DETERMINATION OF DIFFERENTIAL EXCITABILITY 285 



while the natural resting-current was from the less excitable 

 upper to the more excitable lower side, the responsive cur- 

 rent under mechanical stimulation was in the opposite direc- 

 tion namely, from the lower to the upper (p. 112). Using 

 now the electrical form of stimulus, we obtain results which 

 are identical. Fig. 174 gives a series of such responses 

 under equi-alternating electrical shocks. Curiously enough, 

 as pointed out in the last chapter, I have detected a similar 

 plagiotropy in the case of the eel. The head of the fish 

 was cut off, and voluntary action thus eliminated ; electrical 

 mnections were then made, after a period of rest, with the 



dark dorsal upper surface, and the 

 colourless skin of the ventral or 

 lower. A natural current was now 

 found to flow from the upper 



FIG. 174. Photographic Record 

 of Responses of Plagiotropic 

 Stem of Cucurbita to Equi- 

 alternating Electric Shocks 



Direction of responsive current from 

 ventral to dorsal surface. 



FIG. 175. Electrical Responses of 

 Eel to Equi-alternating Electrical 

 Shocks 



Current of response from ventral 

 surface to dorsal. 



surface to the lower, as in the case of the plagiotropic stem 

 of Cucurbita. Electrical excitation was now applied, and 

 the result was a responsive current from the more excitable 

 lower to the less excitable upper surface again, as in the 

 case of Cucurbita. In fig. 175 is seen a series of records in 

 illustration of this. 



Another investigation which I thought might be interest- 

 ing had reference to the variegated colouring of certain 

 foliage leaves. A striking example of this is found in the 





