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THE ANATOMY

OF THE

LYMPHATIC SYSTEM,

BY

E. ^LEm, M.D.

ASSISTANT-PROFESSOR AT THE LABORATORY OF THE
BROWN INSTITUTK^N, LONDON.

L^THE SEROUS MEMBRANES,

LONDON:
SMITH, ELDEE, & CO., 15 WATEELOO PLACE.

1873.

Tx

All rights reserved.

KV)

CONTENTS

SECTION I.
NORMAL CONDITIONS.

CnAPTKR PAGE

Introduction 1

I. The Endothelium of the Free Surface of the Serous Membranes 3
II. The Cellular Elements of the Ground-Substance . . .11

III. The Lymphatic Vessels of the Serous Membranes . . .31

a. Lymphatics of the Omentum and the Pleura Mediastini . . 31

b. The Lymphatic System of the Centrum Tendineum of the

Diaphragm . , . . . . . . . .41

c. The Lymphatic Vessels of the Mesentery 47

d. Relation of the Lymphatic Vessels to the Surface of the

Serous Membranes 49

e. Development of Lymphatic Capillaries 54

IV. Blood-vessels of the Serous Membranes 58

SECTION II.

PATHOLOGICAL CONDITIONS.

Introduction 02

1. The Changes of the Superficial Endothelium . . . .63

2. Alteration of the Cellular Elements op the Matrix . . 73

3. The Blood-vessels and Lymphatic Vessels 81

Bibliography 82

Explanation of Plates 83

fz g *> s^ r;

ANATOMY OF THE LYMrHATIO SYSTEM.

I. THE SEKOUS MEMBEANESJ

Section L--THE NORMAL CONDITIONS,

Since the important discovery of injecting the lymphatic vessels of
the diapliragm from the peritoneal cavity by Recklinghausen, and
since this author has shown that the serous cavities represent great
lymphatic sacs, the serous membranes have become a favourite object
of study. A long series of excellent researches has highly amplified
our knowledge of the normal and pathological histology of the serous
membranes in a relatively short time. The staining with solution of
nitrate of silver, first employed by Recklinghausen, plays a great part
in this advance.

As regards the normal conditions, the attention of histologists has
been chiefly if not wholly directed to three questions : 1. The distri-
bution of the lymphatic vessels in the serous membranes ; 2. The
origin of the lymphatic capillaries from the lymph-canalicular system

' The results of the observations I intend to describe in this memoir have been partly
published by Dr. Burdon-Sanderson and myself, as a preliminary publication, in the
Centralblatt fur medizin. Wissensch. 1872, January 2, 3, and 4. Since that time I
have made a series of observations, which in many respects complete those there de-
scribed, in such a way that the anatomy of the serous membrane, in so far as it refers to
the lymphatic system, may be regarded as complete. I shall have, many times, occasion
to restate what has beea already put down in that preliminary publication, together with
observations of a later date.

These researches were undertaken at the request of Dr. Burdon-Sanderson in connec-
tion with the Pathological Inquiries conducted by him for the Medical Department of the
Privy Council. They are published with the sanction and approval of the medical officer
of the Privy Council, Mr. Simon.

B

2 ANATOMY OF THE LYIVIPHATIC SYSTEM.

of Eecklinghausen ; and 3. The free communication between tlie
lymphatic vessels and the serous cavity by means of stomata.

The following description refers to the minute structure of the
omentum, the centrum tendineum of the diaphragm and the pleura
mediastini. In dealing with these membranes we shall be able,
besides other important facts, to instruct ourselves about the three
questions above mentioned.

In this Section I. we shall treat separately (1) of the endothelium
of the free surface, (2) of the cellular elements of the ground-sub-
stance, (3) of the lymphatic vessels, their distribution and relation
to the tissue and the surface, as well as their development, and (4)
of the blood-vessels.

CHAPTER 1.

THE ENDOTHELIUM OF THE FREE SURFACE OF THE SEROUS MEMBRANES.

A GENERAL description of the endothelium of tlie free surface of tlie
serous membranes is hardly necessary after those given by Reckling-
hausen, Auerbach, Ludwig and Schweigger-Seidel, Dybkovsky and
others.

Some points only will be treated of in this chapter, which have
not yet been sufficiently appreciated.

The endothelium of the free surface is in the normal condition not
everywhere a layer of flattened more or less hyaline cell-plates, but
possesses in many places a different character, which may be described
as follows : the individual cells are polyhedral, club-shaped, or even
short columnar, their substance is distinctly granular, even in the
fresh condition, their nucleus is for the most part, like that of the
ordinary endothelial plates, ovodi, sometimes spherical, clear, sharp-
outlined, with a large shining nucleolus. In many cells, however, the
nucleus is marked by a constriction, or is even perfectly divided into
two.

A portion of the fenestrated part of the fresh omentum of a full-
grown guinea-pig, cat, dog or monkey, mounted in an indifferent fluid,
such as one-half per cent, saline solution, peritoneal fluid, etc., or after
having been stained in one-quarter or one-half per cent, solution of
nitrate of silver and mounted in glycerine, shows often enough on the
surface of the thin trabeculse small gToups of club-shaped or pol}'-
hedral granular cells, projecting from the smface of the trabeculse like
buds. If one follows a large trabecula, which contains either large
blood vessels only, or besides those, also tracts of fat-tissue, one can
always find smaller or larger arose, generally on one surface only, the

« 2

4 ANATOMY OF THE LYMPHATIC SYSTEM.

endothelium of which areae possesses the above-mentioned characters.
As these chief trabeculse project in many instances like folds or
fringes, they afford the best opportimity of studying this germinating
or young endothelium — (we shall use this expression always after-
wards)— from the surface as well as in profile. Especially in the
latter case, one is sure to find, where a large area of germinating
endothelium is focussed, numbers of cells which are raised from the
general surface by means of a stalk, and which possess in theii*
peripheral spherical portion two nuclei or a nucleus in a state of
division ; and fmther, one is sm'e to find there spherical cells just like
lymphoid corpuscles, which are either simply attached to the general
surface 'or are in a state of separating themselves from young endo-
thelial cells. The same character is possessed by the endothelium of
the sm-face of certain nodular or cord-like structures, which are either
isolated or in connection with the chief trabeculae of the fenestrated
part of the omentum, in which larger blood-vessels or fat are contained.
I have come across, several times in the normal as well as in the
chronically inflamed omentum, endothelial cells which presented the
characters of giant-cells — myeloplaxes, that is protoplasmic masses
containing five to ten nuclei. These masses were attached to the
surface by means of a shorter or longer protoplasmic stalk.

A very rich distribution of germinating endothelium is to be found
on the omentum of rabbits. As we shall afterwards see, the omentum
of the rabbit shows remarkable differences as regards the distribution
of the lymphatic and blood-system. These differences are, however, in
general merely differences of development, which are to be explained
by differences of age. Always, however, there are to be found on the
delicate portion of the omentum covering the left part of the stomach,
as well as on the denser part covering the pyloric portion of the
stomach, numerous places, either in the form of more or less isolated
islands of different size or of cords, the surface endothelium of which
possesses the above-mentioned characters, viz. is germinating. Seen
from the surface such areae appear to be covered with cells, which are
raised like buds, with "Shorter or longer stalks. The upper parts of
these buds appear in many instances to imdergo division. That the
germination on these places goes on with some rapidity can be

GERMINATING ENDOTHELIUM. 5

deduced from the fact that besides the appearances of constriction
and division of the polyhedral or club-shaped endothelial cells, there
are always numbers of smaller spherical lymphoid elements to be
found amongst them, which are detached from the surface, that is to
say, which have become perfectly separated.

Grerminating endothelium is to be found just as richly on tlie
omentum of the dog, especially in the non-fenestrated portion, where
it is to be met with in the form of isolated smaller or larger groups.

The pleura mediastini of dogs, cats and monkeys is a very good
object for studying germinating endothelium. On the trabeculiB of
that membrane, as well as on the complicated system of tracts which
extends freely over the surface, there exist numbers of lateral or inter-
calated nodular swellings of various size, the surface of which is
covered abundantly with young endothelium. From the great number
of club-shaped and pedunculated two-nucleated endothelial cells, and
from the number of spherical cells which are more or less loosely
attached to the surface of the above-mentioned swellings, we cannot
but deduce that there is going on a very abundant production of lym-
phoid cells.

Not less instructive is the mesogastrium of the frog. If this
membrane of a female frog during the winter months is examined in
an indifferent fluid or after staining with silver solution, one recog-
nises on the siurface of the dense portion, especially on the trabeculae
of the fenestrated portion, numbers of places where the endothelium
possesses the germinating character : they appear either in small
groups or as nodules which project freely on the surface of the trabe-
culae.

This germinating endothelium, which is similar to that described
in mammals as regards its substance, shape, and nucleus, possesses the
pec^Uarity that the surface of the endothelial cells is provided with a
bunch of cilia. If the membrane is mounted in sermn, and the cover
glass supported by small strips of paper, the ciliary movement can be
observed during three hours and more with equal rapidity. The pro-
liferation of this ciliated endothelial cells takes place in the following
way : one finds not rarely a ciliated cell of a columnar shape which
possesses two nuclei, situated above each other in the longitudinal axis

6 ^ ' ANATOMY OF THE LYMPHATIC SYSTEM.

of the cell ; the cell possesses in some cases a more or less distinct
constriction between the two nuclei, and the cilia of tlie surface have
become very delicate and short.

Finally, there may be seen endothelial cells without cilia, which
consist of two nearly spherical portions held together by a short neck ;
each portion possesses a spherical, sharp-outlined nucleus, with clear
contents and a shining nucleolus.

Mr. Francis Darwin showed to me a preparation of the mesogas-
trium of Rana temporaria, where there were to be seen germinating
endothelial cells that perform distinct amoeboid movements. Fig. 52
shows such young endothelial cells, which bud from a freely-projecting
knob ; the cells are in amoeboid movement.

A similar, but not quite so abimdant, germination may be observed
on the peritoneal surface of the septum cisternae lymphaticae magnse
of the frog, especially on the endothelial cells which surround, or
more correctly speaking, which line the stomata first described by
'^ Dogiel and Schweigger-Seidel.

S These authors found on the peritoneal surface of the septum of

^ female frogs, dviring the spawning season, ciliated endothelial cells of

^ a nearly cylindrical shape, in small groups near the stomata. I shall

J turn to the stomata afterwards. At present I wish only to mention

\ that during the winter months, in some septa besides the germinating

r^ mostly ciliated endothelial cells, there exist shorter or longer tracts,

^". which project more or less freely on the peritoneal surface, and which

jf are covered with polyhedral, sometimes ciliated endothelial cells.

Ludwig and Schweigger-Seidel first called attention to the differ-
ence which exists as regards the endothelium of different portions of
the peritoneal surface of the centrum tendineiun of the diaphragm of
rabbits. These authors have shown that the endothelial cells, which
are situated over the straight lymphatic channels, between the tendon
bundles, are of a smaller size than the endothelial cells which lie over
the tendon bimdles themselves.

They assert also that there exist sometimes groups of lymphoid

^ corpuscles, which are continuous with, or properly speaking, derived

from, those stripes of small endothelial cells previously mentioned.

I am able not only to confirm this latter observation, but also to

GERMINATING ENDOTHELIUM. 7

complete it to the extent that there exist groups or tracts of germi-
nating endothelium in rabbits as well as in guinea-pigs, cats, dogs,
and monkeys, which, as we shall see afterwards, stand in an intimate
relation to lymphatic vessels.

Somewhat different in its arrangement is the germinating endo-
thelium of the mesentery of frogs, cats, dogs, and monkeys, viz. in
these membranes they occur only in groups of less than five endo-
thelial cells, mostly two or three. They are also of a polyhedral
shape, consisting of a distinctly granular protoplasm, with a con-
stricted or double vesicular nucleus ; their size is considerably smaller
than that of the common endothelial plates surrounding them. On
fresh preparations, which have been moimted in serum with great
care, they appear as granular bodies projecting from the surface like
buds; on preparations stained with silver solution, they appear
generally beset with brownish granules. There exists a great variety
as regards the number of such groups in a given field. Searching the
surface of the membrane under a magnifying power of about 200,
one passes two or three fields where there are no groups ; whereas, in
a neighbouring field one meets with half-a-dozen or even a dozen of
them. They are to be found over those parts which contain large
blood-vessels qiute as often as over the intermediate portions.

These structures are not to be confounded with those very small
figures which occur on silver-stained preparations, isolated or in
small groups, amongst the large endothelial fields : a part of those
small fields may correspond to young endothelial cells if they are
distinctly granular.

If one examines carefully the surface of a silver-stained mesentery
of the frog, one will find that the large common endothelial plates,
which in intensely-stained preparations show a clear nucleus in a
brownish cell substance, do not touch each other everywhere by
means of the well-known more or less wavy lines, but that these
silver lines in some places appear to be replaced by a branched cor-
puscle, the body of which is situated at the point of junction of a
number of endothelial cells, and the processes of which stretch
between these endothelial cells so as to become identified with their
silver lines.

8 ANATOMY OF THE LYMPHATIC SYSTEM.

In some of these branched corpuscles a distinct clear nucleus is
to be seen. It is farther to be noticed, on careful examination, that
these branched corpuscles, or let us say at once these branched cells,
exhibit apparently great differences as regards shape, size, processes,
and nucleus, for at one place a corpuscle is like the above-mentioned,
at a neighbouring place the corpuscle has a spindle-shaped form,
the nucleus staff-shaped, and at still another place it is somewhat
elongated, and is provided with a very few processes.

In some preparations, slightly stained with silver, I have been
able to make out with high powers that in some instances the body
of these branched corpuscles lies somewhat deeper than the endothe-
lium, whereas one or the other of the finely granular processes
stretches itself perfectly superficially between the endothelial cells.

The same relations are to be found on the mesentery of cats and
monkeys, over large trabecvdse containing large blood-vessels as well
as on the pleural surface of the centrum tendineum. We shall see
afterwards that they are easier to be found in the inflamed condition.
Most abundantly, however, and chiefly, they are seen to exist on the
omentum of rabbits, on the omentum and pleura mediastini of the
guinea-pig, cat, dog, and monkey, especially on those places where,
as we have seen, the germinating endothelium occurs, viz. on the
above-mentioned nodules and patches, as well as on the tracts which
contain large blood-vessels and fat.

At present I will not describe the minute relations of these branched
corpuscles which project partly or wholly between the endothelium of
the surface, as we shall return to them repeatedly afterwards.

Before leaving this chapter, I wish to say a few words about the
method of investigation by which I have arrived at the foregoing
results. The examination of fresh preparations in serum or other in-
different fluids is of great importance. The membrane, after being
excised with the greatest precautions against pulling or tearing, is
placed in a capsule with somewhat diluted serum or one-half per cent,
saline solution ; after being spread out by slight movement to and
fro, a portion of it is separated with sharp scissors ; a glass slide is
brought in the capsule, and the portion is floated on it, so as to be

GEKMINATING ENDOTHELIUM. 9

perfectly spread out ; the glass slide is raised out of the fluid, and the
preparation is covered with a cover glass.

Equally important are preparations stained with nitrate of silver
solution ; the membrane is excised, together with the organs to which
it is attached, e.g. intestine for the mesentery, sternum and peri-
cardium for the pleura mediastini, costal muscles with their corre-
sponding ribs for the centrum tendineum, stomach spleen and pancreas
for the omentum of guinea-pigs and rabbits (for the omentum of the
cat, dog, and monkey, this is unnecessary). The excised organs are
placed in a large quantity of quarter or half per cent, solution of
nitrate of silver for a few minutes, and then treated in the ordinary
way. In mounting the preparations in glycerine the same precau-
tions are necessary as in mounting the fresh preparations, as above
mentioned, viz. those portions which are to be mounted are spread
out on the glass slide under water, and covered afterwards with a cover
glass, on the under surface of which a drop of glycerine has been pre-
viously applied. A good plan is to pour over the membranes diluted
serum before staining with silver. The risk of mechanical injury is best
avoided by pouring the silver solution on the membranes in situ, and
then cutting them out with their corresponding attachments, so as to
transfer them to water. We may mention at present that in our
farther investigations, especially in those of the cellular structures of
the tissue and of the lymphatics, we have always found that the treat-
ment of the serous membranes requires very great precautions against
even slight mechanical injuries, for only then can the appearances of
irregularities be avoided, which, especially in silver stained prepara-
tions, are apt to confuse the observer. In the contrary cases, there
may be found appearances of not pre-existing structures, even with
some regularity.

It may not be unnecessary to make some remarks about the dark
lines which appear on silver-stained preparations, as the boundaries
of the endothelial cells. Some authors have tried to show that these
lines correspond to a precipitation in a serous fluid which is accu-
mulated in furrows on the surface of the endothelium, the individual
endothelial cells being somewhat convex on their upper surface.
There will scarcely be anyone who will not admit that (1) there

10 ANATO]VIY OF THE LYMPHATIC SYSTEM.

exist such furrows; (2) that the surface of the serous membranes
is always moistened by a serous fluid, and consequently that fluid is
accumulated mostly in the above-mentioned furrows ; (3) that the
silver-salt produces precipitations in albuminous substances. If,
however, anyone concludes from these three circumstances the silver
lines correspond to precipitations in the serous fluid of the surface,
the conclusion is decidedly wrong, as the silver lines do not correspond
only and exclusively to these precipitations, for there exists a niunber
of facts which show that the existence of the silver lines depends also
and chiefly on precipitations in an intercellular albuminous substance,
which holds together the individual endothelial cells. The chief argu-
ment of Schweigger-Seidel, who first expressed the above-mentioned
erroneous opinion, and who defended it with great constancy, was,
that the appearance of the silver lines is prevented by rinsing the
surface of a serous membrane with diluted glycerine, or with diluted
sugar-solution. This assertion, however, I must contradict most
decidedly, as it is not the case either after rinsing with glycerine or
sugar-solution, nor even with water, provided that the membrane has
not been rinsed so much as to remove the endothelium altogether. Of
course, one can hardly expect that the silver lines should be of great
thickness in those instances in which the membrane has been rinsed,
as there exist no precipitations in a serous fluid of the surface which
would increase the precipitations in the intercellular substance. The
presence of various other lines on the surface of the silver-stained
membranes cannot be regarded from what has been said above by any
means as a proof against the silver lines being chiefly dependent on
the intercellular substance. We may mention here as well the very
regular system of silver lines corresponding to intercellular substances
in silver-stained sections of any mucous membrane covered with
laminated epithelium, e.g. cornea, conjunctiva, mucous membrane of
the mouth, sesophagus, larjmx, vagina, &c., in silver-stained sections)
through masses of smooth muscular fibres, in the muscular coat of
silver-stained arteries, and so on. It remains, therefore, for the anta-
gonists of the intercellidar lines only to deny the intercellular sub-
stance of the endothelium altogether, as it has been done by Robinski,
whose assertion it is scarcely necessary to discuss.

u

CHAPTEK IL

THE CELLULAK ELEMENTS OF THE GROUND-SUBSTANCE.

The following description of the cellular elements will be incomplete,
as they will be considered in many ways in the chapter on lymphatic
and blood-vessels. The most instructive and simple object for the
investigation of the cellular elements of the groimd*substance is the
omentum of rabbits, this being flatter, and, for the most part, very
slightly fenestrated compared with that of the guinea-pig, dog, cat,
and monkey.

If one compares the omenta of various rabbits, one finds, on mi-
croscopical observation, some not immaterial differences. One finds,
namely, a great number of omenta of full-grown animals in which
there are richly distributed opaque tracts of different breadth, forming
a network : some of these tracts consist of a row of patches of different
size, mostly oblong, sometimes romidish, which coalesce with each
other more or less.

There are numerous patches which are situated laterally to these
tracts, as well as perfectly isolated ones. Seen under a lens, the tracts
generally follow the course of the larger blood-vessels. In young
animals the network of opaque tracts is less developed than the
isolated patches. But also, on the same omentiun, there exists a
difference between different parts ; while that part of the omentima
which lies upon the anterior wall of the stomach, viz. between the
large and small curvature, contains very abundantly isolated patches
up to such a size that they are hardly visible to the naked eye, we
find on those portions which lie along the great ciu:vature and upon
the pylorus, besides these, also large tracts of fused patches. It may
be said in general, the younger the animal the more isolated small
patches are to be met with ; the older the animal the larger they are,
and the more confluent to tracts. It must not be understood, however.

12 ANATOIVIY OF THE LYMPHATIC SYSTEM.

that in full-grown animals there exist only tracts and large patches,
as there exist also here, as has been already mentioned, smaller patches
situated laterally to the tracts. It may be deduced from this that
in the omentum there is going on a continuous growth and new-
growth of opaque patches, which, by growing in length and coalescing
in the direction of their longitudinal axis, form tracts.

A portion of the fresh omentiun is a very unfit object for the
study of the cellular elements of the ground-substance : besides the
above-mentioned germinating endothelium, only more or less nu-
merous migratory cells can be seen on and in the patches and tracts.
There is only one mode of preparing that gave me good results, that
is, the mode of staining the fresh omentum with silver solution after
having pencilled it gently on one surface. I proceed in the following
way : a rabbit is killed by bleeding, the stomach is exposed ; after
having pushed the intestine to the right side, the free surface of the
omentum is pencilled several times, from the large curvature towards
the diaphragm, with a fine camel's hair pencil moistened with fluid of
the abdominal cavity. After that, a quarter or half per cent, solution
of nitrate of silver is allowed to flow over the omentum from a large
capillary tube, until the membrane has become slightly milky (one
to two minutes are generally sufficient) ; after t"hat, the stomach,
together with the omentum, spleen, pancreas, and a portion of the
duodenum is cut out and transferred to a large capsule with distilled
water ; after some time the water is renewed, and the omentum is
separated under water, together with the spleen and pancreas, from
the stomach with scissors and is transferred to common water. Those
portions of the omentum which are seen to contain small patches are
cut out and mounted, as has been already described. A failure is
more frequent than a success : either the surface has not been pencilled
enough, and then the endothelium of both the surfaces is coloured,
and consequently, hardly anything is to be seen of the cellular ele-
ments of the ground-substance ; or the surface has been pencilled too
hard, and then the arrangement of the ground-substance is altered,
its bundles appear considerably stretched and distinctly fibrillar.
Successful preparations become only slightly yellowish brown, and
can be preserved without alteration for a very long time.

