144 CHEMISTRY OF THE PROTEIDS CHAP. 



even more difficult, because albumins and albumoses are disintegrated 

 by strong caustic soda. Siegfried l has also noticed that the biuret- 

 reaction may be obscured by the presence of other bodies. 



The biuret-reaction is generally supposed to be the most important 

 of all colour tests given by albumins, because biuret, malonamide, 

 oxamide, etc., do not occur in nature, and are not formed during the 

 processes employed by physiological chemists. The reaction is further 

 believed to be given only by true albuminous substances having the 

 structural arrangement described above, and not to be -given by the 

 amino-acids derived from the albumins ; and in this respect the biuret 

 test differs from all the other colour tests. It used also to be held 

 that albumins had been completely disintegrated, by either acids or by 

 ferments, whenever the biuret- test gave negative results ; but this is 

 placing too high a value on the method, for bodies are known to exist 

 which are not amino-acids and yet yield amino-acids on being dissoci- 

 ated bodies which behave therefore as do the peptones, but which 

 do not give the biuret-reaction. Such bodies have been obtained 

 as the result of peptic digestion by Zunz, 2 Pick, 3 Pfaundler, 4 and 

 Reach ; 5 during tryptic digestion, by E. Fischer and Abderhalden ; 6 

 by a combined treatment with hydrochloric acid, trypsin, and barium 

 hydrate, by E. Fischer arid Bergell. 7 Hofmeister 8 calls these bodies 

 peptoids, while E. Fischer 9 calls them peptids, because he considers 

 them to resemble his synthetised amino-acid compounds. As these 

 substances are at least partially dissociated by proteolytic fer- 

 ments, and as they yield the identical amino-acids as do peptones, 9 

 on being dissociated by acids, there is no reason to separate these 

 bodies from peptones simply because they do not give the biuret- 

 reaction. The gradual dissociation of albumins is also discussed 

 in Chapter V. 



3. The Behaviour towards Trypsin. All albumins are dissociated by 

 certain ferments of which the pancreas ferment 10 is the most import- 



1 M. Siegfried, Zeitschr. f. physiol. Chem. 35. 164 (1902). 



2 E. Zunz, ibid. 28. 132 (1899) ; Hofmeister s Beitrcige, 2. 435 (1902), 3. 339 

 (1902). 



3 E. P. Pick, Zeitschr. f. physiol. Chem. 28. 219 (1899). 



4 M. Pfaundler, ibid. 30. 90 (1900). 



5 F. Reach, Hofmeister' s Beitrcige, 4. 139 (1903). 



* E. Fischer and E. Abderhalden, Zeitschr. f. physiol. Chem. 39. 81 (190:5). 



7 E. Fischer and P. Bergell, Chemikerzeitung, 1902, II. 939. (Vortrag von E. Fischer 

 auf der Naturforscherversammlung zu Karlsbad, 1902.) 



8 F. Hofmeister, JErgebnisse der Physiol. von Asher u. Spiro, I. 1. 759 (1902). 



9 E. Fischer and E. Abderhalden, Zeitschr. f. physiol. Chem. 39. 81 (1903) ; E. 

 Fischer and P. Bergell, Chemikerzeitung, 1902, II. 939. (Vortrag von E. Fischer auf der 

 Naturforscherversammlung zu Karlsbad, 1902.) 



10 H. M. Vernon, Journ. of Physiol. 26. 405 (1901). Vernou is of the opinion that 



