1 13 



the same thing. If the calcium is the weakest point then the radiation will cer- 

 tainly find the calcium and that could lead to a break. 



PLATZMAN: It is really not the same thing. However, at the moment 

 I cannot think of a clear criterion for distinguishing between the two in the case 

 before us. 



MAZIA: The reason why I am bringing up this whole question is be- 

 cause I have not seen any discussion of the primary radiochemical action on 

 bonds of the type we have been discussing. They might be very important in the 

 cell. 



PLATZMAN: In the new book edited by Dr. HoUaender, you will find 

 a few sentences that Professor Franck and I wrote on just this point (12). 



POTTER: Can you centrifuge out those little elementary particles? 



MAZIA: Do you mean in solution? 



POTTER: Yes. 



MAZIA: Yes. I am told that it will be a little difficult to study them 

 in more detail by ultracentrifugation because they are not soluble in salt solu- 

 tions. 



SPIEGELMAN: Suppose you have done this. How do you bring the 

 ionic strength up again and what happens to your material? 



MAZIA: Once in solution, it can be precipitated by raising the ionic 

 strength with NaCl and can be redissolved by removing the NaCl. If no Ca is 

 around, precipitation and solution seem to be a matter of the conditions for in- 

 teraction and repulsion of the particles, which is determined by the ionic 

 strength. 



PLATZMAN: Can ultraviolet cause the same type of chromosome 

 breakage? 



HOLLAENDER: To a slight degree only. 



PLATZMAN: Disregarding frequency? 



HOLLAENDER: There is much less chromosome breakage. 



PLATZMAN: Do you still observe the same type of break? 



HOLLAENDER: Yes. 



PLATZMAN: Then it seems to me that might be supportive of heat 

 rather than of ionization. Not that it makes any difference at all at this stage. 



MAZIA: Isn't it still considered to be a fact, Dr. HoUaender, that 

 there is a difference between ultraviolet radiation and ionizing radiation with re- 

 spect to tne chances of producing a break versus the chances of producing a 

 change within the gene? 



PLATZMAN: I would be impressed with that evidence only if someone 

 really did experiments in the vacuum ultraviolet. In fact, however, most experi- 



