nification, is sufficiently explained by their
sojourn in the intestine at the ordinary tem-
perature ; or by the direct effect of this kind
which the pancreatic fluid could produce,
supposing it not overpowered by the gastric
juice. But Bidder and Schmidt offer the fur-
ther suggestion, that even neutral fat is aided
in penetrating the villus by the moistening of
its surface with bile : a view which they
confirm from experiments with capillary tubes
and dead animal membranes.
The continuous absorption of these various
alimentary principles constitutes the chief
share taken by the remainder of the intestinal
canal in the function of digestion. And as
this absorption requires contact, too rapid a
transit of the canal, or too limited an extent
of digestive tube to be traversed, present much
the same appearances in the food, and produce
a very similar effect on the organism. Thus
the fasces expelled in intestinal fistula, on
the one hand, or in diarrhoea on the other,
alike exhibit a large quantity of undigested
starch, protein, and fat ; with unabsorbed bile
and water. And the fatal exhaustion which
often accompanies both* of these states, is
evidence of the virtual starvation which may
thus be brought about.
From the little change undergone by pro-
teinous substances artificially introduced into
the large intestine, as well as from the com-
parative development of this part of the canal
in the carnivorous and herbivorous classes, we
400
STOMACH AND INTESTINE.
may conjecture that its absorptive powers are
chiefly intended to be exercised on the water
of its contents ; and on the sugar and lactic
acid produced by that slow metamorphosis,
which dense starchy substances would here
continue to undergo. But in animals like
the Horse, whose aliment passes quickly
through the stomach and small intestine into an
enormous colon, it is difficult to avoid believ-
ing, that a more or less modified gastric juice
accompanies the insoluble albuminous com-
pounds of the food into this segment of the
canal, and continues its solvent action during
their long sojourn in its interior. It would
otherwise be almost impossible to explain the
nutrition of such animals. How far the
large intestine can take up fat remains un-
known. But it seems certain that its share in
the absorption of this alimentary principle is
very slight compared with that of the small
intestine.
The entire process of digestion might there-
fore be described as consisting in the applica-
tion to the food of a variety of agencies, such
as mechanical division, solution, and metamor-
phosis. In whatever manner these are ap-
plied (either to the food as a whole, or to the
several alimentary principles which form its
constituents), and whether they operate in suc-
cession or combination in any case, they all
work towards the same object : namely, that
of preparing the food for absorption by the
vessels and lacteals which occupy the walls
of the digestive canal. With this act of ab-
sorption, the function of digestion terminates.
The chief agents of this process of division
and solution, we have found to consist of
certain liquid secretions ; which are poured
into the canal, either by the ducts of several
glands, or by the vast compound mucous mem-
brane that lines the various parts of its cavity.
In short, the food received into the intestinal
tube, mingles with a large quantity of a mixed
fluid ; which itself represents the aggregate
contributions of the salivary glands, the
pancreas, the liver, the stomach, and the in-
testine.
But the more accurate researches which
have recently been made on the nature and
amount of these secretions, confirm a suspi-
cion that has long been entertained with
respect to some of them by physiologists.
Comparing their quantity and quality with that
of the faeces and the food, we can now confi-
dently state, that but a very small fraction of
their whole mass leaves the canal with the
excrements ; by far the greater part of it
being reabsorbed into the vessels of the ali-
mentary canal.
This proposition so important to a cor-
rect appreciation of the true office of the in-
testinal canal, and of the relation of digestion
to nutrition has lately been placed in the
clearest light by the admirable researches of
Bidder and Schmidt upon animals. From
their toilsome and accurate experiments, it
would appear, that the total quantity of matter
which thus leaves and returns to the cir-
culation of an adult man, may be esti-
mated at little less* than 20 pounds of liquid
daily ; of which about 3 per cent, consists of
solids in solution. The importance of these
" recrementitious " secretions to the system, is
well shown by the results which follow the
establishment of an artificial biliary fistula.
