34:4 HANDBOOK OF PHYSIOLOGY. 



experiments serve to prove that the chorda contains two sets of nerve 

 fibres, one set (vaso-dilator) which, when stimulated, act upon a local 

 vaso-motor centre for regulating the blood supply, inhibiting its action, 

 and causing the vessels to dilate, and so producing an increased supply of 

 blood to the gland; while another set, which are paralyzed by injection 

 of atropiu, directly stimulate the cells themselves to activity, whereby 

 they secrete and discharge the constituents of the saliva which they 

 produce. These latter fibres very possibly terminate on the salivary cells 

 themselves. If, on the other hand, the sympathetic fibres be divided, 

 stimulation of the tongue by sapid substances, or of the trunk of the 

 lingual, or of the glosso-pharyngeal, continues to produce a flow of saliva. 

 From these experiments it is evident that the chorda tympani nerve is 

 the principal nerve through which efferent impulses proceed from the 

 centre to excite the secretion of this gland. 



The sympathetic nerve also contains two sets of fibres, vaso-coustrictor 

 and secretory. But the flow of saliva, upon stimulating the sympathetic, 

 is scanty, and the saliva itself viscid. At the same time the vessels of 

 the gland are constricted. The secretory fibres may be paralyzed by the 

 administration of atropine. 



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 ob- 

 longata, are, as in the case of the submaxillary gland, the fifth, and the 

 glosso-pharyngeal. The pneumogastric nerves convey a further stimu- 

 lus 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 

 former case, it has been noticed, as has been already described, that 

 during the rest which follows an active secretion the lumen of the alveo- 

 lus 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. 239). 



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 ele- 



