102 



its head was exposed to the sun's rays, but its body was thor- 

 oughly protected by the ventilated air space and walls of the 

 boxes. 1 he monkey was kept in this position and exposed to the 

 sun s rays from early morning till night without any rise of body 

 temperature taking place, or any signs of interference with its 

 health. Ihe same animal was exposed under similar conditions 

 to direct sun's rays for altogether fifty-iour hours within a 

 period of twelve days, and apparently suttered no damage. Dur- 

 ing this period temperatures taken in the hair on the animal's 

 head were frequently found to register as high as 47 "C. 



Some observations were then made as to the effect of sun's 

 rays on the human skin. White and dark brown skins were 

 selected and their normal temperature carefully determined ; this 

 varied between 32.5 "C. and 33.5 "C. There was no constant dif- 

 ference between the two colors. When exposed to the sun the 

 SKin temperatures rapidly rose to 3e).5C or 3/"C. ; on continuing 

 the exposure there was no further rise of temperature, but on 

 the contrary a gradual fall of 0.5 °C. to 1°C. was observed. The 

 fall usually began with the appearance of diaphoresis. The fall 

 was more rapid and greater when active exercise was being taken 

 and there was copious perspiration. If the man had been work- 

 ing hard and perspiring freely before being exposed to the sun's 

 rays, there was only a slight rise of the skin temperature. Dark 

 skins did not, so far as the experiment went, show quite so much 

 rise of temperature as white ones. A possible explanation may 

 be that the dark skin absorbs more heat rays at first, but in con- 

 sequence the sweat glands come into action sooner, and so pre- 

 vent the temperature from rising as high as in the case of white 

 skins. 



Although the effect of the sun's heat on the human body is 

 neutralized by physiological action, this makes certain demands 

 on the human organism. This is shown by one set of observa- 

 tions, in which persons lightly clad were kept at rest but exposed 

 to the sun's rays ; the result of this exposure was to increase the 

 pulse-rate by 8 to 12 beats, and the volume of respiration by 23 

 per cent. Under similar coiKlitions a Philippine weighing 57 kg. 

 lost weight to the extent of 280 grm. in one hour, although no 

 allowance was made for the ])erspirati()n absorl)cd by his clothes. 



When active exercise is being taken the heat produced by mus- 

 cular action ad'ded to that absorbed from the sun's rays may 

 produce a condition of collapse. 



