villus by such numerous communications,
that the two might almost be regarded as
merging into each other.
The substance which forms the ground-
work or basis of the villus resembles, to
some extent, that of the gastric mucous
membrane ; the morphological consti-
tuents of which we have already seen to be
indistinct, except at the bottoms of the
tubes. It rarely presents any definite struc-
ture. Sometimes, however, it is faintly striated.
And occasionally this appearance is so marked,
as to approach a fibrous character. In this re-
spect, it resembles the papillae of the skin and
tongue ; and, especially, those secondary
projections which stud the fungiform papillae
of the latter organ, the basis of which contains
no yellow elastic fibres, but is almost homo-
geneous, and often indistinctly granular.
Mixed with this indistinctly fibrous tissue
are numerous delicate cytoblasts or nuclei
(b, Jigs. 259, 261, 262, 263.). The larger of
these attain the size of coloured blood-cor-
puscles ; while the small merge into granules
by increasing minuteness. The exact re-
lation of these to the basis of the villus is un-
known. Their general effect is to communicate
to the whole villus a more or less mottled and
granular aspect. This appearance (which we
shall find is increased during the period of
intestinal digestion) often obscures, not only
the vague fibrillation just alluded to, but the
whole of the structures which lie beneath the
basement membrane.
As regards the lacteals of the villi, few
anatomical details have been more disputed
than those which relate to the commence-
ment of the chyliferous absorbents within
the substance of these processes. The pro-
gress of microscopical research has, how-
ever, reduced the controversy within very
narrow limits ; and promises at no distant
date, to end it by a final decision. At pre-
sent, almost all trustworthy observers agree
in the statement, that each villus receives
by its base a single (perhaps sometimes a
double) branch of the lacteal system. It is
only as to the further course of this vessel
that opinions differ. Many affirm it to be
continued up the villus as a single tube, which
ends near its apex by a blind and often some-
what dilated extremity. Some authorities
modify this view for the broader villi, by
stating the canal to be double either as a
single loop, or as a bifid and somewhat tor-
tuous tube. While others find that the cen-
tral and simple lacteal canal ends by branching
into a network of more or less complex cha-
racter, like that of the capillaries.
The first of these statements will at any
rate apply to many of the villi. Numerous
observers have verified its accuracy for the
human subject. And it is not difficult to
obtain distinct evidence of its truth in some
other Mammalia. Amongst these the sucking
Rabbit and Calf are especially suitable for
examination. If proper care be taken to
examine the chyliferous villi of these ani-
mals instantly after death, with the aid of
suitable fluids, we may easily convince our-
selves of the presence of a single large lac-
teal tube, with distinct walls, like that repre-
sented in the annexed figure (fig. 26 1.). Such
Fig. 261.
b d d b
Two villi, denuded of epithelium, with the lacteal vessel
in their interior. From the Calf. Magnified 350
diameters. (After Koelliker.}
a, limitary membrane of the villus ; b, matrix or
basis of the same ; c, dilated blind extremity of the
central lacteal ; d, trunk of the same.
single lacteals are generally very large, having
a diameter which often amounts to about one-
third or one-fourth that of the villus itself;
and exhibit a dilated blind extremity, (c,jig.
261.) which nearly doubles their width, hi
man, according to Frerichs *, they are
scarcely more than one-half or two-thirds of
this size.
But it remains to be considered whether this
* Op. dt. p. 751.
STOMACH AND INTESTINE.
353
statement excludes the possibility of a net-
work, such as has been affirmed to exist by
Krause and others. Koelliker, in whose ad-
mirable work * the reader will find a copious
analysis of the latest observations on this
subject, sums them all up very impartially by
acknowledging, that, although he has never
been able to see a trace of such ramifications,
still he cannot venture altogether to deny their
existence. On the contrary, he thinks *it pos-
sible that the above simple mode of commence-
ment, which certainly holds good for the cy-
lindrical villi, ma) be exchanged, in the larger
of these processes, for one involving the pre-
sence of a greater number of lacteal canals, or
the absence of such blind extremities.
