STRUCTURE OF THE EXCRETORY DUCTS. 429 



react through the nerves for many hours, whereby the mucus 

 and the mucus-forming materials are consumed. 



Later inquirers do not agree with me in my opinion regard- 

 ing the demi-lune ; nevertheless, they completely justify 

 it, by each one giving a different interpretation of its nature. 

 C. Ludwig and Gianuzzi ascribed to it a laminated structure, 

 and described the blackening it underwent from the action of 

 perosmic acid, and the reddening with carmine. They were un- 

 able to see nuclei distinctly. Boll and Kolliker described the 

 " half-moon " as composed of connective tissue, which, firmly 

 adherent to the alveolus, represents the cells constituting the 

 reticulum already referred to. Heidenhain maintained that 

 the demi-lune was formed by a layer of young epithelial cells, 

 destined to supply the place of those salivary cells which were 

 undergoing distintegration. I believe this view to be not an 

 unreasonable one, for inasmuch as in the submaxillary gland of 

 the dog the protoplasm of the mucous cells is scarcely, if at all, 

 tinted with solutions of carmine, whilst the small nuclei lying 

 at the periphery, as well as the numerous superimposed long 

 cell processes running outward, are deeply stained, we have 

 a sufficient explanation of the occurrence of a complete mar- 

 ginal zone in the alveolus. But since the term " demi-lune " 

 can possess such different significations, it is better to avoid 

 its use entirely. 



3. THE EXCRETORY DUCTS. In the interior of the gland, 

 besides the- structures already described, are tubes often of con- 

 siderable size, and lined with cylindrical epithelium, to which the 

 name of excretory ducts is applied. Close investigation shows 

 that they must possess great functional . importance. As 

 evidence of this, I would first remark that if a dog be killed as 

 rapidly as possible, and fine sections be prepared from the sub- 

 maxillary gland, transparent drops may be seen exuding from 

 the columnar cells lining the excretory ducts, and some of these 

 having already become detached, lie in the lumen of the 

 tube, appearing in the form of round, sharply defined, clear 

 spherules. These unquestionably proceed from the cylindrical 

 epithelium. But inasmuch as drops, presenting precisely the 



same appearances, are found in freshly secreted saliva, that has 



H H 2 



