280 



PETEK ALEXANDER AND MISS D. I. CONNELL 



EESULTS AND DISCUSSION 



At the time of writing, this experiment has been in progress for just under 

 2 years. Not all of the slides from the mice that have been killed have so far 

 been examined and classified. The present report is therefore limited to the 

 rate of appearance of the following conditions only: (1) benign hepatomas, 

 (2) lung tumours, (3) cataract, (4) papiUonephritis. 



Figure 2 shows that the time of appearance of the benign hepatomas (c/. 

 ConneU and Alexander, 1959) is exactly the same in the irradiated as in the 

 control population. The serial killing technique fully confirms our earlier 



9 12 15 



Age (months) 



Fig. 2. Incidence of hepatomas with increasing age in serially killed control and 

 X-irradiated CBA male mice. 



conclusion, based on examiuation of animals which had been allowed to die, 

 that radiation has no influence on the time-course or incidence of this con- 

 dition. Thus if the appearance of hepatomas is used as a criterion for agemg 

 then radiation does not age. 



Lung tumours would suggest the opposite. Figure 3 shows that radiation 

 has no significant mfluence on the incidence of these tumours, but they 

 appear earlier. It could be argued that radiation had speeded up the "internal 

 clock" of the animal about twice in agreement with the observed life-span 

 shortening; in other words radiation accelerates ageing. 



The appearance of cataracts (see Fig. 4) illustrates another type of response. 

 Radiation reduces the latent period, but also increases the total incidence. The 

 situation is even more complex since the cataracts in the irradiated group are 

 morphologically quite different from senile cataracts (Upton et al., 1960). It 



