J*

s. 
 
 
PRINCIPLES
    HUMAN   PHYSIOLOGY,

WITH THEIR CHIEF APPLICATIONS TO PATHOLOGY, HYGIENE, AND
                    FORENSIC MEDICINE.
                         BY


      WILLIAM  B. CARPENTER, M.D., F.R.S.,
                    J» »
FULLERIAN PROFESSOR OF PHYSIOLOGY IN THE ROYAL INSTITUTION OF GREAT BRITAIN, CORRESPONDING
          MEMBER OF THE AMERICAN PHILOSOPHICAL SOCIETY, AND OF THE
               NATIONAL INSTITUTE OF THE UNITED STATES;
        LECTURER ON PHYSIOLOGY AT THE LONDON HOSPITAL MEDICAL SCHOOL,
                        ETC. ETC.
Eiiixti American, from tjje last SLotrtion STiftfon.
WITH NOTES AND ADDITIONS,
                        BY

           MEREDITH CLYMER, M.D.,

           CONSULTING PHYSICIAN TO THE PHILADELPHIA HOSPITAL ;
LATE PROFESSOR OF THE PRINCIPLES AND PRACTICE OF MEDICINE, AND CLINICAL MEDICINE, IN THE
         FRANKLIN MEDICAL COLLEGE, PHILADELPHIA J  FELLOW OF THE
               COLLEGE OF PHYSICIANS, ETC. ETC. ETC.
                           WITH

THREE HUNDRED AND SEVENTEEN WOOD-CUT AND OTHER ILLUSTRATIONS.
       PHILADELPHIA:
LEA  AND  BLANCHARD
              1847.
03R**£\
;»C.G£tf- 
) <?4  7
            Entered according to Act of Congress, in the year 1845, by
                        LEA   AND BLANCHARD,
in the Office of the Clerk of the District Court for the Eastern District of Pennsylvania.
        PHILADELPHIA :
T. K. AND P. G. COLLINS, PRINTERS. 
                       TO

 WILLIAM  PULTENEY ALISON,

               M.D., F.R.S.E., &c. &c.

PROFESSOR OF THE PRACTICE OF MEDICINE OF THE UNIVERSITY OF EDINBURGH.
My Dear Sir,
  I take the liberty of inscribing the following Work to you, as an ex-
pression of my grateful remembrance of the value of your instructions,
of my respect for those intellectual faculties which render you pre-emi-
nent amongst the Medical Philosophers of our time, and of my admira-
tion for those moral excellencies which call  forth the warm regard of all
who are acquainted with your character.
  In many parts of this Treatise, you will find that doctrines, which you
have long upheld in opposition to almost the whole Physiological world,
are defended with such resources as I could command; and that, in
many instances, such convincing evidence of their truth has been afforded
by recent observations, that further opposition to them would now seem
vain.   And if I have presumed to differ from you on some points, it has
been in the spirit of that independence which you have uniformly encou-
raged in your pupils; yet with a distrust of my own judgment, wherever
it came into collision with yours.
  That you  may long be spared to be the ornament of your University,
and the honour of your City, is the earnest wish of,
                           Dear Sir,
                               Your obliged Pupil,
                                       William B. Carpenter.
1* 
 
EDITOR'S   PREFACE.
   The character of the present Work is too well known and established
to need any commendation.  Within a period of four years, it has passed
through three editions both in this country and Great Britain.  It will
be seen, upon referring to the Author's Preface, that the present edition
has been essentially modified and improved; and, besides  attentive re-
vision, has undergone material alteration in the arrangement.
   Many of the Notes of the American Editor to former editions have
been incorporated by the Author in the text of the present; others remain;
whilst such additions have been made, as the  progress of the science
required.
   By the liberality of the Publishers, the Editor has been enabled to add
numerous additional illustrations;  which, accompanied by copious refer-
ences, will, he trusts, be found to enhance  the value of this edition, and
to peculiarly adapt  it to the Student  of  Physiology.  There  are one
hundred and fifteen more wood-cuts in this than in  the third  English
edition,  and one hundred and one more than in the last American.
  The new matter added by the American Editor is in smaller type, and
is distinguished thus [—M. C]   The  new cuts are  included between
brackets [   ].                                             M.  C.
  230. Spruce Street, Philadelphia,
         September, 1847. 
 
                 PREFACE

                         TO

THE  THIRD  LONDON  EDITION.
   The Author  gladly avails himself of the opportunity afforded him by
the call for a Third Edition of the following work, to express his grateful
acknowledgments for the kind reception it has experienced, both in this
country and  in the United States.   The rapid sale of two large impres-
sions on each side of the Atlantic, has been the most satisfactory proof that
he had not been in error when he supposed that an opening existed for
an additional Treatise on Physiology, notwithstanding  the large number
of those already before the public;  and that he has not been  altogether
unsuccessful in supplying the deficiency.
   The present  Edition has not only undergone a very careful  revision;
but  has in many parts received large additions, and has been in many
others entirely remodelled.  By an increase in the size of the page, and in
the proportion of small type, the quantity of matter has been augmented
by an amount equivalent to the addition of fully a hundred pages.  A
considerable  number of new wood  engravings, of first  rate execution,
have also been  introduced.  Many of these are from original drawings
by Mr. Leonard.
  Among the principal additions will be found a Chapter on the Varie-
ties  of the Human Race;  intended to convey to those, who have not
time or opportunity to peruse Dr. Prichard's elaborate treatises, a general
view of his  arguments and conclusions.   The account  of the Primary
Tissues, also, which was formerly included in the Chapter  on  Nutrition,
has been extended in a degree commensurate with the Author's estimate
of its importance, and  has been made to form a distinct  Chapter nearer
the commencement of the work.  Other additions and  changes, which
constitute, when taken collectively, no inconsiderable  proportion of the
entire  Treatise, are  scattered through the volume.  The materials of
these have been drawn from the numerous contributions to Physiological
Science, which have been made within the last two years, and from 
X
PREFACE.
among which the Author has endeavoured to select the most import-.
ant and the most stable ;—not rashly introducing changes inconsistent
with usually-received  views;—nor, on  the other hand, showing an  un-
willingness to reject the statements of those who have taken much pains
to arrive at accurate  conclusions.  He  trusts that he may be found to
have generally exercised a  sound discretion, both  as  to what he  has
admitted, and what he has rejected; and that his work will  appear to
exhibit on the whole,  a faithful reflection of the present aspect of Phy-
siological Science.  He cannot venture to expect, however, that he  has
succeeded in every instance, so that  each of his readers will be in con-
stant agreement with  him;  since it  is  impossible that they should all
survey the subject from the same point of view.
  Many, however, of  the additions and alterations scattered through the
work, are  the result of the Author's  own investigations.  He has par-
ticularly directed his  attention to the  settlement of points, which  ap-
peared to him to be left doubtful by others; and hence will sometimes be
found to have expressed his views with a degree of confidence, which
the evidence  adduced by them may scarcely appear to warrant.
   The Author feels called upon to express his particular obligations to
the valuable Reports on the Progress of Anatomy and Physiology, con-
tributed by Mr. Paget, to the British  and Foreign  Medical Review;  and
also to those contained in the Half-Yearly Abstract, edited by Dr. Rank-
ing.  He has made a point, however, of consulting the original sources
of information  referred to in these Reports, in every instance in which
he could gain access  to them.  He has derived  much assistance, also,
from Dr. Day's Reports on the Progress of Chemistry, published in the
second of the works  just named; as  well  as from the translation of
Simon's Animal Chemistry, edited by the same gentleman.
   He would be doing injustice to his own feelings, if he did not specially
refer to the  admirable "Anatomical and Pathological Observations" of
Messrs. Goodsir,  as one of the most  valuable  contributions to Physiolo-
gical Science which has been made since the date of his former Edition.
   The subjoined Extracts  from the  First Edition will explain the plan
and scope of his  Treatise to those who may now examine it for the  first
time.
Stoke Newington,
       October,  1846. 
FROM THE
       PREFACE
                 TO

THE  FIRST  EDITION.
   The composition of such a Treatise as the following was a part of the
 original plan of the  Author when  he first came before the Public as a
 writer on Physiology.  Being desirous, however, of making his first  essay
 in the path which had been previously  the most incompletely explored,
 he  deemed it  better  to  await  the verdict  upon this  before proceeding
 further; and he was not without hope, that some Writer, more fully com-
 petent to the task, might in the meantime take up the subject of Human
 Physiology in such a  way as to leave nothing for the Student to desire.
 This,  however, has not been  accomplished.   The previously existing
 Treatises upon it, which have been every year becoming more antiquated,
 have not been replaced by any works,  that can be considered as at the
 same time sufficiently elevated in their character, to represent the present
 condition of Physiological Science,—sufficiently compendious in  their
 bulk for the limited time at the disposal of most  Students,—and  suffi-
 ciently practical in their tendency to lead their readers to  the useful
 applications of the facts and principles they place before them.   This is
 not the opinion of the Author alone,  but that of numerous experienced
 Teachers throughout  the country;  and  he has been  led to regard the
present as a good time for carrying his purpose  into execution.
  The plan and objects of his  Treatise may be gathered from the  pre-
 ceding  statement of the reasons which  have occasioned its production.
In this, as in  his previous work,  it has been  his  object to place the
Reader in the possession of the highest  principles, that can be regarded
 as firmly established, in each department of the  Science;  and  to explain
 and  illustrate these, by the introduction of as many important facts as
could be  included within moderate limits.   In every instance, he  has
endeavoured to make his statements  clear  and precise  without being
formal or dogmatical;  and definite enough to admit of practical applica- 
xu
PREFACE.
 tion without appearing to be unimprovable by further inquiry.  Physiology
 is essentially a science  of progress;  and it  must happen that  much of
 what is now regarded as established  truth, will need great modification
 to be brought into accordance with  the results of new inquiries.  It is
 very desirable, therefore, that the  Student should not be made to think
 so confidently of his acquirements, as  to be indisposed to receive new
 information, even though it should tend to diminish their value.
   The present Treatise  is to be  regarded as complete in itself, and as
 quite independent  of the Author's " Principles of General and Compara-
 tive Physiology."   That it maybe so he has inserted  an introductory
 chapter on the "Place  of Man in the Scale of Being," and numerous
 references  to  the Comparative Physiology of the lower Animals.  Still
 he does not hesitate to express the opinion that, the greater the amount
 of the Student's previous general  knowledge of the Science, the  better
 will he  be prepared to enter upon any department of it, especially that
 peculiarly  complex  and difficult branch, the  Physiology of Man.  On
 every topic, it has  been  the author's  aim to present the  latest and most
 satisfactory information within his reach; and he believes that the Volume
 contains much that will be  new to the Physiologist, whose reading has
 not been tolerably  extensive.   Its materials have been but little derived
 from other  Systematic Treatises on the  subject; and it will not be found
 to bear, as a whole, any  considerable  resemblance to those already before
 the public.  The  author has rather  endeavoured to bring together the
 valuable facts and  principles, scattered through the best of the numerous
Monographs, that  have  been  recently published on special divisions of
Physiology and Medicine; and to reduce these disjecta membra  to that
systematic  form, which  they can only be rightly made to assume, when
brought into  relation with each other, and shown  to be subservient to
principles of still higher generality.  In regard to this, as to his former
 Treatise, the  Author believes that he may claim a  somewhat higher
 character than that of the mere Compiler;  and that even the well-read
Physiologist will find in it  many  facts  and deductions, which have not
been previously brought before him in the same form.
  In apportioning  the amount of space to be devoted to each division of
the subject, the  Author  has had in view  its practical  relations, much
 more  than its merely scientific interest; and he has  on this  account
bestowed a much larger share on the organs of Animal life than some
 may think just when compared with the narrow limits within which other
important topics  are discussed.  But  he has endeavoured to keep always
in view, that he  is  writing for the  guidance of the Student who is to be-
 come a Practitioner, rather than for him who makes the pursuit of Science
 his professed object; and that much that is of the highest interest to the 
PREFACE.
Xlll
latter is  comparatively valueless to  the former.  Hence many topics of
great scientific  interest  are entirely passed over;  and it  is hoped that
such omissions will not be accounted as faults in the estimation of those,
who dread lest the attention of the Student should be too much  drawn off
by the seducing novelties of Science, from his less attractive,  but  more
important objects.
  For a large part of his illustrations, the Author  is indebted to the
valuable and  beautiful Icones Physiologicae  of Prof. Wagner.   He has
indicated the sources of  all which are not original.
  In conclusion, the Author would repeat what he has already had oc-
casion to state;—that  in a work involving many details, it is  not  to be
expected that  no error  should have crept in; but that he has endeavoured
to secure correctness, by relying only upon such authorities as appeared
to him competent, and by comparing their statements with such general
principles  as  he considers well  established.   For the truth of  those
principles, he holds himself responsible; for the correctness of the details,
he  must appeal to  those from whom they are derived, and to  whom he
has generally  referred.   He hopes that he will not be found unwilling to
modify either, wThen they have been proved to be erroneous ;  nor  indis-
posed to profit by criticism, when administered in a friendly spirit.

    Bristol, Feb. 1, 1842,
2 
 
TABLE   OF  CONTENTS.
                           INTRODUCTION.
                                                                     PAGE
Natuhe and Objects or Physiological Science -----     38

                             CHAPTER I.
ON THE PLACE OF MAN IN THE SCALE OF BEING.
1. Distinction between Animals and Plants	-	-	.	39
i 2. General sub-divisions of the Animal Kingdom -	-	-	-	41
3. General characters of Radiata ...	-	-	-	42
4. General characters of Mollusca -	-	-	-	45
5. General characters of Articulata -	-	-	-	48
6. General characters of Vertebrata	-	-	.	50
7. General characters of Fishes -	-	-	-	54
8. General characters of Reptiles -	-	-	-	55
9. General characters of Birds ...	-	-	-	58
10. General characters of Mammalia	-	-	-	62
Hi Chief sub-divisions of Mammalia	-	-	-	65
12. Characteristics of Man - - - -	-	-	-	67
                             CHAPTER II.

  OF THE MUTUAL RELATIONS OF THE DIFFERENT BRANCHES OF THE HUMAN
                                FAMILY.
1. General Considerations  --------76
2. On the Discrimination of Species      ....            -    77
3. On the possible Extent of Variation within the limits of Species      -      -    79
4. On the Extremes of Variation among the Races of Men       -      -      -    81
5. On the value of Physiological and Psychological peculiarities as specific distinc-
     tions   ----------82
6. On the Comparative Peculiarities of the different Races of Mankind   -      -    83
7. Of the Principal Branches of the Human Family      -      -      -      -    91

                            CHAPTER  III.

            OF THE ELEMENTARY PARTS OF THE HUMAN FABRIC.
1. On Organized Structures in General    ------    99
2. On the Original Components of the Animal Fabric     ....   102
3. Of the Elementary Parts of Organized Tissues;—Cells, Membrane, and Fibre  -   108
4i Of the Simple Fibrous Tissues   ...---•   120 
XVI
CONTENTS.
 5. Of simple Cells, floating in the Animal Fluids -
 6. Of Cells developed upon Free Surfaces       .      -      -
 7. Of the Compound Membrano-Fibrous Tissues -
 8. Of Simple Isolated Cells, forming Solid Tissues by their aggregation
 9. Of Tissues consolidated by Earthy deposit.—Bones and Teeth -
10. Of Simple Tubular Tissues.—Capillary Blood-vessels  -
11. Of Compound Tubular Tissues.—Muscle and Nerve   -
PAGE
 124
 137
 147
 150
 161
 188
 192
                              CHAPTER  IV.

                     GENERAL VIEW OF THE FUNCTIONS.
1. Of Vital Actions, and their mutual dependence
2. Functions of Vegetative Life   -      -       -      -
3. Functions of Animal Life     -
216
224
232
                              CHAPTER V.

                    FUNCTIONS  OF THE NERVOUS SYSTEM.
1.  General Summary      -      -       -      -      -      -      •      -     236
2.  Comparative Anatomy and Physiology of the Nervous System in Invertebrata     247
3.  Nervous System of Vertebrata -------     265
4.  Functions of the Spinal Cord and its Nerves.—Reflex Action  -                  285
               Respiratory Movements        -      -      -      -      -     292
               Deglutition and Defecation      -      -      -      -           297
               Movements of the Genital Organs     ....     305
               Protecting Agency of the Spinal Cord  -      -      -      -     305
               Movements of Locomotion     -      -      -      -           307
               Influence on Muscular Tension  -----     307
               Pathological Phenomena        .....     308
               Nerves of the Spinal System   -----     310
5.  Of the Sensory Ganglia and their Functions.—Consensual Movements -      -     326
               Emotional Actions     -      -      -      -      -      -335
               Nerves connected  with the Sensory Ganglia   ...     339
               Consensual Movements of the Eye    ...      -     344
6.  Functions of the Cerebellum   -------     349
7.  Functions of the Cerebrum    .--.--.     357
8.  General Recapitulation, and Pathological Applications -       -      -      -     376
                              CHAPTER  VI.

              OF SENSATION, AND THE ORGANS OF THE SENSES.
1. Of Sensation in General       -
2. Sense of Touch       ---...
3. Sense of Taste        ----..
4. Sense of Smell       ----..
5. Sense of Vision       ---...
6. Sense of Hearing      ----..

                              CHAPTER  VII.

                        OF MUSCULAR CONTRACTILITY.
1. Of Contractility in General     .....
385
395
399
404
407
422
438 
CONTENTS.
XV11
                                                                           PAGE
2.  Of Muscular Irritability ----.-..    439
3.  Of Muscular Tonicity   -       -       -      -      -      -      -       -    449
4.  Energy and Rapidity of Muscular Contraction -----    452


                              CHAPTER  VIII.

                          OF THE VOICE AND SPEECH.
1.  The Larynx, and its Actions   ---....    455
2.  Of Articulate Sounds   --------    464

                               CHAPTER IX.

      INFLUENCE OF THE NERVOUS SYSTEM ON THE  ORGANIC FUNCTIONS.   470


                               CHAPTER X.

                     OF FOOD AND THE DIGESTIVE PROCESS.
1.  Sources of the Demand for  Aliment.—Hunger and Thirst    ...    477
2.  Nature and Destination of the Food of Animals       -      -      -      -    483
3.  Of the Passage of Food along the Alimentary Canal  ---      -    492
                Mastication and Deglutition     -      -      -      -      -    494
                Action of the Stomach  ------    496
                Action of the Intestinal Tube   -      -      -      -      -    501
                Act of Defecation      ------    502
4.  Nature of Chymification and Chylification     .....    503


                               CHAPTER XI.

                     OF ABSORPTION AND SANGUIFICATION.
1.  Absorption  from the Digestive Cavity  ------    509
2.  Absorption  from the Body in general  ------    512
3.  Of the Elaboration of the Nutrient Materials   -      -      -      -      -    517
4.  Composition and Properties of the Chyle and Lymph -      -      -      -    523
5.  Physical and Vital Properties of the Blood     -----    527
6.  Pathological Changes  in the Blood     ------    535


                              CHAPTER XII.

                        OF THE CIRCULATION OF BLOOD.
1.  Of the Circulation in  General  -------    540
2.  Action of the Heart    -      -      -     -      -      -      "      -    546
3.  Movement of the Blood in the Arteries and Capillaries       -      -      -    556
4.  Of the Venous Circulation     ...----    566
5.  Peculiarities of the Circulation in different Parts      -      -      -      -    568


                              CHAPTER XIII.

                               OF RESPIRATION.
1.  Nature of the Function; and Provisions for its Performance  -      -      -    570
2.  Effects of Respiration on the Air      -     -      -      -
                                       2* 
XV1U
CONTENTS.
                                                                           PAGE
 3. Effects of Respiration on the Blood    ------    586
                Exhalation and Absorption by the Lungs       -      -      -    589
 4. Effects of Suspension of the Respiratory Process      ...      -    591

                              CHAPTER  XIV.

                                OF NUTRITION.
 1. General Considerations.—Selective Power of Individual Parts  -      -      -    593
 2. Varying Activity of the Nutritive Processes   -----    596
              Reparative Operations     ------    599
 3. Abnormal Forms of the Nutritive Process     -----    604
 4.  Varying Duration of Different Parts of the Organism   -       -      -      -    609
 5.  Of Death, or Cessation of Nutrition    -      -      -       -      -           612

                              CHAPTER  XV.

                                OF SECRETION.
 1. Of Secretion in General        -       -      -      -       .      .      -    614
 2. The Liver.—Secretion of Bile   ------
 3. The Kidneys.—Secretion of Urine     .....
 4. Mammary Gland.—Secretion of Milk  ------     647
 5. Salivary Glands and Pancreas   -----..     655
 6. Lachrymal Gland      --------     657
 7. The Testis.—Spermatic Fluid   -      -      -       -      .      .       .     657
 8. Cutaneous and Mucous Follicles       -      -       -      .      .       -     661

                             CHAPTER XVI.

      GENERAL REVIEW OF THE NUTRITIVE PROCESSES.--ANIMAL HEAT.
 1. Review of the Nutritive Processes, with Practical Applications       -       -     671
 2. Animal Heat   ------..            ana

                            CHAPTER XVII.

                             OF REPRODUCTION.
1. General Character of  the Function     -      -       .      .      .            ™7
2. Action of the Male     -                                                    „on
                                                         "                  689
3. Action of the Female  ----...            fiq9
4. Development of the Embryo   -                          .                  71„
618
632
                                APPENDIX.
 I. On Phrenology        -
                                                                       -    731
II. On Artificial Somnambulism and Mesmerism     -                        7q„ 
 
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EXPLANATION  OF   PLATES.
                                   PLATE  I.

The  first 16 Figures in this Plate are from Dr. Barry's Embryological Researches in the
                  Philosophical Transactions for 1837, 1839 and 1840.

FIG.
 1. A very early stage  of the formation of the Ovum; the vesicles, the  largest of which
         measures only 1-112 5th of an  inch, are seen in the midst of  dark granules or
         globules  (§ 906).
 2. A stage somewhat more advanced;  the vesicles are surrounded by envelopes of smaller
         vesicles,  amongst which the granules are still seen (§ 906).
 3. A still later stage;  a central vesicle a, is seen, with a spot, b, upon its walls, and sur-
         rounded  with  numerous granules; this  has  now evidently become the Germinal
         Vesicle (§ 906).
 4. Ovisacs from  Human Ovum, l-200th of an inch  and upwards, in diameter; the largest
         exhibits  the Germinal Vesicle, a, very distinctly (§ 906).
 5. Ovisac from Cat, showing its contents when near  maturity;  a, ovisac; b, its contained
         granules; c, zona pellucida; d, granules of the yolk; e, germinal vesicle; /, germinal
         spot; magnified 440 diameters (§ 905).
 6. Ovum of Rabbit at the  periphery of the  Graafian follicle, with part of the membrana
         granulosa removed; g, g, membrana granulosa; ov, ovulum; r, retinacula (§§ 906,
         912).
 7. Ovum with its tunica granulosa and retinacula, removed from the Graafian follicle; a,
         germinal vesicle; b, germinal spot; c, zona pellucida; d, globules of the-yolk; r,r,
         retinacula; t,g, tunica granulosa (§ 906).
 S. Graafian follicle discharging its Ovum, ov, to which the tunica granulosa, tg, and retina-
         cula, r, r, remain attached (§ 912).
 9. Ovarium Ovum in preparation for fecundation: a, germinal spot beginning to resolve it-
         self into cells  at its margin;  b, germinal vesicle; c, elliptical cells in the place of
         the yolk; d, zona pellucida.   100 Diameters (§§ 915, 916.)
10. Ovum nearly ready for fecundation: a, germinal  spot more fully developed into cells, of
         which concentric layers  occupy the germinal vesicle b; c, elliptical discs or cells.;
         rf, zona pellucida; e, outer layer of cells of yolk (§§ 130, 915, 916).
11. Fecundated Ovum of nine hours;  the germinal vesicle, having returned to the centre of
         the ovum, is concealed by the  large elliptical discs, which fill  the cavity of the
         zona pellucida (§ 916).
12. Plan of one of these discs or cells:  its nucleus, a, has developed itself into concentric
         rings of  cells:  and in the most fully developed of these, the nucleus, b, is seen to
         be commencing the same kind of evolution.   In the centre of the original nucleus,
         a pellucid spot, the nucleolus of Schwann and Schleiden, is observed (§§ 130,916). 
XX
EXPLANATION OF PLATES.
PIG.
13. Ovum from the Uterus, measuring about l-68th of an inch in diameter:  a, pair of cells
         now occupying the greater part  of the germinal  vesicle b; c, zona pellucida; d,
         chorion, a new envelope, separated from the last by the fluid it has absorbed
         (§§ 130, 917).
14. Ovum, of which the essential part, a, the pair of cells occupying the  germinal vesicle,
         has advanced further than  in the last  case;  the  other contents of the germinal
         vesicle have undergone liquefaction.  The chorion is here incipient; and the re-
         mains of the cells of which it is composed are seen at cko (§§ 130, 918).
15. More advanced ovum;  the cavity of the germinal vesicle filled with cells, a, mat have
         originated in the  two represented in the last figure; these cells  have nuclei, b,
         which are undergoing a corresponding process  of evolution into secondary cells; c
         and d as in Fig. 13 (§§ 130, 935).
16. Ovum in a state rather more advanced; a, central cell of the germinal mass, now come
         to the surface, and showing the nucleus b with a pellucid centre, from which most
         of the embryonic structures are developed; c, cavity in the germinal mass, caused
         by the approach of its peripheral cells to the enclosing membrane, d (§§ 935, 936).
17. Formation of the Membrana Decidua; a, a, a, interfollicular substance  of the mucous
         membrane of the uterus; b, cavities of the follicles; c, uterine vessels prolonged
         into the decidua and forming loops.  After Baer (§ 919).
18. Human Spermatozoa; a, seminal granules.  After Wagner (§ 902).
19. Cyst of evolution.  After Wagner (§ 902).
20. Capsular bundle  of Spermatozoa, just previous  to their  separation.  After  Wagner
         (§ 902).
21. Globules  from the Chyle; a, ordinary  globules;  b, a globule (cytoblast?) surrounding
         itself with  an envelope  (a forming cell?);  c, minute molecules  of chyle;  d, a
         colourless corpuscle from the blood.  After Wagner (§§ 692, 693).
22. Particles of Blood undergoing multiplication: a, b, c, d, e, successive stages.  After Barry
         (§ 148).
23. Extremity of one of the tufts of foetal vessels forming the Placenta; this includes (like
         a branchial tuft) an artery and vein.  After Reid (§ 922).
24. Plan of the structure of the Placenta, according to Dr. J. Reid's view of it; a, a, portion
         of substance of uterus; b, b, b, b, section of uterine  sinuses, some  of them opening
         on the inner surface into the cavity of the placenta; c, curling artery of uterus; d, d,
         ramifications of foetal vessels, some of them sending down prolonged tufts which
         dip into the uterine sinuses (§ 923).
                                    PLATE II.

25. Uterine Ovum of Rabbit, showing the Area Pellucida, with the annular nucleus of the
         embryonic cell (Fig. 14, 6) now elongated.  In the clear space enclosed by this is a
         well-marked dark groove, occupying the position in which the nervous centres are
         subsequently to be developed.   The cephalic extremity of this is already rounded
         and the caudal extremity pointed.  After Bischoff (§ 937).
26. More advanced ovum, showing the incipient formation of the Vertebral column •  and
         the dilatation of the primitive  groove at  its anterior extremity.   After Bischoff
         (§ 937). 
PLATE n.
fh,   ':>
T.S,>,.?.„Tt l.Xl/1 
 
•   EXPLANATION OF PLATES.
xxi
FIG.
27. More advanced embryo, seen on its ventral side, and showing the first development of
         the Circulating apparatus.  Around the Vascular Area is shown the terminal sinus,
         a, a, a.  The blood returns from this by two superior branches, b, b, and two infe-
         rior, c, c, of the omphalo-meseraic veins, to the heart, d; which is, at this period, a
         tube curved on itself, and presenting the first indication of a division into cavities.
         The two aortic trunks appear, in the abdominal  region, as  the inferior vertebral
         arteries, e, e;  from which are given off the  omphalo-meseraic arteries, /,/, which
          form a network that distributes the blood over the vascular area.  In the cephalic
          region are seen the anterior cerebral vesicles, with the two ocular vesicles, g.  After
          Bischoff (§ 938). 
• 
LIST   OF  WOOD-ENGEAYINGS.
  1. Structure of the Star-fish, after Tiedemann    -----     43
  2. External aspect of Aplysia, after Rang               ....     46
  3. Structure of Aplysia, after Cuvier      ......     47
  4. Section of Cockchafer, after Strauss-Durckheim -----     50
  5. Comparative view of base of Skull of Man, and of Orang-Outan, after Owen -     68
  6. Comparative view of the Skeletons of Man aud the Orang, after Owen      -     71
  7. Views of Prognathous Skull, after Prichard    -----     86
  8. Views of Pyramidal Skull, after Prichard     -----     87
  9. View of Oval Skull, after Prichard     ------     88
 10. Fibrous  structure of Exudation-membrane, after Gerber       -      -      -    107
 11. Fibrous  membrane from the Egg-shell   ------    107
 12. Simple Isolated Cells, containing reproductive Molecules      -      -      -    110
 13. Cells of Zygnema, showing spiral arrangement of nuclear particles, after Hassall   110
 14. Cells of Pelargonium, showing stellate prolongations of nuclei -      -      -    HI
 15. Haematococcus binalis, in various stages of development, after Hassall -      -    111
 16. Coccochloris cystifera, in  various stages of development, after Hassall -      -    111
 17. Haematococcus sanguineus, in various stages of development, after Hassall    -    112
 18. Nostoc macrosporum, in two states, after Hassall      ....    113
 19. Section of branchial Cartilage of young Tadpole, after Schwann      -      -    114
 20. Endogenous cell-growth in cells of a meliceritous tumor, after Goodsir -      -    115
 21. Colorless cells with active molecules and fibres of fibrine, after Addison      -    118
 22. Arrangement of Fibres in Areolar Tissue     -----    120
 23. White Fibrous Tissue, from Ligament  .-----    122
 24. Yellow Fibrous tissue, from Ligamentum nuchas of Calf      -      -      -    122
 25. Elements of Areolar Tissue, after Todd and Bowman  -                        122
 26. Development of Areolar  Tissue, after Schwann       ....    122
 27. Red Corpuscles of Human Blood, after Donne -----    124
 28. Red Corpuscles of Frog's Blood, after Wagner  -----    125
 29. Production of Red Corpuscles in Chick, after Wagner   -      -      -      -    129
 30. Small Venous Trunk, from web of Frog's foot, after Wagner  -      -           132
 31. Vertical  Section of Epidermis, after Wilson    -       -     -      -      -    137
 32. Choroid  Epithelium, with pigment cells, after Todd and Bowman    -      -    139
 33. Cells of  Pigmentum Nigrum   -------    139
 34. Section of the nail and its matrix, after Todd and Bowman   -      -           140
 35. Hairs of Sable and Musk-Deer -------    141
 36. Hair and hair follicles seen in section, after Todd and Bowman       -       -    141
 37. Structure of Human Hair, after Wilson ------    142
 38. Pavement-Epimelium-cells     -------    144
 39. Ciliated  Epithelium    --------    144
 40. Examples of Cilia, after Todd and Bowman   ------    145
 41. Secreting Follicles from the Liver of Crab     .....    146
 42. Capillary Network of Skin, after Berres        .....     148
 43. Capillary Network of Intestinal Villi, after Berres      -                         148
44. Capillary Network of Mucous Membrane, after Berres -      -      -       -     148
45. Diagram of the Structure of Mucous Membrane, after Todd   -      -       -     149
46. Extremity of Intestinal Villi, after Goodsir     -----     151
47. Secreting Cells of Human Liver, after Bowman       -      -      -       -     152
48. Shape of Fat Vesicles in close pressure, after Todd  and Bowman     -       -     152
49. Cells of  Adipose Tissue        -------     153
 50. Blood Vessels of Fat, after Todd and Bowman -       -      -      -       -     153 
XXIV
LIST OF WOOD-ENGRAVINGS.
 51. Fat Vesicles from an emaciated subject, after Todd and Bowman    -            154
 52. Section of Branchial Cartilage of Tadpole, after Schwann    -      -      "      ™
 53. Section of Fibro-Cartilage     -       -             -      -      '      "      «?
 54. Ampullary Loops of Vessels of Cartilage, after Toynbee     -      -      '     ^zl
 55. Nutrient Vessels of Cartilage, after Toynbee   -      -      -      •            15J
 56. Nutrient vessels of the Cornea, after Toynbee        -      -      -            15J
 57. Vertical section of Sclerotica and Cornea, after Todd and Bowman  -      -     158
 58. Tubes of the Cornea of an Ox, injected, after Todd and Bowman    -      -     159
 59. Calcified Areolar Structure from  shell of Echinus     -      -      -      -     161
 60. Cellular Membrane from Shell of Pinna      -      -      -      -      -     161
 61. Section of Bone       ....----     162
 62. Transverse section of a long Bone, after Todd and Bowman  -      -      -     163
 63. Transverse section of a Tibia, after Tomes   -      -      -      -      -     163
 64. Lacunae of Osseous Substance -       -      -      -      -      -      -163
 65. Haversian canals in a long Bone, after Todd and Bowman   ...     164
 66. Section of Cartilage at Seat of Ossification, after Wilson      -      -      -     168
 67. Vertical section of Cartilage, after Todd and Bowman              -      -     168
 68. Scapula of a Fcetus, showing the process- of ossification, after Tomes -      -     170
 69. Longitudinal section of an Incisor and Molar Tooth  -      -      -      -     174
 70. Vertical section of an adult Bicuspid  -      -      -      -      -      -     174
 71. Vertical Section of an imperfectly developed Incisor  -      -      -      -     174
 72. Hexagonal terminations of Fibres of Enamel, after Retzius  -      -      -     174
 73. Fibres of Enamel viewed sideways, after Retzius    ...      -     175
 74. Vertical section of Bicuspid highly magnified -       -      -      -      -     175
 75. Most interior portion of Main Tubes of Dental Bone  -      -      -      -     175
 76. Ramifications of the Main Tubes of Dental Bone     -      -      -      -     175
 77. Transverse section of Crown of  Bicuspid, highly magnified  -      -      -     176
 78. Position of the Main Tubes near the Root of Bicuspid       ...     176
 79. Sections of a Human Incisor, highly magnified, after Todd .and Bowman    -     176
 80. Transverse sections of Tubules of Dentine, after Todd and Bowman -      -     177
 81. Oblique Section of Dentine, after Owen     .....     177
 82. Vessels of Dental Papilla, after Berres       -       -      -      -            180
 83. Diagram of development of Dentine, after Owen     ....     180
 84. Inner surface of cap of dentine, after Owen  -       -      -      -      -     181
 85. Formation of Enamel, after Owen     ------     182
 86. Formation of the Cementum, after Owen    -----     182
 87. First stage of Formation of Teeth, after Goodsir      ....     183
 88. Diagram illustrating subsequent stages of formation of Teeth, after Goodsir  -     183
 89.    Do.                  do.                 do.           after Goodsir  -     184
 90. Capillary network in Frog's foot, after  Wagner       -                          189
 91. Capillary vessels  from pia mater, after Henle -      -      -      -      -     190
 92. Formation of capillaries in germinal membrane, after Wagner       -      -     191
 93. Fasciculus of fibres of Voluntary Muscle, after Baly  -                          193
 94. Portion of Human Muscular Fibre, separating into disks, after Bowman     -     193
 95. Cleavage  of Striped Elementary Fibres      -       -       -      -      -     194
 96. Muscular Fibre broken across, showing Myolemma, after Bowman   -      -     194
 97. Transverse Section of Muscular Fibres of Teal, after Bowman      -      -     196
 98. Fragment of Muscular Fibre from Heart of Ox, after Bowman      -      -     197
 99. Structure  of ultimate fibrillar of striated Muscular Fibre      -      -      -     197
100. Muscular fibre of Dytiscus, contracted in the centre, after Bowman   -      -     198
101. Muscular fibre of Skate, in different stages of contraction, after Bowman    -     199
102. Attachment of Tendon to Muscular Fibre in Skate, after Bowman   -      -     200
103. Non-striated Muscular Fibre, after Bowman  -       -      -      .            200
104.    Do.           showing nodosities, after Wilson   -                          200
105. Muscular Fibres from Fcetus, after Bowman  -       -       -      .      -     202
106.    Do.           treated with tartaric acid, after Wilson     -       -      .     202
107. Capillary network of Muscles, after  Berres   -       -       .       .      •.     904
108. Terminating loops of Nerves in Muscles, after  Burdach      -                   204
109. Structure  of Sympathetic Ganglion, -after Valentin   -                           205
110. Diagram of Tubular Fibre of a Spinal Nerve, after Todd and Bowman     -     206
111. Structure of Nerve-tubes, after Wagner      -                                 207
112. Primitive fibres and ganglionic globules of human brain, after Purkinje     -     208
113. Nerve-vesicles from the Gasserian ganglion, after Todd and Bowman        -     209
114. Caudate nerve-vesicles from the cerebellum and cord, after Todd and Bowman      210 
LIST OF WOOD-ENGRAVINGS.
XXV
*1U*                                                                            PAGE
115. View of piece of Otic ganglion of sheep, after Valentin     -      -      -    210
116. Two views of the vesicular and fibrous matter of the cerebellum, after Todd
         and Bowman      ----....    211
117. Vesicular and fibrous matter in the Gasserian ganglion, after Todd and Bowman  211
118. Primitive Fibres and ganglionic globules, after Wagner      -.      -      -    211
119. Distribution of tactile nerves in skin, after Gerber     -                         212
120. Terminal loops of nerve in the pulp of a tooth, after Valentin       -      -    213
121. Capillary network of nervous centres, after Berres    ....    214
122. Capillary loops in skin of finger, after Berres  -----    214
123. Stages of the development of nerve, after Schwann   -      -      -      -    215
124. Nervous system of Solen, after Blanchard     -       -      -      -      -    251
125. Nervous system of Aplysia, after Cuvier      -                                 254
126. Nervous system of larva of Sphinx ligustri, after Newport   -      -      -    256
127. Portion  of ganglionic tract of Polydesmus, after Newport     -      -      -    257
128. Parts of Nervous System of Articulata, after Newport       -      -      -    259
129. Stomato-gastric  system of Gryllotalpa vulgaris, after Brandt   -      -      -    261
130. A View of the  Great Sympathetic Nerve      -----    267
131. Roots of a dorsal Spinal Nerve, after Todd and Bowman     -      -      -    268
132. Nervous centres in Frog, after Leuret  ------    270
133. Transverse sections of Spinal Cord at different points, after Solly     -      -    271
134. Structure of the Spinal Cord, after Stilling     -       -      -      -      -    272
135. Connection of nerve-roots with the Spinal Cord, after Stilling -      -       -    272
136. A posterior superior view of the Pons Varolii, Cerebellum, &c.      -       -    275
137. An anterior view of the Medulla Oblongata, after Todd and Bowman       -    275
138. A posterior view of the Medulla Oblongata, after Todd and Bowman        -    275
139. Transverse section of the Medulla Oblongata, after Stilling   -      -      -    276
140. Course of the Motor tract, after Sir C. Bell    -----    277
141. Course of the Sensory tract, after Sir C. Bell   -----    278
142. Analytical diagram of the Encephalon, after Mayo    ....    279
143. Brains of Fox-shark, Cod, and Pike, after Leuret      -      -      -      -    281
144. Human Embryo of 6th week, showing rudiments of Brain, after Wagner    -    282
145. Brain of Turtle, after Solly   -------    283
146. Brain of Buzzard, after Leuret        ......    283
147. Brain of Human Embryo at 12th week, after Tiedemann    -      -       -    284
148. Brain of Squirrel laid open, after Solly       .....    284
149. Upper and under surface of Brain of Rabbit, after  Leuret    -      -       -    285
150. Diagram of the distribution of the Fifth Pair  -       -      -      -      -    311
151. A view of the distribution of the Trifacial nerves    ....    312
152. A view of the Third, Fourth, and Sixth Pairs of nerves      -      -       -    313
153. Diagram of the distribution of the Seventh Pair     ....    314
154. Diagram of the distribution of the Eighth Pair      ....    315
155. A view  of the distribution of the Glosso-Pharyngeal, Pneumogastric and Spinal
         Accessory Nerves, or Eighth Pair  -      -      -       -      -       -     316
156. A view  of the course and distribution of the Hypoglossal, or Ninth Pair     -     324
157. Base of  the Cerebrum and Cerebellum with their nerves     -       -       -     327
158. A view of the Optic nerve and the origins of seven other pairs      -       -     340
159. Plan of  the optic tracts and nerves, after Todd and Bowman -     ' -       -     342
160. Course of Fibres in the Chiasma, after Todd and Bowman   -       -       -     342
161. Origin and distribution  of the Portio  Mollis of the Seventh Pair, or Auditory
         Nerve    ---------     343
162. Capillary network at margin of lips, after Berres     ...       -     396
163. Dorsal surface of the Tongue, from Soemmerring     -                          399
164. Simple papillae near the base of the tongue, after Todd  and Bowman -       -     400
165. Vertical section  of one of the circumvallate papillae, after Todd and Bowman     400
166. Compound and simple papillae of Foramen Coecum, after Todd and Bowman     400
167. Capillary network of fungiform papilla of tongue, after Berres       -       -     401
168. Fungiform papilla with its simple papillae and vessels, after Todd and Bowman    401
169. Forms of the conical or filiform papillae, after Todd and Bowman    -       -     401
170. \ A" ffCti°n 0f f^°T and fu,nSiform PaPill3e  I after Todd and Bowman   -     402
     ( b. (structure of filiform papillae              5
171. Nerves of the papillos of the tongue, after Todd and Bowman      -       -     403
172. Distribution of Olfactory nerve on Septum Nasi      ....     405
173. Longitudinal section of globe of the eye     -----     408
174. Horizontal section of the eyeball     ------     409 
XXVI
LIST OF WOOD-ENGRAVINGS.
PAGE
 175. Outer surface of retina of Frog, after Treviranus     -                          412
 176. Capillary network of retina, after Berres     -                                 412
 177. A portion of the retina of an Infant, magnified      -                          ^l2
 178. Vertical section of the Human retina and Hyaloid membrane, after Todd and
          Bowman  --.-----"    413
 179. Membrane of Jacob, after Jacob      ------    413
 180. General section of the Ear, after Scarpa      -----    423
 181. Diagram of the Inner wall of Tympanum, after Todd and Bowman  -       -    424
 182. Axis of Cochlea and Lamina Spiralis ------    425
 183. Cochlea of a newborn Infant,  after Arnold   -----    425
 184. Section of the Cochlea, after Breschet ------    426
 185. Papillae of Auditory nerve on  spiral lamina of cochlea of young mouse      -    426
 186. Auditory nerve taken out of the cochlea      -  ■    -       -       -       -    426
 187. Magnified view of the Lamina Spiralis       -      -       -       -       -    427
 188. Plexiform arrangement of cochlear nerves, after Todd and Bowman -       -    427
 189. Soft parts of  the Vestibule     -------    428
 190. Ampulla of the External Semicircular Membranous Canal    -       -       -    428
 191. Labyrinth laid open, after Breschet    ------    433
 192. Labyrinth of the Left Side                          .....    434
 193. Left Ear in its natural state    -....--    435
 194. Anterior view of the External Ear, Meatus Auditorius, &c.    -       -       -    435
 195. External and Sectional views of the Larynx, after Willis      ...    456
 196. Bird's-eye view of Larynx from above, after Willis   -       -       -       -    457
 197. Diagram of the direction of the muscular forces of the Larynx, after Willis   -    458
 198. Artificial Glottis, after Willis   -      -       -      -       -              -    461
 199. View of the  Organs  of Digestion in their whole length       ...    493
 200. Muscles of the Tongue, Palate, Larynx and Pharynx -       -       -       -    495
 201. Front view of the Stomach distended  ------    499
 202. Interior of the Stomach       ----...    499
 203. Interior of the Stomach and Duodenum       .....    500
 204. Commencement of Lacteal in Villus, after Krause     ....    510
 205. Vessels of Intestinal  Villus of  Hare, after Dollinger   ....    511
 206.    Do.          Do.     of Man, after Krause     .        -       -       -    511
 207. Diagram of Lymphatic Gland,  after Goodsir   -      -       -       .       .    517
 208.  Portion of intra-glandular Lymphatic, after Goodsir   ....    517
 209.  Section showing the anatomy of the Thymus gland, after  Cooper     -       -    521
 210. Microscopic appearance of Inflammatory Blood, after Addison        -       -    534
 211. Web of Frog's foot, slightly magnified, after Wagner  -       -       .       .    541
■212. The anatomy of the  Heart    -------    551
 213. Haemadynamometer of Poisseuille     -       -       .       .       .       .    555
 214. Gill-tuft of Doris, after Alder and Hancock    -                                  573
 215. Lung of Triton, slightly magnified, after Wagner     -       -       .       .     574
 216. Portion of the same more highly magnified, after Wagner     -       -       -     574
 217. Capillary Circulation in lung of living Triton, after Warmer  -       -       -     575
 218. The Larynx, Trachea and Bronchia   --....     g^g
 219. Bronchia and Blood-vessels of the Lungs      -                                  577
 220. Development of Lungs, after Rathke  --..._     g^g
 221. Arrangement of Capillaries in Human Lung   -                                  579
 222. Mammary Gland of Ornithorrhyncus, after Muller    -       -  ■     .       -     616
 223. Exterior of lobule of  liver of Squilla,  after Muller     -       -              .     619
 224. Interior of   do.      do.              do.         -       .       1       -     619
 225. Inferior Surface of the Liver   ---...            g2Q
 226. Three Coats of the Gall Bladder     -       -       .                      [     620
 227. Gall bladder distended, with vessels injected   -                                  fi2i
 228. Nucleated Cells of Parenchyma of Liver      -       .       .      .            fi21
 229. Lobules of Liver, with branches of Hepatic vein, after Kiernan      -            aoo
 230. Horizontal section of  lobules, showing arrangement of their blood-vessels  after
         Kiernan   -      -       -      -       -       .       -      -       -     622
 231. Horizontal section of lobules, showing arrangement of their bile-ducts  after
         Kiernan   -      -      -      -       -       .       .      - '     -     622
 232. Nucleated Cells forming Parenchyma of Liver, after Bowman       .            fi91
 233. Origin of Liver in Chick,  after  Muller ----_[     g2t
 234. Lobules in a state of Aneemia, after Kiernan  -       -       .       _          .  fi9,
 235.   Do.   in first stage  of hepatic-venous congestion, after Kiernan     -      .     62*5 
LIST OF WOOD-ENGRAVINGS.
XXV11
FIG.                                                                            PAGE
236. Lobules in second stage of hepatic-venous congestion, after Kiernan   -       -     625
237.   Do.   in a state of portal-venous congestion, after Kiernan  -       -       -     625
238. Hepatic cells loaded with Fat, after Bowman        -                          627
239. Right Kidney, with Renal Capsule    -      -      -       -       -»           632
240. Section of Kidney after Wilson       ------     632
241. Half a Kidney, divided vertically     ......     633
242. Kidney divided vertically, with Arteries injected     -                          633
243. Section of Kidney, after Wagner     ......     634
244. Portion of Tubulus Uriniferus, after Wagner  .....     634
245. Section of a Pyramid of Malpighi    ......     635
246. Magnified view of small portion of the Kidney, after Wagner        -       -     636
247. Structure of Malpighian Body, after Bowman -----     637
248. Diagram of Circulation in the Kidney, after Bowman -       -       -       -     637
249. Corpora Wolffiana, after Muller        -             -       -       ■»      -     637
250. Mammary Gland     ........     647
251. Vertical section of Mammary Gland  ------     647
252. Distribution of Milk-ducts in Mammary Gland,  after Sir A.  Cooper   -       -     648
253. Termination of portion of milk-duct in a cluster of follicles, after Sir A. Cooper     648
254. Mammary follicles, with contained cells, after Lebert         ...     648
255. Lobule of Parotid Gland,  after Wagner       .....     656
256. Capillary Network of Glandular follicles, after Berres -       -       -       -     656
257. Rudimentary Pancreas of Cod, after Muller  -----     656
258. The Testicle injected  with Mercury  ------     658
259. Minute structure of the Testis        ......     658
260. Human Testis, injected with Mercury, after Lauth   ....     659
261. Diagram of the structure of the same ------     659
262. Sudoriferous Gland, after  Wagner    -      -     . -       -       -       -     661
263. Layer of Sweat-glands of the Axilla, after Todd and Bowman       -       -     662
264. Sweat-gland and its blood-vessels, after Todd and Bowman    -       -       -     662
265. Cuticular portion of a Sweat-duct of the Heel, after Todd and Bowman      -     662
266. Three views of Sebaceous glands and hair-follicles, after Todd and Bowman -     664
267. Cutaneous glands of external Meatus Auditorius, after Wagner       -       -     665
268. Cutaneous follicles of  the Axilla, after Horner       ....     665
269. Gastric glands in Human Stomach, after Wagner     -              -       -     666
270. Horizontal section of a Stomach-cell and tubes, after Todd and Bowman      -     666
271. Vertical sections of mucous membrane of Stomach, after Todd and Bowman -     667
272. Entrances to secreting follicles, after Boyd   -----     667
273. Stomach-cells and Epithelium, after Todd and Bowman      -       -       -     667
274. Villi and follicles of Lieberkuhn on surface of Ileum         -       -       -     668
275. One of the Glandulae solitariae of Peyer, after Boehm         ...     668
276. Mucous coat of Small Intestine, as altered in Fever, after Boehm     -       -     668
277. Glands of Peyer on Small Intestine   -      -      -       -       -       -     669
278. Conglomerate gland of Brunner, after Boehm -----     669
279. Patch of agminated Peyerian glands, after Boehm    ....     670
280. Extremity of Placental Villus, after Goodsir  .....     705
281. External membrane and cells of Placental villus, after Goodsir       -       -     705
282. Diagram of the arrangement of the Placental Decidua, after Goodsir  -       -     706
283. Plan of early Uterine Ovum, after Wagner   -      -       -    >■-       -     715
284. Diagram of Ovum, showing formation of digestive cavity and of amnion, after
         Wagner   ..-------     715
285.   Do.        do.  still more advanced, the allantois beginning to appear, after
         Wagner    ---------     717
286. Diagram of Ovum in  the second month,  showing incipient formation of Pla-
         centa, after Wagner      -      -      -      -       -       -       -     717
287. Section of Uterus, showing ovum, membranes, &c, at the time of formation of
         Placenta, after Wagner    -------     718
288. Diagram illustrating the Foetal Circulation    -      -       -       -       -     721
289. Curve representing  the relative Viability  of Human Male and Female at dif-
         ferent ages, after Quetelet -      -      -      -       -       -       -     727
290   Do.      do.         do.      Heights and Weights  of  the  Human  Male
         and Female at different ages, after Quetelet     -       -       -       -     728
                                       ALSO,
   Two Lithographic Plates, with 27 figures. 
 
INTRODUCTION.
   The object of the science of Physiology is to  bring together, in a sys-
tematic form, the phenomena which normally  present themselves during the
existence of living beings;  and to classify and compare these, in such a man-
ner as to deduce from them the general laivs or  principles, according to which
they take place.
   The term Law having been frequently applied to physical and physiological
phenomena, in a manner very different from that  which sound philosophy
sanctions, it is desirable to explain the acceptation (believed  by the author to
be the only legitimate one) in which  it is here employed.  The  so-called
Laws of  Nature are nothing else than general expressions of the conditions,
under which certain assemblages of phenomena occur; so far as those  con-
ditions are known to us.  Thus  the law of Gravitation, in  General  Physics
(the most universal in  its  action of any with which we are acquainted), is
nothing  else than  a simple  expression of the fact, that, under all  circum-
stances, two masses of matter will attract each other with forces directly pro-
portional to their respective bulks, and inversely  as their distances.  So, again,
the law of  Cell-growth, which seems  to hold  the  same rank in Physiology
with  that of Gravitation  in Physics, embodies  these two general facts,—that
all organised beings originate in cells,—and that the various functions of life
are carried on, even in the adult condition, by the continued growth  and de-
velopment of cells.
   In  no  case  can natural phenomena be correctly said  to  be governed by
laws; since the laws themselves  are nothing else  than manifestations of the
Will of the governing Power.  But they may be  properly said to take place
according to certain laws ;  these laws  being framed by Man as expressions
or descriptions of the slight glimpses he possesses,  of the plan according to
which the Creator sees fit to operate in  the natural world.  Thus understood,
the use of the term Law  can be in no way supposed to imply, that the Deity
stands in any other relation to the phenomena of the  Universe than as  their
direct and constantly-operating Cause.
   In order to  determine  the true laws,  or most general principles,  of  Phy-
siological Science, a very extensive comparison is requisite.  Principles, which
might seem  of paramount importance in regard to  one group  of living beings,
are often  found, on  a  more  general review, to be  quite subordinate.   For
example, the predominance of the Nervous System in the  higher classes of
Animals, and  its evidently close  connection with many of  the functions of
life, has led several Physiologists to the  opinion, that its influence is essential
to the performance of the  functions of Nutrition,  Secretion,  &c.;   but, on
turning our attention to the Vegetable kingdom, in which nothing analogous
to a nervous system can be proved to exist, we  find these functions going on
with even greater activity than in animals.   It  is clear, therefore, they may
be performed without it; and, on a closer examination of the phenomena
    4 
38
INTRODUCTION.
presented by Animals, it  is seen that these may be explained better, on the
principle that the nervous system has a powerful influence on such actions,
than on the idea that it affords a condition essential to them.  Recent inquiries
have shown that the agents immediately concerned in these operations are of
the same nature in  both kingdoms;  the separation  of the  nutrient materials
from the circulating fluids, or the elimination of substances which are to be
withdrawn from it, being performed in the animal, as in the plant, by cells, in
the manner to  be explained hereafter.—This  is only one  out of many in-
stances, which it would be easy to adduce, in proof of the necessity of bring-
ing together all the  phenomena of the same kind, in whatever class of living
beings they may be presented, before we attempt to erect any general princi-
ples in Physiology.
   The object of the present treatise, however, is not to follow out such an
investigation; but to show the detailed application of the principles of which
Physiological science may now be said to consist, to the phenomena exhibited
by the Human being during  the continuance of health or normal life.   These
phenomena, when they occur in  a  disturbed or irregular manner, constitute
disease or abnormal life ; and become the subjects of the science of Pathology.
It is impossible  to draw a precise line of demarcation, between the states of
health and disease ; since  many variations may occur, which do not pass the
limits of what must be called in some individuals the normal state, but which
must be regarded as decidedly abnormal actions in others.   The  sciences of
Physiology and Pathology,  therefore, are very closely related to each other;
and neither can be  pursued with the highest prospect of success, except in
connection with the other.
   Equally close is  the relation between Hygiene,—or  the  art of preserving
the body in health, which is  founded  on  the science  of Physiology,—and
Therapeutics, which is the art of curing disease, founded upon  the science of
Pathology.  In proportion as the science of Physiology  is perfected, will the
simplicity and certainty of its practical applications  increase;  and although
we may not anticipate a return of patriarchal  longevity, yet  the experience of
the last century has amply shown, that  every general increase of attention to
its simple and  universally-acknowledged truths  is attended with a prolonga-
tion of life, and contributes to that not less important object, its  emancipation
from  disease.   In like manner, with  every advance in  Pathological science,
will the art of Therapeutics lose  its  merely empirical character, and become
more  and more rational; that is, the rules  laid down for the treatment of
disease will be less and less  founded upon the results of  a limited experience
as to the  efficacy of particular remedies in  removing certain abnormal  phe-
nomena ;  and will have reference more and more to  the  nature of the morbid
action, which is indicated  by the symptoms.   Thus, when the urine presents
a particular sediment, our  inquiries are directed, not so much to  the condition
of the kidney  itself, as to  the constitutional state which causes  an undue
amount of the  substance in  question to be carried off by the urinary excre-
tion, or which prevents it  from being  (as usual) dissolved in the  fluid.
   In proportion as our treatment of disease thus loses its empirical character,
and is founded  on scientific principles, must it increase in perfection and suc-
cess ;  and in like proportion will the Medical Profession acquire that dignity
to which  the nobility  of  its objects  entitles  it, and that general estimation
which will result from  the enlightened pursuit of them. 
39
                           CHAPTER  I.

             ON THE  PLACE OF  MAN  IX  THE SCALE OF BEING.

               1. Distinction between Jlnimals and Plants.

  1. In entering upon the general survey of the Animal Kingdom, which it
is desirable to take  before we consider in detail any particular member of it,
the  question  naturally arises,—how  is the Animal distinguished from  the
Vegetable ?   There is no  difficulty in replying to this, if we  keep in view
merely the higher  tribes of each division;  no one, for example, would be in
any danger of confounding a Whale  with  a Palm, or  an  Elephant with  an
Oak.   It is when we  descend to the  opposite extremity of the scale, that we
encounter the greatest difficulty; from the  circumstance that the distinguish-
ing characters of each kingdom  disappear, one after another,  until we  are
reduced to those which  seem common  to  both.   So completely is this  the
case, that there are many tribes which cannot, in  the  present state  of  our
knowledge, be referred with certainty to either one division or the other.  We
are accustomed to  think of Animals  as beings,  which not  only  grow and
reproduce themselves, but  which  also possess the power of spontaneously
moving from  place  to  place, and which  are conscious of impressions  made
upon them:  and we usually regard Plants as beings which  are entirely des-
titute of sensibility and of the power  of  spontaneous motion,—going through
all their processes of growth, reproduction and  decay,  alike unconscious of
pleasure and of pain, and devoid  of  all  power of voluntarily changing their
condition.  Such a definition is probably the most correct that we can employ ;
but great difficulties lie in the way of  its  application.  There are many tribes
which  possess a general  structure  more allied to that of beings  known  to  be
Animals, than to that  of  any Plants;  and which yet present no decided indi-
cations, either of sensibility or  of voluntary power.   Such  is the Sponge,
the fabric of  which closely corresponds with that of many Alcyonian Polypes,
whose  animality is undoubted; whilst  there  are no known Vegetables to
which  it presents any near resemblance: and  yet neither observation  nor
experiment has ever succeeded in  proving that the Sponge feels or spontane-
ously moves.  On the other hand, many Vegetables perform evident move-
ments, which, at first  sight, appear to be  spontaneous, as if they indicated
sensibility on the part of the being that executes them.  Such movements,
however,  can in some instances  (as in that of the Sensitive-Plant, or of the
Venus's Fly-trap), be  referred to a sort  of mechanism, the  action of which
does not involve sensibility, and  which may be  compared  with  the many
movements (such as that of the heart) that are constantly taking place in the
bodies  of the highest animals, without their consciousness ; and in other cases
(as in  the Oscillatorise) they are  so  rhythmical,  as to impress the observer
with the idea that they are  rather the result  of some physical, than of any
mental, influence.   In this respect they correspond with the motions of the
constantly-vibrating cilia; which cover the  surface of the mucous membranes
of Animals;  and which  have been recently detected in the reproductive par-
ticles of certain among the  lower tribes of aquatic Plants. 
40
ON THE PLACE OF MAN IN THE SCALE OF BEING.
  2. However difficult it may be for us, owing to our imperfect knowledge,
to draw the line in individual cases, it cannot be doubted that a boundary does
exist;  and, in general, a very simple mark will  suffice  to establish the dis-
tinction.  This mark is  the presence  or  absence of a Stomach, or internal
cavity for the reception of food.   The  possession of a stomach cannot be re-
garded,  however, as in itself  an essential distinction between the two kingdoms
(as  some have represented it); for its presence is merely a result, so to speak,
of the nature of the food of  Animals, and of the mode in which it is obtained.
Vegetables are dependent for their support, upon  those materials only, which
they obtain from the surrounding elements ; carbonic acid, water and ammonia,
duly supplied  to  them, with a small quantity of  certain  mineral ingredients,
affording all the conditions they require for the production of the most mas-
sive fabrics, and the greatest variety of  secretions.   But these same elements,
if supplied to Animals, could  not be converted by them into the materials of
organized structures;  for they  can only employ them as food, after they have
been united into certain peculiar organic compounds ;  and Animals are con-
sequently dependent, either directly or indirectly, upon the Vegetable kingdom
for  their means of support.   Now they cannot incorporate  any alimentary
substance into their own tissues, until  it has been reduced to the fluid  form;
hence they need the means of  effecting this reduction, which  are supplied by
the  stomach.   Again, they cannot be always in immediate relation  with their
food ; they have  to go in search of it, and need a store-room in which it may
be deposited during the intervals ;  this purpose also is supplied by the stomach.
It is evident, moreover, that the  powers of voluntary locomotion and sensa-
tion, which Animals enjoy,  are connected with the peculiar nature of the food
they require;  for if  they were fixed in the ground, like Plants, they would
not be able to obtain that which they require for their support.  It is true that
there  are some, which seem  almost rooted to one spot; but these have the
power  of bringing their food within their reach, though they cannot go in
search of it.   Such is the case with many Polypes,  which use their outspread
tentacula  for this purpose;  and  with  the lower Mollusca, which can  create
currents by means of ciliary action.
  3. A distinction might probably be erected, between the Animal and Vege-
table kingdoms, upon  the mode  in which the first development of the germ
takes  place.   The seed  of  the  Plant, at the time of fertilisation, principally
consists of a  store of nourishment prepared by the parent for the supply of
the  germ, which is introduced  into the  midst of it.  The same may be said of
the  egg of the Animal.  In  both  instances, the first development of the germ
is into a membranous expansion,  which absorbs the alimentary materials with
which it is in  contact; and it prepares  these by assimilation, for the nourish-
ment  of the  embryonic  structure, the  most important parts  of which—the
only permanent  parts  in the higher classes of Animals and in Phanerogamic
Plants—are  in its centre.   Now in Plants,  this membranous expansion (the
single  or double cotyledon) absorbs by its outer surface, which is  applied to
the  albumen  of the  seed, and takes it more or less completely into its own
substance.  In Animals, this expansion is  developed in such a manner, that
it surrounds  the  albumen, inclosing it in a sac,  of which the inner surface
only is  concerned in  absorption.  This sac is, then, the temporary stomach
of the  embryonic structure;  it becomes the  permanent stomach of the Radi-
ata; but in the higher classes, only a portion of it is retained in the fabric of
the adult,—the remainder being cast off, like the cotyledon of Plants, as soon
as  it has performed its function.  Thus, then, the  first nisus of Animal de-
velopment is  towards the formation of a stomach,  for the internal reception
and digestion  of  food; whilst the first  processes of Vegetable evolution tend
to the production of  a leaf-like membrane, which, like the permanent frond of 
GENERAL SUBDIVISIONS OF THE ANIMAL KINGDOM.
41
the lower  classes of Plants, absorbs nourishment by  its expanded  surface
only.
   4.  Some Physiologists have asserted that the nature of the respiratory pro-
cess  affords a ground of distinction between Animals and Plants;—oxygen
being absorbed, and carbonic acid evolved, by the former,—and a converse
change  being effected  in the surrounding air by the latter.  It is not correct,
however, to designate this converse change as a consequence of the respiratory
process ; for in Plants, as in Animals, there  is a continual absorption of oxygen
and evolution of carbonic acid, which constitute the true function of respira-
tion; but  the  effects of this  change are masked (as it were), in  Plants, by
those of the fixation of carbon from the atmosphere,  which only takes place
under the  influence of sun-light, and which is much more analogous to the
digestion of Animals.   The most valid distinction, in doubtful  cases, seems
likely to be  founded on the chemical constitution of the tissues themselves.
In  the plant, the whole of the organized structure, when freed from the pro-
ducts of secretion  which are deposited in it, (many  of these containing the
same proportion of nitrogen  as  exists  in animal flesh,) is found to have the
same composition with  starch; being formed of  oxygen, hydrogen, and  car-
bon only.   In  the animal, on the other hand, the organised tissues  all contain
azote as part  of their proper  substance; non-azotised  compounds, such as
fatty matter, being merely deposited in these, as products of secretion.  Hence
if the chemical composition of the organised tissues themselves can  be  cor-
rectly determined, the Vegetable or Animal nature of  a doubtful  body may be
ascertained.  By this  test, the long-disputed question  of the nature of the
true Corallines has been set at rest; their tissue, when freed from the lime de-
posited  in it, being found to have the composition of that of Plants:  and upon
evidence of the same kind, (the presence of starch in their interior,)  a large
number  of tribes, which have been described by Ehrenberg as  Animalcules,
are now generally referred to the Vegetable kingdom.

            2. General  Subdivisions of the Animal Kingdom.

   5.  The animal kingdom was formerly divided into two primary groups,—the
 Vertebrated and the Invertebrated; the former comprising those which are dis-
tinguished  by the possession of a jointed spinal column, consisting of a num-
ber of internal bones, termed vertebrae ; and the latter including all those  ani-
mals which are destitute of this support.   It was pointed  out by Cuvier,
however, that among the Invertebrata there  are three types  of organization,
as distinct from each other as any of them are from the  Vertebrata; and he
accordingly distributed the whole  under four primary divisions  or  sub-king-
doms: of these, the Vertebrata rank highest;  next, the Articulata  and
the Mollusca, which may be  said to form two parallel series, both of them
inferior  in degree of organization to the Vertebrata, but superior to  the lowest
group ; and lastly, the Radiata, which include those animals that border most
closely, both in external  aspect, and in general character, upon the Vegetable
kingdom.  The members of these groups are readily  separated from each
other by the structure of their skeletons, or organs of support and protection ;
as well  as by many other characters.  In the Vertebrata, the skeleton consists
of a number of internal jointed bones, which are  clothed by the  muscles that
are attached to them and move them ; these bones  are  traversed  by blood-
vessels, and are to be regarded as in all respects analogous to the other living
tissues of the body.  In the Articulata, the soft parts are supported by a hard
external envelope, which is  of  corresponding form  on the two  sides  of the
median  line, and which  is divided into several pieces, jointed or  articulated
together by a membrane, in  such a manner as still to allow  of  free motion; 
42            ON THE PLACE OF MAN IN THE SCALE OF BEING.

and the muscles, which  are numerous and complex, are attached to the inte-
rior of these.  In the Mollusca, the whole body is quite soft; and many spe-
cies exist, in which it has no external protection; in a large proportion of the
group, however, the surface has the power of producing shelly matter, so as
to form a protective habitation, within which the animal can  withdraw its
body, but which does  not  exhibit any very definite type of form.  In  the
Radiata, all the parts are arranged in  a circular manner, the mouth being in
the centre; some of them are protected by firmly-jointed external skeletons,
like those of the Articulata ;  whilst others deposit calcareous matter in the cen-
tre of their soft fleshy structures, as if sketching out the internal skeleton of
the Vertebrata.  The skeletons of most of the Invertebrata differ, however,
from those of  Vertebrate animals, in this important character,—that  they are
not permeated by  vessels,  and are  formed  only  by superficial deposition.
Hence they  are termed extra-vascular : and it is an obvious result of an ar-
rangement of this kind,  that parts once formed are never changed, except by
the ordinary processes of decay, and  that they can only be extended by addi-
tion to their exterior ; whilst in Vertebrata, the bones are subject to alterations
of any kind, whether of removal or addition, throughout their entire substance.
It is not correct to regard them, however, as mere exudations, or as being des-
titute  of vitality ; since  they consist, in all instances, of a regularly-organized
tissue, in which the mineral matter, where such exists, is deposited ; and in
several cases they are traversed by tubes, which seem to convey a fluid  de-
stined for their nutrition, if not actual blood.   Fabrics of this kind are on the
same footing with the dentine and enamel of the teeth of Vertebrata (§§ 209,
210);  to which they sometimes bear  a  very strong resemblance.—A  more
detailed account of the general  structure of these sub-kingdoms will now be
given, beginning with the lowest.

                    3.  General characters of Radiata.

  6. The Radiata possess many points of affinity with the Vegetable  king-
dom ; and of these, the circular arrangement of their parts is one of the most
evident.  Many species of Sea-Anemone, for  instance, present an appearance
so much resembling that of various composite blossoms, as to have been com-
monly termed Animal-flowers,—a designation to  which they further  seem
entitled, from the small  amount of sensibility they manifest, and the  evident
influence of light upon their opening and closing. But it is in the tendency to
the production of compound fabrics,—each containing a number of individu-
als, which have the power of existing independently, but which are to a cer-
tain degree connected with one another,—that we recognise the greatest affinity
in structure, between this group and the Vegetable kingdom.   Every tree is
made  up of a large number of buds, which are composed of leaves arranged
round a common axis ; each bud has  the  power  of preserving its own life,
and of reproducing the original structure, when removed from the parent stem,
if placed in circumstances favourable to its growth ; and yet all are connected
in the growing tree, by a system  of  vessels, which forms  a communication
between them.   This is precisely the nature of the structures formed by the
animals of that class, which may be regarded as the most characteristic of the
Radiate group.   Every mass of Coral is the skeleton of a compound  animal,
consisting of a number of polypes, connected together by a soft flesh, in which
vessels are channelled out;  these  polypes are capable of existing separately,
since  each one, when removed from  the rest, can  in time produce a massive
compound fabric, like that of its parent; but they all contribute to the main-
tenance of the composite structure, so long as they are in connection with it.
In some instances the skeleton is stony, and is formed  by the  deposition of 
GENERAL CHARACTERS OF RADIATA.                  43
calcareous matter—either in the centre of each fleshy column, so as to form a
solid stem,—or on its exterior, so as to form a tube.  In other cases it is horny;
and then it may be a flexible axis, or a  delicate tube.   Both  the stony and
horny  Corals frequently possess  the form of plants or  trees: and  a^  their
skeletons are often found with no obvious traces of the animals to which they
belonged, they have  been accounted Vegetable growths.   There is  not the
least doubt, however, as to the Animal origin of the greater part of these plant-
like structures.
  7. The  affinity between the lowest  Radiata and Plants, in regard to the
vital phenomena they exhibit, is still more close than that manifested  by their
structure.  Although, in the higher  groups, movements  may  be constantly
witnessed, which  evidently indicate  consciousness  and voluntary power, this
is far from being the case in the lower.  There are  many tribes, whose recep-
tion of food, growth, and reproduction, are not known to be accompanied by
any phenomena which distinctly indicate their animal character.  The  most
violent lacerations produce no signs of sensibility ; and the movements occa-
sionally  exhibited  by them have not  so much of a spontaneous  aspect as
those which  are performed by many plants.  This is the case,  for example,
with the Sponge tribe; and also with a number of microscopic species.   So

                                    Fig. 1.
  Asterias aarantiaca, with the upper side of the hard envelope removed ; a, central stomach;  b, cceca
upon its upper surface, probably answering to the liver ; c, c, coecal prolongations of stomach into rays;
e\ c', the same empty ; d, the same opened ; e, under surface, showing vesicles of feet;/, vesicles con-
tracted, showing skeleton between them. 
44
ON THE PLACE OF MAN IN THE SCALE OF BEING.
doubtful is the nature of these beings, that their Animal or Vegetable charac-
ter is rather to be decided  by their affinity with species known to  belong to
one or the other kingdom, and by the chemical  composition of their tissues,
than in any other way.
  8. It is very different, however, in regard to the  higher Radiata.   Even
among the  Zoophytes (as  the plant-like animals just alluded to are com-
monly termed),  there  are some  species which  are unattached  during  the
whole period of  their lives, and which have  a  power  of voluntarily moving
from place to place, such as is never  possessed by plants.   And in the high-
est  class,  the Echinodermata, including the Star-fish,  Sea  Urchin, &c, we
meet with a considerable degree of complexity of structure, and a correspond-
ing variety of actions.  Still, except in those species which connect this group
with others, the same character of  radial or circular symmetry is  maintained
throughout; and in no animal is it  more remarkable than in  the common Star-
fish.  It  is  exhibited alike in its  internal conformation and in its external
aspect.  The mouth, placed in  the  centre of the disk, leads to  a stomach
which occupies  the  greatest part of the  cavity of the  body; and this sends
prolongations into the arms, which are exactly alike  in form, and which  oc-
cupy a precisely similar position in every one.  Each arm is furnished, on its
under side, with a curious apparatus for locomotion, consisting of a series of
short elastic tubes, which  are prolonged  through apertures  in the hard enve-
lope, from a series of vesicles placed along the floor (as it may be termed) of
the ray.   The system of vessels  for absorbing  nutriment  and conveying it
through the system, is also disposed upon the same plan; and the same may
be said of the nervous system, and of the  only organs of special sensation
which this animal appears to possess—the rudimentary eyes, of which one is
found at the extremity of each ray.
  9. Amongst other  results of the repetition  of similar  organs, so remarkable
in the Radiated group, is this,—that one or more of them  may be removed with-
out permanent  injury to the whole  structure, and may even develope them-
selves into an entire fabric.  Thus  in the Star-fish, instances are  known of the
loss of one, two, three, and even  four rays, which have been gradually repro-
duced ; the whole process appearing to be attended with  little inconvenience
to the animal.  In some species of isolated Polypifera, such as the common
Sea-Anemone, and Hydra  (Fresh-water Polype), this power of reproduction
is much greater.   The Hydra may be cut into a large number of pieces (it is
said as many as 40) of which every one shall be capable  of developing itself
in time into a perfect polype.  The Sea-Anemone, when divided either trans-
versely or vertically, still lives; and each half produces  the other, so as to re-
form the perfect animal.  This is another character which shows the  affinity
of the Radiata to the Vegetable kingdom ; and there  is yet another, derived
from their mode  of reproduction.   In many  Polypifera, we observe a  propa-
gation by  buds, in all respects  conformable to  that which  plants effect, and
quite  different from the regular multiplication by distinct germs.  This gem-
miparous reproduction, as  it is called, takes place, not only in the compound
Polypifera, whose plant-like structures are extended by it,  but  also in some
isolated species, such as the Hydra ; from the body of which one or more young
polypes bud forth at  the same time ; and these buds may themselves put forth
another generation, previously to their separation from  their parent.  This
kind of reproduction is not seen anywhere else in the whole Animal kingdom,
except in  a  few of the lowest Mollusca  and Articulata,  which border most
closely on the Radiata.
  10.  In  the lowest animals of this group, such as the  simplest forms  of Po-
lypes, we find the whole body to consist of nothing else than a  stomach, fur- 
                    GENERAL CHARACTERS OF MOLLUSCA.                 45

nished with tentacula for drawing food to its  orifice.*  The nutrient materials
are imbibed by the walls of the stomach, and are transmitted by them to  the
tentacula, without any regular circulation ; and the exposure of the whole of
the soft surface of the body to the  surrounding liquid, affords all the aeration
which is requisite.  In the Medusas, or  Jelly-fish, we often find the stomach
extending itself into a ramified system of tubes, which convey its contents to
the thin border of the umbrella-shaped disk, for more effectual aeration;  but
there is still no separate circulating system, except in a few instances.   In the
class of Echinodermata, however, which includes the highest forms  of Ra-
diated animals (such as the Asterias or Star-fish, Echinus or Sea-Urchin, and
Holothuria  or Sea-Cucumber), we find  the  digestive  cavity restricted within
much narrower limits ; and there is here a distinct system of vessels,  adapted
to absorb  the nutrient fluid from the digestive cavity, and  to convey it to the
remoter parts of the system for their nutrition, as well as to effect its aeration,
by exposing it to the influence of the air contained in the surrounding liquid,
in organs especially adapted for that  purpose.


                    4. General characters of Mollusca.

   11. The range of  Animal forms* comprehended in the Sub-Kingdom Mol-
lusca is  so great, that it would be  difficult to include  them  in any  positive
definition which  should be applicable to all.   They present few traces of the
circular disposition of organs around the mouth, which is characteristic of the
Radiated  classes;  and we seldom  meet with  any marked approach to the
elongation of the  body,—still  seldomer with any indication of that division
into segments,—which are the chief  peculiarities  of the Articulata.  It is by
the  absence of  these, and of  any trace  of the Vertebrated structure,  that the
Mollusca are most readily defined.   The variety of form which  they present,
is less surprising, when it is considered  that  the bulk of their bodies is almost
entirely made up by organs of nutrition; the organs of sensation and locomo-
tion, which they possess, being chiefly subservient to  the supply of these.
We find,  in the  lowest tribes of this group, living beings which are fixed to
one  spot during all but the earliest period of their lives; and  which scarcely
possess within themselves so much power of movement, as that enjoyed by
the individual Polypes in a  compound  polypidom; and yet these exhibit  a
complex and powerful digestive apparatus, a regular circulation of blood, and
an active respiration.    We never find, throughout the whole Animal kingdom,
that the apparatus of organic life is arranged on any definite plan of its own;
its confirmation  being adapted to the type which  predominates in the struc-
ture of each group, and which is principally manifested in the disposition of
the locomotive organs.  Thus, the  stomach of the Star-fish is circular, and
sends a prolongation  into  each ray;  whilst the  digestive cavity of  the  Articu-
lata  is prolonged into a  tube.   In  the  Mollusca, there is no  such  definite
type, the apparatus of nutrition  having  the  predominance over that of loco-
motion ; and the  form of the body is, therefore, extremely variable.  The re-
lative places, even of the  most important organs (such as the gills), are found
to undergo complete changes, as we pass from one tribe to another; although
their general structure is but little altered.
   12. The  lower Mollusca  may be characterised as consisting merely of  a

  * It is usual to speak of the  orifice of the stomach, in the Polypes, as the mouth; and  to
regard the tentacula as prolonged lips.  It appears to  the author much more reasonable, how-
ever, to consider this aperture  as the cardiac orifice of the stomach; and to regard the tenta-
cula in the  light of pharyngeal constrictors, their  office being to grasp the food and convey it
to the stomach.  This view is borne out by  the  conformation of the superadded parts in the
Ciliobrachiate Polypes and Ascidian Molluscs. 
46            ON THE PLACE OF MAN IN THE SCALE OF BEING.
bag of viscera; they have not even any prominence for the mouth, nor any
organs of special sense, such as would distinguish  a head;  and they  are
entirely destitute of symmetry,—the radiated arrangements of parts  seen in
Zoophytes being absent, as well  as  the  bi-lateral  correspondence which is
characteristic of the higher sub-kingdoms.  In  the  more elevated Mollusca,
however, which possess not merely sensitive tentacula, but eyes and even or-
gans of smell and hearing, we find these  disposed in a symmetrical manner;
so that the head, which is the part concerned peculiarly in  animal life, does
present a  bi-lateral equality of parts, even  when  the  remainder of the body
wants it.  Further, in the more active among the  higher classes, we find this
bi-lateral symmetry showing  itself in  the  exterior of the whole  body; evi-
dently bearing a pretty close  relation to  its degree of locomotive power.  It
is most evident and complete in the Cephalopoda  (Cuttle-fish tribe);  many
of which  are  adapted to lead  the life of Fishes,  and resemble them in the
general form of the  body, as also in the  structure of many of the individual
organs.   It is also manifested in many  of the shell-less Gasteropoda, such as
the Slug, or the Aplysia (Sea-Hare) ; as  will be  seen by the accompanying
representation of a species of the latter.   But this symmetry does not extend

                                 Fig.  2.
Aplysia depilans ; a, branchiae or gills.
to the arrangement of the internal organs ;  and appears to be only designed to
adapt the body for more convenient locomotion.
  13. As a  group, however, the Mollusca are to be characterised rather by
the  absence, than  by the possession, of any definite form ; and  there is  a
corresponding absence of any regular  organs  of support, by which such  a
form could  be  maintained.  The name they have received  designates them
as soft animals; and this they are pre-eminently, as every one knows, who
has taken a Slug between his  fingers.  The  shell, where  it exists, is to be
regarded rather in the light of  an appendage, designed for the  mere protec-
tion of the  body, and deriving  its shape from  the latter, than  as a skeleton,
giving attachment to muscles, and regulating the form of the whole structure
It is in no instance a fixed point for the  muscles of locomotion ; and it is onlv
indeed, where the body is uncovered by a  shell, or where a locomotive  orffan
may be projected  beyond  it, that  any  active  movements can  be executed
This locomotive organ,—the foot, as it  is  commonly termed—is nothing else
than a  fleshy mass, formed by the  increased  development of the muscular
portion of one  part of the general envelope  of the body, termed the  mantle
in which the visceral  mass is  loosely included.   The mantle is not essen-
tially different from the skin of other animals ; but it is usually thicker pos-
sessing  a considerable  amount of muscular  fibre  interwoven with it  and its 
GENERAL CHARACTERS OF MOLLUSCA.
47
surface having  frequently a  glandular  character.   This  general  muscular
envelope is the  only locomotive organ possessed by a  large  portion of the
Mollusca; but its contractile properties are usually greatest at some particular
spot, where it is thickened into a  sort of disk, by the  alternate contraction
and  extension of which the animal can slowly propel itself; this is well seen,
by causing a Snail or Slug to crawl over a piece  of glass, so  that the under
surface of the disk may be seen whilst it is in operation.  The  general  cha-
racter of their locomotion, however, is well expressed by the term sluggish;
and  there are scarcely any among the typical Mollusca, whose activity is  such
as to demand for them any higher appellation.
   14. The  general development  of their organs of Nutrition, however, is
  Aplysia cut open, showing the viscera; a, the upper part of oesophagus; b, penis; c, c, salivary glands ;
d, superior or cephalic ganglion; e, e, inferior or sub oesophageal ganglia; /, termination of oesophagus;
g, g, first stomach ; h, third stomach; i, second stomach ; k, intestine ; I, I, I, liver; m, posterior ganglion ;
n, aorta; o, hepatic artery; p, ventricle of heart; g, auricle; r, s, branchia? ; t, testis; k, lower part of
intestine; v, ovary; w, anus. 
48            ON THE PLACE OF MAN IN THE SCALE OF BEING.
much higher than is met with among  the Articulata; and, in proportion to
that of the organs of Locomotion, it is much greater than will be elsewhere
observed throughout the Animal kingdom.  The justice of this statement will
be  made evident by a slight examination of the  preceding figure, in which
the interior  structure of  the Aplysia, showing the general  character of that
of the group, is displayed.   The  only distinct set of muscles, possessed by
this animal, is that connected with  the mouth; which it is able to push for-
wards or to draw back, and which possesses  considerable powers of mastica-
tion, and is furnished with large salivary glands.   The nervous  centres (of
which more will be said  hereafter) are seen to be principally disposed around
the oesophagus.   The whole digestive apparatus is observed to be  very com-
plex and highly developed; the liver alone occupying a considerable part of
the cavity.  The heart  has  distinct muscular walls, and is  divided into  a
separate auricle and  ventricle;  and a large respiratory organ is developed for
the aeration of the  blood.   The position of  the gills, which  are external  to
the cavity, but which are concealed in part  by a  fold of the  mantle, and  in
part by the rudimentary shell, is seen at a, Fig. 2.   The generative apparatus,
also, is highly developed.  Yet with all this  complex organization, the loco-
motive power  of the animal  is not much greater  than that of the Slug; no
other means being provided for the purpose than the contractility of the gene?
ral envelope, which is greatest  in the thickened  portion on the under side of
the body.
  15. The blood of the  Mollusca is white, and the number of corpuscles  in
it is small.   Their temperature is low, being seldom  more than one or two
degrees above  that of the surrounding medium;  but many of  them are capa-
ble  of being subjected to extreme variations  of heat  and cold, without their
vitality being thereby destroyed.  Their respiration  is for the most part aquatic;
and is performed by means of gills, over which a current of water  is con-
stantly being propelled, by the  vibration of the cilia that cover their surface.
Many of them are dependent on the same current for their supplies of food;
part of the  water so introduced  being taken into the stomach; and  a part
flowing over the respiratory surface.  The higher  tribes, however, go  in
search of their food, and have instruments of mastication for reducing it; but
in these, as in the  former, the anal orifice  of the intestine  opens into the
passage through which the  current that has passed  over the respiratory organs
finds egress; so that the  faecal matter from the former, and the fluid that has
served the  purpose  of the latter, are discharged   together.   Although very
voracious when supplies  of food come in their way, most of the Mollusca  are
capable of fasting for long intervals,  where none offer  themselves,—a fact
which is readily explained by that general inertness of their vital  processes,
which has been stated to  be characteristic  of  the group.


                  5. General characters of Articulata.

  16. The members of the sub-kingdom, Articulata, are distinguished, for
the  most part,  by  characters which are exactly opposed to those just  enume-
rated.  Their characteristic form is easily defined ;  and in no instance is there
any wide departure from  it. The body is more or less elongated, and presents
throughout  a most exact bi-lateral symmetry.   It is completely inclosed in an
integument of  greater density than the rest of the structure, which is  divided
into distinct rings or segments ;  these, being held together by a flexible mem-
brane, allow considerable freedom of motion, whilst  they firmly protect the
soft parts, and afford  attachment to numerous  muscles.  It is in the Centipede,
and other such animals, that this division into segments is most distinctly and
regularly marked.   In the lower Articulata, such as the Leech and the Earth- 
GENERAL CHARACTERS OF ARTICULATA.
49
 worm, the integument is altogether so soft, that the intervals of the articulations
 are not very distinct from the rings themselves; and in the highest Crusta-
 cea and Arachnidaf the  segments are  so  closely united together, as to be in
 some instances scarcely recognizable.  In the former, the movements  of the
 body are entirely effected by its  own flexion ;  whilst in the latter, they are
 committed to members developed  for that special purpose.  These members
 also  have an articulated external skeleton.  The bulk of the body  in the Ar-
 ticulata is  made up  of the muscles, by which  the several segments and their
 various appendages  are put in motion ; these muscles have their fixed  points
 on the interior of the hard envelope, just as they are attached in Vertebrated
 animals to the exterior of the bones ; and they form a system of great com-
 plexity.
   17. The development of the organsfbf nutrition in Articulata, would seem
 to be altogether subservient to that of the Locomotive apparatus,—their func-
 tion being chiefly to supply the  nerves and muscles with the aliment necessary
 to maintain their vigour.   The  power of the muscles is so great in proportion
 to the size of the animals, that  in energy and rapidity  of movement, some of
 the Articulated  tribes surpass all other beings.   Their movements are directed
 by organs  of  sensation, which,  although not developed on so high  a plan as
 those of some Mollusca, are evidently very acute in their powers.   There are
 very few instances of Articulated animals being in any way restrained as to
 freedom of locomotion; and these are found in a single group, the Cirrhopoda
 or  Barnacle tribe, which connects this sub-kingdom with the last.  In general,
 they roam freely abroad  in search of food, and are supplied  with  prehensile
 organs for capturing their prey, and with a complex masticating apparatus for
 reducing it.   Their actions are  evidently directed almost solely by instinctive
 propensities, which  are adapted to meet every  ordinary contingency, being of
 similar character in each individual of the same  species, and presenting but
 little appearance of ever being modified by intelligence.  Hence these animals
 seem like machines, contrived to execute a certain set of operations; many of
 them producing immediate results, which even Man, by the highest efforts of
 his reason, has  found it difficult to attain.
   18. All  the  Articulata, save  a few of the very lowest species, possess  a
 distinct head at one  end of the  body, furnished with organs of special sensa-
 tion,  and with lateral jaws for the prehension and reduction of food ; and their
 movements, being principally guided by the  special senses, take place in this
 direction.  The bi-lateral symmetry of the  body is  not confined to its  exte-
 rior ;  for it prevails  most completely in the  whole muscular apparatus ; and
 even  the organs of nutrition present more distinct traces of it than  are to be
 seen elsewhere.  The  compact heart of the  Mollusca, for instance, is here
 replaced by a long tube, the dorsal vessel, placed on the median line; and the
 respiratory organs, which are usually diffused through the whole system, are
 uniform on the two sides.   Even the intestinal canal  partakes of this symme-
 try ;  in some species it runs straight from end to end of the body; and even
 where it is otherwise  disposed, its appendages are nearly equal on the two
 sides.   The respiration of this group is for the most  part aerial;  and the ap-
 paratus for the purpose consists  of a series of chambers or tubes, which are
 dispersed or extended through  the whole body, and which are expanded at
 certain points, in insects  possessing considerable powers of flight, into large
 air-sacs.   By this means, the air,  the blood, and the tissue to be nourished,
 are all brought into contact at  the same points ; and a much less vigorous cir-
culation  is required than would otherwise be needed ; whilst, at  the  same
time,  the specific gravity of the body is diminished, and flight thereby rendered
more  easy.  The whole apparatus of nutrition is comprised within a compa-
ratively small part of the body; and the bulk of the organs  which  compose
    5 
50
ON THE PLACE OF MAN IN THE SCALE OF BEING.
it, is never at all comparable with that which we ordinarily find in the Mol-
lusca.   Thus, the liver, which in the  Oyster forms a large part of the whole
substance, is often scarcely recognizable as such in the Inject; and the intes-
tinal tube seldom makes many convolutions in its course from  one extremity
to the other. The blood is usually white, as in the other Invertebrated classes :
but it contains a larger  number of corpuscles than are seen in that of most of
the Mollusca.  The temperature varies to a certain  degree with that of the
atmosphere ; but  many  Insects have the power of generating a large amount of
independent heat, which is strictly proportionable to  the quantity of oxygen
converted by them  into carbonic acid  in the respiratory process.  All the ac-
tions of the Articulata  are performed with great energy ;  and, at  the time of
the most rapid increase of the body, the demand  for food  is so great, that a
short suspension  of the supply of aliiiient is fatal.  Many of them  are capa-
ble, however, of being submitted to the influence of very extreme temperatures,
with little permanent injury.
   19. The  adjoining figure, which displays the muscular apparatus of the
interior of  the body of  a Cock-chafer, will give an idea of its complexity and
variety, and of the  large portion  of the  trunk which  is occupied by it; and
will also  show the division  of  the  skeleton into  segments, the number of
which in Insects  is limited to thirteen.  These are nearly equal  and .similar
to each other in the Larva ;  but, in the perfect  Insect, the three behind the
head are united into the thorax,  to which  the legs and wings  are  attached;
and the remainder form the abdomen, which has little concern in locomotion.

                                   Fig. 4.
 Section of the trunk of Melolontha vulgaris, (after Strauss-Durckheim,) showing the complexity of the
Muscular system. The first segment of the thorax (2) is chiefly occupied by the muscles of the head,
and by those of the first pair of legs. The second and third segments (3 and 4) contain  the very large
muscles of the wings, and those of tfie other two pairs of legs.  The chief muscles of the abdomen are
the long dorsal and abdominal recti, which move the several segments one upon the other.
                  6.  General characters of Vertebrata.

  20.  In none of the  three preceding divisions of the Animal kingdom, does
the Nervous System attain  such a degree of development, as to give it  that
predominance in  the  whole fabric which it  evidently  possesses in Verte-
brata.  In the Radiata and Mollusca, its functions are obviously restricted to
the maintenance of the nutritive operations ; and to the guidance of the  ani-
mal, by means of its sensory endowments, in the  choice of food, as well  as
(in some instances) in the search for an individual  of the opposite sex: in the 
GENERAL CHARACTERS OF VERTEBRATA.
51
Articulata, its purpose appears similar, but  is carried into effect in a different
manner, the locomotive organs being the parts chiefly supplied by it.   In the
Vertebrata, on the other hand, the development of all the other organs appears
to be subordinate to that of the Nervous System ; their  object being solely  to
give to it  the means of the exercise of its powers.  This statement is  not,  of
course,  as applicable to the lower Vertebrata, as it is to  the higher ;  but  it  is
intended to express the general character of the group.  The predominance
of the nervous system is manifested, not only in the increased size of its cen-
tres, but also in the special  provision which we here find, for the protection
of these from injury.  In the Invertebrated classes, wherever the nervous sys-
tem is inclosed in any protective envelope, that envelope serves equally for
the protection of the whole body.   This is the case, for example, in  regard
to the spiny integument of the Star-fish, the  shell of the Mollusca, and the
firm jointed rings of the Insect.   The only exceptions  occur in a few tribes,
in which the nervous system is much concentrated ; and in which the general
organization  approaches that of the Vertebrata.*  In Vertebrated  animals, we
find that the  skeleton essentially  consists of a  series of parts, which are de-
stined to inclose the nervous centres, and to give attachment on their exterior
to the muscles  by which the body is moved ; hence  it may be  termed the
neuro-skeleton ; in contradistinction to the  dermo-skeleton, which envelopes
the whole body in many Invertebrata, being formed on the basis  of their in-
tegument.  The tissues, bone and cartilage, of which the former is composed,
are more closely connected with the vascular system, than are the hard parts
of Invertebrata ; and are consequently more capable of undergoing interstitial
change.
   21. In  considering the essential character of the skeleton of Vertebrata, we
should look at its simplest forms,—those in which it has the least number  of
superadded parts.  We find these in the Serpent tribe, among Reptiles, and
in the Eel and its allies among Fish.   If we examine their skeletons, we per-
ceive that the Spinal  Column, with  the Cranium at its anterior extremity,
constitutes the essential part of the vertebrated  frame-work ; and  that the de-
velopment of members  is secondary to this.  The Spinal  Column usually
consists of a number of distinct  bones, the Vertebrae ;  each of which is  per-
forated  by a  large aperture, in such a manner that, when the whole is united,
a  continuous tube is formed for  the lodgment of the spinal cord.   The Cra-
nium, which it bears at its upper end, is in reality formed of the same elements
as the vertebra?, instead of differing from them completely in structure, as Ave
might be  led to suppose by examination of its most developed forms only.
The object of this enlargement is to  inclose  the  brain, or mass of cephalic
ganglia, which attains  a greatly-increased size in the Vertebrata; and also  to
afford support and  protection to the organs of special  sense, which are far
more highly  developed among them than they are in the lower classes.   The
true nature of the cranium is best seen  in those animals, in which the brain
bears but a small proportion  to the spinal  cord, such as the lower Reptiles
and Fishes ;  and* an examination of its structure in these satisfactorily proves
the reality of this view, which is further borne out  by  the history of its de-
velopment, and of that of its contained parts, in the higher Vertebrata.
   22. The Vertebral column  at its opposite extremity, is usually contracted
instead  of being dilated,—forming a  tail, or a  rudiment of one, from which
the nervous centres are  entirely  withdrawn ;  the  development of the  tail  is

  * Thus, in the highest Crustacea, there is an internal projection from the shell, on each
side of the median line, which forms a sort of arch inclosing the ventral cord; and in the
naked Cephalopoda, the nervous centres are supported, and in part protected, by cartilagi-
nous plates, which are evidently the rudiments of' the internal skeleton of the Vertebrata. 
52
ON THE PLACE OF MAN IN THE SCALE OF BEING.
commonly seen to be in an  inverse proportion to that of the cranium.   To
this column, the ribs and extremities  are  merely appendages, which we find
more  or less developed in the various tribes, and often entirely absent; whilst
the vertebral column is never wanting, although reduced in some species to a
very rudimentary state.   It is interesting  to compare its  various  conditions,
with those which have been noticed in the external skeleton of the Articulata.
In the lowest animals of the group, locomotion is principally or  even entirely
performed by flexion of the body itself; and here, as  in the worm  tribe, we
find the skeleton extremely flexible, the whole  being comparatively  soft, and
its divisions indistinct.  This is the case, for example, in the Lamprey and
other  Cyclostome fishes : in which there is no distinct division into vertebrae,
the spinal column scarcely possessing even the density  of cartilage.   In pro-
portion, however, as distinct members are developed, and the power of loco-
motion is  committed to them, we find the  firmness of the  spinal column in-
creasing, and its flexibility diminishing ;  and in Birds,—in which, as  in  In-
sects, the  movements of the body through the air are effected by muscles that
must  have very firm points of support,—the vertebral column is much conso-
lidated by the union of its  different parts, so  as to form a solid frame-work.
A.s a general rule, then, the mobility of the extremities, and the firmness  of
the vertebral column, vary  in a like proportion.  The  number  of these ex-
tremities in Vertebrata never exceeds four; and two  of them are not unfre-
quently absent.  The power of locomotion  is not  developed  to nearly the
same  proportional extent, as in the  Articulata;  the swiftest bird, for  example,
not passing through nearly so many times its own length in the same period,
as a large proportion of the Insect tribes :  but it is far greater than that, which
is characteristic of the Mollusca ;  and there is no species that is fixed to one
spot,  without the power of changing its place.  On  the other hand, the high-
est Mollusca approach them very nearly in the development of organs of spe-
cial sense, of which Vertebrata almost invariably possess all four  kinds—sight,
hearing, smell, and  taste.
  23. The  perfection of the Articulate structure has been shown to consist
in the development of those powers which  enable the animal to  perform
actions denoting the highest  instinctive  faculties.   That  of the Vertebrata
evidently tends to remove the  animal from  the dominion of  undiscerning,
uncontrollable, instinct; and  to place all its operations under the dominion of
an intelligent will.   We no longer witness in these operations that uniformity,
which has been  mentioned  as  so remarkable a characteristic  of instinctive
actions.   There is evidently, among the higher Vertebrata especially, a power
of choice and of determination, guided by a perception of the  nature of the
object to  be attained, and of  the  means to  be  employed, constituting the
simplest form of the reasoning faculty ; and the amount of this bears so close
a relation  with the development of  the cerebrum, that it is scarcely possible to
regard the two as unconnected.  In Man,  whose cerebrum is far larger in pro-
portion to his size, as well as more complex  in its structure, than that of any other
animal, the reasoning faculties attain the  highest perfection that we  know to
be  anywhere manifested by them  in connection  with a material instrument;
the instinctive propensities are placed under their subjection; and all his acts,
excepting those immediately  required for the maintenance of his organic func-
tions, are  put under their control.   It is to Man, therefore, that what was just
now stated, of the predominance of the nervous  system in Vertebrata, parti-
cularly applies ;  but the same may be noticed, though in a less striking degree,
throughout the group.   Not only is the influence of  the nervous system to  be
traced, in  the sensible movements which they perform ; but also in various
modifications of the organic functions, which  take place under the influence
of particular states of mind, and the occurrence of which there is no reason 
GENERAL CHARACTERS OF VERTEBRATA.                53
to suspect in the lower tribes of animals.   These are even much more strik-
ing in Man, than in the lower Vertebrata;  indeed the comparative slightness
of the influence of the mind upon the body, is one of the causes  which ren-
der the lower Mammalia more able than Man is to recover from the effects
of severe injuries.  The Mollusca  seem to grow like plants;  their massive
organs increasing by their  own separate vitality, and being but little depend-
ent upon  each other.   Even the act of respiration, which is in  most animals
performed by a series of distinct muscular contractions, is  there principally
effected through the medium of the cilia which clothe the respiratory surface.
But in the Vertebrata, the nervous system possesses a distinct and independ-
ent rank ; its offices are those which more particularly constitute the active
life of the animal; the organic functions have for their chief object, the main-
tenance of the nervous  and muscular apparatus in the condition requisite for
their  activity ; and in consequence, all these different kinds of  apparatus are
so interwoven together, that their mutual dependence is very close.
   24.  The foregoing  remarks will be found to have an  important bearing on
the details subsequently to be  given respecting the  functions of the Nervous
system in Man ;  and it is desirable to set out with clear ideas on this subject,
since there is no department of Physiology, regarding which more error is
prevalent.   There is no valid reason for believing that the Organic  functions
in Animals,  any more than the corresponding changes in Plants, are depend-
ent on the nervous system for their performance;   but common observation
shows, that they are much influenced by it in the higher animals ;  and from
such  a comparison  as that which has been just now briefly made, it would
appear that, the higher  the general  development of the nervous system, the
closer is their relation with it.
   25.  This  general character of the Vertebrata harmonises well with what
may be observed, on  a  cursory glance  at the  structure  of their bodies, as to
the proportion between the organs of Nutritive and those  of Animal life.  The
former, contained in the  cavities of the trunk, are highly developed; but, as in
the Mollusca, they are for the most part unsymmetrically disposed.   Of the
latter, the  nervous system and organs of the senses  occupy the head; whilst
the muscles of locomotion are  principally connected with  the extremities:
both are  symmetrical, as in the Articulata;  but, whilst that part of  the nerv-
ous centres, which is the instrument of reason, is very largely developed, the
portion which is specially destined to locomotion, together with the  muscular
system itself, bears much the  same proportion to the whole bulk of the body,
as it  does in the Articulated series.  Hence we observe that the Vertebrata
unite the unsymmetrical  apparatus of nutrition, characteristic of  the Mollusca,
with the symmetrical system  of nerves and muscles  of locomotion,  which is
the prominent characteristic of the Articulata;  both, however, being rendered
subordinate to the great purpose to be attained in their  fabric,—the develop-
ment of an organ, through which intelligence peculiarly manifests itself.  For
the operations of this, a degree of general perfection  is required, which is
not met with elsewhere.   The higher Vertebrata have a power  of constantly
keeping the  temperature of the body up .to a point, which it can only attain
occasionally, and under  peculiar circumstances, in the Articulata, and which
it never reaches in the Mollusca.  This  involves an  energetic performance of
the functions of respiration and circulation ;  and these again require consider-
able activity of digestion.   All the Vertebrata have red blood,  which is pro-
pelled  through the system by a distinct muscular heart;  and the number of
red corpuscles, which any given amount of the fluid contains, bears a nearly
constant  proportion  to the ordinary temperature  of the animal.   They are
further distinguished from Articulata by a character which seems of little im-
portance, but  which is very constant in each group.   Whilst the mouth of the
                                     5* 
54             ON THE PLACE OF MAN IN THE SCALE OF BEING.

latter is furnished with two or three pairs of jaws which open sideways, that
of the former  has never more than one pair of jaws, which  are placed one
above or before the other;  and these jaws are usually armed with teeth, which
are very analogous in their structure to bone.

                     7.  General characters of Fishes.

  26. The  Vertebrata  are  subdivided into classes, principally according to
their mode of performing the functions of respiration and reproduction.  Thus,
Fishes are  at once separated from all other groups, by  the circumstances of
their being  adapted, like the aquatic  Invertebrata, to aerate  their blood by
gills; and being  hence  enabled to inhabit water during their whole lives,
without the necessity of coming to the  surface to breathe.  The low amount
of their respiration prevents their  bodies  from ever attaining a temperature
much above that of the  surrounding medium; hence they are spoken of as
cold-blooded.   Further, they are oviparous ; an ovum or egg being deposited
by the parent,  from which, in due  time, the young makes its  way;  or if, as
sometimes happens, the ovum is retained within the body of the parent until
it is  hatched, the young  animal, though produced alive, is not subsequently
dependent upon  its parent for support.  In many respects, the organization
of Fishes is not much advanced beyond that of the higher Mollusca.  Their
respiratory apparatus  has the same character; and the organs by which the
blood is depurated of its superfluous azote, rather correspond with the  tem-
porary Corpora Wolffiana of higher animals,  than with their true  Kidneys
(Chap. XV. 3).  The vertebral column itself is often very imperfectly deve-
loped ; in a large proportion of the group, the skeleton is cartilaginous only;
and in the lowest species, it does not even manifest a trace of division into
vertebrae.   Living habitually in an element, which is nearly of the same speci-
fic gravity with their own bodies, Fishes have no weight to support, and have
only to  propel themselves  through the water.  Accordingly  we find their
structure adapted  rather for great freedom of motion, than for firmness and
solidity;  and as progressive motion is chiefly effected by the lateral action of
the spine, the vertebrae are so united, as to move very readily upon one  ano-
ther.   Instead of being articulated together by surfaces nearly  flat, as  in
Mammalia, or by ball-and-socket joints, as in Serpents, they have both their
surfaces concave : and these glide over a bag of fluid  (the representative of the
intervertebral substance  in the higher animals), which is interposed between
each pair.   The  tail is flattened vertically; so as, by its lateral  stroke, to pro-
pel the Fish through the water.   By this character, true Fishes are distin-
guished from those aquatic Mammalia, which are  adapted to inhabit their
element, and which commonly receive  the same  designation;  for the latter,
being air-breathing  Animals, are obliged to come frequently to the surface to
respire; and their tail is flattened horizontally, to enable  them to do this with
facility.   The lateral surface of the body of Fish is further extended above, by
the projection of the dorsal fin, which is supported on the spinous processes of
the vertebrae; and below, by the abdominal fin, which  also is  placed on  the
median line; these will, of course, increase the power of the lateral stroke of
the  body, and can only  be moved with  the  spine.   The pectoral and ventral
fins, on the other hand,—the former of which  answer to the superior extre-
mities, and the  latter to the inferior  extremities, of Man,—serve, by their in-
dependent movements, rather as steering than as propelling organs; and they
also assist in raising  and  depressing  the  animal  through the water.   The
scales with which the bodies of all Fishes  are covered, are frequently of  a
bony hardness, and sometimes form  a firmly-jointed casing,  in  which  the
trunk is completely inclosed;  this is especially the  case, when the  internal 
GENERAL CHARACTERS OF REPTILES.
55
skeleton is  imperfectly developed ;  so that here we have an approach  to the
character of the Invertebrata.
  27.  The  swimming-bladder, as it is commonly termed, of the Fish,  is not
an organ sui generis ; but is ascertained, by comparison with the pulmonary
sacs of the lower Reptiles, to be a rudimentary lung.  It does  not, however,
give any assistance  in the aeration of the blood,  except in a few instances;
but seems to be in general subservient to the  elevation and depression  of the
body in its  element.   The heart of  the  Fish  is extremely simple in its con-
struction, containing two cavities only;  and the course  of  the circulation  is
equally simple.  The blood  which returns from the  body in a venous  condi-
tion, is received into the single auricle or  recipient cavity; and  from  this  it
passes into the ventricle or propellent cavity.   The latter forces it into a large
trunk, which  subdivides  into branches  that  are distributed to the  branchial
arches on each side; and in these it undergoes  aeration.   Being  collected
from the gills by returning vessels, the blood,  now become arterial in its cha-
racter, is transmitted to the large systemic trunk, the aorta, by which it is dis-
tributed through the system,—returning  again to the heart, when it has passed
through  the organs and tissues of the body.   Hence it is evident  that the
whole of the blood passes through the gills, before it goes a second time to the
system;  by which the imperfection of the aerating process itself is in some
degree  compensated.  There is  a  special provision, too,  for renewing by
muscular power the stratum of water in  contact with the gills ; continual cur-
rents being  sent over them from the pharynx, with  which their cavity com-
municates.   It is worth noticing, that whilst,  in the Osseous Fishes, there  is
a single  large external-gill opening on either   side, with a  valve-like opercu-
lum or gill-cover, there are, in the Cartilaginous Fishes, several slits on each
side of the neck, one corresponding with each branchial arch.   Similar aper-
tures in the neck maybe seen in the embryo of Man and of other Mammalia,
as well as of Birds and Reptiles, at the time that the circulation is in the con-
dition of that of the Fish,—the  heart possessing only two cavities, and the
blood being first propelled through a series of branchial  arches.

                    8. General characters of Reptiles.

  28.  The class  of Reptiles  is oviparous  and cold-blooded,  like that of
Fishes;  but the  animals belonging to it  are  formed to breathe air, and to
inhabit the surface  of the earth,—the  few which  are  adapted  to make the
water  their dwelling, being  obliged to come  to the  surface to breathe.  Al-
though they breathe air, however, their respiration is not usually so energetic
as that of Fishes, and their  general  activity is much less.  The  mechanism
for  the  inflation of their lungs is very imperfect.   Being destitute  of  a dia-
phragm, they are obliged  to force air into the chest, by a process resembling
deglutition  or swallowing; so that, strange as  it may seem, a Reptile may be
suffocated by holding its  mouth open.  The   heart possesses  three cavities,
one of which receives the blood from the lungs, and another from the general
system; the arterial and the venous blood, contained in these  two auricles
respectively, are transmitted  to  the  third  or propelling  cavity, the  ventricle,
where they are mixed;  and the half-arterialised  fluid is then  transmitted to
the system at large,  a part being sent  to the lungs.   Thus only  a portion of
the blood expelled from the heart is  exposed to the influence of the air; and
that which is transmitted to the body is very imperfectly arterialised.   In
some of the  higher Reptiles, as the Crocodile, the ventricle is double, as in
the superior Vertebrata; and  the course  of the circulation is so arranged, that
pure arterial blood shall  go to the head, where it is  most required, whilst  a
mixed fluid is  sent to the rest of the body.   This plan  exactly corresponds 
56             ON THE PLACE OF MAN IN THE SCALE OF BEING.

with the one, which is adopted in the circulation of the Human fcetus, from
the time of the formation of the four cavities  in its heart, and of the perma-
nent system of vessels, up to the period of birth.   The imperfect arterialisa-
tion of  the blood in Reptiles, causes a great degree of general inertness  in
their  functions.  Their  motions are principally confined  to  crawling and
swimming; their general habits are sluggish, and their sensations are obtuse;
and their nutritive functions  are  very  slowly performed.  Hence they can
exist  for a long  time, with a very feeble exercise  of these functions, under
circumstances that would be fatal  to animals, in which  they are performed
with greater  activity.  In  cold  and  temperate climes, they pass  the  whole
winter in a state of torpidity; and at other seasons, they may be kept during
a long time from  their due supplies of food and air, without appearing to suf-
fer  much inconvenience.
  29. In regard to the structure of their  skeleton, and the external form  of
the body, there  is a considerable variation among the several orders of Reptiles.
Thus, Tortoises, Lizards, and Serpents, differ from each  other  so widely,
that a common  observer would separate them completely;  and yet they not
only agree in all the foregoing characters, but pass  into one another by links
of transition so  gradual, that it is  even difficult to classify them.  They differ,
however, more  in the configuration of the accessory parts, than in the struc-
ture of  the essential portion of the  skeleton,—the  spinal column.  This  is
characterised by the ball-and-socket articulation of the vertebrae, each vertebra
having one surface convex and the other concave,—a structure which is more
strongly marked in Serpents, whose movements are performed  chiefly by the
flexion of the spinal column itself, than it is  in the other tribes.  The chief
characteristic of the Tortoise tribe, is the shell or case in which the body  is
contained.  The  upper arch of this  shell, termed the carapace, is  formed by
a bony expansion from the edges of the  ribs, which is  covered  by a set  of
horny plates, that are  to be regarded  (like smaller scales) as  epidermic appen-
dages.  The under portion, termed the plastron, is composed of the sternum,
which is in like manner extended laterally.  In the Land-tortoises, this usu-
ally forms a complete floor; but in the  aquatic species, a part is  commonly
absent, the interval being filled up by cartilage and membrane.  The skeleton
of the Lizards is formed more  upon the general plan of that of Mammalia,
but may be readily distinguished from it.   The sternum is usually prolonged
over the front of the  abdomen, and  the ribs are continued  through a much
larger part of the  spinal column; of these abdominal ribs, the white  lines
across the recti muscles in the higher Vertebrata, are evidently the rudiments.
In the higher Lizards, the power of locomotion is  almost entirely .delegated
to the extremities ; but in the less typical species, the  body and tail are much
prolonged, so as to present a serpentiform aspect;  and first one pair of feet,
and then the other, disappear, until the form is altogether that of the Serpent.
Even in  Serpents, however, rudiments of extremities are  frequently to be
found;  but their  mode of progression is very different, and these rudiments
are  of no assistance to them.  The most remarkable feature in the Serpent's
skeleton, besides  the absence of legs, and the large number of ribs and verte-
brae, is the deficiency of a sternum; through the absence of  this, the extremi-
ties of the ribs  are free, and they become in fact the fixed  points, on which
the  animal crawls, when advancing slowly forwards, in a manner which  bears
a strong resemblance to the progression of  the Centipede.
  30. Although the configuration of the cranium varies much in the different
orders of Reptiles, yet there is  a remarkable agreement in certain general cha-
racters,  and  in  the general degree of development.   It consists of  a  much
larger number of parts, than are  to be found in the cranium  of  adult Birds  or
Mammalia ; each principal bone being subdivided, as it were, into smaller ones. 
GENERAL CHARACTERS OF REPTILES.
57
This condition exactly corresponds with that, which may be observed during
the process of  ossification in higher Vertebrata;  for each of the larger bones
of the cranium is formed from several centres of ossification; so that, if  the
cranium of a fcetus or young infant be macerated, it will fall into a number of
pieces nearly corresponding with those  of the Reptile's skull.  The different
orders of Reptiles have a close agreement in various other points ; especially
in the  degree of development of  their several organs of nutrition.   Thus, in
all of them, the lungs, though commonly of large size, are  so  little subdivided,
as really to expose but a small extent of surface.   The glandular structures,
too, are formed upon a much more simple type, than is characteristic of  the
warm-blooded  Vertebrata.   They  all agree, moreover, in having  the body
covered with scales; which, though generally small, are sometimes large flat-
tened plates.
  31.  Between Fishes and  true Reptiles, there  is  a group that remarkably
combines  the characters of both;  being composed  of animals  which come
forth from the egg in the condition of Fishes, but which  afterwards attain a
form  and  structure closely corresponding with that of true  Reptiles.  This
group, consisting of  the Frog and its allies, is sometimes  associated  as an or-
der (Batrachia) of the class of Reptiles ; though it should probably take rank
as a distinct  class, the Amphibia.   The  Tadpole or  larva of the Frog is in
every essential respect a Fish.  Its respiration and circulation, its  digestion
and nutrition, its locomotion and  sensation, are entirely accordant with those
of Fishes.  The body is  destitute of members for progression, but is propelled
through the water by the lateral  undulations of the spinal column, which is
articulated in the same manner as that of Fishes.  At a certain period, a me-
tamorphosis  commences  in which almost every organ in the  body undergoes
an essential change.   Lungs are developed,  which take the  place (in regard
to their function) of the  gills ; and the  latter are atrophied.  The  auricle of
the heart is divided into  two; and the circulation is performed on the plan of
that of the true Reptile.  Two pairs of members are usually formed, to which,
when they are fully developed, the power of progression  is  committed,—the
tail disappearing; in some species, however, the  tail  remains, and  the extre-
mities are small.  The digestive system undergoes a remarkable alteration ;
the intestinal canal, whfch was previously of enormous length  in  proportion
to the  body,  being now considerably shortened, in accordance with the differ-
ent kind of food on which the animal has to subsist.  The  mode  of articu-
lation of the spinal column also, undergoes  a change, which brings it to the
type of that  of Reptiles.  The most obvious point of difference in external
characters, between the higher Amphibia and true Reptiles, is the absence of
scales  or plates on the skin of the former. In this manner, the common Sala-
mander or Water-Newt may be  recognised as belonging to the  Batrachia
though its form would otherwise  lead us to  place it among the  Lizards; and
the Coscilia, which has the form of the  Serpent, is in like manner  known to
be really allied to the Frog.   An acquaintance with the history of these ani-
mals confirms such an arrangement, by  showing that  the Salamander and  the
Ccecilia undergo a metamorphosis ; breathing by gills, and having the general
structure of  Fishes, in the early part of  their lives.
  32.  Besides those animals, however,  which attain the condition of perfect
Reptiles, this  group contains several, whose development is arrested, as it
were, in an intermediate  or transition state ;  their adult form presenting a re-
markable mixture of the  characters of the two classes, which they  thus con-
nect.   This is the case in the Proteus, Siren, and other less known species,
which retain their gills through the whole of their lives, whilst their lungs are
at the same  time developed;  so that, as they can respire in either air  or wa-
ter, they are the only true amphibious animals. In their general organization, 
58
ON THE PLACE OF MAN IN THE SCALE OF BEING.
they correspond with the Tadpole of the Frog at  an advanced period of its
metamorphosis ; and it is a most interesting fact (which has  been established
by the experiments of Dr. W. F. Edwards) that, if Tadpoles be kept in such
a manner, as to be amply supplied with food,  and  exposed  to  a constantly-
renewed current of water, but be secluded from light  and from  the direct in-
fluence of the solar heat, they will continue to grow as Tadpoles ;  their me-
tamorphosis being  checked.   The  metamorphosis of the Batrachia  closely
corresponds with that of Insects ; the young animal, in each  case, at the time
of its emersion from the egg, having a resemblance, in  all essential particulars,
to a class below that to which it is ultimately to belong.  This kind of meta-
morphosis is by no means confined to them, however; for the gradual exten-
sion  of our knowledge  of the early history of  the  different tribes  of animals,
is constantly bringing to light new facts of the same kind.  The Polypes and
lower Mollusca, for instance, come forth from the egg, and swim about for
some time, in  a condition which can scarcely be termed animal;  for there is
not even a mouth leading to  a digestive cavity ; nor are  there any other or-
gans of locomotion than the cilia, the  action of which is involuntary.  And,
in tracing the development of the Human embryo, we shall find that it under-
goes a series of progressive changes equally remarkable;—the principal differ-
ence being, that these  changes are not so arranged  in harmony with  each
other, as to cause the embryo to present, at any one time, the combination of
characters which belong to the Fish, Reptile, &c, or to enable it to sustain an
independent existence.


                    9.  General characters of Birds.

  33. From Reptiles to Birds, the transition would seem rather abrupt; since
the latter class is, in almost every respect, the opposite of the former.   Never-
theless,  it would  seem  to have  been effected by  the now-extinct Pterodac-
tylus, which combined, in  a most remarkable degree, the characters of the
two groups.   Birds are, like  Fishes and Reptiles, oviparous Vertebrata ; but
they differ essentially from both, in being warm-blooded, and in affording as-
sistance by their own heat in the development of the ovum. Birds correspond
with Mammalia, in possessing a heart with four cavities, and a complete dou-
ble circulation ; by which the whole of the blood that has circulated through
the body, is exposed to the influence of the air before  being again  transmitted
to the system.  This high amount of oxygenation  of  the  blood is accompa-
nied  by great activity and energy of all  the organic  functions, acuteness of the
senses, and rapid and powerful locomotion ; as well as by the evolution of a
degree of heat, superior to that which we  ordinarily meet  with  among the
Mammalia.  The temperature of Birds ranges  from about 104° to  112°.  The
lowest is in  the aquatic species, whose general activity is much less than  that
of the tribes which spend most of their time in the air;  the highest is  among
those distinguished for  the  rapidity and energy of their flight, such  as  the
Swallow.
  34. Birds  have been denominated, and not inappropriately, the Insects of
the  Vertebrated series; as  in the  animals  of that class, we find the whole
structure peculiarly adapted to motion, not in water,  nor upon solid ground,
but  in the  elastic and  yielding air.   It is impossible to conceive any more
beautiful series of adaptations of structure to  conditions of existence  than
that  which is exhibited in the conformation of the  Bird, with reference to its
intended mode of life.   In  order to adapt the  Vertebrated animal  to its aerial
residence, its body must be rendered of as low specific gravity as possible.
It is  further necessary that the surface should be capable of being greatly ex-
tended ; and  this by some kind of appendage that should be extremely light, 
GENERAL CHARACTERS OF BIRDS.                    59
arid  at the  same time possessed of considerable resistance.  The degree of
muscular  power  required  for support and propulsion in the air, involves the
necessity  of a very high  amount of respiration (§ 275), for which  it has been
seen that an  express provision exists in Insects;  and as the general  activity
of the vital processes depends greatly upon the high temperature,  which this
energetic  respiration keeps up, a provision  is required for keeping in this heat,
and  not allowing it  to be carried away by the atmosphere, through which the
Bird is rapidly flying.
   35. The  first  and third of these objects,—the lightening of the body, and
the  extension of the respiratory surface,—are beautifully fulfilled  in a mode,
which will be found to correspond with the plan adopted for the same purpose
in Insects.   The air which enters the body, is not restricted to a single pair
of air-sacs or lungs placed near  the throat; but is  transmitted from  the true
lungs, to  a  series of large  air-cells, disposed in the abdomen and in various
other parts of the body.   Even the interior of the bones is made subservient
to the same purpose; being hollow, and lined with a delicate membrane, over
which the blood-vessels are minutely distributed.  In this manner, the respi-
ratory surface is greatly extended; whilst, by the large quantity of air  intro-
duced into the mass, its specific gravity is  diminished.   The subservience of
the  cavities in the bones  to the respiratory function, is curiously shown by
the  fact, which has been ascertained both accidentally and by a designed ex-
periment, that, if the trachea of a Bird be  tied, and an aperture  be made in
one of the long bones, it will respire through this.
   36. The other two objects,—the extension of the surface, and the retention
of the heat within the body,—are also accomplished in combination, by a most
beautiful  and refined contrivance, the covering of feathers.  Like  hair  or
scales, feathers  are to be  regarded as appendages  to  the cutis;  the stem is
formed  from  it by an apparatus, which  may be  likened to a hair-bulb on a
very large scale ; but there are some additional parts for the production of. the
laminae, which form the vane of the feather, and which are joined  to the stem
during its development.  These laminae, when perfectly formed, are connected
by minute barbs at their  edges, which hook into one another, and thus give
the necessary means of resistance to the air.  The substance of which feathers
consists,  is a very bad conductor of heat;  and when they are lying one  over
the other, small quantities of air are included, which still further obstruct  its
transmission by their non-conducting power.  Thus the two chief objects are
fulfilled;—power of resistance and slow-conducting properties being obtained,
in combination  with lightness and elasticity.  At  the two extremes of the
class, however, we  meet  with remarkable modifications in the typical structure
of feathers.   In  the Penguin, those  which  cover  the surface  of the wings
have a strong resemblance to scales ;  and the wings are not employed to raise
this Bird  in the air, but only to propel it through water (as fins would do) by
their action on the liquid.   On the other hand, in the Ostrich  tribe,  the laminae
of the feathers  are separated from each other, so as no longer to form a con-
tinuous surface; the feathers  more resembling branching hairs.   Here the
wings are almost or completely absent; the birds of  this tribe being constantly
upon the ground, propelling themselves  by running,  and  approaching the
Mammalia in many points of their conformation.
   37.  The bony frame-work of Birds presents many remarkable  adaptations
to the same purposes.   In the first place it is to be remarked, that the faculty
of locomotion is here entirely delegated to the extremities; and that the skele-
ton  of the trunk must be consolidated, in proportion to the power  with which
they are  to be  endowed, in order to afford their muscles a firm  attachment
(§ 22).    Just as the segments of the external skeleton  of the  Articulata,
therefore, are consolidated  in Insects, do we find  that the vertebral column 
60
ON THE PLACE OF MAN IN THE SCALE OF BEING.
and its appendages are firmly knit together, in the upper part of the trunk of
Birds.   The vertebrae are closely united to each other; and the ribs are con-
nected with  the  sternum by bony prolongations  of the latter, instead of by
cartilages.   This union  is so arranged, that the state of expansion is  natural
to the thorax, whilst that of contraction is  forced.   The diaphragm is absent
among birds, as among Reptiles ;  except in a few species, which most nearly
approach the Mammalia.  But its deficiency is compensated by this contriv-
ance, which keeps the lungs  and air-sacs always full,—except when the Bird
by a muscular effort,  expels  the air from them, in order that they  may be re-
filled by a fresh supply.  By this means, also, the specific gravity of  the body is
more constantly kept down, than  it  could have been, if the lungs had been
subjected to the constantly-alternating contractions and expansions,  which they
perform  in Mammalia.   It is worthy  of remark, that the air which enters the
bones and the air-sacs, passes through the lungs, both  on its entrance  and
return; so as to yield to their capillaries all the oxygen which they can take
from it,  and  of which  the blood  that it has elsewhere met with  has  not de-
prived it.  It is only  in the lungs,  that it meets with purely venous blood; for
they alone receive the branches of the pulmonary artery; the vessels which
are distributed upon  the respiratory  surface of the  air-sacs and bones, being
a  part of the systematic circulating  apparatus.   Hence  we may regard this
curious provision, as  being partly designed for the aeration of the  blood in its
course through the system (this, it will be  remembered, being the  sole mode
in  which the function is performed in Insects), and partly for supplying the
lungs with air, as from a reservoir, during the violent actions of flight.
   38. The articulation of the  anterior extremity with the trunk exhibits  a
peculiar provision for strength and power, which we find in no other Verte-
brata.  The  two clavicles are united  together on the central line, forming the
furcula or merry-thought; and the use of  this is to  keep the shoulders apart,
notwithstanding the  opposing force exerted by the pectoral  muscles in the
action of flight.  It is generally firm, and  its angle open, in proportion to the
power of  the wings.   Besides  this  bone, there is another connecting the
sternum with the scapula on each  side ; this is the coracoid bone, which in
Man and most other Mammalia is scarcely developed, being merely a short pro-
cess which does not reach the sternum.   The  sternum of Birds  usually ex-
hibits a very remarkale development on the median line ;  an elevated  keel or
ridge being seen on it, which serves for the attachment of the powerful mus-
cles that depress  the  wings.   In the great  development of the sternum, Birds
have some analogy with the  Turtle tribe :  which they also resemble in the
deficiency of teeth, and  in the development of a horny covering to the jaws:
but in these, the lateral elements of the sternum are  the parts most developed;
whilst in Birds it is the  central portion which exhibits the peculiarity.  From
the depth of the keel of the sternum,  a judgment may  be  formed of the thick-
ness  of the pectoral muscles, and thence of the powers of flight ;  in the Os-
trich tribe, where  the wings  are not sufficiently developed to  raise the  bird
off the ground, the sternum is quite flat, as in the Mammalia.   The want of
flexibility in the trunk is counterbalanced by the length and flexibility of the
neck ; the number of cervical vertebrae is very considerable, varyino- from 12
to 23,—the highest number being present in the  Swan  tribe.   They are so
articulated that the head can be turned  completely round, or moved  in any
direction.  The  anterior extremities of Birds being solely adapted to sustain
them in  flight, the posterior are necessarily modified for their  support  on the
ground.   They are usually placed  rather far back; but the spine has a posi-
tion  more inclined than horizontal, so that the weight may not be altogether
thrown forwards.  The trunk is supported  on the thighs by powerful muscles;
and there is  another  series, which  passes  from the lower part of the spine 
GENERAL CHARACTERS OF BIRDS.
61
continuously to the toes, turning  over the knee and heel, in such a  manner
that the flexion of these joints shall tighten the tendons ; by this contrivance,
the simple weight of the body flexes the toes; and Birds are thus enabled to
maintain their position, by grasping  their  perch,  during  sleep, without any
active muscular effort.
   39.  Not only  do Birds resemble  Insects  in  their general structure and
mode of life, but also  in the peculiar development of the instinctive  powers.
Under the direction of these, the  place for their nests appears to be selected ;
their materials collected ;  the nest themselves built, and the young reared in
them ; the migrations  are  performed ; and many curious  stratagems  are em-
ployed to  obtain food.  It is sufficient to  indicate these in  general terms;
since it is well known that the habits of Birds have peculiarities restricted to
each species ; and that in all the  individuals  of each species ;  they are as
precisely  alike as their circumstances will admit.  Nevertheless, there are ob-
served in Birds a degree and kind of adaptation to varying conditions, which
Insects do not possess, and which  display an amount of intelligence far su-
perior  to what is found in  that class (§ 17).  This is evinced also in their edu-
cability;  for no animal can be  taught to  perform  actions  which  are  not
natural to it, unless it possesses in a considerable degree the powers of memory
and association, at least, if not some of the higher mental faculties,  such as
the power of perceiving  and comparing the relations of ideas.  Moreover,
in  the  domesticability of many tribes of Birds, we see this educability com-
bined with a degree of that higher form of attachment to Man, which is so
strikingly exhibited by certain  species  of  Mammalia.  The development of
the senses of Birds varies in different tribes, according to the mode in which
they are adapted to obtain their prey.  The sight is almost always extremely
acute,  and is their chief means of seeking food ;  and  where this would be of
comparatively little service, as  in the nocturnal rapacious  birds, it is compen-
sated by a much higher development of the faculty of hearing, than  is com-
mon  amongst other tribes.  The  senses  of smell, taste, and touch, do not
seem to be usually very acute  in Birds ; but  there  are  particular tribes, in
which each of these is more developed than in the rest.
   40.  As  might  be expected from  the analogy of Birds with Insects, the de-
velopment of their organs of nutrition (excepting that of the respiratory organs)
is much less striking  than is that of the locomotive  apparatus.   The whole
cavity  of the trunk,  especially  in Birds  distinguished for  their powers of
flight,  is small in comparison with that of the body;  but what is  wanting in
the size of the organs, is made up in their energy of function.   Hence the
demand for food is more  active  in them than in any other class  of  animals.
It  is  interesting  to observe, that there is  more  bi-lateral symmetry in the
arrangement of the viscera, than  we usually find in the class above.  This is
evidently connected with their active locomotive  powers ; as  it is obviously
necessary, that the two sides  of the body should be balanced with perfect
equality,  and that their energy should be exactly correspondent.   The lungs
and air-sacs  are precisely  similar in size and situation on the two  sides ; con-
sequently the heart is  placed on the  median line ; and  the mode of origin,
from the aorta, of the trunks supplying the head and upper  extremities, is
alike on the two sides.  The liver, also, is  less asymmetrical than we usually
find it in the Mammalia.
   41.  It  has been remarked,  that the assistance afforded by the  parent, in
the development of the young,  is greater in  Birds  than  in the lower Verte-
brata ;  but is less than in  Mammalia. Whilst Reptiles and Fishes show little
or no concern for their eggs after they have deposited them, Birds sedulously
tend them, affording them not only protection  but warmth, by means of their
powerful heat-producing apparatus.  The yolk-bag of the Bird's  egg is so
     6 
62            ON THE PLACE OF MAN IN THE SCALE OF BEING.

suspended in the midst of the white albumen, that, when the egg is laid upon
its side, it will always rise to the highest part of it;  and the relative weight
of the several parts is further adjusted in such a manner, that the cicatricula
or germ-spot shall always be at the point nearest the  shell, so as to come into
the closest proximity with the source of  heat, and also to be in the most im-
mediate relation with the surrounding air.  There are some Birds, inhabiting
the equatorial region, which do not always incubate their eggs, trusting to the
solar heat for their maturation.  It is said that the Ostriches of the  intertro-
pical deserts  are content with  covering their eggs with a thin layer  of sand,
so as  to admit the action of the sun by  day, and to keep  them warm at night;
but that those living under a  less  constantly elevated  temperature, sit upon
their eggs—if not constantly, at any rate when the solar heat is not sufficient.
This statement has  been  disputed; but its truth seems to be confirmed by a
curious  observation made by Mr. Knight, that a Fly-catcher, which built for
several years in one of his hot-houses, sat upon  its eggs when the temperature
was below  72°, but left them when it rose above that standard.  Certain Birds
inhabiting New Holland, deposit their  eggs in a sort  of hot-bed, composed of
decaying vegetable matter; a number associating together for the construction
of this  artificial incubating apparatus,  although they live separately at other
times.  The degree of assistance afforded by the parent Birds to their young,
after their emersion from the shell, varies much in different tribes ; in general
it may be remarked, however, that it is most prolonged in  those which ulti-
mately attain the highest development, and especially in those whose intelli-
gence becomes  the  greatest.   Thus the Chicken and the Duckling, when just
hatched, are  able to shift for themselves; but among the Raptorial and Inses-
sorial Birds, which rank far higher in the scale, the young is for a long time de-
pendent upon the parent for food ; and in the Parrot tribe, which  unquestion-
ably surpasses all others in intelligence, the parent not only supplies its young
with food which it has  obtained for  them, but partly nourishes them by  a
milky secretion from the interior of the craw;  impregnating  with this the
aliment which it swallows, and which it  afterwards disgorges for its offspring.


                  10. General characters of Mammalia.

   42. The Mammalia are universally regarded as  the highest group in the
Animal kingdom;  not only from being that to  which Man belongs (so far, at
least, as his bodily  structure  is  concerned), but also as  possessing  the most
complex organization, adapted to perform the greatest number and variety of
actions, and  to execute these with the  greatest  intelligence.  The contrast is
here extremely strong between  the reasoning and  the instinctive powers;
even  when we  put Man  out of view.   When  we compare, for example, the
sagacity of a Dog, Monkey, or Elephant, and the  great  variety of circum-
stances in which they will display an intelligent adaptation of means to ends,
with  the limited operations of Insects, over which the judgment and will seem
to have no  control, we cannot help being  struck with the difference.   The
former  are educable in the highest degree next to Man;  the latter could not
be made to change  their  habits, in any essential degree, by the most prolonged
course  of discipline.   Man is actuated, like the lower animals, by instinctive
propensities, which have an immediate bearing  on his corporeal wants; whilst
 they have, like him, the power of adapting their actions to gain certain ends,
 of which they are  conscious.  A Dog or an Elephant may show more real
 wisdom, in controlling for a  time its instinctive propensities, from the desire
 to accomplish  some particular  object, than is  displayed by many Men, who
 give  free scope to the exercise of their sensual passions, although warned by
 their reason of the injurious consequences of such indulgence. 
GENERAL CHARACTERS OF MAMMALIA.
63
   43.  This high development  of the  intelligence in Mammalia, is evidently
 connected with the greatly-prolonged  connection between the parent and the
 offspring, which we find to be a characteristic of this class.  Mammalia are,
 like  Birds, warm-blooded Vertebrata, possessing a complete double circula-
 tion ; and some of them are adapted to lead the life of Birds, passing a large
 part  of their time in darting through  the  air  on wings, in pursuit  of  Insect
 prey.  But  they differ  from  Birds in this  essential  particular, that they are
 not  oviparous, but viviparous;  producing  their  young alive,—that is, in  a
 condition in which they Can perform spontaneous movements, and can appro-
 priate nourishment supplied to  them from without.  But they are not distin-
 guished from all other animals by this character alone;  for  there  are some
 species among Reptiles, Fishes, and even Insects, which produce their young
 alive,—the egg being retained within  the  oviduct and hatched there.   The
 real distinction lies partly in that, which the name  of the class imports,—the
 subsequent nourishment of the  young by suckling;  and partly in  the mode
 in which the  embryo is nourished before its birth.  In Mamniels, the  yolk-
 bag is very small in proportion to its size  in Birds;  and the  contents  of the
 ovum,  instead of furnishing (as in that class) the materials necessary for the
 development  of  the young animal, up to the time when it can ingest food for
 itself, only serve for the  earliest  set of changes in which this process con-
 sists.  In the latter stages of  the evolution  of  the embryo, it is supplied with
 nutriment directly imbibed from  its parent.   This is at first  accomplished
 by means of  a series of root-like tufts, which  are prolonged from the surface
 of  the  ovum, and insinuate themselves among the  maternal vessels, without,
 however, uniting with them.   These  tufts absorb, from the  maternal  fluid,
 the ingredients necessary for the  support  of  the  embryo; and also convey
 back to the parent its effete particles, which are received back into her blood,
 and are then  cast out of her system, by the process of secretion, respiration,
 &c.
   44.  The Mammalia may be divided  into two sub-classes; in  one of which
 the structure  just described is  the greatest advance ever made, in  the  appa-
 ratus by which the foetus is nourished ;  whilst in  the  other  a more concen-
 trated form is subsequently assumed by it.   The ovum of the latter is delayed
 for a longer  period,  in  a cavity formed by the union of the two  oviducts,
 termed  the uterus; which can be scarcely said to be developed in the Marsu-
 pialia and Monotremata, the two orders constituting the first sub-class.   The
 vascular tufts  proceeding from the  chorion become especially developed at one
 point, and the vessels of the uterus are  extremely enlarged in a corresponding
 situation; the tufts  dip down, as it were, into a chamber formed by an exten-
 sion of  the inner lining of these vessels, and serve the  combined purpose of
 the roots of plants  and of the branchiae of aquatic  animals,—absorbing from
 the maternal blood the materials required for the nourishment  of the embryo,
 and aerating the blood of the foetus, by  exposing it  to the  influence of that of
 the parent.  The peculiar organ thus formed is termed the placenta; and the
 two sub-classes of  the Mammalia  have thence received the  appellations of
placental and  non-placental.  The animals belonging to  the latter present
 many points  of affinity  to Birds,  in the structure of their internal organs.
 That of the brain is very nearly allied in these two groups; and their amount
 of intelligence seems, as  far as can be determined, to bear a  close correspond-
 ence.   The Ornithorhyncus in  particular,  has  so many marks of alliance to
 oviparous animals, and its osteology, as well as in  its horny  bill and in less
 important particulars, that  Naturalists  have much  debated  whether it could
 really be termed a Mammiferous animal.  No positive evidence  has  yet been
 obtained that its young are born alive; but on the other hand, there is a strong
 reason to believe  that they come into the world uninclosed in the ovum, al- 
64
ON THE PLACE OF MAN IN THE SCALE OF BEING.
though  in  a very imperfect condition.  Moreover, it  has been satisfactorily
ascertained that  the young are nourished, for some time after their birth, by
a mammary secretion, which the  organization of their  mouth at that period
enables  them  to  obtain  from  the  parent.  In  the  Marsupialia,  there  is a
remarkable compensation for the abrupt termination of the period of uterine
gestation,—the young being received into a pouch or marsupium, within which
the nipple is situated ; this  is extremely prolonged, and the mouth of the foetus
(for so the  being must still  be regarded) is adapted to  receive and hold on by
it; so that  the little  creature, which looks at first more like an earth-worm
than a Mammiferous animal, is  thus suspended within the protective pouch,
until its development is so  far advanced, that it can shift for itself in the same
degree as other new-born animals can do.
  45. The period of gestation in the higher sub-class  of Mammalia, is usually
prolonged,  until the foetus is able, on its entrance into the world,  to execute
regular movements;  some of these being merely indicative of its desire for
food, and others evidently designed for the acquirement of it. In many species,
the young animal seems to  be from the  first in the full possession of its senses,
and has considerable power of  active locomotion; in general, however, it is
very dependent upon its  parent;  only being able to obtain food when this is
placed within its immediate grasp.  Such is the case with the Human infant,
which is closely dependent upon  its  parent, during a larger proportion  of its
existence, than is the young of  any other animal.  Here again, therefore, we
perceive the  application of the  general law, that, the  higher the grade of
development a being is ultimately to  assume, the  more does  it require  to be
assisted during the early stages  of its progress.  In the case of Man, the  pro-
longation of this period has a most important and  evident influence upon the
social condition of the race; being, in fact, one of the chief means, by which
the solitary are bound together in families.
  46. The class Mammalia, taken as  a whole, is not characterized so much
by the possession of any one particular faculty,—like  that which has  been
seen in  Birds,—as by the perfect  combination of the  different powers, which
renders  the animals belonging to  it susceptible of a  much greater variety of
actions,  than any others can perform.   There are  none that can compete with
Birds in acuteness of sight;  but there are few that do not possess  the senses
of smell, taste, and touch in a more elevated degree.   There  are none which
can rival Birds in rapidity of locomotion ; but there are few which cannot per-
form several kinds  of progression.   Several of their movements require  a
considerable amount of flexibility in the spine;  hence the vertebral column,
and the  bony framework of the trunk, are never so much consolidated as they
are in Birds.   On  the other hand, the neck is much less movable; it never
consists of more  than seven vertebrae, and these are always  present; so that
they are sometimes  of great length, as  in  the  Giraffe,  and  sometimes ex-
tremely short, as in the Whale, which seems to  have no neck at all.  In the
greatest number of Mammalia, the body is supported upon all the four  extre-
mities, as in Reptiles ;  being adapted for progression along the surface of the
earth.   There are some species, however, in which the typical structure has
undergone  a metamorphosis, by which it is made to resemble that  of a Bird;
whilst in others it is modified, so  as to conform to the character of the Fish.
In the Bats, the  power of  motion is almost entirely delegated to  the wings,
which are composed of skin, stretched over a bony framework formed of the
widely-extended hand; and the sternum has a projecting keel for  the attach-
ment of the pectoral muscles, as in Birds.  And in the Whale tribe, the power
of locomotion is  almost completely taken from  the extremities,  and  given
back to  the trunk, as in Fishes ; for  the posterior extremities are entirely ab-
sent, and the anterior serve only for  guidance:  there is this important differ- 
CHIEF SUB-DIVISIONS OF MAMMALIA.
65
ence, however, that the tail, which is flattened vertically in Fishes, is flattened
horizontally in the Cetacea, which require the power of frequently coming to
the surface to breathe.
   47.  The  inferior energy of musculan movement in the Mammalia, is ac-
companied by an inferior amount of respiration; the type of the  respiratory
apparatus, however, is higher than in  Birds, a large extent of surface being
comprised within  a smaller space.  The lungs are confined to the cavity of
the thorax; and there is  a provision for the regular renewal of the air received
into them, by the action  of  the diaphragm, which here completely separates
that cavity from the abdomen.  The diminished amount of respiration, again,
involves the production of a lower degree of  animal heat; so that  the tempe-
rature of this class seldom  rises  above  104°.   There is, therefore, less need
of means for effectually confining the caloric,—especially, too, as their greater
average  size causes  their radiating surface to be much less, in proportion to
their bulk, than is that of Birds ; and accordingly, we  find  them provided
only with a  covering of hair or fur, which  is  much less warm than that of
feathers, and which is thin and scanty in Mammals inhabiting tropical climates.
The chief exception to the  last rule is in the case of  the Sloths and  of some
Monkeys, which inhabit situations exposed to the most powerful rays of the
sun, and which are covered with a long but thin and coarse hair; the purpose
of this is evidently the  protection of their skin from the  external heat.   The
inferior energy of the respiration and circulation, involves a diminished activity
of the other functions of nutrition, as compared with those of Birds ; and the
demand for food appears to  be somewhat less constant. Their various organs,
however, are developed upon a higher  plan;  as we have already observed in
regard to those of  respiration.

                  11.  Chief Sub-divisions of Mammalia.
   48.  In sub-dividing the truly Viviparous division of the class, so  as to sepa-
rate Man from the tribes with which he is associated in it, we may be advan-
tageously guided, in the  first place, by the conformation  of the extremities;
since upon the  perfection  of the organs of touch, will depend much of the
address of an animal in  executing the  actions to which it is prompted by its
intelligence.   The degree of this perfection is estimated by the number  and
mobility of the fingers, and by the degree  in which their extremities are  en-
veloped by the nail, claw, or hoof, that terminates them.  When  the fingers
are partly absent, or are  consolidated together, and a hoof envelopes all  that
portion which touches the ground, it is obvious that the  sensibility must be
blunted,  whilst, at  the same time, the member becomes incapacitated for  pre-
hension.  The opposite  extreme is where (as in Man) a thin nail covers only
one side of the extremity of the finger, leaving the other possessed of all its
delicacy;—where  several such fingers  exist, of which one can  be  opposed to
the rest,  so as to render  prehension more perfect, and to  perform a great va-
riety of actions :—and where the  plane of the whole hand can be turned in
any position, by the nature of its attachment to  the fore-arm.   Between these
there are many intermediate gradations.  By these characters, the  viviparous
Mammalia may be divided  into  the  Unguiculated, which have separate  fin-
gers, terminated by distinct nails or claws ; and the Ungulated, in which the
fingers are more or less consolidated, and inclosed at their extremity in a hard
hoof.  Hoofed animals  are necessarily Herbivorous, inasmuch as the  con-
formation of their feet precludes the possibility of their seizing a living prey ;
and  they have flat-crowned grinding teeth for  triturating their food.  The
summits of these teeth are  usually not  covered by a  smooth coat of  enamel,
but present a  series of elevations and  depressions;  these are occasioned by
                                    6* 
66
ON THE PLACE OF MAN IN THE SCALE OF BEING.
the peculiar structure of the teeth, which consist of alternating plates of ena-
mel, ivory or dentine, and cementum or crusta petrosa,—substances  of  three
different degrees of hardness ; and, as the softer portions will of course  wear
down first, the  harder remain  as projecting ridges.  In order to give  effect to
these, there is  usually a considerable power of lateral motion possessed by
the lower jaw ;  so that a regular grinding action may be performed, which is
favourable to  the complete reduction of the tough vegetable substances that
serve as their food.
   49. Animals with Unguiculated fingers are capable of more variety in the cha-
racter of their food. In some it is almost exclusively vegetable, as in the Roden-
tia ;  and here the  power of prehension possessed by the extremities is small,
the fore-arm not being so constructed as to be capable of the motions of pro-
nation and supination.  In this  order, the mouth is  remarkably adapted for
grinding down hard vegetable substances ; the molar teeth being furnished with
transverse ridges of enamel; and the jaws having a powerful movement back-
wards and forwards.* In other orders, again, there is an almost exclusive adap-
tation to  animal food.  The  toes  are  furnished with long and sharp claws ;
and the fore-feet may be placed in a variety of positions,  by the  rotation of
the two bones composing the  lower part of  the. leg.  The grinding teeth are
very narrow, and are  formed with sharp points and  edges, so as to be adapted
for dividing animal flesh ; these are firmly set in short strong jaws, which are
fitted together  like the  blades of a pair of  scissors, having no action  but a
vertical one ; and the constant friction of the edges of the molar teeth against
each other, keeps  them sharp.t  In  the Carnivorous group, too, we  find the
greatest development of the canine teeth, which are commonly absent or but
slightly developed among herbivorous quadrupeds; these are instruments of
great power, serving both for the first attack of their  prey, and  for subse-
quently tearing it  in pieces. It is evident that the whole structure of the  body
must undergo modification, in conformity with the  nature of the food.  The
simple  stomach and intestinal canal of the Carnivorous animal, adapted only
to the digestion of aliment consisting of materials similar to those  of its own
body, would be totally useless to  an animal prevented by its general organi-
zation from obtaining any other than vegetable food ; and,  on the other hand,
the teeth and hoofs of the Herbivorous quadruped would be of little assist-
ance to an animal, whose instincts  and general conformation adapted  it for the
pursuit  of animal prey.  It will be  presently seen that, in regard to his or-
ganization, Man holds an intermediate place between the purely Herbivorous
and  the purely Carnivorous  tribes;  being capable of subsisting  exclusively
upon either kind of diet, but  being obviously intended  by Nature to employ
both in  combination.
   50. The classification of the Mammalia by Linnaeus, although  not strictly
natural, affords us the readiest means of separating Man, zoologically, from all
other animals.   He arranged  under his order Primates, all the unguiculated
Mammalia which have four incisor teeth and two canines in  each jaw; and
thus Man, with the  Monkeys and the Bats, was distinguished from the re-

   * The action of trituration is chiefly performed by the external pteregoid muscles.  When
these  are in operation together, they draw the whole of the lower jaw forwards, so as to
make the lower teeth project beyond the upper; and the jaw being drawn back again by
the digastric muscles, a rapid alternate movement may be thus effected, such as is seen in the
Rodentia.  When only the muscle of one side acts, the condyle of that side is thrown for-
wards • and by the alternating operation of the two, aided by other  muscles, that rotatory
motion is given which we see especially  in  Ruminating Quadrupeds.
   t In Carnivorous animals, the muscles which elevate the lower jaw attain a  very high
decree of development.  This is very remarkably seen in the internal pteregoid, which in
Man is of subordinate size and importance, but which is a very powerful muscle in the Lion,
Tiger, &c. 
CHARACTERISTICS OF MAN.
67
mainder of those Quadrupeds which have separate fingers with distinct nails
or claws.   This  group is now sub-divided into  three orders, corresponding
with the Linnaean genera, Homo,  Simia, and Vespertilio.  The last of these
orders, named Cheiroptera, consists of the Bat tribe, which is easily separated
from all others by the peculiar conformation of the anterior extremities, from
which its name is derived.   The second, termed Quadrumana, comprehends
the Apes, Monkeys, and Baboons, which exhibit a regular series ;  the highest
approaching Man in general conformation;  and the lowest having  much more
of the general organization of the inferior carnivorous quadrupeds.   They are
distinguished from  other  viviparous Mammalia, by possessing an opposable
thumb on all four extremities (whence they are termed four-handed),—a cha-
racter which  is only found elsewhere in the Opossums.  Although some of
the higher  members of this group are capable of maintaining the erect posi-
tion without  difficulty for some time, even whilst walking, it is certainly not
that which  is natural to  them.   The posterior extremity,—being formed on
the plan of a  hand, for prehension rather than for  direct support,—is destitute
of the heel, which  is  characteristic of Man; and although  Apes  can  climb
trees with facility, they cannot  plant the foot firmly on the ground, so as to
resist attempts to  overthrow them;  since the foot rests rather upon the outer
side than upon its sole, and the narrowness of the  pelvis is unfavourable to an
equilibrium.   There are many points of striking resemblance to  Man, how-
ever, in the details of the conformation of the Quadrumana, especially among
the most elevated species; the order being distinguished by the same charac-
ters from most others.   The structure of  their alimentary canal  differs ex-
tremely little from  his.    The eyes  are directed forwards, when the trunk is
erect; and  the orbit is completely separated  from the  temporal  fossae, by a
bony partition.  The  mammae  are situated on the thorax ; and the penis is
pendent.   The coitus, however, is reverse, as in the lower Mammalia.   The
form of the brain in the higher species corresponds with that of Man in  this
remarkable character,—that it is divided into three lobes, of which the poste-
rior is prolonged backwards so as to cover the cerebellum ; this is not the case
in the highest of  the other Mammalia.

                       12. Characteristics of Man.
   51. We  shall  now review, somewhat in detail, the  distinctive characters
that separate  Man from those animals which present the nearest approach to
him in general structure and aspect.  These may be advantageously classified
according to their obvious purposes; and the first series we shall notice con-
sists of those by which  Man is peculiarly  adapted to the erect attitude.  On
examining his cranium we remark that the condyles, by which  it is articulated
with the spinal column,  are so placed that a perpendicular dropped from the
centre  of gravity of the  head would nearly fall  between them, so as  to be
within the base on which it rests.   The foramen magnum is not placed  in the
centre of the base of the skull, but just behind  it; in order to compensate for
the greater  specific gravity of the posterior part of the head, which is entirely
filled with solid matter, whilsf the  anterior part contains  many cavities.  There
is, indeed, a little over-compensation, which gives a slight preponderance to
the front of the head; so that it drops forwards and downwards when all the
muscles are relaxed.  But the muscles which are attached to the back of the
head are far larger and more numerous than those in front of the condyles;
so  that  they are  evidently  intended to  counteract this disposition; and we
find, accordingly, that we can keep up the head for the whole day, with so
slight and involuntary an effort that no fatigue is produced by it.   Moreover,
the surfaces  of the condyles have a horizontal direction when the head is 
68
ON THE PLACE OF MAN IN THE SCALE OF BEING.
upright; and thus the weight of the skull is laid vertically by them upon the
top of the vertebral column.   If these arrangements be  compared with the
position and direction of the occipital  condyles in other Mammalia, it will
be found that these are placed  in the latter much  nearer to the back of the
head, and that  their plane is  more oblique.   Thus, whilst the foramen mag-
num is situated, in Man, just behind the centre of the base of the skull, it is
found in  the Chimpanzee and Orang  Outan to occupy the middle of  the
posterior third ; and, as we descend  through the scale of Mammalia, we ob-
serve that it gradually approaches the back of the skull, and at last  comes
nearly into the line  of its  longest diameter, as we see  in the  Horse.   The
obliquity of the condyles differs in a  similar degree.  In all Mammalia except
Man their plane is oblique; so that, even if the head were equally balanced
upon them, the force  of gravity would tend to carry it forwards and  down-
wards.  In  Man,  the  angle  which  they make  with the horizontal is very
small; in the Orang Outan  it is  as  much  as 37°;  and in the Horse their
plane is vertical, making the  angle 90°.  If, therefore, the natural posture of
Man were horizontal, he would in this respect be circumstanced  like  the
Horse;  for the plane of his condyles, which is nearly horizontal in the erect
position, would then  be vertical:   and the head, instead  of being nearly
balanced in the erect position, would hang at the end of the  neck, so that its
whole weight would have to be supported  by some external  and constantly-
acting power.   But for this there is neither in the skeleton, nor in the muscu-
lar system of Man, any adequate provision.  In other Mammalia the head is
maintained in such a position by a strong and  thick ligament  (the ligamentum
nuchas), which  passes from the spines of the cervical and dorsal vertebrae to
the  most  prominent part of  the occiput; but of this  there  is scarcely any

                                 Fig. 5.
View of the base of skull of Man, compared with that of the Orang Outan.
trace in Man.   In the horizontal position, therefore, he would have the heavi-
est head, with the least power of  supporting it.
  52.  The position of the  face  immediately beneath the brain, so  that its
front is nearly in the same plane  as the forehead, is peculiarly characteristic
of Man ;  for the  crania of the  Chimpanzee  and  Orang, which  approach
nearest to that of Man, are entirely posterior to, and not above, the face.   It
should be remarked  that in  the young Ape there is a much  greater resem-
blance to Man in this respect than there is in the adult.  For at the time of
the second dentition the muzzle of the Ape undergoes a great elongation, so 
                         CHARACTERISTICS OF MAN.                      69

that it projects much more beyond the forehead; this is seen in Fig. 5.  The
whole cast of the features  is altered at the same time, so that it approaches
much more to that  of  the lower Quadrumana than would be  supposed from
observation of the  young  animal only.*  This increased projection  of the
muzzle  is  an evidence of want of perfect adaptation  to  the  erect posture:
whilst the absence of it in Man shows that no other position is natural to him.
Supposing that, with  a head formed  as  at present, he were to  move  on  all
fours, so that his face would be brought into a plane parallel with the ground,
—as  painful an effort would be required to examine with  the eyes an  object
placed in front of the  body, as is now necessary  to keep the eyes fixed  on
the zenith;  the nose would be unable  to perceive any other odours than those
which proceeded from  the earth or from the body itself; and the mouth could
not touch the ground without bringing the forehead and chin also into contact
with it.   The oblique position of the condyles in the Quadrumana enables
them, without much difficulty, to adapt the inclination of their  heads  to the
horizontal or  to the erect position of the body; but the natural position, in
the highest among them, is unquestionably one in which the spinal column is
inclined, the body  being  partially thrown forwards, so as to rest upon the
anterior extremities; and in this position the face is directed forwards without
any effort, owing to the mode in which the head is articulated with the  spine.
  53. The  vertebral  column  in  Man, though not absolutely straight, has its
curves so arranged, that, when the body is in an erect posture, a vertical line
from  its summit would fall exactly  on the centre of  its base.   It increases
considerably in  size in  the lumbar  region, so as to be altogether somewhat
pyramidal  in form.  The lumbar portion, in the Chimpanzee and Orang, is
not of the same proportional strength; and contains but four vertebrae instead
of five.  The processes for the attachment of the  muscles of the back to this
part, are peculiarly large and strong in  Man; and this arrangement is obviously
adapted  to  overcome  the tendency, which the weight of  the viscera in front
of the column would have, to draw  it forwards  and downwards. On the
other hand, the spinous processes of the cervical and dorsal vertebrae,  which
are in other Mammalia large and  strong, for the attachment of the ligamentum
nuchae to support the  head, have in Man but little  prominence, his head being
nearly balanced  on  the top of the column.   The base of the human vertebral
column  is  placed  on  a sacrum of greater proportional breadth, than that of
any other animal;  this sacrum is fixed between  two widely expanded ilia;
and the  whole  pelvis  is thus  peculiarly broad.  In this manner, the femoral
articulations are  thrown very far apart, so as to give a wide basis of support;
and by  the  oblique direction of  the  whole pelvis, the weight of the body is
transmitted almost vertically, from the top of the sacrum to the upper part of
the thigh bones.  The pelvis of  every other species of the class is very dif-
ferently constructed ; as will be seen in the adjoining Figure (6),  in which the
skeleton  of the  Orang is placed in proximity  with that of Man.   It is much
longer and  narrower, having a far smaller space between  the iliac bones and
the lowest ribs ; the sacrum  is lengthened and reduced in width;  the alae of
the ilia are much less expanded;  and the whole pelvis is brought nearly into
a line with the vertebral column.  The position of  the human femur, in  which
it is  most  securely fixed in its deep acetabulum, is  that which it has when
supporting the body in the erect attitude.  In the Chimpanzee and Orang, its
analogous position  is  at an oblique angle to the long axis of the pelvis, with
the body supported obliquely in  front of it;  in many xMammalia, as  in the

  * None but young  specimens of the Chimpanzee and  Orang Outan have ever been
brought alive to this  country; and they have never survived  the period of their second
dentition.
• 
70
ON THE PLACE OF MAN IN THE SCALE OF BEING.
Elephant, it forms nearly a right angle;  and in several others, as the Horse,
Ox, &c, it forms an acute angle with the axis of the pelvis and spinal column.
  54. The lower extremities of  Man are remarkable for their length ; which
is  proportionably greater than that which  we find in any other Mammalia,
except the Kangaroo  tribe.   It  is evident  that there could be no greater ob-
stacle to his prorgession in the  horizontal posture, than this length of what
would then be his hind legs.   Either  Man would be obliged to rest on his
knees, with his thighs so bent towards the  trunk,  that the  attempt to advance
them  would be  inconvenient, his  legs and feet being entirely useless; or he
must  elevate  his trunk  upon the  extremities  of  his toes, throwing his head
downwards, and exerting himself violently  at every attempt to bring forward
the thighs by a rotatory  motion at the hip-joint.  In either case, the only use-
ful joint would be that at the hip;  and the legs would be scarcely superior to
wooden or other rigid  supports.  The chief difference in their proportional
length, between Man and the semi-erect Apes, is seen in the thigh ;  and from
the comparative shortness of his  arms, his hands only reach the middle of the
thighs;  whilst in the Chimpanzee they  hang on  a level with the knees,  and
in the Orang they descend to the ancles.  The human femur is  distinguished
by its form and position as well as by its length.   The obliquity and length
of its neck still further increase the breadth of  the hips; whilst they cause
the lower extremities of these bones to be somewhat obliquely directed towards
each other, so  that the knees are  brought  more into the line of the axis of the
body.   This  position is obviously of great use in walking, when the whole
weight  has to be  alternately supported  on each  limb;  for if the knees  had
been  further apart, the  whole body  must have been swung from side to side
at  each  step, so as to bring the  centre of gravity over the top of each tibia;
and, as  a matter of fact, it  is noticed that  the walk of women, in whom the
pelvis is broader and the knees more separated, is less  steady than that of
men.
  55. There is  a  very marked  contrast  between  the knee-joint of Man,  and
that even of the highest Apes.   In the former, the opposed extremities of the
femur and the tibia are expanded, so as to present a very broad articulating
surface;  and the internal condyle of the femur is  lengthened, so that the  two
are in the same horizontal  plane, in the  usual oblique position  of the femur.
In this  manner, the whole weight of the  body, in  its erect posture, falls verti-
cally  on the top of the tibia, when the joint is in the firmest position in which
it can be placed: and a comparison of the  knee-joint of the Orang with  that
of Man, will make it  at once evident, that the former is not intended to serve
as more than a partial support.  The weight of the body is transmitted through
the tibia, to the upper convex surface of the astragalus, and thence to the other
bones of the foot.   The Human foot is, in proportion to the size of the whole
body, larger, broader,  and stronger, than  that of any other Mammal save the
Kangaroo.  The sole of the foot is concave, so that the weight of the body
falls on  the summit of an arch, of which the os calcis and the metatarsal bones
form  the  two  points of support.  This arched form of the  foot, and the na-
tural contact of the os calcis with the ground, are  peculiar to Man alone.   All
the Apes  have the os calcis small, straight, and more or less raised from the
ground; which they touch when standing erect, with the outer side only of the
foot:  whilst in animals more remote from  Man, the os calcis is brought  still
more  into  the line of the  tibia; and the foot being more elongated and nar-
rowed,  only the  extremities of  the  toes come in contact with the ground.
Hence Man is the only  species of  Mammal, which can stand upon one leg.—
If  we look at the structure of the upper extremity of Man, we observe simi-
lar proofs that it is not intended as an organ of support; being destitute of all
these  adaptations; and  having a conformation obviously  designed  for other 
CHARACTERISTICS OF MAN.
71
Fig.  6.
Comparative view of the Skeleton of Man and that of the Orang Outan. 
72            ON THE PLACE OF MAN IN THE SCALE OF BEING.

purposes, which  could not be  possibly answered, if it were not completely
relieved from the necessity of bearing the weight of the body.   This peculiar
conformation will be subsequently considered.
  56. The other parts  of the  Human body concerned in locomotion are
exactly adapted  to the peculiar construction of the skeleton.   The tibia is
kept erect upon the foot by the very powerful muscles which are attached to
the heel and form the calf of the  leg,—a prominence observed in no other
animal in nearly the same degree.   The flexor longus pollicis pedis, which is
attached  in the Chimpanzee and Orang to the three middle toes, proceeds in
man exclusively to the great toe, on which the weight of the  body is  often
supported.  The extensors of the leg upon trie thigh are much more power-
ful  than the flexors, an arrangement seen in no other animal.   The glutaei, by
which the pelvis is kept erect upon the thigh, are of far  greater size than is
elsewhere seen.   The superior power of the muscles tending to draw the
head and spine backwards, has been already referred to.  In the general form
of the trunk, there is a considerable difference between Man and most other
Mammalia.   His chest is large, but is  flattened in front, and expanded late-
rally, so  that its  transverse diameter is greater than its antero-posterior ;—a
peculiarity in which  only the most Man-like monkeys partake.   His sternum
is short and broad ; and  there is  a considerable  distance between the lower
ribs and  the ilia, in consequence of the small number of ribs, and the length
of the lumbar portion of the vertebral  column.   The viscera in this space,
which in the horizontal  position would be  but insufficiently held up by the
abdominal muscles, are, in the  erect attitude, securely supported by the ex-
panded pelvis.—From all these facts, it is an indisputable conclusion, that the
erect  attitude and biped progression are natural to Man; and we must regard
as in  great degree fabulous, all those histories of supposed wild men, who, it
has been said, were found in woods, dumb, hairy, and crawling on all-fours.
The  most elaborate  investigation* of  the structure of the anthropoid Apes,
and the fullest acquaintance with their  habits, concur in  proving, that their
movements  are  not  easy or agile, unless they employ all their limbs for the
support of their bodies.
  57. The  name Bimana is the most  appropriate that could be found, for an
order constituted by the Human species only ; since Man alone is two-handed.
" That," says Cuvier, " which constitutes the hand, properly so called,  is the
faculty of opposing the thumb  to the  other fingers, so as to seize the  most
minute  objects,—a faculty which  is carried to  its highest degree of perfec-
tion in Man, in whom the whole anterior  extremity is free, and  can be em-
ployed in prehension."  Some  naturalists refuse the term hand to the extremi-
ties of the monkey tribe, preferring to  call them graspers; for it is certainly
true, that, although usually possessing  an opposable thumb, they are destitute
of the power of performing many of those actions which we regard as most
characteristic of the  hand.  Such actions  are chiefly dependent  on the size
and power of the thumb ; which is much more developed in Man than it is
even in the  highest Apes.   The  thumb of the Human hand  can be brought
into exact opposition to the  extremities of  all the fingers, whether singly or
in combination;  whilst in those Quadrumana which  most nearly approach
Man, the thumb  is so  short and weak, and the fingers so long and slender,
that their tips can scarcely be brought  into opposition, and can never be  op-
posed in near contact with each other, with any degree of force.   Hence,
although admirably adapted for clinging round bodies  of a certain size, such
as the small branches of trees, &c, the extremities of the Quadrumana can

  * See especially Mr. Owen's paper on the Chimpanzee and the Orang Outan in the Zoolo-
gical Transactions, vol. i. 
CHARACTERISTICS OF MAN.
73
neither seize very minute objects with such  precision, nor support large ones
with such firmness, as are essential to the dexterous performance of a variety
of operations  for which the hand of Man is admirably  adapted.   Hence
the possession of " four  hands" is not,  as  might be supposed, a character
which raises the animals that exhibit it above two-handed Man; for none of
these four hands are adapted to  the same variety  of actions of prehension of
which his are capable ; and all of them  are in some degree required for sup-
port.   In this respect their character approaches much nearer to  that of the
extremities of the  lower Mammalia ; and there  are several  among  them in
which, the opposable power of  the thumb being deficient, there  is  no very
marked distinction between the  so-called hand, and the foot  of some Carni-
vora.  There is much truth, then, in Sir C. Bell's  remark, that " We ought
to define the hand as belonging exclusively to Man."   There is in him, what
we observe in none of the Mammalia that  approach  him  in other respects,
a complete distinction in the functional character  of the anterior and posterior
extremities; the former being adapted for prehension alone, and the latter for
support alone.  Thus  each function is performed with a much higher degree
of perfection than it can be where two such  opposite purposes  have to be
united.   The  arm of the Ape has as wide a range of motion as  in  Man, so
far as its articulations are concerned; but it is only when the  animal is in the
erect  attitude, that  its arm  can have free play.   Thus the  structure of the
whole frame must conform to  that of the hand, and must act with reference
to it.   But it cannot be said with  truth (as some  have maintained) that Man
owes his superiority to his hand alone ;  for without the directing mind, the
hand  would be comparatively valueless.   His elevated position is due to his
mind and its instruments conjointly; for  if destitute of either, mankind would
be speedily extinguished altogether, or reduced to a very subordinate grade of
existence.
   58. Thus, then, although the order Bimana cannot be separated from the
order Quadrumana  by any single obvious structural distinction, like that which
characterises the Cetacea or  the Cheiroptera, it  is really as far removed by
the minuter, but not less  important, modifications which  have been detailed.
A few other distinctive characters  will now  be noticed.   With one exception
(the fossil genus Anoplotherium, which  is allied  to the Tapir  tribe), Man is
distinguished from all  other animals, by the equality in the  length of all his
teeth, and by the equally close approximation of them all in each jaw. Even
the anthropoid Apes have the canine teeth longer than the others, and an in-
terval in the line of teeth in each side of the jaw, to receive  the canine teeth
of  the opposite jaw.  This is more evident in the  adult than in the young
animal.  The vertical position of the Human teeth, on which one of the most
characteristic features of the Human face—the prominent chin—depends, is
also quite peculiar;  and is intimately connected  both with his erect attitude,
and with the perfection of the hands, by which the food is divided and con-
veyed to the mouth.   He has no  occasion for that protrusion of the muzzle
and lips, which, in  animals  that seize their  food  with the mouth only, is re-
quired to prevent the face from coming into general  contact with it.—The
absence  of any weapons of offence, and of direct means  of defence, are
remarkable characteristics of Man, and  distinguish him from other animals.
On those to whom  Nature has  denied weapons of attack, she has bestowed
the means  either of passive  defence, of concealment, or of flight.  Yet Man,
by his superior reason, has not only been enabled to resist the attacks of other
animals, but even to  bring  them under  subjection to himself.   His intellect
can scarcely suggest the mechanism, which  his hands cannot frame;  and  he
has devised and constructed arms more powerful  than those which any other
creature wields, and defences  so secure  as to defy the assaults of all but his
     7 
74
ON THE PLACE OF MAN IN THE SCALE OF BEING.
fellow-men.—We find, on comparing the brain of Man with that of the lower
Mammalia, that, as might have been  anticipated, its proportional  dimensions
are much greater, and its structure more complex.   The former part of this
statement is easily verified by an examination of the cranium alone, comparing
the size of its cavity with that of the face.  The amount of the facial angle,
taken after the manner of Camper, affords a tolerably correct indication of the
relative sizes of these  parts.  In Man, the facial  angle is, in the average of
Europeans, 80°; in Negroes, it is about 70°.  In the adult Chimpanzee (which
approaches in this respect nearest to Man), the facial angle is only 35°; and
in the Orang, it is no more than 30°.  In other animals it is  still less, except
when it is  increased by the prominence of large  frontal sinuses, or by the
comparative shortness of the jaws.  In regard to the structure of the brain, we
shall here only remark generally, that the Encephalon of Man far exceeds that
of the highest  Quadrumana, in the  size of the cerebral hemispheres, in the
complexity and development of its internal parts, and in the  depth and num-
ber of its convolutions.
   59.  Man cannot be  regarded as distinguished from other Mammalia, how-
ever, either by acuteness of sensibility, or by muscular power.  His swiftness
in running, and agility in leaping, are inferior  to that  of other animals of his
size,—the  full-grown Orang for example.  The smallness of  his face, com-
pared with that of the cranium, shows that the portion of the nervous system
distributed to the organs of sense, is less developed in him than it is in most
other animals ; and the small proportional size of the ganglionic centres, with
which these organs are immediately connected, is another indication of the
same fact.   Accordingly, he is  surpassed by many in acuteness of sensibility
to light, sound, &c;  but he  stands  pre-eminent in the power of comparing
sensations, and of drawing conclusions from them. Moreover, although none
of his senses  are very acute  in his  natural state, they are all moderately so,
which is not the case  in other animals ;  and they are capable (as is  also his
swiftness of  foot) of being much improved by practice, especially when cir-
cumstances strongly call for their exercise.  This power of  adaptation to va-
rieties in external conditions, which makes him to a great extent independent
of them, is manifested in other features  of his structure and economy.  He
is capable  of sustaining the lowest, as well as the highest, extremes of tempe-
rature and of atmospheric pressure.   In the former of these  particulars, he is
strikingly contrasted with the anthropoid Apes, such as the Chimpanzee, which
is  restricted to a few of the hottest  parts of Africa,  and the Orang-Outan,
which is only found in Borneo and Sumatra: these  cannot be kept alive in
temperate  climates, without the  assistance of artificial heat; and even when
this is afforded, they speedily become diseased and die. His diet is naturally
 of a mixed kind; but he can support himself in health and strength, on either
 animal or  vegetable food exclusively.  It is by the demands which his pecu-
 liar condition makes upon the  exercise  of  his  ingenuity, that his mental
 powers  are first called into active  operation; but, when  once aroused, their
 development  has  no  assignable  limit.  The slow growth  of Man, and the
 length of  time  during which he remains in a state of dependence upon his
 parents, have been already mentioned as peculiarities, by  which he is distin-
 guished from all other animals.  He  is  unable to seek his own food, during
 at least the three first years of his life ; and he  does not attain to his full
 stature,  until he is more than twenty years of age.   In proportion to his size,
 too, the whole sum of his life is greater than that of other Mammalia.  The
 greatest age of the Horse, for example, which is an animal of much superior
 bulk, is between thirty and forty years.  That of the Orang, which, when full
 grown,  surpasses Man in stature, is about the same, so far as it can be ascer-
 tained.   The age to which the  life of Man  is frequently prolonged, is well 
GENERAL CONSIDERATIONS.
75
known to be above a hundred years; and instances of such longevity are to be
found in all nations.
  60. Still, however widely Man may be distinguished from other animals,
by these and other peculiarities of his structure and economy, he is  yet more
distinguished by those mental endowments, and  the  habitudes of life and
action thence resulting, which must be regarded as the essential characteris-
tics of humanity.  In the highest among brutes, the mere instinctive propen-
sities (as already defined, §§ 17, 23), are the frequent springs of action; and
although the intelligent will  is called into  exercise to a certain extent, the
character never rises beyond that of the child.  In  fact, the correspondence
between the psychical  endowments of the Chimpanzee, and  those  of the
Human infant before it begins to speak, is very close.  In Man, however, the
instinctive propensities only manifest  themselves strongly, whilst the intellect
is undeveloped; and nearly all the actions of  adult  life are  performed under
the direction of the intelligent will.  From the intelligence of Man results his
mental improvability;  and his improved condition  impresses itself  upon his
organization.   This  capability of improvement in  the bodily as well as the
mental  constitution of  Man,  is the cause of  the  comforts  now enjoyed  by
civilised races, and of the means which they possess of still  further  elevation.
In the processes by which these are attained, we observe a remarkable differ-
ence between the character of  Man, and that of other  animals.  The arts of
which  these last are capable, are limited, and  peculiar  to  each  species ; and
there seems to be no general power of adapting these  to any great  variety of
purposes, or of profiting by the experience of others.  Where a  particular
adaptation  of means to ends, of actions to circumstances, is made by an indi-
vidual  (as is frequently the case, when some amount of intelligence  or ration-
ality exists), the rest do not  seem  to profit by it; so  that there is no proof
that any species or race among  the lower  animals ever makes a  voluntary
advance towards an improvement or alteration  in its condition.  That  modifi-
cations in  structure and instincts may be induced by circumstances, in some
of the most improvable species, such as the Dog, has been shown by abun-
dant evidence; and these modifications, if connected with the original habits
and instincts of the species, maybe hereditarily transmitted.   There is ample
proof that  the  same is the case, in regard both to the corporeal  structure and
the psychical endowments of Man.  Under the influence of education, phy-
sical and mental, continued through successive generations, the  capabilities of
his whole nature, and especially those of his brain, are called out;  so that the
general character of the race is greatly improved.   On  the other hand, under
the influence of a degraded condition, there is an equally certain retrogression;
so that, to bring up the New  Holland Savage,  or the African  Bushman, to the
level of the European, would probably require centuries of civilisation.  One
of the most important aids to the use and development  of the human mind, is
the power  of producing articulate  sounds, or  language; of  which,  as far  as
we know, Man  is the only animal  in possession.   There  is  no doubt, that
many other species have certain powers of communication between individu-
als ; but these are probably very limited, and of a  kind very different  from a
verbal language.
   61.  Although, as we have stated, there is nothing  in Man's  present condi-
tion, which removes him from the pale of the Animal kingdom, and although
his reasoning powers differ rather in  degree than in kind from those of the
inferior animals, he  seems distinguished by one innate tendency;  to which
we have no reason to suppose  that  anything analogous elsewhere exists ; and
which  we might term an instinct, were it not that this designation is  generally
applied to  propensities of a much lower  character.  The tendency here
referred to, is that which seems universal in Man, to believe in some  unseen 
76              MUTUAL RELATIONS OF THE HUMAN FAMILY.

Existence.  This may take various forms, but is never entirely absent from
any race or nation, although (like other innate tendencies) it may be defective
in individuals.  Attempts have  been made by some travellers  to prove, that
particular nations are destitute of it; but  such assertions have been^based
only upon a limited acquaintance with their habits of thought, and with their
outward observances.  For there are probably none, that do  not possess the
idea of some invisible Power external to themselves ; whose favour they seek,
and whose anger they deprecate, by sacrifice and other religious observances.
It requires a higher mental cultivation than is always to  be met with, to con-
ceive of this Power  as having a Spiritual existence; but wherever the  idea
of spirituality  can be defined, it  seems connected with it.  The vulgar readi-
ness to  believe in  demons, ghosts, &c, is only an  irregular or  depraved
manifestation of the same tendency.   Closely connected  with it, is the desire
to share in this spiritual existence;  which has been implanted by the Creator
in the mind of Man; and which, developed as it is by the mental cultivation
that is almost  necessary for the formation of the  idea, has been regarded by
philosophers  in all  ages, as one of the  chief natural  arguments for  the im-
mortality of the soul.  By  this Immortal Soul, the existence of which is thus
guessed by Man, but of whose presence within him he derives  the strongest
assurance from Revelation, Man is connected with beings  of a  higher order,
amongst whom Intelligence exists, unrestrained in its exercise by the imper-
fections of that corporeal mechanism, through which it here operates;  and to
this state,—a  state of more intimate communion of mind with  mind, and of
creatures with their  Creator,—he  is  encouraged to aspire, as  the reward of
his improvement of the talents here committed to his charge.
                          CHAPTER  II.

 OF THE- MUTUAL RELATIONS  OF THE  DIFFERENT BRANCHES OF  THE HUMAN
                                 FAMILY.

                       1.  General Considerations.
   62. Amongst the various tribes of Men, which  people the surface of the
globe, and which are separated from all other animals by the foregoing cha-
racters, there are differences of a very  striking and  important nature.   They
are distinguishable from each other,  not merely by  their language, dress,
manners  and customs, religious belief,  and other acquired peculiarities, but in
the physical conformation of  their bodies; and the difference lies, not merely
in the colour of the skin, the nature  of the  hair, the form  of the soft  parts
(such as  the nose, lips, &c.,)  but in the shape of the skull,  and of other parts
of the bony skeleton, which might be supposed to be less liable to variation.
It is a question of great scientific interest, as well  as  one that  considerably
affects the mode in which we treat the  races that differ from our own,—whe-
ther they are all  of one species, that  is, descended from the same or from
similar parentage,—or whether they are to be  regarded as distinct species,
the first parents of the several races having had the same differences among
themselves, as those now exhibited by  their descendants.
   63. It has been a favourite idea, among those who wished to  excuse the
horrors of slavery, or the extirpation  of savage tribes,  that the races thus 
                    ON THE DISCRIMINATION OF SPECIES.                 77

treated might be considered as inferior species, incapable of being raised by
any treatment to our own elevation; and as thus falling legitimately under the
domination of the superior races, just as the lower animals have been placed
by the Creator in subservience to  Man.  This doctrine, Avhich has had its
origin in the desire to justify as expedient what could  not  be defended as
morally right, finds no  support from scientific  inquiries  conducted in  an  en-
larged spirit.  In order to arrive at a just conclusion on the subject, it is  ne-
cessary to take a very extensive survey of the evidence furnished by a number
of different lines of inquiry.   Thus, in the first place, it is right to  investigate
what are  the  discriminating structural marks, by which species are  distin-
guished among the lower  tribes of animals.—Secondly, it should  be ascer-
tained to what extent variation may proceed among races, which are histori-
cally known to have a common  parentage ; and what are  the  circumstances
which most favour such variations.—Thirdly, the extreme variations, which
present themselves among the  different  races  of men, should be compared
with those which occur among  tribes  of  animals known to be of the same
parentage;  and  it should be  questioned,  at the  same time, whether  the cir-
cumstances which favour the production of varieties in the latter case, are in
operation in the former.—Fourthly, where it is impossible to trace back dis-
tinct races to  their origin, it is to be inquired how far agreement in physiolo-
gical and  psychological peculiarities may be regarded as indicating  specific
identity, even where a considerable  difference  exists in  bodily  conformation;
and this test,  if  it can be determined on, has to be applied to Man.   Fifthly,
it  must be attempted, by a detailed examination of the varieties of the human
race themselves, to ascertain whether  their differences   in conformation  are
constant; or whether there are not occasional manifestations, in each race, of
a tendency to assume the characters of others; so as to prevent a definite line
being drawn between the several tribes, which  together  make  up the (sup-
posed) distinct species.*

                   2.  On the Discrimination  of Species.
   64.  Theirs/ of the foregoing questions is a fertile source of perplexity to
the Naturalist;  owing to the tendency that exists in certain  races  of Plants
and Animals, to exhibit variations of  form much  greater than those which
are relied upon in other instances as  characterizing distinct species.  In our
ignorance as to the history of the origin of the greater part of the dissimilar
forms or races of organized  beings, with which the globe is peopled, we  are
accustomed to regard two races of Plants or animals as of the same species,—
that is, as having had the same or similar progenitors,—when they are not
distinguished  from one  another by any peculiarities, but such as the one may
be supposed to have gained, or  the other to  have  lost, by the influence of
external circumstances during a long period of  time.  On the other hand, two
races are regarded as  constituting distinct species,—that is, are believed to
have descended  from  dissimilar parents,—when a constant well-marked dif-
ference exists between them, such as exhibits no tendency to variation in  the
individuals of either race (being equally characteristic of every one), and is
not affected by the lapse of time or by change in external conditions.
   65.  Thus, if we compare together  the different breeds of  Dogs,  we find

  * This investigation has been  most elaborately, and in the Author's opinion  most suc-
cessfully, worked out by Dr. Prichard, in his profound and philosophical  Treatise on  the
Physical History of Man.  The sketch of the argument given above does little more than
exhibit the conclusions at which he has arrived; and  for the grounds on  which these  are
based, reference ,must be made to that work, or to the abridgment of it published by  Dr.
Prichard, under the title of the Natural History of Man. 
78
MUTUAL RELATIONS OF THE HUMAN FAMILY.
that, although they are  distinguished by very marked  peculiarities, yet that
these peculiarities are by no means constant.  There is historical evidence of
the great change, which  may take place in their  conformation and  habits,
under the influence of a change in their  external circumstances ; in the case,
for example, of the blood-hounds, introduced into the  West Indies  by the
Spaniards, which have  now degenerated into  a wild race of  very different
form, and have lost all the distinctive  characters of the breed.   And there is
not that close agreement in the distinctive characters  of the  several breeds,
among the individuals respectively composing them, which is requisite for the
establishment of  a  definite specific distinction ; the characters being shaded
off, as it were in  individuals, so as to  cause a near approximation between the
less decided forms of the  different races.—On the other hand, in spite of the
varieties of conformation exhibited by the several races of Dog, (which even
affect the number of vertebrae in the tail, as well as the shape and proportions
of the bones, we  never see any which present so strong a resemblance to the
Fox,  as  to be at all  in danger of being  mistaken for that animal; and they
may always be distinguished by this obvious character,—that the pupil of the
eye of the Dog is always round, whilst that of the Fox  is oval when con-
tracted.   This  difference may appear a very trifling one, in comparison with
the important variations presented in the structure of the different  breeds  of
Dogs ; but it is constant; and it  may therefore be  assumed to have existed
in the progenitors of each race, as it exists at present in all their descendants.
   66. There are many instances  of an opposite character, in which the tend-
ency  to  variation is extremely small; and in which the Naturalist feels jus-
tified in assuming  a specific difference, from variations in  size  or  colour,
which in themselves  are very trifling, but which are important in classifica-
tion,  because  they  are  constant.   Thus, among the several species  of  the
genus Felis (or Cat tribe), there is scarcely any perceptible osteological varia-
tion, except in point of size ; so that even  Cuvier was unable to find out a
positive means of distinguishing the skull of the Lion from that of the Tiger;
and the  skeleton of a Wild Cat is a reduced copy of that of the largest Felines.
There are certain species, which  are  distinguished  by no other external indi-
cations, than  the markings upon  their skins;—characters, which are in other
cases subject to extreme  uncertainty; but which are here  so  constant, as to
present  scarcely  the slightest variation amongst  the individuals of each race.
Thus, if a certain patch or stripe  be repeated from generation to generation, in
a wild feline race, the Naturalist  is inclined  to regard this as a sufficient proof
of the specific difference of that race from another which is differently marked.
The Domestic  Cat  is the only one of the group, which is liable to any con-
siderable variation; and in  this  species, as every  one  knows, the  markings
characteristic of the several breeds or races  are not thus constantly repeated,
and therefore cannot be indicative of original difference.  Now it is precisely
in this species  that we should  look for  such variations; since it is the only
one which can be domesticated;  and  the capability of domestication implies
a power in the original constitution of the animal,  to adapt itself to a change
of circumstances, and thus to exhibit various departures from its original type.
   67. This striking contrast, between variable and invariable groups of ani-
mals nearly allied to each other, is found through the whole kingdom ; everv
division  of it appearing to contain some species, which do not change their
forms or other characteristics under  any circumstances, but  which cease  to
exist if  a change  takes place in their conditions, incompatible with the regular
performance of their functions;  whilst it also includes others, in whose phy-
sical  and psychical constitutions there is such a  susceptibility of modification,
that  new forms  and new instincts may arise,  adapted to a great variety of
external conditions, and thus new and very  different races may be originated. 
           EXTENT OF VARIATION IN RACES OF THE SAME SPECIES.         79

Thus, the Feline races, with a few exceptions, are fitted to maintain life only
in tropical climates, and very speedily die in colder countries (unless kept
warm by artificial  means), in consequence of their  deficiency of heat-pro-
ducing power, and the want of a close downy fur adapted to retain the caloric
generated in their bodies.   On  the other hand, the Dog is enabled to accom-
pany Man, in the coldest as well as the hottest regions of the  globe;  his
power of generating  heat being capable of variation, in accordance with  the
external temperature;  and his entire organization  undergoing  modifications,
which  adapt  it to the change in the conditions of its existence.   It appears,
then, that it is quite impossible to fix upon any difference of structural pecu-
liarities, as indications of the distinctness of species;  until  it has  been ascer-
tained by observation, whether  they are  constant and invariable,—the races
neither  exhibiting any  tendency to  change  in successive generations,—nor
showing any disposition to  mutual  approximation, by the  occasional modifi-
cation of the distinctive characters in the individuals composing them.

   3. On the possible Extent of Variation within the Limits  of Species.
   68.  We now  come  to the  second point  of  our  inquiry,—namely,  the
amount of variation which  may  take place  in  races, historically known to
have had a common parentage.   There is considerable  difficulty  in obtaining
the most complete evidence upon this subject; owing to the want of accurate
observation in  the more remote historical  periods, when it  is probable that
most of the varieties or breeds of our domesticated  animals were first origi-
nated.   Still there  is  an adequate  amount of proof, that these  races may
undergo very considerable modifications, in the course of a few generations ;
and that  new  races  or  breeds, distinguished by  marked  peculiarities, may
originate even at the present time.   Our most satisfactory information is  de-
rived from the  changes, which have taken  place in the races of domesticated
animals, introduced into the West  Indies  and South America, by the Span-
iards, three centuries since.  Many of these races  have  multiplied exceed-
ingly, on a soil and under a climate  congenial to their nature;  and several of
them have run wild in the vast forests of America, and  have lost all the most
obvious appearances of domestication.  The wild tribes are found to differ
physically from the domesticated breeds, from which they are known to have
originated ; and there is good reason to  regard this change, as a partial restora-
tion of the primitive characteristics  of the wild stocks, from which the tamed
animals originally descended.  Thus we find  that the Hog, where it has re-
turned  to its wild  state, nearly resembles the Wild  Boar,  which  has never
been in a state of domestication.  The colour loses  the variety found in  the
domestic  breeds ; the Wild  Hogs of the  American forests being uniformly
black.   The thin covering of hair and scattered bristles is replaced by a thick
fur, often somewhat crisp ; beneath which  is found, in  those which inhabit
the colder regions, a species of wool.  The head, too,  becomes much larger
in these wild races, as in the original Boar; and the differences in the conform-
ation of the  cranium, between these and  the domesticated breeds, are fully
equal to anything that is seen in the human race.—The variations which pre-
sent themselves in other races of domesticated animals introduced into South
America at the same period,—such as  the  horse, ass, ox, sheep, goat, dog,
cat, and gallinaceous birds,—are not less striking.—Still  more  remarkable
variations are seen  in certain domesticated breeds, which must without doubt
have sprung from the same  stock with the ordinary ones, although their origin
cannot  be traced historically; thus, in some localities we  find  swine with
solid hoofs ;  in others, the hoof is cleft into  five parts;  and in others, again,
the  toes are developed to a monstrous length. 
so
MUTUAL RELATIONS OF THE HUMAN FAMILY.
   69.  Although the numerous examples furnished by the Vegetable Kingdom
 may seem to  have but a remote bearing on the question, it would still be
 wrong to pass them by without notice;  since the  general principles already
 noticed are recognized by Botanists, as serving for the discrimination or iden-
 tification  of species of Plants; to which they apply equally with Animals.
 We have  abundant evidence, in the case of our cultivated  fruits and flowers,
 of the origination of new and well-marked varieties from stocks originally the
 same; the differences between these  races being such, as would undoubtedly
 have led to their being ranked as  distinct species, if their common parentage
 were not  known.  Thus, of the numerous widely-different  varieties of Apple,
 Pear, Strawberry, Plum, &c,  many have  been produced in our  own time ;
 and there is  no doubt, that all the forms of  each fruit are descended from
 wild stocks, extremely unlike any one of  them.  So the Cowslip, Primrose,
 Oxslip, and Polyanthus, which were formerly regarded as constituting at least
 two distinct species, have  been shown to be all producible  from the seeds of
 one parent.  And a single plant of the Orchideous tribe has borne flowers and
 pseudo-bulbs, which were formerly considered as characteristic  of three dis-
 tinct genera.
  70.  Of the origination of entirely new races  of  animals, distinguished by
 physical peculiarities, and disposed to become permanent under circumstances
 favourable to their perpetuation, we  have frequent examples at the present
 time.   It  is not uncommon to  meet with  individuals among our domesticated
 animals, which differ from others of their kind, in  some  marked feature of
 their conformation.  If this be of a nature which impairs the value of the
 animal, care is taken that it shall not propagate  its race;  but, on the  other
 hand, if it afford a prospect of utility, the skill of the breeder is  employed to
 perpetuate it.  One of the most remarkable examples of this kind, is to  be
 found in the origin of the Ancon or Otter breed  of Sheep, now  common in
 New England.  In the year  1791, one  of the  ewes on  the farm of Seth
 Wright, in the State of Massachusetts, produced a male lamb, remarkable for
 the singular length of its body, the shortness of its limbs, and the crookedness
 of its fore-legs.   This physical conformation, incapacitating the animal from
 leaping fences, appeared to the farmers around so desirable, that they wished
 it continued.   Wright consequently determined  on breeding from this  ram;
 but the first year he obtained only two with the  same peculiarities.  In the
 following  years, he obtained greater numbers; and when they beeame capable
 of breeding with one another, the new race became permanent,—the offspring
 invariably having the Ancon conformation, when both the parents belonged
 to that breed.  In the Human race, it is not  uncommon  to find particular
 families distinguished  by the possession of six  fingers on each hand, and six
 toes on each foot.   If such were to intermarry exclusively with  one another,
 there can  be no reasonable doubt that the children would invariably exhibit
the  same peculiarity;  and  the six-fingered  race, which now tends, whenever
it is originated, to  merge in the more  general form, would then  become per-
manent.  When it is remembered that the influence of a scanty population, in
the  early ages of the world, would  have been precisely the same as that which
is now exercised by the breeders of animals, we can understand  why the va-
rieties, which then arose, should have  had a much greater tendency to become
permanent, than most  of those  which now present themselves. At the present
time, any  peculiarity which may occasionally arise, speedily merges by inter-
mixture with the mass, and returns to the common standard; but when popu-
lation was  scanty, any peculiarities existing in one family would be perpetuated,
by the intermixture of its members, rendered necessary by their isolation from
others;  and thus a new race would originate.
  71.  For the cause of these  occasional variations  from the common type, 
ON THE VALUE OF SPECIFIC DISTINCTIONS.
81
we must look  in part to the original constitution of the species, and in  part
to the influence  of external conditions.  As already  mentioned,  there  is a
marked difference among various species of animals (even those nearly allied,
such as the Domestic Cat and the Tiger), in regard to their respective capa-
cities for variation.  And among the peculiarities of conformation which oc-
casionally present themselves in the  Human and other most variable species,
there are several, which  cannot be  in  any  way attributed to  the  modifying
influence of external conditions;—such, for  example,  as  the development of
additional fingers or toes, the alteration in the number of the vertebrae in the
tail, the unusual consolidation or separation  of the toes, &c.   But it cannot
be doubted, when the known history of the domesticated races is  fairly con-
sidered, that a change of external circumstances is capable of exerting a very
decided influence upon the physical form, upon the habits and instincts, and
upon various functions of life.  The variations thus induced, extend to con-
siderable modifications in the external aspect, such as the  colour, the texture,
and the thickness of the external covering;  to the structure  of limbs, and the
proportional size of parts; to the relative development of the organs of the
senses and of the psychical powers, involving changes in the form  of the cra-
nium; and to acquired propensities, which, within certain limits (depending, it
would appear, on their connection with the natural habits of the species), may
become hereditary.


       4. On the Extremes of Variation among the Races of Men.
   T2.  We have now to inquire, in the  third place, how far the same influ-
ences might be expected to operate in the Human race; and whether the ex-
treme varieties, which we enconuter  among Mankind,  are really greater than
those,  which we  meet with in  the races of  domesticated  animals,  known to
have had a common ancestry.  It must be admitted by every one, that both
of the  conditions just noticed as favouring the origination of peculiarities, ope-
rate to their fullest extent in Man.   There is no other  species of animals, in
which an equal tendency to variation exists.   The different individuals of the
same  breed of Dogs, for  example, resemble each other far more  closely in
physical and mental characters, than the individual men of one nation;  and
there is no species of animals, which possesses an equal power of maintain-
ing life in the remote extremes of climate, atmospheric pressure, &c, which
are encountered at different  parts of the earth's surface, and at different ele-
vations above it.   Again, we should  expect to find  these varieties in external
circumstances,  together with the  change of  habits induced by civilization
(which is far greater than  any change effected by domestication in  the condi-
tion of the lower  animals), producing still more  important alterations in the
physical  form  and constitution of the  Human body, than those effected in
brutes  by a minor degree  of alteration.  And it  may be reasonably antici-
pated, that, as  just now explained, there would be  a greater tendency to the
perpetuation of these varieties,  in other words, to  the  origination  of distinct
races, during the  earlier  ages of the history of the race, than  at the present
time, when, in  fact, by the increasing admixture  of races which  have long
been isolated, there is a tendency to the fusion of all these varieties, and to a
return  to a common type.   Now, when  the extreme varieties which are pre-
sented by the  different races of Man are carefully compared together, it is
found that their differences are all of the same kind as those, which present
themselves among the breeds of domesticated animals;  and  do not by any
means  exceed them (perhaps  not even equalling  them  in degree.   This will
be shown in detail hereafter.
   73.  It appears, then, that the analogical argument derived  from the pheno- 
82
MUTUAL RELATIONS OF THE HUMAN FAMILY.
mena presented by the domesticated species among the lower animals, is de-
cidedly in  favour of the  specific unity of the  Human race;  the  differences
which have sprung up, in course of time, amongst the  inhabitants of different
parts of the world, being such as we have a fair right to attribute—according to
the recognized principles of Zoology—to the modifying influence of external
conditions, acting upon a constitution peculiarly disposed to yield to it.

   5.  On the Value of Physiological and Psychological Peculiarities, as
                          Specific Distinctions.
   74.  We have now to inquire, in the fourth place,  what other arguments in
favour of  this position may be drawn from agreement or difference in  Physi-
ological and Psychological peculiarities.  A comparison of the physiological
history of two races, is often found to afford a better  criterion of their specific
difference  or identity, than the comparison of their  structural  characters.
Now, in every important point of physiological history, there is a  wonderful
agreement amongst the different races of Men ; the variations not being greater
than are those with which we  meet among the  different individuals  of any
one race.   Thus, we not  only find the average duration of life to be every-
where the  same, (making allowance for circumstances which are likely to in-
duce disease), but  the various epochs of life have a  close correspondence,—
such as the times of the first and second dentition, the period  of puberty, the
duration of pregnancy, the intervals of the  catamenia, and  the time of their
final cessation.   And the different  races of Man  are  all subject to the same
diseases, both sporadic, contagious,  and  epidemic;  whilst there are  no two
really-distinct species among the lower animals, which have more than a very
slight conformity in this respect.
   75.  The most important physiological test of specific unity or diversity, is
derived from the phenomena attending the  Reproductive process.   It  is well
known that, in Plants, the stigma of the flower of one species  may be fertil-
ized with the pollen of an allied species; and  that, from the seeds produced,
plants of an intermediate character may be raised.   These hybrid  plants,
however, will not perpetuate the new race ; for, although they may ripen their
seed for one or  two generations, they will  not continue  to  reproduce them-
selves beyond the  third  or fourth.   But, if the  intervention of one of  the pa-
rent species be  employed,—its stigma  being  fertilized by the pollen of the
hybrid, or vice versa,—a  mixed race may be kept up for some time  longer;
but it will  then have a manifest tendency to return to the form of  the parent
whose intervention has been employed.  Where, on the other  hand,  the pa-
rents themselves were  only varieties, the hybrid forms but another variety,
and its powers of  reproduction are rather increased  than diminished;  so that
it may continue to propogate its own race, or may be used for the production
of other varieties,  almost  ad infinitum.  In this way, many beautiful new
varieties of garden  flowers have been obtained ; especially among such  species
as have a natural tendency to  change their aspect.  Amongst Animals, the
limits of hybridity are much more narrow, since the hybrid  is totally unable
to continue its race with one  of its own kind ;* and although it may be fertile
with one of its parent species, the  progeny will  of course approach  in cha-
racter to the pure breed, and  the race will  ultimately merge into it.  On the
other hand, in Animals, as among Plants, the mixed offsprings originating from
different races within the limits of the same species, generally exceed in vi-

  * One or two instances have been stated to occur, in which a Mule has produced offspring
from union with a similar animal;  but this is certainly  the extreme limit, since no one has
ever maintained that the race can be continued further than the second  generation, without
admixture with one of the parent species. 
                DISTINCTIVE PECULIARITIES OF THE RACES OF MAN.           83

   gour, and in the tendency to  multiply, the  parent races from which  they are
   produced, so as to gain ground upon the older varieties, and gradually to su-
   persede them.   In this manner, by the  crossing of the breeds of our domes-
   ticated animals, many new and superior varieties  have been produced.   The
   general principle is, then, that beings of distinct species, or descendants from
   stocks originally different, cannot produce  a mixed race, which shall possess
   the capability of perpetuating itself; whilst the union of varieties has a tend-
   ency to produce a race superior in energy and fertility to its parents.
      76. The application of this principle (if it be admitted as such) to the Hu-
   man races, leaves no doubt with respect to their specific unity; for, as is well
   known, not only do all the races of Men breed freely with each other, but the
   mixed race is generally superior in physical development, and in tendency  to
   rapid multiplication, to either of the parent stocks ;  so that there is much rea-
•   son to believe that, in many countries, the mixed race  between the Aborigines
   and European  colonizers will ultimately become the  dominant power in the
   community.  This is especially the case in India and South America.
      77. Not less conclusive  is the  result of the test, furnished  by agreement
   or difference in psychological characters.  Among the lower animals, we find
   every species characterised by the possession of instincts  and  propensities
   peculiar to itself; and these instincts often differ remarkably in species, which
   present the  closest structural alliance.  On the other hand, in the several
   varieties  of domesticated animals, notwithstanding their strongly-marked di-
   versities of physical  structure, we  may recognize instincts which  are fun-
   damentally  the same, although  they have been modified by  the continued
   influence of Man, and  by the new circumstances in which  the  animals are
   placed.  Now from an impartial survey of the psychological characters of the
   different races  of Men, so far as  our present knowledge extends, the follow-
   ing conclusion  may be drawn.  " We contemplate, among all the diversified
   tribes, who  are endowed wiih reason and speech, the same internal feelings,
   appetencies, and aversions; the same inward convictions, the same sentiments
   of subjection to  invisible powers, and (more  or less fully developed) of ac-
   countableness or responsibility to  unseen  avengers of wrong  and  agents  of
   retributive justice, from whose tribunal men cannot even  by death escape.
   We find everywhere the same susceptibility, though not always  in  the same
   degree of forwardness or ripeness of improvement, of admitting the cultiva-
   tion of those universal endowments, of opening the eyes  of the  mind to the
   more  clear  and luminous views which Christianity unfolds,  of becoming
   moulded to the institutions of religion and of civilised life : in a word, the
   same inward and mental nature is to be recognized in all the races of men.*


     6.  On the  Comparative Peculiarities of the Different Races of Mankind.
      78. We have now  to inquire,fifthly and lastly, whether it is possible, after
   a detailed and careful examination of the ensemble of the characters of the
   different races of Men,  to make  any division of them  into  distinct  groups,
   capable of being defined by such constant  and well-marked features, as shall
   entitle them to  be regarded in the light of distinct species.   The .general re-
   sults, only, of this inquiry, can here be given ; and  this in a very summary
   manner.  They will be almost entirely drawn from the profound and labo-
   rious investigations of Dr. Prichard.
      79. The characters which  are  most relied on for the discrimination of the
   several races of Mankind, are the colour of the skin, the  nature of the hair,
   and  the conformation of the  skull and other parts of  the skeleton.   The Co-
* Prichard's Natural History of Man, p. 546. 
84
MUTUAL RELATIONS OF THE HUMAN FAMILY.
 lour of the skin exists in the  epidermis  only; and it depends  upon the ad-
 mixture of certain peculiar cells, termed pigment-cells, with  the  ordinary
 epidermic cells. These pigment-cells, as will be shown hereafter (§  163), are
 distinguished by their power of generating  or secreting  colouring-matter of
 various hues;  and all the varied shades of colour, presented by the different
 races of men, are  due to the relative  amount  of these cells, and to the parti-
 cular tint  of the  pigment which they form.   It would be easy, by selecting
 well-marked specimens of each race, to make it appear that colour affords
 sufficient distinctive marks for their separation: thus, for example, the fair
 and ruddy Saxon, the jet-black Negro, the olive Mongolian, and the copper-
 coloured North American, would seem positively separated from  each other
 by this character,  propagated,  as it  seems to be, with little or no  perceptible
 change, from generation to generation.  But although  such might appear to
 be the clear and obvious result of a comparison of this kind, yet a more pro- »
 found and comprehensive survey  tends to break down the barrier that would
 be thus established.  For, on tracing this character through the entire family
 of Man, we find the isolated specimens just noticed to be connected by such
 a  series of links, and the transition from one to the other to be so very gradual
 that it is impossible to say where the line is to be drawn.  There is nothing
 here,  then, which  at all approaches to the fixed and definite marks, which have
 been noticed as serving—though  equally trivial in themselves—to  establish
 specific distinctions among other tribes of animals.
   80.  But further, there is  abundant evidence that these distinctions  are far
 from being constantly maintained, even in any one race.   For among all the
 principal subdivisions, albinoism, or  the absence of  pigment-cells, occasion-
 ally presents itself; so that the fair skin of  the European may present itself
 in the offspring of the Negro or of the  Red  Man.   On  the other hand, in-
 stances are by no means rare, of the unusual development  of  pigment-cells
 in individuals  of the  fair-skinned races ; so  that parts of the body are of a
 dark red or brown hue, or are even  quite  black.  Such modifications may
 seem  of little importance to the argument;  since they are  confined to  indi-
 viduals, and may be put aside as accidental.   But  there  is ample evidence,
 that analogous  changes may take  place in the course of  time, which tend to
 produce a great variety of shades of colour, in the  descendants of any one
 stock.   Thus,  in the  great  Indo-Atlantic family, which  may  be  unquestion-
 ably regarded  as having had a  common  origin, we find races with fair com-
 plexion, yellow hair,  and blue eyes,—others presenting the xanthous or olive
 hue,—and others decidedly black.  A similar  diversity may be  seen  among
 the American races, which are equally referrible to one common stock ; and
 it  exists to nearly the same extent among the African  nations, which  are simi-
 larly related to each other.  It may be freely  admitted that, among European
 colonists settled in hot climates, such changes do not present themselves within
 a few generations ; but in many well-known instances of earlier colonization
 they are very clearly manifested.   Thus the wide dispersion of the Jewish
 nation, and their remarkable isolation (maintained by their religious observ-
 ances)  from the people among whom they live, render them peculiarly appro-
 priate subjects for  such observations ; and we accordingly find,  that the bru-
 nette complexion and dark hair, which are usually regarded as characteristic
 of the race, are frequently superseded, in the  Jews of Northern Europe, by
 red or brown hair  and fair complexion; whilst the Jews  who  settled in India
 some centuries  ago, have become  as  dark as the Hindoos  around them.
   81. The relation of the complexions of the different races  of Men  to the
 climates they respectively inhabit, is clearly established by an extended com-
parative survey of both.   From such a  survey the conclusion is  inevitable,
that the intertropical region of the earth is the principal seat of the black races 
             DISTINCTIVE PECULIARITIES OF THE RACES OF MAN.           85

of Men ; whilst the region remote from the tropics is that of the white races;
and that the climates approaching the tropics are generally inhabited by na-
tions, which are of an intermediate complexion.  To this observation it may
be added, that high mountains, and countries of great elevation, are generally
inhabited by people of a lighter colour, than are those of  which the level  is
low, such as swampy or sandy plains upon the sea-coast.  These distinc-
tions are particularly well seen in Africa, where the tropics almost exactly
mark out the limits of the black  complexion of the inhabitants ;  and where
the deepest hue is to be seen among  the Negroes of the Guinea  Coast, whose
residence unites both the conditions just mentioned.
   82. The nature of the Hair is, perhaps, one of the most permanent charac-
teristics of different races.  In regard to its colour, the same statements apply,
as those just made with respect to the colour of the skin; the variety of hue
being given  by pigment-cells, which  may be more  or less developed  under
different circumstances.   But it has  been thought that its texture  afforded a
more valid ground of distinction; and it is commonly said that the substance
which grows on the  head of the African races, and of some other dark-colour-
ed tribes (chiefly inhabiting tropical  climates), is wool, and not hair.  This,
however, is altogether  a mistake:  for microscopic examination  clearly  de-
monstrates, that the  hair of the  Negro has exactly the  same  structure with
that of the European; and that it does not bear any resemblance to wool, save
in its crispness and  tendency to  curl.  Moreover, even  this character is  far
from being a constant one;  for, whilst Europeans are not unfrequently to  be
met with, whose hair is as crisp  as that of the Negro, there is a great variety
amongst the Negro  races themselves, which  present every gradation from a
completely crisp (or what is  termed woolly)  hair, to merely curled or even
flowing locks.   A similar observation holds good in regard to  the natives of
the islands of the great Southern  Ocean, where some individuals possess crisp
hair, whilst others, of the same race,  have it merely curled.  It is evident, then,
that no characters can be drawn from the colour or texture of the hair in Man,
sufficiently fixed and definite to  serve for the  distinction of races: and this
view is borne out by the evident influence  of climate, in producing changes
in the hairy covering of almost every race of domestic animals;—the change
often manifesting itself in the very individuals that are transported from  one
country to another, and showing  itself yet more distinctly in succeeding gene-
rations.
   83. It has been supposed, that varieties in the configuration of the Skeleton
would afford characters for the separation of  the Human races,  more fixed
and definite than these  derived from differences in the form, colour, and tex-
ture of the soft parts which clothe  it.   And attention has been particularly
directed to the skull and the pelvis, as affording such characters.   It has been
generally laid down  as a fundamental principle, that all those  notions which
are found to resemble each  other in  the  shape of their heads, must needs  be
more nearly related to each other, than they are  to tribes of Men who differ
from them  in this  particular.  But if this principle  be rigorously carried out,
it will tend to  bring  together races, which inhabit parts of the  globe very re-
mote from each other, and which  have no other mark of affinity whatever:
whilst, on the other  hand, it will often tend to separate  races, which every
other  character would lead  us to bring together.  It is   to be remembered,
moreover, that the varieties  in the conformation of the skeleton, presented by
the breeds of domesticated animals, are at least equal to those which are ma-
nifested in the conformation and colour of their soft parts; and  we might rea-
sonably expect, therefore, to meet with similar variations  among the Human
races.  It is probable, however, that climate  has not so much influence in
producing such changes in the configuration of the body, as is exerted by the
     8 
86
MUTUAL RELATIONS OF THE HUMAN FAMILY.
peculiar habits and mode of life of the  different races; and Dr. Prichard has
pointed out  a very remarkable  relation of this kind, in regard to the three
principal types of form presented by the skull.
  84.  Among the rudest tribes of Men, hunters and savage inhabitants of fo-
rests, dependent for their supply of food on the accidental produce of the soil
or on the chase,—among whom are the most degraded of the African nations,
and the Australian savages,—a form of head is prevalent, which is  most aptly
distinguished by the term prognathous, indicating a prolongation or forward-
               Profile and basal views of the prognathous skull of a Negro.

extension of the  jaws.  This character is  most strongly marked in the Ne-
groes of the Gold Coast, whose  skulls are usually so  formed, as to give the
idea of lateral compression.  The temporal muscles have a great extent, rising
high on the parietal bones; the cheek-bones project  forward, and not out-
ward ; the upper jaw is lengthened  and projects  forwards, giving a similar
projection  to  the alveolar ridge and to the teeth;  and  the  lower jaw has
somewhat of the  same oblique projection, so that the upper and lower incisor
teeth are set at an obtuse angle to  each other, instead  of  being nearly in pa-
rallel planes, as in the European.  From the shape of the upper jaw alone,
would result a marked diminution in  the  facial angle,  measured according to
the method of Camper; but  this  diminution is far from being sufficient to ap-
proximate the Ethiopian races to the higher Apes, as some have supposed it
to be.  For, whilst the average facial angle of the European may be stated at
80°, and that  of the  Negro at 70°, that of the adult Chimpanzee  is only 35°,
and that of the adult Orang  only 30°.*   Independently of the diminution of
the facial angle, resulting from the projection of the upper jaw, it is quite cer-
tain  that, in the typical prognathous skull, there is a want of elevation of the
forehead;  but it  does not appear that there is a corresponding diminution  in
the capacity of the  cranial cavity,  the retreating form  of  the  forehead being
partly due to  the general elongation of  the  skull in the antero-posterior  direc-
tion.   Nor is  it true, as stated by some, that the position of the foramen  mag-
num  in the Negro is decidedly behind that, which it holds in the European,
—in  this respect  approaching that of the Apes (§ 51): since, if due allowance

   * The different statements made by some writers, who have estimated  the facial angle of
the higher Apes at from 60° to 64°, are due to the measurements having been made upon
young skulls; the projection of the jaws, in these animals, undergoing an extraordinary in-
crease at the time of the second dentition. *
 
             DISTINCTIVE PECULIARITIES OF THE RACES OF MAN.           87

be made for the projection of the upper  jaw, this  aperture  is found to have
the same position  in  the  prognathous skull as in the  oval  one, namely, ex-
actly behind the transverse line bisecting the antero-posterior diameter of the
base of the  cranium.   The prognathous skull is further remarkable for the
large development of the parts connected with the organs of sense, especially
those of smell and hearing.  The aperture  of the nostrils is very wide ;  and
the internal  space allowed for the  expansion of  the Schneiderian membrane,
and for the distribution of the olfactory nerve, is much larger than in most
European heads.   The posterior openings of the nasal cavity are not less re-
markable for their width than the anterior.  The external auditory meatus is
also peculiarly wide and spacious; and the orbital cavities have been thought
to be of more  than ordinary capacity,—but this last is by no means a constant
character.
   85.  A second shape of the head, very different from the preceding, belongs

                                   Fig 8,
              Front and basal views of the pyamidal skull of an Esquimaux.

principally to the nomadic  races, who wander with  their herds  and flocks
over vast plains;  and to the tribes who creep along the shores of the Icy Sea,
and  live partly by fishing, and in part on the  flesh of their reindeer.  This
form, designated by Dr. Prichard as the pyramidal, is typically exhibited by
various nations of Northern and Central Asia;  and is seen in an exaggerated
degree, in the  Esquimaux.   Its most striking character is the lateral or  out-
ward projection of the zygoma, which is due to the form of the malar bones.
These do not project forwards and downwards under  the eyes, as in the pro-
gnathous skull; but take a  direction laterally or outwards, forming, with the
zygomatic process of the temporal bone, a large rounded sweep or segment
of a circle.   From this, in  connection with the narrowness of the forehead,
it results, that lines drawn from the zygomatic arches,  touching the temples on
either side, instead of being parallel (as in Europeans), meet over the forehead,
so as to form with the basis a triangular figure.  The upper  part of the face
being remarkably flat, the nose also being flat, and the nasal bones, as well as
the space between the  eyebrows, being nearly on the same plane with the
cheek-bones, the triangular space bounded by these  lines may be  compared to
one of the faces of a pyramid.   The  orbits are large and deep; and the pecu-
liar conformation  of the bones which  surround  it, gives to the aperture of the
lids  an appearance of obliquity,—the  inner angle seeming  to  be directed
downwards.   The whole  face, instead of presenting an oval form, as  in most
Europeans and Africans, is of a lozenge-shape.   The greater relative develop-
 
88
MUTUAL RELATIONS OE THE HUMAN FAMILY.
ment  of the  zygomatic bones, and of the bones of the face altogether, when
compared with the capacity of the cranium, indicates in the pyramidal skull
a more ample  extension  of the  organs  subservient to sensation;  the same
effect being thus produced by lateral expansion, as by the forward extension
of the facial bones in the prognathous skulls.
  86.  The most civilized races,—those which live by agriculture and the arts
of cultivated life,—all the most intellectually-improved nations of Europe and
Asia,  have a shape of the head, which differs from both the preceding forms,
                                     and  which  may be termed oval or
                                     elliptical.  This  at once approves it-
                                     self as a more symmetrical form; no
                                     part having an excessive prominence;
                                    /whilst on the other hand, there is no-
                                     where  an appearance  of undue flat-
                                     tening or compression.  The head is
                                     altogether of a rounder shape than in
                                     other varieties;  and the forehead is
                                     more  expanded;  while the maxillary
                                     bones and  the  zygomatic arches are
                                     so formed, as to give the face an oval
                                     shape,  "nearly on  a plane  with  the
                                     forehead and cheek-bones, and not
                                     projecting  towards  the lower part.
                                     Owing  to the more perpendicular di-
         Oval skull of a European.          rection  of the alveolar processes, the
                                     front teeth  are fixed in planes, which
are nearly  or  quite parallel  to  each  other.  The  principal  features  in
this form of cranium are thus of  a negative character;  the chief positive dis-
tinction is the large development of the cranial  cavity, and especially the full-
ness  and elevation of the  forehead, in proportion to the size  of the face;—
indicating the  predominance of the intellectual powers over those  merely
instinctive  propensities, which  are  more directly connected with sensations.
Among European nations, the  Greeks have probably displayed the greatest
symmetry and  perfection  in the  form of the head; but various departures
may be traced,  towards the preceding forms, when we compare the  crania of
different races, and even of individuals,  belonging to the same stock,—some
approaching  the  pyramidal form of the  Northern Asiatics,  whilst others ap-
proximate to the  prognathous type of the Negro.
  87. The influence of habits of life, continued  from generation to generation,
upon the form of the head, is remarkably evinced by the transition  from  one
type  to  another, which may be observed in nations that  have undergone a
change in their manners, and customs, and have made an advance in civiliza-
tion.   Thus, to mention but one instance, the Turks at present inhabiting the
Ottoman and Persian empires, are undoubtedly descended from the same stock
with the nomadic races, which are  still  spread through Central Asia.  The
former, however, having conquered  the  countries  which  they now inhabit,
eight centuries  since, have gradually  settled down to the fixed and regular ha-
bits of the  Indo-European race, and have made corresponding  advances in
civilization;  whilst the latter have  continued  their wandering mode of life,
and can scarcely be said to have made any decided  advance during the same
interval.  Now, the long-since civilized Turks have undergone a complete
transformation into the likeness of Europeans ;  whilst their nomadic relatives
retain the pyramidal configuration of the  skull in a very marked degree. Some
have  attributed  this change in the physical structure of the  Turkish race, to
the introduction of Circassian slaves into the harems of the Turks; but this
 
             DISTINCTIVE PECULIARITIES OF THE RACES OF MAN.           89

could only affect the opulent and powerful amongst the  race;  and the great
mass of the Turkish population have always intermarried among themselves.
The difference of religion  and manners must have kept  them  separate from
those Greeks whom they subdued in the new Ottoman countries; and in Per-
sia, the Tajiks, or real Persians, still remain quite distinct from  their Turkish
rulers, belonging to a different  sect among the Mussulmans, and commonly
living apart from them.   In like manner, even the Negro head and face  may
become assimilated to the European, by long subjection to similar influences;
thus, in some of our older West Indian Colonies,  it is not uncommon to meet
with Negroes,—the descendants of those first introduced there,—who exhibit
a very European physiognomy; and  it has even  been asserted  that a Negro
belonging to the Dutch portion of Guiana, may be distinguished from another
belonging to the British settlements, by the similarity of his features and ex-
pression to those which peculiarly characterize his masters.  The effect could
not be here produced,by the intermixture of bloods, since this would be made
apparent by alteration of colour.
  88.  Next to the characters derived from  the form of the head, those which
are founded upon the form  of the pelvis  seem entitled to rank.   These have
been  particularly examined by Professors  Vrolik  and Weber.   The  former
concluded from his examinations of this  part of  the skeleton, that the pelvis
of the Negress, and still more that of the female  Hottentot, approximates to
that of the Simiae in  its general configuration ; especially in its length  and
narrowness,—the iliac bones having a more vertical position, so that the ante-
rior spines approach one another much more closely than  they do in the Euro-
pean ;  and the sacrum also  being longer and narrower.  On the other hand,
Prof. Weber concludes, from a more comprehensive survey, that no particular
figure is a permanent characteristic of any one race.  He groups the principal
varieties which he has met with, according to the form of the upper opening,
—whether oval, round, four-sided, or wedge-shaped.  The first of these is
most frequent in the European races; the second,  among the American races ;
the third, most common among the Mongolian nations, corresponds  remarka-
bly with the form of their  heads ; whilst  the last chiefly occurs among the
races of  Africa, and  is in  like manner  conformable with the oblong com-
pressed form usually presented by their cranium.   But though  there are par-
ticular shapes which are most prevalent in each race, yet there are  numerous
individual deviations; of such  a  nature, that every variety of form presents
itself occasionally in any given race.
  89.  Other variations have been observed by anatomists, in the relative length
of the bones, and in the shape of the  limbs, between the different races of
Man;  but these also seem to have reference to the degree of civilization,  and
to the regularity of the  supply of  wholesome  nutriment.   It is generally to
be observed, that the races least improved by civilization, like the uncultivated
breeds of animals, have slender, lean, and  elongated  limbs; this may be es-
pecially remarked in the natives of Australia.   In nearly all the less civilized
races of Men, the limbs are more crooked and badly formed than the average
of those of Europeans; and  this is particularly the case in the Negro, the
bones of whose legs bow outwards, and whose  feet are remarkably flat.   It
has been generally believed, that the length of the forearm in the Negro is so
much greater than in the European, as to constitute a real character of  ap-
proximation to the Apes.  The difference, however, is in reality extremely
slight; and is not at all  comparable with  that which  exists between the most
uncultivated races of Men and the highest Apes (§  54).  And in regard to all
the  peculiarities here alluded to, it  is to  be observed, that they can only be
discovered by the comparison of large numbers of one race with correspond-
ing  numbers of another; for individuals  are found in every tribe, possessing
                                   8* 
90              MUTUAL RELATIONS OF THE HUMAN FAMILY.

the characters which  distinguish the majority of the other race.  Any such
peculiarities, therefore, are totally useless as the foundation of specific charac-
ters ;  being simply variations from  the ordinary type, resulting from causes
which might affect the entire race, as well as individuals.
  90.  The connection between the general form of the body, on the one hand,
and the degree of civilization (involving the regular supply of nutriment) on
the other, is made apparent, not merely by the improvement which we  per-
ceive  in the form, development, and vigour of the frame, as we advance from
the lowest to the most cultivated of the Human races ; but also by the  degra-
dation which is occasionally to be met with in particular groups of the higher
tribes, which have been subjected for several generations to the influence of
depressing causes.  Of this class of facts, the following is a very  interesting
example :—" On the plantation of Ulster, and afterwards on the successes of
the British against the  rebels of  1641 and 1689, great multitudes  of the na-
tive Irish  were  driven from Armagh and the south of Down, into  the moun-
tainous tract extending from the  barony of Flews eastward to the sea:—on
the other side of the kingdom, the same race were expelled into Leitrim, Sligo
and Mayo.  Here they have been  almost ever since, exposed to  the worst
effects of  hunger and ignorance,  the two  great brutalizers of the human race.
The descendants of these exiles are still readily distinguishable from their
kindred in Meath, and in other districts where they are not in  a state of phy-
sical degradation ; being remarkable for open projecting mouths, with prominent
teeth  and exposed gums;  their advancing cheek-bones and depressed noses
bearing barbarism on their very front.  In Sligo and northern Mayo, the con-
sequences of two centuries of degradation and hardship exhibit themselves in
the whole physical condition of the people;  affecting not only the  features,
but the frame, and giving such an example of human deterioration from known
causes, as almost  compensates, by its value to future ages, for the suffering
and debasement  which past generations have endured in perfecting its appall-
ing lesson.  Five feet two inches upon  an average, pot-bellied, bow-legged,
abortively-featured, their clothing a wisp of rags,—these spectres of a people,
that were once well-grown, able-bodied, and comely, stalk abroad into the day-
light of civilization, the annual apparitions of Irish  ugliness  and Irish want.
In other parts of the  island, where  the population has never undergone the
influence of the  same  causes of physical degradation, it is well known  that
the same race  furnishes the most  perfect  specimens of  human beauty and
vigour, both mental and bodily."*
  91.  From  the foregoing survey of the phenomena, bearing upon the ques-
tion of the specific unity or diversity of the  Human races,  the  following
conclusions may be drawn :—
  1. That the  physical constitution of Man is peculiarly disposed, like that
of the domesticated  animals, to undergo variations; some of which can be
traced to the influence of external causes;  whilst others are not so  explicable,
and must be termed spontaneous.
  II.  That the  extreme variations which  present themselves, between the
races  apparently the most removed from one another, are not greater in degree
than  those which exist between the different breeds of domesticated animals,
which are known to  have descended from a common stock; and that they
are of the same kind  with the variations which present themselves in any
one race of Mankind,—the  difference of degree being clearly attributable, in
the majority of cases, to the respective  conditions under which each  race
exists.
   III. That none of the variations, which have  been pointed out  as existing
* See Dublin University Magazine, No. XLVIII. 
PRINCIPAL BRANCHES OF THE HUMAN FAMILY.
91
 between  the different  races of mankind, have the least claim to be regarded
 as valid  specific distinctions;  being entirely destitute of that fixity, which is
 requisite to entitle them to  such a rank;  and  exhibiting, in certain groups of
 each race, a tendency to pass into the characters of some other.
   IV.  That, in the absence  of any  valid specific distinctions, we are required,
 by the universally-received  principles of zoological science, to regard all the
 races of Mankind  as  belonging to  the  same species, or (in other words) as
 having had either an identical or similar parentage;  and that this  conclusion
 is supported by the positive evidence, afforded by the  agreement of all the
 races in the physiological and psychological characters, that most  distinguish
 them from other species, and especially by the ready propagation of mixed
 breeds or hybrid races.

              7. Principal  Branches of the Human Family.
   92. The above conclusions are found  to be  in entire accordance  with those
 derived from an examination of the relative affinities of the different races" of
 Men at present existing ;  as far as these are deducible from the analogies of their
 language, from their correspondence in peculiar habits and observances, and from
 traditional or other evidence  in regard to their original sources.  For it appears,
 from such investigations, that very great difference in colour, texture of  the hair,
 form of the skull, and other important physical characters, exist among nations,
 which may be referred with great confidence to a common source; whilst on
 the  other hand,  we find traits of physical resemblance, in tribes which exist
 under corresponding circumstances  in remote parts of the world,  and which
 seem to have nothing else in common.   It has been attempted by Blumenbach
 and  Cuvier to arrange the  different races of Men under five principal varie-
 ties; the Caucasian, Mongolian, Ethiopian, Malay, and American.  But, for
 the reason just given, it is impossible to establish any constant distinguishing
 characters, which  shall serve to mark these clearly out; and it moreover ap-
 pears that several additional groups must be created, for the reception of tribes,
 that differ  as much from the preceding as these do from each other.  In the
 following brief enumeration, the views of Dr. Prichard will be adopted.
   93. The Caucasian variety of Blumenbach and Cuvier was so named from the
 idea, that the Caucasian range of mountains might be regarded  as the centre
 or focus of the races belonging to it;  and that the Caucasian people  present
 the  typical conformation of the variety in the most perfect degree.  Neither
 of these  ideas are  correct, however; and some other designation might very
 properly be substituted for that which conveys them.   In this variety are pre-
 sented  all the characters of highest physical perfection of the race, such as
 were, perhaps, most pre-eminently  combined among the Ancient Greeks;  as
 well as those of  intellectual  and moral elevation.   No uniformity exists, how-
 ever, as to colour; for this character presents every intermediate gradation,
 from the fair and  florid hue of the Northern Europeans, to the jet black of
 many tribes in North Africa and Hindustan.   The hair is generally long and
 flexible;  but departures from the  ordinary type  present themselves in this
■ respect, also, both among individuals  and  among whole  tribes.  Although
 there is  general agreement  in  these characters among the nations of South-
 western Asia, Northern Africa, and nearly the whole of Europe,  yet we are
 required by the  evidence of ancient history, as well as by the characters de-
 rived from language, to  separate these nations into two groups; which appeared
 to have  been distinct from  each other at the earliest period of which we have
 any  traces ;  and which we must regard,  therefore, as alike entitled to rank as
 primary branches of the human family.   These are the Syro-Arabian, and the
 Indo-European groups  of nations. 
92              MUTUAL RELATIONS OF THE HUMAN FAMILY.
   94.  The Syro-Arabian nations, distinguished from all others by their very
peculiar  idiom, originally inhabited the region of Asia  intermediate between
the countries of the Indo-European and of  the Egyptian races;  having as its
centre  the region watered by the great rivers of Mesopotamia.  Several of the
nations originally constituting  this group have become extinct, or  nearly so;
and the Arabs, which Originally formed but one subdivision of it, have now
become the dominant race, not only throughout the ancient domain  of the
Syro-Arabian nations, but also in Northern Africa.   In  the opinion of Baron
Larrey, who had ample opportunities for observation, the skulls of the Arabian
race furnish, at present, the most complete  type of the human head; and he
considered the remainder of the physical  frame as  equally distinguished by
its superiority to that of  other races of men.  The  different tribes of Arabs
present very great diversities of colour, which are generally found to coincide
with variations in climate.  Thus the Shegya Arabs, and others living on the
low countries bordering on the Nile, are of a dark-brown or even black hue;
but even  when  quite jetty, they are distinguished from  the  Negro  races by
the brightness of their complexions, by the length and  straightness of their
hair, and by the regularity of their  features.   The  same may be said of the
wandering Arabs of  Northern Africa ;  but  the influence of climate  and cir-
cumstances is still more strongly marked in some of the tribes long settled in
that region, whose descent  may be traced to a distinct branch of the Syro-
Arabian  stock, namely, the Berber, to which  belong the Kabyles of Algiers
and Tunis, the Tuaryks of Sahara, and the Guanches or ancient  population
of the  Canary Isles.  Amongst these  tribes,  whose  affinity is  indisputably
traceable through  their very remarkable language,  every gradation  may be
seen, from the intense blackness of the Negro  skin, to the more swarthy hue
of the inhabitants of the South of Europe.   It is remarkable that some of the
Tuaryk inhabitants of particular Oases in the great desert, who are almost as
insulated  from  communication  with  other races  as are the inhabitants of
islands in a wide  ocean,  have  hair  and features that approach  those of the
Negroes; although they  speak the Berber  language with such purity, as to
forbid the idea of  the introduction of these characters by an intermixture of
races.  The Jews, who are the only remnants now  existing  of the  once pow-
erful Phoenician tribe, and who are now dispersed through nearly every coun-
try on  the face of the earth, present a similar diversity;  having gradually
assimilated in  physical characters to the nations among which they have so
long resided (§ 80).
   95.  The affinity of the  Indo-European  nations, now  spread from the
mouth  of the Ganges to the British Islands and  the Northern extremity of
Scandinavia, is  in  like manner proved by the cognate character of their lan-
guages ; in spite of the differences  in colour and other traits, which present
themselves among the inhabitants of that vast  tract.  The  type of physical
configuration, however, is the  same; and the differences of colour are such,
as may readily be traced to  external agencies.   Thus  among the Hindoo
races we  find that the distinction of castes (perpetuating the same mode of life
in particular families from generation  to generation), the marked differences
of climate (as between the  mountainous regions of Kashmir and Kafiristan,
and the plains bordering  the great rivers of India), and  other circumstances,
are accompanied, as  in the case of the Arabian race, with diversities in phy-
sical conformation, which are now established as belonging to different sections
of the  people.  In many instances, the origin of these varieties can be clearly
traced  by historical  evidence, as well  as  by affinities of language and con-
formation ; and it  cannot be questioned, that Hindoos  as black as Negroes,
others  of a copper-colour, others little darker than the inhabitants of Southern
Europe, and others of fair complexion with blue eyes and auburn or even red 
PRINCIPAL BRANCHES OF THE HUMAN FAMILY.
93
hair, have all had a  common parentage; some having become  darker, and
others lighter than their ancestors, generally in accordance with changes in
their residence and habits.   This group seems to have been early divisible
into two  primary branches; the  northern or Median; and the southern  or
Indian.   Between  the original  languages of these races, a marked resem-
blance can  be traced; and  the traditions of  both races point  to contiguous
regions as their original  seat,—the earliest records of the  Persians  indicating
that they migrated westwards from a spot in the ancient Bactria, not far from
Balkh, to the westward of the Indus;  whilst the traditions of the Brahmans
refer the  origin of the Hindoos to the north-western  part of the country lying
between  the  Himalaya and the  Vindhya mountains, whence they afterwards
moved eastwards and southwards into the Peninsula.   Both these races ap-
pear to have migrated in a north-westerly direction, at a period long preceding
our earliest knowledge of European history ;  for the European languages pre-
sent indications  of affinity  to  the  ancient  languages of  both  Medians and
Indians.   The classical languages of Greece  and Italy appear more referrible
to the  Sanskrit or ancient Indian, than to the Zend or ancient Median ; whilst,
on the other hand, the Germanic languages  would  seem  to have  originated
rather in the  latter.   Of all the  extant  European  dialects, the Lettish and
Lithuanian approach  most nearly to the ancient type.

   a. It may be well to notice here, the nature of the  evidence on which statements  of this
kind are  grounded. The extensive and  profound inquiries which have been  in progress
for many years, have enabled Philologists to distinguish, usually with little difficulty, between
the intermixture of languages, which may arise from the intercourse of any two nations that
happen to be connected by local proximity, commercial intercourse, &c.;  and  that  funda-
mental correspondence, which  indicates original  affinity.  The latter is  to be sought rather
in the analogies of grammatical structure, and in  the laws of combination, or the mechanism
of speech, than in  the vocabulary; and it sometimes happens that a relationship may thus
be traced between languages, which have scarcely a single word in common.  The most
satisfactory evidence, however, is derived from resemblance  in those parts of the vocabu-
lary, which serve to represent the ideas of a people in the most simple state of existence;—
such as terms expressive of family relations; names for the most striking objects of the visi-
ble universe; terms distinguishing different parts of the body; nouns of number, up to 5, 10,
or 20;  verbs descriptive of the  most common sensations and bodily acts, such as  seeing,
hearing, eating, drinking, and sleeping.  As no nation was ever found  destitute of  similar
expressions; and as we know by the observation of facts, in addition to abstract probability,
that tribes however rude, do not exchange their own stock of primitive words for those of a
foreign idiom; it may be inferred that dialects, which correspond  in those parts of their
vocabulary, were originally one speech, or the language of one people.
   6. It has been fully demonstrated, that both these indications of affinity or family relation-
ship exist between the languages of the several races, from which the great mass of the popu-
lation of Europe is derived; and, further, that this affinity not only unites them with each
other, but connects them  all with the common Eastern stock.

   96. The second primary division of the  human family, according  to the
usual  arrangement, is that  commonly  termed  Mongolian.   The  real  Mon-
goles, however, constitute but a single  and not very considerable member of
the group of nations  associated  under this designation;  which is, therefore,
by no means an appropriate one.  The original seat of  these races appears
to have  been the great central  elevated plain of  Asia,  in which all the  great
rivers of that continent have their sources, whatever may  be their subsequent
direction.  Taken  as a whole, this division  of the human family is charac-
terized by the pyramidal form of the skull, and by  a xanthous or olive com-
plexion ; but these characters are only exhibited, in a prominent degree, in
the more typical members of the group, and may become so greatly modified
as to cease altogether to be recognizable.   This has been remarkably the case
with regard  to the Turkish people, now so  extensively distributed.  All  the
most learned writers on Asiatic history are agreed in opinion, that the Turkish 
94
MUTUAL RELATIONS OF THE HUMAN FAMILY.
races are of one  common  stock;  although at present they vary in physical
characters, to  such a  degree that, in some, the original  type has  been alto-
gether changed.  Those which  still inhabit the  ancient  abodes of the  race,
and preserve their pastoral  nomadic life, present the physiognomy  and gene-
ral characteristics which appear to have belonged to the original Turkomans;
and these  are  decidedly referrible  to the so-called Mongolian  type.  Before
the Mohammedan era, however, the Western Turks or Osmanlis had adopted
more settled habits, and had made considerable progress in civilization; and
their  adoption of the  religion of  Islam incited them to still wider  extension,
and  developed that spirit  of conquest, which, during the middle  ages, dis-
played itself with such remarkable vigour.   The  branches of the race, which,
from  their long settlement in Europe, have  made  the greatest progress in
civilization, now exhibit in all essential particulars the physical characters of
the European  model;  and these are particularly apparent in the conformation
of the skull.—In like manner we  find that the Ugorian division, which mi-
grated towards the northwest at  a  very early period, planted a  colony in
Europe, which still tenants the Northern Baltic  countries, forming the races
of Fins and Lappes.  In the time of Tacitus, the Fins were as savage as the
Lappes ; but the former, during the succeeding ages, became so far civilized,
as to  exchange a nomadic  life for one of agricultural pursuits, and have gra-
dually assimilated with  the surrounding  people;  whilst the Lappes, like the
Siberian  tribes of the same race, have ever since continued to be barbarous
nomades, and  have undergone no elevation  in physical characters.   The same
division gave  origin to the  Magyars or Hungarians; a warlike and energetic
people, unlike their kindred in the North; in whom a long abode in the centre
of Europe has, in like manner, developed  the more  elevated characters, phy-
sical and mental, of the European nations.   The  nations inhabiting the south-
eastern portion of Asia, also, appear to  have had their origin in  the Mongolian
or Central Asiatic stock;  although  their  features  and form  of skull by no
means exhibit its characteristic marks,  but  present such departures from it as
are elsewhere observable  in races that are making  advances in civilization.
Even the great peninsula of Hindostan  appears  to have been  peopled, long
previously to  the settlement  of  the present  Hindoo  race, by tribes of the
Central Asiatic stock, so  distinguished by its migratory propensities;  and
remains of these  aborigines  are  still  found in  the hilly parts of  Northern
India, in the Dekhan, and in  Ceylon, constituting numerous tribes, which are
now for the most part isolated from each  other, and which exhibit very dif-
ferent degrees  of civilization.
  97. According to the usual mode of dividing the Human family, the Ethi-
opian or Negro  stock is  made to include all the  nations of Africa, to the
southward of  the Atlas range.  But there is good  reason for  separating the
Hottentots and Bushmen as a distinct race; and for restricting  the designation
of Negroes to  the nations inhabiting the region southward of the Great Desert,
as far as the Hottentot country,—the  inhabitants of the oases of  the  desert
itself being mostly, as already pointed out, of Syro-Arabian origin, although
assimilating closely to the  Negro race in physical  characters.   The  nations
thus in geographical proximity with each  other,  are found to have sufficient
affinities of language, to  justify the belief  in their common origin;  and they
all present, in a more or less evident degree, the  physical peculiarities of the
Negro race. But these are  far from constituting a sufficient ground  for regard-
ing the African nations as  a distinct race, separated from all other families of
men  by a  broad and definite line of  demarcation.   Our idea of  the Negro
character  is principally founded  upon  that division of the  people which in-
habits the low countries of the Western part of Central Africa, and in which
the Negro peculiarities are  most strongly marked.  There are very few nations 
PRINCIPAL BRANCHES OF THE HUMAN FAMILY.
95
which present in a high degree all the characters that are commonly regarded
as typical of the Negro; these  being generally distributed among different
nations  in various ways; and being combined, in  each instance, with more
or fewer of  the characters belonging to the European or Asiatic.  Thus the
race of  Jolofs near the Senegal, and the Guber in the interior of Sudan, have
woolly  hair and deep black  complexions, but fine  forms and regular features
of a European cast; and nearly the same may be said of the darkest of the
Kafirs of Southern Africa.  The Bechuna Kafirs present a  still  nearer ap-
proach  to the  European type;  the complexion being of a light brown, the
hair often not woolly but merely curled, or even in long flowing ringlets, and
the figure and features having  much of the European character.  The nations
of the northeast of Africa, also, present  similar departures from the typical
characters of the Negro.
   98. There  is no  group which presents a  more constant correspondence
between external conditions and physical conformation, than that composed
of  the  African nations.  As  we find  the complexion  becoming gradually
darker,  in passing from  northern to southern Europe, thence to North Africa,
thence  to the borders of the Great  Desert, and thence to the intertropical re-
gion  where alone the  dullest black  is  to be met with,—so do we find, on
passing  southwards  from this, that the hue becomes gradually lighter in pro-
portion as we proceed further from  the  equator,  until we meet with  races
of comparatively fair complexions  among the  nations of Southern  Africa.
Even in the intertropical region, high elevations of the surface have the same
effect, as we have seen them produce  elsewhere, in lightening the complexion.
Thus, the  high parts of Senegambia, where the temperature is moderate and
even cool at  times, are inhabited by Fulahs of a  light copper colour;  whilst
the nations  inhabiting the lower regions around them, are of true Negro black-
ness; and nearly on the same parallel, but at  the opposite side of  Africa, are
the  high planes of Enarea and Kaffa, where the inhabitants are said to be
fairer than  the natives of Southern Europe.  Again, those races which have
the  Negro  character in an exaggerated degree, and which may be  said to ap-
proach to deformity in  persons,—the ugliest blacks, with depressed forehead,
flat noses, and crooked legs,—are in  most instances inhabitants of low coun-
tries, often of swampy tracts near the sea-coast, where many of them have
scarcely any other means of subsistence than shell-fish and the accidental gifts
of the  sea.   Such tribes are uniformly in the lowest stage of society, being
either ferocious  savages, or stupid, sensual, and indolent.   Such are most of
the  tribes along the Slave  Coast.   On the other hand, wherever  we hear of
a Negro state, the inhabitants of which have attained any considerable degree
of improvement in  their social  condition, we constantly find that their phy-
sical characters deviate  considerably from the strongly-marked or exaggerated
type of the Negro.   Such are the  Ashanti, the Sulima, and the Dahomans of
Western Africa; also the Guber of Central Sudan, among which  a consider-
 able  degree of civilization has long existed, which are perhaps the finest race
 of genuine Negroes on the whole continent,  and  which present in their lan-
 guage  distinct traces of original relationship to the Syro-Arabian nations, not
 to be accounted for by  any  subsequent intermixture of races.
   99.  The highest civilization, and the greatest improvement in  physical
 characters, are  to be found  in those nations, which have adopted the Moham-
 medan  religion; this was introduced, three  or four centuries since, into the
 eastern portion of Central Africa;  and it appears  that the same people, which
 were then existing in the savage condition still exhibited by the pagan nations
 further south, have now adopted many of the arts and institutions of civilized
 society, subjecting  themselves to  governments,  practising  agriculture, and
 dwelling in towns of considerable  extent, many of which contain 10,000, and 
96
MUTUAL RELATIONS OF THE HUMAN FAMILY.
some even  30,000 inhabitants; a circumstance  which  implies  a consider-
able advancement in industry, and in the resources of subsistence.  This last
fact affords most striking evidence of the improvability of the  Negro races ;
and, taken in connexion with the many instances that have presented them-
selves, of the advance of individuals, under favourable  circumstances, to  at
least the average degree of mental development among the European nations,
it affords clear proof that the line of demarcation, which has been supposed
to separate  them intellectually and morally from the races that have attained
the greatest  elevation, has no  more real existence than that, which has been
supposed to  be justified by a difference in physical characters, and of which
the fallacy has been demonstrated.
   100.  The  Bushmen or Bojesmen of South Africa are generally regarded
as presenting the most degraded and miserable condition, of which the human
race is  capable:  and  they  have been supposed to present resemblances in
physical characters to the higher Quadrumana.  Yet there is distinct evidence,
that this  degraded  race  is but a branch or subdivision of the once extensive
nation of Hottentots;  and that its present condition is in great part due to the
hardships, to which it has been subjected in consequence of  European colo-
nization.   This race  differs from all other South African nations, both in lan-
guage and in physical conformation.  The language cannot be shown to possess
affinities  with those of any other stock; but in bodily structure there is a re-
markable admixture of the characters of the Mongolian with those of the Ne-
gro.  Thus  the face  presents  the very wide and high cheek-bones, with the
oblique eyes and flat nose, of the Northern Asiatics;  at the same time that, in
the  somewhat prominent muzzle and thick lips, it resembles the countenance
of the  Negro.   The  complexion is of a tawny buff or fawn colour, like that
of the  Negroes diluted with the olive of the Mongoles.   The hair is woolly
like that of the Negroes, but it grows in  small tufts, scattered over the surface
of the  scalp, instead  of covering it uniformly, resembling in its comparative
scantiness that of the Northern Asiatics.   It is most interesting to observe this
remarkable resemblance in physical  characters,  between  the Hottentots and
the Mongolian races ;  in connexion with the similarity that exists between the
circumstances under which they respectively live.   No two.countries can be
more similar, than the vast steppes  of Central Asia, and the karroos of  South-
ern  Africa.  And the inhabitants  of  each were nomadic races, wandering
through deserts remarkable for the wide expansion of their surface, their scanty
herbage, and the dryness of their atmosphere, and feeding upon the milk and
flesh of their horses and cattle.  Of the original pastoral Hottentots, however,
very few now remain.  They have been  gradually driven, by the encroach-
ments of European colonists and  by internal  wars  with each other, to seek
refuge among the inaccessible rocks and deserts of the interior; and they have
thus been converted from a mild unenterprising race of shepherds, into wander-
ing hordes of fierce, suspicious, and vindictive savages, treated as wild beasts
by their fellow-men, until they become really assimilated to wild beasts in their
habits and  dispositions.  This transformation has taken place under the ob-
servation of eye-witnesses, in the Koranas, a tribe of Hottentots well known
to  have been previously the most advanced in  all the improvements which
belong to pastoral life.   Having been plundered by their neighbours and driven
out  into the wilderness to subsist upon fruits, they have adopted the habits of
the  Bushmen, and have become assimilated in  every essential  particular to
that miserable tribe.
   101. The American nations, taken collectively,  form a group  which ap-
pears to have existed  as a separate family of nations from a very early period
in the world's history.   They do not form, however, so distinct a variety, in
regard to physical characters, as some anatomists have endeavoured to prove; 
                PRINCIPAL BRANCHES OF THE HUMAN FAMILY.              97

for, although certain peculiarities have been stated to exist in the skulls of the
aboriginal Americans, yet it is found, on a more extensive examination, that
these peculiarities are very limited in their extent,—the several nations spread
over this vast continent differing from each other in physical  peculiarities, as
much as they do from those of the Old World, so that no typical form can be
made out among them.   In regard to complexion, again, it may  be remarked,
that although the native Americans have  been commonly characterized as
" red men," they are by no means  invariably of a red or coppery hue, some
being as fair as many European  nations, others being yellow or  brown,  and
others nearly, if not quite, as black as the Negroes of Africa; whilst, on the
other hand, there are tribes equally red, and perhaps more  deserving that epi-
thet in Africa and Polynesia.—In spite of all  this diversity of conformation,
it  is  believed that the structure of  their  languages  affords a decided  and
clearly-marked evidence of relationship between them.   The  words, and even
the roots, may differ entirely in the  different groups of American nations;
but there is a  remarkable similarity in grammatical construction amongst them
all, which  is of  a kind not only to demonstrate  their mutual affinity, but to
separate them completely from  all  known languages of  the old continent.
Notwithstanding also their diversities in mode of life, there  are peculiarities
of mental character,  as well as a number of ideas and customs  derived from
tradition, which seem to be common to them all, and which for the most part
indicate a former elevation in the scale of civilization, that  has left its traces
among them even in their present  degraded condition, and  that still distin-
guishes them  from the sensual, volatile, and almost animalized savages, that
are to be met with  in  many  parts of the Old Continent.—The Esquimaux
constitute an exception  to all general accounts of the physical characters of
the American nations;  for in the configuration of their skulls,  in their com-
plexion, and in  their general  physiognomy, they conform  to the Mongolian
type, even presenting it  in an exaggerated degree.   Their  wide extension
along the whole  northern coast of America, and  the  near proximity of this
coast to Kamschatka, certainly lend weight to  the idea, that they derive their
origin from the Northern Asiatic stock; but, on  the other hand, they have a
marked affinity, in regard to language, to the other American nations.   The
Athapascan Indians, various tribes of which inhabit the  country south of the
Esquimaux country, seem intermediate in  physical characters, as they are in
geographical position, between the Esquimaux and the ordinary Americans.
They have a tradition which seems  to indicate, that they are derived from the
North-Eastern Asiatics, with whom they have  many points of accordance in
dress and manners.
   102.  It now remains for us to  notice the Oceanic races, which inhabit the
vast series  of  islands scattered through  the great ocean, that stretches from
Madagascar to Easter Island.   There is no part of the world, which affords a
greater variety of local conditions than this, or which more evidently exhibits
the effects of physical agencies on the  organization of  the human body.
Moreover, it affords a case for the recognition of affinities by means of lan-
guage, that possesses unusual stability;  since the  insulated position of the
various tribes, that people the remote spots of this extensive tract, prevents
them from  exercising that influence upon each  others' forms of speech, which
is  to be observed in  the case of nations united by local  proximity or by fre-
quent intercourse.  Tried by this test, it is found that the  different groups of
people, inhabiting the greater part of these insular tracts, are more nearly con-
nected  together,  although  so  widely scattered, and  so  diverse  in  physical
characters,  than  most of the families of men, occupying continuous tracts of
land on the great continents of the globe.   The inhabitants of Oceanica  seem
divisible into three groups, which are probably to be regarded as  having con-
     9 
98
MUTUAL RELATIONS OF THE HUMAN FAMILY.
stituted distinct races from a very early period; these are the Malayo-Poly-
nesian race, the Pelagian Negroes (commonly termed Papuas), and theAlforas
or Alfourous.
   103. The Malayo-Polynesian group  is by far the  most  extensive of the
three, and comprehends the inhabitants of the  greater part of the Indian and
Polynesian Archipelagoes, with the peninsula of Malacca (which  is the cen-
tre of the Malays proper), and the inhabitants of Madagascar.   These are all
closely united by affinities of language.  The proper Malays  bear a strong
general resemblance to the Mongolian races, and this resemblance  is shared,
in a greater or  less degree, by most of  the  inhabitants of the  Indian Archi-
pelago.  They are of a darker complexion,  as  might be expected from  their
proximity to the equator; but in this complexion, yellow is still a large in-
gredient.  The  Polynesian branch  of  the group presents  a much  wider
diversity; and  if it were not for the community of language, it might be
thought to consist of several races, as distinct  from each other as  from the
Malayan branch.  Thus  the  Tahitians and Marquesans  are  tall and well-
made; their figures combine grace and vigour: their skulls are  usually re-
markably symmetrical;  and their physiognomy presents much of the Euro-
pean cast, with a very slight  admixture of the features of the  Negro.   The
complexion, especially in the females of the higher classes, who are sheltered
from the wind and sun, is of  a clear olive or  brunette,  such as is common
among the natives of Central and Southern Europe;  and the hair, though
generally black, is sometimes brown or auburn, or even red or flaxen. Among
other tribes, as the New Zealanders, and the Tonga, and Friendly Islanders,
there are greater diversities of conformation  and hue;  some being finely pro-
portioned  and vigorous, others  comparatively small and feeble ; some being
of a copper-brown colour, others nearly black, others olive, and  others almost
white.  In fact,  if we once admit a strongly-marked difference in complexion,
features, hair, and general configuration, as  establishing a claim  to  original
distinctness of origin, we  must  admit the application of this   hypothesis to
almost every group of islands in the  Pacific;—an idea of which the essential
community of language seems to afford  a sufficient refutation.  Among the
inhabitants of Madagascar, too, all of which speak dialects of the  same lan-
guage, some bear a strong resemblance  to  the Malayan type,  whilst others
present approaches to that of the Negro.
   104.  The Pelagian-Negro  races  must be regarded as a  group altogether
distinct from the preceding; having  a  marked diversity  of language"; and
presenting more decidedly than any of the Malayo-Polynesians, the characters
df the Negro type.  They form the  predominating population  of New Bri-
tain, New Ireland, the Louisiade  and Solomon Isles, of several of the New
Hebrides, and of New Caledonia; and they seem to extend westwards into
the mountainous interior of the Malayan Peninsula, and into the Andaman
Islands, in the Bay of Bengal.   The Tasmanians, or aborigines of Van Die-
man's Land, which are now almost  completely  exterminated, undoubtedly
belonged to this group.  Very little is  known of them, except through the
reports of the people of Malayo-Polynesian  race inhabiting the same islands;
but it appears that, generally speaking, they have  a very inferior physical de-
velopment, and lead a savage and degraded life.  There is considerable diversity
of physical characters among them ; some approximating closely in hair, com-
plexion, and features,  to  the  Guinea-Coast Negroes ;  whilst  others are  of
yellower tint, straight hair, and better general development.   The Papuans,
who inhabit the northern  coast of New-Guinea, and some  adjacent islands,
and who are remarkable for their large bushy masses of half-woolly hair, have
been supposed  to constitute a distinct race ;  but there is little doubt that they
are of hybrid descent, between the Malays and the Pelagian Negroes. 
                  ON ORGANIZED STRUCTURES IN GENERAL.               99

  105.  Still less  is known of the Alfourous,  or  Alforian race, which  are
considered by some to be the earliest inhabitants  of the greater part of  the
Malayan Archipelago, and to have been supplanted by the more powerful peo-
ple  of the two preceding races, who  have either extirpated them altogether,
or have driven them from the coasts into the mountainous and desert parts of
the  interior.  They are yet to be found in the central parts of the  Moluccas
and  Philippines; and they seem to occupy most of the interior and southern
portion  of New Guinea, where they are termed Endamenes.  They are of
very dark complexion; but their hair, though black and thick, is lank.  They
have a peculiar repulsive physiognomy ; the  nose  is flattened, so as to give
the  nostrils an almost transverse position; the cheek-bones project; the eyes
are  large, the teeth prominent, the lips thick, and the mouth wide.  The limbs
are  long, slender and  misshapen.  From the close resemblance in physical
characters, between the  Endamenes  of New Guinea,  and the  aborigines of
New Holland, and from the proximity  between  the adjacent  coasts  of these
two large islands, it may  be  surmised that  the latter  belong to  the Alforian
race; but too little is known of the language of either, to give this  inference
a sufficient stability.  In the  degradation of their condition and manner of life
the  savages of New Holland fully equal the Bushmen of South Africa ;  and
it is scarcely possible  to imagine human beings, existing in a  condition  more
nearly resembling that of brutes.   But  there  is reason  to believe, that  the
tribes in closest contact with European  settlers are more miserable and savage
than those of the interior; and even with respect to these, increasing acquaint-
ance with their language, and a consequent improved insight into their modes
of thought, tend to raise the very low estimate which  had been formed  and
long maintained, in regard to their extreme mental degradation.  The latest
and most authentic statements enable us to recognize among them the same
principles of a moral  and intellectual nature, which, in more cultivated tribes,
constitute the highest  endowments of humanity, and thus to  show that they
are  not  separated, by any impassable barrier, from the most civilized and cul-
tivated nations of the globe.
                         CHAPTER  III.

           OF  THE ELEMENTARY PARTS  OF THE  HUMAN FABRIC.

                1. On Organized Structures in General.
  106. The Human body, in common with the bodies of all the higher Ani-
mals, is composed  of an immense  number of parts, whose structure and
whose actions are alike dissimilar; but which are yet so arranged, as to make
up a fabric distinguished by its perfect adaptation  to  a great variety of pur-
poses, whilst their actions, though in a great degree independent of each other,
concur in  effecting one common  object,—the maintenance of the integrity of
the  entire  organism.   In the lowest and  simplest  forms of living being, such
as we meet with among the humblest Cellular Plants, we find  a single cell
making up the whole  fabric.  This cell grows from its germ, absorbs and  as-
similates nutriment, converts a part of this into the substance of its own cell-
wall, secretes another portion into  its cavity, and  produces from a third the
reproductive germs that are to continue the race; and having reached its own 
100          OF THE ELEMENTARY PARTS OF THE HUMAN FABRIC.

term of life, and completed the preparation of these germs, it bursts and  sets
them free,—every one of these  being capable, in  its  turn, of going through
the same set of operations.   In  the highest forms  of  Vegetable life, we  find
but a multiplication of similar cells; amongst which these operations are  dis-
tributed, as it were, by a division of labour; so that, by the concurrent labours
of all,  a more complete and permanent effect may be  produced.  If we ana-
lyze the structure of a forest tree, for  example, we find that all the soft  and
growing parts are composed of similar cells; whose office it is, to absorb  and
prepare the nutriment, which is  afterwards to be applied to the extension of
the solid internal skeleton of the trunk and branches.   This latter part is not
concerned in the functions of vegetation, in any other way than as supporting
and connecting the different groups of  cells, which  form the operative  part of
the fabric; and it is composed of two forms of  tissue,—-woody-fibre, and vas-
cular tissue,—each of which may be regarded as originating in the metamor'
phosis  of cells (§ 120).
   107.  At the extremities of the roots of all the more perfect Plants, we find
a set of soft cells, making up those succulent bodies which are known as the
spongioles ;  these are specially  destined to perform the Absorption of nutri-
tious fluid.  This fluid, being conveyed  by the vessels of the stem and branches
to the leaves, is there subjected to the action of the cells which make  up the
parenchyma of those organs.   The crude watery ascending sap  is thus con-
verted, by a variety  of chemical and vital operations, into the thick  glutin-
ous latex;  which, like the  blood of animals, contains  the materials  for the
production of new tissue, and also the elements of the  various  secretions.
This process of conversion includes the  Exhalation  of superfluous liquid;
and also that interchange of gaseous ingredients between the sap and the  air,
which may be termed Aeration ; but it involves, beside these obvious chemi-
cal alterations, a new  molecular arrangement of the particles of the  sap, by
which  a variety of new products  are  generated,—some  of them possessing
such a tendency to pass into the form of solid  organized tissue, as to present
a sort of sketch of this, by a process  of coagulation, when withdrawn from
the living vessels.   To this  peculiar  converting process, which is such an
important step towards the production of  perfect living tissue  from the crude
aliments, the term Assimilation is applied.  As the elaborated  sap or latex
descends in its proper vessels through the stem, it yields up to the growing
parts the nutrient materials they respectively require.   These  growing parts
may be either the  ordinary tissues, of which  the  chief  part of the fabric is
composed, and which are destined to a comparative permanency of duration;
and in  the growth  and  extension of these, the  process  of Nutrition is com-
monly  regarded as  consisting.   On the  other hand, certain  groups  of cells
have for their office the separation of peculiar  products from the sap, such as
oil  (fixed or essential), starch, resin, &c.; which  they store  up  against  the
time when they may be  demanded ; and  these are said to perform the act of
Secretion.   In both  cases,  however, the  act is essentially the  same ;  for the
process of Secretion, like that of  Nutrition, consists  in the growth of a cellular
tissue, and the difference consists only in the destination of the contents of the
cells ; which, in the one case, are adapted merely to give firmness and solidity
to their walls;  whilst, in the other,  they are set apart for some other purpose,
to be given up again when required.
   108.  It is very important to remark, in regard to all the cells thus actively
concerned in the Vegetative functions, by  which the development and exten-
sion of  the permanent fabric is provided for, that they  have but a very transi-
tory life as individuals.  The Absorbent cells at the  extremities  of the rootlets
are continually being  renewed ; some of the  old ones dying and decaying
away, whilst others are converted into the solid texture of the root, and thus 
ON ORGANIZED STRUCTURES IN GENERAL.
101
 contribute to its  progressive elongation.  Of the  transitory duration of the
 Assimilating cells, we have an obvious proof in the " fall of the leaf;" which
 takes place at  intervals  (alike in evergreen and deciduous species), to be fol-
 lowed by the production of a new set of cells, having similar functions.  And
 the  Secreting cells have usually a like transitory duration; being destined to
 give up their contents by the rupture or liquefaction of their walls, whenever
 called upon to do so, by the demand set up  in  the growing  parts of  their
 neighbourhood, for the peculiar products they have set apart.
   109. Not only are the proper organic functions of all Plants thus dependent
 upon the agency of cells ; but their Reproduction is likewise.   In the lowest
 tribes of the Cryptogamia, where each cell is an independent individual, every
 one  has the power of preparing within  itself  the reproductive germs,  from
 which new generations may arise.  In the higher tribes, on the other hand,
 the general principle of the division of labour, which separates the absorbing,
 assimilating and secreting cells, involves also the setting apart of a distinct set
 of cells for the preparation of the reproductive germs ;  these cells are known
 in the  Cryptogamia as spores, and in the Phanerogamia as pollen-grains.  In
 the higher Plants  we find a complex apparatus  superadded  ; for the  purpose
 of aiding the early development of these  germs, by supplying  them with nu-
 triment previously elaborated  by the parent; yet  still this operation is of a
 purely accessory kind, and the essential part of the  process remains the same.
   110. Now we shall find that, although the fabric of Animals appears to be
 formed on a plan entirely different from that of Plants, and although the ob-
jects  to  be  attained  are so  dissimilar, there is a much greater accordance
 amongst their elementary parts, than might have been anticipated.  The starting-
 point of both is the same ; for the embryo of the Animal, up to a certain grade
 of its development, consists, like that of the Plant, of nothing else than an aggre-
 gation of cells (Plate I., Fig. 15). And amongst the  lowest tribes of animals, as
 well as among certain of the highest tribes that retain many  embryonic peculi-
 arities, even in the adult condition, (such as the curious Amphioxus or Lancelot,)
 we find a great proportion of the complete fabric to be possessed of a similar
 constitution.   In most of the  higher animals, however, we find that a large
 proportion of the  fabric consists of tissues in which no distinct trace of a cel-
lular origin is apparent;  and it has been only since improved powers of ob-
 servation have  been brought to bear upon their  analysis, and more especially
since they  have been  examined, not only in their  complete state, but in the
course of their development, that they have been reduced to  the same category
with the tissues of Plants and of the lower Animals.  Other tissues, which
are peculiar to Animals, cannot be referred to the same origin;  but these will
be found to have a grade of organization  even lower than that of simple  iso-
lated cells, and to be referrible to the solidification of the plastic  or organizable
fluid prepared by the  assimilating  cells, and set free by their rupture.   We
shall find, however, that (as in Plants) all the tissues most actively concerned
in the Vital operations, retain  their original cellular form;  and we shall be
able  to refer to  distinct groups of cells in  the bodies of Animals, not merely
the functions of Absorption, Assimilation, Respiration, Secretion, and Repro-
duction, which are common to them with Plants, but  also those of Muscular
Contraction, and Nervous Action, which they alone perform.   Before proceed-
ing to this  investigation, however, it will  be desirable to examine into the na-
ture of the original components at the expense of wrhich  the Animal fabric
is built up. Our knowledge of these is principally derived from the researches
which  have been made into  their character in  Man and the higher Animals;
but there can be little doubt that they are common, with trifling modifications,
perhaps, to the entire kingdom.
                                   9* 
  102         ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.

           2. On the Original Components of the Animal Fabric.
    111. Putting aside, for the present, the inorganic or mineral matters which
  enter into the composition of the Animal body, and which are left in the form
  of an  ash, when the organic  compounds are  decomposed and dissipated by'
  heat, we shall confine our attention  to the  peculiar characters of the latter.
  As already stated (§ 4), the  organized tissues of Plants are found, when en-
  tirely freed from the contents  of their cells, to have a very uniform composi-
  tion; being entirely made up of Carbon united with the elements of Water in
  a  very simple proportion,—that of 8 of the former to 7 of each of the latter;
  and this simplicity in their chemical  character partly accounts for  their com-
  parative durability.  There are various compounds found in the cells of Plants,
  and elaborated by them for the purpose  of  affording food to Animals, which
  do not undergo organization, so long as  they are  contained in the Vegetable
  fabric;  but these very  products, when transferred to the  bodies of Animals,
  form the components of their solid tissues. These substances are distinguished
  by the presence of Azote or Nitrogen, in  considerable amount; and also by the
  large number of atoms of the four components,  which are  united in each of
  them,—giving them a much  more complex  composition, and a much greater
  tendency to decay, this being brought about by the disposition of the compo-
  nents to enter into new compounds of a simpler and  more permanent nature.
  A considerable variety  of such substances exists  in the different parts  of the
  Human body ; but the nature  and composition of these may  be better studied,
  when their structure and actions are being described; and at present  we shall
  confine ourselves  to the fundamental  or original components, of which all the
  others may be regarded as modifications.
    112.  When we  examine the Egg of an   Oviparous  animal, we find that,
  putting aside the fatty matter  of the  yolk (which is destined, not to be con-
  verted into tissue, but to be stored up  in cells), the sole organic constituent is
  that which is known to Chemists as  Albumen.  By the wonderful processes
  of chemical and vital transformation, which take place during the period of
 incubation, and which- are effected by the germ-cell and its  descendants, this
 Albumen is metamorphosed into nerve, muscle, tendon, ligament, membrane,
  areolar tissue, horny substance, feathers,  the organic basis of bone, &c.  The
\ same metamorphosis is continually taking place in the adult animal; for every
|  substance  of similar composition, that is  employed as food,  is reduced to the
 form of Albumen in the digestive process; so that this becomes the essential^
\constituent of whatever fluid is absorbed for the nutrition of the tissues.   It
 is  true that Gelatine, taken in  as food, may be absorbed and carried  into  the'~
 current  of the circulation ; but there is  little  doubt, that it is  incapable of
 being applied to the reconstruction of any but the  gelatinous tissues ; and in
[these it exists in the very lowest form of organization, if organization it  can
 be called.   Moreover, as it is  clear, from what has been  just stated,  that  the
 gelatinous  tissues may be formed at the expense of Albumen, we are justified
 in regarding the latter substance as the common pabulum for all.  Hence Albu-
 men seems to hold very much  the same position in the Animal economy, with
  Gum in the Vegetable.
    113.  The properties of Albumen may  be studied in the White of Egg, or
 in  the Serum of Blood; from  both of which situations it may be obtained in
 a pure state by very simple means.   In the Animal Fluids it exists  in a  so-
 luble state; and even when  it has been dried  (at a temperature of 126°), it
 is  readily  dissolved  again in water, forming a glairy, colourless, and nearly
 tasteless fluid.  In this condition  it is always  combined with  a  small quan-
 tity of free soda;  to the separation of which (whether by the agency of heat
 or  acids), its coagulation is  thought by many Chemists to be due.   On this 
V
COMPONENTS OF THE ANIMAL FABRIC.--ALBUMEN.
103
view, pure Albumen is not soluble in water; its solution being only accom-
plished by union with an alkali.—When dissolved in water,  it  coagulates
at 158° ; a very dilute solution, however, does not  become  turbid until it is
boiled.   When the coagulation of Albumen  takes  place rapidly, a coherent
mass is formed, which shows  no trace whatever of organization; but,  when
the process  is more gradual, minute granules present themselves, which do
not, however, exhibit any tendency towards a higher form of structure.   It is
thrown down from  its solution, in  a  coagulated state, by Alcohol, Creosote,
and by most Acids (particularly nitric)  with the   exception of  the  acetic.
These precipitates  are definite compounds  of the  Acids with  the Albumen,
which here acts the part  of a base.  On  the other hand, coagulated Albumen
dissolves in caustic Alkalies, and  neutralizes  them ; so that it  must here act
as an acid. A solution of Albumen in  water is precipitated by acetate of lead,
and by many other metallic solutions:  and insoluble compounds are formed,
of which one—the albuminate of the chloride of mercury—is of much interest,
as being that which is produced by the mixture of a solution of albumen with
one of corrosive sublimate.  Albumen, both  in its soluble and insoluble state,
always contains  a small  amount of Sulphur,  which  blackens metallic silver;
and also a minute quantity of Phosphorus.  Soluble albumen dissolves  Phos-
phate of Lime ;  and about two per cent, of this salt may be separated from it
in its coagulated state.
   114.  So long as Albumen remains  in  the state  regarded by Chemists as
characteristic of it,  no tendency to become organized can be discerned  in  it;,
but subsequently to its introduction into the  living Animal body, it undergoes
a transformation into a compound, termed Fibrine, which is distinguished from
it by new and peculiar properties.  It appears from the analyses of Mulder
and Scherer, that there is no  essential difference in the ultimate composition
of these two substances; the relative  proportions of the constituents of each
being, according to  them, as follow:—
	Mulder.		ScHEEER.	
	Albumen.	Fibrine.	Albumen.	Fibrine.
Carbon .	. 54-84	54-56	53-850	53-671
Hydrogen	. 7-09	6-90	6-983	6-878
Nitrogen	. 15-83	15-72	15-673	15-763
Oxygen	. 21-23	22-13	)	
Phosphorus .	•33	•33	V 23-494	23-688
Sulphur	•68	•36	>	
	100-00	100-00	100-000	100-000
The wide difference in their properties must be referred, on this view, solely
to a change in the molecular arrangement of their ultimate particles.   Accord-
ing  to Dumas, however, there is a marked difference in composition, between
Fibrine and the various forms of Albumen;—the  former having less Carbon,
and  more Nitrogen, than the latter.   The following are the results of his
analyses:—
	ALBUMEN.		FIBRINE
	From serum.	From eggs.	
Carbon	. 53-32	53-37	52-78
Hydrogen .	7-29	7-10	6-96
Nitrogen	. 15-70	15-77	16-78
Oxygen	}		
Sulphur	. [ 23-69	23-76	23-48
Phosphorus	• >		
100-00     100-00
100-00 
104          ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.

It is not, perhaps, of any great moment whether this difference has a real
existence or not; for the conversion of Albumen into Fibrine  is unquestion-
ably a  process much more of vital than  of chemical  transformation.  We
shall presently see, that Fibrine may be regarded as Albumen, in which the
process of Organization has begun;  its molecules being  ready to assume the
peculiar arrangement that  is  so  designated:  this arrangement  takes  place
most completely, when the fibrinous mass  is in  contact with a living tissue,
and is  therefore to a certain degree under  its influence.   Fibrine, like Albu-
men, may exist in a  soluble or in a coagulated state; its  soluble form  only
occurs,  however, in  certain living animal fluids,—the  Chyle, Lymph, and
Blood;—and it seems to be the intermediate condition between the soluble al-
bumen, and the solid organized substances  which are formed from it.   When
withdrawn from the blood-vessels, the Blood soon coagulates, as do also the
Chyle and Lymph, when they contain sufficient fibrine;  and this coagulation
is entirely due to a  change in  the condition of the Fibrine, the particles of
which have a tendency to aggregation in a  definite manner.  The  Fibrine may
be obtained in a separate form, by stirring fresh-drawn blood with a stick, to
which it adheres in  threads; these contain some  fatty matter, which is to be
washed out with alcohol.  In this condition it possesses the softness and  elas-
ticity which characterize the flesh of animals; and contains about three-fourths
of its weight  of water.  It may be deprived of this water in dry air, and  then
becomes a hard and brittle  substance ;  but, like flesh, it  imbibes water again
when moistened, and recovers  its original softness  and elasticity.   When
burned, it always leaves, like  albumen, a portion of phosphate of lime.  Fi-
brine is insoluble in alcohol and ether, and also, under ordinary circumstances,
in water; but when long boiled in water, especially under pressure, its nature
is altered, and it becomes soluble.   This change, which may be effected also
in coagulated Albumen, is attributed by Mulder to the oxidation of the  Pro-
teine, which is its principal  constituent (§ 116, a).  When  Fibrine is treated
with strong acetic acid, it imbibes the acid, and swells up  into a transparent
colourless jelly,  which is soluble in hot water;  this solution is precipitated by
the addition of another acid.
   115.  Fibrine, like Albumen, unites with acids as  a base, forming  definite
compounds;  and with bases  as an acid.   Its correspondence with Albumen
is further indicated  by the fact (first stated by M. Denis), that it may be en-
tirely dissolved in a solution  of nitrate of potash; and that this solution is
coagulated by heat, and greatly resembles  a solution of Albumen.   This is
only true, however, of the  ordinary Fibrine of  venous blood;  for that which
is obtained from arterial blood or from  the  buffy coat, or which has been ex-
posed for some time  to the  air, is not thus soluble.  This is an important and
interesting circumstance.   The difference  appears to depend upon the larger
quantity of oxygen contained in the latter;  for a solution of  Venous Fibrine in
nitre, contained in a deep cylindrical jar, allows a precipitate in fine flocks to fall
gradually, provided the air have access to the surface, but not if it be prevented
from coming in contact with the fluid; this precipitate is insoluble in the solution
of nitre, and  possesses the  properties  of arterial  fibrine.   Hence  it may be
inferred, that the Fibrine of Venous blood most nearly resembles Albumen;
whilst  that of Arterial blood,  and of the Buffy coat, contains  more oxygen,
and is more highly animalized.—When decomposition commences in a coagu-
lum of  Fibrine withdrawn from the body (and  even in the  greatly-debilitated
living body, in which the Fibrine appears to be imperfectly formed), a granu-
lar mode of aggregation is evident in the particles of the mass,—thus showing
its affinity to  Albumen, when  its  peculiar vital characters have departed,  or
are possessed by it in an inferior degree.
   116.  The  close chemical relation existing between Albumen  and Fibrine 
PROTEINE, AND ITS TRANSFORMATIONS.
105
 is further shown by the fact, that from both of  them (as well as from various
 substances  used as food, which are furnished by  the Vegetable kingdom, §111)
 an identical  substance  may be obtained by a simple process.   If boiled al-
 bumen be  dissolved in  a weak  solution of caustic  alkali, and  the liquid be
 neutralized by an acid,  a precipitate falls down  in grayish-white flocks; this,
 being collected and washed, is gelatinous, of a grayish colour, and semi-trans-
 parent;  and, when dried, it is yeHpwish, hard,  easily pulverized, tasteless, in-
 soluble in water and alcohol, and decomposed by heat without  fusing.   This
 substance  has been termed Proteine, from an  idea that it is the  fundamental
 proximate  principle of which Albumen, Fibrine, &c, are  modifications.   It
 contains the same proportions of Carbon, Hydrogen, Nitrogen and Oxygen, with
 Albumen and Fibrine ; but it has been commonly regarded as destitute of their
 Sulphur and  Phosphorus; the most recent investigations of Liebig, however,
 render it doubtful  whether this is  the case.   According to  Mulder (its dis-
 coverer), its composition may be represented by the  formula 40  C, 31 H, 5 N,
 12 O;  whilst by Liebig it is represented by the formula 48 C, 36 H, 6 N, 14 O.
 Either of these correctly represents the relative proportions of the elements,
 as  deduced  from  analysis ; but the formula of  Mulder is asserted by him to
 represent more  accurately  the combining equivalent of the entire substance,
 as  deduced from the compounds it  forms with others.

   a. According to Mulder, Proteine unites with Oxygen in definite proportions, so as to form
 a binoxide and a tritoxide. These are both produced when Fibrine  is boiled in water for
 some time; the latter being then found  in solution, whilst the former  remains insoluble.
 The tritoxide may also be formed by boiling Albumen for some time in water, when it is in
 like manner taken up in solution;  but the insoluble residue is still albumen.  It is further
 attainable by decomposing the chlorite of proteine with ammonia.  In its properties it some-
 what resembles Gelatine, and has been mistaken  for that substance.  There is reason to
 think that this compound really exists as  such in the blood;  a small quantity of it being
 formed every time that the blood passes through the lungs,  and given  out again when it
 returns to the system;  and a much larger quantity being generated during the inflammatory
 process, so that it may be easily obtained  from the buffy coat by boiling.  It is also said to
 be contained in pus.  The binoxide is quite insoluble in water, but dissolves in dilute  acids.
 It may be obtained by dissolving Hair  in potash, adding a little acid  to throw down the
 proteine, and then adding a large excess of acid, which  precipitates the binoxide. Accord-
 ing to Mulder, this compound also is produced in small quantity at every  respiration; and it
 enters into the normal  composition of several of the animal tissues.—These views, however,
 must still be received with some hesitation.  They are liable  to the fundamental objection,
 advanced against them by Liebig; that the binoxide and  tritoxide, like proteine itself, contain
 the sulphur of albumen and fibrine.  Still, the production of new and peculiar compounds,
 by the  processes indicated, is  an important fact which cannot be overthrown; whatever
 may prove to be the case in regard to the  ultimate composition of these substances.
  b. One of the most characteristic and important properties of Proteine, is the facility with
 which it undergoes decomposition, when  acted on by other chemical substances, especially
 by alkalies.  If aproteine-compound be brought into contact with an alkali,  ammonia is im-
 mediately disengaged; indeed the alkaline solution  can hardly be made weak enough to
 prevent the disengagement of ammonia.   This is a  property, which  must be continually
 acting in the living body; since the blood  has a decidedly alkaline reaction.   If either albu-
 men, or any other proteine compound, be  boiled with potash, it is completely decomposed;
 not, however, being resolved at once into its ultimate constituents, or altogether into simple
 combinations of them;  but in great part into three other organic compounds,—Leucin, Protid,
 and Erythroprotid.  Leucin is a crystalline substance, which forms colourless scales, destitute
 of taste and odour;  it is soluble in water and alcohol, and sublimes unchanged.   It consists
 of 12 Carbon, 12 Hydrogen, 1 Nitrogen, and 4 Oxygen.   There is not at present any evi-
 dence, that it is produced in the living body; but considerable interest attaches to it from the
 fact, that it may be procured from Gelatine, as well as from Proteine; a near relationship
 between these two substances being thus indicated.   The other two compounds, Protid and
 Erythroprotid, are uncrystalline substances; the former of a straw-yellow, the latter of a red-
 dish-brown colour; they belong to the class of bodies which were formerly included under
the vague general term of extractive matter; and they bear a strong  resemblance to Gelatine,
not only in their solubility in waier, but also in their chemical composition, as is  shown by
 the following comparison of their formula?:— 
   106         ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.

                                                   C.    H.    2*r.    o.
           Protid......            13     9     14
           Erythroprotid......    .  13     8     15
           Gelatine.......13    10     2    5
   Besides these substances and Ammonia, Formic and Carbonic Acids  are produced by the
   decomposition of Proteine with potash; the acids unite with the potash, whilst the ammonia
   is set free.
      117.  It  is very important, however, to bear in mind, that however close
   may be the chemical approximation between Albumen and Fibrine, there is  a
   wide  difference between  them, as  regards their  relations to living organized
   structures: and this difference is one of which chemistry takes no cogni-
   zance.  To use a rather  homely illustration, the relation between Albumen,
   Fibrine, and Organized Tissue is somewhat of the same  nature as that which
   exists between  the raw cotton, the spun  yarn, and the woven  fabric.   Albu-
   men  shows no tendency to coagulate, except under the influence of  purely
   chemical agents, and  its coagulum is  entirely destitute of structure, being  a
   mere  homogeneous aggregation of particles.  On  the  other  hand, Fibrine
-  exhibits a constant tendency to pass  into the form of a solid  tissue;  and it
/  seems only restrained  from doing so by certain  influences, whose nature is
   not understood, to which it is subjected whilst contained in  the vessels of the
c  living body.  The conversion of Albumen into Fibrine, therefore, is the first
   great  step in the process  of Nutrition, by which the materials supplied by the
.   food are made to form part of the living tissues of the body ; and  it is the one
  , to which  the term Assimilation may be most appropriately applied.  As
"■  already mentioned, Albumen is always the starting-point; since the  fibrinous
 1  elements of organized tissues  are reduced, by the solvent power of the gas-
   tric fluid, to the same form with the unorganized coagulum of the albumen of
   the egg.  The  first appearance of Fibrine  is in  the Chyle,  or  fluid of the
   Lacteals ;  and when this is examined in the neighbourhood  of the part where
   it has been absorbed, the traces of Fibrine which it presents are very slight.
   As the Chyle flows along the lacteals, however,  the proportion of Fibrine in-
   creases  ; and it reaches  its  maximum at the point where the Chyle is de-
   livered  into the current of the circulating Blood.   The proportion of Fibrine
 •  in the Blood, as indicated by the firmness of the coagulum which it forms, is
   much greater than that contained in  the Chyle,  notwithstanding  that there is
   a constant withdrawal of  this element for the purpose of nutrition.  And in
   certain  disordered  states of the system, in which  the formative powers of the
   Blood are so exalted, as  to produce a tendency  to the formation of tissue in
   abnormal  situations, the proportion of Fibrine  is  found to be  increased to
   twice, thrice, or even four  times its usual amount.   And even  where there is
   no such general increase, a local increase  is made evident  in  the large pro-
   portion  of fibrine, which  exists in the  exudations poured forth for the repara-
   tion of  injuries; these exudations, when possessed of a high formative pro-
   perty (that is, a readiness  to  produce an organized tissue), are  said  to be
   composed ofplastic, or coagulable lymph;  but  this is nothing more than the
   Liquor  Sanguinis, or fluid portion of the Blood, holding in solution an unu-
   sual quantity of Fibrine.   It is evident, from these facts, that  some peculiar
   agency  must exist within the vessels, by which the elaboration of the Fibrine
   from  the Albumen is  effected; and we shall hereafter endeavour to bring
   together certain facts, which seem to indicate its nature.
      118.  The  tissue that  is produced by  the apposition of the  particles of
   Fibrine, when left to themselves, and solely influenced  by  their  own mutual
   attraction, is of a very simple character, being composed of fibres interlaced
   with  each other in various directions.  This arrangement can be seen in the
   ordinary Crassamentum, or clot of healthy  Blood,  by examining thin slices 
FIBRILLATION OF COAGULATED FIBRINE.
107
Fig. 10.
under the microscope;  especially after the clot has been hardened by boiling.
A number of fibres, more or less distinct, may be seen to cross one another;
forming by their interlacement a tolerably regular  network, in the  meshes of
which the red corpuscles are entangled.  This fact was  known to Haller;
but it has been generally overlooked by subsequent Physiologists, until atten-
tion was  drawn to it  by the inquiries of Messrs.  Addison, Gulliver, and
others.   It is in the Buffy Coat, however, that the fibrous arrangement is best
seen; on account,  as it would appear, of  the stronger attraction which  the
particles of fibrine have for one another, when its vitality has  been  raised by
the increased elaboration to which it has been subjected.   That there are va-
rieties of plasticity in the substance, which, on account of  its  power of spon-
taneously coagulating, we must still ca\\ fibrine, appears from  this fact among
others,—that,  in tuberculous  subjects,
the quantity of fibrine  in the blood is
higher than usual (Andral and Gavarret),
although its plasticity is certainly below
par.  It  is as  easy to  understand, that
its plasticity may be increased, as that it
may be  diminished; and  this either in
the general mass of the blood, or  in a
local deposit.   In  fact, the  adhesions
which are formed by the consolidation
of coagulable lymph,—or in other words,
of the fluid portion of the blood, whose
plasticity has  been heightened by  the
vital  actions that take place within  the
capillaries of the part  on which it  has
been effused,'—often acquire  very con-
siderable  firmness, before any vessels
have penetrated them; and  this firmness must depend  upon that mutual
attraction of the particles for  one another,  which in  aplastic  deposits is alto-
gether wanting, and which in cacoplastic deposits is deficient.—A very inte-
resting  example of a structure entirely composed of matted  fibres, and evi-
dently originating  in the simple consolidation of Fibrine, is found in the
membrane adherent to  the interior of the  Egg-shell  (Membrana putaminis);
and also in that which forms  the basis of the Egg-
shell itself.  Between the two, there  is no essen-
tial difference ;  as may be seen by examining " an
egg without shell," as  it  is commonly termed, (or
rather one in which the  shell-membrane has been
unconsolidated  by  the deposition  of  calcareous
matter); or by treating the egg-shell  with dilute
acid, so as to  remove the particles of carbonate of
lime, which are deposited in  the interstices of the
network.  The place of the shell is then found to
be  occupied by a membrane of considerable firm-
ness, closely resembling that  which lines the shell
and surrounds the albumen of the egg, but thicker
and more spongy.  After maceration  for a few
days, either of these membranes may be separated
into  a  number of  laminae, each of which (if suffi-
ciently thin) will show a beautiful  arrangement of reticulated fibres.  It is
impossible to  refuse to such a structure the designation of  an organized tis-
sue, although it contains  no vessels, and must be formed by  the simple con-
solidation of Fibrine, poured out from the lining membrane of the oviduct of
 Fibrous structure of inflammatory exudation
from peritoneum.
11.
  Fibrous membrane from
Egg-shell. 
 108         ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.

 the bird.   It is probably in the same manner, that the Chorion of  the  Mam-
 miferous animal originates; since this is a new envelope, formed around the
 ovum, during its passage along the Fallopian tube.   In the latter, for an ulte-
 rior purpose, vessels are  afterwards developed, by extension from the con-
 tained ovum; and  by the nutrition  they  supply, its  size  is  increased, and
 changes  take place  in its  texture.  But in the Egg-membrane of the Bird,
 there is no need of vessels;  because no subsequent change in its texture is
 required, and its duration is sufficient for the purpose it has  to answer.
   119. The completeness of the transformation of Fibrine into  simple Fi-
 brous Tissue, appears to depend upon two circumstances in particular;—the
 perfect elaboration of the Fibrine itself;  and the vitality of the surface upon
 which the  concretion takes place.   When the Fibrine  is highly elaborated, it
 will coagulate in the form of a definite network of minute fibrillae, even upon
 a dead surface, as  a slip of glass ; this is the case, for instance, with the Fi-
 brine of the buffy coat of the Blood, or with  that of  the  Liquor Sanguinis
 (coagulable lymph) poured out for the reparation of an injured part.   But in
 the ordinary Fibrine of the blood, the fibrillation is less  distinct when the con-
 cretion takes place  upon a dead surface.   When it occurs in contact with a
 living  surface, however,  the  coagulation takes place more  gradually; and it
 seems  as if the particles,  having more time  to arrange themselves, become ag-
gregated into more definite forms, so that a  more regular tissue is produced—
just as crystals are  most perfectly formed  when the crystalline  action takes
 place slowly.  It was formerly imagined that the Muscular  tissue is the only
 one produced at the expense of the  Fibrine of the  blood ; the other tissues
 being formed from its Albumen.  This, however, is unquestionably erroneous.
 There is no proof whatever  that Albumen, as  long as it remains in that con-
 dition, ever becomes organized; whilst, on the other hand,  there is abundant
 evidence, that the plasticity of any fluid deposit—that is, its capability of be-
ing metamorphosed into organized tissue—is in direct relation with the quan-
 tity of Fibrine which it contains.   Thus the Liquor Sanguinis, or Coagulable
 Lymph, thrown out for the reparation of injuries, contains  a large  amount of
 Fibrine ; and this substance is converted, not  at first into muscular fibre, but
 (whatever  may be  the tissue to be  ultimately produced in its place)  into a
 fibrous network, which fills up the breach and  holds together the surrounding
 structure.   This may be regarded as a simple form of areolar tissue ; which
gradually becomes more  perfectly  organized by the  extension of vessels and
nerves into its substance ; and  in which  other forms of tissue may subse-
 quently make their  appearance.   This process will be more  particularly de-
 scribed hereafter; it is at present noticed here  as an illustration of the general
fact, that fibrine is to be regarded as  the plastic element of the nutritive fluids.

 3.  Of the  Elementary Parts of Organized  Tissues;—Cells,  Membrane,
                               and Fibre.
   120.  The cells, which have been spoken of as making up the chief part of
the Vegetable Organism, are minute closed sacs; whose walls are composed
in the  first instance of a delicate membrane, frequently strengthened, at a
period long subsequent to their first formation, by some internal deposit.  The
form of these cells is extremly variable ; and depends chiefly upon the degree
and direction of the pressure, to  which they may have been subjected at the
period of their origin, and subsequently to it.   Sometimes they are spheroidal;
sometimes  cubical or prismatic; sometimes cylindrical; and sometimes very
much prolonged.  These cells may undergo various transformations.—One of
the most common, is the conversion of several into a  continuous tube or Duct.
 This is principally seen in the vessels, through which the sap  ascends the stem; 
DEVELOPMENT AND METAMORPHOSES OF CELLS.
109
these appear to have  been formed  by the breaking-down  of the transverse
partitions, between a regular  series of cylindrical cells laid end to end;  and
the remains  of such partitions may frequently be seen in them.  The ducts
which convey  the ascending  sap, do  not inosculate with each other; their
purpose being merely to carry it direct to the leaves ; but the vessels, through
which the descending or elaborated sap flows, are of very different character;
for their purpose  is to  distribute the  nutritious fluid  through the  tissues;
and they anastomose very freely, just as do the capillaries of Animals.   The
network which they form, however, can be as clearly traced to an origin in cells,
whose cavities were originally distinct, as can the bundles of straight non-
communicating ducts.—Another important transformation  of the original cells,
is that by which  the  Woody Fibres, which compose  nearly all*the fibrous
textures of Vegetables, are produced.  These fibres are stillcells,buttheirformis
very much elongated ; they have a fusiform or spindle shape, being tubes drawn
to a point at each end; at first  they are quite pervious,  like ordinary cells;
but in the older wood, their cavity is filled up by interior deposit.
   121.  Such deposits  may take place in cells of  the ordinary form ;  and they
present many variations in their character, which give corresponding peculi-
arities to the cells which contain them.  In many instances, they consist merely of
concentric layers, one within  the  other, each layer completely lining the  one
which preceded it; and the  cavity  of  the cells being thus gradually but uni-
formly contracted  in every dimension.  In other cases, certain points of the
original external cell-membrane are left uncovered by the  secondary deposits ;
and  thus, the same  vacuities  being  left in the successive  layers, passages are
formed, which  stretch  out from the central cavity to certain spots of the peri-
phery of the cell.   Cells of this character are found in certain parts of plants,
which are required to possess unusual firmness,  without  losing the power of
transmitting  fluid, the  former endowment being conferred by the secondary
deposits;  whilst the latter is retained by the peculiar system of passages just
described,—the thin or uncovered parts of the wall of one  cell being in contact
with corresponding spots on the walls of adjacent cells, as we see in the tissue
of the stones of fruit,  the central gritty matter of the pear, &c.—Lastly, the
new deposit may present the form of a more or less regular spiral fibre, winding
within the cell from end to end ;  and this may present itself  alike in cells of
the ordinary shapes, or  in fusiform cells  (constituting the proper spiral ves-
sels), or in, cells that  have coalesced into continuous  tubes  or ducts.   The
spiral may break  up into rings or irregular pieces; and these may be united
again by additional deposits of  a still more irregular character, so as completely
to obscure their original spiral form.  This spiral fibre is very completely gene-
rated, in some instances, when the cell-wall itself has not acquired any greater
tenacity than that of mucus, very easily dissolved ; which (as we shall presently
see) is a stage in the  production of cells in general.   Such spiral fibres spring
out from  the external coats  of many seeds, when  they  are moistened with
fluids.
   122. So far as is yet known, all  Cells originate  in germs, that have been pre-
pared by some  previously-existing  cell; and these germs may either  be de-
veloped within the parent-cell, or may  be  set free by its rupture, and may be
developed quite independently.   The  latter case, being the simplest, will be
first considered; we have numerous examples of it among the lower Cellular
Plants.  In the first place, the germ, from which the cell originates, is a  mi-
nute granule, only to be  seen  with a good microscope, and apparently quite
homogeneous.   It has the  power of drawing to itself the nutrient elements
around, and of combining these into the proximate principles, that may serve
as the materials for its development.  By the incorporation of these with its
own substance, it gradually increases in size, and  a distinction becomes ap-
     10 
110         ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.
Fisr. 12.
  Simple isolated cells con
taining productive mole
cules.
parent, between its transparent  exterior and its coloured interior.  Thus we
have the first indications of the cell-wall, and the cavity.   As the enlarge-
ment proceeds, the distinction becomes more obvious ; the cell-wall is seen to
be of extreme tenuity, perfectly transparent, and apparently homogeneous in
its texture ;  whilst the contents of the cavity are distinguished by their colour,
which (in the species here alluded to) is commonly either green or bright red.
At first they, too, seem to be homogeneous; but a finely-granular appearance
is then preceptible amongst them ; and a change gradually takes place, which
                      seems  to  consist in  the  aggregation of the  minuter
                      molecules into granules of more distinguishable size and
                      form.   These granules, which are the germs of new
                      cells, seem to be at first attached to the inner wall of the
                      parent-cell; afterwards they separate from it, and move
                      about in its cavity; and at a later period, the parent-
                      cell bursts and sets them free.   Now this  is the ter-
                      mination of the  life of the  parent-cell; but the  com-
                      mencement of the life of a new generation: since every
                      one of these germs may develope itself into a cell, after
                      precisely the foregoing manner ;  and will then, in turn,
                      propagate its  kind by a similar process.
                        123. The  development of  new cells within the pa-
                      rent,—or  what may be termed  the endogenous mode
of cell-growth,—takes place in many instances on a  plan which differs in no
respect from the preceding, except that the parent-cell does not rupture.   The
granules it  contains derive their nutriment from the surrounding fluid, which
is included within the cell;  by their progressive  increase in size, they gradu-
ally fill up the whole cavity of the parent-cell; and by a further increase, they
distend its wall, which becomes thinner and thinner, and at  last ceases  to be
visible around the newly-formed cluster.
   124.  In  other instances, however, we find that the  development of new
               cells  proceeds, not from granules scattered through the whole
               interior of the cell, but  from  a determinate  spot or nucleus,
               which is seen upon its wall.  This nucleus is frequently formed
               very  early, by the aggregation of molecules around the original
               granule or cell-germ, even previously to  the first appearance of
               the distinct cell-membrane; and  by  Schleiden, who  first  ob-
               served this process, it was thought that the body thus produced
               was  essential to  the development of  the new cell,  whence he
               gave  it the name of cytoblast.  It appears, however, from more
               extended  inquiries, that this is not  the case ;  and that the nu-
               cleus is rather concerned with the subsequent operations which
               the cell performs, than with its original  development.   Fre-
               quently the nucleus does  not make its  appearance, until the cell
               itself has been completely  formed.   It is chiefly in the higher
               tribes of Plants, that we  find these nucleated cells; the nucleus
               in the cells of the lower Cryptogamia  being  usually more or
               less expanded or diffused (as it were), through the entire cavity.
               The  destination of the  several forms of cells which make up
               the  complex  structure of the  higher  plants, is very different;
               and their  office seems  in  great measure to depend upon the
               peculiar powers  of the nucleus.   In some instances, this body
               seems to be the centre which attracts new deposits ;  even the
  Cells of Zygne- spiral  filament being probably formed  by  its  agency.    We
 ma, showing spiral have, in some of the  lowest  Cellular Plants, a curious fore-sha-
 arrangementof the dowing of the  spiral vessels  of the  most perfect; the  green
 nuclear particles.
Fig. 13. 
DEVELOPMENT AND MULTIPLICATION OF CELLS.
Ill
Fig. 14.
particles (or diffused nucleus ?) of the cells, in the genus Zygnema, presenting
a regular spiral arrangement at  one  period of their growth  (Fig.  13).   And
in other instances, as in the cells of the petal of
the common Geranium  (Pelargonium), we find
the nucleus sending out curious  stellate or radi-
ating prolongations (Fig. 14.)   These facts  are
of much interest, as illustrating some of the more
obscure changes which are believed to take place
in animal tissues.
   125. But the nucleus may also be  the source
from which the new  cells  arise, that  are  devel-
oped within the cavity of the parent. Several vari-
eties in the mode in which this process takes place,
are presented to our observation in the simplest of
the Cellular Plants, belonging to the group of the
Fresh-water Algae ; the growth of which may be
studied with peculiar facility.   In some of these
the cell is destitute of a nucleus, but is filled with
a very finely-divided  granular  matter, the  en-
dochrome; and the process of cell-multiplication
is effected by the subdivision of this  matter into
two distinct masses, around each of which a pellucid cell-membrane subse-
quently makes  its appearance, thus forming two new cells within  the parent.
By a repetition of the same process, each of  these new cells may again pro-
duce two  new ones; and  thus  the  multiplication  may be  rapidly  effected.
 Cells from the petal of Pelargonium
showing stellate prolongations of the
mftlei.
  Hematococcus binalis, in various stages of devel.
opment; a, a, simple rounded cells; 6, elongated
cell, the endochrome preparing to divide ; c, c, cells
in which the division has taken place; d. large pa-
rent cell, in which the process has been repeated
a second time, so as to form a cluster of  four se-
condary cells, such as is often seen in Cartilage.
  Coccochloris cystifera, showing various stages of
development:—a, simple globular cells, surround-
ed by a well-defined mucous envelope ; b, elon-
gated cell about to divide ; c, cell doubled by di-
vision, both the new cells still enclosed in original
mucous envelope ; d, further stage of the  same
process, one of the secondary cells having again
divided, whilst the other has not  yet undergone
this change, but is about to  do so; e, group of
cells formed  by the  same process, and still re-
tained within the original mucous envelope.
This form of cell-development is best seen  in some of the simplest Algae,
which consist of isolated  cells, and in which the individuals composing the
successive generations are quite independent of one another ; and we have  a
good illustration of it in the Hematococcus  binalis, whose various stages of
cell-multiplication are shown in Fig. 15.  In many other instances, the cells
of successive generations, without losing their individuality, are held together 
112         ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.

by a consistent mucous envelope ; so that we may find two, three, four, or a
larger number, clustered together  within a well-defined  investment, which has
tenacity enough  to  prevent them from  separating.   Of this we have a good
example in Coccochloris cystifera (Fig. 16); and a  yet more remarkable one
in Hematococcus sanguineus (Fig. 17).   The cells  forming such masses  of
vegetation  may be likened  to those of Cartilage, which are similarly enveloped
by an intercellular substance, and which  present the same binary method  of
multiplication (§  129).   In the Confervas we find the cells, which are succes-
sively produced in this manner, remaining in connection with  each other,  so
as to form  articulated filaments.   The  terminal cell of each  filament is con-
tinually undergoing  subdivision in the manner  just described, and thus the
filament is  elongated ; whilst other cells produce regular reproductive granules,
which are  set free by an opening  that forms in the cell-wall, and which devel-
ope themselves into  new individuals  without  any further aid from the  parent
structure, in  the  manner  already described.   The  difference  between these
two modes of propagation seems  to have reference to the age  and degree  of
development of the cell; the binary division being characteristic of cells which
are in a growing  state, and being destined  to extend the  original structure;
whilst the  formation and emission of a number of reproductive  granules is the
function of the mature cell, and is destined to give origin to new  individuals.
These processes  are analogous in the higher plants, the first to the develop-
ment of leaf-buds, the second to the  production  of seeds.  In,  the Nostoc we
find the moniliform  filaments, which are composed of a linear  series of cells,
invested by dense gelatinous sheaths of definite extent, looking almost like

                                     Fig. 17.
  Hematococcus sanguineus in various stages of development,— a, a single cell, enclosed in its mucons
envelope ; b, c, clusters formed by division of parent-cell; d, more numerous cluster, its component cells
in various stages of division ; e, large mass of young cells, formed by continuance of the same process.
and enclosed within common gelatinous envelope.

large parent-cells (Fig. 18, b) ; and the extension of the filaments may so dis-
tend their shealhs as to give them the appearance of capacious globular cells
(Fig.  18,  a).  There is reason to  believe  that the long convoluted filaments
then separate into a cluster of shorter ones,  each having its own share of  the
mucous envelope.
  126.  The history of the Animal cell, in its simplest form, is precisely that
of the Vegetable cell of the lowest kind.  It lives for itself and by itself, and 
DEVELOPMENT AND MULTIPLICATION OF CELLS.            113
 is dependent upon nothing but a due supply of nutriment and a  proper tem-
 perature for the continuance of its growth, and for the due performance of its
 functions, until its  term of life is expired.'   It originates from a  reproductive
 granule, previously formed  by some other cell; this granule attracts to itself,
 assimilates, and organizes, the particles of the nutrient fluid in its neighbour-
 hood ;  and converts some of them into the substance of the cell-wall, whilst
 it draws others into the cavity of the cell.  In this manner the cell  gradually
 increases in size ; and whilst it is
 itself approaching the term  of its                   Fig. 18.
 life, it usually makes preparation                      a.
 for  its  renewal, by the  develop-
 ment of reproductive  granules in
 its interior  ; which may become
 the germs of new cells, when set
 free from the cavity of the parent,
 by the  rupture of its  cell-wall.—
 There is  an important difference,
 however, in the endowments  of
 the  Animal and  Vegetable  cell.
 The latter can in  general  obtain
 its'nutriment, and the materials for
 its secretion,  by itself combining
 inorganic elements into organic
 compounds.  The former,  how-
 ever, is totally destitute of this
 power ; it can  produce no organic
 compound,  and  we  have  yet to
 learn how far  its  power of con-
 verting  one compound into  an-
 other may  extend; its chief en-
 dowment seems to be that  of at-
 tracting or  drawing to itself some
 of the various substances,  which
 are contained in the nutritive fluid
 in relation with it.   This fluid, as
 we shall hereafter see, is a mixture
 of a great number of components ;
 and different sets of cells  appear
 destined severally  to  appropriate
 these, just as the different cells of
 a  parti-coloured  flower have the
 power of drawing  to  themselves
 the element of their several colour-
 ing matters.  As far  as it  is yet
 known, however, the composition
 of the cell-wall is everywhere the
 same, being that  of Proteine.  It
 is  in the nature of the  contents of
 the cell  (as among the  cells of Plants), that the greatest diversity  exists ; and
 we shall find that the purposes of the different groups of cells, in the general
 economy of the Animal, depend upon the nature of the products they secrete,
and upon the length of time during which these products are retained  by them.
   127.  Of  the general account just given, the development of certain  cells,
which float  in the  Chyle, Lymph, and Blood,  may be adduced as  an exam-
ple ; these, which are known as the Chyle and Lymph corpuscles, and as the
                                   10*
  Nostocmacrosporum:—A, a long convoluted filament,
composed of linear series of minute cells, enclosed in
general mucous envelope; b, group of shorter fila-
ments, each with its own gelatinous  envelope, pro-
bably formed by the division of the preceding. 
 114          ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.

 Colourless corpuscles of the Blood, have no single nucleus, but contain seve-
 ral scattered particles, each of which seems to be a reproductive granule;  and
 they emit these by the bursting or liquefaction of their wall,—a change which
 may be effected in them at any time, by the application of chemical reagents.
 The granules thus set free appear to float in the current of fluid, and to be in
 their turn developed into cells at  the expense of the materials it affords.  The
 exudations of the plastic or organizable matter of the blood, which are thrown
 out upon inflamed or wounded surfaces, appear to contain some of these gra-
 nules ;  for similar cells are speedily developed in these exudations, giving rise,
 in their turn, to new generations, when their own term of life is ended.
   128.  In general, however, we find the cells of Animal tissues furnished with
 a nucleus; and  this may be formed, as in Plants, either at an early stage of
 the  development of the cell, by the aggregation of minute molecules around
 the  original granular germ  (which  germ seems to be  the  nucleolus of some
 authors);  or after the cell has attained its full size.   The nucleus, where it
 exists,  appears to be the chief instrument  in  the  functions of  the cell;  the
 cell-membrane  probably having  little  else, than  the  mechanical  office  of
 bounding or limiting the contents of the cell.   In some cells the function is
 restricted to the attraction of certain constituents, by which the cavity of  the
 cell is  filled.  These  constituents may be of a nature to  give  solidity and
 permanence to the texture; thus, the cells of the Epidermis are strengthened
 by a deposit of horny matter, those of Shell by the  deposit of carbonate  of
 lime; those of Bones and Teeth  by a  mixture of mineral  and earthy matter,
 &c.  Or they may be  of a fluid  nature, readily passing into decomposition,
 and destined to be retained only for a short  time; being given up again by
 the  rupture  or liquefaction  of the  cell-wall, as  in  the case with the cells of
 Glandular structures in  general.   Now such cells  do not usually reproduce
 themselves, but successive  crops of them are generated  as fast as required
 from other sources; and the function of their nuclei appears to  be limited to
 their chemical agency upon the materials which they select.  It would seem,
                                       in fact, as if the direction of the nisus
                                       or power of the  cell to this object,
                                       prevented the exercise  of its repro-
                                       ductive powers ;  and where we  find
                                       these  last most strongly manifested,
                                       it is usually observable  that the cell
                                       performs little or no other duty.
                                          129.  In the endogenous develop-
                                       ment  of Animal  cells, the  nucleus
                                       seems always to perform an important
                                       part, where it has  a distinct existence.
                                       In many cases, the multiplication can
                                       be clearly perceived to take place, by
                                       the division of the nucleus  into  two
                                       or more portions  ;  each part giving
                                       origin to a new cell.  This  seems to
                                       be the case, for example, in the ordi-
                                       nary production of Cartilage-cells; for
                                       on examining sections of cartilage that
                                       is undergoing rapid extension, we find
                                       groups of cells, in all respects corre-
                                       sponding with those of the simple
                                       cellular plants, which can be seen  to
                                       increase in the same way.  Thus in
Fig. 19, which represents a section  of  one of the branchial cartilages  of  the
Fig. 19.
  Section of branchial Cartilage of young Tadpole ;
a, b, c, intercellular substance ;  d, single nucleus; e,
nucleus dividing into two; d1, e', two nuclei in one
cell, formed by division of single nucleus;/, second-
ary cell, forming around nucleus g; h, two nuclei
within single secondary cell; i, three secondary
cells, within one primary cell. 
DEVELOPMENT AND METAMORPHOSES OF CELLS.
115
Fig. 20.
Tadpole, we observe, within the large  parent-cells  that are held  together by
intercellular substance, a, b, c, secondary cells in various  stages  of develop-
ment: at d, the nucleus is single ; at e it is dividing  into two ; in the adjoining
cell, the division into two nuclei, d' and e', is complete ; at h, two  such nuclei
are inclosed within a common cell-membrane; at i, we see three new cells
(one  of them elongated, and itself probably about to subdivide)  within the
parent;  and in each of  the two  groups at the top  and bottom of the figure,
we have four  small cells, now  separated  by partitions of intercellular sub-
stance, but having manifestly originated from one parent cell.   (See also Fig.

   130. In other  cases, the granular nucleus subdivides into a greater number
of parts, so  as to  give origin to a cluster of young cells, which may completely
fill the parent-cell; various stages of
this process are  seen  in Fig. 20.
This process seems  to  be adopted,
where rapid multiplication is need-
ed, and where the new or secondary
cells are not destined to possess any
great duration.    The  same  nuclei
or  " germinal centres," continually
drawing  new  materials  from   the
blood, may thus develope many suc-
cessive crops of new cells, when an
opening in  the wall of  the parent-
cell permits them to be discharged
as fast as they are formed ; and this
we shall find to be the way in which
the cells of the secreting  structures
are developed within  the glandular
follicles.  According to Dr. Barry, it
is not uncommon for several annuli
of  young cells to be generated from
the periphery of the nucleus, and to
attain  a certain degree  of develop-
ment within the parent cell, the first-
formed being the largest, as shown
in  Plate I., Fig.  10, a,  b; some  of
these, moreover,  having distinct nu-
clei of their own, from which a third
generation is being developed on  the
same plan (Fig.  12,6); and  yet for all  these to disappear by liquefaction,
leaving the cavity of the parent-cell unoccupied, except by a pair  of cells ori-
ginating in the central part of the  nucleus (Fig. 13).   If  this account be cor-
rect, it is probable that these temporary cells perform the office of preparing
the contents of the parent-cell for  the nutrition of  the offspring  which is to
succeed it;  and each of these twin cells, in its turn,  going through the same
series of  changes (Fig. 14), gives  origin to  a new pair;  the continuance of
which process generates a cluster.  This is the mode, according to Dr. Barry,
in which the first cells of the embryo are developed into the "mulberry mass"
(Fig. 15), by whose subsequent development and metamorphoses, the tissues
and organs  of the fcetus are progressively evolved.
   131. Notwithstanding the numerous varieties  that  exist, in the particular
modes in which the cells are  developed, it seems to be well established as a
simple general principle, that all cells take their origin in  germs prepared by
a previously-existing cell; and that  these germs may be developed, either
  Endogenous cell-growth in cells of a meliceritous
tumour; a, cells presenting nuclei in various stages
of development into a new generation; 6, parent-
cell filled with a  new generation of young cells,
which have originated from the granules of the nu-
cleus. 
116          ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.

within the parent-cell, or when set  free by its  rupture.  The difference ob-
servable  in the several cases that have been enumerated, and in others  that
might be mentioned, seems to have reference chiefly to  the degree of prepara-
tion that is effected in the nutriment with which the young cells are supplied;
—some drawing it directly from the blood; whilst  others receive it through
the medium of the parent-cell, which probably exerts a certain degree of pre-
paring influence upon it;—and others, again, requiring  a further  preparation
to be effected, by the  elaborating or  assimilating influence of a group of tem-
porary cells,  expressly developed for this purpose.
   132.  We shall find, as we proceed, that all  the  tissues most actively con-
cerned in the  maintenance of the  Vital functions of the Human  body,—both
those of a Vegetative nature, and those  which are peculiarly  Animal, are
composed of Cells  which  have undergone no  considerable metamorphosis,
and of which one generation is produced after another  with a rapidity that is
proportioned to the activity of the function.  But there are  other structures
of an accessory character, in which  a  departure from the original type is to
be traced, sometimes so complete, as to prevent their real nature from being
understood, except by a very careful scrutiny into their history.   This depart-
ure is the result of various kinds of metamorphosis of  the cells and of their
nuclei;  of  which the  following are the principal.  The cells, originally sphe-
roidal, oval, or polygonal, may become elongated to such a degree, as to as-
sume the spindle or fusiform shape;  thus  resembling  woody fibres.   They
may at the same  time lose  their nuclei;  and their cavities may be occupied
by internal  deposits, so  that they may be mistaken for solid fibres.  Such
fusiform  cells are often found in exudation-membranes.—Again, the cells may
shoot out prolongations, either  in  a  radiating manner,  so that they assume a
stellate form  ; or in no definite direction, so that their shape becomes altogether
irregular.  Such  forms are seen amongst the pigment-cells of the Batrachia
and Fishes, and among  the vesicles of the gray matter of the nervous system.
Further, the original boundaries of the  cells may be altogether lost, by their
coalescence with each other.  This is the case with many membranes that
seem to have originated in a layer of flat cells ; the  situation of which is rather
to be traced by their nuclei, than by  their former boundaries, which have alto-
gether disappeared.  It is often the case, too, with  the  horny cells, of  which
the nails, hoof, &c, are made up ; and still more with the cells of shell, bone,
tooth, &c, which have been consolidated  by the  deposition of a calcifying
deposit.—Lastly, the character of the original cell may be completely altered
by a solution  in the continuity of its wall, in one  or more spots, so that its
cavity is laid open,  and  coalesces  with  some other.  In this  manner, by the
disappearance of  the  partitions  between  cells laid in apposition,  end to
end, may be  formed a tube;  and this  tube  may coalesce with others, in like
manner, so  as to form a capillary network for the circulation of the blood.
Or the tube may form a simple straight fibre ; and the nuclei of its component
cells may give origin to a new deposit, either in an amorphous condition, as
in the fibrous portion  of nervous tissue, or in  the  form of an aggregation of
new cells, as in the most perfect kind of muscular fibre.   In these cases, also,
the original composition of the tubes may be frequently traced by the  nuclei
that remain in their interior.   In the follicles  of glands, the  solution of con-
tinuity takes  place at one point only, which establishes  a communication be-
tween the cavity of the parent-cell, and some canal by which its contents may
be discharged ; and the nucleus situated at the blind or closed extremity of the
follicle, may  then continue to form successive  generations of secondary cells,
which are discharged by this outlet.
   133.  The  metamorphoses of the  nucleus are not less important, though
not as numerous. In some instances we find it sending out radiating prolonga- 
FIBROUS TISSUES.--BASEMENT MEMBRANE.
117
tions, so that it assumes a stellate form, like that of the cells of the Geranium-
petal ; this seems to be the case in regard to the nuclei of the  Bone-cells.—
In other  instances it appears to resolve itself into a fasciculus of fibres ; and
this  is stated by Henle to be the origin of the yellow fibrous tissue.—Further,
it may separate into a number of distinct fibres, each composed (like those of
the Nostoc, Fig. 18,) of  a linear aggregation of granules;  it seems to be in
this  manner, that the tubuli of the Dental  structure are  formed.—Lastly, it
may disperse itself still more completely into its component granules;  by the
reunion of which, certain peculiar vibrating filaments (the  so-called Sperma-
tozoa) may be formed, possessing  motor  powers analogous to those of the
Oscillatoriae and other corresponding filamentous  products of humble Crypto-
gamic vegetation, but destined to perform most important offices in the func-
tion  of Reproduction.
   134.  We have seen that, in  the Vegetable  structure, the component cells,
tubes, woody fibres (or elongated cells),  &c, are held together by simple ad-
hesion ;  a gummy intercellular substance, which answers  the purpose of a
cement, being often interposed,  sometimes  in  considerable  quantity.  But in
the Animal body, of which the  several parts are destined to  move with greater
or less freedom upon one  another, the aggregations of cells that make up its
chief part, either in their original or  in their metamorphic form, could not be
held together in their constantly-varying  relative positions,  without some in-
tervening substance of an altogether different character.  It must be capable
of resisting tension with  considerable firmness  and  elasticity;  it must admit
free  movement of  the several parts  upon one another; and it must still hold
them sufficiently close  together  to resist any injurious strain upon the  deli-
cate  vessels, nerves, &c, which pass from one to another,  as well as to  pre-
vent any permanent displacement.  Now all these offices are performed  in a
remarkably complete degree, by the  Areolar Tissue (§ 138);  the reason of
whose restriction to the Animal kingdom is thus evident.   And as necessity
arises, in certain parts, for tissues which  shall  exercise a still greater  power
of resistance to tension, and which shall  thus  communicate  motion (as in the
case of Tendons), or shall bind together organs that require to  be united (as
in the case of Ligaments and Fibrous Membranes), so do we find peculiar
tissues developed that shall serve these purposes in the most effectual manner.
Hence these tissues also, although not endowed with any  properties that are
peculiarly animal, are nevertheless  restricted  to  the Animal Kingdom,—as
completely as are the Muscular and Nervous Tissues, which  make  up the
essential parts of  the apparatus of Animal Life.
   135.  That all the  Animal tissues  are  in the first instance developed from
Cells, was the doctrine  put forth by Schwann, who first attempted to gene-
ralize on this subject.  By subsequent research, however, it has been shown
that  this statement was too hasty; and that, although  many tissues retain their
origin cellular type, through  the whole of life, and many more are evidently
generated from Cells and are subsequently metamorphosed, there are some,
in which no other cell-agency can be traced, than that concerned  in the pre-
paration of the plastic material.—This would appear to be the case, in certain
forms of the very delicate structureless  lamella of  membrane, now known
under the name of Basement or Primary Membrane, which is found beneath
the Epidermis or Epithelium, on all  the free surfaces of the body.  In many
specimens of this membrane, no  vestige of cell-structure can be seen;  and it
would rather appear to resemble that, of which the walls of the cells are them-
selves constituted.*  In some instances,  it presents a somewhat granular ap-

  * See a Paper by the Author, on the Microscopic Structure of Shells, &c, in the Annals
of Natural History, Dec. Ib43.  The  inner  layer of the Shells of Mollusca, after treatment 
  118         ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.

 pearance; and it is then supposed by Henle to consist of the coalesced nuclei
 of cells, whose development has been  arrested: or, in  other words, such
 Basement-Membrane is  formed by the consolidation of a layer of the plastic
 element, that includes a large number of the granules, which  may serve for
 the development of new cells.   Other forms of the Basement-Membrane can
 be distinctly seen  to consist of flattened polygonal cells, closely adherent by
 their edges ; every one having its own granular nucleus.*—It seems to be from
 these granular germs, sometimes scattered through the membrane, and  in other
 instances collected into certain spots, that the cells of the  superjacent Epithe-
 lium or Epidermis take their origin; and if this be the case, we must regard
 the Basement-Membrane as a transitional  rather  than as a permanent struc-
 ture,—continually disintegrating, and yielding  up its contained cell-germs on
 its  free surface, and  as constantly being renewed from  the blood beneath.
 For the epidermic structures appear to constitute an exception  to the  general
 rule, that  the  Tissues reproduce themselves; since they are cast off,  without
 leaving their germs behind them;  and the  cells which replace them must be
 derived from new  germs, more directly supplied from  the blood than is else-
 where the case.  In the case of the other tissues, whose disintegration  takes
 place interstitially (so to speak), it would seem  probable  that, in the very
 act of the dissolution of the parent-structure, the germs of the new structures
 destined to replace it are set free; as happens in the  reproduction of the sim-
 ple Cellular Plants.
    136. It would seem doubtful, also, in regard to the simple Fibrous tissues,
 whether they  are generated by a metamorphosis  of Cells, in the same  manner
 as the Osseous, Muscular and Nervous; or whether they are  not produced,
 like the Basement-Membrane, by the  consolidation of a plastic fluid, which
 has  been elaborated  by cells.   The latter view is the one which the Author
 has  been led to regard as most probable, from the results of his own observa-
 tions, coupled with those of Messrs.  Addison and Gulliver previously adverted
 to.   The Membrane of the  Egg-shell, whose  structure  has  been  already
 described (§ 118), appears to him to have essentially the same character with
 the simple Fibrous tissues, which it resembles also in its tenacity (compare
 Fig. 11 with Fig.  22); whilst its origin can scarcely be supposed to be different
 from that of the fibrous  network in the buffy coat of the Blood, or in the
                          bands formed by the coagulation of Lymph upon an
                          inflamed surface.   The  occasional vestiges  of cells,
                          which the purely Fibrous tissues display  (§ 138),
                          and which have  been adduced in  support  of their
                          cellular origin, are  not inconsistent with this view.
                          For in  the  reticulated  structures  just adverted to,
                          certain bodies are seen, which  appear to be nuclei
                          or imperfectly-formed cells (originating probably in
                          germs set free by the rupture of the colourless cor-
                          puscles of the blood), and which closely correspond
                          with the  nuclear corpuscles that may be  brought
                          into view in  the Fibrous tissue.  Mr. Addison's
                          observation,  too,—that  the fibres  formed  in  the
                          Liquor Sanguinis, and in plastic exudations, during
 tive molecules, and fibres, of  coagulation, often seem to radiate from the  remains
 fibrine, from Herpes labiaiis.    of the white corpuscles that  have ruptured, or from
                          the little aggregations of granules they contained,—
• gives the explanation of several of the  appearances, which  have led to  the

  with a dilute acid, yields specimens of Basement-Membrane, in a form well adapted for
  examination.
   *  See J. Goodsir, in " Anatomical and Pathological Observations," Chap. I.
 
