RESPONSE OF ANIMAL AND VEGETAL SKINS 301 



shocks, are seen in fig. 181, the resultant current being seen 

 to be ' up 'that is to say, from the inner to the outer. 



On observing the excitatory after-effect of equi-alternating 

 shocks, the results were found to be the same, the responsive 

 current being now once more from the inner to the outer. 



I next took a series of records of the direct effect of 

 equi-alternating shocks, the results of which were precisely 

 the same as before. On applying stimulation, by exactly 

 equal and alternating shocks, we, as already explained, 



FIG. 1 80. Photographic Record 

 of Electrical Responses of 

 Upper Surface of Intact 

 Human Forefinger to Rotary 

 Mechanical Stimulation. 



Down responses here indicate 

 induced galvanometric posi- 

 tivity. 



FIG. 1 8 1. - Photographic Record of 

 Electrical Responses of Grape-skin 

 to Thermal Shocks at Intervals of a 

 Minute 



Responsive current from inner to outer. 



obtain a result which is due solely to the differential excita- 

 tion of the two opposite surfaces. This is not complicated 

 in any way by the factor of polarisation, although the latter 

 could not have failed to be present if the exciting shocks 

 had been one-directioned. Under the conditions of these 

 equi-alternating shocks, then, a certain effect is often 

 seen, in the phasic variation of the base-line, which is ex- 

 tremely characteristic. We have already seen (p. 98) that 

 when a tissue is subjected to repeated or continuous stimula- 

 tion, its condition undergoes a phasic or periodic variation. 

 Thus from a neutral or positive condition, it may pass into 

 one of maximum contraction or galvanometric negativity, to 



