305 
Vines . — The Proteases of Plants . 
These results show that addition of Na 2 C 0 3 to 2°/ 0 , or of H 3 P 0 4 to 
°‘5 °/o 5 or to o -2% inhibits the digestive action of a io°/ o yeast- 
extract made with 2% NaCl solution. On comparing them with those 
obtained in the corresponding experiments with io°/ o solid yeast (p. 302), 
and with io°/ o aqueous extract (p. 303), there is complete agreement as 
regards the effect of added acid, a matter of importance in relation to 
Bokorny’s experiments ; and as regards the effect of added alkali, the only 
preparation that withstood the action of 2°/ o Na 2 C 0 3 was that containing 
solid yeast. 
The inhibiting effect of added alkali was further investigated by the 
method employed in the corresponding experiments in autolysis (p. 296) 
and peptolysis (p. 300). 
Experiment 3. 10 grms. of dried yeast were extracted on a filter for 3-4 hours 
with 200 cc. 2 % NaCl solution containing 1 % toluol. 50 cc. of the filtrate were 
placed in each of 3 bottles, to which Na 2 C0 3 was added to 1 %, 2 %, 3 % respectively; 
the bottles were then placed in the incubator for 2 hours. On being removed, the con- 
tents of each bottle were divided into 2 equal parts, one of which remained alkaline, 
the other being made slightly acid with HC1. There were then 6 bottles, 3 acid and 3 
alkaline, each containing 25 cc. of liquid : to each was added 0-2 grm. fibrin and 
a little more toluol. 
The 6 bottles were placed in the incubator, together with another bottle, No. 7, 
containing 25 cc. of the original extract, which had not been treated with Na 2 C 0 3 , 
and o° 2 grm. fibrin. 
After 20 hours’ digestion the fibrin had disappeared in bottle No. 7 (natural 
acidity) : but it had not undergone any apparent change in Nos. 1-6, nor had it done 
so after 48 hours’ digestion. 
Thus treatment for two hours with even 1 °/ o of Na 2 C 0 3 sufficed to 
destroy the digestive activity of a 5°/ o yeast-extract made with salt- 
solution, a result that more closely defines the action of alkali than those 
of the preceding experiments, in which it was ascertained that neither 
a 5% yeast-mixture (p. 302) nor a io°/ o watery extract (p. 303) digested 
fibrin in the presence of 2°/ o Na 2 C 0 3 . 
But it has not yet been made clear what is the advantage of a NaCl 
extract over a watery extract of yeast. When the extracts are strong, say 
io°/ o , the advantage is not very marked: the digestive action of both is 
vigorous and rapid, more especially when the period of extraction and 
filtration has been prolonged for many hours. When, however, dilute 
and rapidly prepared extracts are employed, the greater activity of the 
NaCl extract is most apparent, as the following experiment shows. 
Experiment 4 . 1 grm. of dried yeast was treated with 50 cc. toluol-water (1 %); 
1 grm. of yeast was treated with 50 cc. of 2 % NaCl solution : the mixtures were 
at once filtered, so that the preparation of the filtered liquids did not last more than 
2 hours. To each bottle 0-2 grm. fibrin was added, and then they were both put into 
