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The hyperkinetic circulatory state observed in intact anesthetized dogs at the end of a 15 minute period of breathing 6 per cent oxygen in nitrogen was absent in a similar series of dogs acutely adrenalectomized by the ligation technie. Blood removed from intact animals at the end of the anoxic period and infused into normal assay dogs produced a rise in cardiac output in the latter which was not observed with comparable infusions of normal blood or blood removed from adrenalectomized anoxic dogs. The transferable agent demonstrated by this study is considered responsible for the rise in cardiac output in the anoxic donor. It is suggested that this agent arises from the adrenal medulla.

The possibility that the increased cardiac output observed in severe anemia is due to a humoral mechanism was investigated by an assay procedure in which blood from anemic donor dogs was infused into normal assay dogs. Blood removed from anemic donors during the period of augmented cardiac output and infused into assay dogs produced cardiovascular changes which were statistically different from the changes observed with infusions of normal blood or blood removed from anemic donors when the cardiac output was not elevated.