tions, and their necessary mechanical effects.

f The effect of scratching the peritoneal coat
(see opposite page) is perhaps partly due to an
action of this kind.



STOMACH AND INTESTINE.



343



the intestines generally gives them a nodu-
lated or almost moniliform shape, and the
movement gradually ceases. On uncovering
portions of the canal hitherto concealed, all
these appearances are repeated. The con-
tracted state remains for some hours, and
finally again disappears.

Now the tranquillity of these portions of
intestine previously to the admission of air,
the irregular and diffuse nature of the con-
tractions themselves, the final result on the
intestine, and the effect of uncovering fresh
portions all these circumstances together
offer the strongest probability, that the move-
ments witnessed are due to the contact of the
air. And hence, although it is interesting to
notice that these contractions often assume
the form of a peristalsis (that is, of a circular
constriction which travels slowly in a direc-
tion towards the rectum), still they do not
warrant any conclusions as to the nature or
force of those definite movements which are
doubtless executed by the intestines during
life.

Nor are the movements which result from
applying a local irritation to the bowel, under
the same circumstances, much more uniform
or conclusive. Unless excited before the
commencement of the vermicular movements,
or towards their close, they are obviously
liable to be confused with these; which,
indeed, they closely resemble. Thus, when
the surface of the bowel is irritated mechani-
cally, a mere local contraction is sometimes
produced. In other instances, and especially
when the duodenum is the part attacked,
the contraction extends downwards, or even
upwards, from the irritated point. Sometimes
this diffused contraction occurs almost imme-
diately after the application of the stimulus ;
sometimes only after the lapse of a consi-
derable interval of time. Sometimes, without
any repetition of the stimulus, such waves are
repeated; with short intermissions, and of
gradually diminishing strength. Sometimes,
instead of one continuous wave, a broken or
interrupted one is produced ; a condition
which is chiefly seen in the small intestine.
Similar contractions may also be excited by
the mechanical or chemical irritation of the
nerves which immediately supply the intes-
tines. But irritation of the mucous membrane
has little or no effect. Direct galvanic stimu-
lation, by means of the rotary electro-magnetic
apparatus, repeats many of these appearances.
On applying the approximated electrodes to a
given point, a short interval precedes the occur-
rence of a local contraction : and this con-
traction endures after their removal. In some
animals, this local contraction is jwly propa-
gated onwards, for a variable distance, towards
the rectum. This continuous movement may
even be repeated without any fresh appli-
cation of the stimulus. But that more diffuse
irritation which may be produced by stroking
the intestine with the wires gives rise to
none but local contractions. While galvanizing
the nerves reproduces the lively, but general,
movements above alluded to. And finally,



whatever be the form of irritation, it ceases to
have any effect, soon after the lapse of that
period at which the vermicular movements
usually cease. This departure of irritability
may, however, be retarded by warmth, or by
preventing the access of air. And the capacity
for such movements may sometimes be re-
stored by returning the divided and dead
intestine to the belly of the living animal.
Finally, though the repeated irritation of any
one part soon exhausts its contractility, still,
after a short interval of repose, it is at least
partially restored.

On mechanically irritating the exposed
intestines of the living animal, very different
results are obtained. Compressing them
between the fingers produces a local con-
traction, which l?sts some few minutes, and
then disappears. Scratching their peritoneal
surface usually gives rise to elevations, which
are just as local as the preceding depressions.
These elevations, which seem to be due to
relaxation of the outer or longitudinal mus-
cular layer, are accompanied by contractions
of the deeper transverse fibres. And the latter
can still be excited, after all possibility of pro-
ducing the former has been destroyed by
cold. Mechanical or chemical irritation of
the mucous membrane, or pinching or section
of the nerves, produces no movements what-
ever : even where the degree of nervous sti-
mulation is such as to cause convulsive move-
ments of the hind feet of the animal. And
distention of the bowel with water seems to
be equally inefficacious ; indeed, it appears to
leave the ordinary irritability by local stimuli
very little affected.

