474 SALIVA. [CH. xxx. 



term the zymogen, ptyalinogen provisionally, but it has never 

 been satisfactorily separated chemically from ptyalin. 



After secretion, due to the administration of food or of such a 

 drug as pilocarpine, the cells shrink, they stain more readily, their 

 nuclei become more conspicuous, and the outer part of each cell 

 becomes clear and free from granules (fig. 397). 



The Secretory Nerves of Salivary Glands. 



The nerve-fibres which are derived from cranial and sym- 

 pathetic nerves ramify between the gland cells, but have never 

 actually been traced into them. 



These nerves control and regulate the secretion of saliva. 



The general truth concerning the existence of secretory nerves, 

 we have already become acquainted with (p. 164). The subject has 

 been worked out most thoroughly in connection with the salivary 

 glands, particularly the submaxillary gland in dog, rabbit, tfcc., 

 which we will take first. 



The Submaxillary and Sublingual Glands. These glands 

 receive two sets of nerve-fibres ; namely, from the chorda tympani 

 and the sympathetic. 



The chorda tympani is given off from the seventh cranial nerve 

 in the region of the tympanum.* After quitting the temporal 

 bone it passes downwards and forwards, and joins the lingual 

 nerve, with which it is bound up for a short distance. On leaving 

 the lingual nerve it traverses the svbmaxillary ganglion ; it then 

 runs parallel to the duct of the gland, gives off a branch to the 

 sublingual gland, and others to the tongue. The main nerve 

 enters the hilus of the submaxillary gland, where it traverses a 

 second ganglion concealed within the substance of the gland, and 

 which may be called after its discoverer, Langley's ganglion. 



The sympathetic branches to these two glands are derived from 

 the plexus around the facial artery, and accompany the arteries 

 which supply the glands. 



Section of the nerves produces no immediate result ; but after 

 a few days an abundant secretion of thin watery saliva takes 

 place ; this is called paralytic secretion, and is produced either by 

 the activity of the local nervous mechanism, which is then uncon- 

 trolled by impulses from the central nervous system ; or else, 

 it is a degenerative effect analogous to the fibrillar contractions 



* Though the chorda tympani is usually spoken of as a branch of the 

 seventh or facial nerve, it is probable that its fibres are derived from the 

 glosso-pharyngeal, which communicates with the facial in the tympanum. 



