. Ciba Foundation symposium on ionizing radiations and cell metabolism. Radiation -- Physiological effect; Cell metabolism; Radiation -- effects; Radioactivity. 1 226 Barbara E. Holmes mitosis was not seen until 12 hours later. The DNA synthesis could be inhibited by irradiation (800 r whole body) at 12 hours (not later than 24 hours) after poisoning, but even 2000 r could not inhibit the synthesis while it was actively in progress. Another sensitive period for this inhibition was t lOOO c E Q. < £ O4OO o. c o U 200 — Few 4 A Irradiated before operotion X X Irradiated at 12 hours Cont
. Ciba Foundation symposium on ionizing radiations and cell metabolism. Radiation -- Physiological effect; Cell metabolism; Radiation -- effects; Radioactivity. 1 226 Barbara E. Holmes mitosis was not seen until 12 hours later. The DNA synthesis could be inhibited by irradiation (800 r whole body) at 12 hours (not later than 24 hours) after poisoning, but even 2000 r could not inhibit the synthesis while it was actively in progress. Another sensitive period for this inhibition was t lOOO c E Q. < £ O4OO o. c o U 200 — Few 4 A Irradiated before operotion X X Irradiated at 12 hours Control / I (25«/^/x Figures represent mitotic , 0 count/lOOO ] /o Mitos«s showing chromosome fragments ±. 19 6(66%! ^ y A 6 [some] Xr-^' J \ L_ 6 12 15 18 21 24 27 30 33 36 39 42 HOURS AFTER KERATECTOMY. Fig. 1. Rate of DNA synthesis and mitosis in regenerating liver. found by Mrs. Kelly to occur later than 60 hours after poison- ing (Kelly et al, 1955). The curve of regeneration we obtained after hepatectomy (Fig. 1) has some different time relationships. The peak of the DNA synthesis rate seems to be shortly before the first large outburst of mitosis. As soon as large numbers of mitoses are present the rate is diminished. A dose of 2000 r inhibits DNA synthesis by about 50 per cent at any time during the cycle and the effect is immediately apparent. Here our results differ from those obtained by. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Ciba Foundation; Wolstenholme, G. E. W. (Gordon Ethelbert Ward); O'Connor, Cecilia M. (Cecilia Mary), 1927-. Boston, Little, Brown
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