THE LABYRINTH AND THE EIGHTH NERVE 387

During the wars many cases of labyrinthine deafness due to high explosives
came under observation. Sometimes the patients suffered from shock and
presented all the signs of sensorineural deafness. As a rule the deafness and
tinnitus diminish in the weeks following the injury and, when present,
vertigo and disturbances of equilibrium disappear in a few weeks, A degree
of deafness usually remains sometimes with severe loss of the higher fre-
quencies. Such injuries are frequently accompanied by rupture of the tym-
panic membrane (Figs. 199, 204). Treatment consists of complete rest and

Fig. 204. High-explosive shell injury of ear. Horizontal section. Sho\vs rupture of anterior part of
drumhead, with everted edges. 1, Anterior portion of ruptured drumhead (everted); 2, Posterior
margin of rupture, also everted; 3, Malleus; 4, Facial nerve, with stapedius to the left; 5, Smooth end
of posterior vertical canal; 6, Lower part of utricle with crista quarta; 7, Internal meatus; 8, Carotid
canal; 9, Tubal part of tympanum.

administration of sedatives. In a certain number of cases a functional element
is present, especially in those in which examination of the vestibular appar-
atus shows normal reactions. It must not, however, be taken for granted
that deafness—especially when only moderate in amount—in the presence
of normal vestibular responses is necessarily functional. The cochlear
apparatus lies between the oval and round windows, and it is thus more
sensitive to violent commotion of the atmosphere than the vestibular struc-
tures.

'Noise* Deafness. The ever-increasing din to which most of us are exposed
in everyday life constitutes a potential hearing hazard, though individuals
vary greatly in their subjective response to noise. Too little attention is still
paid to the problems of noise control. Constant exposure to loud noises is
a well-known cause of labyrinthine deafness. It is met with in boiler-makers,
coopers, factory workers and service personnel. Miners and others who
use pneumatic or electric drills are also affected. The deafness is due to
degeneration affecting Corti's organ. Most observers hold that the patho-
logical condition is an exhaustion atrophy from over-excitation affecting
primarily that part of the cochlear duct which corresponds to the prevailing
sound. The deafness increases gradually and is not as a rule accompanied
by tinnitus. Men who use a sporting gun occasionally suffer from deafness
in one ear—as a rule the left, as they usually shoot from the right shoulder.

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