ARMY MEDICAL LIBRARY
FOUNDED 1836
&NNE1
WASHINGTON. D.C 
 
/
                   RECOMMENDATIONS.

    From numerous testimonials we  have only space for the
                            following.
 From Charles Anthon, Professor of Greek in Columbia College,  and
   Rector of the Grammar School of Columbia College.
                           Columbia College, August 16th, 1838.
 C. A. Lee, M.D.
   Dear  Sir.—I have examined your unpretending little volume, on
 Physiology with great care,  and have found it so excellent of its kind,
 and so well adapted in every point of view, for the purposes  of educa-
 tion, that I intend to adopt it as a text-book in the grammar-school of
 the college, the moment it appears.  The very popular and  attractive
 view, which you have succeeded in giving of this most important branch
 of knowledge, cannot fail to introduce your work into the most exten-
 sive circulation among  all our  schools both public and private.  I do
 not know when I have met with an elementary treatise that more fully
 accorded with my own  idea of what such a production ought  to be, and
 1  think you have achieved a very proud  victory,  in thus making  the
 stores of a richly furnished mind afford so simple and at the same time
 so invigorating a repast for the youthful intellect.
         I remain,
               With high respect and esteem,
                                   Yours very truly,
                                        CHARLES ANTHON.
   From J. W. Francis, M.D. late Professor in the Rutgers Medical
                             College.
                                 New York, August  16th, 1838.
 C. A. Lee,  M.D.
   Dear Sir,—I have perused your Manual of  Human Physiology.   It
 recommends itself as  a clear and lucid exposition of elementary infor-
 mation on an important branch  of natural science, for those for whom
 it is especially intended ; remarkably free from all ambiguities of thought
 or language and unnecessary digression.  It is well adapted to the ca-
 pacities of youthful learners, and will admirably subserve the intentions
 of the enlightened and benevolent friends of the " American  Common
 School Society."
   With  every wish that your laudable efforts may meet with a  be-
 coming consideration,
                            I  remain, Sir, your friend,
                                        JOHN  W. FRANCIS.
 From A. C. Post, M.D.  late Professor of Clinical Surgery, in the Uni-
                  versity of the city of New York.
   Dear Sir.—The  general ignorance of the community with regard to
the structure and functions of the human body is much to be regretted.
This  ignorance frequently causes men to violate the laws of health,
and it renders them liable to become the victims  of quackery and im-
posture.  I have no knowledge of any remedy which will be  likely to
contribute so much  to the removal of this evil, as the introduction of
popular treatises on Anatomy and Physiology into our common schools.
The  treatise which you have compiled on this subject contains a large
mass of  useful  information  combined with agreeable  and striking il- 
RECOMMENDATIONS.
lustrations.  And  I have no doubt that it will contribute to the diffu-
sion of correct sentiments on the important subjects of which it treats.
                            Yours, sincerely,
                                    ALFRED C. POST, M.D.

                     FROM THE NEW YORKER.
  " Human Physiology, for  the use of Common Schools;  by Charles
A.  Lee,  M.D."—It is an  old objection frequently urged against text
books on most scientific subjects, that they are treated in a manner un-
intelligible to the general reader.  M"uch heavier is this objection when
the work  is intended for children.  No such opposition  however, can
be made to this  work, than which we  never recollect  to have  seen a
better for its proposed object.  The plan is clear, and well arranged, the
divisions of  the subject methodical and scientific, and the style  simple
and familiar.  It is in this last particular, we think the author has been
uncommonly successful.   He has hit to a nicety the proper medium
between childishness and an unnecessary display of learning; and any
child of twelve years of age w>ho cannot master this volume by  dint of
study,  must be allowed  extremely deficient.  Great compression has
been employed so as to confine the volume within certain limits.   This
in itself demanded great skill, and has been executed with correspond-
ent success.   The  work is calculated to be extremely useful, and ought
to be very popular. It should find a place in every school and academy.
It may also be read with great profit by many beyond the age of child--
hood.  We hear the author has an intention of writing similar, though
more  enlarged works on Anatomy  and Comparative Anatomy.   Such
books are much wanted.  We will,  from  the specimen before us, pro-
mise to do—what we rarely care to commit ourselves in saying ;—viz.,
we  promise to read his next work.

From Mr. N. S.  Dodge,  Principal of  the  Pittsfield  Boarding
                   School for Young  Ladies.
                          ^        Pittsfield, Feb. 28th. 1839.
To  Dr.  C. A. Lee.
    Sir.—I  am much obliged by your sending me  through your bro-
ther,  your school  work  on  Physiology.   After looking it carefully
through,  and having put it  into the hands of three of my pupils  who
knew nothing of the  subject, I am convinced  it was just what was
wanted for schools.  In the seven years I have taught, I have found
nothing before on this subject wlTlch I could put into the hands of
young ladies with  safety,  and the only way I could give them any
knowledge of Physiology—a knowledge in my opinion, essentially im-
portant to every  female—was by reading  to  them, page  after page of
Broussais.   For  myself and my school, I  thank you for your book. It
saves me many a weary and  unprofitable hour, and gives  them infor-
mation which  will  make them better educators of our race ; for indeed,
who are the educators of our race but mothers ?   I  shall hereafter use
it in my school,  and as a duty I owe to the rising generation,  I shall
endeavour to have  it introduced into the schools around me.
  With the assurance of my highest regard,  I have the honour to be,
                        Very respect/ully,
                                Yo\ir obedient servant,
                                             N.  S.  DODGE. 
HUMAN   PHYSIOLOGY,
FOR THE USE OF
ELEMENTARY SCHOOLS.
          BY CHARLES A. LEE M. D.,

LATE PROFESSOR OF MATERIA MEDICA AND MEDICAL JURISPRUDENCE, IN
         THE UNIVERSITY OF THE CITY OF NEW YORK.
" The proper study of Mankind is Man.



  ELEVENTH EDITION.':l v
               si
LIPPINCOTT, GRAMBO & CO.
               1854;   .•/'•  v   :*\ 
QT
Entered, according to  Act of Congress, in the year 1847,
                   By W. E. Dean.
In the Clerk's office of the District Court of the  Southern
                 District of New York.
Sterkot'pkd by Smith & Wright, 216 William St. N. Y. 
                TO




 ,  CHARLES ANTHON, L. L. D.




   jay professor of  languages




      in Columbia  College,




       this humble essay,




 i       IS BY PERMISSION,




      GRATEFULLY  INSCRIBED,




IN  TESTIMONY OF PROFOUND RESPECT.
qq 4-2-7 
 
PREFACE TO THE SECOND EDITION.
  In presenting to the public the present stereotype edi-
tion of this  work, it is proper to  state, that no labor or
expense has been  spared to render it still more worthy
of the kind approbation with which it has been received.
A large  proportion  of it  has been entirely re-written,
many corrections  have been made, and numerous and
highly valuable illustrations introduced;  these improve-
ments, together with the  questions at  the  end of each
chapter, cannot but render the work better  adapted to
the objects for which it was written.
  The author flatters himself that this  treatise will be
found to contain the substance of what is yet known on
the subject of Human Physiology, and most that  is
valuable, which is scattered through many  learned and
ponderous  volumes.  In  preparing it,  more than  fifty
different works have been consulted, from all of which
the author  has  freely taken whatever he found adapted
to his purpose.   Originality has not been aimed at, as it
was precluded by the very nature  of the   subject; in-
deed it would have been  unsuited to the object in view 
viil                   PREFACE.
  From the rapid  sale of the first edition, and the nu-
merous orders for the work from all parts of the United
States, it may  safely be concluded,  that Physiology is
henceforth to be one of the common  branches of know-
ledge taught in our schools, academies, and other semi-
naries  of learning.   Indeed it  is  remarkable,  that
sciences, so closely connected with the health and hap-
piness of our race, as those which teach us the structure
and functions of the human body, should so long have
been  confined  to  those  who  intend  to pursue the
practice of medicine and surgery as  a profession, espe-
cially when the practical application  of such knowledge
is daily and hourly of the utmost importance to every
individual, connected as it is, with the preservation of
health and of life.   That such studies are not above the
comprehension of  children I can  testify,  not  only from
my own observation, but from the experience of numer-
ous teachers, such as those whose names are appended
to the testimonials, on the  first pages of this work.  If
this is not sufficient, I have to commend to the attention
of the reader, the  following  extract  from a lecture of
Mr.  George  Combe, the distinguished phrenologist of
Edinburgh, which he was  so kind as  to communicate to
me by letter :
  " I take the liberty to urge very earnestly on  your at-
tention, not only the  advantage, but the necessity of in-
troducing  instruction in  anatomy  and physiology  into
popular education.   The great laws of health cannot be
understood, nor can  their importance be appreciate^1 
                      PREFACE.                    ix
without this knowledge.   I do not mean that you should
teach  your children  all the  minute  details  of these
sciences,  which would  be  necessary if you intended
them for  the  practice of medicine  and surgery:  all I
desire is,  that the structure of the leading organs of the
body should be  explained so far as  to render  the func-
tions of them intelligible, and  that  on  this knowledge
should be founded a clear and practical elucidation  of
the  laws  of health.   I  can certify,  from  observation,
that this instruction  may be  communicated to children
of ten years of age, and upwards, with great success.
The  structure  addresses their observing faculties, and
an explanation of the functions is as interesting to  them
as a romantic story."                             '
   In treating  of physiological subjects, I have unavoid-
ably employed some technical  terms, but only in cases
where  there  was   an   evident  advantage  attending
their use; but  in all such  cases  the  exact meaning
of  the term  has been  assigned  it.   This  explanation
saves the necessity of a  glossary, which was appended
to the first edition, and  it is, therefore, omitted in the
present.
  It will be perceived that the present edition contains
more anatomy than  the  former.   This has  arisen  from
the  full  conviction,  that in  order  to  understand the
functions of an  organ, its structure must first be learn-
ed   To aid  in  the  accomplishment  of this object, nu-
metous well-executed wood cuts have been introduced,
alike  creditable  to the artist and useful to  the learner. 
X                    PREFACE.
The work  is, therefore, presented  to the public in its
present  shape,  with  the hope  and belief,  that it  will
subserve the cause  of  human knowledge and happi-
ness.
    New York, April, 1839.
i 
CONTENTS.
                                                          Page.
Chap. I.—Organic and Inorganic Bodies    ....     13
Chap. II.—Division of the Animal Kingdom    ...       20
Chap. III.—Structure of the Human Body  ....     24
Chap. IV.—Structure of the Human Body continued     .    .   39
Chap. V.—Chemistry of the Human Body       ...      56
Chap. VI.—The Human Skeleton       .....63
Chap. VII.—Properties of Animal Bodies  .                    95
Chap. VIII.—Relation of Animal Bodies to Heat, Light, and
        Electricity........105
Chap. IX.—The Nervous System.....       110
Chap. X.—Intellectual and Moral Faculties      ...     123
Chap. XI.—The Spinal  Marrow and its Functions       .       135
Chap. XII.—The Nerves and their Functions     .     .    .     144
Chap. XIII.—The five Senses—Sense of Touch     .    .       156
Chap. XIV.—Sense of Taste......167
Chap. XV.—Sense of Smell......       177
Chap. XVI.—Sense of Sight......190
Chap. XVII.—Sense of Hearing......225
Chap. XVIII.—Respiration     .      .....237
Chap. XIX.—The Circulation of the Blood     .    .     .    .256
Chap. XX.—Nutritive Functions—Digestion      .    .    .     274
Chap. XXL—Secretion........286
Chap. XXII.—Absorption.......292
Chap. XXIII.—Nutrition.......298
Chap. XXIV.—Animal Heat    ......     304
Chap. XXV.—The Voice.......312
Chap. XXVI.—Locomotion, and its  Organs,    .    .    .      319
Chap. XXVIL—The Teeth*       ......326
Chap. XXXIII.—Sleep and Death.....331
Written by Solomon Brown, A. M. Scientific and Practical Dentist of this city 
 
HUMAN   PHYSIOLOGY.
                     CHAPTER I.

      DEFINITION;--ORGANIC AM) INORGANIC BODIES.

   1. Physiology is "the  science of life," or that branch
of knowledge which explains the uses of the various organs
of living beings.    Vegetable physiology treats of the  func-
tions of plants ; and Comparative physiology, of those of the
inferior orders of animals ;  while Human physiology treats
exclusively of man.
   2. The kingdom  of nature embraces three great classes,
animals, vegetables, and minerals.  According to a more
scientific arrangement, it is composed of organic  and inor-
ganic bodies.   By  organic bodies, we mean those  which
possess organs or instruments for the  performance of certain
functions ;  and by inorganic, those which do not.   It is by
a knowledge of these works of God, that we derive our ideas
of his power, wisdom, and goodness.
   3. Organized bodies are  divided into  two great classes,
animals and vegetables ;  which differ from inorganic matter
in several  respects, the  most  important of which are the
following :—
   4. Organized bodies  have a  certain determinate  form,
peculiar to the species to which they  belong.  Every species
of plant or animal may be known by its external shape ; as
   1                          2 
14                   PHYSIOLOGY.
 a horse, a cow, a tree, or a rose.  They differ so much from
 all  other kinds, that we are seldom  in  danger of mistaking
 them.   This will not apply  to  inorganic bodies,  except,
 perhaps, to a few minerals which  crystallize in a  certain
 shape.
  5. In organized  bodies, we find the parts of  which they
 are composed, distinguished by round or oval forms ;  as the
 body and  leaves of trees ;  the petals of flowers ;  the bodies
 and limbs of animals.  We scarcely ever see straight lines,
 or sharp angles among them, as in mineral  substances.
  Every species of animal or vegetable has its own proper
 size, from which it varies but little.   But  minerals may be
 large  or small;  the  substance  called granite, for example,
 may make a pebble or a mountain.
  6. Inorganic bodies contain either  a single element, as
 carbon, sulphur, &c, or several of the  elementary or simple
 substances, which axe, fifty.two in number, as lime, silex, and
 magnesia ;  while in organized bodies, we find at least three
 of these elements, as carbon, hydrogen, and  oxygen in  veget-
 ables ;  and the same,  with  the addition of  azote  or nitrogen
 in animals.   In organic  bodies, there have  been  discovered
 in all eighteen simple substances, though they generally con-
 tain but three or four.
  7. But  these two classes of substance's, not only differ as
 to the number of the  elements which enter into  their com-
 position, they also  differ,  as  to the mode  in which these
elements are combined.   Thus in  minerals, two  element-
ary substances unite and form a compound, and  this again,
combines either  with another simple substance,, or with  a
compound composed of two other simple substances.   Thus,
for  example, carbonate  of ammonia  is composed  of car-
bon,  oxygen, hydrogen,  and  nitrogen,  but combined  as
follows :—
  The  carbon and oxygen unite to form carbonic acid ;  the
hydrogen and nitrogen, to form ammonia;  these two com-
 pounds thus uniting,  form carbonate of ammonia. 
ORGANIC  and  inorganic  bodies.         15
   In animals, we find the same simple elements uniting, each
with all the others, forming the peculiar principles of organic
bodies, such as fibrin, gelatine, &c.
   8. Organized bodies contain small particles of  matter of
a round or oval shape, both among their solid and fluid parts.
These are supposed, according to their different arrangement,
to make up all the elementary forms of organized bodies ; as
when arranged in lines,  they form  nerves, tendons,  and
muscles ;  in sheets, the various membranes and coats of ves-
sels ; and in masses, the solid substance of the glands, as the
liver, kidneys, and pancreas.
   9. There are but few changes in  inorganic bodies.   The
elements of which they are composed remain at rest.  Rocks
and mountains are the same now, as they were five thousand
years ago.   But in organized bodies, compounds are con-
tinually forming  to be again separated ; animals feed on
vegetables, and vegetables on animals ;

          " See dying vegetables life sustain;
           See life dissolving, vegetate  again ;
           All forms that perish, other forms supply—
           By turns we catch the vital breath and die."

   10. In  organized bodies the parts are mutually  dependen
on each other for support.   If we  cut off the limb of a tree,
it  dies,  because it  can  receive no sap ;  if we  amputate  a
finger, it mortifies, because the  circulation of the  blood  has
ceased ; but if we break off a  piece of marble, it will remain
unchanged as long as the original  mass.
   11. Inorganic  substances exist either in solid, liquid, or
gaseous forms.  They are wholly solid, liquid,  or gaseous.
But organic matter  always presents a combination of solid
and fluid parts.   We find  fluids circulating in regular ves-
sels, and the  solids and  fluids mutually dependent on each
other for support.   In vegetables,  we discover various  parts, 
16
PHYSIOLOGY.
such as wood, bark, leaves, roots, and  flowers;  and in ani-
mals, muscles, nerves,  tendons, vessels—all of which are
organs, or instruments  for  the accomplishment of certain
purposes.  Inorganic bodies are formed of homogeneous parts,
or parts perfectly similar.
   12.  Organic bodies are composed of two kinds of elements,
chemical, such as oxygen, carbon, and hydrogen, which exist
in minerals ; and organic, or proximate, such as albumen, gel-
atine, fibrin, &c, such as are never found  in inorganic mat-
ter.  It is because these organic substances are produced by
the peculiar forces of organic life, and not  by chemical laws,
that we cannot  decompose and then  re-form them,  out of
the same  elements,  as we can minerals.  For example, we
can dissolve alum, salt, or copperas,  and  then  by evapora-
tion, crystalize them in the same shape again.
   13.  The general properties of organic or inorganic bodies
differ in many particulars.   In  the  first place there is  a
constant warfare going on, between the chemical and phys-
ical laws,  which govern  inorganic matter,  and the vital laws
which  maintain animal life.  This conflict commences  at
the first period of our existence, and is kept up to the moment
of our dissolution.   Life  is enabled,  for  wise purposes,  to
wrest  portions of matter from the domain  of  the  laws of
matter, for  a  certain indefinite period ;  for  a while, the
vital powers  maintain a successful contest, but at last they
have to yield, and death  gives over the body to the action
of the chemical forces.
   14.  This power of resisting the mechanical and chemical
laws of matter, is shown by the faculty which animal bodies
possess of maintaining the same degree of temperature, amid
the great changes from heat to cold to which they are exposed;
in the  power  of changing to  chyle and  blood, the various
forms of food on which they subsist;  and also in their power
of forming from these the various tissues and organs of which
they are composed, and  all in opposition to the general laws
of matter. 
            ORGANIC AND INORGANIC BODIES.          17

  15. The growth of organized bodies proceeds from within,
that of inorganic matter from without.  If minerals increase
in size, it is by attracting  matter to their external surface,
while animals  and vegetables  grow by  a process,  called
nutrition ;  that is, laying hold  of nutritious substances and
converting them to their own nature, by  means of internal
organs.
  16. Organized bodies possess the power of being affected
with disease and  recovering from' it.   They also have a
determinate duration, beyond which they do not often live.
This period varies for each species of animal and vegetable.
Some insects live but a single day ; most plants live but a
single year; but some trees, such as the oak and cedar, are
supposed to live more than two thousand years.  The average
duration of human life in this country is not over thirty years.
  17. But the great distinction  between a living being and
an inorganic body is, that the former carries on a number of
processes, not performed by the latter.   A plant, for example,
absorbs food,  converts  it  into  its own  proper  substance,
arranges it into bark,  wood, leaves,  and  other organized
structures, grows, arrives  at maturity,  generates and main-
tains a certain  degree of heat, decays,  and  finally  perishes.
No such phenomena are exhibited by a  stone,  or other inor-
ganic bodies.  These  processes, therefore,  are called vital, be-
cause they are peculiar to a state of life, and afford characters
by which a living being is distinguished from  all others.
  18. Organized beings are divided into two classes, animals
and vegetables,  differing  from each  other  in  several well-
known  features.
  -19.  Sensation and  voluntary motion are possessed by ani-
mals, but not by vegetables.  Had  animals no sensibility or
feeling, they could not know their wants ; and if they knew
them but had not the power of motion, they would perish for
want  of food ; hence  the necessity of these two  faculties
being joined together.
  20. An animal, like a plant, receives food, transforms it into
                              2* 
18                   PHYSIOLOGY.
its own proper substance, and builds it up ir\to certain struc-
tures :  it also generates and maintains a certain degree of
temperature,  and after having arrived at maturity decays
and dies ; but in addition to these vital  processes which are
similar in both, the animal possesses  the faculty of feeling   '
and moving  spontaneously, or according to the dictates of
its will, a property peculiar to itself.
  21.  Vegetables  are nourished by the substances iramedi-
ately around  them, such *as air, water, and the saline proper-
ties of the soil.  They draw their support from without, by
absorption  at their  surface,  or by  means of  roots.   But
animals draw their nutriment from a great variety of sources,
and they  are furnished with  an internal cavity to receive
and prepare it for the purposes of nourishment.
  22. Vegetable matter is composed chiefly of three elements,
viz.  carbon,  hydrogen, and oxygen;  besides  these, animal
matter contains azote, which gives the peculiar smell that we
perceive on burning  flesh, hair, bones,  or feathers.  Eighteen
simple substances, however, have  been found in vegetables,
in very small quantities ; such as lime, sulphur, iodine, silex,
potash, soda,  &c.
  23.  Animals and vegetables both consist of solid and fluid
parts; the fluids,  however, in animals, exist in  much the
largest  proportion.  This is the  reason why decomposition
occurs more  rapidly in animals  than  in vegetables.  Veget-
ables, abounding in fluids, decay sooner than those of a more
solid or fibrous texture.
   24.  Though the differences between animals and  veget-
ables, are in  general sufficiently obvious and  striking, yet
in some few instances, their  distinguishing characteristics
are not so evident.  This  is  apparent from  the  fact, that
some animals have been mistaken for vegetables,  and some
vegetables  for animals.   Some  animals we find  to  be as
firmly attached to the soil, as most vegetables are, as  is the
case in many of the zoophytes, or lowest order of animals,
as the sponge, coral, &c.  ; while on  the other hand, some 
ORGANIC  AND  INORGANIC BODIES.          19
vegetables float  in the  water,  as many kinds of sea-weed,
and are never attached  to the soil.
  Questions.—What is physiology ?  What does vegetable physiology
treat of?  What human ?  What classes does the  kingdom of nature
embrace ?  What other division ?  What is meant by organic  bodies ?
What by inorganic ?   How are organic bodies divided ?   How do or-
ganic and  inorganic  bodies differ  from each other ?   How do  they
differ as to form ?—as to size ?—as to their number of elements ?—as to
their mode of combination ?—as to  the shape of their particles ?—as to
the changes they undergo ?—as to the mutual dependence of parts?—as
to the kinds of elements ?—as to their general properties ?  How as to
their  mode  of growth ? of disease ?   What is  the  grand distinction
between the two classes of bodies ?  How are organized  beings divid.
ed?   How do animals  and  vegetables differ?  How are vegetables
nourished ?  What is vegetable  matter composed of?  Do animals or
vegetables possess the greatest amount of fluids 1  What animals  have
been mistaken for vegetables? 
CHAPTER  II.
            DIVISION of the animal kingdom.

   1. Cuvier has  divided animals  into four great  groups.
 1.  The vertebral.  2. The molluscous.  3. 'The articulated.
 4.  The radiated.   The three last are destitute  of vertebrae,
 or  a connected  series of bones  to  form  a spinal column.
 They  are,  therefore,  called invertebrated, while  the  term
 vertebrated is  applied to  the  former.  The  vertebral are
 again divided into four classes, viz.  1. Mammalia.  2. Birds.
 3.  Reptiles.  4. Fishes.   These  are also  distinguished by
 the  terms  warm, and cold-blooded; the warm-blooded, in-
 cluding the two former, which possess  a  temperature con-
 siderably  above  that  in  which  they live  ; while  the  two
 latter,  or the cold-blooded animals, are but little warmer
 than that  of the medium by  which  they  are surrounded.
 The mammalia are divided  into  nine orders ;  Birds into
 six; while Reptiles  include Tortoises, Lizards,  Serpents,
 and Frogs.   Fishes are divided into the Cartilaginous  and
 Bony.
  2. Molluscous animals,  as the  name  signifies, are those
 which have no  bones  corresponding to those  of the hio-her
 orders of animals.  They include  all  those  animals with soft
 bodies, which dwell  in calcareous habitations, constructed by
 themselves; many of them are  accordingly called shell-fish,
such as the oyster, muscle,  clam, dec.  This  division also
embraces the snail,  slug, and  the nautilus.   The articulated
class includes such animals  as are  furnished with  joints,
with a hard external crust, or skeleton, to which are attach-
ed the organs of motion.   It embraces the annelides, or red.
blooded worms, the Crustacea, (the  lobster and crab,) Spiders,
and Insects.  The Radiated class  includes the Zoophytes, or
Plant animals, so called from  their resemblance to the veget 
PHYSIOLOGY.
21
able kingdom.   Most  of these are of a soft  texture, as the
Polypus, so well known from  its being capable of existing
when turned inside out, and of reproducing any part of its
body when  destroyed  by  accident.  To this class belongs
the Sponge, and the numerous families of the Coral.
   3. The mammalia are  placed at the head of the animal
kingdom ;  not  only because  it is the class  to which man
himself belongs, but because it also enjoys the most numerous
faculties, the most delicate sensations, the most varied powers
of motion, and the highest'degree of intelligence.
   4. The peculiar characters  of these different classes must
be learned from works which treat especially of Comparative
Anatomy.   It  will  be proper, however, in this place,  to
point out some of the  peculiarities which distinguish man.
   5. In structure and external shape, man bears considerable
resemblance to some varieties of the  ape tribe, particularly
the ourang outang.   But we find his  position to be upright;
his foot is large, and the leg placed vertically upon it;  while
the toes are short  and but slightly flexible, and the  great
toe is  horizontal with the others,  so that  his feet is well
adapted to support the body, but cannot be used  for seizing
or climbing.  Apes have thumbs both upon their hands  as
well as feet, so that they can  seize with both  equally well.
The head of man is also very large and heavy, owing to the
magnitude of the brain, and the smallness of the cavities of
the bones ; yet the means of  supporting it, except in a per-
pendicular position  are very  small, as the ligament of the
neck, which in quadrupeds is very thick, in him is almost
wanting.
   6.  Besides this,  the spinal  column is so constructed, that
its flexure forwards is not prevented, so that  should he at-
tempt  to walk on  all-fours, his mouth and eyes would  be
directed towards the earth,  and he could not see before him,
while in an erect attitude he  preserves the use  of his hands,
and at the same time his organs of sense are most favorably
situated for observation. 
22
PHYSIOLOGY.
  7. Though man surpasses all other animals in dexterity, yet
there are many that exceed him in strength, swiftness, and
the acuteness of many of the senses.   The eagle excells him
in acuteness of vision, the grey hound in delicacy of smell,
and a vast number of animals in strength, yet reason makes
up for all other deficiences.   Though physically defenceless,
yet the whole brute creation is subjected to his control.
  8. It was formerly supposed that man, because gifted with
the highest  mental  endowments possessed the largest  of all
brains.   But as elephants and whales surpass him in this
respect, and the  sagacious  monkey and dog  have smaller
brains  than the comparatively stupid ass, hog, and ox, the
opinion was relinquished, and  man was said  only to have
the largest brain in proportion to the size of his body.   But
more extensive observation proved that  canary  and  other
birds, and some varieties of the monkey tribe, have larger
brains  than  man  in  proportion to  the body, and several
mammalia to equal him in this  particular ;  and as rats and
mice too, surpass the dog, horse,  and elephant in the com-
parative bulk of their brains ; this opinion gave way to the
one now generally adopted  by physiologists, viz.  that man
possesses the largest  brain  in comparison  with the nerves
arising from it.
  9. In consequence of the great size of his brain,  man has
a larger facial angle,  which is the space included  by lines
drawn from the centre of the ear to the root of the nose, and
from thence to the  forehead.   In the  best formed human
heads, this angle is equal to  80 or  90 degrees.   In man also,
the chin is more prominent, and the lower front teeth  more
perpendicular ; his teeth also are of the same length, which
is not the case in the inferior animals.   Man only can  adapt
himself to the great varieties of climate, and of food, which
exist on the surface of the earth.
   10. Lastly, man is possessed of faculties  that enable him
to trace effects to their causes, to distinguish between virtue
and vice,  to reflect upon events that have passed, to anti- 
STRUCTURE  OF  THE HUMAN BODY.          23
cipate the issues of the future ;  and, above all, to raise his
mind to  the Supreme Intelligence, the cause of causes, to
whom all nature owes her existence, and to  whom,  with
more or  less clearness of conviction, he feels conscious of
responsibility.
  Questions.—How is the animal kingdom  divided ?  What is meant
by vertebrated,  and what by  invertebrated animals ?   How are the
vertebral divided ?  What is understood by a warm-blooded animal ?
What by a cold-blooded ?  Into how  many  orders are the mammalia
divided ? Birds ?   Reptiles ?  What are molluscous animals ?  What
does the articulated class include ?  What the radiated ?  What  class
is  placed at the head of the  animal kingdom? —and why ?  What
species of animals does man most resemble ?  How does he differ  from
the ape tribe ?  Is man excelled in any respect by the inferior animals ?
Mention some of the peculiarities of man. 
CHAPTER III.
           STRUCTURE  OF THE HUMAN  BODY.

  1. The human  body is composed of solids  and fluids.
These  terms, however,  are  merely relative.   There  is no
fluid which does not contain some solid matter in solution;
and no solid however dense, which does not contain some
fluid.  The nature of both fluids and solids is essentially the
same, for we see one readily passing into the other ; indeed
no fluid long remains a fluid, and no solid  a solid ;  but the
fluid is constantly passing into the solid, and the solid into
the fluid.
  2. The relative proportion of the fluids in  the human
body much exceeds that of the solids, the excess being about
8 to  1.  But the excess varies according to the age.   The
younger the age, the greater  the preponderance of the fluids.
As age increases,  the fluids gradually diminish,  till in old
age,  they become so much lessened, that the body  assumes
a dry, wrinkled, shriveled  and stiff appearance.  In this
manner we explain the softness  and roundness of the body
in infancy and  youth,  and  its hard, unequal and  angular
surface in advanced life.
  3. The fluids, then, are very important, as they furnish
not only the material out of which every part of the body is
formed, but they  also furnish  the medium by which the
noxious and  useless matter is  carried out of the  system.
Every part of the body is a laboratory in which complicated
and  transforming  changes  are constantly going on ; the
fluids are the materials on  which these changes are wrought,
and  the vital forces are the agents by which they are effect-
ed.   The fluids either contribute  to form the blood, or they 
STRUCTURE OF THE HUMAN  BODY.         25
constitute the  blood, or having performed some special office,
as moistening  the various surfaces, are returned  to the blood ;
hence  according to their nature, they are called aqueous,
albuminous, mucous, serous, &c.
  4. The solids are composed of the same chemical  prin-
ciples as the fluids,  and by analysis are reduced to the same
ultimate elements.  In the formation of solids, the particles
of matter are  supposed to be arranged in one of two modes,
viz., either in  the form of minute threads or fibres, or of thin
plates  or laminae;  hence every solid of the body is said  to
he fibrous, or laminated.   These fibres, or laminae are vari-
ously interwoven, and interlaced, so as to form a net-work ;
and the spaces included between them are called areolae,  or
cells.  According to some microscopical observers, the ulti-
mate animal solid is a  minute sphere or globule of matter,
not exceeding an eighth thousandth part of  an inch in diam-
eter.
   5. The  fibrous or laminated matter is often  so arranged
as  to  form a structure,  possessing distinct   and  peculiar
properties ; and each of these modifications is  considered  a
separate form of organized  matter, and is  called a primary
tissue.  These tissues have been variously classified by dif-
ferent  anatomists  and physiologists, some making  them  to
consist of five, viz., the membranous, the cartilaginous, the
osseous,  the muscular, and the nervous; while others  make
but three, the  cellular, the muscular, and the nervous.   An-
other arrangement is  into  filaments, fibres, tissues,  organs,
apparatuses, and systems.
   6. A filament is made up of a series of minute or primi-
tive molecules, arranged in  a row.   A fibre is composed of
several of these filaments united together,  as  the muscular
and nervous fibres.  A tissue is supposed to be composed of
fibres  disposed in planes, forming in this manner an expan-
sion, or when crossing each other, forming spongy solids,
with cells interspersed throughout.   In this  way  are the
cellular  serous, and mucous  membranes   formed.   When
                             3 
26
PHYSIOLOGY.
 these tissues are so arranged as to  form a piece of animal
 mechanism, designed for the performance of a certain office,
 they form what is called an organ, as the lungs, brain, liver,
 dec.  The action of this organ is called its function.  The
 liver, for example, is an organ ; the conversion of the blood
 which passes  through it into bile,  is its function.   When
 several organs are associated together  for the accomplish.
 ment of a common object, such an assemblage is called  an
 apparatus.  The apparatus of digestion consists of the mouth,
 teeth, esophagus, stomach, intestinal canal, liver, pancreas,
 lacteals, dec,  as all these concur in  the process of digestion.
 By system, is understood  an assemblage of organs, possessing
 a  similar structure, as  the  nervous system, the muscular
 system, dec.
   7. Membrane  may be considered  as the  first or  primary
 tissue.  It is the simplest form of organized substance, and
 is extensively  employed in the composition of the body.  In-
 deed, it is the  principal  material used in forming covering,
 containing, protecting, and  fixing  every other  component
 part of it.  It is  this which contains in its  cells  the earthy
 matter which  goes to form the  bones ; the canals in  which
 are  deposited  the substance which  composes the muscular
 and nervous tissues; which forms a covering for the whole
 body ; which  lines all its internal  surfaces ; surrounds  all
 its internal organs ;  which  makes  up  the  solid  portion  of
 every part of the  system; forming the  tubes and vessels,
 such as the arteries and veins ;  it connects  all parts of the
 body together, and fixes them in their several situations ;  in
 short, it is the substratum, or  mould, in which  all the other
 particles are deposited, thus giving  form and outline  to the
 whole body, so  that if every other kind of animal matter
 were removed, this tissue  alone would  preserve the  exact
 figure and present a perfect skeleton of the whole, and  of every
 one of its parts.
   9. There are several kinds of membrane ; the simplest form
of which, and  that from which all the others are supposed to 
           STRUCTURE  OF THE HUMAN BODY.        27

be produced, is termed the cellular.  It is this which I have
already alluded to as entering into the compositions of every
organ, and forming the  basis of the solid  structure of the
body.   Into its cells all other kinds of animal matter are de-
posited as phosphate of lime and gelatine, which form the bones.
It forms sheaths for the muscles and nerves ; composes a great-
er part of the ligaments,  tendons, and cartilages, and even the
hair and nails, thus constituting not only the basis of all the
solids, but serving as a  bond of union  by which the organs
are connected together.   By  its softness and elasticity, and
the oily  fluid  by which its cells are filled, it also promotes
the  mobility of the  parts on one another.   It possesses the
property of contractility, and is composed chiefly of gelatine.
   9. One remarkable circumstance connected with this tis-
sue  is, that as  it  exists throughout the  body, it  forms a con-
nected whole, or an immense  net-work, every where accessi-
ble to air.  This is shown  by forcing air  into its cells, in
any part of the body ; which is found gradually to penetrate
and pervade  every part  till  the  whole  bcdy  is  inflated.
Butchers often avail themselves of a knowledge of this fact,
by blowing their meat, or in other  words, inflating animals
by making a  puncture in some part where the  cellular tissue
is loose, and from  this  one  aperture  forcing the air to the
most distant parts of the body, in  order to give the meat a
fat appearance.  If we  raise up a portion  of cellular mem-
brane, in the form of a thin slice, it  appears as  a semi-trans-
parent and colourless  substance, composed of minute threads
which are seen to cross each other in every possible direction,
leaving spaces  between them, and thus  forming a mesh,
similar to  the spider's web.   As to  the precise  form of these
cells or cavities we have no accurate knowledge.   They are
generally supposed to  be narrow spans  with acute angles, the
sides of which  are flattened, and when  not forcibly expanded,
we may suppose to be in contact.  Some  physiologists in-
deed deny  that any cavities at all exist, but the weight cf
evidence is altogether in favour of their existence. 
28
PHYSIOLOGY.
  A single film of the cellular tissue lifted up, and slightly distended.

  10. In health, the spaces between these lines are filled with
a thin exhalation of a watery nature, which serves to keep
the tissue  always soft  and moist.   This is composed of the
thinner  part of the  blood, which is poured out by a process
called secretion, out is speedily taken up again by absorption.
These two opeiations  exactly balance  each other  in health,
but when  from any cause the equilibrium is disturbed, the
fluid accumulates,  constituting the disease  called  dropsy.
This is often relieved by the operation of tapping, or  draw.
ing off  the water.  Cellular  membrane  is dense  or loose,
coarse or fine, according to its situation and office.   Where
it is subject to  pressure, as in the palm of the hand and sole
of the foot, it is dense  and firm; around the internal organs
it  is more loose  and delicate.  Although cellular tissue en-
ters into the composition  of  all the organs, it  never loses its
own character, nor participates in the functions of the organ,
of which  it forms a part.   Though present in the  nerves it
does not share in  their sensibility, and though it accompa-
nies every muscle and  every muscular  fibre, it nowhere par-
takes of the irritability which belongs to these organs.  The
microscope shows that the minute particles of this tissue are
of a globular figure, arranged like strings  of pearls, as repre-
sented in  the following cut. 
STRUCTURE OF THE HUMAN  BODY.         29
  A portion  of cellular tissue, very highly magnified,  showing  the
strings of globules of which its ultimate fibres are supposed to consist.
   11. The principal varieties of membrane, which are formed
by  the cellular tissue, are the adipose, the serous, the mucous,
the dermoid,  the fibrous, the  cartilaginous, and the osseous.
The adipose is that tissue which contains the fat which is so
disposed as to  form distinct bags in which the fat is con-
tained.   Now it should be recollected, that while the cells of
the cellular tissue are continuous  over  the whole body, each
adipose vesicle is a  distinct bag, having  no communication
whatever with any other.   While also, the cellular tissue is
universally  disposed, the adipose is placed only in particular
  1. A portion of adipose tissue: 2. minute bags containing  the fat:
3. a cluster of the bags, separated and suspended.
                                3* 
30
PHYSIOLOGY.
parts of the body, principally beneath  the skin and the ab-
dominal muscles, and around the heart,  kidneys, dec. while
none is ever found in the  cranium, the brain,  the  eye, the
ear, the nose, and several other organs.
  12.  The Serous Membranes.—These  line all  the closed
cavities, or sacs of the body, and are  reflected over the  or-
gans contained in  them.   Thus the cavities of the brain and
chest, the abdomen and joints, are lined by serous membrane.
By its  external surface, it is united to the walls of the cavity
or the substance of the organ it invests ;  by its internal sur-
face  it  is free and unattached ; whence this surface is in con-
tact only with itself, forming a close cavity, having no com-
munication with the external air.
  13. If it were possible therefore to dissect serous membranes
from off the parts which  they invest,  they  would have  the
form of a sac, without an opening, the organ invested by one
of these folds being altogether external  to the cavity of that
sac; just  as  happens when a double night-cap is worn, of
which  the part immediately covering the  head is analagous
to that portion of the serous membrane which adheres to and
invests  the  organ, whilst the external portion of the cap
represents the  lining of the cavity in which  that  organ is
said  to be contained.  Hence it will readily be  understood
that  the serous membranes  never open, or allow of any per-
foration for  the passage of blood-vessels, nerves, or ducts, to
or from  the enclosed organs ; but that they are always re-
flected over them, forming a sheath around them, and accom-
panying them in their course.   It also  follows as a necessary
consequence, that their free surfaces  completely isolate the
parts between which they intervene.
  14.  The serous membranes are of a whitish, shining col-
our,  and smooth on  their  free or inner surface.  They are
kept constantly  moist  by a fluid  which is   exhaled  in  a
gaseous  state from  the  serum of  the blood,  whence  they
derive their  name.  They are also elastic and extensible,
and  are said  to be destitute of blood-vessels  and  nerves; 
           STRUCTURE OF  THE HUMAN  BODY.         .Si

being composed of condensed  cellular  membrane.   Accord-
ing to Rudolphi, serous membranes line not only the closed
cavities of the body, but the interior of the vessels also,
and  the canals which open  outwardly,  as the alimentary
canal and the  air passages, forming a cuticle over the mu-
cous  membranes, which line  these passages.   The  uses of
the serous membranes  are  to separate different organs, to
diminish friction, and  to  facilitate the motion or gliding of
these parts  upon one  another,  by means of thin  smooth.
moist, and polished surfaces.
  15.  Mucous Membranes.—These  membranes  are  also
another form of the cellular structure, and derive their name
from the nature of the fluid, which it is their office to secrete
by means of numerous minute glands imbedded in their  sub-
stance.   As serous membranes form a shut sac,  completely
excluding the air, mucous membranes on the contrary, line
the various cavities, which are exposed to  the air, such as
the mouth, the nostrils, the windpipe, the gullet, the stomach,
the intestines, and the urinary  organs.   Their internal sur-
face, or that by which they are attached to the passages they
line, is smooth and dense, while their external surface, or that
which  is exposed  to the contact of the air, is soft and pulpy,
like the pile of velvet, or the rind of a ripe peach. 
82                    PHYSIOLOGY.
 A portion of the stomach, showing its internal surface or mucous coat

   16. The mucous coat is the seat of some of the most im-
 portant functions of the economy ; in the lungs, of respira-
 tion ; in the  stomach, of digestion;  and  in the  mouth and
 nose, of taste and smell, dec, and forms, with  scarcely  an
 exception, a  continuous whole.  That portion  which lines
 the eyes and  eye-lids, is connected with that which lines the
 nostrils, by means of the nasal canal ; while that which lines
 the mouth,  meets  in the  throat with  that  which comes
 down from the nose.   In the fauces it divides, and while one
 portion goes  down the windpipe  into the lungs, the other
 passes down the esophagus into the stomach, forming a lining
 for the whole tract of the intestinal canal.
   17. Mucous membranes are of a loose, spongy  texture,  of
a reddish colour, and are largely supplied with blood-vessels
and nerves.   They are also numerously supplied with small
glandular bodies called  mucous glands  or folicles.   The
chief use of these membranes is, to sheath and protect  the
inner surfaces of the body, as the skin does the outer, and by
means of the  mucus, with which they are always covered in
a state of health, to guard them against the contact of irri-
tating substances. 
STRUCTURE OF  THE  HUMAN BODY.         33
  18. We find a remarkable sympathy existing  between all
the mucous membranes ;  accordingly their diseases, particu-
larly the catarrhal affections,  to which they  are often sub-
ject, are very apt to spread in  them.   By reason of this sym-
pathy, the state of one part of these membranes may be as-
certained by examining another part ; the state of the tongue
for example, indicates the condition  of that of the stomach
and intestinal  canal.  There  is  also an extraordinary sym-
pathy between the mucous  membranes  and the respiratory
organs.
   19.   Dermoid Membrane.—This  membrane, called also
cutis or skin, is not only directly continuous with the mu-
cous membranes that line the  internal  passages, but is also
analagous in its structure.  We see them  passing into each
other at the orifices  of the internal canals,  as in  the lips, nos-
trils, eye-lids, external ear, dec.   We find it varying in thick-
ness according to its situation ; in the face and body being
thin and delicate, and on the palms of the hands  and soles of
the feet, considerably firmer and  thicker.  The  skin is
abundantly supplied  with  blood-vessels and nerves; so nume-
rous indeed, that the finest needle cannot  enter  the skin
without piercing many of both, which is proved by the bleed-
ing, as  well as the pain which follow.
   20. The skin, in man, is  made up of four parts, or layers,
the cuticle, rete-mucosum, corpus papillare, and  corium.  It
is covered externally by the  cuticle or epidermis, which is
destitute of nerves and blood-vessels, insensible, and probably
inorganic.  It is the cuticle which is raised by the  applica-
tion of a blister, or by a burn  or scald.   It is  supposed to be
a secretion from the  true skin which concretes  on the surface
becomes dry, and thus offers protection  to the parts beneath,
and also serves to prevent excessive absorption or the escape
of the fluids by evaporation.   It is pierced  by  little pores, for
the passage of hairs, sweat, and the  fluids, taken up by ab-
sorption, although Humboldt asserts that he  could not discover
them  with a  miscroscope which magnified 312,000 times. 
34
PHYSIOLOGY.
   21. The next layer of the skin is the rete  mucosum, or
 mucous web.   It  has been supposed to  consist chiefly  of
 mucus, as  it is of  a soft pulpy texture.   It is the seat of the
 coloring matter in the different races.  In the European, it
 is white, in the African black, and in the Mulatto and Malay,
 copper-coloured.   In  the Ethiopian race, it is much thicker
 than in the light-coloured varieties of the human species, and
 may easily be separated both from the cutis and cuticle, and
 made to appear as a distinct membrane.
   22. The dark color of the skin in the inhabitants of the
 torrid zone, is ascribed by most physiologists,  to the influence
 of the sun  upon the surface of the body ; but the tinge pro.
 duced on  the skin by exposure  to a bright light, appears
 to have no connection with the permanent colour of the
 negro.  Dr. Bostock  states, that the blackest complexions
 are not found in the  hottest  regions,  and  that there are
 some   tribes  nearly  under  the   equator, whose  skin  is
 whiter than that  of  many Europeans.   Besides,  the tinge
 produced  by  the  sun is  not transmitted from  parents  to
 their offspring, whereas the children of negroes are equally
 black in whatever climate they  are born, and their com;
 plexion is not altered  by any number of generations.  When
 a  person  is tanned, as  it  is  called, by the influence of the
 sun, it  is  the cuticle  only which is affected ; if this  be
 removed  by a blister, in  a  few  days new  cuticle will  be
 formed, and the skin in that place will appear as white as it
 ever did.
   23. Albinos.—In the Caucasian race, from  which Europe-
 ans and Americans have descended, there is  usually a mix-
 ture of red or brown,  with white in the complexion ; but
 where the skin is of  a uniform, clear, pearly whiteness, the
individuals are called Albinos, from albus, white.   In  these
persons, the hair is generally white, corresponding  with the
colour of the skin, while the eye  is without  that substance
which gives the various colours to the iris.  The iris, in such 
           STRUCTURE  0E THE HUMAN BODY.        35
cases, is generally of a bright  rose-colour, and  the eyes are
so sensible to light, that they cannot be kept open  in  the
sun-shine, although in the shade, or dusk of the evening, the
vision  is perfect.   It is now well ascertained that the red-
ness of  the eye and the whiteness of the skin in albinos
depends  on the same physical  defect in their organization,
and that it is owing to the absence of the  colouring mat-
ter in  the rete mucosum.   In  the  eye, this  matter,  spread
over the retina, is called  Pigmentum nigrum, or the black
paint.
   24.  What is called the Corpus papillare, is merely a col-
lection of small papillae, formed by the extremities of nerves
and  blood-vessels, and lying immediately under  the mucous
web, dec.  It is in this layer that the sense of touch resides;
the papillae can easily be  seen when the  cuticle has been
removed by a blister.
   25.  The Cutis vera, or true skin, is the  innermost of the
four layers above mentioned.   It is a firm stratum of dense
fibres intersecting each other in every direction, and having
holes for the passage of vessels and nerves.
   26. The true skin is composed chiefly of gelatine, and hence
is used  for the manufacture of glue.  Gelatine combined
with tannin, which is a proximate vegetable principle  ob-
tained  from  oak and other barks, forms a compound that is
insoluble  in  water;  and  it is to this  circumstance  that
leather owes the properties it possesses.  Leather, then, may
be considered as the  product  of  the union of tannin and
gelatine.
   27.  Though the skin consists of four distinct strata, yet
it is only from one-sixth to one-fourth of an inch in diameter.
The true skin is united to the structure  below by cellular
membrane, and this, with the layers above described, consti-
tute  the common integument.   The following sketch  repre-
sents the several layers entering into the composition of the
skin. 
36
PHYSIOLOGY.
1. Cuticle.
2. Rete mucosum.
3. Corpus papillare.
4. Cutis vera.
5. Cellular membrane.
6. Paniculus carnosus,
   There are in certain parts of the body, and especially in
 animals, muscular fibres  passing up  through  the  cellular
 membrane, and inserted obliquely into the-cutis vera,  as at
 6 in the plate.   These form the muscular web, or paniculus
 carnosus.  It is this which raises  the feathers in birds and
 which in the hedgehog and porcupine rolls up the body, and
 erects the  spines ;  and by means of this, animals shake  off
 (lies from their skin.
   28. The skin is defended from the action of moisture, and
 is also kept soft and pliant by an oily fluid, which is separ-
 ated  from  the  blood by numerous sebaceous follicles.   We
 find these  the  most numerous where  there are folds of  the
 skin,  or hairs, or where the surface is exposed  to  friction.
 We sometimes  see the oily matter secreted by these glands
 assume a dark appearance, in the form of black specks, scat-
 tered  over the face, which are called  by many worms, because
 when pressed out they assume that aspect.
   29.  The hair is usually treated of by physiologists as  an
appendage  to the skin.   The  hair takes its origin from the
cellular membrane in the form of bulbs, each bulb consisting
of two parts; an outer, which is vascular, and from which
the hair obtains its nourishment ; an  inner, which is mem-
braneous, and which forms a sheath or tube to the hair during
its  passage through the skin.   The external covering  of
each hair is of  a horny structure, while the  central  part is
1= 
STRUCTURE OF  THE  HUMAN  BODY.         37
soft  and pulpy, and is called medulla, or pith.   The  colour
of the hair varies in different individuals,  and is generally
supposed to depend on the fluids contained in the pith.  The
hair, it is said, has been  known in several instances to have
changed from black to grey in the course of a  single night,
from  the effects  of grief, fear, or some  other  great mental
agitation.   Vauquelin supposes that as the colouring matter
of the hair is destroyed by acids, this phenomenon is owing
to the production of some acid in the system.  Others  sup-
pose that the effect depends  upon the sudden  stagnation of
the vessels  which secrete the  colouring matter,  while the
absorbents continue to act  and remove  that which already
exists.  There are probably  two causes which act in chang-
ing the hair to grey ; the first  is a defective secretion  of a
colouring fluid, and the second, the canals which convey the
fluid into the hair become obliterated.  In the first case, the
hair will remain ; in the last, it inevitably dies and drops
out.
 
38
PHYSIOLOGY.
    30.  The figure on the last page represents the pulp of a
 hair injected ;  1, cut surface of hair ;  2, the pulp ; 3, inject-
 ed vessel  ramifying in  it.  The  figure on the right  shows
 the hair in its fallicle, though the drawing was  made from
 the whisker of a Walrus ;  2, the cutis;  3, external sheath of
 the fallicle ; 4, internal  sheath continuous  with  the  cuticle ;
 5,  pulp ; 6, shaft of hair ; 7, large nerve going to it.
    31.  The nails are also an appendage to  the skin.   Their
 chief use seems to be to  support the pulp of the  finger  while
 it  is exercising touch.   Animals  are provided  with  struc-
 tures analogous in their  physical  and vital properties, such
 as  horns, beaks,  hoofs, nails, spws, scales, dec.  Some physi-
 ologists consider the teeth as  belonging to  the  same  class.
 The various and peculiar functions of the skin, so important
 to  be understood in  order  to the preservation of the health,
 will be fully described hereafter.

  Questions.—Of what is the human body composed ?   What  is said
 of the identity of solids and fluids ?  What proportion do the fluids
 bear to the solids ?  How modified by age ?  What purposes  do  the
 fluids serve ?  What is said of  the solids ?  How are their particles
 arranged to form the different organs ?  How are the areolae formed ?
 Of what shape is the ultimate animal solid ?  What  is a primary tissue ?
 How many primary tissues are there ?  What is a filament ?—a fibre
■—a tissue—an organ—a function ?  Give an  example ?   What is  an
apparatus ?—a system ?—membrane ?   What  are  its uses ?  What is
the  simplest form  of membrane ?—its  use ?  What property does it
possess ?  What its chemical composition ?  What  remarkable circum-
stance connected with it ?  What is the seat of dropsy ?   What varie-
ties of membrane are formed by  the cellular tissue ?  Describe  the
adipose ?  What  are serous  membranes ?—where  found ?—their use ?
structure ?  What are mucous membranes ?  Describe their structure,
situation, use, &c.  What is the skin a continuation of?   Of how many
parts is it composed ?  What is the external layer called ?—what is its
use ?  What is the layer next to the cuticle called ?  Of what is it the
seat ?—the next layer ?—its use ?   Describe  the cutis vera ?   What is
it used for ?   How thick is the skin in man ?  By what contrivance is
the  skin susceptible of motion ?  How is the skin kept soft and pliant?
What is said  of the hair ?—what is its  structure ?—what is its colour
owing to ? What causes it to turn  grey ?   What is said of the  nails 1 
CHAPTER IV.
      STRUCTURE OF  THE  HUMAN BODY CONTINUED.

  1. Another form  of cellular  structure is called fibrous,
from the arrangement of its component parts, which consist
of longitudinal fibres, plainly visible to the naked eye, placed
parallel to each other and  closely united.  These fibres are
sometimes so combined as to form a thin, smooth, dense, and
strong membrane, like that which covers the external surface
of bones, termed  periosteum, or the  internal  surface of the
skull, {dura mater.)  At other  times it forms a firm sheath,
which dips down between the muscles, separating them from
each  other,  or  it may  be  spread over them, binding  them
firmly down in their places.
  2.  In the loins and along the back bone there is a strong
binder of this kind, which  greatly facilitates  the motions of
the body and  powerfully  contributes  to the action  of the
muscles.  Where this is weak, a belt round  the  waist is of
considerable  service,  but in a  well-formed  person it  is  a
clumsy substitute of art for nature, and ultimately tends  to
weaken the back, for exercise strengthens and invigorates all
parts  of the frame, while  artificial  substitutes  invariably
weaken the parts they are  supposed to strengthen.
  3.  It also constitutes the strong, tough, and flexible band,
used for tying parts firmly together, termed ligaments, such
as are found about  the joints,  connecting the bones ;  and  it
also forms those white  cords  in which  muscles  terminate,
called tendons, which  serve  to  attach the  muscles to the
bones,  thus  acting as  mechanical instruments  of motion.
This tissue forms a firm covering or  envelope to the bones,
muscles, tendons,  cartilages,  the eye, kidneys, spleen, and
most of the organs of the body. 
40
PHYSIOLOGY.
   4.  Every joint is enclosed by  a firm fibrous bag, called
the capsular ligament, the internal surface of which secretes a
fluid, termed synovia,  which lubricates the joints, and  serves
the same purpose that oil does in a piece of machinery.   At
the wrist and ankle, and along  the  fingers and toes, the liga-
ments form strong bandages to bind down the muscles  and
tendons, and enables them to act with greater precision  and
steadiness;  otherwise when the muscle contracted,  the  ten-
dons  would start out  like the  string of a bow, and thus not
only destroy the symmetry of the parts, but entirely prevent
motion.  When sprained by  over exertion or accident, an
artificial bandage  becomes necessary ; we then find how su-
perior the natural ligaments are to  any artificial bandage  that
can be contrived.
   5.  Tendon  or  Sinew.—This   well-known structure is
plainly perceptible at the  wrist, on the back of the hand, at
the heel, dec.  They have a  white,  pearly lustre, possess
great strength,  but little elasticity.  They are  composed
of  bundles of parallel  threads, bound  together  by  trans-
verse threads, and they vary .both in figure and extent; some
being cylindrical  and tapering to  the  point of insertion,
and in others forming broad expansions.   So insensible are
tendons, that when ruptured, as the tendon of Achilles at the
heel, not the slightest pain is felt, but the person feels that he
has received a smart blow, or that a part of the floor has given
way under him.
  6. Where force is to be exerted upon some distinct point, it
is transmitted along a tendon,  as forces in machinery are by
ropes.   When a tendon passes over a joint, a bone is formed
sometimes where it crosses, as  the  knee-pan  in front of the
knee joint ;  which is a bone placed directly in the centre of
the tendon, and serves, to throw the  force farther  from the
centre of motion, thereby increasing the  lever, and conse-
quently  the effect.   Similar bones are  often found  in  the
tendons of  the feet. 
STRUCTURE OF THE HUMAN BODY         41
  7. Another primary tissue, or  modification of  cellular
structure, is termed  the cartilaginous.   This seems  to be a
substance intermediate between membrane  and bone.  It is
firm, smooth, highly elastic, of a pearly white colour, and ex-
cept bone, the hardest part of the animal frame.  It is des-
titute of red vessels, and neither nerves nor lymphatics have
been discerned in it; though as it becomes highly sensible,
like the fibrous tissue, by disease, it no doubt is supplied with
nerves.  It is placed at  the ends  of the bones, particularly
about the joints, where by its smooth surface, it facilitates
motion, and by its yielding nature, prevents the shock or jar
which would be produced were the same kind and degree of
motion effected by a rigid and inflexible substance.   Where
strength and  flexibility are required  to be united, we there
find cartilage, as  in the spinal column, between the ribs and
breast bone, in the larynx, the ear, nose, dec.
Portions of cartilage seen in section.
   8. By immersing cartilage in  nitric acid and then in wa-
ter for some little time, we find its  intimate structure so un-
folded, that we can perceive  it to be composed of an infinite
number of minute fibres, arranged perpendicularly like the pile
of velvet.   Thus we see that  in the  construction of the joints,
millions and millions of springs of  the most curious and ex-
cellent contrivance stand perpendicular to the direction of
the force applied, bend  to pressure, and on its removal, regain
                             4* 
42
PHYSIOLOGY.
their form by their elasticity.  When we stand in the erect
posture, the number of minute but efficient springs on which
the weight of the body rests, in the several joints of the back,
in the hip,  knee, and ankle joints, infinitely  surpasses the
powers of the human mind to calculate or even to imagine.
   9. There  is a peculiar tissue, allied to ligament in its tex-
ture,  distinguished by  a high degree of elasticity,  fibrous
structure, and tawny colour, and is hence often called elastic
tissue.   This structure  is very conspicuous  in the neck of
those animals, which have to support a heavy  load horizon-
tally, at the the extremity of a long neck, as in the elephant,
the deer, and our domestic  cattle.   Had their  heads been
supported merely by muscular action, as that is liable to fa-
tigue and requires intervals of rest, as well as the exercise of
volition, the postures could not  have been sustained for any
length  of time without pain and  exhaustion.   This  tissue,
which  is liable to  none of these  objections, is accordingly
substituted for muscular power, in fixing the forms, preserv-
ing the  attitudes,  and  contributing to motion.  The strono-
fibrous band, stretching along the  back part of the neck to
the head of  these animals, enables  them with perfect ease to
support the  head.  It  is  the  elasticity  of this membrane
which causes the head of these animals to be bent back after
death, the action of the muscles having ceased.   It also re-
tracts and  retains  the  sharp claws of the cat tribe  within
their sheath when not in use.   A ligament of this tissue also
retains  the  wings of birds in a bent  position when they are
in a state of rest.
   10.—The osseous fabric—The  osseous or  bony tissue is
another form of cellular matter.   The bones  constitute the
hardest  and  the most solid parts of the whole system, and are
the principal parts that  give it form and stability, forming as
it  were, the  frame work of the  animal machine.  The num.
ber of bones in the human adult, including the teeth, is 245.
When we examine the broken surface of a bone, with a mil
croscope, we find it abundantly supplied with minute  blood- 
STRUCTURE OF  THE HUMAN BODY.        43
vessels, without any  appearance of fibres or  plates.   The
different densities of bones depends on the different mechani-
cal arrangements of the parts composing them.
   11.  The bones not only constitute the  frame work of the
human fabric, but they also  protect  the vital organs, as the
heart and lungs, the brain and  spinal marrow, and also con-
stitute a series  of  levers, by means of which,  through the
agency of muscles, locomotion  is performed.   The  bones in
man also furnish cavities for the secure lodgment of the deli-
cate organs of the senses, as the orbits of the eye, ear, mouth,
and  nostrils.   In man, and the higher order  of animals, the
bones are for the  most part in the interior of the body, and
when near the surface, as in the  skull, they are covered  by
muscles or membranes ;  but in the Crustacea, insects, dec, the
bones compose an  external case within  which  all the soft
parts are contained.
   12.  If we divide any of the long bones longitudinally, we find
two  kinds of structure, the hard or compact, and the alveolar
or spongy.   Indeed there is no bone that does not exhibit to
some extent both of these structures ;  the compact forming
its external,  and the  spongy its  internal part.   These two
formations are clearly seen in  the bones which compose the
skull, (as in the following cut,) with the spongy or cancel-
            a. External plate,  b. c.  Internal plates.
laled structure between them.  This will serve  to illustrate
the structure of all the flat bones.
13. The above cut represents a section of the thigh bone. 
44
PHYSIOLOGY.
a. a.  the extremities having a shell or thin plate of compact
texture, crowded with small cells, diminishing in size, but in-
creasing in number as they approach the articulation ; c, the
cavity for containing the marrow ; b.  b. the walls of the shaft
very firm and solid.  The compact part is thickest near the
middle of the bone where the  greatest strength is required.
This  structure admirably combines the greatest  degree of
strength, with the least degree of weight aud expense of ma-
terial.  It can be mathematically demonstrated that the re-
sistance of a cylindrical body, such as a pillar  or mast, to  a
force  applied transversely  is  increased in proportion to its
diameter.   The same quantity of matter, therefore, placed in
the circumference of a circle produces a stronger bone than
if united in the centre with proportionally diminished diame-
ter.
   14.  How admirably  adapted is  the  arrangement of the
parts  of the  long  bones to the purposes for  which they are
destined.  Their extremities are the fixed points from which
the muscles re-act, and where  greater space was required for
the insertion  of the tendons ;  their diameter  is on  this ac-
count  considerably  increased, and their osseous matter is
disposed in nearly an equal degree through their whole sub-
stance; while  in  the  middle of the  bone,  which  is more
exposed to external violence, and where nothing was want-
ing but mere strength, the bony plates  are all consolidated
together  into  a compact  dense ring,  leaving the  centre
nearly hollow.
   15.  While  the  long bones of the lower  extremities are
adapted for the support of the  body, and its various progres-
sive motions, those of the upper extremities are equally
fitted  for acting upon contiguous bodies, being so attached to
the trunk as to be easily applied to them  in  all directions.
  The flat bones on the other hand offer an extensive sur-
face of defence, as  those of the skullr or for the origin and
insertion of muscles, as the shoulder blade.   The rounded
bones composing the spinal column  and the angular bones of 
           STRUCTURE  OF THE HUMAN BODY.         45
 the wrist and  ankle, have the bony matter extended over a
 considerable  space, in order in the most efficient manner to
 combine  the  properties  of lightness  and strength.  The
 whole assemblage constitutes an apparatus which is capable
 of executing  all the various movements that are necessary for
 the purposes  of life, with a degree  of precision and velocity
 that is truly  wonderful.
   16. The bones are covered with a fibrous  sheathing  of
 dense membrane, called periosteum, which seems to nourish
 the bone, for where it is abraded the bone perishes.   It con-
 tains an abundance of  blood-vessels which run from it into
 the bone ; besides these, a large blood-vessel enters the shafts
 of the long bones near the centre, and branches out in each
 direction, while numerous others enter at  their extremities.
 These blood-vessels, though generally too  minute to convey
 the red particles  of the blood, yet  they readily transmit the
 colouring matter  of madder.   Numerous experiments have
 proved that when animals are supplied with food mixed with
 that substance, in a few days  the bones are coloured red,  or
 of a pinkish  colour, and  on  the  discontinuance of it, in a
 short  time their  natural colour is restored,  showing the
 rapidity with which deposition  and absorption are carried
 on in the healthy state.    This is shown in cases of fracture,
 where the broken ends of a bone become speedily united.  I
 have lately had a case of fractured thigh bone in a child,
 where it became  united with considerable firmness in one
 week.
  17.  Marrow is a species of fat deposited  in the central
 canals of the cylindrical  bones, and in  the lattice work of
 the spongy bones.  It is contained  in the cells  of a delicate
 membranous  web,  and has been supposed  by some to serve
 as a  reservoir of nourishment, and by others,  to keep the
 bones from becoming dry and brittle.  It is found in greater
 quantity  in the adult  and aged than in the young ;  in the
latter,  indeed, its place is occupied by a gelatinous  fluid.
  18.  Chemical examination  shows that bone i3 composed 
46
PHYSIOLOGY.
of earthy and animal matter, the former constituting  about
two-thirds, the remaining one-third  being animal matter.
As we find portions of both these substances in the minutest
particles of bones, both are therefore considered essential to
its composition, and existing in a state of chemical union,
and not as a  mere mechanical mixture.  These two sub-
stances can be readily separated from each  other.   If we
immerse bones  for some time in diluted nitric  acid, or muri-
atic  acid,  though they  retain  their  size  and form,  their
weight  is  considerably diminished,  and  they are rendered
soft, pliable, and elastic.  The earthy portion, phosphate of
lime, has been dissolved, and  is held in solution in the fluid,
and the animal portion, gelatine, remains uninjured.
  Membranous, or gelatinous portion of bone ;  the earthy portion being
so completely removed, that it is capable of being tied in a knot.

