=Tuning Fork Test.=—The normal time rate in seconds set of forks is as
follows:
Fork 32 64 128 512 2048 4096
B. C. 25 30 30 20 10
A. C. tone 70 90 90 40 20
The tuning fork test, carefully made, is the only known method of
measuring the functions of the various structures concerned in audition.
=The Whisper Test= is made by producing a clear whisper from residual
air only, which should be heard about twenty feet by a normal ear.
=The Watch Test= is made by using some loud ticking watch (I prefer
an Ingersoll), holding it first near the ear until the patient
recognizes the tone, and then taking it beyond the hearing distance and
approaching the ear until it is heard. I prefer also to move away from
the ear until the limit is reached and strike an average of this with
the above results. The average eighteen size Ingersoll watch can be
heard for from 100 to 150 inches by the normal ear.
The practical test for the patient is his hearing from the spoken
voice, and is the most reliable so far as permanent results are
concerned.
=Low Tone Limit.=—The lowest limit of hearing is about sixteen double
vibrations per second, but the lowest practical limit is about
thirty-two. There are few people with normal hearing and with musically
trained ears who can recognize a definite tone lower than this, so I
consider the thirty-two fork sufficiently low for all practical tests.
=Conduction Deafness.=—Low tones are lost in tympanic involvement or
conduction deafness, and are diagnostic in such cases, but are of no
particular value in nerve deafness except when that is complicated by
catarrhal deafness.
=Practical Hearing Limits.=—The human voice varies from about 60 to 150
double vibrations per second, and most sounds that we really need to
hear are less than 700 vibrations per second. This is the reason for
using the low forks, 64, 128 and 512.
=Measurement of Nerve Force.=—To measure auditory nerve force, the fork
(say the 128, whose normal B. C. is 30 seconds) is set into vibration
and held gently and with even pressure against the mastoid and the
patient is asked to tell or signal the doctor when he ceases to hear
the tone. Two or more tests may be made to determine the patient’s
personal equation, but the use of control forks (the 64 and 512) will
show any such error. Granting that there is no complicating pathology,
tympanic or labyrinthine, the number of seconds of hearing over 30 will
be the patient’s auditory nerve force. For example, if he hears the
fork 30 seconds his hearing will be thirty-thirtieths or normal. If his
hearing is 25, 20, 15 or 10 seconds, his auditory nerve force will be
respectively 25-30, 20-30, 15-30 or 10-30.
By means of this method an accurate measurement of the functions of
hearing can be made and a definite prognosis can be given. I never use
any of the various named qualitative fork tests for hearing, because
they have no value to one who employs this system.
FOOT NOTE—In the chart T is used, meaning that tone is heard, while S
indicates sound but no tone.
FOOT NOTE—It is not the purpose to give any detailed or differential
methods of diagnosis because if one cares to treat these diseases he
will of course, study a special text on this subject. The methods here
given are only for the general practician who wishes a general idea of
the condition present.