STUDY OF THE INFLUENCE OF OXYGEN ON RADIO-SENSITIVITY 



At room tciiipcratuic our observations of the relation between radio- 

 sensitivity and concentration of dissolved oxygen {Figure 3) may be repre- 

 sented by the formula: 





= (^^-1) 



[O2] 



[0,1 + A' 



(J) 



when m is 2-8 and A' is 5 + 2[xM;'l. In this formula ocn is the aberration 

 coeflicient under strictly anoxic conditions, and [Og] is the concentration of 

 dissolved oxygen. At 37 °C the ()o, of the cells is about five times as high as 

 at IS^C. To obtain the same degree of accuracy in the control of dissolved 

 oxygen in the irradiated fluid as in the room temperature experiments 

 already described, it would therefore be necessary to work with a concentra- 

 tion of tumour cells slightly less than lO** per ml. This was not practicable 



20,- 



2 



OC-CCu. 



-Am-^) 



(0,) 



N i02)*K 



with m=2-7A K=5yM/\. 



50 



200 



-^v- 



1A00 



100 150 



(02)in }iM/[. 

 Figure 3. Ehrlich ascites tumour cells irradiated at 18^C in vitro 



at the time*. Observations made at 37 'C with higher cell concentrations, 

 with an estimated correction for the pressure diflferential between gas and 

 fluid phases conformed, within the limits of experimental error, with equa- 

 tion (7) without any change in the constants. Even though the calculated 

 allowance for the pressure differential is based on the measurements \\hich 

 were made at 18°C, it is subject to some uncertainty, and a substantial 

 diff'erence between the value oi K at 37 °C and at room temperature cannot 

 positively be ruled out. It is very unlikely that K is greater than 10 [j.M/1. 

 at37^C. 



The extremes of radio-sensitivity corresponding to complete anoxia and 

 to full oxygenation were measured at 3"C, 18"'C, and 36 X<, with results 

 given in Table I. The extreme sensitivity ratio m shows no systematic 

 variation over this large range of temperatures. 



* A means of working with concentrations as low as 10* per ml. has since been devised 

 and further work is in progress by the author in collaboration with Dr. Alma Howard and 

 Miss Christine Hawes. 



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