66 BIOLOGICAL ASPECTS OF HUMAN PROBLEMS 



external perception of more than one person, is 

 carried along a bundle of nerve fibers. Now at some 

 period in this passage there occurs a fact ordinarily 

 assumed to be of a wholly different kind, namely, 

 a mental fact within reach of the internal perception 

 of only one person the sensation of having been 

 touched. Nature gives us many examples of strange 

 transmutations of energy, as of heat or electricity 

 into light, or, still more striking, of the change from 

 radium into helium. These are clear examples of the 

 disparateness of the first and second stages of a 

 process, but in none of these cases is the second stage 

 of the process of a radically different order from the 

 first. Helium, though different from radium, is 

 like it an elementary state of matter. The phenome- 

 non of heat and light shade insensibly into each other, 

 and the difference between these forms of energy is 

 apparently mainly one of wave lengths. But here, 

 in the case before us, is an example of an apparently 

 different order between the nerve process of the first 

 stage and that state of consciousness which is the 

 second stage. Where shall we find an example of an 

 equally great difference in quality between the first 

 and second stages of a process? Here, then, is a 

 difficulty of a serious nature; for since we can explain 

 the unknown only in terms of the known, we seem 

 to be shut out from any method of approach, when 

 we venture to deal with consciousness. 



A difficulty which has stood distinctly in the way 

 of clear thought regarding the problem of conscious- 