              CLASSIFICATION OF HUMAN ELEMENTARY TISSUES.          119

belief in the production of the Areolar and other fibrous tissues by Cell-trans-
formation.—An additional argument  in favour of this view, may be found in
the appearances presented by the semi-fibrous Cartilages.  In the Cartilages
of the ribs, for instance, a more or less distinct fibrous appearance may often
be seen in the intercellular substance, which is  elsewhere quite  homogene-
ous ;  this  appearance is sometimes so faint, that it  might be considered  as
an illusion, occasioned by the manipulation to which  the section has been
subjected; but it  is often so  well  defined, as to present  the  aspect of true
fibrous tissue.   No indication of the direct operation  of cells, in the develop-
ment of these fibres, has ever been witnessed; and we can scarcely do other-
wise  than regard them as produced by the regular arrangement and con-
solidation of the particles of  the intercellular substance,  in virtue of its own
inherent powers.
   137. The following arrangement of the Human Tissues will be here adopt-
ed as expressing their respective relations to the  fundamental  elements which
have  been now described; namely, simple Membrane, Fibres, and Cells.
   a. Simple Membranous Tissues.—Of these there are scarcely any examples
in the Human body, except in the posterior layer of the cornea and the cap-
sule of the crystalline lens. The membranous element is largely found, how-
ever, in the compound Membrano-fibrous tissues.
   6.  Simple  Fibrous  Tissues.—Under this head may be  classed the White
and Yellow Fibrous Tissues, and Areolar Tissue.
   c.  Simple Cells floating separately and freely in the fluids.  Such are the
Corpuscles of the Blood, Chyle, and Lymph.
   d.  Simple Cells developed on the free surfaces of the body.  Such are the
Epidermis and Epithelium.
   e.  Compound Membrano-Fibrous Tissues, composed of a  layer of simple
membrane, developing Cells on its free surface,  ajid  united on the other to a
fibrous or areolar structure.—Of this kind  are the Skin, the Mucous  Mem-
branes, the Serous and Synovial membranes, the lining membranes of the
Blood-vessels, &c.
  f.  Simple Isolated Cells, forming solid tissues by their aggregation.—Un-
der this head we may rank the Fat-cells, the Vesicles of Gray Nervous matter,*
the Absorbent cells  at the extremities of the Intestinal villi, and the cellular
parenchyma of the Spleen and similar bodies: the cells  being held together,
in all these cases, by the blood-vessels and areolar tissue which pass in amongst
them.  In Cartilage, and certain tissues allied to it in structure, the cells are
united by intercellular substance, which may be quite homogeneous, or may
have a fibrous character.
   g.  Sclerous or Hard Tissues, in which the cells have been consolidated by
internal deposit, and have more or less completely coalesced with each other.—
 Such is the case with the substance of Hair, Nails, &c,  which may be more
properly  ranked under the Epidemic Tissues ; but the result is most charac-
 teristically seen in Bones and Teeth.
   h.  Simple Tubular Tissues, formed by the coalescence of the cavities of
 cells, without secondary internal deposit.—The  Capillary blood-vessels, and
 probably also the  smallest Lymphatics  and Lacteals, seem to be formed in this
 manner.
   i.  Compound Tubular Tissues ; in which, subsequently to the coalescence
 of the original cells, a new deposit has taken place within their cavities.—In
 the tubuli of the White or Medullary Nervous matter, and in  those of the least

   * As it  is undesirable to separate from each other the  descriptions of the two elementary
 forms of Nervous structure, on account of their close functional connection, the gray or vesi-
 cular nervous matter will be described together with the white or tubular, in the last section
 of this chapter. 
120         ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.
Fig. 22.
perfect form of Muscular Fibre, the secondary deposit has only a granular or
amorphous character ;  but  in  the  striated  Muscular fibre, it is composed ot
minute cells.
  As it is not requisite here  to say anything further  of simple Elementary
Membrane, we shall at once pass on  to the second group of Tissues ; one of
great extent and importance in the bodies of all the higher Animals.

                   4.  Of the Simple Fibrous  Tissues.

  138. A very large proportion of the body, in the higher  Animals, is com-
posed of a tissue, to which the name  of " Cellular" was formerly given.  This
term, however, is  so  much  more  applicable to those  structures,  which are
composed of a congeries of distinct Cells, and the use of it for both purposes
is likely to engender so much confusion, that it is  to be wished that its appli-
cation to this purpose  should be altogether discontinued.—The tissue in ques-
tion, now generally designated the Areolar, is found, when examined under
the Microscope, to consist of  a network  of minute fibres  and bands, inter-
woven in every direction, so as to leave innumerable  interstices, which com-
                               municate  with each  other.   The  two kinds
                               of Fibrous tissue, which elsewhere  exist se-
                               parately,—the white, and the yellow,—may
                               be  detected  in Areolar  tissue;  as was  first
                               pointed out by Messrs. Todd and Bowman.
                               The White presents  itself in  the form of
                               inelastic bands of variable size,  the  largest
                               1-500th of an inch  in  breadth, somewhat
                               wavy in their direction, and marked longitu-
                               dinally by numerous  streaks (Fig. 23); these
                               streaks are rather the indications  of a longi-
                               tudinal creasing, than a true  separation  into
                               component fibres; for it is impossible by any
                               art to tear up the band into  filaments of a de-
                               terminate size, although it manifests a decided
                               tendency   to tear lengthways.   Sometimes,
however, distinct fibres may  be  traced, whose diameter varies from about
l-15,000th  to  l-20,000th of an inch.  The Yellow fibrous  element exists in
the  form of long, single, elastic, branched  filaments, with a  dark decided bor-
der, and disposed to curl when not put on  the stretch (Fig. 24).  These inter-
lace with the others, but appear to have no continuity  of substance  with them.
They are for  the most part  between l-5000th and 1-10,000 of  an  inch in
thickness ;  but they are often met with both larger  and  smaller.   The pro-
portion of this element varies greatly in different parts ; being greatest in those
situations, in which the greatest  elasticity is required.  Sometimes we find
elastic fibres passing round the fasciculi of the white tissue,  constricting them
with distinct rings, or with a  continuous  spiral;  such are  termed by Henle
nucleus-filaments, from his  idea  of their  origin  (§ 133).   This  remarkable
disposition  of the yellow fibres is best  seen in the areolar tissue, that accom-
panies the arteries at the base of the brain.—The  effect of  Acetic acid upon
these two elements is very different; the white  immediately swells  up, and
becomes transparent;  whilst  the yellow remains unchanged.  This agent fre-
 quently brings into view certain  oval  corpuscles, which lie  in the midst of
 the bands and threads, and which sometimes appear to have  delicate prolonga-
 tions among them.  These  are usually supposed  to  be the persistent nuclei
 of the cells, from  which the  tissue  was developed ;  but, as already pointed
 out, it is  doubtful whether the fibres  of this tissue are  ever formed  by the me-

Arrangement of Fibres in Areolar Tissue
      Magnified 135 diameters. 
SIMPLE FIBROUS TISSUES J--AREOLAR TISSUE.
121
 tamorphosis of cells,—their origin being rather, it seems more probable, in the
 fluid blastema (§ 136).—The interstices of Areolar tissue are filled during life
 with a fluid, which resembles a very dilute  Serum  of the blood; it consists
 chiefly of water, but contains a sensible quantity of common salt and albumen,
 and (when concentrated) a trace of alkali sufficient to affect test-paper. The pre-
 sence of this fluid seems to result  from an act of simple physical transudation'
 for it has been found that, when the serum of the blood is made to percolate
 through thin animal membranes, the water charged with saline matter passes
 through them much more readily than the albumen, a part of  which is kept
 back.
   139.  The great use  of Areolar tissue  appears to be, to connect together
 organs and parts of organs, which require a certain degree of motion  upon
 one another: and to envelope, fix, and protect, the blood-vessels, nerves, and
 lymphatics with which these organs are  to be  supplied.  It can scarcely be
 said  to enjoy any vital powers, and is connected solely with physical actions
 (§ 134).   It is extensible in  all directions, and very elastic, in virtue of  the
 physical arrangement of its  elements; and it possesses no contractility, be-
 yond that of the vessels which are distributed through it.  It  cannot be  said
 to be endowed with sensibility ; for the nerves which it contains seem to be
 merely en route to other organs, and not to be distributed to its  own elements.
 And  its asserted powers of absorption and secretion appertain rather to  the
 walls of the capillary blood-vessels, than to  the threads and bands of which
 it is  composed.  It is  regenerated more readily than  any other tissue, save
 the Epithelium;  being produced, it would appear, by the simple consolida-
 tion of the blastema, that is poured out (in the form of organizable lymph) in
 situations where there has been a breach of  substance.  It is also formed in
 the effusions of a similar fluid, which are deposited  on the surfaces, or in
 the substance,  of inflamed tissues.—Areolar tissue yields Gelatine by boiling;
 but this is derived from the  White  Fibrous  element  only ; the Yellow not
 being affected by the process.
   140.  The White Fibrous tissue exists alone in Ligaments, Tendons,  Fi-
 brous Membranes, Aponeuroses, &c. ;  where it presents the same characters
 as those just described,—except that the bands are less wavy, and frequently
 quite straight, so that it is inextensible.   It  receives very  few  blood-vessels,
 and still fewer nerves ; indeed it would seem that, in many structures (as ten-
 dons), it is totally insensible.   It seems  entirely destitute of  any vital pro-
 perty ;  and its chemical nature is such, that  it needs very little  interstitial
 change  to maintain its normal composition. If dried, it has not the  least tend-
 ency  to  putrefy ; and when  moist, it resists  the putrefactive   process more
 strongly than almost any of the softer textures.  The peculiar and important
 property of this tissue, is its  capability of resisting extension ;  and we find it
 in situations, where a firm resistance is  to be made to traction.  If the traction
 be applicable in one direction only, as in Tendons and  most Ligaments, we
 find the bundles of fibres or bands  arranged side by side ; but if it be exerted in
 various directions, the fasciculi cross one  another, as in Fibrous Membranes.
 The reparation of this tissue is effected by the interposition of anew substance,
 every way similar to  the original,  except  that it wants its peculiar  glistening
 aspect,  and is more bulky and transparent.—The Yellow Fibrous tissue exists
 separately  in the middle coat of the Arteries, the Chorda? Vocales, the Liga-
 mentum Nuchse (of quadrupeds) and the  Ligamenta subflava;   and it  enters
 largely  into the composition of some other parts.  It differs remarkably from
 the white, in the possession of a high degree of elasticity; so that the tissues,
 which are composed of it  alone, are among the most elastic  of all known sub-
 stances.   It is, however, much more  brittle  than the white ;  and its fibres
usually  exhibit a marked tendency to curl at their broken ends.  Their  size
     11 
122           ON THE ELEMENTARY PARTS OF  THE HUMAN FABRIC.
varies from about l-4000th, to  l-24,000th of  an  inch; in the  ligamenta  sub-
flava, it  is  usually about  l-7500th.   There  is less tendency to spontaneous
Fig. 23.
Fig. 24.
White Fibrous Tissue, from Ligament.
      Magnified 65 diameters.

                   [Fig. 25.
Yellow Fibrous Tissue, from Ligamentum
 Nucha? of Calf.  Magnified 65 diameters.

                [Fig. 26.
 The two elements of Areolar tissue, in their natural rela-
tions to one another; 1, the white fibrous element, with
cell-nuclei, 9, sparingly visible in it; 2, the yellow fibrous
element, showing the branching or anastomosing charac-
ter of its  fibrillar; 3, fibrillse of the yellow element, far
finer than the rest, but having a similar curly character,
8. nucleolated cell-nuclei, often seen apparently loose.—
From the areolar tissue under the pectoral muscle, mag-
nified 320 diameters.]
  Development of the Areolar tissue,
(white fibrous element;) 4,  nucleated
cells, of a rounded form ; 5, 6,  7, the
same, elongated  in different degrees,
and branching. At 7, the elongated ex-
tremities have joined others, and are
already assuming a distinctly fibrous
character.  (After Schwann.)]
decomposition in this tissue, than in almost any other part of the fabric,—at
least, of its soft and moist portions; it requires but little renovation, therefore)
in the living body ; and is  but very sparingly supplied  with blood-vessels. 
COMPOSITION AND PROPERTIES OF GELATINE.
123
   141. The composition of the White fibrous tissues  is  very different from
that of most others ; for they  yield  to  boiling water the substance  called
Gelatine, which does not  seem  capable of the  same  degree of organization
with the Proteine-compounds.   This  may be obtained by boiling portions of
Skin, Areolar tissue,  Serous membrane, Tendon, Ligament, &c, in water, for
some time ;  after which the decoction is  allowed  to cool, when  it solidifies
into a jelly of greater or less thickness.  Some tissues dissolve readily  in this
manner, and little residual substance is left;  this is especially the  case with
areolar tissue, serous membranes, and (in a less degree) with skin.   Others
require a long boiling for the extraction of any Gelatine ;  and even then it is
obtained in but small quantity;  of this  kind  are  the  Elastic  fibrous  tissue,
and some forms of  Cartilage.   A peculiar  modification  of this principle
exists in most of the permanent cartilages;  and has  received the name of
Chondrine.   Gelatine is not found in  the blood, nor in  any of the healthv
fluids ;  and some Chemists are of opinion, that it is rather a  product  of the
operation practised  to separate it, than a real constituent of the living solids.
This idea seems  inconsistent, however,  with the fact,  that  the  gelatinous tis-
sues will exhibit, without  any preparation, the best marked of the chemical
properties which are  regarded as characteristic of Gelatine,—that, namely, of
forming a peculiar insoluble compound with Tannin ; and the Tanno-Gelatine,
which may be obtained by precipitating Gelatine from a  solution, and that
which results from  the action of Tannin on Animal membrane, appear  to be
precisely analogous in every respect,—save in the presence of structure  in the
latter, which is absent in the former.  Moreover, the  Gelatinous  tissues are
found, when submitted to ultimate analysis, to possess exactly the same com-
position with Gelatine itself.   Still it seems probable, that the arrangement of
the component particles is in some degree altered by the process  of boiling;
for it is found that, the more  distinct  the fibrous structure of the tissue, the
less it is affected by the prolonged action of cold water, and the longer it must
be boiled, before it  is resolved into Gelatine.

  a. Gelatine is very sparingly soluble in cold water;  by contact with which, however, it is
caused to swell up  and soften.  It is readily dissolved by hot water; and forms so strong a
jelly on cooling, that 1  part in 100 of water  becomes  a  consistent solid.  Its reaction with
Tannic acid is so distinct, that 1  part in 5000 of water is at once detected by infusion of
Galls.  The following are the results of four analyses of Gelatine by Scherer and Mulder.
	Sc:	HEHER.		MuLDER. *
Carbon . Hydrogen Nitrogen Oxygen	. 50557 . 6-903 . 18-790 . 23-750		50-774 7-152 18-320 23-754	50-048 50-048 6-477 6-643 18-350 18-388 25-125 24-921
  The  formula deduced by Mulder from this composition, and from  the combinations of
Gelatine with Tannic and Chlorous acids, is 13 C, 10 H,2 N, 5 O.—When Gelatine is boiled
for some time, it loses its power of forming a jelly on cooling; and it is stated by Mulder,
that this is due to its union with an additional amount of water, a true Hydrate of Gelatine
being formed by the combination of 4 Equiv. of Gelatine, with 1 Equiv. of Water.   The
same product is obtained by adding Ammonia to the Chlorite of Gelatine, and  removing by
Alcohol the Sal Ammoniac thus formed.
  b.  It is not  yet known how Gelatine is produced in the Animal body.  There cannot be
a doubt that it may be elaborated from Albumen; since we find a very large  amount of it
in the tissues of young animals, which are entirely formed from albuminous  matter ;  and
also in  the tissues of herbivorous animals, which cannot receive it in their food, since Plants
yield no substance resembling Gelatine in composition.   It has been suggested by Mulder,
that  Gelatine  may be formed by  the decomposition of Proteine, which has been already
mentioned as taking place from the agency of weak alkaline solutions (§ 116 b~), and which
must probably, therefore, be continually occurring in the Blood.  For, if to each atom of Pro-
tid and Erythroprotid, we add one of the atoms of Ammonia which are given off in  that 
124          ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.
decomposition, we have compounds, of which the former differs from Gelatine only by the
presence of two additional atoms of hydrogen and the deficiency of one of oxygen, whilst
the only difference in the latter consists in the presence of one additional atom of hydrogen.
Thus the ammoniated Erythroprotid, when exposed to oxygenation in the lungs, may have
its one superfluous atom of hydrogen  carried off in the form of water, and will then  have
the composition of Gelatine;  and the same result will be attained from the ammoniated
Protid, by the addition of three  atoms of oxygen, which will convert it into Gelatine with
two atoms of water.   According to this formula, the substances produced  from the decom-
position of the proteine in blood, merely through the action of the alkali in the  serum, and
the oxydizing influence of the atmosphere, are—carbonic acid, water, gelatinous tissue, and
leucin.  The carbonic acid passes off through the lungs ; and the water, either by the kid-
neys, or by exhalation from the lungs or skin.  The Gelatine only requires form, to become
Fibrous tissue.  Leucin, however, has not yet been found in the body; and until it  shall
have been discovered, or the  products of its decomposition  shall  have been detected, any
such attempt to explain the formation of Gelatine, must be regarded as altogether theoretical.*
  c. The relation of Gelatine  to the Proteine-compounds is further shown by the fact, that
Leucin  may be produced from the  former, as well as from the latter.  When Gelatine is
boiled, either with alkalies or  with dilute  sulphuric acid, Leucin is formed; together with
extractive matters, and a peculiar sugar termed Glycicoll. This substance crystallizes in large
colourless prisms, which have a sweet taste, and feel gritty between the teeth; it is soluble
in 4 J parts of water, and is taken up in small quantity by Alcohol.  This fact is one of much
interest in regard to certain Pathological relations of Gelatine.

   142. The Yellow Fibrous  tissue, on the contrary,  undergoes scarcely any
change by  long  boiling; a very small quantity of Gelatine being alone yielded
by  it;  and this  being probably derived from the Areolar  tissue, by which  it is
penetrated.   It  is unaffected by  the weaker acids, and undergoes no solution
in the gastric fluid  ;  and it preserves its  elasticity for  an  almost  unlimited pe-
riod.   According  to Scherer, the  yellow fibrous  tissue  from the middle  coat
of  the Arteries  consists of  48 C, 38 H, 6  N,  16  O ;  which  (taking Liebig's
formula for Proteine)  maybe regarded  as 1  Proteine + 2 Water.  When
burned, it leaves 1'7 per cent, of ash.

             5.  Of Simple Cells, floating in the Animal Fluids.

   143. The red colour, which  is characteristic of  the Blood of Vertebrated
animals, is entirely due to the presence, in that  fluid, of a very large number of
floating cells, which  have the power of forming a secretion in their interior,
that is distinguished  by its  peculiar  chemical nature, as well  as  by its hue.
The  red Blood-corpuscles (commonly, but erroneously termed globules) are
                                     flattened Discs,  which, in Man  and most
             Fig. 27.                 of the  Mammalia, have  a distinctly cir-
                                     cular  outline.   In the discs  of  Human
                                     blood, when examined in its natural  con-
                                     dition,  the sides  are  somewhat concave;
                                     and  there  is  a bright spot in the centre,
                                     which has been regarded by many as in-
                                     dicating the existence of a nucleus; though
                                     it is  really nothing else  than an effect of
                                     refraction,  and may be exchanged for a
                                     dark one by slightly  altering  the focus of
                                     the Microscope.   The form of  the  disc
  Red Corpuscles of Human Blood, represent-  •            ,  r,              .
ed at a, as they are seen when rather beyond  lS VerJ mUCn altered  by various reagents :
the focus of the microscope; and at b as they  for the  membrane which composes its eX-
appear when within the focus. Magnified 400  terior or cell-well, is readily permeable by
diameters.                             liquids  ; so as  to  admit a passage of li-
                                     quid, according  to the  laws of Endos-
mose, either inwards  or  outwards, as the  relative density of the  contents of
                         *  See Mulder's Chemistry, p. 326.
 
SIMPLE ISOLATED CELLS ;--RED BLOOD-CORPUSCLES.
125
the cell and of the surrounding fluids may direct.   Thus, if the Red corpus-
cles be treated with water, there is a passage of that liquid into the cell;  the
disc becomes first flat, and then double-convex, so that the central spot disap-
pears ;  and by a continuance of the same process, at last becSmes globular,
and finally bursts, the cell-wall giving way, and allowing the  diffusion of  the
contents through the surrounding liquid.  On  the other hand, when the Red
corpuscles are treated with a thick syrup or solution of albumen, they will be
more or  less completely emptied, and caused to assume  a shrunken appear-
ance ; the first effect of the process being to increase the concavity, and to
render the central spot more distinct. It is probable that the Blood-corpuscles,
even  whilst they are circulating in the living vessels, are  liable to alterations
of this kind, from variations in the density of the  fluid in which they float;
and that such alterations may be constantly connected with certain disordered
states of the  system.*   We hence see the necessity, in examining the Blood
microscopically, for  employing a  fluid  for its dilution, that shall be as nearly
as possible of the same character with ordinary liquor sanguinis.!
   144.  Microscopic observers  have  been much divided  upon the question,
whether or not the Red corpuscles of the Blood of Man and other Mammalia
contain a nucleus.   There  seems every probability from  analogy, that a  nu-
cleus  exists in them, as it does in the  red corpuscles of all other animals;
but it cannot be brought into view by any of the ordinary methods, which
render it distinctly visible in the  oval  blood-discs of Oviparous  Vertebrata;
and of late the general  opinion has been, that nothing resembling  their nuclei
could be present in  the blood-discs of Man and Mammalia.  Dr.  G. O. Rees
states, however,  that, by carefully examining the ruptured cell-walls, which
fall to the bottom  of  the  water  when  red corpuscles  have been  diffused
through  it, he could distinguish appearances on them, that indicated the  ex-
istence of nuclei; although  they escape observation when within the corpus-
cles themselves, on  account of their high  refractive  power.   He  describes
them as  being circular and flattened, like the Red corpuscles themselves ;  and
as about two-thirds  of their 'diameter.
   145.  In all Oviparous Vertebrata, without any known  exception,  the  red
corpuscles are oval,—the proportion between their long and short diameters,
however, being much subject to varia-
tion ;  and their nuclei may always be                 FlS- 28-
brought  into  view,  by  treatment  with
acetic acid, when not at first visible. In
the red particles of the Frog, which are
far larger than those of Man, a nucleus
can be observed to  project somewhat
from  the central portion of the oval,
even  during  their circulation;  and it
is rendered extremely distinct by the
action of acetic acid; this renders the
rpmainder of the  narticle  extremely   Particles of Frog's blood; 1,1, their flatteneI
remainder oi tne  parucie  exiremeiy  face. ^ particle turned near]y edgeways; 3,
transparent,  whilst  it gives  increased  lymph.gi0buie; 4, blood-corpuscles altered by di-
opacity to the nucleus, which  is  then  hue acetic acid. Magnified 500 diameters.
seen to consist of a granular substance.
In the still larger blood-disc of the Proteus and Siren, this appearance is  yet

  * See Dr. G. 0. Rees' Gulstonian Lectures, for 1845.
  f By Wagner, the filtered serum of frog's blood is recommended for this purpose. Weak
solutions of salt or sugar, and urine, answer tolerably well; but Mr. Gulliver  remarks that
all addition must be avoided, when it is intended to measure the corpuscles, or to ascertain
their true forms ; as the serum of one  Mammal reacts injuriously on the blood of another.
See Philos. Magaz., Jan. and Feb. 1840.
                                    11*
 
126          ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.
more distinct;  the structure of the nucleus being so evident without the addi-
tion of acetic acid, that its granules can be counted.*
   146.  The form of the  Red  Corpuscles  is  not unfrequently  seen  to
change during  their circulation;  but this  is  generally  in consequence  of
pressure:  from the effects  of which, however,  they quickly recover them-
selves.  In  the narrow capillary vessels,  they  sometimes  become suddenly
elongated, twisted, or  bent,  through  a narrowing  of the channel;  and this
may take place to such a degree,  as  to  enable  the disc to pass  through  an
aperture, which appears very minute  in  proportion to its diameter.   When
undergoing  spontaneous  decomposition, the blood-discs  become  granulated,
and sometimes (as long ago noticed by Hewson) even mulberry-shaped; and
particles in which these changes appear  to be commencing, may be found  in
the blood at all times.  It  has been ascertained that bile and urea exert a pecu-
liar solvent  power on the  blood-corpuscles;  and  hence  we  can understand
one of the modes in which  a retention of these  substances  in the circulating
fluid (Chap. XV., Sect. 1) proves  so injurious.—The size of the blood-discs
is liable to  considerable variation, even in  the same individual;  some being
met with as much as one-third larger, whilst others are one-third smaller, than
the average.   The diameter of the corpuscles bears no constant relation to the
size of the animal, even within  the  limits of  the same  class; thus,  although
those of the Elephant are the largest among Mammalia (as far as is hitherto
known), those  of  the  Mouse tribe are far from being the smallest,  being  in
fact more than three times the diameter of those of the  Musk Deer.   There
is, however, a  more uniform relation between  the size of  the  animal and that
of its blood-discs, when the comparison is made  within the  limits of the same
order.   In Man, the diameter varies  from  about l-4000th to  l-2800th of  an
inch;  the average diameter is probably about l-3200th.

   a. The following measurements of the blood-discs of various animals are chiefly given
on the authority  of Mr. Gulliver.—The diameter of the corpuscles in the Quadrumana is
generally about the same  with that of the  Human blood-discs; there is, however, a  slight
diminution among the Lemurs, and there is more variation among them, than among  the
Monkeys.  Among the Cheiroptera, the diameter of the corpuscles is somewhat less than in
the preceding order, the average being  about l-4300th of an  inch.   Passing to the Insecti-
vara, we find  the blood-discs of  the Mole to be still smaller, averaging only the l-4747th of
an inch; those of the Hedgehog, however, are larger, being about l-4085th.   In the corpus-
cles of the different families of the Carnivora, there  is  such a well-marked diversity in  the
size of the corpuscles, that the fact may be used as a  help to  classification/}-  In the Seals,

   * As Professor Owen's  interesting account of the blood-discs of the  Siren may not be
generally accessible (Penny Cyclopaedia, Art. Siren),  the leading facts  in it will  be here
stated.   This animal agrees with the Proteus and other species in being perennibranchiate
(§ 32); and, as in all its congeners yet  examined, the blood-discs are of very large dimen-
sions.   They are  usually of an oval  form, the long  diameter being  nearly twice the short;
and the nucleus projects slightly from each of the flattened surfaces.  Considerable variety
in the form of the disc presents itself, some of the corpuscles being  much  less oval than
others; but the nuclei do not partake of these variations in nearly the same degree.  The
nucleus is clearly seen to  consist of a number of moderately-bright spherical granules, of
which  from 20 to 30 could be seen in one plane or  focus, the total  number being of course
much greater.  When removed from the capsule, the nuclei are colourless, and the compo-
nent granules have a high  refracting  power.  Viewed in situ, they present a tinge of colour
lighter  than that  of the surrounding fluid, and dependent upon the  thin  layer of that fluid
interposed between the nucleus and the  capsule.  As the fluid contents of the blood-disc in
part evaporate during the process of desiccation, the capsule falls into folds in the interspace
between the nucleus and the outer margin; these folds generally take the direction of straight
lines three to seven in number, radiating from the nucleus.
   f Two facts of much interest in Zoology have been brought to  light by Mr. Gulliver's
examination of the diameter of the blood-corpuscles of this tribe.   The difference between
those of the Dog  and the Wolf is not greater than that which exists among the varieties of
the Dog; whilst the discs of the  Fox are much  smaller.   The discs of the  Hyaena are  far
more approximate to those of the Canidae, than they are to those of the Felidae. 
                COMPARATIVE SIZES OF RED CORPUSCLES OF BLOOD.            127

the  diameter averages l-3280th  of an inch; in the Dog,  l-3540th;  in the Bear, about
l-3700th; in the Weasel,  l-4200th; in the Cat, l-4400th; and in the Viverrce,  l-5365th.  In
two species only of the Cetacea, have the blood-discs  been yet examined -y the Dolphin, in
which their diameter averages l-3829th of an inqh; and the great Rorqual (the largest known
Mammal), in which they are only l-3100th of an inch, or scarcely larger than  those of Man.
Among the Pachydermata, the average excluding the Elephant (the diameter of whose blood-
discs is about l-2745th of an inch), and the Rhinoceros (in which they are about l-3765th),
may be stated at about l-4200th; and there is less variation than might have been expected,
from the different size and conformation of the several species examined.   Among the Ru-
minantia, the corpuscles are for the most part smaller than in other orders; and there is more
relation between their diameter and  the size of the animal, than is elsewhere observable.
Excluding the Camelidae (which are zoologically intermediate between the Ruminantia and
Pachydermata), we find a range of sizes extending from the l-3777th to the, l-12,325th of
an inch; the former is the diameter in one of the larger Deer;  the  latter in  the Musk Deer,
which is the smallest in the whole order.  In the Camel tribe, the  average  of the long dia-
meter of the corpuscles is about l-3300th of an inch,  whilst that  of the short diameter is
l-6300th; and this is nowhere widely departed  from: the length of the discs is, therefore,
not quite twice their breadth.  Among the Rodentia, the discs are rather large, especially
considering the  small  size of most of the species.   In the  Capybara,  which is  the largest
animal of the order, they average l-3190th; and in the Mouse family (the smallest of Mam-
malia), they are as much  as  l-3814th.   In the Squirrels, the  diameter is rather less;  but in
scarcely any of the whole order is it under l-4000th. Among the Edentata, the Two-toed Sloth
has been found to  have corpuscles of the unusually large diameter of l-2865th of an inch;
whilst in the Armadilloes  they average  about l-3400th.  In the Marsupialia the range is
nearly the same as among the Rodentia.
   b. In Birds, according  to the observations of Mr. Gulliver, the long and  short diameters
of the corpuscles usually bear to  each other the proportion of 1^ or 2, to 1;  and  this is the
general relation among Oviparous Vertebrata, with the exception of some of the Crocodile
tribe, in which the length is sometimes  three times the breadth.   The size of the  corpuscles
of Birds has generally more relation to that of the species, than it  has in Mammalia.  No
instance has yet been  detected, of the occurrence of comparatively small corpuscles  in the
larger species, and of large corpuscles among smaller  animals, which has been seen to  be
common among the former class;  the  blood of the Humming-birds, however, has not yet
been examined. The largest discs are found among  the Cursores; those of the Ostrich have
an average long diameter  of  l-1649th of  an inch, and  a short  diameter of l-3000th; and
among the larger Raptores, Grallatores, and Natatores, the dimensions are but  little inferior.
The least dimensions hitherto observed are among the small Passerine birds;  in  which the
corpuscles have a  long diameter of about  l-2400th of an inch, and a transverse diameter of
from l-3800th to l-4800th.  Circular discs  may be occasionally observed in  some species,
agreeing with the  others in every particular but their form; and every gradation may be no-
ticed between these and the regular oval corpuscles.
   c.  The large size of the blood-discs in  Reptiles,  especially in Batrachia, and  above all,
in the Perennibranchiate species of the latter, has been  of great service to the Physiologist;
by enabling him to  ascertain many particulars regarding their  structure, which could not
have been otherwise determined with  certainty.  Among  other  facilities which this occa-
sions, is that of procuring their separation from the other constituents of  the blood ; for they
are too large  to  pass through  the pores  of ordinary filtering-paper, and are  therefore re-
tained upon it, after the liquor sanguinis has flowed through.  The blood-discs  of the  warm-
blooded Vertebrata cannot be thus separated.  The oval corpuscles of the Frog have a long
diameter of about  1-1108th, and a transverse diameter  of about 1-1800th of an inch; those
of the Salamander or Water-newt are still larger.  The long diameter of the corpuscles of the
Proteus is stated by Wagner at l-337th  of an inch;  that of the Siren is about l-435th, the
short diameter being about l-800th of an inch ; the extremes of variation, however, are very
wide.  The long diameter of the nuclei is about l-1000th or l-1100th, and the short  diame-
ter about l-200Uth; hence it is about three times as long, and nearly twice as broad, as the
entire Human blood-disc, thus having six times its superficies; its thickness is about l-3800th
of an inch.
   d. The number  of Fishes, in which the diameters of the  blood-discs have been examined,
is still inconsiderable. In the common Perch, theyaverage l-2100th  by 1-2824 ; in the Carp,
they are  l-2142nd of an inch  by l-3429th; in the Gold-Fish, though of the same genus and
of much smaller size, they are as much as l-1777th by  l-2824th; in the Pike, l-2000th by
l-3555th; and in the Eel,  l-1745th by l-2842nd.*

  *  A summary of  Mr. Gulliver's numerous and valuable observations  is contained  in the
Proceedings of the Zoological Society, No. clii. 
128         ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.

   147.  In speaking of the Chemical  constitution of the Red Corpuscles  of
Blood, it is necessary to distinguish the substance of their walls  and nuclei
from  their fluid contents.   These  may be separated by  treating  them with
water;  which, as already mentioned", occasions the rupture of the cells, the
walls of which sink to the bottom,  whilst their contents are diffused  through
the liquid.  The substance obtained from the former has been termed Globu-
line; but it does not seem to differ in any essential character from other sub-
stances, that result from the organization of the  proteine-compounds.  The
compound which forms the contents of  the  red  corpuscles, however, and
which gives them their characteristic hue, is very different both in its sensi-
ble properties, and in its composition; and has received the designation  of
Haematine.  When separated from albuminous matter, it is of a dark-brown
hue, and is  tasteless and insoluble in water, alcohol, and ether;  but it is rea-
dily soluble in water or alcohol, that contains alkalies or acids ; whence it may
be  supposed to unite with these,  like  albumen, as an acid or a base.  In
composition, however, it differs considerably from that of the proteine-com-
pounds; its formula being 44 C, 22 H,  3  N, 6 O,  with a single proportional
of iron.   When burned, it yields a notable quantity of peroxide  of iron ; and
one atom of this is considered to be present in combination with  each  equiva-
lent of the animal compound.  The red  colour is not due, however, as for'
merly supposed, to the presence of this  peroxide ; for M. Scherer has  proved,
that the  metal may be  entirely dissolved away by the agency of acids, and
that the animal matter, afterwards boiled in alcohol, colours the spirit intensely
red.  On the other hand, the iron is most certainly united  firmly with the
constituents of the Haematine, as contained in the red corpuscles ; for this sub-
stance may be digested in dilute sulphuric or  muriatic  acid for several days,
without the least diminution in the quantity of iron, the usual amount of which
may be  obtained by combustion from the  Haematine that  has been subjected
to this treatment.  When diffused through water, in the manner just describ-
ed, the Haematine exhibits the same changes of colour under the influence of
oxygen, acids, saline matter, &c, as the Blood undergoes in similar  circum-
stances.
   148.  The question of the origin of the red Blood-corpuscles is a very inte-
resting one, and cannot yet be regarded  as completely determined.  That they
are to be regarded as nucleated cells,—conformable in general character with the
isolated  cells, which constitute  the whole  of the simplest Plants  (§ 125), and
having each an independent life of its own, the duration of which is  limited,
—there  can now be no reasonable doubt.   From this we should infer that they
have the power of reproducing themselves;  and the recent observations of
Dr. Barry and other Microscopists seem to  confirm the statement long ago
made to that effect by Leeuwenhoek.  The first change said to take place,  is
the appearance of delicate radiating lines between  the  nucleus and the peri-
phery ;  dividing the disc into several segments, usually six in number (Plate I.,
Fig. 22.)   The margin is soon  observed to become crenated, by indentations
at corresponding points;  and these indentations become deeper, until  a com-
plete separation takes place,  setting free six young cells or discs (a, b,  c, d, e),
which seem to have been formed around the margin of the nucleus of  the pa-
rent cell.   Between the small newly-generated disc, and the full-sized  corpus-
cle, we should expect to find every intermediate size ; and this is affirmed by
these observers to be the case.—It has been lately asserted by Dr. G. O. Rees,
that, when examining a  portion of Blood maintained at about its natural tem-
perature, he observed some  of the corpuscles to assume an hour-glass form,
by a contraction across their middle ; and that, by the increase of  this contrac-
tion, producing the complete division of the  corpuscles, two unequal-sized
circular bodies were  eventually produced from each; which, when  treated 
ORIGIN AND MULTIPLICATION OF  RED CORPUSCLES.
129
with  a strong saline solution, were emptied of their contents, like ordinary
blood-discs.—It is  not at all improbable, that  both these methods of multi-
plication  may be followed;  and  it can  scarcely be doubted  that, by one  or
both, a continual succession of Red corpuscles is kept up.   That the  corpus-
cles may be generated with great rapidity under peculiar  circumstances, will
hereafter appear (Chap. XL, Sect. 6); and their amount may undergo a rapid
diminution also, without any evident abstraction of them from the circulating
fluid.   This diminution seems to be traceable in some instances to a too low
specific gravity of  the serum ;  which will cause the Red corpuscles to rupture
by endosmose, just as when they are treated with  water.—Appearances have
been seen by Wagner, Gulliver, and others, in the  blood of Batrachia, which
might seem  to indicate  that the  Colourless corpuscles (§ 151) serve as the
nuclei of cells, which, when fully developed, may become Red blood-discs;
but  in the  Mammalia, it is scarcely possible to imagine that this can occur;
since  the diameter of the colourless corpuscles is  very constant;  whilst that
of the Red  blood-discs is so variable, that the  former, though sometimes the
smaller, are  in other instances far larger than the latter.  If it be admitted
that the Red  corpuscles have  the power of reproduction, like other isolated
cells, it does not seem necessary to seek  elsewhere  for the  source of their con-
stant renewal; and various facts, hereafter to be stated, appear to the Author
strongly  indicative of the entire  functional as  well as structural  difference,
between the red and the colourless corpuscles  of the blood of Vertebrata.
   149. That  the Red blood-discs, when first formed in the embryo, have  an
origin common to that of all other tissues, cannot be doubted.   They are pro-
duced, in the  embryo of the Bird, in the portion  of the germinal membrane
which afterwards becomes the area vasculosa ; this consists  of  delicate cells
very uniformly disposed: and  whilst  capillary vessels  are being  formed by
the  union of  the  cavities of these, blood-discs seem  to  be  developed from

                                    Fig. 29.
  Production of blood-corpuscles in Chick, on the fourth day of incubation ; a, particles fully formed;
b, particles in progress of formation; c, similar particles altered by dilute acetic acid, so as to display their
nuclei.

the granules or cell-germs they contain.   These changes take place about the
second or third day of incubation;  but it is  not  until some days afterwards,
that the discs assume their characteristic form.

  a. Mr. Macleod gives the following history of the  development of the blood-corpuscles
in the  Chick.  In blood withdrawn from the heart, on the third day, and diluted with se-
rum, or from the germinal membrane or allantois, and  diluted with fluid albumen,—" a num-
ber of small granules are seen floating about the  field  : these enlarge and become clearer in
the centre; this enlargement goes on very rapidly, and when they have gained to about twice
their original  size, the central clear part becomes dull.  This dullness slightly increases, and
in a short time it is seen to be distinctly granular; whilst the borders are observed to be
well-defined,  smooth, and clearer  than the  central part.  The enlargement of these bodies,
with the granular appearance of their centre, seems  not  to depend on  the aggregation of
granules round a centre one, but on a property which  they have in themselves of enlarging
and presenting that figure.  During all this time they are quite spherical and of good con-
sistence, as they do  not lose their form by considerable  pressure.  In the second stage, the
central  portion gradually becomes less opaque, and ceases to appear granular, the external 
130          ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.

portion at the same  time separating in some degree from the central part.  The blood-cor>
puscle, in this stage  of development, has  the appearance of a slightly flattened round cell,
formed of a somewhat delicate but elastic membrane, with a nucleus in the centre.  At this
time a number of these bodies, being close together in the field, presents a yellowish colour.
The cell is disc-like,  rather concave, but the nucleus convex.  In the third stage, one side of
the corpuscle  gradually elongates, giving it a pear-shaped appearance; the  opposite side then
elongates itself in a  similar manner, and to the same degree.  The concavity between the
nucleus and border disappears, and the whole  becomes slightly convex.  The hue at the
same time gradually becomes redder."*

  The corpuscles  are generally larger in the embryo than in the  adult, espe-
cially soon  after the period of their  first  formation; it was remarked  by M.
Prevost, that in the foetal goat they  were at first twice the size of those of the
mother.   Mr. Gulliver has observed, however, that at a later period of utero-
gestation they are  sometimes smaller than the average dimension of the adult;
but perhaps all such  observations are to be received with hesitation, owing to
the fact mentioned by him, that the variety  in the  magnitude of the foetal cor-
puscles is much greater than in the  full-grown animal.
  150.  In regard  to the uses of the Red corpuscles of the Blood, in the Ani-
mal economy, it appears to the  Author that a definite conclusion may be now
arrived at.  Their existence in  the  circulating fluid is nearly confined  to the
Vertebrated classes ;  the corpuscles which are seen in the blood of the Inver-
tebrated, being mostly analogous rather to the Colourless corpuscles, presently
to be described as  present in the  blood of the  higher animals.   Among the
lower Invertebrata, indeed, the Red  corpuscles seem to be altogether wanting;
and the same may be said of the embryos of the highest animals, at an early
period of their development; as  well as of the early state of parts  that are
being newly formed, at any  period  of their  lives.   Hence  the inference ap-
pears highly probable, that they are not  essentially necessary  to the produc-
tion of the  organizable elements of  the blood, or of the organized tissues; in
other words, to the simple acts  of growth and nutrition. The  Red corpuscles
are most abundant in those classes among Vertebrata, which maintain the
highest temperature ; thus, they are somewhat more numerous, in proportion
to the whole bulk of the Blood, in  Birds than in Mammalia; and far more in
the latter, than in Reptiles  and Fishes.  As it is evident that they undergo
very important changes in the pulmonary and systemic capillaries,—their co-
lour being changed from purple to  red in the former, and from red to  purple
in the latter,—it seems highly probable that they have as their principal office,
the introduction of oxygen into the  blood that circulates through the  systemic
capillaries,  and the removal of the carbonic acid  set  free there; serving, in
fact, as the  medium for bringing  the tissues into relation with the air,  the in-
fluence of which  is necessary for the maintenance of  their vital activity.  In
the Invertebrata generally, whose respiration is very feeble, this end will be
sufficiently  answered by the fluid plasma  of the blood ; the alterations in  which,
under the influence of the air, have been  already noticed (§§ 115, 116 a).  And
in Insects,—the only class whose respiration is at all active, we find  the air
directly conveyed into the tissues ;  the circulating  fluid not being employed as
its carrier (§ 18).  We shall hereafter find, that the influence of oxygen upon
the Nervous and Muscular systems  is essential to  their vital activity ;  and it
seems to be by their agency in  bringing  these into relation, that the Red cor-
puscles possess that intimate connection  with the  Animal functions, which we
find them to possess.   The animals whose temperature is the  highest, are
also those whose  senses are most acute,  and whose movements are most ener-
getic : whilst, on  the other hand, if there be any unusual diminution  in  the
* London and Edinburgh Monthly Journal, September, 1842. 
COLOURLESS CORPUSCLES OF BLOOD.
131
proportion of Red corpuscles, it is invariably accompanied by muscular de-
bility and deficient nervous power.

  a. By Liebig it is supposed, that the iron in the red corpuscles is the  real agent in the
respiratory process : for if its original state be the protoxide, it may become  the peroxide
by uniting with an additional atom of  oxygen,  or  the protocarbonate by the addition of an
atom of carbonic acid.  The former change is supposed by him  to take place in the lungs,
to which the blood comes charged with carbonic acid; the carbonic acid is given up by the
iron, and replaced by an equivalent of oxygen  taken  in from the air: whilst in the syste-
mic capillaries, the converse change takes place,—the oxygen being imparted to  the tissues,
and being replaced by carbonic acid which is given up by them  to be conveyed  out of the
system.  It is stated by Liebig that there is far more than sufficient iron in the whole mass
of the blood, to convey in this manner all the  oxygen and carbonic  acid, which are inter-
changed between the pulmonary and systemic  capillaries.  The  speculation  is certainly an
ingenious one; but it can scarcely be  yet received as a physiological fact.

   151.  Besides the red particles of the Blood, there are others which possess
no colour, and which seem to have a function altogether different;  these are
known  as the White or Colourless corpuscles.  Their  existence  has long
been recognized in the blood of  the lower Vertebrata, where, from being much
smaller than the red  corpuscles, they could readily be  distinguished.  But  it
is only  of late,—chiefly through the researches  of Gulliver, Addison,* and
others, that they have been recognized in the blood of Man and  other  Mam-
malia ;  their size being  nearly the same with that of the red corpuscles; and
the general appearance of the two (owing to the circular form of the latter,
and the absence  of a proper  nucleus,) being  less  distinct.  It is  remarkable
that, notwithstanding the great variations in the size of the red corpuscles in
the different classes of Vertebrata, the dimensions of the colourless corpuscles
are extremely constant throughout; their diameter seldom being much greater
or less than l-3000th of an inch.  This has  been observed even in those ani-
mals,—the Musk-deer, and the Proteus,—which present the widest departure
from the general standard  in the size  of their red corpuscles:  so  that the
colourless corpuscle  is as much  as four times the diameter of  the red, in one
instance; whilst it is not one-eighth of the  long diameter of the red, in the
other.   Hence it would seem very improbable, that the red can never be con-
verted into the white, or the white into  the red.—The aspect of the two, under
the Microscope, is  very different.  Instead   of presenting a  distinct  central
nucleus, like the red corpuscles of the  Oviparous Vertebrata,—or being en-
tirely destitute of granular contents, as are those of Mammalia when unaffected
by reagents, the colourless  corpuscles are  studded   with  minute  granules,
which may be occasionally seen in active  motion within them, and which are
discharged when the corpuscles  are treated with liquor potassae.   They pos-
sess, moreover,  a higher refracting power  than the red corpuscles ; and are
further  distinguished from  them, by their greater firmness, and by the ab-
sence of any disposition to adhere to each other; so that, when a drop of recent
blood is placed  between two strips of glass, and  these are gently  moved over
one another, the white corpuscles may be at once recognized by their soli-
tariness, in the midst of the rows and irregular masses formed by the  aggre-
gation of the red.   This is still  better seen in inflamed blood ; in which the
Red corpuscles  have a peculiar  tendency to adhere to one another, whilst the
White are present in unusual number.
   152.  The Colourless corpuscles  may be  readily distinguished in the cir-
culating Blood, in the capillaries of the Frog's foot;  and it is then observa-
ble, that they occupy the exterior of the current, where the motion of the fluid
is slow, whilst the red corpuscles move rapidly through the centre of the tube.

         * Transactions of  the Provincial Medical Association,  1842 and 1843. 
132
ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.
The Colourless corpuscles, indeed, often  show a disposition to adhere to the
walls of the vessels; which is  manifestly increased on the application of an
irritant.  Hence the idea naturally arises, that (to use the words of Mr. Whar-
                                    ton Jones) "there is some reciprocal re-
                                    lation between the colourless corpuscles,
                                    and the parts outside the vessels, in the
                                    process of nutrition."  What that rela-
                                    tion is, we shall now proceed to inquire.
                                       153. In regard to the purpose of the
                                    Colourless corpuscles in the Animal eco-
                                    nomy, a view has been brought forward
                                    by the Author,* which increased consi-
                                    deration has only served  to strengthen;
                                    and which he advances here, with some
                                    degree of confidence that it will be found,
                                    on attentive examination,  warranted by
                                    a  large number of physiological analo-
                                    gies, though not capable of being direct-
                                    ly proved.  That it may be rightly un-
                                    derstood, a  general sketch  of  certain
                                    known operations of cells  in Plants and
                                    Animals will be first  given.—It is not
                                    difficult, on taking a comprehensive  sur-
                                    vey of the  Assimilating  processes, to
                                    find a number of examples, in which
                                    cells are developed in a temporary man-
                                    ner ;  growing, arriving at  maturity, and
then  disappearing,  apparently  without  having  performed  any particular
function.  In the albumen of the Seed, for instance, this  often takes place to
a remarkable extent.  In the Yolk of  the Egg, there  is  a  similar transitory
development of cells, of which several generations succeed each other, without
any permanent structure being  the result; and we have seen that, according
to Dr. Barry,t a process of  the same nature takes  place within the germinal
vesicle, and  in the primary embryonic  cells and their descendants  (§ 130).
It can scarcely be  imagined by the well-judging Physiologist, that  all  this
cell-life  comes into existence without  some decided purpose;  and if  we can
assign to it an object, the fulfilment of which is consistent with  the facts sup-
plied  by analogy elsewhere, this may be reasonably considered as  having a
fair claim to  be received as a physiological induction.—In all these instances,
and in many more which might be  quoted, the  crude alimentary materials are
being prepared to undergo conversion into permanent and regularly-organized
structures.   We have seen that the very first union of the inorganic elements,
into the  simplest proximate  principles, is effected  by the cell-life of  Plants.
The change of these principles into the peculiar compounds, which form the
characteristic  secretions  of Plants, is  another  result of their cell-life.  And
there  seems equal  ground for the belief that the change of these  proximate
principles into the  peculiar glutinous sap, which is found wherever a forma-
tion of* new tissue is taking  place, is  equally dependent upon the agency of
cells.   Thus, the starchy fluid,  which is contained in the  ovule  previously to
its fecundation, is probably not in  the state in which it  can be immediately
rendered subservient to the nutrition of the embryo;  and the development of
successive generations of cells, which exert upon it their vitalizing influence,

        * Report on Cells, in British and Foreign Medical Review, Jan. 1843.
        | Embryological Researches.  Third Series.
Fig. 30.
  A small venous trunk, a, from the Web of
the Frog's foot, magnified 350 Diam ;  b, b, cells
of the pavement-epithelium, containing nuclei.
In the space between the current of oval blood-
corpuscles, and the walls of the vessel, the rouud
transparent white corpuscles are seen. 
COLOURLESS CORPUSCLES OF BLOOD.
133
may be reasonably regarded  as the means, by which the  requisite change  is
effected.   Exactly the same maybe said of the Albuminous matter contained
in the Yolk of the Egg, which is certainly not in a condition in which it can
be immediately applied to the purposes of nutrition;  and its conversion may
be  regarded as commencing with the development of transitory cells within
its own substance, and as being  completed by means of the cells forming the
inner layer of the germinal membrane, by Avhich it is  subsequently taken up
and introduced into the  current of blood  flowing  through the vascular area
(i§ 149).   A similar purpose is probably answered by the transitory cells de-
veloped within the germinal vesicle;  and by those which appear at a similar
period, in the evolution of  the descendants of the " twin  cells" produced  in
it.—Many similar examples have been elsewhere adduced.

  a. There are probably cases, however, in which cells  are very rapidly called into exist-
ence, without that preparatory elaboration of their nutrient materials, which we regard as
due to the vital operations of a preceding generation.  Thus the Bovista giganteum, a large
fungus of the Puff-ball tribe, has been known to increase, in a single night, from a mere point
to the size of a huge gourd, estimated to contain 47,000,000,000 cellules. In such a case it
is difficult to suppose that any but the most rapid mode of generating cells can have been in
operation;  and the idea that these  could not have been developed by any such elaborate
prpcess as that just alluded to, is borne out by the fact of their extremely transitory charac-
ter,—the decay of such a structure being almost as rapid as its production.  The same may be
remarked of those fungous growths in the Animal body, which sprout  forth most rapidly.
Hence the apparent exception assists in proving the rule.

   154. We have  thus a class of facts, which indicates that the conversion  of
the Chemical compound into the organizable principle—the  aplastic into the
plastic material—is  effected, in the  particular  situations where  it is most
wanted, by the vital agency of transitory cell-life; that is, by the  production
of cells, which are not  themselves  destined to form  an integral part of any
permanent structure, but which, after  attaining a certain maturity, reproduce
themselves and disappear: successive generations thus following one another,
until  the object is  accomplished, after which they altogether vanish.   We
shall  now consider another class of facts, which seem to indicate that a change
of this kind is being continually effected  in the nutritious fluids of Animals,
during their circulation through the body: by Cells, which are either carried
about with them,  or which are developed for the purpose in  particular situa-
tions, as in Plants.   The former is the more common occurrence; since the
conditions of Animal life, usually involving a general movement of the body,
require also a constant general reparation of its parts, and therefore an adapt-
ation of the circulating fluid to the wants of the whole fabric.
   155.  It  is not in the Blood alone, that floating cells are met with; for Cells,
which seem identical with  the Colourless  corpuscles of the blood, are  found
in the  Chyle and  Lymph—fluids in  which,  as  in the  Blood, the  elaboration
of plastic Fibrine  from unorganizable Albumen is continually taking place,  to
make up for the constant withdrawal  of the former substance by the nutrient
processes.  Hence there would  seem  reason for attributing this  important
function to these floating cells; the number  of which present  in the fluids,
seems to bear a very close relation with the energy of the elaborating process.
It is  a fact of great physiological interest  and importance, that, whilst the
colourless corpuscles are to be met with in the nutritious fluids of all Animals
which possess a distinct circulation, the red corpuscles are nearly restricted  to
the blood of Vertebrata.   This  observation, which  was first put  forth  by
Wagner,* has been confirmed by the  Author, who had been previously struck
with  the  very  close analogy  between  the  floating  cells carried  along in the

                * [Elements of Physiology, translated by R. Willis.]
     12 
134         ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.
current of the circulation in some of the very transparent aquatic larva? (espe-
cially those of the Culicidre),  and the lymph-corpuscles of the Frog.  Now
it is evident from this fact, that, as  the Blood of Vertebrata  is distinguished
from their  Chyle chiefly by the presence of red corpuscles in the former, and
by the absence of those  bodies  in the latter, the nutritious fluid of Inverte-
brated animals is rather analogous (as Wagner has remarked) to the Chyle
and  Lymph, than to the  Blood of Vertebrata.  Or, to put the same idea in
another form, the presence of  the  colourless corpuscles in the nutritious fluid
appears to  be the most general fact  in regard to its character throughout the
whole Animal scale; whilst the  presence of  red corpuscles  in  that  fluid is
limited to   the Vertebrated classes  and the higher Invertebrata.   Hence it
would not  be wrong  to infer, that the function of the colourless  corpuscles
must be of  a general character, and intimately connected with the nutritious
properties of the circulating fluid; whilst  the  function of the red corpuscles
must be of  a limited character, being only required in one portion  of  the ani-
mal kingdom.
   156.  Further, it has been noticed  by Mr. Gulliver,  that in the very young
embryo of the Mammalia, the white globules  are nearly as numerous as the
red particles: this, Mr. Gulliver has frequently observed in foetal deer of about
li inch long.  In a  still  smaller fcetus, the blood was pale, from  the  prepon-
derance of the white corpuscles.   It  is, therefore, a fact of much interest,
that, even in the Mammiferous embryo, at the  period when  growth  is most
rapid, the  circulating fluid has a  strong analogy  to that of the  Invertebrata.
It then, too, bears in other respects the most striking analogy to Chyle; since
it consists  of the fluid elaborated from the organizable matter supplied by the
parent,  and directly introduced into  the current of the circulation.  The func-
tion of  the placental vessels may be regarded as double: for they are at the
same time  the channel, through which the alimentary materials supplied by
the parent,  are introduced  into the circulating system of the  fcetus;  and the
medium of aerating  the fluid,  which has  traversed the foetal system.   Hence
the placenta may be regarded as at once the digestive and the respiratory
apparatus of the foetus; and the fluid  circulating through  the cord, as at  once
chyle and  blood.  It is  not  until the pulmonary and  lacteal vessels of the
embryo have commenced their independent operation, that the distinction be-
tween the  blood and the chyle of the  fcetus becomes evident;  and we should
expect, therefore, to  find  that the circulating fluid, up to the time of birth,
contains a large proportion of white corpuscles,—which is  actually the case.
There is a gradual decrease, however, in their proportional number, from the
earlier to the later stages  of embryonic life;  in accordance with the diminish-
ing energy of the formative processes.  The recent observations of Mr. New-
port  upon the Blood of Insects,* present a remarkable correspondence  with
the foregoing.  He  finds  in the  circulating  fluid of the Larva, a number of
"oat-shaped" corpuscles  or floating cells; which he  regards  as analogous to
the  Colourless corpuscles of  Vertebrata.  These are most  numerous at the
period immediately  preceding each  change of skin;  at which time the blood
is extremely coagulable, and evidently possesses the greatest formative power.
 The smallest number are met with  soon after the change of skin; when the
 nutrient matter of the blood has been exhausted in the production of new
 epidermic tissue.  In the Pupa state, the greatest number are found at about
 the third or fourth day subsequent to the  change; when preparations appear
 to be most actively going on, for  the  development of the new parts  that are
 to appear  in the perfect Insect.    After this, there is a gradual diminution; the
 plastic element  being progressively withdrawn by the  formative processes;
Philosophical Magazine, May 1845. 
COLOURLESS CORPUSCLES OF BLOOD.
135
until, in the perfect  Insect, very few  remain.   When the wings are being
expanded, however, and are still soft, a few oat-shaped corpuscles  circulate
through their vessels; but as the wings become  consolidated, these corpuscles
appear to be arrested  and to break down in the circulating passages; supply-
ing, as Mr.  N. thinks, the nutrient material for  the completion of these struc-
tures, which subsequently undergo no change.  In the perfect Insect, a differ-
ent set of corpuscles makes its appearance; which is rather analogous to the
red corpuscles of Vertebrata.   This last  fact  completely harmonizes  with the
views  already expressed; since the formative processes are now reduced  to
their lowest condition in the Insect;  whilst the respiration attains its highest
grade.
   157.  Even in adult animals, however, variations in  formative power may
be detected; which correspond with variations  in  the number of the Colour-
less corpuscles.   Thus  it has been observed by Wagner,* that the number  of
these corpuscles is always remarkably great, in the  blood of  well-fed Frogs
just caught in  the summer season; whilst it is very small in those which have
been  long kept without food, or which are examined during  the winter.  In
the reparation of injuries, too, which is effected in cold-blooded  animals by a
process of simple  growth without inflammation, it would  seem  that the Co-
lourless corpuscles  perform an important part;  as  they are observed in great
numbers, and  in a nearly stationary condition, in the vessels surrounding the
spot where the new tissue is being formed; apparently having the same action
as in the first  development of parts  altogether  new, such  as the toes of the
larva of the Water-Newt.
   158.  A remarkable confirmation of this view of  the connection between the
generation of Colourless corpuscles in  the Blood, and the production of Fi-
brine, is derived from the phenomena of Inflammation.  A decided  increase
in the normal proportion of Fibrine in the Blood (from 2| to 3| parts in 1000),
may probably be looked upon  as the essential  indication of  the existence  of
the Inflammatory condition.   That this production of Fibrine is due to a local
change, can scarcely be doubted ;  since it is frequently observed to commence,
before any constitutional symptoms manifest themselves :  and it may be re-
garded, in fact, as one cause of these symptoms.  Now the microscopic ob-
servations of Mr. Addisont and Dr. Williams,! made  independently of each
other, have established the important fact, that a great accumulation of Colour-
less corpuscles takes  place in the vessels of an inflamed part: this seems  to
be caused at first, by a  determination of those  already existing in the circu-
lating fluid,  towards the affected spot; but partly by an actual increase or
generation of these bodies, which appear  to have the power of  very rapidly
multiplying  themselves.  The accumulation of Colourless corpuscles may be
easily seen,  by applying irritants  to the web of a Frog's foot.   Mr.  Addison
has noticed  it in the Human subject, in blood drawn  by the prick of a needle
from an inflamed pimple, the base of a boil, the skin in scarlatina, &c.  And
the Author, without any knowledge of these observations, had remarked a
very obvious difference  between the  proportions of Colourless corpuscles, in
blood drawn from  a wound in  the skin  of a Frog immediately  upon the in-
cision being made, and in that drawn a few minutes after;  and had been led,
like the observers just quoted, to  refer this difference to  a determination of
Colourless corpuscles to a part irritated.   The absolute increase, sometimes
to a very considerable amount, in the quantity of Colourless corpuscles in the
blood of an inflamed  subject, has  been verified by Mr. Gulliver and several
  * [Elements of Physiology, translated by R. Willis.]
  t Medical Gazette, Dec. 1840; Jan. and March, 1841.
  j Medical Gazette, July, 1841; and Principles of Medicine, [Am. Ed., by Dr. Clymer, pp.
214, 215.] 
 136          ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.

 other observers.   These facts, therefore, afford strong  ground for the belief,
 that the production of Fibrine in the blood is closely connected  with the de-
 velopment of the Colourless corpuscles; and when we consider them in  con-
 nection with the facts  previously urged, there  scarcely appears  to be a  rea-
 sonable doubt that the elaboration of Fibrine is  a consequence of this  form of
 cell-life, and is, in fact, its express  object.
   159.  This view derives  further confirmation  from the  following  recent
 experiment of Mr. Addison's.*   " Provide six or eight  slips of glass,  such as
 are  usually employed  for  mounting  microscopical  objects;  and as many
 smaller pieces.  Having drawn blood  from a  person with  rheumatic fever,
 or any  other inflammatory disease, place a drop of  the  colourless liquor  san-
guinis,  before it fibrillates, on  each of the large  slips of glass;  cover one im-
mediately with one of the smaller slips, and the others one after another at
intervals of thirty or forty  seconds:  then, on examining them by the micro-
scope, the first will  exhibit colourless blood-corpuscles  in  various conditions,
and numerous white molecules distributed through a  more or  less copious
fibrous  network;  and  the last will  be a  tough, coherent,  and  very elastic
membrane, which cannot be broken to pieces nor resolved  into smaller frag-
ments,  however  roughly or  strongly the two pieces of  glass be made  to rub
against each other.   This is a 'glaring instance' of a compact, tough, elastic,
colourless, and fibrous  tissue, forming  from  the  colourless  elements of the
blood;  and  the  several  stages  of its  formation  may  be  actually seen  and
determined.   Numerous corpuscles  may be  observed, in  all these prepara-
tions, to have resolved themselves, or to have fallen down  into a number of
minute molecules, which are spread out over a somewhat larger area than  that
 occupied by the entire corpuscles ; and although still  retaining  a more or less
perfectly circular outline, yet  refracting the light at their edges, in a manner
very different from that in which  the  corpuscles  themselves are  seen to do.
It is from these and  various  other larger and more irregular  masses of mole-
cules or disintegrated corpuscles, that the fibrinous  filaments shoot out on all
sides, as from so many centres; or frequently the filaments  are more copious
 in two  opposite directions."
  a. A different view of the cause of the production of Fibrine, however, has been enter-
tained by some eminent Physiologists; and it does not seem right to allow the opinions of
Wagner, Henle, and Wharton Jones to pass Without notice, even though they appear to the
Author to be easily set  aside.  By  these  observers, the elaboration of Fibrine has been at-
tributed  to the red corpuscles, and has been regarded as one, at least, of their special func-
tions. Nearly all the arguments, however, which  have led us to assign this duty to the
 Colourless corpuscles, tell equally against the doctrine now under consideration.—In the first
place,the contents of the Red corpuscles  have no  resemblance  whatever to liquid Fibrine;
but are characterized by the presence of a substance altogether different: whilst, as shown
above, the Colourless corpuscles emit, on bursting, a fibrillating matter.   If, then, Fibrine be
 elaborated by the Red corpuscles, it must be by forming  part of their walls:  a method alto-
 gether unusual.—Again, the entire absence of Red corpuscles in the  blood of the lower
 Invertebrata, and in that of the larva and pupa of the Insect, the small  proportion in which
they are present in the blood of any Invertebrata, and their occurrence  to any large amount
 in the blood of Vertebrata only, seem  to show that  they  cannot be concerned in a function
 so constant and essential as the elaboration of the plastic element.   The number of the Red
 corpuscles, as stated above, bears a regular proportion to the amount of oxygen introduced
 into the  system, and thus to the heat  developed, and to the activity of the Animal functions;
 but it does not bear the same relation to the  activity of the  formative  processes, which take
 place most energetically in a state of functional quiescence.—Further, although the quantity
 of Fibrine is so remarkably increased in Inflammation, the number of Red corpuscles under-
 goes no  decided change.  Such an augmentation is  even  compatible with a Chlorotic state of
 the blood; the peculiar characteristic of which is a great diminution in the proportion of Red
 corpuscles.  By such  alterations,  the normal  proportion between the Fibrine and the.Red
 corpuscles, which may be stated  as a : b, may be  so much altered as to become, in Inflam-
               * Transactions of the Provincial Medical Association, 1843. 
EPIDERMIC CELLS.
137
Fig. 31.
mation, 4 a: b ; or, in Chlorosis, a:}b.   In Fever, the characteristic alteration in the con-
dition of the blood, appears to be an increase in the amount of Red corpuscles, with a dimi-
nution in the  quantity of Fibrine; yet if  a local inflammation should establish itself during
the course of  a fever, the proportion of fibrine will rise; and this without any change in the
amount of corpuscles.—Lastly, the effect of Loss of Blood has been shown by Andral:s in-
vestigations, to be a marked diminution in the number of Red corpuscles, with no decided
reduction in the quantity of Fibrine, even when this is much above its normal standard; and
in this condition of the blood, it has been observed by Remak that the Colourless corpuscles
are very numerous.

                 6.  Of Cells developed upon Free Surfaces.
   160. Next in independence to the cells  or corpuscles floating in the animal
fluids, are those which cover the free membranous  surfaces of the body, and
which form the Epidermis and Epithelium.   Between these two structures
there is no  essential difference, either  in  regard to their origin,  their  mode of
development, their situation,  or their  individual  history; but there is an im-
portant difference in the  purposes which they respectively serve in  the eco-
nomy.  They both consist of cells, which  are  developed from germs furnished
by the  subjacent  membrane, which are nourished  by its  vessels, and which
are after a time cast off from its free surface to  be replaced by a succeeding
generation ; but the contents of the cells vary in different situations,  and give
peculiar characters to  the tissue.  The  differences, however, are not  more
striking between the Epidermis, or cellular covering of the external surface,
and  the Epithelium, or cellular lining of the internal cavities, than  those which
exist between  the different portions of the Epithelium itself.   For  although
the Epidermis is distinguished by its comparatively
hard, dry, horny character,  whilst the Epithelium
is soft, moist, and deficient in tenacity ;  yet we shall
hereafter find that, as all  the Secretions of the  body
are  elaborated by the agency of  the  cells  of the
latter, there must be  as  many varieties of endow-
ment, in these important bodies, as there are differ-
ences in the results of their action.
   161. The Epidermis,—which  usually forms  a
thin semi-transparent  pellicle, in  close apposition
with the surface of the true Skin, but occasionally
presents a  great increase in thickness,—consists of
a series of  flattened scale-like  cells; which,  when
first formed, are spherical; but which gradually dry
up, their nucleus usually remaining visible.   These
form several  layers;  of which the deeper can be
seen very distinctly to possess the cellular character,
whilst the external  layers are  scaly;  and between
these, all  stages  of transformation may be traced.
The outer layers  are  continually being thrown  off
by desquamation ;  and new ones  are as constantly
being formed below.  They  would seem  to  origi-
nate in germs supplied by the basement-membrane,
on whose surface they make their first appearance;
and  their continued development takes  place at the
expense of nutriment, which  they draw through
that membrane, from the subjacent vessels.   The
Epidermis  is  not  itself  traversed by vessels  or
nerves; but it is  pierced by  the excretory ducts of
the  sebaceous and  sweat glands,  and  also by the
shafts of  the hairs ; being,  however,  at  the  same
                                    12*
 Vertical section of Epidermis,
from palm of the hand;  a, outer
portion,  composed of flattened
scales; b, inner portion, consist-
ing of nucleated cells ;  c, tortu-
ous perspiratory tube, cut across
by the section higher up. Mag-
nified 155 diameters. 
138         ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.
time continuous with the epithelial  linings of these.  The soft layer which
lies in immediate  contact with the true  skin, was formerly supposed to be a
substance of distinct nature, and was described under the name of rete muco-
sum; it  has been proved by microscopic examination, however, to consist of
the same elements with the ordinary epidermis, in an early stage of their
development;  and, so far from being the exclusive  seat of the colour of the
skin, as was formerly supposed, it  only participates with the fully-formed
epidermis in the possession of pigment-cells (§ 163).  The thickness of the
Epidermis, and consequently the number of layers  of which it is composed,
vary greatly in different parts; being usually found to be greatest, where there
is most pressure or friction,—as on the palms of the hands of the labouring
man, and on the soles of the feet, particularly at the heel, and the ball of the
great toe.  It would  seem as if the irritation of the true  skin produced an
augmented determination of blood to the part, and consequently an increased
development of epidermic cells.  The Epidermis covers the whole exterior of
the body, not excepting the Cornea  and  the Conjunctival  membrane;  on the
latter, however, it has more the character of an Epithelium.  This continuity
is well seen in the cast skin  or slough of the Snake; in which the covering
of the front of  the eye is found to be as perfectly exuviated as  that of any part
of the body.
  162. The Epidermis appears solely destined for the protection of the true
Skin, from  the mechanical injury and the pain occasioned by the slightest
abrasion, and from the  irritating influence  of exposure to air and of changes
of temperature.  We perceive the value  of this  protection, when the Epider-
mis has been accidentally removed.   It  is very speedily replaced, however;
the increased determination of blood to the Skin, which is the consequence of
the irritation, being favourable to the rapid  production of Epidermic cells from
its surface.  The peculiar character of the tissue appears to depend upon the
property possessed by its cells, of secreting horny matter into their cavity ;
and this  process seems to take place at a period subsequent to the first forma-
tion of the cells.  For if a thin vertical section of  the Epidermis be  treated
with Acetic acid, or with a strong solution of Potass, it is found that the inner
newly-formed  layers are dissolved by the re-agent, whilst the outer or scaly
ones are  unaffected.  Recent analysis has shown, that the dense Epidermis
from the sole of the foot, and the compact Horny matter of which Nails,
Hoofs, Horns, Hair,  and Wool, are  composed,  have the  same composition;
the formula of all of them  being 48 Carbon, 39 Hydrogen, 7 Nitrogen, and
17 Oxygen.   It is probable that, here as elsewhere, if we could isolate the
ivall of the cell from its contents, we should find the  former to consist of a
proteine-compound.
   163. Mingled with the Epidermic cells, we find  others which  secrete Co-
louring-matter instead of Horn ; these  are termed Pigment-cells.  They are
not readily distinguishable  in the  Epidermis of  the fair  races of mankind,
except in certain parts, such as the areola  around the nipple, and in freckles,
nsevi, &c.  But they are very obvious, on account of their dark  hue, in the
newer layers of the Epidermis of the Negro  and other coloured races; and,
like true Epidermic cells, they dry up and become flattened scales in passing
towards the surface, thus constantly remaining dispersed through its substance,
and giving it a dark tint when it is separated and held up to the light.   In all
races of  men,  however, we find the most remarkable development of Pigment-
cells on  the inner  surface of  the Choroid  coat of the eye: where they form
several layers, known  as the  Pigmentum nigrum.  When examined sepa-
rately, these are found to have a polygonal form, and to have a distinct nucleus
in their interior.   The black colour is given by the accumulation, within the
cell, of a number of flat, rounded or oval  granules, measuring about l-20,000th 
                             PIGMENT-CELLS.                          139

of an inch in diameter, and a quarter as  much in thickness ; these, when
separately viewed, are observed to be transparent, not black and opaque ; and

                [Fig. 32.                                  Fig. 33.
 a. Choroid Epithelium, with the cells filled with               Cells from Pigmentum Ni-
pigment, except at a, where the nuclei are visi-              grum;  a, pigmentary  °ra-
ble. The irregularity of the pigment-cells is seen.              nules  concealing  the  nu-
b. Grains of pigment.                                 cleus; 6, the nucleus distinct.
 b. Pigment-cells from the substance of the Clio-              Magnified 410 diameters.
roid.  A detached nucleus  is  seen. Magnified
320 diameters.]
they exhibit an active movement when set free from the cell, and even whilst
inclosed within it.—The Pigment-cells  are not always of a simple rounded or
polygonal form;  they sometimes present remarkable  stellate prolongations,
such as those seen in the skin of the  Frog (Fig. 88); and occasionally, the
cells being more nearly approximated to each other, these prolongations  com-
municate, so as to form a kind of network.—The Chemical nature of the Black
pigment has not yet been distinctly ascertained ; it has been shown, however,
to have a very close relation with that of the Cuttle-fish ink, or Sepia, which
derives its colour from  the pigment-cells of the ink-bag;  and to include a
larger  proportion of carbon than most  other organic substances,—every 100
parts containing 58^ of that element.
   164. It cannot be doubted that  the  development  of the Pigment-cells of
the skin is very much influenced by exposure to light; and  in  this respect
there   is a remarkable  correspondence between Animals  and Plants,—the
coloration of the  latter, as  is  well  known,  being entirely due to  that agent.
Thus,  it is a matter of familiar  experience, that  the  influence of light  upon
the skin of many individuals, causes it to become spotted with brown freckles ;
these freckles  being  aggregations of brown pigment-cells, which  either  owe
their development to the stimulus of  light, or  are  enabled by its agency to
perform a decided chemical transformation, which  they could not otherwise
effect.   In like manner, the  swarthy hue, which many Europeans acquire
beneath exposure to the sun in tropical climates, is due to a development of
dark pigment-cells, and to this we usually find the greatest disposition in in-
dividuals or races, that are  already of  a somewhat  dark complexion.   The
deep blackness of the Negro skin seems dependent upon nothing  else than  a
similar cause, operating  through  successive generations (§ 80).   It is  well
known that the new-born infants of the negro and other dark races, do not ex-
hibit nearly the same depth of colour in their skins, as that which they present
after the lapse of a few  days, when light  has had time to exert its influence
upon their surface ;  and further, that  in those individuals who  keep them-
selves  during life most secluded from  its  influence, we observe the lightest
hue of the epidermis.   Thus among the intertropical nations, the families of
Chiefs, which are not exposed to the sun in the  same  degree with the  com- 
140         ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.
mon people, almost always present a lighter hue ; and in some of the islands
of the Polynesian Archipelago, bordering on the Equator, they are not darker
than the inhabitants of Southern Europe.—An occasional development of dark
pigment-cells takes place during pregnancy, in some females of the fair races;
thus it is very common to meet with an extremely dark and  broad areola
round the nipple  of  pregnant  women ; and  sometimes large  patches  of  the
cutaneous surface, on the  lower part of the body especially, become almost
as dark as the skin of a Negro.—On the other hand, individuals are occasion-
ally seen with an entire deficiency of pigment-cells, or at least of their proper
secretion; and this not merely in the skin, but in the  eye;  such are termed
Albinoes ; and they are met with alike among the fair, and  among the dark
races.  The absence of colour usually shows  itself also in  the  hair ;  whieh
is almost white.
   165. The Nails, like Hopf, Horn, &c, may be regarded as nothing more
than an altered form of Epidermis.   When their newest and softest portions
are examined, they  are found to  consist of nucleated particles,  resembling
those of the  newer  layers of Epidermis ; in  the more  superficial laminae,
however, no distinct structure can be made out;  but,  when treated with acetic
acid, some traces of  nuclei may be detected in them.  The Nail is produced
from the surface of the true skin that lies beneath it, which is folded into a
                             groove at its root; this surface is highly vascular.
          [Fig. 34.            The increase in length is effected by successive
                             additions at the  root, causing the whole nail to
                             shift onwards ;  but as it moves, it  receives  ad-
                             ditional layers from the subjacent  skin, which
                             increases its thickness.  The nail is continuous
                             with the true Epidermis at every part, except
                             its free projecting edge; and  in the fcetus,  the
                             continuity is maintained there also.
                               166. The Hair,  as originally consisting of
                             Epidermic cells,  may be  properly  described
                             here ; although, when  fully formed, it departs
                             widely (in Man at least) from the cellular type.
  Section of the  skin  on the end of   It has been imagined  until recently, that  the
the finger:—The cuticle, andnaii,n,   Hair,  in common with the other Epidermic  tis-
detachedfromthecutisandmatnx.m.]   Sues, is a mere product of secretion ; its mate-
                             rial, which is  chiefly horny matter of the same
composition with that  of the Epidermis and its  appendages, being elaborated
from the  surface of the pulp at its base.   It is not known, however, to con-
tain a distinctly organized structure; and to be formed by the conversion of
a cellular mass at its root.  The  Hair originates within  a  follicle, which is
formed by a little depression of  the  Skin, and which is lined by a continua-
tion of the Epidermis.  From the  bottom  of this follicle, there  rises up a
cluster of cells, which may be regarded as an  increased development of Epi-
dermic cells ;  the exterior of this cluster, which is the  densest part, is known
as the bulb ; whilst the softer  interior is termed  the pulp.  The follicle itself
is extremely vascular ; and even the bulb is  reddened by minute injection,
though no distinct vessels can  be traced into it.—Although the Hairs of differ-
ent animals vary considerably  in the appearances they present, we may gene-
rally distinguish in them  two elementary parts ;—a cortical or investing sub-
stance, of a fibrous horny texture ;  and a medullary or  pith-like substance,
occupying the interior.  The fullest  development of  both substances is  to be
found in the spiny Hairs of the  Hedgehog, and  in the quills of the Porcu-
pine; which are  but  hairs  on  a  magnified scale.  The cortical  substance
forms a dense horny tube, to which the firmness of the structure seems chiefly
 
STRUCTURE  OF HAIR.
141
due;  whilst the medullary substance is composed of an aggregation  of very
large  cells, which seem  not  to  possess any fluid contents in the part of the
hair which  is  completely formed.  The  structure of the feather of Birds  is
precisely analogous ; the cortical horny tube existing alone in the quill; but
being filled with  a cellular medulla in the stem  of the feather  itself.   In the
hair of the Mouse and other small Rodents, we see the horny tube crossed
at intervals by partitions, which  are sometimes complete, sometimes only par-
tial ;  these are  the walls of the single  or  double line  of cells, of which the
medullary substance is made up.  In  the  Sable,  we sometimes meet with
hairs, in which the medulla is made up of rounded cells;  whilst the cortical
substance  is composed of imbricated Epidermic scales (Fig. 35, b).  In some
instances,  however, there  is scarcely any medulla  to  be traced;  whilst in
other animals, as the Musk-deer (Fig. 35, a), the entire hair seems to be made
up of it.
Fig. 35.
  A, hair of Musk-Deer
consisting almost entirely
of polygonal cells; b, hair
of Sable, showing  large
rounded cells in its  inte-
rior, covered by imbrica-
ted  scales, or  flattened
cells.
[Fig. 36.
  Bulb of a small black hair, from the scrotum, seen
in section, a. Basement membrane of the follicle. 6.
Layer of epidermic cells resting upon it, and becoming
more scaly as they approach c, a layer of imbricated
cells, forming the outer lamina, or cortex, of the hair.
These imbricated cells are seen more flattened and
compressed, the higher they are traced on the bulb.
Within the cortex is the proper substance of the hair,
consisting at the base, where it rests on the base-
ment membrane, of small angular cells scarcely larger
than  their nuclei.  At rf, these cells are more bulky,
and the bulb  consequently thicker; there is also pig-
ment developed in many of them more or less abun-
dantly.  Above d, they assume a decidedly fibrous cha-
racter, and become condensed,  e. A mass of cells in
the axis of the hair, much loaded with pigment]
   167. In the Human hair, the representation of the cortical sheath of the hair
of other animals is found in a thin transparent horny film ; which is composed
of flattened  cells or scales, arranged in an  imbricated manner, their  edges
(Fig. 36) forming delicate lines upon the surface of the hair, which are some-
times  transverse, sometimes oblique, and sometimes  apparently spiral (Fig.
37, a).  Within this, we find a cylinder of  fibrous texture ; which forms the 
142          ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.

principal part of  the  shaft of the hair ; whilst the centre is frequently more
distinctly cellular.   The  constituent fibres of the  shaft are  marked out  by
delicate longitudinal  stripe, which may be traced  in vertical  sections of the
hair (Fig. 37, b.) ;  but they may be still more completely demonstrated  by
crushing the hair, sfter it has been  macerated  for  some time in dilute  acid.
In dark hairs, pigmentary granules are frequently scattered between the fibres;
but they are usually found in greater abundance  in the central cells.   The
Hair of Man is commonly reputed  to  be tubular; but this is seldom if ever
the case, as  is shown  by microscopical examination of thin transverse sec-
tions (Fig. 37, c).   The  mistake has  arisen from  a misinterpretation of the
appearance  of  a dark band in the interior of  the hair, when viewed by trans-
mitted light; which  is really due, partly to the presence of pigmentary mat-
ter in the central portion  of the shaft,  and partly to the refraction of light  by
the cylindrical surface.—The chemical composition of Hair, as already stated,

                                   Fig. 37.
  Structure of Human Hair; a, external surface of the shaft, showing the transverse striae and jagged
boundary, caused by the imbrications of the scaly cortex ; b, longitudinal section of the shaft, showing
the fibrous character of the medullary substance, and the arrangement of the pigmentary matter; c,
transverse sections, showing the distinction between the cortical and medullary substance, and the cen-
tral collection of pigmentary matter, sometimes found in the latter.  Magnified 310 diameters.

is precisely the same with that of the horny Epidermis (§ 162).   Its colour-
ing matter seems related  to  Haematine; it is  bleached by Chlorine; and its
hue appears to be dependent in part upon the presence  of iron, which is found
in larger proportion in  dark than in light hair.
   168. The real nature of the different elements of the  Hair is ascertained,
by  examining them at its base, where  they become continuous with those of
the bulb.  It is then seen, that the fibres of the shaft are identical with the
cells of  the bulb; these undergoing elongation, as they are pushed upwards
towards the mouth of the follicle, by the development of additional  cells be-
neath ; and being proportionably diminished in diameter.   Hence  the shaft of
the hair is considerably narrower than the bulb.   The central part of the hair
which more distinctly exhibits the cellular character, is derived from  the pulp
or internal portion  of the bulb ;  whose constituent cells undergo less change.
And the imbricated layer of cells, that forms its  fibrous envelope, may be said
to be a prolongation of the ordinary Epidermis over the  surface of the hair;
being  developed from the external portion of  the bulb, where it is continuous
with the epidermic lining of the  follicle.—Thus we see that the whole tissue
of  the Hair is  derived  from Epidermic cells, developed in peculiar abundance
from the base of the follicle; some  of these cells, however, retaining their
original  form ;  whilst others are transformed into  fibres, and others converted
(like those  of ordinary Epidermis) into  flattened cells.   They all have the
power, however, of drawing horny matter  into their cavities; and resist the 
STRUCTURE OF HAIR.--EPITHELIUM.
143
solvent power of chemical re-agents, except when these are employed in un-
usual strength.-The Hair is constantly undergoing elongation; by the addi-
tion of  new substance at its base; and the part which has been  once fully
formed, and which has emerged  from the  follicle, usually undergoes no sub-
sequent alteration.   There is evidence, however, that  it may be affected by
changes at its base, the effect of which is propagated along its whole extent ■
thus, it is well known that cases  are not unfrequent, in which, under  the in-
fluence of strong mental  emotion, the whole of the hair has  been turned to
gray or even  to  a silvery white, in  the  course of a single night; a change
which can scarcely be accounted  for in any other way than  by supposing  that
a fluid, capable of chemically affecting the colour, is secreted  at the base of
the hair, and transmitted  by imbibition through the medullary substance to
the opposite extremity.   Another evidence of  their retention of a degree of
vitality, is found  in  the  fact of Hairs  having a tendency to become pointed
after having been cut short off.   In  the hairs  of some animals (particularly
the whiskers of the  Seal and other Carnivora)  the base is  hollow, and con-
tains a true papilla, or elevation of the  cutis, furnished with nerves and blood-
vessels ; this is separated by a layer of basement-membrane from the proper
tissue of the Hair.   In such  cases, there is bleeding from the  stumps of  the
hairs, when they  are shaved off close to  the skin.  There  is an approach to
this  papillary structure in Man;  and it may perhaps be an abnormal develop-
ment of it, which occasions the hair to bleed in the disease termed Plica  Po-
lomca.   The hair of individuals  affected with  it  is further  disposed to split
into  fibres, often  at a  considerable distance from  the  roots, and to exude  a
glutinous  substance; these two causes  unite in occasioning that peculiar mat-
ting of the hair, which has given origin to  the name of the  disease.
   169.  The layer of cells covering the internal free  surfaces of the body, is
known  under the name of Epithelium.  In some instances it appears to serve
to the subjacent membranes, like  the Epidermis to the Cutis, merely as a pro-
tection; whilst in other cases, as  we shall presently find, it answers purposes
of far greater importance.  It has long been known that the epidermic layer
might be traced continuously from the  lips to the  mucous  membrane of  the
mouth,  and thence down  the oesophagus into the stomach; and that, in  the
strong muscular stomach or gizzard of the granivorous birds, it becomes quite
a firm horny lining.   But it  has  been only since  the application of the Mi-
croscope to this investigation, that a continuous  layer of cells has been traced,
not merely along  the whole surface of the  mucous membrane lining the  ali-
mentary canal, but likewise along the free surfaces of all other Mucous Mem-
branes, with their prolongations into  follicles and glands; as well  as on  the
Serous and Synovial membranes,  and the lining membrane of the heart, blood-
vessels, and absorbents.
   170.  The forms presented by the Epithelium cells are various.  The two
chief, however, are the tesselated, forming the pavement-epithelium; and  the
cylindrical, forming  the   cylinder-epithelium.—The Tesselated Epithelium
covers the serous  and synovial membranes,  the lining membrane of  the blood-
vessels, and the ultimate follicles or tubuli  of most glandular structures con-
nected with the skin  or mucous membranes, as  also the mucous membranes
themselves, where the cylinder-epithelium does not exist.  The cells compos-
ing it are  usually flattened and polygonal (Fig. 38, a.) so as to come into con-
tact with each other at their  edges, like the pieces of a tesselated  pavement
(Fig. 30) ; but they sometimes retain their rounded or oval  form, and are  se-
parated from each other by considerable interstices. (Fig. 38, b.)   This last
form seems to be  the commonest,  where the cells are  most actively renewed,
so that  they have  not time (so to speak) to be developed into a continuous
stratum.   The number of layers is commonly small; and sometimes there is 
144          ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.
only a single  one.—The Cylinder-Epithelium is very differently constituted.
Its component cells are cylinders, which are arranged side by side;  one extre-
Fig. 38.
 Separated Epithelium cells, a, with
nuclei, b, and nucleoli, c, from mucous
membrane of mouth.

  Pavement-Epithelium of
the Mucous Membrane of the
smaller bronchial tubes; a,
nuclei with double nucleoli.
mity of each cylinder resting upon  the basement-membrane, whilst the other
forms part of the free surface.  The perfect  cylindrical form is only shown,
however,  when the surface on which the cylinders rest is  flat or  nearly so.
When it is convex, the lower ends or basements of the cells are of much smaller
diameter than the upper or free extremities; and thus each  has the form of a
truncated  cone, rather than of a cylinder; as is well seen on the cells covering
the villi of the intestinal canal.  (Fig. 45.)   On the other hand, where the cy-
linder-epithelium lies upon a concave surface, the  free extremities of the cells
may be smaller than those which are  attached.  Sometimes each cylinder is
formed  from more than  one  cell, as is  shown by its containing two or more
nuclei;  although its cavity seems  to be  continuous from end  to end.   And
occasionally tbe cylinders arise by stalk-like prolongations,  from  a  pavement-
epithelium beneath.   The two forms of Epithelium pass into one another at
various points;  and various transition-forms are  then  seen,—the   tesselated
scales appearing to rise  more and more from the surface, until they project as
long-stalked cells, truncated  cones,  or cylinders.  The  Cylinder-Epithelium
covers the mucous membrane of the alimentary  canal, from  the cardiac orifice
downwards ; it is found also in the  larger ducts  of the glands Avhich open into
it, or upon the external  surface—such as the  ductus choledochus, the salivary
ducts, those, of the prostate and Cowper's glands, the vas deferens, and urethra.
In all these situations, it comes into connection with the Tesselated Epithe-
lium, which usually lines the  more delicate  canals of  the glands,  as well as
their terminal follicles.
   171.  Both these principal forms of Epithelial cells are frequently observed
to be fringed at their  free margins with  delicate filaments, which are termed
Cilio; [from cilium, an eyelash,] and these, although of extreme minuteness,
are organs of great importance in the animal  economy,  through the  extraordi-
nary motor power'with  which they are  endowed.  The form of the Ciliary
                                filaments is usually a  little flattened, and ta-
                                 pering gradually from the base  to the point.
                                 Their size is extremely variable;  the largest
                                that have been observed being about l-500th
                                 of an inch in length,  and  the smallest about
                                 l-13,000th.   When   in  motion,   each  fila-
                                 ment appears  to bend  from its root to its
                                 point, returning  again to  its original  state,
                                 like the stalks of corn when depressed by
                                 the wind;  and when  a number are affected
                                 in succession  with this motion, the appear-
                                 ance of  progressive  waves  following one
Fig. 39.
 Vibratile or ciliated Epithelium ;  a, nu-
cleated cells, resting on their smaller ex-
tremities ; 6, cilia. 
EPITHELIUM ;  CILIARY MOVEMENT.
145
another  is  produced, as when  a corn-field is agitated  by frequent gusts.
When the Ciliary motion is taking place  in full  activity, however, nothing
whatever can be distinguished, but the whirl of particles  in  the  surrounding
fluid;  and it is  only when the rate of movement slackens, that the shape
and size of the  Cilia, and the  manner in which their stroke is made, can  be
clearly seen.  The motion of  the Cilia is not only quite  independent (in  all
the higher animals  at least) of the will of the animal, but is also  independent
even  of the life of the rest of the body; being seen  after  the death of the
animal;  and  proceeding  with  perfect regularity in parts  separated  from the
body.   The isolated epithelium  cells have been seen  to swim about actively
in water, by the agency of their cilia, for  some hours after they have been de-
tached from the mucous surface of the nose;  and the  Ciliary movement has
been seen fifteen days after death in the body of a Tortoise, in which putre-
faction was far advanced.  In the gills of the River-Mussel, which are among
the best objects  for the study of it, the  movement endures  with similar per-
tinacity.
   172. The purpose of this  Ciliary movement is obviously to propel fluids
over the surface on which it takes place; and  it  is consequently limited in
the higher animals  to the  internal surfaces of the body, and always takes
place in  the  direction of the outlets, towards which it aids  in propelling the
various products of secretion.  The case is different, however, among animals
of the  lower classes, especially those inhabiting  the water.   Thus the external
surface of the gills of Fishes, Tadpoles, &c, is furnished with cilia; the con-
tinual  movement of which renews  the water in contact with them, and thus
promotes the aeration of the blood.   In the lower Mollusca, and  in  many
Zoophytes, which pass their lives rooted to one spot, the  motion of the Cilia
serves not merely to produce currents for  respiration, but  likewise to draw
into the  mouth the  minute particles that  serve as food.   [Fig. 107, 2, 5.]
And in the free-moving Animalcules,
of various  kinds, the Cilia are  the
sole instruments which they possess,
not merely for producing those cur-
rents in  the water, which may bring
them the requisite supply of air  and
food, but  also  for  propelling their
own bodies through  the liquid  ele-
ment.   This  is  the  case, too, with
many  larger animals  of the class
Acalepha  (Jelly fish), which  move
through  the water, sometimes with
great  activity, by the combined  ac-
tion of the vast numbers of cilia, that
clothe  the  margins of their external
surfaces.   In these  latter cases, it
would seem as if the  Ciliary move-
ment were more under  the  control
of the  will of the animal, than where
it  is concerned  only  in  the organic
functions.   In what  way the will
can influence it, however, it does
not seem  easy  to say;  since the
ciliated epithelium-cells appear to be perfectly disconnected from the surface
on which they  lie, and cannot, therefore, receive  any direct influence from
their nerves.  Of the cause of the movement of the Cilia themselves, no ac-
count can be given; they are usually far too small to contain even  the minutest
     13
  Examples of Cilia; 1, portion of a bar of the gill of
the sea-mussel, Mytilus edulis, showing cilia at rest
and in motion; 2, ciliated epithelium particles from the
frog's mouth; 3, ciliated epithelium particles from in-
ner surface of human membrana tympani; 4, ditto,
ditto, from the human bronchial mucous membrane •
5, Leucophrys patula, a polygastric infusory animal-
cule; to show its surface covered with cilia, and the
mouth surrounded by them] 
146          ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.
fibrillae, of muscle; and we must regard them as  being, like those fibrillae,
organs sui generis, having their own peculiar endowment,—which is, in  the
higher animals at least, that of continuing  in ceaseless vibration, during  the
whole term of the life of the cells to which they are attached.

  [That this movement is  truly molecular and independent of muscular influence and of
both the Vascular and nervous systems has been proved by experiment.  For, besides continu-
ing to manifest itself in a single particle for  many hours  after  it has  been  isolated  from
the rest of the system, a ciliated surface continues unaffected in  its movements though the
supply of blood to the subjacent  tissues be  completely cut off.  Neither  do hydrocyanic
acid,  opium, strychnine, belladonna, substances which affect powerfully the nervous  sys-
tem, exert any influence on ciliary motion;  this phenomenon continuing  in the bodies of
animals killed by these poisons.  And lastly, shocks of electricity passed through the ciliated
parts, even the removal of the brain and spinal marrow in frogs, extinguishing as it does
muscular motion, do not destroy the action of cilia.—M. C]

   The length of time during which the Ciliary movement continues after the
general death of the body, is much less in the warm-blooded  than  in the cold-
blooded animals;  and  in this respect  it corresponds with  the degree of per-
sistence  of muscular irritability, and of other vital endowments.
   173.  A layer of Ciliated epithelium, of the Tesselated form, is  found upon
the delicate pia mater which lines  the cerebral cavities, not even excepting the
infundibulum and the aqueduct of Sylvius; and it is also found in the termi-
nal ramifications  of the bronchial tubes.  A Cylindrical epithelium furnished
with Cilia is found lining  the nasal cavities, the frontal sinuses, the maxillary
antra, the lachrymal ducts and sac, the posterior surface of the velum  pendu-
lum  palati, and fauces, the Eustachian  tube, the larynx, trachea,  and bronchi
to their finest divisions, the upper portion  of the vagina, the uterus, and  the
Fallopian  tubes.   The function of the  Cilia in all these cases appears to be
the same;  that of propelling the secretions, which would otherwise accumu-
late on these membranes, towards the exterior orifices, whence they may be
carried off.
   174. The Epithelium-cells, like the scales of the Epidermis, are continually
being cast  off and renewed from the  subjacent surface; but the  rapidity of
this renewing process varies  according to the particular function of  the part.
Thus we shall hereafter  find  it  to be  greater on  the Mucous Membranes,
which are  actively engaged in the  introduction of nutrient materials and in the
separation of effete matter, than it is on the Serous surfaces, which are com-
paratively  inert.   The  epithelial cells that  cover  the plane  surfaces, seem to
be developed from granular germs, scattered through the subjacent basement
membrane ;  but it is different in  regard to the cells of the glandular follicles,
which usually  seem to originate in a single " germinal spot," composed of a
mass of granules, at the blind extremity of the follicles.   In fact, each of these
follicles  may be regarded  as  a parent-cell, which was  closed  at an  earlier
period of its existence, and which, even after it has ruptured and given exit
to its  contents, goes on forming  a succession of  new generations  from its
                             nucleus.  The accompanying  figure represents
           Fig. 41.            two follicles of  the  liver of the common Crab,
                             which are seen to be filled with secreting cells;
                              and it is evident, from a comparison of the sizes
                              of the cells at different parts, that they originate
                              at the blind extremity of the follicle, where there
                              is  a germinal  spot; and that, as  they recede
                             from that point and approach the outlet of the
  Two follicles from the liver of Car-  follicle,  they  gradually increase in size and be-
tinus mcenas (Common Crab), with  come filled with their characteristic secretion ' be-
their contained secreting ceils.       ing  at the  same  time pushed  onwards towards
 
            SECRETING CELLS.--SEROUS AND SYNOVIAL MEMBRANES.        147

the outlet, by the continual new growth of cells at the germinal  spot.*—It is
by the continual growth and exuviation of the cells which line  the  glandular
follicles, that the various products of Secretion are separated from the blood;
and it is in cells occupying a similar position, that the Spermatozoa or Repro-
ductive particles are developed (Plate I., Fig. 18).  In each case, the growth
of the  cell, and the nature of its  product,  depend upon  its own  peculiar
vital properties ; and it is a  curious fact that  the seminal cells, in which the
Spermatozoa are formed, are ejected from the gland in the  Decapod Crusta-
ceous animals, not only before they have burst and set free the Spermatozoa,
but even long before the development of the Spermatozoa in their interior is
completed,—the process being perfected, after the cells have been deposited
in the generative passages of the female.t

             7.  Of the  Compound Membrano-Fibrous Tissues.

   175.  Having now considered  the  Elementary components of the Tissues
of the Human body,—namely, Membranes, Fibres, and Cells,—we proceed
to notice certain structures, in which these elements are united in their sim-
plest form ; and, in the first place, those termed Serous and Synovial Mem-
branes.   When examined with the Microscope, their free surface is  found to
be covered with a single layer of  Pavement-Epithelium, which lies  on a con-
tinuous sheet of Basement-Membrane.   Beneath  this last is a layer of con-
densed  Areolar  tissue, which constitutes the chief thickness of the membrane,
confers  upon it  its  strength and elasticity;  this gradually passes  into  that
laxer variety, by which the membrane is  attached  to the parts it lines, and
which  is  commonly known as  the  subserous  tissue.  The yellow fibrous
element enters  largely  into the composition of the membrane  itself; and its
filaments interlace into  a beautiful network, which confers upon it equal elas-
ticity in every direction.  The membrane is traversed by blood-vessels, nerves,
and lymphatics, in varying proportions.   The Serous and Synovial mem-
branes form, as is well known, closed  sacs, which  contain  a greater or less
proportion of fluid.   The liquid effused from  the Serous membranes is nearly
the same with the Serum of the blood; containing as much as 7 or 8 per cent.
of albumen and salts;  and being distinctly  alkaline,  from  the presence of
carbonate or albuminate of soda.   There is no reason for regarding it in any
other light, than as a simple product of transudation.  The fluid contained
in the Synovial capsules, and in the Bursas Mucosae, may be  considered as
serum with from 6 to 10 per cent, of additional albumen ; it shows an  alka-
line reaction.;}:   The fluid of Dropsy (at least in some forms of  this disease)
contains in addition  urea,  and  cholesterine  suspended  in  fine  plates; also
(according to Dr. Kane) stearine  and elaine.
   176.  The general  term Mucous Membrane may be applied  to that great
system of  membranous  expansions, which  forms the external  tegument, or
Skin,—the lining of the internal cavities whose walls are continuous with  it,
or Mucous Membrane proper,—and the prolongations of this into the secre-
ting organs, forming the tubes and follicles of the Glands.  These all consist,
as Mr.  Bowman has justly remarked,§  "of certain elements,  which  the
Anatomist  may detect and discriminate; some of them being essential, others
appended or superadded: and  the broad characteristic  distinctions  between

  * Goodsir, in Anatomical and Pathological Observations, Chap. v.
  f Op. Cit. p. 39.
  j This is probably a true secretion, formed by the agency of the epithelium-cells that cover
certain delicate highly-vascular  fringe-like projections, which hang down into the synovial
capsules.
  § Cyclopaedia of Anatomy and Physiology, vol. iii. p. 485. 
148         ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.
these structures, appreciable  to ordinary sense—as well as  the  innumerable
gradations by which they everywhere blend  insensibly with one another,—
are solely due to various degrees and  kinds of modification wrought in the
form, quantity, and properties  of these respective elementary parts."—The
Mucous  Membrane may be said, like  the  Serous, to  consist of three  chief
parts,—the epithelium or epidermis covering its free surface,—the subjacent
basement-membrane,—and the areolar tissue, with its  vessels,  nerves, &c,
which forms the thickness  of the membrane, and  connects it to  the  adjacent
parts.  Of the  Epithelium and Epidermis, a general description has  been
given in the preceding Section.   The Basement-Membrane  may  be fre-
quently demonstrated  with very little  trouble, in the  tubuli of the  glands,
especially the kidney;  which  are but very slightly adherent, by their exter-
nal surface, to  the  surrounding tissue.  Its existence  on the Skin,  and  on
many parts of the proper Mucous Membrane, has  not  yet been fully  proved;
but there can be no reasonable doubt of its continuity in  these  situations.—
These two elements may be  regarded as the essential constituents of  Mucous
membrane;  which  is thus found to be, strictly speaking, extra-vascular.   Its
difference from  Serous Membrane must be considered,  therefore, as  depend-
ing rather upon its arrangement, and upon the peculiar secretion of its epithe-
lium-cells, than upon any decided anatomical character.
   177.  The tissues appended to these elements, and  less essential to the
character of Mucous  Membrane, are  Capillary  Blood-vessels,  Absorbents,
Fig. 42.
Fig. 43.
		W&Mt	?%&$£$&
	mm	WmmM	lip
	m	WSm Wmt	Hill
mm		slllil?	
Distribution of Capillaries at the sur-
   face of the skin of the finger.
Distribution of Capillaries in the
    Villi of the Intestine.
Fig. 44.
Nerves, and Areolar tissue.  The  former are almost everywhere  abundant;
in the Skin they seem chiefly destined  to supply the nervous papillae, and
thus  minister to  its  acute  sensibility;  whilst in the  Mucous  Membrane
of the Alimentary canal, they seem  more concerned  in  the  functions of Ab-
sorption and Secretion; and in the Glandular organs, they supply the mate-
                            rials for the last-named process.  The Absorb-
                            ents are most abundant, as Lymphatics, in the
                            Skin; and  as Lacteals, in the Mucous  Mem-
                            brane of the first part of  the  Intestinal  canal;
                            but the Lymphatics are also largely distributed
                            through some of the Glandular  organs.  The
                            Skin is the only part of this system, which is
                            largely supplied with Nerves; except the Con-
                            junctival  Membrane,  and  the  Mucous  Mem-
                            brane of the Nose :  hence  the sensibility  of this
                            structure  is usually low, although  its import-
                            ance in the organic functions  is so great.  The
                            Areolar tissue  of Mucous  Membranes usually
makes up the greatest part of their thickness ;  and is so distinct from the sub-
jacent layers, as to be readily separable  from  them.  It differs  not, however,
Distribution of Capillaries around
 follicles of Mucous Membrane. 
                  STRUCTURE AND OFFICES OF MUCOUS MEMBRANE.            149

   in any important particular, from  the same tissue elsewhere; and the white
   and  the  yellow fibrous elements  may be detected  in  it, in  varying propor-
   tions, in different parts,—the latter being especially abundant in the  Skin  and
   the  Lungs, which  owe  to it their peculiar  elasticity.  Hence the Mucous
   Membranes for the most part yield Gelatine, on being boiled.  There is some
   reason  to  believe,  that the Skin also contains nOn-striated muscular fibres
   scattered  through it.—The regeneration of all the  forms of Mucous Mem-
   brane, after loss of substance by disease or injury, is very complete, and takes
   place with considerable rapidity.
      178. The essential character of the Mucous  Membranes, in regard alike to
   their offices and their arrangement, is  altogether different from  that of the
   Serous and  Synovial membranes.  For, whilst the  latter  form  shut sacs,
   whose contents are destined to undergo little change, the former either cover
   the  external surface of  the body, or line tubes and  cavities in its interior,
   which have free outward communications; and they  thus constitute the  me-
   dium, through  which all the changes are effected, that take place between the
   living organism and the external world.  Thus, in the gastro-intestinal mucous
   membrane, we find a provision for reducing the food, by means of  a solvent
   fluid poured out  from its follicles; whilst the villi,  or root-like filaments,
   which are closely set upon the surface of that same membrane, are specially
   adapted to absorb the nutrient materials thus reduced to the liquid state.  This
■v  same membrane, at its lower part, constitutes an outlet through which are  castv
   out,  not merely the indigestible residuum  of the food,  but also the excretions
   from numerous minute glandulae  in the intestinal wall, which result from the

                                     Fig. 45.
  Diagram of the structure of an involuted Mucous Membrane, showing the continuation of its elements
in the follicles and villi; f, f, two follicles; 6, basement membrane; c, submucous tissue; e, epithelium}
v, vascular layer; n, nerve; v, villus, covered with epithelium; v', villus whose epithelium has been shed.
decomposition of the tissues, and which must be separated and cast forth from
them to prevent further decay.  Again, the bronchio-pulmonary mucous mem-
brane serves for the introduction of oxygen from the air, and for the exhala-
tion of water and carbonic acid.  The mucous membranes prolonged into the
                                    13*
8599999999999999999 
 150          ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.

 interior of the'various glands, are the instruments by which  their respective
 products  are eliminated  from the blood.  And  lastly, the Skin is concerned
 in  two great  classes of  changes; the excretion of various matters from  its
 surface, and from  the glandulae in its  substance; and the reception of impres-
 sions upon the nerves, with which it  is so copiously supplied.
   179. The character of the secretions formed by the Mucous Membranes,
 is different in  almost every part; and is dependent, as will  be shown here-
 after, upon the properties of the  Epithelium-cells  which cover them.  These
 cells, instead of forming a comparatively permanent stratum, like  that which
 covers the surface of serous membranes, are  in a state of continual change
 and renewal;  the  older  layers falling off, whilst  new ones  are produced in
 immediate contact with the subjacent  membrane,—and this, not merely  on its
 simple plane surfaces, but on its prolongations, whether these form the cover-
 ings of villi, or the lining of follicles.  The purpose of the cells which form
 the Epidermis, is  simply to protect the sensitive surface of the true skin; and
 these cells have the power of drawing a horny matter into their interior.  On
 the other  hand, the Epithelium cells of the ultimate tubuli or vesicles of glands,
 contain the substances which characterize the secretions of those glands.   It
 is chiefly  on the bronchio-pulmonary and gastro-intestinal mucous membranes,
 that we meet with  the peculiar secretion termed Mucus; which appears to  be
 expressly formed to shield them from the irritation they would suffer through
 the  contact of  air, or of  solids or liquids.   This  secretion is  also found on
 the lining membrane of the larger excretory ducts of most of the glands; and
 it is mixed, in greater or less amount, with most of the secretions discharged
 by them.  It is found  also  upon the lining  membrane  of  the gall-bladder,
 and of the urinary bladder.  When these membranes are in a state of unusual
 irritation,  the  amount  of mucus  which they discharge  is very considerable;
 but it ordinarily forms an extremely thin layer.   The characters of Mucus,
 obtained from various sources, are by no means invariable.  In general, how-
 ever, it may be described as a fluid of peculiar viscidity, either colourless  or
 slightly yellow, transparent or nearly so, incapable of mixing with water, and
 sinking in it, except when  buoyed  up by  bubbles entangled in its  mass,
 which is  commonly the case with the bronchial and  nasal  mucus.  This
 fluid contains  from 4| to 6£ per  cent, of solid matter, of which a small part
 consists of salts resembling those of the blood:  whilst the chief organic con-
 stituent is a substance termed Mucin,  to which the characteristic properties of
the secretion  are due.  This appears  to be an albuminous compound, altered
by  the action of an alkali; for as Dr. Babington has shown, any albuminous
fluid may be made to present the peculiar viscidity of mucus, by treating it
with liquor potassae.  That the  mucin of Mucus  is held in solution by an
alkali,  appears from  this, that it  is readily precipitated by acids, which neu-
tralize the base; and that a sort of faint coagulation may be induced even by
water,  which withdraws  the base from it.   When Mucus is  examined with
the Microscope, it  is found to contain  numerous epithelium-scales (or flattened
cells); together with  round  granular corpuscles, considerably larger than
those of the blood, and closely resembling the nuclei of the epithelium-cells,
which  are commonly termed mucus-corpuscles.   In the more  opaque mucus,
 discharged from membranes in a  state of irritation or inflammation, these cor-
puscles are present in greatly-increased amount; and cells are often developed
around them.


8.  Of Simple Isolated Cells, forming Solid Tissues by their Aggregation.

   180.  We  now  proceed to a class of Cells,  which are equally independent
 of each other, which begin and end their lives as cells without undergoing any 
          PERSISTENT CELLULAR PARENCHYMA.--PLACENTAL CELLS.        151

transformation, but which form part of the substance of the fabric, instead of
lying upon its free surfaces and being continually cast off from them.   Still
their individual history is much the same as that of the cells already noticed;
and  they differ chiefly in regard to the destination of their products.   There
are many animals, in which such aggregations of cells make up a much larger
part of  the fabric, than they do in  Man ;  and this in consequence of their re-
taining  more  of  the embryonic type  of structure in their adult  condition.
Thus in  the  Myxinoid family of  Fishes, there  is no true Vertebral column ;
but its  place  is supplied  by a gelatinous tube,  termed the  chorda dorsalis ;
which consists of nucleated cellular tissue, and  which is precisely  analogous
to the structure  occupying  the same position in the  early embryo of higher
animals.  In the Short Sunfish, a corresponding form of tissue forms a thick
covering  to the body, replacing the true skin.   And  in the Lancelot (a little
Fish  which is deficient in  so many of the characters of the  Vertebrated di-
vision, that  many naturalists have doubted its right to a place in the class), a
considerable portion of the fabric is made up of a like cellular parenchyma.
   181.  The first group of this class deserving a separate notice, is that which
effects the introduction of  aliment into the body;—of those kinds of aliment,
at least, which are not received in solution by any more direct means.   These
cells  (first pointed out by Mr. J. Goodsir) form a cluster at the extremity of
each  of the villi of the intestinal tube;  the origin of  the lacteal being lost in
the midst of  it.   If examined whilst the absorbent process is going on, they
are found to  be  turgid  with a milky  fluid, which is evidently the same with
that  of  the lacteals; and to have a diameter of from l-2000th to 1-1000th of
an inch (Fig. 46, a).   In the intervals of  the digestive process, the extremities
of the villi are comparatively flaccid:  and instead of  cells, they show merely

                                  Fig. 46.
  Extremity of intestinal villus; seen at a, during absorption, and showing absorbent cells and lacteal
trunks, distended with chyle'; at b, during interval of digestion, showing peripheral network of lacteals,
with granular germs of absorbent cells, as yet undeveloped, lying between them.

a collection of granular germs (Fig. 46, b).   These begin to develope them-
selves, as soon as the food has been dissolved in the stomach and transmitted
to the intestine ; and their development goes on so long as they are surrounded
with  nutrient matter.   The cells grow, select, absorb, and prepare the  nu-
tritious  matter, by making it a part of themselves ;  and, when their work is
accomplished, they deliver it to the lacteals by their own rupture or deliques-
cence,—at the same time, it is probable, setting free the germs, from which a
new generation maybe developed, when the next supply of chyle is prepared.
   182.  Although the  mucous  membrane of the intestinal tube is the only
channel, through  which insoluble nutriment can be absorbed in the completely-
formed  Mammal, and  the only situation, therefore, in which  we meet with
these absorbent cells, there are other situations, in which similar cells perform
analogous duties  in the  embryo.  Thus, the Chick derives it nutriment, whilst
in the egg, from the substance of the yolk, by absorption  through the blood-
vessels, spread out in  the vascular layer of the germinal membrane that sur-
rounds it; which vessels  answer to the blood-vessels and lacteals of the per- 
152         ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.
Fig. 47.
manent digestive  cavity, and are  raised into folds or villi, as the contents of
the yolk-bag are  diminished.   Now  the  ends of the vessels  are  separated
from the fluid  contents of the yolk-bag by a  layer of cells, which is  filled
with matter of a  yellow-colour;  and which  seems  to have for its office, to
select and prepare the materials supplied by the yolk, for being received into
the absorbent vessels.   In like manner, the  embryo of the. Mammal is nou-
rished, up to the time of its  birth, through the medium of its  umbilical ves-
sels ; the  ramifications of which  form tufts, that dip down (as it were) into
the maternal blood, and receive from it the materials destined for the nutrition
of the fcetus;  besides effecting the aeration  of the blood of  the  latter, by
exposing  it to the more oxygenated  blood of its mother.   Now around the
capillary loop of the foetal tuft there is a layer of cells,  closely resembling the
absorbent cells of  the villi; and these are inclosed in a cap of basement-mem-
brane, which completes the foetal portion of the tuft, and renders it comparable,
in all essential respects, to the  intestinal villus.   It is again surrounded, however,
by another layer of membrane and of cells,  belonging to the  maternal sys-
tem; the derivation of which will  be explained hereafter (Chap. XVII).
  183.  The cells  which make up the  parenchyma of the Liver in the higher
animals, seem  to  be developed under conditions somewhat similar.  In the
Invertebrata, the Liver is constructed upon the type  of the glands in general;
its secreting cells being developed as an  epithelium upon the inner wall of the
hepatic  ducts.   This does not appear to  be the case, however, in Man and the
Mammalia ; the substance of  whose  liver is  made up of an  aggregation of
                  cells, which lie—so far as  can be ascertained—upon  the
                  outside of the terminal  ramifications of the  hepatic ducts.
                  That these cells are the efficient instruments in the secre-
                  ting  process, is evident from the nature of  their contents,
                  which  consist of biliary matter with  oil  globules.  Their
                  diameter is  usually from l-1500th to l-200th of an inch;
                  and they generally contain  a very distinct nucleus.  Their
                  connexion with the secreting  process is further marked by
                  the fact, that, in some instances in which the bile  has  not
                  been eliminated, and death has been the result,  Microscopic
                  examination has proved that the  hepatic  cells were either
                  very imperfectly formed or were  almost entirely deficient.
Further, in cases of Fatty Liver, the cells have been found to contain an  un-
                          usual amount of Adipose matter.
                             184. The Fat-cells, of which Adipose tissue
                          is composed, also permanently exhibit the original
                          type of structure in its simplest  form.   This  tis-
                          sue is  usually diffused over  the whole body, filling
                          up interstices, and  forming a  kind of pad  or
                          cushion for the support of moveable parts.   Even
                         .in cases  of great emaciation, some Fat is always
                         'left; especially at  the base of the heart, around
                          the origin of the large vessels; in the orbit of the
                          eye ; in the neighbourhood of the  kidney ; in the
                          interior of the bones ; and within  the  spinal ca-
                          nal, between  the  periosteum and the dura mater.
                          The Fat Cells are usually spherical or spheroidal;
  Fat vesicles, assuming the poly-  sometimes, however, when closely pressed toge-
hedrai form from pressure against  tner without the intervention of any intercellular
IS r^^d^m  -bstance, they become polyhedral.   The nucleus
the omentum; magnified about 300  ls  not always to  be distinguished;—perhaps in
diameters.]                  consequence of its having passed to the  interior of
  Secreting Cells of
Human Liver; a, nu-
cleus; 6, nucleus ; c,
oil-particles.
 
fat cells;  composition and uses of fat.              153
Fig. 49.
the cell;  it has been seen, however, in the fat-cells of the embryo.   The dia-
meter of  the greater  number of fat-cells, is  between 1-300th and  1-600th of
an inch ;  but larger and smaller sizes  are frequently to  be met with.-  These
bodies frequently present themselves in an isolated condition, dispersed among
the  meshes  of Areolar  tissue; but when they are aggregated so  as to form
masses of fat, they are first collected into little lobular clusters, each of which
has  a  delicate  membranous invest-
ment ; and these are' again united into
larger clusters, visible  to  the naked
eye.   The aggregation of these often
forms masses of considerable size;
the component parts being held toge-
ther by Areolar tissue, and also by the
blood-vessels which  penetrate them,
and  which  ramify minutely among
them,  forming a  capillary  network,
not  only upon  the  surface  of  the
smallest lobules, but even  (it would
appear) between  their contained fat-
cells.  In some forms of Adipose tis-
sue,  such  as  the marrow of bones, it
would seem  that very little  areolar tissue  exists, or that it is even entirely
absent; and.here the capillary plexus  forms the principal bond of  union be-
tween the fat-cells.  No  lymphatics have  been detected in Adipose tissue ;
and  it would seem to  be equally destitute  of nerves, excepting  such as are
passing through  it on their way to other textures ;—thus accounting for the
known fact of its being insensible, except when those trunks are injured.

                                  [Fig. 50.
Cells of Adipose Tissue ; magnified 135 diameters.
  Blood-vessels of Fat; 1, minute flattened fat-lobule, in which the vessels only are represented ; 3, the
terminal artery ; 4, the primitive vein ; 5, the fat vesicles of one border of the lobule, separately repre-
sented,—magnified 100 diameters; %plano{ the arrangement of the capillaries on the exterior of the
vesicles,—more highly magnified.]

   185. The consistency of the substance contained in the Fat-vesicles,  varies
in different animals, according to  the proportions of the organic elements, that
enter into its composition.   These  elements are  known  under the names of
Stearine, Margarine, and Oleine:  the two former,  which are solid when sepa- 
154          ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.
          [Fig. 51.            rate, being  dissolved  in the latter, at the ordinary
                             temperature of  the body.   That the thick oil thus
       /^^\        .      formed  does  not  escape  from  the fat-cells  during
  t„......-(%^|pi^|r"a      life, may be attributed  to  the  moistening of  their
       !^        J,.....2     walls by the  aqueous fluid circulating through the
      ^^^^^m|         vessels.  In all fixed oils, which are fluid at  com-
  2—%jlp^^         nion temperatures, a portion of"  the solid constitu-
      ^&rj- i             ents 0f fat  exists  ; these may be separated  by ex-
  u ,    ■ ,   ,                 posure to cold, which  congeals  them, leaving the
  Fat vesicles from an emacia-    yuwiyj ""     '             o                   o
led subject;  1,1,the ceii-mem-    Oleine fluid.   All these substances  are regarded
brane; 2,2,2, the solid portion    by chemists in  the light of salts ; being compounds
collected as  a  star-like mass>    0f acids—the Stearic, Margaric, and  Oleic—with
with  the elaine  in  connection    a  common  base, to which, from its sweetish  taste,
with it, but not filling the cell.]     ^ name Qf Q]ycerme  has been given.

  a.  Stearine is the essential constituent of nearly all  solid fats, and preponderates in propor-
tion to their consistence.  It exists largely in  mutton-suet; from this  it may be obtained by
the action of ether, which  takes up all the oily matter.  It is crystalline, like spermaceti;
it is not at all greasy between the fingers, and melts at about 130°.  It is insoluble in water,
and in cold alcohol and ether; but it dissolves in boiling alcohol or ether, crystallizing as it
cools.  Stearic acid (the substance of which the stearine candles are composed) may  be sepa-
rated, by causing it to combine with a stronger base, such as lime or potash, and then setting
it free from this by a stronger acid. It crystallizes in milk-white needles; is soluble in its
own weight of cold  alcohol, and in all proportions at  a boiling heat; and fuses at about 158°.
Its acid powers are sufficient to decompose the  alkaline carbonates.—Margarine  exists in
small quantity, along with Stearine, with most fats ;  but it is the principal solid constituent
of Human  fat, which in this respect resembles olive  oil rather than the other animal fats. It
corresponds with Stearine in many of its properties; but it is much more soluble in alcohol
and ether; and it melts at 116°.   Margaric acid closely resembles stearic acid in most of its
properties; but it is more soluble in cold alcohol; and has a lower melting-point, viz., 140°,
or thereabouts.  It  may be procured from stearic acid, by subjecting  the latter to a dry dis-
tillation.—Oleine exists in small quantity in the various solid fats; but it constitutes the great
mass of the liquid fixed oils.  The tendency of these to solidification by cold, depends upon
the proportion of stearine or margarine they may contain; for oleine itself remains fluid
at the zero of  Fahrenheit's thermometer.  It is soluble in cold  ether, from which it  can only
be separated by the evaporation of the latter.  Oleic acid much resembles oleine in  physical
characters, being colourless, lighter than water, and  not  prone to solidify ;  but it has a dis-
tinct acid reaction, and a sharp taste, and is miscible with  cold alcohol in all  proportions.—
Glycerine, the base of all the fatty acids, may be obtained from any fatty matter, by saponi-
fying it with an alkaline base, by which this compound is set free.  It cannot be  obtained
in a solid form, but  may be brought to the consistence of a thick  syrup.   It dissolves in
water and alcohol;  but is insoluble in ether.  It has a sweetish taste, whence its name is
derived; and  it is remarkable for its solvent powers, which are scarcely inferior to those of
water.—The following table shows the atomic composition of the fatty acids, and of their
base.
               Stearic Acid  ...  .68 Carbon,  66 Hydrogen, 5 Oxygen.
               Margaric Acid  ...   68 Carbon,  66 Hydrogen, 6 Oxygen.
               Oleic Acid   ....   44 Carbon,  39 Hydrogen, 4 Oxygen.
               Glycerine.....6 Carbon,   8 Hydrogen, 6 Oxygen.
   The following results of the ultimate analysis of different  kind of Fat,  show the close
 correspondence in their composition; and at the  same time make apparent the very large
 proportion of  carbon which  they  all contain.
                                Hog's Lard.
             Carbon.....79-098
             Hydrogen ....  11-146
             Oxygen   ....   9-756
button Fat.	Human Fat.
78-996	79-000
11-700	11-416
9-304	9-584
                               100-000        100-000        100-000
   186.  Besides  the support, combined with facility of movement, which Fat
affords to the moving parts of  the body, it answers  the important purpose of
assisting in the  retention of the animal  temperature, by its  non-conducting
power; and the  still more important object, of serving as a kind of  reservoir
of combustible matter against  the time of need.   Herbivorous  animals,  whose 
(..ar-i-^ «*^-
                STRUCTURE AND COMPOSITION OF CARTILAGE.             155

food is scanty during the winter, usually exhibit a strong tendency to such an
accumulation, during the latter part of the  summer, when their food is  most
rich and abundant; and the store thus laid up is consumed during the winter.
This is particularly evident in the hybernating Mammalia, which take little or
no food during their seclusion. Fat appears to be deposited, only where there
is an excess, in the  alimentary matter introduced into the body, of non-azo-
tized compounds which may be converted into it.  But the ingestion of a large
quantity of these  in the food, is by no means  sufficient for the production of
Fat; for they may not be absorbed into the vessels ; and,  if absorbed, there
may be a want of power to generate Adipose tissue,—so  that they would ac-
cumulate  injuriously in  the  blood, if not drawn off by the Liver.  Hence
some persons never become   fat, however large the  quantity of oily matter
ingested ; and it is in such persons, that the tendency to disorder of the Liver
from over-work is most readily manifested ; hence they are  obliged to abstain
from the use of fat-producing articles of food.
   187. In Cartilage, also, the simple cellular structure is very obviously re-
tained, and frequently exists alone ;  although in some forms of this  tissue, it
is united with the fibrous, or  partly
replaced by it.  In  all, however, the                  Fig. 52.
early stage of formation  appears to
be the same.   The structure origi-
nates in cells, analogous to those of
which the rest of the fabric is com-
posed ; but  between  these cells, a
larger quantity than usual of hyaline
or  intercellular  substance is depo-
sited ; and the amount  of  this sub-
stance  continues  increasing,  simul-
taneously with the bulk of the cells.
The original cells are  pushed far-
ther and  farther from one  another ;
but new cells  arise between  them
from germs which  are contained in
the hyaline substance.   The  first
cells frequently produce two or more
young cells from  their  nuclei ; and
thus it is very common to meet with
groups of such cells  or corpuscles, consisting  of two, three, or four.—The
varieties in the permanent Cartilages principally depend  upon the degree of
organization,  which  subsequently
 takes place in the intercellular sub-
 stance.   If a mass of Fibres* analo-
 gous to those of the fibrous  mem-
 branes (§  138), should  originate in
 it, the Cartilage presents a more or
 less fibrous aspect; in some  instan-
 ces the  Fibrous  structure  is  deve-
 loped so  much, at the expense of
 the Cells, that  the latter disappear
 altogether, and the whole  structure
 becomes  fibrous.  Sometimes  the
 fibres  which  are  developed,  are
 rather  analogous to  those  of the
 Elastic tissue (§ 140); these are dis-
 posed  around  the  cells, forming a    Section of Flbr0.Cartilage.  sh0wing disposition of
 kind of network, in the areolae Of   cartilage cells, in areola? of fibrous tissue.
 Section of the Branchial cartilage of Tadpole; a]
group of four cells, separating from each other; 6,
pair of cells in  apposition ; c, c, nuclei of cartilage
cells ; d, cavity containing three cells.
 
156           ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.
which  they lie;  and this  kind of  cartilage  may be  termed the  elastic or
reticular.   The primitive cellular organization is for the  most  part retained
in the ordinary articular cartilages,* the cartilaginous septum narium, the car-
tilages  of the alae and point of the nose, the semilunar  cartilage  of the eye-
lids, the cartilages of the larynx  (with  the exception  of  the  epiglottis), the
cartilage  of the trachea and its branches, the cartilages  of  the  ribs  (in Man)
and the ensiform  cartilage of the  sternum ;  and  it is seen also in the tempo-
rary cartilages, or  those which  are  destined  to  undergo  ossification.  The
fibrous structure is  seen  in all those Cartilages, which unite the  bones by
synchondrosis ;  this  is the  case  in the  vertebral column  and  pelvis,  the
cartilages of which are destitute of corpuscles, except in and  near their  cen-
tres.   In  the lower Vertebrata, however,  and in the early condition of the
higher, the fibrous structure is confined to the exterior, and the whole interior
is occupied by the ordinary cartilaginous corpuscles.  The reticular structure
is best seen in the epiglottis and in the concha auris : in the former of these,
scarcely  any trace of cartilage-cells  remains ; in the latter, the  fibrous net-
work  disappears by degrees  towards the extremity of the  concha, and  the
structure  gradually passes into the cellular form.t

   a. The substance that gives to the Cellular Cartilages their peculiar character, has received
the designation of Chondrine.  It bears much resemblance to ordinary Gelatine, but requires
longer boiling in water for  its solution; the solution fixes on cooling, like that  of gelatine;
and when it becomes dry by evaporation, it has the appearance of solid glue.  Chondrine
is not precipitated, however, by tannic acid; on the other hand, it gives precipitates with
acetic acid, alum, acetate of lead, and proto-sulphate of iron, which do not disturb a solution
of Gelatine.  That the Chondrine obtained by boiling Cartilage is an actual component of
that tissue, and is not a product of the operation, appears from the agreement between its
elementary composition and that of cartilage, when analyzed by combustion.  According to
Mulder, the proportions  of the elements, as deduced  from the definite  compound which
Chondrine forms with Chlorine, are 32 C, 26 H, 4N, 14 0, with  l-10th of an equivalent of
Sulphur.   Chondrine agrees much more nearly with the proteine-compounds, in its element-
ary composition, than does Gelatine; and may be considered as a sort of intermediate stage
between the two.  Chondrine is  not obtainable  from  any of the  Fibro-cartilages; these
yield gelatine, on boiling, exactly similar to that of the  tendons.  The  Elastic  cartilages,
after being boiled for several days, yield a small quantity of an extract, which does not form
a jelly,  but which has the other chemical properties of Chondrine.   The cartilage of Bone,
before ossification, yields only Chondrine ; after ossification, however, it affords only Gelatine;
and it is curious that, even  when  bony deposits take place in the permanent cartilages, the
ossified portion contains  ordinary Gelatine in the place of Chondrine.   Many of the carti-
 lages naturally contain a large  proportion  of mineral  matter; in the costal cartilages, frac-
 tures in which are generally repaired by osseous substance, from 3 to 7 per cent, of ash is
 left by calcination.  This contains a large proportion of the carbonate and sulphate of soda,
 together with carbonate of  lime and a small proportion of phosphate; as age advances, the
 phosphate  of lime predominates, and the soluble compounds diminish.

    188. Cartilage (at least in  its simplest form)  is  nourished,  without coming
 into direct relation with the Blood through the medium of blood-vessels; the
 cellular Cartilages not  being penetrated by vessels in  the healthy state; al-
 though in certain diseased conditions they become distinctly vascular.   They
 are, however, surrounded by  Blood-vessels;  which form large ampullae or
 varicose  dilatations  at their  edges  or on their  surfaces (Fig. 54):  and  from
 these the  Cartilages  derive their nourishment by imbibition  ; in exactly the
 same manner as  the  frond of a Sea-weed  (the structure of which is alike cel-
 lular)  draws into itself  the requisite fluid from the surrounding  medium.   In
 the thicker masses of cartilaginous tissue, however,  such  as  the cartilages of

   *  The articular cartilages, at the points where tendons are implanted into them, have all
 the characters of fibro-cartilage; the fibres of the tendon  being spread through the intercel-
 lular substance of the cartilage, for some distance, and gradually coalescing with it.
   f See Mr. Toynbee's  Memoir on the Non-Vascular Tissues, Phil.  Trans. 1841. 
STRUCTURE AND COMPOSITION OF  CARTILAGE.             157
the ribs, we find canals excavated at wide distances  from each other;  which
are lined by a continuation  of the perichondrium or investing membrane of
the cartilage,  and which thus allow
its vessels  to come into nearer prox-   _              Fig- 54.
no distinction between the  cartilage that is ultimately to become the Osseous
Epiphysis, and that which  is to remain as Articular Cartilage; both are alike
cellular;  and the vessels that  supply them with nutrient  materials penetrate
no further than their surfaces.   At a subsequent period, however, when the
ossification  of  the epiphysal  cartilage  is  about  to  commence, vessels  are
prolonged into it;  and a distinct line of  demarcation is  seen betwixt the vas-
cular portion, which is to be converted into Bone, and the non-vascular part,
which is to remain as Cartilage.   At this period, the  Articular Cartilage is

                                   Fig. 55.
  Vessels situated between the attached synovial membrane, and the articular cartilage, at the point
where the ligamentum teres is inserted in the head of the os femoris of the human subject, between the
third and fourth months of foetal life ; a, the surface of the articular cartilage ; 6, the vessels between the
articular cartilage and the synovial membrane ; c, the surface to which the ligamentum teres was at-
tached ; d, the vein ; e, the artery.

nourished by a plexus of vessels  spread over  its free surface, beneath its sy-
novial membrane; as well as  by the vessels, with which it  comes in contact
at its  attached extremity.  Towards the period of birth, however, the sub-sy-
novial vessels gradually  recede from the surface of the articular cartilage ; and
at adult  age  they have  entirely left it, though they still  form a band which
surrounds  its margin.   The  Fibrous cartilages  are  somewhat vascular ;  but
the vessels do not extend to the cellular portions, where  such exist.
   189. No vessels  can  be traced (according to Mr. Toynbee) into the sub-
stance of the true Cornea;  which, contrary to the statement of Muller, is  a
cellular rather than  a fibrous cartilage.  The cells are not so numerous as are
those of the  articular cartilages; and they are surrounded by a plexus  of bright
     14 
158
ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.
            Fig. 56.              fibres, laxly  connected together, so  as to re-
                                 semble areolar tissue.   Two sets of  vessels, a
                                 superficial and a deep-seated, surround the mar-
                                 gin of the  cornea.  The arteries of the former
                                 are prolonged for  a  short  distance upon  the
                                 Conjunctival membrane, which forms the outer
                                 lamina of the cornea;  but they terminate in
                                 veins at from i  to | a  line from  its margin.
                                 The deep-seated vessels  belong to  the Cornea
                                 proper;  but they do not enter it, the  arteries
                                 terminating in veins just where the  tissue of
                                 the Sclerotic becomes continuous with that of
                                 the Cornea.  In  diseased  conditions  of  the
                                 Cornea (as of the articular cartilages), both sets
                                 of vessels extend  themselves  through it;  the
                                 superficial not unfrequently form a dark band
                                 of  considerable  breadth  round its   margin;
                                 whilst the deep-seated  are  prolonged into its
                                 entire substance.  Notwithstanding the absence
                                 of vessels in the healthy condition of this struc-
                                 ture, incised wounds commonly heal  very rea-
                                 dily, as is  well seen after the operation of  ex-
                                 traction of Cataract;  but the foregoing details
                                 make evident the importance  of not  carrying
the incision further round than is necessary; since  the corneal tissue should
not be cut off from the supply of nourishment, afforded by the vessels in its
immediate proximity.
  [This structure has been recently studied by Messrs. Todd and Bowman, and is described
by them with great accuracy.   We subjoin their  description.   " The  cornea, though a beau-
tifully transparent substance, and appearing  at first sight as homogeneous as glass, is  never-
theless full of elaborate structure.   It is in fact composed of five coats or layers, clearly
distinguishable from one another.   These are, from before backwards, the conjunctival layer
of epithelium, the  anterior elastic lamina, the cornea proper, the posterior elastic lamina, and the
epithelium of the aqueous humour, or posterior epithelium.   The cornea, when uninflamed, con-
tains no blood-vessels; those of the surrounding  parts running back in loops, as they arrive
at its border.
  On the cornea proper, or  lamellated cornea, the thickness and strength of the cornea mainly
depend.  It is a peculiar modification of the white fibrous tissue, continuous with that of the
sclerotic.   At their line of junction (fig. 57), the fibres, which in the sclerotic  have been
                                      Fig. 57.
  Nutrient Vessels of the cornea, a,
superficial vessels belonging to the
Conjunctival membrane, and continu-
ed over the margin of the Cornea; b,
vessels of the Sclerotic, returning at
the margin of the Cornea.
  Vertical section of the Sclerotic and Cornea, showing the continuity of their tissue between the dotted
lines:—o. Cornea,  b. Sclerotic.  In the cornea the tubular spaces are seen cut through, and in the
sclerotic the irregular areolse.  Cell-nuclei, as at c, are seen scattered throughout, rendered more plain
by acetic acid.  Magnified 320 diameters. 
CORNEA, AND CRYSTALLINE LENS.
159
densely interlaced in various directions, and mingled with elastic fibrous tissue, flatten  out
into a membranous form, so as to follow in the main the curvatures of the surfaces of the
cornea, and to constitute a series of more than sixty lamellae, intimately united to one ano-
ther  by very numerous processes of similar structure, passing from one to the other, and
making it impossible to trace any one lamella over even a small portion of the cornea.  The
resulting areolae, which in the sclepotic are irregular, and on all sides open, are converted in
the cornea into tubular spaces, which have a very singular arrangement, hitherto undescribed.
They lie in superposed planes, the contiguous ones of the same plane being for the most part
parallel, but crossing those of the neighbouring planes at an angle, and seldom communica-
ting with them (fig. 58).  The  arrangement and size  of these  tubes can be  shown by

                                     Fig. 58.
Tubes of the Cornea Proper, as shown in the eye of the Ox by mercurial injection. Slightly magnified.

driving mercury, or coloured size, or air, into a small puncture made in the cornea.  They
may also be shown under a high power by moistening a thin section of a dried cornea, and
opening it out by needles.  The tissue forming the parietes of these  tubes is  membranous
rather than fibrous, though  with the best glasses  a fibrous  striation may  be frequently seen,
both in the laminae separating the different series of tubes,  and in that dividing those of the
same layer from each other.  By acetic acid, also, the structure swells, and displays corpus-
cles resembling those apparent in the white fibrous tissue.  Such is the lamellar structure of
the cornea, which mak^s it so much easier to thrust an instrument horizontally than verti-
cally into its substance.   The tubes  or elongated spaces of which we have spoken, are not
distended with any fluid, but are merely moistened in the same way as the  areolse of ordi-
nary areolar tissue.   A perfectly fresh and transparent cornea is rendered opaque by pres-
sure, but it regains  its brilliance on the removal of the compressing force. Some have sup-
posed this to result from the expulsion of fluid from between its laminae; but  that the opa-
city is owing simply to a derangement of the elementary parts of its structure  is plain from
the fact, that the same  phenomena are exhibited by a section, however thin,  immersed in
water, and deranged by stretching.]

   190.  In connection with  the cornea, it is natural to allude  to the Crystal-
line lens and Vitreous  humour, which have a structure essentially the  same.
The structure of the Crystalline lens has long been known to  be  fibrous; and
Sir D. Brewster  has shown,  by the  aid of  polarized light, the very beautiful
manner in which the fibres are arranged.*   They  are united into laminae, by
means of numerous  teeth or sinuosities at  their edges, which lock into one
another.   That these fibres originate  in cells, has been  clearly  ascertained ;
but the nature  of  the metamorphosis has been differently stated  by two emi-
nent  observers, Schwann and Barry.   By the former, the fibres are  considered
to be prolonged cells:  whilst the latter regards them as rather formed upon
the plan of the tubes of muscular fibre (§  235), several cells  coalescing into
one ;  in this  he is supported by Mr. Toynbee, who states  that  he  has  fre-
quently seen the  fibres,  towards the margin  of the lens, made up of such cells.
After it is fully formed,  however, it  is not permeated  by blood-vessels;  these
being confined to the capsule.  During the  early part of  foetal life, and  in in-
flammatory conditions of this membrane, both the  anterior  and posterior por-
tions of the capsule are  distinctly vascular;  but at  a later period,  according to
* Philosophical Transactions, 1833. 
160         ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.

Mr. Toynbee, the posterior half only of the  capsule  has vessels distributed
over it surface;  and  these are derived from  the  Arteria  centralis retinas.
From optical experiments which have been suggested to him by this circum-
stance, he infers  that "objects  (radiating lines for instance), situated on the
anterior surface of the  crystalline lens, produce an indistinctness  in the  image
which is formed upon  the retina;  whereas, when these  lines exist  upon the
posterior surface  of the lens, the image  is clear."  The substance of the Lens
contains about 42 per cent,  of animal matter, with 58 parts of water. Nearly
the whole of the former may be dissolved in cold water by trituration; the
solution is coagulated by heat, and forms  a granular but not coherent  mass;
alcohol and acids produce the same effect.   Hence it appears that  the Lens
chiefly consists of albumen in its soluble  form; and  this may be supposed
to be contained in the  cavities of  the cells, as it is in those of the vitreous
humour.  From the latest  analyses, it appears that the substance of the lens
corresponds most with that modification of albumen, which forms  the Glo-
buline of the blood (§  147).—In the Vitreous humour,  we have an example
of a very loose form of cellular tissue;  strongly resembling that which con-
stitutes the entire structure  of Acalephae (Jelly-fish).   That  the cells  com-
posing it have no open  communication with  each other, is evident  from the
fact  that, when the  general enveloping membrane  is  punctured in several
places, it  is long before the  contained  fluid entirely  drains away.   This
fluid is analogous to  that of the Aqueous humour;  being little else than Wa-
ter, holding a small quantity of Albumen and Saline water in solution.   From
Mr. Toynbee's inquiries it would  appear, that the vessels which pass through
the Vitreous humour do  not send  branches into  its  substance; but  that it is
nourished by the  vessels, which are minutely distributed upon its general en-
velope.   The Ciliary processes of the Choroid membrane are almost entirely
composed of large, plexiform  vessels, closely resembling those  of  synovial
membrane (Fig. 54), which allow a great quantity of blood to circulate through
them ; and  these have probably an important share in the nutrition of the Vi-
treous body.
   191.  Cartilage  is perfectly insensible; and neither nerves nor lymphatics
can be traced into its  substance.   Its functions  are purely mechanical;  the
consolidation of  its texture by internal  deposit  renders it little disposed to
change by spontaneous decay ; and it is protected by its toughness  and elas-
ticity from  those  injuries, to which softer  or more brittle  tissues are liable.
These very circumstances, however, interfere with the  activity of its nutrition.
Cells which are choked up with interior deposit do not readily transmit fluid:
it is doubtful whether any interstitial change can  take place in the interior of
a permanent Cartilage (except when it has  become vascular by disease, or
undergoes ossification), through the whole  of life; and there seems ground to
believe that, when it has been injured by disease  or  accident, the loss of sub-
stance is not repaired by real  cartilaginous tissue.  In the process of ulcera-
tion of Cartilage (as observed by Mr. J. Goodsir), it  appears that the formation
of depressions on the  surface is due, not so  much to  any change originating
in the substance of the cartilage, as to the  eroding  action of the cells of the
false membrane, which is the product of inflammatory action upon its surface;
and it is in this false membrane that  the new vessels  are formed, which dip
down into nipple-like prolongations of the membrane, entering corresponding
hollows excavated in the cartilage.—On the other hand, the softer tissues of
the Eye are capable of complete regeneration.   Every  oculist is aware that
a great loss  of Vitreous humour may take  place without permanent injury;'
and it has been found that even the Crystalline lens may be completely rege-
nerated, after it has been entirely removed  by extraction. 
CALCIFICATION OF FIBRES AND CELLS.
161
 Calcified Areolar Structure, of which the Skele-
ton of the Echinodermata is composed; from the
Spine of an Echinus. Magnified 150 diameters.
      9.  Tissues consolidated by Earthy deposit.—Bones and Teeth.

   192. Both the Fibres and Cells of the Animal tissue, there is reason to be-
lieve, may be consolidated by mineral deposits ; these  being chemically united
with the Gelatine of the Fibres ;  or  secreted, either alone, or in combination
with gelatine, into the cavities  of the
Cells, by their  own inherent powers.                  Fig. 59.
—We have an example of the form-
ation of a skeleton by the consoli-
dation  of  fibres, in the  shell and
other  hard parts of the Echinoder-
mata ; the intimate structure of which,
as shown by the Microscope, strong-
ly reminds us of Areolar  tissue that
might have undergone the calcifying
process.   Again, we have an exam-
ple  of the  formation  of a skeleton
by the deposit of mineral matter in
the  cavities of cells, in the shells of
Mollusca; in many of which  (espe-
cially  among the Bivalves) the cellu-
lar character is permanently shown,
—a consistent membrane being left,
after the  Carbonate of Lime that consolidated the  cell has been  dissolved
away  by an acid.   An arrange-
ment precisely similar, as regards                    Fig. 60.
the  animal constituent, is found
in the Enamel of Teeth (§ 215);
the  only difference being in the
consolidating material, which is
chiefly the Phosphate of Lime,
a mineral far harder than  the
Carbonate.   It  is  not always,
however, that  the original cells
preserve  their character  so dis-
tinctly;  for it is  very commonly
found, that they have  coalesced
with each other, in such a man-
ner as not to  be distinguishable
in the fully-formed  tissue.  We
also frequently  observe,  in  the
skeletons of Vertebrata, that  the
whole substance is not consolidated, but that cavities and channels are left  in
it; which  seem destined to perform  some office connected with the interstitial
changes, that continue to take place  in  the tissues subsequently to their first
formation.   It has been already pointed out (§ 5), that the internal bony ske-
letons of Vertebrated animals are destined  to undergo  a degree of interstitial
change  (in  order  to adapt them to  the progressive growths of the  parts that
cover them), which is not required in the external envelopes of Invertebrated
animals;  these being  capable of sufficient enlargement  by addition  to their
edges merely; or  else being  periodically thrown  off, and renewed  upon  a
'larger scale.  It  is obvious  that, if the whole substance be consolidated by
calcareous deposit, there  can  be  no permeation of nutritive fluid through it;
but, on the other hand, if it be traversed by tubuli, commencing from the  near-
 est vascular surface; or  if a  series of minute chambers, connected  by still
                                    14*
 Cellular membrane, left after the removal of the Cal-
careous matter from the shell of Pinna.  Magnified 185
diameters. 
162         ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.

more minute passages, be excavated in its substance, it is evident that, even
though  blood  cannot circulate through it, a nutritive  fluid drawn from the
blood, may be carried into its minutest parts.   This is the kind of structure
which we find in Bone, and in the principal substance of Teeth.   The mode
in which it is generated, will become the subject of inquiry hereafter.
   193.  When examined with the naked eye, it is  seen that Bone possesses
in some degree a laminated texture : in the long bones, the  external and in-

                                  Fig. 61.
ternal lamina? are arranged concentrically round the medullary canal;  and in
the flat bones, they are parallel to the surface.   Towards the extremities of
the long bones, and between the external plates of  the flat bones, are a num-
ber of cancelli, or small hollows bounded by very thin plates of bone ; these
communicate with  the medullary canal where it exists;  having, like it, an
extremely vascular lining membrane; and their  cavities being filled  with a
peculiar adipose matter.   The hard substance of the bone also is traversed by
canals, on which the name of Haversian  has  been bestowed, after their disco-
verer ; these canals run for the most part in the direction of the laminae ;  but
they have many transverse  communications, both with each  other and with
the medullary cavity, so  that they form  a complete network, which is lined
by a continuation of the membrane of the latter.  Their diameter varies from
l-200th to  1-2000th of an  inch; the average being  probably about 1-500.
The smaller ones contain only  a single capillary vessel; but several such ves-
sels seem  to exist in the larger  ones, together with adipose matter.   When a
thin transverse section of  a long bone  is  made, and is  highly  magnified, it is
seen that the bony matter of the greater  part of  its thickness is  arranged in
concentric circles round the orifices of the canals ;  these  circles are marked
by a series of stellated points; and when  the  latter are  magnified still more
highly, it is seen that they are  cavities or  lacunae of a peculiar form, which
seems characteristic of Bone.  They are  usually oval or lenticular in form;
and are so placed, that one of  their largest surfaces is turned from, and the 
STRUCTURE OF  BONE.
162
other towards, the Haversian canal.   Their long diameter is commonly from

               [Fig. 62.                                     [Fig. 63.
  Transverse section of the compact tissue
of a long Bone ; showing 1, the periosteal
layer; 2, the medullary layer,and the inter-
mediate Haversian systems of lamellae, each
perforated by an Haversian canal.  Mag-
nified about 15 diameters.]
  Transverse section of the compact tissue of a Tibia
from an aged subject, treated with acid ;  showing the
appearance of lamellae surrounding the Haversian ca-
nals.  Portions of several systems of lamellae are seen.
The appearance of the  lacunae, when their pores are
filled with fluid, is also seen, as well as the radiation
from the canals which then remain. From Mr. Tomes.]
l-2400th  to  1-1600th of an inch ;  their short diameter is about one-third, and
their thickness about one-sixth, of their length.

  a. It has been lately shown by Mr. J. Quekett, that there are differences in the form and
size of the lacunae, in the several classes of animals, sufficiently characteristic to allow of the
assignment of minute fragments of bone, with the aid of the microscope, to their proper class.
The lacunae of Reptiles are distinguishable by their large size, and long oval form;  and those
of Fish, by their angular  form and the  fewness of the  radiating canaliculi.  The osseous
lacunae of the Bird may be distinguished from those of the Mammal, partly by their smaller
size, but chiefly by the remarkable tortuosity of their canaliculi, which  wind backwards and
forwards in such a manner, as frequently to  destroy the concentric lamellar appearance.  It
is interesting to remark further, that the sizes of the lacunas in the four classes of the Verte-
brated animals, bear a close  relation to  the  sizes of their blood-corpuscles.   Here, as else-
where, the  dimensions of the ultimate parts of the tissue are tolerably constant in each group
of animals, and show little variation in accordance with  the size of the species; thus there
is little or no perceptible difference  in the size of the elements of  the osseous tissue of the
enormous extinct Iguanodon, and of the smallest Lizard now inhabiting the earth.
G4.
   194.  From all parts of these cavities,
but  especially from  their two  largest
surfaces, proceed  a  large  number of
minute tubuli,  which traverse  the sub-
stance of the  bone,  and  communicate
irregularly  with one  another.  Their
direction, however, possesses  a  certain
degree of  determinateness; for  those
passing off from the inner surface con-
verge towards the  Haversian  canal;
whilst those passing off from the outer
surface diverge  in  the contrary direc-
tion, so as  to meet and inosculate  with
those proceeding  inwards   from  the
cavities  of  the next annulus.  In this  manner, a communication  is kept up
between  the Haversian canal, and  the  most external of its concentric lamellae
  Lacunae of Osseous Substance;  magnified
500 diameters: a, central cavity ; 6, its ramifica-
tions. 
164          ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.
of bone.  It is  not to be imagined, however, that blood  can be conveyed by
                          these tubuli, their size  being far  too  small; for
        [Fig. 65.            their  diameter, at their largest  part, is estimated at
                          from  1-14,000th  to  l-20,000th of an inch, whilst
                          that of the smaller branches is from  l-40,000th to
                          l-60,000th of an  inch ;  so. that  the  blood-corpus-
                          cles could not possibly enter them.   But it may be
                          surmised  that  they draw  fluid  from the nearest
                          blood-vessels, and thus keep up a sort of circulation
                          through the  osseous  substance,  which  may con-
                          tribute to its growth, and may keep it in a state fit
                          for repairing itself, when injured by disease or vio-
                          lence.  The lacunae,  however, do  not seem to be
                          unoccupied in the  living bone;  for each  contains
                          (according to  Mr. J. Goodsir) a minute  grapular
                          substance,  which seems  to be identical  with the
                          nucleus of the original  bone-cell, and which pro-
                          bably serves as a  " nutritive centre,"—attracting to
                          itself, through  its own  system  of canaliculi,  the
                          nutritive materials supplied by the blood-vessels of
                          the nearest surface, and diffusing  these through the
                          surrounding substance.*
                            195.  Although  a large quantity of blood is sent
                          to  Bone, the vessels  do  not penetrate  its minute
                          parts;  being  confined to  the Medullary cavity,
                          and to  the Haversian Canals,  and Cancelli, which
                          are prolongations of it.  The substance of the  Bone,
                          therefore, is really as non-vascular as  that  of  Carti-
                         being, that  it is channelled  out by more numerous
inflexions of the external surface, and that  the vessels are  thus brought into
nearer proximity with its several parts.   The delicate osseous lamellae, which
form the walls of the cancelli, and of the large cells excavated in some of the
cranial bones, have a structure  precisely analogous to that of the cylindrical
laminae surrounding the Haversian canals of the  long bones ; and derive their
nourishment from the vascular membrane covering their  surface, through the
medium of  a similar set of lacunae and canaliculi.   They do not  themselves
contain Haversian canals or cancelli;  because no part of their  substance is far
removed from a vascular membrane.   The cylindrical rods, that make up the
hollow shaft of  a long bone, are  connected  together  by solid  osseous sub-
stance, which is composed of lamellae running parallel to the external surface
of the bone  ; and  these derive their  nutriment either  from the periosteum, or
from the membrane lining  the  great  central medullary cavity; according as
they are nearest to one or to the other.—The membranous lining of the canals
of Bone appears to be supplied with lymphatics, and  also  with nerves; but
with both in a very limited amount.   The  periosteum seems to be scarcely
(if at all) sensible in the state of health, although painfully so when inflamed  ;
and the same may  be said of the membrane  lining the Haversian canals and
cancelli. The membrane lining the central medullary cavity, however, is more

  * The lacunas and canaliculi of Bone were formerly supposed, on  account of the black
appearance they exhibit under the Microscope, "to be filled with  opaque matter; but this ap-
pearance is common to all cavities excavated in a highly-refracting substance (being shown
by a bubble of air in water), and ceases when a very thin section of Bone is examined, es-
pecially if it have been placed in Canada Balsam.  In the Bones of Mummies, they are found
to be filled with a waxen material; and in those which have lain in bogs, they are rendered
peculiarly distinct by the infiltration of some of the surrounding black  matter: so that their
power of imbibing liquids is clearly proved.
  Haversian canals, seen on a
longitudinal section of the com-
pact tissue of the shaft of one of
the long bones: 1, arterial canal;
2, venous canal; 3, dilatation of
another venous canal]

lage ; the only difference 
STRUCTURE AND COMPOSITION OF BONE.
165
sensitive; since unequivocal signs of pain are manifested by an animal, when,
a bone having been sawn across, a probe is passed up the cavity, or an  acrid
fluid  is injected into it.
   196. The ultimate substance of Bone, lying between the lacunae and  cana-
liculi, appears to be usully granular ;  the granules  are  stated by  Mr. Tomes*
to  be  often distinctly visible  without any artificial preparation, in  the sub-
stance of the  delicate  spicula of the  cancelli, when  they are viewed with a
high  power;  and to be made very evident  by prolonged boiling in a Papin's
digester.   They vary in  diameter  from  1-6000th to 1-14,000th  of  an inch ;
their shape  is oval or oblong, often  angular; and they cohere firmly together,
possibly  by the medium of some different  material.   Their  own substance,
however, appears to be perfectly homogeneous ;  but it is made up of  several
components, as appears from the following statements  regarding  the  chemical
composition of Bone.

  a. When the Calcareous matter of Bone has been dissolved away by the action  of an acid,
the Animal substance which remains is almost entirely dissolved by a short boiling in water;
yielding to it a large quantity of Gelatine.  This, indeed, may be obtained  by long boiling
under pressure, from previously-unaltered Bone; and the calcareous matter is then left almost
pure.   The Lime of bones is, for the most part, in the state of Phosphate, especially among
the higher animals; it is  curious,however, that in callus and exostosis,there is a much larger
proportion of  Carbonate of lime, than in the sound bone;  in which respect these formations
correspond with the bones of the lower animals; but in caries, the quantity of the carbonate
is much smaller than usual. The composition of the Phosphate of Lime in Bones is peculiar;
8 equiv. of the base being united with 3 of the acid.  According to Prof.  Graham, it is to be
regarded as a compound  of two tribasic phosphates; namely, 2 Ca, O, H O, P 05-f-2 (3 Ca O,
P 05); with the addition of an equiv. of water,  which is driven off by calcination.  The fol-
lowing are the results of some of the most recent and  careful analyses of Human  Bone, by
Marchand and Lehmann: those of the former were made on the compact substance  of the
femur of a man aged 30; and those of the latter on the long bones of the arm and leg of a
man of 40 years of age.

       Organic matter.                                   Marchand.   Lehmann.
Cardlage insoluble in hydrochloric acid . Cartilage soluble in hydrochloric acid Vessels . .	. 27-23 5-02 1-01	\	32-56
Inorganic matter. Phosphate of lime..... Fluoride of calcium .....	. 52-26 1-00	\	54-61
Carbonate of lime .....	. 10-21		9-41
Phosphate of magnesia ....	.1-05 •92		1-07 1-11
Chloride of sodium .....	0-25		0-38
Oxide of iron and manganese, and loss	1-05		•86
                                                        100-00      100-00

  6. According to Dr. Stark,f the relative proportions of cartilaginous and earthy matter, in
the bones of different animals, in the bones of the same animals at different ages, and in the
different bones of the same body, never depart widely from the preceding standard;  the
amount of earthy matter being always found to be just double that of the cartilaginous basis,
when the bones have been carefully freed from oily matter, and completely dried, previously
to the analysis.  The hardness of bone, he maintains,#does not at all depend upon the pre-
sence of an unusually large proportion of earthy matter; nor does their increased flexibility
and transparency indicate a deficiency of the mineral ingredients; for the transparent readily-
cut bones of fish contain the same amount of earthy matter, in proportion *to their gelatinous
basis,  as do the dense ivory-like leg-bones of the deer or  sheep.   The same holds good of
the bones even of  the so-called  Cartilaginous Fish.  The  difference seems to depend upon
the molecular arrangement of the ultimate particles; and especially, it  seems likely, upon
the relative amount of water which the bones contain.

  * Todd and Bowman's Physiological Anatomy, p. 108,  and Cyclopaedia of Anatomy, art.
Osseous Tissue.
  •J- Edinburgh Med. and Surg.  Journal, April 1845. 
166           OF THE ELEMENTARY PARTS  OF THE  HUMAN FABRIC.
  c.  Probably the most exact and comprehensive analyses yet made of Bone, are those of
Von Bibra ;* whose laborious investigations may be said to have  almost exhausted the sub-
ject.  The following table shows the relative proportions of the principal ingredients in some
of the principal bones of a woman aged 25 years.
		Occipital			Os innomi-		
	Femur.	bone.	Scapula.	Rib.	natum.	Vertebra.	Sternum.
Organic matter.							
Cartilage	29-54	29-87	32-90	33-06	38-26	4344	46-57
Fat ...	1-82	1-40	1-73	2-37	1-77	2-31	2-00
Inorganic matter.							
Phosphate of lime }							
with a little fluo- >	57-42	57-66	54-75	52-91	49-72	44-28	42-63
ride of calcium. )							
Carbonate of lime	8-92	8-75	8-58	S-66	8-08	8-00	7-19
Phosphate of magnesia	1-70	1-69	1-53	1-40	1-57	1-44	1-11
Soluble salts	0-60	0-63	0-51	0-60	0-60	0-53	0-50
                                 100-00   100-00    10000   100-00    100-00   100-00
  The analyses of the long bones of the arm and leg correspond closely with that of the
femur;  but we observe that the  proportions of ingredients  in  the more spongy bones are
widely different.  It is difficult, however, to say how far this variation is due to a difference
in the proportions of gelatine and earthy matter, in the actual osseous  substance; or how far
it may be accounted for by the presence of an increased proportion  of membrane, forming
the  lining of the cancelli.—The same uncertainty must attend the explanation of the differ-
ences that present themselves at different ages; as shown in the following table, which gives
the  comparative analyses of the long bones (generally the  femur) at different ages.
Organic matter. Cartilage .	Foetus 6 months. . 40-38	Foetus 7 months. 34-18	Child 2 months. 33-86	Child 5 years. 31-28	Man 25 years. 29-70	Woman 62 years. 28-03
Fat.....	. a trace	0-63	0-82	0-92	1-33	2-15
Inorganic matter. Phosphate of lime } with a little fluo- >	. 53-46	57-63	57-54	59-96	59-63	63-17
ride of calcium. )						
Carbonate of lime	. 3-06	5-86	6-02	5-91	7-33	4-46
Phosphate of magnesia Soluble salts	. 2-10 . 1-00	1-10 0-60	1-03 0-73	1-24 0-69	1-32 0-69	1-29 0-90
                                 100-00   100-00    100-00   100-00    100-00   100-00
  From this it will be seen that there is a gradual diminution in the proportion of animal
matter, through life; and a corresponding increase in the proportion of the earthy components.
But this is not nearly so great as is  usually supposed ;  and the greater solidity of the bones
of old persons is doubtless owing chiefly to the fact, that their cavities are  progressively con-
tracted, by the addition of new bony matter (§201).
  d. The  following comparative analysis of the bones of different animals, are selected from
the very extensive series given by Von Bibra; which contains 143 of Mammalia (independ-
ently of Man), 151 of Birds, 31  of  Reptiles, and 23 of Fishes.  They were mostly made
upon the long bones ; except in the  case of Fishes, in which they were made upon the Ver-
tebra?.
Sheep.   Horse.   Wolf.   Thrush.   Frog
Cod.   Salmon.
Organic matter.					D'		
Cartilage	. 29-68	27-99	27-44	28-02	30-19	31-90	21-80
Fat ... .	. 0-70	3-11	1-45	1-54	5-31	2-34	38-82
Inorganic matter.							
Phosphate of lime with ")							
a little fluoride of cal- i-	55-94	54-37	57-87	62-65	59-48	57-65	36-84
cium.							
Carbonate of lime	12-18	12-00	11-09	6-05	2-25	4-81	1-01
Phosphate of magnesia	1-00	1-83	1-13	0-90	0-99	2-30	0-70
Soluble salts	0-50	0-70	1-02	0-84	1-78	1-00	0-83
1	100-00	100-00	100-00	100-00	10000	100-00	100-00
  * Chemische Untersuchungen iiber die Knochen und Zahne des Menschen, und der Wir.
belthiere. 
COMPOSITION AND DEVELOPMENT OF BONE.
167
   It will be observed that, in all cases, the proportion between the cartilaginous basis and
 the earthy matter is very nearly the same; being almost exactly as 1 to 2, even where  the
 composition of the bone is most altered, by the presence of an unusual quantity of fatty mat-
 ter.  Hence there is strong reason to believe, that a definite chemical compound  is formed
 by the union of the Gelatine and Earthy salts; and  this  corresponds well with the fact
 already noticed, in regard to the homogeneousness of the ultimate particles of bone.

   197. The first Development of Bone may take place  in the  substance,
 either of Membrane, or of Cartilage.*   The  tabular bones forming  the roof
 of the cranium afford a good example of the first, or intramembranous form
 of Ossification; for  their place is but in part pre-occupied by cartilage ; only
 a membrane being elsewhere interposed between  the dura  mater and the  in-
 teguments.   This membrane is chiefly composed of fibrous fasciculi, corre-
 sponding with those  of the white fibrous tissues ; but amongst these are seen
 numerous cells, some about the size of blood-discs, but others two  or three
 times  larger, containing granular  matter ; and  a  soft  amorphous or  faintly-
 granular matter is also found interposed amidst the fibres and cells.   In cer-
 tain parts, the fibres predominate ; and in others, the cells.  The process of ossi-
 fication here seems at first to consist in the consolidation of the fibres by earthy
 matter ; for the first bony deposit consists of an irregular reticulation, very loose
 and open towards its edges, and there frequently presenting itself in the form
 of distinct spicula, which are continuous with  fasciculi of fibres in the sur-
 rounding membrane.  The limits of the calcifying deposit may be traced  by
 the opaque and granular character of the parts affected by it, and it gradually
 extends itself, involving more and more of the surrounding membrane, until the
 foundation is laid for the  entire bone.    Everywhere the  part most recently
 formed consists of a  very  open reticulation of fibro-calcareous spicula ; whilst
 the older part is rendered harder and  more  compact, by the increase in  the
 number of these spicula, and perhaps also by the calcification of the interve-
 ning cells.  As the process advances, and the plate of bone thickens, a series
 of grooves or furrows, radiating from the ossifying centre, are found upon  its
 surface ; and these by a further increase in thickness, occasioned by a  deposit
 of ossific matter all around them, are gradually converted into closed canals
 (the Haversian), which contain blood-vessels, supported by processes of  the
 investing membrane.  Further deposits subsequently take place in the interior
 of these canals ;  which thus gradually produce a  diminution of their calibre,
 and  a  consolidation of the  bone;  and in this manner its two surfaces  acquire
 their peculiar density, whilst the intervening layer  or diploe retains a charac-
 ter more resembling that of the original  osseous reticulation.—The mode  in
 which the peculiar lacunae  and  canaliculi are formed, in the concentric layers
 around the Haversian canals, probably  corresponds with  that in which they
 are generated in the intracartilaginous form  of ossification, to which we shall
 next proceed.
   198. In a very large proportion of the  skeleton, the appearance of the Bones
 is preceded by that of Cartilages ;  which present the same form, and which
 seem destined to afford a  certain degree  of support, to  the surrounding soft
 parts,  until the  production of Bone has taken place.   As already mentioned
 (§ 187), the temporary cartilages differ in no essential particular from the per-
 manent.  They present the same  irregular scattering of cells through a homo-
 geneous intercellular  substance, and there is the same  absence of any vascu-

  * In recent times, the development of Bone from Cartilage has received almost exclusive
attention; but the older opinion, that Bone is often developed in Membrane, has been lately
brought again into notice by Dr. Sharpey (Introduction to Fifth Edition of Quain's Anatomy),
who  has demonstrated its truth by Microscopic research.  The statements in  the text, upon
this part of the subject, are derived from Dr. Sharpey's  observations, which the author  has
since confirmed. 
168          ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.
larity in the Cartilaginous tissue  itself.   In all considerable masses, how-
ever,  we find a coarse network of canals, lined by an extension  of the peri-
chondrium or investing membrane; and these canals, which may be regarded
as so  many involutions of the external surface, allow the vessels  to come into
nearer relation with  the  interior parts of  the Cartilaginous  structure,  than
they would otherwise do.   They are especially developed at certain  points,
Fig. 66.                              [Fig. 67.
which are to be the* centres of the ossifying process ; and it is always observ-
able, that the vascularity is greatest at the zone, in which  the  conversion of
cartilage into bone is actually taking place.   During the extension of the vas-
cular  canals into the Cartilaginous matrix, certain changes are taking place 
OSSIFICATION OF CARTILAGE.
169
in the  substance of the  latter, which  are  preparatory to its conversion  into
Bone.   Instead of single isolated cells, or groups of two, three, or four, such
as we have seen to be characteristic of ordinary  Cartilage (Fig. 52), we find,
as we approach the centre or line of ossification,  clusters made up of a larger
number arranged in a linear manner; which seem to be formed by a continu-
ance of the same  multiplying process as  that formerly described (Fig.  66).
And when we pass still nearer, we see that these clusters are composed of a
yet greater number of cells, which are arranged in long rows, whose direc-
tion corresponds to the longitudinal axis of the bone; these clusters are still
separated by intercellular substance ;  and it is in  this, that the ossific matter
is first deposited.   If we separate the cartilaginous and the osseous substance
at this stage of the process, we find that the ends of  the  rows  of cartilage-
cells are received into deep narrow cups of bone, formed by the calcification
of the intercellular substance between them.  Thus the  Bone first formed in
the cartilaginous matrix,  is seen to consist of  a series  of lamellae of a  some-
what  cylindrical  form ;  inclosing oblong areolae, or  short  tubular  cavities,
within  which  the  piles  of cartilage-cells yet lie :  and it  thus corresponds
closely  with the reticular structure, which first makes  its appearance in the
intra-membranous form of the process.—So far it  would appear that the blood-
vessels  are not directly concerned in the operation; for although they advance
to the near neighbourhood of the first ossific deposit, they do not make their
way into its substance, or  even into the intervening  areolae.
   199.  This state of things, however, speedily gives  place  to another.  On
examining the subjacent portion, in which the ossifipation has advanced further,
it is found that the original closed cavities have  coalesced to a certain  extent
(probably by the absorption of their walls), both laterally and longitudinally;
and that they now receive numerous blood-vessels, prolonged into them from
the previously-ossified portion.   The groups of cartilage-cells,  which origi-
nally  occupied the cavities, are no longer seen;  and their  place is filled with
a blastema, composed of  cells, containing  a granular  matter, and closely re-
sembling those seen  in the intra-membranous ossification, with a few fibres
scattered  amongst them.    It is by a change in this blastema, that the walls- of
the cavities are  gradually consolidated; new deposits of ossific matter being
formed  in their interior, which occasion the gradual contraction of the cavities,
and give an increasing density to the bone.   The cancellated structure,  which
remains for a time in the interior of the  long bones, and which  continues to
occupy their extremities, represents the  early condition of the ossifying  sub-
stance,  with very little change ;  whilst  the  cavities, which have formed more
regular  communications with each other, and which have been gradually con-
tracted by the subsequent deposit of concentric lamellae, one within  another,
form  the original Haversian  canals.  Thus we  see that  they all form  one
system  in their  origin; as they may be  considered  to  do, notwithstanding
the difference of their form, in the complete bone.
   200.  The original osseous lamellae, formed by the consolidation of the car-
tilaginous substance, are entirely composed of granular matter; and exhibit
none of the lacunae and canaliculi, which are commonly regarded as charac-
teristic of Bone.   These excavations present themselves, however, in all the
subsequent deposits ; and  into the origin of these, we have now to inquire.
According to the views of some  Microscopists, the  cells of the  blastema fill
themselves with ossific matter, except at  the points occupied by the nuclei;
at the same time, they become flattened against  the walls of the canals, and
their nuclei send out radiating prolongations; so that,  when  the calcification
of  the cell has  been completed,  a stellate  cavity is left  in  the hard deposit,
which is occupied by the granular matter of the nucleus.  The centre of this
cavity forms the lacuna, in which the original granular matter may frequently
    15 
170          ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.
 be found remaining, and presenting an appearance as if developed into a cluster
 of minute cells; whilst its prolongations form the canaliculi, from which the
 nuclear matter seems afterwards to disappear altogether.   This view is  sup-
 ported by several considerations; amongst others, by the fact of the existence
 of such stellate nuclei in many Vegetable cells  (Fig. 14); and by the corre-
 sponding appearances witnessed by Professor Owen in the formation of  the
 Cementum of Teeth, a structure  identical with  bone, and  produced by the
 calcification of  the  capsule (§  216).—Others, again, regard the lacunae  and
 their radiating  prolongations as themselves constituting cells;  and examples
 are not wanting of similar forms in bodies known to have this character, as
 the pigment-cells of the skin of Batrachia (Fig. 90, c).—Dr. Sharpey, on the
 other hand, states as the result  of his observations, that the concentric layers
 within the Haversian canals  are formed by a  process analogous to the intra-
 membranous ossification;  namely, by the calcification of successive layers of
 fibres, generated in the  blastema, and possibly derived from the granular cells.
 These fibres, being arranged in  a reticular manner, may here and there include
 an entire  cell or cell-nucleus, the presence of which may determine the posi-
 tion of  a  lacuna;  whilst the canalicula may result from the apposition of the
 minute  apertures, existing between  the  other reticulations of the decussating
 fibres.  This view seems  to derive confirmation from the appearances pre-
 sented by very thin shreds of the gelatinous  matrix, left after the removal of
 the calcareous matter by acid; for these, according to Dr. S., are plainly com-
 posed of  transparent fibres, resembling those of  the white  fibrous tissues, in-
 tersecting one another at acute  angles, and forming a  network, in the meshes
 of which  are minute perforations, that are nothing else than transverse sections
 of the canaliculi.
   201.  In the formation of a long bone, we usually find one centre of ossifi-
 cation in the shaft, and one in each of the epiphyses;  in the flat bones, there
 is one in the middle of the surface, and one in each of the principal processes.
                          The  ossification usually proceeds to a considerable
                          extent, however, in the main centre, before it com-
                          mences in the extremities or processes; and these
                          remain distinct  from the principal mass of the bone,
                          long  after this  has acquired solidity.  During the
                          spread  of the  ossifying process, the cartilaginous
                          matrix  continues  to grow, like  cartilage  in other
                          parts; but after the  bony deposit has  pervaded its
                          entire substance, in the manner just described, a
                          change takes place in  the  method  adopted.  The
                          osseous  laminae, that subdivide  the whole  texture,
                          are removed by absorption  from  the interior of the
                          shaft, so as  to  leave  the great  central medullary
                          cavity; whilst, on the other hand, they receive pro-
                          gressive additions in the external portion, which is
                          thus  gradually  consolidated into the  dense bone,
                          that forms the hollow cylinder of the shaft.  This
                          consolidation is effected by the deposit of  a series
                          of  concentric laminae, one  within another, on  the
                          lining of the Haversian canals.—The bone  con-
                          tinues to increase in diameter, by the formation of
                          new layers upon its exterior; and Dr. Sharpey has
pointed out that these layers  are formed,  not (as  usually stated) in a cartila-
ginous matrix, but in the  substance of  a membrane, consisting of fibres  and
granular cells, and exactly resembling that in which the flat bones of  the roof
of the skull are  developed.  The Haversian canals, too, of these new layers
[Fig. 68.
  Scapula of a Foetus  at the
seventh month ; showing the pro-
gress of ossification.  Natural
size. The light pans are epiphy-
ses as yet cartilaginous.—From
the Museum of King's College,
London.] 
DEVELOPMENT AND GROWTH OF BONE.
171
are formed in the same manner as those of the tabular bones of the skull; the
osseous matter being not only laid on in strata parallel to the surface, but also
being deposited around processes of the vascular membranous tissue, which
extend obliquely from the surface into the substance of the shaft; the canals,
in which these membranous  processes lie, becoming narrowed by the  depo-
sition of concentric osseous  laminae, and  at  last remaining as the Haversian
canals.   Whilst this  new deposition is taking place on  the exterior of  the
shaft, absorption of the  inner and older layers  goes on:  so that  the central
cavity is proportionably enlarged.—The increase of the bone in  length ap-
pears due to the growth of the cartilage between the shaft and the epiphyses,
so long as  this  remains unconsolidated by ossific deposit; and this state con-
tinues, until the bone has acquired nearly its full dimensions.  What further
increase it  gains, seems  chiefly if not entirely due to the progressive ossifica-
tion of  the articular cartilage covering the extremities ; which progressively
diminishes in thickness  during the whole of life, and which in old age some-
times appears to have been almost completely converted into bone.
   202.  It thus  appears  doubtful, whether  there be anything like  a proper
interstitial growth in  bone; that  is, whether  the part, through which  the
ossific process  has made its way, is capable of any further extension than by
addition to its surface.   By the  admirable system of prolongations, however,
by which the vascular membrane is  conveyed into its  intimate substance, we
find this method of superficial deposit adapted to the consolidation of parts, at
first sketched out (as it  were) by a slight osseous reticulation ;  whilst by the
facility with which the bony matter is absorbed in the internal part of the  shaft,
whilst it is being deposited upon its exterior, the same effect is produced, as
if the whole cylinder could enlarge uniformly by a proper interstitial growth,
in the manner of the softer tissues.—Much of our information regarding  the
mode in which new bony matter is deposited, is derived from observations
made nfion the bones of animals that have  been fed with madder; for this
colouring-matter, having  a strong affinity for bone-earth, tinges all those parts
which are  in  close relation  with the vascular surfaces.  In very young ani-
mals, a  single  day serves to colour  the entire   substance of the bones;. for
there is in them  no osseous matter far removed  from  a vascular surface.
At a later period, however, the colouring matter is deposited less rapidly ; and
is found to be  confined  to the innermost of the concentric laminae of  bone,
surrounding  each  Haversian canal,  showing that  this is  the  last formed.
When madder  is given to a growing animal, the  external portion of  the bone
is first reddened; showing that  the new deposit  takes place exclusively in
that situation.  And if, when time has been allowed for this part  to become
tinged, the  administration of the madder be  discontinued, and the animal be
killed some weeks  afterwards, the red stratum is  surrounded by a colourless
one of subsequent formation; whilst the  colourless layer internal to the red
one, and formed previously to it, is thinned by absorption  from within.   By
alternately administering and withholding the madder, a succession of coloured
and colourless  cylinders  may thus  be formed in the  shaft of  a  long bone;
which present  themselves as concentric rings in  its transverse section.
   203.  The nature of the Ossifying process receives some additional light
from the abnormal forms  in which it occasionally presents itself in Cartilages
that are usually permanent;  as  well as in various softer tissues, such as  the
coats of the arteries, fibrous and serous membranes, muscular substance, Sic.
In these cases, the ossific deposit may often be seen to take place, in the first
instance, in the form of distinct granules, which  gradually coalesce ;  or in the
form of spicular fibres, to which additions are   progressively made; until a
solid mass is'produced.   This adventitious bone, however, almost invariably
differs from true or normal bone, in the want of  a regular  Haversian system 
172         ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.

with concentric laminae, and in the absence of the  characteristic lacuna? and
canaliculi.   Irregular cavities, however, are scattered  through  them ;  which
may in some degree answer the same purpose.  The osseous plates not un-
frequently found in the  dura mater, are stated by  Mr. Tomes to possess a
structure more  closely allied  to that of true bone ;  which may be connected
with the  fact that, in some of the lower Mammalia, certain parts of this mem-
brane (the falx  and  tentorium) are normally ossified.
  204. The Regeneration of Bone, after loss of its substance by disease or
injury, is extremely complete;  in  fact, there is no other structure of so com-
plex a nature, which is capable of being so thoroughly repaired.  Much dis-
cussion has  taken place with respect to the  degree  in which  the  different
membranous structures, that surround bone and penetrate its substance, con-
tribute  to its regeneration ;  but the fact seems to  be, that  any or all  these
membranes  may contribute to the formation  of new bone,  in  proportion to
their vascularity,—the new structure, however, being most  readily produced
in continuity with  the old.   Thus, when a portion of the  shaft of the bone
is entirely removed, but the  periosteum is left, the space  is  filled  up with
bony matter in  the  course of a few weeks ;  though, if the periosteum also be
removed, the formation of new  osseous  matter will be confined  to a small
addition in a conical form to the two extremities, a large interspace being left
between  them.   The production of new bony tissue, in this  experiment, as
in cases where  the periosteum has been detached by disease and remains alive
while the shaft dies, is in continuity with minute  spicula of original  bone,
which still adhere to the membrane ; and it is well known that, in comminuted
fractures, every portion of  the  shattered bone, that remains connected with
the vascular membranes, whether these be internal  or  external, becomes the
centre of a new formation ; the loss of substance being filled up the more ra-
pidly, in proportion to the number of such centres.
  205. The most extensive reparation is seen, when the shaft of a long bone
is destroyed by disease.  If violent inflammation occur in its tissue, the death
of the fabric is  frequently the consequence ;  apparently through the blocking-
up of the canals with the products of inflammatory action, and the consequent
cessation of the supply of nutriment.  It is not often that the whole thickness
of the bone becomes necrosed at once ; more commonly this result is confined
to its outer or to its inner layers.   When this is the case, the new formation
takes place  from the part that  remains sound ; the external  layers,  which
receive their vascular supply from the periosteum, and from  the Haversian
canals continued inwards from it, throwing out new matter on  their interior,
which  is gradually  converted into bone;  whilst the internal  layers, if they
should be the parts remaining uninjured, do the same on their exterior, de-
riving their materials from the medullary membrane, and  from  its  prolonga-
tions into their  Haversian canals.  But it sometimes happens  that the  whole
shaft suffers necrosis; and as the medullary membrane arid  the entire Haver-
sian system  have lost their vitality, reparation  can  then only take place from
the splinters of bone which may remain attached to the periosteum, and from
the living bone  at  the two  extremities.   This  is  consequently a very slow
process ; more especially as  the epiphyses, having been originally formed as
distinct parts from  the shaft,  do not  seem able to contribute much to'the re-
generation of the latter.
  , 206.  When  the shaft of a  long bone has been fractured  through, and the
extremities have been brought evenly together, it is  found that the new matter
first ossified is  that which occupies the central  portion of the deposit, and
which thus connects the medullary cavities of the broken ends, forming  a kind
of plug that enters  each.  This  was termed by Dupuytren, by whom  it was
first distinctly described, the provisional  callus, and  it is usually formed in 
REPARATION OF BONE.
173
the course of  five or six weeks, or  less,  in  young persons.  At that period,
however, the contiguous surfaces of the bone itself are not cemented by bony
union;  and the  formation of the permanent callus occupies some months;
during which  the provisional callus  is gradually absorbed, and the  continuity
of the medullary canal is thus restored, in  the manner in which it was first
established.  Mr. Gulliver has  remarked that, when the broken  portions of
bone form an  angle, there is quite a distinct centre of ossification  in the new
matter;  from  which that portion of  it  is  ossified, that lies between the sides
of the angle;  thus  forming what has been termed an accidental  callus, and
giving support to the two portions of the  shaft, in a situation which is exactly
that of the greatest mechanical advantage.   Though for some time quite uncon-  «
nected with the old bone, it soon becomes united  to  the regular callus.  This
instance proves, that continuity with previously-formed bone is not  absolutely
requisite for the production of new osseous  structure; although the process
is decidedly favoured thereby.
   207.  The reparation of Bone, after  disease or  injury,  seems to  take place
upon a plan essentially the same as that  of  its  first formation.  A plastic or
organizable exudation is first poured out from the neighbouring blood-vessels ;
and  thus forms a sort of bed or matrix,  in which the  subsequent  processes
take place.  The next stage, in young animals, is the formation of  a true car-
tilaginous substance, exactly resembling  their temporary cartilages;  and this
is gradually converted  into bone, in  the manner in which  those cartilages are
consolidated in the  first instance. In older animals, however, the  new struc-
ture  appears to be rather of a membranous character; and the ossifying pro-
cess would therefore correspond rather  with that by which the normal in-
crease of their bones  is effected.   Mr. Tomes states* that  he has examined
various cases of fracture of the neck  or  shaft of the femur, in which union
had  not been effected,  in consequence of  the patient's advanced age;  and that
he found in these no intervening cartilage, and but a scanty amount of con-
densed areolar tissue.   In this latter, traces of an attempt at  repair may  be
generally found, in the presence of osseous  matter in granules or granular
masses;  but in these there is no arrangement of tubes or bone-cells  of definite
character; indeed, such osseous masses are generally small, and are deficient
in density, owing to the want of union between the individual granules.      .,  ^
  208.  The Teeth are nearly allied to Bone in structure ; and in some of the ■}•?--? '
lower Vertebrata, there is an  actual continuity between the bone of the jaw, 14^-vu.v
and  the  teeth  projecting  from  it, notwithstanding that the latter form part of  £t c  I -
the dermal skeleton, whilst the former belongs to the neural or internal.   In        ,f
Man and the higher animals, however, there is an obvious difference in their K*•*•%'
structure;  as in their mode of development.  These subjects have lately re-
ceived much attention; and the practical  importance of an acquaintance with
them, renders it desirable that  they  should be here treated somewhat fully.—
The Teeth of Man, and of most of the higher animals, are composed of three
very different substances; Dentine  (known  as ivory in  the tusk of the Ele-
phant), Enamel and Cementum or  Crusta Petrosa.  These are disposed  in
various methods, according to  the purpose which the Tooth is to  serve:  in
Man, the whole of the  crown of the  tooth  is covered with Enamel;  its root or
fang is covered-with Cementum; whilst the substance or body of the tooth is
composed of Dentine.   In the molar Teeth of many Herbivorous animals,
however, the Enamel  and Cementum form  vertical plates, which alternate
with plates of Dentine, and present  their  edges at the grinding surface of the
tooth; and the unequal  wear of these substances,—the Enamel  being the
hardest, and the Cementum the softest,—occasions this surface to be always
kept rough.
              * Cyclopaedia of Anatomy and Physiology, vol. iii,  p. 857.
                                  15* 
174
ON THE ELEMENTARY PARTS OF  THE HUMAN FABIIIC.
[Fig. 69.
[Fig. 70.
  A view of an Incisor and of a Molar Tooth,
given by a longitudinal section, and showing
that the enamel is striated, and that the strise
are all turned to  the centre; the internal
structure is also seen; 1, the enamel; 2, the
ivory  : 3, the cavitas pulpi.}
   209. The Enamel is composed
an inch in  diameter, arranged side
                    [Fig. 71.
        A vertical section of an adult Bicuspid, cut from
      without inwards—magnified 4 times; 1,1, the cor-
      tical substance which surrounds the root up to the
      commencement of  the enamel; 2, 2, the ivory of
      the tooth, in which are seen the  greater parallel
      curvatures, as well as the position of the main
      tubes; 3, apex of the tooth, where the tubes are al-
      most perpendicular; 4,4, the enamel; 5, the cavity
      of the pulp, in  which are seen, by means of the
      glass, the openings of the tubes of the dental bone.]
of solid prisms or fibres,  about  l-5600th of
by side, and closely adherent to  each other;
[Fig. 72.
  A vertical section of an imperfectly developed Incisor,
taken from the follicle in which it was enclosed;  this
section is meant  to show the  position of  the enamel
fibres, and also that a part of the appearances which are
seen in this substance under a  less magnifying power,
originate in  parallel  curvatures of the fibres; 1,1, the
enamel; 2, 2, the dental bone, or ivory; 3, 3, the minute
indentations and points on the  surface of the ivory, on
which the enamel fibres rest; 4, 4, brown parallel fibres;
5, parallel flexions of the fibres of the dental bone in these
stripes ]
  A portion of the surface of the Enamel
on which the hexagonal terminations
of the fibres are shown—highly magni-
fied ; 1, 2, 3, are more strongly marked
dark crooked  crevices,—running be-
tween  the rows  of  the  hexagonal
fibres.] 
STRUCTURE OF TEETH;  ENAMEL, DENTINE.
175
their length corresponds  with the  thickness of the layer which they form;
and the two surfaces of this layer present  the ends of the  prisms, which are
usually more  or less regularly hexagonal.   The course  of these prisms  is
generally wavy; but their curves are for the most part parallel to each other.
In the perfect state, the  Enamel contains but an extremely minute quantity of
animal matter;  but if a  young tooth be examined, it  is found that, after the
[Fig. 73.
[Fig. 74.
  The Fibres of the Enamel viewed sideways
under a magnifying power of 350 times; 1,1,
the enamel fibres ;  2, 2, the transverse stripes
upon them.]
  A small portion of fig. 70 covered with turpentine
varnish, viewed under a magnifying power of 350
times; 1,2,3, are the tubes containing a powdery,
lumpy substance. They are regular, and closely un-
dulating; but the branches do not appear, because
they are penetrated by the varnish.]
calcareous matter of the  tooth has been  dissolved away by an acid, there re-
mains a set of  distinct prismatic cells, which formed (as  it were) the moulds
in which the mineral  substance was deposited.*   The Enamel  is  the  least
constant of the dental  tissues ;  being more frequently absent  than present in
the teeth of Fishes ;  being deficient in the whole order of Serpents; and form-
ing no part of the teeth of the Edentate and Cetacean Mammals.
   210. The Bentinef  consists of a  firm substance, in which  mineral  matter
largely predominates, though to a less degree than in the enamel.   It is tra-
[Fig. 75.
[Fig. 76.
  A view of the most interior portion of the main
tubes of the dental bone in an incisor of a child
two years old, close to their commencement in the
cavitas pulpi, in order to show their first division.]
  A view of the external portion of the tubes of
the same tooth, exhibiting their more minute ra-
mifications, which, for the most part, turn towards
the crown.]
versed by a vast number of very fine cylindrical branching wavy tubuli; which

  * The Author has discovered a structure precisely resembling this, in the shells of many
Mollusca.  See Annals of Natural History, December, 1843.
  ■j- A structure exactly resembling  Dentine has been found by the Author in the shell of
the Crab, especially at the tips of the claws;  and a less regular  structure of the  same kind
in the shells of many Mollusca. (Loc. cit.) 
176
ON THE ELEMENTARY PARTS OF THE  HUMAN FABRIC.
commence  at the  pulp-cavity (on whose wall their openings may be  seen),
and radiate towards the  surface.   In their  course outwards,  the tubuli  occa-
sionally divide dichotomously ; and they frequently give off minute branches,
which  again send off smaller  ones.   In some  animals, these  tubuli may be
traced  at  their extremities  into cells exactly resembling  the lacunae of  bone ;
and here  the Ivory must be considered as presenting a form of transition into
[Fig. 77.
[Fig. 78.
  A view of a small portion of a transverse section of
the crown of the Tooth seen in fig. 70, viewed under a
magnifying power of 350 times ; 1, 2, 3, are the round
openings of the tubes, with parietes of a peculiar sub-
stance ; 4, 5f6, are  the tubes cut more obliquely, in
consequence of their more external position ]
  A view of the position of the same main
tubes, in a transverse section near the root
of a bicuspid, magnified 5 diameters.  The
dark patches in this figure mark the places
in which the bone was especially white and
less transparent than in the clear interme-
diate tracts.]
[Fig. 79.
  Sections of a human incisor, showing:—
  a. Junction of dentine and enamel near the neck of the tooth,  a. Tubes of the dentine, dividing and
ending on b b, the cupped surface on which the enamel rods vertically rest.  c. Free surface of the ena-
mel.  The enamel rods are crossed by transverse lines and also by oblique dark lines.
  b. Bifurcation of the tubuli of the dentine, soon after their commencement on d the surface of the pulp-
cavity.
  c. Branching of the tubuli of the fang, and their termination in the small irregular lacunse of the " gra-
nular layer."
  In these longitudinal views of the tubuli, their cavities only, and not their walls, are visible.
  Magnified 300 diameters.] 
STRUCTURE OF TEETH; ENAMEL, DENTINE.
177
the substance next to be described.   The tubuli, in their radiating course, de-
scribe two, three, or more curvatures, appreciable by a low magnifying power;
these are termed by Prof. Owen, the "primary curvatures."   With  a higher
power, the tubes are seen to be bent, throughout  the  whole of their flexuous
course,  into  minute and  equal oblique undulations,  of which 100  may be
counted within the space  of 1-10th of an inch ; these are the " secondary cur-
vatures" of Prof.  Owen.   Both the primary and the  secondary curvatures of
one  tube are usually parallel with those of  the contiguous  tubes ; and  from
the radiating course of the tubuli,  the rows of curvatures have the  appearance
of lines running parallel  with the external  contour of the  tooth.—The dia-
meter of the  tubuli in their largest part averages about l-10,000th of an inch ;
their smallest branches are  immeasurably fine.   It is impossible that  they
can receive  blood; but it may be surmised  that, like  the canaliculi of bone,
they absorb matter from the vascular lining of the pulp-cavity, which aids in
the nutrition  of the tooth.   Although, when  once fully formed, the Tooth un-
dergoes little or no change, there is evidence that it possesses  a certain power
of repairing the effects  of disease;—a  new  layer of hard matter being some-
times thrown out on  a  surface, which  has been laid bare by  Caries.   It has
been found, too, that the  Dentine is  sometimes tinged by colouring matters
contained in  the blood.   This is most  evident, when   a  young animal is fed
upon madder, during the period of the  formation of the tooth ; but even in an
adult, some tinge will result from a prolonged  use of this  substance; and it
has been noticed that the teeth of persons, who have iong suffered from Jaun-

                  [Fig. 80.                            Fig. 81.
 Transverse sections of tubules of dentine,
showing their cavities, their walls, and the
intertubular tissue.
 a. Ordinary distance apart.              Oblique section of Dentine of human
 6. More crowded.                    tooth, highly magnified, showing the calci-
 c. Another view.                     gerous tubuli, and the outlines of the original
Human molar.—Magnified 400 diameters.]    cells.
dice, sometimes acquire a tinge of bile.   Attention has  been particularly di-
rected  by Prof. Owen, to appearances  which  he regards as  indicating the 
178
ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.
boundaries of the original cells of the dentinal pulp (§ 213) that have not been
obliterated by the process of calcification.*  These  are  particularly evident
in the teeth of the Dugong, and  of the extinct Mylodon; but they occasionally
present themselves in  the  Dentine of  Man (Fig. 81).—In certain Mammals
and Reptiles, and in a large  number of Fishes, the  Dentine is traversed  by
canals, which are prolonged into it from the central pulp-cavity, and which
are lined (like the pulp-cavity itself) by a highly-vascular membrane; and it
is then distinguished as  Vascular Dentine.   These canals are obviously ana-
logous to the  medullary or Haversian canals of  bone ; and the tubuli usually
radiate from them, rather than from  the central cavity.   In some instances,
there is no central  cavity whatever;  but the whole  tooth is  traversed by an
irregular network  of  these medullary canals, which  become continuous with
the Haversian canals of the subjacent bone.—A substance  still more  resem-
bling bone, but formed from the dentinal pulp, is found in the interior of the
teeth of certain  Reptiles  and  Mammalia,  and  occasionally in  the teeth of
Man, especially at  the later  periods  of life.  This  substance possesses not
only vascular or medullary canals, but also the  stellate lacunae and radiating
canaliculi of true bone.  It sometimes occupies the whole of the  cavity of the
pulp, and is  formed by the  ossification  of its cellular parenchyma;  but in
other cases, it forms  merely a thin shell upon  the  interior of the ordinary
Dentine.
   211.  The Cementum or Crusta Petrosa corresponds in all essential parti-
culars with  Bone; possessing its characteristic lacunae;  and being also tra-
versed by vascular medullary canals, wherever it occurs of sufficient thickness,
—as in the exterior of the tooth of the extinct Megatherium, and in the thick
plates interposed within the islands of Enamel in the teeth of Ruminants, Ro-
dents, &c.  The varieties  of microscopic structure presented by the Cemen-
tum  in different classes of animals, correspond with the modifications of the
osseous tissue, which  exist in  the skeletons of those animals respectively.
The Cementum  was  formerly supposed to be restricted  to the compound
teeth of Herbivorous  animals ;  and its  presence in the simple  teeth of Man
and the Carnivora can be shown only by the application  of the Microscope.
In the latter it forms a layer, which invests the fang, and  which  decreases in
thickness as it approaches the  crown  of the tooth;  at the time of the first
emersion of the tooth, it covers the crown  with  a very thin lamina ; but  this
is speedily worn away by use; on the other hand, its thickness around thejj
apex of the fang often undergoes a subsequent increase, especially when chro-
nic inflammation and thickening take place in the membranous contents of the]
socket.
   212.  The following are the results of the most recent  Chemical Analyses
of the component structures of Human Teeth:—t

                           Incisors of Adult  Man.
                                  Dentine.    Enamel.    Cementum.
        Organic matter     .    .     .   28-70       3-59        29-27
        Earthy matter       .     .     71-30      96-41        70-73

                                   100-00     100-00        100-00
  The proportion of these two components varies considerably in different species; thus the
organic basis of the Elephant's tusk forms as much as 43 per cent, of the whole.  It would
seem even to vary considerably in different individuals of the same species: thus in the
molar teeth of one man, Bibra found the organic matter to constitute as little as 21 per cent.,
   * See Prof. Owen's Odontography, Introduction.
  f Op.  Cit.; and Bibra's  "Chemische Untersuchungen iiber die Knochen und Ziihne."' 
COMPOSITION AND DEVELOPMENT OF TEETH.
179
whilst in another it was 28.—The following analyses afford a more particular view of the
components of each substance:—

                            Molars of Adult Man.
	Dentine.	Enamel,
Phosphate, of Lime, with traces of fiuate of lime	. 66-72	89-82
Carbonate of Lime ......	3-36	437
Phosphate of Magnesia .....	108	1-34
	0-83	0-88
		339
Fat.........	0-40	020
	10000	100-00
Incisors of Ox.		
Dentine.	Enamel.	Cement.
Phosphate of Lime, with trace of fiuate		
of lime......59-57	81-86	58-73
Carbonate of Lime . . . 7-00	9-33	7-22
Phosphate of Magnesia . . .0 99	1-20	0-99
Salts......0-91	0-93	0-82
Chondrine.....30-71	6-66	31-31
Fat ...... 0-82	0-02	0-93
100-00	100-00	100-00
  213.  The Dentine and  its  modifications, the Enamel, and the Cementum,
originate in three distinct structures;  which may be termed  respectively, the
dentinal-pulp, the enamel-pulp, and the capsule or cemental-pulp;  the whole
forming the " matrix" from which the entire tooth is evolved.—The Dentinal
pulp is always the first-developed part of the matrix ; and it makes its appear-
ance in the form of  a papilla, budding out from the free surface of a fold or
groove of the mucous membrane of the mouth.   This may be converted into
dentine, without ever becoming inclosed within a capsule; as we  see in the
Shark, whose dentition  never advances beyond this  papillary stage.   The
dentinal pulp consists of a mass of nucleated cells, imbedded in a  semi-fluid
granular blastema, and  the whole inclosed in a dense structureless  pellucid
membrane.   This substance is copiously supplied with  blood-vessels, origin-
ating in a trunk that enters the base of each papilla;  the branches ramify and
diverge in their progress through the  pulp; and at last they form a capillary
network, which terminates in loops  near the apex  of the  pulp  (Fig.  82).
These vessels are accompanied by nerves; which also have looped termina-
tions.—The following is the substance of  the account given by Prof. Owen,
of the conversion of the dentinal pulp into dentine;  based upon his observa-
tion of this process as it occurs in the foetal Shark.   The primary cells, which
are smallest at the base of the  pulp, and have large simple sub-granular nuclei,
soon fall into linear series, directed towards the periphery of the  pulp ; and
those which are nearest to  the periphery become closely aggregated, increase
in size, and present a series of important changes in their interior (Fig. 83, a).
A pellucid point appears in the centre of the nucleus ; and the latter increases
in size,  and becomes more opaque around it.   A  division  of the  nucleus  in
the course of its long axis  is next observed (b);  and in the larger  and more
elongated cells, still nearer the periphery of the pulp, a further subdivision of
the nuclei is observed, in a transverse  as well as a longitudinal direction (c, c),
the subdivisions becoming  elongated,  with their long axes vertical, or nearly
so,  to the surface of the  pulp.   The subdivided and  elongated nuclei become
attached by their extremities to  the corresponding nuclei  of  the cells in ad-
vance; and the attached extremities  become confluent (d); so that  lines or 
180          ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.

            Fig. 82-.                                     Fig. 83.
     Vessels of Dental Papilla.
files of nuclear matter are formed, which
present an unbroken  continuity from
one  primary cell  to another.   While
these changes are proceeding, the cal-
careous  salts  furnished by the blood
begin to be accumulated in the interior
of the cells, and to  be  aggregated in a
semi-transparent state around the cen-
tral granular part of the elongated  nu-
clei, which now present  the character
of rows of minute  secondary cells; and
the salts occupy, in  a still  clearer and
more compact state, the  cavity of the
primary cell not occupied by the trans-
formed nuclei.  The  rows of minute
secondary cells (which appear scarcely
to  advance  beyond  the  condition  of
simple granules) remain uncaleified in
the midst  of the solid  calcareous sub-
stance ;  and thus constitute the tubuli
of the dentine, in which  a  granular or
bead-like aspect may generally be traced.
   214. Around the tubes, in a transverse  section, is a small circular space
(Fig. 84, b,) manifestly distinct from the intertubular substance;  and this is
regarded by Professor Owen as the  indication  of a membrane surrounding
the  elongated and coalesced  secondary cells.   The  traces  of the  original
boundary  of the primary or  parent-cells (Fig. 84, a, a), are  generally  lost;
but, as already remarked  (§210) they are  sometimes  preserved  with  suffi-
cient distinctness  to be quite  recognizable.   The " primary  curvatures" ob-
servable in  the tubuli are due to the arrangement of  the original linear series
  Diagram of development of Dentine ; a, end
of a linear series of primary dentinal cells; 6,
cells with nuclei dividing; c, subdivision and
elongation of nuclear matter; d, elongated
nuclei uniting to form the arese of dentinal
tubes; e, e, calcified cap of dentine, formed by
the intus-susception  of the clear hardening
salts into the walls and cavities of the cells
and intercellular blastema £, e, and  by their
partial exclusion from the moniliform nuclear
tracts/' /'; g, union of two peripheral nucle-
olar or secondary cells with one nearer the
centre of the pulp. 
DEVELOPMENT OF DENTINE.
181
  Inner surface of portion of calcified dentinal pulp,
forming cap of dentine; a, intervals and walls of pri-
mary dentinal cells; b, walls of dentinal tubes ; c, nu-
clear matter, establishing areas of dentinal tubes.
For clearer demonstration, the number of tubes in
the area of each cell is made less than in nature.
of  parent  cells;  whilst  the " se-
condary curvatures" are accounted for
by  the  fact, that the elongated nuclei
usually unite  with each  other at ob-
tuse angles, and not in perfectly straight
lines, (Fig. 83, d.)—Thus we are to
regard the Dentine as composed of the
original cells of the pulp, which have
become consolidated by the calcifying
process, in every part save that which
is occupied by the rows of granules
or incipient cells,  developed from the
metamorphosed nuclei.   The calca-
reous matter appears to be chemically
united,  as in  Bone,  with an  animal
base;  the cavity  of each  cell being
pervaded by both; so that, when the
whole of the calcareous  matter is re-
moved  by dilute acid, a cartilaginous-
looking mass remains, which preserves
the form of the tooth.   The calcifying process takes place first on the exterior
of the pulp, and gradually extends inwards ; and the capillary blood-vessels alto-
gether  retreat from the calcifying portion, and form their terminal loops upon
the surface of  the part which  still remains unconsolidated.   As the  calcifica-
tion extends  inwards,  the pulp,  of course, progressively decreases ; fewer
nuclei are formed in the cells ; and these do  not acquire so large a size.  Here
and there it is seen, that the  inner extremities of two of  the granular tracts,
in the part last calcified,  converge, and connect themselves with a single tract
in the layer nearer the  centre of the pulp, (Fig. 83, g); in which we see the
origin of the  bifurcation of the  tubuli.  This bifurcation  becomes more fre-
quent, as the  calcifying process approximates towards the  centre and base of
the pulp ;  and it is thus that the main tubes are formed.  In some of  the cells,
at and  near the central and basal part of the pulp, the nucleus undergoes no
division ; but it merely elongates, and sometimes becomes angular or radiated,
—thus  showing  a form  of transition to the stellate nucleus of  the bone-cells.
As  already stated, we  occasionally find modifications of  the dentine in this
situation, which closely resemble  true bone  in structure.
  215.   The Enamel-pulp is  not formed  until after the  dental papilla has
become inclosed in a capsule, by the process to be presently described (§  217,
c).   It  differs  from the dentinal pulp, at its first formation, in the more  fluid
state of its blastema; and in  containing fewer and more minute cells.   The
enamel-pulp is derived from the free inner surface of the capsule;  of which
we may regard its cells  as the epithelium.   The cells are  largest and most
numerous in that portion of the pulp which most  nearly approaches the den-
tal  papilla; and many  of them show a nuclear spot (Fig. 85, h, h).   In the
portion of the enamel-pulp most distant from the capsule, the cells, at first
spherical, become  impacted against one another, and are pressed into hexago-
nal or polygonal forms (i, i); the fluid blastema being now almost excluded from
between them.  In the part in closest contiguity with the  surface of the  den-
tinal pulp, the cells increase in length, either by the elongation of each indi-
vidual cell, or by the coalescence of several (j); the nuclei (A;) disappear ; and
the cells, now  forming long prisms (/), absorb into themselves calcareous salts,
which henceforth  completely fill them, in a clear and crystalline form.  These
salts would not seem to be united, as in bone and dentine, with any organic
matters; the small quantity of this existing in Enamel, being probably em-
     16 
182          ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.
Fig. 85.
Fig. 86.
I^^H

  Formation of the Cementum ; m, primary cells; p, their
granular nuclei; n, more minutely granular blastema; o, the
primary cell enlarged, and receiving the hardening salts; n'>
calcified blastema; p',p', stellate nuclei of fully-formed ce-
mental cells.
                              ployed wholly in forming the walls of the pris-
                              matic cells.  The disappearance of the nucleus,
                              previously to  the  calcification of the cell, is
                              evidently the reason of  the absence  of any
                              permanent space or tube in its interior unoccu-
                              pied by mineral matter.   The islands of  Ena-
                              mel, which are found in the midst of the dentine,
                              in the compound teeth of  Herbivorous animals,
                              are formed  from extensions of the  same ena-
                              mel-pulp, with that which gives  origin to the
                              general envelope of  the tooth (§ 217, c).
                                 216. The "Cemental  pulp,"  or  matrix of
                              the Crusta Petrosa, is in fact nothing else than
                              the capsule  itself; in which, at an early period,
                              nucleated  cells  are  found,  distributed  in the
                              midst of a  granular  blastema, which  is  copi-
                              ously supplied  by  vessels.   The process of
                              calcification  begins  in  the portion nearest the
                              dentine;  and  consists,  as  elsewhere,  in the
                              absorption of  calcareous  matter  into the cavi-
                              ties of the cells, in the more close aggregation
of the cells with each other, and in the  changes which take place coincidently
in their nuclei.   These,  which  are at first  large  granular spots of a rounded
form, send out radiating  prolongations, which  extend quite to the  borders of
the cell; and as the calcareous  salts which  penetrate the  cell, are not  depo-
sited in the space occupied by the nuclei,  the  stellate cavities, or lacunae and
diverging canaliculi, are  left, which are so analogous to  those of bone, as to
serve to identify the two tissues.   In the cementum, as  in  Bone and Dentine,
the consolidating substance  appears to  consist  of mineral and organic  matter
in a state of chemical  union.    The boundaries of the original cells usually
disappear in this, as in similar  cases ; so  that nothing remains in the fully-
formed cementum, to  mark its cellular origin,  save  the stellate  lacunee which
represent the positions of the formerly-existing nuclei.
 Formation of Enamel; h, primary
cells suspended in fluid blastemag;
i, the same more fully developed and
become  angular; j, the same be-
coming  prismatic; k,  the nucleus
disappearing; I, the modified pris-
matic cells, filled with calcareous
salts, forming the spicula and fibres
of enamel. 
DEVELOPMENT  OF THE TEETH.
183
   217.  As it is of much practical importance  to understand the origin of the
several kinds of  Human Teeth, and the  times of their  appearance, some de-
tails upon these subjects will be given ;  those which relate to the mode of de-
velopment being principally derived from the researches of  Mr. J.  Goodsir.*

  o. At the sixth  week of Foetal life, a deep narrow groove may be perceived, in the upper
jaw of the Human  embryo, between the lip and the  rudimentary palate; this is speedily
divided into two by a ridge, which afterwards becomes  the external alveolar process; and
it is in the inner groove, that the germs of the teeth subsequently appear.  Hence this may
be  termed the primitive dental groove.   At about the  seventh week, an ovoidal papilla,
consisting of a granular substance, makes its appearance on the  floor of the groove, near
its  posterior termination; this papilla  is the germ of the  Anterior  superior Milk  Molar
tooth.  About the eighth week, a similar papilla, which is  the germ of  the Canine tooth,
arises in front of  this; and during the ninth week the germs of the Incisors make their ap-
pearance under the same form.  During the tenth week, processes from the sides of the
dental groove, particularly the  external one, approach each other, and finally meet  before
and behind the papilla of the  anterior  Molar; so as to  inclose it in a follicle, through the
mouth of which it may be seen.  By a similar process, the
other teeth are gradually inclosed in corresponding follicles.
The germ of the  Posterior milk Molar  also appears during
the tenth week, as a small papilla.   By the thirteenth week,
the follicle of the Posterior Molar is completed;  and the
several papilla? undergo  a gradual change of form.   Instead
of remaining, as hitherto, simple, rounded, blunt masses  of
granular matter, each of them  assumes a particular shape;
the Incisors acquire in some degree  the form of the future
teeth; the Canines  become simple cones; and the Molars
become cones flattened  transversely, somewhat similar  to
carnivorous molars.   During this period, the papillae grow
faster than the follicles;  so that the former protrude from
the mouth of the  latter.   At this  time, the mouths of the
follicles undergo a change, consisting in the development  of
their edges, so as to form  Opercula; which  correspond  in
some measure with the  shape of the crowns of the future
teeth.  There are two of these opercula in the Incisive  follicles, three for the Canines, and
Fig. 87.
  Upper jaw' of human embryo
at 6th week ; showing b, the primi-
tive Dental Groove, behind a, the
Lip.
[  Diagrams illustrative of the formation of a Temporary, and its corresponding Permanent Tooth, from
                                 a Mucous Membrane.

four or five for the Molars.  At the fourteenth week, the inner lip of the dental groove has
increased so much, as to meet and  apply itself in a valvular  manner to the outer lip or

                        * Edin. Med. and Surg. Journal, vol.  Ii. 
184           ON THE ELEMENTARY PARTS OF  THE HUMAN FABRIC.

ridge, which has been also increasing.  The follicles at  this time grow faster than the pa-
pilla?, so that the latter recede into the former.  The primitive dental groove then contains
ten papilla?, inclosed in as many follicles;  and  thus  all necessary provision is made for the
production of the first set of teeth.   (This  series of changes is represented in Fig. 88,  a—g.)
The groove is now situated, however, on a higher level than at first;  and it has undergone
such a change by the  closure of its edges, as  to  entitle  it to the distinctive appellation of
secondary dental groove.  It is in this secondary groove that those structures originate,  which
are destined for  the  development of the   Second  or Permanent set of Teeth,—of those at
least which replace the Milk Teeth.  This is accomplished in the following manner.
   b. At about the fourteenth ox fifteenth week, a little crescentic depression may be observed,
immediately behind the inner  Opercula of each  of the' Milk-tooth  follicles.  This depres-
sion gradually becomes  deeper, and constitutes what maybe  termed a  cavity of reserve;
adapted to furnish delicate mucous membrane, for the future formation of the sacs and pulps
of the ten  anterior Permanent teeth.  These  cavities of reserve  are gradually separated
from the secondary dental groove, by the adhesion  of their edges; and they thus become
minute  compressed sacs, situated between the surface of  the  gum and the milk-sacs.   They
gradually recede, however, from the surface of  the gum,  so as to be posterior instead of in-
ferior to the milk sacs; and at last they imbed themselves in the submucous cellular tissue,
which has all along constituted the external layer of the  milk-sac.  The implantation of the
Permanent tooth-sacs in the walls of the Temporary follicles, gives to the former the appear-
ance of being produced by a gemmiparous process from the latter.   This series of changes
is represented in Fig. 88, g—n.
   c. We now return to the Milk-teeth, the papillae  of which, from the time that their follicles
close, become gradually moulded into their peculiarly Human  shape.  The Molar pulps be-
gin to be perforated by three canals, which, proceeding from the surface  towards the centre,
gradually divide  their primary bases into three secondary bases; and these become  deve-
loped into  the fangs of the future teeth.  Whilst this is going on, the sacs grow  more rapidly
than the papillae, so that there is an intervening space, which is filled with a gelatinous gra-
nular substance—the enamel blastema; this closely applies itself to the surface of the  pa-
pilla, but does not adhere to it.  The branch  of  the dental artery which proceeds to each
sac, ramifies minutely in  its proper membrane, but does not send the  smallest twig into the
granular substance.   At this period, the tubercles and apices of the papillae or pulps become
converted into real dentine or tooth-substance, in the manner already stated (§ 213) ; and the
granular matter is absorbed as fast as this  appears; so that, when the process of conversion
has reached the base of the pulp, the interior of the  dental sac is left in the villous and vas-
cular condition of a true Mucous membrane, having upon it a very thin layer of the granular
substance,  or enamel-pulp, which may be considered as  a sort of Epithelium ; and it is by
the deposition of calcareous matter in the long  prismatic cells of this, that the enamel is

                                         Fig. 89.
  Diagrams illustrative of the formation of the three Permanent Molar teeth, from the non-adherent
                             portion of the Dental Groove.

formed.  The opercula, which close the mouth of the dental sac, attain a much greater  de-
velopment in the Molar teeth of Herbivorous animals; where they dip down into the midst
of the dentinal pulp, and give origin to insulated spots both of  enamel  and  cementum.  It
has been remarked by Mr. Lintott, that  the lines along which the opercula  meet, on  the 
                           DEVELOPMENT OF THE TEETH.                       185

 crown of the Human molar teeth,—that is to say, the groove which separates their tubercles,
 —is by far the most frequent seat of incipient  decay; probably from its tissue having been
 at the first less perfectly formed than that of the remainder.
   d.  Whilst these changes are going on, other important preparations are being made for the
 Permanent set.   The general adhesion of the edges of the Primitive Dental Groove, (§ a)
 does  not invade the portion which is situated behind the Posterior Milk follicle; this retains
 its original appearance for a fortnight or three weeks longer, and affords a nidus for the de-
 velopment of the papilla and follicle of the Anterior  Permanent Molar tooth, which is de-
 veloped in all respects on  the same plan with  the Milk teeth.   After its follicle has closed,
 the edges of the dental groove meet over its mouth; but as the walls of the groove do not
 adhere, a  considerable cavity is left between the  sac of the tooth and the surface of the
 gum.  The cavity is  a reserve of delicate  mucous  membrane, to afford materials for the
 formation  of the Second Permanent Molar, and of the Third Permanent Molar, or Wisdom-
 tooth.  The process just described is represented in Fig. 89, a—c.   It will  be convenient
 here to continue the account of the development of these teeth, although it takes place at a
 much later period.  Towards the end of foetal life, the increase of the bulk of the Milk-tooth
 sacs takes place so much more rapidly than the growth of the jaw, that the sac of the An-
 terior Permanent Molar is  forced  backwards  and upwards, into the maxillary tuberosity;
 and thus it not only draws the surface of the gum in  the  same direction, but lengthens out
 the great cavity of reserve (Fig. 99, d).  During the few months which  succeed birth, how-
 ever, the  jaw is greatly lengthened; and when the infant is eight or nine  months old, the
 Anterior Permanent Molar resumes its former position in the posterior part of the dental
 arch; and the great cavity of reserve returns to  its original size and situation (c).  This
 cavity, however, soon begins to bulge out at its posterior side, and projects itself,  as a sac, into
 the maxillary tuberosity (/) ; a papilla or pulp appears in its fundus; and a process of con-
 traction separates  it from the remainder of the cavity of reserve.  Thus the formation of
 the Second Permanent Molar from the first, takes place on precisely the same plan with the
 formation  of the Permanent Bicuspids  from the Temporary Molars.   The new sac at first
 occupies the maxillary tuberosity (g) ; but the lengthening of the jaw gradually allows it to
 fall downwards and forwards, into the  same line, and on a level, with the rest (ft).  Before
 it leaves the tuberosity altogether, the posterior extremity of the remainder of the cavity of
 reserve sends backwards and upwards its last offset—the sac and pulp of the Wisdom-tooth
 (i);  this speedily occupies the tuberosity after the second molar has  left it (_/);  and ulti-
 mately, when the jaw lengthens for the last time, at the age of nineteen or twenty, it takes
'its place at the posterior extremity of the range of the adult teeth (k).   Thus, the Wisdom-
 teeth are the second products of the posterior or great cavities of reserve; and the final effects
 of development in the secondary dental groove.   In the Elephant, in which there is a con-
 tinual new production of molar  teeth at the back of the  jaw, it is probable that from  each
 sac a cavity of reserve is formed, which  produces the  succeeding tooth; and thus the only
 essential difference between its dentition and that of Man, consists in the degree of continu-
 ance of this gemmiparous process;  which ceases in Man, after being twice  performed, but
 is repeated in the Elephant until nearly the close of its life.
   e. We have thus  sketched the history of the Development of the Teeth,  up to the  time
 when they prepare to make their way through the gum.  The first stage of this  development
 may  be termed the papillary ; and the second the follicular.  The latter terminates when the
 papillae are completely hidden by the closure of the mouths of the follicles, and of the groove
 itself.  The succeeding stage, which has long been known as the saccular, is the one during
 which the whole formation of the  Tooth-substance, and of the Enamel, takes place.   It is
 during this period, also, that the ossification  of the jaw is being effected; and that the bony
 sockets are formed  for the teeth, by the consolidation of the anterior  and posterior ridges
 bounding the alveolar groove  (in which the dental groove was originally imbedded), and of
 the interfollicular septa, which are produced by the meeting of transverse projections from
 these ridges.'—The  history of development in the Lower Jaw is very nearly the same; the
 chief difference being in the origin and situation of  the primitive dental groove.
   /.  We have now only to consider the fourth or eruptive stage,—that in which the Teeth
 make their way through the gum.   This  process chiefly results from the lengthening of the
 fang, by the addition of new  bony matter; and the crown of the tooth is thus made to press
 against the closed mouth of the sac (Fig. 98, m).   This at last gives way, so that the sac as-
 sumes its previous condition of an open follicle.   When the edge of the tooth has once made
 its way through the gum, it advances more rapidly than can well be accounted for by the
 usual rate of lengthening of its  fang; and  this appears to be due to the separation of the
 bottom of the sac from the fundus of the alveolus; so that the whole tooth-apparatus is car-
 ried nearer to the surface, leaving a space at the bottom of the alveolar cavity, in which the
 further lengthening of the root can take place (n).   The open portion of the sac remains as
 the narrow portion of the gum, which  forms a vascular border and groove round  the  neck
 of the perfected tooth (o).  The deeper portion of the sac adheres to the fang of the  tooth,
                                          16* 
186           ON THE ELEMENTARY PARTS OF  THE HUMAN FABRIC.

and  is converted by ossification into the Cementum or Crusta Petrosa (§216).  What is
commonly denominated the Periosteum of the Tooth, really belongs as much to the Alveolus.
It is connected with the tooth by the submucous cellular  tissue, which originally intervened
between the tooth-sac and the walls of the osseous cavity.  It appears from Mr. Nasmyth's
researches, that the inner layer of the portion  of the capsule which covered the crown of
the tooth, remains adherent to it;  forming a  thin coating of Crusta Petrosa (most  of which
is, however, soon worn off) over the Enamel.—During the period that the Milk-teeth  have
been advancing, along with their sockets, to their perfect state and ultimate position, the Per-
manent sacs have been receding in an opposite direction, and have widi their  bony crypts
been enlarging; and at last they occupy a position almost exactly below the former (« and o).
They still retain a communication with the gum, however; the channel by which they  de-
scended  not having completely closed up, and the  neck of the sac  being elongated into a
cord which passes through this.   The channels may afterwards serve as the itinera dentium,
and the cords as gubernacula ;  but it is uncertain whether they really afford any assistance in
directing the future rise of the tooth to the surface ; the successive stages of which  are repre-
sented in Fig.  98,7>—t.   The sacs of the permanent  teeth derive their first vessels from the
gums ; ultimately they receive their proper dental vessels from the Milk-sacs;  and, as they
separate from  the latter into their  own cells,  the newly-formed vessels, conjoining into com-
mon trunks, also retire into permanent dental canals, and gradually become the  most direct
channels for the blood transmitted through the  jaw.
   g. The following interesting generalizations respecting the development of the teeth, result
from Mr. Goodsirs researches.  1. The .MZ&-teeth  are formed on both sides of either jaw
in three divisions,—a Molar, a Canine, and  an Incisive; in  each of which, dentition pro-
ceeds  in  an independent  manner.   2. The dentition of the whole  arch proceeds  from
behind forwards;  the  Molar division commencing before the  Canine, and  the  Canine
before the Incisive.  3. The dentition of each of the  divisions proceeds in a contrary direc-
tion, the Anterior Molar appearing before the Posterior, the  Central Incisor before  the La-
teral.  4. Two of the subordinate phenomena of nutrition also obey this inverse  law;—
the follicles closing by commencing at the  median line and proceeding backwards; and the
dental groove  disappearing in the  same direction.   5. Dentition commences in the Upper
Jaw, and continues in  advance  during the most  important period of its progress.  The
development of the Superior Incisors, however, is retarded by a peculiar cause; so that the
Inferior Incisors have the priority in the time of their completion and appearance.  6. The
germs of the Permanent teeth, with the exception of that of the Anterior Molar, appear in a
direction from the median line backwards.   7. The Milk-teeth originate, or are developed,
from mucous membrane.  8. The Permanent teeth, also  originating from mucous membrane,
are of independent origin, and  have no connection with the milk-teeth.  9.  A tooth-pulp
and its sac must be referred to the same class of organs, as the combined Papilla  and  Folli-
cle from which a hair or feather is developed.
   h. The following is the usual order and period of appearance, of the several pairs of Milk-
teeth.   The Four Central Incisors first present themselves, usually about the seventh month
after birth; but frequently much  earlier or  later:  those of  the Lower Jaw  appear first.
The Lateral Incisors next show themselves, those of the Lower Jaw coming through before
those of the upper; they usually make their appearance between the seventh and tenth months.
After a short  interval, the Anterior  Molars  present themselves.—generally soon after  the
commencement of the Second Year ; and these are followed by the  Canines, which usually
protrude themselves between the fourteenth and twentieth months.  The Posterior Molars are
the last, and the most uncertain  in regard to their  time of appearance; this  varying from
the eighteenth to the thirty-sixth month.  In regard to all except  the front teeth, there  is no
settled rule as to the priority of appearance  of those  in  the  Upper or Under  Jaw; some-
times one precedes, and sometimes the other;  but in general it may be stated, that, when-
ever one makes its appearance, the other cannot be  far  off.   The  same holds good in re-
gard to the two sides, in which development does not always proceed exactly pari passu.—
The period of Dentition is one of considerable risk  to the Infanfs life.  The pressure upon
the nerves of  the  gum, which necessarily precedes the opening of the sac and the eruption
of the tooth, is a fruitful source of irritation; producing disorder of the  whole  system, espe-
cially  of the Digestive organs, and not unfrequently giving origin to fatal Convulsive  affec-
tions.  These  last have been particularly studied by Dr.  M. Hall, who recommends the free
use of the gum-lancet, as a most  important means  of prevention  and  cure.   Even where
Dentition proceeds quite naturally and is not itself a cause of diseased action, it induces  an
irritable state of the whole constitution, which aggravates the effects of other morbific causes.
It is, therefore, of the greatest consequence that the  infant should be withdrawn during this
period, from all injurious influences ; and that  no  irregularity of diet, or deficiency of fresh
air and exercise, should operate to its disadvantage.
   i. After the lapse of a few years, the. further elongation of the jaw permits the appear-
ance of the  First True Molar; which, as already remarked, is really a Milk-tooth, so far as
its formation is concerned.  This commonly  presents itself about the middle or end of the 
DEVELOPMENT OF THE  TEETH.
187
Seventh Year;  sometimes preceding, and sometimes following, the exchange of the Central
Incisors, which takes place about the  same time.  When the Permanent  Teeth have so
much enlarged, that they can no longer be contained within their own alveoli, they press
upon the anterior parietes of those cavities, and  cause their absorption; so that each tooth
is allowed to come forwards, in some  degree, into the lower part of the socket of the  cor-
responding Temporary tooth.   The root of the temporary tooth now begins to  be  absorbed,
generally  at the part nearest its successor; and this absorption proceeds as the new tooth
advances, until the root of the Milk-tooth is complete.ly removed:  when its  crown falls off,
leaving room for the permanent tooth  to supply its place (Fig. 88, p—t).   This absorption
is usually regarded as due to the pressure of the Permanent tooth, but  this  does not appear
to be the case; for it is mentioned by Mr. Bell, that it is not an uncommon occurrence for
the  root of the temporary tooth to be wholly absorbed, and for the crown to fall out spon-
taneously, long before the succeeding tooth has approached the vacant space.  The same
has been remarked by. Mr. Bell, of the cavity in the jaw which is formed for the  reception
of the sac of the Permanent tooth, at the time that it buds off from that of the milk-tooth;
the excavation being often seen to commence before the new sac is formed.  Hence, although
the two processes, growth, and absorption, are usually contemporaneous in each  instance,
they are by no means dependent on each other.   Still it would seem that the existence, if
not the pressure of the new Tooth is necessary  to determine the absorption of the old ; for
cases are not unfrequent, in which the Temporary teeth retain their situation in the mouth,
with considerable  firmness,  until adult age,—the corresponding permanent ones not having
been formed.
  k. In the successive replacement of the Milk-teeth by the Permanent set, a  very regular  -f-
order is usually followed.  The Middle  Inciso'rs are first shed and renewed, and  then the
Lateral Incisors.  The Anterior Milk Molars next follow ; and these are replaced by the An-
terior Bicuspid teeth.   About a year afterwards, the Posterior Milk Molars are shed, and are
replaced in like manner  by Bicuspid teeth.  The Canines are the last of the Milk-teeth  to
be exchanged; the development of the new ones not taking place until the 12th year.  In ■
the succeeding year, the Second pair of the True Molars appears; the third pair, or dentes
sapientice, are seldom developed  until three  or  four  years  subsequently,  and often  much
longer. It has been recently proposed* (and, from the evidence adduced in its favour, the
proposition would seem entitled to considerable  attention) to adopt the successive  stages in
the Second Dentition, as standards  for estimating the physical  capabilities of  Children, es-
pecially in regard to those two periods which the  Factory Laws render  it of the greatest
importance to determine, namely, the ages of nine and thirteen years.   Previously to the for-
mer, a child  is  not permitted to work at  all;  and up to the  latter, it may be only employed '
during 9 hours a day.  The necessities or the cupidity of Parents are continually inducing
them to misrepresent the ages of their children; and it has been  found desirable,  therefore,
to seek for some  test, by which the  capability of the Child may be determined, without a
knowledge of its age.  A standard of Height has been adopted  by the Legislature for this
purpose;  but upon grounds which, Physiologically considered, are very erroneous ; since, as is
well known, the tallest children are frequently the weakliest.  According  to Mr.  Saunders,
the degree of advance of the Second Dentition may be regarded as a much more  correct
standard of the degree of gencjral development of the organic frame, and of its physical
powers; and it appears  from his inquiries, that it may be relied  on as a guide to the  real
age, in a large proportion of cases; whilst no serious or injurious mistake can ever  arise
from its use.  It may happen that  local or constitutional causes  may have  slightly retarded
the development of the Teeth; in  which case  the age of the individual  would  rather be
under-estimated, and no  harm could ensue: on the other hand, instances of premature de-
velopment of the  Teeth very rarely, if ever,  occur :  so that there is no danger of imputing
to a Child a capability for exertion which he does not possess, as  the  test of height is con-
tinually doing.   Moreover, if such an advance in Dentition should occur, it might probably
be regarded as indicative of a corresponding advance in the development  of the whole or-
ganism ; so that the real capability would be such as the teeth represent it.
   /. The  following is Mr. Saunders' statement of tiie Ages at which the Permanent teeth
respectively appear.  The first True Molars usually make their appearance towards the end
of the 7th year.  Occasionally one of them protrudes from the gum at  6, or more frequently
at 6^ years of age; but  the evolution of the whole of them may be regarded as  an almost
infallible  sign of the Child's being 7 years old.   In other instances, however, where the tooth
on one side of the mouth is freely developed, it is fair to reckon the two as having emerged
from their capsule ; since the development of the other must be considered as retarded.  This
rule only holds good, however, in  regard to teeth in the same row; for the development of
the teeth  in either jaw must not be inferred from that of the corresponding  teeth in the other.

   * " The Teeth a Test of Age, considered with reference to the Factory Children."  By
Edwin Saunders. 
188           ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.
With this understanding, the results of the application of the following table will probably
be very near the truth.

            Central Incisors developed at
            Lateral Incisors
            First Bicuspid       . #
            Second Bicuspid
            Canines    ....
            Second Molars

The following  are the results  of the application  of this test,  in a large  number of cases
examined by Mr. Saunders.  Of 708 children of nine years old, 530 would have been pro-
nounced by it to be near the completion of their ninth year; having the central, and either
three or four lateral, incisors fully developed.  Out of the remaining 178, it would have in-
dicated that 126 were 8$  years old, as they presented one or  two of the  Lateral Incisors;
and the 52 others would have been pronounced 8 years old, all having three or four of the
Central Incisors.  So that the extreme deviation is only 12  months ; and this in the incon-
siderable proportion (when compared with the results obtained by other means) of 52 in 708,
or 1\ per cent.   Again, out of 338 children of  13 years of age, 294 might have been pro-
nounced with confidence to be of that age, having the Canines, Bicuspid, and Second Molars,
either entirely developed, or with only the deficiency of one or  two of either class.  Of the
44 others, 36 would have been considered as in their 13th year, having one of the Posterior
Molars developed ;  and 8  as  near the completion of the 12th, having two of the  Canines,
and one or two of the Second Bicuspid.   In a41 these instances, the error is on the favourable
side,—that  is, on the side  on which it is calculated  to prevent injury to the objects of the
inquiry; in no instance did this test cause a Child to be estimated as older or  more fit for
labour than it really  was.
  m. The value of this test, as compared with that of Height, is  manifested  by a striking ex-
ample adduced by Mr. Saunders.  The height of one lad, J. J., aged 8 years and 4  months,
was 4 feet and % of an inch ;  that of another boy, aged  8 years and 7 months, was only 3
feet 7£ inches.   According to the standard of height  adopted by the Factory Commissioners
(namely, 3  feet 10 inches), the  taller lad would have been judged fit for labour, whilst the
shorter would have been rejected.  The  Dentition of the latter, however, was further ad-
vanced than that of the former; for he had two of the Lateral Incisors, whilst the former
had only the Central; and  the determination of their  relative physical powers, which would
have been thus formed, would have been in complete accordance with the truth. The elder
boy, though  shorter  than  the  other by  5$  inches, possessed a much greater degree both of
corporeal and mental  energy, and his  pulse was strong and  regular; whilst that of the
younger lad, who was evidently growing too  fast, was  small  and frequent.—An instance
even more striking has come under the Author's own observation.


                         10. Simple Tubular Tissues.

   218.  We have seen that all the Animal Tissues*, whose structure has been
yet considered, derive the materials  of their growth  and renovation from the
nutrient  fluid; which  is  brought  into a more or less close relation with their
elementary parts, by means of Capillary blood-vessels.   These seem to have
a claim to be regarded  as among the elementary parts  of the fabric;  since they
are formed quite independently of the larger  trunks, and have little in common
with them in  their  function.  All those changes which  take place between
the blood and  the surrounding parts, whether ministering to  the functions of
Nutrition, Secretion, or Respiration, occur  during its movement through the
Capillary vessels: and the function of the larger trunks is merely  to bring to
them a constant  supply of fresh blood, regulated according to the demand
created  by the actions to  which  it  is  subservient;  and to "remove the fluid
which  has circulated through them.   When we examine into  the structure of
the Circulating apparatus  in Plants  and in the lower Animals, we find that
the canals, which convey the nutritive fluid, are  of two kinds ;—either simple
excavations in the solid tissues or unfilled vacuities  ;—or tubes with definite
membranous  walls.   The former are  known, in  Plants, under the name of
inter-cellular passages ;  and, among the lower  tribes in particular, they have
 a large share in the  conveyance of  the nutritious fluid from one  part of the
 8 years.
 9  —
10  —
11  —
12  to 12$
12$ to  14 
STRUCTURE OF CAPILLARY BLOOD-VESSELS.              189
structure to the other.  Similar passages exist to a great extent among the In-
vertebrata ;  the  venous circulation in particular being mainly carried on by
them.   We have an example of them, even in Man, in the Sinuses through
which the venous blood is returned from the Brain ; these sinuses being simple
passages formed by the folds of the Dura Mater. In the higher Plants, however,
the circulation of fluid is for the most part carried on through Ducts, having
distinct membranous parietes;  and these  ducts  may be  either  straight and
simple tubes, as are those of the interior of  the stem through which the sap
ascends;  or they may form a network by their mutual anastomosis, such as
that by which the sa,p descends through the bark and newer wood.  Both of
these forms of  ducts appear to be formed by the coalescence of cells ; the
straight cylindrical ducts  being  formed from cells, arranged in a simple linear
manner; and  the network of vessels for  the descent of the elaborated sap,
being produced by the junction, at various points, of cells of less regular form,
which stretch  out to meet each  other.
   219. In all the higher Animals,—in their adult  condition at  least,—the
Capillary circulation is entirely carried on through tubes having distinct mem-
branous parietes.  These tubes commonly form a minutely-anastomosing net-
work ;  into which the blood is  brought by  the ramifications of the arteries on
one side, and  from which  it is returned by the radicles of the veins on the other.
The  walls  of the tubes  are  composed of a  delicate membrane, in which an
appearance of transverse  striation (as if produced by minute annular fibres)
can sometimes  be discerned.   The diameter of the  Capillaries varies  in dif-
ferent animals,  in accordance  with that of their  blood-corpuscles; thus the

                                  Fig. 90.
Capillary circulation in a portion of the web of a Frog's foot, magnified 110 diameters; 1, trunk of
                      vein ; 2, 2, its branches ; 3, 3, pigment cells.

Capillaries of the Frog  are  of  course much larger than those of Man.   The
diameter of the  latter appears, from the measurements of  Weber, Muller, and
others, to vary from about  the  1-3700th to the 1-2500th of an inch ,- but as
they can only be examined after death, it is probable that these statements are 
190          ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.

not altogether  exact, particularly as  tubes of the smallest of the above sizes
would not admit ordinary blood-corpuscles.  The dimensions of the individual
vessels, indeed, are  by no means  constant;  as  may be seen by watching the
Circulation in  any transparent part, for some little time.  Putting aside the
general  changes, in diameter, which result from  circumstances affecting all the
capillaries  of a part, it may be  observed that a single capillary will sometimes
enlarge  or contract  by itself without any obvious cause.   Thus, the stream
of blood will sometimes be seen to run into passages, which were not before
perceived; and it has hence been supposed that they were new excavations,
formed by the retreating or removal of the solid tissue through which it passes.
But  a more  attentive examination shows, that such passages are real capilla-
ries, which did not, at the time  of the first observation, admit the stream of
blood-corpuscles, in  consequence of the  contraction of their calibre, or of some
other local impediment;  and  that they are  brought into view by the simple
increase in their  diameter.   The compression of one  of the small arteries
will  generally occasion an oscillation of the corpuscles of blood in the small-
est capillaries,  which will be followed by the disappearance of some of them;
but when the obstruction is removed, the blood soon regains its former velocity
and force, and  flows exactly into  the same passages  as before.
   220.  The opinion was long entertained, that there are vessels adapted to sup-
ply the white  or  colourless tissues; carrying from  the  arteries the  Liquor
Sanguinis,  or fluid portion of  the blood;  and leaving the Corpuscles behind,
through  inability to  receive  them.   But such a supposition  is altogether
groundless.  Some  of the white tissues, as  Cartilage, are altogether destitute
of vessels ; and in others, the  supply of blood is so scanty,  as not to commu-
nicate to them  any decided hue.   It is  evident  from what has  been already
stated, that the  idea  that Nutrition can only be carried on by means of Capil-
lary  vessels, is entirely gratuitous.  There is no essential difference, in fact,
between the nutrition of the non-vascular tissues, and that of the islets in the
midst of the network of capillary vessels, which traverses the  most vascular.

                                  Fig. 91.
  Capillary vessels from the pia mater; a, calibre of the tube, partly occupied by oval nuclei, alter-
nately arranged lengthways, and epithelial in their character;  6, 6, 6, nuclei projecting on the exterior
of the tube; c, c, walls, and d, calibre, of a large branch; /,/, oval nuclei, arranged transversely. Mag-
nified 410 diameters. 
FORMATION OF CAPILLARY BLOOD-VESSELS.              191
In both cases, the nutrient materials  conveyed by the blood are absorbed by
the cells or  other  elementary parts of the tissue immediately adjoining  the
vessels, and are imparted by them to others which are further removed ; and
the only variation which exists, is in the amount of the portion of tissue that
has  to be  thus traversed.   There is  great variety in this  respect, as  we
have seen, among the vascular tissues;  and we are  only required to  extend
our ideas, from  the largest of the  islets which we  find  in these, to the still
more isolated structures, of which  the  non-vascular tissues  are  composed.
The distribution of Capillaries through the vascular tissues, and the character
of the reticulation which  they form, vary so greatly in the different parts of
the fabric,  that it is possible to state with tolerable certainty the nature of the
part from  which any specimen  has been detached,—whether  a portion of
skin, mucous membrane, serous  membrane,  muscle,  nerve, fat, areolar tissue,
gland, &c.   But the arrangement  of vessels peculiar to  each evidently  has
reference only  to the convenience of the distribution  of blood among  the
elementary parts of the  tissue, and varies  with their  form.   It is not possible
to imagine that  it has any  other relation  than  this to  their function;  since, as
already shown,  the function of each separate element of the organ, of which
that of the entire  organ is the aggregate, is due to its own  inherent  vital
powers,—the supply of blood being only  required as furnishing the material,
on which these  are to be exercised.
   221. It  has been rendered highly probable, by the  observations of Schwann
and other Physiologists, that the Capillaries  of Animals originate in cells, like
the straight and anastomosing Ducts of Plants.   Bodies  having  the appear-
ance of cell-nuclei may frequently be seen in the walls of the capillaries of
embryos and of tadpoles ; and these are too wide apart to warrant the idea, that
they are the nuclei of  epithelial cells,  such  as those which  line the larger
vessels.   Similar nuclei may be brought into view in the capillaries of adult
animals, by  treating them with acetic  acid ; and they are particularly well
seen in the Pia Mater, which consists almost entirely of a congeries of blood-
vessels (Fig. 91).  The accompanying  figure shows the contrast between the
long oval nuclei b, b, imbedded at intervals in the walls of the true capillaries,
and rather projecting on their exterior;  and the nuclei of the epithelium-cells,
fif, lining the interior of a larger branch, which last are more numerous  and
of less regular form, and are sometimes  placed transversely to  the direction of
the tube.
   222. The first  formation of  the  Capillary  blood-vessels  in the vascular
area in the Bird's egg, is described by Schwann  as  being
affected  entirely by the coalescence of cells, which send       p.   92
off prolongations in various  directions, in the  manner of
stellate pigment-cells, such as those seen  at  c,  c, Fig. 90.
By the junction of these prolongations, a network of tubes
is formed, which is at first very  irregular in  its character;
the  greatest  diameter of the tubes  being  in  the situation
of the centres or bodies of the  original cells;  whilst be-
tween these, at the  points where their prolongations coa-
lesced, they  are much contracted.  The  calibre of the ves-
sels, however, gradually becomes equalized (Fig. 92); and
the network becomes connected with the larger trunks, and
bears a part in the general circulation.—Appearances indica-   First appearance 0f
tive of a similar process, have been seen in the tail of very  blood-vessels  in  the
young Tadpoles; so that it may probably be regarded as the  vascular layer  of the
general  method, by which new  capillaries are formed  in  germinal membrane of
the  natural  process of growth.   Observations upon  the  a jw at the astahour
history  of the  operations, which  are performed  for  the  °  incu
 
192          ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.

repair of injuries, lead to precisely the same conclusions.  The first appear-
ance of the vascular network in the newly-forming  tissue, is  in  the form of
transparent arborescent streaks ;  which push out extensions on all sides ; these
encounter one another, and  form a complete series  of capillary reticulations,
some of which come into connection with the vessels of the surrounding parts.
According  to the observations of Mr. Travers,* isolated corpuscles enter these
newly-formed capillaries, and  perform an oscillating movement  in  them for
some hours, before any series of them passes into  it;  so that we cannot re-
gard the new channel as burrowed out by a string  or file of red corpuscles,
pushed forth from the nearest capillary by vis a tergo, as some have main-
tained.

                    11. Compound Tubular  Tissues.

   223.  There now remain to  be described two elements of the Animal fabric,
to which there is scarcely anything that bears the least analogy in the struc-
ture of Plants ;—namely, the Muscular and Nervous tissues.   We have seen
that, putting aside the  Simple Fibrous tissues, whose function  is purely me-
chanical, the Animal fabric, so far as we  have yet passed its  elements under
review, is constructed  upon the very same type  with that of Plants; all the
parts actively concerned in the processes of nutrition, secretion, reproduction,
&c, retaining their original cellular character; the  vessels that serve for the
conveyance of fluid, having their origin in cells, whose cavities have coalesced ;
whilst  the  more solid portions of the  frame-work are made up of united cells,
whose cavities are  occupied by internal  deposit.—Now the  purpose of the '
Muscular and Nervous system  is entirely different.   The former is  the one,
by which all  the sensible movements of the body are  immediately effected;
and it is only amongst a small  number of Plants, that any such movements
are exhibited.  The latter  serves as the instrument by  which sensations are
received;  and by which the instincts, emotions,  or volitions, excited by these
sensations, act upon  the  muscles:—a class of  functions which we have no
reason whatever to regard as performed by Plants.   In fact, as already pointed
out (§  1—4), the distinction between the two  kingdoms is more properly
founded upon the presence of these functions  and of their instruments in the
Animal, and upon their absence in the Plant,  than upon any other structural
character.
   224. Now it might have not been  unreasonable to expect, that tissues alto-
gether so dissimilar in their properties, and in  the purposes to which they are
destined, should have a structure departing widely from the type  of the simple
Cell.  Yet it does not appear that this is the case.   That portion of the Nerv-
ous matter, by which its most active  functional changes  are  effected, retains
its original cellular character without  alteration;  and  the  so-called fibres,
which constitute the Nerve-trunks, and which convey the influence of these
changes, are in reality tubes, formed as it would seem by the coalescence of
a linear series of ceils, and chiefly distinguished by the peculiar  nature of
their internal  deposit.   In like  manner, we shall find that the ultimate Mus-
cular Fibre is also a tube, formed out of the same elements, and distinguished
by the nature of its contents; which, in  the most perfect form of the tissue,
are composed of linear series of extremely minute  secondary cells.
   225. Muscular tissue exists  under two forms; one  in which the ultimate
fibres are marked by transverse striae ;  and the other in which they are plain
or unstriped.  The  former is chiefly employed in performing the various move-
ments, which are effected through the agency of the Nervous system, and which

               *  Physiology of Inflammation and the Healing Process. 
STRIATED MUSCULAR FIBRE.
193
Fig. 93.
are connected with the peculiarly Animal powers of the being.   The latter is
with  difficulty called  into action through the  nervous  system, but  is  much
more readily excited by stimuli applied to itself; and this is employed to per-
form  various movements, which are more immediately concerned in the Vege-
tative or organic functions.*
   226. When we examine an ordinary Muscle (from one of the extremities,
for example) with the naked  eye, we observe  that it presents  a fibrous  ap-
pearance ;  and that the fibres are arranged with great regularity, in the direc-
tion in which the muscle is to act.   Upon further  examination it is found,
that these fibres are arranged  in fasciculi or bundles of larger or smaller size,
connected by means of areolar tissue; and when the Microscope is applied to
the smallest fibre  which can  be  seen with the naked eye, it is seen itself to
consist of a fasciculus, composed of a number of cylindrical fibres lying in a
parallel direction, and closely bound  to-
gether.   These  primitive  fibres present
two sets of  markings or striae; one  set
longitudinal,—the  other  transverse  or
annular.   By  more   closely examining
these fibres, when  separated from  each
other, it is frequently  seen that each may
be resolved into fibrillae, by the splitting
of its  contents in a longitudinal direction,
as shown in Fig. 93.  These fibrillae have
a peculiar beaded appearance, which will
be presently  noticed  more particularly.—
It not unfrequently happens, however, that
when a  fibre is  drawn apart, its contents
separate  in the direction of the transverse striae; forming a series of discs, as
shown in Figs. 94 and 95.   This cleavage is just as  natural as the  former,
though less frequent;  and it leads us to a view of the composition  of Muscu-
lar Fibre, somewhat different from the one commonly adopted.  To use  the
 Fasciculus of Fibres of Voluntary Muscle;
the fibres separated at one end, into brush-
like bundles of fibrillae.
Fig. 94.
  Portion of Human Muscular fibre, separating into discs, by cleavage in direction of transverse stria?.

words of Mr. Bowman,t it would be as proper to say, "that the  fibre is a pile
of discs, as that it is a bundle offibrillae ; but in fact it is neither the one nor
the other, but a mass in whose structure there is an intimation of the existence
of both, and a tendency to cleave in the two directions.   If there were a gene-
ral disintegration along all the  lines in  both  directions, there would result a
  * By some, the two classes have been spoken of as those of Voluntary and Involuntary
muscles; but this distinction is not correct;  since every muscle ordinarily termed voluntary,
may be called into action involuntarily.
  f See Bowman  on the Minute Structure and Movements of Voluntary Muscle; in Phil.
Trans. 1840.
17 
194          ON THE ELEMENTARY PARTS OF  THE  HUMAN FABRIC.
series of particles, which may be termed primitive particles or  sarcous ele-
ments, the union of which constitutes the mass of the fibre.   These elementary

                                     [Fig. 95.
  Fragments of Striped Elementary Fibres, showing a cleavage in opposite directions;  magnified 300
diameters; 1, longitudinal cleavage; the longitudinal and transverse lines are both seen;  some longitu-
dinal lines are darker and wider than the rest, and are not continuous from end to end; this results from
partial separation of the fibrillae;  6, fibrillar, separated from one another by violence at the broken end
of the fibre, and marked by transverse lines equal in width to those on the fibre ; 7, S represent two ap-
pearances commonly presented by the separated single fibrilla, (more highly magnified;) at 7 the borders
and transverse lines are all perfectly rectilinear, and the included spaces perfectly rectangular; at 8 the
borders are scalloped, the spaces bead-like; when most distinct and definite, the fibrilla presents the
former of these appearances; 2, transverse cleavage ; the longitudinal lines are scarcely visible; 3, in-
complete fracture following the opposite surfaces of a disc, which stretches across the interval and re-
tains the two fragments in connection; the edge and surface of this disc are seen to be minutely granular,
the granules corresponding in size to the thickness of the disc,  and to the distance between the faint
longitudinal lines; 4, another disc nearly detached; 5, detached disc more highly magnified, showing the
sarcous elements.]
particles are arranged and united together  in the two directions.   All the re-
sulting discs, as well as fibrillae, are equal to one another in size;  and con-
tain an equal number of particles.   The  same particles compose both.   To
detach an entire fibrilla, is to abstract a particle of every disc; and  vice versa."
   227.  The elements of Muscular Fibre  are bound together, in  the  perfect
condition of the fibre, by a very delicate tubular sheath.   This cannot always
be readily brought  into view;  but it  is occasionally seen with great distinct-
ness : thus, when the two ends of a  fibre are  drawn apart, its  contents will
                                         sometimes separate without the  rupture
                                         of the sheath, which then becomes evi-
                                         dent ;  and  this, during the act of con-
                                         traction, may sometimes   be  observed
                                         to rise up in wrinkles upon the surface
                                         of the fibre, as seen in Fig. 100.  This
                                         sheath is quite distinct from the areolar
                                         tissue, which binds the fibres into fasci-
                                         culi; and it has  been  termed,  for  the
                                         Its  existence  may be demonstrated in
  Fibre of Human Muscle broken across; the
fragments connected by the untorn Myolemma.
sake of  distinction, the Myolemma.
any Muscular fibre, by subjecting it to the action of fluids, which occasion a
swelling of its contents ; this is especially the effect of acids and alkalies, and
may be  well produced by the citric and tartaric acids, and by potash.   For a
time  the Myolemma yields  to the distention which takes place from within;
but at last it bursts at  particular  points, and  a sort of hernia of its contents
takes place, making the existence of a perfect envelope in all other parts quite 
                        STRIATED MUSCULAR FIBRE.                     195

evident.   This membrane is itself perfectly transparent, and has nothing to do
with the production of either the longitudinal or the transverse striae.  There is
no reason to believe that it is perforated either by nerves or by capillary ves-
sels;  in fact it seems to be an effectual barrier between the real elements of
Muscular structure, and the surrounding parts.   That it has no  share in the
contraction of the fibre, is evident from the fact just mentioned, respecting the
condition which it occasionally presents when the fibre is much shortened.
  228.  Muscular Fibres  are commonly described as cylindrical;  but there is
reason to believe that they are  rather of a polygonal form, their sides  being
flattened against those of  adjoining fibres (Fig. 97).  In some instances the
angles are sharp and decided; in others they are rounded  off,  so as to leave
spaces between the  contiguous fibres for the passage of vessels.   In Insects,
the fibres often present the form of flattened bands.   The average diameter of
the fibres in Man may be stated at about l-400th  of an inch; being somewhat
greater than this in  the Male, and less in the Female.  Their size varies con-
siderably, however, in different classes of animals;  and even in the same ani-
mal, and the same  muscle.  The following table gives illustrations of these
varieties;  the  extremes are  those  met with  by Mr. Bowman himself;  but
other observers speak of  dimensions more widely separated.
Mammalia
Birds .   .
Reptiles .  .
Fish
Insects
It is interesting to  remark, upon this table, that  the Muscular Fibre of Rep-
tiles and Fishes is  upon the whole much larger than that of other Vertebrata,
and that its dimensions present the greatest extremes  of variation;  whilst in
Birds, it is much smaller than in all other Vertebrata, and its  dimensions are
also less variable.   Further, the size of the fibres bears no proportion to that
of the animal;, for we  observe that in the Chaffinch  they are larger than in
the Owl, in the Cat larger than in the Horse, and in the Frog often larger
than in  the Boa.   Moreover  in  Insects, the  diameter of the fibres is even
greater than it is in Mammalia.—The average distance of the transverse striae,
in the muscular fibre of different animals, is very nearly uniform ;  as will be
seen from the following table.  Between the extremes, however, there is  con-
siderable variation; and this will be presently shown to depend upon the  con-
dition of the muscle, at the  time of examination.   The distance is not only
often different in the same muscle and the  same fasciculus, but  even  in  the
same fibre in different parts of its length.  The figures indicate the number of
striae in l-1000th of an inch.   The extremes in the same specimen, however,
are in  no instance so widely apart, as the table indicates for the Class;  the
                     Fractions of an inch.

Human   j fale, "   ■■•***  \°  if*
         I Female   .  .   .  v\z  to  ^

Horse........ttW  t0  ih
Mole  .........  -1,  to   '
1T5
400
XSoJS  IXJ  SJo
__I__tn   l
looo  l"  Joo
 Mouse......
 Ovvl     .......T5Lff  t6v ?
 Chaffinch .......  ^  to  A*
 Her°n........rsVff  to
 Frog........T7rL_  to
 Lizard.......         viv
 B°a........*i*  to  T£,
 Skate........vU  to   &
 Cod........ill  to   &
 Sprat........5,lo  to  ZU
i Staghorn Beetle    .  .  .  .  j{j  to  5}ff
I Blue-bottle Fly.....^  to  ¥iff 
196          ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.
greatest proportion between the maximum and  minimum being, except in In-
sects, as 2 to 1.
	Maximum.	Minimum.	Mean.
Human	. 150	6-0	9-4
Other Mammalia .	. 15-0	6-7	10-9
Birds .	. 14 0	7-0	10-4
Reptiles	. 20-0	6-7	11-7
Fish . . • .	. 18-0	7-5	11-1
Insects	. 160	4-0	95
   229. It has been maintained by some, that each Muscular Fibre  is a hol-
low  bundle of  fibrillae ;  but the  appearance presented by transverse sections
proves that this is not the case, the whole area of  the tube being occupied by
fibrillae, without any trace of central cavity. The extremities of the cut fibrillae,
however, cannot always be distinguished in Mammalia,  in consequence, as it
would seem, of their close and intimate lateral union ;  but they are very evi-

                                  Fig. 97.
Transverse section of Muscular fibres from pectoral muscle of Teal; showing the irregular form of the
      fibres, and the aggregation of circular particles, with which they are completely filled.

dent in Birds, Reptiles, and Fishes (Fig. 97).   The addition of  an acid in-
creases the  distinctness  of  the fibrillae, by  widening  the  interstices between
them.
   230. When the fibrillae are separately  examined, they are found to present
an alternation of dark and  light  spaces, corresponding with the transverse
striae of the fibre, and the lighter intervals between  them.   It is this alterna-
tion, which gives to  the fibrillae the beaded appearance  they present, when
their outline is  not perfectly seen.  When  good  specimens,  however, are
carefully examined under a sufficient magnifying and good defining power, it
is  seen that the border of the fibrillae  is straight or nearly so;  so that the
beaded appearance  is an optical illusion.   Moreover, each of the light spaces
is  seen to be  crossed by a  delicate but distinct line, separating it into two
equal  parts;  and upon  attentive examination  it is  seen, that  a  transparent
border, equal in breadth to either of these parts, is seen at the  sides, as well
as between the ends, of the dark spaces.  Thus each  dark space is completely
surrounded by this pellucid border; and it can scarcely be doubted that the
whole constitutes a complete though minute  cell, and that the  entire fibrilla 
STRIATED MUSCULAR FIBRE.
197
Fig. 98.
Fig. 99.
I
  Fragment of Muscular fibre
from  macerated heart of Ox,
showing formation of striae by
the aggregation of fibrilla?.
is made up of  a linear aggregation  of such cells.*   When the  fibril is in a
state of relaxation, as seen at a, the  diameter of  the  cells  is greatest in the
                          longitudinal  direction ;  but  when it
                          is contracted, the fibril increases  in
                          diameter as it diminishes in length ;
                          so  that  the  transverse  diameter  of
                          each cell equals or even  exceeds the
                          longitudinal  diameter,  as seen  at  b.
                          The  difference  between  the  two
                          states is frequently much more strik-
                          ing  than is represented in the figure.
                          —Thus the act of Muscular  contrac-
                          tion seems to consist in  a change  of
form in the cells of  the ultimate fibrillae, consequent upon an
attraction between the walls of their two  extremities, or per-
haps between  their nuclei;  and it is interesting  to  observe
how very closely it thus corresponds with the  contraction  of
certain Vegetable tissues, of which the component cells change
their form when irritated, and thus produce a movement (§ 1).
The essential difference, therefore, between the striated  mus-
cular tissue of  Animals, and  the contractile tissues of  Plants,
consists in the  subjection of  the former to  nervous influence.
—The diameter of the ultimate fibrillae, and the length of the
component cells,  will of course vary according to the contract-
ed or relaxed condition of the fibre; but they otherwise seem
to be tolerably uniform  in  different  animals.   The  average
diameter may be stated at about l-10,000th  of an inch; but
it has been  observed as  high as l-5000th,  and as low as 1-
20,000th, even when not put upon the stretch. The length of
the component cells corresponds, of course, to the distance of
the striae on the entire fibre ; and this also has been just shown
to average about  1-10,000th of an inch.
   231. The general opinion  as to the disposition of the fibres during the con-
traction of Muscle, has  been, until lately, that  of Prevost  and Dumas, who
stated that they were  thrown into a sinuous or zig-zag flexure.   Recent ob-
servations, however, have fully demonstrated the  incorrectness of this view;
the improbability of which might have been suspected from  the consideration,
  Structure of the
ultimate fibrillae of
striated muscular
fibre :— a, a fibril
in a state of ordi-
nary  relaxation;
6, a fibril in a state
of partial contrac-
tion.
  * This account of the ultimate structure of Muscular Fibre was first published  simulta-
neously (March, 1846), by the Author of this Treatise, in his Manual of Physiology, and by
Dr. Sharpey, in his new edition of Dr. Quain's Anatomy.  Both of these statements, which
were completely independent of each other, were founded upon the examination of the very
beautiful preparations of Muscular Fibre, made by Mr. Lealand the Optician ; who appears
to have been the first to direct attention  to the transverse line dividing  the bright space, and
to the bright border edging the dark spot.  A similar delineation had previously been pub-
lished, however, by Dr. Goodfellow (Physiological Journal, No. IV.) ; but his interpretation
of the appearances was altogether different; for he considered the dark spaces as the " sar-
cous elements" of Mr. Bowman, and regarded them  as separately inclosed within partitions
formed by internal prolongations of the general investing Myolemma.  By  Mr. Erasmus
Wilson, again, the appearances were described as leading to the belief that two kinds of
cells exist in each fibrilla, a dark and a light;  a pair of light cells, separated by the  delicate
transverse line just spoken of, being interposed between each pair of dark  ones [System of
Anatomy, 3d Am. Edit., p. 183].  The  bright edging to the dark spots was overlooked by
him.   The view taken by Dr. Sharpey and the Author has the entire concurrence of several
of the most eminent Microscopists in London and elsewhere; and it is confirmed by the
remarkable similarity between the aspect of the Muscular fibrilla, and that of a minute Con-
ferva,  seen under the same magnifying power,—the cellular constitution of  the latter being
indubitable.
17* 
198          ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.

that fibres in this  state of flexure could scarcely be imagined  to be exerting
any force of traction.  Prof. Owen has noticed that, in the contracted state of
the very transparent muscles of some Entozoa, each separate fibre, which
may be seen with great distinctness, presents a knot or swelling in the middle,
besides being generally thickened; but that it is simply shortened, without
falling out of the straight line.  Dr. A. Thomson remarked the same thing in
the Frog; single fibres, whilst  continuing  in contraction, being simply short-
ened, without falling into  zig-zag lines: and he was led to suspect, from this
and other circumstances, that the zig-zag arrangement was not produced, until
the act of contraction had ceased.   The  recent  inquiries of Mr. Bowman
have proved most satisfactorily, that, in the state of contraction, there is an
approximation of the transverse striae, and a general shortening of the fibre;
and that its  diameter is at the same time increased ;  but that it is never thrown
out of the  straight line, except when it  has ceased to contract, and its  two
extremities  are still held in proximity by the contraction of other fibres.  The
whole process may be distinctly seen under  the Microscope, in a single fibre
isolated from  the rest: it is, of course, desirable to select the specimen  from
those  animals, in  which  the contractility  of the  Muscle is retained for the
longest period after death,—which is  particularly the case in Reptiles among
Vertebrata,  and  in most Invertebrata (Mr.  Bowman particularly recommends
the Crab and Lobster); but  the change has been  fully  proved to differ in no
essential degree, in the warm-blooded Vertebrata.   The  contraction usually
commences  at the extremities of the fibre;  but it frequently occurs also at one
or more intermediate  points.  The first appearance is  a spot more opaque
than the rest, caused by the approximation of  a  few of the  dark points of
some  of the fibrillae:  this  spot usually extends in a short time through the
whole diameter of the fibre; and  the shading, caused by the  approximation
of the transverse  striae, increases in  intensity.  The striae  are found  to be
two, three, or even four times  as numerous, in the contracted, as  in the un-
contracted  part;  and  are  also proportionally  narrower  and  more delicate.
The line of demarcation between the contracted and uncontracted portions is
well defined; but, as  the  process goes  on, fresh striae  are  absorbed  (as it
were) from  the latter into the former.   The contracted part augments in thick-
ness ; but not in a degree commensurate with its  diminished length ; so  that
its solid parts lie in smaller compass than before,—the fluid which  previously
intervened between them, being pressed out in bullae under the myolemma
(Fig.  100).   The force with which the elements of  the fibre thus tend to ap-
proximate is evidently considerable ; for if the two extremities be held apart,
Muscular fibre of Dytiscus, contracted in the centre; the striae approximated ; the breadth of the fibre
              increased; and the sarcolemma raised in bullae on its surface.

the fibre  is not unfrequently ruptured.   This corresponds with the appear-
ances found in the muscles of persons  who  have died from  tetanus; for in
the ruptured fibres of those muscles, which have been the  subjects  of the
spasmodic  action, the striae have been  observed to approximate so closely,
as to be scarcely  distinguishable.   When the contraction is not very decided,
the dark  and elevated  spot appears to play like a wave along the fibre, before
it involves the whole diameter in any part (Fig. 101, 2); and even when con- 
STRIATED MUSCULAR FIBRE.
199
Fig. 101.
1
siderable traction is being exercised, there is continual interchange in the ele-
ments by which  it is effected,—the discs  at one end of  the contracted part
receding from each other, whilst at the other  end new discs  are being re-
ceived into it.
  232.  The foregoing  description is chiefly
derived from the appearances presented by
muscular fibre, when spontaneously passing
into that state of contraction, which is termed
the rigor mortis ; but there can  be no rea-
sonable doubt, that the phenomena of con-
traction, excited by the agency of the nerves,
are precisely similar.   Mr. Bowman has re-
marked, that stimuli of various kinds, direct-
ly applied to them, produce corresponding
effects,  although,  in the case  of  galvanism,
the change  is too rapid for its  steps  to be
followed; and that,  from  the appearances
presented by muscles which have been af-
fected  with  tetanic spasms, the contraction
produced by nervous agency may be inferred
to correspond in character.—It now remains,
therefore, to inquire what is the cause of the
zig-zag arrangement, which is often seen in
the fibres.   This may be easily produced, by
approximating the ends of a fasciculus, after
the irritability of its  fibres  has ceased ; and
it would not seem unlikely, that the passage
of vessels or nerves  should determine the
points  at  which  the  flexures take  place.
Hence it appears, that the sinuous or zig-zag
arrangement is  that  into  which  fibres  are
naturally thrown, if, on elongation following
contraction, they are  not at once  stretched by antagonist muscles.*  Many
facts support the opinion, which has long been held by several Physiologists,
that, when  an entire muscle is contracting, all its fasciculi are not in con-
traction  at  once ; but that there  is  a continual  interchange  in the  parts,
by  which the tension  is effected ;  some relaxing, whilst others are short-
ening.  When the ear is applied to a  muscle in vigorous action, an  exceed-
ingly rapid faint silvery vibration is heard; which seems to be attributable  to
this constant movement in its  substance.   Now, on examining a muscle, of
which some fasciculi present the zig-zag arrangement, others will be seen  (if
the two extremities have not been purposely approximated) to be quite straight,
and in a state of contraction; and it thence appears, that  the former  appear-
ance is  presented by bundles of fibres, which have either not yet entered into
contraction, or which have relaxed after undergoing it; but of which the ex-
tremities are still approximated, by the agency of other contracting fibres.—
The result of various experiments  made for the purpose, leads to the conclu-
sion, that the total bulk of a muscle in contraction is not less than when it is
in a relaxed state ; or that the  difference, if any exist, is extremely trifling.
  233.  Every Muscular Fibre, of  the striated kind  at least, is attached  at its
extremities to white fibrous  tissue ; through the  medium of which it exerts its
contractile power on the bone or other substance, which it is destined to move.
 Muscular"fibre of Skate, in a state of
rest (1), and in three different stages of
contraction (2, 3, 4).
  *  Mr. Bowman's conclusions have recently been confirmed by Prof. E. Weber. (Archives
dAnatomie Generate, Jan. 1846.) 
200          ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.

The whole fasciculus of fibrillae usually seems  to end abruptly in a  perfect
disk ; and the myolemma terminates there.  The tendinous fibres are attached
to the whole surface of the disk;  and probably  become continuous with the

                                  Fig. 102.
Attachment of Tendon to Muscular Fibre, in Skate.
myolemma.  Thus the whole muscle is penetrated by minute fasciculi of tendi-
nous fibres ; and these  collect at its extremities into a Tendon.  Sometimes the
muscular fibres are  attached obliquely to the tendon, which  forms  a broad
band that does not subdivide ;  this is seen in the legs of Insects and Crusta-
cea, in which the muscular fibres have a penniform arrangement; being inserted
into the tendon, on either side, like the laminae of a feather into its stem.
  234. The Muscular Fibre of Organic Life is  very different from the pre-
ceding.  It consists of a series  of tubes, which do  not present transverse
[Fig. 104.]
                                                  4, A muscular fibre
                                                 of Organic Life with
                                                 two of  its nuclei;
                                                 taken from the uri-
                                                 nary bladder, and
                                                 magnified 600 diam-
                                                 eters ;  5, muscular
                                                 fibre of organic life
                                                 from the stomach,
                                                 magnified the same.]


striae,  and in  which the longitudinal  striae  are very faint; these tubes are
usually much  flattened,  and cannot be  shown  to  contain  distinct fibrillae.
Fig. 103.
  Non-striated Muscular Fibre; at
b, in its natural state ; at a, show-
ing the nuclei after the action of
acetic acid. 
NON-STRIATED MUSCULAR FIBRE.
201
Their size is usually much less than that of the fibres of Animal life; but,
owing to the extreme variation in the flattening which they undergo, it  is dif-
ficult to make a precise estimate of their dimensions.   Those of the aliment-
ary canal are stated by Dr. Baly to  measure from about  the l-2500th to the
l-5600th  of an inch; in the foot  of the  common  Mussel, the Author has
found them to be as much as the l-1920th of an inch; whilst in the respira-
tory sac of a Phallusia (an Ascidian Mollusk), their  diameter is no more than
l-8400th.   They sometimes present markings,  which indicate a granular ar-
rangement in their interior ;  and these markings have occasionally a degree
of regularity, which approaches that of the striae on the striped Muscular fibres.
They frequently present nodosities at intervals,  which are the  nuclei of their
original component cells;  and, where these  nuclei  are not otherwise visible,
they may be brought into sight  by acetic acid (Fig. 103, a).   The plain or
non-striated fibres, like those of the other muscles,  are usually arranged in a
parallel manner, into  bands or fasciculi; but these fasciculi are generally in-
terwoven into a  net-work,  not having any fixed points  of attachment, but con-
tracting against each other.   It is of this kind of structure, that the muscular
substance of the walls of the oesophagus, stomach, intestinal  tube, bladder,
and uterus, is composed ;  it occurs also in the bronchial tubes, in the ureters,
and most of the larger gland-ducts, and in the iris.  In the Heart, are  found
various  forms of Muscular fibre; some being distinctly striated, others quite
plain ; and others of  intermediate character.  The average size of the fibres
is less than that of  the fibre, of  which  the voluntary muscles are composed;
and the fasciculi, instead  of being straight and  parallel, are considerably in-
terlaced.  This  intermediate character accords well,  as we shall hereafter see,
with the actions of the organ ; which correspond in their energy and rapidity,
with the contractions of voluntary muscles ;  whilst  they agree with those of
the non-striated  kind, in being  but  little  influenced by the nervous  system.
The middle coat of the Arteries contains a contractile  tissue, very similar to
that of  unstriped muscle;  and fibres of a similar nature are interwoven with
other fibrous tissues in the Skin, and especially  in the Dartos,—giving rise in
the former to the state termed cutis anserina, under  the influence of  cold  or
of depressing emotions ; and in the latter to the wrinkling of the scrotum.
There are certain points, at which the one system of fibres comes into close
connection with the other.  This is  the case, for example, in the oesophagus;
the upper part of which contains striated fibres, and is thrown into contrac-
tion by  nerves ;  whilst the  muscular wall  of the  lower part  seems entirely
composed of non-striated  fibres, and acts for the  most part independently of
the nerves.   The point of transition varies in different animals (§ 386); and
seems not to be  constant among individuals of the human species.
  235.  The Myolemma of the  Muscular Fibre appears  to be the part first
formed ; being distinctly visible long before  any traces of fibrillae can be ob-
served in it.  This tube seems to take its  origin, like the ducts of Plants, in
cells laid end to end, the  cavities of which coalesce, by the disappearance of
the partitions, at a subsequent period ; and the  nuclei of these  original cells
may be distinctly seen, for some time after the appearance of the striae, which
indicate the formation of the fibrillae  in their interior.   In an  early stage of
the development of the fibres, indeed, these bodies project considerably from
their  sides :  in this respect, as well  as in others, there is  a close correspond-
ence between the temporary character of the Muscular fibre of Animal life,
and the permanent condition of that of Organic  life.  In the fully formed
muscle of Animal life, they are not perceptible,  except when a peculiar me-
thod  has been adopted for bringing them into  view.  This method consists in
treating the fibre  with weak acids, which render the nuclei  more opaque,
whilst the surrounding structure becomes more transparent.  They are usually 
202          ON THE ELEMENTARY PARTS OF THE  HUMAN FABRIC.
numerous in proportion to the size of the fibre.   There is every probability
that these nuclei continue to act, like the " germinal spots" of the glandular
Fig. 106.
  Muscular fibres from foetal pectoralis ;
a, from Calf at two months; b, from hu-
man fcetus of nine months.
  Mass of ultimate fibres from
the pectoralis major of the hu-
man fostus,  at  nine  months.
These  fibres have been  im-
mersed in a  solution of tartaric
acid ; and their " numerous cor-
puscles, turned in various direc-
tions,  some  presenting nucle-
oli," are shown.
follicles  or parent-cells,  as centres  of nutrition ;  from  which the  minute
secondary  cells,  that compose the fibrillae,  are  developed as they  are  re-
quired.   The diameter of the  Muscular fibre of the foetus is not above one-
third of that which it possesses in  the adult; and as the size of their ultimate
particles is the same in both cases, their number must be greatly  multiplied
during the  growth of the structure.  But we shall find reason to believe, that
a decay is  continually taking place in the component cells, with  a rapidity
proportional  to the  functional activity  of  the  Muscle, and their  generation,
which occurs  as constantly when the  nutrient operations proceed  in  their
regular course, is probably accomplished  by a development from  these cen-
tres, at the expense of the blood, with which the muscle is copiously supplied.
  236.  From the preceding history it appears, that there is no difference, at
an early stage of development between  the striated and non-striated forms  of
Muscular fibre. Both are simple tubes, containing a granular matter, in which
no definite arrangement can be traced, and presenting enlargements  occasioned
by the presence of the nuclei.  But whilst the striated fibre goes on in its
development, until the fibrillae, with their alternation of light and dark spaces,
are fully produced, the non-striated fibre  retains throughout  life  its original
embryonic character.
  237.  Notwithstanding  the energy of growth in Muscular Fibre, and  the
constant interstitial  change which seems  to take place in its  contents, it is
doubtful if it is ever regenerated, when there has been actual loss of substance.
Wounds of muscles  are  united by Areolar tissue, which gradually becomes
condensed; but its fibres never acquire  any degree of  contractility.
  238.  The Chemical Composition of  Muscular Fibre seems to be very uni-
form, from whatever source it  is obtained.   It  is impossible, however, t6 de-
termine it  with precision ; on  account of the difficulty of completely isolating
the substance of  the  fibres from  the  areolar  tissue, vessels, and  nerves, that
are blended with them.   The proper  muscular  substance differs from  the
simple fibrous tissues, in  not being resolvable into gelatine by the prolonged
action of boiling water;  and in being soluble in  acetic acid, from  which it is 
CHEMICAL COMPOSITION OF MUSCLE.
203
precipitated by ferrocyanide of potassium, showing that it belongs to the pro-
teine-compounds.  The following analyses of Muscle by Berzelius  corre-
sponds very exactly  with those since made by Braconnot, Schultz, Marchand,
and other Chemists :
Fibrine (from the proper muscular substance)
Gelatine (from areolar tissues)
Albumen and haematine
Phosphate of lime, with albumen
Alcoholic extract, with salts (lactates?)
Watery extract, with salts .
Water, and loss
15-80
 1-90
 2-20
  •OS
 1-80*
 1-05
77-17
100-00
Thus something less than 23 percent, of solid matter exists in ordinary meat;
and in 100 parts of this  solid mattter, there are  about 1\ parts of fixed  salts.

  [Krcatine (from Keeac, flesh), originally discovered by Chevreul, in 1835, has been proved
by the recent investigations of Liebig to  be a constant ingredient of the muscles of  all the
higher classes of animals.   Schlossberger found it in the flesh of the alligator.   Its crystals
are colorless, perfectly transparent, and of great  lustre.   They  form groups, the character
of which is exactly similar to that of sugar of lead.  Its formula is C8 N3 Hn 06.   It dissolves
easily in boiling water, and a solution saturated at 212° forms on cooling a mass of small bril-
liant crystals, and is nearly insoluble in cold alcohol.  It is neither acid nor basic.   From the
action of strong mineral acids, a new body of totally different chemical qualities, a true or-
ganic alkali is formed, which Liebig has called Kreatinine.   It is easily obtained from the
hydrochlorate or the sulphate.  Kreatinine is more soluble both in cold and  hot  water than
kreatine; it dissolves in boiling alcohol, and crystallizes  on  cooling.  In its chemical cha-
racter it is analogous  to ammonia.—Its formula is C8 N3  H7 02.—Researches on the Chemistry
of Food, by J. Liebig.—London, 1847.—M. C]
   a. The exact correspondence  in ultimate composition, between dried Muscle, and cfried
Blood, according to the analyses  of Playfair and Bockmann, is not a little  remarkable.  The
following are their results.
	Playfair.		BoCKMAXN.	
	Muscle.	Blood.	Muscle.	Blood
Carbon	. 51-83	51-95	51-89	51-96
Hydrogen .	7-57	7-17	7-59	7-33
Nitrogen	. 15-01	15-07	15-05	1508
Oxygen	. 21-36	21-39	21-24	21-21
Ashes	. 4-23	4-42	4-23	4-42
It may be questioned, from these results, whether the amount of Haematine in Muscle is not
greater than that which is represented by the previous analysis; since a tissue composed of
Fibrine and Albumen alone, could not possess the same ultimate composition with one, in
which Haematine is present in large proportion.
  6.  Some very interesting researches have lately been made by Helmholtz,f on the changes
induced in the tissue  by Muscular action.   Powerful contractions were induced by electricity
in the amputated leg  of a Frog; and were kept  up as long as the irritability was retained.
The  flesh of the two  limbs was then analyzed; and it was found that, in every instance the
water-extractive was  diminished in the electrized muscle, to the extent of from 20 to 24 per
cent.; whilst "the alcoholic extract was increased to about the same amount.—Similar results
were obtained from  experiments on warm-blooded animals; the amount  of change, how-
ever, being less, on account of the shorter  duration of their muscular irritability.

   239.  Muscular  tissue, properly so  called, is  as extra-vascular as cartilage
or dentine;  for  its  fibres are  not penetrated by vessels ;  and the  nutriment
required for the  growth of its contained matter  must be drawn  by absorption
through the  myolemma.  But the  substance of  Muscle, as a  whole, is  ex-

  *  [The recent researches of Liebig make it exceedingly probable that lactic acid is a con-
stituent of muscle.  Its purpose in the animal organism will be alluded to hereafter.—M. C]
  -f Miiller's Arcbiv., 1845. 
204
ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.
tremely vascular, the capillary vessels being distributed in parallel lines, united
                            by transverse branches, in the  minute inter-
          Fig. 107.           spaces between the fibres  (Fig. 107); so that it
                             is probable that there is no fibre, which is not in
                             close relation with a  capillary.  The number
                             of blood-vessels in a given space will of course
                             be greater, where the fibres  and the capilla-
                             ries are  both small, as in  Mammals and  Birds,
                             than where  they  are  of larger diameter, as in
                             Reptiles and Fishes;  and the former condition
                             will  obviously be  the  one most favourable to
                             the performance of active changes between the
   Capillary net-work of Muscle.    blood and the muscle.   These changes consist,
                            it would appear, not merely in the nutrition of
the tissue; but in  the  supply of oxygen, which is  a necessary condition of
the excitement of its  activity.   We shall hereafter see, indeed, that every
muscular contraction probably involves the disintegration of a certain amount
of its substance,  through the union of oxygen,  supplied  by arterial  blood,
with its elements ;  and  that the great  demand for  nutrition, which is occa-
sioned by muscular activity, is for the  purpose of repairing  this loss.  The
muscles of warm-blooded animals speedily lose their  irritability, after the
supply of arterial blood  has been  suspended,  either  through  the cessation of
the general circulation, or by deficient aeration of the fluid.   But the muscles
of cold-blooded animals, which are very inferior in the energy and rapidity
of their action, preserve  their properties for a much longer period, after the
deprivation of their supply of arterial blood;  in accordance with  the general
principle,  that, the lower the usual amount of vital energy,  the longer is its
persistence, after  the withdrawal of the  conditions on which it is dependent.
The very  indisposition to a  change of composition,  on which the less ready
action depends, produces a longer retention of the power of acting.
  240.  The Muscles of Animal life are, of all the tissues  except the skin,
those most copiously supplied with Nerves.  These, like  the blood-vessels,
lie on the  outside of the  Myolemma of the several fibres; and their influence
must consequently be excited through it.  The  general  arrangement of these
nerves is shown in Fig.  108.   Their ultimate fibres or tubes cannot be said

                                 Fig. 108.
Form of the terminating loops of the nerves in the muscles.
to terminate anywhere in the Muscular substance;  for after issuing from the
trunks, they form a series of loops, which return  either to the same trunk, or
 
                nervous system;  its general structure.             205

to an adjacent one.  The occasional appearance of a termination to a nervous
fibril is caused by its dipping down between the muscular fibres, to pass to-
wards another stratum.  The nerves are  almost exclusively  of the  motor
kind;  but a few sensory are blended with them.   We see this  most clearly
in cases in which  the  motor and  sensory trunks supplying the muscles are
distinct; as in the muscles of the orbit.—The non-striated muscles  are very
sparingly supplied with nerves ;  and these are derived (for the most part, if
not  entirely), from the Sympathetic system, rather than from  the Cerebro-
spinal.
   241. We have, lastly, to consider the structure,  composition, actions, and
mode of growth and regeneration of the  Nervous Tissue ; the one which is
most distinctive of the  Animal fabric, and which serves as the instrument of
the operations that are most peculiar to it.  Wherever a distinct Nervous Sys-
tem  can be made out (which has  not yet been found possible  in the  lowest of
those beings, that, from their general structure and habits of life, are unques-
tionably to  be ranked in the Animal Kingdom), it consists of two very different
forms of structure; the presence of both of which, therefore, is essential  to
our idea of it as a whole.   We observe, in the first  place, that it is formed of
trunks, which are distributed to different parts of the body, and especially to
the  muscles  and  to  the  sensory surfaces ; and of ganglia, or masses with
which the  central  terminations of those trunks  come into connexion.  It is
easily established by experiment, that the trunks themselves have no  power
of originating changes ; and  that  they only serve to conduct or convey  the in-
fluence of operations which  take place at their central or peripheral extremi-
ties.  For if a trunk be  divided in any part of its  course, all the parts  to which
the portion thus cast off" from the ganglion is distributed, are completely para-
lyzed ;  that is, no impression made upon them is felt as a sensation ; and no
motion can be excited in them by any act of  the mind.  Or, if the substance
of the ganglion be destroyed, all the parts which are  exclusively supplied by
nervous trunks proceeding  from it, are  in like  manner paralyzed.—But if,

                                  Fig. 109.
  Dorsal ganglion of Sympathetic nerve of Mouse ; a, b, cords of connection with adjacent sympathetic
ganglia; c, c,c, c, branches to the viscera and spinal nerves ; d,ganglionic globules or cells ; e, nervous
fibres traversing the ganglion.

when a trunk is divided, the portion still connected with the ganglion be pinched
or otherwise irritated,  sensations  are felt which are referred to the points sup-
plied by the  separated portion of the trunk ; which shows that the part re-
maining in connexion  with the ganglion is still capable of  conveying impres-
     18 
206         ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.
sions, and that the ganglion itself receives these impressions, and makes them
felt as sensations.   On the other hand, if the separated portion of the  trunk
be irritated, motions  are  excited in the muscles which it supplies;  showing
that it is still  capable of conveying the  motor influence,  though  cut off from
the usual source of that influence.
  242. In the ordinary Nerve-trunks, we find only one form of Nervous tis-
sue ;—that which may  be designated as the fibrous or tubular.  In  the Gan-
glia, we find, in  addition to  this,  a substance  made  up of peculiar cells or
vesicles ; which may be  distinguished  as the vesicular nervous matter.   In
fact, the character of a Ganglionic centre (which is frequently not otherwise
clearly distinguished as  such) is derived from the  presence of this  vesicular
substance.
  243. The ultimate Nerve-fibre, in its most complete form,—such as is pre-
sented to us in the ordinary spinal  nerves,—is distinctly tubular; being com-
posed of an external cylindrical membranous sheath, within which the peculiar
nervous matter is contained.   This membranous tube, like the Myolemma of
muscular fibre, is  extremely delicate and transparent; and is nearly or quite
[Fig. 110.
  B.
  a. Diagram of tubular fibre of a spinal nerve ;—a. Axis cylinder, b. Inner border of white substance.
e, e. Outer border of white substance,  d, d. Tubular membrane,  b. Tubular fibres;  e, in a natural
state, showing the parts as in a.  /. The white substance and axis cylinder interrupted by pressure,
while the tubular membrane remains, g. The same, with varicosities,  h. Various appearances of the
white substance and axis cylinder forced out of the tubular membrane by pressure, i. Broken end of a
tubular fibre, with the white substance closed over it.  k. Lateral bulging of white substance and axis
cylinder, from pressure.  I. The  same more complete, g-'. Varicose fibres of various sizes, from the
cerebellum, c. Gelatinous fibres from the solar plexus, treated with acetic acid, to exhibit their cell-
nuclei. B and c magnified 320 diameters.]

homogeneous.   It  is not penetrated by blood-vessels;  nor is it ever seen to
branch or anastomose with others; so that there is reason to regard it as form- 
TUBULAR NERVOUS TISSUE.
207
ing one continuous sheath, that isolates the contained matter from the surround-
ing tissue, along  the whole  course of the nerve-trunk, from its central to its
peripheral extremity.  When the nerve-fibres are  examined in a very fresh
state, their contents appear pellucid and homogeneous, and of a fluid consist-
ence ;  so that each tube or fibre looks like a cylinder of clear glass, with sim-
ple, well-defined, dark edges.   But a kind of coagulation soon takes, place in
the contained substance, making it easily  distinguishable from the tube  itself;
for the latter is then marked by a double  line, as shown in Fig. Ill, a. The
substance which is in immediate contact with the inner wall of the nerve-tube,
is  more opaque  than that which occupies its centre, and of a different refract-
ing power;  and thus it forms a hollow cylinder, which  surrounds the  latter,
and which is known under the name of the White substance of Schwann. The
centre or axis of the tube is occupied by  a substance that preserves its trans-
parency ; and this  is the axis-cylinder of Rosenthal and Purkinje.   It may be
surmised that the White substance of Schwann, which exhibits much variety
in  thickness in different parts of the  nervous system, chiefly serves, like the
membranous investment, to isolate the interior matter ; which last seems to be
the essential constituent of the nervous fibre.  The whole of the matter con-
tained  in the tubular sheath is extremely soft; yielding to very slight pressure,
and readily escaping from the cut extremities of the tubes. The tubular sheath
itself varies  in density in different parts ;  being stronger in the nervous trunks
than in the substance of the  brain  and spinal cord.   In  the former, it is not
difficult to show that the regular form of  the nerve-tube is a perfect cylinder;
though a little disturbance will cause an alteration in this,—a small excess of
pressure in one part forcing the contents of the tube towards another portion,

                                 Fig. 111.
  Structure of nerve-tubes, magnified 350 diameters,  a, Cylindrical tubuli from nerve,  b, Varicose
tubuli from brain, c, Nerve-tubes, of which one exhibits the remains of nuclei in its walls.

where they are more free to distend it, and thus producing a swelling.  The
greater delicacy of the tubular sheath in the latter, causes this result to take
place with yet more readiness ; so  that a very little  manipulation  exercised
upon the fibres of the Brain or Spinal Cord, or on those of special sense, occa-
sions them to assume a varicose or beaded appearance (Fig. Ill, b), which,
when first observed by Ehrenberg, was thought to be  characteristic of them.
When the fibres  of these parts are examined, however,  without any  such pre-
paration, they are found to be as cylindrical as the others.—The diameter of the
tubular fibres of  the cerebro-spinal nerve-trunks  in Man, usually varies from
about l-2000th to l-4000th of an  inch, being sometimes as great,  however,
as l-1500th  of an inch; and  sometimes  much below the least  of  the above 
208         ON THE ELEMENTARY PARTS OF THE  HUMAN FABRIC.

dimensions.  The fibres decrease in size as they approach  the brain, either
directly, or through the medium of the spinal cord; and in the brain itself they
continue to diminish, as they pass through the medullary towards the cortical
portion; so that they are very commonly found of no more than l-7000th or
l-8000th of an inch in diameter, and sometimes as little as l-14,000th.  Like
most other  elementary structures, they are of considerably larger dimensions
in Reptiles and Fishes ;  varying, according to Dr. Todd, from l-1260th to
l-2280th of an  inch in the Frog;  being in the  Eel as much as the l-1040th
of an inch ; and in the optic nerve of the Cod, no  less than l-650th of an inch
in diameter.*
  244.  Besides these proper tubular nerve-fibres,—of which, in combination
with areolar and fibrous tissue, blood-vessels, &c, a large proportion of  the
cerebro-spinal nerve-trunks are made up,—there are certain other fibres, which
are peculiarly abundant in  the trunks of  the Sympathetic system, and which
are of different character from the preceding.  They are chiefly distinguished
by their small size, their diameter not being above half or one-third of that of
the ordinary nervous tubuli.   They  are destitute of the double contour, which
has been shown to result in the preceding case  from the presence of two dis-
tinct substances within the tubular investment; and their contents appear to
be homogeneous.   And when they are aggregated in bundles, they possess a
yellowish-grey colour.—Although these fine fibres exist in greater proportion
in the Sympathetic  system than  in  the  Cerebro-spinal, yet they are  present
in great numbers in some of the nerves of the latter;  and it is even question-
 Primitive fibres and ganglionic vesicles of human brain, after Purkinje. a, ganglionic vesicles lying
amongst nerve-tubes and blood-vessels, in substance of optic thalamus; a, vesicle more enlarged; b
vascular trunk, b, b, vesicles with variously-formed processes, from dark portion of crus cerebri.  Ma»-
nified 350 diameters.

able, whether they may not be  continuous with the  ordinary tubular  fibres.
They may be traced into the ganglia of the Sympathetic, into the ganglia on
the posterior roots of the Spinal nerves, and  even to the ganglionic matter of
the Brain and Spinal Cord.t

  * Cyclopaedia of Anatomy and Physiology, Vol. in., p. 593.
  f Much controversy has recently taken place  in Germany, regarding the existence of a
set of fibres peculiar to the Sympathetic system.  The grey or gelatinous fibres, described by
Remak, and (following him) by Muller and others, as essentially constituting the Organic
system of Nerves, are now generally admitted not to be entitled to the designation of nerve- 
VESICULAR NERVOUS TISSUE.
209
   245. The second primary element of the Nervous system, without which
the fibrous portion  would seem  to be totally inoperative, is composed of nu-
cleated cells, consisting of a finely granular  substance, and lying somewhat
loosely in the midst of a minute plexus of blood-vessels. Their original  form
may be regarded as globular; whence they have been called ganglion-globules.
This,  however, is liable to alteration; sometimes, perhaps, from external  com-
pression ; but more commonly through their own  irregular mode of growth.
They  frequently extend  themselves  into long  processes, which may give
them (according to  the number thus projecting) a caudate or a stellate aspect,
resembling that of  the pigment-cells of the Batrachia.   These processes are
composed of a finely-granular substance, resembling that of the interior of the
vesicle, with  which they  seem to be distinctly continuous.   They are  very
liable to break off near the vesicle; but if traced to a distance, they are found
to divide  and subdivide, and at last to
give off" some extremely  fine transpa-
rent fibres ; some of which seem to in-
terlace with those of other stellate cells,
whilst others become continuous with
the axis-cylinders  of the nerve-tubes.
Such vesicles  have  been seen alike  in
the ganglionic masses of  the Cerebro-
spinal, and in those  of the Sympathetic
system.*   Besides  the  finely-granular
substance just mentioned, these cells
usually contain a collection of pigment-
granules, which especially cluster round
the nuclei, and give them a reddish or
yellowish-brown colour.  This pigment
seems to  have some resemblance  to
the haematine of the blood ;  and it is
usually,  if  not invariably,  deficient
among the Invertebrata, as well as less
abundant in Reptiles and Fishes.  The
vesicles are sometimes covered with  a
layer of a soft granular substance, which adheres closely to their exterior and
to their processes ;  this is the case in the  outer part of  the cortical substance
of the  human brain.  In other instances, each cell is inclosed in a distinct en-
velope composed of smaller cells, closely  adherent  to  each other, and to the
contained cell; such an arrangement is  common in the smaller ganglia, and
in the inner portion of the cortical substance of the brain.—The diameter of
the vesicles is extremely variable, owing  to  the changes  of form above de-
scribed ;  that of the globular ones is usually  between l-300th and l-1250th of
an inch.
  246. In the central or ganglionic  masses  of the  Nervous  system, we find
these vesicles aggregated together, and imbedded in a finely-granular matter;
the whole being traversed  by  a minute  plexus of capillary blood-vessels.
The entire substance, made up of these distinct elements, is commonly known
as the  cineritious or cortical substance; being distinguished by its colour, in
fibres, but to be a form  of simple fibrous tissue.   The peculiar fibres described above, were
first pointed out by Bidder and Volkmanu;  whose statements in  regard to them have re-
cently been confirmed by the laborious and impartial researches of Kolliker.  (See his work
"Die Selbstilndigkeit und Abhangigkeit des Sympathischen Nervensystoms," 1844; and the
abstract of  his results in Mr. Paget's able Report, in Brit, and For. Med. Review, July, 1846,
p. 271.)
  * See Todd and Bowman s  Physiological  Anatomy, Vol. i.,  p. 214.  See also Kolliker, he.
cit.; and Dr. Radclyffe Hall, in Edinburgh Med. & Surg. Journal, April, 1846.
                                    18*
[Fig  113.
  Nerve-vesicles from the Gasserian ganglion of
the human subject:—a. A globular one with de-
fined border; 6, its nucleus; c, its nucleolus,  d.
Caudate vesicle, e. Elongated vesicle, with two
groups of pigment particles,  f. Vesicle surround-
ed by its sheath, or capsule, of nucleated panicles.
g. The same, the sheath only being in focus.—
Magnified 300 diameters.] 
210
ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.
  Ganglion globules, with their processes, nuclei, and nucleoli:— a. a. From the deeper part of the gray
matter of the convolutions of the cerebellum.  The larger  processes  are directed towards the surface
of the organ, b. Another from the cerebellum, c.d. Others from the post, horn of gray matter of the dor-
sal region of the cord. These contain pigment, which surrounds the nucleus in c. In all these specimens
the processes are more or less broken.—Magnified 200 diameters.]

Man and the higher animals  at least, from the  white  substance composed of
nerve-tubes,  of which the trunks  of the nerves, as well as a large part of the
brain  and spinal cord, are  made up; and occupying in  the  brain  a position
external to the latter, which is often  termed the medullary substance.   This
position, however, is quite  an exceptional one;  for in the spinal cord and in
the scattered ganglia of Vertebrated animals, and in all the  ganglionic centres
of [Invertebrata,—everywhere, in fact,  except in the Brain,—the vesicular
nerve  substance occupies the centres of the ganglia;  consequently the terms
                               cortical and medullary, as applied to the vesi-
                               cular and tubular  substances respectively, are
                               quite inappropriate.   Nor are  the designations
                               that have reference to their colour, much more
                               uniformly correct:  for,  as we  have  seen,
                               the vesicular  substance may be  destitute of
                               internal  pigment-granules, and  the blood in
                               its capillary plexus may be  pale or  colourless,
                               so  that  the  reddish-grey hue,  which  is ex-
                               pressed by the term cineritious, may  be entirely
                               wanting;  whilst, on the other hand, we have
                               seen that certain  of  the nerve-fibres, making
                               up what  is commonly termed the  white sub-
                               stance, are of a grey colour.  Hence the only
                               valid  distinction between  these two kinds of
                               nervous matter, is that which has reference to
                               their  constitution;—as  consisting of  cells or
                               vesicles  on the one hand;  or of  tubes or fibres,
                               on the other.
                                  247. The connection between the  fibrous and
  A small piece of the otic ganglion of
the sheep, slightly compressed; show-
ing the interlacement of the internal
fibres, and the vesicular matter.—
(After Valentin.)] 
CONNECTION OF FIBROUS AND VESICULAR SUBSTANCES.
211
vesicular nervous elements,  in the nervous  centres,  has  not yet been  tho-
    ghly elucidated.   It seems  certain, on  the  one hand,  that some of  the
rou
[Fig. 116.
[Fig. 117.
  a. Blending of the vesicular and fibrous nervous
matter in the  dentate  body of the cerebellum:—a,
Ganglion globule, with its nucleus and nucleolus.
b. Nerve-tube, slightly varicose, in close contact
with the ganglion globule. 6'. Smaller nerve-tubes.
These parts all lie in a finely granular matrix in-
terspersed with nuclei, c.  b. Vesicular and fibrous
matter of the laminae of the cerebellum,  a. Gan-
glion globule.  6. Very  minute nerve-tubes tra-
versing a finely granular  matrix, in  which  are
numerous rounded nuclei, c]
  From the Gasserian ganglion of an adult:—a. a.
Ganglion globules with their nucleus,  nucleated
capsule, and pigment,  t. Tubular fibres, running
among the globules in contact with their capsule.
g. Gelatinous fibres also in contact with the gan-
glion globules.—Magnified 320 diameters.]
fibres come into direct continuity with caudate prolongations of the ganglionic
corpuscles, and may thus be  said to originate from  them.   This appears to
Fig. 118.
  Primitive fibres and ganglionic vesicles,  a, from sympathetic ganglion ;  * a separate vesicle, show-
ing its pellucid nucleus and nucleolus,  b, from grey substance of human cerebellum ; a, b, plexus of
primitive fibres ; c, nucleated globules ;  * a separate globule from human Gasserian ganglion.  Magni-
fied 350 diameters.
be especially the case, with regard to the class offine fibres (§ 244).   On the 
212         ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.
other hand, it seems equally certain that there  are many nerve-tubes which
simply enter the  ganglionic masses, pass round and  amongst  the cells, and
then emerge from  them, without  having undergone any distinct change, save
that they present  a soft  and varicose appearance, whilst threading their way
through the cells.   And it is equally certain  that there are  many ganglionic
corpuscles, which never acquire the caudate prolongations, and which appear
specially destined to act upon  this class of nerve fibres.—Some observations
which have been  made upon  the nervous  system of foetuses, in which  the
brain and spinal cord were wanting, present a remarkable confirmation of this
view.*  The nervous cords were for  the most  part developed ;  and at their
(so called) origins  or central extremities, they  were  found to hang as loose
threads in the cavities of the cranium and spine.   On examining these threads,
it was found that  the nerve-tubes, of  which they consisted, formed  distinct
loops; each of which was composed of a fibre  that entered the cavity, and
then  returned from  it.    These  loops were imbedded  in  granular  matter,
resembling that interposed between the vesicles in the cortical substance of
the brain;  and perhaps  to be regarded as vesicular matter  in an early stage
of its formation.   All that is known of  the laws regulating the formation of
such  irregular  productions, leads to the belief, that we may rightly consider
this  arrangement  of  the nerve-tubes as one which  exists in the nervous cen-
tres, when  they are  normally developed.  But it may not be the only one;
for, as already pointed out, some of the nerve-fibres appear  to originate from
the filamentous prolongations of certain ganglionic cells.  Additional informa-
tion is much needed upon this point.
  248. The  arrangement  of the nerve-fibres, at  their  peripheral  extremities,
seems to be essentially  of the same character.   It  has been  already shown
that  the motor fibres, which are distributed  to  the  muscles, have no proper
terminations;  a series of  loops, returning into  themselves or  joining others,
being formed by the ultimate ramifications of the main  trunks.  The arrange-
ment of  the  sensory fibres seems to  be usually of the same  nature.  The
principal trunks subdivide into numerous anastomosing branches, forming a
sort of plexus in  the substance of the skin ; and from this, single filaments
detach themselves  at intervals, rising up  into the  papillary elevations of its
surface, and then returning again into the  plexus, after making a series of

                                Fig. 119.
in a thin perpendicular section of the skin.
loops,  in  which  a sort of varicose  enlargement of the fibre may often be
noticed.   Similar looped terminations have been traced in the nerves supply-

  * Dr. Lonsdale, in Edinb. Med. and Surg. Journal, No. ctvri.; and Mr. Paget in Brit, and
For. Med. Rev., No. xliii. p. 273. 
CONNECTION OF FIBROUS AND VESICULAR SUBSTANCES.         213
ing the dental sacculi, in the expansions of              [Fig. 120.
the auditory nerve distributed upon the de-
licate membrane lining the  cavities of the
internal ear, and elsewhere.  It would yet,
however, be premature to say, that this ar-
rangement  is  universal.—The peripheral
extremities  may be  really "considered as
the origins  of the  sensory nerves ; since
it  is in  them  that those changes are  ef-
fected which it is the office of the trunks
to conduct towards the centres ; and it may
be  reasonably inquired, whether  anything
like the vesicular substance of the ganglia
can  be detected in them.  In examining
the retina microscopically, it is  found to
be almost entirely  made up of a layer of
ganglionic  cells, very closely resembling
those of the grey matter of the brain; and
these are in apposition with the  vascular
layer;  so that we have here  precisely the
same provision for  exciting a change, that
is to be conducted towards the centres, as
we have in the brain  for exciting  a change,
whose influence is to be conveyed towards
the  periphery.  Something  of  the  same
kind has been seen in connection with the
corresponding  expansions of  the  olfactive
and  auditory nerves ;  and it is   probable
that similar elements exist in the papillae
of the skin and tongue, to which the nerves of taste and touch are distributed.
In these papillae we find loops of capillary  vessels  in  close  contiguity with
the  extremities of  the nerve-tubes.—Hence we may state it as a general fact,
that wherever a change is to  be originated,  we find some form of  Vesicular
matter,  with  capillary blood-vessels ; whilst  for  the conduction of such  a
change to distant parts, the Fibrous structure is alone required.
   249. The Chemical constitution of the Nervous matter is peculiar; and
an acquaintance with its general features  is of importance, in leading us  to
recognize in the excretions the results of its decomposition.
  a.  The following, according to L'Heritier, is the relative proportion of the different con-
stituents in individuals of different classes :—
 Terminal nerves on the sac of the second
molar tooth of the lower jaw in the sheep,
showing the arrangement in loops.—(After
Valentin.)]
				Aged	
	Infants.	Youths.	Adults.	Persons.	Idiots.
Water	82-79	74-26	72-51	73-85	70-93
Albumen	7-00	10-20	9-40	8-65	8-40
Fat .	3-45	5-30	6-10	4-32	5-00
Osmazome (?) and Salts	5-96	8-59	10-19	12-18	14-82
Phosphorus	0-80	1-65	1-80	1-00	0-85
It appears from the researches of M. Fremy, that the Phosphorus is combined with part of
the fatty matter; and forms with it two peculiar fatty acids, termed by him the Cere-brio and
Oleophosphoric.—Cerebric acid, when purified, is white, and presents  itself in crystalline
grains.   It contains a small proportion of Phosphorus;  and differs from the ordinary fatty
matter, in being partly composed of Nitrogen.  It consists of 66-7 per cent, of Carbon,  10-6
of Hydrogen, 2-3 of Nitrogen, 19-5 of Oxygen, and 0-9  of Phosphorus; and thus differs from
ordinary fat, not only in containing Phosphorus and Nitrogen, but in possessing more than
twice their proportion of Oxygen.*—Oleophosphoric acid is separated from the former by its

  *  It is probable that, in the above analysis of L'Heritier, the Cerebric acid, which is not
soluble  in ether, is included under the head of Osmazome; for the analyses of Denis and 
214          ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.

solubility in ether:  it is of a viscid consistence; but when boiled for a long time in water or
alcohol, it  gradually loses its viscidity, and resolves itself into a fluid  oil, which is pure
Oleine, whilst phosphoric acid remains in the liquor.  The proportion of Phosphorus which
this oil contains is about 2 per cent.—Cholesterine has also been extracted from the brain by
M. Fremy in considerable quantity.—The proportion of Fixed  !?alts is small; not being
above 3£ parts in 100 of Dry Cerebral matter; which is less than half the proportion that
exists in Muscle.—According to Lassaigne, the chemical composition of the Cortical and
Medullary  substances  of the  brain  is essentially  different;  the  former  containing 85  per
cent, of water, whilst the latter has only  73; the cortical substance having also 3-7 per cent.
of a red fatty matter, of which the medullary has scarcely any;  and being almost entirely
destitute of the white fatty matter, which exists in large proportion in the latter.

  The  Albuminous matter in  the above analyses,  is probably that of which
the walls of the  nerve-cells  and nerve-tubes, and of  the capillary blood-vessels
are composed.   The contents  of these cells and tubes are represented chiefly,
if not entirely, by the phosphorized  fats; and there are many reasons for  re-
garding these  as the  active agents in the operations of the Nervous system.
It will  be remarked,  that  the  amount of  phosphorus is the greatest at the
period of greatest mental  vigour ;  and that in infancy, old age, and idiocy, the
proportion  is  not above half that  which is  present  during tbe adolescent and
adult periods.
  250.  The Nervous  System  is very copiously supplied  with blood-vessels ;
the arrangement of  which varies according to the form of the elementary parts,
in which  they are distributed.   Thus in the Vesicular  substance of the ner-
vous centres, the  capillaries form a minute net-work,  in the interstices of which
the ganglionic cells are included.   In the tubulo-fibrous substance, the capilla-
ries  are distributed  much  on  the same plan as in Muscular  tissue;  the net-
work  being composed of  straight vessels,  which run along the course  of
the fibres, passing  between the  nerve-tubes, and  which are  connected  at
intervals  by transverse branches.   And at the sensory  extremities of  the

              Fig. 121.                                   Fig. 122.
Capillary net-work of Nervous Centres
nerves  we  find loops of Capillaries arching over their terminal and probably
looped  filaments.—The Brain of Man, taken en masse, has been  estimated to
receive one-sixth of the  whole amount of  blood, although its weight is not
usually more than a-fortieth part of that of the entire body.   Whether or not
this estimate be  precisely correct,  there  can  be no  doubt that it receives  far
more blood, than any other part containing the same amount of solid matter.
Now this copious supply of blood evidently has reference to two distinct ob-
jects ;  first, to supply the necessary conditions for the action of the Nervous
system ; and, secondly, to maintain its nutrition.   Many circumstances lead
to the  conclusion that, in  the  Nervous as in  the  Muscular system, every vital
operation is necessarily connected  with  a certain change of composition, so
other chemists give a much higher proportion to the  phosphorized fat, and  a  much smaller
one to the ill-defined compounds represented by the designation Osmazome.
Distribution of Capillaries at the sur-
  face of the skin of the finger. 
SUPPLY OF BLOOD TO NERVOUS TISSUE.
215
that no manifestation of nervous power can take place, unless this change can
be  effected.   There is strong  reason to believe, further, that this change es-
sentially consists in the union of oxygen conveyed by the arterial blood, with
the elements of the proper nervous matter;  and that this union consequently
involves the death  and disintegration of a certain amount of the nervous tis-
sue,—the  reproduction of which  will be requisite, in  order that the systsm
may be maintained in a state fit for action.   This reproduction is effected by
the nutritive process, which takes place at the expense of other constituents
of the blood;  and it will  proceed  most vigorously in the intervals, when the
active powers of the nervous system are not being called into operation (§§ 292
—296).
   251. The proofs of  this continual  waste and reproduction of the Nervous
substance, will  be partly  found in the appearance of the products of its de-
composition  in  the excretions, and in  the demand which is set up for the ma-
terials  for its reparation;  these being found to accord  in amount,  as will be
shown hereafter, with  the degree of its functional activity.   But evidence of
another kind may be drawn  from the  microscopic  appearances observable in
the cortical substance of the Brain.   It seems probable, from the  observations
of Henle, that there is as  continual a succession of nerve-cells, as there is of
epidermic cells; their  development  commencing  at  the surface, where they
are most copiously supplied with blood-vessels from the pia mater; and pro-
ceeding  as they are carried towards the inner layers, where they  come into
more immediate relation with the tubular portion of the nervous tissue.   This
change of place is  probably due to the continual death  and  disintegration of
the mature cells, where they are  connected with the fibres, and the equally
rapid  production  of new  generations at  the  external  surface;—the newly-
formed epidermic cells being thus carried inwards, in precisely the same man-
ner that the epidermic  cells  are carried outwards.
   252. The first development of the Nerve-tubes appears to take place, like
that of Muscular fibre, by the coalescence of  a number of primary cells into
a  continuous tube;  for although  the primary nervous  cell has not yet been
made out with precision, the nuclei of what seem to be the original cells may
frequently  be  seen in the fully-
formed  tube, lying  between their
membranous walls,  and the white
substance  of Schwann  (111,   c).
When first a nerve-fibre can be re-
cognized as such, it has a strong re-
semblance to the gelatinous fibres
of the sympathetic trunks;  being a
cord of small diameter, without  any
clear distinction between  the  tube
and its contents, of granular consist-
ence, and  having  nuclei at no great
distance  from  each  other.   The
substance  of the  fibre, at this  pe-
riod, seems to correspond  with  the
axis-cylinder of  the  fully-formed
nerve-tube ;  the white substance of
Schwann is  subsequently  deposited
around  it, separating  it  from  the
membranous   tubular  envelope.—
The first  development of the vesi-
cular  substance appears  to take place on the same plan with its subsequent
renewal.
[Fig. 123.
  Various stages of the development of nerve;—a.
Earliest stage.  6. Detached fibre,  c. Nucleated fibre
in the lower part of which, d, the white substance o(
Schwann has begun to be deposited, e. Nucleus in a
more fully-formed fibre between the white substance
and  tubular membrane. /.Displays the tubular mem-
brane, the contained matter having given way.—(After
Schwann.)] 
216                 GENERAL VIEW OF THE FUNCTIONS.

