LIGHT THERAPY MAYER 391 



posure of the germinal layer may lead directly to blistering. There 

 is greater variation in percentage penetration of ultra-violet than 

 in other parts of the spectrum. At 280 millimicrons the absorption 

 in the corneal and prickle cell layers is marked so that the great 

 antirachitic effect of this wave length must occur in or about these 

 layers ; but on both sides of this band, around 300 millimicrons and 

 250 millimicrons, the penetration is greater, more radiation reaching 

 the malpighian layer and corium, thus indicating that erythema 

 production occurs in the germinal layer of the corium under the 

 shadow of the upjjer layers. The corneal and granular layer, there- 

 fore, must play an important part in the light protection of these 

 sensitive layers. From 250 millimicrons down the absorption in 

 the corneal layer increases rapidly and at 200 millimicrons the ab- 

 sorption is so complete as to prevent any radiation from reaching 

 the living layers of the skin.^'* 



Grotthus' law states that a chemical reaction can not occur unless 

 suitable radiations are absorbed. Hemoglobin absorbs ultra-violet 

 rays as well as many of those of longer wave lengths up to approxi- 

 mately 450 millimicrons. Blood serum absorbs the ultra-violet rays, 

 possibly chiefly because of its tyrosine and tryptophan content. The 

 ultra-violet rays necessary for the prevention and healing of rickets 

 and the production of erythema are those below the region of about 

 320 to 313 millimicrons.^^ This region defines also the approximate 

 upper limit of the bactericidal rays, although some experiments 

 have shown bactericidal action with wave lengths at 365 milli- 

 microns.^'' Ultra-violet rays of sunlight extend in their lowest limit 

 to 290 millimicrons,^^ but lamps have some additional bands around 

 260 millimicrons that produce a fleeting erythema, as well as strong 

 bactericidal rays at 265 millimicrons (fig. 2). 



The brownian movement of protoplasmic colloidal particles ceases 

 when exposure to ultra-violet rays coagulates the protoplasm.^^ Egg 

 and serum globulin have been said to be formed from albumin under 

 ultra-violet irradiation. Lens albumin previously sensitized by cer- 

 tain salts, such as calcium, sodium, and magnesium, silicates, or 



"Bachem, A., and Reed, C. I., Amer. Journ. Physiol., vol. 97, p. 86, April, 1931. 



J= Sonne, Carl, and Rekling, Eigil, Hospitalstid, vol. 70, p. 399, Apr. 28, 1927. Hess, 

 A. F., and Weinstock, Mildred, A Study of Light Waves in Their Relation to Rickets, 

 Journ. Amer. Med. Assoc, vol. SO, p. 687, Mar. 10, 1923. Hess, A. F., and Anderson, 

 W. T., The Antirachitic Activity of Monochromatic and Regional Ultra-violet Radiations, 

 idem, vol. 89, p. 1222, Oct. 8, 1927. 



" Coblentz, W. W., and Fulton, H. R., A Radiometric Investigation of the Germicidal 

 Action of Ultra-violet, Amer. Journ. Elcctroth. & Radiol., vol. 43, p. 251, July, 1925. 



" Sheard, Charles, Ultra-violet Radiatien and Its Transmission by Various Substances, 

 Journ. Amer. Med. Assoc, vol. 88, p. 1315, Apr. 23, 1927. 



18 Burge, W. E., Amer. Journ. Physiol., vol. 43, p. 429, June, 1917. Bovie, W. T., Chem. 

 Zeitg., vol. 37, p. 1486, 1913. 



