190 THE PRODUCTS OF ALBUMINOUS DIGESTION. 



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

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

 album! nate, coaguiable albumins, and the albumoses, as already 

 described (page 185). 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. 



Asparaginic Acid. While asparaginic acid is apparently formed 

 from all albuminous substances on digestion with trypsin, the largest 

 amounts are obtained from fibrin and gelatin. 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 asparaginic acid has not been found in the animal 

 body. In the form of its amide asparagin, however, it is widely 

 distributed in the vegetable world, and supposedly plays an im- 

 portant 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. In 

 absolute alcohol it is insoluble. Its aqueous solutions are laBvorota- 

 tory, while in the presence of nitric acid dextrorotation is observed. 



As has been shown (page 86), asparaginic acid is a dibasic acid 

 of the fatty series. It is amido-succinic acid, and is represented by 

 the formula CH r CH(NH 2 ).(COOH) 2 . It can be obtained from 

 asparagin on boiling with hydrochloric acid, as shown in the 

 equation : 



/CONH 2 /COOH 



CH 2 .CH(NH 2 )< + H 2 O == CH 2 .CH(NH 2 )< + NH 3 . 



\COOH \COOH 



Asparagin. 



It has also been produced synthetically. On reduction it yields 

 succinic acid, as has been shown. 



With cupric oxide asparaginic acid forms a crystalline compound 



