The extracellular survival of the malaria parasite Plasmodium lophurae was favored on the 4th day of incubation in vitro by the presence in the medium of added folinic acid at a concentration of about 5 µg. per ml. The development of the human malaria parasite P. falciparum intracellularly in suspensions of human erythrocytes was better in a medium with a high than in one with a low concentration of folic acid.

In the early extracellular development of P. lophurae in vitro erythrocyte extract could be partially replaced by certain yeast protein preparations and by a non-dialyzable fraction, free from hemoglobin, prepared from duck erythrocyte extract by means of starch electrophoresis.

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