Changes in the pool of haemopoietic colony‐forming units (CFUs) of bone marrow and spleen were studied in experiments with mice fed dried thyroid gland (TH) for 21 days, and during the 13 days that followed feeding. After HU treatment, the number of CFUs in DNA synthesis was estimated. As early as the second day of TH treatment, the pool of CFUs is gradually increased, leading to an increase in the total number of splenic and bone marrow CFUs persisting after TH treatment for the period examined. Simultaneously, the numbers of nucleated cells in the bone marrow and spleen are increased. During TH feeding and following its termination, the total number of erythrocytes and the haematocrit values did not change significantly, whereas an increased number of leucocytes was observed in the peripheral blood after TH treatment. Elevation of the proliferative activity of CFUs occurred early in the period of TH treatment, with the maximum attained by end of the first week of TH feeding. This suggests a rapid response of the haemopoietic stem cell compartment to the administration of TH hormones. the participation of humoral factors controlling CFUs compartments in the mechanism of the stimulatory effect of TH hormones on haemopoietic stem cells is discussed.

An increase in the leukocyte number in blood and a decrease in the total cell volume of the bone marrow and spleen were observed in mice after wholebody microwave irradiation (2450 MHz, lambda equals 12.5 cm, 100 mW/cm-2). The number of hematopoietic stem cells increased early after microwave irradiation (1626 plus or minus 53 CFU in bone marrow, 689 plus or minus 86 CFU in the spleen), as compared with that or control (598 plus or minus 92 and 349 plus or minus 79 CFU, respectively). Incorporation of 59Fe in the spleen decreased to 78% of the control value 24 hr after irradiation, which was followed by an increase to 250% on Day 14 after irradiation. After heat exposure, CFUs showed an early decrease in number, whereas the percentage of 59Fe incorporation increased. The different effects of microwaves and externally applied heat on the hematopoietic stem cells suggested that alterations in tissues caused by high-intensity microwave radiation need not be related only to increased internal temperature.

The effect of pretreatment of mice with a single injection of dextran sulphate (DS) on the protective capacity of moderate hypoxia was analysed. Dextran sulphate activated haemopoietic stem cell populations, and irradiation under hypoxia one day after DS injection increased the number of haemopoietic stem cells surviving in the bone marrow of the femur, their recovery after irradiation, and the number of endogenous spleen colonies. A moderate hypoxia (15% O2 and 12% O2) significantly reduced the lethal effect of gamma rays in mice after DS injection and increased the value of LD 50/30.

This paper presents results of experiments on the effects of electromagnetic radiation in the millimeter range (frequency 34.0 +/- 0.1 GHz, power density 20 muW/cm2) emitted by a police radar device. Considering the physical properties of the radiation in millimeter range (skin effects), the experiments were carried out on hairless mice. The main physiological parameters tested were body mass, body temperature, peripheral blood, and mass and cellularity of several important organs. Critical organs, the skin, and cornea were examined by electron microscopy. Differentiation ability of hematopoietic cells, progenitors of granulocytes and macrophages, and DNA synthesis in the cornea were compared in irradiated and nonirradiated animals. None of the parameters tested was affected to an extent that would indicate the start of a pathological process or the risk of damage to genetic material.