METHODS FOR THE STUDY OF FERMENTS 5! 



l-leucin + l-alanyl d-leucin, then we obtain the 

 amino-acids l-leucin and d-alanin, and are left with 

 the compound l-alanyl d-leucin. This is optically 

 active. 



Most interesting results are obtained when optically 

 active polypeptides are chosen for examination in the 

 building up of which several amino-acids take part. 

 As in these bodies the rotation of every possible 

 reduction stage is well known, it is easy to find out, 

 in the most exact and unequivocal manner, at what 

 particular stage the peptolytic ferment of a particular 

 tissue attacks the substrate employed. We have 

 thus a means at hand of comparing ferments of 

 different origins, together with the possibility of 

 recognizing, in the most exact way, all the specifically 

 active peptolytic ferments. Further development 

 of this field of research, by the use of the greatest 

 variety of substrates from all kinds of substances, 

 is required, in order to give an answer to the question 

 of the peculiarities of certain kinds of cells in 

 many directions. It will be possible in future to 

 recognize certain cells by the manner in which they 

 reduce substrates, the synthesis of which, as a matter 

 of course, must be previously fully known to us. 



An example will make clear this method of study- 

 ing cell ferments. 6 The subjoined scheme supplies 



6 'Here we have an enormous field, promising very fruitful 

 results with respect to the most varied problems connected 



