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CHAIRMAN'S OPENING REMARKS 



A. Haddow 



A GREAT deal of work has been carried out on the elucidation 

 of the changes in gross cellular structure produced by ionizing 

 radiations, on the histopathology of radiation damage, and on 

 the cytological and genetical effects. Yet what of the bio- 

 chemical changes, the metabolic changes we have to consider? 

 To quote Dubois and Petersen's review (1954, Annu. Rev. 

 Nuclear Sci., 4, 351), although research on the biochemical 

 effects of ionizing radiations has yielded a vast amount of 

 information, no satisfactory explanation of the exact mechan- 

 ism by which tissue damage is inflicted has yet been obtained. 

 Research on the biochemical mechanisms has been under way 

 for a relatively short period of time. A considerable amount 

 of research on the subject during recent years was of necessity 

 exploratory in nature. Many approaches to the problem of 

 mechanism have been employed. A large number of the earlier 

 studies dealt with in vitro systems. The information obtained 

 from such studies has been valuable in indicating the chemical 

 linkages and groups which are the most susceptible to altera- 

 tion by ionizing radiations. However, attempts to apply in 

 vitro findings with ionizing radiations to intact cells have been 

 generally disappointing. Biologists have therefore turned their 

 attention to the more difficult task of attempting to define 

 radiation damage in terms of interference with biochemical 

 systems, through research on irradiated animals and micro- 

 organisms. My colleague J. A. V. Butler has pointed out that 

 the basic puzzle of radiobiology, one which has been stressed 

 especially by L. H. Gray, is still unsolved — namely that com- 

 paratively small doses of radiation produce marked biological 

 changes, although in general rather large doses are required 

 to produce easily observable chemical changes. In Butler's 



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