DAMAGE IN AEROBIC AND ANAEROBIC SYSTEMS 



37 



Loss of reproductive integrity by mammalian cells 



It is now clear that the radiation-induced loss of reproductive in- 

 tegrity by mammalian cells has much in common with the same phen- 



omenon n\ micro-organisms. 



o 



> 



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{_ 

 Zi 



en 



001 



500 1,000 



Dose (rad ) 



Fig. 6. — Colony-forming ability of human liyer cells after exjiosure to X-rays. (Dewey, 



1960 a) 



Without excej)tion so far, the reported log survival curves are 

 linear for all except the lowest doses and have small extrapolation 

 numbers — mostly ~ 2 and occasionally 4 ~ 6 have been observed. 

 Figure 6 presents the data of Dewey (1960a) for human liver cells 

 cultured and assayed by the technique developed by Puck, and 

 exposed to X-rays under various experimental conditions. 

 Figure 7 presents the data of Hewitt and Wilson (1959) for mouse 

 leukaemia cells grown and exposed to ^OQo y-rays in vivo and 

 tested for the ability of the irradiated cells to regenerate a tumour. 

 The shapes of all the curves in Figs. 6 and 7 are remarkably 

 similar, and for cells irradiated at the same oxygen tension the 

 difference between the slopes of the curves for human liver cells 

 and mouse leukaemia cells is close to that expected on account 

 of the different LET of the radiations to which the cells had been 

 exposed. 



The ratio of aerobic to anaerobic sensitivity for both types of 

 gell is ~ 2-5. In the case of the human liver cells a sensitivity 



