Trichina
in zoölogy, a genus of Nematoidæ, established by Owen for the reception of the minute spiral flesh worm, T. spiralis, discovered in human muscle by Sir James Paget, in 1835, when a student at St. Bartholomew's Hospital, London. Mr. Hilton, of Guy's, had previously noticed gritty particles in human muscles, and recognized them as the results of parasites, afterward shown (by Owen) to be young trichinæ. The trichinæ met with in human muscle are minute immature worms, spirally coiled TRICHINA in small oval cysts, scarcely visible to the naked eye, measuring 1/78 inch in length and 1/136 inch in breadth. Sometimes the worms are not encysted, and measure 1/25 inch in length and 1/360 inch in breadth. The mature and reproductive trichinæ inhabit the intestinal canal of mammals, including man, and live for four or five weeks, attaining ability to reproduce on the second day of their introduction. The male is about 1/18 and the female 1/8 inch long. The eggs are hatched within the female, and as soon as the embryos are expelled they bore their way into the muscles, and there in about 14 days assume the form known as T. spiralis, often setting up trichiniasis. Thus the only way in which trichinæ can get into the human system is by being swallowed alive with pieces, of imperfectly-cooked muscle in which TRICHINOPOLI that the patient experiences the most severe symptoms and stands in greatest danger. Severe pains are experienced at this period in a typical case of trichiniasis, and even breathing may be executed with difficulty owing to the lesions of the muscles. Diarrhea is also prevalent, the symptoms on the whole bearing a resemblance to those of gastric fever.
In about four weeks after the commencement of the symptoms the disease begins to abate. In severe cases the diarrhœa may continue, and often aids a fatal issue, arising from the prostration, together with the total derangement of the secretions. In an acute case of trichiniasis death has been known to occur as early as the fifth day of the disease, while a fatal issue has been allayed as late as the 42d day. Epidemics of trichiniasis have chiefly occurred system disease, while they are encysted. The pig is the great on the Continent, where the habit of source of infection to man, as it is peculiarly liable to the presence of encysted trichinæ.