i68 TEXT-BOOK OF PHYSIOLOGY. 



From this ganglion new nerve-fibers arise, the terminal branches of 

 which become connected with the secretory cells of the gland. 



The effects on the secretion and flow of saliva from the submaxil- 

 lary gland which follow division and stimulation of the chorda tym- 

 pani nerve are shown in the following way : a cannula is inserted into 

 Wharton's duct and the rate of flow estimated; the nerve is then 

 divided, after which the flow ceases. The peripheral end of the 

 nerve is then stimulated with the induced electric current, when a 

 copious secretion of a thin saliva takes place, accompanied by a 

 marked dilatation of the blood-vessels of the gland. The quantity of 

 blood passing through the vessels is so great as to give to the venous 

 blood an arterial hue and to the small veins a distinct pulsation. It 

 would appear from these effects that the chorda contains two sets of 

 fibers, one of which inhibits the action of a local vaso-motor mechan- 

 ism permitting the blood-vessels to dilate (vaso- dilator fibers), the 

 other of which stimulates the secretory cells to activity, either directly 

 or through the intermediation of local ganglia. That local ganglia 

 are involved is shown by the effects which follow the injection 

 of nicotin into the circulation. After a sufficient dose 10 milli- 

 grams for the cat stimulation of the chorda has no effect. Stimu- 

 lation of the nerve-plexus beyond the ganglion, however, is at once 

 followed by vascular dilatation and secretion. 



It might be inferred that the increase in the flow of saliva is due 

 to filtration, the result of the increased blood-supply to the gland, and 

 not to the influence of any true secretory fibers stimulating the 

 activities of the secretory cells. That this is not the case, however, 

 can be demonstrated in several ways: First, the pressure in the duct 

 of the submaxillary gland, as shown by the mercurial manometer, 

 rises, when the gland is secreting, considerably above the pressure in 

 the carotid artery, which could not be the case if it were due to a mere 

 filtration ; for if pressure alone were the cause, the flow of saliva would 

 cease as soon as the pressure in the tube equaled the pressure in the 

 blood-vessels. Second, even in the absence of blood the gland can 

 be made to yield a secretion, as shown by stimulating the nerve in a 

 recently killed animal. Third, after the injection of atropin into the 

 circulation the secretion is abolished, but the local vasomotor mechan- 

 ism is unimpaired, for stimulation of the nerve, as in the previous 

 instance, gives rise to a dilatation of the vessels and an increased 

 blood-supply. There is thus abundant proof that the chorda tym- 

 pani contains two sets of fibers one regulating the blood-supply to 

 the gland, the other stimulating the secretory cells. 



The influence of the auriculo-temporal branch of the fifth nerve 

 upon the parotid gland is similar to the action of the chorda tympani 

 on the submaxillary gland. The active fibers of this nerve are prob- 

 ably derived from the ninth nerve or glossopharyngeal. If the nerve 



