420 PHYSIOLOGICAL FACTORS IN MAMMALS 



P^" in tumor desoxypentose nucleic acid is 1.65 ± 0.52 X 10~^. Thus, 

 irradiation of liver gave a greater depressive effect on tumor desoxy- 

 pentose nucleic acid turnover than muscle irradiation. This has been 

 calculated as equivalent to 0.15 per cent per rep if the radiation had 

 been expended over the whole body. 



The above results of depression of desoxypentose nucleic acid turn- 

 over (11) confirm Hevesy's finding of an indirect effect of radiation on 

 nucleic acid turnover (10). The quantitative effects of irradiation on 

 the proliferative process are summarized as follows: 



Whole-body x-irradiation Depression of white-cell count 1 2"^^ 



Depression of lymphocyte count | ' ° 

 Whole-body x-irradiation Depression of leukemic cells 0.23-2.5% per r 

 Whole-body x-irradiation Depression of white cells in poly- 

 cythemia . 3-0 . 7 % per r 

 Whole-body x-irradiation Depression of red-cell formation 0.3% per r 



Depression of Formation of Desoxypentose Nucleic Acid in Tumor 



Whole-body x-irradiation 0. 18% per r 



Specific-muscle j3-irradiation 0.07% per rep 1 Reps calculated as though 



Specific-liver i3-irradiation 0.15% per rep) ionization had been ex- 



pended on the whole body 



Depression of Formation of Desoxypentose Nucleic Acid in Liver 



Whole-body x-irradiation 0.28% per r 



Specific-muscle /3-irradiation 0.16% per rep Reps calculated as though 



ionization had been ex- 

 pended on the whole body 



Measurements of the turnover of nucleic acid in the specifically ir- 

 radiated liver are suggestive of a greater depression than the equivalent 

 irradiation of whole body or muscle by the same total ionization, but 

 we have not been able to quantify these data because of difficulties of 

 separating the enormous quantity of beta-radiating colloid contained 

 in the livers from the extracted P^^-labeled desoxypentose nucleic acids. 

 Gofman (12), in a preliminary summary of leukemia therapy with radio- 

 active phosphate as contrasted to a colloid of radioactive yttrium that 

 localizes specifically in the bone marrow, indicates that the depression 

 of the leukemia process is essentially related to the ionization directly 

 expended in the marrow. Thus, much smaller radiation dosage of yt- 

 trium colloid is required than in therapy with radioactive phosphate. 

 Probably direct irradiation of tissue is 1.5-2 times as effective in depress- 

 ing the proliferative process as the indirect effects described above. 



