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PHYSIOLOGICAL  ESSAY
OX
DIGESTION,
                   J
                 {
             L SMITH, M. D.
BY NATHAN R.
FROFE SSOR OP ANATOMY AND PHYSIOLOGY, IN  THE  UNIVERSITY

                      OP VERMONT.
  It is no small part of Science to be well acquainted with its real boundaries
but it is necessary also to know what it is which truly exists within these boun^i
ries, and what it is which is only fabled to exist.
                        Preface to Brown on Cause and Effect,
                 NEWARK :
PUBLISHED BV F. BLISS, AND E. WHITE, NO. 123. BROADWAY.
1825. 
Dodd and Manter, Printers, No. 1 Thames Stree 
    TO those whose talents and candour elevate
them above the local and personal partialities and
prejudices, which characterise too many  of our
profession, this Essay is respectfully inscribed, by
one who relies only upon  their unbiassed judg-
ment, and whatever merits the work may contain.
                         THE AUTHOR. 
 
PREFACE
  I WILL not,  in the cant language of authors,
enumerate the embarrassments under which this
small work has been prepared for -the press.   It
would not, however,  have been, at this time, sub-
mitted to the public but by the advice of intelli-
gent friends.
  The  reader will discover that I  am  far from
being orthodox in my opinions, but as there is no-
thing revealed on the subject of Physiology, I trust
that I shall not be denounced as a heretic in me-
dicine ; certainly not, till this Essay has received
a fair and candid examination.
  I  flatter myself that I shall at least call the at-
tention to some  important  defects in the present
mode of reasoning on these subjects.  That I have
a higher object in  view, however, in  presenting
the following pages, I will not deny.
                                    \. R. £ 
 
INTRODUCTION.
  IT is a common remark of those who compare
the Physical and the Physiological Sciences, that
while the former are rapidly rising upon the sure
foundation of correct reasoning, and receiving
additions, which must be co-existent  with  truth
itself, the latter on the other hand, from time to
time, exhibit the downfall of beautiful superstruc-
tures, which  had  been erected upon fallacious
principles.
  The  circumstances which render the progress
of Physiology so uncertain, appear  to  me to be
the  following: 1st, A disregard to the marked
distinction which exists between these sciences;
and 2d, The not determining with sufficient accu-
racy the real boundaries of the latter.
  The  employment of bare hypothesis, in place
of fact, has indeed  been for the most part aban-
doned, and physiologists now uniformly endeavour
to pursue the inductive method,  and to furnish
themselves by observation or  experiment, with
less  perishable data.   It is too often  the  case,
however,  that the  very first  inference drawn
from these facts   is  fallacious, and that,  from 
8
not regarding the essential difference between the
causes or properties, which  produce the effects
or phenomena of one science,  and those which
operate in another.
  When we confine our inquiries to any particular
science, with the laws of which we are acquainted,
and reason from an effect to  a cause, which in its
operations  we know to be  controlled  by  those
laws, there need be no fallacy.  But if we  enter
another field of science, the laws of which we
have not  investigated, and reason from an  effect
to a cause, we shall almost certainly fall  into an
error, for we unconsciously attribute the effect to
a cause with the operations of which we are fami-
liar.   Thus, if  we combine two  inorganic sub-
stances, and after a time, observe  that a remark-
able change has taken place in their properties,
we at once, and with propriety,  attribute it to the
influence of chemical affinities;  for we know that
such substances are exclusively  under the control
of physical properties.  But  if we convey certain
substances into the  stomach  of  an animal,  a
polypus for instance, and upon removing them
after a considerable time, discover that they have
become very much changed, having received new
chemical and sensible properties, it is altogether
unwarrrantable to infer that these changes are
wholly the effect of chemical  influence; for,  as
the stomach of  this and of every other animal  is 
y
indued  with  certain  vital' properties, and as wt
are not yet fully acquainted with their laws or
uniform habits of action, we can not say how much,
in this  instance, is to be attributed  to their in-
fluence.
  That similar effects,  then, in any particular
science are referrible to  the same cause, is gene-
rally true; but that similar effects in two  distinct
sciences,  the cause  being known  in  one, are
referrible to the same cause, is, in principle, false.
  The  other circumstance mentioned  as  having
retarded  the  progress of physiology, is the not
determining, with sufficient accuracy, the limits of
our inquiries.
   In physics,  philosophers have long ago aban-
doned the pursuit of final causes, and have  con-
tented  themselves with  observing and  recording
the uniform laws by which the properties of matter
are  exerted.    In   the  physiological  sciences,
although  it may have been done in principle, it
has rarely been done in practice.
  Undoubtedly, there is in the first attempts which
are made in any science, much difficulty in ascer-
taining what are the proper objects of our inquiry,
and what are beyond the reach of human intellect.
In  the  present improved  state, however, of the
moral and physical sciences, there need be much
less difficulty  than formerly.  The moral sciences
have made us acquainted with the powers of our 
10
minds, and, in some measure, enabled  us to dis-
tinguish the proper objects of their exercise.   The
physical sciences,  although,  as  already stated,
they have,  from our not observing natural distinc-
tions, been eminently prejudicial  to physiological
science, have nevertheless, disciplined our minds
to the true inductive mode of reasoning, and taught
us to distinguish, in those sciences, the attainable
objects.
  These two sciences in some respects, bear an
interesting  analogy  to  each  other.   In  both,
there are discovered certain properties of matter
which, variously modified and combined, produce
all the phenomena which we observe.*  In Phy-
sics, we know the essential nature of these pro-
perties to be beyond  the reach of our  faculties;
we must presume, therefore, those which corres-
pond  to them in the  physiological sciences to
be equally  so.
  How much more happily then  are we circum-
stanced, than were the  earlier physiologists, who
for the want of these simple truths, exhausted the
efforts of many great minds upon subjects  which
the author  of nature has rendered incomprehen-
sible.   For centuries  the  efforts of the human
mind have been lost;  occasionally indeed a trans-
cendant  genius  has intuitively  fallen upon an

 * This analogy probably led to the discovery of the vital property. 
11
important truth, but without being conscious of
the mental process that  led to it, and, of course,
without being able to establish any uniform prin-
ciples of reasoning, which should confirm his own
discoveries  and lead  on to others;  hence the
world  has been but  little benefitted by  those
flashes of truth, which found and  left it in dark-
ness.
   Haller has, perhaps, been the greatest benefac-
tor of physiological science, inasmuch as he was
the first who introduced  any thing like systematic
reasoning, and taught, though not perspicuously, the
distinction between the physical and vital laws, and
also pointed out the proper objects of our inquiry.
Although, in these respects, his system was by no
means complete,  yet  he accomplished so much,
that others were able to  perceive the tendency of
his principles and to continue the  work which he
had begun.   His suggestions have  led to the esta-
blishment of truths which he did not anticipate, and
Bichat and others  have  been much more explicit
on these subjects.
   We may, therefore, after the lapse of so many
centuries of fruitless exertion, consider ourselves in
the possession of the true magnet and chart which
should guide us in our physiological investiga-
tions.  With these facilities, we cannot but antici-
pate with delight the intellectual conquests, which,
in this department of science, the human mind is 
12
destined to achieve.  But error in reasoning is like
the fabled Hydra, and when one fruitful source of
it  is destroyed, another springs  up in our way.
Thus,  it is necessary,  as we advance, that we
should be perpetually on  our guard and  make
frequent application of the  tests of truth.   This
strife with error must prevail while there remains
one truth to be discovered.
   These remarks  are  sufficiently exemplified in
the writings of the physiologists of the  present
day.   Their success has  certainly  been much
less than, from the influence of the present im-
proved mode of reasoning on these subjects, we
might  have  anticipated.   Their  writings  con-
tain many plausible and  ingenious suppositions,
which,  when they are subjected to the rigid but
just ordeal, are " burnt and purged away."   They
do, indeed, begin upon the true principles of induc-
tive reasoning, but on following them a few steps,
we very often discover a sophistry, into which they
are led by a particular set of pre-conceived no-
tions, which, perhaps unconsciously, they are en-
deavouring to establish.  Anticipations in science
have  rarely  proved correct, and yet we are ex-
ceedingly prone to make them. The slow and te-
dious process  by which we arrive  at truth, as we
are conducted  by  facts, is  unsatisfactory to most
minds, and the imagination is allured by the hope of 
13
some brilliant discovery, into regions, where it can*
not be followed by reason.
   The arranging, in their proper order, those phe-
nomena which constitute a science, may be compar-
ed to thelabourof builders, who have prepared,rea-
dy to their hands, all the parts of a regular and spa-
cious edifice.  They may be entirely unacquaint-
ed with the design of the master builder, and una-
ble to predict any thing with regard to the form
which  the work is to assume; and yet, by carefully
observing the form of each  stone  in  relation to
others, and arranging them in different orders, the
proper place of each part will be ascertained.
As the work proceeds, it  will obviously become
less difficult, and at last, the design of the master
builder begins to be developed, and the symmetry
of the whole, together with the beauty of each part,
disappoints and astonishes the beholder.
   In the same manner, should we employ the phe-
nomena which are discovered in nature, not pre-
suming, from the form of a single stone or a pillar,
to anticipate the great designs of the Creator, nor
endeavouring to combine the materials according
to  our own fancy;  but patiently  observing the
adaptation  of one part to another, and changing
their order until an obvious relation is produced.
Should an  error occur, which cannot  at  first be
observed, it will soon be discovered by the diffi-
culty of applying the remaining parts.   If. in thr 
u
progress of the work, for want of the proper feet,
we  interpose a presumption of our own, the sym-
metry of the whole is destroyed, and although we
may continue to  build, yet the plan of the great
Designer never appears.  If, also, we are too intent
upon a plan  of our own imagining, we shall be al-
most certain to produce an incongruity in the ar-
rangement.  In fine, it is not our business to  create
the  materials of the sciences, but  to arrange and
study them.  It is a humble employment, then, in
which even they are engaged, who are capable of
the utmost stretch of human intellect.
  It may not be improper in this place, to remark
for a moment,  upon the sources  from which our
materials are to be drawn.
  Experiments upon living animals, with a view to
multiplying facts in relation to life, appear to  cha-
racterise the researches of the present day.  That
these under  some  circumstances, and performed
with proper precaution  may yield useful matter,
is undeniable; but it is necessary to their success
that we should, to a certain extent, be acquainted
with the properties of life, and the laws by which
the exertion of them is governed; otherwise, we
do not know what effects they may be capable of
accomplishing, and are in danger of attributing
the  results  of our experiments  to  causes  with
which we are  more familiar.  The little progress
which has been made in Physiology by the multi- 
A.i
tude of these experiments, confirms what 1 have
stated.   We  perceive that experimentors, who
may even essentially differ in opinion, find no dif-
ficulty in substantiating their favourite notions, by
the same  series of experiments.  We cannot, by
them, accurately determine, how much is the effect
of physical, and how much of vital properties,
until we know something more of the powers of
the latter.  It would, therefore, be more profitable,
if we  were to direct our  attention  to inquiring
what degree of control they exert over the pheno-
mena of life, rather than to inquiring how much in-
fluence the chemical affinities have over the same.
   Arguments, drawn from analogy, are, when not
carried too far, as I have already stated, often ex-
ceedingly  useful,  particularly on entering a  new
field of inquiry.  Indeed  such are the relations
which the different departments of science  bear
to each other, the moral, the physical, and the phy-
siological, that one cannot comprehend the scope
of any one of them without taking a general view
of the whole.   The existence of those properties
and laws which control inanimate matter, undoubt-
edly suggested to Bichat and others the existence
of corresponding vital principles.   The  analogy
of plants with  animals may be made  much more
particular, for these two orders of beings are class-
ed in  the same department of science,  and are
subject, in part, to the same laws.
                       3 
tb
  Descriptive Anatomy, human and comparative.
has long since arrived at a considerable degree of
perfection.   Every part of the human body has
been scrutinised with the closest attention, and it
appears that  in this department but little remains
to be done.   It is almost unnecessary to say, that
a constant adherence to anatomical facts, is essen-
tial to correct reasoning in physiology.
  Pathology also furnishes us with important data,
for the consequences which result from the defect
of any organ and of its particular function, may in
many instances suggest to us the importance and
the particular use of such organ, and the nature of
its function.
  We must not, however, place too much reliance
upon arguments drawn  from  any  one of these
sources; but if our opinions,  so far from being
pre-conceived, are suggested by facts, if they are
illustrated by the general relation which exists
between different sciences and between parts of
the same, if they are supported by what we know
of the laws  of life, and if they harmonise with
the general anatomy of the  system, and with the
particular structure of those  organs which are
principally concerned, we  may fairly conclude
that we stand upon the rock of truth.
  Before  entering  upon the  immediate  subject
of our inquiries, I think fit to  to make a  few re-
marks  on the relation existing between the phv- 
17
aical and the physiological sciences, that the ge-
neral analogy which connects them, and the cha-
racteristics which distinguish them, may be borne
in mind. 
I 
ESSAY,&c.
          PRELIMINARY OBSERVATIONS.

