The female is a slender round worm, varying in length from to of an inch. The funcrior end presents a bead-like appearance, from which the intestinal canal pro ce•ils. The posterior three-fourths are mainly occupied by the reproductive organ, wltie.t is filled partly with free embryos,. and partly with eggs in various stages of maturity-. When these embryos have attained their full size within the uterus of the parent, they pass out at the genital aperture, and commence life on their own account. Thay are little worms with rounded ends, and presenting no indications of any internal organs. Before entering into the history of their migrations, we may mention that the male worm is seldom more than two-thirds the length of the female. It presents the same beadlike arrangements as the female, and a reproductive organ whose aperture apparently coincides with the anus; while the female sexual aperture is comparatively tie ir the head-end of the worm. The body terminates with two hooks which arc doubt less subsidiary to the reproductive process. The males are less numerous and shorter lived than the females, and probably die after having disehm7ed their natural function. The females continue bringing forth young for a period of two or three weeks. The embryos, according to Leuckart, Cobbold, and all our best helminthologists, penetrate the walls of the intestine, and pass directly into the muscles of their "bearers" or " hosts," where, if the conditions are otherwise favorable, they are developed into the form originally observed hy Owen and Paget. In way, by proceeding along the course of the intermuscular connective tissue, some of them reach the muscles of the extremi ties and other distant parts; but the majority of the wandering embryos (according to Virchow) "remain in those sheathed muscular which arc nearest to the cavity of the body (abdomen and thorax), especially in those which are smaller and most supplied with connective tissue." These embryos penetrate into the interior of the separate mus cular bundles, and in the course of 14 days acquire the size and organization of trichina $pincliq. The surrounding tissues soon become disorganized, and the spot inhabited by the coiled-up worm is converted into a spindle-shaped widening, within which the pre viously described cyst is formed by a hardening and calcification of the exterior. A point of great importance in relation to the distribution of this parasite, and as having .a practical bearing upon the disease known as trichiniasis (q.v.). has been established by
the experiments of Davaine—viz., that while in the adult condition, triclinic° perish in cold water in about an hour, and cannot survive the decease of their host for more than six hours, the larvm remain alive in water for a mouth, and will live for a long time in flesh which has become putrid. In this way, "a carcass near a marsh or rivulet may communicate the parasites to the ruminants that drink the water, or to pigs." In the same year (1860) in which Virchow and Leuckart proved that by feeding an -animal ou flesh containing the trichina 8piraEig, intestinal trichina: were produced, and watched the transformation of the young of the latter into muscular trichinae, a very important corroborative medical case was observed and recorded by Zenker. In this case the patient was a servant-girl, aged '20, and the principal symptoms were loss of appetite, prostration, violent pains, and contraction of the limbs; and finally oedema, which, with a certain amount of phneumouia, terminated fatally in the course of a month. After death, numerous larval trichinae were found in her muscles, while the intestinal canal contained sexually mature worms. Three weeks previously, before the girl had taken ill, she had assisted in killing pigs and making sausages. It was further ascertained that a few days before her illness commenced she had eaten some of the meat in a raw state. On examination it was found that the pork (both hams and sau sages) contained numerous encysted trichinm. It was, moreover, ascertained that the butcher and several members of the girl's family (to whom she had probably given sau sages) were attacked with symptoms similar to those which, in her case, proved fatal. How the pig acquires its trichinae is unknown; but that the larval trichinae contained in putrid flesh, etc., may easily gain admittance to the pig's alimentary tract is a suppo sition at once feasible and of likely kind. Beet-root, earth-worms, moles, and rats have been suggested as their infectors; but on this subject see the advice given by the French commissioners in the next article. The adult trichina is liable to infest the intestinal canal of all animals in which the larvae have been found in the muscles. In this category must be placed man, the dog, cat, rabbit, rat, mouse, mole, hedge-hog, and badger. Whether birds ever contain trichinae is doubtful, and reptiles and fishes are quite free from this parasite.