MUTAGENIC AND CARCINOGENIC AGENTS 



with an effect which, according to Lewis, can be expressed 

 in the form of a Hnear relation to the cumulative dose. In 

 itself this points towards the significance of a single muta- 

 tional event. 



If it is true, as all the data suggest, that some other muta- 

 genic agents are concerned in the continuing rise in leukaemia 

 mortality, their detection and characterization becomes one 

 of the important tasks for research in preventive medicine. 

 So far we have only a few clues to their nature. Like the 

 medical use of X-rays, the unknown factors are increasingly 

 operative in the more advanced countries, in the more 

 economically secure classes and in more recent years. They 

 must be operative at all ages but one or more seem to be 

 particularly potent at the very beginning of life, just before 

 or just after birth. 



There are many things that might be thought of If we 

 judge from bacteria, mutagens are commoner than we 

 thought. Caffeine, for instance, is a potent bacterial muta- 

 gen and I suspect that, like the medical use of X-rays, the 

 amount of caffeine absorbed per head per annum increases 

 with the level of prosperity. It would be ridiculous to 

 start looking askance at coffee and I mention it only to 

 stress the potentialities of changing ways of life for intro- 

 ducing new medical problems. All sorts of things have been 

 happening in the last thirty or fifty years to modify the things 

 we eat and the air we breathe and the way we act. Three 

 diseases are sharply demarcated from the rest — lung cancer, 

 coronary disease and leukaemia — as steadily increasing causes 

 of death. All are increasing because of changing ways of life. 

 We have a fair understanding of the first two. Leukaemia 

 presents an equal challenge. Some first-rate detection work 

 is needed and, as with lung cancer, it must be work done 

 directly with the human problem. Mouse experiments can 

 do no more than offer clues to profitable approaches. In 

 Australia we have felt that an initial step is to see that 

 leukaemia is made a notifiable disease and that an accurate 



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