240 HANDBOOK OF PHYSIOLOGY. 



ganglion is ever the nerve-centre which controls the secretion of the sub- 

 maxillary gland. 



B. On the Parotid Gland. The nerves which influence secretion 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 ordinarily exciting secretion is conveyed to the medulla oblon- 

 gata, 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 

 centre 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 (1) the true salivary, or (2) to the mucous type. In the 



FIG. 179. Alveoli of true salivary gland. A, at rest; B, in the first stage cf secretion; c, after 

 prolonged secretion. (Langley.) 



former case, it has been noticed, as has been already described (p. 232), 

 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 considerable 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 (Fig. 179). 



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

 cell during rest, the second stage consisting of the actual discharge of 

 these granules, with or without previous change. The granules are 

 taken to represent the chief substance of the salivary secretion, i. e., the 

 ferment ptyalin. In the case of the submaxillary gland of the dog, at 

 any rate, the sympathetic nerve-fibres appear to have to do with the first 

 stage of the process, and when stimulated the protoplasm is extremely 

 active in manufacturing the granules, whereas the chorda tympani is 



