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XXIX. On Sounds tnaudihle lij certain Ears. By William 

 Hyde Wollastox, M.D. P.R.S* 



It is not my intention to occupy the time of this Society with 

 the consideration of that mere general dullness to the impression 

 of all kinds of sound which constitutes ordinary deafness, but to 

 request its attention to certain peculiarities that I have observed 

 with respect to partial insensibility in different states of the ear, 

 and in different individuals; for I have found that an ear, which 

 would be considered as perfect with regard to the generality of 

 sounds, may, at the same time, be completely insensible to such 

 as are at one or the other extremity of the scale of musical notes, 

 the hearing or not hearing of which seems to depend wholly on 

 the pitch or frequency of vibration constituting the note, and not 

 upon the intensity or loudness of the noise. 



Indeed, although persons labouring under common deafness 

 have an imperfect perception of all sounds, the degree of indi- 

 stinctness of different sounds is commonly not the same ; for it 

 will be found upon examination, that they usually hear sharp 

 sounds much better than low ones ; they distinguish the voices of 

 women and children better than the deeper tones in which men 

 commonly speak; and it may be remarked, that the generality 

 of persons accustomed to speak to those who are deaf, seem 

 practically aware of this difference, and, even without reflecting 

 upon the motives which guide them, acquire a habit of speaking 

 to deaf persons in a shriller tone of voice, as a method by which 

 they succeed in making them hear more effectually than by 

 merely speaking louder. 



In elucidation of this state of hearing, which casually occurs 

 as a malady, I have observed, that other ears may for a time be 

 reduced to the same condition of insensibility to low sounds. I 

 was originally led to this observation, in endeavouring to investi- 

 gate the cause of deafness in a friend, by trial of different modes 

 of closing, or otherwise lessening the sensibility of my own ears. 

 I remarked that, when the mouth and nose are shut, the tym- 

 panum may be so exhausted by forcible attempt to take breath 

 by expansion of the chest, that the pressure of the external air is 

 strongly felt upon the membrana tympani, and that, in this state 

 of tension from external pressure, the ear becomes insensible to 

 grave tones, without losing in any degree the perception of 

 sharper sounds. 



The state to which the ear is th is reduced by exhaustion, may 

 even be preserved for a certain time without the continued effort 

 of inspiration, and without even stopping the breath, since by 



■• From tlic Transactions of the Royal Society for 1820, Part IF. 



A a 2 sudden 



