4 i8 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 



a given ration is exactly determined in the respiration chamber. 

 Then the marsh gas evolved with the same ration plus fat, pro- 

 tein, starch, crude fiber, or any other nutrient or feed, is 

 determined. The increase or decrease in the quantity of marsh 

 gas evolved, shows the effect of the addition. 



In this way it was found that fat and proteids do not affect 

 the quantity of marsh gas. The methane appears to come en- 

 tirely from the constituents of the nitrogen-free extract and 

 crude fiber. The ratio of protein to non-protein, and other 

 factors, also appears to affect its production. All additions which 

 decrease the digestibility of the nitrogen-free extract decrease 

 the production of methane, but in greater proportion; and addi- 

 tions which increase the digestibility of the nitrogen-free extract 

 increase the production of methane. The various factors which 

 affect the production of methane require further study. 



A considerable portion of the value of the digested nitrogen- 

 free extract and crude fiber is lost as marsh gas, as is seen from 

 the following table : 



A considerable percentage of the material which does not 

 appear in the solid excrement during a digestion experiment is 

 not really digested, i. e., converted into soluble products and 

 absorbed by the body, but is fermented and a portion of its 

 value is lost as marsh gas. 



Organic Matter of the Urine. The digested nitrogenous bodies 

 which have been oxidized by the animal body are excreted in the 

 urine, in the form of urea CO(NH 2 ) 2 , uric acid C 5 H 4 N 4 O 3 , 

 creatin C 4 H 9 N 3 O 2 , or hippuric acid, C 6 H 5 CO.NHCH 2 COOH, 



