Page:Popular Science Monthly Volume 80.djvu/532

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the Negro than for the white man. With the white skin we have the phenomenon of sunburn, with its resultant irritation of the nerve-endings and hyperemia of the peripheral tissues, and this will cause a rise which, apparently, just about offsets the rise in the pigmented brown skin due to the sunlight. To determine definitely the decided difference brought about by the color of the subjects, it was decided to use experimental animals which would show great contrasts; and white, gray and black rabbits gave the data sought. I will select one experiment. When exposed side by side to the sun, the black rabbit reached a maximum subcutaneous temperature of 47°.8 in thirty-one minutes and then died; the gray rabbit a final temperature of 44°.9 in one hour and twenty-six minutes and then died; the white rabbit a final temperature of 45°.7 and when put in the shade it recovered, although much exhausted. None of the animals suffer from sunburn as does the white man, and it is evident that the darker the coat, the greater the heat absorption and the more apparent do the effects of insolation become.

These experiments bring us to the conclusion that, all other things being equal, the Negro will suffer more from the heat effects of the sun than the lighter-skinned races, and all of the work tends to show that the rays of greater refrangibility in the violet and ultraviolet portions of the spectrum are not the important factors, except in so far as they cause sunburn and subsequent excessive pigmentation. However, protection from these rays is easily accomplished and has been accomplished so long as man has worn clothes. These experiments also show that the whiter the clothing the better it is adapted for protection against sunlight and that even in the tropics, if care is taken to seek the shade, no untoward effects can be observed. Indeed, Major W. P. Chamberlain, United States Army Medical Corps, who investigated the systolic blood pressure of a large number of residents in the Philippines, concluded that there is no progressive tendency for the pressure to increase or to decrease with a continued tropical residence covering periods of over three years, beyond which length of time his observations do not extend.

From all of our present studies it would seem legitimate to draw the conclusion that a climate such as we have in the Philippines, where we are surrounded by the sea which modifies the extreme of temperatures and where we have such a large proportion of cloud, is not by any means deleterious to the white man if he takes ordinary precautions which are not as elaborate as those he would take in a northern climate to keep out the cold. In the Philippines the nights are rarely too hot for comfort; they may even be quite cool.

The actual number of hours of insolation per year on the earth's surface, were the sky always clear, is greatest at the equator and diminishes toward the poles, the ratio between 0° and 45° being 1.83 to 1.34,