THE RESPONSE OF TISSUES TO CONTINUOUS IRRADIATION 



215 



At 50 rads/day the white cell count and platelet count, after an initial fall 

 and recovery, are generally maintained at normal levels or at levels only 

 slightly below normal until the animal dies at 150 to 200 days (Fig. 2). Studies 

 with s^Fe (Lamerton et al, 1961) have demonstrated an almost normal 

 erythropoietic activity after 140 days of irradiation. 



Effect of chronic irradiation on hybrid rats. SOrads per day 



I r I I I I I I I \ 1 1 L 



, J \ \ I 



20 40 60 80 100 120 140 160 180 200 



Days 



Fig. 2. Blood changes in young rats (6 to 8 weeks old) during continuous irradiation at 

 50 rads per day. 



It is of interest to study the response to a stress of the blood-forming 

 tissues in a continuously irradiated animal. The stress used has been removal 

 of one-third of the blood volume, by cardiac puncture, and Fig. 3 compares the 

 response of normal animals with those of the same age but irradiated at 

 50 rads/day for 130 days. It can be seen that the rate of haemoglobin recovery 

 is almost the same in normal and irradiated animals. One difference observed 



