in FUNCTION OF MIND AND BRAIN 33 



the expenditure of laborious and painfully conscious effort 

 passes rapidly as it becomes perfect to the margin of the 

 conscious area or altogether beyond its limits. But con- 

 versely in these very exercises, as soon as some conjunction 

 occurs requiring new and perhaps unique adaptation, con- 

 scious attention comes again into play. It is through the 

 elements that come into consciousness as such that we prin- 

 cipally establish new correlations, and we may take as the 

 external sign of the birth of consciousness the appearance of 

 a permanent power of making new combinations, while the 

 measure of the growth of consciousness, and therewith of 

 mind, is in the extent and perfection of the combinations 

 which we can form. In particular we shall find that the 

 extent to which the factors influencing consciousness are 

 themselves brought within the content of consciousness is 

 of special importance in estimating the growth of mind. 



We conceive then of the psycho-physical unity, which is 

 the self, as the seat of mental and of physical phenomena. 

 Under either aspect we can regard it as a unity which sub- 

 sists by processes of adjustment involving the correlation 

 of different experiences and energies. In the nervous 

 system we see the physical basis of such correlation. In 

 the mental life we see it clearly at work, and proceeding at 

 its best through the medium of consciousness. Our busi- 

 ness will be to classify the different forms of adaptive corre- 

 lation and to distinguish the sphere of consciousness in 

 each. We shall thus arrive at a conception of the develop- 

 ment and the sphere of mind which will be true, so far as it 

 goes, whatever interpretation we may ultimately put on the 

 causation of mental phenomena. For this purpose we 

 must first review the general conditions under which the 

 whole psycho-physical unity works. 



(3) The Psycho-Physical Structure in its Development. 



Let us take any commonplace deliverance of conscious- 

 ness and consider the general conditions on which it rests. 

 As I write I hear a lark singing outside. This perception 

 is not the effect of the lark's song alone, nor of the 

 physical waves of air that beat upon the drum of the ear, 

 nor of the vibration of the membrane of Corti, nor of the 



