88 



HUMAN PHYSIOLOGY. 



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.) During the 



FIG. ii. CELLS OP THE ALVEOLI OP A SEROUS OR WATERY SALIVARY GLAND. 



(Langley.") 

 A. After rest. B. After a short period of activity. C. After a prolonged period 



of activity. 



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 



FIG. 12. SECTION OP A Mucous GLAND. (Lavdowsky.) 

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



composed of protoplasm. It would appear that the cells, during rest, 

 elaborate the mucigin, which is discharged 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 presence of salivary 



