ven a third of the descendants of a
mentally unsound individual were to become insane, it would only need a
few generations for that family to be crushed to the wall.

While the descendants of insane persons are distinctly more liable to
become insane than the rest of the community, yet, on account of their
fewness, this tendency probably does not account for more than a small
fraction of the total insanity. We should, by all means, prevent the
marriage of the insane and discourage that of their children, and the
development of any well-defined form of insanity should act at once,
_ipso facto_, as a ground and cause of divorce.

But the consoling fact remains that even of such children, providing, of
course, as usually happens, that the other parent--husband or wife--is
sound and sane, not more than ten or fifteen per cent would probably
become insane. In other words, insanity is acquired and the result of
individual stress and strain at least five times as frequently as it is
inherited. We have absolutely no rational or statistical basis for
gloomy predictions that, at present rates, within a couple of centuries
more, we shall all be shut up in asylums with nobody left to support us
and pay the taxes. The apparent increase of insanity of recent decades
is probably only "on paper," due to better registration.

To put it very roughly, probably ninety-eight per cent of us are so
born, thanks to heredity, that the possibility of our becoming insane,
even under the severest stress, is almost infinitesimal. Of the two per
cent born with this taint, this possible tendency to mental unbalance,
only about one-tenth now become completely insane,[1] and this
percentage might be greatly diminished by general sanitary improvements.
Our alienists now claim that, by checking the reproduction of the
obviously unstable, and careful hygienic treatment and training of the
predisposed two per cent, insanity is almost as preventable as
tuberculosis.

[Footnote 1: The proportion of registered insane in civilized countries
to-day ranges from two to three per 1000 of the population.]

In fine, from all the broad field of pathology, the mists of tradition
which have dimmed the fair name and reputation of heredity are slowly
but surely lifting, until we now behold it, not as our worst enemy, but
as our best friend in the prevention of disease and the upbuilding of
the race.

CHAPTER III

THE PHYSIOGNOMY OF DISEASE: WHAT A DOCTOR C