244 



PHYSIOLOGY 



CHAP. 



" The impulses aroused in the ear by sound impress a wave-image 

 upon the basilar membrane, the special form of which enables the 

 basilar membrane to act as a link in the chain of the conducting 

 apparatus, which is intermediary between the sound and the 

 auditory sensation." 



The facts on which Ewald bases his theory signify a real, 

 positive progress in the difficult problem of audition. We would 

 make . only one objection, with reference to the mechanism by 

 which he conceives the transformation of acoustic images into 

 the psycho-physical process of neural excitation and auditory 

 sensation. From what was said above of 

 the structure of the organ of Corti (p. 

 219) it seems to us fully proved that the 

 true vibrating membrane is not the basilar, 

 which supports the epithelial cells of the 

 peripheral organ of hearing, but the tec- 

 torial, which rests on the ends of the 

 filaments of the hair-cells, and by displace- 

 ment of the hairs excites the nerve -fibres 

 with which these cells are richly provided. 

 Kolmer's recent observations (1905) on 

 the peripheral connection of the fibres of 

 the cochlear nerve with the ciliated hair- 

 cells of the rabbit bring fresh evidence in 

 support of this theory, and show conclu- 

 sively that Corti's hair-cells are true sensory 



Vic,. 100. -Ciliated nerve-cells J ,, J 



of auditory neuro-epithelium nerve-Cells. 



?3UtaL^!3!2 As seen "' Fi g- 100, the fibres of the 

 through which the nerve. coc hlear nerve that are distributed in the 



_* 11" r i 1 i i 



sheath; 2, medullated fibre, auditory neuro-epitnelium ot the rabbit lose 



The fibrils divide into two ,-_ jTii.ii j_i j_i i 



smaller bundles, each of their medullated sheath in passing through 

 :orfin g t e wo to diSt\ n air: the basal membrane, and then arborise in 

 ceiis. The filaments of the the ciliated cells. One single fibre may, by 



hair-cells are not shown. , . . i Tf 



branching, supply two separate hair-cells 



which directly refutes the theory of Helmholtz. The neuro- 

 fibrils of the axon on reaching the base of the hair-cell penetrate 

 into it and form a network with narrow meshes towards the 

 summit of the cell, which, however, they never reach. Kolmer's 

 demonstration gives histological evidence of the theory that the 

 filaments of the hair-cells, which we may conceive to be endowed 

 with exquisite sensibility, are the intermediary through which the 

 vibrations of the tectorial membrane give rise to excitations of 

 the nerve-fibres which, on reaching the centres, arouse auditory 

 sensations. 



With this alteration and amplification, it appears as though 

 Ewald's theory might successfully avoid all the objections to 

 which that of Helmholtz is open. 



