PHYLUM NEMATHELMINTHES 175 



roundworms is that the shiftlessness of the " poor whites " of 

 the South is to a certain degree the result of the attack of the 

 hookworm, Necator americanus. The larvae of the hookworm 

 develop in moist earth and usually find their way into the bodies 

 of human beings by boring through the skin of the foot. In the 

 localities where the hookworm is prevalent, many of the people 

 go barefoot. The larval hookworms enter the veins and pass to 

 the heart; from the heart they reach the lungs, where they make 

 their way through the air passages into the windpipe, and thence 

 into the intestine. To the walls of the intestine the adults at- 

 tach themselves and feed upon, the blood of their host. When 

 the intestinal wall is punctured, a small amount of poison is 

 poured into the wound by the worm. This poison prevents the 

 blood from coagulating, and therefore results in a considerable 

 loss of blood, even after the worm has left the wound. The vic- 

 tims- of the hookworm are anaemic, and also subject to tuber- 

 culosis because of the injury to the lungs. It is estimated that 

 2,000,000 persons are afflicted by this parasite. The hook- 

 worm disease can be cured by thymol (which causes the worm to 

 loosen its hold) followed by Epsom salts. The most important 

 preventive measure is the disposing of human faeces in rural 

 districts, mines, brickyards, etc., in such a manner as to avoid 

 pollution of the soil, thus giving the eggs of the parasites contained 

 in the faeces of infested human beings no opportunity to hatch 

 and develop to the infectious larval stage. 



