RADIATION INJURY AND LETHALITY 



457 



loss of growth capacity following massive exposures in terms of quantita- 

 tive measurements of this component. Another dose-dependent com- 

 ponent of injury is that of chromosome damage, which is considered 

 elsewhere in this volume (18). 



0.075 

 0.070 

 0.065 

 0.060 

 0.055 

 0.050 

 0.045 

 0.040 

 0.035 

 0.030 

 0.025 

 0.020 

 0.015 

 0.010 

 0.005 

 



-B 



__1 L I J J L_ 



10 20 30 40 50 60 



Fig. 



Time, days 

 10. Comparison of directly measured growth respon.se of male rats which re- 



ceived a .single dose of 200 r with the derivative of the response of male rats which 

 received daity exposure at a constant average rate of 13.7 r/day. The two curves 

 show similar phases in about the same time relations, but the single dose response 

 is always positive and does not return to the pretreatment origin. This must be 

 attributed to irreversible effects of large single doses of x-rays. Male Sprague-Dawley 

 rats, age 53 days and weight 150 gm at beginning of treatment. 



The conclusion we can reach on the basis of the above observations 

 is that the responses of physiological systems will in general be linear 

 only for disturbances which produce relatively small displacements from 

 the physiological steady state. 



