SUNBURN 



493 



near 0.25 n, after which it rises toward a new maximum. The general 

 shape of the curves, particularly the maximum at 0.28 /x, resembles that of 

 most unconjugated proteins. It may be concluded that the protein 

 component is principally responsible for the absorption. 



The true attenuation in the epidermis is difficult to estimate because of 

 the high degree of scattering. Different methods have been used for such 

 measurements, those that are optically satisfactory yielding results in 



024 



026 



34 



36 



028 030 32 



WAVE LENGTH.^ 



Fig. 13-2. Absorption by human epidermis. {After Blum, 1941a.) 



Ordinate units are chosen for convenience to bring the data into comparison. The 

 curves for epidermal attenuation, Nos. I, II, III, and IV, are plotted in terms of log 

 /o// in the same units, and are directly comparable. The data are from Lucas (1931) 

 for a sample of human epidermis 0.08 mm thick. Curve I is measured in water, 

 incident light parallel; this curve is dominated by scattering. Curve II, cleared in 

 glycerin, incident light parallel. Curve III, cleared in acetic acid, incident light 

 parallel. Curve IV, cleared in acetic acid, incident light scattered. 



Curve V is a typical protein absorption spectrum plotted in terms of log /o// but 

 with a different unit. Curve VI is the erythemal spectrum plotted as the reciprocal 

 of the erythemal threshold {\/Qt). {After Coblentz et ai, 1932.) 



good general agreement (e.g., Lucas, 1931 ; Pearson and Gair, 1931 ; Kirby- 

 Smith et al., 1942; for additional references including other regions of the 

 spectrum see Blum, 1945). Most measurements have been made on 

 whole epidermis, including both the corneum and malpighian layer. It is 

 possible by various means to strip off the whole epidermal layer (Baum- 

 berger et al., 1942), but separation of the two layers of the epidermis has 

 not been feasible. Pearson and Gair's measurements of the transmission 

 of bits of corneum separated from sunburned skin indicate that the greater 

 part of the incident erythemal radiation is absorbed in this layer, and the 

 character of the corneum and malpighian layer also suggest this (Kirby- 

 Smith et al., 1942). Therefore, probably only a relatively small fraction 



