100 UREA. HIPPURIC ACID. AMINOACIDS 



or by powerful reagents like fuming sulphuric acid. This is 

 one of life's great mysteries. That the living cell, however, 

 after successfully performing the trick of burning protein 

 into C0 2 , H 2 and NH 3 , can finally change the carbonate of 

 ammonium into urea by withdrawal of two molecules of 

 water (carbonate of ammonium necessarily resulting from 

 the combination of the carbonic acid with ammonia in aque- 

 ous solution), is apparently much less inconceivable; and 

 from this stage forward it is rather hard to comprehend 

 why Schmiedeburg's theory should present any particular 

 difficulties. Schmiedeburg's famous pupil, v. Schroeder, 

 whose work was ended by his premature death, was able to 

 show by his frequently-quoted perfusion experiments that 

 the isolated liver is able to transform not only ammonium 

 carbonate but also the ammonium salts of organic acids, as 

 formate of ammonium, into urea. Thereafter Salaskin dem- 

 onstrated that aminoacids are liable to the same change. 

 How this is actually accomplished and what intermediate 

 products are produced are entirely unknown. We have no 

 knowledge, for example, in the oxidation of glycocoll whether 

 the oxygen combines first with the carbon or with the 

 nitrogen, and whether glyoxylic acid (occasionally appear- 

 ing in metabolism) is an intermediate product : 4 



HYDEOXYLAMINOACETIC ACID GLYOXYLIC ACID 



)H COH 



COOHH\ CH 2 .NH.OH 

 COOH 



Ammonium Carbamate. As previously stated, in anhy- 

 dration-p reduction of urea ammonium carbamate, CO<^Q^ H ^ 

 may appear as an intermediate material. For considerable 

 time this compound, occasionally found in the blood, urine 



*H. Eppinger (Hofmeister's Lab., Strasssburg), Hofmeister's Beitr., 6, 481, 

 1905. 



