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 supplied 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 difficult 
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 
