X-Ray Sensitivity 99 



about by environment. Recent studies have shown that the 

 number of Feulgen staining bodies in E. coli is related to the 

 radiation sensitivity. However, it has been found lately that 

 this relationship is quite complicated and requires further 

 investigation. 



Anderson (1951) in our laboratory has studied the effect 

 of oxygen tension on the sensitivity to killing and mutation 



UJ 



o 



a 

 )Li 1.2- 



V) 



UJ 



o 

 I 10- 



6 



IT 



io8- 



< 

 z 

 o 



2 

 O 

 EC 



5o4 



02- 



400r AT50r/MIN. 

 A EXP I - CLONE 3 

 O EXP 2- CLONE 5 



„.-} 



5< n A 1 1 1 ^ 1 I I ' A ? I I 



10 20 30 40 50 60 70 80 90 KDO ioot.OjAT 



lAiR) ABSOLUTE PRESSURE 



PER CENT OXYGEN IN EXPOSURE CHAMBER OFisoomm h». 



Fig. 2. Relation between percentage of oxj-gen in exposure 

 chamber and frequency of chromosomal interchanges per cell in 

 Tradescantia microspores. All exposure to one X-ray dosage- 

 400 r at 50 r/min. Two separate experiments, one with clone 3 

 and one with clone 5 as indicated. Giles and Riley (1950), 

 Proc. Nat. Acad. Sci., Wash., 36, 337. 



production in two biochemical mutants of E. coli B, the 

 streptomycin-requiring and the purine-requiring strains. The 

 mutations produced by X-rays are reversions to streptomycin 

 and purine nondependence. Results of this work indicate 

 that the streptomycin-dependent strain has separate mecha- 

 nisms for X-ray mutation production and for killing; whereas 

 the purine-requiring strain apparently has a similar mecha- 

 nism responsible for both processes. 



