i8o 



PRACTICAL ZOOLOGY 



103, D). One of the most recent discoveries with regard 

 to this parasite is that the shiftlessness of the " poor whites " 

 of the South is to a certain degree the result of its attack. 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. The hookworm is prevalent in many localities 

 where the people go barefoot. The larval hookworms enter the 

 veins and pass to the heart; from the heart they reach the lungs, 



FIG. 102. Trichina. A, Larvae, among muscle fibers not yet encysted. 



B, A single larva encysted. 



C, Piece of pork, natural size, containing many encysted worms. 



D, Adult trichina, much enlarged. (After Leuckart.) 



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 attach 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 pre- 

 vents the blood from coagulating, and therefore results in a con- 

 siderable loss of blood, even after the worm has left the wound. 

 The victims of the hookworm are anaemic, and also subject 

 to tuberculosis because of the injury to the lungs. It is 



