118 SCIENCE PROGRESS 
give us a very good insight as to a very large number of these 
combinations. The only way to arrive at the ultimate solution 
is the isolation of various complexes before complete hydrolysis. 
Pick and Zunz have separated various proteoses and peptones, 
but these are still too complex, as also are the bodies, called 
kyrines, prepared by Siegfried. We must determine the 
combinations of two, of three, of four, as they exist, and their 
possible combinations with each other. A commencement has 
already been made by Fischer and Abderhalden, who have 
isolated three dipeptides. 
A great deal of confusion has for a long time existed con- 
cerning the nature of the proteolytic ferments contained in 
germinating seeds and various plants. By investigating the 
action of these enzymes upon various polypeptides, Abder- 
halden and Schittenhelm found the enzymes of the germinating 
seeds of wheat and lupines contained a tryptic ferment; and 
Abderhalden and Teruuchi showed that the endotryptase of 
yeast and pepsin were like trypsin in their action, whereas 
the juice of Nepenthes contained an enzyme like pepsin in its 
nature. 
V. Tue ISOLATION OF POLYPEPTIDES FROM PROTEINS 
In 1902 Fischer described the results of some experiments 
which he had made in conjunction with Bergel! upon the 
isolation of a dipeptide from silk by means of the combined 
action of acid, alkali, and trypsin. By the action of hydrochloric 
acid upon silk fibrin, a peptone is obtained which gives a marked 
reaction for tyrosine. If this be treated with trypsin, the 
tyrosine is completely split off, and another peptone free from 
tyrosine results, which when acted upon by baryta, loses 
ammonia and yields a dipeptide. This dipeptide was considered 
to be glycylalanine, though the proof could not be satisfactorily 
given at the time. 
This product was not again obtained until quite recently, as 
the exact conditions of its formation could not be repeated ; 
Fischer and Abderhalden then isolated it in the form of its 
diketopiperazine. The silk fibrin was acted upon either by 
sulphuric acid followed by trypsin or by hydrochloric acid ; the 
product was esterified and distilled in the ordinary manner 
at a low temperature, whereby the esters of the monoamino 