CELLULAR ELEMENTS OF THE GROUND-SUBSTANCE. 13

Omitting at present everything except the cellular elements of
the gromid-substance, let us direct our attention to the very smallest
isolated patches recognisable as such under the microscope, and let
us anticipate that there are no capillary blood-vessels in them, and
that the ground-substance is perfectly unstained. The first thing
that strikes one are brownish-coloured structures of an irregular shape,
that is to say, structures which contain larger and smaller brownish
granules ; in most of them an ovoid sharply-outlined nucleus, some-
times with a nucleolus, or a constricted nucleus, or even a few small
nuclei, are to be seen. These brownish cells are of a different size, but
always much larger than colourless blood corpuscles. Their shape is
irregular, as has been already stated : their body is beset with a
variable number of smaller or larger blunt or roundish prominences.
Some of these cells are sharply defined, others are on one side more or
less distinctly continuous with the basis on which they lie. It is
clear that they correspond, as regards shape, to migratory cells. Be-
sides these cells, there is to be found a limited number of small
granular corpuscles, with one or two small nuclei, which are perfectly
like lymphoid corpuscles. In some places they are in such a close
connection with the above-mentioned large cells that they resemble
knobs which are in a state of separation from them.

As we have already mentioned, the ground-substance is imstained.
In it we find a network of a finely granular substance, which is stained
slightly yellowish. This network consists of large plates, connected
with each other by shorter or longer tracts of different breadth. In
the plate-like enlargements one recognises a sharp-outlined oblong
nucleus, with one or two nucleoli, or a constricted nucleus, or a nucleus
which ha& almost divided into two. In the latter instances, the
granular matrix is darker stained in the immediate neighbourhood of
the nuclei. I will refer the reader to Fig. 30, which represents such
a small patch : a represents the network of the finely granular sub-
stance (as this netwo]^ is represented only in one layer, all of the
processes which join the plate-like enlargements are not represented
in the figure) ; h represents the above-mentioned irregular-shapod^
large, coarsely granular cells. It is evident from this figure that we
have before us a network of branched, more or less flattened, cells,

U ANATOMY OF THE LYMPHATIC SYSTEM.

which, on the one hand, undergo division, as at F, and from which, on
the other hand, grow up large coarsely-granular elements.

If we direct our attention to a small patch which is provided with
a system of capillary blood-vessels (see Figs. 24 and 29), we see that
nearly the whole matrix is occupied by a network of finely-granular,
nucleated branched cells, which network is in communication with
the isolated branched cells of the surrounding tissue.

In the same preparation from which Fig. 29 is taken there exist
also patches the ground-substance of which has not remained un-
stained, but is of a slightly brownish colour ; in this ground-substance
we see a rich system of clear lacunae, which communicate with each
other by numerous branched and unbranched canaliculi of dif-
ferent breadth and length. Under a high power, we recognise in
many of the lacunse and canaliculi the finely-granular nucleated
branched cells above described, besides small lymphoid corpuscles.
We need not render it especially prominent that this system of
lacunse and canaliculi corresponds to the well-known lymph-canali-
cular system of Eecklinghausen, and that it represents the spaces in
which the above-mentioned system of branched cells lies. The Fig. 30
may be regarded as a combination of the negative, viz. the clear
lymph-canalicular system, and the positive, viz. the system of
branched cells, the outlines of the former as well as the nucleated
protoplasm of the latter being distinctly recognisable.

In preparations of the dense part of the omentum, e.g, the pyloric
part, prepared in the same way as above, one finds numerous places
quite superficially under the endotheliiun, where the branched cellular
elements and also the lymph-canalicular system show a somewhat dif-
ferent arrangement, the cells being arranged in small groups, and the
individuals of one group being situated round a common centre. In
these cases the cells are either very little branched towards this centre,
or they touch each other even in a straight line, whereas they are
provided with processes in the opposite direction, so as to join the
nt ■v:»'hbouring cells. In silver preparations the ground-substance of
which is stained there are consequently to be found superficial groups
of clear lacunae, which are separated from each other by silver lines,
and which send off canaliculi in the opposite direction. This, to a

CELLULAR ELEMENTS OF THE GROUND-SUBSTANCE. 15

great extent, resembles a group of endothelial plates branching out-
wards. We shall return to these structures afterwards, in the chapter
on Ijrmphatic vessels.^

Besides the above-mentioned small young patches, we find patches
of the following various structure : a smaller or greater number of
capillary blood-vessels are imbedded in a matrix, which contains
besides a limited number of spherical lymphoid cells of different
sizes, branched cells, lying more or less closely by each other ; in
some places, the matrix appears to be completely supplanted by these
latter ones. Where they are not crowded together it is distinctly to
be seen that they are provided with processes which join each other
and those of the neighbouring cells. In the intermediate portions
between the latter and the former the cells become less branched,
their processes much shorter.

On negative silver-stained preparations, viz. in which the lymph-
canalicular system has remained clear, the lacunae of those cells
appear to be separated from each other merely by lines in those
places where the cells lie crowded together. From the fact that in
positive silver-stained preparations the cells of the intermediate
portions possess, instead of the single ovoid clear nucleus, a con-
stricted or even a completely divided nucleus, and secondly, that the
cell bodies themselves exhibit sometimes furrows like marks of

* As the reader may have already observed, I have, as regards the cellular elements
of the omentum, quite the same opinion as Rollett has of those of the cornea. In both
cases the branched cells are more or less flattened parallel to the surface, and in both
cases the lymph-canalicular system corresponds to those cells. In the omentum, as well
as in the cornea, the migratory cells are always found in the lymph-canalicular system,
and, as we shall see afterwards, in the oedematous omentum the lacunae and canaiiculi
may .b© distended by serous fluid and lymphoid corpuscles, which find their way through
the lymph-canalicular system to the lymphatic vessels. Rollett has treated in his paper
the branched corpuscles of the cornea and their lymph-canalicular system in such an
exhaustive manner that it is hardly necessary to enter again into a controversy about the
nature of the connective tissue corpuscles and the lymph-canalicular system of Reckling-
hausen. As regards the serous membranes, there cannot be the slightest doubt about the
cellular elements of the ground-substance being more or less flattened branched-nucleated
protoplasmic cells, and the lymph-canalicular system representing merely the spaces in
the ground-substance for those cells ; and I cannot agree by any means with the assertion
of Schweigger-Seidel and Boll that the connective tissue corpuscles in general represent
elastic plates which play only a passive part. We shall see afterwards that the proto-
plasmic nature of the connective tissue cells of the serous membranes plays an important
part in the normal condition, and still more in chronic inflammation.

16 ANATOMY OF THE LYMPHATIC SYSTEM.

division, we are justified in saying that the fact of the cells being in
some parts of those patches more crowded, smaller, and less branched,
is due to a division of the branched cells, and that in this way such
a patch increases in breadth and thickness.

From what has been said just now it is evident that the last
mentioned patches are, as regards their structure, similar to those
above mentioned, and that they are only further developed.

As regards the spherical cells of different sizes previously men-
tioned, it can be stated : first, that they lie in the lymph-canal icular
system, as may be deduced from the negative silver-stained portions
of these patches ; secondly, that there exist all intermediate sizes
between where a rounded nucleus is surroimded only by a very
thin zone of protoplasm, up to cells which are twice as large as a
common coloiu-less blood-corpuscle. From what has been said at the
commencement of this chapter we must claim also here, for at least
some of the lymphoid cells, that they are derived from the branched
cells of the matrix.

Besides these patches, there exist in the omentum of rabbits a few
other structures, which, although under a lens they do not seem to
differ much from those previously mentioned, yet under a higher
power they exhibit between a network of capillaty blood-vessels a
number of lymphoid corpuscles held together by a delicate reticulum
of branched corpuscles, similar to the reticulum of adenoid tissue.

A last form, which is also very interesting, and which is not very
often to be found, is the following : from a tract which, besides a rich
system of blood-vessels, shows the same structure as the one just before
mentioned, or which tract contains only a larger artery and vein, a
small artery comes off, dissolves itself into a network of capillary
vessels, which join again into venous vessels, which return to the
previously mentioned tract. The matrix in which these capillaries
lie consists merely of a regular beautiful reticulum of nucleated-
branched cells, without having any visible intercellular substance.
Amongst the cells of the reticulum there are to be seen cells which
are apparently spindle-shaped. These are situated generally in a row,
accompanying the capillary vessels ; by lateral branches they seem to
join the branched cells of the reticulum. Looking at these apparently

CELLULAR ELEMENTS OF THE GROUND-SUBSTANCE. 17

spindle-shaped cells carefully under a high power, one soon finds out
that they are only the profile of somewhat flattened branched cells,
exactly the same as the other cells of the reticulum. The meshes of
the reticulum appear perfectly clear, and contain only here and there
a lymphoid corpuscle. We shall return in the chapter on lymphatic
vessels to these patches and cords, where we shall be able to recog-
nise and understand better their intimate structure.

We will, however, anticipate, by calling the patches and tracts
which we have been considering up to the present lymphangial
patches {nodules) and lymphangial tracts.

We may therefore say that there exist in the omentum of the
rabbit two kinds of lymphangial structures :

a. Patches, the matHx of which consists of groups of ordinary,
more or less flattened, more or less branched cells, which on the
one hand multiply by division, in which way the patch increases
in size, and from which, on the other hand, grow up lymphoid
cells. The branched cells lie in the lymph-canalicular system, together
with the lymphoid cells. At an early stage of development these
patches do not contain a special system of blood-vessels ; at a later
time they possess a special rich system of mostly capillary blood-
vessels. By growing in length these patches join so as to form
whole tracts.

b. Patches and tracts, the matrix of ivhich consists of ct recti-
culum, the meshes of ivhich contain a variable number of lymphoid
corpuscles : they are generally provided with more or less abundant
blood-vessels.

We come now to deal with the omentum of the guinea-pig, cat, dog,
and monkey, the omentum of which animals is of a very similar
structure, and at the same time perfectly analogous to that of the
pleura-mediastini. Consequently, what will be said of the former
holds good also for the latter.

In the tissue of the omentum of these animals similar lymphan-
gial structures are to be met with, which, owing to their greater
diameter in thickness, we shall not name patches, but nodules. By
their size we may distinguish them as nodes and nodules, and we
may say as well here as in the rabbit's omentum that they join so as

G

18 ANATOMY OF THE LYIklPHATIC SYSTEM.

to form tracts, and that they project generally only over one surface
of the membrane. The larger ones are provided with a special system
of more or less numerous capillary blood-vessels. They are to be
met with also here, either along the larger blood-vessels, or isolated
at those points to which a number of thin connective-tissue trabe-
culse radiate. The older the animal the larger and more numerous
nodules are to be found, and the thicker and longer are the tracts
they form. In young animals, their number is very limited, and
they are of so small a size that they are to be recognised only under
the microscope.

Before considering their minute structure, we wish to call the
attention of the reader to the following points : — All these nodular
and cord-like structures we have referred to in this cliapter belong,
if I may so say, to the proper ground-substance of the membrane.
We have seen in the first chapter that the germinating endothelium
may form small nodular bodies on the surface of the membrane,
besideslieill^H^btinTiliErthe su^^ structures previously

mentioned.

If we look at a very small, that is a very young nodule, which
can only be discovered under the microscope as such, and is isolated
in the fenestrated membrane, we find in a pencilled silver-stained
preparation, in which, like in those we have described in the rabbit's
omentum, the ground-substance has remained nearly perfectly un-
stained, whereas the cellular elements are distinctly visible by their
yellowish or brownish granules, we find, I say, also here, that the
ground-substance contains more or less flat branched-protoplasmic
cells with oblong nuclei. These cells are more or less crowded
together, and join one another by their processes to form a network.
The nucleus is generally single, and contains one or two nucleoli ;
sometimes the nucleus is constricted, or even divided into two.
MigTatory cells are also to be found in these places, which either
resemble lymphoid cells, or which are large and coarsely granular.
There is one point which we need merely allude to here, having
entered into it fully in speaking of the rabbit's omentum, viz. that
some of the larger migratory cells form a distinct continuum with
one of those branched cells, by means of a longer or shorter neck, tliat

CELLULAR ELEMENTS OF THE GEOUND-SUBSTANCE. 19

is to say, that some of the larger migratory cells have originated from
a branched cell. In negative silver preparations of a corresponding
yoimg nodule it can be made out also that the clear lymph-cana-
b'cular system contains not only the network of branched cells, but
also the migratory cells. Besides the latter, we find also larger
isolated nodules in the fenestrated part of the omentum ; they are
already provided with a system of capillary blood-vessels. As regards
their minute structure, one can determine with certainty in positive
silver preparations that their matrix is occupied by more or less
flattened cells, which, in the same way as in the rabbit's omentum, are
the more branched the nearer they are to the borders of the nodules.
In negative silver preparations we find the lymph-canalicular system
accordingly so transformed that in the central parts of the nodule
the lacunoe communicate with each other only by a few short cana-
liculi or even touch each other in lines ; whereas in the peripheral
parts of the nodule the number and the length of those canaliculi
become greater. We need only add that from those more or less
branched cells of the matrix migratory cells may be seen to grow
up like knobs and become separated.

Besides the nodules just mentioned, we find also here, especially in
the pleura mediastini of the cat, smaller nodules of an elongated shape,
which consist of a delicate reticulum of nucleated branched cells, the
meshes of which are perfectly filled with lymphoid corpuscles.
Finally, we find nodules, and shorter or longer tracts, which possess a
very rich system of capillary blood-vessels. Between these capillary
blood-vessels extends a reticulum of pretty large branched cells, the
meshes of which are either perfectly clear and empty, viz. contain
nothing but fluid, or they contain here and there a smaller or larger
lymphoid cell, which in some instances may be seen to grow up from
those branched cells, viz. we find in one place that from a branched
cell of the reticulum a nucleated rounded knob projects into the
space of an adjacent mesh ; and not far from that we find a similar
appearance, with this difference, that the nucleated knob is raised
from its branched cell by a more or less deep furrow. In a third
case we find the nucleated knob previously mentioned connected with
the branched cell by means of a thin peduncle. From these facts we

c 2

20 ANATOMY OF THE LYMPHATIC SYSTEM.

are justified in concluding that the lymphoid corpuscles which are to
be found in the spaces of the reticulum are offsprings of the cells of
that reticulum.

If we examine one of the above-mentioned membranes without
special preparation we often find nodules and tracts marked only as
an accumulation of lymphoid corpuscles. After what we have stated
in the foregoing pages it would be perfectly erroneous to say that the
nodules and tracts of the omentum represent only accumulations of
lymphoid corpuscles (Knauff, Eecklinghausen) ; and it would be not
less incorrect to say that they resemble follicular tracts of lym-
phatic glands, viz. consist of adenoid tissue (Sanderson). We have
seen, namely, that there exist several marked varieties in the nodules :
a. Simple accumulations of germinating endothelium of the siu-face ;
h. Accumulation of more or less flat branched cells, or what comes to
the same, accumulation of lymph-canalicular systems, the lacunae of
which become by the gradual division of their cells nearer to each
other, and become provided in this way with less niimerous and
shorter canaliculi. Further, we have seen ; c. Nodules which per-
fectly resemble adenoid tissue ; and finally, (d) we have found vascu-
larised nodules, the matrix of which consists of a reticulum of large
more or less flat branched cells, the spaces of which are generally
occupied by fluid, or by a very limited number of lymphoid corpuscles ;
that is to say, the matrix is replaced by a space filled with fluid,
which space is subdivided into a number of small spaces by a reticulum
of branched cells.

As we shall see in the chapter on the lymphatic vessels, the varieties
c and d form one category of nodules and tracts, which, as they develop
in lymphatic vessels, may be called endolymphangial nodules and
tracts, whereas the nodules included in variety b lie outside lym-
phatic vessels, but in close connection with their wall, and may there-
fore be called perilymphangial nodules and tracts.

We must, however, add that we do not intend to draw a hard line
as regards structure between c and d on the one hand and b on the
other hand, at least not for the guinea-pig, cat, dog, or monkey ; for
we have not unfrequently seen nodules and tracts, the peripheral parts
of which consisted of large more or less flat branched cells, which

CELLULAR ELEMENTS OF THE GROUND-SUBSTANCE. 21

were distinctly situated in the lymph-canalicular system, whereas in the
central parts the branched cells were transformed into a delicate
''-ticulum of cells, the bodies of which had become considerably
smaller, and the processes very thin and delicate. The meshes were
filled out nearly completely by lymphoid corpuscles ; and there was
nothing to be seen of an intercellular matrix.

After what has been said about the distribution of those nodules
and tracts it is scarcely necessary to draw the special attention of the
reader to the fact that from their topographical arrangement they
are analogues of the fat tissue of the omentum. We will, therefore,
consider in the following paragraph the structure and the develop-
ment of the fat tissue in so far as it is necessary to show the very
intimate relation between the above-mentioned perilymphangial
structures and the fat tissue of the omentum. Before doing so we
will describe first an organ which is situated in the fossa infra-
orbitalis of young rabbits and guinea-pigs, the structure of which is
able to throw some light on our discussion about the relation of the
fat tissue and the perilymphangial structures.

By the side of the glandula infra-orbitalis lies a mass of fat,
which appears sometimes to be more or less isolated from the gland
as a separate structure, and sometimes to represent only an envelope
of that gland. In young and half-grown animals it is generally
found to consist for the most part of a perfectly hyaline matrix, and
to contain only a few small fat lobules. The older the animal gets
the more fat lobules and the less hyaline substance are to be found
in it.

The best method of preparing this structure for examination is the
following : the skin and subcutaneous tissue are first removed, and
the fascia which bridges over the fossa of the infra-orbital gland is then
slit up. A small portion of the hyaline body, which now protrudes
through the opening, can be snipped off with fine curved scissors, and
mounted in aqueous humor. The following appearances will then be
found under the microscope : in some places, there are a very few thin,
isolated, wavy, shining connective tissue bundles, with here and there
an amoeboid corpuscle ; in other portions very little is to be seen in
the perfectly hyaline matrix, while elsewhere the matrix contains a

22 ANATOMY OF THE LYMPHATIC SYSTEM.

not very limited number of isolated coarsely-g;ranular spindie-sh^ :
looking elements, of a considerable length. They show sometii - ^ :
their thick portion an oblong compressed nucleus ; their extremities
are very delicate, and are seen sometimes to be branched. If the
preparation is protected from evaporation, and if one observes the
hyaline matrix previously mentioned, put under a high power, one is
able to make out after some time has elapsed that granular fields
come into view in which a more or less distinct large oval clear
nucleus-like body may be just perceived. Still later, these granular
fields become more or less distinctly outlined ; it is possible to make out
that they represent plates of different sizes. Grradually, also, the pre-
viously-mentioned nucleus-like body becomes sharply outlined, and is
seen sometimes to contain a distinct nucleolus. If the observation is
still continued, a various number of different processes come into view,
which spring from those plates, and which become in their course so
delicate that they can hardly be followed. The outlines become
gradually more defined, and it is possible to make out that the greater
part of the plate is made of a more or less distinctly fibrillar substance,
and between the fibrils lie single granules, which are continuous with
the masses of granules which surround the nucleus. We can farther
see distinctly that the processes, too, are very finely fibrillated, and
that they are sometimes branched and join those of neighboming
cells after a longer or shorter course. A connection between those
processes and the above-mentioned isolated, wavy, shining connective
tissue bundles is not to be found. Such a connection is already a
priori improbable, from the perfectly different aspect and course of
those connective tissue bundles, provided that the preparation has
been made with the necessary care, and that all rough handling has
been avoided. In a portion which contains only a very few connec-
tive tissue bundles the contrast between the processes of the above-
mentioned cell plates and the connective tissue bimdles is very striking
as regards thickness, com'se, and aspect ; by careful examination it is
hardly possible to imagine how the very delicate processes of the cell-
plates could possibly be transformed into such a connective tissue-
bundle. We need not mention that in those preparations in which
the nimiber of connective tissue-bundles is very large it is very diffi-
cult to come to a decided conclusion.

CELLULAR ELEMENTS OF THE GROUND-SUBSTANCE. 23

The system of cell-plates, with their processes, can be brought into
view very distinctly, and without great loss of time, by moimting the
preparation in diluted Muller's fliud, instead of in serum or humor
aqueus, and they there become visible in fifteen minutes, or even
less.

Not all of the cells which we have designated above as being
branched are flat and of the same size ; generally they are in some
degree flattened. The largest of these latter cover nearly the third
part of a field (Hastnack |), but there are many which are smaller.
The question arises now, in what relation do the first-mentioned
granular spindle-shaped cells stand to those branched more or less
flattened elements.

If one compares a number of preparations it is obvious that in
some of them tlie number of spindle-shaped elements is a very great
one, and that they mostly run in one direction, whereas in some other
ones there are only few to be found. As regards their aspect, these
spindle-shaped cells resemble perfectly those which are to be found
in embryonal connect ive-tissue. If a preparation of the above-men-
tioned substance, containing a great niunber of spindle-shaped ele-
ments, is mounted in a large drop of serum or humor aqueus, and if that
edge of the covering glass which lies parallel to the longitudinal axis of
a certain number of the spindle-shaped elements is pushed slightly
by a needle one can observe the remarkable fact that the coarsely
granular spindle-shaped elements become all converted into pale,
branched, partly finely-granular partly striated, plates, each of which
contains a large flat ovoid nucleus. If, then, the cover-glass is again
allowed to float back, the plates become again converted into spindle-
shaped elements.

In preparations which had been mounted only shortly before, the
placoids which appear instead of the spindle-shaped elements are
very faint, exactly as we saw them previously in fresh preparations,
mounted only a very short time. This manipulation proves that the
coarsely-granular spindle-shaped elements are not, in fact, spindle-
shaped, but are perfectly identical with the above-mentioned placoids
seen edgewise. Under a high power, and using suflBcient care, one
can easily observe, by the above-mentioned manipulation how an in-

24 ANATOMY OF THE LYMPHATIC SYSTEM.

dividual spindle-shaped element rolls on its broadside so as to appear
as a placoid, and vice versa. Having so determined that all the
elements of this gelatinous hyaline body are of the same nature, a
further question arises, What is the significance of those elements ?

From what has been said until now, it is plain that this gelatinous
body is perfectly analogous with what is called ' Schleimgewebe,'
namely, what is regarded as embryonal connective tissue ; but we must
venture to repeat again that we have not been able to discover a
transition of the cellular elements of that gelatinous body into con-
nective tissue bundles. The significance of the placoid cellular ele-
ments of it is to become transformed into fat cells.

If we examine a preparation taken from the perfectly hyaline
part of the neighbourhood of a fat lobule we find the nearer we ap-
proach to the fat lobule the more numerous are the branched placoids,
which contain fat globules, either one large one, or several small ones.
First they appear only isolated, the protoplasmic part and the processes
of the cell are very distinctly recognisable, the nucleus is situated
somewhat peripherally ; then we find them lying in groups, they are
still provided with processes, but contain a very large fat globule.
Here the protoplasm of the cell-body is reduced to a more or less thin
covering of the fat globule. Where cells of that kind lie close beside
each other, their processes can hardly be made out ; but where these
are met with as isolated ones it does not require any high power to
convince one's self that they are still provided with processes.

