FUTURE ANALYSIS OF MEMORY 291 



and every living organ are able to convert energy in 

 but one definite form- -that is, that they are special 

 machines. The determination of the way in which 

 this transformation of energy occurs in the various 

 organs would be the explanation of the specific energy 

 of the various senses. 



Physiology gives us no answer to the latter ques- 

 tion. The idea of specific energy has always been 

 regarded as the terminus for the investigation of the 

 sense-organs. All the more credit is due Mach and 

 Hering for first having advanced beyond that limit 

 with their chemical theory of colour-sensations. Mach 

 has recently expressed the opinion that chemical 

 conditions lie at the foundation of sensations in 

 general (i). 



For the eye we may consider it as probable that 

 light produces chemical effects. Various substances 

 are formed and decomposed in the retina, and the 

 chemical processes of the formation and decomposi- 

 tion of these substances determine the licrht- and 



o 



colour-sensations. The ether-vibrations of certain 

 wave-lengths influence these decompositions in a de- 

 finite manner. The electro-magnetic theory of light 

 will probably in this case lead to further discoveries. 

 Effects similar to those produced by light are also 

 brought about by the electric current. The current 

 itself can pass through the retina only by means of 

 electrolysis, and it may be that the increase in the 

 concentration of ions (wherever their progress is 

 Mocked) brings about the light- and colour-sensations 



