Fifty years ago Baillarger† showed from a study of 453 cases that insanity is one third more frequently transmitted from the mothers to the children than from the fathers, and that in the case of sons the transmission is as frequently from one parent as from the other, and in the case of daughters the disposition to insanity is inherited twice as frequently from the mother as from the father. Leubuscher† apparently referring to some later statistics of Baillarger's dealing with 600 cases, found that:—
Direct inheritance.—(a) Taking all classes of insanity, acquired and congenital, we find that whilst the insane father transmits his mental instability to a greater number of offspring than the insane mother, it is on the daughters that it mostly falls, and where the mother is insane the influence is still more marked in the direction of the daughters; so that whichever parent is insane, more daughters ultimately become insane than sons.
(β) The number of insane mothers is very considerably greater than insane fathers.
Reversional and collateral inheritance.—(a) In both sexes the stronger hereditary influence comes through the maternal branch of the family.
(β) The males have the larger number of brothers insane, the females the larger number of sisters.
Bearing in mind the suggestions previously advanced as to the greater amount of stress that the female is physiologically exposed to, I am inclined to think that the results arrived at in Table III. give us a correct idea concerning the transmission of mental instability.
In this series extraneous circumstances have been excluded to a large extent, and the results are in harmony with Darwin's Law of Heredity. But larger numbers will have to be dealt with before any positive conclusion can be arrived at. Where we deal with all classes, as in Table I., these results are liable to be masked to a certain extent by other causes already mentioned. If such be the case the discrepancy between the two tables will serve to give us an idea of the marked influence that extraneous circumstances have in determining actual insanity in those predisposed to it.
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