VOL. XC.l PHILOSOPHICAL TRANSACTIONS. 629 



an organ becomes imperfect, every agent which can be employed to increase its 

 powers is called into action ; and, in the case here described, the external ear had 

 acquired a distinct motion upward and backward, which was observable whenever 



Mr. P listened to any thing which he did not distinctly hear. This power 



over the muscles was so great, that when desired to raise the ear, or to draw it back- 

 wards, he was capable of moving it in either direction. 



This case is not the only one of this description which has come under my ob- 

 servation ; for another gentleman, Mr. A — , applied to me under a similar com- 

 plaint, but in one ear only, proceeding from suppuration, and producing the same 

 effects. This gentleman has the same power of forcing air through the imperfect 

 ear; suffers equally from bathing, if the meatus auditorius be unprotected; and 

 feels, even from exposure to a stream of cold air, very considerable pain. The only 

 difference I could observe was, that in Mr. A.'s case, the defect of hearing in the 

 diseased organ was somewhat greater than in the former ; for though, when his 

 sound ear was closed, he could hear what was said in a common tone of voice, yet 

 he could not distinguish the notes of a piano-forte at the same distance: a difference 

 which might have in part arisen from the confused noise which is always produced 

 by closing the sound ear ; or because, as he heard well on one side, the imperfect 

 ear had remained unemployed, and consequently had been enfeebled by disuse. 



From these observations it seems to follow, that the loss of the membrana 

 tympani in both ears, far from producing total deafness, occasions only a slight 

 diminution of the powers of hearing. Anatomists who have destroyed this mem- 

 brane in dogs, have asserted, that at first the effect on the sense of hearing was 

 trivial ; but that after a few months a total deafness ensued. Haller also has said, 

 that if the membrane of the tympanum be broken, the person becomes at first hard 

 of hearing, and afterwards perfectly deaf. But in these instances the destruction 

 must have extended further than the membrana tympani ; and the labyrinth must 

 have suffered from the removal of the stapes, and from the consequent discharge of 

 water contained in the cavities of the internal ear ; for it has been very constantly 

 observed, that when all the small bones of the ear have been discharged, a total 

 deafness has ensued. 



It is probable, that in instances in which the membrana tympani is destroyed, the 

 functions of this membrane have been carried on by the merrflbranes of the fenestra 

 ovalis and fenestra rotunda : for as they are placed over the water of the labyrinth, 

 they will, when agitated by the impressions of sound, convey their vibrations to 

 that fluid in a similar manner, though in somewhat an inferior degree, to those 

 which are conveyed by means of the membrana tympani and the small bones which 

 are attached to it; and thus, in the organ of hearing, each part is admirably adapted, 

 not only to the purpose for which it is designed, but also as a provision against ac- 

 cident or disease; so that, whenever any particular part is destroyed, another is 

 substituted for it, and the organ, from this deprivation, surfers but little injury in 

 its functions. It seems that the principal use of the membrana tympani is, to modify 