Where these new fat cells lie in groups a great number of blood-
vessels are to be met with : they form in such places a special system,
which is perfectly analogous to that found in fat lobules. But there
exist similar systems of blood-vessels in groups which do not contain
fat cells, which contain only clusters of the previously-mentioned
placoids : here they are, however, provided only with fewer and shorter
processes. One finds, for instance, an arterial branch breaking up
into a bunch of capillary vessels, which, after anastomosing with each
other, collect themselves into a venous vessel. The hyaline matrix
in which this system of blood-vessels is imbedded contains a great
nimiber of branched placoids. In such places it can be further made

CELLULAR ELEMENTS OF THE GROUND-SUBSTANCE. 25

out, that these placoids undergo rapid divisions ; one finds, namely,
not only cells the nucleus of which is either constricted, or even
divided, but the cells themselves show very distinct notches, and
more or less deep furrows, by which they become separated into two
parts of nearly equal size.

From these facts we can deduce that by division of these placoids
groups of cells result, which lie more or less close to each other, and
which possess shorter and fewer processes than those which are to be
met with in isolated ones.

There are, finally, to be found intermediate stages between such
vascularised lobules, the cells of which are not transformed into fat
cells, and those above-mentioned vascularised true fat lobules. There
can be, consequently, no doubt whatever that this hyaline body be-
comes transformed into fat tissue in the way that its branched flat
placoids become transformed into ordinary fat cells, and that while
doing so they proliferate by division, and that these groups are pro-
vided with a special system of blood-vessels. The latter may already
be found even when the cells of the matrix have not yet transformed
into fat cells.

After having described the development of fat tissue in the gela-
tinous body of the infra-orbital fossa, we shall be able to deal with
that of the omentum and of the mesentery more briefly than we could
otherwise have done, as we find in these membranes exactly the same
relations. As regards the formation of fat cells, we find here the
same relations. We have had the opportunity to remark that peri-
lymphangial vascularised nodules develop from, and consist of, ac-
cumulations of more or less flat and branched cells. We had further
remarked that these nodules join so as to form whole tracts, which
generally follow the course of the larger blood-vessels. We need now
only add that if the branched cells which represent the matrix of
those tracts become converted into fat cells as above described the
result would be what is generally called a vascularised tract of fat
cells. That the tracts of fat cells, as well as the more or less isolated
fat lobules or fat nodules, are only transformed perilymphangial
nodules can be very easily recognised by following a perilym-
phangial tract along a large blood-vessel up to a neighbouring fat tract.

26 ANATOMY OF THE LYMPHATIC SYSTEM.

In that way one will be sure to find smaller or larger nodules, which
are in all stages of conversion into fat tissue. [From this it is also
evident that the fat tracts show here the same relations to the surface
endothelium as the perilymphangial nodules in general]. It is
remarkable that the distribution of the perilymphangial nodules
stands in an opposite relation to that of the fat tracts. The
more perilymphangial nodides and tracts an omentum contains the
smaller is the number of the fat tracts, and vice versa. In well-fed
half and full-grown dogs, and still more in cats and white rats, the
omentum shows only fat tracts and very few lymphangial nodules of
a very small size, in a state where the capillary system is just de-
veloping, whereas, in the omentum of rabbits, seldom, and then only
to a limited extent, fat tracts appear. ^ In the omentum of guinea-
pigs and that of the monkey the lymphangial nodules and fat tracts
are pretty equal, even in the most favourable conditions. In the
pleura mediastini there is a very much smaller tendency for the
lymphangial nodules to become converted into fat tracts, whereas in
the mesentery, even of the rabbit, the tendency is great; from
which it is evident that the conversion of lymphangial nodules into
fat tissue does not take place equally in all serous membranes, nor in
all animals — ^the mesentery has the greatest, the pleura mediastini
the smallest tendency. In cats, dogs, and rats there is a much
greater tendency than in guinea-pigs or monkeys, and the smallest is
to be found in rabbits.

There are two other points with regard to the fat tracts still to be
mentioned, namely : 1. That as long as a lymphangial nodule does not
become converted into a, fat nodule there are always, as we have
seen, numerous lymphoid cells to be found in it, which, as we have
pointed out, are at least partly to be considered as offsprings of the
branched cells of the stroma of the nodule. But as soon as a lym-
phangial nodule becomes converted into a fat nodule the lymphoid
cells become fewer, or, at any rate, are not to be found in the same
number as before. We must therefore conclude that the surplus of
nourishment which the cells of the matrix are provided with is all
consumed in the production of the fat, whereas, previously, it had
been employed for the production of lymph-corpuscles. After what

CELLULAR ELEMENTS OF THE GROUND-SUBSTANCE. 27

has been said above about the transformation of the branched cells
of the stroma into fat cells, it is imnecessary for me to warn the
reader against the possible assumption that in the transformation of
lymphangial nodules into fat nodules the lymph-corpuscles are the
elements which become converted into fat-cells — according to the
previous assertions of histologists — and consequently we could easily
understand why the number of these lymph-corpuscles decreases as
this transformation is going on. For in contradiction to such as-
sertions we have the above stated fact that the fat cells are trans-
formed branched cells of the stroma of the nodule. Besides, the
decrease of the lymph-corpuscles can easily be explained in another
way. We have seen that the branched cells of the stroma of the
nodule lie in the corresponding Ijrmph-canalicular system, together
with the lymph-corpuscles. Under ordinary circumstances, one must
suppose that the lymphoid corpuscles, after they have detached, viz.
constricted, themselves from those branched cells, are carried away
into the lymphatic vessels, into which, as we shall see afterwards,
that lymph-canalicular system leads. As soon as the branched cells
of the matrix become converted into fat cells the production of new
lymph-corpuscles is diminished to a very great extent, and, conse-
quently, there is very little here that can be carried away.

2. The second point we wish to call attention to is the fol-
lowing : the lymphangial nodules and tracts grow relatively quicker
when they are going to become converted into fat tracts. That is seen
best in the mesentery. Here, for example, in cats and in rabbits it is
very easy to find that the number and size of lymphangial nodules
and cords increases very much in the neighbourhood of fat tracts.

It is plain, therefore, after all we have said about the fat tracts,
that we are in agreement with Fleming in saying that fat cells are
transformed branched cells, but that we are not in agreement with
that observer in saying that fat tissue develops in the adventitia of
arteries. What we have already pointed out is that the formation
and growth of the lymphangial nodules is generally, not always
though, closely related to the larger blood-vessels, and we shall see
in one of the following chapters that the development of the lymph-
angial nodides, and consequently also that of the fat nodules and fat

23 ANATOMY OF THE LYMPHATIC SYSTEM.

tracts stands only in so far in a relation to the blood system as a
very active growth of capillary blood-vessels takes place in the
lymphangial nodules. We may say, further, that we consider fat
tissue, in agreement with Toldt, to be a special sort of glandular
tissue, for it develops from a special tissue, i.e, from lymphangial
nodules, which, as we have seen, have very much to do with the for-
mation of lymph-corpuscles, just as a lymphatic gland has.

We have still to make a few remarks about the mesogastrium of
frogs. There are not seldom nodules to be found in the ground-sub-
stance, which are of a spherical shape, sometimes situated so closely to
each other that they almost coalesce, so as to form a cord, and which
are not always near the large blood-vessels. They have a structure
which resembles in all respects that of lymphatic follicles.

As regards the mesentery, there is very little remaining to be said,
partly because we have already discussed the cellular elements of the
omentum, and partly because we shall return to the subject of the
cellular elements of the mesentery in the chapter on inflammation,
the cellular elements in the inflamed state being very much easier
to study than in the normal. This is especially true of frogs and
cats, in which animals chronic inflammation oc<iiirs accidentally, in
consequence of parasites which find their way from the intestine,
through the lymphatics of the mesentery, to the mesenteric glands.

The cellular elements of the ground-substance of the mesentery
are in general more or less flat branched ; in their structure, size, and
nucleus they are not different from those in other serous membranes.
In frogs and monkeys, as well as in cats and dogs, I have not unfre-
quently seen, on pencilled silver preparations, places where the branched
cells of the lymph-canalicular system appeared to undergo division.
In some the nucleus is divided ; in others the body of the cells itself
exhibits a cross mark between the two nuclei, so that then the body
of the cell consists of two halves, touching each other in a straight
line. Sometimes a group of three or four of them were touching each
other in straight lines, either situated all round a common centre, or
arranged in a chain one after the other. In general, these phenomena
are seen to take place near the large blood-vessels. There, also, we

CELLULAR ELEMENTS OF THE GROUND-SUBSTANCE. 29

sometimes find elements which appear like nobs on tlie branched cells
of the lymph-canalicular system, and which perfectly resemble lymph
corpuscles. A fact we have had already opportunity to refer to is
that near the large blood-vessels similar smaller or larger masses of
branched cells are to be found which mostly form oblong nodules and
cords, which begin now to have a special system of blood-vessels of
their own. These nodules and cords are exactly like those described in
the omentum, namely, those which we described under the name of
perilymphangial nodules and tracts. Their intimate structure, their
migratory cells, the relation of these to the branched cells of the
matrix, the relation of these nodules to fat tissue, is here exactly the
same as in the omentum. Especially worthy of notice is the fact
that in guinea-pigs I have met with mesenteries which exhibited an
immense development of these perilymphangial tracts, whereas in
cats and dogs the perilymphangial tracts have a great tendency to
convert themselves into fat tracts.

As regards the cellular elements of the abdominal serosa of the
centrum tendineum, there is very little to be said. They differ in no
respect from those we have found in the mesentery : where the larger
blood-vessels branch, and where, as we shall see, lymph-capillaries
are to be found forming a network, there we find also that the
branched cells of the serosa are situated nearer to each other.
Amongst those we find also here groups of flattened cells, which are
connected with each other only by very few short processes, or even
touch each other end to end. In correspondence with this arrange-
ment, the lymph-canalicular system also becomes modified, namely,
contains groups of lacunae, which communicate with each other by a
few very short canaliculi. The ceils of the pleural serosa of the
centrum tendineum can be recognised more easily on pencilled silver
preparations than those of the abdominal serosa. We there see, close
under the endothelium of the surface, a layer of very large flat,
branched cells, which lie mostly isolated, but in the neighbom'hood of
those places where the vena cava and aorta pass through the dia-
phragm, and also in the median portions of the centrum tendineum, are
foimd in larger groups closely together, so that in many places there

30 ANATOMY OF THE LYMPHATIC SYSTEM.

appears under the endothelium of the general surface a second layer
of large flat cells, arranged very similarly to an endothelium. The
cells consist of an almost hyaline substance, and possess a large clear
ovoid nucleus : the cells which lie deeper in the proper substance of
the serosa are more or less flat and branched. In preparations which
have been stained with nitrate of silver after being pencilled from the
pleural surface, the branched cells of the serosa are not easily recog-
nisable, the lymph-canalicular system of the branched cells being the
chief thing that comes into view ; but by using a high power and
examining a preparation which has been deeply stained in many
places, one is able to distinguish the bodies as well as the processes of
the branched cells, the former occupying the lacunae, the latter the
canaliculi of the lymph-canalicular system. The cell substance is
very pale, distinctly granular round the oblong or spherical sharp
outlined nucleus.

The cells of the islands of the serosa, which are surrounded by
lymphatic vessels (see the following chapter), are very instructive as
regards the processes of division of the branched cells of the lymph-
canalicular system we have already mentioned in a former place. One
finds in the central parts, as well as in the peripheral parts of those
islands, numerous places where the branched celklie in groups, as if
round a common centre or in chains : there the individual cells are
very little or not at all branched where they touch each other, whereas
they are provided with processes on their outer sides. These cells of
the serosa come out very distinctly when the serosa has been slightly
affected by inflammation. Under those circumstances their relation
towards each other and the surroimding parts is much more distinct.
We call the attention of the reader to the figures 14, 16, 17, which
will render our meaning easier to understand than any long descrip-
tion.

31

CHAPTER III.

THE LYMPHATIC VESSELS OF THE SEROUS MEMBRANES.

a. Lymphatics of the Omentum and the Pleura Mediastini.

In the rabbit's omentum the l3niiphatics are easily demonstrated.
Following the above-mentioned method, it is necessary only to pencil
in situ the sm'face of the fresh omentum and then to stain it in silver.
Different portions -of the omentum are differently circumstanced as
regards lymphatics. In the neighbourhood of the greater curvature
of the stomach, and in the portion of omentum covering its pyloric
end, there occurs a rich network' of lymphatics : they are related to
the large blood-vessels in such a way that a group of the latter has
a lymphatic running along both sides and communicating with one
another by transverse and oblique lateral branches. The lymphatics
are also distributed independently of large blood-vessels, chiefly
between and around the lymphatic patches which, as mentioned above,
are met with in great abundance in this part (the pylorus and greater
curvature). Concerning their structure, there is little to add to what
is already known. They are wide vessels, the walls of which consist
only of one layer of endothelial plates ; the latter, in the large lym-
phatics accompanying the blood-vessels, being of a short spindle
shape, almost sinuous. These possess also valves and sacculated dila-
tations corresponding to them, and are to be considered as the main
lymphatic trunks.

The other class, running apart in the tissue, are not different in
calibre, and have also a sinuous endothelium; but they are either
without valves or have them only in a very few places, while they are
provided with sinus-like dilatations springing from their sides. These
are to be considered as the lymphatic capillaries.

32 ANATOMY OF THE LYMPHATIC SYSTEM.

In the portion of omentum covering the anterior wall of the
stomach the conditions are somewhat different. There it will be seen
that the lymphatics rim only in company with the blood-vessels ; large
blood vessels, again, are rare in that part, the vessels of common
occurrence being the smaller arteries and veins, which, however, run
quite isolated, often for a considerable distance. The arrangement
of the lymphatics is as follows. Either a single Ijrmphatic vessel
is accompanied on one side frequently by a vein and sometimes also
by an artery : the lymphatic keeps close to the blood vessel, possesses
at certain points sacciform dilatations, and receives also sometimes a
branch laterally. These are vessels that have mostly a sinuous
endotheliiun. Or, secondly, it may happen that a blood-vessel is
accompanied on both sides by a lymphatic : these are disposed exactly
as in the former case, and commimicate by cross branches. ■ ,

Finally, it occurs not unfrequently that the blood vessel runs
within a lymphatic — that the blood-vessel is invaginated. There
cannot be the slightest doubt that such invaginations occur. They
are of various kinds. One case, for example, which is quite easy to
make out, is that of a vein invaginated for a considerable part of its
course, while, at the same time all its branches, so long as they are
not capillaries, are also invaginated. The chief lyinphatic, containing
the venous trunk, leaves the latter, after a long course, at a point where
this vein opens into a larger trunk, and then unites with the
lymphatic that accompanies this principal venous trunk. It may
also happen, secondly, that the lymphatic leaves the blood-vessel long
before the latter opens into a large trunk : in this case the vein and
lymphatic run side by side to the latter point. Finally, there is a
third case, which, however, in the omentum is much rarer, viz. where
the lymphatic accompanying a blood-vessel (and invaginating it)
suddenly acquires an extensive dilatation, through which the blood-
vessel penetrates, breaking off at an angle, while the lymphatic can be
traced a long way beyond the dilatation.

All these descriptions are drawn from preparations that have been
pencilled and silvered. I have in my possession preparations of
rabbit's omentum where such perivascular lymphatics present them-
selves as large tubes, the walls of them showing the sinuous endothe-

limn distinctly coloured ; in the tube lies the blood-vessel, the wall of
which shows the spindle-shaped endothelium on its inner surface.

In this case, where the lymphatic appears, not, as in the common
silver preparations, in the form of a clear space showing endothelial
markings on a dark ground, but as a wide tube, there is hardly any
possible room for mistake, inasmuch as one can see, even with a low
power, that the blood-vessel is contained, as if it were a thin rod,
within the wide tube. In the iirst case, also, where the lymphatic
shows itself as a clear space with endothelial markings, a mistake will
not readily be made if one has before him an invagination extending
over a long tract ; for in that case it can be seen that the lymphatic
makes certain bends, which affect both sides of it together — that is,
the impression on one side of the vessel has its corresponding and
complementary deflection on the other. The importance of this as
a criterion will appear from the following considerations. The blood-
vessel lying in a lymphatic has that surface which is directed towards
the lumen of the lymphatic also covered by an endothelium. There
appears, therefore, in the optical longitudina^ection on each side of
the vessel, an endothelial membrane, i.e. a membrane with oblong-
nuclei disposed at regular intervals — the endothelium being seen of
course in profile. It presents, therefore, the appearance as if a lym-
phatic ran on each side of the vessel. In this manner the above-
mentioned condition, viz. that the bendings of the lymphatic on both
sides of the blood-vessel correspond to and complement each other,
is of importance for deciding whether we have before us one lymphatic
in which the blood-vessel is invaginated, or a pair of lymphatics.

The lymphatics are also to be seen in the fresh omentum, provided
that the part is mounted in serum and has not been subjected to any
mechanical injury. After having studied the lymphatics in well-
silvered preparations, both those accompanying the blood-vessels as
well as the invaginating variety of them, one may recogTiise them
also in fresh objects. They present themselves as broad tracts which
appear to be bounded by a membrane with oblong nuclei disposed at
regular intervals ; that is, one sees the endothelial membrane in
profile.

34 ANATOMY OF THE LYMPHATIC SYSTEM.

In the lumen of the lymphatic there swim a number of lymph-
corpuscles of various sizes, exhibiting amoeboid movements. How
easy it is to fail to see the lymphatics in the fresh omentum is shown
by the circumstance that, if the membrane is subjected to only a very
slight stretching, the lymphatics collapse completely, and appear as
nothing else than rows of spindle-shaped elements, between which
migratory cells lie here and there. Even in silvered preparations the
same source of error exists. I have seen it happen, in a considerable
number of silver preparations in which the lymphatics were plainly
visible, although their endothelium was only faintly coloured, that, on
removing the preparation from one object-glass to another (necessitated
by an accident), the lymphatics were no longer to be seen. It is only
in the rarest cases that a lymphatic will be seen, unless the omentum
be treated in situ with the proper reagents. And, in my opinion,
this will not appear astonishing, when it is borne in mind, on the one
hand, how delicate and flaccid the lymphatics in this situation are, and
on the other hand, how tender and thin is the ground-substance itself.
How easily, therefore, ^he lymphatics collapse when the membrane is
cut out and the circulation of lymph has ceased. Thus, as regards
the mesentery, there is no possibility of failure in the demonstration
of the large lymphatics running from the intestine to the mesenteric
glands and accompanying the blood-vessels, and which possess muscular
walls ; for in their case, collapse to the extent of their disappearance
cannot occur. On the other hand, demonstration of the lymphatic
proper in the mesentery invariably fails if the mesentery is not
treated in situ with the greatest care. In like manner, it is hard to
fail in demonstrating the lymphatics of the pleural side of the centrum
tendineum, because here the serous membrane is prevented from
shrinking too much by the subjacent tendinous tissue. On the other
hand, want of success in demonstrating the lymphatics of the medias-
tinal pleura is easily intelligible on the same grounds as in the case of
the omentum.

From the circumstances just now mentioned, it follows that one
should be very careful in asserting the existence, in an omentum
whose lymphatics are not apparent, of spindle-shaped elements— and
among them a greater or less number of migratory cells — ranged

THE LYMPHATIC VESSELS OF THE SEROUS IVIEMBRANES. 85

along the sides of the blood-vessels. For it is easy to understand that
this appearance might simply be due to the folded walls of the
collapsed lymphatics, and the migratory cells be actually in the lumen
of the lymphatics. That there actually occiu: near the vascular
trunks occasional aggregation of lymph-canalicular cells and migratory
cells is another and different fact to which we have already directed
attention.

We come now to the important questions — Do the lymphatics in
the rabbit's omentum form a closed vascular system, or do they take
origin among the tissues ? and, In what way do the lymphatics stand
related to the above-mentioned patches and cords ? The answer to
the first question will become obvious when we have first considered
the second question attentively.

We have already mentioned that in negative-pencilled prepara-
tions, as well as in positive, one can convince himself that at certain
points the lacunae, or lymph-canalicular cells respectively, are so
closely pressed together that they come to be arranged in lines ; that
is, they are not united by canals ^r processes in their respective cases,
but simply joined to one another like the cells of an endothelium.
This appearance we shall call that of simple lacunae, understanding
thereby the larger lacunae formed by the fusion of a group of lacunar
spaces of the lymph-canalicular system, and lined, therefore, on one
side with cell-plates arranged like an endothelium. We have already
stated, however, that these isolated simple lymph-lacunae are con-
nected by means of canals with the isolated lacunae of the adjoining
lymph-canalicular system (and the outermost cells, respectively, by
processes with the adjoining cells ;) and we shall now add that those
simple lymph-lacunae are situated quite superficially — that is, under
the endothelium of the surface — and are but seldom met with in the
ground-tissue itself. We may at the same time mention, in connec-
tion with those isolated lacunae, also the simple lymph-lacunae that
occur in the large-sized patches, concerning which we have already
stated that they consist only of an agglomeration of more or less
branched cells, with the young cells belonging to them and lying with
Ihem in the lymph-canalicular system. In this same kind of patches
and cords there is illustrated yet another interesting relation in which

D 2

36 ANATOMY OF THE LYIVIPHATIC SYSTEM.

they stand to the actual Ijmphatic vessels. We have already stated
that the larger patches are provided with a systera of blood-vessels.
Disregarding at present the exact details, we shall merely, mention
that this system consists of an afferent arteriole, efferent veins, and
intermediate capillaries. Regarding, now, the lymphatic system of
these patches, it is always to be observed that the efferent vein, more
seldom also the afferent artery, is accompanied by at least one capil-
lary lymphatic, or is even invaginated in one such. At the point
where the vein becomes the capillary — that is, where it enters the patch
— the lymphatic as such terminates, that is to say, its hitherto
sharply-defined wall and covering of sinuous endothelium ceases,
and only the lymph-canalicular system appears in its place.

There can be no doubt whatever, if a favourable point is closely
observed, that at the point the lumen of the lymphatic vessel on the
one hand loses itself in reality in a labyrinth of spaces, which consist
of lacunae with uniting canals, representing the lymph-canalicular
system, and, on the other hand, the endothelial plates of the lymphatic
are continued as branched cell-plates.

The appearances just now mentioned correspond to what Eeckling-
hausen first described as to the origin of the lymphatic capillaries in
the centriun tendineum of the rabbit, with the adiMtion of the fact
that the endothelium continues itself in the lymph-canalicular sys-
tem as branched cell-plates. We call, therefore, these patches or
nodules peri-lymphangial nodules. When the lymphatic capillary
issuing from the nodule is of the invaginating kind, as in Fig. 40,
one may see at any time several points at which the lymphatic vessel
throws out one or the other of its branches to the lymph-canalicular
system of the surrounding tissue.

We come now to the consideration of the important relation
of that kind of nodules which we have described in Chapter II.
under c.

