THE PHYSIOLOGICAL RESPONSE TO RADIATION AND TO RADIOMIMETIC CHEMICALS 



400-600 r but less often with smaller doses of X-radiation. From about the 

 twelfth day after treatment the animal loses weight fairly steadily for a vary- 

 ing period often extending to about the twentieth day after irradiation. 

 The most important blood effect connected with phase III is the fall in red 

 cells. This fall commences about the middle of phase II but the minimum 

 is reached at about the end of phase III. There is a correlation between the 

 fall in red cells and the second weight drop, and the severity of the anaemia 

 is probably the main factor in determining the magnitude (L2) of this 



8 10 12 -f^ 16 18 20 22 2f- 2e 28 



da_ys 



'-2 2 f 6 

 Figure 1. Weight and Blood Response to X-irradiation 



weight loss. The relation of the anaemia to the fall in platelets which 

 occurs during phases II and III has been discussed by Lamerton and 

 Baxter^. During phase III the lymphocytes and neutrophils continue their 

 rise towards normal values. Phase IV is the final recovery phase. The 

 animal resumes its normal growth at the same rate as before irradiation. 

 Red cells recover steadily and lymphocytes and neutrophils soon regain 

 their normal values. 



With toxic doses of radiation death occurs either during phase I or phase 

 III. Examples of growth curves of individual rats showing variations of 

 pattern which may occur are given in Figure 2. 



236 



