THE CONQUEST OF DISEASE 



was one whose blood continued to remain at a 

 temperature agreeable to the parasite ; but the 

 animal which increased its temperature to a 

 point which was obnoxious to the invading 

 organism survived, propagated its kind, and 

 transmitted to them the very peculiarities by 

 virtue of which it had resisted the enemy. 

 Fever, following infection, is a natural and 

 salutary reaction. It has saved the human 

 race from extinction; and it has been just as 

 much of a protective influence against our 

 microscopic enemies as the green color of the 

 tree-toad, the white of the polar bear, and the 

 sepia of the cuttle fish have been protections 

 against the macroscopic enemies of these ani- 

 mals. Those which developed protective reac- 

 tions survived; those which did not, perished. 



Experiments upon animals are showing that 

 while evolution, natural selection, is adapting 

 the animal to overcome its parasites and ene- 

 mies, the same laws also operate in favor of the 

 latter. So far as the purely vegetative pro- 

 cesses go, nature is as kind to the bacteria as to 

 man; each becomes adapted to new conditions 

 because the survivors transmit their adapta- 

 bility to their offspring. The same natural 

 laws apply to each. Any peculiarity, which 



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