300 COMPARATIVE ELECTRO-PHYSIOLOGY 



skin as alone active, the inner being, to his thinking, in- 

 effective. This particular result may possibly be accounted 

 for by supposing that he used a stimulus intensity which 

 was not sufficiently strong. In my own experiments I 

 obtained clear demonstration of the effectiveness of both 

 surfaces in opposite ways electrically, though the effect 

 obtained from the outer was undoubtedly the more intense 

 of the two. By comparing these two experiments, then, on 

 the grape skin and skin of frog, it will be seen that the 

 inference that the vegetable protoplasm reacts in any way 



Fie. 179. Electrical Response of Frog's Skin to Rotary Mechanical 

 Stimulation 



(a) A, positive response of outer ; B, negative response of inner ; (a') A 

 and B exhibit abolition of response in skin on boiling ; (b) c, current 

 of rest from outer to inner ; R, excitatory response from inner to outer, 

 being summated effect of positive response of outer and negative 

 response of inner. 



essentially different from that of the animal is quite unjus- 

 tified. How widely applicable is the method of mechanical 

 excitation by rotary stimulus will be seen in an attempt, 

 successfully carried out, to determine the very difficult ques- 

 tion of the characteristic response of the intact human skin. 

 This will be seen in the following record of the results 

 obtained with the skin of a forefinger. The responsive elec- 

 trical changes represented by the down records, exhibit induced 

 galvanometric positivity of the excited surface (fig. 180;. 



I shall next describe the results obtained by simultaneous 

 excitation of the inner and outer surfaces of grape-skin. 

 The responses now given, under stimulation by thermal 





