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killing of the animals or represent the initial steps. I would simply like to say 

 that some physiologic and histologic changes, e.g. , lymphopenia and lymphoid 

 involution, apparently reflect the amount of radiation instead of the lethal effect. 

 In other words, the inference that changes observed with low doses are essenti- 

 ally critical for killing does not necessarily follow. 



BARRON: I think DuBois and I are in agreement because of our ex- 

 perience with gases as warfare agents. In order to determine the real mech- 

 anism of these gases, we had to go to doses that were not lethal. 



CURTIS: I think he attempts to find the initial reaction from irradia- 

 tion. 



PATT: That is fine, but there was the additional qualification, namely, 

 that the particular enzyme inactivation that you may get with 200 r, which may 

 be a sublethal exposure, is necessarily critical for killing and to that I object. 



BARRON: I was separating the lethal action of ionizing radiation from 

 the injurious action. 



DUBOIS: According to Dr. Patt's interpretation, I implied that any 

 change that occurs from 200 r might be involved as an important factor in the 

 lethal action of radiation. That is not exactly what was meant, but rather that 

 if a change was found at 1000 r in the rat, for example, and could not be found 

 at 200 r, I would be inclined to suspect that this particular change had nothing 

 to do with the death of the rat after an LD50. In other words, any effect involved 

 in the lethal action at the LD50 level should be detectible at doses below that 

 amount. But this would not mean that a change, which is found, would neces- 

 sarily be involved in the lethal action. 



PATT: Perhaps. 



CURTIS: Let me clear up this point. I gather that you don't agree 

 with this philosophy. Dr. Patt. 



PATT: I think it is fine to use screening procedures. However, the 

 fact that a large exposure, e.g. , 1000 r, does not appear to change a particular 

 reaction does not mean that there may not be a change with lower dosages. This 

 is arguing at the other end. 



DUBOIS: In the same material? 



PATT: Yes, in the same material. This is so because there may be 

 different sorts of effects, differences in recovery, differences in the extent of 

 cellular damage, etc. We know also, that certain pharmacological agents may 

 have one action at low dosages and an entirely different action at high dosages. 



JONES: It might be worth while studying the effect of several doses 

 of radiation. 



PATT: This is essential. The lack of an effect from a high dose does 

 not imply necessarily that an effect will not be seen from a low dose. I will go 

 along with your philosophy as a first approximation but I don't think we can ex- 

 clude the other possibility. 



PLATZMAN: No one has asserted that the primary mechanisms dif- 

 fer at different doses. At least, I hope not. 



