PHYSIOLOGY OF RADIATION INJURY 1001 



there is a negative nitrogen balance (Prosser, Painter, Lisco, et al., 1947; 

 Prosser, Painter, and Swift, 1947). These findings are suggestive of a 

 shift in favor of catabolism. 



Organ weights provide a reasonable index of tissue breakdown and 

 repair after irradiation. The most pronounced changes are seen in the 

 lymphoid organs and testes (Carter, Harris, and Brennan, 1950; Eschen- 

 brenner and Miller, 1950). The weight of the gastrointestinal tract is 

 also decreased (Painter, 1948; Ross and Ely, 1949a) as is the volume of 

 available marrow (Brecher et al., 1948). Muscle and kidney, on the 

 other hand, undergo little change, while the adrenals are increased in 

 size (Patt et al., 1947). Changes in thymus, spleen, and testis are useful 

 as biological dosimeters especially after low dosages; the differences in 

 organ weights are relatively slight, however, over the narrow range from 

 just lethal to completely lethal. 



The finding that weight loss of the irradiated dog cannot be accounted 

 for by decreased food intake (Prosser, Painter, and Swift, 1947) is sug- 

 gestive of an increase in catabolism. In the rat, however, change in 

 body weight appears to be related directly to anorexia (Ely and Ross, 

 1947; D. E. Smith, Tyree, Patt, and Bink, 1951). Identical weight 

 losses have been observed, moreover, in starved and in starved-irradiated 

 rats (D. E. Smith, Tyree, Patt, and Jackson, 1951). Since lethal irradia- 

 tion does not influence the water content of muscle or the entire carcass of 

 the starved rat, it is apparent that water retention cannot be responsible 

 for the failure to find a greater depression of body weight in the starved- 

 irradiated animal. Extracellular water may be increased after lethal 

 irradiation, but the changes in total extracellular space are similar to 

 those seen in starvation (Painter, 1948). Tissue breakdown associated 

 with irradiation, as with starvation, does not result invariably in elevated 

 metabolism. Although direct evidence of an increase in the metabolic 

 rate of irradiated rats has been presented (Kirschner et al., 1949), changes 

 in oxygen consumption do not coincide with weight loss. Other investi- 

 gators have been unable to verify the increase in metabolic rate in mice, 

 rats, guinea pigs, or frogs (D. E. Smith, Tyree, Patt, and Jackson, 1951; 

 W. W. Smith and Smith, 1951b; Pratt et al, 1950; Patt, Swift, and 

 Tyree, 1949) . Measurements of oxygen consumption have not been made 

 during the terminal febrile period in dogs. 



Oxygen utilization may actually be depressed, at least in certain tissues, 

 since the irradiated mouse is said to be more resistant to progressive 

 asphyxia than the nonirradiated (W. W. Smith and Smith, 1951b). It is 

 of interest that the respiratory rate of tissues obtained from irradiated 

 animals or of tissues irradiated in vitro is either unchanged or decreased 

 (Wels, 1924; Crabtree, 1935; Goldfeder and Fershing, 1938; Barron, 

 1946; Barron et al., 1947; DuBois, unpublished observations, 1950). An 

 exception to this is the brief increase in respiration that has been seen in 



