320 



COMPARATIVE PHYSIOLOGY. 



the mucous gland in the resting stage the cells are large, and 

 hold much clear matter in the interspaces of the cell network; 



Fig. 861.— Section of mucous gland (after Lavdowsky). In A, gland at rest; in B, 

 after secreting for some time. 



and, as this does not stain readily, it can not he ordinary 

 protoplasm. This, when the gland is stimulated through its 

 nerves, disappears, leaving the containing cells smaller. It 

 has become mucin, and may itself he called mucinogen. 



It is to be noted that, as the cells become more protoplasmic, 

 less burdened with the products of their activity, the nucleus 

 becomes more prominent, suggestive of its having a probable 

 directive influence over these manufacturing processes. 



Substantially the same chain of events has been established 

 for the serous salivary glands and the stomach, so that we 

 may safely generalize upon these well-established facts. 



It seems clear that a series of changes constructive and, from 

 one point of view, destructive, following the former are con- 



FtG. S62.— Changes in parotid (serous) gland during secretion (after Langley). A, dur- 

 ing rest; B, after moderate, C, after prolonged stimulation. Figures partly dia- 

 grammatic. 



stantly going on in the glands of the digestive organs. Proto- 

 plasm under nerve influence constructs a certain substance, 



