752 SPECIAL SENSES. 



ence of vibrations after the waves of sound cease in the air. This provision 

 enables rapid successions of sounds to be distinctly and acurately repeated. 



The arrangement of the muscles and bones of the middle ear is such that 

 the tension of the membrtina tympani may be regulated and graduated with 

 great nicety. It does not seem to be necessary to perfect audition that this 

 should be done for every single note or combination of notes, but the mem- 

 brane probably is brought by voluntary effort to a definite degree of tension 

 for notes within a certain range as regards pitch or for successions and pro- 

 gressions of sounds in a particular key. As far as the consciousness of this 

 muscular action is concerned, it may be revealed only by the fact of the cor- 

 rect' appreciation of certain musical sounds. Some persons can educate the 

 ear so as to acquire what is called the faculty of absolute pitch ; that is, with- 

 out the aid of a tuning-fork or any musical instrument, they can give the ex- 

 act musical value of any given note. A possible explanation of this is that 

 such persons may have educated the muscles of the ear so as to put the tym- 

 panic membrane in such a condition of tension as to respond to a given note 

 and to recognize the position of this note in the musical scale. Finally, an 

 accomplished musician, in conducting an orchestra, can by a voluntary effort, 

 direct his attention to certain instruments and hear their notes distinctly, 

 separating them from the general volume of sound, can distinguish the 

 faintest discords and can designate a single instrument making a false note. 



Destruction of both tympanic membranes 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, although 

 this is done imperfectly. In a case reported by Astley Cooper, one membrana 

 tympani was entirely destroyed, and the other was nearly gone, there being 

 some parts of its periphery remaining. In this person the hearing was some- 

 what impaired, although he could distinguish ordinary conversation without 

 much difficulty. 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 ex- 

 cellent 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." 



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

 ing 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 accessory action. If the 

 regular waves of a musical sound be conveyed to the terminal filaments of 

 the auditory nerves, these waves make their impression and the sound is cor- 

 rectly appreciated. It makes no difference, except as regards intensity, how 

 these waves are conducted ; the sound 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 