The observations of Schwarzenberg and
Ludwig *, upon dogs in whom intestinal
fistulse had been carefully instituted, afford
much more direct and trustworthy evidence
respecting the normal intestinal movements.
They introduced into the canal balls of wax,
attached to slender lead wires ; and thus
verified the following details. The contents
of the canal are propelled by a slow continuous
peristalsis, which has a definite direction
towards the rectum. And although irritation
always excites a local contraction, it only
gives rise to peristalsis at definite times,
during the intervals of which the intestine
remains at rest. These times have a general
connection with the digestive act : the period
of minimum activity being before a meal ;
while the maximum of movement is usually
from four to six hours after it. But the act
of peristalsis is essentially independent of the
presence of food; since it may be produced
in a starving animal, or in an empty segment
of tube. And not only does this intermittent
character affect the general occurrence of the
propulsive act, but even, to all appearance,
its specific phenomena. For when applied at
the proper period, a single continuous irri-
tation produces a repeated and intermittent
peristalsis. Hence it is obvious that, during

*Zeitschri ft fuer die Rationellen Pathologic, Bd.vii.
p. 315.

z 4



344.



STOMACH AND INTESTINE.



the short intervals of this peristaltic act, the
irritation is incapable of exciting contraction.

We may perhaps sum up all these re-
sults as follows. Direct irritation of this
mass of organic muscle excites loca con-
tractions ; which are of slower access, feebler
power, and longer duration, than those of the
striped fibre. Shortly after death, these con-
tractions of the intestinal coat evince a general
disposition to extend beyond the site of their
origin. But during life, this tendency is so
modified by some governing force, that, in obe-
dience to the requirements of the digestive
organ, it is either exalted into a definite and
effective peristalsis, or altogether suppressed.
This definite peristalsis forms the ordinary mus-
cular action of the bowel; and is the chief
agent in the proper propulsion of its contents.
As regards its intensity, we can only conjec-
ture that it is scarcely more than sufficient to
propel the normal contents. As respects its
character, it is essentially intermittent. As to
its extent, it seems to traverse long segments
of the tube. But it remains very doubtful
whether every or indeed any contraction
proceeds continuously throughout the whole
length of the intestine. Finally, we have a
right to suppose, that at least the more active
forms of peristalsis have in them so much of
rhythm, as to be not only repeated, but self-
repeating, at definite intermissions of time.

But the exact mechanism of this peristalsis
remains in obscurity. Nay, more, the infor-
mation at present at our disposal will not even
enable us to take the first step in that process
of induction by which alone it will probably
be arrived at.

In his admirable Essay on Muscular Move-
ment, E.Weber* haswellillustrated the peculiar
characters of the contractions which are ex-
cited by the irritation of organic muscle. He
has shown that in the Tench (Cyprinus tinea),
in whom the muscular coat of the intestine is
composed of striped or animal fibre, galvaniz-
ing the chief nerves of the tube produces an
immediate, powerful, and cotemporaneous con-
traction, in place of the slow, feeble, intermit-
tent, and enduring action seen in the unstriped
or organic intestinal muscle of the other Cy-
prinoid species. He has also found that the
Iris of various animals repeats the same con-
trast of structure and irritability. Hence he
argues, that the organic muscle is less directly
influenced by the nerves; and that these are
only connected with this contractile tissue in
some such mediate way, as that by which irri-
tation of the sensitive or afferent nerves gives
rise to the reflex movements which are pro-
ducible in voluntary or striped muscle.

But do these facts warrant such a conclu-
sion ? On the contrary, do they not render
it more probable, that the above varieties of
contraction are in some way inherent to the
very structure in which these kindred animals
differ, rather than that they are brought about
by supposed differences of the nervous centres
or trunks : differences (.by the way) such as the
existing state of our knowledge would rather

* Wagner's Handwoerterbuch der Physiologie.



contradict than establish ? In the intestine of a
single Cyprinoid species, the fibre-cell gives
place to the striped fibre. Hence, failing all
proof of other differences, is it not precisely
to this remarkable contrast of structure, that
we must refer the parallel contrast which is
observed in its contraction, when a stimulus
is applied to its nerves ?