                Definition of Ltfe.

   THE material productions of Nature are,  by
Naturalists, divided into two great classes: Organ-
ic and Inorganic.   Organic bodies are those which
possess an internal structure capable of receiving
and assimilating  to  their  own  tissues, inorganic
matter,*  and  of thus increasing and renewing
themselves from within.   Inorganic bodies  are
those  which may be said to  accumulate, but not
to grow;  for they increase by the addition to their
external  surface, of matter already assimilated.
The first  class comprises animals and vegetables.
the second, the mineral kingdom.
   Organized bodies are said to possess life, a term
which has been used with great variety of signifi-
cation at different periods and  by different indi-
viduals.   The ancients, who in their  physiological
investigations, always sought final causes, observing
the uniformity with  which the  functions  of the
different  organs  are  performed, and the harmo-
nious  relations existing between them, were  led
  * Animals feed on substances which were organized, but after their
death, although they retain for a time their structure, yet they obey
only the laws of inorganic matter. 
20
to ascribe organic phenomena to an ethereal
principle, which they supposed to reside in the
centre of the  system, and to  control  it  with
an unerring intelligence.   This is at the present
day the vulgar idea of life, and is such as the mind
naturally adopts, when not disciplined to the true
mode of reasoning on these subjects.  It continued
among men of science, variously modified, but in
principle the same, till a late period in the history
of medicine.
  Modern physiologists have  wisely  abandoned
the pursuit of a final cause or source of anima-
tion, and have been contented with observing the
phenomena manifested by the several organs in
the discharge of their proper offices or functions,
the totality of which  they regard as constituting
life.   Life, therefore, is to be regarded rather as a
result than a cause.
  Every  species of  matter, whether  animate or
inanimate, exists in its present  state and exhibits
its peculiar properties by virtue of certain natural
powers of which  we know nothing  but  by the
effects which they produce.   These  are  always
exercised in a uniform manner, and by  careful
observation we determine the laws by which they
are governed.   Neither the most simple substances
nor the most complex are ever  exempt from their
control;  were  their influence  but for a moment
withheld, all nature  would fall into one chaotic
ma^p. 
•21
  Those powers  which constitute  the class oi
inorganic beings are the attraction of gravitation,
the attraction  of  cohesion,  chemical attraction,
electrical influence, &c. To produce a higher state
of existence other properties are superadded, and
vegetable life is the result.  Animal life  exhibits
a still greater number of vivifying principles.  No
portion of matter, therefore, can  be  said  to be
absolutely dead, though trans-migrating from one
state of existence to another.*  Vegetables  and
animals exhibit so many phenomena in  common,
that they have both been considered as possessing
life, in the common acceptation of that term.

Distinction between  the Physical and  the Physiological
                    Sciences.

  Those properties upon  which the existence of
inorganic bodies depends, are  denominated phys-
ical, as also the sciences which treat of them.  In
contradistinction  to these,  the sciences  which
treat  of the properties of organized beings are
termed physiological.
  Sensibility and  contractility are in the physio-
logical sciences  what attraction, elasticity, &c.
are in  the physical.  From the numerous modifi-
cations and  combinations of these, result the func-
* See Burn3, Bichat, &c. 
22
tions which  are the subjects of physiological in-
quiry.
  Sensibility and contractility are of two  kinds .•
organic and animal: These preside over different
kinds of life; the first over organic, the second over
animal  life.   Organic life  is the result of those
functions which are only concerned in the growth,
preservation and restoration of the structure of the
individual being, without establishing any percep-
tion of bodies exterior to it.  These functions are
digestion, respiration, circulation, exhalation, ab-
sorption, secretion, nutrition, calorification.  They
are employed  in  assimilating foreign  substances
to the structure of the plant or animal, promoting
its growth or renewing its decaying parts and
removing whatever has become useless or hurtful.
It is this species  of life  alone  which belongs to
vegetables, and by the functions which constitute
it, they exist without any consciousess of impres-
sions from surrounding objects.   Far otherwise is
it with  animals, that  move from place to place,
and  sustain an interesting  and  necessary relation
with surrounding beings.   By means of the senses,
the moral faculties take cognizance of whatever
influences the animal frame, and seek or  shun it
as it gives pleasure or pain.
  Both animals and vegetables possess another
class of functions by which they reproduce their
kind and preserve the species. 
fc3
  The organs which are concerned in performing
the functions of organic life, are  the alimentary
canal  and its appendages, the lungs, the heart,
arteries and veins, the exhalents, the absorbents,
the secernents and the nutrients.
   The functions of animal life are performed by
the organs of the senses, by the brain, the nerves,
the muscles, the bones and the organs of the voice.
   The function of digestion, which we are to con-
sider,  is perhaps the most important and interest-
ing of those which constitute organic life.

               Digestion of Plants.

   Every living being, whether animal or vegetable,
possesses an apparatus by which it elects and as-
similates its appropriate  food.  This, in the sim-
plest forms of life, is itself equally simple.  Plants
derive their nourishment from the earth,  by means
of absorbing  tubes  contained   in  their  roots.
These are  continuous with the  sap vessels  or
blood vessels of the  plant, from which the  circu-
 lating mass is conveyed to the leaves, there to be
acted upon by air  and light, and thence  to  be
re-circulated for the purposes of nutrition, secre-
 tion, &c.
   In  what part of the circle it is, that the most
important changes  are effected, is not demon-
strable.  It is undoubtedly, however, accomplished
                       1 
24
somewhere in its course by the peculiar action of
these tubes upon their contents.

              Digestion cf Animals.

   The most imperfect animals are scarcely distin-
guishable from vegetables, the definitions of Natur-
alists having often  proved fallacious.  The most
infallible criterion, however, is their mode of diges-
tion.  Plants feed upon inorganic  matter, and  in
the manner abovementioned.  Animals  are nour-
ished from the animal  or vegetable  kingdom, and
receive their aliment into an internal cavity, where
such parts as are susceptible of animalization, are
elected and assimilated.
   As the structure of some animals differs so little
from that of vegetables, we may fairly infer  that
their digestion differs but little except in the above
particular; thus the  polypus  has no  digestive
apparatus which we can discern, except the cavity
into which its food is conveyed and  from which
it is afterwards disgorged.  May we  not presume
then, from this easy gradation of structure, that a
corresponding one of function  exists, and that the
digestion of the polypus after its food is introduced,
differs but little  from  that of vegetables ?   As we
rise to the higher classes of animals, we find the
digestive apparatus becoming more complicated.
That, which was a mere sack in some of the lower
animals, with a single orifice, and which in others 
2.j
was  little else than a straight  tube, becomes  a
convoluted canal, many times the length of the
body, expanding near its superior extremity to form
the stomach,  and having appended to it many
subsidiary organs indispensable to its functions.

           Theories concerning Digestion.

   The  earliest writers on this  subject, were of
opinion, that the change effected on the aliment in
the stomach was  little else than  the result of pu-
trefaction.  Unsophisticated  in  the logic of the
natural philosophers and chemists,  they suppo-
sed  the food to undergo  the same change which
warmth and moisture effect upon it out of the body.
But when the physical sciences had made some
progress, and men of learning were habituated to
reason  almost exclusively on physical principles,
the mechanism of the system was alone talked of,
and the stomach wrought mechanically upon its
contents.   As chemistry began to assume the cha-
racter  of a science, it also, was very prolific  in
physiological explanations,  and  digestion  was
wholly  chemical.
   It were ridiculous in  us, as it has appeared  in
many writers on this subject, to  inflict,  like  Fal-
staff, a  new stab on these dead  theories, for the
sake of making the  victory, in part, our own. As
shown  in our introduction, they  are obviously in-
consistent  with  principles of medical logic, now 
26
well established.  We enter the field armed with
our sling and stone, (common  sense and truth,)
against a far  more formidable adversary, in the
prime of life, mailed in all the sophistry of the age,
and backed by universal approbation.
  We  shall now proceed to give an account of
what has been regarded for many years past, as
the true explanation of the process of digestion ;
further to inquire what  are the objections which
may be started against it;  and finally, whetheF
there is any more rational mode of accounting for
its phenomena. 
ESSAY, &c.
                  CHAPTER I.

        PHENOMENA AND THEORY OF DIGESTION.

  PREVIOUS to detailing the theory in question, I
shall briefly enumerate the facts, which, in relation
to this subject, may be  considered as well  esta-
blished by  observation or experiment.  This  is
the more necessary, as in elementary physiologi-
cal works, they  are not  well distinguished  from
what is questionable, or  matter of mere  assump-
tion.  We shall find the latter to be frequently em-
ployed  as indisputable facts, having been  con-
sidered as  the property of physiologists by long
possession, but without any well established title.

