FEEDING EXPERIMENTS WITH ABIURET PRODUCTS 45 



tyrosine (Abderhalden and Rona (i i)) were injected combustion was 

 apparently complete, as neither substance was discovered in the 

 urine. Later as the result of both feeding and injecting a dog with 

 the simple amino acids, glycine and alanine, with polypeptides like 

 glycylglycine and diglycylglycine and alanyl-alanine and diketo- 

 piperazines, like glycineanhydride and alanineanhydride, they showed 

 that the breakdown of these substances in the body of this animal 

 was complete, the nitrogen of the different products injected being 

 excreted for the most part as urea. They concluded further that the 

 breakdown of protein in the tissue resembled that which went on 

 in the intestine. Apparently however the proteolytic activity of the 

 tissue enzymes was greater than that of the intestinal ferments as poly- 

 peptides which were resistant to the action of trypsin, glycylglycine and 

 leucylglycine, for example, were broken down to urea (Abderhalden 

 and Babkin (14) ). Another point noted was that the proteolytic 

 tissue enzymes of the dog are apparently much more powerful than 

 those of the rabbit. In support of this observation they quoted Schit- 

 tenhelm and Katzenstein (356) who found that if d. 1. alanine was 

 injected into a dog only a small part of even the 1. alanine was excreted 

 in the urine, whereas Wohlgemuth (421) found when working with the 

 rabbit that only the natural forms of the amino acids were combusted, 

 the abnormal forms being excreted (Abderhalden and Teruuchi (15)). 

 These same authors (i 5) tested extracts obtained from the tissues, 

 and found that liver extract could break down glycylglycine and 

 leucylglycine, both of which are resistant to trypsin. Abderhalden and 

 Hunter (16) also tested the juices obtained by great pressure from 

 different tissues (liver, muscle, kidney) and found that they could 

 decompose various dipeptides (d. 1. leucylglycine, glycyl-d. 1. alanine 

 and glycylglycine). The decomposition took place asymmetrically, 

 the amino acid not found in nature being the one which was not de- 

 composed. Tissue juices were further tested by Abderhalden and 

 Teruuchi (17) with like result. Dog serum was also shown to be cap- 

 able of splitting one dipeptide at least, glycyl-1. tyrosine. Abderhalden 

 and Rona (18) attempted to discover whether these ferments might 

 not be reversible in action, but they found no synthesis. Abder- 

 halden and Schittenhelm (19) tested again the question of the fate of 

 racemic simple amino acids in the body. They found that in the 

 dog the abnormal amino acid was excreted in part. Abderhalden, 

 Gigon and London (46) carried out an excellent experiment on the 

 injection of d. alanine into the jugular vein of a normal dog and 

 of one with an Eck fistula. In each case part of the amino acid was 



