ABSTRACT
Cells obtained from the blood-forming organs of donor animals and injected, under appropriate conditions, into heavily irradiated mice, can colonize, among other organs, the spleen of the hosts, giving rise to discrete and differentiated nodules of haemopoietic tissue (Till & McCulloch, 1961). It has been demonstrated that the number of nodules is directly proportional to the number of injected cells and that such nodules may be regarded as clones arising from single cells (Till & McCulloch, 1961; Becker, McCulloch & Till, 1963). The postulate of classical haematological theories (Maximov & Bloom, 1934; Ferrata, 1935) that a proportion of the cells in blood-forming organs is capable of indefinite division with renewal of the stem line and of differentiation into mature blood cells has thus been experimentally demonstrated.
