COMPOSITION OF FEEDING-STUFFS 7 



proteins was obtained. It was known that this 

 method was not quite correct, for nitrogenous sub- 

 stances of a non-protein nature had already been 

 found in different parts of the plant. The amount 

 of these non-protein materials was considered, 

 though, to be so small as to be negligible. The 

 products obtained in this way by calculation from 

 the nitrogen found in the food were called " crude 

 protein," or " nitrogenous substances." 



It was not until comparatively recently (1879) 

 that the nitrogenous substances of a non-protein 

 nature were shown to be widely distributed in the 

 plant and animal kingdoms, and to be present in 

 considerable quantities in some food-stuffs. This 

 led to a distinction being made between " crude 

 protein," which expresses all the nitrogen-containing 

 compounds, and " pure protein," or, as it is named 

 in some places, "the proteids." When making 

 an analysis of a feeding-stuff advantage is taken of 

 the property which proteins possess of combining 

 with metallic salts or tannic acid, whereas non- 

 proteins do not. In this way protein can be 

 separated from non-protein and the quantities of 

 each determined. For the analysis the finely- 

 ground food-stuff is treated with warm water, and 

 the substance to be used for precipitation is added. 

 The proteins are in this way precipitated, and the 

 nitrogen can then be determined either in the solu- 

 tion which is left after the precipitation, or in the 



