168 THE FEEDING OF ANIMALS 



For this reason the available energy of the digested pro- 

 teins is about one-fourth less than the total. 



247. Loss of food energy in gases. In the third place, 

 there is, with ruminants and horses at least, an escape 

 from the alimentary canal of unconsumed gases, due to 

 the fermentations which take place during digestion. 

 These gases, mostly methane (marsh gas) with some 

 carbon dioxid and from green leguminous plants some 

 hydrogen sulfide and nitrogen, have their source in the 

 carbohydrates and crude fiber, and Kellner found them 

 to represent from 10 to 20 per cent of the total energy 

 value of the dry substance digested from various materials. 

 From twenty experiments, upon five different animals, 

 Kuhn found the loss in methane to be over one-seventh 

 the energy of the digested crude fiber and nitrogen-free 

 extract. 



248. Recent determinations of metabolizable energy. 

 The most accurate and extensive determinations of 

 metabolizable energy that have been made in this coun- 

 try, or perhaps anywhere, are the result of recent inves- 

 tigations by Armsby and Fries with the aid of a respira- 

 tion calorimeter. These involved analysis of the feeds 

 used and determinations of the total energy of the feeds 

 and of the losses through the various avenues indicated 

 above. In carrying on this work, nine steers were used, 

 involving 3,401 experiments. Without giving any atten- 

 tion to the technics of the work, which required a costly 

 and extensive equipment of men and apparatus and 

 involved thousands of accurate chemical analyses of 

 foods and the different forms of excreta, the following may 

 be cited as an example of the necessary computation of 

 losses of chemical energy from a ration through the 

 excreta and the methane: 



