114 SCIENCE- PROGRESS 
result when the proteins are hydrolysed by the proteolytic 
enzymes, pepsin, and trypsin. Even under identical conditions 
it is difficult to determine how far hydrolysis has proceeded 
under their influence, as two preparations are scarcely ever of 
the same strength. Hydrolysis by acids and alkalies is not so 
limited, as they tend to give the ultimate end products which at 
the same time undergo partial racemisation. 
The study of the behaviour of the synthetical polypeptides 
to trypsin throws much more light upon the combinations which 
may actually occur in the protein molecule. Each protein may 
again possess different combinations; their properties, as also 
the various amounts of the same amino acid, obtained by 
hydrolysis, point to a variety of combinations. 
Fischer commenced his investigations upon this subject in 
conjunction with Bergell at a time when only a few of the 
dipeptides had been prepared. The hydrolysis of these by 
trypsin was found to depend upon various factors. Further and 
much more complete investigations were carried out with 
Abderhalden, as the result of which the synthetical polypeptides 
could be divided into two classes : 
Those Hlydrolysed Those not Hydrolysed 
*alanylglycine glycylalanine 
*alanylalanine glyclyglycine 
*alanylleucine A alanylleucine B 
*leucylisoserine A leucylalanine 
glycyl-l-tyrosine leucylglycine 
leucyl-l-tyrosine leucylleucine 
*alanylglycylglycine aminobutyrylglycine 
*leucylglycylglycine aminobutyryl-aminobutyric acid A 
*olycylleucylalanine aminobutyryl-aminobutyric acid B 
*alanylleucylglycine aminoisovaleryl-glycine 
dialanylcystine glycylphenylalanine 
dileucylcystine leucylproline 
tetraglycylglycine diglycylglycine 
triglycylglycinester triglycylglycine 
(Curtius’ biuret base) __dileucylglycylglycine 
The two classes show firstly the endless variety of the 
simple polypeptides, and secondly, on closer examination, that 
* These are racemic compounds. 
