L. H. GRAY 



that some effect could be produced by introducing into the cells some oxidizing 

 agent, like hydrogen peroxide, and things of this kind. I wondered, in the first place, 

 whether anything had been done on those lines, and in this connection, too, could you 

 tell us something about the relation between the respiration in this case and the 

 oxygen? Is it that all these cells are respiring whether or not they are present with 

 oxygen ? Does the respiration have any effect on them or not ? 



Dr. Gray: The first part of your question, I think, concerns the production of perox- 

 ides in the fluid. It is most likely that organic peroxides are produced when you 

 irradiate the ascitic fluid in which these cells are in suspension. If this were so, and 

 if the peroxides were contributing to the observed chromosome damage by their 

 effects on cells during the short period of irradiation, it would be expected that an 

 increased amount of damage would be seen if the cells were allowed to stand in the 

 presence of the fluid after the end of irradiation. This was checked by leaving the 

 cells in the presence of the irradiated plasma for periods of up to three-quarters of an 

 hour, but no increased damage was seen. I suspect that this is because the cells 

 contain catalase. Such after-effects were observed long ago by Alper^ when irradiated 

 virus was allowed to stand in the presence of the irradiated medium, and has been 

 observed quite recently by Adler^ and Adler and Stapleton^ with bacteria which 

 contained no catalase. In each case the effect of the irradiated fluid could be repro- 

 duced by exposing irradiated organisms to other fluid which contained a known 

 amount of hydrogen peroxide. Adler and Stapleton worked with a haemin-deficient 

 mutant strain of Escherichia coli, in which they could control the amount of catalase 

 present in the cells by the composition of the culture medium. They were thus able 

 to show that an after-effect was observed only with the bacteria which contained no 

 catalase. It is interesting also to note that both with the viruses and the bacteria the 

 interaction after the end of irradiation was between peroxides and irradiated organ- 

 isms. Interaction with unirradiated organisms was negligible by comparison. In a 

 paper presented at the recent Atoms for Peace Conference, Kunkel and Schubert* 

 have reported some rather striking protection eflfects observed with cysteamine 

 administered after the end of irradiation. Perhaps the most striking were those 

 observed with a hibernating dormouse. Cysteamine administered to the active dor- 

 mouse before irradiation has a protective effect similar to that observed with mice. 

 When the hibernating dormouse is irradiated, the damaging effects of the radiation 

 only begin to become evident when the dormouse comes out of hibernation. Kunkel 

 and Schubert report that protection against this damage may be obtained by the 

 administration of cysteamine up to 3 weeks after irradiation, provided it is given 

 while the dormouse is still in the hibernating condition. In the same paper they report 

 a very interesting verbal communication from Dittrich. Working with the same 

 tumour cells as those with which Dr. Deschner and I have worked, namely the Ehrlich 

 ascites tumour, Dittrich reports that 'increased chromosomal damage is seen in cells 

 which have been irradiated either in the presence of air or oxygen near 0"C if they 

 are allowed to warm up to 37 '^C in the presence of 2 atm oxygen'. In the course of 

 some studies which Dr. Howard, Miss Hawes, and I were carrying out at 2 °C, we 

 compared the proportion of abnormal anaphases in cells which had been irradiated 

 anaerobically or in the presence of low concentrations of oxygen, and allowed on the 

 one hand to warm up to 37 °C over a period of 20 min in the presence of the gas in 

 which they had been irradiated, or, on the other hand, in the presence of oxygen at 

 1 atm. In a few preliminary experiments of this kind, we have observed no influence 

 of the post-treatment with oxygen at 1 atm pressure. We hope to extend our observa- 

 tions to 2 atm pressure for comparison with the reported observations of Dittrich. 



My colleague, Dr. Dewey, measured the respiration of Ehrlich ascites tumour cells 

 down to partial pressures of about 7 mm mercury without observing any dependence 

 of Qo on the partial pressures of oxygen. In some cells, notably muscle cells, this 

 independence is known to extend to 1 mm mercury, and in bacteria to much lower 



7 85 



