TASTE. 



119 



communicated to it either through the air or otherwise. 

 Many resonators can be excited to vibration not only by 

 their "proper tones," but also by vibrations of approxi- 

 mately the same frequency, in a degree proportional to 

 the approximation. As there is reason to believe that the 

 resonators of the organ of Corti have this property, it 

 enables us to understand how it happens that the number 

 of distinguishable tones exceeds that of the elements 

 which serve to appreciate them. For a tone affects not 

 one, but two or more resonators, each in proportion to its 

 proximity to the tone by which it is excited, so that just 

 as every perception of colour is founded on impressions 

 received through at least three elements, every perception 

 of tone is occasioned by the simultaneous vibration of 

 several elements of the organ of Corti. The power of 

 distinguishing two tones which follow each other at very 

 short intervals of time, is known to vary with their rate 

 of vibration. Thus, whatever be the tone, it has been 

 found that the time intervening between one excitation 

 and its successor must be sufficient for about twenty-two 

 vibrations in order that they may be heard as two. Helm- 

 holtz explains this on the principle that the resonators of 

 the organ of Corti are very readily thrown into vibration, 

 and continue to vibrate only a short time after the excita- 

 tion has ceased. 



Nothing can be stated with certainty as to the functions 

 of the end-organs of the vestibular sacs ; from their 

 analogy with the auditory vesicles of invertebrate animals 

 without cochleae it may be inferred that they have similar 

 functions. (With reference to the ampullae, see p. 97). 



Taste. 



Sensations of taste are occasioned by the access of 

 sapid substances to the tongue, either in the neighbour- 

 hood of the papillae vallatae, or of the papilla foliata of 



