446 PHYSIOLOGY CHAP. 



It is evident that such a clear and exact description, which 

 amounts to a reconstruction and psycho-physiological interpreta- 

 tion of the several factors, could only be given by a physiologist 

 who was at the same time a psychologist. Its scientific value is 

 therefore a hundredfold greater than all the definitions of 

 " conscious and unconscious," " sensation and perception," 

 formulated by eminent metaphysicians ; it is a living page of 

 nascent mental life ; it expresses the minute transitions between 

 the extreme mental states, and gives a precise idea of those 

 intermediate states that may as a whole be termed semi-conscious. 



It would be interesting to have a similar description of the 

 gradual abolition of consciousness, such as must occur on the 

 administration of chloroform for surgical purposes, and of the 

 subsequent gradual return of consciousness. But we have never 

 met with anything relating to this important subject compar- 

 able to Herzen's description and of the same value as a control. 

 Any one who has been chloroformed will bear witness to the 

 gradual clouding and final extinction of consciousness, and its 

 subsequent gradual recovery, without being able to differentiate 

 the characteristics of the respective phases. 



If we attempt to sum up Herzen's auto-observations into 

 a synthetic formula, it may be said that simple sensations pre- 

 dominate in the state of nascent consciousness, as they certainly 

 do in twilight consciousness, while the true perceptions that we 

 only have in full consciousness are absent. In discussing the 

 physiology of the brain and sense-organs we frequently employed 

 these two expressions, " sensation " and " perception," and en- 

 deavoured to differentiate and define them. It is, however, desir- 

 able to return to the subject here, so that we may be better able to 

 comprehend this point, which is often neglected by psychologists. 



As William James points out, " the words sensation and per- 

 ception do not carry very definitely discriminated meanings in 

 popular speech, and in psychology also their meanings run into 

 each other." Both terms stand for processes by which external 

 stimuli, acting on the peripheral sense-organs, cause in them an 

 excitation which affects the cerebral centres, and by which we 

 know of the objective world. "The nearer the object cognised 

 comes to being a simple quantity like ' hot,' ' cold/ ' red,' ' noise,' 

 ' pain,' apprehended irrelatively to other things, the more the 

 state of mind approaches pure sensation. The fuller of relations 

 the object is, on the contrary, the more it is something classed, 

 located, measured, compared, assigned to a function, etc., etc., the 

 more unreservedly do we call the state of mind a perception, and 

 the relatively smaller is the part in it which sensation plays. . . . 

 Sensation, then, . . . differs from perception only in the extreme 

 simplicity of its object or content." l 



1 Psychology, ii. pp. 1-2. 



