182 LECTURE IX. 



of much more importance than the racemic bodies above mentioned. 

 We have, therefore, referred to them here, only because it will be necessary 

 to dwell on them more in detail later, when we consider more fully l 

 the subject of fermentation. It is clear, that we can never tell, a priori, 

 whether the polypeptides constructed from racemic amino acids, comprise 

 the modifications existing in the albumin, or not. It is, therefore, of the 

 greatest importance for the whole future investigation, that Emil Fischer, 

 supported by his satisfactory method of chlorinating the amino acids, is 

 producing polypeptides from active materials exclusively, which he obtains 

 by splitting the racemic compounds into their optically active components. 



We must not forget to mention that the peptide chains, produced from 

 di-amino acids, and especially the di-carboxylic acids, aspartic and glu- 

 tamic acids, give much greater opportunities for variation. In the 

 latter cases the amino acids can attach themselves first to the amino 

 groups, and then, again, at the two carboxyls, thus producing branching 

 chains, as can be shown by the following formula?: 



COOH COOH 



I I / CH 3 



CH . NH . CO . CH 2 . NH 2 CH . NH . CO .(NH 2 )CH . CH 2 CH' 

 | | X CH 3 



CH 2 CH 2 



COOH COOH 



Glycyl-aspartic acid Leucyl-aspartic acid 



COOH CO . NH . CH 2 . COOH 



CH . NH 2 or CH . NH 2 



CH 2 CH 2 



CO . NH . CH 2 . COOH COOH 



Aspargyl-mono-glycine 

 CO.NH. (CH 3 )CH.COOH 



CH . NH 2 

 Ho 



v- 



i 



Jo 



.NH. (CH 3 )CH.COOH 



Aspargyl-dialanine 



These illustrations may suffice to indicate the many possible combina- 

 tions which may arise by introducing these dibasic amino acids into the 

 peptide chains. We will refer here again to a discovery which we have 

 already touched upon. If we hydrolyze albumin, that is, alter the substance 

 by addition of water, either by acids, alkalies, or ferments, ammonia will 



1 Cf . Lecture on Ferments. 



