Electron microscopic study of the shay chloroleukemia.

leukemia. The cells were examined daily under the electron micro scope between the 5th and 15th day following inoculation. The tumorous tissue was found to contain a single type of cells. The polygonal cells were loosely arranged, without intercellular at taching structures between them. Pseudopodia projecting into the intercellular space and rows of pinocytotic intracellular vesi cles pointed to intensive surface activity of the tumor cells. The cells had large nuclei and a comparatively narrow cytoplasmic marginal zone which was rich in homogeneously distributed free ribosomes and polysomes but usually poor in rough-surfaced endoplasmic reticulum. The cytoplasm contained a well-devel oped Golgi apparatus and a varying amount of pigment granules of the dense-core type. The submicroscopic structure of pigment granules and autophagous vacuoles contained in the cytoplasm of the chloroma cells has been described and intensive acid phosphatase activity has been demonstrated on an ultrastructural level in both cytoplasmic inclusions. Acid phosphatase activity was observed in the elements of the Golgi apparatus as well. The origin of pigment granules and autophagous vacuoles is discussed. Pigment granules were occasionally found in the inter cellular space also. Virus-like particles were observed in the inter cellular space as well as in the cavity of large membrane-bounded intracellular vacuoles; they occurred mostly in samples taken from older tumors. These corpuscles had an average diameter of 900 A, included electron-dense nucleoids, and resembled Bernhard's C-type particles.