DETECTION OF PHYSIOLOGICAL ANISOTROPY 109 



We shall next observe what is the electrical mode of 

 response for a tissue which is anisotropic, or unequally ex- 

 citable on two sides. For this purpose we may again take 

 the pulvinus of Mimosa, and make electrical connections at 

 two diametrically opposite points on the upper and lower 

 halves of the pulvinus respectively. It is to be remembered 

 that electrical response takes place on excitation, whether 

 the leaf be free to move, or physically restrained. We may, 

 therefore, hold it in a fixed position ; and indeed this is 

 advisable, in order to avoid that shifting of the electrical 

 contacts which might 

 possibly take place if 

 it were allowed to fall. 



The two contacts 

 are made with two 

 fine straws filled with 

 kaolin paste, moistened 

 in normal saline. On 

 now applying a series 

 of thermal stimuli, on 

 the petiole, near the 

 pulvinus, I obtained the 



responses given in fig. FlG - 7^. Responses of Mimosa to Sunlight of 



79. It will be seen 

 that the 



current flows in the 

 tissue from the rela- 

 tively more excited lower, to the less excited upper, half 

 of the organ. 



We thus arrive at a comprehensive law of the mechanical 

 and electrical response of anisotropic organs : 



Diffuse stimulation induces greater contraction and 

 galvanometric negativity of the more excitable side. 



The laws of electric response in the anisotropic organ 

 may then be detailed as follows : 



1. On simultaneous excitation of two points, A and B, the 

 responsive current flows in the tissue from the more to the less 

 excited, 



not too long Duration 



(a) Light acting on pulvinus from above ; (t>) light 

 responsive acting on pulvinus from below ; (c) light acting 



simultaneously from above and below. Dotted 

 line represents recovery on cessation of light. 



