DIGESTION. 



one of which inhibits the action of a local vaso-motor mechanism permitting 

 the blood-vessels to dilate (vaso-dilatator fibers), the other of which stimu- 

 lates the secretor cells to activity, 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. Stimulation of 

 the nerve-plexus beyond the ganglion, the postganglionic fibers, however, is 

 at once followed by vascular dilatation and secretion, a fact that would 

 indicate that the ganglia are not only stimulated by the chorda tympani but 

 that the conductivity of the nerve endings of the chorda around the ganglia 

 is impaired. 



GlossoJ*/iarynaeal^\ \ / Vf 



/), .> , "l^fe^ 



Utic vanrjl.i 



Parotid Gland, 

 Jaco&sens ^lerut 



Sul-Maxillary Ganqlion_ ~* 



SiibMaxilla.ry Git 



Chorda, Jympanillfertte, 



Sup.Cervical Ganglion 



erces 



FIG. 67. SCHEME OF THE NERVES INVOLVED IN THE SECRETION OF SALIVA. 



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

 tion, ;the result of the increased blood-supply to the gland, and not to the 

 influence of any true secretor fibers stimulating the activities of the secretor 

 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 vaso-motor mechanism is unimpaired, 

 for stimulation of the nerve, as in the previous instance, gives rise to a dilatation 



