ii CHANGES DURING METABOLISM 109 



Stolte l injected one rabbit weighing about 3000 grms. with pure 

 preparations of glycocoll, alanin, aspartic and glutaminic acids, phenyl- 

 alanin, tyrosin, and leucin, with this result : 



1. The aromatic mono-amino-acids (tyrosin and phenylalanin) do 



not give rise to an increased urea output. 



2. Certain mono-amino-acids (alanin, aspartic acid, and glutaminic 



acid) increase the urea output, but appear also partially in 

 the urine. 



3. Certain mono-amino-acids, if given even in large amounts 



(glycocoll and leucin), are broken up so completely in the 



body as practically never to appear in the urine. They, of 



course, give rise to a large increase in the urea output. 



The change which ami no-acids undergo in the body is probably 



over the stage of oxy-acids, as occurs, e.g., in plants and in alcaptonuria 



when tyrosin and phenylalanin are changed into homogentisinic acid 



(see p. 114). It is quite an open question whether the carbon-chain, 



after the splitting off of the nitrogen which forms urea, breaks up 



still further, or whether it is made use of in the building up of other 



non-nitrogenous substances, such as carbohydrates and fat. 



V. Henriques and C. Hansen 2 have fed rats on casein hydrolysed 

 by H 2 S0 4 or HC1 and casein digested by trypsin + erepsin in toluol 

 water, arid found that casein hydrolysed by acids gives rise to 

 products which cannot keep an animal in N-equilibrium ; while the 

 products of casein digestion obtained with trypsin + erepsin not only 

 cover the N-loss, but even allow of N being stored. The nitrogen- 

 equilibrium is also kept up by that fraction of tryptically-digested 

 casein which is not precipitable by phospho-tungstic acid, i.e. by 

 mono-ammo acids. Those compounds of tryptic digestion which 

 are soluble in 96 per cent alcohol heated to 50 also maintain 

 N-equilibrium, while the alcohol-insoluble fraction does not. 



Abderhalden and Rona 3 also find that rats and dogs fed on the 

 products obtained by hydrolysing casein by means of acids only live a 

 few days longer than animals not fed at all, while dogs fed on casein- 

 products digested tryptically till the biuret- reaction is no longer 

 obtainable can maintain their N-equilibrium. 



Wohlgemuth 4 on feeding rabbits with the inactive or racemised 

 mono-amino acids, tyrosin, leucin, aspartic acid, and glutaminic acid, 

 found that the inactive acids became dissociated during metabolism in 



1 Karl Stolte, ffofmeister's Beitrage, 5. 15 (1903). 



2 V. Henriques and C. Hansen, Zeitschr. /. physiol. Chem. 43. 417 (1905). 



3 E. Abderhalden and P. Rona, ibid. 42. 528 (1904), and 44. 198 (1905). 



4 J. Wohlgemuth, Ber. d. deutsch. chem. Gesch. 38. 2064 (1905). 



