366 EFFECTS OF TENSION OF THE TYMPANUM. 



It has been proved by the experiments of Savart and Miiller, that 

 Ofthedeterm- when the tension of the membrana tympani is increased, so- 

 ination of the norous undulations pass with less readiness through it. In- 



intensity of so- 



niferouswaves. deed, this may be yenned by personal experiment, as when, 

 by a strong effort of .expiration or inspiration, the mouth and nostrils be- 

 ing closed, we compress air into the tympanic cavity or withdraw it there- 

 from through the Eustachian tube, and thereby stretch the membrana 

 tympani outwardly or inwardly, the hearing at once becomes indistinct, 

 and sounds are enfeebled. The same ensues on going down in a diving- 

 bell, or suddenly ascending in a balloon. Of the former effect, Dr. Col- 

 Deafness in the ladon gives the following account during a descent in a div- 

 diving-beii. ing-bell at Howth in 1820. "We descended," says he, 

 " so slowly that we did not notice the motion of the bell ; but as soon 

 as the bell was immersed in water, we felt about the ears and forehead a 

 sense of pressure, which continued increasing during some minutes. I did 

 not, however, experience any pain in the ears, but my companion suffered 

 so much that we were obliged to stop our descent for a short time. To 

 remedy. that inconvenience, the workmen instructed us, after having closed 

 our nostrils and mouth, to endeavor to swallow, and to restrain our respi- 

 ration for some moments, in order that, by this exertion, the external air 

 might act on the Eustachian tube. My companion, however, having tried 

 it, found himself very little relieved by this remedy. After some minutes 

 we resumed our descent. My friend suffered considerably : he was pale ; 

 his lips were totally discolored ; his appearance was that of a man on the 

 point of fainting ; he was in involuntary low spirits, owing perhaps to the 

 violence of the pain, added to that kind of apprehension which our situa- 

 tion unavoidably inspired. This appeared to me the more remarkable, as 

 my case was totally the reverse. I was in a state of excitement resem- 

 bling the effect of some spirituous liquor. I suffered no pain. I expe- 

 rienced only a strong pressure around my head, as if an iron circle had 

 been bound about it. I spoke with the workmen, and had some diffi- 

 culty in hearing them. This difficulty of hearing rose to such a height 

 that during three or four minutes I could not hear them speak. I could 

 not, indeed, hear myself speak, though I spoke as loudly as possible, 

 nor did even the great noise caused by the violence of the current against 

 the sides of -the bell reach my ears." 



Under natural circumstances, a stretching of the membrane inwardly 

 Action of the * s accom pli sne( l by the contraction of the tensor tympani mus- 

 musciesofthe cle, the stapedius holding tight contemporaneously on the 

 loop of the stirrup, and preventing disturbance of position of 

 the bony chain at that end, and hindering any outward bulging of the 

 membrane of the fenestra ovalis. When, therefore, the soniferous waves 

 impinge upon the membrana tympani, they tend to throw it into vibra- 



