286 On certain points, etc. [Nov. 27, 1882. 



cardiac muscle ; and it is of course possible to say, that in reality 

 the current acts by stimulating the endings of the vagus in the 

 muscle substance and not directly upon the muscle itself. Un- 

 fortunately in the case of the cardiac muscle this question cannot 

 be decided by the use of curare, yet for other reasons I am inclined 

 to think that both the interrupted current and the atropin pro- 

 duce the effects observed by direct action upon the muscle sub- 

 stance itself. The following consideration especially seems to 

 justify this view. 



If the interrupted current in reality stimulates vagus fibres, 

 then also the single induction shocks must stimulate those same 

 fibres, and therefore the series of single induction shocks ought 

 to produce the same effect upon the muscular strip, as a series of 

 single induction shocks applied to the vagus nerve would produce 

 upon the muscular tissue of the auricle or ventricle respectively. 

 Now single induction shocks applied every five seconds to the strip 

 from the auricle of the tortoise produce regular contractions, 

 which increase to their maximum height and then remain fairly 

 constant at that height; there is no sign of any diminution of 

 force such as is immediately manifested when the interrupted 

 current is sent through the strip. On the other hand, no better 

 stimulus can be desired for the vagus nerve than a series of 

 single induction shocks every five seconds ; the auricular contrac- 

 tions are immediately and very greatly reduced in force, and can 

 be kept small for a long time ; nay more, one single induction 

 shock applied to the vagus is sufficient to reduce most markedly 

 the next five or six auricular contractions. 



Seeing then that the vagus proves itself most sensitive to the 

 stimulus of a series of single induction shocks, while the strip of 

 muscle behaves either with indifference or in exactly the opposite 

 direction to the same kind of stimulation, it seems to me more 

 near the truth to say that the action of the vagus nerve resembles 

 that of a weak interrupted current applied to the muscle itself, 

 than to argue that the interrupted current produces the effect 

 observed because it stimulates vagus fibres in the strip of muscle 

 experimented on. If this view be correct, then the question natu- 

 rally arises, how is it that the vagus possesses only trophic functions 

 and not motor ones, for the interrupted current if strong enough 

 becomes motor in its action ? A question which leads the imagi- 

 nation to wonder whether the presence of ganglion cells in the 

 course of the nerve fibres may prove to be the reason why the 

 vagus is not a motor nerve. 



