DETECTION OF PHYSIOLOGICAL ANISOTROPY 



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stimuli to the two points simultaneously, and then ascertaining 

 the direction of the responsive current. 



For this purpose we might employ any form of stimulus, 

 and it is extremely interesting to find that, however diverse 

 the stimuli, the results obtained by them are always 

 identical. And here we have not merely a means of 

 qualitative demonstration, but in some cases one of quanti- 

 tative also. 



If we take an erect stem of Cucurbita, it being radial 

 and isotropic, all its flanks will be found equally excitable. 

 Hence, if two diametrically opposite contacts are made, there 



FIG. 80. Diametric Method of Stimulation of an Anisotropic Organ 



Diametrically opposite contacts are made at A and B, and tissue subjected 

 to vibrational stimulus. 



will, on diffuse stimulation, be no resultant response. But 

 when such a stem becomes recumbent, the upper side, being 

 now constantly exposed to light, becomes fatigued by over- 

 stimulation, with consequent diminution of its excitability. 

 This is true only when the stimulus has been excessive and 

 long contiaued ; for we have seen moderate stimulus may 

 sometimes enhance the excitability. By the unilateral action 

 of light, then, the organ has been converted from radial into 

 anisotropic, the lower side being that which we shall expect 

 to find the more excitable. 



On mounting such a stem in the vibratory apparatus 

 (fig. 80), and making diametrically opposite contacts on the 

 two anisotropic surfaces, we find that on applying vibration 



