DISCUSSION OF ZIRKLE'S AND TOBIAS' PAPERS 387 



Ephrussi and I, with the collaboration of L'Heritier, have tried the same sort 

 of analysis, but it seemed to us that a simple hypothesis could not account for 

 the results and that many more experimental facts were actually needed. 



Tahmisian : 



The chemists and physicists have ably shown that the effect of an ionizing ray 

 lasts 1 X 10~^^ to 1 X 10"^ sec. To the biologists this has been very discour- 

 aging because the effect of irradiation dosage could be demonstrated several days 

 after the original damage occurred. 



With diaphase grasshopper eggs the irradiated materials could be subjected 

 to 0° for 6 months, after which the irradiation damage could be demonstrated 

 when the eggs were returned to metabolic temperatures. Although 25,000 r 

 destroyed every nucleus in the grasshopper embryo, the utilization of oxygen was 

 not affected; it even increased. We stated that anabolic processes were more 

 susceptible to irradiation than catabolic processes. It was demonstrated that 

 the ability of a resting cell to maintain the status quo was dependent on the pres- 

 ence of a functioning nucleus. 



Clark demonstrated that the maintenance of a dynamic equilibrium in the 

 ameba was dependent on the nucleus. An enucleated ameba could not meet its 

 nitrogen requirements from a medium containing urea and glucose, whereas the 

 control could do this. 



At the symposium on nucleoproteins in Holland the necessity of nucleopro- 

 teins in the cell for the formation and maintenance of enzymes and proteins was 

 clearly brought out. 



Tobias showed that a haploid yeast cell was more susceptible to ionizing 

 radiations than a diploid cell, and the latter than a polyploid. He mentioned that 

 the cytoplasm in these cells must also be injured. Probably the cytoplasm was 

 injured to a much greater extent than the contents of the nucleus, since much 

 more cytoplasm is present. 



In a haploid organism the portion of the cytoplasm which was injured and was 

 under the influence of a destroyed gene could not be repaired. In a diploid or 

 polyploid cell, however, if one gene was destroyed the allele could take over, 

 repair the injury to the cytoplasm, and in turn be able to maintain itself. 



I believe the paper presented by Tobias has finally brought light to the mode 

 of radiation damage to biological material. It also explains why it takes so long 

 to demonstrate injury and why all cells in the proximity of the injured one are 

 differentially affected. Tobias has made a great contribution to the advance- 

 ment of radiobiology. 



Gierlach: 



Throughout the symposium, there has been an evident need for more indi- 

 cators of biological change produced by radiation. With the kind permission of 

 Dr. Zirkle and also of Dr. Sax, I should like to present briefly our results with 

 vital staining techniques. This work has been performed at the Medical De- 

 partment Field Research Laboratory located at Fort Knox, Kentucky, by 

 A. T. Krebs, S. Strugger, and myself. Fluorochromes, as well as diachromes. 



