Z4 THE HISTORY OF BIOLOGY 



Protagoras, likewise a contemporary of Democritus. Protagoras introduced 

 scepticism and subjectivism into Greek thought: "Man is the measure of all 

 things" is one of his fundamental principles; "Contrary assertions are equally 

 true" is another. To such a thinker any consideration of nature was foreign; 

 what he desired to teach was an art of living, such as would free mankind 

 from the fetters which traditional ideas in the sphere of religion and morality 

 had imposed. Highly acclaimed by the younger generation, bitterly hated 

 by the representatives of the past, not least because, in contrast to the earlier 

 philosophers, he taught for payment, which was at that time regarded as 

 equivalent to usury, Protagoras starts an entirely new era in the Greek view 

 of mankind, in relation both to his fellow-creatures and to nature. But be- 

 fore going on to describe this new tendency we must make a brief survey 

 of Greek medical science, at that period a specialized science which had 

 achieved results of lasting value to general biological development. 



