662 THE FORMATION OF UREA 



various oxidising and hydrolysing agents have been so numerous 

 and diverse. Recently' some light has been thrown on this 

 subject from two directions. On the one hand, our knowledge 

 of the constitution of the proteid molecule has received con- 

 siderable additions, partly from the work of Fischer and others 

 who have synthesised proteid-like bodies, the polypeptides, and 

 partly from the work of Kossel and many others who have 

 studied in detail the hydrolytic disintegrations of proteids. On 

 the other hand, it has been discovered that tissues contain 

 proteolytic and other ferments, which presumably exert their 

 action during the normal metabolism of the tissues. The autolytic 

 action of these ferments outside the body on their corresponding 

 tissues is being studied by numerous observers, including Leathes, 

 Hedin, Dakin, Levenne, and others in England and America. 

 As far as the results at present show, the products of autolysis 

 do not differ greatly from those produced by the digestive 

 ferments and other hydrolytic agents. 



The various products into which proteid may be broken up 

 either by oxidation or by hydrolysis with acids, alkalies, or 

 ferments may be roughly classified for our present purpose as 

 follows: (1) The base, ammonia; (2) the mono-amino acids, 

 e.fj. glycin, alanin, leucin, aspartic acid and glutamic acid ; (2a) 

 the aromatic mono-amino acids, e.g. tyrosin and phenyl-alanin ; 

 (2b) the mono-amino acids, containing sulphur, cystein, and 

 cystin; (3) the diamino-acids, e.g. arginin, lysin, ornithin, and 

 histidin ; (4) the chromogenic group, indol and pyrol derivatives ; 

 (5) the purin and pyrimidin bases ; and (6) the carbohydrate 

 group. 



The N of most proteids is found on complete artificial 

 hydrolysis to be distributed over the first three groups and in 

 the following proportions. By hydrolysis of various proteids 

 with acid it has been found that ammonia N forms 8 to 13 

 per cent., diamino-acid N 20 to 30 per cent., and the mono-amino 

 acid N 55 to 75 per cent, of the whole. Cohnheim found that 

 when erepsin acted upon peptone, made from syntonin by pepsin, 

 the distribution of N was much the same ; the ammonia N formed 

 7 per cent., the diamino-acid N 30 per cent., of which a third 

 was present as arginin, and the mono-amino acid N 63 per cent., 

 of the whole. Members of other groups besides those of the first 

 three can be made chemically to yield urea, which is then ob- 



