18 CHEMISTRY OF THE PROTEIDS CHAI-. 



either, while the imide-groups by which the different carbon-chains are 

 kept together are broken, as first suggested as a possibility by Kossel : 1 > 2 



CO - NH - C becomes COOH, NH 2 - C. 



In arginin, according to E. Schulze, 3 a guanidin remainder unites two 

 carbon-chains, and is on the one side next to the carbonyl-group CO. 

 The change produced by acids in guanidin is as follows : 



CO - NH - CNH - NH - C becomes COOH, NH 2 - CNH - NH - C. 



Dissociation by acids resembles that produced by certain ferments. 

 The best method for dissociating albumins by acids is that of Hlasiwetz 

 and Habermann, 4 who use hydrochloric acid with the addition of 

 stannous chloride. F. Bopp 5 and R. Cohn 6 omit the use of a reducing 

 substance such as stannous chloride, but this is, according to Otori, 7 a 

 mistake. The best general account of the hydrolysing action of acids 

 is given by Kossel and Kutscher. 8 



The effect produced by ferments is discussed on pp. 187-199. 



While it is thus possible, on the one hand, to dissociate albumins, 

 E. Fischer, 9 on the other hand, has been successful in linking up two 

 or more of these primary dissociation-products, and has thereby formed 

 imino-compounds, which bear a great resemblance to the simplest of all 

 albumins, namely, the peptones. (Compare Chapter VII.) 



All the other dissociation-products are not formed directly from 

 the albumin molecule, but only secondarily out of the primary dissocia- 

 tion-products, and are therefore only of subordinate importance in all 

 investigations into the constitution of albuminous matter. These 

 secondary products helped us, however, at one time in filling up 

 gaps in our knowledge regarding the primary products, although of 

 late their importance has been greatly diminished. 



Historical Account 



The oldest known dissociation-products of albumins are probably 

 leucin, discovered in 1818 by Proust in cheese and called 'oxide 



%1 A. Kossel, Zeitschr. f. physiol. Chem. 25. 188 (1898). 



v 2 A. Kossel, ibid. 41. 321 (1904). v 3 E. Schulze, ibid. 11. 43 (1886). 



4 Hlasiwetz and Habermann, Liebig's Ann. 159. 304 (1871) and 169. 150 (1873). 



5 F. Bopp, ibid. 69. 16 (1849). 



6 R. Cohn, Zeitsch.f. physiol. Chem. 22. 153 (1896), and 26. 395 (1899). 

 V J. Otori, ibid. 43. 74 (1904). 



^ Kossel and Kutscher, ibid. 31. 165 (1900). 



9 E. Fischer and E. Fourneau, Ber. d. deutsch. chem. Ges. 34. II. 2868 (1901) ; E. 

 Fischer, ibid. 35. I. 1095 (1902) ; E. Fischer, Chemikerzeitung, 1902, II. p. 939 ; E. 

 Fischer, Ber. d. -deutsch. chem. Ges. 36. II. 2094 (1903) ; E. Fischer and E. Otto, ibid. 

 36. II. 2106 (1903), 36. III. 2993 (1903) ; E. Fischer and P. Bergell, ibid. 36. II. 2592 

 (1903) ; E. Fischer, ibid. 36. HI. 2982 (1903). 



