Value of the tuning-fork in the diagnosis of disease of the auditory nerve / by Thomas Barr.

  • Barr, Thomas, 1846-1916.
Date:
[1879]
Catalogue details

Licence: Public Domain Mark

Credit: Value of the tuning-fork in the diagnosis of disease of the auditory nerve / by Thomas Barr. Source: Wellcome Collection.

Provider: This material has been provided by The University of Glasgow Library. The original may be consulted at The University of Glasgow Library.

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    of the head are propagated to the fluid in the bag, sympa- thetic vibrations are set up in the minute hair-like processes and, the terminations of the nerve being thus stimulated the sensation of sound is experienced. The simple membranous bag found in these primitive forms of life becomes evolved in the higher animals, into the complicated arrangements of the membranous labyrinth in the vestibule, semicircular canals and cochlea. This membranous structure is bathed in fluid ' and supports the ramifications of the nerves which are also' sup- posed to terminate in cells with hair-like appendages found at certain parts of the membrane. Sonorous vibrations may reach the terminal nerve-structures in the following different ways:—1st. By the special sound- conducting apparatus provided in man, and in all air breathing animals. This is sometimes called air conduction of sound, because the waves of sound, originating in the vibrating body, are transmitted through the medium of the air to the tym- panic membrane, the vibrations of which are conducted to the fluid in the labyrinth through the malleus, incus, stapes, and membrane of the fenestra ovalis. 2nd. Sonorous vibrations may reach the nerve by the bones of the head, either from direct contact of the vibrating body—direct osseous conduction, or by the waves of, sound reaching the surface of the head through the air—indirect osseous conduction. In either case the vibrations are propagated to the osseous walls of the labyrinth, tympanum, and external auditory canal. The vibrations which reach the osseous walls of the labyrinth are transmitted in part to the perilymph of the vestibule, and thence to the terminations of the nerve, but many also reach the nerve directly through the osseous lamina of the cochlea; while those from the walls of the external auditory canal and tympanum pass to the tympanic membrane, to the ossicles, and to the air contained in the external auditory canal and tympanum, and by these media reach the fluid of the labyrinth through the foramen ovale. The first, the air conduction of sound, is the ordinary mode of hearing in man, and pi'oduces a more powerful impression on the nerve than osseous conduction. This may be easily tested if we place a vibrating tuning-fork on the vertex, and, the moment the vibrations cease to be audible, transfer the fork to a point an inch or two from the ear, when the sound will be heard for some time longer. Vibrations received from the air by the bones of the head have the least effect upon the nerve. This is to be expected if we consider with what diffi- culty sonorous vibrations are transmitted from air to solids,