216 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



In Table U of the Ai)i)eii(lix I bave classified the people of the United States according to the 

 decades in wliich they were born, and have rednced the number born in each decade to a percent- 

 age of the whole. In tlie same table I have classified the 12,154 congenita! deaf mntes mentioned 

 by Mr. Wines in a, similar manner, and also the deaf-mutes who have both parents deaf-mutea. 

 We can tiins examine uikjii the same scale the distribution of the three classes according to age. 

 The results are shown graphi(;ally in the diagram. Fig. 12. 



■ ^The ordinates represent the percentage of the whole wlio were born in the decades indicated 

 by the abscissa. 



If we assume that the numerical relation now existing between congenital deaf-mutes and 

 hearing persons of the same age approximately i-epresents 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 indicatiom are that the congenital deaf-mutes of tlie country are increasing at a greater rate 

 than the population at large; and the deaf-mute children of deaf-mutes at a greater rat^ than the con- 

 genital deaf-mute population. 



