ii PRIMARY DISSOCIATION-PRODUCTS 19 



caseeux,' 1 and glycocoll (or glycin), which was obtained by Braconnot 2 

 in 1820, when he boiled gelatine and meat with sulphuric acid. 

 Braconnot gave to Proust's substance the name leucin in 1820. In 1849 

 Liebig and Hinterberger 3 discovered tyrosin, which they prepared by 

 treating hair with boiling sulphuric acid. In 1865 Cramer 4 added serin, 

 which he obtained from silk glue. In 1867 Kiihne 5 demonstrated the 

 presence of leucin and tyrosin in fibrin by means of tryptic digestion, 

 and since then up till now these substances have remained the most 

 popular of dissociation -products. In 1868-69 Eitthausen 6 obtained 

 aspartic and glutaminic acids from vegetable albumins, and Kreussler 7 

 (1869) and Hlasiwetz and Habermann 8 (1873) showed that they also 

 occur in animal albumins. The just mentioned mono -amino- acids, 

 along with alanin found by Weyl 9 in 1888 in the fibroin of silk, were the 

 only known bodies till E. Schulze 10 in 1892 added amino-valerianic 

 acid. E. and H. Salkowski in 1884 11 and Nencki 12 in 1889 investi- 

 gated the aromatic products which are formed during the bacterial de- 

 composition of albumins, and arrived at the conclusion that tyrosin 

 could not possibly be the only aromatic compound in the albumin 

 molecule, and that phenyl-amino-propionic acid and skatol-amino-acetic 

 acid must also be preformed. Their prophecy has been brilliantly 

 confirmed by the discovery of phenylalanin by E. Schulze, 13 and of 

 tryptophane by Hopkins and Cole, 14 this tryptophane, according to 

 Ellinger, 15 being indol-amino-propionic acid. 



Morner 16 showed further in 1901 that cystin^ which previously had 

 been found only occasionally, was a constant decomposition-product of 

 albumin. 



1 M. Proust, Ann. de Chimie et de Physique, 10. 40 (1818). . 



2 H. Braconnot, ibid, (vou Gay-Lussac and Arago), 13. 113 (1820). 



3 F. Hinterberger, Liebig s Annalen, 71. 70 (1849). 



4 E. Cramer, Journ. f. prakt. Chem. (1) 96. 76 (1865). 



5 \V. Kiihne, Virchow's Arch. 39. 130 (1867), and Verhandl. des Heidelberger nat.- 

 med. Vereitis (N.F.), I. 236, III. 463 (1886). 



6 H. Ritthausen, Journ. f. prakt. Chem. 103. 213 (1868), 106. 445 (1869), 

 107. 218 (1869). 7 W. Kreusler, ibid. 1O7. 240 (1869). 



8 Hlashvetz and J. Habermann, Liebig's Annalen, 169. 150 (1873). 



9 Th. Weyl, Ber. d. deutsch. chem. Ges. 21. II. .1407 and 1529 (1888). 



10 E. Schulze, Zeitschr. f. physiol. Chem. 17. 193 (1892). 



11 E. and H. Salkowski, ibid.*8. 417 (1884), ^9. 8 (1884), U 491 .(1885); 

 E. Salkowski, Die Lehre vom Ham, 1882, and in Ber. d. deutsch. chem. Ges. 34. iii. 

 3884 (1901). 



12 M. Nencki, Monatshefte f. Chem. 1O. 506, 526, 862, 864, 908 (1889). 



13 E. Schulze, Zeitschr. f. physiol. Chem^Q. 63 (1884)^17. 193 (1892). 

 yu F. G. Hopkins and S. W. Cole, Journ. of Physiology, 27. 418 (1901). 



15 A. Ellinger, Berichte d. deutsch. chem. Ges. 37. 1801 (1904) ; and Zeitschr. /. 

 physiol Chem. 43. 325 (1903). y 



** 16 K. A. H. Morner, ibid. 28. 595 (1899), 34. 207 (1901). 



