After examining larger fragments with lower powers, smaller ones are selected, subjected to pressure with cover glass, and examined with higher powers. By compression with cover glass, pushing from side to side, one can isolate almost any structure. One can also then make sure whether a fine fibre is really in connection with any other structure, or only lying above or beneath the same.
The staining with the carmine will generally not attack the fine nerve fibres. To show these up I have used aniline blue dissolved in water. By these means I have brought out very plainly the nerve fibres, in nerve trunks, of considerable size, as well as those along vessels. I took the material prepared as described, broke up a little piece in fragments of the size of mustard seeds, and left them twelve hours in the blue fluid in a watch glass. Glycerine, if necessary, slightly acidulated, will remove the superfluous stain. I was very much pleased with the action of the aniline blue.
Notwithstanding its physiological importance there is among the authorities as yet no uniformity of opinion on the histology of this gland, save that it belongs to the racemose glands, and is made up of epithelial cells.
The question whether there is present a special membrana propria, enveloping the glandular epithelium, as Pflüger teaches, or a network of partly coalesced connective tissue cells, as Kölliker supposes, may not seem very important, but certainly such points must be cleared up before such questions as to how the nerves end can satisfactorily be answered.
This question, the importance of which will be admitted by all, is also a disputed one. In Stricker’s handbook Pflüger has, in the article on the submaxillary gland, given a detailed account of the mode of nerve-ending in this gland. According to his investigations it is of various kinds.
(1.) The medullary fibre approaches an alveolus penetrates this membrane, the axis cylinder breaks up into innumerable fine fibres, and these pass into the body of the gland cell. (2) Or the nerve passes into a pale cell provided with numerous processes, which in their turn form connections with the secreting cells.
These results of Pflüger have, however, not been accepted by all investigators. Thus Kölliker says on this question:
“The investigations on the nerve-endings in the salivary glands are evidently far from being concluded, nevertheless so much can be gathered from the work done that the nerve fibres are in more intimate relations with the glandular elements than has been surmised heretofore. What these relations may be I cannot say, for notwithstanding a very careful investigation of this gland it has not been possible for me to reach views definite and not open to doubt, although frequently enough I have seen fibres and threads of various kinds apparently come in contact with salivary cells. Further, regarding the drawings and descriptions of Pflüger, I must confess, having at the same time nothing but the highest esteem of this investigator, as well as of the care and accuracy he employed in this question, that these do not seem altogether convincing to me.”
MEMBRANA PROPRIA.
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.