We find, for example, a wide lymphatic vessel invaginating a
venous trunk ; the vein collects a small number of capillaries, which
come off from a small arterial branch. The lymphatic vessel, however,
does not cease to exist as such at the point where the capillaries
debouch in the' vein, as in the former case, but continues on to the

THE LYMPHATIC VESSELS OF THE SEROUS MExMBRANES. 37

artery in such a way that the whole system of the capillaries is invagi-
nated in a sacciform dilatation of the lymphatic vessel. Not till the
root of the artery is reached does the lymphatic as such cease to exist,
at which point it loses itself in the lymph-canalicular system ac-
companying the artery. Thus we have before us here a case where a
vein is invaginated in a lymphatic vessel, while the system of capil-
laries belonging to it hangs freely in a lymph-sac, which is a direct
continuation of the lymphatic tube. A modification of this form is
the following : — A lymphatic vessel that simply accompanies a vein
possesses a blind sacciform dilatation, in which the system of capillaries
belonging to the vein is inserted like the glomerulus of a Malphigian
corpuscle of the kidney. We have already mentioned that in the*
case where a blood-vessel is invaginated the blood-vessel itself
possesses on its outer wall, viz. on that diverted towards the lumen of
the lymphatic, an endothelial covering, which exactly resembles that
forming the outer wall of the invaginating lymphatic. On the
invaginated capillaries the same is to be seen, that is to say, besides
the endothelium forming the outer wall of the common lymph-sac,
there is an endothelial covering outside the capillaries. From this it
is clear that the two kinds enumerated of invaginated capillary net-
work are identical. In both cases we have an outer wall of endo-
thelimn for the lymph-sac, and an endothelial wall around the
capillaries.

The second case of invagination of the capillary system is more
frequent than the first, for the reason that the case of a lymphatic
vessel simply accompanying a vein is more frequent than the case in
which the vein is invaginated. So long as the system of capillary blood-
vessels is small there is nothing further in the lymph-sac to be seen,
except here and there a migratory cell. Besides these, however, one
finds nodular structures which resemble those just mentioned in some
respects, but differ from them in other respects. We will direct the
attention of the reader to Fig. 50 on Plate X. and Fig. 43 on Plate
VIII.

In Fig. 50 we see that from the endothelial outer wall of a
capillary vessel branched nucleated protoplasmic bodies extend to that
of a neighbouring capillary ; these occur, therefore, in the lumen of

38 ANATOIVIY OF THE LYMPHATIC SYSTEM.

the lymph-sac, and the lumen is thereby partitioned into a number of
spaces. While at one point this proliferation occurs sparingly, at a
neighbouring point the lumen of the lymphatic-sac may be quite
free, or these branched cells may be so plentiful as to form a tolerably
close network, which differs from a young adenoid reticulum only in
respect of the somewhat greater amount of protoplasm which occurs
round the nuclei at the nodes of the network. From what has been
said, only this conclusion can be drawn, that the growth of a network
of branched cells proceeds from the endothelium of the lymphatic sac,
whereby the lymphatic vessel is transformed into a cavernous or
sinuous structure. It is very easy to make out at all points and in all
'stages of development, with great clearness, that not only from the
endothelium of the wall of the lymphatic vessel, but also from the
branched cells extending across its lumen, lymph corpuscles origi-
nate, which become finally detached and lie in the meshes of the reti-
culum, or in fact in the lumen of the previous lymphatic vessel. In
a completely formed nodule of this sort, which we designate as endo-
lymphangial nodules, one cannot of course any longer determine its
origin ; all that one sees is a delicate reticulum, with lymphoid cells in
its meshes, and supplied with a more or less rich capillary network.
For the same reason, also, in the case of a fully develop ed nodule or cord
of the first form, i.e. a peri-lymphangial nodule or cord, which owes
its origin to an aggregation of lymph-canalicular cells, it is not easy
to distinguish it from an endo-lymphangial noduleor cord, inasmuch as,
as we have already mentioned above, the at first more or less flat cells
gradually transform into an adenoid reticulum, in the meshes of which
lymphoid corpuscles lie, while at the same time the fibrillar ground-
substance disappears. We wish to add here, for the better understand-
ing, two other points, namely, 1. That those lymphatic nodules and
cords which are surrounded by a distinct semicircular lymphatic
vessel, and whose reticulimi is continuous with the endothelium of the
lymphatic vessel, correspond to a peri-lymphangial nodule ; and 2.
That the proliferation of an endo-lymphangial nodule extends more
and more into the lymphatic vessel invaginating or accompanying a
large blood-vessel, so that, therefore, the large blood-vessel seems to
be enclosed in a lymphatic cord. This then comes to resemble

THE LYMPHATIC VESSELS OF THE SEROUS MEMBRANES. 39

the form of cords which originate in the fusion of several peri-lym-
phangial nodules.

To summarise the preceding statements, we may divide the
lymphatic nodules into peri- and endo-lymphangial : the former consti-
tute isolated nodides or patches, and, by fusion, cords ; the latter form
patches and nodules, and, by continuous outgrowt-h, cords. From what
I have seen in the omentum and pleura mediastini of guinea-pigs,
dogs, cats and monkeys, I am inclined to think that along one
lymphatic vessel several endo-lymphangial nodules may originate,
isolated, which afterwards become fused together, so as to form a
cord.

It seems to me that the development of the peri-lymphangial
nodules follows more the arterial vessels, whereas that of the endo-
lymphangial nodules the venous vessels. My researches have, how-
ever, not been carried out so far as to enable me to state this with
certainty.

We come now to the lymphatic system of the omentum and pleura
mediastini of the animals just mentioned. We are able to treat this
part more briefly, since we have stated the essential points in detail
in the preceding, where, in the omentum of the rabbit namely, the
proof of the facts brought forward is considerably easier to adduce
tlian for the first-named animals. The lymphatics in the normal
state are here much more difficult to demonstrate than in the rabbit.
It is desirable to select for studying preparations mounted quite
fresh in serum, and subjected to the least possible tearing. One may
be prepared for ill-success in many cases of staining the omentum
with silver. It is very difficult to pencil accurately the extremely
delicate fenestrated portion of the omentum. The best preparations
are obtained from the guinea-pig, from that part of the omentum in
which the pancreas lies enveloped. It is less difficult to pencil the
omentum of the cat, the rabbit, or the ape, because here the omentum
lies on the small intestine like an apron. It is equally difficult to
obtain a successful preparation of the pleura mediastini of the guinea-
pig as well as of the cat, there being in the latter case an imusual
number of trabeculae, running in all directions free on the surface,
bearing the lymphatic nodules, which trabeoulge interfere to a great

40 ANATOMY OF THE LYMPHATIC SYSTEM.

extent with the pencilling. In the puppy, the pencilling is easier :
the membrane is not too tender, and therefore one succeeds much better
in obtaining a silver preparation in which the lymphatic system may be
successfully studied.

What I shall describe hereafter refers only to a small extent to
silver preparations of the normal membranes ; to a greater extent it
refers to the investigation of fresh normal membranes, and chiefly to
the investigation of membranes — either fresh or silvered — that have
been slightly chronically inflamed. The latter, if the chronic in-
flammation has not reached too high a degree, are especially well
adapted for the study of the lymphatic system, for the simple reason
that here the lymphatics are held distended, either by the fluid of
oedema or by lymphoid corpuscles. Thus the tuberculous omentum
and pleura mediastini of the guinea-pig and ape have been of great
service in many cases in consequence of the cedematous condition.

The lymphatic vessels which accompany the larger blood-vessels
have quite the same relation as we have found them to have in the
rabbit, i.e. they accompany each vessel either singly, or more frequently
in pairs, and are in a few cases of an invaginating character ; the latter
condition, however, being, on the whole, not very frequent. Con-
cerning their structure, there is to be made out only a wall composed
of endothelium ; they follow exactly the course of the venous branches ;
here and there also a lymphatic is seen beside an artery. As regards
those nodules and cords which, by their stroma, may be interpreted
as peri-lymphangial nodules and cords, there exists quite the same
condition as we have already determined for the omentum of the
rabbit ; namely, the lymphatic vessel terminates as such and loses
itself into the densely-aggregated lymph-canalicular system, while
the corresponding system of branched cells is in direct continuity
with the endothelium of the lymphatic vessel. Here, also, we find
amongst the tracts of lymph-canalicular cells which accompany some-
times a small vascular trunk simple lymph-lacunse, that is, a fusion of
several lymph-canaliculi. As in the rabbit, such simple lymph-
lacunse occur also quite superficially in the omentum and pleura
mediastini of the before-mentioned animals. Considerably often,
also, lymph-sinuses, viz. .sacciform dilatations of lymphatic vessels are

THE LYMPHATIC VESSELS OF THE SEROUS MEMBRANES. 41

to be met with. Most generally it is the case where a lymphatic
vessel accompanying a vein gives off a short side-branch, which ends
blindly in the form of a sac. Into this terminal lymph-sac there
exists an invagination of a system of blood capillaries belonging to
that venous trunk. There may occur a growth of the endothelium
of the one wall of the lymph-sac towards the wall of the opposite side
in the form of a cellular network, from which, on the one hand, young
cells become separated, and which, on the other hand, gradually comes
to resemble an adenoid reticulum. In this manner an endo-lymph-
angial nodule is consequently produced. The other form of develop-
ment of endo-lymphangial nodules and cords is also tolerably frequent,
the form, namely, where a lymphatic vessel accompanying a large
blood-vessel possesses a sacciform dilatation in which a number of
capillary blood-vessels lie. By the outgrowth of the endothelial wall
of the lymphatic, in form of a cell network, towards the lumen of the
sac, an endo-lymphangial nodule or cord is formed.

(h.) The Lymphatic System of the Centrum Tendinettm of the

Diaphragm..

Eecklinghausen was the j&rst to assign to the lymphatic vascular
system of the centrum tendineum an adequate importance, having
there previously demonstrated the lymphatics by silver and by natural
filling of these from the peritoneal cavity. Ludwig and Schweigger-
Seidel have amplified the results of Eecklinghausen. My re-
searches do not only confirm those of the authors just mentioned, but
complete them to a considerable extent.

I will first describe the methods by which the lymphatic vessels
of the diaphragm may be demonstrated. First, the method employed
by Eecklinghausen, that is, pencilling the pleural surface of the
centrum tendineum with a fine camel's-hair brush dipped into serum,
and subsequent staining the centrum tendineum with half per cent.
of silver-solution. By this method the lymphatic vessels of the
pleura serosa are shown.

To obtain perfect preparations of these lymphatics, the following

42 ANATOMY OF THE LYJUPHATIC SYSTEM.

is the best plan : the anterior wall of the chest of a just-killed rabbit
or guinea-pig having been removed, the vena cava ascendens is
ligatured near its entrance into the auricel, the pleura separated from
the diaphragm, and the lungs and heart cut out. In this way the
pleural surface of the diaphragm can be exposed without being
smeared with blood. After this, each half of the centrum tendineum
is pencilled separately two or three times with a fine camel's-hair
brush dipped in serum, commencing in the middle line, and carrying
the brush outwards ; a quarter or half per cent, solution of nitrate of
silver is poured on the pencilled siu:face, and is allowed to remain
there for three to j&ve minutes, after which it is replaced by distilled
water : this is changed two or three times. After that the whole
diaphrag-m, together with the ring of cartilage and bone to which it
is attached, is cut out, brought into a large capsule with water. As
soon as the pleural surface assrmies a yellowish-brown colour, the
centrum tendineum is divided into a number of pieces, which are
floated on object glasses and mounted in glycerine. In a similar way
one proceeds if it is intended to demonstrate the lymphatics of the
abdominal surface of the centrum tendineum ; the abdominal surface,
having been exposed, is pencilled and treated as above.

The lymphatics of the diaphragm may be also-injected, either by
Eecklinghausen's method, that is, by injecting a few c.c. of milk into
the abdominal cavity of a living rabbit or guinea-pig, and by killing
the animal after 12 to 24 hours (it is desirable to stain aftei'wards the
centrum tendineiun with silver) ; or by the method of Ludwig and
Schweigger-Seidel, viz. by pouring on the abdominal surface of the
diaphragm of a fresh-killed rabbit a few c.c. of a watery solution of
Berlin blue, in which a fine precipitate of Berlin blue granules had
been effected by the addition of a small quantity of alcohol, and by
carrying an artificial respiration on for 1 5 to 30 minutes. A more simple
method, which gives better results, is the following : into the ab-
dominal cavity of a living middle-sized rabbit or guinea-pig, which had
been left without food for 24 hours, 5 to 10 c.c. of a five per cent, solu-
tion of Brucke's Berlin blue are injected ; after 4 to 8 horn's the animal
is killed by bleeding from the crural artery or by strangulation, and is
allowed to become perfectly cool. In exposing the pleural sm-face of

THE LYMPHATIC VESSELS OF THE SEROUS MEMBRANES. 43

the diaphragm, we find in most cases a complete injection of the
lymphatics. In healthy guinea-pigs the injection is hardly ever so
complete as in rabbits.

From Kecklinghausen it is well known that the very abundant
Ijmiphatics of the centrum tendineiun are distinguishable into lym-
phatic trunks and lymphatic capillaries, the former being provided
with valves and lined by spindle-shaped endothelium, the latter by
their variable lumen, the numerous excavations, their want of valves,
and their sinuous endothelium. Eecklinghausen states that some of
the lymphatic capillaries of the pleural serosa terminate blindly, like
a horn ciurved inwards, and that they dissolve themselves at these
places in the lymph-canalicular system. Lndwig and Schweigger-
Seidel have further shown that the lymphatics of the pleural serosa
of the centrum tendineum of the rabbit stand in communication with
lymphatic vessels, which run between the tendon-bundles; these
being arranged in an abdominal radiating and a plem'al circular
layer, the lymphatics which run between them have, consequently,
a radiating and circular course, and the former are called by L. and
S.S. superficial, the latter, deep lymphatic channels. My researches
teach me the following as regards the distribution of the lymphatics
in the rabbit : the lymphatics of the centrum tendineum are for each
half arranged in two systems, an anterior and posterior. The vessels
of the anterior system are distributed upon the outer and anterior
(that is larger) portion of the anterior quadrant, and upon the outer
(that is smaller) portion of the posterior quadrant. Those of the
posterior system are distributed upon the inner posterior (that is
smaller) portion of the anterior and upon the inner (that is larger)
portion of the posterior quadrant. (The relative number of lymphatics
is greater in the posterior quadrant than in the anterior). The
efferent trunks of the anterior system course along the pars costalis
of the diaphragm, and imite on the posterior surface of the xiphoid
cartilage on each side, usually to one or two large vessels, which run
along with the mammary vessels towards the sternal gland. On their
way they join with those lymphatics that come from the intercostal
spaces. It may be mentioned that the sternal gland is found gene-

44 ANATOMY OF THE LYMPHATIC SYSTEM.

rally completely injected after the natural injection with five per cent.
Berlin blue, as described above.

The efferent trunk of the posterior system is single on each side ;
it mounts obliquely towards the middle line, and opens into the
thoracic duct near the point where the latter emerges from the dia-
phragm. Each system communicates with the corresponding one of
the other side by a few larger vessels. The vessels of each system
have the following characters : the large vessels possess valves and a
wall consisting of spindle-shaped endothelium ; they are situated
chiefly between the pleural serosa and the tendons, or in the depth of
that serosa. The capillaries that run into those vessels have no
valves, are provided with irregular excavations, and their wall consists
of sinuous endothelium. There are two kinds of capillaries : a, such
ones that chiefly lie in the pleural serosa, and are of a variable breadth ;
6, capillaries that lie only between the tendinous tissue. They run,
consequently, in a straight course, in two directions, so that we may
distinguish deep straight capillaries running in a circular direction
and superficial straight capillaries running in a radial direction.
These two kinds of straight lymphatic capillaries communicate with
each other generally at those points where they cross each other in
such a way that an extremely short commuiication-branch exists
where their walls come in contact ; or it is not seldom seen that a
superficial straight capillary bends under a right angle, so as to con-
tinue its com'se as a deep straight capillary. The deep straight
capillaries represent the vessels of communication between the super-
ficial straight capillaries and the lymphatic vessels that lie in the
pleural serosa. As a rule, the deep straight capillaries, before they
join a lymphatic trunk, run a short distance, in a more or less wavy
course, between the tendon and the pleural serosa.

The relation between the straight lymphatic capillaries and those
that lie between the tendon and the pleural serosa, or in the latter,
can also be very clearly demonstrated in preparations prepared in the
following way : the abdominal sm^face of the centrum tendineum of a
rabbit just killed, after having been exposed, is pencilled and covered
with water for a few seconds ; after that, the concavity of the centrum
tendineum is covered with a quarter or half per cent, solution of

THE LITVIPHATIC VESSELS OF THE SEROUS MEMBRANES. 45

nitrate of silver, afid artificial respiration is carried on for fifteen to
twenty minutes, the animal being suspended head downwards. The
centrum tendineum, having been sufficiently washed with water, is
cut out and prepared for microscopic preparations, as mentioned
above. In such preparations the lymphatics present themselves as
dilated sacs and tubes, the endothelial wall of which comes out with
great distinctness. Fig. 36 is taken from such a preparation.

The fact that lymphatic vessels which have a winding course
sink down at once between the tendon-bundles, to continue their course
as straight vessels, is here very obvious.

It can be further made out in such preparations that the horn-like
terminations of lymphatic capillaries, as represented by Eeckling-
hausen, are only apparent, for they correspond to such points where a
lymphatic vessel curves round so as to sink down between tendon-
bundles and to become a straight vessel. In silver preparations
prepared in the ordinary way after pencilling, such horn-like termin-
ations are sometimes pretty common, and can easily be mistaken for
true terminations.

The question presents itself now. What is the physiological value
of the straight lymphatic vessels? Ludwig and Schweigger-Seidel
already attributed to these straight lymphatics an important part in
the absorption. According to those authors they are widely dilated
during the inspiration position of the diaphragm, corresponding to
the action of the muscles and tendons of this latter, whereas they are
compressed during the respiration, the lymphatics of the pleural
surface of the diaphragTQ being quite the reverse. Consequently, the
respiratory movement of the diaphragm acts like a pump on its
lymphatics. (The free communication of the lymphatics with the
peritoneal cavity, by means of stomata, will be discussed hereafter.)'
This, however, is not the only way in which the straight lymphatics
act. We have mentioned before that the lymphatics of the diaphragm
are arranged in an anterior and posterior system, the former dis-
charging itself in trunks that nm towards a gland, the latter in a wide
short trunk that runs directly into the thoracic duct. Now the
straight lymphatic capillaries are the vessels which perform the com-
mimication of those two systems, and this is their chief action. As the

46 ANATOMY OF THE LYMPHATIC SYSTEM.

deep straight lymphatic capillaries and the superficial ones represent,
as we have seen, only one category of vessels, we are justified in saying
that this category of lymphatic capillaries discharges itself in two
directions : one freely in the thoracic duct, and a second less freely
towards the stenial gland. In a following chapter we shall see
that the straight lymphatic capillaries, the deep ones as well as the
superficial ones, stand in free communication with the peritoneal cavity,
by means of vertical lymphatic canals '(stomata of the authors) ;
consequently, we have to substitute for the diagram of L. and S.S.
representing the lymphatics as a single pump, a diagram of a pump
with two cylinders, the one cylinder corresponding to the plem'al
vessels of the anterior system, the other to those of the posterior
system, while the pipe connecting the two cylinders is represented
by the straight capillaries, and the piston tube by the vertical
lymphatic canals. It must be borne in mind, however, that the two
cylinders act simultaneously.

The superficial straight lymphatic capillaries are not. the only
capillaries that are to be met with on the abdominal surface of the
centrum tendineum of the diaphragm of rabbits and guinea-pigs.
Near the median line of the anterior quadrants, and near the large
blood-vessels that pass through the diaphragm, there exist lymphatic
capillaries of a winding course, and provided with numerous dilatation-
sinuses. They stand in communication with the straight lymphatic
capillaries.

In some places two neighbouring superficial straight capillaries
anastomose with each other by means of a transverse branch provided
with sinuses, which belong to the peritoneal serosa.

After what has been said about the relation of the lymphatic
capillaries to the lymph-canalicular system in the omentum, there
remains very little to be said as regards that in the centrum ten-
dineum. We may mention that the continmty of the endothelium
of the pleural lymphatic capillaries with the branched cells of the
lymph-canalicular system of the pleural serosa can be demonstrated
very easily in the centrum tendineum of rabbits and guinea-pigs.
We refer the reader simply to the Figs. 14, 16, and 17, on Plate IV.

THE LYMEIIATIC VESSELS OF THE SEROUS MEMBRANES. 47

These figures, together with their explanation, will undoubtedly
make these relations sufficiently clear.

(c.) The Lymjphatic Vessels of the Mesentery,

The mesentery possesses, as it is known, two kinds of lymphatic
vessels ; first, vessels which run from the intestine to the roots of the
mesentery into the mesenteric glands ; and, secondly, vessels which
belong to the mesentery itself. The vessels of the first kind run in a
radiatory direction and are situated in the chief trabeculse of the
mesentery, together with the large blood-vessels, which run to and
from the intestine. These lymphatic vessels are distinguished by
their numerous valves and by their continuous rich ciicalar muscular
coat. Their endothelium is spindle-shaped, like that in the lymphatic
trunks in general. The vessels of the second kind are : (a) large
lymphatic vessels, which accompany also, like those of the first kind,
the larger blood-vessels. They are either single or, generally, double :
in the former case the lymphatic is situated between the arterial and the
venous trunk ; in the latter the artery and the vein lie both between
the two lymphatics. They are anastomosing with each other by a few
wide branches. Here and there they possess a valve ; they have no
muscular coat ; their coat consists only of one layer of endothelium,
which is more or less elongated, spindle-shaped. In many places the
breadth of the endothelial cells is not much inferior to the longi-
tudinal diameter. The lymphatic vessels of this kind are very often
found to invaginate the arterious or venous trunk for a longer or
shorter distance, especially with their large sacciform dilatations.
These dilatation-sinuses are constantly to be found on the lymphatics
of mammals, as well as in those of frogs. Especially in rana tempo-
raria, and in bufo, I have come across not a few mesenteries
where, instead of lymphatic vessels which accompany the blood-
vessels, there was a system of lymph-sinuses, situated behind each
other and communicating with each other by small openings. This
depends very much upon the arrangement of the ground-substance,
for in these latter cases there were large trabeculaa in which the
large blood-vessels and nerve-trunks were imbedded, from which

48 ANATOMY OF THE LYMPHATIC SYSTEM.

(trabeculae) small branches sprang in regular intervals, anastomosing
with each other and forming a mesh work. Seen from the surface
it looked exactly like a fenestrated membrane. The meshes were
occupied by those above-mentioned lymph-sinuses.

