MINUTE ANATOMY OF THE OMENTUM.
235
divided muscle cells and the nuclei bounding the fibrous
tissue adventitia.
In fig. 2, which represents in transverse section part of
the gland tubule forming one of the ceruminous glands of the
human auditory meatus, the structures described in the two
preceding specimens cannot fail to be recognised. The
appearance of the epithelial lining, however, is peculiar.
Between the free borders of the cells composing it and their
nuclei is a deposit of what appears under the microscope as
brown or yellow granular matter, giving the appearance of
a definite zone internal to the regularly placed nuclei. The
muscular coat is not so well marked as in the last specimen,
but with its darkly stained nuclei still forms a distinct layer
inside the " membrana propria," in this instance well defined.
In a less marked degree similar conditions, with regard to
the position and appearance of the muscular coat, may be
seen in the large sweat-glands of the axilla.
To sum up, then : it would seem that in the sweat-glands
of some animals, as well as in those of man, possessing a
muscular coat, the epithelium, lining the gland, is seated on
the muscular coat without the perceptible intervention of any
membrane; again, that the muscular coat is situated internal
to the membrana propria lying in the inner portion of its
substance ; a priori, it may perhaps be argue'd against the
above, that Histology up till the present time has furnished
no parallel where muscular tissue and epithelium are directly
in contact. Whilst fully admitting the weight of the objection, I would urge that the microscopic appearances detailed
in this paper admit of no other interpretation.
The observations were conducted under the direction of
Dr. Klein.
CONTIMBUTIONS to the MINUTE ANATOMY of the OMENTUTVT.
By Dr. E. K M I N , F.R.S.
(With Plate XVIII).
I PIIOPOSE to describe in this short memoir (1) certain
bud-like structures occurring on the fenestrated portion of
the omentum of rat and dog; (2) the way in which the
fenestrse are produced in the omentum of rodents and carnivorous animals ; and (3) some points referring to the new
formation of blood-vessels in the omentum of guinea-pig.
Before proceeding to detail my observations, I wish to
say a few words as regards the methods used in this in-
236
DR. E. KLEIN.
vestigation. The omen turn is carefully removed from the
freshly killed animal; in the case of mouse, rat, guinea-pig,
and rabbit, the omentum, together with stomach, pancreas,
and spleen, is removed from the animal under fluid ; in the
case of dog or cat a portion of the omentum can be simply
cut off and placed in the proper fluid. This is in all cases a
2 per cent, solution of bichromate of potash. The omentum is
kept in this fluid for from one to two weeks ; small portions of
it are then washed thoroughly in water, and stained in
hsematoxylin, or better first in carmine and then in hsematoxylin. 1 shall have occasion hereafter to point out the advantage of this double staining. The stained preparations
are finally mounted in glycerine.
1. Examining carefully the fenestrated portions of the
omentum of a full-grown rat, larger or smaller bud-like projections are found on the bundles of connective tissue forming
the trabeculse of the fenestree. These buds are covered
with the same endothelium as that lining the trabeculae (see
figs, i—v) ; they are not as a rule in connection with the
connective-tissue bundles, except in later stages, where the
content of the buds becomes itself fibrillar tissue. As regards
the size, they vary very much. Those represented in figs.
i—v are all relatively small, but there are others twice, thrice,
and even more times as large as that represented in fig. iv
or fig. v. The smallest buds are those in figs, i and i i ;
they are either pear-shaped, and by their stalk attached to
the trabeculse, or they are conical with very broad basis, by
means of which it rests on the connective-tissue bundle. An
interesting form is presented by some of them being of more
irregular form and of a plate-like extension, with one or
move spindle-shaped thickenings (see fig. iii). In the young
stages the buds are composed, besides the covering endothelium, of a substance which is very indistinctly granular,
and which stains, somewhat like the connective-tissuebundles,
conspicuously in carmine ; the endothelium, on the other
hand,has a greater affinity to hEEinatoxylin, and hence the usefulness of staining the preparation in carmine and in hsematoxylin. But while the bud-like structures have a greater
affinity to carmine than to hsematoxylin they are not altogether indifferent to the latter; this is especially the case
with the larger examples that we find in the more dense part
of the fenestrated portion, for these assume a peculiar purple
colour which makes them very conspicuous among the rest
of the tissue, and under these circumstances are very easily
distinguished. Not all buds contain, or rather are composed
MINUTE ANATOMY OF THE OMEXTUM.
