AUDITORY SENSATIONS 577 



and then the other telephone be held up to the other unfatigued ear, 

 the sound is at once referred to the unfatigued side. In this localised 

 projection of the sound waves we have a simple means of judging of 

 the presence or absence of the apparatus in one ear or the other. It 

 was pointed out by Bonders that, when one ear was fatigued by a note 

 of 360 vibrations per second, and immediately afterwards a note of 

 .365 vibrations per second was conducted equally to both ears, no trace 

 was perceptible of fatigue, the sound being located exactly in the 

 median line. We are therefore justified in concluding that the end- 

 organ of the nerve fibre which carries the nerve impulses corresponding 

 to a vibration frequency of 360 per second is not the same as the nerve 

 fibre or end apparatus which evokes the sensation corresponding to a 

 note of 365 vibrations per second. If this theory is correct, destruc- 

 tion of the lower part of the cochlea should abolish the power of 

 appreciation of high notes, while damage to the region of the helico- 

 trema should impair sensibility to low notes. Certain results of 

 experiments on dogs afford confirmation of this view, although all 

 such results involving judgment of the powers of appreciation of high 

 or low sounds respectively possessed by animals must be received with 

 caution. A few isolated cases have been recorded in man in which 

 atrophy of the nerve fibres supplying the lower whorl of the cochlea 

 was attended by total want of perception of high tones. 



According to Rutherford, the whole of the basilar membrane, and therefore 

 of the auditory hairs, vibrates equally to every note, just as the plate of a 

 telephone receiver reproduces faithfully the shape of the vibrations impinging 

 on the transmitter of the telephone. This ' telephone theory,' as it has been 

 called, relegates the whole work of analysis to the central nervous system, 

 and gives us no clue as to how such an act of analysis may take place. One 

 would imagine that a much simpler apparatus than that represented by the 

 organ of Corti would be sufficient, if no analysis of the stimulus took place 

 in the peripheral organ. 



When a bow is drawn against the edge of a plate the vibrations affect different 

 parts of the plate unequally, so that lycopodium powder sprinkled on such a 

 plate assumes a complicated pattern. Waller suggests that the basilar mem- 

 brane vibrates as a whole to every tone, but that it presents nodal and inter - 

 nodal points, like the vibrating plate. Since the hair-cells move with the basilar 

 membrane they produce what may be called * pressure patterns ' against 

 the membrana tectoria, so that different combinations of nerve fibres are 

 stimulated according to the pattern, i.e. according to the shape of the com- 

 pound wave. A somewhat similar hypothesis has been put forward by Ewald, 

 but neither of these thepries presents any advantages over the resonator theory 

 of Helmholtz, nor does it account satisfactorily, as the Helmholtz theory does, 

 for the remarkable powers we possess of analysing all kinds of complex sounds. 

 The cochlea becomes more elaborate in structure as we ascend the animal scale, 

 and there is no doubt that this elaboration attains its greatest height in man, 

 who possesses greater powers of analysing sounds than are possessed by any other 

 animal. 



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