8 FEEDING VALUE OF CEREALS. 



The remaining substances sometimes present and included in the 

 nitrogen-free extract, namely, the organic acids, are seldom found in 

 sufficient amount, especially in ordinary fresh foods, to make their 

 consideration necessary. 



CLASSIFICATION OF ALL SEPARATIONS. 



% 



On account, therefore, of differences in digestibility or in nutritive 

 value, the analytical separation of a feeding material as previously 

 given must be enlarged to include part or all of the following sub- 

 stances : 



Proteins : 



True proteins. 

 Amido compounds. 

 Fats: 



True fats. 



Waxes, resins, organic acids, chlorophyl, etc. 

 Carbohydrates : 



Sugars, starch, pentosans, and organic acids. 

 Crude fiber. 



In the case of cereal grains and similar materials this classification 

 for separation may be condensed, because of the small amounts of 

 most of the secondar}^ constituents which are present, as follows: 

 Protein, fat, crude fiber, carbohydrate. In the present investigation 

 these are the determinations that have been made. 



FACTORS USED IN CALCULATING FOOD VALUES. 

 COEFFICIENT OF DIGESTIBILITY. 



The separation of the nutritive constituents of foods into the 

 groups or classes just described is made because of the differences in 

 their relative digestibility. The effect of the general nature of the 

 food on its digestibility must also be considered. Each of the nutri- 

 tive constituents, protein, fat, crude fiber, and carbohydrate, has a 

 coefficient of digestibility which differs for each food in which it 

 occurs. Therefore the coefficient of digestibility of each of these 

 constituents must be known for each food under consideration. 

 Such coefficients have been determined by actual feeding experiments 

 on living animals and factors of digestibility calculated from the 

 results. It has also been shown that it is necessary to consider the 

 animal itself as well as the food and the individual constituents. 

 Such experimental results can not be obtained in all cases, but they 

 have been secured by a few investigators for the more common 

 domestic animals and for a considerable number of foods. From the 

 results of such direct experiments the general factors thus obtained 

 may be applied to a variety of foods. The results obtained by Kell- 

 ner at the Mockern experiment station are considered reliable and 