237
of, that indistinctly granular substance, for in some we may
distinguish under a high power very delicate fibrils, while
in still others the whole mass seems to be composed of a more
or less distinctly fibrillar tissue. In the latter case the fibrils
have either a concentric arrangement, as in fig. v, or they form
a thinner or thicker bundle, much convoluted, and situated
parallel to the surface of the corresponding trabeculse (as in
fig. iv), or vertical to it. The fibrillar nature of such a
bundle is very well shown if in the course of preparing the
specimen the endothelial covering breaks and the bundle of
the bud-like structure becomes uncoiled. It may then be
ascertained that there exists no difference between this
bundle and the ordinary connective-tissue bundles of the
trabeculse. As the contents of the bud-like structures
become more distinctly fibrillar we find that it enters also
into a closer connection with the subjacent connective tissue.
The question presents itself now, How do these bud-like
structures develop ? The earliest, or what appears to be the
earliest, stage is a small prominence due to the presence of
one, two, or three,or probably more, slightly flattened cells,
the substance and hucleus of which places them in the same
category with the endothelial cells of the surface. In the
next stage the substance of these cells, except the one
covering the prominence, becomes indistinctly granular, the
outlines of the cells becoming at the same time indistinct or
altogether lost; whereas the nuclei lose their power of
staining with haematoxylin or carmine ; their outline becomes
soon indistinct, and finally they are altogether lost. In figs.
i, iii, and v very faint outlines of nuclei are still distinguishable.
The description hitherto given applies to the examination
of the omentum of rat, but also in that of half-grown
dog have I observed similar bud-like structures, only these
are less numerous. I should say that those that I have seen,
were of the same kind as that represented in fig.v; they showed
already fibrillar structures, the fibrils being arranged concentrically, and among them were remnants of one or two
nuclei.
So that it appears that bundles of fibrillar connective
tissue are being formed in the omentum by the direct conversion of cells. These cells are in all respects similar to
endothelial cells. This is in conformity with an almost
generally assumed theory ; it is, however, not quite in accordance with what Rollett states ('Strieker's Handbook,'
chapter on Connective Tissue) as regards the development of
the connective-tissue bundles of the fcetal omentum. In my
238
DR. E. KLEIN.
' Anatomy of the Lymphatic System ' (part i, serous
membranes) I slated that under pathological conditions
bud-like and papillary or villous projections grow out from
the surface of the serous membranes (tenestrated as well as
non-fenestrated parts), and that the connective tissue forming
the matrix of the larger or further advanced papillae does
not seem to be produced by the distinct conversion of the
substance of endothelial cells, as stated by Kundrat ('Strieker's Jahrbucher,' 1870), but appears rather as a kind of
secretion. This, however, is certainly not correct in the case
of the projections of the normal omentum as described above,
for here the newly formed connective-tissue bundles are
derived directly from the cell-substance, and it is, therefore,
not unlikely that the same takes place also under the abovementioned pathological conditions.
At one time I was not disinclined to derive some of the
young buds of the omentum of rat, represented in figs, i and
ii, from peculiar large migratory cells, which seem to occur
only in the omentum of white rats. They are conspicuous by
their large size, their coarse granulations, which staine
very deeply in haematoxylin, and also, but to a less degree, in
carmine, and by their clear round nucleus, which was not,
however, stained with the above reagents ; and in this respect
alone they differ markedly from the other cellular elements
of the membrane. These migrants are found in considerable
numbers among the cell-accumulations around the large
blood-vessels, whence they may be traced into the smaller
traheculse of the fenestrated portion. At some places these
cells are changed into fat-cells.
As I said before, I was at first inclined to assume that
some of our buds are derived from these large migrants,
especially those figured in i and ii, by assuming that their
coarse granulations gradually disappear, and that also their
substance undergoes the above-described alterations, but
not being able to find intermediary forms I cannot support
that assumption.
Before concluding this part of the paper I wish to mention
the changes that are observable in the nuclei of the surface
endothelium of the fenestrated portion of the omentum of
rat, consisting in this :—Amongst the ordinary oblong nuclei
of the ordinary endothelial cells (like those represented in
figs, i—v) there are seen occasionally oblong or round nuclei
[the ordinary nuclei are on the average about 0"0135 by
0-0051 millimetres] considerably larger, even twice as large.
