Influence of Chemicals on Radiosensitivity 127 



medium effect. This finding illustrates that both points of 

 view may actually be correct. 



2. Extracts of natural materials (e.g., beef, yeast, or other 

 tissue extracts) yield higher survival than that obtained on a 



y RAYS. 85 kr 



°\ BASAL MEDIUM ♦ YEAST EXTR 



-1 1 r 



18 30 



INCUBATION TEMPERATURE (°C) 



Fig. 6. Comparison of viability on basal 

 medium and basal medium plus yeast extract 

 as a function of postirradiation incubation 

 temperature. (Stapleton, Sbarra and Hol- 

 laender, 1955.) 



simple inorganic salts-glucose (Fig. 7.) medium, although the 

 latter medium is not limiting for normal (non-irradiated) 

 cells. 



3. Attempts to isolate the required materials indicated a 

 multiple requirement. 



4. A complex, chemically defined plating medium (Table 

 I) will, to a high degree, substitute for the natural materials. 



