36 NUTRITION OF FARM ANIMALS 



5. THE NON-PROTEINS 



60. Occurrence. In addition to the proteins, both plants 

 and animals contain a great variety and sometimes relatively 

 considerable amounts of nitrogenous compounds of the most 

 diverse nature. While the occurrence of such compounds, es- 

 pecially in feeding stuffs, was known from an early day, it was 

 long assumed that the amounts present were relatively insignifi- 

 cant and that no material error was involved in regarding all 

 the nitrogen of a feeding stuff as existing in the form of protein. 

 Accordingly, the total nitrogen multiplied by the conventional 

 factor 6.25 and designated as " crude protein " was taken as 

 representing the true protein content of the material. The 

 researches of Scheibler, E. Schulze and Kellner in the seventies, 

 however, showed that this was far from being the case. It 

 was found that nitrogenous substances other than protein 

 were very widely distributed and that sometimes as much as 

 one-third or even one-half of the total nitrogen of feeding 

 stuffs existed in these non-protein compounds. These results 

 have been fully confirmed by subsequent investigations and it 

 has therefore become necessary to distinguish between these 

 substances and the true proteins. 



61. Definition. General properties. While these nitrog- 

 enous compounds other than protein are of the most varied 

 nature, they all differ from the proteins in having a much less 

 complex molecular structure. Many are comparatively simple, 

 crystalline substances, most of them readily soluble in water 

 and diffusible, and they appear distinctly inferior in nutritive 

 value to the proteins. It is a matter of practical convenience, 

 therefore, to have a group name by which to distinguish them 

 and for this purpose the term non-proteins has been proposed. 

 It is, of course, a contraction for non-protein nitrogenous sub- 

 stances and means simply substances which contain nitrogen 

 but are not proteins. It therefore includes a great variety of 

 compounds and may be considered as in a sense a cover for 

 our ignorance of their exact nature. The more important 

 groups of non-proteins are : 



The nitrogenous muscle extractives 

 The nitrogenous lipoids 



