Ten normal guinea pigs each weighing approximately 400 Gm. were given intraperitoneal injections of sterile pyrogen-free saline, and another ten were given injections of saline + 25 mg. of Leukocytosis-Promoting Factor (Menkin). The animals were killed 4 hours after the injection and quantitative studies made on the blood and the bone marrow.
LPF appears to give rise to a considerable discharge of granulocytes from the bone marrow, much greater than can be accounted for by the leukocytosis which develops. The administration of LPF is also associated with a marked increase in the marrow lymphocytes.