THE OUTER AND INNER WORLDS 219 



same kind. Thus a luminous sensation always 

 follows stimulation of the optic nerve. When 

 it is divided by the surgeon, in removal of an 

 eyeball, if the patient is conscious, there is no 

 pain but the consciousness of a flash of light. 

 The same applies to all the other senses. 

 This law has been called the law of the 

 specific energy of the nerves of special sense, 

 but it does not imply that the nerve is anything 

 else than a conductor. The effect is due, as 

 has already been explained, to the arrange- 

 ments at the cerebral end of the nerve, by 

 which the messages are always translated into 

 sensations of the same kind. 



128. Each sense organ works within certain 

 limits. Thus a stimulus may be so feeble as 

 not to produce an effect. This, as regards 

 intensity, is the threshold of sensation. The end- 

 organ is adapted to respond, say to vibrations, 

 within a certain range. Thus, if we look at 

 a spectrum the eye does not recognize light 

 or colour below the lower limit of the red, but 

 we know that there are vibrations in existence 

 that give rise to heat below the red end. The 

 skin may be affected by these low vibrations, 



