214 DIFFERENCES IN THE NERVES 



CHAPTER XXIV. 



LIFE, OR MUSCULAR AND NERVOUS ACTION 



DEPENDENT ON ELECTRIC EXCITATION. 



TTELMHOLTZ thus quotes from Johannes 

 Muller's " Specific Energies of Sense " : 



" ' The difference in the sensations due to the 

 various senses does not depend upon the actions 

 which excite them, but upon the various nervous 

 arrangements which receive them.' 



" According to Thomas Young's hypothesis, 

 there are three kinds of nerve-fibres in the eye 

 with different powers of sensation for feeling red, 

 for feeling green, for feeling violet. In reality, 

 this assumption gives a very simple and perfectly 

 consistent explanation of all the optical phenom- 

 ena depending on color. And by this means the 

 qualitative differences of the sensations of sight 

 are reduced to differences in the nerves which re- 

 ceive the sensations. For the sensations of each 

 individual fibre of the optic nerve, there remain 

 only the quantitative differences of greater or 

 less irritation. 



" The same result is obtained for hearing, by the 

 hypothesis to which the investigation of quality 

 of tone has led us. The qualitative differences 



