ii2 THE CHEMISTRY OF CATTLE FEEDING 



divided. If it be true, as is now generally believed, that 

 the proteins of the food are completely resolved into ammo- 

 acids by tryptic digestion, it follows that animals must possess 

 the power of re-forming protein from these compounds. We 

 should therefore expect that a mixture of amino-acids in 

 which all the necessary ingredients are present in the pro- 

 portions required could be substituted for true protein, and 

 would have the same nutritive value. It is, however, extremely 

 difficult to ensure that any artificially prepared mixture con- 

 tains all the necessary ingredients. It has been shown that 

 the products, as a whole, resulting from the acid hydrolysis 

 of proteins (p. 70) are not an efficient substitute for that 

 substance. 



When amides are ingested, they are rapidly absorbed, and 

 are oxidised in the animal's body ; and it is said that dogs 

 and rats h,ave been kept alive for months on rations which 

 contained no true protein, but it is not asserted that the 

 animals thrived. The whole question requires further in- 

 vestigation. At present, the general consensus of opinion is 

 to the effect that amino-acids do not form an efficient substitute 

 for the whole of the protein. 



It is not quite certain that the proteins of the food are 

 wholly and completely resolved into amino-acids by the 

 processes of digestion. Proteoses, peptones, and peptides, 

 are readily soluble and diffusible, and it is more than probable 

 that some at least of the nitrogenous matter of the food is 

 absorbed in that form. 



When amino-acids are ingested along with true protein 

 they act to some extent in the same manner. It is not known 

 whether they are actually converted into true protein by the 

 action of bacteria, or whether their presence serves merely to 

 protect the true protein from oxidation. There is no doubt 

 that the addition of amides to a food poor in protein increases 

 the- nutritive value of the food. 



The amides of the common foodstuffs roots, tubers 

 etc. probably do not contain all the ingredients necessary 

 for the formation of animal proteins ; but it is believed that 

 they are not entirely without nutritive value. It is generally 



