292 



FACTORS MODIFYING THE SENSITIVITY OF CELLS 



sion and amino acid solutions. However, bacteria become more resistant 

 if irradiated in the presence of these compounds. There is a possibility 

 that the hydrogen peroxide attaches itself to the organic compounds, 

 especially amino acids, and thus makes itself less available to the bac- 

 teria. 



100 



0.001 



0.005 0.01 0.02 



Molar concentration of amino acids 



Fig. 4. Effects of amino acids, prepared immediately before irradiation and added to 



the suspension to be irradiated, on the survival of B/r at 60,000 r. [Hollaender, 



Stapleton, and Martin (11).] 



It appears that radiation probably produces a radical Avhich has a 

 relatively short life but exists long enough to diffuse through the medium 

 and into the bacteria or is produced in the cells themselves and dis- 

 tributed by diffusion. At present this radical could be HO2. However, 

 there may be other compounds formed by irradiation, the existence of 

 which is not yet established. 



