Studies on Malarial Parasites

1. Methods have been described for the preparation and sterilization of a synthetic nutrient medium which supports normal growth during one 24 hour asexual cycle of the erythrocytic form of P. knowlesi. 2. Successive subcultures with good multiplication can be carried out when whole blood or plasma is added to the medium. Data are presented from two such experiments where the sixth and seventh generations, respectively, were injected into normal monkeys. In both cases, the injections produced clinical malaria and in one, an abnormally severe course was observed. 3. A high percentage (95 per cent) of O(2) inhibits multiplication in in vitro cultures. A gas phase approximating alveolar air permits normal development. A lower percentage (0.37 per cent) of O(2) in the gas phase supports growth at least as well. 4. Certain experiments indicate that in vitro growth is better supported in normal monkey plasma than in plasma from parasitized monkeys. Heating of parasitized plasma to 56 degrees C. for 30 minutes removed the deleterious effect. 5. A nutritional need by the parasite for glucose and p-aminobenzoic acid has been shown. Attempts to demonstrate the need for other individual components of the nutrient medium have not been successful though the effect of the absence of blocks of nutrient such as purines and pyrimidines, amino acids, or water-soluble vitamins can be observed. 6. Further assay of the nutritional requirements of the parasite appears to be hampered by the supply of nutrient furnished by the red cells and plasma. Cultivation of parasitized cells washed free of plasma and resuspended in synthetic medium containing 1 per cent serum albumin has been accomplished as one step directed toward the removal of such interfering factors.