            Phenomena of  Digestion.
  The first  change which aliment undergoes  is
comminution by the teeth, and admixture with the
secretions of the mouth, which are mucus and sali-
va.   The former is the common secretion  of all
mucous surfaces; the latter, which  is much  more
abundant, is furnished by appropriate glands.   It
is an exceedingly bland fluid, slightly viscous and 
£8
chemically constituted of four parts of water and one
of albumen, in which are dissolved  phosphates
of soda, lime, and ammonia, and a  small quantity
of common  salt.  It possesses an antiseptic pro-
perty,  and has an affinity  for  oxygen, which are
all the remarkable chemical properties known to
belong to it.
  The secretion of saliva is much increased by
the presence of food in the mouth.  The action of
the  teeth, the  tongue, &c. diffuses the  saliva
through the whole mass of food, which then loses,
in some degree, its sensible  properties.   During
mastication, a small quantity  of air is involved
by the viscid property of this fluid.  If solid food
be swallowed without admixture with the saliva,
and  trituration by the teeth, its digestion is slow
and imperfect.
  The food is next conveyed by deglutition, into
the stomach.  It is not necessary that we should
describe the mechanism of this function.
  The accumulation of food in the stomach imme-
diately appeases the sensation of hunger, and in a
short time the vigour and activity of  the body
are restored.  These effects do not take place in
proportion to the distension of the organ, food
that is highly nutrient satisfying in less quantity.
   According to  Magendie, food remains  in the
stomach about one hour before any change takes
place, except that which arises from mixture with
the fluids. which,duringthis time are copiously pour- 
29
ed into the organ.  The stomach, then contracts
upon its contents, and from this time there is dis-
covered in the pyloric extremity, a fluid supposed
to be the result of digestion, and denominated
chyme.  A lamina of the same is found covering
the mass in the greater curvature of the stomach.
Wilson  Philip  states  " that  this process takes
place only  on, or near the surface of the stomach,
and that in proportion as the food there  situated
undergoes the necessary change, it is, by the mus-
cular powers of the stomach, moved onwards to-
wards the pylorus, making room for  that which
next  succeeds, till the  whole  contents of the sto-
mach  have undergone this process, the digested
contents being regularly  discharged into the duo-
denum as they arrive at the pylorus, till most, and
in some animals, all the contents  of the stomach
are thus removed into that intestine."
   From the moment that food is conveyed into the
stomach, there begins tobe exhaled from the mucous
surface of the organ, mucus, and a fluid resembling
very much, in its sensible  and chemical properties,
saliva.  These  properties must however,  be  very
variable or very obscure, since of the many expe-
rimenters who have carefully analyzed this fluid,
scarce any two give the same results.  Some have
positively declared it to be acid, others with equal
confidence have ascribed to it alkaline properties.
A third class discovering nothing remarkable  m 
30
it, have presumed it to be nothing more than the
residue of former digestions, mingled with saliva
and a similar secretion from the stomach.
  From two circumstances it has been inferred,
and universally believed, that this fluid possesses
an  extraordinary solvent power.   Mr. Hunter
discovered, that  in persons dying  suddenly, and
in whom the function of digestion was progressing
vigorously, there occasionally took place an ero-
sion of the coats of the stomach.  The  same ap-
pearances have since been  observed, and the
fact is  unquestionable.  The  other  circumstance
is the digestion of food contained in hollow balls
and tubes, pierced with  holes, and  introduced
into the stomach, as occured in the experiments of
Spallanzani,  Reaumur, &c.   Spallanzani  and
other experimenters assert that the same results,
though not with the same facility, attended their
experiments on this fluid out of the stomach.  The
more recent experiments of Montegre and others,
performed with more accuracy and precision than
chemical analysis was then capable of, show that
these results were fallacious.
  The aliment, while  in the stomach, is subjected
to gentle pressure by the walls of that organ.
It is also  agitated  by the motions of respiration.
The heat of the stomach during digestion varies
from 98° to  101°.
   After some hours have elapsed from the time 
M
that aliment is taken into the stomach, it is found
to have lost, in a great measure, its sensible  pro-
perties, and  to  be  converted  into a  substance
called chyme.  This is  described as  "a homo-
geneous, pultaceous, greyish mass, of a sweetish
insipid taste and slightly acid."   Its  properties
are by no  means uniform, as they vary with the
food employed, and accurate observers assert that
there are as many kinds of it as of aliments.
  Animal  food  is  more  easily  converted  into
chyme than vegetable.
  The time required for the completion of diges-
tion in the  stomach is from three to five hours.
  It has been acertained by the numerous and
accurate experiments of W. Philip,  that if the
eighth pair of nerves be  divided, the  process of
digestion  is  immediately and  completely sus-
pended.   Violent affections of the mind and of the
body produce the same effect.
  In cases of sudden death, when the process of
digestion is  vigorously going on, food does not
continue to be converted into chyme, although the
stomach may be eroded.
  In digestion, the  chyme does not accumulate in
any quantity at the pyloric end of the stomach, for
its  presence excites a contraction of that portion
of  the organ at the same time that  the  pyloric
sphincter yields, and the contents are conveyed
into the duodenum, which also  contracting pro- 
pels it  along  the whole  tract of the intestines.
Chyme  is not changed in its  properties,  until it
reaches the ductus communis choledochus.  Here,
being combined with the hepatic and pancreatic se-
cretions, it acquires new characteristics, assuming
a bitter taste and yellow colour.   After this, there
will always be found precipitated upon the valvulae
conniventes, a greyish coat adhering to the mucous
membrane.   This has been  thought to  be  the
elements of that fluid, which is discovered in the
lacteals, called  chyle, the  elaboration  of which
has been regarded as the most important result of
digestion.
  These phenomena  are observed in the  two
superior thirds of the small  intestines.
  As the chyme varies exceedingly in the proper-
ties which it exhibits on entering the duodenum,
so the  changes, which are  effected in the small
intestines,  vary  with the  nature of the aliment.
Food, which  has passed the stomach  without
change, undergoes but little  in the intestines.
  It, is  in  the small  intestines  that digestion is
completed, and it is  from  them that those minute
absorbing  vessels, which  we  call lacteals, arise.
They are seen in the mesenteries of animals killed
soon after eating, filled with a milky fluid, which
they convey to the thoracic duct, which transmits
it to the left subclavian vein.
   Although the chyle of  the  intestines is spoken 
J3
of by physiologists, yet nothing is found in them
more nearly resembling it than the  greyish  pre-
cipitate described above.   The chyle, which has
uniformly been the subject of experiment and
description, is that of the lacteals and thoracic
duct.   Magendie  gives  the  following account
of it.  " If  the animal from which  the chyle is
extracted had eaten of fatty vegetable or  animal
substances, the fluid drawn from the thoracic duct
will be of a white milky appearance, rather  hea-
vier than distilled water, of a spermatic odour,
stimulating  the tongue, a little saltish, and percep-
tibly 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  separates into  three parts, one
solid, which is found  at the bottom of the vessel,
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 properties  are the
same; but  instead of being  white and opaque, it
is semi-transparent, and the pellicle  formed on the
surface is less distinctly marked than in  the first
kind of chyle.
   Of the three parts  into which  chyle separates,
when  left  to  itself,  that on  the surface, of an
opaque  white  colour, is a fatty substance: the 
34
 coagulated or solid part is formed of fibrine and
 a little  red colouring matter;  the fluid is analo-
 gous 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 contain  fat  or oil,  while this is hardly
 distinguishable when  the aliments are destitute of
 fat.  The same salts which are  found in the blood
 exist also in the chyle."

      Theory of Digestion by the  Gastric Juice

  In the foregoing sketch, I have not endeavoured
 to enumerate  all  the minutiae relating to the pro-
 cess  of digestion, but  rather  to present  to the
 mind of the reader, in  as concise a manner as pos-
 sible, those important and undeniable facts, which
 bear upon the question about to be agitated ;  for
 more particular information I  refer him to  the ele-
 mentary authors.  In the following pages, I shall
 adduce  other circumstances, both  pro  and con,
perhaps more equivocal,  but &hall endeavour to
give them the precise weight which  their charac-
ter merits.   I shall now proceed to give a concise
account of the theory of digestion at present  re-
ceived. 
35
  Chesselden was the first who suggested that di-
gestion might be accomplished by a solvent fluid
secreted for that purpose, and he conjectured that
it was the saliva.  Reaumur and Spallanzani were
led to a similar anticipation by observing the ef-
fects of chemical solvents in their laboratories, for
chemistry at that time was becoming the fashiona-
ble science  and they were devoted to its pursuits.
With a view to disprove the  mechanical  theory
and to confirm their own anticipations, they introdu-
ced into the stomach, as stated above, hollow balls
and tubes pierced with holes and charged with ali-
ment.  Their contents, upon their being removed
from the stomach at the end of some hours, were
found to have undergone the same change as the
mass in which they were involved.  From that time,
this experiment has been regarded as a complete
confutation  of  all the former hypotheses on this
subject,  and a demonstration that digestion is ef-
fected by the solvent power of a fluid, exhaled from
the stomach, denominated the gastric juice.  This
theory  was  confirmed  by the  erosions of the
stomach, first observed by Hunter, as mentioned
above.   The failures of those who have attempted
artificial digestion, by means of the gastric fluid,
out of  the stomach,  have not  shaken the confi-
dence of physiologists in the powers of this agent.
  The belief, therefore, which prevails is,  that
upon the introduction of food into the stomach, thi- 
36
organ becomes a centre of fluxion, and that there
is then exhaled from its surface the fluid mentioned
above, which, by a chemical agency, converts the
alimentary substances into the homogeneous mass
called chyme.  There is some difference of opi-
nion with regard to the aid which it receives from
the stomach.   Some believe  that the vital powers
of this organ are necessary to digestion, even after
the exhalation of this fluid;  others, that the pro-
cess  is entirely  chemical.    Magendie asserts
that the gastric juice requires no aid but such as
it receives from the precise degree of heat, mois-
ture and motion, to which the aliment is subjected
in the stomach.  W. Philip believes that the vital
powers of the stomach  are only employed in the
elaboration of this fluid, which acts on the food  in-
dependently  of them.
   The conversion of aliment in  the  stomach into
chyme is regarded as far the most important part
of digestion, and as the only office of that  organ.
The chyme, as is generally supposed, is  then con-
veyed into the duodenum to undergo another che-
mical change, by the agency of the hepatic and
pancreatic secretions, the result of which is the pre-
cipitation of the chyle from the mass of the chyme.
I say this is  generally believed, for there is some
difference of opinion on this point, as it is asserted
 by some  that these secretions serve no other pur-
pose than to qualify the residuum, and to stimulate 
                      37

the intestines, while the chyle is elected immedi-
ately from the chyme by the lacteals.
  Such is the theory of digestion  at present univer-
sally received, and which has long since ceased to be
questioned.  So confident are men of science in its
imperishable nature, that all our systems of physio-
logy and pathology  are  founded upon it as their
corner stone.  We are to recollect, however, that
the above experiments and deductions were made
at a time when the rules  of logic, by which we are
guided in speculations of this kind, were less rigid
than they now are. We are to consider, also, that
at that time, the progress of science had shown the
previous theories to be altogether  inadequate to
the  explanation of the  phenomena of digestion,
that the  application  of chemistry in its improved
state to physiological inquiries was then universal,
that, consequently, the ingenious theory  in ques-
tion, offered, as  it was, by men of  high character
and great influence, soon came to be generally re-
ceived, and consequently, ceased to be  the  sub-
ject of that spirited inquiry, which results from dif-
ference of  opinion. 
4 
ESSAY, &c
                 CHAPTER II.

         OBJECTIONS TO THE ABOVE THEORV.

  BUT'are the evidences in favour of digestion, by
the solvent powers of the gastric fluid, sufficient
to check further  inquiry on this subject ?  Is the
mode of reasoning, which  has led to this opinion
conformable to just principles of logic ?  Does the
theory, like that  of Harvey, rest  upon numerous
and unequivocal facts ?  Are the phenomena of
digestion satisfactorily explained by the  suppo-
sition, and does  it harmonize with the  general
anatomy, physiology and pathology of the system.

        Objections to the reasoning employed.

