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Doctor of Medicine of the Faculty of Paris; Professor of Anatomy, Physiology
     and Semeiology; Member of the Socifete Philomatique, and the
          Society M&licale d'Emulation; Associate of the
              Medical Society of Stockholm, &c.
CtanalattU  from  t$e &xmt%
              JOHN REVERE,  M. D.

v rci:-?Tir.fiiDi5KT or thb medical society of Maryland, anb member of thi
            ROYAL PHYSICAL SOCIETY OF EDINBURGH.
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           •Jtolttmom
PUBLISHED BY EDWARD J. COALE 81 CO.
         JOHS D. TOY, PRINTER.
             1822. 
Mi?
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       DISTRICT OF  MARYLAND,  TO  WIT!

    BE IT  REMEMBERED, That on the eighth day of February, In  the forty-sixth year of the Independence of the United States
ef America, Edwaid J. Coale  and  Loudon L. Town send, of  the said District, have deposited in this office the title of a book, the
right whereof they claim as proprietors, in the words following, to wit.

  "A  Summary of Physiology, by F. Magendie, Doctor of Medicine  of the Faculty of Paris; Professor of Anatomy, Physiology,
and Semeiology; Member of  the  Societe Philomatiqu*',  and the Socieie Medicate d'Emulation: Associate of the  Medical Society of
Stockholm, etc.  Translated  from the French, by John  Revere,  M.  D. Vice-Presideat  of  the Medical Society of  Maryland, and
Member  of  the Royal Physical Society of Edinburgh.'*

  In conformity to the Act  of the Congress of the United States, entitled, "An  Act for the encouragement of learning, by securing
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                                                                                                PHILIP  MOORE,
                                                                                       Cltrk of the District of Maryland. 
             TO THE












              OF THE






       eumtetr  States,





           THIS VOLUME,






WHICH I TRUST WILL BE FOUND






       A VALUABLE ADDITION






   TO OUR  PRESENT MEANS OF






     iitrtucal IStruratton,





        IS RESPECTFULLY INSCRIBED.






                    JOHN REVERE. 
 
W1MMT^&
    TPheue have been two different modes pursued in
 investigating the physical sciences.  They may with
 propriety be denominated systematic and theoretic.
   The  first has for its foundation certain gratuitous
 suppositions, or assumed principles, to which known
 facts are applied in such a manner as to explain them.
 Should  any new phenomenon be observed  which does
 not agree with  the fundamental principles  of this sys-
 tem, the fact must be so modified that an  explanation
 of it may be given.  If the supporters of systematic
 science  pay any attention to experience, it is with the
 intention of confirming the system which they  have
 adopted; every thing  which tends to overthrow it is
 neglected,  at least it is not  noticed; they  endeavor to
 find nature as  it should be, according to their pre-
 conceived opinions, not as it is—in a word,  they follow
the synthetic method; descending from hypothesis  to
facts, without  paying any attention  to those general
 principles wThich we ought always to keep  in view, in
 our search after truth.   It is scarcely possible, that un-
der this form natural science  should  make any real
progress
                         2 
X
PREFACE.
   Under the influence of the theoretic mode, the natur-
 al sciences assume an aspect entirely the reverse.  Un-
 der it, facts,—facts alone, serve as the foundation of
 science.  The object of its followers is  to verify, and
 multiply  them as much as possible; and  afterwards to
 study carefully the phenomena which they exhibit, and
 the laws by which  they are governed.   When a person
 gives  himself up  to experimental  researches, it  is to
 augment the number of ascertained facts, or to discover
' their reciprocal relations.  In a word, he follows the
 analytic method: the only guide which conducts us di-
 rectly to  truth.   By this method the sciences are im-
 proved, if not more rapidly, with at least  more cer-
 tainty,  and we may hope to see them approximate  per-
 fection.
   The physical sciences, with scarcely a single excep-
 tion, were  systematic until the  time of Galileo  and
 Bacon.   From that period, and in a great degree from
 the influence of the writings  of the  illustrious  Bacon,
 they  have undergone  a most salutary change.   From
 being systematic and synthetic, they have become theo-
 retic and  analytic;  and from that period  their march
 towards perfection has been extremely rapid.
   It is unpleasant, but  at  the same time it is necessary
to remark, that in the midst of this general progress of
the sciences, physiology, that  important branch of  hu-
man learning,  still retains the systematic form.  If any
one will take the trouble to examine with attention, the
manner in which it is  presented in  the  works of  the
most approved authors, he will find that it rests entirely
on simple suppositions, to which each one has in his
turn attached some of the  numerous phenomena of life. 
PREFACE.
Xi
thinking he has thus given a satisfactory explanation of
them.   What, for example, are "the vital and animal
spirits" of the ancients, "the  Faculties" of Galen, "the
moving and generative principle " of Aristotle, "the
archens" "vital properties,"  &c. which  have been
successively adopted to explain the functions of animal
life,  but arbitrary  suppositions which have served a
long series of generations to conceal that absolute  ig-
norance which has heretofore, and will perhaps always
exist, concerning the cause of life?
  What is the consequence of all this?—It is that phy-
siology, brilliant as it appears in  our modern treatises,
and  notwithstanding the supposed improvements which
it has derived from the talents of many distinguished
men, is a science still in its infancy.—It  is absolutely
necessary to do  something to remove from  it this  re-
proach.  The first step to be  taken in accomplishing
this  object  is, to change the method which has been
heretofore pursued.   It must  be made to  assume  the
analytic method,  and theoretic form. This is indispen-
sable to put  it in the way of improvement, and to place
it on a level with the more advanced of the  physical
sciences.
  My principal  aim in this work is, to contribute some-
thing towards  the  accomplishment of this important
change.  I have endeavored,  as far as possible, to pre-
sent  the science in  the theoretic form, following  the
analytic method, in the explanation of facts.
  One will especially find in  this book facts, the truth
of which I have done all in my power to establish as
definitely  as possible, by observations upon man in a
healthy or morbid state, or by experiments upon living 
Xll
PREFACE.
animals. Among these experiments a considerable num-
ber will be found new.
   I have not however neglected the possible and useful
application of  physical, mechanical and chemical prin-
ciples to the phenomena of  human life.   Perhaps the
application may be found somewhat different from what
has been heretofore  proposed, for I have taken every
care to  arrive at the greatest possible degree of exact-
ness.   Human physiology  is the only  subject which I
have pretended to treat.  Physiology, which in its more
enlarged meaning, comprehends the history of all liv-
ing beings, animal and vegetable, is not sufficiently  ad-
vanced  to be formed into a complete system; and what
is kno'.vn, it would  not  be proper to introduce into  a
work  professedly  elementary.
  In concluding, it is proper to remark, that this book
is  solely designed for  students in medicine.   If they
find here, in terms clear and simple, all which  is posi-
tively known of physiology,  I shall  have accomplished
the object which I have proposed to myself.

 Mote.—I am desirous of expressing publicly my thanks to my friend Doctor
Edwards, who has assisted me in all my experiments, and whose learning and
judgment hare been a very great benefit to me in the preparation of this work. 
A
SUMMARY
01
   Gtf.neral physiology is that natural science, which has for its
object a knowledge of the  phenomena which are peculiar to living
bodies.  It may  be  divided  into vegetable  physiology, which is
confinr-d to vegetables,  comparative physiology^ which treats  of
animals, and  human physiology, the particular object of which is
man.   It is of this last that we propose to treat in the following
work.

          PRELIMINARY  OBSERVATIONS.

             Of Substances and their  Divisions.

   The term substance or body may be applied to every  thing
which  is capable of acting upon  our senses.   Substances are
divided into ponderable and  imponderable.  The first are  those
whifh  act. on  many of our senses, and  the  existence of which
is therefore clearly demonstrable, as solid, liquid, and  gaseous
bodies.  'IV.  >eco*u1 are t'-.ose which  do not  act in  general
upon  more than one  of our  senses, the existence  of which 
14
A  SUMMARY
 has not been demonstrated, and which may perhaps be but a modi-
 fication  of  other bodies, such are caloric, light, the electric and
 magnetic fluids.   Ponderable substances are indued with com-
 mon, or general, and particular or secondary properties.    The
 general properties of substances are  extension, divisibility, im-
 penetrability, and mobility.  A ponderable body  possesses al-
 ways these  four properties united.  The secondary properties are
 different, in different bodies, such as hardness, porosity, elasticity,
 fluidity, &c; they,  together with the general properties, consti-
 tute the state  of  the body.  It is in  acquiring, or  losing these
 secondary properties that bodies change their state,  e. g. VV'ater
 may exist under the form of ice, liquid, or vapour,  although  it is
 still the same body.   To appear  successively under these three
 different  forms, it is only  necessary that they should acquire or
 lose some one of these secondary properties.
   Substances are  simple or compound. Simple substances occur
 rarely in  nature, but are almost always the product of art; indeed
 they are onfy called simple, because no artificial means have been
 discovered of decomposing them.  The following are the names
 of bodies at present considered  simple, viz:  Oxygen,  chlorine,
 iodine, fluorine, sulphur, hydrogen, aluminium, yttrium, glucinium,
 magnesium, zinc, iron, tin, arsenic, molybdenum, chromium, tung-
 stenium, antimony, uranium, cerium, cobalt,  titanium, bismuth,
 copper, tellurium,  nickel, lead, mercury, osmium, silver, rhodium,
 palladium, gold, platina, iridium, borium,  carbon,  phosphorus,
 azote, silicium, zirconium, columbium.
   Compound substances are  found every where; they form  the
 mass  of this globe, and of almost every thing which  we  see upon
 its surface.  There  are some substances, the composition of which
 does  not  undergo  any spontaneous  change; there  are  others, a
 change in the composition of which is constantly  taking place.
 This constitutes a  very important difference in bodies;  they are
 thus very naturally divided into two classes.  Those substances,
 the composition of which  remain constantly the same, are called
 dead,  inert, inorganic bodies; those on  the other hand, the  ele-
 ments of which  are  continually varying, are called living, or-
ganized bodies.
   Organic and inorganic bodies differ from each other in the three
 following respects, viz:—First in form, second  in  composition, 
OF PHYSIOLOGY.
15
third in the laws which govern their changes of state.   The fol-
lowing table exhibits the most remarkable differences.

Differences between dead, inorganic, and living organised bodies'*
Inorganic " Form Angular.        I  Form rounded.      ~) Living
 bodies. £ Volume indeterminate. |  Volume determinate. 5 bodies.
Iliorganic
 bodies.
COMPOSITION.
 ""Sometimes simple.
  Karely formed of more
   than three elements.

  Constant.
\ .ach part can exist in-
   dependent of the rest.
 I Capable  of being de-
 J  composed and restor-
L ed.
Never simple.        ""■
Having at least four ele-
  ments, often eight or
  ten
Variable.
Esicli part more or leas j  bodies.
  dependent on the rest.
Capable of being decom- |
  posed, but not of be- *
  ing restored.       J
Living
LAWS WHICH GOVERN THEM.
        ("Entirely  submissive to
,.     .  J   the laws of attraction,
Inorganic J      d chemical affiuit
 bodies. ^                   J
Partly submissive to at-"*\
  traction and chemical « T . .
   ce -.              V Livinr
  affinity             > ,   ,. °
a  .1        j u     f bodies.
Partly governed by an ',
  unknown power.    J
  Living  bodies arrange themselves  into two classes; the one
includes vegetables and the other animals.

         Differences between vegetables  and  animals.
        VEGETABLES.
Are fixed to the soil.
Have carbon as the principal base
  of their composition.
Composed  of four or  five ele-
  ments.
 Receive from around them their
  aliment ready prepared.
          ANIMALS.
Have the power of locomotion.
Have azote for the base of their
  composition.
Often  composed of eight or ten
  elements
Are compelled to  act upon  their
  aliment to render it suitable to
  nourish them.
Elements which enter into the  Composition  of Animal  Sub-
                             stances.
  A consideration of the elements which enter into the compo-
sition of animal bodies, is not alone interesting in a  physiological
point of view,  but furnishes still more important assistance to the
physician in the treatment of diseases.—These elements consist
of solid, fluid, gaseous, and unconfinable bodies. 
}&                     A SUMMARY

                    The Solid  Elements.
   Phosphorus, sulphur, carbon, iron, magnesia, lime, soda, manga-
nese, potash, si lex, and alumine.

                         The Fluids.
   Muriatic acid, water, which in  this case  may be considered  an
element, constitutes  three, out of four parts, in the organization
of animal bodies.

                     Gaseous Elements.
   Oxygen, hydrogen, and azote.

                    Unconfinable Bodies.
   Caloric, light, electric  fluids.   These different elements being
combined according to  certain laws, at present unknown, form
what may be called the immediate materials of animals.

              Immediate Materials of Animals.
   These are  distinguished into  azotic, and  non-azotic.   The
azotic  principles—are, albumen, fibrine, gelatine, mucus, case-
ous matter, urea, uric acid, osmazome, colouring principle of the
blood.   The non-azotic principles—are,  acetic acid, benzoic acid,
lactic acid, formic acid,  oxalic acid,  rosacic acid, the  sugar  of
milk, the sugar in diabetes, picromel.the yellow colouring princi-
ple of the bile, and other  fluids or solids  which become yellow ac-
cidentally, the vesicating  principle  of  cantharides,  spermaceti,
biliary calculi, odoriferous principle of amber, musk, castor, civet,
&c. of which  but  little  is known but their power of acting  on
the sense of smell.  The  adipose substance  of animals is  not
an immediate  simple principle.   M. Chevreuil has proved that
the adipose substance found in  the human subject, the hog, and
sheep,  is principally formed by two latty  bodies, which present
very different characters, and which may be easily separated. The
butter from the cow is not a simple body; it contains acetic acid,
a yellow colouring principle, and an odoriferous principle,  which
manifests itself  in caseous  matter in  a state of fermentation.
Adipocere—a natural substance found in dead  bodies which have
been long buried, cannot  be reckoned among the number of these 
OF PHYSIOLOGY.
17
immediate materials.  It is composed of margarine, acid of fat,
a yellow colouring principle, and an odoriferous principle.   This
substance must not  be confounded with the spermaceti of the
whale, or biliary  calculi, both of which differ essentially from it.
M. Chevreuil has shewn that it  does not contain a single princi-
ple analogous to  them.

                      Organic  Elements.
   These  materials  combine together,  and from  their combina-
tions arise the  organic elements;  which are  either solids,  or
fluuls.  We are entirely ignorant of the laws, or forces by which
these combinations are effected.

                       Organic Solids.
   The  solids assume  the  form  of tubes, plates, scales, or  mem-
branes.  In man, the  total weight  of the solids  is, in general,
eight or  nine times less  than the fluids;  this  proportion varies
however according to circumstances.
   The ancients believed that all the organic solids of the body
might be traced back to a simple fibre, which they supposed was
formed of earth,  oil, and iron.   Haller, who admitted this idea of
the  ancients, acknowledges that it is  only  perceptible to the
mind's eve; "Invisiblis est ea fibrtt; sola  acie mentis distin^ui-
mus" which is much the same as to have said  that it did  not exist
at all; a thing of which, at the present day, no one doubts.  The
ancients likewise admitted secondary fibres, which they  supposed
were formed by particular modifications of the simple fibre; as the
nervous, muscular, parenchymatous, and osseous fibres. Professor
Chaussier has lately proposed to admit four kinds of fibres; which
he distinguishes  by  the names of laminer, nervous, muscular, and
albugineous.
   The science  was  in this state,  when  M. Pinel  conceived  the
happy idea of  distinguishing the organic solids, not by fibres, but
 by tissues, or systems.*  He founded upon this distinction various
orders of diseases, particularly  the phlegmasise.   Bichat availed
himself of this ingenious  idea,  and applied it to  all the solid
parts of the animal  body.   Those parts of his works which relate

   * The English assert thutthis idea was first suggested by Dr. Carmichael Smith
in 1"88, in a dissertation read before a society in London.
                               3 
18
A  SUMMARY
to this subject may be  accounted among his strongest  claims to
eminence.*  M. Dupuytren perfected the classification of  Bichat;
M. Richerand  has likewise pointed out many of its imperfections.
   The following  is the  classification  of tissues, as corrected by
Messrs. Dupuytren and Richerand:
1	'cellular.		✓■arterial.
2	vascular		-t venous. v.h u.^liatic.
.**	nervous.		< cerebral. £ of the ganglions.
4	osseous.		rfibrous.
Systems.*;	fibrous.		■5 fibro-cartilaginous Ldermoide.
6	muscular.		C voluntary. £ involuntary.
r	erectile.		
8	mucous.		
9	serous.		
10	horny, or	epidermic.	C pilious. (_ epidermic.
11	^parenchymatous.		glandular.
  These different tissues, together with  the  fluids, compose the
organs or instruments  of  life.   When  several  organs  in  their
action tend to one common end, they may together be called an
apparatus.^  The number  of these and their  arrangement consti-
tute the differences between animals.

                 Properties of the  Tissues.
  The tissues which compose the organs  possess certain physical
and chemical properties, which it is important  to study both in the
dead  and living animal  body.   Nearly all the physical properties
which are  found in dead  inorganic  substances  will  be  found
in them; from extreme hardness to  a consistency almost  fluid,
elasticity, transparency, and refrangibility; but  our attention  is
particularly attracted  by  certain properties, which  have  been
called the properties of tissues; such are their extensibility, and
contractility.
   Independently of their  physical properties, the tissues have
been  examined as it respects  their composition;  and it has been

  * See Traite de l'Anatomie Generale.
  t There is no word, that I koow of, in English which perfectly expresses the
idea conveyed by the French word "appareil." I have selected the Arord ap-
paratus as approaching nearest to it.—Trans. 
OF  PHYSIOLOGY.
19
found that some of them are chiefly composed of gelatine, others
of albumen, some of phosphate of lime, others  of  fibrine, &c.
These different tissues  also present in the living body, certain
phenomena, which have attracted  the attention of physiologists.
One branch  of science is  devoted to  the investigation of these
tissues, under the threefold consideration of their physical, chemi-
cal, and vital properties; this is called general anatomy, the study
of which is of the highest importance to physiology.

                  Of the  Fluids  or Humors.
  The fluids of animal bodies, especially man,  greatly exceed the
solid parts.  In the adult, they are as nine to one.  M. Professor
Chaussier  placed  a body  weighing one hundred and twenty
pounds, in an  oven;  after being allowed to dry for several days,
it was found to be reduced to twelve pounds.   It has been long
remarked that dead bodies  which have been found, after having
been  long buried  in  the burning sands  of  Arabia, have under-
gone  an astonishing diminution of weight.   The animal fluids
are sometimes  contained in vessels, in which  they move with a
greater or less degree of rapidity, sometimes in spaces where they
seem to be deposited, at others in large cavities, where they remain
for a longer or shorter time.
  The fluids  of  the human body, which constitute a  principal
object in our present inquiry, are
  1. The blood.
  2. The lymph.
  S. The perspiratory fluids; which comprehend cutaneous trans-
piration, the transpiration  of the mucous,  serous, and synovial
membranes, the cellular, adipose and medullary membranes, and
the interior of the thyroid and thymus glands,  &c.
  4. The follicular fluids;—The fatty humour of the skin, the
cerumen, the sebaceous humour of the eye-lids.   The mucus of
the mucous glands and follicles of the tonsils, the  cardia, and the
parts about the anus, and prostate, &c.
  5. The glandular  fluids;—The tears,  the saliva, the  pancre-
atic juice, the bile, the urine, the fluid of the  glands of Cowper,
the semen, the  milk,  the fluid  contained in the capsulse renales,
and the contents of the mamrnse and testicles  in new born children.
   6.  The chyme and the chyle. 
'20
SUMMARY
  The physical and chemical properties of the fluids are very va-
rious.  Many resemble each other, but no two are precisely alike.
At all times great importance has been attached to a methodical
arrangement of them, and  we  find that different  classifications
have been adopted, according to the  prevailing doctrines of the
schools at different periods.  Thus, the ancients, who laid great
emphasis on the influence of the four elements in the operations of
nature, asserted, that  there were four  principal humours in the
body, viz. the blood, the lymph, the yellow, and  the  black  bile;
and that  these  four humours corresponded to the four elements,
the four seasons of the year, the four parts of the day, and  the four
temperaments.
  In more modern times,  other divisions have been substituted
for  this classification  of the ancients.  Thus, they were at one
time divided into  three classes, viz.  1st, the chyme and chyle;
2nd, the blood;  3d, the humours secreted from the blood.  Some
authors have  thought it  sufficient to  arrange  them  into  two
classes.   1st, fluids which are  useful as aliments; 2nd, those
which are useless in this respect.   The first are called  recremen-
titinl, that is, humours which after their formation are destined to
nourish the body;  the second, excrementitial, or those which are
thrown out of the economy; those humours  which participate in
these two characters,  have for  this reason received the appella-
tion of excremento-recrementitial. Chemists have of late endea-
voured to classify the humours according to their peculiar na-
ture; as the albuminous, fibrous, and aqueous  humours, &c.  But
the classification of Professor Chaussier  will  be found to be the
best.  This has no regard  to the nature of the fluids, or the  use>
to which  they are destined, but is founded on the  mode  of  their
formation, the  only character  which  remains always  the same.
This is the classification that we have followed in the enumera-
tion of the fluids.

     Causes of the Phenomena peculiar to living Bodies.
   From the earliest antiquity it has been observed, that the great-
er number of the phenomena, which  take place in living bodies
are essentially  different from those that occur in  dead inorganic
matter.  One particular cause has been  assigned  to explain the
phenomena observed in  living bodies.   This  cause has received 
OF  PHYSIOLOCY.
21
different names.   It  was denominated  by Hippocrates, <pv<rts-
(nature;) by Aristotle, moving and generative principle; by Boer-
have, impetum faciens; by Van Helmont, archea; by Staal, soul;
others again have called it vis insita, vis vitce, &c.   M. Chaus-
sier, in his learned lectures, and in his synopsis of the characters
of vital  power,  has adopted  the  name "force vitale."—It is not
worth while to endeavour to deceive ourselves by this expression,
"force vitale," or vital power.   It does not, and cannot mean  any
thing else than the unknown cause of vital phenomena.
   In the same manner, say these physiologists, as attraction pre-
sides over the changes of state in dead matter, does the vital pow-
er control the modifications  of organized  bodies.  But they fall
into an error, for vital power and attraction cannot well be com-
pared to each other; the laws of this last are perfectly known; those
of vital  power entirely unknown.  Physiology is, at this time, pre-
cisely in the state  in  which the physical sciences  existed  before
the discoveries of Newton; and it requires a genius of the highest
order to discover the  laws of vital power, in the same  manner as
Newton made known those of attraction.   The glory of this great
man does not consist  in having discovered  attraction, as some be-
lieve, for before his time this cause was  known,  but  in having
shown that this power "acts directly  in proportion to the mass,
and inversely as the squares of the distances."

                       Vital Properties.
   It has not been  supposed sufficient to admit the existence of
this vital  power,  and to allow it to play  an important part in
the explanation of vital  phenomena; but it is asserted that this
power manifests itself by the vital properties;  and on this, some
authors  have founded  not  only physiology, but pathology,  and
therapeutics.
   These vital properties, the existence of  which has been  gener-
ally admitted, have received different names; they have been call-
ed, viz.
   1. Organic, nutritive, vegetative, and  molecular sensibility.
   2. Organic insensible contractility, nutritive  and fibrous  con-
tractility, tone, tonicity.
   3. Cerebral and animal sensibility, and sensibility  from rela-
tion. 
22
A  SUMMARY
   4.  Organic sensible contractility,  irritability  and  vermicular
 motion.
   5.  Voluntary and  animal contractility, contractility from  rela-
 tion,  &c.
   With respect to these properties, some are  common to all liv-
 ing bodies; others are peculiar to certain parts of animals only.
   The first alone deserve the name of vital properties.   It is es-
 sential, however, to remark, that organic sensibility, and organic
 insensible contractility, are not of this description.  These are
 evidently mere suppositions, or modes of conceiving and explain-
 ing the phenomena of life.   They do not in reality exist,  although
 their  existence seems to be universally taken for granted.  Many
 persons are in the habit of speaking of the alterations which these
 vital  properties undergo, and of the necessity of bringing  them
 back  to their natural  state.   It has even been attempted to classi-
 fy the articles of the materia medica,  according to their supposed
 effects upon these properties; and many physicians treat disease
according to  this doctrine.
   There are others of these  properties which are peculiar to cer-
 tain animals, or only to particular parts of them.  Organic sensible
 contractility  is an example of this,  which exists in the heart,
 intestinal canal, and bladder, &c. but is not observed in any other
 part of the animal economy.  Cerebral or animal sensibility, as it
 is called by Bichat, and voluntary contractility, can only  be  reck-
 oned  among the vital properties, by an abuse of terms.   It is
 plain  that these  are but functions, or the results of the action of
 several organs, which in acting have one common  aim.   We shall
 say nothing of the vital power of resistance, of vital affinity, &c.
 because these different properties, although proposed by  men  de-
 servedly distinguished, have not  received the general  assent, nor
 can we perceive any necessity for admitting them.
   Our views, then, concerning the vital properties are  such,  that
 we are induced to reject organic  insensible contractility, and or-
 ganic sensibility, as useless  and dangerous suppositions; to con-
 sider  oiganic sensible contractility as  the action of an  organ; and
 voluntary contractility, as  well as cerebral sensibility, mere func-
 tions. 
OF  PHYSIOLOGY.
S3
              Phenomena of Life in the Fluids.
  The doctrine of the vital properties has not been applied to the
fluids, though it is admitted that they possess life. A method much
more philosophical has been pursued with respect to the fluids than
the solids;  for it was not admitted that they were endowed with
life, until this was proved by the sensible phenomena which they ex-
hibited.  Thus their vitality is inferred from their preserving their
fluidity,  while they remain in certain parts of the living body; and
from the manner in which some of them organize themselves, when
they are thrown  out of the  vessels; and their power of evolving
caloric.  These  are the chief phenomena, which, according to
modern physiologists, prove that the fluids are endowed with life.
It should, however, be recollected that all the fluids do not possess
these characters.  The  blood, chyle, lymph, and a few other fluids
destined to nourish the body, alone present them.  The excremen-
titial fluids, such as the bile, urine, cutaneous transpiration, &c.
do not present any phenomena which are analogous to them; what
is therefore said of the vitality of the fluids, cannot be understood
as applying to these last.
   Before beginning the  examination  of the phenomena of life in
 man, the principal object of  this work, we will make one general
 remark.   Whatever may be the number and diversity  of pheno-
 mena presented by man, during life,  they may be reduced at last
 to these two principal  ones, viz. nutrition and vital action.  A
 few words respecting each of these phenomena are indispensable
 to the proper understanding of those subjects which will hereafter
 fall under our consideration.
    The life of man, and that  of other organized bodies, is pre-
 served  by  the  habitual  assimilation  of a  certain quantity of
 matter, called aliment.   If they are  deprived of this for a given
 period,  it will  be necessarily followed  by  a cessation of  life.
 On the  other hand daily observation shews, that the  organs of
 man, and other living beings,  are constantly losing a certain por-
 tion  of the matter of which  they are  composed.   A  necessity,
 therefore, for repairing the  loss which is thus constantly sustain-
 ed, is the reason why the  habitual use  of aliments is required.
 From these data,  and  from some  other  circumstances,  which we
 shall mention by and by, it  has been justly concluded, that living
 bodies  are not composed, identically, of the same matter at every 
24
A  SUMMARY
period of their existence, but that they undergo a total renovation.
The ancients imagined that this was accomplished in the space of
seven years.   But, without admitting this conjecture  to  its full
extent, it is extremely probable that all  parts of the body, during
life, are undergoing a change, which has the double effect of ex-
pelling those molecules which have served their appointed time in
the composition of the organs, and of replacing them by new mo-
lecules.  It  is this which  constitutes  nutrition.   This  process
does not fall, indeed, under the cognizance of our senses;  but the
effects are  so palpable, that it would  be the height of scepticism
to doubt  it.  In the present state of physiology, this operation can-
not be attributed  to chemical affinity, that power which controls
the action  of minute particles of matter upon  each other in dead
bodies, nor, indeed, do we know of any satisfactory explanation  of
it.   To say that it depends on organic sensibility, or organic in-
sensible contractility, or simply  on vital power, is only to ex-
press the fact in different terms, without giving any explanation of
it.   But  however this may be, we can only attribute  to this pro-
cess of nutrition, the power of living bodies to preserve or change
the physical properties of their organs.   Our different organs be-
ing found to present different  physical  properties, the  process  of
nutrition must  no doubt vary in each.
   Independently of the physical  properties which all parts of the
body present,  there  are a considerable number which  exhibit,
either continually or periodically, a phenomenon which has been
called vital action.  The liver, tor example, is endued with  a pe-
culiar power by which it is  enabled constantly  to form a fluid  call-
ed bile; the same remark may be applied to  the kidneys, in the
formation of urine.   The voluntary muscles under certain circum-
stances,  grow hard, change their  form, and contract;  this is  ano-
ther example of vital action. These vital actions are of great im-
portance in the life of man, and  other  animals, and particularly
demand, therefore, the attention of the physiologist.
   Vital action evidently depends on nutrition, and nutrition is
reciprocally influenced by  vital  action.  Thus an organ which
ceases to receive nutrition, soon loses its power of vital action*
and organs, the action of which  is frequently repeated,  possess
more active powers o! nutrition, while in those on the other  hand
which act but little the piecess of nutrition is evidently slow. 
OF  PHYSIOLOGY.
25
  The precise mode in which vital  action is performed  is un-
known.  There takes  place in the organs, some insensible move-
ment of its molecules,  which can no more  be explained than the
process of nutrition.  No vital action, however  simple it may ap-
pear to be, can be considered an exception to this rule.
  All the phenomena of life, therefore, may  be included under
these two heads, viz. nutrition, and vital action; but as the pecu-
liar action of the particles, which constitutes these two phenome-
na, cannot be perceived by  our  senses, this is  not a point upon
which  we can  profitably bestow much attention.   We must con-
tent ourselves with investigating their results; that is, the physi-
cal properties of the organs, and  the manner in which these con-
cur in the general processes of the livftig body.  This is, in fact,
the end  of physiology, and, to attain this end, the phenomena of
life have been divided  into different classes, or  functions.
   Authors have differed much in their classifications of the func-
tions.   Without stopping to enumerate the different classifica-
tions that  have been  adopted  at  different  epochs  of  science,
which  does not comport  with  the nature  of this work,  we shall
divide the functions, 1st, into those which connect the individual
with surrounding objects; 2nd, those of nutrition; 3d, those which
have  for  their  aim the reproduction of the species.  WTe may
call the first,  functions of relation; the  second, functions of nu-
trition; and the third, functions of generation.
   The method to be pursued in the investigation of a function, is
by no  means a matter  of indifference.   The following is the one
which we have adopted.
   1. General idea of function.
   2. Circumstances which keep  up  the action  of organs, and
which  we call excitants of functions.
   3. Concise anatomical description  of the organs concurring in
any function, and which may be called its apparatus.
   4. The action of each organ  in particular.
   5. A summary shewing the utility  of the function.
   6. The relation of the function to the parts before examined.
   7.  The modifications which the function exhibits, according to
age, sex, temperament, climate, season, and habits.
                              4 
                 OP THE


FUNCTIONS OF RELATION.
   The functions of relation include, sensation,  intelligence,
voice, and motion.

                OF Tlfc SENSATIONS.
  Sensations are those functions which are destined to receive
impressions from external objects, and to convey them to the sen-
sorium.   These functions are five in number, viz. seeing, hearing,
smelling, tasting, and feeling.

                       OF VISION.
  Vision is the function by which we become acquainted with the
size, figure, colour, and  distance of bodies, &c  The organs which
compose the apparatus of virion,  act  under the  influence of a
particular excitant, called light.  We  perceive bodies, and  be-
come acquainted  with many  of  their qualities, although  they
may be at  a  considerable  distance from us;  there must, there-
fore, be some intermediate  agent between these objects and our
eye; this agent is  light.   Light is an  exceedingly subtle fluid,
which emanates from a class  of bodies called luminous; as .for
example, the sun, fixed stars, ignited substances, and  those that
 ne called phosphorescent.  Light is composed  of particles which
move with a prodigious velocity.  It is ascertained that it moves
at the rate of eighty thousand leagues in  a second.  A ray nf
light is  a series of particles succeeding each other without inter-
ruption, in a right line.   The particles  which compose  a ray, are
separated from each  other by considerable intervals, relatively to
their masses.   This may be shewn by  making a large number of
rays cross each other at any given point, when  it will be perceiv-
ed that  the particles  do not strike against each other in meeting. 
OF PHYSIOLOGY.
27
  Light, in  passing  from luminous  bodies, forms diverging rays,
which, if they meet with no obstacles, are prolonged indefinitely.
Natural philosophers have infered from this, that the quantities
of light received from a luminous body in any given spot, is in an
inverse ratio to the squares of the distances  of the surface, from
the luminous body  from which  it arises.   The diverging  rays
formed by light in passing from  luminous bodies, are generally
called  a pencil of rays.   Those  bodies which transmit the light
are called media.   When light  meets in its progress  certain
bodies, called opaque, it is turned from a right line, and the di-
rection given to it is modified by the disposition of the surfaces
of those bodies.   The change of direction which the light under-
goes in this case, is called reflection.   This branch of physics has
received the name of catoptrics.
   Certain bodies transmit light, or suffer it to pass through  them;
for example, glass.   These are said to be transparent, or diaplio-
nous.  In passing through them, the light  undergoes a certain
change, called refraction.  As the utility  of the organ of vision,
from its structure, depends entirely  upon the principles of refrac-
tion, it will be necessary to stop for a moment, for the purpose
of examining the subject.
   The point at which a ray  of  light enters  a medium, is called
the point of immersion; and  that from which  it passes out, the
point of emergence.  If a ray enters perpendicularly the surface
of a medium, it passes through the  medium  preserving its first
direction; but if it strikes obliquely to the surface of the medium,
it is turned from its coarse at the point of  immersion.
   The angle of incidence is that contained between the inci-
dent ray, and a line drawn  perpendicularly  to the surface of the
medium, from the point of immersion.  The angle of refraction is
that contained between the  line described by the refracted ray,
and a  line perpendicular to the refracting  surface at the point of
immersion.
   A ray  of light passing from a  rarer into  a denser medium, is
refracted towards a perpendicular to the surface of the  denser,
drawn from the point  in which the  ray meets the medium; but,
on the contrary, in passing from a  denser info a rarer, it is re-
fracted from  the  perpendicular.   When  a  ray of light  passes
from a rarer through a denser medium, the two surfaces of  which 
28                     A  SUMMARY
are parallel, the ray in passing into the surrounding  air, will
take a direction parallel to that of the incident ray.
   Bodies refract light, in proportion to their density* and com-
bustibility.   Thus, if two bodies be  of  equal  density, but  one
more combustible than the other, the refractive  power of the first
will be found greater than that of the second.   All diaphonous
bodies, at the same time that  they  refract light, reflect it.   In
proportion as bodies possess this last  quality, they are capable of
being used as mirrors.   When  they have  but  little  density, as
for example, the atmospheric air, they are only  visible when they
exist in considerable volumes.
   The form of  refracting bodies has  no  influence upon their re-
fracting power; but it modifies  the  disposition  of the  refracted
rays with respect  to each other.  The perpendiculars at the sur-
face of the refracted body approaching or separating from each
other, according to the form of  the body, the refracted rays must
also converge or diverge from each other.  When, from the form
of a  refracting body, the rays  are  made to converge,  the point
where they  unite is  called the  focus of the  refracting body.
Bodies of a  lenticular form,  or those bodies  which are termin-
ated  by two segments of spheres, present this  phenomenon.  A
refracting body with parallel surfaces, does not  change the direc-
tion of the rays.  A  refracting  body  with  two convex  surfaces,
called a lens, does not possess a greater  refracting power, than a
body  which  is  convex on one  side  and plane on the other, but
the point where the rays unite is nearer.
   The study of refraction makes us acquainted with an extreme-
ly important fact; it teaches us that a beam of  light is  composed
 of a considerable  number of differently  coloured rays, which are
 differently refrangible.  If, in a room previously darkened, we al-
 low a beam  of light to pass through a small aperture, so that it
 will  traverse a prism of glass,  or any other refracting body, the
 surfaces of which are not parallel, and if this be received on any
 plain surface, as for example,  a sheet of  paper, it  will be  seen
 that the beam occupies a considerably larger space than the size
 of the aperture, of an  oblong  form; and instead  of producing a
 white image, a considerable number of  different  colours will be
   *' Density is the relation ot -weight to volume.  It all bodies were of the same
 volume, their relative density might be determined by their -weight. 
OF  PHYSIOLOGY.
29
observed, which run insensibly into each other, and among these
may be distinguished the seven following colours, viz. red, orange,
yellow, green, blue, indigo, and violet.  Neither of these colours
are capable of being decomposed: they are together called the so-
lar spectrum.  Light is not, therefore, homogeneous, but is com-
posed of very differently coloured rays.   On this fact is founded
the explanation of the different colours of bodies.  A white body
reflects light  without decomposing it; a black body does not reflect
light, but totally absorbs it; coloured bodies decompose light and
reflect it; they  absorb some of the rays and reflect others.  Thus
a body will appear red, when the red rays are alone reflected and
the rest absorbed; or will appear  green, when the union  of the
colours reflected  form green.  If, now, it be inquired why certain
bodies reflect one ray and absorb another? it will be replied, that
this phenomenon arises from the peculiar arrangement of the par-
ticles of which the  body is  composed.—This explanation resem-
bles very much what has been given of the phenomena of life, of
which we have before spoken; that is, it is very well as far  as  it
goes, but, in  fact, it explains nothing.  The  discovery  of the ac-
tion of refracting bodies upon light, has not been a mere object of
curiosity; but has led to the construction of ingenious instruments,
by means of  which the sphere of human vision has  been astonish-
ingly extended.

                     Apparatus of Vision.
   The  apparatus of vision is composed  of  three  distinct parts.
The first modifies the light, the second receives the impression of
this fluid,  and the  third transmits this  impression to the senso-
rium.   The  structure of this organ is extremely delicate.   Na-
ture has taken therefore great care  to place before it various parts,
which protect and preserve it in a condition necessary to the free
and easy exercise of its functions.
   The  protecting parts are  the  eye-brows, the eye-lids, and the
apparatus for the secretion and excretion of  the tears.
   The  eye-brows are peculiar to  man, and are formed,
   1. By hairs  of various colours.
   2. By skin.
   3. By sebaceous follicles placed at the root of  each  hair.
   4. By muscles destined to move it, viz. the frontal  portion of 
30
A  SUMMARY
 the occipito-frontalis, the superior edge of the orbicularis palpe-
 brarum, and the corrugator supercilii.
   5.  By numerous blood vessels.
   6.  By nerves.
   Uses of the eye-brows.—The eye-brows have various uses. The
 projection which they form  protects the eye from external vio-
 lence.  The hairs, from their oblique direction, and from the oily
 substance with which they  are covered, prevent the  sweat from
 running into the eye, and  irritating the surface of the organ; they
 direct it towards the temples, and root of the nose.   The colour
 and  number of the  hairs  of the eye-brows  have some influence
 upon  their use.  These are  found  to have some  relation to the
 climate.  The inhabitants of warm climates generally have them
 very thick, and very black.  The inhabitants of cold regions may
 have  them  thick, but they  are  seldom  black.   The eye-brows
 guard the eye from the too vivid impression of light, particularly
 when they are drawn together, as in the act of frowning.
   The eyelids are  two in  number  in man, and are  divided into
 superior and inferior; or great and small; palpebra major and pal-
pebra minor. The form  of the eye-lids is  accommodated to that
 of the globe of the eye, so that when they are brought  together
 they completely cover the anterior surface of that  organ.   They
 do not meet on a  level with  the transverse diameter of the eye,
 but considerably below  it; this was therefore falsely called by
 Haller equator oculi.  The  more extended the  opening that se-
 perates  the eye-lids,  the larger the eye appears; the  opinion we
 form  of the  size of the eye is often, therefore, very incorrect.
 The open edge of the eye-lids is thick, firm and furnished  with
 hairs,  more or   less numerous,  which  are  generally   of  the
 same  colour with the hair of the head.   These hairs  are placed
 very near to each other.   Those of the superior eye-lid  form a
 slight curve upwards, but those of the inferior eye-lid turn in an
 opposite direction. When they are very numerous and very long,
 they are  considered beautiful; an  idea which agrees very well
 with the utility resulting from them. The eye-lashes are covered
 with an unctuous substance,  derived from the small follicles situ-
 ated in the thickest part of the eye-lids, near the roots  of the eye-
 lashes.  They have these in  common with the hair in  most parts
 of the body.   Between the line occupied by the eye-lashes and 
OF  PHYSIOLOGY.
31
*he internal surface, there is a smooth edge  where the  eye-lids
touch each other.  This may be called the margin of the eye-lid.
  The eye-lids are composed of a muscle with semicircular fibres,
the orbicularis  palpebrarum, of a cartilage, of a ligament, the
large ligament  of the  eye-lid,  of a  great number of sebaceous
follicles, meibomian glands, and of a portion of mucous membrane.
All  these parts are connected  together by  cellular membrane,
generally loose  and fine, and containing no  fat.  The  skin of
the eye-lids  is very fine  and semi-transparent; it adapts itself
readily to their movements, and presents transverse folds.  The
muscle  of the eye-lids, by its contraction, approximates them, or,
as we commonly express it, shuts the eye, at the same time that
it presses the eye-lids a little  upon the globe of  the eye.
  The cartilages of the eye-lids are called the tarsi.  That of the
superior  is much  larger than the inferior; their use is  to keep
the eye-lids extended, and constantly accommodated to the form.
of the eye; besides, they  support the  eye-lashes, afford a suitable
situation  for the meibomian glands, and  serve to protect the eye
from external  injury.    The use of the  tarsi, as  respects the
motion  of the eyelids, does  not  appear indispensable, as  they
are  not  found  in  many  animals,  the eye-lids  of which,  never-
theless, perform their functions  well.  The large  ligament  is
nothing more than the cellular  membrane which passes from the
base of the orbit to the superior edge of the cartilage of the tarsus.
It seems  intended to limit the motion by which the eye-lids ap-
proach  each other.
   The  cellular tissue of  the  eye-lids is extremely fine, and deli-
cate, and contains no fat, but is  filled with  a very  thin  serum,
which in  some cases has a greater degree of consistence, and ac-
cumulates in the cells of this tissue;  when this is the  case, the
eye-lids become distended, and of a bluish  colour.  This  colour
and swelling of the eye-lids is frequently observed after excesses
of every kind, after severe diseases, during convalescence, and  in
women during menstruation, &c.  The fineness,  and laxity of the
cellular membrane of the eye-lids, and the absence of fat from its
cells are necessary for their free  motion.   The internal surface
of the eye-lid is covered by a mucous membrane. Besides the parts
already mentioned, the superior  eye-lid has a  muscle proper  to
it, this  is called the elevator  palpeb-fe superiors. 
32
A  SUMMARY.
   Uses of the eye-lids.—The eye-lids cover the eye during sleep,
 and preserve  it from the contact of foreign  bodies which  float
 about in the  atmosphere: they preserve it from blows, by their
 instantaneously closing; by habitually closing, at  nearly  regu-
 lar intervals, they prevent any bad effect from the long continued
 contact of the air, and have likewise the power of  moderating the
 effect of a  too  brilliant light.  By  closing together, they only
 suffer such a quantity of light to pass, as may be necessary for
 vision; but not sufficient to  injure the eye.  On the  other hand-
 when the light is weak, we separate  the eye-lids widely, so as to
 permit the largest quantity of light  possible, to penetrate  to the
 interior of  the eye.   When the eye-lids are near, the eye lashes
 forma sort of grate, which only suffers a certain quantity of light
 to pass  at  a time.   When  the eye-lashes are moist, the small
 drops which cover their surface decompose  the light in the man-
 ner of a prism, and  at the point where the light passes, cause it to
 appear variegated like the rainbow.  The eye-lashes, by dividing
 the light which penetrates into the eye into pencils, cause ignited
 bodies to appear, during the night, as if they were surrounded by
luminous rays.  These appearances vanish as  soon as the eye-lid
is thrown back, or another direction  given  to  the eye-lashes.   It
is supposed that the eye-lashes preserve the eye from the  atoms
 of dust  which are floating in the air.  Vision is  always  more  or
less affected in those persons who have  lost the eye lashes.
   Glands of  Meibomius.—The  compound follicles placed  in
 the thickest part of the tarsi, are called the meibomian glands.
 They are very numerous.   There are  from thirty,  to thirty-six
 in the  upper eyelids,  and  from twenty-four to  thirty in  the
 lower.  In each  compound  follicle there exists a central duct,
 about which are placed the simple follicles, and into which they
 pour the matter which they   secrete.   This duct is  always filled
 with  this matter, in its ordinary  state  is called  the meibomian
 humour, but when  it is thick and  dry is called gum.  After
 sleep, a certain quantity of  this is always found accumulated  at
 the inner an*-!e of the eye, and on  the  margin of  the  eye-lids.
 This matter seems  to be of an unctuous nature,  particular  re-
 searches have  induced me to believe, that it is essentially albu-
 minous.  Each central duct has an opening, hardly visible, on the
 internal surface  of the eye-lid, very near to the margin.  These 
OF  PHYSIOLOGY.                     33
openings are close to each other, and range along the whole length
of the margin.   The meibomian humour  passes out through these
openings when  we compress the  eye-lid lightly;  as they  expe-
rience a sensible pressure on closing  theeye-lid.it  is  probable
that this pressure contributes to  the  excretion of the  humour.
The principal use of this  humour seems to be, to diminish  the
friction of  the eye-lids on the iJobe of the eye. As  the upper eye-
lid  has a greater extent of motion, and   will  of course  produce
more friction, it requires a greater number of these follicles.

                  Apparatus for the Tears.
  The duty of guarding the  eye, and preserving it in a condition
necessary  for the performance of its  functions, is not  confined
exclusively to the eye-brows, or eye lids.  There is  likewise to
be reckoned among the tutamma oculi, a small secretory appar-
atus, of which  the  mechanism  is very  curious, and the utility
very great.  This is the secretory apparatus of the tears.   It is
composed of the lachrymal gland, the excretory ducts, the carun-
cula lachrymalis, the lachrymal ducts, and the  nasal duct.
  Lachrymal gland.'—In the small  fossa, formed at the anterior
and outer  part of the arch of the orbit, is placed  the lachrymal
gland; it is small, and serves to  secrete the  tears.   This gland
was known to the ancients, and was called by them the glandula
superior innominata, in opposition to  the caruncula lachrymalis,
which  they called the  glandula  innominata inferior.   They
attributed  the  formation of tears, partly to  the  caruncula  and
partly to a gland that does not exist in  man, but is found in certain
animals, this is the gland of Harderus.
   Excretory ducts of the lachrymal  gland.—These  are six or
seven in  number.  They  arise from  the small  glandular bodies
that together form this gland.  After  having passed  through the
substance of the gland, they enter the conjunctiva,and pierce this
membrane very near the cartilage of the upper eye-lid, towards its
external extremity.   They may  be rendered visible  by  blowing
into them, or by raising the upper  eye-lid, and compressing the
gland, when the tears will be made to pass out of  the orifices of
the ducts.   This may likewise be  done by macerating them in
water tinged with blood, or by  injecting  them  with  mercury.
5 
34                      A  SUMMARY
 The tears are poured through these orifices, upon the surface of
 the conjunctiva.
   Caruncula lachrymalis.—At  the internal angle of the eye is
 seen  a small projecting, red  body, which  when it  is of a bright
 colour indicates  health  and vigour, when it. is  pale,  debility
 and disease; this is the caruncula lachrymalis.  This small body
 is composed  of seven or eight follicles, ranged  in a semicircular
 line, the convexity within; they  have each  an  opening on  the sur-
 face of the  caruncula  lachrymalis, and  contain  a small  hair.
 These openings are so disposed, that they complete, together with
 the meibomian glands, a circle embracing the  whole anterior part
 of the eye, when the lids are closed.
   Puncta lachrymalia.--At the  point where the eye-lids leave the
 globe of the eye to include the caruncula, on the internal surface,
 near the open edge, on each lid, is seen a small opening; these are
the puncta  lachrymalia, or  external orifices of the  lachrymal
 ducts.  The puncta are always open, with  their orifices directed
towards the eye.  It has been supposed that they possess a  con-
 tractile power, which  may be shewn by touching their  extremity
 with a pointed instrument.  Though I have often  endeavoured,
with great  care, to distinguish these  contractions,  yet I have
never succeeded.   One circumstance should be mentioned which
 is extremely apt to deceive us. When we unsuccessfully  attempt
 to introduce the style, the mucous membrane which covers  the
 puncta becomes soon irritated and  swelled, as would  occur from
 the same violence, at  any other part, when the opening  will  of
 course be diminished.  It is necessary  to distinguish  this  phe-
 nomenon from a contraction of the part.
   The lachrymal ducts arise from the puncta, and terminate in a
 canal extending from the inner canthus of the eye to  the  nasal
 fossae.  The  lachrymal ducts are  very narrow, scarcely suffering
 a hog's  bristle  to pass.   They are from three to  four lines  in
 length, and are placed in the thickest part of the eye-lid, between
 the orbicularis muscle and the conjunctiva.  They terminate some-
times singly,  and sometimes together, in the superior  part of the
 nasal canal.
   Lachrymal sac,  and nasal duct.—The  canal extending from
 the greater angle of the eye  to the inferior passage  of  the  nasal
 fossse, has  been improperly divided by anatomists in two parts. 
OF PHYSIOLOGY.
35
This canal is throughout of the same dimensions—there is nothing
therefore to justify the distinction that has been made, in calling
the upper  part   the  lachrymal  sac, and  the lower the nasal
duct.   This canal is alvvays formed by the mucous membrane of
the nasal fossae  which covers the osseous" duct, passes along the
posterior edge of the projecting apophysis of the maxillary bone,
and the anterior part of the os unguis.  Its use is to conduct the
tears into the rtasal fossee.
   The Membrana  conjunctiva.   This should  be  ranked  among
those organs which constitute the  apparatus  for  the  tears.  This
is a mucous membrane, which  covers the posterior surface  of the
eye-lids, and  is reflected over the anterior surface of  the  ball  of
the <<ye. It is more extensive   tl an the part it covers, and is there-
fore very favourable to  the motion of the eye lids and  the  eye.
The loose manner in which it is attached to the eye-'ids, and the
tunica sclerotica, greatly facilitates their movements. Whether the
conjunctiva passes over the  transparent cornea, or  stops  at  the
circumference of this portion  of  the  eye, and  is then connected
with a distinct membrane which covers this portion of the eye, is
not yet perfectly decided.  The general opinion is, that it covers
the cornea, but M. Ribes, a very  distinguished and expert anato-
mist, contends that  the  cornea  is covered by a  peculiar mem-
brane, united to  the conjunctiva at its circumference, without be-
in** a  continuation of it.  The conjunctiva protects the anterior
parts of the eye; it secretes  a fluid which mixes  with  the tears,
 and appears to have the same use; it likewise possesses the power
 of absorbing,* and, as it is very  smooth and moist, it greatly fa-
 cilitates  the motion of the  eye; lastly it  is the part in  contact
 with the  air, when it is not covered by the tears, of which we are
 now about to speak.

            Secretion of the  Tears and their  Uses.
    This is not the place where we intend to enter into  a  minute
•description of the secretion of the tears, and in what it resembles,
 or differs from other secretions.   It is sufficient here to remark,

   * We may poison  «n animal by applying to the conjunctiva poisonous substances.
 For this reason we  cannot agree with Mr. Adams, the celebrated London  Occu-
 lisf, who thinks that the Belladonna may be continually applied t« the eye with-
 out iaconvenience. 
36
A  SUMMARY
that the lachrymal gland forms them, and  that they  are poured
out, through its excretory ducts, of which we have  spoken, upon
the conjunctiva, at the outer and  superior part  of the eye.   We
shall next inquire  how they proceed, when they have arrived at
this part.  They are  poured  out, we would  observe  in  the  first
place, as well  when we are asleep as awake   In this last state,
the eye lids opening and  shutting alternately, the conjunctiva is
exposed to (he contact of the air, and the eye moves  continually,
neither of which happens during sleep.
   Physiologists have supposed  that the tears run along a  tri-
angular ranal, formed to conduct them towards the inner canthus
of the eye, where they were absorbed by the puncta.   This  ca-
nal, sav fhev, is lormed, first, by the edge of  the eye-lids, the sur-
fa< ts of which being convex, only touch at one point; and, second,
by the anterior face of the eye, which  completes  the triangular
cavity.  This canal has its external extremity more elevated than
its internal.  This arrangement, joined with  the action of the or-
bicularis muscle, the most fixed point of which  is attached to the
projecting apophysis of the os maxillare, directs the tears towards
the puncta lachrymalia.
   But this explanation is defective;  the eye-lids have not  a  con-
vex edge, at the part where they come in contact with each other,
but have plain margins; no such canals, therefore, can exist.   In-
deed, when  we examine the  eye-lids at their posterior surface,
when they are shut, it is  scarcely possible to distinguish the line
where they come  in contact.  But even admitting the existence
of such  a canal, it could serve as a duct for the tears, only durino*.
sleep, and it would still remain necessary to  show, ho'w  they are
disposed of when we are  awake.  During sleep, and  at all  times
when the eye-lids are elided, the tears spread by degrees over the
whole surface, both of  the  ocular  and palpebral  conjunctiva.
They wi.ll, of  course, pass in the largest quantities to  those points
where they meet  with the least  resistance.   The direction where
the resistance  is  least, is the part where  the conjunctiva passes
from  the eye to ihe eve-lids.  In this direction they arrive more
easily at  the  puncta lachrymalia.   The tears  which are  spread
over the conjunctiva, must become mixed with the secreted fluids
of this membrane, and be absorbed together. 
OF  PHYSIOLOGY.                   37
  But when we are awake,  they  do not pass off in this  way.
That  poiiion of the  conjunctiva which  is in contact with the air,
allows the tears which cover it to evaporate, and it would become
dry, if the moisture,were not renewed  by the action of winking.
This seems  *o be the principal use of winking.   The tears, which
thus constantly cover that part of the conjunctiva exposed to the
air. give to  the eye its polish and brilliancy.
  The increase or diminution of the tears influences very  much
the expression of the eyes.   During the excitement  of the pas-
sions, this is very apparent.   In the ordinary state  of the secre-
tion of the tears, they do not  tend, in any  way, to run over the
inferior eye-lid.  I know not how the idea has arisen, that the mei-
bomian humour is Mitended to prevent this,  except from the sup-
posed analogy of oily substances, which when placed on the edge
of a  vessel, prevent  aqueous  fluids from  running  over,  even
when they  rise somewhat above its level.  But  I doubt if this hu-
mour can have such an effect, as it is soluble in the tears.
  The tears which do  not  evaporate, or are not absorbed by the
 conjunctiva, are received  into the puncta, and  conveyed through
 the nasal duct to the nose.    What the power is by  which  this is
 effected, is not  certainly known.  It has been explained on the
 principle of a syphon, capillary attraction, vital properties, &c.
 That of capillary  attraction is,  perhaps,  the  most  probable.
 The  absorption of the tears  by the puncta is not very apparent,
 except when they are very abundant.

                    Of the  Globe of the Eye.
    The situation of  the eye, at the highest part of the body: the ca-
 pacity in man of discerning, at the same time,  with both eyes the
 same object; th^, oblique direction of the base of the orbit; the per-
 fect  protection afforded to  the eye by this cavity, from external
 injury; the great abundance of adipose substance  and cellular
 membrane, which form  an  elastic cushion at-the bottom of  the or-
 bit, &c are curious and  interesting circumstances, which  should
 not be neglected, but which we can only mention in  passing.
    The eye is composed of many different  parts, which perform
 very different offices in the function of vision.   They may be di-
 vided into the refracting and  non-refracting parts  of the eye. 
3S
A  SUMMARY
   The transparent  cornea is a  refracting body, convex on one
side and concave on the other.   In its  form,  transparency, and
mode of insertion, i-t greatly resembles the crystal of a watch.
   The aqueous humour, which fills the chamber of the eve, is not
a  pure watery fluid, as its name implies, but is chiefly composed
of water, with a little albumen.*
   The crystalline humour has been compared  to  a lens.  The
comparison is correct, as far as the form is concerned, but  is  very
defective as respects its structure.  The crystalline humour is
composed of concentric laminae, which increase in density as you
approach the centre, but differ in refrangibility; and  it is  envelop-
ed in a membrane,  which we know, from experience,  to be ex-
tremely important.   On  the other  hand, we know that a  lefts is
homogeneous throughout, and  that  its density  and  refrangibility
in all its parts are the same.   It has been always remarked, that
the convexity of the anterior  surface of the crystalline humour,
differs considerably from its posterior surface.  The last is a part
of a sphere, the diameter of which is much less than that to which
the anterior surface would belong.   It has been generally believed
that this humour was composed chiefly  of albumen; but, from  an
analysis lately made  by M. Berzelius, it appears that it contains
none.  It is formed almost entirely  of water, and a particular sub-
stance, which  has a  greater analogy, in  its  chemical properties,
with the colouring matter of the blood, than with any thing else.
   Behind  the  crystalline is found  the vitreous humour, which is
so called from its supposed resemblance  to melted glass.f
  Each of the parts which we  have pointed out, are  enveloped in
an extremely delicate,  transparent  membrane.  Thus, before the,
cornea is the conjunctiva, behind it the membrane of the aqueous
humour, which covers all the anterior chamber  of the eye; i. e. the
anterior surface of the  iris and the  posterior face of the cornea.
The crystalline is enveloped in its capsule, which adheres at  its
circumference to  the membrane  which  encloses the vitreous hu-
mour.  In passing from its circumference, over its  anterior and
  * According to M. Berzelius, it is composed of water, 98.10; a little albumen;
muriates and lactates, 1.15; soda with a substance only soluble in water, 0.75.
  t According to M. Berzelius, it contains water, 98.40; albumen, 0,16; muriates
and lactates, 1.4*2; soda with animal matter soluble in water only, 0.02; total, lOO.e*. 
OF  PHYSIOLOGY.
39
posterior surfaces, it leaves between the two lamina an interval,
called  the canal of Petit.  It has been generally supposed, that
this canal does not communicate with the chamber of the eye; but
M. Jacobson asserts,  that it presents  a great number- of small
openings, by means of which,  according  to him, the aqueous hu-
mour can enter in or go out;  but I have carefully sought in vain
to find these openings.
   The vitreous humour is surrounded by a membrane called mem-
brana hyaloidea.   This membrane not only surrounds the humour,
but is divided into innumerable cells, which are filled by it.  It is
not necessary to say any thing of the arrangement of these cells,
as this is not of importance in investigating the uses of the vitre-
ous humour.
   The eve is  not only composed  of refracting parts, but likewise
of others, which have each a peculiar destination.
   The tunica sclerotica is a strong fibrous  membrane, which con-
stitutes the external surface of the eye.   Its evident use is to
protect the  internal parts of  the organ; it likewise serves  as a
place of insertion to the muscles which move the eye.
   The  choroid coat abounds  with blood-vessels and nerves, and
is distinctly formed of two  laminee.   It is covered with  a black
substance, which  evidently performs  an  important  part in  the
function of vision.
   The iris is a small circular muscle, which may be seen moving
behind the transparent cornea.  It is of different colours, in dif-
ferent  individuals, and is  pierced in  its centre  by an opening,
called   the  pupil, which  enlarges and  contracts, according  to
circumstances, as we shall hereafter  point out.   The  iris ad-
heres anteriorly, at its  circumference, to the sclerotic coat by a
peculiar cellular tissue, which  is called  the ciliary ligament.  The
posterior  face of the iris is covered  by a b'ack substance  in con-
siderable abundance.   Behind the circumference  of the iris, are
a number of white, radiated lines, which would unite at the cen-
tre of the iris, if they were prolonged; these are the ciliary pro-
cesses.  Anatomists are not yet agreed as  to the nature and uses
of these bodies.  Some consider  them nervous, others muscular,
and others again glandular, or vascular.  The truth is, at present
it is not easy to decide which of these opinions is most probable;
and we shall, by and by, see that their use  is equally unknown. 
40
A  SUMMARY
  The colour of the iris depends on  that of its  tissue, whir.h is
variable, and that of its posterior surface, which is of a dee;; black,
and affects the appearance of its anterior lace.  In blue eye*, for
example, the tissue of the iris is nearly wi.ire, but the deep black,
on the posterior part, modifies this, and determines the colour of
the eyes.  Anatomists vary in their opinions of the nature of the
tissue of the iris,  .^ome consider it similar to that  of the choroid
coat,  that is, they  supi ose  it  to consist chieliy of  vessels and
nerves; others think they can distinguish a great number of mus-
cular  fibres; it has by  some  been  thought  a tissue sui generis;
and  by others confounded  with  the  erectile tissue.  M. Ed-
wards thinks that he can  demonstrate the iris  to be formed of
four distinct laminae, of which  two are a continuation of the la-
minae of the choroid coat, a third pertains to the membrane of the
aqueous humour, and a fourth that  forms  the peculiar tissue  of
the iris.
  Between the membrana hyaloidea and  the  choroid  coat, there
is a membrane chiefly composed of nerves-.   This  is  known by
the name of retina;  it is nearly  transparent, with a very slight
degree of opacity, and appears to be formed by the expansion of
the optic nerve.   M. Ribes, however, thinks differently; he  sup-
poses  it is formed of a distinct membrane,  upon which the optic
nerve is very freely distributed.  There is upon the back part of
the retina, about two lines from the  opfic nerve, a yellow' spot,
and at the side of this there are several fohls.  But these appear-
ances are only found in man, and some species of apes   The eye
receives a large  number of blood-vessels, and many  nerves, the
greater part of which come from the opthalmic ganglion.

                      The Optic Nerve.
  This  is the medium of communication  between the eye and
the brain.   It does  not arise  from  the thalamus nervi  optici,
as many anatomists have thought, but  it derives  its  origin, 1st
from the anterior pair of those tubercles called the quadrugemini;
2nd, from the corpus geniculatum externum, an eminence found
before, and a little to the outer side  of, these tubercles; 3d, from
the laminae of cineritious substance, placed  before the meeting of
the optic nerves, and mamillary eminences, and which  is known by
the name tuber cinereum.  The two  optic nerves approach each 
                      OF  PHYSIOLOGY.                  -41

other,  and  seem to intermix  together  near the superior part
of the sphenoid bone.  The most careful researches  have been
made,  for  the purpose  of ascertaining  if they  decussate, are
in contact, or if  they really intermix with each  other.  Patho-
logy furnishes proofs of all these opinions.  Thus, when the right
eye has been long diseased, the optic nerve of the same side has
been  known to become diseased through its whole extent.  In
another case, where the right  eye was diseased, the anterior por-
tion of the  same side was  found in an evident state of disease,
and the posterior portion of the  left side to present the same ap-
pearance.   Some  have thought, that the crossing of the optic
nerves in fishes, removed every doubt on the  subject; but this can
only be, justly, considered  as amounting to a probability.
   The optic nerve is not formed of  a fibrous envelope, and of a
central pulp, as the ancients believed; but it  is composed of very
fine filaments, placed at the side of  each other, aiid communica-
ting with each other, like other nerves. This  arrangement  is very
evident in that portion of the nerve which extends from the sella
turcica, quite to the eye.

                  Of the Mechanism of Vision.
   To  facilitate the explanation of the manner in  which the light
enters the eye, let  us suppose  a single luminous beam, passing
from a point placed at one  end of a straight line,  which will pass
through the anter*to%-posterior axis of the eye.   We  perceive at
once that there is no other light, but that which falls upon the cor-
nea, that can assist in vision.  That which falls upon the white
of the eye, the eye-lashes, or the eye-lids, can evidently  contri-
bute nothing to this effect.   It is reflected differently, from differ-
ent parts, according to the colour.   The cornea itself does not
receive light through its whole extent, for it  is, generally,  partly
covered above and below by the open edges of the eye-lids.

                      Uses of the Cornea.
   As the cornea is highly polished at its surface, the moment the
 light arrives there,  a part of it is reflected, which contributes  to
 give brilliancy to the eye.  It  is this  which forms the  images
 we observe on the cornea, as it then performs the office of a con-
 vex mirror.   The form «f the cornea shews the eiuct it must have
                                6 
42
A  SUMMARY
 upon the light which  enters into the eye; in consequence of its
 little degree of thickness, it causes  the  rays  of light to converge
 a little toward the axis of the beam.   J n other words, it increases
 the intensity of the light  which penetrates into the anterior cham-
 ber.

                Uses of the Aqueous Humour.
  In traversing the cornea, the rays  of  light have passed from a
 rarer into a denser medium, consequently they are drawn towards
 the perpendicular.  If they  passed out into the air, instead of en-
 tering the anterior chamber of the eye, they  would be refracted
 from the perpendicular, which they had before approached, and, of
 course, would  return  to  their first  degree of  divei^ence.  But
 they enter into the aqueous humour of the eye, a  denser medium
 than the atmosphere;  and are, therefore, less  refracted from the
 perpendicular, and of course diverge less,  than if they had return-
 ed into the air.
  Of all the light entering into the anterior  chamber of the eye,
 that which passes  through the pupil  alone assists  in  performing
 the function of vision.  All  that falls upon the iris is reflected
 across the cornea,  and enables us to distinguish the colour of the
 iris.  The light does not  undergo any new modification in passing
 through the  posterior chamber of the eye, as  the  medium is still
 the same.
               Uses of the Crystalline Humour.
  It is in passing through the crystalline  humour  that  light  un-
 dergoes the  modification  which is most important in the function
 of  vision.  Physicians compare the action of  this  body to that of
 a lens, the use of which is to collect together the rays of light up-
 on a certain part of the retina.   But as  it is very necessary that
 the crystalline humour should have the  lenticular form, wre shall
 confine ourselves  to  simply announcing this  commonly received
 opinion; observing, at  the same time, that  it  is  highly  important
that the subject should be further investigated.  All that can be
positively said  on the subject is, that the  crystalline humour must
 increase the intensity of the light which it directs to the bottom
of the eye, in a much greater degree, from  the circumstance of
 the posterior being more  convex than the anterior surface.   It
 nay likewise be added, that  the  light which passes near the cir- 
OF  PHYSIOLOGY.                   43
cumference of the crystalline  humour, is probably  refracted dif-
ferently from  that  which passes through the centre.  Of conse-
quence the dilatation or contraction of the pupil,  must have an
influence upon the mechanism of vision, which appears to deserve
attention.
  All the light that strikes on the anterior surface  of the crystal-
line, does not pass into the vitrpous humour, but is partly reflected.
A part of this reflected light returns through the aqueous humour
and  cornea, and contributes to form  the  brilliant appearance  of
the eye; another part strikes  upon the posterior surface  of the
iris,  and is absorbed by the black matter which is found there.  It
is probable that some degree  of reflection is produced by each of
the laminae forming this humour.

                 Uses of the Vitreous Humour.
   The vitreous humour possesses a less  degree of refracting pow-
er than the crystalline; of consequence the rays of light  which,
after having traversed  the crystalline, penetrate into the vitreous
humour, are drawn  from the perpendicular at the point of con-
tact.  Its use, then, as respects the direction of the rays in the eye,
is to diminish their convergency.  It may, perhaps, be said that
nature might have arrived at  the same result,  by diminishing the
refractive power of the crystalline humour.  But the presence of
the  vitreous humour in the  eye has another and more important
use; it is to allow a sufficient extent for  the expansion of the  re-
 tina, and thus greatly to extend,  the field of vision.  What  we
 have thus said of a beam of light passing from  a point placed in a
 prolongation of the anterior-posterior axis of the eye, will apply
 with equal truth, to beams passing from every other point, towards
 the  eye, with only this difference; that, in the  first  case, the rays
 tend to unite at  the centre of the  retina, while, in the  other  in-
 stance, they have a tendency to unite at some other point, accord-
 ing to the direction from which they proceed.  Thus, those which
 pass from below, upwards, unite at the superior part of the retina,
 and those which come from above, unite at the inferior part of this
 membrane.  The rays of light thus, form, at the bottom of the eye,
 an exact representation of  each of the objects which are placed
 before it, but with this difference,  that the images  will have a  po-
 sition the reverse of the objects they represent. 
44
A  SUMMARY
  Different methods have been  had recourse  to, to establish this
point.  For a long time experiments  were made with eyes artifi-
cially constructed.  Glass was made to represent the transparent
cornea, and crystalline humour, antl water the aqueous and vitre-
ous humour.  Another mode was  generally employed, before the
publication of my memoir "On the images formed  at  the bottom
of the eye."   It consisted in placing in an aperture  of the window
shutter of a darkened room, the eye of some animal, as for example,
that of an ox or sheep, having first carefully removed the poste-
rior part  of the sclerotica.   There could then  be seen, very dis-
tinctly, upon the retina, the images  of objects placed in such a
manner as to transmit the rays through the pupil.
  I  had  recourse to  a  much more  convenient method  for ac-
complishing this  purpose.  1 took the eyes of rabbits, pigeons,
snail dogs, or  ducks, in  which  the choroid and  sclerotic  coat
are  nearly transparent;  I then removed, carefully,  the  fat and
muscles,  and by directing  the transparent cornea towards  bril-
liant objects, 1 saw distinctly the  images of those objects formed
upon the  retina.  This process was known to Malpighi and  Hal-
ler; the  only circumstance  peculiar to  myself in  this  respect
consists in  my  having selected for  this  purpose  white  rabbits,  m
white pigeons, and white mice;  the eyes of-albinos would proba-
bly  be found equally good.   These will be found much the  most
favourable to the success of this experiment.   The sclerotic coat
is thin, and almost transparent; the choroid  is equally thin, and
as soon as the animal  is dead, the blood which coloured it disap-
pears, and ceases to offer any  perceptible obstacle  to the  passage
of the light.
  The ease and distinctness with which we are thus enabled to
perceive  the images, suggested to  me the idea of making some ex-
periments,  which might  confirm or invalidate the  commonly re-
ceived theory of the mechanism of vision.
  If we  make a small opening in the transparent cornea, and al-
low a small portion of the aqueous humour to escape, the distinct-
ness of the image becomes lost.   The  same  thing  takes  place
when we suffer  a  portion  of 4he vitreous humour to escape, by a
puncture through the sclerotica, which shews that the proportions
of the aqueous and vitreous humours are  such  as to be necessary
to perfect vision.  I have likewise endeavoured to  determine the 
OF  PHYSIOLOGY.                  45
laws of the dimensions of the image, relatively to the distance of
the object;  and I have found that the size of the image  is percep-
tibly  proportional  to the distances.   M. Biot had the  politeness
to confirm  with me this result, which is likewise conformable to
that given by  Le Cat, in his "Treatise on Seasations."   This au-
thor employed artificial eyes in his experiments.
  'I-made  a small  opening at  the circumference  ot the cornea,
near its  junction with the sclerotic coat, and evacuated all the
 aqiuous humour through this aperture.  On  presenting the cor-
 nea towards a  lighted candle, the i.nage appeared to me, other
things being equal, to occupy a much larger  space  than before.
The  image was evidently less distinct, and formed by a  light
much less intense  than  that of the same body, seen in the  other
 eye o! the same animal, that I had placed in a similar situation
 with  respect to the candle, but which I had  preserved whole, for
 the purpose of making the comparison.  This experiment agrees
 with  what we have before said  of  the use of  the aqueous humour,
 in the mechanism  of vision.
   The same  effect wilf'be  produced by removing the  cornea.
 When tins is  done by a circular incision,  made at the point where
 it  unites with  the  sclerotic coat, the image will not  appear to
 change its dimensions, but the light  which  forms  it, loses very
 sensibly its intensity.   We have before remarked  that the size of
 the opening of the  pupil probably influences, to  a  considerable
 degree, the mechanism of vision  After having removed the cor-
 n»a. it is easy to enlarge the  pupil, by a circular incision  made
 into the tissue of  the iris; the image in this case becomes enlarged.
    As the  use of the crystalline humour  is to increase the brilli-
 ancy and distinctness of the image, diminishing at the same time
 its size, we on^ht to expect that the  absence of this body  would
 produce  a reverse effect.   When  we  extract, or  depress this
 humour, by  a process similar to the operation for cataract, the
 image is always formed at the bottom  of the eye, but it is considera-
 bly increased in size. It becomes at least four times larger than that
 produced in  the entire eye, under the same  circumstances.   The
 image is  likewise very indefinite, and  the  light produced very
 weak.  Take away from the same eye the  aqueous and crystal-
  line humours, and  the transparent cornea, and  leave  nothing of
  all the media ef the eye but the  capsule  of the crystalline lens, 
46
A  SUMMARY
and the aqueous  humour, and it will be  found that there is no
longer any image formed upon  the retina.   The light still  passes
very freely, but it no longer affects a particular form, in relation
to that from which it emanates.
   The  greater part of these results agree  very well  with  the
theory of vision, generally admitted at the  present day.   There
is  however, one  point  in  which they differ  essentially.  From
theory we are led to  infer, in order that  the  image may  be dis-
tinct, it is necessary that the form of the eye should vary, or that
the crystalline humour should be carried backwards, or forwards,
according to  the distance  of the object.  These changes  which
have been assumed actually to  take place,  have, by turns, been
attributed to the compression of the  globe of the eye by the recti
and oblique  muscles which  move it, to the  contraction  of the
crystalline humour, or to the  action of the ciliary processes.   Of
late M. Jacobson has asserted that, this effect was produced  by the
aqueous  humour,  entering or passing out  of the canal of Petit.
Now experience contradicts  this theory, and of course all these
explanations fall to the ground.
   It would be very incorrect however, to assert, that every thing
took place in the eye of the living, precisely, as it does in tha?  of
the dead  animal.  There  is this essential difference, that  in the
living animal the pupil dilates or contracts, according  to the in-
tensity of the light, and perhaps according to the distances of ob-
jects.  Observation  shews that  when the light is very brilliant,
the pupil contracts almost to a point, so that the opening can be
scarcely distinguished, which must have the effect to diminish the
size of  the  image.  On  the contrary, when  the  light passing
from  any object  is very  inconsiderable, the pupil dilates very
much, which must produce an enlargement of the image.

                     Motion of the Iris.
   Some assert that the pupil varies  its dimensions according to
the distances of  objects;  but this  point cannot be  considered as
satisfactorily ascertained.  The only circumstance which can be
considered as fully established, in the motion of the  iris,  is the
influence exerted upon it by the intensity of the light.
   The mechanism of the  motions of the iris, has occupied much
*>f the  attention  of physiologists.  Some have supposed it  was 
OF PHYSIOLOGY.
47
composed  of muscular  fibres, and have  explained the motion of
this membrane by the action of its fibres; others have considered
it as being of a peculiar nature.  Mery  and Haller  have refered
its motion  to erection.  According to them the motion  of the iris
is excited  by the sympathetic action of the light upon the retina*
Of  late M. Maunoir, of  Geneva, has distinguished in the iris two
sorts of fibres;  the one  which occupies  the circumference of the
iris, he  calls radiant; the other irregularly  concentric, forming
the  center of the membrane, he calls  the muscle  of the pupil.
M. Maunoir asserts that these fibres are muscular, but brings no
satisfactory proof to support this opinion.*
  It is said that certain individuals have possessed the power  of
controling the motions of the iris by  the will, and  it is  asserted
by  naturalists, that many  birds, such  as parroquets and night
birds, present the same phenomenon.
   A beam of light directed upon the  iris does not cause any mo-
tion of it, which seems to shew, that  the nerves of this part be-
long to the  ganglionic system.  A  section of it, which  is some-
times made  in surgical  operations, is  not painful; but has some-
times been followed by vomiting.   The irritation of the iris with
the point of the needle, in the operation for  cataracts, does not
cause any sensible motion in this membrane, as I have ascertained
from experience.
   Messrs. Fowler  and Ilinhold,  have  found  that  the  galvanic
fluid, when directed  upon the eye of man, and other animals, is
 followed  by contractions of the  iris.   Dr. Nysten  has  likewise
 witnessed the same effect in  the  bodies of criminals, recently
 executed.—But  must  we therefore  necessarily conclude with
 these authors that the movements of  the iris  must  be the result
 of muscular motion? I think not.  In these experiments the retina,
 as well as  the  iris, has  been submitted  to the  influence of the

    *  It has been remarked that the  pupil is very much  enlarged in per-
 sons debilitated by excessive venery and  by those affected with engorgement of
 the abdominal vescera, hydrocephalus, intestinal worms. &c. A single applica-
 tion of certain narcotic plants upon the conjunctiva, particularly the  Belladonna,
 dilates the pupil for  several hours; it is  likewise remarked that in cerebal affec-
 tions, the pupil is either very much enlarged or very much contracted.  The mo-
 lions of the pupil are  in general an index to  the  sensibility of the retina.  At-
 tention to thf motions and state of the iris, is vrry useful in medicine. 
48
A  SUMMARY
galvanic fluid; and they do not prove therefore that the contrac-
tion of the iris was not the result of irritation upou the retina.

               'Uses of the  Choroid Coat.
  The principal use  which this serves in  vision, is absorbing the
light, immediately after it has passed through the retina, by means
of the black matter with  which it is  impregnated.  The effects
found to be produced by a varicose  state of the vessels of this
membrane, must be considered as  a confirmation of this opinion.
In those individuals  who are affected by this disease, the dilated
vessels  remove the black matter with which it is covered, and
every time that the image of the object  falls  upon that  point  of
the retina which corresponds to these vessels, the  object appears
to be spotted red.  The state of vision in certain  white  animals,
and in albinos, where the choroid coat and  iris are not coloured
black,  strongly  sustains  this  assertion.  In them vision  is ex-
tremely imperfect during  the day, so that they can scarcely  see
how to direct themselves.
  M. Le Cat, and some others, have attributed  to  the  choroid
coat the faculty of perceiving light, but this opinion is completely
destitute of proof.

               Uses of the Ciliary Processes.
  There have been no opinions advanced concerning  the  use of
these parts, but  what  are extremely vague and  unsatisfactory;
they are generally  believed to be  contractile.   Some  suppose
that they are destined to  move  the iris, and others to  move for-
ward the crystalline  humour.   M.Jacobson  asserts that  their use
is to dilate the openings  which, according  to  him, the  canal  of
Petit presents anteriorly, for the purpose of allowing the aqueous
humour to enter, or be discharged from this canal, which  would
have the effect to displace the  crystalline  lens.   Some  persons
imagine  that the ciliary  processes are secretory  organs, for  the
production of the black pigment found on the posterior surface of
the iris, and on  the choroid coat, or even of a part of ,the  aqueous
humour.  Mr. Edwards, in a Memoir on the  Anatomy of the Eye,
asserts that they contribute chiefly to the secretion of the aqueous
humour, an opinion  before advanced by  Dr. Young, secretary to
the  lloyal  Society of London, in the Philosophical Transactions. 
                      OF  PHYSIOLOGY.                   49

M. Ribes has promulgated  a similar opinion, with this  difference,
"he supposes that the ciliary processes maintain life and  motion
in the  crystalline, and vitreous humours."  But  there are many
animals which  have no ciliary processes, in  which  the humours
exist.   Haller  supposed  that  they  preserved  the  crystalline
humour  in  the most  favourable  situation.   According  to  this
anatomist, they adhere to the capsule of this humour, both  at their
points and posterior side, by means of the black matter with which
they are covered.

                     Action of the  Retina.
   If we speak here singly of  tlv- action of  the retina in vision,
it is only to facilitate the  study ol this  function.  In reality  no
distinction  exists  between  the  action of  this membrane, and
that of  the  optic  nerve,  much less  of the  sensorium.   The
action of the retina  is  a vital  action,  and  its  mechanism is
completely unknown.  The retina receives the impression  of light*
when  it exists  within  certain  limits of  intensity.  A weak  light
makes no impression upon the  retina,  and  a very  strong  light
disables it from acting.  When too  brilliant  a light  strikes  sud-
denly upon the retina, the effect produced  is  called dazzling;
and the  retina remains for some moments afterwards incapable of
 perceiving  the presence  of light.   This effect is  produced  by
 looking steadily at the sun.  When  we have  remained a long time
 in darkness, even  a weak light  dazzles us.   If the light which
 falls upon the eye  be  extremely weak, and if we still endeavour
 to examine objects, the retina becomes very much fatigued, and
 we soon  feel a sensation  of pain in  the  orbit,  and even in the
 head.
   A light, the  intensity of which is  not very great, but which acts
 during'a certain time on a fixed point of the  retina, causes insen-
 sibility in that point.  If  we fix  for some  time  a white spot upon
 a black surface, and if we then suddenly turn our eyes to a white
 surface, we  seem  to see a black spot.  It is because the retina
 has become  insensible  at the  point  which had  been  fatigued
 by looking at the white spot.  On the other hand when the retina
 has been for  a long time without  acting, in some of its points,
 whilst the others  have acted, the point  which has remained  in a
 State  of repose, becomes possessed of a much greater vde-ree of 
50
A  SUMMARY
sensibility, which causes objects to appear as if they were spotted.
We may explain in this manner how it happens that, after having
viewed  red objects for some time, white bodies appear  spotted
with green.  In this case the retina  has become insensible to the
action of the red ray, and it is well known that when the  red ray
is taken from a beam of  light, it  produces the sensation of green.
Similar  phenomena occur when  we  look for some time on a red
body, or those of any other, colour, and then look suddenly upon
white, or other coloured surfaces.
  We are  enabled to distinguish, with great accuracy, the direc-
tion of  the light which is received upon the retina.   We  believe
instinctively that the light passes in a right line, and that this line
is a prolonga'on of that pursued by the ray, which has entered the
cornea.   Whenever the light, before arriving at the eye, has  been
modified in its course, the impression produced  upon the retina is
inaccurate.  This is a principal  source of those illusions which
often  take place in  vision, and which are therefore  called optical
illusions.
  The retina may receive at the  same time impressions over its
whole extent,  but  then the sensations  which  result  from it  are
very imperfect.   It can only be strongly affected by the image of
one. or two objects, although a much  greater number are painted
there.
  The centre of this membrane appears to enjoy a more exquisite
sensibility than its other  parts.   It is on this part that we  rec ive
the image,  when we wish to examine  an object with attention.
  Does  light act by simple contact with the retina,  or is its pecu-
liar effect  produced  by  traversing this  membrane?   The  pre-
sence of the choroid, or  rather of the  black matter  covering it,
inclines  us to the latter opinion.  It has  been  said that   the
place  that corresponds to the centre of the optic nerve  is insensi-
ble to the impression of light.  1 do  not know of any fact which
directly proves this assertion.  I much  doubt  whether the experi-
ment  of Mariote, which is generally spoken of in medical  books,
be correct; but if it were, 1 think it would  be very  wrong to  con-
clude from this that  the return is insensible  at  the point  which
correspond* to the centre of the optic nerve. 
OP PHYSIOLOGY.
51
                Action of the Optic Nerve.
  There can be no doubt  that the  optic nerve transmits to the
brain, instantaneously, the impressions  made upon the retina by
the light; but we  are absolutely ignorant  of the mode in which
this ts done.  The  manner  in which the two optic nerves run
together, near the sphenoid bone, without doubt, must have a great
influence upon the transmission  of impressions  received by the
eyes.   But it  is not Casy to decide, among the  various opinions
winch have  been advanced on this  point, which is best, a= they all
have some degree of probability.

                     Action of both  Eyes.
  Notwithstanding what has been  sail at different periods, and
the efforts which  have of late been made by M. Gall to prove that
we only see  with one eye at a time; it  apppars to  me to be de-
monstrable,  not only that both eyes concur at the same  time  in
vision, but that it is absolutely necessary that they should act thus
for the  perfect  performance of certain  important acts of this
function. There are however circumstances in which it is  con-
venient to employ but one eye.  For  example, when we wish  to
judge  correctly  of the direction  of  light," to take  aim with  a
gun,  or  to  ascertain if  bodies  are  on a level, or  in a right
line.  There is another situation where  it is convenient to employ
but one eye, it  is when the two organs  are. unequal, either in re-
fractive  power or sensibility.  It  is for the same  reason that we
shut one eye, when we look  through a magnifying glass.
   But with  the exception of these  cases, it is  much more  effectual
to use both  eyes at the same time.    The following experiment of
my own, appears to me to prove  that both eyes see at  the same
time  one object.   Receive into  a darkened  chamber a  beam of
light  upon a plain surface; then take  glasses  of sufti  ient  thick-
ness, each of which  presents one of  the prismatic  colours, and
place them  in  turn   before  the  eyes.   If  the  sight  be good,
and especially if both eyes possess equal power, the  image will
appear  of a dirty white colour, whatever may be the colour of the
glass you employ.  But if one of the eyes be much stronger than
the other; you will see the image of the same colour as the glass.
These results have been confirmed in  the presence of M. Tillaye,
in the cabinet of  physic, of the Faculty of Medicine.  The same 
52
A  SUMMARY
object then produces two impression^, while the brain  perceives
but one: but for this purpose it is necessary that the motions of the
eyes should be in harmony. If, in consequence of disease, the regu-
lar motions of the eyes be interrupted, we then receive two impres-
sions instead of one; and this it  is which constitutes strabismus.
We may likewise voluntarily receive two  impressions instead of
one; we have only to interrupt the harmony in  the motion of the
eyes to  produce this effect.

           On  estimating the  distance of Objects.
   Vision  is essentially  produced by the contact of light with the
retina,  though we are constantly in the habit of referring the cause
of the sensation to the  bodies from which the light passes,  not-
withstanding they  are at a great distance.  It  is plain that this
must be the effect of an intellectual en or.
   Our judgment of the  distances of bodies is very materially af-
fected by  the  distance.  We judge  with accuracy when they
are near us; but it is not so when they are very remotely situ-
ated; then our judgment  is  often most erroneous; but, when ob-
jects are at a very "great distance, we are constantly in error.
   The united action of  both eyes is absolutely necessary to judge
exactly  of the distances of objects, as may be proved by the follow-
ing experiment.   From  a thread suspend a ring, then fix to a rod
a hook,  which will  readily enter the ring.   Place yourself  at a
convenient distance, and endeavour to introduce the hook-   If you
use both eyes, you will readily succeed at each attempt;  but if you
shut one eye, and then endeavour to hook the  ring, you will fail.
The hook will  either go beyond, or fall short of the ring,  and it
wiU  only be, by accident, and after mar.y  fruitless attempts,  that
the hook will be introduced.   Persons whose eyes possess une-
qual power, will not succeed in this experiment, even when they
use both eyes.
   When a person loses  one eye by accident, it often  happens that
they will not be able to judge accurately of distances for more than
a year.   1  once saw a remarkable case of this kind, where the
person,  for several months  afterwards, had to make several at-
tempts before he could seize those objects which were  placed, even
xmy near to him.   Generally speaking, persons who have but one
eye judge very  inaccurately of  di&tances.   The  size of objects, 
OF  PHYSIOLOGY.
53
the intensity of the light which passes from them, the presence of
intermediate objects, &x. influence very much the accuracy of our
judgment with respect to the distances of objects.   Our judg-
ment is much  more exact when  the  objects are placed, on the
same plane  with ourselves.   'Thus  when  we look from  a hi^h
tower upon objects situated below, tlu-y appear to us much small-
er than when the\  are. viewed on the same plane with ourselves.
The same observation applies to objects placed far above us; and
from this we  see  the necessity of giving a considerable volume
to those objects which we place in elevated situations, for the pur-
pose of being seen at a distance  The smaller the object, the more
necessary it is  that it should be placed near to the eye, to be seen
distinctly.   'That which may be called the point of-distinct c'a-ion,
varies very much.   We see distinctly a horse  at  thirty  feet dis-
tance, but we do not see a bird distinctly  at the  same  distance.
If  we wish to  examine a hair, or feather of these animals, they
must be  brought  very near to the eye.  At the same  time, the
same objects may be seen with equal  distinctness at different dis-
 tances.,  For example, it is indifferent to many persons whether
they place a  book,  when  reading, at the distance of one or two
feet from the eye.   1 he  intensity of  lignt thrown upon an  object,
influences, very materially, the distance at which the object may
be seen distinctly.

              On  estimating  the size  of Bodies.
   The correctness of our judgement respecting the size  of bodies
 depends  more upon sagacity  and habit, than upon the particular
 action of the apparatus of vision.   We form our judgment, of the
 dimensions of bodies, from the size  of the image formed at the
 bottom of the eye, the. intensity of  the light which  passes from
 the object, the distance at  which we suppose it to be placed, and
 especially from our  habit of seeing similar objects.  This is the
 reason why  our judgment of the size of bodies (hat we see  for
 the first  time,  is so faulty, when  we do not know the distance.  A
 mountain, seen at a distance for the first time, appears to us gene-
 rally  much  smaller than it really  is, because  we  think it to be
 much nearer than it actually is.  Beyond a very inconsiderable
 distance, we  fall into an illusion  which  the judgment  cannot
 overcome.  That objects at a distance appear infinitely smaller 
54
A  SUMMARY
than they actually are; is sufficiently evident from the appearance
of the celestial bodies.

            On  estimating  the  motion of  Bodies.
   We judge of  the motion of bodies, by that of the image  upon
the retina and by the variations of the size  of this image; or what
amounts to the same, thing, by the change in direction of the light
which arrives at  the eye.
   In order that we may follow the motion, it is necessary that  the
image should not be displaced too rapidly, for then we cannot per-
ceive it.  This is the case with projectiles thrown by fire  arms,
when they pass very near us;  but  when they move at a distance, if
they be of considerable size, as they are exposed for a much longer
time to the eye, the field of vision being greater, we can then dis-
tinguish them.  To jud^e  correctly of the motion  of bodies it is
necessary that we should ourselves  be at rest
   We  distinguish, with difficulty, the motion of bodies which are at
a  distance,  especially if they approach us.   Indeed in this case
we can only  form our judgment of the motion of the body,  by
the variation in the size^of its image.   Now  this variation  being
infinitely  small,  when the body is  at a distance, it is extremely
difficult, and often absolutely impossible, to appreciate it.
   Generally, we distinguish with great diffk ulty, and often we can-
not perceive at all, the motion of birdies which are displaced very
slowly.  This may arise from the real slowness of  the motion, as
in the case of the hand of a watch, or it may arise from the slow-
ness with which  the  image moves  over the retina, as that of the
stars and very distant objects.

                      Optical Illusions.
   From what has been said of the manner that we judge of the
distance, size, and motion of objects, it is easy to perceive that  we
are exposed to numerous errors.  These errors are distinguished
in science by the name  of optical  illusion*.  We  judge, for  the
most part, with  sufficient accuracy of those objects  which are pla-
ced near to us, but are frequently deceived with respect to those
 which  are at a distance.   The illusions into which we  fall, with
 respect to  neighbouring objects, arise  either from the reflection,
 or refraction which the light undergoes, before arriving at the  eye, 
OF PHYSIOLOGY.
55
and to that law which we instinctively establish in our own mind,
namely, that the li<rht passes from the obiVct to the eye in a straight
line.  Tt is to this cause that we must refer the illusions occasion-
ed by mirrors.  We see the object behind the mirror,  in a  prolon-
gation of the line that the ray describes, in directly approaching the
eye.  To this cause must be referred the apparent increase or dim-
inution  of volume  of bodies, seen  through glass.   If the rays are
made to converge, the body will appear to us  larger;  iftodiverge
it wiil appear smaller.   'The use of these  glasses produces  another
illusion.  The objects appear surrounded by the different colours
of the -solar  spectrum, because the surfaces of  glass not being
parallel, decompose the rays of light in the manner of a prism.
  Distant  objects are constantly producing illusions, which  we
cannot prevent, because they necessarily result from certain laws
that govern the animal economy.   An object appears so much the
nearer to us, as its image occupies a more considerable space up-
on the retina, or as the light  passing from it is more intense.  Of
two objects,  of different volume, equally brilliant, and placed at
equal distances, the largest will  appear the nearest;  unless there
be some accidental circumstance  that enables us to judge more
correctly.  If  two objects of equal  volume, be  placed at equal
distances from the eye, but  are  unequally bright, the most bril-
liant will appear the nearest; they will seem  as  if placed at un-
equal distances.   This  any  persons may  convince  themselves
of by observing  a  row of reflectors;  if the  light  of  one be
more intense  than the  rest, it  will  appear the first  of the  row,
while that which is really fiist, will appear last,  if it  be less
bright.   An object which is so placed as  not to  have any thing
between our  eye and it, will  appear nearer than when this is not
the case; the reason of which is,  that intermediate objects enable
us to  compare distances, and thus to form a more exact judgment.
  When our eye is  struck by a  bright object, while those sur-
rounding it are enveloped in darkness,  it appears much  nearer,
than it in reality is.   Every, one  must have noticed this effect of
a single  light at night.  Objects appear  smaller according to
their distances; thus the trees in  a long avenue appear to us to
grow  smaller and approach each  other,  when they are at a con-
siderable distance.  It is by attending to these various sources of
illusions, and the laws of the animal  economy in which they are 
56
A  SUMMARY
 founded,  that artists are enabled to produce  them at pleasure.
 The painter, for example, in many cases, does nothing more than
 transfer to his canvas those optical  illusions into which  we are
 constantly failing.  The construction of optical instruments is al-
 so founded on these principles.   Some augment  the intensity of
 the light; others, by  rendering it divergent,  or  convergent, in-
 crease or  diminish the apparent volume of objects, &c. &c.
   There are some optical illusions which we are  able  to remove
 by experience and the exercise of the other senses.  The  follow-
 ing extremely curious history of a  blind  man restored to sight,
 related by the  celebrated surgeon Cheselden, is  strikingly illus-
 trative of this:—■
  "When he first saw, he was so far from making any judgment
 of distances, that he thought all objects whatever touched  his
 eyes,  as he expressed it, as what he  felt did his skin, and thought
 no objects so agreeable as those which were smooth and regular,
 though he could form no  judgment of  their shape, or guess what
 it was, in  any object, that was pleasing to him:  he knew not the
 shape of any thing, nor any one thing from another, however  dif-
 ferent in shape or magnitude: but upon  being told  what things
 were, whose forms he before knew by feeling, he would carefully
 observe, that he might know them again;  but having too many ob-
jects to learn at once, he  forgot  many of  them; and,  as he said,
 at first he learned to know, and then  forgot a thousand things in
 a day.  One particular only, though it  may  appear trifling, I will re-
 late: having often forgotten which was the cat, and which the do°*,
 he was ashamed to ask;  but catching the cat,  which he knew by
 feeling, he was observed to look at her steadfastly, and, then  set-
 ing her down, said, so puss, I shall know you another time.   He
 was very much  surprised, that those  things which he  had liked
 best, did not appear most agreeable  to his eyes, expecting those
 persons would  appear  most  beautiful  whom he loved most, and
 such things to be most agreeable to his sight that were so to his
 taste.   We  thought he  soon knew  what  pictures represented,
 when  showed to him, but  we found afterwards that we were
 mistaken;  for about  two months after he  was couched, he dis-
 covered that they represented solid bodies, when, to that time, he
 considered them as  party-coloured planes, or surfaces diversified 
OP  PHYSIOLOGY.
57
with variety of paint, but even then  he was  no less surprised,
expecting the pictures would feel  like the things they represent-
ed, and was amazed when he found  those  parts, which by their
light and shadow appeared now round and  uneven, felt only flat
like the rest, and asked, which was the lying  sense, feeling or
seeing?  Being  shewn  his father's picture, in  a locket in his
mother's watch, and told what  it  was, he acknowledged a like-
ness, but was vastly surprised; asking, how it could be. that a large
face could be expressed in so little room, saying, it  should have
seemed as impossible to him, as to put a bushel  of any thing into
a  pint. At first he could bear but very little light, and the things
he saw he thought extremely large; but upon seeing things  larger,
those first seen he conceived less; never being able to imagine any
lines beyond  the bounds he saw;  the room he was in, he «aid, he
knew to  be but part of the house, yet he could  not conceive that
the whole house could  look any bigger.
   "When couched  of his other eye, he says,  that objects at first
appeared large  to this eye,  but not so large as they at first ap-
peared to the other; and looking upon the  same object with both
 eyes, he thought it looked about  twice as  large as with the first
 couched eye only, but not double"*
   This case does not stand alone, but others  very  similar to it
 have  been  witnessed  by  other surgeons; the  results have been
 nearly the same in all.  We may draw the following inferences
 from these facts, viz.  that the exact judsment  which we become
 capable of  forming of the distances, magnitudes, and forms of
 bodies, is the result of experience, or,  what amounts to the same
 thing, of the education of the sense of vision.   This  will be con-
 firmed by considering vision at different periods of life.

               Vision at different Periods  of Life.
    The eyes are the first parts formed in the foetus.  In the em-
 bryo they appear like two black snot«;  at seven months, they be-
 come capable of modifying the light, so as to  form an image up-
 on the retina, as we know from experience; until that period they
 cannot do  this, because the  pupil  is  closed  by the membrana

    * I have preferred an abstract of this case in the language of the venerable
 author, to a translation.—Trans.
                               8 
58                     A SUMMARY
pupillaris.*  At seven months this membrane disappears.  The
common mode of expressing this, is saying, that it is ruptured; it
is probably absorbed.  At this period, the fcetus likewise becomes
capable of  living independently of the mother; it  sometimes hap-
pens, however, that  no trace of this membrane  is  found in the
eyes of the fcetus at six, or even at five months.
  There are some points in  which  the  eyes of the fcetus  and
those of adults  differ; they  are not, however,  very remarkable.
In the first, the  sclerotic  coat is thinner, and even slightly trans-
parent; the choroid is reddish externally, and the black pigment
less thick internally; the  retina is proportionally more developed,
and the aqueous humour  is  more abundant, which causes the  cor-
nea to project; finally, the crystalline humour is much less dense
than  in  the  adult.  Before  birth,  the eye-lids are closed tightly
together, as if they  were glued; in some animals they are even
united by the conjunctiva of the  eye-lids, which  passes from the
one to the  other, and is not  ruptured until after the birth.
  As we advance in life,  the quantity of the humours of  the eye
insensibly  diminish, until the adult age.   After this, they dimin*
ish in a manner much more perceptible; this becomes very palpa-
ble in advanced age.  The crystalline  humour, especially,  not
only  becomes more dense, but it begins to lose its transparency,
and  to assume a yellow colour, which at last becomes quite deep.
At the same time that the crystalline becomes yellow, it becomes
much more dense, and contracts a slight opacity that  increases
with  age, until the opacity becomes complete.
   We learn from experiment, that the eye of the  new born in-
fant then, is extremely  well  adapted to act upon  the light, and to
form images upon the retina.  During the first month of its life,
the infant  gives no evidence of  its being sensible  to  the light.
Its eyes move  slowly, and in a doubtful  manner.   It is not un-
til the seventh week that it exhibits strong proof  of its sensibility
in this respect.   Even then it is only attracted by a very brilliant
  * According to M. Edwards, the membrana pupillaris is formed by a prolonga-
tion of the membrane of the aqueous humour, and by the external lamina ot the
choroid coat.  According to this anatomist, there is no aqueous humour in the an-
terior chamber of the eye, before the rupture of this membrane, but this humour
is aecumulated in the posterior  chamber, which proves, 1st, that the membrane of
the aqueous humour is not the secretory organ of this fluid; 2d, that this organ
exists in the posterior chamber; 3d, that before the seventh month, the membrane 
OP PHYSIOLOGY.                   59
light.  It seems pleased to look upon the sun, at first, but soon it
becomes sensible simply to the light of day. In the mean time, how-
ever, it seems indifferent to other objects; the  first which it no-
tices are generally of a  red, or some other brilliant colour.    At
the end of some days, its  attention is  arrested by  bodies of dif-
ferent colours, but it is  a long time before it becomes capable of
forming any idea  of the  distance, or size of bodies.  It extends
its hands to seize even  the most  remote objects; and, as the first
of its  wants is food, it  endeavours  to carry to its mouth every
thing it gets hold  of, whatever may be  its nature, or dimensions.
It appears, therefore, that vision  is  extremely  imperfect during
this early period  of life,  but from exercise, and especially from  ex-
perience,  resulting from continual mistakes, the sight becomes
perfected by a sort of education.
   It has been asserted that children see objects double and revers-
ed;  this assertion, however, is entirely  unsupported by any proof.
It has been said also, but without any more reason,that the refract-
ing  parts of the  eye being more abundant, they see objects  much
smaller than they actually are.  Vision soon acquires all the per-
fection of which  it is susceptible, and in general it  undergoes  no
modification until the  approach  of  old age.  It is then that the
change we have  pointed  out  in  the humours, tend to render it
more indistinct;  but what principally contributes to this effect, is
the  diminished sensibility of the retina.
   Three causes  affect  vision in  old age, viz.  1st, the diminu-
 tion of the quantity of  the humours of the eye, a circumstance
 that diminishes the refractive powers of the organ, and prevents
 the individual from distinguishing accurately neighbouring  ob-
jects.  He is obliged, in  order to examine them, either to hold them
 at a distance, so that the light which penetrates iuto the eye is less
 divergent, or to  employ convex  glasses,  which  diminish  the  di-
 vergence of the rays; 2nd, commencing opacity of  the crystalline
 humour, which weakens the vision, and, increasing,  tends to  cause
 blindness by producing  the disease, generally known by the  name
 of cataract; 3d, the diminished sensibility of the retina, or if you
 choose, of the  brain, which renders obtuse the perception of im-
 pressions, produced upon the eye, and  often terminates in com-
 plete and incurable blindness.
 of the  aqueous humour presents all the characters of serous membranes, particu-
 larly that of forming a sac without an opening. 
GO
A  SUMMARV
                      OF HEARING.

  Hearing is the function by which  we are made acquainted
with the vibratory motions of bodies.   Sound is to hearing, what
light is to vision.   Sound  is the result of an  impression produced
upon the ear, by the  vibratory motion impressed on the particles
of bodies by percussion, or any other cause.   This word describes
also the vibratory motion  itself.   When  the particles of a body
have been thus put in motion, they communicate it to the elastic
bodies which surround them;  these act again in the same manner,
and thus the vibratory motion is propagated, oftentimes to a con-
siderable distance.  Elastic bodies alone, generally speaking, are
capable of producing and propagating sound.  For the most part,
solid  bodies produce it, while the air is  often the vehicle which
transmits it to our ear.
  We may consider  it according  to its intensity, tone, and mode
of propagation.
  The intensity of sound  depends on the extent of its vibrations.
  The tone depends  on the number of vibrations in a given time,
and may be divided into sharp and«-r«rp.  A grave sound arises
from  few vibrations,  in a sharp sound  they are very numerous.
The most grave sound, that the ear can perceive, is  formed by
thirty vibrations in a  second: the  most sharp, by twelve thousand.
Between these two extremes are included all appreciable sounds,
that is, all sounds of which the ear instinctively perceives the vi-
brations.  Noise differs from  an  appreciable sound in this, that
the ear cannot distinguish the number of vibrations of which it is
formed.
  An appreciable sound, which is composed of double the number
of vibrations of another  sound,  is called its  octave.  Between
these two, are seven intermediate sounds,  called the  diatonic
scale, or gammut; they are distinguished in  France by the names
ut,  re, mi, fas, sol, la, si.
  When we put in   motion a sonorous body, by percussion, we
hear at  first one very distinct sound, more  or less intense, and
more or less sharp, as the  case may be.   This is the fundamental
sound.  With a little attention, one perceives, that it produces at 
OP  PHYSIOLOGY.
61
the same time other sounds, these are called harmonics; this will
be readily observed by striking the cord of an instrument.
  The propagation of sound depends on the nature of the sonorous
body; it  is propagated by all elastic bodies.   The velocity with
which it  move.?, varies according to the body  that serves to propa-
gate it; it  moves through  air at the rate of  forty two  thousand
feet  in a  second;  its transmission is still  more rapid through
water, stone, and wood, &,c*   It generally loses its force in pass-
ing, in a  proportion which is directly as the squares of the distan-
ces.   This however is only in passing through air; sometimes its
intensity is increased in passing; this is the case  when it traver-
ses very  elastic bodies, as certain metals, wood, condensed air, &c.
Sharp, grave, intense, and  weak sounds are propagated with equal
rapidity  and without  being confounded.  It has been  generally
supposed that sound  is  propagated in a right line, forming cones
analogous  to those of light,  with this essential  difference,  that
cones  of sound have only an  oscillatory motion, while  those  of
light are progressive.   When  sound meets with  a body that op-
poses it, it becomes reflected  in the same manner as light,  that
is, the angle of incidence is equal  to the angle of reflection.   The
form of  the body which reflects  sound has a similar  influence.
The slowness with which  sound is propagated, produces certain
phenomena, the reason of which may be easily explained, such for
example as echo, the mysterious chamber, whispering gallery, &c.

