54 LABORATORY WORK IN PHYSIOLOGICAL CHEMISTRY. 



More or less of acid albuminate may be formed during 

 the initial stage of the digestion (first half -hour), but this 

 quickly disappears and apparently does not participate 

 in the future formation of the proteoses, peptones, and 

 "amino" bodies. 



Perform the following tests with the different fractions: 



(a) Try the biuret reaction on each fraction. 



(6) Test Fractions I and // for lead-blackening sulphur. 



(c) Boil Fraction III with 10 per cent H 2 S0 4 for an hour. 

 Cool, neutralize, and test the mixture with Fehling's solu- 

 tion. 



(d) Show, first, that the solutions of Fractions I, II, III t 

 IV are precipitated by nitric, picric, and trichloracetic acids, 

 and that the precipitates so produced disappear when heat 

 is applied and reappear upon cooling; and, second, that 

 they are non-coagulable by heat and respond to the acetic 

 acid and potassium ferrocyanide reaction. 



(e) Prove that the peptones (Fractions V and VI) are 

 not precipitated by nitric or trichloracetic acids; that Millon's 

 and xanthoproteic reactions give indecisive results; that 

 lead-blackening sulphur is absent; and that both tannic and 

 picric acids combine to form insoluble bodies. 



It must be finally emphasized that these various fractions 

 are not to be considered as unit substances. The method of 

 separation just outlined simply attempts to isolate certain 

 mixtures ("fractions") each of which contains in greater 

 part some characteristic component group or complex 

 broken off during the peptic cleavage of the original protein 

 molecule. Thus in Deuteroproteose A the lead-blackening 

 or cystine nucleus predominates, while Deuteroproteose B 

 is characterized by containing the larger part of the carbohy- 

 drate complex. 



