250 FACTORS INFLUENCING CELL RADIOSENSITIVITY 



cells but not among the bacteria (Table 1). The significance of this 

 difference in behavior is not clear, and it probably will be useful to 

 check what happens in haploid yeasts, which (cf. p. 245) give no spon- 

 taneous recovery, whereas the above-mentioned diploid yeast gives some. 



TABLE 1 



Type of Radiation 



I. X-ray, X 1.54 A (Ka of the curve), 

 intensity 6250 r/min 



Yeast 

 A B 



Dose 12,500 r 

 44.8 

 2 22.8 

 5 11.2 



Bacterium 

 A B 



Dose 12,500 r 



77.7 

 2 80.5 

 5 78.6 

 7 83.4 



II. Same radiation 



Dose 5,000 r 

 55.3 



2 



7 



10 



13 



61.6 

 55.4 



68.7 

 60.0 



rDose 700 ergs/mm^ Dose 400 ergs/mm^ 



III. Ultraviolet radiation, X 2537 A, 

 intensity 26 ergs/mm^/sec 



60.0 

 46.4 

 32.0 

 32.4 

 29.0 



3 



7 

 10 



86.9 

 91.8 

 90.2 

 93.4 



A. Time at 5° C (in days). B. Number injured. 



Some Problems of Radio-Oxidations 



sensitization by oxygen 



According to a very early and well-tested observation (cf. 4, 23) 

 microorganisms capable of living either in aerobiosis or in anaerobiosis 

 are appreciably less sensitive to radiation when they live in the absence 

 of oxygen.* The same observation holds for cells of higher organisms 

 (25). This influence of oxygen is probably most evident when mammals 

 completely deprived of oxygen are irradiated in toto. In their experi- 

 ments, Lacassagne and Latarjet (12, 13) have taken advantage of the 

 remarkable capacity of newborn mice to resist for as long as 20 min 

 complete asphyxia with cessation of circulation and respiration and 

 complete anoxia of tissues. The animals can be irradiated during this 



* See Hollaender's paper. 



