Large amounts of plasma from rabbits, rendered anemic by bleeding, were injected into normal rabbits. A significant rise in the number of reticulocytes was observed in these rabbits. Control rabbits receiving the same amount of plasma from normal donor rabbits failed to show any significant change in the reticulocyte count. A definite increase in red blood cell count, hematocrit and per cent nucleated red cells of the bone marrow was noticed in 2 rabbits receiving repeated injections of plasma from anemic rabbits. It is concluded that plasma from rabbits rendered anemic by bleeding contains a factor capable of stimulating red cell production.

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