CH. XXXII.] 



THE SALIVARY GLANDS 



499 



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

 Outside these are smaller, highly granular cells containing no 



Fio. 349. Mucous cells from submaxillary gland of dog. a, from a resting or loaded gland; b, from a 

 gland which has been secreting for some time; a', b', similar cells which have been treated with 

 dilute acid. (Langley.) (From Quain's Anatomy, by permission of Messrs Longmans, Green & Co.) 



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. The 

 demilunes are therefore easily 

 seen in the gland before secretion, 

 owing to the contrast they ex- 

 hibit to the cells loaded with 

 mucin. 



In those alveoli which do not 

 secrete mucin, but a watery non- 

 viscid saliva (parotid, and some of 

 the alveoli of the submaxillary), 

 the cells are filled with small 

 granules of albuminous nature. 

 Such alveoli are called serous or 



albuminous, to distinguish them from the mucous alveoli we have just 

 described. 



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

 substance within the cell is the mother-substance of the enzyme 

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

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

 more fully in connection with the gastric glands and the pancreas, 

 where they have been separated from the enzymes by chemical methods. 

 In the case of saliva we may term the zymogen, ptyalinogen provision- 



Fio. 350. Section through a mucous gland 

 hardened in alcohol. The alveoli are lined 

 with mucous cells, and outside these are the 

 demilunes. (Heidenhain.) 



