650 COMPARATIVE ELECTRO-PHYSIOLOGY 



We turn next to the sensory mode of indication, that is 

 to say, to the psychic effects registered in the central 

 perceiving organ by the positive and negative waves 

 conveyed to it along the afferent nerves. We have already 

 seen that the stimulatory changes induced in these sensory 

 nerves are precisely the same as those which occur in the 

 efferent. What, then, are the effects in the central apparatus 

 induced (i) by that positive impulse which is associated with 

 expansion, and (2) by the negative impulse associated with 

 contraction ? 



It is a matter of universal experience, as already 

 mentioned, that feeble stimulus gives rise to sensations of 

 positive or pleasurable tone, while an intense stimulus of the 

 same kind will induce a responsive sensation which is negative 

 or painful. We have also seen, in the course of the present 

 work, that a feeble stimulus will give rise to a wave of 

 expansion and galvanometric positivity, while the same 

 stimulus, when intense, will give rise to a negative wave. 

 We are therefore justified in regarding the positive impulse, 

 associated with expansion and galvanometric positivity, as 

 pleasure-bearing, and its opposite as pain-bearing or dolori- 

 ferous. Numerous experiments some being of a crucial 

 character will be given, in the course of the present and 

 succeeding chapters, which will be found to lend full support 

 to this conclusion. 



This fact, that the same stimulus may induce positive 

 sensation in the central and expansion in the motile organ, 

 or the negative painful sensation with muscular con- 

 traction, according only to the nature of the indicator, 

 will furnish grounds of reconciliation to those who 

 hold on the one hand that the motor reaction is secon- 

 dary to the mental, and on the other, that sensation 

 is merely an accompaniment of movements reflexly in- 

 duced. 1 



1 Many hold the motor reaction to be secondary to the mental. Of the 

 coarser emotions it has been argued by James that the feeling does not cause, 

 but is caused by, the bodily expression. The bodily changes, according to him, 

 follow directly the perception of the exciting fact, and our feeling of the same 



