654 



NERVOUS SYSTEM. 



diac disturbance, it is often necessary to relieve the respiration by introducing a tube 

 into the trachea. In full-grown dogs, however, the respirations soon become calm, but 

 they are diminished in frequency and become unusually 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 influence 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. 



The influence of the pneumogastrics upon the heart is one of the most interesting 

 points in the physiology of the circulation ; but we can discuss the mechanism of the 

 phenomena following section of the nerves more satisfactorily after we have considered 

 the effects of their galvanization. 



Effects of Galvanizing the Pneumogastrics or their Branches upon the Circulation. 

 The experiments upon the effects of galvanization of the pneumogastrics in the neck on 

 the action of the heart are almost innumerable ; and, although the explanations of the 

 phenomena observed present the widest differences, the facts themselves are sufficiently 



simple. These facts will be discussed under the 

 following heads : 1. The direct influence of galvan- 

 ization of the nerves in the neck, undivided, or of 

 galvanization of the peripheral extremities of the 

 trunks after division. 2. Reflex phenomena follow- 

 ing galvanization of the central ends of the pneu- 

 mogastrics, after their division. 



Direct Influence of tfie Pneumogastrics upon 

 the Heart. In 1846, the brothers Weber noted 

 the important fact, that galvanization of the pneu- 

 mogastrics in the neck rendered the action of 

 the heart slow, and, if the galvanization were suffi- 

 ciently powerful, arrested the heart, which remained 

 flaccid and in diastole for a certain time while the 

 galvanization was continued. This fact has since 

 been confirmed by numerous experimenters. 



While there is no difference of opinion among 

 physiologists with regard to the stoppage of the 

 heart by powerful galvanization, it is stated by 

 some that a very feeble current passed through the 

 peripheral ends of the divided nerves quickens the 

 heart's action ; but it is admitted by all that it is 

 very difficult to regulate the intensity of the current 

 so as to produce this effect. After section of the 

 nerves, the action of the heart is very readily modi- 

 fied by struggles, etc., on the part of the animal 

 under observation ; and, in view of the exceeding 

 FIG. 220. Branches of the pneumogastric to nicety of the reported experiments, it cannot be 

 C, heart ; a, carofld artw^Sng to the brain ; admitted taat tne heart is capable of being excited 

 &<?hSrt es f the pncumo ^ stric in s t{ > to increased rapidity of action, without observations 



of the most positive character. Such facts are 



wanting ; and, farthermore, it has been shown by Dr. Rutherford, in a series of exceed- 

 ingly exact and satisfactory experiments, that whenever a galvanic current passed 

 through the pneumogastrics has any appreciable effect upon the action of the heart, 