In frogs the invagination does happen not only in that way, that
one of the blood-vessels or the nerve-trunk is invaginated in a
Ijnuphatic vessel, but sometimes the whole trabecula which contains
the blood-vessels and the nerve-trunk is invaginated in a lymphatic
vessel.

(yS) Besides those lymphatics which are to be found in and near
the chief trabeculae of the mesentery, there exist other lymphatic
vessels, which belong to that portion of the membrane which stretches
between the chief trabeculae.

These are more or less wide vessels, provided with no valves ; their
wall is a single layer of rhombic endothelium with sinuous outlines.
They correspond to what is generally called l3rmphatic capillaries.
They accompany generally the smaller veins. In the pencilled silver-
stained mesentery of the dog, cat, monkey and frog they are very
easy to demonstrate. They are anastomosing with each other to a
wide net-work, and are also, like those previously-mentioned vessels,
provided with dilatation-sinuses. In those mesenteries where there
is little fat tissue, and consequently the lymphangial plaques and tracts
are clearly seen to consist of branched cells, it is also evident that
these patches and tracts have always on one or both their sides
lymphatic vessels.

In the mesentery of living curarized toads prepared for Cohnheim's
experiment one can very often distinguish the lymphatic vessels with
great ease. In some places they form a rather scarce net-work of
vessels, which run along the blood-vessels ; in some other places they
break up in a dense system of lacunae. In several instances I have
found knobs of different size projecting into the lumen of the lymphatic
vessels from their endothelial wall. These knobs were seen to consist
of an accumulation of germinating endothelial cells ; and, in fact, I have
been able in one instance to observe that these germinating endothelial
cells detach themselves, and are carried away by the lymph-current.
I conclude from this tliat here a local germination of lymphoid cor-

THE LYMPHATIC VESSELS OF THE SEROUS MEMBRANES. 49

puscles is going on from the endothelium of the lymphatics directly
into the lumen of this latter.

(cZ.) Relation of the Lymphatic Vessels to the Surface of the
Serous Membranes,

It is held by many histologists that there exist in many
serous membranes discontinuities between the endothelium of the
surface, by which discontinuities — stomata— a superficial lymphatic
vessel may communicate with the free surface. That there must
exist stomata on the abdominal surface of the centrum tendineum
lias been proved by the well-known experiments of Eeckling-
hausen. After Eecklinghausen, several observers have shown the
absorption of dissolved and undissolved substances, injected into
the serous cavity, from the lymphatics of the serous membrane.
There have been also several observers who tried to show on silver-
stained preparations those stomata. They have, namely, shown that
there exist small circular or angular dark or light fields between the
common large polygonal endothelial cells. These small fields were either
single or in small groups not very far apart from each other ; they
were of different size, and where they appeared to be regularly dis-
tributed they were found to represent the centre of a larger or smaller
group of endothelial cells, radiating towards that centre.

That in many serous membranes stained with nitrate of silver such
figures occur there can be no doubt whatever, but it is a quite dif-
ferent question whether they correspond really to holes. For, on the
one hand, it can be shown that these figures are sometimes to be found
on places, and not very rarely, where there are no lymphatic vessels
just below that part, e.g. on the centrum tendineum : on the other
hand, in the same preparation, they are not to be found where
they ought to be, namely, below where a superficial lymphatic vessel
lies. Besides, from their irregular distribution, their irregular shape
and size, one would be more inclined to take them as accidental than
as anatomical structures.

The histological proof that lymphatic vessels stand freely in
communication with the surface has been brought forward until now,

E

60 ANATOMY OF THE LYMPHATIC SYSTEM.

as far as I can see, only by Dybkovski for the pleura costalis.
DybkoYski has shown on that membrane, after having injected the
lymphatics, that the superficial lymphatic vessels lead freely between
the endothelium of the surface by short vertical branches. Close to
that comes the assertion of Dogiel and Schweigger-Seidel, that the
septum cysternse lymph, magnse in frog is perforated by a numbei;
of canals — stomata — that is to say, that the cysterna Ijmaph. mag-na is
in free communication with the peritoneal cavity. According to
these observers, large flat endothelial cells on both surfaces of the
septum have a radiating arrangement round those stomata; the
nucleus of these radiating endothelial cells lies peripherally in that
portion with which the cells border the stoma, so that each nucleus
causes a roundish projection of the cell into the stoma. We shall see
hereafter that these assertions do not correspond perfectly to the facts.
Finally, Ludwig and Schweigger-Seidel have drawn attention to
the important fact that the peritoneum of the centrum tendineum has
a fenestrated arrangement in those parts which cover the straight
lymphatics. This fact, together with the experience of Eeckling-
hausen, brought many authors to the assumption that those small
irregularly distributed figures amongst the endothelium above the
straight lymphatic channels in silver preparations represent stomata.
We come now to deal with the results of our own researches.
We distinguish two kinds of stomata on the surface of the serous
membranes, namely, stomata vera and stomata spuria or pseudo-sto-
mata. The stomata vera are again of two kinds : a. They represent
the mouth of a vertical lymphatic channel, which is lined by a special
layer of endothelium, and which channel leads into the lumen of a
superficial lymphatic vessel ; b. They represent a discontinuity between
the endothelium of the surface, leading into. a simple lymphatic sinus
near the surface, which, as we have seen, represents a cavity lined
only on one side with an endothelium. Both kinds of stomata vera
are bordered by endothelial elements of a more or less distinct ger-
minating character, namely, the cells are smaller, polyhedral, dis-
tinctly granular, they stain more readily in silver solution, and possess
a single, or a constricted, or a divided nucleus. As regards the dis-

THE LYMPHATIC VESSELS OF THE SEROUS IVEEMBRANES. 51

tribution of the first kind of stomata vera, the following is to be
noticed :

In great numbers they are to be met with on the peritoneal sur-
face of the centrum tendineum. We have had the opportunity to
mention that the straight lymphatic capillaries, the deep ones as well
as the superficial ones, stand in free communication with the peri-
toneal cavity by means of vertical lymphatic channels. The free mouths
of these are the stomata in question. These vertical lymphatic
channels are generally situated in chains behind each other ; they
are more numerous and shorter for the superficial straight lymphatics
than for the deep ones. The vertical lymphatic channels of the latter
exhibit in some rare cases a peculiarity, which consists in this : if from
the deep, straight lymphatic capillary a vertical lymphatic channel
is given off just at the point where the former is covered by a super-
ficial lymph-capillary, then we see that the vertical lymphatic channel
passes simply through the superficial straight vessel, that is to say,
the vertical lymphatic channel appears to be invaginated in the
straight lymphatic vessel.

In the vertical channels of the deep straight lymphatic capillaries,
having a considerable length, it is very easy to recognise that they are
lined by a special layer of endothelium, which in the most cases,
exactly like that of the corresponding stoma, consists of polyhedral
germinating elements. The layer of endothelimn which lines the
vertical channel is also distinguishable in those of the superficial
straight vessels if they are not collapsed. Adjusting from the peri-
toneal surface, one sees first the germinating endothelium of the stoma,
then a similar layer of polyhedral endothelial elements surrounding
the vertical channel like a corona.

Over the above-mentioned excavations and sinuses of the lym-
phatic capillaries of the peritoneal serosa of the centrum tendineum
there exist also stomata vera, i,e, vertical lymphatic channels which,
like those of the superficial straight capillaries, are only of a very
limited length. The endothelium does not differ in any respect from
that of the latter. Quite as numerous are the stomata vera, viz.
the vertical lymphatic canals in the omentum and pleura ; we find
them on the lymphatic capillaries and Ijmaph-sinus^s in the omen-

K 2

52 ANATOMY OF THE LYMPHATIC SYSTEM.

turn and pleura of all animals. They are not quite as numerous
to be seen on the lymphatic capillaries of the mesentery of cat,
monkey, and dog; but they occur relatively often in that of frog
and toad. They are naturally extremely short, in consequence of the
superficial position of the lymphatic capillaries, the membrane being
very thin ; but they are in every case lined by a special layer of
endothelium, which in every respect resembles that of those above
mentioned.

In these membranes — omentum, pleura mediastini and mesentery — -
stomata vera occur on lymphatic capillaries which accompany or in-
vaginate the blood-vessels, as well as on those which have no such
relation to the blood-vessels. It is necessary to mention that these
stomata are generally not so very easy to demonstrate in the normal
omentum, pleura mediastini, and mesentery (except that of the frog
and toad), the lymphatic capillaries not being so easy to demon-
strate. If, however, these membranes are slightly affected with
chronic inflammation, their demonstration does not require any great
skill ; by spreading out the fresh membranes carefully in serum they
may be seen without further preparation. Exactly like the vertical
lymphatic canals, i.e. stomata vera, just mentioned, are those of the
septum cysternaB lymphaticap; magnse of frogs and toads, described
by Dogiel and Schweigger-Seidel. Different from the description
given by these observers, I must mention that tKh vertical lymphatic
canals are lined by a special layer of more or less polyhedral
endothelial cells, which consist of a granular protoplasm. Accord-
ing to D. and S. S., these stomata are bordered by the nuclei of the
common flat large endothelial plates, both on the peritoneal surface
and on that of the cystoma, which nuclei project into the stoma ; but
these projections represent that special lining layer of polyhedral
endothelial cells seen in profile, as it is easily to be recognised on
membranes carefully spread out in the fresh state, and still better
after staining with nitrate of silver. I refer the reader to Figure
3, on Plate L In female frogs and toads the endothelial lining of
these vertical lymphatic canals is provided with ciliae.

In^SiS¥«far female frogs and toads during the winter months I
lave found the endothelium of the stomata of the septum, as well as

THE LYMPHATIC VESSELS OF THE SEROUS MEMBRANES. 53

of the mesentery, in a very active state of germination, the animals
suffering from chronic peritonitis.

A second kind of stoma vermn represents a simple discontinuity
of the endothelium of the surface. They lead into a simple lym-
phatic lacuna, situated superficially beneath the endothelium, and, as
we have seen, lined only on one surface, the lower surface, with an
endothelium. The endothelium of the surface which borders such a
stoma has very often also a germinating character. This kind of
stoma verum is to be found in the omentum of rabbits and the
mesentery of frogs and toads. They are also very much easier to
demonstrate when these membranes are affected with slight chronic
inflammation.

We have already mentioned, at the beginning of this Essay, that
there exist superficial branched cells in the serous membranes which
lie either totally or partially between the endothelium of the surface,
or, as is more commonly the case, only reach the surface by a process
which projects between the superficial endothelium. In the peri-
lymphangial nodules and cords described as occurring in the omen-
tum and pleura this is the case in an extraordinary degree. We
find here a large number of such perpendicular processes, projecting
freely between the endothelium of the surface, which proceed from
the superficial cells of the cell-network of the matrix of these lym-
phatic structures. This may be seen both in the young' and old
structures, in true or optical sections, as well as in surface prepara-
tions. As we have stated that the branched cells which constitute
the matrix of these peri-lymphangial nodules, as well as those of the
ground-tissue of any given part, lie in the lymph-canalicidar system,^
it is a necessary conclusion that the lymph-canalicular system opens

' We must again repeat here that by this we only mean the negative picture whose
position is formed by the branched lymph-canalicular cells themselves, with their pro-
cesses. "We are therefore not in precise agreement with the views of Lavdovsky and
Afonassiew. These authors consider that in the serous membranes a superficial lymph-
canalicular system exists as such, i.e. without the lymph-canalicular cells ; and that this
quasi empty lymph-canalicular system opens freely on the surface by a number of fine
perpendicular canals. We, on the contrary, consider that the branched lymph-canalicular
cells reach the surface through processes ; and as we deny the existence of a lymph-canal-
icular system without cells, and rather consider it only as a negative picture of the latter,
the statement, that the lymph-canalicular system opens freely on the surface by canals, is

54 ANATOMY OF THE LYIVIPHATIC SYSTEM.

freely on the surface, between the endothelium, by perpendicular
canals.

We shall show in the pathological part what great importance must
be ascribed to these freely-projecting cell-processes ; we call them
pseudo-stomata. A peculiar relation exists between these pseudo-
stomata and the young endothelium of the surface of those lymphatic
structures, which consists in the fact that the cell-process representing
the pseudo-stoma buds forth quite distinctly as a young cell. Of this
I have convinced myself in such structures, chiefly in the omentum of
the rabbit, but also in the omentum and pleura of the guinea-pig,
cat, and dog, both in siu*face aspects and also especially in profile
views. The nucleated buds, which, in form, size, and appearance,
are not to be distinguished from young endothelial cells, are seen to
project over the surface by a long thin peduncle. From the fre-
quency with which we see these bud-like young endothelial cells
sending a fine process vertically downwards between the surround-
ing young endothelial cells, we may conclude that a not incon-
siderable part of the young cells which bud forth from the surface of
a lymphangial nodule owe their origin to the pseudo-stomata. This
process, as we shall see, plays an important part in chronic inflam-
mation.

(e.) Development of Lymphatic GapvUaries.

We intend here to consider the development of lymphatic capillaries
only in so far as this takes place normally and to a relatively limited
extent in serous membranes ; in chronic inflammation we shall see
that this development takes place in a far greater degree. We shall

only correct in so far as negative pictures are meant by it. There was consequently no
extreme necessity for Lavdorsky to claim priority for the discovery that the surface of
serous membranes possesses a number of minute openings, which communicate with the
lymph-canalicular system, since we contradict this statement when made with the mean-
ing he applies to it. Least of all can Lavdovsky claim priority for the perpendicular
lymphatic canals, of which we spoke on p. 19 of the preliminary communication of E.
Klein and Burdon-Sanderson, and to which Lavdovsky chiefly referred, as we have seen
that this is something radically different from his own views. What we designated per-
pendicular lymphatic canals were branches of lymphatic vessels lined by endothelium,
and opening freely on the surface.

THE LYMPHATIC VESSELS OF THE SEROUS MEMBRANES. 55

examine the development of lymphatic capillaries in the omentimi of
the rabbit, and in the mesogastrium of the frog, as it may be easily
observed in those places. We have already become acquainted with
the fact that accumulations of branched lymph-canalicular cells form
the foundation of those peri-lymphangial patches and nodules which
are supplied with blood-vessels, as also of those which as yet are with-
out a blood supply. If we examine a number of such patches in suc-
cessful pencilled and silvered preparations, in which the number of
migratory cells is still inconsiderable, we may find, both amongst the
buds which spring from the lymph-canalicular cells, but still remain
connected with them, as also amongst the lymph-canalicular cells
themselves, some individuals in whose interior a vacuole is contained.
They are to be found of the most various size, and in every tran-
sitional stage, from some in which the granular protoplasmic body,
besides the vacuole, contains only a single oblong nucleus, which is
somewhat pushed to one side, to other large elements in which the
protoplasmic body is spread out to form a thin granular mantle, in
which at one point a constricted nucleus lies, or two nuclei, or even a
number of nuclei at equal distances from each other. In the latter
case, the wall appears on optical section to consist of spindle cells
fused together by their extremities. Finally, when these interme-
diate forms have been observed, we can easily understand the large
spherical vesicles, whose wall is distinctly differentiated into separate
endothelial plates. Further, it admits of no doubt that while a cell
grows into such an endothelial vesicle, buds grow out from the proto-
plasm of the cell towards its interior, i.e. towards the vacuole, which
become separated off as young cells. In general, such endothelial vesi-
cles are formed from lumps which bud from the lymph-canalicular cells,
but in many cases also directly from the lymph-canalicular cells them-
selves. In the latter case, we can still recognise, even in those elements
which have already become transformed into vesicles of considerable
size, processes through which the protoplasmic mantle is connected with
the neighbouring lymph-canalicular cells. We have, therefore, here
before us, in optima foi'md, the conversion of lymph-canalicular cells
into endothelial vesicles, quite on the same principle which was shown
by me to obtain in the developing blood-vessels of the embiyo chick.

56 ANATOMY OF THE LYIVIPHATIC SYSTEM.

Further, it is easy to make out that the endothelial vesicles whose wall
shows distinct endothelial plates after treatment with silver occur
chiefly in the immediate neighbourhood of lymphatic capillaries, and
not only solitary, but sometimes scattered in groups, and sometimes
arranged in a linear series, close behind each other. It is already
probable, from what has preceded, that the endothelial vesicles finally
communicate with each other either by fusion, or by extension of the
vacuoles through the protoplasmic processes which connect their
walls ; and also that they communicate in a similar manner with the
lumen of neighbouring lymphatic capillaries, because, as we already
know, the endothelium of the lymphatic capillaries is in direct com-
munication with the lymph-canalicular cells. It is therefore only
necessary that the vacuole of the lymph-canalicular cell should extend
along the process which connects it with the endothelial cell in order
that it should open into the lymphatic capillary. In this manner,
first, a lymphatic capillary may become longer, and secondly, lateral
sinuses or dilatations may be formed. I have not observed these pro-
cesses in the normal omentum of the rabbit, because, as may be easily
conceived, they do not occur with sufficient frequency ; but in chronic
inflammation, on the other hand, I have followed them out in all
serous membranes to so great an extent, and with such intensity, that
I do not hesitate to accept them also as the final result in the case of
the above-described endothelial vesicles.

These endothelial vesicles show a peculiar relation in the mesogas-
trium of the frog. I have described their development in the ' Quarterly
Microscopical Journal,' and have there stated that in female frogs,
in winter, they may be sometimes observed in a very considerable
number, owing to the presence of slight chronic peritonitis. I have
also said that the young vesicles bear cilia, which are directed to
their interior, and that this is sometimes still the case when their
wall is already distinctly differentiated into endothelial plates. So
far as their development is concerned, I have nothing to add to what
I have already said. In many vesicles the development of young cells
towards the lumen is very marked, while in others nothing is to be
seen of this process. I have also shown that these vesicles are not
simple cysts, as stated by Remak, but that they stand in the closest

THE LYMPHATIC VESSELS OF THE SEROUS MEMBRANES. 57

relation to the development of lymphatic sinuses and capillaries ;
indeed, in a mesogastrium in which there is a sufficient number of
such endothelial vesicles in different stages of development, their
connection with lymphatic capillaries may be easily shown. I have
also shown that in a later stage they lose their cilia. Finally, I have
said that an endothelial vesicle may open freely on the surface, and
that in that case a true stoma is formed. There is no difficulty in
understanding this, if we remember what has been said about pseudo-
stomata ; it is only necessary to imagine that if, for instance, a lymph-
canalicular cell, one of whose processes projects freely on the surface,
i,e, forms a pseudo-stoma, becomes converted by vacuolation into an
endothelial vesicle, and the vacuole extends along the process forming
the pseudo-stoma, the process must finally result in the formation of a
true stoma. I may add here that I have observed such endothelial
vesicles also in male frogs and in toads.

We shall see that the new formation of such true stomata takes
place to a very great extent in chronic inflammation of the various
serous membranes of mammals.

According to what we know of the development of endothelial
vesicles, we must express the view that they always ultimately become
connected with lymphatic capillaries.

68 ANATOMY OF THE LYMPHATIC SYSTEM.

CHAPTER IV.

THE BLOOD-VESSELS OF THE SEROUS MEMBRANES.

This is the last subject we shall have to treat of in the section
concerning normal structure. We shall pass over the distribution of
the blood-vessels in general^ as this is so well known and so simple that
we should only weary the reader were we to bring it forward here.
We shall only consider two points in this chapter ; first, the distribu-
tion of blood-vessels in the lymphangial nodules and cords; and
second, the development of blood-capillaries. It is especially the
latter to which we desire to draw the attention of the reader. We
have already mentioned, at the commencement, that in the omentum
and pleura a growth and new formation of lymphatic nodules takes
place, all of which gradually become furnished with a distinct blood-
vascular system, which itself grows with the growth of the nodules,,
and in which the capillaries especially are very richly distributed.
We can therefore observe in these places a contiiaious increase and
new formation of vessels in the adult organism in the normal state.
Concerning the first point, viz. the distribution of blood-A- essels in the
lymphatic nodules and cords, we have to say what follows. Wherever
in a nodude or cord a blood-vascular system can be observed, it con-
sists in general of an afferent small arterial branch, and one or even
two small efierent veins, between which is a network of capillaries,
which is more or less close, according to the size of the nodule. In
isolated cases only a variation may be noticed, where there are two
small arteries and only one vein. I refer the reader to the figures,
which although they represent pathological preparations, are com-
pletely identical so far as the distribution of blood-vessels is concerned,
with full-grown normal nodules. We may often see, coming off from
a small artery which is distributed to such a cord or nodide, a capillary

BLOOD-VESSELS OF THE SEROUS MEMBRANES. 69

which, without joining the other capillaries of the nodule, forms a pool
and passes into a vein. The part to which this capillary loop belongs
may already be clearly recognised to be a young developing nodule.
Now, between this simple capillary loop and the above-mentioned
completely developed blood-vascular system, the most various inter-
mediate stages may be found ; and it becomes a question whether in
time a part of the afferent limb of such a capillary loop becomes an
artery as the growth of the nodule goes on, and whether a portion of
the afferent limb becomes developed into a vein. My researches on
this point have led to no positive result. I could find no stand-point
from which I might arrive at a positive conclusion, for instance, that
the artery of a young nodule had been developed from what was
originally a capillary vessel. I cannot, however, give a decidedly
negative answer, since one is forced to assume, partly from the com-
parison of nodules in different stages of development, and partly from
general embryology, that this really is the case.

We now pass to the consideration of the second point, viz. the
development of capillary blood-vessels in the nodules.

Absolutely the best object for study is the omentum of the rabbit.
Both fresh objects examined in serum, and pencilled preparations
slightly impregnated with silver, give excellent results. If attention
be given to a series of young patches, in which the branched cells of
the matrix are clearly recognisable, and not obscured by the presence
of migratory cells ; and in which, moreover, only a very limited
number of capillaries is formed, we see immediately that the wall of
these capillaries is protoplasmic to a very great extent ; and we can
also see, when we have before us a nucleus on the upper or lower wall
of the capillary, that the part immediately surrounding the nucleus is
distinctly granular, the neighbouring portions gradually less so, until
finally the wall becomes hyaline. In good silvered objects we can
follow the endothelial markings of such capillaries of young nodules
only for a short distance at their commencement and termination,
i,e, at the parts nearest to the artery and vein. In fully-developed
patches the endothelial marking is distinctly to be recognised in the
capillaries. Accordingly, we must consider those capillaries whose
walls still distinctly retain their protoplasmic character as yoimg

60 ANATOMY OF THE LYMPHATIC SYSTEM.

capillaries. But on closer observation another much more important
fact is brought to light ; namely, that the branched cells of the
matrix stand in direct continuity with the protoplasmic wall of these
young capillaries, by their processes. From the extraordinarily com-
mon occurrence of the above fact in various modifications, and from
the clearness with which it may be observed, no error is possible. I
must especially insist upon this now, because in any figure, however
successful, apart from the suspicion one may always feel of a drawing,
this can never be so clearly recognised as it appears de facto under
the microscope.

