BRAIN WEIGHT TO INTELLIGENCE 237 



authors have construed both as if they applied, 

 therefore should it be shown, if possible, that they 

 do not apply. 



The great bulk of the brain mass is white matter. 

 The gray cortex is a smaller proportion of it. It 

 is the principal function of white matter to transmit 

 the impulses issuing from the external world to the 

 cortex, and thence to muscular tissues, thereby pro- 

 ducing motions. 



Obviously, the more complex the outward organs 

 are, the greater must be the variety of possible 

 movements. If creatures possessing such bodies, 

 then, find their best chances of survival in adjust- 

 ments of their movements to the multiform changes 

 in their environment, then brains with exceptionally 

 great masses of white matter must be naturally 

 selected in such forms of life. It is shown, in the 

 paragraphs on the complexity of the human body, 

 in the third chapter, that this applies to primitive 

 man. 



In civilized persons, and more especially in such as 

 are engaged in purely intellectual activities, certain 

 small portions of the white matter of the brain are 

 occupied with somewhat different functions, viz: 

 with mediating between various areas of cortex 

 specialized to the highest purely intellectual pro- 

 cesses. Among these processes are: cognition and 

 recognition, by likeness and difference, classifica- 

 tion, comparison, generalization, abstraction, etc. 



These highest purely intellectual processes, ob- 



