692 THE SENSE OF HEARING. 



branous labj-rinth is ; for, as a solid body insulated by a 

 different medium, it is capable of resonance. 



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 those 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 

 intervals, a noise or rattle is produced ; from a rapid suc- 

 cession 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, 



