158 Mr. Cooper's Observations, &c. 



tympani; and the labyrinth must have suffered from the removal 

 of the stapes, and from the consequent discharge of water con- 

 tained 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 tym- 

 pani is destroyed, the functions of this membrane have been 

 carried on by the membranes of the fenestra ovalis and fenestra 

 rotunda : for, as they are placed over the water of the laby- 

 rinth, 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 accident or disease ; so 

 that, whenever any particular part is destroyed, another is sub- 

 stituted for it, and the organ, from this deprivation, suffers but 

 little injury in its functions. 



It seems that the principal use of the membrana tympani is, 

 to modify the impressions of sound, and to proportion them to 

 the powers and expectation of the organ. Mr. P — had lost this 

 power for a considerable period after the destruction of the 

 membrane; but, in process of time, as the external ear acquired 

 the additional motions I have described, sounds were rendered 

 stronger or weaker by them. When, therefore, he was addressed 

 in a whisper, the ear was seen immediately to move; but, when 

 the tone of voice was louder, it then remained altogether mo- 

 tionless. 



