no doubt an element of
truth in that view. But serious and frequent as are the results of bad
environment and acquired disease in the parentage of the feeble-minded,
they do not form the fundamental factor in the production of the
feeble-minded.[27]

Feeble-mindedness is essentially a germinal variation, belonging to the
same large class as all other biological variations, occurring, for the
most part, in the first place spontaneously, but strongly tending to be
inherited. It thus resembles congenital cataract, deaf-mutism, the
susceptibility to tuberculous infection, etc.[28]

Exact investigation is now showing that feeble-mindedness is passed on
from parent to child to an enormous extent. Some years ago Ashby,
speaking from a large experience in the North of England, estimated that
at least seventy-five per cent of feeble-minded children are born with
an inherited tendency to mental defect. More precise investigation has
since shown that this estimate was under the mark. Tredgold, who in
England has most carefully studied the heredity of the feeble-minded,[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.[30]
Heredity 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, and
is traceable through three generations, though it sometimes skips a
generation. In one family of three hundred and nineteen persons, one
hundred and nineteen were known to be feeble-minded, and only forty-two
known to be normal. The families tended to be large, sometimes very
large, most of them in many cases dying in infancy or growing up
weak-minded.[31]

Not only is feeble-mindedness inherite