The problem of periodicity in the asexual cycle of Plasmodium nucleophilum has been carefully studied in five birds, together with certain other questions, such as the age of the red cell most commonly attacked by the parasite, and the possibility of exoerythrocytic stages in the vertebrate host. The results may be summarized as follows:
1.Periodicity is marked in this species, and the length of the asexual cycle approximates twenty-four hours. There is however much variation in individual birds, and synchronicity is frequently slight. In general, the peak of segmentation occurs between 10 a.m. and 5 p.m.
2.Mature gametocytes may be found at any time during the twenty-four hours. Peaks in gametocyte number tend to follow by a few hours peaks in schizont number, indicating that the time for maturation of the sexual stages is somewhat greater and their length of life longer. It was found that size of the gametocyte, when mature, was somewhat larger than that given in the original description. A further difference, which applies to the asexual as well as the sexual forms, is in the color of the pigment, which is yellowish-brown, particularly when the granules are small.
3.The mean number of merozoites per schizont was found to be 6.09 ± 0.29, with a range of from three to ten.
4.The proportion of schizonts is usually low in this species, even when segmentation is most active, and frequently does not exceed 10 per cent. This is especially true in the later stages of the infection, which suggests that the mortality of the developing parasites is always high, and especially so after the host has had time to set up an effective resistance.
5.The proportion of young parasites in the younger erythrocytes was determined in one bird, from a series of smears made at different times during the twenty-four hours, and found to be high, but nevertheless considerably lower than that found in the other species of avian plasmodia so far critically examined—cathemerium, praecox (relictum), elongatum and circumflexum.
6.Exoerythrocytic stages were searched for in six birds, but without success.