NEKVOUS SYSTEM. 



the ordinary motor nerves of the cerebro-spinal system. 

 Most of the observations made by dividing the nerves have 

 been upon dogs, and the differences in the effects upon other 

 animals are slight and unimportant. The following are the 

 important phenomena presented in typical experiments : 



Section of one of the pneumogastrics in the neck does 

 not produce any very marked effect upon the action of the 

 heart, after the slight disturbance which usually follows the 

 operation has passed away. The number of pulsations is 

 slightly increased, and the cardiac pressure, as shown by a 

 cardiometer fixed in the carotid artery, is slightly dimin- 

 ished ; but this is insignificant compared with the effects of 

 dividing both nerves. 



Section of both pneumogastrics usually produces imme- 

 diate and serious disturbance in the respirations, which are 

 momentarily accelerated. The animal usually becomes agi- 

 tated and suffers from want of air ; and, when it is desired 

 especially to note the cardiac disturbance, it is often neceS' 

 sary to relieve the respiration by introducing a tube into the 

 trachea. In full-grown dogs, however, the respirations soon 

 become calm, but are diminished in frequency, and are un- 

 usually profound. "When the animal is in this condition, 

 the beats of the heart are very much increased in frequency. 

 at least doubled ; but they are inefficient and tremulous. 



An interesting point in this connection is the want of in- 

 fluence of certain medicinal substances over the action of the 

 heart in animals after division of the pneumogastrics. Traube 

 has shown that, while digitalis injected into the veins of a 

 dog was capable in an hour of reducing the pulse to about 

 one-fourth of the normal number of beats per minute, there 

 was no appreciable effect upon the circulation when the 

 injection was made in animals with both pneumogastrics 

 divided. 1 



The influence of the pneumogastrics upon the heart is 



1 TRAUBE, Versuche uber die WirTcung dcr Digitalis. Gesammelte Beitrage zur 

 Pathologic und Physiologic, Berlin, 1871, Bd. i., S. 190, et seg. 



