1 1 92 THE EAR. 



is heard having a pitch equivalent to 40 vibs. per second. Eutherford, 

 indeed, found it possible to employ as many as 352 stimuli per 

 second ; and, on listening over the muscle, to hear a tone of a pitch of 

 that number of vibrations per second. More than 352 stimuli per 

 second did not produce a tone but only a noise. This, however, does 

 not, according to Eutherford, invalidate his theory, for, as he points out, 

 a muscular fibre is a very different thing from a nerve fibre or a nerve 

 cell, and he is of opinion that stimuli of far greater frequency than that 

 recorded might be transmitted along a nerve. Eutherford further 

 instances the case of the insect's wing, such as that of the honey-bee, in 

 which 460 impulses per second pass along the motor nerves to the 

 muscles of the wing. 



The most obvious objection to any theory 1 which dispenses with 

 peripheral analysis, is that it leaves the exceedingly elaborate 

 structure of the organ of Corti, and indeed of the cochlea as a 

 whole, out of account ; or, to put the matter in another light, it 

 assigns to that organ a comparatively simple function (like that of a 

 vibrating membrane), and one which could be performed by a more 

 simple structure. Further, the holder of such a theory, while recognising 

 the analytic powers we undoubtedly possess, must refer these powers to 

 the cortex cerebri, and practically admit that the problem cannot be 

 solved. Ohm's law may be subject to limitations, but at present there 

 is no substitute for it. Moreover, the cochlea becomes more elaborate 

 in all its parts as we ascend the animal scale, until in man, who doubt- 

 less possesses greater powers of analysis than any other animal, the 

 number of hair cells, fibres of the basilar membrane, and arches of Corti, 

 are all much increased. Finally, it has been shown that on purely 

 physical grounds the organ of Corti may be considered to be an analytic 

 apparatus, a view consistent with physical theory, and with all we know 

 of the mode of action of the other peripheral sense organs. 



A further question, however, arises, namely, as to whether it is possible for 

 the cochlea to analyse a compound tone on any other principle than that of 

 sympathetic resonance. Various attempts have been made to explain its mode 

 of action in another way. Hurst 2 has suggested that with each movement 

 inwards and outwards of the stapes, a peculiar wave is generated which travels 

 up the scala vestibuli, through the helicotrema into the scala tympani, and down 

 the basilar membrane to the fenestra rotunda. This wave is not a mere 

 undulation of the basilar membrane, but it causes movements of fluid to and 

 fro in each scala, and these produce a peculiar wave of pressure. As the one 

 wave ascends while the other descends, a movement (or pressure) of the 

 basilar membrane occurs at the point where they meet, and the movement is 

 chiefly in the direction of the tectorial membrane, so that this membrane strikes 

 suddenly on the hair cells and thus irritates the nerves. The point at which 

 the waves meet will depend upon the pitch of the note, or, in other words, upon 

 the time interval between the two waves. In this way, and without sym- 

 pathetic resonance, the cochlea would, within limits, respond to tones of 

 different pitch. The intensity of the movement of the tectorial membrane 

 against the hair cells would, of course, correspond to intensity of tone. The 

 mode of action of the cochlea as an analyser is not, I think, sufficiently ex- 

 plained by this theory. Thus, if c' and g be sounded, we have a fifth, with a 

 vibration ratio of f . A compound wave-movement is transmitted, and this 



1 A full statement of all the speculations of physiologists as to the cochlea will be 

 found in von Stein's book, op. cit., S. 138-155. 



2 "A New Theory of Hearing," Trans. Liverpool Biol. Soc., 1895, vol. ix. pp. 321-353. 



