THE ADULT ANIMAL 176 



HEAT EVOLVED BY DOGS OF DIFFEBENT WEIGHT. 



Thus while the heat evolved, measured in Calories, 

 increased largely with the increased weight of the animal, 

 the heat per unit of body weight (or volume) diminished 

 greatly as the animals became larger. This is due to 

 the fact that small bodies have, in proportion to their 

 weight, a much greater surface than large bodies,^ and 

 it is the extent of surface which determines the rate of 

 cooling. Thus, in the case of the two dogs weighing 

 3 and 24 kilos., their relative weight and volume were 

 clearly 1:8; their relative surface was, however, 1 : 4, 

 and their relative heat production 1 : 3*6. 



If we look back at the daily rations for animals 

 of various weights just given (p. 173), we shall also 

 find that the quantity of food increases at nearly the 



» This fact may be easily grasped by comparing a single cube with 

 another built up of eight similar cubes. The bulk and weight of the 

 large cube are clearly eight times that of the single cube, but its total 

 surface is obviously only four times that of the single cube. 



