10 PRINCIPLES OF FEEDING FARM ANIMALS 



c. Alcohol-soluble proteins are insoluble in water and soluble in 70 to 

 80 per cent, alcohol. To this class belong gliadin found in wheat and rye 

 grain, hordein in barley, and zein in Indian corn. 



d. Ghitelins are insoluble in water, salt solutions and alcohol, and 

 soluble in dilute acids and alkali. Glutenin belonging to this group, with 

 gliadin, forms the gluten of flour; bread dough owes its stickiness to the 

 gluten found therein; grains like rice which contain no gliadin cannot be 

 used for bread making. 



Other simple proteins are albuminoids, histories and protamines; the 

 first substances form the organic basis of bone ; tendon and ligament ; hair, 

 hoof and nails, etc. These are the most resistant groups of protein sub- 

 stances, being insoluble in ordinary chemical solvents, like water, alcohol, 

 salt solutions, etc. 



2. Conjugated Proteins. — These substances have been modified so as 

 .to possess different chemical and physical properties from the simple pro- 

 teins, either through combination with other compounds or through the 

 action of ferments, heat or chemicals. The nucleo-proteins belong to this 

 group of which the best known is casein of milk. They contain phosphorus 

 in addition to the elements that are always found in protein substances. 



3. Derived Proteins. — These are intermediate substances formed in the 

 process of digestion by cleavage of the naturally-occurring proteins; they 

 are diffusible and are assimilated by the living cell for use in the building- 

 up (synthesis) of true proteins. Proteose and peptones are the first repre- 

 sentatives of this class that are formed, when protein is acted upon by 

 enzymes of the digestive juices ( pepsin, trypsin, erepsin ) . On further 

 cleavage these substances are changed into amino-acids, the final decomposi- 

 tion products formed in the digestion of protein substances. 



The amino-acids are the primary building materials out of which 

 the proteins of the animal body are formed. The different protein 

 substances vary greatly in the kinds of amino-acids which they con- 

 tain, and the proportion in which these occur in the protein molecule. 

 The differences in the nutritive value of proteins of different origin 

 that have been observed, appear to be intimately connected with 

 this fact. 



There are eighteen different amino-acids known at present, all of which 

 differ in their chemical constitution and the proportions in which they 

 occur in different- proteins. About one-half of this number are found in 

 plants and plant materials. Among the more important amino-acids may 

 be mentioned: glycine, leucine, glutamic acid, tyrosine, arginine, trypto- 

 phane, lysine and cystine. Zein (the main protein of Indian corn) has been 

 found to contain no glycine, tryptophane or lysine. Glycine is also absent 

 in albumins and in gliadin. The vegetable proteins contain large amounts 

 of glutamic acid, while the animal proteins are high in leucine and also con- 

 tain appreciable amounts of glutamic acid. The amino-acids found in feed- 

 ing stuffs other than the cereals and other seeds have not yet been sys- 

 tematically studied, although a large amount of research work of these 

 substances and their physiological value has been done during late years. 



Amides are a common name for soluble crystallizable protein sub- 

 stances of simpler molecular structure than that of the protein sub- 

 stances and even some of the amino-acids. While the latter usually 

 occur in only small amounts in free form in plants, amides are found 



