THE PRODUCTS OF TRYPTIC DIGESTION. 191 



winch is almost insoluble in cold water, but dissolves in boiling 

 water with comparative ease. This property is utilized for the pur- 

 pose of isolating the substance from the mixture of digestive 

 products. 



Glutaminic Acid. Whether or not glutaminic acid is formed 

 during the tryptic digestion of the albumins in general has not as 

 yet been ascertained. Kutscher claims to have found it in the 

 iso-called antipeptone of Kuhne, which was obtained from fibrin. 

 On boiling with strong mineral acids, however, it is constantly 

 formed. But it is noteworthy that much larger quantities are found 

 if the decomposition of the albumins is effected with hydrochloric 

 .acid than with sulphuric acid. Kutscher thus found only 1.8 per 

 cent, among the decomposition-products of casein when using sul- 

 phuric acid, while Hlasiwez and Habermann obtained as much as 

 29 per cent, when hydrochloric acid was used. This is, of course, 

 remarkable, and it would be exceedingly interesting to ascertain the 

 fate of those radicles which can yield so large an amount of glula- 

 minic acid when decomposition is effected by hydrochloric acid. 



Glutaminic acid crystallizes in small glistening crystals, 

 are soluble with difficulty in cold water, while in boiling water they 

 dissolve with greater ease, but separate out on cooling. With acids 

 and alkalies it combines to form salt-like products, among which the 

 hydrochlorate is conveniently utilized for the purpose of identifying 

 the substance. The melting-point of this compound is 193 C. 



The composition of glutaminic acid is expressed by the formula 

 CH 2 .CH 2 .CH(NH 2 ).(COOH) 2 . It is thus amido-glutaric acid, and 

 bears the same relation to glutamin as that which exists between 

 asparaginic acid and asparagin. This is represented in the equation : 



X CONH 2 /COOH 



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



M3OOH \COOH 



Glutamin. 



On reduction it yields glutaric acid. 



Isolation of Asparaginic 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 asparaginic 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 



