ACTION OF THE TROPICAL SUN. 129 



This increased body temperature probably accounts for many of the 

 accidents which usually are described as sun stroke or heat stroke; how- 

 ever, several strokes of this kind, some even fatal, have been reported 

 with but slight rises in temperature. No reasonable explanation of these 

 in relation to the heat rays have been given. I wish to offer one ex- 

 planation which seems to me quite plausible : Under unfavorable climatic 

 conditions during muscular work, P. Schmidt has observed water losses 

 as great as 1 kilogTam per hour. The body can withstand a loss of water 

 in a maximum of 10 per cent of its weight. An acute loss of 3 to 4 

 kilograms within a few hours, according to our experience with animals 

 (Czerny), necessarily must result in severe disturbances, collapse or even 

 death. It seems quite reasonable to assume that an excessive, continued 

 water evaporation, while avoiding a rise of the body temperature, may 

 lead to collapse, similar to that observed in cholera if the water lost from 

 the body is not replaced. 



SUMMARY. 



1. Under climatic conditions, even during the cooler seasons of the 

 year in Manila, animals, such as rabbits and monkeys which by nature 

 have only a limited power of physical heat regulation, or animals the 

 physical heat regulation of which is artificially inhibited (tracheotomized 

 dogs) die if exposed to the sun, the body temperature rising to febrile 

 heights. If the same animals are protected from the rays of the 

 sun, or if the increase of heat due to radiation from the sun is com- 

 pensated by an increased loss such as would be brought about by a strong 

 wind, then the animals suffer no discomfort. Insolation of the skull alone 

 is without effect if the body temperature is kept within normal limits. 



2. The post-mortem findings on the animals dying as a result of in- 

 solation show decided hsemorrhagic lesions of the meninges in the brain, 

 and in monkeys, in the heart. 



3. In animals without sweat glands the subcutaneous tissues are heated 

 by the radiated heat from the sun to temperatures above those compatible 

 with life. 



4. The himian skin if exposed to the sun is warmed to about 3° to 4° 

 above the normal skin temperature (32°. 5 to 33°. 5). An increase, even 

 to the normal body temperature, is prevented by evaporation of sweat. 

 The cooling effect of the sweat secretion causes a fall of the skin tem- 

 perature even if insolation is continued during longer periods. 



• 5. The brown skin of Malays, while theoretically absorbing more heat 

 in the sun, shows a smaller rise in temperature in the tropical sun than 

 the skin of white men imder similar conditions. As an explanation, it 

 is believed that an earlier and better water evaporation by sweat secretion 

 takes place. 



6. The air in the human hair, especially in black hair, under the 



