INFLUENCE OF NERVES ON THE SUBMAXILLARY GLAND 351 



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). 



FIG. 250. Diagram showing the distribution of the cranial and sympathetic secretory 

 and vase-motor nerves for the parotid and submaxillary glands. The post-ganglionic 

 neurones are in black; the pre-ganglionic neurones including the central neurone of the 

 sympathetic path are in red. (Diagram based on figures by Sheldon, Brubaker, and 

 Starling.) 



The abundant secretion of saliva which follows stimulation of the chorda 

 tympani is not merely the result of a nitration 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 

 some atropine has been previously injected into the veins of the animal ex- 

 perimented upon 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 



