29 found that in over eighty-two per cent cases there is a bad nervous inheritance.
In a large number of cases the bad heredity was associated with alcoholism or consumption in the parentage, but only in a small proportion of cases (about seven per cent) was it probable that alcoholism and consumption alone, and usually combined, had sufficed to produce the defective condition of the children, while environmental conditions only produced mental defect in ten per cent cases.
30Heredity is the chief cause of feeble-mindedness, and a normal child is never born of two feeble-minded parents. The very thorough investigation of the heredity of the feeble-minded which is now being carried on at the institution for their care at Vineland, New Jersey, shows even more decisive results. By making careful pedigrees of the families to which the inmates at Vineland belong it is seen that in a large proportion of cases feeble-mindedness is handed on from generation to generation,