Deafness practically illustrated / [James Yearsley].

  • James Yearsley
Date:
[1849]
Catalogue details

Licence: Public Domain Mark

Credit: Deafness practically illustrated / [James Yearsley]. Source: Wellcome Collection.

    45/200 page 33
    surface. If, on the other hand, the air remains in the tympanum, and becomes expanded beyond the external standard, the membrane is forced outwards, but is pre- vented from assuming a convex form, by its attachment to the handle of the malleus. In either case, whether the pressure be exerted on the membrane of the tym- panum from within or without, imperfection of hearing is the uniform result. This unfortunate contingency admits of a satisfactory elucidation. In the natural and healthy condition of the organ of hearing, the mem- brana tympani closes in the internal ear, being firmly attached by its margin, but without any degree of tension, and in this state is best fitted for the per- formance of its allotted function, which becomes im- peded, when from any cause the membrane is rendered inordinately tense. M. Savart found by actual experi- ment upon a preparation of the membrane of the tym-— panum in the dried state, that when loud sounds were occasioned in its immediate neighbourhood, the vibra- tion of the membrane in a relaxed state was sufficient to throw off from its surface particles of fine sand or minute seeds. M. Savart also found, that when, by means of a small lever, he produced tension of the membrane, sounds of similar intensity occasioned in it more feeble vibrations, and less motion of the dust strewn upon its surface, than when the membrane was suffered to remain in a state of relaxation. The mem- brana tympani may likewise be made tense by a volun- tary effort, and temporary deafness produced by an individual, in whom the sense of hearing is naturally perfect. If the mechanism of blowing be performed forcibly by the cheeks, while the mouth and nostrils are Cc 3
    No text description is available for this image
    No text description is available for this image
    No text description is available for this image