Unless the ensuing loss of bile is compen-
sated by the digestion of a much larger quan-
tity of food, the animal so operated on soon dies
of inanition. And it is probable that the ex-
haustion produced by diarrhaea, or by the
discharge of the intestinal contents through
an abnormal opening in the bowel, may be
partially due to a similar loss of this and other
rich organic fluids, which ought to be reab-
sorbed.
Whether the secretions experience any
change prior to absorption whether any of
them are really modified, and thus far digested
by their colleagues remains at present in
doubt. It may be conjectured, however, that
they are so altered. At any rate, it would
seem that, by provoking these secretions f,
the whole system of a starving animal may
be for a time invigorated and restored. But
the chain of these phenomena is at present
too indistinctly seen, and their connection
with various other organic processes much too
obscure, to justify us in doing more than offer-
ing this conjecture, as one of the most imme-
diate explanations of certain well-known facts.
But we know enough to state that, within
the limits of ingestion and egestion, lie two
corresponding acts of absorption and secre-
tion. Each of these is, so to speak, the co-
efficient of two elements. Absorption takes
up food and secretions : secretion pours out,
not only materials newly devoted to this
purpose by the system, but others which have,
in all probability, already subserved it many
times before. The great mass of the intesti-
nal secretions is thus continually revolving in
a cycle : forming a circulation the channel of
which, placed in the intestinal canal, leaves
and returns to the blood that flows in its
walls ; and only allows a very small offshoot
of its current to reach the outer world, bear-
ing with it certain of its effete particles.
The important chemical details of this cir-
culation have yet to be won by sedulous and
thoughtful " questionings of nature." But
since, for the acquisition of such results, the
liver offers what will probably be the easiest
prize, it may be useful to point out how little
even the vast progress of modern chemistry
has hitherto been able to establish respecting
its true physiological import. The portal blood,
* From the greater proportionate waste of small
animals, it is possible that this estimate (22 Ibs. for
an adult weighing 140 Ibs.) is rather too large.
f Some of the American Indians are alleged to
eat clay with the object of allaying hunger. The
drinking of water is well known to have a similar
effect, and has been shown to increase the quantity
of these secretions without causing a converse dimi-
nution of their density. And the benefit which a
starving person derives from the minutest portion
of food is sometimes so sudden and remarkable,
that we can scarcely avoid referring it to the same
explanation. (Compare 1 Sam. xiv. 27. 29.)
STOMACH AND INTESTINE.
401
charged with the water, fat, albumen, salts,
and extractive, which it has taken up from
the food, and from the secretions of the diges-
tive organs, reaches a large gland. There it
breaks up, as it were, into two streams of fluid:
bile, and hepatic-venous blood. And hence,
the composition of these two fluid products,
compared with its own, might be expected
to give us a clue to the process by which they
originate, if not to the action of the secreting
structure itself.
Such an examination would show that the
hepatic blood has lost almost all the fibrin,
half the albumen, much of the water, and
half the fat (even more of the elain) present
in the portal vein. It has gained in extrac-
tive, and especially (ten to sixteen times as
much) in sugar. And its pale corpuscles are
increased in number.
On the other hand, the organic constituents
of the bile are chiefly fatty substances, espe-
cially the fatty cholic acid and its congeners.
The quantity and quality of most of these sub-
stances show that they have probably been
formed in the liver : and hence that their pre-
sence in the bi e is not to be explained as a
mere transudation of certain dissolved con-
stituents of the blood, followed by their con-
centration in the gland, such as might be
alleged in the case of most of its salts.
But here for the present we rest. Sugar on
the one hand, and certain fatty acids on the
other, appear to be formed in the liver ; at
the expense of fat, albumen, and fibrin. Until
accurate quantitative researches establish
whether the disappearance of the protein-
compounds is sufficiently accounted for by
the total increase of extractive and of pale
corpuscles in the bile and hepatic vein, the
exact source of these substances must re-
main a mystery. Schmidt, indeed, suggests,
that the fat of the portal blood is decomposed
in the liver into the sugar and cholic acid
which its elements would exactly make up.
But while we are justified in giving every
consideration to a view which seems so con-
sonant with the facts hitherto known, we
must be careful to remember that it is on
these facts, and not on the neatness of any
formula, that its value entirely depends. Un-
supported by them, it would be a mere ar-
rangement of certain letters and figures, de-
void of all real significance, and destined
to the oblivion to which thousands of its
predecessors in the literature not the
science of chemistry are daily being con-
signed.
