DIGESTION. yy 



granules disappear from the outer boundary of the cells, which 

 then become clear and distinct. At the end of the secretory activity 

 the cells have been freed of granules and have become smaller and 

 more distinct in outline. It would seem that the granular matter 

 is formed in the cells during the period of rest and discharged into 

 the ducts during the activity of the gland. 



In the mucous glands e. g., submaxillary and sublingual the 

 changes that occur in the cells are somewhat different. (See Fig. 12.) 



FIG. 12. SECTION OF A Mucous GLAND. (Lavdowsky,) 

 A. In a state of rest. B. After it has been for some time actively secreting. 



During the intervals of digestion the cells lining the gland are large, 

 clear, and highly refractive, and contain a large quantity of mucigin. 

 After secretion has taken place the cells exhibit a marked change. 

 The mucigin cells have disappeared, and in their place are cells 

 which are small, dark, and composed of protoplasm. It would ap- 

 pear that the cells, during rest, elaborate the mucigin, which is dis- 

 charged into the tubules during secretory activity, to become part 

 of the secretion. 



Saliva is an opalescent, slightly viscid, alkaline fluid, having a 

 specific gravity of 1.005. Microscopic examination reveals the pres- 

 ence of salivary corpuscles and epithelial cells. Chemically it is 

 composed of water, proteid matter, a ferment (ptyalin), and inor- 

 ganic salts. The amount secreted in twenty-four hours is about 2^ 

 Ibs. Its function is twofold : 

 i. Physical. Softens and moistens the food, agglutinates it, and 



facilitates swallowing. 



