[The activity of growth-regulating substances isolated from the spleen and thymus of healthy cows and of those with hemoblastoses].

Certain agents of the proteoglycan nature possessing organ-specific rather than the species-specific antimitotic chalone activity have been obtained from the normal bovine spleen and thymus. The preparations obtained by the same method from the spleen and the thymus of animals affected by lympholeukemia and lymphosarcoma did not reveal the antimitotic activity; moreover, they were of high mitogenic organ-specific character. A connection between the mitogenic factor produced by lymphocytic cells and the bovine leukemia virus is possible.