                    Apparatus of Hearing.
   This  organ is very complicated, but'we shall not enter into
 minute  anatomical  details, for the reader  is no doubt  already
 well acquainted with the uses of the different parts that constitute
 this sense.
   As  in the apparatus of  vision, so in that of hearing, we find a
 collection of organs, which concur in their physical properties, and
 behind  them a nerve destined to receive, and transmit  impres-
 sions.   The  apparatus  of hearing  is composed  of the external,
 middle  and  internal ear, and  auditory nerve.
   External Ear.—We shall comprehend under this denomina-
 tion, the external cartilage, and the meatus  auditorius externus.
* Yidc Memoirs d'Arcueil, vol. ii. 
62
A  SUMMARY
  The size of the external cartilage is different in different indi-
viduals.   The external face, which in a  well formed ear projects
a little forward, presents five eminences, called  the helix, ante-
helix, tragus, ante-tragus, and  the  lobule.  There  are likewise
three cavities, viz. that of the helix, the scapha, and the concha.
This cartilage is very elastic, the skin which covers it is thin arid
dry, and is attached to the cartilage by  a strong cellular tissue,
which contains  but little adipose substance;  the lobe is chiefly
made up of this cellular substance.  On  the surface of the skin is
seen a large  number of sebaceous follicles, which furnish a white
and shining matter, which gives to the skin its polish, and perhaps
a part of its flexibility.  I here is likewise seen on the different
prominences a few muscular fibres, to which some have given the
names of muscles, but which are really mere vestiges.*  This part
receives many nerves and blood vessels,  is very sensible, and easi-
ly becomes red.   It is attached to the head  by ligaments of cellu-
lar tissue, and muscles called according to their positions, anterior,
superior, and posterior.  These muscles  are very much developed
in many animals, but  in man they can only be considered as ves-
tiges.
  Meatus  auditorius externus.—This   part  extends from  the
concha to the membrana tympani, its length varying according to
the age;  in the adult it is from ten to twelve lines.   It is narrower
at  its extremities, and is slightly curved above  and below.   At
its  external orifice, it is furnished with  hairs like the entrance to
the  other  cavities.  It is  composed of  bone,  and  cartilage;  the
skin with which it is  covered is thin; and is expanded over  the
external surface of the membrana  tympani.   Beneath this skin
there are a great number of sebaceous glands  which secrete  the
cerumen, or  wax,  a yellow, bitter,  and  unctuous substance,  the
uses of which will hereafter be pointed  out.
   Middle  Ear.—The middle, comprehends the  tympanum, the
small bones contained in it, the mastoid  cells, and the eustachian
tube, &c.
   The tympanum is the cavity which separates the external from
the internal ear. Its form is that of  a portion of a cylinder, some-
  * The name  vestiges is given by the French anatomists to those parts of animals
"which are without ai.y perceptible use; but which seem only intended to indicate
the uniform plan that nature has pursued in the construction of auimals, 
                      OP  PHYSTOLOG/Y.                  63

what irregular. Its internal  wall presents an oval hole, called the
foramen ovale, which communicates witft the vestibule and is closed
by  a membrane;  above is a  small projection, and beneath a cleft,
in which is lodged a nervous filament; still lower there is a round
opening called the foramen rotundum, which corresponds to one
of the  scala? of the cochlea, and is also covered by a membrane.
The external opening of the tympanum is covered by a membrane,
called the membrana  tympani.   This menibrane passes  obliquely
downwards and  inwards, it is  tense, very thin, and very trans-
parent; it is  covered  externally by  an expansion  of  the  skin,
and internally by a  mucous membrane; it is also partly covered
on this side, by a nerve, called  the cord of the tympanum. Its
centre gives attachment to the  handle of  the malleus; its circum-
ference is attached to the osseous extremity of the meatus  audi-
 torius externus, and it adheres firmly at every point, affording no
 opening by which the  external, and  middle parts of  the ear can
 communicate with each other.  Its texture is dry, fragile, and has
 nothing analogous to  it in the animal  economy; there cannot be
 distinguished about it either fibres, or blood vessels, or nerves.
    The  circumference of the  tympanum  presents  anteriorly.
 1st.  The eustachian tube by which the tympanum communicates
 with the superior part of the pharynx.  2d. The opening by which
 the tendon of the internal muscle of the  nulleus enters.  Poste-
 riorly is  seen—1st.  The opening into the mastoid cells,  which are
 irregular cavities always filled with air, opening into the thickest
 part of the mastoid process.   2d. The pyramid, a small hollow
 projection which gives attachment to  the muscle of the stapes.
 3d.  The opening by which  the cord of the tympanum enters into
 this cavity.  Below there is a small cleft  called "gleniodale" by
 which  the tendon of  the anterior muscle  of the malleus enters;
 and the  cord of the tympanum  passes out to anastomose with the
 lingual nerves of the fifth pair.  Above there is nothing but small
 openings through which blood vessels pass.  The tympanum, and
 all the openings with which it abounds, are  covered by a very
 delicate mucous membrane.   This cavity is  always filled  with
 air, and  contains four small bones, viz: the malleus, the incus, the
 os orbiculare, and the stapes,  which are so connected together as
 to form  a chain, extending from the membrana tympani, to the
 foramen ovale, where the base  of the stapes is fixed.  There are 
64
A  SUMMARY
 small muscles', destined to move this chain, and  to stretch and
 relax the membranes to which it is attached.   Thus the internal
 muscle of the malleus draws it anteriorly, moves the  whole chain
 of  small bones, and  stretches  the  membrane.   The  anterior
 muscle produces an opposite effect.   We may suppose  also that
 the small muscle lodged in the pyramid, and which is attached to
 the neck of the stapes  may  produce a slight  tension upon  the
 chain, drawing it to its side.
   Internal  Ear or Labyrinth.—This is composed of the cochlea,
 the semicircular canals, and the  vestibule.
   The  Cochlea is a bony canal, of a spiral  form,  which receives
 its  name from its supposed resemblance to the shell of a  snail.
 This is divided into  two cavities, the scalar of the cochlea, which
 are distinguished into internal, and external, and are separated by
 thin partition,  partly osseous and partly membranous.   The  ex-
 ternal scala communicates with the tympanum, through the fora-
 men rotundum; the internal terminates in the vestibule.
  Semicircular Canals.—There are three  cylindrical  canals  of
 a semicircular  form, of which two are arranged  horizontally, and
 the  third vertically;  these canals  terminate  in the  vestibule.
 They contain  bodies of a greyish colour, which enlarge towards
 their extremities.
   Vestibule —'This is the central cavity, or point, where the  other
 parts meet.   It communicates with the tympanum  through  the
foramen ovale, or as it is sometimes called the fenestra ovalis,
 with the internal  scala of the  cochlea, with  the  semicircular
 canals,  and.with the meatus auditorius internits,by a large  num-
 ber  of small openings.   All these  cavities of the internal ear are
 contained in a  very hard bone, from this circumstance called the
 os petrosum.  They are covered  with an extremely delicate mem-
 brane, and are  filled with a thin limpid fluid, called the fluid  of
 Cotunnus, which passes  through two small  apertures, called the
 aqueducts of the cochlea, and  vestibule; they  likewise contain
 the auditory nerve.
  Auditory Nerve.—This nerve arises  from the fourth ventricle
 of the brain; it enters into the labyrinth by foramina at the bottom
 of the rAeatus  auditorius internus.  Having arrived at the vesti-
 bule, it is divided into  several branches, of which one remains in
 the  vestibule, another in  the cochlea, and  two are distributed 
                      OP  PHYSIOLOGY.                   65

through the semicircular canals.  The manner in which these dif-
ferent branches are arranged in the  cavities of the internal  ear
have been  described, with great care, by  Scarpa.   It would  not
be proper to enter here into a more minute detail.
   In terminating this  very concise description  of these parts, it
will be proper  to remark, that  the  internal and  middle ear  arc
traversed by several nervous filaments, which it  is probable do
not assist in the function of hearing.   For  example, the  facial
nerve  passes through a canal hollowed out from the  os  petrosum.
In this canal it  receives a filament of the  vidian nerve, and it sup-
plies  the cord  of the tympanum, which is  spread over this  mem-
brane.  Two other anastomoses are likewise seen in the  ear; to
one of which the attention of  anatomists  has been called by  Mr.
Ribes, the other has been recently discovered by M. Jacobson.

                   Mechanism of Hearing.
   Use of the external  Cartilage nf the Ear.—It collects together
the sonorous rays, and directs them towards  the meatus audito-
rius externus;  this  it more effectually  does, from  its  size  and
elasticity, and  from  its being detached from  the head, and direct-
ed forwards.   Boerhaave. pretended to  have  proved, by an  elabo-
rate calculation, that all the sonorous rays which fall upon the ex-
ternal surface  of the cartilage,  are  necessarily conducted towards
the auditory opening.   This assertion  is, however, evidently in-
correct, at least  in some individuals, because in some   instances
the antehelix is more  prominent than the  helix.  As all the rays
are to be directed towards the concha, what will become of those
that fall  on the posterior  part of the  antehelix in these cases?
This cartilage  however is not  absolutely necessary  for the func-
tion  of hearing; for  in  man, and some  other animals,  it may be
removed  without the  hearing being impaired, for more than a few
 days.
    Uses  of the  Meatus  auditorius externus.—This  transmits
sound to the membrana tympani, like any other tube, partly by its
 walls, and partly by the air contained in it.   The hairs which are
 placed at its entrance, and the cerumen, prevent the introduction
 of foreign  bodies, such  for  example as grains of sand, dust, or
 insects, &c.
                               0 
66
A  SUMMARY
    Uses  i*f lite  Jfsmbrana tympani.—This membrane receives
the sound; which is transmitted to it through the auditory opening.
Under what circumstances this  membrane is rendered tense, by
the action of the internal muscle of the malleus, or relaxed, by the
contraction of the anterior muscle of this small bone, we are at
present entirely ignorant.  An opening made into this membrane
does not very essentially impair  the hearing,*  As it is dry and
elastic, it is peculiarly adapted  to the  transmission of sound to
the air contained within the tympanum, and to the chain of small
bones.  The cord  of the  tympanum  will necessarily participate
in the vibrations, and transmit  to thp brain  certain  impressions.
The contact of a foreign body with this membrane is exceedingly
painful,  a violent noise also occasions  severe pain in this part.
The membrane of the tympanum may be torn, or even  entirely
destroyed, without the hearing being essentially impaired.
   Uses of the Tympanum.—Its principal use  is to  transmit to
the internal, the sounds which it  has  received  from the external
part of the ear.  This transmission of  sound  by  the tympanum
takes place; first, by the  chain  of small bones, which acts  par-
ticularly  on  the  membrane of  the  foramen  ovale;t second, by
the air which tills it, and which  acts  upon the  whole of the os
petrosum,  but especially  upon the membrane  of the foramen
rotundum; third, by the vibration of its walls.
   Uses of the Eustachian Tube.—This  serves to admit  the ex-
ternal  air, so that  the pressure on both  sides  of the  membrana
iyinpani  being equal,  of course  no obstacle  is offered  to the
vibrations of the membrane, by which sound is transmitted to the
internal parts of the ear.  The obliteration  of this tube is a fre-
quent  cause of deafness.  It has been supposed that this  tube
assists in conducting the sound to the  internal parts of the  ear,
but this is a mistake, there being nothing to support the assertion.
It allows the air to escape from the tympanum, when  the  atmos-
phere has been violently agitated by aloud noise, and afterwards

  *For the various opinions which have been formed concerning this membrane,
see the works of  llallrr, vol. 5.
  t We are ignorant of the use  of those  motions which  are produced by the
chain ot small bones.   The loss of these bones  does not necessarily occasion
deafness; it should be  rennrked however, that those individuals who are  in this
c;;uatiun, only preserve this sense for two orihtce years. 
OF  PHYSIOLOGY.
tV7
admits it to this part, and to the  mastoid cells.  The  air in  the
tympanum, being very much  rarified  from the heat of the body,
diminishes the intensity of the sound which it transmits.
   Uses of the  Mastoid  Cells.—This is a point which is not well
ascertained.  It is supposed that  they assist in  augmenting  the
intensity of the sound which arrives at the tymoanum.  If they
produce  this  effect, it must be rather by  the  vibration of the
laminie which  separate the  cells, than  by that of the air  which
they contain.   Sound may reach the tympanum otherwise thar  by
the membrana tvmpani.  The sounds which strike upon the bones
of the head, may be directed  towards the temporal bone, and the
percussion thus arrive at the ear.   We all know how distinctly
the noise arising from the machinery of a watch is perceived by
placing it in contact with the teeth.

                  Uses  of the Internal Ear.
   We are but little  acquainted with the functions of the internal
ear.  We suppose that the sonorous vibrations are propagated  in
various ways, but principally by the membrane of the fenestra
ovalis, that of the foramen rotundum, and  by the internal parietes
of the tympanum, and that the fluid contained within the cavities
of the  internal part of the   ear,  sometimes  called  the fluid of
Cotunnus, must receive vibrations,  which  it transmits to the audi-
tory nerve.  We may likewise suppose that  this  fluid  performs
the  extremely  important function, of breaking the  impulse  of
very intense vibrations,  which would otherwise  essentially injure
the  auditory  nerve.  It is  probable, that in  this  case  the  fluid
 flows  back into the aqueducts of the cochlea,  and vestibule which,
according to this  view, have  considerable analogy  in  their func-
tions with the eustachian tube.
   The external scala of the cochlea, must receive vibrations prin-
 cipally by the membrane of  the foramen rotundum; the vestibule,
by the extremity of the chain of small  bones; the semicircular
 canals, by the walls of the tympanum, and perhaps by  the mastoid
 cells, which are often prolonged  beyond  these canals.   We are,
 however, absolutely ignorant of  the  precise share, which  each
 of the internal parts of the ear take in performing  the function
 of hearing.—The osseo-membranous partition which separates the
 two scalie of the cochlea has given rise t« an  hypothesis which no
 one believes at the present day. 
68
A  SUMMARY
              Action  of the Auditory Nerve.
  This nerve receives impressions and  transmits  them  to  the
brain.   If does this with  a greater or less degree  of exactness in
different individuals.   Many persons are said to have a false ear,
that is, they are  incapable  of accurately distinguishing sounds.
We cannot explain the action of  the auditory nerve, nor that of
the brain  in hearing, but many observations  have been  made  on
this function.
  A  sound, to be distinctly  perceived,  must range within  certain
limits; if it be  too violent, it gives us  pain,  if too weak it causes
no sensation.  We  may perceive  a great number  of sounds  at  a
time.   Appreciable  sounds combined, and succeeding each other
in a certain manner, are a source of agreeable sensations.  There
is one art, the  object  of  which is, to arrange sounds in such  a
manner as to  produce this  effect.  This  art is  music.   Certain
combinations  of sounds  on  the contrary,  cause  disagreeable
sensations.  Very sharp   sounds  wound  the  ear, and those that
are very intense  and  grave, tear the membrana  tympani.  The
absence of the fluid from the cavities of the internal ear destroys
hearing.   When a sound has been long continued, we often think
that we continue to hear  it, even  after  it has ceased.

                    Action of both Ears.
  We receive two impressions from sound, but only perceive one.
It has been said  that we  never use but  one ear at  a time, but  this
is incorrect.   It is true,  that when sound arrives directly at one
ear, it is received with more facility by that, and more imperfect-
ly by  the other, and in this case we only use one ear.  When we
wish to listen, attentively, to  sounds,  which  we  fear to lose, we
place ourselves in such a  situation that  the sonorous rays may en-
ter directly into the concha of one ear;  but when we wish to deter-
mine  from what point  sound proceeds, and  in what direction  it
comes, we are obliged to use both  ears,  because it  is only in com-
paring the intensity of the two impressions, that we ate able to dis-
tinguish the place from which the sound comes.   If for  example,
we stop one ear, and another person makes a slight noise at some
distance, it will  be  impossible for us to determine  the  direction
of the sound, though  we should  succeed every  time with both 
OF PHYSIOLOGY.
69
oars.   Sight greatly assists us in judging of sounds, for in a pro-
found darkness, ev^n with both ears, it is often impossible to de-
eide from what point a noise comes.
   Sound also enables us to judge of the distance by which we are
separated from bodies which produce it.  But in order that our
judgment may be correct in this case, it is necessary that  we
should be familiar with such sounds, otherwise our judgment will
be always erroneous.  In this case our judgment is formed on the
following principle, viz.  that a very intense sound comes from a
neighbouring body, and  a very weak sound from a distant body.
If it  should  happen that the intense sound conies from a distant
body, and  the weak sound from a near one, we  then  fall into an
error of hearing.   Generally, we are easily deceived in judging of
the distance from which sound proceeds; here too vision, material-
ly, assists our judgment.
   The different degrees  of convergence or divergence in the sono-
rous rays, do not appear to influence hearing, nor can we modify
these rays in any other way, but by making a greater number en-
ter into  the ear.   This is the only effect  produced  by  hearing
trumpets which are used  by  the deaf.   It is sometimes necessary
to diminish the intensify of sounds; in this  case we  place a soft
inelastic substance in the meatus auditorius externus.

               Modification of hearing by Age.
   The  ear is formed very early in  the  foetus.  At birth, the
internal ear and  small bones, are  nearly the same as at  any pe-
riod  of  life, but  the parts which belong to the  middle and ex-
ternal ear are not in a  condition to act, which  constitutes an
essential difference between the eye and ear.  The external  car-
tilage is comparatively  very small, and  soft, of course posses-
ses  but  little elasticity, and is  therefore,  but  imperfectly,  pre-
pared to perform  the function, to  which  it is destined. The
panetes of the external passage are in a similar state, the mem-
brana tympani  is very  oblique, and  is therefore badly arranged
to receive the sonorous  rays.  All the external  part of the ear
is covered with a soft, whitish matter, which obstructs its func-
tions.  The tympanum is also proportionally small, and instead of
air, contains  a  thick mucus.  The mastoid  cells do not exist.
But as age advances the auditory apparatus acquires that arrange- 
70
A  SUMMARY
ment, and  perfection, which we have described in the adult.  lu
old age, the changes that take place, in the physical structure of
the ear, are so far from being unfavourable, as happens in the eye,
that they appear on the contrary to improve it.   All the parts be-
come more hard and elastic; the mastoid cells  extend themselves
through the os petrosum, and surround, on all sides, the cavities of
the internal ear.
  The loudest noises have no sensible effect upon  new  born in-
fants, but, after some time, they seem to distinguish sharp sounds;
these are the sort of sounds geneially made use of Oy nurses to at-
tract their attention.  It is  a long time before an  infant judges
correctly of the intensity or direction of sounds, and,especially,
before he attaches any meaning to articulate sounds.   As he pre-
fers the most vivid light, so in the same manner he is pleased, for a
long time, with sounds that are loud arid sharp. But although the
physical structure of the auditory apparatus becomes more perfect
in old age, yet it is nevertheless certain, that the hearing becomes
more imperfect, even at its first approach, and  that there are very
few old men who are not more or less deaf.   This appears to arise
from a diminution of the humour of Cotunnus, and a progressive
loss of sensibility in the auditory nerve.


               SENSE OF SMELLING.

   Tkkuk are many bodies in nature, which suffer to  escape from
them, particles of extreme tenuity, which spread themselves in the
atmosphere, and  are carried, by this vehicle, to a great distance.
These particles constitute odours.   One of the senses is destined
to recognise and appreciate these particles, and thus an important
connexion is established, between animals and them.  Those bo-
dies, the particles of which are fixed, are called inodorous.
   There is a great difference among odorous bodies, in the manner
in which they develope their odours.  Some do not suffer them to
escape, except when they are heated, others when they are rubbed;
some exhale only weak odours, others only those which are stron°*.
Such is the tenuity of these odorous particles, that a body may
exhale them, for a very long time,  without  altering, sensibly, ite
weight. 
OP  PHYSIOLOGY.
71
  Every odorous body has a peculiar odour.  As these bodies are
very numerous,  it has been attempted to class them, but all these
attempts have heretofore  proved fruitless.  We can only distin-
guish odours into weak and  strong, agreeable and disagreeable.
We speak, however, of a  musk-like  odour, aromatic,  and  fetid
odours, &c.  They are,  likewise, sometimes  distinguished into
fugitive and tenacious.   For the most part, however, we can only
designate them by comparing them with that of some known body.
  Nutritious, medicinal, and even poisonous qualifies have been at-
tributed to odours;  but in such cases, these opinions seem to have
been formed  by confounding the influence of odours, with the ef-
fects of absorption.  A man who pounds ja ap for some time, will be
purged, as if he had  taken its substance  into his stomach.   This
effect  cannot be properly referred to the effect of odour, but to
the fine particles of the jalap which are  flonting in the air, and
which are thus introduced into the circulation, either with the
saliva; or in the air which he respires.   It is to  the same cause
which we  must attribute the drunkenness of persons, exposed
for some time to the fumes of spirituous  liquors.  'The  air is the
vehicle by which odours are generally  transported to a distance,
but they are also produced in a vacuum.   There are some bodies
which dart forth their odoriferous particles with a considerable
degree of  force; but  this subject has  not received the attention
which it deserves.   It has not  been fully ascertained,  if odours
observe, in  their  progress, any thing  analogous  to the  conver-
gence and divergence, reflection and refraction of luminous rays.
•Odours attach themselves to, or combine with, many  fluids, as
 well as many solid bodies, a method which is often taken to pre-
 serve them for  a long time.   Liquids, vapours, gases,  and  many
 solid bodies, when  reduced to an impalpable, or even coarse pow-
 der, have likewise the  property of acting upon  the  organs  of
 smell.

                    Apparatus of Smelling.
    The olfactory apparatus may be compared to a sort of sieve,
 placed in a spot over which the current of air, that is introduced
 into the chest in respiration, passes, and which is destined to de-
 tain all the foreign bodies, which  may  happen to be mixed with
 the air, particularly odours. 
7%
A  SUMMARY
   This apparatus is extremely simple.  It differs essentially from
that of vision or hearing in  this, that we  do not find before the
nerve, any  parts which  are  placed there to modify  the  physi-
cal effects of the excitant, the  nerve being, in a great measure,
naked.  The apparatus is composed of the pituitary membrane,
which covers the nasal cavities, of the membrane which lines the
sinuses, and of the olfactory nerve.
   The Pituitary Membrane.—This  covers the whole extent of the
nasal  fossse, increases  very  much  the thickness of its cornets
and is prolonged beyond their edges and  extremities, in such a
manner,  that the air cannot  traverse the nasal fossae, except  by
very narrow and lengthened  passages.  This membrane is thick,
and adheres tenaciously  to the bones and cartilages to which it is
attached.  Its surface presents an infinite  number of  small pro-
jections, which are considered, by  some, as nervous  papillae, but
have been supposed by others to be mucous  cryptee; they are, how-
ever, very vascular.   These  projections give to the  membrane a
velvet-like appearance.  The pituitary membrane is  smooth  to
the touch, soft, and receives a great number of blood-vessels and
nerves.
   The passages which the air passes through, to arrive at the back
part of the mouth, deserve attention.  They are three in  number,
and are divided  by anatomists info  inferior, middle, and  superior
passages. The  inferior is by far the largest, longest, and least
oblique and  tortuous; the mid lie is  narrower, nearly  as long, and
deeper from above, downwards; the  superior is much the shortest,
most oblique, and narrowest.   It also proper ot  add, that a very
narrow interval separates, through  its whole extent, the partition
of the nasal  fossee, from the external walls.  Such is  the  extreme
narrowness of all these canals, that  the least swelling of the pitu-
itary membrane  renders the passage of the air through the nasal
fossae difficult, and, sometimes, impossible.   The two  superior ca-
nals communicate with cavities, which are considerably spacious,
hollowed out of the bones of the head, and are  called  sinuses.
They are the maxillary, palatine, and sphenoidal  sinuses.   I hose
which are found  in the thick part of the ethmoid bone, are some-
times distinguished by the name of cellulee  ethmoidals.
   These  sinuses do not  communicate  with any others than the
two superior canals.  The  frontal sinus, the maxillary,  and the 
OF  PHYSIOLOGY.
73
anterior cells of the ethmoid bone open into the middle passage;
the sphenoidal, and palatine sinuses, and the posterior cells of the
ethmoid  bone open  into the  superior canal.   These sinu-es are
covered with a thin, soft, and apparently mucous membrane, loose-
ly  attached to  their  walls.   They  secrete,  with more or less
abuiiilance, a substance called nasal  mucus, which is coniinually
SpreatI over the surface of  the  pituitary  membrane, and appears
to be useful in smelling.  A considerable < xtent of these sinuses
is always found where this sense, exists i-i great perfection.  This
is, at least, one of the  most  positive results of comparative physi-
ology.
   The Olfactory Nerve.—This arises by three distinct roots from
the posterior, inferior, and interna! part of the anterior lobe of'he
brain.  In passing towards  the cribriform  plate  of the  ethmoid
bone, it is of a  triangular  shape;  here it  becomes  suddenly en-
larged, and is then divided  into a  great number <it small hlaments
which are ramified over the  pituitary membrane, principally at
the superior part of this membrane.
   It is important to remark, that the filaments of the olractorv n^rve
 ha»*e never been traced on the inferior comet or spongy bone, on the
internal face of the middle, nor on any of the sinuses.  The pitui-
tary membrane not only receives the nerves of the first pair, but re-
ceives also a great number  of filaments arising from the spheno-
palatine ganglion; these filaments  are distributed over the inferior
parts of the membrane. It is supplied also by the ethmoidal fila-  '
 ment of the nasal nerve, and  receives from it a  lar-e number of
 small filaments.  The  membrane  which covers the sinuses re-
 ceives also some small nervous branches.
   The nasal  fossse terminate  externally in  tl.e nares, or nos-
 trils, the form, magnitude,  and direction of which vary  in differ-
 ent individuals.   The interior of the anterior nares is  garnish-
 ed with  hairs, and their dimensions are increased and  diminished
 by the action of certain muscles.   The nasal fossse open into the
 pharynx by the posterior nares.

                    Mechanism of Smelling.
    The sense of smell  is exerted at the moment that the air tra-
 verses the nasal toss* in its passage to the lungs.  It is  very  rare
 that we can perceive any odour in  the air, at the moment it escapes
                              10 
74
A  SUMMARY
from this viscus; though this is sometimes observed, especially ia
certain organic affections of the lungs.
  The mechanism of smell is extremely simple; it is only neces-
sary that the odoriferous particles should be stopped, by the pitui-
tary membrane, especially  in those narrow passages  where it re-
ceives the filaments of the  olfactory nerve.   As it is precisely
at the superior part  of the nasal fossse, where the passages are
the narrowest,  that they  are  the most covered  with  mucus, it
is probable  that  this  is  also the spot  where  the odoriferous
particles are stopped.   It  is easy to  understand  the use  of this
mucus; its physical properties appear  to  be  such,  that  it has a
much greater affinity for the odoriferous particles, than for the air.
It, therefore, separates  them  from this fluid,  and  retains them
upon  the pituitary membrane, where they produce the sense of
smell.  It is very important, in the exercise of this function, that
the nasal mucus should  preserve the  same physical properties;
every time they are changed, as happens in the different stages of
corvza, the sense of smell  is either lost or essentially impaired.*
  From  what has been said  of the  distribution of the olfactory
nerves, it is evident that odours, when they come to the superior
part of the nasal cavities,  will  be  more  easily and  vividly per-
ceived.  It is for this purpose  that we modify inspiration, so that
the air shall be  directed upon this point, when we  wish  to per-
ceive vividly or accurately the odour of a body.   It is  for  the
same reason, that those who take snuff endeavour  to place this
substance towards the  upper part of the nasal fossa;.  It would
seem that the internal surfaces of the cornets are extremely well
arranged to stop the  odour, at the moment that the air passes
through; and as their sensibility is very great we are induced  to
believe that they assist in  the  function  of smelling, although  the
filaments of the first pair of  nerves have never been traced upon
them.
  Physiologists are not agreed as to the precise use of the  nose in
smelling; it appears intended  to  direct the air, charged with  the
odorous particles, towards  the  superior  part  of the  nasal fossee.
Persons whose noses are deformed, or have been crushed, and those
  * This is the explanation given in the School of Medicine in Paris.  It seems
at first satisfactory, but, on a nearer examination, it will be found to rtst on
many assumed facts—e. g. the affinity of the na^al mucus for •dours, the deposi-
tion •! the odorous particles on tbe pituitary membrane, &c. 
OF PHYSIOLOGY.
73
who have small  nostrils directed forward,  have generally the
sense of smell very imperfectly.  The loss of the nose, by disease
or by accident, causes nearly an entire loss of this sense.   Ac-
cording to the interesting remark of M. Beclard,  we may restore
the use of this part, in individuals who are in this  situation, by
fitting an artificial nose.
   It has been supposed that  the use  of the sinuses, for the most
part, consists in supplying the  nasal mucus.  But there  are other
uses which may be attributed to them, viztto serve as a depot of the
air charged  with the odorous effluvia, and to increase the surface
to which it may be applied.  Vapours, and gases appear to act in
the manner of odours, on the pituitary membrane; the mode, how-
ever, is probably somewhat different.   Bodies reduced to a coarse
powder, have also a powerful action on this membrane;  their first
contact is even  painful, but habit changes this  pain into plea-
sure, as we see in snuff-takers.   In the practice  of medicine, we
have often recourse to this property of the pituitary  membrane, of
producing instantaneously an acute pain, by the application of
certain pungent odours.
   In speaking of the sense of smelling, it is not proper to be si-
lent concerning  the hairs which  garnish the nostrils;—they are,
perhaps, intended to prevent the foreign bodies, which float in  the
air; from entering the nasal fossse.  Their functions are very analo-
gous to those of the eye-lashes, and of the hairs found at the erf-
 trance of the external passage of the ear.
    It has been  generally admitted,  that the  olfactory nerve is
 especially destined to transmit to  the brain, impressions made by
 odorous bodies; but there is nothing which proves positively tbaj
 the other nerves, which  are expanded  upon the pituitary mem:
 brane, do not concur in this function.

                 Modification of Smell  by Age.
    The olfactory apparatus is  but  imperfectly developed at birth.
 The nasal  cavities, and the different cornets, scarcely  exist; and
 the frontal sinuses cannot be distinguished, though there is reason
 to think that infants are  capable of exercising  this  function. I
 think I have seen children, soon  after birth, exert this sense upo*
 the aliments which were  presented  to them.  With  the progress
 of age, the nasal cavities develope themselves, the sinuses become 
76                     A  SUMMARY

formed, and, in this respect, the olfactory apparatus continues to
grow more perfect, u itil  old age.    The  sense  of  smell  remains
until the la-t  moments  of  life, excepting in  those cases where
there is some organic  a fir ct ion of  the |;art, such,  tor example, as
some change m the secretion of the mucus, &c.
  The »ense .it smell is designed  to make us acquainted with cer-
tain  properties  «,t bodies, especially of the class  of substances
called  aliments.   For  tbe most part, those suus.auces. the odour
of which is (ii-agreeajie, are not  nutritious as alimenis, but  are
frequently  dangerous.   Many animals  appear to have the sense
of smell much more perfectly than ourselves.  'lhi-> sense is also
a source of many iigiei, Lrie sensations,  which have a marked in-
fluence upon the condition and feelings of the  individual.


             ON  THE SENSE OF TASTE.

  Taste is the impression made upon  the tongue  by certain  bo-
dies; those  substances which produce this effect are called  sa-
pid,   it  has been supposed that the degree  of sapidity  in any
bwdy  might be judged of by its solubility.  But there  are some
bodies  which aie insoluble yet have a strong taste,  and there  are
others  which are very soluble that have  scarcely any perceptible
taste.  Sapidity appears  to have some relation to the chemical  na-
ture  of bodies, and  to the general effects which they produce on
the animal  economy.
  'Tastes are very various, and numerous; several  attempts have
been made to divide them into classes, Lut this has never yet been
done  with complete  success; at  the same time we have been ra-
ther more  fortunate in this respect, than with odours.  This  un-
doubtedly arises from the fact, that toe impressions which  we  de-
rive  from the sense of taste, are less transient than those of smell.
The propriety of the following distinctions among sapid bodies is
universally acknowledged, viz: acrid,  acid, bitter; sweet, rowh,
Sj'c.  t'nere  is another division of these bodies which  will  be ad-
mitted  by  e\ery one. because it is founded upon organization; it
it is that of agreeable and  disagreeable.  Animals instinctively
establish this distinction.   This division \- also the more impor-
tant, because  those  Dodies, the t; sic of  which is  agreeable, are 
OF  PHYSIOLOGY.
/ /
usually those that are most nutritious; and on the contrary those,
the taste of which is disagreeable, are often injurious.

                     Apparatus of  Taste.
   The tongue is the principal organ of taste; at the same time the
lips, the internal surface of  the cheeks, the palate, the teeth,'the
the pharynx, the oesophagus,'and the stomach itself, are suscepti-
ble of impressions from the contact of sapid bodies.   The salivary
glands, the excretory ducts of which  open  into the mouth, and
those  follicles which pour  out mucus into  this cavity, concur
powerfully in the function of taste. Independently of the mucous
follicles found on the superior surface of the tongue, which have
received the name of fungous papilla?, there are found still smaller
projections, the most numerous of which are called villous papilla?,
and still others,  less  numerous which are disposed on the side of
the tongue, in two ranges, and are  called conical papillce.
   All the nerves distributed on those parts which are destined to
receive the impression of sapid bodies, must be comprised in the
apparatus of taste.   Thus the inferior maxillary, and  many bran-
ches of the superior maxillary nerves, among which it is proper to
mention the filaments which arise,  from the sphenopalatine gang-
lion, particularly the naso-tml'-dine nerve of Scarpa, the nerves of
the ninth pair, and the  glosso-pharyngeal nerve, &c. all appear to
assist in the function of taste.
   The lingual nerv; s of the fifth pair are those which are usually
 considered by anatomists  as the  principal nerves  of taste; for
 their  filaments,  they assert, may be  traced to the villous and co-
 nical papillae of the tongue.  1 have myself attempted to do this
 but in vain.   Notwithstanding I have employed the most delicate
 instruments,  magnifying glasses,  and  microscopes completed ac-
 cording to the  principles of Mr.  Woolaston, all my  efforts have
 been unsuccessful.   We entirely lose sight of them, the moment
 we arrive at  the exterior membrane  of the tongue.   We  do not
 succeed better*with the other nerves which are distributed over
 this organ.

                     Mechanism  of Taste.
   In order that we may exercise the function of taste perfectly, it
 is necessary that the mucous membrane which covers these organs 
78
A  SUMMARY
should be  in  a state of  integrity, that it  should  be covered
with mucus, and that the saliva should be poured out abundantly.
When this membrane is dry, the taste is very imperfect.  It is
likewise  necessary that these fluids should be in a natural state,
for if the mucus be thick, and yellowish, or if the saliva be acid
or bitter, &c. the taste will be defective.
   Some  authors assert that  the  papillse of the tongue are in a
complete state of erection, during the action of tasting; I believe
however, that this assertion is entirely destitute of foundation.
   It is sufficient that the  body be in  contact with the  organs of
taste, in  order that we may correctly judge respecting it; but, if it
be a solid body, it will be necessary, that it should  be first dissol-
ved  in the saliva, but this is not necessary in liquid or gasseous
bodies.
   It would seem that sapid bodies produce a certain chemical ac-
tion  upon the epidermis of the mucous  membrane of the mouth; this
is at least the case in some instances, e. g. vinegar, mineral acids,
alkalis, a great number of salts, &c.   In these cases the colour
becomes  changed, sometimes it is white, sometimes  yellow,  &c.
They produce analogous effects upon the dead body.   It is proba-
ble that  the manner in which this combination takes place,  has
some relation to the promptitude with  which sapid bodies act,  and
the duration of the impression.
   No satisfactory explanation  has yet  been given why the teeth
are strongly influenced by certain sapid bodies.  It appears from
the researches  of M. de Niel,  a distinguished dentist  of Paris,
that  this is the effect of imbibition.   The experiments  of  this
gentleman  prove, that the teeth  imbibe  promptly the fluids with
which they are in contact.
   The different parts of the mouth appear to have each a peculiar
susceptibility to the  action  of  sapid bodies; for some more  par-
ticularly  affect  the  tongue, some the  teeth, and others the gums.
There is  another class of these bodies, the action of  which seems
to be almost exclusively confined to the palate and pharynx.
   There  are some bodies which leave  for a long time their taste
in the mouth; this is especially the case with aromatic substances.
This remaining taste is sometimes perceived over all the  mouth,
and sometimes occupies only one spot. Acrid bodies, for example,
leave their impression in the pharynx,-acids on the lips and teeth; 
OP  PHYSIOLOGY.
79
 peppermint leaves  an impression  which exists at  the  same time
 in the mouth and pharynx.
   It is necessary that bodies should remain for some time in  the
 mouth, in order that their taste may be appreciated.   When they
 pass  rapidly through this cavity, the impression which they make
 is almost nothing;  this  is the reason  why we swallow quickly
 those substances, the taste of which is disagreeable, and why, on
 the contrary, we allow those things to remain long in the mouth,
 the  taste of which is pleasant.
   When we taste a substance, the flavour of which is strong and
 permanent, vinegar for  example, we  become  insensible  to  the
 action of less pungent bodies.  We often make use of this obser-
 vation to enable our  patients  to avoid  the  disagreeable taste of
 certain medicines.
   Vi e are  capable of perceiving  many tastes,  at the same  time,
 and  of distinguishing their different degrees of intensity.
   By this means we  are sometimes enabled to distinguish very
 exactly the chemical nature of different substances.  The  taste
 however never  arrives at this degree of perfection, but by Ion**
 •xperience, or if you choose, by a complete education.
  I know not any fact which proves that the lingual nerve is ex-
 clusively the nerve  of taste.   The experiment  mentioned by  M.
 Richerand does not  appear to me to  decide this question; this
 seems also to be the opinion of this learned professor.

                Modification  of  Taste by Age.
  It is difficult to  say if taste exists  in  the fcetus; it is certain
 however, that the principal  organ, and  the nerves which are sent
 to it, are fully  developed.  That  this sense exists at the  time  of
 birth, there can be no doubt, as any person may satisfy themselves,
 by rubbing upon the  tongue, or even upon the lips, any bitter or
 9weet  substance.  The impressions of taste appear to be very
 vivid  in children, as is shewn by their repugnance to every thing,
 the flavour of which is strong.
  Taste remains in  the most advanced  age, though it is true that
old persons generally prefer aliments and drinks, the  flavour of
which is strong.  But this is one of the properties of organization,
which  requires very active  excitants, for the maintenance of its
powers, when they have become very weak. 
80
A  SUMMARY
  Taste assists us in the choice of aliments; together with smell,
it enables us to distinguish those  substances which  are injurious,
from those which are useful, it is likewise the sense which enables
us to  form the most correct  judgment  of the chemical  compo-
sition of bodies.
                        OF  TOUCH.

   Touch is the sense which makes us acquainted with the greater
 number of the properties of bodies.   In consequence of its being
 less subject to errors than the other senses, and because in certain
 cases it enables us to detect them, it has been  considered  as the
 most perfect of the senses.  But it will be seen  that its advan-
 tages  have been very much overrated, both by physiologists and
 metaphysicians.
   We must distinguish between feeling and  touch.   Feeling is,
 with   few exceptions,  common  to every part of the  body,  es-
 pecially the cutaneous and mucous surfaces.   It exists in all ani-
 mals, while touch  is evidently confiued to parts, particularly, des-
 tined to this purpose.   This does not exist in all animals, but it
 is nothing more than feeling, united with muscular  contraction,
 and  directed by the will.   In a word, in  the act of  feeling we
 may be considered as being passive, but in exercising the sense of
 touch we are active.

 Of the Physical Properties of bodies which  are the objects of
                          this sense.
   This sense enables us to become acquainted  with nearly all the
 phvsic-il properties  of  bodies.   The  form, dimensions, different
 degrees  of consistence, weight, motion  and vibration  of bodies,
 are all  circumstances of which  we are  enabled  to judge, with
 accuracy, by the sense of touch.
   The  parts destined  to this sense do  not alone  perform  this
 function.   In this respect it  differs  very essentially  from  the
other  senses.   As in  the  greater number of cases, however, it is
the skin  which receives  the impressions  of  touch  from  those
bodies  which surround us, it is necessary to say something con-
cerning its structure. 
OF  PHYSIOLOGY.                  81
   The Skin.—This forms  the envelope of the body; it is lost in
the mucous membranes at the entrance of all the cavities, but it
is incorrect to say, that these membranes are a continuation of it.
  Dermis.—The skin  is principally  formed by the  dermis,  the
texture  of which is fibrous,  and is of different degrees of thick-
ness, according to the parts  which it covers.  It adheres to these
parts, sometimes  by  cellular  membrane, and  sometimes by a
fibrous attachment.  The dermis is nearly always separated from
the subjacent parts by a lamina, which assists in the exercise of
the sense of touch.
  Epidermis.— The external  surface  of  the dermis is  covered
bv  a  solid  substance  secreted  by the skin, called the  epider-
mis.  The epidermis ought  not to be  considered as a membrane;
it is a lamina of  homogeneous substance,  adhering by its internal
surface  to the dermis.  It is pierced  by  an infinite number of
small holes, which allow the  hairs to pass through, and  the  cu-
taneous transpiration to escape, and, at the same time, they assist
in the absorption which is carried on by the skin.  It is proper to
remark  with respect to the epidermis, that it  is insensible, that
it does not possess any of the properties of life,  and that it is  not
subject  to putrefaction.  It  is constantly taken  away and, again
replaced, and its thickness is  increased, according as the situa-
tion of  the parts may  require,   it  cannot be acted upon through
the medium of the digestive organs.
  Rete mucosum, or the mucous substance of Malpighi.—The con-
nexion  between  the dermis and epidermis is intimate, neverthe-
less we  cannot doubt that there is between these two parts a par-
ticular lamina, in which important phenomena take place.  The
organization  of this lamina is still but  little known.   Malpighi
supposed that it was formed by a particular mucus, the existence
of which has been long admitted, and which has been called  the
rete mucosum. or mucous  substance  of Malpighi.   Others  have
considered it, with more reason, as a  network of blood vessels.*
M. Gall compares it to the cineritious substance found in many
parts of the brain.

   * In those cases where vesicatories have been applied to the part sometime be-
fore death, very numerous vessels, very small and filled -with blood, may b« dii-
tinjfuished on the external surface of the dermis.
                                11 
«2
A  SUMMARY
    M. Gautier, in examining with attention the external surface of
 the dermis, observed small reddish projections, arranged in pairs.
 They are easily  recognized  when the dermis is denuded by the
 action of a vesicatory.  These  small bodies ai*p regularly ar-
 ranged in the palm of the hand and the sole  of the foot.   They
 are sensible, and are reproduced w hen thev have been torn away.
 They appear  chiefly mad* up of blood  vessels.   These  bodies
 have been for a long time called cutaneous papilla?, but thev  have
 never been studied with care.  The  epidermis  is  pierced  over
 their top, by a small opening, by which we can observe drops of
 sweat to escape, when the skin is exposed to a  temperature a little
 elevated.   The  skin contains a great  number  of  sebaceous
 follicles;  it  receives many  blood  vessels, and  a great  num-
 ber of nerves, particularly at those  points which are destined
 to exercise the function of touch.   We are entirely ignorant of
 the manner in which the nerves terminate in the skin; all that has
 been said of  the nervous cutaneous papillae, is completely hypo-
 thetical.
  The functions of feeling and touch are assisted by the thinness
 of the dermis, a temperature of the  atmosphere  somewhat ele-
 vated, abundant cutaneous  transpiration, as  well  as a  certain
 thinness and flexibility  of the epidermis.   When  the  reverse of
 these circumstances exist, the sensibility and the touch are always
 more or less imperfect.                                         •■'**

                   Mechanism of Feeling.
  The mechanism of feeling  is extremely simple; it is sufficient
 that the  bodies be in contact  with the skin to enable  us to form
 an idea, more or less exact, of their sensible properties.  We are
 enabled to judge particularly  of temperature  by feeling.  When
 bodies abstract caloric  from us, we say they are cold, and when
 they impart heat, we say they  are warm; thus, according  to the
quantity of caloric  of which  they deprive us, or which they im-
 part to us, we determine their different degrees of temperature.
The judgment which we form  of temperature,  is nevertheless far
from being accurate, in relation to the quantity of caloric  which
our  bodies give  off, or receive; we unconsciously institute  a com-
 parison between the temperature of the surrounding atmosphere,
and those substances which are in contact with our bodies.  If an 
OP  PHYSIOLOGY.
83
object be colder than our body, but warmer than the atmosphere,
it will appear warm to us, although it abstracts caloric when w«
touch it.  This is the reason why such places as caves and wells,
the temperafure o*~ which i« uniform, appear to us cold in summer,
and warm in winter.   The capacity of bodies for caloric,  innuen-
ces also our judgment of temperature:  for example, how different
are the sensations  caused by  iron and  wood, at the same tem-
perature.
   A body sufficiently warm to  decompose chemically our organs,
produces the  sensation of burning.  A body, the temperature of
which is sufficiently low to absorb very rapidlv a great proportion
of the caloric  o'" a part, r-roduces a similar sensation; this  any  one
may satisfy themselves of, by touching concealed  mercury.
  Those bodies which have a  chemical action unon the  epider-
mis, which dissolve it, such as the caustic alkali, and concentrated
acids, produce impressions  peculiar to these bodies, which  may
serve to distinguish them.
  All parts of the skin are not endued  with the same degree of
sensibility: so that a body applied successively on different parts
of the sk*n, will cause a series of very different impressions  The
mucous membranes possess a very delicate sens:bjlity   It seems
hardly  necessary to point out  the great  sensibility of the  lips,
tongue,  conjunctiva, pituitary membrane, and the  mucous mem-
brane of the trachea, ureters, vagina, &c. &c.  The first touch of
those bodies, which are not naturally destined to come in  contact
with  these membranes, is painful, though this effect ceases by
habit.

                   Mechanism  of Touch.
  In  man, the hand  is the  principal organ of touch;  all the  cir-
cumstances which are the most favourable to it are there found
united.   The  epidermis is thin, polished, and very soft, the cuta-
neous transpiration is abundant, and there is likewise an  oily se-
cretion.   The vascular net-work,  called the rete mucosum, is
there in  an unusual quantity, and the dermis is of very inconsidera-
ble thickness; it adheres to the  subjacent aponeurosis, by a fibrous
attachment, and is sustained by an adipose substance and  cellular
membrane,  which is  very  elastic.  It  is at  the^ extremity, or
ball of  the  finger, that all these  arrangements exist in the  highest 
84
A  SUMMARY
degree of perfection.  The motions of the hand are easy and va-
rious, so, in a word, that this  part may be applied to every body,
whatever may be the irregularity of its  figure.  While  the hand
remains immoveable upon the surface of a body, it only  performs
the function  of feeling:  it is necessary, in exercising the  sense
of touch, that it should move over the surfaces of bodies, in order
to make us acquainted with their  form, dimensions, &c. or to
compress them, so that we may form just ideas of their elasticity,
density, &c.   When the dimensions of a body are not very great,
we employ the whole  hand to examine  it, if  on the contrary the
body is very  voluminous, we  only touch it with the extremity of
our finger.  This organ is much  more  perfect in man than in
brutes; his touch is so delicate, that it  has  been considered as
the principal source of his intelligence.
   From the highest antiquity, this sense  has been considered more
perfect than the rest, and has been described  as the cause of hu-
man reason.   This idea is maintained at the present day, and  it
has even been very much extended in the writings of Condillac,
Buffon, and the modern physiologists.   Buffon, in particular, has
attached such  a degree of importance to touch, that he seems to
have thought that  the different degrees in which this sense was
cultivated, was the principal cause of the difference observed in
the minds of men; he enjoins, therefore, the importance of allow-
ing infants the free use of their hands.
   The touch, however, has really no superiority over  the other
senses; and if in some cases it assists us in seeing or hearing, in
others, these  senses afford it equal assistance; nor is  there any
reason  to  believe that the impressions which it excites in the
brain are more vivid than those which arise from the action of the
 other senses.

        Modification* of Feeling  and Touch by  Age.
   It is probable that the  foetus does not exercise this  sense, at
least in its more rigorous acceptation.   It may be  said that the
 first contact of the air with the skin of the new born infant causes
severe pain, which is the reason of its cries.   I believe, however,
 that this idea is unfounded.
   Feeling and touch grow more obtuse with the progress of a°-e.
 In old age they are sensibly diminished; at this period the skin 
OP  PHYSIOLOGY.                   85  %
undergoes changes  which  are  unfavourable to this sense.   The
epidermis is no longer soft and  flexible, the cutaneous transpira-
tion is not abundant, the tat which before sustained the skin is ab-
sorbed, and  it becomes flaccid and rugous.   We can easily ima-
gine that all these causes will impair the functions of feeling and
touch, especially when we  recollect, that the power of receiving
impressions, generally, becomes sensibly diminished in old age.
  By exercise of this sense it may be brought to a very great de-
gree of perfection, as is observed in many professions.  A delicate
touch is indispensable, both in a physician and surgeon.

                   Of Internal  Sensations.
  All the organs, like the skin, possess the faculty of transmitting
to the. brain impressions, when they are brought in contact with
foreign bodies, or when  they are compressed or bruised.  They
may be said, generally, to possess feeling. We must except, how-
ever,  from this remark, the bones, tendons, aponeuroses  and liga-
ments, which, in  a state  of health, are totally insensible, and may
be even cut. burned, or torn, without the brain being affected  by it.
This  important fact was not known  by the  ancients; they con-
sidered all the white parts of the body as nervous, and attributed
to them properties which we now know only pertain to the nerves.
It is to the experiments of Haller, and his disciples, that we are
indebted for this  useful information, which has exerted a powerful
influence upon the progress of modern surgery.
   Without the intervention of any external cause, all the organs
may spontaneously  transmit a great number  of different impres-
sions  to the brain.  They are of three kinds.
   The first  arises when there is a necessity that the organs should
act; these may be  called instinctive desires.   Such are hunger,
thirst, a desire to pass urine, respiration, and the venereal appetite.
   The second take  place during the.action  of the organs; they
are often obscure, buf sometimes very vivid.   Of this number are
the impressions which accompany the different  exertions, e. g.
the impressions  which  we  perceive during the period  of  diges-
tion; thought itself may be included among this sort of impressions.
   The third kind of internal sensations take place when the or-
gans have acted.  To these kind belong the sensation of fatigue,
varying, of course, according to the part affected. 
86
A  SUMMARY
   If is necessary to add to these three kinds of impressions, those
 which  arise from disease; these are very  numerous, and a pro-
 found acquaintance with them, is indispensable to the physician."
 All these  sensations which  arise, independently of the action of
 external  bodies, have  been  designated  as internal  sensations.
 Their consideration was neglected  by the metaphysicians of the
 last cerifurv, but their  study  has of late eneaged the attention of
 many distinguished  authors,  particularly of  Cabanis,  and  M.
 Destutt Tracy;-their history  constitutes  one of the most curious
 parts of ideology.

                  Of a  supposed sixth Sense.
   Buffon, in speaking of the intensity of  those  agreeable sensa-
 tions which are produced by  the approach  of the sexes, has ob-
 served, in  figurative language,  that  they depended  on  a  sixth
 sense.  The professors of animal magnetism, especially  those
 of Germany,  talk much of  a  sense, said  to exist in  persons
 who  talk  in their sleep, that  it is  particularly  developed in
 those persons who are  called somnambulists;  and  that  it  gives
 to  them the power of predicting future events.   This sense
 forms that  instinct of animals, by which they become acquainted
 with dangers which  are near.  It resides in the bones, viscera,
 ganglions, and  the nervous plexus.—To attempt to^nswer such
 silly reveries, would be  only to throw away one's time.
   M. Jacobson having discovered in the os incisivum of animals,
 a particular organ, suspected that it. might be the source of a dis-
 tinct order of sensations; but he has given no proof of this.
   The faculty which bats have  of directing themselves in flying
 in the darkest places, has induced  Spalanzani, and M. Irvine of
 Geneva, to think that these animals are possessed of a sixth sense;
but M. Cuvier has shewn that this power of conducting them-
selves in the dark, is attributable to the sense ef toach.   There
is, therefore, no evidence of a sixth sense. 
OF PHYSIOLOG\.                   87
          OF  SENSATIONS  IN GENERAL.*

  Sensations form the first part of the relations of life, they esta-
blish our  passive relations with  surrounding bodies.  This ex-
pression passive, as any one will  easily perceive, is true only in
a limited sense; for sensation, as well as  the other functions of
the economy, is the result of the action of the organs, and, of con-
sequence, is essentially nctive.  Every substance which exists, is
capable of acting upon our senses; we cannot know positively of
their existence, bui  in  this way.   Sometimes  they act  directly
upon our organs; at others  through the medium  of other bodies,
as light, odours, &c.
  The greater number of bodies  act upon several of our senses;
others, again, only affect one.   The organs of sensation are form-
ed of an exterior part, which exhibits physical properties in com-
mon with other bodies, and of nerves, which receive  impressions
and transmit them to the brain.  The exterior parts of the appa-
ratus of vision  and  hearing are  very  complicated; those of the
others are very simple.   But  in all, the relation between  their
physical properties, and other bodies is such that  the least alter-
ation in these properties, causes a marked  derangement of func-
tion.

                            Nerves.
  The nerves, which form the second part of the instruments of
sensations, are  the  essential organs of sense.  All the nerves
have two extremities; the one  is confounded with the substance
of the brain, the other variously arranged in the organs.  Each of
these extremities have in turn  been  called the origin, and termi-
nation ol the nerves.   Some say,  that all  the nerves arise in the
brain, and terminate in the organs;  others, that they arise in the
organs, and,  bv uniting, form  the  brain.  These modes of expres-
sion a e both improper and convey  very  false ideas.  They can
be only useful  in  the description  of the  organs;  but, as other
  * These general sensations being founded on ou*"> knowledge of particular facts,
we have i'itro.iiie, d them alter ha\i:>jj ex[ iai; .V tl.ese facts.  This course is eov-
formahle to the manner in which our ideas art iorrp'-f*. 
88                      A SUMMARY
  expressions may easily be substituted, without at all obscuring the
  subject, it is desirable that they should be  abandoned.  It is evi-
  dent enough, that the  brain is  not formed by the union of the
  nerves, and it is equally certain that the nerves do not arise from
  the brain.  By these  expressions we merely  mean  to describe,
  metaphorically, the disposition of the two extremities of each
  nerve.
    Cerebral extremity of the nerves.—'The cerebral  extremity of
  the nerves are composed of very fine, and  loose filaments, which
  are continued into the substance of the^rain, for a short distance
  from the  point  where they are first perceived; these filaments,
  when united, form the nerve.
   There is a marked  difference between the  nerves.  Some are
  rounded,  others flattened, others hollowed out  at their sides, a
 great number are very long and  others very short.   It may be
 asserted that, in form, colour, &c. there are no two nerves which
 exactly resemble each other.  In general, they are so placed as
 not  to be exposed to injuries from external causes.   In going to
 the  different parts, the nerves divide into  large, and afterwards
 into smaller  branches;  and they terminate by filaments, so small,
 in the substance  of the organs, that they cannot be  distinguished,
 even by the assistance of the most powerful optical instruments.
 The  nerves   communicate  among  themselves, they  anastomose
 and  thus form what is  called a plexus.
   Organic extremity.—With the  exception of the optic  nerve,
 the organic extremity of which can be easily  distinguished, and
 of the auditory nerve, of which we have tolerably correct notions,
 we are absolutely ignorant of the disposition of the extremities of
 the nervous filaments in the tissue of the organs.  We hear much
 of the nervous extremities, papilla?, &c.  Physiologists  are  still
 in the habit of using  these expressions; but all that is said on  this
 subject is purely imaginary.  It is easy to demonstrate that those
 bodies, which have been, and are still, called nervous papillae, do
 not exist.
  The nerves are in general formed of filaments, excessively deli-
 cate, which are probably reducible into still  finer filaments, if our
 means of division were more perfect.  These filaments,  which
have  been  called  nervoOs  fibres, communicate frequently with
each other,  and affect in the body of the nerve, an  arrangement 
OF  PHYSIOLOGY.
89
similar to what is  found in  a plexus.  It is generally supposed
that a fibre is formed by an envelope, and a central puln, similar
in its nature to  cerebral substance, but I  believe that this is
merely hypothetical.   I have done all in my power to repeat  the
preparations, advised by anatomists to display this structure, but
with all my efforts, I have never been able to distinguish  it  The
tenuity of the  nervous fibres alone, appears tome to »be a most
powerful objection to it.  Since, with the aid of a microscope, we
can scarcely perceive the fibre itself, and may reasonably  suppose,
that this is formed by  fibres, still more delicate; how  I  would
inquire  is it possible to distinguish a cavity  filled with pulp?
  Whatever may be the disposition of the substance, which forms
the parenchyma of the nervous fibres, it is certain that  it possesses
the same chemical  properties as the  cerebral substance,  and  that
each nerve receives very  numerous small branches of arteries,
in proportion to its volume, and a proportionate number  of small
veins.
  The posterior branch of all those  nerves  which arise  from the
spinal  marrow present, not far from the point where they unite
wijth  the anterior  branch, an  enlargement  which  is   called  a
ganglion.   These bodies are of a colour, consistence, and struc-
ture essentially different from those  of the  nerves, and   their use
is unknown.  The  nerves of the eighth  pair, where they  pass out
from the cranium, exhibit enlargements of  this kind.

Of the Mechanism,  or Physiological Explanations  of Sen-
                           sations.
   The physiological  explanation of sensations consists, in the
more or  less  exact  application  of the  laws of physics,  and
chemistry, to the  physical  properties of that  part of the organ,
which  is placed before the nerves, as has been remarked, in  the
particular history of  each sensation. The  moment we  arrive at
the uses of the nerves in these functions, no further explanation
can be given.  It is necessary to adhere rigorously to facts.
   This consequence, so easy to deduce, does  not seem  to have
been perceived but by a very small number of authors; and even
in their works it is expressed very vaguely. All have endeavoured
to explain this action of the nerves.  The  ancients considered
these  organs as  the conductors of the animal  spirits.  At the
                               12 
90
A  SUMMARY
period when physiology was governed by  mechanical ideas, the
nerves were supposed to be vibratory cords, although their physi-
cal condition is such as to prevent their vibration.
  Some very intelligent  men  have supposed that the  nerves
were conductors, and even the secretory organs of a subtle fluid,
which they  have called nervous.  According to them, sensations
are transmitted to the brain, by means of this fluid.  At this mo-
ment, when the  attention is directed  towards the  imponderable
fluids, this opinion has attracted numerous disciples.  I  am ac-
quainted  with men who confer honour on the age, by their genius
and learning, who are inclined to admit that  electricity exerts  a
considerable influence  in the sensations, and other  functions/
To pretend to explain the sensations by referring them to certain
vital properties, which are called animal, perceptive, relative, &c.
is to  have recourse to  a most vicious mode of explanation; it  is
only a  new way of expressing the difficulty, it by no means re-
moves  it.  We  shall therefore class the action of the nerves
among  the  vital actions, which, as has been seen at the  com-
mencement of this work, are not  susceptible of explanation, in
the present state of science.  But that the nerves are  the agents
for the  transmission of those impressions which are received from
the senses, is conclusively demonstrated by  observation and ex-
perience.
  Thus if a man receives a wound which affects a nervous trunk,
the part to which the nerve is distributed becomes insensible.   If
the optic nerve be the one which has suffered, the individual will
become blind, and  if the auditory,  deaf.  We may produce these
effects at  any time upon  brutes, by dividing, or  even  simply  by
compressing the nerves.  When the compression is removed, the
nerve is  restored to its  sensibility as  before.   Jn  man, as in
brutes, the wounding of a nerve  produces severe pain.  In a word,
all  those  diseases  which alter, even slightly, the  tissue of the
nerves,  have a manifest influence  upon their action as agents of
transmission.
  We  are completely  ignorant of the  utility of the numerous
anastomoses which  are observed  among the nerves.  The siopo-
gitions which have been  made to explain  their use, are sufficient
to shew that physiology  is still in its infancy.
* Yide Appendix, No. 1. 
OF PHYSIOLOGY.
91
  Sensations are either vivid or weak. The first time a body acta
tipon our senses, the impression produced is generally vivid.   The
Vivacity of the impression diminishes, if the action of the body be
frequently repeated, and at last it is scarcely perceived. This fact
is expressed when we say, that habit blunts our feelings.   The
existence of  man, being as it were measure/!  out by the vivacity
of his sensations, he is induced to seek continually for new im-
pressions, which are always the most vivid; hence his inconstancy,
inquietude and  ennui, if he remain long exposed to the same
causes of sensation.
   We possess the  power of rendering our sensations more vivid
and distinct.  In order to do this, we dispose the organ of sense
in the most favourable manner,  we receive  but a small number of
sensations at a time, and we direct all our attention to them; thus
arises the important difference between  seeing, and examining,
hearing and listening, the common exercise of the sense of smell,
and snuffing, &c.   JSature has also given us the power of diminish'
ing our sensations.  Thus we draw down the eye-brows, and close
the eye-lids, when the impression produced by the  light is too
vivid, we breathe through the mouth when we  wish to diminish
the effect of a strong odour, &c.
   The  different  sensations also direct, assist, modify, and  may
even mislead each  other.  Smell seems  to be the sentinel and
guide to  taste, and  taste in  its turn exerts a powerful influence
over  smell.  Smell may exercise its functions separately  from
those  of taste, but the  reverse  cannot  be always done; as the
aliments and drinks cannot pass into the mouth without acting,
•more or less, upon the nose; whenever their taste is very disagree-
able, their odour, soon becomes so; again, those aliments, the odour
of which  is most  unpleasant, soon loose this quality when the
taste very vehemently desires them.*
   We know, from numerous observations, that the vivacity of the
impressions received  by the senses is increased by the loss of one
of these organs.   For example, the smell is more delicate in blind
or deaf  persons,  than in those who enjoy all their senses.  1 think
however, that the absence of smell, which we  often meet  with,
4oes not give any increased activity to the other senses.
*• CabaH>*ft 
92                      A  SUMMARY

  Sensations are agreeable or disagreeable; the first, when  they
are vivid, constitute pleasure, and the second pain.  By pl-asure
and pain nature induces us to concur in the order which she has
established among organized  beings.
  Though it may appear like sophistry to say, that pain is but the
shadow of  pleasure, still  it is certain, that  persons  who have ex-
hausted all the sources of pleasure, and have tnus become insensi-
ble to all ordinary sensations, have recourse to the causes of pain,
and gratify themselves by their effects.  Do we not  see, in all  large
cities, that men who are debauched and degraded, find agreeable
sensations where others experience nothing but the  most intoler-
able pain?
   It  is  necessary to  remark, that those sensations which  come
from  the  senses, are  distinct.   All our ideas, and  the know-
ledge  we  have of  nature, are  thus received.   Internal sensa-
tions, or sentiments do not possess these characters.  In general
they are confused, vague,  and often we are  not conscious of them;
they are not engraved  upon  the memory, but are always more  or
less fugitive.
   Y\ henever our organs act  freely, and according to the ordinary
laws of organization, our  thoughts are agreeable, the  pleasure is
sometimes very vivid.  But when  the functions are deranged,
the organs wounded, or diseases  have  impaired their action, our
internal sensations  are painful, according to the nature of tiie
injuiy.  This is the reason  why  pain constitutes  an important
part ox* the study of a physician.
   It is probable, that  the nerves, which pass directly  from the
brain  or  spinal marrow, are the organs for the  transmission of
internal sensations.   The physiologists of the present day, how-
ever, appear t;» attribute this function to the nerve, which is called
the great sympathetic*   We cannot say positively, that it  is not

  * Why should we consider the great  sympathetic as a nerve?  The ganglions
and filaments which pass from it, or lead to  it, have  no analogy with the nerves,
properly so calleu.  Their eolour, form, consistence, disposition, structur.- and
chemical properties, are all different.   Noi Wave they any greater analo >y in
their vital p'.-opertjps. VVe may  scratch, or cut a ganglion, or even tear it without
the animal appearing to be coi.scious ot" it. I hare otten made these experiments
on the ganglions in the necks of horses antl tle^s.  Similar operations perform. d>
mi the  cerebral nerves will produce the most tcrii.ic pain   We may  take :>>■ av-
ail liu- ganglions «t* the neck, and eveu the first ;^»ng1ions of the. thorax, without 
OF PHYSIOLOGY.
93
so; but it is impossible to admit this doctrine, as it is not founded
on any fact, or direct experiment.
  The causes which modify internal and  external sensations are
innumerable.  Age, sex, temperament,  Reasons,  climate,  habit,
and individual   character, each separately modify sensation; but,
when they are  united, the  result  is much  more  manifest.  The
difference of sensations among different individuals  is expressed
by  the common maxim, "every one has his own wav of thinking."
   It is  probable that only internal sensations exist in the  feetus.
We are led to  suppose this by  the motions  which it  executes,
which appear to be the result of impressions arising spontaneous-
ly  in the  organs.   It is well known from experiment, that when
any derangement arises in the circulation or respiration  of  the
mother, it is followed by the motions of the fcetus.  AH the sen-
ses are  not found  to exist at birth, nor  for sometime afterwards.
Taste,  touch, and smell are alone exercised, sight and  hearing
are developed  later, as we have  observed in the  history of each
particular function.  Each sense  must pass through  different, de-
grees, before it can  arrive at perfection.it is indispensable, there-
fore, that each  sense should receive what may be properly called
an education-  If any person will  follow an infant  in the develope-
meht of its senses, he may easily satisfy  himself  of the modifica-
tions they undergo before arriving at perfection.
   In those sensations which are  produced by distant objects, the
 education is slow and difficult; in those which arise from contact,
it is much more prompt, and  appears to be easily effected.   Du-
 ring this education  of the senses, that is, in our infancy, the sen-
sations  are confused and weak.   But afterwards, especially those
of young people, are remarkable for their number and vivacity.

any sensible derangement in the functions, even of those parts to  which we can
trace them.  What reason is there then for considering the system of ganglions as
 constituting a part of the nervous system.' Would it not be  more  philosophical,
 and especi?lly more useful to  the future progress of physiology, to acknowledge
 that at this moment the uses of the great sympathetic are eutirely unknown?  We
 shall be confirmed in this idea by reading on the subject.  Every author has some
 peculiar opinions on this point.  We hear, e. g. the ganglions considered as ner-
 vous centres, small brains, collections of cmeritious substance for the nourish-
 ment of  the nerves, fete. If we inquire after the proof by which  these authors
 establish their doctrines; we are surprised, not to find  any,  but that their  asser-
 tions are mere freaks of the imagination. 
M
A  SUMMARY
At this age they are deeply engraved in the memory; and, of con-"
sequence, are destined to constitute a part of our intellectual ex-
istence, during the remainder of our lives.  With the progress of
age our sensations lose their vivacity, but become more perfect, as
respects exactness,  after arriving at the adult age.  In old  age
the\ grow weak, and are produced  with slowness and  difficulty.
This effect is more remarkable in those senses which make us ac-
quainted with the physical properties of bodies, but much less so in
those by which we become informed of their chemical properties.
These last senses, those of taste and  smell, alone preserve any
activity in decrepitude, the others are nearly extinguished, by the
diminished sensibility, and the succession of physical alterations
which they undergo.


      OF THE FUNCTIONS OF THE  BRAIN.

  The human  understanding exhibits  phenomena so different
from any thing else which natural objects present, that they have
been  referred to a particular being, which  has  been  regarded as
an emanation of the  Deity.  This idea seems too agreeable and
consoling, for us to allow the  physiologist to question its truth.
But the severity of language, or  rather of logic, which physiology
now exacts, requires  that we should treat the human understand-
ing, as if it were the  result of the action of an organ.   By devia-
tinir from this rule, some  men, very justly distinguished for their
intelligence, have fallen into the most serious errors; by following
it, we have, on the contrary, the great advantage of still pursuing
the same  .nethod of study, and of  rendering very plain, things
which have been generally considered as beyond the grasp of the
human mind.

                         The  Brain.
  The brain is the material organ of thought, which is proved by
innumerable facts, and experiments.
  Under the  denomination of  brain, I include  three parts, dis-
tinct from each other, though they are all united at certain  points,
t-hey are the cerebrum, cerebellum, and medulla spinalis. 
OF  PHYSIOLOGY.
95
  In  each of these  principal divisions we find distinct parts,
which have a sort  of separate existence, so that there is nothing
more complicated and difficult in anatomy, than the study of the
organization of the braiij.  In proportion, however, to the impor-
tance of the functions of this organ, anatomists and philosophers
have at all times devoted themselves to its dissection.   The re-
sult of this is, that the anatomical history of the brain, is one of
the most  perfect parts of anatomy.   Very lately this subject has
been  much elucidated  by the publication of the work of Messrs.
Gall  and Spurzeim, and to the investigations to  which it has
given rise.*
   The brain being of an extremely delicate texture, and its func-
tions being easily destroyed by the least derangement, nature has
taken uncommon care to protect it from injuries arising from the
contact of surrounding bodies.
   Among the protecting parts  of the brain which  have  received
the denomination tutamina cerebri, we remark the hair, the scalp,
the muscles, the pericranium, the bones of the skull, and  the dura
mater,  which are particularly  destined to guard  the cerebrum
and cerebellum.
   The Hair.—By its quantity and arrangement, the hair is very
suitable to weaken the effects of blows upon the head. As it is a
bad conductor of caloric, it forms a covering, the texture of which
being loose, intercepts a large number, of small masses of air; it is
well disposed, therefore,  to preserve the head of a uniform  tem-
perature, in some sort  independently  of  the air, or surrounding
bodies.  As it is impregnated with an oily substance, it imbibes
but a small quantity of water and dries rapidly.  The hair being
also a bad conductor of the electric fluid, it in  some degree  insu-
lates the head, hence the head is less likely to  be affected by this
fluid.
   It is easy to conceive how the scalp, the muscles  which cover
the cranium, and the pericranium, concur in protecting the brain;
it will not be  necessary, therefore, to insist on this point.
   The Cranium.—But of all the means of protecting the  brain
the most  efficient, is the collection  of bones, called  the cranium,
which completely envelope  this organ.  In consequence of the
hardness and streigth of this  envelope, and  its spherical  form,
** Vide Appendix, No. C. 
96
A  SUMMARY
all  pressure or percussion, exerted  upon any given part of the
head. <s distributed from this point  to all the rest, and is. there-
fore less felt by the brain.   If, for example, a man receives a blow
from a cane on the top of his head, the motion will be propagated
in every direction, and will extend even  to the middle part of the
base of the cranium,  that  is, even  to  the body  of the sphenoid
bone; if the blow  be given upon the forehead, the motion will be
propagated  towards the middle of the  occipital bone.  In this
transmission of motion through  the bones  of the cranium, it has
been supposed, that  these  bones experienced a  slight,  but  re-
ciprocal displacement, which are  with difficulty distinguished, in
consequence  of  the  disposition  of the different articulations.
There  are, however, good reasons to believe that the cranium re-
sists, as if it were a single bone.
   Changes of form in the brain.—Authors have not dwelt suffi-
ciently upon the  fact, that  it must necessarily  happen, that the
cranium will change  its form, whenever it is  pressed or struck
smartly.  The softness  of the cerebral  mass will enable it  to
endure slight changes in the form of its envelope, without any se-
rious injury.  The softer the brain is, the more able it will be  to
suffer  strong pressure,  or  percussion,  without  inconvenience.
This i» the reason why new-born infants, the bones  of the crani-
um of which  are  very moveable upon each other, often have the
head strongly compressed, and  even sensibly deformed, without
any injurious consequences.   The same things exist, in a degreo,
in children  at a mere advanced age, which receive, without dan-
ger, violent blows upon  the head.  In  the early periods of life,
trhe brain  is much softer than in the adult.*
   Dura Mater.— I he dura mater is so arranged as to  protect the
brain, as it were, against itself.  Indeed, without the folds which
are formed by this membrane, viz. the falciform process, anil the
tentorium, one hemisphere of the  cerebrum would press upon the
other,  when the head  was  inclined to one  side; and the brain

  * II the brain were perfectly fluid  and homogeneous, whatever might be the
changes in  the form of its envelope, the if would not result any injurious effect.
15ul a- the brain is of a soft consist, nee, but not homogeneous, it Allows, that
violent nlows arc often followed by serious accidents, such as concussion, extra-
vasation of blood, abscess, &c. 
OF PHYSIOLOGY.
97
would compress the cerebellum, when the head was erect; so that
the different parts of the organ would destroy each other.
  Medulla Spinalis.—If we compare  the precautions  taken  by
nature, to preserve the cerebrum and cerebellum from  external
injury, with those which we find she has guarded the  spinal mar-
row, we  shall  be led to infer, that this last is of greater impor-
tance than the first; or that its texture,  being more delicate,  re-
quires extreme care.   This is, in fact, the case.   The spinal mar-
row holds a rank in the animal economy,  at least as important as
the cephalic portion of the  nervous  system.  The  least shock
wounds it, the least compression destroys its functions in a mo-
ment.   It was, therefore, necessary that the vertebral canal which
contains it, should  afford a powerful protection.  This end is at-
tained in a manner so perfect, that nothing is more rare than an
injury of the spinal marrow.  The vertebral column necessarily
unites great solidity with great mobility.   It is the  centre of mo-
tion in all  the efforts of the body; it  is also the centre of motion
in  the  action  of the  extremities,  and executes very  extensive
movements itself.
   We cannot here enter into the details  of this admirable mech-
anism.   We refer the  reader to the "Anatomie Descriptive de
Bichat," for a further account of this subject.
   Arachnoides.—Besides the different envelopes of the brain of
which we have spoken, and the dura mater, which  encloses it  in
its whole extent, this organ is surrounded by a very delicate se-
rous membrane, which is called the arachnoides, the principal  use
of which, is to form a very thin  fluid, which lubricates the brain.
The arachnoides penetrates into all the cavities of the brain, and
forms th/re a  perspiratory fluid.
   The Pia Mater.—The manner in which the blood-vessels enter
and pass out from the brain, is extremely curious.  We shall  en-
ter more particularly into a consideration  of this subject, when we
come to treat of the circulation.  We shall only remark here,
that the arteries, before penetrating into the substance of this or-
gan, are reduced to capillary vessels, and  that the veins affect  the
same disposition  in  passing  out from this substance.   As these
very fine blood-vessels  communicate  with each other, by numer-
ous anastamoses, the result is, that there is formed  on the sub-
                              13 
9S
A  "SUMMARY
stance of the brain, a vascular net-work, which has very improper-
ly been called tne pia-mater.   This net-work is introduced into
the cavities of the brain, and  it is this which  forms the plexus
choroides.
   We shall not pretend to give here a description of  the anato-
my of the brain;  but  shall  limit ourselves to some general reflec-
tions on  the subject.   Almost all authors, who have given an ana-
tomical description of the brain, in their works, have neglected to
observe a proper  strictness in the expressions they have  employed,
and  have suffered their minds to be influenced by  preconceived
and  hypothetical opinions.  It is indispensable, for the future
progress of anatomy and physiology, that we should employ terms
which are precise, to  avoid, as  much as possible, hypothetical ex-
pressions, and, above  all, to reject the supposition that the nerves
terminate or unite at any given point of the  brain; that the soul
has its seat  in any particular part  of  this organ; or, that  the ner-
vous fluid is secreted by a certain portion  of the cerebral mass,
while the rest serves  as a conductor of this  fluid, &c.   From ne-
glecting  this method,  those authors who have described  the brain,
have presented false ideas, expressed in an obscure manner.
   When we speak of the  brain, we mean the organ that fills the
cavity of the cranium, and  the vertebral canal.  To facilitate the
study of  it, anatomists have divided  it into three  parts, viz. the
cerebrum, the cerebellum, and  medulla spinalis.  This, however,
is purely a scholastic  distinction; in fact, these  three parts form
but one organ.  The  spinal marrow is but  a prolongation of the
cerebrum and  cerebellum, and these an expansion of the spinal
marrow.
   To say that the cineritious substance of the brain produces the
white part,  is entirely  gratuitous.   In truth, the cineritious, no
more produces the white part  of the  brain,  than the muscle pro-
duces the tendon in which it terminates, or the heart the aorta.
In this respect, the anatomical system of Messrs. Gall and Spur-
ziem is essentially defective.
   In man, that part  which is  properly called the brain, is more
voluminous than  in other animals.   The dimensions of this organ
are proportioned  to those  of  the  head.  Individuals differ very
much in  this respect.  Generally  speaking,  the volume of  the
brain is in a direct proportion  to  the  capacity  of the  mind.   It 
OF  PHYSIOLOGY.
99
would be incorrect, however, to suppose that every man who has
a large head, must, necessarily, be possessed of superior intelli-
gence, because many  causes, besides the  volume of the brain,
may increase the size of the head.  But it is, nevertheless, very
rare that  a man distinguished for his mental faculties, is not
found to have a large head.  The only means of ascertaining the
volume  of the brain in  man,  during life, is to measure the dimen-
sions of the cranium.  No other method, not even that proposed
by  Camper, can be relied upon.
  The brain of man presents more numerous circumvolutions, and
deeper inequalities than other animals.  The number, volume, and
arrangement of the circumvolutions are various.  In some brains
they are very large, and in  others, they are numerous and small.
Their disposition differs in each individual.  Those of the right
side are not arranged like  those of the left.   It would be an in-
teresting  point to  determine, whether  there exists any  relation
between the  number of the circumvolutions, and  the  perfection
or imperfection of the intellectual faculties; between the modifica-
tions of the mind, and  the arrangement of the cerebral  circumvo-
lutions.
  The volume and weight of the cerebellum, differ in different in-
dividuals,  and  at the different periods of life.   In the adult the
cerebellum is equal to the eighth or  ninth  part of the  cerebrum;
but it forms only the sixteenth or eighteenth part in new born in-
fants.   We do not find circumvolutions on the surface of the ce-
rebellum, but it is divided into lamelke, each being separated by
a furrow.  The number and arrangement of these lamellae differ,
in  different individuals.  We may  here  repeat the observation
which was  made  above, in speaking of the cerebral circumvolu-
tions.   An Italian anatomist, Malacarne, is said  to have found
three hundred and twenty four of these lamella; in the cerebellum
of an ideot, while in other  individuals he  found more  than eight
hundred.
   The  substance of the cerebrum is soft and  pulpy;  its form is
easily altered;  in  the  fcetus it is almost fluid;  it  has  more con-
 sistence in childhood,  and still more in the adult.  We find also,
 that the degree of consistence varies at different points of the
organ, and in  different individuals;  the odour is insipid, and 
100                   A SUMMARY

resembles that of the semen, and remains  for many  years  in
dried brains.
  We find two substances in the brain.   The one is grey and the
other white.  The first  is called  the cineritious, and the other,
the medullary substance.  The medullary portion constitutes the
greater part of the organ, it occupies  more particularly the  inte-
rior of it, and that part which  corresponds to the base of the cra-
nium.   It has a fibrous appearance, and possesses  more firmness
than the cineritious part;  and it forms a great  part of the spinal
marrow, particularly near its surface.
  The cineritious substance, which is sometimes called cortical,
forms a thick  lamina on  the external part of the cerebrum and
cerebellum; and  is likewise found in some of the  internal parts.
In some parts, it is  covered by medullary matter, in  others, it
seems intimately combined with it, and sometimes  these two sub-
stances are  disposed in lamin'e or alternate strife.  We find  other
parts in the brain distinguished  by their colour, viz. yellow and
black.
  When we examine the cerebral substance, by means of a micro-
scope, it appears to be formed of an immense number of globules,
of unequal  magnitude, they are about eight  times smaller  than
those of the blood.  In the medullary substance they are disposed
in right lines, and have the appearance of fibres.
  According to M. Vauquelin, there is no difference in the chemi-
cal composition of the different parts of the nervous system.  The
analysis of the cerebrum, cerebellum, spinal marrow, and nerves,
has exhibited the same result.
   The arteries of the brain are large, and are tour  in number, viz.
the two internal  carotids, and the  two vertebrals, they have  a  pe-
culiar arrangement, on which we  shall more particularly  insist
under the article, arterial circulation.   We shall only observe
here, that they are principally placed at the  inferior part of  the
organ, that, by their anastomoses, they form a circle, and that they
are reduced down to capillary vessels before they penetrate into
the substance of the  brain.   It has been computed that the  brain
receives about one eighth of all  the blood which passes from  the
heart   But this  estimate is only an approximation;  the quantity
varying, no doubt, according to a great variety  of  circumstances.
We know from recent dissections, that  the cerebral arteries  are 
OF  PHYSIOLOGY.
101
accompanied by filaments of the great sympathetic nerve; we can
trace  these filaments  with ease, along the principal  branches  of
the arteries.  It is to be presumed, therefore, that they accompany
them  even  in their most minute ramifications.   But it is not to be
concluded, necessarily, from this disposition, which  is common to
all the arteries, that the brain  receives nerves.  The filaments of
the j*reat sympathetic have here, as they have  every where else,
arelatioH to the parietes of the arteries alone.
   The cerebral veins.—These  have also a peculiar arrangement.
Thev occupy the superior parts of the organ, they have  no valvu-
lar structure; and they terminate in canals, situated between the
lamiri'e of the dura mater. We shall particularly investigate this
subject under the head, nervous circulation.  No absorbent vessels
lime  yet been detected in the  brain.

Observations made on the brain of man, and living animals.
   It has been ascertained from the heads of new-born infants,  the
cranium of which is  still membranous, and from those of adults,
where the brain has been  denuded by wounds and disease, that it
has two distinct movements.    The first is evidently synchronous,
with  the pulsation of the heart and arteries, the second, with res-
piration; that is, the organ seems to sink down upon itself, at  the
moment inspiration takes place; the opposite phenomenon occurs
during expiration.  According as the respiration is more or less
6trong, are these motions of the brain manifest.  These two mo-
 tions are very  readily remarked in animals; and it is not easy to
 explain why the existence of  this phenomenon  should lately have
 been called in question.  We must suppose that these motions are
 very distinct when the integrity of the cranium is preserved, and
 that  they  are necessary to the  perfection of the cerebral functions;
 but this is a point which has not been demonstrated.
   The cerebrum and cerebellum exactly fill  the  cavity  of  the
 cranium, in the dead  body;   of consequence, during life,  when
 these parts receive a great quantity of blood, and their vessels are
 distended by  it, and when there is a fluid secretion continually
 forming upon its surface  and  that of its cavities, the organ must
 endure a  considerable pressure, which  will,  of course, vary in
 intensity,  with the quantify of blood  which penetrates  in, and
 passes out from the brain. 
102
A  SUMMARY
  As the spinal marrow does not exactly fill the cavity of the
vertebral canal, it is not as likely to  be compressed, as the cere-
brum and cerebellum.  But the pia mater exerts upon the spinal
marrow a manifest pressure,  so that  this is nearly in the same
condition as the brain, as respects pressure. It appears that  this
pressure is indispensable to the functions of the organ; for when-
ever it is suddenly diminished or increased, the functions are  sus-
pended;  but if this be done gradually, the  cerebral functions con-
tinue.
  Uses of the cerebrum.—The uses of  this organ in the economy
are extremely important and numerous. It is the organ of intelli-
gence; it is the source of all  those means by which we act upon
external bodies; it exercises  an influence, more or less marked,
upon all the  phenomena of life, and it establishes a relation, al-
ways active,  between  the  different organs; or, in  other words, it
is the principal agent  of the sympathies.   We shall now consider
it under the first character.

                       Of Intelligence.
  Whatever  may be the number and diversity of the phenomena
which  pertain to the human understanding, however different they
may appear from  the other phenomena of life, and  though they
may be evidently dependent  upon the soul, it is indispensable to
consider them as the result of  the actions of the brain;  and not to
distinguish them in any way from other  phenomena, which  are
dependent on organic action.  Indeed, the functions of the brain
are absolutely governed  by the  same general  laws as the other
functions; they are developed, and they decay, with the progress
of age; they  are modified by habit, sex, temperament, and indivi-
dual character; they  are deranged,  depressed, and  exalted, by
disease;  and  the physical lesions of  the brain pervert or destroy
them.   In a word,  like every other organic action, they are  not
susceptible of explanation by us; and  in investigating them, lay-
ing aside hypothesis, we must be governed by observation and ex-
perience alone.  It is also necessary to guard ourselves against
the  impression, that  the study of the functions  of the brain is
more difficult than  that of  the other  organs, and  that it belongs
exclusively to metaphysics.  By adhering rigorously to observa-
tion, and scrupulously avoiding all explanations  or conjectures, 
OF PHYSIOLOGY.
103
this  study becomes purely physiological.   Perhaps  it  is even
easier  than many of the other functions, from the facility with
which we are enabled to produce and examine its phenomena.
  The study of the understanding has not heretofore  been consi-
dered  as constituting an essential part of physiology.  One  sci-
ence is specially devoted to this, and is called ideology.   Persons
desirous of examining this interesting  subject  in extenso, may
consult the works of Bacon, Locke, Condillac, Gabanis, and es-
pecially the excellent work of M. Destutt Tracy, entitled  "Ele-
ments of Ideology."   We shall confine ourselves to some  of the
fundamental principles of this science.
   The innumerable phenomena  which  constitute the human un-
derstanding* are but  modifications of the faculty of perception.
W hen  we examine them with attention, we shall find no difficulty
in confirming this observation, the truth of which is generally ad-
mitted by modern metaphysicians.
   We  may divide  the faculty of perception into four principal
modifications.—
   1st.  Sensibility, by which we receive  impressions  from within
 or from without.  2d. Memory, or the faculty of re-producing im-
 pressions, or  sensations previously  received.  3d. The faculty of
 perceiving the relation between sensations, or  judgment.  4th.
 Desire or  will.

                         Of Sensibility.
   All  that we have  said  of sensations  generally, will  apply to
 sensibility; for this reason, we  shall here  limit ourselves to ob-
 serving, that this faculty is exerted in two very different modes.
 In the first,  the  sensation passes  unobserved by us; we do  not
 perceive it.   In the second  we  take notice  of  it, and  are  con-
 scious of  its existence.  It is not sufficient  then, that a body acts
 upon our senses, or that the nerve transmits the impression which
 it has received, to the brain, it is not even sufficient that this or-
 gan receives this  impression.  In order for a  perfect sensation to
 exist.it is necessary that the brain  should perceive the impression

   * The human understanding has been  called  the spirit, the faculties of the
 loul intellectual faculties, cerebral functions, &c. 
104
A  SUMMARY
received by it.   An  impression thus received, is called in  ideo-
logy, a perception, or idea.
   We may easily prove  upon ourselves  the existence of  these
two modes of sensibility.  It is easy to see, for example,  that a
crowd of objects are continually acting  upon our senses, without
our noticing them.   This effect depends in a_great measure upon
habit.
   Sensibility varies infinitely, in different individuals.  In  some
it is very obtuse, in  others it exists in  an extraordinary degree;
generally, in those who  are well constituted; there is a medium
between these two extremes.
   In infancy and youjh, the sensibility is vivid,  and remains
nearly in the same state until the adult age; but as old age ad-
vances,  it becomes  materially diminished; so that the decrepit
are nearly insensible to all the causes of ordinary sensations.

                       Of the Memory.
   The brain is capable, not only of receiving impressions, but also
of re-producing  those, which had before existed.  This cerebral
action, when it  produces recently acquired ideas,  is  called me-
mory.  It is  called recollection,  when the ideas have been  long
acquired.  An old man  who recalls the  events of  his youth,
recollects them;  a man who retraces  the sensations which he has
experienced during the past year, remembers them.
   Reminiscence  is an idea re-produced, which we do not recollect
to have previously received.
   Like sensibility, the memory is very much developed in infancy
and youth. At this period of life the mind acquires knowledge with
the most facility, especially of that kind which does  not require
much reflection; such as  languages, history, and the descriptive
sciences. In the progress of age, the memory becomes  weakened,
it diminishes in  the  adult, and  is almost lost in old  age.   We
sometimes see individuals, however, whose memory remains,even
at the most advanced periods of life. This advautage is generally
derived from constant exercise, as has  been sometimes observed
in actors.  But it is  undoubtedly true, that  it often exists  to the
injury of the other  intellectual  faculties.   The more vivid the
sensations  are, the  more easily are they  remembered.   The 
OP  PHYSIOLOGY.
105
memory of internal sensations, are almost always confused. Cer-
tain diseases of  the brain completely destroy the memory.

                        Of Judgment.
  There can be no doubt, that judgment is  the most important of
the intellectual  faculties.  It  is  by this faculty that we acquire
all  our knowledge.   Without  it oar life would  be purely vegeta-
tive, and we should have no idea of the existence of other bodies,
or  even  of our own, as all our knowledge  is the direct result of
the faculty of judgment.  To  form a judgment, is to establish a
relation between any two ideas, or collections of ideas.   When I
judge that a work is good; I perceive that  the  idea  of  goodness
agrees with  the  bpok which I  have read; I establish a relation, I
form an idea different  from what sensibility, or  memory would
have  enabled  me  to   form.  A series of judgments  connected
together constitute reasoning.   We may  readily conceive how
important it is for U3 to form correct judgments;  that is, that  we
do  not establish any relations but those which really exist.   If
I judge a substance which is poisonous, to be salutary, I incur the
danger of losing my life; the  false judgment which 1 have formed
will be very injurious to me.  The  same  remark will apply  to
all  false judgments.   Nearly  all  the misfortunes to which man is
exposed, morally speaking, have their origin in errors of judgment;
crimes, vices, and bad conduct, are  all the  results of false judg-
ments.
   It is the object of one science, viz. logic, to teach  us to reason
justly.  But sound judgment and good sense,  or erroneous judg-
ment, and mental weakness, are  the results of organization.  It is
impossible  to change in this respect; we  must remain as nature
has formed  us.  Some men are endowed with the valuable gift of
discovering relations which have never before been perceived.  If
these relations should  happen to be important,  so  as  to confer
great benefit on mankind, their possessors  are said  to  be men of
genius;  but if they reiate to oDjecls of less  importance, they  ar«
said to possess wit or imagination.  It is principally  by their man-
 ner of perceiving relations, or judging, that men differ from each
 other.   Vivacity of sensation appears to be injurious to correct
 judgment;  this is the  reason why this faculty becomes more per-
 fect with age.
                               14 
106
A  SUMMARY
                   Of £/ae Desire or Will.
   We give the name of w ill to that modification of the faculty of
 perception, by which we experience desires. In general, it is the
 consequence  of our judgment, and it  is worthy of remark, that
 upon this faculty, our happiness or unhappiness necessarily  de-
 pends.   When our desires are satisfied we  are happy, we are un-
 happy on the  contrary when we cannot gratify them.   It becomes
 us, therefore,  so to direct our desires that we shall be enabled to
 gratify them.  We must avoid desiring, for example, those  things,
 which it is impossible for us to obtain; and it is still more  impor-
 tant for us not to desire those which are injurious, for in this case
 we cannot escape  unhappiness, whether we indulge them,  or not.
 Morality is a  science, the object of which is to give the best di-
 rection to our desires.   Desires have been  generally confounded
 with that cerebral action which  presides over the contraction of
 the voluntary muscles.   1 think it advantageous to  the student
 that this distinction should be established.
   Such are the four principal distinctions into which the  faculty
 of perception has  been divided,  they have been called the  simple
faculties of the mind.   It is the  combination and reaction of these
 faculties upon each other which constitutes the intelligence  of man
 and the higher order of animals. There is, however, this remarkable
 difference between man and other animals; they remain always in
 nearly the same state, their faculties receiving but little improve-
 ment, in the course of their  lives;  but man derives improvement
 from  every object  by which he is surrounded, and is thus enabled
 to attain that  intellectual superiority, by which he is distinguished.
   The faculty of generalising, which consists in creating signs to
 represent ideas, to assist thought by means  of these signs,  and to
 form  abstract  ideas, is characteristic of the human understanding;
 it is this which  enablesjit to acquire that prodigious extension
 which we see in civilized nations.  This faculty of generalising
 can of  course  only  exist  in  a  state of  society.   An indi-
 vidual who  should have lived  alone, who  should not have  had
 any intercourse  with his fellow creatures, even in his early years,
 of which there have been several examples, would not differ much
 from  brute animals, he would only  possess the  four simple facul-
 ties of the mind.  It is the same with  those individuals to whom 
OF PHYSIOLOGY.
107
nature, by a defective organization, has denied the faculty of em-
ploying signs, or of forming these abstractions, or general  ideas;
they remain all their lives in a perfect state of brutality, as we ob-
serve in ideots.
  In  general, the physical circumstances in which a  man finds
himself placed, will have a powerful  influence upon the develope-
ment of his understanding.  If he is enabled to procure subsis-
tence with ease, and to satisfy all his physical wants, he will be in
a situation favourable to the  cultivation of his mind, and a free
developement of his  mental faculties.   But if he can only, with
difficulty, satisfy the demands of nature, his mind being chiefly
directed to that single point, will necessarily remain in a rude and
imperfect state, as is always found to be the case among savages
and slaves.

                         Of Instinct.
  Nature has not abandoned animals to themselves.   It is neces-
sary that each should  exercise a series of actions from which re-
sults that astonishing harmony, which we witness among organized
beings.  To induce animals to concur in this, and  to execute those
actions  for which each is designed,nature has given them instincts,
that is  desires, inclinations, wants, by means of  which they  are
continually and  forcibly compelled to fulfil the designs of nature.
  Instinct may exist in two  different ways, viz.  with,  or without
a knowledge of the end.   The  first may be called intelligent in-
stinct, the second blind, or brutal instinct.  The first is more par-
ticularly the prerogative of man; the  second pertains to  animals.
  In examining with care the numerous phenomena which depend
upon  instinct, we find  that it has two principal objects;  the first
is the preservation of  the  individual, and the second that of the
species.  There  are  as  many instincts as  species of animals,
varying according to their  organization.   As organization varies
among  individuals, these instincts are much more remarkable in
some, than others.
  In man we find two kinds of instincts, the first relates to his
condition as an animal, and is always presented by him in what-
ever situation he is found.   This kind of instinct resembles that
of animals.  The other arises from  the social  state.  Without
doubt it depends, like every other vital  phenomenon,  upon orga- 
108
A  SUMMARY
nization.  But this is never developed but in a state  of civil  so-
ciety, for this purpose it  is necessary that, he should enjoy  those
advantages which accompany this state.
  The first, which may be called a.nimal instinct, includes hun-
ger, thirst, a want of cloathing, and habitation; a desire of happi-'
ness, or of agreeable  sensations, and  the fear of pain  and  death;
a disposition to  destroy  other animals, or even those of his own
species, when dangers are to be  feared  from them, or advantages
to be  derived  from their destruction; the venereal appetite; at-
tachment to children;  tendency to imitation; and a love of society,
which  leads to  civilization,  -Sec.  These  instinctive sentiments
are constantly acting  upon man, and  induce him  to concur in  the
order established among organized beings.   The natural  wants
of man are more numerous  and various than those of  other ani-
mals,  in a direct proportion to his intelligence.   In  every other
respect, he enjoys a decided superiority over all other animals.
  When man  lives in a  state of society, he is enabled easily to
satisfy all  the  wants, «tt which  we have been speaking, he  has
then leisure; in  other words, to satisfy these first wants, requires
but a small portion  of his time and faculties.   Then  arise new
wants, which may be  called social.  Such is our desire to  have a
a very vivid consciousness of our existence; a feeling which,  the
more it is indulged in, the  more difficult  it is to satisfy, because,
as we have already observed, our sensations become weakened by
habit.
  This fondness for  vivid  impressions, joined  to a  continual
diminution in the strength of our sensations, causes inquietude
and vague  desires, which are increased by the importunate recol-
lection of the vivid sensations that we formerly experienced.  For
the purpose of removing  this state, we are compelled  to have  re-
course to a continual  change of objects, or to increase  the inten-
sity of the  same sort of impressions.   From this arises  an  incon-
stancy, which does not permit us  to fix any limits to our wishes,
and a progression of desires  which is annihilated by  indulgence,
but affords  us no gratification; hence arises ennui, that unceasing
source of misery to civilized man, when he has  no employment.
  This desire of vivid sensations,  is counterbalanced  by a love of
repose, or  indolence,  which acts so powerfully on  the  hi°-her
classes of society.  These two opposite sentiments modify each 
OP PHYSIOLOGY.
109
other, and from their action and reaction, result a love of power,
of consideration, and of wealth, which enables us to indulge both.
These two  instinctive  sentiments  are  not  the  only  ones which
arise from the social state; it developes a crowd  of  others,  less
important, indeed, but not less real.  Our natural wants, also, be-
come remarkably  altered; instead of hunger, a most capricious
taste is often substituted; for the venereal desire, feelinus of a very
different nature, &c Natural wants modify social wants, and  vice
versa; and  when, in addition to this, we recollect that, age, sex,
temperament, &c. have a strong influence upon all our desires, we
may form some  idea  of the difficulties which a study of the in-
stinct of man presents.   This part of physiology has been hereto-
fore scarcely noticed.
  We may  at the same time remark, that an  increase of the so-
cial wants,  is always accompanied by a corresponding develope-
ment  of the understandrng.  There is no comparison, as relates
to  the capacity of the mind, between  man in  the more  opulent
class of society, and as he is found in  that condition, where all
his physical energies are barely sufficient to provide for his first
wants.

                       Of the Passions.
  In general, we understand by  the  term passion,  an  extreme
and exclusive instinctive sentiment.  A man in  a passion, neither
sees, hears, or is conscious of  any thing, but the sentiment by
which he is excited; and, as the violence of this sentiment renders
it disagreeable, and even painful, it has received the name of pas-
sion or suffering.  Passions have the same end  as instincts; they in-
duce animals to act according to the general laws of living bodies.
   We see in man, passions, which he  has in  common with other
animals, which  consist in vehement, animal  desires; and others,
which display themselves in a state of society only; these are the   -
social wants, very much increased.
  The animal passions relate to a double end,  as we have before
remarked in speaking of natural instinct, viz. the preservation of
the individual, and that of the species.
  To the preservation of the individual belong, fear, anger, grief,
hatred, and excessive hunger. &c; to that of the species, the vene-
real appetite, jealousy, and furious anger, when the offspring are 
110
A  SUMMARY
 in danger.  Nature has attached great importance to this class of
 passions, which exist  in their full  force in man, in  a state of so-
 ciety.
   The passions peculiar to a state of society, are but the social
 wants carried to an extreme degree.   Ambition is but the excess
 of a love of power; avarice, an excessive desire of fortune; hatr.;l,
 and vengeance  are but natural  and impetuous wishes to  injure
 those who have injured  us; a passion for play, and  almost  every
 other vice, is the result  of a love of violent excitement.     .  •
   Among the  passions, some  weaken  or  extinguish themselves
 when they are satisfied; others, again, only i.c .■■••a'se by imiulgenca.
 Happiness is often diminished by the first, as we sometimes sec
 in love; but unhappiness is necessarily attached  to the last, ex-
 amples of which are constantly furnished by the ambitious, ava-
 ricious, and envious.
   If wants develope  the powers of the understanding, the pas-
 sions are the principal cause of every thing very great which has
 been accomplished by man, either good or bad.  The great  poets,
 heroes, criminals,  and conquerors, have always  been men who
 were strongly under the influence of the passions.
  In speaking of the passions, shall we say with Bichat, that they
 reside in the organic life, or with the ancients and some moderns,
 that anger i* •" the head, courage in the heart, and fear in the se-
 milunar ganglion, &c?  Passions are but internal  sensations, they
 cannot therefore be said to have a seat; they result from  the ac-
 tion of the nervous system, particularly of the brain; they do not,
 therefore, admit of  explanation.  We are capable  of observing di-
 recting, calming or extinguishing them, not of  explaining them.*


                        OF MOTION.

  The functions which  we have now examined, depend  entirely
 on the faculty of perception.  It is  by  this faculty that we arrive
 at a knowledge of the objects which surround us, and of ourselves.
  *  This would be the place to treat of the use of the different parts of the brain
 in intelligence and the instinctive faculties,  but this  subject is very conjectural,
 and  tot) little understood to enter into an elementary work. We have been occu-
pying ourselves with direct  experiments upon this point,  and shall publish the
 results as soon as we think them worthy of public attention. 
01'  PHYSIOLOGY.
Ill
  To terminate the history of the functions of relation, it only re-
mains for us to speak of those functions by  means of which we
act upon foreign bodies, impress upon them the  changes  which we
judge necessary, and express our sentiments and  ideas to those
by whom we are surrounded.  These functions are but different
shades of the same phenomenon, muscular contraction.   So that
the faculty of perception on the one side, and muscular contrac-
tion on  the other, constitute really all our life of  relation.  We
shall first  define muscular contraction in general, after  which,
we shall treat of its principal results, voice and motion.

                  Of Muscular Contraction.
   Muscular contractility, which has also been called animal, and
voluntary  contractility,  is  not a vital property,  at least in the
sense which wc attach to this word.  It results from the success
sive or simultaneous action of several organs, and ought  therefore
to be viewed as a function.

             Apparatus of Muscular Contraction.
   The  organs  which concur in muscular  contraction are  the
brain, nerves, and muscles.  It has not yet been ascertained that
some parts of the brain serve exclusively for sensibility,#nd in-
telligence, and that others are only employed in  muscular con-
traction.   This distinction is without foundation.   For this rea-
son, having spoken above of the brain and nerves in their anatom-
ical relation, we have nothing further to add on this  subject, but
shall now say something of the muscles.

                        Of the Muscles.
   All the muscles taken collectively,  are  called the  muscular
system.  The form and disposition  of the muscles vary infinite-
ly.   Some muscles are formed by the union of a certain number
of muscular fasciculi, which are again composed  of still smaller
bundles.   Others are formed of fasciculi of a smaller volume.
By dividing these fasciculi we get at a fibre extremely small, and
which we can no farther divide, but  which might probably be far-
ther divided if our senses and means of division were more per-
fect.  This fibre which is indivisible by us. is called the  muscular
fibre.  There have been many speculations on its form, volume, 
112                    A SUMMARY
disposition, and the arrangement of the molecules which compose
it.  It is longer or shorter, according to the muscles of which it
constitutes a part; almost always straight, it does not divide, nor
is it confounded with other fibres of the same kind; it is enveloped
in a cellular  tissue extremely delicate; it is soft, and easily torn
in the dead body, but on the contrary in the living body it exhibits
a resistance in proportion to its volume, which is surprising; it is
essentially composed  of fibrine and  osmazome;  it receives much
blood, and at least one nervous filament.  Some anatomists have
pretended to explain how the blood vessels and  nerves act when
they arrive in the tissue of the muscular fibres, but nothing satis-
factory has been advanced upon this point.
  Each muscular fibre is attached at its two extremities by fibrous
prolongations, (tendons or aponeuroses) which are the conductors
of its force when  it contracts itself.  Muscular contraction, as it
exists in the  ordinary state of life, supposes a free and easy exer-
cise of the  brain,  and the nerves  which are  sent to the muscles,
and of the muscles themselves.  Each of these organs must  re-
ceive arterial blood, and the venous blood not be permitted to re-
main in its tissue for too great a length of time, if either of these
conditions  be wanting, muscular contraction,  is either impossi-
ble, perverted, or  very weak.

            Phenomena of Muscular Contraction.
  When a muscle  contracts itself, its fibres grow shorter  and
harder, more or less suddenly, without any oscillation,  or prepa-
ratory hesitation;  they  immediately acquire such  a  degree of
elasticity that they become susceptible of vibrations, or of produ-
cing sounds.  The colour of the muscle does not appear to change
at the moment it contracts, but it has a tendency to displace itself,
which  is counteracted by the aponeurosis.   It has been doubted,
whether a muscle is more voluminous  in a state of contraction or
relaxation; this does  not appear to us to  have been  resolved, hap-
pily it is one of little importance.  All  the sensible phenomena
of muscular contraction  take place in  the muscles themselves;
but it is not the less certain, that these depend upon the action of
the brain and nerves.  Compress the brain of an animal  and it
loses the power of contracting its muscles.  Cut the nerves which
are distributed to a muscle, and it becomes paralysed.   We are 
OF PHYSIOLOGY.
118
■completely ignorant of the changes that take place in the muscu-
lar tissue, during contraction.  In this respect muscular contrac-
tions cannot be separated from the vital actions, of which we can
give no explanation.  Not but there have been many attempts to
explain, not only the action of the muscles, but also that of  the
nerves, and even of the brain, in muscular contraction, but there
is no hypothesis which  has yet been proposed, that can be consi-
dered at all satisfactory.
   Instead  of  consuming  our time in such speculations, which it
is always easy  both to  invent, and to refute, and which should
long since  have been  banished from physiology; we may much
more profitably employ ourselves  in  investigating muscular con-
traction as relates, 1st, to its intensity; 2nd, its  duration; 3d, its
rapidity; 4th, its extent.
   Intensity of Muscular Contraction.—The degree of force with
 which the  muscular fibres shorten  themselves, is generally  re-
 gulated by the  action  of the brain.  It is in general submissive
 to the will  in degrees,  varying in each individual.  A particular
 organization of the muscles is favorable  to the intensity  of its
 contractions, this exists when the fibres are  voluminous, firm, of
 a deep red colour, and presenting  transverse  strise.  With an
 equal effort of the will, they produce greater effects than those
 muscles, the fibres of  which are small, smooth, and of a light
 colour.  Nevertheless, when muscles, the fibres of which are of this
 last description, are placed  strongly under  the influence  of  the
 will, the intensity of the  contraction may be very great; so  that
 cerebral influence, and the disposition of the muscular  tissue.
 are the two elementary principles on which  the intensity of mus-
 cular contraction depends.
    It is rare that we find in the same individual, very energetic
 cerebral action, united with a disposition  of the muscular fibres,
 favourable to  intensity of contractions; it almost always happens
 that these  two principles are opposite to each other.   When  they
 happen to  be united, they produce astonishing effects.  1 his  was
 probably the case with the Athleti of antiquity, and is sometimes
 observed in the jugglers of the present day. By the influence of
 the action  of the brain alone, muscular power  may be exerted to
 an extraordinary degree.  We  know very  well the  astonishing
                                15 
1 H
A  SUMMARY
 strength of some men in anger, that of maniacs, and of persons
 in convulsions, ccc.
   Duration of Muscular  Contraction.— This is in some degree
 dependent upon  the will; but  it cannot be prolonged beyond a
 certain period, which varies in different individuals.   After this
 a  sense  of fatigue is induced,  slight  at first, but which at last
 increases  to such  an extent,  that  the muscle refuses  to eon-
 tract.   The promptitude with which this sensation of fatigue is
 induced, is in proportion to the intensity of the contraction, and
 the  weakness of the individual.  To obviate this inconvenience,
 the different motions of the body are so calculated, that the mus-
 cles act successively, the contraction of each does not, therefore,
 continue long.  We can thus explain why we do not remain long
 in the  same position;  why  an attitude  which requires the strong
 and continued contraction  of a small number  of muscles cannot
 be continued long.  The sense of fatigue, which follows muscular
 contraction, is dissipated  by a  state of repose, after which the
 muscle recovers its power of contraction.
   Rapidity of Muscular Contraction.—To a certain  extent,  ra-
 pidity  of  contractions depends on cerebral influence.   This  is
 proved by  our ordinary  movements; but it also sometimes de-
 pends  upon habit.  Observe, for example, what a difference ex-
 ists, as relates to  rapidity  of muscular contractions, between a
 man who for the first time puts his hand upon the keys of a piano,
 and the same individual after he has been in the habit of practis-
 ing for several years.   We observe  a very remarkable difference
 between individuals, as respects  quickness of contraction, both  in
 the common movements, and in  those  which  require an appro-
 priate  exercise.
  Extent of Muscular Contractions.—This  is directed  by the
 will, but it must necessarily vary with the length of the fibres, for
 long fibres must have a more considerable extent of  contraction
than those which are shorter.
  From what has been said, we  perceive, that in general, the will
has a great influence upon  the contraction of muscles.  But this
is not indispensable.  In a great number of instances, these mo-
tions are executed, not only without its participation, but in op-
 po*ition to it.   We find many remarkable examples of this, in the
effects  of habit, p.-issions and diseases* 
OF PHYSIOLOGY.
115
  We must not confound muscular contraction, such as we have
now described it, with the modifications it  undergoes in certain
diseases, such  as  convulsions, spasms, tetanus, wounds  of  the
brain, &.c*  We must, likewise, take care not to confound  that
contraction, of which we arc  now speaking, with the phenomena
which the muscles present, for some fime after death.   W ithout
doubt, these phenomena  are curious  and worthy of examination,
but they certainly do not merit the  importance which has been   f
attached to them by Haller and  his disciples; especially as it is
not proper to unite them, under the name of irritability, with the
other modes  of contraction,  which are  observed in the  animal
economy, and particularly with that  of muscular contraction.

        Modification of Muscular Contraction by  Age.
   It is only at the commencement  of the second month that we
can distinguish the  muscles  from the gelatinous mass which con-
stitutes the  embryo.   At this period they do not present any of
those characters, by which they  are distinguished  in  the adult.
They  are then of a pale grey  colour, slightly tinged with  red;
and they receive  but a  small quantity of blood comparatively
speaking.  They increase and develope.  themselves with the  pro-
gress of its  growth, though, even  at  the period of birth,  they are
small, flaccid, and indistinct.  We  must except, however, those
which assist in digestion and respiration, which are developed in
a remarkable manner.
   During infancy and  youth, the nutrition of the  muscles be-
comes increased,  and they grow  particularly  in length.   This is
the reason of the slenderness and  agreeable rotundity which we ob-
serve in the forms of children and young men.   When a person ar-
rives at the adult  age, the form undergoes a total change; the mus-
cles increase and project strongly against the skin; the intervals
which separate them being no longer filled  with fat, projections
and depressions are formed, which give to the body an entirely dif-
ferent aspect from that of childhood.   At this age, the muscles
assume a greater  degree  of  consistence, the colour becomes of a
deeper red, and even the chemical characters  are modified.   We
learn from daily experiments, that when the flesh of young  ani-
mals is boiled, that its flavour, colour, and consistence differ very
                      * See Appendix, No. 3. 
116
A  SUMMARY
much from that of an adult animal.  It appears that the muscles
of adult  animals contain more  of  fibrine, osmazome, and the
colouring matter of the blood, of consequence, more of  iron.
   The nourishment of the muscles diminishes sensibly in old age;
they diminish in volume, grow pale, and become flaccid and un-
steady, especially in the extremities, the contractility of the tissue
is weakened, the fibre becomes coriaceous, andis torn  with diffi-
culty.
  Muscular contraction undergoes nearly the same changes as the
nutrition of the muscles.  Weak, and hardly distinguishable in the
fostus, its activity is augmented at birth, increases rapidly in child-
hood and youth, acquires its  highest degree of perfection at the
adult age, and finishes by being nearly lost in the decrepid old man.


