1.Killed P. knowlesi parasites emulsified in paraffin oil containing killed tubercle bacilli protect rhesus monkeys against fatal infection with P. knowlesi. The infection results in the immunized monkey in low grade parasitemia of short duration whereas in the unimmunized monkey almost invariably in high parasitemia and death.
2.No satisfactory substitutes were found for killed tubercle bacilli; cerotic acid gave inconstant results; lipid extracts of mycobacteria, cholesterol and “lecithin” were ineffective. When peanut oil was substituted for paraffin oil and Arlacel for Falba no protection occurred.
3.Preparations containing non-parasitized red blood cells, Falba, paraffin oil and killed tubercle bacilli did not immunize.
4.Killed P. knowlesi induce the production of complement fixing antibodies. When adjuvants are combined with the parasites the antibody titers are higher. In general, the groups of monkeys with higher titers show protection but there is no strict correlation in individual monkeys between antibody titer and protection.