58 A CHEMICAL SIGN OF LIFE 



this region, assuming, of course, that the same strength 

 of current when stimulating in or above the narcotized 

 part is made use of. Since we have no evidence that the 

 resistance of the surrounding sheath of the fiber and 

 that of the conducting medium are the same, we cannot 

 assume that in both experiments the same strength 

 of stimulus was really applied to the conducting portion. 

 The non-transmissibility of the inhibitory state is 

 regarded as another distinction between excitation and 

 conduction. We can abolish excitability at one point 

 without making its neighboring region inexci table. It 

 is rather difficult to consider an analogy between depres- 

 sion and excitation, but the fact is that even if we may 

 not be able to make other than one point inexcitable 

 by one depressing agent, it is doubtful whether we can 

 produce local inexcitability without affecting the con- 

 tiguous parts of the nerve. Waller has demonstrated, 

 in the case of inhibition by heat, that the point of 

 application of gentle heat became electropositive to the 

 rest of the nerve instead of negative, as is the case in 

 ordinary stimulation. According to him, heat does not 

 stimulate the tissue, but depresses it. If this is the 

 case, as he seems to have demonstrated in a variety of 

 tissues, it indicates that although we cannot produce 

 depression at points other than the point of application, 

 yet certain conditions along the nerve must surely be 

 altered through such an inhibition. In any event, we 

 cannot consider non-conductivity of the inhibitory state 

 as evidence that excitability and conductivity are 

 entirely different processes. 



Let us now consider in detail the relation between 

 excitation and conduction. 



