Six birds infected with Plasmodium vaughani were used to study periodicity in the asexual cycle, and in four of them variations in the proportion of reticulocytes and the relative numbers of parasites occurring in reticulocytes at different times were determined. The process of division of the parasite was also investigated. The following conclusions may be drawn:
1.The length of the asexual cycle is 24 hours, with the height of segmentation occurring in the morning. The cycle is not very clearly marked however, and synchronicity is not great. There are variations in different birds, and even in the same bird at different times.
2.On the whole it appears that this species resembles many of the other species of malaria in the tendency of the parasites to invade reticulocytes. But this tendency is less marked than in most of these other species.
3.The proportion of reticulocytes to the total number of erythrocytes varies considerably from time to time both in the same bird, and in different birds, but these variations do not seem to be very consistent or regular. And it does not appear that the periodicity of the parasite bears any direct relationship to periodic changes in the number of reticulocytes, or that variations in the proportion of infected reticulocytes necessarily depend on the number of such red cells available.
4.Division in Plasmodium vaughani appears to occur in three ways: by repeated binary fission of the chromatin, with eventual splitting of the cytoplasm, by the splitting of an elongate parasite into merozoites having a bead-like arrangement, or by the similar breaking-up of a ring-shaped form, with a resulting ring of merozoites.
5.Attempts to transmit infection with this species by Culex pipiens indicate that if this mosquito ever acts as a vector in nature, it must do so very rarely.