1040 



RADIATION BIOLOGY 



and accounts for the fact that during this period erythrocyte, hemoglobin, 

 and hematocrit determinations are frequently within the normal range. 



3. Reduction in red-cell mass results from (a) death of normally aging 

 red cells and (6) the loss of "normal" erythrocytes from the circulation 

 by heightened capillary permeability and thus widespread minute 

 extravasation into lymphatic tissues and tissue spaces. Tagged red cells 

 (Fe 59 and P 32 ), as well as tagged plasma, were found to disappear more 

 rapidly from the circulation of irradiated than from that of nonirradiated 

 animals. The leakage of erythrocytes is a major factor in the production 



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10 20 30 40 50 60 70 80 90 100 110 120 



TIME AFTER EXPOSURE, days 



• 'CONTROL o -o800r »•-— « 500 r 



Fig. 16-6. Effect of single doses of 500 and 800 r of total-body roentgen irradiation on 

 the hemoglobin and erythrocyte values of the peripheral blood of rabbits. 



of anemia. The fate of the red cells thus extravasated as a result of 

 primary or secondary endothelial injury is phagocytosis and eventual 

 hemolysis. 



No significant anemia, as judged by mean averages, has been observed 

 in groups of rabbits exposed to dosages below 500 r. In individual 

 animals, anemia may appear with exposures as low as 300 r. A progres- 

 sively larger fraction develops anemia following exposure to 500 r and 

 above (Jacobson et al., 1947; Jacobson, Marks, and Lorenz, 1949). 

 Figure 16-6 illustrates the anemia observed in rabbits after exposure to 

 800 r. Rats, mice, dogs, cats, swine, and guinea pigs develop anemia in 

 response to lower doses. Figure 16-7 illustrates the anemia in guinea 

 pigs after exposure to 220 r and above. In the absence of gross hemor- 

 rhage the anemia is normochromic and reaches a maximum at about 14 



