390 ANNUAL EEPOET SMITHSONIAN INSTITUTION, 19 32 



fever. The infra-red and visible rays produce, through heating, a 

 dilatation of superficial capillaries and an increased blood flow and 

 exudation of lymph; ^° but, apart from their heating effect, the 

 rays do not destroy cells except when cells which have been sensitized 

 by such substances as eosin and hematoporphyrin are exposed to 

 visible rays." Their heat effects may aid the action of the ultra- 

 violet rays on body cells. 



The heating effect of visible and near infra-red rays must be mild 

 on account of the small absorption in the epidermis and the strong 

 convection by the blood stream. The heat produced by the far 

 infra-red is slowly conducted to the deeper layers and up to the sur- 

 face and carried away by the blood stream and air. Temporary 

 heat erythema is not strictly local, in contrast to the delayed ery- 

 thema of sunburn, which is limited sharply to the exposed area, due 

 to local tissue changes of the nature of degeneration of the prickle 

 cell layer resulting in capillary stasis, diapedesis of leukocytes, and 

 other signs of inflammation to the degree of blistering. Higher tem- 

 peratures have produced increased oxygen consumption and greater 

 local acidity of tissue, which can cause vascular dilatation. 



Irritation of the skin gives rise to three responses; namelj', local 

 vasodilation, a wheal, and finally, under severe action, a local edema 

 and blistering. This triple response, according to Lewis, is provoked 

 directly by a substance (H) similar to, if not identical with, his- 

 tamine. The primary effect of irradiation in producing evidences 

 of inflammation has been concluded by some to be an injury to the 

 capillary endothelium; by others this is considered secondary to 

 irritation by the toxic products of prickle cell degeneration. 



Blister production that results from great increase of permeability 

 may serve a protective function, since the fluid absorbs greatly in 

 the region of 280 millimicrons.^^ 



Ultra-violet rays are rapidly absorbed, in most part, by tissues 

 of a depth of less than 1 mm and produce marked chemical changes. 



In penetrating through human skin visible and near infra-red 

 rays are strongly absorbed by the blood of the corium and sub- 

 cutaneous layers. The local heating effect is rather mild on account 

 of the small absorption in the epidermis and the strong convection 

 by the blood stream. The far infra-red has little penetrating power, 

 most of it being absorbed in the epidermis.^^ The heat produced is 

 slowly conducted away by the blood stream and by air. Overex- 



^0 Hausmann, Walther, and Sonne, Carl. Strahlentheraple, vol. 25, p. 174, 1927. 

 " Hess, A. F., The Ultra-violet Rays of the Sun, Journ. Amer. Med. Assoc, vol. 84, p. 

 1033, Apr. 4, 1925. 



" Bachem and Reed, Arch. Physical Therapy, October, 1931, p. 581. 

 " Miescher, G., Strahlentheraple, vol. 35, p. 403, 1930. 



