40 



PHYSIOLOGY FOR DENTAL STUDENTS. 



compose them are engaged in preparing material to be secreted. 

 By microscopical examination, this material is seen in the proto- 

 plasm of the cells (Fig. 2) as granules, which are extremely 

 small in the serous gland cells, but much larger in the mucous. 

 In both types of gland the granules so crowd the cell that the 

 nucleus becomes indistinct and the cell itself much swollen. 

 After the gland has been active, the granules disappear, being 

 evidently discharged from the cell into the duct of the gland. 

 The granules are believed to represent the precursors of the 

 ptyalin or mucin of saliva hence their name of "zymogen" or 

 "mother of ferment" granules rather than these substances 



A. 



Fig. 2. Cells of parotid gland showing zymogen granules : A, after pro- 

 longed rest ; B, after a moderate secretion ; C, after prolonged secretion. 

 (Langley.) 



themselves. Watery or saline extracts of the glands contain 

 neither mucin nor ptyalin, nor does the addition of acetic acid to 

 a mucous gland cause any precipitate of mucin; indeed, it has 

 an entirely opposite action, it causes the granules to swell. 



The Nerve Supply of the Salivary Glands. The nerve fibers 

 supplying the glands are of the autonomic or visceral type (see 

 p. 277), and they include sympathetic and cerebro-spinal fibers. 

 The sympathetic fibers are derived from cells in the lateral horns 

 of the spinal cord, from which they emerge by the upper three 

 or four thoracic roots, and after ascending as medullated fibers 

 in the cervical sympathetic, terminate as synapses around the 

 cells of the superior cervical ganglion. The axons of these cells 

 proceed as non-medullated post-ganglionic fibers along the near- 

 est vessels to the respective glands. The cerebral autonomic 



