A guide to the study of ear disease / by P. Mcbride.

  • McBride, P. (Peter), 1854-1946.
Date:
[1884]
Catalogue details

Licence: Public Domain Mark

Credit: A guide to the study of ear disease / by P. Mcbride. Source: Wellcome Collection.

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

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    fork be applied to the middle line of the head, either on the brow, the teeth, or lower jaw, it is normally- heard in both ears with equal intensity. The manner in which the sonorous vibrations are perceived when the stem is placed upon the bones of the head, is not the same as when the fork is held at some distance from the ear and so heard. In the latter case the waves of sound impinge upon the tympanic membrane, causing it to vibrate, and with it the whole chain of ossicles, includ- ing the stapes, which communicates the motion to the fluids of the labyrinth, thus acting upon the expansions of the auditory nerve. On the other hand, by placing the stem of the fork on the cranial bones, the vibrations are, to a great extent, conducted directly to the labyrinth, without the intervention of the meatus or tympanum. If, then, the tuning-fork be heard well when placed upon the cranial bones, we are entitled to conclude that the sound-perceiving apparatus is acting, and if deafness be present, that it is due to some lesion in the external or middle ear. In cases where the fault lies in the sound-conducting apparatus, not only is the sound of the vibrating-fork heard well in the affected ear, but is actually heard louder than if the ear were healthy. This fact is best explained for clinical purposes by the hypothesis that the same obstruction in the sound - conducting apparatus which prevents vibrations reaching the labyrinth from the air, also prevents those which have reached it through the cranial bones from escaping, and thus they become intensified. Whether the physics of this explanation are faultless in all cases is doubted by some, but the idea originated with a very excellent physicist, Mack1 If a person with good hearing place a vibrating tuning- 1 A Treatise on the Diseases of the Ear, by St. John Koosa, 4th ed. p. 73.