                    OF THE VOICE.

   We understand by the voice, the sound produced in  the larynx,
at the moment  (he air traverses this organ, either to enter into or
pass out from the trachea.
   For the purpose  of explaining the mechanism  by which the
voice is produced and  modified, we shall say a few words of the
manner in which sound is produced, propagated, and modified in
wind instruments, especially  in those which have the greatest an-
alogy with the  organ of voice.
   In general, a wind instrument is  formed by a straight or curv-
ed tube, in which the air is  thrown into a state of vibration,  by
various processes.  Wind instruments are of two  sorts, the one
is called a mouth and the other a reeded instrument.
   J he mouth  instruments include the  horn, trumpet, flageolet,
flute, and the  flute tube of  the organ.   In all these,  the column
ot air is contained in the tube, which  is the  sonorous  body.  la
order that  it mny  produce  sounds, it  is necessary  that  vibra-
tions should be excited.  The means employed for this purpose,
vary according to  the kind  of  instrument.   The length,  size,
form of the  tube, the openings formed in its side and its extremi-
ties, the force,  and manner with which the vibrations are excited,
are the causes  of the variety of sounds in these different  instru-
 ments. The nature of the substance of which they are formed, 
OF  PHYSIOLOGY.
117
only influences  the  distinctness  of the  sound.  The theory of
these instruments, is precisely similar to that of the longitudinal
vibration of cords.  When ueknow the physical  condition of one
of these instruments, we can determine  with  accuracy, by calcu-
lation, the sound which  it will  produce.  There is nothing ob-
scure in  this  theorv, except some  point relative  to the mouth-
piece, that is,  the manner in  which the vibrations are excited.
There is no very evident resemblance between  this kind of in-
strument  and  that of the voice.
   Reeded instruments.—It is more important for us to understand
reeded instruments, because the organ of the voice  is of this kind.
Unfortunately, their theory is much less perfect than that of mouth
instruments.  We include, in this kind of instruments, the haut-
boy, bassoon,  clarionet, and the  organ of the human voice.   We
may divide this instrument into  the  reed  and the body, or tube;
 the mechanism of these two parts is essentially  different.
   The reed is formed  sometimes of one, and at others of two  thin
 plates, which are susceptible of moving  very rapidly, and the vi-
 biations  of which  are destined alternately  to  intercept,  and
 transmit  a current of air.  This is the reason why the sounds
 thus produced, are not governed  by the same laws, as those form-
 ed by elastic plates, free at one end and fixed at the other, which
 excite  immediately sonorous undulations in  the open  air.  In
 reeded instruments, the reed alone  produces  and  modifies the
 sounds.   If the reed be long, the motions are extensive and slow,
 of consequence, the sounds are grave.   A short reed, on the con-
 trary, produces, necessarily, sharp sounds, because the alternate
  transmission and  repression of the current of air,  are more rapid.
 When we wish to draw from a reeded instrument, a variety  of
 sounds,  it is necessary to  vary  the  length of the reed.  This is
 done by   those who play upon  the bassoon, clarionet, &c. when
 they wish to produce different sounds with these  instruments.
    We may add, however, as an important circumstance, that the
  elevation of  the tone  produced by an instrument depends, in part,
  on the elasticity, weight, and even form of  the reed, and the in-
  tensity of the current of air; for when these circumstances vary,
  the length remaining the same, the tone alters.
     We never employ  the reed alone, but adapt it always to a tube,
  through  which the air passes, when it is forced through the reed, 
118
A  SUMMARY
   and which  must, for  this reason,  be open at both extremities.
   The tube has no influence upon the tone of the sound; it has only
   an influence upon the intensity, distinctness, and the possfftility
   of enabling the reed to form articulate sounds.  Those which pro-
   duce the loudest sounds are conical tubes, which enlarge as they
   approach the part where the air escapes.  If the  cone be revers-
   ed, the sound  becomes  dull.   But if two  equal  cones, opposed
   base to base, are  adjusted  to  a conical  tube,  the  sound becomes
   round and strong.  The reason of these modifications have never
   been given by natural philosophers.
     A column of air vibrating in a tube,  can produce only a cer
   tain number of determinate sounds.  In consequence of this a
   reeded instrument when it is long, can  only  transmit distinctly
   those sounds which it is  intended to produce;  it is also necessary
   to establish at first a certain proportion  between  the reed and the
   body of the instrument. Of consequence, when we wish to draw a
   succession of different sounds  from the same reeded instrument,
   it is necessary  not only  to modify the length  of the reed, but to
   modify also, in a corresponding manner, the length  of the tube;
   now  this end is  attained  by  piercing the sides  of  the  bassoon
   clarionet, &c. with small holes.  By opening or closing these, we
   can make the reed and  the tube bear such a  proportion  to each
   other, as may be convenient. This agreement, likewise, enables us
   more  easily by  means  of the "lips, to give the  instrument  the
   sound which we wish to  produce.  This  influence of the tube is
*  very remarkable in those instruments which are  straight, (clario-
   nets and hautboys.)   It  is even to such an extent that the effect
   produced by the reed is very  imperfect, if the tube be not suited
   to it.  When the tubes are very  large, as in organs, the reeds
   vibrate almost  as freely as in  the open air.   We know not pre-
   cisely what are the movements which take place in the  air con-
   tained in such  tubes, when they transmit the sound produced  by
   the reed.  We have seen  above, that the reverse  is  the  case  in
   mouth instruments.

                    Apparatus of the Voice.
     Inasmuch  as the  passage of the  air through the  larynx, is  a *
   condition absolutely necessary to the formation of the voice, we
   must include all the organs whieh  produce this effect among the 
OF  PHYSIOLOGY.
119
number of the vocal organs.   There are many parts which assist
in the formation or modification of the voice, but before speaking
of them, we shall more particularly insist here  upon the  larynx,
which must be considered, more especially, as the organ of voice.
   The Larynx.—Is placed at the anterior part of the neck, and
forms that remarkable projection which exists  between the tongue
and  the trachea, which varies according to the age and sex.   It
is smaller in children than in females, it is still larger in young
men after the age  of puberty, and  is  much  more developed  in
the adult.  The larynx not only produces the voice, but it is also
the agent of its principal modifications. This is the reason why an
exact knowledge of the anatomy of this organ is indispensable, if
we wish to comprehend  the mechanism of  the  voice.  In conse-
quence of not paying a sufficient attention to this point, very im-
perfect, or even false  ideas have been propagated on this inter-
esting subject.   We  cannot enter here into all the details of the
structure of the larynx;  but we shall dwell  more particularly
upon those  parts which are most necessary to be known, many of
which  are, at present, but  little understood.
   Cartilages of the Larynx.—The larynx  is composed of four
cartilages, and of three fibro-cartilages  The cartilages are  the
cricoid, the thyroid,  and the two arytenoid.  The thyroid is ar-
ticulated  with the cricoid  by  the extremity of its inferior horns.
During life, the thyroid is fixed, relatively to the cricoid cartilage,
which  is contrary to the received opinions on this subject.  Each
arytenoid cartilage is articulated with the cricoid, by means of an
oblong facette, and is concave transversely.  The cricoid presents
a facette, the  disposition  of which  is analogous to that of the
arytenoid cartilage,   with this difference,  that it  is  convex,
where  the  corresponding  part  of the  other  is concave.   Near
the  articulation  is found  a  synovial capsule  closed interiorly
and  posteriorly, but loose laterally.  Before the articulation is the
thyro-arytenoid ligaments, and behind a strong ligamentous fasci-
culus, which may be  called the crico-arytenoid  ligament, from its
attachment.
   Arranged as I have now  described, the articulation will  only
permit  the arytenoid cartilages to  move  laterally  upon the
cricoid.  All motion  anteriorly and posteriorly  is impossible, as
well as a certain  see-saw motion that  is  mentioned in books 
120
A  SUMMARY
on  anatomy, which cannot be  produced by  any muscle.  This
articulation must be  considered as  a simple  lateral  gingly-
mus.   The fibro-cartilages of the larynx, are the epiglottis, and
two small bodies which are  found above the upper part of the
arytenoid cartilages, and which were called by Santorini capitula
cartilaginum arytenoidarum.
  Muscles of the Larynx.—A  great  number of muscles are at-
tached  mediately and  immediately to  the larynx.  These mus-
cles have  been  called extrinsic; they are  destined to  move
the organ as a whole, either to  elevate or depress it, or to carry
it backward or  forwards, &c.  Besides these, the larynx  has
muscles, the use of which is to move one part upon another, these
are called intrinsic.   They are, 1st. The crico-thyroid muscles,
the use of which is not to depress the thyroid  upon the cricoid
cartilage, as has been heretofore believed, but on the  contrary it
elevates the cricoid, making  it approach the thyroid, or even
causing it to pass a little under its inferior edge. 2d. The posterior
crico-arytenoid  and  the  lateral,  crico-arytenoid  muscles,  the
use of  which is to  carry the arytenoid  cartilages  outwardly,
separating them  from each other.  3d. The arytenoid  muscles
which  draw together, and apply to each other the  arytenoid
cartilages.   4th. The thryo-arytenoid, which, is the most impor-
tant to be known of all the muscles of the larynx, inasmuch as it
is that, the vibrations of which produce vocal sounds.  This muscle
forms the lips of  the  glottis, the  inferior walls and the superior,
and lateral ventricles  of the larynx.   5th. Lastly the muscles of
the epiglottis, which are  the  thyro-epiglottis, and the aryteno-
epiglottis, and some fibres which may be viewed as  the vestige of
the glosso-epiglottis, which exists in many animals.   Contraction
has an influence therefore on the position of the epiglottis.
  Mucous\Membrane of the Larynx.—'The larynx  is covered on
its interior surface, by a mucous membrane.  This membrane in
passing from the epiglottis  to  the arytenoid and thyroid carti-
lages, forms  two-folds which  are called the  lateral  ligaments
of the epiglottis, they run together to form the superior  and in-
ferior ligaments of the glottis.   Behind and  in the  tissue of  the
glottis we find a great number of mucous follicles, and some mu-
cous glands.  There exists  in the thickest part of the ligaments of
ihe epiglottis, a collection  of  these bodies  which have been im- 
OP PHYSIOLOGY.
121
properly enough called  the arytenoid glands.   Between the
epiglottis, posteriorly, and the os hyoides and  thyroid  cartilage,
anteriorly, we find  a considerable  bundle, of  very elastic, fatty,
cellular tissue, analogous to  that which is found in the  neigh-
bourhood  of certain joints.   The use  of this  body has not yet
been assigned. I conceive that it serves to facilitate the frequent
gliding  of  the thyroid  cartilage on the posterior face of the os
hyoides, to keep the epiglottis separated superiorly from this bone,
and  at  the same time  to furnish an elastic support, which  may
favour  the  functions which  this fibro-cartilage performs, in  the
voice, and deglutition.
   Vessels and Nerves  of the Larynx.—The  blood  vessels  pre-
sent nothing  very  remarkable.   This remark, however, will  not
apply to the nerves of  this organ,  their distribution deserves  to
be examined with care.   These nerves  are four in  number, viz.
the superior laryngeal, and the recurrents, or  inferior laryngeal.
   The  recurrent nerve  is  distributed to  the posterior crico-
arytenoid, and  to  the  lateral thyroarytenoid muscles; none of
its ramifications are transmitted to the arytenoid, or the crico-
thyroid muscles.  The  superior laryngeal nerve, on  the contrary,
is sent  to the arytenoid  muscle to which  it gives a  considerable
branch; and  to  the crico thyroideus it sends a filament  less re-
markable for its size than the mode of  its transmission.   In some
cases however, this filament does  not  exist, but then the branch
of the external  laryngeal nerve is larger.   The remainder of the
filaments of the laryngeal nerve are distributed to the muscles of
the epiglottis, and to the mucous membrane which covers the en-
trance  of  the larynx.   This part is endued with excessive sensi-
bility.
   Glottis, or Rima Glottidis.—-These  names  are  given to the
opening between  the  thyro-arytenoid  muscles and The aryte-
noid cartilages.  In the dead body, the glottis presents a longitu-
dinal opening or chink, about eight lines  long, and  two or three
wide, and larger at the  posterior, than the anterior part,  where the
two sides approach, so  as to touch at the point where they are at-
tached  to the thyroid cartilage.  The posterior extremity of the
o-lottis  is formed by the arytenoideus muscle.
3 Ligaments of the  Glottis, or the  Vocal Chords.—When  we
bring°the arytenoid cartilages together, so tha* *hoir internal sur-
                              16 
\7\l                    A  SUMMARY

faces  touch, the  g'ottis  is  diminished  about one  third  of its
len"--h; it then  presents an opening not more than from one half,
to a line  in width, and five or six  lines in length.  The sides of
the rima, are called the lips of glottis.   They present a sharp
edge,  and are principally formed by the thyro-arytenoideus mus-
cle, and   by the ligament of the  same name, which covers  like
an aponeurosis, the muscle to which it  is strongly attached, and
itself, covered  by the  mucous membrane, forms essentially  the
thin, or cut edge of the lip.  These lips  of the  glottis  vibrate
during the production of the voice, and may be considered as the
reed of'yjje  instrument.
   Ventricles of the Larynx.—Above the inferior ligaments of the
glottis, are the  ventricles of the  larynx, the cavity of which  is
more  spacious  than if seems to be at  first, the external inferior
and  superior walls of which, are  formed by  the  thyro-arytenoi-
deus  muscle, turned upon itself; the extremity or anterior wall is
formed by the thyroid cartilage.   By  means  of these  ventricles,
the lips  of  the glottis are  perfectly  insulated at their superior
edge.
   Ave see above the opening of the ventricles, two bodies which
have  a great analogy in their arrangement, with the vocal chords,
and which form a second glottis above the first,  these are called
the superior ligameids of  the glottis.  They are formed  by the
superior edge of  the thyro-arytenoid muscle, a little of the fatty,
cellular  tissue, and the mucous membrane of the larynx, which
covers thern before entering into the ventricles.   Such are the ob-
servations which are easily  made  on the larynx in the dead body.
I believe no one lias ever  examined  the glottis in  man  during
life; at least no one to my knowledge, has  ever written  on the
vibjeet.   When we examine it in animals, dogs for example, we
fni'.! tnatit»Mjlargesand diminishes alternately. The arytenoid car-
tila^es are curried outwards at the moment that the air penetrates
into the  lungs, and they approach and appiy themselves to each
other, at the instant the air passes out from this cavity.

         Mechanism of the production  of the  Voice.
   If  we take the trachea  and larynx of an animal,  or man, and
blon   Airongly into the trachea,  towards the larynx, no  sound
 will be produced, but a slight noise resulting from the friction  of 
Ol  PF1YS101.01.V.
11i.i
the air, against the walls of the larynx.  If continuing to blow, we
bring together the arytenoid cartilages, so that their internal sur-
faces are in contact, there will be  produced a sound which has
some resemblance to the  voice of (he animal  from which the la-
rynx was taken.   The  sound will  be more or less sharp or grave,
according as the cartilages aoproach each other with more or lt->s
force;  it will be more intense when we blow into the trachea with
the most force.  It is easy to see, by this experiment, that  it is the
inferior ligament of the glottis, which, by its vibrations, produces
the sound.
   An opening made into  the trachea in  man  and animals  below
the  larynx,  deprives them  of voice; this  will be  restored if the
opening be  stopped  mechanically.   I know a man  who has been
in  this  situation  for many years; he  can only  speak when his
cravat, which closes a  fistulous opening in the larynx, is drawn
tight.  The same effect is produced  when  the larynx is  opened
below the inferior ligaments of the glottis.
   On the contrary, should a wound  exist above the glottis, affect-
ing  the epiglottis  and its  muscles;  the superior ligaments of the
glottis; or even the  superior part  of the arytenoid cartilages, the
voice will still remain.   Indeed,  when  the glottis of a living ani-
mal is laid  bare, when  it cries out, it is easy to  perceive that the
 voice is formed by the vocal chords.*  From this I think  it is pla-
 ced beyond a doubt, that the voice  is produced  in the glottis by
 the movements of  its  inferior ligaments.  If this be  considered
 as well  established, can we, on.philosophical  principles,  account
 for  the  formation of the voice ?  The following explanation ap-
 pears to me the most  probable.   The air forced from the lungs,
 passes at first into  a large canal,  which  soon contracts,  and it is
 then compelled  to pass through a narrow passage or chink, the
 sides of  which are two vibrating  plates, which like the  plates  in
 reeded instruments, permit and intercept alternately  the p:is.*:ige
 of the air,  and  cause at the same time sonorous undulations  in
 the current of air which  is tranMiiitted
   But why then, it may be asked, when we  blow strongly into
 the human trachea  after death, is there no sound produced analo-
 gous to the human  voice?   W by  is the  paralysis of the  intrinsic

         * Tliis is the  name given hv l'Yrrein to the lip- of the glottis. 
124
A  SUMMARY
muscles of this organ always followed by the loss of voice?  and
why is an act of the will required for the formation of vocal
sounds?  The answer is easy.—The  ligaments  of the glottis do
not acquire the power of vibrating like the plates in  reeded in-
struments, except  when the  thyro-arytenoid  muscles are con-
tracted;  of consequence, in all those cases where this is not the
case, no voice will be produced.
  Experiments  upon animals  perfectly agree  with this  doc-
trine.  Divide the  two recurrent  nerves which, as we have  said
before, are distributed  to the thyro-arytenoid muscles,  and the
voice is  immediately lost.   I  have, however, seen many  ani-
mals utter very sharp cries, when they felt severe pain, after the
recurrent nerves had been divided.   But these cries were ex-
tremely analogous to the sounds produced with the larynx of the
animal after death, by  blowing into the trachea, and at the same
time approximating the arytenoid cartilages, a phenomenon which
is readily explained by the distribution of the nerves of the larynx.
The recurrents being divided, the thyro-arytenoid muscles cease
to contract, and the result is aphonia.  But the  arytenoid mus-
cle, which receives its  nerves  from the superior laryngeal,  con-
tracts itself, and at the  moment when a strong expiration takes
place, one of the arytenoid  cartilages being applied to the other,
the rima  glottidis is contracted,  by which the  thyro-arytenoid
muscles are thrown into a state of vibration, though they are not
contracted.

                   Intensity of the Voice.
  This depends like all other sounds, on the extent of the vibra-
tions.  The greater the force with which the air is expelled from
the chest, the greater will be the extent of the vibrations of the
vocal  chords;  and the longer these chords  are, that is, the greater
the capacity of the larynx, the  more considerable will be the ex-
tent of the vibrations.  A strong person,  whose breast is laro-e,
and in whom  the dimensions of the  larynx are considerable, pre-
sents those circumstances which are  the most favourable to inten-
sity of the voice.  But  when this  person  becomes  sick and his
strength  reduced, his voice loses much of its intensity, for  this
simple reason, that  it can no longer  expel  the air from the chest
with great force. 
OF  PHYSIOLOGY.
125
  Children, women, and eunuchs, in whom the larynx is propor-
tionally  smaller than in the adult man, have also naturally the
voice much less intense than his.
  In the ordinary production of the voice, it results from simulta-
neous movements  of  both sides of the glottis.  If one of these
sides loses the faculty of exciting  vibrations in the air, the voice
will necessarily lose the half of its intensity, supposing the expi-
ratory force to remain the same.  We may satisfy ourselves on
this point, by dividing one of the recurrent nerves of a dog, or by
examining the voice of a person attacked with complete hemiplegia.

                  Of the Tones of the  Voice.
   Each  individual possesses a peculiar tone of voice by which he
 is known; the different ages and sexes are marked in this manner.
The tone of the voice then presents infinite modifications.   We
are ignorant of the precise  physical circumstances on which this
depends; the feminine tone, however, which is observed  in chil-
dren and eunuchs, is generally found connected with a peculiarly
soft state of the cartilages of the larynx.   The masculine tone of
voice, which is sometimes observed in females, on the contrary,
seems to be connected  with an osseous state of these cartilages,
particularly the thyroid.
   Tone then is a  modification of sound, of which no very satisfac-
 tory account has yet been given.

        Of the different Notes, or  extent of the Voice.
    The sounds which the larynx in man is  capable of producing
 are extremely numerous.  Many  distinguished  authors have en-
 deavoured to explain their formation, but these when examined,
 will be found to be rather comparisons, than explanations.   Thus
 Ferrein considered the ligaments of the glottis as chords, and he
 explained  the different notes ot  the voice, by the different de-
 grees of tension,  of which he supposed  they  were capable;  &c.
 But all  the explanations which  have heretofore  been  given, err
 radically  in  this, that they are founded  upon  a consideration of
 this organ in the  dead body, while the only true mode of investi-
 gating the subject, is a minute attention to the anatomy  of the
 part, and a careful examination of the phenomena exhibited du- 
126
A  SUMMARY
ring life.  I have endeavoured to supply this deficiency,and will
now state the results which I have obtained.
  I  laid bare  the glottis  of a  dog, making  an incision between
the os hyoides and thyroid cartilage; and examined the part care-
fully while he  was howling.   I  found, when the  sounds were
grave,  that the.  ligaments of  the glottis  vibrated through their
whole length, and that  the expired air passed out  through  the
whole extent of  the glottis.  W hen the sounds were sharp, their
ligaments did  not vibrate  at their anterior, but only at the poste-
rior part, the air  only passing through that portion of the glottis
which vibrated, the opening, of course, being diminished.   When
the sounds became very sharp, the ligaments no longer vibrated,
except at the arytenoid extremity, and the expired air then pass-
ed out at this portion of the glottis.   It appeared that the sharp-
ness of the sound increased until the glottis became entirely closed,
when the  air could  no  longer  pass  through the larynx,  and the
sound  ceased.   The principal use of the arytenoideus muscle
being to close the glottis at its posterior extremity, it must be the
chief agent in producing sharp sounds.  I was desirous of know-
ing what effect would be produced upon the voice by the  division
of the two laryngeal  nerves which supply  this muscle.  I had re-
course to some experiments for this purpose, and found that when
this  was done, the voice of the animal  lost all its sharp sounds;
and  that it likewise acquired an habitual hoarseness which it had
not before possessed.
   The structure of the larynx in man and in the dog is  so much
alike, that we cannot doubt that the same phenomena take place
in both.  There is one  circumstance  which  must have a certain
influence on the tones  of the voice,  it is the contraction of the
thyro-arytenoid  muscles.  The  more strongly  these  muscles
contract, the more will  their elasticity be  increased, and the more
susceptible they will become of vibrating rapidly, and of produc-
ing sharp sounds; on the  contrary, the less  they are contracted,
the more grave the sounds will be.   We may also  presume, that
the contraction of these  muscles concurs powerfully in closing
the glottis, particularly  its anterior half.
   It would appear, then, that the larynx  represents a reeded in-
strument with a double plate, the tones of which are more sharp
;is the plates are shortened, and more  grave as they are elongated. 
OF PHYSIOLOGY.
127
But although the analogy be generally just, it does not necessari-
ly follow, that it is in every respect complete.  In fact, the com-
mon reeds are composed of rectangular plates, fixed on one side
and free on  the other three; in the larynx, the vibrating plates are
nearly rectangular, but they are fixed by three sides instead of
one.  Again, we  raise or fall the notes in the common reeded in-
strument, by varying its length; in  the plates of  the larynx, it is
the size which varies.  Lastly, in  musical instruments we cannot
employ reeds, the plates of which  can, every in»tant> alter their
thickness and elasticity.   From what has been said, it can easily
be conceived, that the larynx may produce the voice and vary its
lone-, somewhat after the manner*t)f  reeded instruments, without
our undertaking minutely  to explain  all  the  particularities in its
mode of action.
   It has heretofore been believed  that the tube, which conveys
 the wind to the  reed, has  no influence  on the sound produced.
 M. Biot relates  an experiment of *M. Grenie, which proves the
 reverse of  this.   It is not impossible that the  lengthening or
 shortening  of the trachea,  which is the tube for conveying the air
 to the larynx, may have some influence in the production of the
 voice, and on its different  tones.
   Having examined the reed of the organ of voice, it will be now
 proper  to consider the tube which the vocal sound traverses, after
 having been produced.  In proceeding from below, upwards, the
 tube is composed, first, of  the interval comprehended between the
 epiglottis, before, and the  lateral  ligaments, in the sides, and the
 posterior walls of the pharynx;  second, of the  pharynx, posterior-
 ly and laterally, and of the most posterior part of the base of the
 tongue, anteriorly; third,  sometimes  of  thy  mouth, sometimes o(
 the nasal cavities, and at  other times of both.
   Thi-> tube may be elongated  or shortened, enlarged or dimin-
 ished; being susceptible of assuming an  infinite number of differ-^
 ent form.-,,  it will fulfil very well  the office of the body of a reed-
 instrument; that is,  it will possess the power of arranging itsell,
 so as to harmonize  with  the larynx, and thu=, favour the produc-
 tion of all  the numerous sounds of which the voice is susceptible;
 it will  increase the intensity of the  vocal sounds by assuming a
 conical form; by enlarging, externally, it will give them an agree- 
128
A  SUMMARY
' able rotundity; or by arranging the external opening convenient-
 ly, it will nearly suppress them, &c.
    Until  natural  philosophy has determined with precision, the
 influence of the tube in reeded instruments,  we can, at best, only
 form probable conjectures respecting the influence  of the tube in
 the formation of the voice.   We can only illustrate this point by
 a small number of experiments, which  relate to those phenomena
 which are the most apparent.
    The  larynx elevates itself during  the  production  of sharp
 sounds, and is depressed when  they are grave; of consequence,
 the i^pcal tube is shortened  in the first case,  and elongated in the
 second.  We may conceive that a short tube  is most favourable
 to the transmission of sharp sounds, and that a long one is most
 advantageous in those which are grave.—At the same time that the
 tube changes its length, it likewise alters its size; a circumstance
 which is remarkable, because, as we have  seen above, the size of
 the tube influences its facility of transmitting sound.
    When the larynx descends, that is, when the vocal tube is elon-
 gated, the thyroid cartilage  is depressed, and separated from the
 os hyoides, to the  whole extent of the thyro-hyoidian membrane.
 By this separation, the  gland of the  epiglottis  is carried forward,
 and comes to lodge itself in the concavity of the posterior face of
 the os hyoides; this gland necessarily draws after it the  epiglottis;
 from  which results a considerable enlargement of the inferior part
 of the vocal tube.
    The opposite phenomenon happens when the larynx is elevated.
 We then  see the thyroid   cartilage  raise  itself  behind the os
 hyoides,* displacing and pushing backward  the gland of the epi-
 glottis, this pushes the epiglottis in its turn, so  that the vocal tube
 becomes thus very much contracted.   In imitating this movement
 upon the dead body, we may satisfy ourselves that this contrac-
 tion may be carried to  five-sixths of the size  of the tube.   Now
 we adapt a large tube  to a  reed  which is to  form grave sounds,
 and, on the contrary, a narrow tube  to one  which is' intended to
 convey sharp sounds.   We  can then, to a certain extent, account
 for the changes of size  which take place in the vocal tube.

   * The thyro-hyoidian muscles appear more particularly destined to produce tr>
 movement by which the thyroid cartilage passes behind the os hyoides. 
OF  PHYSIOLOGY.
129
  The presence  of  the  ventricles of the  larynx, immediately
above the inferior ligaments of the glottis, appears to be intended
to insulate  those ligaments so  that  they  may vibrate  freely.
W hen foreign bodies are introduced into these ventricles, or when
they are  covered  with a tenacious mucous, or a false membrane,
the voice Is either entirely lost, or very much weakened.
  From its  form, position, elasticity, and the movements impress-
ed upon  it by its muscles, the epiglottis seems to constitute an es-
sential part of the. apparatus of voice.   But we may inquire, what
are its uses?  We have seen already, that it assists powerfully in
the contraction of the vocal tube, but  we may suppose that it per-
forms a still more important function.
  M. Grenie, who has invented  so  many  ingenious and useful
modifications of reeded instruments, did not  arrive at these results
by a single  effort, but had to pass  through  a long series of inter-
mediate inquiries.  At one period  of his investigations, he  wished
to augment the intensity of the sound without changing the reed.
To effect this, he was obliged  to  augment, gradually, the intensi-
ty of the current of air; but this,  though  it  rendered the  sounds
stronger, had likewise the effect of elevating the note-  To reme-
dy this inconvenience, M. Grenie could find no other method than
to place, immediately above the reed, a flexible, elastic tongue, re-
sembling very much the epiglottis; we  may suppose, from this, that
the epiglottis assists in giving to man  the power of swelling vocal
sounds, without elevating the tone.
  The intensity  of the voice is  visibly  influenced by  the vocal
tube.  The most intense  sounds  that the voice can produce, re-
quire that the mouth should be opened widely, the tongue  a little
drawn back,  the veil of the palate  a  little raised up,  closing
all communication with  the nasal  fossae.   In this case, the pha-
rynx and the  mouth  evidently perform the  office, and  resemble,
with considerable exactness, those tubes  of reeded instruments
which  enlarge at  the part where the air passes out, and  the effect
of which is to augment the intensity of the sound produced by the
reed.  If the mouth be partly closed,  the lips projected  forwards,
and more or less  drawn together, the  voice will acquire an agree-
able rotundity, but will lose its intensity.   This result is easily
explained by what has been before said of the influence which the
form of the tube exerts in reeded  instruments.  For the same rea-
                             17 
130                    A SUMMARY
sons, every time the vocal sound  passes  the  nasal fossfe, it be*
comes  lower, because the form of these cavities is extremely well
adapted to diminish the  intensity of sounds.  If the mouth and
nose be closed at the same time, no sound will be produced.
  W e  have already seen, in  speaking of the production  of the
voice, that a great number of modifications in the tone arise from
the changes which take place in the thickness and elasticity of
the lips of the glottis.  The tube also produces a great number of
others, varying according to its* length and capacity; the form and
contraction  of the pharynx; the position of the tongue and the veil
of the palate;  according as the sound  passes  out, either entirely
through the  mouth, or nose, or by  these two cavities at the same
time; fhe form of the mouth  and nose of the individual; the pre-
sence or absence of the teeth; the volume of the tongue, &c.—The
tone of the voice, I say, will be modified by all these circumstances.
Whenever,  for example, the sound traverses the  nasal fossae, the
tone will  be disagreeable, or,  as  it is  commonly  called, nasal.
Persons who think that the nasal cavities can augment the inten-
sity  of vocal  sound, by  resounding through them, deceive them-
selves; as these  cavities can only produce the reverse effect.
  Independently of the  numerous modifications determined by
the tube of the vocal organ, a« relates to the intensity and tone of
the voice, it produces another modification, much more important,
by permitting it  or intercepting it alternately.   By  this means,
a vocal sound  is  divided  into small portions, which have each a
distinct character, because each is produced by a particular move-
ment of the  tube.   The influence thus exerted by the vocal tube,
is called the faculty of articulation.
  Thus far we have treated of the human voice, in a general man-
ner; we shall  now  spe..k of its principal  modifications, viz. the
cry, or natural voice; the voice, properly so called, or the acquir-
ed voice; speech, or articulate voice; singing, or appreciable voice.

                Of the natural  Voice, or Cries.
  This is an unappreciable sound, which, like all others  produced
by the  larynx, is susceptible of variety, both in tone and intensi-
ty.   A cry is easily distinguished from  all other  vocal sounds;
but as its character depends upon tone, it is impossible to explain, 
OF  PHYSIOLOGY.
131
physically, the reason of the difference between other vocal sounds
and  it.
   In whatever condition man may be found he is always capable
of uttering this sou ink  The new-born infant and the decriped old
man; the savage and the civilized man; those who have been dumb
from their birth, and  ideots; are all capable of uttering cries.
We  must consider, therefore, crying as essentially depending up-
on organization; this will be still more apparent from examining
its uses.
   Use of Cries.—By a cry, we express vivid sensations, whether
they arise from within or without, whether they  are agreeable or
painful.   By cries we  express our most simple, instinctive wants,
and  natural passions. There are cues of joy and pain; of anger and
of fear, &c.  The social wants and  passions, not being indispen-
sably connected with organization, but requiring  a state of civili-
zation to develope them, have no  peculiar cries.
   Cries generally include the most intense sounds that the organ
of the voice  is capable of  forming.  Most frequently  its  tone
wounds the ear, and acts strongly upon those who are exposed to
its effects.  These establish important relations between  man and
his fellow creatures.   A cry of joy imparts pleasure, a cry of grief
excites pity, and the cry excited  by  fear  carries terror to a dis-
tance, &c.  This kind of language is found among most  animals,
and  is in fact nearly the only one they possess.  The singing of
birds can only be considered  as a modification of their cries.

                      Of Acquired  Voice.
   Man in his ordinary condition, that is in a state of society, and
when he is endowed with  the  sense of hearing, soon perceives,
even in  his early infancy,  that his fellow  creatures  produce
sound*, which are  not cries.  Having remarked  this, by the in-
stinctive  force of imitation, he is soon able to  form analogous
sounds,  this we  call  an acquired voice.  A  deaf child cannot
make these remarks, he,  therefore, can never acquire the  power
of making these sort of sounds.
  The voice does not appear to differ from cries, except  in inten.
sity, and tone; for it is formed of  uuappreciable sounds,  of which
the ear canuot distinguish accurately the intervals. 
132
A  SUMMARY
   Inasmuch as the voice is  the result  of hearing and of an in-
 tellectual  effort, it cannot be  developed unless both  these con-
 ditions exist.   Children who are deaf from birth, cannot form any
 idea of sound; and  ideots are  not  capable of establishing any re-
 lation between the sounds which they hear, and those which they
 are capable of producing, they have therefore no voice; although
 the vocal  apparatus in  both, may be  fitted to  form and modify
 sounds, as well as in those  individuals whose conformation is the
 most perfect.  For  the same reason, those individuals, who  have
 been very improperly called savages, from their having wandered
 in the forest from t! eir  infancy alone, do  not  possess voice be-
 cause the  understanding does not sufficiently  develope  itself in
 this insulated  state, and  no necessity for mental exertion exists.
   The tone, intensity, and notes of the voice  are all  susceptible
 of numerous modifications  by  the  action of the larynx, the vocal
 tube also exerts a powerful influence upon the voice.  Speech and
 singing are  but  modifications of  the acquired  voice.
   It is difficult, perhaps impossible, to say how man has  reached
 that degree of perfection by which he is enabled to represent his
 intellectual  operations by modifications of the  voice, to  compose
 languages, and especially to invent the alphabet. These inquiries
 are undoubtedly curious  and useful, but not indispensable, and
 besides do not properly belong to physiology; it  is the  mechanism
 of the voice which  alone concerns us.
   Language is composed  of  words, which  are the signs of our
 ideas, and words are formed by the letters, or sounds of the alpha-
 bet, which are, for the most part,  but modifications  of the voice,
 Grammarians, distinguish letters into vowels and consonants, but
 this is not a proper physiological distinction. We may distinguish
 them into those  which  are  true modifications  of the  voice, and
 those which are formed independently of the voice.
   Vocal Letters.—The letters which  are formed by the voice  in
 the languages of Europe, are, a, as it is pronounced in English  in
 the word, hall; (French) 6 in hale, and a, e, e, e, French mutes; i, o
 in Italian; o, e, u,eu  in French; and  u, in Italian.  Kach of these let-
ters may be modified; this we express when we say that it is long
or short. The other vocal  letters are, h, and p, (labial consonants;)
d, and t,  (lental consonants;)  I, (palatal consonant;)  g,  and k-
[gutteral  consonants;) m, and n, (nasal consonants.) 
OF  PHYSIOLOGY.
133
   The formation of the vowels requiring the vocal tube to be open,
 deppnds upon the form it affects at the time the voice is produced.
 The vocal consonants suppose that the tube is closed, and result
 from the mannet of its being opened at the moment the voice is
 formed.  The existence of these  last letters is  then instantane-
 ous.
   Non-vocal  Letters.—The other letters/, and v, the two sounds
 of th, in English; s, z, ch, j,  r, h, and  x, in  Spanish, and %, in
 Greek.
   These letters are produced  by  the action of the air against the
 walls  of the  mouth, and are  of consequence  independent  of
 vocal sounds, and  may be prolonged as long  as the air continues
 to pass out from the lungs.
   Each letter, both vowels and consonants, is produced by a cer-
 tain disposition or particular movement of the  vocal  tube: the
 tongue  is the principal agent in the formation of  some; in others
 the lips, and in  others the sound  traverses the nasal fossse, &c.
   In order that  the pronunciation may be correct, it  is necessary
 that the vocal tube should be  well formed.  When there  is any
 lesion of this part, e. g. a perforation of  the vault of the  mouth or
 of  the  uvula, or veil of  the palate; a loss of the teeth;  or a
 swelling or paralysis of the tongue, the power of articulation  be-
 comes altered, and may be even lost.
  The simple noise made by the air in traversing  the larynx may
 be sufficient for pronunciation, as happens when  we speak very
 low.  Persons who have  completely  lost their voice, still  con-
 tinue to pronounce with so much distinctness, as to be understood
 at a certain distance.
  By different  combinations  of  letters  we form sounds more
or less compounded, which are words.  The formation of words
is  different, in different languages.  In  the north of Europe, tiie
consonants are numerous, and the words are rough and difficult to
pronounce.   In the south, the vowels are most numerous; and the
sounds are generally soft and harmonious.
  Accent.—The  same sound is not always continued in the pro-
nunciation  of  words.   In articulating,  the  voice is raised  and
lowered, and its intensity and tone varied, in a  manner which
varies in every language.  The mode  of these variations consti-
tutes accent, or the pronunciation peculiar to each country. 
134
A  SUMMARY
   Speech.—To articulate, or pronounce, is not to speak.   A bird
 may be taught to pronounce words, or even sentences,  but not to
 speak.   Man is alone endowed with the faculty of speech, which
 is the most  powerful means of expressing  his  intelligence;  he
 alone attaches a meaning to the words which he  pronounces, and
 to the arrangement which he gives them. He  would, therefore, not
 possess speech unless he had  understanding.  In fact the greater
 number of ideots never  speak, they articulate sounds vaguely, but
 do not, and cannot attach any meaning to them.

                         Of Singing.
   The  voice in singing differs trom Other sounds  produced by the
 larynx in this,  that it is formed of appreciable sounds, of which
 the  ear  distinguishes easily  the intervals,  and  perceives their
 agreement.  These  characters do not exist either in cries, or  in
 speech,  the sounds of which are  unappreciable.   Dodart has as-
 serted, that in singing, the larynx undergoes  an oscillatory move.
 ment from below, upwards; but his assertion is not confirmed by ex«
 periment. It is probable that in singing the ligaments of the glot-
 tis assume a  particular arrangement, which enables them to form
 appreciable sounds.
   We  remark  very important  differences  among  individuals,
 in the extent, intensity, and tone of  the voice, in singing.  In a
 common voice, there are  about nine notes between its  highest and
 it- lowest tones; the most extensive voice  does not much exceed
 two  octaves,  in full and  well formed sounds.
  There are  two sorts of voices, the grave and the sharp.  They
 differ from each other by about one octave.  In general, men have
 grave voices; those whose voice is the most grave may form sharp
 sounds  by taking what is called the- falsetto.   Women, children,
 and  eunuchs, are generally found to po>ses<  sharp voices.  By
 adding all the notes  of a sharp, to those of a grave voice, they ex-
 tend to  nearly three  octaves.  It does not appear  that any indivi-
dual has ever possessed a voice of this extent, in which the sounds
 were clear and agreeable.
  Singing, like  speech, is an effect of a  state of society;  it sup-
poses the existence of hearing and intelligence.   It is in general,
employed to  paint our instinctive wants, passions, and different
states of mind. 
OF PHYSIOLOGY.                 135
  Singing may also be articulate.   Then  instead  of  expressing
simply sentiments,  it becomes the means of expressing a great
number of the acts of the understanding, but particularly of those
which are connected with the social passions.
  Declamation is a  particular sort of singing; though the intervals
of the tones are not entirely harmonious; and the tones themselves
are  not completely  appreciable.  It appears, that  among the an-
cients, declamation differed much  less from singing, than  among
the  moderns.  It was probably analogous to what is called the
recitative in  modern operas.
  The oriental languages, which are strongly accentuated,  that is,
vary their tones very much in simple pronunciation, are very suit-
able for singing.
  Inspiratory Voice.—All the modifications of the voice which
we  have  examined  are produced  by the air passing out from the
breast.   The voice  may also be formed at  the moment the  air tra-
verses the larynx to penetrate into the trachea.  But this inspira-
tory voice, is hoarse, unequai, and of small extent;  we cannot, but
with difficulty, vary the tones; in a word, from the  very character
of the phenomenon, we can perceive that it  does not  pass according
to the ordinary laws of the animal economy.  We  can both speak
and sing during inspiration.  We  are ignorant of the modifica-
tion which  the lips of the glottis undergo in the  production of in-
spiratory voice.

                 The art of Ventriloquism.
  Inasmuch  as man possesses the power <>f varying indefinitely
the  appreciable and unappreciable sounds of his voice, and  can
change at pleasure, in a thousand ways,  its intensity and tone,
nothing can be easier than  to imitate exactly the different  sounds
which strike  upon his ear; this in fact he executes under a  variety
of circumstances.
  Many persons imitate perfectly the voice and pronunciation of
others; hunters imitate the different cries  of their game, and suc-
ceed  by  these means in attracting them into their snares.  The
faculty which some persons have  of imitating  different sounds,
has  been  made a profession of by some individuals,  who have been
supposed to have  received  from nature an organization different
from  other  men.   But this is a mistake;  they  only  possess  the 
136
A  SUMMARY
 organs of speech and voice well arranged, so that they can readily
 execute the sounds which they wish to produce.
   The principles on which this art rests, are easy lo comprehend.
 We know from experience, that sounds are altered by a variety of
 circumstances; e. g. that they become  weakened, less  dislinct,
 and change their tone when they are at a distance from us.  When
 a.man who descends into a well,  speaks to those who are  above
 him, his voice does not arrive at their ears until it has undergone
 several  modifications, arising from distance, and the form of the
 canal which it has passed through.   If then a person has carefully
 remarked these  modifications, and exerts himself to imitate them,
 after a little practice he will be able to produce this  accoustic il-
 lusion; and we can no more avoid being deceived by  it,  than we
 ean prevent our seeing  objects  larger than  they actually are,
 when we examine them through a magnifying glass.  The decep-
 tion will be complete, if he employs other illusions to distract the
 attention.
   The better the talents of the artist, the more perfect and nume-
 rous the illusions will be; but we must guard ourselves from sup-
 posing that the ventriloquist* produces voice and articulate sounds,
 differently from other persons.  His voice is formed in  the common
 manner, but it is modified by the artist in its volume and tone.  As
 relates to his pronouncing words without moving his lips,  it is be-
 cause he employs words  in which there  are no labial  consonants,
 which unavoidably require the motion of the lips to perform them.
 In one respect we may say that this art is to the ear, what paint-
 ing is to the eye.

             Modification of the  Voice by  Age.
   The laryrtx  is  proportionally very small  in the fcetus,  and the
new born infant; its small volume  is  contrasted with  the  os
hyoides,  the tongue, and  other organs of deglutition, which are
very much  developed; it is rounded, and  the thyroid cartilage
does not  project from the neck.  The lips of the glottis, the ven-
tricles, and superior ligaments are very short, in proportion to

  * The term ventriloquist, and other words of a similar import, were employed
in the infancy of science, but it is evident that we ought not to admit  them now
in scientific  language. 
OF PHYSIOLOGY.
137
what they are afterwards, for the thyroid cartilage being but little
developed, the space which they occupy is necessarily inconsider-
able.  The cartilages are also flexible, and are far  from possessing
the consistence which they afterwards acquire.
  The larynx preserves these characters until about the period of
puberty; at this time, a general revolution takes place in the ani-
mal economy.  The evolution of the genital organs, determines a
rapid increase in the nutrition  of many  of the other organs, es-
pecially that of the voice.  The great  increase in  the nutritive
powers is first apparent in the muscles, afterwards, but more slow-
ly, it is  manifested in the cartilages, when the general form of the
larynx becomes modified.   The  thyroid cartilage  developes itself
at its anterior part, and projects from the neck,  but much more
strongly in the male, than in the female.   From this circumstance
results a considerable  elongation of the lips of the glottis, or  of
the thyro-arytenoid muscles.  This  circumstance is much more
worthy  of remark than the general enlargement of the glottis,
which takes place at the same time.  These changes in the larynx,
though rapid, are not sudden, they require six or eight months be-
fore they are finished.
   After the age of puberty, the  larynx  undergoes  no  other very
remarkable  change;  except that its volume somewhat increases,
and the projection of the thyroid cartilage becomes rather more
prominent. In man, the cartilages ossify  partially; in old age this
process continues, and at last becomes nearly complete; the gland
of the epiglottis decreases, and the  lips of the glottis diminish  in
size, become less deep coloured,  lose their elasticity, and at last
undergo modifications, similar to those of the rest of the muscular
system.
   The production of the voice  being dependent upon the passing
of air into  the  chest,  and the fcetus  being plunged in the fluid
of the amnios, it is of  course incapable of forming  sounds.  But
at the moment of its birth, the  infant produces sharp, and intense
sounds.   Vagitus, is the name which has been given to this cry
of infants, by which it expresses its wants and feelings; we may
recollect that this is the object  of its cries.   Before the end of the
first year, the infant begins to form sounds different from crying.
These sounds are at first vague and irregular, but they soon  be-
come more  and more distinct;  at this  time nurses begin to teach
                               18 
138
A
SUMMARY
them to pronounce the most simple, and at last the  most compli-
cated words.
   The pronunciation of children is different from that of adults;
this  is owing to the great difference which exists in the structure
of their organs.  In children, the teeth are still concealed in the
alveolar  processes; the  tongue is  comparatively large;  the lips
project more than is necessary to  cover the anterior part of the
jav\ - when they are brought in contact; and the nasal cavities are
but little  developed.
   By degrees,  and  in  proportion as  the organs of pronunciation,
approximate those of the adult, children  articulate distinctly the
different combinations of letters.   They do not learn to form ap-
preciable sounds,  or to  sing, for the  most part, until long after
they have acquired the faculty of speech.  These different sounds
are what we have called the acquired voice, and are never formed
by the child when it is deaf.   Until the age of puberty, the larynx
and  lips of the  glottis, remain  proportionally  very small, and the
voice is entirely composed of sounds  which are sharp.   It is then,
physically impossible for the larynx to produce grave sounds.
   At the period of puberty, particularly in men, the voice under-
goes a remarkable modification.  It acquires in a few days, some-
times very suddenly, a grave tone, essentially different from what
it exhibited before; it falls  generally an octave.  In some cases
the voice  is nearly lost, and  does not  entirely return  for  some
weeks; frequently there remains for a time, a remarkable hoarse-
ness, young men often form very sharp  sounds, when they intend
to produce  those which  are grave.   It is  therefore, at this time,
impossible for  them  to produce appreciable sounds; or to sing.
   This state of things continues frequently for a year, after which
the  voice gets its natural tone, which remains during life; but we
sometimes meet with individuals,who,at this time,lose forever the
faculty of singing; and  others, whose  voices  before this period
were  rich  and extensive,  afterwards become  indifferent  and
limited.
   The gravity  which the voice acquires depends,  evidently, on
the developement  of the larynx, and  especially on the elongation
of the lips of the glottis.  As  these parts cannot extend posterior-
ly, they are lengthened anteriorly;  at this period also the larynx 
                     or PHYSIOLOGY.                 139

becomes prominent, forming what is called the pomum adami.
In females, the larynx does not undergo this increase of size, the
voice therefore generally remains sharp.
  The voice preserves  nearly the same  characters from puberty
until  the approach of old  age; at least  its modifications, during
this interval, are inconsiderable, and chiefly respect its tone  and
volume.  But as old age  approaches, the voice becomes essentially
altered; its tone is changed, its extent diminished;  and singing is
more difficult, the sounds resembling tries, and being produced
with difficulty and  labour.  The organs of pronunciation are al-
tered, the teeth being  shorter  and  often lost.  All  these  phe-
nomena become more remarkable as  old  age advances, the voice
becoming weak, tremulous, and broken.  The same  remarks apply
to the singing, the defects in both cases arising from the imper-
fection in the muscular contraction of the part, the slowness in
the movements of  the tougue, the loss of the teeth, and the pro-
portionally  increased length of the lips, &c.  all of which must
necessarily have a strong influence on the pronunciation.

           Relations between Hearing and  Voice.
  We have already spoken of  the  connexion between hearing
and  voice.   It is such, that an  infant deaf from its birth, is  ne-
cessarily dumb; that a person who has a false ear, has  necessarily
a false voice; that an  individual whose hearing is imperfect, is
instinctively induced to talk loud.   But the larynx in those who
have been deaf from birth, is by no means incapable of producing
voice; it has been before observed that they utter cries.  Of  late,
by  different processes, persons deaf and dumb from  their birth
have  been taught to speak so as to maintain a conversation, but
their  voice  is hoarse, rough, and  unequal.   I believe, however,
that there has been no  instance where a deaf and dumb peraon
has been taught to sing.
  There have been some instances of persons who  have acquired
hearing, at an age  when they could give an account of their sen
sations. Among all, the voice has been  developed  soon  after the
individual has acquired  the sense of hearing.
  The Me mo j rs of the  Academy of Sciences for  the  year  1703,
contains an example of this kind; v. Inch occurred in a young man of
Chartres, who was about twenty years of age.   "Who, to the grea' 
140                   A SUMMARY
astonishment of the whole city, began suddenly to speak."  It ap-
pears, from  hit.  account of himself, that about three or  four
months before, he had  heard the bells, and was extremely  sur-
prised by this new and  unknown  sensation.  He observed about
the same time water escape from his left ear, after which he heard
perfectly with  both  ears.  For three  or four months he listened
wi'hout attempting to speak to those about him, accustoming him-
self to repeat, in a very low  voice, those words  which he under-
stood; strengthening himself in the pronunciation, and the ideas
attached to the words.   At last  he broke  silence, and spoke,
though imperfectly. Immediately learned theologians were called
to interrogate, him, &c.
   It is unfortunate for science that this young man was not ob-
served by physicians, perhaps his history might then have been
found more  interesting.
   A similar occurrence took place in Paris, a few years since, a
young man  who  had been deaf and dumb from his  birth, was
cured  of his deafness by doctor  Hard, by  means  of injections
made into the drum, through an opening formed in the membrana
tympani.  He at first heard the sound of the bells  in the neigh-
bourhood, which produced a very  vivid emotion;  he was immedi-
ately seized  with  pain in the head, and vertigo.  The next  day
he was sensible of noises made in his apartment; in twenty-four
hours afterwards, he was able to distinguish the voice of persons;
who *poke to him   Then his delight  became extreme, he could
not satiate himself with  hearing his friends speak, "his eyes" says
Profes>or Percy, "seemed to seek the words upon their lips."  His
voice was not  slow in  developing itself;  it  formed at first but
va^ue  sounds, and in a short time he could stammer  out a few
words, but  he pronounced them  badly and like a child. It was
sometime  before he  could  pronounce compound words, or those
which  contained   many  consonants.  An  organ was suddenly
played in  his presence;  when he immediately began to tremble,
and turned pale, and was near fainting; afterwards he experienced
all  those transports which we can imagine to   be  caused  by a
very vivid, but  unknown pleasure; his flushed cheeks, sparkling
eyes, rapid   respiration, and quick  pulse announced a sort of de-
lirium, an intoxication of pleasurable feelings.   No doubt, many
other surprising  and interesting  phenomena would  have  been 
OP  PHYSIOLOGY.
141
observed in this young man, if disease had not removed him from
the philosophical physicians who attended upon him.

            Of Sounds Independent of the Voice,
  Independently of the voice, man  can produce  at  pleasure a
great number of appreciable, and  unappreciable  sounds; such as
the noise which we make in the act of spitting or  snuffing, that,
by which we call ahorse, and  the imitation of the sound  of draw-
ing a cork from  a bottle, and a multitude of other  noises which
result from the movement of different parts of the mouth, or from
the manner that  the air  penetrates into that cavity, or  passes out
from it.  It is not easy to account for the mechanism of these dif-
ferent  sounds, particularly those which are appreciable, as that of
whistling, we can only approximate this point.


       OF  ATTITUDES AND MOVEMENTS.

   Muscular contraction not only produces the  voice but pre-
side* also oxer our movements and attitudes.
  The explanation of the movements and attitudes  of man con-
sists  in the  application  of  the laws of mechanics to  the organs
which execute them.  Our attitudes and  movements  being exceed-
ingly various, in order to explain  them, it would  be necessary to
have recourse to all the laws of mechanics.  No  one  has ever
executed this labour in a satisfactory manner; they have generally
limited themselves to those movements and  attitudes  which  are
the most frequent, and to the  application of the most simple prin-
ciples of mechanics.

The Mechanical Principles which are necessary to understand
          the Movements and  Attitudes of the Body.
  The line in which the  weight of a body acts, is called the verti-
cal line.   In every part of  a body the vertical line passes through
different points, but there is one point where all these  lines cross
each  other, this is called the centre of gravity.
  The state of equilibrium of a heavy body, placed  upon a hori-
zontal  plane, is when a perpendicular falling through the centre of 
142
A  SUMMARY
gravity upon the horizontal plane, passes between those points on
which the body rests.
  The equilibrium of a heavy body upon a  horizontal plane is
firm, in proportion as the centre of gravity of  the body is near the
plane, and  the surface upon which it rests is  extensive.
  The base of support is the space included between those points
on which a body is applied to the plane.
  Of two hollow columns, formed  of an  equal  quantity of the
same materials, and of the same height, that which has the largest
cavity will be the strongest.
  Of two columns of the same diameter, but of different heights,
the highest will  be the weakest.

                         Of Levers.
  We define a lever to be an inflexible instrument which  turns
upon a fixed point.  We distinguish in this instrument three parts,
viz. the moveable part or fulcrum, the part to which the  resis-
tance, and that to which the power is applied.  According to the
respective positions of the fulcrum, the power, and the resistance,
the  lever is  of the first, second  or third  kind.  In  the lever of
the first kind the fulcrum is between the resistance and the power;
the resistance being at one extremity, and the power at the other.
The second kind of lever is when the resistance is between the
power and the fulcrum; the fulcrum and the power occupying the
two extremities.  Lastly, in the lever of the third kind, the power
is between the resistance, and the fulcrum, the resistance and the
fulcrum being at the two extremities.
  We likewise divide a lever into the arm of the power and that
of the resistance.  The  first comprehends  the portion of the lever
which extends from the  fulcrum  to the  power;  the second is the
portion included between the fulcrum and  the resistance.  When
in  a lever of the first kind, the fulcrum occupies  exactly the mid-
dle of the lever, we then say, that the lever has equal arms; when
the fulcrum is nearer either the power or the  resistance, we then
say, it has unequal arms.
   The length of the arms of the lever gives  more or less advan-
tage, either to the power or to the resistance.   If the arm of the
power, e, g. be  longer  than  that of the  arm of resistance, the 
OF PHYSIOLOGY.
143
increased advantage to the arm of power will be in proportion to
its greater length.  So that if the first of these arms be double or
triple the second, it will be sufficient, if the power be one half or
one third the resistance, to bring these  two forces into a state of
equlibrium.
  In a lever of the second kind, the arm of the power is necessa-
rily longer than that of the resistance, inasmuch as the fulcrum is
at one extremity and the power at the other.  This kind of lever
is always advantageous to the power.   The reverse is the case in
a lever of the  third kind, as  then the power is  between  the  ful-
crum and the resistance.
  A lever of the fir.^t kind is most favourable to an equilibrium,
that of the  second  to overcome resistance, and  a lever of the
third kind conduces most to  rapidity and extent of motion.
  It is important to remark the direction in which the power is
applied  to  a  lever.   The effect of the power is so much  the
more considerable, as  the direction  approaches  nearer to  a per-
pendicular to that of the lever.  * When this is the case, the  whole
force is employed to overcome  the resistance, but when the  direc-
tion is oblique, one part of the  force tends to bring the lever into
a proper  direction, and this portion of the power is lost by the re-
sistance of the fulcrum.

                       Moving Power.
  That general property of matter by which it remains in a etate
of motion or rest, when it is not acted upon by any foreign  cause,
is called its vis inertia.
  The force which produces  motion can only be  measured by the
quantity of motion produced.   This is obtained by multiplying
the mass by the velocity.
  Velocity is acquired  in two ways, viz. either by the continued
action of a force, as in the gravity of bodies, or in consequence of
a force which imparts instantaneously a given velocity.
  From what has been said, it  is easy to infer, that every effort
exerted upon a loose body will  impart motion.  The direction of
the motion, its velocity, and the space it will pass over, must de-
pend upon the mass, the intervals of the action exerted  upon it,
and the forces which act upon it during its motion.  Thus a body 
144
A  SUMMARY
thrown from the hand acquires instantaneously a velocity propor-
tioned to the intensity of the effort, and the mass of the projected
body; the continued  action of gravity modifies incessantly both
the velocity and the direction  of the  motion; the motion is also
retarded by the resistance of the atmosphere, the  effect  of  which
increases with the extent of the surface which strikes against it,
and the specific gravity of the  body.
   Friction is the resistance which a  body is obliged to overcome
in gliding over another body.
   The force which unites two polished surfaces, when brought in
accurate contact with  each other, is called adhesion.  ThU force
is measured by the effort  required to separate them, acting per-
pendicularly to the surfaces.  The more  polished the surfaces in
contact, the greater will be the adhesion, and the less the friction;
when we wish, therefore, two bodies  to glide upon each other, we
polish the surfaces, or interpose some liquid between them.


                      THE  BONES.

   The bones determine the general  form  and dimensions  of the
body   In consequence of their  physical  properties, they fulfil a
very important use in  the different  positions and motions: they
form the different levers which the animal machine  presents, and
serve to transmit the  weight of all  the parts of  our body to the
earth.  They are  employed as  levers of the first,  second,  and
third  kind.  When they are in equilibrio, a lever of the first kind
is almost always employed;  if a considerable resistance  is to be
overcome, they represent a lever of the second kind; and in other
movements they are employed as levers of the third kind; which,as
was before observed, though unfavourable to the action of the pow-
er, conduces very much to the extent and rapidity of the  motions.
The greater part of the projections  and eminences of  the  bones,
serve to change the direction of  the  tendons so that they may be
inserted in a direction less distant from the  perpendicular.
   As means of transmitting weight, the bones  represent hollow
columns, which thus augment, very much, the general resistance
of the skeleton and each bone. 
OF PHYSIOLOGY.
145
                     Form of the Bones.
  The bones are  divided  into  long, short, and flat.  The short
bones are placed  in those  parts  which are very  solid, but have
little mobility, as the feet, and  the vertebral column.   The flat
bones chiefly compose the  walls of the cavities; they concur also,
advantageously, in the movements and attitudes, by the extent of
surface which they present for the insertion of the  muscles.  The
long bones are principally employed in locomotion, and are only
found  in the  extremities.  The  form  of  their body and that of
their extremities is particularly  worthy of  notice.  The body is
always the smallest part of the bones, and is generally rounded;
but, on the contrary, they always grow larger at their extremi-
ties.   This arrangement of the body of the  bones  assists in  giv-
ing form to  the  extremities; and the increased  volume  of  the
articulated extremities, besides this use, gives, also, solidity to the
articulations, and  diminishes the obliquity  of the  insertion of the
tendons upon the bone.
   The short  bones are  very  spongy in their texture,  by which
they present a considerable surface, without much weight.  The
same remark applies to the extremities of the long bones, but their
bodies are very  compact  and  heavy, which impart  to them  a
great power of resistance, which was necessary because these parts
have to sustain all the forces which act upon these bones.
   The spongy tissue of the short, and the extremities of the long
bones are filled with a  medullary fluid;  the  cavities of the long
 bones are filled with a  substance  called marrow.

                  Articulations of the Bones.
   They are distinguished  into those  which permit, and  those
which do not  permit  motion.  The  first presents subdivisions,
founded upon the  form of the articulating surfaces.  The second are
 also subdivided according to the disposition of the articulating sur-
 faces, and the  kind of motions which these articulations permit.
   In the moveable articulations, the bones  are  never in immedi-
 ate contact.   There is  always interposed between them, an elas-
 tic substance, differently disposed,  according to the articulation,
 and destined to support easily  the strongest pressure, to weaken
 shocks and facilitate motion.   Sometimes this substance is homo-
                             iy 
140
A  SUMMARY
geneous in its structure, adheres equally to the surfaces of both
bones, and constitutes what has  been called  the  articulation of
continuity;  it is then of a fibro-cartilaginous nature.   Sometimes
this substance is  formed of a lamina  on each articulating surface;
this is what is called an articulation  of contiguity; in this case,
the substance is cartilaginous.
   It is said  that the substance which  covers the bone in this kind
of articulation, is formed of fibres  arranged at the  side  of each
other, in a  direction perpendicular  to  the surfaces  which they
cover.  This opinion appears  to me, to merit further investiga-
tion.   The cartilages are of a homogeneous lamina.
   The articulations  thus arranged  are  most  favourable to a gli-
ding motion; the surfaces in contact are highly polished, and a
particular liquid, the synovial, is continually  poured out between
them.  For the same reasons, the adhesion  is  very strong, which
adds  to the  solidity  of the articulation.
   In  certain moveable articulations we  find, between the articu-
lated  surfaces, loose fibrocartilaginous  substances.   They have
been supposed to act like cushions, yielding to pressure  and  af-
terwards returning  to their natural  form;  thus protecting those
surfaces with which  they are  in  contact.   For this reason,  it is
said, they are found  in those joints which  sustain the most con-
siderable  pressure.  We  think  this  opinion  is not  sufficiently
proved.  Indeed, they  are  not found in the  hip, nor the ancle
joints, which support,  habitually,  the greatest efforts.  Do they
not rather serve to  favour extent of motion, and to prevent dis-
placement?
   About, and sometimes in the interior  of  joints, we  find fibrous
bodies, which are called ligaments, which perform the double  of-
fice of keeping the bones in their respective situations, and limit-
ing the movements which they execute one upon another.

                      Altitudes  of Man.
   We will now examine man in the different positions which he
can assume; and, first, in that posture which is the most common
to him, that is, upon his feet.
   We see, in the first place, that the  head, united intimately with
the atlas, forms with it  a lever of the first kind, the  fulcrum of
which is in  the articulation of the lateral  masses  ot the atlas, 
OF PHYSIOLOGY.
147
 while the power and the resistance occupy each  an extremity of
 the lever, represented, the one by the face, the other by the occi-
put.  The  fulcrum  being  nearer the occiput than the anterior
 part of the face, the head  tends, by its own, weight, to fall  for-
 wards,  but  it is  retained  in equilibrio  by the contraction  of the
 muscles which are attached to its posterior part.   It is the  verte-
 bral column, then,  which  supports the  head,  and transmits  the
 weight  to its inferior extremity. The  superior extremities, the soft
 parts of ihe neck, the thorax, and the greater part of the abdomi-
 nal viscera, press more or less directly upon the vertebral column.
   In consequence of the great weight of these  parts, it was neces-
 sary that the vertebral column should possess great solidity.  In-
 deed, the bodies of the vertebra, the intervertebral fibro-cartil-
 ages, and the ligaments which bind  these parts  together, form a
 column of great strength.   When we reflect upon the structure
 of the vertebral column, that it is formed of portions of cylinder-
 placed one above another; that it forms a pyramid, the base of  which
 rests upon the sacrum, and that it presents three curvatures in oppo-
 site directions, which cause its power of resistance to be six  times
 greater than if it possessed none, we  can then  form some idea of
 the great resistance of which it is capable.  We know  that it is
 not only capable of supporting the organs which press upon it, but
also burdens of great weight.
   The weight of the organs which the vertebral column sustains,
 causing it to incline forward, there are  muscles  placed  along its
 posterior part which resist this tendency.  Under  these circum-
stances, each vertebra, and  the  parts of which  it  is composed,
represent a lever of the first kind, of which the fulcrum is in  the
fibro-cartilage which sustains the vertebra, the  power in the mus-
cles which draw it  backward, and which are attached to the spi-
nous and transverse processes, and the  weight or resistance in
those parts which draw it forward.
   The vertebral  column, as a whole, represents a lever of  the
third kind, of which the fulcrum is in the articulation of the fifth
lumbar vertebra, with the os sacrum.   In this case the weight, or
resistance, is in those  parts  which tend  to carry the column for-
ward, and the power in the muscles which are  placed  on its pos-
terior part.   As the power acts principally at the inferior part of
the lever, it is there that nature has placed the  strongest muscles; 
148
A  SUMMARY
it is there that the pyramid, represented by the vertebral column,
has the greatest thickness, and that the apophyses of the vertebrae
are more developed and  more  horizontal; it also here that the
sense of fatigue is first perceived, when  we  remain long in an
erect position.
  The muscular power will act  efficiently  in  preserving the equi-
librium, necessary in standing,  in proportion as the spinous pro-
cesses are longer,  and nearer the horizontal direction.
  The weight of the vertebral column, aid the parts which press
upon it, is transmitted directly to the pelvis, which, resting upon
the thigh bones, represents a lever of the first kind, the fulcrum
of which is in the ileo-femoral  articulations, and  the  power and
resistance  are  placed posteriorly and  anteriorly.  The  pelvis
partly sustains the weight of the abdominal viscera, and also sup-
ports the vertebral  column,  transmitting equally to both of the
thigh bones the weight, through the ossa ilii.  The  pelvis is in
equilibrio upon the two heads of the thigh  bones; this equilibrium
results  from a great number of combined efforts.
   On one side, the abdominal viscera, pressing upon  the  pelvis,
incline it forward, tending to depress the pwiis; but the vertebral
column by its weight, acts in an opposite direction.
   The  weight of  the vertebral  column being much greater than
that of the abdominal viscera,  it would  appear necessary to es-
tablish  the equilibrium, that powerful muscles, passing from  the
thigh bones, should  attach  themselves to the pubis, and, by their
contraction, counterbalance the excessive weight  of the vertebral
column.  Such muscles, in fact,  exist,  but it is not the  use of
these muscles  to preserve the  equilibrium of the pelvis upon the
thigh bones; for the pelvis, so  far from  having a  tendency poste-
riorly, rather inclines anteriorly, because the muscles which resist
the tendency of the vertebral  column to  incline  forwani, having
the pelvis for their fixed point,  have a considerable  tendency to
 carry it upward.  There are again those muscles which move the
thigh, bones, on the  posterior part of the pelvis, which prevent its
being elevated, and which are  the principal  agents, in preserving
 the equilibrium of the pelvis  upon the thigh  bones; nature has
 formed these numerous and very powerful.
   The  articulations of the  thigh bones with the ossa-ilii are much
 nearer the  pubis than the  sacrum, from which it happens that the 
OP PHYSIOLOGY.
149
posterior muscles act upon the longest arm of the lever, which is
favourable  to their action.
  In  the erect posture of the  body,  tho thigh bones transmit di-
rectly to the tibiae, the weight  of  the trunk.  They fulfil easily
this use from the strength of  their articulation wiih the ossa ilii.
  Besides  the uses which the neck of the thigh bones perforin in
the  various motions of the body, they are likewise useful in stand-
ing.   As  their head is directed inwards and  upwards, they not
only support the vertical pressure of the  pelvis, but they have a
tendency to prevent the separation of the ossa ilii, thus counter-
acting the  opposite action of the sacrum.
  The thigh bones transmit the weight of the body to the  tibiae,
but,  from  the  manner  in which the pelvis presses upon  their
inferior extremities, they have an inclination forward;  while the
contrary  is the case at their superior  extremities.  In order to
preserve their equilibrium upon the  tibiae, it is necessary, there-
fore, that there  should be powerful  muscles, to oppose this ten-
dency. The  muscles by  which  this is effected, are the rectus,
and  triceps crural* the action of  which  is favoured  by  the
rotula, placed behind  their tendon.  The posterior  muscles of
the leg,  which  are attached to the condyles of the  femur, concur
also in preserving the equilibrium
  The tibiae transmit the weight of the body to the feet, without
any assistance from  the fibulae.   But in  order that the first of
these bones may fulfil, conveniently, this office.it becomes neces-
sary that the muscles should oppose the disposition which exists
at their superior extremities, to be carried forward.  The gastro-
nemii  muscles fulfil this office, in part, but all the muscles situ-
ated on the posterior part of the leg concur.
  The feet sustain the whole  weight of the body, for which their
form  and structure  render them  admirably suited.  The sole of
the foot is very extensive, by which the firmness of the  erect po-
sition  is secured.  The  skin and  epidermis of this part are very
thick.  Beneath the skin is a lamina of fat of considerable thick-
ness at those places where the foot presses upon the earth.   This
fat forms  an elastic  cushion,  which diminishes  the effect  of the
pressure produced by the weight of the body.  The whole inferior
* The author probably refers to the craralis and vasti muscles,
;.—Trans. 
150
A  SUMMARY
 surface of the foot does not touch the ground.   The heel, the ex-
 ternal edge of the foot, the part which corresponds to the anterior
 extremity of the metatarsal bones, and the extremities or balls of
 the toes, are the points which generally press upon the earth, and
 transmit the  weight of the body.  We also find at each of these
 points, fatty masses, of considerable size, which are evidently in-
 tended to prevent  inconvenience from too great pressure; that
 which is placed immediately beneath the head of the os calcis is
 very remarkable; it is attached by its superior  face to the bone,
 but is distinct from the rest of the fatty substance which  adheres
 to the heel. The other fatty masses,  or cushions, are less volumin-
 ous, but are arranged  in a manner completely analogous,
  The tibiae transmit the weight of the body to the  astragalus,
 from which it is again imparted to the rest of the bones of the foot,
 the os calcis receives  the greatest portion, and  the remainder is
 divided between the other points of the foot which press upon the
ground.   The  following  is the  general  mode  by which this is
effected.
  The relation of the os calcis to the  astragalus is such, that it
 transmits the weight partly to the ground, and in part to the os-
cuboides.   This last  and the os-naviculare, through the medium
of the  cuneiform bones, press in their turn upon the metatarsal
bones, which transmit to the ground nearly all  the pressure they
 receive;  the surplus  is propagated  to  the toes.  This  mode of
 transmission  supposes the foot to touch the ground through  the
 whole extent of the sole.
  As the pressure of the tibia is felt over  all the internal part of
the foot, it has a tendency tp press it outwards; the  peroneus
muscle is destined  to counteract this when we  stand in an erect
position.
  We have already seen that the muscles which prevent the head
from falling forwards, arise from the neck; that those which ful-
fil the same office to  the vertebral column, arise from the pelvis;
that those which preserve  the pelvis  in equilibrio, are attached to
the bones of the thighs and legs;  that those which prevent the ro-
tation of the thigh bones  backward, are inserted into the tibia;
and lastly, that those  which retain the  bones of the tibia in their
vertical position, have their fixed point in the feet.   It is then in
 the feet, that all the efforts required in standing, are at last con- 
OF  PHYSIOLOGY.
151
centrated;  it is necessary, therefore, that the feet should present a
resistance proportionate to the efforts which they are destined to
support.   But the feet  have not  any other means  of resistance
than what arises from their weight; all the rest which they exhibit
is communicated by the weight of the body which they support;
so that the same cause which tends to  produce a prostration of the
body, is also that which secures to it firmness in the erect position.
  The space between the feet, as  well as the surface  which they
cover, forms  the  base  of support to  the  body.  The  state of
equilibrium in the erect posture, is a vertical line passing through
the centre of gravity, and falling upon some point included within
the base of support  The position will be firm in proportion to the
extent of this base; in this respect, the size of the feet is far from
being an indifferent circumstance.
   We know from observation, that this posture of the body is most
secure, when the two feet are placed  parallel to  each other, and
•separated by a space equal to the length of one of them.  If we
enlarge, laterally, the base of support, by separating the  feet, the
posture  becomes more secure in that direction,  but we  lose our
firmness anteriorly and  posteriorly.  It is the reverse when we
place one foot before and the other behind.
   The  more the base of support is diminished, the less secure is
the posture, and the greater the muscular power required to pre-
serve it.   This happens when we endeavour to  elevate ourselves
on our toes.  In this case the feet only  touch the  ground in the
space comprehended between the  anterior extremity of the meta-
tarsal bones, and the extremities of the toes. This posture is very
 fatiguing anil cannot long be endured.   Some  persons,  dancers
for example, can elevate themselves upon the extremities of their
toes; a thing which is extremely difficult.  Besides, whatever may
be the  part of the foot which  touches the ground  it is always
comprised  in the four parts which we have mentioned at the com-
 mencement of this article, and we cannot mistake therefore, the
 uses of  the fatty masses which are found there.
   'The position  will also become very difficult, if not impossible,
 when the feet rest upon a very narrow plane;  a tight rope for ex-
 ample.  We may generally  remark,  that whatever contracts the
 base of support, proportionally diminishes  the  firmness of the
 posture; this any one may satisfy himself of, by observing those

                                  « 
152
A  SUMMARY
individuals who have accidentally lost their toes by frost; or the
anterior part of the foot by a partial amputation; those who have
one le"- of wood, or persons walking upon stilts. In this last case
the position is rendered still  more difficult by the distance of the
centre of gravity  from  the  base of support.
   The position upon both  feet  may be  varied infinitely.   The
trunk may be inclined  before or behind, or laterally and the in-
ferior  extremities be bent  in different ways.  Those who under-
stand  all that has been  said  of the  erect posture, will find ne
difficulty in explaining the attitudes here referred to.

                  Standing upon One Foot.
   We sometimes stand on one foot; this attitude  is necessarily
fatiguing.  It requires of the muscles which  surround  the  hip
joint, a strong and continued action, by which the equilibrium of
the pelvis upon one thigh is preserved.  As the  body, and of con-
sequence the pelvis, is inclined  to  fall  to that  side on which  the
leg is not applied to the ground, there  is required of the glutceus
maximus, medius, minimus; tensor vaginae temoris, gemini, pyrami-
dalis, obturatores, and the quadratus femoris, such a contraction, as
will support the  trunk.  We may speak here  of  the use of the
neck of the  thigh bone, and of the projection of the great  tro-
chanter.   It is evident that  they render much less oblique  the
insertion of the muscles which have  been before  spoken of,  and
thus prevent so great a loss  of power as would otherwise be the case
   It is scarcely necessary, to add, that in standing upon one foot,
the  base of support is only represented  by  the  surface of the
ground covered by the foot, and that it must, therefore, be neces-
sarily less secure  than  when we stand  upon both  feet, whatever
maybe the posture.  It will become still more difficult  and tot-
tering, if instead  of applying the whole surface of the foot  to the
ground, we  rest upon  one point of it.  It is quite  impossible to
preserve this position longer than for a few instants.

                           Kneeling.
   The base of support in this posture appears  at first sight to be
very large;  and as the  centre of gravity is brought near the  earth,
one might suppose that it would  be more secure even than stand-
ing.  But the size of the base which  sustains the  weight of the
• 
•   OF  PHYSIOLOGY.
153
body, is  far from being measured  by the whole surface of both
legs which touch the ground.   The patella is  nearly  the  only
part which transmits the weight of the body to the ground.  The
skin also, which covers  this part, is strongly pressed, and not
being covered  with a  fatty cushion as we see on the feet, it soon
b'.'v-omes  injured, if  this position be  long continued.   For this
reason we are  in the habit of placing cushions under the knees,
when we intend to kneel for any considerable length  of time, by
which we transmit the weight of the body to the ground through
an intermediate substance which  increases the  base of support,
and  thus diminishes the effect of pressure.   It is for a  similar
reason, that is to increase the extent of the pressure caused  by
the weight of  the body, that we bend the thighs backwards, and
throw  the  weight upon  the legs and heels.   This situation  is
much more solid and  less fatiguing, because the base of support
is much enlarged, and the centre of gravity nearer the ground.

                      Attitude of Sitting.
  We may sit  in different ways;  on  the ground, for example,
with  the legs extended;  on a  low seat,  the feet touching the
ground, or upon an elevated seat, in which the feet do not touch
the ground but are  suspended, and the back supported, or un-
supported.
  In  all the positions where the back  is not supported, nor the
feet touching, the weight of  the body is transmitted to the ground
by  the pelvis, the size of which at its lower part  is greater than
in any other animal.  'The base of support  by  the trunk becomes
distinct from that of the bones of the  inferior extremities; it  is
represented by the extent which the parts occupy on the resisting
plane which sustains them.   The more voluminous and  fat they
are, the more solid will be the attitude of sitting.
  When in the posture of sitting  the  back is not  supported, it
requires  the permanent contraction  of the posterior muscles  of
the trunk, to  prevent its falling  forward.  The  position  is  on
this account fatiguing, as we observe after sitting on a stool  for
some time, but which is not the case  when the  back is supported,
as in  sitting on a sofa.  Whatever  be  the  manner of sitting,  we
can preserve  this attitude for  a  long  time.   1st.  Because  it  re-
quires the action of but  few muscles.   2d. Because the  base of
                             20 
154
A  SUMMARY
support is  large, and the centre  of gravity  near  the earth
3d. Because the nates, in consequence of the thickness of the
skin, and  the quantity of fat, can support a strong  and  long
continued pressure without inconvenience.

                 Of  the Recumbent  Posture.
  This is  the only  position of the body which does not require
any muscular effort.   This is the attitude of  repose, and  of those
whose muscular  powers are prostrated by disease.  We  can also
endure this attitude for a long time.   The only organ affected  by
this position, is the skin, which corresponds to the base of support.
The pressure of the weight of the body, though very much  divided,
soon causes a sense of uneasiness, and  afterwards  of  pain; and,
if the position remains long the same, as we find in some diseases,
the skin becomes ulcerated, and sometimes gangrenous, particu-
larly at those points which  have the greatest  pressure, as  the
posterior surface of the pelvis, the  great trochanters, &c.   It is to
avoid this inconvenience that we endeavour to procure beds which
are soft, and the elasticity of  which permits  a more equal di-
vision of the pressure upon all those points of the skin which cor-
respond to the base of support.

                         Of Motions.
  There are two kinds  of  motions; the end of the  first is to
change the relative situation of the different  parts of the body.
That of the  second,  to change  the situation cf the whole  body
upon the surface of the earth.  The one is called partial, and  the
other locomotion.

                     Of Partial  Motions.
  The greater number of partial motions make an  inherent part
of different functions.  Many have already been  described, and
the others will be in their turn.   We shall only treat here of those
which may be insulated in the history of the functions.  We shall
successively treat of those of the face, head, trunk, and  superior
and inferior extremities. 
OF PHYSIOLOGY.
155
                Partial  Motions of the Face.
   It is easy to perceive that these motions have two distinct ends.
The first  is to concur in the sensations  of seeing, smelling and
tasting; also, the  receiving of aliments,  mastication, deglutition,
voice and speech. The second indicates the operations of the in-
tellect, and the passions.
   Independently  of those motions of the face which concur  in
vision, smelling,  tasting, voice  and  speech,  of  which  we have
already spoken, and of those  which serve to receive the food, for
mastication, and  deglutition, &c.  of which  we  shall  speak  in
their proper place; the muscles of the face cause in this part mo-
tions, which serve to express certain  intellectual  acts, different
dispositions of the  mind, and instinctive desiros  and  passions.
Pleasure and pain, joy and sadness, desire and fear, anger, hatred,
love, &c. have each an expression in the face  which characterises
them.  'The painful and gloomy affections, and violent desires are
generally accompanied with  a  contraction of the countenance.
The eye-brows are contracted into a frown, and the angles of the
mouth drawn backwards and downwards; on the contrary during
the existence of the mild and amiable affections, gaity, agreeable
sensations, and satisfied desires, the form of the face is expanded,
the eye-brows elevated, the eye-lids separated and  the  angles  of
the  mouth  drawn  upwards  and  backwards, which  produces
smiling.   It is found that persons in whom the different expres-
sions are the most strongly marked, or as it is commonly expressed,
whose physiognomy  is the most remarkable, are usually dis-
tinguished for the vivacity of  their character.
   It is generally  the reverse with persons whose  countenances
are without expression.   When  any particular disposition of the
mind, or passion, is long indulged in, the muscles which are habitu-
ally contracted to express it, acquire a manifest superiority in vo-
lume over the other muscles of the face.  The  physiognomy tnere-
fore preserves  the expression  of the passion, even when it is not
perceived, or a long time after  it has ceased; and is generally a cor-
rect index of the character and habitual passions of the individual.
   The colour of the skin of the  face is also a powerful means of
expressing the intelligence and passions.  We shall treat of this
«ubject under the article capillary circulation. 
J.50
A  SUMMARY
      Motions of the Head  upon the  Vertebral Column.
  The head may be inclined  anteriorly, posteriorly, or  laterally;
it can also execute a rotatory motion, sometimes to the  right and
sometimes to the left.   The  motions  by  which  the  head  is
inclined  forwards or backwards, or sideways, if they are  not ex-
tensive, take place in  the articulation of the  head  with  the first
cervical  vertebra, but  if the extent of motion is  considerable,
all  the  vertebrae of the neck  take  a part  in  it.  The rotatory
motions are  essentially executed  in  the articulation of  the  atlas,
which is evidently  intended  for  this  purpose.   These different
movements, which are frequently  combined together, are perform-
ed by the successive, or simultaneous contraction of the muscles
which extend from the chest and  neck towards the head.
  It is easy  to see that the movements of the head favour vision,
hearing and  smelling;  they are also useful in  the production of
the different tones  of the voice, in  permitting the elongation or
shortening of the trachea, the vocal tube, &c.  These movements
serve also, as a means  of expressing  some of the operations  of
the mind, as approbation, consent,  refusal, &c. which  are  indi-
cated by certain motions of the head  upon  the neck;  certain
passions also induce certain movements or particular attitudes of
the head.

                 Movements  of the  Trunk.
  We shall  only speak in this article of  particular movements of
the vertebral column;  those which are peculiar to the thorax, the
abdomen and the pelvis  will  be exposed hereafter.
  Flexion, extension, lateral inclination, circumduction, and rota-
tion, are the  motions executed by the  vertebral column, as a whole;
these are also executed by each region, and even by each particular
vertebra.   These different motions take place in the interverte-
bral fibro-cartilages; they are,  likewise,  more easy and more ex-
tensive, as these fibro-cartilages are thicker and larger.   For this
reason, the motions  of the cervical, and  lumbar  portions of the
vertebral  column, are evidently more free and  more considerable
than those of the dorsal portion.  It is well  known that the cer-
vical fibro-cartilages, and especially the lumbar, are  proportional-
ly thicker than the dors.il. 
OF PHYSIOLOGY.
157
  In the motions of flexion, either anteriorly, posteriorly, or later-
ally, the fibro-cartilages are pressed down in the direction to-
wards which the flexion is made; of course then, that part which
is thickest will be pressed down  the most; this is one of the rea-
sons why flexion anteriorly is much more extensive in the verte-
bral column than in any other direction.
  In rotation, all the intervertebral bodies must undergo a length-
ening of the plates which comgose them.  The centre of the bodies
of which  we are now  speaking, is soft and almost fluid; the cir-
cumference only, offers a considerable  resistance  in those  mo-
tions  in which the vertebrae are made to approach each other, but
this circumference yields  sufficiently to form a sort ot  pad be-
tween the two bones.  The disposition of the articulating facettes
ot the verteurae, is one of  the circumstances which have most in-
fluence upon the extent, and mode, of the reciprocal motions  of
the vertebrae.
  V\ hen  we consider the   motions  of the vertebral column, as a
whole, it  represents a lever of the third kind, the fulcrum of which
is in the articulation of the fifth lumbar vertebra with the sacrum;
the power is in the muscles which are attached to the vertebra; and
tin' resistance in the weight of the head, the soft parts of the neck,
chest, and partly of the abdomen.   Each  vertebra, on  the other
hand, taken separately, represents a lever of the first kind, the ful-
crum of which is in the middle, upon the vertebra placed directly
underneath, the  power  is  posterior,  and  the  resistance anterior,
or the one to the  right hand, the other to the  left, towards the
extremities of the transverse processes.
  The motions of the vertebral column are frequently accompan-
ied with those of the pelvis  upon the thigh bones, they then ap-
pear to have an extent of motion far greater than they actually
possess.
  'The motions of the vertebral column are often useful in assist-
ing those of the  superior and inferior extremities, and  of render-
ing less fatiguing  the different attitudes  which the body assumes
as a whole.

             Motions of the Superior Extremities.
  The superior  extremities being the principal agents by which
we effect, directly or  indirectly, those changes in surrounding 
158
A  SUMMARY
bodies that  we desire, therefore require extreme mobility to be
united with a  sufficient degree  of solidity.  We  find  in  these
members many long bones, several of which are  of considerable
length, and slender; the short bones are small; and both of them
are light;  the articulating surfaces  are  of small  dimensions;  the
muscles are numerous, and their fibres very long.    The  bones al-
most always represent  levers of the third kind; which are  fa-
vourable,  as has been before  remarked,  to  extent and rapidity of
motion.   When we consider the motions of the superior extremi-
ties as a whole, in relation to the trunk, or those  of the  different
parts  as they respect each other, we readily perceive that they
unite  in a very eminent degree, great extent, rapidity, and variety
of motion.  The solidity of  these members is not  less worthy of
remark   In numerous situations, they have to support consider-
able efforts, as when we support ourselves  upon  a cane, or when
we fall forwards, and the hands receive the whole shock of  the
fall, &c.
  It is impossible for us to enter into all the details  of this won-
derful piece of mechanism.  We refer the  reader,  on this point,
to "L'Anatomie Descriptive" of Bichat, whose genius exerted it-
self with great success  in explaining the mechanism of  animals.
  The superior extremities are essentially useful  in exercising
the sense of touch, of which  the hand is the principal organ.
They  assist us also in exercising the other  senses, they  aid us in
bringing  objects near, or in carrying them to a  distance, or in
placing them under circumstances favourable to the action of the
senses.  Their motions  concur powerfully in expressing certain
intellectual and  instinctive acts.  The  gestures form a true lan-
guage, which is susceptible of  acquiring great perfection, which
may become of the greatest utility, as happens in the deaf and dumb.
In these cases, the gestures not only paint the sentiments, wants,
and passions, but they also express  the slightest  shades in the
faculty of thought.
  The superior extremities are often  useful in the  different atti-
tudes of the  body.  In some cases, they transmit to the earth a
part of its weight, enlarging, of course, the base of  support.   This
is done when we rest upon a cane, or when, being upon our knees,
we place the hands upon the ground; or, when in sitting upon a hor-
izontal plane, we lean upon one or both of our elbows, ike.  They 
OP  PHYSIOLOGY.
159
also increase the security of the posture of standing erect, when
we carry them in a direction opposite to what the body is inclined
to fall by it- own weight.  We see every hour that they are  use-
ful in different modes of progression.

           Movements of the Inferior Extremities.
  Although there is a manifest analogy between the structure of
the superior and inferior extremities, it  is, nevertheless, evident
in the last, that nature has attended much more to their solidity
anil extent of motion, than to their rapidity  and variety.  This
was necessary, for it is rare that  these members move  without
supporting the weight of the body; they are the principal agents
in locomotion.
   When we impress certain modifications upon foreign bodies by
the inferior extremities, they  move independently  of the trunk.
Thus, when we change  the form of a body, by pressing upon  it
with the foot, or when we displace it with a blow of this part, or
when we exercise the  sense of touch with the foot, to judge, for
example, of the  resistance of  the ground  on which we intend to
walk, &c. it is plain that these different motions do not drag the
trunk after them.
   We shall not describe here, particularly, the different, general,
or partial motions  which the  members can effect; we shall only
speak briefly of the different modes of locomotion, that is, of those
motions by which the body is  transported from one place to an-
other, which are, walking, running, leaping, and swimming.

                         Locomotion.
   Of Walking.—The action of walking is not always executed iu
the same manner.   We may walk forwards, or  backwards, or side-
 ways, or in any intermediate direction, we may walk upon an as-
 cending or descending plane, and upon a solid or moveable body;
 walking also differs according to the extent and quickness of the
 steps, &c.  Whatever may be the mode of walking, it is necessa-
 rilv composed of a succession of steps; so that the description of
 walking only relates to the manner in which a series of steps are
 taken.   It is only necessary, therefore, to inquire into the manner
 in which the art of stepping,  with its  various modifications, are
 performed. 
160                    A SUMMARY
   Suppose a man then standing in an erect position, with both
 feet at the side of each other, and  about to walk on a horizontal
 plane, at a common pace both in extent and quickness.   It will be
 necessary  to bend one of the thighs upon  the pelvis, in order to
 raise the foot from the  ground, by a general  shortening of the
 limb.   The flexion of the thigh  throws forward  the whole  limb;
 the foot is then applied to the ground, the heel first touches, and
 afterwards the whole inferior surface of the foot.   When this mo-
 tion is  effected, the pelvis rolls  forward upon the head of the  thigh
 bone, which  is immoveable.  This rotation of the pelvis upon the
 head of the  femur, has for its object,  1st, to carry forward the
 whole of the member  which was  raised from the ground;  2nd, also
 to carry forward the side of the body corresponding to the limb
 which is moved,  while the side  corresponding  to  the  unmoved
 limb remains behind.   These two effects  are hardly  percep'ible
 when the steps are very short; they are remarkable in a common
 walk, but are much more  so when we take  long steps.  Thus far
 there has been no progression, the base of  support is only modi-
 fied; in order that the step may be completed, it is necessary that
 the member remaining behind should be moved up, either in the
 same line,  or beyond that which was first moved   For this pur-
 pose, the foot which is behind is detached from the ground, succes-
 sively  from  the  heel  towards the toe, by  a  rotatory motion, of
 which the centre  is in the articulation of  the bones of the meta-
 tarsus, with the phalanges of the toes,  so that at the end of this
 motion  the foot no longer touches the  ground at its posterior ex-
 tremity.  From this movement of the foot there is an elongation
 of the limb, the effect of which is to carry the corresponding  side
 of the trunk forward, and to  determine the rotation of the pelvis
 upon the head of the femur of the limb first moved.   This motion
 being executed, the limb becomes flexed, the  knee is thrown for-
 ward and the foot detached from  the ground, afterwards, the
 whole limb describes  the  same  motions which had been before
 executed by the limb of the opposite side.
  By this  succession of motions of the inferior extremities, #nd
of the trunk, walking is executed, during which we see that the
heads of the thigh bones, are by  turns fixed points, on which the
pelvis turns as on a pivot,  describing arcs of circles  proportioned
to the extent of the steps. 
OP  PHYSIOLOGY.
161
  In order that we may walk in a right line, it is necessary that
the  arcs of circles described  by the pelvis, and the extension of
the lower limbs, when  they are carried forwards, should be equal;
without this we shall deviate from a right line, and the body will
be directed towards the side opposite  to the limb, the motions of
which are the most extensive.  As it  is difficult to make  the two
limbs execute successively, exactly the same  extent  of  motion,
there is always a tendency to  deviate from a straight line, which
would constantly occur, it this deviation was not corrected by the
sight.   Anv  person may easily  convince  themselves ot  this, by
walking some distance with the eyes closed.
   Having  exposed the mechanism of walking forwards, it will
be no very difficult task to explain walking backwards  or  side-
ways.
  In walking backwards, one of the thighs is bent upon  the pel-
vis, at  the same time the leg is bent upon the thigh, the extension
of the thigh upon the  pelvis succeeds, and the whole of the limb
is carried backward*.  Afterwards the leg is  extended upon the
thigh, the anterior part of the  foot touches the ground, and imme-
diately afterwards the whole of its inferior surface.  At the mo-
ment that the foot  directed backwards is applied to the ground,
that which remains before is raised upon its toe, and the corres-
ponding  member  elongated; the pelvis  is thrown  backwards,
making a rotation  upon the head of  the thigh  bone,  which is di-
rected  backwards.  The limb which is before, is entirely raised
 from the ground, and carried backwards, in order to furnish a fixed
point for a new rotation  of the  pelvis, which will be executed in
 its turn by the opposite member.
   When we wish to execute a  lateral motion, we  bend slightly
one of the thighs upon the pelvis, in  order to raise  the foot from
 the ground;  then  throw the extremity into a state of abduction,
 and apply the foot to  the ground, and immediately afterwards we
 draw  up the other limb  towards the one which had been dis-
 placed; and  so on.
    When we  walk upon an ascending plane, we know that it pro-
 duces great fatigue.   In  this mode of progression,  the flexion  of
 the limb carried first  forward  must be considerable, and the ex-
 tremity remaining behind must not  only execute  the motion of
 rotation upon the  pelvis,  but it is necessary that it should raise
                              21 
162
A  SUMMARY
the whole weight of the body, in order to transport it to the mem-
ber which is before.  The anterior muscles of the thigh  carried
forward, are the principal agents in the transportation of heavy
bodies;  these muscles are also very much fatigued in the action
of passing up a ladder, or any other ascending plane.
  For opposite reasons, walking upon  a descending plane is more
fatiguing than upon a horizontal plane.  Here the posterior mus-
cles of the trunk must act with force,  to prevent  the body from
falling forward.
  All the modes of progression which  we execute rapidly, require
easy movements in all the articulations of the inferior extremities,
and an equal action of every  part of the limbs; the least imper-
fection in the articulating surfaces, or  their mode of gliding upon
each other, the least difference in  the  length, or form, of the ex-
tremities, or the  contractile  force of the  muscles, unavoidably
cause sensible alterations in the progression, and  render it more
or less difficult.

                         Of Leaping.
  If we examine with attention the action  that we are now about
to investigate, we shall perceive, that  during this motion, the body
becomes a projectile, and that  it is  governed by all the  laws
peculiar to them.
   A leap may take place either perpendicularly, anteriorly, pos-
teriorly, or laterally,  &c.  We must  in all  these cases consider
all the  circumstances which accompany it.  Every kind  of leap-
ing must  necessarily be  preceded by a  flexion of one or more of
the articulations of the trunk and inferior extremities; the sudden
extension of these flexed  articulations is the  particular  cause of
the leap.
   Suppose the leap to be made vertically,  which is the most com-
mon; the head is  bent  upon the neck, the vertebral  column is
curved  anteriorly, the pelvis is  bent upon  the thigh, the thigh
upon the  leg,  and  this again upon the foot,  and  the heel either
touches the ground lightly, or not at  all.  This state of general
flexion  is suddenly succeeded by a   universal extension of the
flexed articulations; the different parts  of the body are rapidly
elevated  with a force which surpasses its weight, in a  variable
degree.   Thus the head and chest are directed superiorly by the 
OP PHYSIOLOGY.
163
extension and retraction of the vertebral column; the trunk as a
whole is affected in the same way by the extension  of the pelvis
upon the thigh bones; the thighs being raised suddenly, act upon
the pelvis, and the legs in their turn act upon the thighs. From all
these united, there results a projectile power, by which  the body
is  raised  from the ground, and the elevation will be in the pro-
portion  of the superiority of the power to the weight; after which
it  falls to the ground, presenting the  same phenomena as all other
bodies which are operated  upon  by  the attraction of gravitation.
   In the general retraction by which the leap is produced,  the
muscular contraction does not take  place equally in every part.
It is plain that  it must  be the greatest  where the weight to be
raised is the most considerable.  This is the reason why the mus-
cles which extend  the leg upon the foot, are  those which act with
the most  energy, inasmuch as they  raise the whole weight of the
body, and give  to it an impulse which surpasses its resistance.
These muscles are admirably arranged for this purpose.   They
are extremely powerful,  and are  inserted perpendicularly to  the
lever which they are to move, the os calcis, and act by the arm of
a lever  which has considerable length.
   It is  proper to remark,  that the vertical  leap does not result
from any direct impulse,  but it is a mean  between opposite im-
pulses,  which the trunk  and inferior extremities impart at the in-
stant of the leap.  Indeed  the retraction of the head, the vertebral
column, and the pelvis, have rather a tendency to throw the trunk
posteriorly, than superiorly; the  rotation of  the thigh bones upon
the tibiae, on the contrary, carry the trunk rather anteriorly, than
superiorly;  the motion of  the leg again  has a tendency to throw
the trunk superiorly, and posteriorly.  When the result of the ex-
ertion is a vertical leap, the forces which carry the body forwards
and backwards, destroy each other,  and that which throws the
body upwards, alone takes effect.
   When the leap takes place anteriorly, the motion  of the rota-
tion of the thigh predominates over the impulses posteriorly;
when the leap is made backwards, it is the motion of extension in
the vertebral column, and of the tibia upon the foot, which pro-
duces the effect.
   The  length of the bones of the inferior extremities is advanta-
geous for extending the leap.   We pass oyer the greatest  possible 
164                    A  SUMMARY

distance in  leaping forwards, this  is attributable to the length
of the thigh  bone.  Sometimes we precede the leap by running a
short  distance forward; the impulse which the body thus acquires
is added to that  which it receives at the moment of the leap, by
which its extent is increased.
  The arms are  not entirely useless in leaping. They are brought
towards the  body at the moment when the flexion  of the differ-
ent articulations is math-, preparatory to the act of leaping.  'They
are thrown  out, on the contrary, at the moment when the body
leaves the  ground.   The resistance which  they present to the
muscles which elevate them, enables these muscles to exert some
force  in throwing the trunk upwards, and thus to concur in the
act of leaping.
   The  arms  fulfil  this  purpose  more effectually when they
present  a  firm resistance to  the contraction  of the muscles
which elevate  them.   The ancients  having made this remark
carried  in each hand  weights when they wished to  exert  them-
selves in leaping;  by properly  adjusting the arms, we  can thus
favour a horizontal leap, by giving to  the  superior part  of  the
body, an impulse backwards 01 forwards.
  We are capable of leaping with one foot, or as we commonly
express  it, of hopping.  But this mode of leaping must be neces-
sarily less extensive than when the effort is made simultaneously
by both  limbs.  Sometimes we leap with both feet in contact and
parallel  to each other;  sometimes  one foot  is carried  forwards
during the projection of the body, in whieh case one foot receives
the weight of the body at the moment it touches the ground.
  No impulse will  be communicated  to the  body,  by  the  plane
which sustains it, at the moment of leaping, unless  it be elastic,
and  combines its  reaction with the  effort  of the  muscles.   In
o-eneral, however, the ground serves no other purpose than that of
resisting the  pressure exerted  by the  feet.   Every person knows
that it is almost impossible to  leap when the ground  is soft and
yields to the pressure of the feet.
  The merit of discovering the  true theory of leaping  is  due to
the celebraled Barthez, of Montpelier.  Until his time, the most
incorrect ideas were entertained of this phenomenon.   There is
some  analogy  between the action of an elastic curve, and  that of
the body in leaping. 
OF  PHYSIOLOGY.
165
                        Of Running.
  Running is a combination of walking and leaping; or rather it
consists  of a succession of leaps, executed alternately by each
limb.   We may run with more or less  rapidity, but there is al-
ways a moment when the body is suspended, in consequence of
the impulse communicated  to  it by the limb  which remains be-
hind when we run  forwards.  This  constitutes  the  difference
between  running and walking fast, in which the  foot carried  for-
ward, touches the ground before that which is behind leaves it.
  For the same reasons  which we  have given under the  article
walking, running is least fatiguing  upon a  horizontal plane.
When  it is executed upon an ascending or descending plane, it is
always more or less laborious, and cannot be continued long.
  We  shall not even briefly describe the numerous modifications
in the progressive  motions of man, such  as  climbing, walking
with crutches, stilts, and artificial limbs; or of the different  mo-
tions either in common dancing, or upon a  tight or slack rope; or
those which are executed by tumblers, fencers and  riders, &c. &c.
Considerations of this kind are important, but they can only com-
pose a  part of a complete treatise upon animal mechanics; a work
which still remains to be executed, notwithstanding what has been
done by  Borelli and Bartliez on this subject.  Wre shall only say
a few words of swimming.

                       Of Swimming.
  The body of  man  is specifically heavier  than  water, of conse-
quence, when left in  the midst of a  considerable mass  of  this
fluid, he  will  sink  to the bottom;  this will take  place  with so
much the more  facility as the surface which strikes the  water is of
small extent.  If, for example, the body is placed vertically, the
feet below and  the head above, it will  sink much  more  rapidly
than if the body  was placed  horizontally on  the  surface of the
fluid.   Some  individuals, however,  possess the faculty of render-
ing themsel *es  specifically lighter than the  water, and of conse-
quence, of resting without any effort  upon its  surface.   This is
effected by filling the chest with a large quantity of air, the spe-
cific gravity of  which being much less than the  water, counter- 
166
A  SUMMARY
balances the tendency which there is  in the body to fall to the
bottom.
  It is not, however, by this practice, that swimmers are enabled
to move along the surface of the water, but by the motions which
they execute with  their limbs.   The  object of the motions exe-
cuted by the swimmer, is to sustain the body on the surface of the
water, or to direct its progression.  Whatever may be the inten-
tion of the swimmer, he must act upon the water in such a  man-
ner, that it shall present a sufficient resistance to support his body.
According to this view-, he acts  upon the water  by pressing sud-
denly upon it, before it has  time  to escape, acting rapidly upon a
great number  of points  by the action  of his hands and fct, the
resistance being in proportion  to the  mass of water  displaced.
The motions of  the inferior extremities in the common manner of
swimming are very analogous to those which they execute in leaping.
There are various rootles of swimming, but in all  it is necessary
to strike or press the water  rapidly before it can be displaced.
  It is impossible for a man to Ily; bis specific gravity when com-
pared  with  the atmosphere,  and  the  force exerted oy the con-
traction of his muscles are infinitely too  weak.  All the attempts
heretofore made with this intention, oy machines formed in muta-
tion of the wings of birds,  have been equally unsuccessful.

      Of the Attitudes and Motions  in  Different  Ages.
  From the embryo state to the eighteenth or  twentieth year, the
bones are continually changing their form, volume, 6cc.  Of course
during all the time that the bones are altering their form, the atti-
tudes and motions must exhibit changes analogous to those which
take place in  the skeleton.   We have already seen that the mus-
cles, and  the  muscular contraction are very much  modified  by
age; these circumstances have all an influence upon the  motions.
Ordinarily, by  the twentieth, to the twenty-second year, the  in-
crease of the  long bones is terminated, but they  continue  to  in-
crease in thickness until the adult age is completed, after which
all increase ceases, and the changes which then take place in the
bones, even to the  most advanced old  age, only relate  to the nu-
trition of these organs and  their chemical composition.
   Attitudes of the Fietus.—'The  situation of the  fcetus  in  utero
depends on circumstances  but imperfectly understood.   For the 
OF  PHYSIOLOGY.
167
most part, its head is directed below, this arises probably from its
weight, but why the  occiput corresponds almost always to that
part of the pelvis which is above the acetabulum; or why it some-
times  happens that the breech  is found below, we are entirely
ignorant.
  The thighs  in  the foetus are bent upon  the abdomen  and the
legs upon the thighs, the arms are crossed on the anterior part of
the trunk, and  the head  inclined  upon  the breast  so that it
occupies the  least possible space.   This does not depend upon
muscular contraction, it is the effect of  the  tendency in  the
muscles to relax  themselves:  at  a more advanced  a<;e, we often,
take this position, when we wish to  put all the muscles in a state
of repose.
   At the end of  four months the child  begins to execute  partial
motions, and  perhaps  some slight  motions  which  displace  the
body  wholly.  These  motions are irregular, arising  at various
periods, and  continue until  the end  of pregnancy, and are  fre-
quently exerted  by the inferior extremities, as can be distinguished
at those points  where they  are felt.   WTe cannot suppose that
they depend  upon the will, no  intelligence at  this time existing;
this  is also  evident from the fact  that acephalous infants, that
is those which have no  brain, exhibit  these motions the same as
the most perfectly formed children.
   The new born infant is incapable of assuming any  particular
 position, but  passively  preserves that  which is  given  to it;  we
 however, perceive that lying upon its  back is the most agreeable;
 and  is no doubt most favourable to the feeble state of its muscu-
 lar system.   The extremities  move with facility: but  its  physi-
 ognomy is without expression.  At the end  of two or three months
 it changes its position of its own accord, when  it wishes to be left
 more free.   It lays on its  side or face, turns its head, and  the
 motions of its limbs become more various and powerful. It seizes
 objects with more  strength when  they are  presented  to  it, and
 carries them  to its mouth.  When  it sucks,  it compresses with
 force the breast  of  its nurse, &c. but it remains long incapable of
 supporting itself unpon its feet, or even of sitting. The following
 are the reasons of this; the head  being proportionally  large and
 heavy, and  not supported  by any adequate  muscular  effort, falls
 forward; the  weight  of the viscera of the  chest, and  especially 
163
A  SUMMARY
of the belly, is proportionally great;  the vertebral  column  pre-
sents but one curve, the convexity of  which is behind.   The pos-
terior muscles of the trunk are too weak to resist the disposition
in the vertebral column to fall forwards; besides the spinous pro-
cesses not being developed, the arms of the lever  by which they
act are very short, a circumstance  most  unfavourable to  their
action.  The pelvis is very small, and being very  much inclined
forwards, does not  support the weight of  the abdominal viscera.
The inferior extremities  are but little developed, and are too
weak to sustain the weight of the abdominal viscera; their muscles
are also too weak to balance for a moment the  trunk  while ad-
vancing forwards: every kind of progression is therefore impossi-
ble.
   Soon, however, the'infant, by using both its superior and infe-
rior extremities  at the same time, is able  to transport itself over
short spaces.  From this  circumstance, the extravagant idea has
been advanced, that man is naturally a quadruped, and that stand-
ing upon two feet is the result of living in  a state of society.   If
there were any foundation for this idea, these organs in the adult
would resemble those of the infant, which, as we have before seen,
is not the case.
   Towards the  end of the first year, or at the commencement  of
the second, in consequence of the developement  of the bones,
muscles, &c. and of the alteration in the proportional volume of the
head  and abdominal viscera, the infant becomes able to stand, but
is still unable to walk.  At last, however, he walks alone, though
his gait is tottering and uncertain, the body losing its balance by
the  slightest force.  Walking is the first  kind  of locomotion
which he is able to exert;  it is generally a long time before he is
able to run, or to make even inconsiderable leaps; but as soon  as
the different progressive motions  become   more  firm and steady,
he is in continual motion; he acquires agility, and address; and  he
acquires a taste for the various sports of  children, which almost
always, especially in  boys, serve to exercise the organs of loco-
motion and intelligence.
   In a physiological point of view, the sports of children are well
worthy of notice.   When they are examined with attention, they
will  be found to mimic the actions of manhood.   Wre may also
remark the same feature in the sports of the young in other ani- 
OF  PHYSIOLOGY.                  169
mals, which are generally imitations of those actions  which their
instinct will afterwards impel thern to repeat.
  In the sports of infants, we must not confound those which are
purely instinctive, with those  which are dependent on imitation.
  Fr;>m youth until the adult age, and even beyond it, all the phe-
nomena* which relate to the attitudes and movements of the body are
in perfection; but with the approach of old age, they undergo a re-
markable alteration, which arises fiom a loss of power in the mus-
cular contraction.  The action of the muscles, at this period, is im-
perfect and tremulous, which is very apparent in the attitudes and
motions.  The old  man, whether  walking or standing, is bent for-
ward; the  pelvis is bent upon the thighs, these upon the legs,
and  the legs inclined  forward upon the feet.  This  state of half
flexion tends to weaken still more the power of  the muscles,
which have not  sufficient energy  to  preserve the erect posture of
the body.  The old man endeavours to  make up in  some degree
for these defects, by  means of a  cane, which enlarges  the base of
support, and transmits directly  to the  ground, the  weight of the
superior parts of the body.  In very advanced old age, the motions
become extremely difficult, and  sometimes entirely lost.

