BODY HEAT 55 



nearness to the large bloodvessels and on the conducting 

 power of the intermediate tissues. Were it not for this 

 low conducting power of the body it would be impossible 

 to make use of the local effects of the cautery or of 

 freezing as we do. Fat is the tissue which is the worst 

 conductor of heat,* so that there is some reason in the 

 common belief that a thick layer of subcutaneous fat 

 serves as a blanket, which lessens heat loss. 



Against loss of heat by conduction it is impossible for 

 the body to protect itself by natural means at all, but 

 clothes are of some avail against it (see p. 57). 



3. Convection only comes into play when the body 

 is exposed to the influence of air in motion. Draughts, 

 for instance, produce their local chilling effects by this 

 means, and winds are- even more potent, the combined 

 effect of conduction and convection produced by a cold, 

 damp wind being one of the most chilling influences to 

 which the body can be exposed. 



4. Evaporation stands next to radiation in importance 

 as a mode of heat loss from the skin, 14'5 per cent, of 

 the total surface loss being accounted for in this way. 

 It has been calculated by Erasmus Wilson that the skin 

 contains twenty-one miles of sweat glands, from which 

 about 600 c.c. of sweat are evaporated daily, which will 

 produce a loss of about 350 Calories. During hard 

 exertion this loss is, of course, greatly increased. It has 

 been found, for instance, that stokers may lose 3 pounds 



* For experiments on the conducting power of the different 

 tissues of the body, see Bordier, Archives de Physiol., 1898, 

 xxx. 17 ; also Charrin and Guillemonat (ibid., p. 455). 



