134 THE AMINO ACIDS 



the synthesis of amino acids from ammonia and car- 

 bohydrates has been accomplished directly or in- 

 directly in the laboratory, the possibility of a similar 

 reaction in the body must be reckoned with. Finally, 

 the alleged utilization of urea and other simple nitro- 

 gen derivatives may merely be an instance of unsus- 

 pected retention and delayed excretion. Even so 

 soluble a salt as an iodide may not be entirely recov- 

 ered in the excreta until several days after its adminis- 

 tration has been stopped. Surely no one would look 

 on the temporary deficit as an indication of nutritive 

 'utilization' of the foreign salt." 



Various possibilities therefore present themselves in 

 the interpretation of the alleged utilization of these 

 simple nitrogenous substances. The influence of 

 alimentary bacteria may be eliminated by parenteral 

 feeding of the compounds, which, however, has not 

 been feasible until recently when Henriques succeeded 

 in devising a method whereby a slow constant stream 

 of nutritive solution may be intravenously introduced 

 into the body. Subjecting utilization of urea and 

 ammonium salts to the test by means of this device, 

 Henriques and Anderson have demonstrated that no 

 permanent retention of these nitrogenous compounds 

 occurred. It is therefore exceedingly improbable that 

 the body itself is in a position to transform these sub- 

 stances into amino acids. Amino acid synthesis is 

 not an easy task for the organism nor is there evidence 

 that even the transformation of one amino acid to 

 another is accomplished to any extent. The organism 



