DAMAGE TO REPRODUCTIVE CAPACITY OF HUMAN CELLS 



191 



Melinex bottom. Gas mixtures containing different amounts of O2 and 

 N2 saturated with water vapour were then i)assed over the cells for 

 various lengths of time. No differences in reduction of the sensitivity 

 to X-radiation were observed when the gas mixtures were passed over 

 the cells for 5, 10, 15 and 25 min resi)ectively. It was concluded that a 

 time of 5 min was sufficient for the cells to reach equilibrium with the 

 gas phase. In the experiments summarized in Table I gas was passed 



Table 1. — Relative numbers of cells as percentage of unirradiated con- 

 trols, ivhich have retained the capacity for clone formatio7i after irradiation 

 in gas mixtures of various proportions of oxygen and nitrogen. 



over the cells for 10 min before the irradiation was started. In this table 

 surviving fractions are given for oxygen concentrations in the mixture 

 of 100, 50, 20, 10, 5, 2-8, 1-5, 0-9, 0-3 and per cent. The nitrogen from 

 the cylinder used was found to contain 0-3 per cent O2. This oxygen w^as 

 removed with a "BTS-katalysator"t. It may be concluded that with 

 oxygen concentrations between 10 and 100 per cent no statistically 

 significant differences in radiosensitivity are observed. With gas mix- 

 tures which contain less than 5 per cent O2 the radiosensitivity of the 



t Badische Anilin und Soda Fabrik. 