But in conceding this much, Koelliker
points out what Valentin -f- seems previ-
ously to have suspected, the facility with
which a striated arrangement of the dark
fatty molecules within the chyliferous villus
may be mistaken for lacteal vessels. Nay
more, even the chyle of the central canal
sometimes separates by coagulation into striae,
which closely imitate a branched network. We
may add, that, in the various observations
which have been made on executed criminals,
the possibility of error has probably been in-
creased by the distended state of the vascular
and lacteal canals contained within the delicate
structure of the villus.
Whatever be the case as regards these
conjectures, it seems to me that the large
simple tube, and the minute network, are far
too unlike to be regarded as mere degrees of
development of the same structure in differ-
ent villi. In like manner, the simple loop of
lacteal seen by Henle just beneath the base-
ment membrane is suspicious, not only from
its situation, but also from a fact noticed by
Valentin and Remak, that the central canal
sometimes coexists with it. And when we add
to the foregoing remarks, that the majority
of observers have been unable to see any
such ramifications, it will seem difficult to
avoid concluding, that each villus probably
contains a single large lacteal, which occu-
pies its centre, and ends by a blind extremity.
The muscular constituent of the villus was
first discovered by Bruecke, and has since
been verified by Koelliker in many Birds and
Mammals. Its shape is that of a thin hollow
cone, which closely imitates the form of the
villus enclosing it. Hence, from whatever side
it is examined, it may be seen as a double lon-
gitudinal layer ; which is placed immediately
around both sides of the central lacteal ; and
lies so deeply within the villus, as to be beneath
its vessels, as well as much of its granular basis.
It is more distinct in the lower part of the
villus, and in the larger flat specimens ; but is
easily obscured by oil globules, nuclei, or pig-
ment. The nuclei of its fibre cells are best
seen on the addition of dilute acetic or nitric
acid, when they assume their ordinary charac-
teristic appearance.
The action of this contractile apparatus
during life is at present unknown. Derived,
as it no doubt is, from that general expanse of
Fig. 262.
Supp.
, cit. p. 1GO. et seq.
. cit. p. 684.
VUlus denuded of epithelium, treated iciih acetic acid.
From a young kitten. Magnified 350 diameters.
(After Koelliker.)
a, outline of the villus ; b, nuclei beneath this ;
c, nuclei of the unstriped muscle ; d, roundish nuclei
in the centre of the villus.
unstriped muscular fibre which pervades the
whole mucous membrane of the alimentary
canal, one can hardly avoid ascribing to it a
function which is more or less similar, if not
indeed co-ordinate, with that of the general
stratum. That this function is in some respects
related to the static or passive mechanical cir-
cumstances of the mucous membrane, has
already been conjectured (p. 325.) in speaking
of the stomach. And the little we know of the
ordinary action of the analogous unstriped
element in the skin, rather confirms than con-
tradicts such a supposition. But its pecu-
liar position with respect to the end of the
lacteal trunk in the centre of the viilus,
to which it forms a kind of muscular and
contractile envelope has given rise to the
suspicion, that it effects the propulsion of
the chyle contained in this canal.
How far such a process really obtains must
be determined by future research, which
ought especially to notice the precise con-
nection of this muscular stratum with that
of the mucous membrane generally. In the
meantime, we may notice that, as Koelliker
justly remarks, an active propulsion by these
longitudinal fibres would imply their alternate
contraction and relaxation.* But, assuming
* He also adverts to their apparent want of
nerves, and to the essential independence of organic
muscle of all but mechanical irritations. However
A A
354-
STOMACH AND INTESTINE.
this to occur, it is evident that such a remittent
contraction would not destroy the claims of
the absorptive act itself to be considered
the chief force which propels the chyle. For
in any case, the muscular apparatus would
but limit and remove that diatention of the
lacteal which absorption had previously ef-
fected. It would thus, as it were, merely re-
gulate and transfer the mechanical force of
the latter act ; so as to modify it, either
constantly, or at definite intervals of time.
Some observers have attempted to verify the
action of this delicate muscular apparatus dur-
ing life. Gruby and Delafond first instituted
such observations on a variety of domestic
animals j and they have since been repeated
by Bruecke and Koelliker. AH of these
authorities agree in remarking an alternate
shortening and elongation of the vilius : a
change of form which is so rapid and marked,
that there need be little hesitation in attri-
buting it to a corresponding contraction and
relaxation of these unstriped fibres. But
the phenomena seen in the course of such
vivisections cannot be safely accepted as those
of the healthy animal in its natural state. *
Such a caution is still more applicable
to those contractions by which the villi share
in that irregular movement of the intestine
already described as a kind of rigor mortis.
