THE INTERNAL EAR IN VERTEBRATES 595 



position, variation in size, fibrillar structure, low specific 

 gravity and extreme flexibility, is better fitted than the basilar 

 membrane to respond to every vibration of the endolymph and 

 to be set in motion in its different parts in sympathy with 

 notes of different rapidity and they maintain that it, not the 

 basilar membrane, is the active agent in the stimulation of 

 the sense-cells of the organ of Corti. The sense-cells do not 

 strike the tectorial membrane but the tectorial membrane strikes 

 the sense-cells. 



The actual mode of stimulation of the auditory organ must 

 for the present remain undecided. There is, however, one and 

 that a fundamental question upon which it is possible to speak 

 with more certainty. There is evidence, both clinical and 

 experimental, to show that the cochlea is in itself, in some 

 way, a mechanical analyser of sound. For it is certainly 

 affected in different parts by notes of different pitch. 



In cases of partial deafness (deafness to particular notes) it 

 has been shown by post-mortem examination that particular 

 parts only of the organ of Corti are destroyed. 1 When the 

 deafness is to notes of high pitch it is the basal parts where 

 the elements of the cochlea are at their smallest and shortest, 

 when to notes of low pitch, the apical. 



Similar results have recently been obtained by direct experi- 

 ments upon guinea pigs. 2 Guinea pigs kept during long periods 

 under the influence of one note were found to have part of the 

 organ of Corti destroyed. The higher the note the nearer the 

 base of the cochlea was the spot. 



One can therefore conclude with some degree of safety that 

 the cochlea is the organ by which complex sound vibrations are 

 mechanically sorted and analysed. The perception and appre- 

 ciation of the results of this analysis depend of course upon 

 the brain. The ear can only furnish the brain with the raw 

 material of assorted stimulations; it depends upon the brain 

 by its innate powers and by practice to realise and appreciate 

 the shades of difference there are between these stimulations. 



1 Bezold, Zeits.f. Psych, ic. Phys. d. Sintiesorgatt, 1896, xiii. ; Gruber, Allg . 

 Wien. Med. Ztg. 1864, ix. 



3 Yoshii, Zeits.f. Ohre?iheilk. 58-59, 1909, p. 240. 



