RESPONSE BY POSITIVE VARIATION 165 



found that the so-called ' current of injury ' had in this case, 

 owing to some hitherto unknown cause, undergone a reversal, 

 and was now from the living to the dead, the latter being 

 galvanometrically positive to the former, to the extent of 

 08 volt. The abnormality of the response lay, then, in this 

 fact, that the current of reference had become reversed, and 

 that the responsive current, due to excitation, was now con- 

 cordant with it, instead of antagonistic, thus constituting a 

 positive variation (fig. 112). Later 

 on, I discovered many instances in 

 which the killed end was positive 

 to the unkilled. Since, then, it is 

 possible for the current of reference 

 itself to undergo such obscure and 

 spontaneous reversals, from un- 

 known causes, it is easy to see 

 how uncertain the study of re- 

 sponsive phenomena must become, 

 if we are to depend upon the 

 negative variation as our only FIG. 112. Response by Positive 

 reliable means for their investiga- Variation of Resting Current 

 tion. I next, therefore, turned my The current of injury, shown by 



9 ^ , had in this case become 



attention towards an inquiry into reversed, the killed end having 

 the causes of these anomalous become ga.vanometrical.yposi- 



reversals. 



The subject therefore resolved itself into an investigation 

 as to what conditions determined the negativity or positivity 

 of a tissue at the onset of death. My first attempt, then, was 

 to study a case in which the approach of death was natural, 

 and not the result of any sudden or violent change, such as 

 might conceivably give rise to abnormal reactions. And in 

 my search for suitable specimens, I noticed that often, owing 

 to local mal-nutrition or other causes, the leaves of plants 

 exhibited spots or areas, from which, as centres, death pro- 

 ceeded in constantly widening circles. Thus, in the leaves 

 of Colocasia, for example, we find such dead and dying areas 

 in otherwise fairly healthy leaves. The innermost of these 



