COMPAKATIVE STUDIES OF THE BIOLOGICAL 



EFFECTS OF X-RAYS, NEUTRONS, AND OTHER 



IONIZING RADIATIONS 



L. H. GRAY, M.A., Ph.D. 

 The Mount Vernon Hospital, ISorthicood, Middlesex 



Introduction 



THE immense literature dealing with the biological effects 

 of ionizing radiations is dominated by experiments in 

 which the radiation employed has been therapeutic 

 X-radiation, that is, radiation from tubes operated at voltages of 

 between 80 and 200 kilovolts. This is not surprising, since the 

 majority of the investigations have been undertaken with the 

 object of obtaining information immediately applicable to thera- 

 peutic practice. Of the remainder, the approach has more fre- 

 quently been that of the biologist seeking to explore the effects 

 of radiation on different organisms and on different aspects of 

 cellular activity, than of the physicist attempting to trace one 

 particular lesion — such as a mutation, the breaking of a chromo- 

 some, or the inhibition of mitosis — to the interaction of the 

 radiation with a particular set of atoms within the cell. 



For the former purpose, the type of radiation employed 

 appeared to be of little consequence, and either the gamma rays 

 from radium or therapeutic X-radiation were generally employed 

 as most convenient. For the latter, we need to employ a diversity 

 of radiations, so that we may study the effects of changing in 

 a known manner the distribution of the ions produced through- 

 out the cell. Within fairly recent times, comparative studies 

 with different ionizing radiations, such as gamma rays, X-rays, 

 neutrons, and alpha particles, have led to the establishment of 

 important and often remarkable facts, such as that the death 



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