NEMATHELMINTHES. ROUND- WORMS 



33 



Hookworm. Probably the most widespread 

 and important worm parasite of man is the 

 now popularly known hookworm, of which there 

 are two chief forms, the European, Ankylostoma 

 duodenale, and the American, Necator ameri- 

 canus. The disease caused by this worm is 

 generally known as hookworm disease, or tech- 

 nically as uncinariasis or ankylostomiasis. 



The parasites occur in most parts of the 

 world and practically all tropical countries show 

 the presence of the disease, often in a large per- 

 centage of the population; for example 90 per 

 cent, of the people of Porto Rico formerly were 

 infected. While typical of the tropics, the dis- 

 ease is often common in the temperate zones. / 

 In the southern states of the Union the disease 

 is very prevalent; especially among the poorer 4< __M 

 classes. The disease has t been recognized in 

 tropical countries for three centuries, though its 

 cause was not discovered until past the middle 

 of the nineteenth century. The first case in 

 the United States was reported in Philadelphia 

 in 1893. 



Those who live, or have travelled in the 

 southern states are familiar with the so-called 

 "poor whites" of that region. It has been 

 estimated that, at least until a few years ago, 

 there were some 2,000,000 of these unfortunates. 

 They were formerly considered to be a sort of 

 degenerate race, too lazy or stupid or both to 

 work, who eked out a miserable existence on 

 their pitiful little plantations. These people 

 are pale and anaemic and often thin to emacia- 

 tion; the children are stunted physically and 



FIG. 24. A female Ascaris lumbricoides cut open to 

 show internal structures. x%. I, pharynx; 2, intes- 

 tine; 3, ovary;' 4, uterus; 5, vagina; 6, genital pore; 7, 

 excretory tube; 8, excretory pore. (From Hegner, College 

 Zoology, after Shipley and MacBride.) 

 3 



