ELEMENTARY CHEMICAL PHYSIOLOGY 203 



ammonium sulphate. Naturally they both give the ordinary 

 colour reactions of protein. 



EXPERIMENT. To some diluted egg-white add two or three 

 drops of 10 per cent. HC1. Place in water bath at body temperature 

 for five minutes. Acid meta-protein is formed. 



Note. (a) That no coagulum now appears on heating. 



(b) It is precipitated by making the solution neutral or very 

 faintly alkaline. 



(c) It is salted out by half saturation with ammonium sulphate 

 (like a globulin). 



(d) If neutralised and suspended in water it is coagulated on 

 boiling. 



(b) Proteoses. This group of substances is divided into two, (1) 

 primary and (2) secondary proteoses, which are differentiated by 

 precipitation with ammonium sulphate. 



Primary proteose is a mixture of protoproteose and heteroproteose. 

 Precipitation takes place on half saturation with ammonium 

 sulphate. No coagulation takes place on boiling. A white pre- 

 cipitate forms on the addition of nitric acid ; this precipitate dis- 

 appears on heating, but reappears on cooling. They are almost 

 completely precipitated by alcohol. Salts of the heavy metals like 

 copper sulphate, mercuric chloride, etc., and tannic acid cause 

 precipitation. 



Secondary proteoses, sometimes called deuteroproteoses, are 

 precipitated on full saturation with ammonium sulphate. They 

 behave like primary proteoses except that the nitric acid and copper 

 sulphate tests are negative. 



(c) Peptone. This substance is not precipitated by ammonium 

 sulphate. It gives a very characteristic biuret reaction a definite 

 pink coloration. (If the test is done in the presence of ammonium 

 sulphate a large excess of caustic soda must be added as the alkalinity 

 of the solution must be due to sodium.) It is precipitated by tannic 

 acid and lead acetate. 



EXPERIMENT. Use the solution of Witte's peptone provided and 

 perform the following tests : 



(a) Biuret reaction is pink. (Proteoses and Peptones.) 



(b) On faintly acidifying with acetic acid and boiling no 

 coagulum. 



(c) Add a little HN0 3 a white ring. This dissolves on heating 

 and reappears on cooling. Salicyl-sulphonic acid produces the 

 same effect, but the reaction is more delicate. 



(d) To the solution add an equal amount of (NH 4 ) 2 SO 4 (half satu- 

 rate) . A white precipitate of the primary proteoses is formed. Filter. 



(e) Saturate the filtrate with crystals of (NH 4 ) 2 SO 4 . The 

 secondary proteoses are precipitated. Filter. 



(/) With the filtrate perform Biuret and xanthoproteic tests. 

 As peptones are not precipitated by HNO 3 the xanthoproteic test 

 manifests itself by a yellow colour on heating the solution, turning 



