INFLUENCE OF THE NERVOUS SYSTEM ON THE HEART. 61 



been ascertained that galvanization of the extremities connected with the heart arrests 

 its action, while galvanization of the central extremities has no such effect. Another 

 interesting fact also shows that the influence exerted upon the heart is through the motor 

 filaments of the pneumogastrics. It has been demonstrated by Bernard, in a very curious 

 series of experiments which we shall not fully discuss in this connection, that the woorara 

 poison paralyzes only the motor nerves, leaving the sensory nerves intact. If we expose 

 the heart and the pneumogastric nerves in a warm-blooded animal poisoned with this agent, 

 and continue the pulsations by keeping up artificial respiration, we find that the most 

 powerful current of galvanism passed through the pneumogastrics has no effect upon the 

 heart. 



When we come to the study of the nervous system, we shall see that the inhibitory 

 action of the pneumogastrics upon the heart is derived from the spinal accessory nerves, 

 a fact which has been proven beyond question by a very ingenious series of experiments, 

 which will be fully described hereafter. 



Although galvanization of the pneumogastrics arrests the action of the heart in nearly 

 all animals, there are some in which this does not take place, as in birds ; a fact which is 

 stated by Bernard, but for which he offers no explanation. In some experiments insti- 

 tuted on this subject a few years ago on alligators, we noticed a singular peculiarity which 

 throws some light on the question we are now considering. Desiring to demonstrate to 

 the class at the New Orleans School of Medicine the action of the heart in this animal, 

 an alligator six feet in length was poisoned with woorara and the heart exposed. The 

 animal came under the influence of the poison in about thirty minutes, when the dissec- 

 tion was commenced, and was quite dead when the heart was exposed. The pneumogas- 

 trics were then exposed and galvanized, with the effect of promptly arresting the action 

 of the heart. This observation was verified in another experiment. We were at first at a 

 loss to account for the absence of effect of the woorara on the motor filaments of the 

 pneumogastric nerves ; but on reflection we thought it might be due to slow absorption of 

 the poison in so large a cold-blooded animal. With a view of ascertaining whether there 

 be any difference in the promptness with which different nerves in the body are affected 

 by this agent, we made the following experiment upon a dog : The animal was brought 

 under the influence of ether, and the heart, the pneumogastrics, and the sciatic nerve 

 were exposed. Galvanization of the sciatic produced muscular contraction, and stimula- 

 tion of the pneumogastrics arrested the heart promptly. A grain of woorara, dissolved in 

 water, was then injected under the skin of the thigh. One hour after the injection of 

 the woorara, the sciatic was found insensible to galvanism, but the heart could be ar- 

 rested by galvanization of the pneumogastrics, although it required a powerful current. 

 A weaker current diminished the frequency and increased the force of its pulsations. 

 In this experiment, the operation of opening the chest undoubtedly diminished the ac- 

 tivity of absorption of the poison and consequently retarded its effects upon the nervous 

 system. Taken in connection with the observations on alligators, it shows that the motor 

 nerves are not all affected at the same time, and that the pneumogastrics resist the action 

 of this peculiar poison after the motor nerves generally are paralyzed. 



Our knowledge of the inherent properties of the muscular fibres of the heart and of 

 the effects of the passage of blood through its cavities, which together are competent to 

 keep up for a time regular pulsations without the intervention of the nervous system, 

 taken in connection with the facts just stated concerning the influence of section or gal- 

 vanization of the pneumogastric nerves, enables us to comprehend pretty well the influ- 

 ence of these nerves on the heart. They undoubtedly perform the important function 

 of regulating the force and frequency of its pulsations. Hardly any reflection is necessary 

 to convince us of the importance of such a function, and how it must of necessity be 

 accomplished through the pneumogastrics. It is important, of course, that the heart 

 should act at all times with nearly the same force and frequency. We have seen that 

 the inherent properties of its fibres are competent to make it contract, and the necessary 



