14 R. H. MOLE 



CONCLUSION 



Possible mechanisms for leiikaemogenesis by radiation are listed in 

 Table III. At present there is scientific proof only for an indirect mechanism, 

 defined as a mechanism causing leukaemia to originate in unirradiated cells 

 (Kaplan et al, 1956; Law and Potter, 1956; Barnes et al, 1959). 



Table IIL Mechanisms of radiation-induced leukaemia (cf. Mole, 1962) 



1 Radiation acts directly on cells. Leukaemia stems from the affected cells. 



1.1 Direct action on cellular genetic mechanism. 



1.2 Direct genetic or non-genetic effect increasing susceptibility to infection or other 

 exogenous agent. 



2 Radiation acts indh-ectly to increase the probability of an event which has some chance of 

 occurring all the time. Leukaemia does not originate specifically in irradiated cells. 



2.1 Leukaemia results from a natural instability in the process of cell multiplication. 

 Radiation, by killing cells, increases the rate of cell multiphcation or by altering cell 

 envu-onment favours the instability. 



2.2 Radiation increases susceptibility to infection or exogenous agents by interfering with 

 immune reactions, detoxication mechanisms or in other ways. 



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