This direct reference to the structure of
the organic muscle seems to be most justifi-
able in the case of the local contractions
above alluded to ; many of the peculiarities
of which are almost what might have been
expected from the rudimentary structure, the
little vascularity, and (especially) the mode of
aggregation, of the fibre- cells. But as re-
gards the less local contractions of the un-
striped fibre, their tendency to peristalsis and
intermission soon after death, appears to de-
mand some wider and less continuous connec-
tion of different points and times, than the
tissue itself would directly afford. Such a
means of association suggests itself in the ner-
vous system. And, since the removal of the
mesentery does not deprive the contractions
of this peristaltic character, any supposition
of this kind would appear to refer it to the
nerves within the walls of the intestine. But
it is difficult to believe that these nerves have
ganglia ; nor have any of these essential
elements of a nervous centre ever been seen
in this situation. While it has been pointed
out by Wild, that the excision of a portion of
the oesophagus prevents all propagation of its
peristalsis beyond the interrupted point: a
fact which tends to show that the contraction
of each segment is in some way conditionated
by that of its immediate predecessor. The
latter experiment, however, supposes such a
serious interference with the tube, that any
negative result can hardly be regarded as con-
clusive. And hence, until future researches
bring additional information respecting the
ultimate distribution of the nerves of this un-
striped muscular tunic, and the exact arrange-
ment of its constituent fibre-cells, the relative
share of the muscular and nervous tissues in
these peculiar contractions can hardly be con-
jectured. The stimuli by which we excite them
in our experiments are in reality far too rude,
diffuse, and uncertain in their application, to
afford much ground for a decided preference
of either muscle or nerve, as forming the chief
modulator of that contractility which is, no
doubt, essentially inherent to the sarcous sub-
stance itself.

From the appearances noticed in the healthy
intestine soon after death, it may be doubted,
indeed, whether even this last phrase is quite
specific enough; whether we ought not to
regard* contraction itself (rather than an ab-
stract "contractility") as the inherent pro-
perty of the living organic muscle. In the
observations just mentioned, we have seen
that the death of the animal was soon fol-
lowed by an irregular, but distinct, contrac-

* A contraction answering to what has been phi-
losophically distinguished by Professor Bowman as
"passive" in the case of the striped muscle.



STOMACH AND INTESTINE.



345



tion of the unstriped muscular coat of its in-
testine : a contraction which was apparently
excited by the air, but was certainly indepen-
dent of the nervous centres. This remained
for a time, and then disappeared, never to
return. Hence it seemed, in short, " a kind
of precipitate rigor mortis, hastened by expo-
sure to the air."*

The truth of this analogy between the un-
striped and the striped muscle is confirmed by
observations made on corpses in which all ex-
posure of the intestine has been avoided until
an hour or two after death. A comparison
of such examinations would show that the
death of the intestine, like that of the ar-
teries, is accompanied by the access of a
definite rigor mortis, which is closely analogous
to the stiffening seen in the voluntary muscles.
Both the access and disappearance of this
contraction are, however, more rapid than
in the striped fibres of the proper organs of
locomotion. And its appearances are much
less distinct. In the intestinal canal, it is
chiefly recognized as a narrowing of the tube;
which is attended by an increased thickness of
its walls. But it is sometimes better evi-
denced by intus-susception of the canal; or
by irregular contractions of its calibre.

But whatever the exact relation which the
various contractions producible in the intes-
tine bear to the specific structure that forms its
muscular wall, it seems certain that the true
propulsive peristalsis of the healthy living ani-
mal is a complex and co-ordinate act, which is
at least indirectly dependent upon thecerebro-
spinal centre. And Weber's experiments on
the highly excitable intestine of the Tench
point definitely to the medulla oblongata, as
that segment of the nervous centre by which
this connection is chiefly brought about.
While, as might have been expected, numerous
observations concur to represent the pneumo-
gastric and splanchnic nerves as the channels
by which this central organ influences the
alimentary canal. But the exact degree in
which the various vertebral and prever-
tebral centres of the sympathetic can trans-
mit, modify, or originate the nervous changes
which pass to and from the bowel, is at
present utterly unknown. There are how-
ever various reasons for suspecting, that
neither of the two main ganglia which inter-
vene between any part of the intestinal sur-
face and the cerebro-spinal centre, really limit
the transmission of an afferent, or give origin
to an efferent, change.

