INHERITANCE OF MENTAL DEFECTS AND DISEASE 47 



little unsoundness of mind in the world." Mercier {Sanity and 

 Insanity.) ''The stability or instability of a person's nervous 

 arrangements depend primarily and chiefly upon inheritance." 

 Bianchi {Textbook of Psychiatry), speaking of epilepsy, says 

 "Heredity plays the greatest part, and in most cases is direct and 

 similar." 



The great importance of the hereditary factor is emphasized 

 by Heron who has made an elaborate statistical study of the 

 inheritance of insanity based on data suppHed by Dr. A. R. 

 Urquhart, Superintendent of the James Murray's Royal Asylum, 

 at Perth. "The records which have been compiled by Dr. 

 Urquhart personally," says Heron, "are, therefore, of great value 

 on account of their completeness, uniformity, and the long period 

 over, which they extend." The data showed that where both 

 parents of an insane patient were sane, the ratio of the insane in 

 all the offspring was 314:1179. With one parent insane the off- 

 spring were 93 insane: 299 sane, and when both parents were 

 insane there were 4 insane and 4 sane offspring. Since not all the 

 offspring had reached the age at which latent insanity might be 

 manifested, it is obvious that the relative proportion of insane 

 offspring would be considerably higher. Taking account also of 

 data collected by Pearson, Heron concludes that his results 

 "indicate that if completed histories are taken 40 per cent of 

 insane offspring of insane parents is not an over-estimate, and 

 that in this memoir we have erred on the side of lessening the 

 intensity of inheritance in taking 25 per cent of the offspring of 

 insane persons to be insane." Insanity, according to Heron, is 

 inherited to about the same extent as stature, intelligence, and 

 a number of other traits. 



; The way in which insanity is transmitted is rather more difificult 

 to follow than the mode of inheritance of feeble-mindedness. 

 Unlike the latter trait, insanity is seldom manifested until after 

 the period of adolescence, and very frequently appears in middle 

 life and even in old age. This circumstance creates a difficulty in 

 the way of tracing the operation of any Mendelian factors which 

 may be responsible for the insane diathesis, since a considerable 



