CH. XXX.] SECltETOKY NEKVES 477 



others to the tongue. The main nerve enters the hilus of the sub- 

 maxillary gland, where it traverses a second ganglion concealed within 

 the substance of the gland, and which may be called after its dis- 

 coverer, Langley's ganglion. 



The sympathetic branches to these two glands are derived from the 

 plexus around the facial artery, and accompany the arteries which 

 supply the glands. 



Section of the nerves produces no immediate result ; but after a 

 few days an abundant secretio'n of thin watery saliva takes place; 

 this is called paralytic secretion, and is produced either by the activity 

 of the local nervous mechanism, which is then uncontrolled by impulses 

 from the central nervous system ; or else, it is a degenerative effect 

 analogous to the fibrillar contractions which occur in degenerating 

 muscles after severance of their nerves. If the operation is per- 

 formed 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. 306). Stimulation of the peripheral end of the 

 divided sympathetic causes a scanty secretion of thick viscid saliva, 

 accompanied by vaso-constriction. 



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 considerably 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- 

 dilator) which, when stimulated, 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 sympathetic fibres are also of two kinds, vaso-constrictor and 



* The student should not suppose that the saliva is normally secreted at 

 such high pressure. If it were so the saliva would spurt from the salivary duct 

 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, and indicates what enormous force the secreting cells can exercise. 



