296 
Vines . — The Proteases of Plants. 
marked to justify the inference that a small further addition of alkali would 
arrest autolysis altogether. 
As, however, the time of digestion in this experiment was short, it was 
necessary to ascertain whether similar results were obtainable with more 
prolonged digestion. In the case of HC 1 , a repetition of the foregoing 
experiment showed that no tryptophane-reaction was developed in a 0-5 °/ o 
HC1 liquid after digestion for 20 hours, and only a slight reaction after 
72 hours. In yet another experiment, with 5 °/ o yeast-mixtures containing 
respectively 0-2 °/ 0 , 05%, o-8°/ o , and i°/ o HCl, the tryptophane-reactions 
were — at the end of 24 hours’ digestion — strong in the first, faint in the 
second, and none in the third or fourth ; and at the end of 72 hours, strong 
in the first, distinct in the second, and still none in either the third or 
the fourth. Hence it appears that autolysis was much retarded by 
o* 5 °/ o HC 1 , and altogether inhibited by o-8°/ o *or 1 °/ o . In fact the limit 
of proteolytic activity in the presence of HC1 lies between 0-5 °/ o and o-8 °/ o , 
probably about o*6°/ 0 , for a mixture containing 5 °/ o yeast. 
With regard to alkali, I found that a similar yeast-mixture, to which 
2 °/ Q Na 2 C 0 3 had been added, gave no tryptophane-reaction after digestion 
for 72 hours. In this case I endeavoured to ascertain as nearly as possible 
the minimum time of exposure to the action of alkali required to arrest 
proteolytic action, by the following method : — 
Experiment 4 . 50 cc. of a 5 % yeast-mixture, with toluol, were placed in each 
of 3 bottles, Nos. 1, 2, and 3, to which Na 2 C 0 3 was added to the extent of 1 %, 2 %, 
3 % respectively. The bottles were then placed in the incubator for a certain time. 
At the end of this time the contents of each bottle were divided into two equal 
portions, one of which was left alkaline, whilst to the other half HC 1 was added 
to slight acidity, and the 6 bottles were then returned to the incubator for any 
required number of hours, after which the tryptophane-reactions were compared. 
In the decisive experiment of this kind, the 3 alkaline bottles were digested 
for 2 hours, when the tryptophane-reactions were, in No. 1, distinct ; in No. 2, 
none; in No. 3, none. Half of the contents of each bottle having been acidified, 
the 6 bottles were further digested for 2 2 hours, when the reactions were : — 
No. 1, still alkaline, faint acidified, strong: 
„ 2, „ none „ distinct : 
„ 3, „ none „ none. 
This experiment showed that digestion for two hours with 3 °/ o Na 2 C 0 3 
entirely destroyed proteolytic activity. A similar experiment, in which the 
period of exposure to this degree of alkalinity was only one hour, showed 
that this time did not suffice to destroy proteolytic activity, though it was 
much diminished. 
The foregoing experiments were made with mixtures containing 
usually 5% dried yeast: in none was the proportion less. It seemed 
