TRICHINA. 207 
Trichina,—The formidable Trichina deserves fuller notice. It is 
best known as a parasite in man, pig, and rat, but occurs also in 
hedgehog, fox, marten, 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, boring their way especially 
through connective tissue. The migration causes inflammation and 
fever. In or between the muscle fibres they grow, coil themselves 
Fic. 108.—Trichinz in muscle, Fic. 109.—Trichinz in muscle, 
about to be encapsuled.— encapsuled. There may be 
After Leuckart. 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 Trichine 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 (Zustrongylus 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 
