10 FEEDS AND FEEDING, ABRIDGED 



crude proteins. In addition to carbon, hydrogen, and oxygen, these 

 compounds contain nitrogen, sulfur, and sometimes phosphorus. 

 The nitrogenous compounds are the most complex of all plant com- 

 pounds and are therefore the most difficult to study and classify. 

 For example, the probable molecular composition of legumin, a pro- 

 tein found in the seed of the field pea, is C 718 H 1158 238 N, 14 S 2 . Due to 

 this complexity, and also because of the great number of different 

 nitrogenous compounds found in plants, even after years of effort by 

 able chemists our knowledge of the differences in composition and 

 feeding value of these compounds is still limited. In discussions of 

 feeding stuffs and stock feeding, the terms crude protein, protein, and 

 amids are commonly used for designating the various classes of 

 nitrogenous compounds. 



Crude protein includes all the nitrogenous compounds of the plant. 

 The chemist finds that about 16 per ct. of the plant proteins is 

 nitrogen. Accordingly, he multiplies the nitrogen found in a given 

 plant substance by 6.25 (100 -=- 16 = 6.25) and calls the product crude 

 protein. Crude protein embraces two great groups of nitrogenous 

 plant compounds, proteins and amids. 



The amids may be termed the building stones of the proteins, for 

 from them the plant constructs the more complex proteins, just as a 

 wall is built from stones, and on decomposition the proteins are again 

 broken down into these more simple substances. These compounds 

 are the portable nitrogenous building compounds of the plant, for 

 they are soluble in its juices and hence may be carried wherever 

 needed. Commonly included under the general term amids are com- 

 pounds which the chemist calls amino acids, and others which he 

 terms true amids. In this book, unless otherwise stated, amids will 

 be used to denote both classes of substances. 



Proteins are the more complex forms of crude protein. They are 

 not always soluble, and therefore in many cases not transportable, in 

 the juices of the plant. The proteins form the basis of the proto- 

 plasm, which is the life-holding part of all plants and animals, and 

 so are essential to all life. 



The complexity of the proteins is evident from the fact that 18 

 different amino acids have already been identified which may enter 

 into their composition. Just as the letters of the alphabet may be 

 combined into innumerable words, so the possibility for the combina- 

 tion of the amino acids into different proteins is almost limitless. 

 Thus far, scores of different plant and animal proteins have been 

 separated and examined by the chemists. Some of these, such as 

 egg albumin, contain all the known amino acids, while others, as zein 

 of corn and gliadin of wheat, lack one or more of them. As will be 



