COMPOSITION OF FEEDING STUFFS. 219 



ceding groups of compounds. It includes some of the most val- 

 uable constituents of feeding stuffs, which make up the largest 

 bulk of the food materials; first in importance among these con- 

 stituents are starch and sugar, and, in addition, a number of less 

 well-known substances of similar composition, like pentosans, 

 gums, organic acids, etc. Together with fiber the nitrogen-free 

 extracts forms the group of substances known as carbohydrates. 

 A general name for carbohydrates is heat-producing substances, 

 since this is one Important function which they fill; they are not 

 as valuable for this purpose, pound for pound, as fat, which also 

 Is often used for the purpose by the animal organism, but on ac- 

 count of the large quantities in which the carbohydrates are 

 found in most feeding stuffs they form a group of food materials 

 second to none in importance. Since it has been found that fat 

 will produce on combustion about 2% times as much heat as car- 

 bohydrates, the two components are often considered together in 

 tables of composition of feeding stuffs and in discussions of the 

 feeding value of different foods, the per cent, of fat being multi- 

 plied by 2V4 In such cases, and added to the per cent, of carbo- 

 hydrates (i. c, fiber plus nitrogen-free extract) in the foods. As 

 this renders comparisons much easier, and simplifies calculations 

 for the beginner, we shall adopt this plan in the tables and discus- 

 sions given in this Guide. 



Carbohydrates and fat not only supply heat on being oxidized 

 or burned in the body, but also furnish materials for energy used 

 in muscular action, whether this be voluntary or involuntary. 

 They also in all probability are largely used for the purpose of 

 storing fatty tissue in the body of fattening animals, or of other 

 animals that are fed an excess of nutrients above what is required 

 for the production of the necessary body heat and muscular force. 



To summarize briefly the use of the various food elements: 

 Protein is required for building up muscular tissue, and to supply 

 the breaking-down and waste of nitrogenous components con- 

 stantly taking place in the living body. If fed in excess of this 

 requirement It is used for production of heat and energy. The 

 non-nitrogenous organic components, 1. e., carbohydrates and fat, 

 furnish material for supply of heat and muscular exertion, as well 

 as for the production of fat in the body or in the milk, in case of 

 milk-producing animals. 



