BIOLOGY AND SOCIAL 

 PROBLEMS 



THE NERVOUS SYSTEM 



OF the sixteen hundred millions of human 

 beings that populate the earth to-day expe- 

 rience has shown us that we usually have no 

 difficulty in learning to distinguish one from 

 another with perfect certainty. Physical traits, 

 such as stature, color of hair or eyes, facial 

 form and proportions, are the elements usually 

 employed in this discrimination ; but only a 

 finger print may suffice. When, however, we 

 ask ourselves what constitutes the real in- 

 dividual whom we have learned to know, we 

 are less inclined to dwell on physical traits 

 than on the innumerable characteristic move- 

 ments in the form of common acts, responses, 

 and replies which are habitual with him and 

 which we believe to indicate in him certain 

 mental states and attitudes that we have come 

 to associate with him as part of his nature. 



