XV MAN i8i 



that a particular form of mental ability may depend for 

 its manifestation, not so much upon an essential difference 

 in the structure of the nervous system, as upon the pro- 

 duction by another tissue of some specific poison which 

 causes the nervous system to react in a definite way. 

 We have mentioned these possibilities merely to indicate 

 how complex the problem may turn out to be. Though 

 there is no doubt that mental ability is inherited, what it 

 is that is transmitted, whether factors involving the 

 quality and structure of the nervous system itself, or 

 factors involving the production of specific poisons by 

 other tissues, or both together, is at present uncertain. 

 Little as is known to-day of heredity in man, that little 

 is of extraordinary significance. The qualities of men 

 and women, physical and mental, depend primarily upon 

 the inherent properties of the gametes which went to 

 their making. Within limits these qualities are elastic, 

 and can be modified to a greater or lesser extent by in- 

 fluences brought to bear upon the growing zygote, pro- 

 vided always that the necessary basis is present upon 

 which these influences can work. If the mathematical 

 faculty has been carried in by the gamete, the education 

 of the zygote will enable him to make the most of it. 

 But if the basis is not there, no amount of education can 

 transform that zygote into a mathematician. This is a 

 matter of common experience. Neither is there any 

 reason for supposing that the superior education of a 



