Page:Popular Science Monthly Volume 80.djvu/530

This page has been validated.

that in any one of the places mentioned and which lies outside the tropics, a living body might encounter days in which it would be heated by solar radiation to a much greater extent than in the tropics, and the only question would be whether the possibility of cooling, such as low air temperature, low humidity, winds or other means would compensate to avoid the effects of such insolation.

Our studies were undertaken with animals having fairly well developed means of heat regulation. The most interesting results were obtained with monkeys and human beings. 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. 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. 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. Similar results are obtained if the animals are exposed to full insolation, but care is taken to conduct away the excessive heat increment by means of a brisk current of air from a fan. Under these circumstances the subcutaneous and rectal temperatures remain the same as when the animal is shaded. In this form of experiment the monkey is exposed to all the rays of the sun, including those of lesser refrangibility, heat waves alone being conducted away. If untoward effects are to be attributed to the absorption of the ultraviolet rays, then surely the animal is in the same condition to absorb the latter as he is when no blast of air is present, and their effect should be apparent. 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