e possibilities of its
prevention and the likelihood of its diminution, and then consider the
questions involved in congenital deafness.

ADVENTITIOUS DEAFNESS AND ITS CAUSES

From three-fifths to two-thirds of the cases of deafness are caused
adventitiously--by accident or disease. To accidents, however, only a
very small part are due, probably less than one-fiftieth of the entire
number.[18] Nearly all adventitious deafness results from some disease,
either as a primary disease of the auditory organs, or as a sequence or
product of some disease of the system, often one of infectious
character, the deafness thus constituting a secondary malady or ailment.
The larger portion is of the latter type, probably less than a fourth
resulting from original ear troubles.[19] In either case deafness occurs
usually in infancy or childhood, and does its harm by attacking the
middle or internal ear.

From diseases of the middle ear results over one-fourth (27.2 per cent,
according to the census) of all deafness, and from diseases of the
internal ear, one-fifth (20.7 per cent), very little (0.6 per cent)
being caused by disorders of the outer ear. Of the classified cases of
deafness, according to the census, 56.3 per cent are due to diseases
affecting the middle ear, and 42.7 per cent to diseases affecting the
internal. Of diseases of the middle ear, 72 per cent are of suppurative
character, often with inflammation or abscess, and 28 per cent
non-suppurative, or rather catarrhal in character. Of diseases of the
internal ear, 89 per cent are affections of the nerve, and 10 per cent
of the labyrinth. It is to be noted that when the affection is of the
internal ear, the result is usually total deafness.

By specified diseases, the leading causes of deafness are scarlet fever
(11.1 per cent), meningitis (9.6), brain fever (4.7), catarrh (3.6),
"disease of middle ear" (3.6), measles (2.5), typhoid fever (2.4), colds
(1.6), malarial fever (1.2), influenza (0.7), with smaller proportions
from diphtheria, pneumonia, whooping cough, la grippe, and other
diseases. A large part of deafness is seen to be due to infectious
diseases, the probabilities being that fully one-third is to be so
ascribed, with one-fifth from infectious fevers alone.

After birth and under two years of age, the chief causes of deafness are
meningitis, scarlet fever, disease of middle ear, brain fever, and
measles. From two to five scarlet fever and meningitis are