394 



SCIENCE PROGRESS 



A rise of 2° C. over the normal day body temperature was 

 sufficient to produce much discomfort — a rapid pulse rate, and 

 marked dyspnoea on exertion. A greater rise than this produced 

 alarming symptoms when any considerable exertion was made, 

 as in climbing ladders underground. 



In a good air current the critical wet-bulb temperature was 

 found to be about 2 C. higher. During work, on the other hand, 

 the critical wet-bulb temperature was considerably lower — about 

 26 to 27 with fairly hard work in still air. 



That the wet-bulb temperatures should be the determining 



■v 

 a 



a 



V 



U 



40-5 



4-0 



39-5 



39 



38-S 



38 



37-5 



104-9 



04-0 



103-1 



102-2 



101-3 



a 



22 



1004 



99-5 



i 1 it 2 



Time in hours. 

 p IGi 4. — Variations of rectal temperature during rest, stripped to the waist, at 



various air-temperatures. 

 D = dry-bulb air-temperature. W = wet-bulb air-temperature. 



factor is exactly what might have been predicted on physical 

 grounds ; and as the body, unlike the wet-bulb of a thermometer, 

 is itself a source of heat, it is equally intelligible that moving air 

 raises the critical wet-bulb temperature, and increased heat-pro- 

 duction in the body lowers it. 



A further point brought out strikingly in some of the experi- 

 ments was that the sweating produced by heat depends primarily 

 on the skin temperature, and not on the internal temperature 

 of the body. There is quite commonly a fall in the rectal 

 temperature at the time when most profuse sweating breaks out 

 on going into warm air. On the other hand, sweating does not 



