36 



L. H. URAY 



The fact that a given concentration of glycerine is equally effective 

 in the presence of 1400^moles/l oxygen and in the presence of 14 

 /xmoles/1 oxygen, which is only a little higher than that necessary to 



D 



o 



o 



0-8 m/l. 



f 



k I 2 3 



Glycerine concentration 



-4 ^ 



053 

 0-47 



CO Molar 



Fig. 5. — Effect of glycerine on aerobic and anaerobic sensitivity of Serratin nuircescens. 



(Dewey, 1960 a, b) 



bring the bacteria to their maximum level of sensitivit}^ as far as oxygen 

 is concerned, shows that the mechanism involved is not one in which 

 glycerine and oxygen are competing for a radiation-induced radical. 

 It is fairly clear that the action of the glycerine is antecedent to that at 

 which oxygen enters into the reaction chain. 



One possibility which is at present under investigation is that, at the 

 molarities in question, the alcohol molecules compete with biologically 

 important molecules for radicals which result from the radiolysis of 

 water. If this hypothesis should prove to be correct, then it would 

 follow from the data presented in Fig. 5 that 0"47/r25 ( = 38) per cent 

 of the anoxic sensitivity ofSerratia marcescens is due to energy deposited 

 in the biological molecules themselves and 62 per cent to the radiolysis 

 of water. For cells in-adiated anaerobically the corresponding figures 

 would be 0'53/4: (= 14 per cent) for energy deposited in biological 

 molecules and 86 per cent for t]ie contribution from the radiolysis of 

 \vater, 