On exposing the villi of an animal soon after
death, they gradually become shorter and
Fig. 263.
Villi contracted and shortened so as to offer circular
or transverse wrinkles. From the small intestine of
the dog shortly after death. Magnified 100 diame-
ters ; and examined by reflected light.
wider ; at the same time that their surface
is generally thrown into circular transverse
general this view of the action of unstriped fibre, I
must confess myself very reluctant to accept it on
its present evidence.
* for, to say nothing of the pain, the irritation,
wrinkles or folds. A more minute examination
shows that these folds consist of epithelium,
which has separated from the basement mem-
brane at the points that correspond to the
greatest projection between the contiguous
wrinkles (Jig. 264, 2.) A closer adhesion of
Fig. 264.
Similar villi as seen by transmitted light. The vilius
marked 1, has been partially withdrawn by con-
traction from its investing epithelium, which is thus
left entire like the finger of a glove.
a, epithelium of the vilius; b, granular matrix or
substance of the same.
those columnar cells which occupy the free
extremity of the vilius, frequently causes this
part to be defined, as a shallow funnel, by the
neighbouring separated cells. While in other
instances, a variable length of the whole vilius
withdraws from its cellular investment with
such uniformity, as to leave the extremity of the
latter empty, smooth, and uninjured (fig. 264,
1.), like the finger of a glove. Frequently, how-
ever, some of the epithelial cells are detached.
It is obvious that all these appearances
are referable to a contraction of the un-
striped fibres within the vilius, withdrawing the
substance of the latter from its epithelial in-
vestment. The movements which often ac-
company these changes resemble those above
mentioned as beheld during life ; and consist
of shortening or elongation, to which are some-
times added lateral displacements. The date
of their occurrence is limited to the period
and the exposure, which are involved in such an
opening into the intestine as is necessary to allow a
proper inspection of the villi, Gruby and Delafoud
remark, that their surface becomes wrinkled and
pale at the time of their contraction. Such circum-
stances imply so much disturbance of these soft
structures, as to throw great suspicion upon any
view which would interpret them as part of a normal
process.
STOMACH AND INTESTINE.
355
which immediately succeeds death. And their
duration is rarely protracted beyond a few
minutes.
Changes in the villi during digestion. Dur-
ing the act of digestion, the villi undergo cer-
tain noticeable alterations. At this period,
they receive an increased afflux of blood ;
and become both larger and softer. They ac-
quire a greater opacity ; so as to appear whiter
by reflected, and darker by transmitted, light.
The nuclei and cells which occupy their in-
terior are greatly increased in number and dis-
tinctness. And, finally, after the ingestion of
food containing the usual fatty ingredients,
a portion of these may be found occupying
the interior of the villi themselves.
The process by which fatty matter pene-
trates the villus to enter the lacteal in its
centre, deserves our special attention, from
the fact that it constitutes the origin of the
chyle. At present we shall limit ourselves
to a description of the appearances actually
observed, in connection with the mucous
membrane of the alimentary canal.
The first step towards the absorption of
the fatty matter, consists in its entry into the
epithelium which invests the exterior of the
villus. Each columnar cell of this covering
is gradually filled by a large oil globule ; which
occupies the whole of its cavity, with the ex-
ception of that small portion devoted to its
nucleus. This change first implicates a few
scattered epithelia ; and, by rendering them
Fig. 265.
VWus of the dog about two hours after feeding : show-
ing the entry of fatty into scattered epithelia on its
surface. Magnified about 400 diameters.
a, a, outline of the villus formed by epithelia with
their ordinary contents; b, b, epithelia rendered
bright and refractile by their fatty contents.
more refractile, often causes various parts of
the surface of the villus to offer a curious con-
trast of bright spots (b,fig. 265.) and darker
intervals.* Gradually, however, all the cells
become similarly affected ; so that the entire
vilius assumes the altered appearance just
alluded to.
The next step towards the absorption of the
fatty matter consists in the minute subdivi-
sion of the single oil globule (c^Jig. 266.)
which occupies the epithelial cell. The way
in which this process occurs is unknown :
Fig. 266.
