L. F. LAMERTON AND E. H. BELCHER 



activity assayed in a well-type scintillation counter. The results are given 

 in Figure 2{a). The serial haemoglobin values show the efficiency of the 

 shielding procedure. The percentage of the injected dose of radioactive 

 iron which appears in the spleen, hind limbs and liver, at the time of 4-5 

 hours after injection, is shown. Mean values from control animals of the 

 same age are shown in Figure 2{b). 



In the unshielded animals it can be seen that the uptake in the hind 

 limbs is depressed below normal values even up to 21 days. At 21 days, 

 however, when the haemoglobin curve has begun to rise, the spleen is seen 

 to have an extremely high uptake of the radioactive iron. It appears there- 

 fore that following whole-body irradiation the spleen recovers erythro- 

 poietic function earlier than bone-marrow. This is confirmed histologically. 



The pattern of erythropoiesis is seen to be modified considerably by the 

 shielding of one hind leg. First, the shielded limb has a very high uptake 

 of radioactive iron at 3 days. Secondly, splenic erythropoiesis develops at 

 a much earlier stage than in the case of the unshielded animals. 



Figure 2{b). Mean uptake of ^^Fe, expressed as percentage of 



injected dose, in liver, spleen and hind limbs of unirradiated control 



rats {albino strain) 4-5 hours after subcutaneous injection 



It is possible that these effects are the result of specific humoral factors 

 produced in the shielded limb (Jacobson*^). On the other hand, the pattern 

 of erythropoietic activity may be determined by general physiological 

 changes resulting from the irradiation, perhaps related to the severity of the 

 anaemia produced, or possibly by nervous mechanisms. Further work is 

 being carried out with different doses of radiation, with difTerent strains of 

 rat, and also with splenectomized rats, in an endeavour to elucidate some of 

 the problems involved. 



SUMMARY 



A short progress report is given on the studies of the radiation response of 

 the young growing rat, and the modification produced by procedures such 

 as hind-leg shielding. Platelet changes in irradiated animals have been 

 investigated, and a radioactive iron technique has been used to compare the 

 changes in the pattern of erythropoietic activity in various tissues in rats 

 irradiated with and without shielding procedures. 



ACKNOWLEDGEMENTS 



Our thanks are due to a number of colleagues who are collaborating in these investi- 

 gations, and in particular to Miss E. B. Harriss, Dr. C. F. Baxter, Miss K. Adams 



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