518 PHYSIOLOGY 



a system of stretched strings bound together by a semi-fluid substance. The 

 parts of the membrane near the fenestra rotunda would be adapted for the 

 higher notes, while those near the helicotrema would vibrate to deep tones. 

 Each fibre would, by its vibration, set the overlying part of the organ of 

 Corti into vibration, so that each nerve fibre composing the auditory nerve 

 would be stimulated by a different note. Miiller's law of specific irritability is 

 thus observed, each nerve fibre transmitting an impulse which excites one 

 quality, and only one quality, of sensation. When a compound wave falls on 

 the organ of Corti, it is actually resolved into its simple component waves 

 by the fibres of the basilar membrane, and we therefore get stimulation of a 

 number of nerve fibres and a sensation produced which is a true mixed sensa- 

 tion compounded of a number of simple tone sensations. By an effort of 

 attention therefore it is possible to pick out from a mixed sensation its 

 different components, and in this way we may explain the analytic powers of 

 the ear. 



Certain observations on fatigue of the auditory fibres support the notion 

 that each fibre reacts to notes of one pitch, and only to these notes. If the 

 vibrations of a tuning-fork be conducted by two telephones to both ears 

 the sound appears to come from somewhere in front of the middle line of the 

 body. If the sound be transmitted to one ear for some time so as to produce 

 a condition of slight fatigue, 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 vibra- 

 tions per second was conducted equally to both ears, no trace was per- 

 ceptible 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, destruction of the lower part of the cochlea should 

 abolish the power of appreciation of high notes, while damage to the region 

 of the helicotrema 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 



