INTRODUCTORY. 5 



In accordance with these views, I have en- 

 deavoured throughout this work to avoid speaking 

 of consciousness, or feeling, as the cause of any 

 mental phenomenon.* It has not, however, been 

 convenient always to do so, but I hope that this 

 rule has been adhered to in all important statements. 



Movements and the results of movements, being 

 purely physical actions, are the criteria looked for 

 as indices or expressions of the various brain states. 

 No attempt is made to- form an idea of what life, 

 nutrition, mentation, or any other vital property or 

 process may be ; the signs of vital phenomena are 

 dealt with, not the living origin of those signs. 

 The term " mentation " is used to imply the function 

 discharged by the brain when the phenomena of 

 mind are displayed. 



Frequent reference is made in the succeeding 

 chapters to observations on infants and young 

 children. It appears to me a strictly scientific 

 method to observe and classify the signs which 

 indicate the potentiality for mentation, the early 

 and advancing signs of mentation, and concurrent 

 phenomena. The earliest of these signs are move- 

 ments and the results of movements, and these are 

 purely physical phenomena, capable of being sub- 

 mitted to experimental inquiry. 



Reference is frequently made, by way of illustra- 

 tion, to examples in vegetable life.f If we really 

 accept some form of the evolutionary theory as a 

 working hypothesis, it 'is reasonable to make 



* See " Expression of Consciousness," chap. xiii. 

 t See chaps, ii. and vii. 



