TRICHINA. 



207 



Trichina. The formidable Trichina deserves fuller notice. It is 

 a parasite in man, pig, and rat, but it has been introduced ex- 

 perimentally into hedgehog, fox, dog, cat, rabbit, ox, and horse. 

 The sexual forms live in the intestine, the female about 3 mm. in 

 length, the male less than half as long. After impregnation the 

 female brings forth numerous embryos viviparously, sixty to eighty at a 

 time, and altogether about 1500. These are produced in the wall of 

 the intestine, or in the adjacent lymphatic spaces. Most of them find 

 their way into lymph and blood vessels, and are swept by the blood 

 stream to the muscles ; occasionally some seem to migrate actively, bor- 

 ing their way especially through connective tissue. The migration causes 

 inflammation and fever. In the muscle fibres they grow, coil themselves 



FIG. 1 08. Trichinse in muscle, 

 about to be encapsuled. 

 After Leuckart. 



FIG. 109. Trichinae in muscle, 

 encapsuled. There may be 

 12,000 in a gramme of pig's 

 muscle. After Leuckart. 



spirally, and become encysted within a sheath, at first membranous 

 and afterwards calcareous (Figs. 108 and 109). The cyst is partly due 

 to the muscle, and partly to the parasite. The infected muscle fibre 

 degenerates. In these cysts, which may be sometimes counted in 

 millions, the young Trichinse remain passive, unless the flesh of their 

 host be eaten by another, pig eating rat, man eating pig. In the 

 alimentary canal of the new host the capsule is dissolved, the embryos 

 are set free, and become in two or three days reproductive. The male 

 seems to die after copulation. 



Among the numerous other parasitic Nematodes the following may 

 be noted : The giant palisade worm (Eustrongylus gigas} occurs in the 

 renal region of domestic animals, etc. ; the female may be 3 ft. long. 

 The armed palisade worm (Strongylus armatus} occurs in the intestine 



