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 rnotherdiquors, 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 off; in the filtrate, crystals of aspartic acid separate 
out. 
Glutamic acid is amido-pyrotartaric acid [C 3 H 5 .(NH o ).(C00H) o ], 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 lireuster, 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-H ) X0 4 + HC1) separates out in crystals, which are 
sparingly soluble in saturated hydrochloric acid, but easily soluble in water. 
Xext, 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, glutamic 
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=+31d, 
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./. prakL Chem., Leipzig, 1871, Bd. iii. S. 314. 
2 Ami. <•'. Chem., Leipzig. 1873, Bd. clxix. S. 150. 
3 " Habilitationsschrift," Leipzig, 1892. 4 See p. 423. 
5 Arch. f. Physiol., Leipzig, 1891, S. 254 ; Ber. d. deutsch. cliem. Gesellsch., Berlin, 
1890, Bd. xxiii. S. 3096. 
6 E. Fischer, Arch. f. Physiol.. Leipzig, 1S91, S. 265 ; Max Siegfried, Per. d. deutsch. 
chem. Gesellsch., Berlin, 1891, Bd. xxiv. S. 41S ; Arch. f. Physiol., 1891, S. 270; S. G. 
Hedin, ibid., 1891, S. 273 ; Drechsel and Kriiger, Ber. d. deutsch. chem. Gesellsch., Berlin, 
1892, Bd. xxv. S. 24".4. 
7 Hedin, Arch. f. Anat. v. Physio/., Leipzig, 1891, S. 273. 
