[Number of clonogenic stromal precursor cells in the hematopoietic organs of guinea pigs at different ages].

The content of clonogenic stromal precursors in the femoral bone marrow, spleen and the thymus of guinea pigs of different age was studied by the in vitro colony assay method (monolayer cultivation of hemopoietic and lymphoid tissue). The concentration and the total amount of the stromal precursor cells was shown to be age-dependent. In the femoral bone marrow and in the spleen the amount of fibroblast precursors was maximal by the age of two months; then, with ageing, it remained at the former level in the spleen, but decreased essentially in the bone marrow. The number of stromal precursors was rather constant in the thymus during the period of its active functional activity, but these cells were absent in the thymus of old animals.