Abstract
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 microg. 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.