THE END-PRODUCTS OF ALBUMINOUS DIGESTION. 207 



Isolation of Aspartic Acid and Glutaminic Acid. To isolate the 

 two acids in question among the products of tryptic digestion, the 

 mixture must first be freed from albumins and albumoses, as has 

 been described. The remaining solution is acidified with sulphuric 

 acid and precipitated with phosphotungstic acid. The filtrate is 

 freed from sulphuric acid and any excess of the phosphotungstic 

 acid by means of barium hydrate. From the resulting filtrate 

 leucin and tyrosin are then removed by concentration. The mother- 

 liquor contains the glutaminic acid and aspartic acid. These are 

 now separated from each other in the following manner: the diluted 

 solution is brought to the boiling-point and digested with carbonate 

 of copper. It is filtered while still hot, and precipitated with 

 subacetate of lead, care being taken to avoid an excess. This 

 precipitate is decomposed with hydrogen sulphide, and the filtrate 

 concentrated to a small volume. On standing a crystalline mass is 

 obtained, which is then dissolved in boiling water and digested with 

 an excess of carbonate of copper, as before. The hot filtrate is 

 again concentrated, when on standing the copper salt of aspartic 

 acid separates out in characteristic groups of needles. The filtrate 

 is freed from copper by means of hydrogen sulphide, concentrated, 

 and set aside, when the glutaminic acid crystallizes out. 



Glycocoll. While it is generally known that glycocoll plays an 

 important part in the nitrogenous metabolism of the animal body, 

 and is intimately concerned in the formation of urea, hippuric acid, 

 phenaceturic acid, certain biliary acids, and in birds and reptiles of 

 uric acid, it is of interest to note that the substance has thus far 

 not been met with among the products of pancreatic digestion, 

 although its radicle has been found present in all proteins examined, 

 with the exception of casein and globin, and the so-called Bence- 

 Jones albumin (which see), when hydrolysis was brought about by 

 means of mineral acids. It is especially abundant in silk fibrin, 

 elastin, and collagen. The hetero-albumose of fibrin, according to 

 Spiro, yields a considerable amount of glycocoll, while from the 

 proto-albnmose it cannot be obtained. 



Heretofore the isolation of glycocoll and its recognition as such 

 were attended with great difficulties. A somewhat simpler pro- 

 cedure has recently been suggested by Baum. The method is based 

 upon the observation that glycocoll can be transformed into hippuric 

 acid in the test-tube by treating with benzoyl chloride in the presence 

 of sodium hydrate, and that the formation of the resulting hippuric 

 acid can be readily demonstrated by condensing this with benzalde- 

 hyde in the presence of sodium acetate and acetic anhydride. The 

 lactimide of benzoyl-amino-cinnamic acid is thus formed. On decom- 

 position with sodium hydrate this yields phenyl-pyro-racemic acid, 

 which in ethereal solution gives a green color on treating with 

 chloride of iron. With phenyl-hydrazin, moreover, it forms an 

 osazon which melts at 161 C. These changes may be represented 

 by the equations ; 



