52 THE PROTEINS. [CH. II. 



45. Add concentrated HC1 drop by drop. The precipitate 

 dissolves with the first drop, but generally reappears when an excess 

 is added (see Ex. 21, note 2, and Ex. 40). 



46. Dissolve in a little 0-4 per cent. HC1. Boil the solution : 

 a coagulum is not formed. Cool under the tap and neutralise with 

 0-2 per cent. Na 2 CO 3 . A precipitate is formed which is soluble in an 

 excess of the alkali. 



47. Boil. Cool, and add some 0-4 per cent. HC1. The 

 precipitate does not dissolve, i.e. metaprotein is coagulated when 

 boiled in suspension. 



48. Add a saturated solution of ammonium sulphate drop by 

 drop. The precipitate does not dissolve in any dilution of the salt. 

 The insolubility in dilute solutions of neutral salts is an important 

 distinction between metaproteins and globulins (see Ex. 32 and 34). 



49. Dissolve in a little 0-4 per cent. HC1. Treat the solution 

 with an equal volume of saturated ammonium sulphate solution. 

 The protein is precipitated. 



I. The Albumoses or Proteoses and Peptones. 



These hydrolysed proteins are obtained by the further 

 action of acids or alkalies on globulins, albumins and meta- 

 proteins. They are best formed by the action of pepsin and 

 hydrochloric acid on these proteins. Peptone is the end 

 product of gastric digestion. 



They are prepared on a commercial scale and sold as 



(i.) Witte's peptone, which is prepared from fibrin 

 and consists of a mixture of albumoses and 

 peptone. 



(ii.) Savory and Moore's peptone, which is prepared 

 from meat, and only contains traces of 

 albumoses. 



The following scheme indicates the successive steps 



