128 



ARON. 



seems to be so arranged as to provide for a greater economy in sweating 

 and water evaporation when exposed to the sun, we must conclude 

 tliat the colored man, as regards his physical heat regulation in the 

 tropical sunlight, is in a better position than the white man. 



The temperature conditions surrounding the parts of the body covered 

 by clothes depend principally on the class of clothing worn.^^ It will be 

 important to learn what proportion of the heat rays are absorbed by 

 the clothes, how freely they permit of water evaporation from the skin 

 and how far free circulation of air is possible within them. The ques- 

 tion of the extent to which heat regulation in the Tropics is affected by 

 different kinds of clothing is of great physiologic and hygienic im- 

 portance, and this problem will be considered in future investigations. 



While men, by reason of their superior facilities for evaporating water, 

 are able to counteract the radiated heat from the sun more efficiently 

 than dogs, cats, ralDbits, or monJ^eys, this heat is not without its influence 

 on the human being. The water loss which equalizes the radiated heat 

 is considerable. A man lying quietly in the sun, in one hour lost 280 

 grams in weight. The water actually lost from the body must have been 

 considerably more, because the sweat absorbed by the clothing is not in- 

 cluded in the above figure. The pulse rate of a man sitting quietly in 

 the sun increases on an average about 10 to 12 beats over the number for 

 the same man in the shade. I have proved this by several observations. 

 The quantity of air respired is also increased. An average of a number 

 of observations shows the following : 



Quantity of air respired in liters per minute. 



Number of observations. 



Mini- 

 mum. 



Maxi- 

 mum. 



Aver- 

 age. 



22 in shade 



4.70 

 5.83 



5.98 

 7.90 



5.28 



6.74 



17 in sun 





Therefore, the volume of air respired increases 23 per cent, or from 

 316.8 liters per hour in the shade to 390.4 liters in the sun. 



If heat production within the body is very great, as it is during 

 strenuous muscular work, then, even in a temperate climate, the heat- 

 regulating apparatus is not able to- diminish the heat by water evapora- 

 tion as quickly as it is produced, and as a result rises in the body tem- 

 perature are observed (Zuntz und Schumburg).-^ If at the same time 

 the body is also heated by radiation, the heat accumulatfed must be greater 

 with a corresponding rise in body temperature. 



" Zuntz, Lowy, Miiller und Caspari, Hohenkliraa und Bergwanderungen in 

 ihrer Wirkung auf den Mensehen, Berlin ( 190C) . 



^ Studien zu einer Physiologie des Marsclies, Berlin. 



