ral, and become enclosed in a walled cyst developed 

 by the host. They do not develop further unless host 

 muscle is eaten by another susceptible host and the 

 cyst wall is digested away in the host's stomach or 

 intestine. An ounce of infected sausage may contain 

 more than 100,000 encysted little worms; and the 

 person who eats it may become the sole support of 

 1500 offspring from each female that hatches in the 

 stomach or intestine, so that the body tissues become 

 riddled by more than 100,000,000 larval worms. 

 Since the cysts are microscopic, gross meat inspec- 

 tion does not reveal trichina worm infection. Preven- 

 tion could be greatly aided by careful inspection of 

 pork, as in Chile, or by prohibiting the feeding of 

 garbage to hogs, as in Canada or England. Until bet- 

 ter measures are adopted in the United States, each 

 individual should take care never to eat pork that is 

 not thoroughly cooked. 



Hookworms are tiny worms, only about V2 of an 

 inch long, that live in the human intestine, holding on 

 by clamping the mouth on a bit of intestinal wall, 

 and feeding by sucking in blood and tissue juices. 

 Only recently have these worms been brought under 

 enough control to cede first place to the schistosomes 

 (discussed in the chapter on flatworms) as the most 

 damaging wormlike parasites of man. Necator ainer- 

 icaniis. whose name means "the American killer," 

 probably came to the United States from Africa and 

 is primarily a tropical worm, abundant in middle lat- 

 itudes around the world wherever moderately warm 

 temperatures, moisture, and soil conditions are fa- 

 vorable. Its dependence on warmth and moisture 

 keeps it confined in the United States to the south- 

 eastern states — from Virginia west and southwest to 

 Arkansas and Texas. 



Somewhat more injurious to its hosts is Ancylos- 

 toma diiodenale, chiefly a northern species and the 

 dominant one in Europe, North Africa, western Asia, 

 northern China, and Japan. In most countries farm- 

 ing and mining are the main occupations of hook- 

 worm victims; and in western Europe the worms first 

 attracted attention during the building of the Saint 

 Gotthard tunnel through the Swiss Alps. Afterwards 

 the worms were spread to many European mines. 

 Other species of hookworms occur in cats and dogs 

 and occasionally also in man. The life history has 

 some similarities to that oi Ascaris, but the eggs hatch 

 in the soil and it is the active larval worms that enter 

 the human body, usually burrowing through the skin 

 of bare feet, but also sometimes taking advantage of 

 any other means to penetrate the human skin or en- 

 ter the mouth. Once inside the skin, they enter lymph 

 or blood vessels, are carried to the lungs, coughed up 

 and swallowed, arriving finally in the intestine. There 

 they sap vitality, chiefly through blood loss, of indi- 

 viduals who are malnourished to begin with. The ef- 

 fects of hookworms are not dramatic, but they under- 



/ 





Trichina cyst in hog muscle. The dormant curled-up 

 larva of Trichinella spiralis is about ^j.-, inch long 

 and is enclosed in a wall formed by the host. Stained 

 preparation. ( P. S. Tice ) 



mine whole communities, generation after genera- 

 tion. The wearing of shoes is an important means of 

 protection against ground polluted with hookworms; 

 even light sandals help. 



The guinea worm, Diaciinciilis inedinensis, was 

 referred to earlier. In central Africa, Egypt, the East 

 Indies, and especially from Arabia to India, it is one 

 of the really serious penalties for a way of life in 

 which the same sources of water serve for drinking, 

 bathing, and laundering. The large female worm, 

 only I..-, of an inch wide but up to 4 feet long, lives 

 in the deeper skin layers but comes close to the sur- 

 face to produce a skin ulcer and discharge larval 

 worms whenever an infected arm or leg is suddenly 



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