THE -PROTEINS 371 



Properties. 



The solutions prepared above are known as acid metaprotein or acid 

 albumin and alkali metaprotein or alkali albumin. 



(1) No coagulation occurs on boiling a portion of the solution. 



(2) Metaprotein is insoluble in water. 



On carefully neutralising the solutions with 2N acid or alkali re- 

 spectively, the metaprotein is precipitated when the solution is just 

 acid to litmus ; it redissolves in an excess of either acid or alkali. 

 The precipitate is allowed to settle, the bulk of the water decanted and 

 the remainder filtered. The precipitate is washed with water and ex- 

 amined as follows : 



(3) Metaprotein is soluble in dilute acid or alkali. 



A portion of the precipitate will dissolve in dilute acid or alkali, 

 and will be precipitated on neutralising. 



(4) Metaprotein is coagulated by heating in neutral solution. 



A portion of the precipitate is suspended in water and heated. Coag- 

 ulation occurs. This is verified by adding a drop of dilute acid to the 

 cold solution when the precipitate is no longer found to be soluble. 



(5) Behaviour towards salt solutions. 



Acid metaprotein solutions are precipitated completely on saturat- 

 ing the solution with (a) sodium chloride, (&) magnesium sulphate, or 

 (c) by half saturation with ammonium sulphate. Alkali metaprotein 

 solutions are not precipitated by saturation with sodium chloride, but 

 are precipitated by saturation with magnesium sulphate or half-sat- 

 uration with ammonium sulphate. 



(6) Both solutions give the colour reactions and some of the other 

 general protein reactions. 



PROTEOSES AND PEPTONES. 



A mixture of these substances is formed by the hydrolysis of 

 proteins. They are termed albumose, globulose, caseose, etc., fibrin- 

 peptone, gelatin-peptone, histo-peptone, etc., according to the name of 

 the protein from which they arise. 



Preparation. 



The mixture of proteoses and peptones is most easily prepared by 

 digesting a protein (egg-white, meat, etc.) with 20 parts of -4 per cent hy- 

 drochloric acid and with about 'Oi gm. of pepsin at 37 for several days. 



Witte's peptone is a commercial peptone prepared in this way 

 from fibrin. Similar commercial peptone preparations are made from 

 other proteins. 



Properties. 



The commercial mixtures consist of amorphous powders, white 

 or pale yellow in colour, easily and generally completely soluble in 

 water, but sometimes a small residue remains undissolved. A solution 

 of the mixture (5 per cent.) sho'ws the following reactions : 



