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Speculations on Cellular Actions 

 of Radiations * 



RAYMOND E. ZIRKLE 



Institute of Radiobiology and Biophysics 



University of Chicago 



Chicago, Illinois 



After the foregoing thorough discussions of radiation physics, radia- 

 tion chemistry, and biochemical effects of radiations, it would appear 

 that the tasks of the cellular radiobiology panel are essentially as fol- 

 lows: (1) to review briefly the available data on cellular effects, with 

 special reference to quantitative aspects; (2) to attempt to fit the data 

 with theories, old or new, giving special attention to relations between 

 the cellular effects and the physical and chemical effects; (3) to indicate 

 gaps in our present knowledge and understanding, and to suggest pos- 

 sible methods of eliminating them. This paper will be confined to re- 

 marks about cellular effects in general. Papers by the other contributors 

 deal in more detail with certain important types of cellular effects, about 

 which we now have considerable quantitative information. 



Whenever we carefully ponder the mechanism of any known radio- 

 biological action, we end by admitting that we have substantial direct 

 information only about the very beginning and the very end of the 

 story. The beginning is the act of irradiation, during which charged 

 subatomic particles speed through the biological material, transferring 

 energy to molecules along their paths and thus producing "tracks" of 

 activated (ionized and excited) molecules. All this has been carefully 

 described by the physics panel. The end of the story is the biological 

 end effect, which, if the observations are made on a cellular basis, may 

 be a mutation, a chromosome aberration, an inhibition of cell division, a 

 change in permeability, a change in metabolic rate, or any one of many 

 other deviations from normal structure or function. 



These end effects are of such nature that in no case have we been able 

 to see how they can be directly related to the physical events con- 



* Many of these speculations have been suggested by experimental work done 

 under Contract No. NR-1 16-256 with the Office of Naval Research, Department of 

 the Navy, in cooperation with the Atomic Energy Commission. 



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