Frequencies of CAFC day 28 and 35 in young and old C3H/He, CBA/J, DBA/2, BALB/c, and C57BL/6 mice. (A and B) The mean CAFC frequencies per 10⁵ marrow cells; (C and D) mean numbers of CAFC per femur. For the number of mice per group refer to the legend of Fig 2. Strains are plotted in order of increasing maximal lifespan (indicated below X-axis).