  253.  The regeneration of Nervous tubuli that have been destroyed, takes
place in continuity with that which has been left sound.  This may be more
easily proved by the return of the sensory and motor endowments of the part
whose nerves have been separated, than by microscopic examination of the
reunited trunks themselves, which  is not  always satisfactory.   All our know-
ledge of the functions of the Nervous System leads to the belief, that perfect
continuity of  the nerve-tubes is requisite for the conduction of an impression
of any kind, whether this  be destined to produce motion or sensation; and
various  facts,  well known  to Surgeons,  prove that such restoration may be
complete.   In the various operations which are practised for the restoration
of lost parts, a portion of tissue removed from one spot,  is  grafted as it were
upon another; its original  attachments are more or less  completely severed,
frequently altogether destroyed, and new ones are formed.   Now in such a
part, so long as its original connections exist, and the new ones are not com-
pletely formed, the sensation is referred to the spot from  which it was taken;
thus, when a new nose is made, by partly detaching and bringing down a piece
of skin from the forehead, the patient at first feels, when anything touches the
tip of his  nose, as if the contact were really with the upper part of his fore-
head.   After  time has  been given, however, for the  establishment of new
connections with the parts  into whose neighbourhood it has been brought, the
old connections of the grafted portion are completely severed, and an interval
ensues, during which it frequently loses all sensibility; but after a time its
power of  feeling is restored, and the sensations received through it are referred
to the right spot.—A more familiar case is the regeneration of Skin, contain-
ing sensory nerves, which takes place in the well-managed healing of wounds
involving  loss of substance.  Here there must obviously be, not merely a pro-
longation  of the  nerve-tubes from the subjacent and surrounding trunks, but
also a formation of new sensory papillae.—A still  more striking example of
the regeneration of Nervous tissue, however, is to be found in those cases (of
which there are now several on record),  in which portions of the extremities,
that have been completely severed by accident, have been made to adhere to
the stump, and have, in time, completely recovered their connection with the
Nervous  as with the other systems,—as indicated by the restoration of their
motor and sensory endowments.
                         CHAPTER  IV.

                   GENERAL VIEW OF THE FUNCTIONS.

   1. Of Vital Actions, their conditions, and their mutual dependence.

  254. The idea of Life, in its simplest and most correct acceptation, is that
of Vital  Action; and obviously, therefore, involves that of change.  We do
not consider any being as alive, which is not undergoing some  continual alte-
ration, that may be rendered perceptible to the senses.   This alteration  may
be evidenced only by the growth and extension of the organic structure,  or
the development of  new parts ; and it may take place so slowly as to be im-
perceptible, except by comparing observations  made at long intervals.   Thus
the scaly Lichen, that forms the grey or  yellow spots upon  old walls, might
be thought an inert substance, did  we not know that a sufficiently-prolonged 
CONDITIONS OF VITAL ACTIONS.
217
acquaintance with its history would detect its progressive though tardy exten-
sion, and would ascertain that it multiplies its race by an humble yet effectual
process of fructification.—Or the change may be rather  evidenced, by the
performance of some  kind  of movement, for  which the  ordinary  physical
laws of matter will not account; yet, for the detection of this, a close and
careful scrutiny will be frequently required.  Thus the Oyster that is lying
motionless in its massive bed, or the  Ascidia that clusters  upon the faces of
sea-beaten  rocks, may seem  totally destitute of activity ;  yet it would be found
upon close  examination, that their internal surfaces are  covered with cilia
which are  in continual  vibration,—that by this means  water  is  drawn into
the stomach and caused to  traverse  the  respiratory  organs, yielding  to the
former the animalcules  it may contain, and to the latter  the oxygen  dissolved
in it,—that the food thus introduced into the stomach undergoes digestion, and
is converted into materials adapted to nourish the body, which are then con-
veyed to its different parts by a circulating apparatus,—that in due time em-
bryos are produced,  which  are  endowed  with  powers  of active motion, and
which swim forth from within  the  parent-envelopes and  locate  themselves
elsewhere,—and that,  apathetic as  these creatures may seem, they may be
excited by certain kinds of  stimuli  to movements which seem to  evince sen-
sation ; the Oyster closing its shell,  and the Ascidia contracting its muscular
tunic, when it  receives any kind of mechanical irritation  ; and  the former,
whilst lying undisturbed in  its native haunts, drawing together its valves, if a
shadow passes  between itself and the sun.—From what has been already
stated, regarding the nature  of the actions of the Nervous and Muscular sys-
tems, by which the movements  of Animals  are  chiefly  effected, it would ap-
pear that these, in common  with the Vegetative functions, involve a  chemical
alteration in the structure performing them ; so  that it may be  stated as a
general proposition,  that a change in Chemical composition  is an  essential
condition of every Vital phenomenon.
   255. If change be essential to our idea of Life, it may  be asked, what  is
the condition of a seed, which may remain unaltered during a period of many
centuries;  vegetating  at last, when  placed in  favourable  circumstances, as
if it had only ripened the year before.  Such a seed  is  not alive; for it is not
performing any vital operations. But it is not  dead, for it  has undergone no
decay ; and it is still capable of being aroused into active life, when the proper
stimuli are applied.   And the most correct designation  of  its  state seems to
be that of dormant vitality.—The condition of an animal reduced  to  a state of
complete torpidity and inaction, is  precisely similar; into such a condition,
the Frog may be brought by cold, and the Wheel-Animalcule by deprivation
of moisture. And the condition of  a Human being, during sleep, is precisely
similar, so far as his psychical powers are concerned ;  he is  not  then  a feel-
ing, thinking Man ;  but he is  capable of  feeling  and thinking, when  his
brain is restored to a state of activity, and its powers  are called into operation
by the impressions of external objects.
   256. There can be  no doubt whatever, that, of the  many changes which
take place during the life,  or state of vital activity, of an Organised being,
and which intervene between its first development and  its final decay,  a large
proportion are effected by the direct agency of those forces which  operate in
the Inorganic world;  and there is no necessity whatever for  the  supposition,
that these  forces have any other operation in the living body, than they would
have out of it under similar circumstances.—But after every possible allowance
has been made for the operation of Physical and Chemical  forces  in  the living
Organism, there still remain a large  number of phenomena, which cannot be
in the least explained by them ; and which we can only investigate  with suc-
cess, when we regard them as resulting from the agency of forces, as distinct
     19 
218
GENERAL VIEW OF THE FUNCTIONS.
from those of Physics and Chemistry, as these are from each other.   It is to
such phenomena, that the name  of Vital  is  properly restricted; the forces
from whose operation we  assume them to result, are termed vital forces; and
the properties, which we must attribute to the substances exerting those forces,
are termed vital properties.—Thus we say that the contraction of Muscle  is
a Vital phenomenon ; because its character and conditions appear to be to-
tally distinct from those of Chemical or Physical phenomena.  The act  is
the manifestation of a certain Force;  the possession of which is peculiar to
the muscular structure, and which is named the Contractile force.   Further,
that force may remain dormant (as  it were) in the  muscular structure; not
manifesting itself for a great length of time, and yet resting capable  of being
called into operation at any moment.  This dormant force is termed a Pro-
perty ; thus we regard it as the essential  peculiarity of living muscular tissue,
that it possesses the vital property of Contractility.  Or, to reverse the order,
the Muscle is  said to possess the property of Contractility;  the property,
called into operation by the appropriate stimulus, gives rise to the Contractile
force; and the force produces, if  its operation be unopposed, the act of Con-
traction.
   257. These distinctions, though apparently  verbal only, are of importance
in leading us to the correct method of investigating Vital Phenomena, and of
comparing them with  those  of the  Inorganic world.  It is now almost uni-
versally admitted by  intelligent Physiologists, that we gain nothing by  the
assumption of some  general  controlling agency,  or Vital Principle, distinct
from the  organized  structure itself; and that the Laws of Life are nothing else
than general expressions of the conditions under which Vital operations take
place,—expressions analogous to those  which constitute the laws of Physics
or Chemistry,—and to be arrived at in the  same manner, namely,  by the col-
lection and comparison of phenomena.   The difficulty of thus generalising in
Physiology results  merely from  the complex  nature of the phenomena, and
the consequent difficulty of precisely determining their conditions.   We have
as much  ground for believing in the fixity and constancy of Physiological
phenomena, when the causes  and conditions are the same, as we have in those
of  any  other department of  science ;  and the apparent uncertainty of the
actions of the living body, results merely from the influence of differences in
those conditions, so trivial in appearance as frequently to elude  observation,
and yet  sufficiently powerful in reality to  produce an entire  change in the
result.
   258. All Vital phenomena  are dependent upon at least two sets of condi-
tions;—an Organized structure, possessed of peculiar properties ;—and certain
Stimuli, by which these properties are called  into action.   Thus,  to revert to
the example just  cited, the  Contraction of a Muscle is due to the  inherent
Contractility of the Muscular tissue, called into operation by the stimulus of
innervation;—other conditions, as a certain elevated temperature,  a supply of
oxygen,  &c, being  at the  same time requisite.  The Microscopical  and
Chemical  researches of  recent years,  have given increased stability to the
position, that the  peculiar properties, which  we  term Vital,  are dependent
upon those peculiar modes of combination and aggregation of the elementary
particles, which are characteristic of Organized structures.  We have no evi-
dence of  the  existence of Vital  properties  in any other form  of  matter than
that which we term Organized; whilst, on the other hand, we have no reason
to believe that Organized  matter  can possess its normal  constitution, and be
placed in the requisite   conditions, without  exhibiting Vital Actions.  The
advance  of Pathological science  renders it every day more probable (indeed,
the probability may now  be said to amount almost to positive  certainty), that
derangement in function,—in other words, an imperfect or irregular action,— 
CONDITIONS OF VITAL ACTIONS.
219
always results, either from some change  of structure or composition  in  the
tissue itself, or from some  corresponding  change in the external conditions,
under which the properties of the organ are called into action.   Thus, when
a Muscle has been  long disused, it can  scarcely be excited to contraction by
the usual stimulus,  or may even be altogether powerless ;  and minute  exami-
nation of its structure shows it to have undergone a change, which is obvious
to the Microscope (the  fibres  being as it were shrunken, and the fibrillae in-
distinct), though it may not be  perceptible to the naked eye, and which  results
from  imperfect nutrition.   Or, again,  convulsive or  irregular actions  of the
Nervous System  may be produced, not by any change in its own structure
or composition, but by  the presence of various stimulating  substances in the
blood (such as  urea or strychnine), although their quantity may be so small,
that they cannot be detected without great difficulty.   Further, whenever the
peculiar properties of an Organized structure can no longer  be excited  by the
requisite stimuli, we find that it has undergone some incipient change of com-
position, or that some of the other conditions are wanting.   Thus, the depar-
ture of the  contractility from the muscles of warm-blooded animals, at no  long
period after the cessation of the  circulation, is due in part to the lowering of
their temperature, and in part  to the cessation of the supply of oxygen to the
elementary parts of  their substance;  either of  which would alone  suffice to
prevent their respondence to the  stimuli, that would  ordinarily produce ener-
getic  contractions.—Lastly, we  find special  properties constantly associated
with distinct forms  of organized tissue; thus we never find contractility exist-
ing in the  fibres  of Nerve;  nor do we ever find  the power of conducting
impressions to  exist in the fibres of  Muscle.  The details given in the  pre-
ceding Chapter make it evident that each tissue, distinguished from others by
its  peculiar composition, and  by the form of its elementary parts, has  some-
thing peculiar in its properties ;  and  this is true, as well of properties that are
simply  physical, as of those  that belong  to a  different category:  thus  the
Yellow Fibrous tissue  is distinguished from the White as  much by its elas-
ticity, as by its peculiar composition;  and it does not lose its elasticity, until
it is in a state of  evident decay.
   259.  By the study of the various forms of Elementary Tissue, of  which
the Human fabric (or any other of similar  complexity) is made up, we are led
to the very same  conclusion, with  that which we  should derive  from  the
observation of the  simplest forms of organized being, or from  the  scrutiny
into the  earliest  condition of the most complex;—namely, that the  simple
Cell may be regarded as the  type of  Organization; and  that its actions
constitute the simplest idea of Life.  Between the humblest Confervoid Plant,
and the highest Animal, there is originally no perceptible difference ; they may
be said to have a common starting-point;  and  the subsequent  difference of
their  course  consists essentially  in this,—that the successive generations of
cells,  which are the  descendants  of the former, are all similar to it, each cell
being capable of existing by itself, and therefore ranking as an independent
individual;  whilst  the  subsequent  generations, which originate from  the
latter, undergo various departures from the primary type, and lose the  power
of independent existence, their several actions being mutually dependent upon
each  other, so that  the  integrity  of the whole fabric  is essential to the  con-
tinued life  of any individual cell.  Every individual part, however, even in
the most complex and highly-organized fabric, has its own power of develop-
ment ; and the properties which  it possesses are the result of the exercise of
that power.  But instead of the power of  cell-growth being exerted, as in the
Plant, upon the inorganic  elements  around, it  can  only be put in action, in
the Animal, upon certain peculiar compounds, having the same chemical com-
position with its own substance;  and it is for the reception of these, for their 
220
GENERAL VIEW OF THE FUNCTIONS.
preparation, and for their  maintenance in the requisite state of purity, that a
large part of the fabric of the Animal is destined.  But if we could imagine
its  several tissues to be supplied with nutriment in any other manner, and
maintained in other respects in their normal circumstances (as regards warmth,
air, &c), we have every reason to believe that their independent vitality would
manifest itself,by their continued development, and by the regular exhibition
of  their ordinary properties.  An  approach to this condition is made, in the
experiment  of entirely detaching a limb from  the body, but  keeping up the
circulation of  blood through it, by means of tubes connecting its main artery
and vein witji those of the stump.  Notwithstanding the prejudicial effect of
such severe  injuries, the  increased duration of the muscular irritability in the
separated  part, is a sufficient proof of the continuance of the normal actions of
nutrition,  although  of course  in  a diminished degree.   And  the  occasional
reunion of a member which has been entirely separated,  when decomposing
changes have not yet commenced in it, most clearly shows, that  nothing but
the restoration of its supply of  nutriment is requisite for the preservation of
its vitality, and that its powers of growth and renovation are inherent in itself,
only requiring a due supply of the nutrient material, with certain other con-
current conditions.
  260. In every living structure of a complex nature, therefore, we see a great
variety of actions, resulting from  the exercise of the different properties of its
several component parts.  If we take a general survey of them, with reference
to their mutual relations  to each other, we shall perceive  that they may  be
associated into groups; each  consisting of a  set of actions,  which,  though
different in themselves, concur in  effecting some positive and determined pur-
pose.   These groups of actions  are  termed Functions.   Thus, one of  the
most universal of all the changes  necessary to the continued existence of a
living being, is the exposure of its nutritious fluid to  the air;  by the action of
which  upon it, certain alterations are effected.  For the performance of this
aeration, simple as the change appears, many provisions are required.   In the
first place, there must be an aerating surface, consisting of a thin membrane,
permeable to gases;  on the one side of which the blood may be  spread  out,
whilst  the air is in contact with the other.  Then  there must be a provision
for  continually renewing the blood which is brought to  this surface; in order
that the whole mass of fluid may be equally benefited  by the process.  And,
in like manner, the stratum of air must also be renewed, as frequently as  its
constituents  have undergone any essential change.  We include, therefore, in
speaking of  the Function of Respiration, not only the actual aerating process,
but also the  various changes which are necessary to carry this into effect, and
which  obviously have it for their  ultimate purpose.
  261. On  further  examining and comparing  these Functions, we find that
they are themselves capable of some degree of classification.   Indeed  the dis-
tinction between the groups into which they may be arranged, is one of essen-
tial importance in Animal Physiology.  If we contemplate the history of the
Life of a Plant, we perceive that it grows from a germ to a fabric of sometimes
gigantic size,—generates a large  quantity of  organised  structure, as  well  as
many organic  compounds, which form the products of secretion, but which  do
not undergo organization,—and  multiplies its species, by the production of
germs  similar to that from  which  it originated;—but that it performs all these
complex operations, without (so far as we can perceive) either feeling or think-
ing, without consciousness or will.  All the functions of which its Life is com-
posed, are, therefore, grouped  together under the general designation of Func-
tions of Organic or Vegetative life: and they are subdivided into those  con-
cerned in the maintenance  of the structure of the individual, which are termed
functions  of Nutrition;  and  those to which the Reproduction of the species 
             CLASSIFICATION OF VITAL ACTIONS INTO FUNCTIONS.          221

is  due.—The great feature of the Nutritive operations  in the Plant, is their
constructive character.   They seem as if destined merely for the building-up
and  extension of the fabric; and to this extension there may be no definite
limit.   But it is very important  to  remark, that the growth  of the more per-
manent parts of the structure is only attained by the  continual development,
decay, and renewal of parts, whose existence is  temporary.  No fact is better
established in Vegetable Physiology, than the dependence of the formation of
wood upon the action of the leaves.   It is in their cells, that those important
changes are effected in the sap, by which it is  changed, from a crude watery
fluid containing very little solid matter, to a viscid substance  including a great
variety of organic compounds, destined for the nutrition of the various tissues.
The "fall of the leaf" results merely from the  death and decay of its tissue;
as is evident from the fact, that, for some  time previously, its  regular functions
cease, and that, instead of a fixation  of carbon from the atmosphere, there is a
liberation  of carbonic acid (a result  of their decomposition) in  large amount.
The process takes place in evergreens equally with deciduous trees; the only
difference being, that  the  leaves in the latter are all cast off  and  renewed to-
gether, whilst in the  former they are continually being shed and replaced,  a
few at a time.  It appears as if the nutritious fluid of the higher Plants can
only be prepared by the agency of cells, whose  duration is brief; for we have
no instance, in which the tissue concerned in its elaboration possesses more
than a very limited term of existence.   But by its  active vital operations, it
produces a fluid adapted for the nutrition of parts which are  of a much more
solid and  permanent character, and  which  undergo little change of any kind
subsequently to their complete development;—the want of tendency to decay
being the result of the  very same  peculiarity of constitution as that  which
renders them unfit to participate in the proper vital phenomena of the organism.
Thus the  final cause or purpose of all the Nutritive functions of the Plant, so
far as the  individual is concerned, is to produce an indefinite extension of the
dense, woody, almost inert, and permanent portions of the fabric, by the con-
tinued development,  decay, and  renewal of the  soft,  active, and transitory
cellular parenchyma.—The Nutritive  functions, however,  also  supply the
materials for the continuance of the  race, by the generation of new individuals;
since a new germ cannot be formed, any more than the parent structure can
be extended, without organizable  materials, prepared by the  assimilating pro-
cess, and  supplied to the parts where active changes are going on.
  262. On analyzing the operations which take place in the Animal body, we
find that a large number of them are of essentially the same character with the
foregoing, and differ only in the conditions under which they are  performed ;
so that we may, in fact, readily separate  the Organic  functions, which are
directly concerned in the development and maintenance of the fabric, from the
Animal functions,  which render the  individual conscious of  external impres-
sions, and capable of  executing spontaneous movements.   The  relative de-
velopment of the organs destined to these two  purposes, differs considerably
in the several groups of Animals,  as we have already in part seen (Chap. I.).
The life of a Zoophyte is upon the whole much more vegetative than animal;
and we perceive  in it, not merely the very feeble development of those powers
which are peculiar to the Animal kingdom, but also that tendency to indefinite
extension  which is  characteristic  of the Plant.   In  the Insect we have the
opposite extreme; the most active powers of motion, and sensations of  which
some (at least) are very acute, with a low development of the organs of nutri-
tion.   In Man, and in the higher classes generally, we have less active powers
of locomotion, but a much greater variety of Animal powers  ; and the instru-
ments of the organic or nutritive  operations attain their  highest development,
and their greatest degree of mutual dependence.  We see in the fabric of all
                                   19* 
222
GENERAL VIEW OF THE FUNCTIONS.
things, in which the Animal powers are much  developed, an  almost entire
want of that tendency to indefinite extension, which is so characteristic of the
Plant; and when the large amount of food consumed by them is  considered,
the question naturally arises, to what purpose this food  is applied, and what
is the necessity for the continued activity of the Organic  functions, when once
the fabric has attained the limit of its development.
   263.  The answer to this question  lies in the fact, that the  exercise  of the
Animal functions is essentially destructive of their instruments ; every ope-
ration of the Nervous and Muscular  systems  requiring, as its necessary con-
dition, a disintegration of a certain part of their tissues, probably by their ele-
ments being caused to unite with oxygen.   The  duration of the existence  of
those tissues (as stated in the  preceding Chapter) varies inversely to the use
that is made of them ; being less as their functional activity is greater.  Hence,
when an Animal is very inactive, it requires but  little nutrition; if  in  mode-
rate activity, there is a  moderate  demand  for food ; but if its Nervous and
Muscular energy be frequently and powerfully aroused, the supply must be
increased, in order to maintain  the vigour of the system.   In like manner, the
amount of certain products of  excretion, which result from the disintegration
of the Nervous and Muscular tissues, increases with their activity, and dimin-
ishes in proportion to their freedom from exertion.*  We are not to measure
the activity of the Nervous system, however, like that of the Muscular, only
by the amount of movement to which it gives origin.   For there is equal evi-
dence, that the demand  for blood in the brain, the amount of nutrition it re-
ceives, and the degree of disintegration it undergoes, are  proportional likewise
to the energy of the purely psychical operations ; so that the vigorous exercise
of the intellectual powers, or a  long-continued state of agitation of  the feelings,
produces as great a waste of Nervous matter, as is occasioned by active bodily
exercise.  From this and other considerations, we are almost irresistibly led
to the belief, that every act of  Mind is  inseparably connected, in  our present
state of being, with material changes in the  Nervous  System; a doctrine not
in the least inconsistent with the belief in the separate immaterial existence  of
the Mind itself, nor with the expectation of a future state, in  which the com-
munion of Mind with Mind shall be more direct  and unfettered.
   264. Thus  in the Animal fabric, among the higher classes at least, the func-
tion or purpose of the organs of Vegetative life is not so much  the  extension
of the fabric, for this has certain definite limits, as the maintenance of its in-
tegrity, by the reparation of the  destructive effects of the  exercise  of the
purely Animal powers.   Thus, by the operations of Digestion, Assimilation,
and Circulation, the nutritious materials  are prepared  and conveyed to the
points where they are required  ; the Circulation of Blood also serves to convey
oxygen, which is  introduced by the Respiratory process; and  it has further
for its office to convey away the products of the decomposition of the Muscular
and Nervous tissues that results from their functional activity,—these products
being destined to be  separated  by the Respiratory and other Excreting opera-
tions.  In the performance of the Organic  functions of Animals, as in those
of Plants, there is a continual new production, decay, exuviation, and renewal,
of the cells, by whose instrumentality they are effected ; which altogether effect
a change not less complete than of the leaves in Plants.  But  it takes place  in
the penetralia  of the system, in such a manner as to elude observation, except
that of the most scrutinizing kind;  and it has been in bringing this into view,
that the Microscope has  rendered most essential  service  in Physiology.

  * This doctrine, though propounded in general terms by previous writers, was first point-
edly stated  by Prof. Liebig, so far as regards Muscular  tissue, in his Treatise  on  Animal
Chemistry.  It will be hereafter shown, however, to be  equally applicable to the Nervous
substance. 
MUTUAL DEPENDENCE OF VITAL OPERATIONS.
223
  265. The regular maintenance of the functions of Animal life is thus entirely
dependent upon the due performance of the Nutritive operations; a considera-
tion of great importance in practice, since a very large  proportion of what are
termed functional disorders (of the Nervous system especially) are immediately
dependent upon some abnormal condition of the  Blood.  But there also exists
a connection of an entirely reverse kind, between the Organic and Animal func-
tions ;  for the conditions of Animal existence render the former in great degree
dependent on the latter.   Thus, in regard to the acquisition of food, the Animal
has to make use of its senses, its psychical faculties, and its power of locomotion,
to obtain that which the Plant, from the different provision made for its support,
can derive without any such assistance.  Moreover, the propulsion of the food
along the alimentary canal  is effected  by a series of operations, in which the
Nervous and  Muscular systems  are  together involved at the two extremes;
though simple Muscular contractility is  alone employed  through the greater
part of the intestinal canal.   Thus, the change in the conditions required for
the  ingestion of  food by Animals, has  rendered necessary the introduction of
an additional  element in  the apparatus,  to which nothing comparable was to
be found in  Plants.   Again, in the function of Respiration  as performed in the
higher Animals, the Nervous and  Muscular systems are alike involved; for the
movements, by which the  air in the lungs is being continually renewed, are
dependent upon the action  of both ; and those by which the blood is propelled
through the respiratory organs, are chiefly occasioned by the contractility of a
muscular organ,—the heart.  But in regard to the simple contractility of mus-
cular fibre, upon the direct application of a stimulus to it, which is  the agent
in the movements of the heart and of the alimentary canal,  it may be remarked,
that it does not differ in any  essential particular  from that which is witnessed
in many Vegetables: so that it strictly belongs to the functions of Organic life.
And with respect to those concerned in the act of Respiration, as well as those
which govern the two orifices of  the alimentary tube, it will hereafter appear
that they result, equally with the former, from the application of a stimulus;
and that they  may be performed without any consciousness on the part of the
individual (though ordinarily accompanied  by it):—the difference being, that
in the former the stimulus is  applied to the contractile part itself, whilst in the
latter it  is applied  to an organ with which this is connected by nerves only.
Now we have, even in Vegetables, instances of the propagation of an irritation
from one part to another, so  that a motion results in a part distant from that
stimulated,—as in the case of the Sensitive Plant or Venus's Fly-trap.   The
only essential difference,  therefore, between  those movements of Animals,
which are  thus  closely connected with  the maintenance of the organic func-
tions, and those of Plants, consists in the medium through which  they are
performed,—this being in Animals a distinct Nervous and Muscular apparatus,
whilst in Plants it is only a peculiar modification of the ordinary structure.
  266. From  what has been  said, then, it appears that all the functions of the
Animal body are so completely bound up together, that none can be suspended
without the  cessation of the rest.   The properties of all the tissues and organs
are dependent upon their regular  Nutrition, by a due supply of perfectly-ela-
borated blood;  this  cannot be effected  unless  the functions of  Circulation,
Respiration, and Secretion, be performed with regularity,—the first being ne-
cessary to convey the supply of nutritious fluid, and the two latter to separate
it from its impurities.  The Respiration cannot be maintained without the in-
tegrity of a certain part of the  nervous  system; and the due action of  this,
again, is  dependent upon its  regular nutrition.   The materials necessary for
the replacement of those which are continually being separated from the blood,
can only be derived by the Absorption of ingested aliment; and this cannot
be accomplished without  the preliminary process of Digestion.  The intro- 
224
GENERAL VIEW OF THE FUNCTIONS.
duction of food into the stomach, again, is dependent, like the actions of Re-
spiration, upon the operations of the muscular apparatus and of a part of the
nervous centres; and  the  previous  acquirement of food necessarily involves
the purely Animal powers.  Now it will serve to show the distinction between
these powers, and those which  are  merely subservient to Organic  life, if we
advert to the case, which is of  no unfrequent  occurrence, of a human being,
deprived, by some morbid condition of the brain, of all the powers of Animal
life,—Sensation, Thought, Volition, &c.; and yet capable of maintaining a
vegetative existence,—all the  organic functions going on as usual, the morbid
condition not having  affected the division of the nervous system, that is con-
cerned in the movements on which  some of them  depend.   It is evident that
we can assign no definite limits to such a state, so  long as the necessary food
is  placed within reach of the grasp of the muscles,  that will convey it into the
stomach;  as a matter of fact,  however, it is seldom of long continuance ;
since the disordered state of the brain is sure to extend itself, sooner or later,
to  the rest of the  nervous system.   This condition may be experimentally
imitated, however, by the removal of the brain in many of the lower animals,
whose bodies will  sustain life for many months after  such a mutilation; but
this  can only take place when  that food is  conveyed by  external  agency
within the pharynx, which they would, if in their  natural condition, have ob-
tained for themselves.  A similar experiment is sometimes  made by Nature
for the Physiologist, in the production of foetuses,  as well of the human as of
other species, in which  the brain is absent; these can breathe and  suck and
swallow, and perform all their organic functions ; and there is no  assignable
limit to their existence, so long  as they are duly supplied with food.  Hence
we may learn the exact nature of the dependence of the Organic  functions
upon those  of purely Animal life;  and we  perceive that, though less imme-
diate than it is upon the simple organic operations of the nervous and muscu-
lar systems, it is not less complete.   On  the  other hand, the functions of
Animal life are even more closely dependent upon the Nutritive  actions than
are those of organic life in general; for many tissues will  retain their several
properties, and their power of  growth and  extension, for a much longer pe-
riod  after a general  interruption of the circulation,  than will the Nervous
structure ; which is, indeed, instantaneously affected by a cessation of the due
supply of blood, or by the depravation of its quality.
   267. It is  of little consequence, then, with which  group  of functions we
commence the detailed study of the phenomena, which in their totality make
up the life of Man.  In viewing him  merely as one of the widely-extended
group of organized beings, it would be natural to commence with those phe-
nomena which are common to  all;  and to make, therefore, the Organic func-
tions the first object of our consideration.  On the other hand, regarding Man
as a  being in some degree  isolated  from all these by his  peculiar character-
istics, it seems right to inquire  into the latter in the  first  instance;  more
especially as, in  a general  view of his life, these occupy the most  prominent
place.   It will be necessary, however, previously to entering upon  them, to
take a more detailed survey than we have hitherto done, of the vital  opera-
tions  performed by his several organs, and of their connections with each
other.  We shall commence with those of Vegetative Life.

                    2. Functions of Vegetative  Life.

   268. It is one of the most peculiar characteristics of Organized  structure,
that  its elements have a constant tendency  (under ordinary circumstances at
least) to separate into more simple  combinations; and although it has been
ordinarily considered, that  their living state prevents such a change, and that 
FUNCTIONS OF ORGANIC OR VEGETATIVE LIFE.
225
they have no tendency to it except when dead, reason will hereafter be given
for  the  belief that no such  distinction exists  (Chap. XIV., Sect.  4).  The
maintenance of the vital properties of all organized structure then, requires
either that this  structure should be completely secluded from  air,  moisture,
warmth, and other agents which tend to its decomposition; or that it should
be renewed as fast as it decays.   Now the exclusion of these decomposing
agents would prevent any vital actions from  being called into operation;
since they  are  the ordinary stimuli  which are  necessary to  them.   For
instance, a seed which is buried so deep in the soil as to be excluded  from
the contact of air,  and from the warmth of the sun, will not vegetate, although
it may retain its  power of germinating when  placed in more favourable cir-
cumstances ;  and it will not decay, because secluded from the air and warmth
which are necessary to its decomposition.   But as a certain change of  com-
position  appears  to be a necessary condition of its vital  activity,  it is  obvi-
ously requisite that a provision should  be made, for  removing  from the
organism all those particles which  are manifesting an incipient tendency to
decay, and are thus losing their vital properties; and for replacing these by
newly-combined  particles, which  in their  turn undergo  the same process.
Thus we find that, in the softest parts of the Animal frame-work, as in those
of the Plant, there is much less permanency than there is in those harder and
more solid portions, which often seem altogether to defy  the lapse of  time.
Now it  is in the former that the most active vital changes  take place,—those
of  the  nervous  system,  for example; whilst  of  the  latter, the function is
chiefly, if not entirely, that of giving mechanical  support to the  structure.
The former organs are renewed many times, whilst the fabric of the latter is
not once completely changed;  and thus a very interesting  correspondence is
shown  between the degree in which the action of  any organized structure is
removed from, or is similar to, that of a mere inorganic  substance, and the
amount  of  tendency to  decomposition which  that structure exhibits;  since
this constant  renewal can scarcely serve  any other purpose  than  that of
making up for the effects of decay.
  269.  One of the most important purposes of the supply of aliment, there-
fore, which all living beings continually require, is the replacement of the
portions of the fabric that are thus lost.  The effects of the process  of decay,
when uncompensated by that of renovation, are remarkably seen in cases of
starvation; for it is a very constant indication of this condition, that the  body
exhales a putrescent odour, even before death, and that it subsequently passes
very rapidly into  decomposition.  This, it  may be considered, is the reason
why a constant  supply of aliment  is  still  required for  the maintenance of
every organic structure, though  it may have arrived at its full growth; and it
also affords one source of explanation of the fact, that old people require less
food than adults,  since their  tissues  are more consolidated, and thus become
at the same  time unable to perform their  usual actions with  their pristine
energy, whilst their tendency to decomposition is less.   In the growing  state,
however, an additional important source of demand for food obviously exists,
in the extension which the tissues  themselves are constantly receiving; yet
this, perhaps, does not make so great a difference, as it appears to  do, in the
supply  which is requisite.  For if the addition which is made by  growth to
the  body in any given time, be compared with the  amount of exchange which
has taken place in the same time,—the latter being judged  of by the quantity
of matter excreted from the lungs, liver, kidneys, skin, &c,—it will be found
to bear but a very small proportion to it; except during foetal life, when the
growth is very rapid, and a large proportion of the  effete  particles  are  com-
municated to the maternal blood, to be excreted from it.   The real cause of
the  increased demand for nutriment, during the early part of life, is rather 
226
GENERAL VIEW OF THE FUNCTIONS.
this,-—that the tissues are far from having acquired that firmness and consoli-
dation which they gain at adult age;  and that they are, therefore, more prone
to decomposition, at the same time that their vital activity is greater, as is well
known to be the  case.—The feeling of hunger or desire for food originates,
we shall hereafter find reason to believe  (Chap. X., Sect. 1), not so much in
the stomach itself, as in the system at large; of whose condition, in regard to
the requirement of an increased supply of aliment, it may, during the state of
health, be considered as a pretty faithful  index.  The same may be said  of
thirst.   The feeling of hunger, then, is the stimulus  to the mental operations,
which have for their object  the acquisition of food; whether  these be of a
voluntary or of a purely instinctive  kind.  In Man they are  obviously  the
former, during all but infant life.
   270.  The food received into the mouth, and prepared there  by the acts of
mastication and insalivation (the movements concerned in which  are dependent
upon the brain, and can only be performed when it is in a condition of  some
activity), is  brought by them within reach of the pharyngeal muscles, whose
contraction cannot be effected by the will, but is purely excilo-motor,—result-
ing merely from the impression made upon the fauces  by the contact of  the
substance swallowed, which impression is conveyed to the medulla oblongata
and  reflected back  to  the muscles (§ 383).   By these it is propelled  down
the oesophagus; and, after  their action has ceased, it is taken up (as it were)
by the muscular coat of the  oesophagus itself, and conveyed into the stomach.
How far the movements of the  lower parts  of  the oesophagus  and of  the
stomach  are in Man  dependent  upon  reflex  action, is uncertain;  the facts
which have been  ascertained on this point, by experiment on animals, will be
detailed in their proper place (§ 390).  In the stomach the food is subjected
to the gastric  secretion;  the chemical action of which, aided by the con-
stantly-elevated temperature of the interior of the body, and by the continual
agitation effected by the contractions of the parietes of the organ, effects a
more or less complete solution of it.  The  mixture of the biliary and pan-
creatic secretions  with the chyme thus produced,  occasions a separation  of its
elements into those adapted  for nutrition, and those of which the character is
excrementitious;  and this separation can scarcely  be regarded in any  other
light  than as a chemical precipitation.  By the  agency of  the biliary secre-
tion, moreover, certain elements of the food that would otherwise be rejected,
are reduced  to a form  in which they can be absorbed.   The nutritious por-
tion is taken up by the Blood-vessels and by the Absorbent vessels (or Lac-
teals), which are  distributed on the walls of the alimentary canal; whilst  the
remainder is propelled along the intestinal tube by the simple contractility of
its walls, undergoing at the  same time some further change, by which  the
nutritive materials are  still more  completely extracted  from it.  And at last,
the excrementitious matter,—consisting  not only of a portion  of  the food
taken into the  stomach, but  also  of  part of the secretion of the liver, and of
that of the mucous surface of the intestines and of their glandulae,—is avoided
from the opposite extremity of the  canal, by a muscular  exertion, which is
partly reflex, like that of deglutition, but is partly voluntary, especially (as it
would appear) in Man.
   271.  There  seems no doubt that  fluid containing saline, albuminous, or
other soluble matters, may be absorbed by the Blood-vessels, with which  the
mucous membrane of the alimentary canal is so copiously supplied ; and  this
simple process  of Imbibition probably takes place  according to the physical
laws of Endosmose.   But the Selection  and Absorption of certain nutritious
elements appear to  be performed, not by  vessels, but by the growth and  de-
velopment of cells (§ 181);  which, by their subsequent disintegration, give it
up to the Lacteals.   The absorbed fluid, which  now receives the  name of 
FUNCTIONS OF ORGANIC OR VEGETATIVE LIFE.
227
Chyle, is propelled through the Lacteals, by the contractility of their walls ;
aided in  part, perhaps, by a vis a tergo derived from the force of the absorp-
tion itself.  With the reception of the nutritious fluid into the absorbent ves-
sels, commences its real preparation for  Organization.   Up to that period, it
cannot be said  to be in  any degree vitalised; the changes which it has under-
gone being only of a chemical and physical nature, and such as merely prepare
it for subsequent assimilation.  But in its passage through the long and tor-
tuous system  of absorbent vessels and  glands, it undergoes  changes which,
with little chemical difference, manifest themselves by a decided alteration  in
its properties;  so that the chyle of the thoracic  duct is evidently a very dif-
ferent fluid from the chyle of the lacteals, approaching  much  nearer to blood
in its general characters.   These characters are such as indicate that the pro-
cess of organization and vitilization has commenced; as may  be known alike
from the  microscopic appearance of  the  fluid, and  from  the  actions it  per-
forms when removed from the body.  There is reason  to believe that the
changes, which the Chyle  undergoes in its progress  through  the lacteals, are
due  to the action of certain  cells which are seen to be diffused through the
liquid (§ 155);  these, by their own independent powers of growth, are con-
tinually absorbing into  themselves  the fluid  in which  they float; whilst, by
bursting  or liquefying, as soon as  their term of life is completed, they give
this  back in an altered state.   The Chyle thus modified is conveyed into the
Sanguiferous system of vessels, and flows directly to the heart; by which it is
transmitted with the mass of the blood, to the lungs.   It there has the oppor-
tunity of excreting its superfluous  carbonic acid, and of  absorbing oxygen;
and probably acquires gradually the properties, by which  the  blood previous-
ly formed is distinguished,—thus becoming the pabulum  vitas for the whole
system.
   272.  The  Circulation of  the Blood through the tissues and organs which
it is destined to support, is a process  evidently necessary for the conveyance
to them  of the  nutritious materials, which are provided for the repair of  their
waste ;  and for the removal  of those elements of their fabric,  which are in a
state of  incipient decomposition.   In the lowest classes of organized beings,
every portion of the structure is in direct relation with its nutritive materials ;
it can absorb for itself that which is  required ;  and  it can readily part with
that of which it is desirable to get rid.  Hence in such, no general circulation
is necessary.   In Man, on the other hand, the  digestive cavity occupies  so
small a portion of the body, that the organs at a distance from  it have no  other
means, than their vascular communication  affords, of participating in the re-
sults of its operations; and it  is moreover necessary that  they should  be
continually furnished with the organizable materials, of  which the occasional
operation of the digestive process would otherwise afford only an intermitting
supply.   This  is especially the case, as already mentioned, with the Nervous
system,  which is so predominant a feature in the constitution of Man ; and
we accordingly find both  objects provided  for,  in  the  formation of a large
quantity of a semi-organized product, which  contains within  itself  the mate-
rials of all the  tissues, and is constantly being carried into relation with them.
Blood has been not unaptly  termed chair coulante, or liquid flesh; and  al-
though  it has been heretofore much questioned, whether it could be regarded
as either organized or endowed with  vital properties, there now appears  to  be
sufficient reason for  admitting, that  this is  the  case to a very considerable
extent.   The propulsion of  the blood through the large trunks, which subse-
quently divide into capillary vessels, is due to the contractions of a hollow mus-
cular organ, the Heart;  but  these,  like the peristaltic movements of the ali-
mentary canal, are quite independent of (though frequently influenced by) the 
228
GENERAL VIEW OF THE FUNCTIONS.
agency of the Nervous system;  and are  therefore to be referred to the class
of Organic movements, such as occur in  Vegetables.
  273.  Upon the circulation of the blood through all parts of the fabric, de-
pends, in the first place, the Nutrition of the tissues.  Upon this subject, for-
merly involved in the greatest obscurity, much light has  recently been thrown
by  Microscopic discovery ; it being now understood  (as explained in the
preceding Chapter), that the continued growth and renewal of each tissue are
effected by a continuation of a process of cell-growth, similar to that by which
it was  first  developed.  Even where the primary cells have changed  their
character, their nuclei remain persistent; and may be regarded  (in the lan-
guage of Mr. J. Goodsir) as so many "germinal centres," for giving origin to
new products.  The greatest difficulty, in the present condition of our know-
ledge of this most interesting subject, is to comprehend the reason why such a
variety of products should  spring up ; when the cells in which  they all origi-
nate, appear to be so exactly alike.   The important discoveries now referred
to are not confined to healthy structures; for it has been ascertained, that dis-
eased growths have a similar origin and mode of extension ; and that the ma-
lignant character, assigned to Cancer, Fungus  Haematodes, and other such
productions, is to be traced to the fact, that they are composed of cells which
undergo little metamorphosis, and retain  their reproductive  power ;  so that
from a single cell, as from  that of a  Vegetable Fungus,  a large structure may
rapidly spring  up, the removal of which is by  no means attended with any
certainty that it will not speedily  re-appear, from some  germs left in the sys-
tem.
  274. The  independent character of the cells in which all organized tissues
originate, might be of itself a satisfactory proof that, in Animals, as in Plants,
the  actions of Nutrition are performed by the powers  with  which they are
individually endowed ; and that, whatever influence the Nervous system may
have upon them, they are not in any way essentially dependent upon it. More-
over, there is an evident improbability in the idea, " that any one  of the solid
textures of the living body  should have for its office, to give to any other the
power of taking on any vital actions :" and the improbability becomes an im-
possibility, when the fact is made known, that no formation of nervous matter
takes  place  in the  embryonic structure, until the processes of Organic life
have been for some time in active operation.   The influence which the Nerv-
ous System is known to have upon the Function of Nutrition, is probably ex-
erted, rather through the medium of its power of regulating the diameter of the
arteries and capillaries, by which it controls in some degree the afflux of blood,
and of affecting those preliminary actions on which the quantity and quality of
the  nutritious fluid depend ; than in any more direct manner.   At any rate,
it may be safely asserted, that no  such  proof of its more direct influence, as
is required to counterbalance the manifest improbability which has been shown
to  attend it, has yet been  given;—all the facts which have been adduced in
support of this hypothesis  being equally explicable on the other, which, being
in itself more probable, ought to be preferred.
  275. The  renewal which  the various  tissues of the  body are continually
undergoing, has for its chief object the counteraction of the decay into which
they would otherwise speedily pass;  and  it is  obviously required, that a means
should be  provided  for conveying away the waste, as  well as for supplying
the  new material.  This is partly effected by the Venous circulation; which
takes up a large part of the products of incipient decomposition, and conveys
them to organs of Excretion, by  which they may be separated and cast forth
from the body.  The first product of the decay of all  organized structures,
is  carbonic  acid; and this is the one which  is most constantly and rapidly
accumulating in the system, and the retention of which, therefore, within the 
                FUNCTIONS OF ORGANIC OR VEGETATIVE LIFE.            229

body, is  the most  injurious.   Accordingly, we find two  large  organs—the
Lungs and the Liver—adapted to remove it;  and to both these Venous blood
passes, before it is again sent through the system.  The function of the Lungs
is so important in warm-blooded  animals, that  a  special heart is provided for
propelling the blood through them;  in addition to the one possessed by most
of the lower animals, the  function of which is the propulsion of the blood
through the system.  In these organs, the blood is subjected to the influence
of the atmosphere,  by which the  carbonic acid  with which it was  charged, is
removed and replaced by oxygen ; and this  change takes place, through  the
delicate membrane  that  lines the  air-cells of the lungs, according to the physi-
cal law of the  mutual  diffusion of gases.  The  introduction of  oxygen into
the blood is necessary for the maintenance of those peculiar vivifying  powers,
by which the Nervous and Muscular systems are kept in a state fit for activity ;
and its union with  their elements appears to  be a necessary condition of the
manifestation of their peculiar powers.  Of this  union, carbonic acid is  one
of the chief products ;  and we shall find that the demand for oxygen, and the
excretion of carbonic acid, vary according to the amount of nervous and mus-
cular  action.  The  continual formation of carbonic acid, in this and other in-
terstitial  changes, appears to have a most important purpose in the vital eco-
nomy,—that of  keeping up its temperature to a fixed standard; for the union
of carbon and oxygen in this situation may be  compared to  a process of slow
combustion ; and it is well known that, the more  energetic this is, the higher
is the temperature.   Thus, in Birds, whose muscular and  nervous activity is
so great, and whose respiration is so energetic,  the temperature is constantly
maintained at a point higher than that which other animals ever attain, in the
healthy state at least; whilst in  Reptiles, which  present a  condition exactly
the reverse of this, the  temperature is scarcely  above that of the  surrounding
medium.—The  function of  the  Liver is, like  that of the  lungs, twofold; it
separates from  the blood  a large quantity, of  the superfluous hydro-carbon,
which it acquires  by circulating through the  tissues; and  it combines that
carbon with other  elements, into a secretion,  which, as we have seen, is of
great  importance in the  digestive  process.   The hepatic circulation, however,
is  not kept up  by a  distinct impelling organ;  but the venous blood from the
abdominal viscera (and, in  the  lower Vertebrata, that from  the posterior part
of the body) passes through the Liver on its  return to the heart.
   276. All animal substances have a tendency, during their decomposition,
to throw off nitrogen, as well as carbon ; and this  nitrogen may take the form
either of cyanogen, by  going off in  combination  with  carbon, or of ammo-
nia, by uniting at the  time of its liberation with hydrogen.  The chief function
of the Kidneys is evidently to  separate the azotized products of decay from
the circulating fluid ; for the secretion which is characteristic of them,—namely
urea,—contains  a  larger proportion of nitrogen  than  is found in any other
organic compound; it is identical in its chemical nature with cyanate of am-
monia, and maybe considered as  the result of the union of these two products
of animal decomposition.  The  action of the kidneys is equally essential to
the continued performance  of the other vital functions,  with  that of the lungs
and  liver;  since death  invariably follows its suspension, unless some other
means be provided  by Nature (as occasionally happens), for the separation of
its characteristic excretion from the circulating blood.
   277. There  seems reason  to  believe,  however,  that, of the  products of
decomposition which are set free in the  various  tissues  and  organs of the
body,  only a part is  destined to  be immediately excreted;  and that it is this
part, which is taken up  by the Veins, and conveyed, by the general vascular
apparatus, to the several glands which are to  separate  it.   The  remainder,
consisting of substances which  are fit to be  re-assimilated, appears to be
     20 
230
GENERAL VIEW OF THE FUNCTIONS.
taken up by a distinct system of vessels, termed Lymphatics; which may be
considered as an extension of the Lacteal system through the fabric at large.
There is good reason to believe, that  the special function of the Lymphatics
is, like  that of the Lacteals, to minister to Nutritive  absorption  (although
other substances may find their way into them, by the mere physical process
of imbibition); the latter being especially  destined  to  take  up assimilable
matter from the digestive cavity, whilst the former absorb the products of the
secondary digestion, which seems to be continually going on in every part of
the body.  (See Chap. XL,  Sects. 1 and 2.)   Of these, however, a portion
may still be destined to immediate excretion.
  278.  The  various  Secretions which  have  not  already been adverted to,
appear for the most part to  have  for their object the performance  of some
special  function in the system, rather than the conveyance out of it of  any
substances which  it would be injurious  to retain.  This  is the case, for
example, in regard to the secretion of the Lachrymal, Salivary, and Mam-
mary Glands, as well as  with that of the Mucous  and  Serous Membranes.
The  Excretion  of fluid  from  the cutaneous  surface,  however, appears  to
answer two important purposes,—the removal  from the body of a portion  of
its superfluous fluid,—and the regulation of its temperature.   Just as, by the
action of the Lungs, the conditions are supplied, by which the temperature  of
the body is kept up to a certain  standard, so, by  that of the  Skin, it is  pre-
vented from rising too high; for by the continual  excretion from its surface,
of fluid which has to be  carried off by evaporation, a degree of cold is gene-
rated, which  keeps the  calorific  processes in  check; and  this excretion is
augmented, in proportion  to the elevation of the external  temperature,  which
seems, in fact, the direct  stimulus to the process.—In  all forms of true  Secre-
tion, the selection of the  materials to be separated from  the blood, is accom-
plished, like  selective  Absorption,  by the agency of cells.   These are de-
veloped in the interior of the secreting organ; and when they are  distended
with the fluid they have imbibed, their  term of life appears to have expired,
so that they burst or  liquefy, yielding their  contents to the ducts, by which
the secreted product is conveyed away.  In the case of Adipose tissue, we
have an instance in which the secreted product (separated from the blood by
the cells of which this tissue  essentially consists) is not carried  out of the
body, but  remains to  form a constituent  part of  it.—The  regulation of the
amount of fluid in the vessels, is provided in a kind of safety-valve structure,
which has been lately shown to exist in the  Kidneys.   This readily permits
the escape of aq\\e<ms fluid from the capillary vessels, into the urinary canals,
by a process altogether distinct from  the secretion of the solid matter, which
it is the office of the kidneys to separate from the circulating fluid.  Hence,
if the excretion of fluid from the skin be checked by cold, so that an accumu-
lation would  take  place  in the vessels, the increased  pressure within them
causes an increased  escape of water  through the  kidneys.   The  relation
between the true  process of Secretion, which is performed by the  selective
power of cells, and that of  simple Transudation, is  the same as that which
has been  already pointed out,  between  Selective  Absorption and  simple
Imbibition (§ 271).
   279. There is no sufficient reason  to believe, that the  Nervous System has
any more direct influence on the  process of Secretion, than  it has been stated
to have  on that of Nutrition.  That almost  every secretion in the body is
 affected by states of mind,  which  must  operate through  the nerves, daily
 experience teaches;  but the very remarkable  degree of control, which the
 Nervous system possesses over the Circulation, appears sufficient to explain
any  of these effects, whether  they be local  or general.   The flow of the
secreted fluids through their efferent ducts, seems to be  principally caused  by 
FUNCTIONS OF ORGANIC OR VEGETATIVE LIFE.
231
the proper contractility of these, which (like that of the heart and alimentary
canal)  is  directly stimulated by the contact of their  contents; but there is
also evidence that this  contractility may be  affected (as  it is in those two
instances) by the nervous system; and thus we have an additional means of
influence, by which the nervous system can operate on these processes, since
its  power  is probably not confined to the large ducts, but  extends  to their
ultimate  ramifications.  Where, as happens in the case of the  urinary excre-
tion, there is a reservoir into which it is received as fast as it is formed, for
the purpose of preventing the inconvenience which its constant passage from
the body would  otherwise occasion,—the power of emptying this reservoir is
usually placed in some degree  under  the  dominion  of  the  will, although
chiefly governed  by reflex action.   It is obvious that such a provision is by
no  means essential to the function ; and that it has for its object the adapta-
tion, merely, of that function, to the conditions of Animal existence.
  280. Thus we see that, when we enter, as it were,  into the penetralia of
the Animal system, and study those processes, of which the development and
maintenance of the material fabric essentially consist, we find them performed
under conditions essentially the  same as those which  obtain in Plants ; and
we observe that  the  operations of the  Nervous System have none  but an
indirect influence or control  over  them.  It is, therefore, quite philosophical
to distinguish these Organic Functions, or  phenomena of Vegetative Life,
from those concerned in the  Life of Relation, or Animal  Life.  The distinc-
tion is, indeed, of great practical importance, and lies at the foundation of all
Physiological Science; yet it is seldom accurately made, and a very confused
notion on  the subject is generally prevalent.  It  is  commonly said, for  ex-
ample, that the function of  Respiration  is  the connecting  link between  the
two:—the fact  being, however, that the true process of  Respiration  is no
more a function  of Animal life, than is  any ordinary process of secretion;  but
that, in order to  secure the constant interchange of air, which is necessary to
its performance, the assistance of the nervous and muscular systems is called
in,  though not in a manner which  necessarily involves either  consciousness
or will.
  281.  The process  of Reproduction, like that of Nutrition, has been until
recently involved in great obscurity ; and although it cannot be said .to be  yet
fully elucidated, it has been brought, by late  investigations, far more within
our comprehension, than was formerly deemed possible.   The close connec-
tion between the  Reproductive and Nutritive operations, both as regards their
respective characters, and their dependence upon one  another, has long been
recognized ; and  it is now rendered still more evident.   Nutrition has not been
unaptly designated " a perpetual reproduction ;" and the expression is strictly
correct.  In the  fully-formed organism, the supply of alimentary material to
every part of the fabric, enables it to produce a tissue resembling itself; thus
we only find true bone produced  in continuity with bone, nerve with nerve,
muscle with muscle, and so on.  Hence it would appear that, when a group
of  cells has once taken on a particular kind of development,  it continues to
reproduce  itself on the same  plan.   But in  the Reproductive process it is
different.   A single  cell is  generated  by certain preliminary actions,—from
which single cell, all those which subsequently compose the embryonic struc-
tures, take their  origin; and it is not until a later period, that any distinction
of parts can be traced, in the mass of vesicles which  spring from it.   Hence
the essential character of the process of Reproduction  consists in the  forma-
tion of a cell, which can give origin to others, from which again  others spring ;
—and in the capability of these last to undergo several kinds  of transforma-
tion, so as ultimately  to produce  a  fabric, in  which the number of different
parts is equal to  that'of the  functions to be  performed, every separate part 
232
GENERAL VIEW OF THE FUNCTIONS.
having a purpose distinct from that of the rest.  Such a fabric  is considered
as a very heterogeneous one; and is eminently distinguished from those homo-
geneous organisms, in which every part is but a repetition of the rest.   Of all
Animals, Man possesses, as  already shown, the  greatest variety of endow-
ments,—the greatest number of distinct organs; and yet Man, in common with
the simplest Animal or Plant, takes  his  origin in  a single  cell.   It  is in the
almost homogeneous fabrics of the Cellular Plants, that we find  the  closest
connection between the function of Nutrition, and that of Reproduction; for
every one of the vesicles  which  compose their fabric, is endowed with the
power of generating others similar to itself; and these may either extend the
parent structure, or separate into new and distinct  organisms.   Hence it is
scarcely possible to draw a line, in these cases, between the Nutrition of the
individual, and the Reproduction of the species.
  282.  But, it will be inquired, how and where in the Human  body (and in
the higher Animals in general) is this embryonic vesicle produced,  and what
are the relative offices of the two  sexes in its formation ?   This is a question
which must still be answered with some degree of doubt;  and yet  observed
phenomena, if explained by the aid of analogy, seem to lead to a very direct
conclusion.   The embryonic vesicle itself, like other cells,  must arise from a
germ ; and reasons will  be hereafter given for the belief, that the germ is sup-
plied  by the male parent, and that the female supplies only the materials for
its development.   Here, as in the Nutritive processes, we find that the opera-
tions  immediately concerned in this function,—namely, the act of fecundation,
and the development of the ovum,—are not directly influenced in any way by
the nervous system ; and that the functions of Animal Life  are called  into play,
only in the preliminary and  concluding steps of the process.  In many of the
lower Animals, there is no sexual congress, even where the concurrence of
two sets of organs (as in the Phanerogamic Plants) is necessary for the pro-
cess;  the ova are liberated by one, and  the  spermatozoa by the  other; and
the accidental meeting of the two produces the desired result.   In many Ani-
mals higher in the scale, the impulse which brings the sexes together is of a
purely instinctive kind.   But in Man, it is of a very compound nature.  The
instinctive propensity, unless unduly strong, is controlled  and  guided by the
will, and serves  (like  the  feelings of hunger and thirst)  as a stimulus to the
reasoning processes, by which the means  of gratifying it are obtained;  and a
moral sentiment or affection of a much higher kind is closely connected with
it, which acts as  an  additional incitement.   Those movements,  however,
which are most  closely connected with the essential part of the process, are,
like those of deglutition, respiration, &c, simply reflex and involuntary in their
character; and thus we have another proof of the constancy  of the  principle,
that, where the action of the apparatus  of Animal Life is  brought  into near
connection with  the Organic functions, it is not such as requires the  operation
of the purely  animal powers,—sensation and volition.  Thus, then, as it has
been lucidly remarked, "the Nervous System lives and grows within an Ani-
mal, as a parasitic Plant does in a Vegetable ; with its life and growth, certain
sensations and mental acts, varying in  the different  classes  of Animals, are
connected by  nature in a manner altogether inscrutable to  man; but the ob-
jects of the existence  of Animals require, that these  mental acts should exert
a powerful controlling influence over all the textures and organs of which they
are composed."

                      3.  Functions of Animal Life.

   283. The existence of consciousness, by which the individual (le moi, in
the language of  French physiologists) becomes sensible of impressions made 
FUNCTIONS OF ANIMAL LIFE.
233
 upon its bodily structure,—and the power of spontaneously exciting contrac-
 tions in its tissues, by which evident motions are produced,—have been already
 stated to be«the peculiar attributes of the beings composing the Animal king-
 dom.   The evident motions  exhibited by some Plants, cannot be regarded as
 indicating the existence of any psychical endowments in the beings included
 in the Vegetable kingdom; for they are usually to be referred without difficulty
 to the action, either direct or indirect, of an external stimulus, upon a contrac-
 tile tissue ; and even where no such action evidently takes place, there is good
 reason  to suppose its existence.  To refer, therefore, the movements of Vege-
 tables to a Nervous system, of which no traces can be found,—still more to
 suppose them endowed with  consciousness and will, as some have done,—is
 to violate most grossly a well-known rule in philosophy, which cannot be too
 steadily kept in view in  prosecuting physiological inquiries—non fingere hy-
 potheses.
   284. There  are in Animals, however, many movements which are equally*
 dependent upon  direct stimuli for their production;  such are (as  we have
 seen), even in the highest, the actions of the heart and of the alimentary canal.
 These, in the lowest  tribes, probably bear a  much greater proportion to  the
 whole amount  of those exhibited by the beings, than  they do  in the higher;
 whilst those, which we may  regard as specially dependent on  a nervous sys-
 tem, appear to  constitute but  a small part of their general vital  actions.  The
 life of such beings, therefore, bears a much closer resemblance to that of  the
 Vegetable, than to that of the higher  Animal.  Their organic functions  are
 performed with scarcely more  of sensible movement, than is seen in plants;
 and of  the motions which they do exhibit  (nearly all of them immediately
 concerned in the maintenance of the organic functions), it is probable that
 many are the result  of  the  simple contractility of  their tissues, called into
 action by the stimuli directly applied  to them.   It is scarcely possible to ima-
 gine that such  beings  can enjoy any of those higher  mental powers, which
 Man recognizes by observation on himself, and of which he discerns the ma-
 nifestations in  those tribes, which, from their nearer  relation  to himself, he
 regards as more elevated in the scale of existence.—If we direct our attention
 on the other  hand, to the psychical* operations of Man, as forming part of
 his general vital  actions, we  perceive that  the proportion  is  completely re-
 versed.   So far from his organic  life  exhibiting a predominance, it  appears
 entirely subordinate to his animal functions, and seems  destined only to afford
 the conditions for their performance.   If we could  imagine his nervous and
 muscular systems to be isolated from the remainder of his corporeal structure,
 and endowed in themselves with  the power of retaining their integrity and
 activity, we should have all that is essential to our idea of Man.  But, as at
 present constituted, these organs are dependent, for the maintenance of their
 integrity and  functional activity, upon the nutritive apparatus; and the whole
 object of the latter appears to  be  the  supply of those conditions, which  are
 necessary to the exercise of the peculiarly animal functions.  That his men-
 tal activity should be thus made dependent upon the due  supply of his bodily
 wants, is a part of the general scheme  of his probationary existence ; and  the
 first excitement of his intellectual powers is in a great degree dependent upon
 this arrangement.
  285.  The most simple or elementary function of the  Nervous System is, as
 already observed, the establishment of a communication between a part which
is susceptible of impressions, and another which can perform contractile move-

  * Here and elsewhere this term will be employed in its most extended sense, to designate
all the mental operations,—whether intellectual, emotional or instinctive,—of which Man's
nervous system is  the instrument.
                                  20* 
234
GENERAL VIEW OF THE FUNCTIONS.
ments ; so that a stimulus applied to one may immediately excite a respondent
action in the other, however great may be its distance.  Hence it may be said
to have an internuncial function; but this, so far as it is performed without
the necessary participation of the consciousness or will of the  individual, is
not essentially higher in  character, than the  corresponding function in Plants,
although the latter is affected by a different  apparatus.   The  ministration of
the nervous system to purely Animal life, obviously consists in its rendering
the mind cognizant of that which is taking place around, and in enabling it to
act upon the material world,  by the instruments with which the body is pro-
vided for the purpose.  It is  important to observe, that every  method at pre-
sent known, by which Mind can act upon Mind, requires muscular contraction
as its medium, and sensation as its recipient.  This is  the case, for example,
not only in  tha,t  communication which takes  place by  language, whether
written or spoken; but in the look, the  touch, the gesture, which are so fre-
quently more expressive than any words can be; and thus we trace the limi-
tation, which, even in communication that appears  so  far removed from the
material world, constantly bounds  the operations of the most .powerful  intel-
lect, and the highest flights of the imagination.  That in  a future state of being,
the communion of mind with mind will be more intimate, and that Man will
be admitted into more immediate converse with his Maker, appears to be  alike
the teaching of the most comprehensive Philosophical inquiries, and of the
most direct Revelation of the Divinity.
  286.  The Organs of Sense are instruments, which  are adapted to  enable
particular nerves to receive impressions from without; of a kind, and in  a de-
gree, of which they would not otherwise be sensible.   Thus,  although the
simple contact of  a hard  body with the nerve may be readily conceived to
produce a material change in  it, of such a kind as would be easily propagated
to the central  sensorium, it is evident  that a nerve  must be peculiarly modi-
fied, to receive and conduct sonorous impressions from the undulations of the
air;  still more—to be susceptible of the  impressions produced  by those un-
dulations, to which most Natural Philosophers now attribute the transmission
of light.  And, even  when  this difficulty  has been provided for, by some mo-
dification in the structure of  the nerve itself, there  is  evidently another still
remaining,—that of understanding how distinct images of the form,  colour,
&c, of external objects can be communicated to the nerve of sight; or  ideas
of the direction, pitch, quality, &c, of sonorous undulations, can be obtained
through the auditory nerve.   There is reason to  believe that many among
the lower Animals, which do not see  objects around them, are  conscious of
the influence of light; and thus the distinction between the mere reception of
the impression, and the communication of the optical image, becomes evident.
The former may take place through the intervention of nerves, whose sensory
extremities offer no peculiarities: the latter can only be received through the
medium of  an instrument, which shall, from the mixture of  rays  falling
equally upon  every part of  a  surface, produce an optical  image, and  then
impress it upon the expanded surface of the nerve;  so that each  fibril may
receive a distinct impression, the image presented to the mind being formed
by the combination of the whole.  That this is, in fact, the  share which the
organs of special sense bear in the general endowments of the whole appa-
ratus, may be inferred  especially from  the conformation of  the Eye;  which
is in  every respect a merely optical instrument, of  the greatest beauty and
perfection, adapted to present to the nerve, in the most advantageous manner,
the images of surrounding objects in all their variations.  And  we might con-
ceive that, if it were possible for the interior of the living eye  to be replaced
by one constructed of inorganic materials by the hand of man, without de-
stroying the functional power of the retina,  the  sense  of sight would be but 
FUNCTIONS OF ANIMAL LIFE.
235
little impaired,—except through the incapability, on the part of any piece  of
human mechanism, to  imitate those wondrous  contrivances of Infinite Skill,
which have for their object the adaptation of the instrument to varieties of dis-
tance, of intensity of light, &c   There can be little doubt, that the structure
of the Ear is arranged to do the same  for the  sonorous vibrations, which the
eye does for  the rays  of light; that is, through its means, the  undulations
which strike upon the external surface of the organ are separated and distin-
gished, those of a like kind being brought together  upon one  division of the
nerve, and  those of another order upon a different set  of fibres ;  so that the
different kinds of sound, and the peculiar quality and direction of each, may
be discriminated; whilst, by the concentration of all the impressions of the
same character, a higher amount of force is given to them.   Of the sense  of
Smell, no similar account can be given; since the medium by which odours are
propagated is not known.  If, as is generally believed, this  is accomplished by
the diffusion through space, of minute particles of the  odoriferous body itself
(which supposition  seems to  derive support  from the general fact, that the
most volatile substances are usually most odoriferous), smell may be regarded,
—as taste also is probably to  be considered,—in the light of a  refined kind  of
touch.
  287. Thus, the general rule holds good, here as elsewhere, that the pro-
cesses, by which the organism is immediately brought into relation with the
external world, are  performed in obedience to physical  laws ; the living struc-
ture only affording  certain peculiar conditions, which  may  be imitated in a
great  degree by other means.  This is the case, for example, with regard  to
Digestion, which is in itself a simply  Chemical process, that will take place
out of the body as  well as in  it, if the  materials and the necessary solvent be
submitted to the  same circumstances, as those to which they are  exposed  in
the stomach ;  and in regard  also  to the  act of Respiration, which depends
upon the physical tendency to mutual diffusion, inseparable  from the exist-
ence of gases ; and we  notice the prevalence of the same general fact in the
Animal as in the Organic functions.   We cannot become  cognizant of the
changes, or even of the existence,  of  the  external world, unless some mate-
rial effect be produced by it on our organs of sense; nor can we produce any
alteration  in its  condition, except  by powers which act according to purely
mechanical principles.
  288. In regard to the Muscular System, it has already been  sufficiently
explained  that it forms  a part of the apparatus of Animal life, no otherwise
than as the instrument by  which nervous energy operates  upon  external
objects.  The contractility which it manifests on the application of a stimulus,
is an endowment which it derives  from its  own structure, and not from the
nervous system ; for it will be clearly proved in  its  appropriate  place, that
the presence of  this contractility is connected with the healthy nutrition  of
the tissue, and with its due supply of  arterial  blood ;  and  that the complete
separation of any muscular part from all  its nervous   connections, has  none .
but an indirect influence on its properties. 
236
                            CHAPTER  V.

                      FUNCTIONS OF THE NERVOUS SYSTEM.

                           1. General Summary.

    289. Our fundamental idea of a Nervous System includes a central organ
  or ganglion, essentially composed of vesicles or cells, with a plexus of capil-
  lary vessels distributed  amongst  these ;  and a set of trunks  and ramifying
  branches, composed of tubular fibres, and connecting the ganglion with differ-
  ent parts of the fabric.  These branches are for the most part distributed, on
  the one hand, to the  sensory surfaces and organs  ; and, on the other, to the
  muscles or motor organs.   The former serve for  the conveyance of impres-
  sions, made upon the periphery, towards  the  centre ;  and they may thence
  be denominated afferent fibres.*  The latter, on the other hand, serve to con-
  vey an influence, originating in the central ganglion, to the muscles, which
  are thereby thrown into contraction;  and these are distinguished as efferent
  or motor fibres.   Although the distinctness of these two sets  of fibres has
  only been proved in  the Vertebrata, yet there can be no reasonable doubt of
  its universality.   Now this fundamental idea of a Nervous apparatus, which
  is based upon what are believed to be the relative offices of its several  com-
  ponent parts (as formerly explained § 248), is found to be exactly realized in
  the simple forms of that system, which we find in the lowest animals in which
  Nervous structure can  be  discovered at  all; and even where the apparatus
  has, to all appearance,  a character of much greater complexity, it may still be
  reduced to the same simple idea, by taking it to pieces (so to speak) and exa-
  mining its component parts.  For it will  then  be found, that the multiplica-
  tion  of ganglia and  trunks  is  principally due to the multiplication of the
  organs to  be supplied; as in the case of the  nervous ring of the Star-fish,
  where the ganglia,—all of them apparently identical in function, and similar in
  the distribution of their branches,—are repeated in conformity with the num-
  ber of the radiating parts of the body ; or in the case of the ventral nervous
  cord of an Articulated animal, in which the ganglia are in like  manner re-
  peated longitudinally, in accordance with  the number of segments of the body,
  and of the pairs of members connected with them.  In  other instances, the
  multiplication of ganglia is due  to the increased complexity of the functions
•  performed by a set of  organs;  of this we  shall see numerous examples in
  the higher Vertebrata.  In all cases, the individual ganglia remain to a  great
  extent independent of each other; so that the removal of any one (if it can
  be accomplished without injury to the  rest) affects only  the particular organ
  with which it may be connected, and the  special function of that organ to
  which alone it ministers.
    290. Before proceeding to inquire into the operations of the Nervous  Sys-
  tem as a whole, it is  desirable that we should stop to consider the conditions

    *  Such are commonly denominated sensory fibres; but this designation  is objectionable,
  in as much as many of them serve to excite reflex actions, without necessarily producing
  sensations. 
           DEPENDENCE OF NERVOUS POWER ON SUPPLY OF BLOOD.       237

on which its functional activity is dependent.—The chief of these, is a con-
stant supply of oxygenated blood ; which is  more necessary for the mainte-
nance of the Nervous power, than it is for that of any other tissue whatever.
This supply is peculiarly required at those points at which changes originate ;
not being, it would appear, so  necessary for the mere conduction of impres-
sions.   Consequently we find that the greatest supply of blood is afforded to
the nervous centres, and to the peripheral extremities  or  origins of the affe-
rent nerves; and that the  effects of  any interruption to the supply are  mani-
fested in an immediate and most striking manner.  Thus, if the circulation
through the Brain be suspended but for an instant, insensibility and loss of
voluntary power supervene,  and continue until it is restored.   This was
shown by  the following experiment of Sir A. Cooper's.  After having tied
both carotid arteries in a dog,  he  compressed the Vertebral trunks; and  im-
mediate insensibility came on, the animal at the same time falling powerless.
But convulsive movements occurred at  the same time ;  showing that the func-
tions of the spinal cord were not suspended, but only  deranged.   As soon as
the blood was  re-admitted to the brain, the animal recovered its consciousness
and voluntary  power, and stood on its legs  again ; the convulsive movements
ceased at the  same time.—In Syncope, the  circulation  through the Spinal
cord is weakened, by the  failure of the heart's action, to the same  extent as
the flow  of blood through the Brain; and a general cessation, not merely of
muscular movement, but of all power of exciting it, is the immediate result.
No sooner, however, is the circulation  fully re-established, than the power of
the Nervous centres is restored.—Again, the influence of diminished circula-
tion, at the origins of the  afferent nerves, is shown in the deficient  impressi-
bility of  the nerves, at the part affected.   Thus, if the  movement of  blood
through the capillaries of a limb be stagnated,—whether by pressure on the
arterial trunks, by cold, or by any other cause,—it is at once made apparent
by the numbness of the  surface; and  a complete stagnation produces com-
plete insensibility.  The power of  receiving  impressions, that are  to excite
reflex movements, is diminished in the  same degree.
   291.  On the other hand it  is found,  that increased  circulation through the
same parts, is  attended with an exaltation of their function.  This is particu-
larly noticed in those affections of the  brain and spinal cord, closely border-
ing on inflammation, to which the terms active congestion and determination
of blood have been applied.   We have, in such cases, extreme  acuteness of
sensation, excessive activity of the mental functions, or violent excitement of
the motor powers ;  according (it would seem)  to the particular division  of the
nervous centres most affected.  Again, we find that an increase in the  circu-
lation through any organ, from which afferent nerves arise, increases  their
readiness to receive impressions; thus  the sensibility of the genital organs of
animals during the period of  heat, and  of those of man in a state of venereal
excitement, are greatly augmented;  and the  tendency of impressions, made
upon them, to excite reflex movements, is similarly exalted.
   292.  The due activity of  the  Nervous  System is not merely dependent
upon a constant and ample supply  of  Blood;  but it requires that this blood
should be in a state of extreme  purity, and  more  especially that  it should
contain a due supply of oxygen, and should be depurated of its carbonic acid,
and of other  products of  the  decomposition of the  body.  The final cessa-
tion of nervous power, in  death by Asphyxia, is partly due (as will be shown
hereafter, Chap. XIII., Sect. 3), to a positive deficiency in the supply of blood ;
but the obtuseness of sensibility  which gradually  increases until  a state of
unconsciousness comes on, may be clearly  traced in the first instance to the
deficient aeration of the blood, which is gradually deprived of its  oxygen, and
charged with more and  more  carbonic acid.   Corresponding but less severe 
238
FUNCTIONS OF THE NERVOUS SYSTEM.
 symptoms occur, when the excretion of carbonic acid is not checked, but only
 slightly impeded; provided the impediment be in operation  for a sufficient
 length of time, as in the case of an ill-ventilated  apartment;  an indisposition
 to mental exertion, a deficiency of muscular power, and an obtuseness of the
 intellectual  and moral  faculties, being  the  general result.—These facts  are
 readily explained upon the hypothesis (which seems now to have a sufficiently
 wide foundation, to be  entitled to rank as  physiological truth, although no
 very direct  proof of it can be given), that the functional activity of the nerv^
 ous system is mainly dependent  upon  the  combination of the oxygen sup-
 plied by the blood, with its elements;  the  production of the nervous force,
 whatever be its nature,  being a result of this change  of composition.  The
 chief grounds for this doctrine will now be  enumerated.
   293. In the first place, the dependence of nervous  energy upon the con-
 stant circulation of blood through the tissue, is much more  close and imme-
 diate than can be accounted for on the  idea that the relation  is one of mere
 nutrition  or development.  On the contrary, where  these  last  changes  are
 taking place most actively, we often find  rather a disposition to stagnation of
 the  current, to give time for the elaboration  of the nutrient materials that are
 to be withdrawn from it; and in no case does the process so  instantaneously
 cease, when the flow is  suspended.  From this it would appear, that some
 combination takes place between  the elements of the nervous tissue, and some
 material supplied by the blood; which  is much  more rapid in  its  character,
 than the process of  cell-development;  and  which is essentially concerned in
 the  production and  maintenance of the active condition of the  nervous sys-
 tem.—Again, that the material supplied  by the blood for this purpose is Oxy-
 gen, would appear from a variety of  considerations.  A general  survey of
 the  Animal kingdom shows, that  oxygen is essential  to the  maintenance of
 animal life, as distinct  from vegetative; and  a more particular comparison
 of different tribes demonstrates most unequivocally,  that the  consumption of
 oxygen is in direct relation to the development of the animal powers  in each.
 These facts harmonize completely with what has been just stated,  respecting
 the effects of a suspension of the oxygenating process.
   294. Further, in proof that the activity of the Nervous system is immedi-
 ately dependent, not upon a  process of development or nutrition, but upon
 one of disintegration or destruction, it may  be  urged, that it is impossible for\
 this state of activity to be maintained, in a large  portion of it, without an in-
 terval of  repose, which  we know to be favourable to the vegetative or repa-
 rative processes.  There are certain parts of the Nervous System, particularly
 those that put in action  the respiratory muscles, which  are in a state of un-
 ceasing though moderate activity ; and  in these, the constant nutrition is suffi-
 cient  to  repair the effects of the constant decay.  But those parts which
 operate  in  a more powerful and energetic manner, and which are therefore
 more rapidly disintegrated when  in action,  need  a season of rest for their re-
 paration.   Hence the sense of fatigue  which is experienced when the mind
 has been long acting through  its  instrument,—the Brain; and the  irresistible
 tendency to sleep, which usually supervenes after any unusual exertion of this
 kind. In the healthy state of the body, when the exercise of the nervous system
 by day does not exceed that which the repose of the  night may compensate,
 the Nervous System is maintained in a condition which fits it for constant
 moderate exercise ;  but  unusual demands upon its powers,—whether by long-
 continued and severe exercise of the intellect, by excitement of  the emotions,
• or  by the  combination  of both, in that state of anxiety which the circum-
 stances of man's condition too frequently induce,—occasion an unusual waste,
 and require a prolonged repose and uninterrupted nutrition, for the complete
 restoration  of its  powers.  There can be  no  doubt that (from causes which 

              DISINTEGRATION OF NERVOUS MATTER WITH USE.           239

are not  known) the amount of sleep  required  by different  persons, for the
maintenance of  a healthy condition of  the  Nervous  System, varies consider-
ably ; some being able to dispense with it to a degree which would be exceed-
ingly injurious to other individuals, who do not surpass them in mental activity.
Where a prolonged exertion of the mind has been made, and  the natural tend-
ency to  sleep  has been  habitually resisted, by a strong effort of the will,
injurious results are sure to follow.   The bodily health breaks down; and too
frequently the mind  itself is permanently enfeebled.   It  is obvious that the
Nutrition of the Nervous System becomes completely deranged ; and that the
tissue is no longer formed in a manner requisite  for the discharge  of its healthy
functions.   The same may be said of the state of Mania; in which there is,
for a time, an extraordinary degree of activity (though manifested in an irregu-
lar manner) of the cerebral functions, and an absence of disposition to sleep.
Such a state may continue for some time;  but the subsequent exhaustion of
nervous  power is proportioned to the duration of the excitement, and frequent
attacks of  mania almost invariably subside at last into  imbecility.
   295.  Additional  evidence  for the belief that the functional activity of the
Nervous tissue involves  disintegration of its tissue by the agency of Oxygen,
is found in the increase  of phosphatic  deposits in the urine,—and especially  %■
.of those having  alkaline bases,—when there has been any unusual demand
upon the  nervous power.   No  others of the soft tissues contain any large
amount of phosphorus ;  and the marked increase in these deposits, which has
been continually observed to accompany long-continued wear of mind, whether
by intellectual exertion,  or by the excitement of the feelings,—and which fol-
lows any temporary strain upon its powers, can scarcely be set  down  to  any
other cause.  The most satisfactory proof is to be found in cases, in which
there is a periodical demand upon the mental powers ;  as, for example, among
Clergymen,  in the  preparation for and discharge of their Sunday duties.  This
is found to be almost  invariably followed by the appearance of a large quantity
of the alkaline phosphates in the urine.  And in cases in which constant and
severe intellectual  exertion has impaired  the nutrition of the brain, and has
consequently weakened the mental power, it is found that any  premature at-
tempt to  renew the activity of its  exercise, causes the re-appearance of the
excessive phosphatic discharge indicative of an  undue waste of nervous mat-
ter.*
   296. There is not the same evidence of constant change, however, in re-
gard  to the fibrous element of the Nervous System; and its conducting power
appears  to be much less dependent upon the supply of blood, than is the ori-
ginating power of  the vesicular matter.   It remains, with little decrease, for
some time after death ; especially in cold-blooded animals ; for we can, by
pinching, pricking, or  otherwise stimulating the motor  trunks, give rise to con-
tractions in the  muscles supplied by them, exactly as during life.   Its earlier
departure in warm-blooded animals,  may be partly due to  the  cooling of the
body.
   297.  Of the actual nature of the changes by which impressions are received
upon the peripheral origins of the afferent nerves, or are communicated to the

   * A large amount  of evidence confirmatory of the above views, and showing the  im-
portance of carefully distinguishing between  the alkaline and earthy phosphates, has  been
adduced by Dr. Bence Jones, in a Paper lately read to the Royal Society.   The quantity of
the latter, which is present in the urine, is found to bear a constant relation  to that which is
contained in the food.  On the other hand, the amount of the former varies with  different
conditions of the nervous system, in such a manner as to warrant the inference that its pro-
duction is a result of  the  disintegration of nervous  matter; being due to the union of the
phosphoric  acid thus set free, with alkaline bases present in the blood in a state of feeble
combination. 
240
FUNCTIONS OF THE NERVOUS SYSTEM.
central origins of the motor, and by which they are conducted along each to
their opposite extremities, Physiologists have no  certain knowledge.  That
they are Electrical  in  their character, has been, and still continues to be, a
favourite theory with  some;  and  the  idea seems  to derive support from the
marked degree  in which  Electricity,  transmitted along  the Nervous trunks,
can excite the changes to which  those  nerves are  ordinarily subservient.
Thus, a feeble galvanic current,  transmitted along the motor nerves of an ani-
mal recently killed, will call the muscles supplied by it into contraction ; whilst,
on the other hand,  a similar current transmitted along an  afferent nerve, shall
excite reflex movements through its ganglionic  centre.   Further, if the cur-
rent be transmitted along an afferent  nerve, in a living animal, it  will excite
sensations which are referred to  the  part whence the nerve arises ; and, as
will be shown  hereafter (Chap. VI., Sect. 1), Electricity is capable of thus
producing sensations of a  special kind, as well as those of a general nature.
Moreover, in  the  instantaneousness of the transmission  of Nervous agency
from one  part of the system to another, there is  more analogy  to Electricity,
than to  any other known force.  But these and similar arguments do not prove
the identity of Nervous agency  with Electricity; since the effects of the for-
mer may  be  imitated  to  a certain extent, not merely by Electricity, but by
mechanical and  chemical  stimulation  of  various kinds.   Further, there  are
powerful arguments against such a supposition,  the validity of which cannot
be easily  set aside.  All attempts to prove the existence of an Electric current,
in a Nervous  trunk that is actively engaged in conveying motor influence,
have completely failed, though made with the greatest precaution.  Thus, Mat-
teucci has lately experimented upon the very large crural  nerve of  a Horse,
which was caused, by stimulating  its  roots, to throw the muscles of the leg
into violent contraction ; nevertheless,  although  he used instruments  of such
delicacy, as to be capable  of detecting  an  infinitesimally-small  disturbance of
the electric equilibrium, no such  disturbance was apparent.  Further, it is well
known  that the conducting power of the  nerves is destroyed,  not merely by
dividing the trunk, but also by putting a ligature round it;  which last opera-
tion does  not diminish  its  powers  as a conductor of Electricity.   Moreover,
the various fibrils are not  as completely insulated from each other in regard to
Electricity, as we know them  to be with respect to nervous agency ; Tor the
first of  these forces, when  transmitted  along a  nervous  trunk, cannot be re-
stricted to any fibre or fasciculus  of  fibres, but spreads through  the entire
trunk, and even to  the neighbouring parts in which it is imbedded; whilst the
latter is continually restricted to  a  small portion of the trunk, as is manifested
by its results.  Again, if a small  piece of nervous trunk  be cut out, and be
replaced by an electric  conductor, electricity will  still pass along the nerve;
but no  nervous force, excited  by stimulus  above  the section,  will be propa-
gated through the conductor to the parts  below.  And lastly,  the conducting
power of Nerve  for Electricity is stated  by Matteucci  to be  not more than
one-fourth that of Muscle; whilst  Messrs. Todd and Bowman give it as the
result of their experiments, that  both  Nerve and Muscle are both infinitely
worse conductors than  copper;  their power of conduction not  ranking above
that of  water holding in solution a small quantity of  saline matter.
  a. Although, for the sake of convenience,  Electricity and Nervous power are spoken of,
here and elsewhere, as actual entities or agents, traveling along the  wires or cords that con-
duct them, it must not be forgotten  that the present tendency of scientific inquiry leads us
to abandon such an idea, in the former case at least;  what  is  commonly termed the trans-
mission of electricity being  the  result  of a molecular change, instantaneously occurring  along
the whole length of the conducting body, in virtue of a disturbance, in the polar arrangement
of its particles, at one extremity, which causes a similar disturbance to manifest itself at the
other.  Thus if
                       ab  ab ab   ab   ab  ab  ab  ab 
LAWS OF NERVOUS TRANSMISSION.
241
represent the arrangement of the particles, in the condition of equilibrium or quiescence, and
this condition be disturbed at one extremity, by the operation of a new attraction upon the
first particle a, a new arrangement will instantaneously take place throughout: this may be
represented by
                      a  ba  ba  ba  ba  ba  ba  ba   b
which shows b in a free state at the opposite end, ready to exert its influence upon anything
submitted to it.  It is probable that in this respect there is an analogy between the Nervous
and electrical forces; and that, instead of speaking of the "transmission of nervous influence"
along a nerve, we should describe the change as the production of a "polar state" in the
nervous trunk;  as first pointed out by Messrs. Todd and  Bowman (Physiological Anatomy,
vol. i. p. 240).

   298. Every fibre, there is reason to believe, runs a distinct course between
the central organ, in which  it loses itself  at one extremity, and  the muscle  or
organ of sense in which it terminates at the other.   Each Nervous Trunk is
made up of  several fasciculi of these fibres; and each fasciculus is composed
of a large number of the ultimate fibres  themselves.   Although the fasciculi
occasionally intermix and exchange fibres with one another (as occurs in what
is termed a plexus), the fibres themselves  never inosculate.   Each fibre would
seem,  therefore,  to  have  its appropriate  office,  which  it cannot share with
another.   The objects of a plexus are twofold.  In  some instances it serves
to intermix  fibres,  which  have  endowments fundamentally different:  for
example, the Spinal Accessory nerve, at its origin, appears to be exclusively
motor, and the  roots of  the  Par Vagum  are as  exclusively afferent; but by
the early admixture of these, a large number of  motor  fibres are imparted to
the Par Vagum, and are  distributed in variable  proportion,  with its  different
branches ; whilst few of its sensory filaments seem to enter the Spinal Acces-
sory.—In other instances, the object of a  plexus  appears to be, to give a more
advantageous  distribution to fibres, which all possess corresponding  endow-
ments.   Thus the Brachial plexus mixes together the fibres arising from five
segments of the spinal cord, and sends off five principal trunks to  supply the
arm.   Now if each of these trunks  had arisen  by itself,  from  a distinct seg-
ment of  the spinal cord, so that the parts on which  it is distributed had only
a  single connection with the nervous centres, they would have been  much
more liable to paralysis than at present.  By means  of the plexus, every part
is supplied with fibres arising from each segment of the spinal cord :  and the
functions of the whole must therefore be suspended, before complete paralysis
of any part can occur, from a cause which operates  above the plexus.   Such
a  view is borne out by  direct experiment;  for it  has been ascertained by
Panizza  that, in  Frogs, whose crural plexus  is  much less complicated than
that of Mammalia, section of the roots of one of  the three  nerves which enter
into it, produces little effect on the general movements of the limb; and that,
even when two  are divided, there is no paralysis of any of its actions, all
being weakened in a nearly similar degree.—It  is  not unlikely also that, by
this arrangement, a consentaneousness of action is in some  degree favoured, as
is supposed by Sir  C. Bell;  for comparative anatomy shows that  something
resembling it may be traced, wherever a  similar purpose has to be attained.
Thus, in the Hymenoptera^there is a  similar interlacement between the nerves
of the anterior and  posterior pairs of  wings, which  act very powerfully to-
gether ; whilst in the Coleoptera, in  which the  anterior wings  are converted
into elytra, and are motionless during flight, the nerves supplying each pair
run their course distinctly.   In the Octopus, or Poulp, again, the trunks which
radiate from the  cephalic  mass to the eight large arms  surrounding the  head,
are connected by a circular  band; forming a kind of plexus, which seems to
contribute to the very powerful and  harmonious movements of the arms of
this Cephalopod.
   299.  The  following statements, in which the language of Muller is adopted
    21 
242
FUNCTIONS OF THE NERVOUS SYSTEM.
 with  some  modification, embody the general principles  ascertained by ex-
 periment, respecting  the  transmission of  sensory and motor impressions.
 Their rationale will be at once understood, from the facts already mentioned
 in regard to the isolated  characters of each  fibril, and the identity of  its
 endowments through its whole course,  i. When the whole trunk of a sensory
 nerve is irritated, a sensation is  produced, which is referred  by the  mind to
 the parts to which its branches are ultimately distributed ; and if only part of
 the trunk be irritated, the sensation will be referred to those parts only, which
 are supplied by the fibrils it contains.—This is evidently caused  by  the pro-
 duction of a change in the sensorium, corresponding with that which would
 have  been  transmitted from the  peripheral origins of the  nerves,  had  the
 impression been made upon them.  Such a change only requires the integrity
 of the afferent trunk, between the point irritated and the sensorium; and is"
 not at all dependent upon the state of the  extremity, to which the sensations
 are referred : for this may  have been paralyzed by the  division  of the nerve;
 or altogether separated, as in amputation; or the  relative position  of  its parts
 may have been changed.—It results from the  foregoing, that, when different
 parts  of the thickness of the same trunk are separately  subjected to irritation,
 the sensations are successively referred to the several parts supplied by these
 divisions.   This may be  easily shown by compressing the  ulnar nerve, in
 different directions, where it  passes at the inner side of the elbow-joint.
  n.  The sensation produced by irritation of a branch of the nerve, is con-
 fined  to the  parts to which  that branch is distributed, and does  not affect the
branches which come off from the nerve higher up.  The rationale  of this
law is at once understood:  but it should be mentioned that there are certain
 conditions, in which the irritation of a single nerve will give rise to sensations
 over a great extent of  the  body.   This  seems due, however, to a particular
state of the  central  organs  ;  and  not to any direct  communication among the
sensory fibres.
  in. The motor influence is propagated only in  a centrifugal  direction, never
in a retrograde  course.  It  may  originate  in  a  spontaneous change in  the
central organs:  or  it may  be excited by  an impression conveyed  to them
through afferent nerves;  but in both cases its law is the same.
  iv.  When the whole  trunk of a  motor nerve is  irritated, all the  muscles
which it supplies are caused  to contract: but when only a part of the trunk
or a branch is irritated, the contraction  is  confined to the  muscles, which
receive their nervous fibres from it.   This contraction evidently results from
 the similarity between the effect of an artificial stimulus applied to the trunk
in its  course, and that of the change in the central organs by which the motor
influence is  ordinarily propagated.  In this instance, as in the other, there is
no lateral communication between the  fibrils.
  300.  Various methods of determining the functions of particular nerves
present themselves to the Physiological inquirer.   One source of evidence is
drawn from their anatomical distribution.   For example, if a nervous trunk
 is found to lose itself entirely in the  substance  of muscles, it may be  inferred
 to be  chiefly, if not entirely, motor or efferent.  In this manner,  Willis long
 ago determined that the third, fourth, sixth, portio dura of the seventh, and
ninth cranial nerves, are almost entirely subservient to muscular  movement;
 and the same had been observed of the fibres proceeding from the small root
 of the fifth  pair, before Sir C.  Bell  experimentally determined  the double
 function of  that division of the nerve, into  which  alone  it  enters.   Again,
 where a nerve passes through the muscles, with  little or no ramification among
 them, and proceeds to a cutaneous or mucous surface, on which its branches
 are minutely distributed, there is equal reason to believe that it is of a sensory,
 or rather of an afferent, character.  In this manner Willis came to  the con- 
DETERMINATION OF FUNCTIONS OF NERVES.
243
elusion, that the fifth pair of cranial nerves differs from  those  previously
mentioned, in being partly sensory.  Further, where a nerve is entirely dis-
tributed upon a surface adapted to receive impressions of a special kind,—as
the Schneiderian membrane, the  retina, or the membrane lining the internal
ear,—it may be inferred  that it is not capable of transmitting any other kind
of impressions; for experiment has shown, that the special sensory nerves  do
not possess common sensibility.   The case is different, however, in regard to
the sense of taste, which  originates in impressions not far removed from those
of ordinary touch; and it is probable that the same nerves minister to both.—
Anatomical evidence of this kind is valuable also, not only in reference  to the
functions of a principal trunk, but even  as to those of its  several branches,
which, in some instances, differ considerably.  Thus, some of the branches of
the Par Vagum are especially motor, and others almost exclusively afferent; and
anatomical examination, carefully prosecuted, not only assigns the  reasons for
these functions, when ascertained, but is in itself nearly sufficient to determine
them.  Thus the superior laryngeal branch is distributed almost entirely upon
the mucous surface  of the larynx, the only muscle it supplies being the  crico-
thyroid ; whilst the inferior laryngeal or recurrent is almost exclusively dis-
tributed to  the muscles.   From  this we  should infer, that the former  is  an
afferent, and the latter a motor nerve ; and experimental inquiries (hereafter to
be detailed)  fully confirm this view.  In like manner it may be  shown, that
the Glosso-pharyngeal is chiefly an afferent nerve, since it is distributed  to the
surface of the tongue and pharynx, and scarcely at all to the muscles of those
parts; whilst the pharyngeal branches of the Par Vagum  are chiefly if not
entirely, motor.   Lower down, however, the  branches of the glosso-pharyn-
geal cease, and the oesophageal branches of the par vagum  are distributed both
to the mucous surface and to the muscles; from which it may be inferred that
they are both afferent and motor—a deduction which experiment confirms.
   301.  We  perceive, therefore, that much knowledge of  the function of a
nerve may be obtained,  from the  attentive study of its ultimate distribution:
but it is necessary that this should be very carefully ascertained, before it is
made to serve as the foundation for physiological inferences.  As an example
of former errors in this  respect, may be mentioned  the  description  of  the
Portio Dura of the  seventh, at first  given by Sir C. Bell:  he  stated it  to  be
distributed  to the skin as well as to the  muscles of the  face, and evidently
regarded it as in part an afferent nerve, subservient to respiratory impressions
as well as to motions.   In the same manner, from inaccurate observation  of
the ultimate  distribution  of the Superior Laryngeal nerve, it was long re-
garded as that which stimulated to action the constrictors of the glottis.—But
the knowledge  obtained  by such anatomical examinations alone is of  a very
general kind; and requires to be made particular,—to be corrected and  modi-
fied by other sources of information.  One of these relates to  the connection
of  the trunks with the   central  organs.   The evidence  derived  from this
source,  however, is seldom of a  very  definite character;  and, in  fact,  the
functions of particular  divisions  of  the  nervous centres  have rather been
hitherto judged  of,  by those of the  nerves with which they are  connected,
than  afforded aid in the  determination  of the latter.   Still, this kind  of
examination  is not without its use, when there is reason  to  believe  that a
particular tract of fibrous structure has a certain function, and when the office
of a nerve whose roots  terminate in it  is  doubtful.   Here again, however,
very minute and accurate examination is necessary, before any sound physio-
logical inferences can be  drawn  from  facts of this description;  and  many
instances might be adduced to show, that the real connections of nerves and
nervous centres  are often  very different from their apparent ones.
  302.  Experimental inquiries into the functions of particular nerves are also 
244
FUNCTIONS OF THE NERVOUS SYSTEM.
liable to give fallacious  results, unless they are prosecuted with a full know-
ledge of all the precautions necessary to insure success.   Some of these will
be here explained.   Suppose that, upon irritating the trunk of a nerve, whilst
still in connection with  its centre, muscular movements  are excited; it must
not be hence concluded that the nerve is an efferent one, for it may have no
directly motor powers.   The next step would be to divide the  trunk, and to
irritate each  of the  cut extremities.   If, upon  irritating the end separated
from the centre, muscular contractions are produced, it may be safely  inferred
that the nerve is, in part at least, of an efferent  character.  Should no such
result follow, this would be doubtful.   If, on the other hand, muscular move-
ment should be  produced by irritating  the  extremity in connexion with  the
centre, it will then be evident, that it is occasioned by an impression conveyed
towards  the  centre  by  this trunk, and propagated to the  muscles by some
other; in  other words, to use the  language of Dr. M. Hall, this  nerve is an
excitor of motion, not  a  direct motor  nerve.   The glosso-pharyngeal  nerve
has been  satisfactorily determined  to be  chiefly, if not entirely, an  efferent
nerve, by  experiments of  this kind, performed by Dr. J. Reid.
  303. It has been  from  the want of a proper  mode of experimenting, that
the functions of the  posterior  roots of  the Spinal nerves have been regarded
as in any  degree motor.   If fhey be irritated, without division of either root,
motions are often excited; but if they  be divided, and their separated trunks
be then irritated, no motions ensue; nor are  any movements  produced by
irritation of the roots in connexion with the spinal  cord, if the anterior roots
have been divided.   Hence  it appears that  the motor powers of these  fibres
are not direct, but  that they convey an impression  to  the centre, which is
reflected to the muscles through the anterior roots.  Another source of fallacy
is to  be guarded against, arising from  the  communication to a  nerve, in its
course, of properties it did  not  possess at  its root, by inosculation with  an-
other nerve.   Of this many instances will hereafter present themselves.
  304. The same difficulties do not attend  the determination of the  sensory
properties of nerves.  If, when  the trunk of a nerve  be pricked or pinched,
the animal exhibits signs  of pain, it may  be concluded that the nerve is sen-
sible  to ordinary impressions  at  its  peripheral extremity.  But not unfre-
quently this sensibility  is derived by inosculation with another nerve; as is
the case with  the portio  dura, which is  sensory after it has passed  through
the parotid gland, having received  there a twig from the fifth pair.  A similar
inosculation explains the apparent  sensibility of the anterior  roots of  the
spinal nerves.  If these be irritated, the animal usually gives signs of uneasi-
ness;  but if they be divided, and  the cut ends nearest the centre be irritated,
none  such are exhibited; whilst they are still shown, when the  farther ends
are irritated, but  not if  the posterior roots are divided.  This seems to indi-
cate that, from the point of junction of the  two roots, sensory fibres derived
from the posterior root pass backwards  (or towards the centre) in  the anterior;
and  thus  its apparent sensory endowments are entirely dependent upon its
connexion with the posterior column of the  spinal cord, through  the posterior
roots.
  305. The  fallacies to which all experiments upon the nerves  are subject,
arising from  the partial loss of their powers of receiving and conveying  im-
pressions, and of exciting the muscles  to action, after death, are too obvious
to require particular mention here; yet they are frequently overlooked.  Of
a similar description are those arising from  severe disturbance of the system,
in consequence of operations; which also have not been enough regarded by
experimenters.
  306. All our  positive knowledge of  the functions  of  the Nervous System
in general, save that  which results from  our own consciousness of what passes 
                DETERMINATION OF FUNCTIONS OF NERVES.              245

within ourselves, and that which we obtain from  watching the manifestations
of disease in Man, is derived from  observation of the phenomena exhibited
by animals  made the subjects of experiments; and it is  desirable to preface
our general  summary of the results of these, by some remarks upon the in-
ferences to  be drawn from them.—In the first  place it must be constantly
borne  in  mind  that, except through the  movements consequent upon  them,
we have no  means of ascertaining, whether or not particular changes  in the
Nervous  System, whose character  we  are  endeavoring to determine, are
attended with Sensation; since we have no power of judging whether or not
this has been excited, save by the cries and struggles of the  animal made the
subject of experiment.   Now although such cries  and struggles are ordinarily
considered as indications of pain, yet it is not right so to regard them in  every
instance;  and the  only  unequivocal  evidence  is derived  from observation of
the corresponding phenomena in the Human subject;   since we can  there
ascertain,  by the direct testimony of the individual affected, what impressions
produce sensation, and  what excite  movements  independently  of sensation.
Further, we are not justified in assuming that consciousness is excited  by an
irritation,—still less that the intelligence  and will are called  into exercise by
it,—merely because movements, evidently tending to get  rid  of this, are per-
formed in respondence to it.   We know that the contractions of the  heart
and alimentary tube are ordinarily excited by  a stimulus, without any sensa-
tion being involved;  and these movements, like all that are concerned in the
maintenance of the Organic  functions, have an  obvious design, when con-
sidered either in their immediate effects, or in their more remote consequences.
The character of adaptiveness,  then, in Muscular movements excited by
external stimuli, is  no proof  that they are performed in  obedience to sensa-
tion ;  much less, that they have a voluntary character.   In no  case is this
adaptiveness more remarkable, than  in some  of those actions, whioh are not
only performed without any  effort  of the will,  but which the will cannot
imitate.   This is  the  case, for example, with the  act  of Deglutition;  the
muscles concerned in which cannot be thrown into contraction by a voluntary
impulse, being stimulated  only by impressions conveyed from  the mucous
surface of the fauces to the medulla oblongata, and thence reflected along the
the motor nerves.   No one can swallow  without producing an impression of
some kind upon this surface, to which the  muscular movements will imme-
diately respond.  Now it  is  impossible  to  conceive any movements  more
perfectly adapted to a given purpose than  those of the parts in question; and
yet they are independent, not only of Volition, but of Sensation,—being still
performed  in cases  in  which consciousness is  completely suspended, or
entirely absent.
  307. There is much difficulty, then, in ascertaining the really elementary
functions of the Nervous  System, by experiments upon  animals; and  it is
only when their results are corrected and explained by pathological  observa-
tion on Man,—the sole case in which we can  obtain  satisfactory evidence of
the presence  or absence  of sensation,—that they have much value to the phy-
siological inquirer.  From these combined sources, however, a  vast amount
of knowledge of the functions of the nervous system has recently been gained;
and the general purposes to which it  is subservient,  may be advantageously
stated  in a systematic form, before we enter upon any detailed examination of
them.
  i.  The  Nervous  System receives impressions, which,  being conveyed by
its afferent fibres to the  Sensorium, are there  communicated  to the conscious
Mind,  and thus give origin to Sensations.   The Nervous structure is further
subservient,  in some way, to the acts of that mind; as the result of which, a
motor impulse  is transmitted along the efferent trunks, to particular Muscles,
                                  21* 
246
FUNCTIONS OF THE NERVOUS SYSTEM.
exciting them to contraction.   There  is reason to believe, however, that this
motor impulse may proceed from at least two distinct  sources; being either
the direct consequence of the sensation, acting involuntarily as an  emotional
or instinctive impulse ; or resulting from  a more or less complicated series
of intellectual operations, which terminate  in an act of volition or will.—To
these functions, taken collectively, the Encephalon, and the nerves connected
with  it, are alone subservient; and we may probably assign the group of sim-
ple consensual or involuntary actions to the  ganglia which receive the nerv-
ous trunks from the  organs of sense, and which make up nearly the whole
of the Cephalic masses of ganglia in  the  Invertebrata ; whilst the Cerebral
hemispheres  of Vertebrata are the instruments of the  intellectual operations
and of the mandates of the will.
   n.  Certain parts  of the Nervous  System  receive impressions which  are
propagated along afferent fibres, that terminate in ganglionic centres distinct
from  the sensorium; and in these a reflex motor impulse is excited, which,
being conveyed along the efferent trunks proceeding from  them, excites mus-
cular  contraction, without any  necessary intervention of sensation  or volition.
Of this function (called by Dr.  Hall, to whom the discovery of it is in a great
part due, the reflex function), we shall find that the portion  of the Spinal
Cord of Vertebrata, which is not continuous with the fibrous structure of the
brain, together with the portion of the nervous trunks which  are connected
with it alone, is the instrument: whilst, in  the InvertebraLa, the same office
is performed  by ganglia still more obviously  disconnected from the cephalic
mass.
   m. Another division of the  Nervous System appears to have for its object,
to combine and harmonize the  muscular movements immediately connected
with the maintenance of Organic life;  and to bring these into relation with
certain conditions of the mind.   There is reason to  believe (though this is
less certain) that it also influences, and brings into connection with each other,
the processes of Nutrition, Secretion, &c.; though these, like the muscular
movements just mentioned, are essentially  independent of it.   This portion
of the nervous apparatus is commonly known under the name  of the  Sympa-
thetic system.
   308.  Now, in reference to the first of these classes of operations, it is well
to explain that though  the Physiologist speaks of the intellectual  powers,
moral feelings, &c, as functions of the  Nervous System, they are not so  in
the sense in which the term is employed in regard to other operations of the
bodily frame.  In general, by the function of  an organ, we understand some
change which may  be made evident  to  the senses ; as well  in our own  sys-
tem, as in the body of another.   Sensation, Thought, Emotion, and Volition,
however, are changes imperceptible to our  senses,  by  any means  of observa-
tion we at present possess.  We are cognizant of them in ourselves, without
the intervention of those  processes by which we observe material  changes
external  to our minds ;  but we judge of them  in  others, only by inferences
founded on the actions to which they give rise, when compared with our own.
When we speak of sensation, thought, emotion or volition, therefore, as func-
tions  of the Nervous System,  we mean only that this  system furnishes  the
conditions under which they take place  in the living body ; and we leave the
question entirely open, whether the "Vvxri has or has not an existence independ-
ent of that of the material organism, by which  it operates in  Man, as  he is
at present constituted.
   309.  In regard to the second class of-actions, it may be remarked, that they
are nearly all connected, more or less  closely,  with the maintenance of the
Organic  functions, or with the  protection  of the body from danger.  Thus
the movements of the pharynx supply to the stomach  the alimentary materi- 
            COMPARATIVE ANATOMY AND PHYSIOLOGY.--RADIATA.         247

als, which  it has to prepare for the nutrition of the body; and those of the
muscles of the thorax, &c, maintain that  constant interchange of air in the
lungs, which is  necessary for the aeration of the blood : whilst those,  by
which a limb is involuntarily retracted from any cause of pain or irritation, are
obviously adapted to the latter of these two ends.

   2.  Comparative Anatomy and Physiology of the Nervous System in
                        Invertebrated Animals.

   310.  Although the structure and distribution of the  Nervous System in the
different classes  of Animals have been, until recently, but little  appealed  to
in the determination of its  functions, they are capable of supplying evidence
regarding  some  of  these, not less important in its character than that which,
Comparative Anatomy affords to other departments of Physiology.  Some of
the principal of these contributions will now be pointed out.
   311.  In the lowest tribes of the Radiated division of the animal kingdom,
no  Nervous System has yet been discovered.   These have, therefore, been
separated  by some  naturalists into a  new primary group, to which the desig-
nation  of Acrita has  been given, on account of the (supposed)  "indistinct,
diffused, or molecular character  of  their nervous system."   This idea of a
" diffused  nervous system" seems to be regarded by many—Physiologists  as
well as Naturalists—as the necessary alternative, resulting from the want of
any definite indications of its presence.   It may be said, however, to be based
on  very erroneous notions, as to the true offices of the nervous apparatus.
Its  influence is  not required to endow the  tissues with contractility; a pro-
perty possessed  in  a high degree by the structures of  many Plants,  to which
these beings present a much greater general resemblance, than  they bear to
the higher Animals; and, even in the latter (as will  be shown hereafter), this
property is independent of nervous  agency, although generally  called into
exercise by it.  That  a nervous system is not required by them for the per-
formance  of the  functions  of Nutrition and Reproduction, otherwise than  to
supply, by its locomotive actions, the conditions of those functions,  would
also appear from its absence in Plants.  It is on the sensible movements  of
these beings, that our belief in their possession of a nervous system must  be
founded, when we  cannot  render it cognizable by our senses.  But we must
be careful not to draw hasty inferences from such phenomena.  Sensible move-
ments are, as we have seen, performed by the Dionaea and Sensitive plant, in
respondence to  external stimuli acting on distant organs; and they are also
exhibited, in a very remarkable manner, by the reproductive particles of many
of the simpler Plants,  as well as by numerous beings  now generally referred
to the Vegetable kingdom.   It is to be remarked, however, that such motions
are of a very simple  description.  In objects of the latter class, they are  of
a rhythmical  character, and  do  not seem to be in direct dependence on any
external influences.   And even where they are performed solely in respond-
ence to external stimuli, there is usually such a uniformity in their character,
as indicates that the  means  by which the influence is propagated are of a very
mechanical nature.   On the other hand, those movements of Polypes, which
are performed in respondence to external stimuli, are of a much  more varied
character;  and there are others, which seem to  indicate a certain degree  of
voluntary power, and therefore to display a consciousness of impressions made
upon the  body.  These phenomena, then, would lead us to suspect the ex-
istence  of  a Nervous System in the beings which exhibit them ; not, however,
in a "diffused"  condition, but in the form of connected filaments.  For, what
consentaneousness  of  action can be  looked for in a being  whose nervous
matter is incorporated  in the state of isolated globules with its tissues .'   How 
248                FUNCTIONS OF THE NERVOUS SYSTEM.
should an impression made on one part be propagated by these to a distance ?
And how can that consciousness and will, which are one in each individual,
exist in so many unconnected  particles ?  If, then, we allow any sensibility,
consciousness, and  voluntary power, to  the beings of this group of Acrita—
to deny which would be in effect to exclude them from the Animal Kingdom
—we must regard  these faculties as associated with nervous filaments, of  such
delicacy as to elude our means of research.   When the general softness of
the textures, and the laxity of structure that characterizes the nervous fibres,
in the  lowest animals  in  which  they can be traced, are kept in view,  little
difficulty need be  felt in accounting for their apparent absence.   The case is
very different from that of Vegetable structure; the greater consistency of
which enables  us  to place  much more reliance  upon the negative evidence
afforded by anatomical research.
   312.  The correctness of this view (which has been  here dwelt on the longer,
because it involves a fundamental question in Nervous Physiology), is borne
out by  the fact, that, in those members of the group whose size and consist-
ency  allow  their structures to be sufficiently  examined, a definite  nervous
system  has  been  detected ; in the position  which it might, a priori, be ex-
pected to  occupy, according to the type of the individual.   Thus, in the large
fleshy isolated  polype, commonly known  as  the Sea-Anemone {Actinia), a
nervous ring has been discovered, surrounding the mouth as in otber Radiata,
and sending  off branches to the tentacula, with a minute ganglionic enlarge-
ment  at the base of each.  In the higher Radiata, as the  Star-Fish, the nerv-
ous system  has the same regular form as that which prevails through the
other organs.  The mouth is surrounded by a filamentous ring, which presents
a  regular series of ganglionic enlargements, one of them corresponding with
each segment of the body.   From every one of these, a branch is transmitted
to the corresponding ray ; and two smaller ones proceed to the viscera included
in the central disk.
   313.  The  polypifera being the lowest of the Radiated classes, in which
there  is a regularly-organized digestive apparatus, and which perform move-
ments  of a  character ascribable  only to  a Nervous System, it will be desir-
able to  inquire a little more particularly into the phenomena they exhibit, and
the degree in which these necessarily  involve the possession of the higher
mental  endowments.  In this inquiry we shall refer principally to  the little
Hydra, or fresh-water Polype;  the  habits of which are better known than
those of  any other species.  Although  no nervous  filaments have been de-
tected in  this, we  have a right to infer their presence for the reasons already
given;  and  they probably form  a ring  around the mouth, as in the Actinia,
sending filaments  to the tentacula.  This interesting little being may be re-
garded  as essentially a  stomach;  and the orifice  of this is provided with
tentacula, which contract when  irritated by the touch of any adjacent body,
and endeavour to draw it towards  the entrance   Now, the action in the Hu-
man  body, to which this is most allied,  is evidently that of the muscles of
Deglutition;  which  lay hold, as  it were, of the food that has been conveyed
to the  fauces, and  carry it  into  the stomach.   These muscles are called into
action,  not by an  effort  of  the will, but by the contact of the food with the
lining  membrane  of the pharynx.  This impression  is  propagated by the
glosso-pharyngeal  nerve to the medulla  oblongata, where a respondent motor
impulse is excited, which  is transmitted through the pharyngeal branches of
the par vagum to the muscles of deglutition, and  causes their  contraction.
This  phenomenon will be more fully examined  hereafter; it is here adduced
simply as an instance of the important class of reflex movements, which are
independent  of the brain (though, to a certain extent, controlled by it), which
are altogether involuntary, and which do not necessarily involve the produc- 
MOVEMENTS OF POLYPES.
249
tion of sensation.   There would appear to be little difference in the character
of this movement, between the simple Hydra and the most perfect Vertebrated
animal.  In  the  latter, however, another set of muscles  are  superadded to
these, for the purpose of preparing the aliment by mastication  for the opera-
tion of the stomach, and of bringing it within reach of the pharyngeal con-
striction.—But, it has been urged, the inactivity of the tentacula when  the
Hydra is gorged with food, proves that they are excited to action by the will
of  the  animal.   This inference, however,  may be easily disproved.  The
muscles of deglutition in Man are not  called into action with nearly the  same
readiness  and energy, when the stomach  is distended, as when  it is empty; a
fact of which any  one may convince himself, by observing the relative facility
of swallowing,  at the commencement and the termination of a full meal.    No
one will assert that this variation is an effect of the will; indeed, it is  often
opposed to it;  being one of those beautiful adaptations, by which the welfare
of the economy is  provided for, but which the indulgence of the  sensual appe-
tites opposes.  Most  of the movements  of  this animal, and of others of  the
class, appear to be equally the result  of external stimuli,  with that already
described;  and it  is only  in  a  few instances, principally those  of absolute
locomotion or change of place, that any  evidence of voluntary action can be
discerned.   It may be occasionally remarked, however, that one or more of
the  tentacula are  retracted or extended,  without  the slightest  appreciable
change in any of those external circumstances, which seem  ordinarily to
affect  the motions of  the animal;  and this  action we can  scarcely regard as
otherwise than  voluntary.
   314. Thus in  the  Nervous System of Radiated  Animals, we have an in-
stance of that community of function, which is so remarkable in the organism
of the lower tribes, when contrasted with  the separation, which is perceptible
in those at the  opposite extremity of the scale.   The  visceral  nerves of  the
Asterias are  not  isolated at their central  terminations  from those which  are
connected with the sensorial  and locomotive functions : nor are the  nerves
which minister to the instinctive actions separable from those which convey
the  influence of the Avill.  Every segment  of the body appears  equal in its
character and endowments  to the remainder;  each has a ganglion appropriated
to it; and, as the ganglia, like the segments, are  all alike, neither of them can
be regarded as having any presiding character.
   315.  From the Radiated we now pass to the  Molluscous classes;  the
general character of which, as a natural  group,  is the remarkable  predomi-
nance of the Nutritive system over that of Animal life.  There is not in  the
Mollusca, as  in the Radiata, any repetition of parts around  a common centre;
and  we do not  therefore meet in them  with a number of ganglia, nearly or
altogether alike in endowments.   In some  of the higher  species,  there is a
conformity between the two sides of the body, or a lateral symmetry; which
involves a subdivision of some of the  ganglia, that  are single in the inferior
tribes, into two  masses, which always  remain in connexion with  each other.
With this exception, it may be observed, that all the principal  ganglia, to  the
number of four or five, which we  meet with in  the higher  Mollusca, appear
to have distinct functions; as may be  determined by tracing the  distribution
of their nerves.  Thus we  find a pair of  cephalic ganglia, situated  above  the
oesophagus, connected with the organs of special  sensation, and sending motor
nerves (as we shall see reason to believe) to all  parts of the body.  This is
obviously analogous to the  brain of Vertebrata.  Below the oesophagus there
is  generally a  small ganglion, connected with  the  apparatus of  deglutition,
which may be called  the stomato-gastric ganglion.  In connexion with  the
gills we have always  one ganglion, sometimes a pair, which may be  termed
the branchial ganglion.   Another is found at the base of the foot,  which may 
250
FUNCTIONS OF THE NERVOUS SYSTEM.
be called the pedal ganglion.   And  there is sometimes another, which espe-
cially supplies  the  mantle with nerves; and  this may be called  the palleal
ganglion.—The distribution of their nerves to  the  different  organs, would
alone indicate  the respective  functions of these ganglia; but these are placed
beyond doubt,  by that very great variety in the  disposition of these organs,
which is  characteristic of the  Mollusca.   The development of the  sensory
organs, the  situation of the gills, the structure and position of the foot, the
conformation and uses of the  mantle, are well  known to differ in the most
obvious manner, in genera which are closely allied  to each other.   Hence
the anatomist is enabled, by the discovery of corresponding  changes in the
nervous system, to  satisfy himself of the particular functions  of  its different
centres.*
   316.  It is only in the higher tribes, however, that this separation of function
is evident;  for  in the lowest, we find the Nervous System in  its  least deve-
loped form.  This is the case  in the class tunicata; composed of animals,
in which  the whole body is enclosed in a tunic or bag, having two  orifices,
through one of which  the water is drawn in by ciliary action, whilst  through
the other it is  expelled.   This  bag incloses a large  chamber, the lining of
which is devoted to the respiratory function; and at the bottom of it lies the
mass  of the viscera, on which is the entrance to the stomach.   A part of the
water which is  taken into the respiratory chamber flows into this, and passes
through the intestinal  canal;  being discharged along with  that, which  has
only served the purpose of aerating the blood.  These animals  have no power
of motion, but such as  is  effected by the general contraction of the respiratory
sac; this is effected by a single ganglion placed between its orifices, which is
therefore  chiefly a  branchial ganglion, and is the only nervous centre they
possess.   The  trunks connected with it send branches  over  the muscular
envelope  of the respiratory sac, and to the sphincters which surround its
orifices; whilst other  branches proceed to the membrane lining the  orifices,
and especially to the tentacula, or lips, which are situated at the oral entrance.
The maintenance of the  regular current is effected, as  just stated, by ciliary
action; but when any substance is being drawn in, the  entrance of which
would be  injurious, its  contact with the tentacula  excites a general contraction
of the muscular envelope, and causes a jet of water to issue from one or both
orifices, which  carries  the offending body to a distance.   And, in the same
manner, if the exterior of the body be touched, the mantle suddenly and vio-
lently contracts, and expels the contents of  the sac.—These are the chief, if
not the only actions, which the Nervous System  of these animals is destined
to perform ; and they are evidently of a reflex  character; bearing  a close
correspondence with the  acts of coughing and sneezing in  Man, which are in
like manner destined to  expel  injurious  substances from the respiratory pas-
sages.   By the contact of such substances with  the tentacula  that guard the
oral orifice, or  with the  lining of the respiratory sac, or by irritation of the
external surface of the  body, an impression is produced on  the afferent fibres  ;
which, being conveyed to the central ganglion,  excites there  a reflex motor
impulse;  and the propagation of this impulse along the afferent fibres, to the
muscular  fibres of the  contractile  sac, and to the sphincters, produces  the
movements in question.
   317. In the  conchifera, or Mollusks inhabiting bivalve shells, there are
invariably two  ganglia, having  different functions.  The larger of these (Fig.
124, c), corresponding to the single ganglion of the Tunicata, is situated towards
the posterior end of the body (that is, the end most distant from the mouth),

  * See Mr. Garner on the Nervous System of the Mollusca, in the Linnagan  Transactions,
Vol. xvu. 
NERVOUS SYSTEM OF THE LOWER MOLLUSCA.
251
124.
in the neighbourhood of the posterior adduclor muscle ; and its branches are
distributed to that muscle, to  the  mantle,  to  the gills, and to the siphons
through which the water is introduced
and carried off.   But we find another
ganglion, or rather pair of ganglia,  a,
a, situated near the front of the body,
either  upon the oesophagus, or at its
sides;  these  ganglia  are  connected
with   the  very  sensitive  tentacula
which  guard the mouth; and they
may  be  regarded as  presenting the
first approach,  both in  position and
functions, to the brain  of higher  ani-
mals.   In the Oyster, and others  of
the lower Conchifera which have no
foot,—which  is a muscular tongue-
like  organ, — we find  an additional
ganglion [b) connected  with it.—This
is the  case  in the Solen, or animal of
the Razor-shell; whose foot is  a very
powerful boring instrument, enabling
it to  penetrate  deeply  into the sand.
Here,  then, we have  three distinct
kinds of ganglionic centres ; every one
of which may be doubled, or repeated
on the two sides of the body.   First,
the cephalic ganglia, a, a, which  are
probably the  sole instruments of sen-
sation and of consensual movements;
as well  as  of whatever voluntary
power the animal may possess: these
are  almost  invariably double, being
connected  together  by  a transverse
band,  which arches over the oesopha-
gus.   Second,  the pedal ganglion, b,
which is usually single, in conformity
with the single character of the organ
it supplies ; but in  one very rare  Bi-
valve Mollusk,  the foot is double, and
the pedal ganglion  is  double  also.—
 Third,  the respiratory  ganglion, c,
which frequently presents a form that
indicates a partial  division into two
halves, corresponding  with  the repe-
tition  of the organs  it supplies, on the
two sides of the body.   Besides these
principal centres, we  meet with  nu-
merous smaller ones upon the nervous
cords (/,/, and g, g), which  proceed from them to the different parts of the
general muscular envelope or mantle.
   318.  Now it will be observed, that the two cephalic ganglia a,  a, are con-
nected with the pedal  ganglion, b, by means of a pair of trunks, e,  proceeding
from  the former to the  latter; and that  they are, in like  manner, separately
connected  with  the respiratory or branchial ganglion c.   It is found, upon
  Nervous system of Solen; a. a, cephalic ganj;
connected by a transverse band passing over the
oesophagus; b,  pedal ganglion, the branches of
which are distributed to the powerful muscular
foot; c, branchial ganglion, ihe branches of which
proceed  to the  gills g\ the siphons i. i, and other
parts ; h, anus ; e, trunks connecting cephalic and
branchial ganglia; /,/,//, minute ganglia on the
branches distributed to the mantle. 
252
FUNCTIONS OF THE NERVOUS SYSTEM.
careful dissection, that these  cords do not  serve  merely to bring the ganglia
into relation : but that a part of them pass through the ganglion into the trunks
proceeding from it.   Thus, of the nerves which  supply the large fleshy  foot,
and which appear to proceed from the  pedal ganglion, b, a part are  undoubt-
edly connected with that ganglion alone, coming  into relation  with its vesicu-
lar substance ; but a part also pass on to the cephalic ganglia, by the connecting
trunks,—so that these, rather than the pedal ganglion, constitute their centre.
The same may be  said of the nerves proceeding from the branchial ganglion:
a portion of them having their centre in the vesicular matter of that ganglion;
whilst another portion  has no relation to it whatever (beyond that of prox-
imity), but passes  through or over it, to become connected with the cephalic
ganglia.   There is  good reason to believe, that the pedal and branchial gan-
glia minister  to the  purely  reflex  actions of the organs they respectively sup-
ply; and that they would serve this purpose as well, if altogether cut off from
connection with the cephalic  ganglia:  whilst the  latter,  being the instruments
of the actions which are called forth by sensation (whether these be of a con-
sensual or of a voluntary  nature), exert a general control and direction  over
the  movements of  the animal.
  319.  The  animals of the class gasteropoda, whether furnished with  uni-
valve shells,  or  entirely destitute of such protection, are, for  the  most  part,
much  more  highly organized than  the  preceding; possessing  not merely
greater  locomotive  power,  but organs of special  sense, which are situated in
the  neighbourhood of the mouth,  upon a projecting part of the body, which is
thus constituted a head.  Their nervous system consists of at least three dis-
tinct  centres; the  relative position of which  varies with that of  the  organs
supplied by them.    The anterior or cephalic  ganglia are larger in proportion
to the  rest, than they are in  the Conchifera ;  and they exhibit a tendency to
gain a position anterior  to  the oesophagus, and to approximate towards  each
other, so as to meet and form a single  ganglionic mass on the median  line.
The branchial ganglion is  constantly to be met with ; but its  position is ex-
tremely variable.  This  centre, however, always bears a close  relation  with
the  gills, both in situation and  in degree of  development;  and even where
conjoined, as it frequently  is, with the pedal ganglion, it may be distinguished
from it by the distribution  of its nerves, as well as by its separate connection
with the cephalic ganglia, which is always noticed in such cases.   This  may
be observed in the Patella (limpet) and Umax (slug).  Sometimes  the func-
tions of this  ganglion are subdivided between  two;  of  which one is still ap-
propriated to the branchiae ;  whilst the other is  connected with the general
surface of  the mantle, and  with the respiratory passages which are prolonga-
tions of it, and hence may be called  the palleal  ganglion.  The  position of
the pedal ganglion (which  is  generally double  in  the Gasteropoda, though the
foot is single), also  varies,  but in  a less degree,  since  it is generally in the
neighbourhood of the head.—Besides these nervous centres, we find, in many
of the Gasteropoda, a separate system connected with  a very important set
of organs, the gustatory and  manducatory, which are but slightly shadowed
out among the Conchifera.  In these higher  tribes, the oesophagus  is dilated
at its commencement into a muscular cavity (Fig. 3, a); containing  a curious
rasp-like tongue, often supported  upon cartilages, which serves to reduce the
food; and  sometimes furnished with horny maxilla?.  The nerves which sup-
ply these do not proceed directly from the cephalic ganglia,  but  from a dis-
tinct  centre;  and their  ramifications proceed along  the oesophagus and  sto-
mach, and are occasionally connected with the  other nerves  by inosculating
filaments.  This set of  ganglia  and nerves,  which is  even more important
from  its relative development in some other classes, and into  the analogies of 
NERVOUS SYSTEM OF HIGHER MOLLUSCA.
253
which in the nervous system of Vertebrata we shall hereafter inquire, may be
called, from its distribution, the stomato-gastric system.
  320. The ganglia  first described  may be regarded  as  corresponding with
those parts of the nervous centres in the Vertebrata, the distribution of whose
nerves  is analogous.  Thus the branchial ganglion  obviously corresponds
with that portion of the Medulla Oblongata which is the centre of their respi-
ratory actions ; and the pedal  ganglion  is analogous  to  that division of the
Spinal Cord from which  the nerves of the anterior or posterior extremities
pass off.  It is well known that such portions of the spinal cord may be com-
pletely isolated, without  destroying the functions to  which they minister.
Thus, the brain and  lower part of  the  spinal cord may be removed,—that
portion only of the  cerebro-spinal axis being left, which is connected with the
principal respiratory nerves,  in fact  the respiratory ganglion,—and yet the
animal may continue to exist for some time.   It is  then reduced to a condi-
tion similar to that  of the  Tunicata;  whose single ganglion, though combining
in some degree the  functions of those which  exist separately in the higher
tribes, has evidently the regulation of the respiratory movements for its chief
object.   In  the same manner, the  integrity of the segment of the cord, with
which the nerves of the extremities are connected, will  enable them to execute
those movements of a reflex character, which  depend upon its power as their
centre; even  though it be isolated from every other part of the nervous ap-
paratus.—The cephalic ganglia  must be regarded as chiefly analogous to those
portions of the Encephalon of Vertebrata,  which are  immediately connected
with  the nerves of  sense.   We find nerves of special sensation proceeding
from them, certainly  to eyes  and  an  auditory apparatus,  perhaps  also  to
olfactive organs ; as well  as others of common sensation, supplying the ten-
tacula and mouth.  Hence we must admit, that they perform the functions  of
the optic ganglia of Vertebrata, and perhaps  also of the  olfactory lobes ;  as
well as of the portion of the medulla oblongata, in which  the sensory portion
of  the  fifth pair terminates.  Moreover, they  certainly give origin  also  to
motor nerves ; and must thus perform the functions of  the Medulla Oblongata,
from which the corresponding nerves arise in Vertebrata ;  as  well as, perhaps,
of  the Cerebellum.—It is obvious that the portion of  the Nervous system  of
the Gasteropod  Mollusca, into the analogies of which  we have thus inquired,
cannot in the least be compared as  a whole with the  Sympathetic system  of
the Vertebrata, which it was  formerly imagined to resemble.  The  distribu-
tion of some of its  nerves to the viscera, however, may indicate that it partly
performs the functions of that  system; with  which  it is structurally  inter-
mixed, even in  Vertebrata.  But  the  stomato-gastric  system may,  perhaps,
with more  probability, be considered as executing its offices.  Into the  pecu-
liar character of that system we shall be  more competent to inquire when we
have traced it through other classes  of Invertebrata.
   321. Having thus separately considered the  nervous centres of the Gaste-
ropoda, and determined their special functions  by their structural relations, we
shall inquire into the  mode in which these functions  are combined, so as  to
enable them to act  in harmony.   This is  an inquiry of much interest, in re-
ference to the determination of the offices of the different parts of the nervous
centres in Articulated and Vertebrated animals.  If we examine the  mode  in
which the different ganglia are united by connecting trunks, we are led to per-
ceive the important fact, that, while they have little or no communication with
each other,  they are  all directly connected with the  cephalic ganglia;  which
seem thus  to harmonize and control their individual  actions.   Frequently a
communication with  one another appears to exist, where there is really none.
Thus, in the Aplysia, a cord passes from the branchial  ganglion (Fig. 125, d),
     22 
254
FUNCTIONS OF THE NERVOUS SYSTEM.
which is situated in the posterior part of the body, to the pedal  ganglion of
each side, (c, c).  Where such is  the

               Fig. 125.
  Nervous system of Aplysia. a. pharyngeal gan-
glion ; b, cephalic ganglion. The cephalic is con-
nected, by three distinct cords on each side, with
the lateral masses, c c, which combine the functions
of pedal  and palleal ganglia; these are united with
each other by two transverse bands, between which
the aorta passes.  From the lateral ganglia, a con-
necting  cord passes backwards on each side to the
branchial ganglion, d ; this cord is continuous with
one of the three proceeding from the cephalic gan-
glion.
case, the trunk is not united with that
proceeding from the ganglion through
which it passes; but the two remain
distinct, though running in  the  same
direction.  Moreover, the double func-
tion of a ganglion may be  sometimes
recognized,  by its being  connected
with  the cephalic  mass  by a double
trunk.   Thus, in  the  Aplysia, that
which has been termed the pedal gan-
glion is really made up of a pedal and
palleal ganglion, as is  proved by the
distribution  of its branches; and  in
conformity with this double function,
we find  it  communicating with  the
cephalic mass by two cords, besides
the one which has been just mentioned
as passing through  it, and which ap-
pears  as a  third.    In  the Bullaea,
whose nervous system is disposed on
the same general  plan, the  pedal and
palleal ganglia are separately connected
with the cephalic ; the  cord from the
branchial ganglion passing through the
palleal.
   322.  Further, a careful examination
of these ganglia, and of their connecting
cords, discloses this important fact,
which is peculiarly evident in the case
of the pedal ganglia—that  the  cords
proceeding from the cephalic mass do
not lose themselves in the grey matter
of these ganglia; but divide themselves
into filaments, which mix with those
proceeding  from  them, to form the
nervous trunks which they distribute.
We can scarcely, then, fail to infer,
that the pedal ganglion, with the nerv-
ous fibrils proceeding from itself, is the
source of the reflex actions of this  or-
gan; whilst the filaments which are con-
tinuous with those of  the  connecting
 trunk, and which are thus connected
 with the nucleus of the  cephalic gang-
                                      lia, are the channels of sensory impres-
sions, and of the motor impulses prompted by them.—This is well illustrated
in the curious disposition of parts, which we find in the arms of the Cuttle-fish.
These are provided, it is well known, with a  series of  suckers, which are to
the animal important instruments of locomotion and  prehension.   It has been
observed by Dr. Sharpey, that the nerves which supply these  arms are fur-
nished with  ganglionic enlargements, of which one corresponds  with each
sucker;  and that each trunk consists of two tracts,  in one of which the gan-
glionic enlargements exist; whilst  the  other  passes continuously over these,
but sends off nervous filaments, which help to form  the branches going to  the 
NERVOUS SYSTEM OF MOLLUSCA AND ARTICULATA.           255
several suckers.  When the animal endeavours to embrace any object firmly
with its arm, it brings all the suckers simultaneously to bear upon it.   There
can be little doubt that this action is occasioned by a motor impulse, propa-
gated from the cephalic masses by the non-ganglionic  portion of  the  cord,
which supplies  all the  suckers  alike.  On the  other hand, any individual
sucker may be made to attach itself, by placing a substance in  contact with
it alone ; this action is independent of the cephalic ganglia, as is evident from
the fact, that it will take place when the arm is severed from the body, or even
in a small piece of the arm, if recently separated;  and it can scarcely be doubted,
that it is  due to the reflection of the impression made upon the sucker, through
the small ganglion in its own neighbourhood, where it excites a motor impulse.
The operation of these independent centres appears, in the entire living animal,
to be controlled, directed, and combined, by the cephalic ganglia; through the
medium of the fibrous  band which passes over them, and which  mixes its
branches with theirs.  A very similar  arrangement will  be presently shown
to exist in the double nervous column of the Articulata.
  323. Upon reviewing all the anatomical  facts hitherto stated, it will be per-
ceived that ganglionic masses, characterized by nuclei of grey matter, or of
something equivalent to it, seem to exist, wherever it is desirable that impres-
sions made upon the afferent nerves should excite motions ; and that, as we
rise in the scale, there is an increase in the number of centres possessing a
diversity of functions.   We have seen that sometimes these centres are, for
the sake  of convenient disposition, united into one mass;  whilst on the other
hand, when the organs are multiplied, they also are repeated to a like extent;
especially when it is desirable that they should be able to act independently
of one another, as in the case of the suckers of the Cuttle-fish.  It may further
be remarked, that wherever the presence of special sensory organs, confined
to one part of the body, gives to that part a predominance over the remainder
(the entrance to the alimentary canal being  always in this neighbourhood), we
find the ganglia with which they are connected possessing a special relation
with all the rest, which these do not possess with each  other.  It is obvious
that, where visual organs are developed, the impressions made upon these will
determine the movements of the animal, more than those  of any other kind;
and it would seem to be chiefly owing to the information they communicate,
that the cephalic ganglion has such an evident presiding influence over the rest,
even when smaller than any of  them.  This  is, however, more the case in
animals whose movements are rapid, and in which, therefore, the perception
of distant objects is more important—as in the Insect tribes.  Except in the
Cephalopoda, the subservience of the nervous system to the nutritive functions
of the Mollusca is so great that it might almost be regarded as an appendage to
the digestive organs, destined for the  selection  and  prehension of aliment.
But in the more active members of that class it derives a  more elevated cha-
racter, from the development of organs  of special sensation and of active loco-
motion.
  324. The  animals composing the group  Articulata all present, in a more
or less evident degree, a division into  segments, which have an obvious tend-
ency to resemble one another, as in the Radiata; these are disposed, however,
not in a circle, as in the Radiata, but in a continuous line.   In those in which
these segments differ but little (as in the Centipede,  or the Caterpillar of the
Insect), the nervous system is a repetition  of similar parts;  the most anterior
of the ganglia,  however, has an  evident  predominating influence  over the
rest, for  the  reason just specified;  and this influence will be found, by com-
parison in other classes, to diminish with the loss, and to increase with the de-
velopment, of the faculties  of special sensation, which have their seat there.
The locomotive powers are just  as  predominant in the Articulated series, as 
256
FUNCTIONS OF THE NERVOUS SYSTEM.
Fig. 126.
                                are the nutritive functions among the Mol-
                                lusca.    Accordingly, we find  the  deve-
                                lopment of the  Nervous system to bear a
                                special reference to them ; and the sensori-
                                motor divisions of it can be more distinctly
                                separated, than in  the Mollusca, from the
                                portion which ministers to the organic func-
                                tions.
                                  325. The  general  arrangement of the
                                Nervous  System differs so little, except as
                                to the degree of concentration of the ganglia,
                                in  the different classes  of  this sub-king-
                                dom, that it  is of little consequence what
                                example  we select.  It will be  convenient
                                to  take for illustration that of the Larva of
                                the Sphinx ligustri, or Privet Hawk-Moth,
                                which has been minutely described by Mr.
                                Newport.   Here  we  observe  a  chain  of
                                ganglia running from one extremity of the
                                body to  the other, along the ventral sur-
                                face, and in the median  line.   These gan-
                                glia are  connected by  trunks, which, on
                                close examination, are seen to  consist of
                                two cords closely united.  The cephalic
                                ganglion  is bilobed;  evidently consisting
                                of two masses, which  are united on the
                                median line.  These receive the nerves of the
                                eyes and antennae; but they are still of small
                                size, in  accordance with the  low develop-
                                ment of the  sensory  organs.   The ganglia
                                of the longitudinal cord are nearly equal
                                from  one extremity  of the  body to the
                                other.   Each  sends  off nerves  to its  re-
                                spective segments ; and the branches pro-
                                ceeding from  the different  ganglia  have
                                little communication with each other. The
                                highest  of them,  situated just  beneath the
                                 oesophagus, is connected with the cephalic
                                 masses by two cords ; between which that
                                 canal passes, encircled, as it were, in a ring.
                                    326.  The most detailed account of  the
                                 conformation  of the Nervous  Centres in
                                 the  Articulata, is that  recently given by
                                 Mr. Newport, in regard to the lulus, and
                                 other animals of the  class  myriapoda.*
                                 Their  general  arrangement  corresponds
                                 with that which  has been just described
                                 in the larvae of  the  Sphinx  ligustri;  but
                                 the number of ganglia  is much greater. In
                                 each lateral half of the cord,  two distinct
                                 tracts or layers of fibres can  be detected :
  Nervous System of Larva of Sphinx ligus- of tnese> one—known as the fibrOUS tract
tri, after Newport; a, cephalic ganglia; 1-11, _ig continuous wjth the Cephalic ganglia,
ganglia of the trunk, disposed at nearly equal
distances; the last is formed by the consoli-
dation of the 11th and 12th.
Philosophical Transactions, 1843. 
NERVOUS SYSTEM OF ARTICULATA.
257
Fig. 127.
  Portion of the ganglionic tract of Po-
lydesmus maculalus ; b, inter-ganglionic
cord; c, anterior nerves;  d, posterior
nerves;  f, k, fibres of reinforcement;
g, h, commissural fibres ; i, longitudinal
fibres, softened and enlarged, as they
pass through ganglionic matter.
and contains no vesicular matter; whilst the other known as the ganglionic
tract—has vesicular matter deposited at intervals  amongst its fibres, some of
which are continuous with the brain, whilst others do not reach  it.  (Fig. 128,
a.)  Every nerve that is given off" from this ventral column, is connected with
both tracts ; and thus it has two sets of roots, one proceeding to  the brain,  the
other entering the ganglion near which it arises.  Of this last division, a part
crosses  to the  opposite side, forming  the
commissural fibres which unite  together the
lateral halves  of the cord ;  whilst  another
bundle of fibres runs  along the side of the
ganglionic tract, for a greater or  less propor-
tion of  its length, and  then  emerges again
forming  part of another nervous trunk.   In
Fig. 127 is seen  Mr. N.'s  representation of
one of the ventral ganglia, and part of the
cord, of  Polydesmus maculatus; showing
the longitudinal and commissural  fibres,  to-
gether with those to which  he has given the
name  of fibres of reinforcement.   These
lateral fibres, which do  not pass  on to the
brain, but issue again  from the ventral cord
at a point a little  distant from their entrance,
seem to be more numerous in the hinder part
of  the body of the Centipede tribe, than in
its  front portion :  and thus it is, that the whole
size of  the cord  remains  nearly the same
along its entire length; whilst that of the por-
tion which passes backwards from the brain, must be continually diminishing,
as  it gives off'  fibres to the nerves.
   327. After what has been said of the offices which the ganglia perform in
the Mollusca, and of the relation which they bear to the  cephalic  mass, we
shall have little difficulty in understanding the character  of the nervous appa-
ratus in  the Articulata,  if our minds  be unoccupied by any  preconceived
notion.   When we examine into the actions of the ventral cord, we perceive
that those of all  its ganglia are  similar to each other; being related only to
the movements of their respective segments, and of the members which belong
to them.   In  fact, these  ganglia  may be regarded as  so many repetitions of
the pedal or locomotive  ganglion of the  Mollusca.   It is  easily proved, that
the movements of each pair of feet may be produced by that ganglion alone,
with which it is connected; since a single segment, isolated  from  the rest,
will continue to perform  these movements  for some time, under favourable
circumstances.   But it is evident that they must  be  placed, in the living ani-
mal, under some general control; by which the consentaneousness of action,
that is essential to regular locomotion, may be produced.  This is proved by
the experiments  to  be presently quoted.  We can  scarcely account for  the
exercise  of such  a general control, otherwise than by attributing it to  the
fibrous portion of the  cord,*  which  directly connects  each  of the  nervous
  *  It is believed by Mr. Newport, that the fibrous portion of the ganglionic  tract, which lies
nearest the surface of the body, may be the channel by which sensory impressions are  con-
veyed to the brain; whilst the fibrous tract itself may convey downwards the motor impulses
which originate in the cephalic ganglia.  The chief reason for this supposition, is the corre-
spondence in position,—relatively to each other, and to the rest of the body,—between the
fibrous and ganglionic columns in Articulata, and the portions of the Spinal Cord of Verte-
tebrata, from which the anterior or motor roots, and  the posterior or sensory, respectively
arise.—But the fibres which are peculiar to the ganglionic tract,  obviously form a distinct
system.
                                     22* 
258
FUNCTIONS OF THE NERVOUS SYSTEM.
trunks with the  cephalic ganglia, as in the Mollusca; and  this must, there-
fore, conduct to  the  sensorium (whose  seat is probably in the latter)  the im-
pressions which there produce sensations, and must  convey downwards the
locomotive impulse; whilst the ganglion of each segment, with  the filaments
connected with  its  nucleus, will  form the circle necessary for the  simply-
reflex  actions of its  members.   The independence of the  segments of the
Articulata, as far as their reflex actions are  concerned, and their common sub-
ordination to one presiding centre of the  will, are fully explained on this sup-
position.  It is also quite conformable to the analogy, both  of Mollusca, and
of Vertebrata.
   328. The number and variety of the reflex actions, which take place in the
Articulata after  decapitation, are very remarkable;  and they seem to have a
consentaneousness, proportioned to the closeness of the relation between the
nervous  centres  in the respective species.   Thus, in the  Centipede,  we find
the ganglia of the several segments distinct, but connected by a commissural
trunk.   Here an impression made equally  upon the afferent nerves of all the
ganglia, will produce a consentaneous action.   Thus, if the respiratory ori-
fices on one side of a decapitated Centipede be exposed to an irritating  vapour,
the body will be immediately flexed in the opposite direction; and if the
stigmata of  the  other side  be then similarly irritated, a contrary movement
will occur.   But different actions  may be excited in different parts of the
cord, by the proper disposition of the irritating cause.  In the higher  classes,
however, where  the ganglia of the locomotive organs are much  concentrated,
the same irritation will  produce consentaneous  motions in several members,
similar to those which  the  unmutilated animal performs.   In the  Mantis
religiosa, for example,—which  ordinarily places itself  in a  very  curious
position, especially  when threatened  or  attacked, resting  upon  its  two pos-
terior pairs of legs, and elevating its thorax with the anterior pair, which are
armed  with  powerful claws,—if the anterior segment of  the thorax, with its
attached members, be removed, the posterior part of the body will still remain
balanced upon the four legs which belong to it, resisting any attempts to  over-
throw  it,  recovering its  position when  disturbed, and performing the  same
agitated movements of the wings and elytra, as when the  unmutilated animal
is irritated:  on the other hand, the detached portion of the  thorax, which con-
tains a ganglion, will, when separated from the head, set in motion its long
arms, and impress  their hooks  on the fingers which hold it.   These  facts
prove unequivocally, that the  combined automatic movements of these parts,
which  are performed in direct respondence to external expressions, are only
dependent for their stimulation upon that  ganglionic centre, with which the
nerves that excite them are immediately connected.  Another instance, related
by Burmeister, is still more  satisfactory in regard to the manner in which
these movements are excited.  A specimen of the Dytiscus Sulcatus, from
which  the cephalic ganglia had been  removed,  and which remained in a
motionless condition whilst lying with  its abdomen  on a dry  hard  surface,
executed the usual swimming motions, when  cast into  water, with  great
energy and  rapidity, striking all its comrades to  one side by its violence, and
persisting in this for half an hour.
  329.  These conclusions are also  fully confirmed  by the experiments of
Mr. Newport, upon various  Insects  and  Myriapoda;  the  results of which
have been recently  made public*   The  following, upon the lulus terrestris,
is  particularly interesting.  " The cord  was divided in the fourteenth, and
also the  twentieth segment; and  the  intervening portion was  destroyed, by
breaking it down with a needle.   The animal exhibited in  the  anterior part
* Philos. Trans., 1843, p. 267. 
REFLEX ACTIONS OF ARTICULATA.
259
of its body all the  evidences of perfect  volition.   It moved actively along,
turning  itself  back on  either side repeatedly, as if to examine the  anterior
wounded portion, which it felt again and  again with its antennae: and  when
attempting to escape, frequently turned back as if in pain and aware of  some
hindrance to its  movements; but it seemed  perfectly  unconscious of the
existence of the posterior part of its body,  behind the first incision.   In  those
segments, in which the cord was destroyed, the legs were motionless;  while
those of the posterior division, behind the second  incision, were in constant
but involuntary motion, the movements being  similar to those of walking or
running,  uniformly  continued, but  without any consentaneous action  with
those of the anterior part, by  which locomotion was performed, dragging the
posterior divisions of the body  after them.   When the animal was held by
the posterior segments,  reflex actions were excited in.  the legs, and  powerful
contractions and gyrations of  the whole animal were performed in those seg-
ments ;  but  these movements appeared  to be entirely the  result  of reflex
actions of the muscles, since exactly similar  ones  took place in the whole
body  of decapitated specimens.   At the expiration  of  twelve  hours,  the most
perfectly voluntary acts  were  performed by the head and anterior division of

                                  Fig. 128.
  Parts of Nervous System of Articulata. a, single ganglion of Centipede, much enlarged, showing the
distinctness of the purely fibrous tract, 6, from the ganglionic column, a.  b, portion of the double cord
Irom thorax of Pupa of Sphinx ligustri, showing the respiratory ganglia and nerves, between the gaii-,
glia (2, 3, 4), and  the separated  cords of the symmetrical system,  c, vie'w of two systems combined,
showing their arrangement in the Larva; a, ganglion of ventral column ; 6, fibrous tract passing over
it; cc, respiratory system of nerves distinct from both.

the body,  such  as locomotion forwards or to  either side, avoidance of any
obstacle, touching it with  the antennas, (which  were in rapid action, as in an
uninjured  animal,) and attempting to reach  and to climb up an object pre- 
260
FUNCTIONS OF THE NERVOUS SYSTEM.
 sented  to  it, but not in immediate contact with it.   But reflex  movements
 alone  existed in the posterior division, in which  the legs were very slowly
 moved, even when the animal was not progressing.   Brisk actions were now
 more easily excited in them than at first, either by contact with the segments,
 by irritation of  one or two of the legs themselves, or by a sudden current of
 air.  By these  means, when  the animal was lying  still, actions were imme-
 diately excited in all  the legs of the posterior parts  of the body, anterior and
 posterior to  those  which were  irritated ; and  these actions were induced in
 those of both sides of the body, but appeared to commence on the opposite
 side, in the legs  corresponding to those which were first irritated.   In eighteen
 hours, the  anterior  part of the body was quite dead, so that no motions what-
 ever could be excited in it, either voluntary or  reflex; but reflex actions were
 then readily excited in the posterior, and also slightly so by mechanical irrita-
 tion, even  at twenty-four hours."   It would appear, then, that we  may obtain
 more decided proof, in the  Articulated series,  of the real character of reflex
 actions, and of  their dependence upon a distinct system of nerves, than we
 can draw from  any other class of  animals.  In  the Vertebrata, it is  easy to
 distinguish the  sensory  from the motor—the afferent  from  the  efferent—
 fibres;  but the distinctness of the excito-motor system from the sensori-voli-
 tional, is not so  clearly made  out.  Here, however, the  afferent and efferent
 fibres cannot be readily distinguished; but it is obvious that the reflex actions,
 which manifest  themselves when the communication with the cephalic  ganglia
 is cut off, are to be attributed  to those fibres, which enter the cord under the
 afferent character,—pass into the  et\ge of the ganglion  as the fibres of rein-
forcement, or cross it  as commissural fibres,—and then emerge again as
 efferent fibres, either in the nerves of the same  segment, or in those of another
 more or less distant.   By traversing the  cord  along a part of its  length, and
 thus placing  the several segments in communication with  each other, the
 fibres of reinforcement thus constitute a part of the  longitudinal filaments of
 the cord,—the remainder consisting of the fibres continuous with the cephalic
 ganglia.
   330.  Hitherto we have spoken only of that division of the nervous  system
 of  the Articulata, which may  be regarded as corresponding with the  sensory
 and locomotive  ganglia of the Mollusca ; we have  next  to  inquire what we
 find corresponding  with the branchial ganglion. It is to be recollected,  that the
 respiratory apparatus of Insects is diffused throughout the whole body, so that its
 presiding system of nerves must be proportionally extended; and we are, there-
 fore, prepared to find the branchial ganglion of the  Mollusca  repeated, like
 the pedal,  in each segment.  Besides the nervous trunks proceeding from the
 ventral cord at its ganglionic enlargement, we find,  in most of the  Articulated
 classes, a series  of  smaller nerves,  given  off at intermediate points, without
 any apparent swelling at the points of divergence.   The connections of these
 are most distinctly  traced in the thoracic region, just as the Larva  is passing
 into the Pupa state  ; for the cords of  the ventral column then diverge, so that
 an  additional tract may be seen  which occupies the  central line.  By  a close
 scrutiny, this tract may be found in the perfect Insect, on the superior or vis-
 ceral aspect of the  cord ;  and its nerves are given off from minute ganglionic
 enlargements upon  it.  It seems  to be quite  unconnected, along its whole
 course,  with the colurnn upon which it lies.  Its nerves, however, communi-
 cate with those  of the sensori-motor system ; but they have  a separate distri-
 bution, being transmitted especially to the tracheae, on the parietes of which
 they ramify minutely, and also  to  the muscles concerned in the  respiratory
 movements.   (The latter, however, being a part of the general  locomotive
 apparatus,  are also  supplied from the principal ganglionic column.)   These
 nerves,  then, which are evidently analogous to  those of the gills and siphonic 
RESPIRATORY AND STOMATO-GASTRIC SYSTEMS OF INSECTS.       261
Fig. 129.
>
f
apparatus in the Mollusca, may be regarded as corresponding with the pneu-
monic portion of the Par Vagum in Vertebrata (which is in like manner dis-
tributed on the air passages), and with its associated motor nerves.
  331. In comparing the nervous system of Insects with  that of the higher
Mollusca, it will be seen that they differ  more in the arrangement and in the
relative proportion of  their parts, than in their  essential character.   In both
there is a Cephalic division of the ganglionic centres, in which sensibility and
psychical power appear to reside more particularly, if not entirely.   In both
there is a division specially appropriated to  the Locomotive  apparatus, differ-
ing only in  the multiplication of the centres in Insects, conformably with the
arrangement of the  members they supply ; and sometimes consolidated to
nearly the same degree.   In both, also, we find a division appropriated to the
Respiratory  apparatus, in which  there  is a  corresponding multiplicity of
centres in the Articulata, in harmony with the universal distribution  of their
tracheal system.  And in both, as we  shall now see,
there is a separate  system of nerves, distributed to the
alimentary apparatus,  and supplying the organs of mas-
tication (with the salivary glands), of deglutition, and of
digestion.
  332. Of the stomato-gastric system, some traces may
be found  in  nearly all the Articulated classes.   Thus,
in the Leech, we find a minute ganglion existing at the
base of each of the three teeth which form the  mouth;
these ganglia are connected together, and, to the cephalic
by slender filaments ;  and they  seem also to be  in  con-
nection with other filaments, which may be traced on the
alimentary canal.   As a  specimen of its highly-deve-
loped form, we shall describe  that of the  Gryllotalpa
vulgaris (Common Mole-Cricket). Here we find it con-
sisting of two divisions; one   placed on the  median
line,  which may hence be called  the median system;
the other running  on each side at some little distance,
and hence called the lateral system.—The median sys-
tem appears to originate in a small ganglion, situated an-
teriorly and inferiorly  to the cephalic mass, with which
it communicates by a connecting  branch on  each side.
From this ganglion, nerves proceed to the walls  of the
buccal cavity, the mandibles, &c.   Its principal trunk,
however, (the recurrent of authors,) is sent  backwards
beneath  the  pharynx.   The ramifications of this  are
distributed along the oesophageal tube and dorsal ves-
sel;  whilst the trunk passes downwards  to the stomach,
where its  branches inosculate  with those supplied by
the lateral system, and seem  to  assist in  forming  a
pair of small ganglia, from which most  of the  visceral
nerves radiate.—The ganglia of the lateral system are
two on each side, lying behind and beneath the cephalic
masses.  The anterior pair are  the largest, and meet  on
the median  line, just behind  the cephalic ganglia,  with
which  they communicate.   Posteriorly to these lie the
second pair, which are in connection with them.  Two
cords pass backwards on each  side ;  one derived from
the anterior, the other from the posterior, of these gan-
glia.   They run along the sides of the  oesophagus and
dorsal vessel; and, after inosculating with the branches of the central  system,
 Stomato-gastric system
of  Oryllotalpa vulgaris;
aa, cephalic ganglia; a,
anterior median ganglion
with the recurrent trunk
passing downwards from
it;  bb, and cc, lateral gan-
glia ; d, visceral ganglia. 
262
FUNCTIONS OF THE NERVOUS SYSTEM.
enter the two  coeliac ganglia, from which  branches radiate to the abdominal
viscera.
   333.  This system of ganglia and nerves has an evident affinity  with  the
Sympathetic system of Vertebrata, as well as with some parts of the Cerebro-
spinal system, more especially with the Par Vagum.   It is to be remembered,
that the Pneumogastric  nerve of Vertebrata is distributed to three separate
systems—the  respiratory, the circulating and the digestive.   As we know
that the ultimate  fibrils  of nerves  never anastomose, there can be  no doubt
that these branches might be separately traced backwards into their ganglionic
centres  ; and they  may thus be regarded as functionally three distinct nerves,
though  bound  up in a single trunk.  There is no difficulty, then, in under-
standing that the  respiratory system  of nerves, in Insects, and other  In-
vertebrata, may be analogous with the pneumonic portion of the Par Vagum ;
although it bears no relation with the cardiac and  gastric divisions of  the
nerve.  To the latter divisions, the  analogy of the recurrent nerve  becomes
sufficiently plain, when we look at its distribution  upon  the  dorsal vessel,
oesophagus, and stomach ;* but its commencement in the anterior ganglion,
which also supplies the mouth and pharynx, might seem to place it on a dif-
ferent footing, until we have determined the true analogy of this last centre.
It may be inferred  from its situation, and from the distribution  of its nerves,
that this anterior ganglion is analogous both to the labial  and pharyngeal
ganglia  of the higher Mollusca.   These appear to  form a  division of  the
nervous system, by which the actions immediately concerned  in the prehen-
sion of  food are performed ;  and these  seem  almost as independent of  the
cephalic ganglia, as are those  of respiration.  There is evidently, however,
a greater tendency towards the  union of these centres  with the oesophageal
collar, than of those presiding over the respiratory function, which  is more
independent of the will.
   334.  The  division  of the  nervous system  of Vertebrata with which  the
central  portion of this system  corresponds,  is a question of some  apparent
difficulty; but, if we  bring into comparison  not only the highest but  the
lowest forms of the cerebro-spinal  apparatus, the chief difficulties will be
removed.  The analogies drawn from the distribution of the nervous branches
would lead us to infer, that the third division of the Fifth pair  (including its
sensory and motor origins), the Glosso-Pharyngeal, and the gastric portion of
the Par Vagum, would most nearly represent its central portion.   Now, when
the fifth pair is traced back to  its  true origin, it is found to be not a cerebral
but a spinal nerve; and it is then seen to arise from the Medulla Oblongata,
in such  close approximation with the par vagum and glosso-pharyngeal, as to
show that, if this  portion of the nervous  centres were isolated from the rest,
the nerves which  proceed from it would  form, anatomically as  well as func-
tionally, a natural group.  The fifth  pair,  like other spinal nerves, may act in
a simply-reflex character; although, in Man, it is  usually under  the dominion
of the will.  In the lower animals we find these reflex actions bearing a much
larger proportion to the voluntary,  than  in Man;  and even in him we  not
unfrequently  meet with  cases, in which the functions of the cerebral hemi-
spheres  seem  suspended, whilst those of the spinal cord are unimpaired; so
that the prehension of food by  the lips may take  place without  any effort of
the will.  This has been observed in anencephalous foetuses, in  puppies from
which the brain has been removed, and  in profound apoplexy.   Further, the
connection between the fifth pair and par vagum is very intimate  in fishes;  the
class which approaches  nearest, in  the  character of its  nervous system, to
Invertebrata.   We may reasonably infer, then, that  the  anterior ganglion is
* See Newport, in Phil. Trans., 1832, p. 386. 
STOMATO-GASTRIC SYSTEM OF INVERTEBRATA.
263
the principal centre of the reflex actions of those nerves, which correspond to
the third branch of the fifth pair, to the glosso-pharyngeal, and to the gastric
portion of the  par vagum, in  Vertebrata;  whilst the branches which connect
them with the cephalic ganglia, bring these nerves more or less  under the
influence  of the  latter.—The lateral ganglia seem more  analogous to the
centres of the Sympathetic system in Vertebrata; especially in the connection
of their branches  with all the  other  systems of  nerves;  and in the share
which  they have  in  the formation of the coeliac ganglia.   This view of the
relative functions  of these two divisions  of the  stomato-gastric system, is
strengthened by the fact, that the connection between the Sympathetic system
of Fishes  and the Par Vagum  is much more  intimate than in the higher
Vertebrata; although, even in the latter, as will be shown hereafter, it is by no
means so slight as it appears.*
   335. Upon  taking a general  review of the facts which have  been stated,
and of  the inferences which have been  erected upon them, we perceive that
a gradual elevation may be traced, in the character of the actions  to which the
Nervous System  is subservient, as we ascend from the lower to the higher
parts of the Animal Scale.  In the Radiata and lower Mollusca, in which no
organs of special  sensation exist, all, or  nearly all, of  the  movements which
are witnessed, may be legitimately regarded as simply reflex in their character;
being analogous to those, which are unquestionably so in the higher animals;
and  being performed  by the  instrumentality of  a nervous apparatus, that
seems to  have little  else than an internuncial purpose.   But  when, as in
the higher Mollusca and in  nearly all the Articulata, we meet with distinct
organs of special  sensation, it becomes  evident that the consciousness of the
animal  must be concerned in the direction of its actions; since no impressions
upon these  organs (the  eyes, for example) can exert any motor  influence on
the muscles, except by producing sensations;—that is, if  we may apply to
the lower tribes   the laws deduced from the study of the higher.  Whilst,
therefore, a large  proportion  of the  actions  of the  higher Invertebrata still
continues to  be reflex  (as we  have especially seen in  the Articulata), a new
group is  superadded to these; and  this, consisting of  actions, which are
directly stimulated by  sensations, and in which  no  Reasoning  powers nor
Will  appear to have  any direct participation,  may be  termed consensual.
They require, as their instruments, a set of ganglia to receive the trunks which
originate in the organs of sense, and to issue motor nerves to the several parts
of the  body.   These last are distributed along with  the  trunks, which are
connected with the ganglia belonging to each particular organ; thus the legs
and wings of an Insect  appear to derive  their motor nerves, partly from the
ganglia of the ventral cord, which minister to their reflex actions, and partly
from  the  cephalic ganglia, which seem to harmonize, to control, and even to
antagonize, the influence  of the former.  In like  manner, the  parts of the
body, which are  capable of receiving  sensory impressions, appear to have a
double  connection; one with the ganglia of the ventral cord, for the  purpose
of conveying  thither those impressions  which are destined to  excite reflex
actions; and the other with the cephalic ganglia, in order to originate sensa-
tions.—Of this double system of nerves and ganglia, the one connected solely

  * The view given above  of the comparative structure and offices of the Nervous System,
in the Invertebrated animals, is chiefly abridged from the Author's Prize Thesis on tins
subject;  in which additional details will be found, as well as many other illustrative figures
and references to authorities.  He has there, also, discussed the  physiological explanation
which had been previously  given of the double nervous cord of the Articulata; and having
shown that it is  neither consistent with itself, nor capable  of being applied to  the other
Invertebrata, he has deemed it unnecessary to complicate the present sketch by introducing it. 
264
FUNCTIONS OF THE NERVOUS SYSTEM.
with  the reflex actions, and  the  other with the consensual, the  existence  in
Articulata  seems to  be  clearly  established  by Mr.  Newport's  researches
(§ 326); and although the distinction between the afferent and motor fibres,
of each system respectively,  has  not here been clearly  made out, there can  be
no reasonable doubt of its existence.
   336. The class of consensual actions evidently becomes more predominant,
in proportion as the  special sensory organs  are more  evolved, and  as the
ganglia in immediate connection with them (and altogether forming the cephalic
mass) present  an  increase  in  their  proportionate  development.  This  is
especially the case in the higher  Articulata; in which the Instinctive group of
actions attains  its  highest perfection and  predominance.   The propriety of
referring these to the consensual group, will be obvious  upon a little considera-
tion.   They are as evidently prompted by particular  sensations, as  are the
reflex actions by particular impressions; and the  respondence is as uniform
in the one case, as  in the other.   Although  in these  movements, there is a
most remarkable adaptation of   means to ends, (as in the  construction  of
habitations  by various Insects, and  especially by  the  social  Hymenoptera,)
yet few persons will maintain that this  adaptation is  performed by the reason
of the animal;  since, on this supposition,  every  Bee solves a problem which
has afforded scope  for the laborious inquiries of the „acutest human  mathe-
matician.*  The adaptation is in the  original construction of a nervous system,
which should occasion  particular movements to be  performed  under the in-
fluence of  particular sensations;  and  the constancy  with which  these are
performed by different individuals of the  same  species, when  placed in the
same conditions, leads at once to the belief, that  they must be independent of
any  operations  so variable as those of judgment and  voluntary exertion.
   337. On the other hand,  in the Vertebrata, we shall find the purely reflex
and  consensual movements forming a smaller proportion of their actions, and
brought under a more complete subjection to the Volitional system.   This is
evident, from the greater variety which  the actions exhibit; from the mode in
which they are adapted to peculiar circumstances ; from the degree in which
they may be modified by education; and  from various other indications of a
superior kind of Intelligence.  At last, in  adult Man, we perceive that all the
movements, which  are elsewhere involuntary, but which are not immediately
requisite (as are those of deglutition, respiration, &c.) for the maintenance of

  * The hexagonal form of the cell is the one in which the greatest strength, and the nearest
approach to the cylindrical cavity required for containing the larva, are attained, with the
least  expenditure of material.  But the instinct which directs the Bees in the construction
of the partition that forms the bottom or end of the cell, is of  a nature still more wonderful
than  that which governs its general shape.  The bottom of each cell rests upon three parti-
tions of cells upon the  opposite side of the  comb;  so that it is  rendered much stronger, than
if it merely separated the cavities of two cells opposed to one another. The partition is not
a single plane surface; but is formed by the union of three rhomboidal planes,uniting in the
centre of each cell.  The angles  formed by the sides of these rhombs, were determined by
the measurements of Maraldi to be 109° 28' and 72° 32'; and these have been shown, by
mathematical calculation, to be precisely the angles, at which the  greatest strength and capa-
city can be attained, with the least expenditure of wax.  The solution of the problem was
first attempted by Koenig, a  pupil of the celebrated Bernouilli;  and as his result proved to
differ from the  observed angle by only two minutes of a degree, it was presumed that the
discrepancy was due to an error  of observation, which it was  easy to account  for by the
smallness of  the surfaces whose  inclination had  to be measured.  The question has been
since taken up, however, by  Lord Brougham (Appendix to his Illustrated edition of Paley's
Natural Theology); who has worked it out afresh, and has shown that, when certain small
quantities, neglected by Koenig. are properly  introduced into the calculation, the  result is
exactly accordant with observation,—the Bees being thus proved to be right, and the Mathe-
matician wrong. 
NERVOUS SYSTEM OF VERTEBRATA.
265
 the Organic functions, are placed under the control of the Will, guided by the
 reasoning faculties.  This is especially true of the locomotive organs, whose
 reflex actions are entirely governed by the will; being only distinguishable as
 such, when, from peculiar states  of the  system, the immediate  influence of
 the controlling power is suspended.—We  shall  find ground to  believe, that
 the exercise  of the Reasoning  faculties,  and the  resulting operations of the
 Will, take place through the  instrumentality of another division of the nervous
 centres ;  to which  there is nothing distinctly analogous among  the  Inverte-
 brata ; but which seems to bear a  constant proportion in size and importance,
 among Vertebrated animals, to the development  of the Intelligence and  its
 influence on the movements  of the body :—namely, the Cerebral ganglion.
   338. There is another  aspect,  however, under which we are to consider
 the Nervous System; and this becomes more important in the highest division
 of the Animal kingdom, on  which  we are now about to  dwell.  We have
 hitherto spoken  only of its influence on the contractile properties of the tis-
 sues, to  which  it is distributed.  It has, however,  an  important and direct
 connection with the purely organic functions of Nutrition and Secretion;  and
 we shall see reason to regard it  as the means, not only of placing the animal
 in  relation with  the external world, but  of harmonizing and  controlling the
 organic changes taking place in its own structure, and of bringing these under
 the  influence of particular mental  conditions.  The  opinion is  entertained by
 many, that all the  Organic  Functions  are  dependent upon  the  innervation,
 supplied to them by the system of nerves, which has been termed Sympathetic
 or visceral.  It is incumbent, however, on those who uphold the  necessity of
 this nervous power, to prove it definitively; since all  analogy leads to an
 opposite conclusion.  We may regard the capability of separating a particular
 secretion  from the blood, as a peculiar property inherent in  the glandular cells,
 just as contractility is  the inherent property of  muscular fibre.  But as the
 peculiar  arrangement  of the excitable and contractile tissues  in Animals,
 requires a nervous  system to act as a conductor between them, and to blend
 their actions;  so may the complicated Organic functions of Animals require
 to be harmonized and kept in  sympathy with each other, by some  mode of
 communication  more direct and certain than that  afforded  by the circulating
 system, which is their bond of union in Plants.   We have seen, in the fore-
 going sketch, that the Visceral system does not exist in a distinct form in the
 lower classes of Invertebrated animals; and also  that the nervous system of
 these  classes cannot, as  a whole,  be compared  with it, although it may be
 regarded as containing some rudiments of it.   As the divisions of this system
 become more  evident, however, and the organic functions more complicated,
 some appearance of a separate Sympathetic system presents itself; but this is
 never so distinct as  in Vertebrata.   Hence, it may fairly be inferred that,—as
 the Sympathetic  system is not developed in proportion to the predominant
 activity of the  functions of organic life (which is  so remarkable in the Mol-
 lusca when contracted with the Articulata), but in  proportion to the develop-
 ment of the higher divisions of the nervous system,—its office is  not  to
 contribute  to these  functions  anything essential to their performance; but
 rather to exercise that  general control over them  which becomes the more
 necessary as they become more independent of one another;  and to bring
 them into relation with the system of Animal life.

                    3.  Nervous System of Vertebrata.

  339. When we direct  our  attention to the Nervous System  of the Verte-
brated classes,  we are immediately struck by two remarkable  differences which
its condition presents, from that under which we have seen it to exist in the
     23 
266
FUNCTIONS OF THE NERVOUS SYSTEM,
Invertebrata.   In the latter it has seemed but a mere  appendage to the rest of
the organism,—a mechanism superadded for the purpose of bringing its various
parts into more advantageous relation.   On the other hand, in the Vertebrata
the whole structure appears subservient to  it, and  designed  but to carry its
purposes into  operation.  Again,  in the Invertebrata, we do  not  find any
special adaptation of the organs of support, for the protection  of the Nervous
System.   It is either inclosed, with the other soft parts  of the body, in one
general  hard  tegumentary envelope, as in the Echinodermata  and Articulata;
or it receives a still more  imperfect  protection, as in the Mollusca.  In the
latter, the naked species are  destitute of any means of passive resistance, and
the Nervous System shares the general exposed condition of the whole body ;
and it is not a  little remarkable that, in the  testaceous kinds, the portion of
the body containing the most important nervous centres should be protruded
beyond the shell, whilst the principal  viscera are retained within it.   Now,
in the Vertebrata, we find a special and complex  bony apparatus, adapted in
the most perfect manner for  the protection of the Nervous System ;  and it is,
in fact, the possession of a jointed spinal column, and of its cranial expansion,
which best characterizes the group.
   340. When we look more particularly at the Nervous  Centres  themselves,
we perceive that they combine the general characters of those of the Articulata
with those of  the Mollusca; the locomotive powers  of the former (compara-
tively reduced, however, in  activity) being united with the complex nutritive
system  of the latter; and we  find this combination  manifested,  not only in
the organs themselves, but in  the Nervous System, which stands in so  close
a relation with them.  The Spinal Cord of Vertebrata is evidently the ana-
logue of the ventral columns of Articulata.  It is  a continuous ganglion, con-
taining two portions as distinct as the two tracts in the Articulata;—a fibrous
structure, which  is continuous between the Brain and the spinal  nerves, and
thus resembles the white tract in Insects;—and a ganglionic portion, princi-
pally composed of gray matter.   Into this gray matter, as in  the  ventral gan-
glia of Insects, a part of the roots of the spinal nerves may be traced; whilst
others seem to pass on continuously  to the brain.   At the upper extremity of
the Spinal cord  (commonly termed  the Medulla  Oblongata)  we find the
ganglia  and nerves of special sensation;  and the  organs  which these  supply
are placed in immediate proximity with the entrance to the alimentary canal,
holding the same relation  to it as in the  Mollusca.   But in addition to  these
we find two ganglionic masses in  all Vertebrata, to which we  have no distinct
analogue in the  lower classes—the Cerebral Hemispheres, and the Cerebel-
lum.   With the  development of the former of these, as already remarked,
the perfection  of the reasoning powers appears to hold a close  relation; that
of the latter seems connected  with the necessity which exists, for the adjust-
ment and combination of  the locomotive powers, when the variety of move-
ments  performed  by  the animal is great, and the harmony required among
them  is  more perfect.   Upon these  points, however,  we  shall hereafter
dwell.
   341.  The Visceral system  of nerves now assumes a  more distinct form.
It does not share the protection of the Spinal column; but its ganglia lie for
the most part in the general  cavity of the trunk.  These  ganglia, which
are doubtless  the independent centres of some of the nerve-fibres proceed-
ing from them, are much more numerous than is  commonly supposed.   It
appears  from  recent  researches, that we are to regard  as belonging to the
Visceral or Sympathetic  system, not only the Semilunar and  Cardiac ganglia
(which seem  to  be its principal centres), with the chain of cranial, cervical,
thoracic,  lumbar,  and sacral ganglia, which are  in  nearer proximity to the 
NERVOUS SYSTEM OF VERTEBRATA.
267
Cerebro-spinal system, but also nu-
merous  minute ganglia,  which are
to be found on its branches in vari-
ous parts, and, in addition, the gan-
glia upon the posterior roots of the
Spinal nerves.   If, indeed, we are
to  regard  the  fine  nerve - fibres,
wherever they present themselves,
as belonging  to the  Visceral sys-
tem,  we must  regard this as  still
largely interwoven  with  the  Cere-
bro-spinal  system, notwithstanding
that the  former has its  own set of
ganglionic centres ; since, as already
mentioned  (§  244), these peculiar
fibres   are  found  in  considerable
numbers in all the Cerebro-spinal
nerves, and may be shown to origi-
nate in  the caudate  corpuscles of
the Brain  and  Spinal  Cord.  On
the other  hand, there unquestion-
ably  exist  numerous  fibres in the
Visceral  system,  which   proceed
into it from the Cerebro-spinal sys-
tem ;  these, however, are  not uni-
formly distributed, for some of the
Visceral nerves contain few or none
of them, whilst in  others  they are
numerous.  The branches by which
the Sympathetic system  communi-
cates with  the Cerebro-spinal,  and
which were formerly  considered as
the roots of the  Sympathetic sys-
tem, contain fibres of  both kinds:—
i. e.,  Cerebro-spinal fibres  passing
into  the  Sympathetic,  and  Sym-
pathetic  fibres  passing  into  the
Cerebro - spinal.   The  latter  are
chiefly, if  not  entirely,  transmit-
ted into the anterior branches of
the Spinal  nerves;   the posterior
branches being principally supplied
with fine fibres, from the ganglia on
[Fig. 130.
  A view of the Great Sympathetic Nerve.—1, the plexus on the carotid artery in the carotid foramen ;
2, sixth nerve (motor externus); 3, first branch of the fifth or ophthalmic nerve ; 4. a branch on the sep-
tum narium going to the incisive foramen; 5. the recurrent branch or vidian nerve dividing into the
carotid and petrosal branches; 6, posterior palatine branches; 7, the lingual nerve joined by the corda
tympani; 8, the portio dura of the seventh pair or the  facial nerve; 9, the superior cervical ganglion;
10, the middle cervical ganglion; 11, the inferior cervical ganglion; 12, the roots of the great splanchnic
nerve arising from the dorsal ganglia;  13, the lesser splanchnic nerve; 14, the renal plexus; 15, the solar
plexus; 16, the mesenteric plexus; 17, the lumbar ganglia; 18, the sacral ganglia; 19, the vesical plexus;
20, the rectal plexus;  21, the lumbar plexus (cerebro-spinal); 22, the  rectum; 23, the bladder; 24, the
pubis; 25, the crest of the ileum; 26, the kidney ;  27, the aorta; 28. the diaphragm ; 29, the heart; 30, the
larynx; 31. the sub-maxillary gland; 32, the incisor teeth; 33, nasal septum; 34, globe of the eye; 35,
36, cavity of the*cranium.] 
268
FUNCTIONS OF THE NERVOUS SYSTEM.
               [Fig. 131.                 their posterior roots.  Some of these
                                       last  fibres  also pass, with the ordi-
                                       nary large nerve-tubes,  from  the
                                       Cerebro-spinal into the Sympathetic
                                       system.  By  these communications
                                       the  two systems of  fibres are so
                                       blended with  each other, that it is
                                       impossible  to isolate them;  and all
                                       that can be said is, that the large
                                       tubular fibres predominate  in the
                                       former, and the  fine  homogeneous
                                       fibres in the latter.
                                          342. The  branches  proceeding
                                       from the Semilunar ganglia are dis-
                                       tributed upon the abdominal viscera;
                                       and those  of the Cardiac ganglia
                                       upon the heart and the vessels  pro-
                                       ceeding  from it.  The latter seem
                                       to  accompany  the  arterial  trunks
                                       through  their whole  course, rami-
                                       fying  minutely upon  their  surface;
                                       and it can scarcely be doubted, that
                                       they exercise an  important influ-
                                       ence over  their functions.  What
                                       the  nature  of that influence is, how-
                                       ever,  will  be a subject  for future
                                        inquiry.   It  is  so evidently  con-
                                        nected with the  operations of nutri-
                                        tion,  secretion,  &c, that  the  de-
                                        signation  of "nervous  system of
                                        organic life," as  applied  to this  sys-
                                        tem does  not seem  objectionable,
                                        provided that we do not  understand
it as denoting the dependence of these functions upon it.—Even in  Vertebrata,
however, we do not always find the distribution of the  visceral trunks distinct
from those of the  cerebro-spinal.   In the Cyclostome  Fishes, the  par vagum
supplies the intestinal canal along its whole length,  as  well as the  heart; and
no  appearance of a  distinct sympathetic  can be discovered.   In Serpents,
again, the lower part of the alimentary canal is supplied from the spinal cord,
and the upper part by the par vagum; and  though the  lateral cords of the
sympathetic  may  be traced, they are almost destitute of ganglia.  Even in
the highest Vertebrata, some  of the glands,  of which the secretion is  most
directly influenced by the condition of the mind, are  supplied with most of
their nerves  from  the cerebro-spinal system;  thus, the lachrymal  and sublin-
o-ual glands  receive  large branches from  the fifth  pair,  and the mammary
glands  from the intercostal nerves.  But it appears  probable, from what has
just been stated, that the influence is  conveyed through the visceral fibres,
contained in these nerves, and either originating in the ganglia at  their roots,
or derived from the Sympathetic system.
   343. The Spinal Cord, with its encephalic continuation—the Medulla Ob-
longata,__may be  regarded as constituting the essential part of the nervous
system'of Vertebrata.  Although  the Cerebral Hemispheres in Man bear so
large a  proportion to it in size, that the Spinal Cord seems but  a  mere ap-
pendage to  them,  the case is reversed when we look at the other extremity of
the  scale; the Cerebral Hemispheres, in  many Fishes, being  but ganglionic
 Roots of a dorsal spinal nerve, and its union with
sympathetic:—c, c. Anterior fissure of the spinal cord.
a. Anterior root. p. Posterior root, with its ganglion.
a'. Anterior branch, p'. Posterior branch, s. Sympa-
thetic,  e. Its double junction with the anterior branch
of the spinal nerve by a white and a grey filament.] 
NERVOUS SYSTEM OF VERTEBRATA.
269
protuberances from the Medulla Oblongata.  Moreover, the  fact that animals
are capable of living without the brain, whilst they at once die if deprived of
the spinal cord, sufficiently demonstrates this.   The spinal cord, then, when
viewed in relation to the nervous system of the Invertebrata, may be regarded
as including their respiratory, stomato-gastric, and pedal ganglia.   That these
should be associated together, can scarcely be considered remarkable.   It is
obviously convenient that they should all be inclosed in the bony sheath pro-
vided  for their protection;  and their closer relation favors that sympathy of
action, which  is so  important in  animals of such  complex structure  and
mutually dependent functions, as the higher Vertebrata.  An animal  either
congenitally or experimentally deprived of its cerebral hemispheres, is very
much  in  the condition of one of the Acephalous Mollusca.   It can perform
those  respiratory movements, on which depend the maintenance of its circu-
lation, and  consequently its whole  organic life; it can  swallow food brought
within  its reach, and it can, in some degree, exert its locomotive powers to
obtain it; but it is unconscious of the  direction in which these  can be best
employed, and is  dependent upon the  supplies of food that come within its
grasp.  The Acephalous  Mollusca are so organized, that they find support
from  the particles  brought in by  their respiratory  current;  but the more
highly-organized Vertebrata are  not capable of so existing, and  they must
have their food provided for them by an exertion of the mental powers.  So
long as an anencephalous Vertebrated animal is duly supplied with its requi-
site food, so long may it continue  to exist, although in a state  analogous to
that of profound sleep; and thus it is seen, that the operations of the Brain
are not immediately connected with the maintenance of the organic functions ;
the movements requisite for these being carried on, as  in the lower animals,
through the instrumentality of  ganglionic centres and nerves  specially appro-
priated to them.
   344. It is only in  the Vertebrata, that the difference between the afferent
and efferent fibres of the nerves, has  been satisfactorily determined.   The
merit of this discovery is almost  entirely due to Sir C.  Bell.   He was led to
it by a chain of reasoning  of a  highly philosophical character;  and though
his first experiments  on the Spinal nerves were not satisfactory, he virtually
determined the  respective functions of their two  roots, by experiments and
pathological observations  upon the  cranial nerves, before any other physiolo-
gist came  into the field.*  Subsequently  his general views were  confirmed
by the  very decided  experiments of Muller; but,  until very recently, some
obscurity hung over a portion of  the phenomena.  It was from the first main-
tained  by Magendie,  and has been  subsequently asserted by other physiolo-
gists, that the anterior and  posterior roots of the nerves were both concerned
in the reception of sensations  and in the production  of motions ; for  that,
when the anterior roots were touched,  the animal gave  signs of  pain, at the
same time that convulsive movements were performed; and that, on touching
the posterior roots, not only the sensibility of the animal seemed to be affected,
but muscular motions were excited.   These physiologists were not willing,
therefore, to admit more, than that  the  anterior roots were especially  motor,
and the posterior especially sensory.  But the recently attained knowledge of
the reflex function of the  spinal cord, enables the latter portion of these  phe-
nomena to be easily explained.   The  motions excited by irritating the  pos-
terior root are  entirely dependent upon its connection  with  the spinal cord,
and upon the integrity of the anterior roots and of the trunks  into which they
enter;  whilst they are  not checked  by the separation of the posterior roots
from the peripheral portion of the trunk.   It is evident, therefore, that excita-

          * See British and Foreign Medical Review.  Vol. ix., p. 140, &c.
                                  23* 
270
FUNCTIONS OF THE NERVOUS SYSTEM.
 tion of the posterior root does not act immediately upon the muscles through
 the  trunk of the nerve, which they contribute  to form; but that it excites  a
 motor impulse in the Spinal Cord, which is propagated through the anterior
 roots to the periphery of the system.   The converse phenomenon, the appa-
 rent  sensibility of the anterior roots,  has  been still  more recently explained
 by the  experiments of Dr. Kronenberg;*  which seem to prove, that it is de-
 pendent upon a branch of the posterior root  passing into the anterior  root at
 their point of inosculation, and then directing itself towards the cord (§ 304).
   345. On the other hand, the distinctness of the system of nerves concerned
 in the simply-reflex actions, from those which minister to sensation, emotion,
 and volition by their connection with  the brain, is by no means so obvious as
 in the Invertebrated classes.   When  first pointed out by Dr. Marshall Hall,
 who had  grounded his opinion  more  upon physiological phenomena than
 upon anatomical facts, the statement did not command  general assent; since,
 while the phenomena were admitted, the inferences which he drew from them
 were not  regarded as  necessary results.   When, however, the anatomy of
 the  Nervous centres in Vertebrata was more closely inquired  into (by Mr.
 Grainger,  who had been partly  anticipated  by Bellingeri), it was found to
 present certain  phenomena which might be  regarded as supporting Dr.  M.
 Hall's views; and when the inquiry was extended to the Invertebrated classes,
 the confirmation  was found to  be  still  more decisive.  In our previous  sketch
 these doctrines have been treated as established; since they have been found
 not only to correspond with the facts  disclosed by anatomical research, but to
 be required by them.  We shall now  apply them to  the nervous apparatus of
 the Vertebrata.
                       346.  The Spinal Cord consists of two lateral halves;
                    these are partially separated, in the  higher classes, by
                    the superficial  anterior  and posterior fissures ; and in
                    Fishes by an internal canal, which is continuous with  the
                    fourth ventricle.t   This canal is evidently the indication
                    of that complete  separation of  the two columns,  which
                    exists in the  lower Articulata;  and the fourth  ventricle,
                    which in  many Fishes remains unclosed (the cerebellum
                    not being sufficiently developed to overlap it),  corre-
                    sponds with  the  passage between the cords uniting  the
                    cephalic  ganglia, with the first  sub-"cesophageal, through
                    which  the oesophagus passes   in  all  the   Invertebrata.
                    The two  lateral halves have little  connection with each
                    other in Fishes, and the  pyramidal bodies at their apex
                    scarcely decussate ; but in ascending towards the  higher
                    classes, the communication between the two sides is more
                    intimate,  and a larger proportion of the pyramidal  fibres,
                    crosses to the opposite side.  In all the Vertebrata,  the
                    true Spinal Cord  contains grey  substance, or something
                    equivalent to  it;  thus possessing the character  of  a con-
                    tinuous ganglion.   The proportion of the vertebral column
                    which this ganglionic  portion occupies, is, however,  ex-
                    tremely variable ;  depending principally on  the position
                    of the chief  organs of locomotion.   Thus, in  the Eel,
beiium, so small m not to and other Vermiform Fishes,  it is continued through
cavit^leftV'ne'dive"- the wh°le SPinal  Canal * .whils* ™  the  Lophius and
gence of  the columns of Tetraodon, whose body is less  prolonged, and more
the Spinal Cord.        dependent for its  movements upon the anterior extremi-

  *  Miiller's Archiv., 1839, Heft v.; and Brit, and For. Med. Rev., vol. ix. p. 547.
  f  This canal may be traced in the Spinal Cord of Man and other Mammalia; but it is
nearly obliterated.
Fig. 132.
-u
 Nervous  centres  in
Frog; a, olfactive ganglia;
b, cerebral hemispheres;
c, optic ganglia; d, cere- 
SPINAL CORD OF VERTEBRATA.                    271
ties, the true Spinal  Cord  scarcely passes out of the cranium.   The quan-
tity  of  grey matter  is  nearly  uniform in  every part of  the cord, where
there is  no  great diversity in  the functions  of  the  nerves which originate
from each portion.   In most  Fishes,  for example, the body is propelled
through  the  water more by the lateral  action of the flattened trunk  (whose
surface  is  extended by  the dorsal and  caudal fins   erected upon prolonga-
tions of  its vertebra?), than  by the movements of its extremities,  which serve
principally to guide  it.   Hence we usually find the amount of  grey  mat-
ter varying but little  in  different parts of the  cord.   But in the Flying-fish,
and  others whose pectoral fins are  unusually powerful, a distinct  ganglionic
enlargement  of the cord takes place where the nerves are given off.   In Ser-
pents, again, the  spinal  cord is nearly uniform  throughout its entire  length;
whilst in Amphibia it is so  during the Tadpole condition, but presents enlarge-
ments corresponding  to the anterior and posterior extremities, when these are
developed; at the same time becoming much shortened, as the tail is less im-
portant to  locomotion, or is altogether  atrophied.  In  Birds, the  ganglionic
enlargements  are generally very  perceptible ; and bear  a  close relation in
size, with  the development of the locomotive organs  with which they are
connected.   Thus, in birds of active flight, and short powerless legs, the an-
terior enlargement is  the principal; but  in those which  are  more adapted to
run  on hand than to wing their way through the  air, such as  the  whole tribe
of Struthious birds, the  size of the posterior enlargement is very remarkable.
Hence we have a right to infer, that the increase  in the quantity of grey mat-
ter in the cord has some connection with the amount of power to be supplied ;
and  this  exactly  corresponds with  what has been observed in the Articulated
classes, and especially in watching the metamorphosis of Insects.   In Birds
and  Mammalia, however, the whole amount of the grey matter in the spinal
cord does not bear so large a proportion to the bulk of the nerves proceeding
from it, as in the lower Vertebrata; and  the  reason  of  this seems obvious.
The actions  of the locomotive
organs are less and less of a
reflex character,  and are more
directly  excited  by  the  will,
and consequently by the brain
than in  the inferior tribes; and
just in  proportion,  therefore,
to  the   development of  the
Brain, will it become  the cen-
tre of all the actions performed
by the animal, and the Spinal
Cord a mere appendage  to  it.
Still, in all the Mammalia, even
in Man, do we find these gan-
glionic  enlargements of  the
spinal cord;  and in Man it is
the posterior one (or rather the
inferior),  which  contains the
largest  quantity  of grey mat-
ter.   In the  cord of this class,
too, the lateral halves are much
more intimately united, than in
the classes below; for not  only is  the central canal for the  most part absent,
but the  two crescent-shaped plates of grey matter are united by  a transverse
lamella, which connects their centres like  a commissure.
   347.  TJhe Cord is transversed, not  only by the anterior and posterior fis-
Fig. 133.
 Transverse  sections of human Spinal Cord at different
points, showing the proportional quantity and arrangement
of grey and white matter at each: 1, opposite 11th dorsal ver-
tebra; 2, opposite 10th dorsal; 3, opposite 8th dorsal; 4, op-
posite 5th dorsal; 5, opposite 7th cervical; 6, opposite 4th
cervical; 7, opposite 3d cervical; 8, section of medulla ob-
longata through centre of corpus olivare. 
272
FUNCTIONS OF THE NERVOUS SYSTEM.
sures, but by two furrows on each side, marking out three  columns upon  it.
We have, therefore, on each  half of the cord, an anterior  middle or lateral
and posterior column.   The  points of the crescentic lamellae of grey matter
approach  these furrows pretty  closely ;  but  elsewhere the  grey matter  is
covered deeply by the fibrous columns.   Each spinal nerve arises from two
sets of  roots.   The anterior roots join  the spinal cord, near the  anterior fur-
row ; and the posterior, near the posterior furrow.  Respecting their intimate
connection with the principal divisions of the  cord,  a considerable diversity
has existed among  the  statements  of anatomists ;  but it seems  to be now
generally admitted, that, as in the Articulata, a part of each  root enters the

             [Fig. 134.                                   Fig. 135.
I    i   a
   Transverse section of human spinal cord, close to
 the third and fourth cervical nerves ; magnified ten
 diameters, (from Stilling;)—f. Posterior columns,  ii.
 Gelatinous substance  of the posterior horn.  k. Pos-
 terior root. I. Supposed anterior roots,  a. Anterior
 fissure, c. Posterior fissure.  6. Grey commissure, in
 which a canal is contained, which, according to these
 writers, extends through the length of the cord.  g.
 Anterior horn of grey matter containing caudate vesi-
 cles, e. Antero-lateral column (from k to o)].

grey matter or ganglionic  portion  of the cord, whilst a  part  is  continuous
with its white or fibrous columns.—The course of the fibres which enter the
grey matter, has been lately displayed, in part, at least, by the  researches of
Dr. Stilling.*   It appears that  of the fibres of the posterior roots, some form
loops in the grey matter, and  become continuous with those of the anterior
roots of the same  side, as seen at a, fig. 135.   Others cross the grey matter,
and become continuous  with those of the anterior roots  of the opposite side,
as seen at b.   It can scarcely  be doubted that these fibres, being unconnected,
with the brain, constitute the system to which reflex actions are due.  Although
Dr. Stilling's inquiries  have not proved thefact,t yet it may be inferred from
physiological phenomena, as well  as from the facts recently shown by Mr.
Newport (§ 326), that there are  other fibres, which pass  from the  posterior

  * Ueber die Textur und Function der Medulla Oblongata.
  t It may be thought that the mode of examination which he adopted,—that  of making
very thin transverse sections of the Spinal Cord,—is not well fitted to display the connections
of the roots with bngitudinal fibres.  The subsequent observations of Budge (Muller's  Ar-
chiv. 1844, p. 160), seem to have established the fact of the continuity of a portion of each
root with the longitudinal fibres of  the cord.
  Passage of Nerve-fibres through the
Spinal Cord, according to Stilling; a,
posterior fibres continuous with the
anterior of the same side, through the
nucleus of the cord ; b, posterior fibres
continuous  with the anterior of the
opposite side. 
SPINAL CORD OF VERTEBRATA.
273
 roots into the anterior roots of other nerves above  and below, both  on the
 same side  and on the  opposite.—Of the portions of the roots which are con-
 tinuous with the fibrous columns, the anterior would seem to have a connec-
 tion with both the anterior and lateral columns ; and the posterior cannot be
 said to be  restricted  to the lateral column, some of their fibres entering the
 posterior division of  the cord.
   348. If the white or fibrous portion of the Spinal Cord be really continu-
 ous with the  medullary matter  of the Brain, the roots of the nerves which
 enter it are in reality thus  brought into  connection with  the  Cerebral  Hemi-
 spheres and Cerebellum ;  and the posterior division of these may, therefore,
 be regarded as conducting  to  the  Sensorium those impressions, which* there
 become sensations ; whilst the anterior roots  convey the motive influence,
 which has been propagated, by a voluntary or  emotional impulse, down the
 tract of the  Spinal Cord with which they are continuous.  On the  other hand,
 the passage of one portion of each  set of roots through the grey matter of
 the Cord, completes the nervous circle required for the performance of reflex
 actions ; and by this  they  would seem to take place in  Vertebrated animals,
 just as through the distinct system  of excito-motor fibres  in the Articulata
 (§ 328.)  The fibres  which pass continuously from  the posterior to the ante-
 rior roots of the nerves on the same  side, probably constitute the  channel of
 those reflex actions, which can be excited in apart supplied by any compound
 nerve, by stimulating its afferent fibres, and thus causing a  motor impulse to
 be transmitted from the Spinal Cord along its  afferent portion.   The fibres
 which cross to the opposite side, will produce similar movements in its cor-
 responding parts.  And the fibres, if such  there be, that pass from the pos-
 terior  (afferent) roots  of each nerve, into the anterior (motor) roots of distant
 nerves, would convey to a  great variety of muscles, the influence of a stimulus
 applied to  a single afferent nerve.   It follows, then, on this view qf the  cha-
 racter of the Spinal Cord,  that the continuity of the fibrous  tracts is all that
 is required, to convey the  influence of the brain to  the parts below ;  whilst
 the completeness of the nervous circle is all that is necessary, for the perform-
 ance of reflex actions  excited through it.  This is found to  be  strictly true ;
 the former having been observed  in cases  of disease, and the latter having
 been proved by experiment.   As far as simple  reflex actions are concerned,
 there is as  much segmental independence in Vertebrata, as in the Articulata ;
 but these actions seldom have so completely the character of adaptation, and
 are of a more  irregular and convulsive  nature.  Still, however, there  is an
 essential correspondence between them;  and we may, therefore,  regard  the
 distinction  between the reflex and voluntary movements as the same in each
 group ;  the former predominating in Articulata ; the  latter in  Vertebrata.  On
 this view, then,  each spinal nerve contains at least four sets of fibres.
   i. A  sensory  bundle passing upwards to the Brain.
   n. A motor  set, conveying the influence of volition  and  emotion down-
 wards from the  Brain.
   in. A set of excitor  or  centripetal fibres, terminating  in  the true Spinal
 Cord or ganglion,  and  conveying impressions to it.
   iv. A motor or centifrugal set, arising from  the  same  Ganglionic centre,
 and conveying the motor impulse reflected/rom it to the muscles.
   Of these, the first and third are united in the posterior or afferent roots;
 the second and fourth in the anterior or efferent roots.
   349.  It is difficult to trace the course of the fibres  within the Spinal Cord;
but it is now proved, that Sir C. Bell was not altogether correct in his  idea,
that the functions of the columns of the Cord are respectively similar to those
of the roots connected with them.   Cases, indeed, are of no unfrequent  oc-
currence, in which a portion of one of the columns has been almost entirely 
274                 FUNCTIONS OF THE NERVOUS SYSTEM.
destroyed by injury or disease, without any corresponding loss of the func-
tion attributed to it.*  Such cases have kept alive, in the minds of many emi-
nent practical men, a considerable distrust of the accuracy of Sir C.  Bell's
conclusions.   We have seen that, in regard to the roots of the  nerves, his
first  statements  have been confirmed, and rendered  more precise, by subse-
quent researches; but it is not so in regard to the functions of the anterior
and  posterior divisions of the Spinal Cord.—Bellingeri was led, by experi-
ments  on the spinal cord, to the conclusion, that the anterior roots  of the
nerves were for  the flexion of the various articulations, and  the  posterior for
their extension.   He also was wrong, in extending an inference, founded on
experiments on  the Cord, to the roots of the nerves.—The recent experiments
of Valentin, whilst they fully confirm Sir C. Bell's determination of the func-
tions of the roots of the nerves, coincide, to no small degree, with Bellingeri's
opinion, in regard to  the offices of the anterior and posterior divisions of the
Cord.   He obtained  reason to believe that,  in  the Frog, neither  the superior
nor inferior strand of the cord (posterior and anterior columns in Man) solely
possesses motor functions ; but he found that, when the former were irritated,
sensations predominated; and when the latter, motions were chiefly excited.
He further states that, if the superior  strand  (posterior  column) be irritated
at the point at which the  nerves of either  extremity are  given  off, that ex-
tremity is extended; and  that if  the inferior strand (anterior column) be irri-
tated, the extremity is flexed.  At their entrance  into the spinal cord, there-
fore, it would appear that the motor fibres of the extensors pass towards the
superior stratum (posterior column in  Man), whilst those of the  flexors are
continuous with the inferior stratum  (inferior  column);  their course  being
more altered, however, when they are examined far from the point of issue.
This doctrine was confirmed by  experiments on Mammalia;  and is borne out
(according to Valentin) by pathological phenomena observed in Man. Accord-
ing to this eminent physiologist,  also, relaxation of the sphincters is analogous
to the extended  state of the extremities ; and he has noticed a manifest relaxa-
tion of  the sphincter ani  in the  frog, when the superior part of the spinal
cord was irritated, so as to produce extension  of the limbs.   These  state-
ments are entitled  to considerable  weight, on account  of the  quarter from
which they come ; but they are  not, perhaps, to be  received altogether with-
out hesitation, until confirmed by  other physiologists, especially whilst the
phenomena of reflex action are  still  so imperfectly  known.  For it is quite
possible that, whilst  stimulation of the anterior part of the  cord  may excite
direct motions of flexion, in preference to those of extension, the  movements
of extension produced by stimulating the posterior column may be of a reflex
character.
   350.  There is no reason to believe, that  the functions  of  the Spinal Cord
are essentially different along its whole  length.  Everywhere it  appears to
consist  of a ganglionic centre, supplying nerves  to its particular segment;
and of connecting fibres, by which  the nerves proceeding from any one divi-
sion are brought into relation  with distant portions of the  organ, and with the
large  ganglionic  masses at its anterior extremity.   In this  respect, then, it
corresponds precisely with the  double nervous cord of the Articulata; the
only prominent  difference between the two being, that in  the former the gan-
glionic  matter is continuous from  one extremity of the organ  to the other;
whilst in the latter it is  interrupted  at intervals; and in the Mollusca, the
centres are still  further separated from  each  other.   The connection of the

  * See especially a case recorded by Dr. Webster (Medico-Chirurgical Transactions, vol.
xxvi.), in which there was complete destruction of the posterior columns in the lower part
of the cervical region; which was not attended with loss of sensibility in the parts below,
but, on the contrary, with loss of power of voluntary motion. 
SPINAL CORD OF VERTEBRATA.
275
Spinal  Cord with the large ganglia
contained within  the cavity of the
cranium,  is  effected  by  means of
processes from its  superior extre-
mity, the arrangement of which is
somewhat complex.  This portion
of the cord,  which  also lies within
the cavity of the cranium, has been
termed  the  Medulla  Oblongata.
It has  been  supposed to  be the
peculiar seat of  vitality ;  but the
only real  foundation  of this idea
is,  that it is  the great centre of the
Respiratory actions,  on  the  conti-
nuance  of  which  all   the   other
functions  are  dependent.   The
Brain may be removed from above,
and nearly the whole Spinal  Cord
from below, without  an immediate
check  being put  upon all the phe-
nomena of  life.   In this Medulla
Oblongata,ybwr different parts may
be  distinguished  on each side:—i,
The Anterior Pyramids,  or  Cor-
pora Pyramidalia;   2,  The Oli-
vary Bodies, or  Corpora Oliva-
ria; 3,  The Restiform  bodies, or
 Corpora Restiformia;  otherwise
called  Processus  a  Cerebello ad
Medullam  Oblongatam;  4, The
               [Fig. 137.
[Fig. 136.
  A posterior superior view of the Pons Varolii, the
Cerebellum, and the Medulla Oblongata and Spinalis.
1,1, the crura cerebri; 2, the  pons varolii or tuber-
annularis; 3, its middle fossa; 4, an oblique  band of
medullary matter seen passing from its side; 5, the
external surface of the crus cerebelli in its  natural
state ; 6, the same portion deprived of outer layer; 7,
the nervous matter which united it to 4;  8, the trige-
minus or fifth pair of nerves; 9, portion of the audi-
tory nerve—the white neurine is seen passing from
the oblique band which comes from the corpus resti-
forme to the trigeminus nerve in front, and the auditory
nerve behind ; 10, 11, the superior portion of the hemi-
spheres of the cerebellum; 12, lobulus amygdaloides ;
13, corpus olivare; 14, corpus pyramidale ; 15,  medulla
spinalis.]
[Fig. 138.
  Front view of the medulla oblon-
gata :—p, p. Pyramidal bodies, de-
cussating at d. o,o. Olivary bodies.
r,r. Restiform bodies,  a, a. Arci-
form fibres, v. Lower fibres of the
Pons Varolii]
  Posterior view of the medulla oblongata :—pp. Posterior
pyramids, separated by the posterior fissure,  rr. Restiform
bodies, composed of cc, posterior columns, and dd, lateral
part of the antero-laleral columns of the cord. aa. Olivary
columns, as seen on the floor of the fourth ventricle, sepa-
rated by s, the median fissure, and crossed by some fibres
of origin of nn, the seventh pair of nerves.] 
276                   FUNCTIONS OF THE NERVOUS SYSTEM.

Posterior Pyramids, or  Corpora Pyramidalia Posteriora.  The connections
of these  with the  Brain  above, and with the Spinal  Cord  below, will be now
traced.*

                                        [Fig. 139.
  Transverse section of the medulla oblongata through the lower third of the olivary bodies. (From Stil-
ling.)  Magnified 4 diameters.
  a. Anterior fissure,  b. Fissure of the calamus scriptorius.  c. Raphe\  d. Anterior columns,  e. La-
teral columns, f. Posterior columns,  g. Nucleus of the hypoglossal nerve, containing large vesicles.
ft. Nucleus of the vagus nerve,  i, i. Gelatinous substance, k, k. Roots of the vagus nerve. I. Roots of
Ihe hypoglossal, or ninth nerve, m. A thick bundle of white longitudinal fibres connected with the root
of the vagus,  n. Soft column  (Zartstrang, Stilling),  o. Wedge-like column (Keelstrang, Stilling),  p.
Transverse and arciform fibres,  q. Nucleus of the olivary bodies, r. The large nucleus of the pyramid.
s,s,s.  The small nuclei of the pyramid,  u. A mass of grey  substance near the nucleus of the olives
(Oliven-Nebenkern). u, q, r, are traversed by numerous fibres passing in a transverse semicircular direc-
tion, v, w. Arciform fibres, x.  Grey fibres.]

   351.  As our  object, however, is  rather  Physiological  than purely  Anato-
mical, we  shall commence with  a description of the motor and sensory tracts,
which may, according to Sir C.  Bell,t  be  very distinctly separated in the Pons

  * Great diversities will be found in the accounts given of those  connections by different
Authors; some of which are attributable to a variation in the use of terms, which must not
pass unnoticed.  By the majority of Anatomists, the name of Corpora Restiformia, is given to
the Cerebellar Columns; and its designation, therefore, it  seems advisable to retain.  Some,
however, and amongst them Dr. J. Reid, in  his  late very excellent  description of the Ana-
tomy  of the  Medulla Oblongata (Edinb. Med. &  Surg. Journal, Jan.  1841), give the name to
the columns that pass up from the posterior  division of the spinal cord  into the crus cerebri,
—which are here called  (after Sir C. Bell)  the posterior pyramids;  and apply the terms
Posterior Pyramids to the Cerebellar column.   The truth is that, as Sir C. Bell has justly
observed, all the tracts of fibrous matter connecting the Brain with the Spinal  Cord, have a
somewhat pyramidal form ; and it  might be added'that all have something of  a restiform or
cord-like-aspect.
  t Philosophical Transactions, 1835. 
            STRUCTURE AND CONNECTIONS OF MEDULLA OBLONGATA.        277

Varolii.   The Pons has been correctly designated as  the great Commissure
of the Cerebellum, inclosing the Crura Cerebri;  and its transverse fibres  not
only  surround the longitudinal  bands which connect the Cerebrum with  the
Spinal  Cord, but pass through them ;  so  as in  some degreee to isolate  the

                                     Fig. 140.
  Course of the Motor tract, according to Sir C. Bell, a, a, fibres of the hemispheres, converging to form
the anterior portion of the crus cerebri; b, the same tract where passing the crus cerebri;  c, the right
pyramidal body, a little above the point of decussation ; d, the remaining part of the pons Varolii, a por-
tion having been dissected  off to expose b.—I, olfactory nerve, in outline; 2, union  of optic nerves;
3. motor oculi; 4, 4, patheticus ; 5, 5, trigeminus; 6, 6, its muscular division; 7,7, its sensory root; ?, ori-
gin of sensory root from the posterior part of the medulla oblongata; 9, abducens oculi; 10, auditory
nerve ; 11, facial nerve; 12, eighth pair; 13, hypoglossal; 14, spinal nerves ; 15, spinal accessory of right
side, separated from par vagum and glosso-pharyngeal.

two lateral halves from one  another, and to form a^complete septum between
the anterior and posterior portions  of  each.   The Motor tract is brought  into
view, by simply raising the superficial layer of the Pons, and tracing upwards
and  downwards the longitudinal fibres which then present themselves.  It is
     24 
278
FUNCTIONS OF THE NERVOUS SYSTEM.
then found, that these fibres may be traced upwards, chiefly into the Corpora
Striata, whence they radiate to the Hemispheres ; and downwards, chiefly into
the Anterior Pyramids.  From  this tract arise all the  Motor nerves usually
reckoned  as  Cranial;  as will  be seen  in the accompanying Figure.—The
Sensory tract is displayed, by opening the Medulla Oblongata on its posterior
aspect; and then separating and  turning aside the Restiform Columns, so as
to bring into view the Posterior Pyramids, which lie on the outside  of the ca-
lamus scriptorius.  On tracing their fibres upwards, it is found that  they form
a part of the posterior layer of the Crura Cerebri, ultimately passing on to the
Thalami optici, whence  they radiate to the Hemispheres.  From  this tract,
no motor nerves arise;  but on  tracing it downwards into the Spinal Cord, it
is found that  the sensory root of the fifth pair terminates in it, and that the

                                 Fig. 141.
 Course of the Sensory tract according to Sir C. Bell.  a. Pons Varolii; b, b, sensory tract separated ;
c, union and decussation of posterior columns ; d, d, posterior roots of spinal nerves; e, sensory roots of
fifth pair.

posterior roots of the spinal nerves are evidently connected with its continua-
tion.   Also forming part of the posterior  division of  the crus cerebri, and se-
parated from the anterior by the transverse septum, is a layer of fibres which
ascends  from the Olivary bodies, some  of which  terminate  in  the  Corpora
Quadrigemina.
   352.  On tracing upwards the four divisions  of the Medulla Oblongata, the
following are found to be their chief connections with the  Brain.— 1.  The
fibres of the  Anterior Pyramids  for the most  part enter the Crura Cerebri,
passing  through the Pons  Varolii, and traversing the Optic  Thalami (which,
it  must be carefully borne  in  mind, have scarcely any real  connection  with
the Optic Nerves'; or with  the sense of sight); after which  they diverge and
become intermingled with grey matter, thus forming  the Corpora Striata, and
finally radiate to the convolutions of  the Cerebrum.—2.  The  fibres of the
Olivary body also pass into the Pons Varolii, and there divide into two bands ; 
           STRUCTURE AND CONNECTIONS OF MEDULLA OBLONGATA.        279

of which one proceeds upwards  and  forwards to join  the Crus  Cerebri,
thence to pass to the Optic Thalami;  whilst the other passes  upwards and
backwards into the Corpora Quadrigemina.—3.  Of the true Restiform bodies,
the fibres  pass entirely into  the Cerebellum.—4.  Finally,  of  the  Posterior
Pyramids, the fibres pass directly onwards through  the  Crura Cerebri into
the Thalami,  whence  they radiate to the convolutions.
   353.  The downward course of these fibres  into the Spinal Cord now re-
mains to be traced;  and their arrangement is by no means a simple one.— 1.
The Anterior Pyramids decussate, as is well known, at their lower extremity;

                                 [Fig. 142.
  Analytical diagram of the encephalon—in a vertical section.  (After Mayo.)
  s. Spinal cord. r. Restiform bodies passing to, c the cerebellum,  d. Corpus dentatum of the cerebel-
lum,  o. Olivary body.  /. Columns continuous with the olivary bodies and central part of the medulla
oblongata, and ascending to the tubercular quadrigemina and optic thalami. p. Anterior pyramids,  v.
Pons  Varolii, n, b. Tubercular quadrigemina. g. Geniculate tody of the optic thalamus,  t. Pro-
cessus cerebelli ad testes, a. Anterior lobe of the brain,  q. Posterior lohe of the brain.]
the principal part (but not the whole) of the fibres on each side, passing over
to the other.   The decussating fibres pass  backwards as well as downwards,
and enter, not  the anterior column of the spinal cord, (as commonly stated,)
but the  lateral column.   The smaller bundle of fibres, which do not decus-
sate, passes downwards, along with  those of the olivary bodies, to form the
anterior column.—2. The fibres descending from the Olivary bodies converge 
280
FUNCTIONS OF THE NERVOUS SYSTEM.
as those of the pyramids pass backwards from between them, until they meet
on the median line, forming the greater part of the anterior column.—3. The
fibres of the  Restiform, or Cerebellar columns,—which, like those of the
Olivary columns, do not decussate, mostly pass downwards into the posterior
columns ; but a band (which  has  been termed, from its  curved  aspect, the
arciform  layer) passes  forwards into the anterior columns; and  another
small fasciculus enters the lateral columns.—4. The  fibres  of the Posterior
Pyramids are stated by Sir C. Bell to decussate like those of the anterior;
they pass down chiefly into the posterior part of the lateral column, forming
part also of the posterior.
  354.  The following  tabular view may assist, better than  any delineations
could do, in the comprehension  of this very intricate piece of Anatomy; the
knowledge of which can be readily applied to the explanation of many curious
pathological phenomena, and  cannot but assist in the elucidation of others,
whose rationale is as yet obscure.
  SPINAL COE.D.             MEDULLA OBLONGATA.             BRAIX.
              C Arciform fibres of Cerebellar Columns  .    . ) Cerebellum
Anterior Column 1 Olivary Columns......5 Corpora Quadrigemina
Middle Column

Posterior Column
Non-decussating portion of Ant. Pyramids    . > c    a g^
Decussating portion of Ant. Pyramids  .     . )   r
Post. Pyramidal Columns (decussating?)     . ) rp, .   • o t' '
Portion of Post. Pyramids (non-decussating ?)  . )
Restiform Columns                        Cerebellum
  355.  The Medulla Oblongata is not to be viewed, however, solely as a series
of connecting bands  or commissures, between the Brain and Spinal Cord ; for
it contains vesicular  matter of its own, in  virtue of which it serves as  a gan-
glionic  centre to nerves that are specially connected with it.  The vesicular
matter is partly found in a situation corresponding to that which it occupies
in the spinal cord ;  and it  forms  a tract, which  is continuous above with the
grey nucleus of the Corpora  Quadrigemina, and below with that of the  Spinal
Cord ; and which is opened  out to view (as it were) on the floor of the  fourth
ventricle, forming the calamus  scriptorius.  Besides  this central  portion,
there are other  outlying masses, which are continuous  with  it.   Thus the
bulk of the  Olivary  body is principally due to the presence of a  ganglionic
mass in its interior;  inclosed in  the  fibres of which the olivary column  is
composed, and which, for the most part, pass over and around it without en-
tering it.  This mass consists of a layer of grey matter, spread in a thin pli-
cated stratum over a centre of white substance, and altogether forming what
is known as the corpus dentatum.  There is a considerable  amount  of ve-
sicular substance in the  Restiform bodies also;  and this  is continuous with
the grey matter forming the posterior cornua in the Spinal Cord.
  356. We have now to inquire* into the character of the ganglionic masses,
which form, with the Medulla Oblongata, the Encephalon of Vertebrated ani-
mals.   We should be liable  to form a very erroneous conception of the rela-
tive importance, and  of the  real  nature, of these, if we were  to  study them
only in the  Brain of Man  and of the higher animals; for the  great  develop-
ment of their Cerebrum and Cerebellum throws into the shade (so to  speak)
certain other ganglionic centres, which constitute yet more  essential parts  of
the nervous apparatus.   It is one of the most  interesting results of the com-
parison of the Human Brain with that of the lower tribes of Vertebrata, that
the great change in the relative proportions of the parts, which we encounter
in the latter, makes  evident  the  real  nature and importance of what  would
otherwise have been considered  as subordinate appendages: whilst,  at the
same  time, they afford  us  the connecting links,  by which we are enabled
to trace the real analogies  of the  different  parts of the  Encephalon with the
ganglionic masses which represent it among Invertebrated animals. 
                          ENCEPHALON OF FISHES.                       281

   357. Commencing with Fishes, we find a series  of four distinct ganglionic
masses, arranged in a line which is nearly continuous, from behind forwards,
with that of the  Spinal Cord; of these, the posterior  is  usually single, and
on the median plane, whilst the others are in pairs.  The posterior, from its
position  and connections, is  evidently to be regarded in the light of a Cere-
bellum ;  and it bears a much larger proportion to the rest, in this class, than
in any other.  The pair in front of this are not the hemispheres of the  Ce-
rebrum,  as  their large size in some instances (the  Cod  for  instance) might
lead us to suppose; but they are immediately connected with the Optic nerve,
which, in fact, terminates in  them,  and are therefore to be considered (like the
chief part of the cephalic masses of Invertebrated animals) as Optic Ganglia.
In front of  these are the Cerebral  Hemispheres, which are small, generally
destitute  of convolutions, and  possess  no ventricle in their interior,—except
in the  Sharks and Rays, in which  they  are much more highly developed than
in the  Osseous Fishes.  Anterior  to these is another pair of ganglionic en-
largements, from which the Olfactory nerves arise : and these are,  therefore,
correctly designated as the Olfactive tubercles or ganglia.   In some  instances,
these ganglia are not immediately seated upon the prolonged spinal cord, but
are connected with it by long peduncles ;  this is the case in the Sharks;  and
we are thus led to perceive the real nature of the portion of the trunk  of the
Olfactory nerve in  Man, which  lies within the cranium, and of its bulbous
expansion on the Ethmoid bone.   Besides these principal  ganglionic enlarge-
ments, there are often smaller ones, with which  other nerves are connected.
Thus,  in the Shark,  we find a pair of tubercles of considerable size, at the
origin of  the Trifacial nerves ;  and another pair, in most Fishes, at the roots
of the  Vagi.  In some instances, too, distinct Auditory ganglia present them-
selves ; as in the Carp.
                             Fig. 143.
Pike.               Cod.                        Fox-shark.
 Brains of Fishes, a, olfactive lobes or ganglia; b, cerebral hemispheres;  c, optic lobes ; d, cerebel-
lum j ol, olfactory nerve ; op, optic nerve ; pa, patheticus; mo, motor oculi; ab, abducens;  tri, trifacial;
fa, facial; vag, vagus ; «, tubercles or ganglia of the trifacial; tc, tubercles of the vagus.
  358.  The Optic Lobes of Fishes have no analogy whatever with the  Tha-
lami optici of Mammalia ; the connection of which, with the Optic nerves, is
                                   24* 
282                 FUNCTIONS OF THE NERVOUS SYSTEM.
very slight.  They are rather to be compared with  the  Tubercula Quadri-
gemina, which are the real ganglia of the Optic nerve.   Their analogy is not
so complete, however, to these bodies in the fully formed Brain of Man, as
it is to certain parts which occupy their place at an earlier period. The Third
 Ventricle, which is quite distinct from the Corpora Quadrigemina, is hollowed
out, as it were, from the floor of the Optic Lobes of Fishes; and the Anterior
Commissure bounds its front; hence these  must be considered as  analogous
to the parts surrounding the Third Ventricle, as well as to the Corpora Quad-
rigemina.  This is made evident by the fact, observed by  Muller, that, in the
Lamprey, there is  a distinct Lobe of the third ventricle, replacing  the Optic
Lobes of other  Fishes, and partly giving origin to the optic nerves;  and a
separate vesicle, analogous to the Corpora Quadrigemina.  With this condition,
the early state of the Brain in the embryo of the Bird and Mammiferous ani-
mal, and even in Man himself, bears a very  close correspondence.   The En-
cephalon consists at this time of a series of vesicles, arranged in a line with
                                  each other, of which those that represent
                                  the Cerebrum are  the smallest, whilst that
                                  which represents  the   Cerebellum is the
                                  largest. The latter, as  in Fishes, is single,
                                  covering the fourth ventricle on  the dorsal
                                  surface of  the Medulla Oblongata.   Ante-
                                  rior  to  this,  is  the  single vesicle  of the
                                  Corpora Quadrigemina, from  which the
                                  Optic nerve chiefly arises; this has in its
                                  interior a cavity, the ventricle of Sylvius,
                                  which exists even in the adult Bird, where
                                  the Corpora Quadrigemina are pushed, as
                                  it were,  from each other by the  increased
                                  development of the Cerebral hemispheres.
                                  In front  of this is the vesicle of the Third
                                  Ventricle,  which contains also the  Thala-
                                  mi; as  development  proceeds, this, like
                                  the preceding, is covered  by the enlarged
                                  hemispheres ;  whilst  its roof becomes
                                  cleft  anteriorly on the median  line, so as
                                  to form  the anterior entrance to  the cavity.
                                   Still more anteriorly is the double  vesicle,
                                   which  represents the hemispheres of the
 Cerebrum  ; this has a cavity on each side, the floor of which is formed by the
 corpora striata.   The cavity  of  the cerebral vesicles  has  at first no opening,
 except into that of the third ventricle;  at a later period is  formed  that fissure
 on the inferior  and  posterior side, which (under the name of the fissure of
 Sylvius)enables  the membranes enveloping the brain to  be reflected into the
 lateral ventricles.
   359. Thus it will  be seen that the  real analogy between the brain of the
 Human fcetus, and that of the adult Fish, is not so close  as, from  the resem-
 blance in their external form, might have been supposed.  In the small pro-
 portion which the Cerebral Hemispheres bear to the  other parts, there is evi-
 dently a very close  correspondence ; and this  extends also to the  general
 simplicity  of their structure, the  absence of convolutions, and the deficiency of
 commissures.   But there is  a  much nearer analogy  between the foetal brain
 of the Fish, and the foetal brain of the Mammal;  indeed,  at the earliest period
 of their formation, they could not be distinguished ; during their advance  to the
 permanent condition, however, each undergoes changes, which are so much more
 decided in the higher animals than in the lower, that  in the latter there seems
 but little departure from the foetal condition, whilst in the  former the condition
Fig. 144.
  Human Embryo of sixth week, enlarg-
ed about three times; a, vesicle of corpora
quadrigemina; b, vesicle of cerebral hemi-
spheres; c, vesicle of thalami optici and
third ventricle ;  d, vesicle for cerebellum
and medulla oblongata; e, auditory vesicle ;
f, olfactory fossa; h, liver; ** caudal extre-
mity. 
ENCEPHALON OF REPTILES AND BIRDS.                283
appears entirely changed.   Hence it  is not correct to assert, as is frequently
done,—that the  Brain, or  any other organ,  in  the  higher  animals,  passes
through a series of forms, which  are  parallel to the permanent forms of the
same organ in different parts of the animal scale ;  since the fact is rather, that
the more nearly all are traced back to their first origin,  the closer will their
conformity be found to be ; the subsequent development of each taking place
not only in various degrees, but in different modes  or directions;  so that the
resemblances  presented  by the higher, at different epochs of their evolution,
to the permanent conditions of the lower, are often far from being complete.*
This we have seen to be the case in the present instance ;  the vesicle of the
Corpora Quadrigemina, and that of the  third Ventricle,  uniting  to form the
Optic Lobes of Fishes, whilst in  the higher Vertebrata they remain distinct;
so that there is no single part, with which the Optic  Lobes  can be properly
compared, either in the foetal or perfect state of the  Human Brain.
   360.  The Brain of Reptiles does not  show any considerable advance in
its general  structure above that of Fishes; but the Cerebral Hemispheres are
usually much larger in proportion to  the Optic lobes ; whilst the  Cerebellum
is smaller.   The very low development of the Cerebellum  is especially seen
in the Frog (Fig. 132), in which it is so small  as not even  to cover-in the
Fourth Ventricle; but it is common to  nearly  the whole group.   The defi-
ciency in commissures still exists  to a great extent.  The anterior Commissure
in front of the third ventricle, is the only uniting band which can be distinctly
traced in Fishes ; and Reptiles have, in  addition  to this, a  layer of uniting
fibres which may be  compared to the Fornix; but as yet, there is no vestige
of  a true  Corpus Callosum,  or  great transverse  commissure of the hemi-
spheres.  The distinction between the tubercula quadrigemina, and the parts
inclosing the  third ventricle, is more obvious than in Fishes ;  in fact the Optic
ganglia of Reptiles correspond pretty  closely with the Vesicle of the tubercula
quadrigemina in the brain of the  fcetal Mammal.
Fig. 145.
       Brain of Turtle;  a, olfactive              Brain of Buzzard ; the olfactive ganglia
      ganglia;  b, cerebral hemi-            are concealed beneath b, the hemispheres;
      spheres; c, optic ganglia; d,            c, optic ganglia; d, cerebellum;  g, pineal
      cerebellum.                         gland

  * For a fuller examination of this interesting question, see General and Comparative Phy-
siology, § 244.
Fig. 146.
 
284
FUNCTIONS OF THE NERVOUS SYSTEM.
   361.  This is still more evident in Birds, in whose Encephalon the Tuber-
cula Quadrigemina or Optic Ganglia, and  the  Thalami with their  included
ventricle, are obviously  very distinct  parts.   The  Cerebral Hemispheres
attain a great  increase of  development, and  arch  backwards, so as partly to
cover the Optic ganglia ;  and these  are separated from one another, and thrown
to either side.  The Cerebellum  also is much  increased in size, proportion-
ably to the Medulla Oblongata  and its ganglia; and  it is sometimes marked
with transverse lines, which indicate the intermixture of grey and white mat-
ter in its substance ; there is  as yet, however, no appearance of a division
into hemispheres.   On drawing  apart the hemispheres of the Cerebrum,  the
Corpora Striata, Optic Thalami,  and  Tubercula Quadrigemina or Optic Gan-
glia, are  seen beneath them;  the  size of the last still bears a considerable pro-
portion to that of the whole Encephalon.   The  Optic Ganglia are still hollow,
as they  are in the  embryo condition of Man.  Indeed the Brain of the Human
fcetus about the twelfth week will  bear comparison, in many respects, with
that of the Bird.  The Cerebral hemispheres,  much increased in size, and
arching  back over  the Thalami and Optic ganglia, but destitute of convolutions,
and imperfectly connected by commissures,—the  large cavity still existing in

                                Fig. 147.
14S.
  Brain of Human Embryo at twelfth week, a, seen from behind ; b, side view; c. sectional view; a,
corpora quadrigemina; bb, hemispheres; d, cerebellum; e, medulla oblongata;/, optic thalamus; g,
floor of third ventricle; I, olfactory nerve.,

the Optic ganglia, and freely communicating with  the third ventricle,—and
the imperfect evolution of the Cerebellum,—make the correspondence in the
general condition of the two very considerable.
  362. The  Brain of the  lowest Mammalia presents but a  slight advance
                             upon that of Birds, in regard both  to  the rela-
                             tive proportions of its parts, and to their degree
                             of development.   Thus, in  the Marsupialia, the
                             Cerebral hemispheres exhibit no convolutions;
                             and  the  great   transverse commissure.—the
                             Corpus Callosum,—is deficient.  There is gra-
                             dually  to be noticed, however, in ascending the
                             scale, a backward prolongation of the  Cerebral
                             hemispheres; so  that first  the  Optic ganglia,
                             and then the  Cerebellum, are covered by them.
                             The latter partly shows itself, however, in all
                             but the Quadrumana, when we look at the
                             brain from above downwards;  in  the Rabbit,
                             which  is in  this  respect among the lowest of
                             the true Viviparous   Mammalia,  nearly  the
                             whole  of the Cerebellum   is  uncovered.   In
                             proportion  to  the increase of the  Cerebral
                             hemispheres, there  is a diminution  in the size
                             of the  ganglia immediately connected with the
                             organs  of sense; and this  in comparison, not
                             only with the rest of the Encephalon, but even
  Brain of Squirrel, laid open; the
hemispheres, b, being drawn to either
side to show the subjacent parts;—c,
the optic lobes; d, cerebellum; thai,
thalamus opticus; cs, corpus striatum. 
0
                        ENCEPHALON OF MAMMALIA.                     285

with the Spinal Cord;  so that in Man the Tubercula Quadrigemina are abso-
lutely smaller than they are in many animals of far inferior size.   The inter-

                                  Fig. 149.
 Upper and under surface of Brain of Rabbit, a, b, d, as before ; ol, olfactive lobes; op. optic nerve ;
mo, motor oculi; cm, corpora mamillaria; cc, crus cerebri; pv, pons varolii; pa, patheticus; tri, trifa-
cial ; ab, abducens; fac, facial; au, auditory; vag, vagus ; s, spinal accessory ; hyp, hypoglossal.

nal structure of the hemispheres becomes more complex, in the same propor-
tion as their size and the depth of the convolutions increase;  and in Man all
these conditions present themselves in a far higher degree, than in any other
animal.   In fact it is only among the Ruminantia, Pachydermata, Carnivora,
and Quadrumana, that regular convolutions can be said  to  exist.  The cor-
respondence between the bulbous expansion of the Olfactive Nerves in Mam-
malia, and the Olfactive lobes of the lower Vertebrata, is made evident by the
presence, in both instances, of a cavity which  communicates  with the  lateral
ventricle on  each side ;  it is in Man only that this cavity is wanting.   The
external form of the Corpora Quadrigemina of Mammalia, differs from that of
the Optic ganglia of  Birds, owing to the division  of the  former into anterior
and posterior eminences, (the nates and testes;) and there is also an internal
difference, occasioned by the contraction of the cavity or ventricle, which now
only  remains as  the  Aqueduct of Sylvius.   The Cerebellum is chiefly re-
markable for the development of its lateral parts or hemispheres; the central
portion, sometimes called the vermiform process, is relatively less developed
than in the lower Vertebrata, in which it forms the whole of the organ.

        4.  General Functions  of the Spinal  Cord.—Reflex Action.

   363. The functions of the Nervous System in Vertebrated Animals are so
complex  in  their nature, and our means of analyzing them are so imperfect,
that the inquiry is confessedly one of the greatest difficulty, and needs all the
light  which can be thrown upon it  from any source.   The great accession to
our knowledge of them, which has been made within  the last few years,
chiefly by the  labours of  Sir  C. Bell, and Dr. M. Hall, has so far changed
the aspect of this department of Physiological Science, as to render it neces-
sary for those who had previously studied it, to begin de novo.  This is espe-
cially the case  in regard to the  actions dependent on the Spinal Cord; which
it  seems  desirable to consider  in the first instance, in order that it may be
 
%
286                FUNCTIONS OF THE NERVOUS SYSTEM.

clearly defined what the Brain does not do.  By many, even in recent times,
the Spinal Cord has been considered as  a mere appendage to the Brain ;  but
the phenomena of its independent action render such an idea quite inadmis-
sible.  These  phenomena have been especially pointed out by Dr. M. Hall;
and  it is  mainly owing to his arguments,  that Physiologists are now for the
most part  agreed in the general fact,—that the Spinal  Cord constitutes a  dis-
tinct centre, or rather a collection of centres, of  nervous influence,  and  that
its operations are carried on through the  nervous trunks with which it is con-
nected.   It is further generally admitted that its functions are independent of
the will; and  that they are in effect frequently opposed to those of the Brain,
which operates on the muscles, either  by a  volitional, or by an emotional
impulse.  And lastly, its actions are always (except when excited by a physi-
cal irritation  directly applied to itself) entirely of a reflex character; that is
to say, the motor impulses which originate in it are not spontaneous, but re-
sult from the stimulus of impressions, conveyed to it by the afferent trunks, and
operating upon it, to use the expression of Prochaska, according to certain
"peculiar laws written,  as  it were, by nature on  its medullary pulp."  It is
not,  however, universally admitted  that these actions are independent of sen-
sation; and  some  eminent  physiologists, among whom  may be named Dr.
Alison, still hold that the intervention of sensation is necessary—in  the case
at least,  of the  ordinary associated  movements, which have definite ends in
view, and follow one another in regular succession, as those of  Respiration,—
for an impression to give rise to that organic change in the Spinal Cord, which
shall terminate in a muscular motion.*   It will be desirable, therefore, to con-
sider the evidence upon which  the statement rests, that reflex actions are in-
dependent of  sensation, though ordinarily accompanied by it.
   364.  In the first place, then, it  has  long been well  known that, in  the
Human  being, the  Spinal Cord does not by itself possess, in  the remotest
degree, the power of communicating sensory impressions to the mind; since,
when its lower portion has been severed from the brain by injury or  disease,
there is  complete anjesthesiaTof all the parts of the body, which derive their
nerves exclusively from it.  Hence  it might be inferred, that throughout the
Vertebrated classes, the spinal cord is  equally destitute of sensibility;  and
that any movements produced by stimuli acting through it, are the results of a
physical, and  not of a sensorial change.   This inference, however, has been
disputed ;  and, if unsupported by other evidence, it  would not, perhaps, be
entitled  to rank as an ascertained truth.  The very performance, by decapi-
tated animals  of inferior tribes, of actions which had not been witnessed in
Man under similar  circumstances, has been  held to indicate, that the spinal
cord in them has an endowment which his does not possess.   The possibility
of such  an explanation—however unconformable to that analogy throughout
organized  nature, which the more it is  studied, the more invariably  is found
to guide  to truth—could not be disproved.   Whatever experiments on decapi-
tated animals  were appealed to, in  support of the doctrine that the brain is
the  only seat of sensibility, could be met by a simple denial that the spinal
cord is everywhere as destitute of that endowment, as it appears to be in Man.
The  cases of profound  sleep  and apoplexy might be cited, as examples of
reflex action without consciousness ; and these might be met by the assertion,
that in  such  conditions sensations axe felt, though they are not  remembered.
It is difficult, however, to apply such an  explanation  to the case  of anence-

   *  See Outlines of Physiology, 3d edit., 211.  By many of the German Physiologists, also,
it is maintained that Sensation is a necessary link  in the chain of reflex actions; but as they
employ the term sensation in a sense which does not involve consciousness, it is obvious that
their dissent from Dr. Hall's views is chiefly verbal. 
             FUNCTIONS OF THE SPINAL CORD.--REFLEX ACTION.         287

phalous human infants (in which all the ordinary reflex actions have been ex-
hibited, with an entire absence of brain), without supposing that the Medulla
Oblongata  is the seat of a sensibility which we know that the lower part of
the Spinal  Cord does not possess ;  and of this there is no evidence whatever.
   365. Experiments on the lower animals, then, and observation of the phe-
nomena manifested  by  apoplectic patients and anencephalous infants, might
lead to the conclusion, that the  -Spinal Cord  does  not possess a sensibility,
and that its reflex actions  are independent of sensation.   At  this conclusion,
Prochaska, Sir G.  Blane, Flourens, and other physiologists, had arrived; but
it was not  until special  attention was directed to the  subject by Dr. M. Hall,
that facts were obtained by which a positive statement of it could be supported.
For the question  might have  been continually asked,—If the spinal cord in
Man is precisely analogous in function to that of the lower Vertebrata, why
are not its  reflex phenomena manifested, when a portion of it  is severed from
the rest by disease or injury ?   The answer to this question is  twofold.   In
the first place, simple division  of the  cord with a sharp instrument leaves  the
separated portion in  a state of much  more complete integrity, and therefore
in  a state much more fit for the performance of its  peculiar functions, than it
ordinarily is after disease or violent injury ;  and as the former method of di-
vision  is one with  which the Physiologist is not likely to meet in Man as a
result of accident,  and which he cannot experimentally put  in practice, the
cases in which reflex actions are manifested, are likely to be comparatively few.
But, secondly, a number of such instances have now been accumulated, sufficient
to  prove that the occurrence is by no means  so rare as might  have  been sup-
posed;  and that  nothing  is required but patient observation, to throw great
light on this interesting question, from the  phenomena of disease.  A most
valuable collection of such cases, occurring within his own   experience, has
been published by Dr. W. Budd ;*  and the leading facts observed by him will
be now enumerated.
   366. In  the first case, paraplegia was the result of angular distortion of the
spine in the dorsal region.   The sensibility of the lower  extremities was ex-
tremely feeble, and the  power of voluntary motion was  almost entirely lost.
" When, however, any part of skin is  pinched or pricked, the  limb that is
thus acted on jumps with great vivacity; the toes are retracted towards the
instep, the  foot is  raised on the heel, and the knee so flexed as to raise it off
the bed ; the limb is  maintained in this state of tension for  several seconds
after the withdrawal of the stimulus, and then becomes suddenly relaxed."
" In general, while one leg was convulsed, its fellow remained quiet, unless
stimulus was applied to both at once." "In  these instances, the pricking and
pinching were perceived by the patient; but much more violent contractions
are excited by a stimulus, of whose presence he  is  unconscious.  When a
feather is  passed  lightly over the  skin, in  the hollow of the instep, as if to
tickle, convulsions occur in the corresponding limb, much more vigorous than
those  induced by  pinching or pricking; they succeed one another in a rapid
series  of jerks, which are repeated as long  as the stimulus is maintained."
"When any part  of the limb  is irritated in  the same way, the convulsions
which ensue are very feeble, and much less powerful than those induced by
pricking or pinching."  " Convulsions, identical with  those already described,
are at all  times excited by the  acts of defecation and micturition.   At these
times,  the convulsions are much more vigorous than under any other circum-
stances, insomuch that  the patient has been  obliged to resort to mechanical
means to  secure his person while  engaged in these acts.  During the act of /
expulsion,  the convulsions succeed one another rapidly, the urine is discharged
* Medico-Chirurgical Transactions, vol. xxii. 
288                FUNCTIONS OF THE NERVOUS SYSTEM.

in interrupted jets, and the passage of the faeces suffers a like interruption."
The convulsions are  more  vigorous, the  greater the accumulation of urine;
and  involuntary contractions occur whenever the bladder is distended, and
also when the desire  to relieve the rectum is manifested.  " In all these cir-
cumstances, the convulsions are  perfectly involuntary;  and  he is unable, by
any  effort  of  the  will, to control or moderate them."  The patient subse-
quently regained, in a  gradual  manner, both' the sensibility of the lower ex-
tremities, and voluntary power over  them ;  and as voluntary power  increased,
the susceptibility to involuntary  movements, and the extent and power of these,
diminished.
  367. This case, then, exhibits  an increased tendency to perform reflex actions,
when the control of the  brain was removed; and it  also shows that a  slight
impression upon  the  surface, of which the patient was not conscious, was
more efficacious  in exciting reflex movements, than were others  that more
powerfully affected the sensory organs.   This is constantly observed in ex-
periments upon the lower animals ;  and it harmonizes, also, with the important
fact, that,  when the trunk of an afferent  nerve is pinched, pricked, or other-
wise irritated, the reflex  function will not be nearly so strongly excited, as
when a gentler impression  is made on a surface supplied by the branches of
this  nerve.  The former produces pain, whilst the latter does not; the amount
of sensation, therefore, does not at all correspond with the intensity of reflex
action, but rather  bears a converse  relation to it.  Mr. Grainger found, that
he  could  remove the entire  hind  leg of a  Salamander with the scissors,  with-
out  the creature moving, or giving any expression of suffering, if  the spinal
cord had  been divided:  yet that, by irritation of the  foot, especially by heat,
in an animal similarly  circumstanced, violent convulsive actions in the leg and
tail were excited.—It should be added that, in the foregoing case, the nutrition
of the lower  extremities was  not impaired, as in most cases of paraplegia.
The  rationale of this  phenomenon, which is to be constantly observed  when
the  reflex  actions of the part remain entire, will be hereafter noticed (Chap.
VII.).
   368.  In another case, the paralysis was more  extensive, having  been pro-
duced by an injury (resulting from a fall into the hold  of a vessel) at the lower
part of  the neck.  There was  at first total loss of voluntary power over the
lower extremities, trunk, and hands; slight remaining voluntary power in the
wrists,  rather more in the  elbows,  and  still  more in  the shoulders.   The
intercostal muscles did not participate in the movements of respiration.   The
sensibility of the hands and  feet was greatly impaired.  There were retention
of urine, and involuntary  evacuation of the faeces.  Recovery  took place very
gradually; and during its progress, several remarkable phenomena of reflex
action were observed.   At first, tickling one sole excited  to movement that
limb only which was acted upon ; afterwards, tickling either sole excited both
legs, and, on the 26th  day, not  only the lower  extremities, but the trunk and
other extremities also.   Irritating the soles, by tickling or otherwise, was at
first the only method, and always the most efficient one, by which convulsions
could be excited.  From the 26th to the 69th day, involuntary movements  in
all the palsied parts continued  powerful  and extensive, and  were excited by
the following causes:—In the lower extremities only, by the  passage of flatus
from the bowels, or by  the contact of a cold urinal with the penis; convulsions
in the upper  extremities and  trunk, attended with  sighing,  by plucking the
hair of  the pubes.  On the  41st day, a hot plate  of metal was  applied to the
soles, and found a more powerful excitor of movement than any before  tried.
The movements continued as long as the hot plate was kept applied; but the
same plate, at the common  temperature, excited  no movements after the first
contact.   The contact was distinctly felt  by the  patient; but no sensation of 
             FUNCTIONS OF THE SPINAL CORD.--REFLEX ACTION.          289

heat was  perceived by him, although the  plate was  applied  hot  enough to
cause vesication.  At  three different intervals, the patient took one-eighth of
a grain of strychnia three times a day.   Great increase of susceptibility to
involuntary movements immediately followed, and they  were excited by the
slightest causes.  No convulsions of the upper  extremities could ever be pro-
duced, however, by irritating their integument; though, under the influence of
strychnia, pulling the  hair of  the  head, or tickling the chin, would  occasion
violent spasmodic actions  in them.  Spontaneous convulsions of the palsied
parts, which occurred at other times, were more frequent and more powerful
after  the  use of strychnia.'   On the first return of voluntary  power,  the
patient was enabled to  restrain in some measure the excited movements; but
this required a distinct effort of the will;  and the  first attempts to  walk were
curiously  affected, by the  persistence of the susceptibility to excited involun-
tary movements.   When  he first attempted to  stand, the knees  immediately
became forcibly bent  under him; this action of  the  legs  being  excited by
contact of  the  soles with  the  ground.   On the 95th  day this effect did not
take place, until the  patient  had  made  a few steps; the legs then  had a
tendency  to  bend up, a  movement which  he  counteracted by rubbing the
surface  of the belly: this  rubbing excited the extensors to action, and the legs
became extended with a jerk.   A few more  steps  were  then  made; the
manoeuvre repeated, and so on.  This susceptibility to involuntary movements
from impressions on the  soles, gradually diminished; and on the  141st day,
the patient was able to walk about, supporting himself on the back of a chair
which he  pushed before him ;  but his gait was unsteady, and much resembled
that of chorea.   Sensation improved very slowly : it was  on the 53d day
that he  first slightly perceived the heat of the metal plate.
   369.  This important case suggests many interesting reflections.   Common
sensation  was not so completely abolished as  in the  former instance;  but of
the peculiar kind of impression, which was found  most efficacious  in exciting
reflex  movements,  no consciousness whatever was  experienced.   Not less
interesting was the circumstance, that convulsions  could be readily  excited by
impressions  on surfaces above the seat of injury; as, by pulling the hair of
the scalp,  a sudden noise, and so on.  This  proves  two important points:
first, that a lesion of the cord may be such, as to intercept the transmission of
voluntary influence, and yet may allow the transmission of that reflected from
incident nerves.  Secondly, that  all influences from impressions on incident
nerves are diffused through the cord; for, in the instance adduced, the reflected
influence was undoubtedly not made to deviate into  the cord by the morbid
condition  of that organ,  but followed its natural course of diffusion, being
rendered manifest in this case  by the convulsions which were excited, in con-
sequence of increased  activity of the motor function of the cord.  It is further
interesting to remark, that, in the foregoing case, the reflex actions  were very
feeble during the first seven days, in comparison with their subsequent energy;
being  limited to slight movements of the feet,  which could not always be
excited by tickling the  soles.   In  another case of very  similar character, it was
three days after the accident, before any reflex actions could be produced. It
is evident, then, that the spinal cord must have  been in a state of concussion,
which prevented the  manifestation of its peculiar functions, so long as this
effect lasted; and it is easy,  therefore, to perceive, that  a  still more severe
shock might permanently  destroy its power, so as to prevent the exhibition of
any of  the phenomena of reflex action.
   370. It  seems well  established, then, by such cases, that  the Spinal Cord,
or small segments of it,  may  serve in Man as  the centreof very energetic
reflex actions ; when  the  voluntary power exercised  through the Brain, over
the muscular system,  is   suspended or destroyed.  And  it is further evident,
     25 
290
FUNCTIONS OF THE NERVOUS SYSTEM.
that these movements are produced by a mere physical change in the nervous
centres;  the  consciousness of the individual not being affected in their per-
formance, and sensation having  therefore no necessary participation in them.
As the movements witnessed in  the  lower animals, under the  same circum-
stances, are altogether  of a similar character, there seems no good  reason to
attribute  to their Spinal Cord an attribute, of which it is certainly destitute in
Man.  There is no essential difference, either in structure, or in the nature of
the actions  performed by them, between  the Spinal  Cord and the  Medulla
Oblongata, which can warrant us in assigning to the latter a function that the
former does  not possess: and if the reflexions of the Spinal Cord do not
involve sensation, there is good reason for concluding, that  this change is not
a necessary element in those of  the Medulla Oblongata.  It is  perfectly true,
that it usually accompanies in us the greater number of actions, to which that
division of the centre  is subservient;  for example, those of respiration and
deglutition: and it is  scarcely possible for  such an accident to occur  in the
Human being, as the  separation of the Medulla Oblongata from  the  brain,
without the destruction of the independent functions of both.   It is not likely
that we can ever have the power of ascertaining, by the testimony of a patient
so affected, that the Respiratory  movements  are performed without the  neces-
sary intervention of sensation; as we have been able  to do in regard to other
reflex movements.   But as the general fact is, that there is no positive ground
whatever for regarding  any part of the Spinal Cord as a sensorium independent
of the brain, and that  the Respiratory  movements certainly correspond in all
their conditions with the actions denominated  reflex,—there would seem no
good reason for maintaining that sensation is^in element in their production,
whilst it is admitted to be  not essential in  the case of the less regular con-
vulsive actions already  described. The character of adaptiveness to a designed
end, in regard to their  combination  and succession, which the  movements of
respiration and deglutition exhibit, has been shown  to be no  proof of their
dependence on sensation.
  371.  The question has been often put to  those who advocate this view,—
why the sensation  should be so  constantly  associated with  these changes, if
not essential to produce the motion?  An  objection might fairly be made to
any reasoning from final causes, in a question  of  facts; but the inquiry may
be easily answered. In many instances the production of sensations is the
stimulus necessary for the  excitement  of other actions, which are required
for the continued maintenance of those in question.  This may be rendered
more comprehensible  by a  simple illustration.—A cistern  filled with water
may be speedily emptied by a cock occasionally opened at the bottom; but,
if it communicate with a reservoir, by means  of a valve  opened by  a ball
floating on the surface of the water it contains,  it may be kept constantly full.
The lower cock is  opened, and  the water flows out;  and, in consequence of
the lowering of the surface thus produced, the floating valve above is opened,
and the cistern is refilled from the reservoir.  Now here the action of the ball-
cock at  the  top is  not essential to  the flow of water at the  bottom, but is
rather consecutive upon it.—Just so is it with  regard to those  movements of
Animals, which are concerned in the ingestion  of  their food.   The muscular
contractions required to propel it along the alimentary  canal, from the stomach
downwards, are provided for, without even the intervention of the nervous
system.   To bring it within reach of these, a muscular apparatus is provided,
by which anything that comes within its grasp is  conveyed downwards,
through  a  reflex operation, originating in  the impression made upon the sur-
face of  the  pharynx.   Now this action,  in the ordinary condition, may be
considered as attended with sensation,  in order  that the Animal may be called
upon to execute those other movements, which  will bring food within the 
             FUNCTIONS OF THE SPINAL CORD.—REFLEX ACTION.          291

reach of the  apparatus of deglutition.  The Polype is dependent for its sup-
plies  of aliment, upon what the- currents in the surrounding fluid, or other
chances, bring  into its neighbourhood; but anything which touches  its ten-
tacula,  is entrapped  and conveyed into its stomach.   The  anencephalous
Infant, again, can swallow, and even suck;  but  it can execute no other move-
ments adapted to obtain the supply of food continually necessary for  mainte-
nance, because it has  not a mind which sensations could awake into activity.
   372.  The sensation connected with reflex actions has not only  this  import-
ant end, but it frequently contributes to enjoyment, as in suction and ejaculatio
seminis.  Now there is evidence that the latter of these processes, involving
though  it does  the combined  action of a number of muscles,  and dependent  s
as it  seems upon sensation of a very peculiar  kind, may take place  without
consciousness on the  part of the individual.  Brachet mentions a case of this
kind in  the Human subject, in which the patient's own testimony could be
adduced; and he ascertained  that  emission could be produced  in dogs, in
which the spinal cord had been divided in the  back, and in which, therefore,
it can scarcely be doubted that the sensibility  of  the genital organs was de-
stroyed.  Such cases, it might be thought, are sufficient  to prove, that the
Reflex power, operating  independently of  sensation, is not confined  to  such
irregular convulsive movements as  are seen in Man after disease or  injury;
but is exercised in producing  the regular combined actions which are neces-  ■
sary for the maintenance of the organic functions.  The sensation accompa-
nying these  actions,  moreover, frequently affords  premonition of danger, or
gives excitement to supplementary actions  destined to remove  it, as in the
case of  respiration; for where anything interferes with the due  discharge of
the function, the uneasy  sensation that  ensues occasions unwonted move-
ments,  which are more or less adapted to remove  the impediment, in  propor-
tion as  they are guided  by judgment  as well  as  by consciousness.  Again,
sensation often gives  warning  against inconvenience, as in the excretory  func-
tions; and here it is very evident, that its object is not only (if it be at all) to
excite the associated muscles necessary for the excretion, but actually to make
the Will set up the antagonizing action of the sphincters, as will  be hereafter
explained (§  391).  There is  one unequivocal case, in the  ordinary condition
of the human body, of reflex action without sensation; this is the  muscular
contraction, by which the food is  propelled from  the bottom of  the pharynx
to the stomach.   Unless the morsel be very bulky, so as to press on the sur-
rounding parts, or be  very different in temperature  from the surface it touches,
or have any peculiar  irritating quality, we are not more conscious of  its pre-
sence, whilst it is passing down  the lower part of  the oesophagus, than when
it is being propelled along the intestinal  tube;  and yet, as Dr. J. Reid's ex-
periments* have shown, this  contraction is of a  reflex  character, not being
stimulated by direct contact, but requiring the  completeness of the  nervous
circle for its performance.
   373.  We shall now separately consider  the chief  operations, in which the
Spinal Cord and its system of nerves are usually concerned, in the ordinary
course of the vital actions of the Human body.  Upon taking a  general sur-
vey of  these, it will be found that their principal function is, to supply the
conditions requisite for the maintenance of the various Organic processes.
Thus, the aeration  of the blood, which takes  place whenever   that  fluid is
placed in relation with the atmosphere, can only be carried on, by the  regular
exchange of the small quantity of the gas  contained in  the lungs; if this
cease, the circulation is  soon brought to a stand,  and loss of vitality of the
whole system speedily results.  Hence this is  the most constantly necessary
* Edinb. Med. and Surg. Journ., vol. xlix. 
292
FUNCTIONS OF THE NERVOUS SYSTEM.
   of all the  actions of the  Spinal  Cord; and we find  its maintenance, in spite
   of accident or disease of the spine, remarkably provided for, in the location of
   the  centre of the respiratory movements, which occupies a position where it
   receives the greatest  possible  amount of  protection.   The supply of the di-
   gestive apparatus, again,  is immediately dependent upon the  Spinal system;
   and this, being another  essential function, has  its  centre  equally protected.
   The outlets of the cavities are also controlled by the Spinal system; but this
   control, although essential to the comfort  of life,  is less necessary to its main-
   tenance ;  and  we find it dependent upon a portion of the  Cord, which  is
   more  liable to lose  its powers by disease or injury.   It is possible, as will
   hereafter be shown, that several  actions,  which are at first voluntary, may be
   effected, when so frequently performed  as to become habitual, through the
   medium of the Spinal system;  of this  kind seem  to be the movements of
   locomotion, which are continued involuntarily, when  the whole attention of
   the mind is given to other objects, but which the Will can check at any time.
   We shall commence our  particular survey of the Reflex movements in  Man,
   with the consideration of those  of Respiration, which are well adapted  for
   illustrating their general character.
     374. Respiratory Movements.—The  centre of these is the upper part of
   the  Medulla Oblongata; into this may be traced  the  excitor nerves, that con-
   vey the stimulus on which the movements  are  dependent; and from it pro-
   ceed, either directly or indirectly, the motor nerves by  which they are carried
   into effect.  The chief Excitor of the respiratory movements is unquestion-
   ably the  Par Vagum.  When this is divided on both  sides, according to the
   experiments of Dr. Reid,* the number of respiratory movements is considera-
   bly diminished, usually about one-half.   Now if this nerve excites the motions
   of respiration  by its powerful  action in  producing  sensation, we should ex-
   pect to find its trunk endowed with considerable sensibility, which is not the
   case; for all experimenters agree in stating that, when  its trunk is pinched or
   pricked, the animal does not exhibit  signs of pain  nearly so acute, as when
   the trunks  of the ordinary spinal nerves, or of the fifth pair, are subjected to
   similar treatment.  It  cannot be questioned, however, that its power as an
   excitor of respiration is very great; since, besides the fact of the diminution
   in the number of inspirations  which occurs immediately on section  of it,
/   irritation of its trunk in  the neck is instantly followed by an act of inspira-
   tion.   It is evident  that  this power must arise from impressions made upon
   its peripheral  extremities.  The impression is probably due to the presence
   of venous blood  in the  capillaries of the lungs;  or, as Dr. M. Hall  thinks, to
   the presence of carbonic  acid in the air-cells.   Either or both may be true.—
   The Pneumogastric nerve, however, is not the only  excitor of the respiratory
   movements; since, when the nerve is cut on each  side, they still continue.
   Dr. Reid has satisfactorily shown the statement of many experimenters, that
   the inspirations are increased in frequency after this operation, to be erroneous;
   this  idea having  originated in their very prolonged  and laborious character.
   The removal,of  the Encephalon, also, diminishes the frequency of the respi-
   ratory movements, whether it be performed  before or after the section of the
   Vagi.  Dr. Reid found that, in  a kitten of a day old, in which the inspira-
   tions were 100  per minute, they fell  to  40 when  the Encephalon was  re-
   moved ;  and  on subsequently cutting the Pneumogastrics, the number  of
   inspirations instantly fell to between 3 and 4 in the minute, and continued so
   for  some time.   Hence it appears that the respiratory movements are partly
   dependent upon  sensation, and a motor influence excited by it;  and this may
   also be learned from the  prolonged and laborious character of the inspirations
* Edinb. Med. and Surg. Journ., vol. Ii. 
               REFLEX ACTIONS.--RESPIRATORY MOVEMENTS.            293

during sleep or profound  attention, when  the influence of the Encephalon is
more or less suspended.
  375. But why (it may  be asked) do the movements  continue, when the
Pneumogastrics have been divided, and the Encephalon  has been  removed ?
It is evident that  there must be other excitors to the action of the respiratory
muscles.  Amongst these, the nerves  distributed to the general surface, and
particularly  to the face, probably perform  an important part;  and in exciting
the  first  inspiration, the Fifth pair seems the  principal  agent.   It has  long
been a well-known  fact, that the first inspiratory effort of the new-born infant
is most vigorously performed, when the cool external air comes into contact
with the  face; and  that impressions on the general surface, such as a slap of
the  hand  on the nates, are often  effectual in  exciting the first inspiratory
movements,  when they would not otherwise commence.  Dr. M. Hall relates
an interesting case,  in  which the first inspiration was delayed, simply because
the  face was  protected by  the bed-clothes  from  the atmosphere; and, on lift-
ing  up these, the infant immediately  breathed.  Dr. M. Hall  has recently
mentioned the important fact, that if the cerebrum be removed, and the pneu-
mogastrics be divided, in  a young kitten,  the number of acts of respiration
will be reduced to  four in a minute; but  by directing a stream of  air on the
animal, or by irritating various  parts of the general  surface,  we may excite
twenty or thirty acts  of  respiration within the  same  space of time.   He
further remarks, that in the very young warm-blooded animal, as in the cold-
blooded animal, the  phenomena of the excito-motor power are far more vividly
manifested,  than  in the older and the warm-blooded.   In the very young
kitten, even  when asphyxiated to insensibility, every touch, contact, or slight
blow,—every jar of the table, any sudden impression of the  external air, or
that of a  few drops  of cold water, induces at once energetic reflex movements,
and acts of inspiration.  This may be  looked upon as Nature's provision for
the  first  establishment of  the  acts of inspiration in the  new-born  animal.—
But the influence of the nerves of the general  system is by no means want-
ing in the adult;  as the following  experiment of Dr. J. Reid's demonstrates.
After dividing the pneumogastrics, and removing  the cerebrum and cerebel-
lum, he divided the spinal cord high up in the neck, so as to cut off the com-
munication  between the spinal nerves and the Medulla Oblongata; and he
found  that the frequency of  the  respiratory  movements  was  still further
diminished,  although  they were not even then entirely suspended.—Every-
one knows the fact, that the first  plunge into cold water, the first descent of
the  streams of the shower-bath, or even the dashing  of a glass of cold water
in the face, will produce inspiratory efforts; and this fact has many important
practical applications.   Thus in the treatment of Asphyxia, whether congeni-
tal,  or the result of narcotic poisoning, drowning, &c, the  alternate applica-
tion of cold and  heat is found to be one  of the most efficacious  means  of
restoring the respiratory movements;  and a paroxysm of  hysteric laughter
may be cut  short, by  dashing  a glass of  cold water in the  face.—It may be
surmised that the Sympathetic nerve, which derives many filaments from the
Cerebro-Spinal system, and which especially communicates with the Pneu-
mogastric nerves, is one of the excitors to this  function; and this, perhaps,
not only through its ramifications  in the lungs, which are  considerable, but
also by its distribution on  the systemic vessels;  so that it may convey to the
Spinal Cord the impression of imperfectly-arterialized blood, circulating  in
these, such as the Pneumogastric is believed to  transmit from the lungs.   It
will hereafter be  shown, that an impression of  a corresponding  kind is more
probably the cause  of the sense of  Hunger and  Thirst, than any which origi-
nates in the stomach alone (Chap.  X., Sect. 1).
  376. The Motor or Efferent nerves  concerned  in the function of Respira-
                                  26* 
294
FUNCTIONS OF THE NERVOUS SYSTEM.
tion, are those which  Sir C. Bell  has grouped  together in  his respiratory
system.  The  most important of these, the Phrenic, arises from the upper
part of the  Spinal Cord; the Intercostals much lower down; whilst the Facial
nerve and  the Spinal Accessory, to the  latter of which, as will hereafter  be
stated (§ 408), the motor powers of the par vagum are chiefly due, take their
origin in the Medulla Oblongata itself.  But we must not decide upon  the
connection of a particular nerve with a particular  segment of the Spinal Cord,
simply because it diverges from it at that point.   It has been shown that, in
the Mollusca, a nerve passing to, or proceeding from, one ganglion, frequently
passes through or over another  which lies in its course ; and in the Articulata,
this is a still  more constant occurrence.  It is by no means improbable, then,
that the connection of  the intercostal nerves is  really in part with  the grey
matter of the Medulla Oblongata; at any rate, such a connection has  not been
disproved.   The white columns of the Spinal Cord consist of fibres, which
bring the spinal nerves into connection, not only with the brain, but  also with
other segments of the ganglionic portion of the cord; being analogous in func-
tion, not merely to the distinct  fibrous  tract of the ventral column of the Arti-
culata, but  also to the fibrous bands  that connect the ganglia themselves.  And
as the Medulla Oblongata, in Vertebrated  animals, is  the chief centre of  the
actions of Respiration, it can scarcely be doubted that all the nerves concerned
in that function have a direct structural connection with it.
   377.  That the Respiratory movements, as ordinarily performed, are essen-
tially independent of the Will,  appears not only from our own consciousness,
but also from cases of paralysis; in  some of which, the power  of the will over
the muscles has been lost, whilst the movements  have been  kept up by  the
reflex  action of the Medulla  Oblongata  or respiratory ganglion; whilst in
others, some of the respiratory  muscles have been motionless during ordinary
breathing, and yet have remained under  the power of the will.  Such cases
are mentioned by Sir C. Bell, in the Appendix to his work on the  Nervous
System.   That consciousness  is not a necessary link in the chain of causes,
which  produce the respiratory  movements, we are enabled to  judge  from  the
phenomena presented by the human  being in sleep and coma, by anencephalous
foetuses, and  by decapitated animals.   Further, Dr. Ley* has put on record a
case, which confirms this particular inference, just in the same manner as  the
cases already related confirm the general doctrine of the non-existence of sen-
sibility in the Spinal Cord.   He had  under his care  a patient, in whom  the
par vagum  appeared to be  diseased;  the lungs  suffered in the usual way in
consequence, and the patient had evidently laborious breathing; but he dis-
tinctly said that he felt no uneasiness in his chest.—The experience  of every
one informs  him, that Respiratory movements are partly under the control
and direction of the will, though frequently unrestrainable by it.   In  ordinary
circumstances, when the blood  is being perfectly aerated, and  there is a suffi-
cient amount of arterial blood in the system to  carry  on the functions of  life '
for a short  time, we can suspend the respiratory actions during a few seconds
without any inconvenience.   If, however, we endeavour to prolong the sus-
pension, the  stimulus conveyed by  the excitor  nerves to the Medulla Oblon-
gata becomes too strong, and we cannot avoid making inspiratory efforts ; and
if the suspension be still further prolonged, the whole  body becomes agitated
by movements, which are almost of a convulsive nature ; and  no effort of the
will can then prevent the ingress of air.t   It is  easy to understand why, in

  * On Laryngismus Stridulus, p. 417.
  t It is asserted by M. Bourdon (Recherches sur le Meranisme de la Respiration, p. 81),
that no person  ever committed suicide, though many have attempted to do so, by simply
holding the breath; the control of the will  over the respiratory muscles not being sufficiently
great, to antagonize the stimulus of the " besoin de respirer," when this has become aggra- 
                REFLEX ACTIONS.--RESPIRATORY MOVEMENTS.             295

the higher animals at least, and more especially in Man, the respiratory actions
should be thus placed under  the  control of the will:  since they are  subser-
vient to the production of those  sounds, by which  individuals communicate
their feelings and desires to each other;  and which, when articulate, are capa-
ble of so completely expressing what is  passing in the mind of the speaker.
If the respiratory mucles of Man were no more  under his  control, than they
appear to be in the Insect  or  Molluscous animal, he might be provided with
the most perfect apparatus of speech, and yet he would not be able to employ
it to any advantage.
   378.  The motor power of the Respiratory nerves is  exercised, however,
not only on the muscles which perform  the inspiratory and expiratory move-
ments, but on those which guard the entrance to the windpipe, and also on
certain  other  parts.  The movements  of the  internal respiratory apparatus
are chiefly,  if not entirely, effected  through the medium  of the motor fibres,
which  the Par Vagum  contains.  These motor fibres exist in very different
amount in its different branches.  For example, the pharyngeal and oesopha-
geal branches, by which (as will hereafter appear) the muscles of deglutition
are  excited to contraction, possess  a much larger proportion of them, and
exhibit  much less  sensibility when  irritated, than do  other  divisions of the
trunk.   Between the superior and inferior laryngeal nerves, again, there is an
important difference, which anatomical  and experimental research has now
very clearly demonstrated.   It has long been  known, that section of the Par
Vagum in the  neck, above the inferior  laryngeals, is frequently followed by
suffocation, resulting from closure of the glottis;  and  hence  it has been in-
ferred, that the office of the inferior laryngeals was to  call into action  the
dilators of the larynx, whilst the superior laryngeals were supposed to stimu-
late the constrictors.   This view, however, is incorrect.  It is  inconsistent
with the  results, just stated,  of anatomical examination into the respective
distribution of these two trunks; and it has been completely overthrown by
the  very careful and satisfactory observations and  experiments of Dr. J. Reid,
which have established that, whilst the inferior laryngeal is the motor nerve
of nearly all  the laryngeal muscles, the superior laryngeal is the excitor or
afferent nerve, conveying to the Medulla Oblongata the impressions by which
muscular movements are excited.   Its motor endowments are limited to  the
crico-thyroid  muscle, to which alone of all the muscles  its filaments  can be
traced,  the  remainder being distributed  beneath the  mucous surface of the
larynx;  and its  sensibility is very evident, when it  is  pinched or irritated
during experiments upon it.   On the other hand, the motor character of the
inferior laryngeal branch is shown by its very slight sensibility to injury, its
nearly exclusive distribution to muscles, and its influence in exciting contrac-
tion of  these when  its separated trunk is stimulated.
   379.  It  has been ascertained by  Dr. Reid that, if the  inferior laryngeal
branches  be divided, or the trunk of the par vagum be cut  above their origin
from it, there is no constriction of the glottis, but a paralyzed state of its mus-
cles.  After the first paroxysm occasioned  by the operation,  a period of qui-
escence and freedom from dyspnoea often supervenes, the respirations being
performed with ease, so long as  the animal remains at rest; but an unusual
respiratory  movement, such as takes place at the commencement of a struggle,
induces immediate symptoms of suffocation,—the current of air carrying in-
wards the arytenoid cartilages, which are rendered passive by  the paralyzed

vated by the temporary cessation of the action.  But such persons have succeeded better, by
holding the face beneath the surface of water; because here another set of muscles is called
into action, which are much more under the control of the will, than are those of respiration;
and a strong volition applied to these can prevent all access of air to the lungs, however
violent may be the inspiratory  efforts. 
296                FUNCTIONS OF THE NERVOUS SYSTEM.
state of their muscles;  and these, falling upon the opening of the glottis, like
valves obstruct the entrance of air into the lungs.  The more effort is made,
the greater will be the obstruction:  and accordingly, it is generally necessary
to counteract the tendency to suffocation, when it is desired to prolong the life
of the animal after this operation, by making an opening into  the trachea.  Dr.
Reid further ascertained that  the application of a  stimulus to the inferior
laryngeal  nerves, when separated from the  trunk,  would  occasion distinct
muscular contractions in the larynx; whilst a corresponding stimulus applied
to the  superior laryngeal occasioned no muscular movement, except in the
crico-thyroid muscle.  But when the superior laryngeals were entire, irritation
of the  mucous surface of the larynx, or of the  trunks themselves, produced
contraction of the glottis and efforts  to cough; effects which were at once pre-
vented by dividing those nerves, and thereby cutting off their communication
with the Medulla Oblongata.   There can be no doubt,  then,  that the superior
and inferior laryngeal branches constitute  the  circle of incidents and motor
nerves, by which the aperture of the glottis is governed, and  by which any
irritation of the  larynx  is  made  to  close the passage, so as  to  prevent the
entrance of improper substances;  whilst the superior laryngeal nerve also ex-
cites the muscles of expiration, so as to cause the violent ejection of a blast of
air, by which the offending gas, fluid, or solid, may be carried off.   The effect
of carbonic  acid  in causing spasmodic closure of the  glottis is well known;
and  affords a beautiful example of the protective character of this system of
nerves.  The mucous surface of the trachea and bronchi appears, from the
experiments of Valentin, to be endowed with excitability, so that stimuli ap-
plied to it produce expiratory movements;  and this evidently operates through
the branches  of  the par vagum distributed upon  the  membrane.  Here, as
elsewhere, we find that a stimulus applied to the surface has a much more
decided influence than irritation of the trunk of the nerve supplying it.
   380.  The actions of sighing, yawning, sobbing, laughing, coughing, and
sneezing, are nothing else than simple modifications of the ordinary movements
of respiration, excited either by mental emotions, or by some  stimulus originat-
ing in the respiratory organs themselves.—Sighing is nothing more than a very
long-drawn inspiration, in which a larger quantity of air than usual is made to
enter the lungs.   This is continually taking place to a moderate degree ;  and
we notice it  particularly, when the attention is released, after having  been
fixed upon an object, which has excited it strongly, and which  has  prevented
our feeling the insufficiency of the ordinary movements of respiration. Hence
this action is only occasionally connected with mental emotion.— Yawning is
a still deeper inspiration, which is accompanied  by a kind of spasmodic con-
traction of the muscles of the jaw, and also by  a  very great elevation of the
ribs, in which the scapulae partake.  The purely involuntary character of this
movement is sometimes seen, in a remarkable manner, in cases of palsy; in
which the patient cannot raise his shoulder by an  effort of the will, but does
so in the act of yawning.   Nevertheless  this act may be performed by the
will, though not completely; and it is  one  that is particularly excited by
an involuntary tendency to imitation;  as  every one must have experienced,
who has ever been in company with a set of yawners.—Sobbing is the con-
sequence of a series of short convulsive contractions of the diaphragm ;  and it
is usually accompanied by a closure of the glottis, so that no air really enters.
In Hiccup, the same convulsive respiratory movement occurs; and  the glottis
closes  suddenly  in the midst of it;  the sound is  occasioned by the impulse of
the  column of air in motion, against the glottis.—In  Laughing, a precisely
reverse action takes place: the muscles of expiration are in  convulsive move-
ment, more or less  violent, and  send  out the breath in a series of jerks, the
glottis being  open.  This sometimes  goes on, until the diaphragm is more 
                REFLEX ACTIONS.--RESPIRATORY MOVEMENTS.            297

arched, and the chest is more completely emptied of air, than it could be by
an ordinary movement of expiration.—The act of Crying, though occasioned
by a contrary emotion, is, so far as the respiration is concerned, very nearly
the same as the last.  Every one knows the effect of mixed emotions, in pro-
ducing an expression of them, which is "between a laugh and a cry."—The
greater part of  the preceding movements seem to belong as much  to the con-
sensual or emotional, as to the purely reflex group of actions ; for  whilst they
are sometimes the result of peculiar states  of the respiratory organs, or of the
bodily system  in general, they may also be called forth by influences, which
operate directly through  the  senses, or which  excite  the emotions.  Thus,
whilst Sighing and Yawning often occur as simple results of deficient aeration,
they may be brought on,—the former by a depressed state of the feelings,—
the latter by the mere sight  of  the act in another person.   The actions of
Laughter  and Crying never seem to  originate in the respiratory system; but
to be always  either expressions of the emotions, or simple results of sensa-
tions,—crying being connected with the sense of pain,—and laughter with that
of tickling.   The origin of the act of Hiccup does not seem  very clear; but
the movement is probably of a purely reflex nature.
  381.  The  purposes of the acts of Coughing and  Sneezing are, in  both
instances, to expel substances from the air-passages, which are sources of irri-
tation there;  and this is accomplished  in both, by a violent expiratory effort,
which sends forth a blast of air from the lungs.—Coughing occurs, when the
source of irritation is situated  at the back of  the mouth, in  the trachea, or
bronchial tubes.   The irritation may be  produced by acrid  vapours, or by
liquids or solids, that have found their way into these  passages; or by secre-
tions  which have been poured into them in unusual quantity,  as the result of
disease; or by the simple entrance of air (especially if cold),  when the mem-
brane is in a peculiarly irritable  state.  Any of  these causes may  produce an
impression upon the excitor fibres of the Par Vagum,  which,  being conveyed
to the Medulla Oblongata, shall give rise to the transmission of motor impulses
to the several muscles, that shall combine  them  in the act of coughing.   This
act consists,—1st,  in a long inspiration,  which fills  the lungs;  2d, in the
closure of the glottis at the moment when expiration commences; and 3d, in
the bursting open (as it were) of the glottis, by  the violence of the expiratory
movement; so that a sudden blast of air is forced up the air-passages, carrying
before it  anything that may offer an  obstruction.—The  difference between
coughing and Sneezing consists in this,—that  in the latter, the communication
between the larynx and the mouth is partly or entirely closed, by the drawing
together of the  sides of the velum palati over  the back of the  tongue; so that
the blast of air  is directed, more  or less completely, through the nose, in  such
a way as to carry off any source  of irritation that may.be present there.—It is
difficult to say  how far these  actions are simply reflex; or how far they may
require the stimulus of sensation for their  performance.
   382.  Deglutition and Defecation.—Another  very important function of the
Spinal Cord (and of the ganglia corresponding to it in the Invertebrata), is the
control which it exercises over the entrance and  termination of the  Alimentary
Canal;  and this  reflex action might  probably  be traced in some  animals, in
which the necessity for that of Respiration does not exist.  In all beings which
are unequivocally of an animal character, a stomach or digestive cavity exists;
and  a means  must be provided  for the introduction of food into it.   This is
partly accomplished by the  power, with which  its  entrance  is endowed, of
contracting upon, and of attempting to draw inwards, whatever comes in con-
tact with  it;  as we may readily observe in the Star-Fish, or Sea-Anemone,
where what is  commonly  regarded as the mouth, is really the aperture of the
stomach.  But  we almost always find some more special apparatus, for bring- 
298                FUNCTIONS OF THE NERVOUS SYSTEM.

ing food within  reach of this orifice.   In the Sea-Anemone, the Hydra, and
other Polypes, for example, we find that aperture surrounded by tentacula;
which have an evident tendency to lay hold of anything that touches them, so
as to bring  it, by their  contraction, within reach of the muscles  immediately
surrounding the aperture.  This is just the purpose of the pharyngeal muscles
of Man.  The lower part of the  oesophagus, near its termination in  the sto-
mach, has the same simple tendency to contraction  from above downwards
(so as to convey into the stomach anything which is brought within its reach),
as have the muscles surrounding the mouth of the Polype; but there is need
of some more complex  apparatus, for the purpose of laying hold of the food,
and of conducting it into its grasp.  This is provided for, in the higher animals,
in the muscles of that funnel-like entrance to the oesophagus, which is called
the Pharynx. The actions of these are most distinctly reflex; and it is inte-
resting to remark, that the movements can neither be caused nor controlled  by
the direct influence of the will.  In the  case of the movements of respiration,
we found sufficient provision made for their constant maintenance; and yet,
for secondary purposes, they were placed in a  considerable degree under the
control of the brain.  But here there  are  no secondary purposes to be an-
swered ; the introduction into the stomach of food, brought by the will within
reach of the pharyngeal  muscles, is  the only object contemplated by them;
and they are accordingly placed under the sole government of the Spinal Cord.
   383.  No  attempts, on our own part, will  succeed in  producing  a really
voluntary act of Deglutition.   In order to  excite it, we must supply some
stimulus to the fauces.  A very small particle of solid matter, or a little fluid
(saliva,  for instance), or  the contact of  the back of the tongue itself, will be
sufficient;  but without either of these we cannot swallow at will.   Nor can
we restrain  the tendency, when it is  thus excited by a stimulus; every one
knows how irresistible it is, when the fauces are touched  in any unusual man-
ner ;  and it  is equally beyond the direct control of  the  will, in  the ordinary
process of eating,—voluntary as we commonly  regard this.  The  only mode
in which the will can influence it, is by regulating the approach  of the stimu-
lus necessary to  excite  it; thus, we voluntarily bring a  morsel  of food, or a
little fluid, into contact with the surface of the fauces, and an act of deglutition
is then  involuntarily excited: or we may voluntarily keep all stimulus at a
distance ; and no  effort of the will can  then induce  the action.  Moreover,
this action is performed, like  that of respiration, when the  power  of the will
is suspended, as in profound  sleep, or  in  apoplexy affecting only the brain;
and it does not seem to  be at  all  affected by the entire removal  of the brain,
in an animal that  can sustain the shock of the operation;  being readily ex-
citable,  on stimulating the fauces, so long as  the nervous structure retains its
functions.   This has been  experimentally proved  by Dr. M.  Hall; and it
harmonizes with the natural  experiment sometimes brought under our notice
in the case of an anencephalous infant, in which the power of swallowing
seems as vigorous  as in  the perfect one.  But, if the nervous  circle be de-
stroyed,  either by division of the  trunks, or by injury of any kind to the por-
tion of the nervous centres connected with them, the action can  no longer be
performed;  and thus we see that, when the effects of apoplexy are extending
themselves  from the brain to the  spinal cord, whilst the respiration becomes
stertorous, the power of Deglutition is  lost, and then respiration  also speedily
ceases.
   384.  Our knowledge of the nerves  specially concerned in this  action is
principally due to the very careful and well-conducted experiments of Dr.  J.
Reid.*   The distribution of the Glosso-Pharyngeal evidently points it out as
* Edinb. Med. and Surg. Journ., vol. xlix. 
ACTIONS PRELIMINARY TO DEGLUTITION.
299
in some way connected with it; and this, when carefully examined, discloses
the important fact, that the  nerve  scarcely sends  any of its branches to the
muscles which they enter;  but that these mostly pass through them, to be
distributed to the  superjacent mucous  surface  of the tongue  and fauces.
Further, when the trunk is separated from  the  nervous  centres,  irritation
scarcely ever  produces muscular movements.  Hence it is not in any great
degree an efferent or motor  nerve ;  and its distribution would lead us to sup-
pose its function to be, the conveyance of impressions from the surface of the
Fauces to the Medulla Oblongata.  This inference is fully confirmed by the
fact, that, so long as  its trunk  is  in connection with the  Medulla Oblongata,
and the other  parts are uninjured,  pinching,  or other severe irritation of the
Glosso-Pharyngeal, will often  excite distinct acts of deglutition.   Such irrita-
tion, however, may excite  only  convulsive  twitches,  instead of  the regular
movements of swallowing;  and it is  evident that, here, as elsewhere, the
impressions made upon the extremities of the nerves are much  more power-
ful excitors of reflex movement, than those made upon the trunk, though the
latter are more productive of pain.   It was further observed by Dr. Reid, that
this effect was produced by  pinching the  pharyngeal branches only ;  no irrita-
tion of the lingual division being effectual to the purpose.
   385. If, then, the muscles of deglutition are not immediately stimulated to
contraction by the Glosso-Pharyngeal nerve, it remains to be inquired, by
what nerve the motor influence is conveyed to them from the Medulla Oblon-
gata ; and Dr. Reid has been equally successful in proving, that this function
is chiefly performed by the pharyngeal  branches of the Par Vagum.  Ana-
tomical examination of their distribution  shows, that they lose themselves in
the muscles of the pharynx ;  and whilst no  decided indications of suffering
can be produced by irritating them, evident contractions are occasioned, when
the trunk, separated from  the brain, is pinched or otherwise stimulated.  It
appears,  however,  that neither is  the Glosso-Pharyngeal  the  sole excitor
nerve, nor are the pharyngeal  branches of  the Par Vagum the sole motor
nerves, concerned in deglutition;  for  after the former  has been  perfectly di-
vided on each side, the usual movements can  still be excited, though with less
energy; and, after the latter have been cut, the animal retains  the  means of
forcing small  morsels  through the  pharynx, by the action of the muscles of
the tongue and neck.   From  a careful examination of  the  actions of degluti-
tion, and  of the influence of various  nerves  upon  them, Dr. Reid draws the
following conclusions :—The excitor impressions are conveyed  to the Me-
dulla Oblongata chiefly through  the Glosso-Pharyngeal, but also along the
branches  of the Fifth pair distributed upon the fauces, and probably  along the
branches  of the Superior  Laryngeal  distributed upon the pharynx.   The
motor influence passes chiefly along the  pharyngeal branches of  the Vagus ;
along  the branches of the  Hypo-glossal, distributed  to  the  muscles of the
tongue, and  to the sterno-hyoid,  sterno-thyroid,  and  thyro-hyoid  muscles;
along  the motor filaments  of the  Recurrents, ramifying upon  the larynx;
along some of the branches of the Fifth, supplying the elevator muscles of the
lower jaw ; along the branches of the Portio  Dura, ramifying upon the digas-
tric and stylo-hyoid  muscles,  and upon the muscles of the lower part of the
face ;  and probably along some of the branches of the Cervical plexus, which
unite themselves  to the descendens noni.
   386. When the food has been  propelled downwards  by the  Pharyngeal
muscles as far as their action extends,  its further progress  through  the Oeso-
phagus is effected by  the peristaltic movement of  the muscular  coat of the
tube itself.   This movement is not, however, due only to the direct stimulus
of the muscular fibre by the pressure of  the  food, as it  seems to be in the
lower  part of the alimentary canal; for  Dr.  J. Reid has found,  by repeated 
300
FUNCTIONS OF THE NERVOUS SYSTEM.
experiment, that the continuity of the oesophageal branches of the Par Vagum
with the Spinal Cord, is necessary  for  the rapid  propulsion of the  food; so
that it can scarcely be doubted, that an impression made upon  the mucous
surface of the oesophagus, conveyed by the afferent fibres of these  nerves to
the Medulla Oblongata, and  reflected downwards along  the motor fibres, is
the real cause of the muscular contraction.   If the Par Vagum be divided in
the rabbit, on each  side, above the  oesophageal plexus, but below the pharyn-
geal branches, and the animal be then fed, it is found that the food  is delayed
in  the  oesophagus, which becomes greatly distended.  Further,  if  the lower
extremity of the par vagum  be irritated, distinct contractions are seen in  the
oesophageal tube, proceeding from  above downwards,  and extending over the
cardiac extremity of the stomach.   We have here, then, a distinct  case of
reflex action without  sensation, occurring  as one of  the regular  associated
movements in the natural condition of  the  animal body ;  and it  is  very inte-
resting to find this  following upon  a reflex action with sensation (that of the
pharynx), and  preceding  a  movement which is  altogether unconnected with
the Spinal Cord (that of the lower part of the alimentary canal).   The use of
sensation in the former case will presently appear.  The muscular fibres of
the oesophagus  are also excitable, though usually in a less  degree, by direct
stimulation; for  it appears  that, in  some  animals (the  Dog,  for  example),
section of the pneumogastric does not produce that check to the propulsion of
the food, which it occasions in  the Rabbit;  and  even in the Rabbit, as Dr.
M. Hall* has  remarked,  the simple contractility of the  muscular  fibre occa-
sions a distinct peristaltic movement along the tube, after its nerves have been
divided;  causing it to discharge its  contents, when cut across.  Such a move-
ment, indeed, seems  to take place in something of a rhythmical manner (that
is, at short and tolerably  regular intervals),  whilst a meal is being swallowed;
but as  the  stomach becomes full, the intervals are longer, and  the wave-like
contractions less frequent.—These  movements are reversed in Vomiting ; and
this reversion has  been observed, even after the  separation of  the stomach
from  the oesophagus, as  a consequence of  the injection  of  tartar emetic into
the veins.
   a. It will be desirable here to revert for a short time to the actions, which, in the higher
animals, precede  those of Deglutition.  There can be no doubt that, in the Human being,
the motions adapted to the Ingestion and  Mastication of aliment originally result, in part at
least, from distinct operations of  the Will; but it would appear almost  equally certain that,
in time, they come to be of so habitual a character, that the will only exerts a general con-
trolling influence over them, each individual act being directly excited by sensation.  Every
one is conscious that the act of  mastication  may be performed as well, when  the mind is
attentively dwelling on some other object, as when directed to it; but, in the  former case,
one is rather apt to go on chewing and rechewing what  is  already fit to be swallowed,
 simply because the will does not exert itself to check the action, and to carry the food back-
wards within the reach of the muscles of deglutition. We now see why sensation should
be associated with the latter process, though not essential to it.  The conveyance  of food back-
wards to the fauces is a distinctly voluntary act; and it is necessary that it should be guided
by the sensation, which  there results from the contact it induces.  If the surface of the
pharynx were as destitute of sensation, as is the lower part of the ^'oesophagus, we should not
 know when we had  done what was necessary to  excite its  muscles to operation.—The
 muscles concerned in the Mastication of  food are nearly all supplied by the third  branch of
 the Fifth pair, a large proportion of which is well known to have a motor character.  Many
 of these muscles, especially those of the  cheeks, are  also  supplied by the Portio Dura of the
 Seventh; and yet, if the former  be paralyzed, this cannot stimulate them to the necessary
 combined actions.  Hence we see that the movements are of an associated character, their
 due performance being dependent on the part of the nervous centres, from which the motor
 influence originates.   If the  Fifth pair, on the other  hand, be uninjured, whilst the Portio
 Dura is paralyzed, the movements of Mastication are performed without difficulty; whilst
 those connected  in any way with the Respiratory function, or with  Expression, are para-
 lyzed.
* Third Memoir on the Nervous System, § 201. 
ACTIONS PRELIMINARY TO DEGLUTITION.
301
  b. Comparative Anatomy supplies us with the key to the explanation of these phenomena.
It has been seen that, in the lower animals, the Respiratory organs are completely uncon-
nected with the mouth, and that a very distinct set of muscles is provided to keep  them in
action.  These  muscles have distinct ganglia as the centres of their operations;  and these
ganglia are only connected indirectly with those of the sensori-motor system.  The same
would appear to be the case, in regard to the  introduction of the  food  into  the  digestive
apparatus.  It has been shown that the muscles concerned in this operation have  their own
centres.—the  Stomato-gastric and  Pharyngeal ganglia, which are not very closely connected
with the cephalic, or with the respiratory, or with those of general locomotion.  Now in the
Vertebrata, the  distinct organs have been so far blended together, that the same muscles
serve the purposes of both; but the different sets of movements of these muscles are excited
by different nerves; and the effect of division of either nerve, is to throw the  muscle out of
connection with the function,  to which that nerve  previously rendered it subservient,—as
much as if the muscle were separated  from  the nervous system altogether.  There  is an
apparent exception to this view of the matter, in the case of the Portio Dura; this being the
source of those movements of the upper lip, which, in  many animals, are essential to the
prehension of food.   These movements, however, are dependent upon sensations conveyed
through the Fifth pair,* being  completely checked by division of its infra-orbital trunk; and
it can scarcely be doubted, from their general character, that they are of a strictly voluntary
nature, and are not to be regarded as part of the reflex associated movements in which that
nerve is concerned.
  c. Now although, in the adult Human  being, the movements required to convey the food
to the pharynx are under the control of the Will, if not constantly dependent upon it, there
is good  reason to believe that  this is not the case in regard to those remarkable  associated
movements, which constitute  the act of suction in the Infant.   The experiments  provided
for  us by nature, in the production of  anencephalous  monstrosities, fully prove  that the
nervous connection of the lips  and respiratory organs with the Spinal Cord, is alone sufficient
for  its execution; and  Mr. Grainger has sufficient!^ established the same, by experiment
upon puppies whose brain had been removed.  He adds that, as one of the puppies lay on
its side, sucking the  finger which was  presented to  it,  it pushed out its feet in the same
manner as young pigs exert theirs against the sow's dugs.  On the whole, however, the act
of suction belongs more to the Respiratory ganglion (so to speak) than to the Stomato-gastric
system of nerves; and hence we  can understand why, even in the highest animals, it should'
be purely reflex; the movements of Respiration being so from  the first, whilst those ordi-
narily concerned at a later period in the  Ingestion of the food are more directed by sensa-
tion and volition.   The actions of the  mammary fcetus of the kangaroo, described by Mr.
Morgan, furnish a very interesting exemplification of the same function of the  Spinal Cord;
this creature, resembling an  earth-worm in appearance, and only about fourteen lines in
length, with a brain corresponding in degree of development to  that of a human fcEtus of
the ninth week, executes regular, but slow, movements of respiration, adheres firmly to the
point of the nipple,  and moves its limbs when disturbed.  The milk is forced  into the oeso-
phagus by a compressor muscle, with which the mamma of the parent is provided.  " Can it
be imagined," very justly asks Mr.  Grainger, ':that in this case  there are sensation and vo-
lition, in what can be proved anatomically to be a foetus'?"

   387.  The   Sphincter  muscle,  which  guards the  Cardiac  orifice  of  the
stomach, appears  to be under the  influence of  the Spinal  system  of  nerves.
It is usually closed; but  it  opens when there  is a sufficient  pressure on  it,
made by the accumulated  food  propelled by  the  movements of the  oesophagus
above;  and it then  closes again, so  as to  retain  the  food in  the stomach.
That this closure is due to reflex  action appears from the fact that, when the
nerves supplying the muscle are  divided,  the sphincter  no longer contracts,
and the food  regurgitates  into  the  oesophagus.   The  opening of  the  cardiac
orifice is one  of the  first of the  changes, which occur in the  act of vomiting.—
With regard to the degree, in which the movements of the Stomach, that have
so important a share in  the Digestive operation, are dependent upon the Spinal
system, and are  consequently of a reflex nature, it is difficult to  speak with

  *  Hence originated one of Sir  C. Bell's early errors.   He found that an ass, in which the
infra-orbital branch of  the fifth was divided, would not  pick up oats with its lip, although
they were in  contact with it; hence he concluded that its power of motion was destroyed,—
when it was  in reality only the sensation necessary to excite the will to cause the motion,
that was deficient.
     26 
302
FUNCTIONS OF THE NERVOUS SYSTEM.
 certainty,  owing to the contradictory  results  obtained  by different  experi-
 menters.   These contradictions, however, seem partly due to a diversity in
 the nature of the animals experimented on.  It seems to be well established,
 by the researches of Reid, Valentin, and others, that distinct movements may
 be excited in the Stomach of the Rabbit, if distended with food, by irritating
 the Par Vagum soon after the death of the animal;  these movements seem to
 commence from  the cardiac orifice, and then to spread  themselves in a sort
 of peristaltic manner along the walls of the stomach; but no such movements
 can be excited if the  stomach be empty.   Various experiments  upon living
 animals have led to a similar conclusion; food taken in shortly before or sub-
 sequently to its  division, having  been found to be only dissolved on the sur-
 face of the mass, where it was in contact with  the  mucous membrane.  But
 these experiments  have  been made for the most part upon Herbivorous
 animals, such as horses, asses, and  rabbits; whose  food is bulky and difficult
 of solution, requiring to be  constantly changed in its  position, so  that every
 part of it may be successively brought  to the exterior.  On the  other hand,
 Dr. Reid found, in his  experiments upon  Dogs, that, after the first shock of
 the operation had gone  off, solution  of  the  food in the stomach, and  absorp-
 tion of  chyle, might take place; and hence it may be inferred, that no influ-
 ence of this  nerve upon the muscular parietes of  the  stomach is essential to
 digestion in that species.   This conclusion  harmonizes  well, therefore, with
 the fact already stated respecting the absence of such  influence in the lower
 parts of its oesophagus; and it njay, perhaps, be explained by the considera-
 tion, that the natural  food of the dog is much  less bulky and more  easy of
 solution, than that of the animals already named; so that  there is not so much
 need of the  peculiar  movement, which is in them  so important an aid to  the
.process of reduction.—The muscular walls of the stomach appear to be called
 into reflex contraction in the act of Vomiting;  the  mechanism of which will
 be considered hereafter  (§ 505).
   388.  That the ordinary peristaltic movements of the Intestinal canal, from
 the stomach to the  rectum, may take place without any connection with  the
 nervous system, being  due to  the  direct stimulation of the  contact of food,
 there is now ample evidence; and though some may yet be found to deny  the
 Hallerian doctrine, that muscular fibre  possesses in itself the property of con-
 tractility, so much additional evidence of  its truth has been recently adduced
 whilst the doctrine itself is so conformable to the  analogy supplied by other
 vital phenomena, that it will be here unhesitatingly adopted. (See Chapter  V.)
 Some Physiologists still  suppose, that  the peristaltic  movements of the  ali-
 mentary canal are  due to a sort of reflex action, taking  place  through  the
 ganglia of the Sympathetic system of nerves, especially, of course, the semi-
 lunar.  This supposition, however, has little or no  evidence to support it; for
 it has been  fully proved  that the muscular contractions will continue, long
 after the tube has been separated  from its  nervous connections  through its
 whole extent; and the  only evidence in its  favour is  derived  from the con-
 tractions, which may sometimes be induced in  parts of the tube which are at
 rest, when the Sympathetic nerves supplying them  are  irritated.   The  ex-
 periments of Valentin, however,—by which the fact  that such  contractions
 may be induced (which has been denied  by some) is clearly substantiated,—
 also show that the  motor influence does not originate in the Sympathetic gan-
 glia, but in the Spinal Cord.  The  following are the general results  of  up-
 wards of  three  hundred experiments, so far as they apply to this subject.—
 The pharynx may not  only be excited  to contraction by irritation of the pha-
 ryngeal branches of the Par Vagum, or of the roots of the Spinal Accessory,
 from which their motor power is derived (as will be hereafter explained), but
 also by stimulating the roots of the first two Cervical nerves; and the lower 
                REFLEX ACTIONS.--MOVEMENTS OF STOMACH.             303

part of the  oesophagus in the neck is made  to  contract peristaltically from
above downwards, by  irritation of the roots of the first three  Cervical nerves,
and of the cervical portion of the Sympathetic, through  which last the former
evidently operate.  The thoracic  portion of the oesophagus  is made to  con-
tract, by irritation of the lowest Sympathetic ganglion  of the neck, and of
the higher thoracic ganglia, and also of the roots  of the lower Cervical spinal
nerves.  Muscular contractions of the stomach are produced, by irritation of
the roots of the 4th, 5th, 6th, and 7th Cervical nerves, and  of the  first tho-
racic in the  rabbit;  so  that  a distinct furrow is  evident between the cardiac
and pyloric  portion of the  viscus ;  and the lower  the nerve  irritated, the
nearer the pylorus do the contractions extend.   Irritation of  the first thoracic
ganglion of  the Sympathetic produces the same  effect.  Contractions of the
intestinal tube, varying in place  according to the  part of the  Spinal  Cord ex-
perimented on, may be excited by irritation of the roots of the dorsal, lumbar,
and sacral nerves, and of the trigeminus  ; and similar effects  are produced by
irritation of  the lower part of the  thoracic  portion,  of the lumbar, and of the
sacral portions of the Sympathetic,—also of the  splanchnic, and of the gastric
plexus.
  389.  From these facts it  is evident, that  the  movements of the Intestinal
tube may be  influenced by the  Spinal  Cord ; and that what is commonly
termed the Sympathetic nerve, is the channel of that influence, by the fibres
which  it derives from the Spinal system.  But it by no means thence follows,
that the ordinary peristaltic actions of the muscles in question are dependent
on a stimulus reflected through the spinal  cord, rather  than  on one directly
applied to themselves.   It is clear that, although  these movements are of the
first importance to the welfare of the system, such  means of sustaining them
are feeble, compared to those which we  find provided for the maintenance of
the distinctly-reflex  actions  of  deglutition, respiration,  &c.   The  difficulty
with which  any evidence can be obtained of the connection, is  a  sufficient
proof of this.  On the other hand, we do know that these peristaltic move4-
ments are influenced by particular states of mind, or  by conditions of the bodily
system ; and  the connection just traced satisfactorily accounts for this, and is
itself sufficiently explained.   The intestinal  tube, then,  from the stomach to
the rectum is  not dependent upon  the  Spinal cord for its contractility, but is
enabled to propel its contents by its own inherent powers ; still we  find that
here, as  in other instances,  the  nervous  centres exert a general control  over
even the Organic functions,—doubtless for the purpose of  harmonizing them
with each other, and with the conditions of the organs of Animal life.
  390.  The Muscular Coat of the Bladder appears, like that  of the Intestinal
tube, to be ordinarily  excited to  contraction, rather  by direct  stimulation  than
by the agency of the Spinal nerves.  It  is not, however, altogether  removed
from the influence of the Spinal  Cord; for the experiments of Valentin have
shown that a connection exists, as in the former case, through the Sympathetic
nerve,  affecting not only the bladder but  also the ureters.  That physiologist
states,  that a very distinct and powerful  peristaltic  action of the ureter,  pro-
ceeding from the  kidneys to the bladder, may be produced, by irritating  the
abdominal ganglia of the Sympathetic, or the roots of the superior abdominal
Spinal nerves; and that strong contractions of the bladder are excited, by irri-
tation of the inferior portion of the abdominal Sympathetic, but especially of
its sacral portion, and  of the roots of the middle and inferior nerves of the
Spine.   In these, as in former cases, no  effect is produced by irritation of the
Spinal Nerves, unless the portion of the  Sympathetic  connected with the  par-
ticular organ be entire.
  391.  On examining the outlets by which the excretions are voided, we find
that they are placed, like the entrances, under the guardianship of the Spinal
Cord;  subject, however, to  some  control on  the part of the Will.   In  the 
304
FUNCTIONS OF THE NERVOUS SYSTEM.
lowest animals, the act of discharging excrementitious  matter is probably as
involuntary, as are the acts immediately concerned in the introduction of  nu-
triment ;  and it is performed as  often as  there is anything to be got rid of.
In the higher classes, however, such discharges are much less frequent;  and
reservoirs are provided, in which the excrementitious matter may accumulate
in the intervals.   The associated movements required to  empty  these, are
completely involuntary in their character; and  are  excited by  the quantity,
or stimulating quality, of the contents of the reservoir.   But, had volition  no
control over them, great inconveniences would ensue; hence sensation is ex-
cited by the same stimulus,  which produces  the  movements ; in order that,
by arousing the will, the  otherwise involuntary  motions may be restrained
and directed.—There  can be little  doubt, from  the experiments of Dr. M.
Hall,  as well as from other considerations, that the associated movements, by
which the contents  of the  rectum  and  bladder  are  discharged, correspond
much with those  of  Respiration ; being in their own nature excito-motor, but
capable of a certain  degree  of  voluntary restraint and assistance.  The acts
of Defecation and Urination chiefly depend  upon the combined contraction
of the abdominal  muscles, similar to  that which is concerned in the expiratory
movement; but, the glottis being closed, and the diaphragm fixed, the expulsor
power is restricted to the contents of the abdominal cavity ;  and so long as the
sphincter  of the cardia remains closed, the force  must act downwards, upon
the walls  of the rectum and bladder,—the contents of the one or the other of
these cavities, or  of  both, being expelled, according  to  the  condition of their
respective sphincters.  These actions are doubtless assisted by the contrac-
tion of the walls of the rectum and bladder themselves; for we sometimes find
their agency sufficient to expel the  contents of the  cavities, when  there is  a
total paralysis of the ordinary  expulsors,—provided  that the sphincters be at
the same  time sufficiently relaxed.   This is  more especially the case, when
their  power is augmented  by increased  nutrition.   For example,  in many
cases  of  disease  or  injury of the Spinal Cord, the  bladder ceases to expel
its contents, through the interruption of the circle of reflex  actions; but after
a  time, the necessity for drawing  off the urine  by the catheter is found to
exist  no longer; the  fluid is  constantly expelled as soon as it has accumulated
in small quantities.   In such  cases, the  mucous  coat is  found  after death to
be thickened and inflamed;  and the  muscular coat to be greatly increased in
strength, and contracted upon itself.   It would seem, then,  that the abnormal
irritability of the mucous membrane, and the  increased nutrition of the mus-
cular substance which appears  consequent upon  it, enable the  latter to expel
the urine  without the assistance of the ordinary expulsors.
   392. On the other hand, the sphincters which  antagonize the expellent ac-
tion,  are usually  maintained in a state of moderate contraction, so as to afford
a constant check  to the egress of the contents of  the cavities;  and this  con-
dition has been fully proved by Dr.  M. Hall, to result  from their connection
with  the Spinal Cord, ceasing completely when this is interrupted.   But the
sphincters are certainly in part controlled by the  will, and are made to act in
obedience to  the warning given by sensation ;  and  this voluntary power  is
frequently destroyed by injuries of the Brain, whilst the Spinal  Cord remains
able  to perform  all its  own  functions,  so that  discharge  of  the  urine  and
ieeces occurs.—In their moderate  action, the expulsors and the  sphincters
may  be regarded as  balancing  one  another,  so  far as their reflex action  is
concerned,—the  latter having rather  the predominance, so  as to restrain the
operation of the former.  But, when the quantity or quality of the contents
of the cavity  gives  an  excessive  stimulus  to  the  former, their action pre-
dominates, unless the will is put  in force  to  strengthen  the  resistance of
the sphincter ; this  we are  frequently experiencing, sometimes to our great 
          REFLEX ACTIONS.--MOVEMENTS OF GENITAL ORGANS, ETC.      305

discomfort.   On the  other hand, if the stimulus is  deficient, the will must
aid the expulsors, in order to  overcome that resistance which  is due to  the
reflex contraction of the sphincters; of this also we may convince ourselves,
when a sense of propriety, or a prospective regard to convenience, occasions
us to evacuate the contents of the rectum or bladder without a natural call to
do so.
   393. Movements of the Genital Organs.—The muscular contractions in-
volved in the Emissio Seminis  are clearly  of  a reflex nature ;  being inde-
pendent of the will  and not capable of restraint by it, when once  fully excited;
and being producible in no other way, than (like those concerned in Degluti-
tion)  by a particular local irritation.  That this  irritation need not amount to
a sensation, is proved by cases already referred to (§ 372);  and it  has been
also  shown by  experiment, that section of the  Spinal  Cord  in the lumbar
region does not  prevent the act from being  performed, the lower  division only
being concerned in  the reflexion of the impression.   It further appears, from
the experiments of  Valentin, that the Spinal Cord may operate on the Genital
organs through the  Sympathetic  system.   Contractions  were excited  in  the
vas deferens vesiculae  seminales, especially of the Guinea Pig at the time of
heat,  by irritation of the inferior  lumbar and highest sacral portions  of  the
Sympathetic;  and  the Fallopian  tubes, as well  as the Uterus  itself, may be
excited to contraction,  by irritation of the same  nerves as those  which excite
the rectum,—namely, the lower lumbar and first sacral  nerves of the  Spine.
This  last fact is  important, in regard to the rationale of the operation of  certain
medicines, such as  aloes, which  are known to have an influence"'on both
parts.—In regard to the act of Parturition, there would seem reason to believe,
from  the evidence of cases  of paraplegia, that, of the muscles whose operation
is associated  in it, the diaphragm, abdominal muscles,  &c, are  called  into
action (as in defecation) through the Spinal Cord; but that the contractions
of the Uterus itself are but little dependent  on its connection with the nervous
centres.   Of the reason why the  muscles, which were up to that time inert,
should then combine in this extraordinary manner, and with such remarkable
energy, Physiology can afford  no  certain  information.  There can be little
doubt, however, that the stimulus  usually originates in the uterus, or in some
of the neighbouring organs which are incommoded by the  pressure;  but it
may also  result from  some  condition  of the general system, in which the
uterus itself is but little concerned.  It is an interesting  fact, which  has been
more  than once  observed, that the foetus may be expelled from the dying body
of the mother, even  after the respiratory movements have ceased.   This would
appear due to  the contraction of the Uterine fibres alone, which, like those of
the heart  and alimentary canal, retain their  irritability longer  than  those  of
the muscles supplied  by the cerebro-spinal nerves; and the power  of these
would be unopposed  by the resistance which   they ordinarily have  to en-
counter; since the tension  of all the muscles  surrounding the outlet would be
destroyed, by  the^cessation of the activity of the  Spinal system of  nerves
(§ 398).
  394. Protecting  Agency of  the Spinal Cord.—From the foregoing  details
it appears, that one  of  the chief functions of the  Spinal Cord is to control the
orifices of the various open cavities of the  body; and this function evidently
has safety, as well as convenience, in view.   It has been manifestly designed
by the All-wise  Creator, that the Glottis should close against agents injurious
to the organs within;  and that  the effort to vomit should be  excited by the
attempt to swallow  substances so  nauseous as to induce loathing.—There is
another protective influence exerted by  it, of a still more remarkable nature.
It has been ascertained by Dr. M. Hall  that,  if the functions  of  the Brain be
suspended or  destroyed, without injury to  the Spinal system of nerves, the
                                  26* 
306
FUNCTIONS OF THE NERVOUS SYSTEM.
Orbicularis muscle will contract, so as to occasion the closure of the eyelids,
upon the tarsal margin being touched with a feather.   This fact is interesting
in several points of view.   In the first place, it is a characteristic example of
pure reflex action; occurring under circumstances in which volition cannot be
imagined to guide it, and in which there is no valid reason  to believe that sen-
sation directs it.  Further, it explains the almost irresistible nature of the tend-
ency to winking, which is performed at short intervals by the contraction of the
Orbicularis muscle; this is evidently a Spinal action, capable of being in some
degree restrained (like that of respiration) by the will, but only until such time
as the stimulus (resulting perhaps from  the collection of  minute particles of
dust upon the eyes, or from  the dryness of its surface  in consequence of
evaporation), becomes too strong to  be any longer  resisted.  Again, we have
in sleep or in apoplexy an  example of this  purely spinal  action, unbalanced
by the influence of the will, which,  in  the waking state, antagonizes  it by
calling the levator palpebrae into action.  As soon as the will ceases to act, the
lids droop, and close  over the  eye in order to protect it; and if those of a
sleeping  person be separated by the hand, they.will be  found  presently to
return.   Here, as in  studying the respiratory  and other  movements, we are
led to perceive, that  it is  the Brain alone, which is torpid during sleep,  and
whose functions are  affected by this torpidity.  As Dr. M. Hall very justly
remarks, the Spinal system never sleeps; it is constantly in activity; and it is
thus that, in all periods and phases of Life, the movements  which are essential
to its continued maintenance are kept up without sensible effort.
   395. The closure  of the  Pupil against a strong light, is  another movement
of the same  protective  tendency.    The  channel, through which  that just
named is performed, is  completed by the first branch of the  Fifth  and  the
Portio Dura of the seventh.  The  contraction  of  the  pupil is  immediately
caused by the Third pair, or Motor Oculi; as is easily shown by irritating the
trunk of that nerve and observing the result.  But it is not  easy to speak with
certainty as to the  afferent nerve, by which the motor influence is  excited.
Although the contraction of the  pupil is usually in close accordance with the
sensation occasioned by the impression of light upon  the  retina, yet there is
no want of  evidence to prove that the sensation of light is not always neces-
sary ; for, even when the sight of both eyes has  been entirely destroyed by
amaurosis, the regular actions have been witnessed in the pupil, in accordance
with  varying degrees of  light impinging  on the retina.   This  fact may be
explained in two ways.   It may either be imagined that the requisite stimulus
is not that of light conveyed through the Optic nerve; but that of heat con-
veyed through the ophthalmic branch of the Fifth  pair.  Or it may be  still
supposed, that the motion  results from an impression upon the retina, which
impression, being conducted to the Sensorium, ordinarily produces a sensation;
whilst in these curious cases, no sensation is produced, on account of  a  dis-
ordered state of the  part of the  ganglionic centre in which the Optic nerve
terminates;  though some filaments  of that  nerve, being  connected with the
Third pair by means of a  distinct tract of vesicular  matter, can produce a
reflex action through  it, although no sensation intervene.   In either view, the
rarity of the occurrence  is at once  accounted  for; since in most  cases of
amaurosis, the disease lies in the trunk of the nerve, and thereby checks both
its spinal and its encephalic actions.
   396. The Physiologist  has  not  at present any knowledge of any similar
protective movements, in the Human being, designed to keep the organ of Hear-
ing from injury; but there can be little  doubt that those which we are constantly
witnessing in other animals, possessing large external  ears, are reflex actions
excited by the irritation  applied  to them.   In  regard to the Nose, we find a
remarkably  complex action—that of Sneezing—adapted to  drive off any cause 
              REFLEX ACTIONS.--MOVEMENTS OF LOCOMOTION.           307

of irritation (§ 381).  It will hereafter be shown that the stimulus is conveyed,
in this case, not through the Olfactory nerve, but through the Fifth pair;  so
that it is not dependent upon the excitement of the sensation of Smell.  The
act of Coughing, also, may be regarded as  of a protective character; being
destined to remove  sources of irritation from the air-passages.   The automatic
movements, performed by the limbs of Frogs  and  other  animals, when their
connection with the brain has been  cut off (§§ 306, 370) appear destined to
remove these parts  from sources  of irritation or injury; and they may thus be
rightly placed under the same category.
   397. Movements of Locomotion.—Lastly, we have to inquire how far the
Reflex function of  the Spinal Cord is concerned in the locomotive actions of
the lower  extremities in Man.   It will be  remembered  that, in the Dytiscus
whose head had been removed  (§ 328), the stimulus of the contact of water
immediately excited regular and continued locomotive actions which lasted
for some time.  So in the cases  already quoted (§§ 366—368), when the con-
trol of the will over the lower extremities  was lost, powerful muscular  actions
were  excited  in  them, through  the Spinal Cord alone.   In the healthy con-
dition of the Human system, when the Will is controlling all the movements,
which are not immediately concerned in the maintenance and regulation of
the organic functions, no such actions can  be excited : but in proportion as its
control is lost, does  the independent power of the Spinal Cord  manifest itself.
The more such actions are of a  simple rhythmical character, similar to those
of Respiration, the  more  does it seem that they may with probability be re-
ferred to the  Spinal system;  and if  we attribute to this  (as we can scarcely
help doing) the rapid vibration of the wings of Insects, there seems no reason
why  we should  not  extend the same view  to the  wings  of Birds.  Such an
explanation of their movements  will account for their occasional continuance,
without apparent fatigue, during a period through which no known voluntary
effort  can endure; for it  is one of the  attributes of the Spinal system of
nerves, well pointed out  by Dr. M.  Hall, that the exercise  of the muscles
excited by it does  not occasion  fatigue, the  sense of which is  Cerebral only.
It would seem  to the Author more probable, however, that those movements
which guide the body, and  which must themselves be directed by Sensation,
are to  be  referred  to a class intermediate between  the Voluntary and the Re-
flex, which may be properly termed Consensual.  Numerous actions, in Man,
which  were at first Voluntary, appear at last to be performed as instinctively
or intuitively, as they are  in  the lower animals from the commencement of
their  existence.   (See the next Section.)
   398. Influence on Muscular Tension.—The various muscles of the body,
even  when there  is the  most  complete  absence  of  effort, maintain, in  the
healthy state of the system, a certain  degree of firmness,  by their antagonism
with  each  other; and if any set of muscles be completely paralyzed, the op-
posing muscles will  draw  the  part on which they act, out of its position of
repose;  as is well  seen in the  distortion of the face, which is characteristic
of paralysis of  the facial nerve on one side.   This condition has been desig-
nated as  the tone  of the Muscles; but this term  renders it liable to be con-
founded with their  tonic contraction, which is also concerned  in maintaining
their  firmness, but  which operates in  a very different manner.  The latter is
dependent upon the simple contractility of the muscle ; and is  exhibited alike
by the striated and  the non-striated forms  of muscular fibre, but more espe-
cially by the latter (§ 593).   On the other hand, the condition now alluded  to,
which may perhaps  be appropriately termed  their tension, is  the result of a
moderate though continued excitement of that contractility, through the nerv-
ous centres.  It has been proved by Dr. M. Hall, that the Muscular Tension
is not dependent upon the influence of the Brain ; but upon that of  the Spinal 
308
FUNCTIONS OF THE NERVOUS SYSTEM.
Cord ;  as the following experiments demonstrate.—" Two Rabbits were taken;
from one the head was removed;  from the other also the head was removed,
and the spinal marrow was cautiously destroyed with a sharp instrument: the
limbs of the former  retained a certain  degree  of firmness  and  elasticity;
those of the second were perfectly lax."  Again:—"The limbs and tail of  a
decapitated Turtle possessed a certain degree of firmness  or tone, recoiled on
being drawn from their position, and moved with energy on the application of
a stimulus.   On withdrawing  the spinal marrow gently out  of its canal, all
these phenomena ceased.   The limbs were no longer obedient to stimuli, and
became perfectly flaccid, having lost  all their resilience.  The sphincter lost
its circular form and  contracted state, becoming  lax, flaccid,  and shapeless.
The tail was flaccid, and unmoved on the application of stimuli."  It is further
remarked by Messrs. Todd and Bowman, that ' a decapitated frog will con-
tinue in the sitting posture through the influence of the spinal cord ;  but im-
mediately this organ is removed, the limbs fall apart."
  399.  This operation  of the  Spinal Cord is doubtless but a peculiar mani-
festation of its ordinary reflex function.  We  shall hereafter  see (Section 5)
how much the  influence of the will in producing the active contraction of  a
muscle, is connected with  sensations  received from it; and  it seems highly
probable, that the impression  of the  state  of the muscle, conveyed by the
afferent fibres proceeding from it to the spinal cord, is sufficient to excite this
state of moderate tension  through the motor nerves, arising  from the latter.
Such a view  derives probability from the fact, which must have fallen under
the observation of almost every one, that most reflex actions become increased
in energy if resistance is made to them.  Of this we have familiar examples
in the  action of the  expulsor muscles, which operate in defecation, urination,
and  parturition, if, when they are strongly excited, their  efforts be opposed
by the  will acting on the sphincters,  or by mechanical  means.  Many forms
of convulsive movement exhibit the same tendency ; their violence being pro-
portional to the  mechanical force used to restrain them.*  Here it  is evident
that the impression  of resistance, conveyed  to the Spinal Cord, is the source
of the increased energy of its motor influence;—from which we may  fairly
infer that the moderate resistance, occasioned by the natural antagonism of the
muscles, is  the  source of their continued and moderate tension, whilst they
are  under the influence of the Spinal  Cord.   This constant though gentle
action  serves  to keep up the nutrition of the muscles, which are paralyzed to
the  will; and this is still more completely maintained, if the portion of the
nervous centres, with which they remain connected, is  so unduly irritable,
that the muscles are called into contraction upon the slightest excitation, and
are thus continually exhibiting twitchings, startings, or more powerful convuls-
ive movements.  It is  upon the  state of nutrition of the muscles, that their
contractility depends, as will be  shown hereafter (§ 588) ;  and  hence  the
Spinal  Cord  has  an indirect influence upon this peculiar property, which  is
more likely to be retained, when the muscle  is still subject to  the influence of
the  Spinal Cord, though cut off from that of the Brain, than  when it is com-
pletely paralyzed by the  entire  cessation of  the influence  of the  nervous
centres.
   400. Pathological Phenomena.—It would  not be right to conclude this
account of the principal functions of the Spinal Cord, without adverting to
some of the leading Pathological  applications  of the physiological doctrines

  *  Hence the absurdity of the common practice  of endeavouring  to prevent the move-
ments of the limbs and body, in convulsive paroxysms, by mechanical constraint. Nothing
should be attempted but what is requisite to prevent the sufferer from doing himself an in-
jury. 
REFLEX ACTIONS.--PATHOLOGICAL PHENOMENA.           309
which have  been developed  in  it; although they will  hereafter be passed
under a more general review (Section  8).  A large part  of these were  first
pointed out by Dr. M. Hall;* and they are receiving continual and important
extensions from his  own labours and  those  of other practical inquirers.   It
may be remarked, in the first  place, that the  power of the whole Spinal  sys-
tem is capable of being morbidly diminished  or augmented.  It may even be
for a time almost completely suspended, as in Syncope;  which state may be
induced by sudden and violent impressions,  either of a mental  or physical
nature, that operate upon the whole nervous  system  at once,—commencing,
however, in  the brain.  It is to be remarked  that, in recovering from these, it
is  the Spinal system of which the activity is  first  renewed,—the respiratory
movements  recommencing,  and  the power  of  swallowing  being  restored,
before any voluntary actions can be performed.  A corresponding state may
be induced in particular portions of the system by concussion;  as is seen in
severe injuries of the Spinal  Cord, which are almost invariably followed for
a time by the suspension of its  functions.   Again, the power of the whole
Spinal Cord  may be diminished by various causes, such as enfeebled circula-
tion, pressure, &c.;  and then  we have torpidity of the whole muscular sys-
tem.  If oppression  exists in the Brain, the functions of  the Medulla oblon-
gata will be especially affected; and if it be prolonged and sufficiently severe,
Asphyxia will result from the interruption of the respiratory movements which
it occasions.
   401.  On the other hand, the excitability of the whole Cord, or of particu-
lar parts of it, may be morbidly increased.   This  is  especially seen in ordi-
nary Tetanus and the artificial Tetanus induced by  Strychnine; in which the
slightest external stimulus is sufficient to induce  reflex actions in their most
terrific forms.  It is  interesting to remark, that in this formidable disease the
functions of the muscles controlling the various orifices are those most affected;
and it is by the spasms affecting the organs of respiration or  deglutition,  that
life is commonly terminated.—Various remedial agents will probably be found
to operate, by occasioning increased excitability in some particular segments
of the Cord; so that the  usual stimuli applied  to the  parts connected with
these, will occasion increased  muscular tension.   This seems to be the case,
for example,  in regard to the influence of aloes  on  the  rectum and uterus,
cantharides on the neck of  the bladder and adjoining parts, and secale cornu-
tum on the uterus.   The mode of influence of cantharides is illustrated  by a
curious case, related  by Dr.  M. Hall, of a young lady who lost the power of
retention of urine, in consequence of a  fatty tumour in the spinal  canal, which
gradually severed the Spinal Cord, and induced paraplegia.  The power of
retaining the urine was always  restored for a time by  a dose of  tincture
of cantharides, which augmented the excitability of the segment of the cord,
with which the sphincter vesicae is  connected.—The researches  of Valentin,
when grafted (as it were) on the doctrines of Dr.  M. Hall, afford the key to
the explanation of the numberless  sympathetic  influences of the organs of
nutrition, &c, upon one another; by showing that  they are all connected with
the Spinal  Cord;  and that the muscular  structure, with which  they are all
provided, may be  excited to contraction  through  it.   And, lastly, the more
recent observations of Dr. M. Hall, in regard to the peculiar excitor power
that belongs to the nervous fibres distributed on various  serous  and fibrous
membranes, will probably lead, when they have been fully carried out, to the
explanation of the various convulsive  actions, that result from pressure or
irritation affecting these parts.