  I object to the  mode of reasoning employed on
this subject, as one which  has been  productive of
infinite perplexity and error, and  which has been
uniformly found  inadequate to the explanation of
physiological phenomena.
  It appears  that Chesselden, Reaumur and Spal
                      6 
10
lanzani were led to  anticipate the existence of a
powerful solvent in  the stomach, from comparing
the changes which  the food undergoes  in  that
organ, with results obtained in  their laboratories.
  This was evidently predicting the means by
which Nature should accomplish her  ends, in one
department of science, by observing what she has
done in another, in which the properties of matter,
and the  laws by which they are  exerted, are en-
tirely different.
  It is only in the character of humble enquirers,
who  submit themselves to the  guidance of  such
facts as they may discover, that men have extended
the boundaries of knowledge.
  Were it impossible that the changes effected on
the aliment in the stomach, should be accomplished
in any other way than by a mechanical or chemical
process, their conclusion would be just, for there
could be no fallacy  in reasoning from an effect to
a cause, the operations of which we are acquainted
with. But knowing the distinction which  exists
between  the physical and physiological  sciences,
it is not only possible, but even probable, that this
change is wrought by a cause, the operations of
which, we  are  but  little acquainted with.   It is
incumbent on those, therefore, who  maintain the
above position, not merely to show the effect, but
to demonstrate unequivocally that the gastric fluid
possesses such properties  as are capable of pro- 
II
Cueing the effects attributed to it, or to show thai
they can be accomplished in no other way.
   The chemical powers attributed  to  the gastric
fluid are certainly very extraordinary. It is said, not
merely to  dissolve rapidly the great variety of
aliments which are taken into the stomach, but to
enter into combination with them, and  to produce
a  third  substance.   Should  we  not, therefore,
expect  to  discover something equally  extraor-
dinary in the properties of so  powerful an agent ?
But I have already stated, that this is so far from
being the case, that scarce any two persons give
the same account of its chemical constitution.  Its
analysis  therefore, yields nothing  to support  the
theory in question.
   It was very naturally supposed, by  those  who
attributed these extraordinary powers to the gastric
fluid, that  they would  be manifested, in  some
degree at least, when removed from the stomach;
accordingly, artificial digestion was attempted, the
auxiliary circumstances of heat, motion, &c. being
imitated  as nearly as possible.  Had this  experi-
ment unequivocally  succeeded, it  would  have
been a necessary conclusion, that the solution was
effected  by some property inappreciable  by  the
ordinary chemical tests.  It is obvious, however,
that the experimenter might, in this process, very
easily deceive himself.  Chyme is a substance by
no means possessing  uniform  characteristic pro- 
42
 perties, but is exceedingly variable; by what cri-
 terion therefore, should he ascertain that he had
 accomplished artifical digestion, since we can only
 say of chyme, that it is a " homogeneous, pulta-
 ceous, greyish mass, of a sweetish,  insipid  taste,
 and slightly acid ?"  It certainly would be no diffi-
 cult matter to produce a compound, having these
 properties,  by admixture  and maceration of ali-
 ments, sufficiently comminuted, aided by gentle
 heat and motion.  It does not appear that  these
 experimenters accomplished  any thing more, al-
 though their report of the result was received as
 unequivocal evidence of the solvent powers of the
 gastric fluid.
   The  experiments of Montegre,  performed, as
 we may presume from the reputation of the author,
 with all the nicety and  precision of modern che-
 mistry, tend to show, that the gastric juice, out of
 the stomach, exerts  none of  those  extraordinary
 chemical powers which are attributed to it,  when
 in that  organ, but that it is  as inert as water.
 Allowing that his experiments are not conclusive,
 it is certainly very surprising  that  a fluid, which,
 after death, is supposed to corrode  the stomach,
 without the aid of  a uniform  temperature of 98°
 and of motion, should, to the scrutiny of an able
chemist, yield no evidence of its possessing any
solvent powers whatever.
  Magendie, who nevertheless supports the posi- 
43
   Lion  of  digestion by the gastric fluid, does  not
   believe  that  artificial  digestion  has ever been
   accomplished, and regards the  experiments of
   Montegre as satisfactory proof, that out of the
   stomach, the gastric fluid is perfectly inert.
     It is stated in the foregoing  chapter that there
   are two undeniable facts which contributed greatly
   to  establis the opinion in  question T first, The
   erosion  of the coats of the stomach  after death,
   observed by Hunter, and second,  The  digestion
   of food contained in hollow balls, and introd uced
   into the stomach.
     With regard to the first of these phenomena, it
   appears to me, that the advocates of the theory'"of
   solution  are  not aware of the dilemma to which
   they are reduced, in case it be admitted as an ef-
   fect of the gastric juice.  Magendie, in accounting
   for the inertness of the gastric juice out of the sto-
   mach, attributes it to the absence of certain cir-
   cumstances, which cannot be accurately imitated.
   The  principal of these are uniform heat and  mo-
   tion.   They, it is obvious, are  dependent upon
   vitality,  and must cease with it.   If,  therefore, it
   be asserted  by any, that this fluid acts thus upon
   the dead stomach, with an energy equal to that of
   the most powerful acids, it  is certainly incumbent
   on them to exhibit  its effects  out of  that organ,
   since there can be no reason why they should not
x  He unequivocally demonstrable.   If the negative 
44
 argument be resorted to, that these effects can be
 produced in no other way, I consider the assertion
 to be altogether unwarrantably, and the mode of  *?s
 reasoning to be,  on physiological subjects, alto-
 gether inadmissible.   The changes which take
 place in the human body,  in the article of death,
 have often been observed with astonishment.   So
 numerous and so striking are they, that much cau-
 tion is required  to  distinguish them from those
 changes  which are  the result of disease.   We
 know very well, that if we would discover, after
 death, the morbid evidences of a slight degree of
 inflammation,  the examination must be promptly
 made, or those evidences disappear.  We  know,
 too, that absorption is performed with great energy
 in the article of death, and I believe after appa-
 rent death, or after the animal functions  have
 ceased to be performed.  We have reason,  also,
 to think, that  appearances, resembling  those of
 ulceration,  have  taken  place  after  apparent
 death.
  These post mortem changes are, in a general way,
 accounted for, on the supposition that the organic
functions, particularly those of the capillaries and
 absorbents,  continue to  be performed after  the
 animal functions have ceased.
  Who, therefore, will undertake to say, that the
 abovementioned erosions of the  stomach are ef-
fected by a fluid, secreted by that organ, and pos- 
45
sessing remarkable chemical properties, because
it is  impossible  that  they can  be accomplish-
ed in any  other way ?  We know, very well, the
extreme vascularity  of the stomach and that its
capillary vessels, and  particularly its absorbents,
act  with unparallelled energy.   We know also,
that different portions of the  stomach  derive
their vitality from different  portions of the  ner-
vous system.  Is  it not possible,  therefore, to con-
ceive  that one  part of the stomach, having lost
its vitality, may be acted  upon by anqther which
retains it ? It is by no  means incumbent upon me
to make out, even the probability of this supposi-
tion, the bare possibility of it is obviously sufficient
for my purpose.
  Another objection to the common explanation
of this phenomenon is, that in all  those instances in
which it has been observed, the food, taken into the
organ  a short time  previous to death, has been
found  untouched, however extensive the  erosion
of the stomach may have been.  It is certainly very
singular, that this fluid should produce no effect on
the aliment, which, to prepare it  for its action, ha6
been comminuted by the teeth, mixed with the sa-
liva, macerated by the fluids of the stomach, and
finally imbued with the gastric juice  itself;  and
that it should turn  with  energy upon  the  sto-
mach, which has been influenced by none of those
Hrcumstances, and which  is moreover protected 
46
by an epithet urn, or cuticle, and its own mucous
secretions.
  The experiment of introducing hollow balls or
tubes, filled  with aliment into the stomach, was
first performed with a view to disprove the suppo-
sition of the mechanical action of the walls of the
stomach.  In this respect, it has completely suc-
ceeded ; but it has been also regarded as unequi-
vocal evidence of digestion by the gastric juice,
although  it  by no  means suggested that theory.
Let us candidly examine the circumstances of this
experiment, and see whether the above inference
necessarily  follows.  The balls or tubes, employ-
ed  for this  purpose, must have been small,  and
pierced with holes, either numerous or large, in
order to favour the free access of the gastric juice.
On the introduction of the balls into the stomach,
the progress of the  experiment is entirely hidden
from our view, and we know nothing of it, but from
the result, which, on removal of the balls, is found
to be a  partial  digestion of the aliment contained
in them.  If it can be shown, then, that it is impos-
sible, that the phenomenon can be accomplished in
any other way, the conclusion is just;  but this, as
in the  instance above, is obviously  absurd.  I
hope to make it appear not only possible, but even
probable, that the villi of the stomach  act imme-
diately  on the aliment, and effect the changes that
have been attributed to the gastric juice.   It ie 
47
enough for my present purpose that  such a thing
is obviously possible, and being so, the phenome-
non in question is no  longer proof of the solvent
powers of the gastric juice ; for the villi of the
stomach, being probably capable of elongation,
and  attached to  a  very moveable membrane,
would be capable of seeking the aliment contain-
ed in the stomach  and of coming in contact with
that which is inclosed in the balls ; and it is to be
observed that it is  only that portion, which is in
the  neighbourhood of  the  holes, that  is  found
changed.
  It  is proved by Wilson Philip and others, that
it is only  the surface of the alimentary  mass,
in contact  with the walls of the stomach, that is
changed by the gastric juice: therefore, only that
part of the aliment in the balls, which is reached
by the surface of the stomach, can  be acted upon,
according  to either supposition.  Hence, the fact
is as  much in favour of the one position  as the
other, and  proves nothing.
  A fact, to which  I have already alluded, calcu-
lated to  throw much light upon this obscure  sub-
ject, is that mentioned by Philip, and also by Ma-
gendie.   They both  state, that, in  digestion, no
change takes place in the alimentary mass, (except
such as maceration effects,) until certain motions
are  observed to take  place in  the stomach, by
which its inner  surface is closely applied  to  the 
18
surface of the aliment; that then, the first changes
which are discovered, are on the surface of the
food in contact with the mucous membrane of the
stomach.  A thin layer of aliment is found to be
converted into the  substance which  is called
chyme.  This is then conveyed, by the motions
of the stomach, to the pyloric extremity of the or-
gan and a new surface is presented to the surface
of the stomach to undergo the same change.  To
those who advocate the theory of solution,  the
above must oppose no small difficulty.  The fluid,
which, we are told, begins to be  poured out soon
after the food enters the stomach, and  which,  in
some  instances, is found in considerable quantity
in that organ, must  certainly pervade the whole
mass of the  aliment; why, then, should its effects
be confined to the surface of the alimentary mass ?
and why should  they  be simultaneous  with cer-
tain motions of the stomach ?  It may be said, in-
deed, that this fluid acts with such surprising en-
ergy, that, at the instant of its secretion, it seizes
on the first particle of food with which it comes in
contact  and that thus, it never permeates the mass
of food.   This resort, however, would,  perhaps,
cost our opponents more than they are aware.  It
would amount to an absolute denial of the action
of the gastric juice upon the dead stomach: for,
how could  it act upon that  organ after death,
unless it were accumulated in it. and that, when 
IV»
there is food present upon which it has not acted :
It yvould also follow from this supposition, that the
secretion of the gastric juice does not  commence
until the very moment that digestion is found to
take place.  We might also fairly infer, that its se-
cretion would never take place except food were
present and that  then it would never remain un-
combined in the stomach for a moment.  It yvould,
therefore, be utterly impossible to prove the exist-
ence of such a fluid, and  in advocating it, the abet-
tors  of the theory of solution would abandon all
the arguments usually employed, and gain nothing
but  a supposition.
   Those who believe that the gastric fluid can
only act when aided by certain vital powers resid-
ing in the walls of the  stomach, and account in
this  way, for   digestion taking  place only on the
surface of the mass, in contact with the stomach,
are in the same dilemma.  On such a supposition,
there could be no more proof adduced of the ex-
istence of the gastric juice than of the existence
of the nervous fluid of which  so much was once
said.  We see, indeed, the surface of the aliment
coming in contact with the surface of the stomach,
and a remarkable change effected upon it: but shall
we say, that this is effected by a fluid possessing re-
markable chemical properties poured out at that
instant and enabled to act by the vital powers of
the stomach?  If  its  powers are exerted in no 
50
other way, and at no other  time, what evidence
have our senses,  that there exists any such fluid,
except the effect that is produced  upon the ali-
ment ?  I have already shown that this reasoning
yvould be inadmissible.
  The promptitude with which  digestion is inter-
rupted, by the division of the eighth pair of nerves,
is a sufficient evidence that there is something
more than a mere chemical process going on in the
stomach, for, according to the commonly received
hypothesis, the  gastric juice,  already  secreted,
should continue to operate upon the aliment.
  Having noticed the arguments which are usually
employed in  support of the doctrine of digestion
by  the solvent powers  of  the  gastric juice, we
now proceed to the consideration of circumstances
not immediately suggested by them.

  Changes not  wrought upon large volumes of matter.

