REGULATING THE HEAT 157 



nerve messages are sent out which set the sweat glands 

 in action. The hotter and drier the air, the quicker does 

 evaporation take place and the more rapidly is the body 

 cooled ; when the blood returns to the normal warmth of 

 the body then it ceases to stimulate the controlling nerve 

 centres, and the messages which keep the sweat-glands in 

 action cease to be dispatched. The loss of body fluids, 

 through sweating, gives rise to a feeling of thirst ; a fire- 

 man in the stoke-hole of a steamer will consume 12 pints 

 of fluid in a shift, most of which is evaporated as sweat, 

 and thus the temperature of his body is kept at a normal 

 degree of warmth. If, however, a hot atmosphere — one 

 above 98 — is laden with moisture two things happen : 

 (1) sweat cannot evaporate and thus cool the body ; (2) 

 the body absorbs heat much more rapidly in a hot vapour- 

 laden atmosphere because a moist air is a much better 

 heat conductor than a dry one. Very soon a point is 

 reached when the heat-regulating mechanism of the body 

 breaks down and then " heat-stroke " occurs. The tissues 

 of the brain cease to work when the temperature mounts 

 to 105 ; if it passes above that degree life cannot be 

 maintained for many hours, because the central nerve 

 system undergoes destructive changes. 



There are several other contrivances by means of 

 which the heat of the body is economised. Fat is an 

 excellent non-conductor of heat. We are provided with 

 inner wrappings of this material, particularly one placed 

 just under the skin. Whales, which have to maintain an 

 even body-temperature in Arctic seas, have an enormous 

 subcutaneous covering of fat or blubber. Blubber serves 

 the Greenland whale as house and clothes. Even oil- 

 forming glands — sebaceous glands — are set closely in the 

 human skin to grease its surface, so that moisture may 

 not soak into it and cool the body by evaporation. In 

 spite of all provisions, however, it is a moist-cold wind 

 or air which most taxes our heat-regulating mechanisms. 

 Dr Leonard Hill has shown how an atmosphere, laden with 

 moisture, can steal heat stealthily from our bodies without 

 ever awakening the temperature - regulating mechanism, 



