A 2-year-old Holstein cow had been manifesting such clinical symptoms as suggestive of traumatic pericarditis. Hematological examination revealed a remarkable increase in leukocyte count (37, 000), and a differential leukocyte count consisting of 95.0% lymphocytes, 3.5% neutrophils, 1.0% monocytes, and 0.5% acidophils. With a bad prognosis, the cow was sacrificed.
Postmortem examination revealed tumors in the neck and breast, and marked gelatinous infiltration in the neck, dewlap, and the posterior portion of the breast. A tumor in the neck contained a necrotic focus of fist size. The diaphragmatic, mesenteric, and othe lymph nodes were distinctly enlarged. The heart was covered with voluminous fat masses containing tumors of chicken egg size. The epicardium was thickened. The pericardium contained dark brown fluid.
Histopathologically, the tumors in the neck, anterior portion of the breast, and pericardium were composed of essentially the same tumor tissue. The tumor cells closely resembled lymphocytes. Large numbers of tumor-like cells were present in blood vessels of the sites of tumefaction. Hyaline degeneration occurred in the walls of some of the blood vessels. Argyrophil fibers were generally thick and coarse, and connected with tumor cells generally in a loose manner.
From these results, the cow was diagnosed as a case of lymphatic leukemia. It was the characteristic of this case that the clinical signs manifested had been very close to those of traumatic pericarditis.

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Hog cholera virus isolated from a pig in the field was subjected to alternate or continuous passages through tissue cultures of swine spleen, living rabbits, tissue cultures of swine and bovine testis cells, and swine kidney cells. As a result, it was possible to bring about an attenuation and variation of hog cholera virus.
When swine kidney cells were used for cultivation of this virus, they released about 10^3.5 to 10^4.5 TCID₅₀/0.1 ml of virus. High safety was demonstrated in pigs inoculated subcutaneously with 10^2.5 to 10^5.5 TCID₅₀ of virus. These pigs were protected from challenge with 10, 000 MLD of the ALD strain of hog cholera virus. It was proved that such ability of protecting the inoculated animal from infection had been developed in 3 days after inoculation.

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