190 THE FEEDING OF ANIMALS 



of an animal under given conditions of production. Some 

 of the more recent investigations indicate that the amides 

 should be classed as to function with the true proteins, or, 

 in other words, that they may take part in the synthesis 

 of the proteins that are used constructively in the animal 

 body though probably with not the same percentage of 

 efficiency. Evidence exists, moreover, that the different 

 amides are not of equal value. (See Par. 85.) 



274. Relative nutritive efficiency of the true pro- 

 teins. — ^Notwithstanding possible fimction of the amide 

 compounds in the synthesis of animal proteins, the true 

 proteins of our cattle foods must be regarded as the main 

 flesh-formers. There are, however, many true proteins 

 which are unlike in their constitution. It is desirable 

 to know whether these single proteins differ in nutritive 

 value for specific purposes, like growth or milk forma- 

 tion. Are the alcohol-soluble proteins, such as gliadin 

 and zein of equal value with an albumin, a globulin, or 

 casein? Reference has been made to the fact that while 

 the cleavage products of these various proteins (amino 

 acids), or what are called the building-stones, are to a 

 great extent similar as to kind, these building-stones are 

 not found in the same proportions in the several proteins, 

 and with some proteins certain building-stones are lack- 

 ing. The investigations of Mendell and Osborne, pre- 

 viously mentioned, indicate great unlikeness in nutritive 

 function and value. It is found, for instance, that the 

 gliadin of wheat and rye does not function as does the 

 casein in milk and that zein is particularly inefficient as a 

 means of even sustaining life, and it is significant that 

 the gliadin is deficient in lysine, and that zein is further 

 lacking in tryptophane, whereas the proteins of the animal 

 body contain both of these animo acids. (See Par. 85.) 



