THE END-PRODUCTS OF ALBUMINOUS DIGESTION. 205 



reaction is due to the formation of nitro-tyrosin nitrate, but is not 

 characteristic, as other bodies behave in a similar manner. 



Morner's Test. A small amount of tyrosin, in substance or in 

 solution, is added to a few c.c. of a special reagent which has the 

 composition: formalin, 1 part; distilled water, 45 parts; and con- 

 centrated sulphuric acid, 55 parts. The mixture is boiled, when 

 either at once or a few minutes after boiling has begun a fine green 

 color develops which persists for a long time. Other compounds 

 which are closely related to tyrosin, as also native albumins, albu- 

 moses, and albuminoids, do not give the reaction. With chemically 

 pure jo-oxyphenyl propionic acid and the corresponding acetic acid 

 Morner had not been able to test his reaction. 



Isolation of Leucin and Tyrosin. To isolate leucin and tyrosin 

 among the final products of tryptic digestion, and to separate the 

 two from each other, the digestive mixture is first freed from alkaline 

 albuminate, coagulable albumins, and the albumoses, as already 

 described (page 196). The final filtrate is concentrated to a syrupy 

 consistence, when on cooling leucin and tyrosin crystallize out. The 

 mass of crystals is then boiled with a large quantity of water, to 

 which a sufficient amount of ammonia is added to insure solution of 

 the substances. The boiling solution is treated with subacetate of 

 lead until the resulting precipitate appears almost white. The fil- 

 trate is brought to the boiling-point, neutralized with sulphuric acid, 

 and filtered while boiling hot. On cooling, the tyrosin crystallizes 

 out, while the leucin remains in solution. The former can then be 

 purified by recrystallization from boiling water or from very dilute 

 ammonia. The solution which contains the leucin is freed from lead 

 with hydrogen sulphide, and the filtrate is concentrated and boiled 

 with an excess of freshly precipitated cupric hydrate. A portion of 

 the leucin is thus precipitated, while the rest remains in solution, 

 but partly crystallizes out on cooling as the corresponding copper 

 compound. The precipitate is placed in the copper-containing 

 solution, and is freed from copper with hydrogen sulphide ; the 

 filtrate is then decolorized with animal charcoal, strongly concen- 

 trated, and set aside for crystallization. 



Aspartic Acid. While aspartic acid is apparently formed from 

 all albuminous substances on digestion with trypsin, the largest 

 amounts are obtained from certain vegetable albumins (edestin from 

 hemp-seed, legumin, conglutin of lupinus seed). Like leucin and 

 tyrosin, it likewise results on artificial decomposition of the albu- 

 mins with dilute mineral acids and alkalies, and is also formed 

 during the process of albuminous putrefaction. Outside the in- 

 testinal canal aspartic acid has not been found in the animal body. 

 In the form of its amide asparagin it occurs widely distributed in the 

 vegetable world, and supposedly plays an important role in the 

 synthesis of the vegetable albumins. 



The substance crystallizes in rhombic prisms, which are soluble 

 with difficulty in cold water, but are quite soluble in hot water. 



