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120 PSYCHOBIOLOGY 



otherwise maltreating the tissue; but respond only to the contraction of 

 the tissue. 



The human body is therefore, physiologically considered, but an ex- 

 ceedingly complicated machine, played upon by a great many external 

 forces, and responding to these forces in such a way as to maintain its 

 integrity for a considerable time and to produce other machines similar to 

 itself. The normal physiological performance of such a machine may 

 be summed up under two heads. 1. Reflexes: processes initiated by an 

 external stimulus to a receptor and ending in modification of muscular and 

 glandular activity. 2. Processes contributory to the reflexes. Under this 

 last head go nutritive and similar chemical activities, and the activity of 

 cells essential to the nutrition and protection of the reflex mechanism. 

 Rhythmic, automatic activity of motor ganglion cells (if such activity 

 occurs) is included here. 



Physiology, however, does not exhaust our interest in the organism. It 

 is true, so far as the organ alone is concerned, that when light strikes the 

 eye, all that happens as a result thereof is the contraction of certain 

 muscles, relaxation of certain others, acceleration of certain glandular 

 activity and inhibition of certain others. But another thing also happens 

 which is not to be found in the organism at all. If the eye be my eye, / 

 see the light when this organic reflex occurs. Similarly I am aware of 

 the sound which stimulates my ear, of the sweet which stimulates the taste 

 buds; and of the contraction of the biceps which stimulates the spindles 

 therein. Moreover, I am aware of the activities of my viscera through 

 the operation of the reflexes in which these take part ; an awareness which 

 (in contradistinction to the awareness of those operations which I might 

 have through visual reflexes, for example, if my viscera were laid open for 

 microscopic examination) I call ' having feelings'. 



These awarenesses (which together we call consciousness) depend 

 upon the action of reflexes. Without a reflex from the eye I cannot see 

 light. Without reflexes from my viscera I cannot have ' feelings '. To 

 say that the reflexes cause the consciousness is to make an extrascientific 

 assumption which is not justified, unless we mean by ' cause ' no more than 

 invariably accompany. 



The awarenesses just indicated are perceptual. In addition there is a 

 form of consciousness which we call thought. I can think of red light, 

 when the appropriate stimulus does not fall on the eye, and when there- 

 fore the perceptual light-reflex does not occur. There is, in this case, 

 doubtless a reflex, which, although not initiated in the same receptor as 

 the perceptual light-reflex, has the same termini as the latter. The initia- 

 tion as well as the termination of one of these thought-reflexes is probably 



