135 



found them exceedingly noteworthy. Lastly, I have made certain 

 experiments upon the external auditory canals of the sound ears. 



I compare, then, with one another, the phenomena yielded by a 

 normal ear, an ear with an open Eustachian tube, an ear with the drum 

 impaired in a particular manner, and an ear whose external meatus is 

 in a known altered condition ; calling in facts from other sources in 

 aid; and, finally, endeavour to determine the uses to be assigned 

 to the several structures of the drum in order to embrace all the 

 phenomena*. 



I assure myself that my Eustachian tubes are ordinarily shut, by 

 the difficulty (greater for my left one) of forcing the breath into the 

 drums when I stop my mouth and nose, and the hinderment to its 

 escape till I swallow or eructate, showing that those acts open the 

 tubes. If we mark the sinking-in of the lachrymal sac when we swallow 

 with the mouth and nose stopped, we may see that the naso-guttural 

 cavity enlarges as the glottis is closed in that act, producing a partial 

 vacuum in the drums, and therefore from the greater barometric 

 pressure a feeling of tightness upon the membrana tympani, whilst 

 from loss of usual pressure the Eustachian tubes thereupon close more 

 firmly, and the faucial parts swell and stick together. 



I can readily distinguish the act of opening the Eustachian tube 

 from all other guttural ones, both by hearing and feeling. A tearing 

 sound, or an irregular run of clicks, marks a slower, a sharp click a 

 quicker opening of the tube, a souffle the rush of air through the 

 patent tube, and a small crack the displacement of the membrana 

 tympani. I frequently perceive these phenomena in deglutition, 

 though, owing to the strong pressure of the current of ejected air in 

 the fauces, more especially in eructation. Sometimes also in yawning, 

 showing that a sundering contraction of the muscles of the pharynx 

 and palate attends the opening of the tube. 



With the tube patent I feel the membrana tympani, as expiration 

 and inspiration alternate the greater amount of pressure in its two 

 surfaces, oscillating from outwards to inwards, as the inner canthus 

 of the eye, as reached by the nasal duct, may be seen to do. In 

 violent explosive expirations, the strength of the membrane is 



* A note shows, that though I speak particularly from these sources, the results 

 rest on much hroader grounds ; and mentions how far anything like any portion 

 of this paper has been previously published by myself or others. 



