178 LECTURE IX. 



to say whether they are individual substances or mixtures. Thus far their 

 study has not helped our knowledge regarding the construction of the albu- 

 min molecule. There is no doubt that the product obtained by Emil 

 Fischer and Emil Abderhalden by means of tryptic digestion, which did 

 not give the biuret reaction and was designated as " polypeptide," repre- 

 sents a cleavage product of a lower order of magnitude than the peptones. 

 It is very probably a mixture of various decomposition products. The 

 reason why we have not yet succeeded in getting an idea of the structure 

 of albumin by means of partial decomposition, is due to the fact that with 

 the large number of amino acids we should necessarily expect to find a 

 great many different decomposition products. For instance, in a digest- 

 ing mixture we find, besides peptones and free amino acids, other cleavage- 

 products which do not give the biuret reaction. As it is almost impossible 

 to separate the amino acids already known from such a mixture, it is, there- 

 fore, natural to expect, considering our unfamiliarity with the higher com- 

 plexes, that we can hardly hope to isolate them in a satisfactory manner. 



Recognizing this fact, Emil Fischer 1 recently began to investigate the 

 constitution of the albumins from an entirely different standpoint. He 

 chose the synthetic method. By linking the amino acids together, com- 

 pounds must necessarily result which bear some relation to the albumins. 

 After obtaining a knowledge of the characteristics of these synthetic sub- 

 stances, it should be possible to devise ways and means to produce analo- 

 gous compounds from the albumins. We may say, at the start, that Emil 

 Fischer's early expectations have already been partially realized. While 

 the constitution of albumin was, until recently, very much in darkness, we 

 can now thank Emil Fischer and his students for their extensive researches 

 toward solving this problem. Emil Fischer's work will, undoubtedly, 

 constitute the foundations of both the chemistry and the biology of 

 the albumins. We must return to it in all phases of the question, and 

 shall, therefore, only briefly outline its fundamental characteristics here. 



Emil Fischer started with the assumption that the amino acids in the 

 albumins were combined in the form of an amide-linking. He has shown 

 that the amino acids possess the ability of easily combining among them- 

 selves, thereby splitting off water, the amino group of one amino acid 

 reacting with the carboxyl group of another. The simplest representative 

 of this class of compounds, glycyl-glycine, is produced in the following 

 manner: 



NH 2 .CH 2 .COOH + HNH.CH 2 .COOH H 2 O 



V y ' V "V * 



Glycocoll Glycocoll 



= NH 2 . CH 2 . CO . NH . CH 2 . COOH 



V y- * 



Glycyl-glycine 



1 Cf. E. Fischer: Ber. 39, 530 (1906). 



