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.

3. A considerable part of this deafness is preventable under enlightened
action. Medical science is principally in control of the situation, but
there is also much that can be done in general measures for the
protection of the health. In attacking the problem, the most immediate
practical program lies in the arrest of those diseases, especially
infantile and infectious diseases, that cause deafness.

4. Our evidence is incomplete to determine definitely whether
adventitious deafness is increasing or decreasing relatively among the
population; but it is hardly other than likely that it is decreasing.
Although certain diseases producing deafness fail to show any extensive
signs of abatement, there are other diseases from which there can be
little doubt that deafness is decreasing.

5. In the outlook there is, on the whole, promise, both in respect to
the treatment of deafness itself and of the diseases that lead to
deafness, though it cannot be said in any sense that any large or
general relief is