  * See especially his Treatise on the Diseases and Derangements of the Nervous System. 
310
FUNCTIONS OF THE NERVOUS SYSTEM.
  a. It has been pointed out by Messrs. Todd and Bowman (Physiological Anatomy, Vol. I.
p. 315), that the Spinal  Cord  of the  male frog, at the season of copulation, naturally pos-
sesses a state of most extraordinary excitability.  The thumb of each anterior extremity at
this season, becomes considerably enlarged; as is well known to Naturalists. " This enlarge-
ment is caused principally by a considerable  development of the papillary structure of the
skin which covers it; so that  large papilla?  are formed all over it. A male frog, at this
season, h^s an irresistible propensity to cling to any object, by seizing it between his anterior
extremities.   It  is in this way that he seizes  upon, and clings to the female; fixing his
thumbs to each side of her abdomen, and remaining there for weeks, until the ova have been
completely expelled.  An effort of the Will alone could not Iceep up the grasp uninterrupt-
edly for so long a time, yet so firm is the hold, that it can with difficulty be relaxed.  What-
ever is brought in the way of the thumbs, will  be caught by the forcible contraction ,of the
anterior limbs; and hence we  often find frogs clinging blindly to a piece of wood, or a dead
fish, or some other substance which they may chance to meet  with.  If the finger be placed
between the anterior extremities, they will grasp it firmly; nor will they relax their grasp
until they are separated by force.  If the animal be decapitated, whilst the finger is within
the  grasp of its anterior extremities, they still continue to hold on firmly.  The posterior half
of the body may be cut away, and yet the anterior extremities will still cling to the finger;
but  immediately that  the segment of the cord,  from which the anterior extremities derive
their nerves, has been removed, all their motion ceases.  This curious instinct only exists
during the period of sexual excitement;  for at other periods the excitability of the anterior
extremities is considerably less  than that of the  posterior."
  402. Nerves of the  Spinal System.—The  nerves which minister to the
functions of the Spinal  Cord, conveying to it the impressions  made on the
periphery, and transmitting its motor influence to the muscles,—are not those
alone which are ordinarily designated  as Spinal nerves; for several of those,
which pass forth through  the base of the cranium, and which are commonly
described as  Cephalic  nerves, belong  to the  same  category.   The  general
characters of the  Spinal nerves, their mode  of connection with  the Spinal
Cord by two sets of  roots, and  the  presence  of ganglion upon the posterior
root, have already been adverted to (§ 344).  The anterior roots are usually
the smaller; and this is particularly the case with those of the cervical nerves,
in which the posterior roots  are  of remarkable comparative size.  In the First
Cervical or Sub-occipital pair, the  anterior  roots are sometimes  wanting; but
there is then a derivation  of fibres from the Spinal Accessory, or from the
Hypoglossal, or from both.   The two  roots  of the ordinary Spinal nerves
unite immediately beyond  the ganglion, which is situated on the posterior one;
and the trunk thus formed separates immediately into two divisions,—the an-
terior and posterior,-—each of which contains both afferent and motor fibres.
These divisions, of which  the anterior  is by far the larger, proceed to the ante-
rior and posterior parts of  the body respectively; and are chiefly distributed to
the  skin  and the muscles.  The anterior branch is that which communicates
with the sympathetic nerve.
  403. The pair of nerves commonly designated as the Fifth of the Cephalic
series, or as the Trifacial, is the one which more  nearly resembles the  ordi-
nary Spinal  nerves (as was long since  pointed out by Sir  C.  Bell), than does
any other of those originating within the cranium.   It  possesses two distinct
sets of roots, of which one is much larger than the other ;  on the larger root,
as on the posterior and larger root of the Spinal nerves, is  a distinct ganglion;
and the fibres arising from  the  smaller root do not blend with  the others, until
after the latter have  passed through this ganglion.   The  trunk of the  nerve
separates, as  is well known,  into three divisions,—the  Ophthalmic, the Supe-
rior Maxillary, and  the Inferior Maxillary; and it can be easily shown,  by
careful dissection, that the  fibres of the smaller root pass into the last of these
divisions alone.   When the  distribution of this nerve  is carefully examined,
it is found that the first and second divisions of it  proceed almost entirely to
the skin and  mucous  surfaces; a very small proportion, only, of their  fibres
being lost in the muscles :  whilst of the branches of the third division, a largf
number are  distinctly muscular.  Hence analogy, and the facts supplied by 
SPINAL NERVES.--FIFTH PAIR, OR TRIFACIAL.
311
anatomical research, would lead to the conclusion, that the first two divisions
are nerves of sensation only, and that the third division combines sensory and
motor  endowments.   Such an inference  is fully borne  out by experiment.
When  the whole trunk is divided within the cranium by the penetration of a
sharp instrument (which Magendie, by frequent  practice, has been able to ac-
complish), evident signs of acute pain are given.   After the incision has  been
made through the skin, the  animal  remains  quiet until the nerve is touched;
and when it is pressed or divided,  doleful cries are uttered, which continue
for some time, showing the painful effect of the irritated state  of the cut ex-
tremity.   The common sensibility of all the  parts supplied by this nerve  is
entirely destroyed on the affected side.   The jaw does not hang loosely, be-
cause it is partly kept up by the  muscles of the other side; but it falls in a
slight degree;  and its  movements  are  seen, when carefully observed,  to be
somewhat oblique.   If the  trunk be divided on each side, the whole  head is
deprived of sensibility; and  the animal carries it in a curious vacillating man-
ner, as  if it were a foreign body.

                                    Fig. 150.
  A diagram showing the Fifth pair of nerves with its branches. 1. The origin of the nerve by two roots.
2. The nerve escaping from the crus cerebelli.  3. The Gasserian ganglion.  4. Its ophthalmic division.
5. The frontal nerve, giving off the supra-trochlear branch, and escaping on the forehead through the
supra-orbital foramen.  6. The lachrymal nerve.  7. The nasal nerve, passing at 8 through the anterior
ethmoidal foramen, and giving off the infra-trochlear branch.  9. The communication of the nasal nerve
with the ciliary ganglion. 10. A small portion of the third nerve with which the ganglion is seen com-
municating; the ganglion givesoffthe ciliary branches from its anterior aspect.  11. The superior maxil-
lary nerve. 12. Its orbital branch.  13. The two branches communicating with Meckel's ganglion; the
three branches given off from the lower part of the ganglion are the posterior palatine nerves. 14,14.
The superior dental nerves, posterior, middle, and anterior. 15. The infra-orbital branches distributed
upon the cheek. 16. The inferior maxillary nerve.  17. Its anterior or muscular trunk.  18. The pos-
terior trunk; the two divisions are separated by an arrow.  19. The gustatory nerve. 20. The corda
tympani joining it at an acute angle. 21. The submaxillary ganglion.  22. The inferior dental nerve.
23.  Its mylo-hyoidean branch.  24. The auricular nerve, dividing behind the articulation of the lower
jaw, to reunite and form a single trunk.  25. Its branch of communication with the facial nerve. 26. Its
temporal branch.

   404.  If the anterior or  Ophthalmic branch only be  divided, all the parts
supplied by it are found to have lost  their sensibility, but their  motions  are
unimpaired; and all experiments  and  pathological observations  concur in at- 
312
FUNCTIONS OF THE NERVOUS SYSTEM.
tributing to it sensory endowments only.   The only apparent exception is  in
the case of the Naso-Ciliary branch; since there is good reason to believe that
the long root of the ciliary ganglion, and the long ciliary nerves, possess motor

                                        A view of the distribution of the Trifacial or Fifth
                                      pair; 1, orbit; 2,  antrum highmorianum; 3, tongue;
                                      4, lower jaw-bone; 5, root of the fifth pair, forming
                                      the ganglion of Gasser; 6, first branch of the fifth pair,
                                      or ophthalmic-; 7; second branch of the fifth pair, or
                                      superior maxillary ; 8, third branch of the fifth pair, or
                                      inferior maxillary; 9, frontal branch, dividing into ex-
                                      ternal and internal  frontal nerves; 10, lachrymal
                                      branch of the fifth pair; 11, nasal branch; just under
                                      the figure is the long root of the lenticular or ciliary
                                      ganglion and a few of the ciliary nerves; 12, internal
                                      nasal nerve, disappearing through the anterior eth-
                                      moidal foramen; 13, external nasal nerve; 14, external
                                      and internal frontal nerve;  15, infra-orbitary nerve;
                                      16, posterior dental  branches; 17, middle dental
                                      branch; 18, anterior dental nerve:  19, terminating
                                      branches of the infra-orbital nerve, called the labial
                                      and palpebral nerves; 20, subcutaneous malse, or or-
                                      bitar branch ; 21, pterygoid, or recurrent nerve, from
                                      Meckel's ganglion; 22, five  anterior branches of the
                                      third branch of the fifth pair; 23, lingual branch of the
                                      fifth, joined by the chorda tympani; 24, inferior dental
                                      nerve ; 25, its mental branches; 26, superficial tempo-
                                      ral nerve; 27, auricular branches;  28, mylo-hyoid
                                      branch.]


powers ; but these appear to be derived from the Sympathetic nerve.   When
the whole nerve, or its anterior branch, is divided in  the  rabbit, the pupil is
exceedingly contracted, and remains  immovable; but in dogs and pigeons it
is dilated.   The  pupil of  the other eye is scarcely affected;  or, if its dimen-
sions be changed, it soon returns to  its natural state.   The  eyeball speedily
becomes inflamed, however;  and the inflammation usually runs on  to suppu-
ration and complete disorganization.    The commencement of these changes
may be  commonly noticed within twenty-four hours after the operation;  and
they  appear to be due to the want of the protective secretion, which (as will
be explained when the direct influence of the nervous system upon the organic
functions is considered), is necessary to keep the mucous  surface of the eye
in its healthy condition, and which is not formed when the sensibility of that
surface is  destroyed.—The Superior Maxillary branch, considered in itself,
is equally destitute of motor endowments with the ophthalmic;  but its  con-
nections with other nerves, through the spheno-palatine ganglion and its anas-
tomosing  twigs,  may introduce a  few motor fibres  into  it.—The  Inferior
Maxillary branch is the  only one which possesses motor  as  well as sensory
endowments from its origin; but its different subdivisions possess these endow-
ments in varying proportions, some being almost exclusively motor, and others
as completely of  a  sensory character.  The  latter is  probably the nature of
the Lingual branch; and  there seems good reason to believe, as will hereafter
be shown, that this ministers not only  to the  tactile sensibility of the tongue,
but to the sense of  Taste.  The muscles put in action  by this division of the
Fifth pair, are solely those concerned in  the masticatory movements.
   405.  The Third, Fourth, and Sixth pairs, together make  up  the appara-
tus of motor nerves, by which the  muscles  of the Orbit  are called into  ac-
tion.   The Third pair supplies the greater number of the muscles ; the Fourth
[Fig. 151.
 
CRANIAL NERVES.--THIRD TO SEVENTH.
313
[Fig. 152.
being confined to  the  superior ob-
lique, and the Sixth  to the abdu-
cens.  Of these nerves, the Third
pair is the only one which exhibits
any appearance of sensibility, when
its trunk is irritated ;  but this  sen-
sibility is  not nearly so  great  as
that of the Fifth pair; and it may
be doubted whether it is really pos-
sessed by the Third, in virtue  of
its direct  connection with the nerv-
ous  centres,  or whether it is not
imparted by the anastomosis of that
nerve  with the Fifth,—some  fila-
ments of  which  may pass back-
wards as well as forwards, so as to
confer sensibility  on  the  trunk  of
the Third, above as well as beyond
their point of entrance.—The pe-
culiar mode in  which these motor
nerves ordinarily excite  the  mus-
cles to  action, will be considered
in  the next  Section.   Although
commonly   ranked   as   cephalic
nerves, they  have  no direct  con-
nection with  the  Cerebrum; their
real origin being  from the upper
part of the  Medulla Oblongata, and
those prolongations of it which are
known as the Crura Cerebri.  The
roots of the  Third pair  may  be traced  into direct connection with the Cor-
pora Quadrigemina;  a fact of considerable physiological importance, as will
hereafter  appear.   The chief actions of a purely reflex nature, to which this
group of  nerves ordinarily ministers, are  the government  of the  diameter  of
the pupil,  which is accomplished through  the Third  pair ; and the rolling  of
the eyeball beneath the  upper  lid  during sleep, as well  as in the efforts  of
sneezing, coughing, &c.   But irregular  movements  of the  eyeballs, which
must be referred to the same group, are continually seen to accompany various
other forms of convulsive action.
   406. The Portio  Dura of  the Seventh pair, or Facial  nerve, has  been
supposed, since the first researches  of Sir C.  Bell, to be  a nerve of motion
only; but some recent physiologists have maintained,  that it both  possesses
sensory endowments, and arises  by a double root.  According  to Valentin,
however, who experimented on the roots exposed within the cranium, it pos-
sesses no  sensory endowments at its  origin ; since,  when these roots  were
touched, the animals  gave no  signs  of pain, though  violent muscular move-
ments were excited in the  face.   Subsequently to its  first entrance into the
canal by  which it emerges, however, it anastomoses with other nerves ; and
thus sensory  fibres are introduced into it from many  different sources,—ante-
riorly, from the Fifth pair, and posteriorly, from the Cervical nerves,—which
cause  irritation of several  of its branches to produce pain.   The number
and situation  of the anastomoses  vary  much in  different animals  ; so that it
is impossible to make any very  comprehensive  statement in  regard to them.
—Experimental researches leave no doubt that the Portio Dura is the general
motor nerve of the face ;  ministering to the influence of volition and Emo-
     27
  A view ofthe Third,  Fourth and Sixth pairs of
Nerves; 1, ball ofthe eye and rectus externus muscle;
2, the superior maxilla; 3, the third pair, or motores
oculi, distributed to all the muscles of the eye except
the superior oblique and external rectus; 4, the fourth
pair, or pathetici, going to the superior oblique muscle;
5, one of the branches of the seventh pair; 6, the sixth
pair, or motor externus, distributed to  the external
rectus  muscle;  7, spheno-palatine ganglion and
branches; 8, ciliary nerves from the lenticular gan-
glion, the short root of which is seen to connect it with
the third pair.] 
314
FUNCTIONS OF THE NERVOUS SYSTEM.

               Fig. 153.
  The distribution of the Facial,'nerve, and the branches of the Cervical plexus.  1 .The facial nerve,
escaping from the stylo-mastoid foramen, and crossing the ramus of the lower jaw; the parotid gland
has been removed in order to see the  nerve more distinctly. 2. The posterior auricular branch; the
digastric and stylo-mastoid filaments are seen near the origin of this branch.  3. Temporal branches,
communicating with (4) the branches of the frontal nerve. 5. Facial branches, communicating with
(6) the infra-orbital nerve.  7. Facial  branches, communicating with (8) the mental nerve.  9. Cervico-
facial branches, communicating with  (10) the superficialis colli nerve, and forming a plexus (11) over
the sub-maxillary gland.  The distribution of the branches of the facial in a radiated direction over the
side ofthe face, constitutes the pes anserinus.  12. The auricularius magnus nerve, one ofthe ascending
branches of the cervical plexus. 13. The occipitalis minor, ascending along the posterior border ofthe
sterno-mastoid muscle. 14. The superficial and deep descending branches of the cervical plexus. 15.
The spinal accessory nerve, giving off a branch to the external surface of the trapezius muscle. 16.
The occipitalis major nerve, the posterior branch of the second cervical nerve.

tion, and also being the channel of the Reflex movements concerned  in respi-
ration and other associated movements of  the  muscles;  but not being in the
least concerned in the  act of mastication.

   a. The distinctness of the Spinal and Encephalic actions  of this nerve, is made evident
by the not unfrequent occurrence of paralysis in either of them, without the other being
affected.—Thus we  may see the mouth drawn to one side  (in consequence of the loss of
tone, which the muscles have  experienced), and all the Reflex and Emotional actions of
the face performed only on one side;  and yet Voluntary power may  remain unaffected ; so
that, in ordinary winking, the lid of the affected side does not close; though the patient can
shut the eye by an effort of the will.—On the other hand,  the tension of the muscles may
remain unimpaired, and all their  Reflex and Emotional actions may be performed as usual;
and yet distortion may be at once apparent, when  Voluntary actions  are attempted; in con-
sequence of paralysis of the Cerebral portion of the nerve on one side.

   407. The functions of  the Glosso-Pharyngeal nerve  have been heretofore
alluded to  in part;  but there still remain several questions to be discussed  in
regard to them.   Reasons have  been given for the belief  that  it is chiefly an
afferent nerve,—scarcely having any direct  power of exciting muscular con-
traction, but conveying impressions to  the Medulla Oblongata, which produce
reflex  movements ofthe other nerves  (§ 384).   This view of its function has
been deduced by Dr. Reid  from minute anatomical  investigation, and from  a
large   number of experiments.   Some experimenters  assert, that they have
succeeded in exciting direct  muscular actions through its trunk ;  but these ac-
tions seem to be limited to  the stylo-pharyngei and to the palato-glossi mus- 
FUNCTIONS OF THE PAR VAGUM.
315
cles.  Much controversy has taken place on the question, whether this nerve is to
be regarded as ministering, partly or exclusively, to the sense of  Taste; and
many high authorities have ranged themselves on each side.   The  question
involves that of the function of the Lingual branch of the Fifth pair; and it is
partly to be decided by the anatomical relations of the two nerves respectively.
The glosso-pharyngeal is principally distributed on the mucous surface of the
fauces, and on  the  back of the  tongue.   According to Valentin, it  sends  a
branch forwards, on either side, somewhat beneath the lateral margin, which
supplies the edges and inferior surface of the tip of the tongue, and inosculates
with  the Lingual branch of the Fifth pair.  On the other hand, the upper sur-
face of the front of the tongue is supplied by this lingual branch.  The experi-
ments of Dr. Alcock, whose conclusions  are  borne  out by Dr.  J. Reid, de-
cidedly support the conclusion, that  the  gustative  sensibility of this part of
the tongue is due to the  latter nerve, being evidently impaired by division of
it.  Moreover, cases are by no means rare, in which  the gustative sensibility
of the anterior part of the tongue  has been destroyed, with its tactual sensi-
bility;,, when  there was  no  reason to suppose that any other than the Fifth
pair of nerves was  involved.*  On the other hand, it is equally  certain, that
the sense of taste is  not destroyed by section of the Lingual nerve  on each
side;  and it seems also well ascertained, that it is impaired  by section of the
Glosso-pharyngeal  nerve.  Considering how nearly allied  is the sense  of
Taste to that of Touch, and bearing in mind the  respective distribution of
these two nerves, it  does not seem difficult to arrive at the conclusion, that both
nerves are concerned in  this function  ; but there seems good reason to believe
the Glosso-pharyngeal to  be exclusively that through which the  impressions
made by disagreeable  substances taken into the mouth are propagated to  the
Medulla Oblongata, so as to produce nausea, and to excite efforts  to vomit.
   408. The functions of the Par  Vagum at its roots have lately been made
the subject of particular  examination by various  experimenters; some  of
whom (for instance, Bischoff, Valentin, Longet, and Morganti), have concluded
that it there possesses no motor power, but is entirely a sensory, or rather, an
afferent nerve.  According to these, if the  roots be carefully separated from
those of the Glosso-Pharyngeal, and (which  is  a matter of some difficulty)
from  those of the spinal Accessory  nerve, and be then irritated, no movements
of the organs  supplied by it can be observed;  whilst, if the roots be  irritated
when in  connection with the nervous centres, muscular contractions, evidently
of a reflex character, result from the irritation; and strong evidences  of their
sensibility are also  given.   It has  been further  asserted that, when the roots
of the Spinal  Accessory nerve are irritated,  no indications of sensation  are
given; but that the muscular parts supplied by the Par Vagum, as well as by
its own trunk, are made to contract, even when the roots are  separated from
the nervous centres; so  that these roots must be regarded as the channel of
the motor influence, transmitted to them from the Medulla Oblongata.   When
the Par Vagum swells  into the jugular ganglion,  an interchange of fibres takes
place  between it and the Spinal Accessory;  and  it seems clear that the pha-
ryngeal branches, which  are among  the  most  decidedly motor of all  those
given off from the Pneumogastric, may in great part be traced backwards into
the Spinal Accessory.  These  statements  confirm  the  idea  of  Arnold and
Scarpa,—that  the Par Vagum and Spinal Accessory are  together analogous to
a spinal  nerve, the former answering to the posterior roots, and the  latter to
the anterior.—But, on the other hand, an equally numerous and  trustworthy
set of experimenters (among whom may be mentioned J. Reid, Muller, Volk-
mann, and Stilling) are opposed to  this opinion ;  maintaining that the  Par Va-
gum has  motor roots of its own, and that the Spinal Accessory possesses sen-
* Romberg, in Mailer's Archiv., 1838, Heft in. 
316                     FUNCTIONS  OF THE NERVOUS SYSTEM.
Fig. 154.
[Fig. 155.
r
VA&
  Origin and distribution ofthe Eighth pair of nerves.
1, 3, 4, the medulla oblongata; 1, the corpus pyrami-
dale of one side; 3, the corpus olivare ; 4, the cor-
pus restiforme ; 2, the  pons Varolii; 5, the  facial
nerve ; 6, the origin ofthe glosso-pharyngeal nerve ;
7, the ganglion of Andersch; 8, the trunk ofthe nerve;
9, the spinal accessory nerve; 10, the ganglion ofthe
pneumogastric nerve;  11, its plexiform ganglion;
12, its trunk; 13, its pharyngeal branch forming the
pharyngeal plexus (14) assisted  by a branch from the
glosso-pharyngeal  (8) and one from the superior la-
ryngeal nerve (15); 16, cardiac  branches;  17, recur-
rent laryngeal branch;  18,  anterior  pulmonary
branches;  19, posterior pulmonary branches; 20,
oesophageal plexus ; 21, gastric  branches;  22, origin
ofthe spinal accessory nerve; 23, its branches dis-
tributed to the sterno-mastoid muscle; 24, its branches
to the trapezius muscle.
  A view of the distribution of the Glosso-Pha
ryngeal Pneumogastric  and Spinal Accessory
Nerves, or the Eighth pair ;  1, the inferior max-
illary nerve;  2,  the  gustatory nerve; 3,  the
chorda-tympani ;  4, the  auricular nerve; 5, its
communication with the  portio duTa; 6, the fa-
cial nerve coming out of the stylo-mastoid fora-
men ; 7, the glosso-pharyngeal nerve ; 8, branch-
es to the stylopharyngeus muscle ; 9,  the pha-
ryngeal  branch   of the  pneumogastric nerve
descending to form the pharyngeal plexus; 10,
branches of the  glosso-pharyngeal to the pha-
ryngeal plexus ; 11, the pneumogastric nerve ;
12, the  pharyngeal plexus; 13, the  superior la-
ryngeal branch ;  14, branches to the pharyngeal
plexus; 15, 15, communication ofthe superior
and  inferior  laryngeal  nerves;  16,  cardiac
branches ; 17, cardiac branches  from the right
pneumogastric nerve ; 18, the left cardiac gan-
glion and plexus; 19. the recurrent or inferior
laryngeal nerve;  20, branches  sent  from  the
curve of the recurrent nerve to the pulmonary
plexus;  21, the anterior pulmonary plexus; 22,
22, the  oesophageal plexus.] 
FUNCTIONS OF THE PAR VAGUM.
317
sory roots ; and affirming that irritation of the  roots of the Spinal Accessory
produces little or no effect on the muscles  supplied by the trunk of the Par
Vagum.   The fact appears to  be, that the roots of these two nerves are  so
commingled, that it is difficult to say what belong exclusively to each.   Some
of the fibres usually considered  to belong to the  Spinal  Accessory, are occa-
sionally seen  to  connect themselves with the  roots of the Par Vagum, even
before the ganglion is  found upon it.  And it seems most probable, that  the
roots of the Spinal Accessory are chiefly motor, and those of the Par Vagum
chiefly afferent; that they inosculate with each other in a  degree which may
vary in different  species, and even in different  individuals; and that  the Par
Vagum may thus  derive additional  motor fibres from the Spinal Accessory,
whilst it supplies  that  nerve with additional afferent fibres.—In regard to  its
trunk, there can  be no doubt that  the Par Vagum is to  be considered vas a
nerve of double endowments ; although it  is certain  that these endowments
are very differently distributed amongst its branches.  That the nerve  is capa-
ble of  conveying those  impressions  which become sensations when commu-
nicated to the sensorium, is experimentally proved by the  fact that, when  its
trunk is pinched, the animal gives signs of acute  pain ; but it is also evident
from the painful consciousness we occasionally have of an abnormal condition
of the organs which it supplies.  Thus, the  suspension  of the respiratory
movements  gives  rise  to a feeling of the greatest uneasiness, which must  be
excited by impressions conveyed through this  nerve from  the lungs ;  and  an
inflamed state of  the walls of the  air-passages causes  the contact of cold and
dry air to produce distressing pain and irritation.  Yet, of the ordinary im-
pressions conveyed from these organs, which are concerned in producing the
respiratory movements, and in regulating the actions of the glottis, we are not
conscious.  The  same may be said of the portion of the nerve distributed
upon the alimentary tube.   The  pharyngeal branches are  almost exclusively
motor, the afferent function being performed by the Glosso-pharyngeal; whilst
the oesophageal and gastric are both afferent and motor, conveying impressions
which excite reflex movements in  the muscles of those parts, but which  do
not become sensations  except under  extraordinary circumstances.
   409. The section ofthe Par Vagum produces, as would readily be expected,
great disorder of the functions of Respiration and Digestion, to which it minis-
ters.   It is an operation which has been very frequently performed; and the
statements of its results vary considerably amongst each other, being generally
influenced, in some degree, by the preconceived views of the experimenter. *
The section of the Par Vagum, when practised with the view of ascertaining
the influence of the nerve upon the lungs and stomach, is usually made in the
neck, between the origins of the superior and inferior (or recurrent) laryngeal
branches. Hence the muscles of the  larynx  are paralyzed (§ 379); and, if the
animal should struggle violently, the ingress of air is likely to  be obstructed
by the flapping down  of the arytenoid cartilages, and by the closure of the
glottis.   This is especially the case in young animals, in which the larynx is
small.  But in those that are full grown, and have a large larynx, an adequate
quantity of air may still find its way through the aperture, if the animal refrain
from any violent effort.   In a considerable number of Dr. Reid's experiments,
therefore, he did  not find  it necessary to introduce the trachea-tube, which
other experimenters have generally employed; an opening was made into the
trachea, however, in those instances in which, from any cause, the entrance  of
air was obstructed.

  * The Author employs, as in his opinion the most worthy of confidence, the experiments
of Dr. J. Reid (Edinb. Med. and Surg. Journ., vols. xlix. and li.), on whose accuracy he has
strong personal reasons for placing reliance; and whose anatomical and pathological attain-
ments are such as to render him fully competent to the  task.
                                   27* 
318
FUNCTIONS OF THE  NERVOUS SYSTEM.
   410. The functions of the Pharyngeal and Laryngeal branches ofthe Pneu-
mogastric having been already explained (§§ 378, 379, and 385), Ave may now
proceed to  its Pulmonary division.   In regard to this, we have  to notice,  that
its endowments are chiefly afferent; its most important  office being, to  con-
vey  to  the  Medulla Oblongata the impression produced  by venous  blood in
the capillaries of the lungs, or of carbonic acid in the air-cells.  This impres-
sion  may give rise, as we have seen, to respiratory movements, without pro-
ducing sensation; but if it be from any cause stronger than usual, the sense of
uneasiness  which it occasions is  very distressing.   The  impression may be
imitated by pressure on the nerve; which occasions an immediate inspiratory
movement.   Hence the chief function of the afferent portion of the pulmonary
division of the Par Vagum, is to serve as an excitor  to the respiratory move-
ments ;  which are consequently diminished in frequency, when the trunk is
divided on both sides.—But this division  also contains motor fibres, which
are distributed upon the muscular fibres surrounding  the  bronchial tubes ;  and
the  experiments of Dr. Williams,  which  have been recently  confirmed  by
Longet and Volkmann, agree in proving, that the calibre of the bronchial tubes
can  be caused to contract in a very considerable degree, by stimuli applied to
this  nerve,  and especially by electricity.
   411. Various alterations are produced in the Lungs, by section of the Pneu-
mogastric nerves.   The order in which these arise, and  the causes  to which
they are immediately due, constitute  very interesting subjects of investigation;
and  the knowledge of them will probably throw light upon many ill-understood
morbid phenomena.

   a.  In the first place, it has been fully established by Dr. Reid, that section of the Vagus
on one side  only does not necessarily, or  even generally, induce disease of that lung; and
hence the important inference may be drawn, that the nerve does not exercise any immediate
influence on its functions. When both Vagi are divided, however, the animal rarely survives
long; but its death frequently results from the disorder of the digestive functions.  Never-
theless, the power of digestion is sometimes restored sufficiently to re-invigorate the animals;
and their lives  may then be prolonged for a considerable time.  In fifteen out of seventeen
animals experimented on by Dr. Reid, the lungs were found more or less unfit for the
healthy performance of their functions. The most common morbid changes were a congested
state of the blood-vessels, and an effusion of frothy serum into the air-cells and bronchial tubes.
In eight out of the fifteen, these changes were strongly marked.  In some portions of the
lungs, the quantity of blood was so great as to render them  dense.  The degree of conges-
tion varied in  different parts of the same  lung; but it was generally greatest at the  most
depending portions.  The condensation was generally greater, than could be accounted for
by the mere congestion of blood in the vessels; and probably  arose from the escape of the
solid parts of the blood into the tissue of the lung.   In some  instances the condensation was
so great, that considerable portions of the lung sank in water, and did not crepitate; but
they did not present the granulated appearance of the second stage of ordinary pneumonia.
In five cases  in which the animals had survived a considerable time, portions of the lungs
exhibited the second, and even the third stages of pneumonia, with  puriform  effusion into
the small bronchial tubes; and in two, gangrene had supervened.
   b.  One of the most important points to  ascertain, in an investigation of this kind, is the
first departure from a healthy state;—to decide whether the effusion of frothy reddish serum,
by interfering with the usual change in the lungs, causes the congested state of  the pulmo-
nary vessels  and the laboured  respiration; or whether the effusion is the effect of a pre-
viously congested state of the blood-vessels.  The  former is the opinion of many physiolo-
gists, who have represented the effusion of serum as a process of morbid secretion, directly
resulting from the disorder of that function produced by the  section ofthe nerve; the latter
appears the unavoidable inference from the carefully-noted results of Dr. Reid's experiments.
In several of theset only a very small quantity of frothy serum was found in the air-tubes,
even when the lungs were found loaded with blood, and when the respiration before death
was very laboured.  This naturally leads us to doubt, whether  the frothy serum is the cause
of the laboured respiration, and of the  congested state of the pulmonary vessels, in those
cases where it is present; though there can be no doubt that, when  once it is effused, it must
powerfully tend to increase the difficulty of respiration, and still further to impede the cir-
culation through the lungs.  Dr. R. has satisfied himself of an important point, which has 
FUNCTIONS OF THE PAR VAGUM.
319
been overlooked by others—that this frothy fluid is not mucus, though occasionally mixed
with it; but that it is the frothy serum so  frequently found in cases where the circulation
through the lungs has been impeded  before death.  From this and other facts, Dr. R. con-
cludes " that the congestion of the blood-vessels is the first  departure from the healthy state
of the lung, and that the effusion of'frothy  serum is a subsequent effect."
  c. The next point, therefore, to be inquired into, is the cause of this congestion; and this
is most satisfactorily explained, upon  the general principles regulating the circulation of the
blood, by remembering that section of the  Par Vagum greatly diminishes the frequency of
the respiratory movements, and that the quantity of air introduced into the lungs is, there-
fore, very insufficient for the due aeration of the blood.  "We shall hereafter see reason to
regard it as one of the best established principles in Physiology, that the activity of the
changes which the blood undergoes  in the capillary vessels, does, in some way or other,
regulate its movement through them;—that, when these  changes  are  proceeding with ac-
tivity, the capillary circulation is proportionably accelerated;—and that when they are ab-
normally low in degree, the movement of the blood in the capillaries is stagnated. There
is now abundant evidence, in regard to the  Pulmonary circulation  in particular, that, to pre-
vent the admission of oxygen in the lungs, either by causing the animal to breathe pure
nitrogen or hydrogen, or by occlusion of the  air-passages,  is to bring the circulation through
their capillaries to  a speedy check.   Hence we should at  once be led to infer, that diminu-
tion in the number of Respiratory movements would produce the same effect; and as little
or no difference in their frequency is produced by section  of one Vagus only, the usual ab-
sence of morbid changes in  the lung  supplied by it is fully accounted for.  The  congestion
of the vessels, induced by insufficient aeration, satisfactorily accounts not only for the effusion of
serum, but also for the tendency to  pass  into the inflammatory condition, sometimes  pre-
sented by the lungs, as by other organs similarly affected.   Dr. Reid confirms this view, by
the particulars of cases of disease in the human subject, in which the lungs presented after
death a condition similar to that observed in the lower animals  after section of the Vagi;
and in these individuals, the respiratory movements had been much less frequent than natu-
ral during the latter part of life, owing to  a torpid condition of  the  nervous centres.  The
opinion (held especially by Dr. Wilson Philip) that section of the par vagum produces the
serous effusion, by its direct influence on the function of Secretion, is further invalidated by
the fact stated by Dr. Reid,—that he  always found the bronchial membrane covered with its
true mucus, except when inflammation was present.

   " The experimental  history  of the Par Vagum," it  is justly remarked by
Dr. Reid, "furnishes an excellent illustration of the numerous difficulties with
which the physiologist  has to  contend, from the impossibility of  insulating
any individual organ  from  its mutual actions and reactions, when he wishes
to examine  the  order and  dependence of  its  phenomena."   In  such investi-
gations, no useful inference can be drawn from one or two experiments only;
in order to avoid all  sources  of fallacy, a  large  number  must be made; the
points in which all  agree must be separated from others, in which  there is a
variation of results; and it must be  then inquired, to what the latter is due.
   412.  These observations apply equally to the  other principal subject of in-
quiry  in regard to  the functions of  the Par Vagum,—its influence  upon the
process of Digestion.   The results  obtained  by different  experimenters have
led to differences of opinion  as to its  action, no  less remarkable  than those
which have prevailed on the question just discussed.   Thus, in regard to the
afferent fibres of the  Gastric  division  of the nerve, some  physiologists main-
tain it to be by  impressions on  them alone, that the sense of hunger or satiety
is excited;  whilst others deny that they have  any power of transmitting such
impressions, which, according to them, do not originate in the stomach at all.
Dr. Reid has arrived  at the conclusion, from  his  numerous experiments, that
the Par Vagum is the channel through which the mind becomes cognizant of
the condition of the stomach;  but that it is not the sole excitor of the sense
of hunger.   Animals, which have sustained section of the nerve on both sides,
will eagerly take food,  if they  have  not received too  great a shock from the
operation ; but  they seem  to  experience no  feeling of satiety when the sto-
mach  is loaded.  This inference is confirmed by Valentin, who mentions that
puppies after the operation will take three times the same quantity of milk,
as uninjured individuals of the same age, so as greatly to distend the abdomen. 
320
FUNCTIONS OF THE NERVOUS SYSTEM.
The act of Vomiting has been  proved to  be excitable by impressions trans-
mitted through the Gastric branches of the  Par Vagum ;  although they con-
stitute by no means the only channel, through which the various muscles con-
cerned in it may be called into combined action (§ 505).
   413. The question of the influence of the motor fibres of the Pneumo-
gastric, upon the muscular walls of the stomach, has been already in part dis-
cussed (§  387).   Although it seems unquestionable that they have the power
of stimulating these muscles to contraction, yet there is evidence that the
movements of the stomach, which are most essential to  digestion, may take
place without it.  Thus Dr. Reid found,  in  several of his  experiments, that
food was not only digested in the Stomach, but propelled into the Duodenum,
subsequently to  the operation.   It seems very probable, however, that a tem-
porary suspension of these movements (as of other  independent functions of
the stomach) may be the first effect of tbe operation.
   414. It is necessary here to  stop to notice, on account of the currency
which it has obtained, the  doctrine of Dr. Wilson Philip;—that the Par Va-
gum controls the secretion of the Gastric  fluid;  and that its division  checks
the secretion.  He further stated, that the  influence of Galvanism propagated
along the nerve, would re-establish the secretion. This statement has been quoted
and re-quoted, as an established physiological position ; and, when united with
the well-known  fact, that galvanism would excite muscular contraction, it has
seemed to Dr. W. Philip and other  physiologists  sufficient to establish the
important position, that galvanism and nervous influence are identical.   It has
been  disputed, however, by many other  experimenters;  who  have satisfied
themselves that  the secretion of gastric juice continues  after the operation;
and consequently, that the elaboration  of this product cannot be dependent on
nervous influence supplied by the Par Vagum, though doubtless in part regu-
lated  by it.   The first effects of the operation, however, are almost invariably
found to be  vomiting (in those  animals  capable  of  it), loathing of food, and
arrestment of the digestive process ; and it is not until after four or five days,
that the power seems re-established.   In the animals which died before that
time,  no indication of it could be  discovered by Dr. R.; in those which survived
longer, great emaciation took place; but when life was sufficiently prolonged, the
power of assimilation  seemed  almost completely restored.  This was the
case in four out  of the seventeen dogs experimented on ;  and the evidence of
this restoration consisted in the recovery  of flesh and blood by  the animals,
the vomiting of half-digested food permanently reddening  litmus paper, the
disappearance of a considerable quantity of  alimentary matter from the intes-
tinal canal, and the existence of chyle in the lacteals.   It may serve to account
in some degree  for the contrary results, obtained by other  experimenters, to
state that seven  out of Dr. R.'s  seventeen  experiments were performed before
he obtained  any evidence of digestion after the  operation;  and that the four
which furnished this followed one another almost in succession;  so that it is
easy  to understand why those  who  were satisfied with  a  small number of
experiments, should have been led to deny it altogether.

  [M.  Bernard has instituted fresh experiments to determine  this still-debated  question,
making use of the  artificial fistulous openings into the  stomach, invented by M. Blondlot.
A dog's digestion had been thus watched for eight days, and had always been well  effected.
On the ninth day, after a day's fast, M. Bernard sponged out the stomach, which contracted
on the contact of the sponge, and at once secreted a large quantity of gastric fluid ;  he then
divided the pneumogastric nerves in the middle of the neck, and immediately the mucous
membrane, which  had  been turgid, became  pale, as if exsanguine, its movements ceased,
the secretion of gastric fluid was instantaneously put a stop to, and a  quantity of ropy neutral
mucus was soon produced in its place.  After this, no digestion was duly performed, and
milk was no longer coagulated; raw meat remained unchanged, and the food (meat, milk,
bread and sugar, which the dog had before  thoroughly digested) remained for a long time 
FUNCTIONS OF THE PAR VAGUM.
321
 neutral, and at last  acquired acidity only from its own transformation into lactic acid.  In
 the stomachs of other dogs after the division of the nerves, he traced the transformation of
 cane-sugar  into grape-sugar in three or four hours; and in ten or twelve hours the trans-
 formation into lactic acid was complete.   In others, when the food Was not capable of an
 acid transformation, it remained neutral to the last. In no case did any part of the food pass
 through the peculiar changes of chymification.  In a last experiment, he gave to each of two
 dogs, in one of which he had cut the  nerves, a dose of emulsine, and half an hour after, a
 dose of amygdaline (substances which are innocent alone, but when mixed produce hydro-
 cyanic acid).  The dog, whose nerves were cut, died in a quarter of an hour, the sub-
 stances being absorbed unaltered and mixing in the blood: in the other, the emulsine was
 changed by the action of the gastric fluid  before the amygdaline was administered, and it
 survived.—Gazette Med., Juin 1, 1844,/rwn the Report of the Acad, des Sri., seance du 27 Mai,
 1844.—M. C]
   a. Another series of experim6nts was performed by Dr. Reid, for the purpose of testing
 the validity of  the results obtained by Sir B. Bfodie, relative to the  effects of section of the
 Par Vagum upon the secretions of the stomach, after the introduction of arsenious acid into
 the system.  According to that eminent Surgeon and Physiologist, when  the poison was
 introduced after the Par Vagum had  been divided on each  side, the quantity of the pro-
 tective mucous and  watery secretions was much  less than usuaT", although obvious marks of
 inflammation were present.  In order to avoid error as much as possible, Dr. Reid made five
 sets of experiments, employing two dogs  in each, as nearly as possible of equal size and
 strength, introducing the same quantity of the poison  into the system of each in the same
 manner, but cutting the Vagi in one, and leaving them entire in the other.  This comparative
 mode of experimenting is obviously the only one admissible in such an investigation.  Its
 result was in eveiy instance opposed to the statements of Sir B.  Brodie; the quantity of the
 mucous and watery secretions of the stomach being nearly the same, in each  individual of
 the respective pairs subjected to experiment;  so that  they can no longer be referred to the
 influence of the Eighth pair of nerves.  Moreover, the appearances of inflammation were, in
 four out of the five cases, greatest in the animals whose Vagi were left entire; and this seemed
 to be referrible to the longer duration of their  lives after the arsenic had been introduced.
 The results of Sir B. Brodie's experiments may perhaps, be explained, by the speedy occur-
 rence of death in  the subjects of them, consequent (it  may be) upon the want of suffi-
 ciently free respiration, which was carefully guarded against by Dr. Reid.

   415.  So far as the  results of Dr. Reid's experiments  may be trusted to,
 therefore, (and the Author  is  himself  disposed  to rely on them almost im-
 plicitly,) all the  arguments which have been drawn  in favour of the doctrine
 that Secretion depends upon Nervous agency, from the  effects of lesion of the
 Vagi upon the functions of the Stomach,  must be set aside.   That this nerve
 has  an important influence on the gastric  secretion,  is evident  from the defi-
 ciency in  its  amount  soon  after  the operation, as well as  from other facts.
 But this is a very different proposition from  that  just alluded to; and the
 difference has been  very happily illustrated by Dr.  R.  "The movements of
 a horse," he  observes, " are independent  of the  rider on  his back,—in other
 words, the rider  does not furnish the conditions necessary for the movements
 of the  horse;—but  every one  knows how much these  movements  may be
 influenced by the hand  and  heel of the rider."   It  may  be hoped, then, that
 physiologists will cease  to adduce  the oft-cited  experiments of Dr. Wilson
 Philip, in favour of the hypothesis (for such it must  be termed) that secretion
 is dependent  upon nervous influence, and that  this is identical with  galvan-
 ism.—Additional evidence of their fallacy  is derived from  the fact mentioned
 by Dr. Reid, that the usual  mucous  secretions of the  stomach were  always
 found; and  they are  further invalidated  by  the testimony of  Muller, who
 denies that galvanism has any peculiar influence in re-establishing the gastric
 secretion, when it has been checked  by section of the nerves.
   416.  It only remains to notice  the influence of section of the  Vagi upon
the actions of the Heart.  It has been asserted by Valentin and other experi-
menters, that  mechanical  irritation of these  nerves,  especially at their  roots,
has a tendency to excite or accelerate the  heart's action; other experimenters,
however, have obtained none  but negative results.   Admitting, what seems
probable, that the Cardiac branches of the Pneumogastric have some influence 
322                FUNCTIONS OF THE NERVOUS SYSTEM.
upon the Heart's action, it remains to inquire whether that influence is essen-
tial to its movements;  and whether these nerves  form the channel, through
which  they are affected by emotions of the mind, or by conditions of the
bodily system.  In  regard  to  the  first  point,  no doubt can be  entertained;
since the regular movements of the heart are but little affected by section of
the  Vagi.   With  respect to the  second, there is more difficulty;  since the
number  of  causes, which may influence the  rapidity and pulsations of the
heart, is  very considerable.   For example, when the  blood is forced  on more
rapidly towards the heart, as in exercise, struggling, &c, the stimulus to its
contractions is more frequently renewed, and  they become more frequent;
and when the current  moves on more slowly, as in a state of rest,  their fre-
quency becomes proportionably diminished.  If the contractions of the heart
were not dependent  upon the blood, and their  number were  not  regulated by
the  quantity flowing into its cavities, very serious and  inevitably  fatal  dis-
turbances of the heart's action would soon result.  That this  adjustment takes
place otherwise than through the medium of the nervous centres, is evident
from the fact that, in  a dog, in which the  par vagum and  sympathetic  had
been divided in the  neck on each  side,  violent struggling, induced by alarm,
raised  the number of pulsations from 130  to 260 per minute.   It is difficult
to ascertain, by experiment upon the lower animals, whether simple  emotion,
unattended with struggling or other exertion, would affect the pulsation of the
heart, after section of the Vagi; but when the large proportion of the Sympa-
thetic nerves  proceeding to this organ is considered, and when it is also re-
membered  that irritation of the roots of the upper cervical  nerves stimulates
the action of the heart through these, we can  scarcely doubt  that both may
serve as  the channels of this influence, especially in such  animals as the  dog,
in which the two freely inosculate in the neck.
   417. In regard to the functions  of the Spinal Accessory  nerve, also, there
has been great difference of opinion; the peculiarity of its  origin and course
having led  to the belief, that some very especial purpose is answered by  it.
The predominance  of  motor fibres in its roots, its inosculation  with the Par
Vagum,  and its probable reception of sensory fibres from the latter whilst
imparting to it motor filaments, have been already referred to (§  408).  As  its
trunk passes through the foramen  lacerum, it  divides into two  branches;  of
which the  internal,  after giving off some filaments that assist in forming the
pharyngeal branch of the Par Vagum, becomes incorporated  with the trunk of
that nerve; whilst the  external proceeds  outwards, and is finally  distributed to
the sterno-cleido-mastoideus and  trapezius muscles,  some of  its  filaments
inosculating with those of the  cervical plexus.   When the external branch is
irritated, before it perforates the  sterno-mastoid muscles,  vigorous convulsive
movements of that muscle,  and of the trapezius, are produced; and the animal
does not give any signs of pain, unless the nerve is firmly compressed between
the forceps, or is included in a tight ligature.  Hence it may be  inferred, that
the functions of this nerve are chiefly motor, and that its sensory filaments are
few in number.  Further, when the nerve  has been cut across, or firmly tied,
irritation of the lower end  is attended by the  same convulsive movements of
the muscles;  whilst irritation of the upper end, in connection with  the spinal
cord, is unattended with any muscular movement.  Hence  it is  clear that the
motions occasioned by irritating it are of a direct, not of a reflex  character.
The same  muscular movements  are observed on irritating the nerve in the
recently-killed animal, as during life.

   a. According to Sir C. Bell, the Spinal Accessory is a purely Respiratory nerve, whose office
it is to excite the involuntary or automatic movements of the muscles  it  supplies, which
 share in the act of respiration; and he states that the division of it paralyzes the muscles to
 which it is distributed, as muscles of respiration; though they still perform the voluntary 
HYPOGLOSSAL NERVE.                          323
movements, through the medium of the spinal nerves.  Both Valentin and Dr. Reid, however,
positively deny that this is the case.  Dr. Reids method of experimenting was well adapted
to test the truth of the assertion.  Considering that, in the ordinary condition of the animal,
it might be difficult to distinguish the  actions of particular muscles, beneath the skin, when
those in the neighbourhood were  in operation; and also that the usual automatic movements
might be simulated by voluntary  action, when the breathing might be rendered difficult; he
adopted the following plan :—A small dose of prussic acid was given, to an animal, in which
the Spinal Accessory had been previously divided on one side; and after  the convulsive
movements produced by it had ceased, the animal was generally found in a state similar to
that which we sometimes see in apoplexy,—the action of the heart going on, the respirations
being slow and heaving, and the sensorial functions appearing to be completely suspended.
The Respiratory movements always  ceased before the  action of the heart; but they con-
tinued, in several of the animals experimented on, sufficiently long to allow the muscles of
the anterior part of the neck to  be laid  bare, so that accurate observations could be made
upon their contractions.  In the  dog and cat, the sterno-mastoid does not appear to have
much participation in the ordinary movements of respiration; for in several instances it
could not be seen to contract on either side, though the head was forcibly pulled towards the
chest  at each  inspiratory movement, chiefly by the action of the sterno-hyoid and thyroid
muscles. In two dogs and  one  cat, however, in which the head was fixed,  and these
respiratory movements were particularly vigorous,  distinct contractions were seen in the
exposed sterno-mastoid muscles, synchronous with the other movements of respiration: these
were, perhaps, somewhat weaker on the  side on which the nerve had been cut, but were
still decidedly present.  In  one  of these dogs,  similar  movements were  observed in the
trapezius, on the side on which the nerve had been divided.  As the condition of the animal
forbade the idea that volition could be the cause of these movements, it can scarcely be ques-
tioned that Sir C. Bell's statement was an erroneous one.  As far, therefore, as these experi-
ments afford any positive data, in regard to the functions of this nerve, it may be concluded
that they are  the same as those of the cervical plexus, with which  it anastomoses freely.
"Future anatomical researches," as Dr. Reid justly remarks, "may perhaps explain to us how
it follows this  peculiar course, without obliging us to suppose that it has a reference to any
special  function in the adult of the human  species."   Thus, the study of the history of
development has accounted  satisfactorily for the  peculiar course of the recurrent laryngeal,
which may be traced passing directly from the par vagum to the larynx, at a time when the
neck can scarcely be said to exist, and when that organ is buried in the  thorax.  As this
rises in the neck, the nerve, which  at first came off below the great transverse blood-vessels,
has both its origin and its termination carried upwards; whilst it is still tied down by these
vessels in the middle of its course.

   418. The Hypoglossal nerve, or Motor  Linguae, is the  only one  which,
in the regular order, now remains to be considered.   That the  distribution of
this nerve is restricted  to  the  muscles of  the  tongue, is a point very easily
established by anatomical research; and accordingly we find that, long before
the  time of Sir C. Bell, Willis spoke of it as  the  nerve  of the motions  of
articulation,  whilst to the Lingual  branch of the fifth  pair he  attributed the
power of exercising the  sense  of  taste; and he  distinctly stated,  that the
reason of this organ being  supplied with two  nerves  is its double  function.
The inference that it is chiefly, if not entirely, a motor nerve, which  has been
founded upon its  anatomical distribution, is supported  also by the nature of
its origin, which  is  usually from a single root, corresponding to the anterior
root of the  Spinal  nerves.   Experiment  shows that, when the trunk of the
nerve is stretched, pinched,  or galvanized, violent motions ofthe whole tongue,
even to its tip, are  occasioned;  and also, that similar movements take place
after division of the  nerve,  when the cut end  most distant from the brain is
irritated.  In regard to the degree in which this nerve possesses sensory  pro-
perties, there is some difference of opinion amongst physiologists, founded, as
it would  seem, on  a variation in this  respect between  different  animals.
Indications  of pain are usually  given, when the trunk is irritated after  its exit
from the cranium; but these  may proceed from its free anastomosis with the
cervical nerves, which not  improbably impart  sensory fibres  to it.   But  in
some  Mammalia, the hypoglossal nerve  has  been  found  to possess a small
posterior root with a ganglion: this is the  case in the ox, and also in the rabbit; 
324                 FUNCTIONS OF THE NERVOUS SYSTEM.
and in the latter animal, Valentin states that the two trunks pass out from  the
cranium through separate  orifices, and that, after their  exit, one may be shown

                                   [Fig. 156.
  The course and distribution of the Hypo-Glossal or Ninth pair of nerves; the deep-seated nerves of
the neck are also seen; 1, the hypo-glossal nerve; 2, branches communicating with the gustatory nerve;
3, a branch to the origin of the hyoid muscles; 4, the descendens noni nerve; 5, the loop formed wiih the
branch from the cervical nerves; 6, muscular branches to the depressor muscles of the larynx ; 7, a
filament from the second cervical nerve, and 8, a filament from the third cervical, uniting to form the
communicating branch with the loop from the descendens noni; 9, the auricular nerve; 10, the inferior
dental nerve ; 11, its mylo-hyoidean branch; 12, the gustatory nerve ; 13, the chorda-tympani passing to
the gustatory nerve; 14, the chorda-tympani leaving the gustatory  nerve to join the sub-maxillary
ganglion; 15, the sub-maxillary ganglion; 16, filaments of communication with the lingual nerve; 17,
the glosso-pharyngeal nerve ; 18, the pneumogastric or par vagum nerve; 19, the three upper cervical
nerves; 20, the four inferior cervical nerves; 21, the first dorsal nerve; 22, 23, the  brachial plexus; 24,
25, the phrenic nerve; 26, the carotid artery; 27, the internal jugular vein.]

to be sensory, and the  other  to  be  motor.   Hence, this  nerve, which is the
lowest of those that  originate in the cephalic prolongation of the spinal cord,
generally known as  the medulla oblongata, approaches very closely  in some
animals to the regular type of the  spinal nerves;  and  though in  Man it still
manifests an irregularity, in having only  a single root, yet this irregularity is
often shared by the first cervical nerve, which also has sometimes an anterior
root only.
   419.  The Hypoglossal nerve is distributed not merely to the tongue, but to
the muscles of the neck which are concerned in the movements of the larynx;
and the  purpose of  this distribution  is  probably to  associate  them in those
actions, which are necessary for articulate speech.   Though all the motions
of the tongue are performed through  the  medium of this nerve, yet  it would
appear,  from pathological  phenomena, to have at  least  two distinct connec-
tions with the nervous centres;  for in many cases of paralysis,  the masticatory
movements of the tongue  are but little  affected, when  the power of articula-
tion is much injured or totally destroyed : and the converse may be occasion-
ally noticed.   When  this nerve is paralyzed on  one  side, in hemiplegia, it
will be  generally observed that the tongue, when the patient is directed to put 
CEPHALIC NERVES IN GENERAL.
325
it out, is projected towards  the  palsied side of  the  face: this is due to the
want of action of the lingual muscles of that side, which do not aid in pushing
forward  the tip;  the point  is consequently directed only by the  muscles of
the other side, which will not act in a straight direction, when unantagonized
by  their fellows.   It is a curious fact, however, that  the hypoglossal nerve
seems not  to be always palsied on the same side with the facial, but sometimes
on  the other.   This  has  been suggested  to  be due to the origination of the
roots of this nerve from near the point, at which the pyramids of the medulla
oblongata  decussate;  so  that some of its fibres come off, like those of the
spinal nerves, without crossing;  whilst others are transmitted to the opposite
side, like those of the higher cerebral nerves ;  and the  cause of paralysis  may
affect one or other of these sets of roots  more particularly.   Whatever  may
be  the validity of this explanation, the circumstance is an interesting one, and
well worthy of attention.*
  420. The general character and arrangement of the  Cephalic nerves, as
distinguished  from  the ordinary Spinal, constitute a study of much interest,
when considered in relation  to Comparative  Anatomy,  and to Embryology. It
appears, from  what  has  been already stated, that  the Par Vagum, Spinal
Accessory, Glosso-pharyngeal, and  Hypoglossal nerves,  may be  considered
nearly in the light of ordinary Spinal nerves.   They all take their origin ex-
clusively in the Medulla Oblongata ; and the want of correspondence in posi-
tion, between their roots and those  of  the Spinal nerves, is readily accounted
for by the alteration  in  the direction  of the columns of the Spinal Cord,
which,—as long since pointed out by Rosenthal,  and lately stated prominently
by  Dr. Reid,—not only decussate laterally, but,  as it were, antero-posteriorly
(§ 353)*.   The Hypoglossal, as just stated, not unfrequently possesses a sen-
sory in addition to its motor root.  The  Glosso-pharyngeal,  which is princi-
pally an afferent nerve, is stated  by Arnold and others  to  have  a small motor
root; at any rate, the motor fibres which  answer to it  are to be found in the
Par Vagum.  That  the Par Vagum and   a  portion of the Spinal Accessory
together make up a spinal nerve, has been already stated as probable.
  421. Leaving these nerves out ofthe question, therefore, we proceed to the
rest.   Comparative anatomy, and the study of Embryonic development, alike
show that  the Spinal cord and Medulla Oblongata constitute the  most essen-
tial  part of the nervous  system  in  Vertebrata;  and  that  the Cerebral Hemi-
spheres  are superadded, as  it were,  to  this.   At an  early period of develop-
ment, the  Encephalon consists  chiefly of three vesicles, which  correspond
with  the ganglionic  enlargements of the  nervous  cord of the Articulata, and
mark three divisions of the  cerebro-spinal axis;  and, in accordance with this
view, the Osteologist is able to trace, in  the bones of  the cranium, the same
elements which would form three vertebrae, in a much expanded  and altered
condition.   However improbable such  an idea might seem, when the cranium
of the higher Vertebrata alone is  examined, it  at once reconciles itself to our
reason, when  we  direct  our attention to that of Reptiles   and  Fishes;  in
which classes the size of the Cerebral  or hemispheric  ganglia  is very small,
in comparison with that of the Ganglia  of special sensation ; and in which the
latter evidently form but a  continuation of the Spinal  Cord, modified in its
function;  so that, when we trace upwards  the  cavity of the  spinal column
into that of the cranium, we encounter  no material change, either in its size or

  * It may  be questioned, however, whether the Hypoglossal is really paralyzed on the op-
posite side from the facial in such cases.  An instance has been communicated to the Author
by Dr. W. Budd, in which the hypoglossal nerve was completely  divided on one side; and
yet  the tip of the tongue, when the patient was desired to put it out, was  sometimes directed
from and sometimes  towards the palsied side; showing that the  muscles of either half are
sufficient to  give any required direction to the  whole.
     28 
326                FUNCTIONS OF THE NERVOUS SYSTEM.

direction.   The three  pairs of nerves of  special sensation  make  their way
out through these three cranial vertebra?  respectively.   At a later  period of
development, other nerves are  interposed  between these ; which, being inter-
vertebral, are evidently more analogous to the Spinal nerves, both in situation
and function.   A separation of the primitive fibres of these takes place, how-
ever, during the progress of development, so that their distribution appears
irregular.   Thus the greater part of the sensory fibres are contained  in the
large  division of the Trigeminus;  whilst, of  the motor  fibres, the anterior
ones chiefly pass forwards  as the Oculo-motor and Patheticus; and  of the
posterior,  some  form the small division  of  the Trigeminus, and others unite
with the first pair from the Medulla Oblongata to form  the Facial.   This last
fact explains  the close  union which is  found in Fishes and some Amphibia,
between that nerve and those proceeding  more directly  from the Medulla  Ob-
longata.   According to Valentin, the Glosso-pharyngeal  is the sensory por-
tion ofthe first  pair from the Medulla Oblongata, of which the motor part is
chiefly comprehended in  the Facial nerve.   It  is very interesting to trace this
gradual metamorphosis from the character of the Spinal nerves, which  is ex-
hibited  in the Cephalic, when they  are traced upwards  from the Medulla Ob-
longata ; and this is shown also, in some  degree, in the nerves of special sen-
sation  (§ 446, a).  Although we are accustomed to consider the Fifth pair as
par eminence the Spinal  nerve of the head,  the foregoing statements, founded
upon the history of development, show  that the nerves of the Orbit really
belong to  its motor portion ; they may consequently be regarded as altogether
forming the first of the intervertebral or  Spinal nerves  of the cranium.  The
Facial and Glosso-pharyngeal  appear to constitute the second; whilst the Par
Vagum and Spinal Accessory, forming the third pair,  intervene between this
and the true spinal, of which the  Hypoglossal  may be considered as the first.

5. Of the Sensory  Ganglia and their Functions.—Consensual Movements.

   422. At the  base of the Brain in Man, concealed by the Cerebral Hemi-
spheres, but  still readily distinguishable  from  them, we find a series of gan-
glionic masses; which are in  direct connection with the nerves of Sensation;
and which appear to have functions quite  independent of those of the other
components of the Encephalon.—Thus anteriorly we have  the  Olfactive
ganglia, in what are commonly termed the bulbous expansions of the Olfactive
nerve.  That these are real ganglia, is proved  by their  containing grey or ve-
sicular substance ; and  their separation from the general mass of the Encepha-
lon, by the peduncles or footstalks commonly  termed the trunks ofthe Olfac-
tory nerves, finds its analogy in many species of Fish (§ 357).  The  ganglionic
nature of these masses is more evident in many of the lower  Mammalia, in
which the organ of smell is highly developed, than it is in Man, whose olfac-
tive powers are comparatively moderate.—At some distance behind these, we
have the representatives  of the Optic ganglia, in the Tubercula Quadrigemina,
to which  the principal  part of the roots of the  Optic nerve may be traced.
Although these bodies  are so small in Man, in comparison to the  whole En-
cephalic mass, as to be apparently insignificant, yet they are much larger, and
form a more evidently important part of  it in many of the lower Mammalia;
though still presenting the  same general aspect.—The Auditory ganglia do
not form  distinct lobes or projections ; but are lodged  in the substance of the
 Medulla Oblongata.  Their real character is most evident in certain Fishes, as the
 Carp ; in which we trace the Auditory nerve into a ganglionic centre as distinct
 as the Optic ganglion.   In higher animals, however, and in Man, we are able
 to trace the Auditory nerve into  a small  mass of vesicular matter,  which lies
 on each side of the Fourth Ventricle; and although this is lodged in the midst 
                   SENSORY GANGLIA.--CONSENSUAL ACTIONS.                327

of parts whose  function is  altogether different, yet there  seems no reason for
doubting that it has a character of its own, and that it is really the ganglionic

                                     [Fig. 157.
  A view ofthe base of the Cerebrum and Cerebellum, together with their nerves ; 1, anterior extremity
of the fissure ofthe hemispheres ofthe brain; 2, posterior extremity of the same fissure ; 3, the anterior
lobes of the cerebrum; 4, its middle lobe ; 5, the fissure of Sylvius ; 6, the posterior lobe of the cerebrum;
7, the point of the infundibulum ; 8, its body ; 9, the corpora albicanlia;  10, cineritious matter ;  11, the
crura cerebri; 12, the pons Varolii;  13, the top of the medulla oblongata; 14, posterior prolongation of
the pons Varolii; 15, middle of the cerebellum ; 16, anterior part of the cerebellum; 17, its posterior part
and the fissure of its hemispheres ; 18, superior part of the medulla spinalis ; 19, middle fissure of the
medulla oblongata; 20, the corpus pyramidale ; 21, the corpus restiforme; 22, the corpus olivare ; 23, the
olfactory nerve ; 24, its bulb ; 25, its external root; 26, its middle root; 27, its internal  root; 28, the op-
tic nerve beyond the chiasm; 29, the optic nerve before the chiasm; 30, the motor oculi, or third pair
of nerves ; 31, the fourth pair or pathetic nerves ; 32, the fifth pair, or trigetnini nerves; 33, the sixth
pair, or motor externus ; 34, the facial nerve ; 35, the auditory—the two making the seventh pair ; 36,
37, 38, the eighth pair of nerves. (The ninth pair is not here  seen.)]

centre of the Auditory nerve.—In  like manner, we may probably fix upon a
collection of vesicular matter, imbedded in the  Medulla Oblongata,—which is
considered by  Stilling to be the nucleus of the  Glosso-pharyngeal nerve, and
to which  a portion  of the sensory root of the Fifth pair  may be  traced,—as
representing the Gustatory ganglion.
   423.  At  the  base of  the Cerebral Hemispheres, we find two  other  large
ganglionic  masses, on  either  side ; into which all the  fibres appear  to  pass,
which  connect the Hemispheres with the Medulla Oblongata.   These  are the
Thalami Optici, and  the Corpora Striata.   Now,  although  these are  com-
monly regarded  in  the light of appendages, merely, to  the  Cerebral Hemi-
spheres,  it is evident, from the large quantity of vesicular matter they contain,
that they have an independent character ;  and  that, even if the  Cerebral fibres
simply pass through them, other fibres have their proper ganglionic   centres 
328
FUNCTIONS OF THE NERVOUS SYSTEM.
in them.  Such an idea is further warranted by the history of their develop-
ment; for we find, in the Human embryo of the sixth week, a distinct vesi-
cle for the Thalami Optici, interposed between the vesicle of the Corpora
Quadrigemina, and  that which gives origin  to  the Cerebral Hemispheres;
whilst the Corpora Striata constitute the floor of the cavity or ventricle, which
exists in the latter.—Now, as already pointed out, we may distinguish in the
Medulla Oblongata  and Crura  Cerebri,  a sensory and a motor tract; by
the endowments of  the  nerves which  issue from them.   The sensory tract
may be traced  upwards from the  Olivary columns, until  it almost entirely
spreads itself through the substance of the Thalamus.   Moreover, the Optic
nerves, and the peduncles of the Olfactive, may be  shown to have a  distinct
connection with the Thalami; the former by the direct passage of a  portion
of their roots into these ganglia; and  the latter through the medium of the
Fornix.  Hence we  may fairly regard the Thalami Optici  as the chief focus
of the Sensory nerves; and more especially as  the ganglionic centre of the
nerves of common sensation, which ascend to it from the Medulla Oblongata
and Spinal Cord.—On the other hand, the Corpora  Striata  are implanted on
the motor tracts of the Crura Cerebri, which  descend into the Pyramidal co-
lumns ; and their connection with the motor function is very generally admit-
ted, from the  constancy with which paralysis is observed to accompany lesions
of these bodies, even when they are affected to a very trifling extent.
   424.  The Thalami Optici, and the Corpora Striata, as is well  known, are
very closely connected with each  other  by commissural fibres ; and, if the
preceding account of their respective offices be correct, they may be regarded
as having much the same relation to each  other, as that which exists between
the posterior  and anterior peaks of vesicular matter in  the  Spinal Cord; the
latter issuing motor impulses in respondence to sensations excited through
the former.   They  are  also closely connected with other ganglionic  masses
in their neighbourhood, such as the locus niger, and the vesicular matter of
the pons; which again, are in close  relation with the vesicular matter of the
medulla  oblongata.—Altogether it is very evident, that  an extensive  tract of
ganglionic matter exists at the base of the Encephalon, which is really just as
distinct from  either the Cerebrum  or Cerebellum, as these  are from  each
other; and we have next to inquire, what functions  are to be assigned to it.
   425.  The  determination of  these may seem the  more difficult, as it is im-
possible to make any satisfactory experiments  upon the ganglionic centres in
question, by isolating them from the Cerebral Hemispheres above, and from the
Medulla Oblongata and Spinal Cord below.   But  the evidence derived from
Comparative  Anatomy appears  to  be in this  case particularly  clear; and,
rightly considered, seems to afford  us nearly all the information we require.
In the series  of " experiments  prepared for us by nature," which is presented
to us  in the  descending scale of Animal life, we witness  the effects of the
gradual change of the relative development of the Sensory ganglia and Cerebral
Hemispheres, which are presented to us in the Vertebrated classes ; and the results
of the entire withdrawal of the latter, and of the sole operation of the  former,
which are presented in the higher Invertebrata.  In the sketch already given
of the Comparative Anatomy of the Encephalon in Vertebrata, it has been
shown that the Sensory ganglia gradually increase, whilst the Cerebral hemi-
spheres as regularly diminish, in relative size and importance, as we descend from
the higher Mammalia to the lower,—from these to Birds,—thence to Reptiles,—
from  these, again, to  the  higher Fishes, in which  the aggregate size of the
Sensory ganglia  equals  that of the  Cerebrum,—thence  to  the lower  Fishes,
in which the  size of  the Cerebral lobes is  no greater than that of a single pair
of sensory ganglia, the Optic, and frequently even inferior,—and lastly, to the
Amphioxus  or Lancelot, the  lowest Vertebrated animal of which we have 
FUNCTIONS OF SENSORY GANGLION.
329
 any knowledge, in which there is not  the rudiment of  a Cerebrum, the En-
 cephalon being only represented by a single ganglionic mass, which, from its
 connection with the nerves of sense, must obviously be regarded as analogous
 to the congeries of ganglia that we find in the higher forms of the class.

   a. It has been supposed, from the results of an imperfect examination of this very remarka-
 ble animal, that it is altogether destitute of Encephalon;  and that it possesses no ganglionic
 centre, except the Spinal Cord and  Medulla Oblongata.   The researches of M.  de Quatre-
 fages, however, indicate that the most anterior  of the ganglionic enlargements exhibited bv
 its Cerebro-Spinal axis, is of a more special character than the rest;  uniting in itself the
 characters of several distinct ganglionic centres.  The  ganglionic enlargements, arranged in
 a linear series, which altogether represent the  Spinal Cord, each give origin to a single pair
 of nerves; but the cephalic ganglion is the centre  of five pairs.   Of these, the first  pair is
 distinctly an Optic nerve; being exclusively distributed to an organ, which has the structure
 of a rudimentary Eye, though lodged within the dura mater;—reminding us, in its situation,
 of the Auditory apparatus of the  Gasteropod Mollusks, which is actually imbedded in the
 posterior part of the Cephalic ganglia.  The second pair seems to correspond in its distribu-
 tion with the Facial;  whilst the third represents the Fifth pair and the Pneumogastric con-
 jointly.  The fourth and fifth pairs are distributed to the fin-like  expansion, which forms the
 margin of the head as well as of the body;  and seem to hold the  same relation  to the two
 preceding pairs, as  the dorsal branches of the Spinal nerves bear to the ventral,—or, in Man,
 the posterior to the  anterior. Hence we see that this single ganglion  is made up  of at least
 three centres; of which the first corresponds  to the Optic ganglion of higher Vertebrata;
 whilst the second and third are analogous to certain parts of the Medulla Oblongata in im-
 mediate connection with them.  Moreover, this little  animal possesses an organ of  Smell,
 much more distinct than the rudimentary eye;  and  although its connection with the anterior
 part of the cephalic ganglion has not yet been traced (owing to the extreme minuteness of
 the parts, and the  difficulty  resulting from the  interposition of the dura mater, which is in
 equally close contact with the nervous mass which it incloses, and with the olfactive organ
 which abuts upon its  exterior), there can be little  doubt  that such a connection  exists, and
 that the Cephalic mass unites within itself also the  characters of  an Olfactive ganglion.  But
 no part whatever can be traced, which bears any resemblance to the Cerebral hemispheres;
 and as these, wherever they exist, are completely  isolated  from the Sensory ganglia, their
 absence may be stated as an almost certain fact.  Hence, in this particular, the Amphioxus
 evidently corresponds with the Invertebrata; to which its affinity  is  so close in other particu-
 lars, that many Naturalists have hesitated to assign it a place in the Vertebrated series at all;
 and, as will be seen in  the  next paragraph, the union of several really distinct  ganglionic
 centres into one Cephalic mass, is a fact which is  capable of actual demonstration.  (See
 the Memoir on the  Branchiostoma or Amphioxus, by M. de Quatrefages, in the Annates des
 Sciences Naturelles, 3me Serie, Zoologie, torn, iv.)

   426. Descending  to the Invertebrated  series, we find  that, except in  a few
 of those which  border  most closely upon  Vertebrata  (such,  for  example, as
 the Cuttle-Fish), the whole  Cephalic mass  appears to  be made up of ganglia,
 in immediate  connection with   the nerves  of  sense.   These  may appear to
 form but a  single pair; yet  they  are in reality  composed of  several pairs,
 fused (as it were) into one mass.   Of this  we may judge by determining the
 number of distinct pairs of nerves which issue from them ;  and  also by the
 investigation  of the history of  their development, the results of which bear a
 close correspondence with those obtained in the  preceding method.

   a. Thus, Mr. Newport has shown, by studying the  development of the head in certain
 species of the class  Myriapoda, that it is originally composed of no less than eight  segments;
 each having its peculiar appendages; and each possessing (like  the segments of  the  body)
 its own pair of ganglionic centres.  These segments afterwards coalesce  into two portions;
 of which the most anterior, made up by the union  of four sub-segments, is termed the pro-
 per cephalic; whilst the  posterior, also made  up of  four sub-segments, is termed the basilar.
 The four pairs  of ganglia belonging  to the cephalic portion coalesce into the one pair of
 cephalic ganglia; whilst the other four pairs  unite to form  the first sub-assophageal ganglia.—
 The first of the original  sub-segments had, as its proper appendages, the antennae; and the
ganglia contained in it  were evidently the  proper centres of the antennal  nerves.  The
second had no movable appendages, but contained the eyes; and  its ganglia were evidently
the proper centres  of the optic nerves.   To  the third  belonged  the  first pair of jaws, the
maxillae; and to the fourth, the maxillary palpi: and these organs derived nerves from their
                                       28* 
330
FUNCTIONS OF THE NERVOUS SYSTEM.
own ganglionic centres, belonging to their respective segments.  Now as all these nerves
are found to proceed, in the adult animal from the  single pair of Cephalic ganglia, it is
obvious that these combine the  functions of the ganglionic centres of the nerves of the
antennas, eyes, and palpi, which are all sensory organs, as well as of the maxillary nerves,
which must be chiefly motor.  And it is equally obvious, that there is nothing in such an
animal, which can be compared  to a pair of Cerebral hemispheres; since all the ganglia
of the original  segments are  directly connected with the appendages of those segments
respectively.

   427. It is further to be remarked, that the development of the Cephalic
ganglia in the  Invertebrata always bears an exact proportion to the develop-
ment of the  eyes;  the other organs of special sense  being comparatively
undeveloped; whilst these, in all  the higher classes at least, are instruments
of great perfection, and evidently connected most  intimately with the direc-
tion of the movements of the animals.  Of this fact we have a remarkable
illustration in the history of  the metamorphoses  of Insects ; the eyes being
almost rudimentary, and the Cephalic  ganglia comparatively small, in most
Larvae; whilst both these organs  attain a high development in the Imago, to
whose actions the faculty of sight is essential.
   428. Now upon  making a similar  comparison of the psychical operations
of these different classes of animals, we are led to perceive that, as we de-
scend from the higher to  the lower Vertebrata, we gradually lose the indica-
tions of Intelligence and Will, as the sources of the movements of the animal;
whilst we see a corresponding predominance of those, which are commonly
denominated  Instinctive, and which  are performed  (as  it would appear) in
immediate respondence to certain sensations,—without any intentional adapta-
tion of means to ends on the part of the individual, although such adaptive-
ness doubtless exists in the  actions themselves,  being  a consequence of the
original constitution of the nervous system  of each animal performing them.
It cannot be doubted  by any person who has  attentively studied the charac-
ters of the lower animals, that many  of them possess psychical endowments,
corresponding with those which we term the  intellectual powers  and moral
feelings in Man; but in proportion as these are  undeveloped, in that propor-
tion is the  animal under the dominion  of those  Instinctive  impulses, which,
so far as its own consciousness is concerned, may be designated as blind and
aimless, but which are ordained by the Creator for its protection from  danger,
and for the supply of its natural wants.  The same may be said of the Human
infant, or of the Idiot, in  whom the reasoning powers are undeveloped.  In-
stinctive actions may in general be distinguished  from those which are the
result of voluntary power guided by reason, chiefly by the two following
characters:—1.  Although, in many cases, experience is  required to give the
Will command over  the muscles  concerned in its operations, no experience
or education is required, in order that the different actions, which result from
an Instinctive impulse,  may follow one another with unerring precision.  2.
These actions are always performed  by the same  species of animal, nearly,
if not exactly, in the same manner; presenting no such variation in the means
adapted to the object in view, and admitting of  no such improvement in the
progress of life, or  in  the succession of ages, as we observe in the habits of
individual men, or in the manners and customs of nations, that are  adapted to
the attainment of any particular  ends, by those  voluntary efforts which are
guided by reason.   The faet, too, that these instinctive actions are often seen
to be performed under circumstances rendering them  nugatory, as  reason
informs us, for the ends which they are to  accomplish—(as when the Flesh-fly
deposits her egg on the Carrion-plant instead of a piece  of meat, or when the
Hen sits on  a pebble  instead of her egg)—is an additional proof, that the
Instinctive actions of animals are prompted, like the consensual movements 
SENSORY GANGLIA.--CONSENSUAL ACTIONS.
331
 we have been recently inquiring  into, by an  impulse  which immediately
 results from a particular sensation  being felt, and not by anticipation of the
 effect which the action will produce.
   429.  The highest development of the purely Instinctive tendencies, is to be
 found in the class of Insects;  and above all in the order Hymenoptera, and in
 that of Neuroptera, which is nearly allied  to it.   It is in this division of the
 class, that we  find the highest development of the sensory organs and of the
 cephalic ganglia, and the most active powers of locomotion.  We may  here
 trace the operations of Instinct, with the least possible interference of Intelli-
 gence.   It is, of course, impossible to  draw the line between the two  sources
 of action, with complete precision;  but we  observe, in the habits of Bees and
 other social Insects, every indication of the absence of a power of choice, and
 of the entire domination of instinctive propensities called into action  by sen-
 sations.   Thus, although Bees display the  greatest art in the construction of
 their habitations, and execute a variety of curious contrivances, beautifully
 adapted to variations in their circumstances, the constancy with which indi-
 viduals and communities will act alike  under the same conditions, appears to
 preclude the idea of their possessing any inherent power of spontaneously de-
 parting from the line of action, to which they are tied down by the constitution
 of their Nervous system.  We do  not find one individual or one community
 clever, and  another stupid; nor do we ever witness  a disagreement, or any
 appearance  of indecision, as  to the course of action to be  pursued by the
 several members of any republic*   For a  Bee to  be destitute of its  peculiar
 tendency to build at certain angles,  would  be as remarkable as  for  a  Human
 being  to be  destitute of the desire  to eat,  when his  system should  require
 food.   It may be doubted,  on the other hand, whether there was ever a ease,
 in which an Insect of any kind could be taught to recognize any one, who had
 been in  the habit of feeding it;  or to show  any other unequivocal indications
 of intelligence.

   a. Such anecdotes have been related of  Spiders; but these animals are the highest oi the
 Articulated series, having many points of approach to Vertebrata.  It is probable, therefore,
 that they may possess the rudiment of a Cerebrum; a similar rudiment making its appear-
 ance in the higher Cephalopods, which occupy a  corresponding place in the Molluscous
 series.
   b. The only manifestation of educability, which the Author has ever  noticed, during a
 pretty long familiarity  with the habits of Bees, is the acquirement of a power of distinguish-
 ing the entrance of their hive from that  of others around. When a swarm is first  placed in
 a new box, and the Bees have gone forth in search of food, they often seem puzzled on their
return, as to which is their own habitation; more especially if there be several  hives, with
similar entrances, in one bee-house; and  it has 'been proposed to paint these entrances of
different colours, in order to enable the Bee to distinguish them more readily.  In a short
time, however, even without such aid, the Bees are seen to  dart from a considerable height
in the air, directly down to  their proper entrances; showing that they have learned to  dis-
tinguish these, by a memorial power.  This the Author has observed most remarkably, in a
case in which a hive is placed in the drawing-room of a house, the entrance to it being be-
 neath one ofthe windows; the adjoining houses have windows  precisely similar, except in
the absence of this small passage; and he has often noticed that, when a new stock has been
placed in  this hive, the Bees are some days in  learning the exact  position of their house, con-
siderably annoying the neighbours by flying in at their windows.
  * The community of Bees, though commonly reputed to be a monarchy, governed by a
sovereign, is really a republican which every individual performs its own independent part.
The function of the queen is simply that of breeding; and as (among the Hive-Bees at least)
she is the only female, the purpose of the instinct, which  leads the workers to treat her with
peculiar attention, is very obvious.  But the idea that she directs the operations of the hive,
or exerts any peculiar control over the ordinary Bees, is entirely destitute of foundation.  The
actions of the latter all tend to one common end; simply because they are performed in re-
spondence to impulses, which all alike share. 
332
FUNCTIONS OF THE NERVOUS SYSTEM.
  430. Thus the analysis of such of the actions of these animals, as are evi-
dently of a higher order than the simply-reflex, terminates in referring them to
the immediate directing influence of Sensations ; which, being received by the
cephalic ganglia through the sensory nerves, excite respondent motor impulses,
which are propagated to the various  muscles of the body, through those por-
tions of the motor trunks that issue from  them.   As the term Instinctive  has
been employed in a great variety of significations, and  is very indefinite in its
character, we may more appropriately apply the designation Consensual to the
actions of this group.  We have now to inquire, whether there is any class of
movements in Man and the higher Vertebrata, which seems to possess a simi-
lar character, and which may be regarded as  the special function of the gangli-
onic centres under consideration.—By far the larger part of the movements of
these  animals (putting aside the simply-reflex) are performed under the direc-
tion of the Intelligence ; to which the sensations are communicated ;  by which
a reasoning  process is  founded upon them ; and from  which, at last, issues
that mandate, which is called  the Will.   Consequently, there are compara-
tively few movements, in  the adult at least, which can be clearly distinguished
as neither voluntary, on the  one hand, nor reflex on the other.   Such actions,
however, do exist; and serve to show that, although the  Instinctive propensities
are in great measure superseded by the  Intelligence, they may still operate
independently of it.  As  examples of this group, we may advert to the act of
Vomiting, produced by various causes which act through the organs  of sense;
such  as the sight of a loathsome object, a disagreeable smell, or a  nauseous
taste.   The  excitement of the act of Sneezing by a dazzling light, is another
example of the same kind;  for even if it be granted, that the act of sneezing
is ordinarily excited through the reflex system  alone (which is by no means
certain), there can be no doubt that in this instance it cannot be brought into
play without a sensation actually felt.  The same may be said of the Laughter
which sometimes involuntarily bursts forth, at the provocation of some sight
or sound, to which no distinct ludicrous idea or emotion  can be attached ;  and
of that resulting from the act of tickling, in which case it is most certainly
occasioned by the sensation, and by that alone.
  431. The direct influence of Sensations, in occasioning and governing move-
ments, which are neither reflex nor  voluntary, is most remarkably manifested
in many phenomena of disease.   Thus in cases of excessive irritation of the
retina, wbich renders the eye most painfully sensitive to  even  a feeble amount
of light,—the state designated as photophobia,—the eyelids are drawn together
spasmodically, with such  force as to  resist very powerful efforts to open them ;
and if they be forcibly drawn apart,  the pupil is frequently rolled beneath the
upper lid  (apparently by  the action of the inferior oblique muscle), much  fur-
ther than it could be carried by a voluntary effort.  And in Pleuritis, Pericar-
ditis, and other painful affections of  the parietes of the chest, we may observe
the usual movements of the ribs to be very much abridged ; the dependence of
this abridgement upon the painful sensation which they occasion, being most
evident in those instances in which  the affection is confined to one side,—for
there  is then  a marked curtailment in its  movements, whilst those of the other
side may take place as usual; a difference which cannot be reflex, and which
the Will  cannot imitate.   Again, in some Convulsive disorders, we observe
that the  paroxysms are  excited by causes, which act through the  organs of
special sense;  thus in Hydrophobia, we observe the  immediate influence of
the sight or the sound of liquids, and of  the slightest currents of air; and in
many Hysteric subjects, the sight of a paroxysm in another individual is the
most  certain means of inducing it in themselves.
   432. The results of experiments,  so  far as any reliance can be placed upon
them, confirm  these views; by showing that any disturbance of  the usual 
SENSORY GANGLIA.--CONSENSUAL ACTIONS.             333
actions of the organs of sense, and of the nervous centres with which they are
connected, in animals whose movements are directly governed by the sensations
received  through these, is followed by abnormal movements.  Thus it  has
been ascertained by Flourens, that a vertiginous  movement may be induced in
pigeons, by simply blindfolding one eye ; and Longet has produced the same
effect, by evacuating the humours of one eye.  These vertiginous movements
are more  decided and prolonged, when, instead of blinding one eye, one of
the tubercula quadrigemina  is  removed; the animal continuing to turn itself
towards the injured side, as if rotating on an axis.—The results ofthe experi-
ments of M  Flourens upon the portion of  the  Auditory nerve proceeding to
the Semi-circular canals, are  still more extraordinary.   Section of the hori-
zontal  semi-circular canal in Pigeons, on both  sides, induces a rapid jerking
horizontal movement  of the head, from side to side;  and a tendency to  turn
to one  side, which manifests itself whenever the animal attempts to walk  for-
wards.  Section of a  vertical canal, whether the superior or inferior,  of both
sides, is followed by a violent vertical movement of the head.  And section of
the horizontal and vertical canals  at the same time, causes horizontal and ver-
tical movements.  Section of either canal on one side only, is followed by the
same effect as when the canal is divided on both sides; but this is inferior in
intensity.   The movements continue to be performed during several months.
In Rabbits, section of the horizontal canal is followed  by the same movements,
as those exhibited by pigeons;  and they are even more constant, though less
violent.  Section of the anterior vertical canal causes  the animal to make con-
tinued  forward somersets; whilst section of the posterior vertical canal occa-
sions continual backward somersets.   The movements cease when the animal
is in repose; and they recommence when  it begins to move, increasing in
violence as its motion is more rapid.—These curious results  are supposed by
M. Flourens to indicate, that the nerve supplying the semi-circular canals does
not minister to the sense of hearing, but to the direction of the movements of
the animal: but they are fully explained upon the supposition that the normal
function of the semi-circular canals  is  to indicate to  the animal the direction
of sounds, and that its movements are partly determined by these; so that a
destruction of one or  other of them will produce an irregularity of movement
(resulting, as it would  seem, from a sort of giddiness on the part of the animal),
just as when one of the eyes  of a bird is covered or destroyed, as in  the  ex-
periments just cited.
  433. But we may trace the influence of the Sensory ganglia, not merely in
their direct and independent operation on the muscular system, but also in the
manner in which they participate in all Voluntary actions.  There can be no
doubt that, in every exertion of the will upon  the muscular system, we  are
guided  by the sensations communicated through the afferent nerves, which
indicate to the Sensorium the  state  of the  muscle.  Many  interesting cases
are on record, which show the necessity of this Muscular Sense, for determin-
ing voluntary contraction of the  muscle.  Thus,  Sir C. Bell (who first promi-
nently  directed attention to this class  of facts,  under the  designation of  the
Nervous Circle), mentions an instance of a woman, who was  deprived of it in
her arms, without losing the motor power; and who stated, that she could  not
sustain anything in her hands (not even her child), by  the strongest effort of
her will, unless she kept her eyes constantly fixed upon it; the muscles losing
their power, and the  hands  dropping the object, as  soon as the eyes were
withdrawn from  it.   Here the  employment of  the visual  sense supplied  the
deficiency of the muscular ; but instead of being inseparably connected, as the
latter is in the state of health, with the action ofthe muscle, the former could
be only brought to bear by an effort of the will;  and the sustaining power was
therefore dependent, not upon  the immediate influence of the will upon  the 
334                FUNCTIONS OF THE NERVOUS SYSTEM.

muscle, but upon the voluntary direction ofthe Sight towards the object to be
supported.   Again, in the production of vocal sounds, the nice adjustment of
the muscles of the larynx, which  is requisite to produce determinate tones,
can only be learned  in the first instance under the guidance of the sensation
of the sounds produced, and can only be effected by an act of the will, in
obedience to a mental conception (a sort of  inward sensation)  of the tone to
be uttered,—which conception cannot be formed, unless  the sense of hearing
has previously brought similar tones to the  mind.  Hence it is, that persons
who are born deaf, are also dumb.  They may have no malformation of the
organs of speech;  but they are incapable of uttering distinct vocal sounds or
musical tones, because they have not the guiding conception, or recalled sen-
sation, of the nature of these.   By long training, and by efforts directed by the
muscular sense of the larynx itself, some  persons thus circumstanced have
acquired the power of speech; but  the want of a sufficiently definite control
over the vocal muscles, is always very evident in their use of the organ.
  434. The  conjoint  movements of the two eyes, which concur  to direct
their axes towards  the same object, are among the most interesting of these
actions, in which  Volition and Consensual action are alike  concerned;  and
they afford  an excellent  illustration of the  necessity for guiding  sensations,
to determine  the actions of muscles.   The sensations, however, are not so
much those of the muscles themselves, as those received  through  the visual
organ; but the former  appear capable  of  continuing to guide the harmonious
movements of the  eyeballs, when  the sense of sight has  been lost.  It  is a
striking peculiarity of these  movements, that, in  the majority  of them, two
muscles or  combinations  of  muscles of opposite  action  are in operation at
once;  thus, when  the eyes are  made to rotate in a horizontal  plane, the in-
ternal rectus of one side acts with  the external rectus of the other.   In most
other cases, there is  a difficulty in performing two opposite  movements, on
the two sides at the same time.  Thus, if we move the right hand as if wind-
ing on a reel, and afterwards make the left hand  revolve in a contrary direc-
tion, no difficulty is experienced; but if we attempt to move the  two at the
same time in contrary directions, we shall find it  almost impossible.—As the
Consensual  movements of the Eyes are of  sufficient interest and importance,
to require a detailed  consideration,  they will be examined more fully at the
close  ofthe  present section (§§ 450—456).
  435. If the preceding views be correct, we may regard  the series of Gan-
glionic centres which have been enumerated (§§ 422, 423), as constituting the
real  Sensorium; each  ganglion having  the power of  cummunicating to the
mind  the impressions derived from the organ, with which it is connected, and
of exciting automatic muscular movements in respondence to these sensations.
If this position be denied, we must either refuse the attribute  of consciousness
to those animals, which  possess no other encephalic centres than these; or
we  must believe that the addition of the Cerebral hemispheres, in the Verte-
brated series, alters the endowments of the  Sensory ganglia,—an idea which
is contrary  to all analogy.  So far as the results of experiments can be relied
on, they afford a corroboration of these views.  The degree in which animals
high in the scale of organization can perform the functions of life, without
any other  centre of action than the Ganglia of Special sense, the  Medulla
Oblongata, and the  Cerebellum, appears extraordinary to  those who are accus-
tomed to regard the Cerebral Hemispheres as the centre of all energy.  From
the experiments of Flourens, Hertwig, Magendie, and others, it appears that
not only Reptiles, but Birds and Mammalia,  may survive for many weeks or
months" (if  their physical wants  be duly supplied) after the  removal of the
whole Cerebrum.   It  is  difficult  to  substantiate  the existence in them of
actual Sensation;  but some of their movements appear to be of a higher kind 
         SENSORY GANGLIA.--CONSENSUAL AND EMOTIONAL ACTIONS.      335

than those resulting from mere Reflex action.   One of the most  remarkable
phenomena exhibited by such a being, is the power  of maintaining its equili-
brium, which could scarcely exist without  consciousness.  If it be laid upon
the back, it  rises again;  if pushed, it walks.  If a Bird thus  mutilated  be
thrown into the air, it flies; if a Frog be touched, it  leaps.  It swallows food
and liquid, when they are placed in its mouth; and the digestive operations,
the acts of excretion, &c, take place as usual.  In the case  of a  Pigeon ex-
perimented on by Malacorps, which is recorded  by  Magendie, there appears
sufficient proof of the persistence of a certain amount of sensation.   Although
the animal was  not affected by a strong light suddenly made to fall  upon its
eyes, it was accustomed, when  confined in  a darkened or partially-illuminated
room, to seek out the light parts;  and it avoided objects that lay  in its way.
In the same  manner,  it did not  seem to be  affected by sudden noises; but at
night,  when it slept with  closed  eyes and its head  under its wing, it would
raise  its head in a remarkable manner, and  open  its eyes, on the  slightest
noise;  speedily relapsing into  a state of complete  unconsciousness.    Its
principal occupation was to prune its feathers and  scratch itself.—The con-
dition  of such a being seems to resemble that of a Man, who is in a slumber
sufficiently deep to lose all distinct perception of external objects, but who is
yet conscious of sensations, as appears  from the movements occasioned by
light  or by sounds, or  from those which  he  executes to withdraw  the body
from an uneasy position.*
   436. Among  the ganglia of special  sensation, the  functions of the Optic
Lobes, or  Corpora Quadrigemina, have  been chiefly examined.   The  re-
searches of  Flourens and Hertwig have  shown, that their connection with
the visual  function, which might be inferred from their anatomical  relations,
is substantiated  by experiment.  The partial loss  of the ganglion on  one
side produces partial  loss of power and temporary  blindness on  the opposite
side of the body, without necessarily destroying the  mobility of the pupil;
but  the removal of a larger portion, or complete extirpation of  it,  occasions
permanent blindness and immobility of the pupil, with  temporary muscular
weakness, on the opposite side.   This temporary  disorder of the  muscular
system sometimes manifests itself (as already stated)  in a tendency to move on
the axis, as if the animal were  giddy.   No disturbance of consciousness  ap-
pears  to be produced;  and Hertwig states that he never witnessed the con-
vulsions, which Flourens mentions as a  consequence of the operation, and
which were probably  occasioned  by his  incision  having been  carried  too
deeply.  These  results are  confirmed by pathological phenomena in Man;
for there  are many instances on record, in which blindness  has  been one of
the consequences of diseased alterations  in one  or both tubercles ; and in
some of the cases, in which  the lesion extended to  parts seated  beneath  the
tubercles, disturbed movements were observed.—No definite conclusions can
be drawn,  either from experiment or from  pathological observation, in regard
to the functions of the Thalami Optici and  Corpora Striata;  but there is
nothing in these sources  of information to oppose the views already offered,
which are based on other foundations.
   437. Emotional Actions.—There appears strong reason  for regarding the
Ganglionic tract, which is the instrument of Consensual actions, as the imme-
diate centre  also of those movements which  directly  result  from the excite-
ment ofthe Emotions.  Several considerations tend to establish  this position.

   * It must not be forgotten that, in such experiments, the severity of the operation will of
itself occasion a suspension or disturbance of the functions of  parts that remain ; so that the
loss of a power must not be at once inferred from the absence  of its manifestations. But the
persistence of a power, after the removal of a particular organ, is a clear proof that it cannot
be the peculiar attribute of that organ. 
336
FUNCTIONS OF THE NERVOUS SYSTEM.
In the first  place, that the channel through which the direct impulses of the
Emotions are conveyed to the Muscles, is not the same with that which con-
veys  to  them  the mandates of  the Will, appears sufficiently established by
Pathological observation ;  since cases of paralysis not unfrequently occur, in
which the muscles are obedient to an emotional impulse, though the will exerts
no power over  them;  whilst, on the other  hand, the will may have  its due
influence, and  yet the  emotional state cannot manifest  itself.   This is espe-
cially remarkable  in the different forms of paralysis of the Facial nerve  ; since
the facial muscles manifest the ordinary influence of the Emotions, more evi-
dently than any others.   But it  is  not, however, confined to them; thus, for
example, the arm  of a man,  which no effort of his will could move, has been
seen to be violently agitated  at the sight of a friend.    Dr. M. Hall has inferred
from cases of this kind, that the  Spinal system of nerves constitutes the chan-
nel ofthe Emotional actions; but all which  is proved by  them is, that these
are not effected through the same agency with the Volitional;  and the idea
that they are of the same character with Reflex actions is  distinctly negatived
by the fact, that in a great majority of instances, they are excited through the
organs of special  sense, and that consciousness is  a distinct element in the
series of changes which ends in  their performance.   These facts would lead
us to  infer, that the Emotional actions are dependent on a set of centres, in-
termediate between the Cerebrum and the Spinal Cord;  a position which is
precisely that of the ganglionic tract under consideration.—In the next place
it may be remarked, that the Emotions are so closely linked with Sensations,
as to be regarded by many Metaphysicians  as almost identical with them ; and
this connection is universally recognized  in  the term Feelings popularly ap-
plied  to  both.   Like  the  Instinctive tendencies of  Animals,  the Emotional
states follow directly and  necessarily upon Sensations, without any interven-
ing process of ratiocination  ; and  there  is such a marked correspondence in
the character of the actions,  which flow from these sources, as to point to the
conclusion of the identity of the conditions on  which  they immediately de-
pend.   Of this, an example  will be presently given.  We have  seen that the
SenSory ganglia must necessarily be regarded as the instruments  of  the In-
stinctive actions;  and a probable inference may therefore  be drawn from this
fact, in regard  to  their  relation to those  which (in Man) are designated  as
Emotional.*—A third argument in support of this  view may be drawn from
the fact,  of  the very close connection of  this division of the nervous centres,
with the nervous  trunks, through which  the emotional states are excited, and
the respondent muscular actions  are stimulated.  For the  Sensory ganglia re-
ceive all those nerves, which  communicate the Sensations  through whose
immediate agency the Emotion  is excited;  and the nerves of the Orbit, the
Face, and the  Respiratory organs,—those most concerned in producing the
movements, by which  the emotions are  expressed   or  manifested,—arise in
their  immediate proximity.   It  is chiefly through  these nerves, too, that the

  * It seems by no means certain, that we are always to attribute to the lower animals the
Emotions which we ourselves  feel, because they perform movements analogous to  those by
which we ordinarily  express them: for the movements may be directly excited by the Sen-
sations, without the intervention of the Emotion; just as in ourselves, involuntary laughter
is occasioned by tickling, although no  ludicrous emotion be excited;  or as Vomiting results
from the sight of a loathsome object, rather in respondence to the sensation of nausea, than
to the emotion of disgust which it concurrently excites.  We might, on equally valid grounds,
assert, that the Bee goes through a process of mathematical ratiocination, before it commences
the construction of its cell.  The purpose of the Emotion, in animals possessed of Intelligence,
may be rather to act upwards upon it; and, although closely connected with the sensation
which excites it; it may be no more  necessary to the resulting muscular movement, than
sensation  is to reflex action.—On this view, all  actions of the directly Emotional character
would be in reality purely Consensual. 
EMOTIONAL AND INSTINCTIVE ACTIONS.
337
abnormal  movements are effected, in those disorders of the Nervous centres,
which  may be most distinctly referred to  the  Emotional  system; such  as
Chorea and Hysteria.
   438. The correspondence between the purely Emotional  actions  in Man,
and those  actions in the lower animals to which we give the name of  Instinc-
tive, may be made evident by a  very simple illustration.   The Cuttle-fish is
well known to discharge its ink,  when pursued, and to  tinge the water around
with a colour  so deep, as to enable it to escape under the cloud  thus  formed.
Now it is  not  to be supposed, that the Cuttle-fish  has  any notion of the pur-
pose which this act will serve;  since  its  constancy and uniformity, and the
provision for its performance immediately  on the emersion of the  young ani-
mal from the egg, forbid our regarding it as the result of any act  of reasoning.
Further, the ink is an excretion  which corresponds to  the urine  (having been
found  to contain urea);  and every one knows how strong an impulse to dis-
charge this, is  frequently caused by mental emotion.   The same may be said
of the strongly odorous secretions possessed by many Mammalia, which are
discharged under  similar circumstances, and evidently  with the same object;
though of  that object, the  animal itself be  not  conscious.    The emotion of
fear involuntarily opens the sphincters, and causes the contraction of the recep-
tacle, in one case as in the other; and the great difference between the condi-
tion of Man, and that of the lower animals, in  this respect, is simply that, in
the former, the purely Emotional or Instinctive actions are few in comparison
with the whole, whilst in the latter they constitute by far the largest part; and
also that Man  has  much greater  power of controlling these actions by a volun-
tary effort, than that which the lower animals possess, although even he is not
unfrequently compelled by the  strength of his Emotions to act against his
Will.   Thus,  we see or hear something  ludicrous, which  involuntarily pro-
duces  laughter, although we  may have the strongest motives for desiring to
restrain it.
   a. It is a very interesting question, how far actions at first performed voluntarily by Man,
may by habit cease to require an effort of the Will; being prompted, like the movements of
the Consensual class, by the direct impulse of sensations.  Thus we all know  that, in walking
along an accustomed  road, we frequently occupy our minds with some  continuous train of
thought, and yet  our limbs continue to  move under us with regularity, until we are surprised
by finding ourselves at the place of our destination, or perhaps at some other which we had
not intended to  visit, but to which habit has  conducted us.  Or we may read aloud for a
long time, without having in the least  degree comprehended the meaning of the words  we
have uttered; our attention having been closely engaged by some  engrossing thoughts or
feelings within.  Or a Musician may play a well-known piece of music, whilst carrying on
an animated conversation;—the Author has known a skilful performer who could play at
sight whilst thus  occupied.  Now in such a case it would be  said by some Metaphysicians
(acknowledging,  as most do, that the mind cannot will two different things at the same time)
that the Volition  is in a sort of vibratory condition between the two sets of  actions, now
prompting one, and now the  other.   But it would seem  much more conformable to the
analogy afforded  by other psychical phenomena, to refer the habitual series of actions to the
same operation of the  Nervous System with the Instinctive; and perhaps the  term Automatic
may be fairly applied to the whole of  this group.  It is well known that in cases of severe
injury of the brain, in which Intelligence and Will  seem  completely in abeyance, habitual
actions may be often excited.  Thus, Dr. Perceval, in his Essay on habit, mentions the case
of a snuff-taking Countess, in whom, when seized with apoplexy, irritation of the nose with
a feather produced contraction of the fore-finger and thumb  of the right hand; and Mr.
Traverse has recorded a similar fact in the case of a boy, who, when apparently insensible
from depressed fracture of the skull, assisted in  removing  his clothes, preparatorily to the
required operation.

   439. The purely Emotional actions are not always directly excited, however,
by external sensations;  for they may result from the operations  of the Mind
itself.   Thus involuntary laughter may  result from a ludicrous idea, called up
by some train  of association, and having no obvious  connection with the sen-
     29 
338                FUNCTIONS OF THE NERVOUS SYSTEM.
 sation which first set this process in operation;  and the various movements
 of the face and person, by which Actors endeavour to express strong Emotions,
 are  only effectual in conveying their meaning, when they result from the actual
 working of the emotions in the mind of the performer,  who has, by an effort
 of the will, identified himself (so to speak) with the  character he personates.
 A still more remarkable case is that, in which  paroxysms of Hysterical con-
 vulsion, in themselves beyond the  power of the Will to excite or to control,
 are  brought on by a voluntary effort; which seems to act by "getting up," so
 to speak, the state of feeling, which is the immediate cause of the disordered
 movements.   In all these instances, and others of like nature, it would seem
 as if the agency of the Cerebrum produced the  same condition in the Sensory
 ganglia and their motor fibres, as  that which is more  directly excited by sen-
 sations received through their own afferent nerves.  It may be reasonably
 surmised, that the  Sensory ganglia, like the Cephalic ganglia which are the
 instruments of the Instinctive actions of the lower animals, can only be excited
 to action by stimuli immediately  operating upon them;  but that these stimuli
 may be  either Sensations directly originating in external objects, or Concep-
 tions resulting from the remembrance of those objects, of which there is  strong
 reason to believe that the Cerebrum is the  storehouse.
   440. The Emotions are concerned in Man, however, in many actions, which
 are  in themselves strictly voluntary.  Unless they be strongly  excited, so as
 to get the better of the Will, they  do not operate directly through the nervous
 trunks, but are subservient to  the intellectual operations;  to which they supply
 materials, or motives.  Thus, of  two individuals, with differently constituted
 minds, one shall judge of everything through the medium of a gloomy morose
 temper,  which,  like a darkened glass, represents  to  his judgment the  whole
 world in league to  injure him; and  all  his determinations, being based upon
 this erroneous view, exhibit  the  indications of it  in  his actions; which are
 themselves, nevertheless, of  an entirely voluntary character.   On the  other
 hand, a person of a cheerful, benevolent disposition, looks at the world around
 as through  a Claude Lorraine glass, seeing everything in its  brightest and
 sunniest aspect; and, with intellectual faculties precisely similar to those of
 the  former  individual, he will come to  opposite  conclusions;  because the
 materials, which form the basis of his judgment, are  submitted to it in a very
 different condition.   Various forms of Moral Insanity exhibit the same con-
 trast in a yet  more striking light.   We not  unfrequently meet with individuals,
 still holding their place in society, who  are  accustomed to  act so much upon
feeling,  and  to  be so little guided*by reason,  as  to  be  scarcely regarded as
 sane;  and a very little exaggeration of such a tendency causes the actions to
 be so injurious to the individual himself, or to those around  him, that restraint
 is required, although the intellect  is in no way disordered, nor are any  of the
 feelings  perverted.   Not unfrequently we may  observe similar inconsistencies
 resulting from the  habitual indulgence of  one  particular feeling, or a morbid
 exaggeration of  it.  The mother who, through  weakness of will, yields  to her
 instinctive fondness  for her offspring, in allowing it gratifications which she
 knows  to be injurious to it, is placing herself below the  level of many less
 gifted  beings.   The habit of yielding to a natural infirmity of  temper often
 leads into paroxysms of ungovernable  rage, which, in their turn, pass into a
 state of  maniacal excitement.  It is not unfrequently seen, that a delusion of
 the  intellect (constituting what is  commonly known as Monomania) has in
 reality resulted from a disordered state of the feelings, which have represented
 every occurrence in a wrong  light to the  mind of the individual.  All such
 conditions are of extreme interest, when compared with those which are met
 with amongst idiots, and animals enjoying a much lower degree of intelligence :
 for  the result is much the same, in whatever way the  balance between the 
NERVES OF SPECIAL SENSE.--OLFACTIVE.
339
   feelings and the judgment (which is so beautifully adjusted in the well-ordered
   mind of Man) is disturbed;  whether by a diminution of the intelligence, or
   by an exaltation of the feelings.—These views will  probably be found correct,
   whatever be the truth of the speculation with which they have been here con-
   nected, as to the part of the Nervous  system concerned in the performance of
   the purely Emotional actions.   That their channel is alike distinct, however,
   from that of the Voluntary movements,  and from that of Reflex  operations,
   must be apparent to any one who fairly weighs the evidence.
     441. Nerves connected with  the Sensory Ganglia.—That the First  pair,
   or Olfactory nerves, minister to the  sense of smell, has long  been known,
   yet it could not be predicted without experimental inquiry, that it  is not a
   conductor of the impressions which produce ordinary sensation;  nor that it
   is destitute of  all power of exciting muscular movement, either by direct or
   reflex action.  Anatomical examination of the distribution of this  nerve, proves
   that it is not one which directly conveys  motor influence to any muscles;
   since all its branches are distributed to the membrane lining the nasal cavity.
   Experimental inquiry leads to the same result; for  no irritation of the pedun-
   cles or branches excites any muscular movement.   Further, no irritation  of
   any part of this nerve excites reflex actions through other nerves.  Again, it
   is not a nerve  of common sensation ;  for  animals exhibit no  sign  of pain,
   when it is subjected to any kind of  irritation.   Neither the division of the
   nerve, nor the  destruction  of the  olfactive  ganglia,  seems to inconvenience
,   them materially.  They take their food, move with their accustomed agility,
   and exhibit the usual appetites of their kind.  The  common sensibility of the
   parts contained in the olfactive  organ is in no  decree impaired, as is shown
   by the effect of irritating vapours ; but the animals are  destitute of the sense
   of smell, as is shown by the  way in which  these vapours affect  them.  At
   first they appear indifferent  to  their  presence, and then suddenly and vehe-
   mently avoid them, as soon as the Schneiderian membrane becomes irritated.
   Moreover, if two dogs, with  the  eyes  bandaged,  one  having the olfactory
   nerves  and ganglia sound, and the  other  having  had them destroyed, are
   brought into the neighbourhood of the  dead body Of an animal, the former
   will examine it by  its smell;  whilst the  latter, even if he touches it, pays no
   attention to it.   This experiment Valentin states  that he has  repeated several
   times, and always with the same results.  Further,  common observation
   shows that sensibility to irritants, such as  snuff,  and acuteness of the power
   of smell, bear no  constant proportion to one another ;  and there is ample
   pathological evidence, that the want of this sense  is  connected  with some
   morbid condition of the olfactory nerves  or ganglia.—It is well known that
   Magendie has maintained, that the Fifth pair in some way furnishes conditions
   requisite for the enjoyment of the sense of smell; asserting that, when it is
   cut, the animal is deprived of this.  But his experiments were made  with ir-
   ritating vapours, which excite sternutation or other violent muscular  actions,
   not through the Olfactory nerve, but through the Fifth pair ;  and the experi-
   ments of Valentin,  just related,  fully prove that the animals are  not sensitive
   to odours, strictly so called, after the  Olfactory has been divided.  It is by
   no means improbable, however, that the  acuteness of  the true sense of smell
   may be  diminished by section  of the Fifth pair; since the  olfactory mem-
   brane is no longer  duly moistened by  its proper secretion; and, when dry, it is
   not so susceptible of the impressions made by those minute particles of odori-
   ferous substances, to which the  excitement of the sensation mu6t be referred.
     442.  That the Second pair, or  Optic nerves, have an analogous character,
   appears  alike  from anatomical  and experimental evidence.  No chemical or
   mechanical stimulus of the nerve produces direct muscular motion ; nor  does
   it give rise, as far as can be ascertained, to indications of pain; whence it may 
340                 FUNCTIONS OF THE NERVOUS SYSTEM.
be concluded, that this nerve is not one of common sensation. That the ordi-
nary sensibility of the eyeball remains, when the  functions of the Optic nerve
are completely destroyed, is well known ; as is also the fact, that division of
it puts an end to the power of vision.  Valentin states that,although the Optic
nerve may, like other  nerves, be in appearance completely regenerated, he has
                                       never  been able  to  obtain  any  evi-
                                       dence  that the power  of sight  has
                                       been  in the  least  degree recovered.
                                       He  remarks  that  animals suddenly
                                       made blind exhibit great mental  dis-
                                       turbance,  and perform many unaccus-
                                       tomed movements ; and  that the com-
                                       plete absence of the  power of  vision
                                       is easily ascertained.  Morbid changes
                                       are sometimes observed to take place
                                       in eyes, whose Optic nerve has been
                                       divided ;  but these are  by no means
                                       so constant or so  extensive, as when
                                       the Fifth  pair is paralyzed; and they
                                       may not  improbably be attributed to
                                       the injury, occasioned by the opera-
                                       tion itself, to the parts within the or-
                                       bit.—It is well known that,  when
                                       amaurosis is  produced  by a morbid
                                       condition  of the Optic  nerve  alone,
                                       the eye retains its usual appearance;
                                       but, if the amaurosis  be  complete, the
                                       texture of the  Retina undergoes a re-
                                       markable  change, ceasing to exhibit
                                       that peculiar structure which normally
                                       characterizes  it.   Neither primitive
                                       nervous fibrils, nor nucleated vesicles,
                                       can  be distinguished in it,  and the
                                       yellow spot of  Soemmering becomes
                                       paler, and is at last undistinguishable.
                                       But if a very slight  degree  of  sensi-
                                       bility to light remain, these  changes
                                       are much  less decided.   Further,  it is
                                       well known  that, when  the  sight  is
                                       destroyed by  a  disease  or injury,
which prevents the passage of light through the pupil, the whole eye becomes
more or less atrophied ; and the Retina and Optic nerve, although previously
sound, are found after death, (if the morbid condition have lasted sufficiently
long) to  have lost their characteristic structure.   It seems evident, then,  that
the continuance of the functional  operations of nerves, is a  necessary condi-
tion of the maintenance of their normal organization;  and we can very well
understand that this should be the case, from the analogy of other parts of the
system.
   443. The Optic nerve, though analogous to the Olfactory  in  all the  points
hitherto  mentioned, differs from it in one  important respect;—that it  has the
power of  conveying impressions which shall excite reflex muscular motions.
This is especially the  case in regard to the Iris, the ordinary  actions of which
are regulated by the degree of light impinging on  the retina.  When the optic
nerve  is divided, a contraction of the pupil takes place; but this  does not
occur, if the connection of this nerve with  the third pair, through the nerv-
[Fig. 158.
  A view of the 2d pair or optic, and the origins of
seven other pairs. 1,1. Globe of the eye, the one
on the left hand is perfect, but that on the right has
the sclerotic and choroid removed to show the
retina. 2. The chiasm of the optic nerves. 3. The
corpora albicantia. 4. The infundibulum.  5. The
Pons  Varolii.  6. The medulla oblongata.  The
figure is on the right corpus pyramidale.  7. The
3d pair, motores oculi.  8. 4th pair, pathetici. 9.
5th pair,trigemini. 10. 6th pair, abducentes.  11.
7th pair, auditory and facial.  12. 8th pair, pneumo-
gastric, spinal  accessory, and [glosso-pharyngeal.
13. 9th pair, hypoglossal. ] 
NERVES OF SPECIAL SENSE.--OPTIC.
341
 ous centres, be in any way interrupted.  After such  division (if complete),
 the state of the pupil is not affected by variations in the  degree  of light im-
 pinging on the retina;  except in  particular  cases, in which it is influenced
 through other channels.  Thus, in a patient suffering under amaurosis of one
 eye, the pupil  of  the affected eye is often found to vary in size, in accord-
 ance with that of  the other eye ;  but this effect is produced by the action of
 light on the retina of the sound eye, which produces  a  motor change in the
 third pair  on both sides.  Further, as has been formerly stated  (§ 395), the
 impression only of light upon the retina may give rise to contraction of the
 pupil, by reflex action, when the optic nerve is itself sound ;  whilst  no sen-
 sations are received through the  eye, in consequence of disease  in  the sen-
 sorial portion of the nervous centres.  Although the contraction of the pupil
 is effected by the  influence of motor fibres, which proceed to the sphincter
 of the  Iris from the third pair of nerves, through the Ophthalmic ganglion,
 there is evidence that its dilatation depends  rather upon the influence it de-
 rived from that ganglion itself, and from  the Sympathetic system, of which it
 forms part.—Some have attempted to show, that the actions of the iris are in
 a slight degree voluntary, becatise, by an effort of  the will, they  could  occa-
 sion contraction of the  pupil; but this  so-called voluntary contraction  is  al-
 ways connected with a change in the  place  of the eyeball itself, occasioned
 by an action of some of its muscles.  It is principally noticed under the two
 following conditions:—1. When an object is brought very near the eye, and we
 steadily fix our attention upon it, the axes of the two  eyes are made to  con-
 verge ; and if this  convergence be carried to a considerable extent, so that the
 pupils of both eyes are sensibly directed  towards  the inner canthus, a  con-
 traction of the  pupil takes place.  The final cause or purpose of this  contrac-
 tion is  very evident.  When an object is brought near the eye, the rays pro-
 ceeding from it would enter the pupil (if it  remained of its usual size) at an
 angle of divergence, so much greater than  that which would  allow  them to
 be properly refracted to a focus, that indistinct  vision would necessarily re-
 sult.  By  the contraction of the pupil, however, the extreme  or  most diver-
 gent rays are cut off, and the pencil is reduced within the proper angle.  The
 principle  is precisely the same as that on which the optician  applies a  stop
 behind his lenses, which reduces their aperture in proportion to the shortness
 of  their focal distance.   2.  Contraction  of the pupil is also noticed, when the
 eyeball is  performing that  rotation upwards and inwards, which, when per-
 formed along with  violent respiratory actions,  or during sleep, must be regarded
 as involuntary.  This rotation also takes place, to a slight degree, when the
 eyelid is depressed, as  in ordinary winking  ; and  it is obvious that, in this
 manner, the surface of the eye is more effectually swept free from impurities
 which may have gathered upon it, than it would be by the downward motion
 of the lid alone.   But the pupil is not contracted, when the eyeball  is volun-
 tarily rotated upwards and inwards.
   444. Besides the contractions of the pupil, another action, which has been
 sometimes spoken of as reflex, is produced through  the Optic  nerve,—the
 contraction of the  Orbicularis muscle under the influence of strong light, or
 when a foreign body is  suddenly brought near the eye.   But  this cannot  be
 produced  by any mechanical stimulation, and it evidently involves sensation ;
 in fact, it  is a movement of  a consensual kind, produced by the painful  effect
 of light, which gives rise to the condition  well characterized by the  term
photophobia.   The involuntary character of  it must be evident to every one,
 who has been engaged in the treatment of diseases of the eyes; and the  effect
 of it is  aided by a similarly-involuntary movement of the eyeball itself, which
 is rotated upwards and inwards, to a greater extent than the Will appears able
 to effect.
                                   29 s 
342
FUNCTIONS OF THE NERVOUS SYSTEM.
  445.  There  is a further peculiarity, of a very marked kind, attending the
course of the Optic  nerves; this  is the crossing or decussation which  they
[Fig. 159.
[Fig. 160.
 Plan of the optic nerves on a
small scale, showing their diver-
gence from the chiasma, c, and
their junction with the globe, on
the inner side of the axis of the
humors.]
  Course of fibres in the chiasma, as exhibited by
tearing off the superficial bundles from a specimen
hardened in spirit, a. Anterior fibres, commissural
between the two retinae, p. Posterior fibres, com-
missural between the thalami.  a', p'. Diagram of
the preceding.]
undergo, more or less completely, whilst proceeding from their ganglia to the
eyes.  In some of the lower animals, in which the two eyes (from their lateral
position) have entirely different spheres of vision, the decussation  is complete;
the whole of the fibres from the right optic ganglion passing into the left eye,
and  vice  versa.  This  is  the case, for  example, with most of  the Osseous
Fishes (as the cod, halibut, &c.); and also, in great part at least, with Birds.
In the Human subject, however, and in animals which, like him, have the two
eyes looking in  the same direction,  the decussation seems less complete; but
there is a very remarkable arrangement of the fibres, which seems destined to
bring the two eyes into peculiarly consentaneous action.  The posterior border
of the Optic Chiasma is formed exclusively of commissural fibres, which pass
from one optic ganglion to the other, without entering the real  optic nerve.
Again, the anterior border of the Chiasma is  composed of fibres,  which seem,
in like manner,  to act as a commissure between the two retinae; passing from
one to the other, without any  connection with  the optic ganglia.   The tract
which lies between the two borders, and occupies  the middle of the Chiasma,
is the true Optic Nerve ;  and in this it would appear that a portion of the fibres
decussates, whilst another  portion  passes directly from each Optic  ganglion
into the corresponding eye.  The  fibres which proceed from the ganglia to
the retinae, and  constitute the proper Optic Nerves, may be distinguished into
an internal and  an external tract.   Of these, the external on each side, passes
directly onwards to the eye of that side; whilst the internal crosses over to
the eye of the opposite side.   The distribution of these two  sets of fibres in
the retina of each eye respectively, is such that, according to Mr. Mayo, the
fibres from  either optic ganglion will be distributed to its own  side of both
eyes ; the right  optic ganglion  being thus exclusively connected with the outer
part of the retina of the right eye, and with the inner part of the  retina of the
left eye ;  and the left optic ganglion being, in  like manner, connected exclu-
sively with  the outer side of  the  left retina, and with the inner side of the
right.   Now as either side of  the eye receives the images of objects, which
are on the other side of its axis, it follows, if this account of their distribution
be correct, that in Man, as in  the lower  animals,  each ganglion  receives the
sensations of objects  situated on the opposite sides of the body.  The purpose
of this decussation may  be, to  bring the visual  impressions, which are so im-
portant in directing the movements of the body, into proper harmony with the 
NERVES OF SPECIAL SENSE.--AUDITORY AND GUSTATORY.        343
apparatus;  so that, the decussation of the motor fibres in the pyramids being
accompanied by a decussation of the optic nerves, the  same effect is produced
as if neither decussated,—which last is the case with Invertebrated animals in
general.
   446. The functions of the Auditory nerve, or Portio Mollis of the Seventh,
are easily determined, by anatomical  examination of  its distribution, and by
observation  of  pathological phenomena, to be  analogous to those of the two
preceding,   Atrophy or lesion of the trunk destroys  the sense of Hearing;
whilst irritation of it produces  auditory sensations, but does not occasion pain.
From experiments made upon  the
nerve before  it  leaves the cranial
cavity, it appears satisfactorily as-
certained, that this  nerve  is  not
endowed either with common sen-
sibility,  or  with  the power  of di-
rectly stimulating muscular  move-
ment.  Nor can any obvious reflex
actions be executed  by irritation of
this  nerve;  but it seems neverthe-
less  by no  means improbable, that
the muscles  which regulate the ten-
sion  of the  tympanum,  are  called
into  action  by impressions  made
upon  it and reflected  through  the
auditory ganglion, in the same man-
ner as the diameter of  the  pupil is
regulated through  the Optic  nerve.
—It  has been attempted by  Flou-
rens  to  show, that  the division of
the Auditory nerve, which proceeds
to  the  Semi-circular  canals,  has
functions  altogether  different from
that portion  which supplies the Ves-
tibule and  Cochlea.   This inference, however, is grounded only upon the
movements  exhibited by animals, in  which these nerves are irritated; which
movements are capable of a different explanation (§ 432).

  a. It is interesting to remark, that microscopic examination of the structure of the Audi-
tory nerve clearly indicates its intermediate character between the nerves of special sensa-
tion issuing from  the anterior part of the cranium (namely, the Optic and Olfactory), and
those whose function is to minister, either to common sensation, or to that of Taste, which
approaches nearly to it, (namely, the Fifth pair and the Glosso-pharyngeal,) which issue
from the posterior part of the Encephalon, and  are more nearly analogous to the Spinal
nerves.  The primitive fibres are not so soft as those of the  Olfactive, nor so slender as
those of the Optic; and they  are softer than those ofthe Glosso-pharyngeal.  Moreover, the
Auditory nerve forms a plexus with  the Facial, to which there is no analogy in the Optic
and Olfactive nerves, but to  which a similar  one  exists in the Glosso-pharyngeal.  This
intermediate structural character is  interesting, -when we compare it with  the intermediate
character of the function; for the impressions made upon the sense of Hearing are pro-
duced through vibrations of a material fluid,—instead of being, as in the case of Sight, the
result of changes so subtle  as to be almost  inscrutable to our means of research,—or, as in
the case of Taste and Touch, being produced by the direct contact of the substance which
gives rise to the sensation.

   447. The nerves which  minister  to the sense  of  Taste,  as already men-
tioned, are  destitute of  the  peculiarities  which  distinguish  the  preceding;
being no other than certain  branches of  ordinary afferent nerves,—the Fifth
Pair  and  Glosso-pharyngeal,—the  peculiar endowments of which seem to
[Fig. 161.
  A view of the origin and distribution of the Portio
Mo His of the Seventh pair or Auditory Nerve ; 1, the
medulla oblongata; 2, the pons Varolii; 3, 4. the crura
cerebelli of the right side ; 5, the eighth pair of nerves ;
6, the ninth pair; 7,  the auditory nerve distributed to
the cochlea and  labyrinth; 8, the sixth pair of nerves;
9, the portio dura ofthe seventh pair; 10, the fourth
pair ; 11, the fifth pair.] 
344
FUNCTIONS OF THE NERVOUS SYSTEM.
depend rather upon the structure and actions ofthe papillae at their peripheral
extremities, than upon anything special in their own characters.—From  the
recent observations and experiments  of M. Ch. Bernard, it appears that  the
Facial nerve (Portio  Dura of the 7th) supplies some condition requisite  for
the sense of Taste, through the branch known as the Chorda Tympani, which
is the motor nerve of the  Lingualis  muscle.   When paralysis of the Facial
exists in Man, the  sense of taste is very much impaired on the corresponding
side of the tongue, provided  the cause of the  paralysis be seated above  the
origin ofthe Chorda  Tympani from its trunk.  Similar results have  been  ob-
tained from experiments upon  other  animals.  The nature of the influence
afforded by this nerve is entirely unknown ; and it is the more obscure, as  the
Chorda Tympani contains no sensory filament.
  448. To the sense of Touch, all the afferent nerves  of the body (save  the
nerves of special sense) appear to minister; in virtue—according to the hypo-
thesis here upheld—of the direct connection of certain of their fibrils with the
Sensorium commune.  But the degree in which they are capable of producing
Sensations, does not bear any constant relation to their  power of exciting
Reflex actions.  Thus, the Glosso-pharyngeal is  not  nearly so sensitive as
the Fifth pair; though more powerful as an excitor nerve.  The Par Vagum
appears to have even less power of arousing sensory changes; although it is
the most important of all the excitors to reflex action.   So again, the afferent
nerves of  the inferior extremities, in  Man, are less concerned in ministering
to  sensations, than are those  of the superior; and yet they appear to  be  much
more efficient as excitors to muscular action.—These differences  may be  ac-
counted for, by supposing that  the proportion  which the fibres, having their
centre in the ganglionic matter of the Spinal Cord, bear to  that of the  fibres
which pass on to the Sensorium, is  not constant, but is liable  to variation;
the former predominating in  the  Par Vagum  and the Glosso-pharyngeal;
whilst the latter are more numerous in  the Fifth Pair, and in most of the Spi-
nal nerves.
  449. It appears, from what has been  already stated, that all the motor fibres
ofthe Cerebro-spinal system, not exclusively concerned in Reflex movements,
must be  in connection with the Sensory ganglia; since we  find that their
actions, whether simply  consensual, emotional, or volitional, are dependent
upon guiding sensations.   Of these sensations, the greater  proportion  are
received from the muscles themselves ;  but there are certain cases, as we have
seen, in which  the guiding  influence is communicated  rather by the organs
and zierves of Special sense.   Of these, a  good example is afforded by  the
movements of the  Eyeball, presently to be examined  in detail;  and another
is to be found in those of the Larynx, to  be fully treated of hereafter (Chap.
vm.). The Emotions, in like manner, may operate upon all the motor nerves
of the body;  as  we see in the  violent movements of unrestrained passion, or
in  the increased power given to voluntary efforts, by the simultaneous excite-
ment of certain  emotional states.  But, as already remarked, their  ordinary
action is most displayed through the  motor nerves of the face and respiratory
organs.
  450. Consensual  Movements of the Eye.—It will be recollected that, in
the Human Orbit, six muscles for the mqvements of the eyeball are  found,—
the four recti, and the two oblique muscles.  The precise actions of these are
not easily established by experiment on the lower animals;  for in all those
which ordinarily maintain the horizontal position, there  is an  additional mus-
cle, termed the retractor, which embraces the whole posterior portion  of  the
globe, and passes backwards to be attached to the bottom of the orbit.   This
musclexis most developed in Ruminating animals, which, during their whole
time of feeding, carry their heads in a  dependent  position.   In  most  Carni- 
CONSENSUAL MOVEMENTS OF THE EYE.
345
vorous animals, instead of the complete hollow muscular cone (the base inclos-
ing the eyeball, whilst the apex surrounds the optic nerve) which we find in
the Ruminants, there  are four distinct strips, almost resembling a second set
of recti muscles, but deep-seated, and inserted into the posterior instead of the
anterior portion of the globe.   It  is obvious that  the  actions of these must
greatly affect the results of any operation, which we may perform upon  the
other muscles of the Orbit; and, as  it is  impossible  to divide the former,
without completely separating the eye from its attachments, we have no means
of correcting such results, but by reasoning alone.  Experiments upon ani-
mals of the order of Quadrumana, most nearly allied to Man, would be more
satisfactory ; as in them, the retractor  muscle is almost or entirely absent.—
If the origin and insertion of the  four  Recti muscles be examined, however,
no doubt can remain that each  of them, acting  singly, is capable of causing
the globe to revolve in its own direction,—the superior rectus causing the pupil
to turn upwards,—the internal rectus causing it to roll towards the nose,—and
so on.   A  very easy and direct application  of the laws  of mechanics will fur-
ther make it evident to us, that the combined action of any two of the Recti
muscles will cause the pupil to turn in a direction intermediate between  the
lines of their single action; and that any intermediate  position may thus be
given to the eyeball by  these  muscles alone.  This fact,  which has  not
received the attention  it deserves, leads us  to perceive,  that the Oblique mus-
cles must have some supplementary function.  It may be objected that this is
a theoretical statement only; and that  there may be some practical obstacle
to the performance of diagonal  movements by the Recti muscles, which ren-
ders the assistance of the Obliques essential for this purpose.  But to this it
may be replied, that no single muscle can  direct the ball either downwards
and inwards, or upwards and outwards; and that,  as we have good reason to
believe these movements to be effected by the combination of the Recti mus-
cles, there  is no reason why the other diagonal movements should not also be
due to them.
   451.  The most probable account of the functions of the Oblique muscles of
the eye, seems to be that which was long ago suggested by John Hunter, and
which has  received confirmation from the recent experiments of Dr.  G. John-
son.*—It has been just shown  that the action of the Recti muscles upon the
pupil, is such as to cause it to revolve in any given direction;  and they are
put in action, not merely to alter the range of vision, the head remaining
stationary,  but also to keep the  range of vision the same, and to cause the
images of  the objects, upon which our gaze is fixed, still  to fall upon the
same  parts of the  retinae, by maintaining the position  of the eyes when  the
head is moved upwards, downwards, from side to side, or in any intermediate
direction.   But these muscles are not able to rotate the eyeball upon its antero-
posterior axis; and such rotation is manifestly necessary to preserve the fixed
position of the eyeball, and consequently to keep the image of the object un-
der survey upon the same part  of the retina, when the head is inclined side-
ways, or bowed towards one shoulder and then towards  the other.  It appears
from the experiments of Dr. G. Johnson, that the action of the Oblique mus-
cles is exactly adapted to produce such a rotation;  the Inferior oblique, in its
contraction, causing the eyeball to move upon its antero-posterior axis, in such
a manner that a piece of paper, placed at the outer margin of the cornea, passed
downwards and then inwards  towards the nose; and the Superior oblique
effecting precisely the reverse action, the paper at the outer margin of the cor-
nea passing first upwards  and  then inwards.  There was  not the slightest
appearance, in these  experiments, of elevation, depression, abduction, or ad-
* Cyclopaedia of Anatomy and Physiology, vol. iii. p. 790. 
346
FUNCTIONS OF THE NERVOUS SYSTEM.
duction, of the cornea, as a result of the action of the Oblique muscles;  all
these movements being attributable to the Recti alone.
  452. On studying the conjoint movements of the Eyeball, we  are  led to
observe the very curious fact, that they are not so much symmetrical as har-
monious; that is to say, the corresponding muscles on the  two sides are rarely
in action at once; whilst such a harmony or consent exists between the ac-
tions of the muscles of the two orbits, that they work to one common purpose,
namely, the direction of both eyes towards the required objects.  In order to
study them properly, it is necessary to reduce them to some kind of classifica-
tion.  We may divide  them into the Voluntary and the Involuntary; and the
former, being numerous, require  to be further classified.   They may be ar-
ranged under  two  groups; the first  comprising those which  arealike har-
monious  and symmetrical ; the second including those which are harmonious
but not symmetrical.—To the first  group belong the following:—1. Both
eyeballs are elevated by the contraction of the two Superior Recti.—2. Both
eyeballs are depressed by the conjoint action of the Inferior Recti muscles.—
3. Both  are drawn  directly inwards, or inwards and downwards, as when
we look at an object placed on or near the nose ;  this movement is effected by
the action ofthe Internal Recti of the two sides, with or without the Inferior
Recti. It is  evidently symmetrical, but might seem  at first sight not to be
harmonious, because the eyes do not move together towards one  side or the
other; it is, however, really harmonious, since their axes are directed towards
the same  point.—Now it is to be observed, with regard to these movements,
that we can never effect them in antagonism with each other, or with those of
other muscles.  We cannot, for example, raise one eye and depress the other;
nor can we  raise or depress one eye, when we adduct or abduct the other.
The explanation of this will be found in the fact, that we can never, by so
doing, direct the eyes to the same point.—The harmonious but unsymmetrical
movements, forming the second class, are those in which the Internal  and Ex-
ternal Recti of the two sides are made to act together, either alone, or in con-
junction with the Superior and Inferior Recti. They are as follows.—4. One
eye is made to revolve directly inwards, by the action of its Internal Rectus,
whilst the other is turned outwards by the action of its External Rectus.—5.
One eye  is made to revolve upwards and inwards, by the conjoint action of
the Internal and Superior Recti;  the other, upwards and outwards, by the
conjoint action of the External and Superior Recti.—6. One eye  is  made to
revolve downwards and inwards,  by  the conjoint  action of the Internal  and
Inferior Recti; the other, downwards and outwards, by the conjoint  action
of the External and Inferior Recti.—In these movements, two different mus-
cles, the Abducens and Adducens,  are called into action on the two sides; but
they are so employed for the purpose of directing the axes of the eyes towards
the same point.
  453. The normal Involuntary movements of the eyeballs are only of two
kinds.—1. The rotation of the two eyeballs on their own axes, which takes
place when the head is moved in certain directions (§ 451);  this is effected
in direct respondence  to  certain  guiding sensations, and without any influ-
ence  or control  on the part of the will; it is therefore a purely  consensual
action.—2. The revolution of both eyes upwards  and inwards, which takes
place in the acts of coughing, sneezing, winking, &c.;  this is altogether inde-
pendent  of visual  sensations, and is commonly, like the other  movements
associated in these  actions, of a reflex  nature.—Many abnormal  movements
of the eyeballs, in which there  is  neither harmony nor symmetry in the
actions of the muscles, present themselves in convulsive diseases.
  454. It may be stated as a physiological  fact, that  Single Vision with two
eyes is dependent upon the formation of the image upon parts of the two 
CONSENSUAL MOVEMENTS OF THE EYE.
347
retinas, which are accustomed thus to act with each other.  In many physio-
logical works it is asserted, that single  vision is  the result of the impressions
being  made  on corresponding parts of the  two  retina?,—that is to say, on
parts equally distant from the axis, on  one side or the other :  but this seems
to be disproved by the  fact,  that patients who have been long affected  with
Convergent  Strabismus, and who see equally well with both eyes (as many
do), are not troubled with double vision.   On the other hand, when a person
whose eyes  look  straight before  him, is  the  subject  of a disorder which
renders their motions  in any degree  irregular, he is at once  affected  with
double vision ;  and  the same  has been noticed to be a common  immediate
result of the  successful  operation for the cure of strabismus, where vision is
good in both eyes.   Although the images were previously formed on parts of
the  retinae which were  very far from corresponding with each other, yet no
sooner is the position of the eyes rectified (so that the relation  between the
situation of the images  is the same  as  it would  have been in a sound eye),
than the patient sees double.   Now  in  these cases the difficulty very speedily
diminishes, and the  patient  soon  learns to see  single.  It can  scarcely be
imagined, then, that  to  any  other cause  than  habit,  is  to  be attributed the
long-discussed  phenomenon  of single vision with two eyes.   The  mind  re-
ceives  the two images,  frequently combining them together (as Mr. Wheat-
stone's ingenious  experiments with  the Stereoscope  have most satisfactorily
shown, § 547)  to produce  a picture in relief; and so long as these are  con-
veyed to it in the accustomed manner, it reconciles them together, even if the
parts of the retinae on which they are  formed do not  correspond;  but if any
circumstance break  this  chain, and  cause  the images  to be transmitted to the
sensorium through  a  new  channel, the mind  requires some little  time to
adapt  itself to this impression, as it does by habit to almost every other.
  a. That there is a greater tendency to consent between the images, when they are formed
upon corresponding parts of  the retina-, the Author readily admits ;  and he thinks that this
is a principle of some  importance, in explaining the re-adjustment of the  eyes, after  the
operation for Strabismus.  Every one who has seen much of this operation is aware, that
the re-adjustment of the eye is not always immediate, but that, after  the muscle has been
freely divided,  the eye often remains somewhat inverted for a few days, gradually acquir-
ing its straight position.  The Author has known one case, in which, after such a degree of
temporary inversion as seemed to render the  success of the operation very doubtful, ever-
sion actually took  place for  a short time to a considerable extent; after which the axes be-
came parallel, and have  remained so ever since.
  b. Another argument, derived from the results of this operation, in favour of the  con-
sensual movement being chiefly dependent upon the place of the impressions on the retina,
is, that it is much more  successful in those cases, in which the  sight of the most displaced
eye is good, than  in those in which, (as not unfrequently happens from long disuse) it is
much impaired.  In cases of the latter class, the cure is seldom complete.   There is another
curious fact, which may be adverted to in reference to this subject:  Strabismus not unfre-
quently arises from the formation  of an opaque spot on the centre ofthe cornea, which pre-
vents the  formation of any images on the  retina, except by the oblique rays;  and nature
seems to endeavour (so  to speak) to repair the mischief, by causing the eye to assume  the
position most favourable for the reception of these.
  c. To one more point only, connected with  the subject of Strabismus, would the Author
now allude.  He is well convinced, from repeated observation, that those Surgeons are in the
right, who have  maintained, in a recent controversy, that, in a lqrge proportion of  cases,
strabismus is caused by an affection of both sets of  muscles or nerves, and not of one only;
and that it then requires, for  its perfect cure, the division of  the  corresponding  muscle on
both sides.  Cases will be frequently met with, in which this is evident; the two eyes
being employed to nearly the same extent, and the patient giving to both a slight inward
direction, when desired to look straight forwards.   In  general, however, one  eye usually
lpoks straight forwards,  whilst the other is greatly inverted: and the sight of  the inverted
eye  is  frequently affected to a considerable degree  by disuse; so that, when  the patien;
voluntarily rotates it into its proper axis, his vision with it is far from being distinct.   Some
Surgeons have  maintained, that the  inverted  eye is usually the only one in fault, and con-
sider that the division of the tendon of its Internal Rectus is sufficient for the cure.   They 
348
FUNCTIONS OF THE NERVOUS SYSTEM.
would even divide its other tendons, if the parallelism be not  restored, rather than touch
the other eye.  The Author is himself satisfied, however, that the restriction of the abnor-
mal state to a single eye, is the exception, and not the rule, in all but very slight cases of
strabismus ; and to this opinion he is led both by the  consideration of the mode in which
strabismus first takes place, and by the results of the operations which have come under his
notice.   If the eyes of an infant affected with cerebral disease  be watched, there will fre-
quently be observed in them very irregular movements;  the axes of the two being some-
times extremely convergent, and  then very divergent.   This  irregularity is rarely or never
seen to  be confined to one eye. Now, in a large proportion of cases of Strabismus, the
malady is a consequence of some cerebral affection  during infancy or childhood, which we
can scarcely suppose to have affected one eye only.  Again, in other instances we find the
Strabismus to have resulted from  the constant direction of the eyes to very near objects, as
in short-sighted persons; and here, too, the cause  manifestly affects both.
  d. Now it is easy to understand, why one  eye of the patient should  appear to be in its
natural position,  whilst the other is greatly inverted.  The cause of strabismus usually
affects the two eyes somewhat unequally, so that one is much more inverted than the other.
We will call the  least inverted eye A, and the other B.  In the  ordinary acts of vision, the
patient will make most use of  the least inverted eye, A, because he can most readily look
straight  forwards or outwards with it; but to bring it into the axis, or to rotate it outwards,
necessitates a  still more decided inversion of B.   This  remains the position of things,—the
patient usually looking straight forwards with A, which is the eye constantly employed for
the purposes of vision,—and frequently almost burying under the inner  canthus the other
eye, B, the vision in which is of very little use to him.   When, therefore, the tendon of the
internal rectus of B is divided, the  relative position of  the  two  is not entirely rectified.
Sometimes it appears to be so for a time; but the strabismus then begins to return, and it
can only be checked by division of the tendon of the other eye, A; after which the cure is
generally complete and permanent.   That it has not been  so, in many of the  cases on
which operations have been performed, the Author attributes, without the slightest doubt in
his own mind,.to the neglect of the second operation.   As just now stated, the sight of the
most inverted eye is frequently very imperfect; indeed it is sometimes impaired to such an
extent, that the patients speak of it as entirely useless.   That this impairment results in part
from disuse merely, seems very evident, from the great improvement which often succeeds
the rectification of the axes.  The Author cannot help thinking it probable, however, that
the same cause which produced  the distortion of the  eye may, in some instances at least,
have affected the Optic nerve, as well  as the Motor  nerves  of the orbit; and this  idea is
borne out by the fact of the restoration of sight, in certain cases of Amaurosis, by division of
one or more  tendons, where no  Strabismus previously existed.   (See Adams on Muscular
Amaurosis.)   It  is interesting to remark that, in these  cases, Strabismus was usually the
first effect of the operation ; but that the  eye generally recovered  its ordinary position within
a short time, especially when the  sight was improving.

   455.  If this  be admitted, we gain an important step  in the  explanation of
the Consensual movements of the Eye.  The object to be attained  is evidently
this,—that the  usual axes  of the eye should always be  directed towards the
object to be viewed; and  this,  as  we  have  seen, involves the necessity (in  a
great majority of cases), of  unsymmetrical  movements  being performed by
the two eyeballs.  The combination of  these movements  is involuntary or
automatic;  and  appears to  be regulated  by the sensations  received  through
the retinae.   It  is well known that, in children born  blind, the movements are
not consensual; they are  frequently  very far  from being so, in  cases of con-
genital  cataract, where a  considerable amount of light  is evidently admitted,
but where no distinct image can be formed ; and  in such  cases, the movements
are most consensual where the  object is bright  and luminous, and a more vivid
impression therefore made upon the retina.  It is no objection to  this theory
to say, that persons who have  become blind  may still  move their eyes in "a
consensual  manner;  since,  the  habit of  the association of particular  move-
ments having been once acquired, the guidance of the muscles may be effected
by sensations derived from themselves, in the  manner  in which it  takes place
in the laryngeal movements  of  the deaf and dumb ; and, as a  matter of fact,
a want of consent may be often noticed  where  the blindness is total.   The
peculiar vacant appearance, which may be noticed in the countenances of per-
sons completely deprived of  sight by amaurotic or other affections, which do 
FUNCTIONS OF THE CEREBELLUM.
349
not alter the external aspect ofthe eyes, seems to result from this,—that their
axes are parallel, as if the individual were looking into  distant space, instead
of presenting that slight convergence which  must always exist between them,
when the eyes are fixed upon a definite object.   This  convergence, which  is
of course regulated by the Internal Recti, varies in degree according to the
distance of the object, and it  is astonishing  how minute an alteration in the
axes of the eyes is perceptible to a person observing them.  For instance,  A
sees the eyes of B  directed  towards  his face, but he perceives that B is not
looking at him ;  he knows  this by a sort of intuitive interpretation of the
fact, that his face is not the point of convergence of B's  eyes.  But if B, who
might have been previously looking at something nearer or more remote than
A's face, fix his gaze upon the latter, so that the degree of the convergence  of
the axes is altered, without the general direction of the  eyes being in  the least
affected, the change is at once perceived by the person so regarded ;  and the
eyes ofthe two then meet.
   456.  The foregoing considerations maybe summed up in this simple state-
ment :—that, when we  voluntarily direct  our eyes towards any object, the
actions of the several muscles concerned, are guided by  the visual sensations,
rather than by the ordinary muscular sense, through which other voluntary
movements are regulated.  In this manner are accomplished, not merely the
revolutions of the eyeballs from side  to side, upwards and downwards, or  in
any direction that is required to cause the  image to fall most advantageously
upon the two  retinae ;  but also  that rotation on their axes, which keeps the
images  in the same position upon the  retinae, when the head moves in a plane
perpendicular to their axes;  and  likewise that exact convergence of the  two
axes which shall cause them  to meet in the object  on which the attention  is
fixed, and which consequently varies with its distance.   Of all the movements
of the eyes, there is none which  exhibits  the necessity of  the guiding visual
sensations so much as the revolution  of both  eyes inwards.  Some persons
can effect this voluntarily to a greater extent than others ; but even then, they
can only accomplish it by fixing the gaze  upon some object situated  between
the eyes; and cannot call the adductor muscles  into combined action in per-
fect darkness, or if the lids be closed.   Even those  who have the least power
of effecting this extreme  convergence, by at once directing the eyes towards
a very near object, can accomplish it by looking at  an object placed at a mo-
derate  distance, and  gradually bringing this nearer to  the nose, keeping the
eyes steadily fixed upon it.  The unwonted character of the movement  is
shown  in  this,—that it can only be  maintained, even  for a short time, by a
strong effort, producing a  sense of fatigue.   No  effort whatever can  call into
simultaneous  action  the two  external  Recti;  and this fact is an additional
proof of the necessity of  a guiding visual  sensation ; since it is evident, that
no  object can  ever be placed in such a position, as to  require this action for
the direction of the axes of the eyes towards it.

                     6.  Functions ofthe Cerebellum.

   457.  That the Cerebellum has some special function, distinct from that of
the Cerebral Hemispheres, can scarcely be doubted  ; since  its peculiar struc-
ture and position, its independent connections with the  Medulla  Oblongata,
and its extremely variable size relatively to the remainder of the Encephalon,
point it out as an instrument adapted to some particular purpose.   We shall
inquire  briefly into the  nature of the evidence respecting its function, which
is supplied to us by Comparative Anatomy,  by Experiment, and by Patholo-
gical phenomena. A Cerebellum is found in all Vertebrated animals; although
it is in  some extremely small, looking like a little prominence on the Medulla
     30 
350
FUNCTIONS OF THE NERVOUS SYSTEM.
Oblongata.  When this is the case, it is observed that the whole mass is not
a miniature (so to speak) of the large Cerebellum of Man, but that the central
portion (termed the vermiform process) is the part most developed;  the lobes
not presenting themselves until the organ has acquired an increased dimension.
The following table, constructed from materials contained in M. Serres' most
valuable Comparative Anatomy of the Brain, will afford some idea of the ma-
terials  for speculating on the nature of the function of the Cerebellum, which
we obtain from this source.  The first column gives the diameter of the Spinal
Cord, at the  second  cervical vertebra ; in the two succeeding columns are
stated the transverse and the antero-posterior  diameters of the Cerebellum ;
these dimensions are stated in  hundred-thousandths of a metre.  The fourth
column expresses, in round numbers, the proportion which  the diameters of
the Cerebellum bear to that of the  Spinal Cord ; the latter being reckoned as 1.
Mammalia.	Diam. of Spinal Cord at 2d Cervical Vertebra.	Transverse Diam. of Cerebellum.	Anlero-posterior Diameter of Cerebellum.	Proportions.
Man .	1,100	12,000	6,000	11 — 5i
Si mia Rubra.	900	4,500	2,443	5 —2£
Bear	1,300	5.900	3,500	4£-2£
Dog .	1,100	4J200	2,525	3|—2i
Dromedary .	1,900	7,100	4,600	H—21
Kangaroo	1,200	3,800	2J600	3& 2^
Birds.				
Falcon .	400	1,350	1,100	3J-2|
Swallow	3,175	500	600	3 — 3J
Turkey.	500	1,350	1,600	2|—2^
Ostrich .	700	1,750	2,500	2^-3£
Reptiles.				
Crocodile	300	500	400	lf-li
Frog .	300	300	200	1 __ 2 1 J
. Fishes.				
Shark .	700	1,700	3,100	2h—4$
Cod .	575	1.350	1,700	2i—3
Turbot .	500	750	900	H—H
Lamprey	275	225	100	i-f
1				
  458.  This table affords us much scope for interesting speculation, and may
be applied to the correction of hypotheses  erected upon other foundations.
Before we proceed to these, however, a few general remarks may  be  made
upon it.   In the first place, the proportional development of the Cerebellum
is seen to be  smallest in the Vermiform  Fishes, which approach  most nearly
to the Invertebrata; but it is much greater in the higher Fishes  than it is in
Reptiles.  If we consider in what particular, that may be reasonably supposed
to have a connection with this  organ, the former surpass the latter, we should
at once be struck with their superiority in activity and variety of movement.
Passing on to Birds, we remark that the average dimensions of  the Cerebel-
lum greatly surpass those of the organ in Reptiles ; but that they do not exceed
those occasionally met with in  Fishes.  The  greatest size is not found in those 
FUNCTIONS OF THE CEREBELLUM.
351
species which approach most nearly to the Mammalia in general conformation,
such as the Ostrich; but in those of most active and varied powers of flight.
Lastly, on ascending the scale of Mammiferous  animals, we cannot but be
struck with the rapid advance in the proportional size of the Cerebellum, that
we observe,  as we rise from the lowest, which are surpassed in this respect
by many Birds, towards Man, in whom it attains a development which  appears
enormous, even when contrasted with that of the Quadrumana.
   459.  We  have next  to inquire what evidence can be drawn from  Experi-
mental investigations on the same subject: and in reference to this it is desirable
to remark, in the first place, that the experimental mode of inquiry is  perhaps
more applicable to this organ than to other parts of the Encephalon; inasmuch
as it can be  altogether removed, with little disturbance of the actions imme-
diately essential to life; and the animals  soon recover from the shock of the
operation, and seem but little affected, except in some easily-recognized par-
ticulars.  The principal experimenters upon this subject have been Rolando,
Flourens, Magendie, Hertwig, and Longet.   It is not to be expected, that there
should be an exact conformity  among the results obtained by all.  Every one
who has been  engaged  in physiological experiments, is aware of the  amount
of difference caused by very minute variations in their circumstances; in no
department of inquiry is this  more the case than  in regard to the Nervous
System; and such differences  are yet more likely to occur, in experiments
made upon the Nervous Centres, than in those which concern their trunks.—
The investigations of Flourens  are the most clear and decisive in their  results ;
and of these  we shall accordingly take a general survey.   He found that, when
the Cerebellum was mechanically injured, the animals gave no signs of sensi-
bility, nor were they affected with convulsions.  When the Cerebellum was
being removed by successive slices, the animals became restless, and  their move-
ments were irregular; and by the time that the last portion of the organ was cut
away, the animals  had entirely lost the powers of  springing, flying, walking,
standing, and preserving their equilibrium,—in short, of performing any com-
bined muscular movements, which are not of a simply-reflex character.  When
an animal in this state was laid upon the back, it could not recover its former
posture; but it fluttered its wings and did not lie in a state of stupor.   When
placed in the erect position, it staggered and fell like a drunken man,—not, how-
ever, without making efforts to  maintain its balance.  When threatened with a
blow, it evidently saw it, and endeavoured to avoid it.  It did not seem  that the
animal had in any degree lost voluntary power over its several muscles ; nor did
sensation appear to be impaired.  The faculty of combining the actions of the
muscles in groups, however, was completely destroyed; except so far as those
actions (as that of respiration)  were dependent only upon the Reflex function
of the Spinal Cord.  The experiments afforded the same results, when made
upon each class of Vertebrated animals;  and they have since been repeated,
with corresponding effects, by Bouillaud and Hertwig.  The latter agrees with
Flourens, also, in stating that the removal of one side of the Cerebellum affects
the movements of the  opposite  side of the body;  and  he further mentions
that, if the mutilation of the Cerebellum have been partial only, its  function is
in great degree restored.
   460.  All these results are objected to by those who assert that the Cerebel-
lum  is the seat of the sexual instinct; on the ground that the observed aberra-
tions of the motor functions  are sufficiently accounted for,  by the  general
disturbance  which  an  operation  so severe must  necessarily  induce.  The
fallacy of this objection, however, is shown by the fact, that the much more
severe operation of removing  the  Hemispheres does  not occasion such an
aberration; the power of performing the associated movements, and of main- 
352
FUNCTIONS OF THE NERVOUS SYSTEM.
taining the equilibrium, being remarkably preserved after the loss of them
(§435).
  461. Upon comparing these results with the preceding table, a remarkable
correspondence will be observed between them.  The classes which have the
greatest variety of movements, and which require for them  the most perfect
combination of a large number of separate muscular actions, have,  taken col-
lectively, the largest Cerebellum.  Of all classes of Vertebrata, Reptiles  are
the most  inert; and  their motions require the least co-ordination.  The active
predaceous Fishes far surpass  them  in this respect; and may be  compared
with Birds, in the energy of their  passage through  the water, and in their
facility of changing their direction during the most rapid progression.  The
Cerebellum, accordingly, bears  to the Spinal Cord in  them, very  much  the
same proportion as it does in Birds.  On the other hand, the  Flat Fish, which
lie near the bottom of the ocean, and which have a much less  variety of move-
ment, have a very much smaller cerebellum : and the Vermiform Fishes, which
are almost all completely destitute of fins, and whose progression  is accom-
plished by flexion of the body, have a Cerebellum so small as to be scarcely
discoverable : their motion being, like that of the Articulata, almost  entirely of
a reflex character,—each segment being influenced by its own ganglionic cen-
tre, and the Spinal Cord constituting by far the largest proportion ofthe nervous
centres.   On looking at the class of Birds, we observe that the active preda-
ceous Falcons, and  the Swift-winged Swallows (the perfect control  possessed
by which over their complicated movements must have been observed by every
one), have a Cerebellum much larger in  proportion than that of  the Gallina-
ceous birds, whose  powers of flight are small, or  than  that of the Struthious
tribe, in which they are altogether absent.  Lastly, on  comparing its propor-
tional size in the different orders of Mammalia, with  the number and variety
of muscular actions requiring combined movements, of which  they are respect-
ively capable, we observe an even more remarkable correspondence. In  the
hoofed Quadrupeds, in which the  muscular apparatus of the  extremities is
reduced to its greatest simplicity, and in which the movements of progression
are simple, the Cerebellum is relatively smaller than it is found to be in some
Birds; but in proportion as  the extremities acquire the power of prehension,
and together with this a power of application to a great variety of purposes,—
still  more, in  proportion as the animal  becomes capable of maintaining the
erect posture, in which  a constant muscular exertion, consisting of  a number
of most  elaborately-combined parts, is required,—do we find the size of the
Cerebellum, and the complexity of its structure, undergoing a rapid increase.
Thus, even between the Dog and the Bear there is a marked difference ;  the
latter being capable of remaining for some time in the erect posture, and often
spontaneously assuming it;  whilst  to the former it  is anything  but natural.
In the semi-erect Apes, again, there  is a very great advance in the proportional
size ofthe Cerebellum ; and  those which  most approach Man in the tendency
to preserve habitually the erect posture,  also come nearest to him  in the di-
mensions of this organ.
   462. Now it is evident that Man, although far inferior to many  of the lower
animals  in the power of performing various particular kinds of movement, far
surpasses them all, in the number and variety of the combinations  which he
is capable of executing, and in the complexity of the combinations themselves.
Thus, if  we attentively consider the act of walking in man, we shall find that
there is  scarcely a  muscle of the trunk or extremities which is  not actually
concerned.in it; some being engaged in performing the necessary movements,
and others in maintaining the equilibrium of the body, which is disturbed by
them.  On the  other hand, in the horse or Camel, the muscular movements
are individually numerous, but they do not  require  nearly the same perfect 
FUNCTIONS OF THE CEREBELLUM.
353
co-ordination.  And in the Bird, the number of muscles  employed  in the
movements of flight, and in directing the course of these, is really comparatively
small; as may at once be perceived, by comparing the rigidity ofthe skeleton
of the trunk of the Bird with that of Man, and by remembering the complete
inactivity of the lower  extremities  during the active condition of the  upper.
In fact,, the motions of the wings are so simple and regular, as to suggest the
idea, that, as in Insects, their character is more reflex than directly voluntary:
—an idea which is supported by the length of time during which they  can be
kept up without apparent fatigue, and also by the important facts already men-
tioned, which experimental research has disclosed (§ 435).  It is  seen, then,
that Comparative Anatomy fully confirms the  idea, which Experimental physi-
ology suggests, respecting the chief  functions of the Cerebellum.
  463.  Some of Magendie's  experiments indicate  a further  connection of
this organ with the motor function, the nature of which  is  still obscure.  This
physiologist asserts that, if a wound be inflicted on the Cerebellum, the  animal
seems compelled by an  inward force to  retrograde movement, although ^mak-
ing an effort to advance; and that, if the Crus  Cerebelli on  one side be injured,
the animal is caused to roll over towards the same side.  Sometimes (if Ma-
gendie's  statements can be relied on), the animals make sixty revolutions in a
minute, and  continued this movement for a week without cessation.  Division
of the second Crus Cerebelli restored the equilibrium.  Hertwig observed the
same  phenomenon, when the Pons Varolii  (which  is nothing more than the
commissure of the Cerebellum, surrounding the Crura Cerebri) was injured on
one side; and he has also remarked, that the movements  of the eyes were no
longer consensual.
  464.  On turning to Pathology for evidence of the functions of the Cerebel-
lum, we  meet with much that seems contradictory.  It must be remembered
that a sudden effusion of blood, even to  a small extent, in  any part of the En-
cephalon, is  liable to produce'the phenomena of apoplexy or paralysis; and
inferences founded upon the phenomena exhibited after sudden lesions of this
description are, therefore, much less valid, than those based on the results of
more chronic affections.  In regard to these last, however,  it is to be observed,
that we  are not yet in a condition  to  be able to state with  precision, what
amount of morbid alteration in any part of the nervous centres, is compatible
with but slightly-disturbed  performance of  its function; and that cases are
every now and then occurring, which  would upset all our previous notions, if
we  were not aware, that the same difficulty  presents itself, even  in regard to
the  best-established results  in Neurology.   It is also to be  remembered, that
the  results of disease, occasioning pressure, will be peculiarly liable to affect
the  Medulla oblongata, as well as the  Cerebellum;  and will thus  occasion a
greater loss of motor power than  would be occasioned by the mere suspension
of the function of  the latter.
  465. Pathological  phenomena, when examined  with  these  reservations,
appear to coincide with the results of experiment, in supporting the conclu-
sion, that the Cerebellum is not in any way  the instrument of psychical ope-
rations.  Inflammation of the membranes covering it, if confined to that part,
does not produce  delirium ; and its almost complete destruction  by gradual
softening, does not appear  necessarily to involve  loss of intellectual power.
"But," remarks  Andral, " whilst the  changes  of  intelligence were  variable,
inconstant, and of little  importance, the lesions of motion, on the contrary,
were  observed in all the cases [of softening which had  come under his no-
tice] except one ;  and in this it is not quite certain that motion was not inter-
fered with."  In general, apoplexy of the Cerebellum is accompanied by para-
lysis ; but this is  by no means  usual in cases of chronic  disease, in which
there is rather an irregularity of  movement, with a degree of restlessness re-
                                  30* 
354
FUNCTIONS OF THE NERVOUS SYSTEM.
sembling that described by Flourens as resulting from partial injury of this
organ.  In a few cases in which both  lobes of the  Cerebellum have been
seriously affected, the tendency to retrograde movement hasbeen observed ;
and instances are also on record, of the occurrence of rotatory movement,
which has been found to  be  connected with lesion of the  Crus Cerebelli on
the, same side.  So far as they can be relied on, therefore, the results of the
three  methods of investigation bear a very close correspondence; and it can
scarcely be doubted that they afford us  some approximation to truth.
  466. We have  now to examine, however, another doctrine regarding the
functions of the Cerebellum, which was propounded by Gall,  and which is
supported by the Phrenological school of physiologists.  This doctrine—
that the Cerebellum is the organ of the sexual instinct—is by  no  means in-
compatible with the other; and by some it has been held in combination with
it.  The  greater number of Phrenologists, however, regard  this instinct as the
exclusive function of the Cerebellum;  and assert that they can judge of its
intensity, by the degree of development of the  organ.  We shall now exam-
ine  the evidence in support of this position, afforded by the three methods  of
inquiry which have been already indicated.  The results of fair observation
as to the  comparative size of the Cerebellum in different animals, can scarcely
be regarded as otherwise than very unfavourable to  the doctrine in question.
In the greatest number of Fishes, it is  well known  that no  sexual congress
takes  place ; the seminal fluid being merely effused, like any other excretion,
into the surrounding water;  and being thus brought into  accidental  contact
with the  ova, of which a large proportion are never fertilized.   But there are
certain Fishes, as  the Sharks, Rays and Eels, in which copulation takes place
after the  ordinary method.   Now on contrasting these two groups, we find no
corresponding difference in the size of the Cerebellum.  It is true that this
organ is of large size in the Sharks ; but it is very small  in  the Rays ; and
almost rudimentary in the Eels :—in this respect bearing a precise correspond-
ence with the variety and complexity of their movements.  Further, in many
ordinary  Fishes, which do not copulate, such as the Cod, the Cerebellum is
not  only  larger, but more complex  in  structure, than it is in the generality of
Reptiles, in which the sexual instinct is commonly strong ;—the whole spinal
system of the Frog possessing, at the season of reproduction, an extraordinary
degree of excitability, which is evidently destined to aid in the performance
of the function  (§401, a).   Again,  in comparing  the Gallinaceous Birds,
which are polygamous, with  the Raptorial and Insessorial tribes which live
in pairs,  we find that the former, instead of having a larger cerebellum, have
one of inferior  size.   Further on looking at the  Mammalia, the same dispro-
portion may be noticed.  A  friend who kept some Kangaroos in his garden,
informed the Author that they were the most salacious animals  he ever saw;
yet  their~Cerebellum is one of the smallest to be found in the class.   Every
one knows, again, the salacity of Monkeys ; there are many which are excited
to violent demonstrations by the sight even of a human  female;  and there
are few which do not practise masturbation, when kept in solitary confinement:
yet  in them the Cerebellum is much smaller than in Man, in whom the sexual
impulse is  much less violent.  It has been supposed that the large size of the
organ in Man is connected with his constant possession ofthe appetite, which is
only occasional in others ; but this does not hold good; since among domestic
animals,  there are many which are ready to breed throughout the year,—Cats
and Rabbits for instance;  and in these we do not find any peculiar difference
in the size of the Cerebellum.  It is asserted, however, that the  results  of
observation in Man lead to a positive  conclusion, that  the size of the Cere-
bellum is a measure of the intensity of the sexual instinct in the individual.
This  assertion  has been  met  by  the counter-statement of others,—that no 
FUNCTIONS OF THE CEREBELLUM.
355
such relation exists.  It is  unfortunate that  here, as in many other instances,
each party has registered the observations  favourable  to their own views,
rather than  those  of an opposite  character;  so  that until  some additional
evidence  of a less partial nature has been collected, we must consider the
question  as  sub judice.   The  Author is  by no  means  disposed  to deny
that such a correspondence may exist;  but  on contrasting the  degree of sup-
port which this part of phrenology really derives from pathological evidence,
with that which the upholders of this view represent it to receive, he cannot
but look with much distrust at all their observations on the subject.
   467. It is stated in  Phrenological works, as an  ordinary result of disease
of the Cerebellum, that there is an  affection of the genital organs, manifest-
ing itself in  priapism,  turgescence  of the  testes, and sometimes  in  seminal
emissions.   Now it is  quite true that,  in cases of apoplexy, in which these
symptoms manifest themselves, there  is very commonly  found to be  effusion
upon the  Cerebellum or in its substance ; but it is to be  remembered, that in
all such lesions the Medulla Oblongata  is  involved, and these  symptoms,
equally with paralysis, may be due  to affection of that organ.*   Further, the
converse does  not by any means hold  good; for  the proportion of  cases of
disease of the  Cerebellum, in which  there  is  any manifest  affection of the
sexual  organs, is  really very small, being,  according to  the calculations of
Burdach, not above one in seventeen.  -The  same physiologist states that such
affections do present themselves, although very rarely, when  the Cerebrum is
the seat of the lesion.   A large number of facts adduced by Phrenologists in
support of their views—such as the erections and emissions which often take
place during hanging—may be explained as well, or even better, on the hypo-
thesis that the  Cerebro-spinal axis (that is, the Spinal cord with the Medulla
Oblongata) is the seat of this instinct.  And this hypothesis is much more con-
formable to the results  of experiment and disease, than that which locates it in
the Cerebellum.  For it has  been found that mechanical irritation of the Spinal
Cord, and disease in its substance, much more  frequently produce excitement
of the genital organs, than do lesions of the  Cerebellum.  This view is en-
tertained by Muller, and by most physiologists who have taken a compre-
hensive and  unbiassed  survey of the phenomena in question.
   468. Among the arguments adduced by Gall and his followers in proof of
the connection between the Cerebellum  and the sexual instinct, is one which
would deserve great attention, if the facts stated could be relied on.   It  has
been asserted, over and over again, that the Cerebellum, in animals which have
been castrated when young, is much smaller  than in those which have retained
their virility,—being, in fact, atrophied from want of  power to act.   Now, it
is unfortunate that vague assertion,  founded on estimates formed  by  the  eye
from  the cranium alone, is all on which this position rests ; and it will be pre-
sently shown, how very liable to  error  such an estimate must be. The  fol-
lowing is the result of a series of observations on  this subject, suggested by
M. Leuret,t and carried into effect by  M.  Lassaigne:—The weight of the
Cerebellum,  both absolutely  and as compared with that ofthe Cerebrum, was
adopted as the standard of  comparison.  This was  ascertained in ten Stal-
lions, of the ages of from nine to seventeen  years;  in  twelve Mares, aged

  * A case has been  recently communicated  to the Author, in which  the sexual  desire,
which had been always strong through life, but  which had been controlled within the limits
of decency, manifested itself, during a period of some months preceding death, in a most
extraordinary degree: on post-mortem examination a tumour was found on the Pons Varolii.
This fact harmonizes with the view given in the text (§ 470), that the sexual instinct, if con-
nected with the Cerebellum at all, has its seat in the central lobe: but it also corresponds
equally well with the idea, that the Medulla Oblongata is its centre.
  ■j" Anat. Comp. du Systeme Nerveaux, torn, i., p. 427. 
356
FUNCTIONS OF THE NERVOUS SYSTEM.
from seven to sixteen years; and  in twenty-one  Geldings, aged  from seven
to seventeen  years.   The average weight of the Cerebdpurn *n the Stallions
was 433 grammes; the greatest  being 485 gr., and the least (which was in a
horse of ten  years old) being 350.  The  average weight of the  Cerebellum
was 61 gr. ; the greatest being 65 gr., and the least 56 gr.  The average pro-
portion borne by the weight of the Cerebellum to that ofthe Cerebrum, was,
therefore, 1 to 7*07 ; the highest  (resulting from a very small Cerebrum) being
1 to 6'25; and the lowest (resulting from an unusually large Cerebrum) being
1 to 7*46.  Throughout it might be observed, that the variation in the size of
the Cerebellum was much less than in that of the  Cerebrum.—In the twelve
Mares, the average weight of the  Cerebrum was 402 gr.; the highest being
432 gr., and the lowest 363 gr. That of the Cerebellum was 61 gr.; the high-
est being 66 gr., (which was in  the  individual with the  smallest Cerebrum),
and the lowest 58 gr.   The average proportion of the weight of the Cerebel-
lum to that of the Cerebrum was 1 to 6-59 ; the highest  being 1 to 5'09, and
the lowest 1 to 7.   The proportion was, therefore, considerably higher in the
perfect  female,, than in the perfect male.—In the  twenty-one Geldings, the
average weight of the Cerebrum was 419 gr.; the highest being 566  gr., and
the lowest 346 gr.  The average of the Cerebellum was 70 gr. ; the highest
being 76 gr.,  and the lowest 64 gr.  The average proportion was, therefore,
1 to 5*97; the highest being 1 to 5" 16, and the lowest 1  to 7*44.   It  is curi-
ous, that this  last was  in the individual which had the largest Cerebellum of
the whole ; but the proportional weight of  the Cerebrum was still greater.
  469.  Bringing together the results of  these  observations, they are found to
be  quite opposed  to  the statement of  Gall.  The  weight of  the  Cerebrum,
reckoning the  Cerebellum as 1, is thus expressed in each ofthe foregoing de-
scriptions of  animals:—
                                  Average.    Highest.    Lowest.
          Stallions    ....  7-07        7-46       6-25
          Mares      ....  6-59        7-00       5-09
          Geldings    ....  5-97        7-44       5-16
The average proportional size of the Cerebellum in Geldings, therefore, is so
far  from being less than that which it bears in entire Horses and  Mares, that
it is positively greater;  and this depends not only on diminution in the rela-
tive size of the Cerebrum, but on its own larger dimension, as the following
comparison of absolute weights  will show:—
                                  Average.    Highest.    Lowest.
          Stallions    ....   61          65       56
          Mares      ....   61          66       58
          Geldings    ....   70          76       64
The difference is so  remarkable, and appears, from  examination  of the indi-
vidual results, to be so constant,  that it cannot be attributed to any accidental
circumstance,  arising  out of the  small  number of animals experimented  on.
The average weight of the Cerebellum in the ten Stallions and twelve Mares,
is seen to be the same ; and the extremes  differ but little in the two ; whilst
the average in the Gelding is more than one-seventh higher, and the lowest is
considerably above the average of the preceding, while the highest far  exceeds
the highest amongst the entire  Horses.   It is curious that Gall  would have
been much nearer the truth, if he had said that the dimensions of the Cere-
brum  are usually reduced by castration;  for it  appears from the following
table that this is really the case:—
                                   Average.    Greatest.     Least.
          Stallions    ....   433         485       350
          Mares      .....   402         432      336
          Geldings    ....   419         566      346 
FUNCTIONS OF THE CEREBRUM.
357
The weight of the largest Cerebrum of the Gelding is far above the highest of
the Stallions ; but it seems  to be an extraordinary case, as in no other was the
weight above 490 gr.   If this one be excluded, the average will be reduced
still further, being then  about 412 ;  this may be seen, by looking over the
whole table, to give  a very fair idea of the  usual weight  in  these  animals,
which is therefore less, by about one-twentieth, than the average of  the Stal-
lions.—The increased size of the Cerebellum in Geldings may perhaps be
accounted for by remembering that this class of  horses is solely employed
for its muscular power, and that the constant exercise of the organ is not un-
likely to develop its size;  whilst Stallions, being kept especially for the  pur-
pose of propagation, are  much less  applied to occupations which call forth
their motor  faculties.
   470.  The Author is far from denying in toto, that any peculiar connection
exists between the Cerebellum and the Genital  system ; but if the evidence
at present adduced in support of the Phrenological position be held sufficient
to establish  it, in defiance of so many opposing  considerations, we must bid
adieu to all  safe  reasoning in Physiology.  The  weight of  testimony appears
to him to be quite decided, in regard to the connection of the Cerebellum with
the regulation of the motor function.   How far this  invalidates the moderate
phrenological view, which  does not regard the function of  the Cerebellum as
exclusively  devoted to the  sexual  instinct, is a question well deserving of at-
tention.  There is nothing opposed to such an  idea in the results of the ex-
periments already  adverted to (§ 459) ;  since there is no evidence that sexual
instinct remained after the removal of the Cerebellum ; but,  on the other hand,
there is  no proof that it was destroyed.  A circumstance which  has been
several times mentioned to him,—that great application to gymnastic exercises
diminishes for a time the sexual vigour, and even totally suspends desire,—
seems worthy of consideration in reference to such a view.  If the Cerebellum
be really connected with both kinds of functions, it does not seem unreasona-
ble that the  excessive employment of it upon one should diminish its energy
in regard to the other.  Further, it would seem by no means improbable, that
the Lobes  are specially connected with the  regulation and co-ordination of
movements; whilst the Vermiform processes, which are very large  in many
animals in which the former scarcely present themselves,  are the parts  con-
nected with the  sexual function.  As an additional argument in favour of the
former part  of this view, it may be stated, that in Man the  lobes bear a larger
proportion to the Vermiform  processes  than  in  any other animal;  and that
they undergo their most rapid development  during the first few years of life,
when a large number of  complex voluntary movements are being learned by
experience,  and are  being  associated by means  of the muscular  sensations
accompanying them:  whilst in those animals which have, immediately after
birth, the power of regulating their voluntary movements for definite objects,
with  the greatest  precision, the Cerebellum  is  more fully developed  at  the
time of birth.   In both instances it is well formed and in active operation (so
far as can be judged of by the amount of circulation through it), long  before
the sexual instinct manifests itself in any perceptible degree.

                      7. Functions ofthe Cerebrum.

   471.  We come, in the last  place, to consider  the functions of that portion
of the Nervous  Centres, which is evidently, in  Man, the predominant organ
of his whole system ;  being not merely the instrument of his reasoning facul-
ties, but also possessing a direct or indirect control over nearly all the actions
of his corporeal frame, save those purely vegetative processes, which are most 
358
FUNCTIONS OF THE NERVOUS SYSTEM.
completely isolated from his animal powers.   We should be in great danger,
however, of coming to an erroneous conclusion as to the real character of the
Cerebrum and of its operations, if we confined ourselves to the study of the
Human organism; and the history of Physiological science shows, that every
advance of knowledge respecting its functions, has tended to limit them, whilst
at the same  time rendering them more precise.   Thus the Brain (this term, in
the older Anatomy, being chiefly appropriated to the Cerebrum) was accounted,
not merely the  centre of all motion and  sensation, but also the source of all
vitality ; the different processes of nutrition, secretion, &c, being maintained,
it was supposed, by a constant supply of " animal  spirits," propagated from
the brain,  along the nerves, to each individual part.   The  more modern doc-
trine, that  the Sympathetic System has for its  special function to supply the
nervous influence  requisite for the maintenance of the functions  of  Organic
life, was the first step in the process of limitation ; still the Brain was regarded
as the centre of all the Animal functions ; and no other part was admitted to
possess any power independently of it.   By  experiments  and  pathological
observations, however,  the  powers of the Spinal  Cord as an independent
centre of action were  next  established ;  and it was thus shown, that there is
a large class of motions, in which the Brain has no concern, and  that the re-
moval of the Cerebral  hemispheres is not incompatible (even among the higher
Vertebrata) with the prolonged maintenance of a sort of inert and scarcely
conscious  life.  Still, it has been  usually maintained, and with great show of
reason, that the Cerebrum is the instrument of all psychical operations;  and
of all  the movements which could not be assigned to the reflex action of the
Spinal Cord.  An attempt has  been made, however, in the preceding pages,
to show that this view is not altogether correct;  and  that there is a class of
actions, neither reflex nor voluntary, but  directly consequent .upon Sensations
and  upon the instinctive and  emotional propensities associated with  these,
which  may be justly  assigned to certain  ganglionic centres,  not less inde-
pendent of the Cerebrum than is the Spinal Cord itself.  It has been advanced,
that the Cerebrum must be considered  in the  light of an organ superadded
for a particular purpose or set of  purposes, and not as one which is essential
to life;  that it has no representative among the Invertebrata (except in a few
of the  highest forms, which evidently present a transition towards the Verte-
brated  series);  and that, at its  first introduction, in the class of Fishes, it evi-
dently performs a subordinate part in  the general  actions of the Nervous
System.   Hence,  whatever be the function, or set of  functions, we assign to
the Cerebrum, we must keep in view the special character  of the organ ;  and
must never lose  sight of the fact,  that its predominance in Man does not de-
prive other parts of their independent powers, although it may  keep the exer-
cise of those powers in check, and may considerably modify their manifesta-
tions.
  472. Before proceeding to inquire into the  Physiology  of the Cerebrum,
we may advantageously take notice of some of the leading features  of its struc-
ture.—In the first  place, it forms an exception  to  the  general plan, on  which
the elements of ganglionic centres are arranged ;  in having its vesicular sub-
stance  on  the exterior, instead of  in the central part of the mass.  The pur-
pose of this is probably to  allow the vesicular matter to be disposed in such
a manner, as to present a very large surface, instead  of being aggregated to-
gether in  a more compact  manner ; and  by this means, to admit the more
ready access, on the one side, of  the blood-vessels which are so  essential to
the functional operations of  this tissue, as well as the more ready communi-
cation, on the other, with the vast number of fibres, by which its  influence is
to be propagated.  There is no reason  whatever to believe, that the functions 
FUNCTIONS OF THE CEREBRUM.
359
of the vesicular and fibrous substances are in the least altered by this change
in their relative position ; indeed the results of observation upon the pheno-
mena of disordered Cerebral action are such, as to afford decided confirmation
to the idea already propounded,—that the action of the  vesicular matter con-
stitutes the source of nervous power; whilst the fibrous structure has for its
office, to conduct the influence generated in the preceding, towards the points
at which it is to operate.   The  purpose of this  arrangement is further evi-
denced by the fact, that, in  all the higher forms of Cerebral structure, we find
a provision for a still greater extension of the surface, at which the vesicular
matter and the blood-vessels may come  into relation ; this  being effected, by
the plication of the layer of vesicular matter into  " convolutions,"  into  the
sulci  between which, the highly vascular membrane known as the pia mater
dips down, sending multitudes of small vessels from its  inner surface  into  the
substance it  invests.—In the  fibrous or medullary substance  of which  the
great  mass of the Cerebrum is composed, three  principal sets  of fibres may
be distinguished.  These are,—first, the radiating fibres, which  connect  the
vesicular matter of the cortical substance of the hemispheres  with the Thala-
mi  Optici, and which, if our view of the  function of  the latter be  correct,
may be regarded as  ascending  or sensory;—second,  the radiating fibres,
which connect the  vesicular matter  of  the  cortical substance  of the hemi-
spheres with the Corpora Striata, and which, on  similar grounds, may be re-
garded as descending or motor;—and third, the Commissural fibres, which
establish the  connection between the opposite hemispheres, and between  the
different parts of the vesicular substance of the same side, especially between
that disposed on the surface of each hemisphere, and those  isolated patches
which are found in its interior.  It is  on  the very large  proportion which
the Commissural fibres bear  to  the  rest, that the bulk  of the  Cerebrum of
Man  and of  the higher animals  seems chiefly to depend;  and it is easy to
conceive, that this condition has  an  important relation with the operations of
the Mind, whatever be our  view  of the relative functions of different parts of
the Cerebrum.  It appears  from  the late researches of M. Baillarger,  that  the
surface and the bulk of the cerebral hemispheres are so far from  bearing any
constant proportion to each other, in different animals,  that,  notwithstanding
the depth of  the convolutions  in the Human Cerebrum, its bulk is 1\  times
as great in proportion to its  surface, as it  is in the Rabbit, the surface of whose
Cerebrum is  smooth.   The entire surface of the Human Cerebrum, when  the
convolutions  are unfolded, is estimated by him at about  670 square inches.*
  473. With regard to the Radiating fibres,  which  connect the  Corpora
Striata and Thalami Optici  with  the vesicular surface of the  Cerebral hemi-
spheres, it must be admitted that no positive  proof  has yet been  obtained of
their direct continuity with  those, which enter into the composition of  the
nerves proceeding from the  Spinal  Cord and  Medulla Oblongata  ; and  how-
ever probable such  a continuity may be  regarded on some grounds, there  are
certain phenomena, which may perhaps  be  better explained on the idea, that
these radiating fibres are of  a commissural nature only, serving  to connect the
vesicular matter ofthe Cerebrum with thatof the different portions  ofthe  Cranio-
spinal Axis (under which  term  are  included the Spinal Cord, the  Medulla

  * The inference drawn by M. Baillarger from the facts he has collected,—namely,  that
the proportional surface of vesicular matter in  different animals, whether considered abso-
lutely, or relatively to the volume of the Cerebrum, has no correspondence  with their intel-
lectual capability,—is far too sweeping an assumption; since, as above shown, the increase
in the  commissural fibres, causing an augmentation ofthe bulk of the Cerebrum, may be alike
the cause of increased intelligence and of a diminished proportional amount of vesicular mat-
ter ; though the latter still remains as the original source of power. 
360
FUNCTIONS OF THE NERVOUS SYSTEM.
Oblongata, and the chain  of Sensory Ganglia at the summit of the latter),
and thus brought, through the medium of the latter, into  relation with the cen-
tral terminations of the afferent nerves, and the origins of the motor.  On this
view, the Cerebrum would receive all its  sensory impressions, by the commis-
sural fibres that connect it with the ganglia, which are the real centres of these
nerves ; whilst it would call the motor trunks into action, by exciting, through
another set of commissural fibres, the vesicular matter of the ganglionic cen-
tres from which they pass forth.*—This  question cannot be determined until
it shall have been shown, whether there  is, or is  not, a direct continuity be-
tween any of the fibres of the trunks connected with the Cranio-Spinal  Axis,
and any  of the radiating fibres of the Cerebral hemispheres.   But  the  latter
view is certainly favoured by the very remarkable fact, in  which the results
of all experiments agree, that no  irritation or injury of the Cerebral fibres
themselves, produces either sensation or motion.   Even the Thalami and Cor-
pora Striata may be wounded, without the excitement of convulsive actions;
but if the incisions involve the Tubercula Quadrigemina or the Medulla Ob-
longata, convulsions uniformly occur.  These results are borne out  by patho-
logical observations in Man ;  for it  has  been frequently remarked, when  it
has been necessary to separate protruded portions of the Brain  from the
healthy part, that this has given rise to no sensation, even  in cases  in which
the mind has been perfectly clear at the time.
  474.  The Commissural fibres constitute two principal  groups, the trans-
verse, and the longitudinal; the former connecting the two  Hemispheres with
each other;  the latter uniting the different parts of the same  Hemisphere.—
Of  the transverse commissures, the Corpus Callosum is the most important.
This consists of a mass of fibres very closely interlaced  together; which may
be traced into the substance of the hemispheres on each side, particularly  at
their lower  part, where their connections are the closest  with the Thalami
Optici  and Corpora Striata.   It is difficult, if not impossible, to trace its fibres
any further;  but  there  can be little  doubt that they radiate, with the fibres
proceeding from the bodies just named,  to different parts of the cortical sub-
stance  of the Hemispheres.  This commissure is altogether wanting in  Fish,
Reptiles, and Birds ; and  it is partially or completely wanting in those Mam-
mals, whose Cerebrum is  formed upon the least complex  plan—the Rodents
and Marsupials.  The anterior commissure particularly unites the Corpora
Striata of the two sides:  but  many of its  fibres  pass through  those organs,
and radiate towards the convolutions of the Hemispheres, especially those  of
the middle lobe.  This commissure is particularly large in those Marsupials,
in which the Corpus Callosum is deficient.  The posterior commissure is a
band of fibres which connects together the Thalami optici;  crossing  over from
the posterior extremity of one to that of  the other.   Besides these, there are
other groups of fibres, which  appear to have similar commissural functions,
but which are intermingled with vesicular  substance.   Such  are the soft
commissure, which also extends  between the Thalami;  the Pons Tarini,
which  extends between the  Crura Cerebri;  and the Tuber Cinereum, which
seems to unite the optic tracts with the thalami, the  corpus callosum, the for-
nix, &c, and to be a common point of meeting for several distinct groups  of
fibres.—Ofthe longitudinal commissures, some lie above, and others below,
the Corpus Callosum.   Upon  the transverse fibres of that body, there is a
longitudinal tract on each  side of the median  line,  which serves to connect

  * See Messrs. Todd and Bowman's Physiological Anatomy, Chap.  XI. for  a fuller state-
ment of this view, and of the  arguments in its  favour. See also the General Summary at
the conclusion of the present Chapter. 
FUNCTIONS OF THE CEREBRUM.
361
the convolutions  of the anterior and posterior Cerebral lobes.  Above this,
again, is the superior longitudinal commissure, which is formed by the fibrous
matter of  the great convolutions nearest the  median plane  on the upper sur-
face of the Cerebrum,  and which connects the convolutions of the anterior and
middle lobes with those of the posterior.  Beneath the Corpus Callosum, we
find the most extensive of all the longitudinal commissures, the Fornix.  This
is connected  in front with the Thalami  optici, the  Corpora mammillaria,  the
tuber cinereum, &c.; and behind it spreads its fibres  over the hippocampi
(major and minor), which are nothing  else  than   peculiar convolutions that
project into  the  posterior and  descending  cornua of  the  lateral ventricles.
The  fourth longitudinal  commissure is  the  Taenia semicircularis,  which
forms part of the same system of fibres with  the fornix;  connecting the cor-
pus mammillare and thalamus opticus of each  side with the middle lobe of
the cerebral  hemisphere.  If, as Dr. Todd  has  remarked,* we could take
away  the  corpus callosum, the  grey matter of the internal  convolution, and
the ventricular  prominence of the optic thalami, then all these commissures
would fall together, and would become  united in the same series of longitu-
dinal fibres.—Experiment does  not throw any light upon the particular func-
tions of  the  Corpus  Callosum  and other  Commissures;  since  they can
scarcely be divided  without  severe general injury.  It would appear, how-
ever, that the partial or entire absence of these parts, reducing the Cerebrum
(in this respect at least) to the level of that of the Marsupial Quadruped, or of
the Bird, is by  no means an  unfrequent  cause of deficient intellectual power.
  a. The following case of deficient commissures, lately recorded by Mr. Paget,  is of much
interest.  The middle portion of the Fornix, and the whole of the Septum Lucidum, were
absent; and in place of the Corpus Callosum, there was only a  thin fasciculated layer of
fibrous matter, 1-4 inch in length, but of which the fibres extended to all the parts of the brain,
into which the fibres of the healthy corpus callosum can be traced.  The Middle commissure
was very large; and the lateral parts of the Fornix, with the rest of the Brain,  were quite
healthy. The patient was a servant-girl, who died of pericarditis.  She had displayed, during
her life, nothing very remarkable in her mental condition, beyond a peculiar want of forethought,
and power of judging of the probable event of things.  Her memory was good; and she possessed
as much ordinary knowledge as is commonly acquired by persons in her rank of life.   She
was of good moral character, trustworthy, and fully competent to all the duties of her station,
though somewhat heedless; her temper was good, and disposition cheerful. The  mental de-
ficiencies in the few other cases of which the details have been  recorded, seem to have been
ofthe same order; and this  is exactly what might have been anticipated; since the depriva-
tion of these parts takes away that, which is most characteristic of the Cerebrum of Man and
of the higher Mammalia; and their intellectual operations are peculiarly distinguished by that
application of past experience to the prediction of the future, which  constitutes the highest effort
of Intelligence.

   475. The weight ofthe  entire Encephalon  in the adult Male usually ranges
between 46 and 53 ounces;  and in  the Female, from  41 to 47 ounces.   The
maximum of  the healthy brain seems to  be about 64 ounces, or four pounds ;
and the minimum about 31 oz., or something less  than two pounds.  But in
cases of idiocy, the  amount is sometimes much below this;  as low a weight
as 20 oz. having been  recorded.  It appears, from the recent investigations
of M. Bourgery, that the  relative sizes of the different component  elements
of the Human  Encephalon  are somewhat as follows.   Dividing the  whole
into 204 parts, thei weight ofthe Cerebrum will be  represented by about 170
of those parts, that ofthe Cerebellum by 21, and that of the Medulla Oblon-
gata with the Optic Thalami  and Corpora Striata at 13.  The weight of the
Spinal Cord would be, on  the same  scale, 7 parts.   Hence the Cerebral He-
mispheres of Man include an amount of nervous matter, which is four times

                 * Anatomy of the Brain, Spinal Cord, &c, p. 234.
     31 
362
FUNCTIONS OF THE NERVOUS SYSTEM.
 that of all the rest of the Cerebro-spinal mass, more than eight times that of
 the Cerebellum, thirteen times that of the Medulla Oblongata, &c, and twenty-
four times that of the Spinal Cord.—The average weight  of the whole En-
 cephalon, in proportion to that of the body, in Man, taking the average of a
 great number of observations, is about 1 to 36.  This is a much larger propor-
 tion than  that which obtains in most other animals; thus the average of Mam-
 malia is stated by M. Leuret to be  1 to 186, that of  Birds  1 to 212, that of
 Reptiles 1 to 1321, and that of Fishes 1 to 5668.   It is interesting to remark,
 in reference to  these estimates, that the Encephalic prolongation of the Me-
 dulla Oblongata in Man (being about one-sixteenth of the weight of the whole
 Encephalon) is alone more than twice as heavy in proportion to his body, as
 the entire Encephalon of Reptiles, and ten times as heavy as that of Fish.—
 But there are some animals in which the weight of the Encephalon bears a
 higher proportion to that of the body than it  does in Man;  thus in the Blue-
 headed Tit, the proportion is as 1 to 12, in the Goldfinch as 1 to 24,  and in
 the Field-Mouse as 1 to 31.  It does not hence follow, however, that the  Ce-
 rebrum is larger in proportion; in fact, it is probably not nearly so large;  for
 in Birds and Rodentia, the sensory ganglia form a very considerable propor-
 tion of the entire Encephalon.   The importance of distinguishing between the
 several parts of this  mass, which are  marked out as distinct, alike by their
 structure and connections, as by the history of their development, has not been
 by any means sufficiently attended to.
   476. The Encephalon altogether  receives a supply of Blood, the amount
 of which is very remarkable, when  its comparative bulk is considered;  the
 proportion which  it receives  being, according to the estimate of Haller, as
 much  as  one-fifth of the whole.  The  manner in which  this  blood  is con-
 veyed to the Brain,  and the conditions of its distribution, offer some  pecu-
 liarities worthy of notice.   The two Vertebral and two Carotid arteries, by
 which the blood enters the cavity of the cranium, have a more free communi-
 cation by anastomosis, than any similar set of arteries elsewhere; and this is
 obviously destined  to prevent an obstruction in one trunk from interrupting
 the supply of blood to the parts, through which  its branches  are chiefly  dis-
 tributed,—the  cessation of the circulation through the nervous matter being
 immediately productive  (as formerly shown, § 290)  of  suspension  of its
 functional activity.—Not only must  there be  a sufficient supply of blood, but
 it must make  a  regulated pressure  on the walls of the vessels.  Now the
 Encephalon is differently circumstanced from other vascular organs, in being
 inclosed within an unyielding bony  case; and it has been supposed that the
 total amount of blood circulating through it must  consequently be invariable,
 any disturbance of the circulation being due  to an undue turgidity of the
 arteries and corresponding emptiness of the veins, or vice versa.  But this is
 by no means the  case;  for, independently of the fact that varying states of
 functional activity will doubtless produce a considerable variation in the entire
 bulk of the nervous mass, we find a special provision for equalizing the bulk
 of the contents of the cranial cavity, and for counterbalancing the results of
 differences  in the functional  activity of the brain and in its  supply of blood.
 This  is  the existence of a  fluid,  which is found  beneath  the arachnoid,
 wherever pia mater  exists in  connection with  the  brain  and spinal cord;
 whether on the surfaces of these organs, or in  the  ventricles of the latter.
 The amount of this fluid seems to average about two ounces;  but in  cases of
 atrophy of  the  brain, as much as twelve  ounces of fluid  may sometimes be
 obtained  from the cranio-spinal cavity; whilst in all instances, in which the
 bulk of the brain has undergone an increase, whether from the production of
 additional nervous tissue, or from  undue  turgescence of the vessels, there is 
FUNCTIONS OF THE CEREBRUM.
363
either a diminution or a total absence of this fluid.   It appears from  the ex-
periments of Magendie (to whom our  knowledge of the importance of this
fluid is chiefly due), that its withdrawal in living animals causes great dis-
turbance of the cerebral functions, probably by allowing undue  distention of
the blood-vessels; it is, however, capable of being very rapidly regenerated;
and its reproduction restores  the nervous centres to their natural state.
   477.  As  the  cerebro-spinal  fluid  can readily find its way from the sub-
arachnoid spaces of the cranial  cavity into those of the  spinal, and as the
latter are distensible, to a very considerable extent, it evidently serves as an
equalizer of the amount of pressure within the cranial cavity; admitting the
distention or  contraction of the vessels to take place, within certain  limits,
without  any considerable  change in the  degree of compression to which the
nervous  matter is subjected.  That this  uniformity is of the greatest import-
ance to the  functional exercise of the brain, is evident from a few well-known
facts.  If an aperture be made in the skull, and the protruding portion  of the
brain be subjected to  pressure, the  immediate suspension of the activity of
tile whole organ is the  result; in this  manner, a state  resembling profound
sleep can be  induced in a moment; and  the  normal  activity is renewed as
momentarily, as soon as the pressure is withdrawn.   This  phenomenon has
often been observed in the Human subject, in cases in which a portion ofthe
cranial envelope has been lost by disease or injury.  The various symptoms
of  Cerebral disturbance, which  are  due to a  state  of general  Plethora, are
evidently owing to an excess  of  pressure within the  vessels; but an undue
diminution of pressure is no less injurious, as appears from the disturbance in
the Cerebral functions, which  results from the very opposite  cause, namely,
a depression of  the power of the heart, or a deficiency of blood in the ves-
sels.—It is of  peculiar importance to  bear in mind the disturbance of the
Cerebral functions, which  is  occasioned by internal pressure, when we are
endeavouring to draw inferences from the phenomena presented by disease.
   478.  We shall  now proceed with our Physiological inquiry into the func-
tions of the  Cerebrum; confining ourselves, in the present Section, to certain
general positions, with regard  to which most  Physiologists are agreed; and
referring to  the Appendix for a notice of the more detailed system of Cerebral
Physiology, first propounded by Dr. Gall.—We shall,  as  before, apply to
Comparative Anatomy, to Experiment, and to Pathology, for our chief data.
Any general inferences, founded only upon observation of the phenomena pre-
sented by Man, must be looked upon with suspicion; since every advance in
Comparative Physiology leads us to perceive, how close is the functional rela-
tion between organs, that are really of analogous nature  in different classes of
animals; and  how necessary, therefore, it  is, to examine and contrast all the
facts which  we  can attain  in regard to them, in order to impart to our con-
clusions  the utmost validity of which they are capable.—Our  first general
proposition  is, that the  Cerebrum is the sole instrument of intelligence ; by
which term  is  implied  the intentional adaptation of means to ends, in a man-
ner implying a perception of the  nature of both.   The actions performed by
the lower animals  are often such, as to leave us in  doubt, whether they are
the result of a mere Instinctive impulse, or of an Intelligent adaptation of
means to ends;  and we are guided in our determinations, chiefly by the uni-
formity of  these actions, in the several  individuals of the same species.  If
we analyze  any of our own  instinctive  actions, we  shall perceive the same
absence of design on our own  parts, as that which we attribute  to the  lower
animals.  No one would assert that the tendency to  sexual intercourse is the
result of a knowledge of its  consequences, and of a voluntary adaptation of
means to ends ; or that, if we can imagine a man newly coming into the 
364
FUNCTIONS OF THE NERVOUS SYSTEM.
world in the  full possession of all his powers, he would wait to  eat when
hungry, until experience had taught him  that the swallowing of food would
relieve the uneasy feeling.   It has been  already  shown, that, in the infant,
the act of sucking may be performed even without a Cerebrum (§ 386, c);
and for this and other similar  actions, therefore, it is doubtful whether con-
sciousness is a  requisite  condition.   Adult animals, whose Cerebral hemi-
spheres have been removed, will eat food that is put into their mouths, although
they will  not go to seek it;  and  this is the case with many Human idiots.
When the functions of  the Brain  are disturbed, or in partial abeyance, as in
fever, we  often  see a remarkable return to the  instinctive propensities in
regard to food;  and the Physician frequently derives important guidance as
to the patient's  diet  and regimen (particularly as to  the administration of
wine), from the  inclination or disinclination which he manifests.
  479. The difference between actions of a purely Instinctive character, and
those  which rather result from  the Intellectual  faculties prompted by the in-
stinctive  propensities, is well seen in comparing Birds with Insects.   Their
Instinctive tendencies  are of nearly the same kind; and the usual arts which
they exhibit in the construction of their habitations, in procuring their  fopd,
and in escaping from danger, must be regarded as intuitive, on  account of the
uniformity with  which they are practised by different individuals  of the  same
species, and the perfection with which they  are  exercised  on the very first
occasion.   But in the adaptation of their operations to peculiar circumstances,
Birds display a variety and fertility of resource, far  surpassing that which is
manifested by Insects ; and it is not doubted, by those who have attentively
observed their habits,  that in such adaptations they are often guided by real
Intelligence.  This must  be  the case,  for example, when they make  trial of
several means, and select that one which best answers the purpose ; or when
they make an obvious improvement from year to year in the comforts of their
dwelling; or when they are influenced in  the choice of a situation, by pecu-
liar circumstances, which, in a  state of nature, can scarcely be supposed to
affect them.  The complete domesticability of many Birds is in itself  a proof
of their possessing  a  certain degree of intelligence; but  this alone does not
indicate the possession of more than a very low amount of it;  since many of
the most domesticable animals  are of the  humblest intellectual capacity, and
seem  to become attached to Man, principally as  the source on which they
depend for the  supply of their animal wants.   This is the case with  most
Herbivorous quadrupeds, and with Rabbits, Guinea-pigs, &c.; as well  as with
the Gallinaceous Birds.
  480. The  attachment which is formed  to Man, by certain Mammalia of
higher orders, such as the Dog, the Horse, and the Elephant,  is evidently of
a more elevated  kind, and involves a much larger number of considerations.
The Intelligence of such animals  is peculiarly exhibited in their Educability ;
—that is, in  the facility with which their  natural habits may  be  changed by
the new influences to which they are subjected, and the complication of  the
mental processes which  they appear  to perform under their altered circum-
stances.   Their  actions are evidently the result, in many instances, of a com-
plex train of reasoning, differing in no essential respect from that which Man
would perform  in  similar circumstances;  so that  the epithet, " half  reason-
ing,"  commonly applied to these animals,  does  not express the whole truth;
for their mental processes are of the same  kind with those of Man, and  differ
more  in the degree of control which the animal possesses over them, than they
do in  their own  character.  We have no evidence, however, that any of the
lower animals have a  voluntary power of guiding,  restraining,  or  accelerating
their  mental operations, at all  similar to  that which Man  possesses;  these 
FUNCTIONS OF THE CEREBRUM.
365
operations, indeed, seem  to  be of very much the  same character  as those
which we perform in our dreams, different trains of thought commencing as
they are suggested, and proceeding according to the usual laws, until some other
disturb them.  Although it is  customary to regard the Dog and the Elephant as
the most intelligent among the lower animals, it is  not certain that we do so
with justice; for it is very possible that we are misled by that peculiar attach-
ment to Man, which in them  must be termed an instinct, and which enters as
a motive into a large  proportion of their actions; and that, if we were more
acquainted with the psychical characters of the higher Quadrumana, we should
find in them a  greater degree of mental capability than we now attribute to
them.   One thing is certain,—that,  the  higher  the degree  of intelligence
which we find characteristic of a particular race,—the greater is the degree of
variation which we meet with in the characters of individuals ;  thus every one
knows that there are stupid  Dogs and clever Dogs, ill-tempered Dogs  and
good-tempered Dogs,—as  there are  stupid Men and clever Men, ill-tempered
Men or  good-tempered Men.   But no one could  distinguish between a stupid
Bee and a clever Bee, or between a  good-tempered Wasp and an ill-tempered
Wasp, simply because all their actions are prompted by an unvarying instinct.
  481.  It is important to bear in mind the view  to which we have been con-
ducted,—in regard to  the relative offices of the vesicular and fibrous matter,—
when forming our opinions upon the functions of the Cerebrum  in general, or
of its several parts;  from the various data supplied to us  by Comparative
Anatomy, by the comparison of the Cerebra of different  individuals  of the
Human race with each other and with their respective psychical manifestations,
and by experimental and pathological inquiry.   For in regard  to the  first of
these sources it  is to be remarked, that the size of the brain does  not, con-
sidered  alone,  afford a means of judgment  as to its  power.   The quantity of
vesicular matter on its surface should  rather be our guide; and this we may
judge of, not only by the depth of  the layer, but by the complexity  of the
convolutions by which the surface is extended.  In  no class, save in Mam-
malia, do we  find  the surface  marked with convolutions;  and in  general
we do  not meet with that fissure between the  hemispheres,  which greatly
increases  the  extent of  surface.   In forming comparisons  as to  the" con-
nection  between the  size of  the Cerebrum, and  the Intelligence, in different
animals, we must not be at all guided by its simple proportional dimensions;
since it is very  evident, that  it is rather the proportion of  the bulk  of the
brain to that of the whole body, upon  which  we should found  our  compari-
son.  But even  this  is not altogether  a safe guide;  and many Physiologists
have  endeavoured to  compare the size of the brain, with the aggregate bulk
of the nerves  proceeding from it.   This is  a much fairer measure; but it
cannot be  taken without great difficulty.  For  all practical purposes, trie
comparison of the bulk of the  Cerebrum with that of the Spinal Cord will
probably  answer very well.   The  following table, the materials of  which
are  drawn from M.  Serres' Comparative Anatomy of the  Brain, exhibits
the  three  diameters  of  the  Cerebrum of a number of  different  animals,
and the diameter of the Spinal Cord at  the  second cervical vertebra.  The
last three  columns present  in round numbers, the three  diameters  of the
Cerebrum, reckoning that of  the Spinal Cord as  1, for the sake of easy com-
parison.
                                   31* 
366
FUNCTIONS OF THE NERVOUS SYSTEM.
	1	DIMENSIONS OF CEREBRUM.					
	Diameter of Spinal				Proportional Dime		isions.
							
Man	Cord.	Anti.-post.	Transv.	Vertical.			
	1,100	17,000	7.500	9,000	1—154	1__fiS 1 vs	1-8*
Dolphin	1,100	9,500	5^850	8,200	1—9*	1__54 1 O-g	1—8J
Mandril	950	8,100	3,200	4,900	1—84	1—3*	1—5
Tiger	1,600	9,400	4,250	6,400	1—52	1—2$	1—4
Dromedary	1,900	10,500	5,050	5,800	1—54	1—2*	1—3
Kangaroo	1,200	5,300	2,350	3,800	l_4f	1—2	1-3*
Vulture	800	3,200	2,200	1,550	1—4	1-2$	1—2
Falcon	500	1,900	1,450	1,200	1-3*	1—3	1__0 2 1---£-g
Swallow	175	1,000	600	550	1—5f	1-34	1__Q 1 1--3,
Pie	450	2,000	1,400	1,200	1—4|	1—3	1__92 1 Xij
Turkey	500	1,750	1,250	1,200	1—34	1-24	1-2|
Parroquet	400	2,900	1,400	1,700	1—7*	1-34	1—4*
Tortoise	300	1,600	500		1—5*	1—If	
Crocodile	300	800	500		1—2$	1—If	
Viper	200	600	300		1—2	1-14	
Frog	300	500	400		1__12 1—*-s	i-i*	
Shark	710	2,300	1,100		1—3*	1__14 1--llf	
Cod	575	725	800		i—H	1__12 1--J J	
Lamprey	275	400	300		1-14	l—u	
Angler	400	400	300		l—i	1-1	
  482.  As might be expected, the Cerebrum of Man bears by far the highest
proportion;  but this proportion is not so large in the  transverse and vertical
diameters, as in the antero-posterior;  in  fact, in the proportion ofthe vertical
diameter the Cerebrum of Man is equalled by that ofthe Dolphin, and nearly
so in that of the transverse diameter.   In the complexity of the convolutions,
however,  and  in  the  thickness  of the  grey  matter, the  Cerebrum of Man
far  surpasses that of this  Cetaceous  animal.  In these respects  the higher
Quadrumana present the nearest approach to it; but their brain is much infe-
rior in size.  In descending the scale of  Mammalia, there  may be observed a
gradual simplification  in the general  structure of the Cerebrum, depending
upon a great diminution in the amount  of commissural fibres; until  in  the
Marsupialia the Brain presents nearly the same  condition which it offers in
Birds (§ 361).   These animals manifest a  much  lower degree of Intelligence
than many Birds evidently possess; and  it is interesting to remark, that their
Cerebral hemispheres are proportionably smaller  than those which we find in
many Birds: the diminution in their  relative  size not being counterbalanced
(as  it is in some other instances) by  increased complexity of structure.  In
the class of Birds, we observe that the Vulture and the Falcon, whose preda-
ceous instincts  give them a considerable amount of general energy, are much
inferior in the size of their brains to  the Insessorial Birds, which are more
intelligent;  and that of all, there is none in which the brain is so proportion-
ably large, as it is in the Parrot tribe, the educability of which is familiar to
every one; whilst the easily-domesticable, but unintelligent Turkey, has a brain
of scarcely half the proportional size.   The very small size of the Cerebrum
in  Reptiles  and Fishes, completely  harmonizes  with  the  same view;  these
animals presenting for the most  part but feeble indications of intelligence.
Among Reptiles, the Tortoise has  a Cerebrum  comparable in length to  that
of Birds; but its breadth and depth are far less.  The largest Cerebra among
Fishes are found in the  Shark tribe; the superior  intelligence of which is 
FUNCTIONS OF THE CEREBRUM.
367
well known to those who have had the opportunity of observing their habits :
and it is interesting to  remark, that their surface occasionally presents an ap-
pearance of rudimentary convolutions.
  483.  Comparative Anatomy, then, fully bears out the general doctrine, that
the Cerebrum constitutes the organ of Intelligence, as distinguished from those
mere Instincts, by which many of the lower  animals seem  to be almost en-
tirely guided.  By  Intelligence,  we  do not mean,  however, the  reasoning
faculties only ; but the  combination of those powers which are of an educable
character, and which become the  springs of voluntary action, in varying pro-
portions in  different animals of the  same tribe; as distinguished from those,
which have more immediate relation to the wants of  the corporeal system,
and  which are automatic and invariable in the several individuals of the same
species.—This definition does not leave out of view the operation of the Pas-
sions, Feelings, and Emotions; which are all but modifications of Instinctive
Propensities, to which different names are assigned.  The true character of
these, however, can only be understood, by studying the mode of their action
on the bodily system.  This action is of two kinds;—the one direct, irrational
and involuntary ;—the other indirect, rational, and voluntary.  In the former,
the action is the immediate result of the Emotion, following  closely upon the
Sensation which excited it, and consequently belongs to  the Consensual group
already discussed (Sect. 5);  it is executed without any consciousness of the
purpose to be answered by it; and the power of the Will is only exerted to direct
or restrain it.   In the  latter, as will be presently shown (§ 494), the action
is but remotely the result of the  Emotion, being altogether of the Intelligent
class; it is executed with a view to a distinct purpose, which has been  deter-
mined on by the reasoning powers, and of which, therefore,  the mind is fully
conscious; and it is purely an act of the Will, however strongly the Emotions
may have acted in supplying motives to it and exciting the intellectual powers
to action.
   484.  The general inferences drawn from Comparative Anatomy, are borne
out  by observation  of the  Human  species.  When* the Cerebrum  is  fully
developed, it offers  innumerable diversities of form and size, among various
individuals ; and there  are as many diversities of character.  It may be doubted
if two individuals were ever exactly alike in this respect.  That a Cerebrum
which is greatly under the average size, is incapable of performing its proper
functions, and that the possessor of it must necessarily be more or less idiotic,
there can be no  reasonable doubt.   On the other hand, that a large  well-de-
veloped Cerebrum is found to exist in persons, who have made themselves con-
spicuous in the world by their attainments or their achievements, may be stated
as a proposition of equal generality.   In these opposite cases,  we witness most
distinctly the antagonism between the Instinctive and Voluntary powers. Those
unfortunate beings, in whom the Cerebrum is but little developed, are guided al-
most solely by their instinctive tendencies ; which frequently manifest them-
selves with a degree of strength that would not have been supposed to  exist;
and  occasionally new instincts present themselves, of which the Human being
is ordinarily regarded as destitute.* On the other hand, those who have  obtained
most influence over the understandings of others, have always been themselves
persons of  strong intellectual and volitional powers; in whom the instinctive
tendencies have been subordinate to the reason and will, and who have given
their whole energy to the particular object of their pursuit.—It is very different,

  * A remarkable instance of this has been recently published.  A perfectly idiotic girl, in
Paris, having been seduced by some miscreant, was delivered of  a child without assistance.
It was found  that she had gnawed the umbilical cord in two, in the same manner as is prac-
tised by the lower animals.  It is scarcely to be supposed that she had any idea of the object
of this separation. 
368
FUNCTIONS OF THE NERVOUS SYSTEM.
however, with those who are actuated by what is ordinarily termed genius;
and whose influence is rather upon the feelings, than upon the understandings,
of those around them.  Such persons are often very deficient in the power of
even  comprehending the ordinary affairs of life: and still more commonly,
they show an  extreme want of judgment in the management of them, being
under the immediate influence of their passions and emotions, and not having
brought these under the control of their intelligent will.  The life of a genius,
whether  his bent be towards poetry, music, painting, or  pursuits of  a more
material  character, is seldom one which can be  held  up for imitation.   In
such persons, the general power of the mind being low, the Cerebrum is not
usually found of any great size.—The mere comparative size of the Cerebrum,
however, affords no  accurate measure of the amount of mental power ;  we not
unfrequently meet with men possessing  large and well-formed  heads, whilst
their physical  capability is  not greater than that of others, the dimensions of
whose crania have the  same general proportion, but are of much less absolute
size.  Large brains,  with deficient activity, are commonly found in persons of
what has been termed the phlegmatic temperament, in whom the general pro-
cesses of life seem in a  torpid and indolent state ; whilst small brains and great
activity, betoken what are known as the sanguine  and nervous temperaments.
These distinctions come to be very important, where we  proceed further in
our inquiries, and attempt to determine the particular modes of development
of the Brain, which  coincide with certain manifestations of the mind.
  485. Having now inquired into the evidence of the general functions of the
Cerebrum, which may be derived from examination  of its  Comparative deve-
lopment, we proceed to our other  sources of information; Experiment, and
Pathological phenomena.  From neither of these, however, is much informa-
tion to be derived.—The effects of the entire removal of the Cerebral Hemi-
spheres have been already stated (§ 435),   So far as any inferences  can be
safely drawn from them, they fully bear out the conclusion, that the Cerebrum
is the organ of Intelligence; since the animals which have suffered this muti-
lation appear  to  be  constantly  plunged in  a  profound sleep, from which no
irritation ever seems able to arouse them into full activity.  It  may even be
argued, that the phenomena which they exhibit do not imply the persistence
of consciousness; and that this also must be regarded as the attribute of the
Cerebral hemispheres,  being destroyed by their ablation.  But a careful  ana-
lysis of them seems to show, that sensibility still exists, although it is much
deadened; for in no other  way can we legitimately explain the efforts made
by the animals to balance themselves and maintain their position, which are of
a much higher character than the mere reflex movements exhibited  by the
same  animals  after  the removal of the entire Encephalon,  and which can
scarcely be explained without attributing to  them a degree of sensation.  That
their sensibility should be  greatly blunted,  however, is to be anticipated from
the fact, that it is almost impossible to remove the  Hemispheres, without doing
great  injury to the other ganglionic centres, especially to the Thalami Optici
and Corpora Striata; which, if the preceding views be correct, form a most
important part of the Sensori-Motor apparatus, and which, in the experiments
referred to, appear to have been generally removed with the Cerebral Hemi-
spheres.   The  entire and  permanent removal of all vascular pressure, too,
which is  consequent upon  the laying-open of the cranial cavity, is another
source of permanent disturbance  in the functions of the parts which are left.—
So far as they go, therefore, the results of such experiments confirm the  de-
ductions drawn from Comparative Anatomy, in regard to the general functions
of the Cerebrum ; but we must be careful not to infer too much from them, as
to the extent to which the  animal functions are brought to a close  by the
operation in  question.  In the most recent  experiments, those of MM. Bouil- 
FUNCTIONS OF THE CEREBRUM.
369
 laud  and Longet, it was the opinion of the observers, that  sensibility was
 retained, after the complete removal of the Cerebrum;  although the animals
 appeared unable to attach any ideas to their sensations.*—The results of par-
 tial mutilations are usually, in the first instance, a general disturbance of the
 Cerebral functions; which subsequently, however, more or less subsides, leav-
 ing but little apparent affection of the animal functions, except  muscular weak-
 ness.   The whole of one Hemisphere has been removed in this way, without
 any evident consequence, save a temporary feebleness of  the  limbs  on  the
 opposite side of the body, and what was  supposed to be a deficiency of sight
 through the opposite  eye.   The former was speedily recovered from, and the
 animal performed all its movements  as well as before; the latter,  however,
 was permanent, but the pupil remained active.—When the  upper part, only,
 of both Cerebral Hemispheres was removed by Hertwig, the  animal was re-
 duced, for fifteen days, to nearly the same condition with the one from which
 they  had been  altogether withdrawn;  but afterwards, sensibility evidently re-
 turned, and the muscular power did not appear to be much diminished.
   486.  The information afforded  by Pathological  phenomena is  equally far
 from  being definite.   Many instances are on  record, in which  extensive dis-
 ease has occurred in  one  Hemisphere, so  as almost entirely  to destroy  it,
 without either  any obvious injury to the mental powers, or any interruption
 of the influence of the mind  upon the body.   But there is no case on record
 of severe lesion of both hemispheres, in  which morbid phenomena were not
 evident during  life.   It is true, that in Chronic Hydrocephalus, a very remark-
 able alteration  in the condition of the Brain  sometimes presents itself which
 might a priori have been supposed destructive to its power of activity;—the
 ventricles being so enormously distended with fluid, that  the  cerebral matter
 has seemed like a thin lamina, spread over the interior  of  the  enlarged cra-
 nium.   But there is no proof that  absolute  destruction of any part was  thus
 occasioned ;  and it would  seem that  the  very gradual nature  of the  change,
 gives  to the  structure time for  accommodating itself to it.   This, in fact, is
 to be noticed in all diseases of the Encephalon.   A sudden lesion, so trifling
 as to escape observation, unless this be very carefully conducted, will occasion
 very  severe symptoms; whilst a chronic disease may gradually extend itself,
 without any external manifestation.  It  will usually be found that sudden
 paralysis, of which the seat is in the Brain, results from some slight effusion
 of blood in the substance or neighbourhood of the Corpora Striata ;  whilst,
 if it follow disorder of  the  Brain of long standing, a much greater amount of
 lesion will usually present itself.   In either case, the paralysis  occurs in the
 opposite side of the body, as  we should expect from the decussation of the
 pyramids ; but it may occur either in the  same, or on the opposite side ofthe
face,—the cause of which  is not very apparent.   If convulsions accompany
 the paralysis, we may infer that the  Corpora Quadrigemina, or the parts below,
 are involved  in the injury ; and in  this case it is usually found, that the con-
 vulsions are on the paralyzed side of the body,—the effect of  the lesion, both
 of the Cerebrum and of the Corpora Quadrigemina, being propagated to the
 opposite side, by the decussation of the  Pyramids.  Where, as not unfre-
 quently happens, there is paralysis of one side, accompanying convulsions on
 the other, it is  commonly the result of a lesion affecting the  base of the Brain
 and Medulla Oblongata, on the side on which the convulsions take  place ;—
 here the effect  of the lesion has  to cross from the Brain, whilst its influence

   * It is worthy of remark, also, that M. Flourens, who in the first instance maintained that
 sensation is  altogether destroyed by the removal of the Cerebrum, has  substituted, in the
 Second Edition of his Researches, the word perception for sensation: apparently implying ex-
 actly what is maintained above.—See § 435. 
370
FUNCTIONS OF THE NERVOUS SYSTEM.
on the Medulla Oblongata is shown on the  same side.   Many apparent ano-
malies present themselves, however, which are by no  means  easy of expla-
nation, in the present state of our knowledge.—The disturbance of the Cere-
bral functions, occasioned by those  changes in its  nutrition  which are com-
monly included under the general term  of Inflammation, presents a marked
diversity of character, according to the part it affects.   Thus it is well known
that the delirium of excitement is usually a symptom  of inflammation of the
cortical substance or of the membranes of the hemispheres.   This is  exactly
what  might be anticipated from the foregoing premises, since  this condition
is a perversion of the ordinary mental operations, which are dependent upon
the instrumentality of the vesicular matter; and it is evidently impossible for
the membranes to be affected with inflammation without the nutrition of this
substance being impaired, since it derives all its vessels directly from them.
On the other hand, inflammation of the  fibrous portion of the Cerebrum is
usually attended rather with a state of torpor than with excitement; and with
diminished power of the will over the  muscles.  It is stated by Foville, that
in acute  cases of Insanity, he  has  usually found  the  cortical  substance in-
tensely red, but without adhesion to the membranes ; whilst in chronic cases,
it is indurated and adherent:  but  where the Insanity has been complicated
with Paralysis, he  has  usually found  the  medullary portion  indurated and
congested.
  487.  The  general result of  such investigations is,  that the Cerebrum  is
the organ through which all those impressions are received which  give rise to
the operations of the Intellect; and that  it  affords the power  of occasioning
muscular contraction, in  obedience to the influence of the  Will, which is the
result of those operations.—That  all the operations ofthe  Intellect  are ori-
ginally dependent upon  the  reception of Sensations, is a position  that can
scarcely be denied.   If  it were possible for a Human being to  come into the
world, with a Brain perfectly prepared to be the instrument of mental opera-
tions, but with all the inlets to sensation closed, we have every reason to be-
lieve that the Mind would remain dormant, like a seed buried deep in  the
earth.   For the attentive study of cases, in which there  is congenital defi-
ciency of one or more sensations, makes it evident that the Mind is uttterly
incapable of forming  any definite  ideas,  in regard to those properties of ob-
jects,  of which those sensations are particularly adapted to take cognizance.
Thus the man who is born blind can form no conception of colour;  nor the
congenitally-deaf, of musical tones.  And in those lamentable cases, in which
the sense of touch is the only one through  which ideas can be  introduced, it
is evident that the mental operations would remain of the  simplest and most
limited character, if the utmost attention be not given by a judicious instructor,
to the development of the intellectual faculties,  and the  cultivation of the
moral feelings, through the restricted class of ideas which  there  is a possi-
bility of exciting.—The activity of  the Mind, then, is just  as much the result
of its consciousness of external impressions by which its faculties are called
into play, as the Life of  the body is the consequence of the excitement of its
several vital properties by external stimuli.  If these  stimuli  are prevented
from acting in the first instance, the state  of inaction  continues ; but when
once the mind has been aroused, the sensations which it receives are treasured
up by the  Memory:  and they may thus continue to  be the sources of new
ideas, long after the complete closure of the inlets, by which new sensations
are ordinarily received.   We have  remarkable examples of  this, in the vivid
conceptions which may be formed from the description of a landscape or  a
picture, by those who have once  enjoyed sight; or  in the  composition of
music, even such as involves  new combinations of sounds, by those who have
become  deaf,—as  in the remarkable case of  Beethoven.  The mind thus 
FUNCTIONS OF THE CEREBRUM.
371
feeds, as it were, upon the store which has been laid up  during  the  activity
of its sensory organs; but instead  of diminishing, like  material food, these
sensations become  more and more vivid, the oftener they are  recalled to the
mind.
   488. But the operations ofthe Intellect are immediately founded, not upon
Sensations, but upon the  Ideas  they excite in the  Mind.*   Some  ideas are so
simple, and so constantly excited by certain sensations, that we can scarcely
do otherwise than attribute them to original  or  fundamental properties of the
mind, called into activity by the sensations in question ;  others, however, are
of a  much more complex nature, and vary according to the peculiar character
of the individual mind, the general habits  of thought, and its particular condi-
tion at the time.   In either case, the formation  in the mind of an elementary
notion respecting the  object of  the  Sensation, is  the first operation in which
the Cerebrum can be said to be  necessarily concerned, and is  introductory to
all the rest.  The process, whether simple or complex, is termed Perception;
and the designation is applied, like Secretion, not  merely to the act, but to its
result,—being used to indicate the notion thus produced, whether it be simple
and directly-excited, or more complex and the result of a succession of mental
operations.
   489. The difference between Perception and Sensation maybe easily made
evident.   In order that a sensation should be produced, a conscious  state of
the mind is all that is required.   Its whole attention may be directed towards
some other object,  and the sensation calls up no  new ideas whatever ; yet it
will produce some  change in the Sensorium, which causes it to be (as it were)
registered there for a time, and  which may become the object of subsequent
attention ;  so  that, when the mind  is directed  towards it, that idea or notion
of the cause of the sensation is formed, which constitutes a perception.  For
example, a  student, who is directing his thoughts to some object of earnest
pursuit, does  not receive any  intimation of tbe  passage  of  time, from  the
striking of a clock  in his room.  The  sensation must be produced,  if there
be no defect in his nervous  system ; but it is not attended to, because the mind
is bent upon another object.   It may produce so little impression on the mind,
as not to  recur spontaneously,  when  the  train of thought which  previously
occupied the mind  has been closed, leaving the  attention ready to be directed
to any other object; or, the impression having been stronger, it may so recur,
and at once excite an  idea  in the mind.—Again,  the individual may  then be
able only to say,  that he heard the clock strike; or he may be able to  retrace
the number of strokes.   Now, in either case, a complex perception is  formed,
without his being aware that any mental operation has intervened.  He would
say that he remembers hearing  the  clock  strike ;  but this would not  express
the truth.  That  which he remembers is a certain series of sonorous  impres-
sions, which was communicated to his mind; and he recognizes  them as the
striking of a clock, by a process in which  memory and judgment are com-
bined,—which process may further  inform him, that  the  sounds proceeded
from  his own  particular clock.   If he had never heard a clock strike,  and the
sound produced  by it had  never been described to him, he would not have
been  able to form that notion of the object giving  rise to the sensation, which,
simple as it appears to be at the time, is the  result of complex  mental opera-
tions.   But when these operations have been frequently performed, the per-

  * Some Metaphysicians have spoken of ideas as transformed sensations ;  but this is a gross
absurdity.  The idea is excited by the sensation, in accordance with the original properties of
the mind, and the laws of their operation, just as muscular contraction is excited by the sti-
mulus of electricity or innervation; but it would be just as correct to speak of a muscular
contraction as transformed electricity or innervation, because excited by either of these stimuli,
as it is to call an idea a transformed sensation. 
372
FUNCTIONS OF THE NERVOUS SYSTEM.
ception or notion of the object becomes inseparably connected with the  sen-
sation ; and thus  it is excited by the  latter, without any knowledge on the
part of the individual, that a mental operation has taken place.
  490. Such Perceptions are termed acquired, in  contradistinction to the in-
tuitive perceptions, of which the lower  animals seem to possess a large num-
ber.  The idea of the distance of an  object, for example,  is one derived in
Man from  many  sources, and is the result of a long experience; the  infant,
or the  adult seeing for the first time, has to bring the senses of sight and  of
touch  to  bear  upon one another, in order to  obtain it;  but, when once the
power  of  determining it is acquired, the steps of the process are lost sight of.
In the  lower tribes of animals, however, in which the young  receive no assist-
ance from their  parents, there is  an  evident  necessity for some immediate
power  of  forming this determination; since they would not be able to obtain
their food without it.  Accordingly, they manifest in their  actions a percep-
tion or governing idea of distances, which  can only be  gained by Man after
long experience.   A fly-catcher, for instance, just come out of its shell, has
been seen to peck at an insect,  with an aim as perfect as if it had been all its
life engaged  in learning the art.—In some cases, animals seem to learn  that
by intuitive  perception, at which  Man could only arrive by the most refined
processes  of reasoning, or by the careful application of  the most varied expe-
rience.  Thus, a  little fish, named the Chaetodon  rostratus, is in the habit  of
ejecting from its prolonged snout, drops  of fluid, which strike insects  that hap-
pen to  be  near the surface of the water, and  causes them to fall into it, so  as
to come within its own reach.  Now, by  the laws of refraction of light, the
place of the Insect in the air, will not really be that at which it appears  to
the Fish in the water ; but it will be a little below its apparent place, and to
this point  the aim must be directed.  But  the difference between the real and
the apparent place will not be constant; for the more perpendicularly the rays
enter the water, the  less will  be  the variation; and, on the other hand, the
more oblique the  direction, the  greater will be the difference.   Now it is im-
possible to imagine but that, by an intuitive perception,  the  real place  of the
Insect  is known to the Fish in  every instance, as  perfectly as it could be  to
the most sagacious Human mathematician, or to a clever marksman, who had
learned the requisite allowance in each  case by a long experience.
  490*. In Man, the acquirement of perceptions is clearly a Cerebral opera-
tion ; but  their intuitional formation in the lower  animals  is probably to be
regarded as one of those processes to which the Sensory ganglia are subserv-
ient.   The  same  may be said of  many of the intuitive perceptions in Man;
which, if  analyzed, are found to be connected rather with the instinctive  and
emotional tendencies, than  with  the intellectual powers ;—the  perceptions
which  minister to the exercise of these last, being the  result of  experience.
Thus, it has been well remarked by Dr.  Alison, that the  changes which Emo-
tions occasion in the countenance, gestures, &c, of one individual, are instinc-
tively interpreted  by others ; for these signs of mental affection  are very early
understood by young children, sooner than any associations can be supposed
to have been formed, by experience, of their connection with particular  modes
of conduct; and  they affect us more quickly and  strongly, and with nicer
varieties of feeling, than  when  it is attempted to convey the same feelings  in
words, which are signs addressed to the intellect.
  491. By a certain retentive power, which appears to be peculiar to the
Cerebrum, Sensations and the simple  ideas or Perceptions they excite, are
stored  up  (so to speak) in such a manner, as to become  the subjects of further
mental operations at a time more or less  remote.   They then present them-
selves  as  renewed images of past sensations; and these may recur, either
involuntarily, or by a special direction of the mind towards them  by an effort 
FUNCTIONS OF THE CEREBRUM.
373
of Recollection.  In either case, the Memory of them is probably due to the
operation ofthe principle of Association ; by which sensations and the ideas
they excite become linked together, in such a manner that the recurrence of
one shall be the means of the recal of others which are connected with it.—
There seems much ground for the opinion, that  every Sensation actually ex-
perienced may become the subject of a Perception at any  future time, though
beyond the voluntary power of the memory to retrace; and the phenomena of
dreams and delirium, in which these sensations often recur with extraordinary
vividness, afford much support to this doctrine.   Some of the instances upon
record are remarkable, as proving that the sensations may be thus remembered,
without any perceptions being attached to them ; these sensations having been
of such a nature as not to excite any notion  or idea  in the mind of the indi-
vidual.  A very extraordinary case of this kind has been recorded, in which a
woman, during the delirium of fever, continually repeated sentences  in lan-
guages unknown to those around her, which proved to be Hebrew and Chal-
daic; of these she stated herself, on her recovery, to be perfectly ignorant; but
on tracing her former history, it was  found that, in early life, she had lived as
servant with a  clergyman, who  had  been accustomed to walk up and down
the passage, repeating  or  reading aloud sentences  in these languages, which
she  must have retained  in her memory unconsciously to herself.   Of the
nature of the change, by which sensations are thus registered, it is in vain to
speculate; and it  does  not seem likely that we shall ever  become acquainted
with  it.  This is certain, however,—that disease or injury of the brain will
destroy this power, or will affect it in various remarkable modes.  We not un-
frequently meet with cases in which  the brain has been weakened by attacks
of epilepsy or apoplexy, in such a manner as to prevent the reception of any
new impressions ; so that the patient does not remember anything that passes
from day to  day; whilst the impressions  of events, which happened long
before the  commencement of his malady, recur with greater vividness than
ever.  On  the  other hand, the memory of the  long-since-past is  sometimes
entirely destroyed; whilst that of events which have happened  subsequently
to the malady is but little weakened.  The memory of particular classes of ideas
is frequently destroyed;—that of a certain language, or some branch of science,
for example.   The  loss  of the memory of words is another  very curious
form of this disorder, which is  not unfrequently to be met with: the patient
understands  perfectly well what is said,  but is not able to reply in any other
terms than yes  or no,—not from any  paralysis of the muscles of articulation,
but from the incapability of expressing the ideas in language.  Sometimes the
memory of a particular class of words only, such as  nouns or  verbs, is de-
stroyed ; or it may be impaired  merely, so that the patient  mistakes the proper
terms, and speaks a most curious jargon.  These cases have a peculiar interest,
in reference to the inquiry into  the functions of different  parts of the Cere-
brum.
   492. To the formation of vivid ideas of sensible objects, whether these have
actually presented themselves in the same form at some previous time, or are
modifications of the forms which had a real existence, the  term  Conception is
applied; and this designation, like Perception, is also applied to the result of
the operation, that is, to the idea which is thus formed.  The novelty of the
Conception  may  depend  upon  the new combination or  correlation of the
objects it includes ;  or it  may result from a  sort of decomposition of former
complex ideas, and the re-assemblage of their elements under a different form.
These processes,  like the Memory, of which they are modifications, may be
either spontaneous or voluntary; and in both forms they  are continually em-
ployed by almost every one,—the tendency to the exact reproduction of former
     32 
371
FUNCTIONS OF THE NERVOUS SYSTEM.
ideas, however, being most evident in some minds, whilst the tendency to the
modification of them is more obvious in others.   The latter is one source of
that faculty, to which the term Imagination is given.
  493.  The Mind, however, is not restricted to external sources, for objects
of perception;  since, when  once in activity,  it perceives its own operations,
and traces the various relations and connections among its objects of thought.
The power of doing this  may be termed Internal Perception.   The  mind
often has internal perceptions without any direct effort of the  will, just as  it
receives perceptions from external objects ; but its power of cognizance is not
unfrequently directed inwards by express volition; and the act is  then pecu-
liarly termed Reflection, or perhaps better, Introspection.—Now by this pro-
cess, a new class of  ideas is excited^ of a  very different character from those
which are called up by external objects; and these, being entirely dependent
upon the operation of the Intellectual powers, and having no dependence upon
Sensations  except as the original springs of those operations* may  be termed
Intellectual Ideas, in contradistinction to the Sensational Ideas.  The former,
like the latter, become the subjects ofthe Associating  tendency; and thus are
combined in Trains of Thought.  Some of these intellectual ideas appear to
be so necessarily excited by mental operations, even of the  simplest kind, and
to be so little dependent on individual peculiarities either inherent or acquired,
that they take rank as fundamental axioms or principles of Human Thought.
Such are,—the  belief in our own present existence, or the faith which we re-
pose in the evidence of Consciousness ; this idea being necessarily associated
with every form and condition of mental activity,—the belief  in our past ex-
istence, and in our personal identity  so far as our memory extends, which is
necessarily connected with the act of Recollection;  with this, again, is con-
nected  the general idea of Space:—the belief in the external and independent
existence of the causes of our sensations,  which results from  Perception, or
the direction of the mind  to the ideas originating in them;  with this  is con-
nected  the  general idea of Space:—the belief in the existence of an efficient
cause for the changes which we witness around us, which springs from the
Perception of those changes ;  whence is derived our idea of Power,—the be-
lief in the stability of the order of nature, or in the  invariable  sequence of
similar effects to similar causes, which also springs directly from the Percep-
tion of external changes, and seems prior  to all reasoning upon the results of
observation of them  (being observed  to operate most strongly in those whose
experience  is most scanty, and in relation to subjects that are perfectly new
to them); but which is the foundation of all applications of our own experience
or that of others, to the conduct of our lives, or to the  extension of our know-
ledge :—lastly, the belief in our own free  will, involving the general idea of
Voluntary Power; which is in like  manner a  direct result of our Internal
Perception of those  mental changes which are excited by sensations.  Hence
it is evident, that " the only foundation of much of our belief, and  the only
source of much of our knowledge, is to be found in the  constitution of our own
minds;" but it must be steadily kept in view, that  these  fundamental axioms
are nothing else than expressions  of the general fact, that the ideas in question
are uniformly excited (in all ordinarily-constituted minds, at least) by simple
attention to the changes in which they originate.
  494.  Upon the Sensational  and Intellectual Ideas  thus brought under the
cognizance of the Mind, all acts of reasoning are founded.   These  consist,
for the most part, in  the aggregation  and  collocation of ideas ; the decompo-
sition of complex ideas into more simple ones, and the combination of simple
ideas  into general expressions;  in which  are exercised  the faculty of Com-
parison, by which the relations and connections of ideas are perceived,—that 
FUNCTIONS OF THE CEREBRUM.
375
of Abstraction, by which we fix  our attention on any particular  qualities of
the object of our thought, and isolate it from the rest,—and that of Generali-
zation, by which we fix in our minds some  definite notions in regard to the
general relations of those objects.  These are the processes chiefly concerned
in the simple acquirement of Knowledge; with which  class of operations, the
Emotional part  of our nature has  very little  participation.   But  in  those
modes of exercise of our reasoning powers, which  are chiefly concerned in
the determination of our  actions, the Emotions, &c,  are largely  concerned.
As formerly explained  (§ 440), they chiefly (if not solely) act upon the reason-
ing powers,  by  modifying the form  in which the ideas are  presented to the
mind,—whether these ideas are directly excited by external  sensations, or
whether  they are called up by an  act of the  Memory, or  result from  the
exercise  ofthe Imagination.*  If we closely scrutinize our Emotions, indeed,
we shall find that  they consist chiefly, if not entirely,  of feelings of pleasure
and pain, connected with certain classes of ideas ;  the former producing a
desire  of the objects to which they  relate;  the latter  a repugnance to them.
They thus have  a most important  influence upon  the Judgment, which is
formed by the comparison  of certain kinds of ideas; and  they may conse-
quently modify the Volitional determination, or act of the Will, which is con-
sequent  upon this, and which  may either be  directed  towards the further
operations of the  mind  itself, or may exert an immediate  influence on the
bodily frame, by the agency of the Nervous System.   In either case, it is the
characteristic distinction of a Volitional operation, that means  are intention-
ally adapted to  ends,  in accordance with the belief of  the mind as to their
mutual relations.   Upon the correctness of  that decision, will depend  the
power of the action to accomplish what the mind had  in view.
   495. The faculty of Imagination is in some respects opposed in its  cha-
racter to that of Reason;  being  concerned about fictitious objects, instead of
real ones.   Still it is in a great degree an exercise of the  same powers, though
in a different manner.  Thus it is partly concerned  in framing new combi-
nations of ideas relating to external  objects, and is thus an extended exercise
of  Conception,—placing us, in  idea, in scenes, circumstances, and relations.
in which actual  experience never placed us,—and  thus giving  rise to a new
set of objects of thought.   In fact,  every Conception  of that which has  not
been itself an object of perception, may, strictly speaking, be regarded as the
result of the exercise of Imagination.   Now the new  Conceptions or mental
creations thus formed take their character, in great  degree, from  the Emo-
tional tendencies of the mind; so that the previous development of particular
feelings and affections  will influence, not merely the selection of the objects.
but the mode in which they are thus idealized.  In the higher efforts of the
Imagination, the  mind is concerned, not  so much with the class of Sensa-
tional ideas, but with those of the Intellectual character; and the collocation,
analysis, and comparison of these, by which new forms of  combinations are
suggested to  the mind, involve the exercise of the same powers, as those con-
cerned in  acts  of Reasoning,—but they are exercised in a different way.
Whilst the Imagination thus depends upon  the Intellectual powers for all its
higher operations, the Understanding may be  said to be equally indebted to
the Imagination;  for  the ideal  combinations, which  are the  results of  the
action  of the latter, do not merely  engage  the attention of  the Artist,  who
aims to develop them  in material forms, but are the great sources of the im-

  * The recal of past sensations' and  ideas may produce purely Emotional actions ; by ex-
citing in the centres, from  which those actions proceed, a condition corresponding with that
which would be excited by the present sensation (§ 439). 
376
FUNCTIONS OF THE NERVOUS SYSTEM.
provement of the knowledge and happiness  possessed by our race,—operat-
ing alike in the common affairs of life, by suggesting those pictures of the
future which are ever before our eyes, and are our animating springs of action,
with their visions of enjoyment never perhaps to be fully realized, and  their
prospects of anticipated evil  that  often prove to be an exaggeration of the
reality,—prompting the investigations of Science, that are gradually unfolding
the sublime plan on which the Universe is governed,—and  leading to a con-
tinual aspiration after those highest forms of Moral and Intellectual  beauty,
which are inseparably connected with purity and love.

        8. General Recapitulation and Pathological Applications.

   496.  A general Summary of the views here propounded, in  regard to the
Functions ofthe Cerebro-Spinal division of the Nervous system, may proba-
bly be useful in assisting the  Student to gain clear ideas regarding them.—
The fibres of the nervous  trunks may be divided, according to the direction
of their influence, into two classes,—the afferent or centripetal,—and the effe-
rent or  centrifugal.   The afferent may be said to commence at the periphery,
especially on the skin, mucous surfaces, &c, and to terminate  in the vesicu-
lar matter of the nervous centres ; whilst the efferent originate in that vesicu-
lar matter, and  terminate in the muscles.*  Every fibre runs a distinct course
from  its origin  to  its termination; and it  is  not improbable that there are
several distinct endowments  in the different  fibres  composing each trunk.
There is no evidence that the fibrous structure serves any different purpose
than that of a mere conductor;  and  there seems good  reason to believe that
all the active operations, of which  the nervous system  is the instrument, ori-
ginate in  the vesicular  matter.   A mass of vesicular  matter, connected with
nervous trunks, forms a ganglion.  In  the Invertebrata, the ganglia are fre-
quently numerous, and are scattered through the system, without much con-
nection with each  other;—each having an  independent  action, although its
function may be but a  repetition of  that of others.  In Vertebrated animals,
on the other hand,  they are united into one mass; partly, it would  seem, for
the sake of the protection  afforded them by the bony skeleton;  and partly,
in order that  more complete consentaneousness of action  may be  attained.
Still, certain divisions may be traced in the central masses of the  Cerebro-
spinal  system ; both by the  determination of  their  respective  functions, as
indicated by observation and experiment;  and by the study of the distribution
ofthe nerves proceeding from them.   In this manner we arrive at the know-
ledge of several distinct ganglionic centres, of which  the following may be
considered as a general account.
   i. The True Spinal Cord, consisting of a nucleus of vesicular matter, re-
ceiving afferent fibres, and giving origin to efferent;  by these it is connected
with all parts of the body, but especially with the surface and muscles of the
extremities.  The actions of this centre may he performed without conscious-
ness on the part of the individual;  and they consist in the reflexion of a motor
impulse along an efferent nerve, on the reception of a stimulus conveyed  by an
afferent or excitor  nerve.  These reflex movements can be best excited, when
the muscles are removed from the  control of the Will,  which otherwise gene-
rally antagonizes them.  Some of  them are  connected with the maintenance

   * The terms originate and terminate cannot be used with strict correctness; since, as for-
merly explained (§ 248), many fibres seem to have no actual termination, either in the mus-
cles or in vesicular matter: but they cease to  run in their previous direction, after forming
their terminal loops; and their course as afferent or efferent fibres may consequently be said
to begin or to end at these points. 
GENERAL SUMMARY.                        377
ofthe Organic functions ;* others with locomotion; and others with the pro-
tection or withdrawal of  the body from injury.  Muscular movements  mav
also be excited by a stimulus  directly applied  to  the Spinal Cord itself (§§
363—373).
   ii. The Medulla Oblongata, or cranial  prolongation of the Spinal Cord.
The  actions of this do  not essentially differ from those of the true  Spinal
Cord ;  but  they are connected with different organs.   This  part consists
chiefly of the centres of the  nerves of Respiration and Deglutition,—two
functions, of which the continual maintenance  is essential to the life of the
being;  and it would  seem  as if these were placed within the cranium, to be
more secured from accidental injury.  The movements concerned in Respira-
tion and Deglutition are, like those excited through the true Spinal Cord, of a
strictly reflex character, being in all instances due to an impression or stimulus
originating in the periphery of the system, which, being conveyed to the cen-
tre, excites there a motor impulse; and they, also, are independent of Sensa-
tion (§§ 374—387).
   in.  The Ganglia of the nerves of Sensation, common  and special, which
form, as it were, the  continuation of the Medulla Oblongata.  These  appear
to minister to actions, which, like the Reflex,  are  almost  necessarily excited
by certain  stimuli, and are only  in  a degree  controllable by the Will: but
which differ from those of which  the Spinal Cord is  the centre, in being onlv
excitable through  Sensation.   Reasons  have been given for  the  belief, that
these ganglia  are the centres of those actions, which are commonly termed
instinctive in the lower animals, and consensual and  emotional in ourselves:
these all correspond, in being  performed without any idea of  a purpose, and
without any direction of the Will,—being  frequently in opposition to it (§§
422—460).
   iv. The Cerebral Hemispheres or Ganglia, which  are evidently the  instru-
ments or organs of the intellectual faculties.   It  is  probably  by them alone,
that Ideas or notions  of surrounding objects are acquired, and that these ideas
are made the  groundwork of mental operations.  They would seem, also, to
be the exclusive seat of Memory.   The results of  these operations are mani-
fested on the bodily frame, through the Will; which is capable of acting, in
greater or less degree, on all the  muscles forming  part of the system of Ani-
mal life (§§ 471—495).
   v. The Cerebellum, which appears to be concerned in the regulation and
harmonization of Muscular movements, especially those of a voluntary  cha-
racter (§§ 457—470).
   497.  The  arrangement and connections of these parts maybe thus con-
cisely expressed :—

                       Tabular view of the Nervous Centres.

                              Cerebral Ganglia,
                         the centres of the operations
                           of Intelligence and Will.
Nerves of Special senO          c      n   ,.            f Nerves of Special sen-
sation.- Motor  fibres I          Sensory Ganglia,         J sation. _ Motor fibre,
mingled with  general \   T  the centres of Consensual,      ^ mingied  with  general
motor system (?)•     J   InsUnctlve' and Em0tl0nal actl0ns-   [ motor system (?).
   Cerebellic Ganglia,
for harmonization of general
    muscular actions.
t
32* 
378
FUNCTIONS OF THE NERVOUS SYSTEM.
Afferent and Motor Nerves
of Respiration, Deglutition,
   Respiratory and
Stomato-gastric Ganglia,
in Medulla Oblongata.
( Afferent and Motor Nerves
< of Respiration, Deglutition,
^&c.
Trunks of Spinal nerves, composed of
afferent and motor fibres from true
Spinal Cord and Medulla Oblongata;
and probably also of  sensory and
motor fibres, connected  by the longi-
tudinal strands of the Cord, with the
Sensory Ganglia.
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' Trunks of Spinal Nerves, composed of
 afferent and motor fibres from true
 Spinal Cord and Medulla Oblongata;
 and probably  also of sensory and
 motor  fibres, connected by the longi-
 tudinal strands of the  Cord, with the
 Sensory Ganglia.
  The Spinal  Cord, the Medulla  Oblongata, and Sensory Ganglia, seem to
constitute one continuous group of ganglionic centres; which must be regarded
as the fundamental portion of the Nervous System.   In descending the Verte-
brated series, we find the Cerebrum and Cerebellum gradually diminishing in
size and importance, and at last, in the Amphioxus, disappearing altogether;
and the Cranio-Spinal axis, which then remains, differs in nothing but the
continuity of its vesicular structure, from the nervous system characteristic of
the Articulata, in which the vesicular matter is broken up  (so to speak) into
distinct centres.   In this Cranio-Spinal Axis, all the nerves have their termi-
nation ; and, from what has been ascertained of the anatomy of the gangliated
cord in the  Articulata, there seems  much reason to believe, that  their  fibres
may pass, in the longitudinal strands of the Cord, to great distances from their
points of entrance or emersion ; so that we may have, in the nerves connected
with every  part of the Cord, sensory fibres, whose real  termination  is in the
Sensory ganglia at its summit, and  motor fibres, which originate  from  these
centres, and are the  instruments of all  the actions  to which they minister.
The great difficulty of tracing the individual  fibres of the Spinal Cord, for any
considerable part of its length, renders  it impossible, however, to say with
certainty  that this is their real disposition; but it is  known that  one at least
of  the nerves, the Third pair, has  this double connection with the  Sensory
Ganglia and the Spinal Cord (or rather the  Medulla  Oblongata), and  it  is
likely that the same is true of the  other  motor nerves of the Orbit.   Hence
there is no  improbability in  the idea, that of the afferent  fibres of the Spinal
nerves, some are connected with the vesicular matter of the  part of the Spinal
Cord through which they pass, and others  with  the Sensory Ganglia in the
Encephalon; the relative numbers entering these centres being accordant with
the chief purposes of the trunk, whether as  an excitor of reflex actions, or  as
destined to  arouse sensations:—and that the like is  true of the motor fibres,
the relative proportions of those derived from the two sources having reference
to  the character  of the motions, whether simply-reflex or  consensual,—to
which the trunk is destined to minister.   But  there  is by no  means the  same
evidence, that any fibres contained  in the nerves  actually go on to the Cere-
brum and the Cerebellum;  and  the probability seems rather, that the fibres
which connect these masses with the Cranio-spinal Axis are of a commissural 
GENERAL SUMMARY.
379
nature, and are destined to enable them to receive communications, and to act
on the muscular system, through the mediation of the latter,—than that they
are actually continuous with any of the fibres in the nerve-trunks  connected
with it (see § 473).
  498.  According to these views, the following will be the mechanism  of the
different classes of actions, in which the Cerebro-Spinal apparatus  is  directly
concerned.
  i. In Reflex movements, a stimulus acting through the excitor fibres upon
the vesicular matter of certain parts of the Spinal Cord, causes the transmis-
sion of a  reflex impulse through the motor fibres that proceed from it; and
this gives  occasion to  muscular contraction.—With this  operation, sensation
will be coincident, if the stimulus act upon any of the fibres  that  pass on to
the Sensory ganglia; but this  is not essential to it;  and will not be  aroused
if the connection does not exist, or the Sensory ganglia be in a state of torpor.
  n.  In Sensation, the stimulus acts upon fibres which have their termina-
tion in the chain of ganglia that lies at the base of the cranial cavity in Man,
and is closely  connected with the Medulla  Oblongata.  The series is collect-
ively  termed the Sensorium ; but  it is probable that each is the instrument,
by  which  the animal becomes cognizant of Sensations of a particular  class,—
the Olfactive, Optic,  and  Auditory ganglia, for those of Smell, Light, and
Hearing respectively, the Thalami Optici  for those of Touch, and certain parts
of the Medulla Oblongata for those of Taste.
  m. In Consensual movements, the stimulus conveyed by the Sensory fibres
becomes the direct source of motor impulses ; which are conveyed through the
agency  of fibres that  issue  from the Sensory ganglia and Corpora  Striata.
All the movements which are  neither reflex nor voluntary, seem to belong to
this class; which will  include, therefore, the  instinctive actions of the lower
animals, with the automatic  and purely emotional movements  in Man.
  iv. In the act of Perception, or the formation of ideas from Sensations, in
Memory,  and in all the higher acts of Mind, the Cerebrum seems  to be con-
cerned ; the vesicular matter which constitutes its active portion, receiving the
stimulus to its operations, through the ascending and commissural fibres that
connect its different parts  with the Sensory Ganglia at its base.  As the con-
ducting power of these fibres acts from, not towards, the Sensory ganglia, we
should not expect that irritation of them  should produce Sensation; and this
is precisely what experiment shows to be the case.
  v.  In the act of Voluntary movement, which results from mental operations,
the vesicular  matter of the  Cerebrum  operates, through the descending and
commissural fibres, upon the  motor  portion of  the Sensory ganglia; the
stimulus transmitted downwards  by Volition producing the same kind of state
in its vesicular matter, as that which is  transmitted  upwards by  Sensation.
In the same manner, the recal of past Sensations and Ideas may reproduce, in
the Sensory ganglia, the condition which  gives occasion to  the  purely Emo-
tional movements.
  vi.  The combination and  harmonization of the separate acts  of  Voluntary
Muscular movement, which is the function here attributed to the Cerebellum,
appears to be prompted by the  guiding sensations, of which the Sensory
ganglia are the seat;  the influence of these will be propagated along the com-
missural fibres known as the processus a cerebello ad testes; and  the  motor
influence,  resulting from the  action thus excited in the vesicular matter of the
Cerebellum, will be propagated downwards by its connections with the various
columns of the Spinal Cord.
  499.  The distinctness of the operations of these  several centres is shown
in various ways:  but especially by conditions of the bodily system, in which
one or more of them is  in a state of inaction, whether temporary or permanent; 
380
FUNCTIONS OF THE NERVOUS SYSTEM.
or is prevented, by the  interruption of the usual  channel of communication,
from operating on particular parts.  Thus, in ordinary profound Sleep, which
is a state of complete unconsciousness, it is evident that the Cerebral  Hemi-
spheres, and the Sensory Ganglia, are at rest; as the Cerebellum, also, may be
considered to be: but the Medulla Oblongata and Spinal Cord must be in com-
plete functional activity.  The same is the case in profound Coma, resulting
from effusion of blood, or from narcotic poisons,  but not affecting the power
of breathing or swallowing.   It may  be frequently observed, that the sleep is
not so profound  as  entirely to suspend the consciousness of the individual;
and that various  movements of an adaptive character are performed, tending
to relieve uneasiness resulting from various causes.   In this condition it seems
not improbable, that  the Sensory ganglia are in some degree awake, and that
the movements are of an instinctive nature;—the  mind of the individual not
being sufficiently active to discern the cause of the  uneasiness, or to employ
his intelligence  in  the removal of it.  Whenever  Dreaming takes place, it is
evident that the  Cerebrum  is  in a state of partial activity.  The  states of
Dreaming and  Delirium, and many forms of Insanity, have  considerable
analogy with each other; especially in the absence of the power which is so
characteristic of the well-regulated mind of Man, of controlling and regulating
the current of thought.   One idea calls up another, according to their previous
associations; and the most incongruous combinations are frequently the result;
but it will generally, if not  always, be found,  that the  ideas themselves have
been previously in  the  mind, and that no entirely new train of thought is
started.  Of the degree in which, when the  mind is thus closed to the external
world,  the hidden  stores of Memory are  opened to its  search, many very
curious instances are recorded.
  500. The state of Somnambulism appears  to be nearer to that of wakeful
activity of the whole mind, than is that of Dreaming.  In the latter condition,
the individual is unconscious of external objects ; for, if they produce an effect
upon him, it is in  modifying  the current of  ideas, frequently in some very
extraordinary manner: and he does not form any true perception or idea of
their nature.   But in Somnambulism, his senses are partly awake, so that im-
pressions  made  upon them may be  properly  represented to  the  mind, and
excite there the ideas with which they are connected;  moreover the Cere-
bellum is also awake, so that  the  movements  which the individual performs,
are perfectly adapted to  their  object; indeed, it has frequently occurred, that
the power of balancing the body has been so remarkably exercised in this
condition, that sleep-walkers have  traversed narrow and difficult paths,  over
which they could not have passed in open day, when conscious of their danger.
In Somnambulism, as  in Dreaming, there is  an  evident want  of voluntary
control over the thoughts; their succession is  more influenced, however, by
impressions received from without, than it is in  dreaming ; and hence the mind
may sometimes be  easily guided into a particular  train, by properly  directing
the impressions made upon the sensory organs.  It may often be remarked,
however, that impressions which do not in some  degree harmonize with the
train of ideas, are not received by the mind;  or,  at any rate,  they are  not
applied to the correction  of the  erroneous notions which possess it.  But there
are many different  shades in  the  condition of the mind, between Dreaming
and Somnambulism; the individual being, in some  cases, much less conscious
of external objects, than he is in others.   In  some instances it appears as if
the mind was so wholly engrossed in a particular train of thought, that it could
not be affected by any new sensations, so that there is even an unconsciousness
of those which produce pain; this has its parallel in the waking  state.   A
very remarkable characteristic of the state of Somnambulism, is the  complete
isolation which commonly exists, between the  trains of thought which  then 
             GENERAL SUMMARY.--PATHOLOGICAL APPLICATIONS.         381

occupy the mind, and its operations during the waking hours; so that in neither
state is there a remembrance of what passes  in the other.  There is usually
this difference, however;—that the  mental  operations which take place  in
Somnambulism are, like those of dreaming, frequently suggested by what has
previously been occupying the mind; whilst these seem to leave no impression
to be retraced in the waking  state, though all that passes  in  one  fit of Som-
nambulism  may be recollected in the next.  This has been most  remarkably
observed in the  phenomena of that  curious state, which is known under the
name of Double Consciousness ;* in this, the form of Somnambulism in which
there is a consciousness of external  impressions, seems to alternate with the
condition of ordinary mental activity, and the individual leads (as it were) two
distinct lives, recollecting in each condition what happened in previous states
of the same character, but  knowing nothing of the occurrences of the  other.
—In regard to the curious  forms of  these affections, which are produced by
the so-called Mesmeric influence, the present views of the  Author will be
stated in the Appendix.
   501.  We have thus witnessed several varieties  in  the condition of the bo-
dily system, depending upon  partial  or complete suspension of the functional
activity of the Cerebrum,  Cerebellum, and  Sensory ganglia.  There  is no
normal condition of the Spinal system, which at all corresponds with these;
since its operations are so closely connected with  the maintenance of the Or-
ganic functions,  that the suspension of them necessarily induces the cessation
of the latter.  This is especially the case, however, in regard to the Respira-
tory ganglion; for the whole remainder of the Spinal Cord may be removed,
without the interruption of the movements which are dependent on that seg-
ment of it.  Cases have occurred, however, in which the natural performance
even of these has been partially or entirely suspended ;  and in which the
maintenance of  life has for a time been  effected,  by a voluntary exertion of
the muscles of Respiration.  The influence of the Will upon  the general mo-
tor apparatus of Man, seems  to predominate so greatly over the Reflex  action
of the Spinal Cord, that few phenomena which are  attributable to the latter
ordinarily  present themselves; these are manifested, however, when the in-
fluence of the Brain over any part is cut off, as is seen in certain cases  of pa-
ralysis.  These morbid conditions present us, also, with illustrations  of other
effects of the interruption of the communication between the nervous centres
and particular sets of muscles.  Thus, the influence of the Will  may be cut
off, although that of the Instincts, Emotions, and Reflex Function may remain;
or the respondence of the  muscles to Emotion may be prevented,  whilst they
are still capable  o-f Voluntary control, or of Reflex action.  Such cases seem
to point very clearly to three  distinct primary centres  of  nervous agency;—
and to these, the  Cerebrum Sensory  Ganglia, and Spinal Cord (including the
Medulla Oblongata) have been here  assigned as the  instruments.   We shall
next inquire into some other morbid conditions of the system, which seem
due to the  irregular action of these; and in this we shall be chiefly guided by
the researches of Dr. M. Hall, which  have been already slightly glanced at
(§§ 400,401).
   502.  Of the Convulsive  diseases, it appears that the greater part, if not the
whole, may be attributed to a morbid state of the Spinal  System of nerves.
So completely does  the power of producing convulsive  movements  appear
limited to that and to  the  Sensori-motor system, (no mechanical irritation of
the Cerebral substance being  effectual in exciting such  movements, § 473,)
that, where convulsions present  themselves during  diseases which  appear

  * Much interesting information on this and other subjects, alluded to in this Section, may
be found in Dr. Abercrombie's Treatise on the Intellectual Functions. 
382                FUNCTIONS OF THE NERVOUS SYSTEM.

limited to the Brain, we may infer that one of these systems is involved.  Dr.
M. Hall has  recently pointed out, that this complication is due to the impres-
sions made upon the fibres of the Spinal  nerves  distributed  upon the Dura
Mater, and other serous and fibrous membranes ; for convulsive actions  may
be induced by pinching these membranes, or  otherwise  irritating  them.—Of
the distinct forms or combinations, of which the class of convulsive disorders
is composed, Tetanus  is one of the most interesting and instructive.  This
disease is evidently dependent upon a state of undue excitability of the whole
Spinal System;  and this may be produced by different causes.  That which
is termed the idiopathic form of the  disease has its  origin in the  centres; it
may result in Man from  the  operation  of various predisposing and exciting
causes: and may be artificially induced in Animals  by the administration of
Strychnia.  In the traumatic form  of  the disease, the morbid state has its
origin in a local  injury; and the irritation propagated from this, and operating
through the Spinal Cord, may  be itself a cause of many of the  convulsive
movements.   But, when the  irritable state is once established in the nervous
eentres, convulsive action of  the muscles may be excited  by any stimuli, and
even almost  entirely without external causes.  Hence it is  that, whilst the
amputation of the injured part is not unfrequently the means of saving the
patient, if performed  sufficiently early, it is attended with no benefit if delayed.
The  Cerebral apparatus is entirely unaffected  in this disorder; but the nerves
of deglutition are usually those first influenced  by it; those of  respiration,
however, being soon affected, as also those of the trunk in general.—The
condition termed Hydrophobia is nearly allied to that of  traumatic  Tetanus,
differing chiefly in the  mode in which the cranio-spinal axis is affected.   The
irritable state of the  nervous  centres results from a local  injury  of a peculiar
kind; and here, too,  the early removal of the part is very desirable as a means
of prevention; although, when  the malady has once reached the centres, it is
of no use.   The muscles of respiration  and  deglutition  are, as in  Tetanus,
those spasmodically  affected  in  the  first  instance; but there  is this curious
difference in  the mode in which they are excited to action,—that, whilst in
Tetanus the stimulus operates through the true  Spinal Cord (either centrally, or
by being conveyed from  the-periphery), in Hydrophobia it is often conducted
from the ganglia of Special  Sense, or even from the Cerebrum ;  so that the
sight or sound of fluids, or even the idea of them, occasions—equally with  their
contact, or with that of a current of air—the most distressing convulsions.  It
would seem,  therefore, as if the  Sensori-motor system of nerves  was involved
in it.*—In these and other general convulsive  diseases,  it is probable that the
whole vesicular matter of the centres involved is in so  excitable a state, that
a stimulus applied to any part of it may produce a reaction through the whole.
In no other way would it be  easy to explain the great number and variety of
movements, which a small degree of local irritation may excite.
   503. Epilepsy is another convulsive disease, principally involving the Spinal
Cord, but partly  affecting the  Brain.   The predisposition  to convulsive move-
ments may depend upon many causes ;  but the movements themselves are in
general  immediately excited  by some local irritation, as  by the presence of
undigested matter in the  stomach, of worms in the intestines, &c, although
frequently also from causes purely mental.  The convulsive movements usually
affect the muscular system very extensively; acting especially upon  the mus-
cles of ingestion and egestion.   The Brain is evidently much  concerned in
the disease, however; as is evident from the numerous instances in  which it
has been clearly traced to some  local affection of that organ, as  well as from

  * For an interesting case of the excitement of involuntary muscular movements, by sen-
sations received through the eye and ear, see Dr. Cowan, in Lancet for 1845, Vol. II., p. 3G4. 
             GENERAL SUMMARY.—PATHOLOGICAL APPLICATIONS.          383

the loss of consciousness which  accompanies the convulsion.—Many forms
of that protean  malady, Hysteria, are attended with a similar irritability of
the Nervous Centres ; but there is this remarkable difference in the two cases,
—that the morbid  phenomena of Hysteria, whilst they often simulate those
of Tetanus, Hydrophobia, Epilepsy, &c, are evidently dependent upon a state
of the  system of a much less abnormal  character, being  frequently relieved
by very mild remedies, and being  often  capable  of prevention  by a  strong
effort of the will.   Dr. Hall has pointed out an important distinction between
Epilepsy and Hysteria, which materially influences  the proximate  danger of
the paroxysm of each respectively; in the former, the larynx is convulsively
closed, and partial asphyxia  is the necessary result, if the access of  air be too
long prevented, so  that venous congestion ensues, increasing the disorder of
the nervous centres even to a fatal degree; in  Hysteria, on the contrary, much
as the larynx is  affected, it  is not usually closed.   Cases  sometimes  present
themselves, however, in which the  Hysteric paroxysm assumes the Epileptic
character, the larynx being closed during expiration, so as to produce alarming
results.  The disordered state of the Nervous Centres, to which these con-
vulsive actions are due, seems  to be peculiarly connected with Emotional con-
ditions of the mind, and with functional derangements of the  sexual organs.
  504. The foregoing are the chief general spasmodic diseases in which the
Spinal system of nerves  is evidently involved ;* but there are many others of
a more local character.   Such are the various  forms of Spasmodic Asthma,
the attacks of which generally result  from some  internal irritation, either in
the lungs themselves or in the digestive system, producing a reflex action upon
the muscular fibres of  the bronchial  tubes.   The Croup-like Convulsion, or
Crowing Inspiration of  Infants, again, is an obstruction to the passage of the
air through the glottis, by a  spasmodic contraction of the constrictors of the
larynx.  This spasmodic action may be induced by various kinds of irritation ;
such as that occasioned by teething, by the presence of undigested food, or by
intestinal disorder.  In the crowing inspiration, the larynx is partially closed ;
when the spasm  is  severe,  however, there  is complete occlusion of the pas-
sage ; and forcible efforts at  expiration are made, which induce, as in epilepsy,
a severe  degree  of venous congestion, and this reacts upon the  nervous cen-
tres, aggravating  the previous disorder of their condition.  The present in-
creased knowledge of the functions of the laryngeal nerves, and of the symp-
toms of this disease, appears to render inadmissible the explanation of it given
not long since by Dr. H. Ley, who attributed  it to  paralysis  of the pneumo-
gastric nerves occasioned by pressure.—Spasmodic closure of the larynx may
occur from  other causes.  When the  rima-glottidis is  narrowed, by effusion
of fluid into the substance of its walls, it is very liable to be completely closed,
by spasmodic action, to which the unduly irritable condition of the mucous
membrane will furnish  many sources of excitement.  Choking, again, does
not result so much from the pressure of the  food on the  air-passages  them-

  * Chorea is ranked by Dr. M. Hall as a disease of the Spinal System of nerves; but this
can scarcely be regarded as  a correct  determination.  It is  true that there is considerable
irregularity in the ordinary Reflex  actions; but  the irregularity is still greater in those, to
which Volition or Emotion are the stimuli.  Moreover, the body is at rest during sleep; and
" the Spinal system never sleeps."  The frequent origin of the disease in causes which have
excited strong mental emotions, and the effect of even  moderate excitement of the  feelings
in greatly aggravating the movements of the body, seem to indicate the connection of this
disease with the Sensori-motor system of nerves.  Stammering may be regarded as a sort of
Chorea affecting the muscles of voice; of tins more hereafter (Chap. vi). In Paralysis Agitans,
it may be usually observed, that the voluntary actions are much more affected than the reflex;
the latter, indeed, not in general manifesting any disturbance.  An interesting and well marked
case of this disease  has been mentioned to  the author by Dr. W. Budd,  in which softening
was found in the Crura Cerebri. 
384
FUNCTIONS OF THE NERVOUS SYSTEM.
selves, as from the spasmodic action of the larynx, excited by this; and the
dislodgement of the morsel by an act of vomiting, is the most effectual means
of obtaining relief.—Tenesmus and Strangury are well-known forms of spas-
modic muscular  contraction, excited  by local irritation acting through the
Spinal system.   The abnormal action which  leads  to Abortion  is frequently
excited in the  same manner ;  how far  the uterus itself is called into contrac-
tion  by the ordinary spinal  nerves, is a  question as yet undecided ;  but the
facts  already stated  leave  no doubt, that stimuli operating on these may act
upon it through the Sympathetic, into which their fibres pass (§ 393).   It will
be borne in mind, however, that, in abortion, as in ordinary parturition, many
muscles are called in, to aid the contractions of the uterus, which are strictly
under the dominion of the Spinal system.—There is a form of Incontinence
of urine, which is very analogous  to  the morbid action  just  described; the
sphincter has its due power ; but the stimulus  to the evacuation of the  bladder
is excessive in strength and degree, owing to the acridity of the urine or other
causes.  The  part  of the  bladder  upon  which this appears chiefly to act, is
the trigonum (which  is well known to be more sensitive to  the irritation of
calculi, than tbe rest of the internal surface) ;   and  Sir C. Bell advises  young
persons who suffer  during  the night from  tbis very disagreeable  complaint, to
lie upon  the belly instead  of the back, so  that the contact of the urine with
the trigonum may be delayed as long as possible.
  505. One of the  most familiar examples of the pathological excitement of
the true Spinal system is the act of  Vomiting; and, as Dr. M. Hall justly
remarks, the special function of this system nowhere receives better illustra-
tion.   The act may be excited  in various ways.   Thus, it results from the
tickling of the fauces with a feather or with the finger ; but if the  feather be
carried too far  down, an act of deglutition is induced instead of vomiting.*
In this instance the glosso-pharyngeal, and perhaps also the fifth pair,  are the
nerves by which  the stimulus is conveyed to the Medulla Oblongata.  Vomit-
ing, again, may be  induced by substances  introduced into the stomach; and
here  the pneumogastric is evidently the  excitor.   When  it takes place as a
result of pregnancy, or of some intestinal  irritation, the stimulus  must be con-
veyed, either through one of the ordinary Spinal nerves, or through the Sym-
pathetic.   But it  may also be occasioned by the sight, smell, or taste of any
disagreeable object, or by the mere  conception of it, or by mental emotion
simply.  In this case, the stimulus appears to be received by the  ganglia of
special sense,  and to be transmitted by them to the muscles concerned, as by
the Spinal Cord or  Medulla Oblongata in  the  former case.   When Vomiting
is excited by the  introduction of emetic substances  into the blood, it is proba-
ble that  their  stimulation chiefly operates through  the  extended  plexus of
nerves, spread out by the  Sympathetic upon  the walls of  the blood-vessels ;
but the irritant action of the substance upon the nervous  centres may be also
concerned.—In regard to  the mechanism  by which  the  act of Vomiting is
produced, considerable  difference of opinion  has existed.  The old doctrine
was, that it was  solely occasioned by the  contraction of the stomach itself;
but Magendie  proved that this could not be the case, by substituting a  bladder
for the stomach of an animal, and then injecting a solution  of  tartarized  anti-
mony into its  blood, which immediately caused the emptying  of the bladder,
by the pressure of the surrounding muscles;  these muscles he  considered to

  * This  has been  the cause of many accidents.  Patients have tickled the fauces with a
feather in order to excite vomiting; and, having introduced it too far into the pharynx, it has
been  drawn out of their fingers by the muscles of deglutition, and carried into the oesophagus.
Similar accidents have occurred with the rectum-bougie, and female catheter, as well as with
probes, &c, introduced into the male urethra ; all the orifices being furnished with a kind of
ingestive power, which is clearly the result of Reflex action. 
OF SENSATION IN GENERAL.
385
be the diaphragm and abdominal muscles, the conjoint actions of which would
be a peculiarity observed in no other instance.  By Dr. M. Hall, on the other
hand, it is  maintained that the act of vomiting is, like the expulsion of the
fcetus, urine, faeces, &c, an expiratory effort, modified in its effects by the pe-
culiar condition of the sphincters.  It bears, indeed, great resemblance to the
act of coughing ; differing chiefly in this, that in vomiting, the larynx is closed
during the whole operation, whilst  it is only closed momentarily in coughing;
and also, that in coughing, the cardiac orifice of the stomach  is closed, whilst
in vomiting it is  opened. In this view, the accuracy of which  has been proved
by experiment, the diaphragm is  quite  inert.—A curious case has been re-
corded by Drs. Graves and Stokes,*  in which vomiting  took place from the
stomach of a man, who was found after death to be the subject of a very re-
markable change in the relative position  of the viscera,—the stomach lying in
the thorax, which cavity communicated with the  abdomen, by an opening in
the diaphragm, giving passage to the oesophagus and duodenum.  This case
was regarded  by its reporters as proving  that vomiting might take place by
the action of the stomach alone ;  but  it can scarcely be held  to justify this
conclusion; since, the diaphragm  being entirely passive, the abdominal mus-
cles would  have  the  same power  of emptying  the  stomach, as they would
possess over the lungs.  There can be little doubt, however,  that the walls of
the stomach participate  in the action; for even the resophagus  is thrown into
a state of reversed peristaltic  movement.
                          CHAPTER   VI.

             ON SENSATION, AND THE  ORGANS OF  THE SENSES.

                      1.—Of Sensation in  General.
   506.  By the term Sensation is rightly understood that change in  the con-
dition of the mind, by which we become aware of an impression made upon
some part of the body;  or, in a briefer form of expression, it may be defined
to be the consciousness  of an  impression.   Some physiologists have, it  is
true, spoken  of a  sensation without consciousness; but it seems very de-
sirable thus to limit the term ;  since the word impression may be very well
applied to designate the change produced in the afferent nerves by an external
cause, up to the point at which the mind becomes conscious of it.  We have
seen reason to believe, that the impressions communicated to the Spinal Cord
may there excite motor actions, without occasioning true Sensation ;  and  it
would seem to be  with  the Encephalon  only, that the Mind possesses the
relation necessary  for the production of such a change in it.   Hence this
organ is spoken of as the Sensorium.  For the reasons already given (§ 435),
it seems probable that the ganglia of Special Sensation are rather the essential
instruments of this function, than the Cerebral Hemispheres.   The afferent
nervous fibres, which connect the various parts of the body with the Senso-
rium, are termed sensory.  This term has also been applied to those  which
terminate in the Spinal Cord ;  but as the impressions which these convey do
not produce sensations, it seems desirable to avoid thus designating  them;

                      * Dublin Hospital Reports, Vol.  v.
     33 
386           ON SENSATION, AND THE ORGANS OF THE SENSES.

and the term excitor, proposed by Dr. M. Hall, is  much preferable.   Every
afferent spinal nerve, therefore, is made up of sensory and of excitor fibres ;
and these may be distributed in very different proportions to different parts.
Of the excitor fibres, enough has been already said.  Those parts of the body
which are endowed with sensory fibres, and impressions on which, therefore,
give rise to sensation, are ordinarily spoken of as sensible, and different parts
are spoken of as sensible in different degrees, according to the strength of the
sensation which is produced by a corresponding impression on each.
   507.  In accordance with what was formerly  stated (§ 250) of the  depend-
ence of all nervous  action on the  continuance  of the  capillary Circulation,
especially at the extremities of the fibres, it is found that the  sensory nerves
are distributed pretty much in the  same proportion as the blood-vessels; that
is  to say, in the non-vascular tissues,—such as the epidermis, hair, nails, car-
tilage, and bony substance of the teeth,—no nerves exist, and there is an en-
tire absence of sensibility; and in those whose  vascularity is trifling, the sen-
sibility is  dull, as  is the case with bones, tendons, ligaments, fibrous mem-
branes, and other parts whose functions are simply mechanical, and even with
serous and areolar membranes.  Many of these  textures are acutely sensible,
however, under certain circumstances ; thus, although tendons  and ligaments
may be wounded, burned, &c, with little or no  consciousness of  the  injury,
they cannot be stretched without considerable pain ;  and  the fibrous, serous
and areolar tissues, when their vascularity is increased by inflammation, also
become extremely susceptible of painful impressions.  All very vascular parts,
however, do not possess acute sensibility; the muscles, for instance, are fur-
nished with a large supply of blood, to enable them to perform their peculiar
function ; but they  are  not sensible in by any  means the same proportion.
Even the substance of the  brain and of the nerves of special sensation, ap-
pears to be destitute of  this property; and the same may be said of the mu-
cous membranes, lining the interior ofthe several viscera, which, in the ordi-
nary condition, are  much less sensible than the membranes which cover those
viscera, although so plentifully supplied with blood for their especial purposes.
The most sensible of all parts of the body, is the Skin, in which the sensory
nerves spread themselves out into a minute net-work ; and even of this tissue,
the sensibility differs greatly in different parts.   The organs of special sensa-
tion  are, by the peculiar character of the nerves with which  they are  sup-
plied, rendered sensible to impressions of a particular kind:  thus, the eye is
sensible to light, the ear to sound, &c.; and whatever amount of ordinary
sensibility they possess, is  dependent upon other sensory nerves.   The  eye,
for example, contrary to the usual notions, is a very insensible part of the
body, unless affected with  inflammation ;  for though the mucous membrane
which covers its surface, and which is prolonged from the skin, is acutely
sensible to some kinds of impressions, the interior  is by no means  so, as is
well known to  those who  have operated much on the  eye.   And there are
many parts  of the body, that  are  supplied with the common  sensory nerves
which convey to the mind impressions of particular kinds, with  much greater
readiness  than they communicate those of a different description.
   508. It appears, then, that the vascularity of a part is an essential condition
of its sensibility; but it does not follow that a tissue should be peculiarly sen-
sible, because it is  highly  vascular; since its large supply of blood may be
required for other purposes.  It is not simple vascularity, however, which is
necessary, but rather an active capillary circulation; any cause which retards
this, deadens  the sensibility, as is well seen in regard to cold; and, on  the
other hand, an increase in its energy produces a  corresponding increase in the
sensibility, as is peculiarly evident in  the active congestion which usually pre-
cedes  inflammation.  Acute sensibility to external impressions may arise, 
OF SENSATION IN GENERAL.                      387
however, not only from abnormal activity of  the circulation  in the organ or
part itself, but from the same condition affecting that part of the sensorium in
which  the impressions  are received.   Thus in active congestion and inflam-
mation of the brain, the most ordinary external impressions produce sensations
of  an unbearable  violence;  and  there  are some peculiar conditions of  the
nervous system, known under the name of hysterical, in which  the patients
manifest the same discomfort, even when the circulation  is in a feeble, rather
than  an excited state.   It  is  remarkable that  the  sensibility of the mucous
membranes lining the internal organs, is less exalted by the state of inflamma-
tion,  than  is that of most other parts;  and in this arrangement we may  trace
a wise and beneficent provision ;  since, were it otherwise, the functions neces-
sary  to life  could  not be performed without  extreme distress, with  a  very
moderate amount of disorder in the viscera.   If a joint  is inflamed, we can
give it rest;  but to the actions of the alimentary canal we  can give little volun-
tary respite.
   509. The feelings of Pain or Pleasure, which  are connected with particular
sensations, cannot (for the  most  part  at least) be  explained upon any  other
principle than that of the necessary association of these feelings, by an original
law of our nature, with the sensations in question.  As a general rule, it may
be  stated, that  the violent  excitement of any sensation is disagreeable, even
when the same sensation in a moderate degree may  be  a source of extreme
pleasure.  This is the case  alike with those impressions, which are communi-
cated through the  organs of sight, hearing, smell and taste, as with those that
are received through the nerves of common sensation; and there can be no
doubt that the final cause, or purpose, of the association of painful feelings
with  such violent  excitement, is to stimulate the individual to remove himself
from  what would  be injurious  in  its effects upon the system.  Thus, the pain
resulting from violent pressure  on the cutaneous surface, or from the proximity
of  a heated body, gives warning of the danger of injury, and excites  mental
operations destined to remove  the  part  from  the  influence of the injurious
cause;  and this is shown by the  fact, that loss of sensibility is frequently the
indirect occasion of severe lesions,—the individual not receiving the customary
intimation that an injurious process is  taking place.  Instances have occurred,
in which severe inflammation ofthe membrane  lining  the air-passages  has re-
sulted from the effects of ammoniacal vapours, introduced into them during a
state  of syncope,—the patient not receiving that notice  of the irritation, which
would,  in an active condition of his nervous system, have prevented him  from
inhaling the  noxious agent.

  o. The following case, recorded in the "Journal of a Naturalist," affords a remarkable
instance of this general fact.  The correctness of the statement having been called in question,
it was fully confirrhed by Mr. Richard Smith, the late senior surgeon of the Bristol Infirmary,
under  whose care the sufferer had been.  "A travelling man,  one winter's evening, laid
himself down upon the platform of a lime-kiln, placing his feet, probably numbed with cold,
upon the heap of stones, newly put  on  to burn through the night.  Sleep overcame him in
this situation; the fire gradually rising and increasing, until it ignited the stones upon which
his feet were placed.   Lulled by the warmth, the man slept on;  the fire increased until it
burned one foot (which probably was extended over a vent-hole) and part of the leg  above
the  ankle entirely off, consuming that part so  effectually, that a cinder-like  fragment was
alone remaining,—and still the wretch slept on! and in this state was found by the kiln-man
in the  morning.  Insensible to any pain, and ignorant of his misfortune, he attempted to rise
and pursue his journey, but missing his  shoe, requested to have it found; and when he was
raised, putting his burnt limb to the ground to support his body, the extremity of.his leg-bone,
the  tibia, crumbled into fragments, having been calcined into lime.  Still he expressed no
sense of pain, and probably experienced none; from the gradual operation of the fire, and his
own torpidity during the hours his foot was consuming.  This poor drover survived his mis-
fortunes in the hospital about a fortnight; but the fire having extended to other parts of his
body, recovery was hopeless." 
388           ON SENSATION, AND THE ORGANS OF THE SENSES.

  510.  It is a general rule, with regard to all sensations, that  their intensity
is much affected by habit; being greatly diminished by frequent and continual
repetition.   This is not the case, however, with regard to those sensations to
which the attention is peculiarly directed ; for these lose none of their acute-
ness by frequent repetition; on the contrary, they become much more readily
cognizable by the mind.—We have a good example of both  facts,  in the ef-
fects of sounds upon a sleeping person.  If they are  sounds which  he has
been accustomed to hear, and to disregard, they may not awake him, however
loud they be: thus, the strokes of a forge-hammer,  the firing of  guns, the
shouts of  a multitude, or the loudest music, may neither prevent the acces-
sion of  sleep, nor arouse the already unconscious sleeper;  indeed,  it  oftener
happens that individuals are prevented from  sleeping  by the  want of some
accustomed sound, or are awoke by its cessation.   On the other hand, a very
slight sound, the nature of  which excites the attention, is sufficient to  prevent
sleep ; thus, the buzz of a single musquito, in  the stillness of the night, is
most effectual in dispelling repose ;—and,  in like manner, a person in a state
of the profoundest unconsciousness may be aroused by  a whisper, if the sound
be one to  which he has been accustomed to pay regard.

  a. The following circumstance has been communicated to the Author by a Naval Officer
of high rank:—When a young man he was serving as signal-lieutenant under Lord Hood ;
and being desirous of obtaining the favourable notice of his commander, he devoted  him-
self to his duty with the greatest energy and perseverance, often remaining on deck  nineteen
hours out of the twenty-four, with his attention continually on the stretch.  During the few
hours which he spent in  repose, his sleep was so profound, that no noise of an  ordinary
kind, however loud, would awake him.  But if the word " signal" was softly uttered in his
ear, he was instantly aroused.

  511.  The general law, that Sensations, not attended  to, are blunted by fre-
quent repetition, may perhaps be connected with certain other general facts,
which lie under  the  observation of every one.  It is well known, that the
vividness  of sensations depends rather on the degree of change which they
produce in the system, than on the absolute amount of the  impressing cause;
and this is alike  the  case with regard to the special  and the ordinary sensa-
tions.   Thus, our sensations  of heat and  cold  are entirely governed  by the
previous condition  of the  parts affected; as is shown by the well-known ex-
periment, of putting one hand  in hot water, the other in cold, and then trans-
ferring  both to tepid water, which will seem cool  to one hand, and warm to
the other.  Every one knows, too, how much more we are affected by  a warm
day at the commencement of the summer, than  by an equally hot day later
in the season.  The same  is the case in regard to light and  sound, smell  and
taste.   A person going out of a totally dark room into one moderately bright,
is for the  time painfully impressed by the  light, but soon becomes  habituated
to it; whilst another, who enters it from a room brilliantly illuminated, will
consider it dark and gloomy.   Those who are constantly exposed to very loud
noises,  become almost unconscious of them, and are even undisturbed by them
in illness; and the  medical student well knows, that  even the  effluvia of the
dissecting-room are not perceived, when the organ of smell is habituated to
them, although an  intermission of sufficient  length would,  in either instance,
occasion a renewal of the  first unpleasant feelings, when  the individual is
again subjected to the impression.
  512.  Again, it is a well-known fact, that impressions made upon the organs
of sense continue for  a time,  after  the  cause of the impression  has  ceased.
It is in  this manner that a musical tone, which seems perfectly continuous,
results  from a series of consecutive vibrations,  following each other  with a
certain  rapidity;  and that  a line  or circle of light is produced by a luminous
body moving with a certain velocity.  Now there is  reason  to  believe that 
OF SENSATION IN GENERAL.
389
changes, of which the effects thus transiently remain upon the nerves of sense,
are more permanently  impressed upon the  Sensorium; since,  as  formerly
shown (§ 491), we  can only in this  manner account for the  phenomena of
Memory, and for the effects produced upon this power, by material changes
in the brain.   Hence, the diminution  in the force of sensations, which is the
consequence of their habitual recurrence, may be considered as resulting from
these  two general facts,—the persistence  of the impression made by them
upon the sensorium,—and the consequent  absence of a change  in its state,
when a sensory impression is brought to it, which is of the same nature with
one already registered there : the degree in which  the consciousness is  ex-
cited, being dependent,  as just  stated, not  upon  the absolute  degree  of the
impressing cause, but upon the  amount of change which it produces  in  the
sensorial apparatus.  In this respect  there is a perfect conformity between
the law of sensation, and that of muscular  contraction; for stimuli which ex-
cite the latter, usually lose their force  in proportion to the frequency of their
repetition.  Indeed,  both may be  considered  as results of the  more  general
laws  of vitality; for the actions of other tissues follow the  same rule, as is
shown by the tolerance, that may be  gradually established in the system, of
medicinal agents, poisons, &c,  which would  have at first produced the most
violent effects, when given in the same amount.
   513. It is curious, also, that the feelings  of Pain or Pleasure, which unac-
customed sensations excite, are often exebanged for each other, when the sys-
tem is habituated to  them ; this is especially the case, in regard to  impressions
communicated through the organs of smell and taste.  There are many arti-
cles in common use  among mankind,—such as Tobacco, Fermented Liquors,
Sic, the use of which cannot be  said to produce  a  natural enjoyment, since
it is at first unpleasant to most  persons ; and yet it first becomes tolerable,
then agreeable; and  at last the want of them is felt as a painful privation, and
the stimulus must be applied in an  increasing degree, in order to  produce
the usual effect.
   514. It is through the medium of Sensation, that we acquire a knowledge
of the material world around us; and that its changes excite mental operations
in ourselves.  The various kinds or modes of Sensation excite in us various
ideas  regarding the properties of matter; and these properties  are known  to
us, only through the changes  which they produce in the several organs.  Thus
a man totally blind from birth can form  no idea of the nature of  light  or  co-
lours; nor could one completely  deaf have  any just conception of musical
tones. It is well known that instances exist, in which, from some imperfection
of the organization,  there is  an  incapacity for distinguishing colours or musi-
cal tones, whilst there is no want of sensibility to  light or sound; and  that
some  persons are naturally endowed with  a much greater range  of  the sen-
sory faculties, than others possess. Hence  it does not seem at all  improbable,
that there are  properties of  matter, of which none  of our senses can take
immediate cognizance ;  and which other beings might be formed  to perceive,
in the same manner as we are sensible to light, sound, &c.  Thus, it is well
known, that many animals are affected by atmospheric changes, in  such a
manner, that their actions are regarded by Man as  indications of the probable
state of the weather; and the same  is the case  in a less degree with some
of our own  species; who are peculiarly susceptible of the same influences.
Now  the most universal of all the  qualities or propensities of matter,—
that,  in  fact,  on which  our notion of  it  is  founded,—is  resistance;  and
it is this quality, of which the  knowledge  seems most universally  diffused
throughout the Animal kingdom.  In the lowest tribes,  we find that  contact,
between their surface and some  material body, is required to produce sensa-
                                  33* 
390           ON SENSATION, AND THE ORGANS OF THE SENSES.

tion ; and beings which cannot be made conscious, in  this  manner, of the
existence of something external to themselves, do not deserve to  be ranked
in the Animal kingdom.   Our difficulty lies  (as  heretofore remarked, § 1),
in ascertaining what are to be regarded, in  such beings, as unequivocal indi-
cations of consciousness.  Those animals which are fixed to one spot,  can
have few  other ideas of matter than this  most general one ; but in  those
which  have the  power of locomotion, the  general sensibility of the surface
doubtless communicates to them  some notion of the character of the body
over which they move, in the same manner  as we learn  it by passing the
hand over  its exterior.   We shall  presently see, however, that the idea of
the shape  of a body which we form from the touch, results from a  very com-
plex process ; which animals of the lowest grade can scarcely be supposed
to exercise. There can be no doubt that, next to the mere sense of  resistance,
sensibility to temperature is  the most universally diffused through the Ani-
mal kingdom; and probably  the consciousness of luminosity is the  next in
the extent of its diffusion. There is good reason to believe, from observation
of their habits, that many animals are  susceptible of the  influence,  and  are
directed by the guidance  of light; whilst their organs are not adapted to re-
ceive true  visual  impressions, or to form  optical images ; and such would
seem to be the function of the red spots, frequently seen  on prominent parts
of Animalcules, the lower Articulata and Mollusca, and even of some Radiata.
Wherever these are of sufficient size to allow their structure to be  examined,
they are found to  be largely supplied with nerves, but to be destitute of the
peculiar organization which alone constitutes a true eye.   The sense of Taste
may be considered as a  refined  modification of  that of Touch; and it is
probable that this exists very low down in  the animal scale, being obviously
of great importance in the selection of food ; but the Anatomist has no means
of ascertaining where this refinement exists, and where it does not; since the
organs of taste and  touch are so similar.  The  sense of Hearing does  not
seem to be distinctly present  among the Invertebrate animals, except  in such
as approach most  nearly to  the  Vertebrata; it is not improbable, however,
that sonorous vibrations may produce an effect upon the system of those ani-
mals which do not receive them as sound; and this would  appear, from  a
fact subsequently to be mentioned  (§ 526), to be  not  improbably the case,
with regard especially to aquatic animals.  The sense of Smell, which is con-
cerned with one of the least general  properties of matter, appears  to be  the
least widely diffused among  the whole;  being only possessed in any high
degree by  Vertebrated animals, and being  but feebly present in a  large  pro-
portion of these.
   515. Besides the various kinds of sensibility which have been just enume-
rated, there are  others which are  ordinarily  associated  together, along with
the sense of material resistance (and its several modifications), and the sense
of temperature, under the head of Common Sensation; but several of  them,
especially those which originate in  the body  itself, can  scarcely be regarded
in this light.   Such are the feelings  of  Hunger and Thirst; that of Nausea;
that of distress resulting from suspended aeration of the blood ; that of " sink-
ing at the stomach," as it is vulgarly but expressively described, which results
from strong mental  emotion ; that -of  the venereal excitement, and  perhaps
some others.   Now in regard to all these, it is impossible in the present state
of our knowledge to say, whether their peculiarity results from the particular
constitution ofthe nerves that receive and convey them, or only from a modi-
fication in the impressing causes, and in the mode  in which they  operate.
Thus we have no evidence  that the nervous  fibrils, which convey from the
lungs the sense of distress resulting from deficient  aeration, may not be of a
different  character from those which convey from the surface of the air-pas- 
OF SENSATION IN GENERAL.
391
sages the sense of the contact of a foreign body.   But  as we know that all
the trunks, along which these peculiar impressions travel, do minister to ordi-
nary sensation, whilst the  nerves of truly special  sensation are not sensible
to common impressions, it is evident  that the probability is in favour of the
identity of the fibres, which minister to these sensations, with those of the
usual sensory character.   For the sense of temperature, however, it is not by
any means certain that a special set of fibres does not exist; for many cases
are on record, in which it has been  lost, whilst the ordinary sense of tact
remained;  and it is sometimes preserved, when  the  anaesthesia is in other
respects complete.
   516. With regard to all kinds of Sensation it is  to be remembered, that the
change of which  the  mind is informed, is not the  change at the  peripheral
extremities of the nerves, but the change  communicated to  the sensorium ;
hence it results, that external agencies can give rise to no kind of sensation,
which cannot  also  be  produced  by internal causes, exciting  changes in the
condition of the  nerves in  their course.  This very frequently happens in
regard to  the  senses  of sight  and hearing; flashes of light being  seen, and
ringing sounds in the  ears being heard, when no  external stimulus has pro-
duced such impressions.   The production of odorous and gustative sensations
from  internal  causes, is perhaps less common; but the sense of nausea is
more frequently excited in this manner, than by  the direct contact of the nau-
seating substance with the  tongue or fauces.  The various phases of common
sensibility often originate thus;  and it is an additional evidence in favour of
the distinctness of  the fibres which convey the impressions of temperature,
that these are  frequently affected,—a  person being sensible of  heat or of chil-
liness in some part of his body, without any real alteration of its temperature,
—whilst there is no corresponding affection of the tactual sensations.  The
most common of the internal causes of these subjective sensations (as they
have been termed, in contradistinction to the objective,  which result from  a
real material object), is congestion or inflammation ; and it  is interesting to
remark that this cause, operating through each nerve, produces in the senso-
rium  the changes to which that nerve is usually subservient.   Thus, conges-
tion in the nerves of common sensation gives rise to feelings of pain or un-
easiness ;  but  when occurring in the retina and optic nerve it produces flashes
of light; and in  the auditory nerve  it occasions "a noise in the  ears."—It
may be observed, also, of some external causes, that they may excite changes
in the sensorium  through several different channels; and  that in each case the
sensation is characteristic of the particular nerve, on which the impression is
made.  Thus pressure, which produces through the nerves of common sensa-
tion the feeling of resistance, is well known to occasion,  when exerted on the
eye, the sensation of light  and  colours ;  and, when made with some violence
on the ear, to  produce tinnitus aurium.   It is not so easy to excite sensations
of taste and smell, by mechanical irritation ; and  yet, as Dr. Baly* has shown,
it may readily be accomplished in regard to the former.   The sense of nau-
sea may be  easily produced, as is  familiarly known, by mechanical irritation
of the fauces.  The stimulus of Electricity still more completely possesses
the power of  affecting all the sensory nerves, with the changes which are  pe-
culiar to them; for, by proper management, an  individual may be made con-
scious at the same time of flashes of light, of distinct sounds, of a phosphoric
odour, of a peculiar taste, and of pricking sensations, all excited by the same
cause, the effects of which  are modified, according to the  respective peculi-
arities of  the  instruments  through which it operates.—But although there  are
some stimuli  which can produce sensory impressions on all the  nerves  of
* Translation of Mullers Physiology, p. 1062, note. 
 392          ON SENSATION, AND THE ORGANS OF THE SENSES.

 sensation, it will be found that those, to which any one organ is peculiarly
 fitted to respond, produce little or no effect upon the  rest.   Thus  the ear can-
 not distinguish the slightest difference between a luminous and a  dark object.
 A tuning-fork, which, when laid upon the ear whilst vibrating, produces  a dis-
 tinct musical'tone, excites no other sensation when  placed upon the eye than
 a slight jarring feeling.   The  most delicate  touch  cannot distinguish a sub-
 stance which is  sweet to the taste from one which is bitter; nor can the taste
 (if the communication between the mouth and the  nose be cut off) perceive
 anything peculiar in the  most strongly odoriferous bodies.
   517. It may hence be  inferred that no nerve of special sensation can, by
 any possibility,  take on the function of another.   How far the nerves of com-
 mon  sensation,  can, under any  circumstances, perform  the offices usually
 delegated to those of special  sense, we are not yet in a condition to  deter-
 mine.   Comparative  Anatomy seems to show that,  in the  lowest animals in
 which the rudiments of eyes can be detected, there is no distinction  between
 the nerves  proceeding to these  organs, and the rest;  and there would appear
 some ground for the belief that, as in  other cases, the special organs of  sensi-
 bility are gradually elaborated, in ascending the Animal scale, from the more
 general apparatus, and are not merely superadded to it.  Hence we may con-
 ceive the possibility (though there is no proof of the fact) that states of the
 system might  occur, in which a change in the common  sensory nerves  might
 produce the sensation of light, sound, Sic   But it is quite impossible (so far
 at least as our present knowledge of physical  phenomena permits  us to decide
 upon the impossibility of anything) that distinct visual impressions should be
 communicated to a nerve, except  through  the mediation of such an optical
 instrument as the eye; or distinct sonorous impressions, except through such
 an  acoustic instrument as the ear.   Hence we must  receive with  the greatest
 caution the wonderful accounts of transference of sensation, many of which
 have  undoubtedly been the offspring of deception.  Still it may  be objected
 that, since we are so totally destitute of real knowledge, as to the mode in
 which vision is ordinarily produced by inverted images upon the retina, we
 have no right  to assert  that it may not take  place in some  other way; and
 perhaps  this objection should lead us to consider  the phenomenon rather as
 extremely  improbable,  than  as impossible.   But the improbability may be
 compared to that of  a stone ascending like a  balloon, or a piece of lead float-
 ing on the water; for we have  no  more knowledge of the ultimate  cause of
 that which we term the force of Gravitation, than we have of the  nature of
 Sensation.
   518. The peculiar aptitudes  of the  different Sensory nerves, to receive
 and convey impressions of various kinds, must be regarded as the result of
 properties inherent in themselves; just as we consider the difference between
 the afferent nerves in general, and the motor nerves, to be one belonging to
 their own constitution.   But it  is probable that there are also different locali-
 ties in the  Sensorium, in which the changes to which they give rise are per-
 formed.  This may be judged of from the fact, that the phenomena of sub-
jective sensation frequently originate in peculiar  conditions of the encephalon
 itself, and not in the nervous trunks or organs of sense ;  thus, in dreaming,
 we have frequently very vivid  pictures of external  objects  presented to our
 minds; and we  sometimes distinctly hear voices and musical tones, or have
 perceptions (though this is less common) of tastes  and odours.  The phe-
 nomena of spectral illusions are very nearly  connected with  those of dream-
 ing ; both may be in some degree influenced by external causes,  acting upon
 the organs  of sensation, which are misinterpreted (as it were) by the  mind,
 owing to its state of imperfect operation; but both also may entirely originate
 in the central organs.  There seems to be no difference, in the feelings of the 
OF SENSATION IN GENERAL.
393
individual, between the sensations thus originating, and those which are pro-
duced in the usual manner; for we find that, unless otherwise convinced by
their own reason, persons who witness spectral  illusions believe as firmly in
the reality of the objects that  come before their minds, as if the images of
those objects were actually formed on their retinae.   This is another proof, if
any were wanting, that  the organ of sense, and the nerve belonging to it, are
but the instruments by which certain changes are produced in the sensorium;
of  which changes, and not of the immediate impression of the object, the
sensation really consists.  It seems to be by an innate law of our constitution,
that these subjective sensations, whether originating in  the central organs, or
in the course of the nervous  trunks, should  be referred by the mind to the
ordinary  situations of  the peripheral terminations  of those  nerves; even
though these should not exist, or should be destitute of the power of receiv-
ing impressions.   Thus after  amputations, the  patients are for some time
affected with sensations (originating probably in  the cut extremities of the
nerves),  which they refer to the  removed extremities;  the same has been
noticed in regard  to the eye, as well when it has been  completely extirpated,
as when  its powers have  been destroyed by disease.  The  effects of the
Taliacotian operation also exhibit the  operation of this  law in a curious man-
ner; for  until the flap  of skin, from  which the new nose is formed, obtains
vascular  and nervous connections in its new situation, the sensation produced
by touching it is referred to the forehead.   Another interesting  illustration of
it may be obtained by the following very simple experiment:—if the middle
finger of either hand be crossed behind the fore-finger, so that its extremity is
on the radial side of the latter, and the ends of the two fingers  thus disposed
be  rolled over a marble, pea,  or other round body, a  sensation will be pro-
duced, which, if uncorrected by reason, would  cause the mind  to believe in
the existence of two distinct bodies; this is due to the impression being made
at the same time  upon the radial side of the fore-finger, and the ulnar side of
the middle  finger,—two joints which, in the  natural  position, are at a con-
siderable distance.
   519.  The acuteness of particular sensations is  influenced in a remarkable
degree by the attention  they receive from the mind.  If the mind be entirely
inactive, as in profound sleep, no sensation whatever is produced by ordinary
impressions; on  the other hand, when the mind  is from any cause strongly
directed  upon them, impressions very feeble in themselves produce sensations
of  even  painful  acuteness.  Every one knows how much a slight itching of
some part of the surface may  be magnified, by the direction of the thoughts
to it; whilst as soon as  they are forced by some stronger impression into ano-
ther channel, the irritation is no longer felt.  Every one is aware how vividly
sounds are perceived, when they break in upon the stillness of the night; being
increased in  strength, not only by the contrast, but by absorbing the whole
attention.  An interesting experiment is  mentioned by Muller, which  shows
how completely the mind may be  unconscious of impressions  communicated
to it by one organ of sense, when occupied, even without a distinct effort of
the will, by those received through another.  If we look  at a sheet of white
paper*through two  differently-coloured glasses  at the  same time—one being
placed before each eye,—the resulting sensation is seldom that of a mixture
of  the colours:  if the experiment be  tried with  blue and yellow glasses, for
example, we do not see the paper of  an uniform green;  but the blue is  pre-
dominant at one moment, and  the  yellow at another; or blue nebulous spots
may present themselves on a  yellow field, or yellow  spots on a blue field.
We perceive from this experiment, that the attention may not only be directed
to the impressions made on either retina, to the complete exclusion of those of 
394           ON SENSATION, AND THE ORGANS OF THE SENSES.

the other, but it may be directed to those made on particular spots of either.
This may be noticed, again, in the process by which we make ourselves  ac-
quainted with a landscape or a picture; if our attention be directed to the whole
field of vision at once, we see nothing distinctly ; and it is only by abstracting
ourselves from  the  contemplation of  the greater part of it, and by directing
our attention to smaller portions  in succession, that we can obtain a  definite
conception  of the details.  The same is the case in regard to auditory  impres-
sions ;  and here  the power of attention, in causing one sensation or series  of
sensations to predominate over others which are really more intense, is often
most remarkably manifested.  When we  are listening  to  a piece of music
played by a large orchestra, for example, we may either attend to the combined
effect of  all the  instruments, or we may single  out any one part  in the har-
mony,  and  follow this through all its mazes;  and a person with a practised  ear
(as it is commonly but erroneously termed, it being not the ear but the mind
that is  practised), can even  distinguish the sound of the weakest  instrument
in the  whole band, and can follow its  strain  through  the whole performance.
This attention to a single element can only be given, however, by withdrawing
the mind from the perception of  the rest;  and a musician  who thus  listens,
will have very little idea of  the rest of the harmonic parts,  or of  the  general
effect.   In  fact, when the mind is thus directed, by a strong effort of the will,
into a particular  channel, it may be almost  considered as unconscious quoad
any other impressions.
   520. The effects  of this principle are manifested in regard to the sensations
which  originate within the system; as well  as in respect to those which  are
excited by  external impressions.    Every one is  aware how difficult it is  to
keep the body perfectly quiescent,* especially when there is a particular mo-
tive for doing so, and when  the  attention is strongly directed to  the  object.
This is experienced  even whilst a Photogenic likeness  is being taken, when
the position is chosen by the individual, and a support is adapted to assist
him in retaining it;  and it is still more strongly felt by the performers in  the
Tableaux Vivans, who cannot keep up the effort for more  than three  or four
minutes.   Now  it is well known that, when the attention is strongly directed
to an entirely different object (when we are  listening, for example, to an elo-
quent sermon, or an  interesting lecture), the body may remain perfectly mo-
tionless for a much longer period; the uneasy sensations, which would other-
wise have occasioned the individual to change his position,  not being felt;  but
no sooner is the discourse ended, than a simultaneous movement of the whole
audience takes place, everyone then becoming conscious of some discomfort,
which  he seeks to relieve.  This is the case, also, in regard to the respiratory
sensation ;  in general it may be observed, that the usual reflex  movements  are
not enough for the perfect  aeration of the blood, and that  a  more prolonged
inspiration  prompted by an uneasy feeling, takes place at intervals; but under
such circumstances as those just alluded to, this feeling is not experienced, until
the attention ceases to be engaged by a more powerful stimulus, and  then it
manifests itself by the deep inspirations which accompany, in almost every
individual,  the general movement of the body.
   521. It is curious that the  constant direction of  the  attention to  internal
sensations of a subjective kind, should sometimes occasion actual  disorder of
the parts to which these sensations are referred; and yet this seems the only
w'ay of accounting for some of the phenomena of disease.   Sometimes  the
cause ofthe sensation may exist in the trunk ofthe nerve,  in some part of its
course; whilst in other instances, it may be  confined to the sensorium.  Pain

   * Of course the movements of respiration and winking are left out of the question. 
SENSE OF TOUCH.
395
of the testicle, for example, may be occasioned  by irritation having its seat
in the lower part of the spine, the organ itself being perfectly sound; yet if
that pain  continue, it may become diseased.   The  following  are some very
interesting remarks  on this subject, from  the  able pen  of Dr.  Holland.*
" There is cause to believe  the action of the heart  to be quickened or other-
wise disturbed, by the mere centering of consciousness upon it, without any
emotion or  anxiety."  This  is  especially the  case where its- impulses  are
irregular,  or are so loud as  to  be  audible.   "The  same  may be said of the
parts concerned in respiration.  If this act be expressly made  the  subject of
consciousness, it will be felt to undergo some change; generally to be retarded
at first, and afterwards  quickened."  " The act of  swallowing is  manifestly
rendered more difficult, by  the attention being fixed upon it;  and the same
cause will often be found to render articulation less  distinct, especially when
there exists already some impediment to the function.   A similar direction of
consciousness to the region of the  stomach, creates in this part a sense of
weight, oppression, or other less definite uneasiness ; and, when the stomach
is full, appears greatly  to disturb the due  digestion  of the food.   The state
and action of the bowels are much influenced by the same cause."   A pecu-
liar sense of weight and restlessness approaching to cramp, is felt  in a limb,
to which the attention is particularly directed.   " The attention concentrated,
for so by  an effort of will it may be, on the head or sensorium, gives certain
feelings of tension and uneasiness, caused possibly by some change in  the
circulation of  the part; though it may be an effect, however difficult to be
conceived, on the nervous system itself.  Persistence in this effort, which is
seldom indeed possible beyond a short time without confusion, produces results
of much more complex nature, and scarcely to be defined by any common terms
of language."  These  phenomena have an evident affinity, on the  one hand,
with the exaltation of external or objective sensations,  to  which the attention
is peculiarly directed;  and  on the other with those of  several morbid condi-
tions.  The explanation of them all is probably to be sought in some change
in the circulation of the part,  to which  the sensation is referred.   Thus the
hypochondriac patient," in fixing his consciousness with morbid intentness on
certain organs, creates not merely disordered sensations, but often also disor-
dered actions in them. There  may be palpitation of the heart,  hurried or
choked respiration, flatulence  and other distress of  stomach, irritation of the
bladder; all arising from this  morbid direction  of attention to the organs in
question."  In hysteria, again, " the  instances are frequent, of attacks brought
on  by the mere expectation of them; or by irritation; or  occasionally even a
sort of morbid solicitation  of the  organs to these singular actions."   These
facts go a long way to explain the phenomena of Mesmerism, many of which
are obviously to be referred to the exaggerated operation of the same principle.
(See Appendix.)—We now  proceed to consider in more detail the functions of
the several Organs of the Senses, and shall commence  with that of the most
general character.


