Page:Memoir upon the formation of a deaf variety of the human race (microform) (IA cihm 08831).pdf/45

40 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. In Table U of the Appendix I have classified the people of the United States according to the decades in which they were born, and have reduced the number born in each decade to a percentage of the whole. In the same table I have classified the 12,154 congenital deaf mutes mentioned by Mr. Wines in a similar manner, and also the deaf-mutes who have both parents deaf-mutes. We can thus examine upon the same scale the distribution of the three classes according to age. The results are shown graphically in the diagram, Fig. 12.

The ordinates represent the percentage of the whole who were born in the decades indicated by the abscissæ.

If we assume that the numerical relation now existing between congenital deaf-mutes and hearing persons of the same age approximately represents the proportion of the congenitally deaf to the whole population born at the period when they were born, we have a means of comparing the growth of the congenitally deaf population with that of the population at large.

The indications are that the congenital deaf-mutes of the country are increasing at a greater rate than the population at large; and the deaf-mute children of deaf-mutes at a greater rate than the congenital deaf-mute population.