3 ° 1 
Vines . — The Proteases of Plants. 
After 24 hours’ digestion the tryptophane-reactions were : — 
Na 2 C 0 3 
; I % 
2 % 
3 % 
Alkaline . 
faint 
faint 
none 
Acid .... 
strong 
strong 
marked 
24 hours later they were : — 
Alkaline , 
marked 
faint 
none 
Acid .... 
very strong 
very strong 
strong. 
These experiments with Witte-peptone confirm the conclusion arrived 
at from the autolysis-experiments (see p. 298) — that yeast contains an 
actively peptolytic enzyme, most active at or near the natural acidity 
of the extract, becoming less active, to total arrest, on the addition of either 
acid or alkali. Further, they show that this protease can be very readily 
extracted with water, and that the peptolytic action of a watery extract 
is marked as well as rapid, even when (as in Expt. 1) the extract is dilute 
( 2 %)- 
Peptonization. 
Having ascertained that yeast is actively peptolytic, I proceeded 
to investigate its peptonizing capacity, the test being the complete dis- 
integration of a small quantity of fibrin. The experiments were made 
with (a) solid yeast substance, (b) aqueous extracts, (e) extracts made with 
2 °/ o NaCl solution. 
(a) Experiments with solid yeast substance. The first of these experi- 
ments was of a general character, with the object of ascertaining definitely 
if digestion of fibrin were effected by yeast, and how digestion would be 
influenced by added alkali and acid. 
Experiment 1. In each of 6 bottles were placed 40 cc. distilled water and 
5 grms. of partly dried brewers’ yeast, with toluol as the antiseptic; 0-5 grm. of 
fibrin was added to each, and the bottles were severally treated as follows : — to 
No. 1, nothing further was added ; to No. 2, 1 grm. chalk (reaction remained acid); 
to No. 3, Na 2 CO s to 0-5 % ; to No. 4, HC1 to 0-04 % ; to No. 5, HC 1 to o-i % ; to 
No. 6, HC 1 to o-2 %. 
After 20 hours in the incubator the fibrin had not disappeared in any bottle, 
though in some it had diminished; 24 hours later it had disappeared in Nos. 1 and 
2 ; 24 hours later it had disappeared in No. 3, whilst most of it remained in the 
others. 
In a repetition of this experiment (omitting bottle 6), with 10 grms. of yeast 
(25 %) in each bottle, the fibrin disappeared in all the bottles within 48 hours. 
These experiments show that yeast can digest fibrin ; and that the 
activity of any given mixture, as also its resistance to the retarding action 
of added acid or alkali, depends upon the amount of yeast that it contains. 
These two points were then further investigated. The material used in the 
following experiments was the dried ‘ granular * yeast already mentioned. 
