Page:Defensive Ferments of the Animal Organism (3rd edition).djvu/76

 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 studying cell ferments. The subjoined scheme supplies