Fine Structure of a Transplantable Reticulum Cell Sarcoma. I. Light and Electron Micros- copy of Viable and Necrotic Tumor CeQs 1,2

SUMMARY-A contagious reticulum cell sarcoma of the hamster was studied by light and electron microscopy. There were two basic cell types, principal tumor cells (95%) and macrophage (5%). The cytoplasmic ribosomes of the principal cell were predominantly free in clumps and corresponded to ribosomes described in poorly differentiated cells. Dense bodies consistent with Iysosomes were associated with the Golgi. The macrophage suggested a non-neoplastic cell probably derived from tumor. stroma. Three types of mitochondrial alteration were discussed: mito-chondrial pallor, ruptured mitochondrial membrane, and dense ' matrix degeneration. By light microscopy, necrosis was divided into Four groups: necrobiosis, septal, dermal-epidermal, and thrombotic. Necrobiotic cells were observed early as uniFormly distributed, solitary, rounded cells lying within the phagocytic vacuole of macrophages. Their markedly increased light and electron density led to their designation as "dark cells. " It was suggested that necrobiosis be considered as a possible interpretation of dark cells observed in electron microscope studies. Septal, dermal-epi-dermal, and thrombotic necroses were examples of coagulative necrosis and were qualitatively different from necrobiosis. The fine structure of the cells of coagulative necrosis indicated three cell types designated A, B, and C. The end stage of phagocytized necrotic cells was a cell skeleton rich in dense membranous structures in a state of disarray or arranged as myelin figures. Mechanisms to explain their genesis were discussed.