3^4 Obfcrvathm on the DcJlruStiort 



efe£fcs. This gentleman has the fame power of forcing air 

 through the imperfect ear; fufiers equally from bathing, if 

 the meatus auditorius be unprotected ; and feeJs, even from 

 expofure to a ftrcam of cold air, very coniiderable pain. The . 

 only difference I could obferve was, that in Mr. A.'* cafe, 

 'the defect of hearing in the difcafed organ was fomewhat 

 greater than in the former; for though, when his found ear. 

 was clofed, he could hear what was faid in a common lone 

 of voice, yet he could not diftinguifh the notes of a piano 

 forte at the fame diftance : a difference which might, have in 

 part ariien from the confufed noife which is always produced 

 Tiv doling the found ear; or becaufe, as he heard well on 

 one fide, the imperfect ear had remained unemployed, and 

 consequently had been enfeebled by difule. 



From theie obfervations it feems evidently to follow, that 

 the lofs of the membrana tympani in both ears, far from 

 producing total deafnefs, occafions only a flight diminution 

 of the powers of hearing. 



Anatomifts who have deftroyed this membrane in dogs 

 have afferted, that at firft the effect on the fenfe of hearing 

 was trivial ; but that, after lh° lapfe of a few months, a total 

 deafnefs eni'ued. Baron Hallcr alio has faid, that if the 

 membrane of the tympanum be broken, the perfon becomes 

 at firft hard of hearing, and afterwards perfectly deaf. But, 

 in thefe inftances, the dettruetion muft have extended further 

 than the membrana tympani ; and the labyrinth muft have 

 fuffered from the removal of the ftapes, and from the conse- 

 quent difcharge of water contained in the cavities of the in- 

 ternal car; tor it has been very constantly ohferved, that 

 when all the fmall bones of the ear have been difeharged, a 

 total deafnefs lias enfucd. 



It is probable, that in inftances in which the membrana 

 tympani is deftroyed, the functions of this membrane have 

 been carried on by the membranes of the feneftra ovalis and 

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

 the labyrinth, they will, when agitated by the impreffions of 

 found, convey their vibrations to that fluid in a fnnilar man- 

 ner, though in fomewhat an inferior degree, to thole which 

 are coaveved by means of the membrana tympani and the 



fmaU 



