Within a few days after total-body X-ray irradiation, leu kemia vims particles could be observed in several organs of irradiated C3Hf mice. This was observed not only after frac tionated irradiation (5 X 150 R), but also after a single (250 R) total-body X-ray irradiation. Electron microscopic examina tion of several organs from the irradiated mice, such as spleen, lymph nodes, and bone marrow, revealed the presence of virus particles budding from the cell membranes; mature and im mature type C

more »

... particles were also present in the intercellular spaces. Leukemia virus particles were also consistently present in organs of eight C3Hf mice with radiation-induced leukemia. The distribution of virus particles in organs of mice with radia tion-induced leukemia was similar to that observed in mice with spontaneous or virus-induced leukemia; however, the number of virus particles observed in organs of mice with ra diation-induced leukemia was lower than that observed in mice with passage A (Gross) virus-induced leukemia. These observations contrasted sharply with results of electron microscopic examination of organs of nonirradiated, normal C3Hf mice, which revealed the presence of usually only a few isolated virus particles in the thymus and occasionally also in lymph nodes or in the bone marrow. 1680