For the purpose to study in vivo changes of the mice bearing Ehrlich ascites tumor with special emphasis on the problems of cellular antibody and serum antibody, a series of experiments such as neutralization tests in vivo and in vitro study of the effect of lymph-node cells from the tumor bearing animals on target cells were carried out, and the findings thus obtained are briefly summarized as follows : 1. Regional lymph-node cells from the mouse transplanted with Ehrlich ascites tumor cells

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... ow a marked cytotoxic action on their cultured target cells, JTC-11, synergistically with serum from mouse bearing Ehrlich cancer. 2. The tumor cells inoculated with lymph-node cells from the tumor bearing animals showed a retardation in growth and finally regressed. 3. Spleen and lymph nodes of tumor bearing animals showed a marked increase in weight.