[41] Hereditary deafness is sometimes of a kind that manifests itself some years after birth, often with certain relatives similarly affected. This is especially true of catarrhal and middle ear affections, though their results may more often be partial rather than total deafness.
[42] In a part of such deafness, and also in a portion of that occurring shortly after birth, the cause is said to be syphilis. See Proceedings of International Otological Congress, ix., 1913, p. 49; Volta Review, xiv., 1912, p. 348; xv., 1913, p. 209.
[43] Special Reports, pp. 125, 236. There were 3,341 who failed to answer, and if all had made reply, our percentage would probably be higher yet.
[44] P. 108.
[45] In the Louisiana School 10 per cent of the pupils are said to have parents who were blood relatives; in the Illinois, 5 per cent; and in the Kansas, from 5 to 5.5 per cent. Report of Louisiana School, 1906, p. 17. See also Transactions of American Medical Association, xi., 1858, pp. 321-425; Proceedings of Conference of Principals, iii., 1876, p. 204; Annals, xxii., 1877, p. 242.
[46] On this subject, see Francis Galton. "Natural Inheritance", 1889, p. 132ff. See also G. B. L. Arner, "Consanguineous Marriages", 1908, p. 65ff.; C. B. Davenport, "Heredity in Relation to Eugenics", 1911, p. 124ff.
[47] Special Reports, pp. 128, 235, and passim.
[48] These proportions are further indicated in the succeeding section.
[49] Special Reports, p. 135ff.
[50] Report, 1908, p. 31.