RESONANCE THEORY OF HEARING 



250 



higher particles under the supposed conditions, would fall to the 

 lot of different nerve fibres, and hence l)e produced perfectly, 

 separately and independently. Now, as a matter of fact, later 

 microscopic discoveries respecting the internal construction of 

 the ear, lead to the hypothesis that arrangements exist in the ear 

 similar to those which we have imagined. The end of every 

 fibre of the auditory nerve is connected with small elastic parts 

 which we cannot but assume to be set in sympathetic vibration 

 of the waves of sound." 



He considered that the radial fibres of the basilar membrane 

 constituted this system of resonators. This membrane increases 

 its width (about three 

 times) as it passes from 

 its beginning in the base 

 of the cochlea to its 

 termination in the apex 

 and contains somewhere 

 about 10,000 of these 

 fibres within its sub- 

 stance (Fig. 66). 



To quote again from 

 Helmholtz, " If the 

 tension in the direction 

 of its length is infini- 

 tesimally small in com- 

 parison with the tension 



in the direction of its fig. 66. — interior of right cochlea (human) expo.sed to show 



(«) modiolus, (b) ba.silar membrane, and (c) lamina spiralis 

 breadth then the radial seconuarlus. Between («) and (6) is the lamina spirahs. (E. M. 

 ' ., F'aul.) 



fibres of the basilar 



membrane may be approximately regarded as forming a system of 

 stretched strings, the membranous connection only serving to give 

 a fulcrum to the pressure of the fluid against these strings. In 

 that ease the law of their motion would be the same as if every 

 individual string moved independently of all the others, and 

 obeyed by itself the influence of the periodically alternating 

 pressure of the fluid of the labyrinth contained in the vestibule 

 gallery. Consequently, any exciting tone would set that part of 

 the membrane into sympathetic vibration, for which the proper 

 tone of one of its radial fibres that were stretched and loaded with 

 the various appendages already described corresponds most nearly 

 with the exciting tone ; and thence the Aibrations will extend 

 with rapidly diminishing strength on to the adjacent parts of the 

 membrane." 



That is, three factors are implicated, viz. length, tension and 



17—2 