We need not seek long in a patch in which the number of such
young capillaries is considerable in order to come upon a capillary
which ends csecally. This is either a short lateral branch or a longer
capillary which makes a loop-like bend. At the ca^cal end we can
recognise very clearly the protoplasmic character of the wall. The
lumen becomes more or less suddenly narrowed, the wall finally
becomes solid, and passes into a perfectly ordinary nucleated branched
cell of the matrix. We find all forms of this hollowing out of the
branched cells ; at one time only in a thicker process of a cell, at
another even in the body of the cell itself.

A very common occurrence is, further, that the branched cells, as
we have already had occasion to state, show vacuoles, both in the
body and also in thicker processes. The vacuoles ^.become elongated
towards a capillary branch which is being hollowed out, and finally
fused with it. Capillaries, therefore, are not only formed from pre-
viously existing capillaries by continuous excavation of the branched
cells connected with their walls, but are also formed isolated in the
branched cells themselves, becoming ultimately united with the
former. Isolated vacuolation for the purpose of the formation of
blood-capillaries is a perfectly distinct process from vacuolation for
the purpose of the development of lymphatic capillaries ; for in the
latter case vesicles are developed whose wall almost immediately
shows an endothelial differentiation, even when these vesicles have not
yet come into communication with lymphatic vessels ; in the former
case, on the contrary, this differentiation into endothelial plates does
not take place for a considerable time.

BLOOD-VESSELS OF THE SEROUS MEMBRANES. 61

The principle according to which the formation of capillaries takes
place is similar to that which was first pointed out by Strieker in the
new formation of blood-vessels in the tadpole and in inflammation,
and which was afterwards confirmed in every detail by Arnold. But
we must here remark that in our lymphangial nodules, patches, and
cords, tlie new formation of blood-capillaries does not take place by
the sending forth of protoplasmic buds from the wall of a capillary,
which are then excavated, starting from the vessel ; but this excava-
tion goes on both from the already formed vessel, and also isolated
in the branched lymph-canalicular cells, which are in direct con-
tinuity with the endothelium of the blood-vessels.

Precisely the same mode of development may be shown in the
previously-mentioned gelatinous body of the infra-orbital fossa. Here
a number of places may be found in the neighbourhood of the fat-
body where there is as yet no formation of fat in the groups of
branched cells, and where, nevertheless, an active development of
capillaries is going on. From place to place we find such accumula-
tions of branched cells and yoimg capillaries, in which, on the one
hand, the direct connection of the former with the wall of the latter
may be easily seen, and, on the other hand, the excavation of already
formed capillaries into those cells as well as the isolated vacuolation
of the branched cells may be followed through all stages. It seems,
from what has been said of this hyaline body, and of the development
of fat-tissue in the omentum and the mesentery, to be the general
rule, that the transformation of the branched cells of those cords and
nodules into fat cells is preceded by the development of a correspond-
ing system of capillary blood-vessels.

62 ANATOMY OF THE LYMPHATIC SYSTEM.

Section IL—P A THO LOGICAL CONDITIONS.

Much less attention has been paid to the study of the serous mem-
branes in pathological respects. As regards the changes which the
endothelium of the surface undergoes under morbid conditions, we meet
with the assertions of Eindfleisch, Eanvier and Kundrat. The two last
authors confirm the germination of the endothelium in inflammation
of the serous membranes. The process of germination is, according
to them, exactly the same as it occurs otherwise, and as we had
occasion to see in the normal state ; the cells increase in size, become
more polyhedral, the nuclei are observed to divide, and then the cells
themselves. According to Kundrat the miliary nodules on the serous
membrane in tuberculosis are derived from germinating endothelium.

According to Sanderson there is a pre-existing adenoid tissue in
the omentum in the form of nodules and cords, which increases to an
extraordinary extent in chronic inflammation, so that the nodules and
cords of tubercle which occur in artificial tuberculosis are nothing but
hyperplastic adenoid tissue. According to Knauff small knots and
cords are present even under normal conditions, consisting of a collec-
tion of lymphoid elements. These small knots play the most impor-
tant part in tuberculosis ; it is these that grow and multiply, and
represent the miliary tubercles.

Finally, in respect of the lymphatic vessels, Klebs has declared that
the lymphatic vessels play an important part in artificial tuberculosis ;
since the endothelium of the lymphatic vessels proliferates ; the young
cells originating thus compose the tubercle-knot.

We have already had an opportunity of pointing out in the first
chapter, that on the serous membranes in certain regions, there is

CHANGES OF THE SUPERFICIAL ENDOTHELIUM. 63

normally to be seen a germinating endothelium, a condition, it seems,
overlooked by Ranvier and Kundrat. We have fiu'ther shown, in the
second chapter, that the knots and cords are not exactly to be regarded
as pre-existing adenoid tissue, nor as collections of lymph-corpuscles,
but that they are developed for the most part out of ordinary branched
cells of the tissue — in fact, as peri-lymphangial knots and cords ; and
more, that the farther the development is advanced the more numerous
are the lymph-corpuscles at the spot — the more does the cellular
network assume the character of an adenoid network.

Finally, we have pointed out, in the third chapter, that normally,
in the omentum and the mediastinal pleura, knots and cords originate
by the outgrowth of the endothelium of the lymphatic capillaries as a
network of branched cells, from which young cells spring.

Thus we see that all the views of the authors are applicable to a
certain extent to the normal serous membranes — the views of Kundrat
and Ranvier, of Knauff and Sanderson, and finally of Klebs. We shall
now show in this section how far these views are applicable in patho-
logical relations.

1. The Changes of the Superficial Endothelium.

a. When severe acute peritonitis is produced in a rabbit, guinea-pig,
dog, or cat, for example, by the introduction of ammonia, of a solution
of iodine in hydro-iodic acid, or of toxic pyaemic fluids, which latter
kill the animals in a period varying from twelve to forty-eight hours,
into the peritoneal cavity, the mesentery, the intestinal serosa, the
omentum, and the peritoneum of the centrum tendineum appear ex-
traordinarily hypergemic, if an opportunity is afforded of examining
the animal during the first twenty-four or forty-eight hours. The
abdominal cavity contains mostly, but not always, a greater or smaller
quantity of bloody-coloured fluid, with abundant separation of fibrine.
In these cases of severe acute peritonitis, the endothelium of the surface
exhibits a common character — it appears, that is to say, loosened and
removed over great parts. The fluid contains, accordingly, an abundance
of isolated membranes composed of endothelial cells, and the surface of
many parts is deprived of its endothelium. Many of the endothelial

Gi ANATOMY OF THE LYMPHATIC SYSTEM.

cells, not only those found free in the fluid, but also those still on the
peritoneum, exhibit, in so far, a morphological change, as they appear
larger, as if swelled up, and their protoplasm is occupied by a greater
or smaller number of variously-sized granules. If the fresh membrane
is examined microscopically we may recognise that in the circumference
of those parts which have become deprived of their endothelium, the
individual endothelial cells are distinctly granular, even in the surface
view. On silver preparations these spots are distinguished by the
endothelial cells becoming more deeply coloured (cseteris paribus), i,e,
exhibit a dark granular precipitate. Corresponding to the endothelial
cells being more or less loose, we find instead of the well-known
sharply-defined silver lines, i,e, instead of the stained intercellular lines,
variously-sized, roundish or oblong, dark-coloured, drop-shaped ele-
ments. What appear as cell elements are accordingly separated from
each other by broad or narrow spaces, in which the above-described
bodies lie. I have just said that this substance which appears as black-
coloured drops takes the position in which the cementing substance
should be found. In fact, nothing is easier than to discover the
gradual transition of those broad spaces, filled with the drop-shaped
bodies, into the simple dark silver lines.

The shape, the colouring, the want of every structure, admits of
no other interpretation than that just given, namely, that the indivi-
dual endothelial cells become loosened, and that there is a more or
less fluid substance between them, which has become stained by the
nitrate of silver. Whether these drop-like bodies are offsprings of
the original cementing substance, or whether they belong to the
transudation, would be an idle discussion. From the rapid and
abundant transudation from the blood-vessels the loosening of the
endothelial cells is quite well conceivable as a simply mechanical
result.

A further important fact is that the nuclei of the endotheliarcells
exhibit distinct appearances of division, and this sometimes very ex-
tensively. Not only do we find a great number of flat endothelial cells
in the fluid, in which the nucleus presents the most various appearances
of division, but we especially find, for example, in the centrum
tendineum and mesentery, quite extensive places on which we should

CHANGES OF THE SUPERFICIAL ENDOTHEIJUM. 05

have suspected nothing of the kind in the healthy condition ; tlms,
for example, there is seen on the endothelium, which covers the peri-
toneal side of that portion of the serosa which lies upon the tracts of
tendons, and on which, as we have seen in the first part, proliferation
is not to be observed in the normal condition, an active alteration of
the nuclei over extensive spaces, from the simple constriction to the
division into two or three small nuclei. In the case of the omentum
it is more difficult to furnish a decided opinion, for there, as we have y
seen, an extensive proliferation goes on in the normal condition. x^

Should, however, the inflammation be of a less degree, e.g. in the
case of peritonitis, consequent on the entrance of air after larger or
smaller abdominal wounds by which we expose the peritoneum to the
atmosphere, or by the insertion of threads, of small solid bodies, as
starch (1-2 c.c. of a tolerably concentrated mixture of starch and
water), 5-10 cc of a five per cent. Berlin blue solution, a few c.c.
of oil or oil and starch, or any similar fluid which acts readily as a
foreign body — in these cases, we obtain an appearance somewhat
different from the preceding. Here, indeed, there are also seen, after
twenty-four or forty-eight hours and later, isolated detached endo-
thelial plates in the exudation. The peritoneum, however, exhibits
only a few places where the endothelium is loosened or has disappeared
in masses. On silver-stained preparations the endothelium is more
strongly coloured ; we recognise, in many regions, as on the centrum
tendineum, that the endothelial cells have become granular, are
somewhat swollen in diameter, the nucleus has become more pro-
minent ; in short, they possess more the appearance of epithelium :
the nucleus of many of the cells is in the state of division. On the
omentum, and especially on the fenestrated portion, there may be
demonstrated more easily polyhedral endothelial ceils whose nuclei
are in the state of division. What is most worthy of observation is,
that where we have met with germinating endothelium in the normal
coiiJ'ltion a very active proliferation has taken place. It extends
over the abdominal surface of the centrum tendineum, as well as over
the pseudo-stomata and stomata of the omentum and the mesentery.
In some places the germination of the endothelium is of a very re-
markable extent. Not only occur there bud-like processes which

F

66 ANATOMY OF THE LYMPHATIC SYSTEM.-

consist of young endothelial cells, but the endothelial cells so pro-
liferating arrange themselves into a cord, which stretches freely over
the surface. In the exudation we find a great number of cells, which,
on account of their size, their granulation, and their nucleus, are very
sharply distinguished from the small pale blood or lymph-corpuscles.
In consideration of what we have said above, it will, I think, not meet
any opposition if we consider those corpuscles, reminding one of
endothelial cells, which occur in the exudation, as the products of
the endothelium. Besides, there can be no mistake that also a
large number of cells which are to be found in the exudation, rather
smaller, more or less pale, originate by the division of the former, for
there may be observed on the warm stage amoeboid movements and
division in those larger cells furnished with constricted or double
nucleus.

There are intermediate stages between the forms first cited and
that of acute peritonitis of more moderate degi'ee, just as there is a
complete gradation between acute peritonitis of the severest degree
and of the mildest ; and this depends, as is known, upon the intensity
and extent of the irritation employed, upon the animal itself, and
upon circumstances which we cannot enter upon in detail in this
place, as they lie quite without the boundaries of this description.
What we wish to show is the variety which exists in respect of the
changes of the endothelium that occur when we have to do with
a very intense acute peritonitis, viz. intense hjrperaemia, abundant
emigration of colourless blood corpuscles, and abundant thin exu-
dation fluid ; or with slight acute peritonitis, viz. slight hypergemia,
generally limited to the omentum, peritoneum of the centrum tendi-
neum and intestinal covering, and no marked emigration of colour-
less blood corpuscTes^ For in the latter case it may be observed that
a lively germination of the endothelial cells takes place, limited
chiefly to those places where a germination could be made out
already imder normal circumstances, nama[y7^~t"Ee"centfum ^^n-
dineum around the stomata over the lymphatic capillaries of the
peritoneal surface, on the lymphangial knots and cords of the om^^ntum
and of the mesentery, where we have met with pseudo-stomata and
true stomata in numbers, and, lastly, on the fenestrated parts of

CHANGES OF THE SUPERFICIAL ENDOTHELIUM. 67

the omentum, where we have become acquainted with isolated pseudo-
stomata in the normal state.

(6.) Chronic Peritonitis, — Still more does the condition of limited
endothelial proliferation come into view in chronic inflammation.
If we tuberculise ^ a guinea-pig by the well-kno-svn method of injecting
material of an indurated lymphatic gland into the abdominal cavity,
the most instructive appearances result, as regards germination of the
endothelium, round and about the stomata, especially on the omentum,
on the parietal peritoneum, on the centrum tendineum, and on the
mesentery. The process is most intense on the omentum. Here we
find, as long as the tuberculous process has not yet advanced very
extensively, a very active germination of the endothelium on the
knots and cords frequently mentioned, and whose number and size
have decidedly increased. Under these circumstances the true
stomata can be made out in many cases much easier in fresh prepa-
rations and silver-treated objects than in the normal condition.
Their number, compared with that of the pseudo-stomata, is de-
cidedly smaller. We shall limit ourselves to the smaller lymphatic
knots, for on the larger the process of germination of the endo-
thelium has already advanced so far that it even comprises the endo-
thelium of the thin connective-tissue trabeculae of the neighbourhood,

I do not think it necessary for understanding the matter that I
should once more enumerate all those appearances which indicate
an active germination of the endotheliima. The germination of the
endothelium on the fenestrated portions in the form of small buds
consisting of young endothelium, is also a very active one ; here we
are able to perceive, on account of the great number of such buds,
the presence of a protoplasmic stalk emerging from the matrix, and
representing the centre of these little buds. This protoplasmic
central stalk corresponds completely to a pseudo-stoma. The
germination of young endothelial-looking cells is to be observed on
the pseudo-stomata themselves in great numbers. If we trace, in a
preparation mounted in serum, a thin cord usually projecting towards

» We refer the reader to the detailed account of artificial tuberculosis by Burdon-
Sanderson ; in the same place a detailed account is given of the macroscopic conditions of
the affected organs.

F 2

68 ANATOMY OF THE LYMPHATIC SYSTEM.

one side like a fold, we may convince ourselves, searching at the
edge of this cord, that the germinating polyhedral, or even conical
cells of the surface, are to be referred almost as abundantly to the
pseudo-stomata as to the endothelium of the general surface. At
least, I have often met with appearances, not only in these cords, but
also on the small knots, where, in a given profile \dew, whether
optical-profile or section-profile, a young endothelium cell of the
surface alternated with an endothelial-like bud of a pseudo-stoma.
This distinction in an optical-profile view, such as on a fold, is some-
times combined with great difficulties. I myself considered all these
young endothelial cells of the surface for a long time simply as the
surface endothelium, until, by the frequency of pseudo-stomata on the
lymphatic knots of the rabbit's omentum, and by the discovery that
numerous young cells of the surface, quite resembling endothelial
cells, stand in direct connection with the pseudo-stomata, I became
aware of the inaccuracy of that view. I submitted, therefore, the
young endothelium of the surface of these knots and cords to a subse-
quent exact examination. I have accordingly studied this relation
especially, first upon sections through the large knots and cords of the
pleura of the cat, through the knots and cords of the tuberculous
omentum of the guinea-pig, and have so discovered that, in the first
place, the distribution of pseudo-stomata upon tliese lymphatic knots
is a very extensive one, by far more extensive than I was at first
inclined to accept, and secondly, that a great number of the young
endothelial-looking cells are in continuity with the pseudo-stomata,
that is, with the protoplasmic processes which usually represent the
pseudo-stoma. Once acquainted with the fact itself, I came speedily
into a position to confirm, under all conditions, the fact previously
mentioned, that the proliferation affects not only the endothelium
which surrounds a pseudo-stoma, but that the pseudo-stoma itself
takes part in it. It is clear that there is no necessity to make a
distinction between those young cells which originate from the super-
ficial endotheliuni surrounding a pseudo-stoma, and those of the
latter themselves, since there exists no morphological difference ;
they are quite alike in their appearance, nucleus, form, and size ;

CHANGES OF THE SUPERFICIAL ENDOTHELIUM. 69

they are both situated on the surface of the membrane, and one can
properly speak only of young endothelium.

As has been already indicated, the proliferation of the endothelium
surrounding a true stoma is an active one. Not only do these endo-
thelial cells enlarge, become distinctly granular, and present nuclei
in the act of division, not only do these cells germinate and produce
lymphoid cells, but this change gradually spreads out on the one
hand over the endothelial cells of the surface which are in the
neighbourhood, as well as over those of the vertical lymph-canals, and
further over those of the lymphatic capillaries into which these lymph-
canals open. If we search the abdominal surface of a diaphragm
furnished with abundant knots of tubercle, we shall recognise the
most various appearances of development as regards the proliferation
of the endothelium of the stomata. As the youngest stages, those
are most undoubtedly to be taken where the stoma is surrounded
by a projecting zone of young endothelial cells at both ends, that is
to say, not only at the entrance into the vertical canal, but also at
the exit of the latter into the straight lymphatic capillary.

Besides these, we find other places where this zone has become
already several cells high ; this has then the appearance of a short
cone. Other stages are these : the cone of cells is longer, and at the
same time somewhat thinner and solid ; further, broad, long cones,
which, although the stoma is collapsed, still show a central cavity ;
and, finally, where only a large and broad patch is to be seen, formed
of young endothelial cells. In the latter, the diagnosis that we have
to do with a germination of endothelium round a stoma is generally
not easy. Sometimes it is rendered easy by the following circum-
stances : first, one finds an indication of the opening, close round
which the germination-process has become most intense, for the
smallest cells are found there ; secondly, if the opening itself be not
visible, we can still recognise the spot where the stoma is to be looked
for, from the presence of an amorphous central fibrinous plug very
darkly coloured in silver. Close to this, the smallest elements lie ;
finally, a thick cord of fibrine, which, becoming gradually thinner, is
seen to dip into the point around which the smallest elements lie,
thus indicating the direction and the place of the current of absorp-

70 ANATOI^IY OF THE LYMPHATIC SYSTEM.

tion. When all these conditions are absent, we may perhaps, as long
as the growth has not reached too great an intensity, be able from its
distribution and position to conclude that we have to do with a
germination around the stomata. We shall, however, not undertake
to make such a diagnosis where we find a large patch of germinating
endothelium raised considerably over the surface, and covering nearly
a whole field under the microscope. On a preparation which presents
the appearances previously described there are to be seen many
lymphatic vessels of the peritoneal surface of the centrum tendineum
more or less filled with young cells, and widely distended. In a
vessel of this kind, provided it is only partly filled with cells, we may
recognise some of the latter as being products of endothelial cells on
account of their size, nucleus, and granulation. At the same time
it can be made out, in one place or another, that a growth of the
endothelium of a stoma is going on into the lumen of the lymphatic
capillary in the form of a cone of young cells projecting free into its
lumen, whereas the endothelial cells which represent the wall of the
lymphatic are seen to be enlarged, distinctly granular, and their nuclei
in the act of division. There cannot be the least doubt that (1) the
changes and the growth of the endothelium round the stomata
spread over the endothelium of that portion of the lymphatic vessel
to which the stoma corresponds, and (2) that the young cells which
result from the growth of the endothelium of the stoma fall partly
into the corresponding lymphatic vessel, and partly into the abdo-
minal cavity.

I may now briefly describe the germination of the endothelium
round the true stomata of the omentum of the guinea-pig. We have
previously mentioned that those stomata occur abundantly on the
lymphatic vessels of the omentum, and it may be simply stated in
this place that the germination of their endothelium in animals
which have become tuberculised from the abdominal cavity pro-
ceeds in the same way as in the centrum tendineum. I refer to Figs.
42 and 45, where undoubtedly the fact comes out that the young
cells become detached into the lymphatic vessels. In order to become
acquainted with these conditions, it is necessary not to confine one's self
to parts far advanced in the morbid process, because on them the

CHANGES OF THE SUPERFICIAL ENDOTHELIUM. 71

diagnosis is rendered more difficult by the abundance of new growth,
and by the lymphatics being filled with young cells. The same
occurs as regards the germination of the endothelium round the
stomata when the guin^a-pigs are suffering from chronic inflamma-
tion of the peritoneum, whether this be the result of the introduction
of solid bodies (pieces of gutta-percha, according to Cohnheim and
Froenkel), or of the injection of pysemic fluids and consequent chronic
pyaemia (see Dr. Sanderson's Report, 1872) into the abdominal
cavity.

A fact worth noticing is, that guinea-pigs in which the tuberculi-
zation was induced by subcutaneous injection, or by direct injection
into the blood-vessels, exhibit a marked difference, viz. whereas in
those cases in which the tuberculization has been induced by the
peritoneum, and in which, the peritoneum being more advanced in
the tubercular process than the internal organs (as the lymphatic
glands, spleen, liver, and lungs), the germination of the endothelium
round the stomata or pseudo-stomata is the first and chief change to
be made out at a time when the tubercular process has made very
little progress, one^ does not find this to be the case when the tuber-
culization has been induced subcutaneously or by the vessels, for a
marked growth of the endothelium round the stomata does not take
place until the tuberculosis in general is very advanced.

The same conditions with which we have become acquainted in
the preceding as regards the omentum and centrum tendineum are
to be observed on the mesentery. In those cases, where the mesentery
exhibits moderately far-advanced tuberculous affection, the growth
of the endothelium around the true stomata occurs in a very striking
manner. Figs. 9 and 12 are taken from such a mesentery; here,
over the greatest part of the mesentery, there could be demonstrated
with great ease the stomata vera themselves, as well as the germina-
tion of their endothelium. Besides this, the germination of the
endothelium round the pseudo-stomata and the budding of young
cells from the pseudo-stomata themselves was quite distinct.

What had been said in reference to the change of the endothelium
surrounding true and pseudo-stomata in the guinea-pig, I have found
to be also true of the mesentery and 'omentum of monkeys which

72 ANATOMY OF THE LYMPHATIC SYSTEM.

died in consequence of tuberculosis. The liver, spleen, lungs, and
lymphatic glands contained very numerous tubercles, while the
omentum and the mesentery were disproportionately little affected,
and the centrum tendineum least of all. The same conditions were
found on the mesentery and omentum of cats, which presented the
macroscopic appearances of tuberculosis, viz. grey nodules dissemi-
nated over these membranes, especially over the mesentery. These
were cases of chronic inflammation of the mesentery and omentum
in consequence of a parasitic immigration from the alimentary
canal.

