246 E. Y. GRAYEVSKY, et Cll. 



repeated treatments corresponding to the total dose. This holds true 

 for radiomiitations (Kaufman, 1954) and, apparently, takes place in 

 liver cells resting after irradiation. In this case the number of cells with 

 aberrations (judging from the percentage of cells with anaphase 

 bridges and fragments) did not change during interkinesis and the 

 effects of repeated exposure were additive (Shapiro, 1959). 



The importance of environmental conditions as a factor promoting 

 or preventing the manifestation of radiation damage of cells has been 

 shown also in experiments on P. caudatum (Litvinova, 1959a, b) and 

 on E. coli (Hollaender, 1957). Changing the temperature of incubation 

 (for paramecia) or the concentration of salts in the medium {ior E. coli) 

 significantly altered their reaction to radiation. 



III. SOME QUESTIONS OF RADIATION PROTECTION 



1. The action of protective agents takes place at the cellular level. 

 This conclusion is based on the following data : 



(a) Local cooling of the rat skin (Evans et al., 1942), clamiiing the 

 tail (Howard-Flanders and Wright, 1957), limbs (Zherebrenko et al., 

 1959) or vessels of some internal organs (Weiss, 1959; Osborne and 

 Solem, 1959; Martin, 1960) exert a distinct protective effect on corres- 

 ponding organs and tissues. 



(b) Application or injection of some substances has been shown to 

 lower the radiation injury in the region of treatment (Forssberg, 1950; 

 Kublitska'a, 1951; Fogh, 1960). 



(c) Protective agents decrease the action of radiation on somatic 

 (Bases, 1959) and tumour cells (Gray et al., 1953; Conger, 1956; 

 Tolkacheva, 1959) growing in vitro and on some plant cells (Lea. 1955; 

 Giles and Riley, 1950; Thoday and Read, 1947, 1949), unicellular 

 animals (Bacq et al., 1952) and micro-organisms (Hollaender and 

 Stapleton, 1953). 



According to our data, the action of various radiation protective 

 agents is postulated to be related to the local defence of cells in radio- 

 sensitive systems. Cytological analysis of haematopoietic organs in 

 mice irradiated with 700 to 1000 r in an atmosphere of carbon monoxide 

 showed that (a) the process of cell destruction in the bone-marrow was 

 significantly less: the number of cells preserved was about 1-5 to 2 

 times that in the unprotected control (Barakina, 1957, 1959c); (b) the 

 regeneration of haematopoietic tissue proceeds much more rapidly than 

 in the control (Barakina, 1957). The acceleration of the regeneration 

 in this case is probably related to the preservation of a larger number 

 of viable cells and to their more rapid multiplication judging from the 



