Discussion 



73 



like polymer systems which have been studied previously. It can be 

 protected against irradiation by certain protective substances which will 

 be discussed later, and it can be studied quantitatively. In many ways 

 the preparation resembles the chromosome in the cell, at least as we 

 picture it from microdissection studies. It has, for example, pronounced 

 elasticity. It will break down in response to shearing stress, as Prof. 

 Butler pointed out, but the breakdown need not interfere with the 

 observation of radiation effect. Mr. Fisher, who is now working in our 

 laboratory, has devised a viscometer in which the viscosity may be 

 measured without previously subjecting the preparation to a shearing 



VISCOSITY VS DOSE. RAT THYMUS IN « M NaCI 



50 100 150 200 400 600 



DOSE(r) 



Fig. 1. (HoUaender). Effect of X-rays on viscosity 

 of crude rat thymus preparation (W. Fisher, un- 

 published). 



field. With it he has been able to get very reproducible results. It 

 should be pointed out that sodium deoxyribonucleate is also sensitive to 

 mechanical stresses, and can be broken down during isolation, but it is 

 much more resistant than the nucleoprotein. 



I would like to say that the nucleoprotein which Kaufmann has 

 isolated is in many ways much closer to what exists in the living cell 

 than the pure salt suspension which has been isolated. Unfortunately 

 these nucleoproteins cannot be dried, but it might be possible to reduce 

 them to a very low temperature where a direct effect could be observed. 



Alper: What about the oxygen effect? 



HoUaender: These are very viscous and the moment you bubble 

 oxygen through you break down the pattern in which they are organ- 

 ized. We have not learned how oxygen may be removed and so far it 

 cannot be removed; the moment you bubble nitrogen or any other gas 



