Early exoerythrocytic schizonts of the simian malaria parasite Plasmodium cynomolgi, B strain, have been detected in fixed liver tissue, employing highly specific reagents. Five-day and 4-day schizonts were readily identified by both the indirect fluorescent antibody (IFA) technique and the Giemsa stain, in biopsy material fixed in Carnoy's solution and embedded in paraffin 9.5 years previously. Three-day exoerythrocytic forms were identified by IFA in freshly fixed and embedded tissue, then were re-located in the same sections after staining with Giemsa. The 3-day parasites were within the cytoplasm of hepatic parenchymal cells, measured 5 μ in diameter, and possessed one to three nuclei. Because of the highly specific nature of the immunofluorescent technique, the identification of these early forms is reported here as far more certain than had been possible previously.
Present address: Department of Medicine, USPHS Marine Hospital, 15th Avenue at Lake Street, San Francisco, California 94118.