n 9 o THE EAR. 



affected by the combinational tone itself, according to its frequency. 

 This view will satisfy the theory both as regards differential and 

 summational tones. 



Objections to the theory of Helmholtz. — In addition to those already 

 considered, the following may be mentioned. Eutherford x points 

 out that a compound tone is heard as one sound ; and he argues 

 that if Helmholtz were correct, the note is first analysed by the cochlea 

 into its constituents, and is then reconstructed in the brain, a process 

 apparently unnecessary. The obvious reply is that, as a matter of fact, 

 any compound tone may be analysed by the aid of resonators, and if of 

 sufficient intensity, it does not appear to give rise to a simple sensation ; 

 but by a strong effort of attention the apparently simple sensation can 

 always be more or less fully resolved into sensations corresponding to 

 the partials. Waller 2 adduces the result of an experiment of Hermann 3 

 as a strong objection. Hermann observed that a beat tone might be 

 heard which did not excite a resonator or fork tuned to its pitch. 

 If such be the case, Waller maintains that it is improbable it could 

 act on the fibres of the basilar membrane, if these were supposed 

 to respond as resonators. No doubt if a differential tone really 

 exists in the air, and is not generated in the ear, and yet is unable 

 to set an appropriate resonator in vibration, the theory of hearing 

 founded on sympathetic resonance would receive a severe blow. It 

 does not follow, however, that in Hermann's observation the resonator 

 was unaffected. It did not respond to such an extent as to enable 

 a tone to be heard, although the ear could hear the true differential 

 tone, if sufficiently near the sources of the sounds. This only proves 

 that, with the means at our disposal, the ear is more sensitive 

 than the resonator. Further, as has already been pointed out, it is 

 possible to tune resonators in such a way as to enable them to respond 

 to differential tones, irrespective of the ear. It has also been shown 

 that combinational tones may be generated in the middle ear, in which 

 case it is obvious they would not act on a resonator. Thus, either on 

 the supposition that such tones are generated in the air, or, on the 

 converse, that they are produced in the middle ear, the experiment does 

 not invalidate the sympathetic theory of hearing. 4 



Other theories. — As opposed to the theory of Helmholtz is the 

 one known as the telephone theory, advocated by Eutherford. 

 Einne 5 had already, in 1865, offered cogent objections to the analysis 

 theory, and had suggested that the cochlea acted as a whole. This 

 view was supported twenty years later by Voltolini, 6 and, in 1886, 

 Eutherford 7 stated it with greater fulness, illustrating the function of 

 the cochlea by the analogy of a telephone, and, in particular, attempting 

 to show experimentally that nervous impulses of different rates of 

 frequency can be transmitted along the auditory nerve. 



According to Eutherford, all the hairs of the auditory cells vibrate 



1 Rep. Brit. Ass. Adv. Sc, London, 1886. 2 "Human Physiology," 1891, p. 461. 



3 Arch. f. d. ges. Physiol., Bonn, Bd. xlix. S. 499. 



4 Gray suggests that the intratympanic muscles may act in such a way as to produce 

 differential tones. 



5 Ztschr. f. rat. Med., Dritte Reihe, Bd. xxiv. S. 12-64. An excellent analysis is given 

 in "Die Lehren von den Funktionen dereinzelnen Theile des Ohrlabyrinths," by Stanislaus 

 von Stein, trans, from Russian by C. von Krzywicki, Jena, 1894, S. 141. 



6 Virchotv's Archiv, Bd. c. S. 27-41 ; see also von Stein, op. cit., S. 153. 



7 Rep. Brit. Ass. Adv. Sc. , London, 1886 ; also Journ. Anat. and Physiol., London, vol. xxi. 

 p. 166; see also address on "Tone Sensation, "Brit. Med. Journ., London, 1898, vol. ii. p. 353. 



