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The Dependence of Some Biological Effects 

 of Radiation on the Rate of Energy Loss 



CORNELIUS A. TOBIAS 



Division of Medical Physics 



University of California 



Berkeley, California 



A review of the published theories on biological effects of radiation 

 reveals varying interpretations. Some people favor the so-called hit 

 theory. Many others are inclined to favor the intermediate action theory 

 of Dale. A small group of investigators, some of whom have expanded 

 their views at this symposium, seek to effect a compromise between the 

 two sets of ideas. Still there are some who see futility in attempting to 

 bring order out of the obviously complex physical phenomena and 

 chemical reactions which take place in the chain of events in the biological 

 cell. These people claim that there is no reason at present to make a 

 theory, since any theory would be an oversimplification and could not 

 hope to explain all the facts. For the sake of discussion, one might 

 mention some general arguments in favor of theories and define the 

 scope of usefulness of theoretical interpretation in biology. Theories 

 are usually proposed to reduce the complexity of observations to a few 

 simple, logical processes. Quantitatively the theory is successful if a 

 number of invariant quantities appear in it and if these quantities can 

 be determined by experimentation. These invariants are constants in 

 the equations describing the theory, and they correspond to more or 

 less general laws or properties of the systems under investigation. 



In biology at the present stage of development one must often resort 

 to derivation of theoretical relationships based on experimental obser- 

 vations; thus most of the theories have empirical or semiempirical bases. 

 In a field as highly empirical as biology, one should not immediately aim 

 for theories that have a general validity and that hold true for all living 

 phenomena. Rather, theories should be proposed for a limited range of 

 phenomena and their validity tested with experiments. Thus, a model 

 of the biological effects of radiation is proposed here, not on the assump- 

 tion that it will stand unchanged for a long time to come; rather it is 

 hoped that the model will presently help explain a limited range of 



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