238 Agricultural Chemistry. 



escaping from the alimentary canal, and in the unoxidized com- 

 pounds of the urine. It has been estimated by Kuhn that the 

 loss of energy in the gas, methane, which has its source in the 

 fermentations of the digestive tract, amounts to over one-seventh 

 of the energy of the digested crude fiber and carbohydrates. 

 From, this we see that the available energy of a ration represents 

 the fuel value of the dry matter digested from it, minus the 

 energy in the dry 'matter of the urine and that lost in excreted 

 gases. Such data have been secured on a number of materials 

 by the use of the respiration apparatus an air tight compart- 

 ment in which the animal could live and from which the gases 

 could be removed for analysis. At the same time the urine and 

 feces could also be collected for a complete chemical analysis and 

 for a determination of the energy still contained in them.. 



Net available energy. We have seen that food is not applied 

 to use until it reaches the blood. It must have work done upon 

 it before it is in solution. The processes of mastication, of mov- 

 ing it along the digestive tract, and of bringing it into solution 

 all require the expenditure of a certain amount of energy. Zuntz, 

 working with a horse, has attempted to measure this. His method 

 has been to determine by various devices, how much more oxygen 

 is consumed during mastication and digestion than before or 

 after these operations are accomplished. From this measure of 

 oxygen consumption, he calculated the following heat units, rep- 

 resenting the energy used in chewing certain feeds : 



Cal. 



1 pound corn. (454 grams) 6.3 



1 pound oats 21.0 



1 pound hay ;<,. o 



(/ This is an important finding. Zuntz calculates that in general 

 the coarse feeds have 20 per cent less net energy value than the 

 grains and that the work of mastication and digestion combined 

 is about 48 per cent of the energy value of the digested material 

 from hay and 19.7 per cent of that from oats. We must remem- 

 ber, however, that the wastefulness of fibrous foods shown in 



