ULTRAVIOLET RADIATION— MEIER 377 



serves as a screen by absorbing ultraviolet energy and preventing 

 its further penetration. Degeneration and ulceration of the tissues 

 may be caused by an excessive dose of ultraviolet. Bathers who 

 expose the surface of their bodies to the sun for liours may undergo 

 blood alterations. Bathers should begin their sunbaths gradually, 

 remembering the aphorism of Hippocrates: "To heat or to cool or 

 in any fashion to trouble the body to excess, or suddenly is a danger- 

 ous thing, for excess in everything is the enemy of nature ; but it is 

 prudent to proceed gradually, especially in passing from one stage 

 to another." Forgetfulness or lack of observance of this precept of 

 the father of Naturisme has caused mortal sunburn accidents. 



All travelers in the Tropics have heard of the term "tropical pal- 

 lor." It is applied to white people who, in spite of their sojourn in 

 the hottest climates of the tropical jungles, never seem to become tan; 

 in fact, they appear to be paler than they habitually are in the sum- 

 mertime under the sun of their own temperate climate. Kecent re- 

 search has shown that human sweat partially absorbs ultraviolet 

 light in the spectral region that is effective in producing sunburn or 

 erythema. The scientists placed a drop of perspiration between two 

 flat plates of crystal quartz which transmits ultraviolet light. They 

 placed this over the inner forearm of one of the scientists and then 

 irradiated it with the total radiation of a quartz mercury lamp. The 

 skin under the quartz plates in time developed normal sunburn ex- 

 cept for the small area of about a square centimeter directly under a 

 0.2-mm film of perspiration where the reddening of the skin was 

 markedly less than that of the surrounding region. Spectrophoto- 

 metric measurements indicate that a 0.5-mm film of human sweat 

 transmits only about 75 percent of the solar radiation which is ef- 

 fective in producing sunburn. Is it not possible that, in the Tropics 

 where the humidity is so extreme for a continuous period, the skin 

 is protected by perspiration from the ultraviolet rays that produce 

 sunburn normally in people with white skins? When the same 

 scientist exposed the inner side of the forearm covered with rubber 

 except for a small area of about one square inch to a blast of a 40- 

 mile an hour wind in an experimental wind tunnel, the exposed skin 

 exhibited goose flesh, but at no subsequent time was there the slight- 

 est evidence of reddening or chapping of the exposed area of skin. 

 This experiment seems to indicate that ultraviolet is entirely re- 

 sponsible for sunburn but that the action might be intensified by 

 the secondary effects of the wind, such as a variation of the tempera- 

 ture and moistness of the skin, and a suppression of perspiration 

 which, when present, would protect the skin from the ultraviolet 

 rays. 