  19. If bones are subjected to a strong  heat, as  in a char-
coal fire, on cooling they  appear to have undergone no alter-
ation in figure or  bulk ;  but  they are  rendered white as
chalk;  their weight  is  lessened, and they become  very
brittle.  In this  case, the animal matter has been  wholly
consumed by the fire,  while  the  earthy part remains  un.
changed;  in the former  case, the very reverse happened;
the  animal matter remaining, and  the earthy being remov-d 
STRUCTURE OF  THE  HUMAN  BODY.         47
Earthy portion of bone.
  20. The proportion  between the animal and earthy sub-
stances varies in different individuals, and in the same indi-
vidual at different  periods of life, and under various condi-
tions  of health.  In youth, the former, in old age, the latter
predominates.  The earthy matter is sometimes so deficient
that the  bones have not the  necessary  degree of firmness
and rigidity.   The  consequence is, that those parts of. the
skeleton  which have  to support any considerable  weight
bend  under it, as the spine, the bones of the pelvis, and the
lower limbs.   This is one cause of spinal distortions, though
they  are generally caused by debility  of the muscles from
want of proper exercise.  In many cases of the former kind,
by the subsequent deposition of earthy matter, the bones be-
come sufficiently  dense and compact;  but  the  distortion
remains  fixed and  permanent, and mechanical means, such
as  pulleys, screws, inclined planes, dec, only serve to torture
the patient,  without affording the slightest  prospect  of  a
cure. No one who understands physiology will attempt to
correct  such  distortions by  mechanical  means.  Where
there is  a deficiency  of animal  matter, the bones want  a
poper degree of tenacity, and  are therefore easily fractured
by slight blows or falls.
   21. The ends of  the bones which are  used for  motion, as
already mentioned, are tipped with cartilage or gristle, which
is very smooth and hard ; and  it is constantly wet, in a state
of health, by a fluid which  answers the  same purpose as oil
in machinery, or  tar  upon wagon wheels.   The joints are 
48
PHYSIOLOGY.
enclosed in membranous  bags, and in health the fluid which
moistens them is of just the right quantity and quality ;  but
if we do not take proper exercise, or if we take food or drink
that is  too  heating or irritating,  the joints  grow  stiff, or
rheumatism or gout may be the consequence.
  22". In those parts where bones are to be formed, a mould of
gristle or cartilage is first deposited, of the exact shape that
the future bone is to take; and as bony particles are secret.
ed by the blood, the cartilage is taken up by  the  absorbent
vessels.   In the long round bones, this process begins in the
middle, and in the flat bones, like the shoulder  blade, or those
of the skull,  it begins in the centre and extends gradually
towards the circumference.   But in  the skull, all the bones
are not completely formed, till several  months after  birth.
  23. The bones are variously connected  by joints or arti-
culations, which  admit of different degrees of motion, both
in extent and  variety.  Some  of  these connections allow
free, easy, and conspicuous  motion, as the shoulder  and hip
joints, which  are called ball and  socket joints ;  in others,
there is motion in only two directions, as the knee, elbow,
wrist, and ankle.  These are called hinge-joints, from  their
resemblance to a hinge.   Some bones, like those of the skull,
though connected by a kind of articulation, are nevertheless
immoveable.
  24. Another form of animal matter,  differing essentially
from those  we have been  considering  is,  muscular tissue.
This is familiar to all under the name of flesh.  It  is a sub-
stance of a peculiar nature, arranged in fibres  of extreme
delicacy.   It is  distinguished  from every other texture in
the body, by an  innate  power of contraction ; on  examin-
ing  it with  microscopes of great magnifying power, it  is
found to be composed of filaments so fine as the one forty
thousandth part of an inch in diameter.   These  filaments
collected together, form fibres, which are plainly perceptible
in boiled flesh.  A  collection of these fibres  form a bundle,
and these  bundles  collectively  constitute  a  muscle;  and 
STRUCTURE OF THE HUMAN BODY.        49
muscles appear coarse or fine according to the size  of these
bundles.
  25.  These fibres appear  to  be very uniform as to shape,
size, and general appearance,  being  delicate, soft, flattened,
and though consisting only of a tender pulp, still solid. The
fibrous and fascicular arrangement appears to be chiefly con-
fined  to  muscles of voluntary action, as  they  are  scarcely
perceptible in the  heart, and  not at all in the alimentary
canal, or urinary bladder.   In the stomachs of birds, how-
ever,  the  fibrous  structure is very  distinct, especially in
hawks and owls.
  The appearance of the ultimate fibres and of their transverse lines, as
seen under the microscope of Mr. Lister, when the object is magnified
500 diameters.

  26.  The muscular fibres are every where  penetrated  by
cellular tissue  and numerous blood-vessels and nerves.  The
colour of the muscle of course varies, according to the quan-
tity and quality of the blood. In adult animals it is of various
shades of red ; in young animals, of a cream colour, as in
veal ;  in birds, it varies in different muscles ;  in fowls,  for
example, it is  white on  the breast, and a deep brown on  the
legs ;  while in fishes, it  is  bluish, or white, dec.
  27.  No  part of  the  body except, perhaps, the organs  of
sense,  is so abundantly supplied  with  blood-vessels  and
                              5     /^S*r*€r,,Wi-L
 
50
PHYSIOLOGY.
nerves, as the muscular  tissue.   There is reason to believe
that every filament, however fine, is provided  with the ulti-
mate branch of an artery, vein, aftd nerve.  The direction
of the fibres of muscles varies ; in some, being parallel;  in
others, radiating in different directions.  In some instances,
they  form nearly or  quite  a circle, as  the muscle  which
closes the eye, and  those of the intestinal  canal; in others,
they are penniform, or having their fibres disposed like those
forming the feathery part of a quill.
  Two portions ofmuscle ; one of which, a,  is covered with mem-
brane ; the other, 6, is uncovered ; c, the muscular fibres terminating in
tendon.
  27.  Muscular  tissue  is  supposed  to  consist  chiefly of
fibrin, though some chemists state that it contains albumen,
gelatine, and osmazome.  These latter substances however,
are probably obtained from  the cellular tissue which encloses
and dips down  between  the fibres of muscles.  Fibrin  con-
tains a larger proportion of azote, the element peculiar to the
animal body, than any other  animal  substance.   The  flesh
of young animals affords a large proportion of gelatine, while 
STRUCTURE OF  THE HUMAN  BODY.         51
it  is deficient in fibrin—in adult animals, the  fibrin pre-
dominates, and the gelatine is deficient.
   28.  The peculiar property of muscular tissue is vital, and
consists in the power of diminishing its length, or shortening
on the application of stimulus.   All the motions of the body
are performed  by means of it,  and  without its incessant
action, respiration, digestion, nor circulation could be carried
on for a moment.  Tendons, ligaments, cartilages, and  bones
seem  to  be mechanical contrivances to aid the  muscles in
accomplishing their varied purposes, so that the only source
of motion in the body  is muscular tissue, and the only mode
in which motion is generated is by contractility.
   29.  The last primary  tissue  which we have to  describe, is
termed nervous.   It consists of a soft and pulpy matter, of a
brownish white  colour, and appears to be composed of solid,
elongated threads, differing in  thickness  from that of a hair
to the finest fibre of silk.  Like the muscles, the nerves are
enclosed  in a sheath of condensed cellular membrane,  called
neurilema, or nerve coat; and like  them also, each nerve is
composed of many bundles ; these of many fibres ; and the
fibres of many filaments.  In  one respect  the nervous fibres
differ from the muscular, and  that is, while the muscular fi-
bres generally run parallel to each other, those of the nerves
cross and penetrate each other, so as to form an intimate in-
terlacement, as represented on the following page. When we
come to describe the vascular system, it  will be seen that
either all  the  vessels proceed  from one large trunk, which
goes on   progressively  to  divide and subdivide, until  its
branches become so minute as to be invisible ; or that they
arise  by numerous and invisible branches,  which unite to
form larger and larger vessels, until they  ultimately consti-
tute only a few trunks.  But the muscular and nervous fila-
ments never divide  and subdivide in this manner.  It is the
opinion of the best  anatomists, that there  is a diameter be-
yond which they no longer  diminish.  That  diameter they
maintain is quite uniform in each. 
PHYSIOLOGY.
  Nervous fibres, deprived of their neurilema and unravelled, showing
the smaller threads, or filaments, of which the fibres consist.

   30.  The  nervous tissue is  also  abundantly supplied with
blood-vessels, like the  muscular ; so that  there is not a fibre
or filament, however  minute, which is not supplied by a dis-
tinct blood-vessel.  The  nervous structure forms the brain, 
STRUCTURE OF THE HUMAN BODY.        53
spinal marrow, nerves and their ganglions.  The nervous tis-
sue appears to consist of two substances, which as far as the
eye can distinguish, appear to be entirely distinct from each
other.   The one is called cineritious, or gray, from its col-
our; from its position, cortical, and from its consistence pulpy.
This last appears to be composed  chiefly of blood-vessels.
The other is termed white, or medullary.  It is of firmer
consistence than the pulpy.  This is decidedly fibrous  in its
nature.  In every part of  the nervous system which consti-
tutes a distinct nervous apparatus, both substances are con-
joined.   Neither the pulpy, nor the fibrous alone,  forms a
distinct organ ;  the  union of both is necessary to constitute
an instrument capable of performing a specific function.
   Ultimate fibres of nerve highly magnified; showing the strings of
 globules of which they consist.

   31. Much controversy exists in relation  to the shape of
 the  ultimate particles of nervous matter;  but while micro-
 scopical observations differ as much as they have done hith-
 erto, the question  may fairly be considered as  unsettled.
 The common opinion is, that the ultimate filaments of which
 they are composed, are formed of globules of extreme minute-
 ness.  But then, when we consider the peculiar difficulties
 attending investigations of this nature, that they require un-
 wearied perseverance, extreme accuracy, great patience, and
a dexterity with the hand, united with a delicate discrimina-
tion  of the eye, that belong to few ; and when we consider
moreover, that  these very endowments can only  be acquired
                           5* 
54
PHYSIOLOGY.
by long practice, we shall be led to pause, before we adopt
the opinions of every microscopical enthusiast who enters on
this  very extensive, and deeply fascinating field of discovery.
Portion of the trunk of a nerve dividing into two branches.
  Questions.—Describe the fibrous structure.  What  are its uses?
What are ligaments ?  What is a  capsular ligament ?  What use do
ligaments serve ?  When sprained, what is a good remedy ?  What is
a tendon or sinew ?  Where are  they found ?  What their use ?  Of
what  composed ?   Have they much  sensibility ?  Why are bones
sometimes placed in a  tendon ?  What use does the knee-pan serve ?
Describe  the cartilaginous tissue.   What are its uses ?  How may its
structure be shown ? What is the elastic tissue ?  Where  is it found ?
What are its uses ?  What constitutes the most solid portion of the sys. 
STRUCTURE  OF THE HUMAN BODY.         55
tem ?  What are the uses of the bones ?  How many are there in the
human skeleton ?   Is bone supplied with blood-vessels ?   What is the
different density of bones owing to ?  What  situation do  the bones
occupy in man ?   In the Crustacea and insects ?  Describe the structure
of the long bones ?—of the flat bones ?  What is  the chief use of the
flat bones ?  What covering have the bones ?   What is the structure
of the periosteum ?  What its use ?  How are the bones nourished ?
What effect has madder upon bones when taken internally ?   What is
marrow ? Where is it deposited ?  What its use ?  At what period of
life is it most abundant ?  What is the composition of bone.  What pro-
portion is animal matter ? What earthy ? How are these different sub.
stances  shown ?  Are  their proportions  affected  by  age or health ?
What is the consequence when the earthy matter is deficient ?  What
when the animal ?  How are spinal distortions best remedied ?  How
is bone formed ?   Are all the bones formed  at the time of birth ? What
is muscular tissue ?  By what  property is it distinguished ?—Of what
composed ?  What are fibres ?  What bundles ?   How do the  fibres
appear?  Do all muscles possess the fibrous arrangement?  To what is
the colour of muscle owing?  Of what colour  is the muscle of fishes?
Of what shape are muscles ?  What  is the chemical composition  of
muscular tissue ?   Does age affect the quantity of fibrin  in animals ?
What peculiar property does muscular fibre possess ?  What its use ?
Describe the nervous tissue.  What is the neurilema?  Does nervous
tissue abound with blood-vessels ?  What does it  form ?   How many
kinds of substance is contained in it ?  What is the cineritious  ?  What
their cortical portion ?  Does either alone form any organ ?  What is
said of the shape of the  ultimate particles of matter ? 
CHAPTER  V.
            CHEMISTRY  OF THE HUMAN  BODY.

              Ultimate and Organic Elements.

   1.  By the  chemical  composition of the  body,  is meant
those ultimate elements of which it is made ;  such as oxygen,
carbon, hydrogen, and azote.  By the organic composition,
we mean the  proximate  elements, which are  formed out of
these by the power of the living principle ; such as albumen,
fibrin, gelatine, dec.
   2.  The  ultimate elements  of animal matter  have  been
divided into non-metallic, and metallic substances ; the former
consisting of oxygen, hydrogen, carbon, azote, phosphorus,
sulphur, chlorine, and fluorine ;  the latter, 1, the bases of the
alkalies, viz., potassium,  sodium, and calcium; 2, the bases
of  the  earths, magnesium, silicium,  and aluminum ; 3, the
ponderous metals, iron, manganese,  and copper.
   Of the first class, or the non-metallic substances,  oxygen,
hydrogen, carbon and azote exist in much the largest  pro-
portion, and are in fact the only essential elements of animal
matter.
   3.  All the solids and fluids of the  body contain oxygen.
It is essential  to  all  the proximate elements.  United  with
hydrogen, it forms water, which is calculated to constitute
nine-tenths of the whole weight of the body.   In  union  with
carbon, it forms carbonic acid, which exists in the blood, and
is thrown out by  the lungs and skin.
  3.  Oxygen forms with phosphorus, phosphoric acid, which
with lime constitutes the earthy portion of the bones ; it also
exists in some of the secretions.   In union with their metalic
bases, it forms potash, soda, and lime.   It  also is a consti- 
CHEMISTRY OF  THE  HUMAN  BODY.        57
tuent part of albumen, fibrin, gelatine, and mucus.   Oxygen
is  derived  partly from the air we breathe, and partly from
our food and drinks.  It is given off in all the secretions
and excretions.  The  air contained in the swimming bladder
of fishes, is pure oxygen.
   4. Hydrogen exists in all the fluids and most of the solids,
constituting as it does one element  of water.   In venous
blood, it exists in a larger proportion than in arterial blood,
which contains more  oxygen.  In the bile, it is very abund-
ant,  and in fat and oil, is one of the essential elements.  It
is  this gas which often causes so much distress in a weak
state of the stomach.   Hydrogen  is  introduced  into the
system  by means of  food and drinks, and is discharged in
the same manner as oxygen.
   5. Carbon  abounds in the vegetable as  well  as animal
kingdom.   In oil, fat, albumen, gelatine, fibrin, and mucus,
it  always forms a  part.  In bile, and in venous  blood,  it
exists largely.  If we  burn a piece  of animal  substance,
what is left is found to be  chiefly carbon.   We obtain  it
from our food, and give it off by breathing and the secretions.
It is carbon that makes venous  blood  darker than arterial,
and  the change from purple to bright  crimson which  takes
place in the  lungs, is supposed to be  owing chiefly to the
fact, that  the excess of carbon contained in venous blood  id
discharged by respiration.
   6. Azote exists in large quantities in all animal matter.
It also exists to some extent in a few vegetables, but it is an
essential element in animal substances.  It  is more abund-
ant  in fibrin, of which the muscular flesh is chiefly formed,
than in any other portions of the body, though it  is found
in the  brain  and nerves.   The  peculiar smell of burning
animal matter is owing to azote.   When animal substances
putrefy, it combines with  hydrogen, and forms ammonia or
hartshorn.
   7. Azote is chiefly taken  into  the  system by means  of
animal food.  It  is also taken into the blood  by respiration, 
58
PHYSIOLOGY.
as it forms a  constituent part of the  atmosphere.   This,
however, is denied by some chemists.  It is discharged from
the system in the same  manner as oxygen,  hydrogen, and
carbon ;  though chiefly through the kidneys.
  8. Phosphorus exists  both in animal and  vegetable sub-
stances.   Nearly every part of animal bodies  contain  it,
though it is found more abundantly in the bones.   It gener-
ally exists in  combination with  oxygen, forming phosphoric
acid.   It is discharged mostly  through the kidneys.   The
spontaneous combustion of human bodies, of which we have
some well-attested cases of drunkards, is supposed to be owing
to an accumulation of phosphorus in the system, from some
unknown cause.
  9. Sulphur is always  united, in  animal substances, with
other elements,  as soda and potash.   It is found in albumen,
in the hair and  nails, and in muscular flesh.   It is  given off
by the intestines and by the skin.
  10.  Chlorine is found in most of the animal fluids com.
bined with hydrogen.  This forms hydrochloric  acid.   In
the blood it is  combined with soda  and potash.  It is found
also in the gastric juice, in sweat, milk, saliva, dec.
  11.  Potash exists more abundantly in plants than in ani-
mals.  It is,  however, contained in the  blood,  bile,  urine,
sweat, milk, dec.
  12.  Soda is more abundant in animals  than  plants.  It
exists in  the same fluids in which potash is found ; also  in
bones and muscular flesh.  It is always combined with some
acid.
  13.  Lime forms a large part of the  bones, in union with
phosphoric or carbonic acid.  Silex exists in human hair,
and in  some of the secretions.   Magnesia is contained  in
bones, and in some animal fluids, as milk.  It is also  found
in the brain.   Iron forms the colouring  principle of the red
globules  of the  blood, and  is  therefore  pretty extensively
found in  animal bodies. 
CHEMISTRY OF  THE  HUMAN  BODY         59
   14.  The organic or proximate elements of the body are
formed from the ultimate elements  already described.   We
cannot explain their  formation on any chemical or median-
ical laws, but refer them solely to the influence of the vital
forces.
   15.  These proximate elements are mostly formed  from a
combination of oxygen, carbon, hydrogen, and azote, and are
divided into two classes, acids and oxyds.
   16.  The acids found in the human system are the acetic,
oxalic, the benzoic, and  the  uric.  The three  first are  also
found in the vegetable kingdom, and are composed of oxygen,
hydrogen, and carbon.  When  these organic elements are
made  of three  simple  elements,  they are called ternary
oxyds; such  are sugar, resin,  and the fixed and volatile
oils.
   17.  Milk contains a  considerable quantity of sugar.  It
can be obtained  from whey  by evaporating  it slowly to the
consistence of a  syrup, and then allowing it to cool. It may
then  be  purified by the white  of an egg, or albumen, and
crystalized again.  It has  a different  taste from the sugar
of the cane.
   18.  The bile contains a peculiar resin.  Fat and the mar.
row of the bones contain fixed oils.  But the most important
compounds of the body are  albumen, fibrin,  gelatine, mucus,
and osmazome.
   19.  Albumen  exists in the body, both in a solid and fluid
form.   Combined with water it  forms the white of eggs;
hence its name.  It exists  most abundantly in the serum,
but is found in all the fluids of the body.  It is transparent,
without colour, taste, or smell, and coagulates by heat, acids,
and alcohol.
   20. Solid albumen is also a white and tasteless substance.
It forms the basis of the nerves and brain, and is contained
in the skin, hair, nails, glands,  and  vessels.   Tumours and
wens are mostly composed of albumen.  It is composed of 
60
PHYSIOLOGY.
Carbon 52 parts;  Oxygen  23 parts;  Hydrogen 7  parts,
Azote 15 parts.
  21. Fibrin  is  the  basis  of  muscular flesh ;  and  enters
largely into the formation of the blood, chyle, and lymph.  It
is owing to the presence of fibrin that blood coagulates when
removed from the body.   Fibrin is a solid, white substance,
of a fibrous structure, destitute of smell and taste, and in-
soluble in water.
  22. Fibrin may be obtained  by washing the thick part of
the blood with cold water, and thus separating the colouring
matter,  or the  red  globules.   It differs from  albumen by
possessing the property of coagulating at all temperatures.
Fibrin is composed of  Carbon  43  parts ; Oxygen 19 parts;
Hydrogen 7 parts;  Azote 19 parts.   It contains more azote
and less oxygen than albumen.
  23.  Gelatine is found in none of the fluids of the  human
>ody.   It is, however, found in nearly all the solids.   It is
known  from all the other animal principles by its  readily
dissolving in warm water, forming a  kind of jelly.   When
dry, it forms a hard, shining, brittle substance, called glue.
This is mostly prepared from the skins and hoofs of animals,
by boiling them in water,  and then evaporating the solution.
Isinglass is obtained from the sounds of the sturgeon, and is
a very pure gelatine.
  24.  Gelatine exists  largely  in the skin, cartilages, liga-
ments, tendons, and bones, and  it forms  the  basis  of the
cellular tissue.  As it does not  exist  in the blood, it  is pro-
bably a modification of albumen.   It is composed of Carbon
47  parts ; Oxygen  27 parts ; Hydrogen 7 parts ; Azote 16
parts.
  25. It  appears that  gelatine contains less carbon than
albumen, by 5  or 6 per cent.,  and a  larger proportion of
oxygen in the same  ratio.  Now, if  we suppose, that near
the skin, and in the various tissues of the body, the albumen
of the blood gives off a portion  of its carbon, a part of which 
CHEMISTRY  OF   THE HUMAN BODY.        61
is taken up by the veins, and a part thrown off by the skin,
lungs, and various secretions, we shall see how gelatine may
be formed out of albumen.
  26. Osmazome is an element which exists in all the animal
fluids, and in some of the solids, as the brain and  muscular
fibre.  It is of a reddish brown colour,  of an aromatic smell
and agreeable taste.   It is this which gives  the strong flav-
our of roasted  meat, and  the peculiar taste of the various
kinds of animal food.   It is supposed to be tonic and stimu-
lating, but to possess no nutritive properties.
   27. Mucus is that bland fluid which  moistens the surface
of  all the mucous  membranes.   In some of the hard  parts
of  the body, which are destitute of sensibility, it is found to
exist in considerable quantities,  as  in the nails,  hair, and
cuticle of man, and in the scales, feathers, and wool of dif-
ferent animals.  That part of the skin  called rete mucoscum,
is supposed to be compacted mucus.  Mucus is transparent,
has no colour  or  taste, and has a ropy and viscid consist-
ence.  When  dry, it is insoluble in  water.  It  contains
much azote.
   28. There are some other substances found in the human
body, such as caseine, or that  principle of the milk which
forms the basis of cheese, curd, dec. ;  but they are not of
sufficient importance to need a particular description.
   Questions.—What is meant by the chemical composition of the
body ?  What are some of the ultimate elements ?  What  are some
of the proximate elements ?   How have the ultimate elements been
divided ?  Is oxygen essential to all the proximate elements ? What
is  said of hydrogen ?—Of carbon ?—Of Azote ? How  do  oxygen,
hydrogen, and azote get into the system ?   Is phosphorus found in
animal bodies ? What other elements are met with in animals ? How
are the organic elements of the body formed ?  How  divided ? What
acids are found in animal bodies ?  What  are  the most important
compounds in the body ?   What is said  of albumen  ?  In what  is it
found ?  What is fibrin the basis of?  How may it be obtained from
                             6 
62
PHYSIOLOGY.
blood ?  Of what is  it composed ?  Where is gelatine found  in the
animal body ?  How  known from the other animal principles ?  What
does it form when dried ?   Of what is glue  prepared ?  In what does
gelatine exist ?  How may we account for the  productions of gela-
tine ?  What is osmazome ?   What peculiar properties has it ?  What
is mucus ?  Where found, what is its use ?  Are any other substances
fourd in the human body 1 
CHAPTER VI.
                 THE HUMAN SKELETON.

   1.  Of all the wonderful works of the great Architect, none
bears such  convincing proofs of divine wisdom and good-
ness as the mechanism of the human body.   Every part,
down to the minutest fibre or blood-vessel, bears the impress
of the Creator's hand, aftd the marks of design and contri-
vance are so  obvious throughout, as to lead the mind irre-
sistibly to an all-wise, Omnipotent designer !
   2.   The human skeleton consists of about 252 bones, In-
cluding the  sesamoid, the teeth, and the small  bones of the
ear ;  though they are generally reckoned at 211.  They are
divided into those of the head, trunk, and  extremities, some
of them being single, others in pairs.  When the bones com-
posing the skeleton  are connected together by natural liga-
ments, they form what is called a natural skeleton ;  when by
wires, it is termed  an artificial skeleton.  The latter is the
common and most useful mode of articulation  to the anato-
mist, as the joints can be easily moved and examined.   The
skeleton has  been called the  bony frame work of the body,
because by its form and solidity, it not only retains  every
part of the fabric in  its proper shape, but also affords a hard
surface for the attachment of  muscles, and  the protection of
many  important organs.   If we suppose a plane  to pass
down from the top of the head through the middle of the skele-
ton, the latter  will be divided  into two equal portions,  called)
the right and left side of the body, which are perfectly alikey
in shape and  size.   Those  bones which are  situated in the
centre, such  as the spine  and breast bone, and are  inter-
sected by it, are  said to be symmetrical, because they  are
divided  equally ;  the others, such  as the bones of the arm
and leg, are  in pairs. 
PHYSIOLOGY.
 £f
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Vhf 
THE  HUMAN  SKELETON.
   , The bones of the head are 55 in number, as follows:
              Frontal, (»Os Frontis, a,)            .     .      1
              Parietals, (Ossa Parietalia, 6,)       .     .      2
              Temporal      ....            2
              Occipital, (Os Occipitis)      ...       1
               Sphenoidal, (Os Sphenoides, d,)           .       1
               Ethmoid, (Os Ethmoides)    .      .            1
               Nasal, (Ossa Nasi, e,)  .      .      .     .       2
               Malar, (Ossa malarum /,)   .      .     .       2
               Lachrymal, (Ossa Lachrymalia,)    .     .       2
               Upper Jaw bones, (Ossa maxillaria superiora)     2
               Palate bones, (Ossa palatina)       .     .       2
               Inferior turbinated bones,  (Ossa turbinata) .       2
              Vomer,  ......       1
               Lower Jaw, (Os maxillare inferius, A,)    ,       1
               Teeth, (Dentes)      ....     32
              Tongue bone  (Os hyoidesl   .      .            1
                                                     Total,"55            55
  To these are sometimes added the proper bones of the ear, contained in the tempo-
ral bones.
                         Mallei, (hammer)         2
                         Incudes, (anvil)    .      2
                         Stapedes, (stirrup) .      2
                         Orbicularia, (round bones) 2
                                           Total, "8                        8
  4. The trunk contains 57 bones, viz:
                      Vertebra, (a,)      .     .      24
                      Ribs, Costae, e, f, g,)       .      24
                      Breast bone, (Sternum, c, d,)     2
                      Hip bones, (Ossa innominata, i,)  2
                      Rump bones, (Os sacrum, k,)    1
                      Coccygeal bones, (Osea coceygis)  4
                                              Total,  57"                 57
  5. The upper extremities contain 68 bones, viz:
              Collarbones, (Claviculae, a,)        .      .       2
              Shoulder blades, (Scapulae, b,)      .      .      2
              Arm bones, (Ossa  humeri, c,)       .      .       2
              Fore arm bones, Radii et ulnse, d,«,) .      .      4
              Wrist bones, (Ossa carpi,/,)        .           16
              Hand bones, (Ossa metacarpi, g,    .      .      8
              Finger-bones, (Phalanges digitorum manus, 7t,»', kt) 24
              Thumb bones, (Ossa policis, I,)      .     .      6
              Sessamoid bones, (Ossa sessamoidea) .             4
                                                     Total 68           68
  6 The inferior extremities contain 64 bones, viz:
              Thigh bones, (Ossa femoris, a,)      .     .      2
              Knee-pans, (Patelae, &,)                          2    ,
             Shin bones, (Tibiae, c,)  .      .     .     .      2
             Small bone of the legs, (Fibulas)     .     .      2
             Tarsal, (Ossa tarsi, e,)  .      .     .      .14
             Metatarsal, (Ossa metatarsi,/,)      .      .     10
             Toe bones, (Phalanges digitorum pedis, h, i, k,)   28
              Sessamoid, (Ossa sessamoidea)      .           _4
                                                     Total, 64"           64
6'
Grand Total "255" 
66
PHYSIOLOGY.
 
THE  HUMAN SKELETON.
67
  7* The second plate represents a back view of the male skeleton,
while the first is a front view.
                     a. The parietal bone.
                     6. The occipital bone.
                     c. The temporal bone.
                     d. The cheek bone.
                     e. The lower jaw bone.
                       Neck and Trunk.
                     a. The bones of the neck.
                     6. The bones of the back.
                     c. The bones of the loins.
                     d. The hip bones.
                     e. The sacrum.
                        Upper Extremity.
                     a. The collar bones.
                     b. The blade bone.
                     c. The upper bone of the arm.
                     d. The radius.
                     e. The ulna.
                     f. The bones of the wrist.
                     g. The bones of the hands.
                     h. The first row of finger bones.
                     i*. The second row of finger bones.
                     k. The bones of the thumb.
                        Lower Extremity.
                     a. The thigh bone.
                     6. The large bone of the leg.
                     e. The small bone of the leg.
                     d. The heel bone.
                     e. The bones of the instep.
                     /. The bones of the toes.

   8. It does  not fall within the plan of  the present work to
give a description of the individual  bones which go to make
up the skeleton ;  this must be sought in treatises on anatomy.
Still there are many points connected with the subject of ex-
treme interest  to every reflecting  mind, to which  the atten-
tion of the young may be profitably  directed, particularly as

connected with the marks of  wisdom and design  in  the Al-
mighty architect.   If our curiosity  is excited to see  a piece
of ingenious machinery, or a new engine, shall we neglect to
raise the covering which displays in the body the most stnk-
ing proofs of  design,  surpassing all art in  simplicity  and
effectiveness, and without any thing useless or superfluous. 
68
PHYSIOLOGY.
  9. If we compare the human body, as a work of art, with
any forms of human architecture, how vastly superior does
it appear.  A watch, or a musical automaton are highly in.
genious specimens  of  inventive  skill;  but where  is  the
watch  or the automaton  that  can,  without repair, for  the
space of  80 or 100 years, continue to perform its  movements
with regularity and precision.  And yet  how  much less
complicated is their  machinery, how vastly  more solid, and
durable the materials out of which they are formed !
  10.  If we examine a ship, we find it  built for passive mo.
tion, and for resisting force externally applied ;  a house or a
bridge is constructed  for solidity and firmness, on the prin.
ciple of gravitation; a railroad car is built for rapid motion,
and its wheels so adjusted, that  they may  not run off the
track; but  in the  human body,  we find not  only  securi-
ties against the gravitation  of the parts, provisions to with-
stand shocks and injuries from without, but at the same time,
the frame work is calculated to sustain an  internal impulse
from the muscular force which moves the bones as levers, or
like a hydraulic engine, propels the  fluids through the body.
  11.  The human  fabric is admirably adapted to resist  the
influences to which it  is subjected ;  in  other words, there ia
a nice balance between the  power of exertion and the capa-
bility of resistance.  A deer or a  giraffe is never injured by
any leap which their muscular powers enable them to make,
because the inert power of resisting  the shock, bears a rela-
tion to the muscular power with which they spring ;  and so
it is in man.  The elasticity of his limbs is proportioned very
accurately to his activity; he readily resists shocks and im-
pulses upon the  lower extremities, because they are adapted
to this end ;  but if the same  are applied to the upper, the
bones  are broken or  displaced,  because they are  adapted
rather for extensive and rapid motion, than for resisting vio
lent shocks.
  12.  It has been truly remarked that the foundation of the
Eddystone light-house, the perfection of human architecture 
THE HUMAN SKELETON.
69
 and ingenuity, is not formed on principles so correct, as those
 which have directed the arrangement of the bones of the feet;
 that the most perfect pillar is not adjusted with the accuracy
 of the hollow bones which support our weight;  that the in-
 sertion of a ship's mast into the hull is a clumsy contrivance
 compared with the connexions of the human spine and pel-
 vis ; and that the tendons are  composed in a manner supe
 rior to the improved chain cables of Bloxham.
   13.  As the  head is  the noblest part, and the brain the
 most essential organ of the animal system, let us first direct
 our attention to it.  The brain is liable to injuries, not only
 by sharp bodies touching  and entering it, but by a blow upon
 the head, which shall vibrate through it, without the instru-
 ment piercing the skull;  and such a blow would more effec-
 tually destroy a man's senses, than even if a sword pene-
 trated into  its substance.  It  is  obvious, that  if the bony
 case were soft it would  be  easily pierced ;  if of a brittle
 nature, it would be easily cracked, and if very firm and solid,
 like metal, it would ring and vibrate, and thus communicate
 the concussion to the brain.
   14.  To obviate these dangers, we find the skull composed
 of two plates  of bone, one  external, which is fibrous and
 tough, and one internal, so dense and  hard, that it is called
 by anatomists the glassy  table.   Now, as the brain is liable
 to be hurt  both by sharp and  blunt  instruments, the inner
 table is hard and brittle, calculated to resist any thing pene-
 trating ; while the outer  table is tough to give  consistence,
 and stifle the vibration which would take place,  if the whole
 texture were uniform.  This may be illustrated by  an ex-
 ample.   If  a  soldier's head be covered with a steel  helmet
or cap, the blow of a sword,  which does not penetrate, will
yet bring him to  the ground ;  bu't if it be lined with leather
and  covered with hair, the vibration is not transmitted to
the brain, and the wearer  escapes without injury. 
70
PHYSIOLOGY.
  a, the external,  6, c, the internal table; the intermediate cellular
texture, being soft and spongy, and conveying vessels and nerves from
one part to another.

   15.  It is  worthy of particular remark, how  the changes
in the structure of the bones of the skull are adapted to the
changes in the mind at different periods of life.  At birth,
the skull is  soft and yielding, there being considerable inter-
vals between the adjacent bones  of which it is composed ;
during childhood, it is highly elastic, so that the heedlessness
of that period  may not endanger concussion, to which it is
so often exposed  from falls ;  and during youth and up  to
manhood, the parts which are  exposed to the contact of ex-
ternal bodies, are thicker, and  the bones are still not firmly
consolidated at their  sutures  or seams,  by which they are
united.  As old age approaches, man grows more timid, and
is little  disposed  to  feats of agility or activity ; something
teaches  him that falls or blows, which  could once  be borne
with impunity, can no longer  be encountered  with safety;
and if we examine the skull, we find the two layers of bone
consolidated into one.  The  result of  which  is,  that con-
cussion at this  period would be far more dangerous than in
early life, or at the age of manhood.
   16. The sutures, or joinings of the bones of the skull, in-
terrupts, in a measure, the shock of the vibration  produced
by external violence, and also prevent fractures from extend-
ing as far as they otherwise would do, in one continued bony
 substance.   No one can examine the joinings of two of the
bones of the cranium, without admiring the  minute dove-
 tailing by which  one portion  of the bone  is inserted into,
 and  surrounded by the other, whilst that other pushes  its
 processes out between those of the first in the same manner; 
                THE  HUMAN SKELETON.             71
and tht fibres of the two bones  are  thus  interlaced, as you
might  interlace  your fingers.  But  this dove-tailing exists
only in the external plate ;  on the internal surface the bones
are simply laid in contact.
   17.  Sir Charles  Bell compares the human  skull to the
dome of a building, which is acknowledged to  be  one  of
the most difficult pieces of architecture.  The dome of St.
Sophia, in Constantinople,  built in the time of the Emperor
Justinian, fell three times during its erection; and the dome
of the Cathedral of Florence, stood unfinished 120 years for
want of an architect.  " Yet," says this  writer,  " we  may,
in one sense  say, that every  builder  who tried it, as  well as
every labourer employed, had  the most perfect model in his
own head."  The difficulty  in constructing a dome, is the
tendency of  the weight of its upper part, to disengage the
stones from  each other which form the  lower circle, and
crowd out the circular wall on which  it  rests.  This  is
guarded against, either by soldering  the stones into each
9ther, or by  hooping  them together  by strong iron hoops.
The dome of St. Paul's, in London, is secured  by  several
strong double iron chains, linked together  at the bottom and
along the sides of the cone.   Now, in the  bones which com-
pose the dome of the cranium, we find the edge of a bone at
the suture lying over  the  adjoining bone at one part and
under  it at  another ;  which, with  the dove-tailing  above-
mentioned, holds each bone securely in its place.  But while
a dome is calculated to resist one kind of force, viz. that
acting perpendicularly, or in the direction of gravity, the
skull is equally calculated  to  resist  forces operating in  all
directions.   Thus it can be shown,  that  nc other form  of
equal strength could  be devised.  When we reflect  on the
strength displayed  by the  arched film of an eggshell, we
need not wonder at the severity of blows which  the cranium
can withstand. 
PHYSIOLOGY.
  a, a, the  coronal, suture, from the Latin corona, crown, so called
from its situation on that part of the head, upon which the ancients
placed the laurel, or olive crown, given to the victors in their games.
It connects  the frontal to the parietal bones; b, the sagittal suture,
from a Latin word, signifying arrow, from its straight course.  It runs
from the middle of the frontal to the angle of the occipital bone, con.
necting the  two parietals; c, the lambdoidal suture, extending from
tne sagittal  suture down to the base of the brain on each side ; e, e,
the scaly overlapping of the temporal  upon the parietal bones; hence
called squamous suture.

  18. The frontal bone is one of the most important in the
skull.   It  has been compared to a clam-shell  from its shape,
and it forms the fore-head,  part of the temples, and the roof
of the orbits  of the eyes.  Like  the other bones, it is com-
posed of two plates, which often recede from  each other,
immediately over the nose to a considerable distance, leaving
a space between  them  called  the  frontal sinuses.   These
cavities  communicate with the nose, and are  supposed  to
increase the  intensity of  the sound of the voice, and also  to
render it more melodious.   The change of voice, observable
in a person affected with  a cold, is owing  to a closure of the
passage between the nose and cavity, preventing the access 
THE HUMAN SKELETON.
73
of the sound  to  this reverberating sinus.   Snuff-taking, it
has been supposed, injures  the voice by  obstructing this
canal.
  A front view of the frontal bone ; a, a, frontal sinuses ; b, the tem-
poral arch, beneath which lies the temporal muscle, which closes the
lower jaw ; d, the supra-orbitary hole for a psssage of a branch of the
fifth pair of nerves.

   19.  The shape of the head, as well as its size, varies great-
ly in different individuals.  There are also national peculi-
arities in the form  of the head, constituting a well-marked
national feature.  Thus  the  Caucasian race, to whom we
belong, is  distinguished by  the  beautiful oval  form  of the
head.   To this race the most  civilized  nations  belong, and
those which have ruled  over  the others.   The Mongolian
race, which  inhabits  China  and  Japan, is known  by its
prominent cheek  bones, flat face, narrow and oblique eyes,
straight and black hair, thin beard, and olive complexion.
   20.  The negro race has  a  compressed skull, and a flat.
tened nose, a prominent mouth, and thick lips ;  thus bearing
some resemblance in features  to  the monkey tribe.   The
North American Indian has a  very singular shaped head ;
it being high from the ear upward, and  short from the front
to the back.   The fore-head is not as  largely developed as 
74                   PHYSIOLOGY.
in the Caucasian.   The head of the Hindoo is much smaller
than that of the European, while that of the New-Hollander
is but little superior to that of the ourang outang, who roams
the same forests with  himself.  The New Zealanders have
heads nearly as large  as the  European ;  but the fore-head
is low, and the great preponderance of size  is in the back
part of the  head.
  21.  The heads of the ancient Egyptians, as appears from
an examination of mummies, closely resembled in shape and
size those of modern Europeans. Some of our North American
Indians are in the  habit of flattening their heads by binding
a piece of board on the fore as well as back part of the head,
in infancy.  From this custom, one tribe among the Rocky
Mountains, has received the name of Flat Head Indians.
The Choctaw  tribe were formerly in the habit of flattening
their heads in  the same way ;  but for some years past, they
have discontinued  the practice.  The heads of the different
European nations  differ  somewhat from each other; but a
common  type characterizes them all.
  22.  Not only the size, but the texture of skulls among dif-
ferent nations  varies.   The grain of the New Holland skulls
is extremely rough and  coarse; that of the Hindoos, fine,
smooth, and compact, more closely  resembling ivory.  The
Swiss skulls are open and soft in the grain, while the Greek
are closer, and finer.   It has been suggested that there may
possibly be a corresponding quality of brain in the individu-
als, which  may influence  the  mental, and consequently the
national  character.  This difference is generally attributed
to the effects of temperament.
  23.  The bones of the  cranium increase in extent, thick.
ness, and weight, from  the commencement till the termina-
tion of their development in adult age ; but after this time,
and till old age, they always  diminish in these three rela-
tions.  In advanced life, we often find them reduced to a
mere shell,  and perhaps perforated  in some places.  They
thus become much  lighter than in middle life. Meckel found 
THE HUMAN SKELETON.
75
the skull of a female, seventy  years of age, weigh but four.
teen ounces,  while  that of a girl, twenty years of  age,
weighed twenty-four ounces.  In  the early periods of life,
the whole  form of the head  is much  rounder than at an
advanced age ; owing, perhaps, to  the small development of
the face, which the skull envelopes in every direction.
   24.  The size of the cavity formed  by the bones of the
skull, is  always proportional  to  the  size of  the  organs it
lodges and protects.   The shape and size of the cranium de-
pend on the brain, and not of the brain on the  cranium.  The
soft parts model and adapt to themselves the  hard, and not
the hard, the soft.   The brain is formed before  the  case
which contains it, and it is not till after several years that
the bones of the cranium become perfectly consolidated.  In
a child of ten years of age, afflicted with dropsy in the head
from  infancy, and which was  exhibited a year or two since
in this city as a great curiosity, although the head measured
thirty-two inches in  circumference above the ears, yet nearly
the whole surface  was protected by a bony covering.
   25.  The   Spine.—However  admirably  the skull  may
appear to be adapted to the objects for which it was obviously
designed, the spine exhibits no less evidence of wisdom and
skill in the  divine Architect.  In addition to the firmness
which was required  in  the joinings of the bones of the cra-
nium,  a new principle is now introduced, viz. the attainment
of mobility or pliancy.  The spinal column  indeed serves
three important purposes ; it is the great bond of union be-
tween all the parts of the skeleton ; it  forms  a tube for the
safe lodgment%f the spinal marrow ; and lastly, it is a pillar
to sustain  the head.
   26. In  order to  accomplish these  various purposes, the
back bone, so called,  is composed of twenty-four distinct
bones, or vertebra, from  vertere, to turn, as the body turns on
them,  which are arranged into three classes, the cervical,
dorsal, and lumbar.   The first seven are the cervical, because
they belong to the neck; the next twelve are the dorsal, be- 
76
PHYSIOLOGY.
cause  they  belong to the back ;  and the last  five are the
lumbar, because they are situated  in the loins.  The bones
comprising these classes, differ somewhat from each other in
shape ; a description of the dorsal pieces will prove sufficient
for our purpose.
  A lateral i iew of the spine divided into its cervical, dorsal, and lum
bar portions.


   27.  Each  of these twelve  bones consists 0f a body, foui
articulating processes, two transverse processes, and one spi-
nous process.   The body is formed of soft and spongy  bone,
which  is circular before, flat towards the sides, hollowed out
behind into a crescent shape  for containing the spinal  mar-
row, and concave  above and below for the accommodation
of the intervertebral substance.   On the side of the bone are 
                  THE HUMAN  SKELETON.               77
situated the four articulating processes, each bone being con-
nected  with the two immediately adjoining it.  Two of these
processes are  situated  near  its upper surface  to articulate
with  corresponding processes belonging to the bone above,
and two are placed near its under surface to join with those
of the bone below.  The two superior articulating processes
of one  vertebrae  are  thus connected  with the two  inferior
articulating processes of another, and these points of union
not only co-operate  with  the intervertebral  cartilages in
keeping these two vertebrae  together,  but  permit  a slight
rotatory motion  of the one  upon  the other.   The spinous
process projects directly backwards from the body of the  ver-
tebrae, and may be felt externally by passing the hand along
the spine;  the two transverse stand out on either side, and
have  the ends  of  the  ribs attached to them.
  A vertebra of the neck ; a, body of the bone; b, the spinal process;
c, d, the  transverse processes double, showing circular holes for the
passage of the vertebral artery ; e, e. the superior; /, /, the articular,
or oblique processes; g, the  spinal hole for the spinal marrow.   The
roots of  the articfilar processes are hollowed  out above and below
into notches; and these, when the bones are fitted together, form aper-
tures on each side of the spine, through which the nerves pass out from
the spinal canal.
                                7* 
78
PHYSIOLOGY.
  A vertebra  of the loins ;  a, a, their bodies, larger and more spongy
than those of the others; b,  b, b, the superior ; c, c, c, the inferior ar-
ticular processes, strong and deep, the superior concave ; the inferior
convex ; d, d,  d, the  transverse processes, small  and  long, serving as
levers  for the attachment  of muscles ; e,  e, the spinous  processes,
strong, horizontal, and flattened at the sides; /, the spinal foramen.
  28. The vertebrae, as  I have stated, are not  in  contact,
but separated by  a considerable  interval, which is filled by a
peculiar gristly substance of a  highly elastic  nature, which
is pressed out from betwixt the bones,  and therefore  permits
them to approach, and  play a little in  the motions  of  the
body.  This compressible cushion of cartilage and ligament
serves indeed the triple purpose of uniting the bones to each
other, of diminishing and diffusing the shock  in  walking  or
leaping, and of admitting a greater extent of motion than if
the bones were in more immediate contact.  These  separate
vertebrae are firmly bound to each other in such a way as to 
THE HUMAN SKELETON.
79
admit of flexion and extension, and a certain degree of rota-
tion,  while by their solidity  and firm attachment to each
other, great strength is secured.
  29.  We can now readily perceive how great the influence
of these twenty-four joinings  must be in giving elasticity to
the whole column, and how much this must tend to the pro-
tection  of the brain.   Indeed, were it not  for the  interposi-
tion of  this elastic material, every motion of the body would
produce a jar to  the delicate  texture  of  the brain, and we
should suffer almost  as much in alighting  on  our feet, as in
falling on our head.
   30.  But there  is  another very curious provision  for the
protection of the brain, and that is the curved form of the
spine.  By looking  at the cut, you see that it is shaped like
an  italic f.   Now, suppose it  were straight, and stood per-
pendicularly, it is evident that when we alighted on our feet
it would recoil  with a sudden  jerk,  like a  straight steel
spring  pressed between the hands, from its extremities.  In
such a case, the weight  bearing  equally, the spine would
neither yield to one  side or the other, and consequently, there
would be a  resistance, from the pressure  on all sides  being
balanced.   But shaped as it is, we find it constantly yielding
in the  direction  of its curves ; the pressure is of necessity
more on one side of the  column than on the other, and its
elasticity is immediately  in operation without a  jerk.  It
yields, recoils, and so forms the most perfect spring, admirably
calculated to carry  the  head  without jar or  injury of any
kind.
   31. When we reflect  that the spinal column is  composed
of  so many separate parts, so nicely adapted to each other,
and kept in place by such a complicated  array of ligaments,
tendons, and muscles, we might expect that injuries and dis-
eases of the  structure would be very frequent.  But fortu-
nately  this  is not the case, except where undue  restraint and
confinement are  imposed ; and it is only within a  few years 
80
PHYSIOLOGY.
 since a change has been introduced into the system of edu-
 cation for young ladies, that the spine disease, so called, has
 become a common affection.
   32. Every one who has paid the least attention  to physi-
 ology, is aware that a certain degree of exercise is  as neces-
 sary to the growth and strength of the body, and  of every
 part of it,  as nourishment itself; and that if such exercise
 be withheld during the period of growth, the body never ac-
 quires its due form and proportions, and often is permanently
 crippled.   How cruel it is, then, to repress that overflow of
 life and energy, which nature has given to young creatures,
 to prompt them  to  that exertion which is necessary to the
 full development  of  their  physical  powers ;  and instead of
 allowing the young of both sexes to jump,  and skip,  and
 dance, and  play, as  nature dictates, to curb  all propensity
 to such vulgar activity, for fear that  they may not receive
 the praise of being well-bred.   How preposterous, unnatural,
 and  ruinous is the practice of  confining delicate females for
 hours together  every day to sedentary employment, the sure
 consequence of which will be, weakness of the body generally,
 and of the back in particular, especially if the seat be a stool
 which has no back, or even a narrow chair with a perpen-
 dicular back.
  33.  The effect of such a practice is, that in consequence
 of the fatigue induced by such a posture, the spine gives way
 in some part and bends, and in a  little  time the curvature
 beeomes  permanent.  And often when  a bend  has taken
 place in one direction, there immediately follows an opposite
 bend  above or below, to keep the centre of gravity of  the
 body always  directly over  the  base ;  the  curve accordingly
 thus  becomes double, like an italic /, and the distortion is
rendered  complete.
  34. The means employed to remedy this affection almost
invariably make it  worse.  In the  first place, strong, stiff
stays are put on,  to  support the back, as it is said ; and so
they do, perhaps,  while they are on ;  but as they supersede 
                THE HUMAN SKELETON.              81
the action of the muscles, placed there by nature as the sup.
ports, they cause these to lose their strength ;  and when the
stays are withdrawn, the muscles are found too weak to sup-
port the body.  Other  mechanical expedients may now be
employed, the back may be forcibly stretched by pullies, or
the patient may be kept all day and night lying on an inclin-
ed  plane.  The victim  of fashion may next, perhaps, be
placed under the charge of a regular spine doctor, who, by
means of pulleys, screws, paddings, stays, and close confine-
ment,  destroys what  little  chance there  still remains of a
cure.  A decline now sets in, and  the sufferer sinks into an
early grave.
   35.  Dr. Arnott justly remarks,—" it would be accounted
madness to attempt to improve the strength and shape of a
young race horse or grey hound, by binding  tight splints or
stays round its beautiful young body, and then tying it up
in a stall; but this is the kind  of  absurdity and cruelty
which has been so commonly practised in this  country to-
wards what may well be called the most faultless of created
beings."  This disease  may always be prevented by suitable
exercise,  and  the  same remedy so applied,  as directly to
strengthen the affected  part, will hold  out the best  prospect
of a cure.  Boys never suffer from the spine disease, because
steel and whalebone in them are never made to perform the
office which God designed for the bones and muscles.
   36.  The Chest.—The thorax, or chest extends above from
the first bone of the neck, by which it is connected with the
head, to the diaphragm  below, by which it is divided  from
the abdomen.   It  is  composed of  bones, muscles, and car-
tilages, so disposed  as to sustain and protect the most vital
parts, the heart and lungs, and to turn and twist with perfect
facility in every motion of the body, and to be constantly in
motion in the  act of respiration, without the least cessation
during a whole life.  In front, the chest is  bounded by the
sternum, or  breast-bone ; behind  by the  spinal  column, or
back-bone, and at  the  sides by  the ribs.   Below,  the 
82
PHYSIOLOGY.
diaphragm forms  a  membranous  partition between it  and
the cavity of the abdomen.  It is conical in shape, with its
apex above,  where, indeed, it is so contracted, that there is
barely room in  the  aperture to contain the tubes which go
to the  lungs and stomach, and for the larger  blood-vessels
that go and come from the heart.
  Thorax or chest ; a, the sternum ; b, b, the spine; c, c, the ribs, the
cartilages being in front.

   37.  The ribs are 24  in  number, twelve on each side, of
which the seven upper  are united to the sternum by car-
tilage, and are called true ribs; the cartilages of the other
five are united with each other, and are  not attached to the
sternum ; these are called false ribs ; all of them are con-
nected behind to the spinal column.   The ribs  increase in
length as far as the seventh, by which the cavity of the
chest is enlarged ; from the seventh, they successively dimin-
ish in length,  thus  diminishing  the cavity.   The direction 
THE HUMAN  SKELETON
83
of the ribs from above downwards is oblique, forming, as it
were, a bundle of hoops playing on each other.
   38. The curve  of the  ribs  diminishes considerably from
the first to the twelfth ; the second, however, is usually more
curved than the first.  The inferior ribs are very flat;  the
twelfth is sometimes straight.   The external surface of each
rib is convex, the  internal  concave.   Each rib on its outer
surface near the spine presents an oblique  ridge, occasioned
by the insertion of a muscle ;  and at this  point  there is  a
curvature somewhat abrupt, called the ailgle of the rib.
  Fourth rib; a, vertebral extremity, called the head, which is connect-
ed with the bodies of the two contiguous dorsal vertebrae.  At 6, the
bone is contracted, forming the neck; c, is the tubercle at the back of
the rib, which  is articulated with the transverse process of the ver-
tebrae ; d, the angle ; e, the sternal extremity ; /, a groove for the inter-
costal vessels.   This will serve for a general description  of the ribs.
Twelfth rib, nearly straight.
   39. Sternum.—Between  the forward ends  of the  ribs,
directly in front of the  chest, lies  the sternum, or breast.
bone.   It is light and  spongy,  depending chiefly  for its
strength on the numerous ligaments which cover it.   In the
child,, it is divided  into eight pieces by cartilaginous portions, 
84
PHYSIOLOGY.
which as life advances, are  reduced to three; and, in old
age, are united into one.  It terminates below in a  sharp.
pointed cartilage, which lies  over the stomach, and may be
felt externally.   It  is  somewhat hollowed beneath  at its
upper end for the  passage  of the treachea  or  wind-pipe
which lies directly  under  it; and  on each  side  there  are
seven oval depressions  for admitting the cartilaginous  ex-
tremities of the first seven ribs.
   40. The sternum in this cut consists of two bones.   The
first is broad and thick above, and contracts as it descends.
It is convex before and concave behind.  At the upper angle
a  the collar-bone is articulated ; b, the articular surface for
the cartilage of the first rib ;  b, for second rib ;  c, d, e, f, g,
mark the articular surfaces of the 3d, 4th, 5th, 6th, and 7th
ribs ; h, the ensiform cartilage, terminates the lower extrem- 
THE HUMAN SKELETON.
85
ity of the sternum.   In old people, this cartilage is often
changed into bone.
   41. The  manner  in  which the ribs are attached to the
sternum by  means of slips of elastic cartilage,  is worthy of
particular notice.   It  is  to this  circumstance that  it is
owing, that  the ribs are  so seldom injured by blows and falls ;
for if they were wholly bone from one extremity to the other,
life would be  endangered  by any  accidental fracture,  and
even the rubs and jolts to which we are continually exposed,
would be too  much  for their  delicate and  brittle  texture.
When we lean forward  or to one side, the ribs accommodate
themselves not by a  change of form in the bones, but by the
bending of the cartilages.  It is owing to this elasticity that
the blows of boxers so seldom succeed in fracturing the ribs ;
as they  yield in proportion to  the violence of the force in-
flicted.   But this is  not the case in old age.  Then the car-
tilages of the ribs become bony, and the whole arch unyield-
ing and inelastic ; so that  blows which formerly would have
caused  little or no injury, are now attended with fracture of
the rib.  The influence of the elastic structure  of the ribs,
in the action of breathing, is highly interesting and import-
ant, and will  be  fully explained when we come to treat of
Respiration.
   42. The next division of the trunk is called  the pelvis or
basin, which consists of a circle of large firm bones, situated
between the lower  portion  of  the  trunk and  the inferior
extremities.   They are the sacrum, the coccyx, the ilium, the
ischium, and  the pubis.   The  ilium  forms  the upper, the
ischium the  lower, while the pubis is situated at  the fore part
of the pelvis ; and  each  one of these bones contributes to
form the large and  deep socket, for the head of the thigh
bone.   The pelvis not only affords lodgment for the organs
contained within its cavity, but it also sustains  the entire
weight of the body, and furnishes sockets for the heads of the
thigh bones  to roll in, and a broad surface for numerous mus.
cles to spring  from. 
86
PHYSIOLOGY.
The pelvis.
  43. The last division of the  body comprehends the upper
and lower extremities.  The upper consist of the shoulder,
arm, fore-arm, and hand.  The bones composing the shoulder
are two, the clavicle, or collar bone, and the scapula, or the
blade bone.   The clavicle, named from its resemblance to a
key, resembles the italic s, and extends across the upper part
of the chest, from  the shoulder to the breast bone, and it
serves not only to sustain the upper extremity and  connect
it with the chest, but also  to prevent its falling forward upon
the thorax, and  to afford a fixed point for steadying  the arm
in the performance of its various actions.
  44. The scapula, or  shoulder blade, is a large, flat,  trian-
gular bone placed upon the upper and back part of the  chest,
and extends from the second to the seventh ribs.  It lies em-
bedded in  muscles, and  has no  connection with any  other
bone except the clavicle at a single point.   It is separated
from the thorax  by a  double layer of muscles, on which it is
placed as on a cushion.   It serves for the attachment of six-
teen muscles which  go to the ribs, the bone of the tongue,
the arm, the head, and the spine.   It thus serves not only as
a support, but a fulcrum for every action of the superior
extremity. 
THE HUMAN  SKELETON.
87
  Scapula, a, superior angle ; d, the glenoid cavity, or socket for the
round head of the arm bone ; ?», the aeromion process : n, the coracoid
process, which serve  to protect the joint; /, the base ; g, the costa, or
inferior border, and h, the superior border of the triangle ; I, the spine •
o, the semi-lunar notch, for the passage of an artery, vein, and nerve.

  45. As a general  rule, in the joints, strength and security
are sacrificed,  in  some  degree, to obtain  great freedom and
latitude of motion.   Accordingly, we find  that the  shoulder
joint, which allows of more extensive motion than any other»
is also more frequently dislocated.   In the hinge joints, such
as the knee and  ankle, such an  accident is  comparatively
rare.  Where  a bone is dislocated, a regularly educated sur-
geon should, if possible, always be employed to reduce it, as
there is great danger in  trusting to a natural  bone-setter, so
called, who is entirely ignorant of the anatomy of the parts.
  46. The os  humeri, or arm bone, is of a cylindrical shape,
and  forms at the elbow a  perfect  hinge-joint with  the two 
88
PHYSIOLOGY.
bones of the fore-arm, called radius and ulna.   This bone is
susceptible of all kinds of motion, elevation, depression, ad-
vancing, retreating, circumlocution, and rotation.   Its scap-
ular extremity is lodged in a strong membraneous bag, called
the capsular ligament, and  when  the  arm is raised up, the
bone slides downward in the glenoid cavity, and thus distends
the lower part of the capsular ligament.  In every motion of
the arm,  except in  carrying  it  backwards,  the scapular
readily moves or follows it; it is therefore during motions of
the latter kind, that  dislocations of the joint are most apt to
occur.  If, therefore, the scapula could always  follow the
motions of the  arm, it would  rarely  be forced  out of its
socket, and then only by extreme violence.
   47. In the fore-arm we  find two kinds of motion, one al
the elbow, backward and forward, and also a rotary motion, by
which the  palm is turned upward  or downward, as occasion
requires. These motions are called supination and pronation.
Flexion and extension of the arm are performed by means of
the ulna, which being articulated, with the os humeri, by a
hinge joint, carries the radius  along with it in  all its move-
ments.   Now while the larger part of the ulna  is above, the
larger part of the radius is  below, so  that while the former
presents a large surface for articulation at the elbow, the lat-
ter does the same at the wrist,  and this inverse arrangement
also contributes to  the uniform diameter of the fore-arm.
While the fore-arm is thus attached  to the os humeri, the
radius is attached to the wrist;  so that when  we turn the
palm of the hand, the radius rolls on the ulna  carrying the
hand with it.   Indeed  so admirable is this contrivance, that
both  motions may be performed at the same time, for while
we are  bending the arm, we may also  be rotating or turning
it upon its  axis.  To facilitate  these  motions, it will be
observed that near the elbow, a tubercle of the  radius plays
into a socket of the ulna, whilst  near the wrist,  the radius
finds the socket, and the ulna the tubercle. 
THE HUMAN SKELETON.              89
g, the ulna;  a, the radius.
  48. It has been remarked that the ulna has a hooked pro-
cess, the olecranon, e, which catches round the lower end of the
humerus, forming with it a hinge joint.  The radius also, has
a neat, small, round head, b, bound to the ulna by ligaments,
which, as it turns, carries the hand, which is attached to its
lower extremity along with it.   Now in animals that  have
solid hoofs, such a motion would be useless and a source of
weakness, accordingly we find  these bones united together
and  consolidated in such animals.  By an examination of
these bones alone, the anatomist is able to determine whether
the animal to which they belonged, perhaps thousands of
years  ago,  was carniverous  or  graminiverous,  that  is,
whether he was  an animal or a vegetable feeder ; whether he
had claws or  hoofs.  If he finds merely the end of the radius,
and notices in it a smooth  depression where it bears against
the humerus, and the smooth surface that turns on the cavity
of the ulna, he concludes at once, that the animal had a paw,
and  a  motion of the wrist which implies claws.   It was in
this way that Cuvier and Buckland made those  singular and
interesting  discoveries in  relation to  antediluvian fossil
bones,   which have  given such  importance to geological
researches.
   49.  But let us examine this point a little further.   If the
                          8« 
90
PHYSIOLOGY.
examination of a single bone, or even the end of a bone, like
that of the radius, shows that the animal to which it belonged
was carniverous, like the tiger, lion or leopard, it also shows
the form of all the other bones ; not only that the animal had
teeth to rend his prey, and claws to hold it, but a spinal col-
umn to admit of such motion, such writhing and turning as
is necessary to secure it, and such a stomach and intestines
as are adapted to digest it, in  short, such as belong  to the
carniverous class.   How beautiful is that process of reason.
ing, and  how interesting that science which enables us from
a small portion of a skeleton, to determine the existence of a
carniverous  animal, of a fowl, or a bat, a lizard, or a fish;
which teach us the wisdom and the extent of that plan, which
adapts the members of every creature to its proper office;
which exhibits a system extending through the whole  range
of animated beings, whose motions are conducted by the ope-
ration of muscles and  bones.
  50. Twenty-nine bones enter into the composition  of the
human hand, of which eight constitute the wrist.   The meta-
carpal bones support the fingers, and are  four in  number, the
thumb being directly articulated with the wrist.   From this
arrangement there results great strength, mobility, and elas-
ticity.   Indeed, it  may be said, that on the length, strength,
free lateral motion, and perfect mobility of the  thumb, de-
pends the power of the human hand.   In strength it is said
to be equal to that of all the fingers, hence it is called pollex,
from "pollere" to have much strength.   If we  examine the
thumb of the monkey, we find  that it extends no farther than
to the root of the fingers.   The fingers would be compara-
tively of  little use, were it not for  the fleshy bed of the
thumb. 
THE HUMAN SKELETON.
91
Bones of the hand,
   51.  The bones of the lower extremity consist of the thigh,
leg and foot.  The thigh bone (os femoriz,) is the longest
bone of the human skeleton, and is remarkable for  its great
strength, supporting, as it does, the whole  body, and often
several hundred pounds in addition.  The hip joint is a perfect
specimen  of the ball and socket joint.  This is for the pur-
pose of giving great extent and variety of motion to the legs,
as in walking.   The end of the hip bone  is perfectly round
like a  ball, and  covered  with  a smooth, shining cartilage;
and this is received into a deep cup, also lined with  cartilage
and  moistened with  the synovial  fluid.   Besides  all  this,
there are  strong  ligaments all  around,  binding the bone
firmly  in its place, so that it is a very rare thing  for it to be
dislocated.
   52. The knee is a hinge joint of singular construction. The
rubbing parts are flat and shallow,  and therefore would
easily get out of place, were it not  for the very strong liga-
ments which surround it.  When the ligaments on the inside
of the joint are too weak, a person is said to be knock-kneed,
because the knees knock together.  In weakly children, this
deformity may frequently be cured by exercise.   It can also
be shown that, owing to the air being completely shut out of
the joint, forming what is called a  vacuum, the bones of the
knee are held together by a constant pressure of the atmos-
phere equal to sixty or seventy pounds.   On the fore-part of 
92
PHYSIOLOGY.
the knee, is a movable bone of a flat, round shape, called pa-
tella, or knee-pan, over which a cord or tendon passes, which
is made by a contraction of all the muscles on the fore part
of the thigh.  This serves as  a pulley, and enables the mus-
cles to act to greater advantage, by increasing the distance
of the rope from the centre of motion.
  53.  The leg  below the  knee, is composed of two bones,
tibia  and fibula,  of  a  three-cornered  or  angular shape,
like those of the  fore-arm ; and  the  design no doubt is, to
form  a  pillar   of greater  strength  than  one bone  would
make;  and also to furnish a greater  surface  for the origin
and attachment of the  numerous muscles required  for the
feet.   The ankle, like the wrist,  the elbow, and the knee, is
a perfect hinge of great strength.   In front of it there is a
narrow strap,  or ligament, which  binds  down the cords
which go  to move the toes.   There  is a small  groove  just
within the inner ankle, for the  passage of a tendon, exactly
like a little pulley.  The heel is a lever for those strong mus.
cles to  act by, which form the calf of the leg.  It is the ac-
tion of these muscles, pulling on the heel, that lifts the body,
in walking, dancing, standing on the toes, &c.  In the negro,
the heel is longer than in any other race  of mankind.
   54.  The bones of the  foot  are divided  into the tarsus,
which is composed of seven bones, reaching from the heel
to the middle of the foot.  The metatarsus  consists of five
long  bones, parallel  to each  other, which  extend from the
tarsus to the roots of the toes.  The  bones  of the toes are
called phalanges, from  being  in the form  of  a phalanx.
There are in  all thirty-six bones in  the foot, and  as each
bone  forms a joint, and as  each joint not only permits
motion, but bestows  elasticity, the obvious design  of this
number is to render the  foot elastic, and  thus  save the body
from  shocks.    It should  be recollected  that each bone is
tipped with cartilage, that the fibres composing cartilage
are disposed longitudinally or perpendicularly  to the surface
of the bone and the pressure made upon it;  thus acting like 
THE HUMAN SKELETON.
93
an infinite number of springs of the most delicate structure.
Besides this, the foot is a  double  arch ; it is  arched from
the toes to the heel, and from side  to side, and the bones are
so wedged together, and bound  to each other by ligaments,
that solidity is combined with elasticity and lightness.
  55. In reviewing the human skeleton, we cannot  but re-
mark the nice adaptation of all the parts to each other, and
to the shares which  they have  respectively  to bear ; how
the objects of strength and lightness are combined, and how
the nature and strength of material in different parts are so
admirably  adapted to the  purposes  which  the parts are
designed to serve.   No one can contemplate  the marks of
wisdom  and design displayed in  the osseous fabric, without
being led insensibly to acknowledge the hand  of an all-wise
and benevolent Master Builder. 
94
PHYSIOLOGY.
  Questions.—Of how many bones does the human skeleton consist ?
How are they divided ?  What is a natural skeleton ?  What an arti.
ficial ?  What uses does the skeleton serve ?  What  bones are said to
be symmetrical ?  How many bones are there  in  the  head ?—in the
trunk ?—in the  upper extremities ?—in the  lower ?   How does the
skeleton compare with works of human art ?  How is the  brain pro-
tected from injuries ?  How many plates do the  bones of the  skull
contain  ?  What changes  does age produce  in the bones  of the
skull ?  What are  the  sutures ?—what their use ?   To what does
Sir Charles Bell compare the skull ?  How does it resemble a dome ?
What are the principal  sutures ?   Describe the frontal bone.   What
is said  of the  national  peculiarities in  the shape  of the head ?
What shaped heads had the ancient Egyptians ?  Does the  texture
of skulls vary ?  What changes occur  in the  thickness  and weight
of  the  bones of  the skull ?   What is  said  of the cavity of the
cranium ?  What is formed  first,  the brain or the skull ?  What uses
does  the spine serve ?  Of how many bones does it consist ?  What
are they called ?  How divided ?  Describe a vertebra. What sort of
substance is placed  between the  vertebrae ?—its use ?  Why is the
spine curved like an ft  What is  the spine disease?—its causes?—
its cure ?  What  effect have  mechanical remedies ?  Do boys ever
have it ?  Describe  the  thorax. How many ribs are there ?  What
are true ribs ?   What false ?  Which are the largest ?  Where is the
sternum situated ?   Describe it.  What  is the use of the cartilages
between the sternum and ribs ?  What  is the next  division of the
trunk?  What is the pelvis ?—Of how many bones composed ? What
its use ?  The last division ?  Where is the clavicle ?—its use ?  Des.
cribe the scapula,—its  use ?  Is great  freedom of motion compatible
with great  strength in a joint ?  Describe the os humeri.   Of how
many kinds of motion susceptible ?  Describe the fore arm ?—the radius?
—the ulna.  What  is the contrivance for rotating the arm ?  What is
the olecranon ?—its use ?   In graminiverous  animals, how are these
bones  constructed ?  How  can the anatomist tell to what  kind of
 animal any bone belongs ?   How many bones are there in the hand ?
 —how  many in the wrist ?  What is said of the thumb ?—Of the
 fingers ? What are the bones of the lower extremity ?  Describe  the
 hip joint ?—the knee. Does  the pressure  of the atmosphere affect the
joints ? Describe the leg below the knee?—the ankle.  How are the
 bones  of the foot divided?  How many bones  in the tarsus?—the
 metatarsus ?—the phalanges ?—the foot ?   What is the use of so many
 bones ?  What is the use of the arched form of the  foot ? 
CHAPTER  VII.
             PROPERTIES OF  ANIMAL BODIES.