                           2. Sense of Touch.

   522. By the sense of Touch, as commonly understood, is meant that mo-
dification  of the common sensibility  of the  body, of which the Cutaneous sur-
face is the especial seat.  It derives  its  peculiar power  simply from the large
amount of sensory nervous  fibres, which are distributed in its substance; and
especially  through the terminations (or rather the origins) of these  in the pa-
pillae, which are little elevations of the surface of the cutis, easily perceptible
* Medical Notes and Reflections, Chap. v. 
396
ON SENSATION, AND THE ORGANS OF THE SENSES.
by the aid of a lens, and each chiefly composed of a vascular loop overlapping
                            the extremity of the  nervous fibril.  The pre-
                            cise arrangement of the nerve-fibres in the cuta-
                            neous papillae, has not been indisputably ascer-
                            tained ; but the  opinion  that they form  loops
                            (Fig.  119)  is the one most generally adopted.
                            The number of these  papillae within any given
                            area, pretty closely corresponds with the degree
                            of sensibility of  that part of the surface;  thus
                            we find them most abundant  on the hands, es-
                            pecially towards  the points of the fingers, and
                            on the lips and  tongue.   In  some  animals, es-
                            pecially those of the  Feline  tribe,  the long vi-
                            brissae (commonly termed whiskers) evidently
                           it  has been  demonstrated  that their pulps are
                                                Some interesting observa
  Capillary net-work at margin of
lips.
minister  to  sensation; and
largely supplied with nerves from the fifth pair.
tions have been made by Prof. Weber, on the sensibility of different parts of
the skin.  His mode of ascertaining this, was  to  touch  the  surface with the
legs of a pair of compasses, the points of which were guarded with pieces of
cork ; the eyes being closed at the time, the legs were approximated to each
other, until  they were brought within the smallest distance, at which they
could be felt to be distinct from one another.   The following are some of the
results of the  experiments.  With  the extremities  of  the  fingers and  the
point of  the tongue, the distance could be  distinguished most  easily in the
longitudinal direction ; on the dorsum of the  tongue, the face, neck, and ex-
tremities, the distance could be recognized best when the points were placed
transversely.
                                                                  lines
Point of middle finger .	i	jf a line	Mucous Membrane of gums . 9	
Point of tongue .	i	Df a line	Lower part of forehead	. 10
Palmar surface of third finger	1 line		Lower part of occiput	. 12
Red surface of lips	2 lines		Back of hand .	. 14
Palmar surface of middle finger 2		!)	Neck, under lower jaw	. 15
Dorsal surface of third finger	3	))	Vertex	. 15
Tip of the nose . . ' .	3	!!	Skin" over Patella	. 16
Dorsum and edge of tongue	4	!)	--------Sacrum .	. 18
Part of lips covered by skin	4	.,		18
				
Palm of hand	5	»	Dorsum of foot	. 18
Skin of cheek	5	))	Skin over sternum .	. 20
Extremity of great toe .	5	»	Skin beneath occiput	. 24
Hard palate . .	6	))	Skin over spine, in back	. 30
Dorsal surface of forefinger .	7	„	Middle of the arm .	. 30
Dorsum of hand .	8	I!	------------thigh	. 30
  It is curious that the distance between the legs of the compasses seemed to
be greater (although really so much less), when it was felt by the more sensi-
tive parts, than when it was estimated by parts of less  distinct sensibility.  As
a general fact, it seems that the sensibility of the trunk is greater on the me-
dian line, both before and behind, and less  at the sides.  Differences of tem-
perature, and the weight of bodies, were, according to Prof. Weber's observa-
tions, most accurately recognized at the parts, which were determined to be
most sensible by the foregoing method of inquiry.
  523.  As already stated(§ 514), the only idea communicated to our minds by
the sense of Touch, when exercised in its simplest form, is that of Resistance;
but when the sensory surface and the substance  touched are made  to change
their place in regard to each other, we obtain the additional notion of Extension
or Space.  By the various  degrees  of resistance which the sensory surface
encounters, we estimate the hardness or softness of the body; but in this we 
SENSE OF TOUCH.                         397
are assisted by the muscular sense (§ 433), which makes us conscious of the
degree of pressure we are employing.   By the impressions made upon the
papillae, during the movement of the tactile surface over  that which is being
examined, the roughness, smoothness, or other peculiar characters, of the lat-
ter are estimated.  Our knowledge ofform, however, is a very complex pro-
cess, requiring not merely the exercise of the sense of touch, but also great
attention to the muscular sensations.   It is chiefly, as formerly remarked, in
the variety of movements of which  the hand of Man is  capable, that it is
superior to that of any other animal; and it cannot be doubted that this affords
a very important means of acquiring information  in  regard to  the external
world, and especially of correcting many vague and fallacious notions,  which
we should derive from the sense of Sight, if used alone. On the other  hand,
it must be confessed, that our knowledge would have a very limited range, if
this sense were the only medium, through which we could acquire ideas.  It
is  probably on the sensations communicated through the touch, that the idea
of the  material world, as  something  external to  ourselves, chiefly rests;  but
this idea is by no means a direct result of these sensations, being rather an
instinctive or intuitive perception excited by them.  Every person who directs
the least attention to  the subject  must perceive, how completely different are
those  notions of the  primary or elementary properties of matter, which we
base upon the information thus communicated to us, from the sensations them-
selves ; and, as Dr. Alison has justly remarked, "a decisive proof of this  being
the true representation of this part of our mental constitution, is obtained by
attending to  the  idea of extension or space;  which  is undoubtedly formed
during the exercise of the sense of touch;  and  is  no  sooner formed, than it
' swells in the human mind to Infinity,' to which certainly no human sensation
can bear any resemblance."
   524.  That the conditions under which certain  of the modifications of com-
mon sensation operate, are in some respects different from those of ordinary
Touch, is very easily shown.   Thus, the  feeling of tickling is  excited most
readily in parts, which have the least tactual sensibility,—the armpits, flanks,
and soles of the feet; whilst in the points of the fingers it cannot be excited.
Moreover, the nipple is very moderately endowed with ordinary sensibility;
yet by a particular  kind of irritation, a very strong feeling may be excited
through it.   Again, in regard to temperature, it is  remarked by Weber, that
the left hand  is more sensitive  than the right; although the sense of touch is
undoubtedly  the most acute in the latter.   He states that, if the two hands,
previously of the same temperature, be plunged into separate basins of warm
water, that  in which  the  left hand is immersed will be felt as the warmest,
even though  its  temperature is somewhat  lower than that of  the other.  In
regard to the  sensations of heat and cold, he points out another curious fact,—
that a weaker impression made on a large surface, seems more powerful than
a stronger impression made on a small surface; thus, if the forefinger of one
hand be immersed in water at  104°, and the whole of the other hand be
plunged  in water at   102°, the  cooler  water will  be  thought  the warmer;
whence the well-known fact, that water in which a finger can be held, will
scald the whole hand.  Hence it also follows, that minute differences in tem-
perature, which are imperceptible to a single finger, are appreciated by plung-
ing the whole hand into the water; in this manner, a  difference  of one-third
of a degree may readily  be detected, when the same  hand is  placed succes-
sively in two  vessels.   The judgment is more accurate,  when the temperature
is  not  much  above or below the usual heat of the body; just as sounds are
best discriminated, when neither very acute nor very grave.
  525. The improvement in the sense of Touch, in those persons whose de-
pendence upon it is increased by the loss of other senses, is well  known; this
    34 
398
ON SENSATION, AND THE ORGANS OF THE SENSES.
is doubtless to be  in part attributed (as already remarked) to the increased
attention which is given to the sensations, and in part to an increased develop-
ment of the tactile organs themselves, resulting from the frequent use of them.
The case of Saunderson, who, although he lost his sight at two years old, be-
came Professor of  Mathematics at Cambridge, is well known ; amongst his
most remarkable faculties, was that of  distinguishing genuine  medals from
imitations, which he could do more accurately than many connoisseurs in full
possession of their senses.   The process of the acquirement of the power of
recognizing elevated characters by the touch, is  a remarkable example of  this
improveability.  When a blind person first commences learning to read in this
manner, it is necessary to use a large type ; and every individual  letter must
be felt for some time, before a distinct idea of its form is acquired.   After  a
short period of diligent application, the individual becomes  able to recognize
the combinations of letters in words, without  forming a separate idea of  each
letter;  and can read line after line, by passing the finger over each, with  con-
siderable rapidity.   Now when this power is once thoroughly acquired,  it is
found that the size of the type may be gradually diminished; and this seems
to indicate, that the sensations themselves are  rendered more  acute, by the
frequent application of them in this direction.   As an instance of  the correct
notions which may be conveyed to the  mind, of the forms and surfaces  of  a
great variety of objects, and of the sufficiency of these  notions for accurate
comparison, the Author may mention the case of a blind friend of his own,
who has  acquired a very complete knowledge of Conchology, both recent and
fossil;  and who is not only able to recognize  every one of the numerous spe-
cimens in his own Cabinet, but to mention  the nearest alliances of a Shell
previously unknown to him, when he  has thoroughly examined  it  by his
touch.   Many instances  are on record, of the  acquirement, by the blind, of
the power  of distinguishing the colours of surfaces, which were similar in
other respects; and, however wonderful this may seem, it is by no means
incredible.   For it is to be remembered  that the difference of colour depends
upon the position  and arrangement of  the particles composing the surface,
which  render it capable of reflecting one ray whilst it absorbs all the rest;  and
it is quite consistent with what we know from other sources, to believe  that
the sense of Touch may become so refined, as  to  communicate a perception
of such differences.
   526.  The examples of peculiar  acuteness of this  sense, which we occa-
sionally  meet with among  the lower animals, are very  interesting, when
viewed in connection with its improveability in  Man.  It was found by Spal-
lanzani, that Bats, when deprived of sight, and (as far as possible) of hearing
and  smelling also, still  flew about with equal  certainty and safety, avoiding
every obstacle, passing through passages only  just large enough to admit them,
and  flying about places previously unknown, with the most unerring accuracy,
and  without coming into  collision with the objects near which they passed.
He also stretched threads in various directions across the apartment, with the
same result.   So astonished was he at these curious facts, that he was led to
attribute  the phenomenon to  the possession of a  sixth sense, unknown to Man.
Cuvier was the first to appreciate the real value of these experiments, as afford-
ing a proof of the existence ofthe most exquisite tactile sensibility, over the whole
surface of the flying membrane; the  naked surface and delicate structure of
which, appear well adapted to constitute the seat of so important a function.
From this view, therefore, it would appear that it is by means ofthe pulsation of
the wings on the air, that the propinquity of solid bodies is perceived, through
the manner in which the air reacts on  their  surface.  It is curious  that the
instance  which (so far as we  at  present know) is most analogous to  this,
should be  met with among the inhabitants  of the  deep.   It is  a fact well 
SENSE OF TASTE.                           399
known to Whale-fishers,  especially to  those  who pursue the  Spermaceti
Whale, that these animals have the power of communicating with each other
at great distances.   It  has often been observed, for example, that when a
straggler is attacked, at  the distance of several miles from a shoal, a number
of its fellows bear down to its assistance, in an almost incredibly short space
of time.  It can scarcely be doubted, then, that  the communication must be
made  through the  medium  of  the vibrations of the  water, excited by the
struggles  of the animal, or perhaps by some peculiar movements especially
designed  for this purpose, and propagated through the fluid to the large cuta-
neous  surface of the distant  Whales; and  this idea is fully  confirmed  by
the fact, that the nerves which  proceed  to  the skin,  pass through the inner
layers of blubber with  scarcely any subdivision, but  spread out  into a  net-
work of extreme minuteness, as soon as  they arrive at the surface.
                            3.  Sense of Taste.

  527.  That this sense may be  really considered  as  a peculiar modification
of that of Touch, appears from several considerations.   In the first place, the
actual contact of the object of sense, with the organ through which  the  im-
pression is received, is  here necessary; and  this is the case in regard to  no
other sense.   Moreover  the intimate
structure  of the organ is nearly the
same in both instances.   Again, it ap-
pears from the considerations formerly
alluded to  (§  407), that  there  is  no
special nerve  of taste; the  gustative
impressions made  upon  the front of
the  tongue, being  conveyed by the
lingual branch of the fifth  pair ; whilst
those made  upon the back  of the organ,
are conveyed by the glosso-pharyngeal.
The first of these nerves also ministers
to ordinary tactile  sensibility;  the se-
cond appears  to convey  the impres-
sions which  produce  nausea.   The
papillae of the Tongue are essentially
the same in structure with  those of
the Skin; but many of them are of a
peculiarly complex  nature.

  a. The characters of the papillae of the
tongue have recently undergone a very careful
examination by Messrs. Todd  and Bowman
(Physiological Anatomy, Chap. xv.).   They
may be divided, in the first place, into the
simple and the compound; the former of which
had previously escaped observation, through
not forming any apparent projection.—The
Simple papilla? are scattered in the intervals of
compound, over  the general surface  of the
tongue; and they occupy much ofthe surface
behind the circumvallate variety, where no
compound  papilla? exist.   They are  com-
pletely buried and concealed beneath the
continuous sheet of epithelium, and can only
be detected, when this membrane has been
removed by maceration; they are then  found
[Fig. 163.
 Tongue, seen on its upper surface: a. One of
the circumvallate papilla;,  b. One of the fungi-
form papillae.  Numbers of the conical papillae
are seen about d, and elsewhere,  e. Glottis, epi-
glottis, and glosso-epiglottidean folds of mucous
membrane.—From Soemmering.] 
400              ON SENSATION, AND THE ORGANS  OF  THE SENSES.
to have the general characters of the  cutaneous  papillae, but nerve-tubes have not yet been
detected in them.
  Simple papillae near the base of the tongue:—a. a, concealed under the epithelium'; 6, uncovered by
it.—Magnified 10 diameters,  b. a. Arterial twig, supplying their capillary loops, v.  Vein.  The vessels
are all contained within the line 6, 6, of basement membrane,  c, c.  Deeper epithelial particles resting
on the basement membrane,  d. Scaly epithelium on the surface.  The granular interior of the papillae
is represented at e.  c. Papillae in which the basement membrane is not visible; and the deep layer of
epithelium seems to rest on the capillary loop.—Magnified 200 diam]
'is *165.                     Vertical section of one of the circumvallate
[Fig. 166.
  a. Compound papillae on the side of the foramen caecum, injected:—a, a. Arterial twigs,  v, v. Veins.
The capillary loops indicate the simple papillae; in one of which, b, the injected matter has been extra-
vasated within the basement membrane of the papillae, the outline of which is thus distinguished,  c.
Capillary plexus, where no papillae exist,  e, e.  External  surface  of the epithelium of the papilla.—
Magn. 15 diam.
  b One of the simple papillae of a :—a, v, v. Arterial and venous sides of the capillary loops.   6, b.
Basement membrane,  d. Deeper epithelial particles resting on the basement membrane,  s. Scaly epi-
thelium on the surface—Magnified 300 diameters.] 
SENSE OF TASTE.
401
Fig. 167.
   6. The Compound papilla? are visible to the naked eye; and have been classified, accord-
ing to  their shape, into the circumvallate, the fungiform,  and the filiform.—The  Circumval-
late or calyciform papillae  are eight or  ten in number, and are situated in a V-shaped line
at the  base of the tongue.   Each  consists of a central  flattened circular  projection of the
mucous  membrane, surrounded by a tumid ring of about
the same elevation, from which it is separated  by a narrow
circular  fissure.  The surface of both centre  and  border
is smooth, and  invested by scaly epithelium, which con-
ceals a multitude of simple papillae.—The Fungiform pa-
pilla? are scattered singly over the tongue, chiefly upon its
sides and tip.   They project considerably from the surface,
and are usually narrower at the base than at their summit.
They  contain a complex  capillary plexus, the terminal
loops  of  which enter the numerous simple papilla? that
clothe  the surface of the  fungiform body.  They contain
nerve-tubes, in which a looped arrangement can  be traced;
and the epithelium which covers them is so thin, as to allow
the red colour  of the blood to be seen through it.  In this
manner they are readily distinguished from the filiform pa-
pilla?, among which  they lie.—The Filiform papillae, like the preceding, contain a plexus of
Capillary net-work of fungiform
    papilla of the tongue.
  a. Fungiform papilla, showing the secondary papilla? on its surface, and at a its epithelium covering
them over.—Magnified 35 diameters.
  b. Another, with the capillary loops of its simple papillae injected,  a. Artery, v.  Vein.  The groove
around the base of some of the fungiform papillae is here represented, as well as the capillary loops, c, c,
of some neighbouring simple papilla?.—Magnified 18 diameters.]

capillaries, and a bundle of  nerve-fibres, both terminating in loops, which  enter the simple
papilla? that clothe the surface of the compound body;  but  instead of being covered with
a thin scaly epithelium, they are furnished with bundles of long pointed processes, some of
which approach hairs in their stiffness and structure.   These are immersed in the mucus of
the mouth, and may be  moved in any direction, though they are  generally inclined back-
wards.
[Fig. 169.
                       a'        v       c
  Various forms of the conical compound papillae deprived of their epithelium:—a, b, and especially c,
are the best marked, and were provided with the stiffest and longest epithelium;  their simple papillae
are more acuminated,  d, approaches the fungiform variety : e.f, come near the simple papillae,— Mag-
nified 20 diameters.]
                                          34* 
402             ON SENSATION, AND THE ORGANS OF THE SENSES.
  c.  The Simple papilla? which occur in an isolated  manner, with those which  are aggre-
gated in the Circumvallate and Fungiform bodies, doubtless minister to the sense of Taste;
but there seems much reason to coincide in the opinion of Messrs. Todd and Bowman, with
regard to the different office of the Filiform papillae.   "The comparative thickness of their

                                       [Fig. 170.
  a. Vertical section near the middle of the dorsal surface of the tongue:—a, a. Fungiform papillae, b.
Filiform papilte, with their hair-like processes,  c. Similar ones deprived of their epithelium.—Magni-
fied 2 diameters.
  b. Filiform compound papillae:—a. Artery, v. Vein.  c. Capillary loops ofthe secondary papillae.
b. Line of basement membrane,  d. Secondary papilte, deprived of e, e, the epithelium.  /.  Hair-like
processes of epithelium capping the simple papillae.—Magnified 25 diameters,  g. Separated nucleated
particles of epithelium, magnified 300 diameters.
  1, 2. Hairs found on the surface of the tongue. 3, 4,5. Ends of hair-like epithelial processes, showing
varieties in the imbricated arrangement ofthe particles, but in all a coalescence ofthe particles towards
the point.  5, encloses, a soft hair.—Magnified 160 diameters.]

protective covering, the stiffness and brush-like arrangement of their filamentary productions,
their greater development in  that portion of the dorsum of the  tongue which is chiefly  em-
ployed in  the movements of mastication, all evince the subservience of these papillae to the
latter function, rather than to that of taste;  and it is evident that their isolation and partial
mobility on one another, must render the delicate touch with which they are endowed, more
available in directing the muscular actions of the organ.  The almost manual dexterity of the
organ in dealing with minute particles of food, is probably provided for, as far as sensibility
conduces to it, in the structure and  arrangement of these  papillae."   It may be added, that
the filiform papilla? of Man seem to be the  rudimentary forms of those horny epithelial pro-
cesses which acquire so great a development in the tongues of the Carnivora,and which are
of such importance in the abrasion of their food. 
SENSE OF TASTE.
403
[Fig. 171.
  a. Secondary papilla of the conical class, treated with acetic acid:—a. Its basement membrane, b.
Its nerve-tube forming a loop.  c. Its curly elastic tissue.  The epithelium in this instance is not abund-
ant; but the vertical arrangement of its particles over the apex of the papilla is well seen, d, and illus-
trates the mode of formation ofthe hair-like processes described in the text.—Mag. 160 diam.
  b. A similar papilla, deprived of its epithelium:—a. Basement membrane,  b. Tubular fibre, probably
forming a loop, but its arch not clearly seen,  c, c. Elastic fibrous tissue at its base and in its interior.—
Magnified 320 diameters.
  c. Nerves of a compound papilla near the point of the tongue, in which their loop-like arrangement is
distinctly seen.—Magnified 160 diameters.]

  528.  As a general rule, it is a  necessary condition of the  sense of Taste,
that the object should either be in  a state of  solution,  or should be soluble  in
the moisture covering the tongue;  if this be not  the case, or  if the tongue be
dry, a simple feeling of contact is all  that  is  produced.   As  in the case of
touch, the idea of the character of the sapid body is very imperfect, unless it
is made to move over  the gustative surface; and  thus  the taste is very much
heightened, by the  compression and friction of  the  substance  between the
tongue and  the palate.   From all these  circumstances it  appears indisputable,
that a very strong analogy exists between Taste  and Touch ; indeed it may
be questioned, whether they are not in reality more closely allied, than is the
sense of Temperature with that of Resistance.
   529. Although the Tongue seems to  be  the  chief  seat  of  Gustative sensi-
bility, yet this is also possessed, though  in a less degree, by the palate.   But
it is to be remarked that the  sensations produced by most sapid substances
are of a complex kind;  and  are in great part due to the organ of Smell.   Of
this any one may convince himself, by  closing the nostrils, and inspiring and
expiring through the mouth  only,  when holding  in the mouth, or  even rub-
bing between the tongue and the palate, some sapid substance; of which the
taste is then scarcely recognized, although it is immediately perceived, when
its  effluvia  are  drawn into the nose.   It is well known  too, that, when the 
 404           ON SENSATION, AND THE ORGANS OF THE SENSES.

 sensibility of the Schneiderian membrane  is blunted by inflammation (as in
 an ordinary cold in the head), the power of distinguishing  flavours is very
 much  diminished.   In  fact, some Physiologists are of opinion that all our
 knowledge of the flavor of sapid  substances is received through the Smell;
 and this  is not improbably true: but it is to be remembered, that, besides
flavor, a sapid body may excite various other sensations, as those of irritation
 and pungency ; and of  these, it  seems to be the true  function of the sensory
 surface of the mouth, to take cognizance.  Such sensations are evidently not
 far removed from those of ordinary touch ; and correspond with those which
 may be excited in the nostrils, through the medium of the Fifth pair.  Taken
 in its ordinary compound acceptation, the sense of Taste has for its  object to
 direct us in the choice of food, and to excite the flow of the  mucus and  saliva,
 which are destined to aid in the preparation of the food for Digestion.  Among
 the lower Animals, the  instinctive perceptions connected with  this sense are
 much more remarkable than our  own ; thus an  omnivorous  Monkey will
 seldom  touch fruits of a poisonous character, although their  taste may be
 agreeable; and animals, whose diet is  restricted to  some  one kind of food,
 will decidedly reject all others.   As a  general rule, it may be stated, that
 substances of which the taste  is agreeable to us, are useful in our nutrition;
 and vice versa: but there are many signal exceptions to this.
   530. Like other  senses,  that of Taste is capable of being rendered more
 acute by education;  and this on the principles already laid down in regard to
 touch.  The experienced wine-taster can distinguish differences in age, purity,
 place of  growth, &c, between liquors that to ordinary judgments are alike  ;
 and the epicure can give an exact determination of the spices that are com-
 bined in  a particular sauce, or of the  manner in which the animal, on whose
 flesh he  is feeding, was killed.   As in  the case of  other  senses, moreover,
 impressions made upon the sensory surface remain there for a certain period  :
 and this period is for  the  most part  longer  than  that which is required for
 the departure of the impressions made upon  the eye, the ear, or the  organ of
 smell.   Every one knows  how long  the taste of some powerful substances
 remains in the mouth;  and even of those which  make less decided impres-
 sions, the sensation  remains to such a degree that it  is difficult to  compare
 them at short intervals. Hence if a person  be blindfolded,  and be  made to
 taste substances of distinct, but not widely  different flavours (such as various
 kinds of wine or of spirituous liquors), one after another in rapid succession,
 he soon loses the power of discriminating between them.  In the same man-
 ner, the difficulty of administering very disagreeable medicines may be some-
 times got over, by either previously giving a powerful aromatic, or  by com-
 bining the aromatic with the medicine; its strong impression in both cases
 preventing the unpleasant taste from exciting nausea.

                           4.  Sense of Smell.

   531. Of the nature of Odorous  emanations, the Natural  Philosopher is so
 completely ignorant, that the Physiologist cannot be  expected to give a defi-
 nite account of the  mode, in which they produce sensory impressions.  Al-
 though it may be surmised that they consist of particles of extreme minuteness,
 dissolved  as it were in the air, and-although this idea seems to derive confir-
 mation from the fact that most odorous substances are  volatile, and vice versa,
 —yet the most delicate  experiments have failed to discover any diminution in
 weight, in certain substances (as musk) that have been  impregnating with their
 effluvia a  large quantity of  air  for  several years;  and there are some volatile
 fluids,  such as water,  which  are  entirely inodorous.  The true Olfactory
 nerves pass down from the Olfactory Ganglion (§ 422) in  the  form of very 
SENSE OF SMELL.
405
numerous minute  threads, which  form a plexus upon  the  surface of  the
Schneiderian or  Pituitary  membrane.   Nothing  satisfactory is known in re-
gard to their ultimate arrangement;  but it  is  probable that they form  loops,
  The Olfactory nerve, with its distribution on the septum nasi. The nares have been divided by a longi-
tudinal section made immediately to the  left of the septum, the right nares being preserved entire. 1.
The frontal sinus. 2. The nasal bone. 3. The crista galli process of the ethmoid bone.  4. The sphe-
noidal sinus of the left side.  5. The sella  turcica.  6. The basilar process of the sphenoid and occipital
bones^, 7. The posterior opening ofthe right nares.  8. The opening ofthe Eustachian tube in the upper
part ofthe pharynx.  9. The soft palate, divided through its middle.  10. Cut surface of the hard  palate.
a. The olfactory peduncle.  6. Its three roots of origin,  c. Olfactory ganglion, from which the filaments
proceed that spread out in the substance of the pituitary membrane,  d. The nasal nerve, a branch of
the ophthalmic nerve, descending into the left nares from the anterior foramen ofthe cribriform plate, and
dividing into its external and internal branch,  e. The naso-palatine nerve, a branch ofthe sphenopala-
tine ganglion distributing twigs to the mucous membrane ofthe septum nasi in its course to (/) the ante-
rior palatine foramen, where it forms a smali gangliform swelling (Cloquet's ganglion) by its union with
its fellow of the opposite side. g. Branches of the naso-palatine nerve to the palate.  A. Posterior pala-
tine nerves, i, i. The septum nasi.

similar to those  of the cutaneous nerves.  It would appear that every part of
the Schneiderian  membrane is  not equally endowed  with the  faculty of dis-
tinguishing  odours, which is a very different power from  that of becoming
sensible of irritation from  them.   The  Olfactory nerves  cannot be traced to
the membrane covering the middle and inferior spongy bones, or to that which
lines  the different  sinuses, these  parts of  the  surface being  supplied by  the
Fifth pair only ; and it is a  matter of common experience, that we cannot dis-
tinguish faint odours, unless,  by a peculiar inspiratory effort, we draw the air
charged with them to the upper part of the nose.   In animals  living in  the
air, it is a necessary  condition of the exercise of the sense of Smell, that  the
odorous matter  should be .transmitted  by a respiratory current through  the
nostrils; and  that the membrane  lining these should  be in  a moist   state.
Hence,  by  breathing through the mouth,  we  may  avoid being  affected by
odours even of the strongest and most disagreeable kind;  and in the first stage
of a catarrh, when the ordinary mucous secretion  is  suspended, the sense of
smell is blunted from  this cause, as  it  afterwards is  from the excess in the
quantity of the  fluid,  which  prevents the  odoriferous effluvia from coming
into immediate  relation with  the sensory extremities of the nerves.  Hence
we may easily comprehend, that  section of the Fifth pair, which exercises a 
406           ON SENSATION, AND THE ORGANS OF THE SENSES.

considerable control over the  secretions, will greatly diminish the acuteness of
the smell; and it will have the  further effect of preventing the reception of
any impressions of irritation  from  acrid vapours, which are entirely different
in their character  from true odorous  impressions, and which  are  not  trans-
mitted through the Olfactory nerve (§  441).   The nasal passages may indeed
be considered  as having, in the air-breathing Vertebrata, two  distinct offices;
they constitute  the organ of  smell, through the distribution of the olfactory
nerve upon a part of their surface; but they also constitute the portals of the
respiratory organs, having for their office  to take cognizance of  the aeriform
matter which enters them, and  to give warning of that which would be inju-
rious ; this latter function is performed by the Fifth pair, as by the Par Vagum
in the glottis.  It is  through this nerve, that the act of sneezing is  excitable :
the evident purpose  Of which, is the ejection of a strong blast of air  through
the nasal  passages, in  such a manner as to drive out any offending matter
they may contain.
   532.  The importance  of the  sense of Smell  among many  of  the  lower
Animals,  in guiding  them to  their  food, or in giving them warning of danger
and  also in exciting the sexual feelings, is well known.  To  Man its utility
is very subordinate under ordinary circumstances; but it may be  greatly in-
creased when other  senses are deficient.   Thus, in the well-known case  of
James Mitchell, who was  deaf, blind  and  dumb, from his birth,  it was the
principal  means of distinguishing  persons, and enabled him  at  once to per-
ceive the  entrance of a stranger.   It is recorded that a blind gentleman, who
had  an  antipathy to  cats, was possessed of a sensibility so acute  in this re-
spect, that he perceived the proximity of one that had been accidentally shut
up in a closet adjoining  his room.   Among Savage  tribes, whose  senses are
more cultivated than those of  civilized nations, more direct use being made of
the powers of  observation, the scent is almost as acute as in the lower Mam-
malia; it is asserted by Humboldt,  that the Peruvian Indians in the middle of
the night  can thus distinguish the different races,—whether European, Ameri-
can-Indian, or Negro.*  The agreeable or disagreeable character assigned to
particular  odours, is by  no  means  constant  amongst different  individuals.
Many of  the lower  Animals  pass  their whole  lives in the  midst of odours,
which are to Man (in  his civilized condition  at  least) in the highest degree
revolting; and will even  refuse to  touch food, until it  is far advanced in pu-
tridity.   It more frequently happens  in regard to odours  and savours, than
with respect to other sensory impressions, that habit  makes  that  agreeable,
and even  strongly relished, which was at first avoided; the  taste of the epi-
cure for game that has acquired the fumet,—for olives,—for assafoetida, &c,
are instances of this.   As to the length of time, during which impressions
made upon the organ of smell remain upon it, no  certain knowledge can be
obtained.   It is difficult to say that the effluvia have been completely removed
from the nasal  passages :  since it is not improbable that the odorous particles
(supposing such to exist) are absorbed or dissolved by the mucous  secretion;
it is  probably in this manner that we may account for the fact, well known to
every medical man, that the cadaverous odour is frequently experienced for
days after a post-mortem examination.!

  * The author has been assured by a competent witness, that a  lad  in  the state of Som-
nambulism, had his sense of smell  so remarkably heightened, as  to be able to assign (with-
out the least hesitation) a glove placed in his hand, to its  right owner,—in the midst of
about thirty persons, the boy himself being blindfolded.
  t This may partly be attributed also to the effluvia adhering to the dress.   It has been
remarked that dark cloths retain these more strongly than light. 
SENSE OF VISION.
407
                           5. Sense of  Vision.

   533. The objects of this sense are bodies, which are either in themselves
luminous, or which become so by reflecting the light that proceeds from others.
Whether their light is transmitted by the actual emission of rays, or by the
propagation of undulations  analogous to those of sound, is a jjuestion at pre-
sent keenly debated amongst  Natural Philosophers;  but it is of little conse-
quence to the Physiologist, which is the  true solution;  since it is only with
the laws, which actually regulate the transmission of light, that he is concerned.
These laws it may be desirable here briefly to recapitulate.                  ,
   534. Every point  of a luminous  body sends off a number of  rays, which?
diverge in every direction, so  as to form a cone, of which the luminous poin^
is the apex.   So long as these rays pass through a medium of the same dens-
ity, they proceed in straight lines; but, if they enter a  medium  of different}
density, they are refracted or  bent,—towards the perpendicular to the surface
at the point at which they enter, if they pass from  a rarer  into a denser me-i
dium, and from the perpendicular, when  they pass from  a denser medium
into a rarer.   It is easily shown to be a result of this law, that, when parallel
rays passing through air fall upon a  convex surface of glass, they will-be
made to converge;  so as to meet at the opposite extremity  of the diameter of
the circle, of  which  the curve forms  part.  If, instead of continuing, in  the
glass, they pass out again, through a second convex surface, of which the di-
rection  is the reverse of the first, they will be made to converge still jnore, so
as to meet in the  centre of curvature. Rays which are not parallel, but which
are diverging from a focus, are likewise made to converge to a point or focus ;
but this point will be more  distant from the lens, in  proportion, as the object
is nearer to it, and the angle of  divergence consequently greater.   The rays
diverging from the several points of a luminous object,  are thus brought to a
corresponding focus; and the places of all these foci hold exactly the same re-
lation to each other, with that ofthe points from which  the rays diverged;  so
that a perfect image of the object is  formed upon a screen held in the focus
of the lens.   This image, however, will be inverted;  and  its size, in pro-
portion to that of the object, will depend upon their respective distances from
the lens.  If their distances be the same, their  size will also be the same; if
the object be distant,  and the image near, the latter will be much the smaller;
and vice versa.
   535.  There are two circumstances, however, which interfere with the per-
fection of an image thus formed  by a convex lens.   The one is, that, if  the
lens constitute  a  large part of the  sphere from which  it is taken, the rays
which fall near its margin are  not brought to a focus at  the same point with
those which pass through its  centre; but at a  point  nearer  the lens.   This
difference, which must obviously interfere greatly with the distinctness of the
image, is termed  Spherical Aberration; it may be corrected by the combi-
nation of two or  more lenses, of which the curvatures are calculated to  ba-
lance one another, in such a manner that all the rays shall be brought to  the
same focus;  or by diminishing the aperture of the lens by means of a stop
or diaphragm, in such a manner  that only the central part of it shall be used.
The latter of these methods is the one employed, where  the diminution in
the amount of light transmitted  is not attended with inconvenience.  The
nearer  the object  is to the lens (and the greater, therefore, the angle of diverg-
ence of its rays), the greater will  be the  spherical  aberration, and the more
must the aperture  of the diaphragm be  contracted  in order to counteract it.
The other circumstance that interferes with the  distinctness of the image, is
the unequal  refrangibility  of  the  differently-coloured rays,  which  together 
408
ON SENSATION, AND THE ORGANS OF THE SENSES.
make up white or colourless light; the violet being more  bent from their
course than the  blue, the  blue  more than the yellow, and  the yellow more
than the  red; the 6onsequence  of which will  be, that the violet rays  are
brought to a focus much nearer to the lens  than the blue, and the blue nearer
than the red.  If a screen be held to receive the image, in  the focus of any
of the rays,  the  others will  make  themselves apparent as  fringes  round  its
margin.   This difference is termed Chromatic Aberration.   It is corrected in
practice, by combining together lenses of different substances, of which  the
dispersive power (that is, the power of separating the  coloured rays) differs
considerably.  This is the case with flint and crown glass,  for instance,—the
dispersive power of  the former being much  greater than  that of the latter,
whilst its refractive power is nearly the  same:  so  that, if  a convex lens of
crown glass  be united with  a concave of flint whose curvature is much less,
the dispersion of the rays effected by the former will be counteracted by the
latter, which diminishes in part only its refractive  power.
  536.  The Eye may be  regarded as an  optical  instrument of great perfec-
tion, adapted to produce, on  the expanded surface of the optic nerve, a com-
plete image  or picture of luminous objects brought before it; in which the
forms, colours, lights and shades, Sic, of the object are all  accurately repre-
sented.   By the different refractive powers of the transparent media, through
which the rays of light pass, and  by the curvatures given to their respective
surfaces, both  the Spherical  and Chromatic aberrations are  corrected in a de-
gree sufficient for all  practical purposes:  so  that, in a well-formed eye, the
picture is quite free  from  haziness, and from  false  colours.  The power by
which it  adapts  itself to variations  in  the distance  of the  object,—so as to
form a distinct image of it, whether it be six  inches, six yards, or six miles
off,—is extremely remarkable,  and cannot  be  regarded as hitherto completely
explained.   It is obvious that, if  we fix upon any distance  as  that for which
the eye is naturally  adjusted (say 12 or 14 inches, the  distance  at which we

                                 (Fig. 173.
  A longitudinal section of the globe of the Eye ; 1, the sclerotic, thicker behind than' in front; 2, the
cornea, received within the anterior margin of the  sclerotic, and connected with it by means of a be-
veled edge;  3, the choroid, connected anteriorly with (4) the ciliary ligament, and (5) the ciliary pro-
cesses ; 6, the iris j 7, the pupil; 8, the third layer of the eye, the retina, terminating  anteriorly by an
abrupt border at the commencement of the ciliary processes ; 9, the canal of Petit, which encircles the
lens (12); the thin layer in front of this canal is the zonula ciliaris, a prolongation of the vascular layer
ofthe retina to the lens. 10, the anterior chamber ofthe eye, containing the aqueous humour; the
lining membrane by which the humour is secreted is represented in the diagram ; 11, the posterior; 12,
the lens more convex behind than before, and enclosed in its proper capsule ; 13, the vitreous humour
enclosed in the hyaloid membrane, and in cells formed in its interior by that membrane; 14, a tubular
sheath of the hyaloid membrane, which serves for the passage of the artery of the capsule of the lens ;
15, the neurilemma of the optic nerve ; 16, the arteria centralis retinae, imbedded in  its  centre.] 
SENSE OF VISION.

    [Fig. 174.
409
d    *
  A Horizontal Section of the Eyeball; 1, sclerotic coat; 2, sheath ofthe optic nerve, or canal of Fon-
tana;  3, circular venous sinus of the  iris; 4, proper substance ofthe cornea; 5, arachnoidea oculi; 6,
membrane of the anterior chamber of the aqueous humour;  of the  two dotted lines one points to the
      35 
410           ON SENSATION, AND THE ORGANS OF THE SENSES.

supposed membrane of Descemet, the other to the supposed continuation of that membrane over the
anterior surface ofthe iris; 7. choroid coat; &, annulus albidus; 9, ciliary ligament; 10,10', ciliary body,
consisting of (10') a pars non-fimbriata, and (10) a pars fimbriata formed by the ciliary process ; 11, ora
serrata of the ciliary body ; 12, iris ; 13, pupil; 14. membrane of the pigment; 15, delicate membrane lining
the posterior chamber of the aqueous humour;  16, membrane of Jacob ; 17, the  optic nerve surrounded
by its neurilemma; 17', the fibres ofthe optic nerve consisting of fasciculi of primitivet ubules ; 18, cen-
tral artery of the retina; 19, papilla cornica of the optic nerve ; 20, retina;  the  situation of its vascular
layer is indicated by a dotted line; 21, central transparent point of the retina; 22, vitreous humour; 23,
the hyaloid membrane; 24, canalis hyaloideus; 25, zonula ciliaris; in the plate, none of its fimbriated
part is seen, being concealed by the ciliary processes; 26, canal of Petit; 27, crystalline lens; 28, an-
terior wall ofthe capsule ofthe lens ; 29, posterior wall ofthe capsule ofthe lens; 30, posterior chamber
of the aqueous humour ; 31, anterior chamber of the aqueous humour.]

ordinarily read), the rays  proceeding  from an object, placed  nearer  to the
eye than this, would not be brought  to a focus  upon the retina, but would
converge towards a  point behind it; whilst on the contrary, the rays from an
object at a  greater  distance would  meet before they reached the retina, and
would have again diverged from each other when  they  impinge  upon it; so
that in either case, vision would be indistinct.   Now two methods of adapta-
tion suggest themselves to the  Optician.   Either  he  may  vary the distance
between the refracting surface and the screen on which  the image is formed,
in such a manner, that the  latter shall always be in the focus of the  converg-
ing rays ;  or, the distance of the screen remaining  the  same, he may vary the
convexity of his lens, in such a manner as to adapt it to the distance of the object.
It is not  improbable, that both of these methods  are  employed  in  the Eye,
though no distinct evidence has been obtained of the operation of either.  Seve-
ral hypotheses have  been  proposed,  to  account  for  the phenomenon:  it is
easily proved that no one of them can alone be true; but it cannot be readily
shown that any of  them is entirely false : and it would not seem  unlikely,
therefore, that all may  participate, in  various degrees, in the effect.   The fol-
lowing are the principal of these.—1. An alteration in the form of  the globe
of  the  eye by the action  of the muscles, so that its antero-posterior diameter
may be increased or diminished.*—2. A change  in the convexity of the cor-
nea.  This might be very  well connected with the last; since,  if the  globe
were converted into a spheroid, of which the antero-posterior diameter would
be  the  longest, the curvature of the cornea would be increased ;  whilst, if the
antero-posterior diameter were shortened, the curvature would be diminished.
3.  Change of position of the crystalline lens, by means of the ciliary processes.
4.  Change of figure of the lens itself.   That  one or both of the last two are
concerned in the effect, would appear from the fact, well known to every Oculist,
that, after the removal of  a  cataract, the power  of adapting the eye  to dis-
tances  is greatly diminished.—5.  Change in the  aperture  of the pupil; the
mode in which this  could  assist in accommodating the eye to variations of
distance, is not very obvious.
   537. Some curious  circumstances, relative to the connection between the
optical adaptation of the eye to distances, and the changes in the direction of the
axes of the two  eyes, have  been pointed out by Muller.   When both eyes are
fixed upon an object, their axes must converge (as formerly explained, § 455)
so as to meet in it.   The nearer the object, the greater must be the  degree of
convergence; and when  the object is brought within the ordinary distance of
distinct vision, the  convergence must very rapidly increase.   Now  this is
precisely what takes place, in regard to alterations in the focus of the eye; for
little change is required, when the object is made to approach from a considera-
ble distance to a moderate distance; but, when it is brought near the eye, the

   * The influence of the muscles in altering the form of the globe may be better compre-
hended, now that we know the mode in which this is kept in its place in the front of the
orbit, by a fascia passing behind it, and attached anteriorly to the lids. 
                             SENSE^F VISION.                         411

focus must be considerably lengthened, or the convexity of the eye increased,
to cause the rays to meet on the retina: and hence it may be surmised, that
the same cause is acting to produce both changes.  But that the convergence
of the axes is not itself in any way the occasion of the alteration of the focus
of the eye, is shown by the fact, that the adaptation is as perfect, in a person
who only possesses or uses one  eye, as it is when both are employed; and
also by the power, which is possessed by some persons, of altering the focus
of the eye by an effort of the will, whilst the convergence  remains the same.
In regard  to the adaptation of the eyes to varying distances, it is further to  be
remarked, that, when an object is being viewed as near to the eye as it can  be
distinctly seen, the pupil contracts in  a considerable degree.  The final cause
of this change, is evidently to exclude the outer rays of the cone  or pencil,
which, from the large angle of their divergence, would fall so obliquely on the
convex surface ofthe eye, as to be much affected by the spherical aberration:
and  to allow the Central rays only to enter the eye, so as to preserve the clear-
ness of the image.  The channel through which it is effected is  evidently the
same, as that by which the convergence of the  eyes is  produced,—namely,
the inferior branch of the third  pair of nerves;  to  the action of which, the
sensations upon the retina form  the stimulus, in the same manner as they  do
to the ordinary variation in the diameter of the  pupil under the influence of
light.
   538. The  ordinary  forms of  defective vision, which are known  under the
names of  myopia and presbyopia, or short-sightedness and long-sightedness,
are entirely attributable to defects in the optical adaptation of the eye.  In the
former, its refractive power is too great; the rays from objects  at the usual
distance  are   consequently brought  too soon to a focus, so as to  cross one
another and diverge, before they fall upon the retina;  whilst the eye is adapted
to bring to their proper focus on the  retina,  only those rays which were pre-
viously diverging at a large angle, from an object in its near proximity.   Hence
a short-sighted person, whose shortest limit of distinct vision is not above half
that of a person of ordinary sight, can  see minute  objects  more'clearly;  his
eyes having, in fact, the  same magnifying power, which  those of the other
would possess, if aided by a convex glass, that would enable him  to see the
object distinctly at the shorter distance.  But as the  myopic structure of the
eye  incapacitates its possessor from seeing objects clearly, at even a moderate
distance, it is desirable to apply a correction;  and this  is done, by simply inter-
posing a concave lens, of which  the curvature is properly adapted to compen-
sate for the excess of that of the organ itself, between the object and the eye.
On the othftr hand,  in the presbyopic eye, the curvature and refractive power
are not sufficient to bring to a focus on the retina, rays which were previously
divergent in a considerable or even in a moderate degree; and indistinct vision
in regard  to  all near objects is, therefore, a necessary  consequence, whilst
distant objects are well seen.  This defect is remedied by  the use of convex
lenses, which make up for the deficiency of the curvature.  We commonly
meet with myopia in young  persons, and with presbyopia in old; but this is
by no means the invariable rule; for even aged persons are sometimes short-
sighted;  and  long-sightedness is occasionally met with amongst the young.
In choosing spectacles, for the purpose of  correcting  the errors of the eye, it
is of great consequence  not  to  make an over-compensation; for this  has a
tendency to increase the defect, besides occasioning great fatigue in the employ-
ment of the sight.  It may be easily found,  when a glass of the  right power
has  been selected, by inquiring of the individual, whether it alters the apparent
size of the objects, or only renders  them distinct.   If it  alter the size (in-
creasing it if it be  a convex lens, and  diminishing it if it be a concave),  its
curvature  is too great;  whilst if it do not disperse the haze, it is not sufficiently 
412           ON SENSATION, AND THE ORGANS OF THE SENSES.
powerful.   In general it is better to employ a glass which somewhat under-
compensates the eye, than one which is of a curvature at all too high ; since,
with the advance of years in elderly persons, a progressive increase in power
is required; and, as young persons grow up to adult age, they should endeavour
to  dispense with the aid of spectacles.
   539.  Many other interesting inquiries, respecting  the  action of the eye as
an optical instrument, suggest themselves to the physical philosopher; but the
foregoing are the chief  in which the Physiologist is  concerned; and we shall
now proceed, therefore, to consider  the share, which the  Retina  and Optic
Fig. 175.
Fig. 176.
 Part of the Retina of a Frog, seen
from the outer surface.  Magnified 300
times.
 Distribution of Capillaries in Vascu-
lar layer of Retina.
[Fig. 177.
Nerve perform in the phenomena of vision.—The optic nerve, at its entrance
into the eye, divides  itself  into numerous small fasciculi of ultimate fibrils;
                               and these appear to  spread themselves  out,
                               and to inosculate with each other by an ex-
                               change  of fibrils, so  as to form  a net-like
                               plexus.    There is  considerable  difficulty,
                               however, in the precise  determination of tbe
                               course of  the  nerve-fibres  in the Retina; on
                               account of their minute size, and the absence
                               of their distinctive  characters.   According to
                               Mr. Bowman, the tubular membrane and the
                               white substance  of Schwann  are  deficient;
                               and only the central part of the negve-fibre, or
                               axis-cylinder, is continued into this expansion.
                               The plexus of nerve-fibres comes into relation
                               with a plexus of capillary vessels, very minute-
                               ly distributed;  and also with a layer of cells,
                               so closely resembling those of the cortical  sub-
                               stance of the brain, that there can be no  rea-
                               sonable doubt of their correspondence in func-
                               tion.  This  layer of cells, constitutes the in-
                               ternal layer of the true retina.   We have here,
                               then,  all the elements of an apparatus for the
                               origination of changes in the nervous trunks,
                               in a fully displayed form ; and it can scarcely
                               be doubted that the essential parts of the same
                               structures  exist in the papilla? of the cutaneous
                               and other  sensory surfaces.—The true Retina
                               is covered externally by a very peculiar in-
                               vestment,  the  Membrane  of  Jacob, which
  A portion of the Retina of an Infant,
with its vessels injected and magnified
25 diameters.  An outline ofthe natural
size of this piece is seen just below the
main cut.] 
SENSE OF VISION.                          413
separates it from the pigmentary layer.   This seems to be composed of cells
having a  cylindrical form.  These  are sometimes  arranged vertically to the
[Fig. 178.
occk
  Vertical section of the Human Retina and Hyaloid Membrane, h. Hyaloid membrane, h'. Nuclei
on its inner surface, c. Layer of transparent cells, connecting the hyaloid and retina, c'. Separate
cell enlarged by imbibition of water,  n. Gray nervous layer, with its capillaries.  1. Its fibrous lamina
2. Its vesicular lamina, 1'. Shred of fibrous lamina detached. 2'. Vesicle and nucleus detached, g. Granu-
lar layer.  3. Light lamina frequently seen.  g'. Detached nucleated particle of the granular  layer.
m. Jacob's membrane, m'. Appearance of its particles, when detached, m". Its outer surface.  Mag-
nified 320 diameters.]

surface of the membrane, so that their extremities  only are seen ; whilst in
other instances they are found to present an
imbricated arrangement, lying over each other              £Fig. 179.
obliquely, in which case they are of conside-
rable length (Fig. 175).  They are  remarka-
ble for the rapidity with which  they undergo
alterations after death ;  and especially for the
changes in  their form, which are produced
by the action of water.
   540.  The following statements  on  the
Limits  of Human Vision, in regard to the
possible minuteness of  the objects of which
it can  take  cognizance, comprehend the re-
sult of numerous inquiries made by Ehren-
berg,  with the  view of calculating  the ulti-
mate power  of the Microscope.*  In opposi-  thg
tion to the generally-received opinion, Ehren-  ea.
berg arrived at the conclusion that, in regard
to  the extreme limits of vision,  there is  little difference amongst  persons of
ordinarily good sight, whatever may be the focal distance of their eyes.   The
smallest square magnitude usually visible to  the naked eye, either of white
particles on a black ground, or of black upon a white or light-coloured ground,
is about the  l-405th of  an inch.  It is possible, by  the greatest  condensation
of light,  and excitement of the attention, to recognize magnitudes between the
l-405th  and l-540th of an inch ; but  without sharpness or certainty.  Bodies
which are smaller than  these, cannot be discerned with the naked eye when
single;  bvft may be seen when placed in  a row.   Particles which powerfully
reflect light,  however, may be distinctly seen,  when  not half the size of the

                  * Taylor's Scientific Memoirs.   Vol. i. p. 576.
                                     35*
urface of the Retina, showing
After Jacob.] 
414           ON SENSATION, AND THE ORGANS OF THE SENSES.

least ofthe foregoing; thus, gold dust* ofthe fineness of 1-1125th of an inch,
may be discerned with the naked eye in common daylight.   The delicacy of
vision is far greater for lines than for single articles ; opaque threads of l-4900th
of an inch in diameter may be discerned with  the  naked eye, when held to-
wards the light.  Such threads are about half the diameter of the Silk-worm's
fibre.  The degree in which the attention is directed  to  them, has  a great
influence on the readiness with which very minute  objects can be perceived;
and Ehrenberg remarks that there is a much  greater difference amongst indi-
viduals in this respect, than there is in regard to the absolute limits of vision.
Many persons can distinctly see such objects, when their situation is exactly
pointed out to them, who cannot otherwise  distinguish them;  and the same
is the case with persons of acuter perception, with  respect  to  objects at dis-
tances greater than those,  at which they can  see most clearly.  " I myself,"
says Ehrenberg, " cannot see l-2700th of an inch, black on white, at twelve
inches  distance; but having found it  at from four  to five inches distance, I
can remove it to twelve inches, and still  see the  object plainly."  Similar
phenomena are well known in regard  to a balloon, or a faint star, in a clear
sky; or  a ship in  the horizon: we  easily  see them  after they have been
pointed out to us;  but the faculty of rapidly  descrying  depends on the habit
of using the eyes in search of such objects (§ 519).
  541.  The sense of Vision depends, in  the first  place, on the  transference
to our minds of the picture which is formed upon the retina ; this picture puts
us in possession of  the outlines, lights and shades, colours, and relative posi-
tions of the objects  before us ;  and all the  ideas  respecting the real forms,
distances, Sic, of bodies, which we found upon these data, must be considered
in the light of perceptions, either instinctive or acquired.  Many  of these are
derived  through the combination, in our minds, of the Visual sensations, with
those derived from the sense of Touch.  Thus, to take a most simple illustra-
tion, the idea of smoothness is one  essentially tactile ; and  yet it constantly
occurs to us, on looking at a surface which reflects  light in a particular man-
ner.   But, if it were not  for  the  association, which experience leads us to
form, of the connection between polish as seen by the eye, and  smoothness
as felt by the touch, we should  not  be able to determine, as we now can do,
the existence of both these qualities  from  an  impression communicated to us
through either sense singly.  The general fact that, in Man, the greater part
of those notions of the external world by which his actions in the adult state
are guided, are acquired by the gradual association of the sensations commu-
nicated by the sight and by touch, is substantiated by amply-sufficient evidence.
This evidence  is chiefly derived from observations made upon persons born
blind, to whom sight has been communicated by an operation, at a period of life
which enabled them to give an accurate description  of their  sensations.  The
case recorded  by Cheselden is one of the  most  interesting of these.  The
youth (about 12 years of age), for some time  after tolerably distinct vision had
been obtained,  saw  ewexy thing flat, as in a picture;  simply receiving the con-
sciousness of the impression made upon his retina ;  and it was some time be-
fore  he  acquired the power of judging, by his  sight, of the real forms and
distances of the objects around him.   An amusing  anecdote recorded of him,
shows the complete  want of natural or intuitive connection which there is in
Man, between  the ideas formed through visual and  through  tactile sensations.
He was well acquainted with a Dog and a Cat by feeling ;  but could not re-
member their respective characters when he saw them.   One day,  when thus
puzzled, he took up the Cat in his arms, and felt her  attentively, so as to as-

  * Ehrenberg mentions that he obtained the finest particles of gold, by scraping gilt brass ;
by filing pure gold, he always obtained much coarser particles. 
SENSE OF VISION.
415
sociate the two sets of ideas ; and then, setting her down, said, " So, puss, I
shall know you another  time."   A similar instance has come under the Au-
thor's own knowledge ; but the subject of it was scarcely old enough to  pre-
sent phenomena so striking.  One curious circumstance was remarked of him,
which fully  confirms  (if confirmation were  wanting)  the view here given.
For some time  after the sight was tolerably clear, the lad preferred finding his
way through  his father's house, to which he had  been quite accustomed when
blind, by touch rather than by sight,—the use of the latter sense appearing to
perplex rather than to assist him ;  but, when learning a new locality, he  em-
ployed his sight, and evidently perceived the increase of facility which he de-
rived  from it.
   542.  The  question has been proposed, whether a person born blind, who
was able by the sense of Touch to distinguish a cube from a sphere, would,
on suddenly obtaining his Sight, be  able  to distinguish them  by the latter
sense.  This question was answered by Locke in the negative; and probably
with justice.   It is no real  objection to such a reply, that a new-born animal
seeks the nipple of its mother, when informed of its proximity by sight; for
all that is indicated by this fact is, that the sensation excites an intuitive  feel-
ing of desire, which gives rise to movements adapted to gratify it.   Such in-
stinctive actions, founded upon  intuitive perceptions, are, as already pointed
out, much more numerous in the lower Animals  than in the higher, and in the
young of the  Human species than in the adult (§ 428); and they do not afford
any proof that  definite notions, such as we acquire, of the forms and proper-
ties of external  objects, are possessed by the animals which exhibit them.
We shall now examine, a little  more in detail, into the means by which we
gain such notions, and the data on which they are founded.
   543.  The  first  point  to  be determined, is one which has been a fruitful
source of discussion,—the  cause of erect  vision, the picture upon the retina
being inverted.  Many solutions of it have  been attempted; but they are for the
most  part rather specious than really satisfactory. That which has been of late
years the most in  vogue, is founded upon what was styled the Law of Visible
Direction, which has  been supported by Sir D.  Brewster, and other eminent
Philosophers.  This  law affirms, that every object is seen in the direction of
the perpendicular  to  that point of the retina, on which its image is formed;
or, in other words, that, as all the perpendiculars to the several points of the
inner surface of a  sphere meet in the  centre, the line of  direction of any ob-
ject is identical with the prolonged radius of the  sphere, drawn from the point
at which its image is made upon  the retina.  Upon close examination, how-
ever,  it  is  found that  this law cannot be optically correct; since the lines of
direction cross each other at a point much anterior to the centre of the globe;
as may be determined by drawing a  diagram upon a large scale, and laying
down the course of the rays received by the eye, according to the  curvatures
and refractive powers of its different parts.  In this manner it has been deter-
mined by Volkm'ann,  that the lines of direction  cross each other in a point a
little behind the crystalline lens ; and  that they  will thus fall at such differ-
ent angles on  different points of the  retina, that no general  law can be laid
down respecting them.  It may be questioned, moreover, whether such a law
would afford any assistance  in  explaining the phenomenon ;  since, after all,
it is requisite to assume an intuitive application  of it, in  supposing the mind
to derive its  ideas  of the relative situations of objects, from the imagined line
of direction.—A much  simpler  and more direct  explanation may be given.
We' must remember that, which we have had occasion to notice in regard to all
the other senses,—the broad line of distinction between the sensation and the
perception or elementary notion;  and this is still more clearly shown by the
complete absence  of any relation, but such as experience  developes, between 
416           ON SENSATION, AND THE ORGANS OF THE SENSES.

the perceptions derived through the sight, and those acquired from the touch.
Hence there is no more difficulty in understanding, that  an inverted picture
upon the retina should convey to  us  a notion of the external world, which
harmonizes with  that acquired through the sense of touch, than there is in
comprehending the formation of any of those intuitive perceptions of animals,
which are so much more removed from the teachings of our own experience
(§ 490). It is justly remarked by Muller that, " if we do see objects inverted [or
rather, if the picture on the retina is inverted] the only proof we can possibly
have of it, is that afforded by the study of the laws  of Optics ; and, if everything
is seen reversed, the relative position of the objects remains unchanged.  Hence
it is, also, that no  discordance arises between the sensations of inverted vision
and those  of touch, which perceives everything in its erect position ; for the
images of all  objects, even of our  own limbs, on the retina, are  equally in-
verted, and therefore  maintain the same relative position.   Even the image of
our hand,  when used in touch, is inverted."  From what has been stated, it
would appear quite conceivable, that a  person just endowed with sight, should
not at first know by his visual  powers, whether  a pyramid placed before his
eyes  is the same body, and  in  the same  position, as one with which  he  has
become acquainted by the  touch; and, if this  be admitted, the  inference ne-
cessarily follows, that the notion of erectness, which we form by the combined
use of our eyes and our hands, is really the product of experience in ourselves,
whilst it is probably innate or intuitional in the lower Animals.
  544. The cause of single vision with the two eyes has, in like manner,
been the  subject of much discussion; since the mode in which we are affected
by the two simultaneous impressions, is  quite different from that, in which
we derive our knowledge of external things through the other senses.   Some
have even asserted, that we  do  not really employ both eyes simultaneously,
but that the mind  is  affected by the image communicated  by one only; and
this idea might seem to be  confirmed by the fact heretofore mentioned (§ 519),
respecting the alternate use of  the two eyes, when they are looking through
two differently-coloured media.  But it is  easily disproved  in other ways.—
It will presently be shown, that all our estimates of the forms of bodies, de-
pend on the combination by the mind, of the images simultaneously transmit-
ted by  the two eyes ; and our knowledge of distances is in  great part obtained
in like manner.  The condition of Single Vision has been already stated
(§ 454) to be  probably this,—that the two images of the object should be
formed on parts of the two retina?, which  are accustomed to act in concert;
and reasons were  given for the belief, that  habit is the chief means by which
this conformity is produced.  There can  be no  doubt, however, that double
images are continually being conveyed to our  minds; but that, from their
want of force and distinctness, and from the attention being fixed on something
else,  we do not take  cognizance of them.  This may be shown by a very
simple experiment.   If two fingers be  held up before the eyes, one in front
of the other, and  vision be  directed to the more distant,  so that it is seen
singly, the nearer will appear double ;  while, if  the nearer one be regarded
more particularly, so as to  appear single, the more distant will be seen  double.
A little consideration will show, therefore, that our minds must be continually
affected with  sensations,  which cannot be united into the idea of a single
image ; since, whenever we direct the axes of our eyes towards any object,
everything else will be represented to us as double;  but we do not ordinarily
perceive this, from our minds being fixed upon a  clear and distinct'image, and
disregarding,  therefore, the vague undefined images  formed by objects at a
different focus.  Of this it is very  easy to convince oneself.  It is moreover
evident from this  experiment, that  double vision  cannot result from want of
symmetry in  the position of the images upon the retina, to which some have
* 
SENSE OF VISION.
417
 attributed it;  for it answers equally well, if the line of the two fingers be pre-
 cisly in front of the nose, so that the inclination of both eyes towards either
 object is equal; the position of  the images of the second object must then be
 at the same distance on each side from the central line  of the  retina, and yet
 they are represented to the  mind as double.  It  is, moreover, easily shown,
 that, in the lower animals whose orbits are not directed forwards as in us, but
 sideways in a greater or less degree, whenever an object is so situated as to
 be seen by both eyes, the points of the  two retinae on which its  images are
 formed, must be very far from possessing this symmetry.
   545. Many attempts  have been made to explain the phenomena of Single
 Vision by the peculiar decussation of the Optic nerves (§ 445); and an inte-
 resting correspondence between  the varieties in the degree of decussation, and
 the  position of the  eyes, in several animals, has been pointed out by Mr. Solly
 and Mr. Mayo.  From these and other data, it has been concluded, that each
 nerve is used in looking towards the opposite  side.  This is evidently true of
 the  Osseous Fishes, whose two  eyes, being directed  sideways, have  two en-
 tirely different spheres of vision.  And it is also  true of Man,  if Mr. Mayo's
 account of  the distribution of the nerve  be  correct;  since, when we look at
 an object held directly in front of the face, at the level of the eyes, and at the
 nearest point  for distinct vision,  almost the whole of that portion of the right
 retina, which lies to the outside  of the entrance of the optic nerve,  is directed
 to the left;  and the exactly  different, complementary, or inner portion of the
 left  retina, which is supplied by the same nerve, is  likewise  directed to the
 left.   On this supposition, all the rays entering the two eyes from any one
 point, will  be brought to a focus on fibrils belonging to the nerve of the same
 side; though these are  in Man, as  in other animals whose spheres of vision
 are  nearly or  partly coincident,  distributed  to  distinct visual organs.*  It is
 obvious, however,  that this or any similar explanation, must be insufficient to
 explain the phenomenon of  single vision; since  the images  formed upon the
 two retinae  are necessarily different, and  must be combined or harmonized by
 an act of the  mind, as will be shown in  the succeeding paragraphs.
   546. We shall next consider  the  mode, in which our  notion  of the solid
forms and relative  projection of objects is acquired ; on which great  light has
 recently been thrown  by the interesting experiments of Mr. Wheatstone.t It
 is perfectly evident, both from reason and experience, that the flat picture upon
 the retina, which is the  only object  of our sensation, could not itself convey to
 our  minds any notion, but that of a  corresponding plane surface.  In  fact, any
 notion of solidity, which might  be  formed by a  person, who  had  never had
 the use of more than one eye, would entirely depend upon the combination of
 his visual and tactile sensations.  This  idea is fully confirmed  by  the  case
 already referred to, as recorded  by  Cheselden.  The first visual  idea formed
 by the youth was, that  the  objects around  him  formed a flat surface, which
 touched his eyes, as they had previously been in contact with his hands; and
 after this notion had been corrected, through the education of his sight by his
 touch, he fell  into  the converse error of supposing that a picture, which was
 shown to him, was the object itself represented in relief on a small scale.—But
 where both eyes are employed, it has been ascertained by Mr.  Wheatstone,

   *  The late Dr. Wollaston was subject to a curious affection of vision, which consisted in
 his not being  able to see more than half an object,—the loss being sometimes  on one side,
 and sometimes on the other.  The Author has met with several cases of this disorder, which
 has been termed hemiopia.  Dr. W. thought that they might be explained by the decussation
 of the optic nerve;  but Mr. Mayo states that he has known instances of a parallel affection,
 involving alternately the centre and the circumference ofthe retina, and therefore not attribut-
 able  to any such structural arrangement.
  ■j-  Philosophical  Transactions,  1838. 
418           ON SENSATION, AND THE ORGANS OF THE SENSES.

that  they concur in  exciting the perception of solidity or projection, which
arises from the combination of two different images in the mind.  It is easily
shown, that any near object is seen in two different modes by the two eyes.
Thus let the reader hold up a thin book, in such a manner that its back shall
be exactly in  front of his  nose, and at a moderate distance from it; he will
observe, by closing first one eye and then the other, that his perspective view
of it (or the manner in which he would represent it on a plane surface) is very
different, according to the eye with which he sees it.   With the right eye he
will  see its right side, very  much foreshortened ; with the left, he will  gain a
corresponding view of the left side;  and the apparent angles, and the lengths
of the different lines, will be found to be very different in the two views. On
looking  at either of these  views singly, no other  notion of solidity can be
acquired from it, than that to which the  mind is conducted, by the association
of such a view with the touch ofthe object it represents.  But  it  is capable of
proof, that the mental association of the two different pictures upon the retinae,
does of itself give rise to the idea of solidity.   This proof is afforded by Mr.
Wheatstone's  ingenious instrument, the Stereoscope.
   547. The  Stereoscope essentially consists of two  plane mirrors, inclined
with their backs to one another at an angle of 90°.  If two perspective draw-
ings  of any solid object, as seen at a given distance with the two  eyes respect-
ively, be placed before these mirrors, in  such a manner that their images shall
be made to fall upon the corresponding parts of the  two retinae, in the same
manner  as the two images formed by the  solid object itself would have done,
the mind will perceive, not a single representation of the object, nor a  confused
union of the  two, but a body projecting in relief,—the  exact counterpart of
that  from which the drawings were made.  Mr. Wheatstone further shows by
means of the  Stereoscope,  that similar images, differing to a certain extent in
magnitude, when presented to the corresponding parts of the two retinae, give
rise to the perception of a single object, intermediate  in size between the two
monocular pictures.   Were it not for this, objects would appear single, only
when at an equal distance from both  eyes, so that  their pictures upon the
retina are of the same size;  which will only happen, when they are directly
in front of the median line of the face.  Again, if pictures  of dissimilar objects
be simultaneously presented to  the two  eyes, the consequence will be similar
to that which is experienced, when the  rays come  to the eye through two
differently-coloured media;—the two images do not coalesce,  nor  do  they
appear permanently superposed upon one another: but at one  time one image
predominates  to the exclusion of the other, and then the  other is seen alone ;
and it is only at the moment of change,  that the two seem to be intermingled.
It does not appear to be in  the power of  the will, Mr. Wheatstone remarks,
to determine the appearance of either ; but, if one picture be more illuminated
than the other, it will be seen during a larger proportion of the time.  Many
other curious experiments with this simple instrument  are related  by Mr.
Wheatstone;  and they all go to confirm the general conclusion, that  the com-
bination  of the images furnished  by the  two eyes is a  mental  act,  resulting
from an inherent law of our psychical constitution ; and that our perceptions of
the solidity and projection of objects, near enough to be seen in different views
with the two eyes, result from this cause.  In regard to distant objects, how-
ever, the difference in the images formed  by the two  eyes  is so slight, that it
cannot aid in  the determination;  and hence it is, that, whilst we have no dif-
ficulty in distinguishing a picture, however well painted, from a solid  object,
when placed near our eyes, (since the idea, which might be suggested  by the
image formed on one eye, will then be corrected by the other,) we are very
liable to be misled by a delineation, in which the perspective, light and shade,
Sic, are faithfully depicted, if we are placed at a distance from it, and are pre- 
SENSE OF VISION.
419
vented from perceiving that it is but a picture.  In this case, however, a slight
movement of the head is sufficient to undeceive us;  since  by this movement
a great change would be occasioned in the perspective view of the object, sup-
posing it to possess  an uneven  surface; whilst  it scarcely affects  the image
formed by a picture.  In the same manner, a person who only possesses one eye,
obtains, by  a slight motion of his head, the same  idea  of the form of  a body,
which another would acquire by the simultaneous  use  of his two eyes.
   548.  The appreciation of the distance of objects, may be easily shown to
be principally derived from the association, in the  mind, of visual and tactual
sensations ; assisted, in regard to near objects, by the muscular sensations de-
rived from  the convergence  of the eyes.   Thus, an infant, or a  person who
has but recently acquired sight, evidently forms very  imperfect ideas regarding
the distance of objects; and it is  only after long experience that a correct no-
tion is formed.   The assistance which is given by the joint use of both eyes,
is evident from the fact, that, if we close one eye,  we are unable to  execute
with  certainty many  actions, which require a precise appreciation of  the dis-
tance of near objects,—such  as threading a needle,  or snuffing a  candle.   In
regard to distant objects, our judgment is chiefly founded upon their apparent
size,  if their actual size be known to us ; but, if this  is not the case, and if we
are so situated that we  cannot judge of the intervening space, we principally
form  our estimate from the greater or less distinctness  of their colour and out-
line.   Hence this estimate is liable to be greatly affected by varying states of
the atmosphere;  as is well known to every one who has visited warmer lati-
tudes.  The extreme clearness of the air sometimes brings, into an apparently
near  proximity, a hill  that rises beyond some neighbouring ridge  (the inter-
vening  space  being hidden, so as not to afford any  datum for the estimate of
the distance of the remote hill); and which, by a  slight haziness,  is carried to
three or four times the degree of  apparent remoteness.   It is probable that, in
the lower Animals, the perception of distance is much more intuitive than it is
in ourselves.
   549. Our estimate of the real size of an object  is manifestly connected with
that of its distance.   The apparent size is dependent upon the angle at which
its rays diverge, to impinge upon the cornea; this  angle  increases with the
proximity, and diminishes with the  remoteness, of the object.  Our estimate
of the comparative size of near  objects, of whose distances we  can  become
aware by the inclination of the optic axes, is much more  correct than  that
which we form, when one or both  are far removed; since, when we are un-
certain as to its distance, we cannot form a judgment  of the real size of a body,
from  the angle at which its rays diverge.  Hence  our  estimate of the size of
objects even moderately distant, is much influenced by states ofthe  atmosphere.
Thus, if we walk across a common in a fog, a child approaching us  appears
to have the size of a man, and a man seems like a giant; since the  indistinct-
ness of the outline excites in the mind the  idea of distance;  and  an object
seen under a given visual angle at a distance, must of necessity be  much larger
than one, of which the apparent size is the same, but which is much nearer.
The want of innate power in Man to form a true  conception of either size or
distance, is well  shown by the effect produced on  the mind unprepared for
such delusions, by a skilfully-painted picture;  the view of which is  so con-
trived, that its distance from the eye cannot be estimated in the ordinary man-
ner ;  the objects  it represents are invested by the mind with their  real sizes
and respective distances, as if their  real image was  formed upon the retina.*

  * This delusion has been extremely complete, in some of those who have  seen  the pano-
ramic view of London in the Coliseum.  A lively and interesting account of it is given in
the Journal of the Parsee Shipbuilders, who visited England some time ago. 
420           ON SENSATION, AND THE ORGANS OF THE SENSES.

  550.  From all these considerations, we are led to perceive  the truth of the
quaint observation made by Dr. Brown,—that "vision is, in fact, the  art of
seeing things which are invisible;" that is, of acquiring information, by means
of the eye, which is neither contained in the sensations of sight themselves,
nor logically deducible  from the intimations  which those sensations  really
convey.   We cannot too constantly bear in  mind, in treating of this subject,
that we do not take cognizance by our  optic nerves, as we do by the nerves
of touch, of material bodies themselves, but  of the pictures or images formed
by those objects; and whatever be the notions suggested by the picture, that
can never  be transformed into anything else.   These notions  appear to be, in
the lower  Animals, entirely of an intuitional or instinctive character; in Man
they are so in a much less degree; and although  it is impossible  to come to a
precise conclusion on the subject, from the want of sufficient data, it is indu-
bitable that a large part of the knowledge of the external world, which he de-
rives in the adult condition from the use of his eyes alone, is really dependent
upon  the early education of his  perceptive powers, in which process, the sen-
sations conveyed  by different organs are brought  to bear upon one another.
  551.  The persistence, during a certain interval, of impressions made upon
the retina, gives rise to a number of curious visual phenomena.  The pro-
longation of the impression will be governed, in part, by its previous duration.
Thus, when we rapidly move an ignited point through a circle, the impression
itself is  momentary, and remains but for a short time; whilst, if we have been
for some time looking at a window, and then  close our eyes, the impression of
the dark bars traversing the illuminated space is preserved for  several seconds.
Such  phenomena can here be only briefly adverted to.   One of these is the
combination, into one  image, of two or more objects  presented to the eye in
successive movements; but these must be of a kind which can be united, other-
wise a confused picture is produced. Thus  in a little toy, called the Thauma-
trope, which was introduced some years ago, the  two objects were painted on
the opposite sides of a card,—a bird, for instance, on one, and  a cage on the
other; and, when the card was made (by twisting a pair of strings) to revolve
about one of its diameters, in such a manner as  to be alternately presenting
the two sides to the eye at minute  intervals, the two  pictures were blended,
the bird being  seen in the cage.  A far  more  curious illusion, however, was
that first brought into notice by Mr. Faraday; who showed that, if two toothed
wheels, placed one behind the other, be made to revolve  with equal velocity,
a stationary spectrum will be seen; whilst if one  be  made to revolve more
rapidly  than the other, or the number of  teeth be different, the spectrum also
will revolve.   The same takes  place when a single wheel is made to revolve
before a mirror;  the wheel and its image answering the purpose of the two
wheels  in  the former case.   On  this principle,  a number of very ingenious
toys have been constructed; in some of these, the same figure or object is
seen in  a variety of positions; and  the impressions of these,  passing rapidly
before the eye, give rise by their combination to the idea, that the object is
itself  moving through  these positions.   Similar illusions may be produced in
regard to colour.
  552.  When  the Retina  has  been exposed for some time  to a strong im-
pression of some particular kind,  it seems less susceptible of feebler impres-
sions of the same kind.  Thus, if we look  at any brightly luminous object,
and then turn our eyes on a sheet of white paper, we shall  perceive a dark
spot upon it; the portion of the retina, which had been affected by the bright
image, not being able to receive an impression from the fainter rays reflected
by the paper.  The dark spectrum does  not at once disappear, but assumes
different colours in succession,—these being expressions of the states through
which the retina passes, in its transition to the natural condition.  If the eye 
SENSE OF VISION.
421
has received a strong impression from a coloured object, the spectrum exhibits
the complementary colour;* thus, if the eye be fixed for any length of time
upon a bright red spot on a white  ground,  and be  then suddenly turned so as
to rest upon the white surface, we see a spectrum of a green colour.—The
same explanation  applies to the  curious phenomenon of coloured shadows.
It may not unfrequently be observed at sunset, that, when the light of the sun
acquires  a bright orange colour from the clouds through which it passes, the
shadows cast by it have a blue tint.   Again, in a room with red curtains, the
light which passes through these produces green shadows.   In both instances,
a strong  impression of one colour is made on the general surface of the retina;
and at any particular spots, therefore, at which the light is colourless but very
faint, that colour is not perceived, its  complement only being visible.   The
correctness of this explanation is proved by the fact, that, if the shadow be
viewed through a tube, in such a manner that the coloured ground is excluded,
it seems  like an ordinary shadow.  It is not unlikely  that, as Muller suggests,
the predominant action of one colour  on the  retina  disturbs (as it were) the
equilibrium of its  condition, and excites in it a tendency to the development
of a state, corresponding to that which  is produced by the  impression of the
complementary  colour; for  the  latter  is,  according  to  him, perceived  even
where it does not exist;—as when the eye, after receiving a strong impression
from  a coloured spot, and directed upon a completely dark  surface  or into a
dark cavity, still perceives the spectrum.—Upon  these properties of the eye
are founded the laws of harmonious colouring, which  have an obvious analogy
with those of musical harmony.  All complementary colours have an agreeable
effect, when judiciously disposed in combination;  and all bright colours, which
are not complementary, have a disagreeable effect, if they are predominant:  this  :
is especially the case in regard to the simple colours, strong combinations of
any two  of which, without any colour that is complementary to either of them,
are extremely offensive.  Painters who are ignorant  of these laws, introduce
a large quantity of dull grey into their pictures, in order to diminish the glaring
effects, which they would  otherwise produce; but this benefit is obtained by
a sacrifice of the vividness  and force, which may be  secured in combination
with  the richest harmony, by a proper attention to physiological principles.
   553. Some persons, who  can  perfectly distinguish  forms,  are deficient,
through  some original peculiarity in  the  constitution of the retina, in  the
power of discriminating colours. This is most commonly seen in regard to the
complementary  colours, especially red and  green; such persons  not  being
able to perceive cherries amidst the leaves on a tree, except by the  difference
of their form.   Several distinct varieties of this affection may be distinguished,
however.  These  have been classified by Seebeck and Wartmann.t
   554. Amongst other curious phenomena  of Vision,  is  the  vanishing of
images which fall at the entrance of the optic nerve ;  as is  shown in the fol-
lowing experiment.   Let two black spots  be made upon  a  piece of paper,
about four or five inches apart;  then let the left eye  be closed,  and the right
eye be strongly fixed upon the left-hand spot.  If the paper be  then moved
backwards and forwards, so as to change its distance from the eye, a point will
be found, at which the right-hand spot is no longer visible; though it is clearly
seen, when the paper is brought nearer or removed further.  In this  position
of the eye and object, the rays from the right-hand  spot  cross  to the  nasal

   * By the complementary colour is meant that, which would be required to make white or
colourless  light, when mixed with  the original. As red, blue, and yellow are the primary
or elementary colours, red is the complement of green (which is composed of yellow and
blue) ; blue is the complement of orange (red and yellow); and yellow of purple (red and blue);
and vice versa in all instances.
  f Miiller's Physiology, p. 1213; Taylor's Scientific Memoirs, Vol. iv. p. 156, et seq.
     36 
422           ON SENSATION, AND THE ORGANS OF THE SENSES.

side of the globe, and fall upon the point of the retina, which has just been
mentioned.  The phenomenon is not confined to that spot, however;  nor is
it correct to say, as is sometimes done, that the retina is not sensible to light
at that point;  since,  if such were the case, we  should see a dark spot in  our
field of view,  whenever we use  only one eye.   The  fact is, that a similar
phenomenon may occur under somewhat different conditions, in  any division
of the retina, especially in its lateral parts.   Thus, if we fix the eye for some
time,  until it is fatigued, upon  a strip of coloured paper lying upon  a  white
surface, the image of the coloured object will in a short time disappear,  and
the white  surface will be seen in its  place ;  the disappearance of the image,
however, is only of a few  seconds duration.  The  truth  seems to be,  that
there  is a  tendency in the retina, to the propagation over neighbouring parts,
of impressions which occupy a large proportion of its surface;  and that  this
tendency is the strongest, around  the point at which the optic nerve enters,
so that the state of this part will generally become similar  to  that of the  sur-
rounding portion of the retina.  Hence, when we are using one eye only,
we do not perceive any dark spot in the field, but only a certain degree of in-
distinctness in a portion of the image.
  555.  Under particular circumstances, we may receive a visual representa-
tion of the retina itself;  as is  shown by the experiments of Purkinje.  "If,
in a room otherwise  dark, a lighted candle be moved to and fro, or in a circle,
at a distance of six inches before the eyes, we perceive, after a short time, a
dark arborescent figure ramifying over the whole field of vision; this appear-
ance is produced by  the vasa centralia  distributed  over the retina, or by the
parts  of the retina covered by those vessels.   There are,  properly speaking,
two arborescent figures, the trunks of  which are not coincident, but  on  the
contrary arise in  the right and  left  divisions  of the field, and  immediately
take opposite directions.   One trunk belongs to each eye, but their branches
intersect each other in the common field of vision.  The explanation of  this
phenomenon is as follows :—By the movement  of the candle to and fro, the
light is made to act on the whole extent of the retina, and all the parts of the
membrane which are not immediately covered by the vasa  centralia are feebly
illuminated ; those parts, on the contrary, which are covered with  those vessels
cannot be acted on by the light,  and are perceived, therefore, as  dark arbore-
scent figures.  These figures appear to lie before the eye, and to be suspended
in the field of vision."*   We have  thus  another demonstration  of the  fact
that, in ordinary vision, the immediate  object  of our sensation  is  a  certain
condition  of the  retina,  which  is  excited by the formation of a  luminous
image.

                          6.  Sense of Hearing.

  556.  In the Ear, as in the Eye, the impressions  made  upon the sensory
nerve are  not  at once produced by the  body which originates the  sensation;
but they are propagated to  it, through a medium capable of transmitting them.
Here too, therefore,  we take cognizance by the mind, not of the  sonorous ob-
ject, but of the condition of the  auditory nerve; and all the ideas we form of
sounds, as to  their nature, intensity, direction, &c, must  be  based upon the
changes which they produce  in  it.   The  complex  contrivances, which we
meet with in the  organ of Hearing  among  higher animals, are  evidently in-
tended to give them  greater power of discriminating sounds, than is possessed
by the lower tribes ;  in which last it is reduced to a form so simple, that it may
be questioned whether they can be said to possess  an organ of  hearing, if
by this term we imply anything more  than the mere consciousness of sono-
* Midler's Physiology, p. 1163. 
SENSE OF HEARING.
423
rous vibrations.  There  is a  considerable  difference, however, between  the
Eye and the Ear, in regard to  the special purposes for which they are respect-
ively adapted.  In the former we have seen, that the whole object of  the in-
strument is to direct the rays of light received by it,  in such a manner, as to
occasion them to fall upon the expansion of the optic nerve in a similar rela-
tive position, and  with corresponding proportional  intensity, to  that which
they possessed when issuing from the object.   We have no reason to believe
anything  of this kind to be the purpose of the  Ear; indeed,  it would be in-
consistent  with the laws of the propagation of sound.   Sonorous vibrations
having the most various directions, and the most equal rate of succession, are
transmitted by all media without  modification, however numerous their lines
of intersection ;  and wherever these  undulations fall upon the  auditory nerve,
they must  cause the sensation  of corresponding sounds.   Still it  is probable
that some  portions of the complex organ of hearing, in Man and in the higher
animals, are more adapted than others to  receive impressions  of a particular
character ; and that thus we may be especially informed of the direction of a
sound by one part of  the organ, of its musical tone by another, and of some
other of its qualities by a third. In  our inquiries into this  ill-understood sub-
ject, we shall commence with a brief survey of the  comparative structure of
the organ.
   557.  The essential part of an Organ of Hearing being  obviously a nerve,
endowed with the peculiar property of receiving  and transmitting sonorous
undulations, it is by no means  indispensable that a special provision  should
be made for this purpose; since the  Auditory nerve,  if merely in contact with
the solid parts of the head, will be  affected by  the vibrations, in which it is
continually participating.  Hence we must not imagine the  sense to be absent,
wherever we cannot discover  a special organ.   It is among the highest only
of  the Invertebrate animals, that any such  special organ presents itself; and
then only  in a very simple form.  Thus in the Crustacea  and Cephalopoda,

                                  [Fig. 180.
  General view of the external, middle, and internal ear, as seen in a prepared section through a, the
auditory canal, b. The tympanum or middle ear. c. Eustachian tube, leading to the pharynx, d. Coch-
lea : and e. Semicircular canals and vestibule, see'n on their exterior, as brought into view by dissecting
away the surrounding petrous bone.  The styloid process projects below; and the inner surface of the
carotid canal is seen above the Eustachian tube. From Scarpa.] 
424           ON SENSATION, AND THE ORGANS OF THE SENSES.
the ear consists of a small  cavity excavated in the  solid frame-work  of the
head;  this  cavity is  lined with  a  membrane,  on Avhich  the  nerve is distri-
buted ; and it is filled with  a watery fluid.   In some instances, the cavity is
completely shut in by its solid walls ;  and  the sonorous  vibrations can then
only be communicated through these:  but in the  higher forms of this  appa-
ratus,  there is a  small aperture  covered with  a membrane, upon which the
external medium can at  once act.   In  tracing this  most simple into the more
complex forms, it is at once seen, that the cavity corresponds with the vesti-
bule of the ear of higher animals,  and its  opening with the fenestra ovalis.
In the lowest Cyclostome Fishes, the  organ is but  little more complicated ;
from the vestibule proceeds a single annular  passage, which may be consi-
dered as a semicircular canal; and  the auditory nerve is distributed minutely
upon its lining membrane, as upon that of the vestibule itself.   In  species
a little higher in the scale, two  such  canals exist;  these are present in the
Lamprey.   And in all  the rest of the  class, three  semicircular canals are
found; holding the same direction in regard to  each other, as they do in Man.
Within the vestibular sac of Fishes are found calcareous concretions, which
are pulverulent in the Cartilaginous, but hard and stony in the Osseous tribes;
to these  the name of Otolithes has been given.   Some rudiments of a tympa-
nic cavity may be found in Fishes ; but there  is no  vestige of a  cochlea:  in
several tribes, the organ  of hearing  possesses  a peculiar connection with the
air-bladder, which  appears to be a  foreshadowing of the Eustachian tube of
higher classes.
   558. In the true Reptiles, a considerable advance  is constantly to be found
in the character ofthe Ear;  a tympanic cavity being added, with a drum and
a chain of bones ; and a  rudiment of the cochlea being generally discoverable.
Among  the Amphibia, however, which are  in  so  many respects intermediate

                                  [Fig. 181.
  Diagram of the inner wall of the tympanun after maceration, the outer wall and ossicles being re-
moved,  a. Fenestra ovalis. 6. Fenestra rotunda,  c.  Promontory, d. Pryramid, with the orifice at its
apex. e. Projection of the aqueductus Fallopii.  /. Some of the mastoid cells communicating with the
tympanum,  g. Processus cochleariformis, bounding i, the canal for the tensor tympani muscle: the an-
terior pyramid is broken off, if it existed, h. Commencement of the Eustachian tube.  /. Jugular -fossa,
immediately below the tympanum,  k, k. Carotid canal, with the artery in outline, to.show its course in
relation to the tympanum and Eustachian tube. I. Portio dura ofthe seventh pair of nerves, as it would
be seen in the terminal part of the aqueduct of Fallopius.  m. Chorda tympani, leaving the portio dura,
and entering a short canal, which opens in the tympanum, at the base of the pyramid, n. Grooves for
the tympanic plexus.] 
                              SENSE  OF HEARING.                          425

between the true Reptiles and Fishes, there  is a  remarkable variation in this
respect,—some  having a tympanum, and some being  completely destitute  of
it.  Wherever a tympanic cavity distinctly exists, there is an Eustachian tube
connecting it with the  fauces.   This  cavity, in  the  true  Reptiles, not only
possesses  the fenestra ovalis (or opening into the vestibule), but the fenestra
rotunda (or opening into the cochlea).   The  membrana tympani is usually

                                   [Fig. 182.
  A view of the axis of the Cochlea and the Lamina Spiralis, showing the arrangement of the three
Zones; the osseous zone and the membrane of the vestibule have been removed; 1, the natural size ofthe
parts; the other figure is greatly magnified ; 2, trunk ofthe auditory nerve; 3, the distribution of its fila-
ments in the zona ossea; 4, the nervous anastomosis ofthe zona vesicularis; 5, the zona membranacea;
6, the osseous tissue of the modiolus; 7, the opening between the two scalae.]

visible  externally ;  but it is  sometimes  covered by the skin.—In Birds, the
structure of the ear is essentially  the same  as  in  the higher  Reptiles.   A dis-
tinct  cochlea  exists, though its form is  not spiral but nearly straight: of its
character, however, there can be no doubt; a  division  into  two passages, by
a membranous partition on  which the  nerve is spread out, being evident.
Moreover the tympanum communicates with cavities  in the cranial  bones,
which are thus filled with air; and these, by increasing  the  extent of surface,
produce a more powerful resonance.  There  is  no external ear, except  in  a
few species of nocturnal Birds.—In Mammalia, the organ of hearing is usually
  Cochlea of a new-born infant, opened on the side towards the apex of the petrous bone. It shows the
general arrangement ofthe two scala?, the lamina spiralis, and the distribution ofthe cochlear nerve. At
the apex is seen the modiolus expanding into the cupola, where the spiral canal terminates in a cul-de-
sac. The helicotrema is not visible in this view.  From Arnold.]
                                     36* 
426            ON SENSATION, AND THE ORGANS OF THE SENSES.
formed upon the same plan, as it presents in Man ; in the Monotremata, how-
ever, it more  approaches  that of Birds.  The cochlea of  the Mammalia  in
general is a spiral, forming  about  two turns and  a half;  the  partition which

                                     [Fig. 184.
  The Cochlea divided parallel with its axis, through the centre of the Modiolus; after Breschet; 1, the
modiolus; 2, the infundibulum in which the modiolus terminates ; 3, 3, the cochlear nerve, sending its fila-
ments through the centre of the modiolus; 4, 4, the scala tympani ofthe first turn ofthe cochlea; 5, 5, the
scala vestibula of the first turn; 6, section of the lamina spiralis, its zonula ossea; one of the filaments of
the cochlear nerve is seen passing between the two layers of the lamina spiralis to be distributed upon the
membrane which invests the lamina; 7, the membranous portion of the lamina spiralis; 8, loops formed by
the filaments of the  cochlear nerve; 9,9, scala tympani of the second turn of the cochlea; 10,10, scala
vestibula of the second turn; the septum between the two is the lamina spiralis; 11, the scala tympani of
the remaining half turn ; 12, the remaininghalf turn of the scala vestibula; the dome placed over this half
turn is the cupola: 13, the lamina of bone which forms the  floor of the scala vestibula curving spirally
round to constitute the infundibulum (2); 14, the helicotrema through which a bristle is passed; its lower
extremity issues from the scala tympani of the middle turn of the cochlea.]

divides  its canal is partly osseous, partly membranous;  and its two passages
communicate with the tympanic cavity and the vestibule respectively.   The
cavity  of the tympanum is very large in some species, extending even into the
contiguous bones.   All the Mammalia, except  the aquatic tribes, have an ex-
ternal ear; and this is sometimes of an enormous  size  in  proportion to  the
dimensions of  the body,  as  it  is in  the Bats.   The labyrinth of the higher
Vertebrata contains no otolithes.
   559. The  ultimate  terminations  of the fibres  of the  Auditory  nerve, are

             Fig. 185.                                [Fig. 186.
the cochlea of a young Mouse ; the    The Auditory Nerve taken out of the Cochlea. 1; ,, h
lower portion is the osseous, and the   the trunk of the nerve; ^ 2 hs filaments in the zona ossea
higher the membranous part of the   of lhe lamina spiralis : 3, 3, its  anastomoses in the zona
lamina.  Magnified 300 times.   .     vesicularis.] 
SENSE OF HEARING.                          427
best seen in the lamina spiralis of the cochlea, and its membranous prolon-
gation.  Much diversity exists, however, as to the  interpretation of the  ap-
[Fig. 187.
[Fig. 188.
  A highly magnified view of a small piece ofthe Lamina Spiralis,
showing the globular structure of the Nerves, and the manner in
which they leave their Neurilemma as they anastomose; the natural
size of the piece is seen on the side of the figure; 1, portion of the
auditory nerve, 2, 2, osseous canals in the zona ossea of the lamina
spiralis; 3, 3, anastomoses in the zona mollis; 4, 4, the neurilemma
leaving the nervous loops and interlocking to form the layer ofthe
zona membranacea.]
                                                      Plexiform  arrangement of the
                                                     cochlear nerves seen in the basal
                                                     coil of the lamina spiralis, treated
                                                     with hydrochloric acid.  There
                                                     are no ganglion  globules in this
                                                     plexus, which consists of tubular
                                                     fibres, a. Twig of cochlear nerve
                                                     in the modiolus, its fibres diverging
                                                     and reuniting in 6, a band in the
                                                     plexus taking a direction parallel
                                                     to the zones.   From this other
                                                     twigs radiate, and again and again
                                                     branch and unite as far as the mar-
                                                     gin of the osseous zone c, where
                                                     they terminate. From the sheep.
                                                     Magnified 30 diameters.]

pearances there seen; some  observers affirming that there  are no free or
papillary terminations, and that the nervous fibres all return by loops; whilst
others state that the papillae are clearly to be distinguished.  The fact appears
to be that, as in the retina, the fibres  do form a minute plexus; but that fibres
are connected with this, which  end,  or rather commence  in  papilla?.   The
Auditory nerve is  also very minutely distributed on the membrane lining  the
vestibule and semicircular canals; and  in the  ampullae  or  dilated extremities
of the latter,  there are little projections of this membrane internally, which
are largely supplied with nerves.
   560. In order to gain any definite idea of the uses of different parts of the
Ear, it is necessary to bear in mind,  that sounds may be propagated amongst
solid or fluid bodies in three ways,—by reciprocation, by resonance, and by
conduction.—1. Vibrations of reciprocation are excited  in a sounding body,
when  it is capable of yielding a musical  tone of definite  pitch,  and another
body of the same  pitch is made to sound near it.  Thus  if two strings of the
same length and tension be  placed along side of each other, and one of  them
be sounded with a violin-bow, the other will be thrown into reciprocal vibra-
tion ;  or  if the same tone be produced  near the string in  any other  manner,
as by  a flute, or a tuning-fork, the same effect will  result.—2.  Vibrations of
resonance are of somewhat the same  character; but  they occur when a sound- 
428            ON SENSATION, AND THE  ORGANS OF THE SENSES.

                                      [Fig. 189.
  The soft parts of the Vestibule taken out of their bony case, so as to show the distribution ofthe Nerves
in the Ampullse ; 1, the superior semicircular membranous canal or tube ; 2, the external semicircular
tube; 3, the inferior semicircular tube ; 4, the tube of union of the superior and inferior canals; 5, the
sacculus ellipticus ; 6, the sacculus sphericus ; 7, the portio dura nerve; 8, the anterior fasciculus of the
auditory nerve; 9, the nerve to the sacculus sphericus; 10,10, the nervous fasciculi to the superior and
external ampullse; 11, the nerve to the sacculus ellipticus ; 12, the posterior fasciculus of the auditory
nerve, furnishing 13, the filaments of the sacculus sphericus, and 14, the filaments of the cochlea, cut off.]

                                      [Fig. 190.
  The Ampulla of the External Semicircular Membranous Canal, showing the Mode of termination of its
Nerve.]

ing body is placed in connection with any other, of which one or more parts
may be thrown into  reciprocal vibration, even  though the tone  of the whole
be different, or it be  not capable of producing a definite tone at all.   This is
the case, for example, when a tuning-fork  in vibration is placed upon a sound-
board ;  for even though  the whole board have no  definite  fundamental note,*

  * The fundamental note of a body is the lowest tone which it will  yield, when the whole
of it is in vibration together.  By dividing the body into two or more distinct parts, it may 
SENSE OF HEARING.
429
it will divide itself into a number of parts, which will reciprocate the original
sound, so as greatly to increase its intensity; and the same  sound-board will
act equally well for tuning-forks of several different degrees of pitch.  When
a smaller body is used for resonance", however, it is essential that there  should
be a relation between its fundamental  note and  that of the  sonorous body;
otherwise no distinct resonance is produced.   Thus, if a tuning-fork in vibra-
tion be held over a column of air in a tube, of such a length that the same note
would be given by its vibration, its sound will be reciprocated.   And  if it be
held over a pipe, the column of air in which is a multiple of this, the column
will divide itself into that number of shorter parts, each of which will recipro-
cate the original  sound, and the total action will be one of resonance.  But if
the length of the pipe bear  no such correspondence with the note sounded by
the tuning-fork, no resonance  is given  by the  column  of air it contains.—3.
Vibrations of conduction are the only ones  by which  sounds can strictly be
said to be propagated.  These are  distinguishable  into various kinds, inta
which it is not requisite here  to inquire.   It should be remarked, however,
that all media,  fluid, liquid, or solid, are capable of transmitting sound  in this
manner,—a vacuum  being  the only  space  through which it  cannot pass.
The transmission is  usually much more rapid  through solid  bodies, than
through  liquid ;  and  through liquid,  than  through gaseous.  The greatest
diminution in the intensity  of sound is usually perceived, when a change takes
place in the medium  through which it is propagated, especially from the aeri-
form to the  liquid.
   561. The detailed  application of these principles has  been most elaborately
worked out by Muller; and the following statement of what may be regarded
as the present condition of our knowledge of the subject, is  little more than
an abstract of his results.   Considering it desirable, in the first place, to estab-
lish the  conditions under which those animals hear that are constantly im-
mersed in water, he made a series of experiments, from which he draws the
following conclusions :—i.  Sonorous vibrations, excited  in water, are imparted
with considerable intensity to solid bodies.—n. Sonorous vibrations of solid
bodies are communicated with greater intensity to other solid bodies brought
in contact with  them, than  to water ; but with  much greater  intensity to
water, than  to atmospheric  air.—in. Sonorous vibrations  are  communicated
from air to water with great difficulty,—with very  much greater difficulty
than they are propagated from one part of the air to another; but their  transi-
tion from air to water is much facilitated, by the intervention of  a membrane
extended between them.—iv.  Sonorous vibrations are not only imparted from
water to solid  bodies  with  definite surfaces,  which  are  in contact with the
water, but are also returned with increased intensity by these bodies  to the
water; so that the sound is heard loudly in the vicinity of those bodies, in
situations where, if it had its  origin in  the  conducting  power  of  the water
alone, it would be faint.—v. Sonorous undulations, propagated through  water,
are partially reflected  by the surfaces of solid bodies.—vi. Thin membranes
conduct sound in water  without any loss  of its  intensity, whether they be
tense or lax.—From m., iv., and vi., we learn the mode in which the sound

be made to give a great variety of sounds. Thus, if a stretched string be divided by a bridge
into two equal parts, each will sound the octavo of the fundamental note, or the 8th note
above it.  If it be divided into three parts, each will give the  12th above the fundamental
note; if into four, the 15th or double octave will be heard; if into five, the 17th; if  into six,
the 19th; if into seven, the 20£th (flat seventh above the second  octave); if into eight, the
22d or triple octave.  A  string forcibly set in vibration has a tendency to sound these har-
monics with the fundamental note, by spontaneous division into several distinct segments of
vibration; as may be easily made evident by striking one of the lower keys of the piano,
and listening to the sounds heard whilst the fundamental note is dying away. 
430           ON SENSATION, AND THE ORGANS OF THE SENSES.
 is conducted to the ear,  in aquatic animals  not breathing atmospheric air.
 The labyrinth of such is either entirely inclosed within the  bones of the head,
 as  in the Cephalopoda, and in the Cyclostome and Osseous Fishes; or,  its
 cavity being prolonged to the surface  of the body, it is there brought into
 communication with the conducting medium, by  means of  a membrane,—be-
 sides receiving the vibrations through  the medium of  the solids of the body,
 as is the case in Cartilaginous Fishes  and  Crustacea.   It would seem as if,
 in the Osseous Fishes, the resonance  of the cranial bones, in which the laby-
 rinth is imbedded, were sufficient to give the  requisite increase of intensity to
 the sound ;  whilst in the  Cartilaginous orders, the softness of these bones
 renders some other means necessary.   In addition to this, we find in many
 Fishes a communication with the air-bladder; which  indeed seems to have,
 in these, but little other use.  The mode in which this increases by resonance
 the intensity of  the sounds, will appear from the following experimental con-
 clusions.—vn.  When sonorous  vibrations are communicated from water to
 air inclosed in membranes or solid bodies, a considerable increase  in the in-
 tensity of the sound is  produced, by the resonance  of the air  thus circum-
 scribed.—vm. A body of air  inclosed in a membrane, and surrounded  by
 water, also increases  the intensity of the sound by resonance, when the sono-
 rous undulations are communicated to it by a solid body.   From these ob-
 servations, it may be  concluded, that the air-bladder of Fishes, in addition to
 other uses, serves the purpose of increasing by resonance the intensity of the
 sonorous undulations, communicated from the water to the  body of the Fish.
 Moreover, as the conducting and resonant power of the air in the air-bladder
 is greater in proportion to  its density, the influence of this organ on the per-
 ception of sounds will, of course, be  greater in deep waters, where the  pres-
 sure upon it is considerably increased.
   562. Most animals living in air, are provided with an opening into the ves-
 tibule, covered by a thin membrane;  and, in the majority  of cases, with the
 tympanic apparatus also.   The following experimental  results bear upon the
 manner in which the Ear of such animals is affected  by sound.—ix. Sono-
 rous undulations, in passing from air directly into water, suffer a considerable
 diminution in their  strength;  while, on the contrary,  if a tense membrane
 exists between the air and the water,  the sonorous undulations are communi-
 cated from the former to the  latter medium with great intensity.—x.  The so-
 norous vibrations are also communicated without any perceptible loss of in-
 tensity, from the air to the water; when, to  the membrane forming  the me-
 dium of  communication, there is attached  a short solid body, which  occupies
 the greater part of its surface, and is alone in contact with  the water.—xi. A
small solid body,  fixed in an opening by means of a border of membrane, so
 as to be movable, communicates sonorous vibrations, from air on one side, to
 water or the fluid of the labyrinth on the other, much better than solid media
 not so  constructed.   But  the propagation of sound to the fluid is rendered
 much more perfect, if the solid conductor, thus occupying the opening, is  by
 its  other end fixed to the  middle of the tense membrane, which has atmo-
 spheric air on both sides.—The fact stated in ix. is  evidently one of great im-
 portance in the physiology of hearing;  and  fully explains the nature of the
 process in those animals which receive  the sonorous vibrations  through air,
 but which have no tympanic apparatus.   In x. we have the elucidation of the
 action of the fenestra ovalis, and of the movable  plate of the stapes which
 occupies it, in animals living  in air, but  destitute of tympanic apparatus; this
 is naturally  the case in many Amphibia; and  it  may happen as the result of
 disease in the Human subject.  In xi. we have a very interesting demonstra-
 tion of the purpose and action of the tympanum,  in the more perfect  forms of
 the auditory apparatus.  We are now prepared to inquire, in somewhat more 
SENSE OF HEARING.
431
of detail, into the action of the different parts of this apparatus ; and it will be
better to commence with that of the Internal Ear, the accessory organs being
afterwards considered.
   563.  The object of the Membrana Tympani is evidently to receive the
sonorous undulations from the air, in such a manner as to be  thrown by them
into a recriprocal vibration, which is to be communicated to the chain of bones.
This membrane is, in its usual state, rather lax than tense; and this laxity is
found by experiment to  be, for a small membrane, the best condition  for the
propagation of ordinary sounds.   This  is  easily rendered sensible  in one's
own person ;  for an  increased  tension  may be given to the membrana tym-
pani, either by holding the breath and forcing air into the Eustachian tube, so
as to distend it from within, or by exhausting the  cavity, so as to cause the
external air to make increased pressure upon it.   In either case the hearing is
found immediately to become indistinct.   It is observed, however, that grave
and acute sounds are  not equally affected by this action ; for the experimenter
renders himself deaf to grave sounds, whilst acute sounds  are heard even more
distinctly than before.  This fact is easily understood by referring to the laws
of Acoustics already  mentioned.   The greater the tension to  which the mem-
brana tympani is subjected, the more acute will be its fundamental tone;  and
as no proper reciprocation can  take place in  it, to any sound lower than its
fundamental tone, its  power of repeating perfectly the vibrations proper to the
deeper  notes will diminish.   The  nearer a sound approaches to the funda-
mental note proper to the tense membrane, the more distinctly will it be heard.
On the other hand, when the membrane is in its natural lax condition, its fun-
damental note is very low, and it is capable of repeating a much greater vari-
ety of sounds ; for, when it receives undulations of a higher tone, than those
to which the whole membrane would reciprocate, it divides itself into distinct
segments of vibration, which are separated by  lines  of rest; and every  one of
these reciprocates the sound;* at the same  time rendering it  more intense by
multiplication.   These facts enable us to understand the influence of the ten-
sor tympani muscle, in modifying the tension of the membrane, and thus caus-
ing  it to vibrate in reciprocation  to sounds having a great variety of funda-
mental  notes.  Moreover, the fact that some persons are deaf to grave sounds,
whilst they readily hear the more acute, is thus accounted for.  The tensor
tympani, like the iris, is probably excited to operation by a reflex action; and
it is by no means improbable that one of its functions may be, to prevent the
internal ear from being too violently affected  by loud sounds, by putting the
membrana tympani into such a state of tension, as  not readily to reciprocate
them.
   564.  The uses of the Tympanic cavity are very obvious.   One of its  pur-
poses is, to render the vibrations of the membrane quite  free; and  the other,
to isolate the chain of bones, in such a manner as to prevent their vibrations
from being weakened, by diffusion through the surrounding solid parts.  As to
the objects of the Eustachian tube, however, opinions have been much divided.
From the experiments of Muller it appears, that it does not increase the intens-
ity of  sound, but that it  prevents  a certain degree  of dulness, which  would
attend it, if the cavity of the tympanum were completely closed ; of this dul-
ness we are conscious, when  any tumefaction of the fauces causes an occlusion
of the extremity of the tube.  It  has been supposed  that, among other uses,

   * This is very easily proved by experiments on a membrane  stretched over a resonant
cavity ; if light sand be strewed upon it, and a strong musical tone be produced in its vicinity,
the membrane will immediately be set in vibration, not as a whole (unless its fundamental note
be in unison with that sounded), but in distinct segments, of which every one reciprocates the
sound; from the vibrating parts, the sand will be violently thrown off; but it will settle on the in-
termediate lines of rest, forming a variety of curious figures, which are known as the nodallmes. 
*
432           ON SENSATION, AND THE ORGANS OF THE SENSES.

this canal serves for the conduction of the speaker's voice to his ears ; but this
is certainly not the case in any considerable degree ; for, when the Eustachian
tubes are obstructed by disease, the patient hears  his own voice well, though
other sounds are indistinct; and it  is easily shown, that its transmission is
chiefly accomplished in other ways.   The common idea is,, that  it serves the
same purpose with the hole in  an ordinary drum ; the effect of which is gene-
rally supposed to be, the removal of the impediment to the vibrations of the
membrane, that would be offered by the complete inclosure ofthe air within.
It does not appear, however, that any such impediment is really offered ; and
the effect of the  hole in the drum seems rather to be the  communication, to
the ear of the auditor, of the sonorous vibrations of the contained air; which
are thus transmitted directly through the atmosphere, instead of  being weak-
ened by transmission through the walls of the instrument.  Hence there is no
real  analogy in the two cases.  The principal object of the Eustachian tube
(which  is always found where  there is a tympanic cavity), seems to be, the
maint%nance of the equilibrium between the air within the  tympanum and the
external air; so as to prevent inordinate tension of the membrana tympani,
which would be  produced by too great  or too little pressure on either side,
and  the effect of which would  be imperfection  of hearing.   It also has the
office of conveying away mucus  secreted in the cavity of  the tympanum, by
means of cilia vibrating  on its  lining membrane; and the  deafness, conse-
quent on  occlusion of this  tube, is  in part explicable by the accumulation,
which will then  take place in the tympanum.
  565.  From  what has been stated, it is evident that sonorous undulations
taking place in the air, will be propagated to the fluid contained in the laby-
rinth,—through the tympanum, the chain of bones, and the membrane of the
fenestra ovalis to which the stapes is attached,—without any loss, but rather
an increase, of intensity.  Why water should be chosen as the medium through
which the impression is to be made upon  the nerve, it is impossible for us to
say with anything  like  certainty, in our present  state of ignorance as to the
physical character of that impression.   But, the problem being, to communi-
cate  to water the sonorous undulations of air, the experimental results already
detailed satisfactorily  prove that,—whilst this may be accomplished, in  a de-
gree sufficient for the  wants of the inferior animals, by the simple interposition
of a tense membrane  between  the air and the fluid,—the tympanic apparatus
of the higher classes is most admirably adapted for this purpose.   The fenes-
tra ovalis is not, however, the only channel  of communication between the
tympanum and the labyrinth ; for there is, in most animals, a second aperture,
the fenestra rotunda, leading into  the cochlea, and simply covered with a mem-
brane.  It is generally supposed that, the labyrinth being filled with  a nearly
incompressible fluid,  this second aperture is necessary to allow of the free
vibration of that fluid,—the  membrane of the fenestra rotunda being made to
bulge out, as that of  the fenestra ovalis  is pushed in.  It may,  however, be
easily shown by experiment, as well as by reference to comparative anatomy,
that  no such contrivance is  necessary;  for sonorous undulations may be ex-
cited  in a  non-elastic fluid, completely inclosed within solid walls at  every
part, except where  these  are replaced  by the membrane  through which the
vibrations are propagated; and this is precisely the condition, not only of the
Invertebrated animals, but even of Frogs ; in which last a tympanic apparatus
exists, without a second orifice into the labyrinth.   Moreover it is certain, that
the  vibrations of the air in the cavity of  the tympanum, must of themselves
act upon the membrane of the  fenestra rotunda ; and this is perhaps the most
direct manner in which the  fluid in the cochlea will be affected;  although it
will ultimately be thrown into much more powerful action, by the transmission
of vibrations from the vestibule.   For it has been  satisfactorily determined by 
SENSE OF HEARING.                            433

      [Fig. 191.
  The labyrinth of the Left Ear, laid open in order to show its cavities and the Membranous Labyrinth;
after Breschet;  1, the cavity ofthe vestibule, opened from its anterior aspect in order to show the three-
cornered form of its interior, and the membranous labyrinth which it contains; the figure rests upon the
common saccule of the membranous labyrinth—the sacculus communis; 2, the ampulla of the superior
or perpendicular semicircular canal, receiving a nervous fasciculus from the superior branch of the
vestibular nerve ; 3, 4, the superior or perpendicular canal with its contained membranous canal; 5, the
ampulla of the inferior or horizontal semicircular canal, receiving a nervous fasciculus from the superior
branch ofthe vestibular nerve; 6, the termination ofthe membranous canal ofthe horizontal semicircular
canal in the sacculus communis ; 7, the ampulla ofthe  middle or oblique semicircular canal,(receiving a
nervous fasciculus from  the inferior branch of the vestibular nerve ; 8, the oblique semicircular canal
with its membranous canal;  9, the common canal, resulting from the union of the perpendicular with
the oblique semicircular canal; 10, the membranous common canal terminating in the sacculus com-
munis ; 11, the otoconite ofthe sacculus communis seen through the membranous parietes of that sac ; a
nervous fasciculus from the inferior branch ofthe vestibular nerve is seen to be distributed to the saccu-
lus communis near to the  otoconite ; the extremity of the sacculus above the otoconite is lodged in the
superior ventricle of the vestibule, and that below it in the inferior ventricle; 12,  the sacculus proprius
situated in the anterior ventricle; its otoconite  is seen through its membranous parietes, and a nervous
fasciculus derived from the middle branch ofthe vestibular nerve, is distributed to it; the spaces around
the-membranous labyrinth are occupied by the aqua  labyrinthi; 13, the first turn of the cochlea; the
figure is situated in the scala tympani; 14, the extremity of the scala tympani corresponding with the
fenestra rotunda; 15, the  lamina spiralis; the figure  is  situated in the scala vestibuli; 16, the opening of
the scala vestibuli into the vestibule; 17, the second turn of the cochlea; the figure is placed upon the
lamina spiralis, and, therefore, in the scala vestibuli,  the scala tympani  being beneath the lamina; 18,
the remaining half turn of the  cochlea ; the figure is  placed in the scala tympani; 19, the lamina spiralis
terminating in a falciform extremity; the dark space included within the falciform curve ofthe extremity
of the lamina spiralis is the helicotrema; 20, the infundibulum.]

experiment (xii.), that vibrations  are  transmitted with very much greater in-
tensity to water, when a tense membrane,  and a chain of insulated solid bodies
capable of free movement, are successively the conducting media, than when
the  media of communication  between the vibrating air and  the water are the
same tense  membrane, air, and  a second membrane:—or, to apply this fact
to the organ  of hearing, the same vibrations  of the air act upon  the fluid of the
labyrinth with much greater  intensity,  through the medium of the chain of
auditory bones and  the fenestra  ovalis, than through the medium of the air of
the  tympanum and  the  membrane closing the fenestra rotunda.—The fenestra
rotunda is not to be  considered as having any peculiar relation with the cochlea;
since, in the  Turtle tribe,  the former exists  without the  latter.
   566.  In regard to the functions  of particular parts of the labyrinth, no cer-
tainty can be said  to exist.   From  the  experimental  results already stated, it
appears likely that, the greater the extension of the cavity into the dense  sub-
stance of the bone, the greater will be the resonance  communicated  to the
fluid,  and  thence  transmitted to the nerves exposed to  its influence.—It  is
     37 
434           ON SENSATION, AND THE ORGANS OF THE SENSES.

                                  [Fig. 192.
               A view ofthe labyrinth of the Left Side, laid open in its whole extent so as to show its Structure; these
             figures are all magnified ; 1, the thickness of the outer covering of the cochlea; 2, 2, the scala vestibuli
             or upper layer ofthe lamina spiralis ; 3, 3, the scala tympani or lower layer ofthe lamina spiralis; 4, the
             hamulus cochleae; 5, centre ofthe infundibulum ; 6, the foramen rotundum communicating with the tym-
             panum ; 7, the thickness of the outer layer of the vestibule ; 8, the foramen rotundum ;  9, the fenestra
             ovalis; 10, the orifice of the aqueduct of the vestibule ; 11, the inferior semicircular canal; 12. the superior
             semicircular canal; 13, the external semicircular canal; 14, the  ampulla of the inferior canal; 15, the
             ampulla of the superior canal; 16, the common orifice of the superior and inferior canals; 17, the ampulla
             of the external canal.]

             commonly supposed that the Semicircular Canals have for their peculiar func-
 |v4v£ »***■ £■( tion, the reception of the impressions by which we distinguish the direction of
Cvwa*vv*vv*r;:. sounds;  and it is certainly a powerful argument in support of this view, that,
JitoM/J. w» itu* in  almost every instance in which these parts  exist at  all, they hold the same
, «  -fcc*^*^ ~~relative position to each  other as in Man, their three planes being nearly at
             right angles to one another.  The idea, however, must be regarded as a mere
              speculation, the value of which cannot be decided without an  increased know-
             ledge of the  laws, according to which sonorous vibrations are transmitted.—
              Regarding the special function of the Cochlea, there is precisely the same un-
              certainty.  This part of the organ is peculiar in one respect,—that the expan-
              sion of the auditory nerve is here  spread out (upon  the lamina  spiralis) in
              closer proximity with the bone itself, than it is in any other part of the  laby-
              rinth ; so that the vibrations of the bone will  be  more directly communicated
              to  the nerve.   It is not easy  to see, however,  what can be the peculiar object
              of this disposition, in regard to the function of hearing.   By M. Duges it  is
              surmised, that by the cochlea we are especially enabled to  estimate the pitch
              of sounds, particularly of the voice; and he adduces,  in support of this idea,
              the fact, that the development of the cochlea follows a  very similar proportion
              with the compass of the voice.   This is much the greatest  in the Mammalia;
              less in Birds; and in  Reptiles, which have little true vocal power,  the cochlea
              is  reduced to  its lowest form, disappearing entirely in the Amphibia.   That
              there should be an acoustic relation between the voice and ear of each species
              of animal, cannot be regarded as improbable ;  but  the speculation of M. Duges
              can at present only be received as  a stimulus  to further inquiry.
                 567. We  have now to  consider the functions of  the  accessory parts,—the
              External Ear, and the Meatus.   The Cartilage of the external  ear may pro- 
SENSE OF HEARING.
435
pagate sonorous vibrations in two ways,—by reflection, and by conduction.
In reflection, the concha is the most important part, since it directs the reflected
undulations towards the tragus, whence they are thrown  into  the  auditory
passage.  The other inequalities of the external  ear  cannot promote hearing
by reflection ;  and the purpose of the extension of its cartilage is evidently to
receive the sonorous vibrations from the air, and to conduct them to its point
of attachment.  In this point of view, the inequalities become of importance ;
for those elevations and depressions upon which the undulations fall perpen-
dicularly, will be affected by them in the most intense degree ;  and in conse-

            [Fig. 193.                                    [Fig. 194.
  A view of the Left Ear in its natural state; 1, 2,    An anterior view of the External Ear, as well
the origin and termination of the helix ; 3, the anti-   as of the Meatus Auditorius, Labyrinth, &c.; 1,
helix; 4, the anti-tragus; 5, the tragus; 6, the lobus   the opening into the ear at the bottom of the con-
of the external ear; 7, points to the scapha and is on   cha; 2, the meatus auditorius externus or car-
the front and top of the pinna; 8, the concha; 9, the   tilaginous  canal; 3, the membrana  tympani
meatus auditorius externus.]                    stretching upon its ring; 4, the malleus; 5, the
                                        stapes ; 6. the labyrinth.]
quence of the varied form and position of these inequalities, sonorous undula-
tions, in whatever direction they may come, must fall advantageously upon
some of them.—The functions of the Meatus appear to be threefold.   The
sonorous undulations entering from  the  atmosphere are propagated directly,
without  dispersion, to  the membrana tympani:—the sonorous  undulations
received on the external ear, are conveyed along  the  walls of the meatus  to
the membrana tympani:—the air which it contains, like all insulated masses
of air, increases  the intensity  of  sounds by resonance.  That, in  ordinary
hearing, the  direct transmission of atmospheric vibrations  to  the  membrana
tympani, is the principal means of exciting  the reciprocal vibrations of the
latter, is sufficiently evident; the undulations which directly enter the passage,
will pass straight on to the membrane; whilst those that enter obliquely will
be reflected from side to side, and at last will fall obliquely  on  the membrane,
thus perhaps contributing to the notion of  direction.   The power of the lining
of the meatus to conduct sound from the external  ear, is made evident by the
fact, that, when both ears are closely stopped, the  sound of a pipe having its
lower extremity  covered by a membrane,  is heard more distinctly, when it is
applied to the cartilage of the external ear  itself, than when it is placed in con-
tact with the surface of the head.  The resonant action of  the air in the tube
is  easily demonstrated, by  lengthening  the  passage  by the  introduction  of 
436           ON SENSATION, AND THE ORGANS OF THE SENSES.

another tube; the intensity of external sounds, and also that of the individual's
own voice, as heard by himself, is then much increased.
   568. Many facts  prove, however, that the  fluid of the labyrinth may be
thrown into vibration in other ways, than by the tympanic apparatus.  Thus
in Osseous Fishes, it is only by the vibrations transmitted through the bones
of the head, that hearing can  take place.   There  are many persons, again,
who can distinctly hear sounds which  are thus transmitted to them ;  although,
through some imperfection of the tympanic apparatus, they  are almost insen-
sible to those which they receive in the ordinary way.   It is evident, where
this is the case, that the nerve  must be in a state fully capable of functional
activity;  and, on the  other hand, where sounds cannot  thus  be perceived,
there will be good reason to believe that the nerve is diseased.
   569. A single impulse communicated  to the Auditory nerve, in any of the
foregoing modes, seems to be sufficient to excite the momentary sensation of
sound;  but most frequently a series of such  impulses  is  concerned, there
being  but few sounds which do not  partake, in a  greater or less degree, of
the character of a tone.    Any  continuous sound or tone is dependent upon  a
succession of  such impulses;  and its  acuteness or depth is governed by the
rapidity with which they succeed one another.

  a. It is not difficult to ascertain by experiment, what number of such impulses or undula-
tions are required, to give every tone which the ear can appreciate.  Thus, if a circular plate,
with a number of apertures at regular intervals, be made to revolve over the top of a pipe
through which air is propelled, a succession of short puffs will be allowed to issue from this;
and, if the revolution is sufficiently rapid, these impulses will unite into a definite tone.  In
the same manner, if a spring be fixed near the edge of a revolving toothed wheel, in such
a manner as to be caught by  every tooth as  it passes, a succession of clicks will be heard;
and these too, if the revolution of the wheel be sufficiently rapid, will produce a tone.  The
number of apertures in the plate, which  pass the orifice of the pipe  in a given time, or the
number of teeth which pass the spring, being known, it is easy to see, that this must be the
number of impulses required to produce  the  given tone.  Each impulse produces a double
vibration,—forwards and backwards (as is seen when a string is put in vibration, by pulling
it out of the straight line) ; hence the number of impulses is always half that_of the single
vibrations.  The maximum and minimum of the intervals of successive pulses, still appre-
ciable by the ear as determinate sounds, have also been determined by M. Savart, more satis-
factorily and more accurately than  had  previously been done.  If  their  intensity is great,
sounds are still audible which result from the  succession of 24,000 impulses in a second;
and this, probably, is not the extreme limit to the acuteness of sounds perceptible by the ear.
From some observations of Dr. Wollaston's, it seems probable that the ears of different indi-
viduals are differently constituted in this respect,—some  not  being able to hear very acute
tones produced by Insects, or even Birds, which are distinctly audible to others.   Again, the
sound resulting from 16 impulses per second, is not, as has been usually supposed, the lowest
appreciable note; on the contrary, M. Savart has succeeded in rendering tones distinguisha-
ble, which are produced by  only 7  or 8 impulses in a second; and  continuous sounds of a
still deeper tone could be heard, if the  individual pulses were sufficiently prolonged.  In
regard, however, to the precise time during which a sonorous impression remains upon the
ear, it is difficult to procure exact information, since it departs more gradually than do visual
impressions from the eye.  This is certain, however,—that it is much longer than the interval
between the successive pulses in the production of tones; since it was  found by M. Savart,
that one or even several teeth might be removed from the toothed wheel, without a percep-
tible break in its sound,—showing that, when the tone was once established, the impression
of it remained during an intermission of some length.

   570. The  Ear  may,  like the  Eye, vary  considerably, as regards general
acuteness amongst different individuals; and its power may be much increased
by practice.   A part of this increase depends, however, as in other  instances,
upon  the greater attention which its  fainter indications  receive; but a part,
also, upon an increased  use of the organ.   The power of  hearing  very faint
sounds, is  as  different from the power of distinguishing musical tones, as the
power of discerning very minute objects, or of seeing with very faint degrees
of light, is from that of  distinguishing colours.   Many persons are  altogether 
SENSE OF HEARING.
437
destitute of what is termed a musical ear;  whilst others are endowed "with it
in a degree, which is a source of great discomfort to them, since every discord-
ant sound is  a  positive torment.  The power of distinguishing the direction
of sounds appears to be, in Man, at least, for the most part acquired by habit.
It is some time before the infant seems to know anything of the direction of
noises, which attract his attention.  Now although there can be no question,
that this perception is acquired by attention  to certain variations in the impres-
sion made upon the nerve, through the  medium either of the tympanic appa-
ratus,  or of the bones of the head, yet it is equally evident, that there can be
nothing in these variations themselves adequate to excite the idea, and that it
must therefore be either intuitive or acquired by habit.   This  is a considera-
tion of some  importance, in regard to the similar question as  to the sense of
Visual direction.  In some cases we are probably assisted by  thettelative in-
tensity of the sensations, communicated by the  two ears respectively.  The
idea of the distance of the sonorous body is another acquired  perception, de-
pending  principally upon  the  loudness or faintness of the  sound, when we
have no other indications  to guide us.  In this respect, there is a great simi-
larity between the  perception of the distance of an object, through the Eye,
by its  size,  and through the Ear, by the intensity of its sound.   When we
know the size of the object, or are  acquainted with the  usual  intensity of its
sound, we can judge of its distance ;  and vice versa, when we know its dis-
tance,  we can at once form  an  idea of its real  from its  apparent size, and of
its  real strength of tone from  that which  affects our ears.  In this manner,
the mind may be affected with corresponding deceptions through both senses;
thus, in the  Phantasmagoria, the figure is gradually diminished whilst its dis-
tance remains the same, and it appears to the spectators to recede,—the  illu-
sion being more complete, if its brightness  be  at the same time diminished;
and the  effect of a distant full military band gradually approaching, may be
alike given by a corresponding crescendo of concealed instruments. It is upon
the complete imitation of the conditions which govern our ideas ofthe intensity
and direction, as well as of the character, of sounds,  that the deception^ of the
Ventriloquist  are founded.
   571. Some facts of much interest have lately been ascertained, in regard to
an occasional  variation in the rapidity of the perception of sensory impres-
sions, received through the Eye and through the Ear.   These facts are the
result  of comparisons  made amongst  different astronomical  observers, who
may be watching the same visual phenomena, and timing their observations
by the same clock; for it has been remarked, that some  persons see the same
phenomenon,  a third or even half of  a  second earlier than others.  There is
no reason to suppose from  this, however, that  there is  any difference in the
rate of transmission of the sensory impressions in the two nerves.  The fact
seems  rather to be, that the sensorium does not  readily perceive two different
impressions  with equal distinctness ; and that, when several impressions are
made on the nerves at the same time,  the mind  takes cognizance of one only,
or perceives them in succession.  When, therefore, both sight and  hearing are
directed simultaneously to  one object, the  communication of the  impression
through one sense will  necessarily precede that  made by the other.   The in-
terval between the two sensations is greater in some persons than  in others;
for some  can receive  and be  conscious of many impressions, seemingly at
the same moment;  whilst in others a  perceptible space must elapse.
  572. Amongst other important offices of the  power of Hearing, is that of
supplying the sensations by which the Voice is  regulated.  It is well known
that those who are born entirely deaf, are also dumb,—that is, destitute of the
power  of forming articulate  sounds ;  even though not the least defect exist in
their organs of voice.  Hence it appears that the vocal muscles can only be
                                  37* 
438                    OF MUSCULAR CONTRACTION.
guided in their action by the sensations received through the Ears, in the same
manner as other muscles are guided by the sensations received through them-
selves (§ 433).   On this point, more  will be said hereafter (§ 611).
                        CHAPTER  VII.

         —               OF MUSCULAR ACTION.

                     1.—Of Contractility in General.

  573.  The Nervous System has no power of occasioning movement in any
part of  the  body, save by exciting to contraction certain structures, to which
the  term Muscular is given.   That one tissue should possess within itself the
property of Contractility on the application of a stimulus, is no more wonderful,
than that another should be capable of conveying sensory or  motor influences,
or another of separating a peculiar secretion from the blood.   Such contractile
tissues are found in Vegetables, as well  as in Animals; and  they appear  to
consist, in both  instances, of cells, whose peculiar property it is to change
their form, when subjected to certain kinds of irritation (§  230).  The only
essential difference in function, between the Contractility of  the cells  compos-
ing the  ultimate  fibrillae of Muscular Fibre, and that of  the cells  composing
the  intumescence of  the Sensitive Plant, consists  in the susceptibility of the
former to a stimulus, which does not operate on the latter.  Both can be made
to change their  form  by stimuli of various  kinds,—mechanical, chemical,
electrical,  &c,—directly  applied to themselves; but the contractility of Mus-
cular fibre is excited, in  addition, by the stimulus of Innervation, which has
no operation in the Plant; and it is when its peculiar property is thus excited,
that the Muscular tissue becomes the  instrument of the operation of the Nerv-
ous  system upon the external world, and thus performs an  important part in
the purely Animal Functions.—The  Muscular tissue, however, is  not always
thus called into activity through the medium of the Nervous system ;  for it is
employed to execute numerous movements, which are  immediately connected
with the maintenance of the Organic functions, and in which  the influence of
Innervation seems to be but little concerned; its contractility being excited to
action by stimuli directly applied to itself.—We have seen that there are two
forms of Muscular tissue, the striated and the non-striated, which are appro-
priated  to these  two  purposes;  the former being the kind most readily acted
on  through  the Nervous System, and invariably employed in the Muscles that
are called into action by  its influence ; whilst the  latter (which seems a less
perfectly-developed form ofthe  tissue) is with difficulty excited to contraction
through the Nervous System, and  is usually employed in Muscles, whose
action is altogether uncontrollable by the will (§§ 225—234).
  574. The general property of Contractility shows itself under two forms;
which  are  alike distinct in the mode of their  action, and  in the conditions
requisite for its excitation.—Its  most obvious and  striking manifestations pre-
sent themselves  in the Voluntary muscles and in the Heart;  which,  when in
activity, exhibit powerful contractions tending  to alternate with relaxations.
The modification of contractility which is concerned  in producing  these, is
distinguished as Irritability.—On the other hand, we find that  the muscles 
OF MUSCULAR IRRITABILITY.                    439
exhibit a tendency to  a moderate and permanent contraction, which  is not
shown by them when  they are dead, and which cannot, therefore, be the re-
sult of elasticity, or of any simple physical property; and the contraction,
instead of being a result of stimulation through the nerves, is especially ex-
cited by changes of temperature in the tissue itself.   This endowment, which
seems to  exist  in  the  greatest  amount  in  certain forms of the non-striated
muscle, is called Tonicity.—These two modifications of Muscular Contract-
ility require a separate  consideration.'

                       2.—Of Muscular Irritability.

   575. All Muscular Fibres, which are in possession of vital activity, may be
caused to  contract by stimuli directly applied to themselves ; and these stimuli
may be of different kinds.  The simplest is the contact of a solid substance,
especially if it  be pointed; thus we may excite contractions in  Muscular
fibres, by  simply touching them with the point of a needle or of  a scalpel.
Most substances of strong chemical action, such as acids and alkalies, will ex-
cite  the fibres to  contraction, when  directly applied to  themselves; but the
most powerful agent of all  is Electricity.—If we thus irritate a portion of a
muscle composed of striated fibre, the biceps, for example, the fasciculus of
fibres which is touched will immediately contract, and that one only; and the
contracted fasciculus will soon  relax, without communicating its movements
to any other.   In  fact,  the only way  to call the entire muscle into contraction
at once (since it would be impossible to apply direct irritation  to every fasci-
culus), is to stimulate it through its nerves.   On the other  hand, if we apply
a similar irritation to a portion  of non-striated fibre, as that of the Intestinal
canal, the fasciculus which is stimulated will contract less suddenly, but ulti-
mately to a greater amount; its relaxation will be less speedy ; and, before it
takes place, other fasciculi in the neighbourhood begin to contract;  their con-
traction propagates itself to others;  and so on.  In this  manner, successive
contractions  and relaxations may be produced through a considerable part of
the canal, by a single prick  with a scalpel;  a sort of wave of contraction being
transmitted in the direction of  its length, and being followed by relaxation.
Again, in the  Muscular structure of the Bladder and Uterus (which is of the
non-striated kind), direct irritation excites immediate and powerful contractions,
which extend beyond  the  fasciculus actually irritated, and produce  a great
degree of shortening;  but they do not alternate in the healthy state with any
rapid and decided elongation.   In the Heart, which is composed of a mixture
of striated and non-striated fibre, the  Muscular substance of a large part of the
organ is thrown into rapid and energetic  contraction, by a stimulus applied at
any one point;  and this contraction is speedily followed by relaxation, which
is again  succeeded by a  number of  alternating contractions and relaxations.
And in the muscular tissue of the middle coat of the Arteries,  which is of the
non-striated character, the contraction takes place rather  after the manner of
that of the bladder and  uterus;  a  considerable  degree of shortening  being
effected, by the contraction of other fasciculi than those directly irritated, and
this shortening not giving way speedily to  relaxation; but a prolonged appli-
cation of  the  stimulus is often necessary  to produce the effect.
   576. On the other hand, when the stimuli which excite Muscular Contrac-
tility are  applied to the nerves, which supply any muscle composed of striated
fibre (the Heart only excepted), they produce a simultaneous contraction in the
whole muscle ; the effect of the stimulus  being at once exerted upon every part
of it.  The contraction speedily alternates with relaxation, unless the operation
of the stimulus be continued,—as when an  electric current is propagated with-
out intermission along the nerve-trunks,—in which case the contraction lasts as 
440
OF MUSCULAR CONTRACTION.
long as the stimulus is continuously applied, but ceases as soon as it is with-
drawn.   But  it has been  lately stated  by Volkmann,*  that,  if the  electric
stimulus  be applied to the central organs, from which the  motor nerves arise,
the muscular contraction continues for some time  after its renewal.   If this
should prove to  be a universal fact, it will  afford a valuable means of distin-
guishing  what are  the real centres of  the motor nerves of particular  organs.
Further,  when the continuous electric current was passed  through incident or
excitor nerves, it produced alternating movements of contraction and relaxa-
tion, in the  muscles which were thus  called into  play by reflex stimulation.
The ordinary actions of the non-striated  fibre, on  the other  hand,  are  not
easily excitable by stimuli applied to their nerves ;  indeed  many Physiologists
have denied the  possibility of producing them through this channel.   Positive
evidence  to this  effect, however, has been already given (§ 388).  The results
of Volkmann's recent electrical experiments upon the Heart and the Intesti-
nal Canal are of much interest.   He found that neither of these  organs is
thrown into fixed contraction, when the continuous electric current is applied
to the Brain and Spinal Cord; whence he concludes  that these organs are  not
the centres of their motor nerves.  On  the other hand,  alternating contrac-
tions and relaxations were produced  on applying the continuous current to
the spinal cord,  the par vagum, and the sympathetic nerves ; whence it may
be  concluded that these parts  contain afferent fibres, which  excite motion
through centres  that can scarcely be any others than the  ganglia of the Sym-
pathetic system.   When the  Heart is removed from the body,  and is left  en-
tire, it may be thrown  into a state of fixed contraction, which  lasts  after  the
cessation of the  current;  whence it  may  be  concluded,  that it  contains  the
centre of its own motor nerves.t  These experiments, however, by no means
warrant the conclusion, that the ordinary actions of these muscular organs  are
dependent upon  the agency of their nerves  ; which is opposed by a variety of
evidence.
   577. The general fact, that Muscular Contraction alternates with  Relaxa-
tion at no longer intervals,—is most evident in the rhythmical  movements of
the Heart, and in  the peristaltic action of the Intestinal canal;  since in those
parts, the whole or a large proportion of the fibres seem  to contract together,
and then shortly relax.   But it  is probably no less true, as formerly stated
(§ 232), of the individual fibres of those muscles, which are kept in a state
of contraction by a stimulus  transmitted through their nerves; since none of
them appear, under ordinary circumstances at  least,  to remain in a contracted
state for  any length of time,—a constant interchange  of condition taking place
among the fibres, some contracting whilst others are relaxing, and vice versa.
It is difficult to speak with confidence, however, in regard to the condition of
the individual fibres of a  muscle, that is  thrown into a state  of continued
spasmodic contraction; such as that produced by the application of the elec-
tric current to the centre of its motor  nerves (§ 576).  A  state of this  kind is
often of considerable duration.   Thus the  Author has known a case  of Hys-
teric Trismus, in which the jaws remained closed with the greatest violence
during five days.  Whether the individual  fibres, in  such  instances, maintain
a state of contraction without intermission, or  whether the contraction of the
entire muscle is  kept up by a continual interchange of the fibres actually en-
gaged, is a very curious subject for  inquiry.
   578. Muscles do  not lose their Irritability immediately on  the  general
death of the  system, which must be considered as taking  place, when the  cir-
culation ceases without a power of  renewal; in cold-blooded animals it is re-

  * Mxiller's Archiv., 1844, No. 5, p. 407.
  t Op. cit; and Mr. Paget's Report for 1845, in Brit, and For. Med. Rev., July, 1846. 
       LOSS OF IRRITABILITY BY AFFECTIONS OF THE NERVOUS SYSTEM.    441

tained much longer after this  period than in the higher Vertebrata, in  some
of which it  disappears within  an  hour.  The muscles of young animals
generally retain  their irritability for a longer time  than those of adults ; on
the other hand, those of Birds lose their irritability sooner than those of Mam-
malia.   Hence,  as a general rule, the duration  of  the irritability is inversely
as the amount of respiration.   From experiments on the bodies of  executed
criminals, who were  previously in  good health, Nysten ascertained that, in
the Human subject, the irritability of the several muscular structures departs
in the following time  and order.—The left ventricle of the heart first; the in-
testinal canal at  the end of 45 or 55 minutes ;  the  urinary bladder nearly at
the same time ;  the right ventricle after the lapse of an  hour;  the oesophagus
at the expiration of an hour and a half;  the  iris a  quarter of an hour later ;
the muscles of Animal life  somewhat later; and  lastly, the auricles  of the
heart, especially the  right, which in one instance  contracted under the influ-
ence of galvanism 16| hours after death.
   579. Muscular Irritability is  deadened by many substances, especially by
those which have a narcotic or  sedative action on the  Nervous system.  In
carbonic  acid gas, hydrogen, carbonic oxide, or sulphurous acid gas, muscles
contract  very feebly, or not at all, when stimulated ;  whilst in oxygen they
retain their irritability longer than usual.  Narcotic substances, such as a watery
solution  of opium, when applied directly to the muscles, have an immediate
and powerful effect in diminishing  or even destroying  their irritability; this
effect is  also produced, though in a less powerful  degree, by injecting these
substances into the blood.  In the same manner, venous blood, charged with
carbonic  acid, and  deficient  in  oxygen, has  the  effect of a  poison upon
muscles ; diminishing their irritability, when it continues to circulate through
them, to such a  degree, that they sometimes lose it almost  as soon as the cir-
culation  ceases,  as is  seen in those  who have died  from  gradual and therefore
prolonged  Asphyxia.  The unfavourable influence of  venous  blood is also
shown in the Morbus  Cceruleus; patients affected with which  are incapable
of any considerable muscular exertion.—Although most of the  stimuli which
occasion the contraction of muscles, when directly applied to their fibres, ope-
rate also when applied to their motor nerves, the same  does not hold good in
regard to those  agents which  diminish  irritability.  It  is a fact of some im-
portance, in relation to the disputed question of the connection of muscular
irritability  with  the nervous system, that when, by the application of narcotic
substances to the Nerves, their vital properties are destroyed, the irritability
of the Muscle may remain  for some  time  longer,—showing that the latter
must be  independent of the former.
   580. We find, however, that sudden and  severe injuries of the Nervous
Centres  have power to impair, directly and instantaneously, or even to destroy,
the Contractility of the whole  Muscular system;  so that  death immediately
results, and no  irritability subsequently remains.   It is in this manner, that
the sudden destruction of the  Brain and Spinal Cord, especially of the latter,
occasions the immediate cessation of the Heart's action; though they may be
gradually removed, without any considerable effect upon it.  Severe concus-
sion has the same effect;  hence the Syncope which immediately displays it-
self.   It is sometimes an important question in Forensic Medicine, whether
an individual, who has died from the effects of a  blow  upon the head, could
have moved from the place where the blow  was inflicted.  If there be found,
as is frequently the case, no  sensible disorganization of the Brain, the  death
must be  attributed to  the concussion, and  must have been in that case imme-
diate.  If, on the other hand, effusion of blood has taken place within the
cranium, to any considerable extent, it is probable that  the first  effects of the
blow were  in some  degree  recovered  from, and  that the circulation was re- 
442
OF MUSCULAR CONTRACTION.
established.—It is not essential, however, that the impression should be prima-
rily made upon the Cerebro-Spinal system.   The well-known fact of sudden
death not unfrequently resulting from a blow on the stomach, especially after
a full meal, without any perceptible lesion of the viscera, clearly indicates that
an  impression  upon  the widely-spread  cceliac plexus of Sympathetic nerves
(which will be much more extensively communicated to them,  when the sto-
mach is full, than when it  is  empty), may cause  the immediate cessation of
the Heart's action,  in the  same manner  as  a violent injury  of the Brain or
Spinal  Cord.—Now it is  interesting to remark that, in all  these cases, the
whole vitality of the system  appears to  be  destroyed at once; for the pro-
cesses which would otherwise  succeed the injury, and which, after other kinds
of death, less  sudden in their  character, produce evident changes in the part
of the surface that has immediately received  it, are  here  entirely prevented.
An instance is on record, in which a  criminal under sentence  of death  deter-
mined to anticipate the law by self-destruction.  Having no  other means of
accomplishing his purpose,  he  stooped his head and ran violently against the
wall of his cell; he immediately fell dead ; and  no mark of contusion showed
itself on his forehead. The same absence of the usual results  is to be noticed
in the case of blows on the  stomach.  Yet it is well known, that many  of the
ordinary vital  processes  will take place in the injured parts,  after death of a
more lingering nature ; the vitality of the individual organs not  being destroyed
immediately on the severance of the chain which binds together the different
functions.  Hence  the Irritability of Muscle is not shown, by the foregoing
facts,  to have any closer dependence upon  the Nervous system, than have the
peculiar vital properties of any other tissue.
  581.  The  influence of severe impressions on the Nervous System, in di-
minishing, where it does not altogether destroy, Muscular Irritability, is well
seen in the effect of severe  injuries affecting vital organs, or extending over a
large  part of the surface, in depressing the  Heart's action.  This is a well-
known result of  severe burns, especially in children, whose  nervous system
is more susceptible of such impressions than  that of the  adult;  also of the
rupture of the alimentary canal, of the bladder or uretus; and of the shatter-
ing of one of  the extremities,  by violence affecting  a large part of their sub-
stance.   In all these  cases, the sufferer is in the same condition with one who
has received a  severe blow on the  head, that does not quite  stun him ; the
shock  immediately diminishes the  muscular  contractility  of  the whole  sys-
tem ;  and its  influence on the heart, which of course manifests  itself most
conspicuously, produces a degree of  depression which is frequently never re-
covered  from, and which, at any rate, renders  necessary the  employment of
stimulants, for the purpose of counteracting this very dangerous effect.*—Ex-
cessive mental emotion, of a kind  not in itself  depressing, may occasion the
sudden cessation of  the Heart's action, and a general loss of  muscular  Irrita-
bility ; and  it is well known  that muscular power is greatly diminished by
emotions, which produce no other direct action.
  582.  There  is no evidence that Muscular Irritability can be increased by
any cause operating through the Nervous system.   It is quite true that, under

  * The large quantity of stimulus which can be borne even by children, suffering under
severe burns, is very extraordinary: There can  be  no doubt that many lives have been
saved by the judicious administration of them, to an amount which  would, <i priori, have
been judged in itself fatal; but that  many more have been sacrificed to neglect, even on the
part of those whose duty it is to watch the indications with the closest attention.  The Au-
thor's observation leads him to believe, that Hospital-Nurses very commonly make up their
minds, that children, who have met with severe burns, must die ; and that, unless  closely
watched, they neglect the means of which Science and Experience alike dictate the free em-
ployment. 
INFLUENCE OF ARTERIAL BLOOD.
443
the stimulus of alcohol, nitrous oxide, Sic, or of some purely mental excite-
ment, individuals can  perform actions requiring  a degree of strength, which
they cannot exert under any other circumstances.   But it  does not hence fol-
low, that the irritability is increased ; since the energy of the action may be
due solely to the power of the stimulus by which it is excited, and to the un-
usual number of fibres  called into simultaneous contraction.  It is well known
that stimulating agents, which thus temporarily increase Muscular power, pri-
marily excite the Nervous system;  as is  shown by the increased mental acti-
vity which results from  the moderate use of alcohol, nitrous oxide,  opium,
&c.; and it does not seem necessary, therefore, to go further in search of an
explanation of their  effect on muscular action.—It is worthy of remark that,
whilst the influence of general depressing causes acting through the Nervous
System, is primarily manifested on the muscles of Organic life, that of stimu-
lants chiefly shows itself in the  muscles  subjected to the Will.
   583. There can be no question that, in the  living body, the energy of Mus-
cular contraction is  determined  (other things being equal), by the supply of
Arterial Blood, which  the muscle receives.  It is well known that, when a
ligature is applied to a large arterial trunk in  the Human subject, there is not
only a deficiency of  sensibility in the surface, but also a  partial or complete
suspension of  muscular power, until the collateral circulation is established.
The same result has been constantly attained, in experiments upon the lower
Animals;  the contractility of the  muscle being  impaired or altogether ex-
tinguished, when the flow of blood into it was arrested ; and being recovered
again, when the supply of blood was restored.  The influence of this  supply
of arterial blood is twofold;—it affords  the materials for the nutrition of the
tissue ;—and it furnishes (what  is perhaps more immediately necessary) the
supply of oxygen required for that metamorphosis of the tissue, which seems
to be an essential condition of the generation  of its contractile force.  As this
oxygen is taken in through the lungs, and as  the greater part of it is thrown
off—when united with carbon into  carbonic acid—by the same channel, we
should  expect to find a very close correspondence between the amount of
muscular power developed in an  animal, and the quantity of oxygen consumed
in its Respiration: and this is in reality  the case.   We find, for example, that
in Birds and Insects, whose respiration is the highest, the muscular power is
greater in proportion to their size, than in any other animals.  In the Mam-
malia, and certain Fishes that might be almost called warm-blooded, it  is only
in a degree inferior.   But in the cold-blooded Reptiles, Fishes, and Mollusca,
the muscular power  is comparatively feeble;  though even here we trace gra-
dations, which  accord well with the relative quantities of  oxygen consumed.
But in proportion to the  feebleness of the power, do we usually find its dura-
tion greater (§  578); so  that  it is not so immediately dependent upon the
supply of oxygen, in cold-blooded, as in  warm-blooded animals.   Thus, it is
found that Frogs are still capable of voluntary movement, after the  heart has
been cut out;  they tan move  limbs which are connected with the trunk by
the nerves alone : and that this power is not altogether due to the blood which
may remain in the capillary vessels, is shown  by the experiment of Muller,
who found the muscles still contractile,  after he  had expelled  all the blood,
by forcing a current  of water into an artery, until it escaped from the divided
veins.
   584. It seems probable that the Muscles of Organic life are less dependent
upon a supply of arterialized blood, than are those of Animal life ;  for the
Heart will continue  to contract, when the blood in its vessels is entirely ven-
ous, and when the circulation in it has come to a stand.  Still the dependence
of its action upon a constant supply of arterial blood, is very close; and in all
animals, however different the plans of their  circulation, we find a provision 
444
OF MUSCULAR CONTRACTION.
for this supply, by a special arrangement of the coronary arteries.*  That the
heart's  action  comes  to  an end much sooner, after the destruction of animal
life by pithing, when the coronary arteries have  been  tied, than when  they
are left untouched, has  been  proved by the  experiments  of Mr. Erichsen.t
In an animal that has been pithed, but whose heart has been left  intact, artificial
respiration will easily keep up its action for an hour, or an  hour and  a  half.
But  when the  coronary arteries were  tied, a mean of six experiments gave a
duration,  for the ventricular action, of only 23s minutes after  the  ligatures
were applied, and  32| minutes after the pithing; and in no instance was  it
prolonged more than 31 minutes after  the application of the ligature, or 37
minutes  after the  pithing.   On the other  hand, when the aorta was tied, so
that  the coronary  arteries were distended  with blood, the circulation being
carried on through them alone,  the right ventricle continued to act up to the
82d  minute.
   585. There is a remarkable difference in the degree of Irritability in the two
sides ofthe heart, to which Dr. M. Hall has directed attention.  In the warm-
blooded Vertebrata, the right side ofthe heart will  act on the stimulus of  ven-
ous  blood; whilst  the left side requires the stimulus of arterial.  In Fishes,
on the other hand, whose heart  corresponds to the right side only of  that of
Man, the whole is put in action by venous blood.   In Reptiles, one auricle is
sufficiently stimulated by venous blood, whilst the  other requires arterial; and
the ventricle is  excited to action by a mixed fluid.   In all these cases, there
must be a marked  difference in the properties of the several parts ; some being
sufficiently affected by a stimulus, which is totally inoperative on others.
This is still more remarkably exemplified by the fact, that the muscular  fibre
of Frogs would be thrown into  a  state of permanent and  rigid contraction
(through  the powerful operation of its property of Tonicity), by the stimulus
of a  fluid no  hotter than  the blood,  which  ordinarily bathes the muscles of
Birds.  Now in those warm-blooded animals which pass the winter in a  state
of torpidity, the respiration is very slow and  imperfect, and  the blood is  very
imperfectly arterialized.  There must, therefore, be a change in the properties
of the left ventricle, by which it becomes capable of action on a more feeble
stimulus, thus  resembling the ventricle of Reptiles.

  a.  This  change Dr. M. Hall designates as an  increase  of Irritability; considering that,
if muscular action be excited by a more feeble  stimulus, the property to which that action is
due, must be itself more exalted.  Physiologists have been so long accustomed, however, to
consider the irritability of the muscles in warm-blooded animals as greater than that of cold-
blooded, on account of the greater energy and rapidity of their contractions when excited,
that it seems undesirable to modify the term.-in the manner proposed by Dr. Hall.  No one
will assert that the vitality of the Muscle is exalted, when it is reduced to the condition of that
of the Reptile; and, as Irritability is strictly a vital property, it cannot be correctly spoken of
in that manner.  The general principle, however, laid down by Dr. M. Hall,—that the facility
with which the muscular system may be excited to contraction, or in other words the feeble-
ness  of the stimulus required for the purpose, is inversely as the respiration of the animal,—
is, no doubt, generally correct.                               •

   586. The doctrine, now generally accepted as a Physiological truth, that the
active exercise  of the Contractility of Muscle, is attended with a waste or dis-
integration of its tissue, rests upon a great variety of evidence.   The increase
ofthe demand for food, occasioned by Muscular activity (§ 263), is an indica-
tion that the nutritive operations are excited  by it;  and the  purpose of these
can  scarcely be anything else, than the  reparation of the loss which  the Mus-
cle has sustained.  Again, it has been just shown, that the presence of Oxygen
is essential to  the  development of the Contractile force; and there is evidence
that, in this development, a chemical change is effected in the substance of the

   * Dr. M. Hall's Gulstonian Lectures, pp. 23, 24.     f Medical Gazette, July 8, 1842. 
                DISINTEGRATION AND NUTRITION OF MUSCLE.            445

Muscle, which is of a nature destructive to its integrity as an organized tissue.
For, in  the  first  place, the researches of Helmholtz, formerly referred  to
(§ 238, b), indicate such a change, from the comparative results of Chemical
analysis  of the muscle, before and after the  violent excitement of its contrac-
tility.  But it is still more decidedly shown, by the increase in the excretions,
which is consequent upon Muscular activity; and especially by the augmenta-
tion of the Carbonic acid set free from the respiratory organs, and by that of
the Urea set  free from  the kidneys.  The amount of the latter, indeed, may be
regarded, caeteris paribus, as an approximative  indication  of the quantity of
Muscular tissue which has undergone  disintegration; being increased  or
diminished, in  precise proportion to  the degree of  exertion to which the
Muscular system has been subjected.—It cannot but be regarded as a probable
inference from these facts, that  the development of the  Contractile force is  in
some way dependent upon the  Chemical change, which seems to be so essen-
tial a  condition of it; just as  the  development of the Electric force of the
Galvanic  battery is dependent  upon the new chemical arrangements, which
take place between the bodies brought to act upon one  another in its trough.
   587. The  frequently-renewed exercise of Muscles, by producing a  deter-
mination of blood towards them, occasions  an increase in  their nutrition;  so
that a larger  amount of new tissue becomes developed,5and the muscles are
increased in size and vigour.   This is true, not  only of the whole Muscular
system when equally  exercised; but also of any particular  set of muscles,
which is more exercised than another.   Of the former we have  examples  in
those who practise a system of Gymnastics adapted to call the various mus-
cles alike into play ; and of the latter, in the limbs of individuals who follow
any calling, that habitually requires  the  exertion of either pair, to the partial
exclusion of the other,—as the arms of the Smith, or the  legs of the Opera-
dancer.   But this increased nutrition cannot take place, unless  an adequate
supply of food be afforded ; and if the amount of nutritive  material be insuffi-
cient, the result will be a progressive diminution in the size and power  of the
muscles ; \vhich will manifest itself the  more rapidly, as the amount of exer-
tion, and consequently  the degree of waste, are greater.   Nor can it be effected,
if the  exercise be too  constant;  for it is during the intervals of repose that
the reparation of the muscular tissue occurs; and the  Muscular system, like
the Nervous  (§ 294), may be worn out by too constant use.  The more violent
the action, the longer is the period of subsequent repose, which is required for
the reparation of the tissue :  and the  longest  will, of course, be requisite, when
(as sometimes occurs) the  contractility of  the  muscle is  so completely ex-
hausted by excessive stimulation, that no new manifestation of it can be ex-
cited.  Nevertheless it is certain, that there  must be  a provision in some Mus-
cles, for the continuance of their nutrition during their state of activity;  for in
no other  way could the Heart and Respiratory Muscles, which are in unceas-
ing action during the whole  of  life, be kept  in  a state fit for the  discharge  of
their functions.
   588. On the other hand,  Muscular Irritability, like  the  vital properties  of
other parts, is diminished by want of action; and in this, as in other cases, it
is quite clear that the cause  of  its loss is to  be found in the alteration of the
nutritive  processes, which is the uniform result of the  cessation of the  usual
operations of any part.  The Muscular tissue, like all other soft organized
substances, has  a constant tendency to spontaneous  disintegration, especially
at the high temperature of the body  in warm-blooded animals ; and it is con-
sequently subject to a  slow and regular waste, quite irrespectively of that pro-
duced by its  vital activity.*  Now when a Muscle or set  of Muscles, in a

  * This does not occur with nearly the same  rapidity in cold-blooded Animals, nor in the
     38 
446
OF MUSCULAR CONTRACTION.
warm-blood animal, is reduced to a  state of prolonged inactivity, from what-
ever cause, its supply of blood is diminished, and  its spontaneous decay is
not compensated by an equally active renewal; so that, in time, the  characters
of the structure are changed, and its distinguishing properties  are  no  longer
presented.  Thus in  persons whose lower extremities have been long disused,
the muscles first become pale  and  flabby;  their bulk gradually diminishes ;
their contractile force progressively decreases, and at last departs altogether;
and their proper  structure is  replaced by a deposit of fat, intermixed  with
ordinary fibrous tissue, in which  few or no characteristically-striated muscular
fibres can be detected.
   589.  The  continual  and  evident  influence of the  Nervous  System upon
Muscular Irritability, has led many Physiologists to the belief,  that  the latter
is dependent upon the agency  of the former.  Two views upon this question
have been commonly taught, to both of which it seems necessary to devote a
brief consideration.—The first of these is, that Muscular  Irritability is  derived
from some influence or  energy communicated from the Brain or Spinal Cord.

  a.  This opinion is evidently analogous  to  that which attributes the vital properties of
other parts to the Nervous System alone; and it is open to the same objection, in lamine,
which has been applied to the latter,—the improbability that any one ofthe solid textures ofthe
living body, should have for its  office to give to any other the power of performing any vital
action.  Moreover it is inconsistent with the  fact that, in Vegetables, tissues endowed with
a high degree of contractility exist, and manifest their property when a stimulus is directly
applied  to  themselves; which, nevertheless,  can have  no dependence whatever upon a
nervous system.  In the lower classes of Animals, too, there is good reason to believe, that
the property is much more universally diffused through  their tissues, than nervous agency
can be.   Again, the  action of the heart may be kept up, in the  highest Animals, by taking
care that the current of the circulation be not  interrupted, for a long time after the removal
of)the brain and spinal cord;  it may even continue when completely separated from the
body, which shows that the great centres of the ganglionic system  cannot  supply any influ-
ence necessary to it; and there  are many instances, in which the human foetus has come to
its full size, so that its heart must have regularly acted, without the existence of a brain or
spinal cord. Further, the irritability of muscles of the first class continues for  a long time
after their nerves are divided, and may be called into action by stimuli directly applied to
the parts themselves, or to their nerves below the section, so long as their nutrition is  unim-
paired.
   b. The loss of the  irritability of Muscles, within a few weeks  after the section of their
nerves,—on which great stress has been laid by Muller in support of a modified form  of the
above doctrine, (it being maintained by this distinguished physiologist, that, if muscular irri-
tability is not dependent on the Brain and Spinal Cord, they supply some influence essential
to its exercise,)—is clearly due  to the alteration in their nutrition, consequent upon  their dis-
use.   This has been recently proved to demonstration, by the very ingenious experiments of
Dr. J. Reid.*   "The spinal nerves were cut across, as they lie in  the lower part of the  spinal
canal, in four frogs; and both posterior  extremities were thus insulated from their nervous
connections with the spinal cord.   The muscles of one of the paralyzed limbs were daily
exercised by a weak galvanic battery; while those of the other limb were allowed  to remain
quiescent.  This was continued for  two months; and at the end of that time, the muscles of
the exercised limb retained their original size and firmness and contracted vigorously, while  «
those of  the quiescent limb had shrunk to at least one-half of their former bulk, and pre-
sented a marked contrast with those of the exercised limb.  The  muscles of the  quiescent
limb still retained their contractility, even at the end of two months; but there can be little
doubt that, from their imperfect nutrition, and  the  progressing changes in their physical
structure, this would in no long time have disappeared, had circumstances permitted the
prolongation of the  experiment."f  This experiment  satisfactorily explains  the fact ob-
hybernating condition of certain warm-blooded Mammalia; indeed, when the temperature
of the body is reduced to within a few degrees of the freezing point, no chemical change
seems possible in muscle,—its spontaneous decay, and its vital activity, being alike checked.
  * Edinburgh Monthly Journal of Medical Science, May, 1841.
  f A fact of an exactly parallel character has fallen under the Author's observation, in a
case of Hysteric Paraplegia, in which one leg was occasionally affected with severe cramps.
The muscles of this leg  suffered much less diminution of size  and firmness, than those of 
INHERENT IRRITABILITY OF MUSCULAR FIBRE.
447
served by  Dr. M. Hall, and heretofore adverted to (§  399), that in cases in which the
cause of the paralysis is situated in  the Brain, and  in which the Spinal Cord and  its
nerves are unaffected, the irritability of the muscles of the paralyzed part is not destroyed,
even after a considerable lapse of time.  For, if the capability of performing reflex actions
still exist, on the part of  the nervous system, it is manifest that the  muscles will be  occa-
sionally excited to action through this channel; and that their nutrition and vital properties
will thereby be  preserved, as they were in Dr. Reid's experiments by the artificial excite-
ment of galvanism.  Hence Dr. M. Hall's opinion, that the property of Muscular contrac-
tility is derived from the Spinal Cord, is no more tenable  than  that which locates it in the
Brain.
   e. The loss of irritability from section of the nerves, takes place more speedily in warm-
blooded Vertebrata, all whose vital operations  are performed with a much greater activity,
than in Reptiles, and other  cold-blooded animals.  Dr. Reid found that, in a Rabbit, a por-
tion of whose sciatic nerve had been removed on one side, the muscles of that leg were but
very feebly excited to contraction by Galvanism, after the lapse of seven weeks.   The change
in their nutrition was  evident to the eye, and was made equally apparent by the balance.
The muscles of  the paralyzed limb were much smaller, paler, and  softer, than the corre-
sponding muscles of the opposite leg; and they scarcely weighed more than half,—being
only 170 grains, whilst the others were 327  grains.   It was found, also, that a perceptible
difference existed in the size of  the bones of the leg,  even after so  short an  interval had
elapsed; the  tibia and fibula ofthe paralyzed limb weighing only 81 grains, whilst those of
the sound limb weighed 89 grains.  On examining the muscular fibres with the microscope,
it was found  that those of the paralyzed leg were considerably smaller than  those of  the
sound limb, and presented a somewhat shrivelled appearance; and that the longitudinal and
transverse  striae were much less distinct.
   d. Another equally satisfactory proof, that the loss of Irritability, which follows the sever-
ance of the connection between the Nervous centres and  the Muscle, is not immediately due
to the  interruption of any influence communicated by the former, has been given by the  ex-
periments of Dr. J. Reid.  He has proved, that if the irritability of Muscles be exhausted by
means, which have no tendency to impair their healthy nutrition, and the other conditions
favour the normal performance of the nutrient processes, the irritability is restored, and re-
mains for some time.  His first experiments were on cold-blooded animals, and they would
in themselves be sufficiently satisfactory; but he has since repeated them in the Rabbit, and
established the  fact beyond  all doubt*  "The  sciatic nerve was divided in the  Rabbit,
and a portion of  it removed. One wire from two  galvanic batteries consisting of thirty
pairs of plates, was applied over the course of  the nerve; and the other wire was applied
over  the foot, which was  kept moist, until the muscles had ceased to  contract.  Three
days after  this, a  weaker battery was  used, and the  muscles  of the  limb  had recovered
their contractility, and contracted  powerfully.   The  more powerful battery was used as
before, until  the  muscles  had ceased to respond to  the  excitement;  and three days after
this, they had again recovered their contractility."  It seems  scarcely possible  to draw any
other inference from these experiments, than that Irritability is a property inherent in Mus-
cular  tissue,  and that the agency of the Nervous system upon it is merely to call it into
active operation.

   590. The second doctrine referred  to, as having been  taught by some Phy-
siologists, is, that Muscles,  though not  dependent on nerves for their peculiar
vital power, are yet dependent  upon  them for the exercise of  that power;—
all stimuli,  which excite  muscles to contraction, operating first on the nervous
filaments which enter muscles, and through them on the muscular fibres.

   a. The facts which have been already stated, in regard to the ordinary action of the Mus-
cles of Organic life, furnish a sufficient answer to this hypothesis.  It is with great difficulty
that these can be made to display their irritability, by any stimuli applied to their nerves;
whilst they manifest it strongly,  when the stimulus is directly applied to themselves.  Even
in the Muscles of Animal life, individual fasciculi may be thrown into action in the  same
manner; although the entire mass cannot be put into combined operation, except by a stimu-
lus simultaneously communicated to the whole, which the nerve affords the readiest means
of effecting.  Perhaps the most satisfactory disproof of it, however, is  to be found in the  ob-
the other; so that there was a difference of more than an inch in the circumference of the
limbs.  But since the paraplegia has been recovered from, voluntary power having been es-
tablished in both limbs, and the muscles of both having been exercised in the same degree,
they have greatly improved in size and firmness, and there is no longer any perceptible dif-
ference between them.                                         *  Loc. cit. 
448
OF MUSCULAR CONTRACTION.
servation of Mr. Bowman already cited (§ 231), that a single fibre, completely isolated from
all its connections, may be seen with the microscope to pass into a state of contraction, under
the influence of direct irritation.  Further, it has been experimentally ascertained, that there
are some chemical stimuli, which will produce the contraction of muscles when directly ap-
plied to them, but of which the influence cannot be transmitted through the nerves; this is
especially the case with regard to acids.
   591.  When all these considerations are  allowed their due weight, we  can
scarcely do otherwise than acquiesce fully in the doctrine  of Haller, which
involves no hypothesis, and which is perfectly conformable  to the analogy of
other departments of Physiology.  He regarded every part of the body which
is  endowed with Irritability, as possessing that property in and by itself;  but
considered that the property is subjected to excitement and control from the
Nervous System, the agency of  which is one of the stimuli  that can call it
into  operation.—It maybe desirable briefly to recapitulate the facts, by which
this doctrine is supported.  1. The existence in Vegetables of irritable tissues,
which are excited  to contraction  by stimuli directly applied to themselves,
and which can be in no way dependent  upon, or influenced  by, a  Nervous
system.   2.  The existence in Animals of a form of Muscular tissue, which
is  especially connected with the maintenance of the Organic  functions,  and
which is much more readily excited to action by direct stimulation, than it is
by Nervous agency.  3.  The fact  that, by the  agency of these,  the Organic
functions may go on (as long as their other requisite conditions are supplied)
after the removal of the nervous centres,  and when none  were ever present;
rendering it next to  certain, that their ordinary operations are not dependent
upon any stimuli received through the nerves, but upon those directly applied
to  themselves.  4.  The persistence of  irritability in muscles, for some time
after the nerves have ceased to be able  to convey them the effects of stimuli;
this is constantly seen in regard to the  Sympathetic system of nerves,  and
the muscles  of  Organic life upon which they operate; and  it may also be
shown to occur with respect to the Cerebro-Spinal  system, and  the muscles
of Animal life, by the agency of narcotics.   5.  The persistence of irritability
in  the  muscles, after their complete isolation from the nervous centres, so
long as their nutrition is unimpaired; and the  effects of frequent exercise, in
preventing the  impairment of the nutrition and the loss of irritability.   6.
The recovery of the irritability of muscles, when isolated  from  the nervous
centres, after it has been exhausted by repeated stimulation; this also depends
upon the healthy performance  of the nutritive  actions.   7. The contraction
of" muscular fibre under the microscope, when  completely isolated from all
other tissues.—In the words of  Dr. Alison, then, " the  only ascertained final
cause of all endowments bestowed  on Nerves  in relation to Muscles, in  the
living body, appears to be, not to make Muscles irritable, but  to  subject their
irritability, in different  ways, to  the dominion of the acts and feelings of the
Mind,"—to its volitions, emotions, and instinctive determinations.
   592.  A curious question has been lately raised, the decision on which is of
some importance in our determination of  the nature of the force, by which
the contraction of muscles is occasioned.   This is,—whether the power of a
muscle is greater or less at different degrees of contraction, the same stimulus
being applied.  This seems to have been determined, by the  ingeniously-de-
vised experiments of Schwann.*   He contrived  an  apparatus, which  should
accurately measure the  length of the muscle, and, at the same time, the weight
which it would balance by its  contraction.   Having caused the  muscle of a
Frog to shorten to its extreme point, by the  stimulus of galvanism applied to
the nerve, so  that no further stimulation could lift a weight placed in the oppo-
site scale, he allowed the muscle to  relax  until it was extended to a certain
* MiUler"s Physiology, p. 903. 
                       TONIC CONTRACTION OF MUSCLES.                  449

 point, and then ascertained the weight which would balance its power.   The
 same was several times repeated, as in the following manner:—The length of
 the muscle in  its extreme  state  of contraction, at which no additional force
 could be exerted by it, being represented by 14, it was found that, when it
 had been extended to 17, it would balance a weight of 60; when its  length
 increased to 19*6, it would  balance  a weight of 120;  and  at  22'5,  it would
 balance 180.   In another experiment, the muscle at 13#5, balanced 0; at 18'8,
 it balanced 100 ;  and at 23"4, it balanced 200.  Hence it appears that a uni-
 form increase of force  corresponds  with a  nearly uniform increase  in the
 length of the muscle; or, in other words, that when the muscle is  nearly at
 its full length, its contractile power is the greatest.   In  later  experiments upon
 the same muscle, this  uniform ratio  seemed  to  be departed  from; but, by
 comparing the results in a considerable number of instances, it was constantly
 found that,  in those experiments  which were performed  the soonest  after the
 preparation of the frog, and in which, therefore, the normal conditions  of the
 system were  the  least  disturbed, the  ratio was very closely maintained.  It
 has been ascertained by Valentin, on repeating these experiments, that, by
 repeated equal  irritations, the strength of the muscles in beheaded  frogs de-
 creases in a regular and corresponding ratio ; losing the same amount in each
 successive period of time.   He  also found that, when all the  Irritability has
 ceased, the muscles tear with  a  far less weight, than they were previously
 able,  when  galvanized, to draw.

   a. It has been inferred by Muller, from Schwann's experiments, that the power which
 causes the contraction of a Muscle, must be very different in its  character, from  any of the
 forces of attraction known to us; since  these all increase in energy as the attracted parts ap-
 proach each other, in the inverse ratio  of the square of the distance; so that the  power of a
 Muscle, if operated on by any of these, ought to increase, instead of regularly diminishing,
 with its degree of contraction.  But it is to be remembered  that, as the observations of Mr.
 Bowman have clearly shown, there must be a considerable displacement of the constituents
 of every fibre during contraction (§ 231); so that it  is easy to understand that, the  greater
 the contraction, the more difficult must any further contraction become.  If, between a mag-
 net and a piece of iron attracted by it, there were interposed a spongy elastic tissue, the iron
 would cease to approach the magnet at  a point, at which the attraction  of the magnet would
 be balanced by the force, needed to compress still further the intermediate substance.

                         3.—Of Muscular Tonicity.

   593.  We have  now to consider the  other form of Contractility, which  pro-
 duces a  constant  tendency to contraction (varying, however, as to its degree)
 in the Muscular fibre; but which is  so  far  different from  simple Elasticity,
 that it abates after death, before decomposition has taken place.   This Toni-
 city is to be distinguished from the Muscular Tension, which  is the  result  of
 the reflex operation of the nervous centres (§ 398); being manifested as  well
 when the muscle is altogether removed from nervous influence, as when  sub-
jected to it, and being, like Irritability, an inherent property of the tissue itself,
 the presence of which is characteristic of its living  state.  It manifests itself
 in the retraction which takes place in the ends of  a living muscle, when  it is
 divided  (as is seen in  amputation);  this  retraction  being permanent,  and
 greater than that of a dead muscle.  But its effects are much  more remarkable
 in the non-striated, than in the striated form of Muscular Fibre; and are  par-
 ticularly evident  in  the  contractile coat of the Arteries, causing  the almost
 entire obliteration of  their  tubes, when  they are no longer distended  with
blood.   The disposition to tonic contraction is increased  by any considerable
 change  of temperature ;  the power of  Heat is well  seen  in  the following ex-
periments of John Hunter's :—" As soon as the skin could  be  removed from
a sheep  that was  newly killed, a square  piece of muscle was  cut off, which
                                    38* 
450                    OF MUSCULAR CONTRACTION.
was afterwards divided into three pieces, in  the direction of the fibres;  each
piece was put into a basin of water, the water in each basin being of different
temperatures, viz., one about 125°, about  27° warmer than the animal; an-
other 98°, the heat of the animal;  and the  third 55°, about 43° colder than
the animal.   The muscle in the water heated  to 125° contracted directly, so
as to be half an inch shorter than the other two, and was hard and stiff.  The
muscle in the water  heated to 98° after  six minutes began to contract and
grow stiff; and at the end of twenty minutes it was nearly, though not quite,
as short and hard as the above.   The muscle in the water heated to 55° after
fifteen minutes, began to shorten and grow hard; after twenty minutes it was
nearly as short and as hard as that in the water heated to 98°.  At the end
of twenty-four hours, they were all found to be of the same length and stiff-
ness."*  The agency of Heat in producing this contraction is also remarkably
shown in the  fact, that if a Frog be immersed in water of the temperature of
110°, the muscles of its body and limbs will be thrown into  a state of perma-
nent and rigid contraction.—But it would  seem that  these effects are chiefly,
if not entirely, exerted upon the striated form of Muscular fibre ;  and that the
tonicity of the non-striated fibre is called into play  by Cold, rather than by
heat.  For if a Tadpole or Frog be  immersed  in water, the temperature of
which is gradually raised, until this state of contraction comes  on, the Heart
will be  found to continue  pulsating  for  many hours afterwards, not being
affected by the heat.  On the other hand, if an artery  in a living warm-blooded
animal be exposed to  cold air  for some time, the lowering of its temperature
occasions  its contraction to such an  extent, that its cavity becomes  almost
obliterated.  The influence of warmth in diminishing, and of cold in increas-
ing, the tonicity of  the arterial  system, will be adverted  to hereafter (Chap.
xii., Sect. 3).
   594. The distinctness of the Tonicity of Muscles  from their Irritability, is
further shown by the fact that the former commonly survives the latter; and
that it is not destroyed by treatment, which  occasions  the complete departure
of the Irritability.  The first of these statements finds its proof in the pheno-
mena of the Rigor Mortis, presently to be adverted to.  Of the latter, the fol-
lowing remarkable experiment of John Hunter's is an ample demonstration:—
" From a straight muscle in  a bullock'* neck, a portion, three inches in length,
was taken out immediately after the animal had been knocked down, and was
exposed between  two pieces of lead, to a cold below  0°, for fourteen minutes ;
at the end of this  time it was found  to be frozen  exceedingly hard, was be-
come white, and was  now only two inches long; it was thawed gradually, and
in about six hours after thawing, it contracted so as only to measure one inch
in length;  but irritation did not produce any sensible motion in the fibres.
Here, then, were  the  juices of muscles frozen, so  as to prevent all power of
contraction  in their fibres, without destroying their life; for when thawed,
they showed the  same life which they had before;  this  is exactly similar to
the freezing of blood  too  fast for its  coagulation, which, when  thawed, does
afterwards  coagulate,  as it depends in each on the  life of the part not  being
destroyed."!
   595. The Rigor Mortis, or death-stiffening of the muscles,  is probably to
be regarded as the final manifestation of this property; occurring after all the
Irritability of  the muscles  has departed,  but before  any putrefactive change
has commenced.   This phenomenon is rarely absent; though it may be so
slight, and may last  for so short a time, as to escape observation.  The period
which elapses before its  commencement, is as variable as its duration  ; and

        *  General Principles ofthe Blood,*in Hunter's Works, Vol. iii., p. 110.
       f Op. cit, p. 109. 
RIGOR MORTIS.
451
both appear to be in some degree dependent upon the vital condition of the
body at the time of death.  When the fatal termination has supervened on slow
and wasting disease, occasioning great general depression of the vital powers,
the rigidity usually developes itself very early, and lasts for a short time.  In
diseases which powerfully affect the nervous energy, such as Typhus, this is
often the case ; even though they have not  been of long duration.  Thus,
after death  from Typhus, the limbs have been sometimes known to stiffen
within fifteen  or twenty minutes.   The same is observed in infants and in old
people.  On  the other hand, where  the general energy has been retained  up
to a short period  before  death, the  rigidity is much later in coming on, and
lasts longer;  this happens, for example, in many cases  of Asphyxia and Poi-
soning, in which it has been said not to occur at all.  The commencement of
the rigidity, however, is  not  usually prolonged much  beyond  seven hours;
but twenty or even thirty hours may elapse, before it shows itself.   Its gene-
ral duration  is from twenty-four to thirty-six hours ; but it  may pass off much
more rapidly ; or it may be prolonged through several days.  An attempt has
been made  to connect it with  the  lowering of the  temperature of the dead
body ;  but with this it does not seem to have any relation.   It occurs in cold-
blooded Vertebrata, and even  in Invertebrata, as well as in  warm-blooded ani-
mals ;  and it has frequently been noticed to commence in  the latter, long be-
fore the heat has entirely  departed from the body.  Moreover, it appears first
upon the trunk, which is the region last deserted by the caloric.  It first affects
the neck and lower jaw, and  seems  gradually to  travel downwards; but ac-
cording to some observers, the lower extremities are stiffened before the upper.
In its departure, which is immediately followed by decomposition, the same
order is observed.   It affects all the  muscles nearly alike ;  but the flexors are
usually more  contracted than the extensors, so that the fingers are somewhat
flexed  on the  palm, and the fore-arm on  the arm ;  and the lower jaw, if pre-
viously drooping, is commonly drawn firmly against the upper.   It is remark-
able, that it is equally intense in  muscles which have been paralyzed by He-
miplegia ;  provided  that no  considerable  change has  taken place in  their
nutrition.  When very strong, it renders the muscles prominent, as in volun-
tary contraction.
   596. The ordinary Irritability of  the muscles appears to be almost invaria-
bly lost, or greatly diminished, before the  Rigor  Mortis commences.   This
statement holds  good in regard to animals of different classes, as well as with
respect to  Man under various conditions.  Thus, in Birds, whose  muscles
most speedily lose  their  contractility, the  cadaveric rigidity is  most quickly
exhibited ; whilst in Reptiles it is much longer in  commencing, the irritability
of the  muscles being more persistent.  The interval between the cessation of
the Irritability and the accession of the Rigidity, is sometimes very consider-
able ; and in such cases, the  rigidity, when it does occur, is usually very de-
cided and prolonged.—An attempt has been made to show a correspondence
between the rigor mortis, and the coagulation of the blood in the vessels; and
there is certainly evidence enough to make it appear, that some analogy exists
between these two actions, though they are far from  being  identical.  After
those  forms of death  in which  the   blood  does  not  coagulate,  or  coagulates
feebly, the rigidity commonly manifests  itself least;  but this is by no means
an invariable rule.   It seems probable that, as  the coagulation of the blood
will be shown to be the last act of its vitality, so the stiffening of the muscles
is the  expiring effort of theirs.

   a.  It  is necessary to bear in mind, when the phenomena of cadaveric rigidity are brought
into question in  juridical investigations, that a state at first sight corresponding to it may
supervene immediately upon death, from some peculiar condition of the  nervous and muscular
systems at the moment.  This has been observed in  some cases of Asphyxia; but chiefly
when death has resulted from apoplexy following chronic ramollissement of the brain or spinal 
452
OF MUSCULAR CONTRACTILITY.
 cord.  This contraction, which is obviously of a tetanic character, ceases after a tew hours,
 and is then succeeded by a state of flexibility, after which the ordinary rigidity supervenes.
 The following case illustrates the nature of the inquiries, to which this condition may give
 rise.*  The body of a man was found in a ditch, with the trunk and limbs in such a relative
 position, as could only be maintained by the stiffness of the articulations. This stiffness must
 have come on at  the very moment when the body took that position;  unless  it could be
 imagined  that the  body had been supported by the alleged murderers, until the joints were
 locked by cadaveric stiffness.  A post-mortem examination showed, that there was no neces-
 sity for this supposition,—obviously a very improbable one in itself;—by  affording sufficient
 evidence, that apoplexy, resulting from chronic disease, was the cause of death.  A case
 occurred a few years since in Scotland, in which the same plea was raised. The body was
 found in a position in which it could have only been retained by rigidity of the joints; and
 it was pleaded on  the part of  the prisoner, that death had been natural, and had resulted
 from fracture of the processus dentatus, causing sudden pressure upon the spinal cord, whence
 the spasmodic rigidity would naturally  result.  Proof was deficient, however, as  to  the
 existence of this lesion before death; and the position of the body rather resembled that into
 which it might have been forced during the rigidity, than that  in which it would  probably
 have been at the moment of death.  There were also marks  of violence, and many other
 suspicious circumstances; but  the prisoner was acquitted, chiefly from want of  evidence
 against him.  What seemed to indicate that the rigidity was of the ordinary cadaveric nature,
 was, that there was no evidence of the body having become flexible and again stiffened; as
 it would probably have done, had the rigidity been of the spasmodic character.
   597. As the property of Tonicity manifests  itself most decidedly in the non-
 striated muscles in the living body, so do we find this  post-mortem contraction
 most remarkable in them.   As  soon as the muscular walls  of the several cavi-
 ties lose  their irritability,  they begin to contract firmly upon  their contents,
 and thus become stiff and  firm, though they were previously flaccid.   In this
 manner the ventricles of the heart,  which are  the  first parts  to lose  their
 irritability, become rigid and contracted within an hour or two after death;
 and usually remain  in  that  state  for  ten  or twelve  hours,  sometimes for
 twenty-four  or thirty-six, then again  becoming  relaxed and flaccid.   This
 rigid contracted  state of the heart, in which the walls  are  thickened and the
 cavities  diminished,  was  formerly supposed to  be  a result  of disease, and
 was termed concentric hypertrophy; but it is'now  known, from the inquiries
 of Mr. Paget,  to be the natural condition of the organ, at the period when the
 rigor mortis  occurs in it.—The contraction  of the arterial tubes is so great, as
 to produce for the  time a great  diminution in their calibre ;  and this  doubtless
 contributes to  the passage  of the blood from the arterial into the venous sys-
 tem, which almost  invariably takes place within a  few hours  after death.  The
 arteries then enlarge again, and become quite flaccid, their tubes being emptied
 of their previous contents ; and it  was from  this circumstance, that the  ancient
 Physiologists were led to imagine, that the arteries are not destined to carry
 blood, but air.

           4.—Energy and Rapidity  of Muscular  Contraction.
  598. The  energy of Muscular contraction  is of course to be most remarkably
 observed in those instances in which the continual exercise of particular  parts
 has occasioned an increased  determination of blood towards  them, and  in con-
 sequence a permanent augmentation in  their bulk.   This has  been  the  case,
 for  example, with  persons who have gained  their livelihood  by exhibiting
 feats of strength.  Much will, of course, depend on the mechanically-advantage-
 ous application of  muscular  power; and in this manner, effects  may be pro-
 duced, even  by  persons of ordinary strength, which would not have  been
 thought credible.  In lifting a heavy weight in  each hand, for example, a per-
 son who  keeps his back perfectly rigid, so as  to throw the  pressure vertically
upon  the pelvis, and only uses the powerful  extensors of the thigh  and calf,
by straightening  the knees  (previously somewhat flexed), and bringing the leg
to a right angle with the foot, will have a great advantage over one who uses
                         * Annales d'Hygiene, torn. vii. 
             ENERGY AND RAPIDITY OF MUSCULAR CONTRACTION.         453

his lumbar muscles for the purpose.  A still greater advantage will be gained,
by throwing  the weight more directly upon the  loins, by means of a sort of
girdle, shaped so as to rest upon the top of the sacrum and the ridges of the
ilia;  and by pressing with the hands  upon a frame, so arranged  as to bring
the muscles of the arms to  the assistance of those of the legs : in this manner,
a single Man of ordinary strength may raise a weight of 2000 lbs.; whilst few
who  are unaccustomed to such exertions, can lift more  than 300 lbs. in the
ordinary mode.  A man of great natural strength, however, has been known
to lift 800 lbs. with his  hands; and  the  same individual performed several
other curious feats of strength, which  seem deserving of being here noticed.
" 1.  By the strength of his fingers, he rolled up a very large and strong pewter
dish.  2. He broke several short and strong pieces of tobacco-pipe, with the
force of his middle finger, having laid them on the first and third finger.  3.
Having thrust in under his garter the bowl of a strong tobacco-pipe, his legs
being bent, he broke it to pieces by the tendons of his hams, without altering
the bending of the knee.   4.  He broke such another bowl between his first
and second fingers, by pressing them together sideways.   5. He lifted a table
six feet long, which had half a hundred-weight hanging at the end of it, with
his teeth, and held it in that position for a  considerable time.  It is  true, the
feet of the  table rested against his knees;  but, as the length of the table was
much greater than  its  height, that performance required a great strength to be
exerted by the muscles of his loins, neck, and jaws.  6.  He took an iron
kitchen poker, about a yard long, and three inches in circumference, and, hold-
ing it in his right hand, he struck it on his bare left arm  between the elbow
and the wrist, till he bent the poker nearly to a right angle.  7.  He took such
another poker, and, holding the ends of it  in his hands, and the middle of it
against the back of his neck, he brought both ends of  it together before him ;
and, what was yet more difficult, he pulled it straight again."*   Haller men-
tions an instance of a man, who could raise a weight of 300 lbs. by the action
of the elevator muscles of his jaw:  and that of a slender girl, affected with
tetanic spasm, in whom the extensor muscles of the back, in the state of tonic
contraction or opisthotonos, resisted a weight of 800 lbs., laid on the  abdomen
with the absurd intention of straightening the body.  It  is to be recollected,
that the mechanical application of  the power developed by  muscular contrac-
tion, to the movement of the body, is very commonly disadvantageous as re-
gards force;  being designed  to  cause  the  part moved to pass over a  much
greater space, than that through which  the muscle contracts.  Thus the tem-
poral muscle is attached to  the lower jaw, at about  one-third of the distance
between the condyle  and the  incisors;  so  that a shortening of the muscle to
the amount of half an  inch, will draw up the front of the jaw through an inch
and a half; but a power of 900 lbs. applied by the muscle, would be required
to raise 300 lbs. bearing on the incisors.  In the case of the forearm and leg,
the disproportion  is much greater; the points of attachment of the  muscles,
by which the knee and elbow-joints  are  flexed and  extended, being  much
closer to the fulcrum,  in comparison with the distance  of the points on which
the resistance bears.
   599. The energy of muscular contraction appears to be greater in Insects,
in proportion to their  size, than it is in any other animals.  Thus a Flea has
been known to leap sixty times its own length, and to move as many times
its  own weight.   The short-limbed  Beetles, however,  which  inhabit the
ground, manifest the greatest degree of muscular power.  The Lucanus cer-
vus  (Stag Beetle) has been known to gnaw a hole of an inch diameter, in the
side of an  iron canister in which it had been confined.  The Geotrupes ster-
corarius (Dung or shard-born Beetle) can support uninjured, and even elevate
* Desaguliers' Philosophy. Vol. ii. 
454
OF MUSCULAR CONTRACTILITY.
a weight equal to at least 500 times that of its body.   And a small Carabus
has been seen to draw a weight of 85 grains (about 24 times that of its body)
up a plane of 25° ; and a weight of 125 grains (36  times that of its  body)
up a plane of 5° ;  and in both these instances the  friction was considerable,
the weights being simply laid upon a piece  of paper,  to which the insect was
attached by a string.
  600.  The rapidity of the changes of position  of the component particles
of muscular fibres,  may, as Dr. Alison justly remarks,* be estimated, though
it can hardly be conceived from various well-known facts.  The pulsations of
the heart can sometimes be distinctly numbered in children, at  more than 200
in the minute; and as each contraction of  the ventricles occupies only one-
third of the time of the whole pulsation, it must be accomplished in l-600th
of a minute, or  l-10th  of a second.  Again, it is certain that, by the  move-
ments ofthe tongue and other organs of speech, 1500 letters can be  distinctly
pronounced by some persons in a minute :  each of these must require  a sepa-
rate contraction of muscular fibres ;  and the production and cessation of each
of the  sounds, imply that each separate contraction must be  followed by a
relaxation of equal length; each contraction, therefore, must  have been ef-
fected in 1-1000th part of a  minute, or  in  the 1-10th  of a  second.   Haller
calculated that, in the limbs of a dog at full speed, muscular contractions must
take place in less than the  l-200th of a second, for many minutes at least in
succession.—All these instances, however, are thrown into the shade, by those
which may  be drawn from the class of  Insects.   The rapidity of the vibra-
tions of the wings may be estimated from the musical tone which  they pro-
duce ; it being easily ascertained by experiments, what number of vibrations
are required to produce any note in the scale.  From  these data, it appears
to be the necessary result, that the wings  of many Insects strike the  air many
hundred, or even many thousand, times  in every second.—The minute pre-
cision with which the  degree of  muscular contraction can be  adapted to the
designed effect, is in no instance more remarkable than in the Glottis.  The
musical pitch of the tones produced by it,  is regulated by the  degree of ten-
sion of  the  chordae vocales, which are  possessed of a very considerable de-
gree of elasticity (§ 603).   According to  the observations of Miiller,t the
average length of tbese, in the male, in a state of repose, is about 73-100ths
of an inch;  whilst, in the state of greatest  tension, it is about  93-100ths; the
difference being therefore 20-100ths, or one-fifth of  an inch : in the  female
glottis, the average  dimensions are  about 51-100ths, and  63-100ths respect-
ively ; the difference being thus about one-eighth of an inch.   Now the natu-
ral  compass of the voice, in  most persons  who  have cultivated  the vocal
organ, may  be stated  at about two  octaves, or 24 semitones.   AVithin each
semitone, a singer of ordinary capability could produce  at least ten  distinct
intervals ; so that of the total number, 240 is a very moderate estimate.  There
must, therefore, be  at least 240 different states of tension of the vocal cords,
every one of which is producible by the will, without any previous trial; and
the whole variation in the length of  the  cords being  not more  than one-fifth
of an inch even in man, the variation required to  pass from  one  interval to
another, will not be more  than one twelve-hundredth of an inch.   And yet
this estimate is much below that which might be  truly made  from the  per-
formances of a practised vocalist.J

  * Cyclopaedia of Anatomy and Physiology, Art. Contractility.
  t Physiology, 1018.
  % It is said that the celebrated Made. Mara was able to sound 100 different intervals be-
tween each tone. The compass of her voice was at least three octaves, or 22 tones; so that
the total number of intervals was 2200, all comprised within an extreme variation of one-
eighth of an inch; so that it might be said that she was able to determine the contractions
of her vocal muscles to the seventeen-thousandth of an inch. 
OF THE VOICE AND SPEECH.
455
  601.  Of the different associations of Muscular actions, which are em-
ployed for various purposes in the  living body, it would be out of place here
to speak; since these associations depend upon the Nervous rather than upon
the  muscular system ; and the most important of them have already been con-
sidered  in detail.   It may be mentioned, however, that the aptitude which is
acquired by practice, for the  performance of particular  actions, that were at
first accomplished with  difficulty, seems  to  result as much from a change,
which the  continual repetition of  them occasions  in the Muscle, as  in  the
habit which  the  Nervous system acquires, of exciting their performance.
Thus almost every person learning to play on a musical  instrument, finds a
difficulty in causing the  two shorter  fingers to  move independently of each
other and of  the rest; this is particularly the case in regard to the ring-finger.
Any one may satisfy himself of the difficulty, by laying the palm of the hand
flat on a table, and raising one finger after the other, when it will  be  found,
that the ring-finger cannot be  lifted without  disturbing  the rest,—evidently
from  the difficulty of detaching the  action  of that  portion of the extensor
communis  digitorum, by which the  movement is produced, from that of  the
remainder of the muscle.  Yet to the practised musician, the command  of the
will over all the fingers becomes nearly alike ; and it can scarcely be doubted
that some change takes place in the structure ofthe muscle, which favours  the
isolated operation of its several divisions.
                        CHAPTER  VIII.

                        OF THE VOICE AND SPEECH.

                    1.  The Larynx, and its Actions.

   602.  The sounds produced by the organ of Voice  constitute the most im-
portant  means of communication between Man  and his fellows ; and  the
power of speech has, therefore, a primary influence, as  well on his physical
condition, as on the development of his mental faculties.  Hence,  although it
only depends on one particular  application  of muscular force, comparable
to that  by  which  other volitional or emotional movements are  effected, it
seems right, in treating  of the Physiology of man, to make it an object of
special  consideration.   In order to understand  the  nature of the Organ of
Voice as a generator of  Sound, it is requisite to inquire,  in the first, instance,
into the sources from which sounds at all corresponding to the human voice
are elsewhere obtained.   It is necessary to bear in mind, that Vocal Sounds,
and Speech or Articulate Language, are  two  things  entirely  different;  and
that the former may be produced in great perfection, where there is  no ca-
pability for  the latter.  Hence we should  at once infer, that  the  instrument
for the  production of Vocal  Sounds was  distinct from  that by which these
sounds  are modified  into articulate speech ; and this we  easily discover to be
the case,—the Voice being  unquestionably produced  in the  Larynx, whilst
the modifications of it, by which language  is formed, are  effected for the most
part in the Oral  cavity.   The structure and functions of  the former, then, first
claim  our attention.
   603.  It will be remembered that the Windpipe is  surmounted by  a stout
cartilaginous annulus, termed the Cricoid cartilage ; which serves as a founda- 
456                     OF THE VOICE AND SPEECH.

tion for the  superjacent  mechanism.   This is embraced (as it were) by the
Thyroid, which is articulated to its sides by its  \ower horns, round the ex-
tremities of which it may be regarded as turning, as on a pivot.   In this man-

                                  Fig. 195.
  External and sectional views ofthe Larynx, a n b, the cricoid cartilage ; e c g, the thyroid cartilage;
e, its upper horn ; c, its lower horn, where it is articulated with the cricoid;  f, the arytenoid cartilage;
e, f, the vocal ligament; a k, crico-thyroideus muscle ; f e m, thyro-arytenoideus muscle ; x e, crico-ary-
tenoideus lateralis; s, transverse section of arytenoideus transversus ; m n, space between thyroid and
cricoid; b l, projection of axis of articulation of arytenoid with thyroid.

ner the lower  front border of the thyroid  cartilage, which is ordinarily sepa-
rated by small intervals from the upper margin of the cricoid, may be made to
approach it or recede  from it;  as  any  one may easily ascertain, by placing
his finger against the little depression which may be  readily felt  externally,
and observing its changes of size, whilst a range of different tones is sounded;
it will then be observed that, the higher the note, the more the  two cartilages
are made to approximate,—whilst they seperate in proportion to the depth of
the tones.*  Upon the upper surface of the back of  the cricoid, are seated
the two  small  Arytenoid  cartilages ; these are  fixed  in  one  direction by a
bundle of  strong ligaments, which tie them to the back  of the cricoid ;  but
they have  some power of moving in other directions upon a kind of articulat-
ing surface.   The direction of the surface, and the mode in which these  car-
tilages are otherwise  attached, cause  their movement to be a sort of rotation
in a plane, which is  nearly horizontal, but partly downwards; so  that their
vertical  planes may be made to separate from each other, and at the same
time to assume a slanting position.   This  change  of place will be better  un-
derstood, when the action of the muscles  is described.   To the summit of
the arytenoid cartilages are attached  the chordae vocales  or Vocal  Ligaments,
which stretch  across to the front  of the thyroid cartilage;  and it is upon  the
condition and relative situation of these ligaments, that their action depends. It

  * In making this observation, it is necessary to put out of view the general movement to
the larynx itself, which the finger must be  made to follow up and down. 
STRUCTURE AND ACTIONS OF THE LARYNX.
457
Fig. 196.
is evident that they may be rendered more or less tense by the movement of
the Thyroid  cartilage just described;
being tightened by the depression  of
its front upon the Cricoid cartilage, and
slackened  by  its   elevation.   On the
other hand, they may  be  brought into
more or less close apposition, by the
movement of the Arytenoid cartilages ;
being made to approximate closely,  or
to recede in such  manner as to cause
the rima  glottidis to assume  the  form
of a  narrow  V, by the revolution  of
these cartilages.   We  shall  now  in-
quire into the actions of  the  muscles
upon the several parts of this apparatus;
and first into those  of the larynx alone.
  604.  The depression of the front of
the Thyroid cartilage, and the conse-
quent tension  of the Vocal Ligaments,
are occasioned by the conjoint action of
the Crico-thyroidei on both sides ; and
the chief antagonists  to  these  are the
Thyro-arytenoidei, which  draw  the
front of the Thyroid back towards the
Arytenoid cartilages, and thus relax the
vocal ligaments.  These two pairs  of
muscles may be regarded as  the prin-
cipal governors of the pitch ofthe notes,
which,  as we shall  hereafter  see, is  al-
most  entirely regulated by the  tension
of the  ligaments;   their action  is as-
sisted, however, by that of other muscles
presently to  be mentioned.—The Arytenoid  cartilages  are made to diverge
from  each other, by means of the Crico-arytenoideus posticus of each side,
which  proceeds from  their outer corner, and turns somewhat round the edge
of the  Cricoid, to be attached to the lower  part of its back ; its action is  to
draw  the outer corner backwards  and downwards, so that the points to which
the vocal ligaments are attached, are separated from  one another, and the
Rima Glottidis is thrown open.   This will be at once seen from the succeed-
ing diagram, in which the  direction of traction of the several muscles  is laid
down.—The action of this muscle is partly antagonized  by that of the  Crico-
arytenoideus lateralis, which  runs forwards  and downwards from the outer
corner of the Arytenoid cartilage;  and its action, with that of its fellow, will
be  to bring the anterior points of  the Arytenoid cartilages into the same
straight line, at the  same time depressing them, and thus to close the Glottis.
This  muscle  is assisted by the  Arytenoideus transversus, which  connects
the posterior faces  of  the Arytenoid  cartilages, and which,  by its contraction,
will draw them together.  By the  conjoint action, therefore, of the Crico-ary-
tenoideus lateralis,  and of  the Arytenoideus transversus, the whole of the ad-
jacent  faces of the Arytenoid  cartilages  will be pressed  together; and the
points  to which the vocal ligaments are attached, will  be depressed.—But if
the Arytenoideus be put in action in conjunction with  the Crico-arytenoidei
postici, the tendency of the latter to separate the Arytenoid cartilages being
antagonized by the  former, its backward action only will be  exerted ;  and  thus
it may  be caused  to  aid  the Crico-thyroideus  in rendering tense the vocal
     39
 Bird's-eye view of larynx from above.  6EH,
the thyroid cartilage, embracing the ring of the
cricoid r u x iv, and turning upon the axis x z,
which passes through the lower horns, c, Fig. 113,
n f, n f, the arytenoid cartilages, connected by
the arytenoideus transversus ; t v, t v, the vocal
ligaments; n x, the right crico-arytenoideus late-
ralis (the left being removed); v kf, the left thyro-
arytenoideus (the right being removed); n I, n l}
the crico-arytenoidei postici; b, b, the cricoary-
tenoid ligaments. 
458
OF THE VOICE AND SPEECH.
ligaments.   This  action  will  be further assisted by the  Sterno-thyroideus,
which tends to depress  the Thyroid cartilage, by pulling from a fixed  point
below ;*  and the Thyro-hyoideus will be the antagonist of this, when it acts

                                   Fig. 197.
  Part of Fig. 196 enlarged, to show the direction of the muscular forces, which act on the Arytenoid
cartilage, q n v s, the right Arytenoid cartilage ;  t v, its vocal ligament; b r s, bundle of ligaments unit-
ing it to Cricoid ; o p, projection of its axis of articulation; h g, direction ofthe action of the Thyro-ary-
tenoideus; n x, direction of Crico-arytenoideus lateralis ; N w, direction of Crico-arytenoideus posticus;
N y, direction of Crytenoideus transversus.

from a fixed point above, the  Os Hyoides  being secured by the opposing con-
traction of several other muscles.—The respective actions of these  muscles
will be best comprehended by the following Table.
'A
so C
Crico-Thyroidei
Stehno-Thyroidei

Thyro-Arytenoidei
Thyro-Hyoidei
Govern the pitch of the notes.
           Depress the front of the Thyroid cartilage on the
             Cricoid, and stretch the vocal ligaments; assisted
             by the Arytenoideus and Crico-arytenoidei postici.
           Elevate the front of the Thyroid cartilage, and draw
             it towards the Arytenoids, relaxing the vocal liga-
             ments.
]...
                     Govern the Aperture ofthe Glottis.   .
p   Crico-Arytenoidei Postici.................Open the Glottis.
p
"3
g. < Crico-Arytenoidei Laterales )       i Press together the inner edges of the Ary-
$  \ Arytenoideus                ) '      \   tenoid cartilages, and close the Glottis.

   605. The muscles which stretch or relax the Vocal ligaments, are entirely
concerned in the  production  of Voice; those which govern the aperture of
the  Glottis  have  important  functions  in  connection with  the  Respiratory
actions in general, and  stand  as guards (so to speak) at the entrance to the
lungs.   Their separate  actions  are  easily made evident.   We can close the
aperture of the Glottis, by an  exertion of the  will, either during inspiration or
expiration;  and it is a  kind  of spasmodic movement  of  this sort, which is

   *  This is not usually reckoned as one of the principal muscles concerned in regulating the
voice;  but that it is so, any one may convince himself by placing his finger just above the
sternum, whilst he is sounding high notes;  a strong feeling of muscular tension is then at
once perceived. 
STRUCTURE AND ACTIONS OF THE LARYNX.
459
concerned in the  acts  of Coughing and Sneezing (§ 381), as well as in the
more prolonged impediments to the ingress and egress of air, which have been
already noticed as resulting  from disordered  states  of the Nervous system
(§ 504).   A slight examination of the recent  Larynx is sufficient to make  it
evident that, when once the  borders  of the Rima Glottidis are brought  toge-
ther by muscular action, the  effect of  strong aerial pressure on  either side,—
whether produced by an expulsory blast from below, or by a strong inspiratory
effort, occasioning a partial vacuum  below,  and consequently an increased
pressure  above,—will be  to  force  them  into closer apposition.  With this
action, then, the  muscles which regulate  the  tension of the vocal ligaments
have nothing to do.  In the ordinary condition of rest, it seems probable that
the Arytenoid cartilages are considerably separated from each other; so  as to
cause a wide opening to intervene between their inner faces, and between the
vocal ligaments, through which the air freely passes; and the vocal ligaments
are at the same time  in  a  state  of complete relaxation.  In order to produce
a vocal sound, it is not sufficient to  put the ligaments into a state of tension;
they  must also be brought nearer to each  other.  That the  aperture  of the
Glottis is greatly narrowed during the  production of sounds, is easily made
evident to one's self, by comparing the time occupied by an ordinary expiration,
with  that required  for the passage of the same quantity of  air during the sus-
tenance of a vocal tone.   Further, the size ofthe aperture is made to vary in
accordance with  the  note  which is being produced; of this, too, any one may
convince himself, by noting the time during which he can hold  out a low and
a high note; from which  it will appear, that the aperture of the Glottis is so
much narrowed in producing a high note, as to permit a much less rapid pas-
sage of air, than  is allowed when a low one is sounded.  This adjustment of
the aperture to the tension of the Vocal Ligaments,  is a necessary condition
for the production of a clear  and definite tone.  It further appears  that, in the
narrowing of the Glottis, which is requisite to bring  the vocal ligaments into
the necessary approximation, the upper points of the Arytenoid cartilages are
caused to approximate,  not only by being made to rotate horizontally towards
each other, but also  by a degree of elevation; so that the inner faces of the
Vocal Ligaments are brought into parallelism with each other,—a condition
which may be experimentally shown to be necessary, for  their being thrown
into sonorous vibration.
   606. We have now to inquire what is the operation of the Vocal Ligaments
in the production of sounds;  and  in order to comprehend this, it is necessary
to advert to the conditions under which tones  are produced, by instruments of
various descriptions,  having some analogy with the Larynx.

  a. These are chiefly of three kinds,—strings, flute-pipes, and reeds or tongues. The Vocal
Ligaments were long ago compared by Ferrein to vibrating Strings; and at first sight there
might seem a considerable analogy, the sounds produced by both being elevated by increased
tension.  This resemblance disappears, however, on more accurate comparison; for it may
be easily ascertained by experiment, that no string so short as the vocal ligaments could give
a clear tone, at all to be compared in depth with that of the lowest notes of the human voice;
and also, that the scale of changes produced by increased tension is fundamentally different.
When strings of the same length, but of different tension, are made the subject of comparison,
it is found that the number of vibrations is in proportion to the square  roots of the extending
forces.  Thus, if a string extended by a given weight produce a certain note, a string extended
by four times that weight will give a note, in which the vibrations are twice as rapid,—awl
this will be the octave of the  other.  If nine times the original weight be employed, the
vibrations will be three times as  rapid as  those of the fundamental note, producing the
twelfth above it.  Now by fixing the larynx in such a  manner, that the vocal ligaments can
be extended by a known weight, Muller has ascertained that the sounds produced by a varia-
tion of the extending force  will not follow the same  ratio; and  therefore the condition of
these ligaments cannot be simply that of vibrating cords.  Further, a cord of a certain length,
which is adapted to give out a clear and  distinct note, equal in depth to the lowest of the 
460
OF THE VOICE  AND SPEECH.
human voice, may be made by increased tension to produce all the  superior notes, which,
in stringed instruments, are ordinarily obtained by shortening the strings.*   But it does not
follow that a  short string, which, with  moderate tension, naturally produces a high note,
should be able, by a diminution of the tension, to give out a  deep one; for, although this
might be theoretically possible, yet it cannot be accomplished in practice; since the vibrations
become irregular 6n account of the diminished elasticity.!  These considerations are in them-
selves sufficient to destroy the  supposed analogy; and to prove that the Chordae Vocales can-
not be reduced to the  same category with vibrating strings.
   6. The next kind of instrument, with which  some analogy might be suspected, is  the
Flute-pipe, in which the sound is produced by the vibration of an elastic column of air con-
tained in the tube; and the pitch of the note is determined almost entirely by the length of the
column, although slightly modified by its diameter, and by the nature of the embouchure or
mouth from which it issues.   This is exemplified in the German Flute, and in the English
Flute or Flageolet; in both of which instruments, the acting length of the pipe is determined,
by the interval between the embouchure  and the nearest of the side apertures; by opening
or closing which, therefore, a modification ofthe tone is produced.   In the Organ, of which
the greater number of pipes are constructed upon this plan, there is a distinct pipe for every
note; and their length increases  in a regular scale.  It is, in  fact, with flute-pipes as with
strings,—that a diminution in  length causes an increase in the number of vibrations, in an
inverse proportion;  so that of  two pipes,  one being half the length of the other, the shorter
will give a tone which is the octave above the other, the vibrations of its column of air being
twice as rapid.  Now there is nothing in the form  or dimensions of the column of air be-
tween the larynx and the  mouth, which can be conceived  to render it at all capable of such
vibrations, as are required to produce the tones of the Human voice; though there is some
doubt, whether it is not  the agent in the  musical tones of  certain Birds.  The length of an
open pipe necessary to give the lowest G of the  ordinary bass voice, is nearly six feet; and
the conditions  necessary to produce the higher notes from it, are by no means those which
we find to exist in the process of modulating the human voice.
   c. We now come to  the third class of instruments, in  which sound is  produced by the
vibration of Reeds or Tongues; these may either possess elasticity in themselves, or be made
elastic by tension.  The reeds  of the Mouth-Eolina, Accordion, Seraphine, &c, are examples
of instruments of this character,  in which the lamina vibrates freely in a sort of  frame, that
allows the air  to pass  out on all  sides of it through a  narrow channel, thus increasing the
strength ofthe blast: whilst in the Hautboy, Bassoon, &c, and in Organ-pipes of similar con-
struction, the reed is attached to one end  of a pipe.  In the former kind, the sound is pro-
duced by the vibration of the tongue alone, and is regulated entirely by its length and elasti-
city ; whilst in the latter,  its pitch is dependent upon this  conjointly with the length of the
tube, the column of air contained in which is  thrown  into simultaneous vibration.  Some
interesting researches on the effect produced on the pitch of a sound given by a reed, through
the union of it with  a tube, have been made by M. W. Weber; and, as they are important
in furnishing data, by  which the real  nature of the vocal organ may be  determined, their
chief results will be  here given.—i. The pitch of a reed may be  lowered, but cannot be
raised, by joining it to a tube.  n. The sinking of the pitch of  the reed thus produced, is at
the utmost not more than an octave,  in. The fundamental  note of the reed thus lowered, may
be raised again to its original pitch, by a  further lengthening of the tube: and by a further
increase is again  lowered,  iv. The length of tube, necessary  to lower the  pitch of the in-
strument to any given point, depends on  the relation which exists between the frequency of
the vibrations  of  the tongue of the reed, and those of the column of air in the tube, each
taken separately.—From these data, and  from those of the preceding  paragraph, it follows
that, if a wind-instrument can, by the prolongation of its tube,  be marie to yield tones of any
depth in proportion to the length of the  tube, it  must be regarded as a flute-pipe;  whilst, if
its pitch can only be lowered  an  octave  or less (the embouchure remaining the same) by
lengthening the tube, we may be certain that it is a reed  instrument.  The latter proves to
be the case in regard  to the Larynx.

   607.  It is evident from the foregoing considerations,  that the action of  the
Larynx has  more analogy to that of reed  instruments, than it has to that either

 •  * Thus  in the Piano-forte, where there are strings for each  note, a gradual shortening is
seen from  the lowest  to the highest; and in the Violin the change of tone is produced by
stopping the strings with the finger, so as to diminish their acting length.
   t Thus it would be impossible to produce good Bass notes on the strings of a Violin, by
diminishing their tension; the  length afforded by the Violoncello or Double  Bass is requisite.
The striking difl'erence between the tone of the Bass strings in the Grand Piano-forte and the
small upright Piccolo, is another exemplification of the same principle; being chiefly due to
the length  and tension of the former, as  contrasted with the shortness and slackness of the
latter. 
ACTIONS OF THE LARYNX.
461
of vibrating strings, or of flute pipes.  There would seem, at first sight, to be
a marked difference in character, between the Chordae Vocales, and the tongue
of any reed instrument; but this difference is really by no  means considera-
ble.   In a reed, elasticity is a property of the tongue itself, when fixed at one
end, the other vibrating  freely; but by a  membranous lamina, fixed in  the
same manner, no  tone would be  produced.  If such a lamina, however, be
made elastic by  a moderate degree of tension, and be fixed in such a  manner
as to be advantageously acted on by a current of air, it will give a distinct
tone.  It is  observed by Muller,  that membranous  tongues made elastic by
tension, may have either of three different forms,   i.  That of a band extended
by a cord, and included  between  two firm plates, so that there is a  cleft for
the passage of air  on each  side of the  tongue,  n. The elastic membrane
may be stretched over the half or  any portion of the end of  a short tube, the
other part being occupied  by a solid  plate, between which and the elastic
membrane a narrow fissure  is left.  in. Two elastic membranes may be ex-
tended across the mouth of a short tube, each covering a portion of the opening,
and having a  chink left open between them.—This last is evidently the form
most allied to the Human Glottis; but it may be made to approximate still more
closely, by prolonging the membranes in  a direction parallel to that of the cur-
rent of  air, so that not merely their edges, but their whole planes,  shall be
thrown  into vibration.   Upon this  principle, a kind of artificial Glottis has
been constructed by Mr. Willis;  the conditions of  action, and  the effects of
which, are so nearly allied to that  of the real instrument, that the similar cha-
racter of the  two can scarcely be doubted.  The following  is his description
of it.  " Let a wooden pipe be prepared of the  form of Fig. 198 a, having a
foot, c,  like that of an organ-pipe, and an upper opening, long and narrow, as
at b, with a point a,  rising at  one
end of it.  If a piece  of leather, or                  Fig. 19,8.
still better, of sheet India-rubber, be         a                       0
doubled round this point, and secur-
ed by being  bound round the pipe
at d with strong thread, as in Fig.
198, b,  it will  give us an  artificial
glottis,  with  its upper edges g h,
which may be  made  to vibrate or
not, at  pleasure,  by  inclining  the
planes of the edges.  A couple of
pieces of cork,  e, f, may  be glued
to the corners, to make them more
manageable.   From this machine,
various  notes may be obtained, by
stretching the edges in the  direction
of their length, g h ;  the notes rising
in pitch with the increased  tension,
although the  length of the vibrating
edge is  increased.   It is true, that a
scale of notes equal in  extent to that
of the human voice, cannot be  ob-
tained from  edges of leather;  but
this scale is much greater in India-rubber than in leather ; and  the elasticity
of them both is so much inferior to  that  of the  vocal ligaments, that  we may
readily  infer that the great scale of the latter is due to its greater elastic pow-
ers."  By other experimenters, the tissue forming the middle coat of the arte-
ries has been used for  this purpose, in  the moist s-tate, with great success ;
with this, the tissue of the vocal ligaments is nearly identical.   It is worthy
                                   39*
Artificial Glottis, 
462
OF THE VOICE AND SPEECH.
of remark that, in all such  experiments, it is found that the two membranes
may be thrown into vibration, when inclined towards each other in various
degrees, or even  when  they are in the same  plane, and their edges only ap-
proximate ;  but that the least inclination from each other  (which is  the posi-
tion the vocal ligaments have during the ordinary state of the glottis, § 605,)
completely prevents  any sonorous  vibrations from being produced.
   608.  The pitch of the note produced  by membranous  tongues, may be
affected in several ways.  Thus, an increase in the strength of the blast, which
has  little  influence on  metallic reeds, raises  their pitch very considerably ;
and in this manner the note of a membranous reed may be raised by semitones,
to as much  as a fifth  above the fundamental.   The addition of a pipe  has
nearly the same effect on their pitch, as on that of metallic reeds ; but it can-
not easily be determined with the same precision.   The effect of the junction
of a pipe  with a  double membranous tongue, is  well  shown in the  Trumpet,
Horn, and other instruments ;  which require the vibration of the lips, as well
as a blast of air,  for the production of  their sound, having no  reed of their
own.  By some,  these instruments have been classed with  Flute-pipes ;  but
the conditions of  their action are entirely different.   The  mouth-piece of the
horn or trumpet  is incapable of yielding  any tone, when a current of air is
merely blown through it;  and the  lips are necessary to convert it into a musi-
cal reed, being rendered  tense by the  contraction of their sphincter, partly
antagonized by the slightly-dilating action of other muscles.   The  variation
of the tension of  the lips is  effected by muscular effort; and several different
notes may be produced with a pipe of the same length ; but there is a certain
length of the  column of air, which  is the one best adapted for each tone ; and
different instruments possess various contrivances for changing this.  It has
been recently ascertained,  that the  length of the pipe prefixed to the  reed, has
also  a considerable influence on its tone, rendering it  deeper in proportion as
it is  prolonged, down to nearly the octave of the fundamental note ; but the
pitch then suddenly rises  again, as in the case of the tube placed beyond the
reed. The researches of Muller, however, have  not succeeded in establishing
any very definite  relation  between the length of the two tubes, in  regard to
their influence on the pitch of the  reed placed between them.
   609.  From the foregoing  statements it appears, that the true theory of the
Voice may now be considered  as  well established, in regard to this essential
particular,—that the sound is the result of the vibrations of the vocal ligaments,
which take place  according  to the  same laws  with those of metallic or other
elastic tongues: and that  the  pitch of the notes  is  chiefly governed by the
tension of these laminae.   With respect, however, to the modifications of these
tones, induced by the shape of the air-passages, both above and  below the
larynx,  by the force of the blast, and by other concurrent  circumstances, little
is  certainly known.  Hence it is, that on the theory of the production of what
are called  falsetto notes, there is much difference of opinion amongst Physi-
ologists.  Some have contended, that these tones are  produced by  the vibra-
tion  of the vocal  ligaments along only a part of  their length; but this is cer-
tainly untrue.  By Muller it is believed, that in the falsetto notes merely the
thin  border of the glottis vibrates, so that the fissure remains  distinctly visible;
whilst in the  production of the ordinary vocal tones, the whole breadth of the
vocal ligaments is thrown into strong vibrations, which traverse a wider sphere,
so that a confused motion is seen in the  lips of the glottis,  rendering its fissure
obscure.  That the tension  of the vocal cords is not diminished (as it ought
to be if only a part of their length were  being used), but is progressively in-
creased, as we pass from the ordinary to the falsetto scale, any one  may con-
vince himself, by placing his finger on  the interval between the thyroid and 
ACTIONS OF THE LARYNX.
463
cricoid cartilages, as formerly described (§ 603).*—A very important  adjunct
to the production of the higher notes, has  been pointed out  by Muller/as
being afforded by  the  modification in the space included between the  two
sides of the thyroid cartilage, which is effected by the thyro-arytenoidei.  He
had  experimentally ascertained, that the introduction of a hollow plug into the
upper end of  the pipe beneath his  artificial larynx (and therefore just below
the  reed), by  diminishing  its aperture, produced a  considerable  elevation  of
the tone.   The action may be imitated in the human larynx, when made the
subject of experiment, by  compressing the thyroid cartilage laterally; and  in
this  manner, the natural voice could be made to extend through a range, that
could otherwise be only reached by a falsetto.
   610.  The strength of the tone produced in the larynx, is much increased
by the resonance of the elastic tissue, which it contains in various other parts ;
but still more, perhaps, by that produced by the air  in  the  trachea, bronchi,
and  pulmonary cells.  This comes to be of great importance in the pheno-
mena of auscultation.   The aerial resonance is loudest where any large body
of air is collected together, as in the trachea, the larger bronchi, an emphyse-
matous  dilatation, or a  cavity resulting from  tubercular softening.   On the
other hand, solidification of the pulmonary tissue will produce a resonance  of
a somewhat different kind.   The  influence of the  prefixed  and superadded
tubes, in modifying the  tones produced by the Human larynx, has been found
by Prof. Muller not  to  be at all comparable to that  which  they exercised
over the artificial larynx;  the reason of which difference does not seem very
apparent.   It appears, however, that there is a certain length of the prefixed
tube,—as  there is a certain distance  of  the  vibrating laminae,  and  a certain
length or  form of the tube above,—which  is most favourable  to the produc-
tion of each note; and the downward movement of the whole vocal  organ,
which takes place when we are  sounding deep  notes,  and its rise during the
elevation  of the tones, have been supposed to have the purpose of making this
adjustment in the length of the  trachea;  but this requires  the supposition,
that the real length of the  trachea is shortened whilst it appears extended,—
for which there.seems no  foundation.  It is  considered by Mr. Wheatstone,
that the column of air in the trachea  may divide itself into harmonic lengths,
and  may produce  a reciprocation of  the  tone  given by the  vocal  ligaments
(§ 560);  and  in this  manner  he considers  that the falsetto notes are to be
explained.  It may be added, that  the partial closing of the epiglottis seems
to assist in the production of deep notes, just  as the partial covering of the
top of a short pipe fixed to a reed will lower its tone;  and that something  of
this  kind takes place  during natural vocalization, would appear, from the re-
traction and depression of  the tongue which accompany the  lowering of the
front of the head, when  the very lowest notes are being sounded.   The  arches
of the palate and uvula become contracted  during the formation of the  higher
tones; but no difference can be perceived  in  their state, whether these tones
be falsetto or not; hence it would  appear that  they  have  no concern  in this
peculiarity; and the purpose of their  increased tension  is probably to main-
tain  their  power of resonance.   The  experiments of  Savart have shown, that
a cavity which only responds to a shrill note, when its walls are firm and dry,
may be made  to afford a great variety of lower tones, when its walls are

  * That the falsetto voice differs in some essential particular from the natural, is evident
from this,—that many persons who possess a considerable range of both, are yet unable  to
unite them, so as to sing through the whole scale without a marked  interruption.   Thus a
gentleman of the Author's acquaintance has a bass voice, ranging from the lowest D of the
.Square Piano to  the second D above; and a  falsetto ranging from the A below this to the E
of the octave above, so as to give a compass of more than three octaves on the whole; yet
the two registers cannot be  smoothly blended. 
464
OF THE VOICE AND SPEECH.
moistened and  relaxed in various  degrees.  This observation  may probably
be* applied also to the trachea.
   611.  These and  numerous other muscular actions, which are employed in
the production and  regulation of the voice, are  effected by an impulse which
can scarcely be termed Voluntary, and the nature of which is  a curious sub-
ject for  inquiry.  It may be  safely affirmed, that the production of sounds is
in itself an Instinctive action; although the combination of these, whether into
music or articulate language, is a  matter of acquirement.   Now it might be
supposed that the Will .has  sufficient power over the  vocal muscles, to  put
them  into any state requisite for its purposes, without  any further condition :
but a little self-experiment  will prove that this is not the case.  No definite
tone can be produced by a Voluntary effort, unless that tone be present to the
mind, during however momentary an interval, either  as immediately conveyed
to it by  an  act of Sensation, recalled by  an act of Conception, or anticipated
by an effort of the imagination.   When thus present, the Will can enable the
muscles to assume the condition requisite to  produce it; but under no other
circumstances does this  happen, except by a  particular mode of discipline
presently to be adverted to.   The action  itself, therefore, must be reduced to
the class of  consensual movements; and we  must  suppose that the will is
exercised in  preparing the  conditions requisite for  it, rather than in directly
exciting it.—That  those who  are  unfortunately labouring  under  congenital
deafness, are thence debarred from  learning the use  of Voice in the ordinary
manner, is  well  known;  the  consensual action cannot  be excited,  either
through sensations of the  present, or conceptions of the past; and the imagi-
nation  is entirely destitute of power to  suggest that which has been  in no
shape experienced.  But such persons may be taught to speak in an imperfect
manner, by causing them  to imitate particular  muscular movements, which
they may be made to see;  and it is evident, that they must be guided in the
imitation and ordinary performance of  those  movements, by  the common
muscular sensations which accompany them, and not  by the sensations con-
veyed through the Auditory nerve, which are ordinarily by far the most pre-
cise guides.   Many instances, indeed, are on record,  in which persons entirely
deaf were enabled to carry on  a conversation in the regular way; judging of
what was said, by  the movements  of the lips and tongue, which  they  had
learned  to connect with particular syllables;  and regulating their own voices
in reply, by their voluntary power, guided by muscular sensation.*

  [In the foregoing account of the Physiology of Voice, the author has been  chiefly guided
by the excellent paper by Mr. Willis in  the Transactions of  the Cambridge Philosophical
Society, vol. iv.; and by the elaborate investigations of Muller and his coadjutors, as detailed
in the Fourth Book of his Physiology.]


                       2.—Of  Articulate Sounds.

   612.  The larynx, as now described, is capable of producing those tones of
which  Voice fundamentally consists,  and the  sequence of which becomes
Music:  but Speech consists in the modification of the laryngeal tones, by
other organs, intervening  between the  Glottis  and the Os  Externum ; so as
to produce those articulate sounds, of which Language is formed.  It cannot
be questioned that Music has its language ; and that it is susceptible of ex-
pressing the emotional states of the mind, among  those  at least who have
been accustomed to associate these with  its varied  modes, to  even a higher
degree  than articulate speech.  But it is  incapable of addressing the intellect,
by conveying definite  ideas of objects, properties, actions, &c, in any other
* See Johnstone on Sensation, p. 128. 
OF ARTICULATE SOUNDS.
465
way than by a kind of imitation, which may be compared to the signs used
in hieroglyphic writing.   These ideas it is the peculiar province of articulate
language to convey; and we find that  the  vocal  organ is adapted to  form a
large number of simple sounds, which may be readily combined into groups,
forming words.   The number of combinations which can be thus produced,
is so inexhaustible, that every language has its own peculiar series ;  no dif-
ficulty being found in forming new ones to express new ideas.  There is con-
siderable diversity in different languages, even with regard to the use of the
simplest of these combinations ; some of them  are more easy of formation
than others, and these accordingly enter into the composition of all languages ;
whilst of the more difficult ones, some are employed in one language,  some
in another,—no one language possessing them all.  Without entering into any
detailed account of the mechanism required to produce each of these simple
sounds, a few general considerations  will be offered in regard to  the classifi-
cation  of them; and the  peculiar defect of Articulation, termed Stammering,
will be briefly treated of.
   613. Vocal sounds are divided into Vowels and Consonants ; and the dis-
tinctive characters of these are usually considered to be, that the  Vowels are
produced by the Voice alone, whilst the sound of the Consonants is formed
by some kind of interruption to the voice, so that they cannot be properly
expressed, unless  conjoined  with  a  vowel.  The distinction may be  more
correctly laid down, however, in this manner :—the  Vowel sounds are con-
tinuous tones, modified by the form of the aperture through which they pass
out; whilst in sounding Consonants, the breath  suffers a more  or less  com-
plete interruption, in its passage through parts anterior to the larynx.  Hence
the really simple Vowel sounds are  capable of prolongation during any time
that the breath can sustain  them ; this is not  the  case, however, with the
real Diphthongal sounds (of  which it will presently appear that the English i
is one) ; whilst it is true of some Consonants.   It seems to have been for-
gotten  by many of those who have written upon this subject, that the laryn-
geal voice is  not essential to the  formation of either vowels or consonants; for
all may be  sounded in a whisper.   It is very evident,  therefore, that the
larynx is not primarily concerned in  their production ; and this has been fully
established by the following experiment.   A flexible tube was introduced  by
M. Deleau through his nostril into the pharynx, and air was  impelled  by it
into the fauces ; then, closing the larynx,  he threw the fauces into the differ-
ent positions requisite for producing  articulate sounds, when the air impelled
through the tube became an  audible whisper.  The experiment was repeated,
with this  variation,—that laryngeal  sounds were  allowed to pass into the
fauces; and each articulated letter was then heard  double, in a proper voice
and in a whisper.
   614. That the  Vowels are produced  by simple modifications in the form
of the  external passages, is easily proved, both by observation and by imita-
tive  experiment.   When the mouth is  opened wide, the tongue depressed,
and  the  velum palati elevated, so as to give  the  freest possible  exit to the
voice,  the vowel a in its broadest form (as in ah) is sounded.*  On the other
hand, if the oral aperture be contracted, the tongue being still depressed, the
sound  oo (the continental u) is produced.   If attention be paid to the state of
the buccal cavity, during the pronunciation of the different vowel sounds,  it
will be found to undergo a great variety of modifications, arising from varieties
of position of the tongue, the cheeks, the lips, and velum palati.   The posi-

  * This sound of the vowel a is scarcely used in our. language, though very common in
most of the continental tongues; the nearest approach to it in English is the a in far : but
this is a very perceptible modification, tending towards au. 
466
OF THE VOICE AND SPEECH.
tion of the tongue is, indeed, one of the primary conditions of the variation
of the sound ; for it may be easily  ascertained that, by peculiar inflexions of
this organ, a great diversity of vowel sounds may be produced, the other parts
remaining the same.  Still there  is a certain  position of all the parts, which
is most favourable to the formation  of  each of these sounds ;  but this could
not be expressed without  a  lengthened  description.  The following table,
slightly altered from that of Kempelen, expresses the relative  dimensions of
the buccal cavity and of the oral orifice, for some of the principal of  these;
the number  5 expressing the largest size, and  the others in like proportion:—

          Vowel.
Sound.	Size	of	oral	opening.	Siz	e of	buccal cavity.
as in ah			5				5
as in name			4				2
as in theme			3				1
as in cold			2				4
as in cool			1				5
These are the sounds  of the  five vowels, a, e, i, o, u, in most  Continental
languages ; and it cannot but be admitted, that  the arrangement is a much more
natural one than that of our own vowel series.  The English a has three dis-
tinct sounds capable of prolongation :*—the true broad a of ah, slightly modi-
fied in far; the a offate, corresponding to the e of French; and the a offall,
which should  be really represented by au.  This last is a simple sound, though
commonly reckoned as  a  diphthong.   In Kempelen's scale, the  oral  orifice
required to produce it would be about 3, and  the size  of the buccal cavity 4.t
On the other hand, the sound of the English i cannot, like that of a true vowel,
be prolonged ad libitum;  it is in fact a sort of Diphthong, resulting from the
transition from a  peculiar indefinite murmur to the sound of e, which takes
its place when we attempt to  continue  it.  The sound oy  or oi, as in  oil,
is a good example  of  the true diphthong; being produced by the transition
from au  to e.  In  the same manner, the diphthong ou, which is the same with
ow in owl, is  produced in the  rapid transition from the broad a of ah,  to  the
oo of cool.—Much discussion has  taken place as to  the true character of y,
when it  commences a word, as in yet, yawl, &c.; some having maintained
that  it is a  consonant, (for the very unsatisfactory reason, that we are in the
habit of  employing a rather than an, when we desire  to prefix the indefinite
article to such words,) whilst  others regard it as a peculiar vowel.  A  slight
attention to the position of the vocal organs during  its  pronunciation, makes it
very clear, that its sound  in such words really corresponds  with that  of the
long (English) e;  the pronunciation ofthe word yawl being the same as that
of eaul, when the first sound is not prolonged, but rapidly transformed into
the second.—The sound of the letter  w, moreover,  is  really of the  vowel
character, being formed in the  rapid transition from oo  to the  succeeding
vowel;  thus wall  might be spelt doall.   Many similar  difficulties might be
removed, and  the  conformity between spoken and written language might be
greatly increased (so as to render far more easy the acquirement of the former
from the latter), by due attention to the state of the vocal organs  in the pro-
duction of the  simple sounds.

  * The short vowel  sounds, as a in fat, e in met, o in pot, &c, are not capable of prolonga-
tion.
  | The mode of making a determination of this kind may here be given, for the  sake of
example.  If the broad a be sounded, the mouth and fauces being opened  wide, and we
contract the oral orifice by degrees, at the same time slightly elevating the point of the
tongue, we gradually  come  to the sound of au;  by still further contracting the orifice, and
again depressing the tongue, we form oo. On the other hand, in sounding e,  the tongue is
raised nearly to  the roof of the mouth; if it be depressed, without the position of the lips
being altered, au is given. 
OF ARTICULATE SOUNDS.                      467
  615.  It is  not very difficult to produce a tolerably good artificial imitation
of the Vowel sounds.  This was accomplished by Kempelen, by means of an
India-rubber  ball, with an  orifice at each end, of which  the lower one was
attached to a reed;  by modifying the form of the ball, the different vowels
could be sounded during  the action of the reed.  He also employed a short
funnel-like tube, and obtained the different sounds by covering its  wide open-
ing to a greater  or less  extent.  This last experiment has been repeated by
Mr.  Willis; who has also found that the vowel sounds might be imitated, by
drawing out a long straight tube from the reed.  In this experiment he arrived
at a curious result:—with a tube of a certain length, the series of vowels, i, e,
a, o, u, was obtained, by gradually drawing it out; but, if the length was in-
creased to a certain point, a further gradual increase would produce the same ,
sequence in an inverted order, u, o,  a, e, i;  a still further increase  would pro-
duce a return to  the  first scale,  and  so on.  When the pitch of the reed was
high, and the pipe  short, it was found that the vowels o and u could not be
distinctly formed,—the proper  tone being  injured by the elongation of the
pipe necessary to produce them;  and this, Mr. Willis remarks, is exactly the
case in the Human voice, most singers being unable to pronounce  u and o
upon their highest notes.
  616.  The  most natural  primary  division of the Consonants is into those
which require a total stoppage of  the breath at  the moment  previous to their
being pronounced, and which, therefore, cannot  be  prolonged;  and  those in
pronouncing which the interruption  is partial, and which  can, like the  vowel
sounds, be  prolonged ad  libitum.   The former have received the  designation
of explosive; and the latter of continuous.—In pronouncing the explosive
consonants, the posterior nares  are completely closed, so  that the exit  of air
through the nose is altogether prevented; and the current may be checked in
the mouth in three ways,—by the approximation of the lips,—by the approxi-
mation  of the point of the tongue to the front of the palate,—and  by the ap-
proximation of the middle of the tongue to the arch of the palate.  In the first
of these modes, we pronounce  the  letters b, and p;  in the second, d and t;
in the third, the hard g, and k.  The difference between b, d, and g, on the
one  hand,  and p, t,  and  k,* on the other, seems to depend on this;—that in
the former group the approximating surfaces are larger, and the breath is sent
through them more strongly at the moment of opening, than in the  latter.—
The continuous consonants may be again subdivided, according to the degree
of freedom with which the air is allowed to make its exit, and the compression
which it consequently experiences,  i. The first class includes those, in which
no passage of air takes place through the nose, and in which the parts  of the
mouth that produce the  sound are  nearly approximated together, so that the
compression  is considerable.   This is the case with v and/, which are pro-
duced by approximating  the upper incisors  to the lower lip; and which stand
in nearly the  same relation to each other, as that which exists between d and
t, or 6 and p.  The sibilant sounds  z and s, stand in nearly the same relation
to each other; they are produced by  the passage of air between  the point of
the tongue and the front  of the  palate, the teeth being at the same  time nearly
closed.   The simple  sound sh is formed, by narrowing the channel between
the dorsum of the tongue and the palate; the  former being elevated  towards
the  latter, through  a considerable  part of its length.   If, in sounding s,
we  raise the  point of the tongue a very little, so as  to touch the palate, the
sound of / is evolved; and in the same manner d is produced from z.   This
class also includes the th;  which, being a perfectly simple sound,  ought to be
expressed by a  single letter, as in  Greek; instead of by two, of which the

  *  For the sake of proper comparison, this letter should be sounded not as kay but as key. 
468                     OF THE VOICE AND SPEECH.
combination  does not really produce  anything like  it.   For producing  this
sound, the point of the tongue is applied to the back of the incisors, or to the
front of the palate, as in sounding t;*  but, whilst there is complete contact of
the tip, the air is allowed to pass out  around it.  n.  In the  second class of
continuous consonants, including the letters m, n, I, and r, the nostrils are not
closed; and  the  air thus undergoes very little compression, even though the
passage of air through the oral cavity  is almost or completely checked.   In
pronouncing m and n, the breath passes through the nose alone; and the dif-
ference of the sound of these two letters, must be due to the variation in the
form of the cavity of the mouth, which acts by resonance.  The letter m is a
labial,  like b ; and the  only difference between the two is, that in the former
,the  nasal passage is  open,  whilst the  mouth remains closed; whilst in the
latter,  the  nose  is entirely closed, and the sound is formed  at the moment of
opening the  mouth.  The same correspondence exists between n and /, or n
and  g  (the particular part of the tongue approximated to the palate  not being
of much  consequence in the pronunciation  of n); and hence  it is  that the
transition from n to t, or from n to g,  is so easy, that the combinations nt and
ng are found abundantly in most languages.   The sound of / is produced, by
bringing the tip of the  tongue into contact with the  palate, and allowing the
air to escape around it, at the same time that a vocal  tone is generated in the
larynx;  it differs, therefore, from  th in  the  position  at which the obstruction
is interposed, as well  as in the slight degree of the compression of the air
which it involves.  The sound of the letter r depends on an absolute vibration
of the  point of the tongue, in a narrow  current of air forced between the tongue
itself and  the palate,   in.  The sounds of the third class are scarcely to be
termed consonants, since they are  merely aspirations, caused by an increased
force of breath.   These are h, and the cAt of most foreign languages  (the
Greek %). The first is a simple aspiration ; the second, an aspiration modified
by the elevation of the tongue, causing a slight obstruction  to the passage of
air,  and an increased resonance  in the back of the mouth. This sound would
become either g or k, if the tongue, whilst it is being produced, were carried
up to touch the  palate.J
   617. These distinctions  come to be of much importance, when  we apply
ourselves to the treatment of defects of articulation.   Great as is the number
of muscles employed in the production of definite vocal sounds, the  number
is much greater for those of articulate  language ; and  the varieties of combina-
tion, which we  are continually forming unconsciously to ourselves, would not
be suspected, without a minute analysis of the separate actions.  Thus, in ut-
tering the explosive sounds, we check the passage of air through the  posterior
nares, in the very act of articulating the letter; and yet, this important move-
ment commonly passes unobserved.   We must regard the power of forming
the  several articulate sounds which have been  adverted  to, and their simple
combinations, as so far resulting from  intuition, that it can in  general be more
readily acquired by early practice, than other actions  of the same complexity ;
so that we may consider these  movements  as having somewhat of  the same
consensual character as  that which has been  attributed to the purely vocalizing
 actions (§ 611).   But there is in many individuals  a  deficiency of the power
 of rightly combining them; from which Stammering and other imperfections
 result.
   618.  Many theories regarding the   nature of Stammering  have been  pro-
 posed ; and there can be little doubt, that the impediment may be attributed to
   * Hence it is easy to understand the substitution of t or d, for the English th, by foreigners.
   | The English  ch is merely a combination oft with sh; thus chime  might be spelt tshime.
   \ The general classification proposed by Dr. M. Hall is here adopted, with some modifica-
 tion as to the details. 
OF ARTICULATE SOUNDS.
469
 a great variety of exciting causes.  A  disordered  action of the nervous cen-
 tres must, however, be regarded as the  proximate cause;  though this may be
 (to use the language of Dr. M. Hall) either of centric or of excentric origin,
 —that is, it may result from a morbid  condition of the ganglionic centre, or
 from  an  undue excitement conveyed through its  afferent nerves.   When of
 centric origin (and this is probably the  most general case), the phenomena of
 Stammering and Chorea have a close analogy to each other ; in fact, stammer-
 ing is frequently one of the modes  in which  the disordered condition of the
 nervous system in Chorea manifests itself.  It is in the  pronunciation of the
 Consonants ofthe explosive class, that the stammerer experiences the greatest
 difficulty. The total interruption to the  breath which they occasion, frequently
 becomes  quite spasmodic ; and the whole frame  is thrown into the most dis-
 tressing semi-convulsive movement, until relieved by expiration.*  In the pro-
 nunciation of the  continuous  Consonants  of the  first class, the stammerer
 usually prolongs them, by a spasmodic continuance of the same action; and
 there is, in consequence, an impeded, but not a suspended respiration.   The
 same is the case with  the / and r in the second class.   In pronouncing the m
 and n, on the other hand, as well  as the aspirates and vowels, it is sometimes
 observed  that the stammerer prolongs the sound, by a full and exhausting ex-
 piration.   In all these cases, then, it seems  as if the muscular sense, resulting
 from each particular combination of actions, became  the stimulus to the  invo-
 luntary prolongation of that action.  In some instances, it is possible that the
 defect may result from malformation of the parts about the fauces, producing
 an  abnormal stimulus  of this kind, in some particular positions of the organ;
 and such cases may  be really benefited by an operation for the removal of
 these parts.  But the effect of the operation is  evidently for the most part  upon
 the Nervous System ;  and it coincides with what may be  frequently observed,
 —that the Stammering is increased  under any unusual excitement, especially
 of  the Emotional  kind.
   619. The method proposed by  Dr. Arnott  for the  prevention of Stammer-
 ing, consists in the connection of all the words by  a vocal intonation, in  such
 a manner, that there shall never be an entire stoppage of the breath.   It is
 justly remarked by Muller,  however, that this plan may afford  some benefit,
 but cannot do everything;  since the main impediment occurs in the middle of
 words themselves.  One important remedial means, on which too much stress
 cannot be laid, is  to study carefully the mechanism of the articulation of the
 difficult letters, and to practise their pronunciation repeatedly, slowly, and
 analytically.   The patient would  at first  do well to practise sentences,  from
 which the explosive consonants are omitted; his chief difficulty, arising  from
 ihe spasmodic suspension of the  expiratory movement, being thus avoided.
 Having mastered these, he may pass on to others, in which the difficult letters
 are sparingly introduced; and may finally accustom himself to the use of
 ordinary language.   One of the chief points to be aimed at, is  to make the
 patient feel that he has command  over  his muscles of articulation; and this
 is the  best done, by gradually leading him from  that which he  finds he can
 do, to  that which  he fears he cannot.   The fact  that stammering  people are
 able to sing their words better than to speak them, has been usually explained
 on the supposition that, in  singing, the  glottis is  kept open, so  that there is
 less liability to spasmodic action;  if, however, as here maintained, the spas-
 modic action is not in  the larynx, but in the velum  palati  and the muscles of
 articulation, the difference must be due to the direction of the attention rather

  *  By Dr. Arnott this interruption is represented as taking place in the larynx ; that such is
not the case, the Author believes that a little attention to the ordinary phenomena of voice will
satisfactorily prove.
    40 
470
INFLUENCE OF THE NERVOUS SYSTEM
to the muscles of the larynx than to those of the mouth.  Every one must
have noticed how much the impediment of Stammerers  is increased, when
they are particularly anxious to speak fluently.
                         CHAPTER  IX.

      INFLUENCE OF THE NERVOUS SYSTEM ON THE ORGANIC FUNCTIONS.

  620. Of the modes in which  the Nervous System influences the Organic
Functions, a part have been  already considered.  It has been shown (§ 183)
that it is  concerned in providing the conditions, either immediate or remote,
under which alone  these functions can be  performed ; so that, when its ac-
tivity ceases, they cannot be much longer maintained.   The  first  mode  in
which it  operates upon them  is, therefore, by producing sensible movements
in the Muscles or other contractile organs, which can be stimulated to action
through it; and the contractions thus induced have usually an important effect
upon  them, which  varies, however, in each  individual case.   Thus, the pro-
cess of Nutritive Absorption,  which is the very first stage in the operations of
Vegetative Life, and which is accomplished in  Plants by the accidental con-
tact of the alimentary materials with the radical fibres, cannot take place in
Animals, until the muscular apparatus of prehension has been set in action by
the Will, that  of deglutition by the  Reflex Function, and that of the intestinal
canal  by  direct stimulation,—the two former kinds of contraction being ac-
complished entirely through  the Nervous System, and the latter being  influ-
enced by it.   The Circulation of Blood, too, is chiefly effected, in the higher
Animals at least, by tire contractions of a muscular organ of impulsion ; which
contractions,  though not  essentially dependent upon Nervous action,  are
nevertheless greatly influenced by it.   The function of Respiration, again,
cannot be maintained even for a short time, without muscular movement, ex-
cited through  the Nervous System.  The functions of Nutrition and Secre-
tion are more  independent of it;  taking  place, as  in Plants, so long as the
conditions are supplied by other functions, without any sensible movements
being actually concerned  in  them.   We shall  presently see,  however, that
they are  subject to  a  peculiar kind of Nervous influence, which  does not
manifest itself in obvious  movement, but in altered performance of the inti-
mate processes themselves;  showing itself in the character of the organized
tissue, or of the secreted product.   The act of Excretion is,  like ingestion,
entirely performed by Muscular movement, dependent upon Nervous agency.
Now, wherever such movements of distant organs are usually performed in
connection with each other, there is an obvious channel  for one kind of sym-
pathy between them ; an interesting example of this, is the contraction  of the
Uterus, which may be  frequently made to occur, when that organ is in a re-
laxed state at  the conclusion of labour, by applying suction or  other irritation
to the nipple.
  621. Sympathetic movements of this kind may be excited  either  through
the Cerebro-Spinal, or  the Ganglionic systems ; and we shall be guided in
our determination  of their channel  in each particular  case, by the distribution
of these  systems respectively to the organ affected.   The sympathetic move-
ments of the Muscles of Animal life appear  to be chiefly, if not entirely, ex- 
ON THE ORGANIC FUNCTIONS.
471
cited through the Cerebro-Spinal  system ;  whilst those of the contractile tis-
sues of the  Viscera (§ 234)  are probably excited  through  nerves,  which,
though connected with  the Cerebro-Spinal system, act under peculiar condi-
tions,  and are  commonly spoken of  as  forming part of the Sympathetic
system.   It  has been  shown (§§ 388—393) that all the  contractile  organs,
which may be excited  through the Sympathetic or Visceral system of nerves,
may also be made to act by stimuli applied to the roots of the Spinal nerves;
but that each Cerebro-Spinal  fibre appears to  pass through  several Ganglia,
before being distributed to the organs which it supplies.
  a. Many speculations have been hazarded, as  to the reasons why the Visceral nerves
are destitute of sensibility; and, at the time  when the Sympathetic was supposed to be
merely an offset from the Cerebro-Spinal system, it was imagined that the use of the gan-
glia upon the roots of the spinal nerves was to " cut off sensation" from  those concerned  in
the " vital and  involuntary  motions."  The influence of Bichat's ingenious hypothesis,—that
the Sympathetic system is  complete and independent, ministering to the functions of Or-
ganic Life, as the Cerebro-Spinal does to those of Animal Life—for a time caused  this idea
to be abandoned.  Since, however, it has been anatomically proved, that a large proportion
of the filaments of the visceral  nerves are derived from the Spinal cord, this  opinion has
been revived, in a somewhat modified form.*   Nevertheless  the evidence in its support is
somewhat vague; especially if the truth of the doctrine formerly urged,—that the Spinal
Cord is not itself a centre of sensation,—be admitted.  For it is only necessary to  suppose,
that the white  fibres of the Sympathetic nerve terminate in the true Spinal Cord, without
proceeding to the Brain, to have an explanation of the absence of sensory endowments  in
the organs to which they are distributed, and  of the complete removal  of the muscles sup-
plied by their motor nerves, from voluntary control.  That a few fibres, of which the actions
cannot be excited under ordinary circumstances, pass on to the Brain, would  seem  probable
from the fact of the sensibility of some parts, in disease, which are totally insensible in their
normal condition;—a fact in the explication of which, the hypothesis just alluded to affords
no assistance.
   622. It appears, then, that  it may be stated as a  general  proposition, that
all the evident movements which  can be excited, by irritation  applied to one
part of the  body, in the  contractile  organs  or tissues of another, are really
effected  through  the true Spinal Cord; whether the contractile organ  be a
powerful muscle, or a  thin and feeble layer of fibres around a blood-vessel or
duct.  Upon the reasons why the fibres of the Visceral nerves should be so
peculiarly separated from the rest, we  can at present  only speculate; but it
may not be  considered improbable that, by their peculiar plexiform arrange-
ment in the  various ganglia through  which they pass, connections  are estab-
lished between remote  organs, which  tend to bring  their actions into closer
relation with each other, than would otherwise be the case.    The existence
of such connections for the purpose of harmonizing the  several movements
of the  Viscera, which are concerned in the  various and complex operations of
Digestion and its  attendant processes, may  be inferred  from the perfect con-
formity which exists between them, during all their different  states  of  regular
action; and  still more, perhaps, from the phenomena of their disordered con-
ditions.   The study of these Sympathies is one of those departments  of Phy-
siology, in which it may be expected that much will be gained by patient and
well-directed investigation.
   623. The  movements immediately concerned in the Organic  Functions, how-
ever, are not influenced by Reflex action alone, but also by Emotional condi-
tions of the  mind.  This is most  obvious in regard to the  Heart.   Every one
must have experienced the disturbance  of its pulsations, consequent upon ex-
citement of the feelings, of almost any description.  But other organs probably
experience similar changes, although of a less manifest character.  It is well
known that  the Sympathetic system is  largely distributed upon the trunks  of

  * See Dr. Alison on the Nerves ofthe Orbit; Edin. Phil. Trans., vol. xv.; and Med. Gaz.
vol. xxviii. p.  378. 
472
INFLUENCE OF THE NERVOUS SYSTEM
the blood-vessels, accompanying them to their minutest ramifications ;  and  it
will be hereafter shown (§ 732), that the fibrous tissue of the walls of the ar-
teries is probably susceptible of influence from these nerves.  There  can be
little  doubt, therefore, that they constitute  the  channel through which Emo-
tions operate, in producing sudden distension of particular parts of the vascu-
lar system, as in blushing, erection, Sic.  And to the same kind of influence,
more gradually exerted, we may very probably attribute the regulation of the
supply of blood which passes to  different secreting  organs, in varying condi-
tions of the system.
   624. But the Sympathetic System does not consist of Cerebro-Spinal fila-
ments alone; nor is its influence  exerted only upon the motor or contractile
tissues of the body.  There  is good evidence, that  the Nervous System has
an immediate action upon the molecular changes, which constitute  the func-
tions of Nutrition, Secretion, &c; and the channel  of such  influence is pro-
bably to be found in that system of peculiar fibres formerly described (§ 244),
which constitutes a considerable proportion of the Visceral  nerves, existing
much more  sparingly in most of  the Cerebro-Spinal, but being abundant in
the Fifth pair.  There is  no  valid reason, however,  to believe that any of the
processes of Nutrition and Secretion are dependent  upon this, or any other,
kind  of Nervous agency.   These processes go  on with great rapidity and
energy in the Vegetable kingdom, in which nothing approaching to a Nervous
System exists; and in the Animal kingdom they take place with equal vigour,
long before  the least vestige  of it appears.   The Embryological researches
of Dr. Barry have fully proved, that in the earliest condition of foetal life, the
germ consists  but of a congeries of cells, which have all originated in a single
one;  and from this mass, the several  tissues  are gradually generated, by  a
process which is  technically called  histological* transformation,—one set of
cells being converted into muscular tissue, anther into nervous tissue, another
into mucous membrane, and  so on.   Now  since this is the  case, it is evident
that all these processes of development must take glace, in virtue of  the inhe-
rent properties of the primary tissue itself; since no nervous influence can be
supposed to operate, before nerves are called into existence.   Throughout the
Animal body,  it may be observed that, the  more Vegetative  the nature of any
function, the less is it  connected with the Nervous  System; and all  the ex-
periments, which have been  regarded as proving that the Organic  functions
are dependent upon Nervous  influence, are really explicable, fully as well,
upon the  supposition that they are  capable of being affected  by it, either in
the way of excitement or retardation (see §  415).  Moreover, there  is  abundant
evidence,  that  Secretion may take  place after the death of the general system,
through the persistence of certain molecular changes, of which the essential
conditions are not  immediately altered; thus Mr. T. Bell  mentions that, in
dissecting the poison apparatus of a Rattle-snake, which  had been  dead for
some hours, the poison continued  to be secreted, so fast as  to require being
occasionally dried off.   This is precisely what might have  been  anticipated,
from  the  independent power  of growth in the secreting cells;  and other acts
of Nutrition are recorded  to have occurred  under similar circumstances.  In
such  a case, the Animal body is reduced to the condition  of a Plant; since
the influence of the Nervous system must then be entirely extinct.   Upon
those who maintain that Nervous agency is a condition essential to those mo-
lecular actions, of  which  Nutrition and Secretion  consist,  it is  incumbent,
therefore, to offer some more unexceptionable proof  of their position than has
yet been given;  since their doctrine is opposed by so many considerations of
great weight.

  * This term is used in contradistinction to morphological, which applies to the alterations
in the form of the several parts of the embryo. 
ON THE ORGANIC FUNCTIONS.
473
   625.  That many of the Organic Functions, however, are directly influenced
by the Nervous System, is a matter which does not  admit  of dispute ; and
this influence, exerted, sometimes  in exciting,  sometimes in  checking, and
sometimes in otherwise modifying them, may well  be compared  to that,
which the hand and heel of the  rider have upon his horse, or  which the en-
gine-driver exerts over a locomotive.  It is most remarkably manifested in the
result of  severe injury of the  Nervous centres,—such as concussion of the
Brain, or  of the Solar plexus (§ 580); for this does not merely produce a sus-
pension of the respiratory and other movements, which minister to the or-
ganic functions, and hence a gradual stagnation  of  the latter,—but a sudden
and complete cessation of the whole train of action ;  which cannot be attri-
buted to any other cause than a positive depressing influence  of some kind,
propagated through the Nervous System.  It will  hereafter appear (§ 701),
that  in such cases even the vitality of the Blood is often affected; the usual
coagulation not taking place after death, so long, at least, as the blood remains
within the vessels.  A similar  general depression may result from Mental
Emotion,  operating  through  the  same  channel;  but this more commonly
has rather a local action, or operates more gradually.—The  influence of the
Nervous System is often especially  exerted, in  giving temporary excitement
to a Secreting process;  which need not be  kept in constant  activity, or of
which circumstances may  occasionally  require an  increase.  This  is the
case, for example, in regard to the secretions connected with the process  of
digestion,—the Saliva, Gastric fluid,  Bile, Pancreatic fluid, Sic ; all of these
being excited by the contact of the  substances  on which they act, with the
surfaces on which their respective ducts open.  The secretion  of Milk, again,
in a nursing female,  may be excited by irritation of the  nipple ; and  the de-
termination of blood to the Mammae  during pregnancy, must  be due to in-
creased action in the part, excited by the  changes  occurring in the  Uterus,
which can scarcely operate otherwise than through the Nervous System.  No
other channel of influence can be well imagined for most of  these operations,
than the Sympathetic system of Nerves ; since the organs in question are for
the most part supplied by it.   There is an  apparent  exception, however,  in
the case of the Salivary and Lachrymal glands, which  are  supplied by the
Fifth pair; but this nerve contains so many organic filaments,  and is so inti-
mately connected with the Sympathetic, as evidently to  supply (in the  head)
the place  of a separate ganglionic system.  It is  by  Nervous influence, that
the mucous  secretion covering the membranes is caused to be  regularly formed
for their protection ; for  it is  shown,  by pathological facts, that, when this
influence is interrupted, and the secretion is no longer supplied, the membrane
losing its protection, is irritated by the air or the fluids with  which it may  be
in contact, and  passes into an inflammatory condition.  This is the  explana-
tion of the fact, which has  been well ascertained, that  the  Eye is  liable  to
suppurate  when the Fifth pair  has been divided; and  that the mucous Mem-
brane of the bladder becomes diseased in Paraplegia.
   626. The influence of particular conditions of the mind, in exciting various
Secretions, is a  matter of daily experience.  The flow of Saliva, for exam-
ple, is stimulated by the idea of  food, especially that of  a savoury character.
The Lachrymal secretion, again, which is continually being formed to a small
extent, for the purpose of bathing  the  surface of the  eye, is  poured  out  in
great abundance under the moderate excitement  of the emotions, either  of
joy, tenderness, or grief. It is checked, however, by violent emotions ; hence
in intense grief the tears do not flow. It is a well-known proof of moderated
sorrow, when this takes place; tears, however, do not bring relief, as is com-
monly believed, but  they indicate that it has been brought.   Violent emotion
may also  suspend the Salivary secretion; as is shown by the well-known test,
                                   40* 
474
INFLUENCE  OF THE NERVOUS SYSTEM
often resorted to in India, for the discovery of a thief amongst the servants of
a family,—that of compelling all the parties to hold  a certain quantity of rice
in the mouth during a  few  minutes,—the  offender being  generally distin-
guished  by the comparative  dryness  of his mouthful, at the end of the ex-
periment.   The influence of  the  emotion of love-of-offspring, in increasing
the secretion of Milk, is well known.  The  formation of this fluid is con-
tinually  going on during the  period of lactation ; but  it  is  greatly increased
by the sight of the infant, or even by  the thought of him, especially when as-
sociated with the idea of suckling : this gives rise to  the sudden rush  of blood
to the gland, which  is known by nurses as the draught, and which occasions
a greatly-increased secretion.   The strong  desire to  furnish milk,  together
with the irritation of the gland  through the nipple, has often  been  effectual
in producing the secretion in girls and old women, and even in  men (§ 853, d).
The  quantity of the Gastric  secretion is  increased  by exhilaration ; at least
if we may judge from the increase of the digestive  powers, under such cir-
cumstances.   Freedom  from mental anxiety  favours  the  secretion of fat;
whilst continual solicitude effectually checks  the disposition.  It has been
stated that total despair  has an equal  tendency, with absence of care, to  pro-
duce this effect; persons left long to pine in condemned cells, without a shadow
of hope, frequently becoming remarkably fat in  spite  of their slender fare.*
The  odoriferous secretion of the Skin, which is much  more  powerful in some
individuals than in others, is increased under the influence of certain mental
emotions (as fear or bashfulness), and commonly also by  sexual desire.   The
Sexual secretions  themselves  are strongly influenced by the condition  of the
mind.  When it is frequently and strongly directed towards objects of passion,
these secretions are increased in amount  to a degree which  may cause  them
to be a very injurious drain on  the powers of the system.  On the other hand,
the active employment of the mental powers on other objects, has a tendency
to render less active, or even  to check altogether, the processes by which they
are elaborated.-!"

  * Fletcher's Physiology, Part II., b, p. 11.
  ■J-  This is a simple physiological fact, but of high moral application.  The Author would
say to those of his younger  readers, who urge the wants of Nature as  an excuse for the il-
licit gratification of the  sexual passion: " Try the effects of close mental application to some
of those ennobling pursuits, to which your profession  introduces you,  in combination with
vigorous bodily exercise (for the effects of which see § 470),  before you assert that the ap-
petite is unrestrainable, and act upon that assertion.   Nothing tends so much to increase
the desire, as the continual direction of the mind towards the objects of its gratification.  The
following observations, which the Author believes to be strictly correct, are extracted from
a valuable little work (anonymous) entitled, "Be not deceived," addressed to Young Men;
they are  directed to those who maintain that, the married state being natural to Man, illicit
intercourse is necessary for  those who are prevented by circumstances  from otherwise grati-
fying the sexual passion. " When the appetite is naturally indulged, that is, in marriage, the
necessary energy is supplied by the nervous stimulus of its natural accompaniment of love
before referred to, which prevents  the injury which would otherwise arise from the in-
creased expenditure of animal power: and in like manner, also, the function being in itself
grateful, this personal attachment performs the further necessary office of preventing im-
moderate indulgence, by dividing the attention, through the numerous other sources of sym-
pathy and enjoyment which it simultaneously opens to the mind.  But, when the appetite
is irregularly indulged, that is in fornication, for want of the  healthful vigour of true  love,
its energies become  exhausted; and from  the want of  the numerous  other sympathetic
 sources of enjoyment in true love, in similar thoughts, common pursuits, and above all  in
 common holy hopes, the mere gross animal gratification of lust is resorted to with unnatural
 frequency,  and thus its powers  become still further  exhausted, and, therefore, still more
 unsatisfying, while, at the  same time, a habit is thus created, and these jointly cause an
 increased craving; and the still greater deficiency in the satisfaction experienced in its indulg-
 ence further, continually, ever in a circle, increases—the  habit, demand, indulgence, conse-
 quent exhaustion, diminished satisfaction, and again demand,—till the mind and  body alike
 become disorganized."  Such considerations as these may, to some persons, appear misplaced 
ON THE ORGANIC FUNCTIONS.
475
   627. No  secretion  so evidently exhibits  the influence  of the  depressing
Emotions, as that of the Mammae ; but this may be partly due to the fact, that
the digestive system of the Infant is a more delicate apparatus for testing the
qualities of that secretion, than any which the Chemist can devise;  affording
proof, by disorder of its  function, of changes in the character  of the Milk,
which no examination of its physical properties could detect.  The following
remarks on this subject are abridged from Sir A. Cooper's valuable work  on
the  Breast.   " The secretion of milk proceeds best in  a tranquil state  of
mind, and with a cheerful  temper :  then the milk is regularly abundant, and
agrees well with the child.  On the contrary, a fretful temper lessens the
quantity of milk, makes it thin and serous, and causes it to disturb the child's
bowels, producing intestinal fever and much griping.  Fits of anger produce
a very irritating milk, followed  by griping in  the infant, with  green stools.
Grief has a  great  influence  on lactation, and consequently upon the child.
The loss  of a near and dear relation, or a change of  fortune, will often so
much diminish the  secretion of  milk, as  to render adventitious aid necessary
for the support of the child.   Anxiety of mind diminishes the  quantity, and
alters  the quality of the  milk.  The reception of a letter which leaves the
mind in anxious suspense, lessens the draught, and the breast becomes empty.
If the child be ill, and  the mother is anxious respecting it, she  complains  to
her  medical  attendant  that she has little milk, and that her infant is  griped,
and has frequent green  and frothy motions.   Fear has a powerful  influence
on the secretion of milk.   I am informed by a  medical  man who practices
much  among the  poor, that the  apprehension  of the  brutal  conduct of a
drunken husband, will put a stop for a time  to the secretion of milk.  When
this happens, the breast feels knotted and  hard,  flaccid from the absence  of
milk, and that which  is  secreted  is  highly  irritating, and some time  elapses
before a healthy secretion  returns.   Terror, which is sudden and great fear,
instantly  stops this secretion."  Of this, two  striking instances, in which the
secretion, although  previously abundant, was  completely arrested by this  emo-
tion, are detailed by Sir A. C.   " Those passions which are generally sources
of pleasure, and which, when moderately indulged, are conducive  to  health,
will, when carried  to  excess, alter, and  even  entirely check  the secretion  of
milk."
   a. The following is perhaps the most remarkable instance on record, of the effect of strong
mental excitement on  the Mammary secretion ; the event could hardly be regarded as more
than a simple coincidence, if it were not borne out by the less striking, but equally decisive
facts already mentioned. " A Carpenter fell into a quarrel with a Soldier billeted in his house,
and was set upon by the latter with his drawn sword. The wife of the carpenter at first
trembled from fear and terror, and then suddenly threw herself furiously between the combat-
ants, wrested the sword from the soldier's hand, broke it in pieces, and threw it away.  During
the tumult, some neighbours came in and separated the men.  While  in this state of strong
excitement, the mother took up her  child from the cradle, where  it lay playing, and in the
most perfect health, never having had a moment's illness; she gave it the breast, and in  so
in a Physiological Treatise—yet the Author feels sure that, by his well-judging readers, he
will not be blamed for adverting to this subject, or for the introduction of the above quota-
tion from a writer, of whom he has no personal knowledge, but whose object must be con-
fessed by all to be laudable.  There seems to be  something in the process of training young
men for the Medical Profession, which encourages in them a laxity of thought and expres-
sion on these matters, that generally ends in a laxity of action and of principle.  It might
have been expected that those  who are so  continually witnessing the  melancholy conse-
quences of the violation of the Divine law in this particular, would be the  last to break it
themselves: but this is unfortunately very far from being the case.  The Author regrets to
be obliged further to remark, that some recent works which have issued from the Medical
press, contain much that is calculated to excite, rather than to repress, the propensity; and
that the advice sometimes given by practitioners to their patients is immoral as well as un-
scientific. 
476   INFLUENCE OF THE NERVOUS SYSTEM ON THE ORGANIC FUNCTIONS.

doing sealed its fate.  In a few minutes the infant left off sucking, became restless, panted,
and sank dead upon its mother's bosom.  The physician who was instantly called in, found
the child lying in the cradle, as if asleep, and with its features undisturbed ; but all his re-
sources were fruitless.  It was irrecoverably gone."*  In this interesting case, the milk must
have  undergone a change, which gave  it a powerful sedative action  upon the susceptible
nervous system of the infant.
  b.  The following, which occurred within the Author's own knowledge, is perhaps equally
valuable to the Physiologist, as an example of the similarly-fatal influence of undue emotion
of a different character;  and both should serve  as  a  salutary warning to mothers, not to
indulge  either in the exciting or depressing passions.  A Lady having several children, of
which none  had manifested any particular tendency to cerebral disease, and of which the
youngest was a healthy infant a few months old, heard of the  death (from acute  hydroce-
phalus) of the infant child of a friend residing at a distance, with whom she had been on
terms of close intimacy, and whose  family had increased almost contemporaneously with
her own.  The circumstance naturally made a strong impression on  her mind;  and she
dwelt upon it the more, perhaps, as she happened, at that period, to be separated  from the
rest of her family, and to be much  alone with her babe.  One morning, shortly after having
nursed it,  she laid the infant in its cradle, asleep and apparently in perfect health;  her atten-
tion was shortly attracted  to it by a noise; and, on going to the cradle, she found her infant
in a convulsion, which lasted for a few minutes, and  then left it dead.—Now, although the
influence of the mental emotion is  less unequivocally  displayed  in this case than in the last,
it can scarcely be a matter of doubt;  since it is natural that no feeling should be stronger in
the mother's  mind under such circumstances, than  the fear  that her own beloved  child
should be  taken from her, as  that of  her friend had  been; and it is probable  that she had
been particularly dwelling on it, at the time of nursing the infant on that morning.
  c. Another instance, in  which the maternal influence was less certain, but in which it was
not improbably the immediate cause  of the fatal  termination, occurred  in a family nearly
related to  the Author's.   The mother had lost several children in early infancy, from a con-
vulsive disorder; one infant, however, survived the usually-fatal period; but whilst nursing
him, one morning, she had been strongly dwelling on the fear  of losing him also, although
he appeared a very healthy child.  In a  few minutes after the infant had been transferred
into the arms of the nurse, and whilst she was urging her mistress to take a more cheerful
view, directing her attention to his thriving appearance, he was seized with a convulsion-fit
and died almost instantly.  Now although there was here unquestionably a  predisposing
cause, of which there is no evidence  in the other  cases, it can scarcely be doubted that the
exciting cause of the fatal disorder is to be referred to the mother's anxiety.  This case offers
a valuable suggestion,—which, indeed, would be afforded by other considerations,—that an
infant, under such circumstances, should not be nursed by its mother, but by another woman
of placid temperament, who had reared healthy children of her own.

   628.  Other Secretions are  in like manner  vitiated by mental Emotions, al-
though the influence is  not always so manifest.  Thus, the halitus  from the
lungs is  sometimes  almost instantaneously affected by bad news, so as to pro-
duce foetid breath.   A copious  secretion of foetid  gas not unfrequently  takes
place in  the intestinal canal, under  the  influence  of any disturbing emotion;
or the usual fluid  secretions  from  its walls  are  similarly  disordered.   The
tendency to defecation which is commonly excited under such  circumstances,
is not, therefore, due  simply to the relaxation of the sphincter  ani (as com-
monly  supposed) ; but is partly dependent on the unusually stimulating cha-
racter of the  faeces themselves.  The same  may be said of the tendency to
micturition, which is experienced under similar conditions:  the change in its

  * Dr. Von Ammon, in his treatise " Die ersten Mutterpflichten und die erste Kindespflege,"
quoted in  Dr. Combe's excellent little work on the Management of Infancy.  Similar facts
are recorded by other writers.   Mr.  Wardrop  mentions (Lancet, No.  516), that having re-
moved a small tumour from behind the ear of a mother, all went well, until she fell  into  a
violent passion; and the child, being  suckled soon afterwards, died in convulsions.   He was
sent  for hastily, to see another child in convulsions, after taking the breast of a nurse who
had just been severely reprimanded;  and he was informed by Sir Richard Croft, that he had
seen many similar instances.  Three others are recorded by Burdach (Physiologie, §  522) ;
in one of them, the infant was seized with convulsions on the right side, and hemiplegia on
the left, on sucking immediately after its mother had met with  some distressing occurrence.
Another case was that of a puppy, which was seized with epilepsy, on sucking its mother
after a fit  of rage. 
SOURCES OF DEMAND FOR ALIMENT.
477
character  becomes  perceptible  enough among many animals, in which it ac-
quires a powerfully-disagreeable odour under the influence of fear; and thus
answers the purpose, which is  effected in others by a peculiar secretion.  It
is  a prevalent, and perhaps not an ill-founded opinion, that melancholy and
jealousy have a tendency to increase the quantity, and  to vitiate the quality,
of the biliary fluid ;  perhaps the disorder of the organic function is more com-
monly the source of the former  emotion, than its consequence; but it is  cer-
tain that the indulgence of  these feelings has a decidedly morbific effect, by
disordering the digestive processes, and thus reacts upon the nervous system
by impairing its healthy nutrition.  On the influence  of mental  emotion in
the Mother, on the Foetus  in utero, some remarks  will be offered hereafter
(§ 938).
                          CHAPTER  X.

                   OF FOOD, AND THE DIGESTIVE PROCESS.

      1.—Sources ofthe Demand for Aliment.—Hunger and Thirst.

  629.  The dependence of all Organized beings upon a supply of aliment,—
in the first place for the development of their fabric, and in the second for the
maintenance of their activity,—is a circumstance of such a familiar character,
that it might not seem worth while  to dwell upon it.   Nevertheless the in-
quiry into  the purposes which  the  aliment  serves in the economy,  and into
the relative values of different articles of food, cannot be advantageously pro-
secuted, until we  have  first determined, with  more  precision,  the causes
which occasion the demand to be set up.  These will be now briefly enume-
rated.
  630.  In  the first place, a due  supply of aliment is  required, for the first
development of the germ into the adult fabric.  In all instances, the essen-
tial character of the act of Reproduction appears to  be the liberation or setting-
free of a cell-germ ;  which, according to the character of the being that gave
origin to it, may be destined to evolve, either a simple cell (as in  the lowest
Cryptogamic Plants), a congeries of cells  having a certain degree of variety
of form  and of difference of function  (as in the higher classes of the Vegetable
kingdom), or a  complex  fabric, composed of an  immense variety of  parts,
most of them departing widely,  in appearance at  least, from the original cellu-
lar  type, and destined to perform a vast variety of  actions,— as we see in the
perfectly developed organism of the higher Animals.  The materials which
are subservient to this evolution, are all derived  from the external world;
either immediately, or through the medium of the parent.  The germs of the
lowly Cryptogamia are thrown at once upon  the world (so to speak), to obtain
their own livelihood; and  they themselves occasion the combination of the
inorganic elements, which they there meet with,  into the organic compounds,
which are to be applied  to the development of  their simple organisms.  In
the Flowering Plants, on the other hand, the germ  is at first supplied with a
store of nutriment,  which has   already undergone this  preparation, by the
agency  of  the parent; and this store, laid up in  the seed, is employed in the
development of the fabric of the young plant, until its  organs are sufficiently
evolved  to enable it to perform the same processes  for itself.  The same plan 
478
OF FOOD, AND THE DIGESTIVE PROCESS.
is invariably followed in the development of the Animal;  the nutriment stored
up  in the ovum being usually sufficient for the evolution  of the fabric, until it
acquires the  power of  ingesting food  for  itself;  and where this  is not  the
case (as in  the Mammalia), a further  provision being adopted, by  which  the
supply  is continued during  a lengthened  period.   Even when  thrown upon
its own resources, the  young Animal  is often  far from  having attained even
the form of its parent;  much less its size;  and in the progress of its evolu-
tion, a greater or less  degree of metamorphosis or change of form  is observa-
ble.  This  is  not usually so much  the case  in the  higher animals, as in  the
lower;  because the  supply  of nutriment  is  proportionally greater  in  the
former, and  serves to carry on  the  development to  a later  period; but  the
changes of  condition  which their  germinal  structure  undergoes  within  the
ovum, are really as remarkable as those which are presented in the early em-
bryos of the latter after their emersion from the egg.
  a. The phenomena of metamorphosis are most familiarly known in the case of Insects,
and Frogs, which were formerly thought  to  be exceptions to all general rules; the Insect
coming forth from the egg in the state of a Worm; and the Frog in the condition of a Fish.
But it is now known that changes of form, as complete as these, occur in a large proportion
of the lower tribes of Animals; so that  the absence of them is the exception.  The  true
mode of viewing these early aspects of Animals of the inferior groups, seems  to be to re-
gard them as foetal or embryonic; thus, the Insect, in its larva state, is essentially a fastus,
as regards the grade of  development of its several tissues and organs; but  it  is a foetus
capable of obtaining its own nourishment.  In this condition it attains its full growth as re-
gards size, though its form remains the same; but it then, in passing into the Chrysalis state,
re-assumes (as it were) the condition of the  embryo within the egg,—the development of
various new parts takes place, at the expense of the nutriment stored up in its tissues,—
and it comes forth in the state of the perfect Insect, which henceforth  takes no more food
than is requisite for the maintenance of the fabric thus evolved, or for the preparation of the
stores to  be imparted to the offspring.—In many of the lower tribes, the animal quits the
egg  at a  still earlier period in comparison; thus it has been lately shown by M. Milne  Ed-
wards, that some of the long Marine Worms consist only of  a single  segment, forming a
kind of head, when they leave the egg; and that the other segments, to the number it may
be of several hundred, are gradually developed from this; the  evolution continuing in some
instances during a considerable  part of life.  In some  of the  Radiated tribes, propagation
actually takes place whilst the animal is yet in its first  or  imperfect form; thus the Medusas
begin life as Polypes, and in this condition they increase by germination or budding,  in the
manner of the true or permanent Polypes.

  631.  It is desirable to bear in mind, that the function of  the Germ is sim-
ply that of occasioning  the combination  of the materials  supplied by the
external world, and of directing the appropriation of those materials.  The
several  parts  of the complex fabric of the higher Animals, contain  a great
variety  of materials;  and it is therefore requisite for its  development, that it
should be duly supplied with all these.—The  demand set  up by  the  fabric,
whilst in course of development or evolution, for the materials of its growth,
constitutes,  therefore,  the primary source of the requirement of food ;  and the
nature of this  must be adapted to the  wants of the being.   Thus,  the fabric
of Plants is  essentially  composed of Cellulose, a compound of Oxygen, Hy-  ¥r
drogen, and  Carbon; and the materials required for the production of this are
simply  Carbonic Acid and Water.   But nearly all Plants form some azolized
compound in the interior of their cells ; for the production of which, Ammo-
nia also is required.   And in those  species, which, like the  Cerealia, form a
large quantity  of azotized compounds, and  store them up  in their seeds, a free
supply  of Ammonia is requisite for the production of the greatest  proportion
which they are capable of generating.—In Animals, again, whose tissue chiefly
consists, of these  very  azotized compounds, or  of modifications  of them, a
constant supply of such is required during the whole period of the develop-
ment  of the  fabric, as well as subsequently;  and if they be not afforded in 
SOURCES OF DEMAND FOR ALIMENT.
479
sufficient amount, the evolution of the organism is either retarded or checked
altogether.*  But there is one tissue, namely, Fat, the peculiar characters of
which are derived from the presence of a non-azotized substance in its cells;
and this cannot be developed, unless there be in the food either oily, saccha-
rine, or amylaceous matters, from any of which the fatty compounds may be
generated.
  632. The full  development of the Animal fabric, however, does not by any
means involve the cessation of the demand for food; in fact, during the whole
period of that development, it may be observed that the  amount of nutriment
ingested is far greater than that which is applied  to  the  simple extension of
the structure (§ 269).   One source of this constant demand is to be found in
the continual waste or disintegration of the fabric, which goes on  to a certain
extent under all circumstances, but which varies in degree according  to  cer-
tain conditions not difficult to be  understood.—All organized substances are
liable, from the peculiarity of their chemical compositibn, to interstitial de-
cay ;  and this operates in the living organism, as  much as in the dead body
(§ 268).   The difference  is, that, in the living fabric,  there is a provision for
at once removing the products of decay, so that they may  be cast out of the
system as soon as possible ;  whilst in the dead body they remain, and act as
ferments, accelerating the  decomposition of other parts.  Now the amount of
this interstitial decay varies with the temperature ; being increased by warmth,
and retarded by cold.   It is consequently greatest  in  warm-blooded animals,
the temperature of whose bodies  is  constantly sustained at a high standard ;
it is reduced to its minimum in the torpid  condition of cold-blooded animals,
which is  brought on by  the agency of  cold; and will be  lowered to nearly
the same degree  in the hybernating  state of certain  Mammalia.—There is
another source of waste and decay, which is  common  to Animals, and all but
the simplest Plants ; this results  from the limited duration  of life  in the indi-
vidual parts, which are most actively concerned in the Vegetative Functions.
We   have   seen  that the  essential  instruments  in the  various functions of
Absorption, Assimilation,  Respiration, Secretion, and Reproduction, are cells;
each  of which goes through a certain  series  of processes and then dies  and
decays,—just as  do the isolated cells, which  compose the entire fabric of the
simplest Cryptogamic  Plants. This is evidenced to us in the Vegetable king-
dom  by the " fall of the leaf;" which is nothing else than the result of the
death and decay of the component cells of  that organ,  after having fulfilled
their peculiar functions  ; these consisting in the preparation or elaboration of
the nutritious sap, from which the various tissues and  secretions of the plant
are subsequently  generated.  The same  process  is  continually  taking place,
though in a less obvious manner, in the Animal body ; the rate  of death  and
renewal of each  group of cells  being greater, as the functions to which it
ministers are energetically performed ; whilst the energy of these operations
is mainly dependent upon the demand set up by the exercise of the Animal
functions, for the  reparation of the Nervous  and Muscular  tissues.
  633. The great source  of waste and  decay in the Animal body, and con-
sequently the chief source of the  demand for food, is the disintegration of the
Nervous and Muscular  tissues, which has been shown to be a necessary con-
dition of their functional  activity.   Every manifestation of Nervous power,
of whatever kind, seems to require the combination of Oxygen with the ele-
ments of Nervous matter; the normal composition of which is thus destroyed,

  * The veiy curious discovery has lately been made, in regard to the integuments of the
Tunicated or Ascidian Mollusca (the lowest class of  that sub-kingdom), that they contain a
considerable quantity of Cellulose; a substance which had not been previously supposed to
be a normal constituent of the Animal Fabric.  See Annales des Sciences Naturelles;  3me
Serie, Zool., torn. v. p. 193 et seq. 
480
OF FOOD, AND THE DIGESTIVE PROCESS.
so that it ceases to be fit to form  part of the body, and is cast out by the va-
rious processes of excretion.  The same is the case in regard to  the Muscu-
lar substance ; the waste of which is conformable to the use made of it.  The
demand for the materials of reparation will follow the same proportion;  and
as the preparation of these materials can  only be  effected  by the agency of
the Vegetative or nutritive functions, the rate at which  these  are performed
will be greatly influenced by the activity  of the Animal functions.  Hence
we see the necessity of regulating the supply of food, in accordance with the
state of the latter ; since a diet which would be superfluous and injurious to
an individual of inert habits, is suitable and beneficial to one who  is leading a
life of  continual exertion.  This difference manifests itself remarkably in the
contrast between Animals of different tribes, whose natural instincts lead them
to different modes of life.  The Birds of most active flight, and the Mammals
which are  required to put forth the greatest efforts  to obtain their food, need
the largest and most  constant supplies of nutriment;  but even the least active
of these classes stand in remarkable contrast with  the inert Reptiles, whose
slow and feeble movements are attended with so  little  waste, that they can
sustain life for weeks and even months, with little or no diminution  of their
usual activity, without a fresh supply of food.*
   634.  Finally, there is a most important  cause of demand for food, amongst
the higher Animals, which does not exist either amongst the lower Animals, or
in the Vegetable kingdom, at least to any great degree.  In  the classes of
Mammals  and Birds, and in that of Insects also, we find a capability of sus-
taining the heat of the body at a fixed standard ; which is usually far above
that of the surrounding medium.   This they are  enabled  to  do, as will  be
explained hereafter,  by a process strictly analogous to ordinary combustion ;
the Carbon and Hydrogen, which are directly supplied by their food, or which
have been  employed for a time in the composition of their living tissues and
then set free, being made to combine with  Oxygen introduced  by the  respira-
tory process, and thus giving out the same  heat, as  if the same materials were
burned in  a furnace.   It will be hereafter shown that the immediate cause of
death in a warm-blooded animal, from which the food has been entirely with-
held, is the inability any longer to sustain the temperature which is  requisite for
the performance of its vital operations (Chap. XVL, Sect. 2).  Hence we see
the necessity for a constant supply of aliment, in  the case of warm-blooded
animals, for  this purpose alone;  and the  demand will be  regulated by the
external temperature.   When the heat is rapidly carried off from the surface
by the chilling  influence of  the  surrounding air  or water, a much greater
amount of Carbon and Hydrogen must be consumed within  the body, to main-
tain its proper heat, than when the medium is  nearly  as warm  as the body
itself;  so  that a diet, which is appropriate  in the former  circumstances, is
superfluous and injurious in the latter;  and the food which is amply sufficient
in a warm climate, is utterly destitute of power to enable it to resist the influ-
ence of severe cold.   Substances rich  in  carbon  and hydrogen, and having
little or no oxygen, afford the most efficient heat-sustaining materials; but it
is an essential  condition  of their due action, that  they  should be  of a kind
that renders them capable of being reduced by the solvent  action of the sto-
mach, and of being  absorbed into the system.
   635.  The demand  for food  is increased by any cause  which creates an
unusual drain or waste in the system.  Thus an extensive suppurating action

   * The materials which are required for the reparation of the Muscular tissue, are chiefly
of a fibrinous nature; those employed for  the renovation of the Nervous substance, would
seem to be fatty matter  with Phosphorus.  But from the peculiar composition of the fatty
matters of the Nervous substance (especially the presence of Azote in them), it seems quite
uncertain from which of the constituents of the food they are really formed. 
                DEMAND FOR ALIMENT.--SENSE OF HUNGER.            481

can be  sustained  only by a large  supply of highly nutritious food.   The
mother who has to furnish the  daily supply of milk, which constitutes the
sole support of her offspring, needs an unusual sustenance for  this purpose.
And there are  states of the  system, in which the solid tissues seem to possess
an unusual tendency to decomposition, and in which an increased supply of
aliment is therefore required.  This is the case, for example, in Diabetes ; one
of the first symptoms of which disease is the craving appetite,  that seems as
if it would be never satisfied.  And there can be no  doubt that, putting aside
all the other circumstances  which have been alluded  to,  there is much differ-
ence amongst individuals, in regard  to the rapidity of the changes which  their
organism  undergoes, and the amount  of food consequently required for  its
maintenance.
  636. The want of solid  aliment  is indicated by the sensation of Hunger;
and that of liquid by thirst.  The former of these sensations is  referred to
the  stomach ; and the latter to the fauces: but although  certain conditions of
these  parts may be the immediate cause  of  the  sensations in question,  they
are really indicative of the  requirements of the system at large.   For the in-
tensity of the  feelings bears  no  constant relation to  the amount  of solid  or
liquid aliment in the stomach ; whilst,  on the other hand, it does  correspond
with the  excess of demand in the  system, over the  supply  afforded by the
blood; and it is caused to abate by  the introduction of the requisite materials
into the circulating fluid, even though this be not accomplished in the usual
manner by the  ingestion of food into the  stomach.
  637. That the sense of Hunger, however, is  immediately dependent upon
some  condition of the Stomach, seems to follow from  ;the fact, that  it is abated,
if not arrested, by section  of the Par Vagum (§ 412) ;  and  that  it  maybe
temporarily alleviated, by introducing into the digestive  cavity, matter which
is not alimentary.   Of the  precise nature of that condition, however, we  have
no certain knowledge.  It  is easy  to prove that many of  the  causes which
have been assigned for the  sensation, are but little, if  at all,  concerned in pro-
ducing it.  Thus, mere emptiness of the stomach  cannot occasion it; since,
if the previous meal have  been  ample, the food  passes  from its cavity some
time before a renewal of the uneasy feeling;  and this  emptiness  may continue
(in certain disordered states of the system) for many hours or even days, with-
out a  return of desire for food.   It cannot be due, as  some have supposed, to
the  action of the gastric fluid upon the  coats of the stomach  themselves ; since
this fluid is not poured into the Stomach, except when the production of it is
stimulated by the irritation of its  secreting follicles.   By Dr. Beaumont it is
thought, that  the  distension of these follicles with the  secreted fluid is the
proximate cause of hunger; but there  is no more reason to believe that the
secretion of Gastric fluid is accumulating during the  intervals when it is not
required, than there is  in regard to  Saliva, the Lachrymal fluid, or any other
secretions, which are occasionally poured out in large quantities under the in-
fluence of a particular stimulus;  and, moreover, it is  difficult to imagine  how
mental emotion, or any impression on the nervous  system alone (which is
able, as is well known, to dissipate the  keenest appetite in a moment), can re-
lieve such distension.—It may, perhaps, be a more probable supposition, that
there  is a certain condition  ofthe Capillary circulation in the Stomach, which
is preparatory to the secretion, and  which is  excited by the influence of the
Sympathetic nerves, that communicate  (as it were) the wants of the  general
system.   This condition may be easily imagined to  be the proximate cause
of the sensation of hunger, by acting on the Par Vagum.   When  food is in-
troduced into the stomach, the act of secretion is directly excited ; the capil-
lary vessels are gradually unloaded ; and the immediate  cause of the  impres-
sion on the par vagum is withdrawn.  By the conversion of the  alimentary
    41 
482
OF FOOD, AND THE DIGESTIVE PROCESS.
matter into materials fit for  the  nutrition of  the  system, the  remote  de-
mand also is satisfied;  and  thus it is  that the  condition of the stomach just
referred  to, is permanently relieved  by the ingestion  of substances that  can
serve as food.   But if the ingested matter be not of a kind capable of solution
and assimilation, the feeling of hunger is only temporarily relieved, and soon
returns in greater force than before.—The theory here given seems reconcile-
able with all that has been  said of the conditions of the sense of hunger ;  and
particularly with what  is known  of  the effect produced  upon it by nervous
impressions, which have a  peculiar  influence  upon the capillary circulation.
It also corresponds exactly with what we know of the influence of the nerv-
ous system, and of mental  impressions,  upon other secretions (§ 624).
   638. The sense of Hunger, like other sensations, may not be  taken cogni-
zance of  by the Mind, if its attention be strongly directed towards  other ob-
jects ;  of this fact, almost every one  engaged in  active occupations, whether
mental or bodily, is occasionally conscious. The nocturnal student, who takes
a light and early evening meal, and, after devoting himself to his  pursuits for
several hours uninterruptedly, retires  to rest with a wearied head and an empty
stomach, but without the least sensation  of hunger, is  frequently prevented
from sleeping by an  indescribable feeling of restlessness and deficiency ;  and
the introduction of a small quantity  of  food  into the stomach will almost in-
stantaneously allay this,  and procure comfortable rest.   Many persons, again,
who desire to take active exercise before breakfast, are prevented from doing
so by the lassitude and even faintness which it induces,—the bodily exercise
increasing the demand for food, whilst it draws off the attention from the  sen-
sation of hunger.
   a. The Author may be excused for mentioning  the following circumstance, which some
years ago occurred to himself; and which seems to him a good illustration of the principle,
that the sense of hunger originates in the condition of the general system, and that its mani-
festation through  a peculiar  action in the stomach, is to be regarded as a secondary pheno-
menon,—adapted, under ordinary circumstances, to arouse the mind to the actions necessary
for the supply of the physical wants,—but capable of being overlooked if the attention of
the mind be otherwise directed.  He was  walking alone through a beautiful  country, and
with much to occupy his mind;  and, having expected to meet with some opportunity of ob-
taining refreshment on his road, he had taken no food since his breakfast.  This expectation,
however, was not fulfilled ; but,  as he felt no hunger, he thought little of the disappointment.
It was  evening before he approached the place of his destination, after having walked about
twenty miles, resting frequently  by the way; and he then began to feel a peculiar lassitude,
differing from ordinary fatigue, which rapidly increased, so that during the last mile he could
scarcely support himself.  The " stimulus of necessity," however, kept him  up;  but on ar-
riving at his temporary home, he immediately fainted. It is obvious  that, in this case, the
occupation of the mind on the objects around,  and on its own thoughts, had prevented the
usual warning of hunger from being perceived; and the effect which succeeded was ex-
actly what was to  be anticipated, from the exhaustion of the supply of food occasioned by
the active and prolonged exertion.

   639.  The conditions of  the sense of Thirst appear to be  very  analogous to
those of hunger.   This sense is not  referred, however, to  the stomach, but to
the fauces.   It is generally considered that it immediately results from an im-
 pression on the nerves of the  stomach  ; since, if liquids  are  introduced into
 the stomach through an oesophagus-tube, they  are just as  effectual in allaying
 thirst, as if they are swallowed  in  the ordinary manner.   It may, however,
be doubted, whether the sense of thirst is not even more immediately connect-
 ed with  the state of the general system, than that of  hunger;  for  the imme-
 diate relief afforded by the introduction of liquid into the stomach, is fully ac-
 counted for by the instantaneous  absorption of the fluid into the  veins, which
 is known to take place when there is a  demand for it, not only from Dr. Beau-
 mont's observations, but from many experiments  made with reference to this
 particular  question.   This demand  is  increased  with almost  equal rapidity, 
NATURE AND DESTINATION OF FOOD.
483
by an  excess  in  the  amount of the fluid excretions ;  and it may be satisfied
without the introduction of water into the stomach* (§  677).  Thirst may also
be produced, however, by the impression made by peculiar kinds of food or
drink upon the walls of the alimentary canal; thus salted  or highly-spiced
meat, fermented liquors when too little diluted, and other similarly irritating
agents, excite  thirst; the purpose of which is obviously to cause ingestion of
fluid, by which they may be diluted.

           2.—Nature and Destination of the Food of Animals.

   640. The substances which are required by Animals for the development
and maintenance  of their fabric, are of  two kinds;—the Organic and the In-
organic.   The former alone are commonly reckoned as aliments; but the lat-
ter are really not  less requisite for the sustenance of the body, which speedily
disintegrates, if the attempt be made to support it upon any organic  com-
pounds in a state  of purity.  In all ordinary articles of diet, however, the in-
organic matters are present in  the requisite proportion; and hence they have
very commonly  escaped notice.   The  nature  of these substances, and the
mode in  which they are  introduced into the body, will be considered  here-
after (§  648).  The Organic  matters,  used  as  food  by Animals, are partly
derived from the  Animal, and partly from the Vegetable kingdom;  and  they
may vbe  conveniently  arranged  under  the four following  heads :t—1. The
Saccharine group, including all those  substances, derived from the Vegetable
kingdom, which are analogous in their composition  to Sugar ;—consisting of
oxygen,  hydrogen, and carbon, alone; and having the two first present in the
proportions to form water.  To this group  belong  starch, gum, woody  fibre,
and the various tissues of Plants; which closely resemble each other in the
proportion of  their elements, and which may be converted into Sugar by che-
mical  processes of a simple kind.—2. The Oleaginous group, including oily
matters,  whether  derived from the Vegetable kingdom, or from the fatty por-
tions of Animal  bodies.  The characteristic of  this  class, is the great pre-
dominance of hydrogen and carbon, the small proportion of oxygen, and the
entire  absence of nitrogen.—3.  The Albuminous group, comprising all  those
substances, whether derived  from the Animal  or Vegetable kingdom, which
are closely allied to Albumen, and therefore to  the majority of the Animal
tissues, in their chemical composition.   In this  group, a large proportion of
azote is  united with the oxygen, hydrogen, and  carbon of the preceding.—
4. The Gelatinous group, consisting of substances derived from Animal bodies
only, which are closely allied to Gelatine in  their composition.  These also
contain azote; but the proportion of their components differs from that of the
preceding.
   641. The compounds ofthe  Saccharine group cannot, without undergoing
a metamorphosis, form part of any Animal  tissue ; as there is none which
they resemble in  composition.  It will be shown, however, that they are con-
vertible,  within the Animal body, into those of the Oleaginous group; and,
like them, may be  deposited in the  form of Adipose matter. There  is no
other tissue in the body, into which they can enter without considerable change;
for all others  are  azotized; and it seems extremely improbable that non-azo-
tized compounds can,  under any circumstances, be converted within the  body
into compounds of the albuminous or gelatinous groups.

   * This was among the remarkable results of the injection of fluid into the veins,  in the
Asiatic Cholera.
  f Dr. Prout's  classification of alimentary substances is here adopted, with a slight modifi-
cation ; not as being altogether unexceptionable, but as being, in the Author's opinion, the
most convenient hitherto proposed. 
484               OF FOOD, AND THE DIGESTIVE PROCESS.

   642.  The application of the substances forming the Albuminous group, to
the support of  the Animal body, by affording  the  materials for  the nutrition
and re-formation of its tissues, needs little explanation.   The proportions of
the four ingredients of which they are all composed, are so nearly the same,
that no  essential difference appears to exist among them; and it is a matter of
little consequence, except as far as the gratification of the palate is concerned,
whether we feed upon the flesh of animals (fibrine), upon the white of egg
(albumen), the curd of milk (caseine), the grain of wheat (gluten), or the seed
of the pea (legumin).   All these substances are reduced in the stomach to the
form of albumen; which resembles the gum of Plants, in being the raw ma-
terial, as it were, out of which the various fabrics of the body are constructed.
But the  rule holds good, with regard to these also, that  by being made to
feed constantly on the same substance,-—boiled white of egg, for instance, or
meat deprived of the  principle  (osmazome) that gives it flavour,—an animal
may be effectually starved; its  disgust at the food being such, that even if it
be swallowed, it is not digested.  It is very interesting to remark that, in the
only instance in which Nature  has  provided a single article of food for the
support of the animal body, she has  mingled  articles from the three  first of
the preceding groups.  This is  the case in Milk, which contains a conside-
rable quantity of  an albuminous substance, caseine, which forms its curd ; a
good deal of oily matter, the butter;  and no inconsiderable amount of sugar,
which is dissolved in  the whey.  The proportions of these vary in different
Mammalia; and  they depend in part upon the nature  of the food supplied
to the Animal  that forms the milk ; but the substances are thus combined in
every instance.—Although the greater part of the organized tissue of Animals
is formed at the expense  of the Albumen and Fibrine of their blood, yet
many of them  also contain a large quantity of Gelatine.   It seems certain
that this gelatine may be produced out of fibrine  and albumen;  since in ani-
mals that are supported on these alone, the nutrition of the gelatinous tissues
does not seem to  be impaired.  But  it also appears, that gelatine taken in as
food may be applied to this purpose;  for ordinary experience shows, that be-
nefit is derived from jelly, soup, broth, Sic ; peculiarly by persons who have
been suffering  under exhausting diseases, such as fevers.  But  it also ap-
pears  certain, that it cannot be  applied to the nutrition of  the Albuminous
tissues.   Some important experiments have been  recently made in Paris on
this subject, with a  view of determining how far the soup made from crushed
bones, which constituted a principal  article of diet in the  hospitals of Paris,
was adequate for the  support of the  patients.   The result  of these has been
quite confirmatory of previous  conclusions,—namely, that  Gelatine may be
advantageously mixed with albumen, fibrine, gluten, &c, and  those other in-
gredients which exist in meat-soup and bread;  but that, when taken alone, it
has little more power of sustaining life  than  sugar or starch possesses; and
that, even when bread is united with gelatine-soup, it does not give it the re-
quisite power of nutrition.
   643.  If the non-azotized compounds which exist  so largely in the food of
Herbivorous animals, be not destined to  form part (in any considerable degree
at least)  of their tissues, the question  arises,—what becomes  of them?   It is
not enough to  say that they are  deposited as Fat; since it is only when a large
quantity of them is taken in, that there  is any increase in the quantity of fat
already in  the  body.   We shall  hereafter see, that  they are used up  in the
process of Respiration; being burned-off within the body, for the purpose of
keeping up its temperature.  The process will be hereafter considered more
in detail; and  at present we need only stop  to remark upon the  adaptation
between the food provided for animals in different climates, and the amount
of heat which it is necessary for them to produce.  Thus the bears, and seals, 
NATURE AND DESTINATION OF FOOD.
485
and whales, from which the Esquimaux and the Greenlander derive their sup-
port, have an enormous quantity of fat in their massive bodies:  this fat is as
much esteemed as an article of food among these people, as it would be thought
repulsive by the inhabitants of southern climates; and by the large quantity of
it  they consume, they are  able  to support the bitterness of an Arctic winter,
without appearing to suffer more from the extreme cold, than do  the residents
in more temperate climates during their winter.  On the other hand, the ante-
lopes,  deer, and wild cattle, which form a large proportion of the animal food
of savage or half-cultivated nations inhabiting temperate or tropical regions, pos-
sess very little fat; and the comparatively small supply of carbon and hydro-
gen, whose  combustion is required to keep up  the bodily temperature of the
inhabitants of those regions, is derived from the flesh of those animals, in the
manner that will be presently explained.   Every one knows how much less
vigorous the appetite  becomes,  during the heat of summer, than it is during
the colder portion of the year;  and  this is a natural result of the diminished
demand  for the fuel required to  maintain  the temperature.  And one great
means of preserving the health, during a prolonged residence in a hot climate,
is  to attend to the dictates of Nature, in regard to the quantity of food ingested;
instead of endeavouring (as is the prevalent practice) to stimulate the appetite
by artificial  provocatives.
   644. The maintenance of the bodily temperature  in Carnivorous animals,
appears to depend upon the combustion of the carbon and hydrogen set free
by the disintegration of their Nervous  and Muscular tissues: this disintegra-
tion  taking  place with much more rapidity, in consequence of their almost
unceasing activity, than it does in the Herbivorous animals, which lead com-
paratively inactive lives.  Every one who has visited a menagerie, must have
noticed the continual restlessness of the Tigers, Leopards, Hyaenas, &c, which
keep  pacing from one end of their narrow  cages to the other;  and it would
seem as if this restlessness were  a  natural instinct, impelling them to use mus-
cular exertion sufficient for the metamorphosis of an adequate amount of tissue,
that enough carbon and hydrogen may be set free for the support of the respi-
ratory process.   And we  see a  corresponding activity in the Human hunters
of the  swift-footed Antelope and  agile Deer, which answers a similar purpose;
and which is remarkably contrasted with the stupid inertness of the inhabitants
of the frigid zone, which is only occasionally interrupted by the necessity of
securing the supplies of food afforded by the massive tenants of their seas.—
The nutrition of the Carnivorous  races may, then, be thus described.  The
bodies of the animals upon which they feed contain  flesh, fat, &c, in nearly
the same proportion as their own; and all, or nearly all, the aliment they con-
sume, goes to supply the waste  in the fabric of their own bodies, being con-
verted into its various forms of tissue.  After having remained in this condition
for a certain time, varying according  to the use that is made of them, these
tissues undergo another metamorphosis, which ends in restoring them to inor-
ganic matter;  and  thus give back to the Mineral world the materials which
were drawn off from it by Plants.  Of these Materials, part are burned off, as
it were, within the body, by union with the oxygen of the air, taken in through
the lungs;  and are discharged from these organs, in the form of carbonic acid
and water: the remainder are carried off in the liquid form by other channels.
Hence we  may  briefly express the destination of their food in the following
manner:—
  Food consisting of|        <•  T"  '   ->  A  l th'   f Carbonic acid and Water
  albumen,  fibrine, I Convert- S nT~vmg ,(    , tms  J   thrown off by respiration.
  and other azotized f ed into ) OTsamzea (  metamor- ^ Urea and biliary matter, &c.,
         i                i.  tissue. ) phosed into  ,      ~.,  /,      ' •
  compounds      J        v        JV          \thrown offbyother excretions.
                                  41* 
486
OF FOOD, AND THE DIGESTIVE PROCESS.
   645. But in regard to the Herbivorous animals, the case is different.  They
perspire much more abundantly, and their temperature is thus continually kept
down.  They consequently require  a more  active combustion, to develope
sufficient bodily heat;  and the materials  for this  are  supplied, as we have
seen, by the non-azotized portions of their food, rather than by the metamor-
phosis of their own tissues, which takes place with much less rapidity than in
the Carnivorous tribes.   Hence we may thus express the destination of this
part of their food; that of the azotized matter, here much smaller  in amount,
will be the same as in the preceding  case:—
  Starch, oil,  and ~i   partly   (av     ) but chiefly C Carbonic acid and Water, dis-
  other non-azotized > converted  <    ipose r  tnrown 0g- J engaged by the respiratory
  compounds     )   into   (         ) directly as ( process.

The proportion of the food deposited as fat, will depend in part upon the sur-
plus which remains, after the necessary  supply of materials has been afforded
to the respiratory process.  Hence, the same quantity of food being taken, the
quantity of fat will be increased by  causes that check  the perspiration, and
otherwise prevent  the  temperature of the  body from being lowered, so  that
there is need of less combustion within the  body to keep up its heat.  This is
consistent with the teachings of experience respecting the fattening of cattle;
for it is well known that this may be accomplished much sooner, if the animals
are shut up in a warm dwelling and covered with cloths, than if they are freely
exposed in the open  air.
   646. Now the condition of Man may be regarded as  intermediate between
these two extremes.   The construction of  his digestive apparatus, as well as
his own instinctive propensities, point to a mixed diet  as  that -which is best
suited to his wants.   It does  not appear  that  a diet composed of ordinary
vegetables  only, is favourable to  the full development of either his bodily or
mental powers;  but this cannot be said in  regard to a diet of which bread is
the chief ingredient, since the gluten  it contains appears  to be as well adapted
for the nutrition of the animal tissues, as does the flesh of  animals.   On  the
other hand, a diet composed of animal flesh alone is  the least economical that
can  be conceived; for, since the  greatest demand  for food is created in him
(taking a man of average habits, in regard  to activity and the  climate  he in-
habits), by  the necessity for a supply of carbon and  hydrogen to support his
respiration, this want may be most advantageously fulfilled by the employment
of a certain quantity of non-azotized  food, in which these ingredients predomi-
nate.  Thus  it has been calculated, that, since fifteen pounds of flesh contain
no more carbon  than four pounds of starch, a savage with one carcass  and an
equal weight of  starch, could support life for the same length of time, during
which another restricted to animal food would require five such  carcasses, in
order to procure the carbon  necessary for respiration.  Hence we see the im-
mense advantage as to economy of food, which a fixed agricultural population
possesses  over those wandering tribes of hunters, which still people  a large
part both of the old and new continents.   The mixture of the azotized and
non-azotized  compounds (gluten and starch), that exists  in wheat flour, seems
to be just that which  is most useful to Man; and hence we see the explanation
of the fact, that, from very early ages, bread  has  been regarded as the "staff
of life."  In regard to the nutritious properties of different articles of vegetable
food, these may be generally estimated  by the proportion of azote they con-
tain ; which is in almost every instance less than that existing in good wheat
flour.
   647.  The following  table represents  the relative  quantity of  Nitrogen in
different articles used as food; and thus shows their relative applicability to 
f
NUTRITIVE POWER OF DIFFERENT KINDS OF FOOD.
487
the maintenance and reparation of the body.*  Those which are poorest in
nitrogen, are richest in Carbon and  Hydrogen;  and are, therefore, the best
adapted to serve as the pabulum for the heat-sustaining process.  It is to be
borne in mind, however, that no table of this kind, founded simply upon the
Chemical composition of the various substances,  can indicate their respective
fitness as articles of diet; since this depends also  upon the facility with which
they are reduced by the digestive process, and afterwards assimilated.   Thus
an aliment, abounding in nutritive matter, may be  inferior to one which really
contains a  much  smaller  proportion, if only a part in the first case, and the
whole in the  second, be readily taken up by the system.—In  the following
table, Human Milk is taken as the standard; and the quantity of Nitrogen it
contains is expressed by 100.  But it must be borne  in  mind that this sub-
stance is intended for the nourishment of a being  that passes nearly the whole
of its time in  a quiescent state.; and must not be supposed to be adapted for
the sole maintenance of the Human body in a state of  activity.   In fact, it is
inferior in its proportion of Caseine (the substance of  which  alone the azote
forms a part) to the milk of most, if  not all, other Mammalia ;  their young
bringing their animal functions into exercise at a much earlier period than the
Human infant.
Rice
Potatoes
Turnips
Rye  .
Maize  .
Barley
Human milk
Cow's milk  .
Oyster
Yolk of eggs ,
Cheese
Eel, raw
----boiled
Liver of crab
-Mussel, raw
------boiled
Ox liver, raw
Pork-ham, raw
-------boiled
                 Vegetable.
.  .  81    Oats      .    .    .138
  .  84    White bread  .    .  .  14-2
.  . 106    Wheat    .    .  119-144
  . 196    Carrots      .    .  .  150
100-185    Brown Bread   .    .  166
  . 125    Agaricus cantharellus   201
Peas   .    .    .   . 239
Agaricus russula     . 264
Lentils    .    .     .276
Haricot beans    .   .283
Agaricus deliciosus   _ 289
   100
   237
   305
   305
331-447
  . 434
   428
   471
   528
   660
   570
   539
   807
        Animal.
Salmon, raw
■-----boiled
Liver of Pigeon .
Portable soup
White of Egg   .
Crab, boiled  .
Skate, raw
----boiled  .
Herring, raw
-------boiled"
-------milt of .
Haddock, raw
--------boiled
776
610
742
764
845
859
809
956
910
808
924
920
816
Beans
Flounder, raw
-------■ boiled
Pigeon, raw
------boiled
Lamb, raw
Mutton, raw  .
------boiled
Veal, raw
----boiled
Beef, raw
----boiled
Ox lung
320
954
756.
827
833
773
852
873
911
880
942
931
  648.  Besides these substances, there are certain Mineral ingredients, which
may be said to constitute part of the food of Animals ; being necessary to their
support, in the same manner as other mineral substances are necessary to the
support of Plants.   Of  this kind are common salt, and also phosphorus, sul-
phur, and lime, either in combination or separate.   The uses of Salt are very
numerous and important.   It consists of two substances of opposite qualities,
muriatic acid  and soda ;  and the former is the essential ingredient in the gastric
juice; whilst the latter performs a  very important part in the production of
bile.   Phosphorus is chiefly required to be united with fatty matter, to serve
as the material of the  nervous tissue;  and to be combined with oxygen and
lime, to form  the  bone-earth, by which the bone  is  consolidated.   Sulphur
exists  in  small quantities in  several animal tissues ; but  its  part is by no
means so important, as that performed by phosphorus.  Lime is required for
the consolidation of the  bones;  and for the production of  the shells and other
ihlossberger and Kemp, in Philosophical Magazine.  Nov. 1845. 
%
488               OF FOOD, AND THE DIGESTIVE PROCESS.

hard parts, that form the skeletons of the Invertebrata.  To these  ingredients
we may also add Iron, which is a very important  element in the red blood of
Vertebrated animals.—These substances are contained, more or less  abund-
antly, in most  articles generally used as food ;  and where they are deficient,
the animal suffers in consequence, if they are not  supplied in any other way.
Thus common Salt exists, in  no  inconsiderable  quantity, in the flesh  and
fluids of animals, in milk, and in the egg: it is not so abundant, however, in
plants; and the deficiency is usually supplied to herbivorous animals by some
other means.  Thus salt is purposely mingled with the food of domesticated
animals ; and in most parts of the world inhabited by wild cattle, there are spots
where it exists in the soil, and to which they resort to obtain it.  Such  are the
"buffalo licks" of North America. Phosphorus exists also in the yolk and white
of the Egg, and in Milk,—the substances on which the young animal subsists
during the period of its most rapid  growth ; and it abounds, not only in many
animal substances used as food, but also (in the state of phosphate of lime or
bone-earth) in the seeds of many plants, especially the grasses.  In smaller
quantities it is found in the ashes of almost every plant.  When flesh, bread,
fruit, and husks of grain, are used as the chief articles of food, more phosphorus
is taken into the body than it requires ; and the excess has to be carried out in
the excretions.   Sulphur is derived alike from vegetable and animal substances.
It exists in flesh, eggs, and milk; also in the azotized compounds of plants;
and (in the form of sulphate of lime) in most of the river and spring-water that
we drink.  Iron is found  in the yolk of egg, and in milk, as well as in  animal
flesh; it also exists in small quantities in  most vegetable substances used as
food  by Man,—such as potatoes, cabbage, peas,  cucumbers, mustard, &c.;
and probably in most articles, from which other animals derive their support.
Lime is one of the most universally diffused of all mineral bodies; for there
are very few animal or vegetable substances, in which it  does not exist.   It
is most commonly taken in, among the higher animals, combined with Phos-
phoric acid;  and in this state it exists largely in the seeds of most grasses,
especially in wheat flour.  If it were not for their  deficiency in Phosphate
of lime, some of the Leguminous seeds would be more nutritious than wheaten
flour; the proportion of azotized matter they contain being greater.   A con-
siderable quantity of lime  exists, in the state of carbonate and sulphate, in all
hard water.
  649. The absolute quantity of  food, required for the maintenance  of  the
Human body in health, varies  so  much  with the age, sex, and constitution
of the  individual, and with the circumstances  in  which he  may be  placed,
that it would be absurd to attempt to fix any standard which should apply to
every particular case.  The appetite is the only sure guide for the supply of
the wants of each; but its indications must  not  be  misinterpreted.   To eat
when we are hungry, is an evidently natural disposition; but to  eat as long
as  we are hungry, may not always be prudent.  Since the feeling of hunger
does not depend so much upon the state of fulness or emptiness of the  sto-
mach, as upon the condition of the general system, it appears evident that the
ingestion of food cannot at once produce  the  effect of dissipating it,  though
it will do  so after a short  time ; so  that, if we eat with  undue  rapidity, we
may continue swallowing food long after we have taken as much as will really
be required for the wants  of the system ; and every superfluous  particle is
not merely useless, but injurious.   Hence, besides its other important ends,
the process of thorough  mastication  is important, as  prolonging the meal,
and giving time to the system to become acquainted (as it were) that the sup-
ply of its wants  is in progress ; so that its demand may be abated in due time
to  prevent the ingestion of more than is required.   It is very justly remarked
by Dr. Beaumont, that the cessation of this demand, rather than the positive 
REQUISITE AMOUNT OF FOOD.
489
sense of satiety, is the proper guide.  " There appears to be a sense of per-
fect intelligence conveyed to the encephalic centre, which, in health, invariably
dictates what quantity of aliment (responding to the  sense of  hunger and its
due satisfaction) is naturally required for the purposes of life;  and  which, if
noticed and properly attended to, would  prove the most salutary monitor  of
health, and effectual preventive of disease.  It is not the sense of satiety,
for this is  beyond the point of healthful indulgence,  and is Nature's earliest
indication of an abuse and overburden of her powers  to replenish the system.
It occurs immediately previous to this ; and may be known by the pleasurable
sensations of perfect satisfaction, ease and quiescence of body and mind.   It
is when the stomach says, enough ; and  it is  distinguished from  satiety by
the difference of sensations,—the latter saying too much.''''   Every medical
man is well aware how  generally this rule  is transgressed; some persons
making a regular practice of eating to repletion ; and others  paying far too
little attention to the preliminary operations, and thus ingesting  more than is
good for them, even though  they may actually leave  off with an appetite.
   650.  Although no universal law can be laid down  for individuals, however,
it is a matter of much practical  importance to be able to form a correct ave-
rage estimate.  It is from the experience afforded by the  usual consumption
of food by large bodies of men, that our data are obtained ; and these data
are sufficient to enable us to predict with tolerable accuracy what will be  re-
quired by similar  aggregations, though  they  can afford no guide to the con-
sumption of individuals.—We shall first consider the quantity sufficient for
men in regular active exercise ;  and then inquire how far  that may be safely
reduced for those who lead a more  sedentary life.—The Diet-scale  of the
British Navy may be advantageously taken as a specimen of what is required
for the first class.   It is well known that an  extraordinary improvement has
taken place in the health of seamen during the last 80 years; so that  three
ships can now be kept afloat with only the same number of men, which were
formerly required for two.  This is due to the improvement in the  quality of
the food, in combination with other prophylactic means.   At  present it may
safely be affirmed, that it would not be easy to  conceive of any diet-scale
more adapted to answer the required purpose.  The health  of crews that
have been long  afloat, and  have been exposed to every variety of external
conditions, appears to be preserved (at least when they are under the direc-
tion of judicious  officers), to  the full as well as that of persons subject  to
similar vicissitudes on shore ; and there can be no complaint of insufficiency
of food, although the allowance cannot be regarded as superfluous.   It con-
sists of from 31 to 35£ ounces of dry nutritious matter daily; of this 26 oz.
are vegetable ;  and  the rest  animal;  9 oz. of salt  meat, or 4£ oz. fresh,
being  the  allowance  of the  latter.  This is found  to  be amply  sufficient
for the support of strength ; and  considerable variety is produced, by ex-
changing various parts of the diet for other articles.  This, however, is some-
times done erroneously; thus 8 oz. of fresh vegetables, which  contain only
1| oz. of solid nutriment, are exchanged for  12 oz. of flour, which is almost
all nutritious.   Sugar and Cocoa are also allowed ;  partly in  exchange for  a
portion of the Spirits formerly served out, the  diminution of which, especially
in the case of boys, has been attended with great benefit.
   651. A  considerable reduction  in  this amount is of  course admissible,
where  little bodily exertion is required, and where there  is less exposure  to
low temperatures.  In the case of Prisoners, the diet should of course be as
spare as possible, consistently with health; but it should be  carefully modi-
fied, in individual cases,  according to several  collateral  circumstances, such
as depression of mind, compulsory labour, previous intemperate habits, and
especially  the  length of confinement.  It  has been supposed by some, that 
490               OF FOOD, AND THE DIGESTIVE PROCESS.

prisoners require a fuller diet than  persons at large;  this is probably erro-
neous ;  but more variety is certainly desirable, to counteract, as far as possi-
ble, the depressing influence of their condition  upon  the  digestive powers.
The circumstances which occurred at the Milbank Penitentiary in 1823, form
a lamentable warning against the reduction of the diet-scale to an insufficient
amount.   The allowance to the prisoners  had formerly been from 31 to 33
oz. of dry nutriment daily, and  the  prison was considered  healthy;  but in
1822, it was reduced to 21  oz.  The health of the  prisoners continued  un-
broken for nearly six months ; but scurvy then  showed itself unequivocally,
and out of 860 prisoners, 437, or 52 per cent., were  affected with it.   The
effect of previous confinement here became remarkable; for those were chiefly
attacked, who  had  been  in the prison for two years,  a year, or six months.
Again,  the prisoners  employed in the kitchen, who had 8 oz. of  bread addi-
tional per day, were  not attacked, except three who had only  been  there  a
few days.  After the epidemic had spread to a great extent, it was found that
the addition  of 8 oz. to the  daily allowance of vegetable food,  and £ oz. to
the animal, facilitated the operation of the remedies  which were used for  the
restoration of the health  of the prisoners.—The effects of confinement have
been further shown  in the experience of the Edinburgh House of Refuge,
which was first established in 1832, for  the  reception of beggars during the
cholera, and which has been continued to the present time.   The diet was at
first a quart of oatmeal porridge for  each person, morning and  evening ; and
at dinner 1 oz. of meat,  in broth, with 7 oz. of bread ;  making altogether
about 23 oz. of solid food a day.   During some months, this diet seemed to
answer very well; the people went  out fatter than they came  in, owing to
the diet being better  than that to which they had been accustomed; but after-
wards a proneness to disease manifested  itself  in those who  had been  resi-
dents there for a considerable time, and  the  diet was therefore somewhat in-
creased, with good effect.  The quantity of animal food was probably here
too small; and the  total weight might still have  been  sufficient, if it had
been differently apportioned.—In a Convict-ship, which took out 433 prison-
ers to New Holland  in 1802, the mortality was very trifling, and the general
health good; although these prisoners were  supported on 16 oz. of vegetable
food, and 7£ oz. of animal food per day;  a  quantity which was found to be
perfectly sufficient for them.—The  aged  inmates of work-houses, especially
those who have been accustomed to poor food during their whole lives, re-
quire much less than this ;  their vital functions  being comparatively inactive,
and their amount of labour  or exercise small. In  the Edinburgh work-house,
of which the inmates usually have  good health, they are fed upon oatmeal-
porridge morning and  evening, with barley-broth at dinner ;  the total allow-
ance of dry nutriment  is about 17 oz. ; namely 13 oz. vegetable, and  4 oz.
animal.
   652.  It is a curious  effect of insufficient nutriment, as shown  by the recent
inquiries of  Chossat,* that  it produces an incapability of digesting even the
limited amount supplied.  He found that, when turtle-doves were supplied
with limited quantities  of corn, but with water at discretion, the whole amount
of food taken was scarcely ever actually digested ;  a part of it being rejected by
vomiting, or passing  off by diarrhoea, or accumulating in the crops.  It seems
as if the vital powers  were not sufficient to furnish  the requisite supply of
gastric fluid, when the  body began to be  enfeebled  by insufficient nutrition;
or perhaps we might well say, the materials of the gastric fluid were wanting.
Hence the loathing  of food,  which is  often  manifested by those who  have
been subjected to the influence of an insufficient diet-scale in our prisons and
* Recherches Experimentales sur llnanition, 1843. 
REQUISITE AMOUNT OF FOOD.
491
poor-houses, and which has been set down to caprice or obstinacy, and pun-
ished accordingly, may be  actually a proof of the deficiency of the  supply
which we might expect to have been voraciously devoured, if really less than
the wants of  the system require.
   653*  The smallest quantity of food upon which life is known to have been
supported with vigour, during a prolonged period, is  that on which Cornaro
states himself to have  subsisted.   This  was no more  than  12  oz. a day,
chiefly of vegetable matter, for a period of 58 years.   There is only  one in-
stance on record, in which his plan was followed; and there are probably few
who could long persevere in it, at least among those whose avocations  require
much mental or bodily exertion. It is certain, however, that life with a mode-
rate amount of vigour  may be  preserved for  some time,  with a very  limited
amount of food; this  appears from  the records of shipwreck and similar dis-
asters.  In regard, however, to  those who have been stated to fast for a period
of months or even years, taking no  nutriment, but maintaining an  active con-
dition, it may be safely asserted that they were impostors,—probably possess-
ing unusual powers of abstinence, which  they  took  care to magnify.  The
instances in which the life of Man, or of other Mammalia, has been prolonged
to the greatest extent without water, are those in which, from the peculiarity
of the circumstances,  the cutaneous exhalation  must have been reduced to a
very small amount, or  in which there may have  been an  actual absorption of
water by the skin  and lungs.   Thus, Fodere mentions  that some workmen
were extricated alive,  after fourteen days' confinement in  a cold damp  cavern,
in which they had been buried  under a ruin.   And there is a well-known case
of a Hog, which was buried in its sty for 160 days, under thirty feet of the
chalk of Dover cliff, and was dug out alive at the end of that time, reduced in
weight from 160 lbs. to 40 lbs.: here the temperature would be kept up by the
non-conducting power of the chalk around; and the air  surrounding  the ani-
mal would soon become sufficiently charged with fluid, to resist further evapo-
ration.  The time during which life can be supported under total abstinence,
is usually stated to vary  from 8  to 10 days  :  the period may be  greatly
prolonged, however, by the occasional use of water, and still more by a very
small supply of food.   In a case recorded by Dr. Willan, of a young gentle-
man who starved himself, under the influence of a religious delusion,  life was
prolonged for 60 days; during the whole  of which time  nothing else was
taken than a little orange-juice.  In a somewhat similar  case which occurred
under the Author's notice, in the  person of a young French lady, more than
15 days  elapsed between the  time  that she  ceased to  eat regularly, and
the time of her being compelled to take  nourishment; during this period she
took a great deal of exercise, and her strength seemed to suffer but little, al-
though  she swallowed solid food only once, and  then in small quantity.   If
the cessation of muscular  exertion  be complete, it seems that life is  usually
more prolonged than  where exercise of  any kind is performed ; and this is
what might naturally be expected.—In certain states of the system commonly
known  as Hysterical,  there is frequently a very remarkable disposition for ab-
stinence, and  power of sustaining it.  In a case of this kind which occurred
under the Author's own notice, a young lady, who had suffered severely from
the tetanic form of Hysteria, was unable to take food for three weeks.  The
slightest attempt to introduce a morsel of solid   matter into the stomach, oc-
casioned very  severe vomiting and retching;  and the only nourishment taken
during  the period mentioned, was a cup of tea once or twice a day,—on many
days not even this being swallowed. Yet the  strength of the patient rather
increased  than diminished, during  this period;  her  muscles  became firmer,
and her voice more powerful.—It may be well to remark that,  under such
circumstances, the continual persuasions of anxious friends are very injurious 
492
OF FOOD, AND THE DIGESTIVE PROCESS.
to the patient;  whose return to her usual state will probably take place the
earlier, the more completely she is left to herself.
   654.  Of the  quantity which can be  devoured  at a time, it is scarcely the
place to speak; since such  feats of gluttony only  demonstrate the extraordi-
nary capacity, which the stomach may be made to  attain by continual practice.
Many amusing instances are related by Captain Parry in his Arctic Voyages;
in one case, a young Esquimaux, to whom he had given (for  the sake of cu-
riosity) his full tether, devoured in  four-and-twenty hours, no  less than 35lbs.
of various kinds of aliment, including tallow candles.  A case has recently
been published of a Hindoo, who can eat a whole sheep at a  time ; this pro-
bably surpasses any other instance on record.  The half-breed voyageurs of
Canada, according to Captain Franklin, and the wandering Cossacks of  Sibe-
ria, as testified by Capt. Cochrane, habitually devour  a quantity of animal
food, which would be  soon fatal  to  any one unused to it.   The former are
spoken  of as very  discontented, when put on a  short allowance of 81bs. of
meat a day;  their usual consumption  being from 12 to 20lbs.—That a  much
larger quantity of food  than that formerly specified, may be  taken, with per-
fect freedom from injurious consequences, under a particular  system of  exer-
cise, Sic, appears from the  experience of those who are  trained for feats of
strength, pugilistic  encounters, Sic   The  ordinary belief, that the Athletic
constitution cannot be  long maintained, appears to have  no real foundation;
nor does it appear that  any  ultimate injury results  from the system being per-
severed in  for  some time.  That  trained men often fall into bad health, on
the cessation of the plan, is probably owing in part to the intemperance and
other bad habits of persons of the class  usually subjected to  this  discipline.
The effects of trainers' regimen are  hardness and "firmness  of the muscles,
clearness  of the skin, capability of bearing continued  severe  exercise, and a
feeling of freedom  and  lightness (or " corkiness") in the  limbs.  During the
continuance of the system,  it is found that the body recovers with wonderful
facility from the effects  of injuries ; wounds  heal very rapidly; cutaneous
eruptions usually disappear.   Clearness and vigour of mind, also, are  stated
to be  results of this plan; and it is probable that, where persevering attention
and intense application  are  necessary, a modification of this system, in which
due allowance  should be made for the diminished  quantity of exercise, would
be found advantageous.*


        3.—Of the Passage of Food along the Alimentary Canal.

