PSYCHO-PHYSICS 213 



show that the nervous impulse in plants has the same 

 characteristics as that of animals ; they also demon- 

 strate how the inquiry into the simpler life helps towards 

 the understanding of the more complex. 



Since the tone of sensation is dependent on the intensity 

 of transmitted excitation, Bose next asks himself whether 

 it be possible to control the intensity of nervous impulse 

 at will. He now enters into a new field of inquiry perhaps 

 his most daring. In regard to sensation two extreme 

 cases may be considered : in the first the external stimulus 

 is too feeble for the resulting impulse to cause perception ; 

 here we would desire to exalt the conducting power of 

 the message-bearmg vehicle, the nerve, so that what was 

 subliminal shall become perceptible. Excessively strong 

 external stimulus, on the other hand, on account of its 

 character or intensity causes sensation which is intolerably 

 painful. Could such a message be altogether blocked by 

 arresting the nervous impulse during transit ? The problem 

 is thus stated by Bose : 



There is an apparent resemblance between the conduction 

 of electric impulse by metallic conductor, and the excitatory 

 nervous impulse by a nerve-conductor. In metal the power 

 of conduction is constant, and the electric impulse will depend 

 on the intensity of electric force that is applied. If the con- 

 ducting power of the nerve were constant, then the intensity 

 of the nervous impulse and its resulting sensation will depend 

 inevitably on the intensity of shock which starts the impulse. 

 In that case modification of our sensation would be an im- 

 possibility. But there may be a likelihood that the power of 

 conduction possessed by a nerve is not constant, but capable 

 of change. Should this surmise prove to be correct, then we 

 arrive at the momentous conclusion that sensation itself is 

 modifiable, whatever be the external stimulus, For the modifi- 

 cation of nervous impulse there remains only one alternative, 

 namely, some power to render the vehicle a very much better con- 

 ductor or a non-conductor according to particular requirements. 

 We require the nervous path to become supra-conducting in 

 order that the impulse due to sub-minimal stimulus might be 



