THE SENSES 847 



nerve, which are the physiological counterpart of the aerial 

 waves and the waves of increased and diminished pressure 

 in the liquids of the labyrinth to which they give rise. 

 Thus, a sound of 100 vibrations a second would start 100 

 impulses a second in the auditory nerve ; a loud sound 

 would set up impulses more intense than a feeble sound; 

 and a complex wave, which is the resultant of several sounds 

 of different vibration-frequency, would also in some way 

 or other stamp the impress of its form on the auditory 

 excitation- wave ; just as in a telephone every wave in the air 

 causes a swing of the vibrating plate, and thus sets up a 

 current of corresponding intensity and duration in the wires. 

 This theory evidently abandons the doctrine of specific energy 

 for the particular case of the analysis of pitch, for it assumes 

 that differences of auditory sensation are related to differ- 

 ences in the nature of the impulses travelling up the auditory 

 nerve, and not merely to differences in the anatomical connec- 

 tions (peripheral and central) of the auditory nerve-fibres. 



The statement of Ewald, that after extirpation of the membranous 

 labyrinth on both sides pigeons can still hear, would have an im- 

 portant bearing on the question of the perception of pitch, if it could 

 be definitely accepted, and particularly if it were shown that differ- 

 ences of pitch could still be appreciated. But it has not been proved 

 beyond a doubt that the apparent reaction to sound is due to anything 

 else than stimulation of tactile end-organs. 



The range of hearing is very great. The highest audible tone 

 corresponds to 30,000 to 40,000 vibrations a second, the lowest to 

 about 30. Between these limits as many as 6,000 variations of 

 pitch can be perceived. 



Smell and Taste. 



Smell was defined by Kant as ' taste at a distance ' ; and 

 it is obvious that these two senses not only form a natural 

 group when the quality of the sensations is considered, but 

 are closely associated in their physiological action, especi- 

 ally in connection with the perception of the flavour of the 

 food. The olfactory end-organs in the mucous membrane 

 of the upper part of the nostrils, the so-called regio olfac- 

 toria, have been already described (p. 717). In cases of 

 anosmia, in which the olfactory nerve is absent or paralyzed, 



