ADDENDUM. 



545 



is propagated from cathode or anode as the case may be, at a rate of 

 from 10 to 15 metres per second. As explanatory of the result of 

 his very extended series of experiments, he gives the following 

 diagram. 



\J 



// 



Fig. 24. 



In the diagram, S on the time axis expresses the duration of 

 the closure of the polarising current, which in most of the experi- 

 ments was about T o"- When the distance between the intrapolar 

 tract and the leading off electrodes (which were applied respectively 

 to the natural and end surfaces of the nerve) was about 15 millims. 

 the electrotonic effect began between T fo/' and xlV after the 

 closure of the polarising current, the interval of time being always 

 approximately proportional to the distance. When the current was 

 so directed that the cathode was next the leading off electrodes, the 

 excitatory wave due to the excitation at the cathode was strong 

 enough to reverse the previous negativity of the end surface of 

 the nerve, as shown in the diagram, where the difference of 

 potential between the two leading off contacts is indicated by the 

 distance S y, and the excitatory variation by the loop n g a. The 

 cathelectrotonic effect which is of course in the same direction as the 

 variation, does not begin until the latter has entirely ceased, as 

 indicated by the line k t e. When the anode was next the leading 

 off electrodes, there was also a feeble excitatory effect due to the 

 same cause as before, but in this case its sign was opposed to that of 

 the relatively much stronger anelectrotonic current a t r e. In both 



