HELMHOLTZ IN BONN 



of its radial fibres, which corresponded to the exciting 

 tone, would vibrate, and the vibrations would extend 

 with diminishing strength on the adjacent portions of 

 the membrane. Possibly some of the structures on 

 the surface of the membrane might act as dampers. 

 In this way the parts of the membrane near the base 

 of the cochlea would be adapted for the higher, while 

 those near the vertex of the cochlea would be suitable 

 for the deeper tones. Corti's arches are, therefore, of 

 secondary importance, serving either as supporting 

 structures, or for transmitting vibrations of parts of 

 the basilar membrane to the rows of hair cells placed 

 on their backs. 



Helmholtz also discussed the question as to whether 

 histological evidence as to the number of possible 

 vibratile structures is such as will satisfy the demands 

 of theory. He attempted to answer this question on 

 the basis of E. H. Weber's statement, that practised 

 musicians can * perceive even a difference of pitch 

 for which the vibrational numbers are as 1000 to 

 1001,' or the -$ f th of a semitone, a smaller interval 

 than that between two of Corti's arches, on the 

 assumption that there are about 33^ for each semitone 

 in each cochlea ; and he accounted for the apparent 

 deficiency by the explanation, that if a tone came in 

 between the pitch of two of the arches, 'it would 

 set them both in sympathetic vibration, and the arch 

 would vibrate the more strongly which was nearest 

 in pitch to the proper tone.' This would also ex- 



