strongly inherited, it disappeared entirely
in the next generation with a non-consanguineous marriage. The
inheritance of tendencies or weaknesses may be more common than the
actual inheritance of defects. Dr. Bell's words on this point are
suggestive:

Where a tendency toward ear trouble exists in a family, it may
lie dormant and unsuspected until some serious illness attacks
some member of the family, when the weak spot is revealed and
deafness is produced. We are not all built like that wonderful
one-horse shay that was so perfectly made in all its parts that
when at last it broke down it crumbled into dust. When an
accident occurs it is the weak spot that gives way, and it
would be incorrect to attribute the damage to the accident
alone and ignore the weakness of the part; both undoubtedly are
contributing causes.

In the case, then, of a deaf person who has deaf relatives, the
assigned cause of deafness may not be the only cause involved,
or indeed the true cause at all. It may be the cause simply in
the same sense that the pulling of a trigger is the cause of
the expulsion of a bullet from a rifle, or a spark the cause of
the explosion of a gunpowder magazine; hereditary influences
may be involved.[92]

[Footnote 92: U.S. Census _Report on the Blind and the Deaf_, p. 127.]

It is thus possible to account for the large proportion of deafness
among persons of consanguineous parentage by the simple action of the
laws of heredity. Why then should we go out of our way to look for a
cause of the defect in consanguinity itself? When two explanations are
possible, the simpler explanation is the more probable, other factors
being equal; but in the present problem the factors are not equal, for
the evidence points strongly toward the simpler hypothesis of
intensified heredity, while there is little or no evidence that
consanguinity is a cause _per se_.

As to the probability then of a consanguineous marriage producing deaf
offspring, it will readily be seen to be very slight, and in those
cases where there is actually no trace of hereditary deafness in the
family, perhaps no greater than in non-related marriages. While the
census figures in regard to the deaf are not complete they probably
include a great majority of the deaf in the United States. The 89,287
deaf would mean an average of 12 deaf persons to every 10,000
inhabitants and the 14,472 cong