UTILIZATION OF FOOD 



417 



The nitrogen appears as follows : 



(1) In the undigested residues. 



(2) In the urine. 



(3) In perspiration (very small quantity). 



(4) Used in the production of hair, flesh, milk, etc. 

 The energy is used as follows : 



1 i ) A part appears in the undigested solid excrement. 



(2) A part is used in fermentation and escapes as heat. 



(3) A part is lost in incompletely oxidized organic matter in 

 the urine. 



(4) A part escapes in marsh gas produced by fermentation in 

 the intestines. 



Fig. 87. Curve showing heat production of steers in respiration calorimeter, 



the arrows being pointed up if the animal is standing. 



Pennsylvania Station. 



(5) A portion is used to masticate and digest the food, and is 

 eliminated as heat. 



(6) A portion used for bodily activities, such as beating of 

 the heart, breathing, movements, warming the body, etc., and 

 is eliminated as heat. 



(7) Any portion remaining after the above requirements are 

 satisfied, may be used for external work, stored up in fat or 

 flesh, or used in the production of milk, etc. 



Production of Marsh Gas. The effect of different nutrients or 

 foods upon the production of marsh gas has been studied by the 

 following method. First, the quantity of marsh gas evolved with 