DEVELOPMENT. The development of
the alimentary canal, like that of other or-
gans, offers a series of complicated changes,
the details of which often have but little visible
or direct relation with the future function of
the part. Hence any minute description of the
process would be quite out of place in this
essay. The author therefore limits himself to
a brief sketch of its general outline ; and for
all further details begs to refer the reader to
the article " OVUM."
Supp.
Just as the completely developed intestinal
tube might almost be described as the involu-
tion of an extremely vascular cell-growth, so
its origin distinctly refers it to those two
germinal layers of the embryo from which
such mucous and vascular structures are re-
spectively derived. The centre of the early
ovum consists of three layers ; the upper or
serous, the middle or vascular, and the
under or mucous, lamina. A portion of each
of the two latter is folded inwards, to form the
rudiment of the alimentary canal. And the
whole history of the subsequent development
of this tube is little more than a recital of the
various steps and processes, by which these
mucous and vascular structures are so arranged
as to result in the characteristic form, the nu-
merous segments, and the complex structure,
which have been briefly described in the fore-
going pages.
The formation of the tube begins by the
separation of the united vascular and mucous
layers from the serous lamina immediately
above them. An increase of this separation
prolongs their attachment to the serous layer
into a simple and rudimentary mesentery.
Each end of the canal is then mapped out,
by the conjoined laminae being bent down-
wards and inwards, so as to give rise to two
shallow pits or fossae: which are named the
fovea cardiaca, seu aditus ad intestinum ante-
rior ; and the foveola caudalis, seu adilus ad
intestinum posterior. These two fossae, how-
ever, do not correspond to the future mouth
and anus ; but to the cardiac aperture of the
stomach, and to the middle segment of the
rectum respectively. And between them, a
lateral inflection of the conjoined mucous and
vascular layers gives the canal two sides, the
laminae intestinales ; which, like the similar
vertebral plates of the serous layer, bound
a shallow groove. This groove, the fissura
intestinalis, is rapidly converted into a tube, by
the closing in of its inferior or open surface.
The process of closure begins at each ex-
tremity of the groove, and runs rapidly to-
wards its centre ; but is arrested here, so as
to leave an opening or umbilicus, by means
of which the intestine is connected with the
umbilical vesicle that replaces the vitelline
membrane and yolk. But there does not
seem to be any direct continuity of the vitel-
line and intestinal cavities with each other
through the channel formed by this umbili-
cal ("omphalo-enteric") duct: at least not
such an aperture as to allow of the yolk itself
being immediately received into the intestine.
As the umbilical vesicle gradually removes
from the intestine, this duct undergoes a cor-
responding elongation. Its canal becomes
obliterated prior to the degeneration and dis-
appearance of the tube itself.
The simple straight cylindrical canal, the
development of which has thus been traced
out, resembles the permanent intestinal tube
of many of the lower animals ; with the ex-
ception that, as above stated, it is deficient in
both terminal segments. These it next ac-
quires. And at the same time that it does so,
D D
402
STOMACH AND INTESTINE.
it assumes the length, form, and convolutions,
proper to the perfect intestinal tube.
As it already occupies the whole length of
the abdominal cavity, any elongation of the
canal will of course give it a curved shape.
And since, at this period of fetal life, the
abdomen opens by a wide vertical fissure in
the situation of the future umbilicus, the
first bend of the intestine renders it convex
forwards, and then protrudes it through this
aperture. Here it adjoins the base of the
umbilical duct ; which opens into the point
or angle of this convexity, so that the bowel
appears like a bifurcation of the duct itself.
The two forks of this bifurcation are soon
produced into a spiral coil of intestine;
which still lies outside the abdominal cavity,
and only recedes into it at about the middle
of the third month of uterine life.
At this stage of its evolution, the intestinal
canal may be conveniently described as con-
sisting of three portions : an anterior, which
extends from the beginning of the tube to the
umbilical coil ; a middle, which is formed by
this coil itself; and a posterior, which readies
from the latter segment to the end of the
canal.