They show very often constrictions, as if dividing, or are
nearly completely divided into two or even three smaller
JUNUTG ANATOMY OF THE OMENTUM,
239
nuclei. The presence of two nuclei in one endothelial cell
was, however, seldom met with in the onientum of rat.
The presence of smaller or larger groups of germinating
endothelial cells occurring in various parts of the normal
omentum and pleura of various animals, fully described and
figured in the above-mentioned book, need not here be
mentioned specially.
2. According to Rollet the fenestrse of the omentum are
surrounded by connective-tissue bundles, which return in
themselves, and judging from his fig. 3 in his article on connective tissue, one is led to suppose that in the omentum
there are no other bundles but such as surround the fenestrse
and return in themselves. Ranvier ('Travaux de laboratoire
d'Histologie,' 1874, p. 140) questions this statement, and
maintains on the contrary that there are no bundles returning in themselves, and that the fenestrse originate by the
simple separation of bundles, i. e. are merely holes between
hundles. Ranvier thinks it probable that the holes are produced by migratory cells penetrating through the membrane.
Examining the omentum of young rabbits and guinea pigs,
prepared in the above manner, the origin of the fenestrse
becomes easily understood ; the examination of the omentum
of rats and half-grown dogs gives us also valuable information as regards the arrangemeut of the connective-tissue
bundles in the fenestrated part. There is a considerable
part of the omentum of young guinea pigs (three to four
weeks old), and still more, of young and even full-grown
rabbits, which is of a dense structure, containing only here
and there a few small holes. The omentum of guinea pigs
(three to four weeks old) is especially valuable in this
respect, showing us at once the origin of the holes. In fig.
vfi I have represented a small portion of such an omentum.
As is shown in the figure, the membrane consists of connective-tissue bundles, arranged more or less parallel to each
other; on the surface of the membrane are seen the nuclei
of the endothelium (the outlines of the endothelial cells
becoming of course visible by nitrate of silver). Further,
we see a number.of well-defined holes, a, passing right through
the membrane, these holes being of different sizes. And
finally, we notice in the membrane a number of round
spaces (vacuoles) of different sizes—in some parts their number being very considerable; eome of them contain a small
nucleus, i. e. the nucleus of a connective-tissue cell, the
substance of which may be made out occasionallly as granular
protoplasm situated at and exteuding from the poles of the
240
DR. E. KI.EIN'.
nucleus. On carefully looking over a portion of the omentum
it can be ascertained that the last-named spaces are vacnoles
which open completely on one of the surfaces. I presume
the only interpretation that can be put on these different
appearances is this : there appear smaller or larger vacuoles
in the substance uniting the connective-tissue bundles, vvhicli
ultimately open through the endothelial membrane first of
one then of the other surface. These vacuoles appear not
only at those places between the bundles, where there is
situated a connective-tissue corpuscle—in this case the vacuole
appears to be lined on one side by the cell,—but also
independently of these.
Comparing with the above specimen one that had been
stained in the usual manner with nitrate of silver, we perceive that the smallest examples of those holes which
penetrate completely through the membrane (a in fig. vii)
correspond to the interstitial substance of the endothelial
cells of the surface ; so that the above holes of the omentum
are due to a dehiscence of the interfascicular, and also of the
corresponding parts of the interstitial substance of the surface
endothelium, viz. two substances which, as is well known, are
identical in their chemical characters. That, therefore, the
theory of lianvier, viz. that the holes are caused by migratory cells, is to be dismissed need not be specially insisted
upon. The absence of migratory cells in many parts where
the holes are just being formed—judging from the very
small vacuoles found in the membrane—confirms this conclusively. I presume the above vacuolation is due to the
presence of fluid in the interfascicular substance, probably
liquefaction of part of this substance, and that a similar process in corresponding portions of the interstitial substance of
the endothelium leads to the establishment of complete
boles.
Turning now to the examination of the omentum of young
and half-grown dogs and rats we ascertain the following
important appearances :
(a) Apart from the large trabeculse containing large
blood-vessels, we find some parts in the fenestrated
portion which are of a denser structure; they contain,
besides the surface endothelium, a considerable number of
connective-tissue bundles, arranged parallel with each other ;
between these we find the ordinary connective-tissue corpuscles.
