THE ROUND WORMS 181 



estimated that 2,000,000 persons are afflicted by this parasite. 

 The hookworm 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 feces 

 in rural districts, mines, brickyards, etc., in such a manner as 

 to avoid pollution of the soil, thus giving the eggs of the para- 

 sites contained in the feces of infested human beings no oppor- 

 tunity to hatch and develop to the infectious larval stage. 



Elephantiasis. Another injurious species is Filaria ban- 

 crofti, a parasite in the blood of man. The larvae of this species 

 are about yj-^ of an inch long. During the daytime they live 

 in the lungs and larger arteries, but at night they migrate to 

 the blood vessels in the skin. Mosquitoes, which are active 

 at night, suck up these larvae with the blood of the infected 

 person. The larvae develop in the mosquito's body, becoming 

 about one twentieth of an inch long, make their way into the 

 mouth parts of the insect, and enter the blood of the mosquito's 

 next victim. From the blood they enter the lymphatics and 

 may cause serious disturbances, probably by obstructing the 

 lymph passages. This results in a disease called elephantiasis. 

 The limbs or other regions of the body swell up to an enormous 

 size, but there is very little pain. No successful treatment has 

 yet been discovered, and the results are often fatal. It is said 

 that from 30 per cent to 40 per cent of the natives of certain 

 South Sea islands are more or less seriously afflicted. The 

 parasitic guinea worm has already been described as a parasite 

 of the crustacean, Cyclops (see p. 140). 



Other Roundworms. Parasitic roundworms also attack 

 other animals and plants. One of them, Syngamus (Fig. 103, C), 

 causes the disease known as gapes in poultry and game birds. 

 The birds swallow the young worms, which soon become mature 

 in the windpipe. The stomach worm of sheep (Fig. 103, B) is 

 the most important worm that parasitizes these animals. It 

 lives in the fourth stomach of sheep and goats and causes the 

 death of many animals, especially lambs. The nodular worm of 



