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It is certainly no exaggeration to say that scientific examination and treatment of the ear began with Anton von Troeltsch's method of using a perforated concave mirror reflecting daylight or artificial light into the ear. It is also probably true that since that time, 1855, more time and labor have been spent in attempts to devise satisfactory hearing tests than upon any other question of ctology. Aurists have clearly recognized this lack and have known just what they wished to accomplish.
To give a definition of normal hearing power one must consider the hearing with regard to intensity of sound, ability to hear loud or soft sounds, with regard to the pitch, and the tone, quality and also the distinctness with which rapidly recurring tones or noises can be separated by the ear. It is in consequence impossible at present to establish an absolute standard of normal hearing. Practically,
FISKE GF. THE PHONOGRAPH IN TESTING HEARING.Read before the Chieago Medical Society.. JAMA. 1890;XV(24):854-856. doi:10.1001/jama.1890.02410500010001b