Influence of Radiation on DNA Metabolism 205 



A second method of observing irradiation efTects on DNA 

 synthesis in single cells is that of photometric measurement of 

 the amount of Feulgen stain. Grundmann's (1953) results on 

 bean root meristems at 2 or 4 hours after 200 r, or 4 hours 

 after 800 r, suggest that the changes in DNA classes could 

 be explained by mitotic delay and cell death. 



(3) Analysis of tissue which is synchronized with regard to 

 the mitotic cycle. Such a situation is approached by mam- 

 malian liver regenerating after gross damage such as partial 

 hepatectomy or CCI4 poisoning. Since DNA synthesis begins 

 before mitosis appears, its interruption by moderate doses of 

 radiation cannot be due simply to mitotic inhibition. This 

 tissue thus stands as one for which this simple hypothesis is 

 definitely untenable. Since it is to be discussed in another 

 paper at this meeting, no comments need be made here. 



In conclusion, it appears that in regenerating liver there is 

 some reason to think that DNA synthesis may be specifically 

 interrupted by moderate doses of ionizing radiation. In other 

 tissues, although it is possible that this is so, much more 

 needs to be known about the changes in cell population that 

 result from irradiation before a primary biochemical inter- 

 ference can be established with certainty. Meanwhile, we 

 must recognize that most experimental results can be ex- 

 plained as due simply to mitotic delay and cell death, and do 

 not require us to invoke a biochemical action of radiation on 

 DNA synthesis jper se. 



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Bennett, E. L., and Krueckel, B. J. (1955). Univ. of Calif. Radn. 



Lab. Reports 2827-2828. 

 Bloom, W., ed. (1948a). Histopathology of Irradiation from External 



and Internal Sources, Chaps. 11, 18, 19. New York: McGraw Hill. 

 Bloom, W., ed. (19486). Histopathology of Irradiation from External 



and Internal Sources, Chap. 10. New York: McGraw Hill. 

 Brown, G. B. (1950). Fed. Proc, 9, 517. 



Carlson, J. G. (1948). J. cell. comp. Physiol., 35, Suppl. 1, 89. 

 FoRSSBERG, A., and Klein, G. (1954). Exp. Cell. Res., 7, 480. 

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