Notice of several cases of malformation of the external ear, and of experiments on the state of hearing in such persons, / by Allen Thomson ... Together with an account of the dissection of a similar case of malformation / by Joseph Toynbee.

  • Allen Thomson
Date:
1847
Catalogue details

Licence: Public Domain Mark

Credit: Notice of several cases of malformation of the external ear, and of experiments on the state of hearing in such persons, / by Allen Thomson ... Together with an account of the dissection of a similar case of malformation / by Joseph Toynbee. 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.

    19/24 (page 17)
    1? the top of his head towards the quarter from whence he kne>\' or supposed the sound to proceed. The lad 13. and the other persons similarly affected, hear sounds proceeding from bodies in the air near them (that is not in contact with their head) better with the mouth open than shut; but this is the case with most other persons, and may depend upon two causes. First, that resonance, both of the air in the cavity of the mouth and of the teeth occurs; and second, that the teeth thus become more directly the conductors of sound. Experiments clearly show that no sounds enter the tympanum by the air of the Eustachian tube, and, I need hardly say, that the gaping of the listener is more the effect of the mental act of atten- tion, during which the muscles of the jaw are relaxed, than con- nected with any provision for the increase or conduction of sono- rous vibrations through the Eustachian tube. Neither the lad 13., nor Miss E., had from their sensations ever been led to regard the ears as the seat of hearing; and from the experiments I have performed, I should be inclined to think that other persons, if their external ears were completely stopped, would not readily form that conclusion, which they are so im- mediately led to make, from the varying intensity of the sensations in opposite ears which occurs in the common mode of hearing. When in a person whose ears are natural the external meatus are completely stopped, the sensations of sound appear to affect the whole head, so immediately and equally are they conducted to both cars by the hard parts. Unless, indeed, very marked sounds are made to act close to one or other ear, or unless jarring and painfully intense sounds affect the organ, they are referred indis- tinctly to the whole heaiL Our notion, therefore, of the ears as the seat of hearing, or our power of localizing the impressions of sound, appears to depend upon three circumstances. 1st, Upon the varying intensity of sounds that may affect one ear by turning it in different directions. 2d, Upon the different intensity of sounds affecting opposite ears; and 3d, upon painful sensations accompanying sound. Such pain, however, as is felt from certain sounds, does not pro- bably exist in the auditory nerve itself, but rather in the sensory nerves of the tympanum, and there seems to be a final cause for the existence of these sensations in the increased tension which by re- fiex action they induce in the membrana tympani, and the conse- quent impediment they occasion to the farther or too powerful trans- mission of such sounds to the internal ear, I could not ascertain that such ])ainful sensations had ever been experienced either in the lad 13. or ^liss R., and I am inclined to think that they do not exist in them, in consequence of the absence of the membrana tympani. In the concluding part of this paper it is my intention to trace the malformation I have described to its origin, at an early period c