Similarly I have found the abnormal germination of the endo-
thelium round the stomata, especially round those of the omentum of
the rabbit whose omentum exhibited signs o^^hronic inflammation
in consequence of the presence of parasites in the lymphatics.

I have, however, also induced artificially the abnormal germina-
tion of the endothelium on true stomata and pseudo-stomata on the
omentum and centrum tendineum of the rabbit. If a few c.c. of
starch and oil or starch and water are injected int6 the abdominal
cavity of a well-nourished rabbit, and if the examination of the
omentum and centrum tendineum is undertaken not earlier than
four to eight weeks, we shall find that the alteration of the endo-
thelium is now limited to those places only \\ here we have become
acquainted with stomata and pseudo-stomata, the germination of the
endothelium being here very considerable.

Lastly, I must mention the germination of the endothelium
round the stomata of the mesentery and mesogastrium of a compara-
tively large number of female frogs during the winter months. In
these cases there appeared also on the septum of the cystema-lym-
phatica-magna abundant germination of the endothelium round the
stomata on the peritoneal surface, as well as a germination of the
endothelium spreading from these points. It may be remarked by
the way that the peritoneum of the ovaries and oviducts, and that in
the neighbourhood of the liver, were in these cases covered with more
or less numerous false membranes.

ALTERATION OF CELLULAR ELEMENTS OF MATRIX. 73

2. Alteration of the Cellular Elements of the Matrix.

f (a.) Acute Inftammation. — The object most suited for the study
of the cells of the lymph-canalicular system is afforded by the serous
membranes in the inflamed state, and, above all, the omentum minus
and mesentery in the condition of acute oedema. I have had the
opportunity of examining these membranes in a very large number of
guinea-pigs, rabbits^ and dogs, in a condition where they were swollen
by oedema to five timfes their normal thickness or more ; and here the
best results attende^the examination, both in the fresh condition
and after treatmen^^ith silver. In guinea-pigs, as well as in dogs,
I induced septicaemia by injecting into the abdominal cavity peritoneal
and pleural exudaUon fluids, which were obtained by certain pysemic
processes of an extremely acute process (compare the Report for the
I^jivy Council by Dr. Sanderson, 1872). In rabbits I have seen in
some cases oeJIma of the omentum coming on after the injection of
diluted ammonia into the abdominal cavity, and once after the in-
jection of starch.

After the first twelve to seventy-two hours, cedematous mesen-
teries presented on those places where the oedema was very consider-
able, the connective tissue bundles much separated from each other ;
the cells of the matrix very distinct and isolated. The latter were
recognisable in fresh preparations on account of their protoplasm
being granular : they were distinctly branched, and connected
with each other by processes of extraordinary length. Many appeared
in profile, and presented themselves as granular spindle-shaped cells.
On the spots where the oedema was not very considerable, the investi-
gation was even more instructive, for there the connective tissue
bundles of the matrix were not separated much from each other. They
were only transparent to an extraordinary degree, whereas the lymph-
canalicular system was recognisable as unusually dilated in its lacunae
and connecting canals. Here also there were met with appearances
which correspond to those represented by Schweigger-Seidel on trans-
verse vertical sections through the cornea, namely, the dilated inter-

74 ANATOMY OF THE LYMPHATIC SYSTEM.

fascicular spaces covered on one side only by a spindle-shaped granular
cell, that is by a flat-cell seen in profile ; in other places the latter
was seen to extend through the middle of the space. Besides these
there were also spaces whose cells were seen from*the surface pro-
vided with a number of processes.

In many of the spaces there were found migratory cells in addi-
tion to the branched cells ; and on one preparation I have observed
a migratory cell migrating freely out of such a lymph lacuna into a
neighbouring lymphatic vessel widely dilated and easily recognisable
by its endothelium. #

In mesenteries only a little swollen by oedepia the appearance of
the dilated lymph-canalicular system could b^fix^d very easily by
silver, by first pencilling the membrane carefulFHa one side, and«then
pouring the silver solution over this surface in situ ; after having'
been washed with water, the omentum was kept in situ until the
yellow-brown colour appeared. * • ^

The examination of the cedematous omentum proved of great
value for judging of the normal relations, especiallj^hose of HR
peri-lymphangial nodules and the fat-tissue. In the former, one may
very easily recognise the network of branched cells which form the
matrix of the nodule ; farther, that this stands in direct continuity
with the wall of a lymphatic vessel which exists on the border of the
nodule, and is widely dilated. The endo-lymphangial nodules are
also easily recognisable, their lymphatic vessel, viz. the lymphatic
vessel in which they lie, being dilated by the presence of cedematous
fluid.

We now turn to the question whether the lymph-canalicular
cells exhibit any alteration in acute inflammation, and if so, what
that change is.

I have had the opportunity on several occasions of examining the
centrum tendineum of rabbits after forty-eight hours, in which
peritonitis had been set up by the injection of several minims of
dilute ammonia into the al;dominal cavity ; and on whose centrum
tendineum the endothelium of the abdominal surface had quite
disappeared over tracts of various size. These were simply treated
js^ith silver. The lymph-canalicular system of the abdominal serosa

ALTERATION OF CELLULAR ELEMENTS OF MATRIX. 75

presented itself here with the greatest distinctness on those spots
where the endothelium had become detached. Here one had to do
with a centrum tendineum quasi-pencilled.

In many places the system of lymph-canaliculi of the peritoneal
serosa contained migratory cells ; on other places the branched cells
were also very distinct, besides that the outlines of the lymph-cana-
licular system were recognisable.

On places such as these one could perceive a striking difference
in the individual parts of the lymph-canalicular system in reference
to that of other places. First, it was clear that the lacunae were
larger, the canals were not branched and not so abundant, and
secondly, they appeared wider at many places. When one directed
one's attention to one of the widest of the canals, one could discover
on them one or even several small dilatations. As for the branched
cells of the lymph-canalicular system, it is to be noticed that they
are distinctly recognisable by their granular appearance, and by the
presence of tlieir nucleus. In many of them it was possible to trace
the protoplasm of the cell body, which lay in the lacuna, into the
canals ; in the wide canals which, as above described, were furnished
with lacunae-form bulgings, a swelling corresponding to this bulging
could also be demonstrated on the protoplasm or on the protoplasmic
processes. As for the nuclei, constrictions could be remarked upon
them, and some of the cells were furnished with two nuclei.

From this appearance one is able without doubt to draw the
conclusion that both the lymph-canalicular system and also its
contents, viz. the branched cells, have undergone changes : the
lacunae and canals, or the cell body and cell processes respectively,
were swollen, the canals or cell processes reduced in number, less
branched, and finally, the nuclei of the cells in the act of division.
An objection against these deductions can be made all the less as we
have to do h re w'th a change of the lymph-canalicular system and
of the cells whicr! . iiuot be attributed to any cause of the method
of preparation. H we pass from the places just described to
places where the endothelium of the sm^face is also removefl, and
where consequently colouration of the matrix has occurrei^ but
where the lymph canalicular system contains migratory cells, the

76 ANATOMY OF THE LYIVIPHATIC SYSTEM.

difference in the lymph-canalicular system is even more striking.
If the number of migratory cells is large, then one requires some
time before one is able to interpret such spots ; with a high magni-
fying power (obj. 8), however, and with somewhat more attention, one
can recognise the lacunae of the lymph-canalicular system as being
provided only with a few wide canals. Both in the former and in the
latter, we can recognise lymphoid corpuscles. We shall also be able
to discover here and there in such a dilated canal a smaller or larger
protoplasmic mass surrounding a nucleus, and forming a continuity
with a protoplasmic process, which can be traced into the correspond-
ing lacuna. This nucleated mass of protoplasm appears either as a
terminal or as a lateral bud of a cell process. In the same manner,
one can find one lymph-canalicular cell or another in which the
division of the nucleus has so far advanced that instead of the large
ovoid nucleus one comes upon two or three small nuclei, or that the
cells of the lymph-canalicular system have a swelling placed on one
side, so that the lacuna forms a projection : this swelling is still in
distinct connection with the rest of the cell. We have to do here,
therefore, with a change of the branched lymph-canalicular cells,
as was described of the cornea-corpuscles by Strieker and Norris,
and confirmed by EoUett. It is unnecessary for me to state that
an exudation both of the colourless and coloured corpuscles had taken
place from the blood-vessels, inasmuch as the vessels, especially
the small veins, were to be seen sheathed in compact cords of these ;
they could be followed even into the lymph-canalicular system.

The omentum of such rabbits as these proved to be not less in-
structive. On the cells of the lymph-canalicular system which pre-
sented themselves isolated in the tissue, one could demonstrate on
some places exactly the same change as was described on the centrum
tendineum, namely, the lacuna being larger, the number of the
canals fewer, the canals wider, the cells of the lymph^canalie\ilar
system presenting themselves as granular bodies wij^ pi ocesses, and
their nucleus here and there in the act of divi^on. In the neigh-
bourhood of the blood-vessels numerous migratory cells were met
with in the lymph-canalicular system. If/^e examine carefully the
lymphatic nodules, a distinct increase, of migratory cells could be

ALTERATION OF CELLULAR ELEMENTS OF MATRIX. 77

made out, especially of small finely-granular cells, which may be
taken in all probability as emigrated colourless blood corpuscles.

In lymphatic nodules which lie in the neighbourhood of a vessel,
and which possess either a scanty system of vessels or even none
whatever, and which, according to the description given in Section I.,
are to be regarded as being in an early stage of development, we are
likely to find a number of the lymph-canalicular cells which possess
on their body or on a process, buds of various sizes in such a number
as is not to be found in the uninflamed state ; the condition of their
nucleus is usually that of division, sometimes it is divided into two
or three small nuclei. From these appearances we may conclude
that here also an active inflammatory change had taken place.

Of the greatest importance as regards the changes of the branched
cells of the lymph-canalicular system of the mesentery and omentum
of the guinea-pig and dog was the examination of these membranes
in the oedematous condition during the second or third day of the
inflammation. If, after what I had seen on the centrum tendineura
and omentum of the rabbit, I had had still any doubt about the
active participation of the cells of the lymph-canalicular system in
the production of young cells, the study of the oedematous mesentery
of those animals just mentioned would have cleared up completely
every doubt.

(6.) Chronic Inflammation, — The most important changes in
branched cells of the lymph-canalicular system occur in chronic in-
flammation, which may arise from the most various causes. We will
commence with the centrum tendineum.

Centrum, Tendineum. — If we prepare a centrum tendineum of a
guinea-pig which has tubercular nodules on the centrum tendineum,
by pencilling its pleural surface and subseo^uent staining with silver
solution, we shall obtain a satisfactory understanding of the changes
of the cells of the lymph-canalicular system if the preparation is a
successfiil one, that is, if the system of lymphatic vessels and lymph
canals is plainly and beautifully to be seen. Besides places where
the lymphatic vessels and the system of lymph-canals, as well as the
cells of these, present no deviation from the normal condition, there
are spots to be met with where a distinct change has occurred, the

78 ANATOMY OF THE LYMPHATIC SYSTEM.

branched cells being decidedly more abundant, less branched, their
processes uncommonly broad. In some places the cells are so
closely situated by each other that they resemble an endothelium ;
in this case they are separated from each other by linear inter-
cellular substance. In Fig. 14 this change is very distinctly to
be seen.

This figure is taken from a silver- stained preparation of centrum
tendineum of a guinea-pig suffering from slight chronic inflamma-
tion. At h an important change of the branched lymph-canalicular
cells has taken place, the same being arranged like an endothe-
lium after having imdergone division. To the greatest extent this
change is to be found in the tubercular nodules which have their
seat in the serosa of the pleural surface. Fig. 22 is a silver prepara-
tion of a tuberculous diaphragm of a guinea-pig. The branched
Ijrmph-canalicular cells have all undergone the above-mentioned
change, being now arranged like an endothelium, with the difference,
however, that the cells are for the most part separated by thicker
tracts of intercellular material.

I may mention here that I have frequently succeeded in injecting
the lymph-canalicular system of the peritoneal serosa, as well as of
the tendons of the centrum tendineum, in some cases also that of the
mesentery and the peritoneum parietale, with colouring material ;
namely, in guinea-pigs which suffered from artificial tuberculosis, and
in rabbits in the peritoneal cavity of which starch and water had been
injected several weeks before. In these cases anilin and milk (an
alcoholic solution of anilin is mixed with so much water that the
anilin is precipitated in form of very fine granules), has been intro-
duced into the peritoneal cavity of the affected animals in a quantity
of about 4 c.c. ; after twenty-four to forty-eight hours the animals were
killed. On microscopical preparation of the centrum tendineum
there were many places to be found in which the inflammatory
changes of the branched lymph-canalicular cells were very slight, and
on which places not only the protoplasm of the branched cells and
that of the migratory cells, but also the lymph-canaliculi themselves,
contained more or less numerous anilin granules. To a very great
extent that was the case in a rabbit which suffered from chronic

ALTERATION OF CELLULAR ELEIVIENTS OF MATRIX. 79

peritonitis in consequence of starch-injection into tbe peritoneum,
many of the straight lymphatic capillaries of whose centrum tendineum
were plugged up by lymph-corpuscles.

As regards the peri- and endo-lymphangial nodules and cords of
the omentum, it is to be noticed that in chronic inflammation a very
active proliferation of the elements of those structures takes place.
The best example to ascertain this fact is to be found in the omentum
of guinea-pigs in different stages of the tuberculous process. Here
it can be shown that those structures increase not only in size, but,
what is of greater importance, also in number. Not only the branched
cells of the matrix, but also the lymphoid corpuscles that are in direct
or indirect connection with it, undergo very active proliferation. The
branched cells of the matrix become very much more abundant by
growing into the neighbouring tissue; they are first large in their
body as well as in their processes, but gradually become transformed
into a delicate reticulum. It is very common to find such branched
cells of the matrix whose body is provided with a number of small
constricted nuclei, and amongst the lymphoid corpuscles of the
matrix, multinuclear large elements are oftener to be met with than
in the normal condition.

By the out-growth of tlie branched cells of the matrix very often
secondary nodules and cords are formed, which in some instances pro-
ject over the general surface of the omentum like bridges, villi or
papillae ; they are, as has been stated previously, more or less covered
with germinating endothelium.

After having discovered the pseudo-stomata on the omentum, my
attention was directed to the question, whether in chronic inflamma-
tion the proliferation of the protoplasmic elements representing the
pseudo-stomata plays any part in the development of those smaller
and larger villous projections that are so often to be found on the
omentum as well as on other portions of the peritoneum.

It was soon ascertained that the pseudo-stomata do not only pro-
liferate in the way above stated, viz. budding lymphoid cells to the sur-
face, which resemble young endothelial elements, but also that they
grow out over the general surface as protoplasmic masses, which
carry with them the siurrounding zone of the endothelial cells. As

80 ANATOMY OF THE LYMPHATIC SYSTEM.

long as these villi are small, one recognises a pale granular matrix,
containing two or more nuclei, covered by a layer of endothelial
plates, somewhat thicker than common endothelial cells. In a
still later stage the matrix contains, besides the corpuscles just
mentioned, a substance which is first hyaline, but afterwards be-
comes finely striated connective tissue. In some omenta many villi
are to be found, which consist of a fully-developed connective tissue
matrix, with the corresponding lymph-canalicular system and their
branched cells. The question arises where this connective tissue
matrix originates. Kundrat asserts, that the connective tissue
matrix of those projections and villi of the omentum in chronic in-
flammation take their origin from endothelial elements, which, having
become elongated, become transformed into bundles of connective
tissue. I cannot confirm this statement, for I must on the contrary
mention that the bundles of connective tissue that make their
appearance in these villi are always first hyaline thin bands, which
gradu'lly increase in thickness, whereas the cells of the matrix never
show any transition into these bundles. I possess preparations of the
mesogastrium and the septum cysternse lymphaticae of a female frog,
which suffered from chronic peritonitis, where the development of
villi with a connective tissue matrix can be followed through all its
intermediate stages ; and here it is more likely^ that the connective
tissue bands are mere excretions, either of pseudo-stomata cells or,
as it is oftener the case, of the superficial endothelial cells.

I have come across inniunerable preparations of mesenteries of
guinea-pigs suffering from chronic peritonitis, where the connective
tissue bands of the matrix of the above-mentioned villi and projec-
tions must be taken as excretions of the cells ; in not one single instance
was there to be seen a transformation of cellular substance into these
bands. They always appear as thin hyaline bands of equal diameter,
which gradually increase in thickness, and in a later stage show a
fibrillar structure. I am, therefore, in agreement with Eollett, who
states that in the serous membranes connective-tissue bundles
develope from an inter-cellular substance. We come now to deal
with a point, the significance of which has been until the pre-
sent completely overlooked — we mean the significance of vacuolation

ALTERATION OF CELLULAR ELEMENTS OF MATRIX. 81

of cells in inflammation. We have had already the opportunity to
mention the occurrence and the changes of vacuolated cells in the
normal omentum. We have here only to add that in chronic inflam-
mation very numerous cells of the matrix of the serous membranes
become vacuolated, and change either into lymphatic vessels in the
way previously described, or they become elongated and join a capil-
lary blood-vessel. As regards the former case I had frequently occasion
to see that in some^of them a_formation of lymphoid corpuscles takes
place from the wall of the vesicle into its cavity. Further, I have
met with large multi-nucleated cells (myeloplaxes), in which there
was to be seen the transformation of the central portion into a
number of lymphoid corpuscles, that of the peripheral part into the
nucleated wall of a vesicle — endothelial vesicle.

I refer the reader to Figures 18, 20, 23, 25, 27, 31, 33, and 53.
The most interesting fact as regards the vacuolation of cells I
have observed in the cells of the pseudo-stomata in chronic inflam-
mation. It occurs, namely, that in one of these a vacuolation takes
place, and the vacuole opens on one side free on the surface through
the process that stretches to the surface between the endothelium,
whereas towards the opposite side it becomes connected with a
lymphatic capillary, so that we have then before us the case that a
lymphatic capillary opens freely on the surface of the membrane by
a vertical canal, the entrance opening of which represents a true
stoma. See Figures 27, 33a, 53, and 54.

In Fig. 54, mesogastrium of a common frog, an endo-lymphangial
growth of a branched network is to be noticed in such an isolated
vacuolated cell, from which it can be inferred that endo-lymphangial
nodules develop in lymphatics in their earliest stage.

3. The Blood- Vessels and Lywjphatic Vessels.

What has been said as regards the development of blood capil-
laries in the normal serous membranes is true also for chronic inflam-
mation, of course with greater extensity and intensity.

Finally, we have to notice the intensive growth of a branched
reticulum from the endothelial wall into the lumen of lymphatic

82 ANATOMY OF THE LYMPHATIC SYSTEM.

capillaries, viz. the formation of endo-lymphangial nodules and cords
in chronic inflammation, as it occurs in the omentum and pleura
mediastini of tuberculised guinea-pigs, in the mesentery of tuber-
culous monkeys, in the omentum of rabbits, some of the lymphatics
of which were plugged up by parasites (ova of cysticercus), and in
the mesentery of cats, some of the lymphatics of which contained
ova of nematodes.

BIBLIOQBAPHY,

Recklinghausen : On the Eesorption of Fat. Virchow's Archiv, vol. 36.

BecJcUnghausen : The Lymphatics and theit Eelation to the Connective Tissue. Berlin,

1862.
Schweigger-Seidd and Dogiel : On the Peritoneal Cavity in Frogs, and their Connection

with the Lymphatic System ; in * Arbeiten aus der physiolog. Anstalt zu Leipzig,' 1866.
Jjudmg and Schweigger-Seidel : On the Centrum Tendineum of the Diaphragm. Ibidem.
Schweigger-Seidel : On the Treatment of Animal Tissues with Nitrate of Silver, etc.

Ibidem.
Eollett : Article Cornea in Strieker's Handbook.
Schweigger-Seidel : On the Cornea, in * Arbeiten aus der physiolog. Anstalt zu Leipzig,'

1869.
Boll: On the Structure and Development of the Tissues, in Max Schultze's Archiv,

vol. vii., part 4.
Knauff: Centralblatt fiir medizin. Wissenschaften, August 1867.
Recklinghausen : Article Lymphatics, in Strieker's Handbook.

Flemming : On the Development of Fat-cells. Max Schultze's Archiv, vol. vii., part 1.
Toldt : On the Histology and Physiology of Fat-tissue. Sitzungsber. d. Wiener k. Aca-

demie d. Wissensch., vol. Ixii., part 4, 1870.
Lavdovsky : Centralblatt fiir medizin. Wissensch., 1872.
Afonassiew : Virchow's Archiv, vol. xliv.
Strieker : See Strieker's Handbook, chap, xxxviii.
Arnold : Virchow's Archiv, vol. liii.
Rindflcisch : Pathologische Histologie.

Ranvier: Corveil and Eanvier's Normal and Pathological Histology.
Kundrat : Medicin. Jahrbiicher in Vienna ; ed. by Strieker, vol. i., part 1.
Burden- Sanderson : Report of the medical officer of the Privy Council, 1867 and 1868.
Klebs : Virchow's Archiv, vol. xliv.
E. Klein : Quarterly Journal of Microscopical Science, January 1872.

/.lo^ (jw^ (n^A 0cH^ ^

EXPLANATION OF PLATES.

I have to offer my sincere thanks to the Government Grant Com-
mittee of the Royal Society for having furnished the means for the
execution of the following plates : —

PLATE I.

Fig. 1. Germinating Endothelium of tracts freely projecting over the
surface of the pleura mediastini of a healthy cat. Preparation stained
with nitrate of silver.

M. p. Hastnark, E. p. No. III. Obj. 7.

Fig. 2. Surface of a mesentery of frog, stained with nitrate of silver.
M. p. E. p. III. Obj. 5.

a. Common flat endothelial cells of the surface, amongst which six
couples of cells are to be found, which have stained deeply with
the reagent, and which consist of a granular protoplasm ; these
cells are not flat, but more or less polyhedral — germinating or
young endothelial cells. Between the cells of these couples
more or less distinct openings are to be seen — stomata vera,
which lead into a lymphatic space below ; they are exactly like
the stomata of the epidermis of plants.

Fig. 3. Silver-stained preparation of the septum cysternse lymphaticae-
magn89 of frog.
M. p. III. Obj. 6.

A. Peritoneal surface of that membrane.

B. The surface directed towards the cysterna shows amongst the
common flat endothelial cells, the size and shape of which are
obviously different on the two surfaces, openings of canals, by
which that septum is penetrated. The openings, viz. the
canals are lined with a special layer of polyhedral cells, which have
the character of young germinating endothelial cells.

G 2

84 EXPLANATION OF PLATES.

Fig. 4. Silver-stained preparation of slightly cedematous mesentery of
guinea-pig, suffering from chronic infective peritonitis.