Isolated epithelial cells from a villus^ as seen during the
absorption of fat into the lacteals. (Altered from
KoeUiker.") Magnified 350 diameters.
a, columnar epithelial cell, occupied by fatty
molecules; b, similar cell, containing several small
oil-drops; c, similar cell, enclosing a single oil-
drop ; rf, similar cell completely filled by a larger
oil -drop. The upper or free end of the cell (at d)
js concave.
but the result of the change is to give the
columnar cell a darkly granular appearance
(#, Jig 266.), in which we may often distin-
guish separate, though minute, fatty mole-
cules. These molecules are next found in
the substance of the villus itself, though
chiefly towards its surface and free extre-
mity ; to the apex of which latter part
they are often limited.-f- From the sub-
stance or matrix of the villus, the molecules
of fat are then transferred to the lacteal trunk
occupying its centre ; which, in the most fa-
vourable instances, they define as a slender
column of dark fatty granules.
How far the above process constitutes a
mere act of physical imbibition, it is difficult
at present to determine. But that it is so, at
least in part, can scarcely be doubted. For the
experiments of Matteucci J (which are con-
firmed in all their essential particulars by
Valentin ) prove that, when a dilute alkaline
solution and a faintly alkaline fatty emulsion
are separated from each other by an animal
membrane, diffusion occurs between them.
And the circumstances actually present in
the intestine are even more favourable to
such a transit than those which obtained
in the experiments of these observers. The
lymph and blood are sometimes more alkaline
than the solution which they made use of.
The degree in which the tenuity of the delicate
cell-wail of the villus exceeds that of the
* These appearances, alluded to by Frerichs ( Op.
cit. p. 854.) and detailed by Koelliker (Op. cit. p.
167.), were noticed by me eight years ago in the
human subject.
f The larger drops sometimes seen in this situation
are, I believe, the result of accidental violence to
the specimen.
t Le9ons sur les Phenomenes, &c., pp. 104, 5.
Op. cit. vol. i. p. 379.
A A 2
356
STOMACH AND INTESTINE.
compound membrane forming the diffusive
septum in their experiments, would propor-
tionately favour the resulting transit of the
separated fluids. And since the continuous
movement of the chyle is probably aided by
forces independent of any mere act of dif-
fusion, the force of suction thus added must
itself conditionate a more active transit than
that which they witnessed in the inert en-
dosmometer.
On the other hand, there are good reasons
for regarding the reception of fatty matters
as a much more complex phenomenon, and
the result of what we may venture to call
more vital processes. For the way in which
ether and other solvents act upon the chyle
appears to prove, that the fatty contents of its
molecules are still oily ; and not saponified,
like such diffused fluids. And while the
position of the capillary plexus, and the rapid-
ity and quantity of its stream, render it pro-
bable that any merely diffusive action would
disproportionately affect the blood -which
by the way is often more alkaline than the chyle
-^-a chemical and physical comparison of these
two fluids would seem to show that the re-
verse is actually the case : tbat a larger quan-
tity of fat is taken up by the lacteals than by
the blood-vessels. This view is also con-
firmed by the results of violent inflamma-
tion*, or of great interference with the blood-
vessels j : changes, neither of which would
probably have much direct effect on the physical
action of an independent system of tubes, but
which are nevertheless alleged entirely to pre-
vent the formation of chyle. In any case, it
would seem that there are strict limits to the
quantity of fatty matter which can be absorbed.
Hence when the amount of fat present in any
particular region at all exceeds what its villi
can take up, it is passed on to other portions
of intestine ; failing absorption by which, it is
ultimately discharged unchanged in the faeces.
Intestinal Follicles. ,J We pass on to the
description of a class of structures which are
essentially closed sacs; and which, represented
in the stomach by the lenticular glands, pervade
all the remainder of the intestinal canal under
the two forms of solitary and agminate fol-
licles : the latter being, as their name implies,
essentially clusters of the former.
Agminate follicles. Of the very numer-
ous names which have been bestowed upon
* French s, Loc. cit.
t Fenwick in " Lancet " for 1845, p. 64.
| The etymology of the word "follicle " quite
permits its application to these closed sacs : to which
indeed it seems desirable that we should restrict it^
in speaking of the various constituents of the intes-
tinal mucous membrane.
