NEMATODA 



43 



When the infested flesh, unless thoroughly cooked, is eaten by man the 

 cysts are dissolved, the young entering the small intestine, the worms con- 

 tinue developing and become sexually mature in a few days, the female 

 penetrates into the superficial layer of the intestinal villi, and in the course 

 of a month gives birth to young, and then dies. The young wander 

 through the lymph-vessels and blood-vessels into the capillaries, pass into 

 the muscle and become encysted (Fig. 34), as did the parents in the former 

 host; 1 ounce of infested pork, unless thoroughly cooked, may hberate 

 80,000 worms. If half of these were females, each producing 1000 embryos, 

 40,000,000 worms would shortly begin to migrate into the muscles, causing 

 trichinosis, which may be fatal. The worst epidemic known was in Emmers 

 Leben, Saxony, in 1884, where 364 persons were infected from eating one 

 pig, and 57 persons died within a month. 



The Guinea-worm {Dracun' cuius medinen'sis) is an East India parasite 

 in the subcutaneous connective tissue of man. It is long and slender, 

 sometimes 1 yard long. It forms abscesses under the skin. When the 

 newborn young pass out of their host, if they pass into water, they enter 

 the body of a small crustacean (the Cy- 

 clops), which is necessary to their develop- 

 ment. It is supposed that they reach 

 the human system through the Cyclops, 

 which is swallowed in unfiltered drinking- 

 water. 



Fig. 35. — Eggs of the gape-worm 

 {Syn'garrms trachea'lis) , one of them 

 hatching; enlarged 260 times. 

 (After M^gnin.) 



Fig. 36. — Windpipe of chicken 

 split open to show gape-worms at- 

 tached to its inner surface; en- 

 larged. (After Megnin.) 



The hook-worm (Neca'tor america'nus), of the Southern United States 

 and the West Indies, is thought to have been introduced from Africa by 

 slaves. 



" In hook-worm disease we have ground-itch, tibial ulcer, anemia, inter- 

 ference with physical and mental development, and, in bad cases, dirt 

 eating." ' 



Other Species. — There are various other species. Some, as the pin-worm 

 (Oxyuris vermicularis) and the round-worm (As'caris lumhricoi' des) , are 

 parasitic in man. Some are parasitic in other mammals and some in birds. 

 One of the latter, Syn'gamus trachea'lis (Fig. 35), about \ inch in length, 

 causes '' gapes " in poultry (Fig. 36). 



1 Stitt, 244. 



