USES OF DIFFERENT PARTS OF THE AUDITORY APPARATUS. 839 



muscles of the larynx may act so as to produce successions of notes as rapidly as they can 

 be correctly appreciated. Nor does the fact that we must prepare the tympanic mem- 

 brane for certain notes militate against the theory we have just given, for musical com- 

 positions present melodious successions in a certain scale, the notes of which hear well- 

 defined harmonious relations to each other, and we immediately appreciate a change in 

 the key, which is simply a change in the fundamental. These changes in the key must 

 be made in accordance with the laws of modulation ; otherwise they are harsh and grat- 

 ing. Modulation in music is simply a mode of-passing from one key to another by certain 

 transition-notes or chords, which seem inevitably to lead to a certain key, and to no 

 other. Finally, the laws of vibration by influence show that a single vibrating membrane 

 returns the quality as well as the pitch of tones and of combinations of tones as well. 



The theory we have just given of the possible action of the membrana tympani is an 

 elaboration of the view advanced by Everard Home. Unfortunately for the simplicity of 

 the mechanism of hearing and the idea of division and isolation of function in different 

 parts, which is so seductive to physiologists, there are certain faets and considerations 

 which may prevent some from adopting it absolutely and exclusively as an explanation 

 of the mechanism of the appreciation of musical sounds. These are the following : 



Destruction of both membrane tympani does not necessarily produce total deafness, 

 although this condition involves considerable impairment of hearing. So long as there 

 is simple destruction of these membranes, the bones of the middle ear and the other 

 parts of the auditory apparatus being intact, the waves of sound are conducted to the 

 auditory nerves, though imperfectly. In a remarkable case reported by Sir Astley 

 Cooper, which is cited by most writers upon physiology, one membrana tympani was en- 

 tirely destroyed, and the other was nearly gone, there being some parts of its periphery 

 remaining. In this person, the hearing was somewhat impaired, although he could dis- 

 tinguish ordinary conversation pretty well. Fortunately, he had considerable musical 

 taste, and it was ascertained that his musical ear was not seriously impaired ; " for he 

 played well on the flute and had frequently borne a part in a concert. I speak this, not 

 from his authority only, but also from that of his father, who is an excellent judge of 

 music, and plays well on the violin : he told me, that his son, besides playing on the 

 flute, sung with much taste, and perfectly in tune." This single case, if its details be 

 accurate which we have no reason to doubt shows conclusively that the correct appre- 

 ciation of musical sounds may exist independently of the action of the membrana tym- 

 pani. 



There is one consideration, of the greatest importance, that must be kept in view 

 in studying the functions of any distinct portion of the auditory apparatus, like the 

 membrana tympani. This, like all other parts of the apparatus, except the auditory 

 nerves themselves, has simply an accessory function. If the regular waves of a musical 

 tone be conveyed to the terminal filaments of the auditory nerves, these waves make 

 their impression and the tone is appreciated. It makes no difference, except as regards 

 intensity, how these waves are conducted ; the tone is appreciated by the impression 

 made upon the nerves, and 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 im- 

 pinge upon the retina; as 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 ahsolutely 

 the same, though they be reflected by the concavities of the concha and repeated l>y the 

 tympanic membrane. Even if we assume that the membrane, under normal conditions, 

 repeats musical sounds by vibrations produced by influence, and that this membrane is 

 tuned by voluntary muscular action so that tones are exactly repeated, the position of 

 these tones in the musical scal^ is not and cannot be altered by the action of any of the 

 accessory organs of hearing. The fact that a person may retain his musical ear witli 

 both membranes destroyed is not really an argument against the view that the membrane 

 repeats tones by influence ; for, if musical tones or noisy vibrations be conducted to the 



