300 Royal Society : — 



instant of deglutition, or of the reverse act, eructation, which occludes 

 the glottis. 



From numberless observations, I am able to affirm that the faculty 

 of audition is not at all deteriorated by patency of the tubes, how- 

 ever the ordinary use of the ear may be perplexed by soimds enter- 

 ing the tube. Nor does stretching the membrana tympani, by aug- 

 menting or diminishing the aerial pressure on its inner surface, 

 enfeeble hearing. 



I will now turn to observations made upon my left ear when it 

 was deafened. I show that the external meatus was unaffected ; and 

 if I rubbed my finger over the skin covering the bone behind the ear, 

 or carried the ticking of a watch to the bottom of the meatus by 

 means of a metallic probe, and then did the like to the other ear, I 

 heard well, and as well upon one as the other. Hence the labyrinth 

 and acoustic nerve remained healthy, and the drum alone was 

 affected. Singing noises in the head had been developed just to the 

 same extent as hearing had been blunted, — phenomena that for three 

 weeks before an instantaneous cure remained quite unchanged. 



The noises were caused by the circulation of the blood about the 

 drum, for they rose and fell as the circulation was quick or otherwise. 

 And I was led to the belief that these noises were not created by any 

 morbid change of local circulation, but that, by a moi-lid change in 

 the acoustic properties of the tynipamim, ordinary movements of the 

 blood thereabouts were heard in a nndtiplied manner ; for the 

 click and souffle from air entering the Eustachian tube, as heard 

 in the healthy ear, were wonderfully magnified in the deaf one. 

 The louder souffle, that of eructation, normally but very weak, 

 even when the intruding air strongly forces outwards the membrana 

 tympani, in the deaf ear was always a very pronounced bruit. And 

 a couple of other sounds from distinct sources generated within the 

 site of the membrane are described, which, hardly audible in a normal 

 ear, are loud in an ear thus diseased. 



Thus a grouj) of phenomena beckon to the inference, that this 

 deafness had so modified the acoustic properties of the drum, as both 

 to render all sonorous vibrations affecting the air within it by far 

 more audible than before, and all those entering the meatus audi- 

 torius externus as much less audible than before. What physical 

 cause can bring about these inverse effects ? 



1 . If the fenestra rotunda be the chief portal for sound, no change 

 at it could render one set of sormds more audible Avithout doing so 

 for the other also. 



2. If sound be mainly conveyed to the labyrinth by undulatory 

 displacements of the membrana tympani, causing bodily oscillation 

 of the ossicles, the membrane could not be rendered more responsive 

 to aerial waves falling upon one side of it without becoming equally 

 so for those falling upon its other. 



3. If the fenestra rotunda chiefly afford passage to sound, and the 

 membrana tympani has acquired an abnormally high reflecting 

 power, repelling vibrations that would heretofore have escaped 

 through it from the drum back upon this fenestra, and those that 

 fall upon its outer surface back through the meatus, effects of an in- 



