||P.407 left column bottom paragraph: "What is the source of knowledge about turnover kinetics of the hematopoietic cell renewal systems? It appears legitimate to stress the contribution of nuclear medicine and the utilization of radioactive tracer methods developed during the 1950s and 1960s. It was L.G. Lajtha—himself a pioneer in this field—who published in 1961 the first monograph entitled “The Use of Isotopes in Hematology” (ref 13). At that time, the major radionuclides available and used were 32P, 59Fe, 51Cr, 131I, 60Co, 3H and 35S. During this early period and in the subsequent years, the life span of blood cells was established as indicated in Table 1 (for details see primary sources (1) or (2))."