      Relation of Sensations to the Attitudes and Motions.
   The sensations and motions have a reciprocal and manifest in-
fluence  upon each other.  Vision contributes to the fixedness of
the  greater number of the attitudes of our body: by it we judge of
our comparative position with  surrounding objects.  V\ hen we
 are deprived of this means  of judging of our equilibrium, as when
 we  are on the top of a high edifice, or  upon other elevated  places,
 where we  are only surrounded by the air, the  position of the body
 becomes uncertain, and sometimes we  are totally unable to pre-
 serve it.  The utility of vision  is still more  apparent when  the
 base of support is very narrow. A rope dancer cannot preserve the
 erect posture, unless his sight  is  constantly occupied with the
 position which he wishes to  preserve, so  that the  perpendicular
 which falls through  the centre  of gravity, may pass directly to
 the base of  support.   W hatever may be the attitude which we
 assume, it is very  uncertain, unless we employ vision; this is suf-
 ficiently evident in the posture and attitudes of blind person*.
                             on 
170
A  SUMMARY
  If sight be of great assistance in  the  different attitudes, with
much more reason must  it be useful in the various partial and
locomotions.   Indeed, distinct  vision favours  our motions;  it is
that  which gives to them their  requisite precision and  rapidity;
in almost every instance it directs  them.  If  we bandage the
eyes of an active man, he instantly loses all his agility, his gait is
timid and tottering, especially it he be in a place with which he
is not familiar.   'The absence of vision induces  an indisposition to
motion; the use of this sense, on  the  other hand, excites our ac-
tivity; every one must be conscious of an instinctive  desire of
touching those objects which he sees  for the first time.
  A consideration of the relations between vision and  motions,
leads us to observe; that those motions which are destined to ex-
press our intellectual and instinctive operations,  which are in-
cluded under the generic names of gestures, may be divided into
those which  arise from  organization, and, of consequence, must
exist in man, in whatever condition he is found, and those which
arise from the social state, and become improved with  it.
  The first  are destined  to  express  our most simple  wants,
and  most vivid internal sensations, as joy, grief, and  fear, &c.
Thus, in the expressions of the  animal  passions, gestures are to
the other motions, what  the cry is  to  the  voice.  We observe
them in those persons who are blind from their birth, in the ideot,
and  the  savage, as  well as man in a civilized state, enjoying every
physical and moral advantage.
   The second kind of gestures can only exist in a state of so-
ciety, require  vision and intelligence,  and  are  not  observed
in those who are blind from their birth, or in ideots, savages, or
in those individuals who have lived in an insulated state.  They
may be called acquired or social gestures, from their analogy with
the  acquired voice.  It  is extremely  possible  that, if  we could
restore sight to a person who had been blind from birth, we should
enable him, at the same time, to acquire those  particular gestures
of which we are now speaking.
   It may be said, the gestures  of a person born blind are like
 the  voice of a person  born deaf.  These two phenomena, under
these two different circumstances, are made to supply each other's
place.   The deaf and  dumb make a continual  use  of vestures,
and carry this mode of  communicating  their thoughts  to a won- 
OF  PHYSIOLOGY.
171
derful degree of perfection.   The voice, on the other hand, is the
only means of expressing their thoughts, which are employed  by
the blind; from this arises their fondness for music, and conversa-
tion, and the peculiar accent which they give to their voice.
   Hearing has  some  influence upon the motions.  This sense.
often concurs with vision in directing, and particularly in measur-
ing them; thus causing them to return, after equal intervals, and
producing a certain  number in a given  time;  as we observe in
dancing and  marching.  It  has been  long remarked  that motions
executed by the sound of music, were less fatiguing than without it.
This arises from the regularity with which the muscles contract
and relax alternately, the period of repose being equal  to that of
action;  it may also be  remarked, that music excites  us to motion.
   The  relations of smelling and  tasting with the attitudes,  are
too unimportant to attract much attention.   With respect  to
touch, it is so intimately connected  with  muscular contraction,
that, without  it, this sensation  cannot take place, and it is easy
to  see that  it is intimately connected with all  the phenomena
which depend upon  muscular contraction.
   The  internal  sensations have no less influence upon the differ-
ent attitudes  and motions of the body, than the external.   Who
cannot distinguish, by his gait, and gravity, a man suffering pain or
any other vivid  sensation?  We  can even determine, with  con-
siderable certainty, the particular seat of  the painful affection, by
the arrangement of the body, or the kind of gestures which  the
patient employs.  In a violent cholic, e. g. the chest  is thrown for-
ward upon the pelvis, and  the hands pressed upon the belly; a
violent pain  in  the side naturally induces us to lay on the side
affected;  and  a stone in the  bladder compels the patient frequently
to assume a particular attitude.
    We  thus see the influence of the sensations upon the attitudes
and motions,  and these again react, by influencing the sensations.
The different  attitudes are  favourable, or unfavourable, to the
developement of the external  sensations.   There are  particular
 motions,  peculiar to each sensation,  which  favour its action,  be-
 sides, nearly  all the senses  have particular muscles, which favour
their action, and which  constitute an essential part of the appara-
 tus, a6 we observe in the eve and ear. 
17S
A  SUMMARY
      Relations of the Attitudes and Motions to the Will.
  The attitudes and motions  which we have described, have the
epithet voluntary, applied to them,  because they are said to be
under the immediate influence of the will.  This assertion is true
to a certain extent, but in some respects it is not; we shall, there-
fore, further investigate this point.
  In  consequence of the determination of the will, a motion is
produced, and  there can be no doubt that the  will causes  the de-
velopement of it.  But all the phenomena which take place in the
production of this motion, are not under the  control of the will.
I can move my hand or arm, but I am unable to contract singly,
or together, the muscles of this part, if I have not an idea of the
motion to be produced.   This is equally true of all those muscles
which we consider entirely submissive to the  will.   If we should
undertake to contract the obturator  externus, or any other muscle
which does not produce of itself any determinate motion, we should
find that  this would  be impossible.
  We may then assert, that the cause determining the motion, is
the will;  but that the production of the muscular contraction ne-
cessary to execute this motion, is not dependent upon that cere-
bral action called the w II, but is purely instinctive.
  From these  considerations  it may be inferred, that the  will,
and the action of the brain, which produces directly the contrac-
tion of the muscles, are  two distinct phenomena.   But the direct
experiments of  modern  physiologists, particularly  of Legallois,
have  clearly established  the truth of this. These experiments have
demonstrated,  that the will has its seat in the cerebrum and  cere-
bellum, but the direction of these motions seems  to  reside in  the
spinal marrow.  If we separate the spinal marrow from the rest of
the brain by an incision  near  the occiput, we prevent  the will from
determining and  directing these  motions, though  they are never-
theless executed. As  soon,  however,  as the separation takes
place, they become irregular  in  extent, rapidity, duration, and
direction.
  If the action of the brain which produces muscular contraction
be a phenomenon distinct from the will,  we may easily conceive
why, in certain cases, the motions are not produced, although the
will  commands them, and why,  under  different circumstances, 
OP PHYSIOLOGY.
173
very extensive and powerful motions take place without any par-
ticipation of the will, as we frequently see in di>cises.  For ,he
same reason we may conceive, why it  is very difficult, and often
impossible, for us to assume a new attitude, or to execute a motion
for the first time,  why  the  arts of dancing, fencing, &c. which
depend upon the rapidity and precision of our  motions, are only
acquired by long exercise.  VV hy,  in  a  word, it  frequently hap-
pens, that we execute certain motions  more perfectly, when our
mind is not particularly directed to it, than when our whole at-
tention is concentrated upon it.*

Relations  of the  Attitudes and  Motions to Instinct and  the
                          Passions.
   We have seen  that a great number of what  are  called  the
voluntary  motions  and  attitudes,  are  under  the dominion  of
instinct.   There are a great  number  of attitudes and  motions,
both  partial and general, which essentially depend upon it.
   AH the instinctive sentiments, which  essentially depend upon
organization, such as sadness, fear, joy, hunger, thirst, when car-
ried to a certain degree, induce attitudes and motions which are
peculiar to them, and  indicate their existence.  It is the  same in
the natural passions, and all the instinctive phenomena, which the
social state developes.
   Most  of the passions impel us to move, and increase very much
the intensity of muscular contraction, as we observe in excessive
joy, and anger, and,  in some instances, in fear.  Others of  the pas-
sions  stupify us, and render all kinds of  motion impracticable,
such as great chagrin, and certain sorts of terror; often extreme
joy produces the same effect.  This is the reason why the panto-
mimic art is exercised with so much  success, in exhibiting the
violent passions.

           Relations  of the Motions to the Voice.
   These are intimate, inasmuch as both of the phenomena are the
immediate  effect  of muscular  contraction, with  this  difference,
that in the voice we hear the effect, and see it in the motions.

   * This doctrine has been confirmed by the experiments of Dr.  Wilson Phil-
lip.— Philos. Tvuns. 1815 
174
OF PHYSIOLOGY.
  There  are  eertain  motions  which  essentially  depend upon
organization; they in this respect resemble  a cry.  There are
modes of voice which are  acquired in  social  life, a great number
of motions  are acquired  in  the same  manner.  The voice and
motions unite in the production  of  speech;  these two  are our
principal and almost only means  of expression.  They aid each
other,  and  sometimes  supply each other's place.  A man  who
finds difficulty in expressing  himself, uses  much gesticulation,
but the reverse is generally the case with those whose elocution
is easy.  In the expression of  the more powerful  passions, they
are  united.  It is rare  that in expressing strong  feeling, we do
not unite gesture to speech.
  It has been remarked, that  the modifications which the motions
and  voice undergo by age, are very analogous; we shall find the
same result, if we study the manner in  which  they are modified by
age,  sex, temperament and habit.
  We shall finish with these considerations, the description of
the functions of relation.  These functions possess the common
character of being suspended, or of remaining, during certain in-
tervals, in a state of repose, or sleep.   It would seem, therefore,
proper, that the history of sleep  should immediately follow the
description  of the functions of relation.  But as  the  nutritive
and  generative functions are both influenced  by sleep, we prefer
entering  upon the examination of them first,  which will be done
in the  next  volume.*

  * This is the end of the first volume, which was published in 1816; the second
did not  appear until a year afterwards.  As this division of the work, has no
reference to the  arrangement of its matter, 1  have  thought it sufficient simply
to announce the hct.—Trans. 
OP THE
FUNCTIONS OF NUTRITION.
    J. he common end  to which  the nutritive functions tend, is
the nourishment  of  the  body, by which is meant that  peculiar
internal  motion, by  which all the parts  of animal  bodies  are
decomposed and  recomposed simultaneously.
   These functions are six in number, viz. 1st. Digestion. 2d. Ab-
sorption, and  the course of  the  chyle. 3d. The  course of the
lymph.  4th. The course of the venous  blood.  5th. Respiration.
6th.  The course of the arterial blood.
   After having given a description of these functions, the relation
which they have to each other, and  to those of the functions of
relation,  we shall then examine  the different  secretions, not as
functions, but  as  the  actions of insulated  organs, and  finish by
giving a history of the function of nutrition itself.


                     OF DIGESTION.

   The object of digestion is the  formation of  chyle, a substance
which is destined to repair the loss which the animal economy is
constantly  suffering.  The digestive organs contribute also in
several other ways to  nutrition.

                  Of Aliments and Drinks.
   We give the general appellation of aliment to every substance
which  is capable of nourishing the bedy, when it is submitted to
the action of the digestive organs.   According to this definition,
all aliments are necessarily composed either of animal or vege-
table substances;  for it is only those bodies which  have  enjoyed
life, which are capable  of serving the purposes of nutrition in 
176                     A SUMMARY
 animals.   But this definition of aliment is perhaps too restricted,
 for  it may be fairly  doubted, whether, in  the strictest ser.se, the
'name of aliment should not be applied to those substances, which,
 thou°h  they may not  be said to  nourish the  body, yet concur
 pow ."-fully  in nutrition, inasmuch as they  enter into the  compo-
 sition  of the animal  organs  and  fluids.  Such, for example, as
 m'iriat of soda,  oxyd ot iron, silex, and especially of water, which
 is found in so large a quantity in the bodies of animals, and  is so
 necessary to them.   It will, therefore, be more proper to consider
 every  substance, an  aliment which may assist in  nutrition; pre-
 serving, however, the  important distinction  between  those  sub-
 stances  which are capable of performing tlfts  alone, and  those y*
 which act in concert with them.*
   Of Aliments.—Aliments differ from each other, with respect to
 the  principles  which  predominate in their  composition.   They
 iray be divided  into nine classes,  viz.  1st. Farinaceous aliments,
 wheat,  barley, oats,  rice, rye, indian  corn, potatoes, sago, salop,
 peas, beans, and lentils.   2d.  Mucilaginous  aliments—carrots,
 turnips, asparagus,  cabbage, lettuce,  mushrooms,  melons,  &c.
 3d.  Sweet  aliments—different  kinds of sugar, figs, dried dates
 and  raisins, apricots, &c.  4th. Acid aliments—oranges, gooseber-
 ries, cherries, peaches, raspberries, mulberries, pears, apples,  sor-
 rel,  &c.   5th.  Oily  and  fatty  aliments—cocoa,  olives,  sweet
 almonds, filberts,  walnuts,  animal  tat,  oils   and   butter,  Lie.
 6th.  Cheesy aliments—different kinds  of  milk,  cheese, &c.
 7th. Gelatinous aliments—the  tendons,  aponeuroses,  chorion,
 cellular tissue, and  young  animals, &c.   8th.  Albuminous ali-
 ments—the brain,  nerves, eggs, &c.  9th. Fibrinous aliments—the
 flesh and blood of different animals.

   * It was said by Hipprocates, that there are many kind of aliments, but that
 there is at the same time but one alirnent.  This proposition I have never been
 able clearly to understand.  Did he mean that in every alimentary substance there
 is but one part which is nutritious?  If so, this  part w 11 vary in'each aliment. Or
 did  he mean  that all substances when converted into chyle  are essentially the
 Bame?  This is not  the case, for the qualities of the chyle  vary according tc the
 nature of the food.  Did he mean that the chyle served to renev/ in  the biood a
 particular substance, which  alone  nourishes  the bod), am! which  is the "Qtwd
 7iutrit" of the ancients?  But does any such substance exist? Can we believe that
 there is in all aliments, a particular principle, even  where  the same and essenti-
 ally nutritive?  Nothing is further from being proved. 
OF  PHYSIOLOGY.
177
   We may add to this list a great number of substances  which
are employed as medicines; but which no doubt  have a nutritive
effect, or at least some of their immediate principles, such are
manna, tamarinds, vegetable extracts, sugars, animal and vegeta-
ble decoctions, commonly called ptisans, &c.
   Among the aliments, few are used in the state in which they
naturally exist.  They generally require to be  prepared  before
being  submitted to the action of  the  digestive  organs.  The
mode  of preparation varies infinitely, according to the kmd of
aliments, people, climates, customs, and degree of civilization.
   In  the hands  of  a skilful cook, alimentary substances almost
change entirely  their  nature, form,  consistence, odour,  taste,
colour, and  chemical composition,  &c.   So entirely is the change
effected, that  it is often impossible to recognize the substance
which constitutes the principal ingredient in some  dishes.  The pro-
per object of the art of cookery, is to render the aliments agreeable
to the senses, and to facilitate digestion; but it rarely stops here.
Frequently, among people in an advanced stage of civilization, the
object, as well as the ambition of the artist, is to excite an im-
paired and fastidious appetite, or  to satisfy an eccentric and
capricious taste;  so  far from  being a  useful, it  then becomes a
most pernicious art,  and leads to an  infinite variety of distressing
diseases, or even to  premature death.
   Of Drinks.—By  the term drink, we  understand  some  fluid,
which, when it is introduced into the digestive organs, slakes the
thirst, and  repairs the  loss which  we  habitually sustain, of the
fluid part of our humours.   We must, therefore, consider drinks
as true aliments.
   Drinks are divided according to  their chemical  composition;
1st, water of different kinds, as  spring, well, and  river water;
2nd, syrups, and vegetable and animal infusions, as lemon and
gooseberry syrups, whey, tea, and  coffee, &c.   3d. fermented
liquor?, wine of various kinds, beer, cider and perry; 4th, alcoho-
lic liquors, brandy, alcohol, ether,  rum, &c.

                   Apparatus of Digestion.
   If we judge of the importance  of a  function, from the number
and variety of the organs which concur to effect it, digestion will 
17*
A  SUMMARY
occupy the first rank.  No other function  in the animal economy
presents an apparatus so complicated.
  There exists an evident relation between the  food  of the ani-
mal and  the digestive apparatus.   If the aliments differ essential-
ly in their nature from the elements  which compose  the animal;
if, for example, the  food is herbaceous, the apparatus will be of
large dimensions and  complicated.  If, on  the other hand, the
animal is nourished by flesh, its  digestive  organs will be less nu«
merous and  more simple, as we see. in carnivorous animals.   The
food of man, being  both  animal and vegetable, he  preserves a
medium  between the complicated  apparatus  of herbivorous, and
the  simple apparatus of carnivorous  animals, and  is, therefore,
omnivorous.  It seems hardly necessary to remark, that there are
a great number of substances which are  used as aliments  by ani-
mals, which are of no utility to man, in this respect
  We may describe the digestive apparatus as  a long canal, con-
voluted upon itself, large in some places and small in  others,sus-
ceptible of being enlarged and  diminished, and into which are
poured a great  quantity  of fluids, by  means  of  certain ducts.
Anatomists divide the  digestive  organs  into several portions; 1st,
the mouth; 2nd, the pharynx; 3d, the oesophagus; 4th, the stomach;
5th, the small intestines; 6th, the large  intestines; 7th, the anus.

             Structure of the Digestive Canal.
  The walls of this canal, are formed by two membranous laminae,
through its whole extent.   The internal lamina, which is* destin-
ed to be in contact with the aliments, consists of a mucous  mem-
brane, the aspect and structure  of which vary in different por-
tions of the canal, it is different in the  pharynx from the mouth,
in the  stomach from  the  oesophagus, &c.  At the lips and anus
this membrane is lost in the skin.
  The second lamina, which constitutes the wall of the canal, is
composed of two strata of fibres; the one of which is longitudinal,
and the other circular.  The arrangement, thickness, and nature
of the fibres, which enter into the composition of these strata, are
different, according as they are  observed  in the mouth, oesophagus,
or large intestines, &c.
  A great number of blood-vessels  are sent to, and arise  from
this canal, but the abdominal portion receives  incomparably the 
OF PHYSIOLOOY.                   179
largest part.   The superior part only receives a sufficiency to an-
swer the purposes  of nutrition, and the inconsiderable secretion
of which it is the seat; but the number and volume of the vessels
which appertain to  the  abdominal portion, indicate  that it is in-
tended as the agent of a considerable secretion.   The chyliferous
vessels take  their rise, exclusively, from that  portion of the canal
called the  small  intestines.
  The nerves are distributed  over the canal  in  a reversed order
from the blood-vessels.   That is, the cervical and pectoral parts
receive more than the abdominal portion, with the  exception of
the stomach, where the nerves of the eighth pair terminate. The
remainder of the canal does not receive, scarcely, a branch of the
cerebral  nerves.  The only nerves which  can be distinguished,
proceed from the sub-diaphragmatic ganglions of the great sympa-
thetic. »We shall see, by and  by, the  relation which  exists be-
tween the mode of  distribution of the nerves, and the functions
of the superior and inferior portions of the digestive canal.
  The  bodies which  pour out fluids into the  digestive canal
are, 1st,  the digestive mucous  membrane itself;  2nd,  the in-
sulated follicles, which are scattered in great  number through
the whole extent of this membrane; 3d, agglomerated follicles,
which are met with at the entrance of the oesophagus, between
the  pillars  of the veil  of the  palate, and, sometimes, at the
junction  of the oesophagus and stomach; 4th, the mucous glands,
which exist  in considerable numbers in the walls of the cheeks,
the arch  of  the  palate, near  the  oesophagus; 5th,  the parotid,
submaxillary, and  sublingual glands, which secrete the saliva
that is  poured into  the mouth;  the  liver and pancreas, the first
of which pours out the bile, and the second the pancreatic juice,
by distinct ducts, into  the superior part of the small intestines,
which is called the duodenum.
   All the digestive organs contained in the abdominal cavity, are
immediately covered, in  a manner more  or  less complete, by  a
serous membrane,  called the  peritoneum.  This membrane, from
the manner in which it is arranged, and  its physical and vital
properties,  serves  important  purposes  in the act  of digestion,
either by preserving in the organs their respective relations, or by
favouring their variations of  volume, and preventing any friction
Upon each other, or the neighbouring parte. 
180
A  SUMMARY
  We shall give the necessary details concerning the apparatus
of digestion, after we have explained  their functions.  "Vejshall
confine ourseives, at present, to  some remarks on  the organs of
digestion, considered during life, but at a time when they are not
executing, their peculiar functions.

Remarks on the Digestive Organs of Man and living Animals.
  The surface of the mucous membrane of the digestive  canal, is
always lubricated  by a viscous  substance which  is poured out,
more or less abundantly.   It is observed in  the largest  quantity
in those  parts  where  no follicles  exist; a circumstance  which
seems to shew, that these are not the only secretory organs.  One
part  of the substance, which is generally called mucus, continu-
ally evaporates, so that there constantly exists a certain  quantity
of vapour, in  each part  of  the digestive canal.   The  chemical
nature of this substance is not  well known.  It is transparent,
with  a  slight  greyish  tint;  it  adheres to the membrane  which
forms itrits taste is  salt, and  the application of certain tests
shews that it is acid.   Its formation continues for some time after
death takes place.  That which is formed in  the mouth,  pharynx,
and oesophagus, is propelled into the stomach, and mixed  with the
secretions of the mucous glands and saliva, by the action of deglu-
tition, which frequently takes place.   It would seem from  this,
that the stomach, when there are  no aliments in it, contains  a
considerable quantity of  this mixture of mucus, follicular secre-
tion, and saliva.   This is a  point, however, which is not confirm-
ed  by the  experience  of  most persons.   Nevertheless, it  is  evi-
dent that this exists in some persons, their stomach being  known
in the morning to  contain  several ounces of this mixture.  In
some cases, it is  frothy, very vibcid, and slightly clouded, holding
suspended floculi of mucus.  Its taste is plainly acid,  but not dis-
agreeable, it is .sensibly perceived by the throat, and acts upon the
teeth, so as to diminish the  polish upon their surface, and  to pre-
vent their gliding easily  upon  each other.  This fluid,  when ap-
plied to tiie tincture .tnd  paper of litmus, causes them  to  turn red.
   Under different circumstances, in the same individual, with the
same appearances as relates to  colour, transparency,  and  consis-
tence, this fluid,  when  taken from the stomach, has  neither the
taste nor other properties of acids; sometimes it is slightly salt. 
OF  THYSIOLOHY.                 181
Neither a solution of potash, nor  sulphuric or nitric acids, pro-
duce any apparent effect upon it.*
  (rue of my former pupils, Dr. Pinel, who possessed the faculty
of vomiting at  will, informed me, that  he frequently evacuated
from  the stomach, in  the morning,  three ounces  of this fluid.
Some  of this liquid was examined by M. Thenard, who found it
composed of  a large quantity of  water, some mucus, and some
salts, the base of which were soda and lime;  there was no acidi-
ty perceptible either by the tongue or reagents.  The same phy-
sician, recently, sent me about two ounces of a fluid obtained in
this way.  M. Chevreul analysed it and  found a large portion of
water, a considerable quantity of mucus, the lactic acid of Berze-
lius, and a small  quantity of animal matter, soluble in water, but
insoluble in alcohol, some  hydro-chlorate of ammonia, hydro-
chlorate of potash, and  hydro-chlorate of  soda.
   With respect  to  the quantity of this fluid, M. Pinel observes,
that if he  had swallowed a mouthful of any aliment, he could ob-
tain it in  any quantity, in  a  short  time, even  to half  a pound.
M. Pinel thinks that the taste  of  this  fluid  varies, according to
the sort of aliment he had used the night  before.
   When we examine  the  bodies  of persons who die suddenly,
 and whose stomachs had not recently  received either  food or
 drink, this organ  is only found to contain  a very small quan-
 tity of acid mucus  adhering to its walls, and of which, that part
 which is found in the pyloric  portion  of the viscus, appears re-
 duced into chyme.  It is, then, extremely probable that the fluid
 which passes into the sto.nach is digested, as an alimentary sub-
 stance, which is the reason of its  not accumulating.
    In  animals, the organization of  which  resembles man, as dogs
 and cats, we do  not find any fluid in the stomach, after some days
 of absolute abstinence;  we only find a little viscid mucus adhere-
 ing to its  walls, at the splenic extremity, this substance has a
 very great analogy, in  its physical and chemical properties, with
 what we find in the stomach of man.   But if we cause animals
 to swallow  a body, which is not  susceptible of being digested, a
 pebble for example, there  is formed, at  the end of some time,  in
 the cavity of the stomach, a mucus, acid  fluid, of a greyish colour
* Vide Experiments on Digestion in Man, by S. de Montegre, 1804. 
im
A  SUMMARY
and sensibly salt, which resembles, in its' composition, the mucu«
we often meet with in man, the analysis of which, by  M. Chev-
reul, has already been given.
  The fluid which is composed  of the mucous secretions of the
mouth, pharynx, oesophagus and stomach, with the fluid secreted
by the follicles of these parts, and the saliva, has received from
physiologists the  name of gastric juice, to which they have attri-
buted peculiar properties.
  In  the  small intestines, there is  formed a  large quantity of
mucous substance, which remains constantly attached to their wall.
This differs little, in its sensible qualities, from that which we have
spoken of above, it is  viscid, ropy, and somewhat salt and acid in
its taste; it is very rapidly renewed.   If we lay bare the mucous
membrane of this  intestine in a dog, and remove from it the mucus
which  will be found there, absorbing it  with a sponge, a minute
will  scarcely  pass before it is replaced.  We may repeat  this
experiment as frequently as we choose, until the intestine becomes
inflamed, in consequence of the  contact of air  and other foreign
bodies.   When the mucus penetrates into the cavity of the small
intestines, it is in the form of a pulpy, greyish,  opaque matter,
which has all the  peculiar appearance of chyme.
  The bile and  the  fluid  secreted  by the pancreas, are poured
out into that portion of the canal which is called the duodenum.
I believe that  no one  has ever observed in man, during life, the
manner in  which the  bile and pancreatic  juice are  poured  out.
In animals, dogs for example,  this  fluid  oozes out at  intervals,
that is, about twice ij? a minute,  we see spring from the orifice of
the biliary duct, a drop of bile, which  spreads itself  uniformly
over the surrounding  parts, which are already impregnated by it.
Thus there is always  found in the small intestines,  a certain quan-
tity of bile.  The oozing of the fluid formed  by  the   pancreas,
takes place in a similar manner, but much more  slowly.  A quarter
of an hour often elapses, before  we see a drop of  this fluid  pass
out from the  orifice of the duct, which  pours  it into  the  intes-
tine.  I have,  however, in  some  instances,  observed it  ooze out
with much  more rapidity.
  The different fluids which are deposited in the  small intes-
tines, viz. the chyme which comes from  the stomach, the mucus,
the follicular  fluid,   the  bile and pancreatic  juiee, are mixed 
OF  PHYSIOLOGY.                 1*3
together, but in consequence of its properties, and perhaps of its
proportion,  the  bile predominates, and  gives to the mixture its
colour and taste.  A great part of this mixture descends towards
the large intestines.  In its passage, its consistence  is  increased,
and it becomes of a bright yellow colour, though at first of a deep
yellow, and afterwards green.  There is however, a great differ-
ence in this respect, in different individuals.
   In the large intestines, the mucous and follicular secretion, ap-
pears to be  less active, than in the small intestines.  This mixture
of fluids, after it has arrived at the large intestines, acquires  a
much greater degree of consistency, and a fetid odour, analogous
to that of other fecal matter.
   The knowledge of these  facts  enables us to conceive  how a
person, who has made  no use of  aliments, continues to evacuate
the canal,  and  how, in some  diseases, the quantity  discharged
is very great, although the patient may have been  for a long
time   deprived of every  alimentary  substance,  even   liquid.
Near the  anus, there  are  found  follicles which secrete an oily,
fluid, which has a strong and peculiar odour.   We find, almost
constantly, gas in the intestinal canal; the stomach contains very
little.   The chemical nature of this gas has not yet been examin-
ed with care, but, as the saliva which  we swallow is always im-
pregnated with atmospheric air, it is probable that it is this gas-
seous fluid more or  less  modified; I have ascertained  by experi-
ment,  that it is  partly  composed of carbonic acid.  The small in-
testines contain a very  small quantity of gas;  it is  a  mixture of
carbonic acid, azote and hydrogen.  The large intestine contains
carbonic acid, azote and hydrogen, and sometimes carbonated, and
sometimes sulphuretted, hydrogen.  I  saw ten cubic inches of
this gas in the rectum  of a criminal lately executed,  though the
large intestines did not contain  any fecal matter.
   We may ask, what is the origin of these gases, are they derived
from the external air, or secreted  by the mucous membrane of the
canal, or are they results of the chemical action of the  substances
contained in the canal?  We shall  examine these questions hereaf-
ter; in the meantime we  will remark, that we are in the habit of
swallowing much more atmospheric air than we are aware of.
   The muscular coat  of  the  canal, in relation to  the different
modes of contraction which it exerts must be noticed. The lips, the 
184
A  SUMMARY
jaws, generally the tongue, and the cheeks, move by a contraction,
perfectly analogous to that of locomotion.  The veil of the palate,
the pharynx, oesophagus, and, in some particular circumstances, the
tongue, exhibit motions which have a manifest analogy to muscular
motion, but differ from it, in being executed without the command
of the will. I  have, however, seen some persons who could move
the veil of the palate, and the superior part of the pharynx at will.
   I would  not, however, be understood to say, that the motions of
the parts, of which I have been speaking, take place without nerv-
ous influence, for experience proves the reverse of this.  If, for ex-
ample, we  divide  the nerves which  pass to the oesophagus, we
deprive this part of its contractile power.
   The muscles  of the veil of  the  palate, those  of the pharynx,
and two  thirds of the  superior part of the oesophagus, do not
act as  digestive organs, except when they  thrust forward  sub-
stances from the mouth towards the stomach." The inferior third
of the oesophagus presents a peculiar phenomenon, which  it is im-
portant to  understand.  This is  an  alternate   contraction and
relaxation, which  continually take  place.   This  begins at the
point where the superior two thirds of the canal unites with the
inferior third.   It  is prolonged, with a cprtain degree  of rapidity,
until  the oesophagus is inserted into the stomach.  Once  produced
it continues for  an indefinite time, its medium duration is about
thirty seconds. While the inferior third of the oesophagus is  thus
contracted, it is hard  and elastic as a tense cord. The relaxation
which succeeds this contraction, occurs suddenly and simultane-
ously, through the  whole extent of the contracted fibres, but, in
some  cases, it  seems  to take place from the superior towards the
inferior part.   In  a state of relaxation, the oesophagus presents a
remarkably flaccid appearance, which is  strongly contrasted  with
its state of  contraction.
   This motion of  the oesophagus depends upon the nerves of the
eighth pair.  When  we  divide these  nerves, the oesophagus no
longer contracts, but it does not remain  in the remarkable  state
of relaxation  which  we have described.    Its  fibres,  indepen-
dent  of this nervous influence, continue  to contract  themselves
with a certain  force, and  the canal  remains  in  an intermediate
state  between  contraction  and  relaxation.  The  emptiness or 
OF PHYSIOLOGY.
185
  distension of the stomach  has an influence upon the intensity of
  the contractions of the ceosphagus.*
    From the lower part of the stomach to the end of the rectum,
  the intesi trial  canal exhibits a mode of contraction which differs,
  in almost every respect, from that of the part of  the canal, which
  is above the diaphragm.  This contraction is always made slowly
  and irregularly, an interval of an hour often  takes place without
  our being able to perceive  any trace of  it; at  other times,  many
  portions of it  contract at a time.  It  appears  very little under the
  influence of the nervous system;  it will continue, for example, in
  the stomach alter we have divided the  nerves of the eighth pair;
  it becomes more active by debilitating; animals, and even by death;
  in  somes cases  it  becomes  considerably  accelerated by  it;  it
  remains even  when the intestinal canal  has  been separated  from
  the body.   The pyloric portion of the stomach, and the small  in-
  testines, are the parts of  the canal, where  this  contraction  takes
  place most frequently and  regularly.  This  motion, which results
  from the successive, or simultaneous contraction of the longitu-
  dinal  and circular fibres of the intestinal  canal, has been  desig-
  nated bv different names by authors. It has been called vermicu-
  lar, peristaltic, and organic  sensible contractility.  Whatever it
  may be, the will  does not exert  any sensible influence upon it.
  The muscles of the anus contract voluntarily.
    The super-diaphragmatic portion of  the  canal is not capable of
  undergoing any considerable  dilatation.   It  is easy to see, by its
  structure  and  mode of contraction  in its  muscular coat, that it
  will not permit  aliments to remain  in  its cavity, but that it is
.  rather destined  to  transport these substances  to  the stomach.
  The  stomach  and  large  intestines, on   the  other  hand,  evi-
  dently admit  of great  distension; the substances introduced into
  the canal, also accumulate and remain longer in them,  than  in the
  other  parts.

    * The alternate motion of the interior third of the oesophagus does not take place
  in the horse; but  in this animal, the pillars of  the  diaphragm have a particular
  action  on the cardiac extremity of this duct, which  does not take  place in those
  animals which vomit easily.  See the detail of experiments made by me  on this
  subject and the Report of the Committee of the Institute in the ''Bulletin de la
  Societe t'hilomatique, Anne. 1S15."
                                24 
186
A  SUMMARY
  The diaphragm and abdominal  muscles keep up  a continual
action upon the digestive organs, contained in the abdomen. They
exert upon these organs a continual pressure, which becomes some-
times very considerable.   We shall  see, belov, how these two
causes, singly or together, concur  in the different  acts  of diges-
tion.

                   Of Hunger  and  Thirst.
  Before digestion in man and animals can take place, it is neces-
sary, that a certain number of actions should precede,  by which the
food is seized, triturated and introduced into the stomach.  This
introduction  necessarily ceases  when  the stomach is  full, and
ought only to take place to such an extent, as will satisfy the de-
mands of  the economy; and in general it is best, that  it should not
be  done until the preceding digestion  is  terminated; there are
also other  circumstances where  it is  injurious.  It was therefore *
necessary, that man and animals should be informed of the mo-
ment when it was  proper  to receive solids or liquids into their
stomach, and of the circumstances in which it  was  improper. Na-
ture has effected this important purpose, by imparting to us many
instinctive feelings, which  inform us of  the wants of the economy,
and of the particular state  of the digestive  organs.  These feelings
vary according to their kind.  They may  be  divided into  those
which excite us to use some particular substances,  and into those
which induce us to  desire something remote  and difficult to be
obtained.   The first relate  to hunger and thirst, and the second to
satiety and disgust.

                          Of Hunger.
   The  desire of solid  aliments  is characterized  by a  particu-
lar  sensation in the region of  the  stomach, and  some  degree
of  debility.   In general,  this  sensation   is  produced  when  the
stomach has remained  empty for some time.  The  intensity dif-
fers very  much in different individuals, and even  in  the same
individual. With some, its violence is  extreme, with others, it is
scarcely perceptible; some never experience it, and only eat be-
 cause the hour of repast has arrived; many  persons feel an oppres-
 sion, more or less painful, in the epigrastic region; in others, there 
OF  PHYSIOLOGY.
187
is a gentle heat in the same region, accompanied with yawning, and
a particular noise produced, owing to the displacement of the gas
contained in the intestines, this  noise  is technically called bor-
boryisma.  When this desire is  not  satisfied, it increases  very
much, and at last becomes very painful, and a sensation of general
weakness and  fatigue is induced, which may go to the extent of
rendering locomotion difficult, and perhaps impossible.
   Authors distinguish hunger into local and general  phenomena.
This distinction, is in itself good, and  may perhaps be advanta-
geous to the student; but have not mere gratuitous  suppositions,
the existence of which are barely  possible, been described as the
local  or general phenomena of hunger? This is one of  those
points in physiology in which the deficiency of direct experiment
is most palpably felt.
   The contraction of the stomach  has  been  reckoned  among the
number of the local  phenomena  of hunger.  "The  walls  of the
viscus, it is said, become thicker; it changes its form and situation,
and is drawn a little towards the duodenum.  This cavity contains
the saliva mixed with air, mucus  and  bile which has flowed back
by the action of the duodenum. These different humours are accu-
mulated  in  the  stomach, in proportion to  the  duration  of the
fasting.   The cystic  bile does not run into the  duodenum, but
remains in the gall bladder; and  is more abundant  and black, in
proportion to the duration of the abstinence.  There is a change in
the order of the circulation of the digestive organs; the stomach re-
 ceives less blood, either in  consequence of the flexuous course of
its vessels, then greater because its coats are drawn together, or  in
 consequence of the compression of its nerves from this contraction,
the influence of which upon the circulation will be diminished.  On
the other hand, the  liver, spleen,  and epiploon, in receiving more
blood, perform the office of a diverticulum;  the liver and spleen,
because they are less  supported when the stomach  is empty, and
therefore, offer a more free access to the blood; and the epiploon, be-
 cause then its vessels are less  flexuous, &c."*  The most of these
 propositions are merely  conjectures, and are  nearly destitute of
 proof.   They have  been  already, in   fact, refuted by Bichat,
 though some of the objections of this  ingenious physiologist are
* Vide Dictionarie des Sciences, Medicates, article, digestion. 
188                    A  SUMMARY

themselves exposed to  criticism.   Not being  able  to enter into
the details of this discussion. I shall only relate the experiments
I have made myself on this  subject.
  After twenty-four, forty-eight, and even  sixty hours  of com-
plete abstinence, I have never seen  this  contraction  of  the sto-
mach, of which authors speak.  This organ has always presented
dimensions sufficiently large, especially at its splenic extremity.
Until the  expiration of the  fourth or fifth day, I have not found
the stomach to change its capacity  or to alter  even slightly its
position; even then, the effects  are  not  very remarkable,  except
the fasting has been rigorously observed.
  Bichat thinks that the pressure sustained bv the stomach, when
it is empty, is equal to  what it supports when it is distended, as
the abdominal walls contract, in proportion as the volume  of the
stomach diminishes.  There is no  difficulty in satisfying our-
selves  of the incorrectness of this opinion   If  we introduce our
two fingers into the cavity  of  the  abdomen, after  its walls have
been divided, we shall find, by  direct experiment, that the pres-*
sure upon the viscera of this cavity,  is in proportion to the  disten-
sion of the stomach.  If the stomach be  full, the fingers will be
pressed strongly, and the viscera will be forced through the open-
ing; if it be empty, the pressure  will be  slight, and the effort of
the viscera to  escape, trifling.   We must  not  confound  in this
experiment, the pressure exerted by  the abdominal muscles, when
they are relaxed, with that which is produced  when they contract
forcibly.  Also, when the stomach is empty, all the reservoirs con-
tained in the abdomen,  are  more readily  allowed  to become dis-
tended with their natural contents.  This, I believe, is the princi-
pal cause of the accumulation of the bile in  the vesicula fellis.
With  respect to the presence of the bile in the stomach, which
some persons suppose produces the sensation of hunger, I  believe
that, in certain morbid  conditions, the bile is  not introduced into
this organ, though it  may continue  to be constantly thrown out
into the small  intestines.
   The quantity of mucus existing in  the cavity of  the stomach
becomes less, as the abstinence is  prolonged.   My  experiments
on  this entirely agree with those of Dumas.   With respect to the
quantify of blood sent to the stomach, when it is empty, from the
size of its vessels, and the mode of circulation which takes place 
OP PHYSIOLOGY.
189
there, I am induced to believe, that it receives less of  this fluid
than when it is distended with food.  But instead of differing, in
this respect, from the other abdominal organs, it appears to me
to be common  to them all.
  We have  included, under the general phenomena  of  hunger, a
weakening and diminution of action in all the organs, the circula-
tion and respiration become slower, the heat of the body less, the
secretions diminish, and all the functions are performed with dif-
ficulty.  It  has been said, however, that absorption becomes more
active, but there is no conclusive evidence of this.
  Appetite, which is  the first degree of hunger, must  be  distin-
guished from the inclination we have to prefer one sort of food
to another.  Thesp sensations differ esspntiallv  from hunger,
which is an  expression of the true wants of the economv; thev are
peculiar,  in a great degree, to  civilization, habits, and  certain
idpas relative to the  properties of aliments.  Some arise from
season and climate, and then they become  as natural  as hunger
itself; such  is the  inclination we  have for a vegetable  diet  in
warm  climates, or in  the heat of summer.
  There are some circumstances which render hunger more in-
tense, and cause it to return aftpr  shorter  intervals; such as the
cold and dry air of winter, cold baths, drv fqiction of the skin, ex-
ercise on horse back, walking, fatigue of bodv, and, in eeneral, all
those causes which accelerate the action of  nutrition, with which
hunger is essentially connected.  Some substances when  intro-
duced into  the stomach excite a sensation   analogous to that  of
hunger, but which, however, should not be confounded with it.
   There  are circumstances which  diminish  the intensity of hun-
ger, and which  retard the periods  when it habitually manifests
itself, such  as the moisture or  warmth of the climate, repose of
the  body and  mind,  the gloomy passions; in a word, all those
causes which diminish the action of the other organs, and particu-
larly of nutritition.   We also know that certain substances, when
introduced  into the stomach, prevent the  action of the  organs,
and cause the sense  of hunger to  cease,  as opium and  warm
drinks, &c.
   The proximate causes of hunger have been, in  turn,  attributed
to a great variety of circumstances; as the  foresight of fhe vital
 principle, the friction of the walls of the stomach on each other, 
190
A  SUMMARY
the mechanical action of the liver upon the diaphragm, the acridi-
ty and acidity of the gastric juice, the fatigue of the contracted
fibres of the stomach, the compression of the nerves of this viscus,
&c. &c.  Hunger is  produced, like all other internal sensations,
by the action of the  nervous  system,  and it has  no other seat
than in this system itself, and  no other causes than  the general
laws of organization.  What proves the truth of this  assertion is,
that it continues often when  the stomach  is  distended  with ali-
ment, and again, it does not  occur, although the organ  has been
empty for a long time.  In a word, it is governed  by habit, so as
to cease spontaneously when the hour of repast has passed.  This
is true, not only as relates to the sensation  experienced in the
region of the stomach, but also the general  weakness which ac-
companies  it, and  which, of consequence, cannot be considered
real, at least in the first instance, when it is manifested.
  Many authors  confound hunger with the effects of a  complete
abstinence  prolonged until death is produced.  We shall not fol-
low their example, in this respect.  Hunger, considered  as an in-
stinctive phenomenon, belongs to  physiology, but considered as a
cause of disease, it pertains to  pathology.

                          Of Thirst.
   We give the name of thirst  to that sensation which induces us
to desire drink.  It differs in different individuals, and is not the
same always even in  the same  person, at different times.  In
general, it consists in a sense of dryness, constriction, and heat in
the back part of the mouth, pharynx, oesophagus, and often the
stomach itself.  After thirst has continued, even  for a short time,
these parts  become red and swelled, and the secretion of the mu-
cus ceases almost entirely; that of the follicles  becomes altered,
thick, and  tenacious; the flow  of saliva diminishes, and  its vis-
cidity sensibly increases.  These phenomena are  accompanied
with an indefinite sense  of uneasiness, and general heat, the eyes
become red, the spirits agitated, the motion of the blood acceler-
ated, the respiration short and laborious, the mouth widely  open-
ed, in order to bring the external air in contact with  the irritated
parts, to obtain a momentary relief.
   The desire of drink is increased by certain causes, such as the
heat and dryness of the  atmosphere, which cause a  great loss of 
OF PHYSIOLOGY.
191
the fluid parts of the body, it is also manifest under a great num-
ber of circumstances,  such as  having spoken long, eaten certain
aliments, or having swallowed any substance which remains in
the oesophagus, &c.  The pernicious habit of drinking frequently,
excites a sensation which strongly resembles thirst.
  There are some  persons who never perceive the sensation of
thirst, who seem to drink  merely to  imitate others, but who are
capable of living for a  long time without thinking of it, or feeling
any inconvenience from  being deprived of it.  There are  others,
in whom thirst often takes place, and becomes very imperious, so
as to induce them to drink from twenty to thirty  pounds of  fluid
in the twenty four hours.   We observe a great difference in this
respect in individuals.
   We shall not pretend to go back with some writers to the proxi-
mate cause of thirst, or  suppose that it is  the effect of the  fore-
sight of the soul,  nor  shall  we presume to appoint to  it a place,
either in the nerves of the pharynx, or in the sanguineous, or lym-
phatic vessels;  because  we hope that such considerations will not
hereafter, find a place  in scientific treatises on physiology. Thirst
is an internal sensation, an instinctive sentiment, it is  a result of
organization, and  does not admit of any explanation.  We  shall
not say  more  of  the  morbid phenomena  which accompany, and
precede death, arising from a deprivation  of drink, this entirely
belongs to morbid physiology.

             Of the particular acts of Digestion.
    Those acts which together constitute digestion, are, 1st, prehen-
 sion; 2nd,  mastication;  3rd, secretion of saliva;  4th, deglutition;
3th.  action of the stomach; 6th, action  of the small  intestines;
 Tth,  action of the large intestines;  8th,  expulsion of fecal matter.
    All these  actions  do not equally concur in the  production of
 the chyle;  the action  of the stomach and of the  small intestines
 are alone absolutely indispensable.
    The digestion  of solid  aliments requires these eight digestive
 actions; that of drink is much more simple, it only requires  pre-
 hension, deglution, and  the action of the stomach  and small intes-
 tines.  It  is very rare that fluids  pass to the large  intestines.
 We shall first consider the digestion of aliments, and  afterwards
 that of drinks. 
192
A  SUMMARY
             Of the  Prehension  of solid Aliments.
   The organs of prehension are the superior extremities, and the
 mouth.   We have already spoken of the superior extremities, and
 we now propose to say a few words of the different  parts which
 constitute the mouth.
   Anatomically speaking,  the mouth is that oval cavity formed
 above,  by the  palate and superior  maxillary bone, below, by the
 tongue and inferior maxilla, laterally, by the cheeks, posteriorly
 by the veil of the palate and  pharynx, and anteriorly by the lips.
 The dimensions of the mouth, vary in different individuals, and is
 eapable of being enlarged  in every direction; from above below,
 by the lowering of the tongue, and separation of the jaws;  trans-
 versely, by the separation of the cheeks; and from the anterior to
 the posterior part, by the motion of  the lips  and palate.
   The jaws more particularly influence the form and  dimensions
 of the mouth; the superior constitutes an essential part of the face
 and only  moves  with  the  head, the inferior,  on  the contrary, is
 possessed of great  mobility.   The jaws are garnished  with small
 hard  bodies, called teeth, they are generally considered as bones,
 but they differ from bone in some  important respects, particularly
 in their structure, mode of  formation, uses,  and  from their not
 being altered by the contact-of the air; but they resemble them in
 their hardness and chemical composition.  There are three kinds
 of teeth, the incisors, the canine, and the molares.
   We divide  the teeth into two  parts, the crown and the  root,
 which differ in  their  structure.   As the crowns of the different
 kinds of teeth are required  to perform different  sorts of service,
 their form varies.  That of the molares, or  grinders, is cubical,
 the canine are conical, and the incisors flat, with a cutting edge.
 Whatever is its  form, the crown is excessively hard, but it is worn
 away like dead  matter by constant friction.
   The fangs, or roots  fulfil  in the three kinds of teeth one com-
 mon use, that of  effecting a solid   junction with the ^aws, and of
 transmitting to  them the powerful  impressions  made upon  the
 teeth.   They are received into cavities, which are caded alveolar
processes, and exactly  fill them.   It  would appear that the walls
 of these cavities  exert a considerable pressure  upon the roots of 
OF PHYSIOLOGY.
193
the tooth from the fact that they contract, and at last are filled up
when the roots of the teeth aru removed.
  The incisors and canine teeth  have but one root, the molares
have generally several,  but whatever may be their number,  they
have always the form of a cone, the base of which corresponds to
the crown, and the apex to that part, which ends in the alveolar
process.   In some cases,  they  present  curvatures,  more or less
rematkable.
   The edge of the alveolar process is covered with a thick, fibrous,
resisting coat, which is called the gums; this coat is nicely fitted
round the inferior part of the crown of the teeth, adheres strongly
to them, and thus gives  solidity to the  junction of the teeth with
the jaws. This coat is capable of bearing strong pressure, without
inconvenience, we  readily see the  advantages  which result  from
this arrangement.
   We  must  include in  the number of organs that assist in the
prehension  of the aliments, the muscles which move  the jaws,
particularly the lower jaw; and the tongue, the motions of which
have a considerable influence on the dimensions of the mouth.

       Mechanism of  the Prehension of the Aliments.
   Nothing is more simple than the prehension of the  aliments;
 it  consists in the introduction of alimentary substances into the
 mouth,   lor this  purpose the hands seize the food, and divide it
 into small portions, capable of being contained  in the mouth, and
 then introduce it into this cavity, perhaps, by the  assistance of
 instiuments convenient for this purpose.
   But  in-order that it may  penetrate  into  this cavity,  it  is
 necessary that the jaws should separate, in other words, that the
 mouth  should open. It  was long discussed whether, in opening
 the mouth, the inferior jaw only moved, or whether both jaws sepa-
 rated from each other,  at the same time.  Without entering into
 this  discussion, which  does not  merit the importance that  has
 been attached to it, we  will observe, that it is obvious that the in-
 ferior jaw moves alone  when the mouth is open modera'ely,  but
 when it is opened  very widely, the superior jaw is raised, that is,
 the head is thrown slightly back on the vertebral column.  But, in
 every case, the inferior jaw has much the greatest extent of action,
 unless  its  depresssion is prevented  by some  physical obstacle; 
194
A  SUMMARY
 then the opening of the mouth depends alone upon the retraction
 of the head upon the vertebral column, or what is the same thing,
 upon the elevation of the upper jaw.
   In most cases, when the aliment is introduced into  the mouth,
 the jaws are brought together for the purpose of retaining it. and
 causing it to undergo the process of mastication  and deglutition.
 But sometimes the elevation of the lower jaw assists in the pre-
 hension of the aliments.  We have  one example  of  this in our
 manner of biting fruit; the incisors bury themselves,  in opposite
 directions, in the alimentary substance, and act like the blades of
 scissors, detaching a portion of the mass.  This  motion is princi-
 pally produced by the  contraction of the elevator  muscles of the
 inferior jaw, which represents a lever of the third kind, the power
 being at the insertion of the elevator muscles, the  fulcrum in the
 tempero-maxillary articulation, and the resistance in the substance
 on which the teeth act.*
   The volume of the substance, placed between the incisor teeth,
 influences the force with whicfi they are pressed together.  If the
 volume be small, the force will be much greater, for all the elevator
 muscles are inserted  perpendicularly into the jaw, and the sum
 of their force is employed  to  move the lever which it  represents.
 If the volume of the body be such  that it can  scarcely be intro-
 duced into the mouth, even if the resistance be but  little, the inci-
 sor teeth will be incapable of dividing it, because  the masseter,
 crotophite, and internal  pterygoid muscles, being inserted very
 obliquely into  the jaw, thus lose a great part of the power with
 which they contract.
   When the effort of the muscles of the jaws is not sufficient to
 detach a portion of the alimentary mass, the hands assist in the
 separation.   On the contrary, the mus-les on  the posterior parts
 of the neck draw strongly  the head  backwards,  and,  from  the
 combination of  these two efforts, a portion of the  aliment is de-
 tached and remains in the mouth.  In this mode of prehension, the
 incisor  and canine teeth are employed, but it is rare that  the
 molares assist.
 ^ By the succession of the motions of prehension, the mouth is
 filled, and from the elasticity  of the cheeks, and the depression of

  * In carnivorous animals, where this mode of prehension is frequently emplov-
ed, the three kinds of teeth participate, especially the canine. 
OF  PHYSIOLOGY.
195
the tongue, a  large  quantity  of  aliment may  be accumulated.
When the mouth is fuil, the veil  of the palate is depressed, and
its inferior edge is applied on  the base of the tongue, so that all
communication between the mouth and pharynx is interrupted.

Mastication and mixture of the Saliva with the Aliments.
  Independently of what we have said of the mouth, as relates to
the prehension of aliments, it is necessary to understand the uses it
fulfils in masticating  and mixing the food  with the saliva; it is pro-
per to remark, that fluids, arising from different sources, abound in
the mouth.  The mucous membrane which lines the mouth, the nu-
merous single,  or agglomerated follicles we observe on the inter-
nal surface ol the cheeks, at the junction of the lips with the gums,
the back part  of the  tongue, the anterior surface of the veil of the
palate, and  the uvula, pour out continually the fluid which they
form on the internal  surface of the mouth.  It is  the same of the
mucous glands, which exist, in great number,  in the substance  of
the palate and cheeks.   Lastly, there are six glands, three on each
side, which are called the  parotids, submaxillary,  and sublingual,
that pour out  the saliva they secrete into the  mouth. The first
are placed between the  ear and the jaw,  and have each an excre-
tory duct, which opens on a  level with  the second  upper  molar
teeth.   The ducts of the maxillary glands terminate on each side
of the frenum of the tongue, near which those of the sublingual
glands also open.
   It is probable that  these  fluids  vary in their physical and
chemical properties, according to the  organ  which forms  them,
but chemistry has not yet determined these differences by direct
experiments.  The mixture which we know by the common name
of saliva, has  been carefully analysed.
   Among the  alimentary substances deposited in the mouth, some
traverse this cavity  without undergoing any  change, others, on
the contrary,  remain for  a  considerable time, and   experience
several important modifications.   The first are  soft and nearly
fluid aliments, the temperature of which differs  little  from that of
the body.  The second, are those which  are dry, hard, or fibrous,
and those, the temperature  of which, differs, more or less, from
that peculiar to the animal economy.  They have both, however. 
196
A  SUMMARY
this quality in common, that, in passing through the mouth, they
are appreciated by the organs of taste.
  There are three principal modifications, which the aliments un-
dergo in the mouth, 1st, change of temperature; 2d, admixture with
the fluids which are poured  into the mouth; 3d, pressure, more or
less strong, and comminution, which destroys  the cohesion of the
parts.   They are, besides, easily and frequently transported from
one point of this  cavity to the other.  These  three modes of al-
teration do not take place successively, but simultaneously, each
favouring the other.
  The  change of temperature in  the aliments retained in the
mouth,  is evident; the sensations which they excite, are sufficient
evidence of this.   If they have a very low temperature, they pro-
duce a  vivid sensation of cold; which continues until they have
absorbed a sufficient quantity of caloric to approach the tempera-
ture of the walls  of the mouth.   The reverse takes place when the
temperature is more elevated than  that of its walls.
   Our  judgment, in this instance,  is formed in a  manner similar
to that  by which  we judge  of the  temperature of those  bodies
 which touch the  skin.  We institute a  comparison between the
temperature of the atmosphere, and that  of the body which is  in
 contact with the  mouth;  so that a body, preserving the same tem-
perature, will appear at one time cold, and at another warm, ac-
 cording to the temperature of the bodies which had been before  in
 contact with the mouth.
   The  change of temperature which  the food undergoes in the
 mouth, is a mere accessary  phenomenon.  Its trituration, and in-
 timate  admixture with the fluids poured into this cavity, are the
 circumstances which merit a particular attention.   As soon as
 the aliment is  introduced  into the mouth,  it is pressed by the
 tongue against the palate and the cheeks.  If the aliment has lit-
 tle cohesion, this  simple pressure  of the tongue  is  sufficient to
 spread  it over  the mouth; but, if it be  partly fluid and  partly
 liquid, it presses out the fluid part which is  swallowed, and the
 solid alone remains in the mouth.   The tongu^ produces  this  ef-
 fect readily, as the tissue is muscular,  and as it is supplied with
 a great number of muscles which are destined to move it.
   It seems surprising, that a  body as soft as the tongue, should
 exert an action sufficiently strong to crush a body, which presents 
OP  PHYSIOLOGY.
197
even a slight resistance.  But this is owing to the circumstance,
that it liar-lens at the same time  that it contracts itself; besides,
the mucous  membrane which lines its  superior surface, is com-
posed of a thick, dense, and fibrou9 coat.  Such are the phenome-
na  which  are observed, when the aliments offer  but little resis-
tance, but if thev cohere more strongly, they are then submitted
to the action of the masticating organs.
  The essential  agents of mastication  are,  the  muscles which
move the iaws, the tongue, the cheeks and the lips; the maxillary,
bones, and teeth, can only be considered as instruments.
   Though the action of both  jaws may  assist in mastication, it is
almost entirely performed by the lower  jaw.   This bone is capa-
ble of being elevated  and pressed strongly against  the  upper
jaw, and moved forwards, backwards, and sideways.  These dif-
ferent motions are  produced bv numerous  muscles which  are
attached to the bone; but the jaws could not fulfil the function to
which thev are destined, if they  were  not garnished with teeth,
the nhvsical qualities of which render them  particularly adapted
to this purpose.
   A  few remarks on these bodies are necessary to clearly under-
stand what follows.—The use of the molar  teeth is to grind the
food;  they are twenty in number, ten in  each jaw, five on the right
and five on the left side.   The form of their crown is that of an
irregular cube; the corresponding surfaces are composed  of py-
ramidal eminences, varying in  number in  the  different teeth.
 These asperities and cavities, are so arranged that those  of the
 upper correspond with  those of the lower jaw.
    At the lower and middle  part of the  crown, there exists a cavi-
 ty, filled  with an organ, which,  in the early periods  of life, se-
 cretes the tooth.  The root  is hollowed out into a canal, which
 is  occupied by  an artery, vein,  and filament of a  nerve.   The
 substance which forms the teeth, is of an excessive hardness, par-
 ticularly  its external coat, or enamel.   Being destined  to crush
 bodies, the resistance of  which  is sometimes very great, it is ne-
 cessary that they should  present a proportional  degree  of hard-
 ness; more especially as they are destined to exercise this office
 during life, and it is, therefore, necessary that  they should be
 worn away very slowly.   On this  account, extreme density was 
198                    A  SUMMARY
indispensable, for any body, however hard it  may be, cannot fail
to be worn down by continued friction.
   The substance which forms  the body and root of the teeth, is ho-
mogeneous in all its parts; the enamel, on the contrary, which com-
poses the crown of  the tooth, presents fibres  which are arranged
perpendicularly to the surface of the bony part of the tooth, and
strongly adhering to it.  The phosphate and  carbonate of lime
constitute nearly the whole of the teeth in  man.   In 100 parts,
99.5 are of this  salt, the  remainder  being animal matter.*  In
the enamel, there is scarcely  any animal matter, and it is to this
circumstance that we must attribute its whiteness and excessive
hardness.
   We have already shewn how solid the articulation of the teeth
with  the  jaw is; the molar  teeth, in consequence of the  office
which they perform, possess  this firmness in the highest degree;
their  roots are also more  numerous, though  not  so  large as in
those which  have but  one.   Finally, whether single or double,
their  form is conical, and they are received into cavities to which
they are adapted, which are called alveolar processes; each  tooth
represents a  wedge buried in the jaws.  The teeth in each jaw,
together, form what  are called the dental arches.
   The form of the arch is the half of a parabola, the inferior being
somewhat larger than  the superior.   The inferior edge of the
upper is a little inclined outwards, but that of the lower inwards*
These edges present, at that part  formed by the  molar teeth, a
groove, bounded by two ranges of eminences. When the jaws are
brought together, the incisors and  canine teeth of  the lower jaw
are placed behind the superior.  The external, projecting edge of
the inferior dental  arch enters the groove of the superior arch.
When the edges of the incisors are brought  in contact, there is
an interval left between the molar teeth.  To add firmness to the
junction of the teeth with the jaws, nature has so arranged them
that the sides of nearly all are in contact, which in this way pre-
sent a particular facette.  The result of this  disposition  is, that
  * I have found, from  experiment, that the  proportion of animal matter is
much greater in herbivorous animals.  The proportion of carbonate of lime is
greater in herbivorous animals, tliau  it is in those which are carnivorous or fes
roan, 
OF PHYSIOLOGY.
199
when one of the teeth  is exposed to a considerable pressure, it is
supported by all the teeth which compose the arch.
  These facts  being known, it is easy to understand the explana-
tion of the mechanism  of  mastication.

                 Mechanism of Mastication.
  When mastication begins, the lower jaw is depressed, an effect
which is produced by the relaxation of the elevator and the con-
traction of the depressor muscles.   The food  is then introduced
within the dental arches, by the tongue, or some other means. The
inferior jaw is  then raised by the masseter, internal pterygoid, and
temporal musc^s, the  contraction  of which is proportioned  to
the resistance  of the aliments.   The food  being pressed between
two unequal  surfaces,  the asperities of which grind against each
other, is divided into small portions.
  But a single motion of this kind only affects one part of the
aliments contained in the mouth, ami it is required that all should
undergo this operation.  It is effected by a succession of motions
of the  inferior jaw, by  the contraction of the  muscles of the
«heek, tongue, and  lips, which carry,  successively and promptly,
the aliment between the teeth, when the jaws are separated, so
that it may be crushed  when they are brought together.  When
the food is soft, two or three movements of  the jaws is sufficient,
but the  mastification must be prolonged when the substances are
tough, fibrous  or coriaceous, we then use only the  molar teeth, and
generally those of one side at a time, as if to enable the other to
remain  at rest.  In using the molar teeth, the resisting arm of the
lever, which  is represented  by the lower jaw, is shortened and
thus rendered more favourable to the  power which moves it.
  The teeth are submitted  to a very considerable power during
mastication, which would inevitably loosen, if not displace them,
if they  were not very strongly articulated  with the jaws.  Each
root  acts like a wedge, and transmits to  the alveolar processes,
the force with which it is pressed.
   The advantage arising from the conical form of the root, is by
no means doubtful.  In consequence of this form, the force which
presses  upon   the tooth,  and  tends to thrust  it into the jaw, is
divided, one part having a tendency to separate  the walls of the
alveolar process, the  other to thrust it inwards, thus the force, 
200                    A  SUMMARY
instead of being transmitted to the extremity of the root, which
must have taken place, if it had been cylindrical, is applied to
the whole  alveolar  surface.  The  molar  teeth, which  have to
endure considerable force, have several roots; or at least one very
large root.  The incisor and canine teeth, which have  but  one
root, and that not very  large, are never compelled  to endure a
very strong pressure.
  If the gums had not presented a smooth surface, and of a dense
tissue, placed as they are about the necks of the teeth, and filling
up their intervals, they would have beeu subject every instant to
be torn; for in the mastication of hard substances of an irregular
form, they are every moment exposed  to  be pressed strongly by
the edges and angles of these substances.  This inconvenience is
actually  felt, whenever their tissue  is softened, as in scorbutic
affections.
  During mastification, the  mouth  is  closed  posteriorly by the
veil  of the  palate, the anterior face of which is applied against
the base of  the tongue, anteriorly, the food  is retained  by the
teeth and lips.

                 Admixture of the Aliments.
  When we have  an appetite, the sight of aliments determines a
considerable afflux of saliva to the mouth.   In some persons this
is sufficiently strong for the  saliva to be projected to the distance
of several  feet.  I have actually  seen an  instance  of this.  The
presence of aliment in the mouth, excites this secretion.   While
the aliments are bruised and triturated by  the organs of mastica-
tion, they imbibe these fluids, which are copiously poured into the
mouth at this time, especially the saliva.   It is easy  to conceive,
that the  division of  the  aliment, and  the frequent displacement
which it undergoes during mastication, will  singularly favour its
admixture  with  the  mucus, and  salivary  fluids.  In  their turn,
these fluids facilitate mastication, by softening the aliment.  The
greater number of alimentary substances, when submitted to the
action of the mouth, become dissolved or  suspended, wholly, or
in part, in the saliva, and  at this moment become  proper to be in-
troduced into the stomach, and are soon  swallowed.  In conse-
quence of its viscidity, the  saliva absorbs the air which is com-
bined with it in  the  various  movements which are required  in 
OF PHYSIOLOGY.
201
 mastication, but the quantity of air absorbed in this way is incon-
 siderable, and  has been  generally much exaggerated.
   V\ e  cannot say, positively, what purpose  is answered by  the
 trituration of the food, and  its mixture with the saliva; whether
 it be a simple division,  which renders it more convenient for the
 alteration  v\hich  it  is  destined  to  undergo in  the  stomach, or
 whether it experiences in the mouth some degree of actualization*1
 We will however  remark, that the taste and odour of the aliment
 are  altered  during  mastication, that  when  mastication is  pro-
 longed, it  in general, renders  digestion more  prompt  and easy
 On  the contrary, that persons who do not chew  their aliments,
 have frequently, from this circumstance alone, slow and  imper-
 fect digestion.   We know when mastication and the admixture of
 the saliva are  carried to a sufficient extent, by the degree of re-
 sistance of the aliments, and the taste which they excite. Besides,
 the walls of the mouth, and  especially the  tongue, being endowed
 with  the sense or touch, can  appreciate  the  physical changes
 which take  place in the aliments.  Some authors  have  attributed
 this to the  uvula  of the  palate.*   1  much  doubt, however,  the
 correctness of  this opinion.   The uvula, Irom its situation, has no
 connexion with the aliment during its mastica'ion   1 have often
 noticed persons who  had lost the uvula, either oy a venereal ulcer,
 or by incision,  and  I have never found that their mastication or
 deglutition were the  least deranged.

                Of the Deglutition of Aliments.
   We understand by deglutition, the passage of a solid, liquid, or
 gaseous substance, from the  mouth  into the stomach.   The  de-
 glutition of  solid aliments, will first occupy our attention
   Though apparently simple, deglutition is by far the most com-
 plicated of  all the  muscular actions, which assist in digestion. It
 is produced by the  contraction of a great number of muscles, and
 requires the concurrence of  many  important organs.  All  the
 muscles of the  tongue, those  of the veil of the palate, the pharynx,
 larynx, and the muscular coat of  the oesophagus, assist  in deglu-

   * It is, say they, a vigilant  sentinel, which judges when the aliment can be
 swallowed without inconvenience.  It keeps a  watch upon the organs of deglu-
 tition, and upon the stomach, which, according to the impression it  has re-
ceived, is disposed to receive or reject it.
                               26 
202
A  SUMMARY
tition.   We ought to have an exact and detailed knowledge, if we
wish to  form a just idea of this act. The nature of this work will
not admit of our explaining all the anatomical details.   We shall
limit ourselves to a few remarks, upon the veil of the palate, the
pharynx, and oesophagus.
  The veil of the palate is a sort of valve, attached to the pos-
terior edge of  the arch of the palate; its form is  four sided. The
inferior, or loose edge, is prolonged into a point, which  is called
the uvula.  Like other valves of  the intestinal canal, the veil  of
the palate is essentially formed by a duplicature of the  digestive
mucous membrane; there enters into its composition many mucous
follicles, especially about the uvula.  It is moved by eight muscles,
viz. the two internal  pterygoid, which elevate it; the two exter-
nal pterygoid, which stretch it transversely; the pharyngo staphy-
linus and  the glosso-staphy'inus. which  draw  it down.  These
four last extentl to the  lower part of the throat, and  are  there
covered by the mucous membrane, and  form the pillars of the
veil of  the palate, between  which   are  situated  the  tonsils;  a
collection  of mucous follicles.  The opening  comprehended  be-
tween the  base of the tongue below, the veil of the palate above,
and the lateral pillars is sometimes called  the isthmus oj the
throat.
   By means  of this muscular apparatus, the veil of the palate
undergoes many changes of position.  Its most common situation
is vertical, one  of its faces being anterior,  and the other pos-
terior.  In certain circumstances, it  becomes  horizontal, it then
has a superior and an inferior face, and.its loose  edge corres-
ponds to the concavity of the  pharynx.   This last position is de-
termined   by the contraction of the elevator muscles.
   Bichat asserts, that the elevation of the veil of the palate may
be carried to such an  extent, as to be applied to the opening of the
posterior  nares; this  motion seems to be impossible;  there is no
muscle  arranged in such a mariner as to produce it, and the dispo-
sition of the pillars evidently  opposes it.   The depression of the
veil is executed by the contraction of the muscles which  form the
piliars.   We  have already remarked, that these motions are not
submissive to  the will in a great number of individuals.
   The  pharynx, is a sort of vestibule, into which the nasal fossee,
the eustachian tubes, the mouth, the larynx,and  oesophagus open. 
OP PHYSIOLOGY.
208
It fulfils important  functions in the production of the voice, in
respiration, in hearing  and digestion.   The pharynx  extends
from the. basilary process of the occipital bone, to which it is at-
tached above, to a level with the middle part of the  neck below.
Its transverse dimensions are  limited by  the  os hyoides,  the
larynx, and the aponeurosis of the pterygo-maxillaris, to which
it  is attached.  The mucous membrane, which covers it interiorly,
is  distinguished by the developement of its veins, which form here
a very remarkable net-work.  Near this membrane is the muscu-
lar coat, the circular fibres  of which,  form the three  constrictor
muscles of the pharynx, and the longitudinal fibres of which are
represented by the stylo-pharyngeus, and the pharyngo-staphyli-
nus muscles.   The  contractions  which these muscles execute,
are not in general submissive to the will.
   The oesophagus is immediately attached to the pharynx, and is
prolonged to the  stomach, where it terminates.   Its form is cylin-
drical, it is united to the surrounding parts, by a loose and exten-
sible cellular tissue,  which adapts itself to its dilatation and other
motions.  To penetrate  into the abdomen, the oesophagus passes
between the pillars of  the diaphragm, with which it is intimately
united.
   The mucous membrane of the oesophagus is white, thin, and de-
licate; it forms longitudinal folds, which facilitate its  dilatation.
Above, it is  lost  in  the  pharynx.   Dr.  Rullier has lately called
the attention of anatomists  to several  indentations, formed in its
lower part, which terminates by  a sort of fringed edge,  hanging
loose into the cavity of the stomach.*
   We meet in its substance, a great number of mucous follicles,
and we distinguish on its surface the  orifices of many excretory
ducts of mucous  glands.  The muscular coat of the oesophagus is
thick, and its tissue more dense than the pharynx, its longitudinal
fibres are more external and less numerous, the circular are placed
on the interior, and are very numerous.
   Near the pectoral and  inferior part of the oesophagus, the eighth
pair of nerves form a plexus, which embraces the canal and sends
  * There is between the mucous membrane of the oesophagus and the stomach
as striking a difference, as that which exists between this same membrane in the
cardiac and pyloric half, in the stomach of a horse. 
204                     A  SUMMARY
    many filaments to it.  The contraction of the oesophagus is made
    without any participation of the will.

                     Mechanism  of Deglutition.
      For the better understanding of the subject, we shall divide
    deglutition into three stages.  In the first the aliments pass from
    the mouth into  the  pharynx,  in the second they  pass over the
    openings  of the glottis, and nasal fossee,  and arrive at the oeso-
    phagus, in the third they pass through this canal, into the stomach.*
      Let  us suppose a common case,  that,  for example, we  have
,   swallowed several times a part of the aliment in the mouth, as its
    mastication has been completed.
      As soon as there  is  a  certain quantity of food masticated, it is
    placed  on the superior surface of the tongue, by the action of mas-
    tication, without any necessity, as some have supposed, that the
    apex of this organ should pass into all the angles of the mouth, to
    collect  it together.  Mastication then ceases, the tongue is eleva-
    ted, and  applied to the  arch of the palate, successively, from the
    arch to its base.  The portion  of aliment placed  on its superior
    surface, having no other  way to  escape from the  pressure to which
    it is exposed, is directed  towards the pharynx, where it meets with
    the veil of the palate applied over the base of the tongue, which it
    6auses to be elevated,  the veil becoming horizontal.  The tongue
    continuing to press  the  aliments, they would be carried towards
    the nasal  fosspe; if this was not.  prevented by  the tension which
   'the veil receives from  the peristaphylinus muscles,  and  especially
    by the contraction of its pillars.  It becomes thus  capable of  re-
    sisting the action of the tongue, and of  contributing to  direct the
    aliments towards the pharynx.
      The muscles  which more particularly act in applying the tongue
    to the arch of the palate  and to  the veil of the palate, are the pro-
    per muscles of this organ, aided  by the mylo-hyoideus.  This ter-
    minates the first stage of deglutition. The motions are all volun-
    tary, with the exception  of those of the  veil of  the palate.  The
   phenomena take place  in succession, and with little promptitude,
   they are few in  number and easy to comprehend.

     * For the division of deglutition ity time, see my Thesis, defended in the Schorl
   of Medicine at Paris, 1808. 
OF PHYSIOLOGY.
205
  The same remarks will not apply to the second staze.  There,
the phenomena are simultaneous, multiplied and produced with
such rapidity, that Boerhaave considered them a sort of convul-
sion.   The space which the morsel has to pass over in the second
stage is very short, being only from the upper to the lower part of
the pharynx.   But it  must be prevented  from entering either the
glottis or  the  nasal  fossfe, where  it  would prove injurious.   Be-
sides, its passage must be so rapid as not to  interrupt, but for a
moment, the free communication between the external air and the
larynx.  We shall now see how nature accomplishes this impor-
tant purpose.
  The morsel of food no sooner reaches  the  pharynx than every
part of it is thrown  into action.  It at first  contracts itself, em-
bracing and holding firm the morsel of food;  the veil of the palate,
drawn down  by its pillars, acts at the  same time.   On  the other
side, and  almost at the same  instant, the base  of the tongue, the
os-hyoides, and the larynx are elevated, and approach each other,
that is, the superior edge of  the thyroid cartilage is pressed behind
the body of the os hyoides.  the gland of the  epiglottis is  pushed
backwards, the epiglottis itself depressed, and inclines downwards
and backwards, so as to protect the entrance of the larynx.  The
cricoid  cartilage  executes  a rotation  upon  the inferior horns of
the thyroid,from  which it results, that  the entrance of the larynx
becomes  oblique from above downwards, and  from before, back-
wards.  "The morsel  glides over its surface,  and continuing to be
pressed by the contraction of the pharynx,  and the veil of the
palate, it  arrives at the oesophagus.
   It will  not require  much  consideration to understand the posi-
tion which the epiglottis in this case assumes, if  it be considered as
the only obstacle which prevents the  entrance of the aliments into
the larynx, at the  moment of  deglutition.  But I have shown, by
a series of experiments, that this cause can only be considered as
accessory. We can in fact, entirely remove the  epiglottis from an
animal, without  deglutition  being impeded.   Let us inquire then,
what is the reason why no part of the food is introduced into the
larynx, at the moment of swallowing.   At the instant that the
larynx is elevated, and forced behind the os hvoides, the glottis is
closed with great exactness.  This motion is effected by the  same
muscles which contract the glottis in the production of the voice. 
206
A  SUMMARY
 So that, if we  divide the laryngeal and  recurrent nerves of an
 animal, leaving the  epiglottis  untouched, we render  deglutition
 extremely difficult,  because we have  taken away  the  principal
 cause which  prevents the  introduction of  the  aliment into the
 glottis.  Immediately after the morsel  has passed the  glottis, the
 larynx descends,  the epiglottis  is  raised, and  the glottis again
 opened to give  passage to the air.*
   From this  explanation, it is easy to  comprehend how the ali-
 ments, when  swallowed, arrive  at  the oesophagus, without pene-
 trating into any of those openings which are so  numerous in the
 pharynx.  The veil of the  palate, at the moment when the pha-
 rynx contracts  itself, protects the posterior nares, and  the  orifices
 of the eustachian tubes; the epiglottis, and  especially the  motion
 by which the glottis  is closed, firmly protects the larynx.
   We have  thus finished the description of the second stage of
 deglutition, and traced the morsel of food, as it has passed through
 the mouth and  pharynx, until it has arrived at the upper  part of
 the oesophagus.  All the phenomena exhibited in the second stage,
 take place simultaneously,  and  with great rapidity; they  are not
 controlled by the  will, and differ,  therefore, in many  respects,
 from  the phenomena observed in the first stage.
   The third  stage  of deglutition has  been examined with less
 care; in consequence,  probably,  of  the  situation of the oesopha-
 gus, which it  is  not easy to observe,  except at its cervical portion.
 The  phenomena  are not complicated.  By  its contractions, the
 pharynx pushes the  morsel into the  oesophagus, with  sufficient
 force to dilate the  superior part  of  this organ.   Its superior cir-
 cular  fibres, excited  by the presence of the morsel, contract and
 thrust the  aliment  towards the stomach, causing the distention of
 those parts which are below; these again contract  in  their turn,
 and the thing is repeated; until the morsel arrives at the stomach.
 In the two superior thirds of the  oesophagus, the relaxation of the
 circular fibres immediately  follows the  contraction, by which the
 morsel is displaced.   It is not the same in the inferior third, which
  * I have known  two instances of individuals,  in whom the epiglottis  was en-
tirely wanting, but in  whom deglutition was performed without any difficulty.
 If in laryngeal phthisis, with destruction of the epiglottis, deglutition is imperfect
and laborious, it arises from the arytenoid cartilages being carious, and the edges
of the glottis ulcerated; so that they become incapable of closing exactly.
  See my Memoir upon the Epiglottis, read before the Institute of Paris, 1813. 
OF  PHYSIOLOGY.
207
remains contracted for some time after the introduction of the
food into the stomach.
  We should be  mistaken, if we supposed, that  the  passage  of
the  morsel into the stomach  was  very rapid.  I have been asto-
nished, in my experiments, to find how slow its progress is;  often
two  or three  minutes elapse  before  it reaches the  stomach;  at
other times,it stops and  remains for  a considerable time on each
spot.  1 have seen it, in some instances, rise from the inferior ex-
tremity of the cesophagus towards the upper part,  and afterwards
descend.   When any obstacle prevents its entrance into the sto-
mach, this  motion is repeated a great number of times, before the
aliment is rejected by the mouth.   This explains the sensation
we   often  perceive, of the aliment remaining in  the oesophagus,
which induces us to drink, in  order to make it descend into the
stomach.
   When  the morsel is very large, its progress is still  more slow
and difficult.   It is accompanied  by a vivid  sense  of pain, pro-
duced by the distention  of the nervous filaments,  which surround
the  pectoral  portion of the canal.  Sometimes  the morsel is  ar-
rested entirely, and occasions the most serious accidents.
   Professor Halle observed, in  a woman  affected  by a disease
which enabled him to see the  interior of  the  stomach, that the
arrival of a portion  of aliment in this viscus, was  immediately
followed by the formation of a sort of hood, at the cardiac orifice.
This hood was formed  by the displacement of the mucous mem-
brane of the cesophagus, which was thrust into the stomach by the
contraction ol the circular fibres of the canal.
   The whole extent  that the  morsel has to pass over, during the
three stages of deglutition, is copiously lubricated  by mucus.  The
morsel pressing out  the contents of  the follicles, which it  meets
in its passage, glides easily  along the membrane.   We may  re-
mark, that at those points where the morsel  passes most rapidly,
 and is pressed with the most force,  the mucous secretory organs
 are the most numerous.   For example, in the narrow space where
 the second  stage  of  deglutition  takes place, there are found, the
 tonsils, the fungous papillae at the base of the tongue, the follicles
 of  the veil of the palate, and of the  uvula, those of the epiglottis,
 and the arytenoid glands; in this respect, the saliva, and mucus,
 fulfil  uses analogous  to those of the synovia. 
208                    A  SUMMARY
   Nothing can be easier than to execute deglutition, while nearly
 all the acts which  compose  it, are  beyond the influence of the
 will and  the  dominion of instinct.  We are incapable of alter-
 ing a single motion of  nutrition.   If the substance contained in
 the mouth is  not sufficiently chewed, if it does  not possess the
 form, consistence, and dimensions of the alimentary morsel, and if
 the motions of mastication, which  immediately  precede deglutition,
 have  not been made, with all our exertions, we shall  be  unable to
 swallow it.   How  common a thing is it to see persons incapable
 of swallowing a  pill, and who are  obliged to  have  recourse to
 various means to introduce it into the stomach.
   In  order to form an idea of the part which the will  takes in de-
 glutition, we may make the following experiment upon ourselves.
 Let any one  endeavour to execute five or six motions  of deglu-
 tition, in which he  swallows  the  saliva.  The first, and  even the
 second time, this will be easily  accomplished, but the third  time
 it will be more difficult, because there will remain but little saliva
 in the mouth,  the fourth it will be  impossible to execute until a
 certain  period will elapse, when  new  saliva  will be  thrown into
 the mouth, but the fifth  and sixth will be impossible, because
 there will not be any saliva  to swallow.  Every one may recol-
 lect how difficult deglutition  is, whenever the  mouth and pharynx
 are dry.

                       Of the Abdomen.
   The digestive  actions,  which  remain to be examined  by us,
 take place in the cavity of the abdomen, the disposition of which
 deserves to be studied with attention.
   The abdomen is  the largest of  the cavities of the body, and ad-
 mits of the greatest augmentation of its capacity.  It contains a
 great  number of organs, which are  destined  to perform certain
 important functions, as  generation,  digestion,  secretion of urine,
 &c.   Its walls are chiefly muscular, and have a very  marked ac-
 tion on  the organs they contain.  The form of the abdominal ca-
 vity is irregularly ovoid.  In  consequence of its large dimensions,
and in order to give precision to language, it is divided into seve-
 ral regions, which have each received a particular name.
  To understand this division, which is purely  artificial, it  will
be necessary  to  suppose two horizontal planes, one ot  which 
OF  PHYSIOLOGY.
209
divides the abdomen on a level with the crest of the ilium, and the
other on a  level with the inferior false rib.   The part of the ab-
domen placed beneath  the  first plane, is called the hypogastric
region, that which is found  above the second, the epigastric, and
that comprehended between the two planes, the umbilical.
  Suppose, now, that two vertical planes, passing from the side of
the head, should  tall upon the anterior and inferior spines of the
ilium, dividing the abdomen from  before, backwards, it is plain,
that each of the three abdominal regions, of  which we have been
speaking, will be  subdivided into three compartments, of dimen-
sions nearly equal   It will be found convenient to designate these
subd visions by the following names.   'The middle may be  called
the epigastrium, and the two sides  the hypochondriac regions;
the umbilical region, called right, left, and middle; lastly, we may
give the  name o*  hypogastrium, to the  middle  division of the
hypogastric region, while we call the  sides the iliac regions.
   By means of these  artificial divisions, we may fix, with  exact-
ness, the position and respective relations of the organs contain-
ed in the abdomen;  which will  be  found extremely  convenient,
both in physiology and  medicine.
   Above, the  a domen is separated  from the chest, by the dia-
phragm,  a rnuscie disposed  in  the form  of  an arch,  and the con-
traction of which  has a great influence on the position, and even
upon the action ol the  organs  contained in the  abdomen.  The
circumference of the diaphragm is attached to the edge  of the
false ribs, and the vertebral column.   In a state of relaxation, its
centre is raised to a level with the fifth or sixth true rib, but at
the instant that th-s muscle contracts strongly.it occasions  a con-
siderable diminution of the abdominal cavity, compresses all the
organs which it contains, and distends the soft parts which form
its  walls.
   The inferior part  of  the abdomen is formed by the pelvis, the
firm bones of which  support the weight of  a part of the viscera,
and give a place  of insertion for the muscles, but do not assist in
producing variations in the capacity of the abdomen, except under
circumstances extremely rare.  It is proper to remark, that the space
comprehended between the  coccyx, the tuberosities  of the  ischi-
iua, and the arch of the pubis, is filled with soft parts, and par-
                              27 

A  SUMMARY
ticularly by the ischio-coccygeus, and the elevator and sphincter
ani muscles.
  Anteriorly, and laterally, the walls of the abdomen  are formed
by the abdominal muscles.  These muscles, as we have  already
seen,  concur powerfully in the different attitudes and  motions of
the trunk, and have also effect in  digestion, and generation. &c.
Among these muscles; those which are large, and situated on the
sides, are destined to contract the abdomen, and to compress the
viscera  which are contained in it.
  The  long muscles, situated  anteriorly, are  most generally
the antagonists of the  first.   They  resist their action and may, un-
der certain circumstances, augment the dimensions of the abdo-
men,  and diminish the pressure which the viscera support.
  From the ensiform cartilage,  to the pubis, there exists  a fibrous
cord, formed by  the crossing  of the  fibres of the aponeuroses of
the abdominal muscles; this is called by anatomists the lineaalba.
Its uses will hereafter be explained.
  Most  generally,  the muscles  which  compose  the  abdominal
walls, are directed by the  will, but there are also circumstances,
where they instinctively contract, when  they  display  a  much
greater degree of energy than in ordinary cases.

           Action of the Stomach upon  the Alime7its.
  Thus far we have only seen the physical actions of the diges-
tive organs upon the aliments, we  shall  now examine those ac-
tions which are almost entirely chemical.  In  the stomach, the
aliments are transformed into a substance peculiar  to  animals,
which is called chyme.  But before treating  of  the  phenomena
which its  formation presents, we will  say a few words of the
stomach itself.

                       Of the Stomach.
  The stomach is placed between  the cesophagus and the duode-
num; it occupies, in the abdomen, the epigastric, and a part of the
left hypochondriac  region;  its form, though variable, is,  in gene-
ral, that of  a conoid, curved  upon  itself.  The  left  half of the
stomach is always much larger  than  the right, and, as these two
halves take a different part in  the formation of the chyme, I have
thought it useful to name the one the splenic half, because it is in 
OF  PHYSIOLOGY.
211
 contact with the spleen;  and the other the pyloric half, because
 it corresponds to the pylorus.  These  two parts  are frequently
 separated from each other by a particular contraction.
   The stomach being destined to allow  the aliments to accumulate
 in its cavity, it is evident that its dimensions, situation in the ab-
 domen, and relations with the neighbouring organs, must undergo
 great variations.  This organ has  two orifices;  the one corres-
 ponds  to  the  cesophagus, which is called  the cardiac orifice;  the
 other communicates with the small intestines, and  is called the
 pylorus.
   The three membranes, or tunics, which  surround  the stomach,
 present dispositions  the  most favorable to the variations in the
 volume of the organ.  The exterior, or peritoneal coat, is formed
 of two laminee, slightly adhering  to  the viscus.   These are pro-
 longed, without uniting, for a considerable distance from  its edge,
 and thus form  what is called the epiploon, or omentum, the ex-
 tent of which is, therefore, in an  inverse  ratio  to  the  volume of
 the stomach.
   The mucous membrane of the  stomach  is  of a reddish  white
 and  marbled;  it presents a great  number of irregular folds,  situa-
 ted particularly on the  inferior and  superior edges of the or«an;
 they are also seen on its splenic extremity.  They are the more
 numerous and remarkable when  the  stomach is contracted  upon
 itself.
   There is no part of the digestive mucous membrane, which pre-
 sents so many, and such fine villosities  as the stomach.  It is con-
 stantly covered on its splenic half, by a mucus adhering to its sur-
 face.   VVe also, meet with many follicles  in its substance, but it
 is important to observe, that they  are very  abundant  in  the
 pyloric portion.  We see a certain number in the neighbourhood
 of the cardiac orifice, they are rare in the other parts of the mem-
 brane.
   At  the  pylorus, the mucous membrane  forms a circular fold,
 called the valve of the pylorus. Between its two laminse is found
 a dense, fibrous tissue, designated  by some authors, by the name
 of the pyloric muscle.
   With respect to the muscular coat of the stomach, it  i&  very
thin; its circular and longitudinal  fibres are separated from each 
212
A  SUMM\RY
other, especially on the splenic  part; this  separation increases
or diminishes with the volume of  the stomach.
  There are few  organs which  receive  so much  blood as the
stomach; four arteries, of which  three are  large, are sent exclu-
sively to it. Its nerves are not less numerous, they  are composed
of the  eighth pair, and  of a  great number of filaments coming
from the solar plexus of the great sympathetic.

         Accumulation of Aliments in  the  Stomach.
  Before explaining the changes which  the  aliments  undergo in
the stomach, it  is necessary  to be acquainted with  their accumu-
lation  in this  viscus, and the local  and general  effects  which
result from it.
   The first morsels which are swallowed, are easily lodged in the
stomach.  This organ is but little compressed  by  the  surround-
ing viscera; its walls easily separate, and yield  to the force  with
which  the morsels are thrust into the organ.   But, as new portions
of aliment arrive, its distention   becomes  more difficult, for  it
must be accompanied with a pressure of the other viscera, and an
extension of the abdominal  walls.  It  is, especially towards the
cardiac  extremity, and  the  middle part, that the accumulation
takes place, the pyloric portion is not so readily distended.
   At the same  time  that the  stomach is distended, its form, re-
lations, and even its position become modified.   Instead of  being
flattened, and occupying only the epigastrium, and left hypochon-
driac region, it assumes a rounded form; its  large cul  de sac  is
buried  in  this  hypochondrium, and fills it up, almost entirely.
The large curvature descends towards the umbilicus,  or navel,
especially  on the left side.  The pylorus,  however, fixed  by a fold
of the  peritoneum, preserves its positions and relations with the
surrounding parts.
   In consequence of the resistance  offered  by  the  vertebral
column  posteriorly, the stomach is not dilated  in this  direction.
The result, therefore, is, that the  viscus is  entirely  carried for-
ward;  and, as the pylorus and cesophagus cannot be displaced, in
this direction, it undergoes a rotatory motion, by which  its  large
curvature is directed forward; its posterior face inclined  below,
and its superior upwards. 
OF  PHYSIOLOGY.
213
  In undergoing these changes of relation and position, however,
it preserves a conoid figure, curved upon  itself, which is peculiar
to it.   This arises from the manner in which the three tunics con-
tribute to its dilatation.  The two lamime of the serous membrane
are separated,  and spread over the stomach; and the  mucous
membrane yields, especially in those  parts  where its folds are
most numerous, which it will  be remembered, are the cardiac ex-
trenuty, and along the large curvature.
  The dilatation of the stomach alone, produces important changes.
The whole extent of the cavity is augmente I, the belly  becomes
prominent, the abdominal  viscera compressed with more force,
and often a desire of voiding the foeces and   urine is  felt.   The
diaphragm is crowded into the chest, and  is depressed  with diffi-
culty;  the action of respiration becomes less easy, and those  phe-
nomena  which depend upon it, as speaking  and singing, become
modified, &c.   In some cases, the dilatation  of the stomach may
be carried to  such an extent, that  the abdominal walls become
painfully  distended, and the respiration really difficult.
  For  the production of such  effects, it  is evident, that  the con-
traction  of the  resophagus, which  thrusts the aliment  into the
stomach,  must  be very energetic.   We  have already  spoken of
the considerable thickness of the  muscular coat of this canal, and
the great number of nerves distributed  to it.  There  is nothing
but  this  peculiar  structure, which  can  explain  the  force  with
which  the aliments distend the  stomach.  To satisfy ourselves
of this, we have only to introduce a finger into the cesophagus of
an animal at its cardiac orifice, and we shall be  surprised at the
force with which it contracts. But if the aliments  exert so marked
an influence on the walls of the stomach and abdomen, they  must
themselves undergo a proportionate reaction, and tend to escape
from the  two openings of  the stomach.   It is generally said that
this effect does not take  place, in  consequence  of the  firmness
with which the cardia and pylorus close themselves; but this phe-
nomenon has never been directly investigated.
   The following experiments on this point, were made by myself.
The alternate motion of the oesophagus prevents the return of the
aliments  into its cavity.  The more the stomach is distended, the
more intense  and prolonged is this contraction, and the shorter
the  duration of the relaxation.  The  contraction, for the  most 
214
A  SUMMARY
part, takes place at the moment of inspiration, when the stomach
is very strongly compressed.  The relaxation happens frequently
at the moment of expiration.
  We can form an idea of this mechanism, by laying bare the
Stomach of a dog, and  endeavouring to press back  the  aliments
into the oesophagus, with both  hands.   We  shall find it almost
impossible to do this,  whatever be the force we employ,  if we
make the  attempt at the time  the cesophagus is contracted; but
this will be easily done, if we compress the viscus at the moment
of relaxation.
  The resistance which the pylorus opposes to the aliments, is of
a different kind.  In living animals, whether the stomach be full
or empty, this opening  is closed by the constant contraction of the
fibres, of which it  is composed.  We see  frequently in the sto-
mach another obstruction, one or two  inches distant, which ap-
pears destined to prevent the aliments  from arriving  at the py-
lorus.*  We may distinguish also irregular and peristaltic con-
tractions,  which begin  in the duodenum,  and are prolonged in
the pyloric portion of the stomach, the effect of which is to thrust
the aliments towards  the cardiac  portion.  Besides, when the
pylorus  is not naturally and firmly closed, the aliment has but
little disposition to  introduce itself into this opening, as its  natu-
ral  tendency must be to pass in the direction where the pressure
is least; and this will  of course be as great in  the small intes-
tines as in the stomach, inasmuch as the pressure is  nearly equal
over the whole cavity of the abdomen.
  In  the number of phenomena produced by the presence of ali-
ments in  the  stomach, there are several,  the existence of which,
though generally admitted, have  never been sufficiently demon-
strated.   Such for example, as the diminution of volume in the
spleen, and sanguineous vessels  of the liver and omentum; the
motion of the stomach called by authors the peristole, which pre*
sides over the reception of aliments, distributing them equally,
and exerting upon them a gentle pressure; so that its dilatation,
so  far from being passive,  would be essentially  active.  I have
frequently laid open the abdomen of animals, when the stomach
was filled with aliment; and have often examined the bodies of
  * This structure is very  remarkable in carnivorous animals, and herbivorous
animals with one stomach. 
OF  PHYSIOLOGY.
215
 criminals shortly after death, but I have never seen any thing to
justify these assertions
   The accumulation of aliments in the stomach, is accompanied
 with several  sensations, which it  is proper to notice.  The first
 is the agreeable sensations which we receive in gratifying this na-
 tural  want.  The sensation of hunger is gradually appeased, the
 general weakness which accompanies it, is  replaced  by  a new
 sensation of activity and  vigour.   But if more food be intro-
 duced, a sense  of fulness  and satiety is induced, which shows
 that the  stomach is full.   If, notwithstanding  this instinctive
 warning, we persist in eating more, disgust and nausea supervene,
 and are shortly followed by vomiting.
  These different sensations do not entirely depend upon  the vo-
 lume of the  food; other things being equal, nutritious aliment
 induces  soonest  a sense  of satiety.   A substance which  is but
 little nutritious, calms  but imperfectly the sense of hunger, even
 when it  is taken in considerable  quantity.  The mucous mem-
 brane, therefore, is endued with a  considerable degree of sensibi-
 lity, inasmuch as it distinguishes  the nature of the substances
 brought  in contact  with it.  This quality manifests itself in  a
 very  remarkable  manner,  vvhen   any  poisonous  substance is
 brought  in contact  with it, when  it  produces intense  pain; we
 know also, that it is  sensible to the temperature of aliments.
   From the redness of the mucous  membrane, the quantity of fluid
 which it secretes, and the  size of the vessels which  are ramified
 upon it, we cannot doubt that the presence of  aliments in the sto-
 mach produces an excitement, useful in the process of  chymifica-
 tion.   This excitation  of the   stomach has a powerful  influence
 upon the general state of  the  functions, as will  be  shown here-
 after.
   The aliments  remain in the stomach a considerable length of
 time, generally  for several  hours, during which  they are  formed
 into chyme.   VVe will now  examine the phenomena which attend
 this transformation, which  has been, heretofore, but imperfectly
 investigated.

         Alteration  of the  Aliments  in the  Stomach.
   The aliment remains in the  stomach, generally, about one hour
 before it undergoes any perceptible change, but what arises from 
216
A  SUMMARY
its mixture with the fluids which are continually poured into this
organ.  During this time, the stomach remains uniformly distend-
ed; at last the pyloric portion  contracts itself, through its whole
extent, especially towards the  point  nearest to the  cardiac  por-
tion, during which the aliments are forced  back. From this time,
we find in the  pyloric portion, nothing but chyme, mixed with a
very small portion  of aliment unchanged.
   The highest authorities have agreed in considering chyme as a
homogeneous, pultacious,  greyish  substance, of a  sweetish  in-
sipid taste, slightly acid, which preserves some of the proptrties
of aliments.  But this description is far from  being  perfect.   In-
deed, the circumstances under  which the chyme assumes these
characters, and the sort o?  aliments which had been  used, are not
mentioned, though  it is evidently  important that they should be
known,   there are as many kinds of chyme, as there are sorts
of aliments, it we may judge from their colour-, consistence, aspect,
&c.   This any person may easily satisfy himself of,  by causing
dogs to eat different sorts  of simple  alimentary substances, and
killing them  during the process of digestion.   I  have also repeat-
edly confirmed this observation in  man, upon criminals, and  per-
sons dying suddenly from accidents.
   In general, animal  substances are more easily  and completely
altered than  vegetable.  It happens frequently, that these  last
traverse the whole of the canal, without changing their characters.
I hove often seen in the rectum and small intestines, greens, spin-
nage, &c. which had been added to the soup, preserving  all their
properties,their colour only being altered by tie bile  I he chyme is
particularly formed in the  pyloric portion.  It would appear that
the aliments  are introduced by degrees, and that  during their
stay, they undergo a transformation.  I have, however, often  seen
chymous matter on  the surface  of  the mass of aliments which fill
the cardiac portion; but  generally, the a;iments in this part of the
stomach, preserve their peculiar properties.
   It is difficult to say, why the pyloric portion  is better suited to
the formation of the chyme, than the rest  of (he stomach. Perhaps
the great number of follicles observed  there, induce  some modifi-
cation  in the  quantity or nature of the fluid  secreted.   1 he trans-
formation of alimentary substances into chyme, takes place, gene-
rally, from the  surface towards the centre.  There is  formed on 
OF  PHYSIOLOGY.
217
the surface of the portions of aliment swallowed, a soft coat, easily
detached.  They appear to  be acted upon  by an agent,  which
completely dissolves them.   A morsel of the white of an egg,
boiled  hard, for example, is acted upon as if it had been dipped
in vinegar, or a solution of potash.   Whatever may be the sub-
stance employed, the chyme has  always a sour taste, and smell,
and turns the purple juice of vegetables red.  A very small quan-
tity of gas is found in the stomach, during the formation of chyme,
often it does not exist at all;  sometimes  it is formed like a small
bubble, at the superior part of the cardiac portion.  I have been
able, by great care, in one instance,  in the body of a criminal re-
cently executed, to collect a sufficient  quantity of this gas for
analysis.  M. Chevreul found it composed of
                    Oxygen,        tl.00
                    Carbonic acid,   14.00
                    Pure hydrogen,  3.55
                    Azote,          71.45
                       Total,      100.00
  It is rare that we meet with gas in the stomach of a dog.
  I cannot believe,  with professor Chaussier,  that with each act
of deglutition we swallow a bubble of air, which is thrust into the
stomach with the alimentary  morsel.  If this  were  the case,  we
ought to find in this organ  a considerable quantity of air after
eating, which is not the fact.
  A large quantity  of  chyme does not accumulate in the pyloric
portion of the stomach; the most I have  seen was hardly equiva-
lent, in volume, to two or three ounces of water. It would appear
that the contraction of the stomach has an influence  upon the for-
mation  of the chyme,  from  the  following observations made by
myself-  After having remained for some time immoveable, the
extremity of the duodenum contracts itself, which is  followed by
a similar action in the pyloric portion of the stomach.   This mo-
tion forces the  chyme towards the cardiac portion, but afterwards
the contraction is made  in  an opposite direction; that is, after
being distended, and having permitted the chyme to return anew
into its cavity, the pyloric portion contracts itself from  the left
towards the  right side,  directing the chyme  towards  the duo-
denum, which overcomes the action  of the pylorus, and penetrates
into the intestine.  This phenomenon is  repeated  for  a certain
                              28 
218
A  SUMMARY
 number of times, after which it is stopped, and the same process
 is renewed.  When the stomach contains much aliment, this mo-
 tion is limited to that part of the organ nearest to the pylorus; but, as
 it becomes emptied, the motion extends itself more and more, and
 at last becomes manifest in the cardiac portion, when the stomach
 is nearly empty.   In general, it becomes more distinctly marked
 towards the end of chymification.  Some persons have a distinct
 consciousness of it at the time.
   The pylorus  has been supposed, by some, to act a very impor-
 tant part in  the passage of the chyme, from the stomach  to the in-
 testine.  It judges, according to some, of the degree of chymifica-
 tion of the aliments, it opens, and allows  those parts to  pass
 which possess  the requisite qualities,  but closes itself  against
 those which  do not present them.  We know, however,  from
 daily experience, that undigested  and  indigestible  substances,
 or the stones of  fruit, and  other substances  incapable of being
 converted into  chyme, at last pass easily through it.   These con-
 siderations,  which are in some degree consecrated by the meaning
 of the term pylorus, (a door keeper)  may serve to amuse  us, but
 they are after all mere hypotheses.
   All alimentary substances are not transformed into chyme with
 an equal degree of facility.   In general, fatty substances, tendons,
 cartilages, concrete albumen, and mucilaginous and sweet vegeta-
 bles, resist longer the action of the stomach than those which are
 caseous, fibrous, or glutinous.  Some substances are very difficult
 to digest, such as bone, the epidermis of fruits, and entire kernels
 of grain.   In determining the digestibility of aliments, it is neces-
 sary to take into consideration the size of the portions which are
 swallowed.   I  have often observed that the  largest masses re-
 mained longest  in the stomach.  On  the contrary, a substance
 that is not even digestible, if it be minutely divided, as the stones
 of raisins, do not  remain  long in the stomach, but  pass at once
 with the chyme into the intestine. As regards facility and promp-
 titude, in the formation of the chyme,  there  is a vast difference
among individuals.  It is evident then, from what has been said,
that in order to form an estimate of the precise time required for
the conversion of all the food contained in the stomach into chyme,
it would be necessary to know its quantity, chemical nature, de-
gree of mastication, and the  constitution of the individual.   It is 
OF  PHYSIOLOGY.
219
rare, however, that the transformation of the whole of the aliment
into chyme requires more than five hours.
  We do  not know the  precise nature of the  chemical  changes
which take place in the stomach, though there  have been, at dif-
ferent  periods, many  attempts to  explain them.   The ancient
philosophers supposed that the aliments putrefied in  the stomach;
Hippocrates attributed digestion to coction; Galen supposed that
the stomach possessed certain faculties, which  he called  attrac-
tive, retentive, concoctive. and  expnlsiva;  and thought he  thus
gave an explanation of digestion.   The  doctrine of Galen  was
received by the schools until the seventeenth  century, when  it
was attacked and overthrown  by the chemical sect of philoso-
phers, who established on its ruins, the doctrine of a peculiar fer-
mentation, by means of which the  aliments were macerated, dis-
solved, precipitated, &c.  This system did not retain its  ground
long, but  was replaced by another much less  reasonable.   The
doctrine which succeeded, was that of trituration, or a grinding
down of the aliments, by the contraction of the stomach; it was
also supposed, that an infinite number of small worms attacked
and divided the aliments.  Boerhaave thought he had approached
nearer the truth, when he combined together, the various opinions
on this subject which had prevailed before his time.  Haller aban-
doned  the doctrines of his master, and considered digestion as a
simple maceration.  He  knew that vegetable and animal substan-
ces which are plunged  in water,  are soon covered with a  coat,
soft and homogeneous; and he supposed that the aliments under-
went a similar process,  by  being  macerated in  the saiiva, and
gastric juices.
  If we examine these different systems, by those severe rules of
logic, which should always govern us in physiological inquiries,
we shall be compelled to acknowledge, that they were  mere ef-
forts of the imagination,  which  only served to  conceal the abso-
lute  ignorance  of their inventors.   Was it any advance  in
knowledge to say, that  digestion  was a concoction, a fermenta-
tion, or a  maceration?  Certainly not, as it is impossible that any
one can attach  any precise  meaning  to these  expressions, when
applied to digestion.   But  this was not the  method pursued  by
Reaumur  and Spallanzani.   They  made experiments upon ani-
mals, and demonstrated that all these systems  were false.   They
shewed, that when aliments were inclosed in hollow metallic balls. 
220
A  SUMMARY
and pierced with small holes, that they were digested in the same
manner as if they were floating loose in the  cavity of the stomach.
They proved, that  the stomach  contains a peculiar  fluid, which
they called gastric juice, and that this fluid was the principal
agent in digestion.  But they exaggerated its qualities very much,
and deceived themselves, when they supposed, that they had ex-
plained digestion, by considering it a mere solution; for, from their
not explaining what  they meant by  this solution, they, in fact,
did nothing towards shewing what the precise alteration is which
the food undergoes in the stomach.
  Instead  of stopping to expose and  refute these different hypo-
theses, which would be a very easy task, and  which may be found
in almost every treatise on physiology,  we  shall make some ob-
servations  on the formation  of chyme.  It  is necessary, in inves-
tigating this subject, to attend  to the following  points; first, to
the circumstances in  which the aliments, contained in the sto-
mach, are found to exist;  and,  second, to the chemical nature of
these substances.  The circumstances in which the  aliments are
placed, during the time they remain in the stomach, which re-
quire to be noticed, are few in  number. F"irst, they experience
a pressure, more  or less strong, of the abdominal walls, and of
those of the stomach; second, they are affected  by the motions of
respiration; third, they are exposed  to a  temperature of  from
98° to 104°; fourth, they are exposed to the  action  of the  sali-
va, mucus of the mouth, cesophagus, and  mucous membrane of
the stomach.   This fluid  is slightly  viscid, but it consists  of a
considerable proportion of water, of  mucus, of salts, the base of
which is soda  and ammonia, and of the lactic acid of Berzelius.
   With respect to the  nature of the aliments, we  have already
seen how variable they are, inasmuch as all  the  immediate prin-
ciples of animals and vegetables, may be carried to  the stomach,
in different forms and proportions, for the formation of the chyme.
Can we, therefore, when we take into  consideration the nature
of the aliments, and  the  circumstances under  which they are
placed in  the stomach, account for  the phenomena which are
known to accompany the formation of the chyme? The  particu-
lar temperature, the pressure,  and the agitation which the ali-
ments undergo, cannot be considered as essential  causes  of its
transformation into chyme; it is probable that they merely assist 
OF  PHYSIOLOGY.
221
in the production of this effect.  There  remain, therefore, the ac-
tion of the saliva, and of the peculiar fluid secreted by  the sto-
mach.   But, from the known properties of the saliva, it is incre-
dible that it can attack  and change  the nature  of the aliments,
though it may serve the purpose of diminishing the cohesion of
their particles.  We must,  therefore, attribute  this remarkable
effect, to the fluid formed by the internal membrane  of the sto-
mach.   It appears, then,  that  this is  the agent which, acting
chemically on the alimentary substances, dissolves them from the
surface towards the centre.
   To establish, incontrovertibly, this point, it has been attempted
to produce what has been called, since the time  of Reaumur and
Spallanzani, artificial digestion.  For this purpose, after having
masticated the food, it has been mixed with the gastric juice, and
afterwards exposed in a tube, or  other  vessel, to the same tem-
perature as that  of the  stomach.   Spallanzani has asserted that
they succeeded, and that aliments were reduced to chyme.  But
since the  more recent researches  of  M. Montegre, it appears to
be shewn that this is not the  case, but, on the contrary, that the
substances employed, did not  undergo  any alteration, at all ana-
logous to  that of chymification, which agrees with the experiments
of Reaumur.  But even if the gastric juice does not dissolve the
aliments with which it is enclosed in a tube, we cannot  therefore
conclude, with some, that this fluid does not dissolve the aliment,
when it is introduced  into  the stomach.  The circumstances are
far from  being  the same.   In the stomach, the temperature is
equal;  the aliment pressed and agitated; the saliva and gastric
juice renewed continually; and, as soon as the chyme is formed,
it is forced into the duodenum.  There is nothing of all this takes
place, when the aliment is placed in a tube, or a vessel, and then
mixed  with the gastric juice.  The want of success, therefore, in
artificial digestion, proves  nothing, with respect to  the formation
of chyme.
   How then, it may be asked, can the  same fluid act in a similar-
 manner upon a  great  number of different substances, varying
 essentially from each  other?  The  character of acidity which
 enables it to act upon albumen, for example, would seem to render
 it incapable of dissolving fatty substances.  But to  this it may
 be replied, that  it has  not  been proved that the gastric juice is 
222                    A  SUMMARY
always the same.  The small number of analyses which have been
made, prove, on the contrary, that its properties  vary consider-
ably.  It is possible, that the contact of different aliments with
the mucous membrane of the stomach may have an influence upon
its composition; it is certain, at any rate, that it differs in differ-
ent animals.   That of man, for example, is incapable of attack-
ing  the  tissue of the bones, while the dog digests these  sub-
stances perfectly.*  In general, the action by which the chyme is
formed,  prevents the  reaction of the  constituent  elements of
the food  upon each other; but this is only true when the digestion
is good.  It is found, when the powers of digestion are impaired,
that fermentation, or even putrefaction, may take place.   There
seems reason to believe, that the great quantity of inodorous gas,
which is  thrown off, in some cases, and the sulphuretted hydrogen
which is  disengaged in others, is attributable to this cause.
  For a  long time  the nerves of  the eighth pair have been  sup-
posed to  preside over the act of  chymification.  If, indeed, we
divide these nerves  at the  neck, the substances introduced into
the stomach undergo no further alteration.  The inferences, how-
ever, which have been drawn  from this fact, do  not  seem to be
strictly just.   May we  not  confound  the effects of deranged
respiration  upon the action of  the stomach, with the direct influ-
ence  of  the section of the  nerves of the eighth pair upon this
organ?   I am tempted to believe that this is the case; for if we
divide the  eighth pair of nerves in the  thorax, below where the
branches are given off to the lungs, the aliment which is after-
wards introduced into the  stomach, is  transformed  into  chyme,
and  furnishes  abundant chyle.  Some  persons have supposed,
that electricity has some influence in the  production of  chyme,
and that the nerves, of which we have been speaking, act as con-
ductors.  There  is no positive fact to justify this conjecture.!  A
more probable use of the nerves of the eighth pair is, that they
establish  intimate relations  between the stomach and the brain,
by which the  presence of injurious substances in the aliment is
indicated.

