342 NEKVOUS SYSTEM. 



regards races, the rule is found invariable, when a sufficient 

 number of observations are analyzed, and the same holds 

 true in comparing a large number of individuals of the same 

 race. Average men have an advantage over average women 

 of about six ounces of cerebral substance ; and, while many 

 women are far superior in intellect to many men, such in 

 stances are not sufficiently numerous to invalidate the general 

 law, that the greatest amount of intellectual capacity and 

 mental vigor goes with the greatest quantity of cerebral sub- 

 stance. If we accept the view, which is in every way rea- 

 sonable, that the gray substance of the cerebral hemispheres 

 is the generator of the mind, it would be necessary, in com- 

 paring different individuals with the view of establishing a 

 definite relation between brain-substance and intelligence, 

 to estimate the amount of gray matter ; but it is not easy 

 to see how this can be done with any degree of accuracy. 



It is undoubtedly true that proper training and exercise 

 develop and increase tho vigor of the intellectual faculties ; 

 and that thereby the brain is increased in power, as are the 

 muscles, under analogous conditions. This will perhaps ex- 

 plain some of the exceptions above indicated ; but an addi- 

 tional explanation may be found in differences in the quality 

 of brain-substance in different individuals, independently of 

 the size of the cerebral hemispheres. One evidence that 

 these differences in the quality of intellectual working matter 

 exist is, that some small brains actually accomplish more 

 and better work than some large brains. This fact mny be 

 due to differences in training, to the extraordinary develop- 

 ment in some individuals of certain qualities, to intensity 

 and pertinacity of purpose, capacity for persistent labor in 

 certain directions, a fortunate direction of the mental efforts, 

 opportunity and circumstances, etc. But, aside from these 

 considerations, there are analogies in the muscular system, 

 which render it exceedingly probable that there are impor- 

 tant individual differences in the quality of generating ner- 

 vous matter. 