  Our systems of physiology teach us,  that the
change which the food undergoes in the stomach,
is by far, the most important step in the process of
assimilation or the transition of matter from the
control of physical laws to those of vitality.   We
are told, that  the gastric juice, dissolving and unit-
ing with the  nutrient portions of the food, forms
a new and peculiar  substance,  which must be
considered as highly  animalised,  since no one 
5*
considers that an equally great change is wrought
upon it in the small intestines, or in its passage to
the mass of the blood; nor is it supposed that any
change which it may undergo in the blood vessels,
is equally important with that which takes place
in the stomach.
  If this opinion be correct, digestion is the only
instance  in the animal economy in which an  im-
portant change  is wrought upon a large volume
of matter in any of the large  reservoirs.  All  the
changes, which are effected upon the aliment after
its mingling with the  blood, are  wrought in  the
capillary  vessels of the lungs and the nutrient
vessels of each tissue to which it is appropriated.
In fine, all the  changes which are wrought  upon
the  blood, either for  more perfect animalization,
secretion, exhalation,  or any other purpose,  are
wrought in the  capillary tissues, where  the circu-
lating fluids, becoming exceedingly attenuated,  are
subjected to the  peculiar action of the vessels
which convey them.  No  changes  are wrought
upon the blood in the heart or in any  of the great
blood vessels.
  Glandular structures  appear to be little else
than congeries of minute vessels, for the purpose
of increasing the surface with which the contained
fluids are  in contact  and  thus subjecting them
more fully to their peculiar action.
  Is it not surprising, therefore, that so great a 
o2
 uhange can be effected upon a large mass in the
 stomach, when, to accomplish changes much less
 important, it is necessary, that the matter acted
 upon should be made to pass through  vessels in-
 definitely multiplied ?   It will presently be seen
 that, by the hypothesis which I offer, this difficulty
 is not incurred, since, by that, the more important
 part of digestion itself is effected in the capillary
 vessels.

            Variable properties of chyme.

   The want  of uniformity in the sensible and
 chemical properties of chyme must oppose no small
 difficulty to the advocates of the theory in ques-
 tion.   Magendie  and  others  inform us, that, in
 these respects, it is so variable, that there  are as
 many kinds of chyme as of aliment, it being some-
 times acid, sometimes  alkaline, sometimes of one
 colour and consistence, and sometimes of another.
 If the conversion of aliment  into  chyme  be so
 important  a step in the process of  animalization,
 should we not  expect to discover some uniform
 property or quality, which  shall give evidence of
 its having become in a great degree assimilated ?
 We do, indeed, discover evidences of that kind in
 the chyle,  but never till it has passed through
 the capillary vessels.   The  properties of chyme,
 therefore, although they are very different from
those of the aliment from which it is formed, sug- 
53
gest no such important change, as that said to be
effected by the gastric juice;  on the other hand,
they are  nothing  more  than  might result from
comminution,  admixture and  maceration, of the
contents of the stomach.   The comminution how-
ever, as 1 shall  by and by show, may be such as
cannot be completely effected by art.

          Chyle not found in the intestines.

   Writers speak with great confidence of the for-
mation, in the small intestines, of a fluid denomi-
nated Chyle.  The  most common  opinion with
regard to its formation is, that the chyme, having
already undergone the most important change, is,
on being conveyed into the small intestines, acted
upon by  the  bile  in a  chemical  way and  that
chyle  is  precipitated from the  mass.  Others,
indeed, give different accounts of this process, but
all speak  of the formation of chyle in the small
intestines  with as much confidence as if it were
uniformly  found in  that part of the alimentary
canal, and, taken  from it, had often  been made
the subject of experiments by which its chemical
and animal properties  had been ascertained.  I
will hazard the assertion, however, that there was
never a particle of what was  ascertained  to be
chyle, obtained from any other source than  that of
the lacteals or thoracic  duct.   The existence of
chyle in the intestines has been presumed from the 
54
belief that the lacteals have no power to effect a
change on their contents, and that consequently
they were taken up precisely as they are found in
them.  If this be the case, the conclusion is pal-
pably false, for who can say that the lacteals have
no peculiar  actions by which their contents are
wrought upon ?
  In speaking of the changes which the chyme
undergoes in the small intestines, Magendie states
(page 226,) that " If it consist of animal or vege-
table substances, containing oil, there will bes een
to form, here and there upon its surface, irregular
filaments  flattened or rounded, which  attach
themselves to the valvulae conniventes, and appear
to be imperfectly formed chyle.  I  hope the reader
will recollect that this substance is, what appears
to be, imperfectly formed chyle, and not what has ever
been demonstrated to be chyle, which is also found
in the lacteals.  In another place (page 228,) the
same author remarks  " From what has been said,
it will seem that the chyme in the small intestines
is divided into two parts.   The one is attached to
the walls, and is the chyme in an imperfect state j
the other is destined to be pushed into the large
intestines, and at last entirely rejected."  Without
having  adduced a  single  experiment or  other
circumstance, to show that this substance, which,
in one place he speaks of as only appearing to be
imperfectly formed chyle, and which, in another. 
•JO
he mentions as chyle in an imperfect state, is ac-
tually the  same substance which  is found in the
lacteals, he makes this  final statement, (p. 229,)
" Thus is  accomplished that most important part
of digestion, the production of chyle."  Who will
not  pronounce  the above  conclusion to be alto-
gether unwarrantable ?  / think it may be with safety
asserted, that no animal properties can be demonstrated
hi any substance which has  not  been subjected  to  the
nction of capillary vessels.

   Objections from the Anatomy of parts concerned.

   The theory of digestion, by the solvent power?
of the gastric juice, does not well explain the uses
of certain  anatomical structures met with in the
digestive organs.
   The villi or papillae  of the stomach are, in
their structure, essentially the same as those of
the  small intestines. No material difference in
their organization can be  pointed out, and yet  we
are  told, that their offices are  diametrically oppo-
site, that of the villi of the stomach being to exhale
the  gastric juice, while  those of the intestines
absorb the chyle.
   Bichat  noticed this incongruity, and says, " It
is difficult to conceive how an organ, every where
nearly  similar, can  perform, in different  parts,
functions so  different.  I say  nearly similar,  for
                        8 
5U
we shall see that these papilla? exhibit difference?
of size, length &c. without having any of texture
or structure.
  That the thoracic duct is  the only medium of
communication between the digestive organs and
the mass of  the  blood, is the necessary belief of
those who favour the opinion in question.  It is
conjectured by  some  that  a small  quantity of
nutriment is taken up by the lymphatics, but these
terminate in the  thoracic duct.
  This vessel is  of extremely small size, although
the common trunk of the lacteals and lymphatics.
Its coats are so exceedingly thin and  delicate that
when  collapsed it is  scarely  discernible.    Its
length is very great, as it extends from its origin
in the abdomen, quite through the thorax to the
left subclavian vein.  The track which it pursues
is obliquely across the spine, beneath a  branch
of the vena azygos and  beneath the  aorta.  Hav-
ing gained a situation upon the left of the spine, it
mounts upward in the neck  for a  short distance
beneath the carotid artery and then  curves down-
ward to the place of its termination.
  If the functions of this  little  vessel  are what
they  are supposed to be, it certainly performs an
office of vastly more importance than that of any
duct in the system.  We should expect, therefore,
from observing  the provisions of nature in less
important structures, to find this  organ guarded 
57
with peculiar care, and with*appendages capable
of performing a vicarious office.
  If the proper artery of any part is obliterated,
we find that nature has  anticipated the evil by
furnishing collateral branches.  The same is true
of the nerves.  The organs of the senses are won-
derfully protected  and  exist  in pairs.   How
obvious and how ingenuous  is the guardian care
of nature, in the protection of the brain and  spinal
marrow !  The brain too, consists of hemispheres,
and the spinal marrow sends  off its nerves in pairs,
and these pairs are  constantly interchanging fila-
ments.   The organs most essential to life receive
their  nervous  influence from both the brain and
spinal  marrow and  by  a great  many origins.
These nerves also exist in pairs and  are wonder-
fully protected in their courses.
  The great vessels, the  trachea, the oesophagus
and the intestines, from their size,.their structure
and other circumstances, are but little  liable to
obstructions.
  The digestive organs rarely have their functions
completely  suspended, and  when, from disease,
this does take place, the absorbents are supposed
to feed  on  the reservoirs  of  fat.   The lungs are
organs whose functions cannot be for a moment
suspended;  they, therefore, are carefully protected
and exist in pairs, the functions of one of which 
58
may be  interrupted without materially affecting
those of the other.
  The biliary and pancreatic ducts may be com-
pared  to  the thoracic, but in  case  they  are
obstructed (which occasionally takes place,) the
fluids which they convey may safely be withheld
for a time, or are taken up by the absorbents and
appear in every part of the system.
 How different from all these are the circumstances
of the thoracic duct!   Of all those organs, which
are properly called ducts, I believe it is the long-
est, and of course, in this respect, the most expos-
ed to obstruction.   Its parietes too, are the most
delicate  and unresisting.   It passes in the neigh-
bourhood  of parts,  which, in  certain diseases,
would  be exceedingly liable to  press upon  and
obliterate it.   It has no fellow nor is there any or-
gan which can assume its functions.   It is said, in-
deed, that in some instances, there  are branches
given off from it  in the thorax which enter the
subclavian vein at  different points ;  if, however,
these were  important, we should expect  to find
them uniformly existing.   What appears most like
a provision of nature to protect its  functions, is
the division of the duct in the thorax into several
small branches and their reunion.
  The experiment of tying this duct in the living
animal, I consider to be  neither conclusive for
nor against the opinion which I oppose.  In many 
59
instances  where  it has been tied, the animal has
experienced  no inconvenience.   In others it has
proved fatal.   The former result may, however,
be accounted for by the existence of the collate-
ral branches mentioned above, and the latter, by
the presumption that the performance of so diffi-
cult an experiment would, in many  instances, be
attended with injury of some essential organ.
   It has been long thought by many, that the func-
tions attributed to the liver, by the present theory
of digestion, do not correspond with its magnitude,
its structure  and its pathological importance.   It
is present in  nearly all animals.   The ancients
supposed  it to  be  the organ  of sanguification.
Many modern  physiologists  have suggested that
it might effect some change on the blood  besides
that of the elimination of bile.
   Dr. Rush, in an essay on the functions of the
liver and  spleen, has the following:  " The design
of the liver I believe to  be, to  receive  the blood
from  every part  of the body, in order  to subject
that part  of it, which has not been completely ani-
malized or divested of its chylous properties, to a
secretory process, and after,  to pour the product
of this secretion into the duodenum, to be absorb-
ed or otherwise taken up by the lacteals and con-
veyed with the chyle from the stomach into the
blood-vessels, in order to be completely converted
into red blood, for the purpose of serving  the va- 
60
 t ious and important uses for which that fluid is in-
 tended in the human body."
   Dr. James Johnson, in his Treatise on Tropical
 Climates, says, that  " This immense gland  is the
 the largest in the human frame;  for neither the
 brain, heart, spleen nor kidnies, can be at all com-
 pared with it;  and the lungs, though occupying a
 larger extent when inflated, yet, if condensed to
 equal solidity, would fall short in size and weight.
   Now, since nature, throughout her works, has
 seldom been accused of supererogation, we may
 safely conclude, that the importance of this organ's
 function, in  the animal economy, is commensurate
 with its magnitude."
   The cases of malformation related by Mr. Aber-
nethy  and Mr.  Lawrence, in which  the  vena
portae  terminated, without  division, in  the  vena
cava, are highly interesting.   They render it cer-
 tain that bile may be secreted from arterial blood.
The fact will be again spoken of in answer to an
objection, which it apparently opposes to opinions
soon to be advanced.

            Nutrient effects of aliment.

   It appears to me that  the theory in  question
does not satisfactorily account for the speedy res-
toration of strength and vigour, which one experi-
ences on taking food, who has fasted till weak and
faint.   1 know that many are ready to reply, with 
61
the convenient and magic word sympathy.   W e
are told that the stomach, by its nerves, gives no-
tice to the system of the good things it has in pre-
paration, and that the anticipation of them rouses
its dormant energies.  That stimuli and medicinal
substances partially produce their effects through
the medium of the nerves, I do not deny.   That
the sapid  properties of food have a similar influ-
ence, in a small degree, is equally probable.  The
stimulus of distension may also  have  an  effect
of this kind, though it cannot produce the invigo-
rating effects which we  experience so soon after
taking food, for the effect  is not in proportion to the
quantity, but to the  nutritious qualities of the ali-
ment. That feeling of renewed  strength, yvhich
every one experiences on breaking a long fast, as it
appears to me, is not well accounted for but on the
supposition that some portion of it soon enters the
circulation.  We are told, however, that the pro-
cess of assimilation does  not commence until more
than  an hour after the food is received, and that
during that time, and for  some time after,  so far
from  receiving, the digestive  organs are copiously
imparting.
   Physicians have in some instances attempted to
account for the suddenly invigorating influence  of
food  in the stomach, and also its effects when
thrown into the rectum,  by supposing that some
portions of it were absorbed  by the lymphatics. 
  ■ . y. + i,






.-> *t.(w> 
ESSAY, Ac-
                 chapter hi

 > >1GEST10N BY THE VEINS OF THE STOMACH AND INTESTINES.
                 AND BY THE LIVER.