  1. There are various properties which distinguish living
from dead animal matter.  Both, in common, possess certain
physical properties, such as weight, extensibility, flexibility,
&c. ; but  living matter  has  certain  physiological or  vital
properties  peculiar to it.   It  is these which bring it under
the influence of external agents.
  2. All the phenomena of life are the effect  of impressions
made upon the various organs of the body, by external  or
internal  agents;  and each organ has its own proper sti-
mulus.   Thus the eye  is stimulated by light;  the ear by
sound, the nose by odours, the organs of taste by condi-
ments, &c.
  3. The chick  in its shell is developed by the influence of
heat;  the  seed  germinates under  the combined  effect of
warmth  and moisture ;  and so the growth of the human
body requires the application  of the appropriate stimulants,
such as food, drink, air, exercise, &c.
  4. Every tissue and  organ  has its own mode of activity.
For example, the lungs  react under the influence of the air;
the heart under that of the blood ;  the muscles under that of
the will ; the stomach under that of food, &c.  Every gland,
though  supplied by the same  blood, is excited to secrete  or
form that particular fluid for which it  was so designed ; and
why the liver does not secrete urine and the kidneys bile, it
were useless to inquire.
  5. This property of living matter has three   principal
modifications in the solids and fluids, which have been called
sensitive, motive, and alterative.  By the sensitive powers, are
meant sensibility and its modifications ;  the motive  are  con-
tractility and expansibility; the alterative are those which 
96
PHYSIOLOGY.
preside over the formation  and nutrition of the  different
organs and tissues of the body.
   6.  Sensibility belongs exclusively to animals provided with
a  nervous system.   It enables us  to  receive  impressions
from external objects, or from changes going on in our own
bodies ;  and  to  the  accuracy  of this  power,  we  owe our
ability to guard ourselves  against the influence of noxious
agents.
   7.  Sensibility may be divided into two kinds, general and
special.  By general sensibility is meant, that universal sense,
of which we are  conscious over the  whole body, in the
mouth, &c.  The  same also exists  in  the  interior of the
body, and conveys  to the mind a knowledge of the wants of
the system ;  and when  disease attacks any part, it immedi-
ately  apprizes us of the danger, in order  that we may take
early  measures to remove  it.  By  special  sensibility, we
mean that property which renders the eye sensible to  light,
the ear  to sound,  &c.   Every organ has its  own special
sensibility.
   8.  The  brain  is the common centre of sensibility, both
general and special.  No impression  can be  felt on  any part
or organ, unless it has a connection with the brain.  If the
nerves going from that  organ are divided, or if their  function
is  lost from  palsy or any cause whatever, there can be no
sensation perceived, as  none is excited.
   9.  By perception is  meant, the faculty which the  brain
has of perceiving  or taking notice  of these impressions.
Perception and thought then, are owing to the property of
matter, called  sensibility.   Without  it, we  would be like
stocks or stones, alike unconscious of pleasure or of pain.
   10.  According  to  some  physiologists,  there  is  another
kind of sensibility, which  is termed  organic.  This resides
in  the  several internal  organs, where it is called into  exer-
cise, and does not  require the action  of the  brain.  It de-
pends for nervous influence upon the great sympathetic nerve.
That  such a kind of sensibility exists is very probable, but 
            PROPERTIES OF ANIMAL  BODIES.         97
we have no proof of its existence in our  own  feelings and
consciousness, as we have of the other  kinds of sensibility.
   11.  By organic sensibility, we mean that the stomach  is
sensible  to food, the heart to the blood, &c. ; and that this
feeling is confined to the organ and not  transmitted to the
brain.    It  presides over the process of digestion, circulation,
secretion, absorption, and nutrition.
   12.  Although  the internal  organs  of  the body are not
sensible  to  the presence of the fluids or solids with which
they are usually in contact, yet if foreign  bodies are brought
in  contact with  them, or  substances calculated to injure
them,  we are  immediately made sensible  of it.   Thus let a
person drink  a quantity of brandy, or spirits, to which he
is not accustomed,  and he will at once feel a  sensation of
heat in the  region of  the stomach, altogether  unnatural  to
that organ.  This proves that ardent spirits are not designed
for the drink of man, and are therefore hurtful.
   13.  Certain parts of the body, which, in a healthy  state,
are  nearly  insensible ; yet,  by disease, become the seats of
acute  pain.   This  is  particularly the  case with the  bones,
cartilages,  and ligaments—parts usually wholly destitute of
feeling.
   14.  Contractility,  or the property of contracting, is the chief
motive power of the  system.   It exists  in various degrees,  in
different kinds of animal matter.  That element which pos-
sesses  it in  the greatest  degree  is fibrin; and  those tissues
which have the most fibrin, have the greatest degree of con-
tractility.   The same is true of muscles, for the heart, which
is in constant  motion, is almost pure fibrin.
   15.  It is supposed  that the  coagulation of the blood  is
owing to this contractile power of  fibrin.  In the living
vessels, the  blood  is kept fluid by the vital influence  of the
walls of the vessels  themselves ; but as soon as it is with-
drawn from this influence, the particles of  fibrin immediately
rush together  and form a solid mass.
   16.  Those  tissues which  contain but little fibrin and are
                            9 
»8                    PHYSIOLOGY.
made up  mostly of gelatine,  as  the membranes, cartilages,
skin, vessels, &c, have but a slight  degree of contractility ;
that they possess it, in  some measure, is evident from  the
contraction of blood-vessels by the application of stimulants.
  17. There are two modifications  of contractility ; one of
which depends for its exercise on the  brain, and  the  other
does not.   For example, if we wish  to bend the arm, we have
but to transmit  to the muscles of the arm, through the nerves
with which it is  supplied from  the brain, a volition, or act
of the will, to that effect, and the arm bends.  Here we per-
ceive that the influence of the brain is necessary to contrac
tility or motion.
   18. When  certain muscles are deprived  of this  power of
contracting, they are said to be paralyzed, or the limb is
called paralytic.   When  they have it in excess, they are in
a state of spasm, or convulsion.  We  see such a state often
brought on by excessive drinking.  There is no cure for  this
but by entirely  breaking off the habit.
   19. The other kind of contractility belongs to every part
of the body.   It does not depend  for  its  existence on the
brain, nor is it at all  under the  influence of the will, or
accompanied  with consciousness.   Thus the  heart and the
stomach  contract constantly under the application of their
proper  stimuli,  but the brain is not conscious of it; their
action is  entirely beyond its jurisdiction.  This form of con-
tractility has  been called insensible.
   20. It is owing  to the insensible, organic  contractility,
that the blood circulates in the capillary vessels ;  the  lymph
and the  chyle in  the absorbents and  lacteals, and all the
secreted  fluids  through the vessels  that prepare them.   In
all animals destitute of a heart, the  fluids can only be moved
by this  insensible  contractile  power.   A  similar  force  is
supposed  to exist in the vessels of plants.
   21. These  two kinds of contractility, viz.,  the sensible
and insensible,  have been compared to the hour and minute
hands on the  dial of a clock, which are both moved by the 
PROPERTIES OF  ANIMAL BODIES.          99
same power ; yet the motion of one is insensible to the eye,
while that of the other is distinctly visible.
  22.  By means of the alterative  powers,  all the changes
which take place in the composition of the  solids and fluids
of the body are effected.   By these, the food is changed into
chyme, and then into chyle ;  chyle into blood,  and blood into
bone, muscle, cartilage, &c.   By these, animal  heat  is pre-
served uniform ; and the solids preserve their cohesion, and
the fluids their fluidity.  In short, it is these  powers that
for  a time successfully resist the agency of chemical laws.
  23. Some physiologists attempt to account for every thing
that takes place in  the body, on  chemical  or mechanical
principles.  But the vital laws, or organic forces, form com-
pounds which could never be produced by chemical affinity.
In fact, they are antagonistic  forces, fighting against each
other.  The chemist can decompose  blood, bile, saliva, al-
bumen, gelatine, and fibrin,  but he can not re-form one of
them.   He can no more make a piece of bone, than  he can
make a diamond.
  24. The physical properties of the animal  tissues  are
usually reckoned as five in number, viz. elasticity, extensibil-
ity, flexibility, imbibition, and evaporation.
  25. Elasticity is one of the  physical properties of animal
matter.  It is that power which tends to restore parts that
have been stretched or extended to their former  state.  It is
possessed in the greatest degree by the cellular tissue, which
enters largely into the composition of all the structures in
the body.   All the organs  and membranes  of the  body are
in a constant state of extension.   All the hollow organs, as
the stomach, gall-bladder, and blood-vessels  are kept distend-
ed  by  the  volume  of  their contents.   The extensor and
flexor muscles, when in a state of inaction,  are in a state of
extension.   If such were not the case, all the organs would
contract and shrink to a comparatively small  size.
  26. When  the  stomach is empty,  its sides  contract till
they almost touch  each other.  When a muscle is cut, the 
100
PHYSIOLOGY.
wound  gapes open, owing to the two parts  receding.   The
cartilages of the ribs are highly elastic, and this  facilitates
much the function  of respiration.   The same is true of the
substance of the lungs themselves.  The cartilages between
the bones and the spine are highly elastic.   The loss of this
elasticity makes a difference of an inch or more between the
height of a man in the morning and at  evening.    It is
not unusual for a very tall person  to  lose an inch in height
by  dancing all  the evening.   During sleep, the force of
elasticity restores  these cartilages  to their  usual dimen-
sions.
  27.  The elasticity of the arteries contributes much to the
circulation of the blood.  The blood as it is forced  into these
vessels, is constantly reacted upon,  by their  elastic coats,
and in this way driven  along towards their termination in
the capillary vessels. The same power assists  in circulating
the lymph and chyle in the vessels which contain them. It
is the last function that  ceases to act, and it is not wholly
destroyed even at death.
  28. Flexibility and extensibility are  properties existing in
various degrees in  different parts of the  body.   The  liga-
ments, or little bands, which tie together the bones, are more
flexible than any other part.  By observing the astonishing
feats of the rope-dancer, we see how flexible these  parts are.
The tendons which connect muscles  with  the bones  they
move, are capable of little, if any extension.  If they stretch.
ed, when  the muscles to which they  belong  contract, the
limbs would not move, and the  moving force  would thus be
lost.
  29. Imbibition, is another power possessed by living animal
bodies.  It means the act of drinking in, or taking up fluids,
which may be in contact with any part.   For example, if a
certain  fluid be placed  in  contact with an animal tissue, it
will penetrate into  the latter, as water would into  a sponge,
and this property  is possessed  by all  the soft tissues  to a
greater or less  extent.   All the serous membranes absorb 
PROPERTIES  OF ANIMAL BODIES.        101
with  great  facility.  The epidermis or cuticle  of the skin
permits fluids to pass with difficulty.   That water is taken
up in considerable quantity, however, is proved  by the fact,
which has often been proved by experiment, that a man in-
creases in weight by remaining for a considerable time in a
warm bath.
  30. The following experiments prove the nature of this
process.  If we fill the intestine of a chicken with milk, and
place  it in  water,  we shall see the  milk pass  through its
coats  into the water, and the water will pass  through in an
opposite direction to supply its place.  In the same manner,
if a bladder be filled with hydrogen gas, and suspended  in
the air, in  a  short time it will be found to be mixed with
atmospheric air, which  has passed through its coats.   The
result of all the experiments on this subject seems to show,
that  when  any cavity  containing a fluid is immersed  in
another fluid less dense than the former, there is a tendency
in the membrane to expel the denser, and absorb the thinner
fluid.
  31. Many of the animal tissues are indebted for their
physical properties to the water they imbibe.  If they are
deprived  of this water,  they  are unable to  perform their
proper office and function, until they are again supplied with
it.   Hence  one important reason why the system craves
water, and  why the  want  of  it produces such  distressing
effects.
  32. By the functions  of man, we understand the  opera-
tion of the various organs ; in  other words,  his vital actions.
Life is made up of a constant  series  of these actions, from
the period of birth to the moment of dissolution.  Physiol-
ogists have attempted to define life ; but the best definition we
can give is,  that it is an assemblage of actions.  Indeed, the
essential nature of life is an impenetrable mystery, and not
a proper  subject for  philosophical inquiry.  As the  fluids
are as much endowed with life as the  solids, it cannot be
said that life  is the " effect  of organization ;" besides, a
                              9* 
102
PHYSIOLOGY.
dead man  has the same  organization  as when alive.   It
is, therefore, far better to confess our ignorance, and  say
with John  Hunter,—" life is a property we do  not under-
stand."
  33.  All the actions or functions of the body are mutually
dependent  on each other.  They constitute a  circle, with.
out beginning or end.   The motion of  the blood depends on
the action of the heart and arteries ; the action of the heart
and arteries depends  on the presence of  blood.  The heart
cannot act without the action of the lungs ; the lungs can-
not act without the action of the heart.  Neither lungs nor
heart can act without the influence of  the brain ; the brain
would  have no influence, were it not for the action of  the
lungs and heart.
   34.  Thus the steam of a steam-engine  works a bellows
which blows a fire that produces the steam.  It would be as
difficult in this  case, as  in that  of  the animal  functions to
say, which of these might be easiest dispensed with.  If we
spare the bellows, the fire will not burn ; if we spare the fire,
the steam  will not be raised ; if  we spare the steam, the bel-
lows will not be worked ; so that if we spare either fire, bel-
lows, or steam,  the machinery must stop.   So  it is in  the
human body.
   35.  The functions which fall  within the  scope of this
work  to notice, may be divided into three  classes ;  1, vital;
 2,  nutritive ;  and 3, sensorial.   The vital functions  are those
 which are every moment essential to preserve life. They
 also may  be considered as three in number, viz :  innerva-
 tion, circulation, and  respiration;  or  the functions of the
 nervous system, those of the heart, and  those of the lungs.
    36.  The nutritive functions preside over the growth  and
 nutrition of the body.   By their influence,  the food is as-
 similated,  and becomes a part of our  structures ;  while all
 the waste  materials and worn-out elements are expelled from
 the system.  It thus embraces four functions;  digestion.
 absorption, nutrition,  and secretion. 
PROPERTIES OF ANIMAL BODIES.         103
   37.  The sensorial functions  are  sometimes  called  the
functions of relation, because it is through them that  we
hold  communication with the external  world.  They com-
prise the sensations, intellectual  operations,  and voluntary
motions.   It is the sensorial  functions that raise man  above
all other  animals.   In   proportion  as  they are  more or
less perfect,  organized  beings  ascend  or descend  in  the
scale of  existence.   In  the lower  animals, they  are limit-
ed to the  circle of physical wants  ;  but in man, they con-
fer moral  and  intellectual faculties, which are  his  noblest
attributes.
   38.  These  functions  have  the brain  as  their  common
centre.   They  can  be  improved  to an  almost indefinite
degree  by education  and habit.   We see this in the perfec-
tion which some of the senses  acquire when others are lost;
in the  gigantic intellect of a Newton or a Locke, whose
mental efforts at  first were probably as weak as  those of
other men.   In all  such  cases, individuals  acquire  superi-
ority chiefly by education and constant practice.
  Questions.—How is living animal matter distinguished from dead ?
What properties are possessed in common ?  What are the phenomena
of life owing to ?  What developes the chick ?  What properties does
living matter possess ?  What is understood by the sensitive powers ?
—the motive ?—the alterative ?   What characterizes animals provided
with a nervous  system ?  How many kinds of sensibility are  there ?
What is  meant by  general sensibility ?—by special ?  What is the
common centre of sensibility ? What is perception ?   What is organic
sensibility ?  Are the internal organs sensible  to the presence of their
contents ?  How are such parts affected by disease ? What  is con-
tractility ?  What element possesses it in a great degree ?   How many
kinds of contractility are there ?   When is a limb said to be paralytic ?
When in  spasm ?  What are the alterative powers ?   What their use ?
Is the body under the influence  of chemical laws ?  What are the
physical properties of the animal tissues ?  What office does elasticity
perform ?  Describe  its  operation in cartilages, arteries, &c.  What
are the uses of flexibility and extensibility in the animal body ?   What
is imbibition ?  Do the serous membranes absorb ? What experiments 
104                      PHYSIOLOGY.
prove imbibition ?  What are  understood by the  functions of man ?
What is life ?  Are the  fluids  alive as well as the solids ?  Are the
functions  of the body dependent  on each other?   Illustrate this do.
pendence ?  How  are the functions  divided ?   What are  vital  func.
tions?—nutritive?—sensorial?   What raises man  above all other ani.
mals? 
CHAPTER VIII.
    RELATION OF ANIMAL BODIES TO HEAT, LIGHT, AND
                      ELECTRICITY.

  1. The relations which animal bodies have  to heat, light,
and electricity, are highly interesting, and worthy of particu-
lar notice.   To a certain  extent, all animal bodies  have the
power of regulating their own temperature.   Many of them
develope electricity ;  and some of them, like the lightning-
bug, and other insects, can produce light.  These are singu-
lar properties of living animal matter.
  2. The heat of animal bodies is  produced  within  them-
selves.   It is  not received from without, nor can it be ; as
the natural temperature of the  body is near 100 degrees ;
even when the temperature of the surrounding air is  below
zero.   How this is produced we  shall inquire when we come
to treat especially of animal heat.
  3. Plants have a lower  temperature than animals, and the
higher animals are in the  scale of organized beings, so much
the more animal heat do they produce.  Thus the tempera-
ture of what are called  the cold-blooded animals, such as
fishes, is not much  above that of the  water in which they
live; and although they do not often freeze  to  death in the
winter,  yet they become so torpid as to be incapable of mo-
tion.
  4. It is a favourite sport  in New England  in the winter
season,  to  hunt, on skates, for the  pickerel, and  other  fish,
which abound in the  lakes  and  ponds ; and when found  to
take them, by cutting through the ice with a hatchet ;  and
to spear them  by  torchlight at night.   Now had they the
faculty  of producing  animal  heat, like quadrupeds, or birds,
or man, they would not be rendered  torpid and incapable of
motion  by  cold. 
 106                   PHYSIOLOGY.
                                                *
   5.  Living animal bodies have not only the faculty of pro-
 ducing heat, but they can  also resist heat of a much higher
 temperature than their own bodies.  The heat of the  body
 is kept at its usual standard of 98 degrees, by the  exhalent
 vessels of the skin, which absorb by means of the perspira-
 tion the excess of caloric, and fly off  with it in a state of
 vapour.
   6.  In very hot weather, those functions of the body, such
 as digestion, nutrition,  and secretion, on which the produc-
 tion of animal heat depends, are weakened  by the excessive
 heat, so that in fact less caloric is produced in the system
 than in cold weather.  This is a wise provision of Providence,
 that when much internal heat is wanted to guard against the
 cold,  it is produced; when less is needed, on account of the
 warmth, the system generates less.
   7.  Animal bodies are  also capable of developing electricity;
 as most of the  bodies which surround us are conductors of
 the electric  fluid,  it generally  passes  off as  fast  as  it  is
 formed.   Sparks of fire, however, are often seen in winter,
 on taking off in the dark, silk dresses or stockings, or flannel
 drawers.   Some  physiologists  maintain  that the nervous
 power is nothing but the electric fluid ; but though this may
 not be admitted, there is a very close analogy between them.
   8.  It has also been found that needles plunged into the mid-
 dle of a nerve, become magnetic, and are capable of attracting
 light  substances, such as pieces of paper ; and a physiologist
 by  the name of Weinhold says, that he  has seen sparks
 obtained by bringing the  divided ends  of a  nerve together.
 Muller mentions in his late work on  Physiology, that effi-
 cient galvanic  piles can be constructed from organic sub-
 stances, without any concurrence of metals.   Concentrated
 solutions of organic substances were spread upon thin paper,
 and with disks of this, paper piles constructed, the two layers
of different substances being separated by two thicknesses of
 paper ; electricity  was  developed  by these piles, and tested
by an electrometer.  It would seem  from these experiments, 
      RELATION OF ANIMAL BODIES TO HEAT, &C.    107
that the nervous system is capable of developing  electricity,
under the influence of vitality.
  9. Certain  fishes, such as ,the  torpedo, the electrical  eel,
and five or six other species, are provided with special organs
for  the production of electricity.   In the torpedo they consist
of a large number of prisms, of from three to six sides, stand-
ing close together, near the gills of the fish, and perpendicu-
lar  to the  surface.  They are composed  of membranous
tubes,  divided into numerous  transverse cells,  abundantly
supplied  with blood vessels and nerves.  These vessels are
filled  with a fluid of an  albuminous nature.  These organs
are connected with the brain by three large nerves on each
side.
  10.  In the  gymnotus the electrical apparatus may be com-
pared to a battery of galvanic  troughs.   Two of these  are
found on each side of the spine, separated from each other by
a long ligament, and extending the whole length of the fish
They are composed of horizontal membranous  plates, sepa
rated from one another by a small interval, and crossed in a
perpendicular direction  by membranous partitions, so as to
form a great  number of cells, which are filled with a gelati-
nous fluid.  These organs receive numerous branches  and
nerves from the spinal marrow.
   11.  The resemblance  of these organs to  the galvanic  pile
is very striking.  The latter consists of alternate  plates of
copper and zinc  with a  fluid between them.  Thus we have
in these fishes alternate layers of membranous partitions  and
albuminous fluid.   But is is worthy of particular notice that
these organs lose their electric powers if the nerves which
supply them are divided.  There  can be no doubt then, that
the electric shock which they give is a vital act, depending
on  a nervous  influence, and under the control of the animal's
will.
  12.   The sensation produced by the shock of an electrical
fish, is also similar to that of common electricity. It is pow-
erful enough  to kill small fishes, and is the animal's weapon 
108                   PHYSIOLOGY.
of defence.   Sparks also  have been seen to attend the dis-
charges ; and the shock has been communicated through a
chain consisting of several persons with their hands joined.
   13. Common electricity, and that produced by the organs
of electric animals, are generally believed to be different, but
it has lately been discovered by Dr. Davy, that the  electric
organs of the torpedo affect the galvanometer, render needles
magnetic, and decompose water.
   14. Many animals as  well as  plants are  endowed with
phosphorescent properties.  Every person almost, has seen
rotten wood, or dead fish, shine in the dark ; such are phos.
phorescent.   This phenomenon is probably  owing  to the
fact, that during the decomposition of animal or vegetable
matter  there is  formed a highly inflammable  compound of
carbon,  hydrogen, and oxygen, which like phosphorous, burns
at the ordinary temperature of the air, with an evolution of
light.
   15. But several living animals  exhibit luminous appear-
ances.  Many of the  lower order of animals that inhabit the
sea, and some fishes, are phosphorescent.   It is this  that
causes the  luminous appearance  of the  ocean in warm cli-
mates.  If a vessel be filled with sea-water containing these
animalcula  they immediately become  phosphorescent,  on
shaking the vessel.
   16. It is not uncommon to find insects which have the
faculty of phosphorescence in  a high degree.   It is supposed
to reside in a peculiar albuminous principle, secreted by the
animal,  and that it requires for its manifestation atmospheric
air and  a certain degree of heat.   It is evidently under the
control  of the animal's will,  and  probably depends on the
nervous action.   Some  say,  however, that it is a peculiar
animal  matter  secreted at will, which, combining with the
oxygen of the air gives rise to the  disengagement of light.
Questions.—Have bodies the faculty of regulating their own temper. 
       RELATION OF ANIMAL BODIES TO HEAT, &C.    109

ature ?  What is said of animal heat ?   What is the temperature of
cold blooded animals ?  What preserves the heat of the body uniform ?
Is as much heat produced in the  body in hot as in cold weather?   Do
animal bodies develope electricity.  Can galvanic piles be  made of ani.
mal substances alone ? What kind of fish  are electrical ?   Describe the
electrical  apparatus of the torpedo.   What is a galvanic pile ?  What
effects have the electrical discharges of  the torpedo, &c. ?   In  what
respects like common electricity ?  What is said of the phosphorescent
properties of  animals ?   What animals  have  this property ?  What
does it depend on ?
10 
CHAPTER  IX.
                 THE NERVOUS SYSTEM.

         The Brain, Spinal Marrow, and Nerves.

  1.  There is no  subject, which falls within the range of
physiological enquiry, more interesting  or  more important,
than that of the nervous system.   It is this which furnishes
the material instrument of thought,  the means by which we
become  acquainted with the external world around us, and
also the  channels by  which the will sends forth its commands
to the instruments it employs in their execution.   Besides
this, it presides over  and regulates the functions of the ani.
mal economy, and binds  the various  organs into one sympa-
thizing, harmonious  whole.
  2. The nervous system may be considered  as  embracing,
1st. the brain;  2d.  the  medulla oblongata ; 3d. the spinal
marrow ; 4th. the nerves ; 5th.  the  ganglia.   These are all
embraced under two  general departments, the first consisting
of the  brain and its  dependencies ;  and the second, of the
ganglia  and their nervous connections ;  the first appertain-
ing particularly to animal life, conveying impressions calcu-
lated to  produce sensations, and sending out volitions to its
servants, the organs destined to  receive them ; while the
second supply those  organs not under the  influence of the
will, viz. of digestion, circulation, respiration, and the secre-
tions.
  3. These two grand  divisions  of the  nervous  system,
may be  still further  distinguished by the circumstance, that
the first, or  cerebral department, is  exactly  symmetrical.
The nerves all  go out in pairs from each side of fhe brain
and spinal cord, while the ganglionic system of nerves is dis-
tributed irregularly to all the internal organs.  The nerves 
THE NERVOUS SYSTEM.
Ill
of the first  kind, are either nerves of sensation or of motion.
These nerves, as discovered by Sir Charles Bell, are entirely
distinct, the one  rarely, if ever, performing the function of
the other.   Although these nerves are endowed with different
properties, the common function of both is, to give us correct
intelligence  of  the  relative   condition  of our  existence.
When these functions are  interrupted, as in apoplexy, or
concussion of the brain, the individual is deprived of all feel-
ing and sensibility, hence they are called the nervous depart-
ment  of external or  animal  life.   The  nervous  filaments
which furnish the power of motion, arise from  the anterior
column of the spinal marrow,  while those  in which sensation
resides, are  connected with the posterior column.
   4.  The brain fills the cavity of the cranium or skull, and
in  an adult weighs  between  three and  four pounds.  Its
greatest  length is  about  six  inches, and  its  breadth  five
inches, though its  dimensions vary greatly in different  per-
sons.  In infancy its texture is soft, but it grows harder in
proportion  to the  age.  The  brain is chiefly composed of
two distinct parts, the cerebrum, or brain proper; and the
cerebellum,  or  the  little  brain.  These again  are divided,
each into two distinct lobes.   The  medulla oblongata is the
commencement of the spinal marrow.
   5.  The brain is surrounded by three membranes ; the two
inner ones  thin  and delicate ; the outer one thick and firm,
and called dura mater.  It is a perpendicular fold of the dura
mater, and  divides the brain  into two hemispheres.   It ad-
heres loosely to the bones of the skull; the internal perios-
teum of which it forms.
   6. The other two thin membranes are called arachnoid and
pia mater.  The first is a serous membrane, as the dura mater
is a fibrous membrane ; and forms a completely  closed sac or
bag.   This  membrane, which derives its  name from its
resemblance to a spider's web, spreads over the whole surface
of the brain, without dipping  into any of its furrows or con- 
112
PHYSIOLOGY.
volutions, and  also forms a sheath for all  nerves or blood-
vessels that pass out of, or into the brain.
  a. The scalp, turned down.
  b. The cut edge of the bones of the skull.
  c. The external strong  membrane of the  brain, {dura mater) sua
pended by a hook.
  d. The left hemisphere of the brain, showing its convolutions.
  c. The superior edge of the right hemisphere.
  f. The fissure between the two hemispheres.
   7.  The pia  mater is a loose  cellular membrane, composed
chiefly of blood vessels, which  dips  into all the fissures, and
wraps round all the  convolutions of the brain.  The chief
use of these membranes seems to be to support the different
parts of the brain in their respective places, so that they may
not be injured by sudden shocks and jars, or by compression 
THE NERVOUS SYSTEM.
113
to moisten the brain ;  and furnish a medium of transmitting
blood vessels and absorbents.
   8.  The  outside surface of the brain is cut up, or inter-
sected by deep winding fissures, forming numerous irregular
eminences called convolutions.  These fissures  are generally
about an inch deep.  The brain  on the outer surface, is to a
considerable depth of a grey or ash colour ; hence it is called
the cineritious or ashy portion, and sometimes cortical, from
its position, like the bark surrounding a tree.   The internal
portion is white, and is therefore called the medullary part of
the brain.
   9.  The cortical part of the brain which is  found on the
exterior surface, is on an average about one-sixth of an inch
in depth,  and  dips down every where between the convolu-
tions.   Besides its being of a greyish colour, it is of a firmer
consistence than the medullary matter.  It is full of vessels,
and from this circumstance has been supposed  to nourish the
medullary part.
   10.  There axe four cavities in the  substance  of the brain,
termed ventricles.  Of these the two lateral ventricles are the
largest.  During life a serous exhalation is constantly going
on into their interior, and in health  this fluid is absorbed  or
taken  up, as fast as it is secreted.   In dropsy of the brain,
the water  sometimes accumulates in  these cavities  in im-
mense quantities.  Not long  since, a child, about ten years
of age, was exhibited in this city, whose head  measured two
feet and seven inches in circumference, just above the ears.
The head  was so heavy he could not raise it from the pil-
low.   This was owing to water in the ventricles. The med-
ullary or white matter of the brain  occupies the interior part
of that organ.  It makes up by far the largest portion, and
is fibrous in its structure.
   11.  The  cerebellum or  little brain, is situated at  the base
and back part of the skull, and in weight it is only about one-
eighth or ninth part of that  of the cerebrum.  Like the large
brain,  it is divided into two lateral halves.  It is made up of
                           10* 
114
PHYSIOLOGY.
several little lobes, and if the two hemispheres be divided by
a knife, a beautiful appearance is presented, resembling the
trunk and branches of a tree ;  composed of the white and
grey matter of the brain.   From its shape it has been called
arbor vitm, or tree of life.
  12. The Spinal marrow is a round cord of nervous matter
which passes down through the spine to the loins.   It is di-
vided into two equal lateral parts, by a deep  fissure or groove,
which runs through its  whole length both on its front and
back surface.   Some say that it consists  of four distinct
columns ; others that it is made'up of six white strands, two
before, two behind, and two on the sides ;  proceeding from
the cerebrum, the restiform bodies, and the cerebellum.
  13. There are forty-three pair of nerves, making 86 in all,
proceeding  from  the  brain and  spinal marrow.   These
nerves run to every part of the system, conveying, as already
stated, all sensations and impressions to  the brain, and also
volition from  the  brain, to  all  the voluntary muscles of the
body.  Of these, two pair  go from the cerebrum, viz., those
for smell and sight, or the  olfactory  and optic ; five pair go
from  the pons varolii, which is that round mass of nerve,
which lies between, and seems to connect the  cerebrum and
cerebellum.   Of these, the third, fourth, and sixth pair go to
the muscles of the eye ;  while the fifth and seventh  are dis-
tributed over the face.
   14. The remaining  thirty-six pairs go out from the spinal
marrow, viz., five from the medulla oblongata ; eight  from the
cervical; twelve from the dorsal; five from  the lumbar; and
six from the sacral portion of the spinal cord.   These nerves
supply filaments to every muscular fibre in the system;  or
pass directly to the organs of sense without sending off twigs;
some of them are chiefly employed to form plexuses,  or a net-
work of  nervous threads, woven  closely together, so that it
cannot be unravelled. 
THE  NERVOUS  SYSTEM.
115
  1. Hemispheres of the brain proper, or cerebrum.
  2. Hemispheres of the smaller brain, or cerebellum.
  3. Spinal cord continuous with the brain, and the spinal nerves pro.
ceeding from it on each side. 
116
PHYSIOLOGY.
   15.  The  chief net-works  or ganglia are four in number.
The'first which is called  cervical, is formed  from the second,
third and fourth cervical  nerves ;  lies on the side of the neck
about its middle ; and it gives rise to four large nerves which
go to  the head, neck  and  upper part of the chest.   The
second plexus lies under the pit  of the arm, and gives rise to
eight principal branches  which go to the chest, shoulder and
arms.  The other two  plexuses lie in the pelvis, and give off
branches which supply the viscera contained  in it, and also
the lower extremities.
   16.  A second division of the nervous  system, as I have
stated, has been called by anatomists ganglionic, or the ner.
vous system of organic life.  A ganglion is  a small grayish
white  body, of a roundish or oval  shape, varying in  size,
from a pin's head to an almond.   These ganglions are chief-
ly situated on the sides of the spinal column, throughout its
whole length, and are connected  by nervous threads, which
pass from one to the other,  and also with the nerves which
come out from the spine.  Six of these ganglions are found
in the  head ; three in the neck ;  twelve in  the  dorsal region;
five in the lumbar; and three in the sacral region.
   17.  The principal of the  plexuses are formed by nervous
filaments proceeding from these ganglions.   These are the
cardiac plexus,  the pulmonary plexus,  and the great solar
plexus.  The whole ganglionic system of  nerves is called
the great sympathetic nerve.  This is connected with the brain
by the sixth cerebral nerve and  a branch of the fifth.  It
also  receives  branches  from the seventh, eighth, and ninth,
and all the spinal nerves, to the lower part of the spine, be-
low which it terminates.  We are now prepared to consider
the functions of the nervous system.
   18.  The  brain being the  centre of the  nervous system, is
the most important organ of the  human body.   In the lowest
order of animals, we find but imperfect rudiments of a ner-
vous system ;  but as we  ascend in the scale of animal exist-
ence, we find it more and more developed as we advance, till 
THE NERVOUS SYSTEM.
117
at length we arrive at man, who possesses it in its  highest
form of development.  The functions over which the brain
presides, are the sensations, the voluntary motions, and the
intellectual and moral faculties.
   19.  The mind itself is immaterial—a principle superadded
to matter ; but the brain is the instrument which it employs
in all its operations.  Though it is not matter, yet it works
by means of matter.   In like manner,  the eye is  not sight,
but the instrument of sight ; the ear is not hearing, but the
organ of hearing ;  so the brain is not mind, but the organ
of mind.   Revelation teaches us all we know, with respect
to the  powers and capacities  of mind, when  separate from
the body.
   20.  The spinal  marrow and  the nerves are of subordinate
importance ; as organs  of the nervous  system,  their  use
seems  to  be, to transmit impressions  from  the organs of
sense to the  brain ; or the influence of the brain in a  con-
trary  direction to the  muscles which  are  employed  for
motion.
   21.  The first class of functions which pertain to the brain
are the sensorial.   Though the brain is  the actual seat of
all impressions, yet the organs  of sense and the nerves seem
to be the immediate seats of sensation.  Indeed, no sensation
can be excited in any part or organ, unless its nervous  con-
nection with the brain be entire.   For example, the sense
of touch seems to reside in the ends of the fingers, and that
of sight in the eye, yet  if the nerve which connects these
parts  with  the  brain  be divided,  no impression is felt, no
sensation whatever is excited ; showing conclusively that  it
is the brain that perceives all impressions made on the organs
of sense.
   22.  It is a curious fact connected with  this subject, that
though the  brain is the real seat  of the sensation, yet it  is
always referred to the part or organ, on which the impression
is made, so that there seems to be  a double action, viz., from
the organ to the brain, and from the brain back again to the 
118
PHYSIOLOGY.
organ.  Thus it is not unusual to see persons who have lost
a limb complaining of pain, or some other sensation in the
part which has been  cut off,  and thus they often imagine
that the limb is entire.  Here the sensation existed only in
the mind ;  in the same manner ghosts, hobgoblins, and other
strange sights  are  seen ; but  the sensation is  only in the
brain.
  23.  That the brain is the real seat of all our sensations
may be proved from  other facts.   If a  person receives a
blow upon  the  head so as to stun him, or deprive him of
consciousness, though the organs of sensation and the senses
are wholly uninjured,  he takes no notice of any thing ; he
receives no sensations from any of his senses ;  in  fact, he is
said to be insensible.  The same thing happens if he become
stupid by the use of alcohol, opium, or any narcotic.   If the
quantity is not enough to produce entire torpor of the  brain,
his senses are impaired, his reason is gone ; he is in short a
voluntary mad-man.
  24.  During  sleep,  the senses are said  to be locked up.
But though the eye is closed, the ear is open ; the nerves in
which the sense of touch resides, are still spread out upon
the skin, but yet no impressions are felt; no sensations are
excited ; no notice is taken.   The reason is, the brain is in
a state of repose ; the ship does not obey the rudder, be-
cause the man at the helm is asleep ; the steamboat is not in
motion, for although  she has furnace, boilors, condensers,
paddle-wheels, and all, yet the steam is not up ; so in sleep,
the organs of sense are all sound, yet the  brain, the rudder
of the mind, the moving agent of  the animal  machine, is
dormant;  the messages of its servants, the organs of  sense,
are neither received, noticed, nor acted upon.
  25.  There is another  curious circumstance connected
with the brain ;  it may be so much employed in thought,
or deep meditation, as not to  notice  the impressions made
on the senses.  In  this case,  a person is said to be absent-
minded.  Though the eyes and ears are  open, the brain is 
                 THE NERVOUS SYSTEM.             119
 too busy  about other matters, to take notice of the impres-
 sions made on them ;  accordingly, there are instances known,
 where persons have walked off a precipice, or into the water,
 without noticing the danger till it was too late.
   26. Sensations, then, are the more vivid ;  and the impres.
 sions which they make,  more durable, in proportion to the
 degree of attention with which  the mind is directed towards
 them ; or  the  degree of  activity of the brain.  To obtain
 ideas, which are the pictures of sensible objects painted on
 the brain, we must  therefore endeavour to  concentrate the
 whole attention upon the subject  before us, or  the impres-
 sions we receive will be weak and speedily fade away.   We
 see a great difference in this respect in different persons.
 Two  individuals will  travel  together through the same coun-
 try, and apparently take  the same degree of interest in the
 objects which come under  their notice.  Yet, while one of
 these persons will be able to describe minutely every thing
 he has seen, the other can give only a confused and indistinct
 account of what he has observed.   It is, therefore, not only
 necessary in the acquisition of knowledge that objects should
 make an impression  on the sensual  organs ; but the brain
 must  act upon them, and that not in a slight and  careless
 manner, but  vividly and energetically.
   27. It is possible even  that sensations may be excited  by
 the action of the brain itself, without the intervention of any
 sensible objects.  We see this often in diseases of the brain,
 and especially in that form  of insanity,  called delirium tre-
 mens, or drunken delirium.   Here, the wretched victim  of
 depraved  habit sees  serpents, and  lizards, and bats, and  all
 creeping things, and devils, flying about; and he hears sing-
 ing and  various sounds,  to which  he listens, and calls the
 attention of others, and nothing can break the spell by which
 he is bound, or dispel the illusory  conviction, that what  he
sees and hears is real and not imaginary.
   28. Such  illusory  and false impressions,  are no doubt
sometimes excited in  the minds of those,  who cannot be said 
120
PHYSIOLOGY.
to labour under actual disease ; but their imaginations have
been excited by the influence of fear and  superstition, and
the brain is accordingly excited to act in the same manner
as it would by the actual sight  of some  frightful  object.
Thus a post will appear in the night, to be a robber; a black
stump of a tree, a bear, or a tomb-stone, a ghost; according
to the  idea or apprehension at the time  uppermost  in the
mind.
  29. But though the brain  is the  seat of sensation, yet it
is very remarkable  that it is not itself sensible.  Wounds
in its substance do not seem to excite pain.  The whole of
the cerebrum as well as the cerebellum has been pared  away,
and yet the animal  appeared to suffer no pain ;  but as soon
as that portion of the base of the brain which seems to be
the commencement of the spinal marrow, is touched,  con-
vulsions  immediately  follow.   The  posterior  surface  of the
spinal marrow is also  highly sensible.  This is the substance
of what is yet known  on the subject of sensation.
   30.  Voluntary motion, like  sensation, has also  its  seat in
the brain.  Though  the  muscles are the instruments of
motion, yet all their voluntary motions are performed through
the influence of the brain,  by an act of the will   If the brain
is in a state of repose the body is at rest; if me brain by
an act of violition sends a portion of nervous influence to a
voluntary muscle, it immediately contracts, and  the limb or
organ to which it is attached, moves.  All  we are conscious
of in this process, is, the act of the will and  the motion, which
that act causes.  The volition  and  the motion  seem to be
at the same instant; at least there is no perceptible interval
between them.
  31. But though the  voluntary muscles are excited to action
through  the agency of the brain, yet they are not always
under  the  control of the will.  In  many diseases  of the
brain : in lock jaw, hydrophobia, and other disorders where
the whole nervous system is in  a  state of irritation, the
muscles are excited to violent spasmodic  contraction,  alto- 
THE NERVOUS  SYSTEM              121
 gether beyond the control of the will.  Where convulsions
 arise  from sympathy, as  in teething,  or  irritation  of the
 bowels, the painful impression  is transmitted  to the brain,
 and hence reflected back upon the muscles.  Thus pricking
 the finger with a needle  has thrown a nervous woman into
 spasms, by exciting the brain to action.
   32. If a nerve  which  supplies any voluntary muscle  be
 divided, that muscle will no  longer contract.   This  proves
 that the influence of the brain is necessary.   In palsy, there
 is generally some disease of the brain, as  the  rupture  of a
 small blood-vessel, or tumour growing in its substance.  Here
 the  power of the will, or the faculty of volition is not des-
 troyed ;  but the brain is unable to carry into  execution the
 command  of the will, as when  a person is very willing to
 take a load upon his back, but he happens  not  to have suffi
 cient strength to carry it.
   33. During sleep, all voluntary motion is  suspended, be.
 cause the brain ceases to act.  In those cases where persons
 walk and talk in their sleep, the brain is not entirely dormant.
 Some  of  the  senses seem  to be awake at times, while  the
 others are asleep.   That is, those portions of the brain which
 are excited to action by certain nerves  of sense, are awake
 and active, while  other  portions are dormant  and at rest.
 The brain  needs  repose and relaxation,  as  much as the
muscles.   Periodical cessation of effort is necessary to both,
in order to a vigorous performance of their respective func-
tions.
  Questions.—What functions belong to the nervous system ?  What
does it embrace ?  How many departments ? What affices  does each
perform ? What marks characterize each ?  When their functions are
interrupted,  what happens ?  From what portion  of the sp-inal mar-
row do the nerves of motion arise ?—the  nerves of sensation ?  Des-
cribe the  brain ;—its divisions;—its membranes ;—dura mater ;—pice
mater ;   What are the convolutions of the brain ?  How do the cine-
ritious and medullary portions differ from  each other?   Which is ex
terior ?   How  many cavities in  the brain ?   What are they  called ?
                             11 
122
PHYSIOLOGY.
Describe the cerebellum,—the spinal marrow.   How  many pairs  of
nerves are there ?  How many nerves arise from the cerebrum ?—from
the pons varolii ?—from the spinal marrow ?—from the medulla oblon-
gata ?   How many principal ganglia  ir net-works  of  nerves ?—their
situation ?  What is  a ganglion ?  What are the principal  ganglions
of the nervous system of organic life ?  What is the sympathetic nerve ?
—where situated ? What is the  most important  organ of the body ?
What is said of the brain in the lower animals?  Over  what functions
does the brain preside ?  Is it immaterial ?  What is the first class
of functions over which it presides ?   What  is understood by sensorial
functions ?  What becomes of the senses during sleep ?—during absent-
mindedness ?  What are ideas ?   Is attei tion necessary  in order to im-
press sensations durably on  the  mind ?  May sensations be excited
without the intervention of sensible objects ?  In what disease does this
happen ?  Is the brain itself sensible ?   Where is the seat of voluntary
motion ? How is it  performed ?  What is  volition ?    Are motions
always under the control of the will ?  In what diseases is this not the
case?  What effect has the division  of a nerve?   What happens  in
palsy ?  Why is voluntary motion suspended during  sleep ? 
CHAPTER X.
          INTELLECTUAL AND MORAL  FACULTIES.

   1. The great superiority of the intellectual faculties of
man over those of other animals, has led to a diligent exami-
nation, whether  there be any thing in his anatomical struc
ture which would  seem  to account  for  this  superiority.
Aristotle noticed the great size of the human brain compared
with that of other animals, and laid it down as a general
principle, that the  faculties referred to this organ were in
proportion to its size, compared  with that of the whole body.
Though this rule will hold true in relation to some of the do-
mestic animals,  yet it does not  in relation  to many others,
for accurate researches  have shown that while in man the
ratio of the weight of the brain to that of the whole body is
as 1 to 28, in the dog, it is as  1  to 160, in the horse, as 1 to
400, in the elephant,  1 to 500, in the canary bird, 1 to 14,
and in one species of ape, 1 to 11.
   2. It  is now  generally admitted by physiologists, that the
perfection of the sensitive  functions does not depend on the
absolute  size of  the brain, nor on its proportion to the body
at large,  but upon the proportion  between the size of the
brain, and the aggregate bulk  of  the  nerves that  proceed
from it;  in other words, between the sensorial  and nervous
organs.   For example, the absolute size of  the  brain of the
horse is only about half the size of the human brain, while
the mass of the nerves of the horse at their origin is no less
than ten times larger  than that of man.   Extensive observa-
tions prove that though most of the inferior animals have larger
nerves, and possess  some of the nervous functions in a much
more acute state than  man, yet  man decidedly exceeds them
all in the comparative size of the brain,  and in the perfection
of his intellectual faculties. 
124                  PHYSIOLOGY.
  3. The brain then,  is the organ of the intellectual  and
moral faculties, the material instrument of the mind.   This
is proved not only by comparative anatomy, and experiments
on  animals, but by the history of injuries of the brain, com-
pared with  those  of other  organs.   We know  that  if the
nerves supplying any limb are severed, the will has no  longer
any influence over it;  it is to all useful purposes a dead por-
tion of matter.   The same is true of the spinal marrow.  If
this be compressed by  fracture or dislocation of the  spine,
the whole body below  that point, is deprived both of  sensa-
tion and  motion,  but the  mind loses none of its powers any
more  than if a limb had been amputated.
  4.  If the  brain is  not the  seat of the intellectual faculties,
neither are any  of the other  organs of the  body.    The
lungs, the liver, the spleen, the intestines, or the kidneys,
may  be affected with gangrene, and still the mind remains
clear; though  from sympathy, inflammation of any organ
may  cause  delirium, or other mental affections.  Neither
is the heart the seat of the  mind ; for cronic disease  of that
organ, does not impair  the mental faculties.   Besides the
functions of all these organs are known and cannot be mis-
taken.  If the brain is not  the seat of the intellectual facul-
ties, they cannot be said to have any seat in the body.
   5.  But the effects of injuries of the brain  are very diffe-
rent,  for every cause which disturbs its action suddenly or
slowly, affects at the same time the mind.   Inflammation of
the brain is always attended with delirium, or stupor  ; pres-
sure  on  it,  whether produced  by depressed bone,  foreign
bodies, a tumour,  serum, blood or pus, always gives  rise to
similar  symptoms,  and often destroy both  sensation and
mofion.  In cases of apoplexy, where a person falls in  a fit,
and becomes insensible, we find pressure  on the brain  from
effusion of blood or serum.  In cases of lunatics, we  find in
nearly all cronic cases, structural changes in the brain ; but
if  the case be recent, these changes though they probably
exist, yet may escape our imperfect means of investigation.
Alcohol, opium, and other narcotics affect the mind and the 
        INTELLECTUAL AND MORAL  FACULTIES.      125

nerves through their influence upon the brain.   Whenever
in fact, we see a person become stupid and  insensible, we
may be certain that the brain has  suffered some  physical
change; and where in cases of sickness, we see  the mental
faculties unimpaired to the last, we may be equally sure, that
the brain is not affected.
  6.  The following facts also show that the brain is the or-
gan of the mind.   A man received a blow on his head, and
immediately lost his mental  faculties, and  his  bodily power.
His  appetite and digestion  were good  ; the blood circulated
freely ;  and his breathing and pulse were natural.   He con-
tinued in this state  more than a year, when a surgeon raised
up a piece of bone which had been driven in upon the brain.
His   reason  was immediately restored;  the next day he
spoke, and in a  short  time he recovered entirely;  but he
could recollect nothing of what had happened since  the acci-
dent.  Not long since a beggar exhibited  himself  in Paris,
who had lost a portion of his skull;  his brain was only cov-
ered  by the  skin and membranes.  For  a trifling sum he
would allow any one to press on this exposed part.  As soon
as any pressure was made  he became wholly unconscious;
but his intellect was immediately restored when the pressure
was taken off.
  7.  It has been objected to the brain's being considered the
seat of the  mind, that in some cases, considerable disease
has  been  found  affecting an  entire hemisphere without the
mental faculties having suffered ; but experiments on animals
show that  a sudden lesion of  one hemisphere  only, does  not
immediately  produce  complete stupor, and that this effect
does  not follow  until  both  are removed ;  so that it appears
that one hemisphere aids the other, and compensates  for its
inaction in the operations of the mind.
  8.  But though it is almost universally admitted, that the
brain is the seat of the  higher intellectual faculties,  yet some
physiologists, like  Bichat,  contend  that  the passions  are
seated in the thoracic and abdominal viscera.  It is, however,
                              11* 
126
PHYSIOLOGY.
to be remarked, that the passions, by  means of the change
which takes place in the brain, affect the whole nervous sys-
tem.   We find, for example in nervous females, that the ex-
citing passions give rise to spasmodic action of certain mus-
cles, especially those supplied by nerves  belonging to  the
respiratory system ;  hence the crying, sobbing, sighing, and
the spasmodic distortion of the features.   In the depressing
passions, such as fear and terror, the muscles of the body lose
their tone, because the supply of nervous  influence from the
brain is cut off; the limbs are not able to support the body ;
the features lose their expression ;  and the loss of power may
be so great as to cause complete paralysis of the whole body.
   9.  In like manner is the heart affected by the exciting and
depressing passions.  It throbs irregularly under the influ-
ence of frar and terror; it  beats  high and strong under the
influence  of joy; while its action  is weakened under  the
operation of grief and care; in short,  it  is affected in a
greater or less degree by every emotion which  agitates the
human breast.  But this no more  proves that  the passions
are seated in the heart, than that  they  are seated in the eye,
because grief brings tears into that organ.   Neither has the
liver, as the ancients believed, any relation to the passions of
rage  and  vexation, although a fit of jaundice, may, in some
persons labouring under a disease  of this organ, follow a
paroxysm of these passions.   In  other individuals, a fit of
dyspepsia may follow as a consequence of the same emotions ;
or any other organ, may suffer, according as it is  predis-
posed by  debility, disease, or other  causes.  Such phenome-
na only prove that the whole body is bound up in one indis-
soluble bond of sympathy, or as St.  Paul  expresses it, "God
hath tempered the body together, that there should be no
schism in the body, but that the  members should have  the
same care one for another ; so that,  whether one member suf-
fer, all the members suffer with it, or one member be honored,
all the members rejoice with it."
   10. The brain, like all the other  organs of the body, in- 
         INTELLECTUAL  AND  MORAL  FACULTIES.    127

creases in volume, by the exercise of its  functions.  When
the mind is properly cultivated, the  brain attains  its full
growth and development;  and  where suitable  opportunities
of education have been enjoyed, the intellectual  powers are
generally proportioned  to  the  size of this organ.  Majendi
says,  "The  volume of the brain  is generally in  direct pro-
portion to tin capacity of the mind."  This was also be-
lieved by the ancient Greeks ;  for their  statuaries, or workers
in marble, made the heads  of  their Apollo, and other intel-
lectual gods and heroes, much larger than the heads of their
Hercules, and other heroes, who were  remarkable only for
their  great physical strength.  The heads of idiots are known
to be  extremely small ; some, indeed, are not more  than one-
fifth the average size.
   11. That  the brain is constructed  with  evident  design,
and is composed of a number of curiously wrought parts, all
physiologists admit; yet they have not  been able thoroughly
to penetrate  the intention with which they are formed, or to
agree with respect to the particular functions which  each
part  performs.  It is, however, pretty well ascertained, that
the hemispheres of the large brain, or cerebral  lobes,  are the
instruments by which the intellectual operations  are  carried
on \  in other words, are the seats of the faculties  of thinking,
memoiy, and the will; while the central  parts, such  as the
optic  lobes, and  the medulla oblongata, are principally con-
cerned in sensation ; and that  the cerebellum, or  little brain,
is tne chief sensorial agent in voluntary motion, and the seat
of the animal, or lower propensities.
   12. Many cruel  experiments have been made on  living
animals, to determine the exact functions of particular parts
of the brain  ; but so much violence is done in  these  experi-
ments, that  but little  dependence can  be placed  on them.
Many attempts have been made to determine the exact place
in the brain where  perception  resides, but all such attempts
have  been fruitless.  That it  is placed in the base  of the
brain, or the medulla  oblongata, is very probable, as most of 
128
PHYSIOLOGY.
 the nerves of sense terminate in that part;  but it is difficult
 to prove this by actual experiment.
   13. The brain, like all the organs of the senses, is double ;
 the one side, as in the eyes, ears, and limbs, being exactly
 similar to the other ; so that  it may be said, that we have
 two brains as well as two optic  nerves, and two eyes.  As the
 structure of the brain is fibrous, in order that the two sets
 of fibres may co-operate, and constitute a single organ, the)'
 pass obliquely across from one  side of the brain to  the other,
 and these bridges  constitute what are called the commissures
 of the brain.   It  follows  from  this, that if  the right side of
 the brain  receives an injury,  it will"be felt on the opposite
 side of the body.  The following case proves this.
   14. A piece of wire pierced the brain  of a  boy just over
 the right eye ;  he immediately  lost all motion in the left arm
 and leg, although his sense of feeling was as perfect as ever.
 There are many such cases on record, which conclusively
 show  that  the right side  of  the  brain  furnishes  nerves  of
 sense and  motion to the left side of the body ; and the left
 side of  the brain to the  right side of the body.   If, then, a
 portion of brain is lost by a wound, on one side of the head
 only,  as has often happened, and the intellect does not suffer;
 as the brain is a double  organ, it does not prove, that it  is
 not the  seat of the mental faculties.
  15. The office of the  cerebellum is supposed by many to
 be, to regulate and combine different motions.   For example,
 if the cerebellum be wounded, the animal  cannot  walk with-
 out staggering, and  there will  be a particular weakness on
 that side which is  wounded.  When a person is intoxicated,
his inability of walking in a straight  course, is supposed  to
 be owing to the influence of the alcohol  on  the cerebellum.
In experiments, where the cerebellum  has been wounded  or
divided, the animal has rolled over and over, or whirled  round
and round ; the eyes squinted ;  and all power  of regulating
its motions seems to have been  lost.
  16. Though  man  is infinitely  exalted above  the  brute 
        INTELLECTUAL AND MORAL  FACULTIES.     129
creation, by the endowments  of reason  and a moral  sense,
yet many of the inferior animals excel  him in the perfection
of subordinate powers.  In strength and swiftness, he is sur-
passed by many of the quadrupeds ; in powers of vision, the
eagle and other birds excel  him ;  in acuteness of hearing,
taste, and smell, a large number of animals are  superior to
him.   Man is  indeed a stranger  to those delicate percep-
tions, which teach the lower animals to seek the food  which
is salutary, and avoid that which is injurious, and  has to
depend upon a painful and  hazardous experience for that
knowledge which the brutes possess by instinct.
   17.  "But he has gifts'of  infinitely higher value.   In the
fidelity and tenacity with which impressions are retained in
his memory ;  in  the facility  and strength with which they
are associated ; in grasp of comprehension, in  strength  of
reasoning, in capacity of progressive improvement, he leaves
all other animals at an  immeasurable distance behind.  He
alone enjoys in perfection the gift  of utterance; he alone is
able to clothe  his thoughts in  words ;. in him  alone  do  we
find  implanted the desire of  examining every department of
nature, and  the power  of extending his  views  beyond the
confines of this globe."
   18.  " On him alone have the high privileges been bestow.
ed of recognising and adoring the Power, the Wisdom, and
the Goodness of the Author of the universe, from whom  his
being has emanated, to whom he owes all the blessings which
attend it,  and to whom  he has  been taught to look  forward
to brighter skies, and to purer and more exalted  conditions
of existence."
   19.  Phrenology.—The actual meaning of the term Phren-
ology, is " a discourse about the mind," or, " the doctrine of
the mind."   It professes  indeed  to be a  system of  Mental
Philosophy, and as it is  pretends to be founded in nature and
supported by facts, it certainly  is  not beneath the attention
of the candid inquirer after truth. 
130
PHYSIOLOGY.
  20. The chief doctrines which Phrenology claims to have
established are the following :—•
  1. That the  moral and  the  intellectual faculties are in
nate.
  2. That their exercise, or manifestation, depends on organ-
ization.
  3. That the brain is the organ of all the propensities, sen-
timents, and faculties.
  4. That the  brain is composed of  as  many particular
organs as  there are propensities, sentiments, and  faculties,
which  differ  essentially from each other.   These four pro-
positions may be said  to  constitute the phrenological doc-
trine, and they  are sustained by such numerous experiments,
observations, and facts, that a large proportion of enlighten-
ed physiologists of the  present day acquiesce  in their cor-
rectness.
  21. Another  and a different proposition, however, and one
which, by many, is erroneously supposed, alone, to constitute
Phrenology, is,  that we are able to recognise on the exterior
of the skull, the seats of the particular organs, or intellectual
and moral faculties, and thus determine the character  of in-
dividuals.  This  proposition  has not received that general
concurrence of Physiologists, in  its support, which has at-
tended the former ;  but there are so many zealous  and able
inquirers now in the field, and  such is the  ardour in pursuit
of knowledge, connected with this  subject, that a few years
at farthest, probably, will suffice to overthrow or establish it.
  22. I  have already mentioned some  facts, to prove that
the brain is the organ  of  the  mind, and that the condition
of that organ influences the mind ; let us now inquire whether
the mind, in every act, employs  the whole brain as one oro-an,
or whether separate faculties of the mind are connected with
distinct portions of the brain as their respective organs ?
  23. It is a well established fact in Physiology, that  diffoi -
ent functions are never performed by the same organ, but
that  each function has an organ for itself.  Thus  the eyes 
        INTELLECTUAL AND MORAL FACULTIES.     131

see,  the ears  hear, the  tongue  tastes, the nose smells, the
stomach digests food, the heart circulates the blood, the liver
secretes bile, &c.   Even where the  function is compound,
as in the tongue, where a feeling, taste, and  motion are all
combined, we find a  separate nerve  for each function, and
the same  occurs in every part of the body.   Now,  as no
nerve  performs two functions,  we  may, reasoning  from
analogy, conclude, that it is so in the brain ; different sen-
timents, different faculties, and different propensities, require
for their manifestation different organs or portions of cerebral
matter.
   24. Again, the external senses have for  their  exercise, not
only separate  and external organs, but also as  many separate
internal organs.   Hearing, seeing,  smelling, &c, require
different portions of cerebral substance for their exercise ;
may we not then from analogy, be justified in the conclusion,
that  there are  as  many cerebral, or nervous systems, or
organs, as there are special  internal senses,  and particular
intellectual  and moral  faculties ?  The legitimate inference
then is, that each faculty does possess in the brain a nervous
organ appropriated to its production,  the same as each of the
senses has its particular nervous organ.
   25. The  structure  of the brain is not .homogeneous, but
differs greatly in different parts, both in  composition,  form,
colour,  consistence, and arrangement.   But  what  object
could there be  in  all  this variety, if the brain  acted as a
whole, and there was  but a single intellectual  principle or
faculty ?  A difference of structure shows that there must be
a difference of function, and  as the brain has  been proved to
be the organ of the mind, it follows that different portions or
organs of the brain must be employed by the intellectual and
moral faculties.
  26. The faculties do not all appear  at once, nor do they fail
at once, but they appear in succession, and as a  general rule,
the reflecting or reasoning faculties are the latest in  arriving
at perfection.   So also  the organization of the brain  is un 
132
PHYSIOLOGY.
folded in a slow and gradual manner, and the intellectual fac-
ulties appear in succession only as the structure is perfected.
For example, in infancy, the cerebellum  forms one fifteenth
of the encephalic  mass ;  in adult age about one sixth.   In
childhood the middle parts of the forehead preponderate ; in
later life, the upper  lateral  regions  are  more prominent,
which facts are also in accordance with the periods of unfold-
ing the knowing and reasoning faculties.
  27. Genius is almost always partial;  that is, men gene-
rally  have a taste  or faculty, for  one particular pursuit, or
study, in which alone they have the power of excelling.  One
has a talent  for poetry, another for mechanics, another for
drawing, music, or mathematics, and that is often developed
at a very early age, and  without  the  advantages of educa-
tion, or particular instruction, and these persons may, in all
other pursuits, be  below  mediocrity.  Indeed, nothing  is
more  common than to see in the same individuals some fac-
ulties acute and powerful, while others are feeble and defec-
tive ;  having  an extraordinary memory  for dates, words,
places, &c, while as to other things  it  is deficient.   Such
facts  are not easily explained on the scheme of a single in-
tellectual faculty, and a single organ devoted to its exercise.
  28.  It  is an observation of common notoriety, that when
the mind is fatigued with one kind of occupation or study, it
can engage, with vigour, in one of a different kind, requiring
the exercise  of different faculties ; and thus, instead of fa-
tiguing,  actually acts as a restorative.  Could  this happen,
unless there were a plurality of faculties and organs of the
intellect ?
   29. The phenomena of partial idiocy  and partial insanity
are at variance with the doctrine of a single organ of mind
We often see persons in a state of monomania, that  is,  they
are rational enough on all subjects but one; but in relation
to that, they are entirely mad.  Now, if the brain  be suffi.
ciently sound to manifest all the other faculties in  their per-
fect state, why is  it not also able to manifest this ? 
          INTELLECTUAL  AND MORAL  FACULTIES.      133

   30.  Numerous  cases  are  contained  in  medical  works
 where a wound of the brain was succeeded by the loss of a
! single faculty, and sometimes  by exciting inflammation, be-
 stowed unwonted energy on a single faculty.   Larrey, in his
 surgical memoirs, mentions several cases of wounds made by
 bayonets and swords penetrating the brain  through the orbit
 of the  eye, which entailed the  loss of memory for names, but
 not of things, &c.
   31.  Such are a few of the  arguments adduced by writers
 on this subject, to prove that the brain is not only the organ
 of the  mind, but an  apparatus, a  congeries of organs, each of
 which is the seat of a particular faculty, the organ of a par-
 ticular function.  The evidence to most minds  will appear
 satisfactory and conclusive on this point, though other facts
 and  more  extended investigations  are needed to place the
 science on a permanent foundation.
   Questions.—What was Aristotle's theory in relation to the size of the
 brain ?  How  does its size compare  with that of the body in man ?
 in the dog, the horse ? the elephant ? the canary bird ? the ape ?  What
 is now the received doctrine in relation to the size of the brain ?   How
 is it proved that the brain is  the organ of the intellectual and moral
 powers ?  How do you prove that no other organ than the brain can be
 the seat of the  mind ?  How does inflammation or injuries of the brain
 affect the mind ?  What  cases prove this  connection ?  What objec-
 tions have been raised to the brain being the organ of the mind ?  What
 is said of the passions being situated in the viscera of the chest or abdo-
 men ?   Does the affection of the heart by passion  prove that it is the
 seat of the  mind ?  Why not ?  Does the brain increase in size by ex-
 ercise ?  What was the opinion of the ancient Greeks on this subject ?
 What is sai3 of the functions of particular portions of the brain ?  Is
 much dependance  to be placed on  the experiments made on animals ?
 Where is it supposed perception resides ?   What are the commisseurs
 of the brain ?  When the brain is injured on the right side, which side
of the body is affected ?  What accident proves that the opposite side is
affected ?  What is the office of the cerebellum ?   What effect do we
see in animals when they have been  wounded ?  Is man excelled by ani-
mals in the perfection of the senses ? In what respect does he excel all ani-
                            12 
134
PHYSIOLOGY.
mals ?  What is Phrenology ?  What are its  chief doctrines ?  What
is said of locating the organs on the exterior of the skull ?  What facts
show that the brain does not act as as a whole  in the intellectual opera-
tions?  Have the external  senses separate internal  organs?  What
may we infer from th>s ?  Is the structure of  the brain homogeneous ?
Do the faculties all appear  at  the  same time ?  Is genius generally
partial?  When the mind is  fatigued, what  effect is experienced by
turning the attention to a different  subject ?   What is monomania ?
What do we infer from its existence ?  What is the general conclusion
in relation to the chief doctrines  of Phrenology ? 
CHAPTER  XI.
         THE SPINAL MARROW AND ITS FUNCTIONS.

