21 



these items, which are responsible for biological action, and calling it the sen- 

 sitive volume as far as radiation action is concerned. 



If I think about this from the point of view of the cell, suppose a mito- 

 chondrium is damaged. If an effect is produced at one point in it, I am sure 

 that this will not inactivate the whole mitochondrium . It will probably inactivate 

 a little cytochrome enzyme, 1 of a total of 10. So the effect of this on the total 

 operation of the cell cannot, I believe, be very great. On the other hand, the 

 inactivation of a nucleic acid molecule will also occur, and if you put one ion 

 pair inside the molecule, and if that has transforming properties (it may or may 

 not), biological consequences may follow, and you can estimate them in terms 

 of this very simple idea. That I think is a contribution to radiobiology because, 

 as I say, it enables you to pigeonhole one class of biological action in one 

 corner. 



HOLLAENDER: Do you call that a direct effect or an indirect effect? 



POLLARD: This I call a direct effect. I am speaking of the case 

 where energy is produced and is released inside the molecule. That is my dif- 

 ferentiation between direct and indirect effects. Where does the primary action 

 take place? If it takes place inside the molecule I class it as direct. I am say- 

 ing that, for a first order, if this occurs inside this molecule, you can then say 

 that this same molecule and not its neighbors will cease to have biological func- 

 tion. 



HOLLAENDER: Could you modify this by some secondary treatment; 

 possibly prevent the direct effect. 



POLLARD: I would expect that the direct effect could be modified. 

 That is one thing I want to talk about in a minute, because there are more fea- 

 tures to it than I have been mentioning. I am quite sure that there are ways in 

 which this could be modified on the basis of the picture that I have drawn of the 

 radiation migrating, and the suggestions that Dr. Kamen and Dr. Platzman came 

 up with that you could have groups which, so to speak, absorb the radiation 

 where it does no damage. It could be done deliberately and on occasion some- 

 thing like it does occur. 



However, speaking in the first order only, I should like my pigeonhole 

 to include the statement that the whole molecule, and not its neighbors, in inac- 

 tivated when energy is released inside. By energy, I mean ionization. Clearly, 

 as Dr. Barron correctly says, 80 percent of the matter in this space is water, 

 and what effect results from water action I don't particularly want to debate. I 

 wanted to contribute a part that is not related to water and which I believe to 

 have a part in radiobiological response; certainly not a dominant part. My esti- 

 mate is that it can be between Z5 percent and 75 percent. This is only an esti- 

 mate. 



Now I should like to give the more seamy and, may I say, the more 

 ordinary radiobiological side of this. I should like to describe two experiments 

 that show that you cannot quite accept my overwhelmingly simple concept. 



The first concerns the loss of ability of a virus to combine with anti- 

 serum. We take a virus, T-1, irradiate it and observe whether it will still com- 

 bine with the specific antiserum (16). We let unirradiated and irradiated viruses 

 compete for antibodies and we see whether the competition is interfered with in 

 any way by irradiation. 



