two intermediate iiosts. The eggs must reach water 

 and must be eaten by copepods (tiny crustaceans), 

 which in turn must be eaten by one of a variety of 

 fishes. In the Great Lakes region northern pike and 

 pickerel are most commonly infected, as are also the 

 sauger and yellow perch. Since this region ships great 

 quantities of fish to other localities, the tapeworm has 

 been widely spread. One should therefore not taste 

 raw lake fish during food preparations, or eat smoked 

 fish from infected regions unless it is known to be 

 adequately treated. 



Common in the great cattle- and sheep-raising re- 

 gions of the world, especially in Africa, the Middle 

 East, Australia, and South America, is Echinococcus 

 granulosus, which passes its adult life in dogs and 

 doglike animals but usually develops as a larva in 

 herbivorous animals. The eggs may be passed by the 

 lickings of a friendly dog to the hands and face of 

 man, from where they can reach his mouth. Though 

 the adult is minute in this case, the larva (developing 



into what is called a hydatid cyst) can grow, in the 

 human liver, to the size of a grapefruit or larger. 

 When one or more of these cysts develops in the hu- 

 man brain, the results can be very serious or fatal. 

 The dwarf mouse tapeworm, Hymeiiolepis nana, 

 is the smallest adult tapeworm found in man, but it 

 makes up for its small size by large numbers, perhaps 

 hundreds or thousands in one person. The greater the 

 number present, however, the smaller they grow, so 

 that in heavy infestations they are only about 1 inch 

 long. World-wide in distribution, this is the common- 

 est tapeworm of the southern United States, where it 

 infects from 1 to 2 per cent of the population, espe- 

 cially children. Though difi'erent from almost all 

 other tapeworms in being able to complete its life 

 cycle in a single host, such as man, the rat, or the 

 mouse, it can revert to ancestral habits and use fleas 

 or flour beetles as intermediate hosts. Usually people 

 ingest the eggs by contamination with human feces 

 or in food containing mouse droppings. 



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