The leukocytes, their various activities, their independent life in the circulating blood, and their importance in the human economy have been a subject of medical research ever since the discovery of their existence.
Though leukocytes play an important part in all local processes connected with infection and inflammation, they are produced in only one organic system, namely, in the bone marrow of the short bones (vertebrae, ribs, skull) and in the short bones of the hands and feet. In times of great need, as for instance during acute general infections, such as pneumonia, leukocytes are also formed in the long bones of the extremities, which usually contain only fatty tissue. In studying leukocytosis and the activity of individual leukocytes and especially the cause of the appearance of large numbers of leukocytes of the polymorphonuclear type in such infected areas, an interesting problem presented itself. As far as human beings are