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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    will still be heard almost exclusively on the closed side. Sim- ilar exaggeration of the impression of sound may be noted in our own persons when, in the act of speaking, we close our auditory meatuses—the vibrations of our vocal apparatus transmitted by the cranial bones, will then affect our auditory nerves much more strongly. Lastly, by placing a watch in the mouth, between the teeth of the upper and lower jaws, the sound of the ticking will be heard with much greater inten- sity when we close the ears with the fingers. It is noteworthy that, in stopping the ears, if the finger be pressed into the canal of the ear very firmly, the increase of sound is less marked than when there is closure with only slight pressure, or the sound, instead of being increased, may be actually diminished. The interesting fact, to which Weber was the first to direct attention, that when a vibrating tuning-fork is placed on the vertex, and the external auditory canal of one side is closed with the finger, the sound on that side is much intensified, affords a basis for the application of the tuning fork for the purpose of diflTerential diagnosis. A great amount of labour, by way of experiment and otherwise, has been expended to explain this phenomenon. Politzer, in his recently published volume, gives the following explanation of the increased loudness of the sound on the occluded side:—1st, The increased resonance of the external auditory canal, and the reflection upon the tympanic membrane and ossicles of the vibrations transmitted by the bones of the head to the air in the external passage. 2nd, The hindrance to the passing away from the ear of the waves of sound conducted by the bones of the head to the labyrinth and tympanum. 3rd, The altered tension of the membrane and ossicular chain. This subject is fully treated of, along with that of the effect of very firm pressure in the meatus on osseous conduction, by Politzer, in the ArcJiiv fur Ohrenheilkunde of 1864. The tuning-fork most useful for our purpose should be large sized, and of the pitch C, with 512 vibrations in the second, fitted to produce a sound sufficiently long continued to ensure that the patient has time to recognise on which side he hears the sound best. It yields two simultaneous tones—the funda- mental or deep tone, and the overtone or high tone. The over- tone is usually appreciated more distinctly when the fork is held some distance from the ear; the fundamental tone predom- inates when it is held nearer. The clear overtone is a source of fallacy with some patients sufiering from one-sided deafness, as, when the sounding fork is placed on the head, the overtone, from its great clearness, seems to be heard very distinctly on