  * We should be careful, however, lest we admit too much as respects those
conjectured variations of the animal fluids. The more perfect the science of
chemical analysis becomes, the more constant we find the composition of vegeta-
ble and animal substances are found to be.
  t Vide Appendix. 
OF  PHYSIOLOGY.
223
  In a person whose health is good, the formation of the chyme
takes place without his being conscious of it; he only percieves
that the sense of fullness, and slow respiration,  produced by the
distention of the stomach, by degrees, disappear.  But in persons
of a delicate constitution,  digestion is very frequently accompa-
nied with an indisposition to mental effort, and a general sense of
cold, with slight chills, and drowsiness.   It has been said, that the
vital powers, at this time, are concentrated upon this organ, and
that there is a temporary neglect of the rest.  To these general
effects, may be added the production of gas, which escapes by the
mouth, a sensation of weight,  warmth,  dizziness, and at other
times of  burning about the stomach, with a similar sensation along
the cesophagus,  &c.  These effects are particularly  felt towards
the termination  of chymification, but it is not always found that
slow digestion is attended with injurious effects.

                 Action of the  small intestine.
  This is the longest  portion of the canal, and establishes a com-
munication between the stomach and large intestine.  It is inca-
pable of  great distention, has numerous convolutions, and is very
long.   It is attached to the vertebral column by a fold of the peri-
toneum,  which allows of free motion, but at the  same time limits
it.  Its longitudinal and circular fibres are not separated, as in the
stomach; its mucous membrane, which presents  numerous villosi-
ties, and a large  number of mucous follicles,  forms  folds, irregu-
larly circular, the number of which increases, as we examine the
intestines, near the pyloric orifice;  these folds are called valvulce
conniventes.  The  small intestines are  very  vascular;  and their
nerves arise from ganglions of  the  great sympathetic.   The lac-
teal vessels open upon its internal  surface by very numerous ori-
fices.
  This intestine has been divided into three parts, which are dis-
tinguished by the names of duodenum, jejunum, and  ileum; a
distinction  but  of little use in physiology.  Like the mucous
membrane of the stomach, the  small  intestines  secrete an abun-
dance of mucus; I do not  think it has  ever  been analysed.    I
have found it to be viscid, of a saltish taste, and to change the ve-
getable purple colours red; all the properties which we have before
noticed in the fluid secreted by the  stomach.   Haller gave to tl:U 
224
A  SUMMARY
fluid, the name of intestinal juice;  it has been estimated, that
eight pounds of this fluid  is formed in twenty-four hours.  At a
short distance from the pyloric orifice of the stomach, is found the
common orifice of the biliary ducts, and the pancreatic duct, by
which the fluids secreted  by the liver and  spleen, pass into the
cavity of the intestine.  If the formation of the chyme is still a
mystery, the nature of the  phenomena which  take place in the
small intestines, is by  no means better  understood.   We shall
confine ourselves still to the plan which we  have adopted; that is,
we  shall content ourselves with describing what observation has
proved to us.  We shall  first  speak of  the introduction of the
chyme into the small intestines, and afterwards of the alterations
which it undergoes there.

Accumulation, and  Passage of the  Chyme into  the  Small
                         Intestines.
  I  have  often had occasion  to observe  in  dogs,  the  chyme
passing from the stomach into the duodenum.  The following are
the phenomena which  I have remarked.   At intervals, more or
less remote, we see a contractile motion take  place towards the
middle of the duodenum;  this is rapidly propagated towards the
pylorus; this ring, itself, contracts, as well  as the pyloric  portion
of the stomach. In consequence of this movement, the substances
contained in the duodenum, are thrust towards the pylorus, where
they are stopped by the valve;  and those which are contained in
the pyloric portion of the stomach are forced towards the cardiac.
But this  motion directing the  intestine  towards  the stomach, is
soon replaced by a motion in the opposite direction; which is pro-
pagated from the  stomach, towards  the duodenum,  and which
forces from  the pylorus, a certain quantity  of chyme.  It  appears
to me then,  that the valve of the pylorus serves the purpose, both
of preventing the  substances contained  in the small  intestines
from flowing "back  into the  stomach, and  also, of retaining the
chyme and the aliments in the cavity ot this organ.
  This motion  is repeated, generally, several times in  succession,
varying in the frequency and intensity of the contractions; after
which it ceases for some time.  It is not very distinctly marked,
when the formation of the chyme begins, as the extremity only of
the pyloric portion partakes  in it.   It augments as the stomach 
OF PHYSIOLOGY.
225
becomes emptv, and, towards the end  of chymification, I  have
frequently seen the whole of this organ partake in the action.  I
have ascertained that this motion is not suspended by the division
of the nerves of the eighth  pair.  When the chyme has entered
into the small  intestines, the motion ceases.  In proportion  as it
is repeated,  the chyme becomes  accumulated in the first  portion
of the small intestines,  it distends a little their walls, spreading
itself over the intervals of the valvula? conniventes. Its presence
soon excites the organ to contract, and, by this means, a part is
thrown further into the intestine, and the rest remains  attached to
the surface  of the membrane,  and  takes soon after the  same
direction.  The same phenomenon is continued into the large in-
testines; but as the duodenum receives new portions of chyme, at
a certain  period in the process, the small intestines are filled with
this matter through their whole extent.  We  observe, however,
that it is  much less abundant in  the neighbourhood of  the ccecum,
than at the  extremity of the pylorus.
  The motion which  impels the chyme  through the small intes-
tines, has a very great analogy  with  that of the pylorus   It is
irregular, returns after unequal periods, is made sometimes in one
way, and  sometimes another; and is manifest often in several
parts at the same time. It is always slow, and alters the relations
of the intestinal circumvolutions, and it is entirely free from the
control of the will.  We should form very incorrect ideas on this
suoject, if we confined ourselves to the examination of the small
intestines in an animal recently  killed  It displays  then a degree
of activity far greater than  during life.   But in persons with im-
paired digestion, it acquires an activity and energy  not generally
observed during health.  Whatever may be the manner in which
this motion  is executed, the progress of the chyme  through the
small intestines is very slow; the numerous valves already noticed,
the many asperities  projecting  from  the surface of the mucous
membrane, and the multiplied  curvatures of the canal, must all
have  the effect of retarding  its  progress, but must  favour its
admixture with  the  fluids  contained in  the  intestine, and the
production of the chyle which results from it.
29 
4Hb
A  SUMMARY
Change  which the Chyme undergoes in the Small  Intestines.
  The chyme is not changed in its sensible properties until it ar-
rives at the orifice of the  ductus  communis choledochus, and the
excretory duct of the pancreas. Thus far, it preserves its colour,
semi-fluid consistence, sharp odour, and slightly acid taste; but
on being mixed with  the bile and pancreatic juice, it acquires new
characters.  Its colour becomes yellowish, its tnste bitter, and its
sharp odour  essentially diminished.  If it  consist of animal or
vegetable substances, containing  oil, there will be seen  to form,
here and there upon its surface, irregular filaments, flattened or
rounded, which attach themselves to the surface of the valvular?
conniventes, and appear to be imperfectly formed chyle. VVe do not
remark this, when the chyme consists of aliments which do not con-
tain oil.  There is also, a greyish  coat, that adheres to the mucous
membrane, which appears to  be  the elements of the chyle.  The
same phenomena are observed in the two superior thirds of the
small intestines; but in  the  inferior third, the chyme acquires  a
greater degree of consistence; its yellow colour assumes a deeper
tint; and it  often becomes, at last, of  a greenish  brown, which
pierces through the intestinal walls, and gives  to the ilium an ap-
pearance different from the  duodenum  and jejunum; when the
ccecum is examined,  we  find small whitish strise; these appear to
be nothing more than the residue of the substances which have
served for the formation of the chyle.
   From what has been said  of the varieties which the chyme ex-
hibits, it will be perceived, that the changes, which it undergoes in
the small  intestines, must vary, according to  its properties.  In-
deed, the phenomena of digestion in the small  intestines  vary,
with the nature of the aliment.*  The chyme, however, preserves
its acid property, and if it should happen to contain fragments of
aliments, or  other substances which have resisted the action of
the stomach, these pass through  the small intestines without un-
dergoing any  change.  The same phenomena take place, when
the same  substances are employed.  I  have recently satisfied
myself of this, by examining the  bodies of two criminals, who,

  * We have made many experiments on this subject, but it would have been
improper to hare detailed them in a work professedly elementary. 
OF  PHYSIOLOGY.
227
 two hours before  their execution, had  eaten  the  same food in
 nearly equal quantities. The substances contained in the stomach,
 the chyme in its pyloric portion, and  in the small  intestines, ap-
 peared to me precisely similar in colour, taste, and odour, &c.
   It is rare that we do not meet with  gas in the small intestines,
 during the fermentation of the chyle.  M. Jurine, of Geneva, was
 the first person who examined this  subject with  attention, and
 pointed  out the nature of the gases;  but at the  period that this
 learned physician  wrote, eudiometrical  processes  were far from
 having acquired the degree of perfection, at which  they  have
 since arrived.   I was, therefore, induced to make some new ex-
 periments on this interesting subject.  M. Chevreul assisted me
 in executing this undertaking.  Our experiments were made on
 the bodies of  two criminals, opened a  short time  after death, and
 who, having been young and vigorous, were extremely favourable
 to these researches.  In one, twenty-four years of  age, who had
 eaten two hours before execution, bread and cheese, and drank red
 wine, we found in the small intestines,
                    Carbonic acid,   24.39
                    Hydrogen,       55.53
                    Azote,          20.08
                         Total,    100.00
  In a second subject twenty-three years of age, who had eaten
 of the same food, at the same time, and who had been executed
 at the same time; we found,
                    Carbonic Acid,   40.00
                    Hydrogen,       51.15
                    Azote,          8.85
                        Total,    100.00
  In a third experiment, made upon a young  man twenty-eight
years of  age, and who had eaten four  hours before  his execution,
bread and beef, and lentils, and drank  red wine,  we found in the
small intestines,
                    Carbonic Acid,   25.00
                    Hydrogen,       8.40
                   Azote,           66.6Q
                        Total,    100.00
  We never have observed any other  gas in the small intestines.
This gas may be produced in various  ways; it may either come 
228
A  SUMMARY
from the stomach, with the chyme, or it may be secreted  by the
mucous membrane of the intestine,  or it may be produced by the
reciprocal action of the substances contained in the intestine, or
perhaps, it may arise from all these three causes combined.  The
stomach, however, contains oxygen, with  very little hydrogen;
while in  the small intestines,  we have uniformly met with a con-
siderable portion of hydrogen, but no oxygen.   Daily observation
shews also, that  whenever the stomach contains gas,  it is dis-
charged  by the mouth, towards  the  end of chymification, pro-
bably, because at this time, it most readily passes into the cesopha-
gus.  The secretion of gas by  the mucous membrane, is not known
to take place, except carbonic acid gas, which appears to be form-
ed in this manner, during respiration.
   With  respect to the reciprocal  action of the substances con-
tained in this intestine; I have often observed air bubbles to es-
cape rapidly from the chyme.  This phenomenon has taken place
from the orifice of the ductus communis chotedochus, to  the com-
mencement of the ilium, but no trace of it can  be perceived in
this intestine, nor in the  superior part of the duodenum, or sto-
mach.   1 have made this observation on the body of a  criminal,
four hours after death; it did not present any trace of  putrefac-
tion.  The  alteration that the chyme undergoes  in the  small  in-
testines, is  unknown; it is evident, that it is the result of the ac-
tion of the bile, pancreatic juice, and of the fluid secreted by the
mucous membrane; but what  is the  precise nature of the affinities
exerted  in this operation, which may be considered truly chem-
ical, and how the chyle comes to be precipitated upon the surface
of the valvula? conniventes, whiie the surplus  remains  in the in-
testine,  to be at  last thrown out of the system; is a question of
which we are  completely ignorant.  We know but little of the
time required for the chyme to be sufficiently altered; but it does
not take place very rapidly.   In animals, three or four hours af-
ter eating, it often happens that we do not find that the formation
of the chyle has taken place.
   From  what has been  said,  it will be seen;  that the  chyme in
the small intestines, is  divided into two parts.  The one is at-
tached to the  walls, and  is the chyle in an imperfect state; the
other is destined to be pushed into the large intestines, and at.last 
OF PHYSIOLOGY.
229
entirely rejected.  Thus is accomplished, that most  important
part of digestion, the production of chyle.

                Action of the large Intestines.
  This organ is of considerable extent; it is divided into caecum,
colon, and rectum.   The coecum is situated in the right  iliac  re-
gion, and is connected  with the small intestines.  The colon is
subdivided  into an ascending portion, which  extends from the
coecum to the right hypochondrium,  a transverse portion, which
passes horizontally, from the right to the left hypochondrium, and
a descending portion, which is  prolonged  to the cavity  of  the
pelvis.  The rectum  is  very  short; it begins  where the colon
finishes,  and terminates in the anus.
  The large intestine is bound down  by folds of the peritoneum;
disposed so as to allow of variations in its volume.   Its muscular
coat has  a peculiar arrangement.   Its longitudinal  fibres form
three narrow bands, very distant  from  each other when the in-
testine is dilated.   Its circular fibres, also, are formed  into bands,
much more numerous, but also  separated.  The result is, that
at  a great number of points, the intestine  is only formed by the
peritoneum and the mucous membrane.   These places are gene-
rally arranged  into distinct cavities, where  the fecal matter accu-
mulates.   The  rectum alone, does not exhibit this structure, its
muscular coat  is very thick and uniform, and appears  to contract
with great energy.
   The mucous membrane of the large intestine is  not, like the
small intestine, covered  with villi, but is, on the contrary, smooth,
its colour of a pale red, and we find on  it  but few follicles.   At
the place of its junction with the small intestines, there is found
in  the coecum,  a valve, evidently intended to allow substances to
pass into this intestine, but to prevent their return into the small
intestine; there are few arteries and  veins distributed to this or-
gan; the same remark also applies to the nerves and lymphatics.

Accumulation and Passage of the  Fecal Matter into the large
                          Intestines.
    By the contraction of the inferior portion of the ilium, the mat-
ter contained in it is made to pass into the coecum.  This motion
is  very irregular, and returns at distant  intervals.  It is seldom 
'280                    A  SUMMARY
remarked in living animals, but may be frequently seen in those
which are killed suddenly.  It does not, in any way, resemble the
action of the pylorus.  In proportion as this motion is  repeated,
the matter contained  in  the  ilium  becomes accumulated in the
coecum. It cannot return into the small intestines, in consequence
of the valve  of the coecum, and  can only pass through  the open-
ing which communicates with  the  colon.  Having once passed
into the coecum, it receives the  following names; fecal, or sterco-
racious matter, feces, and  excrement, &c.   After  remaining
sometime in  the coecum, the fecal matter passes into the colon, and
traverses, successively, its different  portions, sometimes forming
one continued  mass, and sometimes forming distinct masses, which
fill one or more of the cavities that the intestine presents, through
its whole  length.
   The progress of the fecal matter \s, almost always, very slow, it
is effected by the contraction of its muscular fibres, and  the pres-
sure which the intestine  suffers, as one of the abdominal viscera;
and it  is  favoured, also, by the mucous  secretion of  its internal
membrane.  Having arrived  at  the  rectum, the matter accumu-
lated there distends its walls, and forms, often, a mass of several
pounds; it cannot pass  beyond this, as  the  anus  is habitually
closed  by the contraction of the two sphincter muscles.  The con-
sistence of the feces in the large intestine is very variable, but, in
a person in good health, it is always greater than in the small in-
testines.  Generally,  its consistence increases as it  approaches
the rectum, but it is made softer by the fluids which the mucous
membrane secretes.

     Changes of the  Fecal Matter in the large Intestines.
   Before  penetrating into the  large intestine, this matter  does
not exhibit the foetid  odour,  peculiar to the human  excrement.
But it contracts  this  odour,  however short the  time  it remains
there.  Its colour, a  brownish yellow,  becomes also  deeper, but
with respect to  consistence,  odour,  colour, &c.  there are many
varieties,  according to  the nature  of the food, the  manner  in
which chymification and  chylification have been performed, and
the peculiar  constitution  of the  individual; there is found in the
excrement all those substances,  which have not been changed by
the action of  the stomach.  Many celebrated  chemists have 
OF PHYSIOLOGY.
231
analysed the human feces. M. Berzelius found them composed of,
     V\ ater,                                         73.3
     Vegetable and animal remains,                    7.0
     Bile,                                            0.9
     Albumen,                                        0*9
     Peculiar extractive matter,                       2.7
     Matter formed from bile, resin, animal matter, &c. 14.0
     Salts,                                          _2£
         Total,                                     100.0
   These analysis, made with the intention of throwing light on
the mysterious nature of digestion, afford us but feeble assistance.
In order to give us  any considerable  advantage,  it would be ne-
cessary to have the circumstances  very  much varied, to know
exactly  the nature and quantity of  food that had been used, to
keep in  view the constitution of  the  individual,  and to analyse
only the feces  which had been  formed from very simple alimenta-
ry substances.  But an undertaking of this kind supposes a de-
gree of perfection in our means of analysis, at which  animal che-
mistry has not yet arrived.
   There exists also in the  large intestine, gases,  enclosed with
the  fecal matter.  M. Jurine long  since determined their nature,
but  he has only made  one satisfactory experiment on this.subject.
In the large intestine of a drunken person, found  frozen to death,
and opened as soon as convenient, he ascertained the existence of
azote, carbonic acid, carburetted and sulphuretted hydrogen.  M.
Chevreul  and myself, examined with care, die gas found in the
large intestine of those criminals of whom we have before spoken.
 In the  subject of the  experiment  first cited, the large intestine
 was found to contain in a hundred  parts of gas,
Carbonic acid,	43.50
Hydrogen carbon, and some traces of sulphuretted hydr»gen, Azote,	5.47 51.03
Total,	100.00
  The subject of the  second experiment, exhibited, in the same
intestine,
       Carbonic acid,                         70.00
       Hydrogen, and carburetted hydrogen,   11.06
       •Vzote,                                18.94
           Total,                           ino.on 
232
A  SUMMARY
In the subject of the third experiment,	we analysed separately
the gas found in the coecum and the rectu	m,the following are the
results:	
Coecum.	
Carbonic acid,	12.50
Hydrogen,	7.50
Carburetted hydrogen,	12.50
Azote,	67.50
Total,	100.00
Rectum.	
Carbonic acid,	42.86
Carburetted hydrogen,	11.18
Azote,	45.96
Total,	100.00
   Some traces of sulphuretted hydrogen were manifested before
this gas was analysed.
   These results, which may be depended on, inasmuch as every
precaution was taken to prevent error, agree very well with those
that had been  made long before by M. Jurine;  but they invalidate
his assertion respecting the carbonic  acid, the quantity  of which,
according to this physician, diminished from  the stomach to the
rectum; but we see on  the contrary,  that the proportion of this
acid increases as you go from the  stomach.  The  same doubts
that we expressed respecting the origin of the gas in the small in-
testines, may  be applied to that produced in the large.    Is  it
received from the small intestine, or is it secreted  by the mu-
cous  membrane, or  formed by the reaction  of  the constituent
principles of the fecal  matter, or does it arise from this  triple
source?  It is not easy to remove these doubts.
   We may however, remark, that this gas differs from that in the
small intestines. In these last, hydrogen predominates, while in
the large intestines it does not exist, but instead of it, carburetted
and sulphuretted hydrogen.
   I have seen  besides, frequently, gas passing out in the form of
innumerable small bubbles,  from the  substance  contained in the
large intestine.
   From what has been said, we may  conclude, that  the action of
the large intestine is  of little importance in the production of the
chyle.  It fulfils, sufficiently well, the office  of a reservoir, where 
OF  PHYSIOLOGY.
233
are deposited for a  certain time, the residue of the chemical ope-
ration of digestion,  fo be  afterwards  expelled.  I conceive the"
digestion is completely effected without the large intestines taking
any part in  it.  Nature  presents this disposition in those  indivi-
duals, with an artificial anus,  which passes out at the coecal ex-
tremity of the small intestine, and from  which those substances
escape that have assisted in the formation of the chyme.

              Expulsion  of the  Fecal Matter.
  The principal agents in  the expulsion of the fecal matter, are
the diaphragm and abdominal  muscles; the colon and rectum co-
operate, but  generally speaking, not in a very efficient manner.
As long as the fecal matter is  not accumulated in the large intes-
tines, especially in  the rectum, we  are not conscious of its exis-
tence;  but when it  is collected in this part, in considerable quan*
tity, it distends the rectum and  produces a vague  sensation of
fulness and uneasiness, over the whole abdomen.  This sensation
is soon replaced by another, much  more vivid, which gives us no-
tice of the necessity of voiding the  fecal matter.   If this notice be
neglected, it  often  ceases for a considerable time; at others, the
sensation is too urgent to be resisted, and the excrement must be
discharged,  notwithstanding all our efforts to  prevent  it.  The
consistence of the fecal matter has an  influence upon the vivacity
of this sensation.   It is almost impossible to resist it, if the fecal
matter be very fluid, but  it is easily overcome  when the contents
of the rectum are hard.
  There is nothing easier to comprehend  than  the mechanism of
the expulsion of the excrement.   In  order that  this  may be ef-
fected, all that is required is, that  the fecal matter accumulated
in the rectum, should be forced forward with a force superior to
the resistance which the muscles of the anus present.  The con-
traction of the rectum alone, cannot produce this effect, notwith-
standing the  great thickness of its muscular coat, it is necessary
that some other power should co-operate.  'This is effected partly
by the diaphragm, which acts directly from above, downwards, upon
the whole mass of the abdominal viscera, and  by the abdominal
muscles which  press them  against  the vertebral  column.   From
these forces combined,  there results a  considerable pressure,
which  forces forward tho stercoracious  matter collected  in the,
                              30 
#34
A  SUMMARY
rectum;  the resistance of the spincters  is overcome; they relax,
and the  matter contained in the rectum is  voided  by the anus.
But as the cavity of the rectum is much more spacious  than the
opening of the anus, which has a constant  tendency  to contract,
the matter passing out through this opening will be moulded to
its size and form.   It will pass the more readily when its consis-
tence  is little, but when the reverse is the case,  great  force is
required to expel it. W hen it is very fluid, the contraction of the
rectum alone, seems sufficient for this purpose.
  A phenomenon analogous to  what we have noticed in  the ceso-
phagus,  has  been observed  in  the rectum by M. Halle.  This
learned professor has remarked, that during  the efforts to void the
fecal matter, the  internal membrane of the rectum is dispaced
and forced down, so as to form a sort of hood near the anus. This
effect must, in a great measure, be produced by the  contraction of
the circular fibres of the rectum.
  The desire of voiding the excrement, returns after  different
intervals, according to the quantity and nature of the  aliments
employed,  and the constitution  of the individual; generally it
doeshot  take place until after several consecutive meals.  In some
persons, it takes place once or twice in the twenty-four hours; but
in others, who  still enjoy health, this  evacuation does  not take
place oftener than once in ten  or nvelve days-   Habit is  one of
the causes  which  have most influence on the regular return of the
excretion'of the fecal matter.  When this habit  is  established, it
returns with great exactness at the same hour.  Many persons,
particularly females, are compelled to have recourse to artificial
means, as enemata, &c. to assist them in performing this function.
  The expulsion of the gas is not periodical. Its progress is much
more rapid and irregular.   Its displacement  being very easy, it
arrives very  soon at the anus, by the  peristaltic motion  of the
large intestine only. It is, however, often necessary for the abdo-
minal walls to contract, in order to expel it.   But  the expulsion
of gas per  anum, is neither regular, nor constant.  In many per-
sons, this but  rarely takes  place, while in  others, it is very fre-
quent.   The  use  of certain aliments, has an influence upon  its
formation; its production, to any considerable extent, is considered
as indicating a bad digestion. 
OF  PHYSIOLOGY.
235
   With the expulsion of the fecal matter, this complex function,
the end of which is the formation of the chyle, is accomplished.
But we  should  have fulfilled  our  task very imperfectly, if, ac-
cording to the example of many distinguished authors, we should
limit  ourselves to treat of the digestion  of  aliments.  There is
another consideration which presents itself, for our  investigation;
this is liquid aliments, or drinks.

                 Of  the Digestion of Drinks.
   It is very remarkable, that though physiologists  have  devoted
much  time  to investigating the digestion of soliij aliments, have
invented systems to explain  it, and experiments to illustrate it;
yet they have  never given any attention to the digestion of drinks;
although the subject  presents  less apparent  difficulty.   Drinks
are generally much more simple than  solid aliments, and are for
the most part nourishing, and easily digested.  The circumstance
that we digest drinks; should have been considered alone, suffici-
ent for rejecting the systems of trituration and  maceration.  In-
deed, we see that  drinks can neither  be bruised, nor macerated,
though they remove hunger, restore vigour, and in a word,nourish
the body.

                Of the Prehension of Drinks.
   The prehension of  drinks may be executed in a variety of ways,
but Petit has shown  that they may  be referred to  two principal
modes.  In the  first,  we pour the  drink into the mouth, which is
effected by  the specific gravity of  the  fluid.   A familiar instance
of this take* place, when we raise the glass to our lips, place  them
in contact with the vessel, and pour the fluid into the mouth.  In
the second mode, we  cause a vacuum to take  place in the cavity of
the  mouth, the  pressure of the atmosphere, at  the same  time,
forcing the fluids to penetrate into it, as for example, in the act of
sipping or sucking.   When we intend to a sip a fluid, it is exe-
cuted in the following manner; the mouth is applied to the surface
of the fluid, we  then  enlarge the chest, by which the pressure of
the atmosphere upon  the portion of the surface of the fluid inter-
cepted by the lips is  diminished, and the fluid therefore, rises into
the place of the air which has been drawn from the  mouth. 
236
A  SUMMARY
  In the act of sucking, the mouth  resembles an air pump, the
opening of which is formed by the lips, the body by  the cheeks,
palate, &c; and  the piston by the tongue.   We apply  the lips
accurately about the body, from which we intend to  extract the
fluid, the tongue  being also in  contact with  it; the tongue then
contracts itself, by which it is carried backwards, and  its volume
diminished; a vacuum is thus formed between its superior surface
and  the p.ilate; the fluid contained  in the body which we  suck,
being  compressed  unequally  by the atmosphere, is displaced,
and  fills the mouth.  Neither mastication, nor  saliva being  re-
quired for the .digestion of drinks, it  is  not necessary that they
should remain  long in the mouth; they are, therefore, swallowed
as soon as they are received.  They undergo no other change in
passing through this cavity, but that of temperature.   If, however,
the taste be strong or disagreeable, or, if  finding it agreeable, we
are desirous of prolonging the pleasure, the presence  of drink in
the mouth, then causes a discharge of saliva to take place, which
is mixed with the fluid.

               Of the Deglutition of Drinks.
  We swallow fluid in the same manner as solid aliments; but as
fluids glide more easily over the mucous membrane of the palate,
tongue, and  pharynx, and as they yield  readily to the  slightest
pressure, they  therefore possess  all the  qualities  which are re-
quired for passing rapidly through the pharynx, and are generally
swallowed with much less difficulty than  solid aliments.  I know
not why the contrary opinion is so generally spread abroad.   It is
supposed  that the particles of  fluids, having a constant tendency
to separate, must present  a greater degree  of resistance to the
action of the organs of deglutition; but daily experience disproves
this assertion.
   Any one may easily prove upon himself, that it is easier to
swallow fluid  than solid  aliments, even after they have been
fully-masticated, and impregnated by the saliva.*   We may call
the portion of  aliment, swallowed during each motion of degluti-
tion, a morsel.  These vary much in volume, but however large

  * We may remark, that in severe inflammations of the throat, persons are only
able to swallow fluids.. 
OF  PHYSIOLOGY.                  237
they may be, when they consist of fluids, they accommodate them-
se\es readily, to the form  of the  pharynx and  oesophagus,  and
therefore never produce any painful distension of these passages,
as is often observed to take place  from  solid aliments.   In the
common method of drinking, the deglutition of fluids exhibits the
three stages, of  which we have before spoken, except when the
fluid is poured directly into the mouth.

Of the Accumulation  of Drinks  in the Stomach, and  of the
                   time they remain there.
   They differ little  in this  respect from solid 'aliments.  Their
action is generally more prompt, more equal, and easier, probably
because the fluids spread  themselves, arid  distend  the stomach
more uniformly.  Like the solid aliments, they occupy more par-
ticularly the left and middle portion of the stomach, the right, or
pyloricportion, seldom containing  much  fluid.   The  distension
of the stomach by fluid, cannot be carried suddenly, to a great ex-
tent, because it will be rejected by  vomiting.   This accident
frequently happens  to  persons  who swallow, in  a short  period,
a  large quantity of drink.   When  a person who  has taken  an
emetic, wishes  to hasten vomiting, there is no  better method of
effecting  this, than  by swallowing  suddenly several glasses of
fluid.  The presence of drink  in  the stomach  produces  effects,
similar to those  which we have  described  under the article, Ac-
cumulation of  Aliments.  The same  changes in  the form and
position of the organ, the  same distension  of the abdomen, the
same obstruction of the pylorus, and contraction  of the cesopha-
gus are observed in both.
   The general  phenomena are different  from  those  which are
produced  by  the solid  aliments.  This  arises  from  the action
of the  fluids  upon  the walls  of the stomach,  and  the  promp-
titude with which they are carried into  the blood.  The fluids
 passing more rapidly through the mouth and oesophagus, than the
 solid food, preserve more perfectly  their original  temperature,
 when they arrive  in the stomach.   It arises from this, that  we
 prefer fluids, when we wish to produce in this organ a sensation
 of heat or cold; and  it is for this reason, that we give a preference
in winter  to warm  drinks, and in  summer to  cold ones.  It is
 well  known,  that  drinks remain a much shorter time in the 
238
A  SUMMARY
stomach, than the solid aliments, but the mode in which they pass
out from this viscus, is but imperfectly understood.  It is gener-
ally believed, that  they traverse  the  pylorus  and pass into the
small intestines, from which  they are absorbed with the chyle.
When a ligature, however, is passed around the pylorus, so as to
prevent their passing into the duodenum, it does not essentially
retard their  disappearance from this cavity.   We shall insist
more on this important point, when we come to  speak  of the ab-
sorption of drinks.

            Alteration of Drinks  in the Stomach.
  In  this respect, drinks may be divided into two classes; first,
those which do not form chyme; and,  second, those which are ca-
pable of being either wholly, or partially converted into this sub-
stance.  To the  first class may be referred pure  water, alcohol
sufficiently diluted  to be considered as a drink, and the vegetable
acids, &c.   Wrhen  water is  received  into  the stomach, its tem-
perature soon becomes  equalized with that of the surrounding vis-
cera; and, at the  same time, it becomes mixed with the mucus, sali-
va, and gastric juice, which are found in this organ, by which it
becomes turbid, and  soon disappears,  without undergoing any
perceptible change; it partly passes into the small intestines, and
is, in part, directly absorbed.   After  its disappearance, there re-
mains a certain  quantity  of  mucus, which  is soon  reduced into
chyme.  We know from  observation, that  water  deprived of at-
mospheric air, as distilled water, or when it is charged with con-
siderable quantities of salts, as  well  water, remains long in the
stomach, producing there a sensation of weight.   Alcohol acts  in
a very different manner.  We at first perceive  a sensation of
warmth, which it impresses as it passes along the mouth, pharynx,
and cesophagus,  which it likewise excites in the stomach, as soon
as it  arrives there.   The effects of this action are to contract the
organ, to irritate the mucous membrane, and augment the secre-
tions of which it is the seat; at the same time, it coagulates all the
albuminous parts of the  alimentary  substances with  which it is
in contact; and, as the different fluids  which are found  in the
stomach, contain a large quantity  of this  matter, the result  is,
that, in a short time after we have  swallowed alcohol, there is,  in
this viscus, a large  quantity  of concreted albumen.  The mucus 
                     OF PHYSIOLOGY.                 23$

undergoes a modification analagous to that of the albumen; it be-
comes hard, and forms irregular elastic filaments, which preserve
a slight degree of transparency.
  In  producing these phenomena,  the alcohol becomes mixed
with the  water contained in the saliva and gastric juice; it dis-
solves, probably, a  part  of the elements which  enter into their
composition, so that it  must become weakened by remaining in
the stomach.   Its  disappearance is  extremely sudden, and  its
general effects are also very rapid, drunkenness or death follow-
ing, almost immediately, the  introduction of a large quantity of
alcohol  into the stomach.  The substances which have been  co-
agulated  by the action of the alcohol  are, after its disappearance,
digested  like solid aliments.
  Among the drinks which are reduced into  chyme, some  are
only changed in part, while others are entirely  transformed into
this substance;  oil is an example of this; it is changed in the  py-
loric portion of the stomach into a substance very analogous to
that which is obtained  after the purification of oils  by the sul-
phuric acid;—this substance is  evidently the chyme  of  oil.  In
consequence of this transformation, oil remains, perhaps, longer
than any other fluid in the stomach.
  It is well known that milk becomes coagulated, shortly after it
is swallowed.   This coagulum  is then a solid aliment, which is
digested  in the  ordinary  way.   Milk  and water can only be con-
sidered as a drink.   The greater number of drinks which we use,
are formed ol water, or alcohol, in which are suspended, or held
in solution, the immediate  principles  of animals and vegetables;
as gelatin, albumen, osmazome, sugar, gum, feecula, and colouring,
or astringent substances.  These  drinks contain, salts of  lime,
soda, potash, &c.  By the results of  many experiments which  I
have  made  upon  animals,  and some observations that I  have
collected upon  man, I  have ascertained, that there takes  place
in the stomach, a separation of the water, or alcohol, from  those
substances which these fluids  held  in solution.   These  last  re-
main in the stomach, where  they are transformed into chyme,
like aliments, while the alcohol, or water, with  which they were
united,  are absorbed, or pass into the small intestines. Those
salts which are held in solution by  the water, do not  abandon
this  fluid, but are absorbed  with it. 
240                   A SUMMARY

  Red wine, for example,  becomes turbid, soon  after it  is swal-
lowed, by its admixture with those secretions which are formed by,
or carried into the stomach.  It soon coagulates the albumen of
these fluids which thus become filled with flocculi; afterwards,
its  colouring  matter, disengaged perhaps, by the mucus and al-
bumen, is deposited upon  the  mucous membrane.   At any rate,
we  see a■ certain quantity  in the  pylorus;  soups  undergo similar
changes; the water which they contain is  absorbed, while the
gelatin, albumen, far, and, probably, the  osmazome, remain in the
stomach, and are reduced  into chyme.

        Action of the Small  Intestines upon   Drinks.
  From what has been said then, it appears that drinks penetrate
into the small  intestines under two different  forms, viz: first, that
of fluid; second, that of chyme.  Except under particular circum-
stances,  the fluids which  pass from  the stomach into  the  intes-
tines, remain but a very short time there.  They do not appear to
undergo any other alteration, except their admixture with the pan-
creatic juice, bile, and other secretions of these organs.  There is
no  chyle formed from them, but they are gentrally absorbed in the
duodenum or commencement of the jejunum, being rarely seen in
the ilium, and still more seldom in the large  intestines.  Indeed
this last circumstance seldom happens, except  in disease, during
the action  of a cathartic, for example.
   The chyme which is formed by drinks follows the same course,
and seems to undergo the same changes as that of the  aliments.
Such are the principal phenomena of the digestion of drinks, and
we perceive the propriety of considering them separately from the
digestion of solid aliments.  But they are not digested separately,
this  vital  operation  is often  carried on, at the same time,  on
both classes  of aliments   Drinks  seem to favor the  digestion
of  solid aliments; it is  probable  that  they produce this effect
in  a variety  of ways.   They  soften  and  dissolve certain ali-
 ments, and aid  in  this  way  their  chymification and  their pas-
 sage through the  pylorus.  Wine  acts in  a similar manner, es-
 pecially on those substances which it  is capable of dissolving;
 it  excites  also by its contact, the mucous membrane of the sto-
 mach, causing an incieased secretion of the gastric juice.  The
 action of alcohol (Strongly resembles that of wine, varying chiefly 
OF  PHYSIOLOGY.
241
in intensity.  The  principal effect  produced by taking  liquors
after dinner, is an increased  excitement of the stomach.

     Remarks upon the  Deglutition of Atmospheric Air.
   Independently of the  faculty of swallowing  fluid, and  solid
aliments,  many  persons  are  capable  of introducing air  into
the stomach by deglutition.   It was long supposed that thi* facul-
ty was  very rare.   M. Gosse, of Geneva, being the only  person,
publicly known,  who possessed this  faculty to any considerable
degree.  I have, however, since ascertained, in a work on this
subject, that it is far from  being uncommon.*  In a hundred
medical  students  I found eight  or  ten  who  possessed  it.  In
the same  work I have shewn, that  we may divide those persons
who are capable of swallowing air into two classes.  Those who
do it with  great facility, and those who only succeed after  great
efforts.   When  persons of the  last description wish to do this,
they in the first nlace expel the air from the chest, as far as possi-
ble;  they then fill the mouth  with air, so as to distend the cheeks,
and  execute deglutition, bringing the chin towards the chest, and
then suddenly drawing it away.  The action is similar to that of
a person wifh a sore throat, who swallows with difficulty.  With
respect to  those persons  who  are  incapable  of  swallowing air,
which consists of a great majority of mankind,  I  may  observe,
that, from exneriments upon myself, and a  great number of medical
students, I have found that, with a little practice, almost any one
can  do this, without great difficulty;  for my own part, I succeed-
ed after trying a few days.   If there should be any good reason
for believing that swallowing air would be useful, as a remedy in
disease,  there can be little  doubt  that patients could be easily
taught to do this.
   In the stomach, the air becomes warmed and rarified, and  soon
distends the organ.   In  some  persons, it excites a sensation of
burning heat, in others it causes a desire  to vomit,  or even sharp
pain.  It is probable that its chemical composition  becomes  al-
tered, but there is nothing positively known on this  subject.   Its
continuance in the stomach is various, generally it returns through
the oesophagus, and  passes out by the mouth.  At other times it

   * Memeir on the deglutition of atmospheric air, read before the Institute.
                              .11 
242
A  SUMMARY
traverses the pylorus, spreads through the whole extent of the in-
testinal canal, and at last  passes out per anum.   In  this last in-
stance, it distends the whole  abdominal cavity, imitating the dis-
ease called ti/mpanites.  I have remarked,  in certain diseases,
that the patients swallowed large quantities  of air without their
appearing to be conscious of  it.  A young physician, a friend of
mine, whose digestion is habitually  bad,  finds considerable relief
from swallowing, occasionally, a mouthful of air.

 Remarks on Regurgitation. Eructation, and  Vomiting, Sfc
  V* e h^ve already seen how the contraction of the  oesophagus
prevents the substances contained in the stomach, and compres-
sed by the abdominal walls, from returning into this canal.   This
however, sometimes takes place, when it receives the names at the
head  of this chapter, according to the extent to  which it may be
carried.   The rejection of all  the  substances  contained  in the
stomach  is  not  effected with equal  facility.  Gas escapes more
readily than liquids, and the  last more easily than solid aliments.
Generally speaking, the more the stomach is distended, the more
easily are its contents rejected by this organ.  When  it contains
gaseous bodies, these necessarily occupy its superior part, and are,
of course, in constant contact with the cardiac  orifice of the sto-
mach. On the slightest relaxation of this  opening, especially when
the stomach is strongly compressed, the gas passes into the oeso-
phagus, and if this tube offer no resistance, it arrives soon at its
superior part, and escapes through the pharynx, causing the edges
ot this opening to vibrate;  this is called  eructation.   It is  proba-
ble, that the oesophagus, by  moving  in  an opposite  direction to
that which is executed in deglutition, assists the  discharge of the
gas through the pharynx.  Wrhen a quantity of vapour or fluid ac-
companies the gas which passes out from the stomach, it is called
card;algia,,or heartburn.  But it is not necessary  that the air dis-
charged in eructation,  should come  directly from  the stomach;
those persons who  possess the faculty of swallowing air, can,
after  it has been forced  through the pharynx, allow it  to return.
   If instead of «as, fluids, or even small masses of solid food, re-
turn from the  stomach  to  the  mouth, this phenomenon may be
called regurgitation.   This  frequently happens in  children in
whom the stomach is habitually distended by a large quantity of 
OF  PHYSIOLOGY.
243
milk.  It also frequently happens in persons who have eaten and
drank very largely, especially when the stomach is strongly com-
pressed by the contraction of the abdominal muscles, in making
efforts  to  go to stool, for example.   Although distention of  the
stomach is favourable to regurgitation; it is also, not rare to meet
with individuals who discharge every morning, one or two mouth-
fuls  of gastric juice  mixed  with bile.   this phenomenon  is
often preceded by eructations, which evacuate  the gas,  that the
stomach also contains.
   When this viscus is full, it is not probable, that its contraction
has much effect in forcing the substances which it contains,  into
the cesophagus; the abdominal walls are the principal agents in pro-
ducing this.  But when the stomach is nearly empty, it  is proba-
ble that the motion of the pylorus has some agency in forcing the
fluids  into  the cesophagus.   This seems the more likely, as the
fluids which are then rejected, are always, more or less, mixed  with
the bile, which  cannot arrive in the stomach, without the contrac-
tion of the duodenum and pyloric  portion ot the stomach.  It will
be recollected, that the oesophagus  contracts with but little energy,
when the stomach is empty.   In most individuals, regurgitation is
entirely involuntary, and only takes place under particular circum-
stances; but there are some persons who can produce this at  will,
and  thus remove  from their stomachs the solid or fluid substances,
which it contains.  In observing  them at the moment when  they
execute this, we  shall  see, they at first, make  an  inspiration,  by
which the diaphragm is depressed;  they then contract the abdo-
minal  muscles, so  as to compress the stomach;  they often assist
this action  by  pressing strongly with the  hands the epigastric re-
gion; they remain in this position immoveable, when, suddenly, the
fluid or aliment  is found to ascend into  the mouth.  It may  he
presumed, that the time  they remain  immoveable, expecting the
appearance  of the substances in  the mouth, is  employed in pro-
ducing a relaxation of the oesophagus, so that the substances which
are  enclosed in  the stomach, may be introduced  into it.  If the
contraction of  the stomach has any effect in expelling these sub-
stances, it can only be considered, in a very remote degree, auxili-
ary to it.   This power of voluntary regurgitaiiou, which some per-
son  possess, is  generally considered  vomiting.    There are  some
individuals, who  after eating, take pleasure in causing the food to 
244'
A  SUMMARY
return into the mouth, to undergo a second mastication, and after*
wards swallow it. Indeed, they perfectly resemble, in this respect,
that class of herbivorous animals which are said to ruminate.
  Vomiting resembles the phenomena of which we have just been
speaking, inasmuch as it has for its end, the expulsion of the sub-
stances contained in the stomach by the mouth.   It differs, how-
ever, from these in some important respects; among others, from
its being announced  by a peculiar sensation; by the efforts  which
accompany it, and the fatigue with which it is always attended.
  We give the name of nausea to  that internal  sensation  which
precedes vomiting; it consists in a general weakness, with a sense
of uneasiness in the head, or in the  epigastric region; the lower lip
becomes  tremulous, and the saliva is copiously poured out into the
mouth. To this state, succeeds suddenly and involuntarily, convul-
sive contractions of  the abdominal muscles, and, at  the same time,
of the diaphragm.  The first are not very intense, but those which
follow are much more so; at last they  come  to such  a degree,
that the substances contained  in the stomach, overcome the resis-
tance of the  cesophagus,  and are thus forced  into the mouth.
The same effect is  produced  frequently; it ceases  afterwards, to
return for a  considerable  time.  I  have  remarked  often, that
animals,  about  the time they are vomiting, swallow  a considerable
quantity of atmospheric air.   This  air seems  destined to favour
the pressure that the abdominal muscles  exert upon the stomach.
It is probable, that the same phenomenon takes place in man.
   At the moment,  when  the substances are driven  from  the
stomach  through the  pharynx and  mouth, the  glottis becomes
closed, the veil of the palate  is raised, and becomes horizontal, as
in deglutition.  In the mean  while, every time we  vomit, there is
introduced a certain quantity of fluid either into the pharynx or
nasal fossse.   It has been  long supposed, that  vomiting depends
upon the sudden and convulsive contraction of the stomach;  but
I have shewn, in a series of experiments, that this  viscus  was
almost entirely passive, and that the true agents of  vomiting were
the diaphragm on one  part, and the large muscles of the abdomen
on the other.   I have even seen it produced,  after substituting a
pig's bladder for the stomach, which I filled with a coloured fluid.*
  * See the details of these experiments, a.\d the report of the committee of tiV
 institute, in my memoir on  vomiting;. Paris, 1813. 
OF PHYSIOLOGY.
245
  In  the  ordinary  state, the diaphragm  and abdominal muscles
co-operate  in  vomiting,  but  they may, however, each  produce it
separately.    For example, an animal  continues to vomit, though
the diaphragm be rendered immoveable, by dividing the diaphrag-
matic  nerves.  It  also  vomits  after  we have divided,  with a
bistory, all the abdominal muscles,-if the precaution be taken of
leaving the linea alba and peritoneum untouched.   I have never
seen the stomach contract itself at the  moment of vomiting; I
eonceive, however, that it is not  impossible, that-the movement of
the pylorus is not seen at this instant.  This was seen  by Haller
in two experiments, and  it induced that illustrious physiologist to
suppose, that  the contraction of the  stomach, was the essential
cause of vomiting.

              Modification of  Digestion by  Age.
   Authors generally represent the digestive organs as inactive
during the foetal state, and that  at the  period of birth, there takes
place a sudden developement of their powers, in order that they
may be prepared to furnish the  necessary materials, for the  nutri-
tion and increase of the body. If, by the term  inactive, they mean
that the digestive organs of  the foetus do not act upon aliments,
there can be no doubt of their correctness; but if they wish to be
understood to the full extent of the expression, i. e. that they are
absolutely inactive, I  think they are mistaken.   It is very probable,
that there takes place in the organs of digestion, in the foetus, an
action very analogous to that of digestion.  But of this subject, we
shall have occasion to speak  more at large, when we come to treat
of the functions of the fcetus.  The same remarks may be applied
to the supposition, that the digestive system is not fully developed,
sit  the period of birth.   If we speak  of the  organs contained
within  the abdomen, it is evident, that  they are  proportionally
more voluminous  than at  a more  advanced age.  But if it be as-
serted, that  the whole digestive apparatus is not so perfect as it
afterwards becomes, the  remark must be  acknowledged to be true;
because the  organs of prehension,  mastication, and excretion of
 fecal matter, are far  from possessing, at birth, the degree of per-
fection which they afterwards acquire.  We cannot suppose that
the energy of the abdominal organs, can supply  the defects of
 those, of which we have been speaking; this is so far  from  being 
246
A  SUMMARY
 the case, that it is necessary that the food of infants should  be
 very delicate, and  easy  of digestion; that  which  is  peculiarly
 adapted to its organs, is the mother's milk;  when it is deprived of
 this,  we all  know  how difficult it is to find any thing that will
 supply its place.  Instead, therefore,  of considering the digestive
 organs of new-born infants, or even of young children, as endowed
 with  great power, we must consider them as much weaker than
 at a later period.  If the  digestive apparatus of children must be
 considered as, in some respects, less perfect than in the adult, ne-
 vertheless, there can be nothing more admirably adapted  to the
 general purposes which it is destined to fulfil.
   Suction is the mode of  prehension  suitable to infants, and  the
 parts which  perform this, are peculiarly fitted for the purpose.
 The  tongue  is large, in comparison with the whole volume of the
 body; the absence of the teeth, allows the lips to be projected  for-
 ward, to a considerable distance, and to embrace,  more exactly
 than can be  done by the adult, the papilla or nipple, from which
 the milk is extracted.  During the first year, the infant is entirely
 destitute of the organs of mastication; the  jaws are small, there
 are no  teeth, the lower jaw is not curved, and does not present
 the same  angle as in the  adult; the elevator muscles,  which are
 the principal agents in mastication, are inserted very  obliquely.
 A sort of pad, formed chiefly of the gums,  supplies the place of
 the teeth.
   Towards the end  of the first year,  and in the course of the se-
 cond, the first or milk teeth pass out  from  the alveolar processes,
 and garnish the jaws.  Their irruption takes place with conside-
 rable regularity, in  pairs.   The two middle incisors of the lower
jaw, generally, first display themselves, then the two superior, and
 successively, and in the same order, the canine and small molares;
 though  the last do not often appear until the third year.   At the
 age of four years, four new teeth appear, these  are the first large
 molares;  they complete  the number of twenty-four,  which the
 child preserves until it is seven years of age.   At this period,
 the irruption of the second teeth takes place.   The first or milk
 teeth, then fall out, generally, in the order they appeared, and are
 successively  replaced by those teeth which are destined to remain
 through life.  At this  time,  four large molares appear, which
 make  twenty-eight teeth.   Between  the  age of  twenty and 
OF  PHYSIOLOGY.
247
twenty-five, though sometimes much later, four more teeth appear,
which are the  sapient teeth, and the number of thirty-two teeth,
proper to man, is then completed.  This renewal of the teeth at
the age of seven years, is necessary,  from the increase which the
jaws  undergo.   The milk teeth being small, those which succeed
them  are larger,  and denser in  their texture;  their roots are
loneer and more numerous,  and thev  are attached more firmly in
the alveolar  processes; arrangements indispensable to the  func-
tions  which thev are  destined to fulfil.
   At the same time that the  jaws increase in  size, they change
their  form.   The inferior jaw is  curved, its  branches becoming
more  vertical, its bodv  assumes  a horizontal direction, and the
angle ?s  more distinctly marked.   When the teeth first  pass out
from  the alveolar processes, and the  instrument is entirely new,
the  incisors have  a sharp  cutting  edge,  the  canine  teeth  are
po nted, and  the face of the molares covered with sharp conical
asnerities; b'lt  in  these resneets  they become somewhat altered
with  age. The teeth rubbing continually against each other, during
mastication, or from bein*r  in contact with bodies more or less
hard, have their form modified bv the  friction.   We  may form
some idea of the a?e of a person bv  his  teeth, but it is so rare
that the *ee<h  are  disposed  with  perfect regularity, and possess
an equal decree of densitv, that  this can  only be remotely ap-
proximated.   Generally, the effect of using the teeth is  first visi-
ble in the inferior incisors:  it is seen afterwards  in the  molares,
but much later in the teeth of the superior jaw.   But the effect of
use upon the teeth is, bv no means, the  most unfavourable change
produced by  a<re.   In  the  first stage  of dotage, they are forced
from the alveolar processes bv  the progress of the ossification of
the jaws, they thus become loose, and at last fall out.   The man-
ner in which this takes place is not regular, as happens in the first
 teeth, but varies in individuals.
   Those who do not lose their teeth, until the period of which we
 are speaking, must be considered  as privileged persons, for, gene-
 rally speaking, they  fall out much earlier, either by accidents,
 such as  blows, or  falls,  which  fracture or  tear them out,  or in
 consequence of the contact of  air, or those substances which are
 habitually introduced into the mouth, by  which  their  texture be-
 comes altered, they exhibit  spots, change  their colour, become 
248
A  SUMMARY
softened, and, at last, fall into fragments.  These  alterations are
improperly enough called, diseases of the teeth; it  is  evident,
however, that they are chemical  changes, as artificial teeth are
found to undergo the  same process.  After the teeth  have fallen
out, the gums become harder, and the alveolar cavities closed up;
an arrangement which, in some sort, supplies  the deficiency of
the teeth.
  Such are the modifications  which the organs of mastication un-
dergo with the  progress of age; those which take place  in the
other digestive organs, are not of sufficient  importance to require
being particularised.  We  shall finish this article by remarking,
that  those voluntary  muscles which assist in digestion undergo,
in consequence of age, the same changes which we have already
pointed out  in speaking of the modifications  produced by this
cause,  in muscular contractions.
  Our knowledge respecting the  modifications  of  digestion in
different ages, is very limited; our information on  this subject is
chiefly  confined to the prehension and mastication  of aliments,
and the excretion ot fecal matter;  the changes which  fhose parts
of the  digestive organs, which are contained in the abdomen, un-
dergo, are nearly unknown.  Hunger seems  to be a  very  acute
sensation in  children, and does not return periodically,  as in
adults, it returns so  often that it seems  to be continual, and it
often appears to exist  when the  stomach is far from being empty.
Sucking is a mode of prehension peculiar  to infants,  and it is
readily executed by  them,  from  the  extent  of their  lips and
tongue.  This action, at least for  the first month, appears to be
entirely instinctive.   Until the appearance of the  teeth, and even
after dentition  has begun, mastication is impossible. If the in-
fant compress those substances, which are placed in  its  mouth, it
is rather to  extract the juice which  they contain, or to favour
their solution, than an attempt at  mastication.  It may, perhaps,
be, that the excessive quantity of  saliva in infants, supersedes, to
a certain degree, the  necessity  of mastication.
   It is necessary to pass to  a consideration  of the  excretion of
fecal matter, in order to be  able to say any thing positive con-
cerning the digestion of young  infants, when compared  with that
of man at the adult  age.  The excretions of infants are much
more frequent than at a more advanced age; they are  almost 
OF PHYSIOLOGY.                 £49
always quite fluid, of a yellowish colour, and do not possess the
peculiar  odour which they afterwards assume, when other ali-
ments than milk are  eaten.   The abdominal muscles, probably,
do not possess sufficient energy at  this age, to expel solid fecal
matter.
  The appearance of the incisor, and even of the canine teeth are
of but little assistance to the infant, in the function of mastication.
It is necessary that the irruption of the molares should take place,
in orderth.it the action should be  efficient; even after this has
occurred, they cannot be exerted upon substances which offer
any  considerable degree  of resistance,  because the elevator mus-
cles of the lower jaw are too weak, and are inserted too obliquely,
to allow  the teeth to act with much  power, upon  substances pos-
sessing a considerable degree of density. It is not until  the se-
cond dentition, and even  some time after, when the angle of the
jaw  has become well  marked,  that mastication acquires  all  the
perfection of which it is  susceptible.   It remains  in this state,
unless molified by use, or the accidental loss  of the teeth, until old
age.  At this period  of life, it is generally found, that nearly  all
of the teeth  have fallen out, and the person  then  masticates with
the  alveolar  edge  of the jaw.  To these causes, w nch  render
mastication  difficult  in old  age, may be added, first; the great
extent of the  lips, which, as soon as the teeth have fallen out,are
longer than  is necessary, to extend  from one jaw to another, and
which, therefore, touching by  their internal surfaces, instead  of
having their edges in contact,  are incapable of retaining the sali«
va.   Second.   The diminution of  the angle of the jaw, which in
 this  respect resembles that of infants; and the curvature of the
 body of this bone, which compels old men to chew with the ante-
 rior and  middle part of  the  alveolar edge,  the only part where
 these edges meet.  Third.   The absence of the teeth, induces a
 neces-ity of chewing with the  lips in contact, which gives, there-
 fore, a  peculiar character to the mastication of persons in  this
 situation.
   The action of the muscles, which concur  in  digestion, undergo
 the same changes, as we have already pointed out, in speaking of
 the influence of different ages upon  muscular contraction.  Feeble
 in the  infant, active  and vigorous in  youth and  manhood,  the
 muscles again loose  their  energy in old   age.  The digestive
                                .■VI 
250
A  SUMMARY
actions, which depend upon muscular contraction, run the same
periods, as any one may satisfy himself, by examining the manner
in which the prehension, mastication  and excretion of  fecal mat-
ter take place, at the different periods of life.   Some old persons
are habitually constipated,  in consequence of the debility of the
muscles.  It has sometimes happened, that persons have been ab-
solutely incapable of expelling the excrement,  in consequence of
which, it  has  become  accumulated in the large intestine to an
enormous extent, so that it becomes  necessary to have recourse
to a surgical operation.
   We know, but  in a very general  sort of way,  the  modifica-
tions  which the  stomach and intestines undergo, at  the different
periods of life.   They appear to be  more active during the in-
crease of the  body,  and afterwards to become more sluggish  in
their  action.  But of all the vital actions, these preserve, until
the last moment of life, the greatest degree  of energy.   We  shall
not enter  here upon the consideration of the modifications, which
arise  in this function from sex, climate,  habits,  temperament, or
the constitution of the individual.  These considerations are no
doubt interesting, but  they more particularly  belong to hygeine;
we shall  therefore limit ourselves to observing, that  digestion
varies in almost every individual, and that  even in  the same per-
son, it is rare that digestion does not  undergo some change daily,
so that a person may digest a substance  to-day, and yet be abso-
lutely incapable of doing this on  a similar substance to-morrow.

   Connexion of Digestion with the Functions of Relation.
   A function so important as digestion, and for the  performance
of which so many different organs co-operate, must necessarily be
intimately connected with the other functions, especially those of
relation.  This connexion exists, indeed; it is even so intimate,
that in most animals, a knowledge of one or more of the organs of
external life, enables us to form  a correct judgment of the dispo-
sition of the digestive organs; and on the contrary, by inspecting
one part of the digestive apparatus, we can form a very just idea
of the arrangement of the organs of sense and voluntary motion.
   The senses point out to us the presence of aliments;  they assist
us in  seizing them, make us acquainted  with their  physical and
chemical  properties, and their  beneficial or ihjurious  qualities. 
OF PHYSIOLOGY.
251
As it is especially in this  last respect, that it is of importance for
us to appreciate aliments, we may consider the  senses of smell
and taste, which perform  this office, as having  more intimate re-
lations  with digestion, than  the otiier senses;  some authors, in-
deed, have classed them among the digestive actions.
  It is  often the  case, that the aspect and odour of food excitec
the appetite, and prepares the organs of digestion for the dis-
charge of their office.   The  reverse, however, is sometimes the
ca»e, i. e. it entirely removes all  desire of food, and  produces a
sensation of disgust.  Generally  speaking, a moderate appetite
imparts to the senses more delicacy and activity; but, as we have
seen above, when hunger is prolonged,  the senses become im-
paired,  so as  at  last to  transmit  only imperfect impressions.
During chymification, they have also less activity, especially if the
stomach be much distended with food.  The relations of muscular
contraction  with digestion, are not  less evident.   We have al-
ready shewn, how the  action of the muscles assists  in the prehen-
sion, mastication,  and deglutition of the aliments, and the excre-
tion of the fecal matter;  besides this, they transport the  body to
procure food,  they excite the appetite by their action, and when
their efforts are  great, they require an abundant nourishment.
In their turn,  they are influenced  by digestion; hunger debilitates
them, and impairs their motions;  and on the contrary, when the
stomach is full, especially in warm climates, and persons in deli-
cate health, there is great indisposition to motion.  But in cold
 countries, and in robust  individuals, the presence  of  food in the
 stomach, increases their vigour and agility.
   We may easily explain the difficulty which is felt in singing or
 speaking, after a generous repast.  The volume of the stomach pre-
 vents the introduction of air into the chest, and the motions of the
 diaphragm, and thus offers an  obstacle to the production of the voice.
The relation between the functions of  the brain and  the  organs
 of digestion are particularly intimate. Hunger  forcibly directs the
 thoughts to the means of obtaining aliment; and on the other hand,
 strong mental excitement, violent chagrin, or sudden fright, often
 take away the appetite, and stop the powers of digestion for some
 days,  so that aliment  which  had  been before introduced into the
 stomach, remains  without undergoing any alteration.   Nothing is
 more common than  to see persons, whose minds are oppressed  by 
252
A  SUMMARY
gloomy affections, in whom the functions of digestion are com-
pletely perverted. Contentment, and gaiety of spirits, on the other
hand, favor digestion; great eaters are seldom subject  to mental
depression.  Every one must  have noticed  the  influence  whioh
digestion exerts upon the operations of the  mind; many  persons
are absolutely incapable of  making any mental  effort during di-
gestion; the accumulation of fecal matter in the large intestines,
has a still more marked influence upon the moral affections.
             COURSE OF THE  CHYLE.

  It would be useless for the digestive organs to form chyle, if this
fluid afterwards remained in  the intestinal canal.  It is therefore,
necessary that the chyle should be transported from the small  in-
testines into the venous system.   This is the end of the function
which we are now about to examine.   To preserve, as far as possi-
ble, the method by which we  have thus far been guided, in the ex-
position of the functions, we shall first speak general ly of the chyle.

                       Of the  Chyle.
  We may consider the chyle in two  different  points of view.
First. When it is mixed with the chyme in  the small  intestines,
and when its characters are such as we  have described, in speak-
ing of the phenomena of its formation.   Second.  Under the firm
of a fluid, moving in the  chyliferous  vessels, and thoracic  duct.
No one having, particularly, investigated  the properties  of the
chyle, during the time it remains in the small intestine,  our  know-
ledge on this point does not extend beyond what has been already
said on  this subject, in speaking of the action  of  this intestine in
digestion.  On  the other hand, the  fluid chyle contained  in the
chyliferous vessels has been examined with great care.
  The best meth6d of procuring this fluid  is, to  give  food to an
animal,  and when a  sufficient time has elapsed, for the digestion
to be going on in its fullest activity, to either strangle the animal,
or to divide  the  spinal marrow behind the  occipital bone.  We
must then lay open the chest, through  its whole extent,  and  pass a
ligature, which shall embrace the aorta, oesophagus,  and  thoracic
duct, as near as possible to the neck.  By turning over the lung, 
OF PHYSIOLOGY.                   253
and  tearing the parts a little, on the left side, we shall then see
the thoracic duct, lying along side of the oesophagus; we then de-
tach tbis above the  ligature,  and by puncturing the duct, we may
permit the chyle to run into  the vessel  which is intended to re-
ceive it.
  The ancients were acquainted  with the existence of the chyle, but
entertained very incorrect ideas concerning it.   At the beginning
of the seventeenth century, considerable attention was directed to
this subject.  It was found to be  of a  white colour, and opaque, and
was therefore compared to milk,  and  the vessels which contained it
were called lactenls; a very incorrect name, inasmuch as there is no
analogy between the chyle and milk, except in colour.  It is only
of late,  and chiefly by the labours'of Dupuytren, Vauquelin, Em-
mert, and  Marcet,  that we have become acquainted with the  po-
sitive qualities of the chyle.  We shall state the observations of
these distinguished  men,  adding  those which  we have made our-
selves.
   If the animal from which  the chyle  is extracted,  had eaten of
fatty animal,  or vegetable substances, the fluid drawn from the
thoracic duct,  will  be of a white milky appearance, rather heavier
than distilled water, of a spermatic  odour, stimulating the tongue,
a little saltish,  anil perceptibly alkaline.   Soon after passing out
from the vessel, in which  it was  lodged, the  chyle runs into a mass,
and acquires a consistence almost solid; after some time, it sepa-
 rates into three parts;  one solid,  which is  found at the bottom of
 the vesse', another fluid  which is  found  above  it, and a third,
 which forms a sort of pellicle on the surface of the fluid;  the chyle,
 at  the  same  time, assumes a bright reddish  tint.   When  it
 consists of aliments, which  do  not contain  fat, its general  proper-
 ties are the same;  but instead of being while, and  opaque, it  is
 semi-transparent,  and the pellicle  formed  on  the surface, is less
 distinctly marked than in the first kind of chyle.  The chyle never
 assumes the colour of those  colouring substances which are mixed
 with the aliment;  as some authors  have asserted.  M. Haile  as-
 certained this, by direct experiments.  I have recently  repeated
 these experiments, with precisely the  same results.   After caus-
 ing animals to eat indigo, saffron, and madder,  I have inspected
 the  chyle, but have never  found that its  colour seemed to have
 any relation to these substances. 
254
A  SUMMARY
  Of the three parts into which the chyle separates, when left to it-
self; that on the surface of an opaque, white colour, is a fatty sub-
stance;  the coagulated, or solid  part, is  formed of fibrine, and a
little red colouring matter; the fluid is analogous to the serum of
the blood. The proportion of these three parts varies, according to
the nature of the aliments. There are various chyles, for example,
that of sugar,  which contains but very little  fibrine; and that of
flesh, which contains much more.  The same remark applies to the
fatty part, which is extremely abundant,  when  the aliments con-
tain fat or oil, while this is hardly distinguishable,  when the ali-
ments  are destitute  of fat.   The same salts which  are  found in
the blood, exist also in  the chyle.   We shall give some further de-
tails relative to the chyle, hereafter.

Of the Apparatus of  Absorption and the Course of the  Chyle,
  This  apparatus is  composed, first, of  those  absorbent vessels,
peculiar to  the small  intestines, which  are called  the  lacteals.
Second, the  Mesenteric glands.   Third, the Thoracic duct.
  The lacteal  vessels  are extremely small, and  very numerous.
They arise from  imperceptible orifices on the surface of the vil-
losities of the mucous  membrane of the intestine, and extend to
the mesenteric glands, in the substance of which they seem to be
lost.  In the walls, and on the surface of  the small intestine, they
are extremely delicate and numerous.  They  inosculate freely, so
as to form a fine and  beautiful  reticulated structure, an arrange-
ment which is especially visible when they are filled  with white
and opaque chyle. They enlarge in size, and  diminish in number
as they go from the  surface of the intestine, and at last form insu-
lated trunks, which  extend to the neighbourhood of the mesenteric
arteries, and sometimes in the  intervals  which separate them, it Ib
in fact,  in this form that they reach the mesenteric glands.
   We give the  name of mesenteric glands, to the small, irregu-
larly formed, lenticular bodies, which are found before the verte-
bral column, between the two laminse of the peritoneum, called
the mesentery.   Their dimensions vary, from two  or three lines
to an inch;  they  are very numerous. But little is known of their
structure; they receive a large  number of blood vessels  in pro-
portion to their size, and are endued  with great sensibility.  On
compressing them between the fingers, we extract a transparent, 
OF PHYSIOLOGY.
255
inodorous fluid, which has never been chemically examined.   It is
especially abundant in the centre of  these bodies. I have observed
a remarkable quantity of it in the bodies of criminals.  The san-
guineous and  lacteal  vessels found in these glands, are reduced
into tubes of extreme tenuity, so  that we are unable to trace the
precise relation  they bear to each other.    It  is however, certain,
that injections forced into either, traverse  the  gland with  the
greatest facility.  There arise from the mesenteric glands, a great
number of vessels of the same  nature  as  the  lacteals, but in
general larger.  These are the roots of the thoracic duct.  They
are directed towards  the vertebral column, and run along with the
aorta and vena cava.  They anastomose frequently, and terminate
in the thoracic duct.
   The name of thoracic duct is given to a vessel, of the same kind
as those which we have just described    It is about the size of a
goose quill, and reaches  from the cavity of the abdomen, where
it commences, to the  left subclavian vein where it terminates.  In
its course, it  passes between the pillars of the diaphragm by the
side of the aorta; it then runs along the vertebral column, until it
arrives opposite to the left subclavian  vein, when  it  turns  of
abruptly, and terminates in that  vessel.   It sometimes opens into
 both  subclavian veins, and sometimes into the right alone.  In the
 interior of the thoracic duct, and lacteal  vessels are found valves,
 so arranged, as to permit the chyle to pass towards the  left  sub-
 clavian vein, but to prevent its moving in an opposite direction;
 true valves however,  are not always found. The walls of the lacteal
 vessels  and  thoracic duct  are  composed  of two distinct mem-
 branes, the one internal, thin and formed into folds, which consti-
 tutes the valves.  The external coat is fibrous, and  possessed of a
 greater  power  of resistance than  would have been  anticipated
 from its great tenuity.
    Before explaining the phenomena of absorption, and the course
 of the chyle, it will be proper to make a few observations  on the
 organs which contain it.  After twelve, twenty-four, or even thirty
 six hours of abstinence, the lacteal vessels of a dog will  be found
 to contain a small quantity of semi-transparent fluid, of a slight
 milky tint, and which exhibits other properties analogous to those
 of the chyle.   This  fluid  which is met with in the lacteal vessels, 
 256                   A SUMMARY

 and thoracic  duct, and  which has never been analysed, appears
 to be chyle, formed from the digestion of the saliva and mucus of
 the stomach.   This seems  the more probable, as the causes which
 increase the  secretion  of  these  fluids,  as acid drinks, diluted
 alcohol, &c. increase  its quantity.  When the animal is deprived
 of nourishment for three or four days, the lacteal vessels get into
 the same situation as  the lymphatics; being sometimes filled  with
 lymph and at  others, perfectly empty.  From these facts, then it
 is evident, that the chyle of aliments, which is extracted  from the
 lacteals, is always either mixed with  the  chyle of digested mucus,
 or with the lymph; the result is the same, if we extract the chyle
 of the thoracic duct which  is constantly filled with  lymph even
 after eight  or more days of abstinence.  "The substance which has
 been examined by chemists under the  name of chyle, is  far from
 consisting  entirely of the extract of alimentary  substances, it is
 evident that they constitute only a certain proportion of it.

                  Absorption  of the  Chyle.
  It cannot be doubted, that the chyle passes  from the cavity of
 the small intestines into the lacteal vessels. How then, it may be
inquired, is this effected?    It would  seem at a first glance, to be
 easy to explain so simple a phenomenon.   But  this is nof the case.
 It has  already been remarked, that  the  situation of  the mouths
 of the lacteal  vessels  is not known, nor is there any thing  better
known of their mode of action, though many persons have under-
taken to explain it.   This  has sometimes  been attributed to the
capillary attraction of  the  orifices of the vessels, and the com-
pression of the chyle  upon the walls of  the small intestines, &c.
Of late it  has been   attributed to a  peculiar  sensibility in  the
mouths of  the absorbents, and the organic insensible contractility,
with which they are  supposed  to be endued.  We  can hardly
imagine how men  of  distinguished minds can  either propose  or
admit  such explanations.   For my own  part, they appear to be
a plain and  simple  acknowledgment of our ignorance of the
nature of this  phenomenon.  'There  is one fact relating to this
subject, which it will  not be useless to mention;  it is that absorp-
tion continues to go on for a considerable time after death.  After
having emptied one or more of the lacteal vessels, in an animai
recently dead, by compression, we shall  again see it, in a short 
OF  PHYSTOLOGY.
257
time,  filled  up anew.  We may repeat this  experiment several
times in succession.   I have myself done it, after the animal has
been dead for two hours.

                     Course  of the Chyle.
  We have alreadv  described the course of the chvle.  Ttat first
passes through  the lacteal vessels, traverses the mesenteric glands,
arrives at the thoracic duct, and is then poured into the left sub-
clavian vein.
  The causes which  give it motion  are, the peculiar  contractility
of the lacteal vessels, the unknown  cause which  produces absorp-
tion,  the pressure  of the abdominal  muscles, especially in  the
motion" of respiration, and  perhaps  the action of the arteries
of the. abdomen.  If we  wish  to form a just idea of  the  ranidity
with which the chyle runs alonsr the thoracic  duct, it w:|l be only
necessary to do, as  I have frequently done, viz to open this canal
in a living animal, at the part where it forms a  junction with the
left  subclavian vein;  we shall  find then, that its rapidity  is not
very  great, but that it is increased every time  the animal  com-
presses the abdominal viscera, by the contraction of the abdominal
muscles;  we may produce a similiar effect  by  compressing the
belly with the  hand.
   It has alvvays appeared to me, that the rapidity with which the
chyle circulates through its  vessels, is  in proportion to  the
quantity which is formed in the small intestines.  This depends
upon the quantity of chyme; so that, if the aliments are abundant,
and easy of digestion, the chyle will  pass along quickly.   If, on
the contrary, the aliments are small in quantity,  or what amounts
to the same thing, if they are difficult of digestion, as there  will
be little chyle formed,  its progress will  be  slow.   It  would be
difficult  to  estimate, accurately, the quantity  of chyle formed
during any given digestion, it is no doubt, however, considerable.
In a dog of an ordinary size, but  who had eaten as much animal
food  as he chose, from an incision made into the thoracic duct in
the neck, the animal being still alive,  there passed out more than
half  an  ounce of this fluid, in five minutes, and it continued to
 ooze out as long as  the chyle was  formed, that is, during several
 hours.
33 
258                    A  SUMMARY
  T do not know, if in the course of the same digestion, the nro«
gress of the chyle varies in rapidity; but, if we suppose it uniform,
it will be  perceived, that there must enter  into the venous system,
six ounces of this fluid in one hour. In man, where the chyliferous
organs are more  voluminous, and  where  digestion is performed
much faster than in the dog, we may presume, that the proportion
of chyle is much more considerable.   The  blood which passes
through the subclavian vein, cannot penetrate into the thoracic duct,
because there exists at its orifice, a valve so disposed as to prevent
this.  For the same reason, in consequence of the  valves in the
thoracic  duct, and  lacteal vessels, the chyle  cannot flow  back
towards the intestinal canal.
   Almost all physiologists have supposed, that the chyle undergoes
some peculiar alterations in  traversing the  mesenteric  glands.
Some have suspected, that these bodies produce a more intimate
admixture of the component parts of the chyle; others have thought
that they add to it a fluid  intended  to  render the  chyle  more
liquid; there are others again, who imagine, on the contrary, that
they take  away something from the elements of the chyle, in order
to purify it.  The truth is, we are entirely ignorant of the influence
which the mesenteric glands exert upon this fluid.  In the same
way, much has been  said of  the variable qualities of this fluid;
according as  the digestion is good or bad. The decay, which takes
place in some diseases, has been attributed to  the formation of a
bad chyle, owing to the nature of  the aliments.   But indeed,  we
know very little of the modifications in its composition  which
take place in the chyle.  Much has been said also of certain  parts
of aliments, which  pass with  the chyle,  into  the blood, without
being altered by the digestive organs. But this is mere conjecture,
without a single positive experiment to support it.
  Dr.  Marcet, who has recently  analysed  the chyle, has  com-
pared that formed  from animal substances, with  that of vege-
tables; he  found, that the last contained three times as much car-
bon, as the chyle produced from animal food.  We learn  from Pro-
fessor  Dupuytren's very ingenious researches, that the thoracic
duct is the only rout by  which the chyle passes, to serve the pur-
poses of nutrition.
  We know from the  experience  of Duverney, from some cases
of obstruction  of the  thoracic duct; and especially  from the 
OP PHYSIOLOGY.
259
experiments  of Flandrin;  of which we have spoken  in another
place;  1 say we know on these authorities, that the thoracic duct
may cease to pour the chyle into the vein, at the point where it
terminates, without producing death.   We know, it is true, that
in some cases a  ligature  upon this  canal has produced  death,
though  we weie   then ignorant of the causes of these different
results; but trie experiments of M. Dupuytren have given  a satis-
factory explanation of them.   This expert surgeon, passed  a liga-
ture about the thoracic duct of several horses, some of them died
in the course of five or six days, while  others preserved every
mark of perfect health.  In those animals which died from  the
effects of the ligature, it  was always  impossible to force any
injection from the lower pait of the duct into the subclavian vein;
it is very pro  able, therefore, that the chyle ceased to be formed in
the venous system, after the application of the ligature.   On the
contrarv,  in  those animals which survived, he always found it
easy 10 make mercurial injections pass, and even other substances,
from the abdominal portion of  the duct into the subclavian vein.
The matter  injected, followed the duct into the  vicinity of the
ligature; there it turned aside, and entered some large lymphatic
vessels, which opened into the  subclavian vein. It is then evident,
that in these  animals, the tying of the thoracic duct had  not pre-
vented the chyle  from mixing  with the  venous blood.
   Inasmuch  as the lacteal  vessels  absorb the chyle, and carry it
into 1he venous system, it  has been assumed, that they fulfil  the
same office for all those substances which are mixed with the ali-
ments, and  which, without being digested, pass into the blood.
Authors  have generally  said, for example, that  drinks  are ab-
sorbed  with  the chyle;  but, as they have  not shewn this to be the
case, by a single  experiment,  we may reject the opinion on  this
ground alone, as  doubtful.—1 have endeavoured to satisfy my own
mind on this point, by direct experiments on  l.ving animals, but I
have not  met with a sii gle instance  in which I could detect the
drink mixed  with the chyle.  When  a dog is made to swallow  a
quantity of diluted alcohol during the digestion of solid aliments;
if, in hall an  hour alterwards, the chyle be extracted, in the manner
I have already pointed out, it will be found that this fluid does not
contain alcohol,  while the blood smells strongly of it, and when 
260
A  SUMMARY
distilled  gives over this substance.  We obtain similar results by
giving a solution of camphor, or any other odorous fluid.
  The modifications which take place in the absorption and course
of the chyle, in different ages, has never been investigated; we only
know, that the mesenteric glands change their colour, diminish in
volume, and  are at last nearly obliterated,  in  old age.  Some au-
thors  have supposed,  that  they  do not suffer the chyle to pass
through them; but this seems to be a mere hold assertion, unsup-
ported by any well authenticated  facts.  We are also completely
ignorant how far sex,  temperament, and habits, modify this func-
tion; nor are we  better informed  respecting  the relations which
exist between this function, and those which we  have already ex-
plained, or which remain  for us to examine.
           ABSORPTION OF THE LYMPH.

  We have just  seen how much remains to be done, in order to
give precision to our ideas of the absorption, and course of the
chyle;  but this Function, a history of which  we are  now about to
give, is still  more imperfectly understood.   \N e know generally
that it exists, but we have scarcely a remote conception of its utility
in the animal economy.  Its apparent object is to  pour the lymph
into the venous system.   It may be presumed that this phenome-
non constitutes but one  point in its utility; nevertheless, when we
come to define  the limits of our knowledge, it is confined to this
alone.
                       Of the Lymph.
  Nothing shews more  strikingly, the  imperfection of our know-
ledge of this function,  than  the  different  opinions  which have
been entertained  by physiologists, of the nature of  the lymph.
Some have  given this name  to the serum of the blood, others to
the  fluid which is  seen on the serous membranes, and others again
to the serosity of the cellular tissue, while some have  considered
the fluid  which oozes from certain scrophulous  ulcers, as lymph.
For ourselves, we intend to  confine the meaning of the term lymph,
to the fluid which is contained in the lymphatic vessels and tho-
racic duct.  It is the more necessary to attach a fixed  meaning to
this word, because,  by admitting other significations, we conse- 
OP PHYSIOLOGY.
261
crate as true,  opinions, than which nothing is further from  being
demonstrated; namely, that the fluids of  the serous membranes,
cellular tissue, &c. are absorbed by  the lymphatic  vessels, and
transported  by these vessels into ihe venous system.
  To procure lymph,  we may have  recourse to two  processes.
The one consists in laying bare a lymphatic vessel, puncturing it,
and collecting the fluid which  passes out.  But  this operation
is difficult  to execute, as the lymphatic  vessels are not  always
filled  with  lymph.   The  other process  consists  in suffering
an  animal  to last, during four or five  days,  and  then  to ex-
tract the  fluid contained  in the thoracic duct, in tne manner  we
have mentioned in speaking of the chyle.   The  fluid which is ob-
tained by either of these methods, is of a reddish colour, and
opaque.   It has  a distinct spermatic odour, a  saline  taste, and
sometimes  exhibits a decidedly yellowish tint,  while at others, it
is of the colour of madder   I think it important to insist on these
details, because a  neglect of them, has probably  induced errors in
the experiments which have been made upon the absorption of co-
louring matter.   But  the lymph does not remain long in a fluid
state, it  soon forms itself into a mass; its  red colour  assumes a
deeper tint, numerous redish  filaments become developed in an
irregular, arborescent form, very analogous to the vessels found
in  the tissue of the organs.   When  we examine with care,  this
mass of coagulated lymph,  we  perceive  that it is formed of two
parts; the one of  which is solid, consist ing of numerous cells, con-
taining the  other part, which is fluid;  if we separate the fluid part,
it again runs into a mass.
   The quantity of lymph  which can be collected in this manner,
from a single animal, is very  inconsiderable, we can obtain from
a large sized dog, scarcely, an ounce  and  an half.   It has appear-
ed to  me that the quantity increased, as the fast is  prolonged.  I
think  also, that I have observed that its colour becomes  redder,
 when  the animal has been long deprived of food.  The solid part
of the lymph, which may be called its coagulum, has a great ana-
 logy with that of  the blood.   It becomes of a scarlet red,  when it
 is  brought in contact  with oxygen gas, and  ot a  purplish  red
 when  it  is  plunged  in carbonic acid gas.  Its specific gravity,
 when compared with distilled water, is :: I02--.28: 1 (00.00.  1 re-
quested M. Chevreul to analyse the lymph of  a dog.   I gave to 
262
A  SUMMARY
him a considerable quantity, which I had  procured, in the man-
ner mentioned above,  after having caused the animal to fast for
several days.  The following are the results obtained by this dis-
tinguished chemist.  A thousand parts of lymph  contained,
               Water,                    926.4.
               Fibrine,                    004.2
               Albumen,                  061.0
               Mur. soda,                 006.1
               Carbon, soda,              001.8
               Phosph. lime and magnesia 1
               I*  K   I                  [000.5
               Larbon. lime,              J
                    Total,                1000.0

    Apparatus of Absorption, and  Course of the  Lymph.
  There is a strong analogy in this respect to the absorption and
sourse of the chyle; or rather, except in  an anatomical  point of
view, they  form parts of  the  same  system.   This  apparatus is
composed of lymphatic vessels,  glands, or lymphatic ganglions,
and  the  thoracic duct; which we   have  already  mentioned in
speaking of the course of the chyle.   The  lymphatic vessels exist
in almost every part of the body.  They are small, anastomose fre-
quently, and have the same reticulated arrangement as the lacteals.
In the extremities they form two planes, the one superficial, and
the other profound.   'The  first is placed in the cellular tissue, be-
tween the skin and the aponeurosis beneath; in general it accom-
panies the  sub-cutaneous veins.   VV he/i  the  vessels which  form
this plane are filled with mercury, and the injection has succeed-
ed  well, they  represent a network, which surrounds  with its
meshes the  whole of the limb.   The  deep seated lymphatics of
the limb are seen, principally, in t|je intervals between the muscles,
and about the nerves, and  large vessels
  Both  the superficial and deep seated lymphatics, as they pass
towards the superior  part of the limb, diminish  in  number, and
terminate soon in the  lymphatic glands of the groin, and arm-pits,
&c. from whence they pass either into the abdomen  or chest. In
the trunk, the lymphatics form, in the same manner, two  lamine,
the one sub-cutaneous, the other placed on  the  internal surface of
the walls of the  cavities.   Each viscus has also two  orders of
lymphatics, the occupying the one surfcae and the other appearing 
                     OP PHYSIOLOGY.                  263

to arise  from the substance of the  organ.   Tt  has  been in vain
attempted to trace these vessels in the brain, spinal marrow and
their envelopes, the eve and  the internal ear, &c.  The lymphatic
vessels of the trunk and extremities accompany the thoracic duct;
but those from  the external parts of the head and neck, terminate
in the  following  manner, viz.  those of the right side  in a large
vessel, which opens  into the ri-jht subclavian vein, and  those  of
the left side into a similar vessel, somewhat smaller, which opens
into the left subclavian vein, a  little  above where  the thoracic
duct discharges itself.
   We are ignorant of the disposition of the  lymphatic vessels at
their origin.  Many  conjectures  have been made  on this Subject,
all equally  destitute of foundation.   That which  seems to be the
most plausible  is, that they arise  bv extremely fine roots from the
substance of the membranes, and cellular tissue, and the parenchy-
ma of the viscera, where thev  appear  to be continued to the last
ramifications of the arteries.  It often  happens,  that an  injection
forced into  an  arterv,  passes into the  lymphatics of the part to
which  it is distributed.
   In  their course, the lymphatics exhibit no regularity, thev in-
crease or diminish in volume, thev are sometimes rounded and
sometimes they present a number of swellings, near to each other.
Their  structure does not, sensiblv, differ from that  of the lacteal
vessels;  like them they are earnished with valves.  In man, each
lymphatic vessel, before arriving1 at  the venous  system,  must tra-
verse  a lymphatic eland.  But this disposition  does  not exist in
any other animals which have lymphatic glands.  These organs
are very numerous,  and, in  form and  structure, entirely resemble
the mesenteric elands; thev are found  particularly in the  armoits,
neck, about the lower jaw,  beneath  the skin of  the  nape of the
neck, in the groin, and in the pelvis, about the larse vessels.  The
lymphatic vessels seem  to bpar the same relation to  them,  as
the lacteal vessels do to  the glands of the mesentery.

               Of the Absorption of the Lymph.
   In order that we may investigate, with advantage, the absorption
of the lymph,  it  is indispensable, to examine the ideas which are
at present received respecting  the origin of this  fluid,  and the ab-
sorbing  faculty  attributed to  the lymphatic vessels.  It will  be 
264
A  SUMMARY
necessary for us,  in doing this, to make use of great caution, and
even sometimes of severity; for, independently of the peculiar dif-
ficult v of the subject, we shall have to discuss an opinion generally
admitted to be true, and sustained  by the most respectable autho-
rities.   But, as the only motive which animates us is a love of
truth, not a fondness for innovation, we hope that no one will fetl
disposed to find  fault with us for  the part we shall take in this
question.
  Let us inquire at  first  respecting the sunposed origin of the
lymph.—According to the best authors, the lymph is the result of
the absorption which the lymphatic vessels exert on the surface
of the mucous, serous, and  synovial membranes, the lamin?e of
the cellular tissue, the skin, and the parenchyma of each organ.
  The above view comprehends two distinct ideas, viz:  first, that
the lymph exists in the different cavities of the body; and second,
that the lymphatic vessels possess the faculty of absorbing it.  Of
these two ideas, the first is entirely incorrect,  and the other de-
serves a  particular examination.  Indeed, although there  is some
analogy between  the appearance of this  fluid,  and that which is
found on the surface of the serous and synovial membranes and
that of  the cellular tissup, &c:  yet we have already shown, that
the lymph differs  from  these fluids, hoth in  its physical and che-
mical characters. And as these different fluids vary among them-
selves, if we admit this origin of the lvmnh, it will  necessarily
consist of different kinds of fluids. Now the lymph has always been
found to possess the same sensible qualities, in all parts of the body.
  Let us next examine the  faculty of absorption, which is attrihu-
ted by authors to the lymphatic vessels. The fluids introduced into
the stomach, and intestines, are promptly absorbed; the same thing
happens in whatever part  of the body the fluid is thrown.  The
skin and the mucous membrane of the lungs possess also the same
property.  The ancients remarked many of these phenomena, but
being ignorant of the existence of the lymphatic vessels, supposed
that the  veins were the agents of absorption.   This opinion  was
maintained  until the middle of the last century, when the nature
of these vessels became better understood.  William Hunter, who
was one of those anatomists who have contributed the most to our
knowledge of these vessels, insisted, most strongly, on their power
of absorption.  This doctrine was propagated, and even enlarged 
OP PHYSIOLOGY.
265
upon, by his brother, and pupils, and, generally, by all  those who
have devoted themselves to the anatomy of the lymphatic v  s^els.
It is  necessary that the proofs upon which  they founded *heir
doctrine, should possess all the strength which they have a^t.ibu-
ted to them.   In  consequence  of the importance of the subject,
we propose entering into some  details.
  To establish that the  lymphatic vessels possessed the power of
absorption, and that the veins are destitute of it, experiment h ive
been made.   But, even supposing them to be exact, which  a» .ve
shall  hereafter see, is far  from being the  case, they are so  few in
number, that it is truly astonishing,  that they  should  ever hive
been  thought sufficient to  overthrow a system, which had |)een so
long and generally admitted.   Of the.^'  experii'ien's, some have
been  made to prove directly, that the lymphatic vessels absorb. . id
others,  again, to show that the  veins Mo not  possess this power.
We shall, for the present, occupy ourselves with the first, and shall
examine the second, under the  article absorption of the. veins.
  John  Hunter, who was  one of the  first who positively d^'ded
the absorption of the veins, and  admitted that  of  the  lympha-
tics,  performed  the  following experiment,  which' appeared to
him very decisive of the question.  He opened the belly of a dog,
and  emptied a portion of the intestines, of the matter  which
it contained.  He  then injected warm  milk into  it,  which was
retained by means of ligatures. The veins which belonged to this
portion of the intestines, were emptied  of their blood, by small
punctures made into their trunks.   The blood was prevented from
going to them, by ligatures on  the arteries which corresponded to
them; in this situation, the parts were returned into the belly.
He allowed them to remain for half* an hour, and then  drew them
out; and, having examined them carefully, he  found, tnat  the veins
were nearly  as empty as when they were  returned  the first i.me,
and that they did not contain  any  white  fluid; while the lacteals
were quite fuil.*   The imperfect state of the art of  performing
physiological  experiments at that time, is the only apology  for this
celebrated anatomist, in not having  perceived how many important
circumstances there  were wanting, supposing it to be  exact, to
enable  him to draw any consequences from  it.  Luleed, in order
that this experiment should be of any use, it would be nece»stfry
          • Sep (Jmiksiiank's Auatoiuv oi* the absorbent vussels.
                              34 
266                    A  SUMMARY
 to  know  if the animal was fasting when it was opened, or was
 then  performing the function of digestion; it  would  have been
 necessary to have examined the state of the lymphatics, in order
 to have ascertained whether they were full of chyle; what changes
 took place in the milk during the time it remained in the intestine;
 upon  what evidence he asserted  that the lacteals were filled with
 milk, at the end of the  experiment, or  whether the fluid  which
 they contained, did not rather consist of chyle.  This experiment
 has been repeated at different times, by  Flandrin, professor in the
 Veterinary  School  of Alzant,  a man justly celebrated for the
 accuracy  of his experiments on living  animals, without having
 obtained any  success; that is, without  having perceived milk in
 the lymphatic vessels. I have myself often repeated this experi-
 ment, and the results which I have  obtained, perfectly agree with
 those  of Flandrin, and  are, of consequence, opposed  to that of
 Hunter.
  Thus the principal experiment of a distinguished author, who
is said to  have seen other fluids than chyle absorbed by the lym-
phatic vessels, appears to be, if not an illusion, at least,so imper-
fect, that  no important inference can be drawn from it.   The
other  experiments of John  Hunter being still less conclusive than
this, I have passed them over in silence.   They have been unsuc-
cessfully repeated by Flandrin, nor  have I myself been more for-
tunate in  attempting them.*
  I have  thought it worth while  to endeavour to  determine,
 whether the lacteal and lymphatic vessels of the intestinal canal
absorb any other fluid, than that  of the chyle. I, in the first place,
 ascertained, that if a dog be made to swallow four ounces of pure
 water, or if it be mixed with a  certain  quantity of  alcohol, or of
 colouring  matter, or salt, at the end of about an hour, the whole of
 the fluid will be absorbed from the intestinal canal.   It is evident,
 that if these different fluids were absorbed by the lymphatic ves-
 sels of the intestines, they would pass through the thoracic  duct;
 if this were the case, then we should find them in this duct, when
 we  collect the lymph of an animal  a half or three-quarters of an
 hour after introducing these fluids into the stomach.
 4 Experiment First.  A dog was made to swallow four ounces of
 a decoction of rhubarb; in half an hour afterwards, the lymph was
 * John Hunter employed but five animals in all his experiments upon absorption. 
                      OF PHYSIOLOGY.                  267

extracted from the thoracic duct.  This fluid did not present any
trace of the rhubarb, although nearly half of the decoction had dis-
apr jared from the intestinal canal; the urine, however,'perceptibly
contained rhubarb.
   Experiment Second.  A dog was compelled to drink six ounces
of a solution of the prussiate  of potash in water; a quarter of
an hour afterwards, the urine was found evidently to contain the
prussiate; the lymph extracted  at  the  same time  from  the tho-
racic duct, manifested  no signs  of it.
   Experiment  Third,  Three ounces of alcohol diluted with wa-
ter, were given to a dog.*  At  the end of a quarter of an  hour,
the blood of the animal exhibited a marked  alcoholic odour;  but
in the lymph nothing of the kind was found.
   Experiment Fourth.  Having passsed a ligature about  the tho-
racic duct of a dog, near the neck; he was made to drink two
ounces of a'decoction  of nux vomica; a liquid  which is extreme-
ly poisonous to animals; the  animal died as suddenly as if the
thoracic  duct had been left perfect.  On opening the body.it was
ascertained that the duct was not double, but that it terminated
singly in the left subclavian vein; and that the  ligature had been
tightly drawn around it.
   Experiment Fifth.   A ligature was passed about the thoracic
duct of a dog, and two ounces  of a decoction of  nux vomica in-
jected into the rectum.  The effects were similar to those which
would have taken place, if the duct had not been tied;  i. e. the
the animal died  almost immediately.  The structure of the duct
was analogous to that in the preceding experiment.
  Experiment Sixth. M. Delille and myself performed the follow-
ing experiment  upon a dog, which seven hours before had been al-
lowed to eat a large quantity of food, in order that  the lacteal ves-
sels might be easily perceived.  We made an incision into the ab-
dominal  walls, and drew out a fold of the  small intestines, upon
which  we  applied two  ligatures,  sixteen  inches  apart.   The
lymphatics which arose from  this portion of the intestine, were
extremely white and distinct, in consequence  of  the chyle with
which  they were distended.    Two  new  ligatures were then
placed upon each of these vessels,  about  four  inches apart; and
•Pure alcoh*l kills dogs almost iinmjfuiatoly. 
268
A  SUMMARY
we then divided these vessels between the two ligatures.  VVe
satisfied  ourselves  also, by every  possible means, that the fold
of the intestines taken from the  abdomen, had no communication
with the  rest of the body by lymphatic vessels.  Five mesenteric
arteries  and veins were sent  to  this  portion of the  intestine.
Four ot these  arteries, and the same number of veins,  were tied
and diviled  in  the same  manner that the lymphatics had been;
afterwards, the  two extremities  of this fold of intestine, were di-
vided, and entirely separated from  the rest of the small intes-
tines.   Thu* v\e  had a  portion  of small  intestine,  about  six-
teen inches  long;  not communicating with the rest  of the  bo-
dy, except by one  mesenteric  artery and vein.  These two ves-
sels were insulated about four  fingers  breadth  in length.   We
removed even the cellular  coat, lest lymphatics should be con-
cealed in it.  We then injected into this fold  of intestine about
two ounces of the  nux vomica, a ligature being applied to prevent
the passing out of the injected fluid.  The fold was then covered
with a piece of fine  linen, and  replaced in the  abdomen.  In
the space of  an hour,  or an hour-arid  six minutes, the effects of the
poison were  manifested  with  their ordinary intensity; so  that
every thing  took  place as if the  fold of  intestine had  been in its
naluial state.
   1 have often repeated each of these experiments, and have va-
ried them in different ways, and  have always found the same re-
sults.  I  think they  are sufficient  to show, positively, that  the
lymphatic vessels are not the only agents of  intestinal  absorption,
and that they are, at least sufficient to render doubtful, the opin-
ion that  these vessels absorb other substances than chyle.  It is
rather from analogy,  than from positive facts, that it has been ad-
mitted, that  lymphatic absorption takes  place  from  the urinary
and  pulmonary  mucous  surfaces, the serous and  synovial mem-
branes, the cellular tissue- the surface of the skin,  and the  sub-
stance of the  organs.   VVe intend, nevertheless, to examine
the  small number of proofs, by  which they have been suppor-
ted by authors.  The lacteal vessels  of the  intestinal   canal, are
the only  effective organs of absorption  in  this  part; the  lym-
phatic vessels then, of the rest of the body, which exhibit a similar
arrangement to the lacteals, must  possess the same power.  Such
is the reasoning ot the* partizans of lymphatic absorption; and, as 
OF  PHYSIOLOGY.
269
 it is known that all the external and internal parts  of the animal
 economy absorb, it has been concluded, that the lymphatic vessels
 were the only instruments of absorption.
   If the faculty of lymphatic absorption of other substances than
 chyle, from  the  intestinal  canal, had been well  demonstrated,
 there wouid be much force in this reasoning.
   But as we have already proved, that there is nothing less certain
 than <hi», we are  obliged to recur to other  facts, or experiments,
 which, as is generally  believed, demonstrate lymphatic absorp-
 tion.
   In animals which had died in consequence  of  pulmonary  or
 abdominal  hemorrhage, C. Mascagni found the  lymphatics of the
 lungs and peritoneum filled with blood.  He concluded, therefore,
 that these vessels  absorbed  the fluid with which they were filled.
 But I have often met, both in animals and  in  men, the lympha-
 tics distended with blood, where  there had  been  no extravasa-
 tion of this fluid; besides, in some cases, there is so  little differ-
 ence between the  lymph and the blood, that it will  be difficult  to
 distinguish them.   The  fact, therefore,  of  Mascagni, has no im-
 portant bearing on the question.
   J'»hn Hunter, after having injected water coloured  with indigo,
 into the peritoneum of an animal, said, that he saw the lymphatics,
 shortly afterwards, filled with a fluid of a blue colour; but this
 fact has been disproved  by the experiments of Flandrin,  upon
 horses.  This author injected into the pleura, and the peritoneum,
 not only a solution of indigo and water, but other coloured fluids,
 but  he never saw them  in  the  lymphatics, though they  were
 promptly absorbed.  M.  Dupuytren and myself, have made more
 than a hundred and fifty experiments, in which we have submit-
 ted a great number of different fluids to the absorption of the se-
rous membranes, but we  have never seen  them, in  a  single in-
stance, introduced  into  the  lymphatic vessels.   The substances
which  were thus introduced into the serous cavities,  produced
very sudden effects, from the rapidity with which they were absor-
bed.  Opium  produced  drowsiness, and wine drunkenness, &c.
I have satisfied myself, by many experiments, that tying the thora-
cic duct does  not diminish  the  promptitude  with which these
effects manifest themselves. 
270
A  SUMMARY
   It is very doubtful  then, whether the lymphatic vessels are the
organs which absorb, in the serous cavities.  We may add, that
the tunica arachnoides, the membrane of the aqueous humour, and
the membrana hyaloidea, the disposition  and structure of which
are very analagous to the serous membranes, and in which no lym-
phatic vessel has ever been detected,  possess a faculty of absorb-
ing, as active as the other membranes of the same kind.
   When  we apply a ligature upon  one of the extremities, that
part of the limb which is most distant from the heart swells, and
the serosity accumulates in the cellular  tissue.   An analogous
phenomenon sometimes  occurs after  extirpating the  mamma,  in
which the operator is obliged to remove all the lymphatic glands
from the axilla.  This phenomenon has been explained by suppos-
ing, that the ligatures, or the removal of the glands from the arm-
pit, prevent the circulation of the lymph, and especially the ab-
sorption in the cellular tissue.  Let us inquire how far this expla-
nation is safisfactory.  In the first place, the  lymph is a very dif-
ferent fluid from the cellular serosity;  again, may not the accumu-
lation of this serosity depend upon other causes, than the obstruct-
ed action of the lymphatics, for example,  the slow  circulation of
the venous blood?  Besides, the removal of the glands  from the
axilla, do not always produce the effect which  we have mentioned;
and we frequently see a complete disorganisation of the glands
of the armpit,  or groin, which are not accompanied with any
cedema.
  Numerous proofs are alleged of the absorption of the lympha-
tic vessels of the skin. It sometimes happens that when a person
punctures his finger, in dissecting a body in a state of putrefaction,
that, two or three days afterwards, the  puncture becomes inflamed,
and the  corresponding glands of the armpit swell and become
painful.  In some rare instances, these effects are accompanied by
a vivid redness, and pain through the whole course of the lympha-
tic trunks of the arm.  Under these circumstances, it is suppos-
ed, that the putrified animal matter is absorbed by the lymphatics
of the finger, that it is transported by them to the  glands  of the
armpit, and that its passage has been marked by the irritation, and
inflammation of the parts  through which it has passed.
  It cannot be  denied that this explanation accounts, plausibly
eaough, for all the appearances, nor shall I pretend  to assert that 
OF PHYSIOLOGY.
271
it is not correct; I suspect even, that  its truth may hereafter be
demonstrated.  But when we reflect, that it is, at this moment, one
of the foundations of therapeutics,  and that it often happens, that
powerful remedies are employed on this principle, I think we do
not go too far in doubting it.  I shall make some reflections upon
this explanation.  In a great majority of instances, a puncture
from a scalpel,  impregnated  with putrid matter, does not produce
any injurious effects.   It  frequently occurs, that a puncture with
a needle, perfectly clean, produces exactly the same phenomena
as those which  have been described; a slight  blow,  by  which the
end of the finger is contused, leads also to precisely the same ef-
fects.  The simple  impression  of cold upon the feet,  causes fre-
quently a swelling of the glands of the groin, and a redness of the
lymphatics, ot  the internal  part of the leg and thigh.  VVe may
also add, that it is common to see the veins  become inflamed,  in
consequence of punctures, and even to concur with the lymphatics.
I saw a very striking, and unfortunate instance of this, in the body
of Professor Lecler.   This estimable philosopher  died, in  conse-
quence of the absorption of putrid miasmata, from a slight scratch
on one of the fingers of the right hand.  The lymphatics and the
glands of the armpit  were inflamed, the glands were of a brown
colour, and evidently  diseased; but the internal membrane of the
veins of the right arm exhibited unequivocal  marks of inflamma-
tion, and the lymphatic glands of the  whole body had undergone
the same alteration as those  of the  right armpit.
  There are also many facts irt»pathology,  which are  alleged  as
proofs of lymphatic absorption.   After an impure coition, an ulcer
appears upon the glans penis, in the course of a few days, one of
the glands of the groin becomes inflamed,  swollen and  painful;
or one of these glands inflame without any preceding ulceration
upon the penis.  This not unfrequently occurs during the first few
days of a severe gonorrhoea.  In these cases, it is supposed, that
the orifices of the lymphatics absorb the venereal virus, and then
transport rt to  the glands, in consequence of which, these parts
are. thrown into a state of inflammation.   As they often return to
a state of health, after the application  of mercurial frictions to the
internal part of the thigh, it has been concluded, that the mercury
is absorbed by the lymphatics of the skin, and  that it  passes.
through  both them and the glands  of  the groin.   These different 
272
A  SUMMARY
facts are of a character to excite a suspicion of  the absorption of
the lymphatic vessels, but they  certainly do not demonstrate it.
This can never be really demonstrated, until the substance, sup-
posed to have been absorbed, is found in these vessels, and as no
one has ever seen, in cases of venereal  ulcer, or gonorrhoea, pus,
or when the mercurial ungent has been applied,  mercury, in the
lymphatic vessels or glands,  it is evident, they  cannot be consi-
dered as demonstrative evidence of lymphatic absorption.   It is a
different thing when we meet with pus,  or mercurial ointment, or
any other substance administered by frictions in these vessels; we
must  then  satisfy ourselves  whether they  have penetrated, by
means of absorption.   VVe shall see hereafter,  with what facility
those  substances which are mixed with  the blood often  pass into
the lymphatic system.                                            i
  Mascagni cites  an  experiment  made upon himself, which he
thinks conclusive; I will literally transl ite it.  "Having kept my
feet plunged in water for several hours, 1 '>bserved a, somewhat,
painful swelling of the inguinal glands,  and fne  transudalion of a
fluid through the gland.  I was seized with a defluxion of the
head,  and had a constant discharge of a salt and acrid  fluid from
my nostrils.  The  following is  the  explanation  which I give of
these  phenomena.  When the lymphatics of the feet were filled
with an unusual quantity of fluid, and the inguinal glands  became
swelled,  the lymphatics of the penis were filled with  more diffi-
culty.   The sanguineous vessels continuing to separate the same
quantity of fluid,  the lymphatic* vessels were insufficient to re-
move  the whole of  it, as their action upon  the  fluid, which they
naturally contain, was retarded; this is the reason  why  the rest
of the secreted  fluid transuded  through the gland.   Again, in
consequence of the abundant absorption of  the lymphatics of the
feet, the  thoracic duct was  distended  with great force,  and the
lymphatics of the pituitary membrane   were incapable of absorb-
ing freely, the fluids  deposited  upon  their  surface; hence the
coryza."  We learn, from this experiment, that Mascagni had the
glands of the groin swelled,  after having suffered his feet to re-
main some time in water;  the explanation which  follows is a mere
conjecture.
  It is not by inference  alone, that absorption of the lymphatic
vessels, in  the  deep seated organs,  has been admitted; but it is 
CP PHYSIOLOGY.
273
maintained by many experiments.  The facts which are alleged in
proof of it,  such as metastasis, the resolution of tumours, the di-
minution of volume in the organs,  &c. establish  clearly enough
the fact of internal absorption; but they by no means prove, that
the lymphatic  vessels execute it.   1  will  mention  a  circum-
stance, which, in my opinion, is much more favourable to the doc-
trine of the absorption of the lymphatic vessels, than any which
I have yet related.   1 am indebted to M. Dupuytren for this fact.
A woman who  had an immense tumour on  the superior, and in-
ternal part of the thigh,  with fluctuation,  died  in the hotel Dieu,
in 1810.  A few days before her death, an  inflammation had ta-
ken place in the sub-cutaneous cellular tissue, on the internal part
of the tumour.   On the  following day,  M.  Dupuytren examined
the body.   He had scarcely divided the skin that covered the tu-
mour, before he remarked white  points upon the  lips of the in-
cision   Surprised at this phenomenon, he carefully dissected the
skin, to a certain extent,  and found white  lines, some of which
were as large as crow quills, running over the sub-cutaneous cel-
lular tissue.  These were evidently lymphatic vessels, tilled with
puriform  matter; the lymphatics were filled with  it as far as the
lumbar glands, but  neither  these glands nor the  thoracic duct,
exhibited any trace of it.
   It will be asked,  if this fact is not enough to  justify us in con-
eluding, that the lymphatics had absorbed the fluid with which
they were distended?  This is probable, but in  order to render it
certain,  it would be necessary to prove the identity of the fluid
contained in the lymphatics, and that of the pus, with which the
cellular tissue  was filled.  We only know this  from appearance.
M. Cruveilhier, who relates  this fact, expresses himself  thus: "I
have said that this  fluid  was pus; it had the opacity,  whitish co-
lour, and consistence of  pus."  Now, the  simple appearance is so
deceitful, that  we  incur much risk in depending  upon it.  Un-
der similar circumstances, two fluids, essentially different  from
each  other,  as  milk and chyle, were for a long time confounded,
merely because they had the same appearance; besides,  we have
no evidence that the lymphatics were not  inflamed, and furnish-
ed the pus themselves, a thing which not unfrequently happens in
the veins. 
274                    A SUMMARY
  Under many similar circumstances, for example, after erysipe-
latous inflammation, with suppuration  of the cellular tissue of the
extremities, I have not been able to distinguish  any marks of pu-
rulent matter in the lymphatic vessels.  Besides, it is not. uncom-
mon to  find, in cases of this kind, the veins which arise from the
diseased part filled with a substance very analogous to  pus.
  In returning to the consideration of the absorbing power of the
lymphatic vessels,  we may  remark, that it is  not  impossible that
it may exist, but still this  is far from being demonstrated; and  as
we  are in possession of a great number of facts which appear, to
us, to establish, positively,  the absorption of  the venous radicles,
we shall consider  the history of the different kinds of absorption,
When we come to  treat of the course  of the venous blood.
  We now  return to the origin of the lymph,  as admitted by phy-
siologists.—If on  the one side,  the fluids which  are supposed  to
be  absorbed by the  lymphatic vessels, differ from the lymph  in
their physical and  chemical properties; and if on  the other hand,
the faculty of absorption  in the lymphatic vessels be a phenome-
non, the existence of which is very doubtful, what can we think
of the received opinion of the origin of the lymph? From whence
then does the fluid arise, which we meet in  these vesse^? or, in
other words, what is the most probable origin of the lymph?  From
the nature of the lymph, which has  a great analogy to the blood;
the communication which anatomy  demonstrates to exist between
the  termination of the arteries and the origin of  the lymphatics;
and from the facility and promptitude with which coloured and
saline fluids are introduced into these vessels;* it appears to  me
very probable,  that the  lymph  is a part of  the blood, which, in-
stead of returning to the  heart by  the veins, follows the rout of
the lymphatic vessels.  This idea  is  not entirely new, it resem-
bles very much that of those anatomists who first discovered  the
lymphatic vessels, and who thought, that these vessels were desti-
 ned to carry back a part of the serum of the  blood to the heart.
   This discussion  of the origin  of the lymph, may appear to some
to be too elaborate; but it was indispensable to avoid the false opin-
ions which  have been entertained, of the absorption  of  this fluid.
It is evident  that it is necessary to form a very different idea on
  * I have established this fact by direct experiments, an account of which 1 shall
 give below. 
                     OP PHYSIOLOGY.                  275

this subject from what is found in works on physiology, and to in-
vestigate the mode in which the lymph passes into the lymphatic
extremities.  But  with what  obscurity is this phenomenon sur-
rounded?  VVe are  ignorant of its cause, mechanism, the disposi-
tion of the instruments  which execute it, and even the circum-
stances under which it takes place.  Indeed, as we have already
remarked, it appears, that it is only under  particular circumstances
that the lymphatics contain lvmph.  There is  nothing about this
obscurity  that should surprise us; we have already seen, and we
shnll  hav<> often occasion hereafter to remark,  that it reigns over
all 'he phenomena  of li*V, to which we cannot applv the laws of
physics, chemistry,  or of mechanics; of conseeuerce,  over  all
those functions which relate to vital action and nutrition.

