976 RADIATION BIOLOGY 



Aberrations in the plasma constituents are rarely related in specific 

 experiments to changes in water distribution, or to renal and gastro- 

 intestinal function, and this aspect of radiation injury deserves study. 

 All the changes that have been described appear to be nonspecific reac- 

 tions to the injury, and some of these are undoubtedly mediated by the 

 pituitary-adrenal system. Yet, differences are apparent between these 

 radiation effects and the alarm reaction (Kohn, 1950, 1951a, b). The 

 pattern of change is said to be similar in young and adult animals and 

 is about equal in the rat and guinea pig after comparable exposure, 

 despite the greater sensitivity of the latter to the lethal action of radiation. 

 The inconsistency of the plasma changes following median lethal irradia- 

 tion, not only among different species but also among animals of the 

 same species, suggests, moreover, that these effects are not critical 

 parameters of radiation injury and probably do not constitute an impor- 

 tant cause of death. 



CARDIOVASCULAR SYSTEM 



The erythematous reaction of skin is not only the most evident but 

 perhaps also the most extensively studied circulatory response to radia- 

 tion, since it plays an important role in determining the course of radia- 

 tion therapy. It is well known that a smaller dosage of low-energy 

 radiation is necessary to produce skin erythema than of high-energy 

 radiation and that the biologic effectiveness decreases with protraction or 

 fractionation of radiation (Shields Warren, 1943c; Schottelndreyer, 

 1949; Larkin, 1941, 1942). The severity of the cutaneous erythema 

 depends, moreover, on the size of the radiation field (Shields Warren, 

 1943c; Jolles, 1941, 1950; Jolles and Mitchell, 1947). Erythema has 

 been described following exposure to the different qualities of radiation, 

 and there is little difference in the reactions that are produced (Miescher, 

 1938; Shields Warren, 1943c; Larkin, 1941, 1942). The 7 -to-X-ray 

 ratio of effectiveness for cutaneous erythema is about 1.3 (Mottram and 

 Gray, 1940). 



Waves of erythema were originally defined by Miescher (1924) and 

 may be seen in human skin during the first day, the second to third 

 week, and at the end of the first month after irradiation. Telangiectasis 

 may appear after heavy irradiation. Similar patterns occur in rabbit 

 skin after local exposure to X rays. With 1000 r, erythema is seen on the 

 first, fifth, and tenth postirradiation days (Painter et at., 1947). The 

 early cutaneous effects have been related to cell injury, the later erythema 

 to alterations in the vascular bed (Shields Warren, 1943c). An increase 

 in the number of patent blood vessels and dilatation of existing capillaries 

 and lymphatics may be noted in irradiated skin (Painter et al., 1947; 

 Borak, 1942a, b, c; Pohle, 1926, 1927; Pendergrass et al, 1944). The 

 bluish cast that is sometimes observed in a hyperemic area after heavy 



