When transplanting the bone marrow cells from adult C57BL mice to the lethally irradiated (CBA X C57BL) F1 hybrids of different age, the decrease of the colony forming activity of the stem haemopoietic cells was observed in the spleen of the older recipients, as compared with the 3 months old ones. The joint transplantation of the bone marrow and thymus cells resulted in both the cases in the stimulation of the growth of colonies. The number of endogenous colonies of haemopoietic cells arising in the spleen of animals following the sublethal irradiation was greater in younger hybrids. After the induction of the "transplant versus host" reaction by the lymph node or spleen cells from the CBA mice, the relative weight of spleen and regional lymph node, respectively, in the older recipients exceeded those in the younger ones.

A study was made of the effect of the hybrid resistance abrogation by means of the lymphoid cell administration on the survival of the lethally irradiated mice protected by the transplantation of the semiallogeneic bone marrow. Injection to the C57BLxCBA recipients of the C57BL lymphoid cells one day before the irradiation and the transplantation of the bone marrow of the same genotype (C57BL) increased the chimera survival in comparison with the untreated recipients; such pretreatment 7 days before the irradiation decreased the chimera survival. Parental spleen lymphocytes administration produced but an insignificant effect on the radioresistance both of the stem hemopoietic cells (by the endocolonisation test) and of the organism as a whole (by the 30-day survival test) of the F1 hybrid. On this basis a conclusion was drawn that the differences in the splenocyte efficacy, when they were injected at different periods before the irradiation, could not be attributed to the changes in radioresistance.

Antidromic potential sin cortical neurons elicited by stimulation of pyramids and different segments of the spinal cord were studied with the aid of extracellular recording in rats. Axons of about 2/3 of the cells under study formed the cortico-spinal tract passing through the ventral portion of the dorsal column up to the lumbar segments of the spinal cord. Conduction velocity along the cortico-spinal axons varied from 2.3 to 17.0 m/sec.

A stimulating influence of thymus cells on the capability of irradiated (from 100 to 500 r) bone marrow of mice of producing colonies in spleen of syngenous recipient has been proven. The intensification of colony formation involves an increased radioresistance of stem cells. It is supposed that radioresistant thymus cells have a stimulating effect. Thymus cells exert their influence not only to the rate of survival of stem cells proliferating in the bone marrow of femur, but also increase their erythropoetic potention.

Migration of stem cells and B-lymphocytes from the bone marrow and of T-lymphocytes from the thymus was studied on special models in mice of the CBA and C57BL lines, responding to sheep erythrocytes oppositely. Genetically-determined differences in the height of the immune response between the CBA and C57BL mice in immunization with sheep erythrocytes depended to a certain extent on different expression of the process of intensification of migration of the stem cells, T- and B-lymphocytes in response to the antigen administration.

A study was made of the dynamics of the colony-forming and migration capacity of the polypotent stem hemopoietic cells of the bone marrow of the F1 (CBA X C57BL) mice after the hydrocortisone administration. The relative count of the stem hemopoietic cells in the bone marrow increased on the 3rd day after the hydrocortisone administration. This elevation was maximal on the 5th day after the hydrocortisone administration. On the 8th day the stem hemopoietic cell count decreased to the normal level.

Materials on the state of hemopoietic organs and peripheral blood of mice and rats kept under hypokinetic conditions for from 1 to 60 days are presented. The changes occurring in the lymphoid tissue (involution of thymo-lymphatic apparatus, lymphopenia and neutrophilosis) have been shown to result from the state of stress. In the bone marrow of animals there occurs activation of erythropoiesis (erythroblasts-polychromatophilic normoblasts) at early (up to 15 days) term of hypokinesia, followed by its inhibition on the 60th day of the experiment. The study of kinetics of the amount of hemopoietic stem cells in the spleen and bone marrow of the femur of mice kept under hypokinesia for 1-45 days suggests the amount of stem cells in the spleen to decrease exponentially while in the bone marrow it changes undulatorily with the maximum on the 1st-3d and 30th-45th days of hypokinesia. Shifts in the number of the stem cell population are accompanied by changes in the direction of their differentiation. The stem cells of the bone marrow manifest higher potencies to form colonies of the erythroid type as compared with the stem cells of intact animals. Possible mechanisms underlying the inhibition of lymph-and erythropoiesis and changes of the stem cell differentiation from the myeloid way to the erythroid way under conditions of hypokinesia are discussed.

The work has shown a number of common features in the structural organization of the brain stem reticular formation in the adult rhesus monkey and man. According to the peculiar features and developmental features the reticular nuclei may be divided into 3 sections (median, medial and lateral) having different genesis. In ontogenesis all the nuclei of the reticular formation undergo differentiation and specialization due to the complication of the brain as a whole. This process, however, goes differently in ontogenesis of the macaque and man which can be seen in the heterochronous rate of their development, namely, in the macaque the terms of maturation of the reticular nuclei are somewhat more accelerated. The work shows changes in the density of cells, the volume of neurones and all the reticular formation in relation to the volume of the brain stem as a whole. However, the differences found in ontogenesis of the macaque and man are mainly of quantitative and idioadaptive character.

Rabbit antisera against antigens of mouse, rabbit, guinea pig and human whole brain cross-reacted in the cytotoxic test with the lymphocytes of the thymus, lymph nodes and the spleen of these animal species. Mouse thymocytes were most sensitive to the antibrain sera (cytotoxic index -- 63--100 per cent); cells from other mouse lymphoid organs and lymphocytes of rabbit, guinea pig and man were more resistant. Bone marrow lymphocytes were not damaged by any of these sera. The antigens which induced the cytotoxic properties of the sera were found only in the human cerebral cortex, but not in the white matter of the brain stem.

A study was made of the effect of benzol on the colony-forming activity in the spleen and the bone marrow of mice in 4 different experimental variants. In benzol hypoplasia of hemopoiesis there was a decrease in the number of the CFU in the hemopoietic organs without any changes in the distribution of their cell types. Incubation of the cells of normal mouse bone marrow with benzol did not induce any decrease of the colony-forming efficiency. Administration of benzol to the lethally irradiated mice after the transplantation of normal bone marrow suspension led to a sharp decrease in the number of CFU with a preponderant depression of the granulocytic colony formation. These data afford to suppose the change in the properties of microenvironment of the hemopoietic stem cells in experimental benzol poisoning.

A determination was made of the number of colonies in the spleen of irradiated mice after administration to them of a culture of mouse bone marrow cells. Colony-forming units proved to persist in the culture only for a short time. Use of preliminarily grown underlayer of fibroblasts of bone marrow origin had no effect on the perservation and dynamics of the changes in the number oc colony-forming units.