EXPERIMENTAL STUDIES ON THE MALARIA OF MONKEYS*

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Abstract
A progress report of work done with L. G. Taliaferro and P. R. Cannon on the morphology, asexual cycle, temp., ordinary course of infection, and acquired immunity to superinfection in the malaria parasite of Panamanian monkeys. Various spp. of monkeys from Panama have been found to be infected with what appears to be a single sp. of a quartan-like parasite which is probably identical with Plasmodium brasilianum, Gonder and Berenberg-Gossler, 1908. The course of initial infection varies with number of parasites injected, but is characterized by acute rise, crisis, and latent period during which relapses of varying degrees of severity may occur. The type of infection encountered, as determined by work on the asexual cycle and on number counts, is the result of a differential mortality of the parasites, which, themselves, reproduce at a constant rate throughout. Thus, before crisis, approximately 7.5 of each brood of about 9 merozoites die (natural resistance of host), whereas at crisis and thereafter, even more die (true acquired immunity). This mortality is correlated with cellular responses on the part of the host. The cellular responses are evidenced by increase in numbers and in phagocytic activity of the differentiated macrophages, especially of the spleen and liver, and by general activation of the more primitive lymphoid tissue, notably in the spleen. No intermediary antibody was found associated with the cellular responses, but a local op-sonizing antibody seems probable, whose concentration in the peripheral blood was too low to be demonstrated by the techniques so far employed. The suggestion is made that these results on acquired immunity against malaria of monkeys so closely parallel those found in avian malaria that it seems not unreasonable to suppose that they may also hold for malaria in man.