nt as
offspring of cousins.

It is interesting to note in this connection that in 1900, Dr. Lee
Wallace Dean, of the University of Iowa examined the 181 blind
children in the Iowa College for the Blind, and found that 9 or nearly
5 per cent were the offspring of first cousin marriages.[78] Dr. Dean
continues,

If we exclude from the list those blind children who were blind
because of blennorrhea neonatorum, sympathetic opthalmia,
trachoma, etc., and consider only those who suffered because of
congenital conditions, we should find that 14 per cent were the
result of consanguineous marriage of the first degree....
Among the pupils who have entered the college since 1900 the
percentage is about the same.

[Footnote 78: _Effect of Consanguinity upon the Organs of Special
Sense_, p. 4.]

This was written in 1903, three years before the publication of Dr.
Bell's report.

Statistics from foreign sources give even larger percentages of the
blind as the offspring of consanguineous marriage. Dr. Feer quotes
fourteen distinct investigations of the etiology of retinitis
pigmentosa, embodying in all 621 cases, of which 167 or 27 per cent
were the offspring of consanguineous parents.[79] Retinitis pigmentosa
is perhaps more generally attributed to consanguineous marriage than
any other specific disease of the eye, and it is to be regretted that
the Census report does not give any data in regard to this cause.
Retinitis pigmentosa in known to be strongly inheritable, as is
albinism and congenital cataract.

[Footnote 79: _Der Einfluss der Blutsverwandschaft der Eltern auf die
Kinder_, p. 14.]

Looking now at the other side of the problem, that of the probability
of consanguineous marriages producing blind offspring, we have as our
data the 2527 blind whose parents were cousins, and a conservative
estimate which may be made from the data in Chapter II that 1,000,000
persons in continental United States are the offspring of cousins
within the degrees included in the Census report.[80] In the general
population 852 per million are reported as blind, and 63 per million
as congenitally blind. The actual figures for the offspring of cousin
marriages are 2527 per million for all blind and 632 per million for
the congenitally so. In other words only 0.25 per cent of the
offspring of cousin marriages are blind and only 0.05 per cent are
congenitally blind. Although the probability that a child of related