108 



What you can conclude from this I don't know. The conclusion I come 

 to is that 100 r does not do anything. To me it is clear that there must be addi- 

 tional factors operating which are multiplicative in character, and what they are 

 I don't know. You can see some of them as physical. For instance, take the 

 matter of area; the fact that the DNA is long and thin whereas I have assumed it 

 to be more or less spherical for this calculation. If DNA is long and thin it will 

 mean that it stands a better chance of being inactivated. This will give a multi- 

 plicative factor of perhaps 4 or 5. But it still does not get us past the fact that 

 we have only about 1 in 500 of the DNA molecules inactivated. 



SPIEGELMAN: If each one of these is unique and uniquely necessary. 



POLLARD: I didn't say that. If I had said it, I would have beenhopped 

 on. You said it. 



SPIEGELMAN: I think that is something that we can reasonably assume 

 to be true. 



POLLARD: I think so, too. 



TOBIAS: Assume that the RNA is distributed somewhat like the DNA so 

 that for synthesis of a given protein you need, say, 9000 RNA molecules. As- 

 sume further, that synthesis in the cell proceeds one step after the other, per- 

 haps on the surface of the RNA. If radiation then inactivates any one RNA mole- 

 cule , e.g. , No. 455, it may be that from then on the rest of them don't count, 

 and protein synthesis is broken down. Under these conditions, you would have a 

 high probability of damaging RNA molecular chains. 



POLLARD: I think there is another point (I believe it is Dr. Barron's) 

 that could make quite a difference. In making the effect in proportion to the 

 area, we have used the smaller molecules that occupy most of the area and we 

 have assumed that nothing happens. Suppose the smaller molecules are actually 

 carriers of radiation energies that are then communicated to the other molecules, 

 which is essentially your point. They may be sort of symbiotic in action. Then 

 you can have a factor of 5 in addition. 



But I feel sure that whatever you do you can never get enough effect in 

 the smaller molecules to account for the effect in the cell. They may be inter- 

 mediary in their action, but the effect you have to look for, I feel sure, is in the 

 larger molecules. I agree, of course, with Dr. Spiegelman, that they are criti- 

 cal. I believe they are in the chain, and I suspect we ought to be looking for those 

 kinds of things. 



HOLLAENDER: This is what I brought up this morning when I said that 

 1 r would interfere with the rate of mitosis. It might be possible that you do in- 

 terfere only with the function of a few enzyme molecules. 



KAPLAN: You have to remember that there are other kinds of cells 

 that are easily knocked off by 100 r. This forces us into some further complica- 

 tions because all the cells in the animal body, with relatively few exceptions, 

 have a normal complement of chromosomes and they have about the same amount 

 of DNA, Even if you postulate that there are 10, 000 kinds of DNA, each of which 

 is unique, presumably all the cells have all of these kinds of DNA because they 

 all got them from a common source. 



This forces us to postulate some kind of amplification system peculiar 

 to certain kinds of cells, in which, so to speak, many roads lead to Rome. Ra- 