The anterior of these three portions may
again be subdivided into three similar seg-
ments. The first, which gradually elongates
from the blind end that was formerly the
fovea cardiaca, is developed during the evolu-
tion of the thorax, so as to form the oeso-
phagus. And it finally opens into the cavity
of the mouth ; which is itself developed from
an involution of the skin, and from the united
ends of the anterior visceral arch. The second
or middle segment dilates, turns on its left
side, and then bends transversely to the axis
of the body, to form the stomach. The
pyloric valve is only visible some time after
this change has occurred. And the third or
lowest portion of this anterior segment is con-
verted into the duodenum.
The middle, umbilical, or extra-abdominal,
part of the canal, is developed into the jeju-
num and ileum, the ccecum, the vermiform
appendix, and part of the colon. In this
process, the change of form undergone by the
small intestine is limited to a mere increase
in its length and in the degree of its con-
volution : an alteration which is accom-
panied by a further elongation of its mesen-
tery. The upper boundary of the large
intestine is first seen as a constriction and
change of calibre, which occupy a point
some distance below the insertion of the
umbilical duct. Such a situation of the
future ccecum conclusively shows, that the
vermiform appendix is not that permanent
intestinal end of the duct, which Oken
supposed it to be. This commencement
of the large intestine next enlarges into
a projecting pouch of uniform width. But
the lower end of this pouch soon ceases to
enlarge, and remains as the vermiform appen-
dix. While its upper part, increasing in size,
becomes the ccecum. The valve appears at
about the tenth week. But the proper shape
and size of the coecum are only acquired
towards the end of foetal life.
The colon is developed from the lower
part of the second, and the upper part of
the third portion of the rudimentary intes-
tine. The ascending colon is at first a simple
straight tube, which, commencing in the
pouch just alluded to, runs forwards along
the spinal column, lying to the left of the
numerous coils of the small intestine. The
succeeding backward bend of this tube has at
first a median position, which renders it par-
allel with (and close to) the ascending colon.
But this part of the canal soon elongates ; and,
passing outwards towards the left side, forms
the transverse and descending portions, as well
as the sigmoid flexure, of the colon. Finally,
the blind end which corresponds to the rec-
tum is continually moved downwards by a
gradual lengthening of the tube; so that it
meets, and at last opens into, a cavity, which
is sent inwards from the skin to form the
future anus. The sacculatioH of the large
intestine only occurs in the latter half of
uterine life. The valvulae conniventes appear
still later, and are but rudimentary at birth.
The development of the various microscopic
constituents of the canal may be almost as
briefly summed up. The cell-growth (which
is derived from the mucous lamina), and the
fibrous tunic (which is developed from the
vascular lamina), are at first very loosely united
to each other. Hence they may be easily
separated into distinct and comparatively
plane strata ; of which the fibrous has
about double or treble the thickness of the
epithelial one. The cells of the latter affect
an elongated or columnar form at a very
early date of foetal life (about the sixth
week). The various offshoots of tubes and
other glands which are contained in the wall of
the canal, are developed from a mass of cell-
growth, which sprouts from the external
surface of the mucous layer, and gradually
acquires the definite form and cavitary ar-
rangement specific to these minute structures.
The larger accessory glands of the liver and
pancreas are produced from a similar mass
which lies external to the bowel: and they
ultimately prolong their ducts so as to
open into the cavity of the intestine.
The fibrous layer, which is at first smooth
and homogeneous, soon becomes roughened
into little projections, which ultimately take
the shape of conical processes. These, as
they enlarge, pass upwards into the mucous
or epithelial layer, Some of these projections
not only separate the various tubes and
glands from each other, but, by a farther
advance and enlargement, carry before them
the general surface of the cell-growth. They
thus form the future villi. While others
and by far the majority affect a lateral,
instead of a vertical, growth ; uniting with
their neighbours by cross ridges, which soon
form a network, that extends between the
tubes at all parts of their height, so as to
constitute a matrix for these and the other
structures derived from the mucous lamina.
STOMACH AND INTESTINE.
