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 2^ with fairly hard work in still air. 



That the wet-bulb temperatures should be the determining 



40-5 



40 



sj 39-5 



^ 39 



38-5 



38 



37-5 



04-9 



104-0 



103-1 



102-2° 1 



101-3 



100-4 



99-5 



2 I l2 2 22 



Time in hours. 



Fig. 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 



