416 Prof. A. M, Mayer's Researches in Acoustics. 



" reverberations or repercussions " take place in a body like the 

 whole apparatus of audition, whose heterogeneous structure must 

 make all of its vibrations^ taken as a mass, forced oscillation s> J 

 do not agree with my distinguished friend in thinking that the 

 difference in the lengths of the scalse could bring about any in- 

 terference except of the most minute and inefficient amount j 

 even if we could agree with Dr. Draper that the intensity of the 

 pulses sent from the fenestra rotunda nearly equal the intensity 

 of those sent up the scala vestibuli from the stapes. The fol- 

 lowing considerations will make clear our objections to the 

 hypothesis of Dr. Draper. If we take the mean wave-length 

 of the sounds which fall upon the ear as that of the treble G of 

 440 vibrations per second, it follows that this wave-length will 

 be 1 metre. But the velocity of sound in the fluid of the scala? 

 is at least 4| times what it is in air of the same temperature j 

 therefore the average length of the sonorous waves which tra* 

 verse the scalse is 4 J metres ; and hence, for two such waves 

 meeting in the helicotrema to completely interfere, one scala 

 would have to exceed the other in length by 2*12 metres. But 

 the entire length of a scala is at the highest only 29 millims. } 

 and the difference in their length, taken at its maximum, is so 

 slight that the diminution in the intensity of the resultant wave 

 produced in the helicotrema is inappreciable ; and especially will 

 it be so considered when we take into account the relatively 

 feeble intensity of the wave which is sent from the tympanic 

 membrane across the air of the drum on to the membrane of 

 the fenestra rotunda, where two sudden changes in density occur 

 before it passes up the scala tympani. 



The following attempt at an explanation of the functions of 

 the spiral stairways of the cochlea is given merely as a suggest 

 tion, and with the hope that I may thereby call the attention of 

 students of physiological acoustics to the consideration of the 

 uses of these peculiar forms. Recent studies in embryology 

 and comparative anatomy have shown that the ductus coch- 

 learis is the essential part of the ear, and that the forms of 

 the scalse are determined by it ; for " the original soft parts of 

 the cochlea are distinct from their osseous capsule, which belongs 

 to the petrous bone ; the scalse are secondary formations around 

 the principal canal of the cochlea, the ductus cochlearis, whose 

 epithelial lining proves eventually to be the germ-centre, so to 

 speak, of the entire apparatus"*. The fact that the ductus con- 

 trols the form of the scalse, and not vice versa, shows that the 

 scalse must bear some very important functional relation to the 

 ductus. This relation will become evident on considering the 

 Waldeyer, "On the Auditory Nerve and Cochlea/' in Strieker's 



Histology 