                    Course nf the Lymph.
   We hive but a few  words to «av on this  subject; authors have
scarcely noticed if, though it is still vague, and our own observa-
tions  on this point will be found  far  from satisfactory.  This  is
an interesting subject of research, and one  entirely new.
   From the general  arrangement of the  lymphatic apparatus, its
termination in  the thoracic duct,  and its cervical trunks, in the
subclavian veins and the form and arrangement of its valves, we
cannot doubt, that the lvmph passes from the different parts of the
body, from which  the lymphatics arise, towards the venous sys-
tem.   But  the  particular phenomena of this motion, its causes,
variations, &c.  have  not yet been investigated.
   The  following remarks are the result  of  my own examination
of this  point.  In  man, and living animals, it is very rare that the
lymphatics of the extremities, head and neck, contain lymph; their
internal surface alone appears to be lubricated with a very  thin
fluid.   In certain  cases,  however,  the ly.noh  i- arrested  in one
or more of these vessels, distends  them and gives to them an ap-
pearance very analogous to that of varicose veins, differing only
in colour.  M.  Soemmering, has seen this often on  the back of the
foot of a female, and I have had occasion to observe a similar in-
stance of it on  the corona glandis.   We find frequently, in dogs,
cats,  and  other livin-r animals, lymphatic vessels full of lymph, on
the surface of the liver,-gall, bladder, the vena  cava of the trunk,
the vena'ports?e,  in the pelvis, and on the sides of the vertebral 
276
A  SUMMARY
column. The cervical trunks are also frequently filled with lymph,
though it is by no means rare that they are found entirely empty.
With respect  to the thoracic duct, I have never seen it empty,
even when the lymphatic vessels of the rest of the body were in a
state of perfect vacuity.
  Why do  these varieties exist  in the presence of the lymph in
the lymphatic vessels? why do those of- the  abdomen  contain it
more frequently than the rest? and  why does the thoracic duct
contain it constantly?—1 acknowledge myself incapable of giving
a satisfactory answer to either of these questions.  The only cir-
cumstance which I  think I have observed, but which  I will not
undertake positively to assert,  is, that  the  lymph  is found most
frequently in the trunks of the lymphatics of  the neck,  when ani-
mals have been long deprived of every kind of aliment.
   As abstinence is  prolonged in a dog,  the lymph becomes more
and more red.  I have  seen  it when its colour was nearly that of
blood,  in dogs which had fasted  eight days.   It has appeared to
me also, that,  in these cases, its quantity is more considerable.
The 'vmph appears to move slowly in  the vessels   If  we punc-
ture it in man, during  life;  (I had once occasion to do this;) the
lymph passes out but slowly and without a jet.   M. Soemmering,
had already made a similar experiment.  When the  lymphatic
trunks of the neck are filled with lymph, we  may easily insulate
them to the  extent of an inch.   VVe may then perceive that the
fluid which fills them, passes along very  gently.   If  we compress
them, so as to make the  lymph, with  which they are  distended,
pass into the subclavian vein, it is often  half an hour before they
become filled anew, and they often remain empty.
   Nevertheless, the lymphatic vessels evidently possess a contrac-
tile power; they empty themselves, frequently, as soon as they are
exposed to the air.  It is  probable that, in consequence of this
contraction, they are almost always  found empty, except the tho-
racic duct, in animals recently dead.  This power is undoubtedly
one of the causes which determine the introduction  of the  lymph
into the venous system.  The pressure which the lymphatics re-
ceive, from the confractibility of the tissue of the skin,  and other
organs, muscular contraction, the pulsation  of the  arteries, &c.
must  have a considerable effect  upon the  course of the lymph.
This is evident in the lymphatics of the  abdominal cavity. 
OF PHYSIOLOGY.
277
  We are completely ignorant of the use of the lymphatic glands;
this is no doubt the  reason why they have been the ooject of so
much speculation.  Malpighi, considered  them  as small hearts,
which  gave a progressive motion to the lymph; others have  sup-
posed that they served to form divisions in the lymphatic vessels,
and to imbibe, like sponges,  the superfluous humours,  to give a
nourishing juice to the nerves, to form fat, &c.  In a word, almost
every one has given on this subject an unbounded freedom to his
imagination.*
   We shall say no more on the  course of the lymph; it may easily
be seen, how  much remains to be done, to throw  light on this phe-
nomenon, and, generally, upon all those which relate to the  func-
tions  of the  lymphatic  system, and  its utility in  the animal
economy.  If our actual knowledge of this subject is so limited, with
what confidence can we receive those medical hypotheses in which
we hear of the thickening of the lymph, the obstruction and  im-
perfect  action  of the  lymphatic »!ands, and of the   defective
action of the -ibsorbent mouths  of the lymphatics, which are sup-
posed to occasion dropsies?  \nd  how  shrill  we determine  to
administer rernedies founded on such reasoning?   The changes of
structure and volume,  which take place in the  lymphatic glands,
from age, must induce us to  presume, that tho  action of the  lym-
phatic system, undergoes modifications in the  different periods of
life;  but there is nothing positively known on the subject.
    COURSE  OF THE BLOOD  IN  THE  VEINS.

  The object of the function which we are now about to examine,
is to transport the venous  blood  from all  parts of the  body and
lungs.   Besides, the organs  which execute if, are  at the  same
time, the principal agents of absorption on the external, and inter-
nal parts of the body;  with the exception of the absorption of the
chvle,  the lymph, and  that which takes place from  the mucous
surfaces of the lungs.
  • I think it unnecessary to notice, particularly, the retrograde motion of the
fluids in the lymphatic vessels; the observations of Darwin, and others, upon this
subject, I conceive to be merely imaginarj. 
278
A  SUMMARY
                    Of the  Venous Blood.
   This name is given  to  that animal fluid which is contained in
the veins, the right side of the  heart, and the pulmonary artery;
organs which, by their union, form the apparatus appropriated to
the venous blood.  This fluid  is of a brownish red colour, so deep,
that it  has received the name of black  blood.   In some cases its
colour is less deep, so  as to be scarlet.   Its odour is sui generis,
its taste is also peculiar; we perceive, however, that it contains
salts, and principally the muriat of soda. .  Its specific  gravity is
something  less  than  water; Haller found  the  medium  to be,
:  : 1.0527 : 1.0000.   Its capacity for caloric, may be expressed by
934. that  of  the arterial  blood  being 9-1,  its  medium tempera-
ture  is 101°  of Far.   The  venous blood,  when  taken from its
vessels, and  left to itself, forms, at the end  of a few moments, a
soft mass; by degrees this mass  separates spontaneously into two
parts, the one a yellowish transparent fluid, called the serum; the
other soft, but nearly solid, of a deep brownish, red colour, which
is called the crassamentum;  the  last occupies the lower part of
the vessel the serum rising above it.   Sometimes there is formed
on the surface of the serum a thin, soft and reddish coat, to which
the name of crust  of the blood,h&?> been very  improperly given.
This spontaneous  separation  of the elements  of the blood, does
not occur until it has remained, for some  time, in a state of rest. If
it be agitated, it retains, for a much  longer time, its homogeneous
appearance.
   When venous blood  is brought in contact with atmospheric air,
or oxygen gas, it  assumes  a Vermillion tint:  with ammonia  it
becomes of a  cherry  red; with azote of a reddish  brown, but
much deeper colour.*   While changing colour, it  absorbs a con-
siderable quantity  of these different gases.   When kept for  some
time  under  a receiver, placed  over  mercury, it exhales a  con-
siderable quantity  of carbonic acid.   M. Vogel  has very recently
made some new researches on this subject.

   * For changes in colour,  which the venous blood undergoes, whea brought in
contact with the different  gases, see vol. iii. of the Chemistry of M. Thenard,
page 513, 
OP PHYSTOLOGY.
279
  According to M. Berzelius, one  thousand parts of the serum
of the human blood contain,
              Water,     -    -     -    -    903.0
              Albumen,     ....   80.0
              r Lactate of soda and extrac-
Substancessoluble )    •       ...                a
  in alcohol.     )   t,ve  ma"er'    "    "    4
              L Muriat of soda and potash   6—10.0
                {Soda  and animal  matter,
                  phosphat of soda,    -    4
                Loss,      -    -           3— 7.0
                     Total,                 10UOO
  The serum sometimes presents a whitish milk-like appearance,
from wiiicii  it has been supposed, that it contains chyle; the sub-
stance that gives to it this appearance resembles oil.
   The crassainentum  of the blood  is chiefly  formed  by the
fibrine and colouring matter. When separated from the colouring
matter, the fibrine is solid, whitish,  insipid, and inodorous; it is
heavier than  water, does not  produce any action upon vegetable
colours.it is elastic when it is humid, and becomes brittle by des-
sication; by distillation it furnishes  a large quantity of the car-
bonat  of  ammonia, and  a large mass  of carbon,  the  ashes  of
which  contain a considerable  quantity of  the  phosphat of lime,
a little of the phosphat of magnesia, carbonat of lime, and car-
bonat  of soda.  One hundred parts of fibrine are composed of,
Carbon,	53.360
Oxygen,	19.685
Hydrogen,	7.021
Azote,	19.934
Total,	100.000
  The colouring  matter is soluble in water, and the serum of the
blood.  When examined by a miscroscope, after being  dissolved
in these fluids, it  appears, like most parts of the fluids in the ani-
mal economy, to  consist of small globu les; when dried and cal-
cined afterwards  in  contact with the air, it melts,  bursts up into
bubbles, burns with a flame, and forms a carbon, which  cannot be
reduced  into  ashes, but with extreme difficulty.  This  carbon,
during ite combustion, disengages ammoniacal gas,  and furnishes 
230
A  SUMMARY
a hundredth part of its  weight of ashes.   It  is composed  of,
           Oxid of iron,                       5£.0
           Pnosphat of lime and a trace of the
             phosphat of magnesia,              8.0
           Pure lime,                          17.5
           Carbonic acid,                     19.5
               Total,                         100.0
  It is important to remark, that  there is not found  in any part
of the blood, either gelatin, or phosphat of iron, as was formerly
believed.  The respective proportions between the quantity of the
serum and the crassamentum; those of the  colouring matter and
fibrine,  have not been carefully examined, as we shall see by arid
by.  It  is probable  that they  are varied  by  an infinite number of
circumstances.
  The coagulation of the  blood, has been, in turn, attributed to
cold, the contact of air, and a state of rest;  but  John  Hunter and
Ht-wson demonstrated  by experiments, that this  phenomenon
could not be referred  to either of  these causes.   Hewson took
fresh blood and froze it, by exposing it to a low  temperature; the
blood was  afterwards melted, and  it  became fluid,  and shortly
coagulated  as  usual.  John  Hunter obtained  a  similar  result.
Thus it was proved, that  coagulation of the blood is not produced
by cold.  It seems  even that a temperature, somewhat high, is fa-
vourable to its coagulation.   Experiment also  proves, that the
blood runs  into a mass, when deprived of the contact of air, and
agitated; in general however, repose, and the contact of air favour
its coagulation.
   But so far from referring the coagulation  of the blood to any
 physical influence, it must undoubtedly  be considered as essen-
tially vital;  that is,  as giving demonstrative evidence, that the
blood is endowed with life.  We shall see, hereafter, of what im-
 portance the property of coagulating, possessed  by the blood and
other fluids, is in many of the phenomena of nutrition.   To form
a more  precise idea of the coagulation of the venous blood, 1 plac-
ed, in the focus of a microscope, a drop of this fluid while it was
still in  a liquid state; it appeared like a  red  mass, but, as soon as
 it began to  coagulate, the edges became transparent and granulat-
 ed;  the solid  part,  being almost opake, formed an infinite number
 of meshes, or cells,  which contained the fluid part; which was the 
OF  PHYSIOLOGY.
281
most transparent part.  It was this disposition which gave to the
edge of the drop  of blood, its granulated aspect. By decrees, *hese
meshes became enlarged, by the retraction of the solid  parts; in
many places they entirely disappeared, and there only  remained,
between the external circumference of the drop of blood, and the
edge  of  the  central coagulum, an arborescent appearance,  very
analogous to what we have described, in speaking  of the lymph;
their divisions communicating with each other, like the vessels and
nerves of leaves.  These experiments must be made by a diffused
or artificial lii-ht, for the direct light of the sun produces dessica-
tion, without  coagulation.   Under many circumstances, the  blood
coagulates, even when contained  in  the  vessels; but in  general,
this  phenomenon arises  from  disease.  Some  authors  thought
they had remarked, that the blood, in coagulating, became warmer,
but John  Hunter, and very recently Mr. J. Davy, have proved,
that there is no  elevation of temperature.
   \t the  period when galvanism attracted so much attention in
France, it was  supposed  that if a  portion of the coagulum,  re-
cently formed,  was submitted to a galvanic current, that it con-
tracted itself  like the  muscular fibres.  I have often endeavoured
to produce this  effect, by  submitting portions of coagulum, at the
moment of their formation, to  the  action of the pile; but I have
never  seen any  thing of the kind.  I have varied  these attempts
in different ways,  but have never been more fortunate   Very re-
cently, I have repeated this experiment, with M. Biot, but the re-
sult was the same.  The analysis of the venous blood, such as we
have already pointed  out, makes us acquainted  with the peculiar
elements of this fluid;  but as all the substances absorbed in the in-
testinal canal, the serous membranes, and the cellular  tissue, are
mixpd immediately with the venous blood, the result must be, that
the composition  of this fluid will vary, in proportion to the matter
absorbed.  There will be found, under different  circumstances,
alcohol, tether, camphor, and salts, which it does  not contain gene-
rally,  when these  substances have been submitted to absorption,
in anv part of the body.   The greater or  less degree of prompti-
tude with which the blood runs into a mass, the solidity of the co-
agulum,  the separation of the serum, the formation of an albumin-
ous  coat  upon its surface, and the particular temperature of the
56 
■28»
A  SUMMARY
fluid, in or out of the vessels, are  phenomena which we shall exa-
mine, in the article urierial blood.

               Apparatus of the Venous Blood.
  This is  composed first of the veins; second of the right auricle*
and  ventricle of the heart; third, of the pulmonary artery.

                        Of the  Veins.
  The  arrangement of the veins in the  tissue of  the organs,  es*
eapes our senses.  When we first begin to distinguish them, they
are presented under the form of an infinite number of small tubes,
exceedingly delicate, communicating with each other in a sort of
very tine  net-work;  they soon  increase  in volume, still preserv-
ing  their  reticulated  arrangement.   They  in  this manner form
vessels, the  capacity,  form, and  disposition  of which,  differ
in each tissue, and even in  each  organ.   Some  organs appear al-
most entirely  formed of venous radicles; such are the spleen, the
cavernous parts of the vagina, the  clitoris, the iris, the nipple,
and  the ureter, &c.   When we force an  injection  into one of  the
veins,  which pass out  from  these different tissues, they become
entirely filled with the injected  matter,  which does not hapoen
when the  injection is  pushed into the arteries.   The incision of
these parts in man, or in living animals, causes blood to be thrown
out,  which has all the appearance of venous blood.
  The  venous extremities  communicate with  the arteries and
lymphatic vessels; anatomy  leaves no doubt on this point;  but it
appears that those  extremities,  the disposition of which is  un-
k'.ovn, are also open on the different surfaces of the membranes,
the  cellular tissue, and even  the  parenchyma  of  the organs.
M. Kibes, having forced mercury into one of the branches of  the
vena portse, saw the villosities of the intestinal mucous  membrane
filled with this  metal,  which spread itself into the cavity  of the
intestine.   In forcing air from the venous trunks, towards their
origin, and overcoming the resistance of the valves, which  is very
easy, in those bodies which are in a state of incipient putrefaction,
the  same anatomist  has alvvays  found the air  spread  with great
facility into the cellular membrane, although no sensible rupture
of fhe  venous  -.vails  had taken t lace,   i stave  n.isde similar  re-
marks  in forcing the air, or other  fluids,  into the veins of  the 
OP PHYSIOLOGY.
286
heart.  These facts,  which have  taken place  since my experi-
ments on  venous absorption, of which I shall  speak  hereafter,
agree perfectly with them.
   The  veins of the brain surround it on every side; they form a
great part of  the  pia  mater, and  penetrate into  the ventricles,
where  they contribute to form  the  plexus choroides.  Those of
the testicle, represent a very fine net-work, which covers the sper-
matic vessels, while those of the kidneys are short and volumin-
ous.  In leaving the organs to  pass  towards the heart,  the veins
affect i very different  arrangement.  In the brain they are lodged
between  fhe laminse of the dura miter, orotecfed by it, and are
known by  the name of sinuses.  In the spermatic cord, they are
flexuous,  anastomosing  frequently,  and  forming the  pampini
form bodies.   \bout  fhe vagina, they are reticulated, in  the
uterus  they  are  verv voluminous,  with numerous flexuosities.
In the extremities, they are distinguished into de.v> -eated,  which
accompany the arteries,  and superficial, which are placed  imme-
diately  under the  skin, in the midst of the lymphatic trunks,
which are  found  there.   In proportion as the veins become  dis-
tant from  the organs,  and approach the heart,  they diminish in
number, and increase in  volume, so that all the veins of the body,
which  are innumerable,  terminate in the  right ventricle  of the
heart, by three trunks, the vena cava  inferior, and superior, and
the coronary vein.
   1  have said, that the small veins communicate with each other,
by frequent anastomoses; this disposition exists also in the large
veins,  and in  the trunks of the veins.   The superficial trunks, in
the extremities, communicate with the deep seated; the veins of
the external part of the  head, with those of the internal; the ex-
ternal,  with the internal jugulars;  and the vena cava superior,
with tin  inferior, &c.   These  anastomoses  are advantageous to
the course of  the blood  in these vessels.  Many veins exhibit, in
their cavities, folds of a parauolic lorm, called valves; they have
two free surfaces, and two edges,  the one of which adheres to the
walls of the vein,  while  the other  is left floating in it.   The first
is more distant from  the heart, and  the other much nearer to it.
The number of the valves are  not always  the same; in general,
thev are the most numerous where the blood has to rue against its
own gravity, aud they have only a weak pressure to support them* 
384
A  SUMMATtY
from the surrounding parts;  they are wanting, on the contrary, ill
those parts where the veins are exposed to an  habi'ual pres«.vre,
whicN favours the circulation of  the  blood,  and in  those  which
consist of canals, not extensible  They  rarely exist in those veins
which are  less than a line  in diameter.  Sometime- the size of
the valves is so great, as  to  fill completely  the cavitv  of the
vein;  but  at  others, they  are evidently  too small to produce this
effect.  All  anatomists have thought that this arrangement de-
pended on primitive organization; but Bichat thought he had dis-
covered that  it arose from the state of contraction,  or dilatation of
the veins, when  death took place.
  I have  endeavoured  to satisfy myself of the  correctness of
Bichat's idea, but 1 acknowledge I have been unable to do it.  I
have not perceived that the distention of the veins had any influ-
ence upon the size of the valves;  it has  seemed to  me, on the con-
trary, that they  remain always the same;  but that  their form was
altered by their  contraction or  dilatation, and it was probably this
which deceived  Bichat.
   the veins  are formed by three  membranes, placed one over the
other.   The  external is cellular, dense, and difficult to rupture.
If we can depend on the  works of anatomists, that which comes
next is formed of parallel  fibres, according  to the length of the
vessel; and that this is easiest  to be  perceived, when  the  vein is
large, and  contracted.  I  have endeavoured, but without success,
to distinguish the fibres of the middle  membrane of the vein.   I
have always  observed excessively numerous filaments  interlaced
in all directions, but which  seemed to assume the appearance of
longitudinal  fibres, when  the vein is  folded longitudinally; a dis-
position which is often observed in the large veins.  The sub-cuta-
neous veins  of the extremities, the walls of which are very thick,
will be found to afford the greatest facility,  in examining the ar-
rangement of this membrane.  We are  ignorant  of the chemical
nature  of the fibrous coat of the veins;  from some experiments
wheh I have made, I suspect it is chiefly fibrine.   It  is extensi-
ble and  firm, and does not present otherwise any peculiarity, in
the living animal, in  which it resembles muscular fibres   When
irritated with the point of a  scalpel, or submitted to a current of
galvanic fluid, it does not exhibit  any sensible contraction.  The
third membrane of the veins, or internal tunic, is extremely  thin, 
OF PHYSIOLOGY.
285
and verv much folded  on  that surface  which is in contact with
the wood;  it is very flexible,  and extensible, at the same time
preset ting a considerable  resistance; it  sunports, for example,
without being ruptured, the pressure of a ligature drawn strongly
around it.  Some of the  veins, for example, the sinuses of thebr;in,
the venous canals o1' the mouth, ami the subhepatic veins have their
their walls alone formed by this membrane, being almost entirely
destitute of the two others.
   These  three funics  to  ether, form a  very elastic tissue.   In
whatever direction the  veins may be enlarged, t>-ey  resume  im-
mediately their primitive form; nor can Limagine on what  ground
Birhat has asserted that they are destitute of elasticity.  Nothing
can be easiei  than to satisfy ourselves that  they  possess this |-hy-
sical  property to a very great  extent.   A large number of small
art* ries and veins, ca'led the vasa vasorum, and filaments of die
great svmpathetic, are  sent  to  the  veins;  they are, therefore, far
from being exempted from those diseases, to which the other parts
of the animal bodv are subject.  They sometimes seem to be af-
fected by inflammation.

               Of the right  Cavities oj the Heart.
   The heart is so well  known, that it seems hardly necessary to
insist much upon its form and  structure.  In man,  the mamalia,
and buds, it is formed  into four cavities; two superior, which are
 called auricles, and two inferior, which are called ventricles.   The
 left auricle  and ventricle  belong  to the apparatus of the  arterial
 blood; the auricle a-.d  ventricle of the right side,  make a part of
 that  of the veuous blood.
   It is not very easy to describe  the form of the right auricle; its
 transverse diameter is the greatest; its cavity exhibits, at its posteri-
 or part, openings from (he vena cava, superior and inferior; internal-
 ly it  presents a depression, called the foramen ovale, which is  Oj>en
 in the fcetus, but  closed in the adult   At the bottom of the  auri-
 cle is  a large opening  which  conducts  into the  right ventricle.
 The internal surface of the auricle presents a  great number of
 fleshy masses or  columns,  which are  rounded  or flattened, and
 which cross each other in various directions, exhibiting a sort of
 spongy tis»ue, spread over the internal surface of rise auricle, .md
 forming a coat of considerable thickness.   At the place where the 
286                    A  SUMMARY
vena cava  inferior is connected with the auricle, is a fold of the
internal membrane, which is called the eusta<-',iaa vdve.
  The right ventricle is a more spacious cavity,  and has thicker
walls than the auricle; it is of a triangular form, the base of which
corresponds to the auricle and pulmonary artery and its apex to
that of the heart; all its surface is covered with large and rounded
projections, which are called columna? carnece, their arrangement
is very irregular, like those of the auricle, they form a reticulated
or cavernous tissue, through the whole extent of the ventricle, par-
ticularly towards its apex.  The columnse earned of the ventri-
cle, being generally larger than those  of the auricle, form also a
net-work, the meshes of which are coarser;  some arising from the
surface of the ventricle, terminate in forming one  or  more ten-
dons, which are attached to the loose edge of the tricuspid valve;
which is placed at the opening, by  which the auricle and ventricle
communicate  with each other. At the side, and a little to the
left of this, is the orifice of the pulmonary artery.  The walls of
the auricle and ventricle are formed of three tunics; the one ex-
terior is of a serous nature, the internal is analogous to that of the
internal membrane of the  veins, and the  middle is chiefly muscu-
lar and contractile: this  coat is thin in the auricle, but of great
thickness and strength in the ventricle.  The innumerable  fibres
which  compose it have a very intricate  arrangement, many res-
pectable  authors have endeavoured,  with great  labour, to ascer-
tain their direction; but,  notwithstanding their patience and  ad-
dress,  the disposition  of these fiores is still  but little  known.
Happily  it  is not necessary  for  us to form  an exact idea  on
this  point, to enable us to comprehend the action  of the auricle
and  ventricle.   The heart has arteries, veins, lymphatic vessels,
and  nerves, which arise from the great sympathetic, and  are  dis-
tributed to its walls and arteries, and perhaps even to its muscular
tissue.

                  Of the Pulmonary  Artery.
  This artery arises from the  right ventricle, and passes towards
the lungs.   At first, it forms  but a single trunk,  soon it becomes
divided into two branches, one of which is sent to the right  and
the other to the left lung;  each of these branches are divided and
subdivided, until  they form an infinite number of small vessels, 
OF PHYSIOLOGY.                 287
the tenuity of which is so great, that they are at  last impercepti-
ble by  our senses.  The divisions and  sub-divisions of each of
these branches of  the  pulmonary artery, are remarkable in this,
that they  do not communicate with each other before  becoming
extremely small, the last divisions appear to be continuous, im-
mediately, with  the roots of the pulmonary veins. The pulmonary
artery  is formed of three  tunics, the external  is very strong, and
of a cellular texture; the internal,  is very smooth on its internal
surface, and is always lubricated  by a thin fluid.  The midd'e tu-
nic  has circular fibres, which are very  elastic, and were long
thought to be muscular, though they evidently do not possess that
character; its chemical nature appears to be nearly all fibrine, when
tested  by  reagents.

                Course  of the Venous Blood.
   According to the most distinguished  physiologists, this  is still
but imperfectly  understood.   We shall only describe, at present,
its most apparent  phenomena, reserving more doubtful  questions
until we speak on the relations which exist between the  course
of the  blood  in the veins and  arteries.   We shall  then speak of
the cause  which determines the entrance of the blood into the ve-
nous extremities.   In order to form a general, but just idea, of
the course of the blood in the veins, it is  necessary to  recollect,
that the sum total of the cavities of the small veins forms a much
larger cavity than  those  of  the  large,  into  which they pour
their contents,  and  these again bear  the same relation  to the
trunks in which  they  terminate.  In  consequence of this,  the
blood  which goes from the extreme  veins, passes  always  from  a
larger  to a smaller cavity.  The following  hydrostatic  principle,
is therefore perfectly applied in this instance.  When a fluid pas-
ses through a tube which  is full, the quantity which traverses in  a
given time the different  sections of the tube, must be always the
same;  but when the tube becomes larger, its velocity diminishes,
and increases when the tube is smaller.
   Kxperience confirms the exactness of this  principle, and  the
justness ol its application to the course of  the  venous  blood.   If
we cut across  a small vein, the blood passes out  very  slowly;
it passes out much more rapidly from a large vein, but its velocity
is very much increased when a venous trunk is  opened.   Many 
288
A  SUMMARY
veins are destined to transport the blood  contained  in  an organ
towards the large trunks.  In consequence of their frequent anas-
tomoses, the compression  of one or  more of the veins does not
prevent, nor even diminish the quantitv of blood  which is re-
turned towards  the  heart; it  only  acquires a greater degree of
velocity,in the veins which remain open.   When  a  ligature is
applied about the arm, preparatory to performing the operation of
bleeding, the following phenomena tak<*  place.   In tne ordinary
state, the blood which is carried to the forearm and hand, returns
towards the heart by four deep seated, and at least as many super-
ficial  veins.  When the  ligature is passed around the arm, the
blood  no longer passes by the sub-cutaneous veins, and traverses,
with difficulty, those which are deep seated.  If one of the veins
be then opened at the  fold of the arm, a  continued jet will be
formed, which lasts as long as  the  ligature remains  tight, and
ceases  when it is removed.
   We  often  find  the  veins   not  much distended with blood;
when,  however,  this  fluid  passes  with the  greatest  rapidity,
the reverse is the case.  In the extreme veins, it is very  little the
case.   For a reason, easy to  be understood, those  circumstances
which  accelerate the motion of the blood  in the veins, increase
also, the distention of the vessels. The introduction of the blood
into  the veins taking place in  a continuous manner, every cause
which  operates as an obstacle to its course, produces a distension
of the  vein, and a greater or  less degree  of stagnation of the
blood.
   The walls of  the veins appear to have a  very feeble  influence
upon the course of the blood.   They yield easily when its quan-
tity is  increased, and contract again when  it is diminished.  But
this contraction is extremely limited, it is not  sufficient to expel
the blood  entirely  from  it; this  is constantly found  to be the
case in the recent  suoject.  I  have often seen the veins empty
in the living animal, and at  other times,  I  have  observed that
the column of fluid was  far from  iiiiiiig ur  entirely the cavity
of the vessel.
   A great number of the veins,  such as  those  of the  mouth,
the sinuses of the  dura mater, and the liver, the walls  of which
form an inflexible  canal, c;>r :m»:  hav  iv.y  influence  upon the
motion of the  blood, that  passes  through their   cavity.  We 
OF  PHYSIOLOGY.
289
must attribute always, the faculty which the veins have of contrac-
ting, when the column of blood  is diminished, to the elasticity of
their walls, and not to a contraction, which has any analogy to that
of the muscles.   This contraction is much  more remarkable in
those  which  have thick  walls, like the superficial veins.   If the
veins  have, of themselves, but little influence upon the course of
the blood, there are many auxiliary causes, the action of which is
very manifest.  All  compression, whether continued or alternate,
exerted upon a vein, can, when  it is sufficiently strong to  flatten
the vein, obstruct the passage of the blood.   If  it  be moderate,
it opposes the dilatation of the vein from the pressure of the blood,
and thus favours its motion.
  The habitual pressure which the skin of the extremities exerts
upon  the veins, running beneath it, is one cause which renders the
course of the blood  in these vessels more  rapid and easy.  We
cannot doubt this, as those circumstances which diminish the con-
tractility of the  tissue of the skin, are, sooner or later, followed
by  a considerable dilatation  of  the  veins, and in some cases the
production  of varices.  It  is  also known,  that an appropriate
bandage restores  the veins to their ordinary  dimensions, and the
course  of the blood to the  internal part.  In the  abdomen, the
veins are submitted to the alternate pressure of the diaphragm
and abdominal muscles; a cause  which  is favourable  to the pro-
gress of the venous  blood  in this part.   The veins of the brain
support  also a considerable  pressure,  which  must produce the
same  result.   Whenever  the blood in the  veins, passes in the
direction of  its weight, its progress is  much easier than  when it
has to mount against  it.  We must not neglect to notice  the re-
lations  of these auxiliary causes to the arrangement of the veins;
where this is the  most remarkable, the veins do not possess valves,
and their walls  are  very thin, as  we notice in the abdomen chest,
eavitv of the cranium, &c.   But where they have the most  influ-
ence, the veins are furnished with valves, and the walls are much
thicker; lastly, where they are very weak, as in the sub-cutaneous
veins, the valves are numerous, and the walls of considerable
thickness.
    If  we wish to form a comparatively exact  idea in this case, we
have  only to examine the internal saphsena, the crural, and the
commencement  of  the  external  iliac veins, on a  level with the 
290                    A  SUMMARY
opening  of the femoral aponeurosis, destined for the passage of
the saphsena vein; the contrast in the thickness of the walls will
be found very striking.  I have lately made this comparison, in
the body of a criminal who was very muscular.   The  walls of the
saphsena were as thick as those of the carotid  artery; the crural,
and  especially  the external iliac, had walls  which  were  much
thinner.
   We must take  care, however, lest we confound these circum-
stances,  favourable to the course of the blood in the veins, with
causes which act in a very different manner. For example, it is ge-
nerally known that the contraction of the muscles of the fore arm
and hand, during bleeding, accelerates  the  motion of the  blood
which escapes through the opening of the vein.   Physiologists as-
sert, that the muscles, in contracting themselves, compress the
deep seated veins, and expel the  blood, which passes  then into
the superficial veins.  If this were the case, the  acceleration would
be only instantaneous, or  at least  of very short duration; while it
is known to continue, in  general, during  the  contraction.   We
shall see  hereafter  how this  phenomenon  can  be explained.
When the feet are plunged, for sometime, in  warm water, the sub-
cutaneous  veins swell;  this is generally attributed to the rare-
faction of the  blood.  The true  cause appears  to me to  be  the
increase in the quantity of the blood which is  carried to the feet,
and especially the skin;  this augmentation  would naturally ac-
celerate the motion of the blood  in the veins, inasmuch as in a
given time they are traversed by a larger quantity of blood.
   From the preceding remarks, we may easily understand, that the
venous  blood must be frequently stopped, or  at least its  course
retarded, either from the too  great pressure  which the veins
experience, in  the different positions that the body assumes; or by
different foreign bodies which are applied to  it, &c.   Hence the
necessity of the numerous anastomoses, which  we have said exist
not only between the extreme veins, but those which are  larger,
and also in the  large trunks.    In consequence of these frequent
communications, should one or more of the veins be  compressed,
so as not to allow the blood  to  pass, this fluid is turned  aside,
and arrives at the heart  by other routs.  One  of the uses  of the
vena azygos appears to be, to establish an  easy communication
 between the vena cava superior and inferior.   1 believe, however. 
OF  PHYSIOLOGY.
291
  its principle use is, to afford a common termination for the greater
  part of the intercostal veins.
    There is nothing very obscure in the action of the valves of the
  veins;  they are  nothing else but true valves, which oppose the
  return  of the blood towards the venous extremities, and which
 fulfil this office  most  perfectly,  when  they  are  large; that is,
 when they are favourably disposed  for closing the  cavity of the
 vein entirely.  The friction of the blood against the walls of the
 veins,  its adhesion to these walls, and its imperfect fluidity, must
  modify the motion of the blood in  the veins, and generally tend
 to retard it.  But it is impossible, in the present state of physio-
 logy and  hydrostatics, to assign, with precision, the particular ef-
 fect of  each of these causes.
    What  we have said of the course of the venous blood, is enough
 to show, that  it is very much modified by an infinite number of
 circumstances.   VVe shall  have occasion to examine  this  more
 particularly hereafter, when we come to examine, generally, the
 circulation  of the  blood, and the differences in quality, between
 that of the arteries and veins.   The  venous blood from every part
 of the body, arrives at  the  right auricle of the heart  by three
 trunks,  which we  have  already  mentioned, viz: two  which are
 very voluminous,  called  the  vena  cava inferior and  superior,
 and a small one, called the coronary vein.   It  is very probable,'
 that the blood passes through each of these  veins with very dif-
 ferent degrees of rapidity.  It is evident that these three columns
 of fluid endeavour to penetrate into the auricle at the same time,
 and that this effort must be considerable.

               Absorption exerted by the Veins.
   Not only do the venous extremities receive blood  directly from
the  extreme arteries, but they present another remarkable  phe-
nomenon.   Every kind of  gas or  fluid, vvhen put in  contact with
the different parts of the body, except the skin, pass  immediately
into the small veins, and arrive soon at the lungs with the venous
blood.   The same thing takes place with all  those solid  sub-
stances, susceptible  of being  dissolved by the blood or secreted
fluids.    In a very short  time  they are introduced  into the
veins, and are transported to the  heart and  lungs.  This intro-
duction  is called venous absorption.  Let us study with care this 
A  SUMMAWY
phenomenon, and take care  that we do not suffer ourselves to be
influenced by the term absorption.  This seems to indicate, that
the substances which pass into the veins are attracted by a  pecu-
liar  force in these vessels.   It is possible  that such a force may
exist, but it is evident that it is impossible at present to demon-
strate it;  it is also very probable, that this introduction is effected
in some other manner.   Without paying any attention, therefore,
to the term absorption, it is only necessary to understand by this
phenomenon, the passage of solid or fluid substances, when placed
in contact with our organs into the extreme veins, the course and
mechanism of which are entirely unknown.
   If we wish to form a distinct idea of this property,  common to
all the veins, we have  only to  introduce an aqueous solution of
camphor into one of the serous or  mucous cavities of the body, or
to bury in the tissue of one of the organs, a morsel of solid cam-
phor.  Soon  after, the air which passes from the lungs of the ani-
mal, will possess, very distinctly, the odour of camphor.   This ex-
periment is easy to be made upon  man, after the administration of
an enema; it is seldom that, in the course of five or six  minutes,
the  breath does not exhibit a strong  odour of this drug.  Almost
all  the  odoriferous substances  which do not combine  with the
blood,  produce similar effects.  In the experiments which  1 have
made upon the absorption of the veins, I have found, that its ra-
 pidity  varied according  to  the different tissues.  It is,  for exam-
 ple, much more rapid  in the serous, than the mucous  membranes;
 it is much more prompt in those tissues, which abound with san-
 guineous vessels, than those which contain few, ike.  The corro-
 sive quality  of the fluids, or solids, submitted to absorption, does
 not prevent this being effected. It appears, on the contrary, to be
 much more prompt than in those substances which do  not attack
 the tissues*
   The intestinal villosities, formed  partly by the venous extremi-
 ties, absorb in the  small intestine, all the fluids except  the chyle.

   * Much is said in modern works of physiology, of the peculiar  sensibility of
 the mouths of the absorbent vessels; they are, say some, endowed with a delicate
 and sure tact, by which they discern those substances which are useful and suita-
 ble to them, and they  refuse those substances which are injurious.  These in-
 genious suppositions, which have a particular charm for minds, eager after new
 ideas, arc destroyed as soon as they are submitted to experiment. 
OF PHYSIOLOGY.
293
It is easy to satisfy ourselves of this, by introducing into the intes-
tine those substances which are  strongly odorous or sapid,  and
susceptible of being absorbed.   As soon as the absorption begins,
and as long as it continues, the properties of these substances may
be recognised, in the blood  taken from the branches of the vena
porta, though we cannot distinguish them in the lymph, until a
considerable  time after the absorption has begun.  We shall show
in the sequel, that they do not arrive at the thoracic duct, through
the medium  of the  lacteal vessels; but through the communica-
tions of the arteries with the lymphatics.  It is well known, that
all  the veins of the digestive organs, unite together  in a single
trunk, which is divided  and subdivided in the tissue of the liver.
This structure  deserves to be noticed.   In consequence  of the
great extent of  the mucous  membrane, with which the drinks and
other fluid's are in contact, and the  rapidity of their absorption, by
the mesenteric veins; a considerable quantity of  fluid, foreign  to
the animal economy, may traverse the venous system of the abdo-
men, in a given time, and alter the composition of  the blood.  If
the fluid, in this state, passed on  to the lungs, and from thence to
the rest of the organs, there would  result the most serious  conse-
quences, as the following experiments will demonstrate.
  I found that fifteen grains of bile forced suddenly  into the crural
vein, generally  killed  the animal in a few minutes.  If a  certain
quantity  of  atmospheric air be introduced, rapidly, into the same
vein, the  same effects will  follow; but an  injection made in the
 same way, into one  of the branches of the vena portse, will not be
found to  produce any inconvenience.   From whence arises the
 difference in these results?  Does the passage of foreign fluids,into
the animal economy, through the innumerable small  vessels of the
 liver, have the effect of  mixing it more  intimately with the blood,
and as it were, diluting  them  with a large quantity of this fluid, so
that their chemical  natures  become somewhat altered?  This be-
comes the more probable, from the circumstance,  that if a quan-
tity of bile or air be injected, very slowly,  into the crural  vein, it
does not produce any sensible  injury.  It is, therefore,  perhaps
necessary, that the  veins arising from the digestive organs, should
pass through the liver, in order that they may mix more intimately
 with the  blood, the substances absorbed in the intestinal canal.
 Whether this effect takes place  or not, it cannot be doubted, that 
294   -                 A SUMMARY
those agents which are absorbed from the stomach and intestines,
do pass  immediately through the liver, and that  they cannot but
have  an influence upon this organ, which merits  the attention of
physicians*   We have said above, that the skin makes an excep-
tion  to the general law, that the veins absorb in every part of the
body.  This proposition merits  a particular examination.
  When the skin is deprived of the  epidermis, and the sanguine-
ous vessels which cover the external surface of the arm are expos-
ed, absorption takes place, as it does in every other part.  After
having applied a blister, if we cover the surface which has been
deprived of its epidermis, with a substance, the effects of which,
upon the animal economy, we  easily observe; a few minutes are
often sufficient for these  to be manifested.  Caustics applied to
ulcerated surfaces, have often produced death.   In order that the
innoculation of the small  pox, or the vaccine disease may succeed,
it is necessary to take care to  place the  substance beneath the
epidermis, and, of consequence, to  place  it  in  contact with the
subjacent sanguineous vessels.
  But it is very different  when the skin remains  covered with its
epidermis.   Unless the substances in contact with it are of a na-
ture to change its chemical composition, or to excite an irritation
in the corresponding sanguineous  vessels, there is no sensible ab-
sorption.  I know that this result is  contrary to the received opin-
ions on  this subject.  WTe think, for example, that when the  body
is plunged in a bath,  that it absorbs the surrounding liquid;  it is
on this idea that the use of nourishing baths of milk and  soup was
founded.  In a  work  recently published,  M.  Seguin  has placed
the fact beyond doubt, that the skin does not absorb water when
placed in it, by a series of very careful experiments.  To satisfy
himself if the same thing would take place with other fluids, this
gentleman made the following experiments upon persons affected
with syphilitic  diseases.—He plunged their feet and legs in baths,

  * It would be curious to inquire,  why,  of all the  vessels'of the liver, the
branches  of the vena portse alone, by the disposition of their external membrane,
called the capsula glissomi, are capable  of contracting upon themselves, when
the quantity of blood which runs through  them diminishes.  Perhaps this ar-
rangement is most favourable to the course  of the venous blood, which, in this
portion of the vena ports, passes from a narrow part into one that is large, while
every where else it passes from a part that is large into one that is narrow. 
OF  PHYSIOLOGY,
295
composed of sixteen pounds of water, with one ounce of corrosive
sublimate, dissolved in it; each bath lasted one or two hours, and
was repeated twice daily. Thirteen patients were submitted to this
treatment during twenty-eight hours, who did not present any evi-
dent marks of absorption; a fourteenth patient presented signs of
this having taken place after the third bath, but he had excorations
on both his legs; two others, who were in the same situation, exhi-
bited the same phenomena.  In general, absorption does not take
place, excepting in those persons where some portion of the epi-
dermis  is removed; however, in a temperature of 72° Faren. the
corrosive sublimate is sometimes absorbed, but the water never.
  Among the experiments of M. Seguin, there is one which appears
to throw great light upon the absorbing faculty of the skin.   After
having  weighed separately, seventy-three grains of calomel, the
same quantity of gamboge, scammony, salt of alembroth and  tar-
tar emetic. M. Seguin caused a patient to lie down on his back, and,
having washed the skin of the abdomen carefully, he applied, with
caution,  upon the surface, these five substances;  he then covered
each of the places with a glass receiver, and kept it in its situa-
tion with a linen bandage.   The heat of the chamber was kept at
about 68° Faren.  M. Seguin remained with  the pafient the whole
time, in order to prevent mistakes; the  experiment lasted during
ten hours and a quarter.  The glasses were then removed, and the
substances collected with great care, and weighed.  The calomel
was reduced  to seventy-one grains  and a  third, the scammony
weighed  seventy-two grains and  three-quarters, the  gamboge,
a little more than seventy-one grains, the salt of alembroth  was
reduced to sixty-two grains; several pustules being developed on
the spot where it was applied; the emetic  tartar weighed sixty-
seven grains.   It is evident from this experiment, that those sub-
stances which  were the  most disposed to irritate the skin, and
combine with the epidermis, were partly absorbed, while with the
others this was not the case.
   But that which does not  take place from a simple application,
may take place from frictions upon the skin with certain sub-
stances.  We cannot  doubt that  mercury, alcohol, opium, cam-
phor, vomits, purgatives, &.c. penetrate  by means of  the  venous
system.  It  appears that these different agents  pass through the
epidermis, either  through the pores, or  arc insinuated into the 
296
A  SFMMA.UY
openings, by which the hairs or insensible transpiration pass out.
Thus in considering the absorption of the skin, we perceive, that
this membrane differs  from the other surfaces of the body only in
bein"* covered by the epidermis.   While this coat remains per-
fect, and is not  perforated by the substances  placed in contact
with the skin, no absorption takes place;  but whenever this is the
case, this action occurs in the skin, as in every other part.
  I am  not ignorant,  that many persons  will be surprised at my
not hesitating to attribute to the veins the faculty of absorption,
while the  general opinion  is, that all absorptions is effected by
the lymphatic vessels.   But from the facts, already related under
the article absorption of the  lymph,  and some others which I am
now about to add, it is impossible for me  to think otherwise.  Be-
sides, the opinion which I support is by no means new.  Rhuysch,
Boerhaave, Mechel, and Swammerdam, professed  it,  and Haller
supported it, though he was not  ignorant of the anatomical labours
of John Hunter.  M. Delille and myself separated  the thigh of
a dog from the body, after having first  stupified him with opium,
for the  purpose  of avoiding the pain, inseparable  from a  tedious
experiment.  We left the crural artery and vein alone untouch-
ed, preserving thus the communication between  the thigh and
trunk.  These two vessels were dissected with very great care,
that is,  they  were insulated  to about the  extent  of two inches;
their cellular coat was removed lest it should  conceal some lym-
phatic  vessels.  Two grains  of a very subtle poison (upastieute)
were then  introduced into the foot.  'The  effects of the poison
were as prompt and severe, as if the thigh  had not been sepa-
rated from the body; so that the  effects were  manifested before
the fourth minute, and the animal died before the  tenth.
   It may be objected, that notwithstanding all the precautions
which were taken, that the walls of the crural artery and vein still
contained  lymphatics, and that these  vessels were  sufficient  to
give passage to  the poison.   To do away this objection,  I  repeat-
ed  upon another dog  the preceding  experiment, with this differ-
ence; I introduced into the crural  artery the  barrel of a small
quill, upon which 1 fixed the vessel  by two ligatures; the artery
was divided  in a circular direction between  the two ligatures; I
then did the same with the  crural vein;  thus all  communication
between the  thigh and the rest of the body was interrupted, 
OF  PHYSIOLOGY.
297
except the arterial blood winch passed to the thigh, and the venous
which  it-turned  from it.  'The poison  introduced into the foot
produced its effects in the ordinary time, for example, about four
minutes.
  From this experiment, we cannot doubt, that the poison did
pass from the toot to the trunk, through  the crural vein.   To ren-
der this phenomenon still more evident, we have only to press the
vein between the fingers, at  the moment when the  poison is be-
ginning to develope  itself;  these  effects cease soon, but they re-
turn as soon as the vein is left free, and  cease  if  we compress
them anew.  We may thus graduate them according to our plea-
sure.  We may add to these facts, which appear  to  me to be de-
cisive, the interesting  experiments  rnade  by Flandrin.  In the
horse, the substances contained most frequently both in the large
and small  intestines, are mixed with a large  quantify  of liquid,
which is  more  or  less abundant,  as we  approach  towards the
rectum; it is  absorbed, as it passes over this part of the  intes-
tinal canal.  Now  Flandrin  ascertained, that the fluid  contained
in the lacteal vessels did not possess any odour analogous to that
of  this intestinal fluid;  but  on the other  hand,  that the venous
blood  of the small intestines  had  sensibly an herbaceous  taste;
that of the coecum had a sharp and slightly urinous taste; that  of
the colon  possessed the same character in a more remarkable de-
gree.  The blood in the other parts  of the body presented nothing
of  the kind.
   A half a pound of assafoetida dissolved in an equal quantity of
honey, was given to ahorse;  the animal  was afterwards  fed in the
usual way, and killed in about sixteen  hours.   The  odour  of the
assafu'tida  was  very distinct  in the veins  of the stomach, small
intestines,  and  ccecum; it  was not remarkable  in  the arterial
blood nor  the  lymph.   I have spoken  under  the article lympha-
tic vessels, of the experiments of John Hunter, to prove that these
vessels are the only  agents  of absorption.  This author has en-
deavoured to demonstrate, that the veins do not absorb; but these
 last  are  not  more satisfactory or  correct, than  those  which  we
 have already mentioned.  I  took, says Hunter, a porlion  of the
 intestine of a sheep,  after having divided the abdominal walls, I
 passed ligatures upon its two extremities, and then filled  it with
 warm  water.  The blood which  returned by the veins of this 
£98
A  SUMMARY
part did not appear to  be more diluted than that of the other
Veins.  It was not swelled, the blood was not more diluted, an I it
did not give any indication of the  presence of the water in its
oavity.  The veins, therefore, do not absorb.
   How many objections present themselves to this experiment in
the minds of those,  who think precision desirable in physiological
inquiries.  How could  John  Hunter know, from the Himile ap-
pearance, immediately after the experiment  was performed, that
the water was not  absorbed, and not mixed with the blood of the
vein?  Again, how  could this author, otherwise so eminent, have
supposed that the action of the vein would continue when a liga-
ture was  passed  around  the  artery?  It would  have  been first
necessary to determine the  effect  of tying  an  artery, upon tie
motion of the blood  in the corresponding^vein; a thin.*; which had
never been  done.   In another experiment, the same physiologist
injected warm milk into a portion ot the intestine; shortly after-
wards he opened the mesenteric vein, and collected  the blood  as
it  passed out,  and because he could not  distinguish  any trace of
the milk, he concluded that no absorption  of this fluid had taken
place by the vein.   But at the time of Hunter, they were far from
possessing any means of  detecting a small quantity of milk in a
certain quantity of  blood.  At the  present period, when animal
chemistry is far more advanced, it is a difficulty not easily over-
come.
   These two experiments, when fairly  considered, ought not to
have any influence  in deciding the doctrine of venous absorption.
The other experiments, the number  of which is  six, are  far from
being conclusive, but on the contrary are still more defective  In a
word, if it were necessary to adduce stronger evidence in favour
of venous absorption, I would refer the reader  to many parts of
the body, in which the most expert  anatomist ha3 never been able
to detect lymphatic vessels, or any  other but blood  vessels, such
as the eye, the brain, the placenta,  &c; though absorption takes
place with the same promptitude, as  in every  other part of the
body. I will add, that all  those animals which do not possess ver-
tebra, have blood, but not lymphatics, while absorption still mani-
festly takes place.   Finally, the thoracic duct is  much too small,
to afford a passage to all  the substances  absorbed  in the  various 
OP PHYSIOLOGY.
299
parts of the body, and particularly the drinks.*  All these pheno-
mena are, at once, satisfactorily explained, when the absorption of
the veins is admitted.   Facts, experiments, and reason, then, con-
cur in favour of the doctrine of venous absorption.t

Passage of the  Venous  Blood through the  large cavities of
                 the right side of the Heart.
   If the heart of a living animal  be exposed, we can readily per-
ceive, that the right auricle and ventricle contract and  dilate al-
ternately.  These motions are so combined,  that the contraction
of the  auricle takes place, at the moment, when  the ventricle is
dilated, and  vice versa;  the  contraction of the  ventricle occurs at
the moment of the dilatation of the auricle. Neither of these cavi-
ties are capable of being dilated, without being at the same  mo-
ment filled with blood;  and  when they  contract,  a part of it  is
necessarily expelled.  But,  such is the structure  of the tricuspid
and sigmoid valves, that the blood  is compelled to pass, succes-
sively,  from  the auricle to the ventricle, and  from  this  last to the
pulmonary artery.   We will  now  enter into a detail of this cu-
rious mechanism.
   I have already observed, that the blood contained in  the three
veins which terminate in the right auricle, make a strong effort to
penetrate into this cavity.    If it is contracted, this effort is una-
vailing; but  when a dilatation  takes place, the blood is precipita-
ted  into  this  cavity,  fills  it completely, and distends its walls
slightly;  it would  penetrate into the ventricle, if this cavity were
not, at  the same moment,  in a state of contraction.  The blood
then is limited, precisely,  to filling at  this moment the  cavity of
the auricle;  but  this soon contracts itself, and  the blood, being
compressed, must escape in that  direction where the resistance is
the least.  Now there are  but  two openings, the one towards the
vena? cava?, and the  other in the direction of* the ventricle.  The
  * Some  persons drink, as  much as twelve pounds of mineral water, in the
course of a few hours, and reject it through the kidneys in the same time.
  t To recapitulate what we have said of the organs of absorption,  in a  genei-al
point of view, we may remark, first, that it is certain that the  lacteal  vessels  ab-
sorb the chyle; second, that  it is  doubtful whether they absorb any thing else;
third, that it has not been demonstrated that the lymphatic vessels  possess the
property of absorption, but it is proved that the veins, are endowed with thi*.
j^o wer. 
JOU
A.  SUMM\UY
sanguineous columns which arrive at the auricle, oppose a certairs
resistance to its passage in the first direction; on the contrary, no
obstacle exists to prevent its entrance into the ventricle, as, from
its beinir  dilated with  force,  it has  a tendency to produce a va-
cuum, and thus to draw the blood from the auricle, instead  of for-
cing it back. All the blood which passes from the auricle does not,
however, enter the ventricle; experiment has shown,  long  since,
that, at each contraction of  the auricle, a certain quantity of this
fluid flows back into the vense cavse.   The undulation, produced by
this cause, may be perceived, as far as the external iliac and jugular
veins; its influence also, upon  the course of the blood is very sen-
sibly seen, in several of the  organs, and especially the brain.
   The quantity of blood which flows back in this  manner  varies,
according to the facility with  which  this fluid is allowed to pene-
trate into the ventricle.  If at the moment  of its dilatation,  the
ventricle contains still  much blood which has  not passed into the
pulmonary artery, it can, of course, receive but a small portion from
the auricle, and its  reflux will, therefore, be much more considera-
ble and extensive.   This occurs, when the blood in the pulmonary
artery is retarded  by obstacles, placed in  the structure  of the
lungs, or  from  the  ventricle having  lost its contractile  power.
The reflux, of which we are speaking, is the cause of the  pulsa-
tion felt in the veins, in certain diseases, and which  has  received
the name of venous  pulsation.  Nothing of the kind occurs in the
coronary  vein, as its mouth  is supplied with a valve, which closes
at the moment the auricle contracts.
   The instant the contraction of the auricle ceases, the  ventricle
contracts, by  which the blood contained in it, being  pressed on
every side, endeavours to  escape;  it would repass,  very  easily,
into the  auricle, did  no obstacle exist, as may be inferred from
what we have already said, this cavity being then in a state of
dilatation.  But this is prevented  by the action of the  tricuspid
valve, which is  placed  at the  opening between the auricle and
ventricle, and will  not  allow of the  reflux of the blood, from the
ventricle to the auricle.  Pressed by the  fluid, with  which  the
ventricle  is distended,  and  which tends to pass into the auricle,
this valve yields until it gets into a line perpendicular to the axis
of the ventricle; then its  three divisions perfectly close the open-
ing, and its fleshy and  tendinous columns will not allow it to go 
OP PHYSIOLOGY.
301
any farther; thus the valve res;sts the effort of the blood, and pre-
vents its passing into the  auricle.  But this is not the case with
tha1  portion of the blood, which, during the dilatation of the ven-
tricle, is placed on that side of the valve which corresponds to the
auricle; it is evident that, when the valve is  raised, this portion
of the blood will be thrown back into the auricle, and mixed  with
that received from the venre cavue,  and coronary vein.  Not be-
ing  able  to  overcome fhe resistance of the tricuspid valve, the
blood of the ventricle is compelled to enter  into the  pulmonary
artery, into which  it passes,  after  having pushed  aside  the  sig-
 moid valves, which support the column of blood contained in this
 arterv, at the moment when the ventricle is dilated.
   We  will now proceed  to  explain  the phenomena  most  appa-
 rent  and best  understood, exhibited by  the  venous blood in
 passing through the right cavities of the heart; there are also other
 circumstances, which  I conceive to be worthy of particular atten-
 tion.  We should have but a very imperfect idea of this subject,
 if we supposed that in each contraction of the ventricle and auri-
 cle of  the heart, that these cavities emptied  themselves complete-
 ly of the blood which they contained.  In observing the heart of
 a living animal, we may distinctly see, at the moment of contrac-
 tion, the auricle or  ventricle  become  sensibly  diminished  in
 volume;  but  it  is  evident, that at the instant  the contraction
 ceases, much  blood  still  remains  in the auricle or ventricle.
  There is only a part  of the  blood  of the  auricle, which  passes
  into the  ventricle when it contracts.  The same is true  of the
  blood of the ventricle, a portion only  of  which passes  into the
  pulmonary artery when the ventricle contracts; these  two cavities,
  therefore, are always filled with blood.  What is the precise por-
  tion of  blood  displaced, it may be inquired, and  how much re-
  mains?   They will  vary, probably,  according to  the force with
  which the ventricle and  auricle contract, the facility with which
  the blood traverses the  pulmonary artery, the quantity of blood
  contained  in the auricle or ventricle, and  the efforts made by the
   three sanguineous columns which empty into the auricle.
     When the  blood  has arrived  at the heart, it is continually
   agitated, pressed and beaten by the motions of this organ; some-
   times it flows back into the vense cavse. or precipitates itself into
   the auricle; again it passes with  rapidity into the ventricle, is 
302
A  SUMMARY
forced back suddenly into the auricle, and returns immediately
afterwards into the ventricle; and again it  penetrates into the
pulmonary artery, and returns afterwards into the ventricle, and
undergoes at each displacement a violent agitation.*   Agitated
and  pressed in this manner,  and  with such prodigious force, the
blood must undergo an intimate admixture of its constituent parts,
during  the time it remains  in the  cavities of the heart and pul-
monary artery.   The chyle and lymph which the subclavian vein
receives, must be distributed equally in the blood of the two vense
cavte.   These two kinds of blood must also be compounded and
completely united.
   1  am  almost tempted to  believe with  Boerrhaave, that  the
fleshy columns of the  right cavities, independently of  their uses
in the  contraction  of these  cavities, must  have a considerable
share in this agitation and admixture of the different elements of
the  blood.   Indeed, the blood which is found in the auricle and
ventricle, not only occupies these large central cavities,  but is also
formed  into small  cells by these columns, of consequence at each
contraction, it is forced partly into these cells, and is replaced at
each dilatation, by a new  portion ol olocd.   Being divided thus
into  a great number of small masses, so as to occupy the cells,
when it is again  united and  expelled; it cannot  tail, from  the
excessive agitation it suffers, that the different elements of winch
it is composed, that have  a great  tendency to separate, become
thus intimately blended and combined.  For the same reason, the
ehyle, lymph, and  drinks, which are carried by  the veins to the
heart, and that have not become intimately mixed with the blood,
must undergo  this change in traversing the right cavities  of the
heart.
   If we wish to form an idea  of the influence of the right side of
the heart, in this respect, we have only to force suddenly a quan-
tity  of air into the jugular vein of a dog, and examine the heart a
few  minutes afterwards, we shall  see the air agitated and beaten
about in the auricle and ventricle, forming a large mass of very
fine  froth.  I have often observed  these phenomena in living ani-
mals; and 1 have lately had  an  opportunity of confirming them

  * It is sufficient to touch but once the heart of a living animal, to form aa idea
of the energy of its contraction. 
                      OP  PHYSIOLOGY.                   308

Upon an horse, the heart of the animal having been exposed,by art
incision on the lateral part of  the thorax.

Passage of the  Venous  Blood through the Pulmonary Artery.
  Notwithstanding the numerous efforts of physiologists, in inves-
tigating the motion of the blood in the arteries, much still remains
to be done on this subject.  Experience and observation are here
our only faithful guides; our explanations must necessarily be im-
perfect, as hydrostatics, the only science which can furnish  them,
has  scarcely  been extended  to  the motions of fluids in flexible
tubes.*  I  shall  not  adopt the  descriptions of other authors, in
giving an account of  the motion and progress of the blood  in  the
pulmonary artery.  I prefer speaking of it at the moment,  when
the relaxation of the  right ventricle takes place, and to see  after*
wards what happens,  vvhen the ventricle contracts, and  forces the
blood into the artery.   This method appears to me to possess the
advantage of placing this phenomenon  in the most striking point
of view; its importance does  not seem, to  me, to be sufficiently
appreciated.
  Let us suppose  the artery  full  of blood, and  left  to itself, the
fluid will be pressed by the walls of the vessel through its  whole
extent, which  will have a tendency to approach each other, and
efface completely its cavity; the blood being thus  compressed,
will endeavour to escape on every side. Now  there are but two
directions in  which this can take place; the one is the orifice next
to the heart, the other the infinite  number of delicate vessels in
which the artery terminates in the tissue of the lung. The  orifice
of the  pulmonary artery, towards the heart being very large, the

  * I cannot resist quoting here, the appropriate remarks of O'Alembert on
this subject. "The mechanism of the human body, the velocity of the blood, and
its action  upon  the vessels, cannot be reduced to a theory.  VVe are  ignorant of
the precise action of the  nerves, the elasticity  of the vessels, their capacity, of
the  tenacity of the blood, and  its different degrees of heat. Were even these
fellings known, the great multitude of other circumstances which would necessarily
enter into such a theory, would probably conduct us to calculations altogether im-
practicable.  It is one of those cases of a compound  problem, one cf the most
"simple parts of which it would be extremely difficult to resolve. When the effects
of nature are too complicated," adds this illustrious philosopher, "to enable us to
submit them to our calculations, experiment is the snly method that remains
for up." 
304
A  SUMMARY
blood would be easily precipitated into the ventricle, if there did
not exist at this orifice, a particular apparatus destined to mvvent
it. I allude to the three sigmoid valves.   At  the instant when the
contraction of the ventricle forces the current of ulood  into the
artery, these valves are Drought in contact with the walls of the
artery, and perpendicular to  its axis;  but the moment that the
blood has a tendency to flow back  into the  ventricle, it places
them in such a situation, that they completely close  up the cavity
of this vessel. From the peculiar form of these valves, beiigthat
of a blind  sac,  the blood  that  enters  into  their cavity,  has  a
tendency to swell them  out, and to give a circular  form to their
fibres.   This valve is divided  into three portions, each of which is
semicircular; now if three  semicircular  bodies be  brought  toge-
ther, there would necessarily exist a space between them.   VVe
might therefore  suppose, that the valves of the pulmonary artery,
when they are pressed back by the blood, would  leave a space by
which the  blood would  flow  back into the  ventricle.  It is un-
doubtedly true,  that if each valve was single, it would assume a
semicircular form; but as there are three, each acted upon by the
blood at the same time, their  sides are brought in contact with
each other, and as they can each only be extended to  a certain
point, in consequence of the smallness of the space in which they
are  contained, they are therefore made  to press each  upon the
other.   The valves are therefore made to assume the form  of a
triangle, the apex of which is at the centre of  the artery,  and
the sides in contact with each other,  so as completely  to  inter-
cept the cavity of the  artery.   Perhaps the small  cartilaginous
masses  which exist at the apex of these triangles,  may be  intended
to close, more accurately, the artery at its centre.
   If we wish to see  the manner in which these three valves are
brought in contact with each other, it  may be done  in the follow-
ing manner; if we inject, gently, wax, or prepared tallow, into the
pulmonary artery, allowing it to pass from the ventricle, when the
artery becomes filled, the valves will be forced into, and  brought
in contact with each other;  so that the orifice of the vessels will be
closed, with sufficient exactness to prevent a single drop of the in-
jection  from returning back into the ventricle.  When the wax or
tallow have become  solid by cooling,  we may examine, at our lei-
sure, the manner by which  the opening of the artery is closed up 
OP  PHYSIOLOGY.
805
by the valve. The blood not being able, therefore, to flow back into
the ventricle, will pass into the ramifications of the pulmonary vein;
into which  the  small  branches of the pulmonary artery are con-
tinued; and  this will continue to be the case, so long as the walls of
the artery press, with  sufficient force, upon the blood which  they
contain; an effect which, with the exception of the trunk and prin-
cipal  branches, continues  until the whole of the blood is expelled.
We mav suppose that the fineness of the small vessels,  in  which
the pulmonary artery terminates, acts as an obstacle to the  blood.
This  would-be the  case if their number was small, or it the sum
of their diameters was less, or  even equal to that of the trunk;
but as they are innumerable, ami  ;is their aggregate capacity is
much greater than that of the  trunk, the current passes on with
ease.   It is,  nevertheless, true, that  a  state  of distention,  or
weakness of the lung, renders  this passage more  or less easy, as
will be more particularly shewn hereafter.
   In  order that the current of blood may  pass with more facility,
it is necessary that the power  of contraction, in the different di-
visions of the artery, should be in proportion to their size.   If for
example, the action of the small vessels was superior to the large,
while the first would expel the blood which  they contained, they
would not be distended by the  blood coming from the second, and
the fiuid would  therefore flow but very  slowly.   Now experiment
shews, that the contrary of this supposition is true.   If  the pul-
monary artery of a living animal be  tied,  immediately beyond the
heart, nearly all the blood contained in the artery, when the liga-
ture was made,  will pass promptly into the pulmonary veins, and
arrive at the other side of the heart.
   We have now observed  what happens,  when the blood contain-
ed in the pulmonary artery, is exposed to  the action of this  vessel
alone; but,  in the ordinary state, at each  contraction of th^ right
ventricle, a  certain  portion of  the blood  is  propelled with force
into the  artery;  the  valves  are instantly  raised;  the artery,
through the whole extent of its divisions, is distended, in propor-
tion to the  force with which the heart contracts, and the  quan-
tity of blood which is thrown into it.  Immediately after its con-
traction, the ventricle  becomes dilated, and  at this instant,  the
walls of the artery re-act upon themselves: the sigmoid valves be-
come depressed, and close the  artery, until a new contraction of
                             39 
306
A  SUMMARY
the ventricle  raises them.  Such is the second cause of the mo-
tion of the blood in the artery, which goes to the lungs;  they are,
as we have seen, alternate, let us  endeavour to appreciate their
effects.   For  this purpose, we will  examine  those phenomena
which are most apparent in the course of the  blood, through  the
pulmonary artery.
   1 have remarked, that at the moment when the ventricle forces
the blood into the artery,  its trunk, and ramifications, of a certain
calibre, undergo an  evident  dilatation.   This phenomenon is
called the pulsation of the artery.  This pulsation  is very strong
near the heart, but grows weaker as you pass from it, anil seems
to cease altogether, when the  artery  becomes subdivided, until it
is very small.    There is another phenomenon observed,  when we
open the artery, which  is  a consequence of the preceding.  If the
opening be near the heart, and in a place where the  pulsations are
very distinct, the blood passes out in a jet, with a jerk, and spreads
itself into a uniform sheet.   VVe see, in the first place, in  these
phenomena, a  new application of the principle of hydrostatics
quoted above, relative to  the  influence which the size of the tube
has upon the fluid, which  runs through it; the larger the tube, the
less the velocity of the fluid passing through it.  As the aggregate
capacity of the ramifications of the  artery increases as  they ap_
proach towards the lungs, the velocity of the blood is necessarily
diminished.
   With  respect to the pulsation of the artery,  and  the jerk of the
blood, as it escapes from an opening in it, we see, evidently, that
these two  effects are the results of  the  contraction of  the right
ventricle, and the introduction of a certain  quantity ol blood  into
the  artery,  which is  thus affected.  Why  are these two effects
weakened at a distance from the heart, and why do they cease al-
together, in the last divisions of the artery?  It is  not impossible,
I think, to give  a satisfactory, mechanical reason for it.   Suppose
acylindrical canal, of a given length,with elastic walls, and tilled
with a fluid; if  a new quantity of  fluid  be  suddenly  introduced
into it,  the pressure will  be felt equally upon every point  of the
walls, which will be equally distended   Suppose, now, that this
canal is divided into two parts, the sections of which,  together,
form a surface equal to that of a section of the main trunk of the
canal; the distention  produced by the sudden introduction of a 
OP PHYSIOLOGY.
307
certain quantity of fluid, will be less perceptible in the two di-
visions, than in the trunk; becnuse, the total circumference of the
two canals, being greater than that of the one canal  alone, its re-
sistance will  be greater.  If  we supoose that these two last are
divided, an'! subdivided, indefinitely, as the sum of the circumfe-
rences of the  small tubes, will  be greatly superior to that of the
great  trunk;  the  same cause which will produce a  sensible dis-
tention in the canal, and its principal divisions, will not be appre-
ciable in  the  smallest subdivisions,  in consequence  of the greater
resistance of their walls.*   'This  phenomenon will  be still more
remarkable, if the  capacity of these divisions, instead of being
equal, is greatly superior to that of  the trunk.
  This last supposition is  realised in the  pulmonary artery; the
capacity of which increases,  as it becomes  divided  arid subdivi-
ded.  It is evident, therefore, that  the effects of trie introduction
of a quantity of blood into this artery, at each  contraction of the
right  ventricle, must  diminish as  it is propagated, and  at  last
cease  altogether,  in the last divisions of the vessel.   It must not
be  forgotten,  that, the  contraction  of the  right ventricle, is the
cause  which keeps constantly in plav, the  elasticity of the walls
of fhe artery;  that is,  which distends them  so as to overcome the
constint  tendency which they  have to approach  towards  each
other, and expel the blood.   From  this, it  will  be perceived, that
there  is.  in fact,  but one cause which uives motion to the blood,
in the pulmonary artery: this is, the  contraction of the ventricle,
that of the artery being but the effect of the distention that it un-
dergoes,  at the instant when a  certain quantity of blood pene-
trates into its cavity, being forced there by the ventricle.
   Authors have thought, that they perceived in the contractions of
the  pulmonary artery, something analogous  to that of the muscles.
But when irritated  with the  point  of an instrument, or caustics,

  * In order to  understand this, it is necessary to recollect, that the surfaces of
circles are proportional to the squares of their circumferences.  Thus, in the di-
vision of the canal into t,wo branches, as we have supposed, if each circumference
was only the half of the principal canal, the surfaces of each of the secondary ca-
nals, would be but the fourth part of the surface of the primitive canal; and these
two  surfaces united,  would  form but the half of this canal; in order that they
shouhl  be equal, therefore, it is necessary that the circumferences of the two di-
visions, taken together, should exceed the circumference of the canal. 
30S
OP  PHYSIOLOGY.
 or when submitted to the influence of a galvanic  stream, no mo-
 tion, analogous to muscular contraction, has ever been observed.
 We must therefore, consider this contraction as an effect of the
 elasticity of the walls of the  vessel.   In order to estimate the im-
 portance of the elasticity of  the walls of the artery, let us suppose
 for an instant, that with its dimensions and ordinary form, it was
 an inflexible canal, so t::at the course of the blood  would be com-
 pletely changed.  Instead of traversing the lungs  in a continued
 stream, it  would only enter the pulmonary veins  at the moment
 that it was propelled  forward by the ventride; at the same time it
 will be necessary to suppose that the artery would  be always per-
 fectly filled with blood; for  if it were  otherwise, it would be re-
 quired that the ventricle should contract itself frequently before
 the blood would  be made to pass into the lungs.   Instead of this,
 obst.ve  what really  takes place; the  ventricle ceases for some
 moi..ents to send blood into the artery; the course  of the blood in
 the lungs, nevertheless continues, as  the artery contracts in pro-
 portion as it is emptied, and  it requires, that the time of emptying
 its, If completely should  be passed over, before the  course of the
 blood into the lungs  is completely stopped; now this suspension
 can never take place during life. The passage of the blood through
 the lungs is necessarily  continued,  and nearly  equally rapid,
 whatever may be the  quantity of blood thrown into the pulmonary
 ai tery at each contraction of the ventricle.
   Various attempts have been made  to determine the quantity of
 blood thrown into the pulmonary artery, at each contraction of the
 ventricle.   In general, the measure of its capacity has  been taken
 on the supposition, ihat all the  blood  found there  passes into the
 a> tery at the moment of its contraction; the  estimate  has been
 considerable.  From what has been said above,  however, it will be
 perceived, how inaccurate this calculation must  be, inasmuch, as
 only a part of the blood contained in the ventricle  is thrown into
the artery, and as it is  impossible to know how much is thrown
out,  and how  much remains,  it is evident that  all  these calcula-
tions are but imperfect guides to truth.   Besides.it is much more
important to know the mechanism, by which  the blood passes from
the ventricle into the artery, and its course  in this  vessel;  the
quantity of  blood  which  passes in a given time, even if it were
known, would not be  a circumstance of much importance. 
OF RESPIRATION,
                             OS
   TR VNSFORMATION OF VENOUS INTO ARTERIAL BLOOD.

  The  blood, in  passing from  the small vessels in  \yhich the
pulmonary artery terminates, and entering into the ramifications
of »!m»  mlmonary veins, becomes changed in its nature, in conse-
quence  of the contact of the air, and acquires the peculiar quali-
ties of the arterial  blood.  It is this change in  fhe properties i^f the
blood, which essentially  constitutes the function  of respiration.
Some authors attach a different idea to respiration; it is often de-
fined,  the  introduction and discharge of air from the  lungs, but
this double motion may take place without the function of respi-
ration being performed.   Others have thought that it consisted in
the passage of the  blood through the lungs; but it often occurs that
this is effected without  respiration.  To study, successfully, this
function,  we must have an exact  knowledge of the structure of
the lungs, and precise notions ot  the chemical and  physical pro-
perties  of the atmospheric air; and we must  understand by what
mechanism this  air is made to penetrate into, and pass out from
the chest.  When we have described each of these points, we shall
then  consider  the phenomenon of the transformation of venous
into arterial blood.

                        Of the Lungs.
   The  lungs are two spongy, and vascular organs of considerable
volume, situated on each side of the chest, their parenchyma is di-
vided and subdivided into lobes and cells, the number, form and
dimensions of which, are difficult to determine. From  an  atten-
tive  examination  of  a  pulmonary cell, we learn that it is formed
of a  spongy  tissue, the  spaces of which  are  so small  that  it re-
quires  a glass of strong magnifying powers to see them distinct-
ly; these spaces communicate with each other, and are enveloped
by a  delicate cellular tissue, which  separates them from the neigh-
bouring cells.  A  portion of  the bronchiee and pulmonary artery 
3iO                    A  SUMMARY
terminates about each  of  the  cells.   The  artery  is distributed
about the tissue of the cells, but in a manner which is not known,
it appears to terminate in an infinite number of minute ramifica-
tions, in the pulmonary vein.   I am myself disposed to believe,
that these numerous small vessels, in which  the pulmonary artery
terminates, and the vein commences, by crossing and anastomosing
with each other in different ways, form the spaces of the cells.*
The small divisions of the bronchiae,  which  end about the cells,
do not  penetrate into their interior, but finish suddenly when they
arrive at the parenchyma.
  This  last circumstance appears to me remarkable, for inasmuch
as the bronchise do  not penetrate into the  spongy tissue of the
lungs, it is improbable, that the surface of the cells with  which the
air is in contact, is covered by  the mucous  membran \   Minute
anatomy) at least, cannot demonstrate its existence in this place.
  A part of the eighth  pair of  nerves, and some  filaments of the
sympathetic are distributed to the  lungs, but we do not know pre-
cisely how  they are  arranged.  The surface  of the  organ  is
covered  by the pleura, a serous  membrane  analogous to the
peritoneum, both in structure and functions.  About the bronchiee
and near the  place where they  enter into the tissue of the Iung9,
there are a certain  number of lymphatic glands, the  colour  of
which is nearly black, and  about which the small  number of lym-
phatic vessels which  arise deep in the pulmonary tissue terminate.
  The art of fine  injections  furnishes us with some  information
relative to the lungs, which must not be omitted.   If  we force an
injection of mercury, or simply of coloured water into the pt\-
monary artery, the substance  injected, will pass into the pulmo-
nary veins, and at the same time, a part  will penetrate into the bron-
chise.and pass out by the trachea. If the injection  be made into the
pulmonary vein, it passes into the pulmonary artery,and in part
into the bronchise. Again, if the injection be introduced through the
trachea, we shall find that it penetrates into both the pulmonary ar-
teries and veins, and  even into the bronchial artery. The lungs fill a
great part of the cavity of the  chest,  enlarging and  contracting
with it; and, as they communicate with the atmosphere, bv the
trachea  and larynx, every time  that the chest is enlarged, they are
distended by  the air;  which is again  expelled  when the chest
* This arrangement exists, more evidently, in the lungs of reptiles. 
OP PHYSIOLOGY.
311
returns to its  former dimensions.   It is necessarry therefore, to
stop a moment to examine this cavity.   The chest or thorax is of
a conical form, the apex  of which is above, and the  base below;
posteriorly, it  is formed by the dorsal vertebrte, anteriorly  by the
sternum, and laterally  by the ribs;  these  last are twelve on each
side; and are  distinguished into true and false.   There are seven
of the first, and five of the last.   The true ribs are  above, they
are articulated posteriorly, with the vertebrae, anteriorly they are
articulated  with the sternum, by means of a prolongation, called
the  cartilages of  the   ribs.   It is the length,  disposition,  and
motion of the ribs upon the vertebrae,  which determine the form,
and  apparent  dimensions of the chest.
   The same  muscle which, as we have already seen, constitutes
the superior wall of the abdomen, forms  also the inferior  wall  of
the thorax,   it is attached, at its circumference, to the lower part
of the chest;  but  its centre  is  elevated  towards this cavity, and
forms, when it is in  a  state of relaxation, an arch, the middle part
of which is on a level  with the inferior extremity of the sternum.
Thus the  cavity  of the thorax  is divided into two portions, a
superior or thoracic, and an inferior, or abdominal portion.  In the
first, indeed,  the  thoracic organs, such  as  the heart, lungs, &c.
only are lodged.   The second  contains, the  liver, spleen and
stomach. Numerous muscles are attached to the bones which form
tbe outline of the thorax;  of these muscles, some are intended  to
render the ribs less  oblique  upon the vertebral column, or  to
enlarge the capacity of the chest;  others depress the ribs, render
them  more oblique upon the vertebrae,  and diminish thus the
capacity of the chest.
   It will be proper for us to investigate the mechanism, by which
the  chest enlarges or  contracts itself,  many of the phenomena of
respiration being intimately connected  with these  variations of
capacity.   The chest  may  be dilated  vertically, laterally, and
from  before  backwards; that  is  to say,  in the direction of its
 principal diameters.  The principal, or to^ speak more correctly,
 the only agent of its  vertical dilatation is the  diaphragm, which,
 in contracting itself, has a tendency to loose its arched form, and
 to become a  plane; a   motion which cannot be  effected,  without
 the thoracic portion of the chest being  increased, and the abdomi-
 nal diminished.   The sides  of this muscle  being; fleshy, and cor- 
312
A  SUMMARY
responding to the lungs, descends more than" the centre, which,
being tendinous, is incapable of making any effort of itself, and is
also retained by its attachment to the sternum, and its union with
the pericardium.  In most cases, this depression of the diaphragm
is sufficient tor the dilatation of the chest; but it sometime- hap-
pens, that the sternum and ribs, by changing the relation between
them and the vertebral column,  produce a sensible augmentation
of the cavity of the thorax.
   Nothing is easier to  conceive, than the mechanism of this mo-
tion, when the physical arrangements  of the parts  is well umi. r-
stood.  It  has, however, been a subject which  has been discussed
with  great animation, by some  distinguished  authors,  who have,
perhaps, given an importance to this question, which it does  not
merit.  If  such controversies lead  to  truth, we shall  not regret
the time which the learned have devoted to them.   But it is rare
that this is the result, at least it has not happened,  as respects  the
dilatation of the thorax.  After a great number of discussions and
experiments,  apparently accurate,  Mailer's opinions, which  ap-
pear to  me far from satisfactory, have  prevailed.   1 will explain
myself upon this point, with all  the deference  which so respecta-
ble an authority demands.
   His explanation of the dilatation of the thorax,  now generally
admitted, reposes upon bases which 1 cannot admit.  He assumes,
that the first rib is nearly immoveable,* and that the thorax  is in-
capable of any motion, as  a whole, either above or  below.f  It is
difficult  to imagine, how so acute  an observer as  Halier, should
have advanced, and supported such an idea; for we have only to
examine upon ourselves the  motions of respiration, in order to
show that the sternum  and first rib  are elevated  during inspira-
tion,  and depressed in  expiration.   The examination of the re-
cent subject, affords the same result; we have only to press  the
sternum superiorly, and  it  will be found, with all the sternal ribs,to   ■%
yield; the first moves upon the vertebral column, and the thorax
is considerably enlarged.

  * Primum par (costarum) firmissimum est, inde ut quseque inferiori loco poni-
tur, ita facilius emovetur, donee innrnia mobilissima fluctuet.  Haller, Element*
Physiologiae, torn. iii. p. S9, lib. viii.
  t Totum tamen pectus, ut nunquam elerari vidi, ita nunquam deprimi.
                                               Haller, he. cit. 
OF PHYSIOLOGY.
313
   After having assumed, that the first rib was nearly immoveable,
Haller asserts, that the second  possesses five or six  times more
motion than the.first;  that the third is greater  than  the second;
and  that their mobility increases as you approach  towards the
lower ribs.   With  respect to the true  ribs,  the  only  ones which
we are at present considering, I believe the fact to be directly the
reverse of that advanced by Haller; that  is, that the first rib is
more moveable than the second, this again-than  the third, and so
on until you arrive  at the seventh.  But to judge  accurately o1 the
degree of mobility of the ribs, we must not confine ourselves to ob-
serving the. motion  they execute at their extremities.   For as they
are of unequal length, a slight motion in the articulation, when the
rib is long, will appear very great in its extremity;  in the same way,
an extensive motion in the articulation of a short rib, would  ap-
pear trifling, if examined at its extremity.   It is  necessary, there-
fore,  in considering the motion of the ribs, to suppose them all of
an equal length; if this be  done, it will  then  be evident, that their
mobility diminishes from the first,  towards  the  seventh, the last
being nearly immoveable.
   The anatomical arrangement of the  posterior  articulations, oc-
casion this difference of mobility.  The first rib  has but one arti-
culating facette at its head, and is only attached  to one vertebra;
it has  no internal  ligament,  nor any costo-transverse ligament.
The posterior ligament of the joint, with the  transverse apophysis,
is  horizontal,  and cannot obstruct either the elevation or depres-
sion of the rib.
   None of these circumstances, which are so favourable to motion,
are found  to exist about the other ribs; they have  each  two articu-
lating  facettes at their head, and are  articulated with two ver-
tebrae    They  have an internal  ligament  in  the  articulation;
which prevents a gliding motion; a costo-transverse ligament at-
tached to the  superior  transverse apophysis, which prevents the
rib from descending; a posterior ligament, directed  from below,
upwards,  is seen behind  the articulation  of the tuberosity, and
prevents the  rib from rising.   Different shades in the disposition
of these different ligaments,  permit the various degrees ot mo-
bility,  of  which we have spoken.  Besides, it is  evident, that the
less  degree of mobility existing in the  long  nbs, th'S  is made up
by the circumstance of their length,  oy  which they are enabled to
                                40 
314
A
SUMMARY
 execute as extensive motion as the first, although they are less
 moveable;  for the same reason, it might be possible that they may
 exhibit even a greater extent of motion.  This compensation  is
 indispensable, as the three ribs, their cartilages,.and the sternum
 can only move  together, arid the motion  of one of these  pieces
 must therefore, follow that of all the rest.  It would follow then,
 that if the  inferior ribs  were the  most  moveable, they would be
 incapable, of  executing  a greater extent of motion, than, that of
 the superior;  and the solidity of the thorax would be diminished,
 without any advantage to its  mobility.
   In most subjects, and'  frequently even  in advanced  age, the
 sternum is composed of two  pieces, articulated by a moveable
 symphisis, on  a level with the cartilage  of the second rib.   This
 arrangement  permitting the  superior extremity of the  inferior
 piece to project a little  forwards, assists in enlarging the chest, in
 a manner which 1 think  has never been remarked.
   But what are the muscles that elevate the sternum and ribs,
 and of  consequence dilate the chest?   According to  Haller, the
 intercostal muscles are the principal agents of this elevation. The
 first intercostals, he  remarks, find  a fixed point  in the first rib,
 which is immoveable, and elevates the second, and  all  the  inter-
 costal muscles, successively, taking the superior rib as their fixed
 point, elevate  the inferior.   But we have just seen th?t the first
 rib is far from  being immoveable; the explanation of  Haller, there-
 fore, necessarily, falls to the ground, and I cannot think  that the
 internal or external intercostals, whatever may have been said to
 the contrary, could produce the elevation of the ribs. The  muscles
 which appear  to me to be destined to this purpose are those,  which
 having one extremity, mediately or immediately attached to the ver-
 tebral column, the head,  or superior extremities, can act, directly
 or indirectly, upon the thorax, so as to elevate  it.  Among these
 muscles, 1 will cite the anterior and  posterior scaleni muscles, the
 muscles of the neck, which are attached to the  sternum, &c.  I
 will also add another muscle, to which no one has ever attributed
this use; I  allude to the  diaphragm.  Tnis muscle  indeed, is
attached at its  circumference, to the inferior  extremity of the
sternum, the seventh true,and all the false ribs; when it contracts,
 it  forces down the abdominal viscera, but, in order to do this, the
 sternum and ribs must present a a resistance sufficient to counter- 
or PHYSIOLOGY.                  315
 act the effort made in. the opposite direction.  Now, this resistance
 can be but imperfect, inasmuch as all  these  parts are moveable;
 for this reason, every time that the diaphragm contracts, it must
 elevate the  thorax, more  or less.  In  general, the extent of the
 elevation; will be  in direct  proportion to the  resistance of the
 abdominal viscera, and the mobility of the ribs.
   In the general elevation of the thorax, the. form of this cavity,
 and the relations of  the bones which compose'it, are necessarily
 altered.  The. cartilages  of the  ribs  appear  to be  peculiarly
 adapted to this"purpose.   As soon as they become ossified  and of
 consequence loose their elasticity, the chest becomes immoveable.
 At the same time, that the sternum is carried  superiorly, its in-
 ferior extremity  >s directed a little anteriorly; it exoeriences  thus
 a slight oscillatory motion; the ribs become less oblique to the ver-
 tebral column; and they separate-a  little,  the cue from the other,
 the inferior  edge being directed  outwards, in  consequence  of a
 slight  inflexion  which the cartilage undergo >s.   VII these  phe-
 nomena can  only be distinctly observed in the superior ribs, they
 are scarcely perceptible in  the inferior.
   There results  from this  elevation  of the thorax, a general  en-
 largement of this cavity,  both  from before, backwards,laterally,
 and from above, downwards.  This  enlargement is called inspira-
 tion;  it exhibits three well  marked degrees.   First, Ordinary in-
 spiration, which  is made by the depression of the diaphragm,  and
 an  almost insensible elevation of  the  thorax.  Second, A deep
 inspiration, in  which  the elevation of the thorax is evident, at the
 same  time  that  the  diaphragm  is  depressed.   Third, Forced
 inspiration, in which the dimensions  of the thorax are augmented
 in every direction, that the physical disposition of this cavity  will
 permit.  To the  dilatation of  the  thorax, succeeds expiration,
 that  is, the return of the  thorax to its  ordinary position  and
 dimensions.  The  mechanism  of this motion  is precisely  the
 reverse of that which we just described.    It is produced  by the
 elasticity of the cartilages  and ligaments of the ribs, which tend
 to react upon themselves,  when the relaxation  of  those muscles
 which elevated the thorax  permit  it, and  finally by the  contrac-
 tion of a great  number of muscles so disposed, that they depress
the thorax, and  draw it back.   Among these  muscles, which  are
 very numerous, it is proper to mention the large muscles of  the 
316                    A  SUMMARY
abdomen, the  great dorsal, the sacro-lumlalis, and the serratus
posticus inferior, &c.
  The contraction  of the  thorax, or  expiration, presents  also
three degrees, first, ordinary expiration, second, deep expiration,
third, forced  expiration.  In ordinary expiration, the  diaphragm
being relaxed, is.crowded up by the abdominal viscera, which are
pressed by the  anterior  muscles of this cavity, and cause a
diminution of  the vertical  diameter of the thorax.   The relaxa-
tion  of the inspiratory, and a slight contraction of the expiratory
muscles,  permit  the  ribs and  sternum to resume their ordinary
relation to the vertebral  column, and thus produce a strong expi-
ration.  But the retraction of the  chest may go still further than
this   If the abdominal  and other expiratory muscles  contract,
forcibly, there will  result from this a more.remarkable crowding
up of the diaphragm, a much greater depression of the ribs, and a
much stronger contraction of the base of the chest, and, of conse-
quence, a  very  considerable diminution  of  the  capacity of the
thorax.   This is called forcible expiration.

                         Of the  Air.
  The earth is surrounded on every side by a very thin and trans-
parent fluid, called  the arr; the whole mass of which is called the
atmosphere.   It extends from  the surface  of the earth to a height
of about lifteen or  sixteen  leagues.  The air is an elastic fluid,
that is, it  possesses, in itself, the property ot exercising a pressure
upon those bodies which it surrounds, and  upon the walls of those
vessels which contain it.  This property supposes in the particles
of which the air is  composed,  a constant tendency to repel  each
»lber.  Another property of the air is  compressibility;  that is,
its  volume may  be diminished, in proportion  to the  pressure to
which it is submitted.  Experiment informs us, that the same  mass
ot air, when subjected successively to different degrees of pres-
sure, occupies spaces or volumes  which are in an inverse ratio to
the degrees of pressure; so that the pressure becoming double,
triple, or quadruple, the volume is reduced one half, one third, or
one  fourth.
  In the atmosphere, the pressure that any given mass of air sup-
per's, '■-,  n proportion to the weight of those strata which are above
it; its weight and density therefore,  diminish as we rise from the 
OP PHYSIOLOGY.
317
earth.  At the surface of the earth, the pressure of the atmosphere
is the result of its total weight.  This pressure is capable of sus-
taining a column  of mercury  thirty-two inches high; the  instru-
ment employed for this purpose, js called a barometer.   Different
physical circumstances cause a slight variation in the atmospheric
pressurt.   It is. for example, weaker at  the summit ofmountains
than in vallies; it is greater when the air is charged with  humid-
ity, than when it is dry.  These variations may be very accurately
appreciated bv means of a barometer.
  Like all other bodies, the air is dilated by heat; its volume aug-
ments 1.266 for everv degree of heat of  the centigrade thermome-
ter.   The air is heavy; this we may satisfy ourselves of, by weigh-
ing at first, a balloon filled with  air, and weighing it afterwards,
when it has been emptied by means of an air-pump.   It has been
found in this wav;  the temperature being at 0, and wlien  the  ba-
rometer was raised to thirty inches, that sixteen cubic inches of air
weighs  19 grains; the same volume of  water weighed  2 pounds,
3 oz. 5 dr.  VV ater is therefore 770 times heavier lhan  air.
  The  atmosphere is more or less charged  with humidity; this
arises from the continual evaporation of those waters which cover
the surface of the earth.   We find from experiment, that water is
changed into vapour at all temperatures, but  this takes place most
rapidly,  when the  temperature is highest.  Further, the  air can
only contain a certain quantity of vapour at a given  temperature;
when it is saturated the humidity is extreme,   The nearer it ap-
proaches this  state the greater is  the humidity; the  instruments
which indicate fhe humidity  of the air. are  called  hygrometers.
When, in consequence of cooling, or any other cause, the air is
incapable of containing all the vapour  which it before  possessed,
this excess assumes the form of mist, or clouds, or is precipitated
in the form of rain or, snow,  &c.   The vapour of  water  being
lighter than air, and causing it to become dilated when it is mixed
with it, the result is, that  humid  is much lighter than dry air.
   Notwithstanding its thinness and transparency, the air refracts,
 intercepts, and reflects light.  In a small mass, we see too few rays
to have  its colour  produce a sensible  impression upon our eyes;
in a large mass the colour is very distinctly blue. The interposi-
tion  of large  masses of air,  gives also a blueish tint  to distant
 objects.   The air is of great  importance in chemical phenomena. 
318
A SUMMARY
 It was regarded for a long time, as an element; its  composition
 was first suspectedby John Key, in the seventeenth century, and
 was afterwards fully established by Lavoisier.  The air is com-
 posed of two gasses. possessing very different properties.   First.
 Oxygen  is a little heavier than  atmospheric air, and combines
 with all simple bodies;  it is one of the elementary principles  of
 water, and vegetable and animal substances; and of the greater
 part of known bodies, it is  necessary  to combustion and respira-
 tion.  Second.  Azote is rather lighter than the air, is one of the
 elements of ammonia, and of animal substances, and extinguishes
 bodies in a state of combustion.
   The proportions of oxygen and azote, which enter into the  com«
 position of air, is determined by  means  of instruments called
 eudiometers.   In these  instruments we  produce the combination
 of oxygen with some combustible body, such as hydrogen or phos-
 phorus, and the result of this combination  makes us acquainted
 with  the quantity of oxygen, that  the air  contained.  It is thus
 found, that a hundred parts of air in wei.hf, contained -?1 parts  of
 oxygen and 79 of azote.  The proportions  are  the same, in all
 places, and at  all heights, and has not  undergone  any sensible
 change in the fifteen year's, which have elapsed,  since chemi-try
 has established this point in a positive manner.  The air contains,
 besides oxygen and azote, and  the vapour of water in a variahle
 quantity, as we have already remarked; a very small quantii*.  of
 carbonic acid: the proportion of which is not fixed in a very rigo-
 rous mariner.  Nearly all combustible bodies decompose the air,
 at a temperature peculiar to each.   In this  decomposition, they
 combine with the oxygen, and leave the azote free.

                 Inspiration and Expiration.
   If we recollect the disposition of the pulmonary cells, the ex-
tensibility of their tissue, their communication with the external
air, by means of the bronchiee, the trachea, and the larynx, we
shall be easily able to conceive that, every time the chest is dilat-
ed, the air rushes into the lungs, in a quantity,  proportioned to
the degree of dilatation.  When the chest contracts itself, a part
of the air  contained in  it is expelled, and rushes  out through the
glottis.  In order "that the air may arrive at the glottis in inspira-
tion, or pass out from it in expiration, it will sometimes traverse 
OP PHYSIOLOGY.
319
the nasal fossre, and sometimes the mouth; the position that the
veil of the palate assumes, on these occasions, deserves attention.
When the air traverses the nasal fossae, and the pharynx, to enter
into the larynx, or to pass out from it, the veil of the palate is ver-
tical;  and applied to the anterior surface of the posterior  part of
the base of the tongue, so that the mouth has no communication
with the pharynx.  When the air traverses the mouth, in inspira-
tion or expiration, the veil of  the palate is horizontal, its posterior
edge embraces the concave surface of the pharynx, and ail  com-
munication is  stopped between  the inferior  part of the pharynx
and the superior part of this canal, as well as the nasal fossse.
Hence the necessity of requesting patients to breathe  through the
mouth, if we wish  to inspect  the tonsil* or  the pharynx.
   These two ways by which  air arrives at the glottis, are neces-
sary,  and eventually supply each other's place*  Thus,  when the
mouth is filled with aliment, the respiration is made  through the
nose;  and it takes place through the mouth when the  nasal fossae
are obstructed by mucus, a slight swelling of the pituitary mem-
brane, or any other cause.  It appears that the number of inspira-
tions  made in a given time,  differs essentially in different indivi-
duals.  Hale  states that there were twenty in the space of a mi-
nute.   A man upon whom Menzies experimented, breathed but
fourteen times in a minute.   Sir Humphrey Davy informs  us that
he respired twenty-six or twenty-seven times in that space.   Mr.
Thompson says, that his ordinary breathing is nineteen times in a
minute;  but I breathe myself fifteen times in the same  period.
Taking twenty, then, as the  medium, we shall have 28,800 inspi-
rations in twenty-four hours.  But it is  probable that  this  number
will vary very  much from a variety of circumstances.   Such as
the duration of  sleep,, motion,  distenrion. of the  stomach by ali-
ment, the capacity of the chest, and the moral affections.
   What quantity of air, it may be  inquired, enters into the  chest
at each inspiration? What quantity passes out at each expiration?
And  how  long  does it  generally remain  there?  Accordng to
Menzies, the medium quantity of air, which enters into the  lung9
at each inspiration, is three  hundred and  twenty cubic inches.
Goodwin thinks, that after a complete expiration, the lungs still
contain .about eight hundred  and eighty  cubic inches.  Menzies 
320
A  SUMMARY
asserts, that the quantity is much greater, and that it amounts to
fourteen hundred and sixty-one cubic inches.
  According to Davy,  after, one  strong expiration, his lungs re-
tain three hundred and thirty-two cub. in.
       After a natural  expiration,              970 cub. in.
       After a natural inspiration,           1106
       After a strong inspiration,            3206
       By strong expiration, after a deep in-
         spiration, there passed out-from the
         lungs,                              1556
       After a natural inspiration,             643
       After a natural.expiration,              353
  Mr. Thomson thinks that we shall not be far from the truth, if
we suppose, that the quantity of air, generally  contained  in the
lungs, to be 2294 cub. in., and that there enters, and passes out of
the chest, at each expiration and  inspiration, SL27 cub.  in.  Thu9,
supposing twenty inspirations in a minute, we should have enter-
in^, and passing out  from the lungs in this time, 6500 cub. in. and
in twenty-four hours, 75556 cub  in. or nearly 48 pounds.
  Chemists have made a great uumber of experiments, to deter-
mine, if the volume  of air diminishes during the rime it remains
in the lungs.  From the most recent experiments it appears, that
in the greater number of instances,  no diminution is observed;
that is, the air expired  represents exactly the same volume as that
inspired.   When this  diminution has taken place, it appears to
have been purely accidental.*
  In  traversing, successively, the mouth,  or nasal, cavities, the
pharynx, the larynx, the trachea and the bronchiae, the inspired air
acquires a temperature nearly equal to that  of the body.   Having
become heated, and of  consequence rarified, the same quantify of
air in  weight, occupies a much greater space  in the  lungs, than
before it was introduced into this viscus.  Besides  this change in
volume, the inspired air  becomes loaded with  the vapour, winch
is continually thrown oft from the mucous menibrane of the lungs;
it is,  therefore, not only warm, but humid, when it arrives at the
pulmonary cells; finally, the portion of  air of which we have spo-
ken,  becomes mixed with that which the lungs before contained.
See Thomson's Chemistry. 
OF  PHYSIOLOGY.
321
But expiration soon succeeds inspiration, a few  seconds ordina-
rily intervene; the air that the  lungs contain, compressed, by the
expiratory powers, escapes in an inverse ratio to the air inspired.
It is proper  here to remark, that the portion of air expired, is not
identically,  that which had  been just inspired, but is a portion of
the mass which the lungs contained before inspiration.  If we com-
pare the  volume of air that the  lungs habitually contain, with that
inspired  and expired at each respiration,  we shall be induced to
believe, that the end of inspiration and expiration, is but to renew,
in part,  the large mass  of air contained in the lungs.   This re-
newal  will  be much  more considerable, wh<n the quantity of air
expired is very great, and the succeeding inspiration strong.

Physical and Chemical changes that the Air undergoes  in the
                           Lungs.
   The air passes out from the  lungs, at about the same tempera-
ture with the body; a great  quantity of vapour, called pulmonary
transpiration, escapes with it;  its chemical composition, is diffe-
rent from that of the air inspired.   The  proportion of azote  is
nearly the same, but the quantity of oxygen and carbonic acid,
are essentially different.  Instead of twenty-one parts of oxygen,
and one  of carbonic acid, in one hundred,  which the atmospheric
air presents, the expired air is  found to contain eighteen or nine-
teen parts of oxygen, and three or four of  carbonic acid.   In ge-
neral, the quantity of carbonic  acid,  represents exactly the quan-
tity of oxygen that has disappeared; the  last experiments, how-
ever, of  Gay Lussac,*and Davy, shew a small excess of  acid, that
is, a little more carbonic acid is formed, than oxygen disappeared.
To estimate the quantity of oxygen consumed by an adult in
twenty-four hours,  it is only necessary to recollect the quantity
of air respired during this interval.  According to Lavoisier, and
Davy,  two hundred and fifty-six cubic inches are consumed in one
minute,  which gives in twenty-four hours, two thousand  nine hun-
dred and eighty cubic inches.
   It is not  difficult to appreciate  the quantity of carbonic acid,
that passes  out from the lungs at  the same time, inasmuch as it is
nearly  equal to the volume  of  oxygen  that has disappeared.
Thompson estimated it at three hundred and twenty cubic inches.
 Though it may be, he remarks, probably  less;  now this quantity
                             41 
322
A  SUMM\HY
of carbonic acid, represents about five thousand two hundred and
seventy grains of carbon.   Some chemists say, that a small quan-
tity of azote disappears during respiration; others have thought,
on the  contrary, that the quantity of this gas was  sensibly in-
creased; but there  is nothing positively (known on  this point.
We are informed of the degree of alteration, that the air under-
goes  in our  lungs, by a sensation  which impels us to renew  it.
This  is hardly perceptible, in common respiration,  because we
hasten to obey this impulse; but it becomes extremely painful, if
this  sensation be not satisfied; it soon causes anxiety and  fear,
which are instinctive evidences of the importance of respiration.
While the air contained in the lungs is  thus modified, both in its
physical and chemical properties,  the venous blood traverses the
ramifications of the  pulmonary  artery, which form,  in part, the
tissue of  the cells of the  lungs.  It then passes into  the ramifica-
tions of the pulmonary veins, and  soon into the veins themselves;
during this, the nature of the blood becomes changed, from venous
to arterial blood.   Let us now examine the phenomena of this
transformation.