   1.  We have  seen, that of all  animals, the brain  of man
has  the  greatest development, in proportion to the spinal
marrow  and nerves ; if we descend to  the  lower animals,
such as reptiles  and fishes, we shall find  that the brain pre-
sents merely a  delicate, anterior termination of the spinal
cord, not much  larger in diameter than the cord itself.   In
these animals, we find the  instincts very limited, and the
displays  of sagacity extremely obscure ;  while they  possess
great tenacity of life.  Frogs, for example, continue to jump
about for many  hours  after  their heart has been torn out;
and the heart of the shark will palpitate  as long after it has
been removed  from the body.   Turtles have  been known to
live for months  after the whole brain has been scooped out.
These facts  prove, that such an  imperfect development  of
the cerebral mass, leaves the different systems of organs less
intimately connected and more independent of each other.
   2.  If we descend still  lower in the scale of invertebrate
animals,  we shall find the different parts still more independ-
ent of each other ; for if we divide their  bodies, so that each
part  will  possess a nervous ganglion, it will become a separ-
ate individual, and  exercise  all the functions performed  by
the entire animal;  and if we descend to zoophytes,  we find
that  in  cutting  them  into  threads, however minute, each
piece will retain life and continue to grow.
   3.  Medulla oblongata.—There is no distinct line of demar-
cation between  the medulla oblongata and the spinal cord.
For  this reason, they are considered and  described  as one
organ.   The medulla oblongata, however,  consisting of six
columns, gives rise to several nerves of distinct function, and 
136
PHYSIOLOGY.
is supposed to be the point at which excitement  to  motion
commences and sensation terminates,  and to possess the
power of originating motion in itself.    Mr.  Mayo infers
this, from the fact that the brain proper, the optic tubercles,
and even the cerebellum may  be  removed by successive por-
tions, and still the animal  live, and exhibit feeling and in-
stinct;  but if the medulla oblongata be removed, all con-
sciousness  is immediately destroyed.   Other  physiologists
say,  that it is the hemispheres  of the  cerebrum  that take
cognizance of sensation, and the source from whence volition
proceeds;  and  that  though  they may  be removed,  layer
after  layer, without  pain,  yet by so  doing, the  senses are
destroyed, memory and intelligence abolished, and  the animal
reduced to an automaton,  destitute of design,  apprehension,
and judgment.   As all the nerves which supply the larynx,
lungs, heart, stomach, and external muscles  of respiration
originate from it, its removal must instantly destroy life.
  4.  The  spinal cord passess  down  through the foramen
magnum, or great hole of the  skull, and the canal  of the ver-
tebra, till it reaches  the second  vertebra of the loins, where
it generally terminates in a tapering  point.   Besides the
bony case in which it is  lodged, the cord  is  enclosed by a
prolongation of  the  dura  mater, which, however, does not
adhere immediately to the bone, as it does  in  the  skull.  It
also  is supplied  with extensions of the  arachnoid and pia
mater ;  between  which, there is  usually  a quantity of serous
fluid, varying from two to six ounces, which seems to impart
a certain degree of support by its pressure and obviates the
effects of concussion.
  5. The  general form of the  spinal cord is cylindrical,
though  somewhat  flattened,  from  its  transverse diameter
being the greatest.   Its thickness, however, is not uniform,
as it  bulges out at the lower part of the  neck, where the
nerves go off to  the arms, and also at the lower part  of the
back, from whence spring  the nerves of the legs.  It is com-
posed of grey and white, or cineritious and medullary mat- 
        THE SPINAL MARROW AND ITS FUNCTIONS.   137
ter, like the brain ; the situation  of the  two is, however,
reversed ; the  medullary matter being disposed in  a thin
layer upon the surface, while the grey portions occupies the
centre.   We,  however,  find the same arrangement in the
medulla oblongata, and  the central parts of the cerebrum
and  cerebellum.   The  chord, as I have  already mention.
ed, is divided into two  lateral halves  by a groove in front
and  a similar groove  behind.   Besides this, there  are on
each  side two  lateral  grooves faintly marked, from which
the anterior and posterior nerves have their origin, so that
in fact, the cord  consists  of four  columns ; from the two
anterior of which, the nerves of motion spring, and from the
two posterior those of sensation.
a, Spinal marrow.
6, Fibres of sensation.
c, Fibres of motion.
e, Nerve.
   6.  There are thirty pairs of nerves that  spring  from the
spinal marrow, viz., eight from the region of the neck, twelve
from that of the back, and five from the pelvis.  By examin-
ing the  above cut, it will be seen that they arise by two
roots, one from  the  anterior, and one from  the  posterior
column.   The fibres of the posterior swell  out into a gang-
lion before they unite with the anterior.
                          12* 
138                  PHYSIOLOGY.
  7. A few years  ago, Sir Charles Bell discovered, that by
opening the  spinal canal in a living animal, and dividing
the posterior roots  of the  nerves, the parts to which they are
distributed are deprived of feeling.   The limb may be prick-
ed or lacerated in any way, without the  animal manifesting
the least feeling, or indication of suffering, while at the same
time the power of motion remains.   He also found that when
the posterior roots were divided,  sensation was  destroyed,
but motion remained.   One of Majendie's  experiments,  is
interesting.  Availing himself of the fact, that the introduc
tion of nux vomica into the system, produces violent spasms,
tremors, and rigidity of the muscles : he administered  it to an
animal, after having severed the anterior roots of  the spinal
nerves.  The consequence was, that while all the muscles,
whose nerves remained -entire, were thrown into  a state of
violent spasm ; those supplied with the nerves,  whose roots
had been divided, remained unaffected.
  8. The spinal cord then serves to connect the brain, which   *
is  the  common  centre of sensation and voluntary motion,
with all the sensible parts of the body, and with the muscles,
the instruments  of motion.   We may view it in  this sense,
as forming a channel  of communication for a  bundle of
nerves running  from the brain to every part of the  system
to carry messages  from the will, and to transmit intelligence
back again, as if all the roads and high-ways in the country
should terminate in  one  grand post-road, connecting them
with the seat of government.
  9. To illustrate, suppose I  seize a hot  iron in my hand,
not knowing it to  be heated ; the painful impression is  im-
mediately  transmitted along  the sensiferous nerves to the
spinal cord, and through that to the brain.  The brain takes
cognizance of it, and a mental determination is immediately
formed to  drop the iron.  The will sends back its command
through the anterior column  of the spinal cord to the motific
nerves, distributed  to the muscles, which go to  the hand.
The muscles instantly obey ; the iron drops, and the whole 
       THE SPINAL MARROW AND ITS FUNCTIONS.    139

process occupies but an instant.  Thus we have two channels
of nervous influence ; the one transmitting intelligence to
the mind, the other conveying the purposes of the will to the
muscles necessary to carry them into effect.
   10.  That such is the chief function of the spinal marrow,
is proved  by  the well-known  fact, that  if it is divided
in any part of its course, that portion of  the body, as well
as  the  limbs,  which  are  situated  below  the seat  of the
injury, will be paralyzed ; that is, all sense and motion will
be lost, while the parts above the injury will  be  unaffected.
If the injury occur very high up in the neck instant death
will ensue, because the nerves, which go the diaphragm and
are necessary to carry on breathing, are separated from their
connection with the brain.   These  leave the  spine as high
as the third vertebra of the neck.
   11.  I have stated  that  it has  been  proved,  that the
principle of  motion  resides  to  some  extent in the  spinal
marrow itself.  This is shown by the following experiment.
If after the spinal cord be divided in the neck, and then lower
down in  the back, we irritate any of the muscles which are
supplied  with nerves from  this isolated segment, motion will
be  produced.   If the foot, or the hand be pricked, it will im-
mediately contract; and this contraction is produced by the
irritation being transmitted to that portion of the spinal mar-
row, from whence  the  nerves of  the part  arise, and  whose
connection with the brain has been  severed, and then an im-
pulse is sent back again from this portion  to the  muscles of
the hand or foot  which  causes them to contract.  Still, all
voluntary motion, as well as  sensation, depend on the brain.
   12. If the medulla oblongata  is  injured, breathing imme-
diately ceases.  If the spinal marrow is  severed opposite the
second bone of the neck, death also speedily follows  ; because
the nerves  of respiration are cut off from their connection
with the part above.   If the spinal cord  be divided, as low as
the fifth cervical bone, then  life will not be immediately de-
stroyed ; but the breathing will be difficult; because the dia- 
140
PHYSIOLOGY.
 phragm is paralyzed, and death sooner or later follows from
 suffocation.   If it be divided about the first dorsal vertebra,
 then life may be maintained for a considerable time, although
 the ribs cannot be elevated, as the intercostal muscles  are
 rendered paralytic.   Breathing is, however, kept up by  the
 action of the diaphragm.   I have  seen a man whose  spine
 was dislocated in this region, live seven or eight weeks.  All
 sensation and motion were lost in the parts below the seat of
 the injury, but his reason and senses were perfect.
   13. As the heart, lungs, larynx, and many of the most im-
 portant organs of the body are supplied  with  nervous  influ-
 ence by the eighth pair of nerves,  or par vagum, why is it
 that  a division of the  spinal marrow causes death ?   This
 question is easily answered, by remembering that one of  the
 functions of the par  vagum is, to convey to  the  brain  the
 sense  of the want  of air, or of respiration,  and  that this
 stimulus reacts upon those parts of the spinal cord which give
 rise to the respiratory nerves of the  chest.  Now if this  com-
 munication  be cut off,  the influence of the brain, or the me-
 dulla  oblongata, cannot be transmitted so as to excite  those
 muscles which are employed  in breathino-.
   14. That this is  the true  answer to the above question is
 also shown  by dividing the par vagum in the  neck.   This
 causes palsy of the lungs, and also of the muscles which  open
 the larynx;  in consequence  of which, the  top of the wind-
 pipe is immediately closed, and death follows from suffocation.
 Besides this, it also prevents transmitting to the medulla ob-
 longata, the  sense of the want of respiration, and thus  pre-
 vents also the reaction of this part upon the spinal marrow.
   15.  Dees  the spinal marrow exert any influence  upon the
 circulation of the blood ?  It is ascertained that  the action  of
 the heart is  nearly independent of the spinal  marrow   Its
 nervous  influence is derived  from  the par vagum and the
great sympathetic nerve, the former of which  has but  little
 connection with the spinal cord.  The whole spinal marrow
 has been removed, and  still the heart has continued to act 
       THE SPINAL MARROW AND ITS FUNCTIONS.    141

Its action, however in such cases is much weakened.   That
the heart is, however, in some measure influenced by the spi-
nal innervation, must be admitted.
  16.  What is called the capillary circulation, or that in the
small vessels, is much under the influence of the spinal mar-
row.   It is found that when any part of it is destroyed, the
blood does not circulate in the small vessels which  derive
their nerves from the portion destroyed.  In these  cases, the
skin becomes purple, and dry ; perspiration ceases, the cuti-
cle peels off,  and the part becomes  sensibly  colder.   The
whole nervous system, however, is concerned in the produc-
tion of animal heat.
   17.  Digestion is  to a considerable  degree under the influ-
ence of the spinal cord.   In all cases of diseases of the spine,
the appetite is poor, and the digestive powers weak.   Colic
and  dyspepsia are frequent attendants upon such complaints.
If the eighth pair of nerves be divided, the  stomach is imme-
diately paralyzed,  and digestion interrupted.  This shows
that the stomach depends for nervous influence on the me.
dulla oblongata, and that it is derived through the medium of
the par vagum.
   18. The spinal marrow exerts an important influence over
the kidneys, more so perhaps than over any of the abdominal
viscera.   Some physiologists also think that it presides over
the  functions of nutrition.   What  seems to  confirm this
opinion, is the fact, that in the Crustacea, insects, and worms,
which have the power of speedily reproducing any  part that
is cut off, the spinal marrow preponderates  over every other
portion of the nervous system.   Nutrition is known to depend
chiefly on  the influence of the great sympathetic nerve, but
its connections with the spinal marrow are so numerous and
intimate, that there can be little doubt, it derives a  consider-
able portion of its nervous energy from the latter.   The fol-
.owing cut represents  the left side of the brain and spinal
marrow, shown by making a section  of the cranium and the
spinal column, and removing the dura mater. 
142
PHYSIOLOGY.
 
         THE SPINAL MARROW AND ITS FUNCTIONS.     143

  a. The convolutions of the cerebrum.
  b. The laminas of the cerebellum.
  e. The pons varolii.
  g. The medulla oblongata.
  c. d. f.  The medulla spinalis, or spinal marrow, extending from the
first cervical to the first lumbar vertebra, and terminating in the cauda
equina.  The cerebrum, it will be  seen, is the largest portion of the
brain, and occupies the whole upper cavity of the skull.  It rests an-
teriorily upon the arches of the orbits; in the centre, upon the middle
fossae  of the  base of the skull, and  posteriorily upon the tentorium
cerebelli.
   Questions.—How do we  find the brain developed in the lower ani-
mals ?  Have they great tenacity of life ?  Will zoophytes live when
divided into pieces ?  What is the medulla oblongata ?  What its func-
tion ?   Describe the  spinal  cord ?—its membranes ? its  shape ?—its
structure ?  How many pair of nerves arise from it ?   How many from
the neck ?—the back ?—the  loins ?  What is the function of the ante-
rior roots ?—the posterior roots ?  What is the use of the spinal cord ?
How is this illustrated ?  How proved ?  What follows, if the spinal
cord be severed opposite the second  bone of the  neck ?—the fifth ?—the
first dorsal ?  Does the principle of motion reside to any extent in the
spinal cord itself?   What experiment proves this?   Why does a divi-
sion of the par vagum or eighth pair cause  death ? Does  the spinal mar-
row exert any influence on the circulation of the blood ?—on the capil.
lary circulation ?—on digestion ?   What proves this ?  Has it any in-
fluence  over the kidneys ?—over nutrition ? 
CHAPTER XII.
           THE NERVES AND THEIR FUNCTIONS.

  1. In describing the nerves and their functions, it will be
necessary to classify them, or to reduce them to such arrange-
ment, as  the present  state of our  knowledge on the subject
will admit.  The following comes as near such a classifica-
tion as it is  possible to make :—1. Nerves of Special Sense.
2. Motific  Nerves.   3. The Respiratory Nerves.   4. The
Regular Nerves,  5. The Ganglionic Nerves.
  2. First  Order.—The nerves which contribute to the
senses of sight, hearing, and smell, constitute the first class,
and are called Nerves of Specific Sense ;  because they are in-
capable of communicating any other impressions, than such
as belong to the respective senses with  which they are con-
nected.   For example, the olfactory can only transmit ideas
of odours, the optic of colours,  the auditory of vibrations,
no matter what  the  stimulants may be which excite them
to action.   If we send an electric shock to the eye, it re-
ceives the impression  of light; to the ear, of sound ; and to
the nose, an odour is perceived :  so also, if we press or strike
the ball of the eye, we experience a vivid sensation of light,
and the same phenomenon occurs when the eye is pierced by
the needle of the surgeon : so also, if we take two pieces of
different  kinds of metal in the mouth, and placing  one over,
and the other under  the  tongue—allow their edges to come
together, we perceive  at once a peculiar taste, excited  by
galvanism.  Thus do these nerves communicate to the mind
that they a're affected in  the only manner of which they are
capable. 
THE NERVES  AND THEIR FUNCTIONS.      145
  This cut represents a portion of nerve, showing the filaments of
which it is composed, and one of them drawn out.

    3.  First, or olfactory.—These  nerves take  their name
from " olfactus^ the smell, as they are essential to this sense.
They are the softest nerves in the body, and more  closely
connected with the hemispheres of the brain than any other.
They lie immediately under the anterior lobes of the brain ;
and as they pass on, they swell into a bulb,  from which
numerous fibres issue, and pass into the nose through a plate
of one of the bones of the skull.   This plate is  pierced with
so many holes for transmitting these twigs of the nerve, that
it has the appearance of a seive ;  and from this circumstance
is called the ethmoid  bone.  The olfactory nerve is spread
out upon the lining  membrane  of the nose,  and is merely
defended by a  thin layer of mucus.   It was  necessary that
these nerves should come to the surface, in  order to come in
contact with the vapours inhaled by  the nostrils.  In  some
animals these nerves are very large, especially in ruminants,
but in others  they are  entirely  wanting, as in whales.  In
fishes, you may see the bulb of the olfactory placed immedi-
ately under the  cup-like nostril.   From the bulb, the nerve
runs  backward along a canal filled  with transparent fluid,
enters the skull, and joins the brain.
    4. The second, or optic.—These  are the largest  of  the
cerebral nerves, and can be traced as far back as the medulla
oblongata at the base of the brain.  They pass along the base
of the brain, and just  before they enter the orbits they unite
with each other, or seem to decussate, or cross each other.
In  some fishes, these  nerves evidently cross without union;
but  in man, it  is now pretty well established,  that a  semi-
decussation takes place ; that is, one half of  the right optic
nerve crosses to the  opposite side, and joins a half  of  the
                            13 
146                   PHYSIOLOGY.
left nerve to proceed to tho left eye ;  so that each eye receives
its optic nerve  from both sides of the brain ;  the right sup.
plying the right side of both eyes, as the left does its cor
responding side of both.  After  the nerve  has entered the
orbit, it proceeds  forwards to the ball of  the eye, and pene-
trating the coats of that organ, expands into a very delicate
web, or nervous net-work, called  the retina,  which  serves to
receive the  image of objects falling upon  it.
   5.  The auditory nerve.—The last nerve of specific sense,
runs along  with another, the two together  being known as
the seventh, of which the auditory forms the soft portion, or
portio  mollis.   It  arises  from  the  medulla oblongata,  and
goes on in contact with the  hard portion, or portio dura, to
the internal auditory passage, which they enter.   Here the
soft portion spreads out into a great many small  branches,
which are distributed over the surface of the internal por-
tions of the ear, and  their  extremities  float in  the water
contained  in the labyrinth,  from which  they receive vibra-
tions which produce the impressions of sound.
   6-  Second  order.—The motiferous nerves, which consti-
tute the second order, consist of  three  nerves ; the third, the
sixth,  and   the ninth, with  perhaps a branch of  the fifth.
These take their  origin at the anterior columns, in the same
line with each other ; but fibrils  of sensation afterwards join
them, so that they are analogous to the double-rooted nerves
of the spinal marrow.
    7. The third pair rise from the crura  of the brain, and
pass  forward  to  a  hole in the bottom of the orbit, through
which they enter, and supply four of the six muscles which
move  the eye, and  also  the  muscle which  moves  the upper
eye-lid, thus placing these muscles under  the command of
the will.   Besides this, a small twig of the fifth nerve swells
out into a ganglion, and  then  joins a twig from  the  third,
which go on together, and penetrate the  coats of the eye, to
which they impart  sensibility, and are connected with the
functions of the iris.   It is  worthy of remark, that here the 
          THE  NERVES AND  THEIR FUNCTIONS.      147
general law is kept, viz., that a ganglion  is formed  in  the
sensific nerves, before they become associated with the fila-
ments of motion.
    8.  The sixth pair arise near the last, and also enter the
orbit;  here they  are  entirely expended upon  the muscle
which  turns the eye towards the temple.  Where this nerve
has been  injured or lost its power, the eye is permanently
turned in towards  the nose ;  and such a person is said to be
cross-eyed.
    9.  The ninth pair  arise  from  the pyramidal bodies, and
passing through holes in the occipital bone, proceed forwards
towards the angle  of the jaw, by the side of the hyoid bone
of the tongue, and  are distributed upon the muscles  between
the lower jaw, hyoid bone, and tongue, the motions of which
it regulates.
  10.  Third Order.—This division embraces what  Sir
Charles Bell calls the respiratory nerves.  These are not only
connected with the function of respiration, but contribute also
to the expression of the passions and emotions of the mind.
They consist of the fourth ;  the portio dura; of the seventh,
or facial; the eighth, or par vagum ;  the phrenic; and the
external respiratory.   As the medulla oblongata,  consists of
three columns ; the nerves of motion arise from the anterior,
those of sensation from the  posterior ; while the respiratory
nerves, already mentioned, spring  from the middle portion,
and all nearly on the same horizontal plane.
  11.  The fourth  nerve supplies the superior oblique muscle
of the  eye, which  rising from the bottom of the orbit, runs
along the ropf of that cavity, till it  comes close to its brim,
where  it terminates in a small tendon, which passes through
a loop or pulley,  then turns  back,  and is inserted into  the
posterior part of the ball, so that  its contraction turns  the
eye in  towards the  nose.   When the will ceases to control
the movements of  the eye, it comes under  the action of the
superior oblique  muscle.    We see  this, in acute  bodily
pain, and at the point of death, when the voluntary muscles 
148
PHYSIOLOGY.
have lost their  power.   This turning  of  the  eye inward
is supposed to indicate great agony ; but  it rather shows
that all suffering has ceased, and that the powers  and sen-
sation  and  motion are lost.   If  we raise  the  eye-lid of a
person asleep, we shall find the eye turned in the same direc-
tion ; also in fainting, and in  cases of suspended animation.
The fourth  nerve is partly then under the  influence of the
will, and partly independent of it.
  12.  The  seventh nerve  consists of two portions, one  of
which, the auditory, has already been described.  The other
portion is called facial, because it is distributed over the face.
Its origin has already been stated, though it receives filaments
from each  column of the medulla  oblongata ;  so  that  its
function  is  complicated.  It seems, in fact, to combine the
character of a regular  nerve and one of instinctive  motion ;
it enters  the internal  auditory  passage  in  connection with
the nerve of hearing, then entering  a canal in the temporal
bone, it comes out just before  the ear, and spreads out over
the face  in  three principal branches, called pes anserina, or
goose's foot, from its resemblance to that object.
  13.  The fifth  nerve is distributed to  the same  parts  on
which  the facial is ramified on the face ;  the one serving for
sensation, the other for expression.   Thus  when the facial
nerve is  divided, or its functions destroyed by disease, the
side affected loses all power of expression, though  sensation
remains unaffected ; on the contrary, if  we divide the fifth
pair, sensation is entirely abolished, while expression remains.
The facial nerve not only communicates the purposes of the
will to the muscles of the face, but at the same time, it calls
them into action under the influence of instinct and sympa-
thy.  On this subject  a late writer  remarks, " How expres-
sive is the  face of man ?  How  clearly it announces the
thoughts  and sentiments of the  mind !   How well depicted
are the passions  on his countenance ! tumultuous rage, abject
fear, devoted love, envy, hatred, grief, and every other emo-
tion, in all their  shades and diversities, are  imprinted there 
          THE  NERVES AND  THEIR  FUNCTIONS.      149
in characters so clear that he that runs may read !  How
difficult, nay, how impossible  is it  to hide or falsify the ex-
pressions which indicate the  internal feelings!   Thus con-
scious guilt shrinks from  detection, innocence  declares  its
confidence, and hope anticipates with bright expectation."
   14. The eighth pair of nerves consist of three  distinct por-
tions ; the first  of which, from its being distributed to the
tongue and throat  is called glossopharyngeal; the second,
from its irregular course is called vagans, or the wandering
nerve ; and the third, from its origin from the spinal marrow,
is called accessory.   These different nerves join  just as they
are about  to escape from the skull, which they  do in  com-
pany with the internal jugular vein, and as soon  as they
emerge they  form connections with the great sympathetic.
   15. The vagans,  on leaving the  skull,  sends off branches
to the pharynx  and esophagus, also to the larynx  and the
muscles which  close the air passage, and the mucous  mem-
brane covering it.  Its trunk  runs down the neck included in
the  same sheath with the carotid  artery and jugular vein,
and  enters the chest under the collar bone.   Here a branch
is given off, which locks round the subclavian artery on one
side, and arch of the aorta on the other, and goes up to the
larynx, hence it is called recurrent.  It supplies those  mus-
cles  particularly which open the  air passage.   The vagans
sends down twigs with the sympathetic which surround the
the divisions  of the wind-pipe, and accompany  them in all
their ramifications  through the lungs.   It also sends numer-
ous  twigs  to the heart,  stomach, liver,  pancreas, spleen, in-
testinal tube, and finally with the sympathetic nerve, and forms
those great nervous centres or ganglia in the abdomen, which
supply all the viscera of that cavity with nervous energy.
   16.  The phrenic nerve derives its name from  its distribu-
tion  to the diaphragm, which  at one time, was considered as
the seat of the soul.   It passes out of the vertebral canal be-
tween the second, third, fourth, and sometimes fifth cervical
                             13* 
150
PHYSIOLOGY.
vertebra?; it runs down the neck, and enters the chest on
the outer side of the internal jugular vein.
   17. The external respiratory  nerve is  distributed to the
intercostal muscles, and those which extend from the ribs to
the shoulder, and which are occasionally employed in labo-
rious breathing.  It is through  the  instrumentality of the
accessory, phrenic, and external respiratory, that  the  mus-
cles employed  in respiration are  brought into action, com-
bined and directed with the proper degree of force, velocity,
and extent, without  the  necessity  of interference of the
mind.   Though to a certain extent, they may be under the
influence of the will, yet it  is only  in a  secondary degree.
No one, for  example, can long  suspend the movements of
respiration,  for in a short time,  instinctive feeling  issues its
irresistible mandates, which neither requires the aid of erring
reason, nor  brooks the capricious interference of the will.
   18. The influence of this order of nerves in the expression
of the passions, is  strikingly depicted in Sir Charles Bell's
Treatise on  the Nervous System.   " In terror," he remarks,
" we can readily conceive why  a man stands  with his  eyes
intently fixed on the object of his fears, the  eye-brows eleva
ted, and the eye-balls largely uncovered ;  or, why with hesi
tating and  bewildered steps,  his eyes  are  rapidly and  wildly
in search of something.   In this  way we only perceive the
intense  application of his mind to the objects of his  appre-
hension, and its direct influence on the outward organs.
But when  we  observe him  farther, there is a spasm in his
breast; he cannot breathe freely ; the chest remains elevated,
and his  respiration is short and rapid; there is  a gasping
and convulsive motion of his  lips, a  tremor on his  hollow
cheeks, a gasping  and  catching of  his throat;  his  hear<
knocks at his ribs, while yet there is no force in  the circu
lation, the lips arjd  cheeks being ashy pale."
   19. "To those I address,  it is unnecessary to go farthei
than  to indicate that the nerves  treated of in these  papers
are the instruments of expression, from  the smile upon the 
         THE NERVES  AND THEIR FUNCTIONS.      151

inlant's cheek to the last  agony  of life.  It is when the
strong man is subdued by this mysterious  influence of soul
on body, and when  the passions may be truly  said to tear
the breast, that we have the most afflicting picture of human
frailty, and  the  most unequivocal proof, that it  is the  order
of functions we  have been considering that is thus affected.
In the first  struggles of the infant  to draw  breath, in the
man recovering  from a state of suffocation, and in the agony
of passion, when the breast labours from the influence at the
heart, the same system of parts is affected, the same nerves,
the same muscles, and the symptoms or characters have a
strict resemblance."
   20.  Fourth  Order.—Regular Nerves.—I have already
stated  that there are thirty pair of regular nerves which go
out from the spine ;  each nerve being composed of two  kinds
of fibres ; those of  the anterior  column  being subsidiary to
motion, and  those from  the posterior to sensation.   With
these,  physiologists  now class the fifth  nerve.  This  large
nerve divides into three principal branches ; the first going to
the eye, is  called opthalmic ; the second to  the upper jaw, is
called superior maxillary; and the third sent to the lower jaw,
is named inferior maxillary.  It is  the  third branch, how-
ever, which  is truly  a compound nerve, as its roots arise both
from  the  anterior  and posterior columns.   The inferior
maxillary  branch,  is a  nerve of  both  sense  and  motion;
its filaments of motion supply the muscles which shut the
jaw,  while  those  of sensation  go to the tongue, salivary
glands, gums, teeth  of the  lower jaw,  external ear, cheek,
chin, and lower  lip.   It is this nerve which gives sensibility
to the face,  and it  is this which is the  seat of  that painful
affection called tic dolouroux, which is sometimes removed by
cutting the nerve affected.   In the cat,  the hare, and  other
animals with large whiskers, the filaments of  this nerve can
be traced to the bulbs of the hairs, which  accounts for the
delicate tact which  these animals  are endowed with, and by
means of which they are enabled  to wind  their  way  in the 
152
PHYSIOLOGY.
 dark, through intricate passages, with the greatest facility
 The fifth nerve  is associated with the organs of the senses
 of smell,  sight, and hearing ; it exercises that  of touch, is
 the immediate  instrument of taste, and  is affected  in some
 degree  by pungent odorous  substances, by  light,  and  by
 sound.
  21.  Spinal nerves.—The nerves of the spinal cord are all
 similar in their  construction, and in the functions which
 they perform.  The two sets of filaments of which they are
 composed, though enclosed in the  same sheath, yet remain
 entirely distinct  throughout their entire course.   They go
 to every muscular  fibre in  the  system, and spread out over
 the entire surface of the body, which possesses, accordingly,
 a  more exquisite  sensibility than  the deep-seated parts.
 Thus in  amputating a limb, the chief pain is in cutting
 through the  external  parts ; for the  bone may  be sawn
 through, the muscles, tendons,  and ligaments  cut  and la-
 cerated, and even  burnt  with a red-hot iron, and  still the
 patient experiences little or no suffering.
  22.  The object of endowing the skin with such a high
 degree of sensibility, is, doubtless, to warn us to avoid,  not
 only what is injurious to the skin itself, but also what might
 endanger  internal parts.   It  thus serves as a  protector to
 the  whole body.   The extremes of heat  and  cold, which
 might  prove  injurious,  produce their  painful impressions;
 mechanical  causes  rouse  by their sharpness, roughness,  or
 hardness ; acrid and corrosive  chemical agents induce un-
 easy sensation—all which  serve to admonish us to shun  the
 causes producing such  effects.   It is  remarkable to notice
 how every part of  the body is endowed with  its own kind
of sensibility.  The skin  feels changes of temperature ;  the
muscles experience only a sense of fatigue ;  the eye is sen-
sible only to light; the ear to sound ;  the  nose to odours ,
the  heart  to  blood ; the stomach to food,  dec. ; and these
sensations are sent along  up  to the brain  by little threads,
in close contact with other threads, which bring back  the 
          THE  NERVES AND THEIR  FUNCTIONS.     153

commands of the will!  Truly may it be said, " man is fear-
fully and wonderfully made."
   23.  The spinal nerves  are  classed according to the por-
tion of the spinal  column from  which they issue ;  as the
neck, back, loins, and pelvis ; forming eight cervical,  twelve
dorsal, five lumbar, and five sacral nerves ; all being con-
nected with the sympathetic.  The four lower cervical and
first dorsal go to the arm-pit, where they form a complicated
plexus, from whence nerves issue to supply the arm and hand.
The dorsal nerves  supply the integuments of  the  body, the
intercostal muscles, and those of the chest.   The lumbar
and sacral nerves supply the muscles of the loins and abdo-
men, together with the lower limbs.
   24.  Fifth Order.—Ganglionic Nerves.—We  have now
considered, somewhat minutely, that  portion of the nervous
system which is called the  cerebro-spinal, embracing the
brain,  the  material  instrument of thought, the source and
channels of voluntary motion, and of instinctive movements
and sympathy.   The ganglionic nerves are sometimes called
great sympathetic, or the great intercostal; but  sympathy
has been shown to be  chiefly independent of it, except  so
far as  it receives  filaments from  the cerebro-spinal nerves;
and it is called great, not so much from its size, as from its
supposed importance.
A plexus of nerves. 
154
PHYSIOLOGY.
   25.  The ganglionic, or great sympathetic nerve, consists in
a series or chain of ganglions, extending from  the  base  of
the  cranium  to  the extremity of the sacrum.   They are
placed on the  lateral part of the bodies of the vertebrae, and
are united to each other by intermediate nervous cords, and
send off  continually filaments  to all the adjacent  organs.
With the exception of the neck, there is a ganglion for each
intervertebral space, both  of the true vertebrae and sacrum.
Besides these, there are other ganglia situated around the
trunks of some of the large vessels of the abdomen.   These
ganglia are composed of a mixture of cineritious and medul-
lary matter, and are supposed to be  the  centres of peculiar
nervous power.
   26.  As to the functions  of this order of nerves, there is
good reason  to believe  that the peculiar vitality of  every
organ  in  the  body directly depends  on them.  Most physi-
ologists believe that they preside over the involuntary func-
tions, as  secretion, nutrition, absorption,  calorification, &c.
Others suppose  that the office of the ganglions is to render
the organs, which are supplied with nerves from them, inde-
pendent of the will.   As branches  from  them, accompany
the blood-vessels throughout their  course, every part of the
body must, to  a certain extent, be under their influence.
   27.  There have been three hypotheses prevalent in respect
to the functions of the nerves.  The first,  that  the  brain
secretes a fine fluid, which circulates through the  nerves,
called animal spirits, and which is the medium of communi-
cation  between  the  different parts of the nervous system ;
the second regards  the  nerves  as cords, which  transmit all
impressions by a kind  of vibration;  and  the third ascribes
nervous influence  to electricity or  galvanism.  But  there
is  no proof whatever  of the  existence  of any such fluid ;
the doctrine of vibrations is pretty much  abandoned ;  while
the electrical   hypothesis,  though   at  first view  perhaps
more plausible,  has probably no better  foundation  to rest
upon. 
           THE  NERVES AND THEIR FUNCTIONS.       155

  Questions.—How are the nerves  classified?   What nerves consti
tute the first order ?  Why called nerves of specific sense ?  Describe
the first or olfactory.  Is it large in animals ?—in  fishes ?—in whales?
—Describe  the second, or optic.  Do the fibres cross each other ?—its
function ?   Describe the auditory nerve.  What nerves constitute  the
second order ? Where do they arise ?  Describe the third pair ;—their
function ?   Describe the sixth pair ;—their function ?—The ninth  pair ;
—their function ?  What compose the third order of nerves ? Describe
the fourth  nerve ;—its function ?  Describe the  seventh nerve ;—its.
function ?   The fifth nerve ;—its function ;—distribution, &c. ?  Des-
cribe the eighth pair of nerves.   What are its three branches called ?
Describe  the vagans ;—the recurrent;—the  phrei ric ;—the  external
respiratory ?  What does Sir Charles Bell say of tin influence of this
order of nerves ?   What compose the fourth order oi nerves ?   Why is
the fifth nerve classed with the  regular nerves ?  Whore does  its first
branch go;—its  second;—its third ?  What  nerve is -effected in tic
doloreaux ;—its function ?  Describe the spinal nerves ;—their  mode
of origin ;—their  distribution ?   Why is the  skin so  sensible ?   Has
any part of the body its own sensibility ?   Illustrate this.  How are the
spinal nerves classed ?   What compose the fifth order ?  What  other
names for the ganglionic nerves ?  Describe them.  What is the func-
tion of the  ganglionic nerves ?   What  hypotheses  have prevailed in
relation to the functions of the nerves ? 
CHAPTER XIII.
          THE  FIVE SENSES.--SENSE OF TOUCH.

   1. A sensation is the perception of an impression made on
some organ.  By our sensati&ns we receive a  knowledge of
what is passing within or without the  body.   They are ac-
cordingly divided into internal  and external.  An internal
sensation, is one which is produced  by causes acting within
the system, as hunger and thirst; but an  external sensation
is  one that is occasioned  by the impression of a body, exter-
nal to the part impressed, as sight, hearing, &c.
   2. No sensation,  we have seen, can be perceived unless it
is  transmitted to th% brain.   When ideas, which have been
called " the images  of sensible objects," are reflected  upon
and compared with  each  other, we exert thought and judg-
ment; and when they are recalled, we are said to exert the
memory.   Thus are the senses avenues to knowledge, though
they do not give rise, as some  have stated, to our intellect
and moral powers.   With every sense an animal discovers
a new world ; thus  creation is to it increased  or diminished,
accordingly as its  senses  are more or less numerous.   A
sensation lasts a certain  time after  the exciting cause  has
ceased.   Thus if a piece of wood, with one  end  ignited is
whirled  round, we see a  luminous ring ; the sensation  pro-
duced by the wood  in each  point of  the circle continuing
till the wood  arrives at that  point again ; a rocket  forms a
train.
   3.  The external  senses  are five  in  number ;  touch, taste,
smell, hearing, and vision.  These are all situated at the sur-
face of the body, so as to be capable of acting  on external
bodies.  Most of them are under the control of  the will ; at
least  they may be exercised actively or passively, and  by 
SENSE OF  TOUCH.
157
directing the attention, the impression may be rendered more
vivid.
  4. The sense of touch is the general  feeling  or sensibility
produced by the skin, and which instructs us regarding the
general qualities of  bodies.  It resides also  to some extent
in mucous  membranes, as in the mouth,  throat, &c, although
in a very  imperfect  degree.   For example,  we cannot  feel
the pulse by placing the tongue over it on the  wrist, as any
one can ascertain by trying  the experiment.   The sense of
touch is distinguished by some writers from  that of feeling,
but they are only modifications of the same sense.
  5. I have already given some account of the structure of
the skin, and stated that  it is divided into four layers, viz.,
the cuticle, mucous web,  papillary body, and true skin;  and
that the cuticle is the thin, transparent pellicle,  or membrane,
which  forms the external incrustment of the body, protecting
those papillae,  in which reside  the  sense of touch.  As no
blood-vessels or nerves have been traced in it,  it is supposed
to be an  unorganized texture, or an albuminous  secretion,
poured out by the subjacent vessels,  and hardened by the in-
fluence of  the air.   This accounts  for its  rapid formation,
when destroyed by a blister,  burn, &c.   When a part of the
body is exposed to irritation, the vessels which pour out the
lymph, from  which the cuticle is derived, have their action
increased,  and  the  cuticle either becomes thickened, as in
the palms of the hand and soles of the feet, or the effusion is
so abundant as to cause a separation between it and the true
skin, causing blisters.
  6. Now, it is a general law, that pressure  promotes ab-
sorption ;  and  we see  this  exemplified daily  in  cases  of
tumours, abscesses,  bandaging for  dropsical effusions, &c.
Had this tissue  been subjected to this general  law, the fric-
tion and pressure  to which the cuticle of the  hands is ex-
posed in manual  labour, and of the feet in walking, would,
in a short  time, have entirely deprived them of protection,
instead of rendering their covering more dense and thicker,
                          14 
158
PHYSIOLOGY.
 that it may more effectually serve as a shield to the parts it
 covers.  As the cuticle is constantly renewed from its inter-
 nal surface, it is also constantly peeling off in the form of a
 fine powder, or thin  scales.  After scarlet fever, and other
 diseases, attended  with great heat of the skin, it is entirely
 removed ; the old scarf-skin, as it is  called, being thrown off
 in large patches.   We find  a cuticle in all organized beings,
 plants, as well as animals, though it differs greatly in struc-
 ture and appearance.   In  many reptiles  and  crustaceous
 animals it is entirely shed at certain periods, presenting an
 exact mould of their bodies, their scales, and other external
 parts, and even their eyes being exactly represented.
   7. The mucous web has already been pretty fully described.
 It is a soft pulpy net-work,  and seems  to  consist chiefly of
 the shaggy extremities of blood-vessels, interlaced and bound
 together by delicate filaments of cellular membrane.  It is
 the seat of those minute globules which constitute the colour-
 ing  matter which  vary  in their tints in different  races.
 These tints are influenced  in a greater or less degree by
 climate, for we find in tropical countries the colours of both
 plants and  animals are more  intense  and brilliant than in
 colder regions, and that exclusion from light produces a pale
 blanched appearance, while exposure to it has  a contrary
 tendency ;  but these  variations  are  neither permanent nor
 do they descend to the offspring.
   8. The dermis,  or  true skin, is the  thickest part of  the
 external integuments, and is composed of an infinite number
 of plates, consisting of filaments inextricably wound together,
 and abundantly supplied  with blood-vessels and nerves. The
 external surface of the cutis is every where studded by very
 minute nipples or papillae, and in several parts, as the palms
 of the hands and the  ends of the fingers, they are arranged
 in symmetrical rows,  which form wavering lines, and separ-
ated by small crevices that admit of the flexions  of the skin
and its adaptation  to the surfaces of external objects.  These
papillae are  the terminations of nerves and  blood-vessels, and 
SENSE OF  TOUCH.
159
are the immediate instruments of touch.  Although covered
by the cuticle and mucous web, yet the removal of these by
blisters or otherwise, does not increase the sense,  but  tends
to destroy and disturb it.  From this arrangement, sensation
is communicated through the hair and nails, as well as the
cuticle.   In  animals, of the cat tribe, which are furnished
with whiskers, these serve as organs of touch, as their roots
terminate in  these nervous papillae.
   9.  The  property of touch  belongs  to  every part of the
body, though the  hand is considered  as its special organ.
The great  number of bones  of which it is composed, make it
susceptible of every variety of motion, by which it changes
its form, and adapts itself to the inequalities of the surfaces
of bodies.   What is called  the pulp  of the fingers, seems
composed  chiefly of a tissue  of blood-vessels and  nerves,
covered  by the  cuticle  and  mucous web, and supported by
the  nails.   The delicacy  of touch is vastly improved by
education  and practice.   This is shown in the case of the
blind, who  often can  distinguish by touch  the different
colours, and  even their different shades.   This will not ap-
pear impossible  when we consider that difference of colour
may depend  on the dispositions,  arrangement, and number
of the little inequalities which roughen the surface of bodies,
even of such as appear the most polished, and thus fit them
to reflect certain rays of light, while they absorb the others.
That the  exercise of this sense  is  a gratification  to the
young, is apparent from the eagerness with which the child
stretches  out his little hands  to  all  the objects within his
reach, and the pleasure he  seems to take in touching  them,
in all their parts, and running over all their surfaces.
   10. I have already mentioned that the external surface of
the  body  is  endowed with  this special sensibility, not only
that it mio-ht furnish us with a  knowledge of the characters
of external objects, and so lead us to avoid dangers which
surround  us, but also to be a  source of positive pleasure.
Though in the acuteness  of the other senses many  animals 
160
PHYSIOLOGY.
 surpass man,, yet in the exquisite sensibility of his skin, man
 stands unrivalled.   " The skin of man," says Majendie,  " is
 more delicate, fuller  of nerves than that of the mammiferse ;
 its surface is  covered  only by the epidermis, insensible in-
 deed, but so thin, that it does not intercept sensation, whilst
 the hairs which cover so thickly the body of quadrupeds, the
 feathers which clothe  that of birds, quite deaden it.   The
 hand  of man, that admirable  instrument of his intelligence,
 of which the structure has appeared to some philosophers, to
 explain  sufficiently  his superiority  over all living species;
 the hand of man, naked, and divided  into  many moveable
 parts, capable of changing every moment its form,  of exactly
 embracing  the surface of  bodies, is  much  fitter   for  as-
 certaining their tangible qualities, than the foot of the quad-
 ruped, inclosed in a  horny  substance, or than that of a bird,
 covered  with scales too thick not to blunt all sensation."
   11. The hand then, is the chief organ of touch, and in  the
 ends of the fingers it resides in the greatest perfection. Thus
 we see that the blind are able to read with facility by passing
 their  fingers over the letters, which are raised by a particu-
 lar kind of type.  In this manner they acquire a knowledge
 of geography, arithmetic, reading, and the usual branches of
 education, not often  met with even in those who have  the
 use of their eyes as well as their  hands.
   12.  Buffon, the celebrated naturalist, thought so much of
 the sense of touch, that he believed  the cause, why one per-
 son has more intellect than  another is, his having made bet-
 ter use of his hands from early infancy.   Other philosophers,
as Majendie states, have ascribed man's superiority over ani-
mals,  and his intelligence, to the fact that he possesses a
hand.  But the hand is  only the instrument of the mind, the
agent of the will; it  can only execute ;  the mind must plan.
Besides, the idiot has  sometimes the sense of touch more deli-
cate than the man of genius, or than the most skilful artist;
while  some of the most ingenious artists have by no  means,
the most delicate touch.  Galen truly says, that  man had 
SENSE OF TOUCH.                161
hands given him because he was the wisest creature ; but he
was not the wisest creature because he had hands.*
   13.  The following cases prove that hands are not indispen-
sable  to genius, and that the human mind can  even triumph
over the imperfections of the  body.  A few  years since a
Miss Biffin was exhibited in London, who was entirely destitute
of both upper and lower extremities; and yet she was very
intelligent  and  ingenious.  She could  hem-stitch with the
greatest  facility, turning the  needle very rapidly  in her
mouth, and inserting  it  by means of her teeth.  She also
painted  miniatures faithfully  and  beautifully,  holding the
pencil between her head and neck.   All her motions in fact
were confined to the tongue and the lips, and to the muscles
of the neck.
   14.  In the year 1825 there  was  a young artist  in Paris,
who had no hands or arms, and only four toes on  each foot;
and yet he sketched and painted beautifully with his feet.   I
have myself seen a young lady, born without arms,  who had
acquired so much skill in the use of the  scissors as to be able,
by holding them in her mouth, to cut  likenesses, watch-pa-
pers, flowers, dec.  She would also draw and write,  and exe-
cute all kinds of needle work with  her  mouth.   A  boy was
not long since  exhibited in the  museum  of  this city, who
performed all  these things with his toes.  This  shows that
other parts of the  body besides the fingers, are  capable of
acquiring great delicacy of  touch.
  *On this subject Dr. Elliotson  remarks, "As  philosophers have
ascribed the superiority of man's intellect to his hand, and of the ele-
phant's to its trunk, the constructiveness of the beaver to its tail, and
the  ferocity of the tiger to its teeth and claws, the poor  man may be
excused who was lately executed at Chelmsford, and left the  following
directions.   " I, Edward Clarke, now in a few hours expecting to die,
do sincerely wish, as my last request, that three of my fingers be given
to my three children, as a warning to them, as my  fingers were the
cause of bringing myself to the gallows, and my children to poverty."
                           14* 
162                  PHYSIOLOGY.
  15.  In  animals, the organ  of touch varies.  In the ape
tribe it is similar to that  of  man.  In some quadrupeds it
is seated in the lips, snout, or  proboscis, as in  the  horse, the
hog, the mole, the  rhinoceros, and the elephant.  Indeed,
the trunk of the elephant comes very near to the human
hand in nicety of  touch, and delicacy of perception.   The
bat is remarkable  for sensibility of touch.   It has been found
that if its eyes  were destroyed and  its ears and nostrils shut
up, it would fly through intricate passages,  without striking
against the walls, and avoid every object placed in its way.
This faculty is supposed to  be  owing to the great delicacy of
touch  residing  in the membrane of the wings, which feels
instantaneously any change produced in the resistance of the
air.
  16.  In  insects, the antenna or feelers, are the  organs of
touch.   These are of a great variety of forms, very flexible;
and constantly in motion, when the insect is walking.  If
the feelers of an insect are  cut off, it either remains motion-
less, or if it attempts to fly, it appears bewildered and lost.
It is by means of their feelers that bees are able to work in
a hive  without light, and build their cells with  the greatest
regularity ;  by them also, they communicate to one another
their impressions  and their wants.
  17.  It is supposed that the  different modes in which ants
touch each other  with  their feelers, when  they  happen to
meet, constitutes a  kind  of natural language, understood by
the whole  tribe.   It is evident that they could not  co-operate
in their labours without some kind of language.  When an
alarm  is given in time of danger, one ant strikes his head
against the corselet of every ant which it chances to meet,
and these repeat  the same  act to all that fall  in  their way,
and so the news is quickly  spread through the whole society.
   18.  Sentinels are always placed on the outside of ants'
nests to apprize the inhabitants of any danger.   When an
enemy approaches,  these  guardians  quickly enter  the nest
and spread the news in the way just  stated, and soon the 
SENSE OF  TOUCH.
163
whole swarm is in motion.  While a larger  proportion of
the ants rush out to repel the attack,  others, who have the
office of guarding the eggs and the larvm, or eggs, hasten to
remove their charge to places of greater  security.   These
acts all depend on the faculty of touch, so that it is as import.
ant to the lower animals as to man.
   19.  Sight, hearing,  and touch, have been called intellec-
tual senses, because they are the means  through which we
obtain our most valuable information, the witnesses that fur-
nish the evidence  of the existence of  external things.  We
can have  no doubt as to the evidence they deliver, if they all
agree in their report.   We find however  that if we depend
on either  alone,  we are liable to be deceived.   Sight is liable
to many illusions ; we may, under the influence of the  ima-
gination,  or of a diseased  brain,  imagine  that  we see  a
thousand  strange  sights, ghosts, hobgoblins, spectres, and
devils ;  or from similar causes, we may believe that we  hear
strange and unearthly sounds ;  but if we attempt to touch
the objects which appear to present themselves to our vision,
or which  discourse such unnatural music, we find that  they
vanish  before us, like  the  ignis fatuus, or jack-o'lantern,
which we may chase " o'er bog, and o'er moor," but we can
never lay  our hands upon it.  I have often watched, with  a
degree  of wonder, the  action of a patient labouring under
drunken delirium ; the unhappy maniac not only sees strange
objects  about his  bed,  and  flitting before his eyes, but he
hears them singing and  talking to him ; he puts out his hand
to grasp  them,—he grasps nothing,—still he is not unde-
ceived,  nothing can make him  believe that what  he sees
and hears are only the phantoms  of a diseased brain ; he per-
sists in endeavouring to seize, to touch the strange objects,
and only  ceases, when  after days  and nights of incessant
vigilance, his strength exhausted, he either sleeps or dies!
  20.  Touch has, therefore, been relied on in every age, as
the most certain of our  senses, and it is well to recollect that
the most important fact that ever occurred on the theatre of 
 164                  PHYSIOLOGY.
 this earth, viz.  the resurrection of the Saviour, is established
 by  the  testimony  of the three intellectual senses.   In the
 gospel of the evangelist  St. John, we read, " But Thomas,
 one of the twelve, called  Didymus, was not with them when
 Jesus came.   The other disciples therefore said unto him, we
 have seen the Lord.   But he said unto them, except I shall
 see  in his hands the print of the nails, and put my finger  into
 the  print of the nails, and thrust my hand into his  side, I will
 not believe.   And  after eight days again his disciples were
 within, and Thomas with them ;  then came Jesus, the door
 being shut, and stood in the midst, and said, peace  be  unto
 you.  Then saith he to Thomas, reach hither thy finger, and
 behold my  hands; and reach hither thy hand, and  thrust  it
 into my side;  and  be  not  faithless but  believing.   And
 Thomas answered and said unto him, my Lord and my God.
 Jesus saith unto him, Thomas, because thou hast seen me,
 thou hast believed ;  blessed are they  that have not seen, and
 yet have believed."   Thus was the fact of the  resurrection
 established by the evidence of so  many of the  senses, as to
 render deception impossible.
  21. In some instances  the touch  itself, is liable to error.
 For example, if we roll a pea, or a  bullet, between two fingers
 crossed, we receive the impression  of two distinct objects,
 though we know there is  only one ; and if we look  at it, at
 the  same time,  the illusion is not removed, though we see at
 once that it is an illusion.   The  organs here are, however,
 placed in an unnatural position.  Another  fallacy occurs
with respect to  heat.  If we place the hand in separate  ves-
sels, the one containing warm, and the other very cold water,
and after some time withdraw  the  hands, and  immediately
 plunge them in  the mixture of both waters, to the one hand
the  mixture  appears warm, and to the other  cold.  So  in a
tropical country, if one person descends a high mountain
from the regions of perpetual snow, and  meets at the middle,
another ascending from the hot valley below, he who is de-
scending will feel  oppressed with heat, while  the  other  is 
SENSE OF  TOUCH.
165
shivering with cold, and both sensations are produced by the
same temperature.  Frozen mercury excites the same sensa-
tion as red hot iron.   A piece of marble will feel colder than
a woollen garment, although both be of the same temperature,
because the marble is a better conductor of heat than wool-
len ; a deep cellar appears warm to us in winter, and cold in
tummer, though its temperature is  nearly  the  same all  the
year round.  During the voyages  made  by Captain Parry
to discover the north-west passage, it was found that after
having lived for some days in a temperature of 15 or 20 de-
grees below zero, it felt quite mild and comfortable when the
thermometer rose to zero and conversely.   The sense, there-
fore, only gives  us  an idea of the relative, not the actual
heat of bodies.
   22.  The sense of feeling may become blunted to an extra-
ordinary degree.   Chabert, the Fire King, was said to have
been in the habit of swallowing forty grains of phosphorus
at  once ; washing his hands in melted lead ; and  drinking
boiling oil, without any apparent injury.   There is a great
difference in the  degree of sensibility of the mucous mem-
brane, in different individuals, some being able without in-
convenience, to   swallow fluids of a temperature  which
would be very uncomfortable to others.
   23.  The tactile power of the skin is not proportionate to
its sensibility.   Thus the arm-pits, flanks, soles of the  feet,
and other parts of the body, have slight power of distinguish.
ing objects  by touch, although they are  very sensible.   It
would be difficult to  make a person laugh by tickling  the
ends of his fingers, and yet we have seen that their sense of
touch is  more delicate than that of  any other portion of the
skin.  All the surfaces and solids of the body possess a kind
of sensibility, peculiar to themselves, and in disease may give
sensations, but this a different property from that of touch.
Questions.—What is a sensation ?  How are they divided ?  What 
166
PHYSIOLOGY.
is an  internal ?   What an external sensation ?   What  are ideas ?
What is the office of the senses ?  How many external senses are there ?
Are they under the control of the will ?  What is touch ?  Is touch the
same as feeling ?   Of how many layers is the skin composed ?  What
is the cuticle ? How formed ?  Its use ?  Is it subjected to the same
law as the other parts of the body  are in  relation  to pressure ?  What
would  have  been the consequence ?  Describe the mucous web.—The
true skin.  Where is the sense of touch chiefly situated ?  Describe the
papillae.  What is the pulp  of the fingers chiefly composed of?  Can
the blind distinguish colours by the touch ?   How  is this  explained ?
Why is the external surface endowed with special sensibility ?  What
does Majendie say of the human skin ?  By what process are the blind
enabled to read ?   What cases show that the  possession of a hand is not
necessary for  the display of intellect and  ingenuity ?  What is the or-
gan of touch in animals ?—in insects ?  What senses are liable to illu-
sions ?   Which is the most certain of the  senses ?  What fact was
established by the senses  of hearing, sight, and touch ?  Is the  touch
ever liable to  error ?  In what cases ?  May the sense of feeling be-
come blunted ?  What facts prove it ?  Are  the tactile  powers of the
skin in proportion to its sensibility ? 
k  CHAPTER XIV.
                     SENSE OF  TASTE.

