I find that the gland cells are enclosed by a membrane (agreeing
altogether with Pflüger) which I look upon as decidedly homogeneous
(histologically speaking, of course), not showing any structure; by no
means being merely a reticulum of connective tissue corpuscles, as
Kölliker suggests.
Further: This membrane is provided with nuclei of an oval form
(generally), reminding me of the nuclei supplying the nerve sheaths.
Finally: This membrana propria sends out from the alveolar walls,
processes, ensheathing—how complete I cannot say—the gland cells. I
cannot otherwise explain the glistening lines, which we see in examining
sections VI extending from the alveolar wall between the cells,
resembling altogether the sections of the alveolar walls. To investigate
this matter more accurately, I have stained sections with carmine, also
with log-wood, and have found that the alveolar wall and these lines
stain the same way. Further breaking up such a section by manipulation
with cover-glass, one can obtain fragments of these processes, thus
demonstrating that these lines are not merely optical illusions.
The nuclei of this membrana propria are situated on its inner surface
and could be distinguished in the gland of the cat, mentioned above, not
only by their more oval, oblong or elliptical form, from the more
roundish nuclei of the gland cells, but just as plainly by the lighter
red or pinkish staining which they take on the nuclei of the gland cells
being stained a deeper red.
Compressing very small fragments of gland-substance (always of course in
glycerine), by means of the cover-glass, beating and pushing it from
side to side, thus bursting the alveolus and tearing the membrane and
isolating it from the contained gland cells, one can prepare for
examination greater or smaller pieces of this membrane. There are by
such means obtainable fragments with all sorts of processes and fringes,
short and long, many and few, which undoubtedly may remind one of
“connective tissue cells.” (See fig. 4.) More convincing than these are
membraneous pieces, which may be obtained of various sizes. (See figs.
5, 6.) I have a drawing of such a fragment, which, if enlarged as figs.
1 and 2, would cover over one-quarter of the page, and to which a number
of nuclei, more than six, are attached. As a rule, this membrane will,
by the manipulations with the cover-glass, not be spread out, but rather
folded up, huddled together inclosing some of the gland cells, forming
an indescribable nest.
I do not know if it will be necessary to mention in this connection that
I consider these nuclei identical with the half-moon cells of Gianuzzi,
and cannot help expressing my surprise at the physiological importance
assigned to them; for they have been considered playing the role of
mother cells, giving origin to glandular epithelium formed to take the
place of cells used up in the process of secretion. The dark staining,
which in section they seem to assume as well as the semilunar form, will
be discussed later. Of course I look upon these nuclei as belonging to
flat epithelial cells, as we find them lining nerve sheaths, and serous
membranes, and consider them of the same physiological importance as the
nuclei of such endothelial cells. A similar ensheathing membrane, or
membrana propria, I find in the ducts; but here I have not been able to
distinguish processes passing in between the cells. If present they must
be exceedingly delicate, for it is not difficult to press out groups of
cells from the ducts so that empty pieces (short ones of course) of such
can be examined.
While the membrana propria of the ducts can be separated rather easily
from the inclosed cells, it is different from the surrounding network of
capillaries. It seems impossible to remove the capillaries from the
duct-walls; while, in the gland-structure proper, among the alveoli, the
separation of the capillary from an alveolus, can with little difficulty
often be accomplished, so that a piece of capillary can be examined
without any other structures lying above or beneath it.