vi NEMATODA FILARIIDAE 147 



When trichinised meat is eaten, unless it has been thoroughly 

 cooked, the cysts are dissolved and the larvae are set free. Within 

 three or four days they become sexually mature and their ova 

 begin to segment. The males after a time leave the body with 

 the excreta and perish, whilst the larvae of the new brood make 

 their way into the tissues of the host. 



Man usually acquires trichinosis by eating uncooked or im- 

 properly-cooked pork, and the disease is so widely spread and of 

 such a serious nature that most civilised countries have adopted 

 rigorous methods for the detection of trichinised meat. The pigs 

 either acquire the disease by eating uncooked swine's flesh, which 

 is frequently given them in the form of offal, or by devouring 

 rats, which are very susceptible to the disease. 



IV. Family Filariidae. 



Mouth with two lips, or without lips. Six oral papillae often 

 present, and sometimes a horny oral capsule. Four pre-anal 

 pairs of papillae, and sometimes an unpaired one as well. Two 

 unequal spicula or a single one. 



G-enera : Filaria, Ichthyonema, Hystrichis, Spiroptera, Dis- 

 pharagus, and others. 



The genus Filaria is a very large one. Like Ascaris, it is 

 confined to Vertebrates, but usually lives in the tissues of the 

 body and not in the intestines. F. (Dracunculus) medinensis 

 Gmel., the guinea-worm, is well known as a human parasite in 

 hot countries ; it also occurs in the horse and dog. The female 

 has an average length of 50 to 80 cm., but gigantic forms with 

 a length of 4 metres have been described. The alimentary canal 

 is degenerate. In adult females the body is completely occupied 

 by a uterus crowded with eggs and embryos, which can only 

 escape by the rupture of the mother's body, as the genital ducts 

 have disappeared. Its original home is tropical Asia and Africa, 

 but it has been introduced into South America with the negroes. 



The female lives coiled up in the subcutaneous tissues, usually 

 in those of the legs. Its presence gives rise to painful tumours. 

 When these break the female protrudes, and may be withdrawn 

 from the body by very carefully rolling it round a stick or pencil. 

 This must be done very slowly, a few inches a day, as the rupture 

 of the body sets free the contained embryos, and may result in 



