The earliest bone marrow precursor cell types, often called stem cells, have a very large
capacity for self renewal. This makes them a useful model system in which to test the
hypothesis that normal somatic cells have a limited proliferative capacity. Marrow precursor
cells differentiate and multiply to replenish the supply of various blood cell types that
constantly turn over. Especially with erythrocyte production, this function is well defined and
can be tested rigorously to determine whether a significant amount of the stem cell …