Deaf_.]

The enumerators of the Twelfth Census reported a total of 101,123
persons as blind, and to each of these Dr. Bell addressed a circular
of inquiry. By this method he obtained verified returns of 64,763
cases of blindness in continental United States or 85.2 per 100,000 of
the total population. In the same way he obtained data in regard to
89,287 persons with seriously impaired powers of hearing, or 117.5 Per
100,000 of the total population.

In each case the following questions among others were asked: "Were
his (or her) parents first cousins? If not first cousins were they
otherwise related by blood to each other, before their marriage? Were
any of his relatives blind? If yes, what relatives? (Father, mother,
grandparents, brothers, sisters, uncles, aunts, and how many of each,
so far as known)." The results of this inquiry give us the best and
most reliable statistical material which has ever been compiled on any
phase of the problem of consanguineous marriage. The investigation of
the deaf was similar to that of the blind, but even more complete.

I. The Blind. The question as to the relationship of the parents was
answered in 56,507 cases, in 2,527 or 4.47 per cent of which the
parents were reported as cousins. Of the 57,726 who answered the
question in regard to blind relatives, 10,967 or 19 per cent replied
in the affirmative.[76] The blind relatives were divided into two
groups: (a) blind brothers, sisters or ancestors, and (b) blind
collateral relatives or descendants. Table XXII concisely expresses
the results most fundamental for this study.

[Footnote 76: U.S. Census, 1900, op. cit., p. 16.]