AUDITORY SENSATIONS. 609 



capable of producing sound vibrations have a proper tone, i. e., 

 that which they produce when struck. When the proper tone of 

 a body capable of vibrating is sounded in its immediate neighbor- 

 hood, this is also set vibrating through the medium of the air. If 

 a clear tone be sung loudly over the strings of a piano, a kind of 

 sympathetic echo will be heard to come from the cords, on account 

 of the strings corresponding to the notes sounded being thrown 

 into sympathetic vibrations. Now, in the basilar membrane we 

 have practically a series of strings of different length since the 

 membrane gets wider as it passes from below upward to the 

 summit of the cochlea and, therefore, a great variety of proper 

 tones. With a high note, then, a fibre of one part of the mem- 

 brane will readily fall into vibration, and with a low note a fibre 

 of another part. Different nerve fibrils are in relation to these 

 different parts, and thus we may conclude that tones of different 

 pitches stimulate distinct nerve terminals, and are conveyed to 

 the brain by separate nerve channels. Impulses arriving at 

 certain brain cells, then, give rise to the idea of high tones, and 

 impulses coming, to others cause the impression of low tones. 

 There are about a sufficient number of fibres in the basilar 

 membrane for all the notes we can hear, viz., from about 30 to 

 4000 waves in the second. 



The rods of Corti cannot be the vibrating agents, because they 

 are too few in number, and they are absent in birds, which 

 appreciate and reproduce various notes. Further, the rods are 

 not elastic, and, therefore, not well suited to vibrate. It may, 

 therefore, be concluded that they only act as levers which convey 

 the vibrations of the fibres of the basilar membrane to the nerve 

 endings in the auditory cells. 



The explanation of our wonderful appreciation of the delicate 

 shades of quality of tones is more difficult. Even persons with 

 indifferently good ears, as musicians say, and no special musical 

 education, can at once distinguish between the quality of the same 

 note when sounded on a violin, a piano and a flute. In examin- 

 ing the resound from a piano when a note is sung. against its 

 strings its becomes obvious that with ever so pure a tone a great 

 number of strings are set vibrating. It will be found that not 



