ADAPTATION OF THE PARASITES 239 



Yet, by doing so, it has ensured its establishment 

 in a most secure manner in the body of man, for it 

 has selected as the instrument of inoculation an insect 

 — the mosquito — precisely the one which is obliged 

 to molest and to follow man in search of its necessary 

 food. 



In all this tliere appears to be such a truly 

 marvellous purposiveness that we see that in the 

 study of parasitism we are face to face with one of 

 the most significant pages which Biology or Medicine 

 has ever presented to our gaze. Further, not only 

 have these minute animal parasites admirably suited 

 themselves to pass their life in our bodies and those 

 of other animals, but we find that as fast as man 

 makes use of remedies to destroy these parasites in 

 his blood, so do the parasites tend apparently to 

 harden themselves to resist these same drugs. 



There is therefore a tendency for the remedies to 

 become less and less efficacious, unless doses so large 

 are administered that they become equally harmful 

 to man. 



Therefore it becomes more evident every day, as 

 our knowledge increases, that the contest between 

 man and animal parasites is a very momentous one — 

 one which has materially helped to mould our develop- 

 ment in the past, and one which to-day continues to 

 limit our progress and development. Considerations 

 like these ought to bring home to every one of us 

 the absolute necessity of combining to eradicate them 

 in the way which nature has herself indicated. This 

 method is summed up in the words "^j?-^L'^;i^zo/i is 