Anti-peiistalsis. The ordinary theory of
intestinal anti-peristalsis may be 'thus stated.
At a certain stage of an intestinal obstruc-
tion, the immoderate irritation which it implies
reverses the natural peristalsis of the bowel ;
so that, instead of proceeding towards the
anus, it passes in the contrary direction. In
this way it impels the contents of the tube
towards the stomach ; whence they are vo-
mited by the aid of an extension or reproduc-
tion of the same action.

About eight years ago, the author { was led

* Author, op. cit. f Op. cit.



to investigate this doctrine, until then uni-
versally accepted. He was thus led to the
conviction, that it ought to be uncondition-
ally rejected ; that it was probably false ; and
certainly had never been proved to be true.
The following were his chief reasons for
coming to such a conclusion :

1. It is difficult even to conjecture any-
thing in the degree or kind of irritation pre-
sent in intestinal obstruction, which should
limit the occurrence of anti-peristalsis to this
state. 2. Since the physical state of occlu-
sion is the necessary condition of faecal
vomiting, it is probable that the causa-
tive process by which this occurrence is
brought about must be physical also. 3. No
anti-peristalsis has ever been observed ; the
movements which occur in the obstructed
bowel after death being similar in their nature to
those witnessed in the healthy intestine under
similar circumstances. 4. The whole of the
appearances seen after death in the obstructed
bowel, show that its contents have been pro-
pelled forwards towards the occlusion, and not
backwards from it. 5. Distention of almost all
the interval between the pylorus and the
occluded part appears to be a condition of
faecal vomiting ; so much so, that the date of
access of this symptom roughly indicates the
locality of the obstruction.

Hence, instead of an imaginary anti-peri-
stalsis, the author ventured to propose a theory
which seemed to deduce the process of faecal
vomiting from the ascertained conditions of
its occurrence.

The complete obstruction of the intestinal
tube at any point, gives rise to an accumu-
lation of its contents above the seat of the
structure. This gradual distention of the
bowel is accompanied by an active propulsion,
which may often be seen and felt through
the wall of the belly, as a violent writhing
peristalsis. After a variable period, vomiting
either occurs for the first time, or if already
present from other causes, it becomes faecal.
But peristalsis in an obstructed tube dis-
tended with fluid, not only implies a forward
movement in the particles that occupy its peri-
phery, but also necessitates more or less of a
backward current in those which are situated
in the axis or centre of the canal. And the
uniform consistence of the distending fluid, or
the return of solid fgeces, through many feet of
tortuous bowel, into theupper part of thecanal,
constitute frequent phenomena, which are best
explained by the mixture and circulation that
these two currents must tend to establish.
On the faecal fluid reaching the stomach, vo-
miting is excited. And it is scarcely neces-
sary to add, that this latter process, as usual,
involves the more or less complete evacuation
not only of the stomach, but also of the upper
part of the distended small intestine.

Mucous membrane. Having thus briefly
described the peritoneal and muscular coats
of the small intestine, we may next proceed
to consider its mucous membrane: the struc-
ture on which its various functions essentially
depend.



346



STOMACH AND INTESTINE.



This tunic everywhere consists of the ordi-
nary elements of a mucous membrane:
namely, a basement membrane, an epithelium,
and a layer of areolar tissue that contains an
admixture of the muscular fibre-cells. But,
instead of forming a simple, flat expanse, it
undergoes numerous modifications; which, un-
der the names of valvuke conniventes, intestinal
tubes, villi, agminate follicles, solitary follicles,
and racemose glands, will especially claim our
notice.

Vahulce conniventes. Almost all the small
intestine is complicated by the presence of
transverse folds of mucous membrane ; which
project from its inner surface into its cavity.
These projections, which were known to many
of the earlier anatomists, were named by
Kerkring the valvulcs conniventes; apparently
from his thinking that they delayed the intes-
tinal contents, but still as it were, connived
at their passage. They begin in the second
portion of the duodenum, and only cease in
the lower fifth or sixth of the small intes-
tine. They are best shown by moderate dis-
tention of the tube with alcohol; which slowly
hardens them, so that they retain their shape,
even after a portion of the wall of the bowel
has been removed to display its interior.

