The Distribution of Haemopoietic Colony-Forming Units in the Mouse Femur, and its Modification by X Rays

A method of dividing mouse femoral bone marrow longitudinally into two groups of cells of varying magnitude has been described. By assaying the haemopoietic colony-forming units (CFU) in two zones of the marrow, their distribution across the diameter of the femur has been determined. It has been shown that the concentration of CFU increases from the longitudinal axis of the femur (20 CFU per 105 bone marrow cells) towards the internal surface of the bone (45 CFU per 105 bone marrow cells), obeying approximately a square law relationship. Relatively few CFU remained in the periostenum or the bone matrix. Using X- and γ-ray CFU survival data, the effects of radiation on the location of CFU in the bone marrow have been determined. The implications of the modified CFU distribution with respect to some experimental situations have been discussed.