FACTORS IN PLASMA CONCERNED IN NATURAL RESISTANCE TO AN AVIAN MALARIA PARASITE (PLASMODIUM LOPHURAE).

The plasma of adult chickens, when injected into young chicks or chick embryos infected with Plasmodium lophurae, lessened the parasitemia. The substances responsible for this effect were inactivated or removed by the heating of adult chicken plasma for (1/2) hour at 65 degrees C., followed by centrifugation to remove the coagulated material; but they were not affected by heating for (1/2) hour at 56 degrees C. The active materials were present in the euglobulin fraction of hen plasma. In similar experiments with ducks, the plasma from each of a series of adult ducks was tested for its effect on the course of infection in young ducklings. The adult ducks were then inoculated with a large dose of parasites. There was a positive correlation between the effectiveness of a plasma in lessening the parasitemia of ducklings treated with it and the resistance on infection exhibited by the duck from which the plasma had been obtained. More than half of the adult female ducks with an active ovary which were tested, but only one of the males, had effective plasmas and also showed relative resistance to the infection.