454 



DIGESTION 



filled with granules or small globules, which are often so numerous as 

 almost entirely to obliterate the nucleus. When the gland becomes active, 

 on the other hand, the granules or globules leave the cells, except for a 

 few which remain toward the lumen border. (Figs. 143 and 144.) 



A.' 



Fig. 143. Cells of parotid gland s.hpwing zymogen granules: A, after prolonged rest; B, after a 

 moderate secretion; C, after prolonged secretion. (From Langley.) 



These observations indicate that the granular or globular material must 

 represent part at least of the secretion of the glands. Sometimes, even 

 before they are extruded, the granules become changed into some differ- 

 ent material, as is indicated by the fact that they stain differently from 



D. 



Fig. 144. Parotid gland of rabbit in varying states of activity examined in fresh state. The 

 upper left-hand acini are resting. The upper right-hand acini are from a gland stimulated to 

 activity by injecting pilocarpine, and the two lower acini from one after stimulation of its sym- 

 pathetic nerve. (After Langley.) 



those of the resting gland. It must not be thought, however, that an 

 extrusion of granules necessarily accompanies secretory activity, for 

 under certain conditions a copious secretion of water and inorganic salts, 

 as well as a certain amount of organic material, may be produced with- 



