808 



FOOD AND DIGESTION 



are constricted. The secretory fibers may be paralyzed by the administration 

 of atropine. 



Nerves of the Parotid Gland. The nerves which influence secre- 

 tion in the parotid gland are branches of the facial (lesser superficial petrosal) 

 and of the sympathetic. The former nerve, after passing through the otic 

 ganglion, joins the auriculo-temporal branch of the fifth cerebral nerve, and, 

 with it, is distributed to the gland. The nerves by which the stimulus ordi- 

 narily exciting secretion is conveyed to the medulla oblongata, are, as in the 

 case of the submaxillary gland, the fifth and the glosso-pharyngeal. The 

 pneumogastric nerves convey a further stimulus to the secretion of saliva when 

 food has entered the stomach; the nerve center is the same as in the case of 

 the submaxillary gland. 



Changes in the Gland Cells. The method by which the salivary 

 cells produce the secretion of saliva appears to be divided into two stages, 

 which differ somewhat according to the class to which the gland belongs, viz., 

 whether to (i) the true salivary, or to (2) the mucous type. In the former 

 case, it has been noticed, as already described, that during the rest which 

 follows an active secretion the lumen of the alveolus becomes smaller, the 

 gland cells larger and very granular. During secretion the alveoli and their 

 cells become smaller, and the granular appearance in the latter to a consider- 

 able extent disappears, and at the end of secretion the granules are confined 

 to the inner part of the cell nearest to the lumen, which is now quite distinct, 

 figure 25 1. 



It is supposed from these appearances that the first stage in the act of 

 secretion consists in the protoplasm of the salivary cell taking up from the 

 lymph certain materials from which it manufactures the elements of its own 



FIG. 251. Alveoli of True Salivary Gland. A, At rest; B, in the first stage of secretion; C, 

 after prolonged secretion. (Langley.) 



secretion, and which are stored up in the form of granules in the cell during 

 rest; the second stage consists of the actual discharge of these granules, with 

 or without previous change. The granules are zymogen granules, and repre- 

 sent the chief substance of the salivary secretion, ptyalin. In the case of the 

 submaxillary gland of the dog, at any rate, the sympathetic nerve fibers appear 

 to have to do with the first stage of the process,, and when stimulated the proto- 



