128 PHYSIOLOGY OF MUSCLES AND NERVES. 



passes from d to c, the influence of the irritant seems, 

 on the contrary, to increase in a h when the current is 

 closed, and to resume its original strength when the 

 current is interrupted. In this case, therefore, it ap- 

 pears that the action of the current tends to increase 

 the excitability. If the wires e f are next connected 

 with the secondary coil of the inductive apparatus, and 

 if the irritants are again applied in such a way that 

 weak but noticeable pulsations occur, these latter are 

 strengthened when the current in the portion c d passes 

 from c to d; and are, on the contrary, weakened when 

 the current is in the opposite direction. In these two 

 series of experiments the irritant was applied in one 

 case above, in the other case below, the constant cur- 

 rent. Both cases showed consistent results. As soon, 

 that is, as the irritant acted on the side of the positive 

 electrode or the anode, through which the current 

 entered the nerve, the excitability was in both cases 

 lowered. But when the irritant was applied on the 

 side of the negative electrode or the kathode, through 

 which the current emerged from the nerve, the irritant 

 being strengthened, the excitability increased. 



These changes in the excitability may be shown 

 throughout the whole length of the nerve ; but they 

 are strongest in the immediate neighbourhood of the 

 portion traversed by the constant current, gradually 

 decreasing upward and downward from the electrodes. 

 In order to find whether a change in the excitability 

 also occurs within the electrodes, the current must be 

 made to traverse a longer portion of the nerve, and the 

 irritant must then be applied to a point within the 

 electrodes. According to the point at which the elec- 

 trode is applied, various changes maybe shown to occur 



