294 COMPARATIVE ELECTRO-PHYSIOLOGY 



tissue with boiling water, when these electro-motive variations 

 were found to disappear. How very reliable these responses 

 can be rendered is shown by the photographic record in 

 fig. 1 80, which is of very special interest, giving as it does the 

 record of responses afforded by the intact human skin. 



Turning now to the nature of the response of the skin, 

 it has been found by Engelmann and others, as already said, 

 that in the frog, while the natural resting current is from the 

 outer surface to the inner, the responsive current is from 

 inner to outer. Dr. Waller, again, undertook to analyse the 

 constituent elements of this response, by passing induction 

 shocks along each of the surfaces, first upper and then lower, 

 and in both directions. He then observed the after-effect 

 at one of the excited points, in relation to an indifferent 

 point. In this way he found that an excited point on the 

 upper surface becomes galvanometrically positive, the current 

 being thus outgoing. The inner surface, however, he found 

 to be ineffective. When an induction shock is passed across 

 the tissue, the resultant response from lower to upper is thus, 

 according to Dr. Waller, due to induced positivity of the 

 upper surface. 



With vegetable specimens, however, such as the outer 

 skin of apple, the results obtained by him were opposite to 

 those of the frog's skin. The responsive currents were here 

 found to be ingoing, the excited point being galvanometrically 

 negative. The explanation offered, in regard to these results, 

 is that living tissues have the peculiarity of responding by 

 ' blaze currents ' to electrical shocks. The use of this phrase, 

 however, as already said, offers no real explanation ; but even 

 apart from this point, the question remains, Why should the 

 blaze currents, so called, be directly opposed in the cases of 

 frog's skin and of the particular vegetable skins which are 

 mentioned, respectively ? In answer to this, the hypothesis 

 put forward by Dr. Waller is, that the difference arises from 

 the different natures of animal and vegetable protoplasms. 1 



1 ' Vegetable protoplasm is in major degree an instrument of synthesis and 

 accumulation, in minor degree the seat of analysis and emission. Animal 



