SALIVARY GLANDS 



73 



two are usually said to be mucous, though they contain both 

 serous and mucous cells. The ducts subdivide into smaller 

 ducts and tubes, until a distinct tubule is distributed to every 

 acinus and becomes the lumen of that acinus. The whole 

 arrangement resembles the branchings of a tree. 



The flow from these glands is greatly increased by masti- 

 cation. From the parotid the flow is much more abundant 

 on that side upon which the 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 



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. 



segment of the cells becomes comparatively clear. It is sup- 

 posed that this is an essential step in the production of the 

 organic constituents of the secretion that the granules con- 

 tain either the ptyalin or the substance necessary to its for- 

 mation. It is also supposed that at the same time that the 

 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 ex- 

 truded, seem to destroy the cell itself. 



