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The Influence of Quantity and Quality 

 of Radiation on the Biologic Effect 



TITUS C. EVANS 



Radiation Research Laboratory 

 State University of Iowa 

 Iowa City, Iowa 



Influence of Quantity on Time and Degree 

 OF Effect per Individual 



Within the usual exposure range for mice (100-1000 r, to determine 

 lethal dose), effects appear more rapidly, become more generalized, and 

 persist for longer periods of time as the amount of irradiation is in- 

 creased. However, if time of death following irradiation is employed 

 as the criterion and the exposure range is extended to include thousands 

 of roentgens, it will be found that the decrease in latent period is pro- 

 portional to the amount of the exposure only in certain parts of the 

 entire curve. This is illustrated in the diagram in Fig. 1, which has been 

 drawn from the data and figures of Krebs (38), Lamarque (39), Lawrence 

 (42), Quastler (52), Evans (13), and Ellinger (9), with liberal translation. 

 The values given are approximations and are included for purposes of 

 illustration. 



As shown in that part of Fig. 1 marked "late death," little or no effect 

 is observed after exposures below 100 r. As the quantity of irradiation 

 is increased, a few individuals will suffer a reduction in survival time. 

 In this low-dose range the findings are not always the same, in that some 

 exhibit aplasia, a few develop neoplasms, some die of acute infection, and 

 others show no evident cause of death. A reduction in leukocytes fol- 

 lows the radiation exposure in some of the individuals suffering the "late 

 death," but this and other moderate changes are usually only temporary. 



After exposures indicated in the part of the curve labeled "early 

 death," the survival time becomes progressively shorter as the amount 

 of irradiation is increased. Only especially sensitive tissue such as in 

 lymphoid organs shows damage at lower doses, but as the exposures in- 

 crease the autopsies indicate more and more aplasia of hematopoietic 

 tissue and widespread sloughing of epithelium. In addition to the 



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