Bauhaus-Universität Weimar

Titel:
The Cyclopaedia of Anatomy and Physiology, vol. 4: Pla [corr.: Ple] - Wri
Person:
Todd, Robert Bentley
PURL:
https://digitalesammlungen.uni-weimar.de/viewer/image/lit29465/455/
SECRETION. 
lacteals are dispersed; and in part of substances 
taken up by the lymphatic or interstitial divi¬ 
sion, and probably consisting chiefly of par¬ 
ticles which are set free by the continual 
disintegration of the living structure, but 
which, not being yet decomposed, are capable 
of being again employed for the purposes of 
nutrition. The materials derived from these 
sources appear to require a considerable pre¬ 
paration or elaboration, before they are fit to 
be introduced into the current of the circula¬ 
tion ; and this elaboration is effected by an 
agency of precisely the same nature with that 
which is concerned in the removal of various 
products of secretion from the blood ; for the 
tubuli of the absorbent system, like those of 
the kidney or the testis, are lined by epithe¬ 
lial cells, and their duty seems to be altogether 
analogous. The alterations which the ab¬ 
sorbed matters undergo during their passage 
along this system of tubes, and the evidence 
that these alterations are in great part due to 
the elaborating action of cells, having been 
heretofore considered (see Nutrition), need 
not be again dwelt on ; but a few words may¬ 
be added respecting the structure and func¬ 
tions of the glandulae or ganglia, with which 
the absorbent vessels of man and the mam¬ 
malia are copiously furnished. These bodies 
are composed of lacteal or lymphatic trunks, 
convoluted into knots, and distended into 
cavities of variable form and size, which are 
known as the “ cells ” of these glands. 
Amongst these cells there is a copious plexus 
of blood-vessels, but there is no direct com¬ 
munication between their cavities. Accord¬ 
ing to Prof. Goodsir *, the epithelium which 
lines the absorbent vessel undergoes a marked 
change where the vessel enters a gland, and 
becomes more like that of the proper glandu¬ 
lar follicles in its character. Instead of being 
flat and scale-like, and forming a single layer 
in close apposition with the basement mem¬ 
brane (as it does in the lacteal tubes before 
they enter the gland, and after they have 
emerged from it), we find it composed, within 
the gland, of numerous layers of spherical 
nucleated cells, of which the superficial ones 
are easily detached, and which appear to be 
identical with the cells that are found floating 
in the chyle and lymph, especially after their 
passage through these bodies. The absorbent 
glands may be regarded, therefore, as concen¬ 
trating within themselves that agency, to 
which the whole system of tubuli is more or 
less subservient. Such an idea is strictly ac¬ 
cordant with the facts of comparative anatomy; 
for in reptiles, in which there are no glands, 
the tubuli or vessels are enormously length¬ 
ened by the convolutions which they present 
along their course, as if to furnish a suffi¬ 
cient extent of epithelial surface. 
There is strong reason for regarding the 
spleen, the thymus and thyroid glands, and 
the supra-renal capsules, as parts of the same 
assimilative apparatus, their office apparently 
* Anatomical and Pathological Observation 
1% 46. 
445 
being, to withdraw certain crude matters from 
the blood, to submit these to an elaborating 
action whereby they shall be rendered more 
fit for the nutrition of the tissues, and then to 
restore them to the circulating current. The 
details of the structure of these organs will be 
found under their respective names; and it 
will be sufficient to state here, that they all 
show an essential correspondence with the 
true and recognised glands in every respect 
but this, that they have no efferent ducts. 
Each of them may be described as consisting 
essentially of a number of vesicles, which are 
either closed and isolated, or open into a 
common reservoir, which is itself closed ; the 
vesicles in either case are lined with epithelial 
cells.* Around these, as around the follicles 
or tubuli of the true glands, blood-vessels are 
copiously distributed ; and the elimination of 
products from the blood appears to be 
effected by their agency, precisely as if these 
products were destined to be cast out of the 
body. The mode in which they are taken 
back into the circulation, after they have been 
subjected to the elaborating process, is not 
very clear; both blood-vessels and absorbents 
have been supposed to participate in the 
operation ; and this idea may not be regarded 
as improbable, when the large size and number 
of the lymphatics distributed to these organs 
is considered. 
Having thus taken a general survey of the 
principal varieties of secretory structure, and 
of the fliief aspects under which the secreting 
function presents itself, we shall pass on to a 
more particular consideration of the mode in 
which this operation is performed, and of the 
instruments by which it is effected. For this 
purpose it will be preferable to select a par¬ 
ticular gland, and to examine the minutiæ of 
its structure in the most diverse forms and 
conditions under which it presents itself; and 
there is none which suits our purpose so well 
as the liver, which is the gland of most 
universal existence throughout the whole 
animal series, and which presents almost 
every leading variety that is found in the 
whole series of glandular structures. And 
we gladly avail ourselves of the opportunity 
thus afforded, of bringing the account already 
given of that gland (see Liver) into con¬ 
formity with the increased knowledge of its 
structure that has been since acquired. 
There are few animals possessed of a dis¬ 
tinct digestive cavity, in which some traces of 
a biliary apparatus (recognisable by the colour 
of the secretion) may not be distinguished. 
Thus in the Hydra, some of the cells that 
form the lining of the stomach contain a 
brownish-yellow matter, strongly resembling 
bile, which is probably poured into the cavity 
on the rupture of the cells. In the walls of 
the stomach of the Actinia, Dr. Thomas Wil¬ 
liams has described sulci formed by du plicatures 
of the lining membrane, in which are lodged 
a set of cells of glandular appearance, some 
* See Prof. Ecker, in Annales des Sciences Na¬ 
turelles, Zoologie, Août, 1847.
        

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