143 



part, corrected by marrow injection in the rat, according to Bond's recent work. 



POTTER: If I get your point correctly, you might think that in X-ray 

 damage you have blasted a piece of the nucleic acid out of the total unit which has 

 not lost its integrity because of hydrogen bonding. And now, if you put in plenty 

 of pieces, say, from marrow nuclei, you may supply at random a piece that can 

 fill the gap in the chain and heal the damage. Is that the point you are making? 



KAPLAN: No, I would not go that far. I would only say that the cells in 

 some of these hematopoietic tissues seem to be incapable of recovery after X 

 irradiation that is about midlethal for the mouse -- they are not capable of re- 

 covery, and by virtue of the impairment of function which results, the animals 

 die because they are vulnerable to infection or hemorrhage, or they lack certain 

 vital functions. This is not important to the discussion. The point is merely 

 that they are unable to recover on their own. If you give them this material, al- 

 most overnight the hennotopoietic tissues recover the ability to start dividing rap- 

 idly. When we shield the spleen or the thigh, or inject bone marrow immediately 

 after irradiation -- of course, the shielding would be during irradiation -- then, 

 within a few days after irradiation, we can show very significant differences in 

 the weight of the thymus between treated and untreated animals. This is a very 

 significant change. Something has happened to those thymus cells which sudden- 

 ly relieves the effect of irradiation and lets them start working again. 



HOLLAENDER: We have conducted similar studies in regard to recov- 

 ery from X irradiation with E. coli. I believe much more is known about this 

 system . 



SPIEGELMAN: What did you supply ? 



HOLLAENDER: E. Coli B/i- can be made to recover from X-ray dam- 

 age to a considerable degree by growing it on yeast or meat extract as mentioned 

 before. A synthetic medium consisting of inorganic salts, glucose, glutamate, 

 uracil, and guanine, will produce as good a recovery at 37^0 as yeast extract. 



SPIEGELMAN: We had an idea along similar lines. It was based on the 

 assumption that demonstration of transformation with certain bacteria stemmed 

 from the fact that the wrong characters were being used. We started by subject- 

 ing the cells to lethal doses of X-rays and then exposing them to DNA from unir- 

 radiated cells. The idea was to reverse the lethal effect with uninjured DNA. 

 The results, however were completely negative. 



HOLLAENDER: We have tried to feed irradiated cells DNA or RNAbut 

 no effect was noticed. Of course, one difficulty might be that these materials 

 can not enter the cell. 



The active material actually was found first by isolating spleen extract 

 by paper chromatography. We found three areas on the paper, extracts of which 

 if combined, could simulate the spleen effect. It appears now that these three 

 materials might be glutamate, uracil, and guanine. Further experimentation is 

 necessary to make this certain (10). 



SHERMAN: In your experiments did it make any difference which kind 

 of spleens you used; whether they were rat spleens or rabbit spleens'' 



HOLLAENDER: Well, actually we used calf spleens for our experi- 

 ments. Of course, we know why the calf spleen did work. 



