CARCINOGENESIS FROM INDEPENDENT EVENTS 



165 



will have occurred just once in each animal. This means that it will be very 

 unhkely indeed that this conjunction or start of a tumour can be recognized 

 morphologically simply because of the problem of sampling. In fact whatever 

 the mechanism of carcinogenesis, if the origin of a tumour is a rare event then 

 any moi'iDhological change which is seen more than once in a whole series of 

 microscopical sections is ipso facto not the relevant change. «■ 



200 



Fig. 4. Age-specific incidence rate of bone tumours in mice given a single injection of ^°Sr 

 (data of Finkel et al, 1960). The bone-tumour rates are plotted against the square of the 

 number of radioactive disintegrations in a manner detailed by Mole (1962). The straight lines 

 are drawn by eye through the origin so that their slopes shaU be proportional to the squares of 

 the injected doses (shown in /xc/kg against each line). 



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Brues, a. M. (1949). J. din. Invest. 28, 1286. 



Dougherty, T. F. (1962). In "Some Aspects of Internallrradation" (T. F. Dougherty, 



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 Finkel, M. P. (1959). Radiation Res. Suppl. 1, 265. 



Finkel, M. P., Bergstrand, P. J., and Biskis, B. 0. (1960a). Radiology 74, 548. 

 FiNKEL, M. P., BiSKis, B. 0., and Bergstrand, P. J. (1960b). In "Radioisotopes in the 



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 Harada, T., and Ishida, M. (1960). J. nat. Cancer Inst. 25, 1253. 

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Mole, R. H. (1962). In "Some Aspects of Internal Irradation" (T. F. Dougherty, 

 ed.). Pergamon Press, Oxford. 



