In the census investigations,[43] of the number who answered on this point, 2,525, or 7.4 per cent, have parents who were cousins. Of these cases, deafness occurred in 87 per cent before the fifth year of age, and in 60 per cent at birth. Of all the deaf born without hearing, 13.5 per cent are the offspring of consanguineous marriages. The proportion of those born deaf is thus nearly twice as great when the parents are cousins as it is among the whole class of the congenitally deaf; and the proportion is also nearly twice as great of the offspring of consanguineous marriages among the congenitally deaf as the proportion of the deaf from such marriages among the total number of the deaf. Moreover, 55.0 per cent of the offspring of cousin-marriages have deaf relatives of some kind, and of the congenitally deaf from cousin-marriages, 65.6 per cent have deaf relatives; while the respective proportions when the parents are not cousins are 25.5 per cent and 40.7 per cent--in the one case less than half, and in the other two-thirds, as great. Further statistics bear out the findings of the census. Dr. E. A. Fay in his "Marriages of the Deaf"[44]--a work we are soon to notice--finds that, though consanguineous marriages form only about one per cent of the total number considered, 30.0 per cent of the children of deaf parents who are cousins are deaf, and that 45.1 per cent of such marriages result in deaf offspring; but that when the parents are not cousins, the respective proportions are 8.3 per cent and 9.3 per cent--only about a fourth and a fifth as great. In the Colorado School, out of 567 pupils in attendance from the beginning to 1912, in 17, or 3 per cent, the parents were related before marriage. In the Kentucky School, out of 83 pupils admitted in 1910 and 1911, 18, or 19.3 per cent, and out of 42 admitted in 1912 and 1913, 8, or 19 per cent, were the offspring of parents who were cousins. In the Iowa School, out of 62 admissions in 1911 and 1912, 4, or 6.5 per cent, and in the Maryland School, out of a total attendance in 1911 of 135, 13, or 9.2 per cent, had parents who were cousins.[45] Consanguineous marriages, so far as the effect on deafness is concerned, are not of relatively frequent occurrence. But where they do take place, there is found a decided connection between them and deafness, the increased tendency thus to transmit a physical abnormality being plain. How far, however, if at all, such deafness is to be directly ascribed to consanguineous marriages, is a matter for question. The main consideration seems to be that in such marriages the chances are at least doubled of the offspring acquiring the characteristics of the parents; and that in them the liability is thus proportionately enhanced of transmitting deafness.[46] THE DEAF HAVING DEAF RELATIVES