NERVE MECHANISM OF SALIVARY SECRETION. 143 



It has been found that section of this nerve, -or of the portio 

 dura near its origin, removes the possibility of exciting the glands 

 to action by stimulating the mouth, so that the cerebro-spinal and 

 not the sympathetic are the channels traversed by the reflected 

 impulse on its way to the gland from its centre. 



The reflex stimuli which were supposed to be elicited through 

 the medium of the sub-maxillary ganglion, probably depended 

 on the escape of the stimulating electric current used, and the 

 reflection from a sporadic ganglion, such as the sub-maxillary, has 

 never been satisfactorily demonstrated. 



It has further been shown that direct stimulation of the chorda 

 tympani nerve, although it be cut off from its central connections, 

 causes a copious secretion of thin, watery saliva, and this increased 

 secretion is accompanied by a great dilatation of the small arte- 

 ries going to the gland, so that a pulsation may be seen in the 

 small veins, and the blood retains its bright arterial color when 

 leaving the organ. 



These two chief results of stimulation, activity of the secreting 

 cells and vascular dilatation, are brought about by different nerve 

 agencies, as appears from the action of atropia which stops the 

 secretion of saliva, but does not prevent the dilatation of the 

 vessels on stimulation of the chorda tympani, from which we 

 conclude that its effect is restricted to a mechanism engaged 

 exclusively in controlling the activity of the gland cells. 



Stimulation of the chorda tympani causes the secretion to be 

 carried on with great energy. The fluid was found to enter the 

 duct with a pressure equal to 200 m.m. (about 8 inches) of mer- 

 cury, while the blood pressure in the carotid artery of the animal 

 was only 112 m.m. (about 4 inches) mercury ; that is to say, the 

 force by means of which secretion is driven outward is nearly 

 twice as great as the pressure in the blood vessels in the gland. 

 The secretion of saliva cannot then be a question of mere filtra- 

 tion, for if the physical agency pressure alone were acting, 

 the saliva would be forced into the blood vessels as soon as the 

 pressure in the duct exceeded that in the vessels. 



The force and rate with which the secretion is produced vary 

 with the strength of the stimulation. The flow of saliva steadily 



