The Ultrastructure of Trophozoites of Entamoeba histolytica with Particular Reference to Spherical Arrangements of Osmiophilic Cylindrical Bodies

SYNOPSIS. Trophozoites of Entamoeba histolytica were cultured under xenic, monoxenic and axenic conditions. Some of the monoxenically cultured trophozoites were grown in the presence of Bacteroides symbiosus and others in the presence of Trypanosoma cruzi (Mexican strain). Other trophozoites were obtained from experimentally produced amebic liver abscesses in hamsters. The trophozoites were centrifuged and prepared for study by electron microscopy. Acid phosphatase activity in the parasites was determined by cytochemical reactions. The various elements of the trophozoites were described and special attention was given to the spherical arrangements of electrons‐dense cylindrical units surrounding finely granular material. Their presence was independent of the strain studied and of the nutrient elements in the culture medium. The cylindrical units probably arise from endoplasmic reticulum elements and their possible function in the digestive processes and aggression mechanisms of the trophozoites is discussed. Acid phosphatase activity was found in round non‐branching intranuclear bodies in trophozoites cultured in various media. Whether these bodies represent part of the lysosomal system of the parasite is unknown. In preliminary work on the action of some amebicidal drugs, a special arrangement of cytomembranes morphologically similar to a Golgi complex was frequently seen in trophozoites of E. histolytica.