104 E. L. POWERS 



being studied to attempt to bridge the gap between our dry system and 

 the wet, metabolizing cell (Webb and Powers, 1961; Tallentire and 

 Powers, 1961). ■]" In this way we hope to make some contribution to the 

 understanding of the interactions between high-energy radiation and 

 functioning, living cells. Even at this time, we can describe a mechanism 

 of action of sulphydryl comjaounds in protecting the bacterial spore, 

 and can wonder as to its applicability to other biological systems. In 

 the case of the spore, the sulphydryl (H2S in this instance) j^rotects by 

 reducing O2 tension and by donating H atoms to free radicals making 

 them harmless. The immediate O2 effect (Class II) cannot take place, 

 and the long-lived radicals (Class III) are scavenged before O2 tension 

 is increased again to the point that O2 can react with the 02-dependent 

 radicals. Also, the 02-independent radicals of short lifetimes can be 

 removed harmlessly as they are formed. Thus, the effect of H2S is the 

 equal of the total oxygen effect, and may exceed it somewhat. 



REFERENCES 



Bachofer, C. S., Ehret, C. F., Mayer, S., and Powers, E. L. (1953). Proc. nat. Acad- 



Set., Wash. 39, 744. 

 Ehret, C. F., Smaller, B., Powers, E. L., and Webb, R. B. (1960). Science, 132, 1768. 

 EiDUS, L. K., and Ganassi, E. E. (1959). Biojjhysics (Riiss.), 4, 215. 

 Gray, L. H. (1957-8). "'Lectures on the Scientific Basis of Medicine," Volume VII, 



pp. 314-347, The Athlone Press, London. 

 Kaleta, B. F. and Powers, E. L. (1958). Report of Division of Biological and Medical 



Research, Argonne National Laboratory. ANL # 6U93 pp. 78-81. 

 Powers, E. L., and Kaleta, B. F. (1960). Science, 132, 959. 



Powers, E. L., Ehret, C. F. and Bannon, Anne (1957). Appl. Microbiol. 5, 61. 

 Powers, E. L., Ehret, C. F. and Smaller, B. (1961). In "Free Radicals in Biological 



Systems", pp. 351-366, Academic Press, New York. 

 Powers, E. L., Webb, R. B. and Ehret, C. F. (1959). E.vp. Cell Res. 17, 550. 

 Powers, E. L., Webb, R. B. and Ehret, C. F. (1960a). Eadn Res. Suppl. 2. pp. 94-121. 

 Powers, E. L., Webb, R. B. and Kaleta, B. F. (1960b). Proc. nat. Acad. Set. Wash. 46, 



984. 

 Tallentire, A., and Powers, E. L. (1961). Radn Res. 14, 510. 

 Webb, R. B., and Powers, E. L. (1961). Radn Res. 14, 515. 

 Webb, R. B., Ehret, C. F., and Powers, E. L. (1958). Experientia, 14, 324. 



DISCUSSION 



bacq: At what dose-rate were the spores irradiated? 



POWERS : In all the experiments reported here the dose-rate was 20,000 r/min. 

 We considered it imjDortant that this condition be always fulfilled. It could be 

 shown that as the dose-rate changes the general picture of the radiosensitivity is 

 altered also. 



t Tlie work of Eidus and his colleagues (Eidus and Ganassi, 1959) is of interest in this 

 connection. The loss of enzymatic activity of aqueous solutions (1 per cent) of mysoin 

 after irradiation parallels our resxxlts on the bacterial spore. They observe an inunediate 

 oxygen effect, and a post-irradiation oxygen effect, tliat correspond closely in magnitude 

 to these effects in the bacterial spore. 



