134 MANUAL OF PHYSIOLOGY. 



The cerebro-spinal parotid branches pass through the lesser 

 superficial petrosal nerve from the tympanic plexus to the otic 

 ganglion, and thence to the auriculo-temporal nerve which sends 

 twigs to the gland. (Fig. 65.) 



I. The effects of experimental stimulation of the cerebro-spinal 

 glandular branches, so far as we know are alike for all the glands. 

 But owing to the greater facility with which the submaxillary 

 gland can be reached and its nerve isolated, research has been 

 chiefly devoted to it, by operating on the chorda tympani and 

 the other nerves supplying the gland. 



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 submaxillary ganglion, probably depended 

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

 reflection from a sporadic ganglion, such as the submaxillary, 

 has never been satisfactorily demonstrated. 



It has further been shown that direct stimulation of the chorda 

 tympaui 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 \ve 

 conclude that its effect is restricted to a mechanism engaged ex- 

 clusively in controlling the activity of the gland cells. 



Stimulation of the chorda tympaui 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- 



