THE REGULATION OF SALIVARY SECRETION. 185 



the periphery into the medulla, and from here over the various 

 nerves to the salivary glands. Most of the peripheral stimuli 

 which call forth a secretion of saliva originate, no doubt, 

 in the mouth. When food is taken into the mouth, it acts 

 upon the gustatory nerve and the glosso-pharyngeal, and 

 these constitute the afferent nerves over which impulses 

 reach the medulla. But many other afferent nerves exist 

 which can bring about a flow of saliva. When the sight of 

 food is effective in this direction, the impulses travel over 

 the optic nerves into the large nuclei at the base of the brain, 

 from where, apparently, connection is made with the medulla. 

 When smell causes a reflex secretion of saliva, the impulses 

 must reach the uncinate gyrus and from here connect with 

 the medulla. Of interest is the great flow of saliva which 

 accompanies feelings of nausea. In certain cases we deal 

 apparently with a stimulation of the endings of the vagus 

 nerve over which impulses travel into the medulla. In 

 others the agencies effective in bringing about the feeling 

 of nausea (as in sea-sickness) may influence the medulla, 

 in part at least, directly. The medulla from which the nerve 

 fibres supplying the salivary glands arise is intimately con- 

 nected with the cerebral cortex. For this reason the mere 

 thought of pleasant or unpleasant things may cause a flow 

 of saliva. As experimental evidence of such a connection we 

 have the well-known fact that stimulation of certain portions 

 of the cerebral cortex causes a free flow of saliva. 



We have thus far limited ourselves to a discussion of the 

 three great pairs of salivary glands. The many small glands 

 scattered throughout the mucous membrane lining the oral 

 cavity give off no inconsiderable secretion as their contri- 

 bution to the ordinary mixed saliva found in the mouth 

 and poured out upon the food. We have little accurate 

 knowledge, however, regarding the means by which the 

 secretion from these small glands is ordinarily controlled. 

 Apparently they are more or less independent of the cen- 

 tral nervous system, for when the ducts of all the large 



