CH. XXX.] 



THE SALIVARY GLANDS 



475 



and some of the alveoli in the human submaxillary) the cells after 

 treatment with water or alcohol are clear and swollen (fig. 395); this 

 is the appearance they usually present in sections of the organ. But 

 if examined in their natural state by teasing a portion of the fresh 



Fio. 304. Section of submaxillary gland of dog. Showing gland-colls, b, and a duct, a, b, in section. 



(Kolliker.) 



gland in serum, they are seen to be occupied by large granules com- 

 posed of a substance known as mucigen or mucinogen. When the 

 gland is active, mucigen is transformed into mucin and discharged as 

 a clear droplet of that substance into the lumen of the alveolus. Out- 

 side these are smaller, highly 

 granular cells containing no 

 mucigen ; these marginal cells 

 stain darkly, and generally form 

 crescentic groups (crescents or 

 demilunes of Gianuzzi) next to 

 the basement membrane. They 

 do not secrete mucin, but are 

 albuminous cells. After secretion 

 their granules are lessened. 



In those alveoli which do not 

 secrete mucin, but a watery non- 

 viscid saliva (parotid, and some 

 of the alveoli of the human sub- 

 maxillary), the cells are filled 

 with small granules of albu- 

 minous nature. Such alveoli are called serous or albuminous, to dis- 

 tinguish them from the mucous alveoli we have just described. 



These yield to the secretion its ferment, ptyalin. The granular 

 substance within the cell is the mother substance of the ferment 

 (zymogeri), not the ferment itself. It is converted into the ferment 

 in the act of secretion. We shall study the question of zymogens 



Fie. 395. Section through a mucous gland 

 hardened in alcohol. The alveoli are lined 

 with transparent mucous cells, and outside 

 these are the demilunes. (Heidenhain.) 



