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A. GLUCKSMANN 



included only those whicli survived for the induction period of the first 

 tumours in the following experiments: a single dose of 11,000 rads at 1-0 MeV; 

 two doses of 2,300 rads each at an interval of two months and eight doses 

 totalling 6,800 rads given over a period of six months at monthly intervals. 

 WhUe the yield of sarcomas is not very different in the DMB A-painted and the 

 irradiated group, the incidence of carcinomas is ten times greater after the 

 DMBA than in the irradiated animals. The difference in the duration of the 



Painting 



o 



E 



80 



60- 



o 



S 40h 



= 20 

 a 



E 



Irradiation 



Papillomas and carcinomas 

 Carcinomas 



200 



400 



600 



Time (days) 



Fig. 7. The induction of skin tumours in mice by weekly applications of benzpyrene and by 

 exposure to a single dose of 8,000 rads at 0-7 MeV. Mice surviving at least seventy days for 

 painting and 400 days for the irradiation are considered "at risk". 



induction time is very striking indeed as Fig. 8 shows. The induction period 

 for the same incidence of sarcomas is about 3 times greater for radiation than 

 for painting while for carcinomas the difference is even greater. Animals 

 given a single dose of 2,300 rads of an electron beam generated at 0-7 MeV — 

 which itself failed to induce any tumours — followed 15 months later by weekly 

 applications of DMBA, show a shortening of the induction period for sar- 

 comas as compared wdth the painting of the unirradiated rats and a lengthen- 

 ing of the induction period and reduction in tumour yield for carcinomas. 

 These effects might be due to the destruction of hair follicles and the reduction 

 in number of epidermal cells by previous irradiation and the increase of ceU 

 population in the unstable dermal scars following irradiation. 



As regards the induction of carcinomas in mice and rats the histogenetic 

 investigation suggests that with carcinogenic hydrocarbons descendants of 

 treated cells produce cancers, while with radiation most if not all the exposed 

 ceUs are killed and cancers are formed in the regenerating tissue involved with 

 repair. The direct action of the chemicals as compared with radiation is also 



