v THE SENSE OF HEARINd 239 



transmit the vibrations they receive to the respective IHT\V- 

 tibres in corresponding frequency, amplitude, and form, just as in 

 a telephone the sound-waves are transformed by the metal plate 

 and magnet into electrical movements which correspond to tin- 

 shocks which produce them. 



According to Rutherford the analysis of tones takes place, 

 not at the peripheral organs, but in the centres, and it is impos- 

 sible to offer any mechanical explanation of it. 



Rutherford's theory of the excitation of the organ of Corti as 

 a whole, by means of sound-waves transmitted from the tympanic 

 apparatus, presents obvious advantages over that of Helmholtz, 

 and avoids the more serious objections to which the latter is open. 

 But it has one grave defect, which almost entirely deprives it of 

 the character and importance of a true theory of audition. It 

 assumes that when stimulated by,, sound-waves the auditory 

 nerve can transmit them to the brain, with all their character- 

 istics of frequency, intensity, and timbre, as though the fibres 

 which compose it were fully analogous to the metal wires of a 

 telephone. 



Rutherford endeavoured to justify his theory experimentally. 

 When a motor nerve is excited by rapid shocks from an induced 

 current there is complete tetanus of the muscle if the number of 

 shocks is 40 per second, and with increased frequency of the 

 stimulus the muscle remains in tetanus. But on auscultating the 

 muscle by suitable means while it is in tetanus a sound is heard, 

 according to Rutherford, the pitch of which varies up to a certain 

 point with the frequency of stimulation ; this was demonstrated 

 by Loven, who considered the sound produced to be the effect 

 of electrotonic variations in the nerve. When, for instance, 40 

 shocks per second are sent into the nerve a deep tone of 40 vibra- 

 tions is heard. Rutherford found that on applying 352 stimuli 

 per second there is a muscle-sound of corresponding pitch. At a 

 still higher frequency of stimulation there is no longer any tone, 

 but only a noise. This does not, according to Rutherford, invalidate 

 his theory, because the muscle-fibre is quite different from the 

 nerve-fibre or cell, which he believes capable of receiving stimuli 

 of far higher frequency than these. He refers in this connection 

 to the wings of insects, as bees, the motor nerves of which are 

 capable of conveying to the muscles fully 460 impulses per second. 

 But even this is far removed from the 40,000-50,000 vibrations 

 of the highest perceptible tones. 



Another very cogent objection which may be raised against 

 all theories which, like Rutherford's, deny the peripheral analysis 

 of tones, and refer this faculty to the cerebral cortex, is that they 

 do not take into account the complex structure of the organ of 

 Corti and the cochlea in general, when they ascribe to it the com- 

 paratively simple function of a vibrating membrane. Comparative 



