1032 



RADIATION BIOLOGY 



be recognized by present methods in any of the various species studied is 

 a reduction in the number of lymphocytes in the peripheral blood. In 

 general, this effect is not significant for doses below 25 r. The pattern 

 of acute radiation response of the rabbit lymphocyte following dosages 

 ranging from 25-800 r is shown in Fig. 16-1. The response of the 

 lymphocytes of the circulating blood of dogs, mice, monkeys, rats, and 

 guinea pigs is fairly comparable to that of rabbits. According to Valen- 

 tine et al. (1947), cats exposed to 200 r respond with a lesser lymphopenia 

 than do the species listed. Lymphocyte values in rabbits fall below 



8000 



CO 

 3hr 



CONTROLS 

 300 r 



6 8 20 40 60 



TIME AFTER EXPOSURE, days 



a m 25 r o a 50 r o 1 



« o 500 r o 



140 



100 r 

 700 r 



200 r 



600r « » 700r « e 800 r 



Fig. 16-1. Effect of single doses of total-body roentgen irradiation on the lymphocyte 

 values of the peripheral blood of rabbits. 



control values after 25 r and return to normal within 24-48 hours. With 

 doses of 50 and 100 r and above, a reduction occurs within 15 minutes, and 

 a maximum depression is reached by 24-48 hours. With dosages of 

 300 r and above, lymphocyte values approach the same minimum, and the 

 time required for recovery is a function of dose. Table 16-1 gives the 

 approximate mean time of recovery of lymphocyte values to normal 

 limits after dosages from 25-800 r. These data are in agreement with 

 those of Hayer (1934), Taylor et al. (1919), Thomas et al. (1919), Clarkson 

 et al. (1938), Linser and Helber (1905), Siegel (1920), Russ et al. (1921), 

 Russ (1921), and others. 



In all species the lymphocyte values of the peripheral blood are gen- 

 erally the last to return to normal levels. After a dose of one-half the 



