THE INHERITANCE OF FAMILY TRAITS 77 



20. Insanity 



If the word epilepsy is a wardrobe then the word insanity 

 is a veritable lumber room, including a great variety of 

 mental diseases which have this in common that they render 

 their victim incompetent and irresponsible before the law. 

 Two great classes of msanity are distinguished: the "or- 

 ganic" and the "functional." The first group includes 

 cases of mental deterioration associated with venereal dis- 

 eases, alcohohsm, degeneration of the blood vessels and 

 trauma; the second includes cases of distinct neuropathic 

 taint which shows itself in the slighter forms as melancholia 

 or manic depressive insanity and in the profounder forms 

 as dementia precox. Concerning heredity in the functional 

 forms there is no doubt. Berze (1910) gives a case of de- 

 mentia precox in a father and three sons; another of two 

 children, their mother and her father; and numerous other 

 cases with two or three to the family — all with a more or 

 less typical form of dementia precox. But the mental de- 

 fect that is "inherited" is not always of the same type. 

 Thus in the same family may be found cases of manic de- 

 pressive insanity, of senile dementia, of alcohohsm and of 

 feeble-mindedness. It would seem to be the neuropathic 

 taint that is inherited. 



This is the conclusion to which Cannon and Rosanoff 

 (1911) have come in their study based on house to houfee 

 investigations of the families of patients at a State Hospital. 

 They omit from consideration the "organic" class of cas^s 

 as "probably purely exogenous in origin." Aside from these 

 they find that when both parents have any form of insanity 

 all of their children will "go insane." If one parent is iiji- 

 sane and the other normal but of insane stock half of the 

 children tend to become insane; when both parents, though 

 normal, belong to an insane stock about one-fourth of the 



