52 LABORATORY WORK IN PHYSIOLOGICAL CHEMISTRY. 



three fractions of proteoses and two of peptones, the pro- 

 cedure for which is the following: 



For the purposes of study, a pepsin-hydrochloric acid 

 digestion of meat or fibrin should be prepared, using 0.3% 

 HC1 and 0.5 grm. pepsin per liter (Grubler's purissimum or 

 Parke-Davis' scale pepsin). Allow the digestion to proceed 

 at 40 C. for three days. After filtration of the digestion 

 mixture and exact neutralization with dilute NaOH the 

 solution is ready for use. Heat a little of it to boiling to 

 show that no coagulable proteins exist in the mixture. 



To a given quantity of the digestion mixture add an 

 equal volume of a saturated solution of (NH 4 ) 2 S0 4 . Stir 

 the solutions together and allow the mixture to stand until 

 the resulting precipitate has settled sufficiently to allow 

 of considerable decantation. Filter the remainder. This 

 precipitate obtained by half saturation of the mixture repre- 

 sents 



Fraction I. It may be further separated into two parts: 

 one soluble in 95 per cent alcohol protoproteose, 

 and the other remaining insoluble heteroproteose. 



In the constitution of protoproteose the aromatic 

 groups predominate, while in heteroproteose the 

 fatty acid radicals are chiefly found. 



To the filtrate from Fraction I add one-half its volume of 

 a saturated solution of (NH 4 ) 2 S0 4 . Allow this to stand 

 and proceed as before. This second precipitate obtained 

 by two-thirds saturation corresponds to 



Fraction II. It consists of Deuteroproteose. A and contains 

 the greater part of the lead-blackening sulphur 

 which was present in the original proteid molecule. 

 On this account it may be termed Thioproteose. 



Completely saturate the filtrate from Fraction II with 



