It is inherent in most fields of investigation that problems which can be expressed in quantitative terms are the most actively pursued. Quantitation permits planned controlled experimentation susceptible to logical reasoning, with eventual understanding. In hematology, techniques for quantitation of normal and abnormal erythropoiesis have been developed, and knowledge concerning red cell disorders has increased concurrently.
Similar techniques for the study of leukopoiesis and leukocyte life span and distribution in normal and abnormal states have only begun to be developed. Part of the difficulty in expressing leukocyte physiology in the same quantitative terms as for the red cell lies in the fact the leukocyte is not confined to the intravascular circulation. Labelled red cells can be followed until their death by sampling the peripheral blood at intervals. The leukocyte, on the other hand, is more difficult to label and, if transferred into a recipient, disappears from the circulation almost immediately.
CRADDOCK CG, PERRY S, LAWRENCE JS. Newer Concepts in Leukocyte Physiology and Their Clinical Significance. AMA Arch Intern Med. 1957;100(2):183-189. doi:10.1001/archinte.1957.00260080009004