Vines. — The Proteases of Plants. : 307 
that may be expressed in the two questions — (1) is there, as is now generally 
held, a single protease in yeast, or is there more than one, and in the latter 
case, how many ? (2) What is the nature of the protease or proteases ? The 
results of my experiments will be briefly considered with a view to a reply. 
Peptolysis. The most important fact that has been brought to light 
is the rapidity with which this process is effected : thus in an autolysis- 
experiment (p. 395) it was found to have proceeded actively in 2I hours ; 
and in a Witte-peptone experiment (p. 299) in 1 hour. Moreover, in the 
latter experiment the watery- extract was very dilute (2 °/ o ) and the time 
of extraction very short (1 hour): therefore the protease concerned is 
readily soluble in water. 
It has been shown, further, that peptolysis is most active at or near 
the natural acidity of the liquid, at a degree of acidity determined by the 
presence of acid phosphates. It is retarded, and eventually arrested, by 
any deviation from this degree of acidity, in the direction either of 
alkalinity or of increased acidity : the effect of added alkali or acid varies 
with the amount of solid yeast present, or with the strength of the extract, 
as also with the length of the exposure to its action. Thus, in the case 
of a 5°/ 0 yeast-mixture, peptolysis was found to be inhibited in the presence 
of either about o *6°/ o HC 1 , or 2% Na 2 C 0 3 , for 24 hours, as also by ex- 
posure to 3°/ o Na 2 C 0 3 for 2 hours (p. 296). Similar results were obtained 
with 5 °/ o watery extracts acting on Witte-peptone (p. 299). 
Peptonization. Under this heading I include the experiments upon 
the digestion of fibrin. 
It has been made clear, in the course of these experiments, that 
peptonization takes place much less rapidly than peptolysis. Even with 
relatively strong yeast-extracts several hours were required for the digestion 
of a small quantity of fibrin : thus 40 cc. of a 5 °/ o yeast-mixture did not 
digest 0-3 grm. fibrin at all in 22 hours, though the fibrin disappeared 
within 24 hours more (p. 302). 
The next point of importance is the relation between watery extracts 
of yeast and NaCl extracts. When the extracts were strong (5% and 
upwards) and the time of extraction long, the difference in the activity 
of the two kinds of extracts was not found to be important ; but when 
the extracts were dilute and the time of extraction short, the difference 
was striking. A rapidly prepared 2 °/ Q watery extract did not digest fibrin 
at all (p. 304), whilst a similarly prepared NaCl extract (p. 305) digested 
the fibrin in about 24 hours. The inference to be drawn is that the 
peptonizing enzyme is not readily soluble in distilled water, but is readily 
soluble in 2 °/ o NaCl solution. 
Peptonization was found, like peptolysis, to proceed most actively 
at or near the natural acidity of the liquid, and to be arrested or retarded 
by the addition of either acid or alkali. But a comparison of the results 
