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The humoral influence of cells of hemopoietic organs of chicken embryos of different terms on the development of the colony and cluster formation of mononuclears of the bone marrow of mice was studied in joint cultivation in two-compartment cylindrical diffuse microchambers. The process of formation of colonies and clusters is inhibited by cells of the yolk sac on the 2nd-4th day of the development, by cells of the liver on the 8th-12th day, of the spleen on the 13th-18th day and of the bone marrow--on the 15th day. The yolk sac cells were found to have most considerable inhibiting influence on proliferation and differentiation of cells on the 2nd day of the development of chicken embryo. The yolk sac cells on the 6th day stimulate the formation of colonies and clusters. The yolk sac, beginning from the 4th day of the development, and the liver release humoral factors promoting the formation of erythroid colonies. The erythroid colonies are formed but when cultivated on the vascular membrane of the chicken embryo; the erythroid colonies are not formed when cultivated in the abdominal cavity of mice. Local erythropoietinoid factors are not synthetized by the spleen and bone marrow cells. A supposition is put forward that a combination of the local inhibiting and erythropoietic effects promotes the erythroid differentiation of cells.

The dependence of colony- and cluster-forming ability (CFA and CLFA) of bone marrow cells on its initial state and the conditions of cultivation was studied. Intact mice and mice with stimulated erythropoiesis were used in the experiment. The bone marrow was separated on a density gradient and cultivated in diffusion chambers (DC) on a plasma clot with addition of the tissue fluid of a chick embryo. Uni- and bicameral milliporous cylindrical microchambers were used. The DC were put into the abdominal cavity of mice first given a cyclophosphamide injection and on the vascular membrane of the chick embryo. The bicameral DC were employed in cocultivation of yolk-sac cells of a 4-week-old chick embryo and bone marrow mononuclears of both experimental groups. The CFA and CLFA of bone marrow mononuclears depend in respect of quantity and quality on the condition of its cultivation rather than on its initial state. It is concluded on the basis of tests for the inductive effects of yolk-sac cells on the CFA and CLFA that in study of cell inductors under conditions of DC and in cultivation in vivo one should take into account the initial state of the hematopoietic target cells, the sensitivity of cells to stimulation, the conditions of cultivation which allow the cells to emerge into the process of this or that differentiation even in the presence of an inductor.

The cells of chick embryo hematopoietic organs were cultivated together with mouse bone marrow cells in bicameral diffusion chambers under normal conditions and in activated erythropoiesis. The yolk sac cells inhibited colony formation on the 2nd, 4th days of development, the hepatic cells--on the 8th, 12th days, the splenic cells--on the 13th, 17th days, and the bone marrow cells--on the 15th day. The cells of the yolk sac sharply intensify the formation of colonies by the marrow mononuclears, in particular, on the 6th developmental day in activated erythropoiesis. The yolk sac (on the 4th, 6th days of development), the liver, and the spleen produce humoral factors which facilitate the formation of erythroid colonies by the marrow cells of mice. The cells of a 4-day-old yolk sac inhibit the formation of granulocytic colonies, and the synthesis of inhibitors ceases in a 6-day-old yolk sac. It is suggested that the synthesis of local humoral inhibitors of the proliferation of colony-forming units controls the intensity of hematopoiesis in the organ and, by reducing proliferation, facilitates the emergency of cells into differentiation independently, according to the law or under the effect of local humoral poetins.