(b) In some extensive portions, however, the meshes of
the fenestrated part are surrounded by thin trabeculse which
are composed of a single connective-tissue bundle, ensheathed
MINUTE ANATOMY OF THE OMENTUM.
241
by the surface endothelium. There are no connective-tissue
corpuscles within this kind of trabeculse.
Between a and b we find all intermediary forms, i. e.
broader or narrower trabeculse, according to the larger or
smaller number of connective-tissue bundles of which they
are composed, and between these lie the corresponding
connective-tissue corpuscles. Examining more carefully one
of the smaller of these intermediary forms of trabeculse,
i. e. one containing a small group of bundles, like the one in
fig. vi, we have two important facts.
First, we see at the points where three or more trabeculse
meet,an accumulation of nuclei; examining these places with
a moderate power we find that the nuclei are due chiefly to
cells situated between the connective-tissue bundles, the
nuclei being surrounded by granular protoplasm. (In preparations prepared with bichromate of potash, and then stained,
as described above, the nuclei belonging to the covering
endothelium cannot be easily distinguished except by very
careful focussing; staining with silver gives satisfactory
information.) A second fact of equally great, importance is
the presence of vacuoles between the bundles of connective tissue. In the drawing under consideration we see
that these vacuoles are between the bundles, and in a more
or less distinct linear arrangement. It is easy to understand
how by the increase in size of these vacuoles a group of
meshes is established, or how by the coalescence of two or
three vacuole meshes of considerable size are formed.
As in the case of the guinea pig (see above), so also
here we find that in some vacuoles are contained nucleated
cells. The examination of a number of places like the one
represented in fig. vi leads one to suppose that the accumulation of nucleated cells at the junction of trabeculse
represents the stock from which cells extend by active
growth between the bundles, and are destined to become
the covering endothelial cells of the latter when this part
becomes feiiestrated.
From the preceding description it appears that the meshes or
holes in the omentum are caused by the separation of the bundles from each other; that is to say, they appear between the
bundles (the connective-tissue corpuscles situated between
these representing the endothelial cells after the fenestration
of the corresponding parts), and that therefore Ranvier is
right against Rollett, according to whom (as mentioned
above) each hole is surrounded by a bundle returning in
itself. Although the statement of Eollett is not correct in
the above form, still it may be rendered correct by slightly
212
DR. E. KLEIN.
modifying it in saying, that there are holes which appear at
first sight to be surrounded by returning bundles, but which
on careful examination are seen to surround only about half
or two thirds of the circumference of the hole.
Staining a portion of omentum of an adult rat in carmine
(after having been kept a few days in the bichromate of potash
solution) and spreading it out with a rather firm hand on an
object glass and mounting and examining it under the microscope, the arrangement of the connective-tissue bundles is very
evident. In some parts we see trabeculse, which arecomposd
of three bundles ; a middle one, and on each side of this a thin
one bordering on a hole and apparently surrounding it. But,
on looking more attentively, it is found that it does not return
in itself, but is a branch of a larger bundle, and, having surrounded the hole for the greater part of its circumference,
joins again another bundle. This condition is quite compatible with the formation of the holes by vacuolation.
3. In my 'Anatomy of the Lymphatics/ I, 1873, p. 11,
.id following, I have minutely described the occurrence of
opaque patches of different sizes (more or less covered with
germinating endothelium) the matrix of which contains a
great abundance of cells. The youngest and smallest of
these milky patches have no blood-vessels, whereas the larger
ones are provided with a special system of capillary vessels.
I have also stated then (1. c , pp. 58, 59, and 60) that in the
omentum of most animals a constant development of new
vessels takes place in these patches of the omentum, either
in connection with already formed vessels by solid protoplasmic processes which become gradually hollowed out (as
described by Strieker and Arnold) or independent of already
formed vessels by vacuolation of some of the connectivetissue corpuscles of the matrix of the above-named patches
(the vacuolation of cells is, as I have pointed out in the
second section of that work, of great importance also in
pathological respect).
Ranvier, a year later, in a paper published in 18741 (1. c ,
p. 148), drewattention to the opaque patches in theomentumof
rabbit and he gave to them a special name, " laches laiteuses."
Those cells of the matrix of these patches of which hloodvessels are developed Ranvier calls " cellule vasoformatives."2
1
Both the reporter in the ' Centralblatt. f. Med. Wisseiisch.,' and the
reporter on "Histology/' ill Virchow's ' Jahrbiiclier,' while reviewing
Ranvier's paper, are quite unaware of my description of the above patches
and2 their importance lor the development of blood-vessels.
