Paul Caspar Freer

“ Therefore, so far as they have gone, our experiments seem to show, as regards rise in temperature upon exposure to the sun, that the white and brown skins are about equal, with a slight factor in favor of the white, but that in the case of the very dark-skinned Negro the temperature, on exposure, reaches a decidedly higher point than it does with either of the others. The dark skin of the Negro obviously will absorb heat more readily than the lighter one of the European, and also will radiate more readily, the heat taken up on the sunny side being rapidly lost on the shady one ”

“ The sun's rays which lie in the portion of the spectrum under discussion, on reaching the atmosphere, suffer molecular scattering, refraction and other changes which modify the proportion of direct sunlight that reaches the earth's surface, and, of course, these changes vary with the condition of the atmosphere. Nevertheless, it is very interesting to observe that even in the tropics the shortest wave-lengths appearing in the spectrum of the sunlight are very close to 291 and that no shorter rays reach the surface of the earth. ”

“ Of course, it must be understood that the monkey's skin is protected by fur and is not sensitive to the irritating effects of the ultraviolet rays as would be the case with the skin of a Caucasian, who, if exposed to the sun, would be sunburnt, whether in a strong blast of air or not. This latter effect is due to the ultraviolet portion of the spectrum, and, as these rays have but little power of penetration, the skin can in time amply protect itself by pigmentation. ”

“ THE subject of the influence of sunlight in the tropics has been the subject of extended discussion for many years, and the general opinion seems to be that the intensity of insolation is the most important factor influencing the physical welfare of the white inhabitants in those parts of the world lying within the regions which are generally considered as having a tropical climate. ”

“ 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 ”

“ The general trend of the discussion in the literature has been that the rays of the sun lying in the region of the spectrum comprising the violet and ultraviolet are of the greatest importance in determining the influence of insolation upon human beings, and these rays have a special, though undeserved, designation as actinic rays. ”

“ If a monkey is exposed to the sunlight in Manila, his subcutaneous and rectal temperatures rise rapidly, the former more rapidly than the latter, and the animal will die within 1 hour and 20 minutes to 1 hour and 50 minutes, the temperatures gradually reaching maxima. Entirely different results are obtained if the animals are shaded, even by such a small area as is produced by an umbrella or a piece of board, all other conditions being similar, except that the direct rays are excluded. Under these circumstances the skin and rectal temperatures never exceed 40° and the animals remain healthy. ”

“ Any one can see that the subject under investigation is so complex and that it is influenced by so many factors that general conclusions at the present time are premature, excepting in so far as they are borne out by experimental evidence. ”

“ As a result we have in the tropics greater absorption and radiation from the earth's surface as a result of direct exposure to the sunlight to augment the influence of the sun's rays, so that, as it has been shown that the heat factor is the chief one to consider, this increment due to radiation from the earth will be of decided influence. ”

“ 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. ”

“ As a consequence, many of the ill effects which are attributed to sunlight may in reality be due to entirely different causes. Again, races native in the tropics, as a rule, do not have access to the complete food supplies of persons in temperate zones, although this statement may sound paradoxical, and this fact in turn may morphologically modify the peoples to a greater extent than other influences. ”

“ 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, although in the longer days in the temperate zone the sunshine reaching the earth when the sun is near sunrise or sunset is only a small proportion of that at midday. ”

“ Experiments on man have shown that the ultraviolet rays are easily guarded against, by shade or even by a white cotton shirt, the heat rays not. In man we have a subject with highly developed sweat glands, so that the means of heat regulation by evaporation are much more complete than in dogs, rabbits or monkeys.
Skin temperatures of men in this climate in the shade under normal conditions, as measured by our apparatus, vary within the extreme limits of 31° to 34°. ”

“ To obtain comparable data, means had to be devised to give accurate and rapid measurements of the temperatures of the skin and of the inner parts of the body, and eventually a very satisfactory apparatus was completed by Dr. Hans Aron, of the department of physiology of the College of Medicine and Surgery, which gave the temperatures by means of specially prepared thermocouples, the changes being read by a tangent galvanometer. Monkeys are naturally at home in the tropics, and we should suppose that they would best be able to withstand the effect of sunlight. ”

“ The races of people native to the tropical zones have no knowledge of bacteriology and pathology which would enable them to understand the measures to be taken to avoid infectious and other diseases, whereas they live in regions where the absence of a pronounced winter is favorable to the rich development of microscopical life. ”

“ On absorption, a large proportion of these rays is presumably converted to heat and conducted away as such, so that it can be assumed that the effects which we observe on exposing these animals to the sun is one of heat, and these conclusions are borne out at autopsy where post-mortem examinations give protocols clearly pointing to heat stroke. Monkeys enclosed in tight boxes, with only the heads exposed, and placed in the full sun, suffer no inconvenience, although the hair temperature on the scalp may reach 47°. ”

“ Therefore it seems evident that the entire question of the influence of insolation upon the inhabitants of the tropics exists as a legitimate field for experimental study and that comparative data from different regions may be obtained so as to solve many of the questions in an impartial manner. The Bureau of Science at Manila is very fortunately situated in regard to this work. ”

“ They have a system of sweat glands, but this is not so highly organized as it is in man, so that their physical heat regulation is brought about not only by evaporation of sweat, but also to a very great extent by water evaporated from the lungs and mouth through increased respiration. ”

“ As mentioned above, we have but few data from Tucson and, therefore, at present we can scarcely make a comparison, but doubtless when a longer series of observation is at hand we shall discover that there are many days in Tucson showing a maximum as high or even higher than Manila, and an average of about the same. The fact is also observed that two days apparently equally clear will show marked differences between each other during corresponding hours, so that the proportion of the rays reaching the earth and lying between 550 and 291 varies from day to day. ”

“ In other words, pronounced differences may be found between the climates of two places in the tropics which may geographically be close together, as may readily be seen by comparing the meteorological data from Alexandria, Cairo and Aswan, in Egypt. Prevailing winds may so modify the climate of a region that during the nights the temperatures may closely correspond to those found in places more favorably placed. ”

“ 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. ”