A Study of Aging, Thermal Killing, and Radiation Damage by Information Theory 305 



by the results obtained for x-ray and thermal kilhng of diploid yeast and other 

 organisms. 



T. H. Wood (24, 25, 39) has reported data on the x-ray survival and thermal 

 killing of yeast, since repeated and verified by Uretz (15). The data for diploid 

 yeast are given in Fig. 4 and A is the time at the indicated temperature or the 



MINUTES AT TEMP 

 10 15 20 



0.002 



0.001 



60 90 120 180 



MINUTES AT 425 r PER MINUTE 



240 



Fig. 4. Thermal and radiation killing of yeast from Wood (25, 39). Note that the 



abscissa is plotted as the square of time at temperature indicated or at 425 r per 



min. Straight lines drawn for comparison only. 



X-ray dose as the case may be. The data have been fitted, using Kimball's 

 method (40), to several curves and the results are shown in Table I. 



The function log ///q = n log [2e 



-M 



— e 



-2k„X 



■'' ] was derived from hit-theory 



by LuRiA and Dulbecco (41) and used by Zirkle and Tobias (20) and by 

 Wood (39). We have fitted Wood's data allowing k^^ to be determined internally 

 by the diploid data and obtain the values shown. When the haploid value 

 nkf^ = 2.49 X 10 * r^^ is imposed on the diploid data n = 21.3; x^ = 5.1; 

 P > 0.5. Wood obtains graphically the slightly different values shown in 

 Table I. It is clear from Fig. 4 and Table I that the term in ?? represents sub- 

 stantially, if not completely, the behavior of the survival curve as a function of 

 dose. The fact that the fit may be made satisfactory by including a small term 

 in either /.^ or A* supports this conclusion. 



