How Science Helps the Body 171 



But there is one infective disease malaria, 

 not induced by bacteria, but by micro- 

 organisms belonging among the protozoa, in 

 which the early dream is realized. For in 

 most cases quinine suffices to destroy the 

 organism without damaging the man. Thus 

 by quinine and mosquito screens and drain- 

 ing the swamps, this pest of many coun- 

 tries and neighborhoods may be effectively 

 suppressed. 



We have thus learned that there is an 

 immunity to infection which faces, species, 

 and individuals naturally enjoy or may acquire 

 by a successfully encountered attack of an 

 infectious disease. We have seen that the 

 body cells possess a marvellous power of 

 adapting themselves to new adverse condi- 

 tions, by the use, to new ends, of capacities 

 by which the usual life is carried on. So 

 when one recovered from diphtheria or typhoid 

 fever is for a time immune, we know that this 

 marks an adaptation of his cells to a new 

 environment, evanescent it is true, but analo- 

 gous with those adjustments by which in the 

 long processes of evolution new traits were 



