PR OB A BLE A CTION OF THE CO CHLEA. 1 1 8 3 



compartment will then represent scala vestibnli and the lower scala tympani. 

 A hole is then cut in the end opposite each scala, and over this hole a 

 thin elastic membrane is stretched. The upper hole is the fenestra ovalis, 

 and the lower the fenestra rotunda. A hole is also cut in the horizontal 

 glass plate, and covered by membrane. This will represent a segment of 

 the basilar membrane. On this membrane a small weight rests, connected 

 with a fine watch-spring, which has its own period of vibration. Then, 

 by means of a horizontal piston, representing the base of the stapes, moved 

 by a wheel, a series of pressures are given to the membrane covering 

 the oval window. With each inward pressure there is a movement down- 

 wards of the membrane in the horizontal glass plate, and a movement outwards 

 of the membrane covering the round window. When the piston moves out- 

 wards there is a reversal of the movements of the membranes. If now the' 

 wheel moving the piston be rotated rapidly, to imitate simple pendular vibra- 

 tions the steel spring, resting on the membrane, representing a segment of the 

 membrana basilaris, at once begins to oscillate at its men period when the 

 number of movements of the piston reach that period. If they go faster, then 

 the spring soon ceases to oscillate. Suppose the period of the spring to be 

 12 per second, and another hole to be cut in the horizontal plate, and covered 

 with membrane, on which rests a weight, with a spring tuned to the octave of 

 the first, that is 24 per second. By means of a wheel having an excentric 

 motion, the piston may be caused to execute a compound movement, produced 

 by two movements in the ratio of 2 : 1 to imitate the movements of the base of 

 the stapes when a sound and its octave act upon it. If, now, the wheel be 

 rotated, when it moves at a rate equal to that of the first spring (12 per second), 

 it is seen that both springs are oscillating ; that is to say, the compound harmonic 

 motion of 2:1 is analysed by the springs, each taking its own period. It 

 would only be a matter of trouble and expense to construct a more complete 

 analyser to imitate the cochlea. 1 



Beauregard and Dupuy 2 find that when the cochlea is stimulated by 

 sound, a current of action occurs in the auditory nerve. Non-polarisable 

 electrodes are placed on the membrana tympani and the cut surface of 

 the peripheral portion of the auditory nerve. In guinea-pigs the current 

 was much less marked when low tones were used than with high ones. 

 The authors maintain that their experiments prove that sound is 

 analysed in the ear. 3 



An obvious question in discussing the Helmholtz theory of the 

 cochlea is as to whether the histological evidence as to the number 

 of possible vibratile structures is such as will satisfy the demands of 

 theory. Helmholtz attempts to answer this question on the basis of 

 E. H. Weber's statement, that practised musicians can " perceive even a 

 difference of pitch for which the vibrational numbers are as 1000 to 

 1001," or the -fa of a semitone, a smaller interval than that between 

 two of Corti's arches, on the assumption that there are about 33£ for 

 each semitone in each cochlea ; and he accounts for the apparent 

 deficiency by the explanation that if a tone came between the pitch of 

 two of the arches " it would set them both in sympathetic vibration, and 

 that arch would vibrate the more strongly which was nearest in pitch to 

 the proper tone." This would also explain how it is that when we listen 



1 No description of the apparatus has been hitherto published ; in its construction I 

 have been much indebted to suggestions made by Professor Criun Brown. 



2 Arch, intcrnat. de laryngol. etc., Paris, July and August 1896. 



3 These observations require repetition. I have myself often searched for such an action 

 current, but without success. 



