“…Case 9 in the pre sent series is interesting in this respect as his marrow, at the time of study, contained many megakaryocytes, and in the,analysable poly ploid cells 2 Ph1 chromosomes were present. It is clear that the Ph1 is not present in the lymphocytic series, as lymphocyte-derived mi toses in cultures of Phytohaemagglutinin-stimulated blood leuco cytes are clearly normal in patients with chronic myeloid leukaemia (6,14,24). These findings tend to indicate separate origins for lymphoid cells and for other blood cells, and is a strong argument against the hypothesis that lymphocytes can act as stem-cells for other cell types.…”