NUMBER OF THE CONGENITALLY DEAF IN 1880, 1890, AND 1900
| Total Number | Congenitally Deaf | Per Cent | Ratio per Million of Population | |
| 1880 | 33,878 | 12,155 | 35.6 | 242 |
| 1890 | 40,562 | 16,866 | 41.2 | 269 |
| 1900 | 37,426 | 12,609 | 33.7 | 166 |
From this it appears that congenital deafness is decreasing both in relation to all deafness, and to the general population.
For further statistics, we may revert to our tables under adventitious deafness. In the tables relating to periods of successive recent years we find in respect to three schools, the New York and Western Pennsylvania institutions and the Maryland School, with certain fluctuations, no great change on the whole, though the last named school shows still a very high proportion. In two schools, the Michigan and Wisconsin, rather an increase is observed. In the Pennsylvania Institution, which covers a period of seventy years, there is a decrease from over 50 per cent to less than 40.
A better test perhaps lies in the comparison of the proportions found for congenital deafness in the tables relating to periods widely separated in time. In these an increase is seen in the single case of the Ohio School; while a decrease is apparent in three, namely, the American and Iowa schools and the New York Institution. These decreases in percentages are respectively from 44.8 and 50.1 to 35.2; from 37.2 to 26.9; and from 42.9 to 38.0.[60]
From the evidence that we have, then, taken together, it seems reasonable to conclude that congenital deafness is, though slowly, becoming less in the course of the years.
Conclusions with Respect to the Elimination or Prevention of Deafness
Most of what has been said in this chapter with respect to the elimination or prevention of deafness may be summed up as follows:
1. There are two kinds of deafness—adventitious and congenital. Of the total number of cases adventitious deafness comprises nearly two-thirds, and congenital deafness a little over one-third.
2. Nearly all adventitious deafness is caused by some disease of infancy or childhood attacking the middle or internal ear, a large part being of infectious character. The two chief diseases causing such deafness are scarlet fever and meningitis, with a less amount from brain fever, typhoid fever, measles, catarrh, diphtheria, whooping cough, etc.