Shielding of the thymic region during x-irradiation: effect on haemopoiesis in mice.

: The course of radiation damage and regeneration of the thymus and haemopoiesis were followed in mice after whole-body X-irradiation and in mice with the shielded thymic region during irradiation with 7 Gy, using several indicators (125IUdR incorporation, thymus weight, cellularity of bone marrow and changes in the peripheral blood leucocyte counts). It was demonstrated that radiation damage, manifested in a significant decrease in the values of the indicators studied immediately after irradiation, followed the same pattern in both groups, shielding, however, accelerated regeneration of the thymus and restoration of haemopoiesis. The favourable effect of thymic shielding was also reflected in a significant increase of LD50/30, and the dose reduction factor was equal to 2.