CHAPTER XL1V 



DISSOCIATION OF COMPLEX SENSATION 



Conversion of pleasurable into painful sensation, and vice versa, by electrotonus 

 The Sensimeter Mechanical stimulation Stimulation by thermal shocks- 

 Chemical stimulation Opposite effects of anode and kathode Normal effects 

 reversed under feeble E.M.F. Negative tone of sensation blocked by alcohol 

 and anaesthetics Separation of positive and negative sensations, by lag of 

 one wave behind the other Dissociation of sensation by depression of con- 

 ductivity Abolition of the negative or painful element by block of conduction. 



I SHALL next proceed to demonstrate, by means of decisive 

 experiments, the fact that sensation and its variations are 

 associated with certain physiological changes and their 

 appropriate modifications. In the mechanical and electrical 

 response of the nerve, we found that while moderate 

 stimulus gave positive response, a stronger stimulus gave 

 negative ; that while the positive was unmixed or elementary, 

 the negative contained a masked positive ; and further, that 

 the velocity of the transmission of the positive was greater 

 than that of the negative wave. 



We shall now study the correspondence of the responsive 

 sensation with these various nervous changes induced by 

 stimulus, and their modifications under different agencies. 

 I shall next, therefore, show, in accordance with the chief aim 

 of this chapter, that the same conditions which determine the 

 exhibition of positive, mechanical, or electrical response, will 

 also, part passu, determine positive tone in the responsive 

 sensation. Those conditions, on the other hand, which bring 

 about a negative mechanical or electrical change in the 

 nerve, will also induce a negative tone in the sensation. The 

 resultant transmitted effect recorded in the responding 

 apparatus, was, as we saw, determined by the receptive ex- 