   1.  The sense of taste is allied to that of smell and touch,
as it  requires the immediate contact of the body with the
organ where  the sense  resides.   The quality of  bodies,
which it teaches us, is called sapidity.  The superior surface
of the tongue is the chief organ of taste ; though the general
lining of the mouth and the upper part of the throat partici-
pate  in  the function.  The tongue is chiefly  composed  of
muscular fibres, running  almost in every direction ;  conse-
quently it possesses great versatility of motion, and can  be
moulded into a great variety of  shapes.   It  may be  con-
sidered as a double organ, as it is formed of two symmetrical
halves, whose  boundaries are marked by a slight  groove in
its  upper surface ; dividing it into right  and left.  From
this groove a membranous  partition extends down through
its  centre, and is attached to the froenum or bridle beneath.
The tongue is not only the organ of taste but also of articu-
lation, and also aids in mastication and deglutition.
  2.  The tongue is abundantly supplied  with blood-vessels ,
and its nerves, as we have seen, are supplied from  three
sources.   There  has  existed great  difference of opinion
among physiologists, as to which of these three  is the special
nerve of taste.  General opinion now holds the fifth as the
proper nerve of taste, as well as of sensibility ; the ninth, as
that of  voluntary motion; and the  eighth, as the  means
whereby thj organ  is brought into  association  with  the
throat, gullet, larynx, &c.   Dr. Elliotson, however, and some
others, think that  the glosso-pharyngeal  is the  nerve of
taste.
  3.  When we examine the surface of the tongue, we  find
it thickly studded with fine papillae, or villi, giving the organ 
168
PHYSIOLOGY.
 a velvety appearance.   There are  three varieties of these
 papillae.  The first are situated near the root of the tongue,
 and belong to the class  of mucous follicles, whose office it is
 to furnish this secretion.   These are much  larger than the
 others, and  are  called lenticular, from being shaped like a
 lens.  It is these,  together with  the almonds of the throat,
 or  ears, as  they  are sometimes called, which afford  the
 mucus  to lubricate the food in the act of  deglutition, and
 also to keep the tongue moist, and in a condition for the due
 performance of  its  function.
   4. The other two sets of papillae are the  instruments  of
 taste.   The one set is  named conical, or filiform, and con
 sists of small  nipple-shaped bodies, broader at the base than
 the top, and scattered over the whole surface of the tongue,
 giving it its  rough or shaggy appearance.  The other set
 of papillae is  larger, and consisting of small  rounded heads,
 supported on short  stalks, something in the shape of a mush.
 room, they have been called fungiform.  These are but few
 compared with  the former.  These sensitive papillae are
 supplied with  numerous blood-vessels as is shown in the next
 cut.  In order for the exercise of taste, it is necessary for the
 mucous membrane  to be in a state of  integrity, for  if it  be
 removed,  we  only  experience a sensation  of pain.   The
 animal papillae,  which abound on the sides  and tip of the
 tongue, appear to be the most exquisitely sensible.  Certain
 bodies seem to  affect one part of the more than another.
 Acids, for example, act especially on the lips and teeth ; acrid
 bodies, like mustard and cayenne pepper, on the pharynx.
 We read of cases in medical works, where, after the tongue
 has been removed by disease, or a  surgical operation, persons
 could still speak, spit,  chew, swallow, and  taste.  In one
 case, the individual could distinguish the bitterness of sal
 ammonial, and the sweetness  of sugar ; and  Blumenbach
 mentions a young man, who was born without a tongue, and
 yet when blindfold, could distinguish  between solutions of
salt and aloes  put upon his palate. 
SENSE OF TASTE.               169
  An upright section of one of the papillae of the tongue very greatly
magnified, and split open, to show the nerves (engraved white) and the
blood-vessels (black.)
  5. The  process  of taste, then,  is as  follows :—When a
fluid is taken into the mouth, these papillae dilate and erect
themselves, being endowed  with the  property of adapting
themselves to the active or passive condition of the sense of
taste.  If a solid portion of food is received, it is first touch-
ed by the tip of the tongue  and brought  into  close  contact
with the papillae ;  when if it be dry or solid, it is carried to
the back  of  the tongue and moistened  with saliva, which
thus becoming impregnated with  its flavour, and  flowing
over the sides of the tongue, gives to the papillae a  percep-
tion of the savoury juices.   The saliva, or spittle, it should
be recollected, is secreted by the  parotid  and other salivary
                            15 
170
PHYSIOLOGY.
 glands, chiefly  during the process of mastication, for  the
 purpose of moistening the food, while the mucous secretion
 is to keep the tongue in a condition to receive the impression
 of sapid bodies.   For example, in sickness, and especially in
 fevers, when the mouth is dry and parched, owing to a sup.
 pression of this secretion, the taste is entirely lost, showing
 that the membrane of the  tongue must be kept moist in order
 to the preservation of the taste.
   6. Insoluble substances are totally insipid, because in order
 to affect the nerves, the substance must be in such a state as
 to penetrate  the spongy  papillae.   It is supposed  that  the
 salts which enter into the composition of the saliva, are very
 efficient agents in reducing substances to a proper condition
 for making an impression on  the  gustatory organ.   In this
 way, we can  account for the fact, that  metals, though  in-
 soluble in water, often impart a peculiar taste.   The organs
 of taste are also powerfully affected by metals, so applied tc
 the mouth as  to call forth electric action.   If we place one.
 kind of metal on the tongue and  another under it, and then
 bring their edges together, a strong sensation is experienced
 If we touch the surface of the  tongue with the point of a
 wire, connected with the  positive  pole of a galvanic battery,
 a sour taste is experienced ; while the negative pole excites
 an alkaline taste.   These phenomena may be owing either
 to the electric action, disengaging from  the saliva an acid
 in one instance, or  an alkali in the other, or the electric  ex-
 citement may call forth the special  sensibility of the gusta-
 tory organ, in  the  same manner as it  causes the special
 sensibility of the other organs.
   7. Savours, like odours, are innumerable, and as they dif-
 fer so much from each other, it is  impossible to classify them
 in any  satisfactory manner.   We  can readily understand
 what is meant by the terms sweet, bitter, sour, saline, acrid,
 &c, yet each of them differs in intensity, as well  as other
shades  of character.  For  example, rectified  sugar, brown
sugar, maple sugar, beet sugar, molasses, honey, &c, are all 
SENSE OF  TASTE.
171
sweet, but the taste of each is different.  Linneus and Booer-
haave both made a  classification  of savours, but they have
never  been  generally adopted  by  physiologists.   Adelon
divides them  into two kinds, the agreeable and disagreeable.
But even this division is not founded in nature ; for we find
the old adage true,  that " one man's meat is another man's
poison."  Every person has some peculiarities of taste, dis
likes to particular articles of food, or shades of difference in
the appreciation of tastes, which may be constitutional, or
caused  by association.   Besides, the taste sometimes  be-
comes unaccountably morbid or  depraved.   We often see
children devouring  chalk, brick-dust, ashes, dirt, and  slate-
pencils, when if, at other times, they were required to swal-
low such articles, as medicine, they  would doubtless deem  it,
a peculiar hardship.
   8.  Savours differ as  to the  permanence or transientness
of impression which they leave upon  the organs of taste.
Aromatic and bitter substances particularly leave their taste
in the mouth for a long time  after they have been swallow-
ed ; the physician, therefore,  when  he  wishes to administer
some nauseous  drug, forestalls the sense of taste, by direct-
ing  one of  these substances to  be held  previously in the
mouth.  There  is a common  experiment on this subject,
which has led  to many bets, viz., giving to a person blind-
fold, brandy, rum, gin, or any other spirituous liquor in rapid
succession, and see  whether  he can tell one  from another.
 In a short time, the nerve becomes  so impregnated with th«
 different substances, that all distinction becomes confounded
 Tasters of wine, tea, &c, understand this principle ; for w«
 see them take up a  small portion and move it over  the wholt
 surface  of the  mouth, so as  to extend its action, and then
 they wait for some  time  after the impression is made  before
 they taste of other  samples.   When a person takes a medi
 cinal draught, he gulps it down as quick as possible, in orde\
 that it may come in contact  with as small a portion as pos
 sible of the organ of taste. 
172
PHYSIOLOGY.
   9. The taste is greatly under the influence of habit.  Many
articles which at first excite disgust, being  taken through
fashion or necessity, at length become highly  grateful.  We
need only name  tobacco, and  perhaps ardent spirits.   The
taste for these substances is altogether artificial, no one be-
ing fond of them, when taken for the first time.  Such per-
version of taste  often becomes national.   Thus garlic forms
a constant ingredient in the dishes of some European coun-
tries.   The  most  celebrated  sauce of antiquity,  was  the
Roman garum,  prepared from the half-putrid intestines of
fish.  Another of their favourite condiments was assafoetida;
and this is still in high repute among many of the orientals.
Rotten eggs are  highly esteemed by the Siamese, and fish in
an advanced state of decomposition is highly  relished in the
northern and  western islands of Scotland.   Dried,  putrid
mutton  is habitually eaten in Iceland, and  epicures in every
country esteem  game and venison a greater luxury, if in a
putrescent state.  To be a fashionable epicure of the present
day, requires that  the taste  should  be educated or trained,
like a sportsman's  setter.   It is then prepared to scent out,
with infallible certainty, what fashion has  taught it to relish
as choice luxuries ; but which simple, unadulterated taste,
rejects as fit only for the kennel or the carrion crow.
   10. The gratification which  we  derive from eating de-
pends chiefly on the state of the  stomach.  If that is not in
a condition to digest food  properly, no matter how much we
may generally relish any particular article ;  it will, at such
times, invariably excite disrelish or even  disgust.  So also
when  we sit  down  with a keen  appetite  to  a meal, as  our
hunger  is appeased, the relish proportionally  diminishes, till
at length we reach  the  point  of satiety, and  if we  persist,
nausea  and  disgust are certain to succeed.    Here then, is
another  wise provision,  informing us  with infallible cer-
tainty  when we have  taken  sufficient  food  to  supply the
wants of the system.   The  ancient  Romans availed them-
selves of a. knowledge of this law, and hence were in the habit 
SENSE OF  TASTE.               173
of leaving  the  table once or twice  during a meal, and after
having, by means of an emetic, unloaded the stomach, of re-
turning again to the charge.
   11.  As a general rule, articles that are  agreeable to the
taste, are safe and nutritious, though  this is not invariably
the case.   For example, prussic acid has a very agreeable
savour, as well as odour, and is accordingly used to impart fla-
vour to dishes and liqueurs, such as noyeau, yet prussic acid
is one of the most powerful poisons in nature.   Many sub-
stances which  at first are  highly agreeable, in a short  time
lose their relish ; we see that grocers understand this prin-
ciple, for instead of forbidding a new apprentice from eating
sugar, raisins, honey, and molasses, he tells him to eat all he
wants, knowing, that in a short time, his  appetite will  be
cloyed, and all  temptation removed.
   12. Among  animals, we find a great difference in the per-
fection of this  sense.  Some enjoy it, doubtless, in as great,
if not a greater degree than man, as they are able by it to
distinguish  plants that are nutritive and good  for food, from
those  which are poisonous ; and  accordingly  it  is  a rare
thing for animals to die from eating such vegetables.  Many
insects feed on the leaves of poisonous plants, and seme ani-
mals eat the leaves of the poison ivy without injury.  There
is an insect which feeds on the leaves of the tobacco,  and the
southern  planter guards against  its  ravages  by a  process
called worming.  The taste  also in animals sometimes be-
comes morbid, as we see  it happen  among our  own  race.
 Mr.  Bennet, in his " Wanderings in New South  Wales"
states, that serious  losses happened  to the  farmers  in  that
 country from the sheep acquiring the habit of licking and
devouring earth impregnated with saline matter.  In a short
 time, he says, their natural innocent dispositions  become
 changed, and they become carniverous and savage,  and de-
 vour the lambs.  Thus  out of a  flock of  twelve hundred
 lambs, eight hundred were devoured by'the sheep themselves.
    13. The sense of taste is most delicate  in youth.  It is
                            15* 
174                  PHYSIOLOGY.
much impaired by  the use of alcoholic drinks, tobacco, and
highly seasoned food ; so that the spirit-drinker, the tobacco.
chewer, and  the epicure often lose this sense to such a de-
gree that they cannot relish plain dressed food.  That  man
relishes his food best who rarely uses powerful stimulants and
narcotics.   Majendie says  that  man  would probably excel
all the other animals in delicacy of taste, if he  did not, at an
early period, impair its  sensibility by strong drinks, or by
the use of spices, and other luxuries.
  14. The taste may  be improved by cultivation like any
of the other senses.  Dr.  Kitchener states that some epicures
are able to  tell from what precise part of the Thames a sal-
mon had  been caught,  when presented at table.   Many
gourmands pretend to be able to pronounce by sipping a few
drops of wine, the  country whence  it comes, as  well as its
age; to tell by the taste, whether  birds put upon the table
are domesticated or wild, &c.  Such  acuteness of taste  is
however, by  no means  desirable, as we are liable, in the
"rough  and tumble" of life, to meet with so much that de-
mands obtuseness  rather than  refinement  of feeling.   The
epicure with his acuteness and delicacy of taste, is liable to
continual annoyances  and  discomforts, while  the man of
simple  and  unsophisticated  taste will  receive  gratification
and pleasure from  the very  same objects which excited dis-
gust in the  former.
  15. If we examine the lower animals, we shall find that  in
none of them is the tongue precisely like that of man.   The
resemblance is the nearest in apes;  but in them, even,  it  is
much elongated. In animals that chew the cud,  or ruminants,
we  find the tongue covered with  a dense cuticle, studded
over with  numerous pointed papillae, especially towards the
root.  These projections, together with the waving ridges on
their palates, are of great use in collecting and swallowing
the  tender herbage  on which they  feed.  In the  cat tribe"
the  sharp, horny prickles on the tongue, enables them to  take
a firm hold.   In the lion and tiger these prickles  are suffi- 
SENSE OF  TASTE.
175
cient to tear off the skin even of large animals.  Ant-eaters
are furnished with a  very long and slender tongue, covered
with a viscid, adhesive secretion, whereby they are able to
seize their prey, on thrusting it into an ant-hill.
   16.  Whales have an enormous tongue, though it has been
doubted whether it is endowed with the sense of taste.  They
have, moreover, projecting downwards from the upper jaw, a
kind of pallisade, consisting of several hundred plates of whale-
bone, the  outer edges of which are sharp, the inner fringed
with  long hair  like  appendages, the spaces  between  the
plates being little more  than half an inch.  The length of
the  plates sometimes exceeds twelve feet.  This pallisade,
when the  mouth is closed, is covered by the enormous fleshy
lower  lip, but when open, it presents  a kind of grating
through  which  the  water loaded  with  medusa and  other
small animals, flows.  Captain Parry states that these medu.
so, or sea-blubber, so  abound  in  the arctic seas, that  when
the  water is  still, and  the surface smooth, they present  a
striking resemblance to a thick snow-fall, when  the flakes are
large and the air calm.  The soft, spongy texture which
forms  the tongue of the whale,  is  thought  to be better
adapted for licking the food from the hairy whale-bone roof,
and transferring it to the gullet, than to  serve  as an instru-
ment of taste.
   17.  The tongue of birds varies much in form and con-
sistence.   In some, it is  horny, as in the toucan, where it is
several inches in length and exceedingly narrow, like a long
strip  of whale-bone;  or  in  the wood-pecker, to  the tip of
whose tongue there is fixed a long, sharp, pointed, spear-like
body with serrated edges, for piercing and seizing on insects
burrowing beneath the bark of trees.  Parrots, which belong
to the same class, have soft fleshy tongues well adapted to the
exercise of taste.
   28.  In  reptiles also, we find  great variety  of forms and
applications of the tongue.   In the  crocodile it is small and
immoveable, so much  so, as to lead some naturalists to deny 
176
PHYSIOLOGY.
 its existence.  In serpents, it is forked, and susceptible ot
 considerable motion ; while in  the frog, it is  folded  back  in
 the  state  of inactivity ;  but when the animal  is about  to
 seize an insect, it suddenly unfolds and projects it out of the
 mouth.   The tongue of a chameleon is contained within a
 sheath, and admits of being projected to  the extent  of six
 inches, and is besmeared with a glutinous  secretion.    In the
 twinkling of an eye it is darted out to catch  its food,  which
 consists chiefly of flies.  Fishes have the mere rudiments of
a tongue, fixed near the throat, which is  often furnished with
teeth.   There is reason to  believe that many  of the  inverte-
brated animals are endowed with taste, such  as bees, wasps,
flies, and leeches.
   Questions.—To what sense is that of taste allied ?  What is sapid-
 ity ?  What is the chief organ of taste ?  What other parts participate
 in the function ?   Describe the structure  of the tongue.   From  what
 source does the tongue derive its nerves ?  Which  is the nerve of
 taste ?  What  are  papillae ?   How  many  kinds are there  on the
 tongue ?   What is the office of the mucous papillae ?—Of the  conical
 and fungiform ?  What is the process of taste ?  Can insoluble  sub-
 stances be tasted ?  Why  not ?  What are the use of  the salts in the
 saliva ?  How do  we taste  metals ?   How is the taste excited by gal-
 vanism explained?  Are  there many  savours?  Name some.  Can
 they be classified ?  Why  not ?  What articles  leave a taste in the
 mouth the longest ?   What use  can  be made  of this  fact ?  How do
 tasters manage ?  Is  taste under the  influence  of habit ?  What  facts
 show this ?   To what is  the pleasure of eating owing ?  How is this
 shown ?  Is  the taste a sure guide to what is safe and nutritious ?  Do
 animals differ as to taste ?  Do they possess it in as great perfection as
 man ?  Does it ever become morbid in them ? When is taste  most
 delicate ?  How is it impaired ?  May the taste be improved ?  Are
the advantages or disadvantages the greatest,  which attend great deli-
cacy of taste ?  Have any of the lower animals a tongue like that of
man ?  Describe some peculiarities ?   What apparatus have whales
for eating small sea animals ?  What is said of  the tongue of birds ?_
of reptiles ? of fishes ?  Do any of the invertebrated animals possess the
faculty of taste ? 
CHAPTER  XV.
                  THE SENSE  OF SMELL.

   1. The sense of smell  takes  cognizance of the odorous
properties of  bodies."  The • seat, or organ, is the muccua
membrane, which lines the nasal cavities, and is called the
schneiderian, or pituitary  membrane.   It  is  covered  with
nervous  papillae,  similar to, but more delicate  than those
which  cover the organ  of taste.  These cavities open  an-
teriority  through the external nostrils,  and posteriorly into
the fauces or throat, to  permit the  air to  traverse them in
its passage  to  the lungs.   The  nasal organ  seems to  be
designed  for the purpose  of collecting the odorous particles ;
and it is  divided  into two  similar cavities, by a bony parti-
tion, called the vomer, which is extended by means of cartilage
to the anterior extremity of the nose.  Each nostril contains
Front view of the nasal fossae. 
178
PHYSIOLOGY.
two  convoluted or turbinated  bones,  of a light spongy tex-
ture, one  being  situated  above the other ; and they divide
the general cavity of the  nostril into  three passages.
  2. In connection with  the nostrils, there are several cavi-
ties,  as in the frontal and upper jaw-bones,  called sinuses.
These  communicate  with the nostrils,  and as they extend
the surface on which  the  lining membrane is expanded, they
are supposed to contribute to the sense of smell, by affording
capacious receptacles for air, loaded  with odorous particles.
Of the 14 bones which enter into the formation of the face,
11 assist in forming  the  cavities of  the nostrils, as do also
three out  of the eight bones  that  form the cranium   Be
Nasal fossae seen from behind, 
SENSE OF  SMELL.
179
sides the cartilage which forms the septum of the nose, two
others of an elastic nature constitute the wings ; and as they
admit of motion, several muscles  are  attached to them, in
order to regulate the  external orifices in accordance with
different conditions of respiration, and also to enable us to
exercise the sense of smell with greater effect, when we wish
voluntarily to employ that function.
   3. The membrane which  lines the nasal fossae, resembles
the mucous  membranes generally, and adheres firmly to the
bones and cartilages which it covers.   Externally, this mem-
brane is continuous with the common  integuments, and pos-
teriorly with the lining membrane  of  the throat.  It varies
somewhat  in appearance  in different situations.   In the
sinuses, it is thin, pale, and  of a smooth surface; but where
it constitutes the immediate seat of smell, it is thicker, more
vascular, and of a redder colour than  mucous membrane in
other situations.  It is studded with mucous follicles, which
yield the secretion with which it is moistened;  though it is
also bathed with the tears that  spread out upon it, after
having been conveyed from the eye through the nasal ducts.
The nasal mucus seems as essential to the sense of smell, as
the secretion from  the mucous membrane of the mouth  to
that of taste.  In  those who use tobacco in the  form of
snuff, this secretion often  becomes so scanty or so changed
in quality, that the  smell  is  much  impaired, and sometimes
entirely lost: the voice also is seriously  injured by the same
 practice.
    4. The olfactory, or first nerve, is the sense of smell.  This
 is spread out on the thick vascular portion of membrane just
 described.   Twigs from the first and second branches of the
 fifth, are plentifully ramified  over  the whole surface of the
 pituitary membrane,  imparting to it common  sensibility.
 The nose is also supplied with branches from the  facial to
 regulate the action of the muscles.  Dr. Majendie says, that
 the organ of smell  ought to be described as a sort of sieve,
 placed  in the passage of the air, as it is introduced  into the 
180
PHYSIOLOGY.
 chest, and intended to stop every foreign body that may be
 mixed with the air, particularly the odours.
   5.  What is called odour, or  smell, resides in nearly all
 bodies, and is given off by moisture, heat, motion, or friction
 Those which do not possess this quality are called inodorous.
 Those little particles which convey the odour, are scattered
 through the air, and in  breathing drawn into the upper part
 of the nostrils, where the sense of smell principally resides.
 If we breathe through the mouth, odours in general will not
 be perceived, unless very pungent.  The fluid which moistens
 the lining membrane of  the nose, is supposed not only to
 render it  more sensitive  and delicate, but also to entangle
 the odorous particles, and in this way detain them longer in
 contact with the olfactory nerve.   The constant evaporation
 which takes place from  the membrane, owing to the  passage
 of the air in respiration, requires  that the secretion should
 be  constant as well as copious ; otherwise the membrane
 would soon become dry  and parched.
   6. It is very difficult  to describe an odour, except  to those
 who have  smelled  it, or  something with which it  may be
 compared.  We can say that  odours are pleasant or dis-
agreeable ; that they are aromatic, or sweet, rancid, or fetid,
 &c. ; but we can  give no correct idea of the peculiar smell
of bodies, such as camphor, musk,  garlic, the rose, &c, with-
out experiencing the sensation which their smell produces.
   7. The odorous particles of bodies must be very small  to
excite  any sensation on  the animal  organs.  A grain of
musk will, it is said, scent  a room  for years, and not lose any
of its weight ; Mr. Boyle  asserts  that the smell of cinnamon,
from Ceylon, is perceived  at sea  at the distance  of twenty.
five miles  from the island.   Scales in which a few grains of
musk have been weighed, have been found to retain the smell
for twenty years, though during all this time, they must have
been constantly giving  off  odorous particles.   Haller kept
some papers forty years, which had been perfumed by a single
grain of amber, and at the end  of that  time they did not 
                       SENSE  OF SMELL.             181
 appear to have lost any of their odour.  But these particles
 cannot be as small as those of light, because we see that glass
 is capable  of retaining the former, but suffers the latter to
 pass through it.  The art of the perfumer consists in fixing
 and preserving odours in the most agreeable and convenient
 vehicles.
   8.  Odours differ very much as to the permanence of the
 impression which they produce.  While that of some is very
 transient, in others the scent remains  for hours  after the
 application of the  substance.   They also  differ, as we have
 seen,  as to  the  extent to which  their influence extends.
 Moisture in the atmosphere is favourable to the diffusion of
 odours, which  would seem  to  show that vapour is a  good
 conductor.   For example,  a flower garden is  never more
 grateful to the smell than in the morning, when the  dew is
 evaporating, or after a warm summer shower.   So also the
 plants of a green-house are more fragrant, just after  they
 have been watered.   Some flowers give  off their odour only
 at certain times, generally after they are fully expanded, and
 their parts in the greatest activity.
   9.  Though the air is the usual vehicle for odours, yet we
 find that  they adhere to solid bodies, and  can even be con-
 veyed through water.  But though the whole  art of per-
 fumery is founded on this fact, it has been strenuously denied
 that they could  be conducted  through water,  and conse-
 quently that fishes  could smell.   Some physiologists state
 that fishes have no olfactory organ ;  that the part commonly
 considered  as such is the organ of taste.  This  opinion is,
 however, erroneous.   " Not many naturalists of the present
 day," says  Dunglison, " will  be hardy enough  to deny, that
 fishes have an organ, or sense of smell.   At all  events, few
 anglers, who have used  their oil of rhodium, or other attrac-
 tive  bait, will  be disposed to give up  the results  of  their
experience, without  stronger grounds  than any that  have
been assigned by the advocates of that  view of the subject."
  10. Fishes are furnished with organs of smell,  but they
                            16 
182
PHYSIOLOGY.
 have no  communication with  the  mouth  or  gullet.   They
 are insulated cavities, covered  with a valvular lid, and lined
 with a plaited membrane, similar  to the  under surface of
 some mushrooms.   This serves to  extend  the surface, while
 it is covered with a viscid mucus.  In the cod-fish, the nerves
 of smell are spread out in a  cavity  filled with fluid, and
 larger than that which contains the brain itself.  "That the
 cod is guided by smell in the selection of food," says Aitkin,
 " must be well  known to every one who  has taken it with
 bait, in circumstances where he could watch the  conduct of
 the fish.  If not very hungry, it may frequently be  observed
 to approach the bait, apparently attracted by the sight, till,
 at a closer distance, it seems distinctly to smell  at it; and
 if not satisfied, turns aside  and  neglects it."  Every  person
 who has been in the habit of fishing much, must have often
 observed the same  fact, in catching common pond-fish, such
 as perch, roach, &c.
   11. It was an opinion formerly entertained, that  odours
 possess  nutritive properties, as  savoury smells  seem to have
 the effect  of allaying hunger, or at least  of satisfying the
 appetite in some degree.   This effect, however, is best ex-
 plained, by referring  it to the  influence  of odours on the
 nervous system, as we see the appetite often instantly des-
 troyed  by unwelcome news.   In   persons  whose digestive
 organs are weak, the  appetite is often destroyed insta'ntane-
 ously by a nauseous odour.  We read that Democritus lived
 three days on  the  vapour  of hot bread ; and Bacon speaks
 of a man, who  was supported several days by inhaling the
 odour of a mixture of aromatic and  aliaceous  herbs.  In
 1638, Dr. Wilkins, the Bishop  of Chester,  published a book,
 the object of which  was, to show that the moon is inhabit-
 able, and that it is possible for us to find a passage thither.
 In this work, he says, " If  we  must needs  feed upon some-
 thing, why may not smells  nourish us ?  Plutarch and  Pliny,
and divers other ancients tell us of a nation in  India, that
lived  only upon pleasing  odours ;  and it  is  the common 
SENSE OF  SMELL.
183
opinion of physicians, that these do strangely both strengthen
and repair the spirits."
   12.  We read an amusing anecdote in Fuller, who lived at
the same  time with the bishop, in relation to this  supposed
nourishing property of odours.  A  poor  man being very
hungry, staid  so  long in a cook's shop, who  was dishing up
the meat,  that his stomach was satisfied  with only  the smell
thereof.   The choleric cook demanded of him to pay for his
breakfast; the poor man denied having had  any ; and  the
controversy was  referred to the decision  of the next man
that should pass  by, who  chanced to be the most notorious
idiot in the  whole city ; he, on  the relation of the matter,
determined that the poor man's money should be put between
two empty dishes, and that the cook  should be recompensed
with the jingling of the money,* as he was satisfied with the
cook's meat.
   13. The sense of smell is closely associated with that of
taste.   It seems  indeed as a sentinel standing on  guard, to
see that no enemy approaches the citadel ; it tells us whether
the  aliment placed  before us,  is agreeable or disagreeable;
of course whether it will agree or disagree with the stomach.
The taste and the smell are hardly ever at loggerheads;  it
does, however, sometimes happen that a substance that is re-
pugnant  to the  smell, is  agreeable to the taste.  In such a
case they soon  come  to  an  understanding, and  the smell
chooses, to make the best of it, and drop its repugnance.  At
any rate, its  aversion,  some way or other, is  soon neutral-
ized.  The smell is, however  more  useful to animals, as a
sentinel,  than it  is to man, whose  reason  is more  than a
match for the instinct of the  brute  creation.  In them, in-
deed, it rarely fails to guide aright.   How wonderful is this
provision which  leads them with unerring certainty to choose
the innocent herb from the  poisonous plant; the nutritious
vegetable from that which is destitute of nutriment; and to
* Dunglison's Physiology. 
184                  PHYSIOLOGY.
reject instinctively, every thing which would prove noxious
or disagreeable.  It is not,  however, infallible  even in the
brute creation ; for we see the flesh-fly attracted by a certain
species of mushroom which admits a cadaverous odour, simi-
lar to putrid flesh;  in these  they  deposit their  eggs, which,
when hatched, perish for want of suitable  food  to nourish
them.
   14. A singular custom, which  prevails among shepherds
in some countries, shows  that the sheep  is  more under the
guidance of smell than sight or any of the other senses.
" When  a  lamb  has  died," says Aitkin, " the  shepherd
wishes to put to the ewe another lamb that may have lost its
dam; if she refuses to foster the stranger, he is sure to suc-
ceed by stripping  off the skin of her own offspring, and tying
it on the back of  the stranger, that she may smell the skin ;
she then entertains and treats it  as her  own.  In this case
she neglects the sense of sight, for nothing can be more un-
couth than the object of her affections ; neither does she
attend to the evidence afforded by hearing ;  however unlike
the bleating of the foster  lamb may be to that  to which she
was first accustomed, her smelling  is satisfied, and she is con-
tent."   The same practice succeeds with the cow.
   15. In the elephant, the tapir, and the  hog, as  well as in
oxen, sheep, deer,  and antelopes, we find  the cavities of the
nose very capacious, and the surface of the pituitary mem-
brane vastly extended ; and accordingly the  sense of smell is
proportipnally acute.  In France  it is customary to employ
the hog to hunt  for  truffles, a species of edible  mushroom
which  grows  at  some distance  below the surface of the
ground.  By  the sense  of smell alone, he is  accurately
guided to the spot where one is' growing, and begins to turn
up the earth with  his snout,  in order to get at it.   The  vege-
table hunter, however, anticipates  him, and driving away the
animal,  digs down, and appropriates it to himself.   In this
way he secures, in a short time,  sufficient  for a family din-
ner. 
SENSE OF  SMELL.
185
   16. The delicacy of this sense in the greyhound is most
 astonishing.  He not only tracks the hare, the fox, or the
 wolf with unerring certainty, long after their footsteps have
 been imprinted, but even  in  a large city, he will trace the
 progress  of his  master through thoroughfares and  thickly
 crowded streets,  distinguishing his footsteps from those of a
 thousand passers-by, and amidst the odorous particles emanat-
 ing from a thousand sources.  When Hispaniola was first dis-
 covered by the Spaniards, they employed  the greyhound in
 hunting the poor  natives, who, unlike the  more fortunate
 Seminoles of Florida, could  find no  ever-glade, no fastness,
 no retreat,  which could save  them from the unerring scent
 of these animals.
   J 7. The organ of smell is universally found in birds,
 though varying  in size.   Rapacious birds and waders, or
 those that live on fish, have it more largely developed than
 any others.   Humboldt relates that in South America, when
 the inhabitants wish  to take the condor, they kill a horse or
 cow, and  in  a  short time, the  odour of the  dead  animal
 attracts those birds  in great numbers, and even  in places
•where  they were  scarcely known to exist.   Some of the
 Roman historians tell us that  vultures went from Asia to the
 field of battle at Pharsalia, a distance  of  several hundred
 miles, attracted thither by the smell of the dead.  Pliny, the
 natural historian, affirms that the vulture and the raven have
 the sense of smell so delicate, that they can foretell the death
 of a man three ddjs beforehand.
   18.  Mr.  Audubon, however, relates two experiments to
 show that vultures are indebted to sight  rather than smell, in
 the discovery of  their prey.   He stuffed a deer's skin with
 hay, allowed it to become as dry as leather, and placed it in a
 field ; in a  few  minutes a vulture made for it, attacked it,
 tore open the  stitches, and pulled out  the hay.  He then put
 a dead  hog into a ditch,- and  covered it over with care; it
 soon putrefied and became intolerably offensive, but the vul-
 tures, which were sailing about in all directions in search of
                            16* 
186
PHYSIOLOGY.
 food, never discovered it, although several dogs had  been
 attracted to it by the scent.   His next experiment  was to
 stick a young pig, and cover it over with  leaves ; vultures
 soon saw the blood, descended to it, and by this  means  soon
 discovered the pig, while it was  still fresh.  The general
 opinion of physiologists at  present is, that  birds of prey,
 have not so acute a sense of smell as has been generally sup.
 posed, and that they are guided chiefly by sight.
   19. It  is stated  by  whale-fishermen, that  in  Greenland,
 when a whale  has been  captured,  although at  the  time
 scarcely a single bird  may be visible, yet  in a short time,
 immense numbers of gulls and other sea-birds hover about,
 and hasten to the spot  from every point of the compass. Al-
 though  these  birds  have the  organ of smell,  and  conse-
 quently the sense itself, largely developed, yet such facts may
 be more satisfactorily explained, than by supposing that they
 are able to smell the flesh of a dead whale,  before putrefac-
 tion has commenced, at a distance of many miles.   A better
 explanation cannot be  given than is contained  in the first
 volume  of " MacGillivray's  History of British  Birds."—
 Speaking of ravens gathering together in immense numbers
 over a  dead carcass, in explanation of the  phenomenon he
 remarks, " A single  raven  might first perceive the carcass.
 Ravens have character in their flight as men have in their
 walk.  A poet sauntering by a river, a conchologist or fish-
woman  looking for  shells  along  the  shore, a  sportsman
searching the  fields, a  footman going on  a message, a lady
running  home  from a  shower, or a gentleman retreating
from a mad bull, move each  in a different manner, suiting
the action to the occasion.   Ravens do  the  same, as well as
other birds ; so those at the next station, perhaps a mile dis-
tant, judging by the flight of their neighbours that they had
a prize in view, might naturally follow.   In this manner the
 intelligence might be communicated over a large extent of
 country, and in a single  day a great number  might assemble.
 We know  from observation that  ravens can perceive an 
SENSE OF  SMELL.
187
 object at a great  distance, but  that  they  can smell food a
 quarter of a mile  off we have no proof whatever;  and as we
 can account for the  phenomenon by their sight, it is unne-
 cessary  to  have recourse to their other faculties."  Every
 person who has seen  the manner  in which crows collect
 together about a dead  animal in the country, will be satis-
 fied that the above is a  correct explanation of the  pheno-
 menon.
   20. The  olfactory  organs of reptiles  are but slightly
 developed.  Frogs have two small holes, which serve as the
 organs of smell.   The pituitary membrane of the turtle is
 of a very dark colour, and the nerve is of considerable size.
 In serpents, they  are  more  elongated,  and in lizards  still
 more so.   The animals of this class have no cavities corres-
 ponding to the sinuses ;  of course the sense of smell cannot
 be very acute.
   21. The smell  can  be greatly  improved by education.
 Humboldt states, that the Peruvian Indians can distinguish
 in the middle of the night the different races by their smell;
 whether  they  are European, negro,  or American Indian.
 By habit, the perfumer  acquires the faculty of distinguishing
 the nicest shades of odours.   We see the influence of educa-
 tion, by the difference between a dog that has been trained
 to the chase, and one that has not.   In the blind, the sense
 of smell is particularly acute.  A boy in Edinburgh, who was
 born blind and deaf, could tell the entrance of a stranger in-
 to the room by the smell alone ;  and he told one person from
 another by smelling at him.
   22.  Dr. Good remarks, that " we occasionally meet among
 mankind with a sort  of sensation altogether wonderful and
 inexplicable.  There  are some persons so peculiarly affected
 by the presence of a  particular object, that is neither seen,
 lasted, smelt, heard, or touched,  as not only to  be  conscious
of its presence, but to be in  agony till it is  removed.  The
vicinity of a cat not  unfrequently produces such an effect;
and I  have been a witness to  the most decisive proofs of this 
188                    PHYSIOLOGY.
in several instances."  There can be no doubt, I think, that
this peculiarity is referable to delicacy of smell.   Dr. Dung-
lison states,  that a  gentleman, blind  from birth,  had  an
extraordinary antipathy  to  cats.   One  day in company, he
suddenly leaped up, got  upon an elevated  seat, and exclaim-
ed, that there was  a  cat in  the room, and  begged them to
remove  it.  It was in  vain  that the company assured him
that he was mistaken.    He persisted in his assertion and in
his state of agitation ;  when, on opening the door of a small
closet in the room, it was found that a  cat had been acci-
dentally shut up in it.
  Questions.—Define the  sense of smell.   Where is it  seated ?  De-
scribe the pituitary membrane ;—the nose.  What cavities are concern-
ed in the sense of smell ?  What is the object of such an extended sur.
face ?  How many bones assist in forming the cavities of the nostrils ?
Why are they supplied with muscles?  Does the  membrane that line
the nostrils resemble the other mucous membrane ?  How is it moist.
ened ?  Do the  tears answer any purpose except washing the eye ?
What effect has snuff-taking on  the  sense of smell ?  What is the
nerve of smell ?  What other nerves send twigs to the nose ;—their func-
tion ?  To what does Majendie compare the organ of smell ?  What
is odour ?  How given off  from bodies ?  Are odours  easily described ?
What facts show that their  particles are very minute ?  What is the
art of perfumery ?  Do odours differ as to the permanence of the im-
pression they produce ?  What favours the diffusion of odours ?  Can
odours be conveyed  through water or other  fluids ?  Have fishes any
organ of smell ?  What facts prove this ?  What article renders bait
attractive to fish ?  Were odours ever believed to be nutritious ?  What
anecdotes in relation to this ?  Are the senses of smell and taste asso-
ciated ?  What  is the use of smell ?  Are any substances disagreeable
to the smell and  agreeable  to the taste ?  Is smell more useful to ani-
mals than man ?. Is it infallible in them ?  What fact proves that it
is not ?  What  singular custom prevails among shepherds ?  What
animals have the sense of smell the most acute ?   How is the smell of
the hog employed in Fiance ?  What is said of this sense in the  grey-
hound ? Was it ever employed to hunt savages ?   When and where ?
Have birds any organ of smell ?   What does Humboldt say of the
condor ?  What  experiments did Audabon try, to prove  that birds of 
SENSE OF  SMELL.
189
prey are guided by sight instead of smell ?  What do whale fishermen
say of birds in Greenland ?   How does  Mr. MacGilivray explain the
gathering together of so many birds over a dead carcase ?   Have rep-
tiles any olfactory organs ?  Can this sense be improved by education ?
What causes  the  singular antipathy to  cats, which we meet with in
some persons ? 
CHAPTER  XVI.
                  the sense of sight

   1. This is the most refined and admirable of all our senses.
 By it especially we hold converse with  the external world ;
 and without it, we should  not only be  deprived of a  large
 portion of the pleasures we now enjoy, but we should be un-
 able to maintain our existence for any length of time.  The
 wisdom, power, and benevolence of God  are  chiefly  mani-
 fested to us through the sense of vision,
   2.  The eye is the organ of sight, and the  most beautiful
 of all the  organs of the senses.  So  admirable is its struc-
 ture, so wonderful the provisions which adapt it to the pur-
 poses for which it was designed by  our  Creator, that I shall
 give as full a description of it as my limits will allow ; and
 in order to an easy and clear comprehension of its structure
 and  function, I  shall  first  describe the coats of the eye, in-
 eluding the retina, or the expansion of the nerve of vision;
 then  the humours of the eye, by  the  agency of which, the
 rays of light are concentrated so as to form an image  upon
 the retina;  and lastly, explain the laws of vision, the motions
 of the eye, and the means of protection against injury.
   3.  The  Coats of the  Eye.—The coats of the  eye are
 generally reckoned as  three in number, viz., the sclerotic, the
 choroid, and the retina; besides  these, there  are  the cornea,
 the iris, and the  ciliary processes, which  are viewed and des-
cribed as appendages to these coats.
   4.  The sclerotic* or outer coat, is the  firm, opaque, fibrous
substance which preserves the globular figure of the eye ; and
besides defending its internal delicate structure, serves for the
attachment of those muscles which move the eye.   It invests
* From a Greek word, signifying hard. 
SENSE OF SIGHT.
191
the eye on every side except the front, forming about  four.
fifths of  the  external  covering,  and  extending from the
entrance of the optic nerve, at its base, to the cornea.  This
coat has  almost the firmness  of leather, and possessing but
little sensibility, it is rarely exposed to inflammation or  other
            Plan of the eye, seen in section.
A, The Sclerotic Coat.         F, The Aqueous Humour.
B, The Choroid  Coat.         G, The Iris.
C, The Retina.               H, The Ciliary Processes.
D, The Optic Nerve.          I, The Crystalline Lens.
E, The Cornea.               K, The Vitreous Humour.
diseases.  The sclerotic coat is much denser in the eyes of
fishes than in the eyes of creatures which live on the surface
of the earth.  In the whale, it is more than an inch  thick,
in order, that when he dives some hundreds of fathoms deep,
the pressure  of the water on the eye may not be greater than
its structure  can withstand.  That this pressure is very great,
is shown by  the common experiment  of corking  an empty
bottle tight, and then letting it down into the sea by a cord ;
the cork will always be found forced in, and  the  bottle full
of water ;  the pressure being equal  to the  weight of the
column of water above it, of which it is the base.  Dr. Buck- 
192
PHYSIOLOGY.
land states, that in  one experiment, a copper  cylinder, con-
taining atmospheric air, was crushed flat under a pressure
of 300 fathoms, and bottles ■ filled with air were crushed in.
stantly.  This shows the necessity of a strong sclerotic coat
in animals that dive far beneath the surface.
            Front and side view of the ball of the eye.

   5.  The  Choroid Coat.*—This  constitutes the second in-
 vesting  membrane of the eye, which is  of a dark  brown
 colour, soft, cellular, and vascular.   This coat  is situated
 on the inner surface of the sclerotic, to which  it is slightly
 attached by means of blood-vessels and nerves, of which in-
 deed it seems to be chiefly composed ; for, on injecting  the
 eye carefully with coloured wax,  it assumes  a  uniform  red
 colour.  The inner as well as outer  surface of this mem-
 brane is covered by the pigmentum nigrum,  or  black paint;
 which seems to absorb  the rays  of light  immediately after
 they have struck  the sensible surface of the retina.   This
 pigment, sometimes called  tapetumf in animals  that see best
 at night, is wanting  in albinos,  as I have already stated ;
 and it  is owing to this  cause  that the iris  and pupil  appear
 of a red colour, and that  their vision is so imperfect, that
 they cannot view objects in a strong light ;  and indeed can
scarcely  see enough to go about  in the day-time.  In ani-
mals that prowl  by night, this pigment is wanting, or of a

           * Choroides, fleecy, like a lamb skin.
           t Tapetum, like cloth, or tapestry. 
SENSE OF  SIGHT.
193
bright green, or silvery whiteness, and the dark pigment is
peculiar to those animals that see in the brightest light of day.
                          Fig. 3.
  The eye, after cutting away the sclerotic coat and cornea, to show
the vessels of the choroid coat; magnified.

  6. The Retina.*—This is  the third and  innermost mem.
brane of the eye, and is  the  expansion  of  the optic  nerve,
and  the  immediate  seat  of vision.   It  is a  soft, thin, and
transparent substance, extending from the optic nerve to the
crystalline lens, and  lining the choroid coat throughout with-
out adhering firmly  to it.  The retina  may be divided into
three layers, viz., serous, nervous, and vascular ;  the former
of which passes on  over  the  surface of the lens, and forms
part of its capsule.  There is a small portion  of the retina,
supposed  to  be  near where  the optic nerve  pierces the
sclerotic coat, which  is  not  susceptible of vision, as may
rje shown  by an experiment hereafter  mentioned.  It  was
formerly supposed, that the retina was endowed with extreme ^
sensibility ;  but  it is now ascertained that it is almost insen-  »
sible to every stimulus  but that of light.  The same is true

                       * Retina, a net.
                           17 
194
PHYSIOLOGY.
of the optic nerve.  The ordinary sensibility of the eye is
derived from the branches of the  fifth  pair of nerves ;  and
we have already seen that several  pairs of nerves are sent to
its muscles.
   7.  The minuteness with which  objects are painted on the
retina is indeed wonderful.   Standing on an  eminence, the
eye takes in a landscape of hundreds of miles in extent;  and
all this is painted on the retina, though, as an English writer
calculates, a portion  of the  castle of Edinburgh, 500  feet
long and 90 feet high, occupies on the retina only the twelve
hundred thousandth part of an inch, when seen at a certain
distance.   " A  whole  printed  sheet  of newspaper," says
Arnott, " may be represented on  the  retina on less surface
than that of a finger nail, and yet not only shall every word
and  letter be separately perceivable, but even  any imperfec-
tion of a single letter ; or, more wonderful still, when at night
an eye is turned up to the blue vault of heaven, there is por-
trayed on the little concave of the retina, the boundless con-
cave of the sky, with every  object in its just proportions.
There a moon in beautiful miniature may be sailing among
her white-edged clouds, and surrounded by a thousand twink-
ling stars, so  that to an animalcule, supposed to be within
and near the pupil, the retina might appear another starry
firmament  with  all its glory.  If the images in the human
eye be thus minute, what must  they be  in the  little eye of a
canary bird, or of another animal smaller still!  How wonder-
ful are the works of nature !"
  8.  The Cornea  is the  term applied to the anterior tran-
sparent portion of the ball.   It resembles a watch crystal in
shape, and it is received  into a groove in the sclerotic coat,
in the same manner  as a watch-glass  is received  into its
case, as in this cut.  It is somewhat thicker than the sclerotic
 
SENSE'OF  SIGHT.              195
coat, and is composed of six concentric plates ;  but its blood-
vessels are so small, that they exclude  the red particles alto-
gether, and admit nothing but serum.  Under the first plate,
little glands are found, perceptible only by aid of the micro-
scope, which are supposed to secrete an oil which gives the
eye its bright, sparkling appearance.   In the last stage of
life, we find this fluid forming a thin pellicle over the cornea.
What is called the ciliary ligament, is the  groove or circle,
where the cornea is inserted  in the sclerotic coat.
   9.  We find the tunics just described  in the lower grades
of animals, as  well as in man, differing of course  in  form,
density, &c,  but  always fitted to the circumstances of the
animal.  Thus in soft, molluscous animals, the defensive coats
of the eye are soft also ; but then their eyes are placed on ten-
tacula, or feelers, so  that they can retract  them within their
shells.  In the  articulata, as  insects, the coverings of the eye
are firmer, and of a horny consistence.  In the Crustacea, such
as crabs, lobsters, &c, the eyes are set in short bony cylinders,
and the cornea is often covered merely by a portion  of skin,
which passes over it.   In fishes, we see the cornea  flat, on
account of the absence of the aqueous  humour.  In  birds,
the  cornea is  conical, corresponding with the  quantity of
aqueous humour ; and it  is more  prominent in rapacious
birds, such as  the hawk, eagle, and  kite, than in  aquatic
birds.  It is remarkable that the solerotica in  birds consists
of three different layers, the middle  one of which  is bone,
and composed  of several plates,  overlapping each other ;
designed doubtless to protect their eyes against  each other's
sharp-pointed  bills,  which they have  to  encounter in their
attacks.   In the higher animals, the coverings of the eye are
similar to those of man.
   10. The Iris, is  a circular membrane, which hangs sus-
pended like a curtain in the aqueous  humour, and is attach-
ed to one of the coats  of the eye at  its circumference.  It
derives its name iris, or rainbow, from the  various colours  it
has in different individuals, such  as dark-brown,  or  black, 
196                  PHYSIOLOGY.
 light-grey,  olue, and  several  shades  and  combinations of
 these.  It is on this  alone that the  colour of the eye de-
 pends.   The colour depends indeed on the  refraction of the
 light, as  it falls on the fleecy or velvet-like  surface  of the
 membrane, and also upon  the degree in  which the black
 paint which  covers its back is seen through it; according as
 the iris is more or less  transparent, will the " colour  of the
 eye" be lighter or darker.
   11.  In many of the  lower animals, especially birds, the
 iris assumes a still greater  variety of colours.   The round
 hole in the centre of the iris is called the pupil, and  it is the
 dark pigment of the choroid coat,  that we see through  this
 when we look into the eye of another.   Aitkin says  that this
 name has been given to it, from the fact that when  we look
 into the eye, we see a small image of our own  face, like a
 very minute child  or pupil.   In albinos, and in animals  that
 see best in the dark, like owls, the dark pigment is  wanting
 not only on the choroid coat, but also on this membrane,  and
 as these parts are very  vascular,  the blood is seen imparting
 a red colour to the eye.
   12. The iris has  the power  of  dilating or contracting in
order to admit  more or less light according as it is needed.
This is effected by muscular fibres.  Of these, there are two
kinds.  The first set converge from the circumference of the
iris to the circular  margin  of the pupil, and are called  the
radiated muscles. When these contract they dilate the pupil.
The other set is composed of circular fibres which go round
the border,  and indeed, form the pupil ;  these are  called
the orbicular muscle;  and when  they contract diminish the
size of the pupil. Now, when more light enters the eye than
is  wanted, the excited retina immediately  gives warnino- of
the danger, and the nerves which  are  plentifully distributed
to the iris, stimulate the orbicular muscle  to contract,  and
the radiated one to relax, by which means the size of the  pu-
pil is instantly lessened.  On the  contrary,  when in the dark
 or twilight, more light  is needed, to transmit a distinct  image 
SENSE OF SIGHT.                 197
of objects to the brain, the orbicular muscle relaxes, and the
radiated one contracts, so as  to enlarge the pupil to its full
extent.   Between these two  muscles is a middle layer, com-
posed of a net-work of blood-vessels and nerves.
  The cut marked I. represents the iris magnified as seen  from the
front, showing the radiated muscle.
  Cut II. is a back view of the same showing the orbicular muscle.

  13. The iris then, regulates the quantity  of light passing
through the pupil.  The pupil during sleep is in an intermediate
state ; in inflammation of the brain it is generally contracted ;
but when the  functions of the brain are interrupted by nar-
cotic poisons, the-pressure of effused fluid, a tumour, or any
other cause, the pupil is dilated.   The  bella  donna, or deadly
night-shade, is employed  by surgeons for  this purpose, when
they wish to couch, or perform other operations on  the eye.
The contraction of the  pupil  is readily  seen by holding a
candle close to the eye of a person, and then withdrawing it
slowly ; or by directing a person to look  at a very  near ob-
ject, and then at one more distant.  Some persons can dilate
and contract the iris at pleasure.  I possess this  faculty  to
a very  great  extent, and  was  conscious  of it before I ac-
tually tried the experiment.   The motion  of the iris  is not at
all associated with that of the lids, as Walker suggests in his
late excellent  work  on  the Philosophy  of Sight,  the lids
remaining the whole time perfectly stationary.  I am, when
contracting the iris, sensible  of an  effort similar to that of
examining a very near object, and when dilating it, like that
                          17* 
198                   PHYSIOLOGY.
of looking on  one at a distance ;  but it  is  not necessary
actually  to look at any object in either case, nor do 1 attempt
it.   If this does  not prove that the muscles  of  the iris are
somewhat  under  the control of the will, then it cannot be
proved that any muscles of the body are so.
  14.  The iris,  in  the  lower animals, not only  presents
great diversities in colour, as  has  been stated, but  also in
form and mobility.   In birds, and  in the cat tribe, its mo-
tions are free  and evidently voluntary ; but in reptiles, its
motions  are obscure ; and in fishes imperceptible.  In rumi-
nants, in the horse, the marmot, in the whale tribe, and in
owls, the goose, and the dove among birds, the pupil is  elon-
gated transversely or  sideways.  In the horse, a small square
curtain hangs down, which intercepts a great portion of the
rays  coming from  above.  In the  cat  tribe, including the
lion, the tiger, leopard, the lynx, the jaguar, &c.  the pupil  is
elongated vertically, as it is also in the crocodile.  Now we
see a wise  design in this arrangement, for in such animals as
have to  watch their  prey, which  is generally  placed  more
above them, as on a tree, than at either side,  the  pupil  is
elongated vertically,  so as to admit of more extended vision
in such direction  ; while in timid animals, like the ox, sheep,
and hare, who have to guard against the insidious approach
of enemies, while quietly grazing the fields, we  find this ar-
rangement reversed, and the pupil admits the greatest num-
ber of lateral rays.
  15.  Ciliary Processes.—These are little folds or fringes of
the choroid coat, which, joining the sclerotica near the cornea,
(which union is termed the ciliary ligament) turn backwards
and inwards, in the form of a  circular, plaited fringe, the lit-
tle threads of which are called  the ciliary processes.  They
are covered, like the choroid, with the black pigment, and
closely embrace the margin of the crystalline lens, forming
round it  an opaque blackened partition, which absorbs all the
side rays of light, which might otherwise have disturbed the
clearness of vision.   These threads or  processes are plaited 
SENSE of  sight.
199
[ike the folds of a ruffle, of which there are about 70 in the
human eye, all arranged in a radiated manner uound the lens,
as represented in the following cut.
                         Fig. 5.
  Section of the eye magnified, showing the ciliary processes, the pig.
mentum nigrum, the retina, and the choroid coat.

   16.  The ciliary processes are  thus  cellular and vascular,
and some have thought muscular, in order to give support to
the weight of the crystalline and vitreous bodies, to  keep
them from falling towards the iris, or into  the aqueous hu-
mour.   To accomplish this, we  find them placed immme-
diately in front of the vitreous humour, and closely embrac-
ing the  circumference of the  crystalline lens, and then to
strengthen the slender materials of which  it is formed, we
find it implanted in little furrows on the surface of the vit-
reous body, glued as  it were to it, and adhering  to it  very
firmly.   We know that very substantial fabrics are made by
plaiting  and matting  together  very slender and  flimsy sub-
stances, as straw, chip, and grass to form hats;  and it  is on
this principle, doubtless, that the ciliary processes are im-
pacted or plaited  together.
  17. Humours  of  the  Eve.—The humours  of the eye* 
200
PHYSIOLOGY.
have  been compared to the glasses of a telescope, and the
coats to the tube which keeps them in their places. They are
three in number, and though all are perfectly  transparent,
they differ in density, and in the space  which  they respec-
tively occupy.
   18. Aqueous Humour.—The aqueous humour  is as clear as
the purest water, from whence its name, although its specific
gravity is  greater ;  containing, as it does, a little albumen,
gelatine, and  muriate of soda.   It fills the entire space be-
tween the cornea and cyrstalline lens.   The iris floats in it,
suspended like a curtain.   The space between  the  iris and
the cornea is called the  anterior chamber ; and that between
the iris and the crystalline lens, the posterior chamber of the
eye.  This fluid is secreted by a very thin, transparent mem-
brane which encloses it, though some say  it exhales from the
vessels of the iris,  and its chief office is to distend the cor-
nea, and preserve the iris in a moist condition, fit for the dis-
charge of its appropriate  functions.  This fluid  is also in a
constant  state  of secretion and  absorption ;  for  when
entirely discharged, in  extracting the lens, for  cataract, we
find that  in a few hours it  will be  restored again.  In old
age, its  quantity is  lessened, and the eye  becomes flatter,
needing the aid of convex glasses.  Fishes have no aqueous
humour at all, as the water, in which they swim, answers the
same  purpose, as this was designed for, in land animals.
   19. Besides this,  the aqueous humour probably  aids  in
adjusting the eye to different distances.   As the  lens lies im-
mediately behind it, it is evident that, when the  quantity  of
fluid is increased, it  will press the lens  back nearer the re-
tina, while, at the same time, it renders  the  cornea more
convex, and the reverse happens when the quantity  is dimi-
nished.   When  the  distension is very great, the  pressure
causes a cloudiness  or  opacity of the cornea, thereby pro-
ducing  blindness.    This  not unfrequently happens  with
horses that have been fed during  the  winter on dry food,
either placed on a  level  with  the head or  above  it.  In the 
SENSE of  sight.
201
spring, when they are turned out to the green pasture, where
their diet is changed from dry to succulent, and where also
the head is held  near the ground to collect the food, a con-
gestion of  the aqueous humour is apt to  occur, sufficient  to
produce temporary blindness.
   20.  The Crystalline Lens.—This  is  placed immediately
behind the aqueous humour, a  short  distance back of the
pupil, and is a double  convex lens, perfectly transparent.   In
shape  it closely resembles the common  burning  glass ;  its
posterior surface is, however, a little more convex than the
exterior, and it approaches nearer to a sphere in  infancy
than in old age.  When the crystalline lens is  first removed
from  an eye, it looks like  a mass of transparent  crystal,
without any trace of organization.   Near the surface it is
much softer than at the centre, which  is  harder  and more
compact.  It is also softer in the young  than in the old.  As
it consists chiefly of albumen, when exposed to heat, as  of
boiling water,  alcohol or acids, it becomes white,  like the
white of an egg.  If we examine  it in  this state, we shall
find that it  consists of an immense number  of concentric
plates or Lamella.  More than  two thousand  of these  have
been counted, disposed in the form of layers like the coat of
an onion, each layer consisting of an  infinite number  of
very minute filaments, wound round in  different  directions,
from  various  centres.  The arrangement of these  fibres
differs in various animals, but is uniform in every individual
of the same species.   In fishes the lens  is nearly  spherical;
in reptiles it is less so, and in birds and  mammalia, it is still
more flattened.   In amphibious  animals, as turtles or frogs,
or those whose  vision is adapted  both for air  and water, as
seals and whales, the lens is more convex than in those which
live entirely in the  water.  When this  lens becomes  so
opaque as to obstruct  the  passage of the  light, either par-
tially or entirely, a person is said to have a cataract.   This
can only be cured by a surgical operation. 
202
PHYSIOLOGY.

   Fig. 6.
  Section of the eye  magnified, showing the Crystalline Lens in its
proper situation, between the aqueous and vitreous humours.
  21.  The Vitreous Humour.—The vitreous body or humour
is so called from its resemblance to melted glass.   It is, like
the other humours, perfectly transparent, and  occupies  the
globe of the eye, of which it constitutes  at  least the poste-
rior two  thirds.   It is surrounded by the retina in nearly its
whole extent, to which, however, it  does not adhere.  It is
composed of a fluid,  contained in cells, formed  of a  mem-
brane  called  the  hyaloid,  which  communicate  with each
other, so that  if it  is punctured, the fluid  with which it is
filled will escape, though slowty in consequence of the intri-
cacy  of the  cellular  structure.  On removing the  vitreous
humour from  the eye, it appears to  be  of about  the consis-
tency of the white  of an egg ; its use  being to afford a sur-
face for  the extension of the expanded  retina, to  keep  the
lens at the requisite distance, and to transmit and refract the
rays of  light. 
SENSE OF  SIGHT.                203

      Fig. 7.
  The vitreous humour and crystalline lens magnified, with the stains
of the pigmentum nigrum left by the  ciliary processes.

  22.  Laws  of Vision.—Light  passes through  the air, or
any  medium of the same  density, in  straight  lines;  but
when it passes  from one medium  into another, it is refracted,
or bent out of a straight course, unless it strikes  the  new
medium in a perpendicular  direction, when it passes directly
through.   Air, water, glass, or any substance through which
light passes, is  called a medium.  When a ray of light passes
from  a thinner or rarer  medium, into one  more dense, as
from air into water, it is bent towards a line drawn perpen-
dicularly to its surface.   The contrary is the case when the
reverse happens.   This  is  shown by  plunging  a  straight
stick into the water, which  will appear crooked.   This  may
be illustrated by the familiar experiment of taking an object,
such as a shilling, and fixing it at the bottom of an empty
basin, then retiring backwards until the brim of the basin
hides it ;  then  let  water be poured into the vessel, and the
coin will again come to light, as  in the following cut.   (See
Fig. 8.)
  Thus the ray of light from the coin will proceed in the di-
rection a, previous to  the addition of the water, but when
water  is poured into the vessel,  the  ray will be  reflected
down to the eye, and the  shilling will appear to occupy the 
204                   PHYSIOLOGY.

                          Fig. 8.
situation b.  In the same way, when  we look  into a river,
the pebbles appear to  be raised in the water, and it looka
shallower than it really, is.   From this circumstance, persons
have often  been  drowned.
  23.  Lenses.—A lens is usually made of glass, its surface
being ground into  some of the following shapes :

                          Fig.  9.
  The first of these on the left hand would be called a plain
lens ; the third, double convex ; the fourth, plano-convex ; the
fifth, double concave ; the sixth, plano-concave; the seventh,
concavo-convex, Sfc.  Now, light  in its passage through these
glasses, would be refracted in proportion to their greater or
less  degrees  of convexity  or concavity;  but in  passing
through a plain  lens, like the first, the rays would not be
bent out of a straight  course.   For example,  if you  place
an object  at the  bottom of a tub of water, and  place the eye
in a  perpendicular  direction over it, the object is seen  pre-
cisely  in  its true situation;  but if you withdraw  a  short
distance, it will appear to be situated where it is not. 
SKNSE  OF  SIGHT.
205
  A, a solid oblong piece of glass; a, a,  a stream of light, which
•trikes the surface of the glass, b, c, and which,  being perpendicular,
suffers it to pass through without  refraction.

  24. Now let us take a concave lens, and see what effect
that will  have on the light.
  A, a solid oblong piece of glass; a, a, a stream of light which strikes
the surface  of the glass b, c, and which being concave, causes the light
in its passage  through it to diverge.

  25.  Now try a convex lens, such  as the  crystalline humour
of the  eye, and see how  that  will affect the rays of light.

                            Fig. 12.
We see that  this  form  of glass causes  the rays of light
                          18 
206
PHYSIOLOGY.
a'a, to converge to a point, or focus at d; and if it was still
more convex, they would come to a point still nearer.   We
are now able fuJly to understand how  it  is that the humours,
or lenses of the eye collect the light from visible objects, and
converge them into an image upon the retina.  These media,
we have seen, are four in number, viz., the cornea, the aqueous
humour, the crystalline  lens, and  the  vitreous humour; each
possessing a different density, different sphericity, and con-
sequently different refractive  powers.
   26. Now let  us examine  the principle on which an image
is  formed.   This may be shown by holding  a common sun-
glass opposite a window in a room, and placing a sheet of
paper behind it.  We immediately see depicted on the paper
a  perfect image of the windojy, diminished according to the
convexity of  the glass,  but inverted.   The greater the con-
convexity, the nearer must the paper be held  to the glass to
receive the  image, and the nearer fo the  window the glass is
held, the larger  will the image appear.

                         Fig. 13
  In this cut, rays of light  pass  from the candle, and the
hand A, B, and falling on the lens at C, are conveyed to the
paper D,  which is consequently illumined with  the  object
in the  same way  as  in the  above  experiment, the window
was painted on  the paper.   In like manner  precisely, are
images painted on the retina, as is shown in  the following
cut. 
SENSE OF  SIGHT.

  . Fig. 14.
  27. Thus the convergence of the rays begins in the aqueous
humour is perfected in the crystalline ; but when they strike
the vitreous humour, which  is concave on its front surface,
and  also  less dense  than the crystalline,  they diverge or
spread out, and are thrown  upon  the back  part of the eye.
The manner in which this is-effected may easily be seen by
the following illustration.
o, the aqueous ; c, the crystalline ;  v, the vitreous humour.
In passing through the crystalline, the rays cross each othei,
so that those rays which  pass from the lower part of an
object are presented uppermost in the bottom of the eye and
the reverse, so that the images of objects are always  invert-
ed, or bottom side upwards.  Any one can see  this  by cut-
ting out  a circular  portion of the outer coat, at  the back
part of the eye of an ox or sheep recently killed, and  holding
it  up at a window ;  he will then  see, on its posterior sur-
face, a perfect but inverted representation of objects whether 
208                 PHYSIOLOGY.

stationary or in motion.   Now, suppose a  person was look-
ing at a church with a  tree standing at its side, he would
have in each eye an actual inverted panorama of the objects,
painted in  a more  beautiful, correct, and delicate manner
than any effort of art can ever hope to exhibit, as follows.
Fig. 16.
  28. But if the images of objects are inverted, why do we
see things erect ?  Locke, Buffon, Diderot, and other great
philosophers, supposed that infants at first see things  upside
down, and afterwards learn to correct their erroneous sensa-
tion, by comparing the information obtained by touch with
that acquired by sight.   And not only this,  they maintain.
ed that infants see every object double, and all at  the same
distance, until experience corrects their errors.   Berkeley,
however, contended, that we judge of the position  of objects
by comparing them with our  own ; and as we see ourselves
as well as every thing  else wrong side  up, or inverted, ex-
ternal bodies are in the same relation to us as if they were
erect.   But in that case, the boy who stoops down  and looks
at objects  between his legs, ought  certainly to  see them
wrong side up ;  but though a little confused perhaps at first,
he soon sees in that  way as well  as  any other.   This diffi-
culty is easily explained by what  is called the law of visible
direction ;  that is, each point of an  object is seen perpendi-
cular to the point of  the retina on which  its image falls.
The surface of the retina being concave, and nearly as pos- 
                      SENSE  OF SIGHT.              209
sible spherical, these lines of visible direction meet and cross
at a point within the eye, which is called the centre of visible
direction ;  the lines from the  upper part of the image go to
the lower part of the object, and those from the  lower part
of the image proceed to the upper part of the object.  Thus
an inverted image necessarily produces an  erect  object, and
the external object is  the thing to which the mind attends,
and  not  the object on the  retina.   The error of all these
philosophers has consisted in this, that they have  imagined
a true picture to be formed on the retina, which is regarded
by the mind, and therefore seen inverted.   But there is no
interior eye to see or take  cognizance of this image ; but
the  mind  accurately  refers  the impression  made  on  the
retina to the object producing it. In  short, the mind stands
behind the retina  and looks  at  objects as  they are through
this screen, but  it does not see the  screen  itself, but judges
of the position of objects by the direction in which the light
comes from them towards  the eye;  and as Arnott  well
remarks,—" no  more deems  an object to be placed  low be-
cause its image may be low in the  eye, than  a man in a
room into which a sun-beam enters by a hole in the window-
shutter,  deems  the  sun low  because its  image  is on the
floor."
   29. Again, why,  as we have two  eyes, does not every
 object appear double ?  The reason is, that in  the two eyes
are corresponding points, so that  when a similar  impres-
 sion is  made on both, the sensation, or  vision,  is single.
 Now, we have the faculty of so directing the axis of the
 eyes, that the image of an  object falls exactly on the same
 point in each ;  but if from any cause there is the least dis-
 turbance,  then  vision  becomes double, as often happens to
 the drunkard.  This is easily  known by slightly  pressing
 a finger on the ball of either eye, so as to prevent its following
 the motion of the other.   Persons who squint  always  have
 double vision, but then they acquire  the power of attending
 to the sensation in one eye at  a time.  Animals  that  have
                           18* 
210
PHYSIOLOGY.
the eyes placed on opposite  sides  of the  head, possess in a
more remarkable degree the faculty of thus attending to one
thing at a time.
   30. It follows then, that the eye itself does not see ;>it  is
only an instrument employed by  the  brain, or  rather the
mind, whose  servant the  brain  is.  The optic nerve is the
channel by which the mind peruses the hand writing of na-
ture on the  retina, and through  which  it transfers to that
material tablet its decisions and  its creations.  There is then
a portion, or  rather an organ of  the brain,  where vision  or
the mind's eye  is seated ; and this portion is sometimes im-
perfectly constituted or organized, as Gall has proved to  be
the case, in  those  who  cannot distinguish  colours.  That
such is a true statement of facts,  we learn from observing that
disease of a given portion of brain produces blindness, whilst
the eye remains perfectly healthy.   Either this was the case
with Milton,  or he  was afflicted with amaurosis, or palsy  of
the retina, for he says,
                         " These eyes, though clear
            To outward view, of blemish, or of spot,
            Bereft of light, their seeing have forgot!
           Nor to their idle orbs doth sight appear
           Of sun, or moon, or star throughout the year!"
We also have the power of internal vision when asleep ; and
those who have lost their eyes perceive spectral illusions, and
other similar phenomena, and they can  also conjure up the
figures  and forms  of various objects familiar to them before
they lost their vision.
   31.  From the principles now laid down we  can understand
why rivers appear  shallower than they are, and why a stick
placed in the  water  appears crooked.   In spearing of fish,
or shooting them in the water, every sportsman knows that
he must'make suitable allowance for this refraction, for the fish
is always nearer to him than it appears.  Bkds that dive  for
fish seem to understand  that  there  is but small chance  of
success if they dive obliquely into the  water, so  like skilful 
SENSE OF SIGHT.
211
opticians, they hover  over,  and when  they see their prey,
dart down perpendicularly, in which direction, as we  have
seen, there is  no refraction.   There is a curious fish in the
East India waters called chactodon, about eight inches  long,
that appears to understand  optics remarkably well.  When
it sees a fly, sitting on the plants that grow in shallow water,
it swims within five or six feet, and then with the dexterity
of a practical marksman, ejects from  its tubular mouth a
single  drop of water which  never  fails  to strike the fly into
the sea, where it  soon becomes its prey.  Dunglison states
that Hommel, the Dutch governor, put some of these fish
into a tub of  water, and  then  pinned a  fly on a stick within
their reach.   He  daily saw the fish shoot at the fly, and they
never  failed to hit their mark.
   32.   Short-sightedness.—This generally  arises  from  too
great convexity of the  cornea,  or excessive  density in  the
structure of the crystalline lens;  either of which will cause
the visual rays from near objects, to converge to a focus,  be-
fore they reach  the retina.   This is remedied by concave
glasses, which, as we have seen, cause the rays to diverge, as
is represented in the following cut.
  A. a short-sighted eye;  B. an arrow which it attempts to perceive,
but  is  prevented  by the convergence of the passage of the visual rays
to foci, at C, before they reach the retina at D.   E. the  same eye. 
212
PHYSIOLOGY
similarly situated, showing how by the intervention of a concave lens,
G., the rays are di-verged, and the image of the arrow, F., accurately
converged to  the retina at A.
  33.  Long-sightedness  is the opposite defect to this, and is
owing to a flattening of the cornea, and a relaxation in  the
structure  of the  crystalline lens, by which its  power of re-
fraction is lessened.   In this case, the rays of light are car-
ried  beyond  the  retina, and therefore do  not  form a distinct
image on  it.   Old persons usually  are subject to this defect;
the only remedy known is convex glasses.   Where persons
have been short-sighted in youth, as the eye grows flatter by
age, they at length are able  to see well, without glasses of any
kind.  This change in the shape of the eye is often  denoted
by a tendency to hold a  book at  a  greater  distance when
reading.  Glasses do for the eye that portion of the labour
of bending  the rays of  light, which it is not able to do for
itself.   By adapting glasses to the successive changes which
age produces in the shape of the eye, the sight may be pro-
longed very often to the  close of life.  After the operation of
extracting the crystalline lens  for  cataract, or  depressing it
by couching, very convex glasses are needed to remedy the
deficiency.
  34.  The sight is often injured by long-protracted attention
to minute and near objects ;  as we see in  the  watch-maker
and engraver; also by watching  for objects at a distance;
as in sailors, and keepers of telegraph stations ; in the one
case  the eye becoming near, and  in the other far-sighted.
During the arbitrary reign of Napoleon,  the young men of
France often produced short-sightedness voluntarily, by wear-
ing very concave glasses, in  order that they might be exempt
from military service.
  35.  Some persons  are unable  to tell one  colour from
another.  Sir David Brewster gives us  the following exam-
ples.   A Mr. Scott  mistook pink for pale blue, and  red for
green.  His  father,  uncle, sister, and two  sons, all mistook
these  colours in th sa  e way.   A  shoemaker named White, 
SENSE OF  SIGHT.
213
could only see two colours, black and white, and he could
never distinguish the cherries on a tree from the leaves.  A
tailor at Plymouth could  only see yellow and  blue.  On one
occasion he repaired a black silk garment with crimson, and
on another, he patched the elbow of a  blue coat with a piece
of red cloth.  M. Nicoll tells us of an officer in the British
navy,  who  purchased  a blue  uniform coat  and waistcoat,
with red  breeches to match.   The cause  of this defect is
believed  to  be a malformation, or deficiency of that portion
of the brain which takes cognizance of colours.
  36.   The lowest  order  of animals have no organs of
vision, or if so, they have  never been detected.  Many in-
sects have two kinds  of  eyes, one kind on each side of the
head, and the other on the top, in a row, or in the form of a
triangle.  The spider  has generally eight of these eyes on
the top of the head.   What are called the  compound eyes
are  placed.on  the side of the head,  and in the wasp and
dragonfly they cover a large part of it.   These eyes are
formed of a large number  of separate cones or cylinders,
closely packed together, each  being a distinct eye, and hex-
agonal, or six-sided in shape, like the cells of a honey-comb.
The ant has about 50 ; the  beetle 3,000 ;  the  silk-worm moth
upwards  of 6,000 ; the dragonfly 12,000 ; and some in-
sects as many as 20,000.
  37.  It is now  ascertained, that each eye forming these
compound eyes of insects, consist of a distinct tube, furnished
with every thing  necessary for complete vision.  The object
of this wonderful arrangement seems to be to compensate for
want of  motion, by the  number of eyes, as the  insect thus
supplied, has an eye pointed towards the object in whatever
direction it may appear,  and  may therefore be truly  called
circumspect.  If we  examine the  wasp and dragon-fly, we
shall find  these compound  eyes to cover a large portion of
each side  of the head.   By examining with  the microscope,
we find each of these conical  tubes covered  with a cornea,
and  containing a crystalline lens, and aqueous and vitreous 
214
PHYSIOLOGY.
humour, an iris, a choroid coat, and a retina; the pigment
running  back around the lens, separating each cylindrical
compartment.  They have no eye-lids, eye-lashes, or tears ;
bat these are compensated for by the great hardness and in-
sensibility of the cornea.
                          Fig. 18.
  Eye of the yellow beetle magnified, composed of 8,820 hexagonal
cylinders, the interior of each tube being round.

