SOME INHABITANTS OP MAN 151 



In heavily infected countries the disease appears to be 

 contracted chiefly from isolated and much-used ponds, or 

 from wells. Probably a further study of the bionomics of the 

 parasite and of its intermediary will show that only certain 

 species of Cyclops act as efficient hosts and that small collec- 

 tions of water can be freed from these small but dangerous 

 crustaceans. 



There is romance even in the lives of worms. I close with 

 the Uf e-story of the ankylostome worms {Ankyhstoma duodenale 

 and Necator americanus), the remarkable wanderings of which 

 were first revealed by a laboratory accident. 



The " ankylostome " or " hookworm " is an intestinal 

 roundworm about half an inch in length, which infests over 

 50 per cent of the inhabitants of tropical and subtropical 

 countries. In Porto Eico, at one period, it was responsible, 

 directly or indirectly, for 30 per cent of the annual mortaKty. 

 Even as a mild infection it is the source of much invalidity 

 and heavy economic loss. The " laziness " and general 

 degeneracy of the " poor white trash," who are said to belong 

 to the purest-blooded English stock in the United States, are 

 due not so much to environment and heredity as to the 

 ravages of these parasites. 



In a public lecture, delivered before the University of 

 Pennsylvania in 1915, Allen J. Smith, citing the factors which 

 have caused the Southern States to lag in American progress, 

 maintained that hookworm disease " stands with malaria as 

 worse than war and the devastation of battles and worse than / 

 all the other pathogenic agencies in combination." Through 

 the influence of these diseases " the men and women of the 

 South, bred from the best American colonial stock, offspring 

 of pioneers, with the blood of BngUsh gentry and continental 

 cavaliers in their veins, sank lower and lower in physical 

 degeneration and squalor ; were derided and denounced as 

 lazy and shiftless and condemned in popular opinion as worth- 

 less and a disgrace." 



The hookworm is one of those roundworms which do not 

 require an intermediary host. The eggs hatch and meta- 



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