LIGHT THERAPY MAYER 397 



is a structure that actively functions in the elaboration of keratin 

 from keratohyalin, and so ultimate explanations may be had as to 

 the effect of light in overcoming derangements from the normal in 

 metabolism. 



Acne vulgaris is less common in tanned skin than in untanned 

 skin. During an epidemic of chicken pox at Kollier's clinic, cutane- 

 ous vesicles were not found on tanned skin, whereas they did appear 

 on unexposed areas beneath plaster casts. Erythema of the skin 

 produced either by heat or by actinic radiations is accompanied by 

 transitory increased bacteriophagic and bacteriolytic power of the 

 blood serum and leukocytes for streptococci, pneumococci, and staphy- 

 lococci.^^ Following exposures to solar radiations and to artificial 

 sources of light, especially with combined exposures to moving air, 

 remarkable muscular tonus has been produced in unused muscles, 

 despite prolonged application of immobilizing casts. 



It is doubtful whether systemic effects resulting from local skin 

 irradiation are due to reflexes arising from stimulation of nerve end- 

 organs. No specialized receptors for ultra-violet rays have been 

 differentiated. Also the vasomotor reactions result just as readily 

 when denervated cutaneous areas are exposed to light. 



It is still debatable whether changes are produced in the blood 

 directly by penetrating rays. If so the visible and near ultra-violet 

 are responsible for systemic effects due to blood changes. 



It seems possible that hormones are produced in the skin because 

 a systemic effect, like the antirachitic, results from irradiation with 

 rays of which only approximately 10 per cent penetrate to the blood 

 vessels.^® 



The action of light on the body is in all probability largely an 

 indirect one by w^ay of the cutaneous cells, nerves, and blood vessels. 

 Ultra-violet rays for the most part are absorbed by the epidermis. 

 Deeper penetration of the longer visible rays and of the shorter 

 infra-red rays may allow of some slight direct action, but there 

 is little cause to believe that this can be of much direct therapeutic 

 value. Therefore, penetration should not be stressed as the factor 

 for the interpretation of physiologic effects. 



Heat rays and heat effects of luminous rays have been shown to 

 increase and hasten the effect of ultra-violet energy, but also experi- 

 ments *° have shown that red rays may act antagonistically to ultra- 

 violet. Thus cholesterol has become activated by ultra-violet rays so 

 as to contain the antirachitic vitamin; thereupon a successive ex- 



38 Eidinon, A., Brit. Journ. Radiology, vol. 31, p. 35, January, 1926. 

 *> See footnote 12. 



"Bovie and Klein (footnote 24). Clausen, Ethel M. L., Proc. Soc. Exper. Biol, and 

 Med., vol. 26, p. 77, November, 1928. Peck, J. L., Physiol. Abstr., vol. 10, p. 374, 1925. 