Fig. 255.




Small intestine distended and hardened by alcohol, and
laid open to sliow the valvulce conniventes occupying
its interior. (From a preparation in the Museum
of King's College.}

Extreme distention greatly diminishes their
size, but never effaces them altogether. And
such a permanent character sufficiently distin-
guishes these folds from those temporary
creasings which are seen generally throughout
the stomach and intestine, and which are
sometimes spoken of as preceding them in
the first part of the duodenum. At first they
are very small and scattered, rise little above
the general mucous surface, extend but a
short distance across the tube, and break up
at their extremities into st'll more minute
creases, which often pass obliquely to join
those next them, above and below. In the
lower part of the duodenum, they gradually
acquire a number and size, which are retained



throughout the whole of the jejunum. But
from the beginning of the ileum, they again
diminish; first in frequency, and latterly in
length and depth. And in the lower third of
this segment, they generally disappear alto-
gether.

Each of these folds consists of a duplica-
ture of mucous membrane, enclosing a process
of the loose areolar tissue which everywhere
separates the mucous from the muscular coat.
Opposite the attached border of the valvula,
this layer is somewhat thicker ; but does not
appear to contain more than its ordinary
small quantity of fibre-cells. The process
which it gives off to each of the folds con-
tains vessels, nerves, and lacteals. The relation
of this tissue to thevalvula is well shown by the
result of its inflation ; which produces a kind
of artificial emphysema, that completely oblite-
rates the whole projection. When the cavity
of the intestine is forcibly distended, the
valvulce are placed vertically to the general
surface. But in the ordinary state of the
bowel, they are easily moved by any ex-
ternal force ; so that their free margin is
generally directed obliquely upwards or down-
wards. Their direction is nearly transverse
to the axis of the tube. Their variable extent
around the wall of the bowel forms one-half,
two-thirds, or even three-fourths of a circle.
Their greatest projection occupies the middle
of their length, where they are often from
one-fourth to half an inch deep. But towards
either extremity, they gradually sink into the
general mucous surface. In doing this, the
valves usually swerve a little from their hither-
to transverse and parallel course ; so that each
joins by one or both ends with the fold imme-
diately before or behind it. And sometimes
a bifurcation of the tapering fold unites its
extremity to two of its neighbours.

The office of these permanent folds has
been a matter of considerable speculation. It
is evident that they increase the extent of the
mucous surface to at least twice or thrice
what it would be in a simple hollow cylinder
of equal size. It is equally obvious, that their
transverse position is peculiarly calculated to
render this enlarged surface an effective one.
For they are at right angles to the direction
of peristalsis, and therefore to the general
course of the intestinal contents. Such an
arrangement of the mucous membrane, taken
in connection with the great mobility of these
folds, must not only insure a thorough ad-
mixture of the various constituents of the
chyme, but, by delaying its direct passage
onwards, bring every portion of it into con-
tact with the greatest possible extent of the
active intestinal surface.

Intestinal tubes. The structure of the
remaining constituents of the intestinal mu-
cous membrane can only be seen distinctly
by the aid of the microscope. Amongst
these minute organs, the intestinal tubes
or, as they are commonly called, the folli-
cles of Lieberkuehn are the first to de-
mand our notice. For, with slight modifica-
tions, they occupy the whole of the small and



STOMACH AND INTESTINE.



347



large intestine. An" allusion has already been
made to the fact that, in many animals, they
appear to usurp a portion of the gastric cavity.
While the importance which this wide distri-
bution would imply, is confirmed by their im-
mense number ; which is such that we may
estimate their aggregate surface as from ten
to fifteen times that of the cylinder of intes-
tine into which they open.

Each tube may be described as a hollow
cylinder, having a length which is about five
times its width, and ending below in a rounded

Fig. 256.




Intestinal tubes from the jejunum, as seen in a vertica

section. (Magnified 80 diameters.}
a, Limitary or basement membrane ; 6, nuclei of
the columnar cells which line its interior; c, calibre