130 Alexander Hollaender and George E. Stapleton 



medium as was obtained on fortified media by cells harvested 

 from nutrient broth. 



2. Cells harvested from basal media to which amino acids 

 or purines and pyrimidines were added showed requirements 

 for these materials after irradiation. Amino acids were most 

 effective. 



3. Cells harvested from nutrient broth showed the most 

 clear-cut dependence of survival on the supplemented medium 

 following irradiation. 



Data on the effect of growth conditions prior to irradiation 

 on the subsequent postirradiation requirements suggested 

 that a sizeable part of the process called "recovery" is related 

 to an adaptive process, and probably involves new enzyme 

 synthesis. Cells that have been grown in a simple medium 

 prior to irradiation might be expected to have a different 

 complement of enzymes from those grown in a nitrogen-rich 

 medium such as beef extract. The former cells have had to 

 synthesize not only all metabolic precursors and inter- 

 mediates from carbon fragments and ammonia but, probably, 

 also the enzymes necessary for these synthetic reactions. 

 The latter cells have had numerous intermediates supplied to 

 them continuously during growth and, therefore, have prob- 

 ably been able to by-pass many synthetic reactions. They are 

 essentially undeveloped or deficient cells. Non-irradiated 

 cells, if transferred from a rich medium to the basal medium 

 can adapt readily to the simple medium; but, interestingly, 

 irradiation appears to interfere with such an adaptation. 

 According to these studies it would seem that under optimal 

 conditions — (1) reduced incubation temperature and (2) 

 the presence in the postirradiation medium of precursors for 

 ribonucleic acid and protein synthesis — a reasonably large 

 fraction of the irradiated population appears to be able to 

 perform the required syntheses. 



Short-term incubation of irradiated cells with extracts of 

 natural materials (15-30 minutes at 37° C) prior to plating, 

 results in loss of dependence of the cells on the plating 

 medium. Quantitatively similar survival is obtained on both 



