36 p. C. KOLLER AND VALERIE WALLIS 



EESULTS 



Cell com'position of peripheral blood 



Table I shows the effect of various doses of total-body irradiation at 1, 6, 

 30 and 60 days after exposure to X-rays. It can be seen that about 30 days 

 are required for the restoration of the normal blood values. The data also 

 show that the number of white cells in the peripheral blood is reduced to 

 nearly the same level after each dose and that the period of recovery is about 

 the same. The number of fractionated doses, i.e. the total amomit of radiation, 

 it seems, does not affect the recovery time. 



Table I. White cell counts in irradiated C57BL mice 



Time after 

 X-rays 1 X 180 r 2 X 180 r 3 X 180 r 4 x 180r Control 



(days) 



7,050 (5 weeks) 

 10,500 (7 weeks) 



Chromosome analysis in the hone-marrow 



Bone-marrow and spleen of irradiated mice were taken at varying 

 intervals and preparations were made for cytological analysis. Dividing cells 

 were, however, extremely rare in the spleen samples and did not provide 

 sufficient data for comparative study. Though many metaphases were seen in 

 the bone-marrow samples, in only a fraction of these cells were the chromo- 

 somes spread well enough to count. Table II shows the frequency of 

 abnormal cells observed in the cell population of the marrow of irradiated 

 mice. It was found that 1 day after receiving 1 X 180 r and 2 X 180 r, nearly 

 half the cells at metaphase were abnormal, with fragmented chromosomes. In 

 the samples taken 6 days after the mice were exposed to these doses, the fre- 

 quency of injured cells was low; in the females, no abnormal cells were seen 

 out of 40 cells analysed. 



When the marrow cells of mice receiving three or four doses of 180 r are 

 considered, it can be seen that, at least in the females, the frequency of 

 abnormal cells is about five times less than in the marrow of females which 

 received only one or two doses of 180 r. This finding is of special interest, 

 because it may indicate that the ceU population after two doses of 180 r had 

 undergone a change, due perhaps to selection, as a result of which it became 

 more radiation resistant. 



