FLATWORMS AND THREADWORMS 



303 



It may take about six 

 weeks for complete encap- 

 sulation, but once encap- 

 sulated they may remain 

 alive for twenty or twenty- 

 five years in the muscle. 



Pigs may be literally 

 "filled" with these parasites, 

 causing what is known as 

 "measly pork," although 

 they may show no external 

 sign of infection. Many 

 countries now insist on pork 

 inspection to prevent a 

 spread of infection. 



The patient usually suf- 

 fers with a fever, anaemia, 

 muscle pains (myositis), 

 which are often mistaken 

 for rheumatism, and intesti- 

 nal disturbances (gastro- 

 enteritis). 



Ankylostoma duodenale in 

 the old world, and Necator 

 americanus in this country 

 are the Hook-worms (Fig. 

 190). The disease caused by 

 hook-worm is variously 

 known as ankylostomiasis, 

 uncinariasis, hook-worm dis- 

 ease, tropical or Egyptian 

 chlorosis, and anaemia of 

 bricklayers and tunnel- 

 workers. 



The old-world animal is 

 small and cylindrical, the 

 male being about 10 mm. in 

 length and the female from 

 10 to 18 mm. There are chitinous plates about the mouth and there 

 are two pairs of sharp, hook-shaped teeth with which the mucosa of the 

 intestine is pierced. On the male there is a prominent caudal, umbrella- 

 like expansion. The American species is slightly more slender, with 

 a globular mouth and a different arrangement of teeth. The eggs of 

 the American form are slightly larger than those of the European forms. 

 The larvae of the hook-worm develop in moist earth and dig their 



Fig. 191. Forms of Worms Parasitic to Man. 



1. Larval stage of Filaria ozzardi (F. demarquayi). 



2. Larval stage of Loa loa (Microfilaria diurna) . 



3. Larval stage of Filaria bancrofti (Microfilaria 

 nocturna ) . 



4. Larval stage of Acanthocheilonema perstans (Mi- 

 crofilaria perstans). 



5. Adult parasite female of Strongyloides stercoralis. 

 6 and 7. Adults, male and female, of the free-living 



generation of Strongyloides stercolaris. 



8. Rhabditiform larva of Strongyloides stercoralis. 

 just hatched from egg. 



9. Filariform infective larva of Strongyloides ster- 

 coralis. 



10. Rhabditiform larva of Ancylostoma duodenale, 

 just hatched from the egg. 



11. Filariform infective larva of Ancylostoma duo- 

 denale. (From Hegner and Cort's "Diagnosis of Proto- 

 zoa and Worms Parasitic to Man" ; 1-4, after Fulleborn ; 

 5-11, after Looss.) 



