7 
Vines . — The Proteases of Plants {VI). 
NaCl-solutions than it is in water; probably the pure peptase would be 
insoluble in pure water. But it must be pointed out that in several experi- 
ments the active peptase-solution gave but a faint xanthoproteic reaction, 
indicating a very small quantity of protein. 
The demonstration of the presence of two distinct proteases in papain 
would be more complete had I succeeded in preparing, not only extracts 
that were exclusively peptonizing, but also extracts that were exclusively 
peptolysing. I have endeavoured to obtain solutions of the latter kind at 
various stages of the methods here described for obtaining those of the 
former kind. For instance, I have treated the papain residue, after extrac- 
tion with 2 per cent. NaCl-solution, with water, and obtained solutions which 
peptolysed Witte-peptone actively, but also had some digestive action on 
fibrin ; similarly, the alcoholic precipitate of the NaCl-solution, when treated 
with water, gave a solution that peptolysed actively, but also peptonized. 
The only liquid that I have found to be exclusively peptolytic is the 
alcoholic liquid filtered off from the alcoholic precipitate of the NaCl-extract. 
I found that some of this liquid, diluted with an equal bulk of water, acted 
upon Witte-peptone so as to cause a distinct tryptophane-reaction, but had 
no effect upon fibrin. Ereptase was clearly present ; but it is not so clear 
that peptase was absent, though probably it was ; for the amount of alcohol 
present was sufficient, as I found by control-experiments, to prevent the 
peptonization of fibrin in liquids known to contain peptase. I anticipate, 
however, that it will be possible to make use of the solubility of ereptase in 
fairly strong (above 60 per cent.) alcohol in devising a method for its 
isolation. 
Yeast {Saccharomyces Cerevisiae). 
The investigation of the proteolytic activity of Yeast began in 1889 
with Salkowski’s observation that, if Yeast be kept in chloroform-water, the 
liquid eventually contains leucin and ty rosin which can only have been formed 
by the digestion of its own proteins. Ten years later (1898-1900) Hahn and 
Geret began the publication of a series of papers (22, 23 ) bearing upon the 
subject ; they found that leucin and tyrosin were formed in the self-digestion 
of the expressed juice of Yeast ; that the juice digested fibrin, egg-albumin, 
casein, with the formation of leucin, tyrosin, and tryptophane among the 
products ; and that digestion was most active in acid medium (0-2 per cent. 
HC 1 ). The name ‘ endotrypsin ’ or ‘ endotryptase ’ was given by them to 
the proteolytic enzyme, on account of the nature of its digestive activity. 
It was, and still is in fact, regarded as a form of 4 vegetable trypsin ’. 
My own observations on Yeast began in 1901, when I tested its 
digestive action in the course of my search for tryptophane as a constant 
product of the proteolysis of plants ( 14 ). The result of these first experi- 
ments was that tryptophane was found in Yeast-digestions when the medium 
was neutral or acid, but not when it was alkaline. 
