B. RAJEWSKY 



respectively with a total dose of l,200r and a time interval of 24 hours 

 between the two part-doses of 600 r each. 



1 ' ' 



. 7200 T A (65 animals) 

 1 t 



600 r BOOrB (66 animals) 



Figure 9. Percentage of animals dead at different limes after single and fractionated 

 whole body irradiation {total dose l,200r). A single irradiation, B fractionated 

 irradiation with two 600 r doses at 24-hours interval 



It is not the mean survival time that is shown in this diagram, but the 

 percentage of animals which died at different days after irradiation. A clear 

 effect of fractionating of the dose is apparent. 



SUMMARY 



The dose-mortality curve for whole body irradiation of white mice has been 

 determined over the range from 250 r to 200,000 r. The dose mortality 

 curve obtained can be divided into several dose ranges and may be connected 

 with difTerent mechanisms of damage. Irradiation of rats and guinea-pigs 

 showed that the dose efTect curves were similar to that found for mice. With 

 very high doses the survival time is decreased to times which correspond 

 practically to instant death. 



The mortality curve in the dose range of approximately l,000r to 1 5,000 r 

 shows a plateau where life span of the irradiated animals remains inde- 

 pendent of the dose. It could be shown by irradiation with lead-shielding 

 of part of the body only that this dose range contains three different constant 

 survival times, corresponding perhaps to three different mechanisms of 

 action : (a) 3-5-day efTect (whole body irradiation and trunk irradiation), 

 (b) 5-day effect (irradiation of the central trunk region), (r) 7-day efTect 

 (irradiation of the head). 



By irradiation of difTerent parts of the body through a slit v/e could localize 

 the efTects mentioned above, in certain regions of the body. Since irradia- 

 tion of certain localized strips of 5 mm width were sufficient to cause these 

 efTects without irradiation of the other parts of the body. 



The irradiation of animals from which single organs had been removed 

 before irradiation and irradiation of some organs in situ have shown that the 

 adrenal and the pituitary glands are of decisive importance in regard to the 

 development of the 3-5-day and the 7-day efTect respectively. In the cases 

 of the adrenalectomized and hypophysectomized animals no dose-inde- 

 pendent ranges were found and survival time was strongly dose dependent. 

 Irradiations of these organs alone (exteriorized or in situ) did not decrease 

 survival time significantly. Apparently not only injury of the organ itself 

 but also disturbances of the functional systems in which it participates are 

 necessary for the lethal efTects to occur. Treatment with cortisone of the 



91 



