i88 UTILISATION OF FOOD BY THE ANIMAL [chap. 



Kellner obtained the following fuel values and heat 

 values for certain typical foods, expressed in calories 

 per gramme of food : — 



Table XVIII.— Energy Developed by Various Foods. 



This table shows us that though in the calorimeter 



go 



fat will develop — =2-15 times as much heat as starch, 



8-8 

 yet in the ox it will develop — = 24 times as much, 



because in the digestion of the starch some of the 

 material is excreted as methane which is still com- 

 bustible and contains energy. Similarly proteins, which 



r.g 



in the calorimeter have a heat value — - = i'4 times 



41 



that of starch .in the animal, possess — = 1-25 times 



the value of starch, because of the comparatively large 

 proportion of undeveloped energy still contained in the 

 excreted urea. We can then take as a basis these 

 experimentally ascertained facts, that the heat value 

 to the animal of a pure digested fat is 2-4 times that 

 of starch, and that of digested protein is 125 times that 

 of starch, and proceed to calculate the heat value of 



