NEMATHELMINTHES. ROUND-WORMS 37 



were infected with hookworms and other intestinal parasites; then a 

 systematic campaign was inaugurated to expel these worms, and when 

 this was done the death rate fell to 13.5 per 1000." 



Trichinella (Trichina) spiralis, Fig. 26, is a small nematode the 

 adult male of which is about 1.5 mm. in length and a female % mm. 

 Both sexes are enlarged somewhat toward the posterior end, where, 

 in the male, are two short, conical protuberances. 



The adults are found in the intestine of man and other animals. 

 The female worm produces a large number of embryos, perhaps 10,000 

 or more, which immediately begin to migrate into the surrounding 

 tissues, finally finding their way, perhaps through the blood and lymph 

 streams, to the muscles of their host where they grow until nearly 

 i mm. in length. As it grows the embryo coils itself into a spiral, 



FIG. 26. Trichinella spiralis encysted among muscle fibres. Highly magnified. 

 (From Hegner, College Zoology, after Shipley and MacBride, from Leuckart.) 



and forms an elliptical cyst around itself as it lies in the connective 

 tissue between the voluntary muscle fibres. It has been estimated 

 that there were from 5,000,000 to 100,000,000, cysts in the bodies of 

 persons who have died of the disease. This cyst, after seven or eight 

 months, begins to degenerate and becomes calcified, and the worm is de- 

 stroyed, though it may take from 2 to 10 years. The adults get into 

 the human intestine from eating uncooked pork in which there are cysts. 

 The cysts dissolve in our intestine, thus liberating the worms which in 

 five or six days are able to produce embryos, and this they may continue 

 to do for a month, if the adults are not gotten rid of by purgatives 

 or by diarrhea; in any case the adult worms usually disappear in five 

 or six weeks. Just how the hog becomes infected is uncertain, probably 

 by eating infected offal, or infected rats; certainly the hog seldom has 

 the opportunity of eating human flesh with or without the trichinella 

 cysts. 



If the disease, Trichiniasis, be recognized before the embryos have 



