WATER ITS RELATION TO METABOLISM 267 



by evaporation of water is thus greater in large than in small 

 animals. In the latter the loss by radiation and conduction is 

 relatively greater. Thus loss of heat is estimated to be in 



The small animals, owing to their great surface exposure, not only 

 do not need to sweat, but have to live at a fast rate to maintain 

 their body heat. On the other hand, large animals must sweat 

 during exercise to keep the great bulk of their bodies at normal 

 temperature, so lessened in them is the surface exposure in 

 proportion to the body mass. 1 



The rate of metabolism of animals is in proportion to the 

 relative surface exposures of their bodies. 



The same proportion has been found to hold good in com- 

 paring men with children and dwarfs. 



In solids of the same shape the surface is proportional 

 to f power of the volume S = &Vf, k being a constant de- 

 termined for any given form. The weight can be put for 

 volume, and then S = fcW. For man fc=12-9, dog 11-2, 

 rabbit 12-9, guinea-pig 8-89, rat 9-13. The formula is only 

 approximately correct, for animals are not of the same geometric 

 figure and vary in specific gravity with the amount of body fat 



1 A dog loses water by opening the mouth and hanging out the tongue. 



