242 PHYSICAL EXPKESSION. 



before giving observations and experiments as 

 proof of points concerning any property or func* 

 tion, to decide upon physical signs which are to 

 be considered as criteria of that function. It is 

 only these physical signs that we can observe or 

 experiment upon. 



The principal properties of the brain necessary 

 to mentation are (1) impressionability, the effect 

 and outcome of the impression varying according 

 to the afferent force or stimulus ; (2) retentiveness 

 or permanent impressionability ; (3) special associa- 

 tion of the outcomings as dependent upon the 

 afferent stimulus. Or we may say that the expres- 

 sion of these properties in part indicates the 

 potentiality for mentation. One method of 

 determining the physical signs of mind is to 

 compare subjects possessed of mind with others 

 devoid of mind, or nearly so. 



It will be granted that an infant at birth does 

 not show well-marked signs of mind ; the principal 

 signs of mind are absent at birth. An adult man 

 who presented no more signs of mind than a child 

 at birth, would be said to be " mindless " in a con- 

 dition of amentia. An infant at birth may be said 

 to possess none of the actual faculties of mind 

 although it is healthy ; it may possess potentialities, 

 but it shows no actual, present signs of mentation. 

 An idiot in growing up from infancy, does not show 

 those objective signs appropriate to its age which 

 indicate potentiality for the functions of mentation. 

 To catalogue the signs which indicate idiocy, is to 

 summarize the signs of the absence of mind (see 



