200 SPECIAL SENSES. 



rubber, when this is introduced. As regards the mere acute- 

 ness of hearing, aside from the pitch of sounds, the explana- 

 tion of the action of the membrane is very simple. As was 

 shown by Miiller, 1 sonorous vibrations are not readily trans- 

 mitted through the atmosphere to solid bodies, like the bones 

 of the ear ; and, when they are thus transmitted, they lose 

 considerably in intensity. When, however, the aerial vibra- 

 tions are received by a delicate membrane, under the condi- 

 tions of the membrana tympani, they are transmitted with 

 very little loss of intensity ; and if this membrane be con- 

 nected with solid bodies, like the bones of the middle ear, 

 the vibrations are readily conveyed to the sensory portions of 

 the auditory apparatus. The parts composing the middle ear 

 are thus admirably adapted to the transmission of sonorous 

 waves to the auditory nerves. The membrane of the tym- 

 panum is delicate in structure, stretched to the proper degree 

 of tension, and vibrates under the influence of the waves of 

 sound, as has been clearly demonstrated by Savart. 2 Attached 

 to this membrane, is the chain of bones, which conducts its 

 vibrations, like the bridge of a violin, to the liquid of the 

 labyrinth. The membrane is fixed at its periphery and has 

 air on both sides, so that it is under the most favorable condi- 

 tions for vibration. 



A study of the mechanism of the ossicles and muscles of 

 the middle ear shows that the membrana tympani is subject 



1 MULLER, Elements of Physiology, London, 1843, vol. ii., p. 1248. Miiller 

 has investigated very closely the physical laws of the transmission of sonorous 

 vibrations through media of different densities. The following paragraph illus- 

 trates the application of these laws to the physiology of the middle ear : 



" A small solid body, fixed in an opening by means of a border of membrane, 

 so as to be movable, communicates sonorous vibrations, from air on one side, 

 to water, or the fluid of the labyrinth, on the other side, much better than solid 

 media not so constructed. But the propagation of sound to the fluid is rendered 

 much more perfect if the solid conductor thus occupying the opening (fenestra 

 of the labyrinth) is by its other end fixed to the middle of a tense membrane 

 which has atmospheric air on both sides." 



2 SAVART, Recherches sur les usages de la membrane du tympan et de Voreille 

 externe, Journal de physiologic, Paris, 1824, tome iv., p. 203, et seq. 



