160 NUTRITION OF FARM ANIMALS 



products of protein katabolism which will be considered in the 

 following section, contains also non-nitrogenous materials, 

 presumably arising from the incomplete katabolism of ingredi- 

 ents of the feed. In the urine of man and of the carnivora these 

 non-nitrogenous substances are chiefly or wholly such as might 

 be derived from the katabolism of proteins (phenols and other 

 compounds of the aromatic series), and their amount is com- 

 paratively small. In the urine of herbivora, particularly of 

 ruminants, however, their quantity is relatively very consid- 

 erable, and it seems impossible to regard any large portion of 

 them as products of protein katabolism. 



225. Origin. Apparently these non-nitrogenous organic 

 substances originate in some way from the roughages. Their 

 proportion in the urine is relatively large when the ration con- 

 sists exclusively of roughage, and the addition of such feeding 

 stuffs to a basal ration causes a marked increase in their amount, 

 while, on the other hand, such concentrates as have been in- 

 vestigated do not produce this effect to any very considerable 

 extent. Furthermore, their amount seems to bear no fixed 

 relation to the protein of the feed. When the amount of the 

 latter ingredient is small, the total organic matter of the urine 

 has in some cases exceeded the digested protein of the feed, thus 

 demonstrating that a portion at least of the non-nitrogenous 

 urinary constituents must have had some other source. As 

 the proportion of protein in the feed increases, the amount of 

 nitrogenous products in the urine likewise increases, while that 

 of the non-nitrogenous products appears to be more constant, 

 so that the ratio of urinary nitrogen to carbon increases. The 

 most plausible explanation of these facts seems to be that the 

 substances in question are derived from some of the non-nitroge- 

 nous ingredients of the roughages, but from what ones, or 

 what is the nature of the products, we are still ignorant. 



4. THE METABOLISM or THE SIMPLE PROTEINS 



Anabolism 



226. Synthesis of proteins from digestive products. The 

 simple proteins are resorbed (139, 152) in the form of com- 

 paratively simple cleavage products; largely as amino acids 

 but in part perhaps as more or less complex polypeptids. Out 



