LIFE-SPAN SHORTENING FROM VARIOUS TISSUE INSULTS 271 



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DISCUSSION 



pochin: One of the problems in this work, I imagine, must be to see what quantitative 

 effect you are getting at a different level of your generalized stresses. I was wondering if 

 3'ou happened to get any information of this sort to give radiation and other generalized 

 stressing agents at an LD50 and study or compare the 50% survival and the length of 

 survival of those surviving the LD50 irradiation as compared with the Ufe-times of those 

 surviving an LD50 from other stresses. 



CURTIS: What we did in every case was to have one group of animals m wliich we deter- 

 mined the lethal dose of the agent in question, and then in the experimental group we 

 gave about half the lethal dose. Thus we were sure in each case that the animals were 

 receiving an almost lethal dose of the agent. 



POCHIN: But the survivors from the LDjq of the other stress agents survived normally? 

 CURTIS: Yes. 



ALEXANDER: I just Wanted to stress that perhaps your experiments had in fact shown 

 that general stress did shorten life-span perhaps not quite so acutely as tetanus toxoid, 

 but maybe just living in America, because your animals had a medium life-span of 400 

 days whereas I don't think many of their genetically identical English counterparts, 

 would live for quite such a short time, so the hectic American hfe seems to have an effect 

 on mice as well! 



CURTIS: We selected this strain of mouse becaue it is quite a short-lived strain so we do 

 not have to wait three years to obtain results. I see no reason to believe that the con- 

 clusions would not be the same for all strains, but would certainly agree that eventually 

 they should be verified on other strains. 



BRiNivMAN: I understand that if one kidney of an animal is removed the other enlarges, 

 unless it is irradiated. So then the capacity for enlargement of the normal kidney is lost 

 by a small amount of irradiation. 



CURTIS: This might be so, but you run into trouble because the hj'perplasia of the kidney 

 can be by both cell enlargement and cell divisiou, and the proportion of the enlargement 

 due to each, changes with age. Radiation acts much more strongly on cell division than 

 on cell elongation, so the interpretation of results may not be so easy. 



