Ill 



though the preliminary spreading at an air-water interface greatly increases 

 radiation sensitivity even though the protein is irradiated dry. We observed 

 about 70 percent inactivation of such films with doses of 3000 r, as measured 

 by the Victoreen meter. The catalase that had not previously been spread was 

 not inactivated by doses available to us with our prehistoric equipment. We 

 are told by people who know more about these matters that the actual value of 

 the dose is not very significant because of backscattering from glass. Never- 

 theless, the relative results remain and suggest that there is something that 

 happens when you open up and cross-link protein molecules at an interface 

 which does increase their susceptibility to inactivation by high energy radiation. 



KAMEN: It increases the sensitivity? 



MAZIA: Yes. There is a question that I should like to raise for my own 

 information. On several occasions during this conference, the idea of local 

 heat effects has come up. This is one of the oldest theories of radiation effects 

 and one which many of us have thought was no longer taken seriously. What 

 is its status ? 



FANO: I think it depends on what you mean by local. 



MAZIA: I am just asking. This is the first time in years that I have heard 

 anyone discuss the so-called "point heat" effects. 



POLLARD: We have given this a lot of careful thought (11). You can 

 measure very carefully the thermal constant for inactivation, let's say, with 

 the wet or dry phase. Which one would not matter in this case, but let's take 

 the dry phase. You can predict what temperature increase would be necessary 

 to produce inactivation in a certain length of time. Then you can calculate the 

 rise in temperature of a molecule due, say, to one primary ionization being 

 put in there and it is plenty high. It goes up to 450° or something like that. 

 But in order to inactivate with the same inactivation constant (and this is the 

 question which may be doubtful) the time that it would have to be kept there is 

 something of the order of 10"2 or 10"3 seconds. There is no mechanism that 

 I can think of by which in the solid state there would actually be temperatures 

 kept up that long. If you put in an ordinary thermal conductivity figure and esti- 

 mate that way, the temperature disappears in time of the order of 10"' and 10"8 

 seconds which gives a discrepancy of 10,000. 



We have looked into this carefully. Not only this work I have described 

 here, but Appleyard (12) has done some on hemoglobin, Setlow (13) on catalase, 

 and the conclusion is that the point heat theory applied literally as such cannot 

 be entertained. However, it does seem to me that there is possibly what might 

 be called "prepartition" heat. In the case of radiation the processes that occur 

 before complete partition may well give you a reaction constant that is lots 

 faster, and I am inclined to maintain that in that time between incomplete par- 

 tition and full thermal action is a place where there is radiobiological action. 

 I feel that some radiobiological action is concerned with that but not with heat. 



MAZIA: Would the reaction system you are describing be dependent on the 

 solid state? 



POLLARD: That is right. You mentioned that there is a possibility that 

 the interface holds up the heat and provides a mechanism by which you can have 

 a little time. Then I think you do possibly bring in this process, as pre-equi- 

 partition or possibly as pure thermal. 



