no 



COMPARATIVE ELECTRO-PHYSIOLOGY 



2. Conversely, if under simultaneous excitation the responsive 

 current be from B to A, then B is the more excitable of these 

 two points. 



These form only an instance of the general law that the 

 responsive current always flows from the more to the less 

 excited. For when a point, B, is excited locally this point, 

 that is to say, being the more excited the responsive 

 current is found to flow away from it to a neutral or in- 

 different point, A, for which any distant point will serve, 

 provided the tissue be non-conducting. Should it be con- 

 ducting, the neutrality of A is maintained by interposing a 



FIG. 79. Transverse Response of Pulvinus of Mimosa 



The petiole is securely held to prevent movement, and diametric electric 

 contacts made in the upper and lower surfaces of pulvinus. Re- 

 sponsive current is from lower to upper surface. 



block. Should the stimulus, however, not be local, but diffuse, 

 a resultant response may still be obtained by injuring or 

 killing the point A, and thus diminishing or abolishing its 

 excitability. On stimulation, the point B is now necessarily 

 the more excited, and the responsive current is still away 

 from B, towards A. And finally, owing to physiological 

 anisotropy, B may be naturally more excitable than A, and 

 on stimulation the responsive current will then be found 

 to flow from the more excited B to the less excited A. 



The comparison of the excitabilities of the two points 

 A and B, therefore, reduces itself to the application of similar 



