The following kinds of mice were infected intravenously with Plasmodium berghei: white Swiss, C 57 Leaden × A, STR × C 57 Black, (C 57 Black × DBA) × DBA. They were examined daily for total per cent parasitemia; per cent mature erythrocytes infected, per cent immature erythrocytes infected, per cent erythrocytes which were immature, and total red cell count.
There was a peak infection of mature erythrocytes at the beginning of the second week, after which infection in these cells declined to a very low level. The infection in immature erythrocytes rose rapidly in all mice and reached a plateau of about 90 per cent in 4 to 6 days. The proportion of immature erythrocytes to total erythrocytes rose after the first week to a plateau of about 60 per cent. Total parasitemia reflected the initial peak of mature erythrocytes followed by the rise in the proportion of immature erythrocytes, most of which were infected.
The red blood cell count began to drop by the third or fourth day after inoculation. It fell more rapidly in Swiss mice than in the others, but there was little difference among the other mice in this respect.
A more detailed examination was made of the course of the infection in mature erythrocytes. The Swiss mice had a mean count on day seven of 51 per cent; (C 57 Black × DBA) × DBA, 21 per cent; C 57 Leaden × A, 11 per cent; STR × C 57 Black, 6 per cent.
In general, the higher the infection in mature erythrocytes, the shorter lived the mice. There were exceptions and these were discussed. Also discussed was the coincidence of peak infection of mature erythrocytes and the first mode of a bimodal survival curve.