   655. The introduction of alimentary matter into  the system, is accomplished
in Animals by the reception of the  food into  an internal cavity, where it is
subjected to a preparatory process,  to which nothing analogous exists in Plants,
and which is termed  Digestion.  This process may be said to have three dif-»
ferent purposes  in view ;—the reduction of the alimentary matter  to a fluid
form, so that it  may become  capable of absorption;—the separation of that

  * The method of training employed by Jackson (a celebrated trainer of prize-fighters in
modern times), as deduced  from his answers to questions put to him by John Bell,  was to
begin on a clear  foundation, by an  emetic and two or three  purges.  Beef and  mutton,
the lean of fat meat being preferred, constituted the principal  food; veal, lamb, and pork
were said to be less digestible (" the last  purges some men").  Fish was said to be a "wa-
tery kind of diet:" and is employed by jockeys who wish to reduce weight by sweating.
Stale bread was the only vegetable food  allowed.  The quantity of fluid permitted was 3£
pints per diem; but fermented liquors were strictly forbidden. Two full meals, with a light
supper, were usually taken.  The quantity of exercise employed was very  considerable, and
such as few men of ordinary strength could endure.  This account corresponds very much
with that which Hunter gave of the North American Indians, when about to set out on a long
march. 
DIGESTIVE APPARATUS.
493
portion of it which is fit to be  assimilated or converted into organized texture,
from that which cannot serve this purpose, and which is at once  rejected ;—
and the  alteration (when required) of the  chemical  constitution of the former,
  A view of the Organs of Digestion, opened in nearly their whole length;  a portion ofthe oesophagus
has been removed on account of want of space in the figure ; the arrows indicate the course of sub-
stances along the canal; 1, the upper lip, turned off the mouth ; 2, its  froenum ; 3, the lower lip, turned
down ;  4, its fraenum; 5, 5, inside ofthe cheeks, covered by the lining membrane ofthe mouth ;  6, points
to the opening of the duct of Steno ;  7, roof of the mouth; 8, lateral half arches ; 9, points to the tonsils;
10, velum  pendulum palati; 11, surface ofthe tongue ; 12, papillee near its point;  13,  a portion of the
trachea ;  14, the oesophagus; 15, its internal surface ;  16, inside of the stomach; 17, its greater extremity
or great cul-de-sac ; 18, its lesser extremity or smaller cul-de-sac ; 19,its lesser curvature; 20, its greater
curvature; 21,  the cardiac orifice;  22, ihe pyloric  orifice; 23, upper portion of duodenum; 24, 25, the
remainder of the duodenum ; 26, its valvulee conniventes ; 27, the gall bladder; 28, the  cystic duct; 29,
division of hepatic ducts in the liver; 30, hepatic duct;  31, ductus communis choledochus ;  32, its open-
ing into the duodenum ; 33, ductus Wirsungii, or pancreatic duct; 34, its opening into the duodenum;
35, upper part  of jejunum; 36, the ileum;  37,  some ofthe valvules conniventes; 38, lower extremity
ofthe ileum; 39, ileo-colic  valve;  40,41, coecum,  or caput coli; 42, appendicula vermiformis; 43,44,
ascending colon ; 45, transverse  colon; 46, 47, descending colon; 48,  sigmoid flexure of the colon;
49, upper portion of the rectum ; 50, its lower extremity ; 51, portion of the levator-ani  muscle ; 52
the anus.]
     42 
494               OF FOOD, AND THE DIGESTIVE PROCESS.
which prepares it  for the important changes it is subsequently to undergo.
The simplest conditions requisite for the accomplishment of these  purposes
are the following:—a fluid capable of performing the solution and of effecting
the required  chemical changes;—a fluid capable of separating the unorganiz-
able matter, by a process analogous to chemical precipitation;—and a cavity
or sac, in which these operations may be performed.  In the lowest Animals,
we find  this cavity formed  on  a very simple plan ; being  evidently nothing
else than an inversion of the external integument, communicating with the
exterior by one  orifice only,  through which the food is drawn in and the ex-
crementitious matter rejected. The fluid necessary to dissolve the food, which
is known by the name of gastric fluid or juice, and that required to separate
the portion which is to be thrown off, which is known as the bile, are secreted
in the walls of the stomach. In the Sea-Anemone, which, affords a very charac-
teristic example of this type of structure, it cannot be ascertained that the very
rapid solution of food, which takes  place  in  the digestive cavity, is assisted
by any movement of its  walls.  In Polypes of a higher conformation, how-
ever, the  digestive cavity is provided with a second orifice ; the stomach opens
into an intestinal tube, through which the excrement is rejected in little pellets ;
and the food, before entering  the true digestive cavity, is submitted to a  pow-
erful gizzard or triturating apparatus.   Still, the bile, like  the gastric juice, is
secreted in the walls ofthe stomach;  as may be distinctly perceived in many
of these animals, on account  of their transparency, and the bright yellow co-
lour of the fluid.  As we ascend  the animal series, we find no essential change
in the character  of the digestive  apparatus.  The biliary follicles are gradu-
ally collected into a glandular  mass, which is altogether removed from the
walls of  the  stomach, and which  pours its  secretion into the intestinal tube,
at a short distance from its commencement; the gastric juice, however, is still
secreted in minute sacs imbedded  in  the substance of the membrane.   Several
accessory glands are added, the uses of which are not accurately known; and
particular modifications of the  apparatus are adapted to peculiarities in the
nature of the food, or in  the mode of its ingestion.   As a general rule it may
be stated, that the digestive apparatus  is most simple in  Carnivorous animals,
in which it has to effect little change upon the aliment  except solution, in or-
der to  bring it to the state fit  for  absorption ; whilst it is most complex in those
that feed upon Vegetable matter,  which needs  to undergo  a greater change,
both in its chemical  composition and in  the  mechanical arrangement  of its
components,  before it can be  rendered subservient to animal nutrition.
  656. Mastication and  Deglutition.—The first step in the process of reduc-
tion, is the Mastication of the food, and the impregnation of  its comminuted
particles  with the Salivary secretion.   Mastication is evidently of great im-
portance, in  preparing the substances to be  afterwards operated on, for the
action  of their solvent;  and it  exactly corresponds with the trituration  to
which the Chemist would submit any solid matter, that he might present it in
the  most advantageous form to a digestive menstruum.   The complete  disin-
tegration of the alimentary matter, therefore, is of great consequence; and, if
imperfectly effected, the subsequent processes are liable to derangement.   This
derangement we continually meet with: for there is not, perhaps, a more fre-
quent source of  Dyspepsia than imperfect mastication, whether resulting from
the haste with which the food is swallowed, or from the want of the proper
instruments.  The disintegration  of the food by mechanical reduction, is  mani-
festly aided by Insalivation:  and  the admixture of Saliva appears further  to
have the effect of commencing the transformation of the amylaceous or starchy
particles  into sugar.  From  recent experiments it would seem that  Saliva, if
acidulated, possesses the  same power of acting on azotized compounds, as that
which characterizes the gastric juice;  and consequently, when introduced into 
MASTICATION AND DEGLUTITION.
495
the  stomach, the Saliva may afford  important aid in  the  digestive process.
(See §§ 668  and 863.)   When  the reduction of the  food  in  the mouth has
been sufficiently accomplished,  it is carried into the oesophagus  by the  action
of Deglutition.  The share which  the nervous system has in this action has
been already stated (§  382);  and  it  here only remains to define more  pre
cisely the different  movements which are concerned in it.   These were  first
described in detail by Magendie; but his account requires  some modification,
through the  more recent observations of Dzondi.*   The first stage in the  pro-
cess is the carrying back of the  food, until it has passed the anterior palatine
arch; this, which  is  effected by the  approximation  of the tongue and the
[Fig. 200.
  A view of the Muscles of the Tongue, Palate, Larynx and Pharynx-as well as the position of the
upper portion ofthe (Esophagus, as shown by a vertical section ofthe head; 1, 1, the vertical section of
the head ; 2, points to the spinal canal; 3, section of the hard palate; 4, inferior spongy bone ; 5. middle
spongy bone; 6, orifice of the right nostril; 7, section ofthe inferior maxilla; 8, section ofthe oshyoides;
9, section ofthe epiglottis; 10, section of the cricoid cartilage; 11, the trachea, covered by its lining mem-
brane ; 12, section of sternum; 13, inside ofthe upper portion of the thorax ; 14, genio-hyo-glossus muscle;
15, its origin ; 16, 17, the fan-like expansion of the fibres of this muscle ; 1P, superficial linguae muscle;
19, verticales lingua? muscle ; 20, genio-hyoideus muscle; 21. mylo-hyoideus muscle; 22, anterior belly
ofdigastricus; 23, section of platysmamyoides; 24, levator menti; 25, orbicularis oris; 26. orifice of Eus-
tachian tube ; 27, levator palati;  28, internal pterygoid ; 29,  section of velum pendulum palati, and  azy-
gos uvulae  muscle; 30, stylo-pharyngeus ; 31, constrictor pharyngis superior ; 32. constrictor pharyngis
medius; 33, insertion stylo-pharyngeus; 34. constrictor pharyngis inferior ; 35, 36, 37, muscular coat of
oesophagus; 38, thyreo-arytenoid muscle and ligaments, and above is the ventricle of Galen: 39, section
of arytenoid cartilage ; 40, border of sterno-hyoideus.]

palate, is a  purely voluntary movement.   In the second stage,  the  tongue is
carried  still  further backwards, and  the larynx is drawn forwards under its
root, so  that the  epiglottis  is  depressed down over the rima glottidis.  The
muscles  of the anterior  palatine  arch contract  after the morsel has passed it,
and assist its passage  backwards;  these, with the  tongue, cut  off completely
the communication between the fauces and the mouth.   At the same time, the
muscles  of the posterior palatine arch contract  in  such a manner, as  to cause
* Mailer's Physiology, p. 501. 
496
OF FOOD, AND THE DIGESTIVE PROCESS.
the sides of the arch to approach each  other like a pair of curtains ; so  that
the passage from the fauces into the posterior nares is nearly closed by them;
and to the cleft between the approximated sides,  the  uvula is applied like a
valve. A sort of inclined plane, directed obliquely downwards and backwards,
is  thus formed;  and  the  morsel slides  along  it into the pharynx, which is
brought up to receive  it.   Some of these acts  may be performed voluntarily;
but the combination of the whole is automatic.   The third stage of the pro-
cess,—the  propulsion of the food down the oesophagus,—then commences.
This  is accomplished  in the upper  part by means of the constrictors of  the
pharynx;  and  in the lower by the muscular  coat  of the oesophagus  itself.
When the morsels are small, and are mixed with much fluid, the undulating
movements  from above  downwards succeed  each other  very  rapidly;  this
may be well  observed in Horses whilst drinking; large morsels, however, are
frequently some time  in making their way  down.  Each portion of food and
drink is included in the contractile walls, which are closely applied to it during
the whole of its transit.   The gurgling sound,  which is observed when drink
is  poured down the throat of a person in articulo mortis, is due  to the want
of this contraction.  The whole of  the third stage is completely involuntary.
At the point  where the oesophagus enters the stomach,—the cardiac orifice of
the latter,—there is a sort of sphincter, which is  usually closed.  This opens
when there is a sufficient pressure on it, made by  accumulated food ; and after-
wards closes, so  as to retain the  food in the  stomach.   The opening of the
cardiac is one  of the first  acts which  takes  place  in vomiting.  When the
sphincter is paralyzed by division of the pneumogastric nerve, the food regur-
gitates into the  oesophagus.
   657. Action of the  Stomach.—A remarkable opportunity of ascertaining the
condition of  the Stomach during Digestion, presented itself, some time since,
in a case in which a large fistulous aperture remained after a  wound that laid
open the cavity, but in which the general  health was completely recovered;
so that the process may be considered as having been normally performed.*
" The inner  coat of the stomach, in its natural and healthy state, is of a light
or pale pink colour, varying in its  hues, according to its full or empty state.
It is of a soft or velvet-like appearance, and is  constantly covered with a  very
thin,  transparent, viscid  mucus, lining  the whole interior of the organ.   By
applying aliment or  other irritants, to the internal  coat of the stomach, and
observing the effect through a magnifying glass, innumerable  lucid points, and
very  fine  nervous or vascular papilla?, can be seen arising  from the villous
membrane, and protruding through the mucous  coat, from which distils a pure,
limpid, colourless, slightly viscid fluid.  The  fluid  thus excited is invariably
distinctly acid.   The mucus of the stomach is less fluid, more  viscid or albu-
minous, semi-opaque, sometimes a little saltish, and does not possess the slight-
est character of acidity.  The gastric fluid never  appears  to be accumulated in
the  cavity of the stomach  while fasting;  and is seldom, if  ever, discharged
from its proper secerning vessels, except when excited by the natural stimulus
of aliment, mechanical irritation of tubes,  or other excitants.   When aliment
is received, the juice is given out in exact proportion to its  requirements for
solution, except when more food has  been taken than  is necessary for the
wants of the system."  That the quantity of the Gastric Juice secreted from

   *  See the case of Alexis St. Martin, with the observations and experiments of Dr. Beau-
mont, republished in this country by Dr. A. Combe.  [A  very extended examination of the
phenomena  of gastric digestion has been made by M. Blondlot,  The chief subject of ex-
periment was a dog, in which he maintained, without affecting the health, a fistulous opening
into the stomach for more than two  years.  His examinations have furnished many new
and important facts, and  have confirmed those of Dr. Beaumont made on  Alexis St. Martin
in nearly every point.—Traite Analytique de la Digestion, Paris, 1844.—M.  C] 
ACTION OF THE STOMACH.
497
the walls of the stomach depends rather upon the general requirements of the
system, than upon the quantity of food introduced into the digestive cavity, is
a principle of the highest practical importance, and cannot be too steadily kept
in view in  Dietetics.  A definite proportion only of aliment can be perfectly
digested in a  given  quantity of the  fluid;  the  action of which, like  that of
other chemical operations, ceases after having been exercised on a fixed and
definite amount of matter.  " When the juice has become saturated, it refuses
to dissolve  more ; and, if an excess of food has been taken, the residue remains
in the stomach, or passes  into the bowels in  a crude  state, and  becomes a
source of nervous irritation, pain, and  disease, for a long time."   The unfa-
vourable effect of an  undue burthen of food upon the stomach itself, interferes
with its healthy action; and thus  the  quantity really apprppriate is not  dis-
solved.   The febrile disturbance is thus increased; and the mucous membrane
of the stomach exhibits  evident indications  of its morbid condition.  The de-
scription of these indications, given by Dr. Beaumont, is peculiarly graphic,
as well  as Hygienically important.
   658.  ^'In disease, or  partial derangement of  the  healthy function, the  mu-
cous membrane presents various  and essentially-different appearances.   In
febrile conditions of the system,  occasioned by  whatever  cause,—obstructed
perspiration, undue  excitement by stimulating liquors, overloading the  sto-
mach with food;  fear, anger, or whatever depresses or disturbs the nervous
system,—the villous  coat becomes sometimes red and dry, at other times pale
and moist,  and loses its  smooth  and healthy appearance;  the  secretions be-
come vitiated,  greatly diminished, or even suppressed; the coat of mucus
scarcely perceptible, the follicles flat and flaccid, with secretions insufficient
to prevent  the papillae from irritation.   There are sometimes  found, on the
internal coat of the  stomach, eruptions  of deep-red pimples, not  numerous,
but distributed here and there upon the villous membrane, rising above the
surface  of the mucous coat.   These  are at first sharp-pointed, and red, but
frequently  become filled with  white  purulent matter.  At other times, irre-
gular, circumscribed red patches, varying in size and extent from half an inch
to an inch and  a half  in circumference,  are  found on  the  internal coat.
These appear to be the effects of congestion in the minute blood-vessels ofthe
stomach.   There are also seen at times small aphthous crusts, in connection
with these  red patches.   Abrasion of the lining membrane, like  the rolling up
of the milcous  coat into small shreds  or strings, leaving the papilla; bare for
an indefinite space, is not an uncommon appearance.   These diseased appear-
ances, when very slight, do not always affect essentially the gastric apparatus.
When considerable, and particularly when there  are corresponding symptoms
of disease,—as dryness  of  the mouth, thirst, accelerated pulse,  &c.—no gas-
tric juice can be  extracted by the alimentary stimulus.  Drinks  are imme-
diately absorbed or otherwise disposed of;  but food taken in this condition of
the stomach remains undigested for twenty-four or forty-eight hours, or more,
increasing  the  derangement of the alimentary canal, and aggravating the gene-
ral symptoms  of disease.  After excessive eating or drinking, chymification is
retarded; and, though the appetite be not always impaired at first, the fluids
become  acrid  and sharp, excoriating the edges  of  the  aperture, and almost
invariably  producing aphthous patches  and  the other indications of a diseased
state of the internal  membrane.  Vitiated  bile is also found in the stomach
under these circumstances, and flocculi of  mucus are more abundant than in
health.   Whenever  this morbid  condition of the  stomach occurs, with the
usual accompanying symptoms of disease,  there is generally a  corresponding
appearance of the tongue.  When a healthy state of the stomach is restored,
the tongue invariably becomes clean."
                                   42* 
498                 OF FOOD, AND THE  DIGESTIVE PROCESS.
   a. Dr. A. Combe's commentary on  the  above passage is  too apposite to be omitted.
" Many persons who obviously live  too freely, protest against the fact, because they feel no
immediate inconvenience, either from the quantity of food, or the stimulants in which they
habitually indulge; or, in other words, because  they experience no pain, sickness, or head-
ache,—nothing, perhaps, except slight fulness and oppression, which soon go off.  Observa-
tion extended over a sufficient length of time, however, shows  that the conclusion drawn is
entirely  fallacious, and that the real amount of injury is not felt at the moment, merely be-
cause, for a wise purpose, nature has deprived  us of any consciousness of either the exist-
ence or the state of the stomach during health.  In  accordance with this, Dr. Beaumont's
experiments prove, that  extensive erythematic inflammation of the  mucous coat of the  sto-
mach was of frequent occurrence in St. Martin after excesses in eating, and especially in
drinking, even when  no marked general symptom was  present to indicate its existence.
Occasionally, febrile heat, nausea, headache, and thirst were complained of, but not always.
Had St.  Martin's stomach, and its inflamed patches, not been visible to the eye, he too might
have been pleased that his temporary excesses did him no harm; but, when they presented
themselves in such legible characters, that Dr. Beaumont could not miss  seeing them, argu-
ment and supposition were at an end, and the broad fact could not be denied."
   b.  The observations of Dr. Beaumont have been confirmed by those of M. Blondlot (Traite
Analytique de la Digestion), and of M. Ch. Bernard (Archiv. d Anat. Gen. et de Physiol.,
Jan. 1846); which were made upon Dogs, in whose stomachs fistulous openings were main-
tained for a length of time.—They found that, although a slight mechanical irritation, applied
directly to the mucous  surface of the stomach, excites at once an abundant flow of gastric
fluid, yet if this irritation be carried beyond certain  limits, so as to produce pain, the secre-
tion, instead of being more abundant, diminishes or ceases entirely;  whilst a ropy mucus is
poured out instead, and the movements of the stomach are considerably increased.  The
animal at the same time appears ill at ease, is agitated, has nausea, and,  if the irritation be
continued, actual vomiting;  and bile has been  observed  to flow into the stomach, and es-
cape by  the fistulous opening.  Similar  disorders of the functions of the stomach result from
violent pain in other  parts of the body; the process of digestion in such cases being sus-
pended, and sometimes vomiting excited.  When accidulated  substances, as food rendered
acid by the addition of a little vinegar,  were introduced  into the stomach, the quantity of
gastric fluid poured out was much  smaller, and the  digestive process consequently slower,
than when similar food, rendered alkaline by a weak solution of carbonate of soda, was in-
troduced.  If, however, instead of a weak solution, carbonate of soda, in crystal or in pow-
der, was introduced into the stomach, a large quantity of mucus and bile, instead of gastric
fluid, flowed into the stomach ; and vomiting and purging very often followed.  When very
cold water, or small pieces of ice, were introduced into the stomach, the  mucous membrane
was at first rendered very pallid; but soon a kind of reaction followed, the membrane be-
came  turgid with blood, and a large quantity of gastric fluid was secreted.   If, however, too
much ice was  employed, the animal appeared ill, and shivered; and digestion, instead of
being rendered more active, was retarded.   Moderate heat, applied to the mucous surface of
the stomach, appeared to have no particular action on digestion;  but a high degree of heat
produced most serious consequences.   Thus, the introduction of a little boiling water threw
the animal at once into a kind of adynamic state, which was followed by death in three or
four hours; the mucous membrane  of  the stomach was  found red  and swollen, whilst an
abundant exudation of blackish blood had taken place into the cavity of the organ.  Similar
injurious effects resulted in a greater or less degree, from the introduction of other irritants,
such as nitrate of silver  or ammonia;  the digestive functions being at once abolished, and
the mucous surface of the organ rendered highly sensitive.

   659.  The food which is propelled along the oesophagus, enters the Stomach
through its cardiac  orifice, in  successive waves: and it  is immediately sub-
jected to a peculiar peristaltic movement, which  has  for its object to produce
the thorough intermixture of the  gastric fluid with the  alimentary mass,  and
also to aid the solution of the latter by the gentle trituration to which it is thus
subjected.   The fasciculi composing the muscular wall of the human stomach,
are so disposed as to shorten  its  diameter  in every  direction  ;  and by the al-
ternate contraction and relaxation of these bands, a great  variety  of motion is
induced in this organ, sometimes  transversely, and  at other  times  lono-itudi-
nally.   "These motions," Dr. Beaumont remarks, "not  only produce a con-
stant disturbance  or churning ofthe  contents ofthe stomach, but they compel
them, at the same time, to revolve about the interior  from point to point,  and
from one extremity to the other."  In  addition  to  these  movements,  there is 
ACTION OF THE STOMACH.
499
[Fig. 201.
  A front view ofthe Stomach, distended by flatus, with the Peritoneal Coat turned off; 1, anterior face
ofthe cesophagus ; 2, the cul-de-sac, or greater extremity ;  3, the lesser or pyloric extremity ; 4, the duo-
denum ; 5, 5. a portion of the peritoneal coat turned back  ; 6, a portion of the longitudinal  fibres of the
muscular coat; 7, the circular fibres of the muscular coat; 8, the oblique muscular fibres, or muscle of
Gav ard ;  9, a portion of the muse ular coat of the duodenum, where its peritoneal coat has been removed. ]

                                     [Fig. 202.
  A view of the interior of the Stomach, as given by the removal of its anterior parietes ; 1, cesophagus;
2. cardiac orifice ofthe stomach;  3, its greater extremity, or cul-de-sac; 4, the greater curvature, 5, line
of the attachment of the omentum majus; 6, the muscular coat; 7, the anterior cut edge of the mucous
coat; 8, the rugns of the mucous coat; 9, the lesser curvature ; 10, the beginning of the duodenum ; 11,
pyloric orifice, or valve ; 12, the first turn of the duodenum downwards.]

a constant  agitation of the  stomach,  produced by  the  respiratory muscles.
The motions of the stomach  itself are not performed on any very exact plan,
and are  much  influenced by  the  character  of the  ingesta,  the  state of  the
general system, and by other circumstances.   The following is the ordinary
course, however, ofthe revolutions ofthe food.   " After passing  the oesopha-
geal ring, it moves from right to left, along the small arch ;  thence, through the
large curvature, from left to right.   The bolus, as it enters the cardia, turns to
the  left, passes  the aperture,* descends into the  splenic extremity, and follows
the  great curvature towards the pyloric end.   It then returns, in the course of
the  smaller curvature, makes its appearance again  at the aperture in its descent
The fistulous orifice in  St. Martins stomach, through which  these observations were
made. 
500
OF FOOD, AND THE DIGESTIVE PROCESS.
[Fig. 203.
  A view ofthe interior of the Stomach and Duodenum in situ, the inferior portion of each having been
removed; 1,1, the under side of the liver; 2, the gall bladder; 3, 3, the lesser curvature and anterior
faces, as seen from below ; 4, the rugae, about the cardiac orifice; 5, the pyloric orifice ; 6, the rugae, and
thickness of this orifice ; 7, 7, the duodenum; 8, lower end ofthe right kidney.]

into  the  great curvature, to perform  similar  revolutions.   These revolutions
are completed in from one to three minutes.   They are  probably  induced in
a great measure, by the circular or transverse muscles of the stomach.  They
are slower at first, than after chymification has considerably advanced;" at
which time  also  there is an increased impulse  towards the  pylorus.  It is
probable that, from the very commencement of chymification,  until the organ
becomes empty, portions of  chyme  are continually passing into  the duode-
num ;  for the bulk  of the alimentary mass  progressively diminishes, and this
the more rapidly as  the process  is  nearer  its completion.   The accelerated
expulsion appears to be effected by a peculiar action of the transverse  mus-
cles  ; and especially of that  portion of them which surrounds  the  stomach at
about four inches from its pyloric extremity.  This band is so forcibly con-
tracted in the latter part of  the digestive process, that it almost separates  the
two  portions of the stomach, into a sort of hour-glass form ;  and Dr.  B. states
that, when he attempted to introduce a long  thermometer tube into the pyloric
portion of the stomach, the bulb  was at first gently resisted, then  allowed to
pass, and then grasped by the muscular parietes  beyond, so as to be drawn
in:  whence it is  evident that the contraction has  for its object, to resist  the
passage of solid bodies into the pyloric extremity of the stomach, at this stage
of digestion ; whilst the  matter which has been reduced to  the  fluid form is
pumped  away (as it were) by the action of that portion of the  viscus. These
peculiar motions continue, until the stomach is perfectly empty, and not a par-
ticle  of food or chyme remains.   Of  the degree in which they are  dependent
upon the influence ofthe Nervous System, some idea  has been already given
(§ 387); there is yet much to be  learned, however, especially in regard to  the
degree in which  the movements  may be checked  or  altered,  by impressions
transmitted through the nervous system.   It is stated by Brachetthat, in some
of his  experiments upon the  Par Vagum some hours after section of the nerve
on both sides, the surface only of the alimentary mass was found to  have  un-
dergone  solution, the remainder of the mass remaining  in the  condition in
which it was at first ingested ; and if this statement can be relied on, it would
appear that  the movements  of the stomach, like  those of the heart, can be
readily affected by  a strong  nervous impression.  It may be partly in this
manner, therefore, and not by acting upon  the secretions  alone, that strong
Emotions influence the digestive  process, as they are well known to  do.   On
the other hand, the  moderate excitement of pleasurable emotions  may be fa- 
ACTION OF THE INTESTINAL TUBE.
501
vourable to the operation ; not only by giving firmness and regularity to the
action of the heart, and thence promoting the  circulation of the blood, and the
increase of the gastric secretion ;  but also in imparting firmness and regularity
to the muscular contractions  of the stomach.
   660.  Action of the Intestinal Tube.—The pulpy substance to which the
aliment is reduced, by the mechanical reduction and chemical  solution it has
undergone in the mouth and  stomach, is termed chyme.   The consistence of
this will of course  vary in some degree  with  thequantity of fluid ingested;
in general it is greyish, semifluid, and homogeneous ;  and possesses a slightly
acid taste, but is otherwise insipid.  Dr. Beaumont describes it as varying in
its aspect,—from that of cream, which it presents when the food  has been of
a rich character,—to that of gruel, which it possesses when the diet has been
farinaceous.   The passage of the chyme through the  pyloric orifice is at first
slow;  but when the digestive process is nearly completed, it is transmitted in
much larger quantities.   From the time that  the ingested matter enters the
intestinal canal, it is propelled by the simple peristaltic action of its muscular
coat, which is directly excited by the contact  either of this matter, or of the
secretions which are mingled with  it;* and all that  is not absorbed  is thus
conducted to the  rectum, its expulsion from  which is due to an  action of a
distinctly reflex  kind, excited through the nervous centres (§ 391).   During
its progress through the  intestinal tube, the product of the gastric operation
undergoes very important changes.  The chyme is mingled in the duodenum
with the biliary and pancreatic secretions, which effect an immediate altera-
tion both in its sensible and chemical properties.   The nature of this altera-
tion can  be best estimated, by mingling  bile with chyme  removed from the
body.   This has been  done  by several experimenters on  the lower animals;
and by Dr.  Beaumont in the case already referred to, which afforded him the
means of obtaining not only chyme, but bile and pancreatic fluid.  The effect
of this admixture was  to separate the chyme  into  three distinct parts,—a red-
dish brown sediment  at the  bottom,—a  whey-coloured fluid in the centre,—
and a creamy pellicle at the top.   The central portion, with the creamy pelli-
cle, seems to constitute the chyle absorbed by  the lacteals ; the creamy matter
being chiefly composed of oily particles; and the wheyey fluid having pro-
teine-compounds, saccharine  and  saline  matters,  in  solution: the sediment,
partly consisting of the  insoluble portion of the food,  and  partly of the biliary
matter itself, is evidently excrementitious.  It is not until the food has passed
the orifice ofthe Ductus Choledochus, that  the absorption of chyle begins,—
the lacteals not being distributed upon the Stomach, or the higher part of the
Duodenum.
   661.  By  the gradual  withdrawal of their fluid portion,  the contents of the
alimentary canal are converted into a mass of greater consistence;  and this,
as it advances through the small intestines, assumes more and more of a  faecal
character.   A part of the faeces, however, may be  derived  from the secretions
of the enteritic mucous membrane, and of its glandulae ; the surface of the for-
mer, with its simple follicles, probably secretes nothing else than mucus  ; but
the glandulae, with which it is  so thickly studded,  appear to serve as the
channel for the elimination of putrescent  matter from the blood.  There can
be no doubt, that a large quantity of fluid is  poured  out  by these glandulae,
when they are in a state of irritation from disease, or from the stimulus of  a
purgative medicine ; since the amount of water discharged from the bowels  is

  * The bile seems to have an important share in producing  this effect;  since, when the
ductus choledochus is tied, constipation always occurs.  The action of mercury as a purgative
appears to take  place through the increase of the hepatic and other secretions which it in-
duces. 
502
OF FOOD, AND THE DIGESTIVE PROCESS.
often much greater than that which has  been ingested, and  must be  derived
from the blood.—The secretion of the coecum has been  ascertained to be, in
herbivorous animals, distinctly acid during digestion;  and there is  reason  to
believe, that the  food there undergoes  a  second process,  analogous  to that to
which  it has been submitted in the stomach, and fitted to extract from it what-
ever undissolved  alimentary matter it may still contain.  There  is  no evi-
dence,  however,  that this is  the case in Man, whose coecum (commonly termed
the appendix coeci vermiformis) is very  small, compared  to that  of  most her-
bivorous animals.
  662.  The act  of Defecation having  been  already  sufficiently considered
(§ 391), it only remains to notice the composition of the  Faeces.  These are
made up of certain parts of the food, which have not been reduced and  ab-
sorbed  ; together with that portion of  the secretions poured  into the aliment-
ary canal between the mouth  and the anus, which has not been taken back
again into  the system.  Of the  former  portion, the constituents may be  in
great part determined by the Microscope.  Thus the cell-walls of the Vegeta-
ble tissues  whose contents  have been extracted, the entire  woody  fibres (on
which  the digestive process has  no influence), the granules of  starch, when
they have  undergone  no preparation  before  being swallowed,—portions  of
tendon, ligament, adipose  tissue, and even  of muscular fibre,—with  other
substances constituting the  undigested residue of the food, may be readily
detected.   Besides these, the microscope  enables us to recognize the brown
colouring-matter of the bile,  epithelium-cells and mucus-corpuscles, and various
saline particles, especially those ofthe ammoniaco-magnesian phosphate, whose
crystals are well-defined; most of which  are derived from  the  secretions.—
The following is the result  of the proximate  analysis of the faeces of an in-
dividual in good health, who had taken  the ordinary diet of this country, as
given by Dr. Percy :—
Substances soluble in ether (brownish yellow fat)
    "       "     alcohol of -830
    "             water (brown resinoid matter)
Organic matter insoluble in the above menstrua  .
Salts soluble in water    ....
Salts insoluble in water  ....
11-95
10-74
11-61
4933
 4-76
11-61
Ultimate analysis of the same  faeces gave the following  as the proportion  of
the components of the Organic constituents ;  Carbon 46"20,  Hydrogen 6'72,
Nitrogen and Oxygen  30*71.—The mineral ash of faecal  matter has been ex-
amined by Enderlin ;  who has given the following as the  proportion of its
ingredients :—                               ;  _
Chloride of sodium and alkaline sulphates
Bibasic phosphate of soda
Phosphates of lime and magnesia
Phosphate of iron .
Sulphate of lime  .
Silica     ....
 1-3G7-)
 2-633 5
80-372 \
 2-090 I
 4-530 f
 7-940 J
Soluble in water.
Insoluble in water.
  It further appears from the inquiries of Enderlin, that a portion of the or-
ganic matter taken  up by alcohol, sometimes (but not constantly) consists of
Choleate of soda, the characteristic ingredient of bile ; and he thinks that this
is more likely to be present, when the faeces have  remained for only a short
period in the large intestine, and when there has been less time for  its re-
absorption.—In the faecal discharges which result from the action of mercu-
rials, large quantities of biliary matter may be detected, very little changed. 
NATURE OF CHYMIFICATION.
503
              4.  Nature of Chymification and Chylification.

  663.  The causes of the  reduction of the  food in the Stomach, have long
been a fruitful source of discussion amongst physiologists; and various hy-
potheses have been devised to account for it.   Some have compared the Sto-
mach of Man to the Gizzard of a fowl, and have supposed that the trituration
of the food between its walls was the essential element in the process ; but
this doctrine is completely incompatible with the fact, that digestible substances,
inclosed in metallic balls with perforations in their sides, are still dissolved by
the power of the gastric fluid, though  the walls of  the  stomach do not come
in contact with them.  Others, again, have imagined that the  process of di-
gestion is one of putrefaction; but this  idea, putting aside its  inherent ab-
surdity, is proved to be incorrect by the  fact that the gastric juice has a de-
cidedly antiseptic quality.  Others, in despair of obtaining any other solution,
have attributed the operation to the direct agency of the vital principle ; for-
getting that, as long as the aliment remains within the stomach  and intestinal
canal, it can no more be the subject of any peculiarly vital process,  than if it
were in contact with the skin, of which the mucous membrane is but an inter-
nal reflexion.  The theory of chemical solution, which was at first regarded
by many as quite untenable, has been of late years so much strengthened by
new facts and arguments, that there  now appears no valid reason  for with-
holding our assent from it; even though  it cannot yet give a complete expla-
nation of the complex phenomena in  question.  The chief opposition to this
theory has arisen from the difficulty  of imagining, that any simply-chemical
solvent should have the power of acting on so great a variety of substances,
and of reducing them to a state so  homogeneous.  This  difficulty, however,
seems now in  a great degree removed, by the discovery  of the close Chemical
relation that subsists, between the  various substances  of each  of the  groups
already enumerated (§ 639) ; which  renders  it easy  to  conceive, that the
changes involved in their reduction may  be of a very simple character.
   664. The first series of facts which will be here adduced, as throwing light
on the process of Chymification, is that  which has been obtained by the ex-
periments of Dr. Beaumont  upon  the individual already alluded  to (§ 658.)
By introducing a tube of India-rubber into the empty stomach, he  was able
to obtain a supply  of Gastric  Juice whenever  he desired it;  for  the tube
served the purpose of stimulating the  follicles to pour  forth their secretion,
and at the same time conveyed it away.   This  fluid, of which the existence
has been denied by some physiologists, is not very unlike saliva in its appear-
ance ; it is, however, distinctly acid to the taste; and chemical analysis shows
that it contains a considerable proportion of  free muriatic acid, and also some
acetic acid.   The former must evidently be derived from the decomposition
of the muriate of soda contained in the blood, the remote source of  which is
the salt ingested with the food.  The latter is an organic compound,  probably
formed at the expense of some of the saccharine matter of the previous'ali-
ment.   Of equal importance with the free acids, is an animal matter, soluble
in cold water, but insoluble in hot, bearing considerable resemblance to albu-
men.   Of this more will be said hereafter.   Besides   these  principal ingre-
dients, the  gastric fluid contains  muriates  and  phosphates  of potass, soda,
magnesia, and lime.   It possesses  the power of coagulating albumen in an
eminent degree ; it is powerfully antiseptic, checking the putrefaction of meat;
and it  is effectually restorative  of  healthy action, when applied  to  old fetid
sores and foul ulcerating surfaces.  It may be kept for  many months, if ex-
cluded from the air without becoming foetid.
  a. The Chemistry of the Gastric Juice has been greatly unsettled by the results of recent 
504
OF FOOD, AND THE DIGESTIVE PROCESS.
inquiries; which seem inconsistent with the statement just given, especially in regard to the
presence of free muriatic acid.  It  may be well, in the first instance, to quote Professor
Dunglison's account of the analysis of the gastric fluid drawn from the  stomach of Alexis
St. Martin, and supplied to him by Dr. Beaumont.  " The quantity of free hydrochloric acid
was surprising ; on distilling the gastric fluid, the acids passed over, the salts and animal mat-
ter remaining in the retort; the amount of chloride of silver  thrown down, on the addition
of nitrate of silver to the distilled fluid, was astonishing. The author had many opportu-
nities of examining the gastric secretion obtained from the case in question.  At all times,
when pure or unmixed, except with  a portion of the mucus of the lining membrane of the
digestive tube, it was a transparent fluid, having a marked smell of hydrochloric acid;  and of
a slightly salt, and very perceptibly acid, taste."   (Human Physiology, Sixth Edition, Vol. I.,
p. 546.)
  6.  From the experiments of MM. Blondipt, Bernard, and Barreswill, and Dr. R. D. Thom-
son, on the other hand, it would seem that no free hydrochloric acid is present in the gastric
fluid; since the fluid which comes over, on distillation at a low temperature, contains none;
whilst the matter remaining in the retort becomes more and more acid with the progress of
the distillation, and may be subjected to a high temperature (300°) without giving off acid
fumes.   It is difficult to account for the discrepancy between these  carefully conducted ex-
periments, and the positive statement of Professor Dunglison, otherwise than by supposing
that the Human gastric fluid differs from that of the Dog and the Pig, which were employed
in the analyses last quoted.—The acid reaction was referred  by Blondlot to the presence of
super-phosphate of lime; but this seems incorrect. Professor Thomson agrees with MM.
Bernard and Barreswill in attributing it chiefly to Lactic acid ; which, contrary to previous
opinions, they regard as generally if  not universally present in the stomach during  healthy
digestion, and it would seem that this acid  may partially decompose  the phosphates and
muriates, which are contained in the secretion : and may thus occasion the phosphoric and
muriatic acids to be set free.  The presence  of a small quantity of free  Acetic acid, also,
seems to have been recognized by them.

  665. The  Gastric Juice  obtained  from  the stomach, was found  by Dr.
Beaumont to possess the  power of dissolving various kinds of alimentary sub-
stances, when these  were submitted to its action at a constant temperature of
100°,  (which is about that  of the  stomach,) and  were  frequently  agitated.
The solution appeared to be in all respects as perfect as that which naturally
takes place in  the stomach ;  but required a longer  time.   This is readily ac-
counted for when we remember, that  no  ordinary agitation can produce the
same effect with the  curious movements  of the stomach ;  and that the conti-
nual removal from its cavity, of the matter which has been already dissolved,
must aid the  operation of the  solvent on the remainder.   The following is
one  out of many experiments detailed by Dr. Beaumont.  "At  lis o'clock,
a. m., after having  kept the lad  fasting for  17 hours, I introduced a gum-elastic
tube, and drew off one ounce of pure gastric liquor, unmixed with  any other
matter, except a small proportion  of mucus, into a  three-ounce vial.   I then
took a  solid piece of boiled recently-salted beef, weighing three drachms, and
put  it  into the liquor in the vial;  corked the vial tight, and  placed it in  a
saucepan  filled with  water, raised to the temperature of 100°, and kept at that
point on  a nicely-regulated sand-bath.  In forty minutes, digestion had dis-
tinctly  commenced  over  the surface of the meat.   In fifty minutes, the  fluid
had  become quite opaque and cloudy;  the'external  texture  began to separate
and  become loose.   In sixty minutes, chyme began to form.   At 1 o'clock,
p.m., (digestion having progressed  with the same regularity as  in the last half-
hour), the cellular texture seemed  to be  entirely destroyed, leaving the mus-
cular fibres loose and unconnected, floating about  in  fine small shreds,  very
tender and soft.  At 3 o'clock, the  muscular  fibres had  diminished one-half,
since the  last examination.  At 5  o'clock, they were  nearly  all digested ;  a
few fibres only remaining.   At 7 o'clock, the muscular texture was completely
broken down,  and only a few of the small fibres could be seen floating in the
fluid.   At 9 o'clock, every part of the meat was completely  digested.    The
gastric juice, when taken from the stomach, was as clear and transparent as
water.  The mixture in the vial was now about the colour of whey.   After 
NATURE OF CHYMIFICATION.
505
standing at rest a few minutes, a fine sediment, of the colour of the meat, sub-
sided to the bottom of the vial.—A piece of beef, exactly similar to that placed
in the vial, was introduced into the stomach, through the aperture, at the same
time.  At  12 o'clock it was withdrawn, and found to be as little affected by
digestion as that in the vial;  there was little or no difference in their  appear-
ance.  It was returned to the stomach; and, on the string being drawn out at
1 o'clock p.m., the meat was found to be all  completely digested and gone.
The effect ofthe gastric juice on the piece of meat suspended in the stomach,
was exactly similar to  that  in the vial, only more  rapid after the first half
hour, and sooner completed.  Digestion commenced on, and was  confined to,
the surface entirely in both situations.  Agitation accelerated the solution in the
vial, by removing the coat  that was digested on the surface,  enveloping the
remainder of the meat in the gastric fluid, and giving this fluid access to the
undigested portions."*   Many variations were made in other experiments ;
some of which  strikingly  displayed  the  effects of thorough  mastication, in
aiding both natural and  artificial digestion.
   666.  The attempt was made by Dr. Beaumont, to determine  the  relative
digestibility of different  articles of diet, by observing the length  of  time re-
quisite for  their solution.   But, as he  himself points out, the rapidity of diges-
tion varies so greatly, according to the quantity eaten, the nature and  amount
of the previous exercise, the interval since the preceding meal, the state of
health, the condition of the mind, and the nature of the weather, that a much
more extended inquiry would be  necessary to arrive at results  to be depended
on.   Some important inferences of  a general  character, however,  may be
drawn from  his inquiries.—It  seems to be a  general rule, that the  flesh of
wild  animals is more easy of  digestion than that of the domesticated races
which approach them most nearly.  This may, perhaps, be partly attributed
to the small quantity of fatty matter that is  mixed up with the flesh of the
former, whilst that of the latter is  largely pervaded  by it.  For  it appears from
Dr. B.'s experiments, that the presence in the stomach of any substance which
is difficult of digestion, interferes with the  solution of food that would other-
wise be soon reduced.   It  seems that, on  the whole, Beef is  more speedily
reduced than Mutton, and Mutton sooner than either Veal or Pork.  Fowls
are far from  possessing the digestibility that is ordinarily imputed to them ;
but Turkey is, of all kinds of flesh except Venison, the most soluble.   Dr.
B.'s experiments further show, that bulk is as necessary for healthy digestion,
as the presence of the nutrient principle itself.   This fact has been long known
by experience to uncivilized  nations.   The Kamschatdales, for example, are
in the habit of mixing earth  or saw-dust with the train-oil, on which alone
they are frequently reduced to live. The Veddahs  or wild hunters of Ceylon,
on the same principle, mingled  the pounded fibres  of soft and decayed wood
with the honey,  on which they feed when meat is  not to be had ;  and on one
of them being asked the reason of the  practice, he replied, " I  cannot tell you,
but I know that  the belly  must  be filled."  It is further shown by  Dr. B.,
that soups and fluid diet  are  not  more readily chymified than  solid  aliment,
and are not alone fit for the support of the system ; and this, also,  is conform-
able to the well-known  results of experience ;  for a dyspeptic  patient will
frequently  reject chicken-broth, when he can  retain solid food  or a richer
soup.  Perhaps, as  Dr.  A. Combe remarks, the  little  support gained  from
fluid diet, is due to the rapid  absorption of the watery part of it; so that the
really nutritious portion is left in too soft and  concentrated a  state, to excite
the  healthy action  of  the stomach.—Dr. Beaumont also ascertained that
moderate exercise facilitates  digestion, though severe and fatiguing  exercise

                     *  Experiments 2 and 3 of First Series.
     43 
506
OF FOOD, AND THE DIGESTIVE PROCESS.
retards it.   If even moderate exercise be taken  immediately after a full meal,
however, it is probably rather injurious than beneficial; but if an hour be per-
mitted to elapse, or if the quantity of food  taken have been small, it is of de-
cided benefit.   The  influence of temperature on  the  process of  solution,  is
remarkably shown in some of Dr. B.'s experiments.  He found that the gas-
tric juice had scarcely any influence on the food submitted to it, when the
bottle was  exposed to the cold air, instead of being kept at a temperature  of
100°.   He observed on  one occasion, that the injection of a single gill  of
water at 50° into the stomach, sufficed to lower its temperature  upwards  of
30° ;  and that its natural  heat was not restored for more  than half an hour.
Hence the  practice of eating  ice  after dinner, or  even of drinking largely  of
cold fluids, is very prejudicial to digestion.
  667.  From the foregoing statements we  may conclude, that the process by
which the  food  is dissolved in the Gastric fluid is of a purely Chemical na-
ture, since  it takes place out of the living body as well as in  it,—allowance
being made for the difference in its physical condition.  That the  natural pro-
cess of digestion is  imitated, when the food is  submitted to the action of the
gastric juice in a vial, not only in regard to the disintegration of  its particles,
but as to the change of character  which they are  made to undergo, is proved
by the fact, that  the artificial chyme thus formed exhibits the  same changes  as
the real chyme, when submitted to the  action of the bile (§ 658).   The pro-
cess of digestion, however, may be freely conceded to be vital, in so far as it
is dependent upon the agency of  a secreted product, which vitality alone (so
far at least as we at present know) can elaborate;  and all  for which it is here
contended  is, that, when this  product is once formed, it has an agency upon
the alimentary matter, which, though not yet fully understood, is conformable,
in all that is known of its operation, to the ordinary laws of chemistry.  Thus,
Digestion is conformable  to Chemical solution,—first, in the  assistance which
both derive from the minute division of the solids  submitted to it;—secondly,
in the assistance which both derive from the successive addition of small por-
tions of the comminuted  solid to the solvent fluid, and from the thorough in-
termixture of the two by  continual agitation;—thirdly, in  the limitation of the
quantity of food on  which a given amount  of gastric juice can operate, which
is  precisely the  case with chemical solvents  ;—fourthly, in the assistance which
both derive from an elevation of temperature,—the beneficial influence of heat
being only limited, in the case of digestion, by its tendency to produce decom-
position of the gastric fluid ;—fifthly, in the different action of the same solvent
upon the various solids submitted to it.
   668. It  may  be  considered  a well-established fact, that diluted acids alone
have no power of  chymifying alimentary substances, although  capable  of
partially dissolving  some of them; but that their presence in the  gastric fluid
is essential to its effectual action.   The active agent in the process appears to
be an Organic compound, to which the name of pepsin has been given.  The
properties  of this have  been investigated by Wasmann, who first succeeded in
obtaining it in an isolated state ; his observations were made upon the mucous
membrane of the stomach  of the  Pig, which greatly resembles that of Man.

   a. When this membrane is  digested in a large quantity of water at from 85° to 95°, many
other matters are removed from it besides pepsin; but if this water be removed, and  the
digestion be continued with fresh water in the cold, very little but pepsin is then taken  up.
Pepsin appears to be but sparingly soluble in water; when its solution is evaporated to dry-
ness, there remains a brown,  grayish, viscid mass, with the odour of glue, and having  the
appearance  of an extract.  The solution of this in water is turbid, and  still possesses appor-
tion of the characteristic power of pepsin, but greatly reduced. When strong alcohol is added
to a fresh solution of pepsin, the latter is precipitated in white flocks, which may be collected
on a filter, and produce a grey compact  mass when dried.   Pepsin enters into chemical com- 
NATURE OF CHYMIFICATION---PEPSIN.
507
bination with many acids, forming compounds which still redden litmus paper;  and it is
when thus united with acetic and muriatic acids, that its solvent powers are the greatest.
  b. " In regard to the solvent power of pepsin  for coagulated albumen, it was observed by
M. Wasmann that a  liquid which contains 17-10,000ths of acetate of pepsia, and 6 drops
of hydrochloric acid per ounce, possesses a very sensible solvent power, so that it will dis-
solve a thin slice of coagulated albumen in the course of 6 or 8 hours' digestion.  With 12
drops of hydrochloric acid  per ounce, the white of  egg is dissolved  in 2 hours.  A liquid
which contains £  gr. of acetate of pepsin, and to which hydrochloric acid and white of egg
are alternately added, so long as the latter dissolves, is capable of taking up 210 grains of
coagulated white of egg at a temperature between  95° and 104°.  It would appear, from
such experiments, that the  hydrochloric acid is the true solvent, and  that the action of the
pepsin is limited to that of disposing the white of egg to dissolve in hydrochloric acid.  The
acid when alone dissolves white of egg by ebullition, just as it does under the  influence of
pepsin; from which it follows that pepsin replaces the effect of a high temperature, which
is not possible in the  stomach.   The same acid with pepsin dissolved blood, fibrine, meat
and cheese; while the isolated acid dissolved  only an insignificant  quantity at  the same
temperature; but when raised to the boiling point, it dissolved  nearly as much, and the part
dissolved appeared to be of the same nature.  The  epidermis, horn, the elastic tissue (such
as the fibrous membrane of arteries) do not dissolve in a dilute acid containing pepsin.  M.
Wasmann has remarked that the pepsin of the stomach of the pig is entirely destitute of the
power to coagulate milk, although the j)e|>sin of the stomach ofthe calf possesses it in a very
high degree; from which he is led to suppose, that the power of the latter depends upon a
particular modification of pepsin, or perhaps upon another substance accompanying it, which
ceases to be formed when the young animal is no longer nourished by the milk of its mother."*

  669. It is considered by Liebig, however, that Pepsin has no proper  ex-
istence as such;  and that it is  nothing else than a proteine-compound in  a
state  of change,—being, when obtained  after the method  of Wasmann,  the
result of  the partial decomposition of the- membrane of the stomach, which
has been induced in it by  exposure to air.  This view accords well with the
fact, recently ascertained by MM. Bernard and Barreswill, that the Saliva and
Pancreatic fluid have an equal solvent power when acidulated.   In  their alka-
line condition, their action  appears  limited to starchy matters; of which they
effect  the conversion into sugar.  In their acid state,  they act, like the gastric
fluid, upon azotized  matters ; and, in  common with it, they are destitute of
power to act upon starch.—We  are further led, by this remarkable fact (the
knowledge of which enables  us  to harmonize many previous results, which
were   apparently discordant),  to  a  belter  understanding of the nature of  the
action of this Organic compound in the  Digestive  process.   Its operation on
starch is precisely that of  the  substance termed  Diastase,  which is found in
Plants, and  which is  the   agent employed  for the  conversion of starch into
sugar, in various processes  of the Vegetable economy.  In so doing, it acts as
a sort of ferment; having the  power of exciting a change in  another substance,
in which  it  does  not itself participate.    This appears to   be  precisely  the
nature of its  operation  upon azotized matters;  in which it produces an in-
cipient change,  that so alters their condition, as to  dispose them to solution in
hydrochloric and acetic  acids, with which they form definite chemical  com-
pounds.—The  analogy  of  the action of Pepsin to that of a  ferment, is further
shown in the power possessed by a very small  quantity of it, to  excite the
required change in an almost unlimited amount of alimentary matters; whilst
only a definite quantity of  these matters, when thus prepared, can  be dissolved
in a limited  amount of dilute  acid; which is  precisely analogous to  the  pro-
cess of chemical solution.   The agency  of Pepsin, in preparing them for that
process, resembles that of Heat; by which it may be  replaced,—the  dilute
acids alone, at  a high temperature, having the power of dissolving azotized
compounds.
  670. We have, in the last place, to consider the changes  which are effected

                * Graham's Elements of Chemistry, [Am. ed. p. 695.] 
508
OF FOOD, AND THE DIGESTIVE PROCESS.
in the nutritive materials, by the admixture of the biliary and pancreatic secre-
tions ; and to inquire into the form in which they are received into the  absorb-
ent vessels.—The substances of the first or saccharine group  consist chiefly
of Sugar and Starch.   It appears from the late researches of MM. Bouchardat
and Sandras, that Sugar is  gradually converted,  during its  passage along the
alimentary canal, into lactic acid;  and that it  is absorbed  in this form alone,
unless it have been administered in considerable quantity or for a long period.
The conversion  of sugar  into lactic  acid, appears  to be  preliminary to the
elimination of that substance by the respiratory process.   The  particles of
Starch, as already mentioned, are but very little acted on by the digestive pro-
cess, at  least in Man and  the Mammalia, unless  their envelopes have been
previously ruptured by heat or chemical agents ; but the triturating  power of
the gizzard in granivorous  Birds, aided by the high temperature and the more
alkaline character of the secretions, enables them to act with more  energy upon
amylaceous substances.  The products of the digestive action upon starch,
are dextrine and grape-sugar; and this is  gradually converted into lactic acid,
in which state it is absorbed.  If sugar be introduced into the blood-vessels
unchanged, it is drawn off by the urine ; and its  heat-sustaining agency, there-
fore, is not exerted.  It is  probably to avoid its too rapid introduction  that
the conversion of amylaceous into saccharine matter is so slowly effected in
the alimentary canal;  this  conversion seems  to begin in the  mouth, to cease
in the stomach during the operation of the acid solvent, and  to  recommence
after the neutralization of the acid by the biliary and pancreatic  fluids,—sub-
sequently continuing during nearly tbe whole of the  passage of the alimentary
matter along the intestinal  tube.—It is now quite certain, that the substances
of this class may be converted, in the living body, into oleaginous matter.  Of
the mode and the situation in which this  conversion  takes place,  nothing
whatever is certainly known; but a clue to an acquaintance with the former
seems to be given by the recently-discovered fact, that the  continued  contact
of bile with saccharine matter occasions the conversion of a portion of the
sugar into an  adipose compound (§ 835).
   671.  The substances forming tbe Oleaginous class do not seem to undergo
any change, except minute division of their particles, until the Chyme is min-
gled with bile; which substance acts as a soap, and renders the oily matters
soluble, or at any rate reduces them to a  condition in  which they can be ab-
sorbed  by the lacteals.  This, indeed, seems to be the main purpose of that
admixture of the bile with the mass in process of digestion, which experiments
and pathological observation abundantly prove to be requisite for the due per-
formance of that function.  Thus, it has been  shown by the experiments of
Schwann, that, if the bile-duct be divided, and be made to discharge  its  con-
tents externally through a fistulous orifice in the walls ofthe abdomen, instead
of into the intestinal canal, those animals which survive the immediate effects
of the operation, subsequently die from  inanition, almost as soon as if they
had been entirely deprived of food.  In like manner, if the flow  ofthe biliary
secretion into the intestine be prevented by  disease,—such as obstruction of
the gall-duct,—the digestive function  is  evidently  disordered, the  peristaltic
action ofthe intestine is not duly performed, the faeces are white and clayey;
and there is an obvious insufficiency in the supply of nutriment prepared for
the absorbent vessels. This deficiency seems  partly due to the want of power
to absorb the oleaginous particles of the  food, which is the result of the non-
intermixture of the bile with the chyme; and partly to the suspension of the
supply of combustible matter, that is afforded  by certain constituents of the
bile itself, which  are destined, not to be  carried out of the system,  but to be
re-absorbed.—The presence of bile in the stomach has the effect of suspend- 
ABSORPTION FROM THE DIGESTIVE CAVITY.
509
ing the solution of the various azotized  principles, and  in regard to them,
therefore, it is injurious; but it seems, from the observations of Dr. Beaumont,
to be a  spontaneous occurrence, whenever the diet has been for a long time,
and in great part, of an oleaginous nature; and it then appears destined to aid
in the reducing process, which is the proper function of the stomach.   It is
suggested by Dr. A. Combe, whether the peculiar digestibility of a piece of
fat bacon, in certain forms  of Dyspepsia, may not be  due  to  the  abnormal
presence of bile in the stomach.  The power of precipitating the proteine-
compounds from their acid solutions, which has  been shown, by the  recent
experiments of Platner, to belong to the peculiar principles of  bile, fully ex-
plains its injurious effects upon the solvent processes, which normally take
place in  the stomach.—In regard to the Albuminous and  Gelatinous articles
of food,  there is no evidence that any other change is effected in them, than
one of simple solution; and they appear to be absorbed in the same condition
as that to which they are reduced by the action of the stomach.
                          CHAPTER   XI.


                   OF ABSORPTION AND  SANGUIFICATION.

               1.—Absorption from the Digestive  Cavity.

   672.  So long as the Alimentary matter is contained in the digestive cavity,
it is as far from being conducive to the nutrition of the system, as if it were in
contact with the external surface.  It is only when absorbed into the vessels,
and carried by the circulating current into  the remote portions of the body,
that it becomes capable of being appropriated by its various tissues and organs.
Among  the Invertebrata, we find the reception of alimentary matter into  the
Circulating system to be entirely accomplished  through the medium of  the
blood-vessels, which are distributed  upon the walls of the digestive cavity.
But in the Vertebrata, we find an additional set of vessels interposed  between
the walls of the intestine and the sanguiferous system; for the purpose, as it
would seem, of taking up that portion of the nutritive matter which  is not in
a state of perfect solution, and of preparing it for being introduced into  the
current of the blood.   These are the lacteals, or absorbents of the intestinal
walls.   That their special office is to take up the  product of the admixture of
the chyme with the biliary  and pancreatic fluids, appears from the fact, that
they are not distributed at all upon the walls of the stomach, nor upon those of
the duodenum above the point of entrance of the hepatic and pancreatic ducts;
but that they are copiously distributed upon  the walls of the remainder of  the
small intestine, and more sparingly  upon those  of the large.   Each lacteal
tube originates in  the interior of one of  the villous processes of  the mucous
membrane lining the intestinal tube.   The accompanying  figure represents  the
appearance offered by the  incipient  lacteals, in a villus of the jejunum of a
young man, who had been hung soon after  taking a full  meal  of farinaceous
food.   The trunk  that  issues from the villus is formed  by the confluence of
                                  43* 
510
OF ABSORPTION AND SANGUIFICATION.
                     several smaller branches, whose  origin it is difficult to
                     trace; but it is probable that they form loops by anasto-
                     mosis with each other, so that there  is no proper free
                     extremity in any case.  It is  quite certain that the lac-
                     teals never  open by free orifices upon the surface ofthe
                     intestine, as was formerly imagined.  From the researches
                     of Mr. J. Goodsir, already referred to  (§ 181), it appears
                     that these loops are imbedded  in a mass of cells, which
                     are the real agents in the selection of  the materials that
                     are destined to  be conveyed into the lacteals.   When
                     these cells have distended themselves, by their inherent
                     power of growth, with the materials which are adapted
  One ofthe intestinal villi,  J   ,  .   °.   .    _    .       , ,         ,   , .,   •  c ,,
with,be commencement  to their selecting function, and have  reached their full
a lacteal.               term of maturity, they appear to yield their contents to
                     the  absorbent  vessels, either  by  bursting  or by deli-
quescence.—It is  thought by Prof. E. Weber, that the  epithelial cells, which
cover the villus, perform a preliminary office; the nutrient  matter being  first
absorbed and partially prepared by them; and then  being drawn, through the
basement membrane of the  villus, into the special absorbent cells which form
part of its substance.  This  seems the more likely,  as we shall hereafter
find that the epithelial  cells of the placental  tufts appear to perform  a  like
function.
  673.  The villi are also furnished with a  minute  plexus  of blood-vessels;
of which the larger branches may be seen with the naked eye, when they are
distended with blood, or with coloured injection (Figs.  205, 206).   The  par-
ticular arrangement of the capillaries of which the plexus is formed, varies in
different animals;  but in all they seem to be most copiously distributed upon
the  surface  of the villus.  The purpose of these may be partly to afford some
of the materials for the development of the absorbent  cells; and this would
seem probable  from the recent  experiments of Mr. Fenwick,* which show
that the lacteals will not absorb alimentary matter from any part of the intes-
tinal canal, in which the blood is not circulating.   But there can be no reason-
able doubt, that the blood-vessels of the mucous membrane lining the digestive
cavity, and  especially those of the villi, perform an important part in the func-
tion of Absorption.   This is established  by the fact, that soluble substances
introduced into the stomach, and prevented from passing beyond  its  pyloric
orifice, are absorbed from its walls.
  674.  In regard to the  degree  in which the function  of  Nutritive Absorp-
tion is performed by  the Lacteals, and by the Sanguiferous System, respect-
ively, considerable  difference of opinion has prevailed.   When the Absorbent
vessels were first  discovered, and their  functional  importance perceived, it
was imagined that the introduction of alimentary fluid  into the vascular  sys-
tem took place by them alone. A slight knowledge of Comparative Anatomy,
however, might have sufficed to correct this error;  since no lacteals exist in
the Invertebrated animals, the function of Absorption being performed by the
Mesenteric blood-vessels only; from which it is evident, that these do  pos-
sess the power of absorption:  and it is scarcely to be supposed  that  they
should not exercise this power in Vertebrated animals  also, since  their dis-
position on  the walls of the intestinal cavity is evidently favourable to it. On
the  other hand, the  introduction of a new and distinct system of vessels would
seem  to indicate, that they must  have some special  purpose; and  there can
be no doubt that the  absorption  of  certain  kinds of nutritive matter  is that
for  which they are peculiarly designed.  The fluid found  in the  lacteals  is
Fig. 204.
* Lancet, Jan. and Feb. 1845. 
 ABSORPTION BY BLOOD-VESSELS OF VILLI.                511

Fig. 205.                            Fig. 206.
                                    A, apex of intestinal vil-
 Vessels of an intestinal villus          lus  from the duodenum of
of a flare, from a dry prepara-          Human female; B, a mesh of
tion by D811inger; 1,  1, veins          the  vascular net-work, 1, 1,
filled with white injection ; 2, 2,          filled up with delicate cellu-
arteries injected red.  Magnified          lar tissue, 2, magnified about
about 45 diameters.                    45 diameters.
almost invariably the same; being  that to which the  name chyle  has been
applied.  It appears from the uniformity of its  composition, which forms a
striking contrast with the diversity of the food from which it is obtained, that
the lacteals (or rather the absorbent cells,  amongst which they originate) have
in some degree the power of selecting the particles of which it is composed;
and  that, whilst they take  up such a proportion of each class of alimentary
materials  as will rightly blend with the rest in the nutritious fluid, they reject
not only the remainder, but also (for the most part at  least) any other ingre-
dients which may be contained  in  the fluid of the intestines.   Such may be
stated as the  general  result of the  experiments that have been made  to de-
termine their function; though it is unquestionable that  extraneous substances,
especially of a saline nature,  occasionally find their way into this system  of
vessels.   This may not improbably be  due to a  correspondence in the size
and  form of the ultimate particles of such substances, with those of  the mate-
rials  normally absorbed by  the lacteals.*
   675. On  the other hand, the  Blood-vessels seem to be  less  concerned  in
nutritive absorption, but take up from  the alimentary canal a portion  of almost
any fluid matters which it may contain.   This seems to have been established
by the carefully-conducted experiments of MM. Tiedemann and Gmelin, who

  * Experiments upon the function of Absorption in Plants, whose radical vessels  have a
corresponding power of selection, appear likely to assist in elucidating this interesting subject.
By the experiments  of Dr. Daubeny it has been ascertained, that if a plant absorb any par-
ticular saline compound, it can also be made to absorb those which are isomorphous with it,
though it will reject most others.—See Princ. of Gen. and Comp. Phys.,§ 294. 
512
OF ABSORPTION AND SANGUIFICATION.
mingled with  the food of animals various substances, which, by their colour,
odour, or chemical properties, might be easily detected in the fluids of the
body.   After  some time the animal was examined; and the result was, that
unequivocal traces of the substances were not unfrequently detected  in  the
venous blood  and in  the urine; whilst it was only in a very few instances,
that any indication of them could be discovered in the chyle.   The colouring
matters employed were various vegetable substances;  such as gamboge, mad-
der, and rhubarb:  the odorous substances were  camphor, musk, assafcetida,
&c.; while, in other  cases, various saline bodies, such as muriate  of barytes,
acetate of lead and of  mercury, and some of the prussi'ates, which might easily
be  detected by  chemical tests, were mixed  with the food.  The colouring
matters, for the most  part, were carried out of the system, without being re-
ceived either  into the veins or lacteals; the odorous substances were  gene-
rally detected  in the  venous blood and in the urine, but not  in  the chyle;
whilst of the  saline  substances, many  were found in  the blood and  in  the
urine,  and  a  very few only in the  chyle.   A similar  conclusion might be
drawn from the numerous instances in which various substances  introduced
into the intestines have been detected in the blood, although the thoracic duct
had been tied; but these results are less satisfactory, because eyen if there is
no  direct communication (as  maintained by  many) between the lacteals arid
the veins in the mesenteric glands, the partitions which separate their respect-
ive contents are evidently so  thin, that transudation  may readily take  place
through them.—It would seem probable, that substances perfectly dissolved
in the  fluids of the stomach, are taken into the blood-vessels so copiously dis-
tributed on its walls, by the  simple and necessary process of Endosmose; in
this manner we may  account  for the fact, that saline substances are for  the
most part readily absorbed into the  blood; and there seems reason to believe
that the Albuminous portion of the chyme, together with the Saccharine prin-
ciples or the products of their transformation, may thus  be introduced directly
into the circulating current, without passing through  the lacteals.—On this
subject there is much  need of further information.

                  2.—Absorption from the Body in general.

  676. The Mucous  Membrane of the  alimentary canal is by no means  the
only channel,  through which nutritive or other substances may be introduced
into the circulating apparatus.  The Lymphatic system is present in all animals
which  have a  lacteal  system ;  and the two evidently constitute  one set of ves-
sels.   The lymphatics, however,  instead of commencing  on the intestinal
walls, are distributed  through  the greater  part of the body, especially  on the
Skin ;  their origins cannot be clearly traced ;  but  they seem in general to form
a plexus in the  substance of the tissues, from which  the convergent  trunks
arise.   After  passing, like the  lacteals, through a series of glandular  bodies
(the precise nature of which will be presently considered, § 682), they  empty
their contents  into  the  same receptacle with the  lacteals; and the mingled
products of both pass into the Sanguiferous  system.—We find in the Skin,
also, a most copious distribution of capillary blood-vessels, the arrangement of
which  is by no means unlike that of the blood-vessels of the alimentary canal;
and its surface is  further extended by the elevations that form the sensory
papillae, which are  in many points comparable to the intestinal villi, although
their special function  is so different.—In the  lowest tribes of animals, and in
the'earliest condition  ofthe higher,  it would  seem as if Absorption by the  ex-
ternal  surface is almost equally important to the  maintenance of life, with
that which  takes place through the internal reflexion of it forming the walls
of the  Digestive cavity.   In  the adult condition of the  higher  animals, how- 
              ABSORPTION THROUGH THE CUTANEOUS SURFACE.          513

ever, the special function ofthe latter is so much exalted, that it usually super-
sedes the necessity of any other  supply ;  and the function of the cutaneous
and pulmonary surfaces  may be considered as rather that of exhalation, than
of absorption.  But there are peculiar conditions of the  system, in which the
imbibition of fluid through  these surfaces  is performed with  great activity,
supplying what would otherwise be  a most important  deficiency.  It may
take place either through the direct application of fluid to the surface, or even
through the medium of the atmosphere, in which a greater or less proportion
of watery vapour is  usually dissolved.   This absorption occurs most  vigor-
ously, when the  system has been drained of its fluid, either by an excess of
the excretions, or by a diminution of the regular supply.
   677. It may be desirable to adduce some  individual cases,  which will set
this function in a  striking  point of view;  and  those may be first noticed, in
which the absorption took place, through the contact of liquids with the skin.
It is well known that shipwrecked sailors,  and others, who are suffering from
thirst, owing to the want of fresh water, find it greatly alleviated, or altogether
relieved, by dipping their clothes into the sea, and putting them on whilst still
wet, or by frequently immersing  their own ,bodies.—Dr. Currie relates the
case of a patient labouring  under dysphagia'in its most advanced stage; the
introduction of any nutriment,  whethersolid or fluid into the stomach, having
become perfectly impracticable.  Under these melancholy circumstances, an
attempt was made to prolong his existence, by the exhibition of nutritive ene-
mata, and by immersion ofthe  body, night  and morning,  in a bath  of milk and
water.   During the continuance of this plan, his weight, which had previously
been rapidly diminishing, remained stationary, although the quantity of the
excretions was increased.   How much of the  absorption, which must have
been effected to replace the amount of excreted fluid, is to be attributed to the
baths, and how much to the enemata, it is  not easy to say ;  but it is important
to remark that " the thirst, which was troublesome during the first days of the
patient's  abstinence, was abated, and, as  he declared, removed by the tepid
bath, in  which he had the most grateful sensations."  " It cannot be doubted,"
Dr.  Currie observes, " that the discharge by stool and  perspiration exceeded
the weight of the clysters ;" and  the  loss  by the urinary excretion, which in-
creased from 24 oz. to 36 oz. under  this system, is only to  be accounted  for
by the cutaneous absorption.—Dr. S. Smith mentions  that a man, who had
lost nearly 3 lbs. by perspiration, during an hour and  a  quarter's labour in a
very hot atmosphere, regained  8 oz. by immersion in a warm bath at 95°,  for
half an hour.—The experiments of Dr. Madden* show that a positive increase
usually takes place in the weight of the body, during immersion in the warm
bath, even though there  is  at the same time a continual loss of weight  by pul-
monary exhalation,  and  by transudationt from the skin.  This increase was,
in some instances, as much as 5  drachms  in half an hour;  whilst the loss of
weight during the previous half hour had been  6j| drachms: so that, if the
same  rate of loss \yjere continued in the bath, the real gain by absorption must
have been nearly an ounce and a half.  Why this gain  was  much less than
in the cases just alluded to, is at once accounted for by the fact that there was
no deficiency, in the latter case, of the fluids naturally present in the body.
   678.  The quantity of water which may be imbibed from the vapour of the
atmosphere, would  exceed belief, were  not the facts on which the assertion
rests, beyond  all question.  Dr. Dill relates  the  case  of a diabetic  patient,

   *  Prize Essay on Cutaneous Absorption, pp. 59—63.
   ■f  That part of the function of cutaneous transpiration, which consists in simple exhalation,
is of course completely checked by such immersion ; but that which is the result of an actual
secreting process in the cutaneous glands  (Chap, xv., Sect. 8)  is increased by heat, even
though this be accompanied with moisture. 
514
OF ABSORPTION AND SANGUIFICATION.
who for five weeks passed 24 lbs. of urine every twenty-four hours ;  his in-
gesta during the same period amounted to 22 lbs.   At the commencement of
the disease he weighed 145 lbs.;  and when he died, 27 lbs. of loss had been
sustained.  The daily excess of the excretions over the ingesta could not have
been less than 4 lbs.; making 140 lbs. for the thirty-five days during which
the complaint lasted.   If from this we deduct the amount of diminution which
the weight of the body sustained during the time, we shall still have 113 lbs.
to be accounted for, which can  only have entered the body from the atmo-
sphere.—A case of ovarian dropsy has been  recorded, in which it was  ob-
served that  the patient, during eighteen days, drank 692 oz. or 43  pints of
fluid, and  that  she discharged by urine and by paracentesis, 1298 oz. or 91
pints, which leaves a  balance of 606 oz. or 38 pints, to be similarly accounted
for.*—The following  remarkable  fact is mentioned by Dr. Watson in his Che-
mical Essays.  " A lad at Newmarket, having been almost starved, in order
that he might be reduced to a proper weight for riding a match,  was weighed
at 9 a. m., and again at 10 a. m. ;  and he was found to have gained nearly 30
oz. in weight  in  the  course of this hour, though  he had only drunk half a
glass of  wine  in the interim."—A parallel  instance was related to the Author
by the late Sir  G. Hill, then Governor of  St. Vincent.   A  jockey had been
for some time in training for a race, in which  that gentleman was much inte-
rested ;  and had been reduced to the proper weight.  On the morning of  the
trial, being much oppressed with  thirst, he  took one cup of tea;  and shortly
afterwards his weight was found to have increased 6 lbs.; so that he was in-
capacitated for  riding.—Nearly the whole of the increase in the former case,
and at least three-fourths of it in the  latter, must  be attributed to cutaneous
absorption ;  which function was  probably stimulated by the wine that  was
taken in the one case, and by  the tea in the other.
   679.  Not only water, but substances dissolved in it, may be thus introduced.
It has been found that, after bathing in infusions of madder, rhubarb, and tur-
meric, the urine was  tinged with  these substances; and that a garlic plaster
affected the breath, when  every care was taken, by breathing through  a tube
connected with the exterior of the apartment, that the odour should not be re-
ceived into the  lungs.t  Gallic acid has been found in the urine, after the ex-
ternal application of a decoction of a bark containing it;  and the soothing influ-
ence in  cases  of neuralgic, pain,  of the  external application of cherry-laurel
water, is well  known.  Many saline  substances  are absorbed  by the skin,
when applied to it in  solution; and it  is interesting to remark, that, contrary
to what happens in regard to the absorption of these from the alimentary ca-
nal, they are  for the  most part  more readily  discoverable in the absorbents
than in the veins.  This  is  probably due to the  fact, that the imbibition of
them is  governed entirely by physical laws; in obedience to which, they pass
most readily into the  vessels which present the thinnest walls and the largest
surface.  In the intestines, the vascular plexus on each villus is far more ex-
tensive than the ramifying lacteal which originates  in it;  and as the walls of
the veins are thin, there is considerable facility for  the entrance  of saline  and
other substances into  the general current of the circulation ;  but in the skin,
the lymphatics are  distributed much more  minutely and extensively than the
veins; and soluble matters, therefore,  enter them  in preference to the veins.
The absorbent power of the Lymphatics of the Skin is well shown by the
following  experiment.  A bandage having been tied by Schreger round the
hind-leg of a Puppy, the limb was kept for twenty-four hours in tepid milk;

   * Madden, loc. cit.—In this case, however,  something is to be allowed for the quantity of
water contained in the solid food ingested.
  t Dunglison's Physiology, [6th. ed., vol. i. p. C47.] 
ABSORPTION FROM THE BODY IN GENERAL.
515
at the expiration of this period, the lymphatics were found full of milk, whilst
the  veins contained none.  In repeating this  experiment upon a young man,
no milk could be detected in the blood drawn from a vein. It has been shown
by Muller that, when the posterior extremities of a Frog were kept for two
hours in a solution of prussiate of potass, the salt  had freely penetrated the
lymphatics, but had not entered the veins.—It does not follow, however, from
these and similar experiments, that in all tissues  the  lymphatics absorb more
readily than the veins ; for as the capillary blood-vessels in the lungs are much
more freely exposed to the surface of the air-cells, than  are the lymphatics,
we  should, on the principles just now stated, expect the former to absorb more
readily.  This appears from experiment to be the fact;  for when a solution
of prussiate of potass was injected by Mayer into the lungs, the salt could be
detected in the serum of the blood  much sooner than in the lymph, and in
the blood of  the left cavities of the  heart, before it had  reached  that of the
right.
  680.  Our inferences with regard to the ordinary functions of the Lymphatic
system, however, must be rather drawn from the nature  of the fluid which it
contains, and from the uses subsequently made of it, than from experiments
such as the preceding.  We shall presently see, that there is a close corre-
spondence in composition between the Chyle ofthe Lacteals, and the Lymph
of the Lymphatics;  the chief difference being the presence in the former, of
a considerable quantity of  fatty matter, and of a larger proportion of the as-
similable substances (albumen and fibrine) which are equally characteristic  of
both (§ 691).  This evident conformity in the nature of the fluid which these
two sets of vessels transmit, joined to the fact of the fluid Lymph, like the
Chyle, being conveyed into the general current of the circulation, just before
the blood is again transmitted to the system  at large, almost inevitably leads
to the inference, that the lymph is, like the chyle, a nutritious fluid, and is not
of an excrementitious character, as formerly  supposed.  On  the other  hand,
the close resemblance  between the contents  of the Lymphatics, and diluted
Liquor Sanguinis, seems to indicate  that the  former are  partly derived from
the fluid portion of the Blood, which has transuded through  the walls of the
Capillary vessels;  and  we shall  presently  see  reason  to  believe that this
transudation  is for the purpose of subjecting certain crude materials, that have
been taken up direct into the blood-vessels,  to an elaborating or preparatory
agency, which it seems to  be the especial object of the Absorbent  system to
exert upon certain of the nutritive components of the circulating fluid.
  681. But it seems not improbable that there may be another source for the
contents of the Lymphatics.  We have  already had to allude, on several oc-
casions, to the disintegration which is continually taking place within the living
body; whether as a result ofthe limited duration ofthe life of its component
parts, or as a consequence  of the decomposing action of Oxygen.  Now the
death of the  tissues by no means involves their  immediate and complete de-
struction ; and there seems no more reason why an animal should not derive
support from its  own dead parts than from  the dead body  of another indi-
vidual.  Whilst, therefore, the matter, which has undergone too  complete a
disintegration to be again employed as nutrient material, is carried off by the
excreting processes that portion which is capable of being again assimilated,
may be taken up by the Lymphatic system.  If this be the case, we may say,
with Dr. Prout, that " a sort of digestion is carried on in all parts of the body."
It may be stated, then, as a general proposition, that the function of  the Ab-
sorbent System is to  take  up, and to convey into  the Circulating apparatus,
such substances  as  are capable  of  appropriation to the nutritive process;
whether these  substances  be directly furnished  by the external world, or  be
derived from the disintegration of the  organism itself.   We have  seen that, 
516
OF ABSORPTION  AND  SANGUIFICATION.
in the Lacteals, the selecting power is such, that these vessels are not disposed
to convey into  the system  any substances but such as  are  destined for this
purpose;  and that extraneous matters are  absorbed in preference by the Me-
senteric  Blood-vessels.   The case is different,  however, with  regard  to  the
Lymphatics; for there is reason to believe, that they are more  disposed than
the veins to the absorption of other  soluble matters;  especially when  these
are brought into relation with the skin, through which the  lymphatic vessels
are very profusely distributed.

  a. Since the time of Hunter, who first brought prominently forward the doctrine  alluded
to, it has been commonly supposed that the function of the Lymphatics is to remove, by in-
terstitial absorption, the effete matter, which is destined to be carried out of the system;  and
any undue activity in this process (such as exists  in ulceration), or any deficiency in its
energy (such as gives rise to dropsical effusions, and  other collections of the same kind),
have been attributed to excess or diminution in the normal operation of the Absorbent Sys-
tem.—From what has been  stated, however, it  appears  that the special function  of the
Lymphatics, like that of the Lacteals, is nutritive absorption ;* and that the reception of any
other substances into their interior, must be looked upon as resulting simply from the  per-
meability of their walls.   This  statement applies to the not unfrequent occurrence of the
absorption of bile, and other fluids, from  the walls of  the cavities in which they were col-
lected: with regard to the absorption of pus, however,  which has been occasionally noticed
to take place, both from internal collections, and from open ulcers, it may be remarked, that
the lymphatic vessels were not  improbably laid open  by ulceration; since in no other way
can be understood the entrance of globules so large as those of pus, into their interior.
  b. If this view of the function of the  Lymphatics be correct,  it follows that we must at-
tribute to the Blood-vessels the  absorption  of the truly effete particles; and in this there
would seem no improbability.  We know that Venous blood contains the  elements of  two
important excretions, that of the lungs and that of the bile, in a far higher amount than does
arterial blood; and we shall hereafter see, that there is a certain portion of the fluid, which
consists of " ill defined animal principles" that seem ready to be thus thrown off.
  c. It may be further remarked, that the reciprocal part which Hunter imagined  the Ar-
  *  The Author, at the time of the publication of the First Edition of this work, believed
this view to be altogether novel;  he has since learned, however, that a similar doctrine had
been put forward by Dr. Moultrie, of South Carolina, in the American Journal of the Medi-
cal Sciences, for the year  1827.
  [In the American Journal of the Medical Sciences, for  1827, Dr. James Moultrie pub-
lished an essay on the " Uses of the Lymph," in which, amongst other things  attempted to
be sustained, will be found the following views.
  1.  The lacteals and lymphatics do not constitute, as they are supposed to do, the absorbent
system of the animal economy; they do not, as the absorbent theory supposes, remove from
the organs the "cast  off molecules" of which they are composed, or carry out of the body
the " effete" particles disintegrated by the act of the assimilative function.   The one is en-
gaged in the preparation and introduction of chyle, and chyle only into the blood; the other
in elaborating an organizable product—a recrementitious  secretion destined to unite with it
for objects of a common and nutritious  nature.  2. The  primary object of the  lymph, and
that for which it is made  to commingle with the chyle in the thoracic duct, is the vitalization
of the  latter fluid.   3. The truly "effete" matter of the body is the carbonaceous element
of the venous blood, to  which may be added the urea or azotic element of the urine.  Than
these, we know of nothing to which that term can be applied.   4. The venous and not the
lacteal  or lymphatic  system, therefore, is the "absorbent  system," in  any  disintegratory or
effete sense of the phrase.  5.  Nature, in eflecting the elimination of excrementitious mat-
ter from the constituency of the solid or fluid parts, appears to aim at restoring to the physi-
cal universe, the matter temporarily borrowed for  subsistence, in a state of elementary sim-
plicity, or an approximation thereto; that is, the carbon as  carbon, the azote as azote, and
hydrogen and oxygen as hydrogen and oxygen.  The lungs she  uses as one medium of es-
cape ; the kidneys as a second ;  and the skin as a third, &c.  Hence, the carbonic  acid  gas
of respiration; the urea of the kidneys, and the aqueous exhalations ofthe skin, pulmonary
transpiration and urine.
  These doctrines have been regularly taught by Dr. M., in  his course of lectures on physi-
ology, delivered in the Medical College of the State of South  Carolina, since the  establish-
ment ofthe  College in 1833. They have also been recently enforced in a brochure published
by Dr.  M., in which he asserts  and vindicates his  claim to their paternity.   On the Organic
Functions of Animals.  By James  Moultbie, M.D., etc., Charleston, S. C. 1844.—M. C.] 
STRUCTURE OF ABSORBENT GLANDULE.
517
teries and Lymphatics to perform in the  function of Nutrition, is quite inconsistent with
what is now known of the  nature of that process: for, as will subsequently appear, it en-
tirely consists in a reaction between the tissues and the nutritious fluid, in which the vessels
have no share save as the channels of supply.  When these channels are obstructed, or the
supply of new matter is cut off in any other way, the removal of the old by interstitial ab-
sorption becomes evident; and that this is accomplished at least as much by the veins as by
the lymphatics, appears from the fact that in some tissues, in which it may take place with
rapidity, lymphatics do not  exist.

             3.—Of the Elaboration of the Nutrient Materials.

   682. The alimentary substances, taken up by the Absorbent vessels, seem
very far from being capable  of immediate application to  the nutrition of the
body; for we find that  they are not conveyed by any means directly into the
Circulating current, but that they first traverse a long series of tubes, convo-
luted at intervals  into ganglia or knots ;*  and that, in the course of this pas-
sage, they undergo considerable changes, which tend to  bring the fluid into
closer relationship with  the Blood.  It  seems probable  that the  materials,
which are directly received into the Blood-vessels, are equally far from being
immediately applicable  to the Nutritive processes ; for we find, in connection
with  the  vascular system,  certain bodies having the essential  structure  of
glands, but destitute of  efferent ducts ; which must restore  to the circulating
current any substances which  they withdraw from  it; and which there are
various reasons  (as will presently appear) for  placing  in the same category
with the glandulae ofthe Absorbent system.—The Absorbent Glandulae, whe-
iher placed upon the Lacteals  in  the Mesentery, or  upon the Lymphatics  in
various parts of  the body, have the same  general structure.  They are made
up of  convoluted knots of absorbent vessels,  the simple cylindrical canals  of
which, however,  are usually dilated into larger cavities, or cells;  and amongst
these, capillary blood-vessels are  minutely distributed.  These  blood-vessels
have  no  direct communication with the  interior of the  absorbents  and the
cavities of the glandulae, being separated from them by the membranous walls
of both sets of tubes;  but  there  can be  no  doubt that transudation  readily
takes  place  from  one  set  of  canals to  the other.   The epithelium, which
lines the  absorbent vessel, undergoes a marked change where  the vessel  en-
ters the gland ;  and becomes more  like that of the  proper glandular follicles
in its character.    Instead of being flat and  scale-like, and forming a single
layer in close apposition with the  basement-membrane, as it does in  the  ab-
sorbents previous to their entrance  into the gland  and  after their emergence
from it, we find it composed of numerous layers of  spherical nucleated cells,
of which the superficial ones are  easily detached, and appear to be identical

                Fig. 207.                                Fig. 208.
  Diagram of a lymphatic gland, showing the           Portion of intra-glandular lymphatic,
intra-glandular network, and the transition         showing along the lower edge the thick-
from the scale-like epithelia ofthe extra-glan-         ness ofthe germinal membrane, and upon
dular lymphatics, to the nucleated cells of the         it, the thick layer of glandular epithelial
intra-glandular.                              cells.
  * In Reptiles, in which there are no glands or ganglia in the Absorbent system, the tubes
are immensely extended in length.
     44 
518
OF ABSORPTION AND SANGUIFICATION.
with the cells found floating in the Chyle.*  Their purpose will be considered
hereafter.
   683.  To the  class  of  Vascular Glands belong the  Spleen, the Thymus
and Thyroid  Glands,  and the supra-Renal Capsules.  With the exception of
the first, they all have  their  origin (as recently ascertained by Mr. J.  Good-
sirt)  in involuted portions of the Germinal membrane; and, at an early  period
of embryonic life, they are in actual continuity with each other.   Their original
identity of function, therefore, cannot be doubted; and the probability  of the
inference, which rests on other grounds, that this  function is to assimilate or
elaborate  the nutrient materials (in  the manner  in  which the cells  of  the
leaves  of Plants prepare their  elaborated  sap), is strengthened by its  exact
conformity with the original function ofthe Germinal membrane.   But there
is no improbability that  they may severally have  some  subsidiary  or supple-
mentary function to perform ; varying  according  to their respective structure,
position, and  connections.  This  seems peculiarly the  case in regard  to  the
Spleen; the origin of which body is not the same with that of the other three.

  a.  According to the account of Dr. Julian Evans,J whose researches appear to have been
more successful  than those of any other Anatomist, the Spleen essentially consists of a fibrous
membrane, which  constitutes its exterior envelope, and which sends prolongations in all
directions across its interior, so as to divide it into a number of minute cavities or lacuna?
of irregular form.   These Splenic lacuna communicate freely with  each other, and with
the Splenic vein; and they are lined by a continuation of the lining membrane ofthe latter,
which is so reflected upon itself, as to leave oval or circular foramina, by which each lacuna
opens into others, or into the splenic vein.  The lacuna?, whose usual diameter is estimated
by Dr. Evans at from half to one-third  of a line, are generally traversed  by filaments of
elastic tissue, imbedded in which a small artery and vein may be frequently observed; over
these filaments,  the lining membrane is  reflected in folds; and in this manner  each lacuna
is incompletely divided into two or more smaller compartments.   There is no direct com-
munication  between the splenic artery and  the interior of the lacuna?; but its branches are
distributed through  the intercellular  parenchyma (which will  be  presently described);  and
the small veins, which collect the blood from the capillaries of the organ, convey it into
these cavities, from which  it is conveyed away by the splenic vein.  The lacunae  may be
readily injected  from the splenic  vein with either air or liquid,—provided  they are not filled
with coagulated blood; and they are so distensible, that the organ may be made to dilate to
many times its original size, with very little force.  This is especially the case in the Spleen
ofthe Herbivora; for the Spleen of a Sheep, weighing 4 ounces, may be easily made to con-
tain 30 ounces of water. That of Man, however, is less capable of this kind of enlargement.
—According to Dr. Evans, the lacuna? ofthe spleen never contain anything but blood ;§ and
he notices that a frequent condition of the Human Spleen  after death, which is sometimes
described as a morbid appearance, consists in the filling of the lacuna? with firmly-coagulated
blood, which gives  a granular appearance to the organ.
  b.  The partitions between the  lacuna? are formed, not only by the membranes  already
mentioned,  but by the peculiar parenchyma of the Spleen; which constitutes a larger part
of the organ in Man than in the Herbivorous Mammalia.   It  presents a  half fluid appear-
ance to the eye; but when an attempt is made to tear it, considerable resistance is expe-
rienced  in consequence of its being intersected by what appear to be minute fibres.  When
a small portion of it is pressed, a liquid is separated; which is that commonly known as the
Liquor Lienis, or Splenic blood; and which is usually described (but erroneously, according
to Dr. E.) as filling the lacuna? of the Spleen.  This liquid, when diluted  with serum and
examined under the Microscope, is found to contain two kinds of corpuscles,—one sort being
apparently  identical with ordinary blood-corpuscles—and  the  other with the  globules cha-
  * See Mr. J. Goodsir's Anatomical and Pathological Researches, p. 46.
  f Proceedings of the Royal Society, 1846.
    Lancet, April 6, 1844.
    "It differs in no respect from venous blood taken  out of any other part of the portal
system.   I have found it fluid or coagulated, as in other parts of the venous system ; and I
have frequently pulled out from the splenic vein colourless coagula. Occasionally a number
of globules may be distinguished in it, resembling those found in the parenchyma; but in
these cases the organ appears to have suffered injury, and these matters appear to have got
into the cells and vein in consequence."   Loc. cit. 
STRUCTURE AND FUNCTIONS OF THE SPLEEN.
519
racteristic of the lymph and abundant in the  lymphatic glands.  The remaining fibrous
substance consists entirely of capillary blood-vessels and lymphatics, with minute corpuscles,
much smaller than blood-corpuscles, varying in  size from about l-6000th to l-7000th of an
inch, of spherical form, and usually corrugated on the surface.  These lie in great numbers
in the meshes of the sanguiferous capillaries; and the minute lymphatics are described by
Dr. E. as connected with the splenic corpuscles, and apparently arising from them.—Lying
in the midst ofthe parenchyma are found a large number of bodies, of about a third of a line
in diameter, which are evidently in close connection with the vascular  system:  these have
long been known as the Malpighian bodies of the spleen, after the name of their discoverer;
but since his time, their existence has been denied, or other appearances have been mistaken
for them.  According to Dr. E., they in all respects resemble the mesenteric or  lymphatic
glands in miniature,—consisting as they do of convoluted masses of blood-vessels and lym-
phatics, united together by elastic  tissue, so as  to possess considerable firmness: and they
further correspond with them in this,—that the  lymph they contain, which was  quite trans-
parent in their afferent lymphatics, now becomes somewhat milky, from containing a large
number of Lymph-globules.
  684.  In regard to the functions of the Spleen, great uncertainty exists.  It
appears from the foregoing account of its structure, that it  may be  regarded
as an organ of duplex  character, and probably of double function.   The cel-
lated structure maybe considered as a multilocular reservoir, capable of great
distention, and lined with a continuation of the inner  membrane of  the  vein;
receiving blood, on  the one hand, from the veins  of the interior of the organ,
and transmitting it onward to the Vena  Portae; and on the other hand, acting
as a reservoir for  the venous blood of the abdomen, when, from any cause,
its passage into the  Vena  Cava is obstructed.  The splenic  parenchyma,  on
the other hand, must be regarded as a complex Lymphatic tissue, essentially
resembling that of the lymphatic glands, but  differently arranged.   In  those
animals in which it predominates, as in  Man, the artery is large ; on the  other
hand, where the cellated structure is  most developed, as  in the Herbivora, the
Vein  is very large,  and the artery comparatively small.—Nothing completely
analogous to a Spleen is found in Invertebrated animals ;  and from the absence
ofthe Lymphatic system in them,  it is evident that the parenchymatous por-
tion can have no existence as such.  Something analogous  to the cellated por-
tion ofthe Spleen, however, exists in the  venous system of many Cephalopoda;
and this circumstance is an additional proof of the duplicity of the character
of this remarkable organ.
  685. Out  of the  numberless theories  of its operation, which have been at
different times brought forwards, the one which seems best  to account for its
cellated structure, is that which  regards  it as a sort of diverticulum or reser-
voir;  which may serve to relieve the  Portal Venous system  from undue dis-
tention, under a great variety of circumstances.   This system is well known
to be  destitute of valves; so that  the Splenic vein has  free communication
with the whole of it.   Hence the Spleen will  be  a ready diverticulum for the
venous  blood, when the  secreting  action of the   Liver  is  feeble, so that the
Portal circulation receives a partial check (§  832).   That any cause of con-
gestion of the Portal system peculiarly affects the Spleen, has been proved  by
experiment; for after the Portal Vein has been tied, the Spleen of an animal,
which previously weighed only 2 ounces, has been found to weigh a pound
and a quarter, or ten times  as  much.   Now it is evident that congestion of
the Portal system is liable to occur, when the alimentary canal is  distended
with food ; and this from two  causes,—the pressure  on the Intestinal veins,
and the quantity of fluid absorbed by these veins.  Hence it may be conceived,
that the Spleen, by affording a reservoir into which the superfluous Venous
blood may be directed, serves an important purpose in  preventing congestion
of other organs.  From the observations of Mr.  Dobson,* it appears that the
* London Med. and Phys. Journal, Oct. 1820. 
520
OF ABSORPTION AND SANGUIFICATION.
Spleen has its maximum volume, at the time when the process of chymifica-
tion is at an end,—namely, about five  hours after food is taken ;  and that it
is small and contains little blood seven hours later,  when  no food has been
taken in the interval.   Hence he inferred, that this organ is the receptacle for
the increased quantity of Blood, which  the system acquires from the food, and
which cannot, without  danger, be admitted into the  blood-vessels generally;
and that it regains its previous dimensions, after the volume of the circulat-
ing fluid has been reduced by secretion.  This view  is confirmed by the fact
noticed by several observers,—that the Spleen  rapidly increases in bulk after
the ingestion of a large quantity  of fluid, which is  absorbed rather  by the
Veins than by the Lacteals.   It has been further stated in  support of this
theory, that animals from which the Spleen has been removed, are very  lia-
ble  to die of apoplexy, if they take a  large quantity of  food  at  a time;  but
that, if they eat moderately and frequently, they do not suffer in this manner.
The use of the Spleen as a  diverticulum for the internal Venous circulation,
is further borne out by its liability to become enlarged in consequence of in-
termittent fever ; during  the cold stage  of which, a great quantity of blood is
driven from  the surface  towards the internal organs; and it may be easily
imagined that, if there were no such reservoir, the congestions in  these would
be much  more dangerous than those which  actually  do  occur.  The perma-
nent enlargement of the organ is of course, on this idea of its use, a result of
its frequent distention.   But besides this safety-valve function, there can be
little doubt that the Spleen performs another, in virtue of the parenchymatous
portion of its structure ;  and that this  function  corresponds with  that of the
Absorbent Glands  in general.  The identity in structure between its  Malpi-
ghian bodies and the ordinary Lymphatic glands, is  such as clearly points to
this inference;  which is  confirmed by  the remarkable fact,  determined by the
recent experiments of Prof. Mayer, that, after the Spleen has  been extirpated,
the lymphatic glands of the neighbourhood increase in size, and  cluster toge-
ther as they enlarge, so as to form an organ which at least  equals the Original
spleen in volume.*  This circumstance explains the  reason of the  almost in-
variable negative  result of  the extirpation  of  the Spleen; for although  the
operation has  been frequently practised, with  the view of  determining  the
functions of the organ by the symptoms presented by animals after its removal,
no decided change in the ordinary course of their vital  phenomena has ever
been observed ; and the health, if at all disturbed for  a time, is afterwards re-
gained.   Now if the functions of the Spleen,—putting aside  the  safety-valve
action of its  distensible  cavities,—be  the  same with that  of the Lymphatic
Glands in general, it is easy to understand, how its loss may  be at once com-
pensated  by an increased action on their part, and how it may be permanently
replaced by an increased development  of some of those  bodies.—Thus, then,
we  may fairly regard the Spleen as concurring in function with the glands of
the Absorbent system, in the Assimilating process, by which the crude nutri-
tive materials are rendered fit to circulate through the system ; the difference
between them appearing to be chiefly this,—that, whilst the latter operate upon
the nutritive substances  taken up by the Lacteals, the Spleen  exerts its influ-
ence upon those which have been received into the  Veins ;  separating them
from the  mass of the blood, and delivering them to  the lymphatic system to
be further elaborated.
   686. The Supra-Renal  Capsules seem to correspond with the Spleen in
their general  structure, and in their connection with  the Lymphatic system;
whilst, in the arrangement of their component parts, they bear more resem-
blance to the Kidney.
* Medical Times, March 29, 1845. 
SUPRA-RENAL CAPSULES.---THYMUS GLAND.
521
  a. In the Supra-Renal Capsules, as in the Kidneys, there is an obvious difference between
the cortical and the medullary substances.  The former is of a yellowish colour; and presents
an appearance, when cut into, as  if it were made up of straight parallel fibres, arranged side
by side.  Of these straight fibres,  however, a part are branches of arteries, which enter this
body at every point of its exterior, from a capillary network covering its surface; and others
are corresponding branches of veins, that  receive the blood from these arteries, and convey
it into a venous plexus which forms the centre of the organ.  Between the radiating blood-
vessels, there are found lying, in the cortical substance, numerous parallel cylinders or elongat-
ed cones, formed by closed sacs of basement-membrane, including nuclei and cells in various
stages of development, with fat-cells.—The medullary substance is partly made up ofthe ve-
nous plexus, dilated into a sort of  cavernous texture, together with empty cavities or lacunse,
that seem destitute of a lining membrane, and contain only a thick grayish-white fluid ; and
partly of an intervening  parenchyma, consisting of cells in various stages of development.
In the Human adult, there is a great predominance of nuclei, which seem as if they did not
attain their full development; but in Ruminant animals, and in the Human subject in early
life, the cells are more or less developed, and then resemble the  ordinary lymph-corpuscles
in size and appearance.  The Lymphatics are of large size, like those of  the Spleen; and
probably convey away the matter  which has been elaborated by these organs, that it may be
mingled with  that which is being taken up and prepared  by other parts  of the Absorbent
system.  The  Supra-Renal capsules attain a very large size early in foetal life, surpassing
the true Kidneys in dimension, up to the tenth or twelfth week: but they  afterwards dimi-
nish relatively to the latter, and are evidently subordinate organs during the whole remainder
of life.

   It does  not seem unlikely that these bodies, like the  Spleen,  have a double
function;  and that, besides participating in the general actions of  the Absorb-
ent glandulae, they may serve as a diverticulum for the Renal circulation, when
from any cause the secreting function of the  Kidneys is retarded or checked,
and the  movement of blood  through them is stagnated.
   687.  The Thymus  Gland is another body which seems referrible  to  the
same  group ;  having all the  essential characters of a true gland, save an excre-
tory duct; and its function being evidently connected, during the  early period
of life  at least, with the elaboration of nutritive  matter, which  is  to be  re-
introduced into  the circulating current.
   a. Its elementary structure may be best understood from the simple form it presents when
it is first capable of being distinguished  in the embryo.   It then consists of a single tube,
closed at both ends, and filled with granular matter; and its subsequent development consists

                                      [Fig. 209.
  A section of the Thymus gland at the eighth month, showing its anatomy ; from a preparation of
Sir A. Cooper's ; 1, the cervical portions ofthe gland; the independence ofthe two lateral glands is
well marked ;  2,  secretory follicles seen upon the surface of the section ; these are observed in all
parts of the section; 3, 3, the pores or openings of the secretory follicles and pouches ; they are seen
covering the whole internal  surface of the great central cavity or reservoir.  The continuity of the
reservoir in the lower or thoracic portion of the gland with the cervical portion, is seen in the figure.]

                                        44* 
522
OF ABSORPTION AND SANGUIFICATION.
in the lateral growth of branching off-shoots from this central tubular  axis.  In its mature
state, therefore, it consists of an assemblage of glandular follicles, which are  surrounded by
a plexus of blood-vessels; and these follicles all communicate with the central reservoir, from
which, however, there is no outlet.  The Lymphatics are  large, and communicate directly
with the Vena Cava; but their immediate connection with the cavity of the Thymus body
has not yet been demonstrated.  The cavities of the  follicles contain a fluid in which a
number of corpuscles are found, giving it a granular appearance.  These corpuscles are, for
the most part, in the condition of nuclei; but fully developed cells are found among them, at
the period when the function of this body seems most active. The chemical nature of the
contents at this period, closely resembles that of the ordinary proteine-compounds.'—It has
been commonly stated, that the Thymus attains its greatest development, in relation to the
rest of the body, during the latter part of foetal life; and it has been considered as an organ
peculiarly connected with the embryonic  condition.  But this is a mistake; for the greatest
activity in the growth of this organ manifests itself in the Human infant, soon after birth;
and it is then, too, that its functional energy seems the greatest.  This rapid state of growth,
however, soon subsides into one of less activity, which merely serves to keep up its propor-
tion to the rest of the body: and its increase usually ceases altogether at the age of about
two  years.  From that  time, during a variable number of years, it remains stationary in
point of size; but, if the individual be adequately nourished, it  gradually assumes the cha-
racter of a mass of fat, by the development of the corpuscles of its interior into fat-cells, which
secrete adipose matter from the blood.  This change in its function is most remarkable in
hybernating Mammals; in which the development of the organ continues, even in an in-
creasing ratio, until the animal reaches adult age, when it includes a large  quantity of fatty
matter.  The same is the case, generally speaking, among Reptiles.   It Is an important fact
in the history of this organ, that it is not to be detected in Fishes;  and does not appear to
exist, either in the tadpole state of the Batrachian reptiles,or in the Perennibranchiate group;
so that we may regard it as essentially connected with pulmonic respiration.*

   688. Various facts lead to the conclusion, that the function of the Thymus,
at the period of its highest development, is that of elaborating and storing up
nutritive  materials, to supply the demand which is peculiarly active during the
early period of extra-uterine life.  The elaborating  action probably corresponds
with that which is exerted  by  the  glands of the Absorbent  system ;   and  the
product, as in the preceding cases, seems to be conveyed away by the lymph-
atics.   The provision of a  store of nutritive matter seems a most valuable one,
under the circumstances in which  it is met with ;  the waste  being more rapid
and  variable than in adults, and the supply not constant.   Thus it has been
noticed that, in over-driven lambs, the thymus soon shrinks  remarkably ;  but
that it becomes as quickly distended again, during rest and plentiful  nourish-
ment.   As  the demand becomes less energetic, and as the supplies furnished
by other  organs become more adequate to meet it, the Thymus diminishes in
size, and no longer performs the same function.   It then  obviously serves to
provide a store of material, not  for the nutrition of the body, but for  the re-
spiratory process, when this has to be carried  on  for long  periods—as in hy-
bernating  Mammals  and in  Reptiles—without a  fresh supply of food.—It is
possible, that the  Thymus gland may further stand in the  same  relation to the
Lungs, as the  Spleen to the Liver, and the Supra-Renal capsules to  the Kid-
neys ; that is,  as  a diverticulum for the blood  transmitted through the bron-
chial arteries (which  are the nutritive  vessels of the Lungs),  before the Luno-s
acquire their full  development in comparison with other organs, or when any
cause subsequently obstructs the circulation through their capillaries.
   689. The Thyroid Gland bears a general analogy to the Thymus; but  its
vesicles are distinct from each  other, and do not communicate with any com-
mon  reservoir.   They are  surrounded, like  the vesicles  of the  true glands,
with  a minute capillary plexus  ; and in the fluid they contain, numerous  cor-
puscles  are found suspended, which appear to  be cell-nuclei, in a   state of
more or less advanced  development.  This body is supplied with  arteries of
considerable size;  and with peculiarly large  lymphatics.   Though  propor-

           * See Mr. Simon's admirable Prize Essay on the Thymus Gland. 
            THYROID GLAND.--ASSIMILATING GLANDS IN GENERAL.         523

tionably larger in the fcetus than in the adult, it remains of considerable  size
during the whole of life.  It appears, from the recent inquiries of Mr. Simon,*
that a Thyroid gland, or some organ representing it in place and office, exists
in all Vertebrated animals.  It presents its simplest form in the class of Fishes ;
in some of which it  appears to  consist  merely of a plexus of capillary ves-
sels, connected with the origin of the cerebral vessels,  and capable, by its dis-
tensibility, of relieving  the latter, in  case of any obstruction to  the  proper
movement of blood through them.  In  the  higher  forms of this organ, the
glandular structure,—consisting  of closed  vesicles over which the  capillary
plexus is distributed, and of their  cellular contents,—is superadded ; and the
organ  then appears, like  the Spleen, to be destined for two different uses;
namely, to serve as a diverticulum to the Cerebral circulation ; and to aid in
the elaboration of nutritive  matter, which is taken up by the Absorbent  sys-
tem, and which is  again poured by it into the general current of  the circula-
tion.
   690.  Thus the Spleen, the Supra-Renal Capsules, the Thymus Gland, and
the Thyroid Gland,  all seem to  share in the preparation of the nutritive ma-
terials of the blood, along with the ordinary glandulae of the Absorbent system.
In fact, we may regard them all as together  constituting an apparatus,  which
is precisely analogous to that of the ordinary glands, but of which the element-
ary parts  are scattered  through the body, instead of being collected into one
compact structure.   Thus if we could imagine any tubular gland,  such as the
Kidney or the Testis, to be unravelled, and its convoluted tubuli to be spread
through the system, yet all discharging their contents by a common outlet, we
should have no unapt representation of the Lymphatic portion of  the Absorb-
ent system.  Its function appears to be, to  separate  the  crude Albuminous
matter from the blood, to  subject it to  an elaborating action performed by the
epithelium-cells lining the  tubes, and then to pour forth this elaborated  pro-
duct,—not as an excretion to be carried out of the body,—but (in  conjunction
with  that, which has been newly taken in by the  Lacteal portion  of the  sys-
tem, and which has undergone elaboration by its glandulae), into the  blood-
vessels, which are to convey it  to the different parts of the body  where  it  is
to be  appropriated.   The four  bodies we have been just considering, appear
to be, so  far as their glandular function is concerned, appendages  to this  sys-
tem.  Their uses as diverticula to the circulation through other organs, render
them liable to occasional distention with blood; and it seems determined that
this blood shall not lie useless, but shall be subservient to the action in  ques-
tion ; the gland-cells that line  the cavities of the organ withdrawing certain
constituents of the blood, to restore them, through the Lymphatic system, in
a state of more complete  preparation for the operations of Nutrition.   Their
function is  very probably vicarious; that is, the determination  of blood  is
greatest (through the state ofthe other organs) at one time to one of these bodies,
and at another time  to another.   Hence the effects of the loss of  any one of
them are not serious ; as  the others are enabled in  great degree to discharge
its duty.

        4.—Composition and Properties of the Chyle and Lymph.

   691. The chief chemical difference between the Chyle and the Lymph,
consists in the much smaller proportion of solid matter in the latter, and in the
almost entire  absence of fat, which is an important constituent of  the former.
This is well shown in the following comparative analyses, performed  by Dr.
G. O. Rees, of the fluids obtained from the lacteal and lymphatic  vessels of a
* Philosophical Transactions, 1844. 
524
OF ABSORPTION AND SANGUIFICATION.
3-516	1-200
0-370	0-120
0-332	0-240
1-233	1.319
3-601	a trace
0-711	0-585
donkey, previously to their entrance into the thoracic duct: the animal having
had a full meal seven hours before its death.
                                                       Chyle.     Lymph.
    Water..........90-237     95536
    Albuminous matter (coagulable by heat)
    Fibrinous matter (spontaneously coagulable)
    Animal extractive  matter, soluble in water and alcohol
    Animal extractive  matter, soluble in water only
    Fatty matter  ........
    Salts;—Alkaline chloride, sulphate and carbonate, with traces of
       alkaline phosphate, oxide of iron    ....

                                                      100-000    100-000

The Lymph obtained from the neck of a horse has been recently analyzed by
Nasse, with nearly the same result.   He  found it  to  contain 95 per cent, of
water;  and the 5  per cent, of solid matter was chiefly composed of albumen
and fibrine, with watery extractive,—scarcely a trace of fat being to be found.
The proportions of saline  matter were found to be remarkably coincident with
those which  exist in the serum of the blood; as  might be expected from  the
fact, that the fluid  portion  of the  lymph must have its origin in that which has
transuded through the blood-vessels :  the absolute quantity, however, is rather
less.—A similar analysis of the Chyle of  a cat by Nasse, has  given results
very closely correspondent With  that of Dr. Rees ; for the proportion of water
was 90'5 per  cent. ; and  ofthe 9*5 parts of solid matter, the albumen, fibrine,
and extractive amounted  to more than 5, and the fat  to more than 3 parts.—
Dr. Rees has  also analyzed the fluid of the Thoracic duct of Man ; and found
it to consist of 90*48 per  cent, of water, 7'08 parts of albumen and fibrine,
1'08 parts  of aqueous and alcoholic extractive, and  0*92  of  fatty matter, with
0*44 per cent, of salines.   Thus the composition of this fluid would seem to
resemble that of the Lymph, rather than that of the Chyle ; the proportion of
the fatty to that ofthe albuminous matter being very small.   This, however,
might have been very probably due to the circumstance,  that the subject from
which  the  fluid was obtained (an executed criminal) had eaten  but little  for
some  hours before his death.
  692.  The characters of the Chyle drawn from  the larger  absorbent trunks,
near their entrance into the Receptaculum Chyli, are very different, however,
from those of the  fluid  as first absorbed  into the Lacteals ; for during its
passage through  these vessels,  and  their ganglia or glands,  it undergoes
important  alterations,  which  gradually assimilate  it  to Blood.   The  chyle
drawn from the lacteals that traverse the intestinal walls, contains Albumen in
a state of complete solution; but it is  generally destitute of the  power of  co-
agulation, no  Fibrine being  present  in it.  The Salts, also, are completely
dissolved;  but the Oily matter presents itself in the form of globules of varia-
ble  size.*   It is  generally supposed, that the milky colour of the chyle is
owing to these; but Mr. Gulliver has recently pointed outf that it is really due
to an immense multitude of far more  minute  particles, which he describes as
forming the molecular base of the chyle.  These molecules are most abundant
in rich,  milky, opaque chyle;  and in  poorer chyle, which is semi-transparent
or opaline, the particles float thinly or separately  in the transparent fluid, and
often exhibit the vivid motions common to  the most minute molecules of vari-
ous substances.   Such is their  minuteness,  that, even with the best instru-

  *  These oily globules are more abundant in the Chyle of Man and of the Carnivora, than
in that of the Herbivora: their diameter has been observed to vary from 1-25 000th to l-2000th
of an inch.
  t Dublin Medical Press, Jan. 1, 1840, and  Gerber's General Anatomy, Appendix, p. 88. ' 
CHARACTERS AND COMPOSITION OF CHYLE.
525
merits, it  's impossible to form  an exact  appreciation either of their form or
their dimensions.   They seem,  however, to be generally spherical; and their
diameter may be estimated at between l-36,000th and 1-24,000th of an inch.
Iheir chemical  nature is as yet uncertain: they are remarkable for their un-
changeableness,  when subjected to the action  of numerous  re-agents;  which
quickly affect the proper Chyle-corpuscles;  and  they are  readily soluble in
Ether, the addition of which causes the whole molecular base instantlv to dis-
appear, not a particle  of  it  remaining; whence it may be inferred that they
consist of oily or fatty matter.   The milky colour,  which the serum of blood
sometimes exhibits, is due to an  admixture of this molecular base with the
circulating fluid ; it is  most common in young animals that are suckling ; but
it is not uncommon in adults, and is not to be attributed to  an absorption of
milk into the chyle, as the physical properties of the two are quite different.
(See § 697, e.)
  693. During the passage of the  Chyle through the absorbents on the intes-
tinal edge  of the  Mesentery, towards the Mesenteric Glands, its character
changes in several important particulars.  The presence of Fibrine begins to
manifest itself, by the slight coagulability of the  fluid when withdrawn from
the vessels ; and while this  ingredient increases, the Albumen and the  Oil-
globules gradually diminish  in  amount.   The Chyle  drawn from  the neigh-
bourhood of the  mesenteric glands exhibits the Corpuscles  regarded as cha-
racteristic  of that fluid; these are peculiarly  abundant in the fluid  drawn from
the glands themselves ; and they are constantly found in it, through its whole
subsequent course. The Chyle-corpuscles  are much larger than  the mole-
cules just described, and an  examination of their character presents no diffi-
culty.  Their diameter  varies  from  1-7110th to  l-2600th of an inch ; the
average being about l-4600th.   They are usually minutely granulated on the
surface, seldom exhibiting any nuclei,  even when treated with acetic acid ; but
sometimes  three  or four central particles  may be distinguished within them.
—During  the  passage of the Chyle  through  the mesenteric glands, a further
increase in the  proportion of Fibrine  takes place; and the resemblance of
the fluid to Blood becomes more apparent.  The Chyle drawn from the vessels
intermediate between  these and the  central  duct, possesses a pale reddish-
yellow colour; and, when  allowed to stand  for a time, undergoes a regular
coagulation, separating into clot and serum.  The former is a consistent gela-
tinous mass, which, when examined with  the  microscope, is found to include
the Chyle-corpuscles,  each of them being surrounded by  a delicate film of
oil: the Fibrine  of which it is principally  composed, differs remarkably from
that of the blood, in  its  inferior tendency to putrefaction ;  whence it may be
inferred that it has not yet undergone its complete vitalization.  The serum
contains the Albumen and Salts in solution, and a  proportion of the Chyle-
corpuscles  suspended in it.  It is  curious,  however, that considerable differ-
ences in the perfection of the  coagulation, and in its duration, should present
themselves in different experiments.   Sometimes the chyle  sets  into a jelly-
like mass, which, without any separation  into coagulum and serum, liquefies
again at the end of half an hour, and remains in this  state.   This change takes
place in the true  coagulum also, if it be kept moist for a sufficient length of
time.   The  Chyle from the Receptaculum  and  Thoracic  Duct coagulates
quickly, often almost  instantaneously; and few or none of the corpuscles re-
main in the serum.—It is to be remembered  that  the Lacteals are the Lym-
phatics  of the intestinal walls  and mesentery;  performing  that  function of
Interstitial Absorption which is elsewhere  accomplished by vessels that are
not concerned  in the introduction of alimentary substances from without.
During the intervals of digestion, they contain a fluid which is in all respects
conformable to the Lymph of the  Lymphatic  trunks. 
526
OF ABSORPTION AND SANGUIFICATION.
  a. The fluid drawn from the Thoracic Duct, and from the Absorbent vessels which empty
their contents into it, is frequently observed to present a decided red tinge, which increases
on exposure to the air.  This tinge is due to the  presence of true Blood-corpuscles;  but
these are somewhat modified in form and size, being a little smaller than the ordinary Blood-
discs, and frequently angular, granulated, or indented at the edges.  By Mr. Lane* it is stated
that this intermixture is accidental; and that it results from the absorption of Blood-particles
into the Lymphatics, at the points where  the\latter are divided, in making the sections ne-
cessary to expose the centres of the Absorbent system; and he mentions a striking fact in
illustration of his view.  He considers that the alteration in the character of the corpuscles
is due to the action of the Chyle on the Blood, since many other fluids will produce analogous
effects; and he states that, shortly after a flow of chyle into the blood, a large number of such
altered discs may be seen in the circulating  fluid.  On the other hand, Mr.  Gulliver  and
several eminent observers, regard these blood-discs as true constituents of  the fluid of  the
absorbents; and suppose  that they are in process of formation.   Reasons have been given,
however, for the belief, that the  red Blood-discs are not formed from the Chyle-corpuscles;
so that Mr. Lane's view is probably the correct one.  Even if the Blood-discs  are not intro-
duced into the Lymphatics during the operation of exposing the Thoracic Duct, it may not
be considered as improbable that, in those animals in which the Lymphatics have several
communications with the veins, they should naturally obtain an entrance  in various parts of
the  system.  Such communications, according to Gerber, decidedly exist in  the Horse; and
it is in the Chyle of that animal,  that the  rosy tint, and the Blood-corpuscles which occasion
it, have been chiefly observed.—The following table, slightly modified from that of Gerber,
presents in a concise form, a view of the relative proportions of the three chief ingredients
in the Chyle, in different parts of the absorbent system, and thus gives an idea of its advance
in the process of assimilation.

In the afferent or peripheral f Fat, in  maximum quantity (numerous fat or oil  globules).
  Lacteals (from the Intes-J Albumen in minimum quantity.
  tines  to  the  Mesenteric | Few or no Chyle-corpuscles.
  glands).                 (^Fibrine almost entire wanting.
In  the  efferent or central f Fat, in  medium quantity (fewer oil globules).
  Lacteals (from the Mesen-J Albumen, in maximum quantity.
  teric glands to the Thoracic | Chyle-corpuscles very numerous, but imperfectly developed.
  Duct).                   (^ Fibrine in medium quantity.
                          f Fat, in minimum quantity (fewer or no oil-globules).
In the  Thoracic  Duct.      J ^bumen, in medium quantity
                          1 Chyle-corpuscles numerous, and more distinctly cellular.
                          ^Fibrine in maximum quantity.

  694. The aspect of the Lymph greatly differs  from that of the  Chyle,  the
former being nearly transparent, whilst the latter is opaque or opalescent;  and
this difference  is readily accounted for, when the assistance of the microscope
is sought,  by  the entire absence from  the Lymph  of  that  molecular base
which is so abundant  in the Chyle.   A considerable number of  corpuscles
are generally present  in it;  and  these seem  to  correspond in all  respects with
the  white  or  colourless  corpuscles  of the  Blood (§ 151).   Their  amount,
however, is extremely  variable; as  is also that  of  the  oil-globules, which
sometimes  occur, whilst in other instances none can be discovered.   Lymph
coagulates  like  chyle;  a colourless  clot being formed,  which incloses  the
greater part of the corpuscles.
  695. The fluid drawn from  the Thoracic Duct, consisting as it  does of an
admixture of Chyle and Lymph, will probably vary in  its character and com-
position, according to  the predominance of the former, or of the latter, of these
fluids.   It  may be noticed, however, that the  floating corpuscles have a more
distinctly cellular character  than have those  of the  chyle and  lymph;  and
that they are of larger size, their  diameter usually ranging from about l-2600th
to l-2900th of an inch.   In these particulars, they correspond with the Colour-
less corpuscles ofthe  Blood; as also in the change they exhibit on the action
of  acetic acid, which  brings into view three  or four large central particles.
Some  observations have been  recently made   by Bidder, on the  amount of

               * Cyclopaedia of Anatomy and Physiology, vol. Hi. p. 220. 
PHYSICAL AND VITAL PROPERTIES OF THE BLOOD.
527
liquid which flows through the Thoracic duct into the venous system;  and if
any inference can be fairly drawn  from the measurement of the quantity de-
livered in the course of a few minutes, it would appear that the total amount
thus transmitted in one day is nearly or quite equal to  the entire mass of the
blood.  At any rate, it so far exceeds the amount of liquid ingested, that we
must believe a large portion of it to be  derived from the circulating current,—
having been withdrawn from it for a time, to be again delivered into its stream,
after having undergone the requisite elaboration.

             5.—Physical and Vital Properties ofthe Blood.

   696.  Having now traced the steps, by which the Blood is  elaborated and
prepared for  circulation through the body, and  having  formerly inquired into
the characters of its chief constituents  (Chap,  m.), we  have now to consider
the fluid as a whole, to study the usual proportions of these constituents, and
the properties which they impart to it.—The  Blood, whilst circulating in the
living vessels,  may be seen  to consist  of a  transparent, nearly colourless,
liquid, termed Liquor  sanguinis; in which the Red Corpuscles, from which
the Blood of Vertebrated animals derives its peculiar hue, as well as the White
or Colourless corpuscles, are freely suspended  and carried along by the cur-
rent.—On the other  hand, when  the Blood has been drawn  from the body,
and is allowed to remain at rest, a spontaneous coagulation takes place, sepa-
rating it into Crassamenlum and  Serum.  The  Crassamentum or Clot  is
composed of a network  of Fibrine, in the meshes  of  which  the Corpuscles,
both red and colourless, are involved, together with a certain amount of serous
fluid.  The Serum, which is  the same  with the Liquor Sanguinis deprived of
its Fibrine,  coagulates by heat, and is  therefore known to contain Albumen;
and if it be exposed to a high  temperature, sufficient to decompose the animal
matter,  a considerable  amount of earthy and alkaline  Salts  remains.—Thus
we have four principal components in the Blood; namely, Fibrine, Albumen,
Corpuscles, and Saline matter.  In the circulating blood, they are thus com-
bined :—

               Fibrine   }
               Albumen  > In solution, forming Liquor Sanguinis.
               Salts      j
               Corpuscles,—suspended in Liquor Sanguinis.

But in coagulated blood,  they are combined as follows:—

                         Crassamentum or Clot.

               c  ,       £ Remaining in solution, forming Serum.
Fibrine
Corpuscles
In the  blood of Man and  the  higher Vertebrata, the Colourless Corpuscles
usually bear so small a proportion to the Red, that they have  until recently
escaped  notice.   In  Reptiles, however,  they attract  attention, from  their
marked difference in size and form, even whilst the blood is moving through
the capillaries; and they are  the more easily watched, owing to the compara-
tively small number of the  Red Corpuscles in those animals.   The blood of
the Invertebrata is usually pale, and contains very few red corpuscles; indeed
they would seem to be absent altogether in the lower Articulata and Mollusca.
On the other hand, the  colourless corpuscles  are frequently very numerous,
especially during the periods of most active  growth.  The blood of these
animals may be likened,  therefore, in  many respects to the Lymph and Chyle
of the  Vertebrata;  and the resemblance is the  more close, as there  is no 
528
OF ABSORPTION AND SANGUIFICATION.
distinction among  the Invertebrata between the  absorbent and sanguiferous
vessels.
   697.  The proportion of the several components of Blood is subject to con-
siderable variations,  within  the limits of health.  Some  of  these variations
may be habitual, depending upon  the constitution  of the  individual, his diet,
mode  of life, Sic,  whilst others are probably referrible to  the  period at which
the last meal was  taken, and the  amount of bodily exertion  made within a
short  time previous to the analysis.

  a.  The discordance in  the results obtained by different experimenters  is doubtless owing
in part to the diversity in their methods  of analysis ;*  but even where the same method is
employed, a wide diversity is apparent;  as  in  the analysis of MM. Becquerel and Rodier.
As there is  a tolerably constant difference between the Male and the Female, it will  be  de-
sirable  to class them separately ; and the results of some of the most recent and trustworthy
analyses of each will be  brought together for the sake of comparison.—The analyses of M.
Lecanu were made on the blood of two  stout and  healthy men; whilst those of MM. Bec-
querel and Rodier give the  maximum, minimum, and mean amount, of each ingredient in
the blood of eleven healthy men, between the ages of 21 and 66 years.
	Lecanu.		MM. Becquerel and Rodier.			Simon.	Nasse.
	i.	n.	Mean.	Maxima.	Minima.		
	780-2	785-6	779-0	8000	760-0	791-9	798-4
	2 1	3-6	2-2	3-5	1-5	20	2-3
Corpuscles . . .	. 133-0	1196	141-1	1520	131-0	114-3	116-5
Albumen . . .	. 66-3	71-5	69-4	73-0	62-0	756	74-2
Extractive mat- }							
ters, Salts, and >	14-6	131	6-8	8-0	5-0	14-2	6-6
loss ;							
Fatty matters . .	3-8	66	1-5	3-2	1-0	2-0	2-0
	1000-0	1000-0	1000.0			1000-0	1000-0
  The following table gives the  results of similar analyses on the blood of Females;  those
of MM. Becquerel and Rodier being made upon eight healthy subjects between the ages of
22 and 58 years.
	MM. Becquerel and Rodier.			Simon.
	Mean.	Maxima.	Minima.	
Water .....	. 791-1	8130	7730	801-4
Fibrine .....	2-2	25	1-8	2-2
Corpuscles ....	. 127-2	137-5	1130	106.1
Albumen .	. 70-5	75-5	65-0	77-6
Extractive matters and Salts	7-4	85	6.2	100
Fatty matters	1-6	2-9	1-0	2-7
	1000-0			1000-0
  6.  Of the Fatty matters of the Blood, a portion seems to correspond with the constituents
of ordinary Fat; another portion seems identical with the Cholesterine, or Biliary Fat; whilst
another contains Phosphorus, and seems allied to the fatty acids of Nervous matter (§ 249).
  c.  Of the nature of the substances  classed under the  head of Extractive, very little  is
known.  It has been lately asserted, that a portion of them consists of binoxide of proteine
(§ 116, a); but as  to the actual existence of this substance, there is still much doubt.  Under
the general  designation of extractive are arranged the " ill-defined animal principles," which
may  include various substances in a state of  change or disintegration, that are being elimi-
nated from the blood by the processes of Excretion.
  d.  The Saline constituents  of the Blood, obtained  by drying and  incinerating the whole
mass, usually amount to between 6 and 7 parts in  1000.   More than half their total quan-
tity is composed of the Chlorides of Sodium and Potassium; and the remainder is  made up
of the tribasic Phosphate of Soda, the Phosphates of Lime and Magnesia, Sulphate of Soda,
  * Thus the small amount of Salts, in the analysis of Nasse  and of MM. Becquerel and
Rodier, as compared with those of MM. Lecanu and Simon, appears due to the fact that the
former express only the free salts, whilst the latter  include  those which are in combination
with the organic constituents. 
               USES OF THE  SEVERAL CONSTITUENTS OF THE BLOOD.          529

 and a  little Phosphate and Oxide  of Iron.  Of these, the chief part are dissolved in  the
 Serum ; but the Earthy Phosphates, which  are insoluble by themselves, are  probably com-
 bined with the Proteine-compounds (§ 113); and the iron is contained, chiefly or entirely,
 in the red corpuscles.—It is difficult to speak with certainty, from  the  examination of  the
 ashes of the blood, as to the state of the Saline constituents of the  circulating fluid.  Thus
 the Serum has an alkaline reaction ;  and this has been  supposed to be due to the presence
 of alkaline Carbonates.  Moreover the presence of the Lactates of potass and  soda has been
 usually asserted.  On the other hand, the recent analyses of Enderlin, which have been con-
 firmed by Liebig, would indicate that the alkaline reaction is  entirely due to the presence of
 the tribasic Phosphate of soda; and that no alkaline carbonates or lactates exist in the blood.
 This discrepancy seems partly due to the mode of analysis employed; for it has been lately
 pointed out by Dr. G. 0. Rees,* that  although the ashes  of the entire mass of blood  do  not
 effervesce on the addition of an acid, effervescence takes place: when acid  is  added  to  the
 ashes of the serum, showing the existence in it, either of alkaline  Carbonates, or of Lactates,
 which  have been reduced to the state of Carbonates by incineration.—It appears that, when
 the  entire mass of blood is incinerated, enough phosphoric acid is produced from the phos-
 phorized fats, to  neutralize  the alkaline carbonates, and thus  to prevent their  presence from
 being recognized.  There can  be  no doubt, however, that the tribasic Phosphate of Soda
 exists as such in the blood, and contributes to its alkaline reaction; and it appears to confer
 upon the liquid a special power of absorbing Carbonic Acid.
  e. Some very interesting observations upon the state of the  blood soon after a meal, have
 been recently made by Drs. Buchanan and R. D. Thompson.  They are confirmatory of  the
 belief generally entertained, that the milky appearance, sometimes presented  by the  Serum,
 is due to the admixture of  Chyle.  When a full meal containing oily matter  is taken after
 a long fast, and a small quantity of blood is  drawn  previously to  the meal and at intervals
 subsequently, the Serum, though quite limpid in the blood first drawn, shows an incipient
 turbidity about half an  hour afterwards ; this turbidity increases for about six hours subse-
 quently, after which it  usually begins to disappear.   The period  at Which the discoloration
 is the greatest,  however, and the  length of time during which it continues, vary  according
 to the kind and quality  of the food, and the state of the digestive functions.  Neither  starch,
 nor sugar, nor proteine-compounds, alone or  combined, occasion  this opacity in the  chyle;
 but it seems entirely dependent upon an admixture of oleaginous  matter with  the food.
 There  are few ordinary meals, however, from which  such matter is altogether  excluded.
 When such milky serum is examined with the Microscope, the opacity is found to be due
 to the presence of an immense number of exceedingly minute granules, resembling  in  ap-
 pearance those which form the " molecular base" of the chyle.  They seem to be composed
 of two chemically-distinct  substances; for when the milky serum is agitated with ether, a
 part is dissolved, whilst another portion remains suspended ;  and this  latter  is  soluble in
 caustic  potass.   The former, therefore, appears to be identical with the  "molecular base" of
 the Chyle, and to be of an oily or fatty nature ; whilst the latter  belongs to  the  proteine-
 compounds.  The Crassamentum of such  blood often  exhibits a pellucid fibrinous crust,
 sometimes interspersed with white dots; and this seems  to consist of an  imperfectly-assi-
 milated proteine-compound, analogous to that found in the serum.  The quantity of this varies
 according to the amount of the  proteine-compounds present in thefood.f—It is evident from
 these  experiments, that  the assimilating process is by  no means completed, at the time of
 the passage of the Chyle into the Blood;  and it would seem  that the  return of the trans-
 parency of the sertfm is due to the gradual removal of the superfluous fatty matter through
 the respiratory process, whilst the proteine-compound, of which  part of the  granules are
 composed, is gradually reduced  to a state of  perfect solution.
  /. The  occasional presence of Sugar, even in healthy blood, when  a large quantity of
 saccharine matter exists in  the food, appears to be  now well established.  But it  seems to
 be commonly transformed, either into lactic acid, or into fatty matter, previously to  its recep-
 tion into the circulating  current.  This last  transformation is partly effected  through the
 agency of the Bile ; as will be shown hereafter (§ 835).

   698. It cannot be doubted  that, upon the due admixture in  the Blood of all
 these elements, the regular  performance of its actions  is dependent.   In regard
 to its physical properties merely, it is  easily shown that a slight alteration may
produce the most injurious consequences; for  a  certain degree of viscidity has
been  found (by the experiments of Poisseuille)  to favour the passage  of fluid
through capillary  tubes; and  thus, if  the viscidity ofthe blood be  diminished
by  a  loss of part of its fibrine, stagnation of the current, and extravasation of a

                  *  On the Analysis of the Blood and Urine, p. 30.
                  | Medical Gazette, Oct. 10, 1845.
     45 
530
OF ABSORPTION AND SANGUIFICATION.
portion of the contents of the vessels, will be the result.  This has been  fully
proved by the numerous experiments of Magendie ;  and the fact is one of very
important Pathological applications (§ 707, b).  But the vital properties ofthe
fluid are still more immediately dependent upon the  Fibrine it contains; since,
as we  have seen reason to believe, it is the material which is most completely
prepared for organization, and which  supplies what is requisite  for the nutri-
tion of the larger proportion of the solid tissues of the body.   It is, therefore,
continually being withdrawn from the blood by the nutritive operations; and
the demand  appears to be supplied, in part by  the influx of Fibrine that has
been prepared  in the  Absorbent system, and in part  by the continued trans-
formation of Albumen, which takes place during the circulation of the Blood,
and of which we have seen reason to  believe that the Colourless Corpuscles
are the instruments (§§ 153—159).—The Albumen of the Blood  is the raw
material, at the expense of which not  only the Fibrine, but many other sub-
stances, are generated during the  nutritive process.  All the Albuminous com-
pounds of  the Secretions, the  Horny matter  of the  Epidermic tissues, the
Gelatine of the simple  Fibrous tissues, and the  Haematine of the Red Cor-
puscles, may be regarded as almost certainly produced by the transformation
of the  Albumen of the Blood ;  and a continual supply of this from the food
is therefore requisite to preserve the due  proportion in the circulating fluid.—
The Red Corpuscles appear to be more connected with  the function of Respira-
tion than with that of Nutrition  (§ 150); and the stimulating action of Arterial
blood,  especially upon the Nervous and  Muscular tissues, appears to depend
upon their presence.    It is  by no means impossible that  their peculiar  con-
nection with  the activity  of the latter  may be  dependent  upon  an  actual
Chemical relation between their contents  and the red matter of the Ganglionic
corpuscles (§ 245); and that a part of their function may be, to prepare the
substance which is  afterwards  to be appropriated as a peculiar nutritive prin-
ciple, by the active instruments of Nervous operations.  It appears  from the
experiments of Dieffenbach  on  transfusion, that the  Red Corpuscles are more
effectual as stimuli to the Heart's action, than is any  other constituent of the
blood.   The rapidity with which they may be decomposed and reconstituted,
is made remarkably evident by the experiments  of Magendie;  who found that,
when  the Blood of one animal was  injected into the veins of another having
discs of very different size and  form  (care being taken to prevent the coagula-
tion of the Fibrine during the operation), the original  Red particles soon dis-
appeared, and were replaced by those characteristic of the species, in whose
veins the fluid was circulating.—The use of the Saline matter is evidently in
part to supply the mineral materials, requisite for the generation of the tissues,
and for the production of the  various secretions.  It is  by the Saline and
Albuminous matters  in  conjunction, that  the  specific gravity of the Liquor
Sanguinis is kept up to the point, at which it is equivalent to that of the con-
tents of the  Red corpuscles; and it is only in this  condition that the latter
present their proper characters.   Thus it has been shown by Dr. G. O. Rees,
that when the quantity of water in the Liquor Sanguinis has been reduced by
copious perspirations or other similar causes, the corpuscles are thin, and very
like those whose contents  have exuded by exosmose into  a denser liquid
around (§143).  On the other  hand, if the Liquor Sanguinis be diluted by the
withdrawal of blood and the injection of an equivalent quantity  of water, the
serum  speedily becomes tinged with the  colouring  matter of the corpuscles;
apparently in  consequence of a rupture  of some of the  cells, by endosmose
from the circumambient liquid,  now  reduced to a lower specific gravity than
that of their contents.—The Fatty matters ofthe Blood are-evidently derived
from the food, either directly, or by the  transformation of its farinaceous in-
gredients ; and they are chiefly appropriated to the maintenance of the com- 
COAGULATION OF THE BLOOD.
531
bustive process.  That which  may be  superfluous, is either deposited in the
cells of Adipose tissue, or it is eliminated by the Liver, the Sebaceous follicles
of the Skin, and (in the nursing female) by the Mammary glands.   How the
peculiar Phosphorized Fats of  the Blood are formed,—whether by the con-
tinuation of the azotized and  phosphorized materials with ordinary fat, or
by the  metamorphosis of albuminous matter,—cannot be said to be yet de-
termined.
  699. When the Blood is drawn from the body, and left to itself, its organic
elements speedily undergo a new arrangement.   The Fibrine coagulates, and
separates itself from  the fluid in which it was previously dissolved; and during
its coagulation it attracts  the  Red particles ; these are included in  areolae or
meshes of the Clot, the substance of which has a tendency to assume a fibrous
arrangement (§ 118) ; and they usually group themselves together in  columnar
masses, resembling piles of money.   The Coagulum  or clot becomes dense,
in proportion to the amount of the Fibrine it contains ; and the Albuminous and
Saline matter still dissolved in the water are separated from it, constituting the
Serum.  This separation  will not occur, however, if the  coagulation  take
place in  a  shallow  vessel;  nor if the amount of Fibrine should be small, or
its vitality low.  A  homogeneous mass, deficient in  firmness, presents  itself
under such  circumstances; though the solid part of this may pass into a state
of more complete condensation, after the lapse of a certain time.—That the
coagulation is due to the Fibrine, and  that  the Red particles are merely passive
in the process, appears from several considerations.   A microscopical exami-
nation of the Clot  shows, that it has  the same texture  with Fibrine, when
coagulating by itself; the Corpuscles clustering together in the interspaces of
the network, and not being uniformly diffused through the whole mass.  Their
Specific Gravity being greater than that of the Fibrine, they are usually  most
abundant at the lower part of  the  clot; and the upper surface is sometimes
nearly colourless, especially when the coagulation has taken place slowly ; yet
this upper  part is much firmer than the under, showing that the Fibrine alone
is the consolidating  agent.—This  has been proved to  demonstration by an
experiment of Muller's.  He  placed  the blood of a Frog, diluted with  water
(or still  better with  a very thin syrup) on a  paper filter, of sufficiently fine
texture to keep back the Corpuscles ;  and the Liquor Sanguinis, having passed
through the filter completely unmixed with them, presented  a distinct coagu-
lum, although  from  the  diluted state of the  fluid, this  did not possess  much
consistency.  Owing to the more minute size of  the  Blood-discs of warm-
blooded animals, this experiment cannot be  so  readily performed with  their
blood.  The sole agency of the Fibrine in coagulation is very easily proved
in another way.  If fresh drawn blood be continually stirred with a  stick, the
Fribrine will adhere to it in strings during  its coagulation ; and the Red parti-
cles will be  left suspended in the serum, without the slightest  tendency to
coagulate.   Moreover, if a solution of any salt, that has  the property of re-
tarding the  coagulation (such as carbonate of  potash or sulphate  of  soda), be
added to the blood, the Corpuscles will have time to sink to the lower stratum
of the fluid, before  the  clot is formed ; the  greater part of  the  Coagulum is
then entirely colourless,  and is found  by the microscope to contain few or no
red particles.
  700.  That the Coagulation of the Blood is not, as some  have supposed, a
proof of its death, but  is rather an act of vitality, appears evident from what
has been already stated (§ 118) of the incipient  organization which may be
detected  even in an ordinary clot; and still  more  from the fact  that, if the
effusion of Fibrine take place upon a living surface, its coagulation is the first
act of its conversion into solid tissues  possessing  a high degree of vitality.  It
is absurd to suppose that the Blood dies,  in order to assume a  higher form. 
532                OF ABSORPTION AND SANGUIFICATION.

A complete demonstration of the  truth of the  Hunterian  doctrine, that the
Blood might become organized, like plastic exudations of " coagulable lymph,"
has  been lately afforded by the researches of Dr.  Zwicky, on  the changes
occurring in the clots of blood which form in blood-vessels, above the points
where they have been  tied.   He has traced the successive  stages ofthe meta-
morphosis ofthe coagulum into fibro-cellular tissue,  and the formation of ves-
sels in its substance; the  whole process taking place exactly as in an  inflam-
matory exudation, and the blood-corpuscles exerting no other influence upon
it, than that of slightly retarding it.
   701.  When the Blood is withdrawn  from  the body, however, its Coagula-
tion is the last act of its life ;  for, if not within the  influence of a living sur-
face,  it  soon passes  into decomposition.   Instances occasionally  present
themselves, in which the Blood does not coagulate  after death ;  and in most
of these, there has been some sudden and violent shock to the  Nervous sys-
tem, which  has destroyed the vitality of solids  and fluids alike.  This is
generally  the case  in men and  animals  killed by lightning, or by  strong elec-
tric shocks ; and in  those poisoned by prussic  acid, or whose life  has been
destroyed by a blow on the epigastrium.  It has also been observed in some
instances  of rupture  of  the heart, or of a large aneurism near it; and a very
interesting phenomenon then not unfrequently presents itself,—the coagulation
ofthe Blood which has been effused into the pericardium (the effusion having
taken place during the  last moments of life), whilst  that in the vessels has re-
mained fluid.   In several of the instances in  which the blood has  been found
uncoagulated in  the vessels, many  hours after death,  a portion withdrawn from
the body has  clotted;  and Dr. Polli  asserts that  the  complete absence of
coagulability is a phenomenon  which has no real occurrence.   During a long
course of researches on this  subject, he has  never yet met with  an instance,
in which the  blood, when left to itself, and duly  protected  from external
destructive  influences,  did not coagulate before becoming putrid.  He has
even more than once caused  blood to coagulate, which  had been  taken in a
fluid state from the veins, thirty-six or forty-eight hours after death.*—It ap-
pears that simple arrestment of Nervous influence favours the coagulation of
the blood in the vessels ;  clots being  found in their trunks, within  a few
minutes after the Brain and Spinal marrow have been broken down.
   702.  The length of time which elapses before Coagulation, and the degree
in which the clot solidifies, vary considerably; in  general, they are  in the
inverse proportion to each other.  Thus, if a large quantity of blood be with-
drawn from the vessels of an animal  at the  same time, or within short inter-
vals, the portions that  last flow coagulate much more rapidly, but much less
firmly, than those  first obtained.   In blood drawn during Inflammatory states,
again, the coagulation is usually slow, but the clot is preternaturally firm ; espe-
cially at its upper part, where the  Buffy coat (§ 704) or  colourless  stratum
of Fibrine, gradually contracts, and produces the cup, which is usually re-
garded  as indicative of a high degree of Inflammation.  Except under the
peculiar circumstances just stated, the Blood  withdrawn from the body always
coagulates;! whether it be kept at rest or in  motion; whether its  temperature
be high or low ; and whether it be excluded from  the air, or be admitted to
free contact with the atmosphere.   The Coagulation may be  accelerated or
retarded,  however, by  variation in these conditions.  Thus, if  the blood be
continually agitated  in a bottle, its coagulation is delayed, though it will at last

  * Ranking's Half-Yearly Abstract, vol. ii. p. 337.
  t Some diseases may perhaps be an exception; non-coagulation of the Blood is said to be
characteristic of the Scurvy, but this is erroneous.  In very severe forms of Typhus, the same
has been stated to occur. 
                COAGULATION OF THE BLOOD.--BUFFY COAT.             533

take place in shreds or insulated portions;  but that rest is not the cause of its
coagulation  (as some have supposed), is  proved by the fact that, if a portion
of blood be included between two ligatures in a living vessel, it will remain
fluid for a long time.  Again, the coagulation is accelerated by moderate heat,
and retarded by cold; but  it is not prevented by even extreme cold; for, if
blood be frozen immediately that it is drawn, it will coagulate on being thawed.
Moreover it is accelerated by exposure to air, but it is not prevented by com-
plete exclusion from it, as is proved by its taking place in a vacuum, or in a
shut sac within the  dead  body:  complete exclusion  from the  air, however,
retards the change;  as has  been  shown by causing Blood to flow into a ves-
sel containing oil, which will form  an impervious coating on  its surface, and
will  occasion the coagulation to  take place so slowly, that  the  Red particles
have time to subside, and  the upper stratum of the clot is colourless.*   A re-
markable case has been put on record by  Dr. Polli, in which complete coagu-
lation of the blood did not take place until fifteen days after it had been with-
drawn  from  the  body; and fifteen days  more  elapsed  before putrefaction
commenced.   The upper  four-fifths of the clot were colourless ; the red cor-
puscles  occupying only the lowest fifth.   It is additionally remarkable, that
the patient (who was suffering under acute pneumonia) being bled very fre-
quently during the succeeding week, the blood gradually lost its indisposition
to coagulate.t  An extrication of Carbonic acid usually  takes place to a slight
degree during coagulation;  but this is  not a constant occurrence; and  the
process  is not prevented, even by agitating Carbonic acid with the  Blood.
   703.  The proportions of Serum  and Clot which present themselves after
coagulation, are liable to great variation, independently of the amount of the
several ingredients characteristic of each;  for  the  Coagulum may include not
only the Fibrine and Red  particles, but also a  large proportion of the Serum,
entangled as it were in its substance. This is particularly the case when the
coagulation  is rapid ; and the clot then  expels little  or none of it by subse-
quent contraction.   On the other hand, if the  coagulation be slow, the parti-
cles of Fibrine seem to become more completely aggregated, the coagulum is
denser at first, and its density is  greatly increased by subsequent contraction.
When a  firm fresh clot is  removed from the fluid in which it is  immersed, its
concretion is found to continue for 24 or even 48 hours, serum being squeezed
out in drops upon its surface; and in  order, therefore, to form  a proper esti-
mate of  the  relative  proportions of Crassamentum and  Serum,  the  former
should be cut into slices, and laid upon bibulous paper, that the  latter may be
pressed  from it as completely as  possible.—According to the experiments of
Mr.  Thrackrah,  Coagulation takes place  sooner in  metallic vessels  than  in
those of  glass or earthenware, and the quantity of Serum separated  is  much
less; in  one instance, the  proportion of  Serum to Clot was as  10 to 24^,
when the blood coagulated in  a glass vessel; whilst a portion of the same
Blood, coagulating in a pewter vessel, gave only 10 of Serum to 175 of Clot.
The Specific Gravity of Blood is no measure of its coagulating  power; for a
high specific gravitv may be due to an excess in the amount of  globules,
which form the heaviest part of the blood ; and  may be accompanied by a
diminution in-the quantity  of fibrine, which is the coagulating element.
   704.  The Crassamentum not  unfrequently exhibits, in  certain disordered
conditions of the Blood, a layer of Fibrine nearly free from colour; and this is
known  as  the  Buffy Coat.  The  presence of this has  been frequently re-
garded as a sign of the existence  of Inflammation, occasioning an undue pre-
dominance of Fibrine; but this idea is far from  being correct, since,  as will pre-

            * Babington in Medico-Chirurgical Transactions, vol. xvi.
            ■j- Mr. Piiget's Report, in Brit, and For. Med. Rev., xix.p. 252.
                                   45* 
534                OF ABSORPTION AND SANGUIFICATION.

sently  appear (§ 705), it may result from  a very opposite condition of the
Blood.   A similar colourless layer of Fibrine is always observable, when the
Coagulation of the blood is retarded by the addition  of agents  that have the
power of delaying it (§ 699); and since, in Inflammatory states of the system,
the blood is generally long in coagulating, it has been supposed that the sepa-
ration of the red particles is due to this cause alone.   Dr. Alison,* however,
maintains that there must be an  absolute tendency to separation between the
two components of the clot, in order to account for the phenomena sometimes
presented by it; and he adduces the two following reasons in support of this
view.  " 1. The formation of the Buffy coat, though  no doubt favoured or
rendered more complete by slow coagulation, is often observed in cases where
the coagulation is more rapid than usual;  and the colouring matter is usually
observed to retire from  the surface of the  fluid in  such cases, before  any
coagulation has commenced.   2.  The  separation of the Fibrine  from the
colouring matter in such cases takes place in films of blood, so thin as not to
admit of a  stratum of the one being laid above the other; they separate  from
each other laterally, and the films acquire a speckled  or mottled appearance,
equally characteristic of the state of the blood with the buffy coat itself."—
It appears from the observations of Mr. Wharton Jones, that the red corpus-
                                    cles  of  Inflammatory  Blood have an
                                    unusual attraction for each other, which
                                    occasions their coalescence in piles and
                                    masses; so that by this character, the
                                    state of the Blood may  be detected,
                                    from the examination of no  more than
                                    a single drop of the fluid.   Now if we
                                    consider, in connection with this in-
                                    crease  in  the mutual attraction of the
                                    Blood-discs, the  increase in the mutual
                                    attraction  of the particles of Fibrine
                                    (which causes the coagulum of Inflam-
                                    matory blood to be so much firmer and
                                    more decidedly fibrous  than that of the
                                    healthy fluid), we  have a cause  suffi-
                                    cient to explain the phenomena noticed
                                    by Dr. Alison;  without the  necessity
                                    of resorting to the idea of an absolute
                                    repulsion being present between the two
                                    constituents.—It is in the Buffy Coat ■
                                     of Inflammatory Blood,  that we see
                                     the clearest indications of organization
                                    ever presented by the circulating  fluid.
The fibrous network is  frequently extremely distinct; and it commonly in-
cludes a large number  of White  Corpuscles in  its  meshes.  Sometimes,
indeed, according to the  observations of  Mr. Addison,  it almost  entirely con-
sists of these bodies.  In its Chemical Composition, the buffy coat of Inflam-
matory blood appears to be peculiar; containing a  larger or  smaller amount
of the substance, readily soluble  in  boiling water, which is  considered by
Mulder to  be  the Tritoxide of Proteine (§ 116, a).
   705. When the Buff  arises  from other causes, however, its appearance is
less characteristic.   It appears from the researches of Andral, that the  usual
condition of its production is an increase in the quantity of Fibrine in propor-
tion to the Red Corpuscles; and not a simple increase of Fibrine.   When the
 The microscopic appearance of a drop of blood
in the inflammatory condition.  The red corpus-
cles lose their circular form and adhere together ■
the white corpuscles remain apart, and are more
abundant than usual.
* Outlines of Physiology, 3d edition, p. 89. 
            BUFFY COAT.--PATHOLOGICAL CHANGES IN THE BLOOD.        535

Blood contains an  excessive  quantity of Fibrine. it  coagulates slowly;  thus
the blood of a patient labouring under Rheumatism  coagulates more slowly
than that of one affected  with Typhoid fever.   The increase  may occur in
two ways;—either by an absolute increase in the Fibrine, the amount of the
corpuscles remaining unchanged, or not  being  augmented  in the  same  pro-
portion ;—or by a diminution of the Corpuscles, the quantity of Fibrine re-
maining the same, or not diminishing in  the  same proportion.   Hence  in
severe Chlorosis, in which the latter condition is strongly developed, the buffy
coat may be  as well marked, as in the severest Inflammation.  Unless the
composition of the blood be  altered  in one of these two ways, it is stated by
Andral that the buffy coat is never formed;  the influence of  circumstances
which favour it, not being  sufficient to produce it when acting alone.   The
absence of these circumstances may prevent it, however, when it would other-
wise have been formed;  thus, when the  Blood flows slowly, the buff is not
properly produced; because the slow discharge gives one  portion time to
coagulate before another; and only the blood last drawn furnishes the Fibrine
at the upper part of the vessel.  Again, in a deep narrow vessel, the buff will
form much more decidedly than  in a broad shallow one;  because the thick-
ness of the Fibrinous crust will be greater.


                 6.—Pathological Changes in the Blood.

   706.  From the part which the Blood performs in the ordinary processes of
Nutrition, it cannot be doubted  that it undergoes important alterations, when
these processes take place in an abnormal manner.   These  alterations  must
be sometimes  the causes, and sometimes the effects, of the morbid phenomena,
which constitute what we term the  Disease.   Thus, when some local cause,
affecting the solid tissues of a certain part of the body, produces Inflammation
in them, their normal relation to the blood is altered; the consequence is, that
the Blood, in passing through them, undergoes a different set of changes  from
those for which it  is originally adapted ; and  thus its own  character under-
goes an alteration, which soon becomes evident throughout the whole mass of
the circulating  fluid, and is,  in  its  turn, the cause of  morbid phenomena in
remote parts of the system.   On the other hand, the strong analogy between
many Constitutional diseases, and the effects of poisonous agents introduced
into the Blood, appears clearly  to point to the inference, that  these diseases
are due to the action of  some morbific matter, which has  been directly intro-
duced into the current of the circulating fluid, and which has affected both its
physical and  its vital properties.*   Here, then, is a wide field for investiga-
tion, of which the  surface can scarcely be  said  to be yet broken up, and
which must yield an abundant harvest to those  who shall cultivate it with in-
telligence and zeal.   The first and most complete series  of connected re-
searches, which have been yet published, on the changes which the blood un-
dergoes in disease, are those of MM. Andral and Gavarret ;t these are confined

   * This doctrine has been brought prominently forward, in a paper on Symmetrical Dis-
eases, read by Dr. William Budd before the Medico-Chirurgical Society, Dec. 16, 1841.  The
Author ingeniously proves, that the symmetry of many diseases (such  as certain forms of
cutaneous eruptions,  rheumatism, &c.) which do  not immediately  depend upon external
causes, necessarily involves the idea of the conveyance ofthe morbific agent in the circulating
fluid; the palsy produced by lead is a very interesting example, in which the agent is known
to be mingled with the blood, and to be deposited in the parts affected, which are generally,
if not always, symmetrical.
  f An account of these inquiries will be found  in the Provincial Medical and Surgical
Journal for May, June, and July  1841; in the Annales des Sciences Naturelles, Dec. 1840,
and March 1841; and in the Ann. de Chimie, tom. Ixxv.  They have since been published 
536
OF ABSORPTION AND SANGUIFICATION.
to the alterations which take place in the proportions of the Organic elements
of the fluid.  Another series of researches of great value, and in almost every
point confirmatory of the preceding, has been since made by MM. Becquerel
and Rodier;* and another by Dr. Karl Popp.t  Numerous other less systematic
analyses have been made by various Chemists and Pathologists.   The follow-
ing outline contains the general results of these.—It is, of course, necessary to
determine,in the first instance, what are  the usual or normal proportions; and
the following may be estimated as  the ordinary  quantity of each element, in
1000 parts of healthy Blood :—
            Fibrine......from  2 to   3J
            Corpuscles......" 110 " 150
            Solid matter of Serum    .     .    .    .  "  72 "   85
  707.  Before  entering upon the consideration of the alterations in the Blood,
which  are effected by particular morbid states,  it is  requisite to notice  the
results of two extraneous causes, usually  operating in disease, which may affect
the proportions  of  its components.   These  are, Abstinence from  food, and
Loss of Blood, as by  Hemorrhage or Venesection.  It has been commonly
supposed, that these causes have a tendency to diminish the proportion of all
the solid elements of the blood; but this is  not  the case; for they affect  the
Corpuscles, chiefly or  exclusively, the quantity of Fibrine and of the solids of
the Serum remaining  nearly the same, unless the  abstinence has  been pro-
longed,  or the loss of  blood  very considerable.—It is probably to the effects
of abstinence, that we are to  attribute the general diminution of the solids of
the blood, which presents  itself in most acute diseases;  thus, on the  average
of 120 cases, MM.  Becquerel and Rodier  found  the average Specific Gravity
of defibrinated blood reduced from 1060  (in Men) and 1057'5 (in  Women), to
1056 (in Men),  and  1055 (in  Women).   The diminution in the proportion of
Corpuscles was well marked;  that of the Albumen was much slighter; there
was on  the whole a slight augmentation  of Cholesterine and Phosphorized
Fat; and a marked increase  in the  Phosphates.   The increase or diminution
of the Fibrine is entirely dependent (as  we shall presently see) on the nature
of the disease.—The  influence of Venesection in impoverishing  the blood is
well shown in the following table of the mean composition of the fluid, at three
successive Venesections in ten persons :—
	First	Second	Third
	Bleeding.	Bleeding.	Bleeding.
Specific Gravity of defibrinated			
Blood.....	1056	1053	1049-6
Water......	793	807-7	823-1
Fibrine .....	3-5	3-8	3-4
Corpuscles . . . . .	129-2	116-3	99-2
Albumen ....	65-0	63-7	64-6
Extractive, free salts, and fatty			
matters . . . . .	9-4	S-5	9-5
Thus we see that  repeated venesections render the blood more watery:  but
this, chiefly by the  diminution  they produce in the amount  of Corpuscles.
They slightly diminish the albumen and fatty matters;  but they exert no per-
ceptible influence on the amount of Fibrine;—a point of the highest practical
importance.
  a. The most important fact substantiated by Andral, is one that had been previously sus-
pected,—the invariable increase in the quantity of Fibrine during acute Inflammatory affec-
tions; the increase being strictly proportional to the intensity of the Inflammation, and to the
in a separate form, under the title of " Essai d'Hematologie Pathologique."  [See Transla-
tion by Drs. Meigs and Stille, Phil. 1844.]
  * Gazette Medicale, 1844, Nos. 47—57.       -j- Ranking's Abstract, vol. iii. p. 306. 
PATHOLOGICAL CHANGES IN THE BLOOD.
537
degree of symptomatic Fever accompanying it.  "The augmentation of the quantity of
Fibrine is so certain a sign of Inflammation, that, if we find more than 5 parts of fibrine in
1000, in  the course of any disease, we may positively affirm  that some local  inflammation
exists.''  Several cases are mentioned, in which an increase  to 7 or 1\ parts took  place,
without any apparent cause; but in which it afterwards proved that severe local  inflamma-
tion was present; and  thus we are furnished with a pathognomonic sign of great importance.
The average proportion of Fibrine in Inflammation  may be  estimated at 7;  the  minimum
at 5; the maximum at 13-3.  The greatest augmentation is  seen in Pneumonia  and  Acute
Rheumatism.  It does  not appear that in robust athletic persons, the proportion of Fibrine is
greater than in those of feeble constitution; in the latter it is the Corpuscles that are deficient;
and it is rather from  this disproportion, than from an absolute excess of Fibrine, that their
greater liability to  Inflammatory affections arises.  Diseases which commence at the same
time as the Inflammation, or co-exist with it, do not prevent the  characteristic increase of the
Fibrine;  thus in Chlorotic females, the proportion rises to 6 or 7, under this influence.  The
augmentation is observed at the very outset of the affection;  the quantity increases with its
progress; and a decrease shows itself when the disease begins to abate.*   When  the* dis-
ease presents alternations of increase and decline, these are marked by precisely correspond-
ing changes in the quantity of Fibrine.  It is a curious fact, that an augmentation is  commonly
observable  during the advanced stage of  Phthisis, in spite of the deterioration which the
blood must then have undergone; this is probably dependent  upon the development of local
inflammation around the tubercular deposits.  In one of Popp's observations, the  proportion
of Fibrine in the blood of a Phthisical patient was not less than 10-7.  Some experiments
performed  by M. Andral  on the blood of pregnant women, seem to  lead to the  conclusion
that, during the first six months, the Fibrine is below the normal standard; and that it sub-
sequently varies, usually undergoing an  augmentation between the sixth and seventh, and
the eighth and ninth months. There is also a diminution in the Corpuscles; and these circum-
stances combined favour the production of the buffy coat (§ 704).  These observations are
confirmed by those of MM. Becquerel and  Rodier.
   b. It appears obvious, from what has been just stated, that the increase in the quantity of
Fibrine is not dependent upon the febrile condition, which is secondary to the  local  inflamma-
tion, but upon the Inflammation itself.  This conclusion is confirmed  by the interesting fact
that, in idiopathic Fever, the proportion of Fibrine is diminished, instead of undergoing an
increase. This diminution was constantly observed by Andral in the premonitory stage of
Continued Fever; in some instances the amount was no more than 1*6 parts in 1000.  The
proportion of Corpuscles was found to have usually, but not constantly, undergone an increase;
as  had also  that of the  sdlid parts of the Serum.   In ordinary Continued Fever, in  which
there was no evident  complication from local disease, the quantity of Fibrin varied from 4-2
to 2-2; that of the  Corpuscles from  185-1 to 103-6 (excluding a case in which their amount
was only 82-5, which was that of a Chlorotic female) ; that of the solid matter of the Serum,
from 98-7 to 909;  and that ofthe Water from 725-6 to 851-9.   Hence the quantity of solid
matter appears to be usually increased; but the peculiar condition ofthe disease may proba-
bly be stated to be, an increase in the proportion of  the Corpuscles to the Fibrine.   When,
however, a local Inflammatory affection developes itself during the course of the  Fever, the
amount  of Fibrine increases; but its augmentation seems  to be kept down by the  febrile
condition.—In Typhoid Fever,-j- the decrease in the proportion of Fibrine is much more de-
cidedly marked; this does not depend upon abstinence;  for it ceases as soon as a  favourable
change occurs in the disease, long before the effect of food could show itself.  In the various
cases examined by Andral, the blood furnished a maximum of 3-7 of Fibrine, and a minimum
of 0-9; in this last case, the Typhoid condition existed in extreme intensity, yet  the patient
recovered.  The proportion of Corpuscles varies considerably; in an early stage of  the disease
it is usually found to be absolutely high; and it always remains high relatively to the amount
of Fibrine.   In Typhoid fever, then, the abnormal condition of the Blood, in regard  to the
  * By experiments on animals, M. Andral  has ascertained that no circumstance  of pre-
vious debility or privation  prevents  this characteristic change.  Having  ascertained the
amount of Fibrine  in the blood of three dogs to be 2-3, 2-2, and l-6 (the  natural range for
these animals), he deprived them, completely or partially, of food.  On the fourteenth day,
the proportion of fibrine had risen, in the first to 4-5: and in the second, to 4: these animals
had  no food.  In the third dog, which was supplied with  a  very small quantity of food
daily, the  same condition developed itself at a later period;  the blood on the fourteenth day
exhibiting only 1-8 parts of fibrine: but on the twenty-second day presenting 3-3 parts—In
all these instances,  the elevation in the proportion of Fibrine was coincident with Inflamma-
tory changes in the stomach.
  f M. Andral confines this term to the species characterized  by ulceration of  the mucous
follicles of the intestinal canal. 
538
OF  ABSORPTION AND SANGUIFICATION.
 disproportion between the Corpuscles and the Fibrine, is more strongly marked than in ordi-
 nary Continued Fever: yet the usual augmentation of Fibrine will take place, if a local in-
 flammation developes itself.—In the Eruptive Fevers, it does not appear that tlte proportion
 between the Fibrine and the Corpuscles undergoes so striking a change, as in ordinary Con-
 tinued Fever;  but the number of cases examined was too small to admit of decided conclu-
 sions.  It was evident, however, that the specific Inflammations proper to, and characteristic
 of, these Fevers, have not the  same effect in occasioning an increase of the Fibrine, as an
 intercurrent Inflammation of an extraneous character.—By the experiments of Magendie it
 has been ascertained that one of the effects of a diminution in the proportion of Fibrine, is a
 tendency to the occurrence of Hemorrhage or of  Congestion, either in the parenchymatous
 tissue, or  on the surface of membranes:  these  conditions  are well known to be of frequent
 occurrence, as complications  of febrile disorders.  A marked diminution  of  Fibrine  was
 noticed also in many cases of the disorder termed Cerebral Congestion, which  commences
 with headache, vertigo, and  tendency to epistaxis, and not unfrequently passes into coma
 and  apoplexy.   In Apoplexy, the diminution of Fibrine was  still more striking; and in gene-
 ral, tTiere was found to be an increase of the Corpuscles.   In one  instance, the quantity of
 Fibrine on the second  day of the attack was found to have fallen to 1-9, whilst that of the
 Corpuscles had risen to 175-5;  but on the third day, when the patient's consciousness began
 to return the quantity of Fibrine was 3-5, whilst  that of the Corpuscles had fallen to 1377.
 It would seem  from  the great change in the character of the Blood, which was noticed in
 this  and in other instances, that  the want of  due proportion between the Fibrine and the
 Corpuscles was the cause, rather than the effect, ofthe Apoplectic attack.
   c.  The amount of Red Corpuscles seems to  be subject to greater variation within the limits
 of ordinary health, than is that of Fibrine.   In the  condition which is ordinarily termed a
 highly sanguineous temperament,  or  Plethora,  it  is chiefly the entire mass of the blood that
 undergoes an increase; but whatever excess there may be in the proportion of its solid  con-
 stituents, affects the  Corpuscles rather than the Fibrine.  Plethoric persons are not more
 prone to Inflammation, than are those of weaker  constitution; but they are liable to Conges-
 tion, especially of the brain, and to Apoplexy or other Hemorrhage.  The effect of Bleeding
 in diminishing this tendency is now intelligible;  since we know that loss  of blood reduces
 tbe proportion of Corpuscles.—On the other hand, in that temperament,*  which, when ex-
 aggerated, becomes Ana?mia, there is a marked diminution of the Corpuscles;  this tempera-
 ment may lead to two different conditions of the system.   In Chlorosis, the Red Corpuscles
 are diminished, whilst the Fibrine remains the same; so that the clot, though small, is firm,
 and not unfrequently  exhibits the buffy coat; in some extreme cases of this disease, the  Cor-
 puscles have been found as  low as 27.  The influence of  the remedial administration of
 Iron, in increasing the quantity of Corpuscles, was  rendered  extremely perceptible by An-
 drei's analyses; in one instance,  after iron had been taken for a short  time, the proportion
 of Corpuscles was found to have risen from 497 to 64-3 ;  whilst in  another, in which it had
 been longer continued, it had risen from 46-6 to 95-7.  On the other hand, Bleeding reduced
 still lower the proportion of Corpuscles; thus in one instance, their amount was found, on a
 second bleeding, to have  sunk from 62-8 to 49.   The full  proportion of  Fibrine in the blood
 of Chlorotic patients  accounts  for the infrequency of Hemorrhage in them;  whilst it also
 leads us to perceive that they may be, equally  with others,  the subjects of acute Inflamma-
 tion, which we know to be the fact.  A diminution  of Corpuscles  may also co-exist with a
 diminution in the amount, or in the degree of elaboration, ofthe Fibrine; and this condition
 seems to be characteristic of Scrofula.  Andral has noticed a diminution in the proportion of
 Corpuscles in other Cachectic states, resulting from the influence of various depressing causes
 on the nutritive powers; as in the case of Diabetes Mellitus,in which the patient was much
 exhausted;—a case of Aneurismal  dilatation of the Heart  inducing Dropsy;—and in several
cases of Cachexia Saturnina.—The increase  in the proportion of Colourless Corpuscles, in
Inflammatory affections, has been  particularly noticed by  Popp; he has found  them espe-
cially abundant in Pneumonia and in Phthisis,—in the former  of which diseases the Fibrine
is invariably, and in the latter generally, increased.
  d.  The  chief class of cases, in which any  marked  change has been  observed in the
amount of solid matter in the Serum, is that of Albuminuria, or Blight's disease of  the Kid-
ney.   The diminished Specific Gravity of the  Serum was long ago pointed out by Dr. Christi-
 son; but Andral remarks that this is not an accurate criterion, since, if there be a diminished
amount of Corpuscles (as is  not unfrequently the case  in this  disease), the proportion of
water in the whole will be  increased, and the specific gravity of  the serum thus lowered,
without any alteration in its proper quantity of solid matter.   According to  Andral, the
diminution in  the amount of Albumen in the Serum is exactly proportional to the quantity
  * The term lymphatic has been applied to this temperament;  by which term was meant
a predominance of lymph in the absorbent vessels. 
PATHOLOGICAL CHANGES IN THE  BLOOD.
539
contained in the urine. A case is related by him, under this head, which affords an interest-
ing exemplification of the general facts that have been already attained by his investigations.
A woman who had been suffering from Erysipelas of the face, and who had lost blood both
by venesection and by leeches, became the subject of Albuminuria.  The blood drawn at
this time exhibited a considerable diminution in the proportion of  Corpuscles, as well as of
Albumen,—a  fact which the previous loss of blood fully accounted for.  After a short period,
during which  she had been allowed a fuller diet, another experimental bleeding exhibited
an increase in the proportion of Corpuscles.  Some time afterwards, when the Albumen had
disappeared from the Urine, some more blood was drawn; and it was then observed that
the Albumen of the Serum had returned to its due proportion, but that  the Corpuscles had
again diminished, whilst there was a marked increase in the quantity of Fibrine.  This altera-
tion was fully accounted for by the fact, that, in the  interval, several Lymphatic ganglia in
the neck had been inflamed and had suppurated; and that the patient had been again placed
on very low diet.  " Thus," observes Andral, " we were enabled to  give a complete explana-
tion of the remarkable oscillations which were presented, in the proportion of the different
elements ofthe blood drawn at three different times from the same individual; and thus it
is that, the more extended are our inquiries, the more easy does it become to refer to general
principles the  causes of all those changes in the composition of the blood, which, from the
frequency and rapidity with which they occur, seem at first sight  to baffle all rules, and to
take place, as it were, at random.  In the midst of this  apparent disorder, there  is but the
fulfilment of laws ; and in order to obtain these, it is only necessary to strip the phenomena
of their complications, and to reduce them to their simplest form."

   708. That the  Blood  is  subject to  a great variety of other  morbid altera-
tions, which are sometimes the causes, and sometimes the results, of Disease,
cannot be for a moment doubted.  But our knowledge of the nature of these
changes is as yet very insufficient.  The great  amount  of attention  which is
being directed by Chemical Pathologists to the  subject,  however, will doubt-
less ere long  produce  some important results.—Among the most  frequent
causes of depravation in the character of this  fluid, we must undoubtedly rank
the retention, in  the Circulating  current, of  matters which  ought to be  re-
moved by the Excreting  processes.   We shall presently see, that a total
interruption  to the  excretion of Carbonic Acid by the  lungs,  will  occasion
death in the  course of a very few  minutes; and  even when only a slight im-
pediment is  offered it, so that the quantity of  Carbonic Acid always contained
in arterial blood is augmented to but a small degree, a  feeling of discomfort
and oppression, increasing with the duration  of  the interruption, is  speedily
produced.   The  results of the  retention  of  the  materials of  the Biliary and
Urinary excretions  will be  hereafter  considered  (Chap, xv.); and at present
it will be only remarked, that such retention  is a most fertile  source  of slight
disorders of  the system, that it is largely concerned in producing many severe
diseases, and that if complete it will most  certainly and  rapidly produce a
fatal result.—The most remarkable cases  of  depravation of the  Blood, by the
introduction  of matters from without, are  those in which these substances act
as ferments,—exciting such Chemical changes in the  constitution ofthe fluid,
that its whole character is  speedily changed, and  its vital properties are alto-
gether destroyed.    Of such an occurrence, we have characteristic examples in
the severe forms of  Typhoid fever, commonly termed malignant; in Plague,
Glanders,  Pustule Maligne, and  several other diseases; in some of which we
can trace the direct introduction of the poison into the blood,  whilst in others
we must infer from the similarity of result) that it has been introduced through
some obscure channel,—probably the lungs.   The final  symptoms which are
common  to  all these  diseases have  been well  described by Dr. Williams,*
under the title of Necroemia, or Death by depravation of  the blood.  " Almost
simultaneously, the heart  loses its  power,   the  pulse becomes very weak,
frequent,  and  unsteady:  the vessels lose their tone,  especially the  capil-
laries of the most vascular organs, and congestions occur to a great  amount;
* Principles of Medicine, [Am. Ed. by Dr. Clymer, p. 373.] 
540
OF THE CIRCULATION OF BLOOD.
the brain becomes inactive, and stupor ensues; the medulla is torpid, and the
powers of respiration and excretion are imperfect: voluntary motion is almost
suspended ;  secretions fail;  molecular nutrition ceases ;  and  at  a  rate  much
more early than in other modes of  death, molecular death follows close on
somatic death,—that is, structures die and begin to run into decomposition as
soon as  the pulse and breath have ceased ;  nay, a partial change of this kind
may even precede the death of the whole body;  and parts running into gan-
grene, as in the carbuncle of plague, the sphacelous throat of malignant scarla-
tina, and the sloughy  sores of the worst forms of typhus, or  the putrid  odour
exhaled even before death by the bodies of those who are the victims of simi-
lar pestilential disease, are so many proofs of the early triumph of dead over
vital chemistry."—"The appearance of petechia? and vibices on the external
surface, the occurrence  of more  extensive  hemorrhage  in internal parts, the
general fluidity of the  blood, and frequently  its unusually dark or otherwise
altered aspect, its poisonous properties as exhibited in its  deleterious operation
on other animals, and its proneness to pass into decomposition, point out the
Blood as the first seat of disorder; and by the failure of its natural properties
and offices as the vivifier of all structure and function, it is plainly the medium
by which death begins in the body."
                        CHAPTER  XII.

                      OF THE CIRCULATION  OF BLOOD.

                    1.—Ofthe Circulation in General.

  709.  The Circulation of nutritive fluid through the body has for its object,
on the one part, to convey to every portion  of the organism the materials for
its growth and renovation, together with  the supply of Oxygen which is re-
quisite for its vital  actions, especially those  of  the  Muscular and Nervous
systems ;  and at the  same time to carry off the particles, which are set free by
the  disintegration or  waste of the tissues, and which are to be removed from
the  body by the Excreting processes.  Of these processes, the one most con-
stantly in operation, as well as most necessary  for the maintenance of the
purity of  the blood,  is the extrication of  Carbonic acid, through the Respira-
tory organs;  and this is made subservient to the introduction of Oxygen into
the  system.  The extent, therefore, to which a Circulating apparatus is de-
veloped in the Animal kingdom, is partly  dependent upon the degree in which
the  function of nutritive Absorption is limited to one  part of the body;  and
partly upon the arrangement of the Excreting surfaces, and especially of the
Respiratory apparatus.   Where the Digestive cavity  extends itself through
the  whole system, so that every part can absorb  at once from its parietes,—
and where the whole external surface is adapted, by its softness and permeability,
to expose  the fluids of the body to  the aerating medium around,—there is no
necessity  for any transmission of fluid from  one part to another;  and accord-
ingly, in the lowest animals, which are thus formed, no true Circulation exists.
Again, in  the Insect tribes,  in whose bodies  the absorption of fluids can only
take place at fixed points, there is a Circulation,  for the purpose  of transmit-
ting the absorbed matter to the remote portions of the  body; but as every part
of the interior is  permeated by  air,  the second of the  above-named purposes 
OF THE CIRCULATION IN GENERAL.
541
is already answered; and the circuit of the blood through the vessels, there-
fore, is not accomplished with the energy and activity which, from the vigor-
ous movements performed by these little beings, might have been supposed
necessary.   On the other hand,  among the Mollusca, in which the absorption
of fluid  and the respiratory  action are alike limited, we find the circulating
apparatus almost as extensive, and the movement of blood as vigorous, as it is
in the lower Vertebrata.  It  is in those animals, in which there  is the greatest
activity in the other functions,—which live, in fact, the fastest,—that the Cir-
culation  is most energetic;  thus the rapid and  energetic  movement of  the
blood in Birds contrasts most strongly with its slow and feeble propulsion  in
Reptiles.  The movement may  vary considerably, however, in the same ani-
mal at different times, according to its state of repose or activity; and in dif-
ferent organs of the same  animal, according  to the energy with which their
functions are being respectively  performed.
  710.  In Man, as in  other Vertebrated animals, there is a regular and con-
tinuous  movement of the nutritive fluid through the vascular system; and upon
the maintenance of this, the activity of all parts of the organism is dependent.
The course of the Blood may be likened to the figure 8 ;  for there  are two
distinct circles of vessels, through which it is transmitted;  and the Heart is
placed at the junction of these.  The Systemic and Pulmonary circulations
are entirely separate, and might be said to  have  distinct  hearts; for the left
and  right sides of the   heart, which are respectively appropriated to these,
have no  direct communication with each other (in  the perfect adult condition,
at least), and are  merely brought together for economy of material.   At «n
early period of foetal life, as in the permanent state of the Dugong, the heart is
so deeply cleft, from the apex towards the base, as almost to give the idea of
two separate organs.   Each system has its  own  set of Arteries or efferent
vessels, and Veins or afferent trunks;  these communicate  at their central ex-
tremity by the Heart; and at their peripheral extremity by the Capillary ves-
sels, which are nothing else than  the minutest ramifications of the two systems,
inosculating into a plexus (§  219).

                                 Fig. 211.
Web of Frog's foot, stretching between two toes, magnified 3 diam.; showing the blood-vessels, and
                    their anastomoses: 1,1, veins; 2, 2, 2, arteries.
    46 
542
OF THE CIRCULATION OF BLOOD.
  a. Although the diameters of the  branches, at each subdivision, together exceed that of
the trunk, yet there is but little real difference in their size.  For, according to a well-known
geometrical law, the areas of circles are as the squares of their diameters; and, as the calibre
of a tube is estimated by its area, not by its  diameter, it follows that, in comparing the size
of a trunk with that of its branches, we are to square the diameter of the  former  and com-
pare the result with the sum of the squares of the diameters of the branches.   When this is
done, there  is found to be a very close correspondence.  The  following table  gives the re-
sult of eight measurements, taken with a view to determine the question,  the first three
were taken from the mesenteric artery of a Sheep; the next three from the aorta and iliac
arteries;  the last two from the  Horse.*
	TRUNK.		BKAJN	uun;s.
	DIAMETER.	SQ.UARE.	DIAMETERS.	SUM OF SQ.UARES
I.	9	81	7.5+5	81.25
II.	7.2	51.64	6+4	52
III.	3.5	12.25	3+2	13
IV.	7.0	49	5+5	50
V.	17	289	10+10-J-9.5	290.25
VI.	10	100	7+7+2	102
VII.	4.5	20.25	3.5+3	21.25
VIII.	8	64	4+7	65
The discrepancy between the two results must be considered extremely small, when it is
stated that the unit, in the above measurements, is no more  than one-fortieth of an inch;
and when it is remembered that any error in  the measurement is greatly increased in the
calculation.
  b. From  Mr. Paget's  observations, however,  it appears that there is seldom an exact
equality between the area of the trunk and that of its branches, but  the area sometimes in-
creases, and sometimes diminishes;—the former being the general rule for the subdivision
of the aorta and  its principal branches in the upper  extremities;—the latter in  the lower.
The following Table shows the relative areas of several arterial trunks, and ofthe branches
proceeding from them.


         Arch of Aorta.....
         Innominata
         Common carotid  .....
         External carotid    ....
         Subclavian  ......
         Abdominal Aorta, to last lumbar art.
                       -, just before dividing  .
TRUNK.	BRANCHES
1	1-055
1	1-147
1	1-013
1	1-190
1	1-055
1	1-183
1	■893
1	•982
1	1-150
        Common Iliac
        External Iliac

  711. That the movement of the Blood through the Arterial trunks and the
Capillary tubes is, in Man, and in other  warm-blooded  animals, chiefly de-
pendent upon the action of the Heart  there can be no doubt whatever.   It can
be easily shown  by experiment, that, if  the  Arterial  current be  checked, the
Capillaries will immediately cease  almost entirely to  deliver  the blood  into
the veins, and the Venous circulation will  be instantaneously arrested.  And
it has  also been proved, that the usual force of the Heart is sufficient to propel
the blood, not only through  the Arterial tubes, but  through the Capillaries,
into the Veins; since even a less force will serve to propel warm water through
the vessels of an animal recently dead.t  But there are  certain "residual phe-
nomena"  even in Man, which clearly indicate that this is not the whole truth;
and that forces existing in the  Blood-vessels have a considerable influence,  in
producing both local and general modifications of the  effects  of the Heart's
action.  There are also indications  of the nature of an influence, in which the
blood-vessels  do not partake, arising from those  changes  occurring between
the Blood and the Tissues, that constitue the processes of Nutrition, Secretion,

               * Ferneley in Medical Gazette, Dec. 7, 1839.
               f See Dr. Williams' Principles of Medicine, p. 143, note. 
MOTION OF THE BLOOD IN THE VESSELS.
543
&c   Such, for  instance, would appear to be the interpretation of the fact,
that whilst any variations  in  the action of the Heart affect the whole  system
alike, there are many variations in the Circulation, which, being very limited
in their extent,  cannot  be  attributed  to such central disturbances, and  must
therefore  be dependent on causes purely local.—Of  the  nature of these in-
fluences, and of the mode of their operation, we shall probably arrive at a
more correct knowledge, if we examine the phenomena of the Circulation in
those beings, in  which the moving power is less  concentrated than it is in  the
higher Animals; for just  as we find in the latter, that the development of
special absorbent vessels does not exclude the  function  of absorption  from
being still performed by the general vascular  system  (§ 675), so may we here
be led to perceive, that  there is a generally-diffused force,  to which  alone  the
Circulation of the  nutritious fluid in the lowest  organisms is due, and which
is not altogether replaced by  the special organ of impulsion, that is developed
in the centre ofthe system in the higher.
   712.  The ascent of the  sap in Vegetables is probably to  be regarded as due,
in part, to the vis a tergo occasioned by the  action of Endosmose at  the
roots;  and in part, to the demand  for fluid, occasioned by the vital  processes
taking place in the leaves.   For if the stem of the Vine,  in which the sap is
rising, be  cut across, the sap will continue to  flow for some time  from the  top
of the lower portion ; and its force of ascent may be shown to  be very con-
siderable, by tying over the  cut  surface  a piece of bladder, which  will be
speedily burst,—or by affixing to it a bent tube, containing a column  of mer-
cury, which will be  raised to the height of forty inches or more.   On  the
other hand, the  attractive force of  the leaves is shown by  the fact, that if  the
lower end of the upper division be put into water, it will  continue to absorb,
as long as the vital actions  of the leaves are being performed  with  vigour;
but,  if the branch be carried into a dark room, the exhalation from the leaves
is immediately checked, and  absorption is  checked also.   The influence of
the actions at the periphery of the circulating system, in maintaining the flow
of fluid towards the part, is  further shown by the fact,  that, if a shoot of an
evergreen species  be grafted on a stock of one with deciduous leaves, a con-
tinual and unwonted  ascent of sap will  be kept up in the latter through  the
winter; this  being evidently due  to the demand occasioned  at its  summit.
Again, the recommencement of the annual flow of sap in an ordinary tree, has
been  found to  take  place in the first instance, not  at its  roots, but in  the
neighbourhood of  the  buds;  for their expansion, under the influence of  the
returning  warmth,  exhausts the fluid from  the vessels of their neighbourhood;
this, again, occasions  a demand from below; and thus the  motion is  gradually
propagated to  the roots.   Now it has been experimentally ascertained, that if
a branch of a vine growing in the open air be trained into  a hot-house, it may
be made  to vegetate  during  the  winter, and to  draw up fluid through  the
stems and roots, whose condition has not  been changed.  It is evident, then,
that  in Plants, the  demand  for fluid, in the organs to which it is distributed by
the vascular system, is one of the chief forces by  which the supply is obtained.
   713. This is  still more evidently the case, in  regard  to the Circulation of
nutritious or  elaborated sap, which takes place  in the  under surface of  the
leaves and in the bark.  The object of this movement is not to convey  the
fluid  in a direct line from  one point to another (as in the case with  the
ascending current), but  to supply every part with materials  for its growth, or
for the production  of its peculiar  secretions.  Hence the vessels in which it
takes place, form a minutely-anastomosing net-work, instead of consisting of a
system of straight and distinct tubes.  Through this net-work, thejatex or
elaborated sap is seen to  move, exactly as does the  blood through the capil-
lary  vessels of animals.   The movement takes place, under favourable  circum- 
544
OF THE CIRCULATION OF BLOOD.
stances, with considerable rapidity ; it is accelerated by heat, and retarded by
cold;  and it is subject to  all those minor irregularities (such as the cessation
of movement, or change in the direction of the current, in a particular chan-
nel), which are so constantly to be noticed by any one who attentively watches
the capillary circulation of Animals, and which clearly prove the operation of
some causes independent  of the heart's action  (§ 734).   The general direction
of the elaborated sap, through this capillary system, is  downwards; but  that
the force of gravity  cannot have much to do with the movement, is  shown by
the fact that,  in dependent branches, it has  to ascend towards the stem, which
it will do without interruption from this cause.   Moreover it may be noticed
that this circulation takes  place most actively, in parts which are undergoing a
rapid developement;  and that its energy corresponds with the vitality of  the
part.  Further; it may be  observed  to  continue  for some time in parts  that
have been  completely detached from the  rest;  and  on which  neither vis a
tergo, nor vis a fronte, can have any influence.   It is  evident, then,  that the
force,—whatever be its nature,—by which this continued movement is kept
up, must be developed  by the  processes to which that movement is subserv-
ient ; in other words, that the changes involved in the acts  of nutrition and
secretion are the real source of the motor power.   The manner in which they
become so, is the next object of our inquiry:  and on this subject, some new
views have recently been put forth by Prof.  Draper,* which seem to  account
well for the phenomena.

  a.  It is capable of being shown, by experiments on inorganic bodies, that, if  two  liquids
communicate with each other through a capillary tube, for  the walls of which they both
have an  affinity, and if this affinity is stronger  in the  one liquid than in the  other, a
movement will ensue;  the liquid which has the  greatest affinity being absorbed most ener-
getically into the tube, and driving the other before it.  The same  result occurs when the
fluid is drawn, not into a  single tube, but into a net-work of  tubes, permeating  a  solid
structure; for if this porous structure be  previously saturated with the fluid, for which it has
the less degree of attraction, this will be driven out and replaced by that for which it has
the greater affinity, when the  latter is permitted to enter it.  Now if, in its passage through
the porous solid, the liquid undergo  such a change, that its  affinity  be diminished, it is ob-
vious that, according to the principle just explained, it must be driven out by a fresh supply
of the original liquid;  and that thus a continual  movement in the same direction  would be
produced.
  b. Now this is  precisely that which seems to take place in the organized tissue, per-
meated by nutritious fluid.  The particles of this fluid, and the solid matter through which
it is distributed, have a certain affinity  for each other; which is exercised in the nutritive
changes, to which the fluid becomes  subservient during the course of  its  circulation.   Cer-
tain matters are drawn from  it, in one  part, for the  support and increase of the woody tis-
sue; in another part, the secreting cells demand the materials which are  requisite for their
growth,—as starch, oil, resin, &c; and thus in every portion that is traversed by the vessels,
there are certain affinities between the solids and the fluids, which are  continually being
newly developed by acts of growth, as fast as  those which  previously existed  are satisfied
or neutralized by the changes that have already occurred.  Thus  in  the circulation of the
elaborated sap, there is a constant attraction of its particles towards  the walls ofthe vessels,
and a continual series of changes produced in the fluid as the result  of that attraction.   The
fluid, which has given up to a certain tissue some of its materials,  no longer has the  same
attraction for that tissue; and it is consequently driven from it by the superior attraction then
possessed by the tissue for another portion of the fluid, which is ready to undergo the  same
changes, to be in its turn rejected for a fresh supply.  Thus in  a growing part, there  js  a
constantly-renewed attraction for the nutritive fluid, which  has not  yet traversed  it; whilst
on the other hand, there is a diminished attraction for the fluid, which has yielded up the
nutritive materials required by the particular tissues of the part; and thus the former is con-
tinually driving the latter before it.
  c. But the fluid, which is thus repelled from one part, may still be attracted towards ano-
ther ; because that portion of its contents, which the latter requires, may not yet have been
removed from it.  And in  this manner, it would  seem that the flow  of  sap is maintained
* On the Forces which produce the Organization of Plants, Chap. in. 
MOTION OF THE BLOOD IN THE VESSELS.
545
through the whole capillary net-work, untili t is a.together exhausted of its nutritive matter.
The source ofthe movement is thus entirely to be looked for in the changes which take place
in the act of growth; and the influence of heat, cold, and other agents, upon the movement
is exercised through their power of accelerating or retarding those changes.

   714. The fluid which thus descends through the stem  and roots, seems to
be at last almost entirely exhausted; a portion of it appears to find its way
into the ascending current, and to be mingled with it;  but all the rest seems
to have been entirely appropriated by the different tissues, through which it
has circulated.   Thus there is  no need of any general  receptacle, into  which
it may be collected, and from which it may take a fresh departure;—such as
is afforded by the heart of the  higher animals.   And as the purpose  of this
circulation is only to supply the  nutritive materials, and  not  to convey oxy-
gen,—this  element being but little required in the vegetative processes, and
being supplied by other means,—the same energy and rapidity are  not re-
quired in it, as need to be provided for in the higher animals.
   715.  In the  lowest Animals, the  movement of the  circulating fluid  seems
as independent of any central organ of impulsion, as it has been  shown to be
in Plants.   Thus,  in the  living Sponge, a  current of water is continually
flowing through the  tubes and  channels, by which its  substance  is  traversed,
the fluid being  taken in by the small orifices, and ejected in powerful streams
from the large ones;  and yet the most attentive examination has  not revealed
any mechanical cause for this movement.  In some of the compound Polypi-
fera, a similar current may be seen;  and it is curious  that, in  many species,
its direction undergoes a periodical change;  being reversed at intervals of a
certain number of seconds.   In the Star-Fish  and Sea-Urchin tribe, a com-
plex circulation of blood takes place, through regular vessels;  and here we
find some indication of a contractile cavity, by the power of which it may be,
in some degree, kept up; but its feeble pulsations  can  scarcely be regarded,
as having any great share in the movement of the fluid  which passes through
it.—In  the Articulated series, there  is, with a  few exceptions, an absence of
any central organ of impulsion, possessed of  power  sufficient to  carry the
blood through the vascular system, by its contractions alone.  In many of the
aquatic worms  and larvae, the  movement of the blood, and the pulsations of
the dorsal vessel, may be distinctly seen: and the thinness ofthe walls ofthe
latter, and the character of its movements, seem clearly to show, that these
can scarcely be regarded as  propulsive, but that  they merely  result from the
variations  in the current which passes through it,—the sides flapping together
when there is an outward flow, and  bulging out when there is an influx.  It
is in these Articulata, in which  there is a provision for respiration throughout
the whole structure,  as is  especially the case  in  Insects,  that the absence of
any central impulsive power is most remarkable.—In the Crustacea, and in
the Mollusca in general, the respiration is aquatic, and  is  restricted to  a par-
ticular organ ; and in these, the heart is found to be more muscular, and the
circulation to be more under its  control.  It is curious to remark, however,
that, in  some of the lower Mollusca, which exhibit a tendency to aggregation
into compound structures, like those of the Polypifera, there is the same want
of definiteness in the course of the circulation, as has been just stated to exist
in the latter group;—the flow of blood, through their complex apparatus of
nutritive organs, being arrested at regular intervals, and then recommencing
in the reverse direction.
  716.  Even in Vertebrated animals, we find  indications of the same defi-
ciency of central power, over the peripheral circulation.  When we look at
the simple, thin-walled heart of Fishes, for example, it seems  impossible that
it should have much  power over  the current of blood flowing back to it by
the veins;  for of this blood, a considerable portion has to pass through three
                                   46* 
546
OF THE CIRCULATION OF BLOOD.
sets of capillaries, between its ejection from the heart, and its return to it.  It
is first transmitted through the respiratory capillaries, for the purpose of aera-
tion ; the confluent vessels, which  collect the arterial blood from these, ter-
minate in the general systemic trunk or  Aorta, in which, as in  the  veins  of
Man, there is an absence  of pulsation, and by these, it  is  distributed  to the
systemic capillaries;  and the blood which, after passing through these, re-
turns from the  posterior part of the body, and from the viscera, passes through
another set of capillaries, those of  the liver and kidneys, before it returns  to
the heart.—Even in the warm-blooded Vertebrata, in which the  respiratory
circiflation is separately performed, the blood which is returned from the in-
testines, passes into  a trunk, the  Vena Portse, which again subdivides into
capillary ramifications, being  transmitted over the plexus of biliary ducts, of
which the liver is chiefly composed ; and thus the Vena Portae, as Hunter
justly observed, should be considered rather  in  the light of an artery,* re-
sembling as it does the aorta of Fishes.   Considering  the  small amount  of
pressure which is exerted by the blood, upon the sides of the vessels that are
formed by the reunion of capillaries, it seems impossible to imagine that the
vis a tergo derived from the impulsive action of the Heart, can be alone suf-
ficient to maintain the portal circulation.


                         2.—Action of the Heart.

  717.  The  Heart is endowed in an  eminent degree  with the property  of
irritability;  by which is  meant,  the capability of being  easily excited  to
movements of  contraction alternating with relaxation (§  574).   Thus, after
the Heart has been removed from  the body, and  has  ceased  to contract, a
slight irritation will cause it to execute, not one movement  only, but a series
of alternate contractions and dilatations, gradually  diminishing in vigour until
they cease.   The contraction begins in the part  irritated, and then extends to
the rest.   It appears  from Mr.  Paget's experiments,! that it is necessary for
the propagation of this irritation, that the parts should be connected by mus-
cular tissue, of which a very narrow isthmus will  suffice ;  and that the pro-
pagation will not take place, if  the connecting isthmus  be  composed  of ten-
don, even though this be a portion  of the auriculo-ventricular ring, which has
been supposed  by some to be peculiarly efficacious  in this conduction.—That
the irritability of the heart is not dependent upon  the Cerebro-spinal system,
appears not merely from the manifestation of it, when the organ is altogether
removed from  the body, but also  from  the fact, that  if the  flood of blood
through the lungs be  kept up by artificial respiration, the heart's action will
continue for a lengthened period, even after the Brain and  Spinal Cord have
been removed,  and when animal life is, therefore, completely extinct.  Hence
we see that the Irritability of this organ  must be an endowment properly be-
longing to it, and not derived from that portion ofthe Nervous System. Like
the contractility of other muscles, it can only  be sustained for any great length
of time, by a supply of Arterial blood to its own tissue (§  584).  It is much
less speedily lost in cold-blooded  animals, however, than  in warm-blooded ;
the heart of the Frog, for  example, will go on pulsating for many hours after
its removal from the body ; and it  is stated by Dr.  MitchellJ that the heart of
a Sturgeon, which he had inflated with air, continued to beat, until the  auricle

  * That it conveys venous blood, is no  reason  to the contrary; since this is the case with
the pulmonary artery.  The character of an artery is derived from the division of its current
into several divergent streams.
  f Brit, and For. Med. Review, vol. xxi. p. 551.
  X American Journal of the Medical Sciences, vol. vii. p. 58. 
ACTION OF THE HEART.
547
had absolutely become  so dry, as to  rustle during its movements.   It has
lately been shown by Mr. Todd, that  the irritability of the  heart is of long
duration after death in very young animals : which, as long since demonstrated
by  Dr. Edwards, agree with the cold-blooded  Vertebrata in their power  of
sustaining life, for a lengthened period, without oxygen.—It is  difficult to ac-
count for the long continuance of the alternate contractions and relaxations of
the muscular parietes of the heart, after  all evident stimuli have ceased to act
upon it;  and many theories  have been offered on the subject, none of  which
afford an adequate explanation.   The  extraordinary tendency to rhythmical
action, which distinguishes the heart from  all other muscles, is shown by. the
fact that not  only do the entire hearts of cold-blooded animals continue to act,
long after their removal from the body, but even  separated portions  of them
will contract and  relax with  great regularity for a long time.   Thus  the auri-
cles will persist in their rhythmical  action, when cut off above the auriculo-
ventricular rings ; and the apex of the heart will do the same, when separated
from the rest of the ventricle.   The stimulus of the contact of  blood  with  the
lining membrane  of the heart, to which  its regular  actions  have been com-
monly  referred, can have no influence  in  producing these  movements; nor
does it appear that the contact of air can take its place; since, as Dr. J. Reid
has shown, the rhythmical contractions  of the heart of  a  frog will  continue
in vacuo.  Nor  is  there any evidence  that the  flow of blood through  the
cavities has the effect of securing the regularity  of their successive  contrac-
tions in the living body:  for this regularity  is equally marked  in the contrac-
tions of the excised  heart, when perfectly emptied of blood,  so long  as  its
movements continue vigorous.  But when its  irritability  is nearly exhausted,
the  usual rhythm is often a  good deal disturbed,  so that the  contractions  of
the  auricles and  ventricles do not regularly alternate with each  other ; and one
set frequently ceases before  the other.
  a. It was  formerly supposed, that the movements of the Heart were dependent upon its
connection with the centres of the Cerebro-Spinal nervous system; and the experiments of
Legallois and others, who found that they were arrested by crushing, or otherwise suddenly
destroying, large portions of these centres, appeared to favour the supposition.   But it has
been shown  by Dr. Wilson Philip and  his successors  in the same  inquiry, that  the whole
Cerebro-Spinal axis  might be gradually removed, without  any such consequence; which
fact harmonizes perfectly with the " experiments prepared for us by Nature," in the  pro-
duction  of monsters  destitute of  these centres, which nevertheless possessed a  regularly-
pulsating heart.  As already mentioned (§ 416), it is difficult to obtain any distinct evidence,
that the actions of the heart  are  affected by any ordinary irritation  of the Par Vagum; but
the recent experiments of MM. Weber have shown that its movements may be immediately
arrested, by the transmission of the electric current from a rotating magnet, either through
the Spinal Cord, or  through the Vagi nerves  divided at their origin.  The same irritation,
however, applied to  a single one of the Vagi, produced no effect.*
  b. It has latterly been the fashion with many, however, to attribute the action of the Heart
to the Sympathetic system ; but of this there is no sufficient evidence.   The possibility of
exciting the action of the heart through the Sympathetic nerve (§ 576), shows that this may
have an influence on its movements; whilst the  great difficulty with which any evidence
to this effect can be procured, seems a sufficient proof, as in the case of the Muscular coat of
the intestines (§ 388), that this influence cannot be nearly adequate  to the constant main-
tenance of a function so energetic.   Some have more recently maintained, that  the move-
ments are of a strictly reflex nature, and that they are effected through the  agency of certain
minute ganglia, belonging to the Sympathetic  system, and scattered  through the substance of
the heart;—in this  way endeavouring to account for the  persistence of the motions of the
organ after its complete removal from the body, and under circumstances which suspend all
reflex movements that have their centre in the cerebro-spinal system.   But this  attempt at
explanation affords no aid  in the  solution of  the cause of the continued rhythmical move-
ments of the organ,  or of its separated portions, after the withdrawal of all stimuli that can
be supposed to operate in exciting them; and the phenomena are just as fully explained by
* Archives dAnat. Gener. et de Physiol., Janv. 1846. 
548
OF THE CIRCULATION OF BLOOD.
attributing them to the independent irritability of the muscular fibre, as by supposing the
nervous system to be concerned in them.
  c. It would appear, however, that changes in  the Ganglionic nerves, like strong impres-
sions upon the Cerebro-spinal system (§580), may have the effect of impeding or even
checking the Heart's action; for a case has  lately been recorded, in which the movements
were occasionally checked for an interval of from 4 to 6 beats, its cessation of action giving
rise to the most fearful sensations of anxiety, and to acute pain passing up to the head from
both sides of the chest,—these symptoms being connected, as it proved on a post-mortem
examination, with the pressure of an enlarged bronchial gland upon the great cardiac nerve.*
It may be surmised, that in many cases of  angina pectoris, in which no lesion sufficient to
account for death could be discovered, some  affection of the cardiac plexus might have been
traced on a more careful examination.

  718.  When the Heart is exposed in a living animal, and its movements are
attentively watched, they are seen  to follow each other with  great regularity.
In an active  and vigorous state of the circulation, however, they are so linked
together, that it is not easy to distinguish them into periods.   A case  has
fallen under  the notice of Prof. Cruveilhier, in which the heart was exterior
to the chest, having escaped from  it  by a perforation in  the  superior  part of
the sternum  ; and his observations upon  it may be perhaps regarded as more
satisfactory than such as are made after the very severe operation required for
the artificial  exposure of the  organ;  although they  are liable to some excep-
tion, from  the very  early  age  of the  subject of  them, which had only been
born nine  hours.  His conclusions  will  be  here adopted ;  with  such addi-
tional remarks as are  suggested by  the  experimental researches of  others,
who have made this  question  a subject of special attention.!   It is universally
admitted, that both Auricles contract,  and also dilate simultaneously ;  and  that
both Ventricles  do the  same:—also that the systole  or contraction of the ven-
tricles corresponds with the projection of blood  into  the  arteries, causing the
pulse; whilst the diastole or  dilatation  of the  ventricles coincides witb the
collapse  of the  arteries.  It is further  admitted, that the contraction of the
Ventricles, and  that  of  the Auricles,  alternate with one another; each taking
place (for the most part, at least), during  the dilatation of the other.  But it
is a question whether there is any interval between  them.   In  the case  just
alluded to, the contraction of  the Ventricles  is  stated to  have been precisely
synchronous with the  dilatation of  the  Auricles;  and the  dilatation of the
Ventricles  to have been performed at the same  time with the contraction of
the Auricles, no period of repose intervening between the two sets of actions.
It appears, however, from the  concurrent testimony of numerous experiment-
ers, that, whilst the contraction of  the Ventricle immediately  succeeds that of
the Auricle, an interval, which  is usually, however, extremely brief, may elapse
between the partial  dilatation  of the  Ventricles and  the succeeding systole of
the Auricles.  The Ventricular dyastole may be  distinguished into two stages,
of  which the first immediately succeeds its systole, and manifests itself in the
recession of the  Heart's apex from the front of the  chest;  whilst the second
is attended with an  enlargement  of  the  heart in all its dimensions, and is
synchronous with the  Auricular contraction.   It is  between these two,  that
the interval of repose  occurs, where it can be observed.   The following
tabular view will, perhaps, make  this account more intelligible;  it is  framed
in such a manner as to commence with the Auricular contraction; but, when
considering the  Sounds of the heart, it will be  necessary to  commence with
the Ventricular  systole.

  • Muller's Archiv. 1841, heft hi.; and Brit, and For. Med.  Rev., Oct. 1841.
  f See also another case, recently observed by M.  Monod,  in Bullet, de l'Acad. de Med.,
Fevr. 1843 ; and Edinb. Med. and Surg. Journ., July 1843. 
ACTION OF THE HEART.
549
                       Auricles.              Ventricles.
                     Contraction.        2d stage of dilatation.
                     Dilatation.         Contraction.—Pu 1 se.
                                      1st stage of dilatation.
                             Brief interval of Repose.
                     Contraction.        2d stage of dilatation.
                     Dilatation.         Contraction.—Pulse.

  719.  The duration  of the  Contraction  of the Ventricles is, according to
Cruveilhier, double that of their Dilatation; and the same holds good of the
Auricles.   In the Systole of the Ventricles, their surface becomes rugous ; the
superficial veins swell; the carneae columnae of the left ventricle are delineated ;
and  the curved fibres of the  conical termination of the left ventricle, which
alone constitutes the apex of the heart, become more manifest.   During their
contraction, every diameter of the  Ventricles is lessened ; their  shortening  is
the most sensible change; but this is owing to the vertical diameter being the
greatest.   The lower  extremity of the left ventricle, or, in other  words, the
apex of the heart, describes  a spiral movement from right to left, and from be-
hind forwards.  It is  to this slow, gradual, and  as it were successive spiral
contraction, that the forward movement of the apex of the heart is owing, and
its consequent percussion against the thoracic parietes.  The ventricular sys-
tole  is not accompanied  by  a projection of the entire heart forwards (as some
have maintained); for it is exclusively the spiral contraction, which determines
the approach of the apex of the heart to the thoracic parietes.   The Diastole
of the heart, according to Cruveilhier, has  the rapidity and energy of an active
movement: triumphing  over pressure exercised upon the  organ, so that the
hand closed upon  it is opened with violence.   This is an observation of great
importance ; but of the cause to which this active dilatation  is due, no  definite
account can be given.   It may partly be explained, perhaps, by the elasticity
of the tissue, interwoven with muscular fibre in the  substance of the heart;
and this may be the cause of the first Ventricular dilatation, the second being
produced by the  ingress of blood occasioned  by the  auricular systole.  But
the dilatation of the Auricles appears to be much greater than can be  accounted
for by any vis a tergo (which, as will hereafter  appear, is extremely small in
the venous system), or by the elasticity of its substance ; for it was observed
in this case to be so great, that the right auricle seemed ready to burst, so great
was its distension,  and so  thin  were  its  walls.  Moreover, the  large Veins
near the heart contract simultaneously with the auricular Systole, and not with
its Diastole; so that they can  have no influence in causing its dilatation.  The
Ventricular diastole is accompanied with a projection of the  heart downwards;
this  motion was at its  maximum  when the child was placed vertically, and
was very strongly marked.
   720.  When the ear is applied over the cardiac region,  during the natural
movements of the  Heart, two  successive sounds are heard; each pair of which
corresponds with one pulsation.  The whole interval between one beat of the
the  Heart, and the  next, may be  divided  into four  parts;  of which  the two
first are occupied by what is commonly known as the first sound;  the third,
by the second sound ;  whilst the fourth is a period of repose.—The first sound
is dull and  prolonged; it is evidently synchronous with the impulse of the
Heart against the  parietes of the chest, and  also with the pulse, as felt near
the  heart;  it must, therefore, be produced  during the Ventricular Systole.—
The second  sound  follows  so immediately upon the conclusion of the first,
that it can scarcely be  imagined to take place during the auricular systole  as
some have supposed, but must be assigned  to the period of the first stage  of
the  Ventricular Diastole.  This, indeed, may now be regarded as clearly esta-
blished; for it has been fully demonstrated, that the second sound is due  to 
550
OF THE CIRCULATION OF BLOOD.
the sudden filling-out of the Semilunar valves of the aorta and pulmonary
artery, with blood; when the outward current through them has ceased, and
the incipient dilatation ofthe ventricles occasions a vacuum behind  them.  If
one of these valves be hooked back by a  curved needle against the side of the
artery, so that a reflux of blood is permitted, the sound is entirely suppressed.
The first sound cannot be so readily or satisfactorily accounted for.  That it
is partly due to the  Impulse of the apex of the  Heart, seems  proved by the
fact, that, when this  impulse is prevented, the sound is much  diminished in
intensity; and also  by the  circumstance  that, when the  Ventricles  contract
with vigour, the greatest intensity of the sound is  over the point of percussion.
But that it is not  entirely due to this  cause is also  evident from tbe fact, that
a sound may still be heard, when the  Heart is contracting out of the body; as
in the case observed by Prof. Cruveilhier.  This sound has been  attributed,
by some experimenters, to the flapping-back of the auriculo-ventricular valves ;
by others to the muscular contraction  of the walls of the ventricles ; by others
again to  the  rush of blood along  the irregular  walls  of the ventricles, and
through the comparatively narrow orifices of the  aorta and pulmonary artery.
This last is probably the most  consistent with truth ; as would appear  from
the following interesting observations made by Cruveilhier.  By applying the
finger to the origin of the pulmonary artery (which is situated  in front of the
aorta, and completely conceals  it), a perfectly  distinct vibratory fremissement
corresponding with the ventricular diastole, was perceived; but no such vibra-
tory thrill could be felt by the finger,  when applied to any part of the base of
the ventricles: whence it was evident, that no action takes place in the mitral
and tricuspid valves, which can give rise to the same palpable effects, as those
produced by the semilunar valves.  The same was ascertained  regarding the
valvular sound, which could be  distinctly heard, by laying the finger against
the origin of the  pulmonary artery, and  applying the ear  to it as to a stetho-
scope:  whilst nothing of the kind could be  perceived in the region of the
auriculo-ventricular valves.  Hence it seems quite certain, that the natural first
sound  cannot  be dependent in any way upon the action of the  mitral and tri-
cuspid valves.  It appeared, on the contrary,  that the maximum intensity of
the first sound was in precisely the same situation as the maximum intensity
of the  second,—namely, at the origin of the large arteries ; and that it dimin-
ished,  as  the  ear was carried from the  base, towards the apex of the  heart.
Moreover, the first sound was observed  to be of exactly  the same character
with the second (the complicating effect of the  impulse being here withdrawn);
except as to its intensity, which was less,—and its duration, which was greater.
   721. Hence, although these  observations do not entitle  us to deny the par-
ticipation of the muscular contraction, and of the movement of the  blood over
the ventricular walls, in  the  production  of the first sound, they establish (if
correct), that  the principal  cause of it  exists at the entrances to  the arterial
trunks; and it does not seem that any other reason can be assigned  for it, than
the prolonged rush of blood through their orifices, and the throwing back of the
Semilunar valves; which, in suddenly flapping down again, produce the second
sound.—That an exaggeration of the first sound,  not essentially differing from
it in character, is often produced by  disease of the sigmoid  valves, which
causes  an obstruction of their  orifice, has long been known ;  and in such
cases,  the character  of the second  sound is also changed.  Indeed, M. Cru-
veilhier states it as, in his opinion, an uniform occurrence, that disease of the
Semilunar valves alters both sounds.   When  this disease is such as to prevent
the valves from effectually closing, a reflux of blood takes place into the ven-
tricle at the time of  its  diastole; causing a rushing sound, more or less  pro-
longed, to be  heard in the intervals of the pulse, instead  of with  it.  These
considerations appear to prove almost incontestably, that the cause of the first 
ACTION OF THE HEART.
551
sound, and that of the second, are very closely allied ;  and this view, which if
correct  is  of great importance  in  the explanation of numerous morbid  phe-
nomena, harmonizes  well with  the  known  effect  of a slight  obstruction in a
tube, through which fluid is being rapidly forced, in producing a  prolonged
sound, very analogous  to the first  sound of  the  heart.   The following  table
may assist the  student  in connecting the sounds  of the Heart with its move-
ments.
First Sound.    Ventricular Systole, and Auricular Diastole.   Impulse of apex against
                      parietes of chest.   Pulsation in arteries.
Second Sound.   First stage of Ventricular Diastole.
Interval.        Short repose; then Auricular Systole, and second stage of Ventricular
                      Diastole.
   722.  The  course of the circulating fluid  through the Heart, and  the action
of  its different valves, will  now  be  briefly described.   The  Venous  blood,
which is  returned  by the ascending and  descending Vena Cava, enters the
right Auricle during  its  diastole ;  and, when it contracts, is  forced between
the Tricuspid valves, into the Ventricle.   The reflux of blood into the veins,
during the auricular systole, is prevented by the  valves with which  they are
furnished ; but these valves  are so formed, as  not  to  close  accurately, espe-

                                     [Fig. 212.
  The Anatomy of the Heart; 1, the right auricle; 2, the  entrance of the superior vena cava; 3, the
entrance of the inferior cava; 4, the opening of the coronary vein, half closed by the coronary valve ;
5, the Eustachian valve ; 6, the fossa ovalis, surrounded by the annulis ovalis; 7, the tuberculum Low-
eri ; 8, the musculi pectinati in the  appendix auricula?;  9, the auriculo-ventricular opening; 10, the
cavity of the right ventricle; 11, the tricuspid valve, attached by the  chordae tendineae to the carneae
columnae (12); 13, the pulmonary artery, guarded at its commencement by three semilunar valves; 14,
the right pulmonary artery, passing beneath the arch and behind the ascending aorta; 15, the left pulmo-
nary artery, crossing in front of the descending aorta; *, the remains of the ductus arteriosus, acting aa
a ligament between the pulmonary artery and  arch ofthe aorta; the arrows mark  the course of the
venous blood through the right side of the heart; entering the auricle by the superior and infeiior cava,
it passes through the auriculo-ventricular opening into the ventricle, and thence through the pulmonary
artery to the lungs ; 16, the left auricle ; 17, the openings of the four pulmonary veins ; 18, the  auriculo-
ventricular opening; 19, the left ventricle ; 20, the mitral valve, attached by its chordae tendineae to two
large columnae carneae, which project from the walls of the ventricle; 21, the commencement and course
of the ascending aorta behind the pulmonary artery, marked toy an arrow;  the entrance of the vessel
is guarded by three semilunar valves ; 22, the arch of the aorta.  The comparative thickness of the two
ventricles is shown in the diagram. The course of the arterial blood through the left side of the heart
is marked by arrows. The blood is  brought from  the lungs by the four pulmonary veins into the left
auricle, and passes through the auriculo-ventricular opening into the left ventricle, whence it is con-
veyed by the aorta to every part of the body.] 
552
OF THE CIRCULATION OF BLOOD.
cially, when the tubes are distended ; so that a small amount of reflux usually
takes place, and  this is much  increased when there is any obstruction to the
pulmonary circulation.   Whilst the right Ventricle is  contracting upon the
blood that has entered it, the carneae columnae, which contract simultaneously
with its proper walls, put the  chordae tendineae, upon the  stretch; and these
draw the flaps of the Tricuspid valve into the auriculo-ventricular  axis.   The
blood then getting behind them, and being compressed  by the contraction of
the ventricle, forces the flaps together in such a manner as  to close the orifice ;
but they do not fall suddenly against each other, as is the case with the semi-
lunar valves, since they are restrained by  the chordae tendineae; whence it is,
that no sound is produced by their  closure.  The  blood is expelled by the
ventricular systole  into the  Pulmonary  Artery, which it  distends,  passing
freely through the  Semilunar valves;  but as  soon  as the  vis a tergo ceases,
and reflux might take place by the contraction of the arterial walls, the valves
are filled out by the  backward  tendency of the blood, and completely check
the return of any portion of it into the ventricle.   The blood, after having cir-
culated through the lungs, returns as Arterial blood, by the Pulmonary Veins,
to the left Auricle;  whence it  passes through  the  mitral  valves into the left
Ventricle, and  thence into the Aorta,—in the same manner with that  on the
other side, as just described.
   723.  There are, however, some important differences in  the structure and
functional actions of the  two  divisions of the  Heart, which should be  here
adverted to.
  a. The walls of the left Ventricle are considerably thicker than  those of the right; and
its force of contraction is much  greater.  The  following are the comparative results  of M.
Bizot's  recent measurements, taking the average of males from 16 to 89 years.

                                    BASE.          MIDDLE.            APEX.
       Left Ventricle                4£ lines        5^ lines          3| lines
       Right Ventricle              ljf lines       1| lines           l^L lines
In the female, the average thickness  is somewhat less.  It will  be  seen that  the point of
greatest thickness in the left Ventricle is near  its middle; while in the right, it is nearer the
base.  The thickness of the former goes on increasing during all periods of life, from youth
to advanced age ; whilst that of the right is nearly stationary.  The left Auricle is somewhat
thicker than the  right; the average thickness of the former  being,  according to Bouillaud,
a line and a half; whilst that of the latter is only a line.  In regard to the relative capaci-
ties of the right and left cavities, much difference of opinion has prevailed.   The right Au-
ricle is generally allowed to be more capacious  than the left; and  the same is commonly
taught of the right Ventricle.  So much fallacy may arise, however, from the peculiar condi-
tion of the animal at the moment of death, that this is not easily proved, and is, indeed, by
no means certain.
  b. Many eminent Anatomists maintain, that the two cavities are equal.   The capacity of
each of the cavities may be estimated, in the full-sized Heart, at  about two ounces; that of
the Auricles being probably a little less; and that of the Ventricles  a little greater.  That
the Ventricles receive more blood from the Auricles, than the latter  could transmit, to them
by simply emptying themselves once, seems, therefore, probable;  and may be accounted for
by the fact already  stated, regarding the slight intermission in the Ventricular Diastole, during
which more blood may enter the Auricle from the veins.
  c.  There is a well-known anatomical difference between the Auriculo-Ventricular valves,
on the two sides, which has given rise to the diversity of name.   This seems, from the re-
searches of Mr. King,* to be connected with an important functional difference.  The  Mitral
valve closes much more perfectly than the Tricuspid ;  and the latter is so constructed, as to
allow of considerable  reflux, when the cavities are  greatly distended.  Many occasional
causes tend to produce an accumulation of blood in the venous system, and in the right side
of the  Heart;  thus, any obstruction to the pulmonary circulation, cold, compression  of the
venous  system by muscular action, &c, are known to favour such  a condition.  This is a
state of peculiar danger, from the liability which over-distension of the Ventricular  cavity
has, to produce a state of muscular paralysis; and in the structure of the Heart itself, there
seems to be a provision against it.  For, when the ventricle is thus distended, the Tricuspid
* Guy's Hospital Reports, vol. ii. 
ACTION OF THE HEART.
553
valves do not close properly; and a reflux of blood is  permitted, not only into the Auricle,
but also (through the imperfect closure of their valves under the same circumstances), into
the large veins.  This  is proved by the fact, several times observed by Dr. J. Reid, in his
experiments upon Asphyxia, &c, that, when the action of the Right  Ventricle had  ceased
from over-distension, he could frequently re-excite it, not merely by puncturing its walls, but
by making an opening in the jugular vein.  This fact evidently affords an indication of great
importance in the treatment of Asphyxia;  and it explains the reflux of blood, or venous
pulse, which is frequently observed in cases of  pulmonary disease, and which, according to
Mr. King, always exists, though in a less striking degree.

   724. It is not quite certain whether the Ventricles empty themselves com-
pletely at each  contraction ; but it seems probable that the blood which  they
contain, is not entirely forced into the arteries.  The quantity which is pro-
pelled by each Ventricle, at every stroke, may be estimated, therefore, at from
1| oz. to 2 oz.  If we adopt the lower  of these  numbers, we shall find that,
reckoning  75 pulsations of the Heart to  a minute, 112 oz., or 7  lbs., of blood
pass through each ventricle in  that  time; and, on the higher estimate, 150
oz.,  or 9 lbs. 6 oz., would  pass through  in the same period.  Now the whole
quantity of blood  contained in  the human body, according to the estimate of
Haller (which is considered by Dr. Allen Thomson to be  near  the truth), is
about  one-fifth  of the weight of the  body, or  28 lbs.  in  a person weighing
140  lbs.*  This quantity  would pass through the Heart, therefore, in four
minutes, on  the lower of the two preceding estimates, or in three minutes on
the higher; and would circulate afresh, fifteen or twenty times in an hour. It
would appear, however, that this estimate  of the rapidity of the  circulation is
very far from the truth; for recent experiments  have shown, that substances
introduced into the  Venous circulation, may be detected in the remotest parts
of the Arterial circulation, even in animals larger  than  Man, in less than half
a  minute.—The earliest of  such experiments were those of Hering,t who en-
deavoured to ascertain the  rapidity of the circulation, by introducing Prussiate
of Potash  into one part of the system, and drawing blood from another.  He
states  that he delected this salt, in blood drawn from one of the Jugular veins
of the  Horse, within 20 or 30 seconds  after  it had been  introduced into the
other;  in  which brief space the blood must have  been  received by the Heart,
must have been transmitted through  the Lungs, have returned  to the  Heart
again, have been  sent through  the Carotid artery, and  have traversed its ca-
pillaries.   From experiments  of  a similar nature upon other veins, he  states
that the salt passed from the Jugular vein into  the  Saphena in  20 seconds;
into the  Masseteric  artery in from 15 to 20 seconds;  into the External Max-
illary artery in  from 10  to 25 seconds ;  and into the Metatarsal artery in from
20 to 40 seconds.  An attempt has  been made  to  invalidate the inference
which seems inevitably  to  flow from  these experiments, in regard to the rate
of the circulation, by attributing  the  transmission of the salt to  the permea-
bility ofthe  animal  tissues ;J but it has never been shown, that even Prussiate
of Potash (which is probably  more  transmissible through  this channel than
any  other salt), can be carried from one  part to another, with a rapidity at all
proportional to this.  The only mode  in which  this property can  be con-
ceived materially to facilitate the transmission of the salt through  the vascular
system, would be by allowing it to pass through the septum of  the auricles,
and  thus to make its way  from the right to the left side of the heart, without
passing through the pulmonary circulation;  and this  it could scarcely  do, to
the large amount which  is evidently transmitted, in so short a time.
   725. The  experiments of Hering  have been recently fully confirmed by

     *  Valentin's estimate,  founded upon different data, closely corresponds  with this.
     f Tietlemann's Zeitschrift, vol. iii. p. 85.
     j See Dr. Allen Thomson, he. cit.
     47 
554
OF THE CIRCULATION OF BLOOD.
those of Mr. Blake;* who varied them  by employing  different  substances,
and  took other precautions  against sources of fallacy.   Ten seconds  after
having injected a solution of Nitrate of Baryta into the Jugular vein of ahorse,
he drew blood from  the Carotid artery of  the opposite side; after allowing
this to flow for five seconds, he substituted another vessel, which received the
blood that flowed during the five ensuing seconds ; and the blood  that flowed
after the twentieth second, by which time the action of the Heart had stopped,
was  received into  a third vessel.   These different specimens were carefully
analyzed.  No trace of Baryta could be detected  in the blood,  which had
escaped from the artery between the tenth  and fifteenth second after the in-
jection of the poison ; but in that which was drawn  between the fifteenth and
the twentieth second, the salt was  found  to be present, and in  greater abun-
dance  than in  the blood  which  had subsequently flowed.  Moreover, the
coincidence between  the cessation of the Heart's  action, and the  diffusion of
the salt through the arterial blood, bear a striking correspondence ;  and it may
be hence inferred, that the arrestment of its  muscular movement is due to the
effect of this agent upon its  tissue,  when immediately  operating upon it,
through the capillaries of the coronary artery.   This conclusion is borne out
by a variety of other experiments; which  show that the time of  the agency
of other poisons, that suddenly check the Heart's  action (which  is the espe-
cial property of mineral poisons), nearly coincides, in different  animals, with
that which is required to convey them  into the Arterial capillaries.   And it
seems to derive full confirmation from the fact, that poisons, which act locally
on other parts, give the first indications of their operation, in the same period
after they have been  introduced into  the Venous circulation.   Thus, in the
Horse, the time that  is  required  for the  blood to pass from the Jugular vein
into the capillary terminations of  the Coronary arteries,  is  16 seconds; as is
shown by  the power of Nitrate of Potass  to arrest the Heart's action within
that time :  and Nitrate of Strychnia, injected into  a  vein, gave  the first mani-
festation of its  action on the  Spinal  Cord, in precisely the same number of
seconds. In  the Dog, the Heart's action was arrested by the Nitrate of Potass
in 11 or 12 seconds; and the  tetanic convulsions  occasioned  by Strychnia,
also  commenced  in  12 seconds.   In the  Fowl, the former  period was 6
seconds, and the latter Qk ;  in the Rabbit, the first was 4, and the other 4|
seconds.  From these experiments, it seems difficult to resist the conclusion,
that the rapidity of the Circulation is very  much underrated, in any  estimate
that we found upon the capacity of the Heart,  and its number of pulsations in
a given time; and  that  some  other force, than its  contractions, must have a
share in producing the movement of the blood  through the vessels.
  726.  The force  with which the  Heart propels the Blood, may be estimated
in two ways;—either by ascertaining the height of the column of that fluid,
which its  contractile action will  support;—or by  causing  the blood to  act
upon a  shorter column of mercury.—The former method was the one adopted
by Hales, who introduced a long pipe into the Carotid artery of a Horse, and
found that  the blood would sometimes rise in it to the height of  10 feet. From
parallel experiments upon Sheep, Oxen, Dogs,  and other animals, and by
comparing the calibre of their respective vessels with that of the Human aorta,
Hales concluded, that the usual force of the Heart in Man would sustain a
column of blood 7£  feet high, the weight of which would  be about 4 lbs. 6
oz.—The second  method is  that more  recently adopted by Poisseuille; and
the instrument which he contrived for carrying it into practice (termed by him
the Haemadynamometer) has been the means  of aiding  many valuable inqui-
ries  on the physiology of the Circulation.   The  result of his experiments is
* Edinb. Med. and Surg. Journal, Oct. 1841. 
ACTION OF THE HEART.
555
very nearly the same as that of Hales ;  his estimate of the force, with which

                                                              [Fig. 213.
  Ha?madynamometer of Poisseuille. A
bent glass tube, filled with mercury in
the lower part, a d e. The horizontal
part 6, is provided with a brass head,
which fits  into the artery.  A small
quantity of a solution of the carbonate
of soda is interposed between the mer-
cury and the blood, to prevent its coagu-
lation. When the blood presses on the
fluid in the horizontal limb, the rise of
the mercury towards e, measured from
the level to which it has fallen towards
a, gives the pressure under which the
blood moves.]
  c. The effect of muscular exertion in raising the pulse is well known;  as is also the fact,
which is one exemplification of it, that the pulse varies considerably with the posture of the
body.   The amount of this variation has been made the subject of extensive inquiry by Dr.
Guy; and the following are his results.  In 100 healthy Males, of the mean age of 27 years,
in a state of rest, the average frequency of the pulse was, when standing, 79,—when sitting,
70,—and when lying, 67 per minute.   Several exceptions occurred, however, to the general
law; and  when these were excluded, the average numbers were,—standing, 81,—sitting,
71,—and lying, 66; so that the difference between standing and sitting was 10 beats, or
l-8th of the whole; the difference between  sitting and lying was 5 beats, or 1-13th of the
whole;  and the difference between standing and lying was  15 beats, or l-5th ofthe  whole.
In 50 healthy Females, of the same mean age, the average pulse, when standing, was 89,—
  * The extreme latitude of the estimates which have been made of this force, has been a
subject of not undeserved ridicule.  Borelli imagined it to be 180,000 lbs.; whilst by Keill it
was supposed to be no more than from 5 to 8 ounces.
  -f Guy's Hospital Reports, vol. iii. p. 312.
the blood is propelled into the Aorta, being 4
lbs.  3 oz.  The backward pressure upon the
walls  of the  Heart,  or  in  other  words the
force which  they  have  to overcome in pro-
pelling  the blood,  is properly  estimated,  by
multiplying the pressure of blood in the aorta,
into the surface of a plane  passing  through
the base and apex of the left  ventricle ;  by
which calculation  it is  found to be about 13
lbs.*  The pressure appears, from  the experi-
ments of Poisseuille, to  be very nearly equal
for equal surfaces, throughout the  larger arte-
rial  branches;  since it  diminishes regularly
in proportion  to their  calibre;  in  the  radial
artery at the  wrist,  it was estimated by him
at 4 drachms.
   727.  The  number of contractions of  the
Heart in a given time, is liable  to great varia-
tion, within  the  limits  of  ordinary  health,
from several  causes;  the chief of these are,
diversities  of  Age, of Sex, of Muscular  exer-
tion, of the condition of the Mind,  of the state
of the Digestive system, and of the Period of
the day.
   a. Putting aside the other causes of uncertainty, the
following table may be regarded as an approximation
to the average frequency of the Pulse, at the several
ages  specified in it.
                              BEATS  PER MINUTE.
                                    140 — 150
                                    130 — 140
                                    115— 130
                                    100 — 115
                                     90 — 100
                                     85 — 90
                                     80— 85
                                     70— 80
                                     50— 65
  In the fcetus in utero
  Newly-born infant
  During the First year
  During the Second year
  During the Third year
  About the Seventh year
  Age of Puberty
  Manhood  .
  Old age
  b. The difference caused by sex is very considerable,
especially in adult age; it appears from the inquiries
of Dr. Guy,"!" that the  pulse of the adult Female ex-
ceeds in frequency the  pulse of the adult Male, at the
same mean age, by from 10 to 14 beats in a minute. 
556
OF THE CIRCULATION QF BLOOD.
when sitting, 81,—and when lying, 80.   When the exceptions (which were more numerous
in proportion than in males) were excluded, the averages were, standing, 91,—sitting, 8 1,—
lying, 79; the difference between standing and  sitting was thus 7 beats, or 1—13th of the
whole;  that between sitting  and lying  was 4, or 1-21st  of the whole; and that between
standing and lying  was 11, or l-8th of tbe whole.   In both sexes, the effect produced by
change of posture increases with the usual frequency of the pulse; whilst the exceptions to
the general rule are more numerous, as  the pulse is less frequent.   The  variation is tem-
porarily increased by the muscular effort, involved in the absolute  change of the posture;
and it is only by  the use of a revolving board, by which the position of the body can be
altered, without any exertion on the part of the subject of the observation, that correct results
can be obtained.  That the difference between standing and sitting  should be greater than
that between sitting and lying, is just what we should  expect; when we compare the
amount of muscular effort required in the maintenance of the two former  positions respect-
ively.
  d. The Pulse is well known to be much accelerated by Mental excitement, especially by
that ofthe Emotions; it  is also quicker during Digestion; but on neither of these points can
any exact numerical statement be given.
  e. The diurnal variation of the pulse, however,  has been made the subject of observation
by Dr. Guy ;* and, as the results of his inquiries have much interest, although (from having
been made only on his  own  person) they may ultimately require some modification, they
will be here stated.   '•]. The pulse of a  healthy male in a state of rest, unexcited either by
food or exercise, is most frequent in  the  morning, and gradually diminishes  as  the day ad-
vances.   2.  The  pulse diminishes in  frequency more  rapidly in the  evening, than in the
morning.  3. The diminution in the frequency  ofthe pulse (after excitement) is more regu-
lar and progressive in the evening than in the morning.  4. The effect of  food is  greater
and more lasting in the morning, than in  the evening; and in some instances, the same food,
which in the morning produces an effect considerable both in amount and duration, has no
effect whatever in the evening."  It may be hoped that, ere  long, this interesting  and im-
portant  subject  will receive further elucidation.
  [/. Dr. \ alleix has recently published  a series of interesting observations  on  the  fre-
quency of the pulse in newly-born infants, and in children aged from  seven months to six
years.   He obtained the  following results:  1. At birth the pulse is less frequent than at six
months;  the number of  beats in a minute  may be stated  with  considerable exactness to be
between 90 and 100.  2. Increase  of temperature, even in the  slightest degree, invariably
produces a notable acceleration of the pulse.   The exact ratio between the degree of eleva-
tion  of  temperature and the increase in  the  frequency of the pulse, is not yet accurately
ascertained.   3. Although the observations of Dr. Valleix show a progressive diurnal diminu-
tion  in the frequency of the pulse, still, he thinks, it would be premature  to  conclude that
these facts support  those of Dr. Guy.  Dr. Valleix  examined his patients in the morning
after they had been eating, and  to this fact, he thinks, should be attributed the acceleration
of the pulse in  the  early part of the day, and its subsequent  diminution  towards evening.
4. The slightest muscular effort in children is sufficient to augment considerably the number
of pulsations.   The same is true of any moral emotion.  5. The influence  of sex  on  the
pulse is very marked in  young children.  The pulse  is  much more  frequent in young girls
than in boys ofthe same age.   6. During sleep there is a decided diminution in the  number
of beats.  7. Between 7  and 27 months there is no sensible change in the  frequency of the
pulse.  Its mean may be stated at 126 beats  in the  minute, without distinction  of sex.  If
sex be considered, it would be 121 for males and 128 for females.  These  numbers express
the frequency of the pulse at this age under ordinary circumstances, but if  a  state of perfect
calm is supposed, the numbers would be 119 for the males, and 124  for females.  8. After
some observations, not very numerous, however, the  pulse would appear to range a little
above 100 till six years of age.  9.  The mean number of inspirations in  a minute in chil-
dren aged from 7 months to two years and a half, is between 30 and 32, and is to  number
of pulsations : :  1 : 4.—M. C]


         3.—Movement  of the Blood in  the Arteries and  Capillaries.

   728.  We have next to  consider the  influence  of the Arterial  tubes  on  the
flow of Blood  through them.   This influence  is exerted by  the middle  or
fibrous  coat, which alone  is possessed of contractile  properties.   We  find in
this coat, a layer of  annular fibres, possessing no small resemblance to  that
of which the muscular coat of the alimentary canal is  composed.   On the out-
* Op. cit., vol. iv. p. 69. 
MOTION OF THE BLOOD IN THE ARTERIES.
557
side of this, is a layer of yellow elastic  tissue, which is much, thicker in the
larger arteries, in proportion to their size, than in the smaller.  To this last
tissue  is due  the  simple elasticity of the  arterial walls, which is a physical
property that  persists after death, until a serious  change takes place in  their
composition :  whilst to the one first mentioned, we are to attribute the property
which they unquestionably possess—in common with proper muscular tissue,
—of contracting on the application of a stimulus, so long as their vitality re-
mains.   These two endowments exist, in various proportional degrees, in the
different parts of the Arterial system.  Thus it was justly remarked by Hun-
ter, that elasticity, being the property by which  the  interrupted force of the
Heart is made equable  and continuous, is most seen in the large vessels more
immediately connected  with that organ.  On the other hand, the contractility
is most observable in the smaller vessels, where it is more required for regu-
lating the flow of blood towards particular organs.
  729. It  is  easily shown that  the action of the Elasticity of  the Arterial
tubes,  is one of a  purely  physical character;  and that its purpose is to  con-
vert the intermitting impulses, which the fluid receives from the heart, into a
continuous current.  The former are very evident in the larger trunks; but
they diminish with the  subdivision  of these, until  they entirely disappear in
the capillaries, in which the stream is usually equable or nearly so.  We may
imagine a powerful forcing-pump injecting water, by successive strokes, into
a system of tubes  with  unyielding walls ;—the flow of fluid at the farther ex-
tremities of these tubes, would be  as much  interrupted as its entrance into
them.   But if  an  air-vessel (like that  of  a  fire-engine) were placed at  their
commencement, the flow would be in  a  great degree equalized;  since a part
of the force of each stroke would be spent upon the  compression of the air
included in it; and this  force would be restored by the elasticity of the air
during the interval, which would propel the stream, until directly renewed by
the  next impulse.  A much closer imitation  of  the  natural apparatus would
be  afforded, by a  pipe which had  elastic walls of  its  own; if  water  were
forced by a syringe into a long tube of  caoutchouc, for example,  the  stream
would be equalized before it had proceeded  far.   This effect is  found to be
accomplished, at any point of the Arterial circulation, in a degree proportionate
to its distance from the Heart; and it is  another effect ofthe same cause, that
the pressure of the blood upon  the wall of the arteries (as  shown by the ex-
periments of Poisseuille)  is nearly the  same all over the system.   It is to the
distension  of the   arterial tubes, both  in their length and  calibre, that  their
pulsation is due.   Their elongation is the more considerable of the two effects;
and it causes the artery to be lifted from its' seat and to become curved.  The
transverse  dilatation has been denied by some  physiologists; but it has  been
recently proved to  take place,  by an ingenious experiment of Poisseuille's.
The increase of capacity, however, is  not  more than  l-10th;  so that the in-
crease  of diameter will not be  so much as l-20th,—a quantity scarcely per-
ceptible  to  ordinary  measurement.   The  transmission  of the  pulse-wave
through the whole system is not  instantaneous, but takes place in an appre-
ciable time.  The pulsation of the large  arteries near the Heart, is synchron-
ous with the Ventricular systole; but that of other arteries is somewhat later,
—the difference varying with their distance, and amounting in some  instances
to between l-6th and  l-7th of a second.
  730.  It has been denied by many Physiologists, that the middle coat of the
Arteries possesses   any property which can be likened to Muscular  Contrac-
tility; and it  will  therefore be  desirable  to enter  somewhat in detail into the
question.  That it cannot be readily stimulated to contraction, through the
medium  of its  nerves,  is universally admitted ; but  the same is the case in
regard to the  Muscular coat of  the alimentary canal, which contracts most
                                   47* 
558
OF THE CIRCULATION OF BLOOD.
 vigorously on  the  direct application of stimuli  to  itself; and  Valentin and
 others have recently succeeded in producing evident contractions in the Aorta,
 by irritation of the Sympathetic  nerve,  and of certain  roots  of the Spinal
 nerves.  Further, although  many experiments have  failed in producing con-
 tractions of this  tissue, by stimuli  directly applied to itself, yet others have
 distinctly witnessed them;  and, in any  question  of this kind, the positive
 evidence must  be held to outweigh the negative.   Thus Verschuir states, that
 he has seen arteries contract, when stimulated by the mineral acids, by elec-
 tricity, and  by the application  of the point of a scalpel.  Dr. Thomson also
 saw them contract, on the application of ammonia, and when punctured with
 the point of a fine needle, in the living body.   It has been ascertained by the
 direct and careful experiments  of Poisseuille, that, when  the artery  is dilated
 by the blood injected into it from  the heart, it reacts with a force superior to
 the impressing impulse; and he has also shown that, if a  portion of an artery
 from an animal  recently dead (in which the vital  contractility seems to be
 preserved), and one from an animal that has been dead some days (in which
 nothing but the elasticity remains), be distended with an  equal  force, the for-
 mer becomes much more contracted than the latter, after the distending force
 is removed.
   731.  Several experiments also indicate the  existence of that power of slow
 contraction in the arteries, which  has  been distinguished by the appellation
 Tonicity; but which does not seem anything  else than a  particular manifesta-
 tion of the general property of vital contractility, and is certainly of a nature
 quite distinct from ordinary elasticity.   Thus, when a ligature is placed upon
 an artery in a living animal, the part of the artery beyond  the ligature becomes
 gradually smaller, and  is emptied to a certain  degree, if not completely, of the
 blood it contained.  Again, when part of an artery in a living animal is isolated
 by means of two ligatures, and  is punctured, the blood issues from the orifice,
 and the inclosed  portion of the artery is almost completely emptied of its
 contents.   The exposure of arteries to the air was found by Hunter to occa-
 sion their contraction, to such an extent, that obliteration of their  tube was
 the result; and this statement has  been subsequently confirmed.  Further,
 every Surgeon  knows, that the contraction of divided arteries  is an efficient
 means of  the arrest of hemorrhage from them, especially  when they are of
 small calibre;  so that, in  the  case of the temporal  artery, for  example, the
 complete division of the  tube is often the readiest means of checking the flow
 of blood from it, when it has been once wounded.   This contraction is much
greater than could be accounted for by the simple elasticity of the tissue ; and
 is more decided in small, than In large vessels.  The empty condition of the
 arteries, generally found within a short time  after death, seems to be in part
 due  to the same cause; since their  calibre is usually much diminished, and is
 sometimes completely  obliterated.  A remarkable example of the same slow
 contraction, is that which takes place  in the  end of the  upper portion of an
 arterial trunk, when the passage of blood through it  is interrupted  by a liga-
 ture ; for the current of blood  then passes  off  by the  nearest large  lateral
 branch ;  and the  tube of the artery shrivels,  and soon becomes  impervious,
 from the  point at which the  ligature is applied, back to  the  origin of that
 branch.  This  last fact is important, as proving how little influence the vis a
 tergo possesses over the calibre of arterial tubes ; since, without any interrup-
 tion to the pressure of blood occasioned by it,  the tube becomes impervious.—
 It is to the moderate action of  the  Tonicity of arteries, that their contraction
 upon the  stream of blood  passing through them (which serves to  keep the
 tubes always full) is due.  If the tonicity be excessive, the pulse is hard and
 wiry; but if it be deficient, the pulse is very  compressible, though bounding,
 and  the flow of  blood  through the arteries  is  retarded.  Dr.  Williams has 
MOTION OF THE BLOOD IN THE ARTERIES.
559
performed some ingenious experiments, which prove  that the force required
to propel fluid through a tube, whose sides are yielding, is very much greater
than that which will carry it through a tube of even smaller  size, with  rigid
parietes; consequently, a loss of tonicity in the blood-vessels retards the flow
of blood through them;  whilst an increase hastens it.  The Tonicity of the
arteries differs from their ordinary Contractility, in being augmented  by  cold,
and  diminished by warmth.  Hence  cold and heat  are two  most valuable
remedial agents, when this property is deficient or in excess.
   732.  It is still to be inquired, in what manner the Contractility of the Arte-
ries is to be regarded as influencing the flow of Blood through them.  It is at
once  evident, that  any general contraction of the arterial tubes would  have
rather the effect of opposing, than  of assisting the  flow; but if the fibrous
coat of the Arteries is in some degree disposed to the alternate contraction and
relaxation, which are so remarkable in the Heart, they may exert a force which
shall  be supplementary to  that of the Heart's impulse,—relaxing to receive
the blood from it,  and contracting upon their contents, with a power superior
to that by which they were distended.   It is  difficult to  say whether or not
this be the case ; though there would certainly appear some evidence in favour
of the supposition.  The loss of the  Heart's power over the currents of blood,
in proportion to their degree of subdivision, occasioned by the increased fric-
tion to which they will be subjected, would seem to require some compensat-
ing power, in  order that  the perfect  equality of pressure may be obtained
which has been spoken of as existing in all parts of the arterial system.  In
no other way than this can  the  fibrous coat  of the Arteries be regarded as
having any propulsive power over their contents; except by a peristaltic or
vermicular movement, resembling that which takes place in the alimentary
canal;  and of such there is no evidence whatever.—A very important use
may  be assigned to this muscular coat, which has been generally overlooked
by Physiologists,—that of regulating the diameter of the tubes, in accord-
ance with the quantity of blood to  be conducted through them to any  part;
which will depend upon its peculiar circumstances  at the time.   Such  local
changes are continually to be observed, in the various phases  of normal life,
as well as in diseased states; and they will be found to be constantly in har-
mony with the particular condition  of the processes of Nutrition, Secretion,
Sic,  to which  the Capillary circulation ministers.  Of this kind are the en-
largement of the trunks of the Uterine and Mammary arteries, at the epochs
of pregnancy and lactation ;—the enlargement and strongly-increased pulsa-
tion of the Radial artery, -whfcn there is any active inflammation in the thumb ;
■—the enormous diameter which the Spermatic  artery will attain, when the
testicle  is greatly increased in size by diseased action; and many other simi-
lar phenomena.   In such  cases, it cannot  be  the action of the Heart that in-
creases  the calibre of the  vessels;  since this is  commonly unaltered, and  is
itself unable, as we have just seen, even to maintain  their permeability.   It
must, therefore, be by a power inherent in themselves, that their dilatation is
effected.  The minute  distribution  of the Sympathetic nerve upon the  walls
of the arteries,—the known power which  this has of  producing contractions,
alike in their fibrous coat,  and in the muscular tunic of the intestinal  canal,—
and various phenomena, which indicate the  power  of certain states  of  mind
over the dimensions of the arteries, in particular parts of the body at least,—
render it highly probable that the calibre of the arteries is regulated in no in-
considerable degree through its intervention.*  The permanent dilatation,
however, which is seen in the arteries  supplying parts that are  undergoing

   * For Anatomical evidence to this effect, see  Henle on the Contractility of the  Blood-
vessels, in Casper's Wochenschrift, May 1840, and Brit, and For. Med. Rev., vol. x. p. 551. 
560
OF THE CIRCULATION OF BLOOD.
enlargement, must be due, not  to  simple  dilatation merely, but to  increased
nutrition; since we find that their walls are  thickened as well  as extended.
And, on the other  side, when  slow contraction occurs in these tubes, as a
consequence of disease, it must be  in part occasioned  by atrophy;  since
their nutrition is so much  diminished, that in  time they almost entirely disap-
pear,—a portion of a large artery occasionally shriveling  into a ligamentous
band.
   733.  We now come to  the last head of the inquiry into the powers which
convey the  blood through the  capillary system;—that, namely, which con-
cerns the agencies existing in the Capillaries  themselves.   Many discussions
on this subject may be found in Physiological writings ; and it has so imme-
diate a  bearing on  one of the  most important  questions  in Pathology,—the
nature of Inflammation,—that it deserves the fullest attention.   The chief
question in debate, is the  degree in which the Capillary  circulation is  influ-
enced by any other agency than the contractile power of the Heart and Arte-
rial  system;—some Physiologists  maintaining that  this alone is  sufficient
to account for all  the  phenomena  of the Capillary circulation;—and others
asserting that it is necessary to  admit  some supplementary force, which may
be exerted either to assist, retard, or regulate  the flow of blood from the Arte-
ries into the Veins.   We  shall first consider what evidence there  is of the
existence of any such force; and,  when led to an  affirmative conclusion, we
shall examine into its nature.—No  physiological fact is more clearly proved
than the existence, in the  lower classes of Animals, as well as in Plants, of
some power independent of a vis  a tergo, by which the circulating fluid is
caused to move through their vessels  (§§ 712—716).   This power seems to
originate in themselves, and to be closely connected with the state of the
Nutritive and Secreting processes :  since anything which  stimulates  these to
increased energy, accelerates the circulation;  whilst any check to them occa-
sions a corresponding stagnation.  It may be convenient to designate this
motor  force by  the name  of capillary power; it being  clearly understood,
however, that no mechanical propulsion is thence implied.  On ascending the
Animal scale,  we find the  power which, in the lower organisms, is diffused
through  the whole  system, gradually concentrated in a single  part; a new
force, that of  the Heart, being  brought into operation,  and the Circulation
placed, in a  greater  or less degree, under its control.   Still there is evidence,
that the movement of blood through the capillaries  is not entirely due to this ;
since it may continue after the cessation of the Heart's  action,—may itself
cease in particular organs  when the Heart is  still acting vigorously,—and is
constantly being affected in amount and rapidity, by causes originating in the
part  itself, and in no way affecting the  Heart.  The chief proofs  of these
statements will now be adverted to.
  734.  When the flow of blood through the Capillaries of a transparent part,
such as the web of a Frog's foot, is observed  with  the Microscope, it appears
at first to take place with great evenness and regularity.   But on watching the
movement for some time, various changes may be observed, which cannot be
attributed to the  Heart's influence, and which show that a certain regulating
or distributive power exists in the walls of the capillaries, or in the tissues
which they traverse.  Some of these changes, involving variations in the size
of the  Capillary tubes, have been already referred  to (§ 219).  Others, how-
ever, are manifested in great and sudden alterations in the velocity of the cur-
rent ; which cause a marked difference in the rates of the movement of the
blood through the several  parts of the area  under observation.  Sometimes
this variation extends even to the entire reversion, for  a time, of  the direction
of the movement, in certain of the transverse or communicating branches ; the
flow always taking place, of course, from the stronger towards the weaker cur- 
MOTION OF THE BLOOD IN THE ARTERIES.
561
rent.   Not unfrequently an entire stagnation of the current, in some particular
tube, precedes this reversal of its direction.  Irregularities of this kind, how-
ever, are more frequent when the Heart's  action is  partially interrupted ;  as
it usually is by the pressure, to which the Tadpole or other animal must  be
subjected, in order to allow  microscopic observations to be made upon its cir-
culation.  Under such circumstances, the varieties in  the capillary circulation,
induced  by  causes  purely local, become  very conspicuous;  for  when the
whole  current has nearly stagnated, and a fresh impulse from the heart re-
news it, the movement is not by any means uniform (as  it might have been
expected to be) through the whole plexus supplied by one arterial trunk, but
is much greater in some of the tubes than it is in others ; the variation being
in no degree connected with  their size, and being very different  at short in-
tervals.
  735. The movement of the blood in the  Capillaries  of cold-blooded ani-
mals, after complete  excision of the Heart, has been repeatedly witnessed.
In warm-blooded animals, this cannot be  satisfactorily established by experi-
ment, since the shock occasioned by so severe an operation much sooner de-
stroys  the general vitality of the system ; but it  may be proved in other ways
to take place.    After most kinds  of natural  death, the arterial  system  is
found, subsequently to the lapse of a few hours,  almost or completely emptied
of blood ;  this  is partly, no doubt,  the effect of the tonic contraction  of the
tubes themselves  ; but the emptying is commonly more complete than could  be
thus accounted for, and must, therefore, be partly due to the  continuance  of
the capillary circulation.  Moreover, when death  has taken place suddenly
from some cause (as, for instance, a violent electric shock), that destroys the
vitality of the whole system at once, the  arterial tubes  are found to  contain
their due proportion of blood.  Further, it has  been well ascertained that a
real process of secretion not unfrequently  continues  after general or somatic
death ; urine has been poured out  by the ureters, sweat excluded from the
skin, and other peculiar secretions formed  by their glands; and these changes
could  not have taken place unless the capillary  circulation were still continu-
ing.   In the early embryonic condition of the highest animals, the  movement
of blood seems to be unquestionably due to some diffused power, independent
of any central impulsion ;  for it may be seen to commence in  the Vascular
Area, before the  development of the Heart.  The first movement is towards
instead of from,  the centre ;  and even for some  time after the  circulation is
fairly established, the  walls  of the  Heart  consist merely of cells loosely  at-
tached together,  and  can hardly be  supposed to have any great contractile
power.
  736. The last of these facts may be said not  to have any direct bearing  on
the question, whether the Capillary power  has any existence in the adult con-
dition ; but the phenomena  occasionally presented by the  Fcetus, at  a later
stage, appear decisive.  Cases are of no very unfrequent  occurrence, in which
the heart is absent during the whole of embryonic life, and yet the greater part
of the  organs are well developed.   In most or all of these cases, however, a
perfect twin fcetus exists ; of which the placenta  is in  some degree united with
that of the imperfect one;  and it has been customary to attribute the  circula-
tion in the latter, to  the influence  of the heart of the former, propagated
through  the placental vessels.  This  supposition  has  not been disproved
(however improbable  it might seem) until recently; when  a  case  of this
kind occurred, which  was submitted  to the most careful examination  by  an
accomplished anatomist ;* and this decisive result was obtained, that it seemed

  * See Dr. Houston in the Dublin Medical Journal, 1837.  An attempt has been recently
made by Dr. M. Hall (Edinb. Monthly Journal, 1843) to disprove Dr.Houston's inferences; 
562
OF THE CIRCULATION OF BLOOD.
impossible for the heart of the twin fcetus to have occasioned the movement
of blood in the imperfect one; and that some cause present in the latter, must
have been sufficient for the propulsion of blood through its  vessels.   It was
a very curious anomaly in this  case, that the usual functions of  the Arteries
and Veins must have been reversed; for the Vena  Cava, receiving  its blood
from  the Umbilical  Vein nearly as usual,  had no communication  with  the
Arterial system (the Heart being absent), except through the  Systemic Capil-
laries ; to which, therefore, the blood must have next proceeded,  returning to
the placenta by the Umbilical Artery.   This view of the course  of the blood
was confirmed by the fact, that the veins were everywhere destitute of valves.
■—It is evident, that a single case of this kind, if unequivocally demonstrated,
furnishes all the proof that can be needed, of the existence, even  in the high-
est animals, of a capillary power; which, though usually subordinate  to  the
Heart's action, is sufficiently strong to maintain the  circulation by itself, when
the power of the central organ is diminished.  In this, as in many other cases,
we  may observe a remarkable power in the living  system, to adapt itself to
exigencies.  In  the acardiac Fcetus, the capillary power  supplies the place
of the Heart, up  to the period of birth ; after which, of course, the circula-
tion ceases, for want of due aeration of the  blood.   It  has occasionally been
noticed, that a gradual degeneration in the structure  of the  Heart has  taken
place  during life, to such an extent that scarcely any muscular tissue could at
last be detected in it; without any  such interruption  to  the circulation, as
must have been anticipated, if it furnished the sole impelling force.
  737.  Further, it is a general principle, unquestioned by any Physiologist,
and embodied in  the ancient aphorism XIbi stimulus, ibi fluxus, that, when
there  is any local excitement to the processes of Nutrition, Secretion, &c, a
determination of blood towards the part speedily takes place, and the  motion
of blood through it is increased inTapidity; and although it might be urged,
that this  increased determination may not be the effect, but the cause, of the
increased local action, such an opinion could not be sustained, without many
inconsistencies  with positive facts.  For it is known that such local determi-
nations may take place, not only as a part of the regular phenomena of growth
and development (as in the  case of the entire  genital system at the time of
puberty and of periodical heat, the uterus after conception, and  the mammae
after parturition), but also as  a  consequence of a strictly local cause.  Thus,
the student is well aware  that, after  several hours'  close application, there is
commonly an increased determination  of blood to  the brain, causing a sense
of oppression, a feeling of heat, and frequently a diminished action in other
parts;  and, again, when the capillary circulation is  being examined under the
microscope, it is  seen to be  quickened by moderate stimuli, and equally re-
tarded by depressing agents.   All these facts harmonize completely with the
phenomena, which are yet more striking in the lower classes of organized
beings, and which are evidently the results of the same laws.
  738.  It is  equally capable of proof, on the  other  hand, that  an  influence
generated in the Capillaries  may afford a complete check to the circulation
in the part ; even when the Heart's  action is unimpaired, and no mechanical
impediment exists to the transmission of blood.   Thus, cases of spontaneous
gangrene of the lower extremities are of no unfrequent occurrence, in which
the death of the solid tissues is clearly connected with a  local decline of the
circulation ; and in which it has been shown, by examination of the limb after
its  removal, that both  the larger tubes  and the capillaries  were completely

but a most satisfactory reply has been made by Dr. Houston, at the Meeting of the British
Association, August 1843, and published in the Dublin Journal, Jan. 1844. See also Edinb.
Med. and Surg. Journ. July 1844. 
MOTION OF THE BLOOD IN THE CAPILLARIES.
563
pervious; so that the cessation of the flow of blood could not be attributed to
any impediment, except that arising from the cessation of some power which
exists in the capillaries, and which is  necessary for  the maintenance of the
current through  them.   The influence  of the prolonged  application of Cold
to a part,  may be quoted in support of the same general  proposition ;  for, al-
though the calibre of the vessels  may be diminished  by  this agent, yet their
contraction  is not sufficient to account  for that complete  cessation of the flow
of blood through them which is well known to occur, and to terminate in the
loss of their vitality.  The most remarkable evidence on this point, however,
is derived from  the phenomena of Asphyxia, which  will be more  fully ex-
plained in the succeeding Chapter.  At  present it  may  be  stated  as  a fact,
which has  now been very satisfactorily  ascertained, that, if  admission of air
into the lungs be prevented, the circulation through them will be brought to a
stand, as soon as the  air which they contain has been to a great  degree de-
prived of its oxygen, or rather has become loaded with carbonic  acid;  and
this stagnation will, of course, be communicated to all the rest ofthe system.
Yet, if it have not continued sufficiently long, to cause  the loss of vitality in
the nervous centres, the  movement may be renewed  by  the  admission of air
into  the lungs.  Now, although it has  been asserted that the  stagnation is due
to a mechanical impediment, resulting from  the contracted state of the lungs in
such  cases, this has been clearly proved  not to  be the fact, by causing animals
to breathe a gas destitute of oxygen, so as to produce Asphyxia in a different
manner;  the same stagnation results as in the other case.
   739. If the phenomena which have been here  brought  together, be con-
sidered as establishing the existence, in all classes of  beings  possessing a cir-
culating apparatus, of a Capillary power, which affords a necessary condition
for the movement of the nutritious fluid, through those parts in which it comes
into more  immediate  relation with the solids,—the question  still  remains
open, as to  its nature.   That the Capillaries possess  a contractile power, far
higher in degree than that of the large Arteries, and more easily excited than
that of the  smaller, appears  scarcely to  admit of doubt;  though to what it is
due,   may  be  reasonably questioned.   It has been  recently asserted  by
Schwann, that they possess  the same kind  of fibrous tissue  in their walls, as
do the large vessels: and  this cannot be regarded  as improbable.   It is not
possible, however, that their contractility could have any influence in aiding
the continuous motion of  blood through them ; unless it were exercised in a
very  different manner from that of which observation  affords  us  evidence.
For,  when  we are microscopically examining the Capillary circulation of any
part,  it is at once seen, that  the vessels  present no obvious  movement; and
that the  stream, now rendered continuous by the elasticity of the arteries,
passes through  them, as through unelastic  tubes. The only method, in which
the contractility of the  Capillaries could produce a  regular influence on the
current of blood, would be  an alternate contraction and dilatation, or a peri-
staltic movement;  and of neither of these can the least traces be discerned.
Hence we should altogether  dismiss from our minds the  idea of any mechani-
cal assistance, afforded by the  action of the Capillaries, to the  movement of
the blood.  That the contractile  coat of the Capillaries has for its office, to
regulate the calibre of the vessels, can  scarcely be doubted; but any general
permanent  contraction  would only occasion an obstacle to the circulation,—
as is shown by the effects of stimulating injections, which, if thrown into the
vessels before their vitality has been lost, will not pass through the  capillaries.
It would appear, therefore, to be through their action on this coat, that local
 stimuli occasion a contraction of the capillaries ; their effect, however, is dif-
 ferent from what might have been anticipated;  for,  instead of the capillary
 circulation  being retarded, it is accelerated, at least until an abnormal condition 
564
OF THE CIRCULATION OF BLOOD.
results from their continued operation.   Here, again, is another evidence, that
something different from mechanical power must be the agent, that operates
in all the foregoing cases.
  740.  It appears, from the preceding facts, that the conditions, under which
the power in question uniformly operates, may be  thus  simply and definitely
expressed:—Whilst the injection of blood into the Capillary vessels of every
part of the system, is due  to  the  action of  the Heart, its  rate of  passage
through those vessels is greatly modified by the degree  of activity in the pro-
cesses,  to which  it should  normally be subservient in them ;—the current
being rendered more rapid by an increase in their activity, and being stagnated
by their depression or total  cessation.—Thus  it seems  that " the capillaries
possess a distributive power over the blood, regulating  the  local circulation,
independently of  the central organ, in obedience to the necessities of each
part."  If this be true, it  is evident that the  dilatation  or contraction of the
Capillaries will only have a secondary influence on  the movement of the blood
through them.   The  former condition is usually an  indication of diminished
vital energy; and when it is observed, it is almost  invariably accompanied by
a retardation or partial stagnation of  the current; on the other hand, the ap-
plication of a moderate stimulus, which excites  the contractility, accelerates
for a  time the motion  of the blood, by rendering more energetic that reaction
between the fluids and the  surrounding tissues, which  is the condition that
really has the most influence over the  current.—That alterations in the chemi-
cal state ofthe blood  (involving, of course, important changes in  its vital pro-
perties) are capable of exercising a most important  effect on  the Capillary cir-
culation, is shown, not merely by the stagnation of the Pulmonary Circulation
in Asphyxia  (§ 780), but by the curious  fact ascertained  by Dr. J. Reid,—that
the blood, when imperfectly arterialized, is  retarded in  the  systemic capilla-
ries, causing  an  increased pressure on the walls of the arteries.  He found that,
when the ingress of air through the trachea  of a Dog was prevented, and the
Asphyxia was proceeding  to the stage of insensibility,— the  attemps at  inspi-
ration being few and laboured, and the blood in an  exposed artery being quite
venous  in its character,—the pressure upon  the Arterial  walls, as  indicated by
the hannadynamometer applied to the Femoral artery, was much  greater than
usual.  Upon applying a  similar  test to a Vein, however, it was found that
the pressure was proportionably diminished; whence it became apparent,that
there was an unusual  obstruction to the  passage of venous blood through the
systemic  capillaries.   After  this period, however, the mercury in the h?ema-
dynamometer applied  to the artery began to fall steadily, and at  last rapidly,
in consequence ofthe diminished force ofthe heart, and the  retardation of the
blood in the  pulmonic capillaries;  but, if atmospheric air was admitted, the
mercury rose very speedily, showing that the renewal ofthe proper chemical
state of the blood, restored the condition necessary for its circulation through
the Capillaries.
  741.  The  principles already noticed  (§ 713) as  put forth by Prof. Draper,
seem fully adequate to explain  these phenomena.

  a. The arterial blood,—containing oxygen with which  it is ready to  part, and being pre-
pared to receive in exchange the carbonic acid which the tissues  set free,—must obviously
have a greater affinity for  the tissues, than venous blood; in  which both these changes have
already been effected. Consequently upon mere physical principles, the arterial blood which
enters the systemic Capillaries on one side, must drive before it, and expel on the other side
of the net-work, the blood which has become venous whilst traversing it.  But if the blood
which enters the Capillaries have no such affinity, no such motor power can  be developed.
  b. On  the other hand, in the Capillaries of the lungs the opposite affinities prevail.  The
venous blood and the air in the pulmonary cells have a mutual attraction, which is satisfied
by the exchange of oxygen and carbonic acid that takes place through the walls of the capil-
laries ; and when the blood has  become arterialized, it no longer  has any attraction  for the 
MOTION OF THE BLOOD IN THE CAPILLARIES.             565
 air.  Upon the very same principle, therefore, the venous blood will drive the arterial before
 it, in the pulmonary capillaries, whilst respiration is properly going on: but if the supply of
 oxygen be interrupted, so that the blood is no longer aerated, no change in the affinities takes
 place whilst it traverses the capillary net-work; the blood continuing venous, still retains its
 need of a change, and its attraction for the walls  of the capillaries; and its egress into  the
 pulmonary veins is thus resisted, rather than aided, by the force generated in the lun«s.
   c. The change in the condition of the blood,  in regard to the relative proportions of its
 oxygen and carbonic acid, is the only one to which the Pulmonary Circulation is subservient-
 but in the Systemic Circulation, the  changes are of a much more complex nature;—every
 distinct  organ attracting to  itself the peculiar substances which  it requires as the materials
 of its own nutrition; and the nature of the affinities thus generated being consequently differ-
 ent in each case.  But the same law holds good in all instances.  Thus the blood conveyed
 to the liver by the portal vein, contains the materials at the expense of which the bile-secret-
 ing cells are developed; consequently the tissue of the liver, which is principally made up
 of these cells, possesses a  certain degree  of affinity or attraction for blood containing these
 materials; and this is  diminished, so soon as they have been drawn from it into the cells
 around.  Consequently the blood of the portal vein will drive before it, into the hepatic vein,
 the blood which has traversed the capillaries ofthe portal system, and which has given  up,
 in doing so, the elements of bile to the solid tissues of the liver.—The same principle holds
 good in  every other case.

   742. It can be scarcely doubted, that  it  is by some influence exercised over
 the  molecular actions, to which the Blood  is  subject  in  the Capillaries, that
 the Nervous  system can operate on the  functions of Nutrition,  Secretion, Sic,
 in the  manner already  alluded to (Chap, vn.); and this influence may be not
 improperly termed  vital, if  by so  designating it  we  merely  imply that  its
 nature  and mode of operation  are unknown, but  that it is closely connected
 with those actions which are altogether peculiar to living beings.  The follow-
 ing experiment, made by Dr. Wilson Philip, exhibits  in a convincing  manner
 the possibility of such  an influence.  "  The web of one of the hind legs of a
 frog was brought before the microscope; and while Dr. Hastings observed the
 circulation, which was  vigorous, the brain  was crushed by the blow of a ham-
 mer.   The vessels of the web instantly lost their power, the circulation ceas-
 ing ;  an effect which cannot arise,  as we have seen, from the  ceasing of the
 action of the  heart.  [Dr. P. here refers  to  experiments, by which it was ascer-
 tained, that the circulation in the capillary vessels of the frog will continue for
 several minutes,  after the interruption ofthe heart's action.]   In a short time
 the  blood again  began  to  move, but with less force.   This experiment was
 repeated, with the same result.  If the brain is not completely crushed, although
 the animal is killed, the blow, instead of destroying the circulation, increases
 its rapidity."*   We are  not hence  to  conclude, however, that the Nervous
 system supplies  any influence, which  is  essential  to the continuance of the
 Circulation ; since it is  only by such sudden  and severe injuries  to the nervous
 centres, as instantaneously destroy the vitality of the  wbole system (§ 735),
 that the movement of the blood is arrested.   The experiments of Muller and
others  satisfactorily  prove, that  mere action of the  Nerves  does not produce
any direct effect  upon the Capillary circulation; and this corresponds with the
well-known fact, that the Nutritive processes may continue as usual, after this
action has been  suspended.  All  the facts, which bear upon the question  of
the connection between Nervous  agency and the forces maintaining the
Capillary Circulation, have an equal relation to the functions of Nutrition and
Secretion  in  general; and as already shown, the Nervous System  also influ-
ences these, by the  control  it exerts over the diameter of the blood-vessels
(§ 730).

    * Experimental Inquiry into the Laws of  the Vital Functions, 4th edition, p. 52.
     48 
566
OF THE CIRCULATION OF BLOOD.
                     4.—Of the Venous Circulation.

  743.  The Venous system takes its  origin  in  the small  trunks  that are
formed by the re-union of the Capillaries; and it returns the blood from these
to the Heart.   The structure of the Veins is essentially the same with that of
the Arteries; but the fibrous tissue, of which their middle coat is made up,
bears more resemblance to the  areolar tissue of the skin, than it does either
to muscular fibre, or to  the true elastic tissue.   The Elasticity of the Veins,
however, is shown by the jet of blood, which at first  spouts  out in ordinary
venesection ; when, by means of the ligature, a distension has  been occasioned
in the  tubes  below it.   A slight Contractility on  the application of stimuli,
and on irritation of the  Sympathetic nervous fibres, has been observed ; but
this is not so decided as in the Arteries.   The whole capacity of the Venous
system is considerably greater than that of the Arterial;  the former is usually
estimated to contain from 2 or  3  times  as much  blood as  the latter, in the
ordinary condition  of the  circulation; and when we consider the great pro-
portion, which the  Veins in almost every part of the body bear to the arteries,
we shall scarcely regard even  the  larger of these  ratios as exaggerated.  Of
course the rapidity of the movement  of the blood  in the two systems, will
bear an inverse ratio to their respective capacities ;  thus if, in a given length,
the Veins  contain  three times as much blood  as  the Arteries, the fluid will
move with only one-third  of  the  velocity.   Even at  their origins  in the
Capillary plexus, the Veins  are larger than the Arteries which terminate in
the same  plexus;  so that, wherever the arterial and venous  net-works  form
distinct strata, they are readily distinguished from each other.   The Veins
are remarkable for  the number of valves which they contain, formed  of dupli-
catures  or loose folds of the internal tunic, between the  component laminae of
which, contractile fibres are interposed; and also  for the dilatations behind
these, which, when distended, give them a varicose appearance.   The valves
are single in  the  small veins,  the free edge of the flap  closing  against the
opposite  wall of the vein;  in  the  larger  trunks  they are double ;  and in a
few instances they are  composed of  three flaps.   The object of  these valves
is evidently to prevent  the reflux of blood; and we shall presently see that
they are of important use in assisting in  the maintenance of the venous circu-
lation.   They  are  most numerous in those Veins which run  among  parts
affected by muscular movement; and they are  not found in  the veins of the
lungs of the abdominal viscera  or of the brain.
   744.  The movement of  the  blood through  the Veins is, without doubt,
chiefly effected  by the vis a tergo or propulsive  force ; which  results from
the action of the Heart and  Arteries, and from the  additional  power generated
in the Capillary vessels.  This is shown by the  immediate  arrestment  of it,
which takes place when  these forces are suspended.   There  are some con-
current causes, however, which are supposed by some to have much influence
upon it, and of  which the consideration  must not  be neglected.

   a. One of these is  the suction-power attributed to the Heart; acting as a vis  a fronte, in
drawing the blood towards it.  It is very doubtful how far the Auricles have such a power
of active  dilatation, as that which would be required  for this purpose; and no sufficient
evidence has been given, that the current of blood at any distance from the Heart is affected
by it.  Indeed, for a reason to  be presently stated, this may be regarded  as impossible.
  b. Another important agency  has been  found by some Physiologists in the  Inspiratory
movement; this is supposed to draw the blood of  the Veins into  the chest, in order to sup-
ply the vacuum which is created there, at the  moment of the descent of the Diaphragm.
That the movement in question has some influence on the flow  of Venous blood into the
chest, is evident from the occurrence of the respiratory pulse, long ago described by Haller;
which may be seen in the veins of the neck and shoulder in thin persons, and in those
especially who are suffering from pulmonary diseases. During  Inspiration,  the Veins are 
VENOUS CIRCULATION.
567
seen to  be partially emptied; whilst during Expiration they become turgid, partly in con-
sequence of the accumulation from behind, and of the check in  front; and partly (it may
be) in some cases, through an absolute reflux from  the veins within the chest (§  723, c).
The fact that, in the immediate neighbourhood  of the chest, the flow of blood towards the
heart is aided by Inspiration and impeded by Expiration, is further proved by Sir D. Barry's
experiment, which consisted in introducing one extremity of  a tube into the Jugular vein of
a Horse, and  the other into water, which exhibited an  alternate elevation and  depression
with inspiration and expiration; this has been repeated and  confirmed by several Physiolo-
gists.  On the other  hand, the expiratory movement, while it directly causes accumulation
in the Veins, will assist the Heart  in propelling the blood into the Arteries; and by the com-
bined action of these two causes are produced, among other effects, the rising and sinking of
the Brain, synchronously with expiration and inspiration, which  are observed when a por-
tion of the cranium is  removed.   Several considerations, however, agree  in pointing to the
conclusion, that no great efficacy can be rightly attributed to the Respiratory movements, as
exerting any  general influence over the Venous  circulation.  The Pulmonary circulation,
being entirely within  the chest, cannot be affected  by variations in atmospheric pressure ;
and it may be further  remarked, that the whole mechanism  of respiration is so different in
Birds, from that which  exists  in Mammalia, that no vacuum can ever be said  to  exist in
their chests, although the venous circulation  is performed as actively  as usual.  The  Venous
circulation of  the fcetus, also, is independent of any such agency.  Again, it has been shown
experimentally by Dr.  Arnott  and  others, that no suction-power exerted at the farther end
of a long tube, whose  walls are so deficient in firmness as are those of the Veins, can  oc-
casion any acceleration in a current of fluid transmitted through it; for the effect of the
suction is destroyed, at no great distance from the point at which it is applied, by the flap-
ping together of the sides of the vessel.
   c. One of the most powerful of the general causes which  influence the Venous  circula-
tion, is doubtless the frequently-recurring action of the Muscles upon their trunks.   In every
instance that Muscular movement takes place, a portion of the Veins  of the part will undergo
compression;  and as the blood is  prevented, by the  valves in the veins, from being driven
back into the small  vessels, it is necessarily forced  on towards the  Heart.  As each set of
muscles is relaxed, the Veins  compressed by it fill out again,—to be again compressed  by
the renewal of the force.  That the general Muscular movement is an  important agent in
maintaining the Circulation, at a point above that, at which it would be kept by the action
of  the Heart  and Capillaries alone, appears from several considerations.  The pulsations
are diminished  in frequency by rest, accelerated by  exertion, and very much quickened by
violent effort.   In all  kinds of exercise, and in almost every sort  of effort, there  is that
alternate contraction and relaxation of particular groups of  Muscles, which has been just
mentioned, as effecting the flow of blood through  the Veins; and there can be little doubt,
that the increased rapidity ofthe return of blood through them, is of itself  a sufficient cause
for the accelerated movements of  the Heart.  When a large number of Muscles are put in
action after repose, as is the case  when we rise up  from a recumbent or  a sitting posture,
the blood is driven to the Heart with  a very strong impetus;  and if that organ should be
diseased, it may arrive there in a  quantity larger than can be disposed of; so that sudden
death may be the result.  Hence the necessity for the avoidance of  all sudden and violent
movements, on the part of those who labour  under either a functional or structural disease of
the centre of the circulation.

   745. The Venous circulation is much more  liable than the  Arterial, to be
influenced by the force of Gravity;  and this influence  is  particularly notice-
able, when the tonicity of the vessels is  deficient.

  a. The following experiments performed  by Dr.  Williams, to  elucidate  the influence  of
deficient firmness in the walls of the vessels, and of gravitation, over  the movement of fluids
through tubes, throw great light on the causes of  Venous Congestion.—A tube with two
equal arms having been fitted to a syringe, a brass tube two feet  long, having several right
angles in its course, was adapted to one of them, whilst to the other was tied a portion of a
rabbit's intestine four  feet long, and of calibre double that  of  the brass tube,  this being
arranged in curves and coils, but without angles and crossings. When the two tubes were
raised to the same height, the  small metal tube discharged from two  to five times the quan-
tity of water discharged in a given time by the larger but membranous tube; the difference
being greatest, when the strokes of the piston were most forcible  and sudden, by which the
intestine was much dilated at its syringe end, but  conveyed very little more water.  When
the discharging ends were raised a few inches higher, the difference  increased considerably,
the amount of fluid discharged by the gut being much diminished; and when the ends were
raised to the height of eight  or ten inches, the gut ceased to discharge, each stroke only
moving the column of  water in it, and this  subsiding again, without rising high  enough to 
568
OF THE CIRCULATION OF  BLOOD.
overflow.  When the force of the stroke increased, the part of the intestine nearest the
syringe burst.
  b. From these experiments  it is easy to understand, how any deficiency of tone in the
Venous System will tend to prevent the ascent of the blood from the depending parts of the
body, and will consequently occasion an increased pressure on the walls of the vessels, and
an augmentation in the quantity of blood they contain.   All these conditions are peculiarly
favourable to the escape of the watery part of the blood from the  small vessels; and this
may either infiltrate  into the  areolar tissue, or it may be poured into some neighbouring
serous cavity, producing dropsy.  Thus it happens, that  such effusions may often be traced
to that state of deficient vigour of the system, which peculiarly manifests itself in want of
tone of the blood-vessels;  and that it is relieved by remedies which restore this.  In many
young females of leuco-phlegmatic temperament,  for example, there is a tendency to swell-
ing of the feet, by cedematous effusion into the areolar tissue, in consequence of the depend-
ing position of the limbs; the cedema disappears during the night, but returns during the day,
and is at its maximum in the evening.  And the congestion which frequently manifests
itself in the posterior  parts of the body, towards the close  of exhausting diseases, in which
the  patient has lain much upon his back, is attributable to a similar cause; of such conges-
tion, effusions into the various  serous cavities are frequent results; and such effusions, taking
place during the last hours of life, are often erroneously regarded as the cause of death.  To
the  same cause we are to attribute the varicose state of the veins of the leg, which  is so
common amongst persons of  relaxed fibre,  and  especially in those  whose habits require
them to be much in the erect posture; and this distension occasionally proceeds to complete
rupture, the causes of which are fully  elucidated by the experiments just cited.

           5.—Peculiarities of the Circulation  in different Parts.

  746. In several portions of the Human body, there  are certain varieties in
the  distribution  and in  the functional actions  of the  Blood-Vessels, which
should not be omitted in a general account of the Circulation.   Of these, we
have in the first place to notice the apparatus for the Pulmonary circulation;
the chief peculiarity of which is, that venous blood is sent from  the heart,
through a tube which is  Arterial in its  structure, whilst arterial blood is re-
turned to the heart, through a vessel whose entire character is that of  a  Vein.
The movement  of the  blood through these is considerably affected by  the
physical state of the Lungs themselves ; being retarded by any causes, which
can occasion  pressure  on the vessels (such as over-distension of the cells with
air,  obstruction of their cavity by solid or  fluid  depositions, or by foreign sub-
stances injected into them, &c); and proceeding with the greatest energy  and
regularity, when the respiratory movements  are freely performed.—The Por-
tal  circulation, again, is peculiar, in being a kind of offset from the general or
systemic  circulation;  and also  in  being  destitute of valves;  and  it may be
surmised with much probability, that the purpose of their absence is, to allow
of an unusually free passage of blood from one  part of that system to another,
during the very varying conditions to  which it is subjected (§ 685).
  747.  Another very important modification of the Circulating system, is that
which presents  itself within  the Cranium.   From  the  circumstance  of the
cranium being a closed cavity, which must be always filled with  the  same
total amount of contents, the flow of blood through its vessels is attended with
some peculiarities.   The  pressure of the atmosphere is here exerted, rather
to keep the blood in the head, than to force it out;  and it  might accordingly
be inferred that, whilst the quantity of cerebral matter  remains the  same, the
amount of blood in the cranial vessels must also  be  invariable.   This  infer-
ence appeared to derive support from  the experiments  of  Dr. Kellie.*   On
bleeding animals to death, he found that,  whilst the remainder of the  body was
completely exsanguine, the usual quantity of blood remained  in  the  arteries
and veins of the cranium ;  but that, if an opening was made in the skull, these
vessels were then as completely emptied as  the rest.   It is not to be hence
* Edinburgh Medico-Chirurgical Transactions, vol. i. 
PECULIARITIES OF CIRCULATION.                   569
inferred, however, that the absolute quantity of  blood within  the cranium is
not subject to variation; and that in the states of inflammation, congestion, or
other morbid  affections, there  is only a disturbance  of the  usual balance of
the arterial and venous circulation.   The fact in  all probability is rather, that
the softness of the Cerebral tissue,  and its varying functional activity, render
it peculiarly liable to undergo alterations in bulk; and that the amount of the
cerebro-spinal fluid varies  considerably at different times (§ 476); so that the
quantity of blood may thus, even in  the healthy condition, be continually
changing.  Moreover, in disordered  states of the circulation, the quantity of
blood in the vessels of the  cranium  may be for a  time diminished by a sudden
extravasation, either of blood or serum, into  the cerebral substance; and the
amount of interior pressure upon  the  walls of  the vessels may also be con-
siderably altered, even when there  is no difference in  the quantity of fluid
contained in them.*
  748.  The  Erectile tissues constitute another curious modification of the
ordinary vascular apparatus.  The chief of  these are the Corpora Cavernosa
in the penis of the  male,  and in the clitoris  of  the female; the  collection of
similar tissues round the vagina, and in the nymphse, of the female; and the
nipple in both sexes.   In  all these situations, erection  may be  produced by
local irritation ; or it may take place as a result of certain emotional conditions
of the mind; the influence  of which is probably  transmitted  through  the
Sympathetic nerve,  as  it  may be  experienced  even in cases  of paraplegia.
The erectile tissue appears essentially to consist of a plexus of varicose Veins,
inclosed in a fibrous  envelope.   According to Gerber,t this plexus is traversed
by^numerous contractile fibres, which  are analogous to those that form the
dartos; and to the contraction of these is probably to be attributed that ob-
struction to the return  of blood by the Veins,  which is the occasion of the
turgescence.   The  proximate  cause of the  erection of the Penis, has been
stated by some to be the action of the Ischio-Cavernosi muscles  ; and by others
it has  been attributed to the compression of the Vena dorsalis penis against
the Symphysis pubis.  But  it is obvious that nothing  analogous to this  can
apply to the other erectile organs,  especially to  the  Nipple.  In the  Penis,
according to Muller,  there are two  sets of arteries; of which one, destined for
the nutrition  of the tissues, communicates with  the veins in the usual way,
through a capillary net-work ; whilst the others pass off as large branches, and
penetrate the cavernous substance  in a helicine manner, communicating ab-
ruptly with the venous cells.  It would seem not improbable, that  these last
are not ordinarily pervious to blood; but that the same change in the contrac-
tile fibres,  which impedes the  return  of the blood  by the veins,  may also
permit it to enter more freely from the helicine  arteries.  This  double com-
munication, however, is denied by Valentin,  who gives a different explanation
of the appearances described by Muller.—The  arteries are protected in such
a manner, that, even when the veins are most compressed, and  the erection
most complete, they  are still quite pervious.

  *  The results of the more recent experiments of Dr. G. Burrows (Med. Gaz., April and
May, 1843) fully confirm the views stated above.
  | General Anatomy, p. 298.
                                   48* 
570                         OF RESPIRATION.
                         CHAPTER  XIII.

                             OF RESPIRATION.

     1.—Nature of the Function: and Provisions for its Performance.

   749.  It is  obvious  that the  Nutritive fluid, in its circulation through the
capillaries of the system, must undergo great alterations, both in its physical
constitution, and its vital properties.   It  gives up to the tissues with which it
is brought into contact, some of its most important elements ;  and, at the same
time, it is made the vehicle of the removal, from these tissues, of ingredients
which are no longer in the state of combination, that fits them for their offices
in the Animal Economy.   To separate these ingredients from the general cur-
rent of the circulation, and to carry them out of the system, is the great object
of the Excretory organs ; and it is very evident  that the  importance of the
respective functions of these will vary with  the amount of the  ingredient
which they have to separate, and with the  deleterious  influence which its re-
tention would  exert on the welfare of the system at large.   Of all these injuri-
ous  ingredients, Carbonic Acid is without doubt the one  most  abundantly
introduced into  the nutritive fluid; and it is also most deleterious in its effects
on the system, if allowed to accumulate.—We find, accordingly, that the pro-
vision for the  removal of  Carbonic Acid from  the Blood,  is  one of peculiar
extent and importance, especially in  the higher forms of Animals ; and further,
that instead of being effected by an operation peculiarly  vital (like other acts
of Excretion), its performance is secured by being made to depend upon simple
physical laws, and is not nearly so susceptible of derangement from disorder
of other processes, as it would be if its conditions  were less simple.   All that
is requisite for it, as we  shall presently see,  is the exposure of the Blood to
the influence of the Atmospheric air, or of Air dissolved in  water, through the
medium of a membrane  that shall permit the diffusion of gases; and an inter-
change  then takes place between the gaseous matters on  the two sides,—Car-
bonic acid being exhaled from the Blood, and being replaced by Oxygen.
Thus the extrication of Carbonic  acid is effected  in a manner, that renders it
subservient  to the  introduction of the element which is required for all the
most active manifestations of vital  power; and it is in these two processes
conjointly, not in either alone, that the function of Respiration essentially con-
sists.—We  shall now inquire  into the sources from which  Carbonic acid is
produced in the living body; and the causes  ofthe demand for Oxygen.
   750.  All  organized bodies, as  already  explained, are liable  to continual
decay, even whilst  they are most actively engaged in performing the actions
of Life ;  and  one of the  chief products of that decay is Carbonic Acid.  A
large quantity of this gas is set free, during the decomposition of almost every
kind of organized matter; the Carbon of the substance being united with the
oxygen supplied by the air.   Hence we find, that the formation and liberation
of carbonic Acid go on with great  rapidity after death, both in the Plant and
in the Animal;  and that they take  place,  also, to a very great extent, in the
period that often precedes the death of  the body, during which a o-eneral de-
composition of  the tissues is occurring.   Thus  in Plants, as soon as they
become unhealthy, the extrication of carbon in the form of carbonic acid takes 
SOURCES OF CARBONIC ACID.
571
place in greater amount than its fixation from the carbonic acid of the atmo-
sphere ; and the same change normally occurs during the period that immedi-
ately precedes  the annual fall of the leaves, their tissue being no longer able
to perform its proper functions, and giving rise, by its incipient decay, to a
large increase  in  the quantity of carbonic acid set free.   The same  thing
happens in the Animal body, during the progress of many diseases which are
attended with an unusual tendency to  decomposition in the solids and fluids,
-—such as eruptive fevers ;—the quantity of carbonic acid set free in Respira-
tion is greatly increased, although the-body remains completely at rest; and
notwithstanding this, the blood frequently exhibits a very dark hue, indicating
that it  has not been freed from  the  unusual amount of  that substance which
it has received  from the tissues.—Hence the first object of the Respiratory
process, which is common to all forms of organized being, is to extricate from
the  body the carbonic acid, which is one of the products of the continual de-
composition of its tissues.   The softness of many of the tissues of Animals,
and  the large quantity of fluid contained in their bodies,  render them more
prone than Plants to this kind of decomposition; and in warm-blooded animals,
the   high  temperature  at which the fabric is usually maintained, adds  con-
siderably to the degree of  this tendency, so that the waste of their tissues,
from this cause alone, is as much greater than that of cold-blooded  animals,
as the  latter is than that of Plants.  But when the temperature of the Reptile
is raised by external heat  to  the level of that of  the  Mammal, its need for
respiration increases, owing to the augmented waste of its tissues.  When, on
the other hand, the warm-blooded Mammal is reduced,  in the state of hyber-
nation, to the level of the cold-blooded Reptile, the waste of its tissues dimin-
ishes to such an extent, as  to require but a very small exertion of the respira-
tory process to get rid of the carbonic acid, which is one of its chief products.
And in those animals which are capable of retaining their vitality, when they
are frozen, or when their tissues are  completely dried up, the decomposition
is for the time  entirely suspended, and consequently there is no carbonic acid
to be set free.
  751. But another source of Carbonic acid to be set free by the Respiratory
process, and one which  is peculiar to animals, consists  in the rapid changes
which take  place in the Muscular and Nervous  tissues, during the period of
their activity.  It has been already shown (§ 586), that  there is strong reason
to believe the waste or  decomposition of the muscular  tissue to be  in  exact
proportion to the degree in which it is exerted;  every development of muscu-
lar force being accompanied by a change in the condition of a certain amount
of tissue.   In order that this change may take place, the presence of Oxygen
is essential; and one of the products of the union of oxygen with the elements
of muscular fibre is  carbonic  acid.  The same may probably be said of the
Nervous tissue (§ 292).  Hence  it may be stated as a general principle, that
the  peculiar waste of the Muscular and Nervous substances, which is a con-
dition of their functional activity, and which  is altogether distinct from the
general slow decay that is common to these tissues with others, is  another
source of the carbonic acid which is set free from the animal body;  and that
the amount thus generated will consequently depend upon the degree in which
these tissues are exercised.   In animals which are chiefly made up of the
organs  of vegetative life, in whose  bodies  the nervous  and muscular tissues
form but a very small part, and in whose tranquil plant-like existence there is
but  very little demand upon the exercise of these structures, the quantity of
carbonic acid thus liberated will be extremely small.  On the other hand, in
animals, whose bodies are chiefly composed of muscle, and whose life  is an
almost ceaseless round of exertion, the quantity of carbonic  acid thus liberated
is very considerable. 
572                         OF RESPIRATION.
  752.  Besides  these  sources  of  Carbonic acid, which are common to  all
Animals, there  is  another, which  appears  to be peculiar to the two highest
classes, Birds and Mammals.   These are capable of maintaining a constantly
elevated temperature, so  long  as they are  supplied with a proper amount of
appropriate  food;  and  their power of doing so appears to depend upon the
direct combination of certain elements of the food, with the oxygen of the air,
by a process analogous to combustion ;  these elements having been introduced
into  the blood for that purpose, but not having formed a part of  any of the
solid tissues of the body/ unless they have  been deposited in the form of fat.
The nature  of these substances has been already noticed (§641).   It is  quite
clear that they cannot be applied in their original form, to the nutrition of the
tissues that originate in proteine compounds; and it is  tolerably certain that,
in the  ordinary condition of the body, they undergo  no such conversion, as
would adapt them  to that purpose.   The Liver seems to afford a  channel, by
which some ofthe fatty matters are drawn off from the blood;  but even these
seem, in part  at least, to be reabsorbed (§  671), and to be thrown off by the
respiratory process.
  753.  The quantity of carbonic acid, that is generated  directly from the
elements of the food, seems to vary considerably in different animals, and in
different states of the same individual.  In the Carnivorous tribes, which spend
the greater part of  their time in a state of activity, it is  probable that the quan-
tity which is generated by the  waste or metamorphosis of the  tissues is suffi-
cient for the maintenance of the required temperature,—and that little or  none
of the carbonic acid  set free in respiration is derived from the  direct combus-
tion of the materials of the food.  But in Herbivorous animals of comparatively
inert habits, the amount of metamorphosis of the tissues is far from being suf-
ficient;  and a large part of the food, consisting as  it does of substances that
cannot be applied  to  the  nutrition of the tissues, is made to enter into direct
combination with the oxygen of the air, and thus to compensate  for the de-
ficiency. In Man and other animals, which  can sustain considerable variations
of climate, and can adapt  themselves to  a great diversity of habits, the quantity
of carbonic acid formed by the direct combination of the elements of the food
with the oxygen of the air, will differ extremely under  different circumstances.
It will  serve as the  complement of that which is  formed in other ways;  so
that  it will diminish with the increase, and  will increase with the  diminution
of muscular activity.  On the  other hand it will vary, in accordance with the
external temperature; increasing with its diminution, as more heat must then
be generated;  and diminishing with its increase.—In all cases, if  a sufficient
supply of food be not furnished, the store of fat is drawn upon: and if this be
exhausted, the animal dies of cold  (§ 896).
  754.  To recapitulate, then, the sources of Carbonic Acid in the animal body
are threefold.—i.  The continual decay of the tissues; which is common to
all organized bodies; which is  diminished by cold and dryness, and increased
by warmth  and  moisture; which  takes place with increased  rapidity at the
approach of death, whether this affect the body at large, or only an individual
part; and which goes on  unchecked when the  actions of nutrition have ceased
altogether.—n. The  Metamorphosis, which is  peculiar to  the Nervous and
Muscular tissues;  which is the very condition of their activity, and which
therefore bears a direct relation to  the degree in which they are exerted.—hi.
The direct conversion of the carbon of the  food into carbonic acid; which is
peculiar to warm-blooded animals  ; and which seems to vary  in  quantity, in
accordance with the amount of heat to be generated.—We shall now examine
into  the manner in which this compound is  set free, in the principal groups of
the Animal kingdom.
  755.  Notwithstanding  their diversity in  external form, the organs of Re- 
GENERAL STRUCTURE OF THE RESPIRATORY ORGANS.          573
spiration are always formed upon the same general plan;  being essentially
composed of a membranous prolongation of the external surface, adapted, by
its vascularity and permeability, to bring the blood into close relation with the
surrounding  medium.   But as this medium  may be either air or water,  we
find two principal forms of the apparatus; one of them adapted for each kind
of respiration.  In aquatic animals, the membrane is usually prolonged ex-
ternally into tufts or fringes, which are so arranged as to expose the greatest
amount of surface to the water; each  filament of which these are composed,
includes an afferent and efferent capillary vessel; and it is whilst the  fluid is
passing through  them, that its aeration is accomplished.   The collection of
tufts or fringes constitutes what are known as gills;
and though their arrangement varies considerably, their         Fig. 214.
essential character is but little different, throughout the
classes of animals  that possess them.   On the other
hand, in air-breathing Animals, the aerating surface
is reflected inwardly,  forming  passages or chambers
into which the air is received, and on the walls  of
which the blood is distributed in a minute  capillary
net-work.   Such a conformation is found even among
some of the lower Articulata, which have a series  of
air-sacs disposed along each side of the body, one for
every segment.  In Insects we  find,  instead of the
sacs, a system of prolonged tubes, ramifying  through
the body,  and  carrying  air  into  its   minutest  por-
tions.   Even in some Mollusca, such  as  the Snail   One ofthe arborescent pro-
     d,,         A ■  , r*         ,      /•  i       • •     cesses, forming the prills of
    other terrestrial Gasteropods,  we find a provision  Doris Johnstoni> separated
for aerial respiration;  a large cavity being  formed in  and enlarged.
the back, communicating with the air, and having a
beautifully-reticulated  plexus  of  blood-vessels on its  walls.   In  none of
the Invertebrata, however, does the respiratory apparatus  communicate with
the mouth;  which is an organ solely appropriated, in them, to the  ingestion
of  food.   In the Mollusca,  indeed, the  channel through  which the  water,
that has passed  over  the  aerating surface, leaves  the chamber (formed  by
a fold of the mantle  or general  envelope) which  contains the gills,  is the
same as that through  which the  excrementitious  matter is discharged from
the intestine;  and  the  gills themselves  are  very commonly situated  in the
neighbourhood of the  anal orifice.  This fact is interesting in  regard  to the
character of  the temporary respiratory apparatus  of the Human embryo.  In
Fishes and the larvae of Batrachia, which are the highest animals that  breathe
by gills, these  organs  are  so  disposed in connecting with  the  cavity of the
mouth, that fresh currents of water are continually being forced over them by
its muscles;  and thus  the energy of their action is  greatly  increased.   More-
over the whole blood,  which is propelled from the  heart, proceeds first to the
respiratory organs;  instead of  passing  through them on its return  from the
systemic circulation, as in  most  of the  aquatic Invertebrata.   Still,  as the
quantity of oxygen which  the blood can  obtain in  this  manner is very small,
being limited to that contained in  the atmospheric air dissolved in the water,
the amount of aeration must be considered as low.
  756.  In the lowest Vertebrata that possess anything like a pulmonary cavity,
this has a structure as  simple as that of the air-sac  of the Snail.   This is the
case in  many Fishes,  where it is  known as  the  air-bladder; it is frequently
single in this class, and communicates  with the intestinal canal near the sto-
mach, or is  altogether  destitute of outlet.  In others, however, it is double,
and its duct opens  into the oesophagus  near the mouth; so that its analogy to
the lungs  of higher animals is very evident.  The Batrachia begin life as 
»
574                          OF RESPIRATION.

Fishes, breathing by gills during their tadpole state;  but at the time that the
legs  are developed  and the tail has decreased, the  pulmonary organs also are
evolved, and the course of the  blood is altered, so that it is no longer trans-
mitted through the gills, which speedily  shrivel and disappear (§ 3l).  There
are some species, however, whose metamorphosis  is checked, so that in their
permanent condition both lungs and gills are present; but the former are then
present in a very rudimentary form, not  being more developed than the air-
sacs  of many Fishes.  The  lungs of Reptiles are, for the most  part, simple
sacs; into which the bronchial tubes open freely; and on the walls of which,
the pulmonary vessels are distributed.   The extent of surface is considerably
increased, however, by the formation of a number of little pits or sacculi  on
the inner wall of the cavity,  especially at its upper part; and between these,
we observe  a sort of cartilaginous frame-work, which is continuous with the
cartilage ofthe bronchus on either side.   The Turtles and their allies are the
only Reptiles, in which the cavity of the lung is itself divided by membranous
partitions;  and thus it happens that, excepting in these, the net-work of pul-
monary capillaries, in the  class of  Reptiles, is exposed only on one side to
the influence of the air.  The general distribution of these vessels is shown
in the accompanying figures.   It will be seen that the trunk of the pulmonary
artery runs along one side of the sac, and that of the pulmonary vein along
the other (Fig. 215); and that numerous branches  arise from the former,
which  subdivide into capillaries that  ramify over the whole surface, and then
reunite into  small veins which terminate in the latter.   The islets of paren-
chyma left between  the capillary vessels, are seen to be much smaller than
those which are usually to be observed in the systemic circulation  (Figs.
216, 217); so that the membrane is more copiously traversed by vessels, than

                                                    [Fig. 216.
                                                   of the lung of the same animal,
                                           more highly magnified ; the vessels, finely-
 Lung of Triton cristatus, magnified               injected with size and vermilion, form a
about 3 diameters ; a, pulmonary artery;               net-work so minute, that the parenchyma is
b, pulmonary vein.                              only seen in small islets in its interstices.
Fig. 215.
;; :
«j
Portio 
             GENERAL STRUCTURE OF THE RESPIRATORY ORGANS.          575

any other that is known.  The walls of the capillaries, moreover, are much
less distinct than  those  of the systemic  circulation.   These two  conditions
are obviously favourable to  the  exposure of the  largest possible quantity of
blood to the  influence of the air; but as the surface is not an extensive one,
the amount which can be thus exposed at any one time is very limited;  and
the pulmonary artery is in fact one of the smaller branches of the aorta, which
conveys a mixed fluid to the system at  large.

                                 Fig. 217.
 Portion of the lung of a living Triton, as seen under the microscope with the power of 150 diam.; a,
b, pulmonary vein, receiving blood from the large trunk c, and a smaller vessel d.

  757.  In the warm-blooded Vertebrata, which have a complete  double cir-
culation,—namely, Birds and Mammalia,—a much larger extent of- surface is
provided for the aeration of the blood; the whole  current of which is trans-
mitted to the lungs, before circulating again through the  system.   This  in-
crease is provided in Birds, partly by the greater extension of surface in the
lungs themselves,—these  cavities being subdivided by partitions into numerous
smaller chambers, each having pitted walls, and resembling the entire lung  of
a Reptile;—and partly by the addition of  a number  of large  air-sacs, which
are disposed in various parts of the body, and even in the  interior of the long
bones.   Hence  it happens, that the amount of Respiration is greater in  this
class  than in any other;  although the form of the  apparatus is not nearly  so
concentrated as  in the Mammalia ; nor is the mechanism of the chest so well
adapted to a constant exchange of the air contained in its cavities (§ 37).   In
Mammalia the lungs are  proportionally  smaller ;  and  the whole respiratory 
576
OF RESPIRATION.
apparatus is restricted to the thorax: but the minute subdivision of their cavity,
and the mechanism by which a continual  interchange  of air  is provided for,
render them very efficient for their designed purpose.—The  following, accord-
ing  to the latest  researches,  especially those of Mr. Rainey,* appears to be
the nature of the ultimate structure of the lungs in Man and the  Mammalia
in general.  The bronchial tubes  divide and subdivide, like  the branches of a
tree, still retaining  their ordinary characters, until they are no  more than from
l-50th to l-30th  of an inch in diameter;  and  in these the longitudinal  and
annular fibres, together with the  ciliated  epithelium, come  to  an  abrupt  ter-
mination.   Beyond this boundary, the tubular  form of the  air-passages con-
tinued from the  bronchi  is  retained for  some  distance ;  but  it  is gradually
changed by the irregular branching of the passages, and by the  increase of
the number of apertures in  their walls, which lead to the air-cells.   Thus, at
last, each minute division of the air-passages  becomes quite irregular in form ;
air-cells opening  into every  part of it,  and almost constituting its walls; until
it terminates, almost without dilatation, in  an air-cell.   This terminal portion
of the air-passage,  with its  surrounding  cluster of air-cells, may be regarded
as forming a sort of lobule, and as representing the entire lung of a Frog or

                                    [Fig. 218.
  The Larynx, Trachea and Bronchia;, deprived of their fibrous covering, and with the outline of the
Lungs ;  1,1, outline of the upper lobes of the lungs ; 2, outline ofthe middle lobe of the right lung ; 3, 3,
outline of the inferior lobes of both lungs ; 4, outline ofthe ninth dorsal vertebra, showing its relation to
the lungs and the vertebral column ; 5, thyroid cartilage ; 6, cricoid cartilage ; 7, trachea; 8, right bron-
chus ; 9, left bronchus ; 10, crico-thyroid ligament; 11,12, rings of the trachea; 13, first ring of the tra-
chea; 14, last ring of the trachea, which is corset-shaped; 15, 16, a complete bronchial cartilaginous
ring; 17, one which is bifurcated ; 18, double bifurcated bronchial rings; 19,19, smaller bronchial rings;
20, depressions for the course of the large blood-vessels.]
* Medico-Chirurgical Transactions, vol. xxviii. 
STRUCTURE AND DEVELOPMENT OF HUMAN LUNG.
577
[Fig. 219.
  A view ofthe Bronchia; and Blood-Vessels of the Lungs as shown by dissection, as well as the rela-
 tive position of the Lungs to the Heart; 1. end of the left auricle of the heart; 2, the right auricle; 3,
 the left ventricle with its vessels; 4, the right ventricle with its vessels; 5, the pulmonary artery; 6,
 arch of the aorta; 7, superior vena cava; 8, arteria innominata ; 9. left primitive carotid artery; 10, left
 subclavian artery; 11, the trachea; 12, the larynx ; 13, upper lobe of the right lung; 14, upper lobe of the
 left lung; 15, trunk of the right pulmonary artery ; 16, lower lobes of the lungs.  The distribution of the
 bronchia and of the arteries and veins, as well as some of the air-cells of the lungs, is also shown in
 this dissection.]

 other Reptile; the whole lung of the Mammal being  made up of a multitude
 of  such lobules, which are almost exact repetitions of each other.   There is,
 however, this  difference;—that the air-cells in the lung of the Reptile are mere
 sacculated depressions in the walls of the cavity, opening very  freely into it;
 —whilst the air-cells of  each lobule of the lung of  the Mammal are arranged
 around the central  passage  in  such  numbers, that the  outer  ones  can only
 communicate with this passage through the medium of those which are nearer
 the middle of  the cluster.  Those cells which communicate directly with the
 bronchial tubes and intercellular passages, open into  them by large circular
 apertures ; and they are themselves similarly opened into by other cells, which
 again communicate with  others  beyond  them;  so that each of  the openings
 in the air-passage leads to a series of air-cells, extending from it  to the surface
 of the lobule.   These cells have also lateral communications with each other.
 The walls  of  the  air-cells are formed of a very thin and transparent mem-
brane, which  is folded   sharply  at the  orifices of  communication, so  as  to
form a very definite border to them; and the capillary plexus  is  so placed
between the two layers, which form the walls of two  adjacent air-cells,  as  to
expose one of its surfaces each;  by  which provision,  the full influence ofthe
air upon it is secured.
     49 
578
OF RESPIRATION.
  a. It appears from the researches of M. Bourgery,* that the  development of the air-cells
continues in the human subject up to  the  age of thirty, at which time the capacity for re-
spiration is  the  greatest; it subsequently decreases, especially in persons who suffer from
cough,—the  violence of which expiratory effort  frequently causes  rupture of the air-cells,
and thus gradually produces that emphysematous state of the lungs, which is so common in
elderly persons.  The power of increasing the volume of air taken in, by a forced inspira-
tion, is much less in the old person than in the child, though the  average  amount of air in-
spired may be the same; hence the young person possesses a greater capacity of respiration,
as it were, in reserve;  whilst the old  man has little, and is, therefore, unfit for great exer-
tisn.
  b. The Lungs are developed, in the first  instance, as diverticula from the oesophageal tube.
In the Chick, about the fourth day, a little sacculus is described as shooting forth  at its pos-
terior and inferior part; and this  soon subdivides at its lower  part  into two; at the same
time becoming more separated from the tube, by a constriction around the  neck, which soon
elongates so as to form the trachea.  On the fifth or sixth day, the lung of one side is com-
                                          pletely distinct from that of the other, and each
                                          is attached to the common pedicle by a pecu-
                                          liar branch, the future  bronchus.  The upper
                                          portion has much thicker walls than the lower;
                                          and these  appear to contain a large quantity
                                          of vesicular  parenchyma, in which the rami-
                                           fications of the bronchial  tubes  subsequently
                                           extend themselves.  About the  tenth or ele-
                                           venth day  of incubation, these  ramifications
                                           possess nearly their permanent character and
                                           situation.  The first trace of the Glottis  ap-
  First appearance of the lungs ; a, in a Fowl at   pears about the fifth day;  it is  then a mere
four days ; b, in a Fowl at six days ;  c, termina-   slit in the walls of the cesophagus, resembling
tion of bronchus in a very young Pig.            that by which the ductus pneumaticus of some
                                           Fishes, opens into the alimentary canal. The
formation of the cartilaginous rings of the trachea does not commence until after the twelfth
day, when they first appear as transverse  stria? on the median line of the front only; they
gradually become solid, and extend themselves on either side, until they nearly meet at last
on the median line on  the back or vertebral side of the tube.
  c. The history of the process in the Human embryo, appears to be very nearly the same.
The first appearance of the Lungs takes place about the sixth week, at  which time they are
simple vesicular prolongations ofthe oesophageal membrane.  Their surface, however, soon
becomes  studded with  numerous little wart-like projections;  and these are caused  by the
formation of corresponding enlargements of their cavity.  These enlargements soon become
prolonged, and develope corresponding bud-like enlargements from their sides; and  in this
manner,  the form of the organs is gradually changed, a progressive  increase in  their bulk
taking place  from  above downwards, in consequence of the extension of the bronchial ra-
mifications from the single tube at the apex.  At the same time, however, a corresponding
increase  in the amount of the parenchymatous tissue of the lung is taking place;  for this is
deposited in all the interstices between the bronchial ramifications, and might be compared
with the soil filling up the spaces amongst the roots of a tree.   It is in this parenchyma that
the pulmonary vessels  are distributed ; and the portion of it which  extends beyond the ter-
minations of the bronchial tubes, seems to act as  the nidus for their further extension.  It
can be easily shown that, up to a late  period of the development of the lungs, the  dilated
terminations of the  bronchi constitute the only air-cells (Fig. 220, c): but, as already men-
tioned, the parenchyma subsequently has additional cavities formed within it.—It is a  fact
of some  interest, as an example of the tendency of certain diseased conditions to  produce a
return to forms which are natural to the foetal organism, or which present themselves in other
animals,—that up to a late period in the development of the Human embryo, the lungs do
not nearly fill the cavity of the chest,  and the  pleura of each  side contains a good deal of
serous fluid.

