B. RAJEWSKY 



Three interrelations for the 3 • 5-day effect seem possible : 

 (7) An important organ of the body is critically injured after application of 

 a certain dose. The injury requires a latent period of 3-5 days until death 

 takes place. Further injuries, which appear when the dose is increased, 

 take a longer time to be lethal and are therefore without any significance 

 as regards the 3 • 5 day effect. 



(2) After reaching the minimum dose in the independent range a process 

 is started in the body of the irradiated animal by various irradiation injuries, 

 which finally causes the death of the animal within 3-5 days. 



(3) The changes produced in the body in the dose-independent range are 

 of such kind that continued injuries are compensated by the function of one 

 or several organs. This system of compensation breaks down if a much too 

 large dose is applied. 



Based on the studies of Miller, Hammond, Tompkins and Shorter^, 

 injury of the intestine, leading to an increased permeability to bacteria and 

 consequently to bacteraemia, appears as a possible mechanism, and 

 Quastler (verbal communication), after confirming the 3-5-day effect, 



Table I. — Effect of antibiotics on survival time 



believed that it is mainly due to damage of the intestinal epithelia. It was 

 necessary, therefore, to examine this question. For this purpose white rats 

 and white mice were treated with penicillin and streptomycin before 

 irradiation and then were irradiated with different doses. The 3-5-day 

 effect was maintained and the treated animals showed no significant differ- 

 ence from the untreated animals [see Table I). Blood cultures from the 

 control and antibiotic-treated animals were all negative. 



Consequently bacteraemia cannot be the cause of the 3-5-day effect. 



The two other possibilities mentioned above were therefore examined 

 using a different technique of lead shielding. The experiments were 

 carried out in such a way that in one series the amount of shielding of the 

 animal's body was increased progressively from the cranial end. In the 

 other series shielding was started at the caudal end portion and increased 

 towards the head. 



As can be seen from Figure 4A the two injury curves overlap at a point 

 which corresponds to a life span of 3-5 days ; (/) shows both the 3-5-day 

 and the 7-day effect, while from the other curve (//) only the 3 • 5-day effect 

 can be observed, which hides the 7-day effect in whole body irradiation. 



85 



