342 GENERAL DISCUSSION 



polymerization and other chain reactions. I think we can conclude safely that polymer- 

 ization isn't lilvely to be a very important lesion in damaging the cell. There might be 

 oxidation changes mvolved where dose-rate does come in, but this seems improbable. I 

 would say that the most probable thing is that the initial injury, defined as a chemical 

 event, is dose-rate independent. When you have 10^ or so r/sec then there is a slight 

 dose rate dependence but for many radiation-induced chemical reactions in the dose- 

 rate region about which we are talking the initial injury is almost certamly the same, 

 whatever the rate. 



RUSSELL: I would say essentially the same thing, although I would distinguish between 

 pre-mutational damage and the actual completion of the mutation. We don't claim that 

 there is recovery from mutation. Therefore, in one termmology this is less damage. But 

 if one is referring to the pre-mutational effect, there must be recovery, as I see it, in the 

 sense expressed by Dr. Upton and Dr. Alexander. The primary damage presumably is the 

 same, from the point of view of the number of ionizations, but since the total effect of 

 this on mutation is less at low dose-rates, there must have been recovery in the inter- 

 mediate processes. 



berenblum: I tliinli it is important to consider both injury and recovery as separate 

 entities because one can surely visualize two kinds of injury — one wliich is reparable and 

 one wliich is not. If you give a dose of radiation such that the injury is uTeversible and 

 the cell dies you will obviously get no mutations. Are you talking of recovery of the cell 

 itself, or are you talking of recovery of the tissue? 

 BACQ: The cell itself. 



BERENBLUM: Yes, but is it always possible to distinguish this? Can't you conceive a 

 situation where, with a particular dose of radiation, all the cells that are injured are 

 kUled. The cells that are not injured, presumably they are less sensitive, will also show 

 no mutations. One can visualize here a large dose producing less mutations because it has 

 killed off all the cells, whereas a smaller dose wUl produce a higher incidence of mutations 

 because not all the cells have been killed. Is that possible? I'm just putting it forward as a 

 thesis. 



RUSSELL: Yes, we have postulated that it is exactly this effect which accounts for a 

 reduction in mutation rate when the close increases from 600 r to 1 000 r. 

 ROTBLAT: This work was done at a high dose-rate. Do you thmk you would get a drop at 

 a lower dose-rate? 



RUSSELL: No. At a lower dose-rate there is no drop. 



ROTBLAT: This fits in with what has just been said about the difference in kilUng effect 

 and mutation. 



Damage to Vessels 



BACQ: May we take up now this question of injury to blood vessels? Just to start the 

 discussion I will tell you of one human case which has been presented by A. Massart 

 in January of tliis year in Essen, at the meeting of the Veremgung deutscher Strahlen- 

 schutzartze f where I happened to be present. A man received accidentally diu-ing 

 manipulation of radioisotope a rather big dose on a hand. He got the usual oedema 

 which subsided, but one year and a half (or two years) afterwards, there began to show the 

 usual atrophy of the skin, beginning of gangrene even, and the surgeons were ready to 

 amputate at least two fingers. The physician in charge thought that before amputation 

 one should try one long-lasting vasodilator substance kallicrem which is present in an 

 extract of the pancreas called Padutin. He injected the drug three times a week regularly. 



fSee "Strahlenschutz in Forschung und Praxis", Band 2. Verlag Rombach, Freiburg- 

 im-Breisgau, 1963. 



