LATE EFFECTS OF EADIOMIMETIC AGENTS 175 



trpTON: This is conceivable I thinlj. We have endeavoured to correct statistically the 

 incidence of lung tumours so as to allow for difference in survival, but this doesn't restore 

 the incidence to normal. I think there is an effect, certainly, of intercurrent mortahty, 

 but I am not sure it is the whole explanation for the differences in tumour incidence. 

 ALEXANDER: But you see; we have found that the latent period for these lung adenomas, 

 particularly with radiomimetic chemicals, was of the order of 550 days. So that cutting 

 off 150 daj's might lose you all j^our lung adenomas. 



rotblat: I would like to support that, because there are data with X-rays on mice where 

 you find a decrease with dose, but after adjustment for the time of the occurrence there is 

 no change with dose at all. 



LEJEUNE: I would like to ask a question about the meaning of life-span. If the mice were 

 as well examined as human beings are, would you say that this life-span reduction is 

 specific such as we could detect in man, or is it some general effect that you carmot define 

 at aU? 



UPTON: We are making a preliminary attempt to answer Dr. Lejeune's question, but I 

 regret to say that the state of the art isn't very advanced yet; that is, we don't, unfor- 

 tunately, know very much about our dead mice. We are endeavouring now to do serial 

 sacrifice experiments so that we are not limited to autopsy material. Frequently it's not 

 possible, however, at least in my experience, to say confidently why a given mouse died. 

 Replying to your question about the death rate in relation to age: again, only lookmg at 

 the mice with lung tumours at the time of death we see that this neoplasm is a late- 

 occurring disease, and the curve is of the same general character as the so called "Gom- 

 pertz type" curve. Nitrogen mustard displaces the curve to the left, and TEM even more 

 markedly. Now one thing worth noting is that the death rate with lung tumours in the 

 X-ray group is not as greatly displaced as it should be, if effects on the age-distribution of 

 lung tumours parallel the effects on over-all survival, that is, you recall the life-table for 

 all the X-ray mice was displaced much further to the left. So I think in answer to your 

 question, Dr. Alexander, there is in fact less advancement in the age-distribution of lung 

 tumours, m other words, many mice are dying from other causes before they have had a 

 chance to develop lung tumours. 



