266 WATER ITS RELATION TO METABOLISM 



The quantity of heat furnished by an animal in a given time 

 depends on the coefficient of cooling, and this' depends not only 

 on the form, but on the surface of the body, as is seen in calori- 

 metric experiments where the body is varnished or covered with 

 oil or glycerine. The varnished surface loses heat so rapidly that 

 the animal dies from cooling. Similarly the relative dryness or 

 moisture of the skin can modify the coefficient of cooling. 

 So, too, the colour, for white rabbits lose only 75 per cent, of 

 the heat lost by black or grey. The loss of heat before and 

 after shaving off the fur of a rabbit is as 100 to 150-160 (Richet, 

 Laulanie). 



C0 2 . H 2 0. 



Sheep before shearing excreted 719*6 grm. 1939 grm. 

 ,, after 725'1 grm. 434 grm. 



Man modifies his heat loss by clothing, shelter, artificial heat, 

 and so extends his adaptation to wider limits of climate. 



Clothes lessen the heat loss 47 per cent. (Rubner). D'Arsonval 

 found a 74 kg. man at 18 C. 



Lost 79 Cal. per hour clothed. 

 124 naked. 



Clothes are formed of substances of feeble conductivity and 

 entangle air in the mesh. If the conductivity of silver be taken 

 as 493, that of wool or cotton relatively is 0'04, and of air 0'000288. 

 The power of clothes to imbibe sweat modifies their worth, as 

 water is a far better conductor than air. White is a feeble 

 absorbent of radiant heat, and thus is chosen for tropical climates. 

 In the night, on the other hand, white loses less body heat, and 

 is thus warmer than black. 



The loss of heat from an animal is not as simple as that 

 from the surface of a metal vessel of water, for the deeper parts 

 of the body where the temperature is constant are separated from 

 the air by layers of fat, skin, fur, or feathers. Thus the peripheral 

 temperature differs notably from that of the central parts. Fat 

 has about half the conductivity of muscle for heat. The 

 diathermancy of white skin is twice that of black skin. Thus 

 his black skin protects the deeper tissues of the negro from the 

 sun's rays (P. Schmidt). 



The water excreted per kg. of body weight is about the same 

 in small and large animals. The relative amount of heat lost 



