[Ultrastructural changes in the red bone marrow in hyper- and hypokinesia].

Changes were looked for in the bone marrow of rats, put for a long period of ontogenesis under different degrees of muscular activity. The experiment was carried out on three groups of animals of the same age--those for the purpose of control, those loaded with movements, and those immobilized. The ultrastructural picture of the bone marrow with the rats loaded with movements showed an active hematopoiesis which was especially pronounced in the erythrocyte row. We found also an increased activity all over the cellular surface, pinocyte invaginations and vesicles, which were a sign of an intense exchange between the cells and the environment. A lower erythropoietic activity was found in the marrow of the immobilized animals. In this group no erythroblastic isles were found, which is typical of normal erythropoesis. Some young cells showed reduced small organs, whereas others were characterized by a more pronounced vacuolation of the cytoplasm.