: Feer, op. cit., pp. 13-14.]

From these tables we may infer that consanguinity influences idiocy
far more than it does insanity, but it is not entirely clear why the
number of hereditary cases should be relatively smaller among the
idiotic. Since insanity is more likely to have some more definitely
assignable cause than idiocy, we should expect the percentage due to
heredity to be lower and consequently the influence of consanguinity
less.

It is generally admitted that a tendency toward insanity is
inheritable, and it seems probable that this tendency as well as other
neuroses may be intensified through double heredity. A case in point
can be found in the Shattuck genealogy.[74] For four generations in
the S. family there is no indication of neurosis. The average number
of children to a family had been eight, few children died young and
all were prosperous farmers. But in 1719 J.S. married E.C. and their
son Z.S. is thus described: "He was sometimes subject to depression of
spirits; and some peculiar traits of character in a few branches of
his family seem to have originated with him." He married A.C., a niece
of his mother. They both lived to be over 80 and had ten children, of
whom three were insane; only six married, and of these only two are
known to have left surviving children. One of these a daughter, S.S.,
married E.S., a nephew of her father, and himself the offspring of a
second cousin marriage within the S. blood. E.S. and S.S. had five
children, all of whom married, and there is no further mention of
insanity. We may suppose, then, that the C. stock was neurotic, and
that a consanguineous marriage within that stock, although of the S.
surname, intensified the tendency into insanity, but with a further
infusion of the normal S. blood the morbidity was eliminated. It is
very evident that the heredity and not the consanguinity was the cause
of these three cases of insanity.

[Footnote 74: _Shattuck Memorials_, p. 118.]

CHAPTER VI

CONSANGUINITY AND THE SPECIAL SENSES

The most important source for this chapter is the special report on
the Blind and the Deaf in the Twelfth Census of the United States.[75]
This report was prepared under the direction of Dr. Alexander Graham
Bell, as Expert Special Agent of the Census Office.

[Footnote 75: U.S. Census, 1900, _Special Report on the Blind and the
Deaf_.]

The enumerators of the Twelfth Census reported a total of 101,123
persons as blind, and