303 Royal Society : — 



to their escape into the air in the drum, and equally repels vibra- 

 tions that fall upon it from this air. Thus, when dise.ise nuUifies 

 the great reflecting qualities of the inner surface, much of the sound 

 from without passes into the drum and is wasted, or deafness results ; 

 whilst much ofthatinthe drum enters the membrane, and some of it 

 finds its way along the ossicles, and noises in the head are engendered. 



Now I find that the cutaneous surface of the drum-head admits 

 vibrations from air with very much greater facility than water does, 

 that is, readily ; for on filling the external meatus of the sound ear 

 with water, and then letting it leak out again, I remarked that for more 

 than half an hour afterwards septa of water were constantly forming 

 themselves across the canal and producing much deafness, and then 

 breaking again with a loud noise, and the deafness vanishing. After 

 some evaporation the following instructive effects alone took place : — ■ 

 the membrane would attract a film of water over its surface, and 

 deafness ensue ; but on a gust of air plunging into the drum through 

 the Eustachian tube, the membrane spj-inging outwards with a smart 

 smack, would throw off the fluid, and the hearing as instantaneously 

 be restored. This would yradually wane away again by the re- 

 attraction of the water, to be instantaneously regained again, and so 

 on. But since the transition is easy between the membrane's outer 

 surface and air, svhat has been said above shows that it must be diffi- 

 cult between the inner surface and air, and the statement in (4.) is 

 demonstrated. 



Accordingly the external layer of the membrane is formed of skin, 

 a drv tissue of loose texture, penetrable by air, and coming into in- 

 timate relation with it ; whilst the mucous membrane of the drum 

 is, as it were, unparalleled not only for tenuit}-, but compactness and 

 high vascularity, though it is barely possible to verify the presence of 

 mucous exudation upon it, affording a glassy surface which is a for- 

 midable barrier to the passage of vibrations from it to air, and vice 

 versa ; and this is so reflected, that the membrane and ossicles lead- 

 ing to the labyrinth lie without it, confining useful vibrations to 

 their destined jiath, and excluding hurtful ones from it ; and the 

 mastoid cells help to further stifle such vibrations as by any accident 

 intrude upon the air in the drum. The membrane of the fenestra 

 rotunda, by its elasticity, protects the acoustic nerve from undue 

 compression, &c. The membrana tympaui avails acoustically by its 

 area, whilst its flexibility, the joints in the ossicular chain, &:c., are 

 mere machinery for conveying, under all contingencies, vibrations to 

 the fenestra ovalis, and provision against mechanical accidents. The 

 structure of the labyrinth admits of explanation, in a great degree, 

 upon like principles. 



The personal case of deafness studied in this paper was from a 

 cold draught on tlie ear, a mere inflammation of the mucous lining 

 of the drum, ultimately forming a layer of dried mucus upon the 

 membrana tympani, which originally involving much air-bubbles, 

 remained very permeable by air, and assimilated acoustically the 

 inner face of the membrane to the cuticular outer one. The instan- 

 taneous dispersion of the noises and deafness was caused by the 

 sudden peeling off of this false cuticle ; whilst a film of water upon 