   758.  The network of vessels  on the  walls of the air-cells  is  so  minute, that
the diameter of the meshes is scarcely so great  as that of the  capillary ves-
sels  which inclose  them.   According  to Mr. Addison, the  capillaries  in  the
lung of a Toad admit, in their natural state, no more than one,  or  at most two
rows of blood-corpuscles  ; and the  islets of tissue between  them are compa-
* Archives Generates de Medecine, Mars 1843. 
STRUCTURE AND DEVELOPMENT OF HUMAN LUNG.
579
ratively  large ;  whilst, if the lung                Fig. 221.
be  congested or  inflamed, five or
six rows of  corpuscles are seen in
the vessels ;  and the islets of tissue
are  almost  entirely  obliterated.—
The  diameter of the  Human  air-
cells  is  about twenty times  greater
than  that of the  capillaries  which
are distributed upon  their parietes  ;
varying  (according to the measure-
ment of  Weber) from the 1-200th
to the l-70th of  an inch.   It has
been  calculated by M. Rochoux, that
as  many  as 17,790 air-cells  are
grouped  around each terminal bron-
chus  ; and  that their total number  Arrangement of the Capillaries of the air-cells of
amounts to  no  less  than 600 mil-              the Human Lung.
lions.
  759. The fibrous coat of the bronchial tubes possesses a considerable amount
of contractility, which can scarcely be  regarded as otherwise than muscular.
From the experiments of Dr. C.  B. Williams,* it appears  that all the air-
tubes are endowed with  a considerable amount of contractility, which may
be  excited by electrical,  chemical, or mechanical stimuli, applied  to  them-
selves ;  but this is  not so readily excitable through their nerves, although the
experiments  of Volkmann and Longet have clearly shown the possibility  of
thus calling  it into action  (§  410).  This contractility resembles that of the
intestines or arteries, more than that of the voluntary muscles or heart; the
contraction and relaxation being more gradual than that of the latter, though
less tardy than  that of the former.  It is  chiefly manifested in the smaller
bronchial tubes ; since, in the trachea and the larger bronchi, the cartilaginous
rings prevent any decided diminution in the calibre of the tube.   Wedemeyer
did not succeed in producing  any distinct contraction of the  fibres of the tra-
chea  and larger bronchi;  but he states  that  tubes of less than a line in dia-
meter could be perceived to  contract gradually under the stimulus of galva-
nism, until their ca,vity was nearly obliterated. It is remarked  by Dr. Williams,
that the contractility ofthe bronchial muscles  is soon exhausted by the action
of a stimulus; but that it  may in some degree be restored by rest, even when
the lung is removed from the  body.  When the stimulation is long continued,
however, as  by intense irritation  of the  mucous  membrane  during life, the
contractile tissue passes into  a state which  resembles that of the tonic con-
traction of muscular  fibre (§  593).  The  contractility is greatly affected by
the mode of  death, and is remarkably diminished by the action of  vegetable
narcotics, particularly stramonium and belladonna; whilst it seems to be scarcely
at all affected by  hydrocyanic acid.—These  facts  are  very important, as
throwing light upon certain diseased conditions.  It has long been  suspected,
that the dyspnoea of Spasmodic Asthma depends  upon a constricted state  of
the smaller bronchial tubes, excited through the nervous  system, frequently
by a  stimulating cause at some distance;  and there can now be little doubt
that this  is the case.   The peculiar influence of stramonium and belladonna,
in diminishing the  contractility of  these fibres, harmonizes remarkably with
the well-known fact of the relief frequently afforded by them in this distress-
ing malady.
  760.  The  Lungs themselves are to  be regarded, as quite passive in the

      * Athenaeum Report of the  Meeting of the British Association, 1840, p. 802.
 
580                            OF RESPIRATION.
movements of respiration ;  the renewal of their  contained air being accom-
plished by the action of the muscles external to the thorax, or partly forming
its  parietes.   The lung completely fills  the  cavity  of the pleura, in the healthy
state at least; so  that,  when this is enlarged, a vacuum  is produced, which
can only be  filled by a corresponding enlargement  of the  lung;  and to pro-
duce this, the air rushes down the trachea, and passes to the remotest air-cells.

  a. The distension of the whole tissue  of the lung, which is effected in this manner, is
much more complete than that, which could be occasioned by simple insufflation from  the
trachea;—a fact of which it has been proposed to  take advantage in juridical inquiries in
regard to suspected cases of Infanticide, where the  lungs are found to float, and the defence
is set up that the child was still-born, and that  air was blown into the chest for the purpose
of resuscitating it.   It has been ascertained by the  experiments of Mr. Jennings,* that if a
piece of lung,  which has been filled with air  by insufflation, be exposed to  great pressure,
the air may be expelled from it sufficiently to cause it to sink in water; but that no pressure
can produce the same effect upon that which has been filled by a natural inspiratory effort.
It is a serious objection to the use of this test  of juridical  investigations, however, that  the
early inspiratory efforts of the infant are often so feeble, as to produce but a  very imperfect
dilatation ofthe air-cells; so that the lung of an infant which has naturally inspired cannot,
by such means, be distinguished from one that has been artificially inflated.  The fact ascer-
tained by Mr. J., however, is one of much physiological interest.—Owing to the freedom
with which the air enters  the lungs, when  there  is no abnormal obstruction, the external
surface is  always  in contact with the walls  of the chest, so that the  pulmonary and costal
pleurae glide over one  another with every inspiration and  expiration.  The smooth and
moistened character of their surface prevents the movement from producing any sound;  but
it becomes evident when the friction is increased, either by the dryness that is commonly
one of the early changes produced by inflammation, or by the  rough deposit that subsequently
appears.
  b. The complete dependence of the expansion  of the Lungs upon the production of a
vacuum in the  chest, is well shown by the effect of admission of air into the pleural cavity.
When an  aperture  is made on either side, so that the air rushes in at each inspiratory
movement, the expansion of the lung on that side is diminished, or entirely prevented, in
proportion to the size ofthe aperture.  If air can enter through it more readily than through
the trachea, an entire collapse of the lung takes place; and by making such an aperture on
each side, complete asphyxia is produced.  But if  it be too' small to  admit the very ready
passage of air, the  vacuum produced by the inspiratory movement is more easily filled by the
distension of the lungs, than by the rush of air into the pleural cavity; so that a sufficient
amount of change takes place  for the maintenance  of life.  This is frequently observed in
the case of penetrating wounds of the thorax, in  the  surgical treatment of which, it is of
great importance to close the aperture as completely as possible ; when this has been accom-
plished, the air that  had found its way into the cavity is  soon  absorbed, and the lung re-
sumes its full play.  When one lung is obstructed by tubercular deposit, or is prevented in
any other way from  rightly discharging its function, an opening that freely admits air into
the pleural cavity  ofthe other  side, is necessarily attended  with an immediately fatal result;
and in this manner it not unfrequently happens, that chronic pulmonary diseases suddenly
terminate in Asphyxia, a communication being opened by ulceration between a bronchial
tube and the cavity of the thorax.

   761.  The dilatation of the chest during Inspiration, is chiefly accomplished
by the  contraction of the  Diaphragm, which, from the high arch that it pre-
viously formed, becomes nearly  plane;  in this change  of figure, it presses on
the abdominal viscera,  so  as to cause  them to protrude, which they are ena-
bled to do  by the relaxation of  the  abdominal muscles.   In ordinary tranquil
breathing, the action of the diaphragm is  alone  nearly sufficient to produce
the necessary exchange of air;  but,  when a full  inspiration is required,  the
cavity of the chest is dilated laterally, as well as  inferiorly.  This is accom-
plished  by the  Intercostal muscles, the Scaleni,  Serrati,  and others;  which,
by elevating  the  ribs, bring  them and  their cartilages more nearly into  the
same direction, and thus  separate  them more widely from the  median line.
Expiration is chiefly effected by the contraction  of  the  abdominal muscles,
which at the same time force up the diaphragm by their pressure on the vis-

        * Transactions of the Provincial Medical and Surgical Association, vol. ii. 
ACTION OF THE LUNGS IN RESPIRATION.
581
 cera, and depress the ribs; in the latter movement they are  aided by the
 Longissimus Dorsi, Sacrolumbalis, &c, and also by the elasticity of the car-
 tilages of the ribs, with that of the air-cells and air-tubes themselves.
   762. It is difficult to form an estimate by observations on one's self, of the
 usual number and degree of the respiratory movements; since the direction of
 the attention to them is certain to  increase their frequency and amount.   In
 general it may be stated, that from 14 to 18 alternations usually occur  in a
 minute; of these the ordinary inspirations involve but little movement of the
 thorax ; but a greater exertion is made at about every fifth recurrence.   The
 average numerical proportion of the respiratory movements, to the pulsations
 of the  heart, is about 1 to 5 or 4§ ; and when this  proportion  is widely de-
 parted from, there is reason to suspect some obstruction to the aeration of the
 blood, or some disorder of the nervous system.   Thus in Pneumonia, in which
 a greater or less amount of the lung is unfit for its office, the number of respira-
 tions increases in a more rapid proportion than  the acceleration  of the pulse;
 so that the ratio becomes as 1 to 3, or even 1 to 2, in accordance with the de-
 gree  of engorgement.*  In Hysterical patients, however, a similar increase,
 or even  a greater one, may take place without  any serious cause; thus Dr.
 Elliotsont mentions a case, in which  the  respiratory movements of a young
 female, through nervous affection, were 98  or even 106, whilst the pulse was
 104.  On the other hand, the respirations in  certain typhoid conditions and
 in narcotic poisoning become abnormally slow, owing to the torpid condition of
 the nervous centres, the proportion being 1 to 6, or  even 1 to  8; and in  such
 cases, the lungs not unfrequently become cedematous, from the cause formerly
 mentioned (§ 411).
   763. The amount, also, of the Respiratory Movements is affected by  vari-
 ous  morbid conditions ;  thus  when dislocation of the spine takes place above
 the origin of the intercostal nerves, but below that of the phrenic, so that the
 former are paralyzed, the respiratory movement is confined to the diaphragm ;
 and  as this  is insufficient, serum is effused into the lungs, and a slow Asphyxia
 supervenes, which  usually proves fatal in  from three to seven  days.  Even
 where the muscles  and nerves are  all  capable of action, the full performance
 of the  inspiratory movements is prevented, by the  solidification or engorge-
 ment of any part of the lung,  which interferes with its free distension; or  by
 adhesions between  the pleural surfaces, which offer a still more direct impedi-
 ment. When these adhesions are of long standing, they are commonly stretched
 into  bands, by the continual  tension to which they are  subjected.  If the
 impeding cause  affect both sides, the movements of both will be alike inter-
 fered with;  but if one  side only is affected, its movements will be diminished,
 whilst those of the  other remain natural;  and the physician hence  frequently
 derives  an indication of great value, in regard to the  degree in which the  lung
 is incapable of  performing its functions.  It is  to be remembered, however,
 that the action both of the diaphragm and of the elevators of the ribs may  be
 prevented, by pain either in the muscles themselves or in the parts which  they
 move; thus the descent of the diaphragm is checked by inflammation of the
 abdominal viscera or of the peritoneum ; and that of the intercostals by rheu-
 matism, pleuritis, pericarditis, or other painful disorders of the parts forming
 the parietes ofthe thorax (§ 431).
   764.  The capacity of  the Lungs for air varies considerably in different in-
 dividuals ; and as the most complete expiration does  not  by any means empty

  * See a Paper by Dr. Hooker, on the Relation between the Respiratory  and Circulating
Functions, in the Boston (N. E.) Medical and SurgicalJoumal; an abstract of which will be
found in British and Foreign Medical Review, vol. vi. p. 263.
  f Physiology, p. 215. note.
                                   49* 
582
OF RESPIRATION.
them, it is not possible to ascertain it with accuracy.  But the amount which
can be expelled by a forcible expiration, after a full inspiration, may be taken
as a measure of the comparative " capacity of respiration" in different indi-
viduals ;  and the researches of Mr. Hutchinson have shown that, in the state
of health, this bears a very constant proportion to the height.  Thus he found
that the average capacity of men of 5 ft. 7 in.  is about 224 cubic inches, whilst
that of men  of 5 ft. 2  in. is about 173 cubic inches, and that of men of 6 feet,
about 255 cubic inches.   The size of the chest affords no good indication of
the capacity of expiration.  The results  of such  examinations are so  nearly
uniform, that disease  may be suspected  in any man, who cannot blow  out
nearly so many cubic inches as the average of those of the same height;  the
only exceptions among  healthy subjects,  being in the case of fat men, whose
capacity  is always low.—It is obvious from these facts, that the amount of air
ordinarily respired will vary greatly in different individuals ; and this is doubt-
less tme source of the discrepancy of the results of the various  experiments,
which have  been made to determine  this  point.   Some of the most recent  ex-
periments on the subject are those of Mr. Coathupe,* in which the Author has
much reason to feel confidence.  According to his estimate, about 266^ cubic
feet, or 460,224 cubic inches of air,  pass through the lungs of a middle-sized
man in 24 hours; reckoning the average number of inspirations at  16  per
minute, this  would give 20 cubic inches as the amount inhaled at each.


                  2.—Effects of Respiration on the Air.

  765. We  naturally pass from the foregoing inquiries, to those that relate to
the alterations in the Air, which are effected  by Respiration.  These mainly
consist in the removal of a portion of  the Oxygen, and the substitution of a
quantity  of  Carbonic  Acid, rather  less in bulk  than the Oxygen which  has
disappeared.   The proportion of the air thus changed appears to vary accord-
ing to the frequency of the respirations.  Thus Vierordt found that, if  he only
respired  six times in a minute, the quantity of  Carbonic acid was  5*5  per
cent, of the  whole  air exhaled; with  twelve respirations, it was 4"2; with
twenty-four, it was 3'3; with forty-eight, it was 3*0 ; and with  ninety-six, it
was 2*6 per cent.   In some of the. experiments of Messrs. Allen and Pepys,
it was as much as 8 per cent.   Probably about 4  per  cent, may be taken as
the average,  at the ordinary rate of respiration.—It appears, however, from the
researches of the last-named experimenters, that if the air be already  charged
in some  degree with Carbonic acid, the  quantity  exhaled is much less ;  for
when 300 cubic inches  of air were respired for three minutes, only  28| cubic
inches (9| per cent.) of Carbonic acid were found  in it; although the previous
rate of its production, when fresh air was taken in at  every respiration, was
32 cubic inches in a  minute.   Knowing, then, the necessity of a free excre-
tion of carbonic acid,  we are led by this fact to perceive the high importance
of ventilation; for  it is not sufficient for health, that a room should contain the
quantity of air requisite  for the support of its inhabitants during a given time;
since after they have  remained in it but a part of that  time, the quantity of
carbonic acid which its  atmosphere will contain, will be large enough to inter-
fere greatly  with the due aeration of their blood, and will thus cause  oppres-
sion of the brain and  the other morbid affections that result from the accumu-
lation of carbonic acid in the circulating fluid.—On the other hand, it has been
ascertained by the recent experiments of Dr. Boswell Reid that, if the carbonic
acid be removed  as fast as it is formed, an animal may remain in a  limited
quantity of  air, without much inconvenience,  until nearly the whole of its

        * Athenaeum Report of Meeting of the British Association, 1839; p. 707. 
EXCHANGE OF OXYGEN AND CARBONIC ACID.             583
oxygen is exhausted ;—thus showing that the respirability of air does not de-
pend so much upon the proportion of oxygen it contains, as upon its freedom
from contamination with carbonic acid or other poisonous gases.
   766.  The reaction which thus takes place between the Air and the Blood,
is easily explained upon physical principles.  If the Blood come to the Lungs
charged with Carbonic  acid, and is exposed in their cells to the  influence of
atmospheric air, which  is  a mixture of Oxygen and Nitrogen, an endosmose
and  exosmose of gases will take place, according to certain fixed laws.*   The
Carbonic acid of the blood will pass out, to be replaced by Oxygen and Ni-
trogen ; and the quantity of the former which enters will be much greater than
that  of the latter, on account of the  superior facility with which oxygen passes
through porous membranes.   If the venous blood also contain  Nitrogen as
well as  carbonic acid, this also will  pass out, to be replaced by the Oxygen of
the air.   Thus, there will  be a  continual Exosmose of Carbonic acid and Ni-
trogen, and a continual Endosmose of Oxygen and Nitrogen,  The exhalation
and  absorption of Nitrogen appear  usually to balance each other; so that the
amount of this gas in the respired air undergoes little or no change.  But the
case  is  different in regard to  the  exchange of Carbonic  acid and Oxygen.
According to the law of mutual diffusion of gases, the volume of Oxygen that
is taken in,  should exceed that of the Carbonic acid which passes out, in the
proportion of 1174 to  1000.   This  calculation, deduced from the relative
densities of the two gases, corresponds so  closely with the actual results of
experiments upon the respiration of Man, that the interchange may be regarded
as always taking place  in accordance with the law of mutual diffusion;  so
that, from the amount of Carbonic  acid exhaled, the  quantity of  Oxygen ab-
sorbed may be  readily  calculated.!   Now as Carbonic acid contains its own
bulk of Oxygen, it follows that the amount of  Oxygen absorbed exceeds that
which is given off, by 174 parts in  every 1000; so that a quantity of oxygen,
equal to more than one-sixth of that which is converted into  Carbonic acid, is
employed in the system for other purposes.  It appears probable  that a part
of this additional Oxygen is made to combine with Hydrogen furnished by the
food or by the disintegration of the tissues ; and that the water thus generated
forms part of that exhaled from the lungs; whilst another part will be applied
to the oxidation of the  Sulphur and Phosphorus, which are taken in as such
in the food, and which, after forming part of the solid tissues, are excreted in
the condition of Sulphuric and Phosphoric acids,—chiefly through the kidneys.
   767.  The absolute quantity of Carbonic Acid exhaled  from the  Lungs is
liable to variation from so many  sources, that no  fixed  standard  can be
assigned for it.   The   mean of  a  great number of observations,  however,
made in different modes, and under different circumstances,  would give  about
160  grains of Carbon per hour as the amount  set free by  a well-grown  adult
man, under ordinary circumstances.   Taking this  as the average  of  the
twenty-four  hours, the  total quantity of Carbon thus daily expired from  the
Lungs would be 3840  grains, or 8  oz. Troy.   The chief causes of variation
are,—the Temperature  of the  surrounding  medium,  Age, Sex, Development
of the body, state of Health or Disease, Muscular Exertion or Repose,  Sleep
or Watchfulness, Period  of  the Day,  and  state of the  Digestive process.
These will now be considered in detail.
  a.  Temperature of surrounding Medium. — The  amount of Carbonic Acid exhaled  by
warm-blooded animals is greatly increased by external  Cold, and diminished by  Heat; as is
shown by the  following results of comparative experiments upon the quantity set free  by
the same animals, at low, medium, and high temperatures, in periods of an hour (Letellier).
* See Principles of General and Comparative Physiology, §§ 437—9.
f Valentin's Lehrbuch der Physiologie, vol. i., pp. 507-580. 
584
OF RESPIRATION.
                          Temp, about 32°.      Temp. 59°—68°.   Temp. 86°—106°.
                               Grammes.            Grammes.           Grammes.
       A Canary  -    -    -    0-325                0-250                0-129
       A Turtle-Dove  -    -    0-974                0-684                0-336
       Two Mice -    -    -    0-531                0-498                0-268
       A Guinea-Pig   -    -    3-006                2-080                1-453

From this table it appears that the quantity of carbonic acid exhaled by Mammals between
86° and 106° is less than half that set free  near the freezing-point; whilst that which is
exhaled between 59° and 68° is but little more than two-thirds of the same amount.  The
diminution occasioned  by heat is  still more remarkable in Birds; which  exhaled at the
highest temperature scarcely more  than one-third of  that set free at the  lowest.  The ob-
servations of Vierordt upon himself show that the same is true of the Human subject; a
difference of 10° Fahr., according to him, producing a variation of rather more than two
cubic inches in the amount of Carbonic Acid hourly expired.
  b.  Age.—The amount of Carbonic Acid exhaled increases in both sexes up to about the
thirtieth year; it remains stationary until about the forty-fifth;  and then diminishes.  The
following are the comparative  results of experiments  upon males of different ages, and of a
moderate degree of  muscular development (Andral and Gavarret).
	Carbon exhaled		Carbon exhaled
Age.	per hour.	Age.	per hour.
8 years -	77-0 grains	37 years -	- 164-7 grains.
12 "	- 113-9 "	48 "	- 161-7 "
14 "	- 126-2 "	59 "	- 154-0 «
20 "	- 166-3 "	68 "	- 147-8 "
26 "	- 169-4 "	76 "	- 92-4 "
  c. Sex.—At all ages beyond  eight years, the exhalation is greater in Males than  in Fe-
males.  Nearly the same proportionate increase takes place, however, in females, up to the
time of puberty; when the quantity abruptly ceases to  increase, and  remains  stationary so
long as they continue to menstruate.  When, however, menstruation has ceased, the exhala-
tion of carbonic acid begins again to augment; and then again diminishes, with the advance
of years, as in men.   Should menstruation temporarily  cease at any time, the exhalation of
carbonic  acid  immediately undergoes an increase, precisely as at the final cessation of the
function.   And during pregnancy, the exhalation increases in like  manner.   The following
table of the comparative  respiration  of females at different ages, will serve  at the same
time for comparison with the preceding, so as to exhibit the general difference between the
two  sexes, at  ages  nearly corresponding; and also to  indicate the peculiar modifications
induced by the operations of the genital system (Andral and Gavarret).

                      Carbon exhaled            After Cessation of Catamenia.
        Age.             per hour.                              Carbon exhaled
       10 years  -    -  92-4  grains
       13  "    -    -  97-0    «
           During Menstrual life.
       15£ years -    -  97-0  grains.
       26   "   -    -  97-0    "
       32   «   -    -  95-4    "
       45   "   -    -  95-4    "
            During Pregnancy.
       22 years  -    - 129-3  grains.
       32  "    -    - 126-7    "
       42  "    -    - 120-3    "

  d. Development of the Body.—The  more robust the individual,  ceteris  paribus, the more
Carbonic Acid is exhaled;  and the variation is much more influenced by the development
of the muscular system, than by the height^ or weight, capacity of the  chest, &c.   Thus, a
very strong man of twenty-six years of age  exhaled at the rate of 217-1 grains per hour;
when a man of moderate muscular power set free but 169-4 grains in the same time.  An-
other robust man of sixty years of age exhaled at the rate of 209-4 per hour; another of
similar constitution, and sixty-three years of age, at the rate of 190-9 grains  per hour; and
an old man of 92 years, who  still  preserved an  uncommon degree of energy, and* who  in
his younger days had boasted of extraordinary muscular powers, exhaled at the, rate of 135-5
grains per hour.  So also, a remarkably vigorous  young woman of nineteen  years  exhaled
at the rate  of 107-8 grains per  hour; another of twenty-two years, rather less powerful, at
the rate of 103-1 grains; and a strong woman of forty-four years (who had ceased to men-
struate) 152-4 grains.—On  the other hand, a  slender man of  forty-five years, in the enjoy-
Age.	per hour.
38 years -	- 120-3 grains
49 "	- 113-9 "
52 «	- 115-5 "
56 "	- 119-3 "
66 «	- 104-7 «
76 "	- 101-4 "
82 "	- 92-4 "
 
AMOUNT OF CARBONIC ACID EXHALED.
585
ment of good  health, only exhaled at the rate of 132-4  grains per hour (Andral and  Ga-
varret).
  e.  State of Health or Disease.—Upon this very important cause of variation, few accurate
researches have yet been made.  The per  centage of carbonic acid in the expired air has
been found to be unusually great in  the  Exanthemata, and  in chronic skin diseases (Mac-
gregor) ;  and it has been stated to be diminished in typhus (Malcolm).—Thus, the  average
proportion in  health being about 3-96 per cent. (Prout), it has been seen at 8 per  cent, in
confluent  small-pox, at 5 percent, in measles, and at 7-2 per cent, in a severe case of icthyosis
which terminated  fatally; whilst in  Typhus the per centage has been found  to range from
1-18 to 2-50.  But  these statements do not indicate the total quantity exhaled in each case.—
The remarkable increase of  the exhalation in  cases of Chlorosis, has been already noticed;
in four cases recorded by Hannover, the hourly expiration was 1236, 1186, 1169, and 106-3
grains,—the absolute quantity diminishing as the respirations increased in rapidity.—In chronic
diseases of the respiratory organs, as might be  anticipated, the amount of Carbonic acid ex-
haled  undergoes a sensible diminution (Nysten  and Hannover).—Further researches  are
much needed on this subject; but, for obvious reasons, they cannot be readily made in severe
forms of disease.
  /.  Muscular  Exertion or Repose.—The effect of bodily exercise, in moderation, is to produce
a considerable increase in the amount of  carbonic acid exhaled, both during its continuance,
and for some little time  subsequently to its cessation.  According to the observations of Vie-
rordt, the  increase  amounts to one-third of the  quantity exhaled during rest; and it lasts for
more than an hour afterwards, being manifested in the greater quantity of air respired, and
in the  larger per centage of carbonic acid  contained in it.   If  the exercise be prolonged,
however,  so as to occasion fatigue, it is succeeded by a diminished exhalation.—The connec-
tion  between  muscular  exertion and the exhalation of carbonic acid, is most remarkably
shown in Insects;  in which animals we may witness  the rapid transition between the op-
posite  conditions of extreme muscular exertion, and tranquil repose; and in which the effects
of these upon the  respiratory process are not  masked  by that exhalation of carbonic acid,
which is required  in warm-blooded animals  simply for the maintenance of a fixed tempera-
ture.   Thus a Humble-Bee has been found to produce one-third of a cubic inch of carbonic
acid, in the course  of a  single hour, during which its whole body was in a state of constant
movement, from the excitement resulting from  its capture; and yet, during the whole twenty-
four hours of the succeeding day, which it passed in a state of comparative rest, the quantity
of carbonic acid generated by it was  absolutely less.
   g. Sleep or Watchfulness.—The amount of carbonic acid exhaled during sleep is considera-
bly less than that  set free in the waking state.   This is particularly shown by the experi-
ments of ^charting; who confined the  subjects  of them in an air-tight chamber, within
which they could sleep, take their meals, &c.  Thus in one case, the hourly exhalation sank
from 160  to 100, in another from 194-7 to 122-3, and in another from 99 to 75-1.   The cause
of this result is partly to be  sought in the cessation of all muscular exertion (save that con-
cerned in the maintenance of the respiration) ;  and partly in the diminution in the dissipa-
tion of the heat of the body itself.
  h. State of the Digestive Process.—It  is well established, that  the exhalation of carbonic acid
is greatly  increased by eating, and that it is diminished  by  fasting.  Thus Prof. Scharling
states the  hourly exhalation to have increased in one instance from  145  to 190, after break-
fast and a walk; in another from 140 to 177  after breakfast alone; and in another from 111-9
to  188'9, after dinner.  It is  remarkable that alcoholic drinks have a tendency to diminish the
exhalation of carbonic acid, especially when  taken into an empty stomach; and strong tea is
said to have the same effect  (Prout, Vierordt).—The quantity  is also increased by exhilarating
emotions, and  decreased by depressing affections of the mind (Prout).
  i. Period of  the Day.—Independently of these variations, which  have their source in the
condition of the individual, there appears to be a slight tendency  to increase in the quantity
of carbonic acid exhaled during the early part  of the day, and a  steady decrease  during the
afternoon; so that,  in the evening the quantity is decidedly less than in the morning.   It is
very difficult to separate the  effects of this influence, however, from those of the causes pre-
viously adverted to.

   768.  The aeration of the  blood may take  place,  not only by means of the
Lungs, but also  through the medium of the Cutaneous  surface.   In some of
the  lower tribes of  animals, indeed,  this  is  a  very important  part of their
respiratory process :  and even  in some Vertebrata,  the cutaneous  respiration
is  capable of supporting life for  a considerable time.   This  is especially the
case  in  the  Batrachia, whose skin is  soft, thin, and moist;  and the effect is
here the greater, since the blood which  circulates through the system is, from 
586
OF RESPIRATION.
the small proportion of it that has passed through the lungs, very imperfectly
arterialized.  By the experiments of Bischoff it was ascertained that, even
after the lungs of a Frog had been removed, a quarter of a cubic inch of car-
bonic acid was exhaled from the skin, during eight hours.  Experiments which
have been made on the  Human subject leave no room for doubt, that a similar
process is effected through  the medium of his general surface;  for, when a
limb has  been inclosed  for some hours in an air-tight vessel containing atmo-
spheric air freed from carbonic acid, a sensible  amount of this gas has been
found to be generated.  Moreover, it has been observed not unfrequently, that
the livid tint of the skin which supervenes in Asphyxia, owing to  the non-
arterialization of the blood in  the lungs, has given  place  after death to the
fresh hue of health, owing  to  the reddening of the  blood in  the cutaneous
capillaries by the action of the atmosphere upon them.  We have no means
of ascertaining the usual amount of  carbonic acid excreted through the Skin,
except by determining the whole quantity disengaged from  the body, and sub-
tracting the portion exhaled from the lungs; and no sufficiently precise experi-
ments upon this subject have yet been made.   The  only way to separate the
results of the pulmonary and cutaneous exhalation of carbonic acid, would be
to confine the body in a close chamber, into which the product of the cutaneous
respiration might freely pass;  whilst the  pulmonary respiration during the
same period should be measured  by a distinct apparatus.  It is not improbable
that, in cases of obstruction to the  due action of the lungs, the exhalation of
carbonic acid through the skin may  undergo  a considerable increase; for we
find a similar disposition to vicarious action in other parts  of the excreting
apparatus.  Moreover, there is evidence, that the interchange of gases between
the air and the blood, through the skin, has an important share in keeping up
the temperature of the  body (Chap, xvi., Sect. 2);  and we find the tempera-
ture of the surface much  elevated in many cases of pneumonia, phthisis, &c,
in which the  lungs seem to perform their function very insufficiently.

                3.—Effects of Respiration on the Blood.

   769. That an important change is effected in the character of the Blood, by
exposure to Atmospheric  air in the lungs, has been known, from  the time
when it was first ascertained that it is  regularly transmitted  to those  organs.
The most obvious part of this change is the alteration in its colour, from the
dark purple of the venous fluid,  to the rich crimson of the arterial.  But this
alteration is only the index of changes far  more important, which occur in its
chemical constitution.   Respecting  the nature of these  changes,  there has
been, as  formerly stated, much difference of opinion;  some maintaining that
the carbonic acid exhaled is formed  in the  lungs;  and others,  that it is  con-
tained in the  venous blood, and is truly excreted from it.   The latter opinion,
which was long since  brought forward by La Grange and  Hassenfratz, has
recently obtained such  full confirmation, from the experiments of Spallanzani,
Edwards, Muller, Bischoff, Magnus, and others, as  to  have  a  full claim for
adoption as a physiological truth.  These  experiments are of two kinds ; first,
those which show that an exhalation of carbonic acid may  continue for a long
time, when the animal is breathing an atmosphere in which no oxygen exists;
and, secondly, those which prove that much more  carbonic acid exists in an
uncombined state in venous blood than in  arterial, whilst  more oxygen exists
in a similar condition in arterial blood than in venous.  The results of these
will now be briefly stated.—It was  shown by Spallanzani, that Snails might
be kept for a long period in Hydrogen, without apparent injury to them; and
that during this period they disengaged a considerable amount of Carbonic
acid.   Dr. Edwards subsequently ascertained  that,  when Frogs were kept in 
                 EFFECTS OF RESPIRATION ON THE BLOOD.               587

hydrogen for several hours, the quantity of carbonic acid exhaled was fully as
great as it would have been in atmospheric air, or even greater; this latter fact,
if correct, may be accounted for, by the superior displacing power, which (on
the laws of the diffusion  of gases) hydrogen  possesses  for  carbonic acid.
Collard de Martigny repeated this experiment in nitrogen, with the same re-
sults.  In both sets of experiments, the precaution was used of compressing
the flanks of the animal, previously to immersing it in  the gas, so as to expel
from the lungs whatever mixture of oxygen  they might contain.   These ex-
periments have been since repeated by Muller and Bergemann, who took the
additional precaution of removing, by means of the  air-pump, all the atmo-
spheric air that the lungs of the frog might previously contain, together with the
carbonic acid that might exist in the alimentary canal.  They found in one of
their experiments, that the quantity of carbonic acid exhaled in hydrogen  was
nearly a cubic inch in 65 hours;  and  in another, that nearly the same  amount
was given off in nitrogen ; but this required rather a longer period.  It appears
from the table of their results,* that the amount was not ordinarily greater in
the experiments which  were  prolonged  for twelve or fourteen hours,  than in
those which were terminated in half the time ;  hence it may be inferred,  that the
quantity which the blood is itself capable of  disengaging is limited, and  that
the absorption of oxygen is necessary to enable carbon  to be set free from the
tissues.—It is impossible, however, for an adult Bird  or Mammal to  sustain
life for any  considerable time, in an atmosphere deprived of oxygen; since the
greatly-increased rapidity and energy of all  their vital operations, necessitate
a much more constant  supply of this vivifying agent,  than is needed by the
inferior tribes; and, as  we sball  presently see, the capillary action necessary
for the passage of the blood  through  the lungs will not take place without it.
But Dr. Edwards  has  shown, that young Mammalia can sustain life in an
atmosphere of hydrogen or nitrogen, for a sufficient length of time to exhale a
sensible amount of carbonic acid ; so that the character of the process is clearly
proved to be the same in them, as in  Reptiles and Invertebrata.
   770.  That the changes which Venous Blood undergoes  in the lungs, are to
be explained upon principles of a purely chemical  and  physical nature, is evi-
dent from the fact, that the same changes  will take place when it is exposed
to the air out of the body, even through the medium of a thick membrane, such
as a bladder.  Such changes, however, only affect the surface of the fluid; but
this is exactly what we should expect, since  the air has no access to the  part
beneath.  The Blood, whilst  circulating through the capillaries of the Lungs,
is divided into an innumerable multitude of  minute streamlets, each so small
as  to  admit but a  single layer of its corpuscles;  and  in these, therefore, the
surface which is placed in contact with the air is so enormously extended, as
to be  almost beyond calculation.  Hence, then, we can  at once understand
how such a change may be  instantaneously effected  in it, as would  occupy
several hours, when the blood is  less  advantageously exposed to the influence
of oxygen.—In studying the nature of these alterations, it is very necessary
to ascertain whether Oxygen and Carbonic Acid exist in  a  free state in the
Blood; and  to what extent their proportions differ in Venous and  Arterial
blood.   The late  researches  of Professor Magnus have  shown  that Blood
possesses a very remarkable  absorbing power for these gases, especially for
Carbonic acid.   By freely exposing  it to the  latter gas,  it was found that it
could  take up as much as 1| times its bulk;  and that after  all its Oxygen and
Nitrogen had been thus displaced, it could  still absorb as much as 16 per
cent, of its volume of Oxygen, and 6*3 of Nitrogen, on  being exposed to those
gases  respectively.   The usual quantity of Oxygen present in arterial blood
* Muller's Physiology, p. 341. 
588
OF RESPIRATION.
is, according to the experiments of Magnus, about 10  per cent.; but  while
passing through the systemic capillaries, this is diminished about one-half, so
that Venous  blood does not contain more than 5 per cent, of its volume of
Oxygen.   On the other hand, the Carbonic acid of Arterial blood is  about 20
per cent, of its volume; and this proportion is increased in Venous  blood to
nearly 25 per cent.  The amount of Nitrogen varies considerably, being some-
times  as little  as  1*7  per  cent, of the volume of the blood, and  sometimes
nearly double that proportion; it does not appear to  differ, according to any
constant law, in arterial and venous blood.*
  771. There can be little doubt, then, that the changes which the function
of Respiration  effects in the Blood have reference in  great part to the relative
proportions of  the  different gases, which it holds in solution.   And  although
it might appear that the change of colour, which the Red Corpuscles  undergo,
is a proof of a change of composition in the  Haematine which they contain,
yet such a supposition  is not borne  out by experiment; for no difference of
composition has been detected, between the Haematine of Venous and that of
Arterial blood ;  and it appears from the researches of Peligot on the  action of
the protoxide of nitrogen upon solutions of the salts  of the protoxide of iron,
that liquids may have their colour changed by the  absorption of gases, which
form no chemical  union with them.—There seems reason to conclude, how-
ever, from the statements formerly quoted (§ 115)  in regard to the difference
between the Fibrine of Venous and that of Arterial  blood, that Oxygen derived
from the inspired  air enters  into actual combination with this element; and
the  same may very probably be true of other constituents of  the blood:—so
that we are to regard the influence of Respiration as partly exerted in modify-
ing  the proportions of the gases dissolved in the blood, substituting Oxygen
for a portion of its Carbonic Acid; and partly in enabling  the  ingredients of
the  liquid to enter into new combinations with the Oxygen of the air.   For
the  reasons  formerly stated (§ 150) it appears probable that,  whether or not
their Hsematine be chemically affected by  the change, the Red Corpuscles are
the chief carriers of the two gases to  be interchanged, between the pulmonary
and systemic capillaries.
  772. Although the alteration in the relative proportions of Oxygen  and Car-
bonic acid which it contains, is doubtless the  essential change effected in the
Blood by the Respiratory  process, the  alteration in its colour is the  most ob-
vious;  and this is, under ordinary circumstances, an indication that  the other
change has taken place. Thus, if Arterial blood be exposed, out of the body,
to carbonic acid, it will acquire the  dark hue of venous blood; and Venous
blood  exposed to  it becomes  darker still.  On the  other hand,  if Venous
blood be exposed to Oxygen, it acquires the Arterial hue.   The presence of a
certain amount of saline matter appears, from the experiments of Dr. Stevens
and others, to be a condition necessary for the due influence of oxygen upon
the colour of the blood; since, if it be deficient, the contact  of oxygen will not
produce its  usual  effect.   On the other  hand, the addition of saline  matter
(especially nitre) will occasion a decided change of hue in venous blood, with-
out any extrication of  carbonic acid or absorption of oxygen.

  * For the latest researches of Prof. Magnus, which have had their origin in the objections
of M. Gay Lussac to  those previously published by him, see the Annalen der Physik und
Chemie, vol. lxvi., p. 177, and an Abstract in the Philosophical Magazine, Dec. 1845, Suppl.
In these researches, far greater  success was obtained in removing the gases from the blood,
than in any previous  experiments; and the account of their proportions, therefore, is more
satisfactory.  It is extremely difficult to avoid all sources of error, in such researches; but
the constancy of the results obtained by Magnus indicates that we may place much  confidence
in them. 
ABSORPTION THROUGH THE LUNGS.
5^9
   a. It has recently been attempted, by Mulder and others, to account for the change of hue
 under the influence of carbonic acid, oxygen, and saline matter, by a change of form in the
 red corpuscles; which are supposed to be bi-concave and reflecting in bright coloured blood,
 and bi-convex and refracting in blood presenting the venous tint.  But the supposition is not
 borne out by minute and careful observations on the forms of the corpuscles, nor by varied
 experiments on the effects of re-agents.  As Dr. G. 0. Rees has shown, the blood-corpuscles
 maybe changed in  form, without  any consequent change of colour; whilst, on the other
 hand, the blood is reddened by saline solutions, whether they produce endosmose or exos-
 mose in the red corpuscles, thus either filling or emptying them, and rendering them either
 bi-convex or bi-concave.

   773. Exhalation  and Absorption by the Lungs.—The  alteration  in the
 proportions of its usual gaseous ingredients,  is by no means the only change
 which the Blood  undergoes  in the Lungs.   It parts also, with a considerable
 amount of water, in  the form  of vapour;  this usually contains a certain pro-
 portion of animal  matter; and  it is sometimes charged with volatile substances,
 which have been elsewhere  introduced into the blood, or  which have been
 formed during its assimilation.  It may  also absorb from the  atmosphere vola-
 tile matter diffused through it.  Both these  changes are probably to be ex-
 plained upon simple physical  principles; being dependent on the exposure  of
 the  blood  to the atmosphere, over a very  extensive surface,  and  through a
 membrane  of great  permeability.  Of  the  fluid  ordinarily exhaled with the
 breath, a part doubtless proceeds from the moist lining of the nostrils, fauces,
 &c.;  but  it is  indisputable that the greater proportion of it comes from the
 lungs, since, when the respiration is entirely performed through a canula intro-
 duced into the trachea, the amount of watery vapour which the breath contains,
 is still very considerable.  The quantity which thus passes off is by no means
 trifling; probably between 16 and 20 ounces in the  twenty-four hours.  It is
 not so liable to variation under the influence of temperature,  the movement  of
 the  surrounding air, and other  similar  causes, as is  the cutaneous transpira-
 tion ;  for  air, which has  found its way into the air-cells  of the  lungs, is,
 under almost all circumstances, nearly the same in regard to such conditions,
 and becomes charged with that amount  of watery vapour which saturates it  at
 the temperature of the body.   It is considered by Dr. Prout, that the principal
 source of  this vapour is not the blood properly so called, but the chyle and
 lymph which have just been introduced into it from the thoracic duct;  a loss
 of a portion of their fluid being required, to give  them sufficient concentration.
 A process very analogous takes place in Plants; for a very large proportion of
 the water taken up in the crude  sap, is  parted with in the leaves.   But it  is
 probable that a part, at least, of the water thrown off by the lungs is generated
 by the union of Oxygen and Hydrogen  during the course of the Circulation.
   774. The fluid thrown off from the Lungs is  not  pure  water.  It  holds in
 solution, as might  have been expected, a considerable amount of carbonic acid,
 and also some animal matter;  the exact nature of the latter, which, according
 to Collard  de  Martigny, constitutes about 3 parts in 1000, has not been ascer-
 tained.   If the fluid  be  kept in a closed  vessel, and be exposed to an elevated
 temperature, a very evident putrid odour is exhaled by it.  Every one knows
 that the breath, itself has, occasionally in  some  persons, and constantly in
 others, a fetid taint;  when this  does not proceed from carious teeth, ulcerations
 in the  air-passages, disease in the lungs, or other similar causes, it must result
 from the excretion of the odorous matter, in combination with watery vapour,
 from the pulmonary surface.  That this is the true account of it seems evident,
 from the analogous phenomenon of the excretion of turpentine, camphor, alco-
hol, and other odorous substances, which have been introduced into the venous
 system, either by  natural absorption, or  by direct  injection; and also from the
suddenness with which it manifests  itself,  when the digestive apparatus  is
slightly disordered.
     50 
590
OF RESPIRATION.
  775.  The  Lungs are capable, under peculiar  circumstances, of absorbing
fluid from the atmosphere.  Thus Dr. Madden* has shown that, if the vapour
of hot water be inhaled for some  time together, the loss by exhalation  is  found
to be so much less than usual, as to indicate that the cutaneous transpiration
is partly counterbalanced by pulmonary absorption; the pulmonary exhalation
being at the same time entirely checked.  It is probable that, if the  quantity
of fluid in the blood had been previously diminished by excessive sweating,
or by other copious fluid secretions, the pulmonary absorption would have
been much greater.   Still in the cases formerly mentioned (§ 678), in  which
a large  increase in weight could only be accounted for on the supposition of
absorption of water from the atmosphere, it seems probable that the cutaneous
surface  was chiefly concerned: for it can only be  when the air introduced into
the lungs is saturated with watery vapour, that the usual exhalation will  be
checked, or that any absorption  can take place.
  776.  That absorption of other volatile  matters diffused through the  air is,
however,  continually taking  place by the lungs, is easily demonstrated.  A
familiar example, is  the effect of the inhalation of the vapour  of Turpentine
upon the  urinary excretion.  It can only be  in this manner that those gases
act upon the system, which have a noxious  or poisonous effect, when min-
gled in  small quantities in the atmosphere.  Of these, Sulphuretted Hydrogen
is one of  the most powerful in  its action ; for it has been found that air im-
pregnated with l-1500th part of it, will kill a bird  in a very short time ; and
that  a quantity but little more than double, namely l-800th part, will soon kill
a dog.  This gas is  exhaled in  large  quantities  from many forms  of decom-
posing animal and vegetable matter; and  it has recently been shown  (by Pro-
fessor Daniell) to be absorbed by the water of the estuaries of those African
rivers, whose mouths are regarded as  among the  most pestilential spots upon
the surface of  the globe.—Carburetted hydrogen is another gas whose  effects
are similar ;  but a larger  proportion is required to destroy life.—Carbonic
acid  gas, also, appears  to  be absorbed by the lungs, when a large proportion
of it  is  contained in the atmosphere.   The accumulation of this gas in the
blood, when the respired  air is charged with it even  to a moderate amount,
might be attributed to the impediments thus offered to its ordinary exhalation:
but the  following experiment appears to prove, that it may be  actually  absorbed
into  the blood; and that it will thus exert a real poisonous influence, and not
merely  produce an asphyxiating effect.  It  was found by Rolando, that the
air-tube of one lung of the land-tortoise may  be  tied,  without  apparently
doing any material injury to the animal, as the respiration performed  by the
other is sufficient to maintain life for some time ; but, having contrived to make
a tortoise  inhale carbonic acid by one lung, whilst it breathed air by the other,
he found  that the  animal died  in a  few hours.t—Cyanogen  is another gas
which has an  actively-poisonous influence upon  animals, when absorbed into
the lungs; its agency,  also, is of a narcotic character.
  777.  It is singular that the effects of the respiration of pure Oxygen  should
not be dissimilar.   At  first, the  rapidity of the  pulse and the number of  the
respirations are increased, and the animal appears  to suffer little or no  incon-
venience for an hour;  but symptoms of  coma then gradually develop  them-
selves, and death  ensues  in  six, ten, or  twelve  hours.  If the animals  are

  * Prize Essay on Cutaneous Absorption, p. 55.
  f The fatal result of breathing the  fumes of charcoal is, therefore, not simple asphyxia,
such as would result from  breathing hydrogen or nitrogen.  Other volatile products are set
free in the combustion of  charcoal, besides carbonic acid.  Mr. Coathupe  (loc.  cit.) states
these to be Carbonate, Muriate  and Sulphate of Ammonia, Carbonic Oxide, Oxygen, Nitro-
gen, Watery vapour, and Empyreumatic Oil:  to these Sulphurous acid may appear to be
properly added. 
EFFECTS OF SUSPENSION OF RESPIRATION.
591
removed into the air before the insensibility is considerable, they then quickly
recover.  When the  body is  examined, the  heart is seen beating strongly
while the diaphragm is motionless; the whole blood in the veins, as well as
in the arteries, is of a bright scarlet colour;  and several  of the membranous
surfaces have the  same  tint.  The blood is  observed to coagulate with re-
markable rapidity ;  and it is to the alteration  in its  properties, occasioned by
the hyper-arterialization,  and indicated by  this condition, that we  are proba-
bly to attribute the fatal result.   There can be no doubt that in this instance
an undue amount  of oxygen is absorbed ; and it does not seem unlikely that
one cause of the fatal result, is a stagnation of the blood in the systemic capil-
laries, consequent upon the want of sufficient change in its condition.—When
Nitrogen or Hydrogen is breathed, for any length of time, death results from
the deprivation of Oxygen, rather than from  any deleterious influence which
these gases  themselves  exert.—Death  is  also  caused by the inhalation  of
several gases of an irritant character, such as  Sulphurous, Nitrous, and Muria-
tic  acids:  but it is doubtful how far they  are absorbed;  or  how far their
injurious  effects  are due to the abnormal action, which they excite  in  the
lining membrane of the air-cells and tubes.—It cannot be doubted, that mias-
mata  and  other morbific agents diffused through the atmosphere, are  more
readily introduced into  the system through  the pulmonary surface than by
any other;  and our aim should therefore be directed to the discovery of some
counteracting agents,  which can  be  introduced  in the same manner.   The
pulmonary surface affords a channel for the introduction of certain medicines
that can be raised in vapour, when it is desired to affect the system  with them
speedily and powerfully ; such are iodine, mercury; tobacco, stramonium, &c.

                 4.—Effects of Suspension  of Respiration.

   778. We have now to consider  the results of the cessation ofthe Respira-
tory function, and the  consequent retention of carbonic acid in the blood.   If
this be  sufficiently prolonged, a  condition  ensues, to which the name  of
Asphyxia has been given;  the essential character of which is  the cessation
of muscular movement, and shortly  afterwards of the circulation ; Math an
accumulation of blood in the venous  system.   The time which is necessary
for life  to be destroyed by asphyxia varies much, not only in different animals,
but in different states  of  the same.  Thus  Warm-blooded animals  are  much
sooner asphyxiated than Reptiles or Invertebrata; on the other hand, a hyber-
nating Mammal supports life for many months, with a respiration  sufficiently
low to produce speedy asphyxia if it were  in a state of activity.   And among
Mammalia and Birds,  there  are many species which are adapted, by peculiari-
ties of conformation, to sustain a deprivation  of  air for much more than the
average period.*   Excluding these, it may  be stated as a general fact, that, if
a warm-blooded animal in a state of activity be deprived of respiratory power,
its muscular movements  (with the  exception  of the contraction of the heart)
will cease within five  minutes,  often  within  three ;  and that the  circulation
generally fails within ten minutes.   Many persons, however, are  capable of
sustaining a deprivation  of  air for  three, four, or even five minutes,  without
insensibility or any other injury; but this  power, which  seems possessed to

  * Thus, the Cetacea contain far more blood in their vessels, than  do any other Mamma-
lia ; and these vessels are so arranged that both arteries and veins are in connection with
large reservoirs or diverticula.  The reservoirs belonging to the former are usually full; but
when the Whale remains  long under water,  the blood which they contain is  gradually in-
troduced into the circulation, and, after becoming venous, accumulates in the reservoirs con-
nected with  the venous system.   By means of this provision, the Whale can remain under
water for more than an hour. 
592
OF RESPIRATION.
the greatest degree by the divers of Ceylon, can only be acquired by habit.
The period during which remedial  means may be successful in restoring the
activity of the vital and animal  functions, is not, however, restricted  to this.
Cases are not unfrequent, of the revival of drowned persons after  a submer-
sion of  half an hour;  and more than one has been credibly recorded, in which
above three-quarters of an hour had elapsed.  It is not improbable, however,
that in some of these  cases a state of Syncope had  come on at the moment
of immersion, through the influence of fear or other mental  emotion, concus-
sion of  the brain, &c.; so that, when the  circulation was thus enfeebled, the
deprivation of air  would not  have  the same injurious  effect, as  when this
function was  in full activity.   The  case would then  closely resemble  that of
a hybernating animal; for in  both  instances the being  might be  said  to live
very slowly, and would therefore not require the usual amount of vital stimuli.
The condition of the still-born infant is in some respects the same;.  and re-
animation has been successfully attempted, when nearly half an  hour had
intervened between birth and the employment of resuscitating means, and when
probably a much longer time  had elapsed from  the period of the suspension
of the circulation.
  779.  It has now been sufficiently proved, both by experiment  and  by pa-
thological observation, that  the  first effect  of the non-arterialization  of the
blood in the lungs, is  the retardation of the fluid in  their capillaries (§ 738);
of which  the accumulation in  the venous system, and the deficient supply to
the arterial, are the necessary  consequences.  It is  some time, however, be-
fore a complete stagnation takes place from  this cause: since, as  long as the
proportion of oxygen which remains in the air in the lungs is considerable,
and  that of the  carbonic acid is small, so  long will some  imperfectly-arte-
rialized  blood find  its  way back to the heart, and be  transmitted to the system.
This blood will have a depressing influence upon the  functions of the brain
and of the muscular system; which influence is aided by the diminution that
gradually  takes place, in the quantity of blood propelled through  the  aorta ;
and the actions of the  respiratory muscles and  of the heart will therefore
soon become  enfeebled.   The  cessation of the  heart's contraction  is  due to
two  distinct causes, acting on  the two sides ; for on the right side it is the
result of the over-distension of the walls of the ventricle, owing to the accu-
mulation of venous blood; and on  the left  to deficiency of the stimulus ne-
cessary to excite the movement.  The property of  contractility is not  finally
lost, nearly as soon as the movements  cease;  for the action of the right ven-
tricle may be renewed, for some  time after it has ceased, by withdrawing a
portion  of its contents,—either  through  the pulmonary artery, their  natural
channel,—or, more directly, by an opening  made in its own parietes,  in the
auricle,  or in  the jugular vein ( § 723, c).  On the other hand, the left ventricle
may be again  set in  action,  by renewing  its appropriate stimulus of  arterial
blood.   Hence, if  the stoppage of the circulation have not been of too long
continuance, it may be renewed by artifical respiration : for the replacement
of the carbonic acid by oxygen in the  air-cells of the lungs, restores  the cir-
culation through the pulmonary capillaries ;  and thus at the same time relieves
the distension of the right ventricle and conveys to the left the due stimulus to
its actions.
   780.  Of the mode  in which the pulmonary circulation is stagnated by the
want of oxygen, and renewed  by its ingress into the lungs, no other explana-
tion can be given, than that which has been heretofore offered of the capillary
circulation in general;—namely, that the performance of the normal reaction
between the blood  and the  surrounding medium  (whether this be air, water,
or solid organized  tissue) is  a  condition necessary to the regular  movement 
               GENERAL VIEW OF THE PROCESS OF NUTRITION.            593

of the blood through the extreme vessels.*  This view has recently obtained
additional support from the experiments of Dr. J. Reid on the Respiration of
Azote.t  He found that, when the ordinary respiration of an animal is inter-
rupted, and the Asphyxia is proceeding to the stage of insensibility, the first
effect upon the arterial system is an increased distension  (as indicated by the
haemadynamometer), even  although the blood  is at that time nearly venous in
its character ; this indicates that the fluid, now so perverted, is unable to pass
with facility through the systemic capillaries, in consequence of its not being
in a state fit for the performance of its normal actions.  As the stagnation in
the pulmonary capillaries  becomes  more complete,  however, less and less
blood is returned from  the lungs to  the heart;  and, the systemic arteries
being gradually unloaded without being  refilled, the  pressure  of the  blood
upon their  walls  diminishes, and is at last no longer  experienced.  Its dimi-
nution is not arrested by causing the animal to breathe nitrogen, although the
respiratory movements are renewed,—thus proving that the stagnation of the
blood in  the capillaries of  the lungs is not due (as some  have supposed) to a
mechanical  impediment: but the  pressure is immediately increased by the
admission of atmospheric air, which occasions the renewal of the pulmonary
circulation, and the consequent increase in the supply of  aerated blood to the
systemic arteries.—It has  been shown by Mr. Wharton Jones,:); that the ca-
pillary circulation in a frog's foot is retarded  or  even checked, by the  direc-
tion of a stream of carbonic acid gas against the membrane ; and he attributes
this stagnation to the disposition thus  produced in the red corpuscles, to ag-
gregate together and to adhere  to the walls of the vessel, so as to choke up
its calibre.
                         CHAPTER  XIV.

                              OF NUTRITION.

    1.—General Considerations.—Selective Power of Individual Parts.

   781. The function of Nutrition, considered in the widest acceptation of the
term, includes the whole series of processes, by which the fluid alimentary
materials,—prepared by the Digestive process, introduced into the system by
Absorption, and carried into its penetralia  by the Circulation,—are converted
into Organized tissue;  by which  conversion it is caused to  manifest a set of
properties  altogether new, which, being neither Physical nor Chemical, are
termed Vital.   Thus Albumen, which is a perfectly dead or inert  substance,
and of which the distinguishing properties  are entirely attributable to its pecu-
liar composition, is transformed by the Nutritive process into Muscular Fibre,
possessed of the remarkable Vital  property of Contractility.—But this  process
of conversion commences in the nutritive  materials whilst they are still  in  a
fluid condition, and are moving through the vessels; for we have seen that, at
this stage  of the  operation, the unorganizable Albumen is  transformed  into

  * For a fuller discussion of the Pathology of Asphyxia, see the Author's essay on the sub-
ject in the Library of Practical Medicine, vol. iii.
  f Edinb. Med. and Surg. Journal, April  1841.
  j British and Foreign Medical Review, vol. xiv., p. 600.
                                   50* 
594
OF NUTRITION.
Fibrine,—a substance which possesses a tendency to spontaneous organization,
and which must be regarded as endowed with Vital properties.  It is convenient
to speak of it, therefore, under a distinct designation; and the term Assimilation
has been  applied to it.  In its more restricted  sense, the term Nutrition  is
applied to the growth of the various  tissues of the body, at the expense of the
materials  prepared by the Assimilating process, and supplied by the Circu-
lating current.
   782. It appears evident, from what has been formerly stated  (Chap, in.),
that the process of Nutrition mainly consists in the growth of the individual
cells  composing  the fabric; and that  these  derive  their  support  from the
organic compounds  with  which they are supplied by the  blood, just as the
cells composing the  simplest Plants  derive theirs from the inorganic elements
which surround them.  And as different species ofthe  latter  select  and com-
bine these in such  modes  and proportions  as  to give rise to  organisms  of
very diversified forms and  properties, so is it easily intelligible  that the dif-
ferent parts of the fabric of the highest Animals should exercise  a similar
selective   power, in  regard  to  the materials  with which the blood  supplies
them.  The  structure  composing every separate portion  of the body has
(what may be termed) an elective affinity for some particular constituents  of
the blood; causing it to abstract from that fluid, and to convert  into its own
substance, certain of its elements.   The property by which  the cells of the
Animal or Vegetable structure  are enabled to perform it, is one of which we
are not likely soon to know more.   It will probably long remain an ultimate
fact in Physiology, that cells have the power of growing from germs, of under-
going certain transformations, and of producing germs that will develope other
cells  similar to themselves;—just as it is an ultimate fact in Physics, that
masses of matter attract each other; or in Chemistry, that the molecules  of
different substances  have a tendency to unite, so as to  form a compound dif-
ferent from either of the elements.  It is of  such ultimate  facts as these, that
the science of Vitality essentially consists: since the Physical and  Chemical
phenomena which occur in living bodies, are not strictly removable from the
laws of Inorganic Nature.   The  conditions  under which  this appropriating
power operates, however, are  freely open to our investigation;  and it is a
great  step in  the progress of the inquiry, to become  aware that  these are  so
closely conformable, throughout the  organized  world,  as they have  been
shown to  be.   It may be stated, as a general fact, that in assimilating, or con-
verting into its own  substance,  matter which  was previously unable to exhibit
any of the manifestations  of life, every cell thereby participates in the process
of organization and  vitalization;  for, by the  new circumstances  in which the
matter is placed, its properties undergo a change,—or, to speak more correctly,
properties which were previously dormant are caused to manifest themselves.
No matter, that is not in a state of Organization, can exhibit those properties,
which, from their being peculiar to living bodies, and altogether different from
Physical  and Chemical, are termed Vital; and it may also be  asserted that
no  matter, which  exhibits  perfect  organization, is  destitute of the peculiar
vital  properties belonging to its  kind of structure.*  As a corollary to this
general fact, it may be stated, that no organism  can be produced by any
fortuitous  combination of inorganic matter;  since, even for the generation of
the simplest  cell,  there is required  a cell  previously existing, to furnish the
germ.

  * For a fuller consideration of this question, and  the grounds upon which this view is
supported, the reader is referred to the Article Life in the Cyclopedia  of Anatomy and Phy-
siology; and to the Chapter on the "Nature  and Causes of Vital Actions," in his Principles of
General and Comparative Physiology. 
SELECTIVE POWER OF INDIVIDUAL PARTS.
595
   783. We have seen that, in some  cases, the germs are prepared by pre-
viously-existing cells of the same kind; thus the Red and colourless corpuscles
of the  Blood, the Cartilage-cells, the cells of Vesicular  Nervous  matter, and
those  of many other tissues, appear  to be the  offspring  of parents exactly
similar to themselves.  In  other cases, however, the germs seem to be fur-
nished by certain " nutritive centres," which appear to be  constantly  engaged
in the preparation of them, deriving their materials from  the blood.*  Thus
the Epidermic and Epithelial cells  are produced, not from preceding cells of
a  similar character (for  these  are  thrown  off without  performing any such
reproductive act), but from germs derived from the basement or primary mem-
brane  beneath;  and,  in like manner, the  minute cells, of  which the  ultimate
fibrillae of Muscle  are. composed, appear to originate in  nuclei or germinal
centres, belonging to the tubular Myolemma.   But even these germinal centres
may probably be considered as nothing else than the nuclei of  certain parent-
cells, which, instead  of producing their like, give  origin to a new generation
having different  properties.   Thus, the basement  or primary-membrane  has
been  already stated (§ 135) to exhibit not unfrequently the indications of a
cellular constitution ; the germinal centres which it contains being the nuclei
of its component cells: and its character is particularly well seen where it is
inverted so  as to form secreting  follicles; for, as we have seen (§ 174), each
of these follicles  may be regarded as a single  parent-cell, which opens at the
extremity farthest from the nucleus, and continues to discharge from its orifice
successive generations of  cells, having their origin in its nucleus, which thus
acts as a permanent  " germinal centre."   And  in like manner, the germinal
centres of Muscular Fibre may be regarded as the nuclei of the  cells, of which
it was originally composed.
   784. The Selecting power, which is possessed by the germs of each kind
of tissue, and which enables them to draw from the Blood the materials which
they severally require for their development, manifests itself also in the mode
in which substances, that are abnormally present in the Blood, affect  the con-
dition and development of the solid tissues.   Thus we find that the presence
of a certain quantity  of Arsenic in the Blood, will produce a state of irritation
of all the Mucous membranes in the body.  The continued introduction of
Lead into the circulating system, occasions a modification in the nutrition of
the extensor muscles of tbe forearm,  producing the form of partial paralysis
commonly termed wrist-drop;  and the existence of this modification is shown
by the fact (disclosed by Chemical analysis) of the actual presence of lead in
the palsied muscles.—Here we have to remark the  Symmetrical nature of the
affection, consequent upon the occurrence of the same disorder in the corre-
sponding parts of the two sides of the  body; for these muscles appear to have
the same kind of tendency to attract  Lead from the circulating current, in a
degree that is equal  on the two  sides, as  they have to  draw from the  blood
the materials of their  regular growth, and to develope themselves in an exactly
similar manner.  In  like  manner, the cutaneous  eruptions, which are occa-
sionally produced by the internal exhibition of iodide of potassium, are found
to be almost precisely symmetrical; the presence ofthe medicine in the blood
being the occasion of a disordered nutrition of certain parts of the skin;  and
the selecting power of particular spots being evinced by the exact correspond-
ence of the  parts affected on the two sides.
   785. The same  appears to be the  case with  regard to  substances, whose
presence  in  the  blood is rather the result of a disordered  condition of the
digestive  and assimilating processes,  than  of their direct introduction from
without.  Thus in Lepra and Psoriasis,—chronic diseases of the Skin, which

          *  See Goodsir's Anatomical and Pathological Observations, Chap. i. 
596
OF NUTRITION.
seem to have their origin in a disordered state of the Blood, rather than in the
solid tissues affected,—we find a remarkable tendency to the repetition of the
patches, on the two  sides  of the  body, or on the corresponding parts of the
limbs; and this we must attribute to the peculiar attraction subsisting between
the solid  tissues  of those parts, and the morbid matter  circulating through
them.—So in those chronic forms  of  Gout  and Rheumatism, which  modify
the nutrition  of the joints, producing a deposit of "chalk stones," or perma-
nent distortion and stiffening from an alteration ofthe tissues, ofthe joint, we
almost invariably find  the corresponding joints of the two sides affected.—
The chief exceptions to the general principle, that the presence of morbid or
extraneous matters in the blood affects all  parts alike,  are  found to occur
where there  is much febrile  disturbance, or where local causes  produce  a
peculiar tendency to disorder of a single  part.  The  nearer the  approach
presented by the morbid process, in point of rate and character, to the ordi-
nary nutritive operations of the part, the more does it tend to approach these,
in the symmetry with which it developes itself.*


2.— Varying Activity of the Nutritive Processes.—Reparative Operations.

   786. Without any change in the character of the Nutritive processes, there
may be considerable variations in their degree of activity; and this, either as
regards the entire organism, or individual  parts, though most commonly the
latter. These  variations  maybe so considerable as  to constitute Disease;
though there  are some which take place as part of the regular series of Phy-
siological  phenomena.  Thus, the  Nutritive processes  should have a degree
of activity more than sufficient to supply the Waste of the body during the
whole period of infancy, childhood and  adolescence, until, in  fact,  its full
dimensions are  obtained; whilst, on  the  other hand, they are  usually  less
rapid than the disintegrating processes in old age, so that the bulk of the body
diminishes.  Now  as the Waste of the body, so far from being more rapid in
old age than  in childhood, is  much less so, it follows  that the difference in
the activity of the Nutritive processes in these  two states must be very con-
siderable ; and this  is manifested, not only in  the greater demand for food
which exists  in the  child  (relatively to  the bulk of its body), but also in the
greater quickness and facility with which injuries are repaired.   Local varia-
tions may also occur, as part of the regular train of vital actions in the adult;
thus we perceive  an enormous increase in the amount  of tissue contained in
the Uterus and Mammary glands  during pregnancy, and a decrease in the
bulk of the Thymus gland after the period of infancy.   Now in these cases
we see, that increased Nutrition is invariably connected with increased Func-
tional activity;  and diminished  nutrition with diminished functional activity:
and this we shall  find to be the constant rule, in regard also to those variations
which must be considered as abnormal.
   787. Increased Nutrition, or Hypertrophy, is  never  known to affect the
ivhole body,  to a degree  sufficient  to constitute disease.   It cannot be  pro-
duced as a consequence of the ingestion of an undue supply of food:  for this
does not increase the formative activity of the tissues, but merely renders the
blood richer in nutritive materials; a part of which the excreting organs are
called on  to be continually removing, without its being rendered subservient to
the wants ofthe body (§ 819); whilst another part may be  employed in the
nutrition  of one  particular  tissue, the  Adipose, which has a tendency to in-
crease with  the  superfluity of  non-azotized food, provided that  the requi-

  * See Dr. W. Budd's valuable paper on the  " Symmetry of Disease," in vol. xxv. of the
Medico-Chirurgical Transactions. 
VARYING ACTIVITY OF THE NUTRITIVE PROCESSES.           597
site amount of cellular tissue  be generated  to  hold the  fatty matter (§ 184).
But examples of Hypertrophy of particular tissues or organs are very com-
mon.   Thus any particular set of Muscles, which is subjected to frequent and
energetic use, acquires a great increase in bulk ;  as we see in the arms of a
Blacksmith or Waterman, the legs of an Opera-dancer, &c.  The hypertrophy
of these muscles is a consequence of their increased functional  activity ; which,
being produced by an  exertion of the  will, and unaccompanied  with any in-
jurious effects on the system, can scarcely be regarded as morbid.  But there
are many  instances, in  which  the involuntary muscles  acquire  a greatly-
increased strength, in  consequence of an obstruction to  their action, which
results from disease.   Thus we  see the right ventricle of the Heart become
hypertrophied (and dilated  at the same time), where  chronic pulmonary dis-
ease produces a difficulty in the  propulsion  of the blood  through the vessels
of the lungs; the muscular fibres of the Bladder become enormously hyper-
trophied, when stricture, diseased prostate, or other causes produce a demand
for increased expulsive  force on  the  part of that  organ; and  those of the
Stomach also become so, in cases  of stricture of the pylorus.  As an instance
of hypertrophy of a Secreting organ in consequence of an undue excitement
of its function, we may notice the  enlargement which usually takes place in
the Kidney,  when its  fellow is  incapacitated by disease.   And  the Nervous
system presents us  with a very remarkable case of hypertrophy of a part,
resulting from  over-excitement of its  function;  for  if young persons, who
naturally show precocity of intellect, are  encouraged rather than checked in
the use of  their brain, the increased nutrition of the organ (which grows faster
than its bony case) occasions  pressure upon its vessels, it becomes  indurated
and inactive, and fatuity  and coma are the result.
   788. Local hypertrophy may be induced  also by local congestions; but in
such cases it will usually be found, that the form of tissue produced is of the
lowest kind, unless  the  functional activity of the  part be increased by the
congestion.  Thus, when disease  of the Heart produces long-continued con-
gestion of  the Lungs, Liver, Spleen, &c, the bulk of these organs increases;
but chiefly by the production of an additional  amount of interstitial Areolar
tissue, which may result (as we have seen) from  the simple  consolidation of
Fibrine ; and partly also (in the case of the spleen especially) by the gorging
of their  distensible veins with blood.—One of the least explicable cases of
Hypertrophy, is that which takes place in the  Thyroid gland, causing Bron-
chocele.  So little is known of  the normal office  of this organ,  that it cannot
be determined, whether  its increased size be due to  an  increased activity of
its functional operations, or to  an unusual  formative activity   in its tissue,
depending  on  some hidden  cause.  The connection of this disorder with
causes which affect the whole constitution rather than individual parts, would
seem to indicate the former.
   789. When  the Waste of the Tissues is more rapid than their replacement
by Nutrition, Atrophy is said to take place; and  this  may  affect either  the
whole body, or individual parts.   General Atrophy, Marasmus, or emaciation,
may result from an insufficient supply of plastic matter, from want of forma-
tive power in  the tissues  themselves, or  from their  too rapid disintegration.'
The insufficiency  of the supply of nutritive matter may depend either on de-
ficiency in the azotized substances ingested as food, or on imperfect perform-
ance  of those processes by which they  are  converted  into the plastic ele-
ment,—Fibrine.   Hence,  even  when there  is  an  ample  supply  of  food,
atrophy may take place to a very severe extent, in consequence  of disordered
digestion, or a  want of vital power in the fibrine-elaborating cells.  Again, we
have reason  to believe that the formative power in the tissues themselves  may
be diminished, so  as to check the process of Nutrition, even  when the plastic 
598                          OF NUTRITION.
material is supplied ; thus there seems to be a complete stoppage of this action
in Fever, and  a  diminution of it in that irritable state of the  system, which
results from excessive and prolonged bodily exertion or  anxiety of mind, es-
pecially when accompanied by want of sleep.   It is difficult to separate this
cause, however, from  mal-assimilation on  the one  hand, or from  too rapid
decay of the tissues on the other:  for we know that, in such states, there is a
tendency to imperfect elaboration of the Fibrinous element, and at the same
time an unusually rapid disintegration, as manifested by the  increased amount
of Urea in the urine.   The influence of excessive waste in causing Atrophy
of the body, is well shown in the cases of  Diabetes mellitus and colliquative
Diarrhosa;  in both these, the  increase and  depravation of the secretions are
undoubtedly to be regarded as the  effects, and  not the causes, of the textural
changes with which they are associated.   Colliquative Diarrhoea is a constant
occurrence on the last day or two of life, in animals reduced  by Starvation;
and  is accompanied by that  foetid odour of the body, which  indicates that
decomposition is already going  on  throughout the system.  The same thing
occurs as the ordinary termination  to many diseases of exhaustion; in which
Inanition is unquestionably the immediate cause of death.
   790.  Partial Atrophy may occur in consequence  of  disuse  of the organ
affected, occasioning inactivity in its formative processes; or as a result of a
deficiency of nutriment, occasioned by an obstruction to the circulation.  Of
the operation of  the former cause, we have many examples in  the ordinary
processes of the economy.  Thus  the Uterus  is  atrophied, relatively to its
previous condition, as soon as parturition has taken  place ; and the Mammary
glands, when lactation has been discontinued.   It is probably in part to this
cause, and  in part to the diversion  of the blood  into other channels, that we
are to attribute the atrophy of many parts, as the development of the system
advances, which at an  earlier period were of large comparative size,—such as
the  Corpora Wolffiana, the  Suprarenal capsules,  and the Thymus gland.
Many instances might be adverted  to, of the influence of  suspension of func-
tional activity, as  a  result of disease or  injury, in producing local  atrophy.
One of the most common cases, is the atrophy of Muscles which is conse-
quent upon their disuse.   This disuse will produce the same effect, whether
it be occasioned  by paralysis, which prevents the nervous centres from excit-
ing the muscles to contraction;  or by anchylosis, which interposes a mechani-
cal impediment to their use ;  or by fractures or other accidents, the reparation
of which requires  the limb to be kept at rest.   Or even  if, without having
suffered from any  injury, a limb be fixed during some time  in one posture, its
muscles will become atrophied, as  is  seen  in  the case of the Indian Fakirs.
(See § 588).   Similar facts may be adduced, in regard to Atrophy of Nerves,
from interruption of their normal function.   Thus when  the Cornea has been
rendered so opaque by accident or disease, that  no light  can penetrate  to the
interior of  the eye, the Retina and the Optic nerve lose, after a time, their
characteristic structure ; so that scarcely a trace of the peculiar globules of the
former, or of the nerve-tubes  of the latter, can be found in them.   These and
similar  facts are readily understood, when  connected by  the general principle
formerly- laid  down,—that every proper vital operation involves  an  act of
nutrition ;  in such a  manner that, whilst  the vital  properties  of any part are
dependent  upon  its due nutrition, the amount of its nutrition will in return
depend upon the degree in which these properties are exercised.
   791.  Partial Atrophy may depend, however, upon causes of  a purely me-
chanical nature; such, for example, as produce an interruption of the current
of Blood through the part.  This  may result from changes in the  Arteries
supplying it;  such as  ossification,  or other forms of obstruction.   Or it may
be consequent upon disease in the  part itself;  as when the deposits produced 
              VARYING ACTIVITY OF THE NUTRITIVE PROCESSES.          599

by Inflammation tend to  contract, and thus to press upon  the vascular struc-
ture, which frequently happens in the lungs, liver, and kidneys; or when the
inflammation occurs in the vessels themselves, causing adhesion of their walls,
and obliteration of their tubes; or when a new growth absorbs into itself all
the nutritive materials which the Blood supplies.*
  792.  The nutritive operations take place, with  extraordinary energy and
rapidity, in the process  of Reparation ; by which losses of substance, occa-
sioned by injury or  disease, are made good.  In its most  perfect  form, this
process is exactly analogous to that of the first development of the correspond-
ing parts ; and its results are as complete in the one case as in the other.  In
fact, among the lowest  tribes of  Animals,  we find  these two conditions
blended, as it were, together;  for the process of reparation may be carried in
them to such an extent, as to regenerate the whole organism from a very small
portion  of it.  In the Hydra, or Fresh-water  Polype, there would seem to be
scarcely any limit to this power;  for,  if the body of the  animal be minced
into the smallest possible fragments, every one of these can produce a new
and perfect being.  In this  manner no less  than forty have been artificially
generated from a single  individual.—In  ascending  the Animal scale, we find
this  reparative power less conspicuous, because  exercised with  regard  to
smaller parts only of the  body; but the greater complexity of  the  changes
involved in the process, renders it in reality not less considerable than in  the
lower classes.  Thus, the  restoration of a Bone destroyed by Necrosis is  a
much more extraordinary operation, than the growth of an entire Polype from
a single fragment:  since it involves a far  greater amount  and variety of
actions.  Numerous and well-authenticated  instances are  on  record, of the
reunion  of parts that had been entirely  separated from the body, and of the
restoration of all their vital properties : and this could only take place, through
the perfect reproduction of a large number of very different structures.   The
reappearance of Fungous growths, whose organization is of a low character,
is a fact with which every surgeon is familiar; and cases occasionally, though
rarely, present themselves, in which reproduction  of a whole  member takes
place even in the Human subject.!
  793.  It is the general opinion among British surgeons (founded upon what
they believe, but erroneously, to have been the  doctrine of Hunter), that In-
flammation is essential to the process of Reparation.  There is no doubt that,
as usually conducted, the healing of wounds  is attended by a greater or less
degree  of Inflammation; but it does not thence follow that this  morbid con-
dition  is essential to the renewal of the healthy state;  and in fact it can be
shown that, in the majority of cases, the Inflammation is  injurious rather than
beneficial.   The  following important conclusions are  drawn by Dr. Macart-
ney;]; from a very philosophical comparative survey of the operations of Re-
paration and Inflammation, as performed in the different classes  of  animals :
—" That the powers of Reparation and Reproduction are in proportion to the
indisposition or incapacity for Inflammation;—that Inflammation is so far
from being necessary to the Reparation of parts, that, in proportion as it exists,
the latter is impeded, retarded, or prevented;—that, when Inflammation  does
not exist, the Reparative power is equal to the  original tendency to produce
and maintain organic form and structure ;—and that it then becomes a natural
function, like the growth of the individual, or the reproduction of the species."
  794.  Guided chiefly  by Dr. Macartney's  views, which  have  derived  im-

  * See on this subject Dr. Williams' Elements of Medicine, chap. iv.; to which the Author
is partly indebted for the preceding paragraphs.
  f See, on the whole of the subject of the comparative powers of Reparation in the Ani-
mal series, the Author's Principles of Gen. and Comp. Physiol. §§ 586, 587.
  J Treatise on Inflammation, p. 7. 
600
OF NUTRITION.
portant confirmation from recent observations, we shall treat of the reparative
processes under three distinct heads :—First, the adhesion of the sides  of a
wound by a medium of coagulable lymph, or of a clot  of blood.   Second,
reparation without any medium of lymph or granulations, the  cavity of the
wound being filled by a natural process of growth from its  walls.  Third,
reparation by means of a  new, vascular, and organized substance, termed
Granulations.—The first of these modes of Reparation, is that which is ordi-
narily termed union by the first intention; of this kind of adhesion, the heal-
ing of the incision made in venesection, which usually takes  place almost
without consciousness on  the  part of the patient, and  with scarcely any In-
flammation's a characteristic  example: the white line  of cicatrix which is
left, marks the formation of new substance;  and is the result of the want of
that perfect approximation of the lips of the wound, which may  frequently be
obtained in parts, where pressure  can be more firmly applied, and where the
space to be filled up is  proportionably thinner.  This mode of union is ordi-
narily considered by British Surgeons to be the result of  an adhesive inflam-
mation.   In  so  regarding it, they conceive  that they are following out  the
views of Hunter; but he expressly states that  wounds  may heal without any
pain or constitutional disturbance, the reunion proceeding "as if nothing had
happened ;" so that he in  effect admits, that reparation of this kind may take
place without Inflammation.  It is well known that if a slight wound, which
is  thus healing, be provoked to an increased degree of Inflammation, its pro-
gress is interrupted; and all the means which the Surgeon employs to  pro-
mote union, are  such  as  tend to prevent the accession of this state.   The
doctrine that the effusion of Lymph for the Reparation of the tissues, is not
to be regarded as necessarily a result of the Inflammatory process, is not so
novel as its opponents have regarded it;  since it has been  maintained by many
eminent observers, even from  the earliest  times.   The  only case  in which
the occurrence of Inflammation can be regarded as  salutary, is  that in which
there is a  deficiency of Fibrine in the  blood,  causing  a  deficient  organiza-
bility of the lymph.  It has been seen that the amount of Fibrine is rapidly
increased by inflammation; and the  Surgeon well knows  that a wound  with
pale flabby edges, in a depressed state of the system, will not heal, until some
degree of Inflammation has commenced.
   795.  When  the Liquor Sanguinis  of the  Blood, known as Coagulable
Lymph, is effused between the two edges of a wound, or upon  the surface of
a membrane lining a closed sac, the following appears to  be the history of its
organization.  The new matter,  which is poured  out in a  fluid state,  and
which seems to have been subjected  to  the peculiar  influence of the Colour-
less  Corpuscles that rapidly collect  in large  numbers at the injured spot, un-
dergoes a Coagulation resembling that  of Blood; the Serum, being set free
by the concretion of the  Fibrine, is absorbed;  and the  fibrinous coagulum
speedily attains an almost membranous  density.   If examined  with a Micro-
scope at the commencement of the process of  organization, it is seen to con-
tain a large number of cells, which sometimes closely resemble the Colourless
Corpuscles of the Blood;  and in other  instances (especially where there has
been active Inflammation) present greater similarity to Pus-corpuscles ; these
cells, which are known as exudation-corpuscles, probably originate in granules
set free from the Colourless Corpuscles of the circulating blood, and exuded
with the  Liquor Sanguinis.   In  a short  time, these corpuscles present the
appearance of regular cells, disposed in layers, and adhering together by an
intermediate unorganized substance ; bearing, in fact, a strong resemblance to
the cells of tesselated  epithelium.  Some hours later, the mass exhibits an
evidently-fibrous character ; which is probably due to the further elaboration
of the plastic material, by the  cells  just mentioned.   Between the fibres, a 
REPARATIVE PROCESSES.
601
considerable amount of unorganized substance yet remains ; and they maybe
readily separated, or  torn in any direction.   A vascular  rete next makes its
appearance, in connection with the vessels of the subjacent surface; the first
appearance  of this network  is in  the form of transparent arborescent streaks,
which push out extensions on all sides;  these encounter  one another,  and
form a complete series of capillary reticulations, the distribution of which very
nearly resembles that which has  been seen in  the villi of the intestines (Fig.
204).—From the observations of  Mr. Travers* it appears, that isolated glob-
ules enter these  capillary tubes, and perform an oscillatory motion in them
for some  hours, before  any series of them passes into it; so that we  cannot
regard the new channel as burrowed  out by a string or file of red corpuscles,
pushed out from the nearest capillary by vis a tergo, as some have maintained.
And he has further established two important facts, in the history of the  Re-
paration of  Tissues, which  correspond with the observation  just cited:—1.
That the Liquor  Sanguinis  first effused is not sufficiently organizable to be-
come an entirely new and permanent tissue ; although adequate both to afford
nutrition to  the old, and to form  a new tissue of temporary character:—and,
2.  That the generation of the new tissues is preceded by the collection of a
large number  of  white corpuscles, in a nearly stationary condition, in  the
blood-vessels immediately subjacent; and by the appearance of a large number
of  similar cells in the newly-forming tissue ; the  two together constituting
what Mr. T. has  aptly called " the  new lymph-bed  of organization."   The
views formerly advanced (§§ 154-159) respecting the function of the Colour-
less Corpuscles, are  thus strikingly  confirmed.—This process of Reparation
appears to be  conformable, in all essential particulars, with  that which  has
been observed  in the  first Development of new parts,—such as the toes of the
larva of the Water-Newt.
   796. Although many have doubted whether effusions of Blood could thus
become organized, there seems no valid reason to think that its Fibrine would
comport itself in any other  way, when Red particles are included in its coa-
gulum, than when they are  absent.   That large masses of extravasated Blood
should exhibit little or no  tendency to organization, will not be considered
surprising;  when it is remembered that only their  surface  can be in that re-
lation with a living membrane, which has been stated to  be essential  to  the
further vitalization of the effused Fibrine (§119).  It has been  proved in many
instances, however, that Coagula of Blood completely inclosed within the body
possess an incipient vascularity, being capable of injection from the surface
beneath (§ 700);t  and there is no valid reason to deny that the thin layer of
Blood which remains between the lips of an  incised wound,  when these  are
closely brought together, is the medium of their reunion.  It is  unquestionable,
however,  that the Fibrine of an ordinary  Blood-clot is less highly-elaborated,
and consequently less  susceptible of organization, than  that of the Liquor
Sanguinis, which is poured forth after an injury, and which has been subjected
to the local  action that is its immediate result.
  797. To the second mode of Reparation, attention has recently been strongly
directed by  Dr. Macartney ; and as this, too, is a strictly Physiological action,
and is  one which the  Surgeon should aim at producing,  it will be here  dis-
cussed somewhat in detail.   The Surgeon has, until recently, regarded  the
processes  of Granulation and  Suppuration, which  are attended with  much
local Inflammation, and with a considerable amount of Constitutional disturb-
ance when the surface is large, as the only means by which an open wound

  *  Physiology of Inflammation  and the Healing Process.
  f For well-established  cases of this  sort, see communications by Mr. Dalrymple in the
Medico-Chirurgical Transactions, vol. xxiii.; and in Lancet, March 23, 1844.
     51 
602
OF NUTRITION.
can be filled up.   Occasional  instances, however, have  not been wanting, in
which large open wounds have closed up under the dry clot of blood, by which
they were at first covered over, without any suppuration, or other symptom
of inflammation;  and in these it has been found, that  the  new surface much
more nearly resembles the ordinary one, than does the Cicatrix which follows
granulation.  To Dr. Macartney, however, is due the merit of explaining the
rationale of this  action ; which is precisely analogous  to  that which is  con-
cerned in the ordinary processes of growth, and to that reproduction of whole
parts which takes place in  the lower animals without Inflammation.   It is
termed by him the modelling process; and  he remarks as  characteristic of it
that, when it goes on perfectly, and without Inflammation, the patients are so
completely free from uneasy sensations, as only to be aware of the extent of the
injury by their own  examination.  In this process, the surfaces of the wound
do not unite by vascular connection, even when they lie in contact; nor is the
space between them filled up with coagulable  lymph; but they are smooth
and red,  moistened with  a fluid, and presenting the  appearance of one of the
natural mucous membranes.  " It  might be anticipated that, as  this mode of
reparation bears so strong a  resemblance to the natural formation and develop-
ment of parts, it is the slowest mode ; but this is of little account, when com-
pared with its great advantages in  being unattended with pain, inflammation,
and  constitutional sympathy, and  leaving behind  it the best description of
cicatrix."  In the case of large burns on the trunk in children, the difference
between  the two modes  of Reparation will frequently be that of life and death;
for it often  happens that  the patient sinks under the great constitutional dis-
turbance  occasioned  by a large Suppurating  surface, although he  has survived
the immediate shock of the  injury.
  798. The most effectual means  of promoting this kind of Reparative pro-
cess, and of preventing the  interference  of Inflammation,  vary  according to
the nature  of the injury.   The exclusion  of air  from the surface, and  the
regulation of the temperature, appear the two points of chief importance.   By
Dr. Macartney, the constant application of moisture is  also insisted on.*   He
states that the immediate effects of injuries, especially of such as act severely
upon the sentient extremities of the  nerves, are best abated by the action of
"steam  at a high  but  comfortable  temperature, the  influence  of which is
gently stimulant,  and at  the same time extremely  soothing.  After the  pain
and  sense  of injury have passed  away, the steam, at "a lower  temperature,
may be continued;  and,  according to Dr. M., no local application can com-
pete with this, when the Inflammation  is of an active character.    For subse-
quently  restraining this, however, so  as  to  promote the  simple Reparative
process,  Water-dressing will, he considers, answer sufficiently well; its prin-
cipal  object being the constant production of a moderate degree of Cold,
which diminishes,  whilst  it  does not extinguish, sensibility  and vascular
action, and allows the Reparative  process to be carried on as in the inferior
tribes of animals.  The reduction of the heat in  an  extreme  degree, as by
the application of ice or iced water,  is not here  called  for, and would be
positively injurious; since  it not only  renders the existence of  Inflammation
in the part  impossible, but, being a direct sedative to all vital actions, suspends
also the  process  of  restoration.  The efficacy of Water-dressing in injuries
of the severest character, and in those which are  most likely to be attended
with violent Inflammation (especially  wounds  of the  large joints)  has  now
been  established  beyond all question; and its  employment is  continually
becoming more general.t—Other plans have been proposed, however, which

  * Treatise on Inflammation, p. 178.
  f See an account of the results of this treatment by Dr. Gilchrist,  in Brit, and For Med
Rev., July  1846, p. 242. 
ORIGIN OF THE SOLID TISSUES.
603
 seem in particular cases to be equally effectual.   To Dr. Greenhow, of New-
 castle, for instance, it was accidentally suggested, a few years since,* to cover
 the surface of recent burns  with  a liquefied resinous ointment;  and he states
 that in  this manner Suppuration may be prevented, even where large sloughs
 are formed;  the hollow being gradually filled up by new tissue, which is  so
 like that which  has been destroyed, that no change in the surface manifests
 itself, and none of that contraction, which ordinarily occurs  even under the
 best management,  subsequently  takes  place.  A plan has, moreover,  been
 proposed for preventing suppuration, and promoting reparation by the model-
 ling process,  which consists  in the  application of warm dry air to the wounded
 surface.  The experiments made  on this have not been entirely satisfactory,
 but they seem to  show that, though the  process of healing is  much  slower
 under  treatment of this kind, it is attended with less constitutional  disturb-
 ance than is unavoidable in the ordinary method; and it may, therefore, be
 advantageously put in practice in those cases  in which the condition of the
 patient  requires  every precaution  against such an  additional burthen,—as after
 amputation  in a strumous subject.  But  of the superiority of this treatment
 to the water-dressing, no evidence has yet been adduced.
   799.  The  third method of Reparation,—that by Granulation—appears to
 be a means employed by Nature for the purpose, under the unfavourable cir-
 cumstances of Irritation or a continuance of Inflammation; proving that parts
 previously in a  healthy state, are  disposed to heal, in  despite of many impe-
 diments thrown  in their way.  The Granulation-structure is a special  one,
 formed for a temporary purpose.  It is endowed with higher vascularity and
 a  more  rapid power of growth,  than  is possessed by any modification  of
 ordinary  tissue;  but  it is very easily  destroyed by  injury, or by a higher
 degree of inflammation.  The existence of Granulations  has  been supposed
 to be necessary to fill up deficiencies;  this, however,  is not altogether true;
 as we occasionally find very considerable vacancies filled with lymph, which
 gradually becomes organized, without being converted into granulations; and
 the void may be also supplied by the process of natural growth just described.
 Moreover, it  is only in the  beginning that granulations take the place  of the
 natural  structure; for the approximation of the edges  of a wound filled  with
 them, requires that they should be removed by interstitial  absorption;  so that
 wounds healed by this  process do not exhibit any remains of  the new me-
 dium.   This approximation somewhat  resembles that which occurs in open
 wounds that have never inflamed,  being the result of the natural processes  of
 growth; and it does not take place until the Inflammation has in great degree
 subsided: but it differs from the modelling processes in this,—that, as the wound
 is  occupied by granulations, its closure takes  place prematurely, as it were;
 so that, when the granulations are subsequently absorbed altogether,  a  con-
 tracted cicatrix is the  result.—It will be  presently seen that the formation  of
 the Granulation-structure is  intimately connected with the elaboration of Pus;
 and this  process, accompanied as it is with such  great constitutional disturb-
 ance, and involving such a loss of nutritious material, cannot but be regarded
 as an action to be altogether avoided, if  possible.
  800.  We shall now consider, more in detail, the  nature  of the process  of
 Granulation, and of the Suppuration which usually accompanies it. Its com-
mencement is exactly conformable  to the first stage of ordinary reunion  by the
first intention ; for Liquor Sanguinis is thrown out, in which Exudation-cor-
puscles  present themselves in large numbers.   According to Gerber, the trans-
formation of these into  a sort of imperfect Epithelium may be seen to take
place within half an hour.   New layers are in the mean time developed; and
* Medical Gazette, Oct. 13, 1838. 
604
OF NUTRITION.
the most superficial of the  Exudation-corpuscles, which are  exposed to the
contact of air, change their character (in the mode to be presently described,
§ 805), and become Pus-Globules ; whilst those in close contact with the sub-
jacent surface take a  share  in  the  process  of reparation.  A new layer of
exudation-corpuscles is next deposited over this :  of which the outer portion
degenerates as before  into pus-globules,  whilst the inner  part gives origin to
a kind of areolar tissue, forming Granulations.  These Granulations are them-
selves extremely vascular;  and, as recently shown  by Mr. Liston,* the ves-
sels of the subjacent tissue are  much enlarged, and assume a varicose charac-
ter.   The bright red colour of the Granulations,  however, does  not  depend
on  their  vascularity alone ;  for the  cells themselves,  especially those  most
recently evolved, are of nearly  as deep  a colour as the  blood-globules ; and
the superficial bleeding which follows even the  slightest touch of  the granu-
lating surface, does not proceed from blood shed from the newly-formed vessels
only ;  for the red fluid shed in this manner  contains, besides blood-discs,
newly-developed red cells, ruddy cytoblasts, pale granules and reddish serum.
It is a common property of  animal cytoblasts, that  they present a  red colour
on  their  first formation, when in  contact with oxygen; but this hue they
lose again, whether they advance to perfect development and  become integral
parts of a living tissue, or die and degenerate.
  801. The  process  of  Granulation and  Suppuration appears to  differ from
that of simple Reparation (the modelling process of Dr. Macartney) in this,
—that a large part of the Exudation-corpuscles  deposited on the wounded
surface degenerate into Pus in  the former case, whilst none are thus wasted
in the latter ;—but that the existence of Inflammation occasions a more co-
pious supply of Fibrine  in the  former case, and increases its tendency to be-
come organized ;  the filling-up of a wound with Granulations being thus a
much  more rapid process than that renewal of the completely-formed Tissues,
which may take place in the absence of Inflammation.   The imperfect cha-
racter of the  Granulation-structure is shown, by  the almost  complete disap-
pearance of it after the wound has closed over.  The portion of it in immediate
contact with  the subjacent tissue, however, appears to undergo a higher organi-
zation ; for it becomes the medium by which the Cicatrix is  made to adhere
to  the bottom  of the wound.   It is very liable to undergo  changes which
end in its disintegration ; as is  evident from the known tendency to re-open-
ing, in wounds that have been closed in this manner.


             3.—Abnormal Forms of the Nutritive Process.

   802. Under the  preceding head, we  have  considered the  chief variations
in the degree of activity, that are witnessed  in the ordinary or normal condi-
tions of the Nutritive process,—that is,  those conditions in  which  the pro-
ducts  are adapted, by their  similarity  of character, to  replace those which
have been removed by  disintegration.   But we have now to consider  those
forms of this process,—in which the products are abnormal,—being different
from the tissues they ought to replace.   We shall confine ourselves to a brief
examination  of the two most important  of these states ;—that which is termed
Inflammation ;—and  that  which gives  rise  to  Tubercular deposit.  The
former results from an excess of the plastic element in  the blood  ;  the latter
from a depraved condition of it, whereby its plasticity is impaired  or destroy-
ed.—Notwithstanding all the attention which has been  given to the state  of
the vessels in Inflammation, a careful consideration of its phenomena, with the
light which recent investigations have thrown upon these, leads us  to attach
* Medicc-Chirurgical Transactions, vol. xxiii. 
ABNORMAL FORMS OF THE NUTRITIVE PROCESS.
605
comparatively little importance to this, and to seek for the essential character of
the process elsewhere.   The researches of  Addison, Williams, Barry, Gulli-
ver, Andral, and others, all seem to point to the following  conclusions:—1.
That there is a peculiar afflux or determination of the White Corpuscles  of
the Blood towards the inflamed  part.   2. That the total  amount of these cor-
puscles in  the  circulating blood undergoes a great increase.   3. That the
quantity of Fibrine in the Blood augments, in proportion to the extent and
intensity of the Inflammation ; and this, even when it was previously, from
the  influence  of some  other morbid  condition,  below  the usual standard.
With its quantity, its plasticity,  or tendency to organization, also increases  in
a  healthy subject.—Now when these facts  are  compared together,  and are
connected with those formerly  adduced, in regard to  the probable  function
of the White Corpuscles of the blood, they lead almost irresistibly to the con-
clusion, that the  process  of Inflammation essentially  consists  in an  undue
stagnation of these corpuscles in the vessels of the part, an excessive  multi-
plication of them by tbe  ordinary  process  of generation,  and a consequent
over production of  Fibrine.   By these changes, and by the results which fol-
low them, Inflammation may be distinguished from the various forms of Hy-
peremia and Congestion.   To the results, then, we  shall next direct our at-
tention.
   803.  It may be inferred from various phenomena, that whilst the forma-
tive power of the Blood is increased in Inflammation,  that of the Tissues  is
diminished.  Certainly this is the case in regard to the system at large, when
febrile irritation has been established; for, notwithstanding the increased Plas-
ticity of the Blood, we see the body wasting, instead of  increasing in vigour.
And  it  may be inferred also, in regard to the tissues  of  the part  affected,
from the  tendency to Atrophy  and Disintegration which they  exhibit; and
which is greater (leading even to the death of whole parts) in  proportion  as
the inflammation  is more  intense, and as the tendency to the deposit of new
products is the more decided.   That a  Stagnation  of Blood takes  place  in
the vessels of the inflamed part, is  another general  fact, which throws some
light upon the nature of  the  process ;  for this stagnation is obviously favour-
able to the transudation of the fluid Plasma of the  blood, through the walls
of the vessels, into the  surrounding tissue,  or upon a neighbouring surface.
This deposition of  the Fibrinous element, possessing a high degree of plasti-
city, and capable  of spontaneously passing into simple forms of tissue (which
may be gradually replaced by higher forms, when penetrated by vessels from
the surrounding parts), may  be  regarded as the first characteristic  result  of
Inflammation.  It is by the deposition, and subsequent organization, of plas-
tic matter in the substance of organs, that their tissues become consolidated ;
and  by its deposition and subsequent organization upon  their free surfaces,
that false membranes and adhesions are  formed.   It appears probable, from
the recent inquiries of Mr. Robinson,* that  this deposition may be attributed
to physical causes.   It is well known, that  simple  Congestion will  occasion
transudation of the serous portion of the  Blood ;  and  if the  return  of the
Blood by  the veins of a part be completely prevented, a greater or less  pro-
portion of fibrine also may be poured forth.  Now  when the quantity of Fi-
brine in the blood is greatly augmented,  and the firmness of the walls of the
vessels  in the inflamed part is diminished by the alterations taking  place  in
their tissue, it is easy to understand that the disposition to the effusion of Fi-
brine will be much increased.   Sometimes the Fibrine is diluted with a large
quantity of Serum ; and is poured into a cavity (as that of a serous sac)  in
the form of  a liquid, which afterwards separates into clot and serum.

                * Medico-Chirurgical Transactions, vol. xxvi. p. 51.
                                   51* 
606
OF NUTRITION.
   804. Should the Inflammation increase in intensity, a complete stagnation
 of blood in the tissue most affected, or even in an  entire organ, will be the
 result; and this will occasion  its death.   If  a large  part be thus entirely de-
 stroyed at once, the process is termed Gangrene; and it separates from the
 living part, at a line where the Inflammation is less  intense, and where there
 is a deposit of Fibrine, which serves  the important purpose of closing the
 mouths of the blood-vessels that are laid open by the  process.  If the destruc-
 tion of tissue, however, be interstitial, the dead parts are not thus thrown off,
 but are taken up by the absorbent process ; and thus  the cavity of an Abscess,
 or of an Ulcer is formed.   This cavity is'usually bounded by tissue, that has
 been consolidated  by the effusion of Fibrine ;—a fact readily accounted for on
 the principles just stated.  For the death  and removal  of tissue take place,
 where the Inflammation has been most intense and the  stagnation most com-
 plete, which is in  the centre of the  inflamed spot; and the fibrinous effusion,
 the result  of  moderate inflammation, is poured  into  the  surrounding  tissue.
 The elements of Liquor Sanguinis  are poured into the central, as well as the
 peripheral, portion ofthe  inflamed tissue; but they assume a different form—
 that of Pus.   It would appear as if the influence of the surrounding death and
 decay produces a degradation of their character; so that they become entirely
 aplastic or unorganizable, although immediately derived  from  Blood  highly
 charged with  Fibrine.
   805. Between Coagulable Lymph and  Purulent effusions, there are many
 degrees of transition;  the very same deposit being  frequently organizable  at
 one part,—presenting the character of a tough fibrous membrane, interspersed
 with corpuscles,—whilst it is friable in another, from want of complete fibril-
 lation in the fluid  portion of the effusion,—and is entirely destitute of tenacity
 in a third portion, especially the superficial part, or free surface, of the deposit.
 When examined by the Microscope, Pus  is found to  be  characterized  by the
 presence of a number of cells  of a peculiar aspect, having a very tuberculated
 or mulberry surface; these are  seen floating in a fluid, termed liquor puris,
 which is of an albuminous or low fibrinous character, being entirely destitute
 of organizability.   Now the production of Pus in an  inflamed part, or in other
 words, the act of Suppuration, may be due to one of three causes, viz.—the
 intensity of the inflammation; the presence of air, which becomes a source of
 irritation;  and a  previously vitiated  state  of the blood.  Various  attempts
 have been made to show that the Pus-globule is a  degenerated red or white
 corpuscle of the  Blood ;  it seems  more  probable, however, that  it does not
 escape  from the vessels  as a complete cell, but as   a cell-germ, which may
 have  had  its  origin in a white corpuscle of the blood ;  and  which, under
 favourable circumstances, might have produced an Exudation-corpuscle (§ 800).
 At any rate, it must  be regarded as a degenerated form of cell; and the liquor
puris must be considered  as  analogous to the plasma of the Blood  in a de-
 generated state.
   806.  In what manner  the  Inflammatory process determines the formation
 of the Pus-cell, and the  consequent degradation of the  product, we are at
 present unable to  state ;  but that the degree of irritation in  the part  has  an
 influence upon it, is  evident from the effects of the contact of air upon inflamed
 surfaces, causing those elements to  take the form of  Pus, which would other-
 wise have been thrown out as a plastic deposit.  This  circumstance would
 seem to indicate, beyond all doubt, that the Exudation and Pus-corpuscles,
 the plastic Lymph and the aplastic Liquor puris have the same origin;  but
 that their  character is determined  by local circumstances.   There  is great
 reason to  believe,  that when Pus is introduced  into the Blood, it may induce
 such a change in the character of the fluid, as speedily to impair its vital pro-
 perties ; so that the  Pus-corpuscles will rapidly propagate themselves in  the 
ABNORMAL FORMS OF THE NUTRITIVE PROCESS.
607
Blood, and the plasticity of the Liquor Sanguinis will be diminished.  In this
manner the whole system will be seriously affected, and there will be a tend-
ency to deposits of Pus in various organs—especially in those which, like the
Lungs and Liver, serve as emunctories to  the  system—without any previous
inflammatory changes in these parts.   It has been ascertained by Mr. Addi-
son, that if a drop of Pus be treated with Liquor Potassae, it entirely loses its
opaque character, and becomes clear and transparent, like Mucus,—with whose
tenacity and elasticity also it becomes endowed.   If it be then treated with
acetic acid, it recovers somewhat of its former opacity;  and, when pressed
into a thin film, exhibits a distinct fibrillation.
  807. In persons  of that peculiar constitution, which  is termed Scrofulous
or Strumous, we find an imperfectly-organizable or Caco-plastic  deposit, or
even an altogether aplastic product, known by the designation of Tubercular
matter, frequently taking the place of the normal  elements of Tissue ; both
in the ordinary process of Nutrition, and still  more when  Inflammation is set
up.  From an examination of the Blood of Tuberculous  subjects it appears,
that the Fibrinous element is not deficient in amount,  but that it is not duly
elaborated;  so that the coagulum is loose, and the red corpuscles  are found
to bear an abnormally low proportion to  it.   We can understand, therefore,
that such a constant deficiency in Plasticity must affect the ordinary nutritive
process;  and that  there will  be a liability to the deposit of cacoplastic pro-
ducts,  without Inflammation, instead ofthe normal elements of tissue.   Such
appears to be the history of the formation  of Tubercles in  the lungs and other
organs, when it occurs as a kind of metamorphosis of  the ordinary Nutritive
process ;  and in this manner it may proceed  insidiously for a long period, so
that a large part of the tissue of the lungs shall be replaced by an amorphous
deposit,  without any  other  ostensible sign  than  an increasing  difficulty of
respiration.   It  is  in the different forms  of  Tubercular deposit, that we see
the gradation most  strikingly displayed between the plastic  and the  aplastic
formations.   In the semi-transparent, miliary, gray, and tough yellow  forms
of Tubercle, we  find traces of organization in the  form of cells and  fibres,
more or less  obvious ; these being sometimes almost as  perfectly formed as
those of Plastic Lymph, at least on  the superficial part of the deposit, which
is in immediate relation with the  living structures around; and sometimes so
degenerated, as scarcely to be distinguishable.  In no instances  do such de-
posits ever undergo further organization; and therefore they must be regarded
as caco-plastic.   But in the opaque, crude, or yellow  Tubercle, we do not
find even these traces  of definite structure; for the  matter of which  it con-
sists is altogether granular, more resembling  that which we  find  in an albu-
minous coagulum.   The larger the  proportion of this kind of  matter  in  a
tubercular deposit,  the more is it prone to soften, whilst  the semi-organized
tubercle has more tendency to contraction.  This is entirely aplastic.
  808.  Now although Tubercular matter  may be slowly  and insidiously de-
posited, by a  kind of degradation  of the ordinary Nutritive process, yet it can-
not be doubted that Inflammation has a great  tendency to  favour it; so  that  a
larger quantity may be produced  in the lungs, after  a Pneumonia has existed
for  a day or  two, than it would have required years to generate  in the pre-
vious mode.   But the character of the deposit still remains the same ; and its
relation to the plastic element of the blood is  shown  by the interesting fact, of
no  unfrequent  occurrence,—that, in a Pneumonia  affecting  a Tuberculous
subject, Plastic Lymph is thrown out in one part, whilst Tubercular matter is
deposited in  another.   Now  Inflammation, producing a  rapid deposition  of
Tubercular matter, is  peculiarly  liable to arise in organs, which have  been
previously affected  with chronic Tubercular  deposits, by an impairment of
the process of textural  Nutrition ; for these deposits, acting like foreign bodies, 
608
OF NUTRITION.
may of themselves become sources  of irritation; and the perversion of  the
structure  and  functions of  the  part renders it peculiarly susceptible of  the
influence of external morbific causes.—These views,  at which several recent
Physiologists and Pathologists have arrived on independent grounds, seem to
reconcile or supersede all the discordant opinions which have been upheld at
different times regarding the nature of Tubercle; and lead to the soundest
views with respect to the treatment  of the  Diathesis.
  809.  We frequently meet with abnormal growths  of a Fatty, Cartilaginous,
Fibrous, or even Bony structure;  which result from the development of these
tissues in unusual situations, and appear to originate in some perverted action
of the parts themselves.—But there is another remarkable form of  disordered
Nutrition, which is concerned in producing  what have been termed  hetero-
logous growths,—that is, masses  of tissue, differing  in character from any
which is  normally present  in the body.   Most  of  these are included under
the general designation of  Cancerous or Fungous structures ; and  it has been
shown by Muller and others, that the new growth consists of a mass of cells;
which, like the Vegetable Fungi, develope themselves  with great rapidity; and
which destroy the surrounding tissues  by their pressure, as well as by ab-
stracting  from the  Blood  the  nourishment which was  destined for them.
These parasitic masses have a completely  independent  power of growth and
reproduction;  and it  seems  difficult to  refuse them  the character of  distinct
existences.  They can be  propagated by inoculation, which conveys into the
tissues of  the animal  operated on, the germs of the peculiar cells  that consti-
tute the morbid  growth ; and these soon  develope  themselves  into  a new
mass.   It seems to be by  the  diffusion of the  germs produced in one part,
through the whole fabric,  by the circulating current,  that the tendency  to re-
appearance (which is one  great feature in  the  malignant character of  these
diseases)  is occasioned.  Yet there is  no  evidence, that  the  first  production
of a Cancerous growth is due to germs introduced  from  without;  in  fact, as
it appears to the Author, the history of its origin,  as well  as the analogy of
similar cases, makes  it far more probable, that the Cancer-cell is but an abnor-
mal form of the ordinary tissue-cells of the body,—being, in fact, a cell which
possesses  to an unusual  degree the  power of reproduction, instead of under-
going those transformations  by which  it  would be converted  into  other
kinds of tissue.
  a. Several instances have been recently published, of the occurrence of Vegetable organ-
isms as parasites upon the Animal body.   That in some of these a true Plant, possessing a
regular apparatus of nutrition and reproduction, has arisen from a germ introduced from
without, there can be little question; but in other instances (as in the case of the crusts of
Porrigo favosa), it has been assumed that  the organization is Vegetable, merely because it
consists of a mass of cells capable of extending themselves by  the ordinary process of mul-
tiplication.   But it must be remembered, that the cellular organization is common to Ani-
mals as well as to Plants; being the only form that manifests itself at an early period of
development in either kingdom, and  remaining throughout life in those parts which have
not  undergone a metamorphosis for special purposes.  Hence to speak of Porrigo favosa, or
any similar disease, as produced by the growth of a Plant within the Animal body, appears
to the Author a very arbitrary assumption; the simple fact being, in regard to this and many
other structures of a low type, that they present the simplest or most general kind of organ-
ization.  Their nature must be  decided by their Chemical constitution;  and this, in the case
of the Porrigo favosa, appears to be unquestionably Animal.
  b. There seems a strong probability in the idea, that the propagation of many diseases by
inoculation, essentially consists  in the transplanting of cell-germs from the body of one ani-
mal to that of another.   Thus the Vaccine Vesicle appears to be made up of an aggregation
of distinct cells, to which we may very fairly attribute an origin of this kind. But this seems
rather true of diseases which manifest themselves by a local development of cellular struc-
tures,—such as Cancer and Cow-pox,—than of such as Hydrophobia, Plague, Poisoning by
Serpents, &c, in which the symptoms are referrible, more or less clearly, to an alteration in
the character of the Blood, by the introduction of a  substance acting as a ferment (§ 708). 
VARYING DURATION OF CELL-LIFE.
609
        4.— Varying duration of different parts of the Organism.

   810.  From the foregoing details the obvious  inference results,—that each
part of  the organism has an individual Life of its own, whilst contributing  to
uphold  the  general  Life  of  the  entire being.   This Life, or  state of Vital
Action,  depends upon the due performance of the functions of all the subordi-
nate parts, which are closely connected together.  The lowest classes of or-
ganized beings are made up of repetitions of the same  elements;  and each
part, therefore, can perform its functions in great degree independently of the
rest.  But, in ascending the scale, we find that the lives of the individual parts
become gradually merged (so to  speak) in  the  general life of the structure ;
for these parts gradually become more and  more different in  function, and
therefore more and more dependent on each other for their means of support;
so that  the activity of all is necessary  for the  maintenance of any one.
   811.  The doctrine of Development from Cells gives us a clearer idea of the
nature ofthe continual process of decay and renewal, which take place in the
Animal  body.  Every Cell has, to a certain degree, an individual life of its
own.  This individuality is much more decided in the lower forms of organ-
ized being, where each cell can maintain an  independent existence, than it is
in the higher, in whose fabric a  large number having different  functions are
united  into  one structure, the combined activity of the whole of  which  is
necessary to the life of  any one.  But, even in the highest, it is evident that
each cell will possess a certain duration of its  own; and that, from its  first
period of development, all the changes which it undergoes are governed by
laws peculiar  to it.   In the various parts of the  Vegetable, as in those of the
Animal, we find a great difference in  the duration of the existence of the cells
composing them.  These differences  may be reduced to five heads.
   i. Cells may be generated, which  have a very transient existence,  and
which disappear again, without undergoing any transformation.   This may be
seen in  the Vegetable ovule, and in the Germinal Vesicle of the Animal Ovum ;
as well  as in many other parts.  Thus we  have Absorbent Cells  (§ 181),
Secreting Cells (§ 179), and probably Assimilating  or Fibrine-elaborating
Cells (§ 154); all of which originate  in pre-existing germs, attain  their full
development (in the course of which they perform their  allotted function),
and then disappear by rupture or liquefaction.  In such instances it is obvious
that, from their first origin, the cells are subject to a law of limited duration,
and  that their  death and decay are as  much the  result of their inherent consti-
tution, as are those of each entire Animal or Vegetable organism.
   n. The contrary extreme to this may be found in those Cells, of which the
function, instead of being transient, is to be indefinitely prolonged; such are
those of which the organs of  mechanical support are usually formed.  Here
the cell, instead of changing its form, or of giving origin to new cells within
itself, becomes the subject of an  internal deposit of hard matter, which lines
its walls, and cuts  it off, more or less completely, from  the general  course  of
Vital Action.  When this is the  case, and the hard matter is not itself liable
lo decomposition, the duration of the  cell-walls,  which  are protected by their
peculiar aggregation from exposure to decomposing agents, may undergo little
or no change for an almost indefinite period.  Thus the heart-wood of Plants,
the Bones of Animals, and still more  their Hair, Hoofs, Horns, Sic, may re-
main unaltered through a long series of years.   Of some of these parts it can
scarcely be said that they are less alive, when removed from the organism to
which they belonged, than when included in it.   In the heart-wood of a Plant,
for example, no vital change takes place, from the time  that the woody tubes
and cells are once consolidated by internal deposition;  it may decay, whilst 
610
OF NUTRITION.
still forming part of the stem, without interfering with the nutritive operations
of the tree ;  and if we could possibly remove it entirely, without doing injury
by the operation to the rest of the structure, its absence  would be productive
of no  other  evil consequences than those which would necessarily result
from  the  withdrawal of the mechanical support  afforded by it.   The same
may be said of the Epidermic Appendages  of  Animals,  and of the  External
Skeletons of many Invertebrata;  which remain equally  unchanged  from the
time of their first formation.—Now as long as  these structures hold  together,
it is evident that the organized  part of them must have undergone little change
from the condition in  which it  existed in  the living fabric; and that their
death takes  place, in  reality, only when the structures   decay,—this decay
being, in  fact,  the consequence of it.   The law  of existence of such  cells,
therefore, is that of indefinitely-prolonged duration;  this law must have been
impressed upon them from their origin; and the power by which their walls
secrete and deposit the consolidating materials,  appears to be the chief means
of keeping it in operation.
   m. In  all the higher forms of Animal structure, the Cells originally com-
posing it are only the  means of generating  tissues of other kinds, in which
the Cellular character is less obvious.   Thus the  Muscular and Nervous tis-
sues  have their origin  in cells, which at first  appear in  no respect  different
from others,  but which subsequently undergo a peculiar  metamorphosis, and
themselves no longer exist as  such.   Upon all these primordial cells, there-
fore, a law of transformation  is  impressed, from  the time of their first  pro-
duction.   In  their original aspect, they cannot be distinguished  from the cells
which are not destined  to undergo any  such metamorphosis; but, just as  the
first cell of the embryo, from which Man is produced, must have some real
though not apparent difference  from that in which the Polype originates, so
must the cell which is afterwards developed into Muscular Fibre, be inherently
different from that which is subsequently converted into Nervous tissue.
   iv.  The tissues, thus formed by the transforming processes to which certain
Cells  are subject, are  evidently governed by the  same  laws of Nutrition as
those  which regulate ordinary Cell-growth;  these are modified in their action,
however, by  the conditions in  which they are placed, in regard to the activity
ofthe function  which the Tissue is called upon to perform.   In all instances,
however, these  Tissues have a limited period of existence.   They are gene-
rated, they grow  from the alimentary materials  with which they are supplied,
they arrive at maturity, they decline, they die, and they decay ; just as do the
isolated vesicles  constituting the humblest  forms  of vegetation.   For all of
them there is an appointed duration of life, just as there is for the  entire Man.
—Now on this view we can explain  many  physiological phenomena, which
cannot otherwise be  very satisfactorily accounted for.  It  is owing to the con-
tinual death and decay of its component cells, that the process of decomposition
goes on with such constancy and uniformity in the  living  body; whilst, on the
other hand, it is by  the continual reproduction of  new cells, in  the  place of
those which  have disappeared, that the normal organization is  maintained.
The limited  duration of the life of the cells  composing the  various tissues is
further made  evident, by the rapid disappearance of the  normal organization,
and by the loss of the functional power of  those tissues, when the cessation
of their activity prevents the development of the  new cells, by which  alone
their character  can be maintained.  Of  the  change of structure  and loss of
power which result from disuse and consequent want of nutrition in Muscular
and Nervous tissues, instances have  already been given (§§ 588 and  790).
The ordinary processes of Decomposition and Interstitial Absorption are pro-
bably less rapid than usual under such  circumstances; so that the length of
time required  for the  disappearance of the characteristic structure, and  the 
VARYING DURATION OF DIFFERENT PARTS.
611
consequent loss of functional power, affords us some idea of the limit to the
duration of the  life  of the  tissue.   It may be  stated, then, as a general  pro-
position, that the interstitial change, which the whole structure of the body is
continually undergoing, in its normal or physiological condition, is due to the
regularly-occurring death and  reproduction of  its component cells, of which
every  one has  its own  limit  of duration.  We uniformly find  that  those
Tissues, in which the  most active vital  changes are going on  (such as  the
Nervous and  Muscular), are those  in which the duration of the individual
component portions is the least;  as  is shown by the rapidity of the  changes
of removal and reposition, which are continually taking place in them.   The
converse holds good also.  Further it may be remarked,—and this is a matter
of much practical importance,—that anything which increases  the functional
activity of any particular tissue, thus causing it to live faster, diminishes  the
duration of  its life; as is shown in the  increased rapidity of disintegration,
which results  from  the  continued  exercise of the  Muscular  and  Nervous
systems.
  v. There  is yet another phase, under which Cellular life presents itself as
a natural condition in the lower organisms, and in the early condition of the
higher; but which constitutes  a morbid  state  in the adult condition of  the
latter.   This is when  cells  reproduce themselves with  extreme rapidity,—
neither the primary nor  secondary cells  undergoing any further transforma-
tion,—and the duration of each individual being limited by the development
of its progeny within it, causing its own distension and final rupture or dis-
appearance.   The growth of the lower Fungi offers a striking example of this
in the  Vegetable kingdom ;  and  the  early processes of development in  the
Ovum of the highest Animals,  exhibit the same character.  Every cell, as it
is generated, proceeds at once to the work of multiplication,  for  which it
seems specially destined; and  thus it is  subject  from the first to the law of
Reproduction.   It is this which distinguishes  the Fungoid diseases; which
derive the character designated by the Surgeon as malignancy, simply from
their tendency to propagation, and his want of  power to control  it.   It seems
probable that  many other changes of structure are due  to a corresponding
cause.
  812. The duration of the existence of the individual Cells in corresponding
parts, is further  subject to variation,  in accordance with the period of life of
the entire organism.   Thus all the tissues, even those most consolidated, are
undergoing continual changes in the  young animal, in which the processes of
decay and renewal go on  much faster than in the adult;  and in the adult, than
in the aged person.  Even the  cells ofthe Bony structure, which in the adult
are almost permanent, and in  the aged person  are subject to extremely little
change, are liable in the infant  to an  early decomposition; their places being
filled up by others, of which the form adapts itself to the growth of the struc-*
ture.   This  may be partly accounted for  by the imperfect  degree, in which,
so long as the  entire organism is undergoing rapid increase, the normal struc-
ture is developed in any  one portion of it;  for the degree of  consolidation
being less, the tendency to decay will naturally  be greater.   But  this explana-
tion is not in itself sufficient; and  we  must  be content for the  present to
regard it as a general law (which may ultimately prove to be but a result of
some  more general principle) that the duration  of the existence  of individual
cells increases, caeteris paribus, with the advance of life.   At the same time,
their functional activity diminishes.   They may be said to live more slowly.
The dull perceptions, and slow and feeble  movements, of the aged  man, form
a striking contrast with the acute sensibility, and the rapid and vigorous mus-
cular actions, of the child; and  the same change may be noticed in the organic
functions.  Hence it may be stated as a general law, that the vital activity of 
612                          OF NUTRITION.
the Cells (and of the tissues produced  by their transformation) diminishes in
proportion to the prolongation of the general life of the system; and this law
exactly corresponds with what has just been observed, as to the comparison
of the tissues of different kinds, which are present in the  same body.

                5.—Of Death, or Cessation  of Nutrition.

   813. It is a necessary consequence of that  intimate mutual dependence of
the several  operations, which  is characteristic of the higher  organisms, that
the interruption of the function of any one important part is followed by the
Death of the whole structure; because it interferes with the elaboration, cir-
culation,  or depuration of that nutritive fluid, which supplies the pabulum for
the growth and reproduction of each portion  of the system.  But the  lives
of individual parts may be prolonged for a greater  or less duration, after the
suspension of the regular  series of their combined operations; hence  it is
that Molecular Death is not always an immediate result of Somatic Death.—
But, on the other hand, if the  function of the part have no immediate relation
to the  indispensable actions just  alluded to,  it  may cease  without affecting
them;  so that Molecular death may take place to a considerable extent (as in
entire limbs, or in the muscles and integuments of  the head and trunk) with-
out Somatic death necessarily resulting.
   814. The permanent and complete cessation of  the Circulating current, is
that which essentially constitutes Somatic  Death;  and this  may be traced to
several distinct causes.—In the first place, it may be due to  failure in the pro-
pulsive power of the Heart, which constitutes Syncope;  and this may result
from a variety of causes, which cannot be here  particularized.—Secondly, it
may be occasioned  by an obstruction to  the flow of blood through the capil-
laries of the lungs, constituting Asphyxia; and  this, as we have seen,  may
be consequent upon disordered states of the  lungs  themselves, or upon  sus-
pension  of  the respiratory movements, through  affections  of the Nervous
centres.  It  is in this mode that most fatal  disorders of  the Nervous System
produce death;  except when  a sudden and violent  impression (as from  con-
cussion of the  brain, or a blow on the epigastrium) occasions a cessation of
the heart's power.  Thus in Apoplexy, Narcotic Poisoning,  &c, death results
from the paralyzed condition of the Medulla Oblongata; whilst in the  con-
vulsive diseases, the  fatal result  ensues upon  a spasmodic  fixation of the
respiratory muscles.—Thirdly, Somatic  death may be  occasioned by a  dis-
ordered condition of the Blood itself, which  at  the same time weakens the
power of the Heart, impairs the activity of the Nervous system, and prevents
the performance of those changes in the systemic  capillaries, which afford  a
powerful auxiliary to the circulation. This is Death by Necraemia.—Fourthly,
Somatic death may result directly from the agency of Cold, which stagnates
all the vital operations of the system. Where the cooling is due to the agency
of an extremely low external  temperature, which acts first upon the super-
ficial parts, there is reason to think- that the congestion of the internal vessels
thereby induced, occasions a torpid condition  of the nervous centres, and that
the cessation of the Circulation is immediately due to Asphyxia.   But when
the cooling is gradual, and the loss of heat is nearly equally  rapid throughout,
it is obvious that the  stagnation will be universal, and that no cessation of
activity in any one  part is the occasion  of  the stagnation in the functions of
the remainder.  It is in this  manner that death results from Starvation; and
not by the weakening of the heart's action,  as  commonly supposed.   The
proofs of this will be stated hereafter (§ 896).
   815. That Molecular death should speedily follow Somatic death, is not
surprising; when it is borne in mind how  constant is the dependence of all 
OF DEATH, OR CESSATION OF NUTRITION.
613
those functional  operations, in  which vital  activity  consists, upon the due
supply of the circulating fluid.  And as a general rule we find, that the more
active the changes which  normally take  place  in  any tissue during life, the
more speedily is  its complete loss of activity, or Death, when the requisite
conditions of its vital action are no longer supplied to it.  We  may observe
that, in  Cold-blooded animals, the supervention of Molecular upon Somatic
death is  much less speedy than it  is in Birds  and Mammals.   This seems
due to two causes.   In the first place, the tissues of the former, being at  all
times possessed of a lower degree of vital  activity than those  of  the latter,
are disposed to retain it  for a longer time; according to the principle  already
laid down.  And, secondly, as the maintenance of a high temperature is  an
essential condition  of the  vital  activity of the tissues of warm-blooded ani-
mals, the rapid cooling of the body after Somatic death is calculated to extin-
guish it speedily;  and that  this  cause has a  real operation, is evinced by the
influence of artificial warmth in sustaining  the vital properties of separated
parts.—The rapidity with  which Molecular death follows the cessation of the
general  circulation, will  be influenced by a  variety of causes; but  especially
by the degree in which the condition of the solids and fluids of the body has
been impaired by the  mode of  death.  Thus in Necraemia, and in death  by
gradual  cooling, Molecular and  Somatic death may be said to  be  simultane-
ous ; and the same appears to be true of death by sudden and violent impres-
sions on the Nervous System.   But in many cases of death by causes, which
suddenly operate in producing  Syncope  or Asphyxia, the tissues  and blood
having been previously in a healthy condition, Molecular death may be  long
postponed.   We cannot be quite certain that it has supervened,  until signs of
actual decomposition present themselves.
   816.  When Molecular death  takes place  in an isolated part, it must result
from  some  condition peculiar to that  part; and not primarily affecting the
body in general.  Thus  we may have Gangrene or Mortification of a limb as
a  direct  result of the application of severe cold, or of an  agent capable of
producing chemical changes in its  substance, or of violent  contusions occa-
sioning mechanical injury; or, again, from  an interruption to the current of
nutritive fluid; or,  further, from some  ill-understood stagnation of the nutri-
tive process, which  manifests itself in  the  spontaneous death of the  tissues
without any assignable  cause, as in some cases of Senile Gangrene.   Some-
times we are enabled to trace this  stagnation to some disordered condition  of
the circulating fluid; as in the Gangrene resulting from the continued  use  of
the Ergot of Rye or Wheat; but we can give no other  account  of the  almost
invariable commencement  of such  gangrene in the extremities, than we can
of the  selection of  Lead, introduced  into the blood, by the extensors  of the
fore-arm.—When Mortification or Molecular Death is once established  in any
part, it tends to spread, both to contiguous and to distant portions of the body.
—Thus we  have continually to witness  the extension  of Gangrene  of the
lower extremities, resulting  from severe injury or from the use of the  Ergot,
from the small part  first affected, until  the whole limb is involved; and this
extension is easily accounted for  by our knowledge ofthe tendency of organic
substances  in the act of  decomposition, to produce a similar change in other
organic substances subjected to their influence.  And the propagation  of the
Gangrenous tendency to  other parts, is obviously due to the perversion ofthe
qualities  of  the Blood, which results from a similar  cause.  It is not, how-
ever, until some organ is affected,  whose  action is essential to the due main-
tenance  of the Vegetative functions, that Molecular death becomes a Cause  of
Somatic  death; and very extensive ravages  may thus take place without the
extinction of the  sufferer's life.
    52 
614                          OF SECRETION.
                        CHAPTER  XV.

                             OF SECRETION.

                      1.—Of Secretion in General.

  817.  The literal meaning of the term Secretion is separation;  and this is
nearly its true acceptation in  Physiology.  We have seen that the Nutritive
materials, which are received  into the  living body, are combined in a certain
proportion in the circulating fluid;  and that they are carried in its current  to
every part of the structure.  Of the elements of the Blood, some are being
continually separated from  it, to be introduced into the solid textures, of which
they become constituents;  forming, as it were, the  organized frame-work, in
the interstices of which various  other matters (also  separated from the blood)
are deposited in  an inorganic  condition.  This separation, the object of which
is to build up a living fabric, has been already considered  under the head  of
Nutrition; but it may be here  remarked, that  the  deposition of Calcareous
matter in the Bones  and Teeth,  of Chondrine and Gelatine in the Bones and
Cartilages, and of Horny matter in the  cells of the Epithelium and  its  ap-
pendages (Hair, Nails, Hoofs, Sic), is accomplished by a process analogous
in all respects to that  concerned in the separation  of those  other products
which are ordinarily considered  as Secretions.  The same may be said of the
Serous fluid, which  distends the interspaces of Areolar tissue, the Oily matter
contained in  the Fat-cells,  the Albuminous fluid of the Humours of the Eye,
and other analogous constituents of the living fabric.
   818. But we  have chiefly to  consider under  the present  head, the nature
and origin of those  products which are continually being  cast forth from the
living body; the amount of  which is usually equal, in the  adult animal, to
that of the solids and  fluids  ingested,  after allowance  has been made for  the
portion rejected, in the form  of  faeces, as indigestible.   The  experiments of
Dr. Dalton* on  his own person, give  the following as the  proportional quan-
tities discharged through the principal  channels of excretion.   The mean
quantity of solid and  liquid Aliment taken into  the system  daily (during 14
days in spring) being 91 oz.,  or about 5f lbs., the average amount of Faeces
(including part of the solid matter of the bile) was 5 oz.; the  average amount
of  Urine was 48£ oz. daily; and,  as  the total weight of the body remained
the same, the quantity of fluid and solid matter excreted by the Skin and the
Lungs must have been 37s oz.  At other periods of the year, a variation was
observed ; especially in the relative amount of fluid passing off by the Urine,
and by Cutaneous exhalation.
   819. It can scarcely be  questioned, that the chief source ofthe Excretions
is to be found in the continued Decomposition  of the various tissues of the
body, which has been several times alluded to (§§ 275 and 811); and it is pro-
bable, from considerations  heretofore  adduced, that they are derived, not so
much from the fluid returned into the  blood  by the Lymphatics (as formerly
supposed), as from the Blood itself (§  680).  It has been pointed out by Lie-
big, that there is a remarkable  correspondence between the elements of  the
Blood, and those of the Bile and Urine  taken  together; so that the Tissues,
* Edinburgh New Philosophical Journal, 1832, 1833. 
OF SECRETION IN GENERAL.
615
which are all formed from the  nutritive  fluid, may be regarded  as  resolving
themselves, by  their ultimate decomposition,  into  these two  excretions.
Moreover, the Blood, during its circulation, gives up one portion of its con-
stituents in one part of the body—another at a different situation,—and so on.
Thus, the elaboration of Gelatine, which  is deposited so largely in  the  solid
tissues, must occasion a considerable alteration in the blood: since, in its pro-
duction from Albumen, a  certain residuum must be left (§  141, b, c).   This
residuum is probably another important source of the products of Excretion.
The same may be remarked in regard to the Nutrition  of  the Nervous Sys-
tem (§ 249).  In several  other instances, peculiarities  of action in different
parts  will deprive the Blood that passes  through them, of its due proportion
of certain of its  constituents ;  these are  partly restored by its admixture in
the Heart, with the Blood that has returned from other parts ; but still  a gene-
ral alteration in the character of the  Blood is the result of its Circulation ; and
for this alteration, it is the province  of the Excretory function to  compensate.
A striking illustration may be found, in the change  of the colour, and of the
proportional amount of free Oxygen and Carbonic Acid, which takes place
in the Systemic capillaries,  and which is reversed in the passage  of the Blood
through the Lungs (§ 766).—Moreover it appears  that two, at  least, of the
Excreting organs have for their function to prevent the  accumulation, in the
Blood, of matters which have  been taken  in as food, but for which there is
no demand in  the  economy.  Thus the Liver appears to be  the peculiar
channel for the elimination  of superfluous non-azotized matter (§ 833) ;  and
the Kidney of  these  azotized compounds, which cannot be worked  up (so
to speak) into tissue (§ 842).  Particular  sources for the respective contents
of other Excretions will be pointed out, when they  are considered in  detail.
   820. A  distinction  has already been  drawn  (§278) between the  proper
Excretions, the retention of which in the Blood would be positively injurious,
and those Secretions which are destined  for particular purposes within ihe
system, and the cessation of which has no immediate influence on any  but the
function to which they are destined.  This distinction is one of great  import-
ance, especially when it is considered with reference to the Chemical Elements,
that are found in  the two classes of fluids respectively.   The solid matter dis-
solved in those of the latter class, is little else than  a portion of  the constitu-
ents ofthe Blood, either pure, or but slightly altered ; thus, in the Lachrymal
fluid, the Saliva,  the Pancreatic juice, the Serous fluid of areolar tissue and
of serous  and synovial membranes, we find little else than Albuminous and
Saline matter, derived at once  from the blood.   The Caseine, which is the
most  characteristic  ingredient of Milk (§ 854 b), is but a slightly-altered form
of Albumen; and some curious evidence has recently been obtained, that this
alteration commences  in the Blood, and goes on during pregnancy  as a pre-
paration for lactation.*  On  the other hand, the characteristic ingredients of the
Excretions are very different in  character from  the normal elements of the
Blood.  They are all  of  them completely unorganizable;  and they possess,
for the most part, a simple atomic constitution.   Some  of  them  also, have a
tendency to assume a crystalline form ; which is considered by Dr. Prout to
indicate their unfitness to  enter into the composition  of organized  tissues.
With regard to some of the chief of these, there is sufficient evidence  of their
existence, in small  quantity, in the circulating Blood; but it is also, clear, that
they exist there as  products of decomposition,  and  that they are destined to
be separated from it as speedily as possible. If their separation be prevented,
they  accumulate, and communicate  to the  circulating fluid a positively delete-
rious character.   Of this, we  have already seen a striking example in the
* See Dr. G. Bird, in Guy's Hospital Reports, vol. v. 
616
OF SECRETION.
case of Asphyxia (§ 779); and the history of the other two principal Excre-
tions, the Bile and  Urine, will furnish evidence  to  the same effect.—As  a
general fact, then, it may be  stated, that the  materials of the Secretions pre-
exist in the Blood, in a state  nearly resembling that in which they are thrown
off by the-secreting organs: but that the materials of those secretions, which
are only destined  to perform  some  particular function in the economy, are
derived from the substances which are appropriated to its general purposes;
whilst those  of the excretions are the result of the changes that have taken
place in the system, and cannot be retained in it without injury.
   821. Of the reason why certain compounds forming part of the circulating
Blood, are separated from it by one  organ, and others by  a different one, no
other account  can be given, than that which refers them to the special endow-
ments  of the cells, which are the real instruments of the process.  When the
ultimate structure of Glands is considered, it is found to be  neither more nor
less than a vascular  membrane, covered with epithelium-cells, and made up
into various forms for convenience of packing.  Of such  a membrane, in its
most expanded state, that which composes the walls of the  Serous cavities, or
of the  Synovial capsules, affords a  good example.   Of Mucous membrane
(§ 178), the structure is  in some instances  almost equally simple ;  but in gene-
ral the secreting surface is extended, by the  inversion of the membrane, into
a large number of little  open  sacs or follicles (Fig. 45), which are lined with
epithelium-cells, and copiously  supplied  with  blood-vessels,  and which  are
equally concerned with  the external superficies, in the elaboration of the pro-
tective secretion that covers these membranes.  In the most complex form of
gland,  we  find  nothing but  a very obvious  modification  of this structure.
Either the sacs are prolonged  into cceca or blind tubes, as  is the case in  the
Human Kidney or Testis; or they are very  greatly multiplied, and  are clus-
tered together  (just like  currants upon a stalk) upon efferent ducts common to
several of them, as is seen in  the Parotid.   Now, that the particular modifica-
tion of structure, which the Gland may present, has no essential connection
with the character ofthe Secretion it is destined to form, is  evident from this
circumstance,—that almost every gland may be found under a variety of forms,
in different parts of the Animal series.  The Secreting system, like every
other, is far simpler in  the lower classes  of  Animals than  in the higher; the
number of effete compounds, to be excreted from the circulating fluid, is  much
smaller; and the variety of purposes, for which special secretions are required,
is much less.   Hence, for almost every Gland, there  is a part of the Animal
scale below which it does not exist; and  when it  makes its first appearance,
it almost invariably presents a character nearly as simple, as that of  the least
complex glanular structures in the higher animals.  Thus the  Pancreas in
Fishes (Fig. 257), the Mammary Gland in the Ornithorhyncus (Fig. 222), the
                                   Salivary glands  in  the Echinodermata,
             Fig. 222.               and  the Urinary organs of Insects,  are
                                   nothing more than follicles more or less
                                   extended, and having  separate orifices.
                                   Again,  in Insects, we find  that all  the
                                   glands,—the Liver and Salivary glands,
                                   as  well as  the  Kidneys  and Testes,
                                   —have the  form of  prolonged  tubes;
                                   Whilst  in  Mollusca, all  the  secret-
    Mammary Gland of Ornithorhyncus,     ing  organs,—the Urinary  and  Genital,
                                   as well as the Biliary and Salivary,—
consist of multiplied vesicles connected with a ramifying duct.   Moreover, it
is a well-ascertained fact that,  even in the  highest organisms, the functions of
Glandular structures (especially of those  concerned  in  Excretion)  are to  a
 
OF SECRETION IN GENERAL.
617
certain degree vicarious with each other ; so that, when the secretion from one
of them is checked, the system makes an effort to throw off, by another chan-
nel, the injurious  products that  would otherwise  accumulate  in the Blood.
What is the nature of the change in any secreting organ, that causes it thus to
take upon itself a  new function,  is  a question upon which we can at present
only speculate;  we have no more  certain  knowledge of it, than we have of
the cause which occasions their normal actions.
   822. It has been recently proved, beyond  all reasonable doubt, that in all
secreting organs, the Cells which cover the membranous surfaces, and line the
follicles and tubes, constitute the  really operative part.   The  simplest condi-
tion of a Secreting Cell, in the Animal Body, is that in which it exists in Adi-
pose tissue ;  every cell of which possesses the power of secreting or separat-
ing Fatty matter from the Blood.   In this case, the secreted product remains
stored up in the cavity of the cell, as it usually does in the Cellular tissue of
Plants ;—not being poured forth, as it generally is  elsewhere, by the subse-
quent bursting or liquefaction of  the cell.   But when the Secreting Cells are
disposed on the surface of a membrane, instead of being aggregated in a mass,
it is obvious that, if they burst or dissolve away, their contents will be poured
into the cavity bounded by that membrane ; and this is the case in the ordinary
Secreting processes.  Thus the Mucus, which covers the surface of  the  Mu-
cous membranes,  and  which is  being continually  renewed, is the product of
the elaboration  performed by the Epithelium-cells, which cover their free sur-
faces, and line their follicles.  These cells are being continually cast off, and
replaced by a fresh growth, which has its origin in germs supplied by the
subjacent membrane ; and thus it is by the act of Cell-growth, that the Secret-
ing process is accomplished.  For just as the cells at the extremities of the
Intestinal Villi  select, from the contents of the alimentary tube, the nutritious
portion which is to be introduced into the absorbent vessels,—so do the cells
of the Secreting Tubuli or Follicles select from the Blood those effete particles
which it is their peculiar province  to assimilate, and then discharge them into
the canals by which they will be carried out of the system.*   Hence, as Mr.
Goodsir justly remarks, " there are not, as has been hitherto supposed, two
vital processes  going  on at the same  time, viz., growth  and secretion; but
only one, viz., growth.   The only difference between this kind of growth,
and that which  occurs in other organs is, that a portion of the product is, from
the anatomical condition  of the part, thrown out of the  system."
   823. From the  study of the  changes  which  take place in the Glandular
organs, during their first  development and their continued activity, Mr. Good-
sir has  arrived at the conclusion, that the follicles  may be considered as pa-
rent-cells ;  and  that the secreting cells in their interior may be regarded as a
second  generation, developed from the nuclei or germinal spots on the walls
of the first.   Now the successive production and  development of the latter,
in which the process of secretion essentially consists, may take place on two
different plans.

  a.  In one class of Glands, the  parent-cell, having begun to develope new cells in its inte-
rior, gives way at one point, and bursts into the excretory duct, so as to become an open fol-
licle, instead of a closed cell; its contained or secondary cells, in the progress of their own
growth, draw into  themselves the matters to be  eliminated from the blood, and, having at-
tained their full term of life, burst or liquefy, so as to discharge their contents into the cavity
of the follicle, whence they pass by its  open orifice into the excretory duct; and a continual
new production of secondary cells takes place from the germinal spot or nucleus at the ex-
tremity of the follicle,  which is here a permanent structure.  In this form of gland, we may
frequently observe the secreting cells existing in various stages of development, within a
  * We shall hereafter meet with an  instance (§ 829) in which, from the position of the
cells secreting it, Adipose matter is discharged from the body as an Excretion.
                                     52* 
618
OF SECRETION.
 single follicle;  their size increasing, and the character of their contents becoming more dis-
 tinct, in proportion to their distance from the germinal spot (which is at the blind termina-
 tion of the follicle), and their consequent proximity to the outlet (Fig. 41).  In some varieties
 of such glands,  however, especially when the follicles are extended into prolonged tubes, the
 production of new cells does not take place from a single germinal spot at the extremity of
 the follicle, but from a number of points scattered through its entire length.
   b. In the second type of Glandular structures, the parent-cell does not remain as a perma-
 nent follicle; but, having  come to maturity, and formed a connection with the excretory
 duct, it discharges its entire contents into the latter, and then shrivels up  and disappears, to
 be replaced by newly-developed follicles.  In each parent-cell of a gland formed upon this
 type, we shall find all its secondary or secreting cells at nearly the same  grade of develop-
 ment ;  but the several parent-cells, of which the parenchyma of  the gland is composed, are
 in very different stages of growth at any one period—some  having discharged their contents,
 and being in progress of disappearance, whilst others are just arriving at maturity, and con-
 necting themselves with the excretory duct; others exhibiting an earlier  degree of develop-
 ment in the secondary cells; others presenting the latter in their  incipient condition; whilst
 others are themselves just starting into existence, and as yet exhibit no traces of the second
 generation, which they are destined subsequently to develope.
  c. The former of these seems to  be  the usual type of the ordinary glands; the latter is
 chiefly, if not entirely, to be met with among the Spermatic Glands.*

   824.  It is  important to bear in  mind, that  an essential difference exists be-
 tween the vital power  concerned  in the true Secreting process, and the phy-
 sical property  which  occasions fluid Exhalation or Transudation.   This dif-
 ference is  precisely the same   as  that which exists between  the vital act of
 Selective Absorption, and the physical  operation of Endosmose or Imbibition.
 By Imbibition  and Transudation,  certain  fluids  may  pass through  organic
 membranes, in the  dead  as well  as in  the living body;  and this passage de-
 pends merely upon the physical condition of the part, in regard to the amount
 and the  nature of the  fluid it contains, and the permeability of its tissues.
 Not only does water  thus  transude, but various  substances  that  are held in
 complete solution  in it, especially albumen  and  saline matter: it  is in this
 manner that  the Blood absorbs  fluids from the digestive cavity (§ 675), and
 pours  out the serous fluid which occupies the interspaces of the  areolar tissue
 and the serous  cavities.  The transudation of the watery portion of the blood
is much increased  by  any impediment  to  its flow through the vessels, as in
 Congestion and  Inflammation; and also  by any causes that  produce a dimi-
 nished resistance in  their walls.—We shall hereafter see, in examining the
 Physiology of  the  Urinary secretion, a very  striking example of the contrast
 between physical Transudation and vital Secretion (§  840).


                     2.— The Liver.—Secretion of Bile.

   825. The  Liver  is  probably more  universally found, throughout  the Ani-
mal scale, than any other gland.   Its form  varies  so greatly, however, in dif-
ferent  tribes,  that, without a knowledge  of its  essential structure,  we should be
disposed to  question whether  any identity of character exists  amongst the
several organs which we include under  this designation.

  a. In the higher Polypes, for example, we find it  to consist of a number of distinct folli-
cles, lodged within the walls of the stomach, and pouring  their  secretion into its cavity by
as many separate orifices;  and it is  more by the peculiar character of their secretion, than
by any other  distinction, that these follicles are recognized as Hepatic.—In the lower Articu-
lata, a very similar conformation is met with ; but in the higher classes of  this series, such
as Insects, the follicles are prolonged into tubes of considerable  extent.   It is very curious
 to observe, in animals of such complex structure, that a few long tubes,  closed at one end,
and opening  at the other into the alimentary canal, are  all  which  they have to represent  a
 Liver;  but the  wonder is readily accounted for by keeping in view  the extremely active
* See Goodsir's Anatomical and Pathological Researches, Chap. v.
■livS"-- 
THE LIVER---SECRETION OF BILE.
619
Respiration of these beings, which renders unnecessary any other complex apparatus for ela-
borating carbon from the system.
  b. On the other hand, among the Mollusca, the Liver attains a much greater development.
Instead of the follicles  being prolonged into tubes (which is the usual form of the glandular
system in Insects),  they are very much increased in number, and arranged on the sides  of
canals or efferent ducts, which either separately pour their fluid into the intestine, or partially
unite with each other  before doing so.  The Liver thus acquires a lobulated character, each
lobe consisting of a duct with its branching follicles; and the whole  organ forms  a consider-
able proportion  of the mass of the viscera, and is evidently of great importance in the
economy of the animal.—It is interesting to compare this complex  structure with the very
simple condition presented by the Liver in insects; and, when we keep in view the relative
amount of  Respiration in the two groups of animals, we are at once struck with the fact,
that the development  of the Liver bears an inverse proportion to the opportunity afforded
by the Respiratory organs for the aeration of the blood;  it being peculiarly extended, when
these, either from their small  size, or from their employment in an aquatic medium, cannot
perform their function with  great  activity.  This conclusion is confirmed in an  interesting
manner by the fact, that the Crustacea, which have the general organization of Insects, but
which inhabit the water and breathe by gills instead of by a complex system of air-tubes,

                    Fig. 223.                           Fig. 224.
   Lobule of Liver of Squilla Mantis; exterior.     Lobule of Liver of Squilla Mantis cut open.

possess a Liver  corresponding in  form and in degree  of development with that  of the
Mollusca.
  c.  In the Vertebrated Sub-kingdom, we may trace the operation of the same principle;
but the internal structure of the Liver, in the adult condition at least, is less  easily demon-
strated, than  it is in the lower classes; owing to its increased complexity of  structure, and
the closer union between its different parts.  In Fishes and Reptiles, the Liver is of consider-
able  size, and seems to perform a very important part in the decarbonization of the  blood:
its form is adapted to that of the cavity in which  it is lodged, sometimes one lobe only being
developed. In Birds, on tbe other hand, whose respiration is so much more active, it is much
smaller, but is placed on the median line, in conformity with the general symmetry of their
internal as well as external organs  (§ 40).   In Mammalia, also, it is comparatively  small;
but, though reduced in proportional  size, it is at  the same time much more compact and
firm than in  the lower Vertebrata.
  d.  The Liver of Man  is much less developed than that of many other Mammalia; and
presents, as rudimentary indications, certain organs which are elsewhere  fully developed.
The  whole mass, which we are accustomed to  describe as consisting of a right and left lobe,
does in reality form but one (there being no real division between its two  portions), which
must be regarded as the Central lobe; the Lobulus Spigelii is the rudiment of a second or
right lobe, and the Lobulus Caudatus  is a Lobule developed from it.  In the Carnivora and
Rodentia, which present the most complex form of Liver that we meet with  among Mam-
malia, there  are  five distinct  parts;—a central or principal  lobe, corresponding with the
principal part of the liver of Man; a right lateral lobe with a lobular appendage, correspond-
ing to the Lobulus Spigelii and Lobulus Caudatus;  and a similar lobe and lobule on the left
side.
  e.  The Gall-bladder is an appendage to the  Liver, of which we find  no traces  in the
Invertebrata.  It may be regarded as simply a  dilatation of the efferent duct, more  or less
prolonged from it, adapted to store up the hepatic-secretion against the time when it may be
required. In Fishes it frequently, but by no means  constantly, presents itself; in Reptiles,
on the  other hand, it invariably exists.  In Birds  it is occasionally absent, even  in species 
620
OF SECRETION.
[Fig. 225.
  The inferior or concave surface ofthe Liver, showing its subdivisions into lobes; 1, centre ofthe right
lobe ; 2, centre ofthe left lobe; 3, its anterior, inferior or thin margin; 4, its posterior, thick or diaphragm-
atic portion; 5, the right extremity; 6, the left extremity; 7, the  notch in the  anterior margin; 8, the
umbilical or longitudinal fissure; 9, the round ligament or remains ofthe umbilical vein;  10, the portion
ofthe suspensory ligament in  connection with  the round ligament;  11, pons hepatis, or band of liver
across the umbilical fissure; 12, posterior end of longitudinal fissure ; 13,14, attachment ofthe obliterated
ductus venosus to the ascending vena cava; 15, transverse fissure ; 16, section of the hepatic duct; 17,
hepatic artery; 18, its branches; 19, venaportarum ; 20, its sinus, or division into right and left branches;
21, fibrous remains of the ductus venosus;  22, gall-bladder:  23, its neck; 24, lobulus quartus ; 25, lobulus
spigelii; 26, lobulus caudatus ;  27, inferior vena cava; 28, curvature of liver to fit the ascending colon;
29, depression to fit the right kidney ; 30, upper portion of its right concave surface over the renal cap-
sule ; 31, portion of liver uncovered by the peritoneum; 32, inferior edge ofthe coronary ligament in the
liver; 33, depression made by the vertebral column.]
[Fig. 226.
closely allied to others that possess it, and without any marked difference in the food, habits,
&c. of the two.  In Mammalia, again, it is frequently absent, especially among herbivorous
animals; sometimes,  on the other hand, two are present, a second or accessory gall-bladder
                                                        being formed upon the Ductus com-
                                                        munis  choledochus,  which  else-
                                                        where not unfrequently presents a
                                                        dilatation in the same situation.  In
                                                        the  first  Giraffe  dissected  by Mr.
                                                        Owen, no gall-bladder was  found;
                                                        in the second there were two.
                                                          /. In the Human species the gall-
                                                        bladder  is  rarely absent, except in
                                                        cases  of malformation depending
                                                        upon general arrest of development,
                                                        in  which several  organs  are  in-
                                                        volved.   The Excretory Ducts of
                                                        the  Liver  and  Gall-bladder  have
                                                        three coats,—an internal or mucous,
                                                        a middle or fibrous, and an external
                                                        or areolar.  The internal coat is con-
                                                        tinuous with the Mucous membrane
                                                        of the intestinal tube, into which it
                                                        opens;  and  the  whole  glandular
                                                        structure  may indeed be considered
                                                        as a complex prolongation of this,
                                                        copiously supplied with blood-ves-
                                                        sels, and  packed into the smallest
                                                        possible compass.  The middle or
  Shows  the three coats of the Gall-Bladder separated from  fibrous  coat  bears a considerable
each other; 1, the external or peritoneal coat; 2, the cellular  resemblance in aspect to that of the
coat with its vessels injected; 3, the mucous coat  covered  Arteries; in its properties, however,
with wrinkles; 4, 4, valves formed by this coat in the neck of  it is still more nearly allied  to true
the gall-bladder; 5,5, orifices ofthe mucous follicles at this  muscle, being capable of exhibiting
point.]                                                   contraction on the application of
999994 
THE LIVER---SECRETION OF BILE.
621
stimuli to the  Sympathetic  nerves
supplying it; and in some instances
of obstruction,  it has  presented an
appearance very closely resembling
that  of  the  muscular coat  of  the
alimentary canal.*   Dr.  Davy has
pointed out, that the mucous coat of
the Ductus communis is disposed in
valve-like folds; in such a manner,
as to prevent the reflux of the bile,
or of the contents of the intestine.
[Fig. 227.
   826. The Liver may be re-
garded as  essentially consist-
ing of a mass of cells, in con-
nection with the ramifications
                                   A view of the Gall-Bladder distended with air, and with its
                                 vessels injected; 1, cystic artery ; 2, the branches of it which
                                 supply the peritoneal coat of the liver; 3, the branch of the
                                 hepatic artery which goes to the gall-bladder j 4, the lymphatics
ofthe Hepatic Duct: and these  of the gaii-biadder.]
are  in  close relation with the
ramifications  of the  Portal  Vein and  Hepatic Artery, that  serve  to  con-
vey blood  to  the  minutest  parts  of this  organ;   and  with  those  of  the
Hepatic Vein, which return  it to  the  heart, after it  has been subservient to
the  Nutrition of the  structure and to the  elaboration of the Secretion.   Be-
sides these, the Liver contains Lymphatics and Nerves;  the latter are chiefly
derived from the Sympathetic  system, and are distributed on the walls of the
vessels  and  ducts.    These various  portions of  the  structure  are connected
together by a fibrous  tissue, to  which the name of Glisson's Capsule has been
given.   For our  present knowledge  of their ultimate  arrangement, we  are
almost entirely indebted to Mr. Kiernan,t whose account of them will be here
followed,—his researches having  been confirmed, in all essential particulars,
by other Anatomists.
   a. When a Liver is closely examined with the naked eye, it is seen to be made up of a
great number of small granular bodies, about the size of a millet seed, of an irregular form,
and  presenting  a number of rounded projecting
processes upon their surfaces.  These are com-
monly termed lobules, although by some Anatomists
they are spoken of as acini.  When divided longi-
tudinally, they have a  somewhat foliated appear-
ance (Fig. 229), arising  from the distribution  of
the Hepatic Vein ; which, passing into the centre
of each  division, is termed the mfra-lobular vein.
The exterior of each Lobule is covered by a pro-
cess of the capsule of Glisson; which is very dense
in the Pig and other animals; but which is so thin
as to be almost undistinguishable in the Human
liver. Its substance is composed of the minute
ramifications of the  before-mentioned vessels, arranged in the manner presently to be de-
scribed ; the spaces between which are filled up  with a parenchyma, composed of nucleated
cells, like those shown in Fig. 232.  The structure of each lobule, then, gives us the essential
characters of the whole gland.
   b. The Lobules, when  transversely divided, are  usually  found to present somewhat of a
pentagonal or a hexagonal  shape; the angles being  generally  somewhat rounded, so as to
form a series of passages, or mter-lobular spaces: in these lie the branches of the Vena Portae,
and of the Hepatic Artery and Duct, from which are derived the plexuses that compose the
lobules.   Each Lobule, when examined with  the microscope, is found to be apparently com-
posed of numerous minute  bodies of yellowish  colour, and of  various forms, connected to-
gether by vessels ,- to these the name of acini was given by Malpighi; and to these, if they
deserve a name, it ought to be  restricted.  They will  be  presently shown, however, to be
nothing else than the irregular islets, left between the meshes  of the plexus formed by the
ultimate ramifications of the Portal Vein.  The  Vena Porta?, it will be recollected, is formed
[Fig. 228.
  1, Nucleated cells composing the parenchy-
ma of the gland; 2, lobules of human liver
with ramifications ofthe hepatic vein.]
\ C\ uv
■J^O^A/^
* In the Horse and Dog this coat is clearly muscular.
f Philosophical Transactions, 1833. 
622
OF  SECRETION.
by the convergence of the veins, which return the blood from the chylopoietic viscera; and
there is reason to believe that it also receives the  blood, which is conveyed to the Liver for
Fig. 229.
Fig. 230.
  Connection ofthe lobules of the liver with
the hepatic vein; 1, a trunk ofthe vein; 2, 2,
lobules depending from its branches,  like
leaves on a tree; the centre of each being
occupied by a venous twig,—the Intra-lobu-
lar Vein.
  Horizontal section of three superficial lobules,
showing the two principal systems of Blood-Ves-
sels; 1,1, iw«ra-lobular veins, proceeding from the
Hepatic veins; 2, 2, inter-lobular plexus, formed
by branches of the Portal veins.
the purposes of Nutrition, by the Hepatic Artery.  As it is an  afferent, not an  efferent ves-
sel, it has a strong claim to the character of an Artery; even although it conveys Venous
blood.   Like an artery, it gradually subdivides into smaller  and yet  smaller branches; and
at last forms a plexus of vessels, which lie in the  inter-lobular spaces, and spread with the
freest inosculation, throughout the entire Liver.  To these vessels, the name of inter-lobular
Veins is given by Mr. Kiernan.  They ramify in the capsules of  the lobules, covering with
their ramifications the whole external surface  of these; and then enter their substance.
When they enter the Lobules, they are termed lobular veins; and the plexus formed by their
convergence, from the circumference of each lobule towards its centre (where their ultimate
ramifications terminate  in those of the intra-lobular or hepatic vein), is designated as the
Lobular  Venous plexus.   In the islets of this plexus (the acini of Malpighi) the ramifications
of the hepatic duct are distributed  in the manner next to be described.
   c. The Hepatic duct forms,  by its subdivision and ramification, an Interlobular plexus of a
very similar character; but the anastomosis between the branches going to the different lobules
                                                   is less intimate  than  that of the  inter-
Fig. 231.
  Horizontal section of two superficial Lobules, show-
ing the interlobular  plexus of biliary ducts; 1,1, intra-
lobular veins; 2, 2, trunks of biliary ducts, proceeding
from the plexus which traverses the lobules ; 3, inter-
lobular tissue ; 4, parenchyma of the  lobules.
lobular veins, and cannot be directly
demonstrated; although  Mr. Kiernan
thinks that his experiments  leave but
little  doubt of its  existence,—a  com-
munication (which cannot be seen to be
established by any nearer channel) be-
ing proved to  exist between  the right
and left  primary  subdivisions of the
duct.   The Interlobular Ducts ramify
upon the capsular surface of the lobules,
with  the branches of the Portal Vein
and Hepatic Artery; they then enter its
substance, and subdivide into minute
branches, which anastomose  with each
other,  and form a  reticulated plexus,
termed by Mr.  K., the Lobular Biliary
plexus.  This plexus constitutes the prin-
cipal  part ofthe substance of the lobule;
and when seen through the meshes of
the Portal plexus, gives rise  to the ap- 
                         THE  LIVER---SECRETION OF BILE.                     623

pearance of ccecal terminations  of ducts.   The  ultimate terminations of these  ducts  have
not, however, been traced in the adult Liver of any of the higher animals, although they are
sufficiently evident in the embryonic condition.  From the analogy of other organs,  there
would seem good reason to believe, that  the  ultimate ramifications of  the hepatic  ducts
anastomose freely together,  and that they form  a  network,  in which their terminations are
lost, as it were, without forming true cceca.  This  view of the matter finds confirmation in
the curious fact pointed out by  Mr. Kiernan, that, in the left lateral ligament, the  essential
parts of a lobe are found in the simplest form and arrangement.  From the edge of the liver
next to the ligament, numerous Ducts emerge, which ramify between the two layers of peri-
toneum of which the ligament is  composed.   They are accompanied by branches of the Portal
and Hepatic Veins, and of the Hepatic Artery; which also ramify in this ligament, especially
around the parietes of the ducts.  These Ducts, of  which some are occasionally of considera-
ble size, divide, subdivide, and anastomose with each other;  and the meshes formed by the
network of larger or excreting  Ducts, are  occupied by minute plexuses of their  ultimate
ramifications or secreting Ducts.
   d. The Hepatic Artery sends  branches to every part of the Liver, supplying the walls of
the Portal and Hepatic Veins, and of the Hepatic Ducts, as well as Glisson's capsule.  The
principal  distribution of its  branches, however,  is  to  the Lobules, which they reach, in the
same manner with the Portal  vessels and Biliary Ducts, by spreading themselves through the
interlobular spaces.  There  they ramify upon the  interlobular ducts, and upon the capsular
surface of the lobules, which they then penetrate; their minuteness prevents their distribu-
tion within the lobules  from being clearly demonstrable; but, as they enter along with the
biliary ducts, there can be little doubt that, here  as elsewhere, they are principally distributed
upon the  walls of these.  As  to the  ultimate termination of the capillaries of the Hepatic
Artery,—whether they enter  the Portal plexus, or the  Hepatic Vein,—there is a difference
of opinion amongst anatomists; the former view being upheld by Kiernan, the  latter by
Muller.   The question is a  very interesting one in a physiological point of view;  since, if
the former account be the true one, the Blood which is brought to the Liver by the Hepatic
Artery becomes subservient to the  secretion of  Bile, only by passing into the Portal plexus;
whilst, if the latter be the correct statement, either the arterial Blood is not at all subservient
to the formation of Bile, or the secretion can be elaborated from the arterial capillaries.  The
experiments of Mr. Kiernan have satisfaotorily proved, that the Intralobular or Hepatic  Veins
cannot be filled  by injection from the Hepatic Artery, though they maybe readily filled from
the Portal plexus; whilst, on the other hand, there is reason to believe, that a very fine in-
jection into the Hepatic arteries, will find its way  into the Portal plexus*   It is certain that
all the branches of the Hepatic artery, of  which  the termination can be ascertained, end in
the Vena Porta?;  a free capillary communication existing between their two systems of
branches, on the walls of the  larger blood-vessels  and ducts.  According to Muller, there is
an ultimate plexus of capillary vessels, with which all the three systems freely communicate;
but for this idea there is no adequate foundation; and it is inconsistent with the fact just stated,
that injection into the Hepatic Artery does  not return by the Hepatic vein.  And the views
of Mr.  Kiernan  have  lately  received important  confirmation from the researches of Mr.
Bowman  on the circulation  in the Kidney (§ 841).
   e.  It now only remains to describe the Hepatic Veins, the branches of which occupy the
interior of the Lobules, and  are termed intralobular veins (1, 1, Figs. 230 and 231).  On
making a transverse  section of  a lobule, it is seen that the  central vessel is formed by the
convergence of from four to  six or eight minute  venules, which arise  from the processes
upon the  surface of the lobule.   In the  superficial lobules, (by which term are designated
those lobules which lie upon the exterior of the glandular substance, not only upon the sur-
face of the Liver, but also against the walls of the larger vessels, ducts, &c.,) the Intralobular
Veins commence directly from their surface; and the minute venules of which each is com-
posed may be seen in an  ordinary injection, converging from  the circumference towards
the centre, as in the transverse section of other lobules.  The Intralobular Veins terminate in
the larger trunks, which pass along  the bases of the lobules, collecting from  them their
venous blood;  these  are called by Mr. Kiernan sublobular veins.  The  main trunk of the
Hepatic Vein terminates in the  ascending  Vena Cava.
   /.  In regard to the  mode in  which the nucleated Cells,  that  are  the  real agents in  the
Secreting process, are arranged  in the Liver of  Man and the higher animals, there is  much
uncertainty; owing especially  to  our want of  acquaintance   with the mode  in which
the Hepatic Ducts terminate.   They would seem to form  the  greatest part of the Paren-
chyma, which  fills  up  the interstices  between  the reticulations  of  the  Blood-vessels
and Ducts; but it is  obvious, from  their functional operation, that they must have a more
  * This is stated to have been the case in the injections of Lieberkuhn, although Mr. Kier-
nan has not succeeded in effecting it. 
624
OF SECRETION.
     Fig. 232.        close  relation  to  the latter than to the former.'  Their  diameter
                    is usually from 1-1500th to l-2000th of an inch; and they are conse-
                    quently  easily recognized, whenever a  portion of the substance of
                    the Liver is torn  up and  examined with the higher powers of the
 ^^^^^^^^'     Microscope.  Their shape is usually spheroidal.  They have a distinct
 ^^^^Sl^^""    biliary tinge;  and contain  a granular amorphous  matter, with a few
                    small  adipose globules.
                      g. In regard to the Embryonic Development  of the Human Liver,
                    a considerable  part of our information must  necessarily  be  derived
                    from the  study of that of other animals; and this not so much from
                    Mammalia, as from Birds ; since the development of this organ com-
                    mences  so  early in the former, its phases  are so rapidly hurried
                    through, and its evolution is so soon completed, that the process cannot
be continuously watched.—In the Chick, the rudiments ofthe Liver are found at the commence-
                                           ment of the third day of incubation, in  the
  Glandular cells  of
Liver; a, nucleus ; 6,
nucleolus (?); c, adi-
pose particles.
Fig. 233.
  Origin of the Liver from the intestinal wall, in
the embryo of the Fowl, on the fourth day of incu-
bation ;— a, heart; 6, intestines ; e, everted portion
giving origin to the liver;  d, liver; e, portion of
yolk-bag.
                                           form of two ccecal pouches, which are pro-
                                           longed from the Intestinal tube; these carry
                                           before them a fold of the vascular layer, from
                                           which the blood-vessels  subsequently origin-
                                           ate ;  and they soon begin to ramify in this,
                                           sending off branches, of which tbe ccecal ex-
                                           tremities are still evident.  At the end ofthe
                                           fourth day, the tubuli and their ramifications
                                           have attained a considerable  size ; and they
                                           approach each other and coalesce at the base,
                                           entering the intestine by an orifice common
                                           to the two.  In this process, it is easy to re-
                                           cognize the  analogy to  the succession  of
                                           forms, which we encounter in ascending the
                                           animal scale.  The size and density of the
                                           organ are gradually increased; but it is not
                                           until several days  afterwards, that the gall-
                                           bladder is developed.—In the Human Em-
                                           bryo, the formation of the  Liver begins at
about the third week of intra-uterine existence ; the  organ is from the first of very large
size, when compared with that of the body; and between the third and the fifth week, it is
one-half the weight  of the  entire  embryo.  It  is at that period divided into several lobes.
By the third lunar month, the liver extends nearly to the  pelvis, and almost fills the abdo-
men ; the right side now begins to gain upon the left; the gall-bladder begins to appear at
this time.   The subsequent changes chiefly consist in the consolidation of the viscus, and the
diminution of its proportional size.  Up to the  period of birth, however, the bulk of the
Liver, relatively to that of the entire body, is much greater than in the adult; the proportion
being as 1  to 18 or 20 in the new-born  child, whilst it is about 1 to 36 in  the adult: and
the difference between  the right and left sides is still inconsiderable.  During the first year of
extra-uterine life, however, a great change takes  place; the right lobe increases a little or re-
mains stationary, whilst the left lobe undergoes an absolute diminution, being reduced nearly
one-half; and as, during the  same period, the bulk of the rest of  the body has been rapidly
increasing,  the proportion is much more reduced during that period, than in any subsequent
one of the same length.  According to  Meckel, the liver of the  newly-born infant weighs
one-fourth  heavier than that  of a  child of eight or ten months old; and as the weight of the
whole body is more than doubled, during the  same time, it is obvious that the change in the
proportion of the two must be principally effected at this epoch.

   827. The knowledge  of the distribution of the Biliary ducts, and  of the two
chief systems of Blood-vessels,  in the  Lobules of the Liver,  has  enabled Mr.
Kiernan  to give  a  most satisfactory explanation of appearances, by  which
Pathological anatomists  had been previously much perplexed.   When the
Liver is in a state  of Anaemia (which  rarely "happens as a natural condition,
although  it may be induced by  bleeding  an animal to  death), the whole sub-
stance  of the lobules  is pale, as  represented in Fig. 234.    In general, how-
ever, the  Liver is  more  or less  congested at the moment of  death;  and this
congestion may manifest itself in  several ways.   The  whole substance may
be congested; in which case  the lobules present a nearly uniform dark  colour
throughout their substance, their centres being usually  more  deeply-coloured 
SECRETION OF BILE.
625
Fig. 234.                                       Fig. 235.
4, interlobular veins, occupying the centres of       1, rounded lobules in first stage of Hepatic Ve-
the lobules;  5, smaller veins, terminating in the     nous congestion, as they appear on the surface
central veins.                                ofthe liver; 2, interlobular spaces and fissures.
than the margins.   An appearance  more frequently offered after death, how-
ever, is that represented at Fig. 235, and termed by Mr. Kiernan the first stage
of Hepatic Venous congestion. In this, the isolated centres of the Lobules alone
present the colour of sanguineous congestion; and the surrounding substance
varies  from  a  yellowish-white, yellow, or greenish colour, according  to  the
quantity and quality of the Bile which it contains.   This accumulation of the
blood in the Hepatic Veins, and the emptiness ofthe Portal plexus, seem due
to the  continuance of capillary action  after the general circulation has ceased;
—a circumstance to which we find an exact parallel, in  the emptiness of the
systemic arteries, and  the fulness of the veins, after most kinds of death.   In
the second stage of Hepatic Venous congestion, the accumulation of blood is
found not only in  the  Intralobular Veins, but  even in parts  of the Portal or
Lobular Venous plexus.   The parts which are  freest from it are  those sur-
  a., lobules in the second stage of Hepatic Venous       a, lobules as they appearonthe surface in a
congestion; b, andc, interlobular spaces;i>,con-     state of Portal Venous congestion;  b, interlo
gested intralobular veins; e, congested patches,     bular spaces and fissures; c, intralobular hepatic
extending to the circumference ofthe lobules;     veins, containing no blood; d, the central por-
F, non-congested portions of lobules.              tions in a state of anasmia; E, the marginal por-
                                          tions in a congested state.
53 
626
OF SECRETION.
rounding  the  interlobular spaces; so  that the non-congested  substance here
appears in the form of circular or irregular patches, in the midst of which  the
spaces and fissures are seen (Fig. 236).*   Although the Portal as well as  the
Hepatic venous system is  thus involved in this form  of congestion, yet, as
the obstruction evidently originates  in the latter, the term given by Mr. Kier-
nan is still applicable ; and it is important to distinguish this appearance from
that next to be described.  The second stage of Hepatic venous congestion very
commonly attends disease  of  the heart, and other disorders in which there is
an impediment to  the venous  circulation;  and in  combination with  accumu-
lation in the biliary ducts,  it gives  rise to those various appearances, which
are known  under the  name of dram-drinkers' or  nutmeg liver.  The other
form of partial congestion arises from an accumulation of blood in the Portal
veins, with a reverse condition  of the Hepatic  or intralobular veins; in this
condition, which Mr. K. designates as portal venous congestion, the  marginal
portions of the lobules are of deeper colour than usual, and form a continuous
network, the isolated spaces between which are occupied by the non-congested
portions (Fig. 237).  This is a very rare occurrence ; having been seen by Mr.
K. in children only.—These differences fully explain the diversity of  the state-
ments of  different anatomists, as to the relative position of the so-called  red
and yellow substances; for it  now  appears, that the red substance is the con-
gested portion of the  lobules, which may be either  interior or  exterior, or
irregularly disposed;  whilst the yellow  is the  non-congested part,  in which
the Biliary plexus shows itself more or less distinctly.
  828.  Another very interesting form of Pathological change in the  aspect of
the Liver, which the knowledge of the structure of the Lobules enables us to
comprehend, is that  to which  the name of Cirrhosis  has been given.   This
has been erroneously attributed to the  presence of a new deposit, analogous to
that of Tubercular matter; but it is really due to Atrophy and partial Con-
gestion in the Liver itself.   It is described by Laennec as usually presenting
itself in small masses, varying in size from a cherry-stone  to a millet-seed,
and scattered through the substance of the Liver.  When these  are minute,
and closely set, they impart what appears at first to be a uniform brownish-
yellow tint to the  divided surface of the Liver; but when the tissue is more
attentively examined, their separation  becomes evident.   These small masses
are not distinct  lobules in a variable  state of hypertrophy (as supposed by
Cruveilhier); but small uncongested  patches, composed of  parts of several
adjoining lobules, and having one  or more interlobular  spaces for a centre;
and the biliary plexuses of these, being filled with bile, give them their yellow
colour.   On the other hand, there  is  an atrophy, more or less complete, of
the portions of the substance of the liver intervening between them; so that
the bulk of the whole  organ is much diminished, very commonly to  one-half,
and sometimes to  one-third, of its original  size.
  829.  The application ofthe Microscope to the Hepatic Cells, in various states
of disease, has afforded many  facts of great interest.   The fatty liver, which
is often found in the bodies of  persons  who have died from diseases obstructing
the pulmonary circulation, has been  shown by Mr. Bowmanf  to depend
upon the presence of  a large quantity of  fatty  matter in the interior of the
cells;  which frequently appear as if gorged with it.   This would seem to
be occasioned by the want of elimination of the fatty matter through  the
respiratory process; and the consequent accumulation of it in the Blood, by

  * This very common aspect of the Liver, which presents numerous modifications, has been
a source of great perplexity to those who have studied the minute anatomy of this organ, and
has even led Anatomists of the highest eminence into serious errors.  See Cyclop, of Anat.
and Physiol., vol. iii. pp. 185,186.
  •f Medical Gazette, January 1842. 
SECRETION OF BILE.
627
which the burden of separating it is thrown upon the Liver.—Dr. Williams*
mentions,  that,  in  a  case  of  obstruction  of  the  ductus
choledochus by malignant disease,—which occasioned com-      Fig. 238.
plete  interruption  to  the passage  of bile, and  consequent
jaundice,—scarcely  an entire nucleated  cell  could be  dis-
covered by attentive examination of a large part of the organ.
Nothing more  than  minute free particles of fat, and  free float-
ing amorphous granular matter, could be detected.  He further
states that, in a case of fever, the hepatic  cells were found to     Hepatic  Cells
be  almost entirely destitute of  fatty particles;  and that  in   gorged with Fat:
what  is known as "granular liver;" the granules (which have   "ieus™& Adipose
much  the appearance  of tubercles) consist of  cells,  which   globules.'
strongly resemble the ordinary cells of the parenchyma of the
Liver  in every respect, except that they are almost  or completely destitute of
yellow contents.   Similar observations have  been  also recorded by Dr. G.
Budd.—In two cases of jaundice examined by Mr.  Gulliver, the hepatic  cells
were  gorged with biliary matter; some of them  to such an extent,  that  they
had become nearly opaque.   Perhaps if this condition had continued, these
cells  would  have been all ruptured, and  the  state of the organ would  have
resembled that described by Dr. Williams.
   830. Previously to birth, the Liver is the only decarbonizing organ in the
system, the Lungs being at that time inert; but as  soon  as  tbe latter come
into play, they separate from  the Venous blood a large proportion of the car-
bon with  which it is charged, and less blood is transmitted to the  Liver for
this purpose.   The diminution in the quantity ofthe Blood circulating through
this organ, is  extremely rapid;  and it is usually very evident  within a short
time after birth, in the comparative paleness of the substance of the gland.  It
has been  proposed to give this fact  a practical bearing, in those judicial in-
quiries which are directed to the determination  of  the question, whether or
not an Infant has respired after birth; it having  been conceived,  that the
diversion  of the current of the Blood from  the Liver to the Lungs, consequent
upon  the  first inspiration,  would be sufficient to make a certain difference in
their relative weights, if that inspiration had taken place.   More careful  and
extended  observations, however, have satisfactorily  proved that, although an
increase in the weight of the Lupgs, and a diminution of that of the Liver, are
generally  found to exist after respiration has been fully established, they are
not by any means  constantly produced when the inspirations have been feeble,
as they frequently are for  some hours or days after birth ; whilst, on  the other
hand, it is not uncommon to meet, in  infants that have not breathed, with Lungs
as heavy,  and Livers as light, as in the average of those which have respired.t
  831. We have now  to consider the conditions, under which the secretion
of Bile takes place; and one of the most important of these, is the character
of the Blood with which  the  organ is supplied.   We have seen that there is
anatomical reason for the belief, that the blood supplied by the Hepatic Artery
is  not directly concerned in the  Secretion ; but  that it first  serves for the
Nutrition  of the organ, and then, passing into the  Portal system (in the same
manner as does the blood  of the mesenteric and other arteries), forms part of
the mass of Venous  Blood, from which the secreting cells elaborate their  pro-
duct.   This view is borne out by the results of Experiment, and of  Patholo-
gical observation.  Thus, if the Vena Portae be tied, the secretion of bile  still
continues, though in diminished quantity;  and several cases are on record, in
which, through a malformation, the Vena Portae terminated in the Vena Cava

          *  Guy's Hospital Reports, 1843.
          |  See Dr. Guy, in Edinb. Med. and Surg. Journal,  vols. lvi. and lvii. 
628
OF SECRETION.
without ramifying through  the  liver,  and in which secretion  of Bile  took
place,—evidently from the blood of the Hepatic Artery, which had become
venous by circulating  through the  substance of the Liver; and  this blood
appears* to have passed into the ramifications of the Umbilical Vein, which
formed a plexus in the lobules, exactly resembling the ordinary portal plexus.
It must be remembered,  however, that  in  all these instances, the  arterial
Blood will become abnormally charged with  the elements of Bile; since the
blood of the chylopoietic viscera, from which it ought to have been separated,
returns to the heart without  undergoing any such purification: and the secre-
tion of Bile from the blood supplied by the Hepatic Artery under such circum-
stances cannot,  therefore, be considered as proving that the arterial  blood is
ordinarily concerned in the secretion to the same degree.
   832. That the proximate elements  of  the Bile accumulate in  the Blood,
when from any cause  the secretion  is suspended, is a fact now  well ascer-
tained ; and this satisfactorily accounts for the disturbance of the  other func-
tions, especially those  of  the Nervous system, which  then ensues.  When
the suppression is  complete, the  patient suddenly  becomes  jaundiced, the
powers of that system  are speedily lowered (almost as by a narcotic poison),
and death rapidly supervenes.!  When the  secretion  is diminished, but not
suspended, the  same symptoms present themselves in a less aggravated form.
It is probable that much of the disorder in the functions of the  Brain, which
so constantly accompanies deranged  action of the Digestive system, is due to
the less severe operation of  the same cause,—the partial retention within the
Blood, of certain constituents of the Bile, which should have been eliminated
from the  circulating fluid.   In such  a  condition, we derive great benefit  from.
the use of mercurial  medicines;  which, by stimulating the Liver to increased
action, cause  the removal  of the morbific agent from  the blood.   Deficient
secretion of  the Liver may be recognized as the cause of this and of  other
diseases, by the paleness of the alvine  evacuations, the diffused yellowness of
the surface of  the body, the yellowish-brown fur upon the tongue, and the
congestion ofthe portal system; this last results from the same cause, as that
which stagnates the  blood in the Lungs when there is deficient Respiration
(§ 738), and frequently occasions Ascites, and other disorders of the contents
ofthe abdomen.  An abnormal accumulation of the  elements  of the Bile in
the Blood, is  habitual in some persons; and it produces a degree of indisposi-
tion to bodily or mental exertion, which it is difficult to counteract.  It  may
often be recognized by the accumulation of dark mucus having distinctly the
taste of bile, on the surface  of the  tongue, especially during  the  night;  this
secretion being apparently eliminated by the mucous  membrane of the tongue,
when the function of the liver is not duly performed.
   833. Much discussion has  taken  place among  Chemists, in  regard to the
proximate  principles of the Biliary secretion ; a large number of analyses hav-
ing been made, amongst the  results of which there is  great want of conformity.
The discrepancies principally arise  from this source,—that the secretion is
acted on with great facility by chemical reagents; so that many of the  com-
ponent parts  which have been enumerated, are  not true educts ; but are pro-
ducts of the  operations, to which the fluid has been  subjected.  The propor-
tion of solid  matter is usually from 9 to 12 per cent.; and nearly the whole of
this consists  of  substances peculiar to  Bile.

   a. The following are the general results of the analyses made by Berzelius, of Human
Bile, and of that of the Ox:—
  * This, at least, was found to be the case, in the only instance in which the liver
examined with sufficient care.
  f See Dr. Alison in Edinburgh Medical and Surgical Journal, vol. xliv. p  287. 
SECRETION OF BILE.
629
	Max.	Ox.
Water ......	90-44	92-84
Biliary matter .....	800	5-00
Mucus ......	•30	•23
Alkali (in combination with fatty acids)	•41	
Chloride of sodium, and extractive	•74	1-50
Phosphates and sulphates of soda and lime	•11	•43
	100-00	100-00
In the Biliary matter, we are to distinguish at  least three distinct substances ; Cholesterine,
Bilic acid, and Colouring matter.—In healthy bile, the proportion of Cholesterine appears to
be very small;  but in many disordered  states of the  secretion, and especially in disease of
the Gall-bladder, this substance is present in much larger amount; and it usually forms the
principal, if not the sole, ingredient in biliary concretions.   It is a white crystallizable fatty
matter, somewhat resembling Spermaceti;  free from taste and odour; not soluble in water,
but dissolving freely in  alcohol, from which it is deposited on cooling in pearly scales.  It
is almost entirely composed of  Carbon and Hydrogen; its  constitution being 36 Carbon, 32
Hydrogen, 1 Oxygen.  It may be obtained by a chemical process of no great  complexity,
from the Serum of the Blood; and it is not unfrequently deposited as a result of diseased ac-
tion in other parts of the body, especially in the fluids of local Dropsies, as hydrocele, ovarian
dropsy, &c.
  6. The principal constituent of Bile is a  compound of soda  with a peculiar organic body;
which is.now generally  regarded in the  light of a fatty acid, and named Bilic acid.  Accord-
ing to Platner, this bilic acid and the bibilate of soda may be  obtained in a pure crystalline
state from fresh bile; a yellowish-brown syrup  being left, which seems principally to consist
of colouring matter diffused through the  water.   No analysis has yet been made of bilic acid
thus purified; that of Dr. Kemp, made upon an impure bilic acid, gives as its ultimate com-
position 48 Carbon, 42 Hydrogen, 13 Oxygen, and 1 Nitrogen. This is the substance described
by different Chemists (doubtless under various modifications, according to the process used
to obtain it), as Choleic acid, Bilin, Picromel, &c.  It is very readily altered by reagents, espe-
cially by acids;  and a great variety of products may be formed by its decomposition.  Some
of these appear to present themselves in the living body, as results  of disordered conditions
of the secreting process.
  c.  The colouring matter of the bile is now termed Biliverdin. That of the Ox contains no
azote; and appears to be identical  with  the Chlorophyl of plants.   That of Man, however,
contains about 7 per cent, of Azote, with 68 parts of Carbon, 7^ of Hydrogen, and  17| of
Oxygen;  and it cannot be  derived so  directly from the food.   When exposed to the air, it
becomes of a deep green absorbing oxygen; and the same change is produced by nitric acid,
—the liquor soon passing, however, to a red hue. This frequently takes  place within the
body, in cases of Jaundice; but more especially in the urine.   Though the colouring matter
is usually present but in small  quantity  during health, it sometimes accumulates in disease,
so as to produce solid masses, which include little else.

   834. The  amount of the secretion  of Bile appears to bear some proportion
to that of the Food digested.    That its  formation is continually going on to a
certain degree appears  unquestionable; but that its quantity is greatly increased
during the solution of food in  the  stomach, appears also to be well established.
In those  animals" which are most  constantly ingesting food, we find no  Gall-
bladder : for  in them, the Bile may be poured into the Intestine  as fast as it is
formed.  In  those which only take  food occasionally, on the other  hand, and
which are provided  with  a Gall-bladder,  the  Bile, when not required  in the
Intestine, flows back into that reservoir.   This reflex would appear due  to the
valve-like termination of the Ductus  Choledochus in the walls of the  Intestine;
by which a certain resistance is offered  to the entrance of  the fluid, unless it
be propelled  by some decided force.  The flow of Bile into the Intestinal tube,
when its action is needed  there, is commonly imputed to the pressure of the
distended Duodenum against the  Gall-bladder; it may be doubted, however,
whether  the  contractile power of the Duct itself does not afford important aid
in the process;  and  it is easy to understand, from  the known influence ofthe
Sympathetic system of nerves upon it  (§ 825,/), that peristaltic movements
may be thus excited at the time when  they are needed.—It is an interesting
fact, proving how completely the passage  of Bile into the Intestine is depend- 
630
OF SECRETION.
 ent upon the presence of aliment in the latter, that the Gall-bladder is almost
 invariably found turgid in persons who have died  of starvation; the secretion
 formed at the ordinary slow rate having gradually accumulated, for  want of
 demand.   This fact is important in juridical inquiries.
 .  835. The Bile, as already shown (§ 660), has an important operation to
 effect in the Digestive process;—that of  reducing the oily matter of the food
 to a state  in which  it may be taken  up by the Absorbent vessels.  This it
 effects by means of  its soapy character;  which, notwithstanding  the doubts
 of Chemists, seems  to be proved  by familiar facts.   Thus, Ox-Gall  is com-
 monly employed to remove grease spots ; and the bile of the Sea-Wolf (Anar-
 rhicas lupus)  is  ordinarily used  as  soap by the  Icelanders.   Moreover, the
 small quantity of Cholesterine contained in healthy Bile, is certainly in a state
 of complete solution; the biliary  soap  having the  same action upon it, as
 upon the oleaginous constituents ofthe chyme.—From the recent experiments
 of H. Meckel, however, it appears that  the  Bile  may perform another very
 important office,—the transformation  of  sugar into fatty matter.   He  found
 that, when bile was mingled  with grape-sugar, and allowed to remain in con-
 tact with it for some  time, a much larger quantity of fatty matter  existed in
 the mixture, than could have been present in the bile ; and that the transfor-
 mation is much aided by heat.  Thus, the amount of fat, contained in an equal
 amount of the bile employed, having been ascertained from parallel experi-
 ments to be from "48 to '54 grammes, the amount obtained from the  mixture
 of bile and grape-sugar, after five hours'  exposure to  the  warmth of  an incu-
 bating machine, was *87 grammes ; and after twenty-four hours' exposure, 1'84
 grammes.*  It seems probable that this transformation may take place in the
 Liver itself; for in animals fed upon grape-sugar,  this substance has been de-
 tected in the blood of the portal vein, but not in that  of the hepatic vein.  It
 will take effect,  not merely upon  the  Sugar introduced  as such in the food,
 but also  upon the amylaceous substances, which have been converted into
 sugar by the action of the Salivary and Pancreatic fluids  (§ 670).
  836.  There can be no doubt, however,  that the  Bile is partly an  excremen-
 titious fluid; a portion of it being destined  to be at  once  carried  out of the
 system, by  the intestinal canal, although another portion is  destined to  be re-
 absorbed, for the purpose (as it would seem) of being ultimately  carried off
 by the respiratory process.   The former part probably includes the whole of
 the colouring matter; the presence of which  in the faeces is sufficiently ob-
 vious.  The latter seems usually to comprise the  fatty or soapy portion ; no
 distinct indications of which  can be generally found in the faeces, unless they
 have rapidly passed through the alimentary canal  (§  662).  But in particular
 states of the system,  the faeces may contain a very large quantity of bile; the
 presence of which almost unchanged, may be recognized in the  evacuations
 in  bilious  diarrhrea,  and in  the  stools  which  follow mercurial  purgatives.
 Hence the Bile may be a completely excrementitious product; and the idea
 of the action of the Liver, as one of the great purifiers of the body from the
 results of its decay, is not at all invalidated by the observation, that a large
 part of  its secretion is ordinarily destined for immediate  re-absorption.   The
 composition of the secretion  clearly indicates, that it is especially intended to
 eliminate from the blood its  superfluous  Hydro-Carbon,—whether this  have
 been absorbed as such from the aliment, or have been taken up by the  Blood
 as  effete matter, during the course of the  circulation.
  a. If more non-azotized food be taken into the system, than can be got rid of by the
Respiratory process, and if there be not a sufficiently rapid production of Adipose tissue to
admit of its being deposited as Fat, it would accumulate in the Blood, unless separated by

         *  Mr. Paget's Report, in Brit, and For. Med. Rev., July 1846, p. 261. 
SECRETION OF BILE.
631
the Liver.   If too much work be thrown upon this organ, its function becomes disordered,
from its inability to separate from the Blood, all that it should draw off:  the injurious sub-
stances accumulate in the Blood, therefore, producing various symptoms that are known un-
der the general term of bilious. This is particularly liable to happen in warm climates, in
consequence of the diminished excretion through the Lungs,—occasioned by the warmth of
the surrounding air, and the small  quantity of exercise  usually taken.   To remove these
symptoms, medicines are required, which shall stimulate the liver to increased action.  The
constant use of such, however, has a very pernicious effect upon  the constitution; and care-
ful attention to the regulation of the  diet,—especially the avoidance of a superfluity of oily
or farinaceous matter,—together with the employment of an increased amount of exercise,
will probably answer the same end in a much better manner.

   Besides the source of Biliary matter already pointed out in the decompo-
sition  of  the  Fibrinous tissues  (§ 819), it seems probable that there is another
very important one in the continual waste of Nervous matter, which more
nearly approaches Bile in composition (§ 249);  especially if,  as  asserted  by
Fremy, the peculiar acids of the  Brain  may be  detected in the Liver.   In
cases of slow Asphyxia, the amount of  the Biliary secretion is much increased;
as might  be  expected, from what has just been stated of its purpose.
   837. It would not seem improbable, that  the  Liver acts towards the ab-
sorbed matters  which enter the blood by the Mesenteric Veins, the same part
which the Lungs perform for those which are introduced through the Lymph-
atic  system ;  namely, the affording an opportunity for the excretion of super-
fluous  or injurious  substances  contained  in  the absorbed  fluid,  before it
enters the general current of  the Circulation.  There  is every reason to be-
lieve,  that the conversion  of Chyle into Blood is  a slow process, requiring the
prolonged influence of the latter fluid upon the former;  during this  influence
many  chemical changes take place, which are almost  certain  to  be attended
with an extrication of Carbon  and Hydrogen, these being the  ingredients of
which the Chyle contains most when compared with blood ; and for the extrica-
tion of these, the Lungs and Liver afford ready means.  Hence  we see why the
Lacteal system should terminate in a Venous trunk near the Heart, so that the
fluid discharged by it will proceed at once to the Lungs ; and why the Liver,
wherever it  has a distinct circulation, should receive the blood from  the walls
of the Intestines.   Among the Mollusca,  in which the chyle  is  absorbed  by
the mesenteric veins, (there being no separate lacteal system,) these veins, in-
stead of returning to the heart through the liver, terminate in  the  branchial
vessels ;  and the process of depuration is effected by  the gills.   Their liver
is supplied only by the  hepatic artery.
  a.  This view derives interesting confirmation from the experiments of Cruveilhier, on
the artificial production of purulent deposits by injection of Mercury into the veins.  He found
that,  when the  mercury was introduced into any part ofthe general venous system, abscesses
in the Lungs were induced; each inclosing a globule, the irritation occasioned by which
was the cause of the purulent  deposit.   When the mercury was  introduced into one of the
Intestinal veins, on the other hand, similar purulent deposits occurred in the Liver.  It is
well  known that abscesses in the Lungs and Liver are very common sequelae of wounds of
the head, and of surgical operations, especially those involving bones; and  there seems good
reason to believe, that in such cases Pus (or some of its elements, which may act the part of
& ferment in exciting suppuration elsewhere), is actually carried along with the current of blood
in the Lungs and Liver; and that, like the globules of mercury, not being susceptible of elimi-
nation by these two great emunctories, it acts  as a disturbing cause, and occasions disease of
their  tissue. The fact that a considerable amount of Copper may  be detected in the substance
of the Liver, after the prolonged introduction of its salts into the system, seems to add weight
to this view of its function.  It is yet to be ascertained, however, why some substances should
be arrested in this organ, whilst others are allowed to pass. 
632
OF SECRETION.
                  3.—The Kidneys—Secretion of  Urine.

   838. The Kidneys cannot  be regarded  as inferior in  importance  to the
Liver, when considered merely as excreting organs;  but their function  only
consists in separating from the blood certain effete substances, which are to
be thrown off from it; and has no direct connection  with any ofthe nutritive
operations, concerned in the introduction of aliment into the system.  Organs
destined to the elaboration of  a  Urinary secretion may be traced very low
down  in the Animal  scale.  Among many of the Mollusca we find a small
sac, filled with a semi-fluid secretion which has been shown to contain uric
acid, opening  into the intestine, near its anal orifice.  In  Insects, we  often
meet with prolonged  tubes, resembling the biliary vessels in form, but termi-
nating in a lower part of the intestinal tube ; in some species these are  dilated
near their extremity into a receptacle for their secretion, or a urinary bladder.
Throughout the Vertebrated classes, they exist  in a still more  evident form.
They are uniformly composed of a congeries of prolonged tubes, subdividing
and  ramifying more or less ;  which spring from  the ureter or efferent  duct,
and terminate  either in blind extremities, or in a plexus formed by their  inos-
culation.  There are considerable variations  in the arrangement of these tubes,
however, in different  tribes of animals.  In Fishes,  the Kidneys  very  com-
monly extend  the whole length of the abdomen ;  and they consist of tufts of
uniform-sized tubules, which shoot out transversely at intervals from the long
ureter.   These tubes  frequently divide into pairs, but without  any great alte-
ration in their  diameter.  They appear to terminate in ccecal extremities, with-
out any inosculation;  the number of bifurcations, and the degree of convolu-

            [Fig. 239.                                  [Fig. 240.
  A view of the Right Kidney with its Renal
Capsule; 1, anterior face of the kidney ; 2, exter-
nal or convex edge; 3, its internal edge ; 4, hilum
renale; 5, inferior extremity ofthe kidney; 6, pel-
vis of the ureter;  7, ureter; 8, 9, superior and in-
ferior branches of the eraulgent artery ; 10,11,12,
the three branches of the emulgent vein ; 13, an-
terior face of the  renal capsule; 14, its superior
edge; 15, its external edge ; 16, its internal ex-
tremity; 17, the fissure on the anterior face ofthe
capsule.]
  A section of the Kidney, surmounted by the
Supra-Renal  Capsule; 1, the supra-renal cap-
sule ; 2, the vascular portion; 3, 3, its tubular
portion, consisting of cones; 4, 4, two of the
calices receiving the apex of their correspond-
ing cones ; 5,5, 5, the three infundibula ; 6, the
pelvis; 7, the ureter.] 
THE KIDNEYS--SECRETION OF URINE.
633
[Fig. 241.
[Fig. 242.
  Represents the half of a Kidney di-
vided vertically, and with its arteries
injected;  the matter has also passed
into the excretory ducts; 1, 2, branches
of the emulgent artery ;  3, 3, hilum re-
nale; 4, 4, cortical substance, as essen-
tially formed by the capillary termina-
tions of the vessels of the kidney; 5,
medullary or tubular portion.]
  A view of half a Kidney divided vertically from its con-
vex to its concave edge ; one of its extremities is perfect;
1,1, the lobes which form the kidney ; 2, 2, the lines of se-
paration of these lobes; 3, the cortical substance ; 4, 5. the
pyramids of Malpighi; 6, the hilum renale split up and
cleared of its vessels; 7, 7, points to the tubes of Bellini;
8, one of the papillae ; 9,10, two other papillae, uncut, but
deprivedofthe calicesthat surrounded them; 11, one ofthe
foveolae in the papilla; 12,12, the vascular  circle sur-
rounding the papillae; 13, circumference of the tubular
portion; 14, external surface ofthe kidney; 15, the por-
tion of its external surface on a line with its fissure.]

tion, vary greatly in different species.   The uriniferous  tubes are connected
together by a very loose  areolar web.—The structure of the gland in Reptiles
appears to  be  essentially the same; its form, however,  varies considerably
in the different tribes, being greatly prolonged in the Serpents, and abbreviated
in the Tortoises.  In the Crocodile, the distinction between the  cortical and
medullary portion begins to show itself; the tubes being nearly straight where
they issue  from the ureter,  and being convoluted near the surface only of the
lobes.  The Corpora Malpighiana (§  839,  b), however, where they exist in this
class, are scattered through  the whole substance;  not  being  confined, as  in
higher animals, to the cortical  portion.—In Birds,  the urinary  tubes, forming
the several clusters, are  more closely united together;  they  frequently ramify
to a considerable degree.—In the Mammalia, as in Man,.there is  an  evident
distinction  between  the straight and the convoluted  portions  of  the  system  of
tubes;  the former character is seen in the medullary substance ; the latter in
the cortical.   In nearly all below the  Mammalia, the kidneys  present exter-
nally a lobulated aspect; resulting from the want of union between the differ-
ent  bundles of tubes, which arise from separate parts of the ureter.   In the
kidney of the Mammalia, however, the ureter dilates into a capacious  recep-
tacle, towards which the  several bundles  of  uriniferous  tubes converge, so
that they open into it in close proximity  with each  other;  and  the lobules
formed by  these bundles are so closely brought together,  that  no  appearance
of a division  presents itself, until a section of  the gland is made.   Among
some Mammalia, however, the lower form is still retained ; and it is presented
in the Human species also, at an early period  of its fetal development.
  839.  The following is an account of the structure of the Kidney, according
to the most recent investigations.*

  * See Bowman in  Philosophical Transactions, 1S42; also Gerlach,  in Muller's Archiy.,
Hefl 4, 1845, and in Ranking's  Abstract, vol. iii. p. 307. 
634
OF  SECRETION.
  a. The distinction between the cortical and medullary parts of the Kidney essentially con-
sists in this,—that the former is by far the most vascular, and the plexus formed by the
tubuli uriniferi seems to  come into  the closest relation with that of the sanguiferous capil-
laries, so that it is probably the  seat of the greater part of the process of secretion; whilst
the latter is principally composed of tubes, passing in a straight line from the former towards
their point of entrance into the  ureter.   In this respect  there is a considerable analogy of
structure and comparative function, between the two parts of the kidney and the two parts
of the brain. The adjoined figure represents the  appearances presented by a portion of an

                   Fig.  243.                                        Fig. 244.
  Portion of the Kidney of a new-born infant; a, natural       Portion of one ofthe tubuli uriniferi,
size; 1,1, corpora Malpighiana, as dispersed points in the     from the kidney of an adult; showing
cortical substance; 2,2, papilla; b, a smaller part magni-     its tesselated epithelium.   Magnified
fied ; 1,1, corpora Malpighiana; 2, 2, tubuli uriniferi.           250 diameters.
 injected kidney, as seen by the naked eye, and under a low magnifying power.  The tubuli
 uriniferi, in passing outwards from the calices, increase in number by divarication, to a con-
 siderable extent, as shown in Fig. 246; but their diameter remains the same.  When they
 arrive in the cortical substance, their previously straight direction is departed from, and they
 become much convoluted.  The closeness of the texture formed by their interlacement with
 the blood-vessels, renders it difficult  to obtain a clear view of their mode of termination.
 They seem to inosculate with each other, forming a plexus, with  a free extremity, or more
 probably a loop, here and there (Fig. 246); the number of these free extremities, however,
 does not appear to be nearly equal to that of the uriniferous tubes themselves.
   b. Scattered through the plexus formed by the blood-vessels and uriniferous tubes, a num-
 ber of little dark points may be seen with the naked eye, to which the designation of Cor-
 pora Malpighiana has been given, after  the name of their discoverer.  Each one of these,
 when examined with a high  magnifying power, is  found to  consist of a mass of minute
 blood-vessels (Fig. 246, 7) ; somewhat resembling those convoluted masses of Absorbents,
 termed Lymphatic  Glands.  Each of these is included in an offshoot from one of the tubuli
 uriniferi, which swells  into a flask-like dilatation to receive it (Fig. 247); and every tube
 may have several such  lateral offshoots.  The Epithelium which  elsewhere lines the tube
 (whose usual character is shown  in  Fig. 244)  is altered in appearance, where the tube is
 continuous with this capsular dilatation  (Fig. 247, 2'); being there more transparent, and
 furnished with  cilia (as shown at  2"), which in the Frog may be seen, for many hours after
 death, in very active motion, directing a current down the tube.  Further within the capsule,
 the Epithelium is excessively delicate;  but  it may be  clearly seen to cover the convoluted
 knot of vessels, which  constitutes the Malpighian body*—The Renal Artery, on entering
 the Kidney,  divides itself into minute twigs, which are  the afferent  vessels of the Malpighian
 tufts (Fig. 248, af).  After it has pierced the capsule, the twig dilates; and suddenly divides
 and subdivides itself into several minute branches, terminating in  convoluted capillaries,
 which are collected in the form of a ball  (rn. m) ; and from the interior of the ball, the soli-
 tary efferent vessel, e f arises, which passes out of the capsule by the side of the single affe-
 rent vessel.   This ball  seems to lie loose  and bare in the capsule, being attached to it only
»by its afferent and efferent vessels (Fig. 248, m); but it appears in reality to be enveloped
 in a reflexion of the membrane that forms the capsule;  and from this are probably generated
 the epithelium-cells, by which it is covered.   The efferent vessels, on leaving the Malpighian
 bodies, separately enter the plexus of capillaries, p, surrounding the tubuli uriniferi, st, and
 supply that plexus  with blood:  from  this plexus the Renal vein arises.—In Mr. Bowman's
  * On this point, which is one of difference between Mr.  Bowman and Dr. Gerlach, the
Author's own observations lead him unhesitatingly to concur with the latter. 
SECRETION OF URINE.                             635

        [Fig. 245.
   A section of one of the Pyramids of Malpighi,  and of its corresponding cortical substance, as seen
 under the microscope ; 1, portion of the surface of the kidney; 2, from this figure up to 1, is the cortical
 substance of the kidney: 3, from 2 to this number is the tubular portion ; 4, the foveola; 5, 6, arteries
 and veins ramifying through the kidney; 7, arteries to the acina of the kidney ; 8, capillary extremities
 of veins  anastomosing with corresponding arterioles; 9, tortuous extremities ofthe arteries directed
 into the interior of the gland ; 10, bases of the cones of the cortical and pyramidal substance of the kid-
 ney ; from 10 to 4 is a collection of these cones; 11, the envelop of the cortical layer; 12, prolongations
 of the tubular portion ; 13, tortuous tubes, or those of  Ferrien ; 14, straight tubes, or those of Bellini; 15,
 vessels which wind between them; 16, course of the uriniferous tubes in the tubular  portion; 17, the
 matter between these tubes ; 18, bifurcation  of the straight tubes ; 19, sections of these  tubes; 20, their
 orifices.]

 opinion, all the  free extremities of the tubuli uriniferi thus  include  Corpora  Malpighiana;
and the appearance of ccecal terminations, such  as those represented at a and  c, Fig. 246, he
regards as an optical illusion, caused by a change in the direction of the tubuli, which occa-
sions them to dip away suddenly from the observer. 
636                                OF SECRETION.

                                        Fig. 246.
  A small portion of the Kidney, magnified about 60 times; 1, supposed ccecal extremity of a tubulus
uriniferus • 3, 3, recurrent loops of tubuli; 5, 5, bifurcations of tubuli; 4, 5, 6, tubuli converging towards
the papilla • 7, 7, 7> Corpora Malpighiana, seen to consist of plexuses of blood-vessels, connected with a
capillary net-work; 8, arterial trunk.

  c  The Embryological Development of the Urinary organs in Vertebrated animals is a
subject of peculiar interest; owing to  the correspondence which may be traced between the
transitory forms they present in the higher classes, and  their permanent  condition in the
lower.  In this respect there is an evident analogy with  the Respiratory system.  The first 
THE KIDNEYS---SECRETION OF URINE.
637
appearance of anything resembling a Urinary apparatus  in the Chick, is seen on the second
half of the third day.  The form at the time presented by it is that of a long canal, extend-
ing on each side of the Spinal Column, from the region of the heart, towards the Allantois;
and the sides of this  present a series  of elevations and depressions, indicative of the com-
mencing development of cceca.  On the fourth day, the Corpora Wolffiana, as they then are
termed, are distinctly recognized, as composed of a series of ccecal appendages, which are
attached along the whole course  of the first-mentioned canal, opening into its  outer side. On
the fifth day these appendages  are  convoluted; and the body which they form acquires
increased breadth and thickness.   They  evidently then possess a secreting function; and the
fluid which they separate  is poured by the long straight canal into the cloaca.  Between
their component shut sacs, numbers of small  points appear, which consist of little clusters
of convoluted vessels, exactly analogous  to the  Corpora  Malpighiana of the kidney.—The
Fig. 247.
Fig. 248.
Fig. 249.
  Uriniferous Tube, Malpighian
Tuft, and Capsule, from Kidney
of Frog: a, cavity of the tube;
6, epithelium of the  tube;  b',
ciliated epithelium of the  neck
of the  capsule; b", detached
epithelium  scale; e,  basement
membrane of tube ; e', basement
membrane of capsule. Magnified
about 320 diam.
  Distribution of the Renal ves-
sels ; from Kidney of Horse; a,
branch of Renal artery; af,
afferent vessel; m, m, Malpig-
hian tufts; ef, ef, efferent ves-
sels; p, vascular plexus sur-
rounding  the tubes ; st, straight
tube; ct, convoluted tube. Mag-
nified about 30 diam.
  Corpora Wolffiana, with kid-
ney and testes, from embryo of
Bird; 1, kidney; 2,2, ureters; 3,
corpus Wolffianum; 4, its ex-
cretory duct;  5, 5, testicles;  at
the summit are seen the supra-
renal capsules.
Corpora Wolffiana, however, have only a temporary existence in the higher Vertebrata;
although it seems that, in Fishes, they constitute the permanent kidney.*  The development
of the true Kidneys commences in the Chick  about  the fifth day.  They are seen on the
sixth, as lobulated grayish masses, which sprout from the outer edges of the Wolffian bodies;
and they gradually increase, the temporary organs diminishing in the same proportion. The
sexual organs, as will be hereafter explained (§ 866,6), also originate in the Wolffian bodies;
and at the end of foetal life, the only vestige of the latter is to be found as a shrunk rudi-
ment situated near the testes of the male.—The progress of development in the Human
embryo seems closely conformable to the foregoing account.  The Wolffian bodies  begin to
appear towards the end of the first month; and it is in the course  of the  seventh week,
that the true Kidneys first present themselves.  From the beginning of the third month the
diminution in the sizeof the Wolffian bodies goes on pari passu with the increase ofthe Kidneys;
and at tire time of birth scarcely any traces of them can be  found.  At the end of the third
* See Principles of General and Comparative Physiology, § 659.
54 
638
OF SECRETION.
month, the kidneys consist of seven or eight lobes, the future pyramids; their excretory
ducts still terminate in the same canal, which receives those of the Wolffian bodies and of
the sexual organs;  and this opens, with the rectum, into a sort of cloaca, or sinus urogeni-
tals, analogous to that which is permanent in the oviparous  Vertebrata.   The Kidneys are
at this  time covered  by the  Supra-Renal  Capsules, which are very large; about the sixth
month, however, these have decreased, whilst the kidneys have increased, so that their pro-
portional weight is as 1 to 4|.  At birth  the weight of the  Kidneys is about three times
that of the Supra-Renal Capsules; and they bear to the whole body the proportion of 1 to
80; in  the adult, however, they are no more than 1 to 240.  The Corpora Wolffiana are,
when at their greatest development, the most vascular parts of the body next to the liver;
four or five branches from the aorta are distributed to each, and two veins are returned from
each to the vena cava. The upper veins and  their corresponding arteries are converted
into the Renal or emulgent vessels; and the lower into Spermatic vessels.  The lobulated
appearance of the kidney gradually disappears; partly in consequence of the condensation
of the areolar tissue, which connects the  different parts;  and  partly through the  develop-
ment of additional tubuli in the interstices.  The Urinary Bladder is formed  quite inde-
pendently of the secreting apparatus, being a part of the allantoic, which is first developed
as a large caecum or diverticulum from the lower  extremity of the alimentary canal (Chap.
xvn.).   The part of the tube below this  forms the Cloaca,  or common termination of the
intestinal and vesical  apparatus.  The sides of this cloaca, however, gradually approach
one another, so as  to form a transverse  partition, which  separates  the Rectum from the
Genito-urinary canal;  and the urethra of the female is afterwards separated from the Vagina
by a similar process.

   840. The researches of Mr. Bowman on the  structure of the  Malpighian
bodies, and on the vascular apparatus of  the Kidney,  have thrown great light
upon the mode  in  which the Urinary secretion  is elaborated.  One  of the
most remarkable circumstances  attending this excretion, in the Mammalia
particularly, is the large  but  variable quantity of water, which is thus got rid
of,—the amount of which bears no constant proportion to that of the solid
matter  dissolved in it.   The Kidneys, in  fact, seem  to  form a kind of regu-
lating valve, by which  the quantity of water in the system is kept to its proper
amount.  The Exhalation from the Skin,  which is  the other principal means
of removing the  superfluous  liquid from the blood, is liable to great variations,
from the temperature of the  air around (§ 870): hence, if there were not some
other means of adjusting the quantity of fluid in the  Blood-vessels, it would
be liable to  continual and very injurious variation.   This  important function
is performed by the Kidneys; which allow such a quantity of water to pass
into the urinary  tubes, as may keep the pressure within the vessels nearly at
a uniform standard.  The quantity of water which is passed off by the kid-
neys, therefore, will depend in part  upon that exhaled by the  Skin;  being
greatest when this is least, and vice versa: but the quantity of solid matter to
be conveyed away  in the secretion has little  to do with  this; being dependent
upon the amount of waste in the  system, and upon  the quantity of  surplus
azotized aliment which has to be discharged through the channel.—The Kid-
ney contains two very distinct provisions for these purposes.   The cells lining
the Tubuli  Uriniferi are probably here, as elsewhere, the instruments by which
the solid matter of the secretion is  elaborated; whilst it can scarcely be doubted
that the office of the Corpora Malpighiana is to allow the transudation of the
superfluous fluid through the thin-walled and naked capillaries of which they
are composed.   "It would,  indeed," Mr.  Bowman remarks, "be difficult to
conceive a disposition of  parts more calculated to favour the escape of  water
from the blood, than that of  the Malpighian  body.  A large artery breaks up
in a very direct manner  into a number  of minute  branches;  each of which
suddenly opens into an assemblage  of vessels of far  greater aggregate capacity
than itself,  and from which there is  but one narrow exit.   Hence must arise
a very abrupt retardation in the velocity of the current of blood.  The vessels
in which this delay occurs are uncovered by any structure.   They lie bare in
a cell, from which there is but one outlet, the orifice  of the tube.  This orifice 
THE KIDNEYS--SECRETION OF URINE.
639
  is encircled by cilia, in active motion, directing a current towards the tube.
  These exquisite organs must not only serve to carry forward the fluid which
  is already in the cell, and in which the vascular tuft is bathed; but must tend
  to remove  pressure from the free surface of  the vessels, and so to encourage
* the escanp of their more fluid contents."
     841. There is a striking  analogy between  the  mode  in which th^* Tubuli
  Uriniferi are supplied  with  Blood, for the purpose of elaborating their secre-
  tion,  and the plan  on which the Hepatic  circulation  is carried on.  The
  secretion of the Liver is formed from  blood conveyed to it by one large vessel,
  the Vena Portae, which has collected it  from the Venous capillaries of the
  chylopoietic  viscera, and which  subdivides  again to distribute it through the
  liver.  The secretion of the Kidney, in like manner, is elaborated from blood
  which has already passed through  one set of capillary vessels,—those of the
  Malpighian tufts;  this  blood is collected and conveyed to the proper secreting
  surface, not by one large trunk (which would  have  been a very inconvenient
  arrangement), but  by a multitude of  small ones,—the efferent  vessels of the
  Malpighian bodies, which   may be regarded  as collectively representing the
  Vena Portae, since they convey the blood from the systemic to the secreting
  capillaries.   Hence the Kidney  may be said to have  a portal system within
  itself.—This ingenious view of Mr.  Bowman's finds support from the fact,
  that in Reptiles (in which,  as in Fishes, the Portal trunk receives the blood
  from  the whole posterior part  of the body, and supplies the  Kidneys as well
  as the Liver), the  efferent vessels of the  Malpighian  bodies—which  receive
  their  blood, as elsewhere, from the Renal Artery—unite  with  the branches
  of the Portal vein, to  form  the secreting  plexus around the Tubuli Uriniferi.
  Here, therefore, the blood of the secreting plexus has a double source; the
  vessels which supply it receiving their blood in part from the capillaries of the
  organ itself, and in part from those of viscera external  to it;  just as, in the
  Liver, the secreting plexus  is supplied in  part by the blood conveyed from the
  chylopoietic  viscera through  tbe  Vena  Porta?, and in part by the nutritive
  capillaries  of the  organ itself, which receive  their blood from the  Hepatic
  Artery.
     842. The nature and purposes ofthe Urinary secretion, and the alterations
  which it is liable to undergo in various conditions of the system, are much
  better understood than are those of the Bile;  this is owing, in  great part, to
  the circumstance, that  it may  be readily collected in a state of purity ; and
  that its ingredients are of such a nature, as to be  easily and definitely sepa-
  rated  from each other  by simple chemical means.  There can be no doubt
  that the chief purpose of this excretion, is  to remove from the system the effete
  azotized  matters which the  blood takes up in the course of the circulation, or
  which may have been  produced by changes occurring in itself.   This is evi-
  dent from  the large proportion of  Nitrogen  which  is contained in the solid
  matter dissolved in it;  and  from the  crystalline form  presented by this solid
  matter when separated,—a form which indicates that its state of combination
  is such, as to prevent it from conducing to the nutrition of the system.  The
  injurious effects of the retention in the Blood, of the components of the Uri-
  nary  secretion,  are fully demonstrated by the results of its cessation; whether
  this be made to take place experimentally (as by tying the renal artery), or be
  the consequence of a disordered condition of the kidney.   Symptoms of great
  disorder of the nervous centres, analogous to those  produced by many narcotic
  poisons, soon exhibit themselves ; and the patient dies comatose, if the secre-
  tion be not restored.   In such cases, Urea (the characteristic ingredient of the
  urine) is found to have accumulated in the Blood ; and it may even be detected
  by the smell, in the fluid effused into the Ventricles of the Brain.  The con-
  clusion which may be  drawn from this circumstance, regarding the pre-exist- 
640
OF SECRETION.
ence of the components of the secretion in the Blood, is strengthened by the
fact that, even in the healthy state, Urea maybe detected in the blood; it only
exists  there  normally, however, in very small quantity; but, when  there is
any impediment to its excretion, it goes on accumulating, and produces conse-
quences more or less serious  in proportion  to its amount.  It is  not improba-
ble thatf*as in the case of the retention of Bile in the Blood (§ 832^many of
the minor as well as of the severer forms of sympathetic disturbance, connected
with disordered secretion from the Kidney, are due to the  directly poisonous
operation of  the elements of  the Urine, upon the several organs whose func-
tion is disturbed; and  that many complaints, in  which no such  agency has
been until recently suspected,—especially Convulsive affections  arising from
a disordered action of the Nervous centres,—are due to the insufficient  elimi-
nation of Urea from the Blood.
  843.  In order to form a correct opinion of the state of the Urinary secretion
in morbid conditions of the system, it is desirable to be acquainted with  every
leading particular  regarding  its  healthy  characters.—The average Quantity,
during 24 hours, has been variously estimated:  it differs, of course, with the
amount of fluid ingested, and  it is influenced also by the external temperature,
—a much smaller amount of the superfluous fluid of the body  being set free
from the skin in winter than in summer, and a larger proportion being carried
off by the kidneys.   Probably we shall be  pretty near the truth, in estimating
the amount at from about 30  oz. in summer,  to 40 oz. in winter, for a person
who does not drink more  than the  simple wants of nature require.—The
Specific Gravity comes to be a  very important  character,  in various morbid
conditions of  the urine :  and it is therefore desirable to estimate it correctly.
This  also is, of course, liable to the same causes of variation; since,  when
the same amount of solid matter is dissolved in a larger or  smaller quantity of
water, the specific gravity will  be proportionably lower or  higher.   The
average, according to Dr. Prout, in  a  healthy person, taking the whole year
round, is about 1020; the standard rising  in summer (on account of the greater
discharge of  fluid by perspiration) to 1025; and being lowered in winter to
1015.   Simon, however, states the  average specific  gravity at  no more than
1012.   It will depend, in each individual case, upon the amount of fluid habitu-
ally ingested, as compared with that dissipated by cutaneous exhalation;  and
it will also vary with the period that has  elapsed since the last introduction of
liquid into the stomach.   From these and other causes, the  proportion of solid
matter in  1000 parts of Urine may vary from 20 to 70.  The following table
expresses the relative amounts of the different components, in every 100 parts
of this solid matter; according to the analyses of different  Chemists.
erzelius.	Lehmann.	Simon.	Marchand.
45-10	4968	33-80	48-91
1-50	1-61	1-40	1-59
3630	28-95	42-60	32-49
10-30	11-58	8-14	10-18
6-88	5-96	6-50	4-57
1-50	1-97	1-59	1-81
  We shall presently find the causes of some of these variations in the nature
of the ingesta, and in the  amount of exercise  taken by the individual.__The
Urine in health usually exhibits an acid  reaction; this  depends, however,
upon  certain conditions furnished by the aliment; and may be altered (as will
presently appear) by a change in tbe ingesta.
  844.  The most important of the  above ingredients (constituting from one-
third to one-half of the whole solid matters of the Urine) is evidently that
which, from its being the principal cause of the characteristic properties  of the
Urea.....
Uric Acid  .....
Extractive matter, Ammonia-salts, \
  and Chloride of sodium       \
Alkaline Sulphates
Alkaline Phosphates
Phosphates of Lime and Magnesia 
SECRETION OF TRINE.
641
 secretion, is termed Urea.  This maybe readily separated from Urine, in the
 form of transparent colourless crystals;'which have a faint and peculiar, but
 not urinous odour:  and, as already mentioned, it is distinctly traceable in the
 Blood, where it rapidly accumulates, if its continual elimination be in any way
 interfered with.   It is very soluble in water, and combines with acids without
 neutralizing them.  In its chemical composition,  it is  identical with cyanate
 of ammonia; this composition being 2 Carbon, 4 Hydrogen, 2 Nitrogen, and
 2 Oxygen,—a formula  much more simple  than that of  almost any  other
 organic substance.  The amount of Urea excreted in  twenty-four hours has
 been made the subject of examination by Lecanu ;* and the following are his
 results, as deduced from a series of 120  analyses:—
                                        Minimum.     Mean.     Maximum.
 By men........357-51  grs.   433-13 grs.    510-36 grs.
 By women........153-25       295-15       437-06
 By old men (84 to 86 years)   ....   61-08       12522       295-15
 By children of eight years.....161-78       207-99       254-20
 By children of four years.....57-28       69-55        81-83
   It is very interesting to perceive, in  this table, how large an amount of Urea
 is excreted by children ; and how small a quantity, in proportion to their bulk,
 by old men.   This  corresponds precisely with  the  rapidity of interstitial
 change at different periods of life.   (See § 812.)   Moreover, as this  continual
 disintegration is very much accelerated by increased vital activity of the Tis-
 sues, the amount of Urea undergoes a like augmentation; so that—other cir-
 cumstances being equal—the amount of Urea  excreted may fairly serve as a
 measure of the waste of the tissues, and consequently of the degree in which
 they have been exercised.   This will  be especially the case in  regard  to the
 Muscular Tissue ; which constitutes so  large a part of the fabric.   In  some
 experiments recently made on the influence of various causes upon the con-
 stitution of Urine, Dr. Lehmann found that, by the substitution of violent for
 moderate exercise, the quantity of Urea was raised from 32|  to  45j parts;
 and Simon  found that, by two hours' violent exercise, the  proportion of  the
 urea in the urine passed half an hour subsequently was double that contained
 in the morning urine.   If such increased waste  be  not compensated by in-
 creased nutrition, a  diminution in the  bulk of the body is the necessary con-
 sequence.
   845. The next important  ingredient,  Uric or LAthic Acid, exists  much
 more largely in the Urine ofthe lower Vertebrata, than in that of Mammalia;
 thus the nearly solid urinary excretion of Serpents, and the semi-fluid  urine
 of  Birds, is almost entirely composed of this acid, in combination with Am-
 monia.  Its presence has not yet been detected in healthy blood; but when
 it is imperfectly eliminated, we are assured of its accumulation  in the  circu-
 lating fluid, by its deposition, in combination with  Soda, in the neighbourhood
 of the joints,—forming Gouty Concretions, or Chalk-stones.   Pure Lithic acid
 crystallizes in fine scales of a brilliant white  colour, and  silky lustre ; it is
 tasteless  and inodorous, and is  so sparingly soluble  in water, that at least
 10,000 times its own weight is required  to dissolve it.   As it exists  in a state
 of perfect solution in healthy Urine,  it must be  in  combination with  some
 base; and that this is the case, is at once^proved by the fact, that it is precipi-
tated  immediately on the addition of a  small quantity of any acid,  even the
Carbonic.  It is generally believed, that the base is  Ammonia;  but it has
recently been  affirmed by  Liebig,t that the  Uric acid  (with the Hippuric) is
held in solution by the 'Phosphate  of Soda,—which, from being bibasic or
alkaline, is rendered acid,  by  yielding up a part of its  soda to these organic

    *  Journal de Pharmacie, tom. xxv.                  t Lancet, June 8, 1844.
                                   54* 
642
OF SECRETION.
acids, which are thereby rendered soluble.   It is in this manner that he partly
explains the usually acid reaction of healthy urine ;  the other causes of which
will be presently noticed.—If there be an undue proportion of Lithic acid in
the urine, it will be precipitated on cooling;  because  it  is  less  soluble in a
cold than  in a warm solution of phosphate of soda; and the same  result will
happen, if there be a predominance of other  acids  in the  urine, which will
seize upon its base, as  soon  as its  own affinity for it  is diminished by the
lowering of its temperature.   By Dr. Prout it is believed  that Lactic acid, ex-
isting in  the Blood or in  the Urine in  excess, is  an ordinary source  of this
deposit;  but the presence of this acid  is altogether  denied by  Liebig (§ 846).
—The composition of Lithic Acid  is  as follows:—10 Carbon, 4 Hydrogen,
4 Nitrogen, 6 Oxygen.   The amount of it  usually  excreted  in the Urine of
Man is but very small; it  is occasionally,  however, considerably  increased;
but the circumstances under which  this increase takes place have not yet been
exactly determined.
   a. Uric acid is replaced in the Herbivorous animals by the Hippuric;  the composition and
properties of which are very different from those presented by that substance.   When pure,
it forms long transparent four-sided prisms; it is soluble in 400 parts of cold water, and dis-
solves readily at a boiling heat;  and it has a strong acid reaction, and bitterish taste.  Its
formula is 18 Carbon, 8 Hydrogen, 1 Nitrogen, and 5  Oxygen, with 1 equiv. of Water.   It
has very curious relations with  Benzoic acid; which it yields, together with Benzoate of
Ammonia, when acted upon by a high temperature, or during the putrefaction of the urine
of which it forms a part.  According to Liebig, the Hippuric acid in the urine of the Horse
and Ox is replaced by Benzoic acid, when the animal  is subjected to hard labour.—It appears
from his recent experiments,* that we are to regard Hippuric acid as a normal element of
Human urine; for he has detected Benzoic acid among the products of its putrefaction; and
as we know that the latter does not exist in the Urine of Man, and as there is no other sub-
stance at the expense of  which it can be formed during the putrefactive process, we can
scarcely hesitate to admit that such must be the case.   It is a very curious fact, that the intro-
duction of Benzoic acid into the system causes a large increase in the amount of  Hippuric
acid in  the Urine; and if this be formed at the expense of the elements, which would other-
wise have produced Uric acid, an easy method is pointed out for the elimination of the latter
substance from  the blood, when it has accumulated there,—the salts of Hippuric acid being
so much more soluble  than those of the Uric.  According to Keller,-)" whose experiments
were made upon himself, both Urea and Uric acid existed in normal quantity in  his urine,
though  a large quantity of Hippuric acid was being excreted;  whilst Mr. Alexander Ure
states,J that he has succeeded, by the administration  of Benzoic acid, in  preventing the de-
position of Gouty concretions, and even in removing them when they had been formed.
   b. Many remarkable changes are effected in Lithic acid, by the operation of other chemi-
cal agents; and these changes are very important, in their bearing on pathological conditions
of the Urine.  When Uric acid  is subjected to the action of Oxygen, it is first resolved into
Urea and a compound termed Alloxan.  Now this Alloxan, when acted on by a new supply
of Oxygen, is resolved into  Urea and Oxalic acid; or, with a  still further amount of Oxygen,
into Urea and Carbonic acid:—a fact, which has a very important bearing on the production
of Calculi composed  of Uric and Oxalic acids, and which explains the remarkable alterna-
tions which are often observed in the layers of these concretions.   It is affirmed by Liebig,
that the calculi which are composed of Urate of Ammonia, or of Oxalate of Lime, occur in
persons, in whom, from want of exercise, or from other causes, the quantity of Oxygen intro-
duced into the system is beneath what it ought to be.  When patients suffering under Uric
acid Calculi take more exercise, the Urates are replaced by Oxalates, in consequence of the
larger amount of Oxygen introduced  into the system; and if the oxygenation could be carried
still further, the latter would cease to be deposited, their elements passing off in the form of
 Urea and Carbonic acid.  These views are  borne  out by the results of Lehmann's experi-
 ments upon himself; for he found that the violent exercise, which raised the  proportion of
 Urea in the urine by more than one-third'(§ 844)  brought down the amount of  Uric acid
from 1-18 to -642, or nearly one-half.
   c. Another change is that which  gives rise to the peculiar compound  termed  Allantoin;
 which naturally exists in the fluid of the Allantois of the festal calf.   This may be formed
 artificially by boiling Uric acid with peroxide of lead; from which process there result an

            *  Loc. cit.                  t  Liebig's Animal Chemistry, p. 327.
            J  Medico-Chirurgical Transactions, vol. xxiv. 
SECRETION OF URINE.
643
Oxalate of the protoxide of lead, Urea and Allantoin; the composition of which last substance
is very different from that of urea or uric acid, being 8 Carbon, 5 Hydrogen, 4 Nitrogen, and
5 Oxygen.
  d. By the operation of Nitric Acid upon Uric acid, several new products  are generated,
some of which are of much practical interest.  To one of these  the name of Murexid has
been given, on account of its reddish purple colour (resembling that of the Tyrian dye which
was obtained from a species of Murex); this is a crystalline subslance, sparingly soluble  in
cold water, but copiously soluble in warm, imparting to it its vivid colour.  By Dr. Prout it
was long since described as consisting of a peculiar acid,  the Purpuric, in combination with
Ammonia; this view of its composition is not generally received by German  Chemists ; but
it has lately been supported by Fritzche, who has shown the real existence  of the acid,  by
obtaining  Purpurates of other  bases. This substance is  one source of the  colours of the
pink and lateritious sediments  which so often present themselves  in the Urine ; these hues
partly depend, however, on the influence of nitric acid upon the  peculiar Colouring princi-
ples of the urine, the nature of which principles is not yet fully understood.

   846. It was supposed until recently, that Lactic acid is a normal constitu-
ent of Human Urine.   It appears to have been  demonstrated  by the experi-
ments of Liebig, however, that this is not the case ;  and that another organic
substance, which forms a  crystalline compound with zinc, very similar to the
lactate, has been mistaken for it.   The composition of  this substance, which
usually forms about  one part in 200 of Urine, has been recently determined
to be 8 Carbon, 8 Hydrogen, 3 Nitrogen, and 3 Oxygen.  It thus differs from
Lactic acid in containing Nitrogen;  as well as in proportion of its other com-
ponents.
   847. It has been shown (§ 843), that  the Urine contains a considerable
amount of Saline matter;  the excretion  of  which from  the system appears  to
be one of the principal offices of the Kidney.   Various saline compounds,
and the  bases of others, are being continually introduced with the  food (§ 648);
and these, after performing their part in the organism, must be eliminated from
the  circulating fluid, in order  to prevent injurious accumulation.   Of these
we shall now examine the chief sources.—The  mode in which the Muriates
find their way into the Urine is easily understood.   Of the Common Salt in-
gested, a considerable  part is  decomposed into Muriatic Acid and  Soda; the
former being found uncombined in the Gastric juice ;  and the latter in  the  Bile.
By the mixture of the Bile with  the Chyme, a re-union of these two consti-
tuents takes place;  and Salt is again formed, which is  received  into the Cir-
culation that it may be eliminated (its part in the economy having been now per-
formed) by the Kidney.—The quantity of the Sulphates present in the Urine,
 appears to have no relation with that of the amount of Sulphuric acid ingested ;
 for it much surpasses what could be thus accounted for,—being often consi-
 derable, when no Sulphate whatever can be detected in the  food.   But  most
of the  azotized  compounds employed as food have Sulphur in combination
 with them ; and there can be no doubt, that this undergoes oxidation within
 the  system, and thus  generates  Sulphuric acid, which unites with  any free
 or weakly-combined bases it may meet with, to form  the Sulphates present in
 the  Urine.—The Phosphates  are  probably derived  in' part from the Phos-
 phates taken in with the  food, and  in part  from the  free Phosphorus, which
 its elements contain.   Of the latter, great  use  is made in the production of
 Nervous matter  (§ 249) ;  the  continual waste of which must set it free again.
 When thus set free, there is obviously no channel for its elimination, save  by
its conversion  into  Phosphoric  acid, and  its union with an  alkaline base.*
 That this is really the case, would appear from  the fact noticed by Dr. Prout,
 and confirmed by many others,—that mental or bodily labour which involves

   *  This circumstance has been  entirely overlooked by Liebig, in his late discussion (loc.
cit.)  ofthe Constitution of the  Urine; the Phosphates being regarded by him as having their
 sole origin in the Phosphates of the ingesta. 
644
OF SECRETION.
much waste of the Nervous System, is followed by an increase in the quan-
tity of the  alkaline Phosphates in the Urine (§ 295).  This increase cannot
proceed  from the  waste  of the Muscular system ; for this would  set  free
Phosphate of Lime, which chiefly passes off by the faeces.
   848.  The alkaline or  acid reaction of the Urine, therefore, will not only
depend upon the quantity of alkaline Phosphates converted into acid Phos-
phates by the Uric and Hippuric  acids (§ 845); but also upon the amount of
the bases  in the ingesta, compared  with that of the  permanent Acids intro-
duced into the system or generated within it.   The Urine of animals which
live chiefly or entirely upon Vegetable  food, is almost invariably alkaline;
because this food contains  a large quantity of alkaline  bases, in  combination
with Citric, Tartaric, Oxalic, and other acids, which  are decomposed within
the system; and the  amount of Sulphuric and  Phosphoric acids produced is
not sufficient to  neutralize  them.  On the other hand, the  food of Carnivo-
rous animals contains no free or weakly-combined bases ; and as its  Sulphur
and Phosphorus, when oxidized in the system, produce a considerable quan-
tity of free acids, which share the bases with the Muriatic acid already there,
the Urine  must  necessarily have an  acid reaction.   The  character of the
Urine of Man, in this  respect, is considered by Liebig to depend entirely upon
that of the food ingested. .
  a. Proceeding upon his determination that no Lactic acid is ever present in the Urine, he
remarks: " The acid, neutral, or alkaline reaction of Urine of healthy individuals, does not
depend on any difference in the processes of digestion, respiration, or  secretion,  in the va-
rious classes of animals, but upon the  constitution of the aliments, and upon the alkaline
bases which  enter the organism through the medium of these aliments.  If the amount of
these bases is sufficiently large  to neutralize the acids formed in  the  organism, or supplied
by the aliments; the urine  is neutral;  whilst it manifests an alkaline reaction, when the
amount of alkaline bases thus supplied to the organism is more than sufficient to  neu-
tralize the acids; but in all these cases, the urine accords with the nature pf the aliments
taken."  The varying amount of Uric Acid,—which, on  Prof. Liebig's own showing, is very
much influenced by the respiration,—is altogether left out of consideration in this sweeping
generalization.
  849. The amount of Azotized matter  in the Urine, also, is greatly influ-
enced by the nature of the  food ingested, whilst the  constitution of  the Ani-
mal frame remains  nearly the same; hence it appears,  that  a certain portion
of it must be derived from the unassimilated materials which have been taken
into the blood, and  which, being superfluous, are injurious.   It is well known
that the ingestion of an over-supply of azotized matter  does not occasion an
increased production of the fibrinous or gelatinous tissues; and it  may be
hence inferred that, as there is no  means by which the superfluous amount
can be stored up in the system (in the mode that non-azotized matter  is stored
up as Fat), it must be continually eliminated from the Blood.  And there can
be no  doubt that the Kidneys are the principal channel by  which this is ef-
fected ; the  amount of azote thrown  off in a given time, in the various com-
pounds which they excrete, being equal to 10-1 lths of the whole  quantity
ingested.—The  following  are  the results of the most  satisfactory inquiries
that have yet been made, in regard to the influence of  various  kinds of  Ali-
ment upon  the amount of the solid matters in the Urine.  These experiments
were performed by Dr. Lehmann of Leipsig, upon himself.  In the first series,
Dr. L. adopted an ordinary mixed diet;  but he took no more solid or liquid
aliment than was needed  to appease hunger or thirst, and abstained from fer-
mented  drinks.   Every two hours  he took exercise in the open air, but he
avoided immoderate exertion of every kind.   The average result of  the exa-
mination of the Urine passed under  these circumstances,  for fifteen days, is
given in the first line  of the subsequent Table.—In a second  series  of experi-
ments, Dr. L. lived for twelve days  on an exclusively  Animal diet; and for 
SECRETION OF URINE.
645
the last  six of these, it  consisted solely of eggs.  He took 32  eggs daily;
which contained 189*7 grammes of dry albumen, and 157*48 of fatty matters;
or about  228*75 grammes of carbon, and 30*16 of azote.   The amount of
Urea  is  shown, in the second line of the Table, to have undergone a very
large increase ; and it contained more than five-sixths of the  whole azote in-
gested.—In a third series of experiments, Dr. L. lived for twelve days on a
Vegetable diet;  and its effect upon the solid matter of  the Urine  is shown in
the third  line of the  Table.—In  a fourth, he lived for two  days upon pure
farinaceous and  oleaginous substances, without  azotized  food  of any kind ;
and the  azotized  matter of the Urine must, therefore, have been solely the
result of the disintegration of the tissues.   It is seen to undergo a very marked
diminution under this regimen, as is shown in the fourth line of the Table.
His health was so seriously affected, however, by this diet, that he was una-
ble to continue it longer.
		Solid Matters.	Urea.	Uric Acid.	Lactic Acid (?) and Lactates.	Extractive Matters.
I. II. III. IV.	Mixed diet Animal diet Vegetable diet . Non-Azotized diet	. 67-82 . 87-44 . 59-24 . 41-68	32-498 53-198 22-481 15-408	1-183 1-478 1-021 0735	2-257 2-167 2-669 5-276	10-480 5-145 16-499 11-854
  850. The following inferences are drawn by Dr. Lehmann, from these
experiments:—" 1. Animal articles of diet augment  the  solid matters of the
Urine.  Vegetable substances, and still more such  as are deprived of azote,
on the contrary, diminish it.—2. Although Azote be a product of decomposi-
tion of the organism, yet its proportions in the urine depend also on the food,
for we find a richly-azotized diet augment considerably the quantity of Urea.
In the above experiments, the proportion of the  Urea to  the other solid mat-
ters was as 100 to 116  in a mixed  diet; as 100 to 63  in an  animal diet; as
100 to 156 in a vegetable diet;  and as 100 to 170  in a non-azotized diet.—3.
The quantity of Uric Acid depends less on  the nature  of the diet, than on
other circumstances; the differences observed in it being too slight to warrant
us in ascribing them to the former cause.—4. The combinations of Proteine,
and consequently the azote of the food, are absorbed in the intestinal canal;
and what is not employed in the formation of the tissues, is  thrown off by
the  Kidneys in the form of Urea or Uric acid,—these organs  being the chief
if not the sole, channel  through  which the system  frees itself of its excess of
azote.—5. The urine contains  quantities of Sulphates and Phosphates pro-
portional to the azotized matters which have been absorbed;  and the propor-
tion of these salts is sensibly increased under  the use of a large amount of
those.—6. In the same  circumstances, the Extractive matters  diminish, while
their quantity is increased by the use of vegetable  diet,—a  fact which proves
the  influence of vegetable aliment over the production of these matters in the
urine.—7. Under an animal diet, the quantity of Lactic acid diminishes ;  but
the  greater part of this acid is free.   It is the reverse under a vegetable diet;
there is more lactic acid, but it is united to bases.  The largest production of
lactic  acid is under a non-azotized diet;  and most of it is  then combined with
ammonia.  Therefore the lactic acid eliminated with the urine, is in great part
the  product of non-azotized substances not entirely assimilated; but it results
also in part from the decomposition of the azotized  substances entering into
the  composition of the body and the food.—8.  The  Kidneys not only sepa-
rate certain constituent parts of the organs, which have become inadequate for
the  maintenance of life, but they also expel the superfluous nutritive  matters
that may have been absorbed."*  It must be remarked, with  regard to these
* L'Experience, Dec. 7, 1843; and Edinb. Monthly Journal, March, 1844. 
646
OF SECRETION.
inferences, that the statements concerning the amount of Lactic acid and the
Lactates, must be considered as invalidated by the discoveries of Liebig al-
ready referred to (§ 846).  The most unequivocal facts determined by Dr.
Lehmann's  inquiries, are those which relate to the influence of Diet on the
amount of  Urea excreted.   The experiments  upon a  purely non-azotized
diet were  not continued  long enough for a satisfactory result to be obtained;
but it is evident that, so  long as the ingesta  contain  no azote, the whole of
that element in the Urine must be attributed to the disintegration or waste of
the tissues, and may be fairly taken as a measure of its amount.
   851.  The fact of the pre-existence  ofthe chief constituents  of Urine in the
Blood, is important as explaining the facility with which the secreting function
appears to be transferred  to other membranes, in some of the cases in which
the Kidney does not perform its function.   Doubtless there has been much
error on this subject, arising out of deceptions practised  by impostors ; but a
sufficient number of indubitably genuine cases are on record, to put it beyond
doubt that such transferences have taken place,—urinous fluid being secreted
from the  stomach,  mammae, umbilicus, nose, Sic*—On the  other hand, the
Kidney may serve  as  the channel for  the  elimination  of substances which
are usually drawn off by other organs.  Thus, when the secreting action of
the Liver has been  gradually impaired by structural disease, the  Kidneys ap-
pear to  have performed its function, in separating some (at least) of  the  ele-
ments of Bile.   And a case has recently been mentioned, in  which the urine
of a parturient female, who did not suckle her infant, was found to contain a
considerable amount of Butyric acid, during  several  days.  The elimination
of Kiesteine by the Kidney during pregnancy will be presently noticed (§ 859).
   852.  The facility with which  substances taken into the  current of the
Circulation pass into the Urinary  secretion, varies extremely; and no general
law can be stated  in regard to it.   It appears from Wohler's  elaborate re-
searches on this subject, that the salts which are most readily  excreted are
those which excite the  action  of the kidneys.t  The  rapidity with which
absorption and elimination take place is often extremely remarkable; Prus-
siate of Potash having been detected  in the urine,  within two minutes after it
had been introduced into the stomach.  The variations  in this respect would
appear to  depend chiefly on the degree of concentration  of the  saline solution,
which will affect the rapidity of its absorption, according to the  laws of En-
dosmose ;—its reception  into the blood being more rapid, in proportion  as its
density is lower, in comparison with that of the circulating fluid.  Pure water,
or water containing but a small admixture of saline matter, is readily absorbed
into the blood-vessels  of the Intestinal villi; but it  is  as readily drawn off
through the Kidneys (by the agency, as  it  would seem, of  the Malpighian
bodies, § 840);  and consequently a large  amount  may  be ingested in a  short
time.   But if the water contain an amount  of saline matter equal to that of
the Serum, no absorption of it takes  place;  it remains in the intestinal  tube;
and it is voided by the rectum.   Further, if the quantity of  saline matter in
the solution be greater  than that of the  Serum, not only will no absorption
take place, but there will be an endosmose of the water  of the blood towards
the solution;  so that a large quantity of fluid is discharged by the  Intestinal
canal.  This simple  explanation, first  offered by Liebig,J accounts well for
the diuretic effect of most weak saline solutions, and  the purgative qualities of
stronger ones.—For the  transit of the peculiar principles of Vegetables, how-
ever, it appears that from one to two  hours are  usually required.  The  effect

   * For a scientific explanation of this fact, see Princ. of Gen. and Comp. Phys., § 539.
    See Miiller's Physiology, p. 589.
    Chemistry applied to Agriculture and Physiology, Part ii.
 
MAMMARY GLANDS--SECRETION OF MILK.
647
of Oil of Turpentine, and probably of other volatile agents, is produced much
more  rapidly;  the  characteristic odour  of violets being perceptible in  the
Urine passed but a few minutes after  the  vapour of the oil had  been received
into the lungs.
                 4.—Mammary Glands.—Secretion of Milk.

   853.  We now come  to  those Glands, whose  action is rather to elaborate
from the Blood certain  products,  which are destined for special uses  in the
economy, than  to eliminate matters, whose retention in the circulating current
would be injurious.   Pre-eminent  amongst these in  size and importance, at
least during  their period of  activity, are  the  Mammary Glands; which are
found only in the animals  of  the  Class  Mammalia, and which present  them-
selves in an almost rudimentary state in some of the non-placental subdivisions
ofthe class (§ 44).

  a. The structure of the Human Mammary Gland, which  has been  recently investigated
fully by Sir A. Cooper, is very  simple, and easily described.   It consists of a series of ducts
passing inwards from their termination in the nipple, and then ramifying like the roots of a
tree, their ultimate subdivisions terminating in minute follicles.  The  mamillary tubes are
usually about ten or twelve  in number;  they are straight  ducts, of somewhat variable size;
and their orifices,  which are situated in  the centre.of the nipple, and are usually concealed
by the overlapping of its  sides, are  narrower than the tubes themselves.  At the base of the
nipple, these tubes dilate into reservoirs, which extend beneath the areola and to some dis-
tance into the gland, when the breast is in a state of lactation. These are much larger in
many of the lower Mammalia  than they are in the Human female; their use is to supply
the immediate wants of the child  when it is first applied to the breast,  so that it shall not
be disappointed, but shall be induced to proceed with sucking until the draught be occasioned
(§ 626).  From each of  these reservoirs commence five or six main branches of the lacti-
ferous tubes, each  of which speedily subdivides into smaller ones; and  these again divari-
cate, until their size is very  much reduced, and their extent greatly increased.  The propor-
tional size of the trunk and of  its branches, appears to follow the same law which governs
that of the blood-vessels. The breast is not formed into  regular lobes by the ramifications
of the ducts; because they ramify between, and intermix with each other  so as to destroy
[Fig. 250.
[Fig. 251.
  The Mammary Gland after the removal of the
skin, as taken from the subject three days after
delivery; 1, the surface of the chest; 2, subcuta-
neous fat; 3, the skin covering the gland; 4, cir-
cumference ofthe gland; 5, its lobules separated
by fat; 6, the lactiferous ducts converging to unite
in the nipple; 7, the nipple slightly raised and
showing the openingsof the tubes atitsextremity.]
  A vertical section of the Mammary Gland,
showing its thickness and the origins ofthe lacti-
ferous ducts; 1,2,3 its pectoral surface; 4, section
ofthe skin on the surface ofthe gland; 5, the thin
skin covering the nipple; 6, the lobules and lobes
composing the gland ; 7, the lactiferous tubes com-
ing from the lobules; 8, the same tubes collected
in the nipple] 
648
OF  SECRETION.
Fig. 252.
Distribution of the milk-ducts in the Mamma of the Human female, during lactation; the ducts
                                  injected with wax.
the simplicity and uniformity of their divisions.   It is very rarely, however, that  they inos-
culate.  The mammary ducts are composed of a fibrous coat lined by a mucous membrane;
the latter is highly vascular, and forms a secretion of its own, which sometimes collects  in
considerable quantity when the milk ceaseSfto be produced.
   b. The gland itself is composed of the union of a number of glandules, which are con-
nected by means of the fibrous or fascial tissue  of the gland; it is between these, that the
mammary  tubes may be observed to ramify; and from them their branches spring.  When
the glandules are filled with injection, and for a  long  time macerated in water and un-
ravelled, they are found to be disposed in lobuli; and when a branch of mammary tube is
separated, with the glandules attached, the part appears like a bunch of fruit hanging by its
stalk.  When the lactiferous tube proceeding from a glandule is minutely injected, the latter
will be found to be composed of numerous  follicles, in which the ultimate  ramifications of
the  former terminate, or rather originate.  Their size, in full  lactation, is that  of a hole
Fig. 253.                                   Fig. 254.
  Termination of portion of milk-
duct in a cluster of follicles ; from                 Ultimate follicles of Mammary
a mercurial injection;  enlarged               gland, with their secreting cells,
four times.                                  o, a;—b, b, the nuclei. 
MAMMARY GLANDS---SECRETION  OF MILK.
649
pricked in paper by the point of a very fine pin;  so that the follicles  are, when distended
with quicksilver or milk, just visible to the naked eye.   At other times, however, the follicles
do not admit of being injected, though the  lactiferous tubes may have been completely filled.
They are lined  by a continuation of the same membrane, with that which lines the ducts;
and this possesses a high vascularity.  The arteries which supply the glandules with blood,
become very large during lactation; and their  divisions spread themselves minutely on the
follicles.  From the  blood which they convey,  the milk is  secreted and  poured into the
follicles, whence it flows into the ducts.  From the researches of Mr. Goodsir it appears,
that, in common with other  glandular structures, the inner surface of the  milk-follicles is
covered with a layer of epithelium-cells;  which, being seen  to contain milk-globules, may
be without doubt regarded as the real agents  in the secreting process.  Absorbent vessels
are seen to arise in large numbers in  the  neighbourhood of the follicles;  their function ap-
pears to be, to absorb the more watery part of the  milk contained in the follicles and tubes,
so as to render it more nutrient than it is as first secreted; and also to relieve the distention
which would occur, during the absence of the child, from the continuance  of the secreting
process.
  c.  The  Mammary gland may be  detected at  an early period  of fcetal existence;  being
easily distinguishable  from the surrounding parts,  by the redness of its colour and  its high
vascularity, especially when  the whole is injected.   At this period it presents no difference
in the  male and female; and it  is not .until near  the  period of puberty, that  any striking
change manifests  itself,—the gland continuing to grow, in each sex, in proportion to the
body  at large.  About the  age of thirteen, however,  the enlargement of the gland  com-
mences in the Female; and  by sixteen years, it is  greatly evolved, and some of the lactife-
rous tubes  can  be injected.   At about  the age of twenty, the  gland attains  its full size
previous to lactation;  but the milk  follicles cannot even  then  be injected  from the  tubes.
During pregnancy, the mammas receive a greatly-increased quantity of blood.  This  deter-
mination often commences very early, and produces a  feeling of  tenderness and distention,
which is a valuable sign (where it exists in connection with  others) of the commencement
of gestation.  The Areola at this time  becomes darker in its colour, and thicker in sub-
stance, and more extended;  its papilla? become more  developed, and the secretion from its
follicles increased.  The vascularity of the gland  continues to increase during pregnancy;
and at  the  time of parturition, its tabulated character  can be distinctly felt.  The  follicles
are not, however,  developed  sufficiently for injection, until lactation  has commenced.  After
the cessation of  the catamenia from age, so that pregnancy is no longer possible, the lactife-
rous ducts continue open, but the milk follicles  are incapable of receiving injection.   The
substance of the glandules gradually disappears, so that in old age only portions of the ducts
remain, which are usually loaded with mucus; but the place of the glandules is commonly
filled up by adipose  tissue,  so that the form  of the breast  is preserved.  Sir A. Cooper
notices a curious change, which  he states to be almost invariable with age,—namely, the
ossification of the arteries of the breast, the large  trunks  as well as the branches; so that
their calibre is greatly diminished, or even obliterated.
   d. The Mammary gland of the Male is a sort of miniature picture of that of the female.
It varies extremely in its magnitude,  being in some  persons of the size  of a large  pea;
whilst in  others it is an inch, or even two inches in diameter.   In  its structure it  corre-
sponds exactly with that of the female, but is altogether on a  smaller scale.  It  is composed
of lobules containing follicles, from which ducts arise;  and these follicles and ducts are not
too minute to be injected, although with difficulty.   The evolution of the gland  goes on pari
passu with that ofthe body, not undergoing an increase at any particular period; it is  some-
times of considerable size in old  age.  A fluid, which is probably mucus, may be  pressed
from the nipple in many persons; and this in the dead  body, with even more facility than in
the living.   That the essential character ofthe gland is the same in the male as in the female,
is shown by the instances, of which there  are now several on record, in which  infants have
been suckled by men.  The  following is given by Dr.  Dunglison.*  " Professor Hall, of the
University of Maryland, exhibited to his Obstetrical class, in the year 1837, a coloured man,
fifty-five years of  age, who had large, soft, well-formed mammas, rather more  conical than
those of the female, and projecting fully seven inches from the chest; with perfect and large
nipples.  The glandular structure seemed to the touch  to be exactly like that of the female.
This man had officiated as wet-nurse, for several  years, in the family of his mistress; and
he represented that the secretion of milk was induced  by applying the children entrusted to
his care to the breasts during the night.  When the milk was no longer required, great dif-
  *  Dunglisons Physiology, [sixth ed., vol. ii. p. 480.]   See also the case described by the
Bishop of Cork, in the Philosophical Transactions, vol. xli. p. 813: one mentioned by Cap-
tain  Franklin (Narrative of a Journey to the Polar Sea, p. 157); and one which fell under
the notice of the celebrated traveller Humboldt  (Personal Narrative, vol.  iii. p. 58).
      55 
650
OF SECRETION.
ficulty was experienced in arresting the secretion.   His genital organs were fully deve
loped.''—Corresponding facts are also recorded of the male of several of the lower animals

   854. The secretion  of  Milk  consists of Water holding in solution Sugar,
various  Saline ingredients, and  a  peculiar albuminous substance termed
Caseine; and  having Oleaginous particles suspended in it.   The constitution
of this fluid is made  evident by the  ordinary processes, to  which it is sub-
jected in domestic economy.  If it be  allowed to stand for some time, exposed
to the air, a large part of the oleaginous  globules come to the surface, being
of less specific gravity than the fluid through  which they are diffused.   At
the same time there is reason  to  believe that they undergo a change which
will be presently  described. The cream  thus formed does not, however, con-
sist  of oily particles alone; but includes a  considerable amount  of caseine,
with the  sugar and  salts  of the milk.   These  are further  separated by the
continued agitation of the cream;  which, by rupturing the  envelopes of the
oil-globules, separates  it into butter, formed by their aggregation,  and butter-
milk, containing the caseine, sugar, Sic  A considerable quantity of caseine,
however, is entangled  with the  oleaginous matter; and this has a tendency to
decompose, so as to render the butter rancid. It may be separated by melting
the butter at the temperature of 180°;  when the caseine will fall to the bot-
tom, leaving the butter pure, and much less liable to change.—The milk, after
the cream has  been removed, still contains the greatest part of its caseine and
sugar.  If it be kept long enough, spontaneous  change takes place in its com-
position; the sugar is converted into lactic acid, and this coagulates the caseine,
precipitating it in small flakes.  The same precipitation may be accomplished
at any time, by the addition of an acid; all tbe acids,  however, which  act
upon albumen, do not  precipitate caseine, as will presently be pointed out in
detail;  the most  effectual is that  contained in  the dried stomach of a calf,
known as rennet.   This  exerts so powerful an influence  over it, that, accord-
ing to the experiments of Berzelius, a piece of the membrane coagulated the
caseine of  1800 times  its weight of milk, with  the loss of only l"17th part of
its own weight; so that the active principle, dissolved from the rennet, must
have collected the  caseine  of about 30,000 times  its weight  of milk.   The
whey left after the curd has been separated, contains  a large proportion of the
saccharine  and saline  matter, entering into the original composition  of  the
milk.   This may be readily separated by evaporation.*

  a.  When Milk is  examined with the Microscope, it is seen  to contain a large number of
particles of irregular size and form, suspended in a somewhat turbid  fluid; these particles
(according to the measurement  of Donnef/) vary in size from about the  l-12,700tli to the
l-3040th of an inch; and they are termed milk-globules.  They are not affected by the mere
contact of ether  or alkalies; but if these reagents are shaken with them, an immediate solu-
tion  is the result.  The  same  effect happens,  if they are first treated with acetic acid.
Hence it is evident, that the globules consist of oily matter, inclosed in an envelope of some
kind; and an extremely delicate pellicle may, ir^ fact, be distinguished after the removal of
the oily matter by ether; or, after the globules have been ruptured, and their contents pressed
out, by rubbing a drop of  milk between two plates of glass.   No proof of the organization
of this pellicle has, however,  been detected; and it is probably to be regarded as the simple
result of the contact of oil with albuminous matter, which is known to give rise to  a mem-
branous film.—Besides these milk-globules, other globules of much  smaller size are  seen in
milk; and these present the peculiar movement, which is exhibited by molecules in gene-
ral.  Most of them seem  to consist of oily matter, not inclosed in an envelope, as they are
at once dissolved, when the fluid is treated with ether; but, according to the statements of
Donne, it would  seem that a portion of them  are composed of caseine, suspended,  not dis-
solved, in  the fluid.  It may be reasonably doubted, however, whether these were not in
* A considerable quantity is thus obtained for household purposes in Switzerland.
■j- Cours de Microscopie, Douzieme Legon. 
MAMMARY GLANDS---SECRETION OF MILK.
651
a state of change; whether from  their own decomposition, or from incipient coagulation;
either of which  might have taken place during the processes  of filtration, &c, that were
required  to determine their nature.  In addition to the foregoing particles, there are found in
the Colostrum, or milk first secreted after delivery, large yellow granulated corpuscles, which
are described by Donne as composed of a multitude of small grains aggregated together, and
frequently including a true globule of milk in their centre: these are for the most part solu-
ble in ether;  but traces of some adhesive matter, probably mucus, holding together the par-
ticles, are then seen.  They are considered by some as exudation-corpuscles; to which they
certainly bear a close  resemblance.   Lamellae  of epithelium  are also found in the milk.—
All the larger globules may be removed by repeated filtration; and the fluid is then  nearly
transparent.  This, in fact, is the simplest way of separating the oleaginous from the other
constituents of the  milk; as little caseine then adheres to the former.  That the transparent
fluid which has passed through the filter contains nearly the whole amount of the caseine
of the milk, appears a sufficient proof that this is, for the most part, truly dissolved  in  the
fluid.
   b. We shall now consider the chemical characters of each of  the foregoing ingredients.—
The Oleaginous matter of milk  principally consists, like fatty matter in general, of the two
substances, elaine and stearine; which are  converted in the  process of saponification into
the elaic, stearic, and margaric acids: but it also contains another substance peculiar to it,
which yields  in saponification  three volatile acids,  of strong animal odour, to which Chev-
reul has  given the  names of butyric, caproic, and capric  acids;  whilst the fatty substance
itself, to which the peculiar smell and taste of butter are due, is designated as butyruie. The
peculiar acids are not  only formed when the butyrine is treated with alkalies;  but are pro-
duced by the  ordinary decomposition of this principle, which is favoured by time and mode-
rate warmth.—The Caseine or  cheesy matter of  milk, which  is  obtained with  some slight
admixture of fatty matter in the production  of cheese from  skimmed milk, is chiefly distin-
guished from Albumen, by the peculiar readiness  with which  it is precipitated by feeble
organic acids, such as the lactic and acetic; and by its non-coagulability by heat alone.  The
Caseine of Human milk, however, is much less  precipitable by acids, than is that  of the
Cow;  very commonly resisting the action of the mineral acids, and even that of the acetic;
but being always coagulated by rennet, though the curd is long in collecting.  It  is remarked
by Dr. G. O. Rees,* that the caseine of  human milk thus bears somewhat the same relation
to that of the  cow, that the albumen of chyle bears to that of the  blood.—The Sugar of milk,
which may be obtained by evaporating  whey to the consistence of a syrup and then setting
it aside to crystallize, contains a large proportion  (12 per cent.) of water, so that it may be
considered  as really a  hydrate of sugar; it is nearly identical in  its composition  with starch,
and may, like it, be converted into true  sugar by the action of sulphuric acid; and  when in
contact with a. ferment, or decomposing  azotized compound, it is extremely prone to be con-
verted into lactic acid, by appropriating to itself the elements of water.  It is, in fact, through
this process, that the coagulation of the caseine is effected, by means of rennet;  for as soon
as a very minute quantity of lactic acid  is generated, it withdraws from the caseine the free
alkali which kept it in solution, and  the  caseine is consequently precipitated.   The  same
effect will be produced by incipient decomposition  of the caseine itself; which will soon
occasion  lactic acid to  be generated from the sugar,  in sufficient quantity to give to  the milk
a distinctly acid reaction.—The Saline matter contained in milk, appears to be nearly iden-
tical with that of the blood; with a larger proportion of the phosphates of lime and mag-
nesia, which amount to 2 or 2§ parts in  1000.  These phosphates are held in solution chiefly
by the Caseine;  which seems to have a power of combining with them, even greater than
that of Albumen:  the presence of a minute proportion of free alkali, also, assists their solu-
tion.  A  small portion of iron in the  state of phosphate,  together with the chlorides of
potassium and sodium, may also be detected in milk.-j-

   855.  The proportion of these different constituents  is liable to great varia-
tion, from several causes.   Thus, the whole amount of  the  solid constituents
may vary from 86  to 138*6 parts  in 1000;  the difference being partly due to
individual constitution, but in  great  part, also, to  the  amount and  character
of  the ingesta.   The average seems to be between  100  and 120 parts.   The
following are the results   of the  analyses of  Simon;  the first column being
the average of fourteen observations  upon the same woman;  the second giv-
ing the  maximum of each ingredient;  and the third the minimum:—
* Art. Milk, in the Cyclopaedia of Anatomy and Physiology.
| Haidlen, in Annalen der Chemie und Pharmacie, xlv. p. 263. 
OF SECRETION.
	i.	n.	in.
Water ......	883-6	914-0	801-4
Butter......	25-3	54-0	8-0
Caseine ......	34-3	452	19-6
Sugar of Milk and Extractive Matters	48-2	62-4	39-2
Fixed salts .....	2-3	2-7	1-6
It also appears from the analyses of Simon, that the proportion of the differ-
ent ingredients is liable to variation, according to the time which has elapsed
since parturition.  The quantity of Caseine is at  its minimum at the com-
mencement of lactation, and then gradually rises until it attains a nearly fixed
proportion.  The quantity of Sugar, on  the  contrary, is at its maximum  at
first, and gradually diminishes.  The amount of Butter (as appears  from the
wide extremes  shown in the above tables) is more  variable than  that of any
other constituent—.That  some  of the  variations are due, moreover, to the
character of the ingesta, and others to the external temperature, amount  of
exercise, and other circumstances affecting the individual, is  proved  by the
recent inquiries of Dr. Playfair upon the Milk of  the Cow.   He has shown
that the amount of butter depends in part upon the quantity of oily matter  in
the food;  and in part upon  the  amount  of exercise which  the animal takes,
and the warmth of the atmosphere in which  it is kept.  Exercise  and cold,
by  increasing the respiration, eliminate part of the oily matter in the  form  of
carbonic acid and water;  whilst rest and warmth, by diminishing this drain,
favour its passage into the milk.—The  proportion of  Caseine, on the other
hand, is increased by exercise; which would seem  to  show that this ingre-
dient is derived from the disintegration of Muscular tissue,—and thus adds
strength to the  Author's view  (§ 681)  that of the matter thus  set free, a part
only  is destined  to immediate excretion,  and that a  part  may again be
subservient to the operations of Nutrition.  Dr. Playfair's experience on this
head seems to  correspond with  the results of common observation in Swit-
zerland, where they pasture cattle in very exposed situations, and are obliged
to use a great deal of muscular exertion.   The quantity of  Butter yielded by
them is very small; whilst the Cheese is in unusually large proportion.  But
these very cattle, when stall-fed, give a large  quantity of Butter and very little
Cheese.
  856.  The  change which naturally takes place, from  the condition of Co-
lostrum to that  of true Milk, during the first  week of lactation, is a very im-
portant one.   The Colostrum has a purgative effect upon the child,  which is
very useful in clearing its bowels of the meconium that loads them at birth;
and thus the necessity of any other purgative is generally superseded.  Oc-
casionally, however, the colostric  character  is retained by the  milk, during
an  abnormally long period; and the health of the  infant is  then  severely af-
fected.   It is  important to know that this  may occur, even though  the  milk
may present all the  usual appearances  of the healthy secretion ;  but the mi-
croscope at once detects the difference.*   The return to the character of the
early milk, which has been stated to take  place after the expiration of about
twelve months, seems to indicate that Nature designs the secretion no longer
to be encouraged.  The mother's milk  cannot then be so  nutritious to the
child as other food ;t  and every medical man is  familiar with  the  injurious
consequences, to which she renders  herself liable by unduly prolonging lac-
tation.:]:

  *  See Donne, "Du Lait, et en particulier celui des Nourrices;" and Brit, and For. Med.
Review, vol. vi. p. 181.
  t On the  whole subject of Infant Nutrition, the Author would strongly recommend the
excellent little work of Dr. A. Combe, formerly referred to.
  X One of these, which has particularly fallen under the Author's notice, is debility of the 
MAMMARY GLANDS--SECRETION OF MILK.
653
  857.  It is very interesting to observe that Milk contains the three classes
of principles which are required for human food,—the Albuminous, Oleagi-
nous, and Saccharine ;  and it is the only secreted fluid, in which  these all
exist in any considerable amount.   It is, therefore, the food  most perfectly
adapted for the young animal; and is the only single article supplied by na-
ture, in which such a combination exists.   Our artificial combinations will be
suitable to replace it, just in proportion  as they imitate its  character; but in
none  of them can we advantageously dispense with milk, under some form
or other.  It should be remembered that the saline ingredients of Milk, espe-
cially the phosphates of lime, magnesia,  and iron, have a  very important
function in the nutrition of the infant,—affording the material for the consoli-
dation of its bones, and  for the  production of its red blood-corpuscles;  and
any fluid substituted for milk, which  does not contain these, is deficient in
essential constituents.   It  is very justly remarked by Dr. Rees, that of all
the secreted fluids, Milk is most nearly allied in its composition to blood.
  858.  The proportion of the different  ingredients in the Milk of different
animals, is subject to considerable variation:  and this fact is of much practi-
cal importance in guiding our selection, when good Human milk cannot be
conveniently obtained for the nourishment of an infant.   The first point to
be inquired into, is the quantity of  solid matter contained  in  each kind; this
may be determined either  by evaporation, or by the specific  gravity of  the
fluid.  The Specific  Gravity of  Human  milk is stated  by Dr. Rees to vary
between 1030  and 1035;  others, however, have  estimated  it much lower.
That of the Cow appears to be  usually about the same ;  that of the cream,
however, being 1024,  and that of the skimmed milk about 1035.  The varia-
tion will in part depend (as in the case of the urine) upon the quantity of fluid
ingested, and in part, it is probable, upon the manner in  which  the  milk is
drawn ; for it is well known to milkers, that the last milk they obtain is much
richer than that with  which  the  udder  is distended at the  commencement.
The quantity of solid matter, obtainable from Human  and from Cow's Milk
by evaporation, seems, like the specific gravities of the fluids, to be nearly the
same.   In the relative proportion of the  ingredients, however, there is a con-
siderable difference ; there being much more sugar, and less caseine in Human
Milk  than in that of the Cow.   The following table exhibits the relative pro-
portion  of the different ingredients, in the Milk of various animals, from which
it is commonly obtained:—
                                   Cow.    Goat.    Sheep.    Ass.     Mare.
Water ....	. 861-0	868-0	856-2	907-0	896-3
Butter ....	. 380	33-2	42-0	12-10	traces
Caseine ....	. 68-0	402	45-0	16-74	162
Sugar of Milk and Extractive Matters Fixed Salts	. 29-0 6-1	52-8 5-8	50-0 ) 6-8 S	62-31	87-5
It appears from this, that, whilst  the  milk of the Cow, Goat, and Sheep  do
not differ from each other in any very prominent degree, that of the Ass and
Mare is a fluid of very dissimilar character, containing  a comparatively small
proportion of caseine and butter, and  abounding in  sugar.   Hence it  is, that
it is much more disposed to ferment than other milk ; indeed  the sugar of
Mare's milk is so  abundant, that the  Tartars  prepare  from it  a spirituous
liquor, to which they give the name of koumiss.   It appears from these de-
tails that no milk  more nearly approaches that of the Human  female, than
that of the Sheep and Goat; these both possess, however, a larger proportion
of caseine, which forms a peculiarly dense curd;  and the milk of the  Goat

retina, sometimes proceeding to complete amaurosis; this, if treated in time, is most commonly
relieved by discontinuance of lactation, generous diet, and quinine.
                                   55* 
654
OF SECRETION.
 is tainted with the peculiar odour of the animal, which is more intense if the
 individual be dark-coloured.   The milk ofthe Cow will usually answer very
 well for the food of the infant;  care being taken to dilute it properly, accord-
 ing to the age of the child, and to add a little sugar.  It is an interesting cir-
 cumstance, lately ascertained, that the milk of Carnivorous Mammals, fed ex-
 clusively on animal diet, contains scarcely a trace  of sugar, whilst the caseine
 and butter are abundant.
   859.  From what has been stated of the close correspondence between the
 elements ofthe Blood and those of the Milk, it is evident that we can scarcely
 expect to  trace  the existence of the latter, as such, in the  circulating fluid.
 To what degree  the change, in which  their  elaboration consists, is accom-
 plished in the Mammary gland, or during the course of the  circulation, there
 is no certain means of ascertaining.   The recent discovery of the usual pre-
 sence of the organic compound named kiesteine (which  is  nearly related to
 caseine), in the urine of pregnant women, seems to indicate that the conversion
 of albumen into caseine takes place in the blood,—this curious excretion being
 the means  of preventing its accumulation in the  circulating fluid, previously
 to the time when it is  secreted by the mamma?.*   It is evident that this secre-
 tion cannot serve as the channel for the deportation of any element, the accu-
 mulation of which  would be injurious to the system;  since it does not occur
 in the male at all; and is present in the female at particular times only.  Yet
 there is  reason to believe that if, whilst the process is going on, it be suddenly
 checked, the retention of  the material in the blood, or the reabsorption of the
 secreted  fluid, is attended  with  injurious  consequences.   Thus if,  when the
 milk is first secreted, the child be  not put to the breast,  an accumulation takes
 place, which, if not relieved, occasions great general disturbance of the system.
 The narrowness of the orifice of the milk-tubes obstructs the spontaneous exit
 ofthe fluid, especially in primiparae; the reservoirs and ducts become loaded;
 further secretion is  prevented ;  and a state of congestion of the vessels of the
 gland, tending  to inflammation, is induced.  The accompanying fever is partly
 due, no doubt, to the  local disturbance;  but  in part also, there seems  reason
 to believe, to the reabsorption of the milk into the  blood;  this cannot  but  be
 injurious, since, although  but little  altered, the constitution of milk is  essen-
 tially different, especially  in  regard  to the  quantity of crystallizable  matter
 (sugar) which  it contains.  The instances of the vicarious  secretion of milk
 are not numerous ;  and in no instance is there any proof  that the elements of
 the fluid were  pre-existent in the blood.  Some ofthe most curious are those
 in which it has been poured  out from a gland in the groin; but  it is probable
 that this was  in consequence of the  existence  of a real repetition, in that
 place, of the true mammary structure,—this being the situation  ofthe mammae
 of many of the inferior animals, of which the analogues in Man are usually
 undeveloped.

  a. The  following is a more  unequivocal case of vicarious secretion; and it is peculiarly
 interesting as exhibiting the injurious effects of the  re-absorption of the secretion,  and  the
 relief which the system  experienced when it was  separated from  the blood by the new
 channel.  "A lady of delicate  constitution (with a predisposition to pneumonia) was pre-
vented from suckling her child, as she desired, by the following circumstance.   Soon after
 her delivery she had a severe fever, during which her breasts became very  large and hard;
the  nipples were swollen and firm; and  there was evidently  an abundant secretion of
 milk; but neither the sucking of  the infant, nor any artificial means, could draw  a single
drop of fluid from the swollen glands.  It was clear that the milk-tubes were closed; and as
the  breasts continued to grow larger  and more painful, purgatives and other means were
employed to check the secretion of milk.  After three days  the fever somewhat diminished,
and was replaced by a constant cough, which was at first dry, but soon after was followed
* See Dr. Golding Bird, in Guy's Hosp. Rep., vol. v. 
SALIVARY GLANDS AND PANCREAS.
655
by the expectoration of simple mucus.  After this, the cough diminished in severity, and the
expectoration became easy; but the sputa were no longer mucous, but were composed of a
liquid, which had all the physical characters of genuine milk.   This continued for fifteen
days; the quantity of milk expectorated amounting to three ounces or more in the twenty-
four hours.  The breasts gradually diminished in size: and by the time that the expectoration
ceased, they had regained their natural  dimensions.  The same complete obstacle to the
flow of milk from the nipples recurred after the births of four  children successively, with
the same  sequelae.  After the sixth, she had the same symptoms of  fever, but this time
they were not followed by bronchitis or  the expectoration of  milk;  she had in their  stead
copious sweatings, which, with other severe symptoms, reduced her to a cachectic state, and
terminated fatally in a fortnight.''*
  860.  Of the  quantity of Milk  ordinarily secreted  by, a good Nurse,  it is
impossible to gain  any definite idea; as the amount  which can be  artificially
drawn, affords no criterion of that which is secreted at the time of the draught
(§ 626).   The quantity which can be squeezed from either breast at any one
time, and which, therefore, must have  been contained in its tubes  and reser-
voirs, is  about two  ounces.   The amount secreted is greatly influenced by
the mental and physical condition  of the female, and also by the  quantity and
character of the ingesta.   In regard to the influence  of the mental  state  upon
this secretion,  ample  details have already been  given (Chap.  ix.).  With
respect to the physical state most favourable  to the production of an ample
supply of  this important fluid, it may be stated generally, that sound health,
a vigorous but  not plethoric constitution, regular habits, moderate but not
fatiguing exercise,  and an adequate  but  not excessive amount of nutritious
food, furnish the conditions most required.   It is  seldom  that stimulating
liquors, which are so commonly indulged in, are anything but prejudicial; but
the unmeasured condemnation of them in which some writers have indulged,
is certainly injudicious ; as experience amply demonstrates the improvement
in the condition both of mother and infant, which occasionally results from the
moderate employment of them.
  861.  The-influence of various  Medicines  upon  the Milk, is another im-
portant  question, which  has  not  yet been sufficiently  investigated.   As a
general rule, it appears that the most soluble saline  compounds pass into the
milk as into other secretions; but there are many exceptions.  Common salt,
the sesqui-carbonate of soda, sulphate of soda, iodide  of  potassium, oxide of
zinc, tris-nitrate  of  bismuth, and sesqui-oxide of iron, have  been readily de-
tected in the  milk,  when these substances were experimentally administered
to an ass;  and ordinary experience shows, that the  human  infant is affected
by many of these, when they are administered to the mother.  The influence
of mercurial medicines taken by the mother,  in removing from the infant a
syphilitic taint possessed by both, is  also well known.   The vegetable purga-
tives, especially  castor oil, senna, and  colocynth, have little  effect  upon the
milk ; hence they are to be preferred to the saline  aperients, when it is  not
desired to act upon the bowels of the child.

                    5.—Salivary  Glands and Pancreas.

  862.  The  structure of the Salivary Glands and  Pancreas in Man,  bears
considerable resemblance to  that of the  Mammary  glands.   In some of the
lower tribes,  however, they are much simpler.   Thus, in the Echinodermata
and  in Insects,  the Salivary glands have  the character of prolonged cceca,
more or  less convoluted; and the Pancreas of Fishes presents  itself in the
form of a cluster of short cceca  round the pyloric extremity of  the stomach,
and opening into it by distinct orifices.   The  accompanying figure will give

  *  Bullctino delle Scienze Mediche, Apr. 1839; and Brit,  and For. Med. Review, Jan.
1840. 
656
OF SECRETION.
Fig. 255.
Fig. 256.
 Lobule of Parotid gland of a new-born infant
injected with mercury. Magnified 50 diam.
  Distribution of Capillaries around the
follicles of Parotid Gland.
Fig. 257.
a sufficient idea of the structure of these glands in Man;  the follicles are
                              very minute, having a diameter  only about
                              three times greater than that of the capillary
                              blood-vessels. Their development  commences
                              from a simple canal, sending off bud-like pro-
                              cesses, which opens  from the mouth, and lies
                              amidst a cellular blastema.   As development
                              proceeds, the canal becomes  more and more
                              ramified, and communicates with.the enlarged
                              parent-cells of the blastema, which remain as
                              the  terminal  follicles of the branches  of the
                              gland-duct (§ 823).
                                863.  The Salivary secretion is by no  means
                              necessarily constant;  being almost or com-
                              pletely suspended by cessation  of the  move-
                              ment of the masticator  muscles  and tongue, if
                              unexcited by any nervous stimulus.    Hence
                              it is, that the secretion is checked during sleep;
                              so that, if the mouth be kept open, its surface
                              is almost  dried up by the  atmosphere.  The
                              mode in which the secretion is excited through
the influence of the nervous system has already been considered (§§ 625, 626).
The quantity of Saliva formed during the twenty-four hours has been estimated
at about 15 or 20 ounces ; but on this point it is evidently impossible to speak
with certainty.  The fluid obtained from the mouth  is of a more viscous cha-
racter than the true saliva secreted by the glands ; being mingled with mucus.
The salivary fluid varies as to its chemical reaction; being sometimes slightly
acid, and  sometimes slightly alkaline  ; but it  is seldom precisely neutral.
According to Huenefeld, it will  at the same time  strike a blue  colour with
reddened litmus-paper ; and turn blue  litmus-paper  red ;  but the saliva ex-
amined directly before, and during, the act of eating, is always alkaline.   It
seems  probable that the acid reaction  is due  to the  mucus  of the  mouth ;
which, at times when only a small  amount of saliva is excreted, is not neu-
tralized by  its alkali.  The specific gravity of Saliva varies from T006  to
1-009.  It contains a small  number of  corpuscles,' which  seem to be partly
epithelium-cells from the mucous surface of the mouth, and partly the  secret-
ing cells  of the salivary  vesicles.  The solid matter contained in  Saliva
amounts to  from  10 to 13 parts in 1000.   The animal principles of which
 Rudimentary Pancreas from Cod :—
o, pyloric extremity of stomach; 6, in-
testine. 
LACHRYMAL GLAND--THE TESTIS.
657
this is composed are Albumen, Mucus, and a peculiar substance termed Ptya-
lin, which is soluble in water, insoluble in  alcohol, and yet is different either
from albumen or  gelatin.   A considerable  proportion of  saline and earthy
matter exists in the solid residue of saliva;  this is nearly of the same  cha-
racter as that which the blood contains, being chiefly composed of the phos-
phate of lime and  soda, the chlorides of sodium and potassium, and the lac-
tates of soda and potash.   One remarkable property of the salivary secretion,
is its formation of a rust-red precipitate when  mixed with a solution of  per-
salt of iron.  This is supposed to be due to the  presence in it of  the prin-
ciple termed sulpho-cyanogen.  The tartar which collects on  the human teeth
consists principally of the earthy phosphates, the particles  of which are  held
together by  about 20 per cent, of animal matter;  and  nearly the  same  may
be said of the salivary concretions which occasionally obstruct the ducts.—It
appears from various  recent experiments, that  the  peculiar animal  matter of
the Saliva has a decided effect in metamorphosing certain alimentary  sub-
stances, and thus performs the first part of the digestive process.   Starcb  may
be converted into sugar, and sugar into lactic  acid, by its agency ; and if acidu-
lated, it has a solvent power for caseine, animal flesh, and other albuminous
substances (§ 669).
   864.  The Pancreatic  Secretion of Man cannot, of course, be  readily ob-
tained for analysis; that which is procured from the lower animals, however,
probably gives a sufficiently correct idea of its character.  It seems to be of
a nearly similar nature with saliva, but usually  contains a much larger propor-
tion of  solid matter;  in that of the Dog as much  as 87 parts in 1000  have
been found ; and in that of the Sheep, 40 parts.   The probable offices of this
secretion in the digestive process,  have been  already noticed  (§§ 669, 670).

                          6.—Lachrymal Gland.
   865.  The Lachrymal glands and their secretion  may be  next mentioned ;
but neither  require any lengthened description.  The gland in Man  is formed
very much  on the plan of the Parotid, being  composed of  branched canals
terminating in follicles, the ultimate ramifications of the several  branches
forming lobules or divisions of the glands.   The  lachrymal fluid has not re-
cently undergone  any accurate analysis; and all that can be  stated respecting
it is the general fact,  that the quantity of solid matter in it is  extremely small,
and that  this consists  chiefly of saline, and  either mucous or  albuminous
compounds.  It seems probable that the  secretion  of the  lachrymal  gland
itself is very little else than the serum of the blood, deprived of  a great part
of its albumen ; and that the mucus of  the tears is  secreted  from the surface
of the conjunctival membrane.  This  secretion has a slightly alkaline  reac-
tion.  It is being  constantly formed in moderate amount,  for the purpose of
cleansing the surface of  the eye from the  impurities which would otherwise
rest upon it; and  it is then absorbed by the open orifices of the nasal  duct,
and carried into the nose,  as fast as it is poured out.   The  cause of this  ab-
sorption does not seem very  clear.  Capillary attraction is  probably in part
concerned; and it has been thought that the momentary partial vacuum, oc-
casioned by the inspiratory effort in all the air-passages, will  cause the empty-
ing of the nasal duct below, and a consequent in-draught  above.   The influ-
ence of the nervous system upon this secretion has been already adverted to
(§§ 625, 626).

                    7.—The Testis.—Spermatic Fluid.
   866. In  the  Testes we return  to  the tubular form  of glandular  structure,
which' so remarkably distinguishes  the Kidney from all the  other glands 
658
OF SECRETION.
hitherto mentioned.  The external forms presented by these  glands through-
out the Animal kingdom, are extremely various;  but their composition is for
the most part very uniform.  The object is sometimes  attained by a simple
but  much  elongated canal;  sometimes  by shorter  branched tubes;  and  in
other instances, again, by numerous aggregated cceca, which are often rounded
into cells.  In regard to this, as to many other glands, it may be stated that,
whilst its general form  in Insects is that  of  prolonged tubes, the  required ex-
tension of surface is given  in the  Mollusca  by the multiplication of cells, so
that the structure has a compact spongy character.   It is  interesting to  remark
that, in some of  the lowest Fishes, this  organ consists of a mass of vesicles
which  have no  efferent duct;  and  that  the  secretion  formed  within  these
escapes by the rupture of the vesicles, allowing it to  escape into the abdomi-
nal cavity,  whence it  passes by openings that lead directly  to  the exterior.
In these Fishes, the ova are discharged from the ovarium in a very similar man-
ner ;  a modification of which plan is followed in all the higher Vertebrata,—
the ovum being in  them also discharged, by the rupture of its containing vesi-
cle or ovisac, into  the  abdominal cavity, but being immediately received and
conveyed away by the  funnel-shaped internal prolongation of the  external ori-
fice, which is known as the fimbriated extremity of the Fallopian tube.*
  a. The Testis in Man has in every respect, however, a distinctly glandular character.  It
consists of several lobules, which are separated from each other by processes of the tunica
albuginea that pass down between them, and also by an extremely delicate  membrane (de-
scribed by Sir A. Cooper under the name of tunica vasculosa) consisting of minute ramifica-
tions ofthe spermatic  vessels united by areolar tissue.  Each lobule is composed of a mass
of convoluted Tubuli  Seminiferi, throughout which blood-vessels are minutely distributed.

                [Fig. 258.                              [Fig. 259.
  The Testicle injected with mercuTy; 1, tunica
albuginea; 2, seminiferous tubes; 3, the rete vas-
culosum testis; 4, a globule of mercury which has
ruptured the tubes; 5, the vasa efTerentia which
form the coni vasculosi; 6, coni vasculosi forming
the head of the epididymis; 7, epididymis ; 8, glo-
bus minor of the epididymis; 9, vas deferens.]
 A view of the minute structure of the Testis ;
1,1, tunica albuginea; 2, 2, corpus highmorianum;
3, 3, tubuli seminiferi convoluted into lobules; 4,
vasa recta; 5, rete testis; 6, vasa efTerentia; 7,
coni vasculosi constituting the globus major of
the epididymis; 8, body of the epididymis; 9, its
globus minor; 10, vas deferens  11, vasculum
aberrans or blind duct.]
* See Principles of General and Comparative Physiology, § 641. 
THE TESTIS—SPERMATIC  FLUID.
659
The lobules differ greatly in size, some containing one, and  others many of the tubuli;  the
total number of the lobules is estimated at about 450 in each testis, and that of the tubuli at
840.  The convolutions of the tubuli are so arranged, that each lobule forms a sort of cone,
the apex of which is directed towards the Rete Testis.   It  is  difficult to trace the free ex-
tremities of the Seminiferous tubes, owing to the frequency of their anastomoses with each
other; in this respect, therefore, the structure of the testis accords closely with that of the

                                           Fig. 260.
  Human Testis, injected  with mercury as completely as possible; 1,1, lobules formed of the semini-
ferous tubes; 2, rete testis; 3, vasa efTerentia; 4, flexures of the efferent vessels passing into the hea(l,
5, 5, ofthe epididymis ; 6, body ofthe epididymis;  7, appendix ;  8, cauda; 9, vas deferens.

                                        Fig. 261.
Plan of the  structure of the Testis and Epididymis; a, a. seminiferous tubes; a*, a*,
l0aes; the other references as in the last figure. 
660
OF SECRETION.
Kidney.  The diameter ofthe Tubuli is for the most part very uniform; in the natural con-
dition they seem to vary from about the l-195th to the  l-10th of an inch; but when injected
with mercury they are distended to a size nearly double the smaller of these dimensions.
When they have  reached to within a line or two of the Rete Testis, they cease to be con-
voluted, several unite  together into tubes of larger diameter, and these enter the rete testis
under the name of tubuli  recti.   The rete testis consists of from seven to thirteen vessels,
which  run in a waving course,  anastomose with  each other, and  again divide, being  all
connected together.  The  vasa efferentia which pass to the head of the epididymis are at
first straight, but soon  become convoluted, each forming a sort of cone, of which the apex is
directed towards the rete testis, the base  to the head of the epididymis.   The number of
these  is stated to vary from nine to thirty;  and their length to be about eight inches.  The
epididymis itself consists of a very convoluted canal, the length of which is about twenty-one
feet.   Into its lower extremity, that is, the angle  which it makes where it terminates in the
vas deferens, is poured the secretion of the vasculum  aberrans or appendix;  which seems
like a testis in miniature, closely resembling a single lobule in its structure.  Its special func-
tion is unknown.
  b. The Testicles originate, in the Embryo, from the  lower part of the Corpora Wolffiana
(§ 839, c) ;  arising from their lower and inner sides,  whilst the Kidneys spring from their
upper and outer parts.  They make their first appearance in the Chick about the fourth day,
as delicate striae on the Wolffian bodies; and at this period no difference can be detected be-
tween the Testes and the  Ovaria, which originate in precisely the same  manner.   Like
the kidneys, the germ-preparing organs  increase in proportion  with the diminution in the
temporary structures,  at first their efferent ducts  open  into those  of the Wolffian bodies, but
they are subsequently separated  by the  formation  of a partition, like that which separates
the rectum from the cloaca.  In the Human embryo, the rudiments of the sexual organs,—
whether testes or ovaria,—first present themselves soon after the kidneys make their appear-
ance, that is, towards the end of the seventh week.  They are at first much prolonged, and
seem to consist of a kind of soft, homogeneous blastema, in which the tubular structure subse-
quently developes itself.  The Ovary at that period has the same aspect and texture; but its
subsequent course of development is different.  The Testis gradually assumes its permanent
form ; the epididymis appears in  the tenth week;  and the gubernaculum, (a membranous
process from the filamentous tissue of the scrotum, analogous to  the round ligament arising
from the labium, and  attached to the ovary, of the female,) which is originally attached to
the vas deferens, gradually fixes  itself to the lower  end of the testis or  epididymis.  The
Testes begin to descend at about the middle period of pregnancy; at the seventh month
they reach the inner ring ; in the eighth they enter the passage; and in the ninth they usually
descend into the scrotum.   The cause of this descent is not very clear.  It can scarcely be
due merely, as some have supposed, to the contraction ofthe gubernaculum; since that does
not contain any fibrous structure,  until after the lowering of the testes has commenced.  It
is well known that the testes  are not always found in the scrotum at the time of birth, even
at the full period.   Upon an examination of 97 new-born infants, Wrisberg found both testes
in the scrotum in 67,—one or both in the canal in 17,—in 8 one testis in the abdomen,—and
in 3 both testes within the cavity.  Sometimes one or both testes  remain in the abdomen
during the whole of life ; but this circumstance does not seem to impair their function.  This
condition is natural, indeed, in the Ram.

   867.  The fluid  secreted by the Testes  is thick, tenacious, and of  a greyish
or yellowish  colour.   It  is mingled, during  or before emission, with  fluid
secreted by the  Prostate, Cowper's  glands, Sic ;  and it cannot, therefore, be
obtained pure, but by  drawing it  from the testicle itself;  hence no  accurate
analysis can be made of it in the Human subject.   The so-called Spermatozoa
and  Seminal Granules, which form the most important  and characteristic parts
of the Semen, are so  intimately connected with  the Reproductive Function,
that they will be more  appropriately described under that head.  It maybe here
remarked,  however, that  they correspond most exactly  with other Secretions,
in their mode of  production ;  for, as will be shown hereafter, they are elaborated
by cells, which lie within the tubuli, and which rupture so as to set them free,
when they are mature  (§ 902).   The  peculiar odour which the  Semen pos-
sesses, does not  appear to belong to the proper spermatic fluid ; but is probably
derived from one  or other of the  secretions with which it is  mingled.   The
chemical analyses which have been  made of this  fluid are all defective,  inas-
much as they do not distinguish the real secretion of the testes from the mucus,
prostatic fluid, &c, with  which it is  mingled.   It may be stated, however, that 
CUTANEOUS AND MUCOUS FOLLICLES.
661
it has an alkaline reaction, and contains albumen, with a peculiar animal prin-
ciple termed Spermatine ; and also saline matter, consisting chiefly of muriates
and phosphates, especially the latter, which form crystals  when the fluid has
stood for some little time.
                   8.—Cutaneous and Mucous Follicles.

   868.  Having now described  the  structure             Fig. 262.
and  functions of the principal Glands, which
are composed of aggregated masses of secret-
ing cells or tubes, we may proceed to those in
which the glandulae are more  scattered, but
are still, in their aggregate amount, of sufficient
importance  to  claim particular notice.   This
is especially the case in the  Skin, and its in-
ternal prolongations, forming Mucous  Mem-
branes.   The Skin is the seat of various secre-
tions , for  each of which  it is  provided with
special organs.  Of these  the most important
is the Perspiration;  which is formed in small
glandular organs seated just beneath  the cutis,
and  diffused over the  whole surface of the
body.   The efferent ducts of these Glandubje
open by minute pores in the Epidermis, which
are seen in elevated lines  on the skin of the
palm of the hand and the sole of the foot; they
penetrate  the  epidermis rather  obliquely, so
that  a sort of little valve is formed by it, which
is lifted  up by the excreted  fluid as  it issues.
The ducts  pass through the Epidermis and
Cutis in a spiral direction;  and then enter the
glands,  which  consist of the convolutions of
the ducts, more or less  subdivided, on which
blood-vessels  are  distributed.    Where  the
Epidermis is thin, the canal is straighter.'—On
the palm of the  hand, the sole of the  foot, and
the extremities of the fingers, the apertures of
the perspiratory ducts are visible to the naked
eye ; being situated at regular distances along
the little ridges of sensory papillae, and giving
to the latter the appearance of being crossed
by transverse lines.  According  to Mr. Eras-
mus Wilson,*  as many  as 3528  of these
glandulae exist in  a square inch of surface on   Sudoriferous Gland from the palm of
the palm of the hand ; and as every tube, when the hand) magnjfied 40 diameters; 1,1,
straightened out, is about a quarter of an inch contorted tubes, composing the gland,
in length, it follows  that, in  a Square inch of and uniting into two excretory ducts, 2,
skin from the palm of the hand,  there exists a *>which™"^w«JJ«
             r    i. ooo -i       nni c „*  perforates the epidermis at 3, anaopen.-
lengthof tube equal to 883 inches, or  73^ feet. onitssurface at4; the gland is imbedded
The number of glandulae in other parts of the m fat-vesicles, which are seen at 5,5.
skin, is  sometimes greater, but generally less
than this;  and  according  to  Mr. Wilson, about 2800  may be taken  as the
average  number of pores in each  square inch throughout the body.   Now the
Practical Treatise on Healthy Skin, p. 42.
56 
662                              OF SECRETION.
[Fig. 263.
[Fig. 265.
  Vertical section of the skin
and sweat-glands of the axilla;
—a. Layer of glands with their
ducts traversing 6, the cutis and
cuticle, c.  Small hair,  d, d.
Portions of  larger  hairs.—
Magn. one and a half diam.]
[Fig. 264.
  Sweat-gland  and the commencement of its
duct :—a. Venous radicles  on the wall of the
cell in which the gland rests.  This vein anas-
tomoses with others in the vicinity. 6. Capilla-
ries of the gland separately represented, arising
from  their  arteries, which  also anastomose.
The blood-vessels are all situated on the outside
or deep surface of the tube, in contact with the
basement-membrane.—Magn. 35 diam.]
  a. Vertical section of the cuticle from the heel,
detached by maceration.  The epithelium of the
sweat-duct, continuous with the cuticle, has been
drawn out of the tube of basement-membrane, as
far as the gland, where it begins to be contorted.
The cavity of the duct is seen dilating as it enters
the cuticle, and then stretching up to the surface
through the epidermic laminae. The deep surface
of the duct is continuous with the surface of the
cavities in which the papillae are lodged.—Magn.
35 diameters.
  b. Duct at its entrance into the cuticle.—More
highly magnified.]
number of square inches of surface, in  a man of  ordinary stature, is  about
2500;  the total  number of pores, therefore, may be  about seven millions;
and the length of the perspiratory tubing would  thus be  1,750,000 inches, or
145,833 feet, or 48,611 yards ; or nearly 28 miles.
   869. The Secretion of fluid by these  Glands is continually taking place;
but this fluid, being  usually carried off in the form of vapour as  fast as it is
separated, does  not  accumulate and become sensible.   If", however, from the
increased amount of the secretion, or  from the  condition  of the surrounding
air  the whole  fluid  thus poured out  should not evaporate, it accumulates in 
CUTANEOUS AND MUCOUS FOLLICLES.
663
minute drops upon the surface of the skin.  Thus the Sudoriferous excretion
may take the form  either of sensible or insensible transpiration; the latter
being constant, the former occasional.  It is difficult to  obtain enough of this
secretion for analysis, free from the  sebaceous and other matters which accu-
mulate on the surface of the skin; and its character can only, therefore, be
stated approximately.  It has  usually an  acid reaction, which seems due to
the presence of acetic acid;  and to this,  or to lactic acid, we are probably to
attribute  the sour smell which it has, especially in some disordered states of
the system.  The proportion of solid matter, according to Anselmino, varies
between  5 and 12*5  parts in  1000.   The greatest part of it consists of animal
matter, which is apparently a  proteine-compound in a state of incipient decom-
position.  The remainder consists of saline compounds ;  of which the chlorides
of potassium and sodium appear to be pretty constantly present; whilst the
muriate of ammonia, free acetic acid, and acetate of soda, have also been said
to occur  in it.—The proportion of these  ingredients would probably be found
larger in the fluid of the Sudoriferous glands, if we had the means of collecting
it separately; for of the whole fluid which passes off from the surface of the
skin, only a small proportion can be properly said to be secreted by the Sudo-
riferous glands; the greater part,  under ordinary circumstances, being the
product of simple Evaporation, by which, of course, nothing but pure watery
vapour is dissipated.
   870. The entire amount of fluid which is insensibly lost from the Cutaneous
and Pulmonary surfaces, is estimated by Seguin at 18 grains per minute ;  of
which 11 grains pass off by the skin, and 7 by the  lungs.  The  maximum
loss by Exhalation,  cutaneous and pulmonary, during twenty-four hours, (ex-
cept under very peculiar circumstances,) is 5 lbs.;  the minimum  1§ lb.   It
varies  greatly, according to the condition of the atmosphere, and that of the
body itself. 'The manner and degree in which it is influenced by atmospheric
conditions,  will be better discussed  under the head of Animal Heat (§ 897);
since this influence has a most important effect  in the regulation of the tem-
perature of the body.   As  already pointed out, the  Urinary excretion is  in
great degree vicarious with it, in regard to the  amount  of fluid discharged,—
the  urine  being more watery in proportion as the Cutaneous Exhalation is
diminished in  amount,—and vice versa  (§ 840).  But we are  also to look at
these two excretions  as vicarious, in regard to the deportation (or getting rid)
of  the products of the waste of the system.   The share which the Skin has
in  this  office  has  probably been generally under-rated.  There  is reason to
believe that at least  100  grains  of azotized matter are excreted from it daily;
and any cause which checks this excretion, must throw additional labour on
the kidneys, and will be likely  to produce disorders of their function.
   871. The Exhalant action  of the Skin  is influenced by general conditions of
the vascular and nervous systems; which are as yet ill understood.  It is quite
certain, however, that through  the  influence of  the latter the  secretion may
be excited or suspended ; this is seen on  the one hand in the  state of syncope,
and the effects of depressing emotions, especially fear, and its more aggravated
condition, terror;  and on the  other in  the dry condition of the skin during
states of high nervous excitement.  It is  very probable that, in  many forms of
fever, the suppression of the perspiration is a cause,  rather than an effect, of
disordered vascular action; for there are several morbid conditions of large
parts of  the surface, in which the suppression of the transpiration  appears to
be one of the chief sources of danger, having a tendency to produce congestion
and inflammation of internal organs.  From the recent  experiments  of Dr.
Fourcault,* it appears that complete suppression of the Perspiration in animals,

       *  Comptes Rendus  de l'Academie, May, 1844;  and Lancet, June 8, 1844. 
664
OF SECRETION.
by means of a varnish applied over the skin, gives rise to  a state termed by
him Cutaneous Asphyxia ; which is marked by imperfect arterialization ofthe
blood, and  considerable fall of temperature (§§ 768, 891); and which, as it
produces  death in  the  lower animals, would probably do  the same in Man.
A partial suppression by the same means gives rise to Febrile symptoms, and
to Albuminuria.
  872.  The Skin is likewise furnished with numerous  Sebaceous glands, also
distributed more or less closely throughout the whole surface of the body.   By
these  an Adipose secretion is  poured forth,  which  keeps the skin from being
dried  and cracked by the action of the sun and air.  It is especially abundant
in the races  which are formed to inhabit warm climates.  Some of these glan-

                                 [Fig. 266.
 Sebaceous glands, showing their size and relation to the hair-follicles:—a and b from the nose ; cfrom
the beard.  In the latter the cutis sends down an investment of the hair-follicle.—Magn. 18 diam.]

dulas  are simple follicles lined with secreting cells, and contained in the sub-
stance of the Skin itself; whilst others are formed out of similar follicles, more
or less branched, elongated, and convoluted; and others, again, seem to con-
sist of little else than clusters of Fat cells, from one part of which an excretory
duct arises: these last commonly  open into  the passage,  by which the Hair
makes its way outwards.  Besides  these  there are  other glands situated in
particular parts of the body, and having special functions.  Such are the Ceru-
minous glands situated beneath the  skin  of the auditory meatus;  these are
closely analogous in  form to  the sudoriferous  glands, as the accompanying
figure shows; but  their  secretion is very different, being nearly solid, and
having somewhat of a resinous  character.—A peculiar  series  of glandulae,
bearing a general resemblance  to the sudoriferous glands, but of larger size,
have  lately been discovered by Prof. Horner*  and M. Robin  to exist in the
human  axillae;  where  they probably serve  to  secrete  the peculiar odorous
matter, characteristic of that part.  In many of the lower animals, such  glands
may be detected, having a structure of considerable complexity.   The odorous
secretion would appear to be elaborated from the blood by a simple chemical
change;  for it may be made evident even in  blood that has been dried  up, by
* [Am. Journ. Med. Science, Jan. 1846, p. 13.] 
CUTANEOUS AND MUCOUS FOLLICLES.
665
Fig. 267.
  Cutaneous glands of external meatus auditorius.—1. Section of the skin, magnified three diameters ;
2, 2, hairs ; 3, 3, superficial sebaceous glands ; 1,1, larger and deeper-seated glands, by which the ceru-
men is secreted.—2.  A hair, perforating the epidermis at 3;  1,1, sebaceous glands, with their excretory
ducts 2,2; 4, base of the hair, in its double follicle 5,5.-3.  Cerumen-gland, formed by the  contorted
tube, 1,1, of the excretory duct, 2; 3, vascular trunk  and  ramifications.—The last two figures highly
magnified.

                                     [Fig. 268.
Cutaneous Follicles or Glands of the Axilla, magnified one-third.—(Horner.)]
treating it with sulphuric acid.   This aromatic principle  differs sufficiently in
the  blood  of  different animals, to enable a  person with a  delicate sense of
smell to  determine from what animal any specimen has been  procured ;  and
this fact  has been applied with success to juridical investigations.  It has even
                                         56* 
666
OF SECRETION.
been stated that the blood of the human Male may be distinguished from that
of the Female, by its more powerful odour; but this does not appear to be
the case,—at least with sufficient certainty for medico-legal inquiries.*
  873. Besides the crypts or  follicles, which have been spoken of as gene-
rally existing in Mucous Membranes (§ 178), there exist, in that of the Intes-
tinal Canal, numerous glandulae in various parts, for the elaboration of par-
ticular  secretions.  In the Stomach,  for example, a large  number  of these
secreting  organs,  some  of them  possessing rather a  complex structure, are
included in the thickness of its walls, composing, indeed, the greater part of
the mucous membrane.   If this be divided by a  section  perpendicular to its
surface, it is seen to be made up of a number of tubuli closely applied to each
other, their blind  extremities being in  contact with the submucous tissue, and
their open ends being directed towards the cavity of the stomach.  In some
situations, these tubuli  are short and straight;  in other parts they are longer,
and  present an appearance of irregular dilatation or partial convolution.  This,
indeed, is their usual character, especially towards the cardiac orifice of the
Fig. 269.            •                   [Fig. 270.
tubes proceeding from a single cell.  The
letters refer to corresponding- parts.   The
epithelium is glandular; the nuclei very
delicate ; the cavity of the tubes very small,
and in some cases not visible.
                                   From the dog, after twelve hours' fasting.
                                  Magnified 200 diameters.]

* See Annales d'Hygiene, vol. i. pp. 267 and 548; vol. ii. p. 217; vol. x. p. 160, &c. 
CUTANEOUS AND MUCOUS FOLLICLES.
667
stomach.  On  the other  hand, towards the  pyloric extremity, they have  a
much more complex structure.   Betweeen  the tubuli, blood-vessels  pass up
from the sub-mucous  tissue, and  form  a vascular  net-work  on its  surface.
From the examination of these horizontal sections of the mucous membrane
at various depths, Dr. Todd*  has ascertained that the tubuli are arranged in
bundles  or groups,  surrounded  and bound  together by a fine areolar mem-
brane ;  the size of the  bundles, and the number of tubules contained  in them,
vary considerably.   The tubes  do not, in general,  open  directly upon  the
surface,  but  into the bottom of small depressions or pits, which may be  seen
to cover the membrane.   These pits are more or  less  circular in form, and
are separated from one  another by partition-like elevations of the membrane,
which vary  in  depth ; and  sometimes  even  by pointed  processes, that  have
been mistaken  by some  anatomists  for  villi.   The diameter of these pits
varies from about l-100th to l-250th of an  inch;  it is always greatest near
[Fig. 271.
Fig. 272.
[Fig. 273.
  Portion of the mucous
membrane ofthe stomach,
showing entrances to the
secreting tubes, in pits
upon its surface.
oi^bp-
oo1
nQ-

  Vertical section of a stomach cell, with its
tubes : a in the middle region, b in the pyloric
region, a a. Orifices of the cells on the inner
surface ofthe stomach. 6 6. Different depths at
which the columnar epithelium is exchanged
for glandular,  c. Pyloric tube, or prolonged
stomach cell.  d. Pyloric  tubes, terminating
variously, and  lined to their extremities with
sub-columnar epithelium.
  From the  dog, after twelve hours'  fasting.
Magnified 200 diameters.]
  a. Inner surface of the stomach, showing
the cells after the mucus has been washed
out. Magnified 25 diameters.
  b. Columnar epithelium of the inner sur-
face and cells of the stomach:—a. Free
ends of the epithelial  particles, seen on
looking down upon the membrane.  6. Nu-
clei visible at a deeper level, c. The free
ends seen obliquely, d. Deep or attached
ends ofthe same. The oval nuclei are seen
near the deeper ends.
  From the dog.  Magnified 300 diameters.]
  * Gul^tonian  Lectures on the Physiology of the  Stomach, in Medical Gazette, 1839.
See also Dr. Sprott Boyd's Inaugural Dissertation on the Mucous Membrane of the Stomach,
in Edinb. Med. and Surg. Journal, vol. xlvi. 
668
OF SECRETION.
[Fig. 274.
the pylorus.  When the surface of the membrane, cleansed  from mucus and
epithelium-scales, is examined with a  sufficient magnifying power, it is seen
that from three to five perforations exist in the bottom of each pit; and these
are the openings ofthe secreting tubes.   The Gastric fluid, elaborated by this
apparatus, having been already made a subject of special consideration (§ 664)
need not be here described.
                                               874. The  whole  Mucous sur-
                                            face of the Intestinal canal is fur-
                                            nished  with glandular  follicles of
                                            a very similar character; of which
                                            some approach those  of  the sto-
                                            mach in complexity of structure;
                                            whilst  others  evidently corre-
                                            spond with the crypts of ordinary
                                            Mucous Membrane.  An innu-
                                            merable multitude  of pores  are
                                            easily seen, by the aid of a sim-
                                            ple lens, to  cover the whole in-
                                            ternal surface of  the large Intes-
                                            tine; and these are the entrances
                                            to tubular follicles, closely resem-
                                            bling those  of the  stomach,  but
                                            more simple in structure.   Their
                                            ccecal extremities abut against the
                                            sub-mucous tissue:  towards  the
                                            end  of the  Rectum,  however,
                                            they are  much  prolonged, and
                                             constitute  a  peculiar layer  be-
                                             tween the mucous  and muscular
                                             coats;  the tubes which are there
                                             visible  to  the naked  eye, being
                                             erect, parallel, and densely crowd-
                                            ed.   These glands probably form
                                            the peculiarly thick and tenacious
                                            mucus  of the large intestine.   In
                                            the small  intestine,  on the other
                                            hand, the cceca are less deep and
                                            their apertures are smaller. These
                                            apertures are, for the most part,
                                            situated around  the  bases of the
villi: in the fcetus and newly-born child, they are so abundant as to be almost
  A section of the Ileum, inverted so as to show the ap-
pearance and arrangement of the villi on an extended
surface, as well as the follicles of Lieberkiihn ; the whole
seen under the microscope.  A close examination of this
cut will show a great number  of black points in the
spaces between the projections of villi: these are the
follicles of Lieberkiihn.]
Fig. 275.
Fig. 276.
  One of the glandular majores sim-
plices, viewed from above at a, and
seen in section at b ; from the large
intestine.
  Mucous coat of small intestines as
altered in fever; the follicles of Lie-
berkiihn filled with tenacious white
secretion. 
CUTANEOUS AND MUCOUS FOLLICLES.
669
[Fig. 277.
in contact; but in the adult, the intervals  increase, so as to  occupy more
space than the apertures.   The glandulae of  the  small intestines  have long
been known under the name of the follicles of  Lieberkiihn ;  they become
particularly evident (Fig. 275) when the mucous membrane is inflamed, being
then filled with an opaque whitish secre-
tion, which is absent in the healthy state.
—Besides the  foregoing descriptions of
solitary glandulae, the Coecum  and the
lower part of the Rectum contain a num-
ber of simple and large follicles, which
produce slight rounded  elevations on the
surface of the  mucous  membrane; the
centre of each of these elevations is per-
forated by an aperture of the follicle; and
around this are  seen  the  orifices of the
tubular coeca,  which closely  envelope
the globular  follicle (Fig. 270).   These
seem most abundant where the largest
quantity of mucus is required.   They
have been confounded with the glands of
Brunner ; but are rather analogous to the
solitary Peyerian glands, presently to be
noticed.
   875. The  true glands of Brunner are   A section of the small Intestine containing
chiefly situated in the Duodenum ; and sorae of the slands of Peyer> as shown under
„i_   v    .  •   .r           ,   .  •  ,i   the  microscope.  These glands appear to be
they lie not  in the mucous but  in the     „ .  ..  f       ,.  „    '.„:„;„„ „„
   '         .              ip      small lenticular excavations, containing, ac-
sub-mucous  tissue, where they  form a cording t0 Boehrrl) a white, milky and rather
Continuous layer  Of  white  bodies SUr- thick fluid, with numerous round corpuscles of
rounding the whole intestine.   Their various sizes, but mostly smaller than blood-
size, Unless diseased, is Scarcely that of g'°bules- The meshes seen in Ihe cut are the
a hemp-seed; each  consists of nume- °'dinary jripe-iike  folds °f *• "~ c°at'
       f      1,1    r  i • i  i   i     and not the venous texture spoken of under the
rous minute  lobules, of which the ducts f0niCies.i
open  into a common  excretory tube ;
and in the lobules may be  distinguished the  minute ramifications  of these
ducts, with clusters of follicles  forming acini, of which about  six  hundred
are computed to exist in each.   Hence these glands
are of complex structure, much resembling that of the
Salivary  glands and Pancreas,  and entirely differing
from all the other glandulae of  the walls of the ali-
mentary canal.   Of the peculiar nature of their secre-
tion nothing is known.
   876. The so  called Peyerian glands constitute,
when aggregated together, large patches on the mucous
membrane of  the small intestine,  where  they are
known as the  glandulae ctgminatae;  and it is  to
these  alone  that  Peyer's name is usually applied.
Similar  bodies,  however,  known as  the  glandulae
solitariae, exist separately in  the lower part of the
small  intestines ;  where they have been confounded with the glands of Brun-
ner, which do not extend beyond the  commencement of the Jejunum.   The
glands of Peyer, when examined in  a healthy mucous membrane, present the
appearance  of circular white slightly-raised spots,  about a line in diameter,
over which the membrane is usually less set with villi, and very often entirely
free from them.   Each of these white spots, of which a large number are
contained in the agminated glands, is  surrounded  by a zone of openings like
Fig. 278.
 Conglomerate gland  of
Brunner, from commence-
ment of duodenum; mag-
nified a hundred  times. 
670
OF SECRETION.
 Portion of one of the patches of Peyer's glands,
from the end of the Ileum, highly magnified ; the villi
are also displayed.
those of the follicles of Lieberkiihn,  which  lead (as do  those) into tubular
cceca.   On rupturing the surface of one of  the white bodies, there is found a
                                        cavity, corresponding in extent with
              Fig. 279.                   the  spot, and of considerable extent;
                                        but  this cavity has  usually no  ex-
                                        cretory opening, and the tubular fol-
                                        licles  by  which  it  is  surrounded,
                                        have no connection  with it.  In its
                                        interior is found  a  grayish-white
                                        mucous matter, interspersed with
                                        cells in various  stages  of  develop-
                                        ment.  There is reason to believe
                                        that, at a certain period of the  ex-
                                        istence of  each of these  glandulae,
                                        an excretory orifice is formed, by a
                                        sort of dehiscence in the wall of the
                                        cavity; and that,  through this,  the
                                        product secreted by  the  contained
                                        cells may be  poured forth.  Each
                                        of them may be compared, on this
                                        view, to  one of the  ultimate folli-
                                        cles, which constitutes the secreting
                                        portion of any one  of the  larger
glands (§ 823);  the only difference being,  that the latter are situated at  the
extremities of the ramifying ducts, by which their product  is collected  and
conveyed away;  whilst the former pour  their secretion at once  into  the
cavity of the intestine.—The membrane which  covers  in the cavity is  ex-
tremely thin, and is very liable to be destroyed by ulceration ; hence it is, that,
after inflammation of the  enteritic  mucous membrane,  the patches of  Peyer
are often to be seen as a congeries of shallow  open  cells  or follicles.
  877.  Although the particular use of each variety of the Intestinal glandulae
cannot yet be determined, there seems  little doubt that their general function
is, to eliminate  from the Blood those putrescent  matters which would  other-
wise accumulate in it; whether as  one of the results of the  normal waste of
the system, or as produced by various  morbific causes, which act as ferments,
and thus occasion an unusual tendency to decomposition in the  solids  and
fluids of the body.  That the putrescent elements of the faeces are not  imme-
diately derived  from the food taken in, so much  as from the excreting  action
of the Intestinal Glandulae, appears from this  consideration, among others;—
that faecal matter is still  discharged, even in considerable quantities, long after
the intestinal tube has  been  completely emptied of its alimentary contents.
We see this in  the course of many diseases, when food is not taken for many
days, during which time the bowels have been  completely  emptied of their
previous contents by repeated evacuations; and whatever then passes,  in  ad-
dition to the biliary and pancreatic fluids, must be derived from the intestinal
walls themselves.   Sometimes a copious flux of putrescent  matter continues
to take place  spontaneously;  whilst it is  often produced by the  agency of
purgative medicine.  The "colliquative diarrhoea,"  which frequently comes
on at the close of  exhausting diseases, and  which usually precedes death by
starvation, appears to depend, not so much  upon a disordered  state of the
intestinal glandulae themselves, as upon the  general disintegration of the solids
of the body, which calls them into  extraordinary activity for  the purpose of
separating the decomposing matter. 
GENERAL REVIEW OF THE NUTRITIVE PROCESSES.
671
                        CHAPTER  XVI.

     GENERAL REVIEW OF  THE NUTRITIVE PROCESSES.--ANIMAL HEAT.

   1.—Review of the Nutritive Processes, with Practical Applications.

