PHYSIOLOGY OF THE MIDDLE EAR. 191 



produced by the stretching of the membrane, so as to put it in unison 

 with the sound produced. Independently, however, of the experiments 

 of M. Savart, which show, that unison is not necessary for the produc- 

 tion of vibrations, the fact, that we are capable of distinguishing several 

 sounds at the same time, would seem to negative the supposition. Nor 

 can we easily conceive, that the membrane could admit of as many 

 distinct vibrations as the ear is capable of accurately appreciating 

 tones, amounting to about eight octaves. Bichat thought, that the 

 degree of tension of the membrane corresponded with the intensity of 

 sounds; and that by it the sonorous vibrations attained the internal 

 ear in a degree sufficiently strong to excite the appropriate impression, 

 but not so strong as to cause pain, the membrane becoming more tense 

 for a feeble sound, and relaxed for one too strong. In support of this 

 view, Bichat cites the case of several persons, who could not hear ordi- 

 nary sounds, until the ear had been impressed by louder, which, accord- 

 ing to him, roused the. membrane to tension. M. Savart, on the other 

 hand, from the fact that every membrane vibrates with more difficulty, 

 and less extensively, according to its tension, conjectures that the mem- 

 brane is relaxed in the case of very feeble or agreeable sounds, and is 

 rendered tense to transmit the too powerful or disagreeable. 



Again, it has been conceived that the tension varies with the tone 

 of the sound, being augmented according to some physiologists, in 

 acute, according to others, in grave sounds. Sir Everard Home, 1 it 

 has been remarked, esteems the membrane to be muscular: and he 

 affirms, that it is chiefly by means of this muscle, that accurate per- 

 ceptions of sound are made by the internal organ ; and that the mem- 

 brane can alter its degree of tension. It has been before observed, 

 that the muscles, attached to the small bones, are capable of varying 

 this tension ; that the internal muscle of the malleus or tensor tympani, 

 for example, by its contraction, renders it more tense. Sir Everard 

 admits, " that the membrana tympani is relaxed by the muscle of the 

 malleus, but not for the purpose alleged in the commonly received 

 theory. It is stretched in order to bring the radiated muscle of the 

 membrane itself into a state capable of acting, and of giving those 

 different degrees of tension to the membrane, which empower it to cor- 

 respond with the variety of external tremors: when the membrane is 

 relaxed, the radiated muscle cannot act with any effect, and external 

 tremors make less accurate impressions." The reader is referred to the 

 remarks already made on the views of Sir Everard in their anatomical 

 relations. His speculations do not, however, end here. He employs 

 the discovery to account for the difference between a "musical ear," as 

 it is usually termed, and one which is incapable of discriminating, or 

 feeling pleasure from, the succession of musical tones, with what suc- 

 cess we shall inquire presently. The truth is, that none of the conjec- 

 tures, which have been proposed regarding the precise effects of tension 

 or relaxation of this membrane, can be looked upon in any other light 

 than as ingenious speculations, based, generally, upon the fact, that the 

 membrane seems certainly capable of being varied in its tension by the 



1 Lect. on Comp. Anat., iii. 265. 



