CHAP, in.] HEARING, SMELL, AND TASTE. 561 



are not discrete ; the vibrations corresponding to the fundamental 

 tone and overtones do not travel as so many separate waves ; they 

 all together form one complex disturbance of the medium; and it 

 is as one composite wave that the sound falls on the membrana 

 tympani, and passing through the auditory apparatus, breaks on 

 the terminations of the auditory nerve. And when two or more 

 musical sounds are heard at the same time, the same fusion of the 

 waves occurs. Since we can distinguish several tones reaching our 

 ear at the same time, it is clear that we must possess in our minds 

 or in our ears some means of analysing these composite waves 

 of sound which fall on our acoustic organs, and of sorting out their 

 constituent vibrations. 



There is at hand a simple and easy physical method of analysing 

 composite sounds. If a person standing before an open piano sings 

 out any note, it will be observed that a number of the strings of 

 the piano will be thrown into vibration, and on examination it will 

 be found that those strings which are thus set going correspond in 

 pitch to the fundamental tone and to the several overtones of the 

 note sung. The note sung reaches the strings as a complex wave, 

 but these strings are able to analyse the wave into its constituent 

 vibrations, each string taking up those vibrations and those vibra- 

 tions only which belong to the tone given forth by itself when 

 struck. If we suppose that each terminal fibril of the auditory 

 nerve is connected with an organ so far like a piano-string that it 

 will readily vibrate in response to a series of vibrating impulses of 

 a given period and to none other, and that we possess a number of 

 such terminal organs sufficient for the analysis of all the sounds 

 which we can analyse, and that each terminal organ so affected by 

 particular vibrations gives rise to a sensory impulse and thus to a 

 sensation of a distinct character if we suppose these organs to 

 exist, our appreciation of sounds is in a large measure explained. 

 In the organ of Corti we find structures the arrangement of which 

 irresistibly suggests to us that these are the organs we are seeking. 

 We have only to suppose that of the long series of rods of Corti, 

 varying regularly as these do from the bottom to the top of the 

 spiral, in length and in the span of their arch, each pair will 

 vibrate in response to a particular tone, and the whole matter 

 seems explained. But the more the subject is inquired into, the 

 more complex and difficult it appears; and we are obliged to 

 conclude that the part played by the rods of Corti is only a sub- 

 ordinate part of the function of the whole organ of Corti. 



In the first place, it is difficult to see how the rods of Corti, 

 even if they are thrown into vibration, can originate sensory 

 impulses, for the fibrils of the auditory nerve terminate in the 

 inner and outer hair-cells, and it is in these cells, and not along the 

 course of the fibrils as they pass under and between the rods 

 of Corti, that the sensory impulses must begin. In the second 

 place, the variation in length of the fibres along the series is 



F. 36 



