Discussion 159 



rather crude polynucleotide RNA fraction from Esch. coli and found it 

 was stimulatory in recovery of Esch. coli. We tried this same preparation 

 injected into irradiated mice, and it seemed to work in mice too. These 

 experiments are extremely preliminary, but it looks as if the same sort 

 of preparation injected repeatedly into animals might bring about 

 something of the order of 20 per cent survival in mice irradiated with a 

 supralethal dose. We have had a lot of variability among samples pre- 

 pared similarly. Some fractions have been toxic. We hope that when 

 we iron out some of the difficulties concerning toxicity of some of this 

 material prepared from bacteria, we can then give a better answer than 

 we can at the present time. There is no possibility here, of course, of 

 repopulation. 



Stocken : I think that Dr. Loutit used very careful but accurate words 

 when he said that the humoral factor was not the initiating mechanism. 

 I think that this completely covers it. 



Stapleton: One reason why I hesitated to say anything about this 

 bacterial fraction was the fact that people have found increased survival 

 somewhat like we have found by injecting materials such as ground 

 glass, charcoal, and so on, following irradiation. 



Butler: Then what is the status of Cole's nucleoprotein fraction? Is 

 the effect due to cells? 



Loutit: With Stocken we have made preparations according to the 

 Cole recipe, using one of these marker chromosomes and the recovering 

 marrow in those animals contains the marker. That suggests to me 

 either that the residual number of whole cells are the effective thing, or 

 if it is the nuclei, that they can reform their own cytoplasm and get 

 cracking again from that. I find that a little far-fetched. 



Stocken: In self-defence, I think that this preparation here has been 

 reasonably well done. All the cells have been counted. We have used 

 various techniques for looking at nuclei, and I don't think that Cole had 

 these advantages. I do think that his material was probably contamin- 

 ated with whole cells. 



Alexander: An impressive argument which Cole used was that he said 

 that his "nuclear" preparations could be inactivated by treatment 

 with DNAse, whereas the cellular preparations could not. This would 

 show that the activity of the "nuclear" preparations is not due to con- 

 tamination with whole cells, since these should not be inactivated by 

 DNAse. But Dr. Jacobson told me last year in Chicago that although 

 DNAse does not inactivate preparations containing large numbers of 

 cells (of the order of several million), it does destroy the activity of 

 suspension containing 10* or so cells per mi. Since this number of cells 

 is sufficient to produce appreciable effects and is also the amount of 

 contamination to be expected in preparations of nuclei, the DNAse test 

 can no longer be considered as decisive proof for the nuclear hypothesis. 



Stocken: We have done these experiments too, on the same prepara- 

 tion and there is no recovery with the DNAse-treated preparation. 



Spiegelman: Have these cells been stained to see whether they still 

 have DNA material? 



Stocken: No. They have been examined by phase contrast microscopy 



