PHYSIOLOGICAL CHEMISTRY 311 



EXPERIMENT XIV. Render dilute egg-white alkaline, and treat as 

 above. Alkali meta-protein is prepared. It gives similar reactions to 

 acid meta-protein. As, however, in making alkali meta-protein some of 

 the loosely combined nitrogen and sulphur are split off, it cannot be 

 changed into acid meta-protein. The reverse change is, however, 

 possible. Acid meta-protein when prepared from muscle (myosin) 

 is often called syntonin. Alkali meta-protein when prepared by the 

 action of strong alkalis on protein is termed " Lieberkiihn's Jelly.' 

 Acid meta-protein is one of the first products of peptic digestion of 

 protein, alkali meta-protein of tryptic digestion. 



Proteoses and Peptones. These occur as the first stages of protein 

 cleavage under the action of such agents as mineral acids, superheated 

 steam, the proteolytic enzymes. They will be more fully studied 

 under Digestion. (See p. 384). 



EXPERIMENT XV. 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 Am 2 SO 4 (half saturate). 



A white precipitate of the primary proteoses (except hetero- 

 proteose) which are salted out Filter. 



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



proteoses are salted out. ' Filter. 



(/) With the filtrate perform Biuret and xanthoproteic tests 

 To obtain the Biuret test in the presence of a large quantity 

 of Am 2 S0 4 a large excess of caustic soda is required. As 

 peptones are not precipitated by HNO 3 the xanthoproteic 

 test manifests itself by a yellow colour on heating the 

 solution, turning orange with ammonia. The positive results 

 show the presence of peptones. 



From these experiments we learn : 



(1) That proteoses and peptones give a pink Biuret. 



(2) That they are not coagulable by heat. 



(3) That proteoses give a precipitate with HN0 3 soluble on 



heating. Therefore, in the presence of other proteins, 

 precipitated by HN0 3 , such as albumin and globulin, they 

 can be separated by warming the solution and filtering hot. 



