530 COMPARATIVE ELECTRO-PHYSIOLOGY 



isolation, its conductivity was below par, and the responses 

 obtained were positive. After a series of stimulations, 

 however, the true excitatory wave was transmitted, with the 

 concomitant negative or contractile responses. In order to 

 demonstrate the effect of fatigue on conductivity, the 

 recording of this series was commenced only after many 

 normal responses had already been given. In the series 

 recorded we can see that the responses at first exhibit 

 periodic fatigue. The accentuation of fatigue is then mani- 

 fested by a rapid decline in the amplitude of the responses. 

 A remarkable change next begins to appear. It has been 



FIG. 325. Record, obtained on Smoked Glass, 01 Transmitted Effect 

 of Stimulation on Nerve of Gecko 



Note here the progressive effect of fatigue, seen first as periodic fatigue ; 

 second as diphasic effect ; and third as reversal into abnormal positive. 



shown that the true excitatory negative response contains a 

 masked positive element. Owing now to growing fatigue, the 

 exhibition of the negative is delayed, and the positive thus 

 shows itself as a preliminary down-curve in a diphasic response. 

 Afterwards, the excitatory negative is completely abolished, 

 and the positive response by expansion alone remains, as 

 seen in the last of the series. Ultimately, when the nerve is 

 killed, by excessive stimulation, even the positive response 

 disappears. 



We may notice here the interesting fact that nerve, which 

 is regarded as a conductor, par excellence^ will sometimes 