M. p. IIL 5.

a. The endothelium of the general surface ; below the endothe-
lium close to the surface a large dilated lymphatic vessel c is
to be seen, through which passes an artery d and a nerve
trunk e (Invagination) ; the lymphatic vessel stands in free
communication with free surface, viz. the peritoneal cavity,
by a number of stomata vera, which are lined with young
endothelium.

FiQ. 5. Silver- stained preparation of the omentum majus of dog.

M. p. III. 8. (Tube drawn in.)

Shows amongst the flat endothelium of the surface small and
large groups of germinating endothelium, between which
numbers of small stomata are to be seen.

PLATE II.

Fig. 6. Silver-stained preparation of the omentum of rabbit.
M. p. II. 7. (Tube half drawn out.)

a. Common flat endothelium of the general surface.

b. A tract projecting somewhat over the surface, covered with

an endothelium, the cells of which are of smaller size;
amongst these smaller or larger groups of small cells are
to be seen, which are not flat but polyhedral, which
consist of a distinctly granular protoplasm, and which are
arranged more or less regularly round stomata.

Fig. 7. Silver preparation of centrum tendineum of rabbit. Peritoneal
surface.

M.p. m. 7.

a. Common flat endothelium of the peritoneal serosa, which

covers the tendon-bundles.

b. Smaller endothelium, which covers straight lymphatic vessels

which lie between the tendon-bundles.

c. Stomata vera, some widely open, some collapsed, which lead

to those straight lymphatic vessels j these stomata are lined

EXPLANATION OF PLATES. 85

with endothelial cells, wHich, as in Fig. 6, are of a germina-
ting character.
d. Represent sinuses of those straight lymphatic vessels.

Fig. 8. Peritoneal surface of a silver preparation of a centrum tendineum
of a guinea-pig which suffered from chronic infect, peritonitis (artificial
tuberculosis.)

M. p. III. 7.

a — a and a, — a^ Indicate the straight lymphatic vessels between
the tendon bundles, as in Fig. 7.

h. Represent stomata which are plugged up by a substance which
has become darkly stained by the reagent (fibrinous plug) ;
the endothelium which surrounds the stomata is in a state
of intensive germination, forming buds and villi, freely pro-
jecting over the surface ; on the latter ones cells are seen
to be in the state of detaching themselves by constriction
(lymphoid cells).

Fig. 9. Silver preparation of the mesentery of guinea-pig in the same
morbid condition as that of Fig. 8.

M. p. III. 7.

a. Common endothelium of the surface.

d. The upper wall of a lymphatic sinus, which has become

freely exposed to the surface ; the endothelial marking of

that wall is clearly to be seen.
h. Stomata, which lead obliquely into the cavity of the lymphatic

sinus.
c. Germinating endothelium round these stomata, forming buds,

which project over the free surface.

PLATE III.

Fig. 10. Silver preparation of the omentum of a guinea-pig suffering
from chronic infective inflammation.

M. p. III. 7.

a. The trabeculsB of the fenestrated portion of the omentum, with

its endothelial covering.
h. Freely-projecting villi, the top of which is covered with c

germinating endothelium.

86 EXPLANATION OF PLATES.

Fig. 11. Silver preparation of the peritoneal surface of the centmm ten-
din eum of the diaphragm of rabbit, as in Fig. 7.
M. p. III. 6.

t. Endothelium which covers the serosa over the tendon-
bundles.
8. Stomata over the straight lymphatic vessels, some of them
open, some collapsed; the surrounding endothelium of a
germinating character.

Fig. 12. Silver preparation from the same mesentery as Fig. 9.
M. p. in. 5.

a. Stomata, the surrounding endothelium c of vrhich, as well as

of lymphatic sinuses 6, is intensively germinating.
h. The endothelium of lymphatic sinuses, the stomata of which
are widely open, so that the endothelium of their bottom
can be seen.
d. Common flat endothelium of the general surface.

Fig. 13. Silver preparation of the fenestrated portion of omentum of
guinea-pig suffering from chronic peritonitis.
M. p. III. 7.

a. Thin trabeculee covered with common flat endothelium.

h. Abundant germination of endothelium, springing off from the

surface of a larger trabecula c, and continuing on the

smaller secondary trabeculas. ;

PLATE IV.

Fig. 14. Silver preparation of the pencilled pleural surface of the centrum
tendineum of a guinea-pig suffering from slight chronic inflammation
of the serous membranes.
M. p. III. 7.

a. The endothelium of lymphatic-capillaries,
c. The lymph-canalicular system of the pleural- serosa ; the
branched cells, which occupy that 1. c. system, are in some
places distinctly to be seen.
At ft, these cells (respectively the lacunae of the 1. c. system)

have become more numerous by division.
At tZ, the continuation of the endothelium of the lymphatic ca-
pillaries with the cells of the 1. c. system is clearly to be seen.

EXPLANATION OF PLATES. 87

Fia. 15. From a preparation similar to that shown in Fig. 14 ; there was
a little more inflammation in the serous membranes.
M. p. ni. 7. (Tube half drawn out).

a. Endothelium of lymphatic capillaries.
h. The same somewhat altered.

c. Continuation between it and the cells of the lymph-canali-
cular system.

Fig. 16. A preparation similar to that shown in Fig. 14).
M. p. III. 7.

a, hf and c as in Fig. 14.

Fig. 17. Silver preparation of the pencilled pleural-surface of tho
normal centrum tendineum of rabbit.
M. p. III. 7.

I. Endothelium of lymphatic capillaries.

c. Lymph- canalicular system of the serosa.

8. The same, in which only the nuclei of the branched cells are

to be seen.
At t, continuation of the endothelium of the lymphatic vessels
with the lymph-canalicular system, or, properly speaking, with
their branched cells.

Fig. 18. From a silver- stained preparation of the mesogastrium of a frog,
representing a node projecting freely from the surface of a large
trabecula t.
M. p. III. 8.

a. Cihated endothelium which covers the surface of that node.
h. A vacuolated cell of the matrix of the node ; fine ciliaa are
projecting into the vacuole.

c. A vacuolated cell, the wall of which has already differentiated

in individual endothelial plates.

d. A vacaolated cell filled with nucleated young cells.

Fig. 19. From a silver preparation of a pencilled mesentery of ape suf-
fering from chronic peritonitis.
M. p. III. 8.
M. Connective-tissue matrix not represented.

a. The lymph-canalicular system, with its corresponding branched

cells.
h. Large migratory cells which lie in that 1. c. system beside
the branched cells.

88 EXPLANATION OF PLATES.

Fig. 20. From the lumbar portion of the peritoneum parietale of a rabbit
suffering from chronic peritonitis.

M. p. III. 8.

a. Enlarged branched cells of the ground-substance, provided
with a vacuole c, in which lie fat globules dj and young
(lymph) cells e.

I. The nuclei of the branched cells.

Fig. 21. From the mesentery of ape suffering from chronic peritonitis.

M. p. in. 8.

a. Enlarged branched cells of the ground-substance, filled with
fat globules h. The ground-substance 31 is not represented.

PLATE V.

Fig. 22. From the centrum tendineum of a guinea-pig suffering from arti-
ficial tuberculosis of the serous membranes (including the centrum
tendineum). The preparation had been pencilled from the pleural
surface and stained with nitrate of silver.
M. p. III. 7. (Tube not drawn out.)

Showing a patch in pleural serosa (ycung tubercle), which

owes its origin to an intensive proliferation of the branched

cells of the lymph-canalicular system.

At A. the connection of that patch with the lymphatic capillaries,

which bend in another layer than that represented in the

figure.

Fig. 23. From a silver-stained omentum, of a guinea-pig suffering from
chronic infective peritonitis.

M. p. III. 7.

F. Ground-substance of the fenestrated portion of the omentum, over
the surface of which a villus is projecting freely : A its radix,
by which it is connected with the membrane ; B its summit.
a. Common flat endothelium of the general surface of the villus.
h. Germinating endothelium.

c. Vacuolated cells in the ground-substance of the villus.

d. The same, containing young cells.

EXPLANATION OF PLATES. 89

Fig. 24. From a silver-stained preparation of normal omentum of
rabbit, representing a vascular patch, the ground- substance of which
F has remained unstained by the silver, whereas the very rich net-
work of the branched cells e have become very distinct.
M. p. III. 7.

a. Capillary blood-vessels.

h. Growing capillaries ; the growth takes place by hollowing

of the branched cells which are in connection with the wall of

the capillary vessels d.
c. Vacuolation in the branched cells, as the first step of becoming

hollowed out and afterwards to become continuous with the

lumen of a capillary vessel.

Fig. 25. From a silver-stained preparation of the mesentery of a monkey
suffering from chronic peritonitis.

M. p. II. 7.

F. Ground- substance not represented.

a. Different stages of vacuolation of apparently not branched
cells of the matrix. Such vacuolated cells becoming united
from tubes, the wall of which becomes differentiated in en-
dothelial plates a.

h. Small, c larger nucleated elements of the matrix.

Fig. 26. From a silver- stained preparation of the omentum of a guinea-
pig, as in Fig. 23, representing a villus which projects freely over the
surface. Optical longitudinal section.

M. p. III. 10 a I'immersion.

a. Ground substance of the villus, consisting of finely fibrillated
connective tissue, containing large granular spindle-shaped
looking cells, which in many places, c, are projecting between
the enlarged and germinating endothelium h and c freely
up to the surface — ^Pseudo-stomata ; from them also young
cells grow up, d.

Fig. 27. From a silver- stained preparation of the centrum tendineum
of a guinea-pig as in Fig. 22. Pleural surface.

M. p. in. 5.

a. Common endothelium of the general surface; below it a
vacuolated cell, which forms a stoma verum with the surface.

..^.^'IS*,^

90 EXPLANATION OF PLATES.

Fig. 28. From the same mesentery of monkey as Fig. 25.

M. p. III. 8.

F. Ground- substance not represented.

a. Large, coarsely-granular nucleated elements, wHcli contain
a various number of spherical or irregular globules of
different sizes, which are homogeneous in structure, and are
somewhat similar to fat globules, although they refract light
differently.

PLATE VI.

Fig. 29. A preparation similar to that shown in Fig. 24.
A vascularised patch of the normal omentum of rabbit.
M. p. III. 8.

a. Capillary blood-vessels.

At 6, their connection with the branched cells of the ground-
substance ; these places represent at the same time where
young capillaries are formed.

c. The branched cells of the matrix.

d. Similar ones of the ground-substance of the neighbourhood of

the patch.

Fig. 30. From a pencilled silver-stained normal omentum of rabbit.
M. p. IV. 8.

Representing a young patch, the ground-substance of which M is un-
stained.

a. The lymph-canalicular system, with the correspondingbranched

nucleated cells.
h. Migratory cells, either perfectly detached from those branched

cells or in a state of growing from them.
c. Vacuolated element, which is a mere knob of a branched cell.
In d the vacuolation has gone so far that a vesicle is formed,

the wall of which has differentiated in endothelial plates.

(Development of a lymphatic vessel.)
At F division of the branched cells.

Fig. 31. From a silver-stained mesentery of a monkey suffering from
chronic infective peritonitis. Representing a sprout freely projecting
over the surface.

EXPLANATION OF PLATES. 91

a. Pedrinculus of the sprout.

h. Summit of it. The endothelium which covers this sprout,
especially that of the summit, is of a germinating character.

c. A vacuolated cell of the matrix.

d. Young cells of the matrix.

Fig. 32. From a pencilled portion of the mesentery of the same monkey
as Fig. 31.

M. p. lY. 8.

a. Migratory cells not yet perfectly detached from the nucleated
branched cells, which lie in the lymph-canalicular system h.

c. The nuclei of those branched cells. There are numbers of
small elements and particles in the lymph-canalicular system
to be seen, which owe their origin probably to the nuclei of
the branched cells as well as to the migratory cells.

F. Matrix unstained.

Fig. 33. From the silver-stained mesentery of the same monkey.

M. p. II. 7.

In A a vacuolated cell is to be seen which lies below the endothelium
of the surface : its wall has already become differentiated into endo-
thelial plates a, and at the same time its cavity has opened, so as
to communicate with the free surface of the mesentery by a stoma
verum h.

In B a sprout is to be seen, which projects between the endothelium
of the general surface a freely outwards : it stands in communication
with the tissue below the endothelium of the surface by means of a
protoplasmic pedunculus c ; its body is formed by a vacuolated cell
6, which in fact represents only the cell of a pseudo- stoma.

Fig. 34. From a pencilled silver- stained preparation of normal omentum
of rabbit.
M. p. III. 7.

a. Lymphatic-capillary vessel, showing the endothehal markings

of its walls.
h. An artery.

c. Capillary blood-vessels ; and d, branched cells of a surrounding
patch.

e. A place where the endothelium of the lymphatic vessel

becomes continuous with those branched cells.

f. Migratory cells.

92 EXPLANATION OF PLATES.

PLATE yil.

FiQ. 35. Silver- stained preparation of a pencilled centrum tendineum of
normal rabbit.
M. p. III. 2.

a. Large lymphatic vessels, with valve.

h. Lymphatic capillaries.

c. Lymphatic capillaries, which dip down between tendons.

Fig. 36. Preparation of centrum tendineum (normal) of rabbit, the dia-
phragm of which had been injected with nitrate of silver by Ludwig's
experiment, the ground- substance nearly unstained.

M. p. III. 5.

a. Large lymphatics of the pleural side.

b. Lymphatic capillaries which run between the tendon-bundles,

straight lymphatic capillaries.

Fig. 37. Natural injection of the lymphatics of the centrum tendineum
of rabbit with five per cent. Berlin-blue solution ; seen from the abdo-
minal side.

M. p. ni. 4.

a. Large lymphatics of the pleural side.
h. Straight lymphatic capillaries.

Fig. 39. From a pencilled silver preparation of the omentum of rabbit.

M. p. IIL 5.

a. Lymphatic vessels showing their endothelium.
h. Valyes of the lymphatics.

c. A large trabecula containing large blood-vessels (not repre-

sented).

d. Ground-substance (not represented).

PLATE VIII.

Fig. 38. Silver preparation of a centrum tendineum (pencilled from the
abdominal surface) of rabbit.
M. p. HI. 4.
Showing lymphatic capillaries of the peritoneal surface.

EXPLANATION OF PLATES. 93

Fig. 40. Silver preparation of a pencilled omentum of rabbit.

M. p. II. 7.

a, A vein filled with blood.
h. Capillary blood-vessel.

c. Lymphatic capillary vessels showing their endothelium ; the

blood-vessels are invaginated in these lymphatics.

d. Branches of the lymphatic vessel, which are in communication

with the lymph-canalicular system of the ground-substance e.
f. The lymph-canalicular system of a lymphatic patch, which
system is also in communication with the lymphatic vessel
at^.

Fig. 41. Fresh preparation of an cedematous omentum of a guinea-pig
suffering from chronic peritonitis.
M. p. III. 7.

a. A lymphatic vessel.

h. A portion of a peri-lymphangial nodule.

c. The endothelial wall of the lymphatic vessel seen in profile.

d. Blood capillaries of the nodule.

e. Lymph corpuscles. It is seen that the reticulum of nucleated

branched cells which forms the stroma of that nodule is
in continuation with the endothelial wall of the lymphatic
vessel.

Fig. 42. Silver preparation of omentum of guinea-pig suffering from
chronic peritonitis.

M. p. III. 7

The figure represents a large trabecula, which projects over the general
surface like a fringe.

a. A venous blood-vessel, its endothelium distinctly to be seen.

d. Accumulation of lymph- corpuscles, probably in lymphatic
vessels which accompany the vein.

h. An open stoma verura, surrounded by germinating endo-
thelium ; the stoma leads into a lymphatic space, which,
as far as it can be traced, shows its endothelial wall in
profile ; the lymphatic space is, except a few large lymph-
corpuscles, filled with clear fluid ; it is probable that the
lymph-corpuscles which project to the right and left side
of this lymphatic space lie in the continuation of it.

c. A sprout of germinating endothelium, round a stoma, which

94 EXPLANATION OF PLATES.

is plugged up by a darkly-stained substance (fibrin) ; it is
probable that also here this stoma leads to a lymphatic
vessel, which is filled with lymph- corpuscles.

/. Endothehum of the general surface.

e. Enlarged endothelium seen in profile at the edge of the
fringe.

Fig. 43. Fresh preparation of the same omentum as Fig. 4] .

M. p. III. 7.

a. A venous capillary vessel, filled with blood.
h. An invaginating lymphatic vessel.

c. Outer endothelial wall.

e. Inner (covering the blood-vessel) endothelial wall of the
lymphatic vessel.

d. Endo-lymphangial reticulum, which is continuous with the

endothelial wall of the lymphatic vessel. In this way endo-
lymphangial nodules and tracts are formed.

Fig. 44. From an cedematous omentum of a monkey suffering from
chronic peritonitis.

M. p. ni. 7.

a. An artery

h. A vein filled with blood (not fully represented).

c. A lymphatic vessel in which both the veins and the artery are

invaginated. Many of the endothelial cells of the wall of
the lymphatic vessel are seen to be enlarged.

d. Lymph-corpuscles which nearly have plugged up the lym-

phatic vessel.

PLATE IX.

Fig. 45. A silver preparation of the centrum tendineum of a guinea-pig,
suffering from chronic infective inflammation of the serous membranes.

M. p. III. 5.
Surface view of a portion of the peritoneal surface.

a. The upper endothelial wall of a sacciform dilatation of a super-
ficial straight lymphatic capillary vessel ; the [endothehum
of the general surface of the serosa is somehow removed.
h. Large open stomata vera.

EXPLANATION OF PLATES. 95

c. Germinating endothelium; at 5 a sprout of germinating endo-

thelium c is growing into the cavity of the lymphatic
vessel.

d. Common endothelium of the general surface.

Fig. 46. From an omentum of a guinea-pig suffering from chronic infec-
tive peritonitis. The omentum had been kept in cpirit and stained with
carmine.

M. p. II. 8.

a. A capillary vein.

h. Matrix of the fenestrated portion, containing numerous nu-
cleated cells. About the intimate relation of these nucleated
cells nothing can be made out distinctly.

Fia. 47. From the fenestrated portion of an injected omentum of guinea-
pig suffering from slight chronic infective peritonitis.

M. p. III. 5.
To show the distribution of blood-vessels in the lymphatic nodules.
a. Arteries.
V. Veins.

c. Capillary vessels.

d. Matrix of the fenestrated portion of the membrane.

e. Germinating endothelium covering a freely-projecting nodule.
/. Holes of the membrane.

Fig. 48. From the same, omentum as Fig. 47.
M. p. III. 5.
A freely-projecting large lymphatic nodule.

ft. Arteries.
6. Veins.

c. Capillary vessels.

d. Matrix.

e. Holes of the latter.

96 EXPLANATION OF PLATES.

PLATE X.

Fig. 49. From a pencilled silver- stained mesentery of frog; slight
chronic peritonitis.

M. p. III. 7.

a. Small blood-vessels, showing distinctly their endothelinm.

i. Lymphatic vessels, showing their endothelial wall; the
lumen of the vessels contains numerous colourless cor-
puscles c.

At (Z,and towards the left side of the preparation, a lymphatic vessel
is seen to be in continuity with the lymph- canalicular system
of the ground-substance, in which system also numerous
colourless corpuscles are to be found. To the left-hand side
of the preparation, where* the drawing is taken from, an
abundant emigration of colourless blood-corpuscles can be
seen to have taken place from the appearance in which the
blood-vessels and the surrounding tissue is found : these
colourless corpuscles are seen to pass through the lymph-
canalicular system into the lymphatic vessels towards the
right-hand side.

/. Ground- substance, not represented.

Fig. 50. From the same omentum as Fig. 43.

M. p. IIL 7.

a. Vein.
h. Artery.

c. Capillaries.

d. A lymphatic vessel, in which this whole system of blood-

vessels is invaginated.

e. Reticulum of nucleated branched cells growing from the en-

dothelial wall of the lymphatic vessel into the cavity of the
vessel.

Fig. 61. From a fresh preparation of oedematous pleura mediastini of
cat, representing a lymphatic cord in profile.

M. p. IIL 7.

a. Germinating endothelium of the surface of the cords.
h. Nucleated buds which are direct offsprings of the reticulum of
the matrix. There are seen numbers of such protoplasmic

EXPLANATION OF PLATES. 97

processes which project from the reticulated-branched cells
of the matrix up to the free surface between the endothelium
of the latter (Pseudo-stomata).

c. Branched cells of the reticulum, which form, so to speak, the

matrix of the chord.

d. Lymph-corpuscles occupying the meshes of the reticulum.

Fig. 52. From a fresh mesogastrium of rana temporaria.
M. p. III. 8.

A. A knob freely projecting over the surface of the membrane, con-
sisting of a clear matrix, in which some granular cellular ele-
ments are to be seen ; the knob is covered with an endothelium
c, which is not so flat as the endothelium in general.
a. The root of the knob. With the endothelial covering of this
knob there are in direct continuity four cells, which spring
from a common protoplasmic peduncle by means of long
thin protoplasmic filaments.
The cells h have shown for a considerable length of time active

amoeboid movements.
The cell d was also in continuity with the endothelium a of a fold
of the membrane.
There cannot be any doubt that these cells are endothehal
cells, and consequently that they are in a state where they
are already amoeboid cells (lymph corpuscles), although they
have not yet perfectly separated from the endothelial
matrix.

Fig. 53. From a fresh mesogastrium of rana temporaria.
M. p. III. 7.

1, 2, and 3. Vesicles of the tissues, the interior of which is lined
with cili^ ; the wall consists of a nucleated protoplasm ;
each of these vesicles develops from one cell of the tissue
by vacuolation ; in 3, three granular cells are to be seen
two of which are provided with cilia3. These could only
have been brought into the cavity of the vesicles from
outside, because some of the germinating endothelial cells of
the surface are provided with cilias.

In 4 the summit of such a vesicle is adjusted, which shows
a stoma ; so that the interior of the vesicle communicates
with the free surface of the mesogastrium. This stoma is
H

98 EXPLANATION OF PLATES.

also lined with ciliae. It is very probable that such a
ciliated vesicle opens towards the free surface in the course
of its development.

Fig. 54. From the same preparation as Fig. 53.
M. p. III. 8.
A vesicle which has already lost its ciliary lining. The protoplasmic
wall of the vesicle grows towards the cavity in form of a protoplasmic
reticulum like that in Fig. 50. In that way gradually a nodule may
result which possesses the structure of a lymph-follicle— endo-lym-
phangial nodule.

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Sixth Edition. With 146 Engravings on Wood. Small 8vo. 125. Gd.

ON THE CONNECTION OF BRIGHT'S DISEASE WITH CHANGES IN THE
VASCULAR SYSTEM:

WITH ILLUSTRATIONS FROM THE SPHYGMOGRAPH.

By A. L. GALABIN, M.A., M„D., Fellow of Trinity College, Cambridge.
Demy Svo. Is. 6^.

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