THE CHEMICAL COMPOSITION OF FEEDINGSTUFFS 11 



to life itself, while others are essential to growth only. 

 Therefore different proteins may differ considerably in 

 nutritive value. For example, an animal will starve to 

 death on the protein, gelatin, because it is lacking in two 

 of the amino acids which are essential to the animal organ- 

 ism, viz., tyrosine, and tryptophane. Another example is 

 zein, the principal protein of corn, which is lacking in two 

 essential amino acids, lysine and tryptophane. Conse- 

 quently, in practical feeding it is well that the feeder 

 should know something about the amino acid content of 

 the proteins in order to make sure that he is providing the 

 proper kind as well as the proper amount of protein in 

 the ration. 



Non-proteins. — The non-proteins are substances which 

 contain the element nitrogen but which are not proteins. 

 In most cases, the non-proteins are simply proteins in the 

 process of formation or decomposition. They consist, 

 principally, of amino acids, amides, ammonia, and other 

 compounds, which nature ultimately would build up into 

 the complex proteins ; or else they are the products of 

 complex proteins which have been decomposed and broken 

 down \vith the formation of amino acids and other simpler 

 substances. Thus non-proteins are especially abundant 

 in immature plants, where the protein formation has not 

 been completed, and in fermented feeds, as silage, where 

 the proteins have been decomposed partially. Ripe grains 

 are comparatively low in them. The nutritive value of 

 a proper mixture of the non-proteins is equal to that of the 

 true proteins. However, if they are not present in the 

 proper proportions, the non-proteins ^vill not be as valuable 

 as most proteins. 



