Currents on Transmission of Excitation. 



497 



Part II. — Influence of Direction of Electric Current on Conduction 

 of Excitation in Animal Nerve. 

 I shall now take up the question whether an electrical current induced 

 any selective variation of conductivity in the animal nerve, similar to that 

 induced in the conducting tissue of the plant. 



1. The Method oj Experiment. 



In the experiments which I am about to describe, arrangements were 

 specially made so that (1) the excitation had not to traverse the polar 

 region, and (2) the point of stimulation was at a relatively great distance 

 from either pole. The fulfilment of the latter condition ensured the point 

 of stimulation being placed at the neutral region. 



In the choice of experimental specimens I was fortunate enough to secure 

 frogs of unusually large size, locally known as "golden frogs" (Rana 

 tigrina). A preparation was made of the spine, the attached nerve, the 

 muscle and the tendon. The polarising electrodes were applied at the 

 extreme ends, on the spine and on the tendon (fig. 6). The following are 

 the measurements, in a typical case, of the different parts of the preparation. 



Fig. 6. — Experimental arrangement for study of variation of conductivity of nerve by 

 the directive action of an electric current, n n', nerve ; S, point of application of 

 stimulus in the middle or indifferent region. 



