NERVOUS SYSTEM AND HEREDITY 211 



to produce descendants with greater intellect. The 

 intellect is not proportional to chemical changes, like 

 muscular activity. In the brain of an idiot and of a 

 genius the same chemical changes may occur. The 

 difference between the two, however, is that the idiot 

 fails to notice valuable associations of ideas while the 

 brain of the genius retains them. We arrive thus at 



o 



the conclusion that a transmission of hereditary char- 

 acteristics through the egg is only possible in the 

 form of specific chemical substances, and that the 

 central nervous system could only influence heredity, 

 if it could bring about the formation of special sub- 

 stances in the egg (by influencing metabolism). It 

 would, of course, first have to be proved that the cen- 

 tral nervous system has such an influence upon the 

 sexual cells, and this is extremely doubtful. For this 

 reason we should not be justified in maintaining that 

 the activity of a generation can produce an heredi- 

 tary increase of the ability and tendencies in the same 

 direction. Herbert Spencer gives as a proof of this last 

 possibility the fact that the circles of touch in the tip 

 of our toncrue are the smallest. He believes that 



o 



this is due to the fact that from time immemorial man 

 had the tendency to examine the spaces between the 

 teeth with the tongue, and this is supposed to have 

 caused an hereditary increase in the nerve-endings of 

 the tongue. Spencer overlooks the fact that in the tip 

 of the nose the circles of touch are also a comparative 

 minimum, and it is certain that this organ has not 

 been used for such a purpose since time immemorial. 



