298 COMPARATIVE ELECTRO-PHYSIOLOGY 



response of each surface is displayed separately, without 

 either being affected by the other. There is here, moreover, 

 no complication due to the polarisation factor, inevitable 

 when uni-directioned induction shocks are employed for 

 excitation. Thus, after the individual responses of each 

 surface have been analysed, we are able to arrive at a definite 

 conclusion as to what would be the character of the resultant 

 response if both the surfaces were simultaneously excited. 

 This conclusion is then submitted to three other tests. Thus, 

 (2) the two surfaces of the specimen are subjected simul- 

 taneously to the same thermal shocks, according to the 

 method already described. Again, (3) the Method of 

 the After Effect under equi-alternating shocks is employed. 

 And, finally, (4) the Direct Effect of these equi-alternating 

 shocks of moderate intensity is recorded. The results 

 obtained by all these diverse methods are in complete 

 concordance with each other, and fully support the theo- 

 retical inferences which have already been made. 



I took the skin of a ripe muscatel grape, such as are 

 available in Calcutta. On making the galvanometric con- 

 nections with the outer and inner surfaces, a resting current, 

 C, was found to flow in the skin from the outer to the 

 inner, just as in the skin of the frog (right-hand diagram, 

 fig- !78). The grape skin was now mounted in the rotary 

 stimulating apparatus, first, for the stimulation of the outer 

 or epidermal surface, with the outer layer placed upwards. 

 The distance between the two electrodes was always the 

 same namely, 2 cm. On now stimulating one of the two 

 contacts, response took place by the induced galvanometric 

 positivity of that point. That is to say, the current was 

 'outgoing,' into the galvanometer circuit, from the surface 

 of the skin. When the second point was now stimulated the 

 deflection previously obtained was reversed, the second contact 

 thus also exhibiting galvanometric positivity on excitation. 



The position of the skin in the apparatus was now 

 changed, the inner surface being placed upwards. In this 

 way points diametrically opposite to those in the last case 



