746 



RADIATION BIOLOGY 



4. The percentage of increase in aberration frequency above this base 

 line depends on the percentage of oxygen present during irradiation. 

 This relationship is approximately linear between and 10 per cent oxy- 

 gen, after which the increase in aberration frequency becomes more 

 gradual, until an approximate plateau is reached at 21 per cent. Data 

 for chromosome interchanges at a constant dose are given in Fig. 10-10. 

 Similar results have been reported by Baker (Hollaender, Baker, and 

 Anderson, 1952) for reciprocal translocations detected genetically in 

 Drosophila virilis. 



5. The effect of oxygen in increasing the yield of X-ray-induced 

 aberrations is an immediate one. This has been demonstrated by experi- 



O 



or 



UJ 

 Q. 



to 



LlJ 



< 

 O 



1.1 - 



0.9 



0.7 



0.5 



o 



o 



o 

 q: 

 i 

 o 



0.3 



0.1 



AA A 7, A I I " I "" 



10 20 30 40 50 

 (AIR) 



60 70 80 90 



— TT 



100 



PERCENTAGE OF OXYGEN IN EXPOSURE CHAMBER, 

 NORMAL ATMOSPHERIC PRESSURE 



Fig. 10-10. Relation between percentage of oxygen and yield of X-ray-induced 

 chromosome interchanges (400 r at 50 r/min). (Giles and Beatty, 1950. Figure 

 reproduced by permission of the authors and the editor of Science.) 



ments in which a rapid introduction of oxygen into cells during irradi- 

 ation is effected. It has also been shown that the removal of oxygen 

 during irradiation results in a decreased aberration yield. Data for 

 chromosome interchanges are presented in Table 10-2. 



6. The effect of pressure during irradiation depends on the amount of 

 oxygen present in the gas mixture used. These studies provide further 

 evidence that the increase in aberration frequency is related to the actual 

 amount of oxygen dissolved in the cells. 



7. Irradiation in pure hydrogen at normal pressure and under three 

 atmospheres of pressure effects little or no significant decrease in aber- 

 ration yield. 