   AFTER perusing the foregoing remarks, I trust
that the reader  will not be astonished at the title
of this  chapter.   The objections to a false hypo-
thesis, if they are  founded in fact arid properly
urged, must involve  some of those  circumstan-
ces which contribute to the explanation of what-
ever phenomena are the  subjects of our inquiry.
We will, therefore, commit ourselves to the  gui-
dance  of such  facts  as  have been  mentioned
above, and such  others as do notrequire to be tor-
tured into an accordance with our sentiments.

        Agency of the Mucous Membrane.

  In the foregoing chapter it appears, that no im-
portant change is effected on the aliment until  it
comes in contact with the mucous membrane of the
stomach.  I trust that I have also shown the exist-
ence of a gastric liquor possessing the powers so 
64
long attributed  to it, to be a fallacy.   As I have
before stated, we see the aliment come in contact
with the walls of the stomach,  and an important
change  immediately taking place upon it.  If I
understand the relation between cause and  effect,
we are not to interpose a new link in the chain of
sequents,  for the sake of aiding the imagination,
or for completing our preconceived notions.   The
presumption is, then, until some new intervening
cause can  be pointed out, that the change in ques-
tion is effected by immediate agency of the mucous
membrane of the stomach.  If we go beyond this,
and assert that the change is effected by a particu-
lar portion, or set of  vessels,  contained  in this
organ, we require further proof.  My proposition
is, that the first step in the process of digestion is
effected by capillary veins,  originating in the villi
of the stomach with  absorbing extremities, and
terminating in the great branches of the vena por-
tae.    The arguments  in favour of it  are  drawn
from the results of certain  experiments, from the
nature of the change effected on the aliment, from
the analogy of plants with  animals  and Trom the
anatomy and pathology of the digestive organs.

            Absorption by the  Veins.

  Much credit is due to those  who have  revived
and  so  ably  maintained the  ancient doctrine of
absorption by the  venous extremities.   It  is very 
O.J
evident that so  important a fact,  for I no longci
consider it questionable, must have an important
bearing on other physiological questions.  To them
I acknowledge myself indebted for the most im-
portant circumstances, which led  to the  opinion
I entertain with regard to digestion.  If there are
any who,  after scrutinizing the  experiments  of
Magendie and his pupils, are disposed to doubt on
this subject, I refer them to a series of experiments
detailed in the Philadelphia Journal of the Medical
and Physical  sciences,  as performed, apparently
with great labour and accuracy, by Messrs. Law-
rence and Coates.   I refer them, also, to the expe-
riments and opinions of a great majority of those
whose circumstances have given them an opportu-
nity to investigate the subject experimentally, for
their own satisfaction.   It will be found, that  in
many of  these experiments, certain  fluids, intro-
duced into the stomach, were conveyed  into the
mass of the blood, although every communication
of the absorbents with the blood vessels was cut off
by tying the thoracic duct and the lymphatic trunks
which enter the subclavian vein.   All that can be
expected  from  experiments upon the living isystem
is certainly accomplished in these instances, and
their results are as conclusive as the nature of the
vital laws will admit.  If any reliance is to be placed
upon arguments drawn from such a  source,  thev
certainly  furnish irresistible proof, that  at feast 
66
-some substances are taken into the circulation by
the medium of the veins of the stomach.
  If any, however, are so fastidious as still to
doubt, let them produce equally strong evidence
that the lympatics do actually perform the function
so long attributed to them.  We should not suffer
the revered names of Monro, Hunter, Cruikshank
and others, to cast a spell over this subject, and to
deter us from free inquiry.   Let the physiologist
adduce, from the writings of these men, evidence
that the  lymphatics absorb, equally strong with
that upon which Magendie and others have found-
ed  their opinions.
  I would not be understood to deny the function
which the  lymphatic and  lacteal  absorbents are
supposed to perform.  It would seem,  however,
that the  lymphatics performed some other  office.
Their contents, so far from appearing to be excre-
mentitious matters, consist of a fluid which is uni-
form  in its sensible and chemical properties and
which appears to be highly animalized, and resem-
bling the most important constituent principle of
the blood.
  If the lymphatics exert no influence on their
contents, but exist merely for the purpose of taking
up that which has become useless, and conveying
it into the  mass of the blood, why,  since nature
accomplishes her ends by the simplest means, do
not the absorbent branches terminate in the near- 
67
 est veins, instead of traversing so great a distance
 to reach the left subclavian ?
    From the length of these vessels, which is greatly
 increased by the convolutions which probably take
 place in the lymphatic glands, from the nature of
 their contents and other circumstances, we are led
 to inquire whether  they  are not concerned in  the
 important process of animalization, receiving cer-
 tain parts of the blood from the capillary arteries,
 yvhich they exalt to a higher degree of organic life.
 The manner in which their contents combine with
 the chyle in the thoracic duct, harmonises with  the
 supposition;  for  we may rationally suppose that
 they  exert an influence on the partially animalized,
 though comparatively crude fluid, introduced by
 the lacteals.  By the  theory at present received,
 the only fluid that nourishes the system, is here
 mingled with the  refuse matters.

          Different  substances absorbed.

  It being proved that certain coloured fluids are
taken up by the veins of the stomach, we may fairly
presume that the sudden, and hitherto unaccounta-
ble, disappearance of water, alcohol, &c. from the
stomach,  and its sudden appearance, under some
circumstances, in the blood and the urine, is owing
to its being thus absorbed.   This phenomenon has
been heretofore  explained by attributing extraor-
dinary energy of  action to the absorbents of the 
68
stomach, or by supposing the existence of a direct
communication between the stomach and bladder.
Who, however, on being made acquainted with the
fact that the veins of the stomach do absorb, and
that  they are incomparably more numerous than
the absorbents, will not account for it by the suppo-
sition that these organs are principally concerned ?
  But if the veins absorb water, alcohol, and the
prussiate of potash, it is certain that they will take
up those simple aliments which  are soluble  in wa-
ter.   A solution  of gelatin, for instance, must be
presumed to be as readily taken  up as the prussiate
of potash, and so also all the fluid parts of animal
substances.  Many other substances are also capa-
ble of yielding their  nutrient parts to water,  and
may also be taken up.
  Again,  if the  veins of the stomach absorb any
fluid substances except mere water, we do no vio-
lence to reason to say that they will, in  some way
or other, take up such substances as are insoluble,
so far as we know, by any thing contained in the
stomach.   Most physiologists believe, that certain
medicinal substances which are insoluble are,  ne-
vertheless, taken into the circulation by the absor-
bents.  The fact appears to me  to be  supported
by abundant proof.   We know, also,  very well,
that the bones and other solid parts of the system,
are  sometimes taken up by either the absorbents
or veins, with surprising rapidity.   In some instan- 
69
ces, the most intractable substances, when lodged
in the flesh, have  been  absorbed and  removed.
* Plants, by their roots,  decompose  the soils on
which they feed, and take up  substances which
are the most insoluble in nature.
   How it  is that  these  phenomena are  accom-
plished,  we cannot say.   Perhaps they may be
taken  up in a state of extreme comminution, and
perhaps  they  may  be resolved,  by the  powers of
life, into their ultimate, or in some instances, their
proximate  principles.
   That our food, solid and fluid,  should be taken
up by the veins of the stomach with  sufficient ra-
pidity to be subservient to digestion, is certainly not
absurd.  Vascular  and nervous as the stomach is,
we are to  presume that its vital energies,  in this
respect,  are far superior to those of any other tis-
sues in the system.   The surface  too, which it
presents to the food, when we consider its folds and
its papillae, must be very  great.
   The villi of the  intestines are known  to peform
absorption with great energy, and that  of a sub-
stance which  does not  appear to be altogether
fluid.  The villi of the stomach are certainly more
numerous than those of the intestines and, a priori,
we might  fairly presume, from their anatomical
  * I would observe that this analogy is not objectionable on the
ground that it is drawn from another kingdom.  The organic function^
*re common to both plants and animal?. 
70
structure, that they performed the same function
with greater energy.  But by the prevailing theory
of solution  by the gastric juice, their function is
entirely  different,  a  circumstance  noticed  by
Bichat as mentioned above.

            Sensible properties of chyme.

  The sensible properties of the  chyme  I  have
already mentioned as furnishing arguments against
the opinion in question.   They are not less im-
portant in the support which they yield our hypo-
thesis.  On the supposition that the villi of the
stomach act upon  the aliment as  suggested above,
electing from it such principles as are subservient
to nutrition, the appearances  of the chyme are
precisely what we should expect.   The sensible
properties   of chyme  suggested to some  of the
older anatomists the idea that the aliment was, in
the stomach, attacked by a myriad of small worms
which reduced it  to the  uniform pulpy mass of
this substance.*
  That this may be effected by a myriad of ab-
sorbing mouths, the changes which take place in
the aliment render not improbable.   An extremely
minute mechanical division would  of course  be
  * Perhaps they were as near the truth as  those who consider the
process to be performed by a chemical agent,  for neither the existence
of these wonderful worms, nor of the not less wonderful fluid  can be
proved, and if we reason from the effect alone, we should with more
propriety ascribe it to the former. 
; j
effected  upon it, and perhaps many substances
would be decomposed, some of their  proximate
principles being taken up. A change in the sensible
and chemical properties  equivalent to what we
actually  discover  would  of course take  place.
We should also expect that the chyme would be
variable  in its appearance as the food employed
varies.
  The manner in which different portions of ali-
ment are successively changed is also much more
satisfactorily explained by our hypothesis, for  that
only can be  acted upon which is in contact with
the surface of the stomach.  This, as stated by W.
Philip, by the peculiar action of the muscular coat
of  the stomach, is made to give place to another
layer and the digested portion is conveyed to the
pyloric extremity.  The appropriate motions of
the stomach are  constantly evolving the central
parts of  the  mass and bringing them in contact
with the  surface.

    Effects of division of the eighth pair of nerves.

  The results of the experiments of W.  Philip
harmonize much more perfectly with the opinion
which we offer, than  with the theory of Solution.
In  mentioning the phenomena which result from
the division of the eighth pair of nerves, we could
not but admire how the process of digestion should
                      10 
72
be  immediately  suspended, even  although the
food in the stomach be imbued with the gastric
liquor; particularly, as it is stated by the advocates
of the latter theory, that the  gastric fluid does,
after death, corrode  the walls of the  stomach.
If the most important influence exerted on the food
is by the absorbing powers of  the villi, and if the
villi receive their power  to act, as they undoubt-
edly-do, from the eighth  pair of nerves, the diffi-
culty is at once solved.

        Vegetables and Animals  compared.

