THE BIOLOGICAL EFFECTS OF PENETRATING 



RADIATIONS 



F. G. SPEAR, M.A., M.D., D.M.R.E. 



Straii^eways Research Laboratory, Cambridge, and Member of the 

 Scientific Staff, Medical Research Council 



Introduclion 



WHIL.E Planck was putting forward his theory of energy 

 quanta, Becquerel, by accident, and Curie and Asch- 

 kinass, by design, made experiments upon themselves 

 and, with others, demonstrated the destructive action of radium 

 and X-rays on Hving tissues. As a consequence, the biological 

 effects of penetrating radiations became widely studied, in part 

 to satisfy a natural curiosity, but also to determine how the rays 

 might be usefully employed in medicine. The fiftieth anniversary 

 of the discovery (in November 1895) of X-rays seems a fitting 

 time to review the trends and some of the achievements in this 

 now vast field of experimental radiobiology, which was born 

 so soon after Rontgen's momentous announcement. 



For roughly 25 years, biological observations were mainly 

 qualitative and were concerned with the changes, seen in a 

 great variety of biological material, after exposure to arbitrarily 

 chosen and crudely measured doses, of radiation. By this seem- 

 ingly haphazard method, however, many facts of fundamental 

 importance were learned. For example, the selective action of 

 radiation was recognized in the discovery that the cells of some 

 tissues were more affected by a given dose of radiation than the 

 cells of other tissues exposed to the same dose under identical 

 conditions. It was also found that the same dose produced a 

 different result according to whether it was given at a high 

 intensity for a short time or a low intensity for a longer time. It 



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