894: OF NERVOUS IRK1TABILTTY 



nervous connection hanging between. (Fig. 134.) If the positive 

 pole, a. of the battery be now placed in the vessel which holds leg 

 No. 1, and the negative pole, b, in that containing leg No. 2, it will 

 be seen that the galvanic current will traverse the two legs in op- 

 posite directions. In No. 1, it will pass in a direction contrary to 

 the course of its nervous fibres, that is, it will be for this leg an 



Fig. 134. 



inverse current ; while in No. 2 it will pass in the same direction 

 with that of the nervous fibres, that is, it will be for this leg a direct 

 current. It will now be found that at the moment when the cir- 

 cuit is completed, a contraction takes place in No. 2 by the direct 

 current, while No. 1 remains at rest ; but at the time the circuit is 

 broken, a contraction is produced in No. 1 by the inverse current, 

 but no movement takes place in No. 2. A succession of alternate 

 contractions may thus be produced in the two legs by repeatedly 

 closing and opening the circuit. If the position of the poles, a, b, 

 be reversed, the effects of the current will be changed in a corre- 

 sponding manner. 



After a nerve has become exhausted by the direct current, it is 

 still sensitive to the inverse ; and after exhaustion by the inverse, 

 it is still sensitive to the direct. It has even been found by Mat- 

 teucci that after a nerve has been exhausted for the time by the direct 

 current, the return of its irritability is hastened by the subsequent 

 passage of the inverse current ; so that it will become again sensi- 

 tive to the direct current sooner than if allowed to remain at rest. 

 Nothing, accordingly, is so exciting to a nerve as the passage of 

 direct and inverse currents, alternating with each other in rapid 

 succession. Such a mode of applying the electric stimulus is that 