Until a more uniform nomenclature is adopted,
it seems advisable to enumerate a few of these
names. Such are the titles of glandulee Peyerianee ;
agmina Peyeri ; glandulee aggregates ; glandules, agmi-
nate ; vesicularum agmina ; plexus intestinaks ; plaques
gaufrees; and finally, Peyer's patches. The latter
uncouth designation is, perhaps, that most com-
monly made use of in this country. But as Peyer
appears to have been anticipated b}' our countryman
Grew in the discovery of these structures, there is
the less need of clinging to one of those unmeaning
these follicles, that above made use of seems
preferable ; since it best connotes both
their structure and arrangement. There are
generally about twenty clusters of these
agminate follicles scattered throughout the
small intestine. Their shape is commonly
that of an oval, having a length about twice
its width. They are situated on the free
border of the bowel, or opposite to the
attachment of its mesentery ; and usually
correspond to about the lower three-fifths of
the small intestine, or to that part of it which
is regarded as the ileum. Hence they have
been looked upon as, in a certain sense,
characteristic of this region. But they some-
times extend into the jejunum, being scattered
sparingly throughout its lowest segments.
And they may rarely be found even in
the duodenum. In such cases, their entire
number is usually about twice or thrice that of
the average given above.
But amid all their variations of number,
size, and extent, the agminate follicles seem
to retain a certain predominant relation to
the end of the ileum. For it is here that they
are both largest and most numerous. And
while in the remainder of the small intestine,
their length is usually rather under than over
an inch, nothing is more common than to find
the immediate neighbourhood of the ilio-caecal
valve occupied by a single irregular cluster ;
which has a length of two, three, or even four
inches, and a width which carries it round
ils or fths of the inner circumference of the
intestinal tube.
Fig. 267.
Agminate follicles as seen by reflected light. Magni-
fied 4 diameters. (After Kodliher.}
_ a, general mucous surface with villi ; b, depres-
sions leading to the several follicles; c, intervals
between them, covered by small villi.
On examining the mucous membrane of the
surnames, which every practical teacher of anatomy
will probably agree with the author in thinking
very objectionable.
STOMACH AND INTESTINE.
bowel by reflected light, at a place corre-
sponding to a cluster of agminate follicles, we
see that its surface (which is raised above
the rest of the intestine, but has no very
sharp line of demarcation from it) is occu-
pied by a number of irregular shallow de-
pressions (6,j%. 267.), at tolerably uniform dis-
tances from each other. But when inspected
by transmitted light, these fossae are replaced
Fig. 268.
Agminate follicles as seen by transmitted light Mag-
nified about 5 diameters. (After Boehm.)
a, general mucous surface of the ileum ; b t b, opaque
grains corresponding to the several follicles.
by comparatively opaque grains (b^b,^g. 268.),
of about the size of a millet seed ; the aggre-
gation of which renders the whole cluster
very distinctly visible by this mode of exami-
nation. Finally, the cluster may often be
recognised externally, from the bulging of the
peritoneal coat which it causes in this situa-
tion. Indeed, its constituent follicles may
sometimes be seen glimmering through the
delicate muscular tunic.
Each such cluster is composed of a number
of follicles, varying from twenty or thirty in
the smaller, to at least one or two hundred in
the larger, specimens. A careful examination of
the mucous surface shows that the depressions
just mentioned do not lead to any apertures,
but are terminated by a smooth surface, the
convexity of which somewhat diminishes their
own depth. It is only at the margins, and in
the intervals, of these fossae, that we find
the tubes and villi proper to the small in-
testine. And both of these latter structures
are somewhat modified. Those tubes which
immediately surround each depression have
a circular or elliptical arrangement ; so
that their orifices generally form a ring
of ten to twenty tubes in the fossa
(around a, Jig. 269.), and thus give rise to a
357
very characteristic appearance.* In like
manner, the villi in their immediate neigh-
bourhood often appear to radiate outwards
Fig. 269.
; >^^
Portion of a cluster of agminate follicles.
a, a, follicles encircled by apertures of the intes-
tinal tubes in the form of a ring ; 6, short and ob-
tuse villi, occupying the intervals of the follicles ;