268 COMPARATIVE ELECTRO-PHYSIOLOGY 



in fig. 169. In this particular specimen, owing to growing 

 fatigue, the responses are seen to undergo diminution. In the 

 sheathing petiole of Musa also, we found, as will be remem- 

 bered, that the inner or concave surface was more excitable 

 than the outer or convex. In taking records of the responses 

 of such a specimen to equi-alternating electrical shocks, the 

 direction of the responsive current was found to be from the 

 more excitable inner to the less excitable outer surface. 



It is now evident that in the 

 structure of any single element of 

 an electrical organ, the essential 

 question is not as to the corre- 

 spondence of one part or another 

 with muscle, nerve, or gland, but 

 merely that of anisotropy. Any 

 tissue which is anisotropic is 

 potentially an electrical element. 

 Thus a stem of Cucurbita origin- 

 ally radial, becomes physiologically 

 anisotropic when it happens to 

 assume the recumbent posture, 

 owing to the a-symmetrical action 

 FIG. 169. Response of Pulvinus o f environmental stimuli. Such 

 Ele^Shoc qUi ' iilternating an anisotropic organ, when elec- 



Responsive current from more trically excited, gives a One- 



excitable lower to less excit- ^irectioned responsive current 



able upper. 



from the lower or ventral to the 



upper or dorsal surface. A similar reaction is, curiously enough, 

 shown by the body of the Eel, which also, on excitation, gives 

 a responsive current from the ventral surface to the dorsal. 



The responsive peculiarity of the constituent elements of 

 the electrical organ is thus not unique. The extraordinary 

 character of the organ depends merely upon the serial 

 arrangement of innumerable such elements, connected with 

 a nerve-trunk, by means of which a voluntary impulse is 

 enabled to bring about the excitatory discharge of the 

 electrical pile, and so convert it into a weapon of offence. 



