Ability of osteogenic precursors of bone marrow from intact and induced (by implantation of decalcified bone matrix) bones to support themselves was compared by transplantation in diffusion chambers. Osteogenesis continued for several months in bone marrow transplants from intact bones whereas in transplants from induced bone tissue active osteogenesis, although still observed after 12–20 days, ceased after 2 months. Fibroblasts from the second passage from cultures of hematopoietic tissue of induced bones, unlike fibroblasts from cultures of intact bone marrow, were virtually without osteogenic powers. These results confirm that induced osteogenic tissue has limited ability of self-support after the action of the inducer has ceased, compared with intact bone tissue.

The capacity for self-maintenance of the bone marrow osteogenic precursor cells from the skeletal bones and from the bones induced by implantation of decalcified bone matrix is compared. Transplantation in diffusion chambers is employed as the test system. Osteogenesis in the bone marrow transplants isolated from the skeletal bone lasts several months, whereas osteogenesis in the bone marrow transplants isolated from induced bone stops after the second month. Fibroblasts arising in the monolayer cultures of the skeletal bone marrow retained their osteogenic potencies after repeated passages. On the contrary, fibroblasts from the monolayer cultures of induced bone marrow lost their osteogenic capacity after the second passage. Thus, contrary to osteogenic precursors of the skeletal bone, osteogenic precursors of induced bone tissue had a very limited self-maintaining capacity after the cessation of induction.

Guinea pig and rabbit thymus cells showed a marked capacity for bone formation under the influence of transitional epithelium and decalcified bone matrix and were much superior in that respect to all the other populations of lymphoid and hemopoietic cells studied. Diffusion chambers containing the reacting cells together with inductors of osteogenesis were used.

ABSTRACT In monolayer cultures of guinea‐pig bone marrow and spleen the development of discrete fibroblast colonies takes place on days 9–12. The linear increase in the number of colonies with increasing numbers of explanted cells and the distribution of male and female cells in mixed cultures support the view that fibroblast colonies are clones. The concentration of colony‐forming cells in bone marrow and spleen is approximately 10 ‐5 . Bone marrow culture (but not spleen culture) fibroblasts are capable of spontaneous bone formation in diffusion chambers. Fibroblasts from both bone marrow and spleen cultures are inducible to osteogenesis in diffusion chambers in the presence of transitional epithelium.

In transplanting the mucous membrane of the urinary bladder to rats under the fascia of the anterior abdominal wall osteogenesis was induced not earlier than in 18–20 days, whereas in guinea pigs — in 10 days; the bone tissue development occurs in about 10% of the cases. Morphology and histochemistry of osteogenesis induction are very much alike in guinea pigs and rats. Low inducing activity of the rat transitional epithelium may be explained by the close contact of transitional epithelium and the vascular network in these animals. Such relationship is easily explained if to accept that the production of the inducing substance-factor from the epithelium is constant.