GASTRIC DIGESTION. 53 



(NH 4 ) 2 S0 4 (in substance), allow the mixture to stand, and 

 treat as previously. 



Fraction III. This precipitate is termed Deuteroproteose B or 

 Synproteose. It contains the greater part of the car- 

 bohydrate nucleus of the original protein molecule 

 and is, therefore, sometimes called Glycoproteose. 



To the filtrate from Fraction III add T V its volume of a 



N 



H 2 S0 4 solution, which is saturated with (NH 4 ) 2 S0 4 . Pro- 

 ceed with the precipitation and filtration as before. 



Fraction IV. This fraction, which in the case of some 

 proteins is absent, is designated as Deuteroproteose C. 



The acid-saturaled filtrate from Fraction IV is treated 

 with a solution of iodo-potassium iodide (saturated with 

 (NH 4 ) 2 SO 4 ) until no further precipitate results. This is 

 allowed to settle and is then filtered off. This precipitate 

 upon treatment with 95 per cent alcohol subdivides into a 

 soluble and insoluble fraction. If the insoluble residue 

 is filtered off it forms 



Fraction V, denoted as Peptone A; and 



Fraction VI, which consists of the alcoholic filtrate from 

 Fraction V, is called Peptone B. 



Very little is known regarding the character of 

 these two peptone fractions. Undoubtedly they 

 contain peptides of varying complexity mixed with 

 amino acids. Fraction V gives the biuret reaction 

 while Fraction VI does not; hence the former frac- 

 tion must possess the most complex polypeptides. 



The "amino" bodies are precipitable with phospho- 

 tungstic acid and remain in greater part in the filtrate sub- 

 sequent to the treatment with iodo-potassium iodide. 



