SALIVARY GLANDS 73 



lumen of that acinus. The whole arrangement resembles the 

 branchings of a tree. 



The flow from these glands is greatly increased by mastica- 

 tion. From the parotid the flow is much more abundant on that 

 side upon which mastication takes place. During activity it 

 can be shown that the granules of the serous cells accumulate 

 toward the lumen of the acinus while the outer segment of the 

 cells becomes comparatively clear. It is supposed that this is 

 an essential step in the production of the organic constituents of 



FIG. 34. Section of a mucous gland. (Brubaker after Lavdowsky.) 

 A, in a state of rest; B, after it has been for some time actively secreting. 



the secretion that the granules contain either the ptyalin or the 

 substance necessary to its formation. It is also supposed that at 

 the same time that ptyalin is being thus produced and discharged, 

 very active constructive changes are occurring in the clear zone 

 of the cells. During activity some at least of the mucous cells 

 seem to break down, but it is probable that the granules in the 

 cell protoplasm become converted into mucin, which, being 

 extruded, seem to destroy the cell itself. 



Composition and Properties of Saliva. While it is possible 

 to draw certain distinctions between the saliva from the different 

 glands, these distinctions are comparatively unimportant, so far 



