STUDY OF rm: influence of oxygen on R.\1)I0-SENSITI\ l iy 



Table 2. Composition of gas in <<|iiilil)iiiiiii wiili lliiid In the I'ciitDiical (a\ily 

 of mice and rdalcd alxuatidii locliiciciits 



quantities of hydrogen peroxide are introduced into the peritoneal cavity 

 the fluid becomes a mass of small bubbles of oxygen, resulting mainly from 

 a decomposition of the hydrogen peroxide by the catalase present in the 

 red blood cells. This was found to be a very effective way of raising the 

 oxygen tension throughout the cavity, but was obviously incompatible with 

 a measurement of the actual oxygen tension in the cavity by our bubble 

 technique. The treatment did not raise the spontaneous aberration fre- 

 quency appreciably above the usual 5 per cent level. The radio-sensitivity 

 of tumour cells irradiated in the peritoneal cavity in the presence of hydrogen 

 peroxide are shown in Table 2. The value of the anaerobic aberration coeffi- 

 cient a^i is that observed in vitro. It is seen that the average sensitivity of 

 tumour cells in the peritoneal cavity of an animal breathing 8-5 per cent 

 oxygen barely exceeds the completely anaerobic value, and is only 20 per 

 cent greater than the anaerobic value in an animal breathing air. Admin- 

 istration of oxygen increases the average sensitivity to 60 per cent above the 

 anaerobic value. By the administration of hydrogen peroxide, the average 

 sensitivity may be raised to a level only slightly below that of cells irradiated 

 in vitro in the fully oxygenated condition. 



When values of radio-sensitivity and of the bubble oxygen tension in the 

 peritoneal cavity in each of the 44 irradiated animals are compared indi- 

 vidually, however {Figure 4), a very wide scatter is revealed. In only a few 

 animals did the radio-sensitivity approach the value, shown by the upper 

 broken line, which would have been observed in vitro for cells at the oxygen 

 tension recorded by the bubble. In most animals, radio-sensitivity is much 

 lower than that corresponding to the bubble oxygen tension, Init in none 

 is it significantly below the in vitro anaerobic level. Since most, and in some 

 cases all the fiuid in the peritoneal cavity of an irradiated animal was injected 

 into new hosts and scored for chromosome abnormality, the mean of all such 

 scores must relate to the average condition of the whole fluid. We have noted 



82 



