538 COMPARATIVE ELECTRO-PHYSIOLOGY 



excitations, the indications of which were afforded by the 

 nerve-and-muscle preparation. 



The only perplexing feature of these responses was the 

 abnormally long period of ten to fifteen seconds which was 

 generally found to elapse between the application of the 

 strong stimulus to the plant nerve, and the response subse- 

 quently given by the terminal muscle. Here it must be 

 remembered that the excitation applied at one end of the 

 plant nerve has to travel the entire length before its excita- 

 tory electrical variation can be communicated to the nerve 

 of the frog-preparation. The transmitted excitatory varia- 

 tion in the primary has, moreover, to reach a certain intensity 

 before it can effectively excite the secondary preparation. We 

 know, further, that an isolated piece of nerve is liable to fall 

 into a sub-tonic or depressed condition, in which its conducting 

 power is much lowered, to be gradually restored again under 

 strong or long-continued stimulation. These considerations 

 will probably be found to account for the delay in the occur- 

 rence of the first of these responses. It would thus appear from 

 the last experiment that a nerve, when subjected to a single 

 strong stimulus, will give a multiple series of responses. In 

 order to test this by direct experiment I employed the highly 

 magnifying Kunchangraph, and subjected an experimental 

 nerve of frog to a single strong thermal stimulation. This 

 gave rise, at first, either to an abnormal positive response or 

 to a moderate negative. But there followed, after a longer or 

 shorter pause, a series of multiple contractile responses, which 

 generally grew in intensity for a considerable time. There 

 were in the series a number of short pauses, each followed by 

 a veritable storm of excitation, in which individual responses 

 were so rapid that the up or down movement of the spot of 

 light appeared as brief flashes, in which all distinctness was 

 obliterated. This experiment conclusively shows that the 

 nerve, like certain other tissues, is susceptible of multiple 

 excitation. 



If the nerve in a nerve-and-muscle preparation be 

 allowed to dry, the muscle is seen to be thrown into a series 



