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DISCUSSION 



ALEXANDER: Dr. Cottier whetted our appetites by saying that he'd seen membrane 

 changes and then that he wasn't so sure whether they were real. This was exactly the 

 position which we reached at this Institute, when Drs. Birbeck and Mercer examined a 

 whole lot of irradiated tissues aiid were at first very enthusiastic aboiit changes in the 

 membranes. However, after lookmg at a really large number of sections of control 

 material, one just couldn't be sure. Do you think from your studies that one could make 

 this electron microscopic morphology quantitative so that one could say that the 

 uumber of membrane abnormalities is increased as a result of irradiation? It seems to me 

 that at the present time electron microscopy can only given us a positive or negative 

 answer, and if the radiation change is sometliing similar to the sort of change that may 

 happen in the handling of the cell, then one can't be sure unless one can make it quantita- 

 tive. Do you think it should be possible to do this? 



COTTIER: It seems possible that by serial sectioning and constructing a tliree- dimensional 

 model of the ceU, one should be able to differentiate between actual membrane defects 

 and membrane folding. For in vivo studies of this kind the thymic cortex may be parti- 

 cularly suitable since it is composed mainly of the radiosensitive small lymphocytes and 

 does not show the same degree of spontaneous cell death as is seen in spleen and lymph 

 nodes. 



ALEXANDER: We tried to examine this in what we thought would be an even more simple 

 system, namely with cells in tissue culture. The mteresting thmg with these cells is that 

 one doesn't even get any gross abnormaUty until after about 24-36 hours. It's only 

 when one irradiates the same ceUs in vivo that one gets — as you showed with your liver 

 cells — these gross abnormaUties, so these must be due to an abscopal effect. The disap- 

 pointing thing really is that not only does the electron microscope not pick up anything 

 immediately with certainty — it doesn't even pick anything up with certainty after 24 

 hours. 



UPTON: May I comment briefly on some work which Dr. Parsons carried out at Oak 

 Ridge with the electron microscope, in which, following up the observations of Burke and 

 Russell on the very high radiosensitivity of the early oocytes m the immature mouse, he 

 chose to look at oocytes within a few miimtes of low doses of the order of 10 to 15 r. 

 After gomg to great pains to eliminate artifacts he was able to find quite dramatic general 

 changes in mitochondria within just a few minutes after doses of less than 10 r. Tliis of 

 course is the LD50 for oocytes, a big dose for this type of cell, but a small dose in terms of 

 whole-body irradiation. These changes occurred very early and the cells that survived 

 appeared to be normal. He wasn't able to determine whether the mitochondrial changes 

 preceded the earliest detectable nuclear changes. He was anxious to try to see whether 

 nuclear changes could be seen earlier, but this point could not be resolved with the tech- 

 niques that were available. 



COTTIER: Mitochondrial swelling of a variable degree is often seen in lymphocytes. On the 

 basis of our findings we could not decide whether it precedes or follows nuclear damage. 



