ROUNDW ORMS— THE NEMATHELMINTHES 163 



meat for cooking. If these scraps contain the encysted larvae, the hogs 

 can readily become infected. Because of repeated cases of human infection, 

 some regions require thorough cooking of all garbage before it is fed to 

 hogs. 



The Pinworm 



One of the most widespread of the roundworms is the pinworm, En- 

 terobius vermicularis. It is found in all parts of the world and is espe- 

 cially abundant among children in the United States. The adult worms, 

 about half an inch long, live in the large intestine and the females have a 

 habit of migrating down and laying their eggs around the anal opening. 

 This causes an intense itching and desire to scratch so that children easily 

 get the eggs on their hands and, thus, can reinfect themselves. The eggs 

 make a direct trip through the digestive system and hatch and grow to 

 maturity when they reach the large intestine. They live only a few 

 weeks so, if reinfection can be prevented, they will disappear from the 

 body within this period of time. It is very difficult to prevent reinfec- 

 tion, however, because the eggs are very small and light in weight and 

 easily spread, so medical treatment to expel them seems to be advisable. 



Perhaps this recital of the life histories of these common parasites has 

 somewhat shocked the more squeamish of you, yet a knowledge of their 

 life histories will help protect you from them. Certainly it would be 

 more shocking to have them in your body than to read about them, and, 

 no matter how fastidious you may be, you have no assurance that you 

 will not have the opportunity to acquire some of them during your life. 



Elephantiasis 



One of the most repulsive diseases of tropical regions is known as 

 elephantiasis in which certain parts of the body increase in size tremen- 

 dously. An ankle may swell until it is as big as a person's waist ; a single 

 finger may enlarge until it is larger than the wrist ; the male genital or- 

 gans may swell until a man cannot walk. These symptoms are caused 

 by an accumulation of small roundworms in the lymph spaces and the 

 consequent interference with the free flow of lymph through these re- 

 gions. This causes the lymph to accumulate and causes a temporary 

 swelling which is followed by a growth of connective tissue that makes 

 the swelling permanent. Wucheria bancrofti is the genus and species name 

 of the worm causing this condition. The females may be about three 

 inches long, but only about as thick as a coarse sewing thread, while the 

 males are about half this length. They are found in great tangles in the 



