332 



FOOD AND DIGESTION 



The veins may even pulsate, and the blood contained within them is more 

 arterial than venous in character. 



When, on the other hand, the stimulus is applied to the sympathetic fila- 

 ments (mere division producing no apparent effect), the arteries contract, 

 and the blood stream is in consequence much diminished; and only a sluggish 

 stream of dark blood escapes from the veins. The saliva, instead of being 

 abundant and watery, becomes scanty and tenacious. If both chorda tym- 

 pani and sympathetic branches be divided, the gland, released from nervous 

 control, may secrete continuously and abundantly (paralytic secretion). 



.ortx 



FIG. 250. Showing the distribution of the divisions of the fifth, seventh, and ninth cranial. 



(Sheldon.) 



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 

 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 previ- 

 ously injected, stimulation of the peripheral end of the divided chorda pro- 

 duces all the vascular effects as before, without any secretion of saliva accom- 

 panying them. Again, if an animal's head be cut off, and the chorda be 

 rapidly exposed and stimulated with an interrupted current, a secretion of 



