CARCINOGENESIS 129 



of the necessary conditions for carcinogenesis, but that the presence of one 

 functioning ovary or treatment with oestrogens can prevent, or at least 

 delay, the tumour formation wliile for the thymoma the irradiation of the 

 thymus does not appear to be one of the necessary conditions. The point I 

 wanted to make, is that even in the induction of tumours by locally acting 

 carcinogens systemic factors play a major role and that the process of 

 carcinogenesis due to local radiation may be an indirect one. 



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Deeinger, M. K., Lorenz, E., and Uphoff, D. E. (1955). J. nat. Cancer Inst. 15, 931. 



Frieben (1902). Fortschr. Bontgenstr. 6, 106. 



Gardner, W. U. (1950). Proc. Soc. exp. Biol. N.Y. 75, 434. 



Gardner, W. U. (1953). "Advances in Cancer Research", Vol. 1, p. 173. (A. Haddow, 



and J. P. Greenstein, eds.), Academic Press, New York. 

 Kaplan, H. S. (1950). J. nat. Cancer Inst. 11, 125. 

 Kaplan, H. S., and Brown, M. B. (1954). Science 119, 439. 



Krebs, C, Rask-Nielsen, H. C, and Wagner, A. (1930). Acta Radiol. Suppl. X. 

 Lick, L., Kjerschbafm, A., and Mixer, H. (1949). Caricer Res. 9, 35. 

 Mabie, p., Clfnet, J., and Raulot-Lapionte, G. (1910). Bull. Ass.frang. cancer 3, 404. 

 Martland, H. S. (1931). Amer. J. Cancer 15, 2435. 

 Sarin, F. R., Doan, C. A., and Forkner, C. E. (1932). J. exp. Med. 56, 267. 



DISCUSSION 



ALEXANDER: In producing skin cancers by irradiation, do you inevitably have to produce 



this chain of events of shedding of the irradiated tissue and scar formation? If you 



rearrange your dosage schedule of irradiation in such a way as to avoid it, do you then 



never get skin cancers or can you still get cancers sometimes? 



GLtfcKSMANN: I have never been able to get it without such previous local damage. There 



are some experiments with a-particles of very low penetration which do not cause 



ulceration and which Professor Lamerton has used. Did you get any cancers? 



lamerton: We did not get any tumours in these experiments. 



berenblum: I did not quite understand the irradiation procedure. Was the dose given 



as a single exposure? 



glucksmann: In most of the experiments the dose was given as a single dose, but we have 



given two equal doses at intervals of two months in rats and also suppUed X-rays in 



eight doses at monthly intervals over a period of six months. Henshaw et at. have given 



daily fractions of ^-rays to mice and rats at various dose levels and also single doses and 



found that single exposures were more efficient in producing skin tumours than the 



fractionated regime. 



casarett: Were the doses of radiation which reduced the yield of chemically induced 



carcmomas and delayed the time of their onset large doses? Have you any idea of what 



the mechanism of this delay or inhibition might be? 



glucksmann: The doses were of the order of 2,300 rads in the skin and almost the same for 



the genital tract. I do not know what the mechanism of the delay or inliibition of 



carcinogenesis may be. Under certain conditions, in the vulva for instance, we get a 



