tary defect, hereditary insanity, but very
little of hereditary powers of recovery, of inherited vigor, and the
fact that ninety-nine and seven-tenths per cent of us are sane.

One instance of hereditary defect, of inherited degeneracy, fills us
with horror and stirs us to move Heaven and earth to prevent another
such. The inheritance of vigor, of healthfulness, and of sanity we
placidly accept as a matter of course and bank upon it in our plans for
the future, without so much as a thank you to the force that underlies
it.

When once we clear away these inherited misconceptions and look the
facts of the situation squarely in the face, we find that heredity is at
least ten times as potent and as frequently concerned in the
transmission and securing of health and vigor as of disease and
weakness; that its influence on the perpetuation of bodily and mental
defects has been enormously exaggerated and that there are exceedingly
few hereditary diseases.

It is not necessary for our present purpose to enter into a discussion
of the innumerable theories of that inevitable tendency of like to beget
like, of child to resemble parent, which we call heredity. One
reference, however, may be permitted to the controversy that has
divided the scientific world: whether _acquired_ characters, changes
occurring during the lifetime of the individual, can be inherited.
Disease is nine times out of ten an acquired character; hence, instead
of the probabilities being that it would be inherited, the balance of
evidence to date points in exactly the opposite direction. The burden of
proof as to the inheritance of disease is absolutely upon those who
believe in its possibility.

Another fundamental fact which renders the inheritance of disease upon a
_priori_ grounds improbable and upon practical grounds obviously
difficult, is that characters or peculiarities, in order to be inherited
certainly for more than a few generations, must be beneficial and
helpful in the struggle. A moment's reflection will show this to be
mathematically necessary, in that any family or race which tended to
inherit defects and injurious characters would rapidly go down in the
struggle for survival and become extinct. An inherited disease of any
seriousness could not run for more than two or three generations in any
family, simply for the reason that by the end of that time there would
be no family left for it to run in. A slight defect or small peculiarity
of und