SENSIBILITY OF THE AUDITORY NERVE. 543 



The rods of Corti are probably arranged so that each is set 

 to vibrate in unison with a particular tone, and thus strike a 

 particular note, the sensation of which is carried to the brain 

 by those filaments of the auditory nerve with which the little 

 vibrating rod is connected. 



The distinctive function therefore of these minute bodies is, 

 probably, to render sensible to the brain the various musical 

 notes and tones, one of them answering to one tone, and one to 

 another ; while perhaps the other parts of the organ of hearing 

 discriminate between the intensities of different sounds, rather 

 than their qualities. 



Sensibility of the Auditory Nerve. 



Most frequently, several undulations or impulses on the 

 auditory nerve concur in the production of the impressions of 

 sound. 



By the rapid succession of several impulses at unequal inter- 

 vals, a noise or rattle is produced ; from a rapid succession of 

 several impulses at equal intervals, a musical sound results, 

 the height or acuteness of which increases with the number of 

 the impulses communicated to the ear within a given time. A 

 sound of definite musical value is also produced when each one 

 of the impulses, succeeding another thus at regular intervals, 

 is itself compounded of several undulations, in such a way that, 

 heard alone, it would give the impression of an unmusical 

 sound; that is to say, by a sufficiently rapid succession of 

 short unmusical sounds at regular intervals, a musical sound 

 is generated. 



It would appear that two impulses, which are equivalent to 

 four single or half vibrations, are sufficient to produce a definite 

 note, audible as such through the auditory nerve. The note 

 produced by the shocks of the teeth of a revolving wheel, at 

 regular intervals upon a solid body, is still heard when the 

 teeth of the wheel are removed in succession, until two only 

 are left ; the sound produced by the impulse of these two teeth 

 has still the same definite value in the scale of music. 



The maximum and minimum of the intervals of successive 

 impulses still appreciable through the auditory nerve as de- 

 terminate sounds, have been determined by M. Savart. If 

 their intensity is sufficiently great, sounds are still audible 

 which result from the succession of 48,000 half vibrations, or 

 24,000 impulses in a second ; and this, probably, is not the 

 extreme limit in acuteness of sounds perceptible by the ear. 

 For the opposite extreme, he has succeeded in rendering sounds 

 audible which were produced by only fourteen or eighteen half 



