BY JAMES M. PETRIE. 117 



solutions were kept cool by standing in water. This reagent 

 precipitates the largest amount of protein, and the filtrates 

 were biuret-fi'ee. With regard to the nature of this protein, 

 the following authorities are quoted: — 



Sebelit'M,* ISSiJ, jn't'parcd proteins by salting out egg-all )uiii in, 

 casein, etc., and found that these were completely precipitated 

 from solution liy tannic acid, giving nitrogen-free filtrates. He 

 used a solution of tannic-acetic acids and alcohol. 



Effront, t 1<^99, showed that the end-products of peptic diges- 

 tion of fibrin escape precipitation with tannic acid, and that, 

 besides peptones, some albumoses remain in solution. 



Neumeister:J: states that this reagent precipitates all proteins, 

 including proteoses and peptones. 



Simon,§ separated the total i)roteins of milk completely by a 

 solution of tannic-acetit" acids and alcohol, but found that, with 

 tainiic acid alone, ([uantitative results could not be obtained; also 

 that good results ensued oidy when sufficient inorganic salts were 

 present. 



Hedin, II 1901, b}' using a tannin-salt-acetic acid solution, 

 showed that the amount precipitated varied with the concenti-a- 

 tion of the protein-solution; and further, that the tannin-filtrate 

 contained peptones and low-er products of digestion. 



Mack,^ 1904, after preparing pure peptones by Siegfried's 

 method, showed that they were precipitated from strong solutions 

 by tannic acid, the precipitates being soluble in acetic acid. 



Winterstein and Bissegger**, 1906, used the tannic-acetic acidx 

 alcohol-mixture to pre<;ipitate the total protein of clieese-extracts, 

 and found that the results were influenced by the amount of 



* Skbelien— Zeit. physiol. Cliein. 13, 1889, 135. 

 t Effront— Chein. Ztg., 24, 1899, 770, 783. 

 J Nkumkistkr— Lehrl). H. ph3'sioI. Chem. ii., 234. 

 § SiMo.N— Zeit. pliysiol. Cheni. 33, 1901, 470. 

 II Hkdin— Journ. Plij'siol. 30, 1904, 156, 195. 

 U Mack— Zeit. physiol. Chem. 42, 1904, 259. 

 ** WiNTERSTKIN 11. BiSSEGGER. — r6id. 47, 1906, 38. 