                         Fig. 19.
   Eye of the phalaena or butterfly, magnified,  consisting of 11,300
 square sections. The eye of the mordella is similar, containing 25,088
 prisms.

   38. Motions of the Eye.—We have seen that the eye is a
 perfect optical  instrument, infinitely surpassing the boasted
 specimens of human skill;  but without the power of motion,
 of adapting it to the  varied objects which surround us, we
 should derive but a very small proportion of that gratification
 and  pleasure, of which it is now the source.   We shall  per-
 ceive the great advantages we enjoy from  this benevolent
 provision, if we contemplate the movements of a telescope ;
 how difficult it is to direct it to any object, so as to obtain a
 view of it, and  what  complicated and cumbrous machinery
are required to effect it.  But  all the various motions of the
eye are produced by six little muscles! 
SENSE OF  SIGHT.              '215
  39. Four of the muscles of the eye are called straight or
recti muscles ; the other two are named the oblique muscles.
The first four arise from the back part of the orbit, and are
inserted  by  broad  thin  tendons into  the four  sides of the
globes near  the junction of  the  cornea  with the sclerotic
coat.  The white pearly appearance of the eye is caused  by
these tendons.   The oblique muscles arise from the front and
inner side of the orbit, and pass to the eye-ball at right angles
from the straight muscles, one passing over its upper surface,
and the other upon its under surface, and both are inserted
into its outer side, one a little  above its horizontal axis, the
other a little below it.  The superior oblique muscle is, how-
ever, worthy of more particular notice,  as no part of the
body exhibits clearer marks of design and contrivance.  It
arises as I have said, from the bottom of the orbit, it proceeds
forwards  and becomes tendinous, and when it reaches near
the margin of the orbit, it passes through a little  cartilagi-
nous pulley,  by which the direction  of  its action is changed,
precisely as  we see done by a  pulley among the ropes of a
ship ; after passing through  this little loop, which is dense,
smooth, and  elastic, and furnished with a  lubricating fluid to
diminish  friction, the  tendon runs obliquely backwards and
towards  the internal angle to be inserted into the ball.  When
mis muscle acts, the eye is  rolled directly inwards.  Thus
the muscle pulls in a direction contrary to its own action, as
when a man raises himself by a  rope  thrown over a beam.
The other, or inferior  oblique muscle, rolls the eye  outwards
towards  the temple.   When  they both act together,  the eye
is steadily carried  forwards.   The  recti  muscles  move the
eye in four directions, upwards, downwards, to the right, and
to the left, each movement being affected  by its appropriate
muscle.   When the four act together, the eye is drawn back
towards  the bottom of the orbit. 
216
PHYSIOLOGY.
Fig. 20
    Side view of the muscles of the eye in their natural positions,  a. o.
  c. d. the four straight muscles,  a. is turned up to prevent the others
  from being hidden,  e. the superior oblique muscle. /. the optic nerve.
  The other oblique muscle is not  shown, but it lies on the other side of
  the  ball, and comes round, and is inserted near the superior oblique; so
  that they pull opposite ways, like  two men sawing timber.  By the com-
  bined action of all these muscles, an infinite variety of motions of the
  eye  can be produced.

    40. In order  to facilitate  the motions  of the  eye* it  is
  lodged securely on a soft bed  of fat.   This is contained  in
  very large  cells at the  bottom of the  orbits, and is  more
  fluid than fat in general, and is less affected than any other
  part of the  body  by those  causes, which  produce general
  emaciation.   The eye-ball may therefore be said to move  in
  a fluid medium, fully adequate to give  every necessary sup.
  port, and at the same time affording the least possible resist-
»  ance.
    41. Defences and Appendages  of the  Eye.—These are 
SENSE OF  SIGHT.              217
the orbit, the eyebrows, the eyelashes, the eyelids, and the
lachrymal apparatus.  The orbit is a four-sided vault, com-
posed of seven bones, and shaped like a pyramid  or  cone,
the apex pointing  backwards.  The eyeball  and the orbit
seem  exactly made  for each other; the one being globular,
the other rounded to receive it.   At the bottom of the orbit
are holes fc<r the passage  of the  blood-vessels  and nerves.
Now  this cavity is not scooped out of the skull, as a  boy
would make a hole  in a block of wood,  but  the seven bones,
which enter into its composition, are so curiously dove-tailed
together as just to leave  this space for  the  reception of the
eye and  its  appendages.   What  mechanic  could  place
seven irregular, jagged bones together so as to form a smooth,
polished cavity, for  such  a delicate organ as the eye to roll
in !  So securely is the eye protected  by its bony house or
encasement, that it is a very rare thing for it to be injured,
except by some sharp pointed object.
   42. The eye then is surrounded on every side with bone,
except  the  front;  now,  what have we here to serve as a
means of defence ?   It would not have  answered our  pur-
pose to have had it entirely shut up in a box of bones, or
even  to have left a little hole just to peep through.  As we
cannot draw our heads into a shell when danger  threatens,
like a snail or  turtle, we  are furnished  with  a couple of
moveable  curtains  or  eyelids, placed before the  eyes, which
we can let down or raise  up  just when  we  please.   If the
eyes are "the  windows of the  soul," then I  would call the
lids a pair of  inimitable window shutters, for  they exclude
the light whenever  its presence would be disagreeable to us.
   43. The eyelids  are composed  of a  thin skin, externally ;
internally of cellular  membrane,—its  cells filled  with a soft
semi-transparent fluid ; while their inner surface, in contact
with  the eye,  is lined with  a delicate mucous  membrane,
continuous with the skin, called  conjunctiva.   Besides these
there are beneath the skin, two sets of muscular fibres; one
cal ed orbicular, running round the lid  horizontally, whose
                            19 
21S                   PHYSIOLOGY.
contraction serves to close the eye ;  the other lying beneath,
are the fibres of the levator miscle, which serves to raise the
lid, or open the eye.  These two muscles are well  e 'hibited
in the following cut:
                          Fig. 21.
  Muscles of the eyelids, the elevator passing back into the orbit; the
sphincter, or orbicular muscle surrounding the eye.

  44.  Around the margin  of each lid, there  is a  delicate
elastic cartilage placed, which serves  to  preserve  the shape
of the lid ; and into this, as is shown  in  the cut, the fibres
of the elevator muscle, are inserted.   In  contact and around
each cartilage, on its anterior surface, at the root of the eye-
lashes, is  situated a row of little bags  or  follicles, which
secrete an oily fluid, to keep the parts soft  and pliant, and
prevent the lids from sticking together.   It is this matter
which we often find in the  morning, collected on the margin
of the lids, or in the internal angle of the eye.        •
  45.  Now, mark this difference ;  the levator muscle, which
rises from the bottom of  the orbit, is  entirely under the con-
trol of the will;  the orbicular muscle is not.   See  the ad-
vantage of this.   If we had  always to issue a command of
the will  to  shut  the eyes, before  going  to  sleep, I imagine
there are a good many in this lazy world who  would forget
to shut their eyes, and so go  to  sleep with them wide open.
To what dangers would  they be exposed, an 1  what  injuries
might they  not sustain  in  consequence!   But  watch  a 
SENSE OF  SIGHT.
219
sleepy person.   No sooner does he begin  to  grow  drowsy,
than his eyes begin to close; in other  words,  " they grow
heavy."  If he wishes to keep awake he makes a desperate ef-
fort to open his lids ; and in the drunkard, whose involuntary
muscles overpower the voluntary ones, it  is quite ludicrous to
watch the expression of countenance, and see how quick the
disobedient, rebel lids close, upon the oft-repeated efforts to
keep them open.
  46. The opening  and closure of the lids ordinarily occu-
pies about the eighth  part  of  a second, so that there is no
interruption to the continuance of  vision.  Besides serving
as a curtain to protect the  eye, the lids serve, by their  mo-
tions to diffuse the tears and mucous secretions, thus keep-
ing  the  surface of  the  cornea moist, and wiping  off  any
foreign matter, as dust, that may be lodged on it. Th« eye-
lids when closed, do not entirely prevent the transmission of
light  ; for when we have been refreshed by sleep, the stimulus
of the light falling upon the lids, is sufficient to arouse  sen.
sibility and awake us.
   47. It is a curious fact, that while the upper eye-lid falls,
the lower eye-lid is  moved towards the nose, and thus  aids
in collecting all offensive particles in the corner of the eye.
This can readily be  shown by  marking  the edges of the lids
with  a black spot ;  when the lids are opened  and closed, the
spot on the upper eye-lid will rise  and fall perpendicularly,
while that on the  lower one  will play horizontally  like a
weaver's shuttle.  When any  thing gets into the eye, there
is this continual play  of the lids maintained,  till the offend-
ing  particles have been driven  into the  inner corner  of the
eye, when  relief is at once obtained.   When the object  is
very small,  or not  sufficiently irritating to  excite these
muscles of the lids to action, it is common to place an  eye-
stone, which  is  a smooth  piece of sulphate  of lime in the
eye.   This not only  excites an abundant secretion  of tears,
but also causes the necessary  motions of the lids, by which
the object is soon washed into  the angle of the eye. 
220                  PHYSIOLOGY.
  48. Many animals have what may be called a  third  eye-
lid, called  the  nicitating membrane.   This slides from one
angle of the eye to the opposite side, under the lids, whether
open  or  shut.  Its use is  to  clear  away all  matter which
might be irritating to the eye.  Birds that see best by night,
such as  owls, defend their eyes  against the light of the sun,
by drawing this curtain over them.
  49. The eye-lashes, or cilia, also aid in  the protection of
the eye.   They ward off insects, protect the  eye from  par-
ticles floating in the air, and also break the intensity'of light.
Indeed,  when moist, as they often are with perspiration, the
little drops serve to decompose the rays of light,  causing the
appearance of aluminous zone around the flame of a candle.
The eye-brows are  composed  of loose  cellular substance,
covered with skin,  from which  spring  short bristly hairs
projecting outwards.  Like  all hairs, they penetrate  little
follicles, and become besmeared with an oily secretion, which
preserves their glossiness, so that the drops of sweat which
may accumulate on the brow are prevented  from  trickling
over the eye-lids, where they might interfere with vision.
  50. Lachrymal Apparatus.—The tears are secreted by the
lachrymal gland, which is a small spongy body of a flatten-
ed form, seated in the  hollow of the bone, in  the upper and
outer part of the  orbit, just beneath the  outer  end of the
bone.  These serve as fountains, as well as laboratories  or
distilleries, separating,  as they do, a pure water from the red
blood, and discharging it by means of seven  or  eight -little
tubes, upon  the inner surface of  the upper eye-lid,  from
whence it is spread along with  the mucus from the con-
junctiva over  the  eye, by the movements of the lids.  But
what becomes of the tears ?  In the inner corner of the eye
are two very minute apertures,  one in each  lid, which are
the orifices of two  canals, which communicate with a  pipe,
by which the superfluous moisture is drained off into the
nostrils.  This process is constantly going on without notice
But when there is much irritation, then the  natural chan 
SENSE  OF SIGHT
221
nels are insufficient for their escape, and  the tears roll over
the cheek.
                             Fig. 22.
  a, the eye-ball, and b, b, are the upper and lower sides.  Now in order
to prevent dust and other bodies from working their way between  the
Dall and the lid, through passages at c, c, into the  socket of the eye,
where  they would excite great inconvenience and  pain, we find  the
common skin of the eye-lids d, d, after covering their edges, turn in a
little .way between the lid and  the ball, and  then  turn back and  are
reflected over the surface of the  cornea ; where, to prevent the obstruc.
'ion of vision, it becomes perfectly transparent.
                            Fig. 23.
  The eye-lids separated, and viewed from behind ; a, the lachrymal
gland ; b, the ducts from the lachrymal gland ; c, the mouths of these
ducts; d, the  puncta  lachrymalia;  e, the meibomian glands,  which
»ecrete the oily fluid.
                                19* 
222
PHYSIOLOGY.
   51.  There is a striking proof of design  in the manner in
which  the opaque, lining  membrane of the  eye-lids becomes
transparent, as it is reflected over  the cornea.   But we can
illustrate this  more clearly by means of the following  dia-
gram.
                          Fig.  24.
  The eye-lids viewed from before; a, a, the lachrymal canals;  b, the
larchrymal sack.  The lachrymal sack is a bag of an oval shape, fixed
to the end of the double canal, and lies in a depression of the nasal
bones.  It terminates in a tube called the duct, which passes through
a hole made for it, in the bones of the  nose, and  opens into the nos-
tril.

  52.  It is now well ascertained  that  a  belief in superna-
tural appearances, and  stories in  relation  to  seeing  ghosts,
hobgoblins, and spectres, have  arisen from optical  illusion.
We have seen  how a person  in  delirium  tremens, imagines
that he sees a thousand unreal objects, and hears a thousand
strange voices; the same phenomenon, though less in  degree,
may happen to a person in health, owing  to an  excitement
in some  portion of the  brain.   I have  heard  an aged  rela-
tive, who  believed  in  witchcraft,  tell of frequently having
seen the  ghost of some  deceased friend, and once of having
fired at  a  deer three  times, in the  twilight, while he  was
cropping the  tender grain just springing  out of a newly 
SENSE OF  SIGHT.
223
sown field,  without frightening  the animal;  and when at
length he suddenly disappeared, no  tracks or traces of him
could be discovered on the soft mould.  Nothing could con-
vince the old gentleman  that his sight had  deceived him,
that these objects had only existed in his brain.
   53.  One source of deception  lies  in the fact that, indirect
as  well as  direct  vision is  intermittent,  as any  one may
learn by attempting to read  small print by moonshine, or in
twilight, or by looking  at a single star for some time, when
it will be found to  vanish often  and reappear.  In  an ob-
scure light we find that a painful effort is required to  distin-
guish objects ; and after  all  they appear and  disappear, be-
cause  the impression they  make  upon  the retina  is  not
sufficiently vivid to be continuous.  We  can easily imagine
therefore, that in the dusk, to a person who is ignorant of
this fact, the sudden disappearance  and  reappearance of
objects must seem  very extraordinary
   54.  Dr.  Paley remarks that,  " were there  no example in
 the world of contrivance except that of the eye, it would be,
 alone, sufficient to support the  conclusions which we draw
 from it, as to the necessity of an intelligent Creator."  When
 we  look at  a telescope, and see how  it consists  of  a  tube
 composed  of various pieces,  containing  several glasses or
 lenses placed at different distances in order to refract the
 rays of light, and bring them to  a focus ; how,  within it,
 there is a partition of metal, through which is a round  hole
 in the  centre for the purpose of lessening the surface of the
 lens on which the rays of light strike ; and when, in addi-
 tion to all this, we see the inside painted black, to absorb the
 oblique and scattering  rays  that  would  otherwise  render
 objects confused  and indistinct;  when we see all these
 things, we  immediately say, here are marks  of design, here
 is  evidence of wise  and skilful contrivance ! and yet the
 telescope is  but a close imitation of the human eye, which
 had God for its  designer.   When,  also, we look at the ca-
 mera obscura and see a tight, dark  box, with a  lens fitted in- 
224
PHYSIOLOGY.
to it, through  which  the light, passing, falls  upon a screen
behind, forming an inverted image of the object represented,
we say at once here is design !   But this  instrument also is
cppied from the human eye !
   Questions.—What is said of the sense of sight ?  What are the coata
of the eye ? Describe the scelerotic ?—the choroid ?  What is the pig-
mentum nigrum ? Is it ever absent ? Describe the retina ? Illustrate the
minuteness with which objects are painted on it ? Describe the cornea 7
—the ciliary ligament ?  What is said of these tunics in the lower
order of animals ?  What is the iris ?   How does  it contract and di-
late ?  Are the muscles ever  under the control of the will ?  What  is
said  of the iris among the  lower animals ?  Describe the ciliary pro.
cesses ?  What are the humours of the eye ?   Describe the  aqueous ?
the crystalline ?—the vitreous ?   Explain some  of the laws of vision ?
What is a lens ?  How  many,  and  what kinds of lenses are there ?
What effect on light has a concave ?  a convex ? a plain lens ?  Illus.
trate this by the humours of the eye.  Are images erect on the retina ?
Where do the rays cross ?  How do you  explain why we do  not see
objects inverted ?   Why do  we  not  see objects double ?  Why do riv-
ers appear shallower than  they are?   To what  is  short-sightedness
owing ?  How may it be corrected ? What is long-sightedness ?  What
is the remedy ?  Are  there persons who cannot distinguish colours ?
To what  is this owing ?  What is  said  of compound eyes ?  How
many muscles are there to move the eye ?   Describe them ; the recti;
the oblique.  What are the  defences of the eye ?  Describe the orbit;
the eyelids ; the muscles of the lids.  Are  they voluntary  muscles ?
How are objects carried  into the angle of the eye ?   What is  the use
of eyelashes ?—of eyebrows?  How  are the tears  secreted?  How
carried out of the eye ?  What  has led to a belief in  supernatural ap.
pearances  ? 
CHAPTER XVII.
                 THE SENSE  OF HEARING.

   1. Through  the sense  of hearing, we obtain a know.
 ledge of the peculiar vibrations  of sonorous  bodies, which
 constitute sounds.   The organ  of hearing is very compli-
 cated, like that of sight, and  the precise office of the differ-
 ent  parts is not  yet fully known ;  it is, however generally
 divided into the  outer, the  middle,  and  the inner part, and
 the auditory nerve.
   2. The External Ear.—The outer part  of the organ  of
 hearing consists of  what is called the external  ear, and the
 cavity which leads to the ear-drum; and is composed chiefly
 of cartilage, covered with the skin,  and supplied with blood-
 vessels  and  nerves.   Its use is to collect sound, or rather the
 vibrations of the air, and transmit  them  through the tube
 that leads to the ear-drum.   For this purpose it is admirably
 contrived ;  its  surface being smooth and folded into grooves,
 which,  assisted  by a raised  border  and  several concave
 spaces,  conduct whatever sounds fall upon  it, with the great-
 est certainty, directly to the drum of the ear.  The external
 ear  is furnished with muscles, and savages are  said to  have
 the  power of raising or bringing forwards their ears, like a
 horse, to  catch sounds as they come from different direc-
 tions ; but the  habits of civilized life destroy this  facultv.
 The following  cut  represents  the external ear, and the  mus-
 cles by  which it is  moved.  (See Fig. 1.)
   3.  Various names are assigned  to the  different portions
of the external  ear, such as helix to the outer border, scapha,
the large boat-like depression, die. ;  but passing these by, as
of little importance, we remark that the external ear  is  con-
fined to the  class  mammalia, nor does it always  exist  among
them, for the mole, the water-shrew, and other diving animals, 
226                 PHYSIOLOGY.
External Ear and Muscles.
seals and whales, are destitute of it.  Indeed, as water  is a
much better conductor of sound than air, there would seem
to be little occasion for the external ear in them ; but they
suffer in consequence, when they attempt to  live with their
heads out of water.  Owing  to  this  obtuseness of hearing
in the whale, he is easily approached  by the whaler, and be-
fore he hears the oars of his enemy, the harpoon is fixed
into his unwieldy carcass.  In like manner,  the walrus and
the seal remain unconscious of the footsteps of their foe, till
it is too late to retreat.   In land animals that are timid, as
the hare and rabbit, the ear is very large, so  that  they  may
be apprized of the approach of their  enemy in time  to  flee
to a place of safety.
  4.  The  Tube of the External Ear.—This  is the passage,
called by anatomists meatus  auditorius externus, which ex-
tends from the  outer ear to the tympanum or drum, which is
stretched across its inner end.  This passage is  about ten
lines, or nearly an inch in length ;  and pursues a  somewhat
winding course inwards, a little forwards and downwards ;
its external portion being composed of cartilage, and its in-
ternal of bono.  The width, as well as tension of this tube,
are effected by the motions of the jaw, as  any one can learn 
THE SENSE OF HEARING.            227
by placing his little  finger in his ear, and then opening and
closing the mouth.   This is, no  doubt, one  reason  why a
person stands with his  mouth open when he  is listening at-
tentively.  This tube being constantly open, is liable to the
entrance of foreign bodies, such  as dust, insects, and the
like.   But, like the eye, it is  not left without means of de-
fence,  for  on  its  inside, there  are numerous fine  bristles,
which  interlace and  prevent the entrance of any thing but
sound ; while between  the roots of these hairs, there are
numerous little glands, which secrete a nauseous  bitter wax,
which  by its offensiveness, either  deters insects from  enter-
ing, or if they do, entangles  them, and thus prevents  any
further advance.  This wax  often becomes hard, and ob.
structs the tube, causing  more or less deafness.  This form
of deafness is  easily cured, although.it may have  existed
even for years.   When the ear  is dry, from a deficiency of
wax, the hearing also becomes  imperfect, as  also when it is
thin and purulent.
                          Fig. 2.
General sectional view of the structure of the ear;  a, ih? meatus 
228
PHYSIOLOGY.
auditorius externus ;  b, the tympanum ; c, the malleus ;  d, the incus ,
e, the os orbiculare; /, the stapes ; g, the semicircular canals ; A, the
cochlea ; i, the meatus auditorius internus; k, the-eustachian tube.

  5. Membrane of the Drum, stretched across  the inner end
of the auditory tube, is a membrane, called by anatomists the
membrane of the tympanum, (membrana tympani,) or drum of
the  ear.   It is somewhat oval in  shape, but hollowed out, or
depressed at  the centre, where, as we shall presently see, it
is fastened to the  end of a small bone.   This membrane  is
tense like a drum-head, thin, and transparent.  Its use is to
convey the vibrations of the atmosphere to the expansion of
the  optic nerve in  the internal ear.   It does not seem entire-
ly essential to the  function of hearing, as  the hearing some-
times remains after it is destroyed.   When it is ruptured, a
person can force the air out of his ear ; but while it remains
entire, it is impossible for insects or other bodies to get into
the drum, as is generally believed.   The  drum is capable of
being rendered  more or less tense, and  thus  of  moderating
the intensity of vibrations transmitted to it.
  6.  The Drum.—What is called  the drum, or* tympanum,
is an irregular cylindrical cavity, separated from  the external
passage by the membrane of the drum. It contains the little
bones of the ear, the openings to the labyrinth and  other
parts of the organ.   Anteriorly a passage leads  from  this
cavity, forwards  and downwards to the  throat, called  the
Eustachian tube.  Posteriorly there are several openings into
osseous cells, called the mastoid cells, which are situated in
that projecting  process of bone immediately back of the ear.
This cavity  then is filled with  air.
 7 Eustachian Tube.—I have stated that this tube leads from
the drum into the mouth, and serves  for the introduction of
air into  the  internal ear.   The necessity of  such a contri-
vance is obvious from the fact, that sounds cannot be trans-
mitted through a  vacuum, as is  shown in the common ex-
periment of ringing  a bell  in an exhausted  receiver, when
no  sound is made.  So in a drum,  there  is an air-hole, else 
THE SENSE OF HEARING.             229
the sound would be flat, and the head liable to be ruptured.
When this  tube  is obstructed by the  swelling of its lining
membrane from cold, or the accumulation of secretion in the
passage, deafness  is the consequence.   This passage is about
an inch and a half in length, and widens from the ear to the
throat like  a  trumpet.  When deafness  occurs  from com-
plete  closure of this  tube, hearing may be restored by per-
forating the membrane of  the  drum.  We may ascertain
with a good degree of certainty-whether deafness  arises from
this cause, by  placing  a watch between the teeth, if its mo-
tions  are audible, we may conclude that the essential organ
of hearing is unaffected.
  8.  Bones of the Ear.—These are four in number, and are
so connected with each other  in the dr»um, that they serve
to transmit vibrations of the membrane of the tympanum to
the  internal ear.  From their  shape, they are  called  the
mallet, the anvil, the orbicular, and the stirrup bones, and are
exhibited in nearly the natural size in the following cut.
Mallens, Incus, and Orbiculare, Stapes.
Bones of the ear.
These bones are very hard and brittle, have no cartilage on
their  articular  surfaces like other bones ;  neither  are  they
furnished with  ligaments or synovia, but  their  dry and
polished surfaces are accurately  fitted to each other in the
form of a bent lever ; and in this way, being connected and
held together by the little muscles, by which they are moved
and attached to each other, the intensity of vibration which
they receive from the membrane of the drum is not blunted.
                            20 
230
PHYSIOLOGY.
The handle of the mallet is attached to the membrane of the
drum, and  its other extremity rests on the anvil, which is
connected with the orbicular bone,  the smallest in the  body,
and  not much  larger than a grain  of sand.   This is  inter-
posed between  the  round bone and the stapes, whose base
rests  upon the membrane of  the oval fenestra.  Now the
contraction of the muscles which connect these bones, puts
the drum-head on the stretch, and thus adapts it for the  ready
transmission of sound.
   9. Mastoid Cells.—These are seated in the hard  portion
of the temporal bone, and are also filled with  air.  The ear
is thus  surrounded with an atmosphere of its  own.  In the
elephant, the two tables of the skull are separated from each
other by a  bony cellular structure to the extent of upwards
of a foot, and these cells are filled with air which communi-
cate with the drum of the ear.   We find  in the cat tribe, in
dogs, and in gnawing animals, that  there is a hollow sphere
of very  hard  bone attached to the  drum, shaped something
like a conch, and well  adapted for  reflecting  the vibrations
of sound, and rendering  them  more intense, like the sound-
ing board of a piano-forte.  A similar hard conch is  found
in the whale tribe.   The two tables of the skull in birds are
also widely separated, thus rendering them lighter,  and  as
the cells communicate with the drum, doubtless for the pur-
pose of increasing the volume of  air. for the  reception of
vibration.
   10. Petrous Portion.—The  internal ear is  situated  in a
portion  of  the temporal  bone,  called petrous,  from petra, a
rock, because of  its solid structure.  The object of this is
evident  from the fact, that hard elastic  substances transmit
vibrations of sound  far better than matter  of a  softer  texture.
This portion of  the temporal possesses  indeed  almost an
ivory hardness, being  the  densest  structure  in the animal
body, next to the enamel  of the teeth ; and in this solid body
the labyrinth of the ear is situated.  Now in whales, the
skeleton is  formed of loose spongy bones, with a considerable 
THE  SENSE  OF HEARING.
231
quantity of oil, collected in their cells.   To  compensate for
this soft  structure, whales are furnished  with  a sounding
board, or the dense  conch, above mentioned.   In fishes, we
often find several of these little bony concretions, of a smooth
and polished appearance, and hard and  brittle as porcelain.
These are often seen in  cutting up boiled  fish, when  placed
upon the table, but few are aware  of the uses they serve in
perfecting the organ of hearing.
   11. In order, however, to understand the precise  function
of  these bones, it  will be necessary to examine a little more
into their situation and connection.   In the  following plan,
they are  represented, greatly  magnified,  but each bone in its
natural position.
                             Fig. 4.
  A, the malleus, or mallet, with its long handle running down, to
touch with its delicate extremity the membrane of the drum.  B, is the
incus, or anvil, nicely fitted to the mallet, and showing C, the orbicular
bone placed between its termination, and D, the stirrup. The line  a, b,
represents the centre of motion of the malleus, and c,  d, the centre of
motion of the incus.  Now this chain of bones acts on the principle of
a long lever, as a small motion at one end of a long pole serve to move
it through a wide space at the other.  As Sir Charles Bell  explains it,
the head of the malleus is so articulated with the body of the incus,
that the centre of motion of the incus is a line drawn through the centre
7f its body,  and consequently the extremity  of the long  process, to 
232
PHi'SIOLuuY.
which the orbicular and stirrup bones are attached, moves  through a
greater space than that which receives the impulse of the head of the
malleus.   Thus a very small degree  of motion, communicated by the
head of the  malleus to the body  of the  incus, is greatly increased in
the extremity of the long process of the incus ; and consequently this
mechanism assists greatly in giving strength to  the vibrations trans
mitted to the internal ear.

  12. Now in distinguishing low  sounds,  the  drum head is
supposed to be  put upon the stretch, chiefly by the aid of one
little muscle,  called tensor tympani, which is attached to the
malleus, and  the centre of the  membrane, so that when it
acts, it pulls the long handle of that bone, and draws the tym-
panum inwards.  Thus being made tense,  it is prepared for
the reception of low sounds.   When  sounds are so acute as
to be  painful, and we wish to diminish their  intensity,  this
muscle relaxes, and the tympanum becoming  comparatively
flaccid, a deadened  muffled impression is transmitted to the
brain, precisely as  when we  muffle a drum. This relaxation
is also aided  by a muscle expressly prepared for that pur-
pose,  called laxator tympani,  which arises from the temporal
bone and is inserted into the handle of the malleus, so as to
pull it forwards.
  13. We traced the progress of sound through the external
ear, the  auditory  passage, and  the chain   of bones, to the
stapes.   Now, if the reader will look at plate II., he will see
that  the  base  of  the stirrup-bone  is  smooth and flat  ;
this is placed directly  upon  the passage into the labyrinth,
called foramen ovale, as a seal is placed on  an impression, or
a valve upon a hole.   The cavities we  have described are
filled  with  air, those now to be mentioned are filled with  wa-
ter.  The labyrinth then, which has been called  the audience
chamber of the ear,  consists of three parts,  viz.,  the vesti.
bule or  lobby, which may be compared  to the porch of a
building; three semi-circular canals shaped like three hoops
tied together  at one point, and  their opposite points  wide!)
aeparated ; and lastly,  the cochlea,  which  closely resemblei 
THE SENSE OF  HEARING.
233
a snail shell, consisting  of two spiral  canals, which  wind
round a central  pillar twice and a half,  and also  separated
by a spiral partition.
Section of the Cochlea.
  14. The stapes then rests upon the membrane  which  is
placed across the opening  into the labyrinth.  When the
tympanum, or drum-head, is impressed by the vibrations of
the  air, the  vibration  is communicated to the little  bones,
and through them to the membrane of the labyrinth, which
causes  corresponding  tremors in the fluid  which fills  its
winding canals,  and the spiral  passages of the  cochlea ;
upon  which  the  auditory nerve  is spread out like  a fine
pulpy web, in the same manner as the retina is spread out
upon the  choroid coat of the eye, or the  olfactory  nerve
upon the mucous membrane  of the nose, and thus is sound
conveyed by the  nerve to the brain.
  15. The  object of  these   spiral  passages  returning into
themselves is,  doubtless, to furnish  an  extensive surface,
within a  small space,   for the expansion  of the auditory
nerve, and also that the undulations of the fluid which fills
them after passing from the  oval fenestra along the winding
                            20* 
234
PHYSIOLOGY.
 passages, and up the spiral staircase of the cochlea, might
 come down to the  round fenestra, whose elastic membrane
 would transmit the vibration  in  the  opposite direction.—
 When the sounds, therefore, have done their  office, in  order
 that the  hearing  might not be  rendered  confused by a pro-
 longed vibration of the fluid, as an echo is repeated between
 two mountains, as  they strike  the above  named  membrane,
 they are given off to the air in the tympanum, and there the
 vibrations end; for we  have seen that  it is  probably the
 bones in the tympanum chiefly, and not the air, which trans-
 mits impressions to the fluids of the labyrinth, and that  they
 receive their impulse from the drum of the ear.
   16.  Sound.—Sound has no  distinct existence, but is the
 result  of certain conditions of bodies.   We see how, by
 throwing a pebble into a lake of water at rest, the undula-
 tions spread in every direction, in  the form of a circle, until
 the impulse is lost in the distance.   So in air, frequent vi-
 brations  produce sound ; and hearing has been  defined to be
 that function by which  we obtain a knowledge of the vibra-
 tory motions  of bodies.  These motions  produce waves or
 undulations in the air, which are  propagated in every direc-
 tion, as  the circular  waves  are  produced in  the lake, by
 throwing in the pebble.
   17. Aii is  the common vehicle of sound, though all elastic
 bodies are capable of conveying it.  Water conveys  sound
 better than air, and some solid bodies better than  either.  If
 two stones are struck together under water, a person whose
head is under the  surface may hear the sound at a great dis-
 tance.   A blow struck with a hammer by a workman  in a
diving bell, far below the surface of the water,  is heard dis-
tinctly many fathoms  above.   So  also if  the ear  be applied
to the end of a long stick of timber a slight scratch made at
the other extremity will be distinctly heard.  The report of
a cannon is heard to a much greater distance over the frozen
surface of snow ;  and,  under  such circumstances, firing has
been heard from one to two  hundred  miles.  Savages are 
THE SENSE OF HEARING.
235
acquainted with this fact, for  they apply their ears  to  the
ground to hear the  approaching footsteps of their enemy or
their prey.  An easy way to tell whether a tea-ketlle boils,
is to touch it  with a stick, and place the  other end to  the
ear. On this principle, I suppose, watchmen strike the curb
stone with their clubs, as the sound is communicated much
farther than it was  formerly by means of their rattle.   So
also a musical box, when held in the hand is scarcely heard,
but when placed  on  a  bureau or  sounding  board, it "dis-
courseth most eloquent  music."  The stethoscope now used
by  physicians to assist  in determining the  nature of many
diseases  is derived from a knowledge of this principle.  It is
merely a cylinder of wood, about an  inch in  diameter, one
end of which is placed  on the  surface of the body over the
diseased  part, and the other applied to the ear; sound is thus
carried along the tube, and most important aid is derived to
the skilful physician, in  ascertaining  the nature and seat of
all  diseases of the heart and lungs.
   18.  The transmission of sound  is  affected  materially by
the condition of the atmosphere, with  respect to tempera-
ture, moisture, &c.   During the night, when  the air is still,
and of uniform density  and  temperature, sounds are heard
to a great distance ;  but when  it is loaded with vapors, as in
a fall of snow or rain, sounds are more limited, and rendered
confused and indistinct.
   19.  The density of  the air has a great effect upon  the
transmission of sound..   In a  dry, cold atmosphere, at  the
level of the sea, sounds are transmitted to vast distances,
 while on high mountains, such as  the Andes, or even Mont
Blanc, the report of a pistol is not louder  than  that of an
 Indian cracker.   The  wind, also,  has a great influence in
aiding or retarding the transmission of sound.   Sound is
also reflected like  light, and indeed  is  subject to the same
laws, for the angle of reflection is  always equal to the angle
 of incidence.   Reflected sound  is  termed an echo.   The
  •oiling of thunder is supposed  to depend partly on the sound 
236
PHYSIOLOGY.
being reflected from  cloud to cloud, and through strata of
air of different densities, though  it also arises  from a dis-
charge of electricity, through a wide extent of air.  In this
case, as the sound from the point nearest the hearer reaches
his ear first, and  some moments elapse before that from  the
more distant arrives, there must consequently be a continued
peal.   Some of  our  large public houses and  manufactories
are fitted with pipes  for conveying intelligence to distant
apartments, attention being attracted by ringing a bell.
   20. It has been doubted whether sound can be propagated
from one  medium to  another, as from air to  water.  It is
now known, however, that if a musket  is discharged over a
person who is under water, he will hear  the report.  The
question has also arisen, whether  sound  can be propagated
from water to the air again.  This is easily proved by strik-
ing two stones together .under water, although  we are told
that persons in a diving-bell under water,  could not hear a
musket discharged immediately over it.   But here the sound
had to be communicated from the air to the water, and from
the water to the  air  again.   Sound travels at the  rate of
eleven hundred and forty-two feet in a second,  or a mile in
four seconds.  As light travels much faster, we  see the flash
of a  gun before  we hear the report.   This will enable us to
tell in a thunder storm how far we are from a thunder-cloud;
as we have only to allow eleven  hundred feet  for each  se-
cond, between the time when  the flash is  seen and the report
heard, and  one beat of the pulse for a second.   In this way,
too, the distance of a ship of  war at sea is often ascertained
by those on board of the vessel she is in pursuit of.   Solids
and fluids  convey sound not  only more perfectly, but also
more  rapidly than air.  It  is  found that  the  velocity of
sound in water, is about four  thousand nine hundred feet in
a second, being between four  and five times more rapid than
it  is through air.  Sound  passes  through tin at the  rate of
eight thousand one hundred and seventy-five feet, and through
iron, glass  and wood, eighteen thousand five hundred and 
THE SENSE OF  HEARING.            237
thirty feet in a second.   This explains why, when a gun is
fired at a distance over the surface of a frozen lake, we hear
two reports  after we see the  flash; first a  sharp  and loud
one, transmitted by  the  solid  ice, and then a  weaker and
duller  one,  through  the  air.  Franklin,  however, found by
his experiments, that, after  travelling about a mile  through
the water, sound lost  some of its intensity, which indeed
might be expected.  Musical tones are said to be acute when
the intervals  between the vibrations  are short, and grave
when they are long.   Thus a flute called an octave produces
a shriller sound than the  common flute; a fiddle than a bass
viol.   The strings, too, of a violin, which are designed for
high or acute notes, are smaller than  the others, that  their
vibrations may be more rapid; while those  which make the
grave tones are large, and wound  round sometimes with fine
wire, to increase the  weight, and  make them  vibrate more
slowly.   It is the quality and  variety of the sounds which,
in musical tones, gives the hearer so much pleasure.
   21.  In  the lower  order of animals, hearing  is performed
by means of an apparatus, much more simple than in man.
Some of them have merely a membranous sac, supplied with
nervous threads.   This is even the case in fishes, which re-
quire neither tympanum nor bones, nor any of the accessory
parts found in land animals, as the undulations of water strike
with greater force upon  the organ of hearing than  those of
air.   The apparatus of hearing in the frog is very singular,
and  designed so as to enable the  animal  to hear both in air
and water.
   22.  Animals with long ears are  able  to move  them by
muscles for  that purpose, and turn them to the point whence
the sound proceeds.  This may be seen in the  horse, which
turns his ear always  in the direction of the sound.   In stage
horses, we often see the leaders turn their ears   forward,
while those behind turn  theirs backward.  Some men also
have the  power of moving their ears.
   23.  Like all our other senses, that of hearing is capable 
238                   PHYSIOLOGY.
of much improvement' by cultivation.   The Indian in the
forest, accustomed  to  listen to the approach of his enemies,
or of his prey, acquires such  acuteness of  this sense, as  to
hear sounds which would  be  inaudible to those who live amid
the din of civilized life.  The blind  also excel in the acute.
ness of hearing, and for this reason especially, acquire great
skill  in performing on  musical  instruments.   Shakspeare
thus describes a person destitute  of musical taste.
         " The man that hath no music in his soul,
          Nor is not moved with concord  of sweet sounds,
          Is fit for treasons, stratagems, and spoils ;
          The motions of his spirit are dull as night,
          And his affections dark as Erebus ;
          Let no such man  be trusted."
   Questions.—What  are sounds?  Describe the external ear;—the
tube of the external ear ;—the membrana tympani;—the drum, or tym
panum;—the eustachian tube.  How many little bones of the ear are
there ?  Their names and office ?  How are low sounds perceived ?
What is  the use of-the spiral passages ?  How is sound eonveyed ?  Is
it conveyed by solids ;—by water ?  What  is the stethoscope ?  Can
sound be propagated from one medium to another ?  At what rate does
it travel ?  How can we tell  the distance of sound ?   What effect has
the density of air on sound ?  How is  the lengthened  peal of thunder
explained ?  How is hearing performed irUhe lower order of animals ?
Can hearing be improved by cultivation ? 
CHAPTER  XVIII
                      RESPIRATION.

  1. By Respiration, is meant the process of taking air into
the  lungs and throwing it out again.  Inspiration is the act
of drawing the air in ; expiration, that of forcing it out.
Respiration is essential to all animal existence.   It is in the
lungs that the last change is produced in the assimilation of
the food, by which  it is converted into that vital fluid, which
carries  life, and strength, and nourishment to every fibre in
the animal system.
  2. The parts concerned  in respiration may be arranged
into three divisions, viz., 1,  the bones which  form the respir-
atory cavity ; 2, the muscles by which these bones are moved,

                          Fig. 1.
Thorax, or chest; a, the sternum ;  b, b, the spine ;  c, c, tne ribs. 
240
PHYSIOLOGY.
and the size of the cavity regulated ;  3, the respiratory organs
contained within the cavity.
   3.  The  bones which  enter  into  the  composition of the'
chest, are the sternum, or breast-bone ; twelve dorsal vertebrae,
and twenty four ribs.   By examining  the preceding plate,
Fig, 1., the sternum will be seen to terminate at its lower
part in a triangular piece of cartilage, which  lies directly
over  the stomach,  and may be  felt externally ; the seven
uppermost, or true ribs, will  be seen  to  extend the whole
distance from the spine to  the sternum, strips of elastic car-
tilage being  interposed between the breast-bone and  their
anterior extremities, while  the five lower, or false ribs, are
merely attached to each other by slips of cartilage ; the two
lower, indeed, float  loosely, without any attachment to the
others, except by means of muscles.
   4.  I have already stated  that the ribs are attached to the
6pine at an acute angle, so that they cannot be moved out
of their ordinary position,  without enlarging the dimensions
of the chest.   The articulation of the ribs, both at the spine
and sternum, is effected by means of cartilage, thus  allowing
sufficient degree of motion for the purposes of respiration in
a healthy state.   The  chest expands during  inspiration for
the reception of air ;  and during expiration, it  contracts to
expel  air, which  is  no longer useful.   There are, therefore,
two motions  required, an upward and an outward ;  the first
increases the distance  between the  spine and sternum ; the
last, that between the ribs.  Now  these  motions are both
effected by the ribs, and  they are  so articulated, that  they
cannot  perform  the one without the  other.  By looking at
the cut, then, it will readily be seen how where the ribs rise,
the sternum will be pushed out, and of course the cavity of
the chest enlarged.
   5.  The Muscles.—All the muscles which are attached to
the bones just described,  aid  more or less in   respiration,
though the intercostal  muscles are  those chiefly concerned.
These run  from  one rib to another,  filling  up  the spaces be- 
RESPIRATION.
241
tween them.  These muscles, though thin, consist of a double
layer of fibres, the external and the internal, which  pass in
inverse directions, one layer from above downwards, the other
from behind forwards, from edge to edge of the ribs, crossing
each other.   Now, the first rib being fixed, the second move-
able, but less so than the third, the third less than the fourth,
and so on through the  whole series; the contraction of the
intircostals  must consequently elevate the whole  series, as
the upper ribs  serve as fixed points for the action of the
muscles.
   6. The  chief muscle,  however, of  respiration, is the
diaphragm.   By the aid of this, the capacity of the  chest is
enlarged downwards, as we have seen it  to  have been up-
wards  and outwards by that of the ribs.  The diaphragm,
or midriff, is a circular muscle,  placed  transversely across
the trunk, nearly at its centre, dividing the cavity of the
thorax from that of the abdomen.   It is attached to the in-
side of the breast-bone and the  cartilages of the false  ribs,
and is fleshy all around its border, but tendinous towards its
centre ;  the  surface towards the abdomen  is concave, and
that towards the chest  convex.   Even  when  it is not in
action, its upper surface forms an arch, the convexity of
which is towards the  thorax, and  reaches as high as the
fourth rib.   The central, or tendinous  portion of  the dia-
phragm, is attached to the pericardium supporting the heart;
and is nearly, or quite  immoveable, in order to afford a fixed
point for the action of the muscular fibres, which constitute
its sides.  Owing  to this arrangement, its motions do not
interfere with those of the heart.
                            21 
242                   PHYSIOLOGY.

                           Fig. 2.
  Yiew of the diaphragm"; 1, cavity of the thorax ; 2, diaphragm sep.
arating the cavity of the thorax from that of the abdomen ; 3, cavity
of the pelvis.
  7. During the act of inspiration, the  diaphragm contracts;
the muscular fibres shorten themselves, and the muscle de-
scends, passing from the  fourth  rib to  below the  seventh,
losing the arched form, as represented in the  cut.   At the
same time,  the muscles  of the  abdomen are  protruded  for-
wards,  and the viscera in  its cavity pushed downwards.
The degree  in which the capacity of the chest  is enlarged by
these movements is very satisfactorily  shown  in the follow
ing cut. 
RESPIRATION.                  243
  Fig. Ill, diaphragm in its state of greatest descent in inspiration;
2, muscles of the abdomen, showing  the extent of their protrusion in
the  action of inspiration.  Fig  IV, diaphragm in  the state of its
greatest  ascent in expiration ; 2, muscles  of the abdomen in action
forcing the viscera and diaphragm upwards.
  8.  We have  now seen how the capacity of the chest is
enlarged by inspiration, how is its capacity diminished  by
expiration ?   The descent of the  ribs is occasioned  by the
elasticity of the cartilages and ligaments which join them
to the sternum and the spine.  Indeed the  natural condition
of the chest is  that which obtains after a full expiration ;
and  therefore we may consider the  bones which form the
walls of the chest, and the muscles which  cover those bones,
as anatagonizing or opposite forces.   The ribs, then, have a
natural  tendency to fall, owing to their peculiar  structure,
as well  as their position ; while  their expansion  is effected
by the specific action of their muscles.   Besides  this, when
the diaphragm  relaxes, the abdominal muscles  contract and
push the abdominal viscera, and  the  diaphragm also, up  to- 
244                  PHYSIOLOGY.
wards the cavity of the chest;  and thus by the descent of
the ribs and  the ascent of the  diaphragm, the capacity of
the thorax is  diminished, and the  motion of expiration is
completed.
   9. The third division of our subject embraces the  respir-
atory organs, or the lungs.  These are of a spongy texture
and  conical shape, and  fill the cavity of the chest, being
composed chiefly  of  blood-vessels,  and  air-vessels, with a
small portion  of cellular  tissue.  They  are called  lights in
the lower animals.  There are two lungs, one in the right,
the other in the left side of the  thorax ; and each of these
lungs is divided  into several lobes.  A serous membrane
called the pleura surrounds the  lungs, and is reflected upon
the walls of the chest, so as to form a shut sac, into which
a  thin watery fluid is constantly exhaled, to keep the sur-
faces moist and slippery.   It is this membrane which is the
seat of pleurisy.   There  are  two pleurae, each of which is
confined to its own side of the chest, lining its cavity,  and
covering  the  lung.   Behind  the breast-bone,  they  form a
partition, called  mediastinum; between  the sides of which,
the heart and pericardium are situated.   The pleurae serve
to attach the  lungs by their roots  to their respective cavi-
ties, and to facilitate  their movements, by means of the fluid
exhaled from  their surfaces.  Each lung is attached  to the
spine by its  roots, where blood-vessels,  nerves, lymphatics,
and a branch  of the windpipe  enter it.   (See Fig.  5.)
   10. Thus we perceive that  the chest is divided into threu
compartments, one on each  side, containing  a lung ; the
middle one, the heart.  Between these there is no communi.
cation; so that if a fluid is thrown into  one of  them, it  does
not find its way into  the others.  As the  heart lies  chiefly
on the left side, the lung of that side is smaller than  the on*
on the right, and divided into  only two lobes, while the othei
is divided into three.   The lungs are the lightest texture in
the human body, owing to the air  which  they contain, and
their aspect varies with the age.  In infancy they are  of * 
RESPR1ATION.
245
  a,  the cut edges of the ribs,  forming the lateral boundaries of the
cavity of the thorax; 6, the diaphragm, forming the inferior boundary
of the thorax, and the  division between the thorax and the abdomen ;
c, the cut edges of the abdominal muscles, turned aside, exposing the
general cavity of the abdomen.
  Fig. 1, the cut edge  of the pericardium turned aside ; 2, the heart;
3,  the  great vessels in immediate connexion with  the heart; 4, the
trachea, or  wind-pipe ; 5, the  lungs;  6, the  liver; 7, the stomach;
8, tne large  intestine ; 9, the small intestines ; 10, the urinary bladder.

pale red, in youth of a  darker colour, and in  old age of a
livid blue.
   11.  The air enters the lungs through the trachea or wind*
                             21* 
&46                  PHYSIOLOGY.
pipe.   This is a tube, made up  of little rings, cartilaginous
in front, and muscular or fibrous behind ; and is about eight
or ten inches in length.   It lies immediately on the gullet or
esophagus, and extends from the larynx to the third vertebra
of the  back.   Here it  divides into two  branches, called
bronchia, one of which goes to the right, the other  to  the
left lobe of the lungs.   The right branch divides again into
three principle branches, as soon  as it enters the lung ; and
the left into two ;  corresponding to the number of lobes in>
each  lung; then they subdivide into an  innumerable number
of small twigs, like the branch of  a tree,  until they termi-
nate in those small cells already mentioned.  These cells are
about the one hundredth  of an inch in diameter.
   12. The  bronchial tubes then, terminate in minute  vesi-
cles of unequal size, which are of a  cylindrical and some-
what rounded figure.  These vesicles are large enough to be
visible to the naked eye, and  present something of the ap-
pearance of a  cluster of currants attached to their stem, as
shown  in the following cut:
                    Fig. 6.
View of the Bronchial Tubes, terminating in Air vesicles.
External view.—1. Bronchial tube. |     The Bronchial tube and  Air
              2. Air vesicles.      vesicles laid open.

  It should be borne in mind that the office of respiration is
to bring the blood in contact  with the air, and, accordingly,
the  lungs are so constructed as to allow the largest  possible 
RESPIRATION.
247
quantity of deteriorated blood, to enjoy the fullest intercourse
with the largest possible quantity of vital  air;  and all  the
mechanism of bones and  muscles which  I have described,
are only subservient to th s end.   Now it has  been calcula-
ted by Hales, that each air cell is the one hundredth part of
an inch in diameter, and that the amount of surface furnish-
ed by them, collectively, is equal to twenty thousand square
inches.  Other physiologists have calculated the surface to
be over fifteen hundred cubic feet, and Munroe states that it
is thirty times the surface of the human body.
  1.  The  larynx;  2. The  trachea;  3. Right bronchia;  4.  Left
bronchia ; 5. Left lung divided into three lobes ; 7. Large bronchial
tubes; 8. Small bronchial tubes ending in air cells or vesicles.

  13.  Such is the structure of the vessel which conveys the
air to the blood; let us examine how the  blood gets to the
air.   This is  effected by  means  of the pulmonary artery,
which springs  from the  right  ventricle of  the  heart, divides 
248
PHYSIOLOGY.
into two branches, one for each lung, and again subdivides,
and ramifies through the organ in a manner  precisely simi-
lar to the bronchial  tubes.  Every  bronchus, or branch of
the  trachea, thus has a corresponding  blood-vessel,  which
tracks it throughout its entire course until it reaches the air
vesicles, upon the  surface  of  which the minute vessels ex-
pand and  ramify, forming a net-work  so beautiful, that the
anatomist who first observed it, called it the rete mirabile, or
the wonderful net-work.   Thus the air is on one  side, and
the blood on the other, of an immense surface of membrane,
finer than the most  delicate  lace or  gauze ; and as such
membranes are permeable to air and other gases, the oxygen
of the  air penetrates it and unites with  the  blood, while  a
portion of carbon and  water are  given  off by exhalation.
Thus does the blood  lose its dark  venous character, and as-
sume a florid, arterial hue, and become fitted to carry life
and vigour to every  part of the system.
  14. Thus we see that the lungs and all their  complicated
machinery of bones, ligaments, muscles and cartilages, were
formed for the sake of these little air-cells ; for it is through
their agency that the blood undergoes the necessary changes
and alterations.  When  we reflect upon the relative extent
of the actual respiratory surface, compared with the dimen-
sions of the  lungs  themselves, that a stratum of blood seve-
ral  hundred  feet in  surface, is exposed to a stratum  of air
still more extensive, and all  compressed within the  compass
of a few inches, we  are filled with admiration and astonish.
ment at the wisdom displayed in such a structure, and search
in vain, among all  the contrivances of human  skill and
genius, for a counterpart !
  15. We are now prepared to trace the successive acts of
respiration,  accomplished  through  the  agency  of the me-
chanism just described.   About one second and a half after
expiration, the muscles of inspiration begin to act, the inter-
costals contract, and, by elevating the ribs, increase the dis.
tance between the spine and sternum.   As the ribs rise, the 
RESPIRATION.
249
diaphragm descends, and  thus the cavity of the  chest is en-
larged in every direction.  This expansion, like  that  of a
bellows, causes a vacuum, and  as the  lungs are passive, the
air consequently  rushes in through  the  mouth  and  nostrils
to fill it, and this influx of air continues until the density of
the internal, is equal to that of the external  air, when the
act of inspiration  is  at  an end.   Again, the  intercostal
muscles relax, and  the ribs, by their elasticity, are restored
to their natural position,  while,  at the same moment, the dia-
phragm relaxes, and  allows the abdominal  muscles  to  con-
tract and thrust it  up  into the chest.  Thus the lungs being
pressed upon in every direction, below  by the diaphragm,
before by the sternum and ribs, and behind by the spine and
ribs, the air within them  is pressed  out    Such  is the beau-
tiful and complicated mechanism of respiration.
                          Fig. 8.
  The cut upon the left represents the natural shape of the chest, and
that upon the right, the contracted state of it, owing to tight lacirrg.

   16.  Now we can easily understand how tight-lacing alters
the shape and diminishes the capacity  of the  chest.  By
looking at the cut, we see that the figure of the chest is that
of an irregular cone, with a convex  projection on each  side,
and flattened  before  and  behind.   By  compressing it, how-
ever, by corsets,  it is changed into a cylinder, its lower part
being forced in, so that its transverse diameter is diminished 
250
PHYSIOLOGY.
nearly, or quite, one half.  Now, in this state  of things, it
is  very clear  that  the ribs cannot  be  raised upwards and
outwards, as they are in  natural and free  respiration, and,
consequently, the capacity of the chest cannot  be enlarged
in these directions.   How, then, is  life supported ?  Clearly
by the play of the  diaphragm alone, which, by its  descent,
enlarges the cavity  of the chest in  its long diameter.  But
even the action of this muscle is cramped  by this unnatural
practice ; for, as the compressing apparatus extends  down
over the loins behind, and in  front over all the soft parts, or
the organs below the chest, it acts like a solid wall, prevent.
ing, by its resistance, the protrusion of these organs, and
thus restrains  the  diaphragm  above, in its attempt to de-
scend ; so that in  fact, the  beautiful mechanism, contrived
by a Supreme architect, for performing a function indispen-
sable  to life, health, beauty  and enjoyment,  is  confined,
in every direction, and life, consequently, sapped at  its very
fountain head!
   17.  If an  opening  be  made  into  the cavity of the
chest, the lung upon that side  immediately collapses, and is
no longer useful in  breathing.  How is this explained?  The
lungs have  a constant tendency to collapse, and they are
only kept from doing so,  by the pressure of the  air contained
within them.   If a hole  be  made in the walls of the chest,
so as  to allow the  atmospheric air  to come in contact with
the external surface of the lungs, and thus make the  pressure
on the external and internal surface equal,  they immediately
collapse and  shrink to that  size which is natural to them,
and which they assume when removed from the chest.  This
operation, of opening the cavity of the chest, has been pro-
posed as a remedy for  consumption ; as the lung in a state
of rest would  be more  likely to heal than  when in constant
motion.
   18. The atmosphere is an  invisible elastic fluid, surround-
ing the earth to the height of about forty miles.   Water is
seven hundred  times heavier  than air ;  and yet a column  of 
RESPIRATION.
251
air a foot in diameter, and  extending  to  the  top  of the at-
mosphere, would be equal in weight to a column of water of
the same diameter  thirty-two feet high, or to a  column of
mercury twenty-eight inches high.   The  pressure of the at-
mosphere then, upon  the  body of a common  sized  man, is
equal to between  thirty and forty thousand pounds.   Atmos-
pheric air is composed of oxygen, azote and carbonic acid,
in the  proportion of 20 parts of oxygen, 78 of azote, and 2
of carbonic acid.
   19.  Oxygen is  an invisible air, or gas, and enters into the
composition of air, water, and all  animal and vegetable sub-
stances.  It is the  supporter of combustion, and  no animal
can live without it.  What are called  acids and oxyds in
chemistry, are  oxygen  combined  with  other substances, as
sulphur, salt, nitre, &c.   Azote can neither support combus
tion  nor respiration, at least in  man ;  though it is an ele-
ment in all  animal matter, and  in  some  vegetables.  In
these cases it is obtained, both from focd and the  air.
   20.  It is now fully ascertained, that  while the chemical
composition of the blood is essentially changed, its weight
always remains the same ; as the  carbon discharged is pre-
cisely  equal to the united  weight of the oxygen  and  azote
absorbed, and the same change is effected by the  respiration
of all animals, whatever be their rank in the scale of organ-
ization.   It is  worthy of remark,  that  plants  and animals
produce directly  opposite changes in the chemical constitu-
tion of the air.   The carbonic acid given off by animals is
composed of oxygen  and carbon ; this is decomposed by
vegetables, which absorb the carbon and give off  the oxygen
to the air, which in its turn is absorbed bv animals, and car-
bonic  acid  given off:  so  these two great  departments ui
organized structure furnish  food for each other,  renovating
the air, and preserving it in a state of constant purity. The
immense quantity of oxyen given off by vegetables, may be
inferred from the following  experiment.   About fifty leaves
were enclosed in  a jar of air ; the surface of the whole being 
252                 PHYSIOLOGY.
about 300 square inches ;  by adding some  carbonic acid to
the jar, in a short time 26  cubic  inches  of oxygen  were
evolved.   What then must be the amount  given off by an
entire tree, especially in cities, where carbonic acid abounds ;
hence how important it is that cities should  be thickly plant-
ed with trees, not only for the sake  of ornament, but much
more for that of utility.
  21.  The quantity of oxygen  consumed  by a man  in a
minute, is about 30 cubic inches.  He breathes 20  times in
a minute ; and every time he breathes, takes  into his lungs 15
cubic inches of atmospheric air, which contains  three cubic
inches of oxygen, so that one half of that which is  inspired
disappears in every act of respiration.  This will amount to
about 2,000 cubic inches in an hour, and 45,000 cubic inches
in 24 hours.  Thus one man will consume, in 24 hours, all
the oxygen contained in a space of 312 square feet; or in 12
hours, in 156 square feet.  And still our churches, and school-
rooms, and dwelling-houses, are constructed with no view to
a renovation of the air we breathe !
  22.  Dr. Southwood Smith has lately  performed a series
of very interesting experiments, from which he deduces the
following general results :—" 1. The volume of air ordinarily
present in  the  lungs is about 12 pints.   2. The volume of
air received by  the lungs at an ordinary inspiration is one
pint.   3. The volume of air expelled  from the lungs at an
ordinary expiration, is a little less than one pint.  4. Of the
volume of air received by the lungs  at one  inspiration,  only
one-fourth part  is decomposed at one action  of the heart, and
this is so decomposed in the  five-sixth parts of  one second
of time.  5.  The blood  circulates through  the  system, and
returns to the heart in 160 seconds of time,  which is exactly
i.w uine in which the whole volume of air in the lungs is de-
composed.  These circuits are performed every eight minutes,
540 circuits are performed every 24 hours.   6.  The whole
volume of air decomposed in 24 hours is 221,882 cubic inches,
exactly 540 times the volume of the contents of the lun^s. 
RESPIRATION.                  253
7. The quantity of blood that flows to the lungs to be acted
upon by the air at one action of the heart is two ounces, and
this is  acted on  in  less than  one second of time.  8. The
quantity of blood in the whole body of the  human  adult  is
24  pounds avoirdupois, or  20 pints.  9.  In  24 hours  57
hogsheads of air flow to the lungs.   10.  In the same  time,
24 hogsheads of blood are presented in the lungs to this quan-
tity of air.   11.  In the mutual action that takes place be-
tween  these quantities of air and  blood, the  air loses 328
ounces of oxygen, and the blood 10 ounces  of  carbon."
  23.  The blood, as it goes the round of  the system, leav-
ing a little bony matter here, a little  muscular  there; sup-
plying the nails, and the hair, and  the skin, and  every thing,
with the particles which, in the wear and tear of the ma-
chine,  they have  lost; loses by degrees its bright arterial
colour, and  by the  time it comes round again to the  lungs,
it is no longer fit to perform its duty ;  it has been robbed  of
all its principles most  essential  to  life, and it must be  re-
newed  and prepared afresh,  before  it can be of any further
use.  This is done  in the lungs :  and this   process is  what
physiologists call  the vital part of respiration.
  24.  All animals have not lungs.   Insects absorb the  air
from the surface of the body ; so also do many of the family
of zoophytes.  Some  have  feathery tufts,  like  a plume of
feathers,  which they keep  in constant  motion ; while the
common earth-worm, or  angle-worm,  has  a single row  of
holes along its back, about one hundred and twenty in num.
ber, which open each of them into a small respiratory bag,
situated between  the skin and the intestine.  The  leech  or
blood-sucker, and the  lamprey eel, have the same kind  of
apparatus for breathing.
  25.  In fishes, the gills, which are their lungs,  are made  up
of an infinite number of little fibres, or filaments, set close
too-ether, like  the teeth of a  fine  comb, or the barbs of a
feather;  and these are covered  with  innumerable   small
processes, crowded  together  like the nap of velvet, and over
                         22 
254
PHYSIOLOGY.
these are spread myriads of blood-vessels, like a  fine net.
work.   The air which is contained  in the  water,  is drawn
in with it by the mouth, and forced, by the muscles of the
throat, through  the opening leading to the gills, the filaments
of which are expanded and  separated by the same process,
so that theyireceive the full  action of the fluid as  it passes
by them.   When a fish is taken out  of water, the reason he
cannot breathe is, that  these  filaments collapse, and adhere
together in a mass,  and the air  cannot separate them.
  26. The  seal, porpoise, dolphin and whale, belong to the
class mammalia, and therefore have to  rise to the surface of
the water to get air to  breathe.   It  is this  necessity which
exposes the  whale to  the harpoon  of the   fisherman; for
such are his  strength  and swiftness, that, could he live en-
tirely under water, he  might defy the utmost  ingenuity of
man to capture  him.

                          Fig.  9.
  The above cut shows the mode of respiration in fishes.  The gillfl
are seen bent over in the form of a feather: d is the auricle of the
heart; e, the  ventricle; /, the bronchial artery ; g, g, the gills.  The 
RESPIRATION.
255
heart of a fish throws the blood only to the gills, and not to the rest of
the body as in other animals.  This is the reason why the gills are red,
while the  other parts of a fish are  white.   Respiration  in fishes  is,
therefore, performed by  taking water into the  mouth, and forcing it
through  the  gills;  in  this manner the air  contained in the water is
brought in contact with  the thin coats of the blood-vessels, through
which the oaygen is absorbed.
   Questions.— -What is  meant by respiration ?—by inspiration?.—by
expiration ?   How  are the  parts  concerned in respiration arranged ?
What bones are concerned ?   Describe the position of the ribs.  What
muscles are chiefly concerned in respiration ?  Describe  the  intercos-
tals,—the diaphragm.  How  does the diaphragm act in inspiration ?
In expiration ?   What causes  the  deecent of the ribs  in expiration ?
Describe the structure of the lungs. What called in the lower animals ?
What are the pleurae ?—the mediastinum ?  How many compartments
is  the chest divided into ?   In which  is  the  heart ?  What is  the
trachea ?  What does it end in ?  How large are the air cells ?  What
is the office of respiration ?  What amount of surface do the air cells
present ?  How does  the blood get in contact with the  air ?   Describe
the process of respiration.  How does tight lacing injure the health ?
What happens if a  hole is made into the  cavity of the  chest ?  What
is the weight of the  atmosphere equal to ?  Of what gases is it com.
posed ?   What effect do vegetables have on air ?   What is oxygen ?—
azote 1  What is the effect of respiration on air ?   How much oxygen
is consumed by a man in twenty-four hours ? How do insects  breathe?
—the earth-worm ?—fishes ?—birds ?—the whale ? &c 
CHAPTER XIX.
           THE CIRCULATION OF THE BLOOD.

