Some of the factors that produce a diminution in the number of parasites in P. lophurae infected ducks have been discussed. It has been shown that an increase in the carbon dioxide content of the plasma occurs with the increase in the degree of parasitemia. It appears that carbon dioxide may be a very important factor in producing the death of plasmodia following the time of the peak of the parasitemia. Furthermore in support of the opinion that factors other than immunologic play a significant role in regard to the degree of parasitemia it has been shown elsewhere that the number of parasites may be prevented from decreasing by the intravenous injection of large numbers of red blood cells. The number of parasites is greater in polycythemic than normal ducks. These plasmodia also prefer adult erythrocytes to young red blood cells. Phagocytosis occurs in ducks infected with P. lophurae and no doubt certain immunological substances are produced, however, these alone do not appear to be adequate to account for the phenomenon of the rapid decrease in the degree of parasitemia following the peak of infection.
Present address: Dept. of Pathology, School of Medicine, University of Texas, Galveston, Texas.