1 70 NUTRITION OF FARM ANIMALS 



growth of rats through two generations was secured on purin- 

 and pyrimidin-free feed. Another fact pointing in the same 

 direction is that the body does not appear to require a supply 

 of phosphorus in organic combination but can build up its 

 organic compounds from phosphates (258). 



239. Regeneration from, cleavage products. In view of 

 the capacity of the body to produce nucleoproteins in the 

 entire absence of their constituent " building stones " may it 

 be supposed that when the latter are supplied in the feed they 

 may be recombined in the cells somewhat as are the ' amino 

 acids of the simple proteins? 



No positive answer can be given to this question. It would 

 seem, however, that the first steps in the autogenesis of the 

 nucleoproteins must be the formation of pentoses and of the 

 purin and pyrimidin bases, i.e., of precisely those substances 

 which result from the digestive cleavages. Even though it be 

 assumed that, in the former case, they are produced within the 

 cells where they are further synthesized to nucleic acid, it is 

 not altogether clear why the same substances brought to the 

 cell by the blood current should not be available for the same 

 purpose. Provisionally, at least, it seems perfectly possible to 

 regard the entire stock of these " building stones " contained 

 in the body, whether derived from the feed or produced by the 

 body cells, as potentially available for the regeneration of 

 nucleic acids. From this point of view, the increased excretion 

 of purins which results from their ingestion would be con- 

 sidered as a consequence of their increased concentration in 

 the blood and as analogous to the increased excretion of urea 

 which follows the ingestion of simple proteins or of amino 

 acids (402). 



Katabolism 



240. Cleavages. The katabolism of the nucleic acids 

 bears a close general resemblance to that of the simple pro- 

 teins. As in the case of the latter, the first general stage of the 

 process consists of a series of enzymatic cleavages. These 

 cleavages are quite analogous to those of the simple proteins 

 and yield as final products the comparatively simple " building 

 stones " of the nucleic acids. Since it is to be supposed that 

 the autogenesis (238) of these compounds is via these same 