It seems to be necessary to have always in readiness a few new names,
otherwise your descriptions will be left unnoticed.
MINUTE ANATOMV Of THE OMENTUM.
243
Ranvier's description of the mode of the formation of bloodvessels in these patches varies somewhat from that described
by myself. After a new investigation of the development of
blood-vessels in similar patches of the omentum of very young
guinea pigs, I have come to the conclusion that the mode of
development of blood-vessels in the young animal corresponds
to that described by me of those in the rabbit and not to that
maintained by Ranvier. If a preparation be prepared in the
above manner (2 percent, bichrom. of potash for eight to ten
days, washing in water and then staining in haematoxylin or
carmine and hsematoxylin) from the omentum of a young
guinea-pig (not older than three or four weeks) and the vicinity
of large vessels be examined, numerous places may be sought
out in which a development of new blood-capillaries can be
easily discovered.
Fig. 8 accompanying this paper is taken from such a part.
In this figure there are two capillary vessels which are still
in a young condition ; they still show the cells by whose
vacuolation and fusion the vessel has been formed. In close
vicinity to the vessels we find very numerous cells, the
greater number of which are vacuolated in various ways, as
is shown in the figure. These vacuolated cells have a more
or less distinct linear arrangement, and we have only to
imagine that those parts by which they are in contact become
absorbed or disappear, to obtain a portion of a capillary
vessel. Although the number of vacuolated cells is smaller
in most patches where the development of blood-vessels has
begun, than that represented in figure 8, still it is so large in
my specimens that their importance for the development of
blood-vessels cannot be overlooked. Besides, the condition
and aspect of the young capillaries like those represented in
fig. 8 strongly support the view just mentioned.
To say that the vacuolated cells and the above condition
of the young capillaries is due to the influence of the reagent
used (2 per cent, solution of bichromate of potash), would
be against all our experience of the action of that fluid.
From the foregoing we see that vacuolation is important for
the origin of the holes at the fenestrated omentum in general
and also for the development of capillary vessels in the patches
and nodules, in the omentum of the young guinea pig ; in
the former case the vacuolation takes place in the interstitial
substance of the connective-tissue stroma, in the latter case
in the cells of the matrix ; and by fusion of the vacuolated
cells capillary vessels are formed.
The omentum of the above case has not been feneslrated
yet; it contained only indications of it in the form of a few
214
DR. R. KLEIN.
holes, as described in paragraph 2. If the omen turn be
already fenestrated, the vacuolated cells become very few,
although development of capillary vessels is still going on.
I refer to the examination of the omen turn of a guinea pig
about six weeks old, which omentum is abundantly feuestrated, almost like that of an adult animal. Although I do not
see here any such conspicuous appearances of vacuolated cells
near the capillary blood-vessels, as in the former case, still
there are capillary vessels to be met with in small patches,
the wall of which still shows traces of its mode of development, viz. by fusion of vacuolated cells, like the capillaries in
fig. 8. There are, however, other appearances which are in
perfect harmony with the vaeuolation theory. Thus I have
before me a small patch with a network of capillaries, from
the Avail of one of which solid protoplasmic threads of
great fineness extend, running in a slightly curved manner
over a distance of one to three millimetres, and eadiug in the
wall of a capillary vessel of a distant patch. The thread in
question contains seven spindle-shaped swellings, whicli
contain either a single nucleus or a small number of nuclei
(two, three, or four) ; in the latter case the fusiform swelling
shows more or less advanced vaeuolation. There can be no
doubt that this thread will finally become converted into
a blood-vessel, for other such threads may be found in different
stages of development. Thus is explained the presence of
solitary capillary vessels found in the omentum, and extending from one vascular cell-patch to another, sometimes for a
conspicuous distance a distance occasionally to be measured
by the inch-measure. Besides the above nucleated protoplasmic vaso-formative threads there are other fine nucleated
protoplasmic threads, which appear to lose themselves in
the connective tissue of the matrix; they are at some places
of jfreat length (I—3 mm.), and contain a nucleus at several
places at regular intervals ; they are probably nerves. I
believe I have seen them in connection, or what appears to
be a connection, with the vaso-formative threads.