METABOLISM OF THE NUCLEIC ACIDS 433 



indicated a drop of about 30 % in the uptake of isotope by both PNA and 

 DNA of the irradiated cells as compared with the controls. There is there- 

 fore a contrast between the results obtained by purely chemical analysis 

 and those from the isotope measurements since with DNA the chemical 

 method indicates a fall in the rate of DNA synthesis after irradiation to 

 about 33 % of that in the controls, while the isotope method suggests that 

 DNA synthesis falls to about 70% of the control level. Similarly, chemical 

 measurements with PNA indicate an undiminished rate of synthesis after 

 irradiation, while isotope methods show a fall in renewal of PNA to about 

 70 % of the control value. 



The effect of X-irradiation (1000 r.) of rabbit abdominal viscera and 

 femora on the blood cell population and on the uptake of P^- by the DNA, 

 nPNA, and cPNA of appendix, bone marrow, kidney, and thymus has been 

 studied by Smellie et a/.-'^-'^ Although the erythrocyte pattern was not 

 greatly altered until about 49 hr. after irradiation, the proportion of 

 lymphocytes fell rapidly within 2 hr. of treatment and there was an initial 

 sharp increase in the granulocytes. 



DNA synthesis in appendix and bone marrow was reduced to about 35 % 

 and 65%, respectively, of the normal level within 2 hr. of exposure to the 

 X-rays, the values at 20 hr. being 17 % and 23 % and at 49 hr. 33 % and 

 76%. In thymus DNA turnover was not affected at 2 hr. but by 20 hr. 

 was reduced to 37% of the normal, recovering by 49 hr. to 46%. 



The activities of the nPNA and cPNA of appendix and bone marrow 

 were depressed within 2 hr. of irradiation and remained low even after 49 

 hr. In kidney both nPNA and cPNA showed slightly elevated activities 

 2 hr. after irradiation but by 20 hr. and 49 hr. the values were below nor- 

 mal. Thymus nPNA and cPNA were little affected by 2 hr. but fell mark- 

 edly 20 hr. and 49 hr. after exposure to the X-rays. 



The incorporation of P^- into the DNA, nPNA, and cPNA of appendix, 

 bone marrow, spleen, and thymus of rabbits which had been treated with 

 phenylhydrazine to induce hemolytic anemia and hyperplasia of the bone 

 marrow has been studied.-^^-'^ The activity of bone marrow DNA was 

 increased to approximately twice the control value, while in spleen a ten- 

 fold increase in activity was recorded. The cPNA of bone marrow and 

 spleen exhibits a considerable increase in activity while the turnover of 

 nPNA is also slightly elevated. The nucleic acids of appendix and thymus 

 were unchanged in the anemic animals. 



In the field of bacterial viruses, several extensive review articles have 

 appeared in recent months: Putnam,^'* Cohen ,21^ Hershey,^"*' and Kozloff.-^^ 



"» F. W. Putnam, Advances in Protein Chem. 8, 175 (1953). 



219 S. S. Cohen, Cold Spring Harbor Symposia Quant. Biol. 18, 221 (1953). 



220 A. D. Hershey, Cold Spring Harbor Symposia Quant. Biol. 18, 135 (195"^). 



