CH. xxx.] SECRETORY NERVES. 475 



which occur in degenerating muscles after severance of their 

 nerves. If the operation is performed on one side, the glands 

 of the opposite side also show a similar condition, and the thin 

 saliva secreted there is called the antilytic secretion. 



Stimulation of the peripheral end of the divided chorda 

 tympani produces an abundant secretion of saliva, which is 

 accompanied by vaso-dilatation (see p. 308). 



Stimulation of the peripheral end of the divided sympathetic 

 causes a scanty secretion of thick viscid saliva, accompanied by 

 vaso-constrictiou. 



The abundant secretion of saliva, which follows stimulation of 

 the chorda tympani, is not merely the result of a filtration of fluid 

 from the blood-vessels, in consequence of the largely increased 

 circulation through them. This is proved by the fact that, when 

 the main duct is obstructed, the pressure within it may consider- 

 ably exceed the blood pressure in the arteries,* and also that when 

 into the veins of the animal experimented upon, some atropine has 

 been previously injected, stimulation of the peripheral end of the 

 divided chorda produces all the vascular effects as before, without 

 any secretion of saliva accompanying them. Again, if an animal's 

 head is cut off, and the chorda be rapidly exposed and stimulated 

 with an interrupted current, a secretion of saliva ensues for a 

 short time, although the blood flow is necessarily absent. 

 These experiments serve to prove that the chorda contains two 

 sets of nerve fibres, one set (vaso-dilatator) which, when stimu- 

 lated, cause the vessels to dilate ; while another set, which are 

 paralysed by atropine, directly stimulate the cells themselves to 

 activity, whereby they secrete and discharge the constituents of 

 the saliva which they produce. On the other hand, the sym- 

 pathetic fibres are also of two kinds, vaso-constrictor and 

 secretory, the latter being paralysed by atropine. The chorda 

 tympani nerve is, however, the principal nerve through which 

 efferent impulses proceed from the central nervous system to 

 excite the secretion of these glands. 



The function of the ganglia has been made out by Langley by 

 the nicotine method (see p. 301). At one time the submaxillary 

 ganglion was supposed to be the seat of reflex action for the 

 secretion. This, however, is not the case. The ganglia are cell- 

 stations on the course of the fibres to the submaxillary and 



* The student should not fall into the error of supposing that the saliva 

 is normally secreted, at such high pressure. If it were so the saliva would 

 spnrt from the salivary <luct with greater force than the blood would spurt 

 from the arteries when they are cut. The high pressure alluded to in the 

 text only occurs when the duct is obstructed. 



