304 
Vines . — The Proteases of Plants . 
with solid yeast, it is clear that the resistance of solid yeast to acid and 
alkali is greater than that of the filtered extracts. 
The following experiment shows that a dilute and rapidly prepared 
watery extract has little or no action on fibrin : — 
Experiment 3 , 2 grms. of dried yeast were extracted on a filter with 100 cc. 
toluol-water (1 %), the whole process being completed in 2 hours. 50 cc. of the 
filtrate were put into a bottle with 0*2 grm. fibrin. The fibrin had not disappeared 
after digestion in the incubator for 5 days. 
Having observed that the digestion of boiled fibrin took place in the 
presence of solid yeast, I made an experiment of this kind with yeast- 
extract, and with the same result: 60 cc. of a 2 o°/ o yeast-extract digested 
0-2, grm. fibrin in 4 days. 
(c) Experiments with 2, °/ o NaCl extracts. It occurred to me that 
it should be possible to prepare yeast-extracts that would digest fibrin 
more actively than did the aqueous extracts, by the use of some solvent 
other than distilled water. I found such a solvent in a 2°/ o solution of 
common salt (NaCl): extracts made with this liquid, even when rapidly 
prepared, can be depended upon to digest fibrin, and are therefore specially 
suitable for the investigation of the digestive action of yeast upon this 
proteid. 
The following experiment, with a io°/ o yeast-extract, gives a general 
indication of the effect of various antiseptics and of HC 1 upon the digestion 
of fibrin : — 
Experiment 1. 20 grms. of dried yeast were extracted for several hours on 
a filter with 200 cc. of 2 % NaCl solution. 25 cc. of the filtrate were placed in each 
of 6 bottles, treated respectively as follows: — No. 1, nothing further added; No. 2, 
added HCN to 0-2 % ; No. 3, added NaF to 1 % ; No. 4, added chloroform to 0-5 %; 
No. 5, added toluol to 0*5 % ; No. 6, added HC 1 to 0*2 % : to each added 0*2 grm. 
fibrin. 
After 26 hours in the incubator the fibrin had disappeared in all the bottles 
except No. 6, where it seemed to be quite unaltered. 
The following experiment demonstrates the inhibiting action of added 
acid and alkali : — 
Experiment 2. 40 grms. of dried yeast were extracted for several hours with 
400 cc. of 2 % NaCl solution containing 1 % toluol. 40 cc. of the filtered liquid, with 
the addition of a little more toluol, were put into each of 9 bottles with 0-3 grm. fibrin : 
the further additions were — to No. 1, nothing ; to No. 2, 2 grms. precipitated chalk; 
to Nos. 3, 4, 5, HClto o* 1 %, 0.2 %, 0-5 % respectively ; to No. 6, H 3 P 0 4 to 0-5 % ; 
to Nos. 7, 8, 9, Na 2 C 0 3 to 1 %, 2 %, 3 % respectively. 
After 5 hours in the incubator the fibrin in Nos. 1, 2, 3 showed signs of solution. 
After 24 hours it had disappeared in Nos. 1, 2, 3, and 7 : it had not perceptibly 
diminished in any of the others, nor had it done so 72 hours later. 
