110 NERVOTJS SYSTEM. 



that, with this arrangement, the current will pass through 

 both nerves, being direct for the one and inverse for the 

 other. In this case, if the irritability of the nerves be not 

 too intense, ther'e will be a contraction in the leg in which 

 tho current is direct at the time of making the circuit, while 

 the other leg will contract when the circuit is broken. 1 This 

 experiment has been modified by Chauveau, and applied to 

 the two facial nerves in a living horse. A Leyden jar is 

 very feebly charged with electricity, and the two facials are 

 exposed. The current is then passed instantaneously through 

 both the nerves, which gives but a single stimulus and that 

 corresponds to the time of making the circuit with the con- 

 stant current. In this experiment, the current is direc't for 

 one nerve and inverse for the other, and contraction takes 

 place only in those muscles supplied with the nerve for 

 which the current is direct. 3 



The muscular contraction produced by galvanic stimula- 

 tion of the nerve is more vigorous the greater the extent of 

 the nerve included between the poles of the battery. This 

 fact has long been observed, and its accuracy is easily veri- 

 fied. It would naturally be expected that the greater the 

 amount of stimulation the more marked would be the mus- 

 cular action ; and the stimulation seems to be increased in 

 proportion to the extent of nerve through which the gal- 

 vanic current is made to pass. 



The irritability of a nerve, it is well known, may be ex- 

 hausted by the repeated application of electricity, whatever 

 be the direction of the current, and is more or less com- 

 pletely restored by repose. It is a curious fact, in this con- 

 nection, that when the irritability of a nerve has been ex- 

 hausted for the direct current, it will respond to the inverse 

 current, and vice versa / and it is even more remarkable that 

 after the irritability has been exhausted by the direct cur- 



1 MATTEUCCI, Lemons sur les phenomena physiques des corps vivants, Paris, 

 1847, p. 233. 



8 CHAUVEAU, op. cit. Journal de la physiologic, Paris, 1860, tome iii., p. 67. 



