78 MENTAL EVOLUTION IN ANIMALS. 



CHAPTER VIL 



Sensation. 



By Sensation I mean simply Feeling aroused by a stimulus. 

 In my usage, therefore, the term is of course exclusive of 

 all the metaphorical meanings which it presents in such 

 applications as " sensitive plates," &c. It is also exclusive, on 

 the one hand, of Eeflex Action, as well as of non-nervous 

 adjustments, and on the other, of Perception. Thus, too, it is 

 exclusive of the carefully defined meaning which it bears in 

 the writings of Lewes. He defined Sensation as the reaction 

 of a sense-organ, whether or not accompanied by Feeling, and 

 thus he habitually speaks of unfelt sensations. In his nomen- 

 clature, therefore, Sensation is a process of a purely physical 

 kind, with which consciousness may or may not be involved. 

 In my opinion, however, it is most desirable, notwithstanding 

 his elaborate justification of this use of the term, to abide by 

 its original signification, which I have explained. AVhen I 

 have occasion to speak of the physical reaction of a sense- 

 organ, I shall speak of it as a physical reaction, and not as a 

 sensation. The distinction which, in common with other 

 psychologists, I draw between a Sensation and a Perception, 

 I shall explain more fully in the chapter where I shall have 

 to treat of Perception. Meanwhile it is enough to say that 

 the great distinction consists in Perception involving an 

 element of Cognition as well as the element of Feeling. 



It is more difficult to draw the distinction between 

 Sensation and non-nervous adjustments, and still more so 

 between Sensation and nervous adjustments which are un- 

 felt (Pieflex Action). Here, however, we are but again 

 encountering the difficulty which we have already con- 

 sidered, viz.^ that of drawing the line where consciousness 

 begins ; and, as we have previously seen, this difficulty has 

 nothing to do with the validity of a classification of psychical 



