Haemopoietic Changes in the Rat during Growth and during Continuous Gamma Irradiation of the Adult Animal

I n this report, the changing patterns of cell proliferation in the various haemopoietic tissues (in particular the bone marrow and the spleen of the rat) are studied in relation to one another and to the changing requirements for blood production during growth. Particular attention is given to the erythropoietic system. In addition, haemopoiesis during growth involves maintaining the cellular content of an expanding blood volume and previous work (Lamerton, Pontifex, Blackett and Adams, 1960; Lord, 1964) has shown that the cellular content of the blood can be maintained in spite of a greatly depleted marrow cell population. Therefore, changes in cell proliferation in the bone marrow and spleen of adult rats following doses of continuous whole‐body γ‐irradiation are also studied. These changes are compared with those taking place during growth.