  878. The  detailed survey  which has  been now taken,  of the different
Functional  operations concerned  in maintaining  the life of the individual,
may suggest to us some  general views that have important practical applica-
tions.   In the first place, it has been shown, that the province of the Animal
is not to combine Inorganic elements into Organic  compounds, fit to be  ap-
plied to the purposes of Nutrition; but to use those which are prepared for
it by the Plant.  The nutritive materials thus obtained  may be divided into
two great classes, the azotized and the non-azotized.  The former have been
shown (§ 642) to be so nearly identical in composition with  the  proximate
principles of  which the Animal body is composed, that no great amount of
chemical transformation can be required to prepare  them for being appropri-
ated by it.   The latter are altogether different in  character; and whether or
not they can, by any process  of transformation, be  made subservient  to  the
nutrition of the Azotized tissues, it is unquestionable  that their ordinary use
is to serve  as the materials for the Respiratory process, and  for the mainte-
nance of Animal heat.   The  demand for these several articles in the system
will depend, in regard to the  former, upon the amount of Tissue which  has
been disintegrated and needs  repair; and with respect to the latter, upon  the
amount of  Heat which it is necessary to  generate,  to keep up the tempera-
ture of the body to its  regular standard.   Hence  a  highly-azotized  diet is
most required when  the greatest amount of muscular exertion is being used;
whilst a diet, in  which non-azotized substances are predominant, will serve
to sustain the Animal Heat in a  cold  atmosphere.   The adjustment of the
diet to the  wants of the system, is a matter of the greatest importance for
the preservation  of health.   If too great an amount of  azotized food be in-
gested, and the superfluity be thrown upon the Kidneys to eliminate (§ 850),
disorder of the Urinary Secretion  is almost certain, sooner or later, to mani-
fest itself.   The  quantity of Lithic Acid, in particular, undergoes considerable
increase; and, by the removal of  its bases through  the  increased  production
of other acids, it is very likely to pass out in an insoluble state, giving rise to
Gravelly deposits.   Or  it may accumulate in the Blood, and  there combine
with Soda; forming  a salt which is deposited in  various  parts (especially in
the neighbourhood of the smaller joints), forming concretions, which are com-
monly known under the name of "chalk-stones."   These  deposits usually
take place, however, after severe attacks of a peculiar  Inflammation, known
as Gout; and this inflammation seems to be connected with the accumulation
of Lithate  of Soda in the  Blood.—Over this  disease a careful regulation of
the diet exercises  a  powerful control.  A patient  affected with the " Lithic
Acid diathesis," may palliate, if not altogether cure his disorder, by rigorously
abstaining  from  the  use of any superfluous amount of azotized  compounds
as food; and by subsisting as much as possible upon those belonging to the
Farinaceous  group.  It is by no  means every case, however, that is capable
of alleviation by treatment of this  sort; in fact, it  can  seldom be rigorously 
672          GENERAL REVIEW OF THE NUTRITIVE PROCESSES.

enforced, except in early life, or at any rate when the  constitution is unbroken
by disease or intemperance.  Not unfrequently it will be found, that the per-
sistence in a diet of this kind, occasions so much disorder of the stomach, as
to be quite out of the  question.—On the other hand, in the " Strumous dia-
thesis," there would seem to be  a low condition of those vital powers, which
are concerned in the conversion of the Albuminous materials  prepared by
the Digestive process, into  the Fibrinous matter which  is ready for assimila-
tion ; so that, by a  perversion of the ordinary nutrient actions, Albuminous
Tubercle is deposited in the interstices  of the tissues, instead of these tissues
being themselves regenerated  by Organizable  Fibrine; and  the same may
take place in a more rapid manner,  in consequence of that disturbance of the
nutrient processes, which is known in  healthy constitutions as Inflammation
(§ 802).   It is  obvious, then, that  the  treatment of  the Strumous Diathesis
should be directed towards  the invigoration of  the general powers of the sys-
tem ;  and although, when disease of the Chest has once established  itself, a
warm moist atmosphere  may be necessary as  a preventive of inflammatory
affections, it is a great mistake  to  imagine that such a  plan  is applicable to
those in whom there is merely a strumous  predisposition;  for this should be
combated by such means as are calculated rather to brace than to relax the
system,—especially out-door exercise, a nutritious diet in  which easily-digested
proteine-compounds  should predominate, and  a dry and well-ventilated  habi-
tation. There can be no doubt that the Tuberculous  Cachexia is encouraged,
and developed, by injudicious management during  the  early ages of life, in
many cases where it might have been avoided.*
   879.  Equally important  is the regulation of the diet, in regard to its non-
azotized constituents.  If these  are in excess, the elimination of them from
the Blood falls especially upon  the Liver  (§ 836);  and a continued excess
gives rise to disorders  in its function, which a diminution in the quantity of
Farinaceous or Oleaginous  matter  ingested would prevent or  cure.   This is
especially liable to happen to Europeans proceeding  to  warm climates ;  who
are not warned by their decrease of appetite, that there is no longer a necessity
for the same supply ;  but force themselves  to eat much  more than they have
any real occasion for.—There is a  very remarkable condition of the  system,
in which there is a tendency to the presence of a large amount of Sugar within
the vessels; either through the absence of  power to convert that which has
been taken in ;  or through the actual production of that compound, as a result
ofthe waste of the system.   We have seen that Sugar may be detected in
the Serum of healthy blood, drawn soon after a meal;  but that it soon becomes
untraceable,—probably in consequence of  its being  carried off by the respi-
ratory process (§ 697).  In  the  disease termed Diabetes, or the " saccharine
diathesis," there is a much larger  amount  of Sugar  in  the Blood: and this
appears to be constantly present, as if, from  some cause, "its elimination by
the usual channel were retarded.  The Sugar  makes its appearance,  also, in
the Urine; the Kidneys taking-on  the unusual office of separating this  com-
pound, that it may not accumulate in  the Blood.—Some late researches on
the exclusive employment  of  azotized principles as  articles of diet, in the
treatment ofthe  Saccharine diathesis, have given very favourable results. The
plan was long since proposed by Dr. Rollo ; and when the diseased condition
has been uncomplicated by other maladies (as  is not  unfrequently the case),
the rigorous enforcement of such  a diet  has been  attended with success in
numerous instances.   One of the greatest difficulties  in  the application of the
system, however, has  arisen from  the longing which  the patients experience

  * See the excellent works of Sir James Clark, in which the importance of Hygienic treat-
ment is strongly insisted on. 
GENERAL REVIEW OF THE NUTRITIVE PROCESSES.
673
for Vegetable food; since this tempts them to gratify their appetites, to the
complete prejudice of the remedial system,—a very small amount of farina-
ceous matter being sufficient  to cause the  re-appearance of the Sugar, after it
had seemed  to be entirely got rid of.  It has been proposed, however, by M.
Bouchardat  to gratify this longing  to a certain degree, by allowing the use of
bread made  of wheaten flower, from which nearly all the Fecula has  been
separated,—the Gluten  only being left, with such a small amount of Fecula
as may serve to make  it rise in fermentation; so that it  is as free from un-
azotized  constituents, as the  average of animal substances.   This  plan has
been very successfully practiced;  having frequently kept  the disease in  com-
plete  check, where, from the advanced  period of life, the  duration of the
morbid state, and other circumstances, a perfect cure could not be reasonably
expected.
   880. From  what has been stated in Chap. xn. respecting the nature of the
Function of Circulation, it is evident that primary disorders of that  function
are not  nearly so frequent as they are ordinarily supposed to be;  and that
the proximate cause of morbid phenomena is seldom to  be found  in 'them.
By the action  of  the Heart and  Blood-vessels, the  nutrient fluid, which has
been prepared from the alimentary materials submitted to the digestive appara-
tus, is conveyed to the tissues which it is  to nourish; but the true process  of
Nutrition is independent of  this, and may take place after the motion of the
fluid  has ceased,  just as it commences  before any movement shows itself.
For the tissue which exists in the  Embryo during  the early period of its de-
velopment, and also in any newly-forming part, is destitute of vessels, consist-
ing only of  cells ; and  these grow and reproduce them'selves at  the expense
of the nutritive materials supplied  to them from without, just  as  does the
whole mass of a Cellular Plant.   Moreover it has been  shown (§ 740), that
the activity  of the nutrient processes has much to do with the movement of
the fluid through  the smaller vessels, and  is a cause rather than a consequence
of it.  If the action of the Heart cease, the whole circulation must obviously
come to  a stand ere long; but in many animals the Capillary movement may
continue for some time after  the general circulation  has been checked;  and,
so long as blood is supplied to the parts, so long may their nutrition continue,
provided other circumstances be favourable.   It is  unquestionably true, that
the cessation of the Circulation is  usually  the immediate cause of Death; and
that, when the suspension is  permanent, the loss of the vitality of the system,
considered both as a whole, and as made  up of distinct parts, is  a necessary
consequence.   But still, we find that the cause of this cessation seldom  origi-
nates in  the Circulating apparatus  itself;   and  in  general,  a disturbed state of
the Circulation is to  be looked upon rather  as  a result, than as a  cause, of
diseased action.    An extreme case of such  a disturbance, which, when suffi-
ciently prolonged, is attended with fatal results, is to be found in Asphyxia-;
in which the cessation of the action of the Lungs induces a stagnation of the
Blood in  their capillaries; and as, in warm-blooded  animals, the whole cur-
rent of Blood  has  to pass through  the Lungs,  before  proceeding  again to the
system, a total suspension of the Circulation necessarily results from this inter-
ruption (§§ 738 and 779).  Now if we take this (which it appears reasonable
to do) as a type of a great number of morbid conditions  of different organs,
we are led to  see  why a serious disturbance of the movement in any one part
should affect the entire circulating apparatus, and  should thus  influence  its
flow through almost every other organ.    There are no other organs, however,
in which a stagnation can be so serious as in the Lungs; since there  are none
through which the whole current flows.    The Liver ranks next in importance,
since all the  venous blood  collected  from the  Chylopoietic viscera  passes
through  it;  and every practical man is aware how frequently derangement of
     57 
674
GENERAL REVIEW OF THE NUTRITIVE PROCESSES.
the circulation through the Liver, originating in an unhealthy state of the gland
itself, is a cause of serious disorders in the abdominal viscera.—Minor irregu-
larities in the Circulation, in various parts, not unfrequently become causes of
serious inconvenience.   Thus, few conditions  are  more common, especially
amongst persons of active minds but inert habits, than undue determination of
blood to  the Head, conjoined with torpor of the circulation through  the Skin,
especially that of the extremities, which are  ordinarily cold.  The obvious
indication here is, to endeavour to restore the balance of the Circulation ;  and
excitement of the flow of blood  through the Skin, by frictions, moderately-
stimulating applications, exercise, &c, will commonly prove of great utility.
   881.  There  are many disorders commonly regarded as affections of the
Circulation, which  evidently consist in reality of a morbid alteration in the
Nutritive processes : among these there can be little doubt that we  are to rank
local Determinations and Congestions, which result from an exalted or dimi-
nished activity of the formative actions;  and Inflammation, in which these
actions are perverted.  Much has been said and written, to very little purpose,
respecting the essential nature of this process; it has been  attributed by some
to disordered action of the  vessels, and by others to an injurious  impression
on the nerves,—the  fact, that Inflammation may occur in  tissues  which con-
tain neither vessels nor nerves, having been entirely overlooked.   The  only
view of  the character of Inflammation  that  seems  likely to account for it's
phenomena, is that which regards it as essentially consisting in a  disturbance
of the due  relation  between  the living Tissue and the  nutrient  materials
contained in the Blood ;  in other words,  as an abnormal form of the ordinary
nutritive  process (§§ '802—806).   A similar  remark may  be made, in regard
to those productions formerly termed  " Heterologous transformations" of
tissue; which are rather to be regarded  as  new  growths, that  have appro-
priated the nutriment designed for the support of the proper tissues, and  have
therefore become developed at the  expense  of these.   It is quite  as absurd
to attempt to  account for the growth of Scirrhus, Carcinoma, &c, by any
peculiar action of the vessels of the part, as it  would be to  attribute the secre-
tion of fatty matter  by the  cells of  one tissue, or of  phosphate  of lime by
those of  another, to  the peculiar  distribution of their vessels.  The progress
of research obviously leads to the conclusion, that in every part of  the living
body there is an inherent and independent vitality, which enables it to grow
and maintain its normal  structure and constitution, so long as it  is supplied
with the  requisite materials; and that changes in the character of the tissue
can be referred to nothing else than to alterations  in its properties, resulting
from  external  agencies,  or to alterations in  the  materials supplied for its
renewal.  Of these  two morbific causes, the latter is  undoubtedly the  most
frequent; and the tendency  which is now gaining ground, to seek in the Blood
for indications of pathological changes, when  there is no obvious  general dis-
turbance  of the  system,  will probably lead to a greatly-increased knowledge
of the real nature of diseased  states; in spite of the opposition which  any
return to the Humoral Pathology is sure to excite, in the minds of those who
regard it as an exploded  and pernicious system.
  882. The  Sympathy between different parts of the system, which espe-
cially manifests itself in the tendency to simultaneous affection with the same
Disease,  affords an excellent illustration of this principle.   Of those Sympa-
thetic  actions, which result from the Nervous connections of  the various
organs, this  is  not the place  to speak;  since we  are  at  present concerned
with those perversions of the Nutritive processes, which give rise to Inflam-
matory and other diseases.   Where a certain tissue, throughout the body, is
similarly affected, there is strong reason to presume  that the morbific cause
is conveyed to it in the Blood; this is the case, for example, with  regard to 
GENERAL REVIEW OF THE NUTRITIVE PROCESSES.
675
the Mucous membranes, which all manifest a tendency to Inflammation, when
Arsenic has been received into  the system: and certain forms of the disease
commonly termed Influenza, are marked by a similar disposition.   The same
may be said  in  regard to  Inflammation of the Fibrous membranes, Areolar
tissue, Serous membranes, and  other structures.  It has  been considered a
sufficient  account of these  consentaneous affections, to  say that they result
from Sympathy,—a mere verbal quibble,  which explains nothing.   If, on the
other hand, we regard the disease as a perversion of the  ordinary processes
of Nutrition, Secretion, Sic, and as dependent upon an abnormal condition of
the Blood (such  as is induced  by the introduction  of a  poison into it), the
rationale of the  sympathetic disturbance  becomes apparent;—since all the
tissues of the same kind will of necessity be similarly affected, although some
local cause may occasion one to suffer more severely than another.  In  the
ingenious  paper by Dr. W. Budd, already  referred  to (§ 785), the perfect cor-
respondence, which not unfrequently manifests itself between the diseased
actions on the two sides of the  body, is adduced in support of the same view,
to which it is made to afford very striking confirmation.   The fact that  this
kind of Sympathy not unfrequently manifests itself between tissues  having
an  analogous  structure, but very different function, is  another argument in
favour of the same view ;  of this fact, the  sympathy of which every practical
man is  aware, between the Skin and  Mucous Membranes, is a  very good
example.   The sympathy of the different tissues forming any individual organ,
by which disease in one becomes a cause  of disorder in the rest, is, however,
to be very differently explained.  We have examples of this in  Inflammatory
affections  ofthe  Mucous membranes, which usually extend themselves to the
remaining constituents of the organs of which  they form a part; and in those
of the Serous membranes, which almost  always follow inflammation of the
organs they invest.  Here the local disturbance of one part appears sufficient
to account for the extension of  it to another, that is closely connected with it
by vessels and nerves; this has been termed the Sympathy of Contiguity.
The Fibrous membranes are less liable to  be affected in this manner, than are
most other tissues ; and the  reason appears simply this,—that there  is usually
less vascular connection between them and the adjacent  parts, than there is
in the case of the Serous  membranes.  Hence the Fibrous membranes  fre-
quently act as insulators, preventing  the spread of disease to adjacent parts.
   883.  The  general  characters of the processes of Nutrition and  Secretion
are so nearly allied, that what has been stated of the Pathological states of the
former, is nearly as applicable to those of  the  latter.   Although it  is unques-
tionable that disordered Secretion may result from  a purely local cause, acting
on the solid tissue of the part affected, yet there is also increasing reason to
believe, that in a large number  of cases, the abnormal character of the  pro-
duct is in  reality a result of the abnormal state of the Blood  from which it
is separated; and  that the organ itself is  still  performing  a healthy function,
in separating  from the blood  that  which would  be  injurious to   it.   This
leads us to refer  such disorders to causes much more remote than those
which were formerly supposed to operate ; but they are  undoubtedly nearer
the true ones.  Such a view has been prosecuted  by Dr. Prout in regard to
the abnormal conditions of  the Urine, with great success;  and  there can be
little doubt that  it is  also  applicable to  the  Biliary secretion, on the  true
chemical nature of which there  is scarcely yet an agreement among  Chemists,
and  whose  pathological conditions, therefore, are, and  must  long remain,
comparatively obscure.  It  is  obvious that, if the Assimilation of  Nutritive
matter be  in any respect wrongly performed, the products  of the Decomposi-
tion of the Tissues (in which these excretions probably originate, § 819), must
also be different; and our  remedial measures must often be directed, therefore,
not so much to the Secreting organ, as towards the previous operations. 
676           GENERAL REVIEW OF THE NUTRITIVE PROCESSES.

  884.  These considerations are of the highest importance in the treatment
of Disease; the success of which will greatly depend  upon  the  degree in
which the Physician follows the indications of Nature, instead of putting him-
self in antagonism to her course of operation.   If we pay but a slight attention
to those phenomena which result from the  introduction of  poisons into the
system, we perceive that there is almost invariably an increased excretion of
some kind, which tends to eliminate them from the blood.  Even where there
is no other obvious means for their removal, we can have little doubt that the
Respiratory function gives  important aid in their separation  ; when we keep
in view that from five to eight ounces  of solid  carbon, to  say  nothing of the
hydrogen, are  thrown off from  the  lungs in the course of every twenty-four
hours.  It is important to bear this circumstance in mind ; since it enables us
to understand how, if time be given, the system frees itself from such noxious
substances;  and it  points out the duty of the medical attendant to be rather
that of supporting  the powers of the body by judiciously-devised means, and
of aiding in the elimination of the noxious matter by a copious supply of pure
air, than of interfering more actively to promote that which Nature is already
effecting in the most advantageous  manner.   We see the results of  this ope-
ration in the case of Narcotic poisoning; in which, if the Respiratory process
can be artificially kept up for a  sufficient length  of time, the powers of the
nervous system  are gradually restored, even after what seemed to be  their
complete and final cessation.—There can be no  doubt that, in like manner,
the system makes  an effort to rid itself of other noxious substances, the pre-
sence of which in the blood  results from  morbid processes going on in the
body itself, and which, if retained,  would  produce the  most serious conse-
quences.  Thus a copious discharge of  Lithic acid by the Urine will frequently
avert or curtail an attack of  Gout.  The copious acid  perspirations, which
occur in certain forms of Rheumatism, are the means by which the Lactic acid
(which  seems  to be the materies morbi of this  disease) is  separated from the
blood.  And there can be no doubt that an attack of Diarrhoea often prevents
more serious disease, by removing an  unusual  accumulation of the elements
of bile, or by eliminating an undue amount of putrescent  matter, the continued
presence of which in the circulating fluid would induce the  most serious dis-
orders in the nervous system.—There  can  be no doubt that a due regulation
of the Excreting processes  is one of the most important  means, by which the
Physician can counteract the results of disordered actions in the system.  They
may frequently require to be  gently stimulated,  in order to remove some mor-
bific elements  from the blood.  But it will be seldom that it will be desirable
to check them, even when apparently excessive, unless there be strong reason
to believe, that the excess proceeds from a disordered state of the organ itself,
produced by local  causes only.
                           2.—Animal Heat.

  885. All the vital actions that have been considered in the preceding pages,
require a certain amount of Heat as a condition of their performance;  and in
the more elevated tribes of animals, in which  (for the very purposes of their
creation) a high degree of constancy and regularity is required in these actions,
there is a provision within themselves for the maintenance of their temperature
at a certain standard.  We shall inquire, in the first place, into the amount of
Heat thus generated by Man; and then into the sources of its production.
  886.  Our present knowledge of the Temperature of the Human body under
different circumstances, is  chiefly  due to  the  investigations of Dr. J. Davy.
Much additional information may be expected, however, from  inquiries which 
ANIMAL HEAT.                           67?
are at present in progress.   Dr. Davy's observations* have  included 114 in-
dividuals of both sexes, of different ages, and among various races, in different
latitudes, and under various temperatures; the external temperature, however,
was in no instance very low, and  the variations were by no means  extreme.
The mean of the ages of all the individuals was 27 years.   The following is
a general statement of the results, the temperature of the  body being ascer-
tained by a thermometer placed under the tongue.
  Temperature of the air      60°    Average temperature of the body  91-28°
                           69°     "      "      "     »      98-15°
                   "       78°     "      "      "     "      98-85°
                           79.50    „      ,,      »     »      99-21°
                   n       80o     •>      »      >,     »      99-67°
                           82°     "      "      "     "      99-9°
  Mean of all the experiments  74°    Mean of all the experiments     100°
  Highest temperature of air   82°    Highest temperature of body     102°
  Lowest temperature of air    60°    Lowest temperature of body      96-5°
From this we  see that the variations noted by Dr. Davy, which were evidently
in part the consequence  of variations in external temperature, but which were
also partly attributable to individual peculiarities, amounted to 55 degrees ; the
lower extreme would probably undergo still further depression, if the inquiries
were carried on  in very cold climates.—The Temperature of the body may
be affected by internal as well as by external causes;  thus in diseases which
involve an accelerated pulse and an augmented respiration, the temperature is
generally higher  than usual,  even though a large  portion of the lung may be
unfit for its function.   This is often remarkably seen in  the last  stages of
Phthisis, when the inspirations are extremely rapid, and the  pulse so quick as
scarcely to admit of being  counted; the  skin, in  such cases, often  becomes
almost painfully hot.   On the other hand, in diseases of the contrary character,
such as Asthma  and the Asiatic Cholera, the  temperature of the body falls,
sometimes, to  the extent of 20 degrees.  The following observations have been
made on this  subject by M. Donne ;t it is much to be  desired, however, that
fuller data could  be collected on the subject.   In  a case of Puerperal Fever,
the pulse being 168, and the respiration 48  per minute, the temperature was
104°.   In a case of Hypertrophy  of the Heart, the pulse  being  150 and the
respirations 34, the temperature was 103°.  In a case  of Typhoid Fever, the
pulse being 136,  and the respirations 50, the temperature was 104°.   And in
a case of Phthisis,  the pulse being 140, and the respirations 62, the  tempera-
ture was 102°.   On the other hand, in a case  of Jaundice, in which the pulse
was but 52, the temperature  was only 96'40°;  but the same temperature was
observed in a  case of Diabetes, in  which the pulse was 84.  The limited re-
sults of Mons. D.'s experiments, whilst they clearly indicate that a  general
relation exists  between  the  temperature of the body and the rapidity of the
pulse, also show  that this  relation is by no  means invariable, but that it is
liable to be affected by several causes, of which our knowledge is as yet very
limited.  Dr. Dunglison speaks of having frequently seen the thermometer at
106° in Scarlatina and Typhus ; and Dr. Edwards mentions a case of Tetanus,
in which it rose to  HOf.J

  *  Phil. Trans., 1814; republished in Anatomical and Physiological Researches.
  t  Archives Generates, Oct. 1835 ;  and Brit, and For. Med. Rev., vol. ii. p. 248.
  X  [An extensive series of observations has been made by M. Roger* on the temperature
of children in health and various diseases.
  In nine examinations of infants from  one to twenty minutes after birth, the temperature
(observed in these and in all the other cases, in the axilla), was from 9995 to 9545.  Im-
Arch. Gen. de Medecinc, Juillet, Aout, &c, 1844.
                 57* 
678            GENERAL REVIEW OF THE NUTRITIVE PROCESSES.
  887. Although there appears to be, for all species  of animals, a  distinct
limit to the variations  of bodily temperature, under which their vital opera-
tions can be carried on, this limitation does not prevent animals from  existing
in the midst of great diversities of external conditions ; since they have within
themselves the power of compensating for these, in a very extraordinary de-
gree.   This power seems  to  exist in Man to a higher amount than  in most
other animals;  since he can not only support, but enjoy, life under extremes,
either of which would be fatal to many.   In many parts of the  tropical zone,
the thermometer rises  every day through a large  portion of the  year to 110°;
and in  British India it is said to be seen occasionally at 130°.   On the other
hand, the  degree of cold frequently  sustained by Arctic voyagers, and quite
endurable  under proper precautions, appears much more  astonishing; by
Capt. Parry, the  thermometer has  been seen as low as —55°, or 87° below
the  freezing point; by  Capt. Franklin  at—58°, or 90° below the   freezing
point;  and by Capt. Back at —70°, or 102° below the freezing point.   In both
cases, the  effect of the atmospheric temperature  on the body is greatly influ-
enced by the condition  of  the air  as  to motion  or rest; thus, every  one has
heard of the almost unbearable oppressiveness of  the  sirocco or hot  wind of
Sicily and Italy, the actual temperature of  which is not higher  than has often
been experienced without any great discomfort, when the air is  calm : and, on
the other side, it may be mentioned that, in the experience of many Arctic voya-
gers, a temperature of—50° may be sustained, when the air is  perfectly still,
with less inconvenience than is  caused by air in motion at  a temperature fifty
degrees higher.   This  is quite  conformable to what might be  anticipated on
physical principles.
  888. Again, the degree of moisture contained in a heated atmosphere, makes
a great difference in the degree of elevation of temperature, which may be  sus-

mediately after birth the  temperature was at  the highest; but  it quickly fell to near the
lowest of those above stated; but, by the next day, it was again  completely or nearly what
it was before.  The rapidity of the pulse and of respiration  appeared to have no certain re-
lation to the temperature.
  In thirty-three infants of from one  to seven days old, the  most frequent  temperature was
98-6; the average was 98-75; the maximum (in one case only)  102-2; the minimum  (also
observed only once) 96°-8.  All the  infants were healthy.  The frequency of respiration
had no  evident or constant relation to the temperature.  A few of the infants were of a
weakly habit; their average was 97-7: the others were strong, and their average tempera-
ture  was 99°-534.  The age of the  infant  (in this short  period) had no influence on its
temperature; neither  had its sex, nor its state of sleep or waking, nor  the period  after
suckling.      t
  In twenty-four children, chiefly boys, from four months  to fourteen years  old, the most fre-
quent temperature was above 98°-6 ;  the average was 98°-978,  the minimum was 98°-15;
the maximum  99°-95. The average temperature of those  six years old or under, was
98°-798; of those above six years old, 99°-158.  The average number of  pulsations in the
minute was in those under six years old  102; in those above that age 77;  yet the tempera-
ture  of the latter was higher than that of the former, or of younger infants. There was no
evident relation between  the temperature and the frequency of respiration;  nor in a few
examinations, was the temperature affected in a regular way, by active exercise for a short
time, or by the stage of digestion.
  As already said, in all  the examinations  from  which these  results were  obtained, the
thermometer was held in  the axilla; comparative examinations proved that the tempera-
ture of the axilla (though lower than that of internal organs), was higher  than that of any
other part of the surface of the skin.  Of the other parts examined, the warmest was the
abdomen, then in succession, the cavity of the mouth, the bend of the arm, the  hands, the
feet; of which last, the average  temperature, in four examinations, was only 87°-35.  (These
results correspond sufficiently with those obtained  by Dr.  John Davy.)
  In diseased states, (to the illustration of which the greater part of the memoir is devoted,)
the temperature of the skin  in children may descend to 74°-3,  and may  ascend to 108°-5.
Its range of variation is therefore much greater than in adults, in whom M. Andral found it
to vary  in different diseases not more than from 95° to 107°-6.—M. C] 
ANIMAL HEAT.
679
tained without inconvenience.   Many instances are on record, of a heat of
from 250° to 280° being endured in dry air for a, considerable length of time,
even by persons unaccustomed to  a particularly high temperature ; and per-
sons whose occupations are such as to require it, can sustain a much higher
degree of heat, though not perhaps for any long period.  The workmen of
the late Sir F. Chantrey have been accustomed to enter a furnace in which
his moulds were dried, whilst the floor was red-hot, and  a  thermometer  in the
air stood at 350°; and Chabert, the " Fire-king," was in the habit of entering
an oven, whose temperature was from 400° to 600°.   It is possible that these
feats might be easily matched by many workmen who are habitually exposed
to high  temperatures; such  as those  employed in Iron-foundries, Glass-
houses, and  Gas-works.  In all these  instances, the dryness  of the air facili-
tates the rapidity of the vaporization of the fluid, of which the heat occasions
the secretion by the Cutaneous glands; and the large amount of caloric  which
becomes latent in the process, is for the most part withdrawn from the body,
the temperature of which is  thus kept down.  Exposure to a very elevated
temperature, however, if  continued for a sufficient length of time, does pro-
duce a certain elevation of that of  the body; as might be expected from the
statements already made  in regard to  the  variation in the heat  of the body
with  changes in  atmospheric  temperature  (§ 886).   In the experiments of
MM. Berger and Delaroche, it was found tbat, after  the  body had been  ex-
posed to  air  of 120° during 17 minutes, a thermometer placed in the mouth
rose nearly 6 degrees above  the ordinary temperature;  it may be remarked,
however, that as the body was immersed in a close box, from which  the head
projected (in order to avoid the direct influence of the heated air on  the tem-
perature ofthe mouth), the air had  probably become charged with the vapour
exhaled from the surface, and had therefore somewhat of the effects of a moist
atmosphere.   At  any rate, the  temperature of the body  does not appear to
rise, under any circumstances, to a degree very much greater than  this.   In
one of the experiments of Drs. Fordyce and Blagden,  the  temperature of a
Dog, that had been shut  up for half-an-hour in a chamber of which the tem-
perature  was between 220° and 236°, was found to  have risen from 101° to
about 108°.   MM. Delaroche and  Berger tried several experiments on  differ-
ent species of animals, in order to ascertain the highest temperature to  which
the body could be raised  without the destruction of life, by inclosing them in
air heated from 122° to 201°, until they died: the result was very uniform,
the temperature of the body at the  end  of the experiment  only varying
in  the different species  between 11°  and  13° above  their natural standard:
whence it  may be  inferred, that an elevation to this degree must  be fatal.
This  elevation would be attained comparatively  soon  in a  moist  atmo-
sphere ;  partly  because  of the greater conducting  power  of the  medium;
but principally on  account  of the  check which is put  upon the  vapor-
ization  of the fluid secreted  by the skin.  Even here, however, custom
and acquired constitution have  a very striking influence; for whilst the in-
habitants of  this country are  unable  to sustain, during  more than 10 or 12
minutes, immersion in a vapour-bath of the temperature of 110° or 120°, the
Finnish peasantry remain for half-an-hour or  more in a  vapour-bath, the tem-
perature  of which finally rises even to 158° or 167°.—Accurate experiments
are yet wanting, to determine the influence of humidity on the effects of cold
air.   From  experiments  on  young Birds incapable of maintaining their own
temperature, of which some were placed in cold dry air, and others in cold air
charged with moisture, it was found by Dr. Edwards that  the loss of heat was
in both instances the same;  the effect of the  evaporation from the surface in
the former case, being counter-balanced in  the latter by the  depressing influ-
ence of the cold moisture.  This influence, the existence of which is  a mat- 
680
GENERAL REVIEW OF THE NUTRITIVE PROCESSES.
ter  of ordinary  experience, is probably exerted directly  upon  the nervous
system.
   889. Having thus considered the  general  facts which indicate the faculty
possessed by the living system, in the higher Animals, of keeping up its tem-
perature to an elevated standard, and of preventing  it from  being  raised  much
beyond it by any degree of external  heat, we have next to inquire to what
this faculty is due.   We shall be more likely to arrive at accurate results in
such an inquiry, the more comprehensive  is  our survey of the phenomena to
which it relates.*

   a. The most recent experiments on the temperature  of Plants (those made by MM. Bec-
querel and Breschet with the thermo-multiplier) have  demonstrated, that in those parts in
which the vital processes are taking place with activity, a sensible amount of caloric is being
constantly evolved.   The amount of this evolution of heat is generally very  low, not more,
in fact, than a single degree (Fahr.); and as it does not more than counterbalance the effect
of the evaporation, which is continually taking place from the surface, there is no sensible
difference between the temperature of  the plant  and that of the surrounding air.  At the
time of Flowering, however, a  much  greater degree of heat is generated in many plants,
especially in those in which  a large number of flowers are crowded together, as in the case
of the Arum tribe:  thus a thermometer placed in the midst of twelve spadixes has been
seen to rise to 121°, whilst the temperature of the air was only 66°.  During the Germina-
tion of seeds, again, a considerable development  of heat takes place;  this,  which  is  soon
carried off from a single seed, becomes very sensible when a large number are heaped toge-
ther, as in malting; the thermometer plunged into a heap of germinating barley having been
seen to rise to 110°.
   b. These facts are of more importance than might appear at first sight;  for they indicate
unequivocally, that the source of the heat is to be  looked for  in the Organic functions, not in
those of Animal life.   The evolution of Caloric has been attributed  by many physiologists
to the Nervous system ; the influence which this  system  evidently possesses over the func-
tion, being mistaken for the efficient cause of it.  As has been remarked on  several former
occasions, however,—the fact that any change takes place in Vegetables, to the same degree
(under certain conditions,) with that in which it ever presents itself  in Animal^, is a suffi-
cient proof that it cannot be dependent upon nervous agency, although it may be influenced by
it.  Moreover, it may be remarked that the production of Heat is an operation of an entirely
physical character, and that it may be referred to  physical causes; whilst the operations in
which the Nervous system is concerned, are such as we cannot liken in any degree to physical
phenomena, and are of a purely vital character.—In our inquiry into the sources of the Heat
evolved by living beings, we are limited, therefore, to those which can operate in the Vege-
table kingdom; and on examining into  the phenomena which present any relation to  this,
we are at once  struck with the fact, that an absorption  of Oxygen from the air, with an ex-
trication of Carbonic acid, is  continually taking place (constituting the true Respiratory pro-
cess of Plants, § 750);  and  that these  changes occur with  excessive activity, at the  very
periods at which the evolution of Heat is most remarkable,—those, namely, of germination
and flowering.  The quantity of Oxygen consumed  by flowers  is enormous—those  of the
Arum Italicum  having been found to convert 40 times their own bulk of that gas into Carbonic
acid, between the periods of their first appearance and their final decay ; and of this, the far
larger proportion is consumed by the sexual apparatus, which has been found to consume 132
times its own bulk of Oxygen in 24 hours.  That this change  is a condition necessary for the'
production of Heat, is fully proved by the  fact, that no caloric is evolved when the flowers
are excluded from the contact of Oxygen;  whilst the substitution of pure oxygen for atmo-
spheric air occasions the elevation of temperature to be more rapid and considerable  than
usual.t  The same may be said of the heat liberated by seeds in the  act of Germination: a
large amount of oxygen is absorbed, and of carbonic acid given out, during this process; and
the evolution of Heat may be easily shown to be  as  dependent  upon this change, as in the
instance just quoted.
   c.  When the phenomena  of Calorification in Animals are carefully examined, they are
found to harmonize completely with this view.  Throughout the whole kingdom, an exact
conformity may be perceived between  the amount of Oxygen  consumed and of Carbonic
acid given off, and the degree of Heat liberated.  In the cold-blooded animals, whose tem-
  * This subject is more fully treated in the Author's Principles of General and Compara-
tive Physiology, §§ 548—567.
  t See the very interesting experiments of MM. Vrolik and Vriese, in the Ann. des Sci.
Nat., N. S. Botan., tom. xi., p. 551. 
DEVELOPMENT OF HEAT.
681
perature is almost entirely dependent upon that of the surrounding element, the respiration
is feeble, being carried on, for the most part, through the medium of water.  In the warm-
blooded Vertebrata, however, which have tbe power of keeping up the heat of their bodies to
an elevated standard, even when that of the surrounding air is far beneath it, the quantity of
Oxygen consumed is very large; and that required by Birds is more, in proportion to their size,
than that employed by Mammalia; as we should expect  from the more elevated tempera-
ture of the former.  In the class of Insects, we  have  a very remarkable illustration of the
same  general fact.   It appears, from the researches of  Mr. Newport, that  Insects, during
their larva and pupa  states, and even in their perfect condition when at rest, are to be re-
garded as truly cold-blooded animals ; their temperature rising and falling with that of the
surrounding medium, and being at no time more than a degree or two above it.  In a state
of activity, however, the temperature of the body attains a considerable elevation,—fre-
quently as much as 10° or 15° above that  of the air.  It must be remembered that, owing
to their larger extent  of surface in proportion to their  bulk, small animals are cooled much
more rapidly than large ones; and the  temperature of Insects would probably rise much
higher, if it were not for the loss they are thus  continually experiencing, which is greatly
increased by  the action of the wings.  In one of Mr. N.'s experiments, a single Humble-bee,
in a state of  violent excitement, communicated to  three cubic inches of air as much as 4°
of heat within five minutes; its own temperature being raised 7° in the same time. When
several individuals in a state of excitement, however, are clustered together, so that the loss
of heat is prevented,  the elevation of temperature is much more considerable; thus a ther-
mometer introduced  among seven "Nursing-Bees" stood at  92^°, whilst the  external air
was only 70°; and the temperature of a hive was raised by disturbing  it, during winter,
from 48^° to 102°, the temperature of the air being only 34^ at the  time!   In all these
instances, the amount of Oxygen consumed bears an exact proportion to that of the Heat
evolved.

   890.  In  the higher  animals, as  in the lower,  exercise has  a considerable
effect in producing an elevation of temperature;  and, that this is not merely
due to  the acceleration of the circulation, is shown  by the very curious  fact,
that the exercise  of a particular  muscle will cause an increase in  the heat
liberated from it, as shown by needles plunged in its substance, and connected
with  the thermo-multiplier.*  It may, indeed, be stated as a general proposi-
tion,  applicable as well  to  different parts of the same being, as  to different
individuals, that the development of Heat is proportional to the activity of the
molecular processes  which constitute the  functions of Nutrition,  Secretion,
&c.; increasing with their activity,  and diminishing with their torpor.  It is
very  easy to explain, on this principle, the  known  influence of  the  Neiwous
system on  the calorific function: since, although the molecular  changes in the
organized fabric are not dependent upon  the agency of that system, they are
very  much influenced by it;  and  thus we can readily understand how a state
of nervous excitement may produce an elevation of temperature, whilst a de-
pression of nervous power occasions a  cooling of the body.  The experi-
ments  of Sir  B.  Brodie, Chossat, and others,—in  which  a  greater  or less
portion of  the nervous centres was  removed, and the animal cooled notwith-
standing the maintenance  of the  circulation,—by no  means prove  that  the
Nervous system is directly concerned in the production  of  heat; since in all
such  experiments, there is a gradual loss of those other vital  powers, which
are concerned in the function of calorification.   From the experiments of Dr.
W. Philip  and Dr. Hastings, it appears that an animal whose nervous centres
have  been  removed, cools  much  faster when left to  itself,  than when Artifi-
cial Respiration is practised;  and that, if the cooling have made much  pro-
gress before the artificial respiration is caused to commence, the temperature
may  be raised;—and this, too, in  spite of the very imperfect manner in which
natural Respiration is replaced by movements artificially effected.
   891.  That the  maintenance of Animal Heat is due in part to those molecu-
lar changes, to which the Cutaneous Respiration is  subservient, appears from

  * See the  experiments of MM. Becquerel and Breschet, in Ann. des Sci. Nat. N. S. ZooL,
tom. vi. 
682
GENERAL REVIEW OF THE NUTRITIVE PROCESSES.
the following experiments recently performed by MM. Becquerel and Bres-
chet.   The  hair of Rabbits was shaved  off, and  a composition of glue, suet,
and resin, forming a coating through which air could  not pass, was applied
over the whole surface.   It might seem natural to suppose tbat, by preventing
the evaporation of the sweat, the  temperature  of the  tissues would be very
sensibly increased ; and that, by this increase of the temperature of the whole
body, a high state of fever would be engendered, with the symptoms of which
the animal would at last die.  But the contrary occurred.  In the first Rabbit,
which had a temperature of 100°  before being shaved and plastered, it had
fallen to 89|° by the time the  material spread  over him was dry.  An hour
after,  the thermometer placed in the same parts (the muscles of the thigh and
chest) had descended to 76°.   In  another Rabbit, prepared with  more  care,
by the time  that the plaster was dry, the  temperature of the body was not
more  than 5§° above that ofthe surrounding medium, which was  at that time
69j°;  and in an hour after this, the animal died.  These experiments place
in a very striking point of view the importance of the Cutaneous surface as a
respiratory organ, even in the  higher animals:  and they enable us to under-
stand  how, when the  secreting power of the  Lungs is nearly destroyed by
disease, the  heat of the body is kept up  to its natural  standard by the action
of the Skin.   A valuable therapeutic indication, also, is  derivable from the
knowledge which we thus gain, of the importance of the Cutaneous Respira-
tion;  for it leads us to perceive the desirableness of keeping the  skin moist,
in those febrile diseases in which there are great heat and  dryness of the sur-
face, since secretion cannot properly take place through a dry membrane.  Of
the relief afforded by cold  or  tepid  sponging  in  such cases, experience has
given  ample  evidence.
  892. All the foregoing facts  point to the formation of Carbonic Acid, by the
union of  the Oxygen absorbed from the air with Carbon set free from the
body, as the main  source of the  evolution of  Heat within the Animal sys-
tem.  The precise mode in which  this union is accomplished,  is not yet
known; but it is certain that, in whatever  manner the  combination may take
place, a certain measure of caloric must be generated.  The combustion of
from 5 to  10 oz. of Carbon per day, however, would  be  by no means  suffi-
cient to keep up  the temperature of the Human body to its proper standard;
for it has been experimentally  ascertained, that  the amount of Caloric set free
by a warm-blooded animal in a given  time is more than can be thus accounted
for.   It does not hence follow,  however,  that we are to look to any other than
Chemical processes, for the explanation of this most important function; since
there can be no doubt that there are many other changes of composition, con-
tinually taking place in the living body, which have  their share in the pro-
duction of the effect.  These take place, for the most part, at the expense of
the surplus of Oxygen absorbed over that which is given out in the form of
Carbonic Acid; this  surplus amounting  to as  much  as 15 per cent, of the
whole (§ 766).   Of the manner in which this surplus is employed, no precise
account can be given; but there can be little doubt that part of it is expended
in uniting  with Hydrogen, to form a portion of  the watery vapour which  is
exhaled from the lungs;  and that another part unites with the Phosphorus
and Sulphur which are taken  in as food (forming part of the proteine-com-
pounds (§ 114), to be excreted  as Phosphates and Sulphates (§ 847).  These
and other changes, in which the absorbed Oxygen participates, will be attended
with the evolution of Caloric;  and thus  we are probably to  account for the
excess of  Heat generated by a warm-blooded  animal  in  a given  time, above
that which would be produced  by the combustion of  the  amount of Carbon
exhaled by it during the same period; as  shown in the experiments of Dulong 
DEVELOPMENT OF HEAT.
683
and Despretz.*   Although, therefore, the Chemical doctrine of Calorification
cannot be regarded as yet perfected as to its details, there can be no reasonable
doubt that it is altogether sufficient to account for the phenomena in question.
And it may be stated  as  a general fact, that the production of Animal Heat is
due  to  the various changes  in  Chemical composition,  that  are  continually
taking place within the system;  of which changes, the  absorption  of Oxygen,
and the disengagement of Carbonic Acid, are the two chief external manifesta-
tions:—and that the degree of Caloric liberated bears  a close relation to  the
activity of these changes, either  in regard  to  the  body  at large, or tb any
portion of it.
   893.  The researches  of Dr. Edwards upon Animal Heat have brought to
light some very interesting  facts, regarding  the diversity which  exists  as to
the  power of generating  heat, in the  same species of animal, at different ages,
and at different periods of the year.

   a. It appears to be  a general fact, that the younger the animal, the less is its independent
calorifying power.  The development of the embryo  of oviparous animals is entirely de-
pendent upon the amount of  external warmth supplied to it; and there are many kinds of
Birds, which, at the time they issue from the egg, are so deficient  in tbe power of generating
heat, that their temperature rapidly falls, when they are removed from the nest and placed
in a cold atmosphere.  It was shown by collateral  experiments, that the loss of heat  was
not to be attributed to the absence  of feathers, nor to the extent of surface exposed in com-
parison with the  bulk of the body;  and that nothing but an absolute deficiency in the power
of generating  it,  would account for the fall of temperature.  This is quite conformable to
facts well ascertained in  regard to Mammalia.  The  fcetus, during intra-uterine life, has
little power of keeping up its own temperature; and in many cases it is much dependent
on external warmth, for some time after birth.  The degree of this dependence, however,
differs greatly in  the various  species of Mammalia, as among Birds: being less, in propor-
tion as the  general development  is advanced.   Thus, young Guinea pigs, which can  run
about and pick up food for themselves almost as soon as they are born, are  from the  first
independent of parental warmth;  whilst, on the  other hand, the young of Dogs, Cats, Rab-
bits,  &c, which are born blind, and which do not, for a fortnight  or more, acquire the same
development with the preceding, rapidly lose their heat when withdrawn from contact with
the body of the mother.
  b.  In the Human species  it is well known,  that external warmth is necessary for the
Infant; but the fact is too  often neglected (under the erroneous  idea of hardening the con-
stitution) during  the early years of childhood.   It is to be carefully remembered, that the
development of Man is slower than that of any other animal; and that  his  calorifying
power is closely  connected with  his general bodily vigour.   In  the case of children born
very prematurely, the greatest attention must be given to the sustenance of the heat of the
body (§ 932); and though  the  infant becomes more  independent of it as  development
advances, it is many years  before the standard can  be  maintained  without  assistance,
throughout the ordinary vicissitudes of  external temperature.   The  calorifying power,
which is fully possessed by adults,  decreases again in advanced age.  Old people complain
that their " blood  is chill;" and they suffer greatly from exposure  to cold, the temperature of
their whole body  being lowered by it.
  c. These facts  have a very interesting connection with the results of statistical inquiries,
as to the average  number of deaths at different seasons, recorded by M. Quetelet.-|-
  * It has been recently shown by Liebig, that the discrepancy between the actual amount
of heat generated, and  the amount which was calculated to have been  produced by the
union of Carbon and Hydrogen with Oxygen, to form the Carbonic Acid and Water exhaled,
in these experiments, may be nearly reconciled by adopting a more correct estimate of the
heat generated by combustion of given quantities of Carbon and Hydrogen respectively.  But
all these calculations proceed upon  the  supposition, that the  whole amount  of Oxygen ab-
sorbed, which is not exhaled as Carbonic acid, is exhaled in combination with Hydrogen, as
Water'- and thus no account is taken of other combustion-processes going on in the body, by
which'a greater amount of heat maybe generated, than by the  combustion of Hydrogen.
We have no means whatever of ascertaining how much of the watery vapour thrown off
by the lungs and skin is actually formed within the body, and how much is the mere super-
fluity  ofthe liquid ingested.
  t Essai de Physique Sociale, tom. i. p. 197. 
684
GENERAL REVIEW OF THE NUTRITIVE PROCESSES.
	First	2—3	8—12	25—30	50—65	90 Years
January	Month.	Years.	Years.	Years.	Years.	and above.
	1-39	1-22	1-08	1-05	1-30	1-58
February	1-28	1-13	1-06	1-04	122	1-48
March	1-21	1-30	1-27	1-11	111	1-25
April	1-02	1-27	1-34	1-06	1-02	0-96
May	0-93	1-12	1-21	1-02	0-93	0-84
June	0-83	094	099	1-02	0-85	0-75
July	0-78	0-82	0-88	0-91	0-77	0-64
August	0-79	073	0-82	0-96	0-85	0-66
September	0-86	076	0-81	0-95	089	0-76
October-	0-91	0-78	0-76	093	0-90	0-74
November	093	091	0-80	0-97	1-00	1-03
December	107	1-01	0-96	0-97	1-15	1-29 -------
We see from this table that, during the first  month of infant life, the external temperature
has a very marked  influence;  for the average mortality during each of the three summer
months being 80, that of January is nearly 140, and the average of February and March is
125.  This  is confirmed by the result obtained by MM. Villerme and  Milne-Edwards, in
their researches  on the mortality of the children conveyed to the Foundling Hospitals in
the different towns in France;  for they not only ascertained that the mortality is much the
greatest during the first three months in the year, but also that it varies in different parts of
the kingdom, according to the relative severity of the winter.  As childhood advances, how-
ever, the winter mortality diminishes, whilst that of the spring undergoes an increase;  this
is probably due  to the greater  prevalence of certain epidemics at the latter season; for the
same condition is observed, in  a still more  remarkable degree, between the ages of 8 and 12
years,—the time when children are most severely affected by such  epidemics.  As the con-
stitution acquires greater vigour, and the  bodily structure  attains its  full development, the
influence of the  season upon  mortality becomes less apparent; so that  at the age of from
25 to 30 years, the difference between the  summer and winter mortality is very slight. This
difference reappears, however, in a very marked degree, at  a later period, when the general
vigour, and the calorifying power, undergo a gradual  diminution.   Between the ages of 50
and 65  it is nearly as  great as in early infancy; and it gradually becomes more striking,
until, at the  age of 90 and upwards, the deaths in January  are 158, for every 64  in July (a
proportion of 2^ to  1); and the average of the three  winter months is  145, whilst that of
the three summer months is only 68, or less than one-half.

   894. Not only does the same individual possess different degrees of calori-
fying power, at different  periods of his life, but  also at different seasons of
the year.

  a. Dr. Edwards found that Sparrows, when exposed for  some time to a temperature of
32° during the summer, rapidly lost heat,  the refrigeration  during 3 hours being from  6 to
21 degrees;  but  that, when they were placed in the same circumstances during winter (after
having been accustomed to a warm temperature) the refrigeration was much less, not being
in any instance more than 2° in 3 hours.  . Although it would be  difficult to prove the  fact
experimentally in regard to Man, there can be little  doubt that he shares with the other
Mammalia in this variation.  It is well known that the general vigour of the system is less
in summer than  in winter;  in hot climates than in moderately cold.   Moreover, we  con-
tinually experience  the great discomforts of a  cold day in summer; when, our system not
being prepared for it, we can less readily maintain our temperature at its normal standard.
The practical inference,—that we should be much on our  guard against exposure  to  low
temperatures during summer,—is one of much importance; and  its value has  been fully
confirmed by experience.  The same principle may also be applied to  the  explanation of
the well-known fact, that those who have been long resident in warm climates feel the cold
acutely; whilst those who have been inured to cold are able to resist it much better, than
those who are exposed to it for the first time.   The former have a continued summer  con-
stitution; and their system not  being called upon by its external conditions to produce much
heat, the power  is after a time partially lost.  On  the other hand, those who live in  cold
climates have a perpetual winter  constitution (as it were) established; and  the  amount of
heat generated by them is much greater.  It will be obvious that this must be the case, if
Man's capability of living under the  greatest varieties of climate be sufficiently considered.
From Dr. E.'s experiments it appears, that every month makes an evident  difference  in the 
DEVELOPMENT OF HEAT.
685
seasonal degree; the heat lost by Sparrows in August being much less than that lost by
birds of the same species in July.

  895. Our knowledge of  the dependence of all the vital processes in warm-
blooded animals, upon  the Heat of their  bodies,—and of the dependence of
their  Calorifying power upon  the  due supply of material for the Chemical
changes which  generate Heat,—has lately received  some very  remarkable
additions from the experiments of M. Chossat.*  He  found that Birds, when
totally deprived  of food and drink, suffered a progressive, though  slight, daily
diminution of temperature.   This diminution was not so much shown by a
fall of their maximum heat, as by an increase in the diurnal variation, which
he ascertained to occur even in the  normal state.  The amount of this varia-
tion, in Birds properly supplied with  food, is about U°  Fahf. daily; the
maximum  being about noon, and  the  minimum at  midnight.   In the  in-
anitiated  state,  however,  the  average  variation was about  6°, gradually
increasing as the animal became weaker: moreover, the gradual  rise of tem-
perature, which should have taken  place between midnight and noon, was
retarded;  whilst the fall subsequently to noon commenced much  earlier than
in the healthy state;  so that the average of the whole day was  lowered by
 about 4.'° between the first and the penultimate days of this condition.   On
 the last day, the production of Heat diminished very rapidly, and the ther-
 mometer  fell from hour to hour, until death supervened; the whole loss on
 that  day  being  about 25°  Fahr.,  making the  total depression about 29§°.
 This depression appears, from the considerations to be presently  stated, to be
 the immediate cause of Death.—On examining the amount of loss sustained
 by the different organs of the body, it was found that 93 per cent, of the Fat
 had disappeared,—all, in fact, which could be removed;  whilst the Nervous
 Centres scarcely exhibited any  diminution in weight.   The loss  of weight of
 the whole body averaged about 40  per  cent.; and that of the various other
 component tissues was very much what might have been anticipated.  From
 the constant coincidence between the entire consumption of the Fat, and the
 depression of Temperature,—joined to the fact that the duration  of life under
 the inanitiating  process evidently varied (other things being equal) with the
 amount of Fat  previously  accumulated in the body,—the inference  seems
 irresistible, that  the Calorifying power depended chiefly, if not  entirely, on
 the materials  supplied  by this  substance.  The maintenance of the normal
 amount of matter in  the  Nervous  centres,  is  a  very  remarkable  fact; and
 seems to  countenance the idea,  that the substances peculiar to Nervous tissue
 may be  formed from Fatty matter, rather than from  a Proteine-compound
 (§  249).
   896. Whenever, therefore, the store of combustible  matter in the system was
 exhausted,—whether by the Respiratory process alone, or by this in conjunc-
 tion  with the conversion of Adipose matter into the materials for  the Nervous
 or other tissues,—the inanitiated animals died, by the cooling of their bodies
 consequent upon the loss of Calorifying  power.  That this is the real expla-
 nation of the fact, is shown by  the results of a series of very remarkable ex-
 periments performed  by M. Chossat, with a view of testing  the correctness
 of this view.   When inanitiated animals whose death seemed impending (in
 several instances death actually took place, whilst the  preliminary processes
 of weighing, the application of  the thermometer, &c, were being performed;,
 were subjected to artificial heat, they were almost uniformly restored  trom a
 state of insensibility and want of muscular power to a condition of compara-
 tive  activity; their temperature  rose, their muscular power returned, they tlew

   * Recherches Experimental sur llnanition, Paris, 1843.  See, also, the Brit, and For.
 Med. Rev. for April, 1844.
      58 
686           GENERAL REVIEW OF THE NUTRITIVE PROCESSES.
about the room and took food when it was presented to them ; and, if the ar-
tificial assistance was sufficiently prolonged, and they were not again subjected
to the starving process, most of them  recovered.   If they were  left to them-
selves too early, however, the digestive process was not performed, and they
ultimately died.   Up to the time when they began to take food,  their weight
continued to diminish; the secretions  being renewed, under the  influence  of
artificial  heat,  sometimes to a considerable amount.  It was not until Diges-
tion had  actually taken place (which, owing to the weakened functional power,
was commonly many hours subsequently to the ingestion of the  food), that
the animal regained  its  power of generating  heat; so that, if  the  external
source of heat was withdrawn, the body at once cooled:  and it was not until
the quantity-of food actually digested was sufficient to  support the wants  of
the body, that its independent power of  Calorification returned.  It is to be
remembered that, in such cases, the resources of the body are on the point  of
being completely exhausted, when the  attempt at re-animation is made; con-
sequently it has nothing whatever to fall back upon ; and the leaving it to itself
at any time until fresh resources have been  provided for it, is  consequently
as certain a cause of death, as  it would have been in the  first  instance.—It
can scarcely be  questioned, from the similarity of the phenomena, that Inani-
tion, with its consequent depression of temperature, is the immediate cause
of death  in various  Diseases of Exhaustion ; and it seems probable that there
are many cases, in  which the  depressing cause is of a temporary nature, and
in which a judicious and timely application of artificial  Heat might prolong
life until it has passed off,—just as artificial Respiration is serviceable in cases
of Narcotic Poisoning (§ 885).  It is  especially, perhaps, in those  forms  of
Febrile disease, in which no decided lesion can be discovered after death, that
this view has  the strongest claim to reception ; but many  other cases will
occur to  the intelligent Practitioner.*
   897. Having  thus considered the means, by which the degree of Heat ne-
cessary for the  performance of the functions of the Human system  is gene-
rated, we have to inquire how its temperature  is prevented from being raised
too high; in other words, what Frigorifying means there are, to counter-
balance the influence of causes, which in excess would otherwise be fatal, by
raising the heat of the body to an  undue degree.   How is  it,  for example,
that, when a  person enters a room whose  atmosphere  is heated to one  or
two hundred degrees above  his body, the latter does not partake of the eleva-
tion, even though exposed to the heat for some time ? Or, since the inhabitants
of a climate where the thermometer averages 100° for many weeks together,
are continually generating additional heat in their own  bodies,  how is it that
this does not accumulate, and raise them  to an undue elevation ?  The means
provided by Nature for cooling the body  when necessary, are of the simplest
possible  character.   From the whole of its soft moist surface, simple Evapo-
ration will take place  at all times, as from an inorganic body in  the same cir-
cumstances ; and the  amount of this will be  regulated merely by the condi-
tion of the atmosphere as to warmth and  dryness.   The more readily watery
vapour can be dissolved in atmospheric air, the more will be  lost from the

  * The beneficial result of the administration of Alcohol in such conditions, and the large
amount in which it may be given with impunity, may probably be accounted for on this
principle.  That it is a specific stimulus to the Nervous system, cannot  be doubted from its
effects on  the healthy body; but that it serves as a fuel to keep up the  Calorifying process,
appears equally certain.  Now its great efficacy in such cases seems to depend  upon  the
readiness  with which it will be taken into the Circulation, by a simple act of Endosmotic
Imbibition, when the special Absorbent process dependent upon the peculiar powers of  the
cells of the villi  (§ 181), is in abeyance.  There is no other combustible fluid, whose density,
relatively  to that of the Blood, will permit of its rapid Absorption by the ^simple physical
process adverted to. 
OF REPRODUCTION.
687
surface of the body in this manner.   In cold weather, very little is thus carried
off, even though  the  air be  dry : and a  warm atmosphere, already charged
with dampness, will be nearly as ineffectual.   But simple evaporation is not
the chief  means  by which the  temperature of the body is regulated.  The
Skin, as already mentioned (§ 868), contains a large number of glandulae, the
office of which is to secrete an aqueous fluid;  and the amount of this Exha-
lation appears to  depend solely or  chiefly upon  the temperature of the sur-
rounding air.   Thus, when  the external heat is very great, a considerable
amount of fluid is transuded from the skin; and this, in evaporating, converts
into latent  heat a large quantity of the free  caloric, which would  otherwise
raise the temperature of the body.  If the atmosphere be hot and dry, and
also be in  motion, both Exhalation and Evaporation go on  with great rapidity.
If it be cold, both are  checked,—the  former almost entirely so; but if it be
dry, some evaporation still continues.  On the other hand, in a hot atmosphere,
saturated with moisture, Exhalation continues, though Evaporation is almost
entirely checked; and the fluid poured out by the exhalant glands accumulates
on the skin.   There  is reason to believe that the secretion continues, even
when the  body is immersed in  water, provided its temperature be high.—We
learn from these facts the great importance of not suddenly checking Exhala-
tion, by exposure of the surface to cold,  when the secretion is being actively
performed ; since a great disturbance of the circulation  will be likely to ensue,
similar  to  that which has been already mentioned, as occurring when  other
important secretions are suddenly suspended.
CHAPTER  XVII,
OF REPRODUCTION.
                 1.—General Character of the Function.

  898. The  Function of Reproduction  has been  commonly regarded as so
entirely different in character from  the ordinary Nutritive  processes, that no
analogy can be drawn between them.  The results of late inquiries, however,
leave no doubt that the difference between them is extremely small,—having,
in fact, a relation rather to the object of the action, than to the mode in which
it is performed.  In  the  ordinary function  of Nutrition,  there is a  continual
regeneration or reproduction of the tissues  and organs of the body;  but the
new parts  are destined still to constitute the same whole.   On the other hand,
in Reproduction, the newly-formed parts  are destined from the first to be cast
off from the parent structure, and to become new individuals.  Still, their ori-
gin is essentially the same  in both instances ; as appears  from  the mode in
which the multiplication of the lower Plants and Animals takes place.  Thus
in the  simplest Cryptogamia, such as the Yeast Fungus,* every single cell
may be regarded as a distinct individual; since it is capable of living by itself,
and of generating new cells; and thus the production  of a new cell, in con-
nection with the original one, may be regarded as alike  an act  of  Nutrition
and of Reproduction. So again, in the Hydra  and  other Polypes, the remark-
able power of reparation which is  manifested in  their  Nutritive operations,

           *  See Principles of General and Comparative Physiology, § 98. 
688                         OF REPRODUCTION.

may be employed in generating new individuals ;  since, when the body is
divided into numerous parts, each  one of  these has the power of developing
all the rest of  the structure, and thus  of becoming  a  complete animal (§ 9).
Still we find in most Plants, and in all Animals, some portion of the structure
specially designed to form and to set free germs, which are destined to become
new individuals ;  and it is in the liberation and development of these, that the
function of Reproduction essentially consists.
  899.  In Plants it is  very evident that  these  germs  differ but  little  from
those which elsewhere  produce new  cells (§ 122) ; and that the first aspect
of the new being is neither more nor  less than a single cell, in which all the
other cells of  the structure subsequently originate.  In the Cryptogamia, the
cell-germs are  contained in what is termed the spore;  and, when liberated
from the parent, they are developed into  cells without any further assistance
than that which they  derive from the  air,  moisture, Sic, that surround them.
In Flowering Plants,  on the other hand, the  cell-germs are conveyed into a
new set of organs, in which they are  supplied with nutriment previously ela-
borated for them by the parent; and, in this manner, they are enabled to attain
an ultimate development which is much higher than that of the Cryptogamia.
It is now well established, that the pollen-grain of Phanerogamia is analogous
to the spore of Cryptogamia; since it contains the reproductive granules, which
are the germs  of the first cells of the new individual.  When the pollen-grains
are cast upon the stigmatic surface, they project one or more long tubes, which
insinuate themselves down the  soft loose tissue of the style, and reach  the
ovarium.  Into these  tubes, the granules which  the pollen-grain contained are
seen to pass;  and they are  thus conveyed  into the  ovules, the foramina of
which are penetrated by the  extremities of the pollen-tubes.  The ovules
previously contained  nothing but  starchy matter; but from the time that the
pollen-tubes have thus  implanted (as it were) their contents in their cavity,
they may be considered as fecundated. The subsequent growth of the embryo
from  the  first-formed cells, takes  place according  to  the principles already
stated, under the  head of Nutrition;  and thus it is seen, that the mysterious
process of Reproduction evidently consists, in  Flowering Plants,  of nothing
else than the implantation of a cell-germ  prepared by the male organs,  in a
nidus or receptacle adapted to aid its  early development, which nidus consti-
tutes the essential part of the female system.
  900.  There is  now good  reason to believe that, in no Animals, is the Re-
productive apparatus  less  simple than it is in the  higher Plants ;—that is to
say, in every instance, two sets of organs, a germ-preparing, and a germ-
nourishing, are present.  These organs differ much  in form and complexity
of structure in the various tribes of Animals ; but their  essential function is
the same in all.  Those which are termed Male  organs prepare and set free
certain bodies, which, having an  inherent power of  motion, have been  sup-
posed to be independent Animalcules, and have been termed Spermatozoa;
there is but little reason,, however, to  regard  them in  this light, since ciliated
epithelium-cells may  exhibit as much  activity;  and there is no evidence that
their function  is any higher than that  ofthe pollen-tube of Plants, which con-
veys into the ovulum the germs of the first cells of the embryo. This view of
the character of the Spermatozoa  rests  alike upon the nature of  their move-
ments, and the mode  of their production.*  Dr. Barry's observations on the
history of the Ovum, and on the nature of the act of Fecundation (which will
be presently given in  some  detail) have left scarcely any doubt, that this act
consists  in the introduction of some new element into the Ovule, through the
medium of the Spermatozoa; the arrival of which at the surface of the ovary

           * See Principles of General and Comparative Physiology, § 606. 
ACTION OF THE MALE.
689
had been more than once previously seen, and the penetration of which to the
Ovum there was good reason to suspect:  and these have been confirmed by
the observations of Dr. A. Farre on the Ovum of the Earth-worm, which he
has distinctly seen to be penetrated by Spermatozoa.   The act of Fecunda-
tion is evidently analogous, therefore, in Animals, to the process which has
been  described  as  taking  place in the Flowering Plants.  In many of the
lower tribes of Animals, the spermatic fluid  effused by an individual of one
sex, comes into direct contact with the ova previously deposited by the other;
but in all the higher tribes, as in Man, the act of fecundation is performed be-
fore, or shortly after the ova quit the ovarium.   With these general views, we
shall now be prepared to consider the share which each sex has in the Function
of Reproduction.

                          2.  Action ofthe Male.

   901.  The Spermatic  fluid secreted by the Testes of the Male (§ 867), differs
from  all other secretions, in containing a large number of very minute bodies,
only discernible with  a high power of the Microscope ; and these, in ordinary
cases, remain in active motion for  some time after they have quitted the living
body.  The  Human Spermatozoon (of which representations are  given in
Plate I., Fig. 18), consists of  a little oval flattened body from the l-600th to
the l-800th of a line in length, from which proceeds a long filiform tail gradu-
ally tapering to the  finest point, of l-50th or at most l-40th of a line in length.
The whole is perfectly  transparent; and nothing  that can be termed structure
can be satisfactorily distinguished within it.*   The movements are principally
executed by the tail, which has a kind of vibratile undulating motion.  They
may continue for many hours  after the emission of the fluid ; and they are not
checked  by its  admixture with other  secretions, such as the  urine  and  the
prostatic fluid.   Thus, in cases of nocturnal emission, the Spermatozoa may
not unfrequently be found actively moving through the urine in the morning;
and those contained in the seminal fluid collected from females that have just
copulated, are frequently found to live many days.   Their presence may be
readily detected by a Microscope  of sufficient power, even when they have
long ceased to move,  and are  broken into fragments; and the Physician and
the Medical Jurist will frequently derive much assistance  from  an  examination
of this kind.   Thus, cases are of no uncommon occurrence, especially among\
those who have been too much addicted to sexual  indulgence, in which seminal
emissions take  place unconsciously and frequently, and produce great general
derangement of  the health; and the true  nature  of the complaint is obscure, ,■
until the fact has been detected by ocular examination.   Again, in charges of
rape,  in which  evidence of actual  emission is required, a microscopic exami-
nation of the stiffened spots left on the linen will seldom fail in obtaining proof,
if the act have  been completed: in such cases, however, we must not expect
to meet with more than  fragments of Spermatozoa; but these are so unlike
anything else, that little doubt need be entertained regarding them.   It has
been proposed to employ the same test, in juridical inquiries respecting doubt-
ful cases of death by suspension: seminal emissions being  not unfrequent
results of this kind of violence:  but there are many obvious objections which
should prevent  much  confidence being placed in it.t

  * It  has been asserted that distinct oral and anal orifices, with appearances of internal
organs, have been seen in the Spermatozoa of certain  Mammalia; but these observations
have not been confirmed; and  they are not borne out by the attentive examination of the
larger Spermatozoa of other animals.
  -j- See the Author's  Article "Asphyxia," in the Library of Practical Medicine, and the
authorities there referred to.
                                   58* 
690
OF REPRODUCTION.
   902. The mode of Evolution of Spermatozoa, which has been recently
discovered by Wagner, is so different from the  ordinary method of produc-
tion amongst Animalcules, as of itself to indicate that  the former  cannot be
referred to the same category with the latter.   It may be best studied in those
animals which  only have a periodical fertility; and the Passerine Birds are
among the most convenient subjects for the purpose.   During the winter, the
testes are small  and almost  bloodless, and no trace of Spermatozoa can be
detected within  them; on the return of spring, however, they undergo great
enlargement and become almost gorged with blood, and  the gradual steps of
the evolution of the Spermatozoa may be easily  observed.   The fluid drawn
from them is first seen to contain a number of granular corpuscles, resembling
those known as the Seminal Granules in the human semen (delineated at a,
Fig. 18, Plate I.);  and in a  short  time  there  are seen, in  addition to  these,
numerous rounded transparent vesicles, at first having but one nucleus, and
afterwards presenting   several.   These nuclei bear a close resemblance to the
granular corpuscles just mentioned; and it is probable that the former are to
be  regarded  as  cytoblasts, from which  the Spermatoferous cells (shown, as
existing in the human semen, in Fig. 19, Plate I.) are  evolved.   The nuclei
seem afterwards to resolve themselves into a fine granular matter, which is
diffused through the whole vesicle or " cyst of evolution;" and in this, a linear
arrangement soon becomes  perceptible.   The lines become more  and more
distinct, and are at last seen  to be evidently produced  by the arrangement of
the Spermatozoa, which lie side by side within the vesicle;  and the form of
this changes from a  sphere to a long oval.   After a time  they break  forth,
but still adhere to each other for a short period, forming bundles, such as may
often be  met with  in  the human  semen, when taken directly from the testis
(Fig. 20, Plate I.).*  That the Spermatozoa are  the essential elements ofthe
spermatic fluid, has been reasonably inferred from several circumstances, such
as their absence or imperfect development in hybrid animals, which are nearly
or entirely sterile:  and the  fact that Fecundation essentially consists in the
direct communication  of one of them with a certain point in the  Ovum, ap-
pears too well established to admit of further  doubt.   Regarding the uses of
the other constituents  of the Semen, no sufficient  account can be given.
  903. The power of procreation does not usually exist in  the Human Male,
until the age of from  14 to 16 years;  and it may be considered probable that
no  Spermatozoa are produced until that period, although a fluid is  secreted by
the testes.   At this epoch, which is ordinarily designated  as that of Puberty, a
considerable change takes place in the bodily constitution:  the sexual organs
undergo a much-increased development; various parts of the surface, especially
the chin and the pubes, become  covered with hair; the larynx enlarges, and
the voice becomes lower in pitch, as well as rougher and  more powerful; and
new feelings and desires are awakened in the mind.  Instances, however, are
by  no means rare, in which these changes  take place at  a  much earlier
period; the full development of the generative organs, with  manifestations of
the sexual passion, having been  observed in children of but a few years old.
The procreative power may last, if not abused, during a  very  prolonged
period.  Undoubted instances of virility at the age  of more than 100 years
are on record; but in  these cases, the general bodily vigour  was preserved in
a very remarkable degree.  The ordinary  rule seems to be, that sexual power
is not retained by the  male in any considerable degree, after  the age of 60 or
65  years.  To the  use of the sexual  organs for  the continuance of his  race,

  * For a fuller account, with illustrations, of the  development of the Spermatozoa, and its
analogy with the formation of other tissues, see  Princ. of Gen. and  Comp. Phys., §§ 430
and 607. 
ACTION OF THE MALE.
691
Man is prompted by a powerful Instinctive desire, which he shares with the
lower animals.   This  Instinct, like the others  formerly alluded to (§428—
430), is excited by sensations;  and these  may either  originate  in the sexual
organs themselves, or may be excited through the organs of special sensation.
Thus in Man it is most powerfully aroused by impressions conveyed through
the sight or the touch: in many other animals, the auditory and olfactive organs
communicate impressions which  have  an  equal  power; and it  is not impro-
bable that, in certain morbidly-excited states of  feeling, the same may be the
case in ourselves.  That local impressions have also a very powerful effect in
exciting sexual desire,  must have  been  within the experience of almost every
one;  the fact is most remarkable, however, in cases of Satyriasis, which dis-
ease is generally found to be connected with some obvious cause of irritation
ofthe generative system, such as pruritus,  active congestion, &c.   That some
part of the  Encephalon is the seat of this  as of  other  instinctive propensities,
appears from the considerations formerly  adduced; but that  the Cerebellum
is the part  in which this function is specially located, cannot be regarded as
by any means sufficiently proved (§§ 466—470).   The instinct, when  once
aroused (even though very obscurely felt),  acts upon  the mental faculties and
moral feelings; and thus becomes the source,  though almost unconsciously so
to the individual, ofthe tendency to form that kind of  attachment towards one
of the opposite sex, which is known as love.  This  tendency cannot be re-
garded as a simple passion or emotion, since it is the  result  of the combined
operations of the reason, the imagination, and the moral feelings; and it is in
the engraftment  (so to  speak)  of the  psychical  attachment, upon  the mere
corporeal instinct, that  a difference exists between the  sexual relations of Man
and those of the lower animals.  In proportion  as the Human  being makes
the temporary gratification of the mere sexual appetite his chief object, and
overlooks the happiness arising from spiritual communion, which is not only
purer but more  permanent, and of which a  renewal  may be anticipated in
another world,—does he degrade himself to the  level of the brutes that perish.
Yet how lamentably frequent is this degradation!
   904.  When impelled by sexual excitement, the Male seeks intercourse with
the Female, the erectile tissue of the genital organs becomes turgid with blood
(§ 748), and the  surface acquires a much-increased sensibility ; this is espe-
cially acute in the Glans penis.  By the friction of the Glans against the rugous
walls of the Vagina, the excitement is increased; and the  impression which
is thus produced at last  becomes  so  strong, that  it  produces, through the
medium of the  Spinal Cord, a reflex  contraction of the muscles which  sur-
round  the  Vesiculae Seminales (§ 393).  These receptacles discharge their
contents (partly consisting of semen and partly of a secretion of their own)
into the Urethra; and  from this they are expelled with some degree of force,
and with a  kind  of convulsive action, by its own Compressor muscles.  Now
although the sensations concerned in this act are ordinarily most acutely plea-
surable, there appears sufficient evidence that they are by no means essential to
its performance; and that the impression which is conveyed to the Spinal Cord
need not give rise to a sensation, in order  to produce the reflex contraction of
the Ejaculator  muscles (§ 372).    The high degree  of nervous excitement
which the act of coition involves, produces a subsequent depression of corre-
sponding amount; and the too frequent repetition of it is productive of conse-
quences very injurious  to the general health.  This is still more the case with
the solitary indulgence, which  (it is to be feared) is  practised  by too many
youths; for this, substituting an unnatural degree of one kind of excitement,
for that which is wanting in  another, cannot  but be  still more trying to the
bodily powers.   The secretion of seminal fluid  being, like other secretions,
very much under the control ofthe nervous system, will be increased by the 
692
OF REPRODUCTION.
 continual direction of the mind towards objects which awaken the sexual pro-
 pensity (§ 626, note); and thus, if intercourse be very frequent, a much larger
 quantity will altogether be produced, although the  amount emitted  at each
 period will be less.   The formation of the secretion seems of itself to be a
 much greater tax upon  the corporeal powers, than might have been supposed
 a priori: and it is a well-known fact, that the highest degree of bodily vigour
 is inconsistent with  more than a very moderate indulgence  in  sexual inter-
 course ; whilst nothing is more  certain to reduce the powers, both of body
 and mind, than excess in this respect.   These principles, which are of great
 importance in the regulation of the health, are but results of  the general law,
 which prevails equally in  the  Vegetable and  Animal  kingdoms,—that  the
 Development of the Individual, and the  Reproduction of the Species, stand
 in an inverse ratio to each other.

                        3.—Action of the Female.

   905. The essential part of the Female Generative system is that in which
 the  Ova are prepared;  the other organs are merely accessory, and are not to
 be found in a large proportion of  the Animal kingdom.  In many of the lower
 animals, the Ovaria  and Testes are so extremely like each other, that the  dif-
 ference between them can scarcely be distinguisbed ; and the  same has already
 been stated, regarding the condition of these organs in Man, at an early period
 of development (§ 866 b).  The fact is one of no small interest.  In tbe lower
 animals, the Ovarium consists of a loose tissue containing  many cells, in which
 the  Ova are formed, and from which they escape by the rupture of the cell-
 walls ; in the higher animals, as in the Human female, the tissue of the Ova-
 rium  is more compact, forming what is known as the stroma; and the Ova,
 except when they are approaching maturity, can only be distinguished in the
 interstices of this, by the aid of  a high magnifying power.   We owe  to  Dr.
 Barry the discovery of the  earliest stages in the production  of the Ovum and
 its accessory parts,  in Mammalia and other Vertebrata.  In order to under-
 stand his account, however, it will be necessary that the parts of which the
 ovum consists should be previously understood.—Taking the Fowl's Egg as a
 familiar illustration, it  must be remarked, in the first place, that neither the
 albumen which forms the white, nor the  shell-membrane with its testaceous
 covering, exist in  the Ovarian Ovum ;  these  portions being added during its
 passage along the oviduct. ]  The parts which  we have to  analyze, are  the
1 Yolk-membrane and its contents.  Within the Yolk-membrane, we find in the
 first place,  the Yolk itself; a substance consisting in part of albuminous gran-
■ ules, and in part of  oily globules.  Towards  the centre, the character of the
; Yolk in some degree changes; its colour being lighter, and the granules pre-
 senting more the appearance of cells, with minuter globules  in  their interior.
 The central portion  is termed the discus vitellinus.  Occupying the centre of
 the  yolk (in the immature ovulum) is a large cell, very distinct in aspect from
 the  rest, and having a well-marked nucleus upon its walls.  This is termed
 the  germinal vesicle; and the nucleus, the germinal spot.—The Mammalian
 Ovum contains exactly the  same parts; but the yolk is much smaller in pro-
 portion, and  corresponds in character rather with the discus vitellinus, than
 with the whole yolk of the  Bird's egg.  The Ovum in all Vertebrated animals
 is produced within  a capsule or  bag, the  exterior of which  is in contact with
 the  stroma  ofthe  ovarium ; this has been termed in  Mammalia, the Graafian
follicle, after the  name of its first discoverer; but the more general  and ap-
 propriate designation of Ovisac has been  given  to it by Dr. Barry, who  has
 shown that it exists in  other classes of Vertebrata.   Between the  Ovum  and
 the  Ovisac, in Oviparous animals, there is scarcely any interval; but in the 
ACTION OF THE FEMALE.                      6D3
Mammalia, a large amount of granular matter is present;  and this arranges
itself into some peculiar structures discovered by  Dr. Barry, and presently to
be described.   The membrane which surrounds the yolk  in Mammalia  has
received, on account of its thickness and peculiar transparency, the designation
of zona pellucida.—The several parts of the Ovum now described are shown
in Fig. 5, Plate I.
   906.  From  the researches  of Dr.  Barry on the early development of the
Ovum, it appears that the  Germinal  Vesicle is  the  part which can first be
distinctly traced.   In Fig.  1 (Plate I.) is seen  a representation of one of its
incipient stages in the Rabbit; there is nothing here visible, but a collection
of very transparent vesicles, surrounded by a mass of dark  granules.   In the
succeeding stage, represented  in Fig. 2, some of the vesicles  have  enlarged,
and the  granules immediately surrounding them have become developed into
cells.   A more advanced condition is  represented (on a smaller scale) in Fig.
3; in which a distinct spot  (b)  is seen on the central vesicle (a), marking it as
the Germinal Vesicle; whilst  many of the granules surrounding it  have be-
come  cells, and have taken-on a very regular  arrangement.   After a time, a
membrane forms around each cluster of granules, separating  it  from the stroma
of the ovarium ; this is the  Ovisac.  At a later period, a separation takes place
between the inner and outer portions  of the mass of granular matter, included
between the ovisac and the germinal vesicle ; and the separation is completed
by the development of a  membrane, which envelopes the inner stratum. This
stratum becomes the Yolk, and includes most of the oil-particles which pre-
viously existed within the  ovisac; whilst  the  portion of the granular mass,
exterior to  this, gives origin in Mammalia to certain structures  of a very pe-
culiar character, which seem  to be concerned in the  liberation of the ovum
from the Graafian follicle or Ovisac.   The appearance of the Human Ovisac
and its  contents  is seen in Fig. 4.  The granules immediately surrounding
the Ovum  assume the appearance  of  cells;  and these unite to form a sort of
membrane, to  which the name of tunica granulosa has been  given.   This is
seen at t g (Fig. 7).  The granules lining the Ovisac also  combine themselves
into a membranous structure; to which Dr. Barry has given the designation
of membrana granulosa (g g, Fig. 6).  These are connected by four band-
like extensions of the same cellulo-membranous structure, which seem to  sus-
pend  the ovum in its place; and these are called retinacula (r r, Figs. 6 and
7). The space between  the Tunica Granulosa and the Membrana Granulosa,
which  is not occupied by the  Retinacula, is filled with fluid,  in which few or
no cells can be seen.   The uses of this structure, so far as  they are apparent,
will be described, when the processes by which the Ovum escapes from the
Ovary  are  detailed.
   907. The Ovisac does not form the entire structure which has been described
as the Graafian  follicle; for this consists of two layers, of which the inner
one is the true  Ovisac, whilst  the outer results from a thickening and conden-
sation of the surrounding layer of the Stroma of the Ovarium.  It is the outer
layer  only which is vascular; the inner presents no trace of structure;  and
the increase of the ovum must take place by simple imbibition, through it, of
the supply of nutritive matter brought into contact with its  exterior.  The
Ovarium may be seen, even in the ftetal animal, to contain  immature Ova; in
which  the  several parts can be clearly distinguished.   At a later period, how-
ever, the number of Ova greatly increases ;  and the development of some ad-
vances, whilst  others degenerate.   According to  the recent valuable inquiries
of Dr. Ritchie,* it appears that, even during the period  of childhood, there is a
continual rupture of Ovisacs, and discharge of Ova, at the surface of the
* London Medical Gazette, 1844. 
694
OF REPRODUCTION.
Ovarium.  The  Ovaria are studded with numerous minute copper-coloured
maculae; and their surface presents delicate vesicular elevations, which  are
occasioned by the most matured ovisacs : the dehiscence of these takes place
by minute punctiform openings  in the peritoneal coat; and no cicatrix is  left.
At the  period of puberty, the stroma ofthe ovarium is  crowded with Ovisacs;
which  are still so minute,  that in the Ox (according to Dr. Barry's computa-
tion) a cubic inch would contain 200 millions of them.  The greatest advance
is seen in those which are situated  nearest  the  surface of the Ovarium;  and
in these, the  Graafian follicle with its two coats, may be distinctly traced.  It
is curious that the outer wall (which is itself a  part of the condensed stroma
of  the  ovarium) should  contain  an  immense  number  of minute ovisacs; so
that this, in  the  adult animal, is the most convenient situation in which to
view them: these ovisacs have been termed  by Dr. Barry " parasitic ovisacs."
In those animals  whose aptitude for conception  is periodical, the development
of the  Ova, to  such  a degree that  they become  prepared for fecundation,, is
periodical also.   This development becomes evident, when the parts are  ex-
amined in  an animal which is  " in heat,"  by the projection of the Graafian
follicles from the surface;  and it consists not merely in an increase of size,
but in certain internal changes presently to  be described.
   908. In  the  Human female, the period of Puberty, or of commencing apti-
tude for procreation, is usually between the 13th and 16th  year; it is earlier
in warm climates  than in cold;* and in densely-populated manufacturing towns,
than  in thinly  peopled  agricultural  districts.   The mental and  bodily habits
of  the  individual have  also a  considerable influence  upon  the time of its
occurrence ;  girls brought  up in  the midst of luxury or sensual indulgence,
undergoing this change earlier than  those reared in hardihood  and self-denial.
The changes in which Puberty  consists,  are for the most part  connected with
the Reproductive system.   The  external  and  internal  organs of generation

  [*It has been stated, by almost all physiological writers, that women reach maturity, and
that menstruation commences much earlier in  hot climates, particularly between the tropics,
than in temperate and very cold countries. Haller states that in the warm regions of Asia,
the catamenia appear from the 8th to the 10th year; and in Switzerland,  Britain, and other
temperate regions, at the age of 12 or 13, and  later the farther we ascend  towards the north.
The same view has been held by nearly all subsequent writers on the subject, and they infer
that animals, like plants, reach maturity sooner in hot than in cold climates. Dewees says
that menstruation occurs  later  in our northern than in our southern states.   From many
elaborate and interesting  papers which have  been published within a few years, especially
from those of Mr.  Roberton of Manchester, it would seem that the natural period of puberty
in women occurs in a much more extended range of ages, and  is much  more  equally dis-
tributed through that range than others have alleged, and that, in other countries, the parallel
between plants and  fruits does not hold good.
  At Gottingen, Osiander  ascertained  the ages at which 137 women began to menstruate.
In 21 of these the catamenia appeared at 14;  in 32 at 15; in 24 at 16; 9 at 12;  and  1 not
before the 24th year.  The Indian girls in Canada, and  in our north-western states and ter-
ritories, begin to menstruate  frequently at 12, 13 and 14.  From the statement of Baron
Humboldt, the same is equally true of the Korriacs, and the tribes of northern Asia, where
girls of 10 years are sometimes found mothers.  The notion that women  in Lapland do not
menstruate till  20, and then  only during summer, is founded on a mistake in Linnseus's
Flora Lapponica.  Tooke states that the Sclavonian, or native Russians, reach puberty at an
early age;  and  Dr. Robert Lee, who was in the Crimea,  and all the Russian provinces along
the Black Sea, and in the Ukraine, and whose opportunities of observation were extensive,
says that his conviction is, that over the whole south of Russia the period of puberty is the
same as in Great Britain; and  that women cease to bear children at the same age.  The
same would appear to hold good in Java, and in all the islands of the Indian Archipelago, and
in Sierra Leone;  and the difference  said  to exist in Arabia in  this respect is due to the
early marriages, and universal licentiousness  and depravity of morals in that country.  It
would appear from observations made in the' West  India Islands, that menstruation occurs
there about the same period, and that the alleged difference in this respect between the
negress and the white female does not exist.—M. C] 
ACTION OF THE FEMALE.
695
 undergo a considerable increase of size ;  the mammary glands enlarge ; and a
 deposition of fat takes place in the mammae and on the pubes, as well as over
 the whole surface of  the body,—giving to the person that roundness and ful-
 ness, which are so attractive to the opposite sex, at the period of commencing
 Womanhood.   The first appearance of the Catamenia usually occurs whilst
 these changes  are  in progress, and is a decided indication of the arrival of the
 period of Puberty; but it is  not unfrequently delayed much longer; and its
 absence is by  no  means to be  regarded as a proof of the want of aptitude  for
 procreation, since  many women have borne large families, without having ever
 menstruated.  The Catamenial discharge  appears normally to consist of blood
 deprived of its fibrine; the fluid being composed of serum, in which red cor-
 puscles are  suspended, and being readily distinguishable from true blood  by
 its want of power to clot.  When clots are found in it, therefore, a morbid
 condition of the secreting surface must be inferred.   The interval which usu-
 ally elapses between the successive appearances ofthe secretion, is about four
 weeks; and the duration of the flow is from three to six days.  There  is,
 however, great variety in this  respect  among the inhabitants of different cli-
 mates, and among individuals;  in general, the appearance is more frequent,
 and the duration of the flow greater, among the  residents in warm countries,
 and among individuals of luxurious habits and relaxed frame, than among the
 inhabitants of  colder climes, or among individuals inured  to bodily exertion.
 The first appearance of the discharge is usually preceded and accompanied  by
 considerable general disturbance of the system; especially pain  in the loins
 and a sense of fatigue in the  lower extremities; and its periodical return is
 usually attended with the  same  symptoms, which are more or less severe  in
 different individuals.
  909.  Much  discussion has taken place respecting the causes  and purposes
 of the Menstrual  flow; and  recent inquiries have thrown much light upon
 them.   The state of  the Female Generative  system, during its continuance,
 appears to be analogous to the heat  of  the  lower animals; many of which
 have  a  sero-sanguinolent  discharge at that period.   There is good reason to
 believe  that in Women the sexual feeling becomes stronger at that epoch;
 and it is quite certain that there is a greater aptitude for Conception, imme-
 diately before'and  after Menstruation, than there is at any intermediate period.
 Observations to this effect were made  by  Hippocrates, and were confirmed  by
 Boerhaave and Haller; indeed coitus  immediately after menstruation appears
 to have  been  frequently recommended as a  cure  for sterility, and to have
 proved successful.  It is well known that, among many of the lower animals,
 the Ova are entirely  extruded by the Female, before the  Spermatic fluid of
 the Male reaches  them ; and that even in Birds,  this occasionally takes place.
 This  question has been recently made the subject of special inquiry by M.
 Raciborski;  who  affirms  that tbe exceptions to the  rule—that Conception
 occurs immediately before  or  after, or during, Menstruation—are not more
 than 6 or 7 per cent.  Indeed,  in his latest work  on this subject,* he gives the
 details of 15 cases, in which the date of Conception could be accurately fixed,
 and the time of the last appearance of the Catamenia was also known ; and in
 all  but one  of them,  the correspondence between the two periods was very
 close.   Even  in  the  exceptional case, the  Catamenia made their appearance
 shortly after the Coitus ; which took place at about the middle of the interval
between the two regular periods.  When Conception occurs immediately be-
fore the Menstrual period, the  Catamenia sometimes appear, and sometimes
are  absent; if they appear, their duration is generally less  than usual.   The
fact that Conception often takes place immediately before the last appearance
* Sur la Ponte des Mammiferes.  Paris, 1844. 
696
OF REPRODUCTION.
of the Catamenia (and not after it, as commonly imagined), is one well known
to practical men.   Numerous  cases  have been collected by Mr. Girdwood,
Dr. Robert Lee, MM. Gendrin, Negrier, Raciborski, and others, in which the
Menstrual period was evidently connected with the maturation and  discharge
of Ova; but the most complete observations yet made upon this subject, are
those of Dr. Ritchie (loc. cit.)   He states that about the period of Puberty a
marked change usually takes place in the mode in which the Ovisacs discharge
their contents ; but that this change does not necessarily occur simultaneously
with the first appearance of the Catamenia; as in some cases the conditions,
which obtain in the period before puberty, are extended into that of menstrua-
tion.  The Ovaries now receive a much larger supply of blood; and the Ovi-
sacs show a great increase in bulk and vascularity ; so that, when they appear
at the surface of the ovary, they  present themselves  as pisiform turgid eleva-
tions ; and the discharge of their contents leaves a much larger cicatrix, and
is accompanied by an effusion of blood into their cavity, with other subsequent
changes, to be presently described.  It would appear, however, that although
such a discharge takes place most frequently at the Menstrual period, yet that
the two occurrences are not necessarily co-existent;  for menstruation may
take place  without any such rupture; whilst, on the other hand, the  matura-
tion and discharge  of mature ova may occur in the intervals of Menstruation,
and even  at  periods of life when that  function is not taking place.  The
essential condition of  Menstruation  itself  would appear to be  tbe increased
turgescence of the vessels of  the Uterus ; and the  appearance,  on its internal
surface, of a  meshwork of deciduous  villous vessels, which may remain for at
least two weeks.   It is evident that  this is a preparation for tbe formation of
the Decidua (§ 919).
   910. The duration of the period of  aptitude for procreation, as marked by
the persistence of the  Catamenia, is more limited in Women  than  in Men;
usually terminating at about the 45th year; it is sometimes prolonged, how-
ever, for ten or even fifteen years longer; but cases are rare in  which women
above 50 years of  age  have borne children.   There is usually no Menstrual
flow during Pregnancy and Lactation ; in fact, the cessation of the Catamenia
is generally one of the  first signs, indicating that Conception has taken place.
But it  is by no  means uncommon for them  to appear once or twice subse-
quently to Conception; and in some women, there  is a regular monthly dis-
charge, though probably not of the usual secretion, through the whole period.
Some very  anomalous  cases  are  recorded,  in  which the Catamenia never
appeared at  any other  time than during Pregnancy ; and  were then regular.
The  absence of the Catamenia during  Lactation is by no means  constant,
especially  if the  period be prolonged;  when  the Menstrual discharge recurs,
it may  be considered as indicating an aptitude for Conception;  and it is well
known that, although   Pregnancy seldom recurs during  the  continuance of
Lactation, the  rule is by no means invariable.
   911. The function of the Female,  during the coitus, is entirely of a passive
character.   When the  sexual feeling is strongly excited, there  is a considera-
ble degree of turgescence in  the erectile tissue surrounding  the vagina, and
composing the greater  part of the nymphae and the clitoris ; and there is also
an increased secretion from the mucous follicles.*   But these changes are by

   [* The glands of Duverney have been lately (1840) very •accurately described by Profes-
sor Tiedemann, his attention having been directed to  these organs by the late Dr. Fricke, of
Hamburg.   These glands are situated at either side of the entrance of the vagina, beneath
the integument covering the inferior part of the vagina, as well as the superficial perineal
fascia, and the constrictor vaginss muscle.  The space they occupy lies between the lower
end of the vagina, the ascending ramus of the ischium, the crus clitoridis, and the erector
clitoridis muscle.  Superiorly are the  fibres of the  levator ani which are attached to the 
ACTION OF THE FEMALE.
697
no means  necessary for effectual coition; since it is a fact well  established,
that fruitful intercourse may take place, when  the female is in a state of nar-
cotism, of somnambulism, or even of profound ordinary sleep.   It  has been
supposed by some, that the os uteri dilates, by a kind of reflex action, to re-
ceive the semen; but  of this  there is  no  evidence.  The introduction of a
small quantity of the  fluid just within  the  Vagina, appears to  be all  that is
absolutely necessary for conception;  for there are many cases  on record, in
which pregnancy has occurred, in spite of the closure of the  entrance to the
vagina  by a strong membrane, in which but  a  very small aperture  existed.
That the Spermatozoa make their way towards  the Ovarium,  and fecundate
the Ovum either before it entirely quits the Ovisac or very shortly afterwards,
appears to be the general rule in  regard to the Mammalia;  and the question
naturally arises,—by  what means do they arrive there.  It has been supposed,
that the action  of the  cilia, which line the  Fallopian tubes, might account for
their transit; but the direction of this is from the Ovaria towards the Uterus,
and would therefore be opposed  to it.   A peristaltic action  of the Fallopian
tubes themselves may generally be noticed  in  animals killed soon after sexual
intercourse; and in those which "have a two-horned membranous Uterus, such
as is evidently but a dilatation of the  Fallopian tube, this partakes of the same
movement, as may be well seen  in the  Rabbit:  in  animals,  however, which
have a single Uterus with thicker walls (as  in  the Human female), it must
evidently be unavailable.   Among the tribes whose  Ova  are  fertilized out of
 the  body, the power of movement inherent in the Spermatozoa is  obviously
 the means by which  they are  brought  in  contact with the Ova:  and it does
 not seem unreasonable to suppose, that the  same is  the case  in regard to the
 higher classes;  and that the transit  of these curious  particles, from the Va-
 gina to the Ovaries,  is effected by  the  same kind  of action  as that which
 causes them to traverse the field of the  microscope.—We shall now  consider
 the  changes in  the Ovum  and its appendages, by  which it is  prepared for
 fecundation.
   912. Up to the period when the Ovum is nearly  brought to  maturity, it re-
 mains  in the centre of the Ovisac or inner layer ofthe Graafian follicle ; and
 it is supported in its place by  the Retinacula, which connect its  Tunica
 Granulosa with the Membrana Granulosa  that lines the ovisac.  (See Fig. 6,

 ischium, and behind these are the transversi-perinei muscles.   They are  surrounded by very
 loose cellular tissue.  They are  rounded,  but somewhat elongated, being flat and bean-
 shaped.  Their long diameter  is from 5 to 10 lines; their transverse diameter 2j to 4£ lines,
 and they are from 2} to 3 lines thick.  The excretory duct is at the anterior edge of the
 superior part of the gland, and runs beneath the  constrictor vaginoe, horizontally forwards
 and inwards, to the inner face ofthe nympha, opening in front of the carunculae myrtiformes,
 in the midst of a number of small mucous follicles.  These glands were first discovered by
 Duverney in the cow, about the middle of the seventeenth century.  Barthohnus subse-
 quently found them in the human female, and his observations were confirmed by Duver-
 ney,  Morgagni, Santorini, Peyer, &c.  Haller  denied their existence;  and  such  structure
 seems to have been forgotten until they  were again  described by Mr. Taylor (Dublin
 Journal, vol. xiii. 1838).   They are analogous to Cowper's glands in the male, according to
 Tiedemann, and  like them are sometimes wanting, and differ in size.  In  advanced  age
 they are said to diminish in size, and even disappear.  They are present in the females of
 all animals, where Cowper's glands exist  in the  males.  They secrete a thick, tenacious,
 grayish-white fluid, which is emitted in large quantities, at the termination ofthe sexual act,
 most likelv from the spasmodic contraction of the constrictor vaginae muscle, under wnicn.
 thev lie  Its admixture with the male semen is supposed to probably have some connection
 with impregnation, and it has been suggested that it may be the vehicle of the fecundating
 prnTcSof the semen.   These glands were probably known to the ancients, and it is doubt-
 fess their secretion which Hippocrates and others  describe as the female semen-(1843.)
 Tnese  glands have lately been described  by Huguier of Paris, in ^eAr^Anatomu.
 His description corresponds in every respect with that given above.—(1847.;—Jl. L.j
      59 
698
OF REPRODUCTION.
Plate I.)   The Ovum  then begins to move towards  the  periphery of the
Graafian follicle;  and always towards that point  of it which is nearest the
surface of the Ovary.   This movement appears to be due, in the first instance,
to the shortening of the Retinacula  in that direction;  and whilst the Ovum
lies against the membrane of the Ovisac, a gradual  thinning of the latter seems
to take place.   At the same time an important change is  occurring in the outer
wall of  the  Graafian follicle, especially at the part most deeply imbedded in
the  Ovary; its vascularity  is greatly increased, and  its substance appears
thickened.  This  thickening is  probably due to the deposition of blood in a
state ready to become more highly organized, upon the exterior of the Ovisac;
and  the consequence of it is, that considerable pressure is made upon the con-
tents of the follicle, the effect of which is, of course, exerted most upon the
thinnest part of it.  Thus, a sort of vis a tergo is exercised against the Ovum
and  the Disc (consisting of the  tunica granulosa and the central part  of the
retinacula) in which it  is imbedded;  and the whole is forced, by the rupture
ofthe Graafian follicle,  into the funnel-shaped entrance  ofthe Fallopian tube,
—the Retinacula  being gradually detached from  the Membrana  Granulosa,
which  is left behind.   This  action is represented in Fig. 8, Plate I.  What
becomes of the Ovisac is  not certain.   Dr. Barry affirms that he has some-
times known it to be subsequently expelled from  the ovary;  but it appears
more commonly to coalesce with the  surrounding envelope, and to constitute,
together with it, the lining of the cavity, which is usually found in  the Corpus
Luteum.   The substance known under this name  is found in the Ovary, after
the Ovum has  escaped  from it;  and the  importance of the question, how far
its presence may be  regarded as an indication that  Conception has taken
place, requires that we  should have clear ideas respecting its nature.
   913.  The term Corpus Luteum has been usually applied to a reddish-yel-
low  substance, glandular in  aspect, friable  in consistence, and very vascular;
which occupies the part of  the Ovary from which the germ has escaped, and
is larger or smaller according to the length of time  that has elapsed since con-
ception.   At first it is usually so large as to occasion a considerable projection
on the  surface of the  Ovary; its form is oval, or resembles  that of a bean.
When  cut across, its dimensions are usually found to be from 4 to 5-8ths of
an inch in its  long diameter, and from 3 to 4-8ths in its short; and it thus
occupies from a fourth to a  half of the whole area of the ovarium; but these
dimensions  are not unfrequently exceeded.  The centre of this substance  is
hollow;  and by a proper acquaintance with this  character, the true  Corpus
Luteum may be distinguished from substances, bearing  a general resemblance
to it, but very different in  their character.  The following  is  Dr.  Mont-
gomery's account of it.  " Its centre  exhibits either a cavity, or a radiated or
branching white line, according  to the period  at  which  the  examination is
made.   If within the first three  or four months after conception, we shall, I
believe, always find the cavity still existing, and of such a size as to be capable
of containing a grain of wheat at least, and very often of much greater dimen-
sions ;  this  cavity is  surrounded by  a strong white  cyst;  and  as gestation
proceeds, the opposite  parts of this cyst approximate, and at length close to-
gether, by which  the cavity is completely obliterated, and in  its place there
remains  an irregular white line, whose form is best expressed by calling  it
radiated  or stelliform.   This is  visible as long  as any distinct trace  of the
Corpus Luteum remains."*   The true Corpus Luteum is further distinguished
by its capability of being injected from the vessels of  the Ovary ;  which is
not  the case with Tubercular deposits, or other substances which may stimu-
late  it.   After Delivery, the size of the  Corpus Luteum rapidly diminishes;
                         * Signs of Pregnancy, p. 226. 
ACTION OF THE FEMALE.
699
and in a few months it ceases to be recognizable  as such.   The cicatrix by
which the  Ovum has escaped is visible for some time longer; but this too,
according  to  the  careful researches  of Dr. Montgomery,  cannot be distin-
guished at a subsequent period.   Hence there is no correspondence between
the number of Corpora Lutea found in the  ovaries of a woman, or of Cica-
trices on their surface, and the number of children she may have borne.  The
number of  Corpora Lutea must always be less, when there have been  many
conceptions; but the number of Cicatrices maybe greater; for several causes,
such as the  escape of  unimpregnated  ova, or the bursting  of  little abscesses,
may give rise to such appearances.
   914. Much  discussion  has taken  place  amongst  Embryologists,  as  to
whether the substance  of the Corpus Luteum is deposited within the Graafian
follicle, externally to it, or between  its layers.   The first  is  the  opinion  of
Baer, Bischoff, and others; who regarded it as a growth from the inner layer
of the Graafian follicle.   The second is the opinion  of  Dr. R.  Lee and Mr.
Wharton Jones.  The third is the doctrine taught by Drs. Montgomery and
Barry; the  former regarding it, however, as deposited between the two layers,
of which the  cellulo-vascular layer of the  Graafian follicle (which  are both
derived from the condensed stroma of the ovarium) consist;  whilst  the latter
maintains that the deposit takes place between the true Ovisac and its Ovarian
envelopes.   The  recent inquiries  of Dr. Ritchie*  throw great  light on this
question ; by showing  that a great variety of changes may  take place, after the
discharge of the Ovum from the  Ovisac;  amongst which may be included all
the appearances described by the several writers just quoted.   The following
is an abstract of the results of Dr. R.'s researches.

  a. The appearances presented by the Ovaries, Graafian follicles, and by the blood which
is contained in the latter subsequent to  their rupture, vary according to  the time at which
they are examined, and the absorbing power of the  individual.—In cases of the recent dis-
charge of an Ovum, the Peritoneal coat of the Ovary is marked by a jagged slit or opening,
having a florid vascular areola; in those of longer standing, the opening is covered over,—
with the exception of a minute circular foramen in the centre, (or where the  slit has been of
great length)  of two  such openings,—with new tissue, surrounded by a claret-coloured mar-
gin ; and in those still more  ancient, the whole is healed up into a cicatrix, which is more
or less superficial and free from discoloration, according to its age.
  b. With respect  to the Blood, which is generally contained in the  ruptured follicles, it is
seen first as a florid  coagulum; next, having only its centre scarlet-coloured, and its peri-
phery more or less black, and perhaps furrowed; frequently the clot  has  a gamboge colour
from the decomposition of its red corpuscles, or has become pale from their absorption; and
lastly, the clot is found in different stages of absorption.  But it sometimes also happens,—
and that indifferently in every variety of the uterine state,—that  the ruptured follicles are
found empty, or containing only an aqueous fluid.
  c. The coats of the  ruptured Follicles have been found in four different general conditions,
apparently dependent on  their relative degree of organization; and each class presenting,
also, modifications of their respective characteristics, proceeding in part from the same cause,
and in part also from changes connected with the  period of their progress in which they
were examined.
  r. The first class was distinguished by the  attenuated state of the  coats of the ruptured
Follicle; and by the total absence of any organic changes in these, different from their con-
dition previous to  their discharge.  The only alterations observable resulted from the me-
chanical dyeing of their coats of an inky-black, or of a yellow colour, proceeding from their
contact with  decomposed blood.—The first class of appearance was found indifferently in
all ages and states, subsequent to puberty.
  n. The  second general  class of ruptured Follicles was characterized, in  addition to  the
appearances  just described, by organic changes  in  their coats; consisting, progressively, of
an increased vascularity, a thickening, a  whitening  of the colour, and finally, a corrugation
of their tissue.  The  white bodies thus formed, to which Dr. R.  has given the designation of
Corpora Albida, may  exist  under two distinct forms:—1. As soft bodies of a yellowish fatty
aspect having the outer coat  much thickened, whilst their inner remains as a delicate dia-
* Medical Gazette, 1844. 
700
OF REPRODUCTION.
phanous pellicle; these, after a lengthened period, present themselves as yellowish-white,
and generally globular bodies, more or less fissured from their contraction, and sometimes in
process  of absorption, having a granular-looking  structure, and seldom being divisible into
laminae  by simple dissection:—and 2.  As dense bodies of a whitish, shining, firm structure,
their inner coat being the seat of these changes, and  their outer adhering loosely as a
transparent peculiar layer; the ipner layer  presents  itself  as a thick, opaque, deeply-
wrinkled or corrugated, and rocky cyst, or is sometimes partially diaphanous, and of a shin-
ing pearly aspect, and  very white colour; and  it sometimes contains a yellow,  greenish,
transparent fluid, or a clot of blood, either unchanged, or converted into a yellow or black
pigment.  This second variety appears to be the Corpus Luteum  of Baer.—These white
bodies, or Corpora Albida, were found by Dr. R. in every variety of uterine condition, subse-
quent to the establishment  of menstruation, but never before it; and the dense kind, espe-
cially, were persistent for a long period.   They had no necessary connection with the gravid
condition; but they were occasionally (especially the  dense variety)  the only specialty ob-
servable in the ovaries of the puerperal female, some time after delivery.
  in. The third class was  characterized  by the  presence of an  organized yellow-coloured
brain-like, granular matter; forming bodies to  which Dr. R. has  giyen the name of Corpora
Cephaloidea.  These differed, according as  the cerebriform, matter was deposited  between
the layers of ruptured Follicles, having transparent pellicular walls, as in Class i., or having
either their inner or outer coat thickened, as  in  Class n.;—or according as  the cerebriform
matter was deposited externally to the two inner layers of the Follicle.—The former of those
varieties was found by Dr. Ritchie in menstruating females;  also during the first months of
the gravid  state; and sometimes even in the  period of lactation.   In some  instances, only
one or two of the cerebriform  bodies were found; but in others, five or six.  Their struc-
ture, especially in the more perfectly-organized specimens, presented  a striking resemblance
to the convoluted reddish-yellow surface of the brain, covered by its  inner membranes, and
painted  with its scarlet-coloured and dark vessels.  These cephaloid bodies undergo diminu-
tion in proportion to  their age, and the absorbing power of the female.   In those possessed
of only thin coats, or having the outer layer as the seat of the thickening, the inner walls of
the cysts speedily contracted and coalesced; so that their centres exhibited a delicate opaque
streak:  or, in those better  developed, a serrated, curved, and well-marked white line, ac-
cording  as the cyst was of elliptical or of a globular form.  This variety of cerebriform cyst
was  met with in a recent state as well in immediate  connection with the existence of men-
struation, as during the first seven months of pregnancy ; and in this latter case, by under-
going a  conversion in its form presently to be  noticed  (iv), they constituted the Corpora
Lutea of Dr. Montgomery.—In the second variety of Cephaloid bodies, the two inner layers
ofthe Graafian Follicle were converted into a dense white body, surrounded by an  envelope
of yellow matter.  Such cysts  (the Corpora Lutea of Dr. Lee) were never observed as an
effect of menstruation simply, but were met with exclusively in the gravid female;  although
two  were seen (as were also the cephaloid bodies of the preceding order) to be present in
some cases of single  conception.  This form of Cephaloid bodies was generally distinguished
by large, persistent, white,  glistening cavities.  The  granular cephaloid matter was some-
times found quite  absorbed within a  few days after  parturition;  but in other instances it
underwent the metamorphosis characteristic of the next class.
  iv. The fourth general state of the ruptured Graafian  follicle was peculiar to the impreg-
nated and lactating female, in  the period between the 8th and 13th months after concep-
tion ; and appeared to be a conversion of the  Corpora Cephaloidea  already described, arising
out of a higher and more perfect organization.   Down to the 7th month of pregnancy, the
cysts contained in  the  Ovaries did not  differ in  any respect from the  cerebriform bodies
found in the unimpregnated state; except that they were sometimes plumper, more vascu-
lar, better developed, and had their inner  layer more frequently thickened.  A change in
the hue  of the  granular matter then commences, which becomes more decided as time
elapses; so that by the  end of the  1st month after delivery, it  becomes of a decided rose
colour, changing to a still more florid hue on exposure to air.  Its cavity also contracts, so as
to leave but a stellated point, or a curved groove: and a fibrous appearance (probably de-
pendent on the  traction thus  exercised) is seen in the surrounding substance.   Although
these bodies, termed  by Dr. Ritchie Corpora rubra, are found exclusively in the later months
of pregnancy, or in the puerperal state, yet they  are not always present in those conditions.

The number  of  cases examined by Dr.  Ritchie is not,  perhaps, sufficient to
enable us to found any positive statements upon the results of  his examina-
tion of them ;  but the following inductions appear highly probable :—1.  That
the  presence  of Corpora  Rubra may  be regarded  as  indicative, not  only of
conception, but  also of an advanced state  of pregnancy, or of recent delivery;
but  that their absence is not to be  regarded as any proof to the contrary.__2. 
ACTION OF THE FEMALE.
701
That the presence of Corpora Cephaloidea  of the second order is to be re-
garded as indicative of conception.—3. That the  presence  of the Corpora
Cephaloidea of the first order, or of Corpora Albida, cannot be regarded as
in the  least degree indicative of Conception ; as they may result from  the
simple discharge of an Ovum, in  the  ordinary course  of those changes to
which  the Ovarium is  subject.—The excess of  Corpora Albida above every
other appearance is due, not  merely to their being an ordinary result of  the
discharge of unimpregnated Ova;  but also to the frequency  of  their produc-
tion as degenerated forms (so  to speak) of the Corpora Cephaloidea and Cor-
pora Rubra of the gravid female ;  and also to their occasional existence as,
from the first, the only Ovarian change following upon Conception.
   915. The  object of the changes which have  been  already described, is to
bring the Ovum within reach of the fecundating influence;  and to convey it
into^the Uterus  after it has  been fertilized.   We have  now to consider  the
changes in the. Ovum  itself, which take place during the same epoch.   At
about; the same period that the  Ovum moves towards the  periphery of  the
Graafian follicle, the Germinal Vesicle moves towards the  periphery of  the
yolk-bag; and it always takes up  its position at the precise point of the Zona
Pellucida which is nearest the Ovisac, and which is closest, therefore, to the
surface of the Ovary.   Moreover,  the Germinal  Spot is always on that part
of the Germinal Vesicle, which is in closest contact with the Zona Pellucida.
(See a, Figs. 9 and 10, Plate I.)   Thus, the Germinal Spot is  very near the
exterior of the Ovary ; but is separated from it by the peritoneal coat of the
latter,  by a thin layer of its stroma forming the external layer of the Graafian
follicle, by the ovisac forming its internal membrane, and by the zona pellu-
cida.   We have already seen how the obstacle interposed by the three former
to the  entrance  of the Spermatozoon, is overcome;  we  shall presently find
that the Zona Pellucida undergoes a similar change.
   916. Whilst the Ovum  is being prepared for fecundation, a series of very
important actions takes place in the Germinal Vesicle.  The exterior or peri-
pheral portion of the Spot, which previously consisted of a collection of very
minute granules, begins to develope itself into a ring of new cells of extreme
delicacy (Fig. 9, a);  these gradually enlarge, and  a second ring of cells is
developed within it, pushing the first-formed cells further away from the cen-
tre.   Many successive  rings of cells are thus formed ; and  at last the whole
 Germinal Vesicle  is filled with them, as shown  at b,  Fig. 10.  Still there
remains a pellucid space in the centre of the  Germinal Spot (resembling  that
seen at a, Y\«. 12); in which no cells are developed.  The  first-formed  cells
 that have been  pushed outwards,  are so much compressed by those subse-
 quently formed, as frequently to undergo liquefaction ;  and during the  time
that the Ova are being matured for fertilization,  there is  a continual new pro-
 duction of cells at the centre, and  a degeneration at  the circumference.—At
 the  same time, the Yolk undergoes changes  somewhat analogous; for it
 ceases to contain  separate oil-globules; and large elliptical discs  or cells are
 seen in it, especially just beneath the Zona Pellucida  (Fig. 9, c).*   Here, too,
the formation of new cells takes place from the periphery towards the centre ;
the peripheral ones gradually undergo liquefaction,  as  is seen in the outer
lave? of those in Fig. 10, which are becoming indistinct; and they are replaced
by a new layer pushed outwards  from the centre.   The same process  sub-
 sequently continues in the Yolk, for  some  time after fecundation;  and this
 not only in regard to the yolk as a whole, but in respect to its individual cells,

   * Tt i  to be remembered that the observations of Dr. Barry,  here quoted, were made on
 the Raobif: andTie  therefore, probably applicable equally to other Mammaha, but  not to
 Oviparous Animals.
59' 
702
OF REPRODUCTION.
as is shown in Fig. 11, where concentric  rings of new cells are seen in each
of the parent vesicles.  Even in the most advanced of these secondary cells,
another generation may be seen, and these are developed upon the same plan
with those of  the Germinal Vesicle:  thus in Fig. 12, the pellucid  centre of
the original nucleus of the parent disc is seen at a, and is surrounded by seve-
ral concentric  rings of cells, increasing in size from within outwards ; and at
b is represented the condition of the outer and older cells, in which  the same
process is undergoing repetition.   (Although the figure only represents one
secondary cell as in the act of producing others, the others of the same age
are alike engaged in the process of multiplication.)—The foregoing history is
equally applicable to the  cells, from which the Embryo subsequently origi-
nates ; and it  is probably  the general  mode in which the process takes place.
   917. At the time when the interior  of the Germinal Vesicle is being pre-
pared for  the reception  of the fecundating influence, the  portion of the Zona
Pellucida  against which it lies becomes attenuated; and a chink then forms in
it, just above what was the pellucid centre of the Germinal Spot.   Through
this chink, the Spermatozoon can reach the Germinal Vesicle; and that it does
so, we are now entitled to affirm, not only from analogy, but also from actual
observation (§ 900).   What is the nature ofthe influence communicated by it
is less certain; but from the known character ofthe process of fecundation in
Plants, we shall have little difficulty  in  concluding, that  it deposits  in the
Germinal Vesicle the rudiments of the first cells, which are subsequently to
be developed into the Embryonic  structure.  It  is certain that none of the
cells previously contained in  the Germinal Vesicle subsequently form part of
it; in fact, they all liquefy after a time,  and  disappear entirely.  But in the
previously pellucid  centre of what was the Germinal Spot, two new cells are
seen after fecundation;  these enlarge  at  the  expense of the rest;  and from
them, all the permanent structures originate.   This  pair  of cells is seen at a,
Figs. 13 and 14; in the former some ofthe cells ofthe Germinal Vesicle are
still left;  in the latter, they have been all absorbed.   The Germinal Vesicle
returns after fecundation to the centre of the Yolk, being at first entirely con-
cealed by its discs (Fig. 11);  and the cleft in the Zona Pellucida soon closes,
so as to be no longer distinguishable.   The two new cells and the other con-
tents  of the Germinal Vesicle, undergo such a rapid increase in size, that they
soon fill the whole interior of the Zona Pellucida; and the cells of the Yolk
being reduced by the pressure into a liquid form,  their elements are  absorbed
by the new cells of the Embryonic structure.   This, at least, is the case  in
the Mammalia; among which the Yolk performs but a very subordinate part,
having only to serve for the development of  the  Embryo during a very brief
period.—In each of  the  two primary Germ-cells  (as they  may be  called) a
series of changes takes place, exactly conformable to that already described as
occurring  in the Germinal Vesicle ;—that is to say,—a ring of new cells origi-
nates in the margin of its nucleus,—this  increases in size, and is pushed out-
wards by  another ring nearer  the  centre, thisagain by another, and so on,—
and at last, two cells appear in the pellucid central space, which are developed
at the expense of all the  rest, and are  to  be  regarded as the real permanent
offspring of the parent.   These changes  may be seen in  progress in Figs.  13
and 14;  in the former, the original cells of the Germinal Vesicle  have not
quite disappeared, although their liquefaction is in progress; in the latter,  no
vestige of them is left, the whole cavity being occupied by  the twin-cells.
   918. These changes commence during the passage of  the Ovum along the
Fallopian tube; and during its transit to  the  Uterus, it acquires a sort of gela-
tinous envelope, which is,inclosed in a membrane  of fibrous texture, termed
•the Chorion.   The gelatinous envelope is probably of an albuminous nature
in reality, corresponding with the white of the Bird's egg;  whilst the fibrous 
ACTION OF THE FEMALE.
703
texture of Chorion seems to be produced, like the membranous basis of the
egg-shell of the Bird (§ 118), by the exudation  of Fibrine from  the lining
membrane  of the  Fallopian tube  or Oviduct.   The  outer layer of this en-
velope, in the egg of the Bird, is consolidated by the deposition of particles of
Carbonate  of Lime in its  areola?;  but it undergoes no  higher organization.
The Chorion  of the Mammal,  on the other hand, subsequently  undergoes
changes of a much higher order; which adapt it  for participating,  to a  most
important degree, in the nutrition of the included  embryo.—The  first of  these
changes consists in the extension of the surface of the membrane into a  num-
ber of villous prolongations, which give it a spongy or shaggy appearance.
These serve  as absorbing radicles,  and form  the channel through  which the
embryo is nourished by the fluids of the parent, until a more perfect commu-
nication is formed,  in the manner to be presently explained.
   919.  We have  now  to  speak of  the changes in the Uterus, which take
place in consequence of Conception, and which prepare it  to receive the
Ovum.   Of these the most important is the  formation of the  Membrana De-
cidua, so called from its being cast off at each parturition.  This  membrane
has been usually supposed to be a new formation;  and has been described as
originating in coagulable lymph thrown out on the inner surface of the Uterus,
 into  which vessels are  prolonged from  the  subjacent surface.   It appears,
 however, from the  late researches of Dr. Sharpey and Prof. Weber,* that this
 is not the true account of it;  and that the Decidua is really composed of the
 inner portion of the Mucous membrane itself, which undergoes a considerable
 change in its character.  The Mucous membrane of the Uterus  had been ob-
 served by Dr. J. Reid to possess, on its free surface, a tubular structure; not
 very unlike that which has been described as existing in the lining membrane
 of the stomach (§ 873 and Fig. 269).   This tubular portion becomes thickened
 and increased in vascularity, within a short time after conception; and  when
 the inner surface  of a  newly-impregnated  Uterus is examined with   a low
 magnifying power, the orifices of its  tubes  (Plate I., Fig. 17,  b,  b) are very
 distinctly seen, being lined with a white epithelium.  The blood-vessels (c, c)
 form a  very minute net-work, which extends  in  loops  from  the subjacent
 portion  of the  membrane.  According to the recent  observations of Mr.  J.
 Goodsir,t the interfollicular spaces (a, a, a) also are  crowded with nucleated
 particles ; and it is to the development of this interfollicular substance, as well
 as to the enlargement of the follicles themselves, and the copious development
 of epithelial cells in their interior, that the mucous membrane in  this condition
 owes its  increased thickness.   At  a later period, the  Decidua  may be found
 to consist of two distinct layers; the Decidua vera, lining the uterus; and the
 Decidua reflexa, covering the exterior of the ovum.  It was formerly supposed
 that the latter is a portion  of  the former, which has been pushed before the
 ovum at its entrance into  the uterus; but the  two layers are so  different in
 texture, that they cannot be supposed to have the same origin.   The difficulty
 appears to be solved by the observations, of Mr. Gpodsir   " From what has
 now been  stated," he remarks, "it appears  that the  Decidua consists of two
 distinct elements; the mucous membrane of the uterus, thickened by a pecu-
 liar  development; and a  non-vascular cellular substance  the product  of the
 uterine follicles.   The former constitutes, at a later period, the  greater  part o
 the decidua vera; the latter,  the  decidua reflexa   This view .of the  consti
 tution of the Decidua clears up the doubts  which were entertained regarding
  he  arrangement of these membranes at the os uteri and entrances of the Fallo-
 oian tubes   i" is evident that these orifices  will be open or closed, just as the
* Muller's Physiology, pp. 1574-1580.
| Anatomical and Pathological Observations, Lhap. ix. 
704
OF REPRODUCTION.
cellular secretion is more or less plentiful, or in a state of more or less vigor-
ous development."—" When the ovum enters the cavity of the uterus, the
cellular decidua surrounds it, and becomes what has been named the decidua
reflexa, by a continuation of the same action, by which it had been increasing
in quantity before the arrival of the ovum.  The cellular decidua grows around
the ovum by the formation of new cells, the product of those in whose vicinity
the ovum happens  to be situated."
   920.  When the  Ovum has arrived in the Uterus, therefore, and the villous
tufts of the Chorion are developed, these come  into  contact, in the first in-
stance, with the layer of cellular decidua, which intervenes  between them
and  the  vascular decidua.   Through this cellular membrane, therefore, the
ovum must  derive  its nutriment from the vascular surface;  and it cannot be
deemed improbable, that the office of its component cells is to  draw from the
subjacent vessels the materials which are to  serve for the nutrition of the
ovum, and to present it  to the villous tufts of the  chorion.   Each of these is
composed (according to the observations of Mr. J. Goodsir) of an assemblage
of nucleated cells, which  are  found in various stages of  development; and
these are  always  inclosed within a  layer of basement-membrane, which
seems to be itself composed of flattened cells united by their edges.   At the
free  extremity of each  villus,  is a  bulbous  expansion,  the  cells composing
which are arranged round a central spot;  and it is at  this point that the most
active processes  of growth take place, the villus  elongating by the develop-
ment of new cells from its germinal spot, and (like the spongiole of the plant)
drawing  in nutriment from  the  soil in which it is imbedded.—In its  earliest
grade of development, the chorion and its villi contain  no vessels;  and the
fluid drawn in by the tufts is communicated to the embryo, by the absorbing
powers of the germinal membrane of the latter.   But when the tufts are pe-
netrated by blood-vessels, and their communication with the embryo becomes
more direct, the  means by which they communicate with the parent are found
to be still essentially the same;—namely, a double layer of  nucleated cells,
one layer belonging to the fostal tuft,  and the other to the vascular  maternal
surface.  It is from these elements that the Placenta is formed, in the manner
next to be described.
   921.  The first stage in this process consists in  the extension of the foetal
vessels into the villi of the Chorion over its entire surface, in the manner here-
after to be  detailed (§ 941); so that the  nutriment which these villi imbibe,
instead of being merely added to the  albuminous fluid surrounding  the yolk-
bag, is now conveyed directly to the embryo.  This,—the earliest and simplest
mode by which the Foetus effects a new connection with the parent,—is the
only one in which it ever takes place in the lower Mammalia, which are hence
properly designated as " non-placental," rather than as ovo-viviparous (§ 44).
In the higher Mammalia, however, there soon occurs a great extension of the
vascular  tufts of the  fcetal  Chorion, at  certain points;  and a corresponding
adaptation, on the  part of .the Uterine structure, to afford  them an increased
supply of nutritious fluid.  These specially-prolonged portions are scattered,
in the Ruminantia  and some other Mammalia, over the  whole surface of the
Chorion, forming what are termed the Cotyledons ; but in the higher orders,
and in Man, they are concentrated  in one spot,  forming  the Placenta.   In
some of the lower tribes, the maternal and the fcetal portions of the Placenta
may be very easily separated; the former consisting of the thickened Decidua;
and the latter being composed of the  prolonged  and ramifying vascular tufts
of the Chorion, dipping down  into it.  But in the Human  Placenta, the two
elements are mingled together through its whole substance.
   922.  On looking at the Fcetal surface of the Human Placenta, we perceive
that the umbilical vessels diverge in every direction from  the  point at which
* 
ACTION OF THE FEMALE.
705
they enter it;  and their  subdivisions  ramify very minutely, forming a large
part of its substance.   The terminal ramifications are represented by Dr. J.
Reid*  as having the digitated aspect represented  in Fig. 23, (Plate I.) ;  but
this is  one  of the more complex forms.  In  its simplest character, each
villus  is cylindrical or nearly so; and  the digitated villi are only solitary villi
grouped together at the extremity of a  primary branch.   Each  villus contains
a capillary vessel,  which forms  a series  of loops,  communicating with  an
artery  on one side and with a vein on  the other; but the  same capillary may
pass into several villi, before re-entering a  larger vessel.   The vessels of the
villi are covered, as in the Chorion, by a layer of  cells (Fig. 280/), inclosed
Fig. 280.
Fig. 2S1.
  Portion of the external membrane,
with the external cells, of a placental
villus:— a. cells seen through the mem-
brane ; 6, cells seen from within the
villus; e, cells seen in profile along the
edge of the villus.
      Extremity of a placental villus :— a, exter-
    nal membrane of the villus, continuous with
    the lining membrane of the vascular  system
    of the mother ; 6, external cells of the villus,
    belonging to the placental decidua; c, c, ger-
    minal centres of the external cells; d, the
    space between the maternal and foetal  por-
    tions ofthe villus; e, the internal membrane of
    the villus, continuous with the external mem-
    brane ofthe chorion;/, the internal cells ofthe
    villus, belonging to the chorion; g, the loop of
    umbilical vessels.

in basement-membrane (e); but the foetal tuft thus formed is  inclosed in a se-
cond series of envelopes (a, b, c), derived from  the maternal  portion  of the
Placenta,—a space  (d) being left, however, between the two, at the extremity
of the tuft.
   923.  Whilst the foetal portion of the Placenta is thus  being generated by
the extension of the  vascular tufts of  the Chorion, the Maternal  portion is
formed  by the enlargement  of the vessels of the decidua, between which  they
dip down.  " These vessels assume the  character of sinuses ;  and at last swell
out (so  to speak)  around and between  the villi;  so that finally the villi are
completely bound up  or covered  by the  membrane which constitutes the walls
of the vessels, this  membrane following the  contour of all the villi, and  even
passing to a certain extent over the branches  and stems of the tufts.   Between
this membrane, or wall of the enlarged decidual vessels, and the internal mem-
brane of the villi, there still remains a layer of the cells of the decidua."t   In
this manner is formed the Maternal portion of the Placenta, which may be re-
garded in its adult state (as was well  pointed out by Dr.  J. Reid) in the  light
of a large sac formed by a prolongation of the inner coat of the Uterine vessels ;
against "the foetal surface  of which sac, the  tufts just described may be said to
push  themselves, so as to dip down into it, carrying before them a portion of
its thin  wall, which constitutes a  sheath  to each tuft.  Now as every extension

            * Edinb. Med. and Surg. Journal, Jan. 1S41.
            ■j- Good6ir's Anatomical  and Pathological Observations, p. 60. 
706
OF REPRODUCTION.
of the uterine vessels carries the decidua before it, every one of  the vascular
tufts that dips down into it will be covered with a layer of the  cellular struc-
ture ofthe latter; and the foetal portion of each tuft will thus be inclosed in a
layer of maternal cells  and basement-membrane (Fig.  280, a, b,  c; and Fig.
281, a, b, e).   In this manner, the whole interior ofthe placental  cavity "is in-
tersected by numerous tufts of foetal vessels, disposed  in  fringes, and  bound
down by reflections ofthe delicate membrane that forms its proper wall; just
as the intestines  are held in their places by reflections of the peritoneum that
covers them.   This view was suggested to Dr. R. by the very interesting fact,
that the  tufts of fcetal  vessels not unfrequently extend beyond the uterine sur-
face of the  Placenta,  and dip down into the uterine sinuses; where they  are
still covered, and held in their places, by reflections of the same membrane <
(Plate I., Fig. 24).   All the bands which connect and tie down the tufts (Fig.
282, g), are formed of the same elements as the envelopes of the tufts them-
selves ;  namely, a fold of the lining membrane of the decidual  sinuses, and a
layer of the cellular decidua.

                                   Fig. 282.
 Diagram illustrating the arrangement of the placental decidua :—a, decidua in contact with the interior
of the uterus ; 6, venous sinus passing obliquely through it by a valvular opening; c, a curling artery
passing in the same direction; d, the lining membrane ofthe maternal vascular system, passing in from
the artery and vein, lining the bag of the placenta, and covering e, e, the foetal tufts, passing on to them
from their stems from the fcetal side of the cavity, also by the terminal decidual bars/./', from the uterine
side, and from one tuft to the other by the lateral bar, g ; h, h, separated foetal tufts, showing the internal
membrane and cells, which, with the loops of umbilical vessels, constitute the true foetal portion of the
tufts.

   924.  The blood is  conveyed into the  Placental cavity by the "curling
arteries"  of the Uterus; and is returned from it by the large veins, that are
commonly designated  as  sinuses.   The foetal vessels, being bathed  in  this
blood, as the branchiae of aquatic animals are in the water that surrounds them,
not only enable the foetal blood to exchange its venous character for the  arte-
rial, by parting with its  carbonic  acid  to  the  maternal  blood, and receiving
oxygen from it;  but they also serve as  rootlets, by which  certain nutritious
elements of the maternal blood (probably those composing the liquor sanguinis)
are taken into the system of the Foetus.  In this they closely correspond with
the villi of the Intestinal canal; and there is this further very striking analogy,
—that the nutrient material is selected and prepared by two sets  of cells, one
of which (the maternal) transmits it to the other (the fcetal),  in the  same man-
ner as the epithelial  cells of the intestinal villi seem  to  take  up  and prepare
the  nutrient matter, which is  destined to be  still further assimilated  by the
special absorbing cells of their interior (§ 672).   There is  no  more direct
communication between the  Mother and Foetus than this; all the  observations
which have been supposed to prove the existence of real vascular continuity, 
ACTION OF THE FEMALE.
70T
having been falsified by the  extravasation of fluid, consequent upon the force
used in injecting the vessels.  Moreover, the different size of the blood-corpus-
cles in the Foetus and in the Parent (§ 149) shows the  non-existence of  any
such communication.
  925. The formation of the  Placenta, in the  manner just described, com-
mences in the latter part  of the second  month;  during the third, it acquires
its proper character; and it  subsequently goes on increasing, in accordance
with the growth of the ovum.   Towards the  end of the term of  gestation,
however, it  becomes more dense  and less vascular;  owing, it would seem, to
the obliteration of several of the minuter vessels, which are converted  into
hard fibrous filaments.  The vessels of the Uterus undergo great enlargement
throughout,  but especially at the part to which the Placenta is attached;  and
the blood  in  moving  through  them  produces a peculiar  murmur, which is
usually distinctly audible at an early period of Pregnancy, and may be regarded
 (when due care is taken to avoid sources  of fallacy), as one of its most unequi-
 vocal  positive signs.   The  Placental bruit is thus described by Dr. Mont-
 gomery.*   " The characters of  this phenomenon are, a low murmuring or
 somewhat cooing sound, resembling that made by blowing gently over the lip
 of a wide-mouthed phial,  and accompanied by a  slight rushing noise, but with-
 out any sensation of impulse.  The sound is, in its return, exactly synchronous
 with the pulse of the  mother at the time of examination; and  varies in the
 frequency of  its repetitions, with  any accidental variation which may occur
 in  the maternal  circulation.  Its situation does  not  vary during the course of
 the same pregnancy; but in whatever region of the uterus it is first heard, it
 will in future be found, if recognized  at all,—for it is liable to intermissions,—
 at  least  we  shall  occasionally be  unable to hear it where we have already
 heard it a short time before, and where  we shall shortly again recognize it.
 According to  my experience, it will be most frequently heard about the situa-
 tion of the Fallopian tube of the right side; but it may be detected in any of
 the lateral  or anterior parts of the uterus."  That the cause of this sound
 exists in the  Uterus itself, is distinctly  proved  by  the fact, that it  has  been
 heard when that  organ was so completely ant everted, that  the fundus  hung
 down between the patient's  thighs.  A sound so much resembling this,  as to
 be scarcely distinguishable  from it, may be  occasioned, however, by a cause
 of a very different nature,—namely, an  abdominal tumour, pressing upon the
 aorta, iliac  arteries, or enlarged vessels  of its own;  and, in doubtful cases, it
 is  necessary to give full weight to the possibility of such an explanation.   The
 sound may be imitated at any time,  by  pressing the stethoscope on  the  iliac
 arteries.  The  Placental bruit has been not unfrequently heard in the   11th
 week;  but it cannot generally be detected before the fourth month, when the
 fundus uteri rises above  the anterior wall of the pelvis.
    926.  The  amount  of the peculiar tissue of the  Uterus (§ 234) greatly
 increases during pregnancy.  At the same time, the Mammary gland and its
 appendages undergo a fuller development;  and from this a valuable, but not
 unequivocal, indication  of  pregnancy may be drawn.   Occasional shooting
 pains in the  Mammae are not unfrequently experienced within a short period
 after  conception ; and more continued tenderness is also not unusual.  A sense
 of distension is very  commonly experienced at about the end of the second
 month; and  from that time  a distinct " knottiness" usually begins  to present
 itself, increasing  with  the  advance of Pregnancy.   In  many instances, how-
 ever, these mammary sympathies are entirely absent; and they may be  simu-
 lated by changes that take place in consequence of various  affections of the
 Uterus.  A  change  of  colour  in the  areola  is a very common,  but not an
* Op. cit., p. 121. 
708
OF REPRODUCTION.
invariable, occurrence in the early months of pregnancy;  but another sign is
afforded by the areola and nipple, which is of more value because more con-
stant,—namely,  a  puffy  turgescence, and an increased development of the
little glandular follicles, or tubercles, which  commonly secrete a dewy mois-
ture.—The presence or  absence of kiesteine in the Urine (§ 859) also may
probably be regarded as  a valuable diagnostic sign.   This substance appears
on the surface of the fluid, after it has stood for two or three days, in the form
of a thin 'pellicle of a somewhat fatty aspect; it is preceded  by a sediment
which has very much the appearance of cotton wool; and it disappears when
the urine is  decomposing, at  the  same  time  emitting an  odour like  that of
putrid cheese.*—Many  other changes in the constitution take place during
Pregnancy; indicated by the  buffiness of the blood, the irritability of the sto-
mach, and  the  increased excitability of the  mind.  All these, however, are
discussed with sufficient  amplification, in works on Obstetric Medicine.
   927.  The act of Conception, being one of  a purely  organic  nature, is not
attended with any consciousness  on the part of the mother;  but there are
some women, in whom it is attended with certain sympathetic affections, such
as faintness, vertigo, Sic, that enable them to fix upon the particular  time at
which it has  taken place.  From that  period, however, the Mother  has no
direct consciousness of the change going on in the Uterus (save by the effects
of its increasing pressure on  other  parts), until the occurrence of what is
termed  " Quickening."  This  is generally described as a  kind of fluttering
movement, attended with some degree  of syncope or vertigo.  After it has
once  occurred, and has  strongly excited attention, it is occasionally renewed
once  or twice, and then gives place to the ordinary movements of the foetus.
Not unfrequently, however, no movement whatever is  felt, until near  the end
of the term of gestation,  or even through the  whole of  it.   As  to the cause of
the sensation, Obstetricians  are much  divided;  and no satisfactory  account
has  been given of it.    It has  been vulgarly  supposed to be due to  the first
movement of the Foetus, which was imagined then to become possessed of an
independent  life:  and the English law recognizes the  truth of this doctrine,
in varying the punishment of an attempt to  procure  Abortion, according to
whether the woman be " quick with child" or not; and in delaying execution
when a woman  can be proved to be so, though it is made to proceed if she is
not, even if she be unquestionably pregnant.   Whether or not the first sensible
motions of the Foetus  are the cause of the peculiar feeling in question, there
can be no doubt that the Embryo  has as much independent vitality before, as
after, the quickening.  From the time that the Ovum quits the Ovary, it ceases
to be a part of  the Parent, and is dependent on it only for a  due supply of
nourishment, which it converts, by its  own  inherent  powers, into its proper
fabric.   This dependence cannot be  said to cease at the moment of quicken-
ing;  for the connection  must be prolonged during several weeks, before the
Foetus can be said to be capable of living without such,assistance.  The earliest
period at which this may occur, will be presently considered  (§ 932).
   928. At the conclusion of about nine (solar) months  from the period of con-
ception, the time of Parturition arrives.  The Uterus,  by its own efforts, and
by the assistance of the  muscles  of Expiration, expels its contents;  and the
 membranes of  the Ovum being usually ruptured before it  is  entirely dis-
 charged, the Foetus comes at once into the world.  Although  there can be  no
 doubt that, as already  stated  (§ 393), the contractile fibres of  the Uterus may
 be called into effectual action without Nervous influence, yet it is equally cer-
 tain  that Uterine  contractions  may be induced through the Spinal system of

   * [See an excellent paper on this subject in Am. Journ. of  Med. Sci.. vol iv  N S  bv
 Elisha Kane, M. D.—M. C] 
ACTION OF THE FEMALE.
709
 nerves.   For in no other way can we account  for many phenomena which
 are obviously of a reflex character; such  as the sudden contraction of the Ute-
 rus, previously distended and inactive, when  cold  is  applied to the external
 surface of the  body, or  when the child is  applied to the nipple.   In the first
 stage of labour, the Uterine contractions  appear to  be alone concerned; and
 it is not until the  head  of  the child is passing through the Os Uteri, and  is
 entering the Vagina, that the assistance of the Expiratory muscles is called
 in.  The excitor fibres, which convey to the  Spinal Cord the stimulus that
 calls them into action, must originate, therefore,  rather in the Vagina  than in
 the Uterus itself.   Whilst the fibres of the fundus and body of the Uterus are
 in powerful  contraction, those of the Cervix Uteri and Vagina must be in a
 state of dilatation; and this  dilatation appears to  be in  some respects different
 from the mere  yielding to the pressure of the child's head.  A slow contrac-
 tion of the  fibres of the fundus  and body of the Uterus, and a yielding of
 those of the cervix, usually take  place during  some  days previous  to Par-
 turition ; so that the child lies lower, and the size ofthe abdomen diminishes.*
   929. As to the reason why the period of Parturition should be just nine
 months after that of Conception,  we know nothing  more than we do of that
 of similar facts in the  physical history of Man—such as the periodical return
 of the Gatamenia,—the  renewal  of the Teeth,—the recurrence of the tend-
 ency to Sleep, &c.  That it is immediately dependent upon sofne state ofthe
 constitution, rather than  upon  the condition  of the Uterus, appears from the
 fact that, in cases of Extra-uterine pregnancy, contractions resembling those
 of labour take  place in  its  walls.  Moreover,  various  states  of the constitu-
 tion, especially that which is designated  as irritability, may induce the occur-
 rence of the parturient efforts at an earlier period; and this constitutes Abor-
 tion, or Premature delivery, according to the viability of the child.  There
 are some women, in whom  this regularly happens at a certain month, so that it
 seems  to be an action natural to them ; but it is  always to be prevented, if pos-
 sible, being injurious alike to the mother and child;  and this prevention is to
 be attempted by rest and  tranquillity of mind and  body, and by a careful avoid-
 ance of all the exciting  causes, which may produce Uterine contractions  by
 their operation on the Nervous system.   For  it is to be  remembered that,
 although the muscular fibres of the Uterus are capable, like those of the ali-
 mentary canal, of an independent  action, they are likely to be excited to ope-
 ration through  the Nervous system, and  especially  through the Sympathetic
 (§ 393).  The same action which expels the Foetus, also detaches the Pla-
 centa ;  and  if the Uterus contract with sufficient force after this has been
 thrown off, the orifices  of  the vessels which communicated with it  are so
 effectually closed, that little  or no hemorrhage takes place.   If, however, the
 Uterus  does not contract, or relaxes after  having contracted, a large amount
 of blood may be lost in  a short time from the open orifices.   For some little
 time after  Parturition, a sero-sanguineous  discharge,  termed  the  Lochia, is
 poured  out from the Uterus; and this  commonly contains  shreds  of the De-
 ciduous membrane, which had not been  previously detached.  Within a few
 weeks  after delivery, the Uterus regains (at least in a healthy subject)  its pre-
 vious condition;  and it is probable that the portion of its mucous Membrane,
 which had been thrown off as Decidua, is very early reproduced.
  930.  Although  the  duration of Pregnancy is commonly  stated  at nine
 solar months, it would be more correct to fix the period at 40  weeks, or 280
 days ;  which  exceeds  nine  months by from  5  to 7 days, according to  the
months included.  This, at  least, is the average result of observation, in cases

  * See some interesting Papers on the Physiology of Parturition, by Dr. W. Tyler Smith,
in the Lancet, July 6 and 13, 1844.
60 
710
OF REPRODUCTION.
in which the period of Conception could be fixed from peculiar circumstances,
with  something like  certainty.  The  mode of reckoning  customary among
women, is to date from the middle of  the  month after the last appearance  of
the Catamenia; but it is certain  that Conception  is much more likely to take
place soon after they have ceased  to flow, or even before their access, than at
a later period (§ 909);  so that, in  most instances, it would  be most correct to
expect Labour at forty weeks and  a few days  after the last recurrence of the
Menses.   The period  of Quickening may  be relied on in some women, in
whom it occurs with great regularity  in  a certain  week of  Pregnancy; but
there is  in general great latitude  as to the time of its  occurrence.  The usual
or average time is probably about  the  18th week.
   931.  The question of the extreme limits of Gestation, is one of great import-
ance  both to the Practitioner  and  to the Medical Jurist; but it is one which
cannot yet be regarded as satisfactorily decided.  Many persons, whose expe-
rience should  give much weight to their opinion, maintain  that  the regular
period of 40 weeks is never extended for more than two or three days ; whilst,
on the other hand, there  are numerous cases on record, which,  if testimony is
to be believed at all, (and in many of  these, the character  and circumstances
of the parties placed them above suspicion,) furnish ample  evidence that Ges-
tation may be prolonged  for  at  least three weeks  beyond  the regular term.*
The  English law fixes no precise  limit; and  the  decisions which have been
given in our courts, when questions of this  kind have been raised, have been
mostly formed  upon the collateral circumstances.   The law of France pro-
vides that the  legitimacy of a child born  within  300  days after the  death  or
departure of the husband, shall not be  questioned ; and a child born after more
than  300 days  is not declared a bastard, but its legitimacy may be contested.
By the  Scotch law, a  child  is not  declared a bastard, unless  born  after the
tenth month from the death or departure of the husband.

   a.  The analogical evidence drawn from observations on the lower animals is extremely
strong.  The observations of  Tessier,  which were continued during a period of forty years,
with every precaution against inaccuracy, have furnished a body of results, which seems
quite decisive.   In the Cow, the  ordinary period of gestation  is about the same as in the
Human female; but out of 577 individuals, no less than 20 calved beyond the 298th day, and
of these, some went on to the 321st, making an excess of nearly six weeks.  Of 447 Mares,
whose natural period of gestation is about 335 days, 42 foaled between the 359th and the 419th
day, the greatest protraction being  thus 84 days, or just one-fourth of the  usual term. Of 912
Sheep, whose natural period is about  151 days, 90 yeaned beyond  the 153d day; and of
these, 7 went on until the 157th day, making an excess of 6 days. Of 161 Rabbits, whose
natural period is about 30 days, no fewer than 25 littered between the 32d and 35th;  the
greatest protraction was  here one-sixth  of the whole period, and the proportion in which
there was a manifest prolongation was also nearly one-sixth of the total number of indi-
viduals.  In the  incubation of the common Hen, Tessier found that there was  not unfre-
quently a prolongation to the amount of three days, or one-seventh ofthe whole period.
   b.  In regard to Cows, the observations of Tessier have been recently confirmed by those
of Earl Spencer, who has publishedf a table of the period of gestation as observed in 764
individuals; he considers the average period to be 284 or 285 days: but no fewer than 310
calved after the 285th day; and of these, 3 went on to the 306th day, and  1 to the 313th.
It is curious that,  among the  calves born between the 290th and 300th days, there was a
decided preponderance of males,—these being 74, to 32 females; whilst all of those born
after  the 300th day were females.
   c.  It appears, however, from some recent statements published on the authority of Earl
Spencer, that the Male parent may exert an important influence on the period of gestation.
Of 75 Cows in calf by a particular^bull, the average period was 288£ days, or four days'
more than the usual period.  Of the 704 cows previously mentioned, 185 (nearly one-fourth)
went less than 281 days; whilst not one of the cows in calf to this bull did so. On the
  * A good collection of such cases will be found in Dr. Montgomery's excellent work
the Signs of Pregnancy.
  •j- Journal ofthe English Agricultural Society, 1839. 
ACTION OF THE FEMALE.
711
other hand, ofthe 764 cows first mentioned, 111 (rather more than one-seventh) went above
289 days; while, of the cows in calf by this bull, 29 out of 75 (nearly two-fifths) went above
289 days.*                                                          '
  d. Another series of observations has recently been published by Mr. C. N. Bement of
Albany, U. S.,f who has recorded the period of gestation  of 62 Cows.  The longest period
was 336 days; the shortest, 213 days.  The  average period for male calves was 288 days;
and for females, 282 days.

These variations  are probably to be regarded  as due, not so much to  a pro-
longation of the period of C^ero-gestation, as to  various circumstances  which
may have  a retarding influence on the  process  of Fecundation, and  on  the
transmission of the Ovum through the Fallopian tube.   These have been well
pointed out by Dr. Montgomery 4  It may be added that, in Dr. Barry's  ob-
servations  on  the  early changes that take  place  in the Ovum of Rabbits, he
has noticed several  irregularities  of this description.—On the whole, it may
be considered  that, in regard to  the  Human female, the French law is  a very
reasonable one.   It  is probable, from  the circumstances alluded to in the pre-
ceding  paragraph, that Gestation is protracted to the  extent of a week,  ten
days, or a fortnight, much more frequently than  is commonly supposed.   In
several of the cases in which  the protraction appeared indubitable, the  Infant
was unusually large and  vigorous.
   932. In  regard to the shortest period  at which Gestation may terminate,
consistently with  the viability of the Child, there is a still greater degree of
uncertainty.   Most  practitioners are of opinion, that it is next to impossible
for a Child to live and grow to  maturity, which has not nearly completed its
seventh month; but it is almost unquestionable that Infants, which have been
born at a much earlier period, have  lived for  some  months.   It is rare in such
cases, however, that the  date of Conception  can  be fixed with  sufficient pre-
cision to enable a definite statement to be given.   Of the importance  of  the
question, a case which recently occurred in  Scotland affords sufficient  proof.
A vast  amount of contradictory evidence was  adduced on this trial; but, on
the general rule of  accepting positive in preference to negative testimony, it
seems that we ought to  consider it possible, that a child may live for some
months, which has been  born at the conclusion of 24 weeks of gestation.   In
the case in question, the  Presbytery decided in favour  of  the legitimacy of an
Infant born alive  within  25 weeks after marriage.§
  a. A very interesting case  is on  record,|| in which the  mother (who had borne five chil-
dren) was confident that her period of gestation was less  than 19 weeks; the facts stated
respecting the development of the  child are necessarily very imperfect, as it was important
to avoid exposing his body, in order that his temperature might be kept up; but at the age
of three weeks, he was only 13 inches in length, and his weight was no more than 29 oz.
At that time, he might be regarded, according to the calculation of the mother, as correspond-
ing with an infant of 22 weeks or 5^ months; but the length and weight were greater than
is usual  at that period, and he must have been probably born at  about the 25th week.   It is
an interesting feature in this case,  that the calorific  power of the Infant was so low,  that
artificial heat was constantly needed to sustain it; but that, under the influence of the heat
of the fire, he evidently became weaker,  whilst the warmth of a person in bed rendered
him lively and comparatively strong.  During the first week, it was extremely difficult to
get him  to swallow;  and it was nearly a  month before he  could suck.  At the time of the
report, he was four months old, and his health appeared very good.
  b. Another case of very early viability has been more  recently  put on  record  by  Mr.
Dodd:1I  in this, as in the former instance, the determination of the child's  age rests chiefly
on the opinion of the mother; but there appears no reason for suspecting any fallacy.  The
* Dr. J. C. Hall, in Medical Gazette, May 6, 1842.
t American Journal ofthe Medical Sciences, October, 1845.        X °P- cit» P- 272-
§ Report of Proceedings against the Rev. Fergus Jardine, Edin., 1839.
|| Edinb. Med. and Surg. Journal, vol. xi.
IT Provincial Medical and Surgical Journal, vol. ii. p. 474. 
712
OF REPRODUCTION.
child seems to have been born at the  26th or 27th week of gestation;  and having been
placed under judicious management, it has thriven well.
  c. One of the most satisfactory cases on record, is that detailed by Dr. Outrepont (Professor
of Obstetrics at Wurtzburgh), and stated by Dr. Christison in his evidence on the case just
alluded to.  The evidence is as complete as it is possible to be in any case of the kind; being
derived not only from the date assigned by the Mother to her Conception, but also from the
structure and history of the Child.  The Gestation could have only lasted 27 weeks, and was
very probably less.  The length ofthe child was 13^ inches, and its weight was 24 oz.  Its
development was altogether slow; and at the age of eleven years, the child seemed no more
advanced in body or mind, than most other lads of seven years old.  In this last point, there
is a very striking  correspondence with  the results of other observations upon very prema-
ture children, made at an earlier age: and these all harmonize with the general principle
already more than once alluded to,—that the shorter the period during which  the early de-
velopment of the embryo takes place at the expense of nourishment supplied by the parent,
the lower is the degree of development it will  ultimately attain (§ 45).
,  d. To these may be added another case of recent occurrence in America: in which a
woman,  who believed herself to be  in the sixth month of pregnancy, was prematurely de-
livered in  consequence of a fall.   The child  seemed barely alive, showing  scarcely any
motion, and being too feeble to cry. It had no nails on its hands or feet, nor hair on the scalp ;
and the cranium was imperfectly ossified.  At the end of seven weeks it was weighed for
the first time, and found to weigh only 26 oz.   When ten months old, it was playful, lively,
and healthy; and weighed 10^ lbs.   The reporter of this case regrets that he did not take
more particular notice of the state  of the  Child at birth, which  he was prevented  from
doing by the daily expectation of its death.*

   933.  There is another question regarding  the Function of  the Female  in
the Reproductive act,  which is of great  interest in a scientific point  of view,
and which may become of importance  in Juridical inquiries;—namely, the
possibility of Superfcetation, that is, of two distinct conceptions at an interval
of greater or less duration ; so  that two  foetuses of different ages, the offspring
perhaps of different parents,  may  exist in the  Uterus at the  same time.—The
simplest case of Superfcetation, the frequent-occurrence  of which places it be-
yond reasonable doubt, is that  in  which a female  has intercourse on the same
day with two Males of different complexions, and bears twins at the full time;
the two infants resembling the two parents respectively.  Thus, in the slave-
states of America, it is not uncommon for a black woman to bear at the same
time  a  black  and  a  mulatto child;  the former being the offspring of her black
husband, and the latter of her white paramour.   The converse has occasionally
though less frequently, occurred ;  a  white woman bearing  at the same time  a
white and a  mulatto  child.  There  is  no  difficulty in  accounting for  such
facts, when it is remembered that nothing has  occurred to prevent the Uterus
and Ovaria from being as ready for the second conception as for the first; since
the orifice of the former is not  yet closed up ; and, at the time when one ovum
is matured for fecundation, there are usually more in the same condition.
But it is not  easy thus to  account for  the birth of two  children, each appa-
rently mature, at an interval of five or six months; since it might have been
supposed that the uterus was so completely occupied with  the first Ovum,  as
not to allow of the transmission of the seminal fluid, necessary for the fecun-
dation of the second.   In cases where  two children have  been produced  at
the same time, one  of which was fully-formed, whilst the other was small and
seemingly premature, there  is  no occasion whatever to  imagine that the two
were conceived at  different periods; since the smaller  foetus  may have been
" blighted," and its development retarded, as  not unfrequently happens in other
cases.  Nor is it necessary to  infer the  occurrence of Superfcetation  in every
case,  in which a living child has been produced a month or  two after  the birth
of another;  since the latter may have been premature,  whilst the former has
been  carried  to the full term.   But such a difference can scarcely be, at the
* American Journal of the Medical Sciences, April 1843. 
t-yj/r
s~
                      DEVELOPMENT OF THE EMBRYO.                  713

most, more than 2£ or three months;  and there are several cases now on re-
cord, in which  the  interval was from  110 to 170 days, whilst neither of the
children  was premature  in appearance;  so that the possibility  of a second
Conception, when the Uterus already contains an Ovum of several months,
can scarcely be denied, however improbable it may seem.  ~

                     4.—Development of the Embryo.

   934.  Under this  head  it is intended to state, not so much the details of the
process of Development, as those leading  facts, the knowledge of which is
desirable in itself, as well as essential to the due comprehension of the former.
It is difficult to see  what  practical benefit can result from a minute acquaint-
ance with all the steps of the evolution of the Embryo,  however interesting
these may be in a scientific point of view;  and the time of the ordinary Stu-
dent, on which there are so many pressing calls, may be much better occupied
than in committing  them to memory.   In the following  sketch, little will be
said respecting the latter stages of the process, or the development of particular
organs, since these  have been  already noticed under their severally distinct
heads.   Our attention will first be given  to the  formation of the Embryonic
mass, and of the membranes surrounding the Yolk-bag;  and then to the ori-
gin ofthe Vertebral column, Digestive organs, and Circulating apparatus.
   935. The Ovum, when  it quits the Ovarium, has been stated to  contain
within the Germinal Vesicle, two cells which did not exist there previously
to fecundation;  and from each  of these, two new cells are subsequently pro-
duced, which in their turn give birth to eight others (§ 917).   In this manner,
the number of vesicles originating in the twin-cells of the Germ is continually
increased, until at last they become too numerous to be  counted, and form a
cluster resembling  a  Mulberry in  appearance;  this mulberry-like structure
may be conveniently termed the Germinal  Mass (Plate I., Fig. 15, a).  In the
centre of this mass  there is found a peculiar Cell, differing from the rest in its
greater size, and in possessing a very well-defined annular nucleus, with a
pellucid cavity in its centre (Fig. 16,  a, b).   From this  peculiar Cell, all the
parts which enter  permanently into the composition of the  Embryo are de-
veloped ; the vesicles forming  the exterior of the germinal mass being sub-
servient to a merely temporary purpose.  This  central or Embryonic Cell is
gradually brought to the  surface of the Germinal Mass, by the formation of a
cavity  c in the interior of the latter; for the layer of cells within which this
cavity is  formed, progressively extends  itself, until it comes into contact with
the inner surface of the  Yolk-bag, having  absorbed the yolk  into the hollow
thus left.  Thus out of  the  periphery  of  the Mulberry-mass, appears  to be
formed the exterior  layer of what is termed the  Germinal Membrane: this
membrane is first seen as an epithelium-like layer of cells, covering the Yolk;
but beneath this layer, which is afterwards  known as the serous lamina of the
Germinal membrane, two others are  subsequently produced from the central
portion of the Germinal mass.   Now it is highly interesting to observe, that
this Germinal Membrane, which in the higher animals is  a mere temporary
structure, subservient only to a temporary function, forms, in the lower tribes,
the greater part of  the permanent fabric of the body.  Thus, in the Polypes,
the cavity in which the  Yolk is inclosed becomes a Stomach ;  the  external
laver of the Germinal Membrane becomes the integument; whilst the internal
forms the lining of the  Digestive cavity, of which the  mouth  is formed by
absorption of its wall at one point.  Here the Yolk is directly  absorbed and
assimilated by the  surrounding membrane.   In the higher Oviparous animals,
the  Germinal Membrane serves to absorb nutritious  matter from the  \ oik,
and to prepare it for  the use ofthe Embryo itself, by converting it into  Blood
                                    60* 
714                        OF REPRODUCTION.
(§ 938);  but, after the Yolk has been  exhausted, the Yolk-bag is taken into
the body, and  is  gradually removed by absorption.   In Mammalia,  these
structures are of less importance.  The store of Yolk, laid up for the nutrition
of the Embryo, is  comparatively inconsiderable; being only destined to serve
for the short time that elapses, before  the Ovum forms  its new connection
with the  Parent, through the  medium of the  Chorion; and the Yolk-bag  is
ultimately separated from the Embryo,  and thrown off as useless.   Still the
early processes are the  same in Mammiferous, as they are in Oviparous ani-
mals ;  and the  Development of Man, of a Bird, of  a Reptile, or of a Fish,
takes place, up to a certain point, upon  the same general plan.
   936. The Embryonic Cell, and the cluster of cells that surrounds it, hav-
ing arrived on the  surface of  the Yolk by the  movement just described, con-
stitute  what is known in the Bird's egg under the name  of the Cicatricula.
This is a semi-opaque disc, composed of numerous flattened cells; and in the
midst of it is seen a round  transparent space, termed the Area Pellucida,
which  is  nothing else than the place  occupied  by the large Embryonic Cell,
now become flattened, and still  retaining its clearness.  In the centre of this
is seen a very faint line, which is termed the Primitive Trace; and this  is
the large  annular Nucleus (Plate I., Fig. 16, b) of the Embryonic Cell, now
become elongated,  and itself beginning to be developed into cells.  The same
process then takes place within the Embryonic  Cell, which has been described
as occurring within the Germinal Vesicle (§ 916); the granules forming the
periphery of  the nucleus are first developed into  cells, and  these are  pushed
outwards by a new series subsequently generated near the centre.  From the
mass of  cells thus  formed, a hollow process passes down  into the Yolk; and
this gradually extends itself in the  same manner as did that formed from the
Mulberry-mass, until it includes the whole Yolk, and  comes into contact with
the inner surface of the layer of cells  already mentioned as forming the serous
or external lamina of  the Germinal Membrane.  This  second layer of cells
is probably that which forms the vascular lamina of the  Germinal Membrane.
A third process seems to be afterwards  sent down, from a part of the nucleus
somewhat interior  to that from  which the last proceeded: and  this becomes
the mucous or internal lamina ofthe  Germinal Membrane.
   937. The cell-germs forming  the periphery of the Nucleus having been thus
developed, those nearer the centre then begin to exhibit a corresponding acti-
vity.   Their evolution follows exactly the  same plan as that which has been
described in  regard to the contents  of the Germinal Vesicle (§ 916); with
the exception that  these are arranged in an elongated and  not  in a circular
form.  The shape of  the nucleus at this time may be compared to that of a
pear; the large end marking the situation of  the Head ; whilst the prolonged
portion is the rudiment of the body.   On the  median line  is seen a  groove,
occupying the situation in which the  Nervous Centres are to be  subsequently
evolved (Fig. 25, Plate II.).   These,  when first developed, are surrounded by
a tubular structure, which has but a temporary existence in the higher Verte-
brata, but which is permanent in the lower Fishes : this structure, termed the
Chorda Dorsalis,  is  found,  wherever it exists, to  be entirely  composed  of
nucleated cells.   From the cells which  are exterior to these, is  produced the
Vertebral Column; and the  mode  in which this originates is somewhat  as
follows.  The cells on either side of the central space (in which the elements
of the  nervous system  are not yet developed) rise up in a ridge, so that the
central space becomes  a groove; these  two ridges gradually rise up  and ap-
proach one another, and they are then  observed to  contain, in what subse-
quently becomes the thoracic region, a few  pairs of small  opaque plates.
The ridges (termed plicae dorsales, or dorsal laminae) continue inclining towards
each other, until they coalesce, so that a complete tube is formed ; and in this 
DEVELOPMENT OF THE EMBRYO.
715
tube an indication is soon perceived of a division into vertebra?, of which the
plates just mentioned are the incipient arches (Fig. 26,  Plate II.).  Towards
the anterior extremity, however, the dorsal laminae do  not at once close  in;
and the large cells, in which the great divisions of the  Encephalon originate
(§ 358), may be seen between them.  From the Dorsal Lamina on either side,
a prolongation passes outwards and then downwards, forming what is known
as the ventral lamina; in this are developed the Ribs and the transverse pro-
cesses of the Vertebrae ;  and the two have the same tendency to meet on the
median  line, and  thus  to  close in  the abdominal cavity, which the dorsal
laminae have to inclose the spinal cord.  At the same time  the  layers of the
Germinal Membrane, which lie beyond  the extremities of the Embryo, are
folded in, so as to  make  a  depression on  the yolk;  and their folded margins
gradually approach one another under  the abdomen.  In  these two modes, a
cavity is formed beneath the Embryonic  mass, which is separated from  the
general cavity of the Yolk  by the folds just described;  but  these still leave a
passage which, in  the Bird, remains of considerable  size until  a much later
period, but which, in the Mammiferous Ovum, is soon  obliterated.  For  the
sac which contains the yolk, and from which the abdominal cavity is pinched
off (as  it were) at a very early period, is destined, in the Mammiferous ani-
mal, to be entirely cast away; the purpose which it has to serve being one of
a very temporary character.
   938.  Whilst these  new  structures are  being  produced, a very remarkable
change is taking place in that part of the  Serous lamina, which surrounds the
Area Pellucida.  This rises up on either side in two folds;  and these gradually
approach one  another, at last meeting in the space between the general  en-
velope  and  the  embryo, and thus  forming an additional investment to  the
latter.  As each fold  contains  two layers of membrane, a double envelope
is thus formed;  of this, the  outer lamina adheres to the general envelope;
whilst the inner remains as a distinct  sac, to which  the name of Amnion is
given.   (See Figs. 284, 285, and 286.)   This takes place  during the third
day in the Chick.; the period at which  it  occurs in the Human Ovum is diffi-
cult to be ascertained, owing to the small number of normal specimens which
have come  under observation at a  sufficiently early stage.—During the same

               Fig. 283.                           Fig. 284.
 Plan of early uterine Ovum.  Within the      Diagram of ovum at later stage; the digestive ca-
external ring, or zona pellucida, are the serous    vity beginning to be  separated from the yolk-sac,
lamina, o; the yolk, b; and the incipient em-    and the amnion beginning to be formed; a, chorion;
bryo c] '                              b, yolk-sac; c, embryo; d, and e, folds of the serous
                                     layer rising up to form the Amnion.

period, a very important provision for the future support of the Embryo begins
to be made; by the development of Blood-vessels and the formation of Blood.
Hitherto, the Embryonic structure has been nourished by direct absorption of 
716
OF REPRODUCTION.
the alimentary materials supplied to it  by the Yolk; in the same manner as
the simplest Cellular  plant is developed at the expense of the  carbonic acid,
moisture, Sic, which it obtains for itself from the surrounding elements.   But
its increasing size, and the  necessity for a more free communication between
its parts than any structure  consisting of  cells  alone can permit, call for  the
development of Vessels, through which the nutritious fluid may be conveyed.
These vessels are first seen  in that part of  the Vascular lamina of the Germinal
Membrane, which immediately surrounds the embryo;  and  they form a  net-
work, bounded by a circular channel, which  is known under the name of the
Vascular Area (Fig. 27, Plate II.).  This gradually extends itself, until  the
vessels spread over the whole of the membrane  containing the yolk.   The
first blood-discs appear to be  formed from the nuclei of  the cells, whose
cavities have become continuous with each other to  form the vessels (§ 222);
and from these, all subsequent blood-discs are probably generated.  This  net-
work of blood-vessels  serves the purposes of absorbing the  nutritious matter
of the Yolk, and of conveying it towards  the embryonic structures, which are
now in process of rapid development.   The first movement of the fluid is
towards the embryo;  and  this can be  witnessed  before any distinct heart is
evolved.   The same process of  absorption from  the Yolk, and of conversion
into Blood, probably continues as long  as there is any alimentary material left
in the sac.
   939. The  Yolk-sac is early separated  in the Mammalia, by a constriction
of the portion which is continuous with the  abdomen of the Embryo;  and it
is known from that time under the name of the  Umbilical Vesicle.  The com-
munication, however, remains open for  a time through the constricted portion,
which is  termed the Vitelline Duct;  and even after this has been cut off, the
trunks which connected the circulating system of the Embryo with that of the
Vascular Area, are still discernible; these  are  called  Omphalo-Mesenteric,
Meseraic, or Vitelline vessels.  It was  formerly believed, that the  nutrient
matter of the yolk passes directly through the  Vitelline duct, into the (future)
digestive cavity of the Embryo, and is  from it absorbed into.its  structure; but
there can now be little doubt, that the  Vitelline vessels are the real agents of
its absorption, and that they convey it  to the tissues in process of formation.
They do, in fact, correspond to the Mesenteric veins of Invertebrated  animals,
which are the sole agents in the absorption of nutriment from  their digestive
cavity (§ 674); and the yolk-bag, as already remarked, is the temporary  sto-
mach of  the Embryo,—remaining as the permanent stomach in the Radiated
tribes.  Previously to the ninth day of incubation (in the Fowl's egg), a series
of folds are formed by the  lining  membrane of  the yolk-bag,  which project
into its cavity;  these become gradually deeper and more crowded, as the bag
diminishes in size by the  absorption of its contents.   The Vitelline vessels,
that ramify upon the yolk-bag,  send into these folds (or valvulae conniventes)
a series of inosculating loops, which immensely increase the  extent of  this
absorbing apparatus.  But  these minute  vessels  are not in immediate contact
with the  yolk; for there intervenes between them a layer of nucleated cells,
which is easily washed away.  It was from the colour of these, communicated
to the  vessels beneath, that Haller termed  the latter  vasa lutea; when the
layer is removed, the vessels present their usual colour.  There seems good
reason to believe, that these cells, like those of the Intestinal  Villi in the adult
(§ 672), are the real agents in the  process of absorbing and assimilating the
nutritive  matter of the yolk; and that  they  deliver this up to the vessels, by
themselves undergoing rupture  or dissolution, being replaced by new layers.
   940. The formation of the Heart takes place in the Vascular layer, beneath
the upper part of the Spinal Column; it at first appears as a mere cavity in its
substance, surrounded only by cells; but its walls gradually acquire  firmness 
DEVELOPMENT OF THE EMBRYO.                   717
and distinctness, and become sufficiently powerful to propel the blood through
the vessels of the  Embryo  and those of the Vascular Area.   The first ap-
pearance of the Heart in the Chick is at about the 27th hour;  the time of its
formation in Mammalia  has not  been distinctly ascertained.  In its earliest
form, it has the same simple character, which is  presented  by the central im-
pelling cavity of the lower Invertebrata;  being a  mere prolonged canal, which
at its posterior  extremity  receives the veins, and  at its anterior sends forth the
arteries.   After a short time, however, it becomes bent upon itself (Plate II.,
Fig. 27, d) ; and it is soon subdivided into three cavities, which  exist  in  all
Vertebrata,—a  simple auricle or receiving cavity, a simple  ventricle or pro-
pelling cavity, and a bulbus arteriosus at the origin of the aorta.  The  circu-
lation is at  first carried  on  exactly  upon  the  plan, which is permanently
exhibited by Fishes.   The Aorta subdivides into four or five arches on either
side of the  neck;  and these are  separated  by slits or fissures, much resem-
bling  those  which form the entrances  to  the  gill-cavities of Cartilaginous
Fishes.   These arches reunite to form the descending aorta, which transmits
branches to  all parts of the body.   Such is  the  first  phase or aspect of the
Circulating Apparatus, which is common to all Vertebrata during the earliest
period of  their development, and which  may, therefore, be considered as  its
most general form.   It remains  permanent in the  class of Fishes; and in them
the vascular system undergoes further development on the same type, a num-
ber of minute tufts being sent forth from each of the arches, which enter the
filaments of the  gills, and serve  for  the  aeration of the blood.  In higher
Vertebrata, however, the plan of the circulation is  afterwards entirely changed,
by the formation of new  cavities in the heart, and by the production of new
vessels; these changes will be presently  described.  It is incorrect, therefore,
to speak of  the vascular arches  in  their necks as branchial arches; since  no
branchiae or gills are  ever developed  from them.  The clefts  between them
may be  very distinctly seen  in the Human Foetus towards the end of the first
month;  during the  second, they usually close up and disappear.
   941.  With the evolution  of  a  Circulating  apparatus,  adapted to absorb
nourishment from the store prepared  for the  use  of the Embryo, and to  con-
vey it to its  different tissues, it becomes necessary that a respiratory apparatus
 The Amnion in process of formation, by the
arching over of the serous lamina; a, the
chorion; 6, the yolk-bag, surrounded by se-
rous and vascular laminae;  c, the embryo;
d, e, and/, external and internal folds of the
serous layer, forming the amnion ; g, incipi-
ent allantois.
Fig. 286.
 Diagram representing a Human Ovum in
second month;  a. 1, smooth portion of cho-
rion ;  a. 2, villous poriion of chorion; k, k,
elongated villi, beginning to collect into Pla
centa; b, yolk-sac or umbilical vesicle; c, em
bryo;/, amnion (inner layer); g, allantois;
h, outer layer of amnion, coalescing with
chorion. 
718
OF REPRODUCTION.
should  also be provided, for  unloading the blood of the  carbonic acid with
which it becomes charged  during the course of its circulation.   The tempo-
rary Respiratory apparatus now  to be  described, bears a strong resemblance
in its own character, and especially in its vascular connections, with the gills
of the  Mollusca; which  are  prolongations of the external surface (usually
near the  termination  of the  intestinal  canal),  and which almost  invariably
receive their vessels from that part of the system.  This apparatus is termed
the Allantois.  It consists at  first of a kind  of diverticulum or prolongation of
the lower part of the Digestive cavity, the formation of which has been already
described.  This is  at  first  seen as  a single vesicle, of no great  size  (Fig.
285, g);  and in the Foetus of Mammalia, which is soon provided with other
means  of aerating its blood, it seldom attains  any considerable  dimensions.
In Birds, however, it  becomes so large as  to extend  itself around  the  whole
Yolk-sac, intervening between it  and the membrane of the shell;  and through
the latter it comes into relation with the external air.  The preceding diagram
(Fig. 286) will serve  to explain  its origin  and position in the Human ovum.
The chief office of the  Allantois in Mammalia is to convey the vessels of the

                                  [Fig.  287.
 Diagram of Human Ovum, at the time of formation of Placenta; a, muco-gelatinous substance, block-
ing up os uteri; b, b, Fallopian tubes; c,c, Decidua vera, prolonged at c 2, into Fallopian tube ; ^cavity
of uterus, almost completely occupied by ovum; e, e, angles at which Decidua vera is reflected'; /, De-
cidua serotina; g, allantois; h, umbilical vesicle ; i, amnion ; k, chorion, lined with outer fold of serous
tunic. 
                      DEVELOPMENT OF THE EMBRYO.                  719

embryo to the  Chorion; and its  extent bears a pretty close  correspondence
with the extent of surface, through which  the Chorion comes into vascular
connection with the Decidua.  Thus, in  the Carnivora, whose Placenta ex-
tends like a band around the whole Ovum, the Allantois also lines the whole
inner surface of the Chorion, except where the Umbilical Vesicle comes in
contact with it.  On the other hand,  in  Man and the Quadrumana, whose
Placenta is restricted  to one spot, the Allantois is small, and conveys the
foetal vessels to one portion only  of the Chorion.  When these vessels have
reached the Chorion, they  ramify in its substance, and send filaments into its
villi; and in proportion as these  villi form that connection with the uterine
structure, which has been  already described, do the vessels increase in  size.
They then  pass directly from the Foetus  to  the Chorion;  and the Allantois,
being no longer of any use, shrivels up, and remains as a minute vesicle, only
to be detected by careful examination.   The same thing happens  in regard to
the Umbilical vesicle, from which the entire contents  have been by this time
exhausted; and from henceforth  the F.cetus is completely dependent for the
materials of its growth, upon the  supply it receives through the  Placenta,
which is conducted to  it by the vessels of the Umbilical Cord.  This state of
things is represented in  the preceding diagram.—The Allantois has a  corre-
spondence in situation with the  Urinary Bladder; but it  is only the  lower
part of it, pinched off, as it were, from the rest, that  remains as  such.  The
duct by which it is  connected with the abdomen gradually shrivels;  and  a
vestige of this  is permanent, forming the  Urachus or  suspensory ligament of
the Bladder, by which it is connected with the Umbilicus.   Before this takes
place, however, the Allantois is the receptacle for the  secretion ofthe Corpora
 Wolffiana, and of the  true Kidneys, when they are formed.
   942. It will be seen from the  preceding  diagram, that the Umbilical  Cord
receives an investment  from the Amnion,  which forms  a  kind of tubular
 sheath around it; it is continuous at the  Umbilicus  with the  integument of
 the  foetus;  and at the  point where the cord enters the Placenta, it is reflected
 over its  internal  or foetal  surface.   The  Amnion (which thus forms a  shut
 sac, like  that of  the Pleura, Arachnoid, &c.) contains a  fluid  known  as  the
liquor amnii; this  consists of water holding in solution a small quantity of
 albumen  and saline matter, and resembling, therefore,  very diluted serum.
 During the first two months of gestation, the Amnion and the inner surface
 of the Chorion (which is really  the reflected layer of the  Amnion, just as the
 lining of the abdominal cavity is formed by the peritoneum) are separated by a
 gelatinous-looking substance; which may perhaps be  considered as represent-
 ing  the white  of the egg in Birds; and which probably aids in the  nutrition
 of the Embryo, previously to the formation of the  Placenta (§  918).  This
 is absorbed during the second month;  and the Amnion  is then  found imme-
 diately beneath the  Chorion.—In the Umbilical Cord, when it is completely
 formed, the following  parts may be traced.   1. The tubular  sheath afforded
 by the Amnion.  2.  The  Umbilical Vesicle, with its pedicle, or  Omphalo-
 Enteric duct.  2.  The  Vasa Omphalo-Meseraica, or mesenteric vessels of
 the  Embryo, by which the Yolk was absorbed into the body of the Foetus;
 these  accompany the pedicle.  4. The Urachus, and  remains ofthe Allantois.
 5. The Vasa  Umbilicalia, which, in the later period of gestation, constitute
 the  chief part of the  Cord.  These last vessels consist in Man  of two Arte-
 ries and one Vein.  The  Arteries are the main branches  of the Hypogastric;
 and they convey to the Placenta the blood which has to be aerated and other-
 wise revivified, by being brought into  relation with that of the Mother.  The
 Vein  returns  this  to  the  Foetus, and discharges  a  part  of  it into  the Vena
 Portae, and a part  directly through the Ductus Venosus into the Aorta. 
720
OF REPRODUCTION.
   943.  A change  in the type of the Circulating systeil of the foetus, from
that at first  presented  by it (§ 940), takes place at a very early period.  At
about the 4th week, in the  Human Embryo, a septum begins to be formed in
the Ventricle;  and by  the end of the 8th week it is complete.  The Septum
Auriculorum is formed at a somewhat later period, and it remains incomplete
during the whole of foetal life ;  it is partly closed by the valvular fold cover-
ing  the  Foramen  Ovale, which fold is  developed during the third  month.
During the  same period, a transformation takes place  in the arrangement of
the large vessels proceeding from the Heart;  which ends in their assumption
of the form they present until the end of Foetal life;  and this undergoes but
a slight alteration,  when the plan of  the circulation is changed at the moment
of the first  inspiration.  The number of Aortic arches on  each side, which
was five at first, soon becomes reduced in the Mammalia to three, by the
obliteration  of the two highest pairs.  The Bulbus Arteriosus is subdivided,
by the adhesion of its  walls at opposite points, into two tubes, of which one
becomes the Aorta and the other the Pulmonary Artery;  and of  the  three
pairs of (branchial) arches, the highest,  being connected with the Aortic trunk,
contributes to the formation of the Subclavian and Carotid arteries; whilst of
the middle pair, the arch on the right  side is obliterated, the other becoming
the Arch of the Aorta.   The lowest pair arises from  the Pulmonary trunk,
and  forms the Pulmonary artery on each side; that on the left side, however,
goes on to join the descending Aorta  as before, and thus constitutes the Ductus
Arteriosus.
   944.  The following is the course of the circulation of the blood in the
Foetus.   The fluid brought from the Placenta by the Umbilical Vein is partly
conveyed at once  to  the Vena Cava  ascendens, by means  of the  Ductus
Venosus, and partly flows through the  Vena Portae into the Liver, whence it
reaches the  ascending  Cava by the Hepatic Vein.  Having thus been trans-
mitted through  the two great depurating organs, the  Placenta and the foetal
Liver, it is in the condition of arterial blood; but, being mixed in the vessels
with that which has been returned from the trunk and lower extremities, it
loses this character in  some degree  by the time that  it arrives in the Heart.
In the  right Auricle, which it then enters, it would be also mixed with the
venous  blood conveyed by the descending Cava; were it not that a very curi-
ous provision exists, to prevent (in great degree,  if not entirely) any such fur-
ther dilution.   The Eustachian valve has  been found, by the experiments of
Dr. J. Reid,* to serve the purpose of directing the arterial blood, which flows
upwards from the ascending Cava, through the  Foramen Ovale, into the left
Auricle, whence it passes into the Ventricle; whilst it also directs the Venous
blood, that has been returned by the descending  Cava  into  the right Ven-
tricle.   When the  Ventricles contract,  the Arterial blood  which the left con-
tains is propelled  into  the ascending Aorta, and supplies the  branches  that
proceed  to  the head and upper extremities, before it undergoes any admix-
ture ; whilst the Venous blood, contained in  the  right Ventricle,  is  forced
through  the Pulmonary  artery and  Ductus Arteriosus into the  descending
Aorta, mingling with the arterial current which that  vessel previously con-
veyed, and passing thus to the trunk and lower extremities.   Hence the Head
and superior extremities,  whose  development is required  to be in advance of
that  of the lower, are supplied with blood nearly as pure as that which returns
from the  Placenta: whilst the  rest of the body receives a mixture of this,
with what has previously circulated through the system;  and of this mixture
a portion is transmitted to the Placenta, to be renovated by coming into rela-
tion with the maternal fluid.  At birth, the course of  the current is  entirely
* Edinb. Med. and Surg. Journal, vol. xliii. 
DEVELOPMENT OF THE EMBRYO.

            [Fig. 288.
721
u  u
  The Postal Circulation; 1, the umbilical  cord, consisting of the umbilical vein and two umbilical
arteries; proceeding from the placenta (2); 3, the umbilical vein dividing into three branches; two (4, 4)
to be distributed to the liver ; and one (5), the ductus venosus, which enters the inferior vena cava (6);
7, the portal vein, returning the blood from the intestines, and uniting with the right hepatic branch; 8,
the right auricle; the course of the blood is denoted by the arrow, proceeding from 8 to 9, the left auricle;
10, the left ventricle; the blood following the arrow to the arch ofthe aorta (11), to be distributed through
the branches given off by the arch to the head and upper extremities.  The arrows, 12 and 13, represent
the return of the blood from the  head and upper  extremities through the jugular and subclavian veins,
to the superior vena  cava (14), to the right auricle (8), and in the course of the arrow through the right
ventricle (15), to the pulmonary artery (16); 17, the ductus arteriosus, which appears to be a proper con-
tinuation of the pulmonary artery—the  offsets at each side are the right and  left pulmonary artery cut
off; these are of extremely small size as compared with the ductus arteriosus. The ductus arteriosus
joins the descending aorta (18, 1^), which divides into the common iliacs, and these into the  internal
iliacs, which become the umbilical  arteries (19), and  return the blood  along the umbilical cord to the
placenta; while the  other divisions, the external iliacs (20), are continued into the lower extremities.
The arrows at the termination of these vessels mark the return of the venous blood by the veins to the
inferior cava.]

changed by its diversion into the Lungs;  which takes  place  immediately on
the first inspiration.   The Ductus Venosus  and Ductus Arteriosus soon shrivel
into ligaments;  the  Foramen Ovale becomes  closed  by its  valve; and the
circulation, which was before carried on upon the plan of that of the higher
Reptiles, now becomes  that of the  complete Bird  or Mammal.   It is  by no
means unfrequent, however, for  some  arrest of development to  prevent the
     61 
722
OF REPRODUCTION.
completion of these changes ; and various malformations, involving an imper-
fect discharge of the function, may hence result.*
  945. The Alimentary Canal has been shown to have its origin in the Yolk-
sac or Umbilical Vesicle; being a portion pinched off (as it were) from that
part of it, which is just beneath the Spinal Column of the Embryo  (§ 937).
At first it  is  merely a long narrow tube, nearly straight, and communicating
with the Umbilical Vesicle at about the middle of its length; thus it may be
regarded as composed of the union of two, an  upper and a lower division.
At first, neither Mouth nor Anus exists ;  but  these  are  formed early in the
second month, if not before.  The tube gradually manifests a distinction into
its special parts, Oesophagus, Stomach, Small Intestine, and Large Intestine;
and the first change in its position occurs in the Stomach, which, from being
disposed in the line of the  body, takes  an oblique direction.  The curves of
the large and small intestines present themselves at a later period.  It is at the
lower part of the  small Intestine, near its termination in the large, that the
entrance of the Omphalo-Enteric duct exists;  and a remnant of this canal is
not unfrequently preserved throughout life, in  the form of a small pouch or
diverticulum from that part of the intestine.  The various Glandular structures
connected with the alimentary canal, originate in diverticula from its walls, in
the manner already described in regard to the Liver (§ 826,  g).   The Lungs
and Respiratory apparatus  are formed in like manner, as diverticula from the
(Esophagus (§ 757, b, c).
  946. The mode in  which the chief organs of the Human embryo originate
having been thus  described, and sufficient particulars in regard to  their subse-
quent development having been already given  under distinct heads, it is un-
necessary  here  to add more on  this very interesting but complex subject; be-
cause for practical purposes there is  little or no advantage to be gained from
the most perfect aquaintance with it.   The most important of all the facts that
have come under  our  review, is that which has  been stated as in the highest
degree probable, if not yet absolutely proved, in regard to the relative offices
of the Male and Female in this hitberto  mysterious  process.  According to
the view here given, the Male furnishes the  germ; and  the Female  supplies
it with Nutriment, during the whole period of its early development.   There
is no  difficulty in  reconciling such a  doctrine with the well-known fact, that
the offspring commonly bears a resemblance to both parents (of which the
production of a hybrid between distinct species is the most striking example);
since  numerous phenomena prove that, in this earliest and simplest condition
of the organism, the form it will ultimately assume very much depends upon
circumstances external to it;  among which circumstances, the kind  of nutri-
ment  supplied will be one of the most important.!  Upon the same principle
we may account for the influence ofthe mental condition of the Mother upon
her Offspring, during a  later period of pregnancy.   That such influence may
occur, there can be no reasonable doubt.  " We have demonstrative evidence,"
says Dr. A. Combe,! "  that a fit of passion in  a nurse vitiates the quality of
the milk to  such  a degree, as to cause colic and indigestion [or even  death]
in the suckling infant.  If, in the child already born, and  in so far independent
of its  parent, the relation between the  two is thus strong, is it unreasonable to
suppose that it should be yet stronger, when  the infant lies in its  mother's
womb, is  nourished indirectly by its mother's blood, and is, to all intents and
purposes, a part of her own body ?  If a sudden and powerful emotion of her
own mind exerts  such an influence upon  her stomach as to excite immediate

          *  See Principles of General and Comparative Physiology, Chap. vi.
          f  See Principles of General and Comparative Physiology, § 665.
          X On the Management of Infancy, p. 76. 
DEVELOPMENT OF THE EMBRYO.
723
vomiting, and upon her heart as almost to arrest its motion and induce fainting,
can we believe that it will have no effect on her womb and the fragile being
contained within it ?   Facts and reason,  then, alike demonstrate the reality of
the influence: and much practical advantage would result to both parent and
child, were the conditions  and extent of its operations better understood."
Among facts  of  this  class, there  is, perhaps, none more striking than  that
quoted by the same Author from Baron  Percy, as  having occurred after the
siege of  Landau  in 1793.   In  addition to a violent  cannonading, which kept
the women for some  time in a constant state  of  alarm, the arsenal blew up
with a terrific explosion, which few could hear with unshaken nerves.   Out
of 92  children born  in that district within a few months afterwards, Baron
Percy  states  that 16 died at the instant of birth;  33 languished for from  8 to
10 months, and then died; 8 became idiotic, and died before the age of 5 years ;
and 2 came into the world with numerous fractures of the bones of the limbs,
caused by the cannonading and explosion.   Here, then, is a total of 59 chil-
dren out of 92, or within a trifle of 2 out of every 3, actually killed through the
medium  of the Mother's alarm and the  natural consequences  upon her own
organization,—an experiment (for such it is to the Physiologist) upon too large
a scale for its results to be set down as mere " coincidences."   No soundly-
judging Physiologist  of the present day is likely to fall into the popular error,
of supposing that marks upon the Infant  are to be referred to some transient
though strong impression upon the imagination of the Mother; but there ap-
pear to be a sufficient number of facts on  record, to prove that habitual mental
conditions on the part of the  Mother may have influence enough, at an early
period of gestation, to produce evident bodily deformity, or peculiar tendencies
of the  mind.   But whatever be the nature and degree of the  influence thus
transmitted, it must be such as can act by modifying the character of  the nu-
tritive materials supplied by the Mother  to the Foetus; since there is no other
channel  by which  any influence  can  be propagated.   The  absurdity of the
vulgar notion just alluded to, is sufficiently evident from this fact alone ; as it
is impossible  to  suppose that a sudden  fright, speedily forgotten, can exert
such a continued influence on the nutrition of the Embryo, as to occasion any
personal peculiarity.*  The view here stated is one which ought to have great
weight, in making manifest the importance of careful management of the health
of the  Mother, both  corporeal  and mental, during  the  period of pregnancy;
since the constitution of the offspring so  much depends upon the impressions
then made upon its most impressible structure.
  947.  It  is  frequently of great importance, both to the Practitioner and to
the Medical Jurist, to be able to determine the age of a Foetus, from the physi-
cal characters which  it presents;  and the following table has been framed by
Devergiet in order to  facilitate such determination.   It is to be remarked, how-
ever, that the  absolute Length and Weight of the Embryo are much less  safe
criteria, than its degree of Development,—as indicated by the relative evolution
of the  several parts, which  make  their appearance successively.   Thus  it is
very possible for one child, born  at the full time, to weigh less than another,
born at 8 or even at  7 months ; its length, too, may be no greater;  but the
position  of the middle point of the body will usually afford sufficient ground

  *  For some valuable observations  on this subject, see Montgomery on the Signs of Preg-
nancy.  Numerous  cases have been  recorded, during the last few years (especially in the
Lancet and Provincial Medical Journal) in which malformations in the  Infant appeared
distinctly traceable to strong impressions made  on the mind of the Mother, some months
previously to parturition; these impressions having been persistent during the remaining
period of pregnancy, and giving rise to a full expectation on the part of the Mother, that the
child would be affected in the particular manner which actually occurred.
  | Medecine Legale, vol. i. p. 495. 
724
OF  REPRODUCTION.
for the  determination; since, during the two latter months of pregnancy, the
increasing development of the lower extremities throws it lower down.

  Embryo 3 to 4 weeks.—It has the form of a serpent;—its length from  three to five lines;
its head  indicated by a swelling; its caudal extremity (in which is  seen a white line, indi-
cating the continuation of the medulla spinalis), slender, and terminating in the umbilical
cord;—the mouth indicated by a cleft;—the  eyes by two black points ;  the members begin
to appear as nipple-like protuberances;—the liver occupies the whole abdomen;—the bladder
is very large.  The chorion is villous, but its villosities are still diffused over the whole surface.
  Embryo of 6  weeks.—Its length from 7 to 10 lines;—its weight from  40 to 75 grains;—
face distinct from cranium;—aperture of nose, mouth, eyes, and ears  perceptible;—head
distinct from thorax ;—hands and fore-arms in the middle of  the  length, fingers distinct;—
legs and  feet situated near the anus;—clavicle and maxillary bone present a point of ossifi-
cation ;—distinct umbilicus for attachment of cord, which at  that time  consists  of  the om-
phalo-meseraic vessels, of a portion of the urachus,  of  a part of the intestinal tube, and of
filaments which represent the  umbilical vessels.  The placenta begins to be formed;—the
chorion still separated from the amnion;—the umbilical vesicle very large.
  Embryo of 2  months.—Length from 16 to 19 lines; weight from 150  to 300  grains; the
elbows and arms detached from the trunk;—heels  and knees  also isolated;—rudiments  of
the nose  and of the lips;—palpebral circle beginning  to show itself;—clitoris or penis ap-
parent; anus marked by a dark spot; rudiments of lungs, spleen, and supra-renal capsules;
—ccecum placed behind  the umbilicus ;—digestive canal withdrawn into the abdomen;—
urachus visible;—osseous points in the frontal bone  and in the ribs.—Chorion commencing
to touch  the amnion  at the point opposite the insertion of the placenta; placenta begins  to
assume its regular form;—umbilical vessels commence  twisting.
  Embryo of 3  months.—Length from 2 to 1\ inches;—weight from 1 oz. to 1 \ oz.  (Troy);
—head voluminous;—eyelids in contact by their free margin: membrana pupillaris  visible;
—mouth closed;—fingers completely separated;—inferior extremities of greater length than
rudimentary tail;—clitoris  and penis very long;—thymus  as  well as supra-renal capsules
present;—ccecum placed below the umbilicus;—cerebrum 5 lines, cerebellum 4 lines, me-
dulla oblongata 1^ line, and medulla  spinalis J of a line, in  diameter;—two ventricles  of
heart distinct.—The decidua reflexa and decidua uterina in contact:—funis contains umbili-
cal vessels and a little of  the gelatine of Warthon ;—placenta completely isolated;—umbilical
vesicle, allantois, and omphalo-mesenteric vessels have  disappeared.
  Foztus of A months.—Length  5  to  6 inches;—weight 2J to 3 oz.;—skin  rosy, tolerably
dense;—mouth very large and open;—membrana pupillaris very evident; nails begin to
appear:—genital organ and sex distinct;—ccecum placed near the right kidney;—gall-bladder
appearing;—meconium in duodenum; coscal valve visible;  umbilicus placed near pubis;—
ossicula  auditoria  ossified;—points  of ossification in superior part of sacrum;—membrane
forming  at  point of insertion  of placenta  on  uterus;—complete contact of chorion with
amnion.
  Fcetus of 5 months.—Length 6 to 7 inches;  weight 5  to 7 oz.;—volume of head still com-
paratively great;—nails  very distinct;—hair beginning  to appear;—skin without sebaceous
covering;—white  substance in cerebellum;  heart and kidneys very voluminous;—coecum
situated  at inferior part of right kidney;—gall-bladder  distinct;—germs  of permanent teeth
appear;—points of ossification in pubis and calcaneum;—meconium has a yellowish-green
tint, and  occupies commencement of large intestine.
   Fcetus of 6 months.—Length 9 to 10 inches:—weight 1 lb.;—skin presents some appear-
ance  of fibrous structure;—eyelids still agglutinated, and membrana pupillaris  remains;—
sacculi begin to appear  in colon;—funis inserted a  little above pubis;—face of a purplish
red;—hair white or silvery;—sebaceous covering begins  to  present  itself;—meconium in
large intestines;—liver of dark red;—gall-bladder contains serous fluid destitute of bitter-
ness;—testes near kidneys ;—points of ossification  in four  divisions of sternum;—middle
point at  lower, end of sternum.
   Foztus of] months.—Length 13 to 15 inches;  weight 3 to 4 lbs.;—skin of rosy hue, thick,
and fibrous;—sebaceous  covering begins  to appear;—nails do not yet reach extremities of
fingers;—eyelids no longer adherent;—membrana pupillaris disappearing;—a point of ossi-
fication in the astragalus;—meconium occupies nearly the whole of large  intestine •__valvules
conniventes beginning to  appear;—ccecum  placed  in right iliac fossa;—left lobe  of liver
almost as large as right;—gall-bladder contains bile;—brain possesses more consistency •__
testicles  more distant from kidneys;—middle point at a little below end  of sternum.
   Fcetus of 8  months.—Length 14 to  16 inches;—weight 4  or 5 lbs.;—skin covered with
well-marked sebaceous.envelope ; nails reach extremities of fingers;—membrana pupillaris
becomes invisible during this month:—a point of ossification in last vertebra of sacrum •__
cartilage of inferior  extremity of femur presents no  centre of ossification ;—brain has some 
PROPORTION OF SEXES.
725
indications of convolutions;—testicles descend into internal ring;—middle point nearer the
umbilicus than the sternum.
  Fcetus of 9 months, the full term.—Length from 17 to 21  inches:—weight from 5 to 9 lbs.,
the average probably about 6£  lbs.;—head covered with hair in greater or less quantity, of
from 9 to 12 lines  in  length;—skin covered with sebaceous matter, especially at bends  of
joints;—membrana pupillaris no longer exists;—external auditory meatus still cartilaginous;
—four portions of occipital bone remain distinct;—os hyoides not yet ossified; point of ossi-
fication in the centre of cartilage at lower extremity of femur;—white and grey substances
of brain  become distinct;—liver descends to umbilicus;—testes have passed inguinal ring,
and are frequently found in scrotum;—meconium at termination of large intestine;—middle
point of body at umbilicus, or a little below it.

   948.  Even at Birth, there is a manifest difference in the physical conditions
of Infants of different sexes;  for, in the average of a large number, there is  a
decided preponderance on the side  of the  Males, both  as to  the Length and
the Weight of the  body.

   a. The Length of the body in fifteen new-born infants of each sex, as ascertained by Que-
telet,* was as follows:—

          From 16 to 17 inchest (French)
                17 to 18
                18 to 19
                19 to 20
            -   20 to 21
From these observations, the mean and the extremes of the Lengths of the Male and Female
respectively, were  calculated to be,—
                                     Males.                    Females.
          Minimum    .    .    16 inches, 2 lines           16 inches, 2 lines
          Mean        .    .    18        6               18         li
          Maximum   .    .    19        8               20        6
Notwithstanding that the  maximum is here on the side of the Female (this being an acci-
dental result, which would probably have  been  otherwise, had a larger number been  ex-
amined), the average shows a difference  of 4$ lines in favour of the Male.
   b. The inequality in the Weight of the two is even more remarkable; the observations of
M. QueteletJ were made upon 63 male and 56 female infants.
          Infants  weighing  from                     Males.   Females.  Total.
              1  to li kilog.§.....0        1        1
Males.	Females.	Total.
2	4	6
8	19	27
. 28	18	46
12	8	20
0	1	1
li to 2
0        1        1
             2  to2i......3        7       10
             2ito3......13       14       27
             3  to 3J......28       23       51
             3ito4......14        7       21
             4to4i......5        3        8

The extremes and means were as follows:—
                                                Males.      Females.
                 Minimum      .     .    .     2-34 kilog.       1-12
                 Mean    ....     3-20             2-91
                 Maximum     .     .    •     4-50             425

  c. The average weight of infants of both sexes, as  determined by these inquiries, is 3-05
kilog. or 6-7 lbs. ° and this corresponds almost exactly with the statement of Chaussier, whose
observations were made upon more than -20,000 infants.  The mean obtained by him, with-
out reference to distinction of sex, was 6-75 lbs.; the maximum being 11-3 lbs., and the mini-
mum  3-2 lbs.||  The average in this country is probably rather higher; according to  Dr.
Joseph Clarke,H whose  inquiries were made  on 60 males and 60 females, the  average of

  * Sur L'Homme, tom. ii. p. 8.
  t The French inch is about one-fifteenth more than the English.
  X Op. cit., tom. ii. p. 35.
  $ The kilogramme is equal to 2j lbs. avoirdupois.
  H These numbers have been erroneously stated in many Physiological works; owing to
the difference  between the French and English pound not having been allowed  for.
  IT  Philosophical Transactions, vol. lxxvi.
                                         61* 
726
OF REPRODUCTION.
Male children is 7£ lbs.: and that of Females 6$ lbs.  He adds that children which at the
full time weigh less than 5 lbs. rarely thrive; being generally feeble in their actions, and
dying within a short time. Several instances are on record, of infants whose weight at birth
exceeded 15 lbs.  It appears that  healthy females, living in, the country, and engaged in
active but not over-fatiguing occupations, have generally the largest children; and this is
what might be expected a priori from the superior activity of their nutritive functions.
   949.  Notwithstanding that, in  any ordinary population, there is a decided
preponderance  in the number  of Females, the  number of  Male births is con-
siderably greater than that  of females.   Taking the average of the whole of
Europe, the  proportion  is about 106 Males to 100 Females.   It is  curious,
however, that this proportion  is considerably different for  legitimate  and for
illegitimate  births; the average of the  latter being only 102^ to 100, in the
places where that of the former was 105f to  100.  This is  probably to be
accounted for by the fact, which is one of the  most remarkable  contributions
that have yet been made by Statistics to  Physiology, that the  Sex of the off-
spring is influenced by the relative ages of the parents.  The following table
expresses the average results obtained by M. Hofacker* in Germany, and by
Mr. Sadlert in  Britain; between which  it will be seen that there is a manifest
correspondence, although both were drawn from a too limited series of observa-
tions.   The  numbers indicate the  proportion of Male births to 100 Females,
under the several conditions mentioned in the  first  column.
                             Hofacker.                                 Sadler.
Father younger than Mother  .     .   90-6   Father younger than Mother  .    .    86-5
Father and Mother of equal age     .   90-0   Father and Mother of equal age   .    94-8
Father older by 1 to 6 years   .     . 103-4  Father older  by 1 to 6 years   .    .   103-7
             6 to 9   .    .     . 124-7       .    .     6 to 11  .    .    .   126-7
             9 to 18   .    .     . 143-7       .    .    11 to 16  .    .    .   147-7
             18 and more   .     . 200-0      .    .    16 and more   .    .   163-2
From this  it appears, that  the more advanced age of the Male parent has a
very decided influence in occasioning a preponderance in the number of Male
infants ; and as the state of society generally involves a condition of this kind
in regard to marriages, whilst in the  case of illegitimate children the same
does not hold good, the difference in the  proportional number of male  births
is accounted for.  We  are not likely to obtain data equally satisfactory in
regard to the influence of more advanced age on the  part of the Female parent;
as a difference  of 10 or  15  years on that side  is not so  common.  If it exist
to the same extent, it is probable that the same law would be found to prevail
in regard  to Female  children born under such  circumstances, as has been
stated with respect to the Male;—namely, that the mortality is greater during
embryonic life  and early infancy, so that  the preponderance is reduced.
   950.  There  appears  to be, from the first, a difference in the viability (or
probability of life) of Male and Female children ; for, out of the total number
born dead, there are 3 Males to 2  Females: this proportion  gradually lessens,
however, during early infancy ; being about 4 to 3 during the first two months,
and about 4 to  5 during the next three  months ;  after which time the  deaths
are  nearly in proportion to the numbers of the  two sexes respectively, until
the  age of puberty.   The  viability of the two  sexes  continues to  increase
during childhood; and attains  its maximum between the 13th and 14th  years.
For a short time after  this epoch has been  passed, the rate of mortality is
higher  in  Females than in Males; but  from about the age of 18 to 28, the
mortality is  much greater  in  Males, being at its  maximum at 25, when the
viability is only half what it is at  puberty.  This fact is a very striking one;
and shows most forcibly that the indulgence of the  passions  not only weakens
the health, but  in a great number of instances is the cause  of a very premature

  * Annales d'Hygiene, Cvt. 1829.                f Law of Population, vol. ii. p. 343. 
PROPORTION OF SEXES.
727
death.   From the age  of 28 to that of  50, the mortality is greater, and the
viability less, on  the  side of the Female;  this  is what would be anticipated
from the increased risk, to which  she  is liable during the parturient period.
After the age of 50, the mortality is  nearly the same for both.
  a.  These facts have been expressed by Quetelet in a form which brings them prominently
before the eye  (Fig.  289).  The relative viability of the Male at different ages is represented
by a  curved line; the elevation  of which indicates  its  degree, at the respective  periods
marked along the base line.  The dotted  line which follows a different curve, represents
the viability of the Female.  Starting from a, the period of birth, we  arrive at  the maxi-
mum of viability for both at b; from this point, the Female curve steadily descends towards

                                     Fig. 289.
     Diagram representing the comparative Viability of the Male and Female at different Ages.

n, at first very rapidly, but afterwards more gradually;  whilst the Male curve does not de-
scend quite so soon, but afterwards falls much lower, its minimum being c, which corresponds
with the age of 25 years.   It afterwards ascends to d, which is the maximum of viability
subsequently to the age of puberty; this point is attained at the age of 30 years, from which
period, up to 50, the probability of life  is greater in  the Male than  in the Female.  In the
decline of life there seems little difference for the two sexes.

  951.  Similar diagrams have been  constructed  by Quetelet, to indicate the
relative Heights and Weights  of the  two sexes  (Fig. 290).

  a. In regard  to Height it may be observed, that the  increase is  most  rapid in the first
year, and that it afterwards diminishes gradually;  between the ages of 5 and 16 years, the
annual increase is very regular.  The difference between the Height of the Male and Fe-
male, which has been already stated  to present itself at birth, continues to increase during
infancy and youth;  it is not very decided, however, until  about the 15th year, after which
the  growth of the Female  proceeds at a much diminished  rate, whilst that of the  Male con-
tinues in nearly the same  degree, until about the age of 19 years.  It appears, then, that the
Female comes to her full development in regard to Height, earlier than does the Male.  It
seems probable, from  the  observations  of Quetelet. that the full height of the Male is not 
728
OF REPRODUCTION.
generally attained until the age of 25 years.  At about the age of 50, both Male and Female
undergo a diminution of their stature, which continues during the latter part of life.
  b. The proportional  Weight of the two sexes at different periods, corresponds pretty
closely with their height.  Starting from birth, the predominance then exhibited by the Male
gradually increases during the first few years;  but towards the period  of puberty, the pro-
portional weight of the Female increases; and at the age of 12 years, there is no difference
between the two sexes in this respect.   The weight of the Male, however, then increases
much more rapidly than that of the Female,  especially between the  ages of 15 and 20
years; after the  latter  period, there  is no considerable  increase on the side of the Male,
though his maximum is not attained  until the  age of 40; and there is an absolute diminu-
tion on the part of the Female, whose weight remains less during nearly the whole period of
child-bearing.  After the termination of the parturient period, the weight of the Female again
undergoes an increase, and  its maximum is attained about 50.  In old age, the weight of
both sexes undergoes a diminution in nearly the same degree.  The average Weights of the
Male  and Female, that have attained their full development, are twenty times those of  the
new-born Infant of the two sexes respectively.   The Height, on the other hand, is about 3£
times  as much.
Fig. 290.
   952.  The chief differences in  the Constitution of the two sexes manifest
themselves during the period, when the Generative function of  each is in the
greatest vigour.   Many of these  distinctions have been already alluded to;
but  there  are others  of too great importance to  be overlooked; and  these
chiefly relate to the Nervous System and its functions.   There  is no obvious
structural  difference in the Nervous  System of the two sexes (putting  aside
the local peculiarities of its distribution to the organs of generation); save the
inferior  size of  the Cerebral Hemispheres in the Female.   This difference,
which is not observed in other parts  of the Encephalon, is readily accounted
for on the principles formerly stated; when we  compare the physical charac-
ter of Woman, with that of Man.  For there can be no doubt  that—putting
aside the exceptional cases which  now and then occur—the intellectual  pow-
ers of Woman are inferior to those of Man.  Although her perceptive facul-
ties  are  more acute, her capability of sustained mental exertion is much less •
and  though her views are  often peculiarly distinguished by clearness and deci-
sion, they  are  generally deficient in that comprehensiveness which is neces-
sary for their stability. ^ With less of the  volitional powers than Man pos-
sesses, she has the emotional and instinctive in a much stronger degree   The
emotions therefore predominate;  and  more frequently  become the leading- 
PROPORTION OF SEXES.
729
springs of action, than they are in Man.   By their direct influence upon the
bodily frame, they produce changes in the organic functions, which far sur-
pass in degree anything of the same kind that we ordinarily witness in  Man;
and they thus not unfrequently occasion symptoms  of an anomalous  kind,
which are very perplexing to the Medical practitioner, but  very interesting to
the Physiological  observer.  But they also  act as powerful  motives  to the
Will; and, when strongly called forth, produce a degree of vigour and  deter-
mination, which is very surprising to those who  have usually seen the  indi-
vidual under a different aspect.   But this vigour, being due to the  strong
excitement of the Feelings, and not to any  inherent strength of Intellect, is
only sustained during the persistence of  the motive, and fails as soon as it
subsides.  The  feelings of Woman,  being frequently called forth by the
occurrences  she witnesses around her, are naturally more  disinterested than
those of Man;  his energy is more concentrated upon one object; and to this
his intellect  is directed with an earnestness that  too frequently either blunts
his feelings, or carries them  along in the same channel,—thus rendering them
selfish.   The  intuitive powers of Woman  are certainly greater than those
of Man.   Her perceptions are more acute, her  apprehension quicker;  and
she has  a remarkable power of  interpreting the feelings of others, which
gives to  her, not  only a  much more ready sympathy with  these, but  that
power of guiding her actions so as to be in accordance with them, which we
 call tact.  This tact bears a close correspondence with the  adaptiveness to
 particular ends, which we see in Instinctive actions.   In  regard to the infe-
 rior development of her Intellectual powers, therefore, and  in the  predomi-
 nance of the Instinctive, Woman must be considered as ranking  below Man;
 but in the  superior purity  and elevation of her Feelings, she is  as  highly
 raised above him.  Her whole character, Psychical as well  as Corporeal, is
 beautifully adapted to supply what is deficient in Man; and to  elevate and
 refine those powers, which might otherwise be directed  to  low and selfish
 objects. 
 
APPENDIX.
                               I.—ON PHRENOLOGY.

  Without entering into a general discussion of the merits of the system of Phrenology at
present in vogue, which would be misplaced in a Treatise like the present, the Author feels
it desirable to express the opinion, which a recent careful examination of the  chief questions
at issue between Phrenologists and their opponents have led him to entertain.
  That the different portions of the Cerebral mass should have different parts to perform in
that wonderful series of operations, by which the Brain as a whole becomes the instrument
of the Mind, does not seem to him in  the least improbable.  Nor, if we duly consider  the
general plan of construction of the nervous centres in Vertebrated animals, is it a legitimate
objection to such a view, that there is no mechanical distinction of "organs" either upon
the surface or in the interior of the Cerebrum; for in the  Spinal Cord  and Medulla Oblon-
gata, there is a continuous tract of grey matter, which is really made up of an assemblage of
ganglia having dissimilar functions, although  there  are no  external indications of the dis-
tinctness of these ganglia.  Further, it  appears to be quite legitimate to judge of  the com-
parative powers of  different parts of the Cerebrum,  or of the same portions in different in-
dividuals, by their comparative  sizes;  due allowance being made for other circumstances of
difference.  And if the development of a particular  part of the Cerebrum were constantly
found to be in harmony with the manifestation of a certain feature of psychical character,
there would be strong  ground for regarding such a  part as the instrument of the mental
operation in question.  The attempt to  establish a system of Cerebral Physiology by com-
parative observations of this nature, appears  to the Author, therefore, a  most  legitimate one;
and his objections to the  present system  of Phrenology are based  only on the very imperfect
manner in which it has been  constructed;  the foundations on which  it  rests being (in his
opinion)  of a very  insecure character; and  the superstructure having been built up of the
slightest possible materials.   The following  are  the  chief points on which he feels called
upon to express his dissent.
  1.  The present system of Phrenology  is founded only on comparative observation of the
psychical character and cerebral conformation in different individuals of the Human species
alone; evidence  derived  from Comparative Anatomy being admitted only so far as it corre-
sponds with the  system thus constructed.  When the fundamental importance of the study
of Comparative Anatomy in the determination of the functions of all other  organs, and of
other parts of the Nervous  System itself, is  duly considered, the Author cannot regard  any
system of Cerebral Physiology as having a claim to a place in a scientific treatise,  which is
not founded on this basis.
  2.  The present system of Phrenology is altogether inconsistent with well-ascertained facts,
regarding the Comparative  Anatomy and Embryological Development of the Cerebrum. It
is clearly established by anatomical research, that the posterior  lobes of the Cerebrum are
relatively much smaller in the Quadrumana  than they are in Man, and that they disappear
altogether in the Carnivora, not a vestige of them being discoverable in any of the lower
Mammalia; and that the middle lobes, though they may be traced in the lowest of the Mam-
malian Class, are altogether wanting in Birds, Reptiles,  and Fishes.  The  Cerebrum of these
animals, therefore, is the rudiment of the anterior lobe only of that of Mammalia.—Further,
it has been lately shown by Prof. Retzius (whose researches on  this head are confirmatory
of those of Tiedemann, at the same time being more  full and precise), that the development
ofthe Cerebrum ofthe Human Embryo takes place  on the same plan.  In the first period,
which corresponds  with the second and third months, only the anterior lobes form;  in  the
second period which is  comprised in  the end of the  third  month, in the fourth,  and  in a
small portion of the fifth, the two middle lobes appear; and it is not until the latter part of
the fifth  month, that the development of the posterior lobes properly commences.  They
sprout, as it were, from the posterior extremity of the middle lobes; from which  they are
divided, on the brain ofthe mature fcetus, as well as occasionally in that of adults,  by a dis-
tinct furrow.—The exact mutual confirmation afforded by these two sources of knowledge, 
732
APPENDIX.
proves the complete inadmissibility of the ordinary Phrenological interpretation of the in-
creased development of the posterior lobes  in Man,—namely, that they are present in all
Vertebrata, but that they are pushed backwards  in the  higher forms by the increased de-
velopment of the anterior portion of the Cerebrum.  Now as the Instincts and Propensities
are located, according to the present system of Phrenology, in the posterior and middle lobes
of the Cerebrum, which are altogether wanting in the Oviparous Classes in  which these In-
stincts and Propensities most strongly manifest themselves, it would appear that some funda-
mental  error must exist in the allocation.
   3. The present system of Phrenology takes no account whatever of the series of ganglionic
masses, which He at the base of the Cerebrum in Man, and which are thrown into the shade
(as it were) by its excessive development; but which increase in relative size and import-
ance as we descend the scale, until, in the lower Fishes and Invertebrata generally, they
come to constitute the  whole Brain.  We have seen that, in the  Cod, the rudiment of the
Cerebrum is much smaller than  a single pair of these ganglia,—the Optic;  and as this rudi-.-
ment does not possess a ventricle (which is present in the Sharks, &c, dividing the rudiment
of the hemisphere which arches over it,  from the corpus striatum  which lies at its base), it
is probably to  be regarded as not really analogous to  any part of the Cerebrum strictly so
called, but to the Corpus Striatum, which (with the Thalamus) constitutes  an independent
organ.  Thus  we have the Cerebrum entirely disappearing in the Osseous Fishes;  and the
whole Brain made up of the  Sensory Ganglia and the Cerebellum.—In the Invertebrata, not
the rudiment of a Cerebrum can be discovered; the cephalic masses of nervous matter being
made up of ganglia in immediate  connection with the  organs of sense and motion.   It is
obvious, therefore, that these  organs must be of  primary importance as centres of nervous
action;  and that the functions of the Cerebrum, whatever be their  nature, must be of a super-
added, and  of a non-essential character.—The view which the Author takes of these pheno-
mena will  be  found at large in  the  Text.   He regards the Sensory Ganglia as the seat of
Sensation (each kind of sensation being communicated through  its  own  ganglion) and of
the simple feelings of  pleasure  and pain connected with those sensations; and also as the
instrument of  those consensual movements, which  follow immediately and  necessarily upon
sensations.   To this category he would refer the purely Instinctive  actions, which are imme-
diately prompted by sensations, which seem to involve no idea of the purpose towards which
they are directed, and which  cannot be said (the idea of the object being deficient) to spring
from a desire  or propensity.  Probably all or nearly all  the actions of Invertebrata and of
the lower Fishes are of this class.  The  emotions and propensities of Man and of the higher
Mammalia, which form the chief springs of action in them, may be regarded as involving
the combined  operation of  the Sensory Ganglia and the  Cerebrum; the latter affording the
ideas, whilst the former invest these ideas with the pleasure or pain, which gives them the
form of passions, desires, or  propensities, and which  causes  them to become the  moving
springs  of a great part  of the intellectual  operations, which are purely Cerebral.  The action
of the Cerebrum in the passions, emotions, &c, is limited, therefore, on this view of their
nature, to its instrumentality in furnishing the several classes of ideas to which those emotions
respectively relate.  If the Phrenological system be thus modified, there will no longer be
the same difficulty in  reconciling it with the facts of Comparative Anatomy; since in those
animals which are unpossessed of  the posterior lobes, the actions, which in Man and the
higher Mammalia result from desires or propensities involving a distinct idea or conception
of the object, may be purely instinctive, and may thus be performed through the medium of
the Sensory Ganglia alone, without the participation of the Cerebrum.
  4. The present system of Phrenology leaves undetermined a very large proportion of the
Cerebral surface in Man,—probably not less than  one-half;  namely the whole series  of
convolutions covering the  opposing median surfaces of the hemispheres, the convolutions of
nearly the  whole of the base of the Cerebrum, and  those of the fissure  of Sylvius.  Yet
not the  slightest ground can be  adduced for  the  supposition that Uiese unappropriated por-
tions have  any less participation in the operations of the intellect,  the exercise of the moral
feelings, or the influence of the animal propensities, than  have the  external and superior
portions of the respective lobes.   No admission of the imperfection of the  present system
of Phrenology can be  a sufficient explanation of this fact, which would  seem to  indicate
some fundamental error in the method employed; since one of the great claims which is set
up in behalf of that system is the completeness of the system of Psychical philosophy which
it presents; so that, if there were every facility for  observing the relative development ofthe
parts of the Cerebral surface in  question, there would seem to be no "organs" left to distri-
bute over it
   5. If it be urged, however, that  none of these objections  are sufficient to overthrow the
position, now  established by  a long  course of  observation, that a  constant correspondence
exists in Man between the development of  certain parts of  the  Cerebrum, and  particular
Psychical characteristics, and that the present system must consequently be true, in spite of
its inconsistency with the facts of Comparative Anatomy, it becomes necessary to inquire in 
APPENDIX.
733
more detail into the character of the evidence adduced in its behalf.—The following objec-
tions may be urged upon this subject.   The greater part ofthe observations upon which the
present system of  Phrenology rests, have  been made  upon crania alone, or  upon casts of
crania; not upon the  cerebrum itself.  In this method of observation there are many falla-
cies; especially those arising from the  indisputable fact, that the cerebrum may be moulded
in such a manner as to undergo considerable alteration in form, without any  change in its
internal structure or in the relative development of its several parts.  And an extensive
comparison of the crania of different nations shows that their differences of  form have in
many instances no relation whatever to their psychical character.  That the form of the cra-
nium is to a certain extent independent of that of the brain, and may impress  itself upon its
contents, appears further from a comparison between the cerebral and cranial conformations
of different species of animals.  It is found that, even when closely-allied species are com-
pared  together, similar projections of the cranium may cover different convolutions; the
general form of the cranium being modified by its instrumentality in other functions, espe-
cially in mastication, and by its position upon the trunk and its mode of muscular connection
with it.  There is  a peculiar uncertainty attending all estimates of the comparative size of
the Cerebellum, from inspection of the  exterior of the cranium; for the  observations of Prof.
Retzius upon the varieties of form which the cranium presents in different races, have in-
dicated this fact among others,-—that the position of the cerebellum may vary considerably,
being much more horizontal in one case and more vertical in another; so that cerebella of
the same size may exist in crania having very different amounts of occipital  protuberance;
and vice versa.—Further, after  dismissing the sources of error already mentioned, there yet
remain many, arising from want of precision in the cranioscopical observations, and want of
opportunity of forming a  correct estimate of the characters of the individuals whose " deve-
lopments" have been examined.   The difficulty of precisely estimating the relative sizes of
different organs by any system  of measurement, which has been acknowledged and regretted
by candid phrenologists, often leads to the formation of very different inferences from the
same data, as the Author can vouch from his own knowledge.  And when the estimate of
the character has been formed from craniological  indications, there  are many difficulties in
the way of a  faithful comparison with the real  character of the individual, of which the
manifestation in his ostensible conduct can generally reveal but a small part.  Now  there
can be little doubt, that the habit of attending-to and of recording coincidences  between cere-
bral developments and psychical manifestations, without  due regard to the cases in which
there is no coincidence, has been far too prevalent amongst professed phrenologists.  Unless
the failures are duly chronicled with the successes, no value can be attached to any series
of observations, however numerous and  satisfactory.  Many such failures, upon points in
regard to which there could be no misapprehension or evasion, have come under the Author's
knowledge; and have tended  to prevent his reception of the present phrenological system;
but they find no place in formal treatises on Phrenology, which lead their readers to suppose
that the coincidences are invariable.  The connection of the  Sexual  propensity with the
Cerebellum has been usually regarded  by  Phrenologists as one of the best-ascertained of its
whole series of dogmata; and yet we have seen how little this  determination can stand the
test of a careful scrutiny.
   Those who are desirous  of  studying the Phrenological system at present in  vogue, as ex-
pounded by an intelligent  and  unfettered partisan, may be referred to Mr. Noble's recent
treatise, entitled " The Brain and its Physiology;"  whilst the  objections summed up in this
Appendix are stated more  at large in a critique on that work in the British and Foreign Me-
dical Review, for October, 1846.


           H._ON  ARTIFICIAL  SOMNAMBULISM AND MESMERISM.

   It appears to the Author that  the time has now come, when a tolerably definite opinion
may be formed regarding a large number of the phenomena commonly included in the term
"Mesmerism."  Notwithstanding  the  exposures of  various pretenders, which have taken
place from time to time,  there  remains a  considerable mass of phenomena,  which cannot
be so readily disposed of, and  which appear to him  to have as just a title to the attention of
the scientific Physiologist, as that which is possessed by any other class of well-ascertained
facts.                                                                              ,
   Passing over, for the present, the inquiry into the manner in which  these effects may be
induced, the Author  may briefly enumerate the principal  phenomena which  he regards as
having been veritably presented in a sufficient number of instances, to entitle them to be
considered as genuine and regular manifestations of the peculiar bodily and mental condition
under  discussion.                                              .  .
   1 A state of complete Coma or perfect insensibility, analogous in its mode  of access and
departure to  that which is known  as the "Hysteric  Coma," and (like it) usually distin-
      62 
734
APPENDIX.
guishable from the Coma of Cerebral oppression by a constant twinkling movement of the
eyelids.  In this condition, severe  surgical  operations may be performed, without any con-
sciousness on the part of the patient; and it is not unfrequently found that the state of tor-
por extends from the Cerebrum and Sensory Ganglia to the Medulla Oblongata, so that  the
respiratory movements  become  seriously interfered with, and a state of partial  asphyxia
supervenes.
  2. A state of Somnambulism or Sleep-waking, which may present all the varieties of the
natural Somnambulism, from a very limited awakening of the mental powers, to the state
of complete double Consciousness (§ 500), in which the individual manifests all the  ordi-
nary powers of his mind, but remembers nothing of what has passed when restored to his
natural waking state.   This state of Somnambulism, in the form which it commonly takes,
is characterized by the facility with which the  thoughts are directed into any channel which
the observer may desire, by the principle of " suggestion;" and  by the want of  power, on
the part of the Somnambulist, to apply the teachings of ordinary experience to the correction
of the erroneous ideas which are thus made to  occupy the mind.  In these  particulars, this
condition  closely corresponds with that of Dreaming; and differs from it chiefly in  the
readiness With which ideas are excited through the ordinary channels of sensation, and with
which the bodily powers are called into action to give effect to the ideas thus aroused.  The
emotional states are more easily brought into play, than the purely intellectual  operations.
It is a peculiar characteristic  of this condition, that  the whole attention may be so completely
fixed upon one object, that there  is an insensibility to all impressions  unconnected with it,
although every thing which bears upon it  is fully appreciated.   In this respect  there is  a
complete correspondence with the phenomena of ordinary somnambulism;  but there is this
difference,—that,  from  the greater subjection of the mind to external influences, it may be
more readily played upon (so to speak) by the observer, and may thus be exclusively fixed
upon any object which  he may direct.  In  this manner, a state of insensibility to pain may
be brought about, nearly as complete as that which occurs in the comatose state, by causing
the mind to be  strongly and exclusively directed towards another object.   This condition
finds its parallel  in that of Reverie; in which strong  impressions upon the body may be
unfelt, so long as the mind is engrossed upon some different train of thought.
  3. A frequent phenomenon of this condition, and one which has its parallel in Natural
Somnambulism, is a remarkable exaltation of one  or more of the Senses, so that the indi-
vidual becomes susceptible of influences, which, in his natural condition, would not be in
the  least perceived.  The Author has referred to a case  (§ 532, note) in which such an
exaltation of the sense of Smell was manifested; and in  the same case, as  in many others.
there was a similar exaltation of the sense of Temperature.   The exaltation of the Muscular
Sense, by which  various actions that  ordinarily require the guidance of vision, are directed
independently of it,  is  a common phenomenon of the  Mesmeric  or Artificial, as of the
Natural, Somnambulism.
  4. The Muscular  system  may also  be  excited to  action in unusual modes, and with
unusual energy.  Notwithstanding the fallacy of many of the  cases of Cataleptic  rigidity
which have been publicly exhibited, the  Author  is satisfied, from investigations privately
made, of the  possibility of  artificially inducing this condition.   A slight irritation of the
muscles themselves, or of the skin which  covers them,—as by drawing the points of the
fingers over them, or even wafting currents of air over  the surface,—is  sufficient to excite
the  tonic muscular  contraction, which may continue in sufficient force to suspend a con-
siderable weight, for a longer period than it could be  kept up  by any conceivable  effort  of
voluntary power.  Further, by directing the attention exclusively to any set of muscles, and
by impressing the mind ofthe Somnambulist with the  facility ofthe action to be performed,
a very extraordinary degree of muscular  power may be called forth, even in very feeble
individuals.  Thus the  Author has seen a man of extremely low muscular development and
small stature,  not only lift up a 28 lb. weight upon his little finger, but even swing  it round
his head with the greatest apparent facility,—having been previously assured that it was  as
light as  a  feather.  Upon  taking up the  same weight upon their own little  fingers, the
Author and his friends were very glad  to lay it down after raising it a foot from the ground;
and the subject of the experiment (a respectable middle-aged man, who  was not a regular
" exhibitor," and upon whom no suspicion of any kind rested) declined, when in his waking
state,  even attempting to lift the weight, on the ground  that it would strain him too  much.
   These are the principal phenomena  of Artificial Somnambulism, in regard to which the
Author feels his mind made up.  He does not see why any discredit should be .attached to
them, since they correspond in all essential particulars with those of states, which naturally
 or  spontaneously occur in many individuals,  and which he has  had opportunities of per-
 sonally observing, in cases in which  the well-known characters of the parties placed them
 above suspicion.  When the facility with which the mind of the Somnambulist is played on
 by suggestions conveyed either in language or by other  sensations which  excite associated
 ideas, and the absence of the corrective power ordinarily supplied by past experience, are 
APPENDIX.
735
duly kept  m view, many of the  supposed «higher  phenomena" of Mesmerism  may be
accounted tor, without regarding the patient on the one hand as possessed of extraordinary
powers ol  divination, or on  the other as practising a deception.  Thus,  bearing in  mind
tfiat Oomnambuhsm is an acted dream, the course of which is governed by external  impres-
sions, it is easy to understand how the subject of it may be directed by leading questions to
enter buildings which he has never seen, and to describe scenes which he  has never wit-
nessed, without any intentional deceit.   The love of tbe marvellous  so strongly possessed
by many of the witnesses of such exhibitions, prompts them to grasp at and to exaggerate
the coincidences in all such  performances, and  to neglect the  failures; and hence reports
are given to the public, which, when the real truth of them is known, prove to have been
the results of a series of guesses, the correctness of which is in direct relation to the  amount
of guidance afforded by the questions themselves.  In  like manner the manifestations of the
excitement of the " phrenological organs" seem to depend upon the conveyance of a sug-
gestion to the patient, either  through- his knowledge of their supposed seat, or through the
anticipations expressed by the by-standers.  Many  instances are  recorded, in which  the
intention has been  stated of  exciting one organ,  whilst the finger has been  placed upon or
pointed at another; and the resulting manifestation has always been that which would flow
from the former.   It does not hence follow that intentional deception is being  practised by
the Somnambulist;  since the condition  of mind already referred to, causes it to respond to
the suggestion which is most strongly conveyed to it.  Many of the  emotional states  are •
readily excitable, by placing  the  muscles in the position which naturally expresses them;
thus the combative tendency may  be called forth by gently flexing  the fingers, so as to
double the fist; a cheerful hilarious mood may be induced by drawing outwards  the  cor-
ners of the mouth as in laughter; and this may  be exchanged for the  reverse state of gloom
and ill-temper, by drawing the eyebrows downwards and towards each other, as in frown-
ing.  In like manner, on putting the hand upon the  vertex, the Somnambulist draws him-
self up, and shows the  manifestation of self-esteem; whilst  the  depression of the head into
the position of humility calls forth the corresponding emotion.   Those who have carefully
observed the habits of infants and young children, must perceive the accordance of  these
phenomena with those which continually present themselves at that early period of life,
when the condition of the mind is  so completely under the government of suggestions re-
ceived from without.
  In regard to the alleged powers, which are said  to be possessed by many Somnambulists,
of reading with the eyes completely covered, or of discerning words enclosed in opaque
boxes, the Author need only here express his complete conviction that no case of  this de-
scription has ever stood the test of a searching investigation.
  The modes in which the Artificial Somnambulism  may be induced, are extremely vari-
ous.  The experiments of Mr. Braid have shown,  that one of the most effectual is the con-
tinued convergence of the eyes upon a bright  object, held at a small distance above and in
front of them, and gradually approximated towards them.  The mere steady  direction of the
eyes towards a distant  object, in persons who have often practised the former  method,  fre-
quently serves to induce the state.  All the phenomena  described in the preceding  para-
graphs, have been  witnessed by the Author in individuals thus "hypnotized;" and he
considers that this curious class of observations cannot be better  prosecuted than by the em-
ployment of that  method.  He is  not yet satisfied that, in the ordinary " Mesmeric " process,
any other influence  than this is  really exerted; but the patient is sent to  sleep with  the
dominant idea that  some special influence is exerted by the Mesmerizer, and  this idea affects
all the subsequent phenomena,—producing, for example, in some cases, insensibility to every-
thing but what is said by the mesmerizer or by an individual placed by him  en rapport with
the  Somnambulist.   It will generally be found, that the degree  of this supposed connection
depends upon the notions of it previously formed by the  individual Mesmerized.  In the
hypnotic state, there is an entire absence of any such peculiar influence; the Somnambulist
being equally conscious of what is said or done by  every bystander.
  The Author may refer to an Article in the British and Foreign Medical Review for April,
1845, as on the whole  expressing (although not written by himself) his opinions upon this
curious and interesting subject. 
 
INDEX.
The Numbers refer to the Paragraphs.
A.
 Aberration, spherical, 535; chromatic, 535
 Abnormal forms of nutritive process, 802—809
 Abortion, 929
 Abscess, 804
 Absorbent cells, 181, 182
 ---------vessels, see Lacteals, and Lympha-
   tics
 Absorption
   Nutritive, general account of, 107, 271; by
     intestinal surface, 672—675; by lacteals,
     672, 674; by  blood-vessels, 673, 675; by
     general surface, 676—681 ; by skin, 676—
     679 ;  by lungs, 678, 775, 776
   Interstitial, by lymphatics, 680,681; by veins,
     681 6
   Of gases and vapours by lungs, 775, 776
 Abstinence, cases of, 653
 Actinia, nervous system of, 312, 313
 Activity, varying, of nutritive processes, 786—
   791
 Adaptiveness of movements, no proof of sensa-
   tion,  306
 Addison, Mr., his observations on  blood-cor-
   puscles  referred to, 151, 158, 159; on fibril-
   lation of liquor sanguinis, 136 ; on blood-ves-
   sels of lungs, 758; on pus, 806
 Adhesion, 793, 794
 Adipose tissue, see Fat-cells
 Aeration,  107 ; see Respiration
 Afferent nerves, 2S9, 344
 Age, influence of, on pulse, 727 a; on excretion
   of carbonic acid, 767 b; on excretion of urea,
   844;  on activity of nutritive processes, 786,
   812 ;  on power of calorification, 893
 Air, influence of respiration  on, 765—768
 Air-cells of lungs, 757, 758
 Albinoism, 80
 Albumen, 112; composition of, 114;  properties
   of, 113—115 ;  conversion of into fibrine, 114,
   117, 153—158; proportion of in blood, 697,
  706; purposes of, 698; diminution of in blood,
  707 d; predominance of in tubercular depo-
  sits, 878
Albuminous principles of food, 640, 857 ; ap-
  plication of in  the animal body, 642
Albuminuria, 707 d
Alcock, Dr., his experiments on nerves of taste,
  407
Alcohol, use of in supporting heat, 896 note
Alfourous, 105
Aliment, causes of demand for, 629—635; see
  Food
Alimentary materials, 640 ; see Food
Allantoin, 845 c
Allantois, origin and uses of, 839 c
Allen and Pepys, their researches on respira-
  tion, 765
American nations, 101
Amphibia, 31
Amphioxus, 110, 180; nervous centres of, 42."
Anaamia, 707 c
Andral, M., on amount of carbonic acid excret-
  ed, 767 ; on pathological changes in  blood,
  706, 707
Animal Heat, see Heat
Animal kingdom, primary subdivisions of, 5
Animal magnetism, Appendix II.
Animals, distinguished from Plants, 1—4
--------early development of, 3
Anselmino, on solid  matters of cutaneous ex-
     halation, 869
   Aplastic deposits, 804, 807
   Aplysia, 12, 15; nervous system of, 321
   Apoplexy, decrease of fibrine in, 707 c; death
     by, 814
   Arabian nations, 94
   Arciform fibres of medulla oblongata, 353
   Area pellucida, 936
   Areolar tissue, 138, 139
   Areas, comparative, of arteries, 710
   Arnott, Dr., on  stammering, 619 ;  on the ven-
     ous circulation, 744 b
   Arteries, distribution  of,  710;   area of, 710;
     structure and properties of, 728—732 ; elas-
     ticity of, 729 ;  their contractility, proofs  of,
     730; its influence in regulating the circula-
     tion, 732; their  tonicity, 731; influence of
     nerves upon, 623, 732
   Articulata, 5, 16—19; segmental  division  of,
     16 ;  animal powers of,  17 ; nutrition of, 18 ;
     bi-lateral sympathy of, 16; respiration and
     heat of,  18 ;  nervous system  of,  324—334
   Articulate  sounds, 612—619;  vowels,  613—
     615; consonants, 616, 617
   Articulation, movements  of, guided by sensa-
     tion, 611, 617
   Asphyxia, nature of, 778; phenomena of, 779:
     780 ; referred to, 738, 740, 814,  820
   Assimilation in  Plants, 107; in Animals, 271;
     781
   Asthma, spasmodic, 504, 759
   Atrophy, 789—791

62* 
738
INDEX.
                           The Numbers refer

Attention, effects of, on sensations, 519—521
Auditory ganglia, in Fishes, 357; in Man, 422
Auditory nerve, 446; terminations  of, in ear,
  559
Auricles of heart, action of, 718, 719; capacity
  of, 723 6                           V   3
Automatic actions, 438 a
Azote, absorption and exhalation of, 766;  ex-
  cretion of, in urine, 819, 842—850; respira-
  tion in, 769, 780
B.
Barry, Dr. M., his researches on the blood-
   corpuscles referred to, 148; his embryologi-
   cal researches referred to, 130, 900—918
Barry, Sir D., his experiments on the  venous
   circulation, 744 6
Basement-membrane, 135
Bat, peculiar sensibility of, 526
Batrachia, 31, 32;  metamorphosis of, 32
Beaumont, Dr., his experiments and observa-
   tions on digestion, 637,649, 657—660, 664—
   666
Becquerel on the heat of Plants, 889 a; on the
   heat of Animals, 891; on the heat of Muscle,
   890
Bee, perfection of instinct of, 336; construction
   of hexagonal cell by, 336 note;  uneducability
   of, 429 6; temperature of, 889 c
Bell, Sir C, his discoveries referred to, 344,
  349,351,376,377,433
Bell, Mr. T., on the development ofthe teeth,
  217 i ;  on secretion after death, 624
Bellingeri, on the Spinal Cord, 349
Berger and Delaroche, their experiments  on
  Animal Heat, 888
Berber race, 94
Bernard, M. Ch., his researches  on digestion,
  658 b, 664 6, 669
Bibra, Von, his analyses of Bone, 196; of Teeth,
  212
Bile,  secretion of, 831—837; composition of,
  833; amount of, 834;  formed from  venous
  blood, 831; partly an excrementitious fluid,
  836;  effects of  non-elimination  of, 836;
  sources of, 836;  purposes of, in  digestive
  process, 660, 670, 671, 835
Birds, 33—41; skeleton of, 37, 38 ; respiration
  and heat of, 33, 757, 889 c;  covering  of, 36 ;
  instinctive powers and  intelligence  of,  39,
  479, nutritive system in, 40; bi-lateral sym-
  metry in,  40; development of young  in, 41;
  blood-corpuscles of, 146 b, 149 ; brain of, 361
Bischoff, his experiments on respiration, 768
Bladder,  contraction of, 390
Blake, Mr., his experiments on the Circulation,
  725
Blind persons, acuteness of touch in, 525
Blondlot, M., his researches on digestion, 658
  b, 664 6
Blood,
  Physical  and vital properties of, 696—708 ;
    composed  of  liquor  sanguinis and cor-
    puscles, 696 ;  proportion  of components
    of, in health, 697 ; purposes of, 698; total
    amount of in body, 724
  Structure  of Red Corpuscles, 143, 144; form
    of corpuscles, 145,146; size of corpuscles,
to the Paragraphs.

     146;  chemical constitution of corpuscles,
     147 ; origin of, from each other, 148;  first
     production of, in  embryo, 149; purposes
     of, in animal economy, 150
  Colourless corpuscles, 151, 152; their uses
     in the economy, 153—159
  Serum, composition  of, 697 ; milky, 697 e
  Coagulation  of,  699—705; due to fibrine
     alone,  117, 118(^S99;  an act  of vitality,
     118,700,701; causes influencing, 701, 702;
     proportions of serum and clot, 703; buffy
     coat, causes of, 704, 705; composition of,
     116a;  artificially  producible, by retarding
     coagulation, 699
  Pathological changes in, 706—708; normal
     proportion of chief constituents, 706;  in-
     fluence  of abstinence  and  hemorrhage,
     707; increase  of  fibrine in  inflammation,
     158,  707 a, 802;  deficiency of fibrine in
     fever and hemorrhagic diseases, 707 b; in-
     crease  of  corpuscles in plethora, 707 c;
     diminution in chlorosis, anaemia, &c, 707
     c;  decrease of albumen in Bright's disease,
     707 d; general depravation of, 708; imper-
     fect elaboration of, in tuberculous cachexia,
     807
  Changes produced in, by respiration, 769—
     772;  difference of arterial and  venous
     blood, 769; excretion of carbonic acid from,
     769 ; absorption of oxygen by, 766 ; gases
     extracted  from, 770; change of colour,
     causes of, 771, 772; aeration of, by gene-
     ral surface, 768
  Organization of, 118, 700, 796
  Movement of through vessels, see Circulation
 Blood-discs, see Corpuscles
 Blood-vessels,  see Arteries, Capillaries,  and
  Veins
 Bone, 192—207; structure of, 192—196; form-
  ation of, in  membrane,  197;  in cartilage,
  198—200 ; chemical composition  of,  196 ;
  growth of, 201—203; regeneration of, 204
  —207
 Bouchardat, M., his researches  on digestion,
  670
 Bovista giganteum, 153 a
 Bourgery, M., his observations on air-cells of
  lungs, 757 a
 Bowman, Mr., his observations on muscular
  fibre, 226, 228, 231,  232, 590 a;  on mucous
  membrane, 176; on  structure  ofthe kidney,
  839—841; on fatty liver, 929
 Brain, see Encephalon, Cerebrum, Cerebellum,
  &c.
 Brewster, Sir D., his law  of visible direction,
  543
 Bright's disease of the Kidney, 707 d
 Brodie, Sir B., his experiments on the Par Va-
  gum, 414,a; on  animal heat,  890
 Bronchial tubes, contractility of, 410, 759
 Brunner's glands, S75
 Buchanan, Dr., his  researches on the  blood re-
  ferred to, 697 e
 Budd, Dr. W.,  his  cases  of reflex action  re-
  ferred  to, 365—369; his observations on
  symmetrical diseases referred  to, 7S5, 882
 Buffy coat, 704, 705
 Bulbus arteriosus, 940, 943
 Bushmen, 70 
INDEX.
739
The Numbers refer to the Paragraphs.
Cacoplastic deposits, 807
Callus, formation of, 206
Cancer, 809, 881
Capacity of respiration, 764
Capillary vessels, distribution and size of, 219,
  220 ; origin of, 221, 222 ; properties of their
  walls, 739 ; absent in some tissues, 220 ;  in-
  dependent  movement  of  blood  in, 733;
  proofs of, 734—739
Capillary circulation, 733—742; phenomena
  of, 734; continues after cessation of heart's
  action, 735; in acardiac fcetus, 736; stagna-
  tion  of, in Asphyxia,  &c, 738; influence of
  local  excitement on,  737;  laws regulating,
  739—741; connection of, with nervous  in-
  fluence, 742
Carbonic acid, excretion of, 749; sources  of,
  750—754 ; amount of, 765—767;  made sub-
  servient to introduction of oxygen, 766;
  effected through the  skin,  768; contained
  in venous blood, 770; expiration of, in hy-
  drogen, 769 ; influence of on colour of blood,
  771, 772;  effects of its retention in the sys-
  tem, 778—780
--------, absorption of, by lungs, 776
Carnivorous animals, nutrition of, 644
Cartilage, structure of, 187—191; composition
  of, 177, a; nutrition of, 188, 191; ulceration
  and reparation of, 191 ; ossification of, 198
  —200
Catamenia, 908, 909
Caucasian race, 93
Cells, the types of Organization, 259 ; compose
    bulk of fabric of Vegetables,  106—109;
    origin  of, 122—124; transformations  of,
    120,121
  Origin of animal structures in, 110;  indi-
    vidual  growth of, in animals,  126,  127;
    history  of  development  of,  128—131;
    transformations  of,  132,  133, 223;  indi-
    vidual life  of,  126, 811;  continual death
    of, in living body, 108, 261, 811; varying
    duration of, 811, 812
  Functions of,  general,  110, 126, 132,259;
    in Absorption, 181, 182, 271, 672; in As-
    similation,  153, 154, 271;  in  Secretion,
    174, 179, 278,  821—823;  in Reproduc-
    tion, 174,281,902
  Persistence  of,  in animal  tissues,  180; in
    pigment, 163, 164; in fat, 184; in shell,
    192 ; in epidermis  and epithelium, 160—
    174 ; in cartilage,  187; in  muscle,  230;
    in nerve, 245
  Replacement of by Fibres, 134, 136
Cellular Plants, 106
Cellular tissue,  see Areolar tissue
Cellulose, Vegetable, 4, 111
Cementum  of teeth, structure  of, 208,  211;
  composition of, 212;  development of, 216
Centipede, nervous system and actions of,  326
  __329
Cerebellum, 340, 457—470 ; of Fishes, 357 ; of
  Reptiles, 360; of Birds, 361;  of Mammalia,
  362 ;  of Human embryo, 358, 359, 361;  re-
  lative dimensions of,  457, 458, 461 ;  experi-
  ments on, 459,  460, 463;  observations on
  size of, in castrated animals, 468, 469; con-
  nection  of, with motor power,  459—465;
  with sexual instinct, 466—470;  pathological
  changes in, 464, 465, 467; phrenological ac-
  count of, 470
Cerebro-spinal fluid, 476, 477
Cerebrum, 340, 471—495; general structure
  of, 472—474; of Fishes, 357 ;  of Reptiles,
  360 ;  of Birds,  361 ; of Mammalia, 362; of
  Human embryo, 358,  359,  361 ;  general
  functions of, 478—480;  relative dimensions
  of, 481—484; experiments on, 485; patholo-
  gical  changes in, 486 ;  connection  of, with
  intelligence, 485—495;  with  the will, 487,
  494; distinct functions  of several parts of,
  Appendix I.; peculiar conditions of, in sleep,
  somnambulism, &c, 499, 500, Appendix II.
Ceruminous glands, 872
Chsetodon rostratus, 490
Change, involved  in idea of life, 254
Cheselden's case of cataract, 541
Chimpanzee, 51—59
Chlorosis, 707 c
Chondrine, composition and properties of, 141,
  187 a
Chorda dorsalis, ISO, 937
Chordae vocales, 603, 605,  607
Chorea, 504 note
Chorion, production of, 918; subsequent changes
  in, 918, 920—923
Chossat, his experiments on inanition, 652, 895,
  896
Chyle, 674; formation of, in intestines, 660; ab-
  sorption of, 181,672; analysis of, 691; aspect
  of, 692;  changes of, in  progress  through
  lacteals,  692,  693; globules contained in,
  their  nature and source,  155,  693;  their
  destination, 154—159, 693 ; chyle from tho-
  racic  duct,  693, 695;  relative constitution
  of, 691
Chyme, formed by digestive process, 657—660
Chymification, 663—669;  a chemical action,
  667
Cicatricula, 936
Cilia, 171—173
Cineritious matter, 246
Circulation
  General account of, 272;  objects of,  709;
     course of, in Man, 710; arterial trunks,
     710; capillaries, 219,  710;  veins, 710
  In Plants, 712—714; in  lower Animals, 715,
     716
  Action of Heart, 719—727;  connection of,
     with  nervous system,  416,  576,  580,
     717; rhythmical movements of, 717—719;
     sounds of, 720, 721 ;  course  of blood in,
     722 ; differences of two sides, 723 ;  quan-
     tity of blood impelled by, 724, 725; force
     of contractions, 726 ;  number of contrac-
     tions, 727
  Action of  Arteries,  728—732; their  elas-
     ticity and contractility, 728; influence of
     their elasticity, 729 ;  proofs of their con-
     tractility, 730; their  tonicity, 731; influ-
     ence of their contractility, 732
  Independent motion  in capillaries,  733—
     742; proofs  of, 734—738;  stagnation in,
     738, 740; influence of capillaries in regu-
     lating amount of flow,  740 ;  contractility of
     capillaries, 739; general principles of their
     action, 751;  influence of nerves on capil-
     lary circulation, 742 
>EX.
740

                           The Numbers refer

  Motion of Blood in Veins, 743—745 ; struc-
    ture and properties of veins, 743 ; causes
    of flow of blood through, 744; influence
    of gravity upon,  745
  Peculiarities of circulation, in lungs, 746 ; in
    portal system, 685,  746 ; in cranium, 476,
    747;  in erectile tissue, 748;  in fcetus,
    early state of, 938—940 ; subsequent con-
    dition of, 943—944
  Disorders of circulation, 881
Civilization, influence of,  on development  of
  human body, 87—90
Clot, of Blood, see  Crassamentum
------------, organization of, 118, 119, 700,
  796
Coagulable lymph, see Liquor Sanguinis
Coagulation, of blood, 699—705; due to fibrine
  alone, 117, 118,  699;  an act of vitality, 118,
  700, 701;  circumstances  influencing,  701,
  702; proportion  of serum  and clot, 703 ;  of
  chyle, 117, 693;  of lymph, 694 ; of fibrine,
  117—119
Coathupe, Mr., hie experiments on respiration,
  764; on products of combustion of charcoal,
  776 note
Coccochloris, 125
Cochlea, 566
Cockchafer, 19
Ccecilia, 31
Coition, act of, in Male, 904; in Female, 911
Cold, degree of, endurable by Man, 987 ; death
  by, 814, 895, 896  ; means of producing, in
  the living body, 897; influence of, on young
  animals, 893, 894
Collard  de Martigny, his  experiments on re-
  spiration, 769, 774
Colostrum, 854 a, 856
Colour of Skin, 79—81 (see Pigment-cells)
Colourless corpuscles in blood, 151—158
Colours, impressions  made by,  552;  comple-
  mentary, 552; deficiency of power of distin-
  guishing, 553
Combe, Dr. A., quoted from, 658 a, 666, 671
Crmmissures  of Brain, 474; deficiency of,
  474 a
Complementary colours, 552
Conception, aptitude for, 909;  act  of, 911,
  927
Conchifera, nervous system in, 317, 318
Concussion of brain, effects of, 580, 625
Consciousness, double, 500
Consensual movements, 335; of  Articulata,
  336; of Vertebrata, 337, 430—436;  of Eye-
  balls, 450—456
Consonants, 616
Contractility of Muscle, 573;  two forms of,
  574;  of arteries, 730, 731; of Capillaries,
  739 ; of bronchial  tubes, 410, 759 (see Irri-
  tability)
Contraction  of Muscle, mode  of, 230,  575,
  576; causes of,  575,  576; alternating  with
  relaxation, 575,577; after  death, 578, 595—
  597; dependent on arterial blood, 583, 584 ;
  power of, the  same at different degrees  of
  extension, 592; energy of, in Man,  598;  in
  Insects, 599; rapidity of, 600
Convolutions of Brain, 472
Convulsive diseases, 502—504
Cooling power of cutaneous exhalation, 897
Cooper, Sir A., his experiments on circulation
to the Paragraphs.

  through  cranium, 290;  his  researches  on
  mammary gland and its secretion, 853
Coral, 6
Corallines, 4
Cornaro, his diet, 653
Cornea, structure and nutrition of, 189
Corpora Albida, 914
------ Cephaloidea, 914
------ Lutea, 912-914
------ Malpighiana, of Spleen, 683;  of Kid-
  ney, 839 b
------ Olivaria, 352, 353
------ Pyramidalia, 352, 353
------ Quadrigemina, 422, 436
------ Restiformia, 352, 353
------ Rubra, 914
------ Striata, 423, 424
------ Wolffiana, 26, 839 c
Corpus Callosum, 474
Corpuscles, Red,  of Blood, 143—150; struc-
  ture of, 143, 144; form of, 145, 146; size of,
  in Mammalia, 146a; in Birds, 1466; in Rep-
  tiles, 146 c; in Fishes, 146 a"; chemical con-
  stitution of, 147; origin of, 148; production
  of in embryo, 149; large in fcetus, 149; uses
  of, in animal economy, 150, 698;  proportion
  of in Blood, 697; increase of, in plethora,
  707 c; diminution of, in chlorosis, 707 c
----------, Colourless, of Blood,  151—159 ;
  characters of, 151;  movement of, 152; uses
  of, 153—159
----------of Chyle, 155
----------of Lymph, 155
----------of Spleen, 684 6
----------of Supra-Renal Capsules, 686
Cortical Substance, of Brain, 472
----------------, of Kidney, S39 a
Convulsive diseases, 501—504
Cotyledons of Ruminants, 921
Coughing, act of, 381
Cranium, circulation in, 476, 747; forms of in
  different races of Men, 81—S7
Crassamentum of Blood, 696
Crowing inspiration of infants, 504
Crusta petrosa of teeth, 208, 211, 212, 216
Cruveilhier, M., his observations  on heart, 718
  —722; on purulent deposits, 837 a
Crying, act of, 380
Cryptogamia, reproduction in, 899
Crystalline lens, 190
Currie, Dr., case of dysphagia related  by, 677
Cutaneous  follicles, perspiratory,  868—870;
  sebaceous, 872
Cuttle-fish, nerves of arms in, 322,  323;  ejec-
  tion of ink by, 438
Cutis anserina, 234
Cyclostome Fishes, 22
Cylinder-epithelium, 170
                    D.

Dartos, contractility of, 234
Davy, Dr. J., his researches on  animal heat,
  886
Death, somatic and molecular, 813—816,880;
  death of individual cells, 811, 812 ; by as-
  phyxia, 814; by cold, 814, 895 ; by syncope,
  814; by necraemia, 814; by retention of se-
  cretions, 278, 832,842 
INDEX.
741
                           The Numbers refer
Decay, constant in Animal body, 268,632, 633,
  750 (see Disintegration)
Decidua, formation of, 919
Decomposition, continual, in living beings, 268,
  632, 633 (see Disintegration)
Decussation, of optic nerves, 445
Defecation, movements concerned in, 391, 392
Degeneration, of nervous structure, 263,292—
  296; of muscular fibre, 239, 263,586; of ele-
  ments of blood into pus,  800, 805; into tu-
  bercle, 807, 808
Deglutition, 382—386;  a reflex  action, 382,
  383 ; nerves concerned in, 384, 385;  actions
  preceding, 386 a-c;  in Polypes, 382
Delaroche  and Berger,  their experiments on
  Animal Heat,  888
Dental groove, 217
Dentine, 208; structure  of,  210; composition
  of, 212;  development of,  213, 214
Dermo-skeleton, 20
Despretz, M.,  his researches on  animal heat,
  892
Devergie, M., his table of development of foetus
  at different ages, 947
Diabetes, 879
Diaphragm, movements of, 761
Diathesis, gouty, 878, 884; saccharine,  879;
  tubercular,  878
Diet-scale, see Food
Digestion,
  General account of, 270;  in lower Animals,
     655 ; alimentary  materials, 641; their re-
     spective destinations, 642—647; inorganic
     substances,  648; relative digestibility of
     different kinds of food, 666;  importance of
     bulk, 666
  Processes  of,  656—662;  mastication and
     insalivation, 656; deglutition,  656; con-
     dition of stomach in, during health, 657 ;
     disorder of, 658  ; entrance  of food into
     stomach, 659; movements  of stomach,
     659 ; expulsion into duodenum, 660; pas-
     sage  along  intestines, 661;  discharge of
     faeces, 662
  Chemical phenomena of, 663—671; compo-
     sition and properties of gastric juice, 664;
     its chemical action, 665, 667 ; artificial so-
     lution of food, 668; Wasmann's researches
     on pepsin, 668 ;  Bernard and Barreswill's
     researches,  669 ;  conversion of saccharine
     and  oleaginous principles, 670, 671
  Influence of nerves upon, 387, 413—415
  Interstitial, according  to Dr. Prout, 681
Digestive cavity in lower animals, 655; origin
  and formation of, 937, 945
Direction, law of visible, 543
Discs, of Blood, see Corpuscles
Disintegration of Muscular tissue, 239, 263,
  586 ; of Nervous tissue, 263, 292—296
Distance, adaptation  of  eye to, 536 ; estimate
  of, 548
Diving animals, 778
Dobson,Mr., his experiments on the  Spleen,

Domesticability of Animals, 39, 42
Donne, M., his  observations on  Milk, 854  a,
   856; on temperature in disease, 886
Doris, gills of, 755
Dormant Vitality, 255
Dorsal vessel of Articulata,  18
to the Paragraphs.

 Double consciousness, 500
 Draper, Professor, on Capillary Circulation 713,
   741
 Dreaming, 499
 Dugong, heart of, 710
 Dulong, M., his researches  on animal heat,
   892
 Dumas, his analysis of fibrine, 114
 Duration of life in individual parts, 810—812
 Dytiscus, experiments on, 328
 Dzondi, on deglutition, 656
E.
Ear, general action of, 556; comparative struc-
  ture of, 557, 558;  distribution of auditory
  nerve in, 559 ;  uses of membrana tympani,
  563; of tympanic cavity, 564;  of labyrinth,
  565, 566 ;  of external ear and  meatus, 567,
  568
Echinodermata, 7—10; shell of,  192
Educability, of Birds, 39, 479; of Mammalia,
  42, 480 ; of Man, 60
Edwards, Dr., his experiments on respiration,
  769; on animal heat, 888, 893, 894
Efferent nerves, 289, 344
Egg, see Ovum
Egg-shell, Membrane  of, 118
Ehrenberg, on limits of vision, 540
Eighth Pair of Nerves, see Glosso-pharyngeal,
  Par Vagum, and Spinal Accessory
Ejaculatio seminis, 372, 393, 904
Elaboration of fibrine, 116,  154—159
Elasticity of arterial walls, 728, 729
Elastic tissues, 138, 139
Electricity, not identical with nervous power,
  297
Embryo, early development of, 915—917, 934
  —945 ; formation of germinal mass, 935 ;  of
  germinal membrane, 935, 936; of vertebral
  column, 937 ;  of amnion, 938 ;  of vascular
  area and  umbilical vessels,  938, 939;  of
  heart and  branchial arches, 940;  of allan-
  tois, 941; of umbilical cord, 941, 942; later
  circulation in,  943, 944; influence of mo-
  ther on, 946 ;  table of development, 947 ;
  size and weight of at birth, 948; proportion
  of males and females, 949 ; relative viability
  of,  950
Embryonic cell, 935, 936
Embryonic development,  of brain, 358, 359,
  361; of cephalic nerves,  420, 421; of lungs,
  757 b, c ; of blood-corpuscles, 149 ; of liver,
  826 g;  of kidney, 839 c; of heart, 940 ;  of
  circulating apparatus, 940, 943, 944 ; of di-
  gestive cavity, 945
Emissio seminis,  372, 393
Emotions, influence  of on Intelligence and
  Will, 440; on nutrition and secretion, 625—
  628
Emotional actions, 437—440
Enamel, 208; structure of, 209;  composition
  of, 212 ; development of, 215
Endosmose, 271, 675
Encephalon, 356 ; comparative anatomy of, 357
  __362; weight of,  in  proportion to  entire
  body, 475;  proportions  of different  parts,
  in  Fishes, 357—359; in Reptiles, 360 ;  in
  Birds, 361; in  Mammalia, 362; in Human 
742
INDEX.
The Numbers refer to the Paragraphs.
   embryo, 358, 359, 361; supply of blood to,
   476,477
 Epidermic tissues, 160—174;  epidermis, 161,
   162 ; hair, 166—168 ; nails, 162, 165; epithe-
   lium, 169—174; nutrition of, 135, 161, 174;
   functions of, 162, 174
 Epilepsy, 503
 Epithelium, 169—174; the real secreting struc-
   ture, 174; cylindrical, 170; tesselated, 170;
   ciliated, 171—173
 Erect vision, 543
 Erectile tissue, 748
 Ethiopian nations, 97—99
 Eustachian tube, uses of, 564
 Eustachian valve, uses of, 944
 Evans, Dr. Julian on the structure ofthe Spleen,
   683, 684
 Excretion,
   Objects of, 275;  of carbon, 275, 833 ; of ni-
    trogen, 276, 842; result of decomposition,
    275,819; elements of, previously in blood,
    820, 832,  842
 Excretions, outlets of, guarded by spinal cord,
   391
 Exhalation, in  Plants, 107; by lungs, 773, 774;
   influenced by mental state, 774; from skin,
   870, 871
 Experiments on nerves, fallacies of, 302—306
 Expiration, act of, 761
 External Ear, uses of, 567
 Exudation corpuscles, 800, 805
Eye, general action of, 536; an optical instru-
  ment, 536; adaptation of, to distance, 536,
  537 ; defects of, 538 ; optical powers of, 540;
  consensual movements of, 450—456
Facial nerve, 406
Faeces, composition of, 662
Fallopian  tubes,  passage  of  Spermatozoa
  through, 911;  passage of ova along, 911,
  918; contractions  of, produced by  nervous
  agency, 393
Falsetto notes, how produced, 609
Faraday, Mr., optical illusion discovered by,
  551
Farre, Dr. A.,  discovery of Spermatozoa in
  Ovum, 900
Fat-cells, 184; contents of, 185; uses  of, 186;
  formation of, 186
Fatty livers, 829
Feathers, 166
Fecundation in Plants, 899;  in Animals, 900
Fever, state of blood in, 707 b
Fenestra ovalis, 557, 558
-------rotunda, 558
Fenwick, Mr., his experiments on absorption,
  673
Ferments,  action of, in  digestion, 669:  in
  blood, 70S, 877
Ferneley, Mr., on areas of arteries, 710 a
Fibres,  origin of, 118, 119, 136; white, 138,
  140; yellow, 138, 142; mixture of in areolar
  tissue, 138; in serous  and  synovial mem-
  branes, 175; in mucous membrane and skin,
  176, 177
------ of Muscle and Nerve, see Muscular
  Fibre, and Nervous tissue
 Fibrillae,  ultimate of Muscle, cellular nature
   of, 230
 Fibrine, composition of, 114;  properties of,
   114, 115; coagulation of, 117—119;  elabo-
   ration of, 117, 158, 159; in chyle, 693; in
   blood, 696—705;  increase of, in inflamma-
   tion,  158, 707 a, 802; diminution of, in fever
   and hemorrhagic diseases, 707 b ; imperfect
   elaboration  of, in strumous diathesis,  807,
   878;  formed at expense of albumen, 114—
   117;  effusion  of, 803;  organization of, 119,
   700, 795, 796
 Fibro-cartilage,  187
 Fibrous tissues, simple, 138—142; origin of,
   118,119,136
 Fifth Pair of nerves, 403, 404 ; lingual branch
   of, 404, 407;  development of, 421;  influ-
   ence of, on  organic processes, 625
 Fishes, 26, 27; skeleton of, 26 ; respiration of,
   27, 755; air-bladder  of, 27,  755;  kidneys
   of, 838, 839 c; encephalon  of,  357, 358;
   circulation in, 27, 716; blood-corpuscles of,
   146, d
 Flourens, M., his experiments on the  nervous
   system, 432, 435, 436, 459
 Fluids,  absorption  of,  by intestinal  surface,
   674, 675; by general surface, 676,  677; by
   veins, 675,  676;  by lacteals,  674,675; by
   lymphatics, 679
 Fly-catcher, incubation  of, 41
 Foetus, table of development  of, 947;  circula-
   tion in, 940, 943,  944; brain  of, compared
   with  that of lower animals, 358, 359, 361;
   see Embryo
 Follicles of Lieberkiihn, 874
 Food, causes of demand for, 629—635 ;  differ-
   ent kinds of, 640, 648; relative amount of
   azote in each, 647;  destination of,  641—
   646;  desire for, 636—639; relative digesti-
   bility of different kinds of, 666; mechanical
   reduction of, 656 ; action of stomach upon,
   657—659; passage of, into intestine, 660;
   passage  of, through  intestinal canal, 661 ;
   ejection of insoluble portion of, 662; mode
   of solution  of, 663—671; smallest  quantity
   of, on which  life  can  be  supported, 653;
   greatest quantity that can be devoured, 654;
   supply of, required by Man, 650, 651; suf-
   ficiency of, indicated by satiety, 649 ; allow-
   ance of, in Navy, 650;  in Milbank Peniten-
   tiary, 651; in  Edinburgh House of Refuge,
   651;  in  Convict-ship, 651 ; effects of insuf-
   ficient supply of, 651, 652
 Form, mode  of  acquiring knowledge of, by
   touch, 523 ; by sight,  541, 542, 546, 547
 Fourth pair of nerves, 405
 Fourth ventricle, 346, 355
 Foville, Dr., his observations on  brain, 486
 Freckles,  164
 Fremy,  M., his analysis of Nervous matter,
   249
 Frog, metamorphoses of, 31; excitable state
   of spinal cord in, 401 a
Functions, 260 ;  division of, into organic and
   animal, 261, 262;  connection of, 263—267;
   of Animal life, 283—288;  of Organic  life,
   268—282                               '
Fungous growths, 809 
INDEX.
743
The Numbers refer to the Paragraphs.
Gall, Dr., his statements respecting the Cere-
  bellum, 468
Gall-bladder, 825 e,f
Ganglia, structure of, 252, 245—247
------- of Special sense in Vertebrata, 422—
  425
-------of Sympathetic, 314, 342
Gangrene, 804
Gases, contained in blood, 770; absorption of,
  by lungs, 775—777
Gasteropoda, Nervous System of, 319—321
Gastric  fluid, composition and  properties of,
  664; action of, 665;  secretion  of,  propor-
  tional to wants of the system, 657;  not de-
  pendent on nervous influence, 414, 415; but
  affected by it, 626, 637
Gelatine, composition of, 141
-------, of cartilage, 187 a; of bone, 196
Gelatinous principles of food, 640;  application
  of, in  the animal body, 642
Gerber,  Prof., referred to, 693 a
Germinal mass, 935
--------membrane, 935; serous layer,  936 ;
  mucous and vascular layers, 936
--------spot, 905, 915
         vesicle, 905, 906, 915—917
Gestation, signs of, 926; ordinary duration  of,
  928—930; protracted, 931; shortest period
  of, 932
Gills, respiration by, 755
Glands, general structure of, 821—823
------, lymphatic, 682
------, vascular, 683—690
Globules, see Corpuscles
Globuline, composition of, 147
Glosso-pharyngeal  nerve, functions of, 384,
  407 ;  development of, 420, 421
Glycerine, composition and properties of, 185 a
Glycicoll, 141 c
Goodsir, Mr.,  his observations  on  primary
  membrane, 135;  on  the Teeth, 217;  on
  Bone, 194;  on ulceration  of Cartilage, 191;
  on Absorption,  181, 672;   on  Vascular
  Glands, 683; on  Secretion,  822, 823;  on
  Milk-cells, 853 b; on formation of Decidua,
  919;  on structure of Placenta, 921—923
Gouty diathesis, 878, 884
Graafian follicle, 905, 912—914
Grainger, Mr., referred to, 345, 367
Granulation, process of, 799—801
Gravity, influence  of on Circulation, 745
Greenhow,  Dr., his plan of treating burns,
  798
Grey matter of Nervous system, 245, 246; of
  Brain, 472
Gryllotalpa, nervous system  of, 332
Gulliver, Mr., his  observations  on.  blood-cor-
  puscles referred  to, 146, 149, 151, 156,158;
  on reparation of bone, 206; on chyle, 692
Guy, Dr., his researches on the Pulse, 727
H.
Habitual movements, 438
Haematine, 147
Haematococcus, 125
Hair, characters of, in different human races,
  82; structure, growth, and  composition of,
  166—168
Hales, Dr., his experiments on the circulation,
  726
Hall, Dr. M., his  discoveries  on  the  Nervous
  system, 307,  345, 363, 365, 374, 375, 383,
  386, 392, 394, 398, 4)0, 505;  his views on
  muscular irritability, 585, 589 b
Haller,  his doctrine  of  muscular  irritability,

Hastings,  Dr.,  his experiments  on capillary
  circulation, 717 a; on animal heat, 890
Haversian canals, 19*; formation of, 197,199,
  201
Hearing, sense of, 556—572; physical  condi-
  tions  of, 557, 560—562 ; use of tympanum,
  563;  tympanic cavity  and Eustachian "tube,
  564;  chain of bines,  565;  labyrinth, 566;
  external  ear, 567;  auditory  nerve, 559;
  tones  produced by succession of sounds,
  569 ;  estimate cf degree, direction, and dis-
  tance  of sounds, 570;  rapidity of perception
  by, compared with  sight, 571;  uses  of, in
  regulating voice, 572,  611
Heart, 111; muscular fibre of, 234;  inherent
  contractility of 717; rhythmical movements
  of, 717—719; influence  of  nerves  on, 416,
  576,717 a-c; sounds  of, 720,  721; course
  of blood through, 722; differences of struc-
  ture  in two  sides  of, 723;  difference  of
  valves, 723 (; quantity  of  blood propelled
  by, 724, 725; force  of contraction  of, 726
  number of contractions of, 727; variou
  causes influencing, 727 a-e  ; origin of, 940
  subsequent development of, 943
Heat, Animal, amount of, developed by Man
  885, 886; in disease, 886; dependence  of
  on  formation of carbonic acid,  889—892
  development  of, in Plants, 889 a,  b;  in
  lower animals, 889, c; effect of exercise on
  890 ;  partly maintained by artificial respira
  tion, 896; dependent in  part on cutaneous
  respiration, 891; chemical  theory of, 892
  heat of young animals, 893 ;  variations  in
  power of generating,  at different  seasons,
  894; loss of, during inanition, 895, 896 ; pro-
  visions against excess, 897
Heat, external, influence of, on incubation  of
  Birds, 41; influence of,  on vital actions  in
  general, 885; extremes  of, endurable by
  Man,  887,  888; power  of resisting,  887,
  888, 897
Heat, sexual, 909
Helmholtz, his observations on composition of
  muscle, 238 b, 586
Hemiopia, 545 note
Hepatic  artery, 826 d
-------cells, 183, 826/
     — duct, 826 c
        vein, 826 a, e
Herbivorous animals, nutrition of, 645
Hering, experiments of, on  circulation, 724
Heterologous growths, 809, 881
Hiccup, act of, 380.
Hippuric acid, 845 a
Holland, Dr., referred to, 521
Horny matter, composition of,  162
Horses, cerebella of, 468.
Hottentots, 100
Houston, Dr., on acardiac foetus, 736 
744
INDEX.
                           The Numbers refer
Hunger, sense of, 412, 636—638
Hunter, John, on muscular tonicity, 593, 594;
  on functions of lymphatics, 681 a, c; on con-
  tractility of arteriei, 731; on union by  ad-
  hesion, 794
Hutchison, Mr., on capacity of respiration, 764
Hydra, 9 ; movements of, 313 ;  reproduction
  of parts in, 9, 792
Hydrophobia, 502.
Hymenoptera, nerves of wings  of, 298;  in-
  stincts of, 336, 429
Hypertrophy, 787, 788
Hypoglossal nerve, functions of, 418, 419 ;  de-
  velopment of, 420, 421
Hysteria, 503; remarkable abstinence in, 653
Ideas, formation of, 488.
Idiots, actions of, 428, 474, 478, 484
Improvability of Man, 60
Inanition, Chossat's experiments on, 895, 896
Incontinence of urine, 401, £04
Indo-European nations, 95
Indian nations, 95
Infants, inferior calorifying pover of, 893, 932 a
Inflammation, increase of fibrine of blood in,
  707 a, 802 ;  diminished vitally ofthe tissues
  in, 803 ; results of, 804— 80C ; generally un-
  favourable to  reparation,  793,  799—801;
  prevention of,  after injuries, 798; how far
  concerned in deposition of tubercle, 808
Ingestion  of food, actions concerned  in, 382,
  656
Insalivation, 656
Insects, Muscular apparatus of, 19 ; strength of,
  599 ; instincts of, 17, 429, 479;  heat deve-
  loped by, 889 c ; nervous  system of,  325—
  336; reflex actions of, 328, 329 ;  consensual
  actions  of, 336; circulation in, 715; respira-
  tion  in,  755
Inspiration, act of, 761
Instinctive actions,  characters of, 428
Instincts,  of Articulata, 17,  336, 429, 479; of
  Birds, 479;  of Mammalia, 42, 480;  of Man,
  428,437—440, 484; of Cuttlefish, 438 ; of In-
  fants and Idiots, 428, 484
Intelligence, of Vertebrata, 23, 482 ; of Birds,
  479; of Mammalia, 480; of Man, 484; gene-
  ral absence of, in Invertebrata, 429; seat of,
  in the Cerebrum,  478
Intercellular passages, 218
Intervertebral  nerves, 421
Intestines, peristaltic movements of, 388, 389;
  passage of food through, 660, 661; glandular
  of, 661, 874—876 ;  secretions of, 661, 877
Intuitive perceptions, 490
Invertebrata, general absence of red corpus-
  cles  in,  150; character of blood  of, 155
Iron,  contained in  food, 648 ; in blood-discs,
  147 ; administration of, in chlorosis, 707 c
Irritability, of muscular fibre, see Muscle
lulus, nervous system and actions of, 326, 329
Jennings, Mr., on artificial insufflation of lungs,
  760 a
to the Paragraphs.

Jewish nation, 80, 94
Jones, Dr. Bence, his  observations on phos-
  phatic deposits, 295 note
Jones, Mr. Wharton, his observations on blood-
  corpuscles, 152, 159 a ; on effects of inflam-
  mation, 704; on capillary circulation, 780
K.
Kellie, Dr., his experiments on circulation in
  cranium, 747
Kidneys, general function of, 276, 819 ;  struc-
  ture of, 838,839; cortical and medullary sub-
  stances, 839 a ; tubuli uriniferi, 839 a ; Mal-
  pighian bodies in, 839 b; circulation in, 840;
  embryological development of, 839 c; see
  Urine.
Kiernan, Mr., on the liver, 826, 827
Kiesteine, in urine of pregnant women, 859,
  926
Knight, Mr., observation on incubation of Fly-
  catcher, 41
Kronenberg, Dr., on roots of spinal nerves, 304,
  344
Lachrymal gland, 865
            secretion, 865;  influence of nerv-
  ous system on, 625, 626
Lacteals, origin and distribution of, 672 ; func-
  tions of, 674, 675
Lactic acid, present in stomach during diges-
  tion, 664 b; not a constituent of urine, 846
Lacunae of bone, 193,194
Lamina spiralis, 559
Lamprey, 22
Lane, Mr., his investigations on chyle, 693 a
Language, indication of affinity of races, 95 a
Laryngeal nerves, 378
Larynx, structure of, 602—604; action of, 604
  —611; muscles of, 604, 605              *
Laughing, act of, 380
Lecanu, M., his analysis of blood, 697 a; his
  observations on urine, 844
Lehmann, his experiments on composition  of
  urine, 844, 849, 850
Letellier, M., his  researches on  respiration,
  767 a
Leuret, M., his observations  on  Cerebellum,
  468, 469
Liebig,  Prof., on digestive  process, 669;  on
  red corpuscles of  blood, 150 a; on compo-
  sition of  urine, 845—848; on uric acid, 845
Life, idea of, involves change, 254, 255 ; dura-
  tion of, in individual parts, 259, 810—812
Ligaments, structure of, 140; vocal, 140
Ligamentum nuchas,  140
Light, laws of refraction of, 533—535; rapidity
  of perception of, compared with sound, 571;
  influence  of, on metamorphosis, 32; effect
  of, on pupil, 395, 443; influence of,  on pig-
  ment-cells, 164
Lime, an element of animal structures„648
Lingual branch of fifth pair, 407
Lintott, Mr., his observations on  the teeth,
  217 c
Liquor sanguinis, 696 : organization of, 117—
  119,795,796 
INDEX.
745
                           The Numbers refer

Liver, general function of, 275, 819;  univer-
  sally*present in Animal  Kingdom, 825; size
  and form of, in Vertebrata, 825 c, d ; gene-
  ral structure of,  826 ; component cells  of,
  183, 826 /; distribution of  portal vessels,
  826 b; of hepatic artery, 826 d; of  hepatic
  vein, 826 a, e ;  of hepatic ducts, 826  c ; con-
  gestion of, 327 ;  cirrhosis of, 828 ; embryo-
  nic  development of, 826  g;  proportional
  size of, before  and after birth, 826 g, 830 ;
  secretion of bile  by, 831—836, see Bile;
  other depurating  actions of, 837
Lizards, 29
Locomotive actions, 397
Looped terminations of Nerves, 240, 248
Lungs, structure  of, in lower Vertebrata, 756;
  in Man, 737 ; development of, 757 a-c ;  ac-
  tion of, in respiration, 760 ; capacity  of, 764;
  chemical changes in, 765—767 ; exhalation
  by, 773, 774 ; absorption by, 775, 776
Lymph, composition of, 691;  elaboration  of,
  682; globules in, 155, 694 ; purposes of,  154
  —159
Lymph, coagulable, see Liquor Sanguinis
Lymphatic glands,  structure of, 682
Lymphatics, distribution of, through the body,
  676 ; function  of, 679, 680 ; specially con-
  cerned in nutritive absorption, 680, 681
                    M.

Macartney, Dr., his views on the reparative
  processes, 793—801
Macleod, Dr., on  first production of blood-cor-
  puscles, 149 a
Madden, Dr., his  experiments upon absorption,
  677, 775
Madder, effect of, on bones, 202 ; on teeth, 210
Magnetism, Animal, Appendix II.
Magnus, his experiments on the blood, 770
Malayo-Polynesian race, 103
Malignant growths,  809, 881
Mammalia, 42—50 ; sub-classes of, 44; skele-
  ton of, 46 ; respiration and heat  of, 47, 757 ;
  subdivisions of, 48 ; brain of,  362; intelli-
  gence of, 42, 485; blood-corpuscles of, 146 a
Mammary gland, 853 ; structure of glandula?,
  853, a, b; development of, 853,  c; structure
  of in male, 853 d ;  secretion of, 854—861;
  see Milk
Man, characteristics of, 51—61 ; erect attitude
  of,  51—57 ; hand of, 57 ;  other distinctive
  characters of, 58 ; sensibility and locomotive
  power of, 59 ;  intelligence of, 60; soul  of,
  61; psychical operations in, 283—2S6; sub-
  division of into races, 62, 63, 78—105; com-
  mon  origin of, 91 ; extremes  of variation
  amongst races of, 72 ; proper food of, 646
Mantis, nervous system of, 328
Margarine,composition and properties of, 185 a
Mastication, 656             ,,,.••,  ocn
Matteucci, his experiments on Electricity, 297
Mayer, Prof., his experiments on  the  Spleen,
  685
Median nations, 95
Medulla Oblongata,  350 ; structure  and connec-
  tions of, 351—355 ; ganglionic character of,
  355; general  functions  of, 370, 374, 384;
      63
to the Paragraphs.

  centre of respiratory movements, 374 ;  cen-
  tre of acts of deglutition, 384, 385
Medullary matter of nervous system, structure
  of, 243, 246 ; functions of, 248
Melolontha vulgaris, 19
Membrana granulosa, 906, 912
Membrana tympani, uses of, 563
Membrane, basement or primary, 135 ; fibrous,
   140; mucous, 176—179;  serous and syno-
  vial, 175
Membrane, development of bone in, 197
Memory, 491
Menstruation, 908, 909
Metamorphosis of Batrachia, &c, 32, 630 a
Milk, peculiarity of as  alimentary  substance,
   642, 647 ; general composition of, 854, 857 ;
   microscopic characters of, 854 a ; constitu-
   ents of, 854 6 ;  proportion  of constituents in
   human milk, 855 ;  in milk of different ani-
   mals, 858 ; quantity of, 860 ;  change in cha-
   racter of, during nursing, 856 ; consequences
   of retention of, 859 ; transference of secre-
   tion, 859 a; foreign substances entering,
   861 ; influence of emotions on, 627 ; secre-
   tion of, in male, 853 c
 Milky aspect of Chyle, 692
 -----serum, 697 e
 Milbank Penitentiary, 651
 Mind, elementary operations of, 487—495; in-
   fluence of, on nutrition and secretion, 625—
   628
 Mineral ingredients of Food, 648
 Mitchell, James, case of, 532
 Modelling process, 797, 798
 Molecular base of Chyle, 692
 Molecular death, 813, 815, 816
 Mollusca, 5, 11—15; deficiency of symmetry
   in,  11—13; organs  of locomotion  in, 13;
   organs of nutrition in, 14; blood and respira-
   tion of, 15 ; shells of, 192 ; nervous  system
   in, 315—322; circulation in, 715; respiration
   in, 755
 Mongolian nations, 96
 Montgomery, Dr., on Corpus luteum, 913,914;
   on placental bruit, 925
 Mother, influence of, on foetus, 946
 Motions of Plants, 1, 230
 Motor influence, laws of propagation of, 299
 Motor lingua?, 418, 419
 ----- oculi, 405
 -----nerves, determination  of, 300—303
        tract of Sir C. Bell, 351
Mucous layer of germinal membrane, 936
Mucous Membrane,  176—179;  of stomach,
  appearance  of, in health, 657; in disease,
  658; intestinal, structure of, 661; glandulae
  of, in stomach, 873 ; in intestines, 874—877
Mucus, properties of, 179
Mulder, his  analysis of albumen and  fibrine,
  114;  of proteine  and its oxides, 116; of
  gelatine, 141 a
Muller, Prof., his researches on vision referred
  to, 519,537, 543, 552; on hearing, 561, 562,
  564; on blood, 699; on voice, 606—610; on
  respiration, 769; on cancer, 809
Muscular Fibre, 223—240; chemical composi-
    tion of,  238
  Structure of, 224, 225; in muscles of Animal
    life, 225—233; arrangement of, in fasci- 
746                                    INDEX.


                           The Numbers refer to the Paragraphs.
    culi,226; composed of fibrilla?, 226 ;  en-
    veloped in sheath, 227; form and com-
    parative dimensions of, 228,229; structure
    of ultimate fibrillae, 230; state of, in con-
    traction, 231, 233; origin  of, 235, 236;
    reparation of, 237; supply of blood-vessels
    to, 239; supply of nerves to, 240; struc-
    ture  of, in  Muscles of Organic life, 234;
    development of, 235,  236; disintegration
    of, from use, 239, 263, 586
  Contractility of, 573,574; irritability of, 575;
    contraction  alternating with  relaxation,
    576, 577;  persistence  of after death, 578 ;
    depressed by  sedatives, 579;  by violent
    nervous impressions, 580, 581; increased
    by stimuli, 582; dependent on arterialized
    blood, 583—585;  increased  by habitual
    employment of particular muscles, 587;
    diminished by want of  action, 5S8;  in-
    fluence  of nerves  on, 589—591;  loss of,
    from section of nerves, 589 b, c ; restored
    after  exhaustion, 589 d; an independent
    endowment,  591; difference of,  on two
    sides of heart, 585; the same  at different
    degrees of contraction, 592 ; power gene-
    rated by, in Man, 598 ; in Insects, 599
  Tonicity of,  593—597;   effect of heat and
    cold  upon, 593, 594
  Contraction of, after death, 595—597
Muscular Contraction, influence of, on Circu-
  lation, 744 c
Muscular Sense, 433, 434
-------- Tension, maintained through Spinal
  Cord, 398, 399
Musk-deer,  blood-corpuscles of, 146  a, 151;
  hair of, 166
Myolemma, 227, 235
Myopia, 538
Myxinoid fishes, 180
Myriapoda, nervous system of, 326; develop-
  ment of head of, 426 a
                    N.

Nails, 162, 165
Necraemia, 70S
Negro races, 97—99
Nerves, origin of, in ganglia, 246, 247; termi-
  nations of, in muscles, 239 ;  in skin and
  sensory organs, 248 ; mode  of determining
  functions of,  300—306
Nervous agency, hypothesis on its nature, 297;
  laws  of  its transmission, 298, 299; not es-
  sential to Nutrition and Secretion, 620, 624 ;
  influence of,  on organic functions, 625—628
Nervous circle, 433
Nervous System, general functions of, 289, 307;
  elementary structure of, 241—253 ;  fibrous
  matter of, 242—244; vesicular matter of, 245,
  246 ;  arrangement of fibres in ganglia, 246,
  247 ; afferent and efferent fibres of, 289,344 ;
  use of plexuses in, 298; isolated course  of
  single fibres, 298; general purposes  of, 307
  —309; dependence of its activity upon supply
  of blood, 290, 291; functional  activity of, in-
  volves disintegration,  292—296; nature of
  changes in, 297;  existence of in lowest Ani-
  mals,  311, 312; general  recapitulation  of
  functions, 496—498; peculiar conditions of,
  499—501; pathological states of,.501—505
Nervous system of Radiata, 313, 314; of Mol-
  lusca, 315—323; of Articulata, 324—336; of
  Vertebrata, 337—362
Nervous tissue, 241—253; fibrous element of,
  242—244; cellular element of, 245, 246; re-
  lation of two structures in, 246—248; com-
  position of, 249; nutrition of, 250, 251; first
  development  of, 252; regeneration of, 253;
  disintegration of, with use, 292—296; decay
  of, when not  employed, 442
Neuro-skeleton, 20
Newport, Mr., his observations on the blood-
  corpuscles of Insects, 156; on their nervous
  system, 325—330 ;  on their  temperature,
  889 c; on development of head  of Myria-
  poda, 426 a
Nitrogen, proportion of, in different  articles of
  food, 647;  exhalation and absorption of,
  766 ; respiration in, 769, 780; amount of, in
  blood, 770
Nostoc, 125
Nucleus, 124; its offices and  metamorphosis,
  in Plants, 124, 125; in Animals,  128—133
Nucleus-filaments, 138
Nutrition,
  General account of, 273, 274, 781; connec-
    tion of, with nervous system, 279; not de-
    pendent upon nervous  agency, 624; but
    influenced  by it, 624, 625
  Essential  nature  of, 782;  a continuous pro-
    cess of cell development, 782, 783; select-
    ing power  of individual parts, 784, 785
  Varying activity  of, 7S6—791 ; affected  by
    age, 786; hypertrophy, 787, 788 ; atrophy,
    789—791
  Reparative processes, 792—801; reproduc-
    tion of parts in lower Animals, 792; union
   ■ by first intention, 793, 794;  organization
    of liquor sanguinis, 119,795; organization
    of blood, 700,  796; modelling  process  of
    Dr. Macartney, 797; circumstances favour-
    able to, 798; granulation, 799—801
  Abnormal forms of Nutritive processes, 802
    —809 ; inflammation, 802—804; suppura-
    tion,  805,  806;  tubercular deposit, 807,
    808;  cancerous growths, 809
  Varying duration of different parts,  810—
    812;  limited term of existence of cells,
    811;  variation of, with period of life, 812
  Death, or Cessation of Nutrition,  813—816;
    somatic and  molecular, 813; somatic, by
    Syncope, 814; by Asphyxia, 814; by Cold,
    814; Molecular, consequent upon somatic,
    815;  dependent on local change, 816
                    O.

Oblique muscles of orbit, 451
Oceanic races, 102 ,
Octopus, nerves of, 298
Odoriferous glandulae, 872
Odorous matter in blood, 872
Odours, sensibility to, 531, 532
CEsophagus, descent of food through, 386, 656
Oleaginous principles of food,  640, 641; de-
  stination of, in Animal body, 643—646, 671 
INDEX.
747
     r
                           The Numbers refer
Oleine, composition  and properties of, 185 a
Olfactory lobes, in Fishes, 357—359; in Rep-
  tiles, 360;  in Birds, 361;  in  Mammalia,
  362 ;  in Man, 422
Olfactive nerves, functions of, 331
Olivary bodies, 350—354
Omphalo-Meseraic vessels, 939
Optic lobes, in Fishes, 357—359 ; in Reptiles,
  360;  in Birds, 361 ; in  Mammalia, 362; in
  Human  embryo,  358, 359,  361;  in Man,
  422 ;  functions of, 436  •
Optic Nerve, 442—445; an excitor of motion,
  443 ;  decussation of, 445; termination of, in
  retina, 539
Optic Thalami, 423,424
Orang Outan compared with Man, 50—60
Orbicularis muscle, reflex action of, 394
Orbit, motor nerves  of, 405;  muscles of, 450,
  451
Organic fibres of Nervous System,  244, 247,
  341
Organization, connection of, with vital proper-
  ties, 781 ; incipient in liquor sanguinis, 117
  —119 ; in coagulable lymph, 117, 795
Organs of Sense, their mode of operation, see
  Ear, Eye, &c.
Ornithorrhyncus, 44; mammary gland of, 821
Ossification, in  membrane, 197, 201;  in carti-
  lage, 198—201
Ostrich, incubation of, 41
Otter-breed, origination of, 70
Ovarium, origin  of  ova in, 905—907; corpus
  luteum in, 913, 914
Ovisac, 907, 908
Ovum, component parts of, 905 ; origin of, 906,
  907;  maturation of, 909; arrival of sperma-
  tozoa at, 900, 911; discharge of, from ovary,
  912; first  changes  in, 915—918;  later
  changes in, 934—947
Owen, Mr., on  blood-corpuscles of Siren, 145
  note; on structure  of dentine, 210 ; on forma-
  tion  of dentine, 213, 214;  on formation of
  enamel, 215;  on formation of crusta petrosa,
  216
Oxygen, introduction of,  in respiration, 766;
  presence of, in arterial blood, 770, 771 ; in-
  fluence  of, on colour of blood,  771, 772 ;
  effect of respiration of, 777
                     P.

Paget, Mr. J., on areas of arteries, 710 6; on
  concentric hypertrophy of heart,  597;  on
  absence  of corpus  callosum, 474 a; on ac-
  tion of heart, 717
Pancreas, structure of, 862 ; secretion of, 669,
  670, 863
Papillae, of skin, 522; of tongue, 527
Papuans, 104
Paralysis agitans, 381 note
Paraplegia, cases of, showing  reflex  action,
  366—369
Parturition, 393, 928, 929
Par Vagum, 408; the excitor of respiratory
  movements, 374, 375;  influence of, on pha-
  rynx, 385 ; on oesophagus, 386; on stomach,
  3S7 ; chief excitor  of sense of hunger, 412,
to the Paragraphs.

  637;  effects of section  of, on lungs, 409—
  411;  on digestion, 412—415; on heart, 416
Pelagian-Negro races, 104
Pelvis,  various forms of in different races of
  Men, 88
Pepsin, 668, 669
Perception, 488—490
Perenni-branchiate Batrachia, 32
Peristaltic  movements of intestines, 388, 575,
  660;  independent of nervous agency, 3SS;
  influenced by spinal cord through  sympa-
  thetic, 388, 389
Peyerian glands, 874, 876
Philip, Dr. Wilson, his experiments on  the Par
  Vagum, 414, 415;  on connection of Nervous
  System with heart, 717 a,- with Capillaries,
  742 ;  on animal heat, 890
Phosphorus, an element of food, 648 ;  in pro-
  teine-compounds,  113, 114; oxidation of, in
  system, S47
Photophobia, 431
Phrenological doctrines regarding Cerebellum,
  466—470
Phrenology, observations  on, Appendix I.
Physiology, objects of the science, and mode
  of pursuing it, Introduction.
Pigment-cells, 163, 164
Piementum nigrum,  164
Placenta, 44 ; formation and structure  of, 920
  —924
Placental souffle, 925
Plants,  see  Vegetables
Playfair, Dr., his observations on Milk, 855
Plethora,  increase  of  blood-corpuscles  in,
  708 c
Plexus of nerves, use of, 298
Plica Polonica, 168
Plicae dorsales, 937
Pneumogastric nerve, see Par Vagum
Poisseuille, M., his experiments on the circu-
  lation, 726, 729, 730
Polli, Dr., his observations on blood, 701, 702
Polydesmus, nervous system of, 326
Polynesian races, 103
Polypes, 6—10 ; circulation in, 715 ; reproduc-
  tion of parts in, 9, 792;  movements  of, 313
Porrigo favosa, 809 a
Portal  circulation,  685,  746;  in liver, 826,
  827 ;  in kidneys, 839 6—841
Portio dura, 406
Posterior roots of spinal nerves, 344
Pregnancy, signs of, 926; see Gestation
Presbyopia, 538
Prichard, Dr., his ethnographical researches
  referred to, 63 note, 77, 92
Primitive trace, 936
Protecting agency  of Spinal Cord,  394—396
Proteine, composition and properties of, 116
Proteus, 32; blood-corpuscles of,  146 c, 151
Prout, Dr.,  his classification of alimentary sub-
  stances, 640 ; his observations on secondary
  digestion, 681; on amount of carbonic acid
  excreted, 767 ;  on watery exhalation from
  the lungs, 773 ; on urine, 845 d; on general
  disorders of secretion, 883
Puberty, in Male, 903; in Female, 908
Pulsation of heart, 717
--------of arteries, 729
Pulse, average frequency  of, at different ages, 
748
INDEX.
                           The Numbers refer to the Paragraphs.
  727; variations of,  under different circum-
  stances, 727 a-e; proportion of to respira-
  tory movements, 762
Pulse, respiratory, 744 b
-----venous, 723 c
Pupil, action of, 395
Purkinje, optical experiment of, 555
Pus, production of of, 779, 800, 805, 806
Pyramids, anterior and posterior, 350—354
                    Q-

Quadrumana,50
Quekett, Mr. J.,, his observations on bone re-
  ferred to,  194 a
Quetelet, M., his researches on  relative mor-
  tality at different  seasons, 699  c ; on length
  and weight of infants at birth, 948 ; on rela-
  tive viability of males and females, 950 ; on
  comparative heights  of males  and females,
  951
Quickening, 927
R.
Racieorski, his researches on Conception, 909
Radiata, 5—10; general structure of, 5; affi-
  nity with vegetables, 6, 7 ;  symmetry in, 8 ;
  reproduction of parts in, 9; nutritive organs
  in, 10;  nervous system in, 311—314
Rainey, Mr.,  his researches on  structure  of
  lungs, 757
Recti muscles of orbit, 450
Red Corpuscles of Blood, see Corpuscles, Red
Reeds, vibrating, laws of, 606 c
Rees, Dr. G. O., his observations on blood-cor-
  puscles referred to, 143, 144, 148; on com-
  position of Chyle and Lymph, 691; on Saline
  matter of Blood, 697 d
Reflex action, 313, 363 ; in Mollusca, 316, 317,
  322;  in Articulata,  327—329,335; in Ver-
  tebrata, 337, 364—373
-----------,  cases of in Man, without sensa-
  tion,  365—370
Regeneration  of parts, in lower Animals, 9,
  792;  of  bone,  204—207,  792; of nervous
  substance, 253
Reid, Dr. J.,  his  researches on respiratory
  movements, 374, 375;  on  movements of
  deglutition, 384—386; on movements of sto-
   mach, 387; on glosso-pharyngeal nerve, 407;
   on pneumogastric, 408—416 ;  on  laryngeal
   nerves, 378, 379 ; on spinal accessory, 417;
   on muscular contractility, 589; on irritabi-
   lity  of heart, 717;  on  Asphyxia,  723 c,
   780; on  capillary circulation,  740;  on mu-
   cous membrane of uterus, 919 ; on structure
   of placenta, 922
 Reid, Dr. D. B., his researches on respiration,
   765
1 Reinforcement, fibres of, 326
 Reparative processes, 792—801; Dr. Macart-
   ney's views of, 793—801 ; union  by first in-
   tention,  794; process of  organization of
   liquor  sanguinis,  119, 795; organization of
   blood, 700, 796; modelling process,  797;
  causes favourable to, 798 ;  granulation, 799
  —801
Repetition of parts  in  Radiata, 6—9; in Ar-
  ticulata, 324, 330
Reproduction,
  General account of, 281, 282, 898 ; in Plants,
    109, 898, 899 ;  in Animals, 900
  History of,  in  Male, 901—904; spermatic
    fluid, 867, 901; evolution of spermatozoa,
    902 ; power of, 903 ; coitus, 904
  History of,  in  Female, 905—933; general
    account of ovum, 905; first development
    of, 906,  907 ;  menstruation, 908, 909;
    aptitude for conception, 909, 910 ; coitus,
    911 ; escape of ovum, 912 ; corpus luteum,
    913, 914;  first changes  in  ovum, 915—
    917;  addition of chorion, 918; formation
    of decidua, 919 ;  formation and structure
    of placenta, 920—924; sound  of, 925 ; in-
    crease of tissue of uterus, 926 ; quicken-
    ing, 927 ; parturition, 928, 929; ordinary
    duration of gestation, 930; protracted ges-
    tation,  931 ; shortest term of gestation,
    932; superfcetation,  933
   Development of embryo, see Embryo
   Reproduction of  lost parts, 9, 792
 Reptiles, 28—32; respiration and circulation
    in, 28, 756; different orders  of, 29,  30;
    connected with Fishes by Batrachia, 31,
    32; brain of,  360;   blood-corpuscles of,
     145, 146 c ; lungs of, 756
 Resistance, sense of, 514
 Respiration,
   General purposes of,  749—754;  necessity
     for, 749; in  Plants, 750;  in Animals,
     generally, 751 ; in  warm-blooded Verte-
     brata, 752; variation in degree of, 753,
     754
   Structure and action of Respiratory organs,
     in Invertebrata, 755 ; in lower Vertebrata,
     756 ; structure and development of lungs
     in Man, 757 ; arrangement of their blood-
     vessels,  758;  contractility  of bronchial
     tubes, 758 ;  movements concerned in ex-
     change  of air, 760, 761; number and ex-
     tent of, 762, 763 ; capacity of lungs, 764
   Chemical  phenomena, 765—768 ;  carbonic
     acid exhaled, 765 ;  proportional amount
     of oxygen absorbed, 766; absolute quan-
     tity of carbon set free, 767; variations in,
     767  a-i; azote  absorbed and exhaled,
     766; cutaneous respiration, 768
   Effects  on the blood, 769—772;  carbonic
     acid in venous blood, 769, 770; exhala-
     tion of, in hydrogen and azote, 769 ; com-
     parative analysis  of free gases in arterial
     and venous blood, 770 ; causes of change
     of colour, 771, 772
   To be regarded  as  an Excretion, 275, 749 ;
     consequences of retention  of carbonic
     acid, 778—780 ; phenomena  of Asphyxia,
     779 ; its immediate causes, 780
   Movements of,  760—763 ;  dependent  on
     Nervous agency, 374, 375; centre of, in
     Medulla oblongata, 376; nerves concerned
     in, 374—376 ; independent of will and of
     consciousness, 377 ; guard to entrances of
     lungs, 378, 379; modifications of, 379—
     381; influence of pain od, 431, 763; num- 
INDEX.
749
                           The Numbers refer
    ber of, 762, 763; share of lungs and air-
    passages in, 759, 760; various influences
    affecting, 763
Res^ratory  Circulation,  710;  peculiarity of,

Respiratory pulse, 744 b
Restiform bodies, 350—354
Rete mucosum, 161
Retma, structure  of,  539; <he recipient  of
  visual  impressions, 536;  inversion of pic-
  tures upon, 543; persistence  of  impressions
  on, 551, 552 ;  vanishing of images on, 554 ;
  visual representation of, 555
Retinacula, 906, 912
Rigor Mortis, 232, 595—597
Ritchie,  Dr., his researches  on development
  of ova, 907 ;  on Menstruation, 909 ;  on the
  Corpus luteum, 914
Robinson, Mr., on effusion of fibrine, 803
Saccharine principles of food, 640 ; destina-
  tion of, 641, 643, 645, 670
Saliva, properties of, 656, 668, 863 ; incorpo-
  ration of with food, 656
Salivary glands, structure of, 862 ; secretion
  of,  863; influence  of nervous system  on,
  625, 626
Saunders,  Mr.  E., his  researches  upon  the
  teeth, 217 k-m
Savart, M., his researches upon sound, 469 a
Scharling, Prof., his researches on respiration,
  767
Schleiden, his researches on  the development
  of cells in Plants, 124
Schwann,  his  experiments on muscular con-
  traction, 592; his observations on  cellular
  origin of Animal structures, 135
Seasons, influence  of on Calorification, 894
Sebaceous glands,  872
Secretion, general nature of, 275—278, 817;
  structures adapted  for, 821—823;  essen-
  tially composed  of cells, 821—823 ; disor-
  ders of, connected with nutritive processes,
  882; not dependent on nervous agency,620,
  624 ; influence of nervous system on, 625—
  628
Secretions, amount of, 818 ;  sources of, 819 ;
  elements of, pre-existing in the blood, 820 ;
  some of them used in the system, 820;  see
  Bile, Urine, Milk, &c.
Seguin, on cutaneous exhalation, 870
Selecting power, of individual parts, 7S2—785
Semicircular canals, 366
Seminal secretion, 867, 901, 904; influenced
  by state of feeling, 626 note
Sensation,  307,  308; characteristic  of Ani-
  mals, 283, 284;  why  associated with reflex
  actions, 371, 372; dependent on Capillary
  Circulation, 290, 507, 508 ; the originator of
  consensual movements, 430—432 ; the guide
  of voluntary movements, 433
Sensations, nature  of, 506; different kinds of,
  507;  dependence of on supply  of blood,
  50S ;  pain or pleasure connected with, 509 ;
  influence  of habit on, 510—513;  special,
to the Paragraphs?

   514,  518; common, 514, 515;  subjective
   and objective, 516,  518,  521;  transference
   of, 517 ; influence of attention on, 519—521;
   knowledge gained from, 487—490
 Sense, Muscular, 433,  434
 Sensibility in different parts, 507,  508
 Sensitive Plant, movements  of,  1
 Sensorium, 435
 Sensory ganglia, 422—427 ; functions  of, 428
   —440
 -------nerves, 441—449; terminations of, 248
         tract of Sir C. Bell, 351
Serous membranes, 175
Serpents, 29
Serres, his measurements of Cerebellum, 457 ;
  of Cerebrum, 481
Serum of blood, 696;  composition  of, 697;
  proportion of, to clot, 703 ;  milky,  697 e
Seventh pair,  portio  mollis of, 446;  portio
  dura of, 406
Sexual instinct, 903, 909 ;  its  supposed loca-
  tion in the Cerebellum, 466—470
Sharpey, Dr., his observations on development
  of bone, 197—201  ;  on  muscular fibrillae,
  230, note; on nerves of Cuttlefish, 322; on
  decidua, 919
Shell, structure of, in Echinodermata, 192 ; in
  Mollusca, 192
Siege of Landau, 946
Sighing, act of, 380
Sight, sense of, see Vision
Simon, Mr., on Thymus and Thyroid Glands,
  687, 688
Single vision with two eyes, 545—547
Siren, 32 ; blood-corpuscles of, 145 note
Sixth pair of nerves, 405
Size, mode of estimating by vision, 549
Skin, structure of, 176, 177 ; contractility of,
  234 ; absorbing power of, 676—679; respi-
  ratory power  of,  768 ;  exhaling apparatus
  in, 868 ; transpiration from, 869—871; seba-
  ceous and ceruminous glands in, 872 ; exu-
  dation from, increased by heat, 897
Skull, forms of, in different races of  Men, 83
  —87
Sleep, 499
Smell, sense of,  531, 532 ;  seat of, 531 ; con-
  ditions of, 531; acuteness of, in some Ani-
  mals and Men, 532
Sneezing, act of, 381,  531
Sobbing, act of, 380
Solen, nervous system of, 317, 318
Somatic death, 813, 814
Somnambulism, 500, Appendix II.
Sound, laws of propagation  of,  560—562; suc-
  cessive pulses  of, 569 ; mode  of estimating
  direction, distance,  and  intensity of, 570 ;
  rapidity  of  perception of,  compared with
  that of light, 571 ; use of in regulating voice,
  572, 611
Sounds, articulate, 612—619
      , of heart, 720,  721;  of placenta, 925
Spasmodic diseases, 501—504
Species, discrimination of,  64—67; variation
  within  limits of, 6S—73; distinguished by
  physiological and psychological characters,
  74—77
Spencer, Earl, on the duration of gestation in
  Cattle, 931 
750
INDEX.
The Numbers refer to the Paragraphs.
Spermatic fluid, 867
Spermatozoa, 900, 901;  function of, 900, 911,
  917 ; development of, 902
Sphincters, action of, 391, 392
Sphinx ligustri, Nervous system of, 325
Spinal accessory nerve, 4l7
Spinal Cord of Vertebrata, 346—350 ; its com-
  parative  anatomy, 346; its  divisions, 346,
  347; its  connections with the nerves, 347,
  348 ; functions of several parts of, 349, 350;
  general functions  of, 363—373 ; absence of
  proper sensibility in, 365 ; protecting agency
  of, 394—396;  maintenance of muscular ten-
  sion through,  398, 399;  influence of,  on
  heart, 717 a;  power of sustaining locomo-
  tive actions, 397 ;  pathological conditions of,
  400, 401, 501—504
Spinal nerves, double roots of, 344
Spinal system, nerves of, 402—421
Spleen, structure of, 683 ;  functions of, 684,
  685
Sponges, 1, 7
Spongioles of Plants, 107
Stammering, causes of, 617,  618;  treatment
  of, 619
Star-fish, structure of, 8—10 ; nervous system
  of, 312, 314
Stark, Dr., his analysis of Bone, 196 6
Stearine, composition and properties of, 185 a
Stereoscope, 546, 547
Stilling,  Dr.,  his researches  on the  Spinal
  Cord, 347
Stomach, presence  of, characteristic of Ani-
  mals, 2 ; general characters of, 655; state
  of, in health, 657; in disease, 758 ; sense of
  hunger referred to, 637 ; movements of, 387,
  413, 659;  influenced by nerves, 387, 413 ;
  secretions of, 665, 873 ; influence of nerves
  on, 414, 415 ;  effects of blows on, 580, 625
Stomato-gastric system, of Mollusca, 319, 320;
  of Articulata,  332—334
Strabismus, 454  a-d
Strangury, 504
Strings, vibrating, laws of, 606 a
Strumous diathesis,  878 (see Tubercle)
Subjective  sensations, 516, 518, 521
Suction, act of, 386 c
Sudoriferous glandulae, 868 ; their  secretion,
  869, 870
Sulphur, contained  in food, 648;  in proteine-
  compounds, 113,  114; oxidation of,  in sys-
  tem, 847
Superfcetation, 933
Suppuration, 799—801
Supra-renal capsules, 686
Swimming-bladder,  27
Symmetrical diseases, 784, 785
Symmetry, radiate,  8 ;  bilateral, of Articulata,
  18; of Vertebrata,  25;  deficiency  of,  in
  Mollusca, 12
Sympathetic System, peculiar  fibres  of, 244 ;
  general  structure of, 338, 341, 342; influ-
  ence of, on movements of intestinal canal,
  388, 389 ;  on  ureter and  muscular coat of
  bladder, 390; on uterus and fallopian tubes,
  393;  on heart and vessels, 416, 623, 717 6,
  730,  732;  on ductus  choledochus,  825/;
  on  processes of organic life, 620—628
Sympathies, motor, 620—623;  organic, 625—
  628
Syncope, 580, 814
Synovial Membranes, 175
Syro-Arabian nations, 94
T.
Taliacotian operation, 253
Taste, nerves of, 407, 447
Taste, sense of, 527—530; nerves concerned
  in, 407, 447; conditions of, 528 :  partly de-
  pendent on smell, 529; educability of, 530 ;
  purposes of, 529
Teeth, 208—217 ;  component  tissues of,  208
  —216; development of,  in  Human  infant,
  217, a-i ; a test of age, 217 k, I, m
Temperature, sense of, 514, 524 ;  ordinary, of
  the human  body, 886 ; extremes of sustain-
  able by Man, 887, 888 ; (see Heat)
Tendons, structure of, 140 ; attachment of to
  muscle, 233
Tenesmus, 504
Tension of Muscles, 398, 399
Tetanus, 401,502
Testis, structure of, 866 ; development of, 866
  6 ;  secretion of,  867
Tessier's experiments on duration of gestation,
  931
Thackrah, Mr., his observations  on coagula-
  tion of blood, 703
Thalami Optici, 423, 424
Thaumatrope, 551
Third pair of Cranial Nerves, 405
      ventricle of Brain, 358, 359
Thirst, sense of, 639
Thorax,  movements of,  in respiration, 760,
  761
Thymus gland, 687, 688
Thyroid gland, 689
Tiedemann, his researches on absorption, 675
Tissues, elementary, classification of, 137
Todd, Dr., on mucous membrane, 873
Tomes, Mr., his  observations on bone referred
  to, 196, 203, 207
Tongue,  papilla  of, 527; movements of, 418,
  419
Tonicity  of muscles, 593—597 ;  of arteries,
  731; effects of deficiency of, 745
Tortoises, 29
Touch, nerves of, 448
Touch, sense of,  522—826 ; varying  acuteness
  of, in different parts, 522;  ideas derived from,
  514,523; peculiarities of, 524; improvability
  of, 525;  modifications  of, in  different ani-
  mals, 526 ; connection of, with vision, 541,
  542
Toynbee, Mr., his researches on non-vascular
  tissues, 187—190
Trainers' diet, 654
Transudation, 824
Travers, Mr., his observations on formation of
  new vessels, 222 ;  on production of new tis-
  sue, 795
Trifacial  nerve, 403, 404
Tubercula  Quadrigemina, 422, 436
Tubercular matter, 807, 808 ; tendency in the
  system to deposit, 878
Tubular tissues, simple, 218—222; compound,
   223—253 
                                        IND

                           The Numbers refer
Tunica granulosa, 906, 912
Turkish race, 96
Tunicata, nervous system and actions of, 316
Tympanum, membrane of, 563 ; cavity of, 564
                     U.

Umbilical cord, 941, 942
----------vesicle, 939, 941
Unguiculated Mammalia, 48, 49
Ungulated Mammalia, 48, 49
Unity, specific, of human races, 91
Urea, composition of, 844; increase of by ex-
  ercise, 844
Uric acid, composition of, 845;  pathological
  changes in, 845 a-d
Urine, nature and purposes of its secretion, 842
  —852; effects  of its retention, 842; com-
  position of, in health, 843;  amount of urea
  contained  in, 844; uric acid in, 845; hippu-
  ric  acid' in, 845 a; no  lactic acid in,  846;
  saline compounds in, 847; alkaline or acid
  reaction of, 848 ;  amount of azotized matter
  in, 849 ; influence of diet on, 849,850 ; trans-
  ference of secretion, 851; excretion of saline
  matter with, 852
Uterus, changes  of, preparatory to gestation,
  919; increase in substance during gestation,
  926 ; contractions of, how far dependent  on
  nervous agency, 393, 928
                    V.

Vagus nerve, see Par Vagum
Valentin, his researches on Spinal Cord, 349 ;
  on movements of Stomach, 387 ; on the Sym-
  pathetic, 388, 390, 393,  730; on  Olfactory
  nerve, 441;  on Optic nerve, 442 ; on Portio
  Dura, 406 ; on Par Vagum, 408, 416 ; on Spi-
  nal Accessory, 417; on  Hypoglossal, 418;
  on quantity of blood  in system, 724
Valves of heart, actions of,  722, 723 c; sounds
  produced  by, 720, 721
Vapour, exhalation of,  from lungs, 773,  774
Variation, extremes  of in species, 68—71; in
  Man, 72, 73
Varicose nerve-tubes, 243
Vasa lutea, 939
Vascular area, 938
--------lamina of Germinal  Membrane, 936,
  938, 940
Vegetable proximate principles, 111
Vegetables, distinguished  from Animals,  1—4;
  food of, 2 ; movements of, 1, 283 ;  early de-
  velopment of, 3; formation of cells in, 106—
  109, 120—125;  general  functions of, 107,
  261;  circulation  in, 712—714;  respiration
  in, 750 ; reproduction in, 899
Veins, distribution of, 710; structure of, 743;
  movement of blood in, 744;  causes of con-
  gestion  in, 745;  pulsation in, 723 c
Ventricles of heart,  contraction of, 718—721 ;
  force of, 726; thickness of, 723 ;  capacity of,
  724
Ventricles of brain, third, 358; fourth, 346,
  358
Vertebrae, 21;  origin of, 937
ex.                                    75i

to the Paragraphs.

Vertebral column in Fishes, 26
 Vertebrata, 5, 20—25; skeleton of, 21, 22; ex-
   tremities of,  22 ;  predominance of nervous
   system in, 20,23 ;  organs of animal and vege-
   tative life in, 25; symmetry in, 25; intelli-
   gence of, 23 ;  nervous  system  of, 339—362
 Vesicles of Brain in  Embryo, 358
 Vessels, formation of, in  Plants,  218 ; in Ani-
   mals, 221, 222
 Viability of Infant, earliest period of, 932
 Vierordt, his researches  on  respiration, 765,
   767
 Villi of Mucous Membrane, 178,  472, 473
 Visceral system of nerves, see Sympathetic
 Visible direction, law of, 543
 Vision, sense of, 533—555; optical conditions
   of, 534—537; defective, 538; limits of, 540;
   mental conditions of,  541;  connection  of,
   with touch, 541,542; erect, 543; single, 544,
   545 ; appreciation of form by, 546, 547;  of
   distance, 548 ; of size, 549 ; persistence  of
   impressions, 551; complementary colours,
   552; want of power to distinguish colours,
   553; vanishing of images, 554; visual per-
   ception of retina,  555
 Vital Action involves change, 254    '
-----------dependence of, on external stimuli.
   255, 258
 Vital Actions, classifications of, into Functions,
   260
 Vital forces, 256
 Vitality, duration of in  individual parts, 810—
   812; dormant, 255
 ------of general system, destroyed by sudden
   shock,  580, 735, 742
 Vital properties, 256, 258 ; retention of, 259
 Vitelline  vessels, 939
 Vitreous humour, 190
 Voice, 602—619 ; conformation of larynx, 603
   —605;   sounds  resembling  produced  by
   strings, 606 a; by flute-pipes, 606 b; by reeds,
   606 c;  action of chordae vocales, 607; arti-
   ficial larynx, 607;  pitch, how regulated, 608 ;
   falsetto notes, how produced, 609; influence
   of air-passages on, 610; movements concern-
   ed in, how directed, 611
 Volkmann, his experiments on Muscular con-
   traction, 576
 Voluntary actions, distinguished from automa-
   tic, 483 ;  originate in Cerebrum, 483, 495
 Vomiting, 505
 Vowel sounds, 614,  615
                    W.

Wagner,his observations on blood-corpuscles,
  148, 155, 157, 159 a; his account of develop-
  ment of Spermatozoa, 902
Wasmann, his researches on pepsin 668
Waste of Animal tissues, see Decay, and  Dis-
  integration
Weber, Prof., his researches on sensation, 522 ;
  on absorption, 672; on  movements of heart,
  717a
Whale, Spermaceti, peculiar sensibility of, 526
Wheatstone, Prof., his Stereoscope, 546, 547
White corpuscles of blood, 151—159
White fibrous tissue, 13S—141 
752
INDEX.
                          The Numbers refer

White matter of nervous system, 242, 243
Williams, Dr., on contractility of bronchi, 759;
  on Necraemia, 708; on Inflammation,  158;
  on causes of Venous Congestion, 745
Willis, Mr., his researches on the Voice, 604:—
  608
Wilson, Mr. Erasmus, on cutaneous follicles,
  868
Wings of Insects, interlacement of nerves sup-
  plying, 298; rapidity of motion of, 600
Wollaston, Dr., his observations upon sound,
  569 a; upon hemiopia, 545 note
to the Paragraphs.

                    Y.

Yawning, act of, 390
Yellow fibrous tissue, 138—142
Yolk, 905, 935, 939
Yolk-bag, 905, 935, 939
Young animals, low calorifying power of, 893,
  932 a; influence of cold upon, 893 c

                     Z.

Zona pellucida, 905,917
Zwicky, Dr., on organization of thrombus, 700
THE  END. 
 
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NLM031925152