526 THE POPULAR SCIENCE MONTHLY 



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 compen- 

 sate to avoid the effects of such insolation. 



Our studies were undertaken with animals having fairly well de- 

 veloped 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. En- 

 tirely 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 ex- 

 ceed 40° and the animals remain healthy. Similar results are obtained 

 if the animals are exposed to full insolation, but care is taken to con- 

 duct 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 con- 

 ducted 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 



