DEATH RATE AFTER IONIZING RADIATION 293 



It appears noteworthy that the increase in age-specific mortality associated 

 with pulmonary tumours was less marked in irradiated mice than in those 

 treated with radiomimetic chemicals, despite the greater over-all life-shorten- 

 ing in the former. This may be correlated with the failure of radiation to 

 induce lung tumours. 



These results serve to illustrate the complexity of the effects of radiation 

 on the life-span. The variation of the age-specific death rate of different 

 diseases and the effects of radiation on the age distribution of such diseases 

 cannot be characterized by a single simple formula. Nor is it possible to 

 comprehend changes in the incidence of any one disease without taking into 

 account other intercurrent diseases affecting survival, as stressed earlier 

 (KimbaU, 1958). The generalization that irradiation advances the onset of 

 senescent diseases is consistent with the effects of radiation on the over-all 

 age-specific death rate but is an oversimplification in the light of variations 

 among specific lesions. 



CONCLUSIONS 



1. The age-specific death rate increases irregularly with age in mice, 

 tending to rise exponentially with time beyond a certain age. 



2. Radiation and radiomimetic chemicals administered early in life 

 increase the over-all age-specific death rate in a manner suggestive of ageing. 



3. When the age-specific death rates for individual diseases are analysed, 

 the curves are found to vary in shape and slope, and the effects of radiation 

 appear quantitatively, if not qualitatively, variable. 



4. Age-specific death rates from radiogenic leukaemias (thymic lymphoma 

 and myeloid leukaemia) appear unusual in that mortality from these diseases 

 becomes maximal relatively early. 



5. Analysis of the age-specific death rates for various other diseases, 

 including non-neoplastic lesions, indicates that the life-shortening effects of 

 radiation are not confined to induction of neoplasia or any other specific type 

 of pathological change. Instead, they appear to be correlated with a general 

 advancement in the age distribution of diseases otherwise associated with 

 senescence. 



6. The results emphasize the complexity of the relation between the 

 incidence of a disease and the radiation dose, owing to effects of radiation on 

 intercurrent diseases affecting the survival of the population at risk. 



REFERENCES 



ICiMBALL, A. W. (1958). Bull. Int. Statist. Inst. 36, 193. 

 Kimball, A. W. (I960). Biometrics 16, 505. 

 Mole, R. H. (1957). Nature, Lond. 180, 456. 



