REACTIONS OF THE HEMATOPOIETIC SYSTEM TO INFECTION

An increase in the number of leukocytes of the peripheral blood is so frequent a manifestation of infection that infection must always be sought when the leukocyte count is raised above the normal average. Usually the number of the polymorphonuclear neutrophils is augmented, both relatively and absolutely. Arneth, Schilling and others have attached significance to the increase in the proportion of young polymorphonuclear neutrophils in the hyperleukocytosis of infection; even myelocytes may appear in the peripheral blood. The occurrence of young granular leukocytes and of myelocytes outside the bone marrow indicates not merely that the hyperleukocytosis is a matter of altered distribution of the circulating leukocytes but that these cells are produced in increased numbers in the hematopoietic system as the result of reaction to the stimulus of the infection. A sudden increase in the number of young, undifferentiated precursors of the granulocytes and their persistence characterizes certain forms of