THE ENERGY BALANCE. 89 



area which is less than double (two surfaces having been brought 

 together). Its greater tendency to cool explains why small ani- 

 mals ahouM so much more quickly succumb to cold than those 

 that are larger, and why slim persons shrniM feel the cold more 

 keenly than those that are stout. 



Other things, such as diet, external temperature, etc., being 

 the same, it is therefore surface area and not body weight ivhich 

 determines the energy production, a fact which is clearly dem- 

 onstrated by finding that the calorie output for different animals 

 is constant when it is calculated for each square metre of sur- 

 face. Thus, a horse produces only 14.5 C. per kg. of body 

 weight in 24 hours, whereas a mouse produces 452 C., but if 

 we calculate according to square metre of surface the dif- 

 ferences practically vanish. These facts, however, do not apply 

 when the differences in size are due to age. This fact has been 

 most strikingly demonstrated in the case of man, for it has been 

 found that the calorie requirement per unit of surface is very 

 distinctly greater in the early years of life than later. Thus, tak- 

 ing the discharge of carbon dioxide as a criterion of the energy 

 discharge, the following results have been obtained from indi- 

 viduals sitting down : 



Carbon dioxide discharged, per 



Average age Average weight square meter of surface 



(years) "(kilogrammes) and hour (grammes) 



\Males 



9 2/3 28 29.9 



12 1/2 34 26.5 



15 1/2 51 23.5 



19 1/2 60 21.8 



25 68 18.5 



35 68 16.9 



45 77 16.3 



58 85 14.2 

 Females 



8 22 26.6 



12 36 20.1 



15 49 16.0 



17 2/3 54 14.8 



30 54 16.3 



45 67 17.9 



