418 



PHYSIOLOGICAL FACTORS IN MAMMALS 



incorporation of iron into the circulating red blood cells in the normal 

 and the irradiated rat. Two criteria of red-cell formation can be used: 



(1) the relative uptake of labeled iron by the marrow-red-cell system 

 compared with deposition in the inactive pool of iron in the liver; 



(2) the rate of appearance of labeled iron in the circulating blood. The 

 data of Hennesy and Huff (9) have been recalculated on this basis, and 

 it can be seen (Fig. 3) that the uptake of iron by the marrow decreases 

 by 50 per cent at an irradiation dose of 150 r. The general level of the 

 decrease in red-cell formation is 0.3 per cent per roentgen, which is com- 

 parable to the depression of leukocyte formation. It is worth noting, 



100 



1i 60 



Q- 40 



20 



10 



50 



100 150 



Dose, r 



200 



250 



Fig. 3. The half time of the appearance of a tracer dose of radioactive iron in the 

 circulating of blood and the fraction of the dose that enters the marrow during the 

 first 25 days. Both are functions of the rate of red-cell formation. The lower the 

 half time of entry into the blood and the greater the amount of radioiron reaching the 

 circulating blood, the more rapidly new cells are being formed. [Calculated from 



Hennesy and Huff (9).] 



however, that the erythrocyte study (9) deals with acutely irradiated 

 rats, whereas the leukocyte response is based upon a less intense dosage 

 rate spread over several days. Both criteria of red-cell formation indi- 

 cate an irradiation effect in the range of 5-25 r. 



Effects Relative to the Desoxypentose Nucleic Acid 



Molecule 



Significant differences have been observed in the turnover of desoxy- 

 ribose nucleic acid. These studies follow the general method of Hevesy 

 (10). Whole-body irradiation depresses formation of nucleic acid as 

 measured by the rate of incorporation of radioactive phosphate into 



