10 PRINCIPLES OF FEEDING FARM ANIMALS 
e. Alcohol-soluble proteims 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. Glutelins are insoluble in water, salt solutions and alcohol, and 
soluble in dilute acids and alkali. Glutenin belonging to this group, with 
gliadin, formsthe 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 albwminoids, histones 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 
