/6 THE PHYSIOLOGY OF DIGESTION AND ABSORPTION 



maxillary and sublingual glands by stimulation of the chorda 

 tympani and the sympathetic fibers. 



It would seem at first, in the light of the vascular changes 

 accompanying stimulation of the two supplies to all these 

 glands, that the resultant phenomena could be explained en- 

 tirely by variations in the amount of blood, and that the ner- 

 vous system influences their secretion only by contraction and 

 dilatation of the vessels. However, a number of circum- 

 stances, which it is unnecessary to relate here, prove that the 

 secretory fibers exert an influence directly upon the cells 

 themselves, causing them to secrete. The mere distribution 

 of these fibers to the gland cells presupposes some such func- 

 tion on their part ; and it can actually be shown that the se- 

 cretion can be increased when the blood supply is cut off, or 

 without dilatation of the vessels. Such action, however, is 

 of course only temporary, for the materials for secretion 

 must be supplied by the blood. The exact method of ter- 

 mination of the secretory fibers has not been determined. 

 It is probable that they end between and around the cells and 

 do not penetrate their substance. 



Section of the chorda tympani causes a continuous flow 

 of saliva from the submaxillary and sublingual glands for 

 several weeks. This has been termed paralytic secretion, 

 and is supposed to be due to the fact that the chorda fibers 

 do not themselves run directly to the glands, but are distrib- 

 uted to sympathetic ganglia (the submaxillary or others in 

 the gland substance). Section of the chorda, then, causes 

 degeneration of its fibers only as far as these ganglia, and 

 their cells are thought to be subject, in some obscure way, to 

 continuous irritation (luring the period for which the para- 

 lytic secretion continues. 



Function. The function of this secretion is twofold, (a) 

 mechanical, and (b) chemical. 



(a) From a mechanical standpoint (i) it facilitates pho- 

 nation, mastication and gustation by maintaining a proper 

 degree of moisture in the mouth; (2) its more watery parts 



