[Effect of different leukocyte pyrogen fractions on hemopoiesis]

Fractionation of leukocyte pyrogen on a column of Sephadex G-75 made it possible to obtain separately the fraction stimulating the hemopoiesis and the fraction possessing the pyrogenic activity and inhibiting the hemopoiesis. Judging by the elution profile of Sephadex column G-75, substances of high molecular weight produced a stimulating action, and of low molecular weight--pyrogenic and inhibitory action. Possibly pyrogenic and inhibitory activities are connected with different substances. The nature of the inhibitory factor requires further investigation. It may be supposed that it is a substance of chalone type.