THE DIGESTION OF FEEDS 33 



amount of urea excreted in the urine, say during a day, we are 

 able to ascertain the amount of protein substances in the feed or 

 of body tissues that have been decomposed during the day (see 

 p. 44). 



Metabolism. The chemical changes that occur within the body inci- 

 dent to the exercise of vital functions and to growth are included under the 

 general term metabolism. Metabolic processes in the animal body are of 

 two kinds: Katabolic or destructive, those by which the food materials 

 are broken into compounds of simpler structure, and anabolic or construc- 

 tive, by which these simpler compounds are again built up into complex 

 substances. The formation of peptones and amino acids from the proteins 

 is a katabolic process, while the reverse change, the building up of these 

 simpler compounds into body protein, albumen, globulin, etc., is a con- 

 structive process. Both kinds of processes take place continuously in the 

 living body, as we have seen; they are essential to life, and are discontinued 

 only when life ceases. 



QUESTIONS 



1. Give the various groups of substances found in the animal body and 



state their main characteristics. 



2. Why is it necessary to give salt to farm animals? 



3. Name the various digestive fluids in the animal body, and state the 



changes which different components of feed undergo in the process of 

 digestion. 



4. What is the difference between ruminants and non-ruminants? 



5. Name the American farm animals that belong to each group. 



C. Describe the difference between the digestive apparatus of ruminants and 



non-ruminants. 

 7. Describe the process of absorption of the digested protein substances, 



carbohydrates and fat. 