  1. That the  blood  is constantly circulating throughout
the  human body, was unknown till  Harvey made the  disco-
very,  two hundred years ago.   Before  this time, air  was
supposed to circulate  through the  arteries, or air tubes;
hence their name.  The reason why this great  truth  was
not found out sooner, was, that on  examining  dead bodies,
the  arteries were always found  empty of blood ;  owing  to
the  contractile force with which they are endowed.
  2. The circulation is called one of the  vital  functions,
because  it is  essential to life.   Its suspension for a short
time throughout the body is certainly fatal.   Hence we find
that diseases of the heart and great vessels are apt to termi-
nate in sudden death, while in other diseases the approach
of death is gradual.
  3. Life, in all the organs,  is maintained  by the presence
of arterial blood.   Without it they could not be  nourished,
nor could they perform their appropriate functions.   The
moment any part of the body is deprived of blood, from that
time it ceases to grow ; it withers and decays, and soon be-
comes a mass of dead matter.  If the arteries which supply
any of the limbs with  blood  are tied, the limb soon grows
black,  and mortifies.   In the same  way, if we  stop the cir-
culation of sap in a tree by girding or dividing the vessels
which convey this fluid to the branches,  the tree immediate-
ly dies.  Blades of grass and corn are  often  destroyed  by
worms  severing  the  same  vessels  with  their  teeth ;  and
peach  and  other  fruit  trees,  are  generally short  lived from
the same cause.
  4. Some animals are  destitute of a circulation, such as in-
sects, worms, &c.  Air and food are essential to the existence 
THE CIRCULATION OF THE BLOOD.        257
of life, but the food cannot be changed into blood before the
air has acted on it by one  of its principles, oxygen.   Now,
if these two principles are  not introduced into the system in
the same place, but in  separate organs, it is evident  they
cannot be employed in nutrition till they are brought toge-
ther ; which is done in  the  lungs ;  the  blood is there fitted
to carry nourishment and  life to every part of the  system.
Every animal then, that has a local  respiration, must  also
have a circulation.
   5. The organs of the  circulation are the heart, arteries,
the veins, and the capillary vessels.  The arteries and veins,
or the arterial and  venous  systems as they are called, have
been compared to  two trees, the  one  scarlet and the other
purple,  whose  trunks  are  united at the heart, and  whose
branches are connected  at their  extremities, thus forming a
regular circle.   The blood is then forced  out of the heart
by the contraction  of that  organ, into the arteries, by  which
it is  distributed throughout the body;  from whence it is re-
turned by the veins.  Between the ends of the  arteries and
the commencement of the  veins, are the small hair-like ves-
sels called capillaries.
   6. The heart is a hollow organ of a muscular and fibrous
structure, and somewhat conical in shape.   It is placed in
the fore  part of the cavity of the chest, inclined to the left
side.   It rests on  the midriff or diaphragm, which  is the
muscle that separates the chest from the abdomen ; and it is
supported also at its base which  is  uppermost, by means of
the large blood-vessels connected with it.  The  heart is sur-
rounded  by  a  strong  membranous  bag, called the pericar-
dium, by which  it  is, in a measure,  protected.   This  bag is
the seat of dropsy of the  heart, and  is generally found to
contain more or less water after death.
   7. In  the human species, and  throughout the class mam-
malia, the heart is a double organ ; consisting in fact of two
single hearts, each of which gives motion to a different kind
of blood.  One of these, the right heart, receives the  dark
                            22* 
258
PHYSIOLOGY.
venous blood which is returned from all parts of the body,
and sends it through  the  lungs, from whence  it returns to
the left side of the heart  changed  to  bright  arterial blood,
and is distributed by the aorta, or great artery, through the
system.  The right heart then may be called the venous or
pulmonary heart, the left, the arterial heart.  Both, however,
are so united together, as to form in appearance  but one
heart.
                         Fig. 1.
 
THE CIRCULATION  OF THE BLOOD.         259
which, by contracting,  force it out, are called ventricles.
The walls of the heart are composed  of strong muscular or
fleshy fibres, crossing and interlacing one another, and those
of the ventricles are  much  thicker than those of the auri-
cles.
  9. The cavities in  the right side of the heart are trian-
gular in shape, and  those  of the  left, oval.   Each cavity
will hold about two  ounces of blood.   Between each of
these two cavities or  chambers, there is a passage, which  is
closed with  a valve;  so that when the ventricles contract,
the blood, instead  of passing through  into  the  auricle,  is
poured into the arteries.   This valve is formed by the  dou-
bling of a  thin, transparent membrane, which  lines the
cavities, and extends  both through the veins and  arteries.
The valve in the right side  of the  heart  is called  tricuspid,
and that in the left, bicuspid or mitral.
   10.  There are also valves placed at the  orifice  of the
great arteries of the heart, the pulmonary and aorta, as  they
are given off from the right and left ventricles.  They differ
somewhat from the former, by being of a half-moon or semi-
lunar shape, and formed by folds of the lining membrane  of
the arteries.  These  are  called sigmoid valves ;  and  their
use is to prevent the  blood from flowing back from the  arte-
ries into  the ventricles.   Where the vena cava, or the great
vein  which returns  all the  blood, empties  into  the   right
auricle of the heart, there is another valve, called the Eusta-
 chian valve.   (See Fig. 2.)
   11. The arteries are the  vessels  into which the blood is
 immediately propelled by the action of the heart, and which
 distribute it to all the parts  of the  body.  The pulmonary
 artery or the artery of the right side of the heart, circulates
 dark-coloured or venous blood through the  lungs, where  by
 exposure to the air, it becomes a bright scarlet.  This  is  re-
 turned into the left auricle,  which forces it into the left ven-
 tricle, whence it is sent through the aorta to every part  of
 the system. 
260
PHYSIOLOGY.
Fig.  2.
  View of the heart with its several chambers  exposed and  the ves.
sels in connection with  them.   1. The  superior vena cava.   2. The
inferior vena cava.  3. The chamber called the auricle.  4. The right
ventricle.  5. The line marking the passage between the two cham
bers, and the points of attachment of one margin of the valve.  6. The
septum between the two ventricles.  7. The pulmonary artery, arising
from the right ventricle, and dividing at 8 into  right and left, for the
corresponding lungs.   9. The four pulmonary veins, bringing the blood
from the lungs into 10, the left auricle.   11. The left ventricle.  12.
The aorta, arising from the left ventricle, and passing down behind the
heart, to distribute blood to every part of the system.  Thus the blood
moves in a double circle, one from the heart to the body, and from the
body back to the heart, called the systemic circle;  the other, from
the heart to the lung, and from the  lung back to the heart, called the
pulmonic circle.

  12.  The arteries are very strong and elastic, of a yellow-
ish white colour, and have three coats, the  outer one of which
is called cellular, the middle, the fibrous coat, and the inter-
nal,  serous.  It is very important that  arteries  should be
elastic and capable of  stretching,  because, if they were not,
every time a limb was  broken, the  artery  would Ijc ruptured,
and  the  person bleed  to death.   (See Fig. 3.)
  13.  The veins which return the blood to the heart consti-
tute two systems like  the  arteries; the   one brings  all  the
dark-coloured  blood from the head, trunk and limbs, and in-
ternal organs, to the  right side of the heart, into  which it
opens by the  two  great  trunks, called the  upper and  lower 
THE CIRCULATION  OF THE  BLOOD.        '261

                Fig. 3,
The Arterial system.
vena cava.  The other conveys the scarlet-coloured or arte-
rial blood, from the lungs to the  left auricle, into which it
issues  by four  large  trunks, called pulmonary veins.   The
veins are strong and  flexible, but not  elastic  like  arteries.
They are furnished with little valves  placed at short dis.
tances from each other, so as to prevent the blood from flow. 
262                  physiology.
ing back again.   Like the arteries, they are supplied with
nerves from the great sympathetic nerve.
  Portion of an artery, showing the several coats of which it is com-
posed, separated from each other.  1. The internal or serous coat; 2.
The middle or fibrous coat; 3.  The external or cellular coat.

  14.  The capillary system, so called from the vessels  being
small, like hairs, presents two modifications.  The first con-
sists of little  tubes, furnished  with proper  coats or  walls,
which are the termination  of the arteries and the commence-
ment of the veins.   But a part  of these small vessels do not
terminate in veins, but in the  very substance  of the  flesh,
and the organs themselves.  These are even smaller  chan-
nels  than the first, and permit only a single globule of  blood
to pass out at a time.   They are probably  formed by the
fine arterial vessels, gradually losing their proper coats, and
becoming confounded with the cellular tissue.
  15.  In  the capillary  system, the functions  of secretion,
nutrition, absorption and calorification, or the production ot
animal  heat, are performed.   It is often divided into two
sections, the general and the  pulmonary.  The first has al-
ready been described.   The  other exists only in the  lungs,
and connects the pulmonary arteries and veins.   In this the
blood is changed  from venous to arterial.
  16.  The account which has been given of the  circulation
applies to the human species, mammalia and birds.  Reptiles
have but one heart, containing one ventricle  and  one or two 
THE CIRCULATION  OF THE BLOOD.        263
auricles, which receive arterial blood from  the  lungs, and
venous  blood  from  the body, and in its cavity both are
mixed together.  The main artery going from the heart, di-
vides into two branches, one of which goes to the lungs, the
other is distributed throughout  the body.  In some of the
other classes of animals, such as worms, there is  no heart,
and  the circulation consists in the  passage of the blood from
the surface, where are seated the organs of respiration, to
all parts of the animal and back again, which is performed
exclusively by  vessels.  Fishes have a single heart, designed
only to circulate venous blood, which it conveys to the gills,
or lungs;  and  from thence it is carried to every part of the
body, by an artery which rises from the gills themselves.
Shell-fish have also a single heart, but  this  only circulates
arterial blood.
   17.  The following facts were brought forward by Harvey
to prove the circulation of the blood.   If the  chest  of a
cold-blooded animal be opened, the  heart will be seen dilating
and  contracting.   The valves are  so situated throughout the
circulating system, as to promote the  circulation.   Between
the auricles and ventricles they are so placed as to allow the
blood to pass freely from the former into the latter, and to
prevent its return.  The valves  placed at the orifice of the
arteries, permits the blood to enter them from the ventricles,
but prevents it getting back into the heart.   The valves in
the veins allow the blood to go towards the  heart, but pre-
vent it  from going in  the other direction.
   18.  In bleeding, a bandage or ligature is placed round the
arm, above the point  where the arm  is  to be  opened.   The
blood, in its  return toward the heart, is interrupted, but the
artery which carries the blood  to  it  is  not compressed, be-
cause it lies deeper.   Sometimes, however, the ligature is so
tight that  the blood will not flow  till  it has  been loosened.
If the vein be  opened below the  ligature it will bleed freely,
but no blood is obtained if it be opened above.
   19.  When a limb is amputated  by a surgeon, he only ties 
264                  PHYSIOLOGY.
the arteries.  The reason is, that as these  convey the blood
from the heart, the patient would soon  bleed to death unless
some means were  adopted to prevent it.   But, although the
veins  are as  large as  the arteries,  yet, as they carry the
blood back to  the heart, they do not bleed, although they are
not tied.

                          Fig. 5.
The Venous System 
          THE  CIRCULATION  OF THE  BLOOD.        265
  20. The blood can also be seen to move  in the small ca-
pillaries by means of a microscope.   The fine  web  of  a
frog's foot is generally used for this  purpose.   Microscopi-
cal observations, however, should be  received with great al-
lowance, for no  two  observers have ever found the same ap-
pearances.  One makes out  the globules of the  blood  to be
round, another square,  and  another  tubular.   Some physi-
ologists, it is to  be feared, find just what they  wish  to find.
Owing to  the  refraction of light, the microscope is  little to
be depended on  in examining the minute structure of bodiws.
  21.  The motion of the blood is  chiefly owing  to the ac-
tion  of the heart.   This contracts  with great force, and in
the following manner.  The  auricles  both  contract at the
same instant, forcing the blood  which  is received from the
lungs, and the general circulation, into the ventricles ;  these
then contract at the same moment; the right one  sending
the blood  through  the  lungs,  the left one through  the  aorta.
This alternate action is constant, as long as life  continues.
The reason why the auricles  act together, and  the ventricles
the  same, is probably owing  to the fact, that both have a
common septum or dividing wall, so that one cannot contract
without the other.
  22.  The ventricles contract more suddenly and powerfully
than the  auricles, and  they are three times as long in dila-
ting or expanding, as contracting.   When  the ventricles
contract,  the apex or point of  the heart rises up  and strikes
against the left wall  of the chest,  between  the sixth and
seventh ribs, and this can be felt by placing the hand on the
left side.   The  left ventricle  has much thicker and  stronger
walls  than  the right, because  it has a greater  distance  to
throw the blood ;  but the right ventricle will hold more than
the left, because the venous  system is more capacious than
the arterial.
   23. The velocity of the blood in the arterial system grows
slower in proportion  to its  distance from the heart,  while
that in the veins is  accelerated the  nearer  it approaches the
                          23 
266
PHYSIOLOGY.
heart.   The reason why the blood moves slower in the arte.
ries  as  it  recedes  from the heart, is owing, probably, to
friction, and  the  increased capacity of the  vessels, for  the
arterial system is compared to a cone, whose apex is at  the
heart.   The course of blood in the arteries  is intermittent,
or by jets; not that it does not flow all the time, but its flow
is more  or less  rapid, according as the ventricles are con-
tracting or dilating.
   24. The force with which the blood is thrown from  the
heart is variously estimated.  Hales computed that the  left
ventricle of a horse exerted a force equal to 113 pounds,  and
that of a man at 51 pounds.  Some think that the contrac-
tion must overcome the whole pressure of  the air  upon  the
body, which is equal to forty thousand pounds.  As we can-
not, however, correctly estimate  the  influence of breathing
and  other causes, we  cannot, with  any degree of certainty,
tell  what degree of  power is exerted by the  heart.   Dr.
Arnott thinks, however, that the heart acts with a force of
about six pounds on every square inch, and as the left cham-
ber of the heart has about ten square inches, the whole force
exerted is sixty pounds.
   25. The Blood.—The blood is not necessarily  red, it may
be white, as in the fish ;  transparent, as  in the  insect;  yel-
lowish, as in the reptile; and indeed there is no  animal in
which the blood  is red in all the parts of its body.
   26. In a short time after blood is taken from the body it
separates into two portions, by a process called  coagulation,
viz.  1.  a watery portion called  serum,  and a solid portion
called coagulum  or clot; the white substance which forms
the upper part of the clot is called fibrin, and the  red mass
under it, the red particles.  The  fibrin is the material from
which all the solids of the body are formed.   (See Fig.  6.)
   27. The red particles owe their colour, it is supposed, to
the presence of iron;  though some say it depends on an  ani-
mal substance of a  gelatinous  nature.   These are usually
described as being minute  globules, but the latest microsco- 
THE CIRCULATION OF  THE BLOOD.        26?

               Fig. 6.
  A portion of fibrin, showing its fibrous structure and the net-lika
arrangement of its fibres.

pic observations show that  they are flattened  cakes, having
rounded  and  slightly thickened margins, as  shown in the
following cut:
                          Fig. 7.
pEpji
  1. A particle of human blood  as it appears when transparent ana
floating.  2. The same, seen as illuminated. 3. The same, one half
illuminated.  4.  A  particle  of  frog's  blood floating.  5. The same,
seen edge-wavs. All these objects are magnified five hundred diam-
eters.

  28.  The blood  constitutes about  one fifth part  of  the
weight of the whole  body ;  so  that  the  whole quantity of
blood  in  the body  of  an adult may be estimated  at between
thirty and  forty pounds.  A complete revolution  of  the
blood  takes  place  every  three minutes, and  there are about
five hundred and fifty revolutions every twenty-four hours.
The contractions of the  ventricles, or the  pulse,  is  about
6eventy-five  times  in a minute, in a grown person, and one
hundred and forty  in an infant; in   old age about sixty. 
268
PHYSIOLOGY.
 Now as two ounces of blood are thrown out of the heart at
 each beat, thirty five pounds on an average, must pass through
 the  heart every three minutes ; seven hundred pounds every
 hour; and  sixteen thousand pounds,  or eight tons, every
 twenty-four hours.
   29. Dr. Barry  states,  that  the quicker  the blond circu-
 lates the sooner will the machine wear out.  Now,  suppose
 that  the pulse of  a temperate  man be seventy in  a minute,
 and  by  the use of ardent spirits he forces it up  to eighty-
 five, then instead of living seventy years, his number of pul-
 sations will be finished at the age of fifty-six ; thus cutting
 short his life fourteen years.
   30. The  heart   beats  more than  one  hundred thousand
 times in twenty-four hours, and sometimes continues to beat
 thus  for one hundred years.  What other machine  so com-
 plicated, could last as long ?  And still it is  made of nothing
 but  flesh.   How strange  that  it should act so  long,  without
 growing weary ! Truly is it said, that " man is fearfully and
 wonderfully made !"
   31. Some physiologists consider  the  heart the only mo-
 ving power  of the  circulation  : Others think that the arte-
 ries aid by their contractile power.   Others still believe that
 the capillary vessels have  a kind of absorbing and  propelling
 force,  independent of the heart  and arteries, while a last
 class  ascribe  the  circulation  to a self-moving power in the
 blood itself.  All these theories may have some  truth in them,
 but they err in being too exclusive.
   32.  That the heart is  the   chief moving power of the
 blood is generally  admitted.   If the heart  of a frog be ta-
 ken  from the body and  placed in warm water, it will  con-
 continue to contract  and dilate with great force  for a  con-
siderable time.  This  would seem  to prove that  its action
does  not depend on the contact of air and blood.  In  ser-
 pents the heart retains this power a long time after death;
and  it has been known to contract at least four days after
life appeared extinct.   The heart of a sturgeon was cut out 
THE CIRCULATION OF THE BLOOD.       269
and  laid on  the  ground, and after it ceased to beat it was
blown  up and ordered to be dried.   It  was then hung up
when it  began to move again and continued to beat, though
more slowly, for ten hours ; and it continued to contract till
it  became so dry as to rustle with the motion.   If the heart
of any  animal  be taken from the  body immediately after
death and carefully washed, it will continue to act for some
time ; showing that  this alternation of action is natural to
its irritable fibre, and results directly from its structure.
  33. The arteries have not an equal power of contraction,
with the heart, though they are generally found more or less
contracted after death.  The pulse, which may be felt by
placing  the  fingers on the side of the wrist, takes place at
the  very instant  the  heart  contracts,  and is not probably
owing  to the contraction or  dilitation of the artery, but
chiefly  to the jet of blood,  which  is sent along the tube.
When  arteries are changed into bone, the pulse is still felt.
No pulse exists in animals destitute of a heart.
  34. That the arteries are not only elastic, but contract so
as to assist the heart in circulating the blood, is evident from
the following facts.  If an artery be laid bare, and two lig-
atures  applied so as to cut off all communication, and then
a small  opening  made  between the ligatures,  the blood will
spirt out with  considerable  force, and  the artery become
much contracted.   When a person or animal  is bleeding to
death, the arteries always contract in proportion to the loss
of blood ; after death they relax again.  Arteries too will
contract  by the application of stimulants or irritating sub-
stances.
  35. Besides these facts  to prove that arteries contract,
We  may mention the following.   We read  of cases of pal-
sv, where in  the  paralytic limb no pulse could be felt, al-
though the heart beat  as strongly as ever.  We read of oth-
er cases  where  the arteries continued to beat after the pul-
sations  of the heart ceased.  In diseases of the heart, we
sometimes have a weak pulse, although the heart beats very
                             23* 
270                  PHYSIOLOGY.
strongly.   And  in apoplexy the pulse is often strong,  when
the heart  acts feebly.  Burns relates cases where the pulse
at the wrist did not correspond with the contractions of the
heart: and it cannot be denied that in some animals a cir-
culation exists, although they have no heart.  Although fish-
es have  a heart,  their blood  is moved  through the body by
vessels.   After the heart is taken out of the body, the blood
is still seen to flow in the small vessels.
   36. I  have stated that arteries contract by an irritating
substance being applied to them.   Hartshorn, or ammonia,
will make an artery shrink so as to lose one eighth of its cir-
cumference.  A  partial enlargement of an artery  takes place
in a living animal  by exposing it, and rubbing it between
the finger and  thumb, but in  general no pulsation will be
seen in an artery thus exposed.
   37. The capillary vessels have an action independent of
the heart.   When the blood has reached the ends of the ar-
teries, or the capillary vessels, the force of the heart and ar-
teries is probably nearly,  if not quite exhausted.  Dr. Ar-
nott says  that  the  blood  is  driven into them, by a force
equal to four pounds to the square inch.   There  is no doubt
that the action  of the heart  is sufficient to force the blood
through the arteries into the veins; for  when the heart acts
feebly the  surface of the  body is pale and cold.  But  the
blood is known  to move in a  backward or retrograde direc-
tion.  When a leech  is applied to the skin, the blood  flows to
the spot from all quarters.   In blushing, the capillaries of
the cheek  dilate instantly and admit more blood; under  the
influence  of fear they contract, and the face becomes pale ;
tears will  gush  from the eye in a moment and suddenly dis-
appear ;  now  all these things could not  happen if these ves-
sels did  not act independent of the heart.
   38. It is probably capillary action which moves the fluids
in all  animals that have no heart.  Persons have lain in a
swoon apparently dead for days together and then revived.
In these cases life was preserved in the capillary circulation, 
THE CIRCULATION OF THE BLOOD.       271
I have seen a case of this kind, where a young lady of this
city,  was kept a  fortnight after she  was supposed to have
died ;  her looks being so natural that her parents were  un-
willing  to  bury her, for fear she would come to life.   Al-
though she lay in a room without a fire in the winter season,
yet her body retained  its natural warmth for several days,
her cheeks their florid colour,  and her limbs their usual flex-
ibility.  These singular phenomena were perhaps owing to
a continuance of the capillary circulation.
  40. The capillary vessels are the last part of the body that,
continues to act.   After the breathing and the action of the
heart  have  ceased, they still  continue to act like innumera-
ble  little pumps, drawing the blood out of the arteries and
substance of the  organs, and  forcing it into the veins.  As
nutrition and secretion  are performed by that portion of the
capillary system which acts independently  of the heart and
arteries, the continuance of  action in this system accounts
for  the growth of the beard and the hair, which takes place
after  death.   It is owing to the same reason, that the arte-
ries are always found empty after death.
  41. Physiologists  are not agreed as to  the cause of the
motion of blood in the veins.  The veins have thinner coats
than the arteries and are destitute of elasticity.  As they are
wanting in elasticity, if they  had no irritability, they  could
not act  upon the blood contained in them, and accordingly
could exert no active force in  circulating the  blood.   But  it
is found by  experiments that  the veins are not mere passive
tubes ; they possess a certain  degree of contractile power, as
is shown  in the  shrinking of the veins on the back of the
hands in  cold weather; besides, if a vein  be punctured be-
tween two ligatures, the blood  will spirt  out.   The veins
then assist the circulation by a sli ht degree of  contractile
power.
  42. A^ain : when the heart dilates, the blood is sucked
up in  the veins precisely as it is in a pump.   This is denied
by some, who say, that if the end of a syringe be placed in a 
272
PHYSIOLOGY.
tube of eel-skin,  or any thing which is not elastic, and you
attempt to pump the water out of it, supposing it to be filled,
the sides will be brought together,  and the tube closed, so
that the water cannot escape.  This, however, will not hap-
pen, if, as in the veins, the fluid is forced in at the other end.
  43.  The expansion of the  chest in  breathing, also aids in
circulating the blood  in the veins.  When the chest is dila-
ted, both air and blood rush into it.   This may be seen by
watching the jugular  veins in the neck, which empty them-
selves  during  inspiration.   Dr. Barry placed one end of a
tube in the jugular vein, and  the other in a coloured fluid.
During inspiration, the fluid was sucked from the vessel into
the vein ; during expiration, it remained stationary.  It should
be remembered, that during one act of respiration, the heart
beats  five or six times.
  44.  One other cause remains to circulate the blood in the
veins,  and that is, the action of the muscles.  When the
muscles contract, they press  upon the veins  in contact with,
or near them, and  so force  the  blood along their cavities.
This  can be  seen  in bleeding from  the arm ;  if a  person
grasps a stick, the blood flows much  more freely than when
the muscles are relaxed.   It is  in this way, that exercise
proves so beneficial to health, by promoting the circulation
of the blood through the system ; and  we account  in this
way also, for the fact that sedentary habits so often lay the
foundation  for incurable diseases.
  45.  The heart is not so dependent on the brain  for its ac
tion as many other organs.   Monsters, born without head*.
sometimes  live for several  days.   Snakes have  lived six
months without a head ; and any animal may live for some
time in the same condition, if the blood-vessels of the neck
are tied. If the breathing be kept  up by artificial respiration,
life may be continued for a long time.  I have myself kept
a child alive two hours, that had its neck broken, by keeping
up artificial breathing ;  persons have been saved in the same
way, who had taken large doses of laudanum. 
THE  CIRCULATION  OF  THE BLOOD.        273
  46.  In fainting, the heart ceases to act.  It may be owing
to various causes, acting on  the nervous system, or on the
blood-vessels.   Mental emotion, loss  of. blood, or any thing
that renders the  blood-vessels about the  heart  less full or
tense than usual, will cause a  person to faint.   This state is
soonest  relieved  by lying down, probably because the action
of the  heart is sufficient to force the blood along horizontal
tubes, but  not to raise it in a perpendicular position. Where
blood has  been lost in sufficient quantity to endanger life,  it
has been supplied from the  veins of another person, by a pro-
cess called transfusion.
   Questions.—When  was the circulation of the blood discovered ?
and by whom ?  Why not  discovered before ?  Why is the circulation
called  a vital function ?   How is life maintained"?   Have all animals
a circulation ?  Describe the structure of the heart.   What is the peri-
cardium ?   In what animals is the heart double ?   Describe the cavi-
ties of the heart—the valves.  What is their use ?  What are arteries ?
How many coats have they ?   Describe the venous system.   Have the
veins valves ? What is the capillary system ?  Describe the circulation
in reptiles—worms—fishes.  What  facts did  Harvey bring forward to
prove  the  circulation of the blood ?  What is the motion of the blood
chiefly owing to ?  Are the ven'.ricles thicker than the auricles ? Why ?
What  is said of  the  velocity  of the blood ?  Of the force of the
heart ?  Describe  the  composition of the blood ?  What proportion of
the body does it constitute ?   How long is the blood in performing a
revolution ?  What is the last part of the body that continues to act?
Why are the arteries found empty after death ?   What circulates the
blood  in the  veins 1   What  aids in this process ?  Does the  heart de.
pend on the brain for its action ?  What facts connected with this sub.
ject?   What occurs in fainting ?   What position is  most favorable in
recovering from fainting ? 
CHAPTER  XX.
           NUTRITIVE  FUNCTIONS.--DIGESTION.

  1. Digestion, absorption, secretion, and nutrition constitute
what are called the nutritive functions.   Digestion is that
process by which the food is brought into a state in which
it may be  taken  up by the lacteal  vessels and carried into
the blood.   The  digestive apparatus consists  of the  mouth
and its appendages ;  the pharynx ; esophagus ; the stomach
and intestines;  the  whole  tract making  what is called the
alimentary canal.   Besides these,  there  are  the salivary
glands ;  the liver ; the pancreas, or sweet-bread of animals ;
all  of which  aid in the  process of digestion.
   2. The  parts  which compose the mouth,  are the lips,
cheeks, palate, tongue, teeth, and salivary glands.   There are
six salivary glands, which secrete saliva, viz.: the parotid;
sub-maxillary; and  the sub-lingual.  The  parotid gland is
situated  on the cheek before the ear; the sub-maxillary im-
mediately beneath the lower jaw , and the sub-lingual under
the tongue.   They all pour forth a fluid, during mastication,
into the mouth  to moisten the food, and prepare it for the
change  it is to undergo in the stomach.   A swelling of the
parotid gland is  called the mumps.
   3.  In a grown person, there are thirty-two teeth ; four in-
cisor, or cutting  teeth,  two canine or dog teeth, ten molar or
grinders in each jaw.   The first set of teeth begin to come,
when  the child is about six months old, and by the time it  is
two years and a half old, it has twenty;  about the  seventh
year,  they all become  loose and fall out, and  their place  is
supplied by  another set.  The teeth are  the hardest part of
the body ; their internal  parts resemble bone;  the external
consist  of a  very hard and highly polished substance, called
enamel,  which is very  durable. 
NDTRITIVE FUNCTIONS--DIGESTION.      275

                Fig. 1.
  Half of the lower jaw ; a, the base ; 6, the angle ; c, the ramus; d,
the condyle; e, the coronard  process; h, the two incisors or cutting
teeth; i, one canine or dog tooth; k, two small molar; I, three large
molar or grinding teeth.

  4. The jaws perform an important part, in fitting the food
for the stomach.  The lower jaw only has motion ;  being
moved by means of strong muscles, which rise from the tern-
pies and upper jaw ;  and it not only moves directly upwards
and downwards, but  sideways,  so as  to grind the food be-
tween  the teeth, as grain is ground between two mill-stones.
  5. The tongue  is likewise  very useful in  the process of
mastication,  as it removes the food from  one part of the
mouth to  another, so as to bring every  portion between the
teeth; and then it forms  it into a suitable shape for swal-
lowing.  The tongue is made up by different muscles,  and is
supplied by nerves, chiefly from the eleventh pair.
  6. The esophagus or meat-pipe, lies directly  behind the
wind-pipe, and is about one inch in diameter.   It connects
what is called the pharynx, with the stomach.  All these or-
gans are lined by a soft, velvet-like membrane, termed mucous
membrane, because it is always covered  in health, with a vi-
scid fluid, called mucus. 
276
PHYSIOLOGY.
   7.  The  stomach is the largest organ of digestion.   It lies
immediately under the  false ribs, on the left side, below the
midriff, and is shaped somewhat like a bag-pipe. It has two
openings, the  upper one, which admits the food, is called car-
diac,  and the  lower one, the pyloric orifice.  In a middle sized
man,  this organ is about ten inches long, and three or four  in
diameter, and holds from three to six pints.
   8.  The stomach has four distinct  coats ;  the inner one  is
called mucous or  villous; being thin, soft, and spongy ; the
second vascular;  as it  is made up chiefly of blood vessels •
the third muscular',  composed  of muscular fibres, and very
strong ;  the fourth serous; as it secretes a serous or watery
fluid.   The stomach is freely  supplied with blood vessels and
nerves;  the latter being furnished  partly  from the  spinal
marrow,  and partly from the  brain.
  The human stomach : a, the esophagus or gullet; b, the cardiac por-
tion ; c, the left extremity ; d, the small extremity ; e, the pylorus tied ;
g g, the omentum or caul,  which  is attached to the outside of the
stomach, and falls over the intestines like a curtain. 
           NUTRITIVE FUNCTIONS--DIGESTION.      277
  9. The  intestines in  man, are from five to six times the
length of the body ;  and are divided into large and small in-
testines;  the  latter making about four fifths of the whole.
The small intestines are  divided into duodenum, jejunum,
and ileon.  The duodenum is so called because  it is about
twelve  finger's-breadth in length ; the jejunum from its gene-
rally being found empty ; the ducts  or  canals from the liver
and pancreas enter the duodenum near the  middle, and it is
abundantly supplied with lacteals.   The different portions
of the  large intestine are called coecum, colon, and rectum.
  10.  The Uver is the largest gland in the body ;  and it lies
directly under the ribs, on the right side, and reaching be-
low them.  In a grown person, it is about ten inches in diam-
eter, and weighs not far from four pounds.   It  secretes the
bile, which is poured out into a bag called gall-bladder, con-
nected with it; from thence it is carried into the duodenum.
The liver is found in all the vertebrated animals and in the
mollusca;  in birds, reptiles and fishes, its size is greater in
proportion to that of the body than in the  human species.
It is attached to the diaphragm, which lies above  it, by a
fold of the peritoneum, called the suspensory ligament of the
liver.
  11.  The pancreas is a gland about five inches in  length,
of a whitish colour, lying immediately behind the stomach.
It is supplied, like the stomach, with numerous  blood-vessels
and  nerves.   It secretes a fluid, called the  pancreatic fluid,
which  is  white,  viscid, inodorous,  slightly saline, and con.
tains a large proportion of albumen.   This gland is found
in all the  mammalia, in birds, and in amphibious animals, or
such as live both in air and  water, like the  frog; but it ia
much larger in animals that live on  vegetables, than in those
that feed  on  flesh.  Hence, the fluid which it secretes, is
supposed to aid in difficult digestion.  (See Fig.  3.)
                          21 
27S
rilYiTOLOGY.
Fig. 3.
  The above cut represents the whole  tract of the intestinal canal, nol
exactly in its natural position, but spread out so as to show the relativt
proportions ; /, the sesophagus; ^,cardia ; h, pylorus ; i, i, the duodenum,
about twelve fingers' breadth in  length; k, hepatic duct; I, gall  blad 
NUTRITIVE FUNCTIONS---DIGESTION.       279
der ; m, cystic duct; n, ductus communis, formed by the union of both;
o, the opening of this duct into the duodenum; p, pancreatic duct;  q,
its opening into the duodenum; r, jejunum; s, ilium; these constitute
the small intestines, and are about twenty-six feet in length, or five
times the length of the body; t, termination of ilium  in the coecum;
m, superior fold of valve of colon ; v, inferior do.;  w, coecum ; x, ver-
miform process; y, y, colon; z, rectum.   The coecum, colon, and
rectum, form the large intestines, and are about six feet in length ; the
coecum being about 4 inches long, and the same in diameter.  The
arrows show the direction which the food takes in digestion.

   12.  Hunger and  thirst are sensations designed to teach us
the necessity of supplying those  losses which the  system is
constantly undergoing  by the  different secretions and excre-
tions, amounting to several  pounds in the course of twenty-
four hours.  The  blood first feels  the loss, and then  the
solids,  whose particles  are continually taken  up by the  ab-
sorbents, and carried into the blood, and thus ejected from
the system; and were not these losses supplied by the timely
introduction of food, the  body would  rapidly  emaciate, till
death closed the scene.   Hunger is supposed  to be owing to
a peculiar affection of  the nerves of the stomach; for when
the nerve which goes from the brain to the stomach (the par-
vagum,) is  divided, the sensation of hunger  is lost, or at
least the appetite  for food is destroyed.
   13.  While the food is undergoing the process of mastica-
tion, that is, of being divided and ground down by the teeth,
it is thoroughly mixed  with a  quantity of saliva, amounting
it is supposed to between eight and  ten  ounces.  The food
is thus brought into a  condition to be easily swallowed, and
readily dissolved by the  action of the  stomach.   It is very
important, therefore, that the food should be slowly chewed,
and reduced to as  fine a state as possible  in  the  mouth, in
order that  digestion may be  easy.   Too great  rapidity in
eating, probably  lays the foundation  of many cases of indi-
gestion.
  14.  After the food  has been  sufficiently masticated, it  is
carried down the aesophagus  into the  stomach, first by the 
280
PHYSIOLOGY.
contraction of the muscles  of the  pharynx, and then by a
successive  contraction of the circular fibres of the gullet it-
self, from above downwards.   That the morsel is not carried
down merely by its own weight, is proved by  the fact, that
a man can swallow with his head downwards.
   15. In the  stomach, the food is converted into a soft, grey,
pulpy  mass,  called chyme.  This process has  been called
chymosis.  It is  produced  by the motions  of  the stomach,
together with the agency of the secretions, which are thrown
out by the  gastric vessels.   These motions have been called
vermicular  or worm-like; and undulatory, or like wave sue-
ceeding  wave.   The  crawling of a worm furnishes a very
good illustration of the successive contractions of the muscu-
lar fibres of the stomach, commencing, as  they do, at the seso.
phagus, and proceeding onwards to the pylorus, and so back
again.  These motions of course bring every portion of  the
contents of the stomach in  contact with all  parts of its sur-
face; and so they become intimately  mixed  with the gastric
fluid.
   16.  The food is thus carried round the  interior of the sto-
mach,  from one  extremity  to  the other ; and  from one  to
three minutes are employed in  each revolution.  In the mean
time, both orifices are closed; so that the contents cannot
escape.  During  this  process,  the gastric  fluid is secreted in
large  quantities,  and  becomes mixed with  the  food as it
passes  round.  In a short  time, the  taste, smell, and other
sensible properties of the food, are entirely  changed.  This
is  produced by the agency of the gastric juice, which sub-
verts the chemical affinities  of the food ;  and with  its ele-
ments  forms new  combinations.
   17.  The gastric fluid is a clear, transparent fluid, produced
by arterial  exhalation ; acid to the taste, slightly saline, and
free from odour.   It possesses the singular  property of  co-
agulating albumen ; resists  the putrefaction of  animal  mat-
ter ; and dissolves nearly every kind of alimentary substance.
Its acid properties are owing to the muriatic  and acetic acids 
              NUTRITIVE  FUNCTIONS--DIGESTION.      281
    which it contains.   The  gastric fluid  is found  to  contain
    more acid,  in  proportion as the  food  is  more  difficult of
    digestion.   It is  only secreted, when food is present in the
    stomach.
      18. The  aliment then is converted into chyme, chiefly by
    the gastric fluid ; aided, however, by the motions of  the sto-
    mach.  This is  proved by the fact, that this fluid will dis-
    solve alimentary  substances out of the stomach :  the chyme
    which is prepared by artificial digestion, presenting the same
    sensible properties  as that which  is found in the stomach.
    Such is the power  of the gastric  fluid, that  it will  dissolve
    bones, not only in  the stomach, but out of it.  It  curdles
    milk; and for this  purpose  the  rennet, or stomach of the
    calf, is used by farmers in making cheese.   But every thing
,   which is coagulated in the stomach, is dissolved again, in its
    conversion into chyme.
      19. But  digestion is a vital and  not a chemical  process.
    Though aliment  may be reduced to a substance  resembling
    chyme, by the  action of gastric  fluid out of the body;  yet
    it is destitute of  all those peculiar properties which  assimi-
    late  it to  the  nature of  a living animal.   The food  may
    doubtless  be brought to a fluid state  by a chemical  process,
    and  even alimentary principles may in  the same  way be
    changed into each other, as starch into  sugar and gum;  but
    there is still  another  power, which  may be  called vitalizing
    or organization, by  which  alimentary substances are  brought
    into such  a  condition as adapts them for an  intimate union
    with  the living body.   Such a power is beyond the reach of
    chemical action.
      20. The time which is required to  change food into chyme,
    varies according  to the nature of the food.   Animal food is
    digested sooner than vegetable.  The average time required,
    is about three hours and a half.   A  good deal depends, also,
    on the degree of mastication it has undergone.  If swallowed
    in large masses its solution must go on slowly.
      21  \s fast as the aliment is changed into chyme, it pass.
                              24* 
282 '                PHYSIOLOGY.
es out of the stomach into  the  duodenum, and  it  generally
stays in the stomach  until it has undergone this change.
Indigestible substances  have thus been  vomited  up,  more
than a week  after they were swallowed.   All fluids which
are swallowed, are supposed to be taken up  by absorption.
   22. If the par-vagum, or nerve which goes from the brain
to the stomach, be divided,  digestion is impaired or suspend-
ed.  The same happens under the influence of mental  emo-
tions, such as grief, anger, &c.  Some  physiologists  have
thought that this nerve presides over the  secretion of the
gastric juice ; others, that it stimulates the muscular motions
of the  stomach;  while  a  third  class  consider it  to be the
seat of sensation  in the  stomach, giving rise to hunger and
thirst.   But it is  not  yet fully settled  what  particular influ-
ence this nerve exerts ever digestion.
   23. The chyme, on passing from the stomach, is received
into the duodenum.   This, like  the stomach, has a serous,
muscular, and mucous coat, and has a  mucous, as well  as se-
rous, secretion.   In this portion of intestine, the  chyme in
its passage meets  with the  pancreatic and the biliary fluids;
the irritating properties of  the acid chyme, cause  these
fluids to be poured out in  great abundance, as well as the
other secretions  ; and  these  are thoroughly  mixed  with
the chyme  by the contraction  of the intestine.   It now be-
comes  of a yellowish, instead  of a  gray  colour; its  acid
properties  disappear,  and  large quantities  of albumen are
developed.   This  is supposed, by some, to  be derived  from
the pancreatic fluid, which contains a large proportion  of it.
   24. As it becomes  intimately mixed with the biliary and
pancreatic  secretions, the substance called chyle is produced.
Though some say it is not to be found in  the duodenum—but
only the elements out  of which it is  formed.  But albumen,
which is  the basis of  chyle, exists abundantly in the duode
num ; and so also do particles of fibrin.   By the microscope,
globules also may be detected in the chyme, similar to  those
which are found in the chyle. 
          NUTRITIVE  FUNCTIONS--DIGESTION.       283
  25. It would seem, then, that the great business of diges-
tion is to change the food into  albuminous  matter, which
forms the basis of the chyle as well as the blood ; and it is
certain that no albumen is formed in the stomach; though
the change which the food there  undergoes, is  an approach
to the nature of albumen.   As the  bile is alkaline, it doubt-
less combines with, and n-sutralizes the acid  properties of
the chyme, which would  precipitate the mucus of the bile,
and leave it in a state of coagulation.
   26.  Chyle  then  is the fluid, which is taken up by the ab-
sorbent vessels, called lacteals, whether it exists ready formed
in the chyme, or is manufactured  out of it, by the action of
these  vessels  themselves.   It is usually of a milk white co-
lour, but varies in appearance in different animals ; and ac-
cording  to the nature of the food.   In animals that feed on
flesh,  it is opaque ;  in such as live on vegetables, it is trans-
parent ;  in  birds  and fishes, thin, serous, and clear like wa-
ter.   It is saltish, and somewhat  sweet to the taste ;  heavier
than water but less so than blood.   It  coagulates on stand-
ing,  like blood, and separates into three portions; a fluid, a
coagulum, and a  fatty substance.  The fluid portion  is chief-
ly of  albumen and coagulates like the serum  of the blood by
heat,  acids, and  alcohol ;  the coagulum  consists of fibrin,
and a coloring matter, which is white.
   27.  Whatever the food may consist of, physiologists are
now pretty well  agreed, that the chyle will always  be com-
posed of fibrin,  albumen,  a. fat  matter, muriate of soda, and
phosphate of  lime, though  in  variable  proportions.   Food
that contains much azote, such as that of animals, it is sup-
posed will form  chyle, which contains a greater portion of
fibrin than that of vegetables, as azote is one of the chief ele.
ments of fibrin. Dr. Marcet states  that chyle produced from
vegetable aliments contains three times  as  much carbon  as
that formed out of animal substances.   It  is certain that
chyle  from animal food is milky ; and that from vegetables
traasparent.  As both however  are composed of the same 
284
PHYSIOLOGY.
essential  elements, we may be assured, that man can live on
either animal or vegetable diet,  as  it may be most conve-
nient.   As the most important part of digestion seems to be
completed in the small intestines,  we shall not follow the pro-
cess any farther.
  28. A few years since, a man  in the United States army
received  a gun-shot wound,  which made a hole in his sto-
mach ; and which left an opening into the cavity of that or-
gan, so that the whijle process of  digestion could be seen, as
it  was going on.  Dr. Beaumont, a physician in the army,
availed  himself of this singular  case, and performed many
curious experiments which occupied him for several  years.
The following are the most  important inferences, which he
drew from his experiments.
   29.  " Animal and farinaceous aliments are more easy of
digestion  than vegetables.   Digestion  is facilitated by mi-
nuteness of  division and tenderness of fibre;  hence the im-
portance  of  thoroughly chewing  the  food.   The  ultimate
principles of aliment  are always the same, from whatever
kind of,food  they may be obtained, whether  vegetable or an-
imal.  The  quantity of food generally  taken "into the sto-
mach, is greater than the system  requires.  Solid food is ea-
sier of digestion than fluid. Stimulating condiments, such as
spices, are hurtful to a healthy stomach.
   30.  The continued  use of ardent spirits always  produces
diseases  of the stomach.   Hunger is the effect of the dis-
tension of the vessels, which secrete the gastric juice.  The
temperature  of the  stomach is 100 degrees of Fahrenheit.
The gastric juice dissolves the food, and alters its properties.
It also coagulates, or renders solid, albumen, and afterwards
dissolves it.
   31.  The gastric juice is a clear and transparent fluid;  a
little saltish, and somewhat  sour to the taste.   When pure,
it suffers no  change  by keeping.   Gentle exercise assists the
digestion of the food.  Water, ardent spirits, and most other
fluids are not  affected by the gastric juice, but  disappear
from the stomach soon after  they are received." 
            NUTRITIVE  FUNCTIONS---DIGESTION.       285

  Questions.—What constitute the nutritive functions?   What the di-
gestive  apparatus?  What the  mouth?  How  many salivary  glands
are  there ?  How  many teeth are there in an adult ?  How divided ?
When  do they begin to appear ?   When are they shed ?  What is the
outside of the tooth called ?   How is the tongue useful in  mastication ?
Describe the esophagus—the stomach—the intestines—the liver—the
pancreas—hunger  and thirst.  Describe  the process of digestion. What
is the gastric juice ?  Chyme ?  Chyle  ?  What is rennet—what used
for ?  Is digestion a  chemical process  ?  How  long does it generally
take to convert food into chyme ?   What influence has the  par vagum
nerve on digestion  ?  Where  do the pancreatic and biliary fluids enter
the  intestines ? their use ?  Is the nature of chyle changed by the kind
of food ?  Of what is it always composed ?   What are the principle re-
sults of Beaumont's experiments in relation to digestion ? 
CHAPTER XXI.
                       SECRETION.

  1. Secretion  is one  of the most  obscure  and mysterious
functions in the animal economy. To secrete means to sepa.
rate ;  but most  of the fluids formed by this  process, did not
previously  exist in the blood, but  only the elements out of
which they are  made.  It is purely a vital and not a mechan-
ical process, like straining through a seive, to which some
have compared it: and the vessels by which it is accom-
plished may well  be called  the architects and chemists of the
system ; for out  of the same  material, the  blood, they con-
struct a variety of wonderful fabrics, and  chemical com-
pounds.
  2. We  see the same wonderful  power possessed also by
vegetables—for, out of the same materials, the  olive pre-
pares its oil; the  cocoa-nut its milk ; the cane its sugar ; the
poppy  its  narcotic juice ; the henbane its poison ; the oak
its green pulpy leaves, its light pith, and its dense woody fi-
bre : all composed of the same, few simple elements, only ar-
ranged in different order and proportions.
  3. In  like manner,  we  find the vessels in animal bodies,
capable of forming all the various textures and  substances
which make up  the frame; the cellular tissue ; the mem-
branes ; the ligaments ; the cartilages ; the  bones ;  the mar-
row ; the muscles,  with  their tendons ; the  lubricating fluid
of the joints ; the pulp of the brain ; the transparent jelly of
the eye ;  in short,  all  the textures of the various organs  of
which the body  is composed;  and still all  are made out  of
the same blood; and consist of  the same ultimate elements.
   4.  The  most simple form of secretion, however, seems to
be, the mere separation of some principle, which previously
existed in  the blood ; as serum is deposited in most of the ca-
vities, by a kind  of exhalation.   Some other principles also 
                       SECRETION.                  287
exist  in  the blood, which are found in the  secretions, as fi.
brin,  a fatty substance; and  some  of the elements of the
bile.   Some physiologists believe, that many of the secre-
tions  do exist ready formed in the blood, but cannot be de-
tected by analysis. In  proof of this, two ounces of bile have
been  injected  into the veins of a dog, but the blood of the
animal, which was analyzed a few moments after, exhibited
not a  trace of bile.
   5.  That  secretion  is a vital  process and not a chemical
one,  is evident from the fact, that it is so  much under the
influence  of the nervous system.   For example,  sorrow and
grief change the qualities of the bile: a fit of anger  some-
times causes an excessive flow of it :  it will also  change the
nature of milk to  such  a degree, as to produce colic, vomit-
ing, and  even convulsions in the infant  that swallows it.
Grief will also suspend  the secretion of the gastric fluid, and
thus destroy the appetite ;  while fear causes a cold sweat to
break out, all over the surface of the  body.  If the nerves go-
ing to any  organ  are divided, the function  of secretion will
be suspended.  It  is doubtless owing  in a great degree to the
changeful states  of the nervous system, that the secretions
vary  so much  in  quality as well as quantity at different pe-
riods.
   6.  Though  we are able to understand but little of the true
nature of secretion, we know  that there are  three  kinds of se.
cretory organs, viz., exhalent vessels ; follicles ; and glands.
The exhalents are believed to be the termination of the arte-
ries, or capillaries; and they are of two kinds, internal and
external;  the former terminating on all the surfaces within
the body ;  and the latter on the outside.   Their use is to
soften and lubricate these parts.
   7.  The fluid, which  is thrown out by  the serous mem-
brane which surrounds  the brain, the lungs,  and the contents
of the abdomen, as well as into the cavities  of  the joints, is
very similar to the water of the blood, and its use is, to  keep
the parts in a moist state, and enable  the organs to move ea- 
288
PHYSIOLOGY.
 sily on each other.  Fat is also a secretion, which is thrown
 out  in a fluid state, from the cellular tissue, into little cells;
 and it is mostly found immediately under the skin, between
 that  and the flesh.  Its use seems to be, to lubricate the so-
 lids and facilitate their movements ; to f >rm a cushion around
 the body, and protect it  from external injuries as well as the
 extremes of heat and cold.
   8.  During sickness,  when we take little or no food  into
 the stomach, life is supported by the absorption of the fat,
 which is taken up by little vessels and again poured into the
 blood, to nourish the body; also in  animals which lie in
 their burrows,  in a half torpid state during the winter, their
 nourishment is derived from the  same source.
   9.  Marrow which fills all the cavities of the long bones,
 is very much like fat, and this also is a secretion from a thin,
 delicate  membrane, that lines  the  cavities of the  bones.
 These are the  principal  internal exhalations, or secretions.
   10.  The external  secretions are two in number; the  first
 and most important from the skin is called, when insensible,
perspiration ; and when  it is visible, is called sweat;  the se-
 cond  is from the lungs, and can  be seen in the form of a va-
 pour in a frosty morning.  The fluid which escapes from the
 skin, is chiefly water, containing  a little acid and some salts,
 with a small quantity of animal matter.
   11.  The  skin  is covered with an innumerable number of
 pores,  so small  indeed, as  to be invisible to the naked eye,
 through which the insensible  perspiration is constantly pour-
 ing,  amounting  in  weight to more than one half of all the
 food and drink taken into the stomach, and much exceeding
 that lost by  all the other excretions.
   12.  From a vast number of experiments performed by dif-
ferent persons, it appears that the largest amount of insensi-
ble perspiration amounts  to five pounds in twenty-four hours,
and the smallest to thirty-two ounces.   Now, when we con.
eider  that the skin, serves  as one of the chief outlets, by
which the old and useless particles are got  rid of, out of  the 
SECRETION.
289
blood, and that checked perspiration is one of the most pow.
erful causes of disease and death, we shall see how important
it is to keep the pores  of the skin  free, by frequent washing
and bathing at all seasons of the year.
  13.  When the surface also is c-hilled  by cold, and reaction
does not follow, the blood-vessels become contracted all over
the skin, and  the  blood retreats  to the  inner parts of the
body ;  the  29  ounces  of waste and noxious matter, which
ought to be discharged, are kept in the  system, and sickness
is the consequence.  Accordin-gly, we  find that it is a good
remedy, in most cases of disease, to excite a perspiration and
keep it up for some time.
   14.  The  uses  of transpiration  by the skin, are, not only
to carry out of the body the noxious properties of the blood,
but also to render the skin soft  and  pliable, the sense  of
touch  delicate, and also to cool the body when exposed  to
great heat.
   15.  The  exhalation  from  the lungs closely resembles that
from  the skin.   It was once  supposed to be formed in the
lungs,  by the union of hydrogen  from  the blood, and  oxy-
gen from the  air, thus forming water ;  but  it is the opinion
of  most physiologists at present, that it is either the watery
part of the mucus secreted by the  mucous coat of the lungs
and air passages, or  that  it  is given  off directly from the
blood.
   16.  The Follicles, are small sacks or bags, found in the
skin, and the mucous membranes.    The pores which we see
on the skin are only the outlets of these follicles.   Their use
is  to secrete an oily matter to mix with the perspiration, and
help to keep the skin soft and moist; when these outlets are
closed, sometimes there appear small black specks on the skin,
sometimes  called  worms, but  they are nothing  more  than
hardened mucus.   Every hair has a follicle at its root, and
the wax which collects in the ears, is secreted by follicles.
   17.  The chief agents  of  secretion in the body, are the
elands, which are bodies of  various  size, generally  of a
6                         25 
290
PHYSIOLOGY.
rounded form ; and the fluids they secrete, are very different
from each other, and also from the blood which furnishes the
same  materials  to all.   For instance,  the liver secretes the
yellow, ropy fluid, called bile ; the kidneys, secreft urine ; the
lachrymal gland, which is  placed  immediately over the  eye
in the orbit, secretes the  tears ; and the spittle or saliva is
poured out from the salivary glands.
  18. Glands are formed of a large number of arteries, veins,
nerves, and  lymphatics, disposed in  a peculiar manner, and
connected together by a tissue of cellular membrane.  When
in a cavity, they  are  covered on their external surface by a
coat, derived from the membrane that lines the cavity, and
they  are  also provided with a canal, called excretory duct,
which is  lined with mucous membrane.  There are seven
kinds of glandular secretions.
  19. The secreted fluids  have been divided  into serous or
watery, albuminous mucous, oily, and the mixed; such as sa-
liva, bile, tears, <Stc. They  have  also been divided into recre-
menlitious and  the excrementiiious, or those  which are  des-
lined  to be absorbed and returned into the mass of the blood,
and  which  are  deposited  in cavities that have no external
opening;  and the second, those which are designed, after
their formation, to be  expelled from the  system.
  20. When any substance is taken up by the absorbents,
and carried into the blood,  which cannot be converted, to any
useful purpose in the system, it is immediately discharged by
means of  the secretions.   Not many years ago, a man was
carried into a London hospital,  who was picked up drunk in
the  streets.  He lived but a short time,  and on examining
his brain, nearly a half a   gill of fluid strongly impregnated
with gin, was found in the ventricles.  This was secreted.
  21. Unless the secretions all go on, we cannot enjoy good
health.  If that from, the skin is stopped, fever, or some  in-
ternal inflammation  is the consequence.  If the bile ceases
to flow,  we cannot properly digest our  food ; and  so if any
of the others are interrupted, some serious disease will be the 
                          SECRETION.                      291

result.   The use of ardent spirits deranges all the secretions,
and this is one reason why they shorten life so much.
  Questions.—What  is Secretion ?  Is it a vital process ? Have vege-
tables the same property of secretion ? Illustrate this. What is the use
of this function ?   What is the most simple form of secretion ?   How
is it proved that secretion is a vital process ?   How many kinds of se-
cretory organs are there ?  What are  exhalents ?—their use ?   What
is fat?  How is life supported in sickness ?  What is marrow ?   What
are  the  external secretions ?   How much does the insensible perspira-
tion amount to in 24 hours ?  What important inference do we derive
from  this in relation  to health ?   What is use of transpiration by the
skin ?  What is the  exhalation from the lungs owing to ?  What are
follicles?  What  are the chief agents of secretion?  What are glands
composed of ?—their structure ?  How are the secreted fluids divided ?
V/hat becomes of useless substances carried  by  absorption into the
blood ? Can health be maintained if the secretions be checked ? 
CHAPTER  XXII.
                       ABSORPTION.

   1.  Absorption is another  function of the animal body,
immediately connected with nutrition.   By it is meant that
process by which food and drinks, designed for the nourish-
ment and growth of the body, are taken up and carried into
the blood ; and also those particles and  materials that have
been  already deposited, and have  become  either  useless  or
injurious, are conveyed into the general mass of the circula-
ting fluids, and thus removed from the system.   The first is
effected by the lacteal vessels; the second by the lymphatics.
   2.  The absorbent system, so  called, consists  of the lym-
phatic vessels, the lymphatic glands, and the thoracic duct.
The lymphatic  vessels arise, not only from all  the mucous
surfaces, but also from the whole surface of the body;  the
intimate tissue of every  structure ; and from  all cavities,
such as the chest, abdomen, the joints, the  pericardium, and
even  the  ventricles of the brain.   They  are  exceedingly
small at their origin, but by  uniting, form larger and larger
trunks as  they proceed, which is generally in  the  course of
the veins, till they finally discharge their contents, either in-
to the thoracic  duct, or some  of the large veins  near  the
heart.  Throughout their whole extent, they are provided
with numerous valves, which, when they are distended with
lymph, causes them to resemble a string of beads.
   3.  Every part  of the  body is supposed  to  be  furnished
with absorbent  vessels, with the exception of the  nails, the
hair, the'cuticle, and the enamel of the teeth.  And even in
these, it is not  impossible  that they may exist;  only they
are too small  to be detected.
   4.  The lymphatics of the small  intestines, called lacteals,
are the agpnis of digestive absorption.   They arise from the 
                      ABSORPTION.                   293
surface of the  mucous coat, pass  between the  serous and
muscular coats, and proceed to the small glands or ganglions
of the mesentery.   As they emerge from these, they increase
rapidly in size, till they finally  unite in a large trunk, which
passes up along  the spine, and at last empties its contents
into the left subclavian vein near the heart.   Many physi-
ologists are of  opinion that the lacteals not only terminate
in the thoracic duct, but  also in numerous  veins in the ab-
domen.
  5.  The chyle, which is the fluid taken up by the lacteals,
does not exist ready formed in the chyme, but is formed  or
manufactured out of the nutrient principles contained in  it,
by a specific action of the lacteal vessels  themselves.   In
like manner, the sap which is contained in vegetables, does
not previously exist ready made in the materials which are
absorbed from the ground, but is formed  by the peculiar ac-
tion of the roots.   No  chyle  has ever been  found  in the
intestines.
  6.  As the chyle passes  on towards the heart, it undergoes
important changes.  It loses some of its albuminous quali-
ties ;  while its fatty matter, its fibrin,  and cruor, considera-
bly increase.   Its tendency  to   coagulate,  also  becomes
greater as it approaches  the venous system, and it  becomes
clearer and  more transparent.   What is the precise  nature
of the change which the chyle undergoes in passing through
the glands is unknown.
  7." Absorption  not only takes place from the small intes-
tines, but from  the whole tract of the intestinal canal, inclu-
ding the mouth and aesophagus.  But those  vessels  which
absorb chyle, are chiefly found  in  the small intestines.   It
is highly probable that alimentary substances may be directly
absorbed  from  the  intestines, without  undergoing any  pre-
vious chancre or assimilation, like alcohol or water ; but that
in their passage through the absorbent system, they undergo
a species of digestion, and become  in a good  degree fitted
for the replenishment of the blood.   To  this, however, alco-
                          25* 
294
PHYSIOLOGY.
hol is an exception, as  it frequently, if not always,  passes
into the blood unchanged.
   8.  Various medicinal substances are  absorbed, and  enter
the circulation, nearly  or  wholly  unchanged.   Colouring
matter, such as madder, is  taken  up and  carried  into the
blood, and  even  tinges the  bones.   Oderiferous  particles,
such as of garlic,  camphor, asparagus, &c, are also readily
absorbed, and in this way the  blood derives  its saline proper-
ties.  It is  pretty well  established, that  articles not  of an
alimentary nature, which are  absorbed, are  chiefly taken up
by the veins, while  the  lacteals absorb  chyle  more readily
than any other substances.
   9.  Absorption  takes place  from the external surface or
skin.   This  is  proved  by  many  facts.   Thirst   may  be
quenched  by applying  moist cloths to the skin, or  by bath-
ing.  The body increases in weight by the  use of the  bath ;
and it has been found  that the hand, immersed to the wrist
in warm water, will  absorb from 90 to 100 grains of fluid
in the space  of one  hour.  The saliva has become  bitter by
the absorption of  sea  water ;  and it  is stated  that  patients
have been supported  by baths  of milk or  broth.
   10. Medicinal substances are often absorbed  by  the skin.
Mercury, Spanish  fly, morphine, and many other articles are
frequently introduced  into  the system  through  the  skin.
Metallic quicksilver  has  been  found in the bones of persons
who had been  subjected to  mecurial frictions ; and it  has
also been obtained by distilling the blood. of rabbits, dogs,
and cats, which had  been rubbed with this  mineral.  Gases
are also absorbed by the  skin.
  11. As  every part of  the body is subject to constant re-
novation and change, absorption  must be continually  goino-
on among the particles and substance  of which each or<mn
is  composed.   This  is called  interstitial absorption.   It is
this which counterbalances  the action of the nutrient ves-
sels, and preserves the form and size of every part of the
body.   When it is too active, the  body emaciates ;  when it 
                      ABSORPTION.                   295
is deficient, plethora  is the result.   In the later periods  of
life it is more active  than nutrition, and the body dwindles
in size ;  in youth the reverse is the case.
   12.  Foreign bodies, introduced into the substance of or-
gans, are also absorbed.   Wens an-d tumours of considera-
ble size, often  disappear  from  the same  cause.  Instances
are known where the absorbent vessels have set to work and
removed the whole bone  of a  limb ;  and  but  lately a case
occurred in Boston, in  which  every particle of bone in the
arm was  thus  taken up  and carried  away, after a fracture
had  occurred.    How  admirable is that  arrangement  by
which the vessels  of absorption and secretion so act as to
balance  each other; and how  soon  would a loss  of this
balance produce derangement, disease, and even death.
   13.  Another form of absorption  is called  respiratory,
which we have already considered under the subject of res-
piration.   We understand by it, merely the introduction  of
oxygen into  the  blood, through  the pulmonary cells.  Sub-
stances, however, in a state of vapour, or  fine dust, are also
readily imbibed when drawn into the lungs;  such as metal-
lic vapours, oderiferous particles, marsh and other effluvia.
It is in this way, probably,  that contagious  diseases are
caught.
   14.  It is by means of what  physiologists call recrementi-
tial  absorption, that  fluids are  removed  from the  system
which are secreted  upon surfaces that have no external out-
let ;  as in the cavity  of the  chest, abdomen, brain,  &c.
These fluids are various : such as the serous fluids ;  the sy-
novia of the joints ; the fat ; the marrow,  and the humours
of the eye.  It is this which prevents dropsies in these vari-
ous cavities ; and also removes  them when already existing.
This form of absorption is also  proved  by the fact, that fo-
reign substances, placed in contact with these surfaces, in a
short time disappear.
   15.  Another variety of absorption  has been called excre-
mentitial; as  it  relates to the fluids which  have been excreted. 
29G
PHYSIOLOGY.
These are liable to be absorbed; at least the more fluid parts
of them, by which they are again  carried into the  mass of
the circulating  fluids, and  such parts selected as are fit for
the uses of the animal economy, such is the case with  the
fluids  exhaled by  the skin ;  the mucous  membranes;  the
saliva ; the bile;  the gastric and pancreatic fluids ; the milk,
&c.  Thus,  has it been  remarked, does nature choose  to
subject the materials of decomposition to a careful revision,
before rejecting them finally from the body.
   16.  All these varieties of absorption are constantly going
on from the moment  of birth to that of dissolution, and all
the fluids which are absorbed, are changed  in their charac-
ter, and fitted to repair the  wastes of the system.   Thus,
by absorption in the lungs, oxygen is  converted into one of
the elements  of  the blood;  in  the  intestines, chyme  is
changed into  chyle;  in the tissues of the  organs, solid par-
tides are converted into fluid  lymph;  and from  the cavities
secreted and excreted fluids  are again  taken up and thrown
into the circulation, to be once more revised and elaborated.
  17.  Frogs,  and several other amphibious animals, are fur-
nished with large receptacles for  the lymph, situated imme-
diately  under  the  skin, which  exhibit distinct  and regular
pulsations like those of the heart.   The use of these lympha-
tic hearts is evidently to propel the lymph along the lympha-
tic vessels.  The  frog  has four  of these  organs; the  two
posterior being situated behind the joint of the hip ;  and the
two anterior ones on each  side of the third vertebra.  These
organs  have also been  discovered in the  toad, salamander,
and lizard.
  Questions.—What is meant by absorption ?  What composes the ab-
sorbent system ?  Where do the  lymphatic vessels arise ?  Describe
their structure.  Are they found in every part of the body ? What are
the agents of digestive absorption ?  Describe the  lacteals.  What is
chyle ?  Does it exist ready formed in  chyme ?  What changes does
it undergo in  its passage to the  heart ?  Where are  the chyliferoua 
ABSORPTION.
297
vessels chiefly found ? Arc alimentary substances absorbed without be-
ing previously changed into chyle ?   Is alcohol digested ?  Are medi-
cinal substances absorbed ?  How is this proved ? Does absorption take
place from the skin ?  What is interstitial absorption ?  What is ema.
ciation owing to ?—plethora ?  Are foreign  bodies  absorbed  when in-
troduced into the substance of organs ?   Are the bones ever absorbed ?
What is respiratory absorption ?  What  is recrementitial absorption ?
What excrementitial ?  Are these processes  always going on ?  What
peculiarity is there in the lymphatic  system  of frogs ? 
CHAPTER  XXIII.
                       NUTRITION.