  I have already suggested an analogy between
the digestion of Plants and of Animals.  This com-
parison may with  propriety   be  carried much
farther.
  Vegetable life is under the control of the same
ultimate properties which preside over the organic
life of animals.   Organic sensibility and contractility,
variously modified, produce in both the functions
of  assimilation, circulation, nutrition,  secretion,
&c.  Our logic  therefore, does  not forbid  the
employment of analogies  drawn from the vegetable
kingdom, the functions of which are less complex.
  One  of the characteristic differences between
plants and animals is, that  the former are fixed to
the earth by their roots, the radicles of which take
from the soil  whatever  affords nutriment to the
plant and convey it immediately into the circula- 
7tf
 lion, where it becomes assimilated to the different
 textures of the plant.  Animals on the other hand,
 must have locomotion, and to render this consist-
 ent with digestion, the animal is furnished with an
 internal cavity capable of receiving  those sub-
 stances which yield aliment, though  in a  much
 more concentrated state than they are  presented
 to the roots of plants.
   Plants, it has been  often observed, do, in their
 general structure  as well as in their organic pro-
 perties,  bear  a rude resemblance to animals.
 They  have  a  cuticle, a  cutis and a skeleton.
 Their sap vessels too,  perform a circulation more
 simple, indeed, but  not unlike  that of  the  blood
 vessels of animals, and their leaves  are obviously
 their lungs, in which their blood is attenuated and
 exposed to the action  of the air.  They have also
 their secernents and exhalents.  But  to what in
 the animal economy shall we compare the radicles
 of vegetables ?  1 think it  will appear that  there
 is no forced resemblance  between them and  the
 villi of the stomach.  The  roots of plants, indeed,
 are of comparatively great  length and necessarily
 so, for plants having no prehensive apparatus by
 which their proper aliment is elected and brought
 in contact  with their roots, the latter must go  in
quest of it, ramifying to a considerable extent from
the stalk of the plant  and drawing nourishment
from a great volume of soil.  Hence also the root? 
74
of plants are constantly  elongating  and multi-
plying.  The radicles of vegetables are indefinitely
small and  numerous, much  more  So than one
would imagine, who has merely examined such as
are torn from the earth.  If they are raised with a
large volume of earth and this be carefully washed
away, they will be found as minute and numerous
as the villi of the stomach.   The radicles of the
stomach are very differently circumstanced.  The
substances from which they are to elect food are,
in a much more concentrated  state, conveyed into
the cavity of the organ, and by  its  muscular
motions successively applied to iter* surface.  Yet
they probably have, in some degree, the power of
seeking their food by elongating themselves, and
by the mobility of the surface to which they are
attached.
  By the prevailing theory of digestion, however,
an action, by no means analogous to that of the ra-
dicles of plants, is  attributed to the villi of the
stomach, for these last are supposed merely to ex-
hale a fluid which acts chemically upon the con-
tents of the organ.  Thus too the digestion of an
animal must be less under the control of vital or
organic properties than that of the humblest plant;
for in the latter, nothing appears to  be left to the
agency  of  physical  properties, but  all to be ac-
complished by  the  vital or organic  powers.
The radicles of plants are endued with the sur- 
15
prising power of acting upon the most intractibie
substances and conveying them into  the circula-
tion, thus silex is detected in the textures of some
plants.
  We should expect, in rising from the lower to
the higher grades of existence, to find the functions
more purely and exclusively under the control of
those laws which constitute  life, but if the above
theory be true, the laws of inorganic matter have,
so far as we can ascertain, more influence over the
animal  than  the  vegetable  functions.   Is  it not
then  more rational to infer from the analogy of
structure which I have pointed out,  a correspond-
ing one of action, and that the villi of the stomach
are endued with the power of electing and absor-
bing alimentary substances ?
  If the above analogy does not carry with it con-
viction, yet  I am  persuaded that  to those  who
take  a comprehensive view  of the works of nature
and the relations which the  different orders of be-
ings bear to each  other, it  will at least be a cor-
roborating circumstance.

         Digestion of the inferior animals.

   The phenomena attending  the  digestion per-
formed by some of the inferior  animals are highly
interesting,  and  as  the  process  in them  may
be  presumed to be  more  simple,  they may as-
sist  to elucidate  our subject.    I  have  already1 
16
spoken of the digestion of the polypus.   From its
being properly classed with animals it  has been
presumed that its digestion is performed in a simi-
lar way, and that the substances taken into its ca-
vity are acted upon by a  gastric juice secreted
for that purpose ; yet no one has ever demonstra-
ted this fluid, or  that the digestion of the polypus
is effected by it.
  This animal is, by its structure, scarcely distin-
guished from vegetables.   The only circumstance,
which characterises it as  an  animal, is the fact
that  instead of deriving its nourishment  by means
of roots from the earth, it takes it up from an in-
ternal cavity into whiqh  it is  conveyed.  If then
we are to presume any thing with regard to the
digestion of this  animal, is  it not more rational to
suppose that the digestion  of a being which only
differs from a vegetable in the nature of its food, and
in its taking it up by an internal instead of an ex-
ternal surface, will perform this function nearly in
the same manner with a vegetable ?  This suppo-
sition furnishes  us with a beautiful and  easy gra-
dation of function, as well as of structure, from the
vegetable to the animal kingdom.
  But there are animals which  may be regarded
as of a still lower order  than the polypus, and
which do not even  possess the internal cavity of
that animal, but take up their nourishment by
means of a kind of placental surface.   Does any 
i '
                       i I

one believe that they perform digestion by means
of a gastric juice ?
   While amusing myself with angling, I once took
a trout which had swallowed one of its  own spe-
cies of half its own length.  The tail was still out
of its mouth, and only the head and a small part of
the body  were  in the  stomach, and  these parts
were  considerably  digested.   The  appearance
which it presented was something different from
what I had anticipated on the supposition that di-
gestion  is performed by the  gastric juice.   It
appeared as if a considerable  part  of the sub-
stance of the fish had been eaten away, while that
which remained upon the bones was altogether
unchanged.    In  the stomach was  nothing like
chyme nor chyle, that I could discover, but merely
a frothy mucus.   I  had at that time no favourite
theory to support, and even then, the circumstance
staggered very, much, my belief in the commonly
received theory  of digestion.*

       Assimilation effected by capillary vessels.

  But I fancy that my opponents are impatient to
inquire of me in what manner the changes of  as-

 * In the writings of Sir William Jones is to be found an account of an
animal named the Pangolin, the stomach of which was frequently exa-
mined by the author, and never any thing but mineral substances found
in it.  The singular circumstance led him to query whether the animal
did not derive its nourishment from this source, and by a process in the
stomach similar to that performed by the roots of plant*. 
                      78
                       «
limitation are wrought, and what apparatus is ap-
propriated to that function, in case the process is
so little effected in  the cavity of the stomach.  I
reply, that it is accomplished in the capillary and
other vessels, through which the aliment  is made
to pass before it is added to the circulating mass
of the blood.
  It is obvious that whatever  is absorbed by the
veins of the stomach will be first conveyed through
the tissue  of vessels  indefinitely  minute, which
may be said to compose the villi  of the organ;
next through the branches which ramify in the cel-
lular coat, through the long tortuous vessels of sen-
sible magnitude meandering upon the suface of
the stomach and between the laminae of the peri-
toneum.
  This, however, is not the most interesting part of
its course.  On reaching the trunk of the vena por-
tarum, along which it is slowly propelled, proba-
bly by the action of that, vessel, it  is conveyed to
the great fissure of the liver, to be diffused through
that large and important viscus, having first  been
mingled with the returning  blood of the spleen,
the pancreas, the omentum, &c.  It is then again
subjected to the action of a congeries of capilla-
ries constituting the substance of the liver.
  Here, then, is an ample opportunity for all those
changes to be wrought, which may be deemed ne-
cessary for the conversion of aliment into blood. 
79
This supposition  too, accords well with what we
observe in the performance of other functions, by
which changes are wrought in the properties of
circulating fluids, viz. that they are accomplished
not upon lage volumes and in large reservoirs, but
upon attenuated streams and in minute vessels.
   I have heretofore objected to the prevailing the-
ory, that it does not appreciate the importance of
the liver nor attribute to it an office corresponding
to its magnitude, structure and pathological con-
sequence.  The hypothesis which we offer exalts
it to the highest degree of physiological impor-
tance, regarding  it as, perhaps, the most efficient
organ concerned in animalization.

        Circulation of the vena portarum.

  Anatomists have heretofore had no settled opi-
nions with regard to the end for which the blood
is circulated  through the vena portarum.  Some
have supposed it to be merely preparatory to the
secretion of bile; others, that it is for the purpose
of preserving an  equilibrium in the circulation of
the blood. With regard to the first opinion, the
secretion  of bile does not appear tobe a matter of
sufficient importance to  account for all this appro-
priation of apparatus.   The latter does not bet-
ter comport with what we observe of the means
which  nature employs  to  accomplish her  ends.
                     11 
ao
That a system of vessels is furnished merely for
the purpose of keeping a portion of the blood for
a time out of the general circulation, is too  much
like the belief that the spleen is packed into the
abdomen just to fill up the vacant space and to
make all snug, and for the same reason that a
traveller tucks an old coat into his trunk.  These
minor  objects are undoubtedly accomplished in
the animal economy, but never at such an expense
of means.   Such a  wonderful harmony  pervades
the whole, that  these circumstances must be pre-
sumed to  follow in the train  of those which are
more important.
  In some respects the circulation through the ab-
dominal vessels is even more  interesting than that
through  the lungs.   Their  contents  are  made
twice to pass through capillary vessels, the trunk
of the vena portarum performing between them an
office something like that of a heart.

