The Beginnings of Intelligence 133 



of a lessened nervous discharge. An act which 

 brings pleasure causes an influx of nervous energy 

 to the centers concerned in the movement; the lines 

 of discharge become "more permeable," and upon 

 a repetition of the conditions the same act follows 

 with greater readiness than before; If the act is 

 followed by pain with its concomitant of lessened 

 nervous discharge, the diminution of nervous energy 

 serves to prevent the performance of the act in re- 

 sponse to the same conditions. Closely similar ex- 

 planations of the physiology of the pleasure-pain re- 

 sponse have been given by Bain and by Baldwin, the 

 latter declaring that "pleasure and pain can be agents 

 of accommodation and development only if the one, 

 pleasure, carry with it the phenomenon of motor ex- 

 cess — and the other, pain, the reverse — probably 

 some form of inhibition or of antagonistic contrac- 

 tion." 



The physiological concomitants of pleasure and 

 pain have afforded a subject for numerous labora- 

 tory studies and almost no end of theories. It has 

 been impossible thus far to discover that either of 

 these states is invariably accompanied by any defi- 

 nite physiological condition. The theory of Spen-' 

 cer and Bain is open to obvious criticism, for the 

 man who steps on a tack undoubtedly has a "height- 

 ened nervous discharge," as much as a man who 

 shouts for joy. And I believe I am safe in saying 

 that no theory of the physiology of pleasure and 

 pain is on a sufficiently firm basis to warrant its b?- 



