This section is from the book "The Home Hand-Book of Domestic Hygiene and Rational Medicine. Volume 2.", by J. H. Kellogg, M.D.. Also available from Amazon: The Home Hand-Book of Domestic Hygiene and Rational Medicine, Volume 2.
Quite a variety of instruments have been invented for the purpose of intensifying sound for the benefit of tlmse who are hard of hearing, in cases in which the middle ear is the seat of the disease, the auditory nerve remaining intact. Two of the nmst useful instruments are shown in Figs. 460 and 461. Auricles, Fig. 462, are of rather doubtful value. The conversation tube, Fig. 463, is a very serviceable instrument. Fig. 464 shows at a and b, small silver cornets, which are recommended on account of the ease with which they can bo concealed. They are, however, of little value as aids to hearing. Some years ago the discovery was made that a small bit of moist cotton in the ear adds greatly to the hearing power when the drum membrane is ruptured. Artificial drum membranes, Fig. 465 are now made and are often very serviceable, in some cases, though all are not benefited by them.
Fig. 460. Dipper Trumpet.
Fig. 461. Ear Trumpet.
Fig. 462. Auricles.
Fig. 463. Conversation Tube.
Fig. 464. Small Silver Cornets.
Fig. 465. Artificial Drum Membrane.
Fig. 466. The Audiphone.
The audiphone, Fig. 466, is a recent invention, which is of service in some cases of deafness, though it is by no means so universally applicable as has been claimed by its inventor. It is composed of a sheet of gutta-percha attached to a handle and made tense by means of a cord. In use, the upper edge is placed against the front teeth, through which the vibrations of sound are communicated to the bones of the skull and to the auditory apparatus. The principal objection is its price, which is very exorbitant when compared with its actual cost. A sheet of card-board eight or ten inches square may be used in the same way as the audiphone. The dentaphone is practically the same as the audiphone, the only difference being that it may be folded so as to be convenient to carry in the pocket. The megaphone, an instrument by which very distant sounds may be distinctly heard when wholly imperceptible to the unaided ear, is one of the numerous inventions of Mr. Thos. A. Edison. The instrument constructed by him, the marvelous powers of which were exhibited to us by his laboratory assistant, is of such mammoth proportions as to be of no particular value for the relief of deafness. It is quite doubtful whether it can be sufficiently reduced in size to be of any value for this purpose.