Influence of Chemicals on Radiosensitivity 131 



media. This incubation period is not sufficient to allow cell 

 division to occur. Apparently, some nutritional factor is 

 present in these extracts which either partially reverses the 

 potential damage brought about by X- or gamma-rays or aids 

 in the adaptive process involved. These two suggested 

 mechanisms may actually be identical in the bacterial system. 

 The synthesis of ribonucleic and deoxyribonucleic acids, 

 and of proteins, was followed in non-irradiated and in irradi- 

 ated cells under the best and worst conditions for recovery, 



6.0 



4.0- 



53 



o 



tr 



LJ 

 M 



3 0- 



> 



DC 



± 2.0 



o 

 o 



1.0 



7 



I 



rU 



m 



7 



30 60 90 120 

 ACID- SOLUBLE 



30 60 90 120 30 60 90 120 30 60 90 120 

 RNA ONA PROTEIN-N 



INCUBATION TIME(min) 



Fig. 8. Relative rates of synthesis of nucleic acids and 



protein by irradiated (0) and non-irradiated (□) Esch. 



coli B/r on basal medium at 37° C. 



i.e., incubation at 18° C in a complete medium and at 37° C in 

 basal medium, respectively (Fig. 8) (Stapleton and Woodbury, 

 1955). Similar aliquots of cell suspension were inoculated into 

 the two media at the two temperatures; and after various 

 incubation periods the cells were- harvested, washed, and 

 extracted with trichloracetic acid, and analysed by the 

 Schneider technique as used by Morse and Carter. Irradiated 

 cells held in the basal medium at 18° C show no net synthesis of 

 deoxyribonucleic acid or acid-soluble components and a 

 reduced rate of synthesis of protein and acid-insoluble ribo- 

 nucleic acid. On the other hand, irradiated cells incubated 



