CHAPTER XLIII 



CERTAIN PSYCHO-PHYSIOLOGICAL PHENOMENA THE ;.< 

 PHYSICAL BASIS OF SENSATION 



Indications of stimulatory changes in nerve: I, Electrical; 2, Mechanical- 

 Transmission in both directions Stimulatory changes in motor and sensory 

 nerves similar Responsive molecular changes and the correlated tones of 

 sensation Two kinds of nervous impulse, and their characteristics Different 

 manifestations of the same nervous impulse determined by nature of indicator 

 Electrical, motile, and sensory responses, and their mutual relations The 

 brain as a perceiving apparatus Weber-Fechner's Law Elimination ot 

 psychic assumption from explanation of particular relation between stimulus 

 and resultant sensation Explanation of the factor of quality in sensation 

 Explanation of conversion from positive to negative tone of sensation after 

 tetanisation Various effects of progressive molecular change in nerve Effects 

 of attention and inhibition Polar variations of tonus, inducing acceleration 

 and retardation. 



IT is admitted that the molecular changes induced in the 

 nerve by stimulus, are followed by sensations perceived in 

 the brain. The question as to the nature of these antecedent 

 changes induced in the nerve, and the quality of the sensation 

 that succeeds them, falls properly, then, within the scope of a 

 physiological inquiry ; and it is certain aspects of this which 

 will be treated in the present chapter. I may here point out 

 that the results which I have to describe consist of deductions 

 drawn from direct experiment. They will in some cases 

 lend support to the psychological hypotheses already ad- 

 vanced ; while in others they will be found to be opposed. 

 In such cases, therefore, it is perhaps not too much to hope, 

 from their strictly experimental character, that they will 

 prove of use in deciding between rival theories ; while in 

 others they will be found to introduce facts and considera- 

 tions which are entirely new. 



