ORGAN AND BODY SYSTEMS 479 



Ultra-violet rays have so slight a power of penetration that their 

 effects are limited to the skin and superficial structures (191). Other 

 effects, such as chemical changes induced in the blood, must come about 

 through the absorption of the radiation in the capillary screen imme- 

 diately beneath the skin. Keller (173, 174, 175) reviews in detail the 

 literature on the histological changes in the skin produced by these 

 rays, and adds some observations of his own. The first change appears 

 5 hr. after exposure. The skin is sharply red, and leucocytes begin to 

 infiltrate among the cells of the papillae and the superficial layers. 

 Oxydase-reaction granules appear around the vessels which are full of 

 blood. In 30 hr. the reaction is increased. The nuclei of the superficial 

 cells, occupying a zone from 0.05 to 1.0 mm. in thickness are dimly 

 stained, while adjacent cells show a deeply stained protoplasm with their 

 nuclei lying in an unstained area. Degenerating cells and leucocytes 

 appear. The basal cells show httle colloid degeneration; the pigment 

 layer is somewhat disturbed; and here and there the cutis is separated 

 from the epidermis. The blood vessels are still dilated and the oxydase 

 reaction well marked. 



During the next few days the general reaction subsides. But the 

 greatest amount of swelling of connective-tissue cells occurs on the third 

 day after exposure. The epithelium becomes much reduced in thickness, 

 and is divided into two layers, the outer being deeply stained and the 

 inner composed of a normal layer in which no signs of degeneration can 

 be seen. The blood vessels and connective-tissue cells gradually assume 

 their normal state. At no time do the sweat glands and hair papillae 

 show any reaction. For a detailed account of these phenomena and 

 for a discussion of the general reaction of the body to ultra-violet rays, 

 the original paper should be consulted. 



Sensitivity to ultra-violet rays depends on the color of the skin and 

 hair, on the age of the individual, and on the time of the year when 

 exposure occurs. During menstruation and pregnancy it is increased 

 (21, 22, 43, 91, 92). The intensity of the reaction to ultra-violet radia- 

 tion is apparently only a question of dosage, for with high dosage the 

 deeper structures are damaged, even the endotheUal cells, capillary 

 loops, and fibroblasts. Degeneration and ulceration may be carried 

 to extremes by increased dosage (306). 



The pigmentation which develops after exposure serves as a screen 

 by absorbing ultra-violet energy and preventing its further penetration 

 (9, 10, 132, 191, 232, 233, 358, 397). 



Many workers believe that the chemical content of the skin is not 

 only changed by the irradiation but also is apt to influence the result 

 (116). Adler (3, 4, 5) thought there was a fall in the Ca and K content 

 with increasing doses of roentgen rays. Uhlmann (359) thinks that the 

 acid-base shift in the blood has an important influence on epilation by 