403
Finally, the unstriped muscular fibres, and
the white and yellow fibrous elements, repeat
the ordinary steps seen in the development
of these tissues generally.
ABNORMAL ANATOMY.
Malformations. The malformations of the
digestive canal may be conveniently arranged
in three groups: 1. Those which appear
to depend on an arrested or deficient de-
velopment. 2. Those which are attended by
an excess of size. 3. Those which can only
be referred to errors of development, the
causes of which are unknown ; or to mal-
formations of adjacent parts.
(1.) A deficient development of the whole
tube may diminish either its calibre, its length,
or both of these dimensions simultaneously.
But malformations of this kind are rarely seen,
in that marked degree in which alone they can
be distinguished from from the differences
which doubtless obtain in different indivi-
duals.
Among the results of a local failure of de-
velopment, by far the most common is one,
which we might expect to be so, both from
the history of the evolution of the digestive
canal, and from the analogy of malformations
in other parts ; namely, the absence of one or
both of the terminal orifices of the tube, to-
gether with more or less of its adjacent seg-
ments.
Thus the imperforate anus, which is some-
times limited to the mere occlusion of the
lower orifice of the bowel by a thin mem-
brane, is, in other instances, associated with
the absence of a variable extent of the rec-
tum, and even of the colon, ileum, or jeju-
num. In such cases, a cord of more or less
dense fibrous tissue generally replaces a vari-
able extent of the absent segment of tube.
The canal itself is usually dilated above its
closed extremity. It may, however, com-
municate with the neighbouring urinary or
genital cavities ; or it may even open at the
umbilicus.*
The analogous deficiency of the oesopha-
gus is of less frequent occurrence than the
preceding, and is but very rarely associated
with it. Here the pharynx ends below in a
blind extremity ; generally forming a pouch,
which sometimes communicates anteriorly
with the adjacent trachea. The oesophagus
below this pouch begins in a similar but nar-
rower sac, which is separated from the pha-
rynx, either by a membrane, or by a fibrous
cord, or by an absolute interval of varying
length.
The deficiency of the stomach occurs
chiefly in acephalous monsters. It is some-
times accompanied by the absence of the
duodenum, or part of the jejunum.
* In that class of double monsters in which the
trunks are distinct below, but united above in the
upper part of the belly, a variable length of their
two small intestines is sometimes similarly fused
into a single tube, which bifurcates above and
below. The seat of the lower bifurcation is some-
times occupied by a (probably true) diverticulum.
An incomplete evolution of the remainder
of the tube is evinced, either by a local nar-
rowness of variable* extent and situation, or
by a closure and interruption which (mutatis
mutandis) repeat the various grades of this
malformation seen in the occluded oesophagus
and anus. Or it may exhibit a somewhat
analogous tendency of the more complex parts
of the canal towards the simply tubular shape.
Thus the stomach may be devoid, either of
its cardiac sac, or of its pyloric valve; or
may present a cylindrical form, precisely like
that of the small intestine. Or the valve or
pouch of the projecting ccecum, or its vermi-
form appendix, may similarly disappear.-f-
The maximum of this imperfection renders
the whole intestine a narrow cylindrical tube,
in which it is impossible to distinguish be-
tween the large and small bowel.
Almost all the foregoing malformations,
where excessive, are accompanied by other
deformities, which affect the neighbouring or-
gans. Thus the deficiency of part of the
rectum is a common coincident of the mo-
nopodous state, in which the two lower limbs
are fused into one.
(2.) The excess of development to which
we may refer the second class of malforma-
tions of the digestive canal, consists in an
increased length or width of the whole tube,
or of any particular part of it. In the latter
case, the large intestine, the ccecum, and the
stomach are the segments most frequently
affected. The other local malformations
which we may ascribe to such an excess, are
those of subdivision of the canal on the one
hand, and the production of diverticula or
supplementary tubes on the other.
Very few of the transverse subdivisions of
the tube can, however, be regarded as really
belonging to the category of excessive de-
velopment. For even where these, as in the
stomach, subdivide the cavity of the canal by
imperfect septa, into abnormal portions, still
the latter generally exhibit a diminished,