        Phenomena of the Festal circulation.
  A reference to the phenomena of the foetal cir-
culation will, as  I think, tend to  confirm what I
have advanced with regard to the functions of the
liver and the vena portarum,  and also  to display
a beautiful correspondence between the changes
which at the time of birth, take place in this cir-
culation  and that  of the  lungs, that, so far as I
know, has not been heretofore pointed out. 
ai
  It is welt known that previous to birth the liver
predominates  over all the other  viscera.   It is
undoubtedly thus early developed for important
purposes, performing, at that time, some indispen-
sable office in the foetal system.  It is conjectured
by some that at that time it exerts an influence on
the blood which is subsequently assumed by the
lungs.   The  blood which is  received from the
maternal system is conveyed to the liver by the
umbilical vein.  It there  enters the  portal sinus,
a part of it being taken up by the ductus venosus,
while a large proportion is conveyed by the  rami-
fications of the vena portarum through the  glan-
dular structure  of this organ.  It is not in  vain
that the feetal blood is  thus  circulated through
the liver, it is undoubtedly for the  purpose  of its
being wrought upon by  the  capillaries of that
gland, and it is  for this purpose that the liver is
thus early perfected.
  In the foetal state the system of the vena portae
is organized at the same time with the digestive
organs,^but, like the vasuclar system of the lungs,
it  is in  a great degree dormant, the  quantity of
blood which it conveys being merely sufficient for
their nutrition.   The  moment, however, that di-
gestion  begins to take place  after birth,  these
organs  become centres of fluxion, and the vena
portarum becomes charged with blood possessing 
82
peculiar properties which, in some way or other,,
it receives in the stomach, intestines &c.
  At birth the circulation  by the umbilical  vein
immediately ceases, and its place, as soon as di-
gestion commences, is  supplied by  that  of the
blood of the vena portarum.  Must we not infer,
then, that this last is circulated  through the  liver
for  the same purposes as the  former? for  it is
conveyed in the  same  vessels, and we  cannot
suppose  that they are at once endued with a new
action, entirely different from that which they had
before performed and which is merely for the pur-
pose of furnishing bile, a fluid which is not needed
in the foetal state, as no digestion then takes place.
  Here, then, as well as in the lungs, we see a
surprising change  taking place in the circulation
at  the time of birth, not so  promptly, indeed, as
that of the lungs, nor so immediately essential to
the continuance of life, but  not  less so in its ulti-
mate effects.  We have  every reason to think that,
as  is the case  often in the lungs, so also in the
portal  system an  imperfect  establishment of  its
circulation, either  from organic defect in the  liver
or some other organ, is often the cause of infantile
diseases  marked with  indigestion and  imperfect
assimilation  and which often terminate  fatally.
Who, that has been engaged in extensive practice,
has  not  witnessed the  frequent  occurrence  of
infa/itile  jaundice, and that too taking  place  as 
83
soon as digestion has commenced, and in children
born apparently healthy.
   An interesting  case of the  kind has recently
occurred in my own practice.   The birth of the
child was supposed to be premature by three or four
yveeks, and occasioned by a rupture of the mem-
branes and discharge of water, at first unattended
with pains.  The child, when born, was  of the
natural  complexion  and apparently well;  but  as
soon as it  began to take the milk of the mother
the skin began to assume a deep yellow hue, the
abdomen swelled and digestion appeared  to go
on  imperfectly.   The  bowels were obstinately
costive.  By the use of the blue pill, accompanied
with other laxatives, the health was in a measure
restored, the skin assuming a healthy complexion
and the digestive organs performing their functions
more perfectly.   Still, however, all was not right;
the bowels  remained tumid, and the costiveness
such as to require the occasional use of a cathar-
tic.  The  birth  of the child occurred  in the
spring.  These  symptoms continued during the
summer and following winter;  the child  grew,
however, and was thought by the  parents to be
otherwise  well.   At the age of one year, by my
advice, the child was weaned.   This change ap-
peared, for a time, to be favourable to  its health.
It was found necessary, however, to restrict it  to
the most simple and easily assimilated articles. 
84
Cows milk it could never take.  The article which
appeared to be most suitable was arrow root, and
this was for a time almost exclusively used.
  In the summer, however, bowel  complaints be-
gan to prevail among children.  It is to be ob-
served also, that at Burlington, Vt, where the case
occurred and  in its neighbourhood, intermittent
fevers occasionally  happen,  and in the summer
most diseases exhibit a bilious character.  At this
time the little sufferer became afflicted with a
kind of lintery, its food appearing to glide through
the alimentary canal  without  having  undergone
any  change, and accompanied with  a copious
secretion  of mucus.   The treatment which  I
found successful  in similar cases proved unavail-
ing.  I then directed that it should be  removed
into the country remote from the  atmosphere  of
the lake;  in this also we were disappointed.  At
this  time, and when we  had  given up all  confi-
dence in medicine, and almost entirely our hope
of its recovery, the mother suggested to  me that
the child had manifested a desire for the breast.
I immediately advised that  a healthy wet nurse
should be procured, but the child would not suffer
itself to be taken by any woman but its mother.
I then directed that it should be fed with the milk
of a healthy woman, whose child was six months
of age and perfectly healthy.   Immediately every
thing was changed;  the diarrhoea ceased: the rest- 
85
 lessness, which had been extreme, was succeeded
 by refreshing  sleep; the appetite improved and
 the child took eagerly of the breast milk, although
 it would not swallow a drop of cows milk.
   The  little patient gradually recovered  health
 and strength,  but  whenever any other food was
 substituted, the same symptoms recurred.
   On the approach of cool weather, however, the
 breast milk yvas gradually  withdrawn, and  the
 digestion of the most simple aliments appeared to
 go on in the regular and healthy manner, and the
 child was restored to perfect health.
   I know very well, that these causes are not un-
 accountable upon the supposition that digestion is
 effected by the gastric juice, and that the most im-
 portant function of the liver is the secretion of bile ;
 but are they thus accounted for in an equally satis-
 factory way ? and does the explanation harmonize
 equally well with what we discover in the anatomy
 of these organs ?  We have shown,  that the secre-
 tion of bile is  probably  effected from the arterial
 blood  of the liver.  The circulation of this, we
 know, is perfect in the foetal state, and that no
 great change is effected in it at  birth ;   but as a
 new circulation by the vena portarum occurs, and
 as by our hypothesis, the blood conveyed by it is
 charged with alimentary matters  which may be
 presumed to produce a new excitement in the liver,
it is easy to conceive, that any  organic  defect in 
86
the liver  or an imperfect preparatory assimilation
in the branches of the vena portarum, which ori-
ginate in the stomach and intestines, may derange
all  the functions of the organ.  Pathological and
physiological  phenomena  harmonize  beautifully
with the supposition, and certainly furnish us with
very plausible arguments.  That they may be duly
appreciated and receive their proper weight, is all
that I ask.
  In conclusion of this section, I would  point out
an interesting analogy which follows from our hy-
pothesis, between what may be called digestion in
the foetal state, and digestion after birth.  It is
pretty well ascertained and if I mistake not,  gene-
rally believed, that the  foetus must be  nourished
from the  blood of the  mother,  by means of the
absorbing powers  of the capillary veins in  which
the umbilical vein terminates, and which appear to
constitute a considerable part of the foetal portion
of the placenta.   By our hypothesis the function
at birth, is transferred to the capillary veins of the
vena portae, which as above, appears to perform
precisely  the same office in relation to the liver,
that the  umbilical vein does  before birth.   Let it
be carefully noticed too, that they are the opposite
extremes of the same continuous vessel.
  Another circumstance which  strengthens the
analogy between the nourishment of  the  foetus 
87
 and digestion after birth is,  that as a part of the
 nutriment in the latter case is, without circulating
 through the liver, as I shall by and by more par-
 ticularly state, conveyed by the thoracic duct into
 the venous  blood,  to  be circulated  through  the
 lungs before it serves the  purposes of nutrition ;
 so also in the former, a portion of the foetal blood,
 by the ductus venosus, immediately enters the heart,
 and as it has in the plaeenta undergone that change
 which after birth is effected by the  lungs, it is im-
 mediately  fit for  nutrition and is   distributed for
 that purpose.
   In considering this subject, we are very naturally
 led to inquire whether the blood of the vena porta?
 exhibits any properties which would  favour  tlie
 belief that the veins of the stomach and intestines
 do largely  absorb alimentary substances.  The
 unbiassed observations of many, furnish us with a
 satisfactory reply.  Dr. Rush, who quotes authori-
 ties in support  of the assertion, tells us that the
 blood  of the vena portae  is more crude than  the
 blood of other veins, that it coagulates more slowly,
 and that it undergoes putrefaction less  readily;
 circumstances which decidedly indicate a less  de-
 gree of animalization.   I believe  it is commonly
thought by physiologists,  that the  blood of this
 system differs more from arterial blood than thai
of other veins.
                       1? 
88
  Haller asserts that he detected oil in the blood
of the vena portae.   We may have the more confi-
dence in his observation, as he was not at the time
searching for appearances of this kind for the pur-
pose of substantiating a favourite hypothesis.
  The experiments of Flandrin, as quoted by Ma-
gendie, are decidedly in point.  " In the horse, the
substances  contained both in the large and  small
intestines, are generally mixed with a large quan-
tity 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 intestinal 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 in-
testines 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  degree.  The blood in the other
parts of the body presented nothing of the  kind.
A half pound of assafoetida dissolved in an equal
quantity of honey, was given to  a horse ; the ani-
mal was afterwards fed in the usual way, and killed
in about sixteen hours.   The odour of the assa-
foetida was very distinct in the veins of the stomach,
small intestines, and coecum ; it was not remarka-
ble in the arterial  blood nor the lymph."  p. 307 
8U
   It appears to me surprising that the result of
these experiments, which are of such  a decided
character, did not suggest the hypothesis which, I
think I may say without vanity, we have found at
least very plausible, upon other grounds.
   It is not to be supposed, however, that, under
ordinary circumstances, the presence of aliment in
the vena portae is to be easily demonstrated.  We
must recollect that, during digestion, the circula-
tion in the exceedingly vascular organs concerned,
is much increased, that the alimentary matters are
also mingled with the returning blood of the spleen,
pancreas, &c, and that hence, it must be greatly
diluted.
   Another inference which  may be drawn from
the above experiments is,  that the portion of the
aliment which  is found in the vena portae is in a
much  more crude state than that of the thoracic
duct.

    Objections to the hypothesis of Absorption.

   The arguments which would seem to oppose the
opinions which I have endeavoured in the forego-
ing pages to substantiate, are many of them  the
same which favour the  theory of solution by  the
o-astric fluid.  I have already attempted a refuta-
tion of them.   Other difficulties which appear to
arise from the structure of the organs concerned 
90
in this  function, I have endeavoured to solve.
There are some, however,  whieh present them-
selves, of which we have not found occasion to
speak.
  It might, perhaps, be thought that if the veins of
the stomach, in addition to  their transmitting the
blood which they receive from the arteries, do also
absorb and  convey so great a volume of aliment,
they should be  found in greater number, in pro-
portion to the arteries, than in other organs.
  In reply, it is only necessary to call to mind that
the arteries of the  stomach  during digestion are
exhaling as great a volume of fluid as is absorbed
by the veins.  Here  we may notice, too, in the
supposition, an  interesting correspondence of ac-
tion which supports the  doctrine of venous absorp-
tion.
  That the arteries of many organs copiously ex-
hale, no one doubts.   That the veins absorb is not
so demonstrable; but when  we take into conside-
ration the relation between the arteries and veins,
that the arteries convey  the blood from the centre
of the system, and that the veins return it, absorp-
tion is certainly the function which, in the veins,
corresponds to  exhalation of the arteries.
  That we shall be able to  prove or disprove the
function which I attribute to the villi of the stomach,
by comparing the weight of the food taken in, with 
91
what remains at the time that it begins to be trans-
mitted  to  the  intestines, I think very doubtful.
Its consistence  is, as we have  stated, entirely
changed, and its volume and weight are so much
increased by the exhaled fluids, that the removal of
its more nutrient parts might not be appreciable.
  The cases of mal-formation, related by Abertheny
and Lawrence, would, at first view, operate against
our hypothesis.  I think, however, that they are
capable of an explanation which gives it additional
weight.  It will be remembered that the hepatic
artery, in these cases, was much larger than usual.
Now it is obvious, that the whole mass  of blood
must have been in a  short time subjected  to the
action of the liver.  Usually the aliment is conveyed
by  the  vena portae to be acted upon by  the  liver
before it is added to the  mass of the  blood.  In
the above cases there is this difference, that the
aliment must first have been mingled with the mass
of the blood, after having undergone the action of
the absorbing veins of the stomach and intestines,
before it was acted upon  by the liver.
   These cases, then, bear a striking resemblance
to those of mal-formation of the heart, in which life
is for a  long time supported,  although but a small
proportion of blood passes through the lungs.   The
spleen  and the pancreas would,  probably, under
snch circumstances, vicariouslv assist the  liver. 
92
  I presume that it will be inferred, from what has
already been said, that I by no means deny in toto
the functions attributed to the lacteals.  Their of-
fice is, undoubtedly, to take up a portion of the ali-
ment, to subject it to their own action and that of
the mesenteric glands, and finally to pour it into
the mass of the blood.  They probably absorb
that part of our food which  is capable of being
converted into some one of the constituent parts of
the blood, without undergoing the action of the
liver.   What  part of this  fluid it is which is fur-
nished by the  lacteals, and what by the liver, I am
unable to say.  It has been supposed by some, that
the latter organ was concerned in elaborating the
red globules.  That it assists in completing some
one or more of the constituent parts of the blood,
I think will follow from what has been said.
  The argument against the theory of solution and
that in favour of immediate absorption, will recip-
rocally aid each other.   If the objections against
the former are founded in  truth,  they render the
latter the more probable;  and  if the latter hypo-
thesis is supported by analogy and by fact, the ob-
jections to the former are the stronger.   I have to
request of the reader that he will view this attempt
in all its parts, and estimate their united weight. 
y3
  In conclusion of this essay I would observe, that
I am aware of the caution with which objections to
a long established system are received.
  It was said by a distinguished logician, Dr. John-
son, that "After a system is well established upon
positive evidence, a few partial objections ought
not to shake  it.  The human  mind is so limited
that it cannot take in all the parts of a subject, so
that there may be objections raised against any
thing."
  We cannot, indeed, be too  well guarded against
perplexing sophistries of this kind, but if the reader
will take the trouble to review the objections which
have been adduced against the theory of digestion
by  the gastric juice, he  will discover that so far
from being partial, they have  a very general bear-
ing upon the system in question, and that they are
intended  to meet the arguments upon  which  it
chiefly relies.   It is to be recollected too, that this
system is by no means founded  upon positive evi-
dence, but such as is, at best, equivocal. 
 
                     ERRATA.

1'age  7.   2d line,  for and (the physiological, 6cc.) read
           with (the physiological, &c.)
  „   54.   7th  line  from  the  bottom,  for  chyme, read
           chyle.
  .,   66.   5th line, for lympatics, read Itjmphatics.
I 
/