90 CHEMISTRY OF THE PROTEIDS CHAP. 



the ammonia, which is formed simultaneously, and thereby gives rise 

 to humin. 



Schmiedeberg has drawn attention to the fact that humins, as far 

 as appearance, properties, and composition are concerned, show a great 

 resemblance to the melanin s or the normally occurring dark pigments 

 of the hair, skin, etc. He therefore calls them melanoidins, and those 

 with acid characters melanoidinic acids. According to the recent 

 account of Spiegler, 1 however, melanins may show quite different 

 chemical reactions. The darkening of urine which occurs on boiling it 

 with acids depends, according to v. Udransky, on the formation of 

 humin out of the reducing substances in the urine ; he calls the dark 

 pigment seen in urine after poisoning with carbolic acid also humin. 

 Hlasiwetz 2 has pointed out that some relation exists between humin 

 substances and the deeply coloured bodies in the bark, etc., of plants, 

 and has called these dark bodies phlobaphenes. 



The melanotic pigments found during pathological conditions have 

 been investigated by Zdarek and Zeynek, 3 Brandl and Pfeiffer, 4 and 

 Wolff. 5 



C. SECONDARY DISSOCIATION-PRODUCTS DERIVED FROM THE 

 AMINO-ACIDS 



Before discussing how the primary dissociation - products are 

 linked together, and how thereby the configuration of the aibuu^ 

 molecule is determined, it is necessary to study the secondary dissocia- 

 tion-products, by which we mean those substances which result from 

 a disintegration of the primary products, namely, the amino -acids. 

 These secondary products were at one time of the highest importance 

 for the study of the chemistry of albumins, while now they are of 

 especial interest in connection with physiological research. 



(a) The Disintegration of Albumins by means of Boiling Alkalies 



Schiitzenberger 6 was the first to disintegrate albuminous substances 

 with barium hydrate under pressure ; he was followed by Schulze and 

 Bosshard, 7 while later Maly 8 and Bernert 9 used the same method in 



1 E. Spiegler, Hofmeisters Beitr. 4. 40 (1903). 



2 H. Hlasiwetz, Liebig's Ann. 143. 290 (1867). 



3 Zdarek and Zeynek, Zeitschr. f. physiol. Chem. 36. 493 (1902). 



4 Brandl and Pfeiffer, Zeitschr. f. Biol 26. 348 (1890). 



5 Hans Wolff, ffofmeister's Beitr. 5. 476 (1904). 



6 P. Schiitzenberger, Bull, de la Soc. chimique, 23 and 24. (1875). 



7 E. Schulze and E. Bosshard, Zeitschr. f. physiol. Chem. 9. 63 (1884). 



8 R. Maly, Monatshefte /. Chem. Q. 107 (1885), 9. 258 (1888). 



9 R. Bernert, Zeitschr. f. physiol. Chem. 26. 272 (1898). 



