On the StruBure and Ufes of the Afemhrana Tympam. 93 



The third and moft general method is the fermentation of wine. In this procefs neither 

 water nor carbonic acid is produced ; but an abforption of oxygen takes place : this acetous 

 acid contains tartar, alcohol, and colouring matter. 



The fourth mode, which is nearly fimilar to the third, the difference, perhaps, being 

 only becaufe it is no longer the vegetable fluid called lume which produces the acetous acid, 

 is a particular fermentation which takes place in certain animal or vegetable produ£ls 

 above-mentioned, but efpecially in urines. This acid is always combined with ammonia. 



III. 



On the StruBure and Ufes of the Memhrana Tympani of the Ear. By EvERARD HoME, 



Efq. F.R.S.* 



T. 



HE fubjed of inquiry appointed by the Croonlan Inftitution, has been greatly 

 elucidated at different times by ingenious members of this learned Society. A large field, 

 however, Hill remained open ; and, refpecling future inveftigations, I (hall have occafion 

 to offer a frefh proof of the aid to be derived from comparative anatomy, in afcertaining 

 the ftrudure of parts which, from their minutenefs and fituation in the human body 

 admit with much difficulty of being explored. 



The principal obje£i: of the prefent le£lure is to communicate a difcovery of the 

 flrudturc of the membrana tympani ; which, in fome refpedls, affords a new and very 

 curious inftance of the application of mufcular action, and may conduce to account for 

 certain phaenomena in the fenfe of hearing, in a more fatisfaftory manner than has hitherto 

 been propofed. 



The membrana tympani has always been confidered as a common membrane, which, by 

 means of mufcles belonging to the malleus being ftretched or relaxed, became fitted, in its- 

 various degrees of tenfion, to convey the vaft variety of external founds to the internal 

 organ. Its fhape, fituation, and office, have procured it the name of drum of the ear j 

 and the mufcles of the malleus having been deemed fufficient for bracing and unbracing it, 

 lefs attention was beftowed on the ftrudture of the membrane itfelf: to which may be 

 added, that in the human ear, and generally in the ear of quadrupeds, the membrane is fo 

 extremely fmall and thin, and in its fituation fo peculiarly confined,, as. not to be got at for 

 infpedion but with much difficulty. 



The cafe is different in the elephant, where this membrane is fo very large, that the part* 

 of which it is compofed are readily diflinguifhed : they are even confpicuous to thejiakcd 

 eye *, and mufcular fibres are feen paffing along the membrane, in a radiated mannerj from 

 the bony rim which furrounds it, towards the handle of the malleus, to which the central. 

 I^art of the membrane is firmly attached. 



• fhilof, Tranfaaions, 1800,. 



Thl&, 



