Clinical, histopathological, and electron microsco pical observations were performed on a case of lymphoid leukemia in a calf encountered in the Chitose area in Hokkaido in 1971. This case was diagnosed as the “small lymphoid cell type” (lymphocytic lymphosarcoma) of bovine malignantlym phoma. It was also classified into the “calf multic entric type” from clinical aspects. It should be emphasized from an epidemiological point of view that the disease occurred to a three-day-old animal.

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Seventy-day-old chicks were inoculated with a single intraocular (IO) or intracloacal (IC) dose of the Asian type of Newcastle disease virus and examined for lesions of lymphatic organs, including the bursa of Fabricius (BF), thymus, spleen, and cecal tonsils. They Were killed one after another every day from I to 6 days after the inoculation. Some chicks died before autopsy.
1. The acute symptoms of the Asian type, such as depression, gasping, severe green diarrhea, and ticking, began to appear 3 days after the inoculation. Macroscopic observation revealed hemorrhage and ulceration in the digestive tract, congestion or hemorrhage in the trachea, collagenic edema in the neck hypodermis, and swelling, necrosis, and atrophy of lymphatic organs.
2. Histopathologic examination showed selected necrosis of lymphocytes and the replacement of vanishing lymphocytes by proliferated reticulum cells In every lymphatic organ observed. In the severe case, necrosis also appeared in other components, such as blood vessels and reticulum cells. Occasionally, wide areas of non-selected necrosis were scattered in the lymphnodes. Finally, in the thymus, spleen, and cecal tonsils, regeneration of lymphocytes occurred to the sites of reticular fibers or newlyformed blood vessels. BF remained atrophic, showing the formation of a duct-like structure by epithelial cells and no reproductin of lymphocytes. The atrophy of the BF was more marked in the IO than in the IC group.
3. The presence of viral antigen in the cytoplasm of epithelial and reticulum cells was confirmed by the direct fluorescent antibody technique.
4. In the thymus and spleen, the virus titer reached 10^6.0-10^7.0 TCID 50/0.1 ml in both groups. In the BF, it was considerably low in the 10 group.

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