The Use of Roentgen Radiation in locating an Origin of Host Resistance to Trichinella spiralis Infections.

It has been demonstrated by Ducas (1), McCoy (2, 3), and Fischthal (4), and in experiments included in this investigation, that rats once infected with Trichilella spiralis may be highly resistant to subsequent infections. Trichienlla infections consist of a primary intestinal phase and a secondary muscle invasion. The question has arisen as to whether the host resistance to re-infection is elicited by the penetration of the adult parasites into the intestinal mucosa, the mligration of the larvae to the muscles, or both phases. This series of experiments was designed for the purpose of locating the origin of the resistance, and to demonstrate the use of roentgen radiation as a tool in resistance studies. Tyzzer and Honeij (5), in 1916, Schwartz (6), in 1921, and Semrad (7), in 1937, demonstrated that radium or roentgen irradiation of Trichi,ella larvae, before feeding to a suitable host, would either destroy the larvae before they grew to maturity in the intestine of the host or else prevent the formation of young in the adult female worms that did develop. The extent of injury to the parasites was apparently proportional to the dosage of irradiation. The present authors (8, 9), employing quantitative methods, have determined the range of dosages of radiation which allows the trichina larvae to grow to maturity in the intestine without producing offspring. In this way, an intestinal infection without the consequent muscle invasion could be achieved. The aim of the present experiments is to determine whether an intestinal infection alone will produce resistance to a second infection of trichina.