  1. Nutrition may be  considered  as  the completion of
the  functions of digestion.  It is that process by which the
waste of the organs is repaired, and by which their develop-
ment  and growth are maintained.   Respiration, digestion,
circulation, absorption, and  secretion, are but separate links
in the  chain  of nutrition ; which would  be instantly de-
stroyed by the absence of any one of them.
  2. In  the construction of a machine, or an instrument,
designed to last for many  years, the mechanist  seeks for the
most durable materials.   In making a watch, for instance,
he forms the wheels of brass, the spring and  barrel-chain of
steel, and for the pivot, which is subject to incessant friction,
he employs the hardest of all materials—the diamond.   The
necessity for this arises from the fact, that such instruments
do  not contain, within themselves, the power of repairing
their own losses.
  3. But far different is the case with the animal machine.
In order to qualify it for  exercising the functions of life, it
mist be so constructed  as to render it capable of continual
alterations, displacements  and adjustments ;  and these sub-
ject to continual variation, according to the stage of growth,
and also to the  different  circumstances in  which it may be
placed.  Instead,  therefore, of a  few  elementary  bodies, or
their simpler combinations,  nature has employed such com-
pounds as admit  of greater change,  and  a more variable
proportion of ingredients, and greater diversity in the mode
of combination.   It is  nutrition that moulds  these  plustic
materials, and forms these  ever-changing  compounds ;  and
so  preserves the  animal machine,  amid   all  the var'ing
changes of condition to which it is subject. 
NUTRITION.
299
  4. No one  can doubt that the system is continually un-
dergoing changes.  This is proved by the losses to which it
is  subjected ;  by the necessity  of frequent supplies of ali-
ment ;  by the rapid wasting of flesh on  the withdrawal  of
food ; and by the emaciation caused by sickness and old age.
It  is also shewn by  an experiment, which has  often been
made,  viz. of giving madder to animals mixed with their
food;  which in a short time tinges their  bones of a red
colour.  If the madder be withdrawn, the red colour in a few
days disappears  from the  bones; evidently from the effects
of absorption.
  5. Every  part of the body  is subject to  this constant
change of matter.   While  one  set  of vessels, the  lympha-
tics, are taking  to  pieces  and  carrying away the various
parts  of which  the machine is composed, another set, viz.,
the capillaries, are constantly  at work,  repairing the loss,
depositing bone,  muscle, cartilage, nerve, tendon, fat, mem-
brane,  ligament, hair, nails, &c. where each is wanted, and
this with such regularity and order, as to preserve the shape,
size, and appearance of every organ, so that, though after an
interval of a  few years there may not remain in the body a
single  particle of  which, at the former  period, it was made
up ; still, the individual preserves the same form and features ;
his personal identity is never lost.
  6. Those  animals,  which are the most complicated  in
their structure, and are  distinguished by  the greatest variety
of vital manifestations, are subject to the most rapid changes
of matter.  Such animals require more frequent, and more
abundant supplies of food,  and in proportion as they are  ex-
posed  to  a greater number of external impressions,  so will
be  the rapidity in this change of matter.  The frog, for in-
stance, has been dug from the earth many feet below its sur-
face * and even taken from cavities in solid limestone, where
he had been shut up probably for centuries, and still exhibit-
ed sifns of life when exposed to the  open air.  As he was so
situated as to  lose nothing, by  secretion or evaporation, of 
300"
PHYSIOLOGY.
course he required nothing to supply any loss, but how the
vital principle was preserved  for such a length of lime, is a
mystery not easy to  be explained.
  7. The blood contains all the materials of nutrition.   The
process by which the food is changed into blood has been al-
ready explained.  As  it goes the round of circulation, the
nutrient capillary vessels select and secrete those parts which
are similar to the nature of the structure, and the other por-
tions pass on ; so that every tissue takes up and converts  to
its  own use  the very  principles  which  it  requires for its
growth ;  or in other words, as  the vital current  approaches
each organ, the particles appropriate to it,  feel its attractive
force ; obey it ;  quit the stream ; mingle with the substance
of its tissue, and are  changed into  its own true  and proper
nature.
  8. Before  the  body has attained its full growth, the func-
tion of nutrition  is  very active ; a  large amount of food is
taken, being not only sufficient to supply the place of what
is lost by the action of the  absorbents, but also to contribute
to the growth of the body.   In middle age, nutrition and ab-
sorption are more equal ; but in old age the  absorbents are
more active than the nutrient vessels ;  the size consequently
diminishes ; the parts grow weaker; the bones more brittle ;
the body bends forward ; and every  function exhibits marks
of decay and  dissolution.
  9. A few years ago, a man by the name of Calvin Edson,
of Vermont, commonly called the living skeleton, exhibited
himself through the country for money.  From having been
a large man, he had wasted away by degrees, so that instead
of  his usual weight, he weighed but sixty pounds.   He had
been gradually losing flesh for eighteen  years ; and he attri-
buted it  to having  taken  cold from sleeping on the ground.
This emaciation was  owing  to  the absorbent vessels being
more active  than  those of nutrition ; whatever may have
been the cause of the loss of balance. 
                       NUTRITION.                  301
  10. On the other hand, when the nutrient vessels are the
most active, the person  grows fleshy and corpulent, as in the
case of Daniel  Lambert, who weighed  seven hundred and
thirty-nine pounds at the age of forty ; or in that of a Lon-
don butcher,  who weighed eight hundred pounds.  There are
several cases on record, where men weighed eight  hundred
pounds.
  11. The degree of nutrition, depends much on the quanti-
ty and quality  of the food.  A person who confines himself
chiefly to animal diet, and drinks freely of ale and other malt
liquors, will  usually  grow  fat;  but  this does not indicate
strength  but  weakness.   It shows  that  there is not only a
weakness of the absorbents, which are not ab'e to take up
and remove the fat; but also a muscular debility, and a want
of force in the circulation.   Motion is impeded ;  the heart
is loaded and  oppressed; the breathing is laborious ; the
blood accumulates in the  brain, and the person is every mo-
ment exposed to apoplexy.  In all such  cases,  a sparing diet
of vegetables,  with  proper  exercise, will  prove an  effectual
remedy.  Bv sweating, horse-riding, and a  low diet, jockeys
have not  unfrequenlly reduced themselves 15 or 20 pounds,
in a week or ten days.
   12.  Large accumulations of fat, it is  said, sometimes take
place, as the sudden effect of the influence of the atmosphere.
Thus, in the short space of twenty-four hours, it is stated by
writers on natural history, that a  mist will occasionally fatten
thrushes, robins, &c, to such a degree, than they can hard.
ly get out of the way of the sportsman's gun.  This however
is not fat, but the appearance is owing to a fulness of the
vessels, from a suspension of evaporation.
   13.  The hump of  the camel appears to form a sort of re-
serve,  by  which, the Arabs say, he is nourished, during his
lono- journeys.   In a period of plenty, the rapid secretion of
fat converts  it  into a pyramid, equalling a fourth of the ani-
mal's entire bulk ;  but  a journey  through the desert gradual.
Jy lowers it,  so that it becomes scarcely visible.  Tie camel
                            26 
    1
302                 PHYSIOLOGY.

then gives out, and can travel no further  till the store is re-
plenished by rest and food.*
   14.  Tumours, wens, and other morbid growths are the con-
sequence of an error in nutrition.   The nutritious vessels de-
oosite fat where it is not wanted, and occasionally bony mat-
ter, where fibrin should be left or  something else.  In this
way  only can we  account  for the bony concretions and
scales  which are sometimes  met with about the heart and
blood-vessels ;  for the chalky deposits about the joints,  in
cases of gout and rheumatism, and  even for horny projec-
tions, which  have in a few cases been known to sprout out
from  the head.  A few years ago, there were exhibited in
London, several individuals called the porcupine family, who
were all covered with dark colored horny excrescences; which
they shed annually  in the autumn or winter.  These curious
organic peculiarities, resembled  the quills of the porcupine,
and were  two or three inches in length.  But these are only
exceptions to the usual regularity of nature's operations, and
ought, instead of lessening, to increase our admiration at the
admirable symmetry and uniformity  that prevail, through
every department of organized being.
   15.  The activity of muscular nutrition, depends much on
exercise.  The arm of  a blacksmith,  or a stone-cutter, for
instance, is generally large and brawny, because  their  mus-
cles are almost in  constant  use.  The same is true of the
muscles of the  leg, in  rope-dancers and tumblers, also  in
great walkers.  Let any one examine the muscles of the Ra-
vel Family, so celebrated for strength and agility  in all gym-
nastic  exercises, and he will find them not only unusually de-
veloped, but also hard and firm.  If  a  person meet with an
accident so that he  is unable to walk, although his appetite
remains, his muscles dwindle  away for want of exercise.   If
then,  a person who leads a sedentary life be corpulent, the
excess  is not to be considered sound  muscle or flesh, but fat,
which, I have before stated, is a sign of weakness.
* Burkhardt's travels. 
                           NUTRITION.                     303

  Question,.—Wliil is nutrition ?  What is sought for in constructing
a machine ?  Why the necessity for this ?  How  is it in  the animal
machine ?  Is the system constantly  undergoing changes ?   How is
this shown ?  What vessels repair the losses of the system ? What ani.
mals are subject to the most rapid changes of matter ?  What contains
the materials of nutrition ?  When is  nutrition most  active ?—when
least so ?   What is the consequence ?  What does the degree of  nutri-
tion depend on ?  Does fatness indicate strength ?  Why not ?   What
use docs the  hump of the camel serve ?  What are tumours and wens
owing  to ?  What causes muscular nutrition ? 
CHAPTER  XXIV.
                     ANIMAL HEAT.

  1. Calorification,  is a function of  animal bodies, not yet
thoroughly understood.   We see certain phenomena, but the
causes are hidden from our view.  It is very doubtful wheth-
er  we shall  ever be able  to  penetrate the veil which con-
ceals the wonderful operations of vital chemistry ;  and per-
haps it would lead to no useful  result if  we could ; should
we  ever  attain to the knowledge of  all the natural laws of
life, we shall then be assured that it is only in consequence
of  their violation that man pays, by suffering, sickness  and
premature death,  the penalty of their transgression.
  2. What causes the temperature  of the body to be main-
tained  at an average of ninety-eight degrees, and this, too,
under all climates,  and at  all seasons ?  In the first place,
respiration  is much  concerned  in  the production of animal
heat.   It  was once  indeed  believed, that  the chief office of
respiration was to cool the blood; and that the heart was the
great furnace of the system, where all  the heat was pro-
duced.
  3. When it was discovered that both in combustion and
respiration, carbonic acid  was produced, and  oxygen  ab-
sorbed, it was at once surmised, that breathing must be a kind
of  combustion by which all  the hea«t of the body  is generat-
ed.  But it was objected to this, that  if the heat was all pro.
duced in the lungs,  why were  not the lungs hotter than the
other parts of the body, as those parts of a stove in contact
with the fuel,  are hotter than those at a distance.
   4.  This objection to Mr. Black's  hypothesis,  led Mr.
Crawford to  propose the following solution.  Although ani-
mal heat is produced in the  lungs by  the" process  of respira-
tion, yet as arterial  blood has a greater capacity for caloric 
                     ANIMAL  HEAT.                  305
than venous, that is, requires more calorit to preserve  it at
the same temperature,  the heat becomes latent in saturating
this increased capacity of arterial blood ; and  is gradually
given off in every part of the body, as the blood assumes the
venous character.   But unfortunately for this theory, it has
been ascertained that there is no difference, and that arterial
and venous blood have an equal capacity for heat.
   5. But however it  may  be explained, no  one can doubt,
that calorification is closely connected Vith respiration.  If
the latter is increased by any cause, the heat of the body is
also increased.  When it is impeded, as in asthma, fainting,
breathing deleterious gases, and suffocation,  the animal heat
is sensibly diminished. Those animals whose respiratory ap-
paratus is the most perfect and the best developed, have the
highest temperature, as we see in birds, whose bodies are sev-
eral degrees warmer than the human species.
   6. On the  contrary, if we  look at the cold-blooded ani-
mals, we shall find that a large proportion of them  live in
water, where  the  supply  of oxygen is  but scanty, and that
their respiration  is  very imperfect;  while in animals  that
lie torpid during  the winter, and are quite cold, respiration
is almost if  not quite suspended.  According to Majendie,
respiration  produces  four-fifths of the heat in  herbivorous
animals;  three-fourths in  carniverous, and the same  in
birds.
   7. It is found by experiment, that arterial blood is warmer
than venous.  The blood is found to acquire one degree of
heat in passing through the lungs, and as the  whole mass
of the  blood passes through  the lungs twenty times an hour,
it follows, that the system receives from respiration twenty
deo-rees of heat in  an hour, or two hundred and forty degrees
every twelve hours.   Respiration, then, is one of the chief
sources of animal  heat.
   8. Another theory in  relation  to animal heat  is, that it is
produced bv, or depends on,  nervous influence.   This is
26* 
306
PHYSIOLOGY.
supported by a few experiments of Mr. Brodie, who kept up
artificial respiration in animals after cutting off their heads.
He found  that, notwithstanding, the usual  changes  took
place  in the blood, and in the air introduced  into the lungs,
yet the  temperature fell even faster  than in another animal
killed at the same time, in which respiration  was not  kept
up.  This experiment, however, is not conclusive, as  an ani-
mal may be cooled by forcing too much air into the lungs;
and if less be introduced the heat may be preserved for some
time.
   9. Another theory is,  that  animal heat is generated in
the capillary system.   This is supported by  the fact, that
some parts of the body are often hotter  than others, as in
inflammation ; that it is always proportioned  to the ener-
getic  action of any organ, as  the head  becomes hotter  by
hard study ; and a glass of spirits excites a feeling of warmth
in the stomach.
   10. It may be laid down as  an axiom, or admitted truth,
that all  movements  among the  particles  of  bodies which
cause a change of state, are attended with change of tem-
perature.   This  is  the  case  in  combustion, which  is a
union of oxygen  with  the  inflammable  body, and  the
production of carbonic acid ; and so also when two liquids
are mixed together, which chemically unite, heat is  always
evolved.   Now, in all  the processes  of nutrition, secretion,
digestion, respiration,  &c, such  changes  are constantly
going on.  In respiration, a part  of  the blood is thrown off
in a gaseous form, while  a quantity of oxygen unites  with
the remaining portion.  This  process, according  to  all the
known laws of caloric, must  be attended with an  elevation
of temperature.   And this proves to be the fact.
   11. By the function of nutrition, fluids are changed into
solids ; and  by absorption, solids are changed into fluids;  by
secretion, new chemical compounds are formed out of a  few
simple elements contained in the blood; and by digestion, a 
ANIMAL HEAT.
307
new fluid, chyle, is formed out of the solids, which constitute
the food.  By all these processes, animal heat must necessa-
rily be generated.
   12.  But in order to the production of animal heat, by the
action of the capillary vessels, two conditions are necessary.
One is, the presence  of arterial blood ;  the other, the action
of the nervous system.   That arterial blood is necessary, is
shown by the operation of tying the vessels which supply a
limb with blood.   The consequence always is, that the tem-
perature immediately falls, and  such limbs have to be wrap-
ped in cotton, and other means  used to preserve a comforta-
ble  degree  of warmth.    That nervous influence  is also
productive of animal heat,  is  shown by dividing, in like
manner, the nerves which go  to any part. The temperature
of a  paralytic limb is always lower than that of the sound
one.
   13. It may  be  concluded  then, that  respiration, circula-
tion, and  nervous influence, all  co-operate  in  producing
animal heat, or that they are  conditions essential to this
phenomenon.   We here also perceive a circle of actions ;
or a chain, composed of many  links, no  one  of which can
be  spared.   Each one contributes to a result essential  to
organic existence, and one of the most curious and wonder-
ful which the mind can contemplate.
   14. If these principles  be correct, we should expect  to
find  the greatest  heat in  those animals  whose  structure  is
the most complex; whose organic  or  vital actions  are  the
most intense; and  whose changes are the most rapid.  Now
all these conditions belong to the warm-blooded animals es-
pecially, and  particularly   to birds,  whose  temperature
exceeds, by  several  degrees, that of man.   In them, as  I
have already stated,  respiration is more  perfect, and the cir-
culation more rapid.
   15.  Upon the same  principles, it  would also follow, that
animal heat would be the  highest  in those portions of the
body where the organic  actions are most active.  And such 
308
PHYSIOLOGY.
is actually the case.   If a thermometer be placed over the
chest, the stomach,  or  the  liver, it  will indicate a higher
temperature by some degrees than exists in the extremities,
because it is near the seat of respiration, digestion, and the
largest secretory organ  in the  body.   The temperature  of
different parts of the animal body ranges  from  91 to 100
degrees ; and in fever to 112, which  is marked "fever heat"
on the thermometer.
  16. Those animals that  belong to  the  class mammalia,
and which live  in water, such as the whale, the  dolphin, and
the porpoise, have a temperature as high as that  of  man.
Captain Scoresby found  the temperature of a whale, in the
Arctic Ocean, to be  104 degrees ; whjle  that  of the  polar
bear and wolf were no greater.  Warm-blooded animals are
generally  covered with  hair or feathers,  to protect  them
from the cold ;  cold-blooded  animals  need  no protection, as
they can live in a temperature  as low as the freezing  point
of water.  Seals, bears and walruses  in the Northern Ocean,
are protected by a coating of hair ;  the whale is protected
by the great thickness of its skin and the stratum of fat im-
mediately beneath it. Dr. Edwards  states that frogs, which
can live in  water at 32 degrees, will die in a short time in
water at 105 degrees.
   17.  But this does not seem to be  the  case  in  all  cold-
blooded animals.   In some  of  the warm  springs in Brazil,
which  have  a temperature of 88,  many small fishes are
found;  and also in a  hot  spring at  the Manillas, which
raises  the  thermometer to  158 degrees;  and Humboldt, in
his travels, tells us  that in the  province of Quito, in South
America, he saw fishes thrown  up from the bottom of a vol-
cano, along with water  and  heated vapour, which raised  the
thermometer to 210, or only two degrees short of the boiling
point.   Lord Bute saw  beetles in the boiling springs of  Al-
bano, which died when plunged  into cold water;  and Dr.
Elliotson states that a gentleman of  his acquaintance boiled
some honeycomb two years old, and after extracting all  tlio 
ANIMAL HEAT.
309
honey, threw the refuse into a stable, which was  soon filled
with bees.
  18.  Warm-blooded animals have the faculty of preserv.
ing the same degree of heat in  nearly every variety of cli-
mate.   During  Captain Parry's voyage to the Arctic seas,
in quest of the northwest passage, the crews of his vessels
were  often  exposed  to a temperature  of fifty degrees below
zero, or one hundred and  fifty degrees below  that of their
own bodies, and still they were  able to resist it, and escape
being  frost bitten.  When the  temperature was  thirty-two
degrees  below  zero, they found that of an Arctic fox  one
hundred and six degrees, which  shows what a strong coun-
teracting energy there is in  animals, against  the effects of
cold.
   19.  The human body can also resist great heat as well as
cold.   In summer we are often exposed, when in  the sun, to
a temperature many degrees above that of the body, but the
heat  of the  body is not  elevated.   Chantry,  the sculptor,
often entered his furnace when heated for  drying his moulds,
when  the  thermometer in it stood  at three  hundred  and
twenty ; and his workmen did the same when the tempera-
ture  was  three hundred  and  forty degrees.   Dunglison
states that Chabert entered an oven  with  impunity, the
heat of  which  was  from four hundred to six hundred de-
grees.   In all these  cases, where even water was  boiled, and
meat cooked to  a crisp, the heat of the body was  raised but
a few degrees.
   20. In these  cases the heat of the  body is kept down to
near  the natural standard, by exhalation, or sweating.  This
carries off the heat  in a state of vapour as fast as it is  pro-
duced.  For the same reason, water cannot be heated above
two hundred and twelve degrees, as  it then escapes in the
form  of vapour.  By evaporation, also, bottles of wine are
cooled  in  summer, by wrapping them round   with  wet
cloths.  In India, it is said, that ice is produced in  a simi.
 lar manner.  If an animal be saturated  with  moisture, and 
310
PHYSIOLOGY.
placed in a  hot  oven, it  soon dies, because the  exhalation,
from the body is prevented.   It is for this reason, also, that
we feel the heat more in damp weather than in dry, although
the temperature  be  lower.   Such weather is called  sultry,
close,  muggy,  Sec,  because  the  saturation of  the  air by
moisture, prevents the  escape of heat by evaporation from
our  bodies.
   21. In infancy, the faculty of generating animal  heat is
much less than in adult age.   This is the chief cause why
so many perish during the first years of life, and particular.
ly in winter, during  the first  few days.    At this period, the
temperature  of infants  is only about  ninety-three degrees,
and  in some  instances not more than eighty, and is  rapidly
diminished by  slight exposures.  This shows the great  im-
portance  of  guarding against the effect  of cold, by proper
clothing,  and  a  regulated temperature  of houses.   Man
has no natural protection against the influence of cold,  but
reason  was given  him as a  substitute.   How few appear
to employ this  faculty,  in  guarding  against  atmospheric
vicissitudes  by a  proper adaptation  of  the  dress;  and  in
consequence, how  many,  instead of consulting their health,
comfort, and  usefulness, fall victims to negligence or fashion !
  Questions.—What is calorification ?  What are the causes of animal
heat ?  Why was it surmised that respiration was  concerned in this
process ?  What objections to this ? What was Crawford's hypothesis ?
What occurs when respiration  is impeded ?  What  occurs in cold-
blooded animals ?  How much heat, according to Magendie, is produced
by respiration in  herbiverous animals ?—in carniverous ?—in birds ?
Is arterial blood warmer than venous ? How much heat does the blood
acquire in passing through the lungs?  How many degrees does the
system acquire from this source  in 24 hours ?  What is Brodie's theory
with respect to animal heat ?  What facts  in favour of it ?  What  is
said of animal heat being generated in the capillary system ?  What
axiom in relation to a change in the  particles of bodies  has a bearing
on this subject ?  What conditions are necessary to the production of
animal heat by the action of the capillaries ?   How is this proved 7 
ANIMAL  HEAT-
311
What functions co-operate in the production of animal heat ?  In what
animals is heat the greatest ?  Why ?  In what parts of the body is it
the highest ?  Why ?  What is the temperature of the mammalia that
live in water ?  What effect does a change of temperature  have  on
cold-blooded animals ?   Can warm-blooded animals preserve the same
temperature in every climate ?  How  is this effected ?  What effect
will checking evaporation  have ?  Is  the faculty of generating heat
less in infancy ?   What inference  do we draw from this fact ? 
CHAPTER XXV.
                       THE VOICE.

  1. The voice is a sound produced in the larynx, or wind-
pipe, by the passage of air, either to or from the lungs.  It
is generally caused in the act of  respiration, and its seat is
the  larynx, which forms the  very top of the wind-pipe, and
externally  makes that prominence at the  fore-part of the
neck, called Adam's apple.   It is connected  above with the
bone of the throat, by means of small muscles, and behind
with the esophagus, or passage to  the stomach.
  2. The larynx is composed of four cartilages, closely con-
nected by membranes;  these are  called the thyroid, the cri-
coid, and the two arytenoid cartilages.  The thyroid cartilage
is shaped somewhat  like  a shield,  and hence its name.  It
forms the front and lateral part of the larynx, being broader
in front than behind, and  made up  of two parts which join
in the front of  the neck at an  acute angle, thus making the
prominence spoken of above.   It  has two projections above,
and two below; the former  connect it with  the bone of the
tongue, and are called the  upper  horns ;  by  the latter which
are called the lower horns, it  is  united with the cricoid carti-
lage, by means of ligaments.
  3.  The  cricoid cartilage is so called from  its resemblance
to a ring.   It  lies immediately below the thyroid cartilage,
being broad at  its sides, narrow in front, and connected with
the thyroid cartilage behind by a still broader surface.  In
front it is not connected with the thyroid cartilage;  but the
space is occupied by the lining membrane of the  larynx,
covered with the common integuments.
  4.  The arytenoid cartilages are much smaller than  the oth-
ers, and are situated at*the back  part of the larynx, in con-
nection with  the cricoid  cartilage.  They  have small mus. 
                       THE VOICE.                   313
cles attached to them, by which they are moved sideways,
and it is by these  motions  that the opening in the larynx,
called the  glottis,  is enlarged or contracted.   Two  fibrous
ligaments connect  these  cartilages with the thyroid ; these
two  are called vocal  chords, as  they are supposed  to  be
particularly concerned in the  production of voice.   They
pass from the artenoid cartilages to the angle formed  by the
two side pieces of the thyroid, and are about half an inch in
length.   The opening between them is called glottis, rima-
gloltidis, or chink of the glottis.
   5. The  epiglottis is  the little moveable cartilage ; which
lies over the top of the wind-pipe, at  the root  of the tongue,
and has been compared to a trap-door  It prevents the food
from passing  into the wind-pipe  when we swallow.   From
its elasticity, its position  is usually perpendicular, except in
the very act of swallowing, when the tongue is carried back-
wards, so as to bring it exactly over  the opening ; this pre-
vents the passage of foreign bodies into the lungs.
   6. The  larynx  is  abundantly supplied with nerves which
are given off from the eighth pair.   The thyroid gland is a
body  consisting of  two  lobes, lying one on each  side, and
somewhat below the larynx ; the use of which is unknown;
it  is the seat of the  disease called goitre, or swelled neck, so
common in Switzerland, and some other countries.
   7. Such is the description of the organs immediately con-
cerned  in  the  voice ; the whole  vocal apparatus, however,
comprises  the  muscles  concerned in breathing, the  mouth,
and nasal cavities, as well as the parts above mentioned.  It
is  essential to  the  production of voice that the  air should
pass from  the lungs through the larynx ; for if an opening
be made in the wind-pipe, so that the air escapes, the voice
is  lost.   I  lately witnessed this in a  man who undertook to
destroy  his life by cutting his throat.  He succeeded in cut-
tin"- the wind-pipe completely off,  but as no large  blood ves-
sels were divided, he got  well.  This man could not utter a
                         27 
314
PHYSIOLOGY.
 syllable, not even  in  a whisper, until the wind-pipe healed
 up ; his voice was then restored to its former condition.
   8. Volition is  necessary to the production of vcice.   If
 the  nerves  going to the larynx are cut, the voice will be
 lost.   Palsy of the muscles of the larynx, also causes dumb-
 ness ;  and  fear effects the voice by  paralyzing muscular ef-
 fort.   The  epiglottis is found not to be concerned in the pro-
 duction of the voice, as it may be removed without affecting
 it; its sole office  being to guard the wind-pipe against the in-
 traduction of foreign substances.
   9.  It has been proved by experiments, that  nearly all the
 larynx  except the chorda vocales, or vocal chords, may be
 removed without  destroying the voice.   These are the small
 ligaments that pass from the arytenoid cartilages to the thy.
 roid cartilages, and are usually  called the inferior ligaments,
 or the lower vocal chords.
   10.  It  is  now ascertained that these  chords perform  the
 principal part in  the production of the voice.   In what way
 this  is done, is not  precisely known  ; but, we may suppose
 that the air in passing from the lungs in expiration, is forced
 out of small cavities, as  the air-cells and minute branches of
 the  wind-pipe, into the main channel; it it is thence sent
 through a narrow passage, on each side of which is a vibra-
 tory chord ; the vibrations of which, by the action of the air
 produces voice or sound.
   11.  It has been said that if this theory of the voice be cor-
 rect, there ought to be sound produced by forcing air through
 the wind-pipe of a dead animal.  But this takes for granted
what is  not true, namely, that the  voice is the result of a
purely mechanical  process ; instead  of  which, it is a vital
function,  performed  by  living  agents, and therefore  under
the control of voluntary action.
   12. In producing sound, there can be no doubt that nume-
rous voluntary muscles are put in action, bringing the ary-
tenoid cartilages  in  contact with  each other,  thus putting
upon the stretch the  lower vocal chords  which are attached 
                      THE VOICE.                   315
 to  them.   It  is  therefore  by no means  strange that vocal
 sound cannot  be  made by forcing air through the larynx of
 a dead animal.
   13. It has often been disputed whether  the  larynx was a
 wind or stringed  instrument.  Most physiologists at the pre-
 sent time,  regard it as a wind instrument of the reed kind,
 such  as  the clarionet, hautboy, &c, and they differ chiefly
 in explaining the various modifications of the tone and qua-
 lity of the voice.  There is, however, great reason to believe
 that it partakes of the character of both.
   14. The strength of the voice depends on the extent of the
 vibrations, of course on  the size of the larynx, and partly
 also on the force with which the air is sent from the lungs.
 Thus the voice of men is much stronger than that of wo-
 men and  children ; and  that of a well person stronger than
 that of a feeble individual.  The change of voice at the pe.
 riod of manhood, is owing  to the increase in size of the la-
 rynx.
   15. The tone of the voice can be almost infinitely varied :
 indeed, nothing can exceed the human organ of voice in va-
 riety  and execution.   We may perhaps safely  calculate the
 number of changes  that can be 'produced in the organ, at
 least to be equal to the number of muscles employed, togeth-
 er  with  all the combinations of which they  are capable.
 Now, the muscles immediately concerned in the function of
 voice are seven pair.  Besides these, however, there are fif-
teen other pair, which are  connected with the larynx, and
 have more or less to do in regulating the motions of the car-
 tilages, keeping them steady or moving them in different di-
rections.
  16. Now, if there were only  seven pair of muscles con-
cerned, the  different  movements which their varied action
would produce, will  amount to more than sixteen thousand.
Takin<>-  the whole number of muscles into account, the dif-
ferent combinations  will be more than one thousand million.
But besides these, there are the midriff, or diaphragm, the ab- 
316
PHYSIOLOGY.
dominal, and the intercostal muscles, all of which are con-
cerned  in  the  production of voice !   " How  wonderful is
man !   How passing wonder, He that made him such !"
   17. The precise manner in which such  an infinite varie-
ty of tones is produced, is unknown ; physiologists explain-
ing the matter according to their respective theories, wheth-
er  the  larynx  be  a wind or  stringed instrument.  The
glottis doubtless contracts  for  the  production  of  acute or
sharp tones ; but how grave ones  are  produced,  admits of
doubt, whether  it be owing to a  lengthening of the trachea,
or the relaxation of the  vocal chords.  Perhaps it  would be
near the truth to  say,  that both these circumstances take
place, but that  the grave notes  are chiefly caused by  the
latter.
   18. Ventriloquism consists in making the voice appear to
proceed from other  persons in various places, either in or out
of the room. To do this with success the performer first di-
rects the attention of the audience to the place from whence
he  wishes to  have his  voice appear  to proceed ; he then
changes his voice in such  a  manner as makes it sound like
that of another person, or the noise  of the animal he designs
to imitate, and in doing  so, avoids all the words which have
labials, or which require the use of the lips.  This modifica-
tion of  voice is supposed to be  performed by the muscles of
the larynx, and this is known to be  the sole organ  of  all  the
natural  cries.
   19. There are generally considered to be  two kinds of
voice, the natural and acquired.   The former is possessed in
common with man,  by the inferior animals, but the latter is
enjoyed  by  man alone to any extent.  The natural voice
consists  in mere cries,  and  is  possessed  by the  infant as
soon as  it  is born, and also  by idiots, and  by those who
are born dumb.  It is  seated  entirely in the larynx,  and
does not depend on  intellect, or  hearing.
  20. The acquired voice, on  the contrary, is  the result ol
imitation, and enables us to express our ideas  in  words oi 
THE VOICE.
317
articulate  sounds.   In this way the child learns to imitate
the sounds  which  he hears, and if he is deaf, of course he
will never  learn to  speak :  children therefore  are  dumb,
because they are deaf.   Idiots also are dumb, although they
can hear;  intellectual faculties, therefore, are necessary  to
speech  as  well  as  hearing; and it is probably owing to a
want of intellect that infants do not speak at an  earlier
age.  For  the  same reason, the ourang outang  cannot ac-
quire the  faculty  of speech.   In  the acquired  voice, the
tongue  and lips are brought into exercise, but neither of
them can  be regarded as absolutely essential to the faculty
of speech.
   21.  Whistling is  caused by  the expired air being broken
or  divided  by  the lips, which act  the part of the glottis  in
the production  of  the voice.   Wliispering consists  in the
articulation of the  air  of expiration, and  is  wholly per-
formed  in the  vocal tube; hence the impossibility of sing-
ing in  a whisper—singing being produced  in the  glottis.
Sighing is produced by the rushing of the air along the air
passages;  and the  voice is also concerned in laughing, cry-
ing, coughing,  sneezing,  yawning, and sobbing, modified  by
the mode of respiration.
   22. Singing  is a very  useful  art, and ought to be learned
by every person.   It not only contributes to our intellectual
gratification, but  is also  of  essential benefit  to the bodily
health.   For these reasons, and because it  conduces to be-
get an habitual  cheerfulness of mind, it ought to be  taught
in all schools  and academies, and  made a part of  the daily
exercises,  as it is in Germany,  and  in  our own  infant
schools.
  Questions. —What is voice ?  Where is its seat ?  What is the la-
rynx composed of?  What is the shape of the thyroid cartilage ? De-
scribe its structure ?  The cricoid ?—its structure and situation ?  De-
scribe the arytenoid cartilages? What is the glottis?—the epiglottis?
What is the thyroid gland ?—its use ?—the  seat of what  disease ?
                            27- 
318
PHYSIOLOGY.
What does the whole vocal apparatus comprise ?  What is essential
to the production of voice ?  What effect has cutting the nerves which
go to the larynx ?  What part  of the larynx can be removed without
effecting the voice ?  What are chiefly concerned in the production of
voice ?  Is the larynx a wind or stringed instrument ?  What docs the
strength of the voice depend on ?   What is a change of voice owing
to ? What is said of the tone of the voice ?  How many muscles are con-
cerned ? How many combinations can they produce ?  How are acute
sounds produced ?   How grave ones ?  What is ventriloquism ?  What
is natural voice ?  What acquired ?   Why are deaf children dumb ?
Why are idiots ?  What  is whistling ?—whispering ?—sighing, &c?
What is said of singing ? 
CHAPTER XXVI.
              LOCOMOTION AND ITS ORGANS.

   1.  Man is distinguished from  the vegetable  world, not
only  by his  possessing a nervous system, organs of sense,
and voice, but also by the  power of locomotion, or moving
from  place to place.   This power connects him with the
external world, enlarges his sphere  of action and increases
his means of acquiring knowledge.   It implies that he has
a will, and that these  motive organs are under the influence
of volition; else he would be the sport of chance and  wan-
der about without a motive.
   2.  Many of the functions of the body are not under the
control of the will ; such are  digestion, absorption, circula-
tion, respiration,  and  secretion, which go on as  well when
we are asleep as when awake.    They are  possessed, at least
some  of them, by vegetables  as well as animals, and are
therefore called organic functions.
   3.  The agents of locomotion are the bones and muscles;
but they would be useless for motion were they not supplied
with  nerves of voluntary motion, and thus brought  under
the influence of the  will.   The bones are tied together by
means of strong  fibrous ligaments or  cords, allowing the
joints great freedom and extent of motion, as we see in the
shoulder and  hip joints.
  4.  We then have  the  bones, which act as levers ; the
muscles  are the  moving  power, and  the  brain and nerves
are the vital  agents,  which set the  machinery in motion.
Muscles alone have the power  of contraction, and it is  one
of the most remarkable properties of, life.  Were it not for
this, the food could not be digested, the  blood could not  be 
320
PHYSIOLOGY.
circulated, and the iris could not  guard the eye against the
admission of too much  light, which would speedily destroy
the vision.
   5. The shape of muscles is various, some are round, some
flat, and the fibres of which they  are composed, are con-
nected by  means  of cellular membrane.  Some  are penni-
form, or made of bundles of fibres, diverging  from a central
line, like  the feathers of a  quill.   Muscles compose a  large
part of  the bulk of the body ; and when  they  contract, the
fibres shorten and become harder, as may easily be perceived
by placing one hand on the middle  of  the arm  and bending
the elbow, or  on  the temple and' closing firmly the  lower
jaw.
   6. The force  with which a muscle contracts, depends  on
the physical condition  of the muscle and the energy of the
brain.   When the fibres  of the  muscle are large  and firm,
they will contract with more force than when  they are  small,
soft, and delicate.  We see some  persons, who labour under
great  mental  excitement,  perform  astonishing  feats  of
strength, although, perhaps, they  may not have muscles  of
the ordinary size.
   7. The knee-pan has often been split in two by the con-
traction of the muscles of the leg; a horse has been known
to break its under jaw by biting a piece of iron.  Men have
been known to lift eight  and  nine hundred pounds  weight;
to break ropes two inches in  circumference, and  to bend a
round piece of iron, a yard  long, and three inches  in circum-
ference, to a right angle, by striking it across the left arm,
between the shoulder and the  wrist, with  the right hand.*
   8. The force of muscular contraction is greatly increased
by exercise.  The strength of an active man  labouring to
the greatest possible advantage, is estimated  to  be sufficient
to raise  ten  pounds, ten feet in a  second, for ten  hours in a
day ;  or to raise one hundred pounds, one foot  in a second,
* See Dunglison's Physiology. 
LOCOMOTION AND. ITS ORGANS.         321
or thirty-six  thousand feet in a day ;  or three  millions, six
hundred thousand pounds, or four hundred and thirty-two
thousand gallons, one foot  in a day.   The  weakest men in
health can generally lift about one hundred and twenty-five
pounds, and  the strongest of ordinary men four hundred
pounds.  The daily work of a horse is equal  to that of five
or six men.
   9. There is much  difference in the  velocity of muscular
contraction,  as  it is regulated entirely by the will.  The
swiftest race-horse on record was capable of going a  mile in
a minute; yet this is trifling compared  with the velocity of
birds, or even of many small  insects.  It  has been ascer-
tained  that a pigeon-hawk can fly one hundred miles in  an
hour ; the eider-duck ninety miles an hour, and the common
crow, twenty-five miles an hour.   The swallow flies ninety-
two miles an  hour, and the swift  is said to fly two hundred
and fifty miles in the same space  of time.
   10. A falcon belonging to Henry IV. of France, escaped
from Fontainbleau, and  in twenty-four hours  after  was in
Malta, a distance of one  thousand three hundred and fifty
miles, making a velocity of fifty-seven miles an  hour, sup-
posing him to have been on the  wing all the time ;  but as
such birds do not fly by night, his flight was probably at the
rate of seventy-five miles per hour.  This will give us some
idea of the  wonderful velocity  of the  contractions of the
muscles of  the wings of  birds of  rapid flight.
   11. But  this rapidity of motion is much under the influ-
ence of habit.    How awkward  are  the first attempts at
writing, drawing, dancing, or  playing on musical  instru-
ments, and with what ease and  grace are they  performed
after a little  practice.  The  same  is  true with  regard to
public speaking, or any thing which  requires voluntary  mo
tion.
   12. It is a law of the human system, that relaxation must
follow contraction,—or rest, exercise;  and although  the du-
ration  of action of the voluntary muscles  is in a  great de- 
322
PHYSIOLOGY.
gree under the control of the will, yet it cannot be continued
long.  This duration will  be shorter  in proportion as the
contraction is violent or moderate.  All muscles do not act
at the same time, for as some are contracting, such as the
flexors, or those that bend  the  limbs, the extensors, or those
that straighten them, are relaxed.
   13. It is  by the constant action of the muscles, that the
body is kept in an erect position.  If a person gets asleep
while sitting or standing up, the  head falls forwards, and if
he did not  wake, the  body would fall likewise.  The same
happens when a person is deprived of sense,  by a  fit of
apoplexy  or palsy,  or  by the intemperate  use  of ardent
spirits.
   J4.  We see that  it  requires a long time  for children to
learn to walk securely.   The reason is, that the base of sup-
port for  the  body is small;  being only the  space between
the feet and that on which the feet rest.   The larger the
base, the easier it is to maintain  an erect position ;  so that
persons with small feet  do  not  stand as firmly as those  with
large ones.   This accounts for the difficulty  of standing  on
our toes, or  of walking  on a rope.  It is practice  and in-
stinct  which teaches children  where to place their feet in
order to be most  secure when erect; their muscles also are
still weak, for want of exercise.
   15.  Walking consists in a succession  of steps.   We first
balance the  body on one foot, then bending the opposite foot
on the leg, and the  leg  on  the  thigh, we bend the thiah on
the pelvis, and so shorten  the limb.   In this  way the  leg is
brought forward,  and the foot is then brought to  the ground
resting first on the  heel; the body is then partially rotated
on the head  of the  thigh  bone, and the other leg is raised,
bent, and  carried forward  in the  same manner, and  the foot
placed in advance of the other.   The legs thus act as levers
to propel the body along, and the longer the levers the more
rapid will space be measured over.
  16.  The utility of walking excels that  of all other modes 
LOCOMOTION AND ITS  ORGANS.          323
of progression.   While  the  able  pedestrian is independent
of stage coaches and hired horses, he alone fully enjoys the
scenes through which he passes, and is free to dispose of his
time as he pleases.  To counteract these advantages, greater
fatigue is doubtless attendant on  walking; but this fatigue
is really the result of previous inactivity; for daily exercise,
gradually  increased by rendering walking more easy  and
agreeable,  and inducing  its more frequent  practice,  dimi-
nishes fatigue  in such a degree,  that very great distances
may be accomplished with pleasure, instead of painful exer-
tion.
   17.  The power of walking  great distances, without  fa-
tigue  is unfortunately in this country a rare accomplish-
ment.  A good  walker will do six miles an hour, for one hour,
on a good road.  If in  good  training,  he  may do  twelve
miles in two  hours.  Eighteen miles in three hours  have
been achieved, though rarely.   At the rate of five miles an
hour,  pedestrians of the  first  class  will do  forty miles in
eight  hours, and perhaps fifty in  ten.   Captain Barclay
walked 180 miles without resting ;  and  also 1000 miles in
1000 successive hours.
   18.  In the act of leaping, the whole  body is raised from
the ground, and for a short time suspended in the air.   It is
performed by bending  the head upon the body, the body on
the thighs, these on  the legs, and  the legs on the feet.   The
feet do not stand firmly on  the ground, as in  walking, but
the heel is raised, or  perhaps  slightly touches the  ground.
The muscles are all  in a state of flexion.   They are sudden-
ly contracted at the same instant ;  the consequence is,  that
the feet are raised from the ground and carried  forward, and
the body with  them, until it  is  brought to the earth by the
force of gravitation.  The distance passed  over, is in  pro-
portion to the  power and suddenness with which the muscles
contract.
   19.  The muscles which form the calf of the leg, act with
the greatest power in leaping, as they have to raise the whole 
324
PHYSIOLOGY.
 body.   Their great strength is  shown  by raising the body
 upon the toes, together  with a large additional weight; and
 this power is not only owing to  their great  size, but also  to
 the manner in which they are  inserted into the  heel, thus
 having the advantage of the long arm of a  lever.
   20.  The muscular powers exhibited  by many small ani-
 mals and insects is astonishing.  Small animals  can leap
 much farther than large ones, according to their size.  The
 flea and the locust leap two hundred times their own length,
 as if a man should leap  twelve  hundred feet high.  Others
 leap three hundred  times their  length,  and if man  was as
 strong  in proportion, he ought to leap more than  a quarter
 of a mile.  We read of an  English mechanic, who made a
 golden chain as long as the finger, with  a  lock  and key,
 which  was dragged  by a flea, and of another flea  dragging
 a silver cannon  on  wheels, that was twenty-four  times its
 own weight.   This cannon  was charged  with powder and
 fired without the flea seeming to be alarmed.   A cockroach,
 or an ant is six times as strong, for its size, as a horse; and,
 if an elephant were as strong in proportion, he  would  be
 able to tear up rocks and level mountains.
  21.  Hopping is merely leaping on one foot.  As but half
 the muscular power  is exerted, a man  ought  to be able to
 leap twice as far  as he can  hop.  Running  consists of a
 succession of low leaps, performed  by each  leg alternately.
 It differs from walking, in the body being thrown forward at
 each step, and the hind foot  being raised before the fore foot
 touches the ground.   A person cannot stop running instant-
 ly, as he can  walking, because his  velocity is so great as to
 carry him forward a certain distance, whether he uses his
 muscles or not, and thus occasions him to fall.
  22. The practice  of running  may be carried to a great
degree  of perfection.  A  quarter of a mile in a minute  is
good running; and a mile in four  minutes, at four starts, is
excellent.  A  mile was perhaps never run in four  minutes;
but it has been done  in four minutes  and a half.  A mile in 
LOCOMOTION AND  ITS  ORGANS.        325
five minutes is called very good running; two miles in ten
minutes is but rarely accomplished.  Ten miles an  hour is
done by all the best runners.   Forty miles, in four hours
and three quarters has been done by one individual.   Some
Indians, it is said, will run at this rate for several hours, but
it is very doubtful.
   23.  Swimming is very much like  leaping ; at  least the
same muscles  are brought  into action in the  lower limbs.
While the hands are brought to a point before the  head, the
legs are drawn up and suddenly extended, as in  leaping.  By
the resistance  of the water, the body is projected  forwards.
The hands are now carried,  with a  circular  motion, the
palms  being turned outwards, till they reach the sides of the
body, and thus the  impulse through the water is kept up by
a constant succession of these  movements.  A boat  is pro-
pelled on the same principle.  Indeed the body may be com-
pared to the boat itself, and the hands and feet to  the  oars.
A good swimmer ought to make three miles an hour.
   24.  The human body is very nearly of the  same specific
gravity as water; that is, it is  of the same weight as a body
of water  of the same bulk.  Dr. Franklin says if a person
avoids struggling and plunging, he may lie on  his back with
his mouth and face out of water, without difficulty,  even if
he cannot swim.   As swimming therefore, is a highly useful
art, and an agreeable and healthy exercise, it should be made
a necessary part  of the education of boys.
   25.  The importance of gymnastic  exercises  will only be
questioned by those  who are not aware that the health and
vigour of all the bodily orga*ns depend on the  proportioned
exercise of each.   Such exercises  ensure  the development
of all the locomotive organs; and they prevent or  correct
all the deformities to which those organs are liable.   They
are the best calculated to produce strength and activity, and
to bestow  invariable health.  At the same time  they confer
beauty of form, and contribute to impart an elegant air and
graceful manners.
                             28 
CHAPTER  XXVII.
                       THE TEETH.

   1. is  the  teeth are the only bones in the human frame
 whicr. are exposed to the immediate action of foreign bodies,
 they tiwit distinct and special consideration in this treatise
 on the General Physiology  of man.   The most remarkable
 fact in th^ir history is,  that unlike the other bones, the teeth
 which make their appearance  in infancy, are removed at the
 age of seven  or  thereabouts, and another set come forward
 to supply iheir places.
   2. The virst set called temporary teeth, are just twenty  in
 number, tei* in each jaw.  The two front teeth above and be-
 low, are known as central incisors, because they serve to cut
 the food.  The teeth adjoining these are denominated lateral
 incisors,  nest to which come  the  canine  or dog  teeth,  of
 which those in the upper jaw are called eye teeth.   Back of
 these at either extremity of each dental arch are two larger
 teeth known as grinders from the fact that they operate like
 mill-stones, in reducing the food to very minute  particles  in
 preparation for quick  and easy digestion.
   3.  The second  or  permanent set  has  twelve additional
 teeth, six above  and  six below, making  thirty-two in all.
 The two  next  back  of each eye tooth,  are  styled  bicuspids,
 because they terminate in two points ; and the four extreme
 grinders are sometimes called wisdom teeth, because they do
 not generally appear until the  individual arrives at mature
 age.  Thus, there are twelve grinders or molar teeth in the
 second set instead of eight as  in the first set ; and there are
eight bicuspids which are  not found among the temporary
 teeth at all.
  4.  Each tooth consists  of  two distinct parts, called the
 crown and root;  the former  being  that portion which pro- 
THE TEETH.
327
 jects from the gum into the cavity of the mouth, and the lat-
 ter that which  is  buried in the socket.  The incisors, eye
 teeth  and  bicuspids have one root each, the upper grinders
 three and the lower grinders two.  The roots of the wisdom
• teeth  are commonly compressed into one  mass having little
 or no  divergency, and  in rare  instances the bicuspids have
 two distinct fangs, while the  upper molars have been known
 to have four or five distinct roots.
    5. Every human tooth is  composed of two distinctly or-
 ganised substances, namely the enamel covering  the crown,
 and the osseous or bonv portion  which constitutes the  re-
 remainder of the tooth.   The osseous part is scarcely distin-
 guishable from  other bony  structures excepting  from its
 greater density.   The enamel  on the contrary, is remarka-
 ble for its extreme hardness resulting from its chrystaline
 structure.   It consists  of needle-formed  crystals,, one  ex-
 tremity  of  which  rests upon the bone  beneath,  while  the
 other is  presented to the food.
    6. The teeth are found by chemical analysis to consist of
 nearly the same elementary  substances as the  other bones ;
 namely, phosphorus,  lime, magnesia, soda, carbon,  oxygen,
 chlorine, gelatine and water.   As  the teeth  are a part of the
 living  system, they are supplied  with  nerves, blood vessels
 and absorbents,  not only by a central cavity extending from
 the point of each root to the middle of the crown, but by a
 membranous sheath enveloping the root called the periosteum,
 as is true of the other bones.
    7. The teeth are firmly attached  to the  jaw or maxillary
 bone, by means of sockets called alveoli.   In case of extrac-
 tion the alveoli yield to moderate  pressure and  suffer  the
 teeth to escape without any injury to the adjacent parts ;
 and as soon as the teeth are  removed the investigating bone
 is sufficient to produce  immediate  absorbtion.
    8. The first set  of teeth begin  to make their appearance
 through the gums, between the sixth and eighth month, and
 before  the infant arrives at the  thirtieth month all the teeth 
328
PHYSIOLOGY.
have assumed their natural position.   The  second dentition
commences  about the  seventh year, and is commonly per-
fected before the fourteenth.
  9. When the teeth are so  much  crowded  as  to  disturb
their regular arrangement ; or  when they press so hard upon
each other as to destroy  the enamel, one or more should be
removed  without  delay.   If this precaution should  be ne-
glected, an unsightly mal-arrangement, or inevitable destruc-
tion  of several of the  teeth, will be the melancholy result.
The  removal of a sound tooth causes very little pain com-
pared with the agony attending  those which are suffered to
become diseased.   •
  10. It  is impossible,  under ordinary circumstances, to
preserve  the teeth for many  years  without keeping them
very clean.   Food lodges between them at every meal, and
undergoes decomposition if not removed.  A substance, called
tartar, or salivary  calculus, which  is  deposited from  the
saliva, adheres to the teeth, becomes  very  hard, and finally
assumes a dark colour,  if not constantly washed away with
a brush and water.   If food be suffered  to  putrefy in spaces
between the teeth the process of mortification  is extended to
the teeth  themselves; and if tartar collect in solid  masses,
the teeth become loose  in their sockets and are thus  utterly
lost.
   11.  In  order to keep the teeth and gums perfectly clean
and healthy, it is  necessary to wash them with a stiff brush
and water several times  in a day.  No person of ordinary
neatness would consent to eat  with knives,  forks and  spoons,
unless they  were  cleansed after every meal.  The teeth are
more liable  to accumulate  filth than  any of these domestic
utensils, and therefore need at least equally frequent washing.
In the morning, after each meal, and  before retiring to  rest,
are not too  many times to purify the  teeth with a brush and
water, and once in each  week  with good tooth powder.
   12. The  Dentifrice  or Tooth  Powder, which I would  re.
commend in preference to all others which I have ever seen, 
THE TEETH.                   329
is composed of the following ingredients, well  pulverised in
a mortar, and intimately mixed together:
  Loaf sugar, half an ounce,
  Cinnamon, half an ounce,
  Gum Kino, quarter of an ounce,
  Peruvian bark, three ounces,
  Prepared chalk, six ounces,
  Armenian Bole, five and a half ounces;
     making one pound avoirdupoise.
  13.  In addition  to  the  above described  dentifrice, every
person  should  be  provided  with a good tooth  brush, which
should be laid aside as useless whenever it loses its  stiffness
and elasticity.   A  piece of gloss-silk, well  waxed, should be
employed to cleanse the open spaces between the teeth, inas-
much as these are  not easily cleansed with  the brush alone.
If tooth-picks are used  at all, they should be made  of  wood
or quill, since those formed of any of the metals, particularly
of steel or iron, are quite too hard, and therefore destructive
to the teeth and gums.
  14.  If brushing  the teeth and  using the other methods of
keeping  them  in order  as  above  described, should fail  of
effecting the desired  purpose, the assistance  of the dentist
should be put in requisition.  With his scaling instruments,
he can effectually  remove every vestige of tartar,  together
with any other impurities lodged upon the teeth.   Above all,
abstain from the use  of all kinds of powders and washes
which render the  teeth  white  by chemical action.  These
contain acid in one form or another, and are  therefore de-
structive to the teeth.
  15.  Persons desirous of preserving their  teeth in a  sound
and healthy state for many  years, should consult their  gene-
ral health in all their habits of life, especially in relation to
food and drinks.   Neither solid nor  fluid aliment should be
taken into the mouth at either  very high or very low tem-
perature, because sudden transitions from  heat to  cold, or
from cold to heat, are liable to crack the enamel of the teeth
                            28* 
330                  PHYSIOLOGY.
by unequal expansion and contraction, as is readily ascer-
tained by  the  assistance of the microscope.   Teeth  thus
injured, almost  always decay in consequence  of the exposure
of the bony substance of the tooth to  the action of corro-
sive fluids.
  16. There are three  prevalent  general causes of the de-
struction of human teeth, besides occasional accident: viz.
accumulation of tartar, ulceration  of the fangs, and dental
gangrene.   Ulcers of the  fangs  extend to the  alveoli  or
sockets, which  are  also destroyed, together  with the  invest-
ing gum.   The well informed dentist can best prescribe and
apply the proper remedies for all  these forms of dental dis-
ease. 
CHAPTER XXVIII.
                   SLEEP AND DEATH.

   1.  Sleep is the periodical  and temporary suspension of
those functions that connect us with the external  world.
Man  is  so constituted, that the functions  of sensibility, vol-
untary  motion, and the intellectual  faculties cannot  be in-
dulged for any length of time without fatigue.  The nervous
energy, which seems  essential to their exercise, becomes ex-
hausted ; the  muscles can no  longer contract;  the external
senses  cannot receive  impressions;  the  brain, and  conse-
quently the mind, becomes  torpid ; and a person sinks into
a state of torpor and  inaction, called sleep.
  2.  The approach  of sleep  is  announced  by an internal
sensation, termed drowsiness,  which gradually  increases  in
strength, till at length it becomes irresistible. Great languor
of the muscles and heaviness  of the  eyes are experienced;
the sight yields first;  next the smell; then the hearing; and
lastly, the sense of touch ; while at the same  time, all  the
internal sensations, such as  hunger and thirst, are no longer
felt.  The will ceases to control the functions that are under
its influence, till finally all power  of volition is  wholly lost.
Respiration is still carried on, but chiefly by means  of the
diaphragm, which is an involuntary muscle; it  is,  however,
somewhat slower, as well as  the circulation, than  in  the
waking  condition.
  3.  During perfect sleep, the functions of the brain are en-
tirely suspended.   In such a state, dreams do  not happen ;
for  as the brain is in  a state of complete inaction, the intel-
ectual  operations are consequently  dormant.    When  the
brain is not in a state of complete repose, objects and images
may float confusedly through  the mind, which are often the
result of external impressions  imperfectly perceived, as they
excite but an imperfect reaction in the brain. 
332                   PHYSIOLOGY.
  4. The organic  or nutritial  functions  continue during
sleep, but with  diminished energy.   The  circulation and
respiration are  not  only slower, but digestion is  retarded,
and  secretion,  nutrition, and calorification, are  less active
than when awake.   The  temperature of the  body is also
lowered during  sleep, which may perhaps  be  owing to  the
facts above mentioned.
  5. The duration  of sleep  is  influenced by  a variety of
circumstances.   The average  time  of regular, periodical
sleep, in adults, is from five to eight hours.  Infants require
twice as much  sleep  as  grown  persons.   The quantity of
sleep required, depends very much upon habit.  It is said of
Pichegru, one  of Buonaparte's  generals, that, for  a whole
year, he had not more than one hour of sleep in twenty-four
hours.   Buonaparte  himself, when on active  duty, seldom
slept more than three hours in twenty-four; often  but one
hour.   Men of active minds, who  are engaged in a series
of interesting  employments, sleep much less than  the lazy
and the listless.  The intellectual and moral faculties seem
to require a longer  period of repose  than the functions of
voluntary motion.
  6. Though the night is the proper season for sleep, owing
to the  absence  of light, diminished  warmth, its comparative
stillness, as well as the exhaustion  caused by the labours of
the day, yet some animals,  which pursue their prey  by night,
sleep during the day, as the  cat, fox, wolf, otter,  owl, and
bat.  Hybernating animals sleep for  several months during
the winter, such as the bear, hedge-hog, marmot, &c.   Some
birds, also, such as bats and swallows, sleep during  the win-
ter, or hybernate.   During this state their temperature is di-
minished, their  secretions  nearly checked, their excretions
suppressed, their respiration slow, and scarcely perceptible,
their circulation very languid, and sensibility to external im-
pressions  entirely suspended.  The arterial blood of hyber-
nating  animals, differs but  little from venous blood.
   7.  Dreams  are  now  considered  by  physiologists  to be 
SLEEP AND DEATH.               333
owing to an irregular action of the brain, in which the con-
trolling power of the will is lost, and  the  memory and the
imagination bear unlimited  sway.  Indeed all the faculties
of the mind may be in exercise.   The mind reasons, judges,
wills, and experiences all the various emotions.  We seem
to hear, see, walk, talk, and perform the usual offices of life.
Sometimes  the voluntary muscles are thrown into action,
and the dreamer moves, speaks, groans, cries, or sings; but
the moment consciousness is roused, he is awake.   Dreams,
therefore, have well been said to be  " a portion of animal
life, escaping from the torpor  in  which  the  rest  of it  lies
buried."
   8.  Before  the functions of the  brain  were  understood,
dreams were  regarded as supernatural, and  even now are
considered  in  this  light by  the ignorant  and superstitious.
Mr.  Baxter, as well as Bishop Newton divided them into two
kinds, good and evil, because they believed  that  good and
evil spirits  were concerned in their production, according as
one  or the  other obtained the ascendancy.   It  is supposed
that animals dream, especially the dog ;  are they subject to
supernatural influence 1
   9.  It is a singular circumstance in  relation to our dreams,
that we mistake our  ideas for actual perceptions, and sup-
pose that the train of images that passes through our minds,
represents scenes which really exist. This is doubtless owing
to the fact  that, during sleep, the senses do not admit exter-
nal impressions, and  of course we are  unable to compare the
ideas that arise in our minds with sensible impressions, and
thus perceive the difference between them.  Our only con-
sciousness  consists in the images  and ideas actually present
in the mind ; and it  is therefore  unavoidable that we should
believe that our ideas represent objects actually existing.
   10. There is a kind of dreaming, in some cases of imper-
fect sleep, where the will retains its power over the muscles
of voluntary motion, while the external senses remain buried 
334                  PHYSIOLOGY.
in partia. or complete repose.   This is called somnambulism
or sleep-walking.
   11.  Many remarkable cases  of somnambulism have been
lately published, as the effects of animal magnetism;  but in
many of these, it is to  be  feared, credulity existed  on one
side, and imposition was  practised on the other.   That som-
nambulism, or a state nearly similar, is brought about by  the
practices of magnetizers in  persons of acute sensibility, and
highly excitable nervous  temperament, would seem scarcely
to admit of a doubt.  Still, all such cases should be regarded
with great  circumspection, and every means  employed to
detect imposition and fraud.
   12.  Somnambulism seems to differ from the waking state,
only in consciousness being absent.  The person appears to
enjoy the  full exercise of all his faculties ; he can converse,
walk, sing, compose verses, and perform various  operations ;
and  yet in the waking state he has no recollection of  what
has occurred.   In this respect somnambulism  differs from
dreaming, and resembles  a morbid state; indeed, it is a state
of disease analagous to trance,  catalepsy, or epilepsy.
   13. A state, the reverse of somnambulism, is  called  incu-
bus, or nightmare.  In this  affection, a person feels a sense
of weight and suffocation, as  if there was a heavy load  on
his stomach  or chest, and imagines that seme frightful object
is seated there.   This is owing to  some oppression of  the
digestive,  circulatory, and respiratory  organs, most usually
occasioned  by a late,  hearty  supper  of indigestible  food.
Frightful  dreams denote ill  health, and are often caused  by
a  derangement of some important organ, as of the heart,
stomach, or  liver, exciting  the  brain to sympathetic  action.
To dream immediately on going to sleep, is always a mark
of disease.
  14. There is still another state which bears a close resem-
blance  to somnambulism, and this is termed revery, absence
of mind, or  brown study.   In this, the attention is  so  com- 
SLEEP AND DEATH.
335
 pletely riveted to some particular subject,  that the person is
 entirely insensible to the presence of surrounding objects.
   15. One great object of education is to give the will power
 over the attention.   The mind that  cannot command this
 faculty, is in a  deplorable condition for all the higher pur-
 poses of reflection and knowledge for which it is intended.
 Without it, perception exercises itself in vain ; the memory
 can lay up no store of ideas;  the judgment draw forth no
 comparisons ;   the  imagination must become blighted and
 barren ; and in proportion  as  a person has  no  command
 over his attention, in  that degree must he be an idiot.
   16. It is the  will  of Providence that all organized beings
 must perish.  For a while, life  maintains a successful con-
 flict with the chemical laws  of  matter ;  but at length its re-
 sistance becomes weaker  and  weaker, till, sooner or  later,
 those functions  cease which  have enabled  us to withstand
 the destructive influences  by which we are surrounded.
   17. The duration of life varies, not only in the animal but
 in the  vegetable kingdom.  As a general rule, where the
 growth  is  slow, the  period of decrease  is proportionably
 slow; and  where it is rapid, decay as  rapidly supervenes.
 The gourd  that  sprang up  in  a night, perished also in a
 night.
   18. There are two kinds of death, natural and accidental.
 Natural death, or that of old  age, is caused  by a gradual
 decay and  wearing out of all the  organs ;  accidental death,
 or such as  is occasioned by accident, cuts off existence pre-
 maturely.   The  natural  period of life  differs  in  different
 individuals; being influenced by a variety of circumstances ;
 such  as  the  original constitution ; habits of life ; and the
 health of the locality where a person is situated.
  19. The natural period  of life,  has not materially differed
since the time of the flood.   " The days  of our years," savs
the Psalmist, " are threescore and ten ; and if by reason of
strength they be fourscore  years, 5ret is their strength labour
and sorrow, for it is soon  cut off and  we fly away."  This 
336
PHYSIOLOGY.
description  is as  applicable now,  as  it  was four thousand
years ago.
   20.  Those  who die from old age are few;  being, in  the
city of New York,  but  one  in thirty-four.  In  New En-
gland, generally,  the proportion  is  rather greater.   The
mean duration of life in New York is but twenty-five years;
while the average  rate of mortality, according to population,
is  one in thirty-five.   The diseases to  which man is  subject,
from  the earliest  to the latest period of his existence, are
numerous, and many of them  of a  fatal character.   Syden-
ham estimates that two thirds of mankind die of  acute dis-
eases ; and that  of the remaining,  one third, or two ninths
of the whole, die of consumption, leaving only one ninth to
perish from other chronic maladies, and from pure old age.
   20.  As age approaches, the functions  are all performed
with less energy.  The teeth  fall out,  and their sockets are
absorbed ; respiration is not  as readily accomplished ; the
valves of the heart,  and  the coats of many of the  arteries
become changed into bone, thus obstructing the circulation,
and  often causing  an intermittent  pulse; nutrition  lan-
guishes ;  the senses are blunted ;  animal  heat diminishes, so
that warmer  clothing is demanded ;  the muscular  system
loses its power, and the body bends forward ; the limbs totter,
the mental as  well as corporeal faculties often fail ;  and the
individual is  reduced to second childhood, so well described
by Shakspeare.

                     " Last scene of all,
      That ends this strange, eventful history,
      Is second childishness,  and mere oblivion ;
      Sans teeth; Sans eyes, Sans taste, Sans everything."

As the other functions cease their  office, sensibility gradual.
ly becomes  extinct,  a^^hTqj almosT imperceptibly takes its
flight.           /W^             ^£\
 
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