152 CHEMISTRY OF THE PROTEIDS CHAP. 



may remain behind which does not give the biuret-reaction. Therefore 

 at present both views have an equal right to be considered. 



Why some of the complexes dissociate so much more readily than 

 do others we, as yet, do not know. Whatever the reason may be, 

 there cannot be any doubt that some relationship exists between the 

 ease with which dissociation occurs and the presence of definite 

 dissociation-products in a given albumin. This view is borne out by 

 a study of Pick's albumoses, and also by comparing different albumins 

 with one another. Casein and globin, which are very readily digested, 

 do not contain any glycocoll, but much tyrosin and tryptophane, while 

 serum -globulin contains much glycocoll and is not readily digested, 

 according to E. Fischer and Abderhalden and Umber; 1 gelatine 

 contains the largest amount of glycocoll, no tyrosin and no tryptophane, 

 and yields, according to Reich-Herzberge, 2 mere traces of leucin on 

 being digested with trypsin. Thus the chemical character of an albumin 

 is partly determined by the quantitative amounts of amino- acids 

 present, and partly by the manner in which the amino -acids are 

 distributed over the anti- and the hemi-groups. 



The whole of the nitrogen is present as amide, and none in the 

 form of nitro-, nitroso-, or azo-nitrogen, as is proved by the fact that 

 proteids 3 and their dissociation-products give ' approximately ' the same 

 nitrogen value when they are examined by either Kjeldahl's method 

 or by that of Dumas. 4 



The carbon is contained partly in fatty and partly in aromatic 

 compounds. In both it is arranged in the same manner. The 

 heterocyclic groups are represented by a-pyrrolidin-carboxylic acid, 

 and by oxy-a-pyrrolidin-carboxylic acid. That histidin also contains 

 an imido-azol nucleus has now been proved. 



Diacipiperazin is also almost certainly a primary product according 

 to E. Fischer 5 (see p. 55). 



Hydroxyl-groups are present in serin, in tetra-oxy-amino-caproic-, 

 in trioxy-di-amino-dodecanoic-, in oxy-a-pyrrolidin-carboxylic-, in oxy- 

 amino-suberic-, in oxy-amino-succinic-acids, and in tyrosin. 



Aldehyde and ketone groups are absent in albumins, according to 

 Low 6 and v. Lorenz, 7 and so are the groups 0-CH 3 and 0-C 2 H 5 , 

 according to v. Lorenz. 



F. Umber, Zeitschr.f. physiol. Chem. 25. 258 (1898). 

 F. Reich-Herzberge, ibid. 34. 119 (1901). 



J. Munk, Arch. /. (Anat. u.) Physiol. 1895, p. 551 ; F. Soldner and Camerer, 

 Zeitschr.f. Biol. 33. 66 (1896). 



See, however, note about Kjeldahl's method on pp. 81, 82. 

 E. Fischer, Ber. d. deutsch: chem. Ges. 38. 605 (1905). 



6 0. Low, Journ. f. prakt. Chem. (2) 31. 129 (1885. 



7 J. v. Lorenz, Zeitschr. f. physiol. Chem. 17- 457 (1892). ' 



