156 HEREDITY AND EUGENICS 



but a step from insanity to genius. Indeed, many 

 geniuses would pass with any psychiatrist as true 

 insanities. The diagnosis may depend on whether 

 the aberration is useful or dangerous. But it is 

 impossible to graft genius on to feeblemindedness, and 

 the loss of a whole feebleminded stock would not 

 involve the suppression of a single genius. For in 

 feebleminded families even the " normals " are 

 usually of low-grade intelligence, and they are as a 

 rule correspondingh' low in social grade. Notwith- 

 standing this, it is clear that the condition of the 

 feebleminded does not result from their environment, 

 but rather that their lack of capacity causes them to 

 gravitate into squalid conditions, since the}- cannot 

 grapple adequately with the complexities and subtle- 

 ties of modern civilised life. Urquhart (1909) 

 classifies insanitv as melancholia, mania or dementia 

 which are acquired, and idioc}^ and imbecility which 

 are congenital. The latter conditions are, usually 

 at least, accompanied by gross physical deficiencies. 

 The pedigrees of insanity are usually unsatisfactory 

 in failing to distinguish betw^een different types, and 

 so they give no general rule of inheritance, although 

 many of them run through three generations. 



Holmes (1921) has pointed out that the germ plasm 

 of neurotic stocks may be affected in a variet}" of 

 wa^^s in different individuals. He says (p. 49): 

 " Charts of the inheritance of insanity show that the 

 afflicted individuals exhibit a great diversity of 

 symptoms in successive generations." Particular 

 types of insanity, however, tend to run in certain 

 families. This is particularl}- true of dementia 

 prsecox (see p. 158) and periodical insanity. Unlike 

 most forms of insanity, Huntingdon's chorea* appears 



* Chronic chorea or St. Vitus' dance is a convulsive nervous 

 disease with irregular movements, dementia, and disturbance of 

 speech. 



