Page:Popular Science Monthly Volume 27.djvu/31

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That this is not peculiar to the pupils of this particular institution, and that it holds true of deaf-mutes in general, is shown by the following table, compiled from the records of six institutions:

The table shows that, among 5,823 deaf-mutes taken from different parts of the country, 1,719, or 29$1/2$ per cent, are known to have had deaf-mute relatives, and that this is due to the influence of heredity is well shown when we contrast those who were born deaf with those who had afterward lost their hearing. Many of those who lose their hearing by accident or disease have no hereditary tendency to deafness, but a considerable number of those who lose their hearing at some time after birth are born with an hereditary predisposition to deafness. If, therefore, we contrast the congenitally deaf with those who have become deaf, we should expect the latter class to have a much smaller percentage of deaf relatives than the former class, but a greater percentage than the community at large.

Professor Bell has compiled the following two tables from the one which is given above, and they show that, while only about 13 per cent of the pupils which were not born deaf have deaf relatives, more than 54 per cent of the congenitally deaf pupils are recorded as having such relatives: