THE MEMBRANA TYMPANI 739 



There is an important consideration that must be kept in view in 

 studying the uses of any distinct portion of the auditory apparatus, like 

 the membrana tympani. This membrane, like all other parts of the 

 apparatus, except the auditory nerves themselves, has simply an acces- 

 sory action. If the regular waves of a musical sound are conveyed to 

 the terminal filaments of the auditory nerves, these waves make their 

 impression and the sound is correctly appreciated. It makes no differ- 

 ence, except as regards intensity, how these waves are conducted ; the 

 sound is appreciated by the impression made on the nerves, and on the 

 nerves only. The waves of sound are not like the waves of light, 

 refracted, decomposed, perhaps, and necessarily brought to a focus as 

 they impinge on the retina ; but so far as the action of the accessory 

 parts of the ear are concerned, the waves of sound are unaltered ; that 

 is, the rate of their succession remains the same, though they are reflected 

 by the concavities of the concha and repeated by the tympanic membrane. 

 Even if it be assumed that the membrane under normal conditions repeats 

 musical sounds by vibrations produced by influence, and that sounds are 

 exactly repeated, the position of these sounds in the musical scale is not 

 and can not be altered by the action of any of the accessory organs of 

 hearing. The fact that a person may retain his musical ear with both 

 membranes destroyed is not an argument against the view that the mem- 

 brane repeats sounds by influence ; for if musical sounds or irregular 

 vibrations are conducted to the auditory nerves, the impression produced 

 must of necessity be dependent exclusively on the character, regularity 

 and number of the sonorous vibrations. And again, the physical laws of 

 sound teach that a membrane like the membrana tympani must repro- 

 duce sounds with which it is more or less closely in unison much better 

 than discordant or irregular vibrations. In a loud confusion of sounds, 

 one can readily distinguish melody or harmony, even when the vibrations 

 of the latter are comparatively feeble. 



It has been shown that the appreciation of the pitch of sounds bears 

 a certain relation to the degree of tension of the tympanic membrane. 

 When the membrane is rendered tense, there is insensibility to low 

 notes. When the membrane is brought to the highest degree of tension 

 by voluntary contraction of the tensor tympani, the limit of appreciation 

 of high notes may be raised from three thousand to five thousand vibra- 

 tions. It is a fact in the physics of the membrana tympani that the 

 vibrations are more intense the nearer the membrane approaches to a 

 vertical position ; and it has been observed that the membrane has a 

 position more nearly vertical in musicians than in persons with an 

 imperfect musical ear (Troltsch). 



Experiments have shown that the tympanic membrane vibrates more 



