107 



800 r, there was no appreciable change ir> the respiration of those particular 

 tissues. 



CURTIS- To get back to the second part of your question, if I under- 

 stood it. it was that a 5 or 10 percent change in all the enzymes might somehow 

 add up to the lethal effect. 



JONES- Yes, I also anticipate a difference from cell to cell. There 

 maybe great individual differences in the enzyme content of each cell and parts 

 ^f ceils for any particular type of enzymes; on a random basis, some should go 

 UP and some should go down, but in this case you have shown us that every en- 

 zyme is somewhat depressed. Could this in itself describe a total change that 

 mS be of greater consequence to cell function than the apparent average 5 to 10 

 percent depression of all the effects? 



CURTIS: Do you think that this is the case? 



JONES: No. I just brought up the question. What do others here think 

 about it as a possibility? 



BENNETT: This is being investigated by Miss Hughes in our laborato- 

 rv Acetate-C^'i is given to animals that have been irradiated, and the rate ot 

 excretion of C 140, is determined. The experiments have really just been imti- 

 a?ed bu^he rate 'appears to be closely comparable to that of the normal animal. 



If irradiation is affecting the Krebs cycle and all the rates were de- 

 creased to 90 percent of normal, one might expect that excre ion of COz would 

 be down to something like a quarter of normal. This does not ^PP^^^. ^° J?^^^^^^_ 

 case in the whole animal. But there are limitations. One might not be observ 

 ing the metabolism at the critical time, etc. 



CURTIS- I think we might come back to a point that Dr. Pollard 

 brought up this morning. That is. that very few molecules are disrupted by a 

 lethal dose of radiation In that case, we were talking about large molecules 

 Is it not true that this afternoon we are talking about much smaller molecules? 



DUBOIS: Yes. 



CURTIS- If that is correct, then the smaller the molecule, the less is 

 the probability that enough of these molecules will be f^l?^]f^.Xlt"JT^^^^^ 

 radiation to be of importance. This means a lower probability that we are deal 

 ing here with a fundamental aspect of the whole radiation problem. 



POLLARD: I have just made a few scratch-pad calculations that might 

 be interesting. Take a cell of a length of 5jx and a radius of 1^. Roughly speak- 

 ing there are 9, 000 RNA molecules in it and 900 DNA. This is calculating that 

 DnX molecules kave a weight of 10^ and RNA molecules of 105 and that their 

 proportion is that given for yeast this morning. 



If vou suppose that 100 r are distributed proportionately to the area that 

 these things cover -- incidentally, this is assuming the effect to be purely in- 

 direct --ff you assume it direct, it goes in volume - for this type of action you 

 can say that you are going to get 1 /3 of a DNA molecule inactivated per cell, 



10 RNA per 'ell and fo protein per cell. You started out with ^OO' 000 pro tern 

 molecules So you have 1 in 10,000 protein molecules inactivated. You started 

 Tt wUh 9 000 RNA and you have 10 of those inactivated. So you have about 1 m 



1000 of those and maybe 1 in 1000 of the DNA. 



