.500 



RADIATION BIOLOGY 



suhso<nieiit lilistoriiifi and (l('s(|uaniali()ii tlial followed the liiji;h doses of 

 the longer waxc Iciiglhs likewise showed no such optimum. It therefore 

 .seems that only the erytiiema is inhibited, not the underlyinf; photo- 

 chemical reaction as reflected in other aspects of sunburn. This point of 

 view was supported by results of furthei- experiments. Doses of short- 

 wa\-e-leiigth erythemal radiation (0.2537 n) sufricicnt to elicit erythema 

 were first given (A,B,C). Then, before the erythema had had time to 

 develop, doses of the longer wave lengths of the erythemal spectrum 

 (^0.29 0.32 /i) were applied across the same areas (D,E,F). The 



B: 

 C: 

 D: 

 E: 

 F: 



Fig. 13-6. Result of exposure to the longer wave lengths of mereury arc (filtered 

 through pyrex) (D,E,F), after exposure to wave length 0.2537 fx (.\,li,C). 

 A: 1.1 ergs cm"^ X 10* of "erythemal effective energy" 

 3.9 ergs cm~- X 10* of "er3^thenial effective energy" 

 8.3 ergs cm"^ X 10* of "erythemal effective energy" 

 15.4 ergs cm~^ X 10* of "erythemal effective energy" 

 35.2 ergs cm"^ X 10* of "erythemal effective energy" 

 52.2 ergs cm"^ X 10* of "erythemal effective energy" 

 Doses D, E, and F were applied approximately 15 min after A, B, and C. The 

 diagram represents the various degrees of erythema 2^^ hr after the last exposure. 

 Note inhibition of erj'thema in areas 5, 6, 8, and 9. {After Blum and Terus, 1946a.) 



latter inhibited the erythema ordinarily resulting from the former, as 

 indicated in Fig. 13-6. The whole of the areas that received the heavy 

 doses of the longer-wave-length radiation subsequently underwent 

 blistering and destjuamation. 



The inhibition of erythema without inhibition of sunburn as a wh()l(\ 

 was interpreted as resulting from a direct effect of the longer wave lengths 

 of the erythemal spec^trum on the minute vessels of the skin, limiting their 

 response to the dilator substance formed in the epidermis. The trans- 

 mission spectra for human epidermis presented in Fig. 13-7 show that the 

 longer wave lengths of the erythemal spectrum do penetrate below the 

 epidermis to a certain extent and could act directly on the mirmte vessels. 

 The inhibition of erythema would seem comparable to the inhibition of 



