8 
Vines . — The Proteases of Plants (VI). 
A year later, I returned to the study of Yeast-digestion, and pursued it 
in greater detail. The material used was chiefly dried Yeast. The results 
which I obtained were these ( 17 ) — 
(1) dilute watery extracts of Yeast digested Witte-peptone but not fibrin ; 
(2) dilute extracts of Yeast made with NaCl-solution (2 per cent.) 
readily digested both fibrin and Witte-peptone ; 
(fi) peptolysis and peptonization were influenced in the same manner, 
but not in the same degree, by the addition of acid or alkali. 
These results raised the important issue that may be best expressed 
in two questions : (1) Is there, as is generally held, a single protease in 
Yeast, or is there more than one ? (2) In the latter case, how many proteases 
are there, and what is their nature ? 
My answer to these questions was that ‘the two digestive processes 
—that is, the digestion of fibrin (peptonization) and the digestion of Witte- 
peptone (peptolysis) — are not effected by one and the same protease. On 
the contrary, the facts described in this paper indicate the presence of two 
proteases ; the one exclusively peptolytic, readily soluble in water [ereptase] ; 
the other exclusively peptonizing, less soluble in water, but readily soluble 
in 2 per cent. NaCl-solution [peptase] ’. 
After completing the investigation of the Hemp-seed and of papain, 
with the results already described, I turned yet once more to Yeast, to see 
if it might not be possible here also to effect the separation of the two 
enzymes, of which the distinct individuality had been so strongly suggested 
by my previous experiments. 
These experiments had, in fact, already demonstrated that, on making 
a dilute extract of Yeast with distilled water, and filtering it, a solution is 
obtained which has no action upon fibrin, but readily digests Witte-peptone 
with the formation of tryptophane. Clearly such a solution contains only 
ereptase. This being so, what remained to be done in the new experiments 
was to obtain a solution from Yeast which would digest fibrin but not 
Witte-peptone, a solution which should, in fact, contain peptase. 
I have now, after many and long-continued experiments, succeeded in 
preparing such a solution from both fresh and dried Yeast. In illustration 
of the method employed, I give a description of an experiment made with 
fresh Yeast. 
About a litre of yeast was obtained from the brewery : it was placed upon a 
filter to allow the beer to drain off, and it was washed by running water through it. 
After allowing it to drain until no more water dropped from it, the solid residue was 
of the consistence of thick paste and amounted to about nine large table-spoonfuls. 
This was removed from the filter and thoroughly mixed with 500 cc. 5 percent. NaCl- 
solution ; to the mixture was added chloroform enough to give the strength of chloro- 
form-water (0-5 per cent.), and it was left standing all night in a covered jar kept in a 
cold room. It was noticed next morning that the mixture in the jar had frothed up 