          Change of the  Venous,  into Arterial Blood.
   At the moment when the blood  passes through the minute ves-
 sels, which cover the pulmonary or air cells, it  assumes a bright
 scarlet colour; its odour is stronger,  its taste more  distinct, and
 its temperature elevated about one degree.  One part of the se-
 rum  escapes in the form of vapour, into the air cells, and mixes
 with the air. Its tendency to coagulate, sensibly augments.  This
 fact  is generally expressed by saying, that its {plasticite) is much
 greater;  its specific gravity, and its capacity for caloric, are both
 diminished.  When the venous blood has acquired these charac-
 ters, it becomes arterial.  In order that we may render more evi-
 dent, the differences between arterial and venous blood, we shall
 recapitulate them in the following table. 
                    OP PHYSIOLOGY.                  323

  Principal differences  between Venous and Arterial  Blood.
                            Venous Blond     Arterial Bind.
      Colour,              a modena red,   bright scarlet.
      Odour,               weak,           strong.
      Temperature,        98° Far.         nearly 100.
      Capacity for caloric,  852*            839
      Specific gravity,      1051*           1049
      Coagulation,          less prompt,     more prompt.
      Serum,               more abundant,  less abundant.
  I have  already described the changes that the air undergoes^
in the lungs;  and am now about to  notice  those which take place-
in the venous blood, in traversing  these organs;  let us now  see
what  connexion exists between  these two orders of phenomena.
The colour of the  blood evidently  denends  upon  its immediate
contact with  the oxvgen; for, if any other  gas exists in the lungs,
or if the atmospheric air be not renewed, this change in colour no
longer  fakes place.  But it manifests itself anew, as soon  as  we
permit  the introduction of oxygen gas into the air cells of the
lunu-s.  It s  easy to see the phenomenon  of the change, in colour
of the venous blood, even  in the dead subject.   At  the approach
of death,  the venous blood  often accumulates in the vessels of the
lungs;  the bronchite being  deprived of air. it preserves the venous
properties long after death.  If the atmospheric air be forced into
the  trachea, in such a manner as to  distend the tissue  of  the
lun *s. it causes a change of colour  in  the  blood, from the modena
 red to a bright vermiliion tint.
    The same phenomenon  is observed whenever the  venous blood
 is brought in contact with  oxygen,  or atmospheric air.  Blood
 drawn  from a  vein anil  exposed  to the air, assumes a brighter
 tint; immediate  contact is  not  necessary;  the same  blood  con-
 tained  in a bladder, and plunged into oxygen gas, becomes scarlet
 over its whole  surface.   Thus, the very delicate vascular walls
 which, in the lungs, separate the atmospheric  air, and  the blood,
 cannot be considered as an obsia-leto this change of colour.  But,
 it may be inquired, how does oxygen gas produce this change of
 colour in  the venous blood?   Chemists are not agreed  upon this
 point.  Some think that it combines directly with the blood; others

                   • Water being as 1000----J. Davy. 
324
A  SUMMARY
that it removes from  the blood  a certain quantity of carbon; and
there are others again, who are inclined to believe, that both these
effects take place; but neither of these explanations will satisfac-
torily  account for the change  of colour.   Many chemist* have
attributed the peculiar colour of the blood to the presence of iron,
but  this opinion is  now  rejected as  extremely doubtful; it will
however, seem less  unreasonable, when it  is recollected, that if
this  metal be  separated  from the coloured  part of  the blood, it
looses the property  of becoming scarlet, on  being exposed  to
oxygen gas.*
   We may easily imagine the loss of serum which the blood  un-
dergoes in respiration. It is very probable, that a certain quantity
of serum  escapes from the extreme ramifications, and evaporates
into the air which the cells contain. This vapour afterwards passes
out  with the expired air, under the denomination of pulmonary
transpiration, but it does not  necessarily  follow,  that  all  the
vapour which passes  out from the blood, during  expiration, arises
from the pulmonary  artery.   I  have remarked above, that a con-
siderable portion of  this vapour is thrown off by the arterial blood,
which  is distributed  to the mucous membrane of the  bronchise.
In  his first  researches  upon   respiration,  Lavoisier   believed,
that a combination  of hydrogen  and oxygen took  place  in  the
lungs, from which resulted the formation of a certain quantity of
wa*ter.  This  idea however, is not at  present admitted, but this
transpiration  is  considered as  the result  of the  passage of the
serum into the air cells of the bronchiae. as it passes through the
pulmonary artery. Anatomy seems to confirm this, water injected
into  the pulmonary artery, passes, under the  form of  innumerable
small  drops  almost  imperceptible, into the  air cells, and mixes
with the air which they contain.
  In living animals, we may increase  at will, the quantity of pul-
monary transpiration, by injecting distilled water at  the tempera-
ture  of the body, into the venous system, as the following experi-
ment will  prove.  Take a small dog, and inject, at different times,
a considerable  volume of water; the animal  will  at first be in a
perfect state  of  plethora, its vessels  will be so completely dis-

  ' We must not confound  the  colouring matter  of  the blood, described  by
Messrs. Biamleand Vaui[uelin with hamutine, the colouring  matter of logwood,
which was described by M. (Jhevreal. 
OF PHYSIOLOGY.
325
tended, that it will move with difficulty; but, at the end of some of
moments, its respiration will  become considerably accelerated,
and there will be poured out a great abundance of fluid from the
throat, the source of which is evidently the  pulmonary transpira-
tion, considerably augmented.   It is not only the aqueous part of
the blood, which  escapes  by pulmonary transpiration.   I have
shewn,  by direct experiments, that many substances introduced
into the veins, either by absorption or direct injection, soon pass
out by the lungs. Diluted alcohol, a solution  of camphor, of nether
or other odoriferous substances, introduced  into the cavity of the
peritoneum, or any other part, is soon absorbed  by the veins, and
transported  to the  lungs, it then passes into the bronchiae, and
may be recognized by the peculiar  odour of the expired air.
   Phosphorus acts in the same manner, its odour is not only sen-
sible in the expired air, but its presence is still more easily shown,
and in the most  positive manner. Inject into the crural vein of a
dog, h-If an ounce of oil, in which phosphorous has been dissolved,
you will scarcely  have performed  this operation, when there will
pass  out from the nostrils  of  the animal, a dense, white  vapour
which is the phosphoric acid.  It appears, from the experiments of
Dr Nysten, that gases act  in  nearly the same  manner; that is,
that after they have  been  injected into the veins, they  pass out
with the expired air.
   Some attempts have been made  to determine  the  quantity of
vapour that  escapes from the  lungs of an adult,  in twenty-four
hours.  The latest, performed  by  Mr. Thomson, fix it at about
eighteen ounces; Lavoisier and  Seguin, formerly estimated it at
something less than this.   It is  probable, that it is varied  by  an
infinite number of circumstances.
   It  is not vet, considered as settled, in what mode  the carbonic
acid contained in the  expired air,  is formed.  It is  thought  by
some, that it exists, ready formed, in the venous blood, and that it
is exhaled by this fluid, at the moment of  its passage through the
lungs; by others, that it is the  result of the  direct combination of
the carbon of  the venous blood  with  the oxygen; but neither of
these opinions can  be considered  as fully established; perhaps
both these effects mav take place at the same time.  From our ig-
norance  of the mode of formation  of the carbonic acid,  we are
unable to fix the precise part  performed, by the oxygen in resn: 
326                     A  SUMMARY

ration.  Some assert that it is employed to combine with the car-
bon of the venous blood; others, that it  passes into the pulmonary
veins, and there is still another class who believe that it performs
both these offices,  at  the  same time.   All  this part  of  animal
chemistry requires  further investigation; so long as we have not
any positive knowledge concerning the formation of carbonic acid,
and the disappearance of oxygen, it  will be difficult  to  determine
the cause of the elevation of temperature, which  takes place in
the blood, in  passing through the lungs.   It is probab'e, however,
that the oxygen combines with  the  carbon of the  blood, and, as
every formation of this kind is accompanied by a considerable evo-
lution of caloric, it is probable, that  this is the cause of the increa-
sed heat of the arterial blood.  If we suppose, also,  that the oxy-
gen is absorbed and  passes into the  pulmonary  veins, and  that it
combines  afterwards directly with  the blood;  we  may then ac-
count for  the elevation in the temperature of the blood;  for every
combination of oxygen with  a combustible  body, is accompanied
with an evolution of caloric*
  The slight diminution in the specific gravity of the blood,  and
its capacity for heat, arises, probably, from the loss  of water, from
the surface of the air cells.   With respect to the other  properties
that the venous blood acquires in traversing the lungs, such as its
odour, peculiarity of taste, &c  that our opinions on this  point may
be accurate, it  is necessary that an exact and comparative analy-
sis of the venous and arterial blood, should make us precisely ac-
quainted with these differences.  This is a service, for which phy-
siology looks to the science of chemistry.

            Respiration of  various kinds  of Gas.
   We must not rest satisfied with studying the effects of the res-
piration of atmospheric air, we are naturally desirous of knowing
what  would be the result of the respiration of other kinds of gas.
Animals have been plunged into them, men have voluntarily res-
pired  them, and it is thus known,  that atmospheric air alone, can,
for any  considerable  time,  serve  the  purposes  of respiration.
Every other  uas destroys animal  life, more  or  less  promptly;
even oxygen  itself, when it is pure, is fatal,  and when it is mixed
* See article, animal heat. 
OP PHYSIOLOGY.                  327
with azote, but in proportions different from  the common air, it,
sooner or later, causes the death of those animals that  respire'it.
From making these different experiments, we are induced  to di-
vide gases, as they relate to respiration, into  two classes.   First,
those that are respirable;  second, those that are deleterious.
   V\\e fi< st, to which belong the protoxide of azote, hydrogen, &c.
d'siroy animals,  only, because they are incapable of fulfilling the
offi. e *»( oxygen.   Among these  gases, there is one,  the protoxide
of azote, or nitrous oxide, which produces very remarkable effects,
and  which should perhaps be considered as belonging to the second
class,  ."-tir II Davy was the first who examined the effects of this
upon himself.  After having expired the  air from  his lungs, he
breathed about five pounds of the nitrous oxide; the first sensations
which he experienced were those of vertigo,  at  the end  of about
haif a minute, continuing still to respire this air, these effects gra-
dually  diminished;  and  were succeeded by a sensation analogous
to a gentle  pressure, accompanied by a slight, but very agreeable
trembling, particularly in the chest and extremities. Surrounding
objects  appeared to him to be of a dazzling brigh+ness, and  his
hearing to be more acute; towards the last respirations, the agita-
tion augmented,  his muscular force seemed much increased, and
he felt an irresistible propensity to put himself in motion.   These*
 effects ceased,as soon as Mr. Davy had discontinued to  respire the
gas, and. in the course of ten minutes, he found himself in a natural
 situation.
   These effects, are not,  however, always the  same;  Vauquelin
 and  1'henard, who also  respired this gas, did not perceive all the
 phenomena described  by  Davy,  but others analogous to  them.
 The deleterious gases are those which are not only incapable of
 respiration, but destroy, more or less rapidly,  man and  animals
 that respire them, even when   mixed  with certain portions of at-
 mospheric  air.   Uf this number are all the acid gases, ammoniacal
 gas, sulpuretted hydrogen, &c. &c.

 Influence of the Nerves  of the eighth pair upon Respiration.

    The nerves of the eighth pair are the only cerebral nerves which
 send filaments to the tissue of the lungs; this  has induced  phy-
 siologists to divide them, to examine the effects that would result
 from it. This easy experiment was made often by the ancients, 
328
A  SUMMARY
and there are few modern physiologists who have not repeated the
experiment.  Every animal, in which the nerves in question are
divided, dies,  more  or  less  suddenly; sometimes, death  takes
place instantly  after the division.  It never survives more than
three or four days.   Death  has  been attributed, by  authors, in
turn,  to the cessation pf the motions of the  heart, imperfect di-
gestion, inflammation of the lungs, &c.   VVe are indebted to the
recent inquiries of Messrs. Dupuytren,  Dumas, Blainville, Pro-
vencal, and Legallois, for  the interesting information they have
given us on this subject.  I will now give an abstract of their re-
searches.
  A division of the nerves of the  eighth pair,  in the neck, on a
level  with  the thyroid gland, or  even lower,  has an influence;
first, upon the larynx, second, upon the lungs.  These  two classes
of effects must  be distinguished.   In treating  of the  voice, we
have said,  that  the divisions of  the recurrent  nerves, produced
sudden aphonia, or  loss of  the voice.  The same  phenomenon
takes place, after the division of the eighth pair of nerves, which
is easy to understand, as the recurrents are but  branches of these
nerves.  But in addition to the loss of voice, it  is not  uncommon,
that a section of the nerves of the eighth pair, is followed by such
an approximation of the  edges of  the glottis, that the air is inca-
pable of penetrating into the larynx, and that sudden death hap-
pens, as is  always the case in an animal, which is incapable of re-
newing the air of its lungs.  In ordinary cases, the sides  of the
glottis are  not brought so exactly together, as to entirely exclude
the air from entering into the larynx, for the purposes of respira-
tion.  But  as the glottis has lost its peculiar motion, the air enters
into, and passes out from the chest, in a more irregular and con*
strained manner.
  At the time when these observations were made, it  would have
been impossible  to have  explained, satisfactorily, these different
phenomena.  But since the reader  is acquainted with the  man-
ner in which the  recurrent and laryngeal nerves are distributed
to the muscles of the  larynx;  the subject presents no further dif-
ficulty.  By the division of the eighth pair, at the  lower part of
the neck, the dilator  muscles of the glottis  are paralised.   This
opening no longer enlarges itself at the instant of  inspiration,
which  the constrictors, which receive  their  nerves from the 
OP PHYSIOLOGY.
329
superior  laryngeal, preserve  their action,  and close the glottis,
more or Us.-, completely.  When the section of the eighth pair is
not followed by  such a  constriction  of the glottis, as  to  cause
instantaneous death, other phenomena are developed, and death
does not  occur until the end  of  three or four days.
  Respiration is at first constrained, the motion of inspiration is
more i xtensive, and the animal seems to pay a particular attention
to it; he  is not inclined to move, is evidently fatigued by exertion,
and will  often preserve a perfect state of  repose.   The forma-
tion  of arterial blood  is not  prevented, for a short time after
the  operation, but  soon, the second day, for example, the laborious
respiration  increases,  and   the efforts  in  inspiration become
greater.   The  arterial  blood has no  longer the Vermillion  tint
that  is peculiar to it, it is deeper coloured, and  its temperature
becomes  diminished; at last all these symptoms increase, respiration
can onlv be made  by all the  inspiratory powers; the arterial blood
becomes of a dull red, and  similar to-venous blood; the arteries
containing but  little of it, a  chilliness becomes manifest, and the
animal soon dies; on* opening the chest, we find the bronchi*, and
sometimes the  trachea itself, filled with a frothy fluid, sometimes
bloody; the tissue  of the lungs is engorged and swollen,  the raini-
ficarioris, and even the trunk, of the pulmonary artery, are strongly
distended with blood, of nearly a bUck colour; there is likewise
found a coHsideraule effusion  of serosity, or even of blood, into the
parenchyma ot  the lungs.  On the other hand, experiments show,
that in pioportiou  as tins series of phenomena become developed,
the animals  consume  less  oxygen, and  form a less  quantity
ol carbonic acid,  it has been supposed, with reason, that in this
case, the animals perished, because respiration could  not be per-
formed,  the  structure of tue  lungs  being  so altered,  that the
inspired  air could  not arrive  at the air cells.   1 think we may add
to this cause,  the difficulty  which the blood from the  pulmo-
nary artery, experiences in passing into the vein; a difficulty which
appears to me, to  be the cause  of the  distension of the venous
system alter Ueath, and of the small quantity of blood which the
arterial system contains, sometime before this event happens.'
   The section of  one of the nerves of the  eighth pair, produces
these effects upon  one of the  lungs only, and  life may be continued
4:^ 
330                 OP  PHYSIOLOGY.

by the action of the other of these organs, the animal not perishing.
1 have seen animals live in this state many months.

                   Of Artificial Respiration.
  The principal object of the motion of the thorax, is to draw air
into the  lungs, and afterwards to expel it  from these organs.
Whenever these  motions are stopped, the air of the lungs being
no longer renewed, respiration necessarily ceases, and death soon
follows.   But we may supply, for a certain time, the action of the
thorax, by .introducing air artificially into the lungs.  Both ancient
and  modern anatomists have often practised this.   The air has
been  gradually introduced with bellows, or  bladders, &c.  This
may also be done with a syringe, with  a small  hole on the side of
its  tube.  The end  of the tube is  introduced  into the  trachea,
and fixed there by a ligature; afterwards we draw the piston, in
order to fill the syringe  with  air;  we then apply one finger upon
this small hole, to prevent the air from passing out through it; the
piston is then forced down, and' the air of  the syringe passes into
the lungs.  We then withdraw the piston, and the syringe becomes
filled with air from the lungs; we now raise the finger placed
upon  the small hole, and by pushing down the piston, cause the air
to escape, which has already performed  the purposes of respira-
tion;  we draw immediately the piston, to fill the instrument with
pure air, leaving  the little  hole open, &c.  By repeating regularly
these motions, we  are able to protract the life of an animal, in
which the  thorax has become immoveable, either from a division
of the spinal marrow, behind the occipital bone, or even where the
head  has been  entirely cut off.  It however, fulfils, but very imper-
fectly, the function of  respiration, and can  never  be prolonged
beyond a few hours.  Frequently the lungs become engorged  by
the blood, or are torn by the air; this fluid is also introduced into
the pulmonary veins, and spreads itself into the cellular tissue, so'
as to prevent the dilatation of the  air cells. 
      COURSE OF THE  ARTERIAL  BLOOD.


  This function has for its object, to transport the arterial blood
from the lungs to every part of the body.

                   Of the Arterial  Blood.
  From what has been already said  of the arterial blood, under.
the article respiration, there remains for us but little  to add re-
specting this fluid.  It will be proper to observe, that the learned
piofessor  Vauquelin has recently found in this  fluid, a considera-
ble quantify of oily matter, of a yellowish colour, of a bland taste,
and of a soft consistence,  and which, of consequence, in appear-
ance, at least, has great analogy to fat.  When by the aid of a
strong magnifying glass, or a microscope, we examine the trans-
parent parts of cold blooded animals, we discover, in  the  sangui-
neous vessels,  an  innumerable multitude of small  rounded par-
ticles, which  swim  in  the serum,  rolling one over the  other, as
they pass from  the arteries to the veins."
  Similar observations have never been made  upon warm blooded
animals, because the  membranes  and  walls of the sanguineous
vessels are opaque.   Rut, as by diluting a drop  of blood  in water,
we can distinguish, bv means of a microscope,  particles of a round-
ed form, the existence of globules has been admitted, both in ani-
mals and man.   Very  wonderful thinirs  have been  «aid of these
globules..  According to Lewenhoeck, a thousand million of these
globules are not larger than a grain of sand.  Haller, in speaking
of cold blooded animals,  (for he  had never  seen these globules
in warm blooded,)  says, they are  so-00 part  of an inch  in di-
ameter.  Some have  thought, that they were of the same diame-
ter and  form in all animals; others, on the contrary,  have main-
tained  that they have a peculiar size  and form in each animal;
some say, that  they are spherical, and  whole;  others, that they
are flattened, with a  hole pierced  through their centre;  finally,
there have been some,  who have  thought  that a globule,  was a
small bladder which contained a certain number of small globule?. 
334
A SUMMARY
   I think there is much fancy, error, and optical  illusion, in all
these different opinions.   I  have  made a great number of  micro-
scopic experiments, to clear up this point.   I have never seen, in
the blood of man, diluted in water, any thing more than particles
of coloured  matter, generally rounded, and of  different sizes,
which, according as they were placed, accurately or otherwise, in
the focus of the  microscope, appeared sometimes spherical, some-
times flattened,  and at others, as  if they were pierced through the
centre. All these appearances may be produced, at  pleasure, by
varying the  position of the particles, in relation to the instrument.
I believe also, that air bubbles have been often described and de-
signed in books, for globules of blood.  Nothing,  at least,  resem-
bles more, certain  figures of Hewson, for  example, than  small
bubbles of air, which may be produced by  agitating slightly the
fiuid submitted to the microscope.

              Apparatus of the Arterial Blood.
  It is composed first, of the pulmonary veins, second of the left
cavities of the heart, third, of the arteries.

                      Pulmonary Veins.
  They arise  like veins, properly so called,  in the tissue  of the
lungs, that is, they consist  at first of an infinite number of small
branches,  which appear to be a  continuation of the pulmonary
artery; these small branches uniting,  form  small trunks, which
gradually  become larger.   At last, all these trunks terminate in
four vessels, which, after running a short distance, open into the
left  auricle  of the heart.   The pulmonary  veins differ from all
other veins in  this,  that they do not  anastomose  with each other
when  they have acquired a certain  size.  We have  observed  a
similar disposition in  the divisions of the artery, which is distri-
buted to the lungs.   The  pulmonary  veins  have no valves, but
their structure,  in  other  respects, is similar to  the  other veins;
their middle membrane is, however, a little thicker, and seems to
possess a greater degree of elasticity.

                  Left cavities of the Heart.
  The form and  size  of the left auricle, differ  but little  from
the  right, its  surface only is smoother, and does  not  present 
OF PHYSIOLOGY.
333
any  fleshy  column,  (except in the appendix called oricule.)
It communicates, bv an  oval  opening,  with the left'ventricle,
which is distinguished  from the right,  by the greater degree of
thickness of its walls, and the number, volume, and disposition of
its fleshy columns.   The opening bv which  the auricle and ven-
tricle communicate,  is garnished by  what is called  the  mitral
valve, which is very analogous to the tricuspid valve.  The ven-
tricle gives origin  to the  artery colled the aorta; the orifice of
which  presents three semi-lunar valves, very  similar  to the pul-
monary artery.

                       Of the  Arteries.
  The aorta is to the left ventricle, what the pulmonary artery is
to the right, though it differs in many important particulars.   Its
capacity and extent are much greater; nearly all its divisions are
considered as  arteries,  and have each received particular  names.
Its branches  anastomose with each other in  various modes;  they
often present  numerous  and remarkable ffexosities.  They are
distributed to every nart of the body, and affect, in each, a peculiar
arrangement;  they  communicate with  the veins and  lympha-
tic vessels.  Tn other respects, the structure of the aorta  strong-
ly resembles the  pulmonary artery; its middle membrane,  is how-
ever, much thicker and more elastic.  Through nearly its whole
extent, the aorta is  accompanied  by filaments, arising from the
ganglions of fhe great sympathetic nerve. These filaments appear
to be distributed to its  walls.

    Course of the Arterial Blood in the Pulmonary  Veins.
   In treating of the course of the blood, in the pulmonary artery,
we pointed out, how this fluid arrived at the extreme  branches of
this vessel.  The blood does not stop there, it passes into the ex-
treme branches of the  pulmonary vein, and soon  into the trunks
 of this  vein; in its passage, its motion is gradually accelerated as
 it passes from the small, into the large veins.  It  does not run
 with a jerk, and  is nearly  of equal rapidity in  the four pulmonary
 veins.   But let us inquire what cause determines the  progress of
 the blood in these veins? we naturally refer this to the contrac-
 tion of  the right ventricle, and the elasticity of the walls of the
  ulmonary artery.   Indeed, having forced the blood to the extreme 
;?3i
A  SUMMARY
ramifications of the pulmonary artery, we cannot  conceive  why
the«e two causes should  not  continue its  motion even  in  the
pulmonary veins.
  This was the opinion of Harvey, who first demonstrated the true
course ot  the blood;  but modern physiologists have found this ex-
planation  too simple, and it is now generally admitted, that when
the blood  has arrived at the extreme ramifications of the  pulmo-
nary artery, and entered those of the pulmonary veins, or as they
are more  commonly  called, capillary vessels of the lungs,  the
blood no longer moves from the influence of the heart, but by an
action peculiar to the small vessels that it traverses.  This idea
of the action of  the  capillary vessels is  extremely convenient in
physiology; after the  vital  properties, there is nothing which more
facilitates our explanation  of the most obscure phenomena.   Let
us therefore examine it with attention; ami first, has this action of
the capillaries been witnessed by any observer?  does it fall within
the scope  of our senses? No, no one pretends to have seen  it, it is
only a thing supposed.   But let us admit  for an instant the exis-
tence of  this capillary action; in  what does it consist? is  it  a
greater or less degree of  contraction, by  which the blood  with
which they are filled, is forced forward?  in contracting from  their
elasticity, they would undoubtedly  propel  the blood: but can  any
reason be assigned why fhey should direct  it rather towards the
veins, than arteries? finally,  when the small  vessels  are  once
emptied,  how would they be filled again? this can onlv be. by the
force of the heart propelling blood  into them, or else, from  their
dilating in such a manner as to attract this  fluid  from the neigh-
bouring vessels; according to this supposition, it would be as like-
ly to attract the blood from the veins as from the arteries.  If we
admit, therefore, a position, which  is merely gratuitous, that the
capillary  vessels  dilate and  contract themselves alternately, we
still should not be able to explain the function attributed to them.
That they may perform this function, it would  be necessary  that
each capillary vessel should be arranged in a manner analogous ta
the heart, that it should be composed of two parts, in which, one
dilated while the other contracted itself, and that there  shouhl be
between them, a valve analogous to the mitral valve.   Yet even
with this  complicated apparatus, the course of  the blood in these
vessels would not be uniform. 
OF  PHYSIOLOGY.
o35"
  In whatever point of view, therefore, we examine this action of
the capillary vessels,  it is found  vague and contradictory.  In
reptiles also, where by the  aid of a microscope  it is easy to dis-
tinguish the blood of the pulmonary artery passing into the veins,
no motion can be perceived, at that point, where the  artery ter-
minates in the vein, the motion of the blood is nevertheless mani-
fest, and even rapid.  VVe must conclude then,  that the capillary
action of the vessels of the lungs,  giving  motion to  the blood in
the pulmonary veins, is a mere supposition, an effort of the imagi-
nation, in a  word, purely hypothetical, and that  the true  cause of
the passage of the blood in the pulmonary artery and veins,  is the
contraction  of the right ventricle of the heart.
  I  am far from thinking,  that the small vessels, at all times,
equally favour the passage of the  blood;  we  have a proof to the
contrary, at each inspiration and expiration.  When the lungs are
distended with air, its passage is easy, but when the chest is con-
tracted, the lungs containing but little air, it  becomes more diffi-
cult. It is besides, extremely probable, that they  dilate themselves,
according to the quantity of blood which traverses the lungs, and
many other circumstances.   I am  ready to believe that, according
as they are distended or contracted, they may  influence  the pro-
gress of the fluid  that traverses  them; but 1 cannot admit  that
they are capable of modifying the course of the blood, or that they
are the sole agents of  its motion.
   The eighth pair of nerves appears to have a great influence upon
the  passage of the blood through the lungs.   It is very probable,
that it modifies the disposition  of the capillary vessels  of these
organs; when  we inject water into the pulmonary artery, in the
dead body, it passes immediately  into the veins; a part of it, how-
ever, escapes into the cells of the bronchiae, where  it mixes with
the  air, and forms  froth; another portion escapes, and  becomes
infiltrated  into  the cellular tissue of the lungs.  After a certain
time,  when this infiltration has become somewhat considerable, it
then becomes impossible to force the injection further into the pul-
 monary veins.   Similar phenomena occur, when instead of  water,
blood is injected into the  pulmonary artery.  These phenomena,
 as we have seen, have a  great analogy,  with those produced by
 fhe section of the eighth pair of nerves in living animals.    The 
336
A  SUMMARY
pulmonary veins are not so extensible as the other veins, they pour
out promptly, into the left auricle the blood which passes through
them.

            Absorption  of the Pulmonary  Veins.
  Like the other veins, the pulmonary veins absorb, and carry to
the heart, those  substances which are in contact with  the spongy
tissue of the air cells of  the lungs. It is sufficient to inspire once,
air charged with odoriferous particles, in order that it may become
manifest in the animal economy.  The deleterious gases, medicinal
substances  spread through  the air, contagious miasmata,  cer-
tain poisons, or  medicines applied to the tongue, produce  effects
which  astonish us by their promptitude.  The mode of this absorp-
tion is  no  better understood,  than that of venous absorption
generally.

Passage  of the  Arterial Blood through the Left Cavities of
                          the Heart.
   The mechanism  by which the blood traverses the  left auricle
and ventricle, is the same, as that by which the venous blood tra-
verses the  right cavities of the heart.   When  the  left auricle
dilates, the blood is poured in, by the.pulmonary veins, and fills it.
When afterwards it contracts itself,  one part of the blood  passes
into the  ventricle, another  flows back into the pulmonary veins,
When the ventricle dilates, it receives blood from the auricle, and
a small portion from the aorta. When it contracts itself,  the mitral
yalve is raised, it closes the opening between the auricle and  ven-
tricle,  so that the blood cannot return into the auricle; it is there-
fore, forced into the aorta, pushing before it the .semilunar valves,
with which the vessel  had  been closed, during the  dilatation
of the ventricle.
   It is proper  however, to remark, that as there are  no fleshy
columns existing in the left auricle, it cannot be supposed to  have
the  same influence upon the  blood, that  we have supposed to be
exerted by  the right;  and as  the  left ventricle has much thicker
walls than the right, it must compress the blood \\ itii much greater
force,  which is indispensable, from the great distance this fluid has
to pass over. 
OP PHYSIOLOGY.
337
    Course  of the  Blood in  the  Aorta, and  its Divisions.
   Notwithstanding the differences which exist between this and
the pulmonary artery, the phenomena of the course of the blood,
are nearly the same.   'Thus a ligature  being  applied  upon this
vessel, near to the heart, in a living animal, it becomes contracted
through  its whole extent, and the blood, with the exception of a
certain quantity, which remains in the principal arteries, passes in
a few moments into the veins.
   Some  authors have called in question  the  fact, of the contrac-
tion of  the arteries, under  these  circumstances.  We may  de-
monstrate this, by the  following experiment.  Lay bare the  ca-
rotid  artery in a living animal,  for several  inches in extent;
take,  with a compass,  the transverse dimensions of the vessel, tie
it at  two different  points,  you will then have a portion of  the
artery full of blood;  make into the walls of this portion of the ar-
tery a small opening, and you will immediately see the  blood al-
most entirely  pass out. darting even to some distance.   Measure
afterwards the size,  with a compass, and you will not then doubt
that the  artery is very much contracted, if the prompt expulsion
of the blood had not  already convinced you.   This experiment
proves also, contrary to the opinion of Bichat, that the force with
which the arteries re-act upon  themselves, is  sufficient to expel
the blood they contain. 1 will  immediately give other proofs of
this.  During life, this total expulsion cannot take place, because
the left  ventricle throws out, at every moment, new  masses of
blood into the aorta, and this blood  replaces that which is con-
tinually  passing into the veins.
   Every time that the  ventricle forces blood into the aorta, it is
distended, as  well  as  all  its ramifications  of a  certain calibre.
But this  dilatation becomes less as the  arteries become smaller,
and it ceases  altogether, in those which are very small.  These
phenomena are, as we  see, the same already described in speaking
of the pulmonary artery.  The explanations that  we  then  gave,
may with propriety be applied here.
   The polished surface of the interior  of the arteries, must be
very favourable to the motion of the blood; we know, at least, that
it diminishes when this is removed by certain diseases; the course
of the fluid becomes  slower, and sometimes  ceases  altogether.
                              43 
338
A  SUMMARY
This is probably, also,  the  reason why blood will not  pass long
through a tube, introduced  into the extremity of an open artery.
It is very probable, that the friction of the blood against, the walls
of the arteries, its adhesion to these walls,  its viscid nature, &c.
must have great influence upon its motion.   But it is impossible,
justly to appreciate these different causes, either together or sepa-
rate.  Independently of these phenomena, common to both the ar-
teries, there are some which are peculiar to the aorta,  and which
depend upon the anastomoses existing between its branches, and
the innumerable  curvatures which are found in the  greater num-
ber of them.
   Whenever an artery presents a curvature, there is, every time
the ventricle contracts, a tendency in it to assume a straight line;
this tendency  manifests itself by an apparent motion, called by
some authors locomotion of the artery, and which may be consi-
dered as a principal cause of  the pulse.   This motion is most re-
markable, when it is observed near the heart, and  in one of  the
large arteries.   In  the  arch of the aorta, it  is most apparent.   It
may  be easily explained.   One consequence to be deduced from
this fact is, that it  is mechanically impossible, that the windings
of the artery, particularly when they are sudden, should not re-
tard the course of the blood.  Bichat is entirely mistaken in this
respect, when he asserts, that  these meanderings of  the artery
have no influence.  This could not happen, he says,  unless  the
arteries were empty, when the heart sent  forward its blood to
them, but, as they are constantly filled,  this  effect cannot take
place.  Now, inasmuch as  each curve of the  artery has such a
force expended upon it, as to give the vessel a tendency to  be-
come straightened,  there will be, necessarily, less  force for the
motion  of  the fluid,  and, of consequence, its motion will be  re-
tarded.
   It  is  much  more difficult to explain the influence of the diffe-
rent anastomoses.  Their  utility is very evident; through  them
the arteries mutually supply each other, and distribute blood to
the organs; but we are unable to say,  with  accuracy, what  influ-
ence  they exert upon the progress  of the blood.  If the dimen-
sions, curves, and anastomoses of the arteries, essentially modify
the course of the blood; it is impossible, that the organs, in which
each of these circumstances  exist, in  different  degrees, should 
OF PHYSIOLOGY.
339
i-eceive the blood, with the same degree of rapidity, and, of conse-
quence, with the same  force.   The brain, for  example, receives
four large arteries for itself alone; but the arteries run in a very
tortuous direction, with many suddeu turns, before they penetrate
the cranium; when they have arrived there, they anastomose very
frequently;  and finally, they  do not enter into the tissue of the
organ until they have become extremely small.   The blood must,
therefore, circulate but very slowly in this  organ.  The kidney,
on th.^ contrary, has but one artery, which is short and volumin-
ous, which at once buries itself in its parenchyma, and is divided
into large  branches;  the  blood  must,  therefore, pass through it
with great rapidity.
   Thus,  by all  the concurrent  circumstances  which modify the
course of the arterial  blood, it becomes resolved into a very com-
plicated hydraulic problem, viz.   The continued distribution of a
fluid, varying >ssentially  in quantity  and  rapidity,  in  different
parts,  through a single system of tubes, of  unequal capacity, by
means of a  single agent of alternate impulsion.
   In the number of phenomena  exhibited in the course of the ar-
terial blood,  we have placed the dilatation and contraction of the
arteries.   Bichat does not admit the  existence of these pheno-
mena.  This author will  not allow, that the arteries dilate at the
instant when the ventricle contracts; and he formally denies,
that they contract, to force the blood into the different parts.. I
think, however, that with a little attention, it  is  possible to see,
distinctly,  these two phenomena, when the  artery  is divided.
They are, for example, evident in the  large arteries,  such as the
thoracic, and abdominal aorta, especially in large animals; but to
render them apparent upon smaller arteries,   we may make the
following experiment.  Lay bare the crural  artery and vein of a
dog, to a  certain extent;  then pass behind these two vessels, a
ligature,  which must be drawn very tight over  the posterior  part
of the thigh.  The arterial blood  will  thus be prevented from ar-
riving at the limb, except  through the crural artery, and can only
return through the crural vein.   Measure with a compass, the di-
ameter of the artery,  afterwards, press it between the finger and
thumb, so as to  intercept  the  blood, and you  will see, in a short
time, that part of the artery which is beyond the fingers,  become
emptied  of  the blood which it contained.   Allow the blood 
340                    A  SUMMARY

afterwards to penetrate into the artery, by removing the compres-
sion, you  will then see it again become distended with blood,  at
each contraction of the ventricle, and resume its former dimen-
sions.
  But  although  I consider the contraction and dilatation  of the
arteries, a point completely ascertained, I am far  from thinking,
with some authors of the last century, that they dilate themselves,
and that they are contracted  by muscular fibres.  I think on the
contrary,  that they are passive in both cases, that  is, that their
dilatation and contraction, are simply the effects of the elasticity of
their walls, acted upon  by the blood, which is continually forced into
their cavity, by the contraction  of the left ventricle of the heart.
  There is a difference in this respect, between the large and small
arteries. I have proved by direct experiments, that the arteries do
not exhibit any evidences of irritability, that is, they remain im-
moveable  under the application  of pointed instruments, caustics,
and a stream of the galvanic fluid.  Not being able  to detect the
contractility of the walls of the arteries, Bichat thought it neces-
sary to deny the important phenomenon which he supposed, to be
the effect of it.   He did  not believe, that the blood ran on in a
continued stream in these vessels, but he supposed that the entire
mass of fluid was displaced at the instant that the ventricle con-
tracts,  and was immoveable when  it was in a state of rtlaxation
as would happen, if the walls of the arteries  were  inflexible. This
opinion has  been supported  very recently by Dr. Johnson,  an
English physician.  He has even constructed a  machine, which
according to him, renders this thing evident.   But it is sufficient,
to open the artery in  a living animal, to see  that the  blood will
pass out in a continued stream, with a jerk if the artery is large
and uniformly if the artery be small.  Now, the action  of the heart
being  intermitting, it  is impossible that it should produce a con-
tinued  stream.  'The arteries must  therefore act upon the blood.
  The elasticity of the arterial walls, represents those of a resor-
voir of air in certain  pumps, which act  alternately, and which
therefore, furnish the fluid in a continued stream.   We know, in
general, in mechanics, that  every intermitting  motion  may  be
transferred into a continued one, by  employing the force that pro-
duces  it, to compress  the receiver, which  re-acts  in a continued
manner. 
OP PHYSIOLOGY.
341
       Passage of the  Arterial Blood into the  Veins.
  When an injection is forced into an artery in the dead body, it
returns promptly by the corresponding vein. The same thing takes
place, and with still greater facility, if the injection be made into
the  artery of a living animal.   In cold blooded  animals, by the
aid of a microscope, we can distinguish the blood passing from the
arteries  into the veins;* the communication between these  two
kinds of vessels is  then, direct and extremely easy.  It is natural
to suppose that when  the heart has forced the blood into the ex-
treme  arteries,  that it continues to give  it motion, after it has
reached  the branches, and even the trunks of the  veins.  Harvey,
and a great number of distinguished anatomists  have thought the
same.   Bichat has of late opposed, with great force, this doctrine;
and has  endeavoured  to fix limits to the influence of the heart.
He  supposes that this action ceases at the point where the arteries
terminate  in  the  veins.  According to him, the  action  of these
small vessels alone is the cause of the motion of  the blood.
   We have already combatted this supposition, in speaking of the
course of the blood in the lungs; the same reasoning applies per-
fectly here.   Bichat asserts that this capillary action consists in a
kind of oscillation or insensible vibration  of the walls of these
vessels.  Now I ask how an oscillation or insensible vibration of
the walls can determine the motion of a fluid contained in a canal?
 Again, if this vibration  be insensible, who can undertake to decide
upon its existence?  Let us not, therefore, render complicated, a
simple question, by suppositions vague and destitute of proof, but
let us admit an explanation which presents itself naturally to the
mind; viz. that the contraction of the heart, is the principal cause
of the motion of the  blood, both in the arteries and veins.
   The following experiments, appear to me, to  render this phe-
nomenon very evident.   After having passed a ligature about the
thigh of a dog, in  the mode just pointed  out, that is, without in-
 cluding either the crural  artery or vein, apply a  ligature separ-
 ately upon the vein near the groin, and make a slight puncture in
 the vessel; the blood  will  then escape, forming a jet.  Press then
 the artery between the finger and  thumb, so as to prevent the

   * Cowper assirts, that he witnessed the same phenomenon in warm hlooded
 animals; 1 have repeated his experiment*, without success. 
342
A  SUMMARY
arterial blood from passing to the limb; the jet of venous blood will
not stop instantly, but it will continue for a few moments. At last,
however, the column will  diminish, and  finally stop, though the
vein may be full through its whole extent.  If, during the produc-
tion of these phenomena, we examine the artery, we shall see that
it  becomes gradually contracted, and at last completely  empty.
At this period  of the experiment, let the compression  upon the
artery be removed, the blood  will be  propelled by the heart, and
will  soon arrive at the extreme ramifications ot  the artery; the
column of blood  will  now  be. soon seen, to pass out  from the
opening in the vein, and, by degrees, the jet will become perfectly
established  as  before.    Compress  anew  the artery,  until  it
becomes empty, afterwards allow the blood to penetrate slowly.
Under these circumstances, the blood will continue to pass out in
a small stream  from the vein, but not in a jet, which will however
take place, when the artery is left entirely free.  Analogous results
may  be obtained, by forcing an injection of  warm water into the
artery, instead  of allowing the blood to penetrate  it;  the  more
force  used  in pushing forward the injection, the more  promptly
will the fluid pass out from the vein.
   I observed, in speaking of the lymphatic vessels, that they com-
municate  with  the arteries,  and  that   injections  pass  readily
from one into the other.   This communication becomes still  more
evident, when we inject saline or coloured fluids into the veins in
a  living animal.  1 have  satisfied myself often,  that these sub-
stances pass into the lymphatic vessels, in the  course  of two or
three minutes, and that their presence may easily be demonstrated
in  the lymph extracted from these vessels.
   As long as the veins  which pass out from the organs are free,
the blood which arrives by the arteries, traverses their parenchyma,
and is not accumulated.  But if the veins are compressed, or are
unable to empty themselves of fhe blood which they contain, this
fluid still continuing to arrive by the arteries, and finding no op-
portunity to escape into  the  veins,  becomes accumulated in the
tissue of the organ, distends the sanguineous  vessels,  and aug-
ments, more or less, its volume, especially, if its physical qualities
are such as to  favour these changes.   This  phenomenon  may be
observed in many organs, but,  as it is most apparent  in the brain,
it  has been most  frequently remarked there.  This swelling of 
OP PHYSIOLOGY.
343
the brain, from an obstruction in the circulation, happens, when-
ever the course of the blood through the lungs is interrupted; and
as this takes place, generally, during expiration, the brain at this
moment becomes swollen, in proportion as the expiration is longer
and more complete.   In young animals, where the brain receives
proportionally  more arterial blood,  the swelling is much  more
remarkable.

             Jlemarks on the motions of the Heart.
   The  right auricle and ventricle, and the left auricle and ven-
tricle, the  actions of  which we have investigated separately,
really form but one organ, the heart.  The auricles contract and di-
late themselves at the same moment; the  motion of the ventricles
is also simultaneous.  When we speak of the contraction of  the
heart, it is  of  the ventricles that we  particularly speak.   Their
contraction is called the systole, and their dilatation the diastole
of the heart.
   Every time that the  ventricles contract, the whole of the heart
is thrown suddenly forward, and Hie appx of this  organ strikes
against  the walls of the left side of  the chest, near the space be-
tween the sixth and  seventh true ribs.  This displacement ante-
riorly of the heart, during its systole, has given occasion to a long
and spirited controversy.  Some contend that the heart becomes
shortened during its contraction; others maintain that it becomes
elongated, and that  thi* i«» necessarily the case, otherwise it could
not strike against the walls of the thorax, inasmuch as it is more
than an inch distant from it during its diastole.  A. great number
of animals  were uselessly sacrificed, in examining this motion of
the heart: at the same moment,  some asserted that they saw the
heart shortened, while others as strongly affirmed the reverse.
 What experiments could rot determine, a very simple reasoning
 makes clear.  Bossuet interfered in the controversy, and showed,
 that if the heart were elonp-ated in  its systole, the mitral and tri-
 cuspid valves  being retained  bv the fleshy  columns, could not
 close the opening-s  between the ventricles  and auricles.  The
 partisans in favour of the lengthening of the  heart, persisted no
 further;  but it remained to be shown, how the ventricle could be
 shortened,  as the heart was carried  forward  Senac proved,  that
 this depended  upon three  causes.   First, the dilatation  of the 
344
A  SUMMARY
auricle, which takes place during the contraction of the ventricle;
Second, the dilatation of the aorta and pulmonary artery, in con-
sequence  of  the  blood introduced  into  them by the  ventricles;
Third, the tendency in the arch of  the aorta to  be thrown into a
straight line by the contraction of the left ventricle.
  The number of pulsations of the  heart  is considerable, and is
greatest in the early periods of life.
At birth, it is from 150 to 140 in a minute.	
At one year, 120	130.
At two years, 100	110.
At three years, 90	100.
At seven years, 85	90.
At fourteen years, 80	85.
At the adult age, 75	80.
In old age, 65	75.
Extreme old age, 60	65.
  But these numbers vary  according to an infinite number of cir-
cumstances,  such as sex, temperament, individual  disposition,
&c.   The affections of  the mind have a great influence upon the
rapidity of the contractions of the  heart; every one  knows, that
an emotion, however slight, modifies these contractions, and  often
accelerates  them.  Diseases  produce  great  changes  in  this re-
spect.
  Many researche%have been made, to ascertain  the force with
which the ventricles contract.  To appreciate that of the  left ven-
tricle,  an  experiment has been made, which consist  in  crossing
the legs,  placing the ham of one leg upon the  knee of the  other
and  suspending, at the end of the  foot, a weight  of  fifty-five
pounds.  This  considerable  weight,  though placed  at  the ex-
tremity of so long  a lever, is raised at every contraction of the
ventricle,  in consequence  of the tendency  to become  straight,
which operates upon this accidental curve of the popliteal artery,
when the legs  are  crossed  in this  manner.  This  experiment
shows, that the  contractile force of the heart  is  very great, though
it does not enable us to form  any accurate  estimate  of  it.  The
mechanical physiologists, made great efforts to express it in num-
bers;  Borelli, compared the force with which  the  circulation  is
carried on, to a power that would be necessary to raise a weight  of
180,000 pounds; Haller supposed it to be 51  pounds 5  ounces, 
OF PHYSIOLOGY.
315
and Keil reduced it to five or eight ounces. Which shall we con-
sider the truth among such palpable contradictions?  It appears to
be impossible to know, exactly, the force exerted by the  heart,
when it contracts itself.   It  is probable, that it is varied  by nu-
merous causes, such as age, volume of the organ, size of the indi-
vidual, peculiar constitution, quantity of the blood, state of the
nervous system, the action of the organs, and a  state of  health or
disease, &c. All that has  been said of the force of the heart, relates
only to its contraction; its dilatation has often been considered as
a passive state, a sort of repose of the fibres.   However,  when the
ventricles  dilate, it is with great force, capable,  for example, of
raising a weight of  twenty pounds, as I have often remarked in
animals recently dead.   When  we seize with the hand,  the heart
of a living animal, however small its size, i.t is  impossible, what-
ever force we may  exert,  to prevent the dilation of the ventricles.
Tiie dilatation  of the heart, cannot therefore, be  considered a state
of repose, or inaction.
  From  the first moment of the existence  of the embryo,  until
death  takes  place   from  decrepitude, the  heart  continues  to
beat.  What is the cause of this?   Tins question  has often  been
proposed  both  by  ancient and  modern  philosophers  and  physi-
ologists.  The  causes of phenomena are  not easily to be given
in physiology.  It almost  always happens, that what is considered
such, is  nothing more than  a description of these phenomena in
different  terms.   But it  is  curious to  remark the facility, with
which we suffer ourselves to be abused in this respect; the differ-
ent explanations of the  motion  of the heart, are most palpable
proofs  of this.  The ancients  asserted  that there  was  in  the
heart a peculiar  virtue,  a concentrated fire, which gave  motion
to this organ.   Descartes imagined, that there took place in the
ventricles, a sudden explosion like that  from gun powder.  The
motion of the heart was afterwards  attributed  to  the  animal
spirits, the nervous  fluid, the prases systematis nervosi, and the
archeus; Haller considered it, as an effect of irritability. Recently,
M. Legallois has endeavoured  to  prove by  experiments that the
principal cause of the  motion  of  the heart, had its  seat  in the
spinal marrow.
   These  experiments of M. Legallois  consisted in destroying
successively, in living animals, the spinal marrow, by introducing
                             44 
346
A  SUMMARY
a metallic  staff into the vertebral canal.  The result is, that the
force with which the left ventricle  contracts, diminishes in pro-
portion  to the destruction of the spinal marrow, and  when  it is
complete, the heart no longer possesses power to propel the blood
forward to  the extremities.  From these experiments, which have
been  multiplied, and  varied  with  great ingenuity, M. Legallois
concludes, that the cause of the  motion of the heart exists in the
spinal marrow.  As it has been remarked, that this organ con-
tinues to contract, for  a considerable  time after  the complete
destruction of the spinal  marrow, that its  motions even continue
regularly after it has been separated from the body; M. Legallois
remarks on these facts, that these  motions are not the true con-
tractions of the heart, that they  are only the simple effects of the
irritability  of the organ.
   To make good this explanation  of M. Legallois, it would be
necessary to show by experiments, in what the difference between
the irritability of muscular fibres, and  their contraction consists'
This important distinction not having yet been established,  I con-
ceive, that  we cannot conclude from the labours of  M. Legallois
any thing more, than that the spinal marrow has an influence upon
the force with which the heart contracts; but we can by no means
infer, that it is the cause of the motions of  the heart.
   The  organs which transmit to the heart, the influence  of the
brain and  spinal marrow, are nervous filaments coming from the
eighth pair, and perhapsagreat number of filaments of  the cervical
ganglions of  the great sympathetic.  M. Dupuytren and myself,
have endeavoured, for several years, to determine by the excision of
 the cervical ganglions, and even the first of the thorax, the action
 of the ganglions upon the motion of the heart.  But our efforts have
been thus far unsatisfactory.  The animals have nearly all died,
 in consequence  of the wound  unavoidable in  extracting  them.
 We  have never remarked any direct influence upon the heart.

           Remarks on the  Circulation of the Blood.
   Wre   are now  acquainted with  all the links  that form the
 chain,  which  the sanguineous  system  represents.   We know
 how the blood is carried to the lungs, and every part of the body,
 and how it returns again to the  heart.   Let us now examine theso 
OF PHYSIOLOGY.
347
phenomena in a general manner, that we may impress  the most
important of them, more strongly upon our minds.
   The quantity of blood contained in the sanguineous  system is
very considerable.   It  has  been estimated, by  many  authors, at
from twenty-four to thirty pounds.   This estimate cannot be very
exact, as the quantity must  vary  according to a variety of causes.
We know but little better, the  d.ffereuce between the mass of
arterial and venous  blood.  The last being contained  in vessels,
the capacity of which is superior to the arteries, must necessarily
contain  the most, though we  cannot say, exactly, how much  it
exceeds.
   The circle through which the blood passes, being uninterrupted,
and the capacity of the canal being very variable, the rapidity of this
fluid must be very different; because the same quantity must pass
through every part in a given time, which is confirmed by observa-
tion.  The rapidity is greatest in the trunk and principal branches
of the  aorta, and pulmonary artery; it diminishes  much in the
secondary branches, and still more at the point  where the arteries
terminate in the veins.   It afterwards augments, as the  blood
passes from the extreme vessels into the larger trunks of the  veins,
but its rapidity is never as great in the venpe  cavse, as in the aorta.
    In the trunks and principal divisions of the  artery, the motion
of the blood is continued, not only by  the influence of the elastic
power of the arteries, but it is also thrown out in a jerk, by the
contraction  of the ventricles; this jerk manifests itself  in  the
arteries by a simple dilatation, in those which are straight, and by
a dilatation and  an effort to become  straightened in  those  which
are flexuous.  The first phenomenon with which this second cir-
 cumstance is connected, is the pulse.   It is not easy to study this
 in man or  animals, except in  those places  where the arteries run
 upon the  bones, because there they do not move  from the  finger
 applied over them, as  is the case  with those which  float in the
 midst of  soft parts.
    The pulse frequently makes us  acquainted with the principal
 modifications of the contraction of the left ventricle, its prompti-
 tude, intensity,  weakness, and regularity or  irregularity.  We
 know, also, by the pulse, the quantity  of the blood; if it be great,
 the artery is rounded, large, and resisting; if  little, the artery is
 small, and easily compressed. Certain dispositions in the arteries, 
348
A  SUMMARY
influence the pulse, and  may render it  different in the principal
arteries.
  The pulsations of the arteries are, necessarily, perceptible in the
neighbouring organs, in proportion as the  arteries  are large, and
the  organs yield easily.   The  agitation they experience, is  con-
sidered  favourable to  their  action, though there  is  no positive
proof of this.   In this respect, no organ  is influenced more than
the brain.   The four  cerebral arteries, uniting  in  circles at the
base of the cranium, elevate the  brain at each contraction of the
ventricle,  as may be  easily seen  bv laving bare the brain of an
animal,  or by observing this organ in wounds of the head.   It is
probably to moderate this agitation, that the  numerous curves  of
the  internal  carotid  and  vertebral  arteries are   made,  before
their entrance into the cranium.   These flexuosities must, necessa-
rily, retard the  course of the blood through these vessels.   When
the arteries penetrate, into the parenchyma  of  organs,  in large
trunks, as the liver, kidney,  &c.  the organ must undergo a great
agitation at each contraction of the heart.   The organs where the
vessels do not  penetrate, until  they have become divided,  and
subdivided, do not experience this.
  All the blood that arrives from the lungs to the  left auricle of the
heart,  is of the same nature; it, however, sometimes happens, that
it is not precisely  similar in the  four pulmonary veins.*  If, for
example, a portion of the lungs is altered to  such an  extent, that
the air cannot penetrate into its air  cells, the blood  that traverses
it, will not be changed  from venous to arterial  blood; but it will
arrive  at the heart without having undergone this transformation.
In  its passage,  however,  through the left cavities, it will be  inti-
mately mixed with the rest of the blood.   The blood which comes
from the left ventricle,  must necessarily  be  homogenous, until it
reaches  the furthest branches of  the aorta; but  vvhen it arrives at
the smallest vessels, its elements  become separated.  There exist
a great number of parts, such as  the-serous membranes, the cellu-
lar tissue,  the tendons, the aponeuroses, the fibrous  membranes,
&c. in which we cannot distinguish the  red blood, and where the
capillary vessels contain only serum,  This division of the ele-
ments of the blood, is only found  in a state of health.   When the
* See the experiments of Legallois. 
OF PHYSIOLOGY.
349
parts, iiist mentioned, become diseased, it often occurs, that their
small vessels are filled with red blood.
  It has been attempted, to  explain this analysis of the blood in
the small vessels. Boerrhaave, who admitted the existence of seve-
ral  kinds  of globules, of different  sizes, in the blood, asserts, that
globules of a-certain size, can only pass into vessels  of a  given
calibre.  We have already seen, that the globules, as described by
Boerrhaave, do  not  exist.  Bichat believed, that there existed in
the small vessels a peculiar sensibility, in consequence of which,
thev would receive onlv that part  of the blood  adapted to  them.
W> have already frequently combatted  ideas of this  kind; they
are not admissible here, because  the most irritating fluids,  when
introduced into the arteries, pass immediately into  the  veins,
without their passage hein«-opposed bv the capillary vessels.
   Tn traversing the small vessels,  the blood is deprived of its ele-
ments:  sometimes the serum esranes,  and spreads itself over the
surface of the membrane, at others,  the fat is  deposited  in its
cells: here it is the  mucous, there the fibrine;  and  besides, there
mav be foreign substances,  that have become accidentally  mixed
with the arterial blood.   By loosing these different elements, this
fluid  approaches-the character of venous blood.   At the  same
time that the arterial blood  supplies those parts which are lost,
the small veins absorb the suhstances  in contact with  them. For
example,  in  the intestinal canal, they take up  the drinks; on the
other hand, the lymphatic trunks  pour the  lvmph and chyle into
the venous system.   It is certain, therefore, that the venous blood
cannot be homogeneous, and that its romposition must vary in the
different  veins.  But having arrived at the heart, by  the motions
of the risrht auricle and ventricle,  and  the dispositmn of the fleshy
column?,  all its elements become intimately mixed before it  passes
into the pulmonary  artery.
   There  is a general law of the economy, that no organ can con-
tinue to act, unless'it  receives arterial blood; the  result,  there-
fore is, that  all  the other functions are dependent  upon the cir-
culation.   But in its turn, the circulation is dependent upon the
respiration-, which  forms the arterial blood; nor can if exist without
the action of the nervous svstem, which has a great influence upon
the rapidity  of the course of the blood, and its distribution to the
organs.   In  fact,  under the influence of the nervous  system, the 
350
A  SUMMARY
motions of the heart increase or diminish, and, of consequence,
the general course of the blood is increased or retarded.  Again,
when the  organs act voluntarily,  or involuntarily, they  receive
an increased  quantity of blood, without the general circulation
being at all accelerated; if their action be very considerable, the
arteries leading to  them have  their action  increased;  if, on the
contrary,  their action diminishes, the arteries are retracted, and
only allow a small portion of blood to arrive at the organ.  These
phenomena are manifest in the  muscles; the  circulation becomes
more rapid when they contract;  if they often contract, these arte-
ries increase in volume; if they are paralysed, the arteries become
very small, and the pulse scarcely perceptible.
  The nervous system, then, influences the circulation in three
ways.  First, in  modifying the  motions of the heart; Second,  in
modifying the capillaries of the organs, so as to accelerate, or re-
tard the course of the blood.   Third, in producing the same ef-
fects in the lungs,  that is,  in rendering  more or less  .easy, the
course of the blood  through this organ.   The acceleration of the
motions of the heart, becomes perceptible to us, from the pulsation
of its apex against the walls of the chest; an obstruction in the
capillary circulation is known, by a sensation of numbness, and a
particular sort of pricking.  When the pulmonary circulation '19
difficult, we are aware of it, from a sense of oppression or suffo-
cation.  It is probable, that the distribution of  the  filaments of
the great sympathetic nerves, to the walls of the arteries, answers
some important purpose, we are completely ignorant of their use;
experiment has thrown no light upon this point.

Of the  Transfusion of Blood, and the Infusion of Medicinal
                           Agents.
   Such is the opposition that men of genius have always met from
their cotemporaries, that it was thirty years before the discovery
of Harvey, the proofs of which were then niQSt evident, was ac-
knowledged.  But as soon as the circulation was admitted; a soft
of delirium seems to have seized upon the profession; it was sup-
posed that the means of curing all diseases and rendering man
immortal  were discovered. The causes of all our diseases were  at-
tributed to the blood.   To cure them, therefore, nothing more was 
OF PHYSIOLOGY.
351
required than  to remove the bad blood, and to replace it with that
which was pure, taken from a healthy animal.
  The first attempts were made upon  animals, and  were very
successful.  A dog having lost a large quantity of blood, received
by transfusion, that of a sheep, and was perfectly restored; ano-
ther dog, old  and deaf, recovered by  this means the use of his
hearing, and seemed to renew  his youth.  A horse, twenty-six
years old, having received into his veins the blood of four lambs,
acquired new  vigour.  The  experiment of transfusion was now
tried upon man.  Denys and Emerez, the one a physician and the
other a  surgeon, of Paris, were the first who made  the attempt.
They introduced into the  veins of an insane young man, the blood
of  a calf, in a larger quantity than had been taken from him;  he
recovered his  reason.  A  case of leprosy, and a quartan fever,
were cured by this means; and many cases  of transfusion were
tried upon men in health, without any injurious result.
   But some sad  accidents, soon calmed the  general enthusiasm,
excited  by these  few  successful cases.  The  young  man, soon
after the experiment, became frantic; he was the second time sub-
jected to transfusion, and soon died  with a discharge of blood,
and in  a state of stupor.   A prince of the blood royal, having also
fallen a victim to this practice, it was forbidden by the parliament
of Paris.  A  short time  afterwards, G. Riva, having performed
the operation  of  transfusion upon two  individuals, who died, in
Italy, the Pope forbade it. From  that period,  transfusion has been
considered as not only useless,"  but dangerous; but as it seems to
have succeeded in some cases, it would be an interesting inquiry
for a person skilled in such experiments, to pursue the subject
 further.  1 have had occasion to make  a certain  number  of these
 experiments,  but have never known any instance  where the intro-
 duction of the blood of one animal, into the veins of another, was
 attended by any serious inconvenience, even  when the quantity of
 blood thus introduced, was much greater than before.
    A short time after the  discovery of the circulation, it was at-
 tempted to introduce medicines directly  into the  veins. Some
 advantages resulted from  it in some instances, and inconveniences
 in others, and it soon fell  into discredit; but it has been tried with
 success in some experiments upon animals. It is an  excellent way
 of judging promptly of  the mode of  action  of a medicine or 
352                    A SUMMARY
poison.   This process is  employed in administering  medicine to
large animals, in tue Veterinary School at Copenhagen; great benefit
is found from the promptitude of its action, and great economy in
the quantity of medicine *  employed.  This  mode, if used with
intelligence, might be found very efficient in those extreme cases
where the ordinary modes of treatment  are found  totally  in-
efficient.
                   OF  SECRETIONS.

  In  traversing the  innumerable small  vessels,  by which  the
arteries and veins communicate, one  part  of the elements bf the
blood spreads itself over all the external ami internal surfaces of
the body, another is deposited in the small hollow organs, si'uated
in the substance of  the skin  and mucous membranes, a third is
distributed to the parenchyma of those organs called glands, un-
dergoes a  particular  elaboration, and  is afterwards poured  out,
under certain circumstances, on  the surface of the mucous  mem-
branes or skin.
   We give the generic name  of secretion, to that phenomenon by
which a part  of the blood escapes, and is afterwards poured  out,
either externally of internally, whether it preserves its chemical
properties, or whether its elements have undergone  a new order
of combinations.  We generally distinguish  the secretions  into
three kinds; the exhalations, and follicular, and  glandular  sfcre-
tions.   But  this division,  as  it  respects secreting organs,  and
secreted fluids, is very imperfect.  Many  organs  which secrete
cannot be referred either to follicles or glands; what are  generally
called follicles or glands, are organs  which differ  so much from
each other in their  form, structure, and the  fluids they secrete,
that it  would perhaps be  best, not  to  confound them  under the
same denomination.  Nevertheless, to avoid  every thing like an
unnecessary  spirit of  innovation, We  shall hereafter speak of the
secretions, according  to this classification.   We shall  not  dwell
on this  article, for were we to allow  it the extension of which it
is susceptible, we should  greatly exceed the bounds to which, we
have limited  ourselves in this work. 
OF  PHYSIOLOGY.
353
                     Of the Exhalations.
  The exhalations take  place, either within or without the body;
upon the skin or mucous membranes. Hence their distinction iuto
external and internal.

                   Internal  Exhalations.
  Wherever large or small surfaces are in contact, an exhalation
takes p'ace; whenever fluids are accumulated in a cavity, without
an apparent opening,  they are deposited by exhalation; the phe-
nomenon  of exhalation, also, manifests  itself  in  almost every
part of the animal economy.   It exists in  the  serous, synovial,
and  mucous membranes, the cellular  tissue, the interior of the
vessels, and the adipose cells, the  internal  parts of the eyes and
ears, and the parenchyma of many organs, such as the thymus and
thyroid glands, and the capsulse renales, &c.   It is by exhalation
that the aqueous and  vitreous humours, and the fluid contained in
the  labyrinth, are formed and  renewed.  The fluids exhaled in
these different parts, have not all been analysed; among those that
have, many are found  to resemble, more or less, the  elements
of the blood, and particularly the serum; such are the fluids of
the serous membranes, of the cellular tissue, and chambers ot the
eye.   Others differ more, e. g. the synovia, fat, &c.

                     Serous Exhalation.
   All the organs  of  the  head, chest  and abdomen, are covered
with a serous membrane, which is also  extended  over the walls of
these cavites; so that the organs are not in contact with the walls,
or  neighbouring viscera;  but  through  the medium of this  mem-
brane.  As this membrane is very highly polished, the organs can
move easily upon each other, and upon the walls.  The principal
cause  that  preserves the  fine polish,  is this exhalation.  There
passes continually from every point of  this membrane, a very thin
fluid, which spreads  itself over the neighbouring parts, fonmng a
humid  coat, which favours  the  motion of the organs upon  each
other.
   It appears that  this power of gliding upon each other, is  very
favourable to the action of the organs.   Whenever they are de-
prived of this by a disease of the serous memorane, their functions
                              45 
354
A  SUMMARY
 are disturbed and sometimes cease altogether. In a state of health,
 the fluid secreted by  the  serous membranes, nearly resembles
 the serum of the blood, with a certain quantity of albumen.

          Serous  Exhalation of the  Cellular  Tissue.
   The cellular  tissue is  spread over almost  every part of the
 animal economy.  It serves sometimes to  separate, and at others
 to  unite different organs, and the parts of  the same organ.   This
 every where consists of very small delicate membranes,  crossing
 each other  in a thousand different directions, so as to form cells.
 The size and arrangement of these membranes vary, in different
 parts  of the body.  In some they are larger, thicker, and  form
 large cells; in others they are very small, thin, and form extremely
 small  cells.  In some places,  the  tissue  is very  extensible, in
 others, it is rigid, offering considerable resistance.   But whatever
 may be the disposition of the cellular tissue, it exhales  from its
 surfaces, a fluid very analogous  to that of  the serous membranes,
 which appears to serve the  same  purposes. Its use is to facilitate
 the motion of these membranes upon each other, and of conse-
 quence, to favour the  reciprocal  motions of the organs,  and the
 changes of  relation in their different parts.

          Adipose Exhalation  of the Cellular Tissue.
   Besides the serosity, we find in the cellular tissue, in many parts,
 a fluid of a very different nature;  this is fat.  As respects the pre-
 sence of fat, the cellular tissue may be  divided into three kinds;
 viz. that  which contains it  constantly; that which contains it oc-
 casionally;  and that in which it  is never  found.  The orbit, the
 sole of the foot, the ball of the fingers and  toes, are always found to
 exhibit fat.   The subcutaneous  cellular tissue, and that found on
 the surface  of the heart, loins, &c. present  it often; but that of the
 eyelids, and scrotum, and interior of the cranium, never contain it.
  The fat is contained in distinct cells,  which  do not  communi-
cate with  the  neighbouring ones.  This has led  to the belief, that
the tissue containing  the fat, differed from that  containing  the
serum; but as no one has yet demonstrated these  fatty cells, un-
less they were filled with fat, this anatomical distinction appears
to  me  to be very doubtful.   The size, form, and disposition of 
OF  PHYSIOLOGY.
355
these cells, do not differ more than the  total quantity of fat that
they contain; in  some  individuals there  are but a few ounces;
while in others there are many pounds.  From the experiments of
M. Chevreul, it appears that the human  fat  is  almost always yel-
low; it is inodorous, and congeals at from fifteen to twenty-five
of Reaumer.   It is composed of two parts, the one fluid, and  the
other concrete; which are again  composed of two new immediate
principles, but in different proportions,  discovered by  M. Chev-
reul, who calls them "ela'ine," and "stearine."1
  It is principally by its physical qualities, that the  fat appears
to be useful in the animal economy.   In the orbit,  it forms a sort
of elastic  cushion, upon  which the eye moves with facility; on the
sole of the foot, and the nates, it forms a cushion, which prevents
the skin from being injuted by the pressure  of the body, in stand-
ing or sitting.   Its presence  beneath the skin,  assists  in giving
rotundity to the form,  diminishing the projection of the bones
and  muscles, and thus increasing the beauty of the body.  As all
fatty substances are bad conductors of caloric, it is useful in this
respect;  fat  persons seldom suffering from cold  in winter.  Age,
and  mode of life, have  great influence  on the production of  this
substance; young infants are generally fat.   It  is  seldom that it
is much developed in young persons; but after  the age  of thirty,
especially if the food be nutritious, and  the  mode of living seden-
tary, its  quantity augments very much.  The abdomen, at  this
period, becomes prominent,  and  the nates and mammae, in  fe-
males become large.   The yellow colour  of this substance  in-
creases in old age.

                    Synovial Exhalation.
  About the moveable  joints, we find a very delicate membrane,
having great analogy to the serous membranes; but differing from
them in having small, redish  prolongations, containing  numerous
sanguineous vessels; they have  been called /ranges synoviales.
They are very visible in the large articulations of the extremities.
It has been long believed by anatomists, and there are  some who
still think, that the capsules of the joints are folded over  the move-
able cartilages, and cover the  surfaces to which  they correspond.
I have lately satisfied myself, that these membranes do not extend 
356
A  SUMMARY
beyond the circumferences of the cartilages. We have spoken of
the uses of the synovia, in treating of motions.

           Exhalation in the interior of the Eye.
  The different humours of the eye are also  formed by exhala-
tion.  They are each enveloped by a membrane, which appears to
be destined to exhale and absorb them.   The humours of the eye
are, the aqueous humour, at present supposed to be formed by the
ciliary processes; the vitreous  humour, secreted by the membrana
hyaloidea;  the  crystalline; the black matter of the choroid  coat,
and that  on the posterior surface of the iris.
  The chemical composition of the aqueous and crystalline, and
vitreous  humours, have been explained in the article vision.  The
black matter of the iris and choroid coat, has been analysed by M.
Berzelius   Tt  is insoluble in  water and acids:  the caustic  alkali
dissolves it, and  the acids precipitate  it from this  solution.   It
burns like  vegetable matter, leaving a ferruginous cinder.  Expe-
rience informs us, that the aqueous and viferous humours are ra-
pidly renewed, when pus or blo*»d have been extravasated into the
eye. In a few days they disappear, arid the humours resume, by de-
grees, their transparency.  It  does not appear that the crystalline
or choroid  humour can be re-produced,  at  least nothing shows it.

                  Sanguineous Exhalations.
   In all  the exhalations that we have now considered, only a part
of  the principles of the  blood pass out from  the vessels.   The
blood  itself, appears to  be poured out  into several of the organs,
and to fill  up the cellular tissue that forms their parenchyma; such
are fhe cavernous bodies of the vagina and  clitoris.   The spleen
and the  mammary processes, &c.  The anatomical examination of
these different tissues, seems to show, that they are habitually
filled with venous blood, the quantity of which, differs in different
circumstances, particularly, according to the state of action  or in-
action of the organs.  There exist many other  exhalations  of in-
ternal parts, among which I would mention, the cavities of the
internal  ear, of  the parenchyma  of  the  thymus, and  thyroid
gla>:d; and of the capsula; renales, &c   But  we are scarcely ac-
quainted with the fluids formed in these different parts, they have
 never been analysed, and then uses are unknown. 
OP  PHYSIOLOGY.
357
  Phv«inlngists have often endeavoured to exp'ain the phenome-
non of exhalation.   Indeed, each one has given his own opinions
on this subject.  Some  admit the existence of exhaling mouths,
others of lateral pores   Bichat  has  created  particular vessels,
that he calls exhatnnts.  1 s.iy he  has  created  them, for  he ac-
knowledges these vessels cannot be seen; anti as the existence of
these pores, mouths, and exhalants, are not sufficient to explain
the diversity in the exhalations, they  have  been supposed to pos-
sess  a  peculiar  sensibility, and  particular motions, in virtue of
which they suffer certain parts of the blood to pass, and refuse a
passage to the others.   VVe have little to remark on explanations
of this  kind.
  It is vety certain, however, that the physical disposition of the
small vessels  has an influence upon exhalation, as the following
facts will show.   When we inject, in the dead body, warm water
into an  artery passing to a  serous  membrane,  as  soon as the
stream  is established in the artery and vein, there will be seen
upon the membrane, a multitude of small  drops which evaporate
promptly.   Has not this phenomenon great analogy with exhala-
tion? If we employ a solution of gelatin, coloured with vermillion,
to inject a whole body, it frequently  happens  that the gelatin is
deposited  about  the  circumvolutions, and inequalities ol the
cerebrum, without the colouring  matter having escaped from the
ves-els; the injection spreads itself, on the  contrary, over the ex-
ternal and internal surface of the choroid coat.  If we employ
linseed oil, coloured with vermillion, we often find the colouring
matter separated from  the oil, and deposited  in the synovial cap-
sules of  the large  joints, while there is no transudation  on the
surface of  the brain, or the interior of the eye.

                    External Exhalations.
   They consist only of the exhalations of the  mucous membranes,
and of the skin, or cutaneous transpiration.

           Exhalation of the Mucous Membranes.
   There are two mucous membranes; the  one covers the surface
of the eye, the lachrymal passages, the nasal  cavities, the middle
ear, the  mouth, the whole  of the  intestinal canal, the excretory
ducts, which terminate in it,  and  lastly the  larynx, the trachea, 
358
A  SUMMARY
and the bronchise;  the other mucous membrane covers the surface
of the organs  of generation, and the  urinary apparatus.   These
two membranes are constantly lubricated by a fluid  they  secrete,
called the mucus.   This fluid is transparent, viscid and of a salt-
ish taste; it reddens litmus paper, contains much water,  muriat
of potash, and soda, lactat of lime, soda, and  phosphat of lime.
According to  Fourcroy, and Vauquelin, the mucus is the same in
all  the mucous membranes.  M. Berzelius thinks, on the contrary,
that it varies much, according to the parts from which it is taken.
Many persons suppose, that the mucus  is formed exclusively  by
the follicles of the  mucous membranes.  I am satisfied, however,
by  recent experiments, that it  is formed in  the parts where the
follicles do not exist; 1 have also already remarked, that  it conti-
nues to be formed for some time after death.
  The mucus  forms a covering of various degrees of thickness,
on the surface of the mucous membranes, and  is frequently re-
newed.   Its water evaporates under the name of mucous exhala-
tion.  It protects  the  niembrane  from the action of the air, ali-
ments, and various glandular fluids;  it seems, indeed, to  perform
the same office for these membranes, as  the epidermis, for the
skin.  Independently of its general uses, its functions are modi-
fied, according to the particular parts of these membranes. Thus
the nasal mucus assists  the sense of smell, that of the mouth fa-
cilitates taste, that of  the stomach and intestines concurs in di-
gestion, and that of the genital and urinary passages assists in the
functions of generation and urinary excretion.  A  great part of
the mucus is  absorbed by the membranes which secrete it; the
rest is either thrown off alone, as when we spit, or is mixed with
pulmonary transpiration, fecal matter, urine, &c.

                  Cutaneous  Transpiration.
  There is a transparent fluid, with an odour  more or less strong,
and of a salt and acid taste, constantly passing through the innu-
merable openings, with which  the epidermis is pierced.  Most
frequently, this fluid evaporates, as soon as it is brought in  con-
tact with the air, but sometimes it runs over the surface of the
skin.   In  the  first  instance, it is imperceptible  to the sight, and
it is then called insensible perspiration; in the second, it is called
sweat.  Whatever may be the form assumed by this fluid, when it 
OF PHYSIOLOGY.
359
escapes from the skin, it is composed, according to M. Thenard,
of a large proportion  of water, a small quantity of acetic acid,
muriat  of soda  and potash, a little phosphat ol lime, an atom of
the  oxid of  iron, and a trace of animal  matter.  M. Berzelius
conceives the  acid of the  sweat not to be  the acetic acid, but the
lactic acid of Scheele.  The skin also exhales an  oily substance
and the carbonic acid.
  A great number of experiments have been made, to determine
the  quantity of transpiration, formed  in  a  given  time,  and  the
range of its variations, under different circumstances.  The first
attempts of  this  kind were made by Sanctorius, who, for thirty
years, with extreme care, and unwearied patience, weighed his
aliments, drinks, solid and fluid excretions, and afterwards him-
self.  But notwithstanding his  zeal  and perseverance, Sancto-
rius never arrived at any very precise results. Since his time,
the subject  has  been examined with  more success; the  most re-
markable efforts  on  this  subject, were  made  by Lavoisier  and
Seguin.  These gentlemen were the  first, who distinguished  be-
tween the loss from pulmonary and cutaneous transpiration.  Se-
guin enclosed  himself in  an  oiled cloth bag, that covered  the
head, with an opening  for the  mouth; the  edges  of which were
made to adhere about  the mouth, by  a mixture of pitch  and  tur-
pentine.  In this way, the pulmonary  transpiration alone escaped
into the atmosphere.  To  ascertain the quantity, it was  only ne-
cessary to weigh himself with the  sack, at the beginning and  end
of the  experiment,  with  a very  delicate balance.   By weigh-
ing himself out  of the sack, he determined  the  total quantity
of the  transpired humour; so that, saying nothing of the fluid,
which he knew had passed out from the lungs, he  was in posses-
sion of the  quantity  of humour exhaled by the skin.   He kept,
besides, an accurate account of his food, solid  and  fluid excre-
tions, and in  general, of  all those causes  that might influence
transpiration.
  The  following are the results of the inquiries of Lavoisier  and
Seguin.
   1.  The largest quantity of insensible  perspiration, including
that of the lungs, is thirty-two grains per minute.
  2. The least loss, was eleven grains in a minute. 
360
A  SUMMARY
  3. During digestion, the loss of weight, occasioned by insensi-
ble  transpiration, was at its minimum.
  4. Immediately after dinner, the transpiration was at its max-
imum.
  5. The  medium  quantity  of insensible  transpiration, was
eighteen grains in a minute; of these, eleven depended upon cuta-
neous, and  seven on pulmonary transpiration.
  6. Cutaneous  transpiration  only  varied,  during, and after
eating.
  7. Whatever  might be  the quantity of  food taken by any one,
or whatever the variations of tie atmosphere, the same indivi-
dual, after having increased in weight, to the amount of the whole
quantity of food taken, returned every day at the end of twenty-
four hours,  to nearly the same weight that he was before;  provid
ed,  that he was not at the time growing, nor had committed any
excess.
  It is to be regretted, that  this important undertaking  was not
continued,  and that these  authors limited themselves to the inves-
tigation of  insensible transpiration, without extending their obser-
vations to  the sweat.  Whenever cutaneous transpiration is not
reduced to  vapour, as soon as it is brought in contact with the air,
it appears on the surface of the skin, in  the form of a liquid; now
this effect  may occur either from the abundance of the transpira-
tion, or from the dissolving power of the air being diminished. We
sweat readily in a warm and moist atmosphere, by the influence of
these two causes, but we sweat much less easily in a warm and dry
air. Certain parts of the i>o.ly transpire more abundantly, and sweat
more easily than others; such  as the hands, feet, arm-pits, groins,
forehead, &c.  In general,  the skin of these prrts, receives, propor-
tionally, a  much greater  quantity of blood;  and some  of them,
the arm-pit, sole or the foot, &c. are excluded from the air. The
sweat does not appear the same in every part;  every one kntK.s
that its odour varies in different parts of the body, the same is true
of its acidity;  this appears to be much greater in the arm-pits and
soles of the feet than in other parts.
  Cutaneous transpiration has various uses in the animal  econo-
my; it preserves the softness of the skin,  arid is favourable to the
sense of touch.   Bv  its  evaporation, together  with pulmonary
transpiration,  it is the principal means of cooling  the body, and 
OP PHYSIOLOGY.
361
 preserving  it at a certain temperature.  It would  appear, that
 its expulsion from the economy is very importan ; as, whe'iever
 it is  diminished or suspended, derangement of the health fol-
 lows, ami many diseases do not yield,  until copious  perspiration
 is produced.

                     Follicular Secretions.
   We give the name of follicles to the  small, hollow organs,
 lodged in the skin and mucous membranes, and which hav«*!'cr this
 reason b-ei distinguished, into mucous and cutaneous;  the folli-
 cles are also divided into simple and compound.

                Mucous Follicular Secretions.
   The simple mucous follicles are  found over nearly the whole ex-
 tent of the mucous membranes, more  or less abundant;  there are,
 however, parts of these membranes of considerable extent, where
 they cannot be detected.  Those bodies, called the fungous pa  il-
 lee of  the tongue, the amygdalae, the glands of the  cardia, pros-
 tate, &c.  are considered by anatomists as  collections of simple
 follicles.  Perhaps this opinion is not well  founded, we know little
 of the fluid  they secrete, it appears to be analogous to the mucus,
 and to answer the same purposes.

               Cutaneous  Follicular Secretions.
   In almost every part of the skin, there exist  small  openings,
 the orifices  of small, hollow organs, with  membranous walls, ha-
 bitually filled with  albuminous and fatty  matter, the consistence,
 colour, odour, and even taste  of which, vary in different parts  of
 the body, and  are  continually  poured  upon the  surface of the
 skin.   'These small organs are  called  the  follicles of  the  skin;
 there  is at least  one at the  base of each  hair; the hairs indeed  of-
 ten traverse the cavity of a follicle in passing out.  The follicles
 form that shining fatty substance,  that we  see upon the scalp and
 cartilage of the ear.   The follicles secrete the wax, in the meatus
auditorious externus, and likewise the thick, whitish matter that
 we force out from the  skin of the face,  by pressing it, under the
 form of  small worms.  This substance, from its external surface
being in contact with the air, becomes blackened, and produces the
                           46 
362
A  SUMMARY
numerous spots that we see in the face of some persons, particu-
larly about the nostrils and cheeks.
  It appears also, that these follicles  secrete  the white, odorous
matter, that is  continually renewed  about the parts of genera-
tion.   From being spread  upon the surface of the skin, hair, &c.
this substance preserves the softness and elasticity of these parts,
renders their surface  smooth and polished, and favours  their mo-
tion upon each other.  Inconsequence of its unctuous nature, it
in some measure, defends them from humidity.

                    Glandular Secretions.
  We give the name of gland, to a secretory organ, which pours
the fluid  formed by it, over the  surface of a mucous membrane or
the skin, by one or  more excretory ducts.   The number of glands
is \ery considerable; their action has received the name of glandu-
lar secretion.  There are six secretions of this kind, the tears, the
saliva, the bile, the  pancreatic juice, the urine, the semen, and the
milk.  We may, perhaps,add ■•> these  the secretions of the mucous
glands, and of the glands of Cowper.

                     Secretion of Tears.
  The gland that forms the tears, is very small; it is situated is
the upper and outer part of the orbit, and a little on the  outside
of the eye; it is composed of small  granulated masses, united by
a cellular tissue.  Its excretory ducts, small  and numerous, pass
out at the posterior part  of  the upper eye-lid; it receives  a small
artery, a branch  of the opthalmic, and a nerve derived from the
fifth pair.  In health,  the tears are not very abundant; the fluid is
limpid, inodorous, and of a saltish taste.  They were analysed by
Fourcroy  and Vauquelin, who found  them composed  of  a great
proportion of water, some  hundredths  of  mucus, and muriat, and
phosphat  of  soda;  a very little soda and pure lime.   What  is
generally called the tears, is not, however, the fluid secreted en-
tirely by the lachrymal gland; it is a mixture of this fluid with the
matter secreted, by the conjunctiva;  and probably, that  of the
glands of Meibomius.
  The tears  form a covering to the conjunctiva of the eye, and
defend it from  the contact of the air; they facilitate the motion
of the eye-hds upon  the eye,, favour the expulsion  of foreign 
OP PHYSIOLOGY.
363
bodies,  and prevent the action of irritating substances upon the
conjunctiva; under these  circumstances,  their quantity becomes
suddenly  very much increased.   They also assist  in express-
ing the passions;  disappointment,  grief, joy, and pleasure, cause
the tears to be poured out in  abundance; their secretion, it is
manifest, is strongly influenced by the nervous system.  This .a-
fluv'nce takes place, probably, through  the  medium of the nerve
sent to the lachrymal gland from the fifth pair of cerebral nerves.

                    Secretion of the Saliva.
  The salivary glands are, First, the two parotids, situated before
the ear, and behind the neck, and ascending process of the infe-
rior maxillary  bone.  Second,  the sub-maxillary gland, situated
beneath, and on  the surface ot this bone.  Third, the sub-lingui-
nal, placed immediately  below the tongue..  The  parotids, and
sub-maxillary glands, have each only one excretory duct, the sub-
linguals have several.   All these glands are formed of granulated
masses, of different form  and  size.  They receive arteries of con-
siderable  size, in proportion to their volume; and are amply sup-
plied with nerves, derived from  the brain and spinal marrow.
The saliva secreted by these glands, is continually running into
the mouth, and occupies  its lower part.  It is placed between the
inferior and  lateral parts of the  tongue, at  first, and  when this
space is filled, it  is lodged between the inferior lip, the  cheek,
and the external side of  the lower jaw.  When deposited in the
mouth, it becomes mixed  with the fluids secreted by the mucous
membrane and follicles.
   No one has ever analysed the fluid of the salivary glands sepa-
rately, but only the fluid  found in the mouth, which is, to be sure,
almost entirely composed of saliva.  It is limpid, viscid, without
colour, or smell,  of a bland taste, and somewhat heavier than wa-
ter.  Berzelius asserts, that it is composed of 992.9 of water; 2.9
of  a particular animal  matter; 1.4 of muriat of  potash and soda;
0.9 of tart, of sod. and animal matter, and 0.2 of soda.  It is pro-
bable, that the composition of the saliva varies, as it is sometimes
sensibly acid.  The saliva is one of the fluids  most useful in di-
gestion;  it favours the  mastication  anil division of  fhe  aliments;
it assists in  deglutition and the formation of chyme; and facili-
tates the motion  of the tongue, in speech and singing. The greater 
364
A  SUMMARY
part of this fluid is carried into the stomach, by the action of de-
glu'i ion;  a small part passes out with the expired air, and evapo-
rates.

               Secretion of the Pancreatic Juice.
  The pancreas, is situated in the abdomen, behind the stomach;
its  excretory duct opens  into  the duodenum, near to that of the
liver   From the granulated structure of  this organ, it has been
considered a salivary gland; but it differs  from them in the  size
of the arteries  it receives, and from its not having any cerebral
nerve.
  De Graff', the celebrated Dutch anatomist, discovered a mode of
collecting the pancreatic  juice; it consisted in introducing  into
the intestinal extremity of the excretory duct, the barrel of a small
quill, which terminated in  a little bottle, .laced in the abdomen of
the animal.  I have often  attempted to repeat  this  process, but
have alvvays failed.   The quill,  and every  other tube, wounded
the mucous membrane of  the duct, and  the blood,  oozing out,
gradually  clo.-ed up the mouth of the tube   1  had therefore re-
course  to a much more simph method; having  laid  bare the ori-
fice ol tiie  duct in a dog. I wiped, carefully, with a  piece  of fine
linen,  the sui n ui dirij; mucous membrane, arid then  waired urtil
a drop of the juice passed  out.   As soon as it appeared, 1 sucked
it up by means of a peculiar sort of pipe, (pipette,) an instrument
used in chemisiry.   In this way, I have been able to collect seve-
ral  drops of this fluid at a  time, but never a sufficient quantity to
make a regular analysis.   I have found it of a light yellow colour,
of a saltish taste, and without odour; it possessed alkaline proper-
ties, and  was  partly coagulated  by heat.*   The circumstance
which ha^ appeared the most remarkable to me, in endeavouring
to procure this fluid, is the small quantity in which it seems to be
formed.   It frequently happens, that a drop  will not pass out,
once  in a halt  hour; and  1 have  sometimes waited  for  a much
longer  period, before it  has  appeared.   Its secretion does  not
seem to be increased  during digestion, but on the coutrary, rather

  * fu bints which have two organs of this kind, 1 have remarked that the excre-
tor) ductb are endowed with a constant peristaltic motion.  The pancreatic juice
is also much more abundant; it is almost entirely albuminous, at least it hardens,
like albumen, by heat- 
OF PHYSIOLOGY.
365
retarded.   In  general, 1 think it  is most abundant in very young
animals.   It is impossible to form any very precise  notions of the
uses of the pancreatic juice.

                    Secretion of the  Bile.
  The liver is the largest gland in the body; and  it differs from
all the other secretory organs still more, in being constantly tra-
versed by a large  quantity of venous blood, besides the arterial
blood, sent to tins, as to every other part.   Its  parenchyma does
not resemble the other glands, and  its secretions differ essentially
from all other glandular fluids.
  The excretory duct of the  liver, terminates  in the duodenum,
but before reaching this part, it communicates with a small mem-
branous sac, called the ce<icula fellis; which is almost constant-
ly  filled  with bile.  There  are  few fluids,  which so  materially
differ  from  the blood as the bile.  Its  colour is  greenish;  its
taste extremely bitter; it is viscid, stringy, sometimes transparent
and sometimes clouded.   It contains water, albumen, a substance
called by chemists resin, a yellow  colouring principle, soda, and
salts,  viz.  muriat, siilphat   and phosphat of soda, phosphat of
 lime, and  oxide of iron.    These  properties are particularly found
in the bile contained  in the gall bladder.   'That which passes di^
rectly from the liver, and  which is called the hepatic bile, has never
been analysed.  It is not of  so  deep a colour,  is less  viscid, and
 bitter than the cystic bile.   'The  formation  of bile seems to be
 continual.   Whatever may  be  the circumstances in which  the
 animal  is placed, if  the orifice of the duct,  called  the  ductus
 communis choledochus. be laid bare, we can distinguish this fluid,
 passing drop by drop over the surface of the intestine. It appears
 that the gall  bladder becomes filled when the stomach is  empty;
 and the abdominal pressure  is least   It has always appeared to
 me, that it was more distended  at this time, but it does not lose
 all  its contents  when  the  stomach is full.  The  circumstance
 which contributes most to the expulsion of the bile,  is vomiting.
 I have often  found it empty in animals which have died in conse-
 quence of poisons, producing vomiting.
    'The liver receiving at the same time venous blood by the vena
  port*,  and  arterial blood by the hepatic artery,  physiologists
  have found  great difficulty in  determining which,  of these  two 
366                   A  SUMMARY
 sorts of blood, serves in the formation of bile.  Some have thought
 that the blood of the vena portse, having more carbon and hydrogen
 than that of  the hepatic artery, was more suitable for furnishing
 the elements of the bile.  Bichat has opposed  this opinion with
 success; he has shown, that the quantity of arterial blood sent to
 the liver bore a nearer proportion to the  quantity of bile formed,
 than the venous blood; that the volume  of the hepatic duct was
 not in proportion  to the vena portse; that the fat, a fluid contain-
 ing much hydrogen, was secreted from tha arterial blood, &c. He
 might have added, fhat nothing proves the blood  of the vena  portse
 to be more analogous to the bile than the arterial  blood.  We shall
 not take a part in this controversy; the two opinions are equally
 destitute of proof.   Besides,  it is not improbable that  the two
 sorts  of blood  may serve the purposes of secretion.  Anatomy
 seems to prove this, for injections show that all  the vessels  of the
 liver, arterial, venous, lymphatic and excretory, communicate with
 each other.
   The bile assists in digestion, but the mode is entirely unknown.
 From our ignorance of the causes of disease, we often  attribute
 pernicious qualities to the bile, that it, very probably, is far from
 possessing.

                     Secretion of Urine.
   The secretion,  to which we are now about to call the attention
 of the reader, differs in many respects from the preceding.   The
 fluid which is the result of it, is much more abundant than that of
 any other gland, and instead of performing any further uses  in the
 economy, it is destined to be expelled.   We are informed of the
 necessity of doing this, by a peculiar sensation,  which, like  other
 instinctive phenomena of this kind, becomes very vivid and pain-
ful; if it be not  satisfied promptly, its retention is accompanied by
the most troublesome consequences. There are .few of the organs
of secretion  so complicated  as that of  the  urine.  It is composed
of the two kidneys,  the calices, the pelves, the ureters, the urinary
bladder, and the urethra.  The abdominal muscles, also concur in
the action of these  different parts; the kidneys  alone secrete the
urine, the others only serve the purposes of retaining, transport-
ing and  expelling it. 
OP PHY9IOLOGY.
367
  The kidneys are small in proportion to the quantity of fluid
they secrete.  They are generally surrounded  with a large quantity
of fat, and are situated, on  the  sides of the vertebral  column,
before the  last of the false  ribs, and the quadratus lumborum.
Their parenchyma is generally composed of  two substances; the
exterior which is very  vascular, and  is called  the cortical; the
other part, called medullary  or  tubular, is arranged  into  a cer-
tain  number of cones, the bases  of  which correspond to the sur-
face  of the organ, and  the apices  unite in a membranus  cavity
called the pelvis.   These  cones appear to be formed by a large
number of small hollow  fibres, which  are excretory ducts of a
particular kind, and  are constantly filled with urine.   There is no
organ which receives so much blood,.in proportion to its volume, as
the  kidney.   The artery is short  and  large, and arises directly
from the aorta;  it communicates, very freely, with the  veins and
tubular substance, as may easily be shewn, by  injections of> the
coarsest kind, which, when pushed into the renal artery, pass into
the  veins and pelvis, after having filled the cortical substance.
Filaments  of the great sympathetic, are the only nerves  distri-
bributed to the kidney.
  The calices, pelvis, and ureters form together  a  canal, which
passes from the kidney, where it embraces the papillae, and termi-
nates in the bladder.  This  last organ is an extensible and con-
tractile sac, destined to receive the  fluid secreted by the kidney,
and  which communicates externally, by a canal called the urethra;
tfliis  is long in man,  but short in the female.   The posterior ex-
tremity of the urethra  in  man, is  surrounded by  the prostate
gland, which  has been considered by some anatomists, as a mass
of mucous follicles.  Two small  glands placed before the anus,
pour  out a particular fluid into this canal.   Two muscles, de-
scend  from the pubis towards the rectum, pass along  the  sides
of that part of the  bladder, which terminates in  the urethra,
approach  each other posteriorly, and  thus form an  arch  which
embraces the neck of the bladder, and raise or depress  it.
  If we divide the pelvis  of the kidney,  in a living animal, we
can  perceive  the urine oozing out slowly  from  the papillae; this
fluid is deposited in the cavity of the calices, afterwards in that
of the pelvis, and gradually in the ureter, through  which it at last
peuetrates, to the bladder  into which it continues constantly to 
368
A  SUMMARY
 trickle, as it is easy to perceive in persons affected by a deformity,
 called a retroversion of tit- bladder, in which the internal surface
 of this organ is  exposed to view.   A slight compression of the
 papillfe forces the urine out in a considerable quantity, but instead
 of being  limpid, as  it is naturally, it  is thick ai<d  turbid    It
 appears therefore to be filtered, by  the hollow fibres of the tubu-
 lar substance.   Neitner the pelvis nor the ureter be ng contractile,
 it is probable  that  the  force  which  determines  its progress,  is
 partly that by which it  is poured into the pelvis, and partly the
 pressure of the abdominal muscles, to which may be added, when
 the body is erect, the weight  of the  fluid.   Under the  influence
 of these causes,  the urine is introduced  into the bladder, and  by
 degrees distends this organ, sometimes to a considerable extent,
 the extensibility of its different membranes, permitting this accu-
 mulation.*
   Why does the urine  accumulate in  the  bladder, why does it
 not  immediately pass out  by the urethra, or  flow back  into the
 ureters?   The answer, as respects the ureters,  is very easy; these
 ducts pass for a considerable distance, through the substance of
 the walls of the bladder.  In proportion, therefore, as the urine
 distends this organ, it flattens the ureters, and closes them more
 exactly, when it is  abundant.  This effect takes place, as well in
 the living, as the dead  body; a liquid, or even air, pushed  with
 great force into  the bladder, cannot be introduced *nto the ureters.
 It is, then, by a mechanism  analogous to that of certain valves,
 that the urine does not return towards the kidney.
   It is not so easy to explain the reason, why the urine is not im-
 mediately  poured into  the urethra;  many causes seem to concur
in producing this effect.   The walls of  the canal, especially to-
 wards the  bladder,  tend  continually to  re-act upon themselves,
and to efface its cavity; but this cause alone would  be insufficient
to resist a considerable effort  of the urine to escape, when the
bladder is  distended.   In the  dead body, where the same dispo-
sition exists in  the canal, the  resistance  is very weak, and does
not prevent the fluid from passing out, however slightly the blad-
der may be compressed.   The angle made  by the urethra with

  * As it is proved, that the heart and the elasticity of the arteries, have a marked
influence on the course of the Wood, in the capillaries and veius, may not these
causes act upon the fluids in certain excretory  ducts? 
OF PHYSIOLOGY.
369
the bladder, when it is much distended, may also act as an obsta-
cle to the passage ot the urine.   But I believe  the principal cau-e
which prevents this effect, is the contraction of the elevator mus-
cles of the anus, which, either from the disposition in their fibres to
shorten  themselves, or from their contraction, under the direct in-
fluence  of the brain, press the urethra from below, upwards, thus
bringing its walls in contact, and closing its posterior orifice.

                   Excretion of the Urine.
   When  the  urine is accumulated in certain  quantities in  the
bladder, we feel a desire to expel it.   The mechanism by which
this is effected, deserves particular attention, as it has not been
always  rightly understood.  If the urine  be not  constantly pass-
ino- out, this is not owing to any want of contraction in the blad-
der, for this organ has always a tendency to re-act upon itself.
But, by the influence of causes, that we  shall now point out, the
internal orifice of the urethra resists this with a force, that the con-
traction of the bladder is incapable of overcoming.  This condi-
tion of  things is removed by the will, first, by adding  to the con-
traction of the bladder, that of the abdominal muscles;  second, by
relaxing the elevator  muscles of the anus, which close the ure-
thra.   When this  resistance is once overcome, the  contraction
of  the bladder is sufficient for the complete expulsion of the urine
which it contains;  but if the action of the abdominal  muscles be
added, the force and size of the stream is much increased.   We
can suddenly stop the flowing of  the urine, by contracting the
levatores ani muscles.
   The  contraction of the bladder is not voluntary, although by
 the action of the  abdominal  muscles and the levatores ani mus-
 cles, we can permit its contraction at pleasure.   What urine re-
 mains in the urethra, after the bladder is emptied, is  expelled by
 the contraction of the muscles, called the acceleratores urinaz.
    Though the quantity of this fluid is very abundant, and though
 it  contains many immediate principles, not found in  the  blood,
 and which are, therefore, formed  by some  chemical action in the
 kidneys, the secretion of urine is very rapid.   During health, the
 urine is of a yellow colour, more  or less deep, its taste  saltish,
 and a  little acrid, and its odour peculiar.  It is composed of wa-
 ter, mucus, probably derived  from  the mucous membrane of the
                              ±7 
370
A  SUMMARY
urinary passages, of another animal  substance, uric  acid, phos-
phoric acid, lactic acid, muriat of soda and ammonia, phosphat of
soda and  ammonia, lime, magnesia, sulphat  of  potash, lactat of
ammonia and  silex.   The  physical properties  of the  urine, are
Subject to great variations.   If we  make use  of  rhubarb or mad-
der, it becomes of a  deep yellow;  if  we respire air, loaded with
the vapours arising from  turpentine, or if we take this drug inter-
nally, the urine assumes  an odour like violets;  every one knows
the disagreeable odour of the urine, after eating asparagus.
   Its chemical composition is equally variable.  The more water
we drink, the  greater the proportion of water  in  the urine; and
the reverse.  'The uric  acid  becomes  abundant, when the diet is
very generous, while the person exercises but little; but this acid
diminishes, and may even be made to disappear entirely, by the
continued and exclusive  use of non-azotic aliments; such as su-
gar, gum,  and  butter, &c.   Some  salts, when introduced into the
stomach, even in small quantity, are  found in a very short time,
in the urine.   'The extreme  rapidity  with which this is effected,
has given rise to  the belief, that there exists a direct communica-
tion from the stomach to the bladder;  even at this time, there are
many persons of this opinion    For a  still  longer time it has been
suspected, that there was  a duct passing from the  stomach to
the bladder;  but  no such part has  ever been demonstrated.  Some
have  thought,  but without adducing any proof as to the fact, that
this took place through the cellular tissue, by the  anastomoses of
the lymphatic vessels.
   Darwin  having given to one of his friends a  few grains of the
nitrat of  potash,  collected  the urine at the  end of a few hours,
ami then  bled him.  'The salt was found  in  the  urine,  but could
not be recognised in the  blood.  M. Brande, made a similar obser-
vation with the prussiat of potash, and he  concluded, that the cir-
culation is not the only medium  of communication between the
stomach anti  bladder, but he did not undertake  to explain what
this medium was   Sir Everard Home, is  likewise  of the same
opinion.   I have made some experiments, with a wish to throw
some light on  this  important  question, and  1 have found, first,
that when we inject fhe prussiat of  potash into the veins, or into
those parts where it  will  be rapidly absorbed, as the intestines or
serous cavities, it soon passes into the bladder, where  it may be 
OP PHYSIOLOGY.
371
recognised mixed with the urine.  Second, if the quantity inject-
ed be very great, its existence in the blood  may be demonstrated
by reagents;  but, if the quantity used be very small, it is impossi-
ble to detect its presence by any known method.   Fourth,  we can
detect the existence of  this salt in the blood, in all proportions in
the urine   There  is nothing  very  remarkable,  therefore, in the
fact, that Darwin and lirande could not find this substance in the
blood,  though its presence  in the urine was distinctly perceived.
   With  respect to those organs which transport the fluids ot the
stomach  and intestines into the circulating system, from what has
been already said, in speaking of the lacteal vessels, and  the ab-
sorption  of the veins, it is evident, that the veins absorb the fluids
directly, and transport them to  the liver and heart.  'The rout
which  the  fluids pass through, therefore, to  arrive at the kidneys,
is much  shorter than is  generally supposed; that  is, through the
lymphatic  vessels, mesenteric glands, and thoracic duct.
  In explaining glandular secretion,  physiologists have  given a
loose rein  to their imaginations.  The  glands  have been  succes-
si>ely con-ulered as sieves, filters and fermenting vats.  Botdeu,
and more recently, Bichat, have  attributed to their molecules, a
sensibility, and particular  motion, by which  they  elect,  from the
blood which traverses them, the particles proper to enter into the
composition of the fluids  they are  destined to secrete.*   Some
have given to them atmospheres,  departments; others have sup-
posed them susceptible of erection, sleep, &c.   But notwithstand-
ing the efforts of many very eminent men, it must be  acknow-
ledged, that  we are at  present entirely  ignorant of what takes
place in a gland when it acts. Chemical phenomena  are, necessarily
developed.   Many secreted fluids are acid, while  the blood is al-
kaline; many of them contain immediate principles, which do not
exist in the blood, and which  are formed in the glands;  but the
particular mode of these combinations is unknown.
   But  we will not comound among these hypotheses of the action
of the  glands, a very ingenious suggestion of Mr. V\ olaston.  I his
distinguished chemist, bting under an impression  that electricity,
even when very weak, might  have a decided influence upon the
secretions; had  recourse  to the following  curious experiment.
  * Bordeu acknowledges that this is a mere metaphorical mode of expression.
Vide Researches on the Glands. 
372                    A SUMMARY
He took a tube of glass about two  inches  high, and  about  three
quarters of an inch in diameter, and closed one extremity with a
piece of bladder.  He then  poured into the  tube  a  little water,
with  1.240 part of its weight of muriat of soda, he  then moist-
ened  the  biadder,  placed it upon  a  bit  of  silver,  and  bent a
piece of zinc wire so that one of its extremities touched the  piece
of metal,  and the other penetrated  into the tube to the depth  of
about one inch.  At this moment the external  face of  the bladder,
indicated the presence of pure  soda.   There was, therefore, from
this very weak action of the electric fluid, a decomposition of  the
marine salt, and at the same  moment, the soda separated from  the
acid and penetrated through the bladder.  Mr. Wolaston thinks
that it is not impossible that  something analogous,  takes place in
the secretions.   It will be perceived, that before this  idea can  be
fully admitted, many other proofs must be  required.*
   Many organs, such as the thyroid and thymus, the  spleen and  the
capsulse renales, have been called glands by anatomists.   Profes-
sor Chaussier, has substituted for this  denomination, glandiform-
ganglions.  We are totally ignorant of the uses of those parts; as
they are, in general, more voluminous in the  fcetus;  it is thought
they perform some important function  during that state; but there
is no absolute proof of this.   The works of physiologists contain a
great number  of hypotheses,  constructed for the purpose  of ex-
plaining their functions.
                     OF NUTRITION.

  We know that the blood  supplies the materials for all the
secretions, internal and external; that its powers are preserved by
general absorption, and by the chyle and drink.  It remains  for
us now, to examine what takes place in the parenchyma  of the
organs and tissues during life; this is called nutrition.   From the
earliest periods of life to advanced old age, the body is constantly
changing in weight and volume. The  different organs and  tissues
present infinite  varieties in  consistence, colour, elasticity, and,
frequently, chemical composition. The volume of organs augments

       *  For the secretion of the semen and  milk, see Generation. 
OP PHYSIOLOGY.
373
when they are frequently in action; on the contrary, their dimen-
sions diminish much, when they remain long in a state of repose.
By the influence of one or other of these causes, their physical and
chemical properties exhibit surprising variations;  a great  number
of diseases produce, often in a very short time, very remarkable
changes in the conformation and structure of a great number of
organs.  If we  mix madder with the food  of an animal, during
fifreen or twenty days, the bones present  a red tint, which disap-
pears when it is omitted.
   There  exists, then, in  the  very  substance of the organs, an
insensible motion of their particles, which  produces all these modi-
fications.  It is this intestine motion, of the nature of which we are
ignorant,  to which  we  give the name of  nutrition.   This phe-
nomenon, which the observing spirit of the ancients did not allow
them to overlook, has  been the  object of many ingenious suppo-
sitions, that are still admitted by some at this day.  It is said, for
example,  that by means of nutrition, the whole body is renewed,
so that at any given moment, it is not formed of a single  particle
that composed it at some  former period.  Limits have even been
assigned to this total tenovation. Some  have  fixed three years,
others think it cannot be completed  in  less than seven;  but there
is nothing tojustify these  conjectures; on the contrary, some well
established facts appear to do away this idea.
   Every body knows  that soldiers, sailors, and savages, are in the
habit of colouring their skin, which  they  introduce into the tissue
of this membrane.  The figures  thus traced, preserve  their form
and colour during life, except under very peculiar circumstances.
How does this  phenomenon agree with  this idea of renovation,
which, according to authors, takes place in the skin.*
   In considering the suppositions, of which we have now spoken,
 it is understood in the metaphorical language at present used in
 physiology, that the particles of  organs cannot serve but a certain

   * The recent employment of the nitrat of silver, internally, in the  treatment
 of epilepsy, has furnished a new phenomenon of this kind. After this remedy has
 been used for several months, the skin of many patients has become of a greyish
 blue colour, probably owing to this salt being deposited in the tissue of this mem-
 brane, where it  is placed  in immediate contact with the air.  Several individuals
 have remained in this state for many years, without the colour being diminished.
 In others, it has by degrees diminished, and  disappeared at the end of two or
 three years. 
374
A  SUMMARY
 time in their composition; and, being no longer suitable to com-
 pose  the  organs, they are then  absorbed, and  replaced  by new
 molecules, arising from the aliment.  It may  be added, that the
 animal  substances which  compose our excretions,  are the  de-
 molished organs, and that they are principally composed of par-
 ticles, no  longer capable of  serving in the composition  ol  the
 body, &c.
   Instead  of discussing these  hypotheses,  let us  examine  the
 few facts  which  are ascertained  on the  subjrct  of nutrition.
 In  observing  the promptitude with  which  the  organs  change
 their  chemical  and physical  properties by diseases and  age, it
 appears that nutrition is more or  less rapid, according to the par-
 ticular tissue.  The glands, muscles, skin, &c. change their volume,
 colour, and  consistence with  great rapidity; the tendons, fibrous
 membranes, the  bones  and cartilages, appear  to have a  much
 slower nutrition, as  their physical properties change  but slowly,
 in consequence  of age or disease.
  If we take into consideration the  quantity  of aliments  con-
 sumed, in  proportion to the weight of the body, it appears, that the
 action of nutrition is much more  rapid in infancy and youth, than
in the adult or advanced  a^e; it  is accelerated by  the action of
the organs, and  retarded by  their remaining  in  a state of rest.
 Children and young persons, consume more food than adults, and
 old persons; the last preserve their  faculties with a  very small
 quantity of aliment.  All exertions of the  body,  render a more
abundant and  nutritious diet necessary; a state of perfect repose,
 on the contrary, will permit a prolonged abstinence.
  The blood appears to contain  the greater part ot the principles
necessary  to the nutrition of the organs; the fibrine, the albumen,
the fat, salts, &c. which enter into the composition of the tissues,
 are found  in the blood.  They appear to be deposited  in their pa-
renchyma, at  the moment v\ hen  the  blood  passes through  them;
the mode of this deposition is entirely unknown.  There exists an
evident connexion, between the activity of the nutrition of  an or-
gan, and the quantity of blood it receives.  The tissues, the nutri-
 tion of which  is rapid, have large arteries;  vvhen the-act ion of an
 organ has determined an increased  nutrition,  the  arteries and
veins  grow larger.  There are many  immediate principles  enter-
 ing into the composition of organs, which are not found  in  the 
OF PHYSIOLOGY.
375
blood, such are osmazome, cerebral matter, gelatine, &c.  They
are forme I  at  the  expense of  the  other principles in the paren-
chyma of the  organs, by a chemical action, the mode of which is
unknown.
   Since the nature of the different tissues of the animal economy
ha- been ascertained by chemical  analysis, we know that they all
contain a large portion of azote.   Our aliments being,  also, com-
posed in part of  this simple  substance, it was probable that the
azote of the organs was derived from them; but many respectable
authors think, that it arises from respiration, and others, that it is
entirely formed by the influence of life.   Both these opinions are
supported,  particularly, by the example  of herbivorous animals,
which feed exclusively on substances not  containing azote; or the
history of certain  nations, whose  inhabitants  live entirely on rice
and maize; or that of negroes, who live lor a long time upon sugar,
and finally, on what  is said of caravans,  who, in  traversing the
d.'sert, have little other food  for a long time than gum.  If these
facts prove, indeed, that men are  capable of living for a long time
without azotic aliments, it would seem necessary to acknowledge,
that  the azote of the organs  has some oilier origin than the ali-
ments.  But  in  fact, nearly  all the vegetables employed  for the
nutrition of man and  animals, contain more or less azote.  For
example, the raw sugar eaten by the negroes, is composed of
it in a considerable  proportion; with respect to those people who
are said to live on rice and maize, it is well known that they add
to this diet, milk  and cheese; now cheese, of all the  immediate
 nutritive principles, has the most azote.
   I  have thought, that we might  acquire more exact  notions on
 this  subject, by  subletting animals, for  a sufficient  period, to a
 particular  diet, the chemical   composition  of  which, should be de-
 terminate, and rigorously pursued.  Dogs were very  proper for
 these experiments,  is like man, they are  nourished by vegetable
 and  animal substances. Every one knows, that a dog can live for
 a lomr time on bread alone; but from this  fact, nothing can be con-
 clusively inferred, relative to the  production of azote  in the ani-
 mal  economy; for the  gluten contained in the  bread,  abounds in
 azote.  To obtain a satisfactory  result, it would be necessary to
 feed one of these animals with a substance considered  nutritious,
 but which does not contain azote. 
376
A  SUMMARY
  With this intention, I  put a dog about three years old, fat and
healthy, upon  a diet exclusively  of pure white sugar, with dis-
tilled water for drink; he had thein both  without any limit.  For
seven or eight days he appeared to be very well; he was sprightly,
ate with avidity, and drank as usual.  He began to grow thin, the
second  week, although his appetite was good, and he  ate six  or
eight ounces of the sugar in twenty-four hours.  His alvine excre-
tions were neither frequent nor copious, and the urine was in suf-
ficient abundance.   The emaciation increased in the third  week,
the strength diminished, the animal  lost its spirit, and its appetite
became less. At this period there happened, first upon one eye, and
then upon the other, a small ulcer on the centre of the transparent
cornea; it augmented rapidly, and, at the end of a few days, it was
about a line in diameter, its depth  increasing in the same ratio;
the  cornea became soon  perforated, and  the humours of the eye
discharged.  This singular phenomenon was accompanied with an
abundant  secretion  of the glands about the eye-lids.
   In the mean time, the  emaciation continued to increase, and the
strength to be diminished, and, though the animal  ate daily three
or  four ounces of  sugar, its weakness became  so great, that it
could neither chew nor swallow, of course, every other motion was
impossible. It expired on the  twenty-second day of the experi-
ment.   I examined  the body, with every possible precaution, there
was no fat to be found; the  muscles were reduced more than
five sixths of their ordinary volume,  the  stomach and  intes-
tines were much diminished in size, and strongly contracted. The
gall and urinary bladder were distended  by the fluids peculiar to
them.   I requested M. Chevreul to  examine them;  he found them
possessing nearly all the characters belonging to the  urine and
bile of herbivorous  animals; that is, the urine, instead of being
acid, like that of carnivorous  animals, was  sensibly alkaline, not
exhibiting any trace of uric or phosphoric acid.   The  bile con-
tained a considerable portion of pycromel, a substance peculiar to
the bile of the ox, and in general  of all herbivorous animals. The
excrements were also examined by M. Chevreul,  they contained
very little azote, though they  ordinarily exhibit much  of this
substance.
   Such a result deserved to be verified by new experiments; I ^yas
therefore,  induced to submit a second dog  to the  same regimen, 
OF  PHYSIOLOGY.
377
namely, sugar and distilled water.  The phenomena were similar
to those just described, except that the  eyes did not begin to ul-
cerate until the twenty-fifth day, and the animal died before the
ulcer had penetrated into the cavity of the eye, as occurred  in the
dog that was the subject of the first experiment.  In other respects,
the same emaciation and debility, followed by death on the thirty-
fourth day, occurred;  and on opening the body,  the same state of
the muscles and abdominal viscera, especially   the same charac-
ters in the  excrements, bile and urine were discovered.   A third
experiment afforded exactly similar  results, and I was therefore
induced  to believe, that sugar alone is incapable  of nourishing
dogs.
  It was interesting to determine whether the defective nutritious
qualities, were  peculiar to <ugar,  or whether they existed, in com-
mon with other non-azotic substances, generally esteemed nourish-
ing.  I took two dogs, young  and vigorous, but small  in  size;  I
o-ave them  for food, very good olive oil and distilled  water, as their
constant diet.   They appeared  to  be  perfectly well,  for about
fifteen davs; after which  they experienced a  series of symptoms
similar to those related, of the animals that  were fed on sugar.
No ulceration  of the cornea, however, took place;  but they died
towards the thirty-sixth day of the  experiment, they  presented  a
similar state of the organs; and  in the composition of  the urine
and bile, the same phenomena as in the preceding cases.
   Gum is  another substance which does not contain azote, but is
generally considered nourishing; we might presume that it would
act like sugar and oil, but it seemed desirable to  determine this
by direct experiment.  With  this view, I fed  several dogs upon
 gum,  and  the phenomena I observed did not sensibly differ from
 those,  of  which I have  already given an account.  I have re-
 cently repeated the experiment upon a dog with butter, an  animal
 substance  destitute of azote.   Like the animals in the  preceding
 cases, he at first supported this diet very well; but at the end of
 fifteen days, he began to lose his  flesh and strength.  He died on
 the thirty-sixth day, although, until the thirty-second, I gave him
 this food as freely as he would eat it, and though he continued to
 eat until two days before his death.  The right eye of this animal
 exhibited an ulcer of the cornea, similar to that mentioned  to have
 taken place in the animals fed upon sugar.  On opening the body,
                              48 
378
A  SUMMARY
the  same  modifications  of the bile and  urine  were  noticed.
Although the nature of the excretions of these animals, shewed
that they digested the substances which they had eaten,  I was de-
sirous of satisfying myself,  more positively, on'this  point.  For
this purpose, after having fed several  dogs upon oil, gum, or sugar,
I opened them and  found that these substances were reduced into
a particular chyme, and that they afterwards furnished an abun-
dant chyle.  That which came from the oil was of a white, milky
appearance, the chyle produced by the gum or sugar, was trans-
parent, and more watery, than that of the oil. It is evident, there-
fore, that if these different substances do not  nourish  the body,
it cannot be attributed to their not being digested.
  These facts appear important in more than one respect; in the
first place, they  render  it  very probable, that the azote of the
organs is primarily  derived from  the  aliments; and  they throw
some light  on the causes  and treatment of the gout  and gravel.*
  A great  number of tissues in the economy do not appear to un-
dergo the process of nutrition,  properly  so called; for  example,
the epidermis, the nails, the hair, the colouring matter of the skin,
and  perhaps the  cartilages.  These different parts are  really  se-
creted, either by  particular  organs, as the teeth and  hair, or  by
parts which perform, at the same time, other functions,as the nails
and  epidermis.  These  parts, seem to be formed to  prevent the
friction of foreign bodies, and are renewed proportionally; when
completely removed they are reproduced.   It is a singular fact,
that they continue to grow for several days after death; we have
had  occasion  to  mention a  similar  phenomenon  respecting the
mucus.  After these few observations on the principal phenomena
of nutrition, it will  be proper to examine, a very important phe-
nomenon, which appears to be intimately connected with nutrition,
and respiration; I refer to the  production of heat in the human
body.

