228 NERVOUS SYSTEM. 



pneumogastrics ; but it has been conclusively demonstrated 

 that they -are really derived from the spinal accessories, the 

 upper filaments of origin of which are situated just below 

 the roots of the pneumogastrics. 



The action of the spinal accessories upon the heart has 

 already been considered. 1 The connection between these 

 nerves and their influence over the heart may be briefly 

 repeated, as follows : 



It has been shown that powerful galvanization of one 

 pneumogastric will arrest the heart's action. "Waller, after 

 extirpating the spinal accessory nerve upon one side, found 

 that galvanization of the pneumogastric upon that side had 

 no effect upon the heart, provided that from ten to twelve 

 days had elapsed after extirpation of the spinal accessory, 

 a sufficient time to secure disorganization and loss of irrita- 

 bility of its fibres. These experiments show conclusively 

 that the motor filaments contained in the pneumogastric, 

 which act directly upon the heart, are derived exclusively 

 from the communicating branch of the spinal accessory. 



Reflex Influence, through the Pneumogastrics^ upon tlie 

 Circulation. Galvanization of the central ends of the pneu- 

 mogastrics, after their division in the neck, does not influ- 

 ence the action of the heart, except as the pulsations are 

 affected by the modifications in respiration. In experiments 

 made upon this point by Bernard, the difference in the ef- 

 fects of galvanization of the central and the peripheral ends 

 was distinctly noted. When the central ends were stimu- 

 lated in dogs, the pupils became dilated, the eyes protruded, 

 sometimes vomiting occurred, and always the number of 

 respiratory acts was diminished, and, with a powerful cur- 

 rent, were arrested in inspiration ; but the pulsations of the 

 heart were not affected. 3 



1 See p. 204. 



2 BERNARD, Systems nerveux, Paris, 1858, tome ii., p. 382, et seq. 



The arrest of respiration, particularly the action of the diaphnagm, was first 



