The foregoing results lend no support to the supposed greater 

 digestive capacity of the pure-bred animal. 



Metabolizable Energy. 



Feed may be regarded as the fuel of the animal body, supply- 

 ing energy for its operation much as coal or other fuel does for 

 those of the engine. The feed of domestic animals, however, is 

 very incompletely oxidized in the body, much of its potential energy 

 escaping unused in the unburned matter excreted in the feces and 

 urine,and in the gaseous products of fermentation, especially methan. 

 It is clear that only that portion of the total energy remaining 

 after the subtraction of the amount carried or! in the excreta 

 can possibly be of use to the body. This portion of the total energy 

 has been called by the writers metabolizable energy, the term sig- 

 nifying that portion of the total energy which can be converted 

 into the kinetic form in the body. It is equivalent to the energy 

 of the feed minus the energy of the excreta. The term fuel values 

 has also sometimes been employed for it because it is equivalent to 

 the total amount of heat capable of being produced in the body by 

 the oxidation of the feed. 



In these investigations, the determinations of the energy of 

 feces, urine and methan in the respiration calorimeter experiments 

 afford the basis for comparing the percentage of the total energy of 

 the feeding stuffs which was metabolized by the two animals, the 

 average results being as follows : 



Table j. Average Percentage of Feed Energy Metabolizable. 



(7) 



