472 



JOHN W. G O W E N 



the number of genes not affected is equal to y, the original number of 

 genes is N, the X-ray dose in r. units is d, and 6 is a constant, this 

 equation becomes: 



y = Ne-"'^ 



The exposure of the blood cells of an organism to X rays is known 

 to change the frequency of the leucocytes in the blood. These 



tr 



UJ 



a. 



50 



:v 



20 



10 



\ 



\ 



^. 



DOSE 100 

 BACTERIA 



\ Ba 

 ^ 



\ 



200 400 



X RAY DOSE, r. 



600 



Fig. 8. Effect of X radiation in lowering the resistance of different mouse 

 strains to given doses of typhoid organisms. 



changes have pronounced effects on the resistance of the organisms. 

 Radiant energy has been used as a tool, for example, in altering re- 

 sistance to mouse typhoid disease. Mice of resistant and susceptible 

 strains have been irradiated and then inoculated with the disease 

 organisms. A plot of the results is sho^vn in Figm^e 8. The data are 

 quite irregular because of the difficulty of getting sufficient material 

 for test. A general linear trend downward in resistance is evident 

 wdth increased- irradiation. This would be expected if the X rays 



