RANK OF DIFFERENT NATIONS 187 



ideas began expanding the horizon of thought and 

 provoked many controversies, which for the time 

 were often bitter, but, in many instances, resulted 

 in freeing the mind from the bonds of inherited and 

 traditional superstitions. 



Gradually all animal life came to be looked on as 

 the result of an orderly progress with no place for 

 the idea of chance. The idea of the constancy of 

 nature was established. Then arrived, in the last 

 half of the nineteenth century, largely as the result 

 of zoological progress, the doctrine of organic 

 evolution which produced a mental revolution. It is 

 generally recognized that from the time of the re- 

 vival of scientific learning to the present, while all 

 scientific study was making towards enlightenment, 

 still, the investigation of problems involving animal 

 life had unusually broad influence in promoting 

 intellectual progress. 



The controversies engendered were often against 

 theological opinion, but these flashes of enlighten- 

 ment were by no means confined to that territory. 

 Scientific dogma (as that of the fixity of species) and 

 medical tradition (as to the source and the nature 

 of disease) also gave way to investigations of a 

 biological character. 



