236 PHYSIOLOGY CHAP. 



periphery as afc the central end. The same occurs in a pianoforte 

 when the dampers are raised. If the sound-wave of a powerful 

 note is directed against the strings by a musical instrument or 

 by the human voice, all, and only, those strings vibrate simultane- 

 ously of which the tones are contained in the note sounded. If, 

 writes Helmholtz, every string of a piano could be joined to a 

 nerve-fibre so as to throw it into excitation, each sound produced 

 by the instrument would (as is the case in the ear) call forth a 

 series of sensations exactly corresponding to the pendular vibrations 

 into which the original movement of the air was decomposed, and 

 the presence of each of the constituent harmonies would be 

 perceived in exactly the same way as in the ear. 



Numerous objections can be raised to this inviting theory. 



We have seen that the membrane of the organ of Corti which 

 can vibrate most easily is not the basilar, but the tectorial mem- 

 brane, which is normally stretched over the end of the filaments of 

 the hair -cells. The extreme shortness of the elastic radial fibres of 

 the basilar membrane (fractions of a millimetre) makes it incon- 

 ceivable that they can be tuned and capable of vibrating to the 

 different notes of the musical scale, particularly to the lowest 

 notes which require very long, thick strings. On the other 

 hand, even if we admit that the number of radial fibres in 

 the basilar membrane is sufficient to fulfil the requirements of 

 this theory, it is highly improbable that there can be a correspond- 

 ing number of specifically differentiated nerve-fibres. Granting, 

 with Helmholtz, that 4200 resonators are enough to cover the 

 seven octaves used in music and another 300 resonators the other 

 extreme, non-musical tones, the organ of Corti must as a whole 

 comprise 4500 distinct resonators, with as many specifically 

 differentiated nerve-fibres and central organs ! 



Another objection arises from the fact that the basilar 

 membrane is in reality not a system of radially stretched strings, 

 but a continuous membrane, the elements of which are not suited 

 to receive the waves corresponding to the respective notes, and 

 to transmit the separate impulses they excite to the brain. The 

 vibrations of any element of such a membrane must, no matter 

 how weakened they may become, be transmitted to the other 

 elements. Even when any given tone impinges on a series of 

 resonators, not only are those corresponding to it thrown into 

 vibration, but those in which the vibration-number differs only 

 slightly from that of the given tone vibrate as well. 



Finally, Helmholtz' theory encounters grave objections when 

 it is considered from the phylogenetic standpoint. The excessively 

 numerous specific differentiations of the fibres of the auditory 

 nerve demanded on the resonance theory, according to which a 

 well-developed and perfectly trained ear is capable of perceiving 

 all tones and sounds, could not have been developed simul- 



