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medium, the membrane. As no substance can be applied over tbe 

 meatus, however it be done, which does not hinder our hearing of 

 external sounds just as much as it occasions resonance of parietal 

 ones, the membrane on this supposition must in some degree or 

 other be a positive detriment to the auditory function. Besides, were 

 hearing aided by resonance within the drum, a patent Eustachian 

 tube by allowing vibrations to disperse must impair hearing, which 

 I know not to be the case. Again, if we assume the membrane to 

 but slightly arrest the transition of sound from the outer to the 

 tympanic air, to be, in short, an unavoidable impediment to hearing, 

 fulfilling some non-acoustic purpose, the loss of it would not prove 

 at once, as it does, a serious detriment to hearing rather than some 

 benefit. I may append too, that were it but a trifling obstacle, the 

 group of sounds occurring within it, so described, should be aug- 

 mented by resonance in the external meatus, on its outlet being 

 stopped ; yet I can detect nothing of the sort. Further, I squeezed 

 a plug of chewed brown paper, and one of dry paper, firmly into the 

 bottom of the meatus of the healthy ear, against the membrane, co- 

 vered the membrane with a stratum of wax, and filled the meatus 

 with water ; but in not one of these experiments were the said group 

 of sounds rendered louder. So that it appears that the application to 

 the membrane of even a highly reflecting surface fails to intercept 

 and cause to return intra- tympanic sounds, which can only be be- 

 cause the membrane is difficult for such sound to pass through. But 

 if the membrane highly resists the transition of aerial vibrations, it 

 (the fenestra rotunda being the chief portal) is a serious detriment 

 to hearing. Hence this fenestra cannot be of this acoustic conse- 

 quence. And we must have recourse to the only other theory which 

 suggests itself, which is 



4. That the membrane and ossicles form the essential path for 

 sonorous vibrations, which traverse it by the mode of condensation 

 and rarefaction ; that aerial ones impinging upon the outer surface 

 of the membrane easily impress themselves upon its substance, and pass 

 into the ossicles, whilst the inner surface presents a great obstacle 

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

 tions that fall upon it from this air. Thus, when disease nullifies 

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

 from without passes into the drum and is wasted, or deafness re- 



