HISTOLOGICAL CHARACTERS. 

 The following table is taken from Colin : l 



477 



SOME HISTOLOGICAL CHARACTERS OF THE SALIVARY GLANDS. 



It would be outside the scope of this account to give a detailed 

 description of the ducts, ductules, terminal tubes, lymphatics, and other 

 histological features of the several glands. But some of the histological 

 features have so intimate a relation to physiological observations, that it 

 is not advisable to pass them by without notice. 



The narrow ductule, proceeding from a duct, commonly divides, and 

 each secondary ductule widens more or less suddenly into a tube of 

 secreting cells ; each tube gives off curved branches, and these also may 

 give off similar branches ; thus, a clump of tubes is formed around the 

 primary ductule. The terminal tubes are usually called alveoli, and their 

 cells alveolar cells. 



The alveolar cells may be classified according to the chemical nature 

 of the substances they secrete. A step in this direction was taken by 

 Heidenhain, who divided the cells into mucous cells which secrete mucin, 

 and albuminous cells which secrete some form of proteid. There is good 

 evidence that the typical albuminous cell does not secrete any mucin, 

 and there is some evidence that the typical mucous cell does not secrete 

 any proteid, and on this basis it is apt to be assumed that all the alveolar 

 cells secrete either mucin only, or proteid only. It should, however, be 

 remembered that this is an assumption ; it is possible that some alveolar 

 cells secrete both mucin. and proteid. 



In any one salivary gland all the alveolar cells may be mucous or 

 all may be albuminous, or some of them may be mucous and some 

 albuminous. Further, in different glands, the relative number of the 

 two kinds of cells varies in nearly all possible proportions. The 

 nomenclature in use takes notice of the broad distinctions only. Glands 

 which consist almost entirely of albuminous cells are called albuminous 

 glands, those which consist chiefly of mucous cells are called mucous 

 glands. The glands of intermediate structure are commonly placed 

 in the class of mucous glands, unless the proportion of mucous to 

 albuminous cells is very small. 



The term "mixed gland" was introduced for certain special cases; for example, 

 the submaxillary gland of the guinea-pig, in which one or more lobules were 

 said to be mucous and the rest to be albuminous. But in the guinea-pig, and 

 possibly in the other cases, the mucous lobule appears to be a separate gland 

 (cf. above, p. 476). It would probably be more convenient to use the term 

 " mixed," for a gland in which the mucous and albuminous cells are present 

 in approximately equal proportions. And we might have the following scale, 

 passing from entirely albuminous to entirely mucous : albuminous glands, 

 1 "Traite" de pliysiol. compare'e des animaux," 3rd edition, 1886, tome i. 



