232 CIRCULATION. 



writers have denied this fact, but it is confirmed by the testi- 

 mony of nearly all experimenters. To anticipate a little in 

 the history of the pneumogastric nerves, it may be stated that 

 while they are exclusively sensitive at their origin, they receive 

 after having emerged from the cranial cavity a number of 

 filaments from various motor nerves. That they influence 

 certain muscles, is shown by their paralysis after division of 

 the nerves in the neck; as, for example, the arrest of the 

 movements of the glottis. 



Having this double property of motion and sensation, and 

 being distributed in part to an organ composed almost exclu- 

 sively of muscular fibres, which, as we have seen, is not en- 

 dowed with general sensibility, we should expect that their 

 section would arrest, or at least diminish, the frequency of 

 the heart's action. What explanation, then, can we offer for 

 the fact that this seems actually to excite the movements 

 of the heart? We will be better prepared to answer this 

 question after we have studied the effects of galvanization of 

 the nerves in a living animal, or one in which the action of 

 the heart is kept up by artificial respiration. 



Numerous experiments have been made with reference to 

 the effects on the heart of galvanic currents, both feeble and 

 powerful, passed through the pneumogastrics before division, 

 of currents passed through the upper and lower extremities 

 after division, etc., a full detail of which belongs properly to 

 the physiological history of the nervous system. In this con- 

 nection, a few of these facts only need be stated. 



It has been shown by repeated experiments, which we 

 have frequently confirmed, that a moderately powerful cur- 

 rent of galvanism passed through both pneumogastrics will 

 arrest the action of the heart, and that the organ will cease 

 its contractions as long as the current is continued. This 

 experiment has been performed upon living animals, both 

 with and without exposure of the heart. The arrest is not 

 due to violent and continued contraction of the muscular 

 fibres ; on the contrary, the heart is relaxed, its ventricles are 