                      Of Animal Heat.
  A dead body, which does not change its  state, when  placed in
the  midst of other  bodies, soon acquires the same temperature,
  *  Persons attacked with those diseases, are generally great eaters ot meat, fish,
milk and  other substances abounding in  azote; gravel, urinary, and arthritic
calculi are formed by uric acid, a principle  that contains much azute.  Perhaps by
diminishing the proportion of azotic aliments, we may prevent these  diseases. 
OP PHYSIOLOGY.
379
in consequence of the tendency of caloric to arrive at an equilib-
rium.  The human body acts  differently; when surrounded by
bodies warmer than itself, it preserves, during life, a lower tempera-
ture;  when surrounded by bodies of a lower temperature  than
itself, its temperature remains more elevated.   There is, then, in
the animal economy, two distinct and different properties, the one
producing  heat and the other cold.  Let us  examine these two
properties, and  inquire, in the first place, how heat is produced.
The principal, or" rather the  most evident  cause,  is  respira-
tion.  Experiment demonstrates to us, in fact, that the blood be-
comes heated about one degree, in passing through the lungs; and
as it is  carried  from  the  lungs to  every part of the body, it
carries every where warmth, and imparts it to the organs.   We
have already seen that the venous blood is colder than the arterial-
   This developement of heat in respiration, appears  to arise, as
we have already observed, from the formation of carbonic  acid,
whether this takes place directly in  the lungs, or in  the paren-
chyma of the organs.  The very beautiful experiments of Lavoi-
sier and Laplace, lead to this conclusion;  they placed in a calori-
moter, animals, and compared the quantity of heat produced, with
the quantity of carbonic acid  formed  in a given time; within a
very small  propoltion, the heat produced was such as would neces-
sarily be evolved, from the quantity of carbonic acid formed.
   The experiments of Messrs. Brodie, Thillage, and Legallois,
also prove, that if the  respiration of an animal be  obstructed,
either by placing it in a fatiguing posture, or in making it respire
artificially, its temperature is diminished, and the quantity of car-
bonic acid  formed, less.  In those diseases where the respiration
is accelerated, the  animal heat is augmented, except  under par-
ticular circumstances.  Respiration is, therefore, a centre  from
which the animal heat is developed.   In considering  this, as the
source of heat in  the animal body, we see that the caloric must be
distributed to the different parts of the body, in an unequal  man-
ner. Those parts which are most distant from the heart, or receive
less blood,  or which cool the easiest, must be generally colder,
than those  which present a contrary arrangement. This in fact, is
found to be actually the case.  The limbs are  colder  than the
trunk; they are often found at 88° or 90° Far. and even less, while
the cavity  of the thorax approaches 104°.  But  the  extremities 
380
A  SUMMARY
have a considerable extent of surface, in proportion to their mass*
they are more distant from the heart, and receive  less blood than
most of the organs of the trunk.   From  the extent of their surface,
and their distance from the heart, it is probable, that the feet and
hands would have a still lower temperature, than what is observed
generally, if these parts did not receive a large quantity of olood.
The same disposition exists in all the external organs, the surface
of which is very extensive, the nose, cartilage of the ear, &c. their
temperature is higher than would be anticipated,  from  their sur-
face and distance from the heart.
   But notwithstanding  this  foresight of  nature,  the parts  with
large surfaces, lose their caloric more  easily, and are  habitually
colder than the  rest; the temperature of  the  hands and  feet is
frequently reduced in winter, much below that of the  neighbour-
ing parts; this is the reason why we expose  them  more freely to
the fire.  Among the means we  instinctively  use, to  prevent or
remove the cold,  are running, walking, leaping, &c. which accele-
rate  the circulation;  and blows  and pressure  upon  the skin,
which draw into the tissue of this membrane a large quantity of
blood.  Another  means,  equally  efficacious, is diminishing  the
surface in contact with the body which conveys away the caloric,
as flexion of the different extremities upon each other,  or placing
them in contact  with the trunk.  Children and  weak persons,
often adopt this  when they lie down,* for this, among other rea-
sons, it is improper  to dress children in swaddling clothes, when
they are to lie down in the cold.   Our clothes preserve the heat,
for the materials which  compose  them, being  bad conductors of
heat, do not allow it to escape from the body.
   From what has been said, it appears, that the  combination of the
oxygen of the air, with the carbon of the blood, is  sufficient to ex-
plain most of the phenomena which  occur in  the production of
animal heat;  but there are some, which,  if real, cannot be ex-
plained in this way.  It has been observed,  by persons worthy of
belief, that, in certain local diseases, the temperature of the part
diseased, becomes greater than that of  the blood,  taken from the
left auricle, by several degrees.  If it be so, the continual return
of the arterial blood, will not be sufficient to explain this increase

    * See :\ Memoir of .*A. Cies, iu the Journal de .\I;A;z'.r.z, Annee, 1317. 
OF PHYSIOLOGY.
381
of heat.  This  second source of heat, must be connected with the
nutritive phenomena, which  take place in the  diseased  part.
There is nothing forced in this supposition, for chemical combina-
tions generally give rise  to elevations of temperature, and  we
cannot doubt that, both in secretion and nutrition, combinations
of this  kind, take place in the depths of the organs.
   By means of these two  sources of heat, life may  be preserved,
although the body be exposed to a very low temperature, as that of
winter in polar regions, where the thermometer dften fills to 108°
or 9° below zero.   In  general, we  support  with  difficulty,  such
excessive cold, and it often happens, that those parts  which are
cooled  the soonest, become  frozen and  mortify;  this was  ex-
perienced by many of the soldiers in the Russian  wars.   How-
ever, as we are capable of resisting, easily, a low temperature, it
is evident  we possess the power of evolving heat  to a great de-
gree.
   That of producing cold, or  in more precise terms, of resisting
h«at, is more limited.  In tropical  countries, it  has often hap-
pened, that men have died suddenly, apparently  from the  heat,
when  the thermometer has risen to 120° Far.   But our power of
resisting heat, is by no means limited  to this.   Messrs.  Banks,
Blagden, and Fordyce, exposed  themselves to a temperature of
nearly 257°, and found that their bodies preserved  nearly its or-
dinary  temperature.   The more recent experiments of Berger,
and Delaroche have shewn,  that the heat of the body could be
raised, by these means, several degrees. It is not necessary, even
for this effect, that the surrounding temperature should be very
high.  Having placed themselves in a stove, at 119°, their  tempe-
rature  was raised  about  3 degrees.   M  Delaroche, having re-
mained sixteen minutes in a dry stove, at 176°, found an increase
of 4° in his person.
   Franklin, to whom the  physical and moral sciences are indebt-
ed,  for many important discoveries, and ingenious observations,
was the first who explained how the body resists excessive heat.
He shewed, that this was the effect of the co-operation of the pul-
monary and  cutaneous transpiration, and that, in this respect, the
bodies of  animals resemble porous vases, called alcarrazas.
These vases, used in warm countries, allow the water they contain,
to ooze out and thu6 to keep their surface  constantly  wet,  from 
382
OF  PHYSIOLOGY.
which arises a rapid evaporation, which cools  the fluid they con-
tain.  To confirm this important fact, M.  Delaroche  placed ani-
mals in  a warm atmosphere, saturated with humidity, so that
evaporation could not take place.  These animals could not sup-
port but  a moderate degree of heat, and  become warmed, as if
they had no means of cooling themselves.  It is thus placed be-
yond doubt, that cutaneous and  pulmonary evaporation are the
causes by which man and animals resist a great degree of heat,
this explanation is still more confirmed, by the great loss of weight
that the  body  undergoes, when it is exposed  to a high tempera-
ture.
  From the facts which have thus been exposed, it is evident, that
the authors who have represented animal heat as fixed, are very
far from  the  truth.   To judge correctly,  it is necessary to take
into consideration the temperature and humidity of the surround-
ing atmosphere.  It  is also necessary  to  consider the tempera-
ture of the different parts, and not to judge of one by that of ano-
ther.  Few observations have been made on the temperature pe-
culiar to the  human  body; Messrs. Edwards and Gentil, have
most recently investigated the subject.  These authors have re*
marked,  that the place most favourable to judge of the heat of the
body is the arm pit.  They have remarked a difference, of nearly
a degree, between the heat of a young man and that  of a young
girl; the hand of the last presented a temperature somewhat less
than 98°, that of the young man was nearly 99°. The same authors
have observed remarkable differences in the  heat of persons of
different temperaments.  There are diurnal variations, the tem-
perature varies two or three degrees from morning to evening. In
general this subject requires further experiments. 
OF GENERATION.
   The functions of relation, and those of nutrition, are neces-
sary to the existence of the individual; but like all other animals,
man is called on to exercise another very important function, the
reproduction of his species.  In its object, generation differs, very
essentially, from the functions of -elation and nutrition; but it
differs still more essentially in this, that the organs which co-ope-
rate in it, do not exist in the same individual; this constitutes the
principal difference between the sexes.

                  Apparatus of Generation.
  It is composed of the organs proper to man, and those peculiar
to the female.

               Organs  of Generation in Man.
  These organs are, the testicles, vesiculm  seminales, prostate,
and penis.
  Testicles.—These are  two in number;  the cases related by au-
thors, who  assert  that they have  seen three and even four, are
very doubtful. Their form is ovoid, their size inconsiderable; their
parenchyma consists of an infinite number  of small vessels folded
and rolled  upon themselves, called tubuli seminiferi, and  are di-
rected towards a point of the surface, called the head of the epidi-
dymus.   Here they  meet and anastomose, at  the same time di-
minishing in number, and finish  by forming a convoluted canal,
called the  epididymis.   It  soon  leaves  the organ; when it re-
ceives the  name ot vas de/erens.  It then rises up towards the
inguinal riug, plunges into  the pelvis, and arrives at last at the
interior and anterior part of the bladder; there it communicates
with  the vesiculse seminales, and the  prustate  portion  of the
urethra. 
384
A  SUMMARY
  The parenchyma of the testicle is enveloped by a strong fibrous
membrane; it is also covered, first, by a serous membrane, called
the tunica vaginalis testis;  winch  in trie iceius makes a part of
the peritoneum; second, Oy a muscular membrane, wnich is capa-
ble of elevating  the testicle, and  applying  it against the  ring;
third, by the darios, a layer of loose cellular tissue, which appears
to be contractile; fourth, by a rugous skin of a dark colour, wnich
forms the scrotum.
  The arterial blood arrives at the testicle bv a small artery, de-
rived from the aorta, near the emulgent  arteries.  The vems of
this organ are  large,  tortuous, and  numerous; have  frequent
anastomoses, and have together  received  the name pampiniform
bodies.   Although the sensibility of the testicle is very great, it
does  not appear that any nerve can be traced to it,  either  from
the brain or ganglions.
   The name vesicular seminales has been  given to two small, cel-
lular bodies, below the bas/ond of the bladder, and wnich appear
to be destined to contain the fluid secreted by the testicle. Their
walls are thin, covered internally by a  mucous membrane, and
externally by a fibrous coat; we do not know whether the  inter-
mediate membrane  is,  or  is  not  contractile.   The  anterior ex-
tremity of these small vesicles, communicate with  the vas  de-
ferens and  urethra, by a very short and narrow canal, called  the
ejaculator*.
   The penis is the only part of  the male organs of generation,
which remains to be described.  It  is formed by the cavernous
bodies>the  spongy portion  0/ the urethra, ami the  glans  penis.
The cavernous bodies principally determine  the form and dimen-
sions of the penis.  They commence on the internal part of the
rami  ischii, approach each  other, and  soon  unite  to form the
body ol the  penis.   They  are separated  from  each  other by
a fibrous partition, pierced  with several  openings; their external
membrane is fibrous, thick,  hard, and very strong.  Their interior
consists of  laminse,  crossing each other in various directions,
which together form a sort of sponge, in which the olood  is  extra-
vasated. The urethra and glans,  which  are also essential parts
 of the penis, have  a  similar structure;  but are  not surrounded
 by a fibrous membrane.   Six  arteries are distributed to the penis; 
OP  PHYSIOLOGY.
385
this part also  receives many nervous filaments, arising from  the
neives of the sacrum.
  The genital  organs in man really consist of but one  apparatus
of glandular secretion, of which the testicles are the glands,  the
vesicular seminales the  reservoir, and the vas deferens and ure-
thra the excretory duct.   This secretion is indispensable for ge-
neration.  We give the name of semen to the fluid  secreted by
the testicles   The small  volume of these glands, the  number of
the spermatic  ducts, the small  quantity of  blood carried by the
spermatic arteries, and the length and extreme narrowness of the
vas deferens,  render it probable, that  the  quantity secre'ed is
very small;  and that it is propelled towards  the vesiculse semi-
nales  very slowly.  It is probable  also, that the secretion is con-
stant, but is increased by venereal  excitement, the use  of certain
aliment, and the frequent indulgence of the venereal appetite.
It is extremely difficult to explain, how the semen is made to  tra-
verse  the  tubuli seminiferi, epidydimis, and vas deferens.  Per-
haps it may be the effect of capillar) attraction, an idea which
appears to  receive some  support  from the small size of these
parts, and thickness and strength of their walls.  It is somewhat
easier to understand how  the  semen, having arrived at the extre-
mity of the  vas deferens,  can  penetrate into  the vesiculse semi-
nales.  The ejaculatory ducts embraced, together with the neck
of the  bladder, by the levatores ani muscles, will resist at first the
fluid, v/hich  will find a more ready access into the vesiculse semi-
nales.
  The semen, as it passes from the testicles, has never been ana-
lysed; the fluid which  has been  examined under this name, is
formed by the  semen,  the  fluid secreted  by the mucous mem-
brane  of the vesiculte seminales,  the prostate, and  perhaps the
glands of Covvper.  At the moment when this fluid passes from
the urethra,  it  is  composed of two substances,  the  one fluid,
and the  other thick and nearly opaque.   When left to  them-
selves, these  substances  mix, and the mass liquefies in  a  few
minutes.   The odour of  the semen is strong and  peculiar; its
taste saltish, and even  a little  acrid.  Professor Vauquelin,  who
analysed it,  found it composed of  900 parts of water,  60 of ani-
mal mucilage,  10 of soda, 30  of phosphat  of lime.    When exa-
mined by a microscope, there  can be distinguished a multitude of
                              49 
386                   A  SUMMARY

small animalculse, which appear  to have  a  rounded head, and a
long tail.  These animalculae move with a certain degree of  ra-
pidity; they appear to avoid the light, and to delight in the shade.
  The secretion of the  semen  commences at the age of puberty;
before  this period, the testicles secrete a viscid transparent fluid,
which  has never been analysed, but which, to judge  from  appear-
ance, differs essentially from  semen.   The  revolution which  the
whole  economy undergoes at this period,  such as the tone of  the
voice, the developement of hairs, the increase of the muscles and
bones, &c. are intimately connected  with  the existence of  the
testicles, and the secretion of this fluid.  Eunuchs  preserve  the
same form as in childhood; their larynx does not increase, their
chin is not covered with hair, and their disposition is generally
timid; and finally, their physical and moral character very nearly
resembles that of females.   Nevertheless,  many of them take
delight in venereal intercourse, and  give  themselves up  with ar-
dour to a connexion, which must  always be  unfruitful. In a state
of health, before an emission of semen takes  place, the  spongy
tissue  of the penis becomes  warm, hardened and  distended in
every  direction; in a word, in a state of erection.   In this state,
every  thing shows, that the blood has been thrown into the penis,
in large  quantity; its arteries are enlarged, and  beat with more
force;  its veins are swelled, and its  temperature sensibly aug-
mented.  These different  phenomena are evidently  under the in-
fluence of the  nervous  system.
   Different explanations  have been given  of erection.   It  has
been referred  to the  compression  of the pudic  veins by  the
 muscles of the penis;  and to the constriction of the veins by ner-
vous influence, &c.  But  as  erection  is  an action purely vital,
can it be explained?  It may be  produced by many and  very  dif-
 ferent causes, such as  mechanical excitement, venereal  desires,
the  fulness of the vesiculee seminales, the use of certain aliments,
some medicines, and even certain poisons.  It is  also excited by
 several diseases, flagellation, &c.  But of all  these causes, the
imagination is  by far the most prompt.  One of the  most  remark-
able phenomena which  attend erection, is, undoubtedly, the great
 rapidity with which it  is reproduced,  or ceases, in  certain cases.
 Generally, erection is  attended  with oozing of a viscid  transpa-
 rent fluid, said to come from the  prostate. 
OP  PHYSIOLOGY.
387
  The circumstances  which lead to the excretion  of the semen,
and  tiie  sensation  which accompanies it, are sufficiently well
known; but the mechanism of  its evacuation is much less under-
stood.   Are  the vesiculee seminales emptied entirely, or in part,
at the moment of emission?  Is it their middle tunic which con-
tracts itself, or are they all compressed by other causes? Are the
levatores relaxed at this instant?  Is it  the contact of the  semen
which  excites the sensation  which  accompanies  its  expulsion?
&c. &c.  We know not of any positive answers to these questions.

               Female  Organs  0/ Generation.
  They are the ovaria, fallopian tubes, uterus and vagina, at least-
these are the essential organs.
  Ovaria.—From the time of Stenon, the  term ovaria has been
applied to two small bodies, situated in  the cavity of the pelvis, on
each side of the uterus.  Each ovarium is formed by an external
fibrous membrane, and the interior by a peculiar cellular tissue, in
the midst of which are fifteen, or twenty vesicles,  of which some
are larger than others, and correspond, by one of their sides, to the
external  membrane, which is more.thin in that  part.  These  ve-
sicles appear  to contain  the rudiments of the germ, and to bear
the same relation to women, that the eggs do  to birds, reptiles and
fishes.  They are formed by two  membranous envelopes, and  by
a fluid which runs into a mass, and becomes hardened like albumen.
When the ovaria are not developed,  as sometimes happens  in
some individuals, it exerts an influence upon the economy, which
to be sure, is not similar, but analogous to emasculation upon  the
male.  Sterile women, for this reason, have  often a form resem-
bling men, with  hair upon the chin,  and about the  mouth, and
with a disposition and character like that of men.   In  such per-
sons, the voice is often grave and sonorous, and the clitoris larger
than natural.  In this kind of imperfect woman (called a Virago,)
is often found inclinations, in themselves immoral, and  which are
generally, peculiar to man; which are interesting in a  physiologi-
cal  point of view.
  Fallopian  Tubes.—These are. two  narrow canals,  the one on
the right, and  the other on the left side of the uterus,  which are
media of communication between  the  internal part of the uterus
and  ovaria.   Their external extremity  is  uneven and ragged, and 
388
A  SUMMARY
narrow, through the rest  of  their extent.  Their tissue, especial-
ly towards the uterus, is very analogous to the vas deferens.
   Uterus—In the cavity of the pelvis, between the bladder and
rectum, is found the uterus;  it is pyriform, and small, in the ordi-
nary state, but undergoes a  surprising enlargement, during preg-
nancy.  We  may divide  it into body  and  neck; the last  is em-
braced by  the vagina;  it has three orifices,two at the fundus of the
uterus, communicating with the fallopian tubes, and one below, with
the vagina.  The  tissue of the uterus is peculiar, there is nothing
analogous to it in the animal economy, except  some slight resem-
blance in  the heart.   Its  structure  is  more easily  studied in an
advanced  state of pregnancy, than the ordinary condition. There
are two prolongations of this tissue, sent to the inguinal rings, un-
der the name of round ligaments; which spread themselves at the
sides of the labia.  A  great  part of the surface of the uterus is
covered by the peritoneum,  which forms many remarkable folds
about the organ.   The internal surface is covered by  a  mucous
membrane; when  we examine  this surface  with  a magnifying
glass of considerable power, we can perceive a multitude of small
openings,  of  which some, less numerous but larger, belong to the
veins of the organ, and others more numerous, appear to belong to
the capillary  arteries. The  arteries  of the uterus  are flexuous,
and large, in proportion to  its volume; the veins are likewise
numerous and large.   They  form in  the substance of the tissue,
what has been improperly called by anatomists, uterine sinuses;
the  nerves are less numerous,  and come from the hypogastric
plexus.
   Vagina.—The  cavity  of the uterus communicates  externally
with the vagina, a membranous  canal placed nearly vertically in
the cavity of the pelvis.  It is from six to seven inches long,  and
its size various, depending upon the circumstance of the individual
having had children.   Its internal surface, especially at the lower
part, has  numerous transverse  folds  which allow the vagina to
become stretched  in  pregnancy.  At  the  inferior part of the va-
gina is the hymen, a delicate membrane, which nearly closes up
the tube.  The tissue of the vagina is composed of greyish fibres,
crossing each other in various directions,  somewhat analogous to
those of the uterus.  Below it is surrounded by numerous veins,
which resemble the tissue of the cavernous bodies of the penis, and 
OF  PHYSIOLOGY.
389
which form a retiform-ple.vus.  It is supposed  that  this part of
the vagina is susceptible of erection.  All the internal surface of
this  organ is covered with a membrane containing many mucous
and sebaceous follicles.
  The external  female  organs are the labia,  and nymphce,  folds
in the skin,  which are destined to become effaced during parturi-
tion, and the clitoris, which is a kind of small, imperfect penis,
convposed of two cavernous bodies, and of a sort of glans, covered
with a prepuce.   It is endued with great sensibility, and under-
goes an erection similar to that of the penis.

                       Of Menstruation.
  In most  women, an  aptitude for generation is indicated, by a
periodical, sanguineous  discharge, which takes place from the in-
ternal  surface of the uterus, and  is a true sanguineous exhalation.
It is called  menstruation, because it returns regularly at the end
of a  month.  Ther .> are, however, some women in whom this dis-
charge recurs at the  end of every fifteen days, others once in two
months, others again in whom it has no fixed period, and some few
cases in which it never  appears.  The approach of this discharge
is indicated by  particular signs, such as a sense of weight in the
loins, lassitude in  the limbs, and  pricking and pain in the nipples.
Its first appearance is sometimes marked by serious  accidents, at
others, the discharge suddenly takes  place, without  any previous
indication.
  The duration  of the discharge, its mode, the  quantity of  blood
exhaled, its colour and  consistence, are equally variable.   With
some women, the  quantity of menstrual blood  is  considerable,
sometimes to the extent of several  pounds.   When  menstruation
continues for eight or  ten days,  the  discharge  acquires  all the
qualities of arterial blood.   In some individuals, only a few  drops
of blood are discharged, which is frequently watery,  and destitute
of fibrine, in others it has all the characters of venous blood; the
evacuation  continues hardly  a  day,  or stops and returns again.
During  menstruation,  the  susceptibility  of females  is   much
increased;  the least noise frightens, a slight contradiction affects
them, and they are particularly irascible.
   The regularity or irregularity of the return of the courses, the
nature and  quantity of the blood evacuated, and the duration of 
390
A  SUMMARY
the evacuation, are intimately connected with the health of the in-
dividual; all deserve the particular attention of the physician.  It
has been shewn, by the dissection of  women who have died dur-
ing menstruation, that the blood escaped from the internal surface
of  the  uterus, the vessels of  which were found red, and filled
with blood, which readily  ran into the cavity, by slight pressure.
Although the menstrual discharge takes place from the uterus, yet
this is not always  the  case, many instances have been  known
where this  evacuation occurred in the mucous membrane of the
large  intestines,  stomach, lungs, and even  the eye. Different
parts  of the skin have also been known to discharge  blood, peri-
odically; thus it  has been  known to  issue monthly, from  one  or
more  of the fingers, the cheek, the skin of the abdomen, &c.
   Some distinguished authors, in their anxiety to find the imme-
diate  cause of menstruation, have attributed it to the  influence of
the moon, to the vertical  position of  the body, and  to a generous
diet.  The period at which menstruation first takes place, in this
climate, is towards  the thirteenth or fourteenth year;  it is earlier
in warm, and later in cold climates.   In equatorial  regions, girls
often  arrive at  puberty by the age of seven or eight years.  To-
wards the age of fifty, but later  in the northerly,  and earlier in
warm climates, menstruation ceases; and with it finishes the apti-
tude for generation. This period is called critical, and  is often
marked by  the developement of alarming  diseases.   What we
have said of menstruation, is liable to many exceptions.   Young
girls have been often known  to conceive, before menstruation has
taken place;  old  women, in whom the courses had  ceased  at the
ordinary period, have had them re-appear at the age of sixty or
seventy, and they have  become mothers; lastly,  women in whom
menstruation has never been observed, have nevertheless become
impregnated.

                 Copulation and Fecundation.
   Wre have  already remarked,  that  our individual existence is
protected by certain instinctive sentiments.   A sentiment of the
same nature, but much more  vivid and imperious, because its end
is more important, secures the  preservation of the species, by  in-
ducing  the sexes to approach each other, for the purpose of coi-
tion.  The  part  performed by man, in the act of re-production, 
OF PHYSIOLOGY.
391
consists in depositing in the vagina, as near as possible to  the os
uteri, the semen.   The  part performed by the female is more ob-
scure; a  great  number, perceive at this moment  the  most vivid
sensation  of pleasure, while others appear  insensible, and some
even  experience pain and disgust.  Some discharge a large quan-
tity of mucus, at  the instant when the pleasure is  most exquisite,
while in the greater number of females, nothing of the kind  is ob-
served.   In all these respects,  there  are not, perhaps, any two
who resemble each other.   These different phenomena take place
in common copulations,  i.e.  those which  are  not followed  by
fecundation.
  We will now  inquire  what takes place  in fecundation.  Ac-
cording to the  latest physiologists, the uterus inhales the semen,
and directs it to the ovaria, through the fallopian tubes, the  ragged
extremity of which embraces closely this organ.*  The contact of
the semen, causes  the  rupture of one of these vesicles, and the
fluid  which passes out, or the vesicle itself, is carried into the ute-
rus, where the embryo becomes developed.  However satisfactory
this  explanation  may  appear, we must take care how we too
readily admit it; for it is purely hypothetical, and contrary even
to the experiments of  the most careful observers.  In the  nume-
rous experiments made upon animals, by Harvey, De  Graaf, Va-
lisnieri, &c. the semen could  never be detected in the cavity of
the uterus, much less in the fallopian tubes and ovaria.  It is the
same .with the  motion,  by which the fallopian tubes embraces the
ovaria; it has never been shewn by experiment.   If we admit that
the semen penetrates  into the uterus, at the moment of coition,
which is not impossible, though it has never been observed, it will
be then,  difficult  to comprehend  how the fluid can pass through
the  fallopian  tubes, to the ovaria.  The uterus, when empty,  is
not contractile; the uterine orifices of the tubes are extremely
small, and these have  no sensible motion.
  From the difficulty of conceiving how the semen could be trans-
ported to the ovaria, some authors have imagined, that it was not
this substance that was carried to the  ovaria, but only the  vapour
exhaled  from  it,  which they  called  the aura seminalis.   Others

  * I pass over the various hypotheses, both of the ancients and moderns, on ge-
neration.  Why should the mind of the medical student be overloaded  by these
brilliant reveries, which have inconceivably retarded the progress of science? 
392                    A  SUMMARY
have thought, that the semen was absorbed from the vagina, passed
into the venous system, and arrived at the ovaria i>y the arteries.*
The phenomena which accompany fecundaiion  in women, then,
are but little understood;  an equal obscurity rests on the fecun-
dation of  the females of  other  mammiferous  animals.  With
these, however,  it will  be much easier  to conceive of the passage
of the semen to the ovaria, inasmuch  as the uterus and ovaria are
capable of a  peristaltic motion,  similar to that  of the intestines.
Fecundation in fishes, reptiles, and birds, is effected by contact of
the semen  with the ova; it may be presumed, that nature em-
ploys the same mode with the mammalia.  We  may consider it,
therefore, as highly probable, that  the semen passes, either at the
moment of  coition,  or some  time  afterwards,  to the  ovarium,
where it performs  its specific  action upon the vesicle,  which is
afterwards to be developed.
   But even if it be acknowledged, that  the semen finds its way to
the vesicle of the ovarium, it still remains to be  shewn, how its
contact animates the germ.  Jsow this  is a phenomenon, of which
it is impossible that our senses should take cognizance.  It is one
of those mysteries which at present are, and will probably always
remain, inexplicable.!   But we have  the experiments of  Spallan-
zani on this subject, which have done as much towards removing
the difficulty, as perhaps  can ever be effected.   This illustrious
naturalist has  proved, by a great number of experiments; first,
that three grains of semen dissolved in  two pounds of water, still
preserved its fecundating power.  Second, that spermatic ani-
malculse,  are not necessary to fecundation, as  several  authors,
particularly Buffon, supposed.   Third, that the seminal  vapour
has no fecundating property.  Fourth,  that a bitch may be fecun-
dated  by  injecting semen into the vagina with a syringe, &c. &c.
   We must consider as conjectural, what is said by authors of the
general signs of  fecundation.  At the moment of conception, it is
said, that, the woman experiences a universal thrilling sensation,
accompanied with a feeling of extreme pleasure, which continues

  * If there was any truth in this idea, a female might be fecundated by i.jecting
the semen into the veins.   This would be a curious experiment to try.
  t The same obscurity surrounds this, as we find in the physical and moral re-
semblance observed between parents and children, the transmission of diseases,
the sex of the new individual, &c. 
OF  PHYSIOLOGY.
393
for some time.   The countenance  becomes altered, the eyes lose
their brilliancy, the pupil is dilated, and the face pale, &c.  With-
out doubt, fecundation is often accompanied by these signs; but
how many mothers are there, who  have never experienced them;
and who have arrived at the third month  of  pregnancy without
suspecting their situation?  Our ideas of the changes which take
place in the ovaria after fecundation, are more exact.  The most
accurate observers have  described a body  of  a yellowish colour,
which is developed  in the ovaria of fecundated  females, which
is at  first rather large, but diminishes in  size as  pregnancy ad-
vances.  But this phenomenon belongs to the history of gestation,
which we are now about to investigate.

                  Of Pregnancy  or Gestation.
   The period which elapses between  fecundation and parturition,
 is called pregnancy or gestation;  it is generally nine months, or
 two hundred and seventy days.  All this time is required for  the
 evolution of the organs  of the new individual.  To form precise
 notions of pregnancy, it is  necessary to study successively  the
 phenomena  which take place in  the  ovaria, after fecundation,
 those of the  fallopian tubes, of the uterus and adjacent parts, those
 of the economy generally, and finally, those which are peculiar to
 the fcetus.
    Ovaria.—Notwithstanding the numerous works of anatomists
 and  physiologists, on the changes which take place in the ovaria
 after fecundation, we have still  much to learn  on this subject.
 The difficulty  consists in knowing, what  is  detached  from  the
 ovarium to  pass into the uterus.  Some  assert, that  they have
 seen a small vesicle detached from the ovarium, and pass into the
 fallopian tube; while others  maintain, that nothing of the kind
 has ever been observed.  I am now about to state the result  of my
 own  observations on this point. Twenty-four  or thirty hours
 after a productive coition,  the  vesicles of  the  ovarium,  which
  were the most developed, augment sensibly in volume.   The tis-
  sue  of the ovarium which surrounds them, becomes more consis-
  tent, and changed to a greyish yellow colour.   In this state, the
  tissue of the  ovarium takes the name  of corpus luteum, y^iow
  body.  The vesicle continues to grow  larger, until  the second,
  third, or fourth day;  and the corpus luteum grows in  the iame
                              50 
394
A  SUMMARY
proportion; it contains a whitish opaque  fluid, similar to milk in
appearance.  After this, the vesicle ruptures the external tunic of
the ovarium, and is carried to its surface, where it adheres by one
of its sides.  I have seen, in bitches,  vesicles thus pass out from
the ovarium, which had attained fhe volume of an ordinary hazel
nut.  In this  state  they present no  appearance internally, that
can be considered a  germ; their surface is smooth, and  the fluid
they contain does not run into a mass, as before fecundation.
   After the escape of the vesicle, the corpus luteum  remains in
the ovarium, it presents in its centre a cavity which is large in pro-
portion  as it is  near  the period of conception; but in  time  it be-
comes diminished, like the corpus luteum itself.   This  diminution
however, is very slow, and the ovaria always contain those of  the
preceding generation.  Thus the first effects of  fecundation take
place in the ovaria, and consist in the developement of one or more
vesicles, and as many corpora lutea.  Sometimes the vesicles are
found  filled with  blood; they appear to  have been too strongly
affected by the semen. It appears also, that, in  certain cases, the
vesicle  of one or more of the corpora lutea  become ruptured,
before their entire developement; for it is not rare to find more
corpora lutea in  the ovarium, than vesicles at its surface.

                Action of the Fallopian Tubes.
   Among the vesicles on the  surface of the ovarium,  there is or-
dinarily one which adheres to the open and mucous mouth of one
of these tubes, the tissue of which is softened  and gorged with
blood, and exhibits a peristaltic motion.  I  have never  directly
detected the vesicle in the tube; but  I have often seen the vesicle
after it was descended towards the  inferior part of the horn of
the uterus, while another had contracted adhesions with the  ex-
tremity of the tube.   At  this moment, the  body of the tube was
enlarged  to nearly half an inch in diameter; it, of consequence,
was sufficiently large to allow the vesicle to pass.
   The  period at which the vesicle  traverses the tube, appears to
vary, in different kinds of animals.  In hares it  appears to take
place on the third or fourth day; in dogs the sixth or  eighth.   It
is probable that it is still  later in women;  and that  it does not
take  place until the twelfth.   Dr. Maygrier assured me, that he
had seen the product of fecundation thrown  off' by an  abortion, of 
OP PHYSIOLOGY.
395
the  twelfth day; it was a small vesicle, filled with a transparent
fluid.  The vascular appendices, in which the tubes terminate in
the human subject, are probably intended  to  contract adhesions
with  the  vesicle, after it is detached from the ovarium; and to
pour  upon it a fluid that favours its developement.  After the
vesicle has  passed, the tube contracts  and resumes its ordinary
size.  Having arrived at  the uterus, the ovum unites itself,inti-
mately, with the internal surface of this organ;  it there receives
the materials necessary to its growth, and acquires a considerable
volume.   The uterus accommodates itself to this change of form,
and volume, &c.

             Alteration of the Uterus in Gestation.
  During the three first months of pregnancy, the  developement
is inconsiderable, and is made in the cavity of the pelvis;  but. in
the fourth, it increases more rapidly, and becoming too large to be
contained in the pelvis, it rises into the hypogastric region.  The
organ continues  to increase during the  fifth, sixth, seventh, and
eighth month; it occupies, gradually, a larger space in  the abdo-
men, compressing and displacing the neighbouring organs, crowd-
ing them into the hypochondriac and iliac regions. At the end
of the eighth month, it fills  itself, the hypogastric  and   umbilical
region, and  its  fundus approaches the   epigastric region.  After
this the fundus sinks, and approaches the umbilicus.  The neck of
the uterus undergoes but little change in the seven first months of
gestation; the viscus preserves, during  this  time, a conoid form.
After this, the length  of the neck is diminished, and at last be-
comes nearly effaced,  and the uterus assumes an ovoid form; its
volume, according to  Haller, is  nearly twelve times larger than
when empty.
  It is impossible that the  uterus should become  altered  so re-
markably in its form, volume, and situation, without its relations
to the neighbouring parts  being essentially altered.  In  fact, the
peritoneal coat,  which forms the  broad ligameuts,  is  stretched,
and the vagina elongated.   The ovaria, retained by their arteries
and veins, cannot rise with  the fundus of fhe uterus;  they are
therefore  applied to  its side, together  with the  fallopian  tubes.
The round ligaments  accommodate themselves to their  situation,
tending however, to carry  the fundus of the uterus forward, which 
396
A  SUMMARY
must have a favourable effect on the abdominal circulation, by di-
minishing the pressure on the large vessels.  The abdominal walk
undergo  a considerable extension; hence the rugous appearance
opon the abdomen of women who have borne children.
  In proportion as the uterus developes itself, its  tissue loses its
consistence; it assumes a deep red colour, and a spongy texture;
its structure becomes more distinctly fibrous.  We see, externally,
longitudinal fibres passing from the fundus towards  the neck,
which are intersected at right angles by circular fibres.   Beneath
this tunic, the tissue of the uterus presents an inexplicable interlace-
ment of fibres, in which no regular arrangement can be discovered.
In this state, the organ appears to be endowed with a peculiar con-
tractility, which, in  animals, has a great analogy  with  the peris-
taltic motion of the  intestines.  Its  internal  surface, soon after
fecundation, presents an albuminous coat, adhering strongly to it.
This coat increases with the organ,  in the early periods of preg-
nancy, but afterwards disappears, in a great measure.   Dr.  Wil-
liam Hunter,* who first described it  carefully, called it the mem-
brana decidua.   It appears  destined  to favour the adhesion of
the ovum, to the internal surface of the uterus.
   These changes in the volume and structure of the uterus, ne-
 cessarily modify its circulation.  Its arteries undergo a considera-
 ble dilatation,  the  veins become enlarged, and  form  in the pa-
 renchyma of  the organ what has been, improperly, called uterine
 sinuses; the lymphatic vessels also become very voluminous.  It
 must be evident, that  the quantity of  blood  which traverses the
 uterus in a given time, is proportioned to the changes it has under-
 gone, and the new functions it is called upon to perform.

              General Phenomena  of Pregnancy.
    While all these phenomena occur in  the uterus, important mo-
 difications take  place in the functions of the mother, and com-
 mence  often  immediately after fecundation.  Menstruation  does
 not reappear, the mamma; swell, and, if in  a state of lactation, the
 mitk  becomes serous, and  is frequently injurious to  the  infant.
 The eye-lids are swelled  and of a blueish  colour, and  the counte-
 nance  altered;  the cutaneous transpiration assumes  a peculiar
 odour; a general paleness,  with a diminished or capricious appe-
" See his magnificent work, De Utero Gravido. 
OP PHYSIOLOGY.
-397
tite,  are also  often observed; sometimes  continual nausea, with
violent pain of the head, followed by distressing vomiting, occur.
The abdomen is often affected with an extreme sensibility, and
at first becomes  flattened; some females lose their  sleep, and
are unable to leave a recumbent posture, without experiencing a
sense of extreme fatigue; on the other hand, persons of a delicate
constitution, and valetudinarians, often,  have their health very
much improved;  serious diseases are sometimes arrested in the
mid«t of their course, and do not again resume it, until after par-
turition.
   In general, the intellectual  faculties of pregnant females are
weakened, and  they  are  affected, to an unusual degree, by the
most trifling  events;  hence  the necessity  of those  kindnesses,
 and attentions, which this peculiar situation demands.  To these
 different symptoms, which it is impossible to explain, are added
 phenomena, evidently arising from an augmentation of volume in
 the uterus; such as cramps in the limbs, swelling of the superficial
 veins of the thighs and legs, and a sensation of numbness or prick-
 ing, arising from an obstruction in the  circulation.  In the later
 period of pregnancy, the bladder and rectum  being strongly com-
 pressed, the  desire of passing urine and going to stool, are fre-
 quent.   We shall not add  to these phenomena, the existence of
 which  is certain, suppositions  destitute of  proof; such for exam-
 ple, that fractures in pregnant women are attended with  more
 difficulty than in other women;  the contrary of which is shewn by
 experience.

           Developement of the Ovum in the Uterus.
    At first the ovum is loose in the uterus;  its volume is nearly as
  small as when it heftjthe ovarium; but, in the course of the second
  month, its dimensions increase, and  it is  covered by long fila-
  ments of about a line in length, which ramify in the manner of
  sanguineous vessels, running into the  membrana decidua.  In
  the third month,  we perceive them only  on one side of the
  ovum, those on the. other having nearly disappeared; but those
  which remain have acquired an increased size and consistence,
  and  are implanted more deeply in the decidua, and at last con-
  stitute the placenta; over the remainder of  its surface, the ovum
  presents a soft, shaggy coat,  called  the decidua refle.ra.  The 
398
A  SUMMARY
ovum continues to increase and develope itself, until the termina-
tion of pregnancy, when its volume equals that of the inside of the
uterus; but  its structure has experienced changes  which we are
■ow about to examine.
  At  first, its two  membranes are thick and  strong.  The  ex-
ternal is  called the chorion, and the internal  the  amnios.  Tbe
fluid contained in the last, augments in proportion to tbe volume of
the ovum; according to  M. Vauquelin, it exhioits, at the same
time,  acid and alkaline properties.  It is formed or water, acu-
men,  muriat of soda, and phosphat of  lime.  M. Berzelius s.tys,
that he  has detected in it the fluoric acid.  Perhaps it is not the
same, at  different periods of gestation,   there is also a  Ho id be-
tween the chorion and  amnios, in the second month  of pregr.ancy,
but it disappears  during the third.
   Until the end of the third  week, the ovum  exhibits no appear-
ance of the germ; the fluid it contains  is transparent and tartly
coagulable as before.  At  this period,  we begin to perceive that
the side  of the  ovum adheres to the uterus, being a slightly
opaque  gelatinous mass, all the parts  of which appear  homoge-
neous.  Soon, some points become more opaque, and  there are
two distinct vesicles of nearly equal size, united by a  peduncle,
or sort of foot stalk, one of these  vesicles adheres to the amnois
by a small filament.  About the same  time, there appears in the
middle of the last a red  point, from  which yellowish  filaments
are  seen  to  pass  off; this  is  the  heart and principal  blood
vessels.   At the  commencement of the second  month, the head is
visible, the  eyes  forming two black points, quite large, in propor-
tion to the volume of the head.  Small  openings  indicate the
place of the ears and nostrils; the mouth is at  first  large, but be-
comes contracted as the lips become developed, which  happens
towards the sixtieth day;  at  this time, the ears, nose, and limbs,
are likewise perceptible.
   By the end of about the  fourth month, all the principal organs
have become  successively  developed.   At this time, the embryo
 state ceases, and the fcetal state begins, wfcich is continued  until
 the  end of pregnancy.  During this time, all  the parts  increase
 with more or less rapidity, and approach the state they exhibit  at
 birth.  We have already spoken sufficiently of the peculiarities of 
OF  PHYSIOLOGY.
399
the functions of relation, and we shall now say something respect-
ing those of nutrition.
   Before the sixth month, the lungs are very small; the heart is
lar-je, but its  four cavities  are  confounded, at least difficult to
distinguish; the liver is large, and occupies a great part of the ab-
domen; the gall bladder is not full of bile, but of a colourless fluid,
which is not bitter; at its lower part, the small intestine contains
a yellowish matter, in small quantity,  called the meconium; the
testicles are  placed on the sides of the lumbar vertebra;, and the
ovaria occupy the same  position.  At  the  end of the seventh
month, the lungs  assume a redish tint, which they had not before;
the cavities of the heart become  distinct; the  liver  preserves its
large dimensions,  but is a  little above the umbilicus; the bile ap-
pears  in the gall  bladder;  the meconium is more abundant, and
descends more in  the large intestine;  the ovaria approach the
pelvis, and the testicles the  rings.   At this period, the  fa*tus be-
comes capable of living, independently, of the mother; it continues
to grow  more perfect  until the  eighth or ninth month, when it is
expelled from the uterus.   We cannot give here the  interesting
details of this increase of the organs; they belong to anatomy; but
we shall occupy ourselves, for a short time, with the physiological
phenomena to which they relate.

              Functions 0/ the Ovum  and Foetus.
   Soon after the ovum has arrived in the cavity of the uterus, its
 rough surface is transformed into sanguineous vessels; life, there-
 fore, exists in the ovum.  But we have no idea of this mode of ex-
 istence; it  is probable, that the surface absorbs the  fluids  with
which it is in contact,  and that these,  having undergone a par-
 ticular elaboration  by the  membranes, are  afterwards poured
into the cavity of the  amnios.   What,  we  may inquire, was the
germ before its appearance?  Did it before exist, or is it formed at
 this moment?  Does the small, slightly opaque mass which com-
poses it, contain the rudiments of all the organs of the fcetus and
adult, or are they created at the instant when they first appear?
 W hat can be a nutrition so complicated, so  important, which is
 formed without vessels, or nerves, or apparent circulation? How
 does the heart begin to move, without the appearance of a nervous
 system?  From whence comes the yellow blood which  it at first 
400
A  SUMMARY
 contains, &c. &c.  In the present state of science, it is impossi-
 ble to give any satisfactory answers to these questions.
   We are ignorant of what takes place in the embryo, while the
 organs are imperfectly formed; there is, however, a sort of circu-
 lation.   The  heart sends  the  blood into the large vessels, and
 newly formed placenta; and, it is probable, that the  blood  is re-
 turned to the heart by the veins, &c.   But, when  the new  being
 has arrived at the foetal state, and the greater number of the or-
 gans have appeared, it is then possible to recognise some of the
 functions peculiar to this state.   Of the different functions of the
 fcetus, the circulation is best understood.  It is more complicated
 than in the adult and is entirely different.   In the first place,  it
 would be impossible to make the division of the blood vessels into
 arterial and venous; for the blood of  the fcetus has every where
 the same appearance, it is of a brownish red tint; in other respects,
 it resembles the blood of the adult,  it  coagulates, separates into
 crassamentum and serum, &c.  I do not know why some distin-
 guished chemists have asserted, that it does not contain fibrine.
   Placenta.—The most singular, and  the most important organ
 of the fcetus, is the placenta; it succeeds those filaments which,
during the first month of gestation, cover the ovum.   At first, it
is very small, but soon acquires considerable magnitude. By its
external surface it  adheres to the uterus, presenting  irregular
furrows, which divide it into several lobes or  cotyledons, the num-
ber and form of which is not fixed; its foetal surface is covered by
the chorion and amnios, except at it centre, which gives insertion
to the umbilical cord.  Sanguineous  vessels divided and subdi-
vided, form its parenchyma; they belong to the umbilical arteries
and vein. The vessels of one lobe do not communicate with those
of the neighbouring lobes, but those of the same cotyledon have fre-
quent anastomoses, and nothing is easier than to make injections
pass from one to the other.
   Umbilical Cord.—-This extends from the centre of the placenta
to the umbilicus of the infant; its length is often two feet; it  is
formed  by  the two umbilical  arteries and  the umbilical  vein,
united by a dense cellular tissue.   It is covered by the two mem-
branes of the ovum.  In the first months of gestation, a vesicle, to
which some small vessels,  prolongations of the mesenteric artery
 and vein, are sent, are found in the thickness  of the cord, betwee* 
OP PHYSIOLOGY.                 401
the  chorion  and  amnios, not  far  from  the  umbilicus.    This
membrane  is  not analogous to  the allantois,  but more  nearly
resembles  the yellow membrane of birds and  reptiles, and the
umbilical vesicles of mainniiferous animals.  It contains a yellow-
ish fluid, which  appears to be absorbed  by the veins expanded
over its walls.*
   Having  arisen at the placenta, and  arrived  at  the umbilicus,
the umbilical vein enters the abdomen, and passes  into the lower
surface of the  liver, there it divides into  two large branches, of
which one is distributed to the liver with  the vena porta;, and  the
other terminates suddenly in  the vena cava, under the name of
ductus venosus.  This  vein has two valves, the one at the place
of its  bifurcation, and  the other at its junction  with the vena
cava.  The heart and  large vessels  of the.  fcetus, after the se-
venth  month, are very  different from  what they are after birth.
The valve of  the vena  cava is very  much  developed, the partition
of the auricles is perforated with a large  opening,  garnished with
a valve, called the J'oramen ovale.  The  pulmonary artery, after
having sent two small  branches to the lungs, terminates in the
aorta;  it is called  in this place the ductus arteriosus.
   Another character peculiar to the circulation of the fcetus, is
the existence of the umbilical arteries, which arise from the inter-
nal  iliacs, run along  the sides  of the  bladder,  pass out from
the abdomen through the  umbilicus, to the placenta, where  they
are  distributed in the  manner before  described.   From  this ar-
rangement of the circulating apparatus  of the fcetus, it  is evi-
dent, that  the course of the blood must be very different from that
of the adult.   If we suppose that  the blood goes from the pla-
centa, it is evident  that it passes through the umbilical  vein to
the liver;  there a part of the blood is directed  to the liver, and
another to the vena  cava, these  two parts lead to the heart, by
the vena cava inferior;  having arrived  at  this organ, it penetrates
into the right and left auricle, traversing the foramen ovale at the
moment they are dilated.   At this  moment the blood of the vena
cava inferior unavoidably  mixes  with that of the vena cava supe-
rior.  Indeed, how  could two fluids, of nearly the same nature,
   * See the Memoir of M. Dutrochet on the envelopes of the egg, inserted
among those of the Medical  Society of  Emulation, -.ol. viii. and the interesting
researches pf M. Cuvier oh the same subject.  (Annales de Museum, IS17.)
                              51 
402
OP PHYSIOLOGY.
 remain separate in a cavity, where they arrive at the same time,
 and which contracts to expel them?  I am not ignorant, that Sa-
 batier, in his beautiful Memoir on  the  Circulation  of the Foetus,
 has  maintained a contrary opinion;  but 1 confess,  his reasons
 have, by no means, altered my opinion in this respect.
   'The  contraction of the auricles succeeds  their dilatation, and
 the blood  is forced  into  the  ventricles; these in their turn con-
 tract and expel the blood, the left  into the  aorta, and the right
 into the  pulmonary artery;  but this  artery  terminates in  the
 aorta, with the exception  of a very small branch, which goes to the
 lungs.   Under  the  influence of these  two agents of impulsion,
 the biood passes through all the divisions of the aorta, and returns
 to the heart by the vena;  cava:; but it is partly carried to the pla-
 centa, by the umbilical arteries, and returned by  the  vein.   It is
 easy to conceive the utility of the foramen ovale and the ductus
 arteriosus.  The left  auricle receiving but little blood from  the
 lungs, could  not supply the ventricle, if it did not receive it from
 the foramen ovale.   On the other hand, the lungs not having any
 functions to perform, if all the blood of the pulmonary artery was
 sent to them, the action of the right ventricle would be lost; whereas
 by means of the ductus arteriosus, the force  of the  two ventri-
 cles is employed, to propel the blood  in the  aorta;  without this
 action of both ventricles, it is probable  that  the blood could not
 arrive at the placenta, and return again to the heart.
  The motions of the heart are very rapid  in  the fcetus;  they ge-
 nerally exceed one hundred  and twenty pulsations in a minute;
 the circulation  is of course  proportionally  quick.  A  question
 now pre&enis itself,  which is extremely difficult, viz.—What rela-
 tion does the circulation  of the mother bear to that of the fcetus?
 To arrive at any thing like a satisfactory answer, it is in  the first
 place necessary to examine the mode by  which  the placenta is
 united with the uterus.   Anatomists have varied   in  opinion on
 this point.  It was for a long time believed, that the uterine arte-
 teries anastomosed directly with the  branches of  the umbilical
 veins, and that  the last divisions of the  placenta terminated in the
 veins ot the uterus.  But the impossibility of making injections
 pass from the umbilical  vein  into  the uterine arteries, and vice
versa, being demonstrated, this idea  was abandoned.   It is gene-
rally admitted  now, that, there  does not exist any anastomosis 
OP PHYSIOLOGY.
403
between the sanguineous vessels of the placenta, and those of the
uterus.  I have made some researches on  this point, and the fol-
lowing are the results:—
   I at first repeated the attempts to  inject the placenta from the
uterine  vessels,  but without success; I have even made them in
living animals without being more fortunate; I have used poison-
ous substances, the effects of which I  was before acquainted  with,
odorous  substances,  &c. but  I have seen  nothing which has
induced  me to  suspect, that there is any direct communication.
In  bitches, towards the middle of gestation, a great number of
small arteries maybe distinguished, passing out from the tissue of
the uterus, and  dividing into  numerous  ramifications.  At this
period, it  is impossible to separate these two organs without tear-
ing these  small arteries, and  producing considerable hemorrhage.
But towards the end of gestation,  in removing the placenta  how-
ever  freely, these small vessels separate,  without the  extravasa-
tion of blood.  When  we inject into  the veins of a dog, a cei tain
quantity of camphor, the blood becomes of a strong campiWous
odour.  After having done this on a slut, in the latter period of
gestation, I took a fcetus from  the uterus, at  the  end of three or
four minutes, its blood had not  the odour of camphor.  But that of
a second fcetns, extracted after a quarter of an hour, had the odour
of camphor, very distinctly.  The same was  found to be the case
with  the other foetuses.
   Thus, notwithstanding there is no direct anastomosis between
the vessels of the  uterus and  placenta, it cannot be doubted that
the blood of the mother, or some of its parts, passes to the fcetus
with  a certain degree of promptitude.   It is probably deposited by
the uterine vessels on the surface, or in the tissue of the placenta,
and absorbed by the extreme branches of the umbilical vein.
   It  is much more difficult to determine if the blood of the fcetus
returns to the mother.  Among the small  vessels which go in ani-
mals from the uterus to the  placenta, we  see nothing which has
the appearance  of a vein.  In women, there are large openings,
which communicate with the uterine  veins, seen in that part of the
Uterus,  which adheres to the placenta.   But we are ignorant
whether these venous orifices are  destined to absorb the blood of
the fcetus, or to allow the blood of the mother to escape to the sur-
face of the placenta; we may admit  this last idea to be true, but 
404                    A  SUMMARY
there is no evidence of it.  I have introduced into the vessels of
the umbilical  cord, active poisons, directing thetn  towards  the
placenta; but 1 have never seen the mother experience any effects,
and even when she has died of hemorrhage, the vessels of  the
fetus remained full of blood.
  As no anastomosis with the vessels of the uterus exists, it is pro-
bable that the circulation of  the  mother  has no other influence
upon that of the fcetus than pouring blood into the fissures of the
placenta.  The heart of the  fetus is the  principal moving power
of its blood.   It is, however,  asserted, that well formed  foetuses
have been  born without any  heart; but can these  observations be
depended on? There have been well authenticated  cases where
the placenta was entirely separated from  the dead foetus, while it
has continued to develope itself.   M. Ribes, recently observed a
case where the umbilical  cord was ruptured  and perfectly cica-
trised;  how was the circulation carried  on in this organ?   We
must conclude, therefore, that the  relations  between the circula-
tion of the  mother and that of the fcetus,  require new experi-
ments.
   Some authors have asserted that the placenta was to the foetus,
what the lungs are to the adult; others have endeavoured to ex-
plain the large  volume of the liver, by attributing to it  the same
use.  These assertions  are entirely unsupported by proof.    The
functions of the capsulse  renales, thymus and thyroid glands, the
dimensions of which in the fetus are considerable, are also at  pre-
sent involved  in  impenetrable obscurity.   This subject has often
exercised the  imaginations of physiologists, but without any  real
benefit to science.
   Notwithstanding the imposing authority of Boerrhave, it is im-
possible to admit,  that the foetus  continually swallows the water
of the amnios, that it digests it, and is nourished by it.  Its sto-
mach, it is true, contains a viscid matter in considerable quantity;
but it resembles, in no respect, the liquor amnii, it is very  acid
and gelatinous; towards the  pilorus it is  greyish and opaque.  It
appears, that  it is formed in the stomach, that  it passes into the
small intestines,  where, after having undergone the  action of the
bile, and perhaps the pancreatic  juice, it  furnishes a particular
chyle.   The  remainder  descends towards  the  large intestines,
where  it forms the meconium, which  is evidently  the result of 
OP PHYSIOLOGY.
405
digestion carried  on during pregnancy.  Whence, it may be in-
quired, arises this digested  matter?  It appears probable, that, it is
secreted by the stomach itself, or that it descends from the ceso-
phagus; there  is nothing, however, opposed to the idea, that in
certain cases, the fetus may swallow some mouthfuls of the liquor
amnii; the fact that  hairs similar to those of the skin, are some-
times found in the meconium seems to prove this.  It is important
to remark, that the  meconium is a substance that has little azote.
   Nothing is  at present known, respecting the use of this diges-
tion in the fetus;  it is not probable, that it is essential to  its de-
velopement, inasmuch as it cannot  exist in those instances where
there is no stomach; nor any  thing which answers to  it.   Some
persons assert, that  they have seen the chyle in  the thoracic duct
of the fetus.   1 have never seen any thing of the kind; in living
animals, this  canal and the lymphatics contain a fluid which ap-
pears to be analogous to the lymph, and which coagulates sponta-
neously like it-  I have made some attempts to satisfy myself, by
direct experiments,  whether venous absorption  took  place in the
fcetus in utero.   I have injected into the pleura, peritoneum, and
the cellular tissue,  active poisonous substances, but I could not
obtain any satisfactory result, as the nervous system of the fetus,
when it has not respired, appears to be insensible to the action of
poisons.  It appears certain, that  exhalations take  place  in the
fetus, as all  its  surfaces  are  lubricated nearly as  they are after-
 wards; the fat is  abundant, and the humours of  the eye exist.  It
 is  also probable, that  cutaneous transpiration takes place, and is
 continually mixed  with the liquor amnii.   With  respect to this
 last fluid, it is difficult to say whence it is derived;  no sanguine-
 ous vessels appear on the  amnios, it is nevertheless probable, that
this membrane is its secretory organ.
    The cutaneous and mucous follicles are developed, and appear
 to have a powerful action, especially after the seventh month; the
 skin is then covered by a thick coat of fatty matter, secreted by
 the follicles.   Many authors have  considered this as a deposition
 from the liquor amnii; the mucus is also very abundant in  the two
 last months of gestation.   All the glands, which  assist in diges-
 tion, are  of considerable size, and appear to have a certain degree
 of activity; we know but  little of  the  others.  We  are ignorant,
 for example,  whether  the kidneys form urine, and  whether this 
406
A  SUMMARY
fluid is thrown out by  the urethra into  the cavity of the amnios.
The testicles-and mammse appear to form a fluid, which does not
resemble  either semen or milk, which  is found in the vesicula;
seminales, and lactiferous ducts.
   What  then, can we say  of  the nutrition of the fetus?  Physio-
logical works, contain only vague conjectures on this  point.   It
appears certain, that the  placenta receives  from  the mother, the
materials necessary to the developement  of the organs; but we
are ignorant of the  nature of these materials,  and how they are
obtained.  Respiration not having taken place before birth, its
heat cannot  depend upon this.  Experience has shown, that it
does not  rise above 94° or 95° of Faren.;  it is said to be  more
elevated  when the fetus  in utero is dead.   If this  be true, the
fcetus  must have a means of cooling itself,  which does not exist
after  birth.   This is all we know of the nutritive  functions  of the
fcetus; what  relates  to the functions of relation, has been  already
explained.
   As the mother transmits to  the fetus the materials  necessary
to its nutrition, it will be  necessarily modified by the nature and
quantity of the materials transmitted. If the quality be good, and
the quantity sufficient, the growtn will  be natural, but if  the
proportion be small, or if the quality be not proper, the  fetus will
be badly  nourished, and will either cease to be developed, or even
perish.   Now the moral condition of the mother must modify the
nature and properties  of these elements, which pass to the pla-
centa; it is true, therefore, that her imagination has an influence
upon the  fetus.   It  is thus that sudden terror, violent chagrin, or
immoderate joy,  may  cause the death of the fetus, or retard its
growth.  Physical causes,  such as blows, falls,  the action of cer-
tain medicinal  agents, and the bad quality  of the  aliments, may
have the  same result, because they injure or prevent the transmis-
sion  of the  nutritive materials of the  fetus.   If the  mother be
affected by a  contagious disease, the fetus has likewise  symptoms
of it;  thus the  life of  the fetus is in an evident  state  of depen-
dence upon that of the mother.
   Independently of the lesions which  arise from this source, the
fetus is  frequently attacked with spontaneous  diseases,  such as
dropsies, ulcers,  fractures, gangrenes,  cutaneous  eruptions,  the
separation of one or more of the limbs, and many other internal 
OP PHYSIOLOGY.                 407
diseases, both local and general. They often die of these diseases
before  birth, and if they are permitted to  live uutil  after birth,
they are then incapable any longer of supporting life.  The mem-
branes  of the ovum, the placenta, and liquor amnii, are also some-
times found in a morbid state.
  0/ Monstrosities.— In consequence of some unknown causes,
the  different  parts of the fetus  develope  themselves, sometimes
in a preternatural manner; so that  one or more  of the natural
emuuctories of the body do not exist, or are closed  by membranes.
Somitimes the  lungs, stomach, bladder, kidnies, liver, and  even
brain, are entirely wanting, or arranged in an unusual manner.
In general, according to the remark  of AL Beclard, when a nerve
is wanting, the  parts to which  it should  be distributed  do not
exist.   1 here are other malformations or monstrosities, which de-
pend on unknown causes,  and seem to arise from a confusion of
two germs, from whrch result children with two  heads  and one
trunk,  or two trunks and one head,  or one trunk and four arms,
ami four legs well formed.   'There have been often found, fetuses
not developed,  in the  bellies of  individuals in   advanced  age.
There is no reason  for  believing  that the imagination of the
mother can have any influence in  the formation of these  mon-
sters;  besides, productions of this kind are daily observed  in the
offsprings of other animals, and  even in plants.
  It is not very unusual for the uterus to  contain  two, instead of
one foetus.  In Trance, this occurs as often as one in twenty-four;
it appears to  be more  frequent in England.  Three fetuses in
one uestation is much more  rare; in  thirty-six thousand labours
in  the "Hospice de  la Maternite," in Paris, only  twenty-four
cases of this kind happened.   There have been some well authen-
ticated  instances, where women have had four  fetuses in one
gestation; but, beyond this,  the instances related by authors appear
to be fabulous.   In cases of plurality of children, the volume and
weight of the children are in  proportion to the number; twins are
smaller  than common children, &c, but  whatever may be their
size, they are each surrounded  with a  separate amnios and cho-
rion, and have a distinct placenta.   Their functions are sepaiate,
so  that one may die while the others continue to become devel-
oped.   There is nothing to countenance the belief, that in  case
of  plurality of  children, fecundation  took  place  at two or three 
408
A  SUMMARY
different times, and that there really exist instances of superfeta-
tion.   The histories of this, which have been related, are far from
resting on the degree of evidence, which is necessary in a science
of facts.

                       Of Parturition.
  At the end of the seventh month  of gestation, the fetus is in a
condition to respire and exercise its digestive functions; it is then
capable of an independent existence.   It is rare, however, that
parturition takes place at this time; it generally  occurs  at the
end of nine kaleudar months.  There have been examples cited,
of the birth of children  at the end of ten full months of gestation,
but these cases are very doubtful, as it is so extremely difficult to
determine  the  precise  period of conception.   According  to the
French Code, however, it is an established principle, that parturi-
tion may take place at the end of  two hundred and ninety-nine
days  of gestation.
  Nothing is more curious,  than the  mechanism by  which the
foetus is expelled;  every thing seems to have  been foreseen and
provided for, with an admirable precision, so as to favour its pas-
sage through the  pelvis and organs of generation.  The physical
causes by which this is  effected are, the contraction of the uterus
and abdominal muscles;  through their  agency, the membranes
are ruptured, the water of the amnios discharged, and the head of
the fetus  forced  into  the pelvis, and passes through the vulva,
the folds of which are effaced.  These different phenomena take
place in a regular succession, and are accompanied by pains, more
or less severe, by swelling and relaxation of the soft parts  about
the pelvis, and the external organs of generation, and an abundant
mucous secretion in the cavity of the vagina.   All these circum-
stances, each in its particular way, favour the passage of the fetus.
To facilitate the study of this complicated operation, it is neces-
sary to divide it into several stages, or periods.
  First stage of Parturition.—It consists of premonitory signs.
Two  or three days before parturition,  an  unusual discharge of
mucus from the vagina, is observed  to take place;  the  genital or-
gans  are swollen, and become relaxed,  and it is the same of the
ligaments which  unite the bones  of the pelvis.   The neck of the
uterus becomes flattened, its opening  enlarged, and  its  edges 
OF PHYSIOLOGY.
409
thinner; and slight pains, which are known  in France under the
name of mouches,  or flee bites, are noticed in the loins and belly.
  Second stage.—Pains  of a different kind  are  soon developed;
they  appear to begin in the  loins,  are propagated either  to-
wards the fundus, or neck of the uterus, and are renewed after
considerable intervals, e. g. a quarter or half an hour.  Each is
accompanied by an evident contraction ol the body of the uterus,
a manifest  tension of its neck, and a  dilatation  of its mouth,
or os tinea?.  If the finger be now introduced into the vagina, we
can  distinguish the envelopes of the  fetus, projecting from  fhe
os tincse.   The contractions gradually become stronger, and  the
pains more severe, by which the membranes are at  last ruptured,
and  the  water discharged; when the  action of the uterus  is di-
rectly applied to the fetus.
  Third stage.—The pains and contractions of  the uterus, now
considerably increase, and are instinctively accompanied with
contractions of fhe abdominal muscles.  Women, perceiving their
effect, are induced often, to make  all the  muscular efforts  that
they are capable of.   The pulse is also frequently increased,  the
countenance animated, and the whole body  in extreme agitation,
the sweat pouring from the surface  in great abundance.  The
head  being engaged  in  the pelvis,  the  face towards the sacrum,
and  the occiput presenting, glides  under the arch of the pubis.
  Fourth stage.—After some instants of repose, the expulsive ef-
forts  recommence; the head presents at the vulva, and endeavours
to pass through, which is at last effected by a strong effort.  When
once  the head  is disengaged, the rest of the body soon follows.
The umoilical cord is now tied, and divided, at a short distance
from  the navel
  Fifth stage.—If the accoucheur does not  immediately proceed
to extract the placenta,  in a short time, slight pains are observed
again; the uterus  contracts  feebly, but  with  sufficient force to
expel the placenta and membranes;  th s has  received the name of
deliverance.  During twelve or fifteen days, which succeed par-
turition, the uterus resumes, gradually, its original size and form,
the woman  perspires freely, and  the mamma; become distended
with  milk.  A discharge, at first bloody, and afterwards whitish,
called the lochia,  takes  place  from the vagina, which indicates
that the organs are returning to their natural state. 
410
A  SUMMARY
  As soon as it is separated from  its mother, and sometimes be-
fore, the chest of the infant dilates, and the lungs are distended
with air;  and this motion continues to be repeated for the remain-
der of  life.  The lungs being distended by air, permit the blood
to pass through the pulmonary artery, so that the ductus arterio-
sus, and foramen  ovale, receiving less blood, contract gradually,
and  at  last become  obliterated.  The same thing takes  place in
the umbilical vein and arteries,  which are transformed into a sort
of fibrous ligaments.   The infant, at birth, is  from eighteen to
twenty inches in  length, and weighs five or  six pounds.  In ge-
neral, the number of male is greater than that of female children.
The number of children that may be  born of one mother, cannot
exceed  the number  of vesicles  contained  in  the ovum,  that is
about forty.

                        Of Lactation.
  The painful act that we have  now described, does not terminate
the duties of the mother;  the infant now requires care of a diffe-
rent kind;  it must  be protected against the weather, and great
attention  is required for its preservation, and  for its  moral and
physical  education;  lastly, nature  has confided to her the power
of furnishing its  first aliment, and  the only one suitable to the
feebleness of its organs.  'This  aliment is milk, it is secreted by
the mammae; the number, form, and situation of which are among
the  distinctive characters of the human species.   Their paren-
chyma  is entirely different from that of the other secretoiy or-
gans.  Each mamma has twelve or fifteen secretory ducts, which
open at the top  and sides of  the mammary process, or nipple.
The arteries which are distributed to the mam in.e, are small, but
very numerous;  they abound with  lymphatic vessels and nerves,
and are endued with a vivid sensibility.  The mammary process,
in particular, is very sensible, and  is susceptible of a  state analo-
gous to erection.
   Until the period of fecundation, the mamma;  remain inactive,
not exercising any apparent secretion.  But in  the early periods
of  pregnancy, the woman observes peculiar pricking  and darting
pains, and  the  organs become swelled.   After a certain period
especially as the end of gestation approaches, a serous  fluid, some-
times  in  considerable quantity, is  discharged from the nipple. 
OP  PHYSIOLOGY.                  411
The secretion often preserves the same characters for two  or
three days after delivery; but  the  milk,  properly so called, does
not appear until the end of that time.
  The milk  is one of the most azotic  of  the  glandular fluids; its
smell, colour, and taste, are  well known.  According to M. Ber-
zelius, it is composed of cream and milk, properly so called; the
last contains, 928.75 parts of water; 28.00 of caseous matter, with
sugar; 35.00 of sugar of milk; 1.70 of muriat of potash; 0.25  of
phosphat; 6.00  of  the  lactic  acid; acetat  of potash, and lactat
of iron, 0.30.  The cream contains butter 4.5, cheese  3.5, petit-
lait 92.0.
  It has been long observed, that the  quantity and nature of the
milk changes with the quantity and nature of the aliments; this
has given rise to the singular opinion, that the lymphatics were the
vessels destined to carry to  the  mammse, the materials  of their
secretion.  But it  is the  same with the milk,  as  it is with the
urine, the properties of which  vary with the solid or fluid substan-
ces introduced into the stomach.   For example, the milk is more
abundant,  thicker and  less acid, if the woman is  nourished with
animal substances;  it is less abundant, thinner, and more acid, if
the diet be vegetable.  The milk also assumes particular qualities,
if the woman has taken medicinal substances,  it becomes purga-
tive, for example, when rhuoarb, jalap, &c.  have been used.  The
secretion of milk is prolonged  until the organs of mastication shall
become sufficiently  developed to prepare  the aliment for diges-
tion;  it does not  cease until the course of  the second  year;
although the  secretion of milk  seems peculiar to parturient fe-
males, it has  sometimes been observed in young virgins, and even
men.*

                          Of Sleep.
  In terminating the history of the functions of relation, we re-
marked, that these  functions were periodically  suspended, and
we are now  about  to examine this phenomenon.   After having
been awake for sixteen or eighteen hours, we experience a general
  * I have not thought proper to introduce into this work, a particufar description
of the different  ages, sexes,  temperaments, zoological character of man, &c.
These considerations properly belong to hygiene and natural  history.  See the
article Hygiene, in the Encyclopedic Methodique,  and the new work of M. Cu>
vier, oo the Animal Kingdom. 
412
A  SUMMARY
sensation of fatigue and  weakness.  Our motions become more
difficult, our  senses lose  their activity, and  the understanding
itself becomes  disturbed, perceiving sensations  imperfectly, and
commanding the  contract.ons of  the  muscles  with difficulty.
From these signs we perceive the necessity of giving ourselves up
to sleep; we choose a position that requires no effort to preserve
it, we seek darkness and  silence, and then abandon ourselves to
repose.
   In sleep, we lose successively the use of our senses;  vision is
prevented  by the eye-lids being brought  together; smell ceases
after taste, hearing after smell, and touch after hearing;  the mus-
cles of the extremities become relaxed, and  cease to act before
those of the head and  spine.   In proportion as these phenomena
take  place,  respiration becomes  slower and  more profound;  the
circulation is retarded,  more  blood is  carried to  the  head,  the
animal heat is diminished, and the secretions less abundant. How-
ever, when man is plunged into this state, he does not lose a sense
of his existence, he is still conscious of many of the changes which
take  place  around  him, which  is not without its charms; ideas,
more or  less  incoherent, succeed.  At  last he  entirely ceas-
es to be  conscious of  his existence,  he is then  asleep.   During
sleep, the circulation, respiration, and the  different secretions, re-
main slower,  of  consequence digestion  is  effected with less
promptitude.   I  do not know* on  what plausible ground  many au-
thors have asserted that absorption alone acquires new energy. As
the nutritive functions continue in  sleep, it  is evident, that the
brain only ceases to act as the organ of intelligence and muscular
contraction, but that it continues to influence the muscles of res-
piration, the heart, the arteries, the secretions, and nutrition.
   Profound sleep exists, when it is  necessary to  employ strong
excitants to remove it; it is  light, when it ceases easily.  Com-
plete sleep is such as  I have described, i. e. it is the result of the
suspension of the action of the organs  of  relation, and of the di-
minished action of the nutritive functions.  But it is not rare that
many of the organs of relation preserve their activity during sleep,
as when we sleep standing.   It is frequent also, that one or more
of the senses remain awake,  and  transmit to the brain impressions
 which they receive; it is still more common  for the brain to take
 cognizance ot the different internal sensations  which are developed 
GP PHYSIOLOGY.
41$
during sleep, such  as  wants, desires, grief, &c.   The under-
standing may exert itself during sleep, either in an irregular and
incoherent manner, or regularly aiid logically, as we meet with in
some individuals.
  The direction that the ideas take in sleep, or the nature of the
dreams, depend very much on the state of the  organs.  If the
stomach  be overcharged with  undigested aliment, or if  the respi-
ration be difficult, from the  position or other causes, the dreams
will  be disagreeable and fatiguing.  A sensation of hunger will
caese us to dream of agreeable repasts, &c.  The habitual occu-
py turn of the mind will not have  a  'ess influence upon the train
of our ideas; the ambitious dream of success or disgrace, the poet
makes verses,  and the lover sees  his mistress.   It is because the
ji'(!«.':irent  exerts  itself in  its full strength  during our dreams,
relatively to  future  events, that this has been  imputed  to divina-
tion  by the superstitious.
  There is nothing more  curious  in the study of sleep than the
state  of  somnambulists.   These individuals first sleep  pro-
foundly, they then  rise up suddenly, dress themselves, under-
stand, see, speak,  use their hands with address,  give themselves
up to different exercises, write, compose, and  return to bed, and
on awakening the  next day, preserve no recollection of  any  thing
that  has  happened.   V\ hat difference is there, then,  between a
somnambulist of this kind, and a man awake?  There is only one
evident difference;  the last  is conscious of his  existence, and
the other is without it.  We  shall not, with some authors, seek
after the proximate cause  of sleep, and find it  in  a weakening of
certain parts of the cerebellum, the  afflux  of the  blood to the
brain, &c.  Sleep  being an immediate effect of  the laws  of organi-
zation, cannot  depend  on any physical cause  of this kind.  Its
regular return  is  one  of those circumstances which contribute
most to the preservation of the health;  when  it  is long prevent-
ed, it is often followed by serious inconveniences; and in no case
can be carried beyond certain  limits.                          «
  The ordinary duration of sleep is variable, in general  it is from
six to eight hours; fatigue of the muscular system, great agitation
of mind, numerous vivid sensations, indolent habits, the immode-
rate  use of wine and substantial food have a tendency to prolong
it.   In infancy and youth, the functions of relation being very 
414                 OP PHYSIOLOGY.
 active, more rest is required. Mature age, more avaricious of time,
 and surrounded by cares, requires much less. In old age, the two
 opposite extremes generally exist, either almost continual somno-
 lency, or but very little disposition to sleep.  By a quiet uninter-
 rupted sleep, and restrained within due limits, the  powers of  the
 body are restored, and the  organs resume their aptitude to  act
 with  facility.  But if disagreeable  dreams, or painful impressions
 disturb our sleep, or simply if they are prolonged beyond a suita-
 ble limit, so far from restoring, it  diminishes the forces, fatigues
 the organs, and becomes often a cause of serious diseases.

                           Of Death.
   The  individual existence of all organised bodies  is temporary;
 none escape the hard necessity of  ceasing to be, or dying;  nor is
 man exempt from this.  The particular history of each function
 shows, that in  the first  periods of  old age, and  often before, the
 organs become deteriorated, that many completely cease to act;
 that others are absorbed  and  disappear;  and lastly, that  in de-
 crepitude, life is Reduced  to a few miserable remnants of the vital
 functions,  and some of the nutritive functions in  an imperfect
 state.   In this condition the  most  trifling external  cause, the
slightest blow  or fall,  is  sufficient  to arrest one  of the  func-
tions indispensable to life, when death immediately follows, as the
last degree in  the destruction of the organs and functions.  But
a small number of persons die  solely through the effects of age;
it scarcely happens  to  one  in  a million; the remainder  die  at
every period of life, by accidents  and diseases;  and this  great
destruction  of human life, by causes apparently accidental, ap-
pears to be provided for by nature, with  as much care, as she
 takes to insure the reproduction of the species.
THE EN©. 
AfflHBSniMtS*
                          No. I.

    1 he following experiment of Dr. Wilson Philip, made under
circumstances which seem scarcely to allow of error, shew that
there is nothing very preposterous in  admitting  "that electricity
may exert a  considerable influence in the  sensations,  and  other
functions."
  "Having at the  request of Dr. W. Philip, divided the eighth
pair of nerves in the neck of two small dogs, which were allowed
to eat  as  much  lean  raw mutton, cut into small pieces, as they
chose, immediately before the experiment, after having fasted for
many hours, I subjected  one  of them to the galvanic influence,
by coating the lower parts of  the divided nerves with tinfoil, and
connecting it with one end of the galvanic trough; while the other
end of the trough was connected with the region of  the stomach,
which before the experiment,  had been shaved, and a three shilling
piece bound upon  it.  The power of the  galvanism was such as to
occasion a twitching  of  the fore limbs during the whole experi-
ment.   The  dog  which  was not  galvanised,  was  immediately
seized  with  dyspnoea, and efforts to vomit.  In the other, neither
was observed in the slightest  degree, at  any period of the experi-
ment, except when for a few  seconds the galvanic influence was
intentionally discontinued, during which  the  breathing became
very laborious, again becoming free as soon  as the galvanism was
restored.  This dog lived about two hours.  The other dog was
still alive, though extremely weak,  at the  end  of four hours, at
which time it was  killed by a  blow  on the head. 
416
APPENDIX.
   "On examining the stomach of the galvanised dog, fhe mnftoi
 was found in a soft, half-dissolved state, all  character of muscular
 fibre having disappeared.  The lungs, on examination, were  found
 perfectly  healthy, but  rather  of a florid colour.  In the stomach
 of the other dog the bits of mutton  still retained their firmness,
 and on being cut into, displayed both  the  red colour and  fibrous
 appearance  of the  muscle, which did not seem to be at all dimin-
 ished.   The lungs were found greatly congested, and collapsed
 very imperfectly, the surface being covered with patches of a dark
 red colour.
   "'the above experiment was made in presence of the house sur-
 geon and  pupils of the infirmary, who all  examined the state of
 the stomach and  lunjts, and expressed  themselves satisfied with
 the result.   The accuracy of the above statement I am ready.to
 attest in any way  in which 1 may be required to do it.
         (Signed)                JAMES P. SHEPPARD."
   "Worcester, Feb. 7th, 1820."


                           No.  II.
   The  author of the Summary,  &c. has not entered  into a con-
 sideration of the physiology of the  brain very fully, but has de-
ferred to some future opportunity, his observations on this  point.
 There is one department of it which has excited considerable in-
 terest among, scientific  men, which  he has scarcely touched;  I
 allude to Dr. Gall's System of Craniology.   To have entered fully
into the consideration of this subject, involved, as it is, with much
that is visionary and fanciful, would  not have comported with the
 spirit of this book.  But as there is much in this system which is
 curious  and  worthy of attention, and  as  I do not know of any
 source, generally accessible in  this country, where a knowledge of
it may  be acquirer!, I have thought that this  work, which  is de-
 s  ne'l  for  the  American  medical  student,  would be rendered
 more complete  by appending to it a brief  abstract of these doc-
 trines, and  the facts and reasonings on which they are founded.
  Although from  the very constitution of man, one of the first
 reflections   he  must' make,   when  contemplating  himself,  it
 the remarkable relation which exists between  his brain anil the
 operations of his intellect; yet the attempt to trace a connexion 
APPENDIX.
417
between the volume and form of this organ, and the character of
the individual, and to reduce  it to a science, is of  quite modern
date.  The first elaborate essay on this subject, was made by Dau-
benton. in  a memoir  on the situation of the foramen magnum of
the occipital bone, in man and animals, read before the French
academy,  in 176S.  About thirty years afterwards, the subject
was taken up by Camper,  who endeavoured to lay down rules by
which we might judge of the nation and intellect of the individual,
from the mechanual form  of the cranium, measured in certain di-
rections.   For this purpose, he collected together a great number
of skulls from different countries, and having compared them, at
length proposed as a rule  for solving this problem, what he called
the facial angle.  This is formed by the two following lines,  viz.
one passing from the  anterior part of the alveolar margin of the
upper jaw, to the most prominent part of the forehead, above the
nose, and  the other  from the  first mentioned point, through the
meatus auditonusexternus.  It will be seen from this, that as the
forehead becomes full and prominent, that the angle formed by
these lines increases, and  on the contrary, that when the forehead
is retreating, and the  bones of  the face prominent, this angle  will
diminish.   As  the facial  angle is  increased,  the sublimity  and
beauty of the outline of the human head increases, until it reaches
100°, but if the  angle be  increased beyond this, it produces de-
formity;  on the contrary,  as the angle diminishes, the outline ap-
proaches that of the brute. It has been found  by extensive obser-
vation, that the facial angle  in man, actually ranges from 70° to
80°.  It is about 70 in the Carib  and Negro, and  about  bO in the
European.  It would seem, from  experience, that the facial angle
of Camper indicates, with considerable fidelity, the capacity of
the cranium,  and  the  intellectual* character of the individual.
But it is not without objections;  one of the most obvious is, that,
as it refers to the dimensions of the cranium in one direction only,
it must shew its capacity but imperfectly.
   The system of Doctors Gall and ^purzeim goes much farther;
it professes not only to point out, generally, the intellectual cha-
racter of the individual, but to determine with precision, the dis-
position and propensities of the person, from the form of the  cra-
nium, and  certain prominences about it.  Instead of dissecting
the brain, like  other anatomists, with a sharp instrument,  and
                              5S 
418
APPENDIX.
shewing its structure by successive sections, beginning at the top
of the cerebrum and proceeding downwards, they employ a blunt
instrument,  beginning at  the  base  and proceeding upwards,  by
which they are enabled to follow, with more accuracy, the natural
arrangement  and texture of the organ.  From this  mode of dis-
seciion, they  are led to infer,  that the brain is  not  homogeneous,
as some have supposed, but demonstratively fibrous. Among the
peculiar opinions arising from  this mode of dissection, is the doc-
trine, that the encephalon is not a mere pulpy mass, but a mem-
brane;  in this way they account for the intelligence frequently ob-
served in  hydrocephalic patients, even when there is an apparent
disorganisation of the brain.
   "It may be proved by anatomy,"  say they, 'that the  fibres of
the brain  are directed vertically,  or perpendicularly  upwards,
from the cerebral cavities; and that every convolution consists of
two layers, applied  vertically, one to  another, and separable from
each other.   If,  therefore, a great quantity of water be accumula-
ted in the cerebral cavities, and act against the convolutions placed
around these cavities, it gradually separates the two layers whose
natural position is vertical, till at last their situation is horizontal.
In this manner, in large hydrocephalic skulls, the convolutions are
entirely unfolded, and  present a smooth surface and membranous
expansion.
   "Thus the cerebrum is made up of  thin convolutions of medul-
lary and cortical substance, surrounding the two lateral ventricles,
which are unfolded when the  cavities of those two ventricles are
enlarged,  and in this unfolded state, the functions of this part of
the organ  can be carried  on."
   With these and some other  peculiar views, as to the anatomical
structure  of  the brain, they endeavour to prove, first, that it is
"the seat  ot the soul," the "organ of the feelings and intellectual
faculties," though this is denied by some, and even by the high and
modern authority  of Bichat.   Taking it then as an established
point, that the brain is the seat of thought, they endeavour to shew
that it is  not a single organ,  but is composed "of as many single
organs as there are particular and independent manifestations of
mind."   They contend,  that  when  these  different parts of the
brain, or, as they call therm, organs, become developed in a remark-
able degree, that this is manifested not only in the intellectual char- 
APPENDIX.
419
 acter of the individual, but likewise in the increased prominence
 of  that  particular  part of the cranium.  By very  careful and
 extensive observation, they conceive it practicable to  determine
 with considerable precision, the relative position of these different
 organs, and that in tact they have already  ascertained this.  They
 have accordingly divided the cranium into thirty-three  parts, and
 have given a  name to each, indicative of  the peculiar  quality of
 mind manifested in those individuals in whom this particular part
 or organ has been observed to be remarkably developed.
  Our limits will not permit our giving more than this very brief
 and imperfect outline of the system of craniology, of Drs. Gall and
 Spurzeim.  Indeed, after more deliberately perusing the cautions
 of the author of the "Summary," on the dangerous tendency of in-
 dulging a spirit of speculation in  physiological inquiries, I have
 almost regretted  our having at all entered  upon the subject.
  It cannot be denied that there is something extravagant and in-
 credible in the first  aspect of this system, yet it is equally  true,
 that these gentlemen have investigated the subject with singular
industry,  and  have collected  together a great number ot curious
 and  remarkable  facts, to  illustrate and prove the truth of their
 doctrines. It will also be confessed, that their researches have
given rise to some original views of the anatomical  structure of
 the brain, which  explain,  plausibly enough, some surprising cir-
 cumstances in the pathology  of  this organ.  Lastly, I will  ob-
 serve, that the doctrines are elaborately illustrated  from morbid
 phenomena, dissections of the brains of ideots, known experiments
 on living  animals, natural history, and comparative anatomy.*
                                                    [Trans,

                           No.  III.
  The classifications of the functions by Magendie, is essentially
the  same  as that of Bichat.  By the first they are  divided into
those of relation, nutrition, and generation; by the last into the
functions  of animal and organic  life, and generation.  In  fact,
they differ only in name.   There  are certain  remarkable distinc-
 tive characters, possessed by the two first classes of  functions,
 or modes of life, which are  much insisted upon  by Bichat, but
 are scarcely noticed  by Magendie.   They appear to  me  to be
* Vide Physiognomical System of Drs. Gall and Spurzeim. 
420
APPENDIX.
curious, and well worthy of a place in an  elementary treatise on
physiology.   After having enumerated these two classes of or-
gans, I will state, very concisely, some of these differences.
  The organs of animal life  are,  1st  those  of locomotion, and
2d. those of the voice; the two modes by  which animals commu-
nicate voluntarily  with surrounding objects.   3d. The external
senses, which  receive external  impressions.   4th. Internal sen-
sations, which perceive, reflect, and combine them, and in conse-
quence  form  volitions.  5th. The organs  for  the transmission of
sensation and motion, which establish the communication between
the external  senses  which receive, and the internal, which per-
ceive impressions; between those  which  form  volitions, and the
vocal and locomotive organs which execute them.
  The organs of  organic  life are, 1st. Those of digestion.  2d.
Those of respiration,  which  receive from the  air certain  prin-
ciples necessary to  the blood, to enable it to nourish the organs,
and reject others.   3d.  Those of the circulation which carry to
all  the organs nutritive substances.  4th. Those of absorption.
5th. Those of secretion.*
  The most  remarkable circumstances which distinguish the or-
gans of animal, from those of organic life are, the symmetry of the
one, and the irregularity of the other. The organs of animal life, are
very equally divided into pairs,  between  which the  most perfect
symmetry and resemblance prevail.   The body is, in this respect,
divided  into two parts, with mathematical precision, the line of
demarkation being indicated at various points,  viz. the fissure be-
neath the nose, the  chin, the  raphe of the perineum, &c.  The
brain is divided in a similar manner, and  the nerves passing out
from it to the agents of locomotion and  voice, the organs of ani-
mal life  are  also  arranged in  symmetrical pairs,  with  the  most
perfect regularity.   But the reverse  of all this is found  to exist
in the organs of organic life.  The heart and arteries, the organs of
respiration, the digestive viscera, absorbents, &c. are all  irregu-
larly disposed; and, unlike the organs of  animal life, this irregu-
larity in the arrangement of one side, never  affects the functions
of  the other.  The sources from which the nerves, distributed to
these two classes of organs, are derived, is a circumstance worthy
* Vide Anatomie'Descriptive, par Bichat. 
APPENDIX.
421
of notice.  "It is well known, that the animal functions, sensa-
tion, locomotion, and voice, are under the direction of the cere-
bral nerves; on the contrary, that most of the organs of organic
life receive their nerves, and, with them, their principle of action,
from the ganglions."  (Great sympathetic.)*
  The necessary consequence of the symmetrical arrangement of
the organs of animal life, is, that, as  they are alike in structure,
they must resemble each other  in their mode of action, and if one
be stronger than the other, the function will be imperfect.   If one
eye be stronger than the  other, vision is imperfect, &c. &c  But
the reverse is the case in the organs of organic life; if one kidney
be stronger than the  other, or one lung more vigorous  than its fel-
low, no derangement is produced in the exercise of the respective
functions  of these organs   Hence  it  often happens, that there
are great irregularities in structure, and defects in the conforma-
tion of the organs of organic life, without any disturbance in the
functions.
   There is another  remarkable difference in these two functions,
to which we would   more particularly call  the attention of the
reader.  It is the periodical intermissions necessary in the  animal
organs, and their  uninterrupted continuance in those of organic
life.  The first class are capable of acting  for a certain length
of  time, after  which their power becomes  exhausted, and  they
must then remain, for a considerable  period, in a state  of repose.
All the  senses, after having been long active, become unfit to re-
ceive new impressions, until they are refreshed by rest; the  same
remark  applies to the imagination, perception, and other faculties
of the mind.  All the  muscles of voluntary motion, require pe-
riods of relaxation and repose; hence the necessary intermissions
of locomotion and  voice.  The same  remark applies to all the
functions  of  relation.   But on the other hand, the  organs  of or-
ganic life continue  their unwearied  action,  from  their first  deve-
 lopement, until death takes place.   There are  moments,  when
 their powers languish from disease, but they never entirely  cease
 but with life.   The heart  and arteries continue to pulsate, the
 lungs to play, the abdominal viscera  to secrete, and  the  lympha-
 tics to absorb, until  death interrupts their functions.
                                                     f_Trans.
              * See  Bichat's Researches on Life and Death 
 
iw®as;»
Definition of Physiology,           -        -  t
Preliminary Observations,      -
Substances and their Divisions
Differences between dead and living Bodies,
Differences between Vegetables and Animals,
Elements which enter into the Composition of Animal
    Substances,      -
Immediate Materials of Animals,
Organic Elements,   -
Organic Solids,           -
Properties of  Tissues,         •
Of the Fluids or Humours,
Causes of the Phenomena peculiar to living Bodies,
Vital Properties,     -
Phenomena of Life in the Fluids,
Functions of  Relation,
Of Sensations,
Of Vision,  -
Apparatus of Vision,
Eye-brow6,          -
 Eye-lids,       -
 Glands of Meibomius,         -
 Apparatus for the Tears,    -
 Caruncula lachrymalis,                  *
 Puncta lachrymalia,       -
 Lachrymal Ducts,    - 
424
INDEX.
Lachrymal Sac, and Nasal Duct,
Membrana Conjunctiva,
Secretion of the Tears, and their Uses,
Globe of the Eye.
Crystalline Humour,
Optic Nerve,
Mechanism of Vision,
Uses of the Cornea,
Uses of the Aqueous Humour,
Uses of the Crystalline Humour,
Uses of the Vitreous Humour,
Motion of the Iris,
Uses of the Choroid Coat,
Uses of the Ciliary  Processes,
Action of the Retina,
Action of the Optic Nerve,
Action of both Eyes,
On estimating the Distance of Objects,
On estimating the Size of Bodies,
On estimating the Motion of Bodies,
Optical  Illusions,
Vision at different Periods of Life,
Of Hearing,     -
Apparatus of Hearing,
Meatus auditorius externus,
Internal ear or labyrinth,
Cochlea,   -
Semicircular canals,
Vestibule,
Auditory  Nerve,
Mechanism of Hearing,
Uses of the External Ear,
Uses of the Tympanum,
Uses of the Internal Ear,
Action of the Auditory  Nerve,
Action of both Ears,
Modification of Hearing by Age,
Sense of Smelling,
Apparatus of Smelling, 
INDEX.
425
Pituitary Membrane,     -        -        -         -     72
Olfactory Nerve,     .        -        ..        -         73
Mechanism of Smelling,  -        -        -         -     ib.
Modification of Smell by Age,          -        -         75
On the Sense of Taste,   -        -        -         -     76
Apparatus of Taste,          -         -        -         7?
Mechanism of Taste,     -        -        -         -     ib.
Modification of Taste by Age,           -        -         79
Of 'Touch,     -         -         -         -         -     80
Physical Properties of Bodies, which are the objects of
     this Sense        -         -         -         -         ib.
Dermis,       -         -         -         -         -     81
Epidermis,          -         -         -         -         ib.
Rete Mucosum,          -         -         -         -     ib.
Mechanism of Feeling,         ...         82
Mechanism of  Touch,    -         -        -        -85'
Modifications of Feeling and Touch by Age,       -         84
Of Internal Sensations,            -        -        l    85
Of a supposed Sixth Sense,     .         .         -         86
Of Sensations in general,          -        -        -    87
Nerves,   -----        ib.
Cerebral Extremity,      -         -        -        -    88
Organic Extremity,                    -        -        ib.
Of the Mechanism of Sensations,    -        -        -    89
 Appendix, No. 1,              -        -        -        90
 Of the  Functions of the Brain,      -        -        -    94
 Brain,      -----        ib.
 Hair,          -        -        -        -        "    95
 Cranium,            -            ,     -        -        m'
 Dura Mater,    -        -        -                 -    96
 Medulla Spinalis,    -        -        -        -        97
 Arachnoides,   -                                         •"•
 Pia Mater,          -                  -        -        ib.
 Observations on the Brain of Man and Animals,        -    101
 Intelligence,         -
 Sensibility,     -
 Memory,            -
 Judgment,     -        -        -        -        -   105
 Desire or  Will,       -        -                 -        lo6
                             54
103
104 
426
INDEX.
Instinct,       -         -        -         -         -   107
Passions,   -----        109
Of Motion,     -        -         -         -         -   110
Muscular Contraction,          -         -        -       111
Apparatus of Muscular Contraction,          -         -    ib.
Musi les,                                                ib.
Phenomena of Muscular Contraction,         -         -   112
Intensity of Muscular Contraction,       -        -       113
Duration of Muscular Contraction,           -         -   114
Rapidity of Muscular Contraction,       -         -        ib.
Extent of Muscular Contraction,   -         -         -   ib.
Modification  of Muscular Contraction by Age,     -       115
Of the Voice,  -         -         -         -        -   116
Reeded Instruments,          -         -        -       117
Apparatus of the Voice,   -         -         -             118
Larynx,   -         -         -         -        -       If 9
Cartilages of the Larynx,          -         -         -    ib.
Muscles of the Larynx,        ...       120
Mucous Membrane of the Larynx,  -         -         -    ib.
Vessels and Nerves of the Larynx,      -        -        121
Glottis,        -         -         -         _         -    ib
Ligaments of the Glottis,       -         -        -        ib.
Mechanism of the  production of the Voice,    -         -   122
Intensity of  the Voice,         -                          124
Tones of the Voice,       -                               125
Notes of  the Voice,            **         -        -        ib.
Of the  Natural Voice,     -         -         -         -   130
Of Acquired  Voice,            -          -         -       131
Of Singing,     -         -        -        -         -   134
Of the Art of Ventriloquism,   -                          155
Modification of the Voice by Age,  -                     136
Relations between Hearing and Voice,     •         -       139
Sounds independent of the Vpice,   -                      141
Attitudes and Movements,     -         -        -        ib.
 Mechanical Principles necessary  to understand the move-
     ments and attitudes of the Body,        -         -    jD,
 Levers,    -        -        .         .         .        142
Moving Power,          -                               143
 Bones,    -                                    *        J44 
INDEX.
Form of the Bones,
Articulations,            -
Attitudes of Man,   •-
Standing upon One Foot,
Kneeling,          ...
Attitude of Sitting,
Recumbent  Posture,
Motions,      -
Partial,   -
Motions of thp Trunk,
Motions of the Superior Extremities,
Motions of the Inferior Extremities,
Loromotion,       -
Leaping,       -         -        -         -
Running,          -
Swimming,   -
Attitudes and Motions in Different Ages,
Relations of Sensations to the Attitudes and Motions,
Relations of the Attitudes and Motions to the Will,
Relations of the Attitudes and Motions to  Instinct and
     the Passions,       -
Relations of the Motions to the Voice,  -
End of the First Volume,          -
Functions of Nutrition,       -
Digestion,     -
Aliments and Drinks,         -
 Apparatus of Digestion,           -
 Structure of the Digestive Canal,
 Remarks on  the  Digestive Organs of Man and Living
     Animals,           -
 Hunger and Thirst,          -
 Of  Hunger,   -        -         -         -        -
 Of  Thirst,         -
 Of the Particular  Acts of Digestion,
 Of the Prehension of Solid Aliments,
 Of the Mechanism of the Prehension of Aliments,
 Mastication and Mixture of the Saliva with the Aliments,
 Mechanism of Mastication,        -
 Admixture of the Aliments,   -
145
ib.
146
152
ib.
153
154
ib.
ib.
156
157
159
ib.
162
165
ib.
166
169
172

173
 ib.
174
175
 ib.
 ib.
177
178

180
186
 ib.
 190
191
192
 193
 195
 199
200 
4S8
INDEX.
Deglutition of Aliments,          -         -         -    201
Mechanism of  Deglutition,    -                           204
Of the Abdomen,        .        -         -              208
Action of the Stomach upon the Aliments,        -        210
Of the Stomach,         -        -         -         -    ib.
Accumulation of Aliments in the stomach,        -        212
Alteration of the Aliments in the Stomach,   -         -    215
Action of the Small  Intestines,         -        -        223
Passage of the Chyme into the Small  Intestines,       -    224
Change which the Chyme undergoes in the small Intestines,  226
Action of the Large Intestines,         -        -        229
Passage of the Fecal Matter into the Large Intestines,  -    ib.
Changes of the Fecal Matter in the Large intestines,       230
Expulsion of the Fecal Matter,    -         -         -    25S
Of the Digestion of Drinks,   -         -        -        235
Prehension of Drinks,   -        -         -         -    ib.
Deglutition of Drinks,        -                           236
Of the Accumulation of Drinks in the Stomach, and the
    time they remain there,       -                       237
Alteration of Dnnk> in the Stomach,     -         -        238
Action of the Small Intestines upon  Drinks,           -    240
Remarks upon the Deglutition of Atmospheric  Air,         241
Remarks on Regurgitation, Eructation, and  Vomiting, &c.    242
Modification of Digestion by  Age,       -         -        245
Connexion of Digestion with the Functions of Relation,     250
Course of the Chyle,     -        -        -         -    252
Of the Chyle,       -                                    ib.
Of the Apparatus of Absorption, and the Course of the
    Chyle,    -         -        -         -         -    254
Absorption of the Chyle,      -                           256
Course of the Chyle,    -        -         -         -    257
Absorption of the  Lymph,    ...        260
Of the Lymph,          -        -         -          -     ib.
Apparatus of Absorption, and Course of the Lymph,        262
Of the Absorption of the Lymph,  -                      263
Course of the Lymph,         ...        275
Course of the Blood in the Veins,           -         -    277
Of the Venous Blood,        ...        278
Apparatus of the Venous Blood,   -                      282 
                           INDEX.                      429
Of the Veins,            -         -        .         .     282
Of the Right Cavities of the Heart,      -         -         285
Pulmonary Artery,      -                                 286
Course of the Venous Blood,  -                            287
Absorption exerted by the Veins,  -                       291
Passage of the Venous Blood through the Cavities of the
     right side of the Heart,       -                       299
Passage of the Venous Blood through the Pulmonary Artery,  SOS
Of Respiration,     -                                     309
Of the Lungs,           -        -         -        -     ib.
Of the Air,                                               316
Inspiration and Expiration,        -        -         -     318
Physical and Chemical changes that the Air undergoes
     in the Lungs,   -                                     321
Change of the Venous into Arterial Blood,    -         -     322
Respiration  of various kinds of Gas,     -         -         326
Influence of the Nerves of the eighth pair upon Respiration,    327
Of Artificial Respiration,          -                       330
Course of the Arterial Blood,  -                            331
Of the Arterial Blood,  -         -        -        -     ib.
Apparatus of the Arterial Blood,        -         -         332
Pulmonary Veins,       -        -         -         -     ib.
Left Cavities of the Heart,    -                            ib.
Of the Arteries,          -                                 333
Course of the Arterial Blood in the Pulmonary Veins,        ib.
Absorption of the Pulmonary Veins,         -        -     336
Passage of the Arterial Blood through the Cavities of the
     Heart,         -                   -                   ib.
Course of the Blood in the Aorta and its Divisions,     -     337
Passage of the Arterial Blood into the  Veins,     -         341
Remarks on the Motions of the Heart,        -         -     343
Remarks on the  Circulation  of the Blood,         -         S46
Transfusion of Blood, and Infusion of Medicinal Agents,     350
Of Secretions,       ...         -         352
Internal Exhalations,     •                                 S53
Serous Exhalations,   -                                   ib.
Serous Exhalation of the Cellular Tissue,    -        -     354
Adipose Exhalation of the Cellular Tissue,        -         ib.
Synovial Exhalation,    -         -        -        -     3 
430
INDEX.
Exhalation in the Interior of the Eye,        - '        -    356
Sanguineous Exhalations,     -                            ib.
External Exhalations,             -                      357
Exhalation of the Mucous Membranes,   -        -         ib.
Cutaneous Transpiration,         -                      358
Mucous Follicular Secretions,           -        -        361
Cutaneous Follicular Secretions,   -        -         -     ib.
Glandular Secretions,        -                          362
Secretion of Tears,      -         -        -         -     ib.
Secretion of Saliva,           ...        363
Secretion of the Pancreatic Juice,                     -    364
Secretion of the Bile,         ...        365
Secretion of the Urine,   -                               366
Excretion of the Urine,       -                          369
Of Nutrition,           -        -        -         -    372
Of Animal  Heat,                                        378
Of Generation,          -        -        -             383
Apparatus of Generation,     -                           ib.
Organs of Generation in Man,      -        -         -     ib.
Female Organs of Generation,          -        -        387
Of Menstruation,        ...         -    389
Copulation and Fecundation,            -        -        390
Of Gestation or  Pregnancy,        ...    393
Action of the Fallopian Tubes,          -        -        394
Alteration of the Uterus in Gestation,       -         -    395
General Phenomena of Pregnancy,      -        -        396
Developement of the Ovum in the Uterus,    -         -    397
Functions of the Ovum and Fcetus,      -        -        399
Of Parturition,          -        -        .         .    408
Of Lactation,       -         -^J^L'S^fJS..   -        410
Of Sleep,     -         ->*>~:     ^TA       .    411
Of Death,          -    V-<"_        ' 1  J  -        414
Appendix, No. 1,      ' -  I       .    ^ifvf        "    4l5
         N„. 2,    -    vciBgNprA.   -        416
         No. 3,        -      *  .-—^ ■  „Y       .    419