STUDY OF THE EFFECT OF TROPICAL SUNLIGHT. 93 



the dark-skinned races can withstand the sunlit^ht belter than 

 those of hghter skin and experimental evidence bearing on this 

 fact, is introduced in the experimental part of this paper. Since 

 man has at his command means such as clothing, artificial heat, 

 refrigeration, and dwellings to aid him in uncongenial climates, 

 transported individuals survive where many of the lower animals 

 perish; moreover, the temperature-regulating devices of human 

 beings are more sensitive than those of most animals. 



In the sun of this region, at least, the skin temperature of 

 men rises above the normal blood temperature, the subcutaneous 

 temperatures of monkeys and rabbits rise more rapidly and to 

 a much higher figure and death ensues. Since the skin charac- 

 teristics are probably the most important in determining the 

 survival of individuals and races, the measurements on skin 

 temperatures so far made will be considered first. 



Aron ' has summarized the prior work and by means of ther- 

 mocouples has extended the observations to a number of subjects 

 in Manila. I have continued his work in much the same way 

 in Baguio, employing as subjects a number of men, monkeys, 

 and several differently colored rabbits, with striking results. 



With men, higher skin temperatures were obtained than any 

 yet recorded. 



The lighter-colored skins reach a maximum in a shorter time 

 than the darker, but the darker skins finally attain maxima 

 higher than those of the lighter color. The protective value 

 of the darker skins would seem to be somewhat nullified by 

 these observations, but I believe this can be explained by the 

 greater radiating power of the darker colors. In full sunlight 

 the proportion of the body w^hich is exposed to the rays of the 

 sun is the lesser fraction of the whole, and while the part in 

 the sun is absorbing heat rapidly, the radiation from the parts 

 in the shade is correspondingly rapid. Moreover, counts now 

 being made by Mr. Elbert Clark of the department of anatomy, 

 College of Medicine and Surgery of the University of the Phil- 

 ippines, results to be published latter, show that the darker 

 skins contain a larger percentage of sweat glands than the 

 lighter. Another advantage which the darker skins have over 

 the lighter, is that the former are not so subject to irritation 

 by the rays of the sun, and the consequent effect upon the nerves 

 and blood vessels, which is so pronounced in the case of white 



'This Journal, See. B (1911), 6, 101. 



