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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 the 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 

 the cuticular face assimilates that to the inner one, when the ear 

 excludes both tympanic and outej sounds from the labyrinth. Deaf- 

 ness produced by disease in the external meatus only yields noises 

 when it propagates irritation so as to excite secretion of mucus on 

 the inner face of the drum-head. Simple perforation of the drum- 

 head only deafens in proportion to the extent of surface removed. 

 If there co-exist a more or less fluid discharge from the drum, this 

 spoils hearing by covering the cuticular surface of the membrane, 

 though it may not deviate so much acoustically from that lined by 

 mucous membrane as to very materially damage it. To remedy such 

 deafness mechanically, we should first essay to rescue the cuticular 

 face from the fluid by placing some material to draw off the discharge 

 from it, so as to keep the membrane fit for its duties, and still ex- 

 posed to aerial vibrations. If the mischief is so extensive that we 

 are obliged to employ some disc to rest against the remaining ossicles 

 as a substitute for the true membrane, we should try to form one 

 with surfaces acoustically imitating those of the membrane itself. 



The paper concludes by pointing out how the various injuries which 

 have been known to occur by disease or otherwise to the different 

 parts of the tympanum, are readily accounted for by the functional 

 hypothesis here submitted. 



