i66 HEREDITY AND EUGENICS 



how the bodily functions have their effect on the 

 mind, and an\^ defect is unconsciously compensated 

 for b}^ the individual. This may ultimately lead to 

 a pathological condition of the mind, in other words, 

 insanity, particularly in a time of mental stress, 

 and under some conditions a psychoanalysis may 

 restore the mental balance. The development of 

 insanity is thus closely wrapped up with bodily con- 

 ditions. That there is also an element of inheritance 

 in man}^ cases of insanit}- is undeniable, but it remains 

 to be determined precisely what that element is in 

 different cases. The situation is obscure in com- 

 parison with feeblemindedness where the nature of 

 the inheritance is clear. Insanities also show a 

 greater variety of types, and they cannot be graded 

 in a simple series like the mental-age series of the 

 feebleminded. The compelling force of the excessive 

 development or derangement of some autonomic 

 bodily function will usually furnish the immediate 

 cause of an insane manifestation. Various inherited 

 derangements of the nervous control of the bod}' 

 may then provide the basis for the development of an 

 insane diathesis. 



Inherited mental differences, no doubt, go back 

 to germinal changes affecting the nervous system. 

 Traced backwards in the ontogeny, they must have 

 a purety physical basis like other germinal changes.* 

 The description of a breed of goats in Kentucky 

 (Hooper, 191 6) is instructive in this connection. 

 When frightened, their forelegs become stiff, and 

 they hop along, dragging their hind legs. If much 

 frightened, the latter also become stiff, and the animal 

 falls over. Such a breed must have arisen through a 

 germinal change affecting chiefly the nervous system. 



* Yerkes has shown that in crosses between wild and tame rats 

 wildness will appear in the offspring even when the father was 

 wild and the young were reared by tame mothers. 



