426 CHEMISTR Y OF THE DIGESTIVE PROCESSES. 



Aspartic acid is soluble with difficulty in cold water, easily soluble in. boiling 

 water, and insoluble in alcohol. It crystallises in rhombic prisms ; its solutions 

 are optically active, and curiously when in acid solution it is dextrorotatory, 

 but laevorotatory when in alkaline solution. It forms a crystalline compound 

 with copper, which may be used for purifying it. After leucine and tyrosine 

 have crystallised out from the products of a proteid decomposition, they 

 are separated from the mother-liquors, and these are further concentrated 

 and treated with a small quantity of alcohol, when after a time a new 

 crust of crystals forms. These are dissolved in water, the solution is 

 boiled with freshly precipitated cupric hydrate and filtered ; in the filtrate, 

 on cooling, crystals are deposited of the copper salt of aspartic acid just 

 mentioned. These crystals are dissolved in hydrochloric acid, the copper 

 is thrown out by a stream of sulphuretted hydrogen, and the copper 

 sulphide filtered oft'; in the filtrate, ^crystals of aspartic acid separate 

 out. 



Glutamic acid is amido-pyrotartaric acid [C 3 H 5 .(NH 2 ).(COOH). 2 ], and is 

 homologous with aspartic acid, being the next higher member in the series, 

 It occurs in minute quantities in the artificial decomposition of proteids, but 

 has not yet been shown to be formed in the decomposition brought about by 

 pancreatic digestion. It has been obtained by Kitthausen and Kreuster, 1 in 

 the decomposition of vegetable proteid by dilute sulphuric acid ; from casein 

 when decomposed by stannous chloride and hydrochloric acid, by Hlasiwetz 

 and Habermann; 2 and from reticulin, by Siegfried. 3 



It may be obtained by saturating its ice-cold solution with hydrochloric 

 acid gas, and then keeping in a freezing mixture until the compound with 

 hydrochloric acid (C 5 H 9 NO 4 + HC1) separates out in crystals, which are 

 sparingly soluble in saturated hydrochloric acid, but easily soluble in water. 

 Next, these crystals are dissolved in warm water, and the boiling solution 

 is treated with freshly precipitated moist silver oxide, which removes the 

 hydrochloric acid by forming silver chloride ; the filtrate is freed of silver 

 by a stream of sulphuretted hydrogen, and concentrated. On standing, glutainic 

 acid separates in crystals which form rhombic tetrahedra or octahedra, 

 sparingly soluble in cold, readily soluble in hot water, but insoluble in 

 alcohol or ether. Solutions of the acid are dextrorotatory (a)D.= +31*1, 

 and it shows the same phenomena with regard to rotation as are described 

 for leucine. 4 



Organic bases formed in tryptic digestion. Lysine and lysatine 

 or lysatinine. Two organic bases, lysine and lysatine or lysatinine, have been 

 recently isolated from the products of artificial decomposition of proteids, by 

 means of a modification of the method of Hlasiwetz and Habermann, in which 

 metallic zinc was added in addition to stannous chloride and hydrochloric acid, 

 and means taken to exclude oxygen during the operation. These substances 

 were first isolated from casein by Drechsel, 5 and afterwards extensively studied 

 by himself and others. 6 They have since been found among the products of 

 tryptic digestion. 7 



Lysine and lysatine are both precipitated by a hot saturated solution of 

 phosphotungstic acid, which does not precipitate the amido-acids, and so 

 furnishes a means of separating the two from the other products of a proteid 



1 Journ.f. prakt. Chem., Leipzig, 1871, Bd. iii. S. 314. 



2 Ann. d. Chem., Leipzig, 1873, Bd. clxix. S. 150. 



3 ;< Habilitationsschrif't," Leipzig, 1892. 4 See p. 423. 



5 Arch. f. Physiol., Leipzig, 1891, S. 254; Ber. d. deutsch. diem. Gesellsch., Berlin, 

 1890, Bd. xxiii. S. 3096. 



6 E. Fischer, Arch. f. Physiol., Leipzig, 1891, S. 265 ; Max Siegfried, Ber. d. deutsch. 

 diem. Gesellsch., Berlin, 1891, Bd. xxiv. S. 418 ; Arch. f. Physiol., 1891, S. 270; S. G. 

 Hedin, ibid., 1891, S. 273 ; Drechsel and Kriiger, Ber. d. deutsch. chcm. Gesellsch., Berlin, 

 1892, Bd. xxv. S. 2454. 



7 Hedin, Arch. f. Anat. u. Physiol., Leipzig, 1891, S. 273. 



