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The Effect of Ionizing Radiations 

 on Some Systems of Biological Importance 



E. S. GUZMAN BARRON 



Biology Division, Argonne National Laboratory 



and Department of Medicine, University of Chicago 



Chicago, Illinois 



A quarter of a century ago a great controversy arose in the field of 

 cellular respiration. On one side were the partisans of the theory of 

 activation of oxygen as the all-important process, and, on the other, 

 the partisans of the theory of hydrogen activation. The controversy 

 became more and more heated with neither side willing to retreat. 

 Even the late Sir Frederic Hopkins' oration at the Physiology Congress 

 of Stockholm, advocating that both sides were right, did not bring 

 the necessary calm. Years had to pass to demonstrate that, in fact, 

 both theories could be harmonized into one. The same sort of contro- 

 versy has been going on in the field of ionizing radiations in biology 

 between the partisans of the "target" or "one-hit theory" and those 

 of the "indirect action." As in the case of cellular respiration, indi- 

 cations are that both theories are partly correct. The definite progress 

 made during the last ten years has, in fact, demonstrated that both 

 processes occur when ionizing radiations strike living cells. The cell 

 components may obviously be affected by direct collision with the 

 ionizing radiations. They will also be affected by the products of 

 ionization of water and of oxygen. The contribution of each one of 

 these actions will depend on a number of factors, such as stability of 

 the components, nature of the environment, and reactivity towards the 

 products of ionization of water. In calculating the part played by these 

 two actions, however, it must not be forgotten that water comprises 

 80 per cent of the total body weight, and that this fluid is permanently 

 saturated with molecular oxygen. The radiochemical reactions of bio- 

 logical importance are, then, those taking place in an aqueous, oxy- 

 genated milieu. 



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