ACTION OF ELECTRICITY UTON THE NERVES. 107 



application of electricity to an exposed nerve are the action 

 of constant currents of different degrees of intensity, the 

 phenomena observed on making and breaking the circuit, 

 and the effects of an interrupted current. 



During the passage of a feeble constant current through 

 an exposed nerve, whatever be its direction, there are no 

 convulsive movements and no evidences of pain. This fact 

 has long been recognized by physiologists, who at first 

 limited the effects of electricity upon the nerves to two 

 periods, one at the making of the circuit and the other at its 

 interruption. We shall see, however, that the passage of 

 electricity through a portion of a nervous trunk produces a 

 peculiar condition in parts of the nerve not included between 

 the poles of the battery, described by Du Bois-Reymond 

 under the name of electrotonus ; but the fact that neither 

 motion nor sensation is excited in a mixed nerve .during the 

 actual passage of a feeble constant current is not invalidated. 



If a sufficiently powerful constant current be passed 

 through a nerve, disorganization of its tissue takes place, and 

 the nerve finally loses its excitability, as it does when 

 bruised, ligatured, or when its structure is destroyed in any 

 other way. 1 It was thought by Galvani, and the idea has 

 been adopted by Matteucci, Guerard, and Longet, 9 that a 

 current directed exactly across a nerve, so as to pass at right 

 angles to its fibres, does not give rise to muscular contrac- 

 tion ; but it is doubtful whether this can be accepted as a 

 demonstrated fact. Chauveau has found that a transverse 

 current passed through the exposed facial nerve of a horse 

 produces well-marked muscular action. He is of the opinion 

 that the experiments of Galvani and his followers, made upon 

 frogs, are faulty, inasmuch as the nerve is so small that but 

 little if any of the galvanic current passes through its sub- 

 stance, being conducted from one pole to the other through 



1 BERNARD, Lerons sur la physiologic et la pathologie dusysteme nerveux, Paris, 

 1858, tome i.,p. 162. 



8 LOXGET, Traile de physiologic, Paris, 1869, tome iii., p. 193. 



