6 FEEDING VALUE OF CEREALS. 



NUTRIENTS ON WHICH THE FEEDING VALUE IS BASED. 



PROTEINS. 



This class of substances includes the true proteins, which are of an 

 organic nitrogenous nature, very complex and similar in composition 

 and properties to white of egg or lean meat. They are of very great 

 importance, for from them the animal derives the nitrogenous mate- 

 rial from which its own muscular tissue is built. The separation of the 

 proteins into individuals or even into classes is very difficult and, 

 though they are not all equal in nutritive value, the investigations 

 throwing light upon this question are so recent and incomplete that 

 it is impossible, at present, to attempt any separation. With vegetable 

 foods the proteins may be left as a group, because those present are 

 the simple proteins and are similar to each other. 



There is, however, another class of nitrogenous organic bodies which 

 are not proteins, but which are included with them in determinations 

 made by the usual methods. These substances are the amido com- 

 pounds. Many of the proteins contain approximately 16 per cent 

 of nitrogen, and it is customary in analyzing protein foods to deter- 

 mine simply the amount of nitrogen present. The result obtained 

 by multiplying this amount by 6.25 is called crude protein. When 

 determined in this way, crude protein includes the amido compounds, 

 which do not contain as much nitrogen as the proteins, nor do they 

 furnish as much, if any, nutriment to the animal. In cereal grains 

 the amount of these amido compounds present is very small, even 

 within the limits of error of the method of separation used, a and on 

 this account they are disregarded and the crude protein is considered 

 as true protein. 5 



FATS. 



The method for the determination of fats is that of extraction with 

 ether, and all substances soluble in ether, such as chlorophyll, organic 

 acids, waxes, resins, etc., are included. In some materials allowance 

 would have to be made for such a mixture, but in grains and a great 

 number of ordinary stock foods it is not necessary. The extracted 

 product is not always a pure fat or a mixture of pure fats, but when 

 waxes or resins are present they are in small quantities and their 

 nutritive value is probably almost the same as that of true fats. Xo 

 great error is introduced, therefore, if the extract is considered as fat, 

 and this is usually done. On account of the impure nature of the 

 extract, the name "ether extract" is often used instead of the term 



a Stutzer's method. 



b The protein factor used in this investigation, except in the case of wheat, is the 

 common one, viz, 6.25. With wheat the now accepted factor of 5.7 has been adopted. 



