TONE AND NOISE PERCEPTION IN WHITE RAT 329 



explain Hunter's results, in case they prove to be correct, we 

 need only posit a lack in the rat's ear of suitable structures for 

 resonance, thus making possible only forced, or highly inelastic, 

 movement of cells in the cochlea. The basilar membrane may 

 consist of tissue, for instance, too loose and flabby for resonance ; 

 or there may be ossification under the basilar membrane, as has 

 been found by Shambaugh to be the case under the narrower 

 end of the basilar membrane of the pig's ear. Various other 

 conditions may be responsible for the lack of sympathetic reso- 

 nance in the white rat's cochlea, but it is useless to speculate on 

 them further. It is sufficient, in our present ignorance of the 

 real nature of the rat's cochlea, merely to set the hypothesis 

 so as to direct the attention of anatomists to matters which are 

 crucial and which have not infrequently been overlooked in 

 anatomical investigations. 



If there are no structures in the white rat's ear suitable to 

 serve as resonators periodic vibrations will have very slight 

 stimulating effect. Noises coming with richer and more irregular 

 pulsations would therefore be audible even though tones are 

 inaudible. It would be interesting to try periodic vibrations of 

 very low frequencies, near man's lower limit. The intensity of 

 all tones should be as great as possible. Miss Barber used as 

 a control an interrupted organ pipe without, I believe, giving 

 the period of interruption. Further experiments along this line 

 with various frequencies, both of the interrupted tones and of 

 the interruptions themselves, might give significant results The 

 periods of interruption should doubtless be below the frequency 

 of the lower audible limit. Noises of a slightly different kind 

 from those used might be produced by the irregular striking of 

 the keys of the piano or organ. Can the rat be made to respond 

 to such " noises "? 



Even the results already obtained on the white rat, indicat- 

 ing certainly considerable difference in the perception of noises 

 and of tones, will present difficulties of no small importance to 

 non-resonance theories of hearing. 



