750 HEARING [CH. LIV. 



stimulus is conducted to the brain. If two tones are sounded 

 together, the two appropriate fibres respond, and the analysis of the 

 now more complex stimulus is performed in the cochlea. The fibres 

 of the basilar membrane increase in radial length from the base 

 towards the apex of the cochlea. According to the resonance-theory, 

 the upper part of the organ would thus be affected by low tones, the 

 lower part by high tones. 



The first of these two classes of theory makes it difficult or 

 impossible for us to explain our ability to analyse complex chords 

 into their component tones. The full acceptance of the second is 

 difficult in the face of the small difference of length (at most 1 : 12) 

 between the shortest and the longest of the basilar fibres. On the 

 other hand, it accounts for nearly all the phenomena which require 

 explanation, and gains support from the effects of experiment on, 

 and disease of, different portions of the cochlea. For instance, the 

 deafness to high pitched tones (seen in boiler makers) is associated 

 with disease of the lower whorl of the cochlea. 



