On the erythropoietic principle in the blood of rabbits made severely anemic with phenylhydrazine.

TRUE POLYCYTHEMIA can be produced in normal, adult rats at ordinary altitudes by injection of the filtrate of boiled plasma of rabbits made severely anemic with phenylhydrazine. 7 All the criteria of polycythemia are observed: increases in red cell count, hematocrit and hemoglobin concentration, as well as reticulocytosis and evidence in the bone marrow of stimulation of erythropoiesis. An extract of such anemic rabbit plasma is effective not only in the normal adult rat, but also in mice.8 Anemic dog plasma is active in the rat.9 The active principle is clearly not species specific. Gordon et al.3 have related the potency of the plasma filtrate to the degree of reticubocytosis in the donor rabbit; Jacobsen et al.’#{176} to the presence of liver damage with the anemia. In our experience neither of these is an invariable criterion for obtaining a highly active plasma filtrate. Accordingly, we describe below the method we now use that has always given us a highly active extract. Whereas the plasma filtrate produces a polycythemia, the parent plasma if injected for a few days causes a drop in hemoglobin. Some experiments are described below which explain the effect of boiling in destroying or removing the agent responsible for the decrease while the erythropoietic principle is preserved. In our early experiments on the erythropoietic factor the assay was based on production of polycythemia in adult rats. With only four rats this assay consumed about 250 ml. of active plasma filtrate, and the time required was two weeks. In order to conserve material and shorten the time we have employed two other assay procedures. One is based on producing a reticulocytosis in normal adult mice, the other on increased uptake of Fe5#{176} in the blood of starved rats.’2 These two tests were used mainly as a guide in the fractionation procedure. The active fraction is predominantly mucoprotein.