Notes on the mechanism of leukocytosis.

I N THE LITERATURE one frequently encounters the opinion that leukocytosis is due to stimulation of the bone marrow. Leukocytosis generally develops so rapidly that the increase in circulating neutrophils cannot be due to an increase in their rate of maturation. Many chemical and physical agents have been shown to be causes of leukocytosis. Tullis’ is of the opinion that there is probably more than one mechanism of white cell stimulation and that leukocytosis is a nonspecific response to any of several demands. In previous work we found that a significant increase occurred in leukocyte motility and in the absolute nummber of neutrophils after the intramuscular administration of ACTH. A hypothesis was formulated, postulating that leukocytosis is the result of increased motility of the polynuclears, which migrate in larger numbers from the bone marrow into the peripheral blood.2’3 A number of experiments were carried out to test this hypothesis.