THE PHLEBOTOMY of the healthy donor is the simplest approach to the study of blood regeneration, since there is a controlled, known amount of blood loss and no impairment of hemopoiesis from disease. However, the measurement of blood regeneration after a single phlebotomy of 500 ml. is difficult because of the small change in red cell values, and this change is easily obscured by physiological fluctuations. Estimates of recovery time range from a few days1 to several months.2 Marked individual variation is found within any one group of donors; for example, Fowler and Barer2b noted recovery times of from 21 to 98 days among 63 subjects. In the present study repeated phlebotomies of donors have made it possible to establish a pattern of response, which can be applied to blood loss in general, be it of small or large amount.
Normal subjects and patients with increased