93(5 RADIATION BIOLOGY 



retarding effects of irradiation and also to increase the number of 

 dominant lethal mutations in irradiated Drosophila (Mottram, 1935a; 

 Crabtree and Cramer, 1933; Baker and Sgourakis, 1950). In larger 

 animals the results are equally confusing. Sensitivity of newborn mice 

 and rats to irradiation of the whole body or of the skin is decreased when 

 the ambient temperature is lowered during exposure (Lacassagne, 1942; 

 Hempelmann et al., 1949; Evans, Goodrich, and Slaughter, 1941; Evans, 

 Robbie, et al., 1941). Chilling of the adult animal does not increase the 

 survival rate, however (Hempelmann et al., 1949). Moreover, lethality 

 and cytological damage in the frog and tadpole are not influenced by a 

 change in body temperature during irradiation (Patt and Swift, 1948; 

 Aliens al., 1950). 



Evaluation of temperature effects during irradiation is complicated 

 since temperature may alter the quality as well as the quantity of cellular 

 activity, which, in turn, may modify the response to irradiation. Fur- 

 ther, reactions of injury and of recovery must rapidly follow the primary 

 events that are associated with the absorption of energy, and it is probable 

 that these secondary metabolic reactions appear in some degree even 

 before the irradiation is terminated. Since the time course and tempera- 

 ture coefficients of the subsequent biochemical changes may vary for the 

 different effects and systems, it is perhaps not surprising that many types 

 of temperature responses have been described. When there is little 

 metabolic activity initially, as in the unfertilized eggs of Nereis, the 

 temperature coefficient of the events occurring during irradiation, which 

 result ultimately in a lethal action, is found to be about 1.1 (Redfield 

 et al, 1924). 



Certain temperature effects may be attributed more directly to specific 

 changes, e.g., in blood flow or in oxygen tension. Sensitivity to radiation 

 is dependent upon the blood flow to the exposed area, and the beneficial 

 effects of chilling the skin can be ascribed to changes in the vascular bed 

 (Carty, 1930). Likewise, the decreased lethality of the chilled newborn 

 mammal may be a consequence of lowered oxygen tension resulting from 

 the relatively greater depression of breathing than of tissue respiration 

 in the cold. In contrast, the increase in dominant lethal mutations in 

 Drosophila irradiated in oxygen at 2°C over those treated in oxygen at 

 27°C has been related to the higher oxygen tension within the irradiated 

 sperm at the lower temperature (Baker and Sgourakis, 1950). Actually, 

 these two views are not incompatible. 



While it is true that fern spores and certain pollens show an enhanced 

 radioresistance at liquid air temperatures, perhaps because of altered 

 formation and diffusion of free radicals or of some change in the con- 

 figuration of organic molecules, there is reasonable evidence that less 

 extreme temperature changes do not directly influence the immediate 

 radiation reactions in living systems. Temperature independence over 



