DAMAGE TO REPRODUCTIVE CAPACITY OF HUMAN CELLS 



193 



with other systems namely that the oxygen effect is smaller for radi- 

 ations of high LET than for radiations of low LET Bora, 1958; Gray 

 et al, 1958; Neary et al, 1959). 



In Fig. 5 the sensitivity of these cells to :20() kV X-radiatioii is 

 given as a function of the oxygen concentration, whereby the sensi- 

 tivity of cells in equilibrium with pure nitrogen is taken as unity. The 



3 



- 2 



4-1 '■ 



o 



10 30 50 70 90 



120 



160 



200 382 760 



mm Hg 



Oxygen pressure in gas mixture of oxygen + nitrogen 



Y\G. 5. — Sensitivity to 200 kV X-radiation of human cells in equilibrium with gas mix- 

 tures which contain different percentages of O2 and N2. Sensitivity of cells in ec^uili- 



brium with pure nitrogen is taken as unity. 



shape of this curve is very similar to curves obtained with other 

 systems (Gray et al., 1958; Howard-Flanders, 1958). It can be repre- 

 sented api)roximately by 



8 7v+m[02] 



.S'„ (A'+[02]) 



where S is the radiosensitivity (l/i^s?) of cells in equilibrium with 

 oxygen concentration [O2], ^S'^ is the radiosensitivity in nitrogen and 

 m and K are constants. The value found from our curve for K is about 

 7 /xmoles/1. 



REFERENCES 



Barendsen, G. W., and Beusker, T. L. J., (1960). Radn Res. 13, 841. 



Bora. K. C. (1958). Proc. 2nd. Inf. Conf. Peaceful Uses Atomic Energy, Geneva, 195S. 22, 



88. 

 Elkind, M. M. and Sutton. H. (1959). Nature, Lond. 184, 1293. 

 Gray, L. H., Chase, H. B., Dkschner, E. E., Hunt, J. W., and Scott, (). C. A. (1958). 



Proc. '2nd. Int. Co7if. Peaceful Uses Atomic Energy, Geneva, 1958, 22, 413. 

 Hood. S. L. and Norris, G. (1959). Biochini. hiophys. Acta.. 36, 275. 

 Howard-Flanders, P. (1958). Advanc. biol. med. P/iys. 6, 553. 

 MoRKOviN, D., and Feldman, A. (1959). Brit. J. Radiol. 32, 282. 

 Neary, G. J., Tonkinson, S. M., and Williamson, F. S. (1959). Int. J. radn Biol. 1, 201, 



