SUNBURN 



501 



flushing after severe superficial burn from heat, when the skin may be 

 blanched in the area of the burn. Although the inhibition of erythema is 

 experimentally demonstrable only with severe doses of these longer wave 

 lengths of the erythemal spectrum, it seems reasonable to assume that 

 they exert some inhibitory effect even at much lower doses and hence may 

 influence the erythemal threshold when determined with polychromatic 

 radiation. Partial inhibition of dilation of the minute vessels by the 

 longer wave lengths would raise the observable erythemal threshold to 



24 



026 



028 



034 



36 



038 



30 32 



WAVE LENGTH,// 



Fig. 13-7. Transmission of human and of mouse epidermis. Mi is from ear of normal 

 young mouse; M^ from ear of mouse subjected to repeated exposures to ultraviolet 

 radiation. Hi from untanned volar surface of human forearm; Ho from slightly 

 tanned volar surface of the same forearm; H3 from heavily tanned dorsal surface of 

 forearm. All measurements are for transmitted radiation collected at 45°, epidermis 

 not cleared. The transmitted radiation collected at 180° would be somewhat greater. 

 (After Kirhxj-Smith et al, 1942.) 



these wave lengths. This would in effect negate Eq. (13-14) by making 

 the response to the dilator substance effectively wave-length dependent. 

 Another explanation may now be based on the finding by Rottier (1952) 

 and Rottier and Mullink (1952) that dilator substance is formed in the 

 corneum. Our simple model does not take this into account, but could be 

 extended to do so by making additional assumptions. If the dilator sub- 

 stance formed in the corneum were different from that formed in the mal- 

 pighian layer and its action on the vessels differed quantitatively, or if the 

 rate of formation and diffusion to the vessels were quite different in the 

 two cases, the relation in Eq. (13-14) need not hold. This is another 

 possible explanation of the discrepancy that has been bothering us; per- 

 haps both explanations are pertinent to the complex response studied 

 in sunburn. 



