Vines. — The Proteases of Plants. 315 
Now as to the nature of the peptonizing enzyme. It may be either 
a pepsin or a trypsin, but the question is, which ? This question is more 
easy to put than to answer, because there is at present no method by which 
the enzyme can be obtained free from the associated erepsin ; and until that 
is done, no direct answer can be forthcoming. But it is possible to form an 
opinion upon indirect evidence. It should be borne in mind that, as I have 
elsewhere stated, there is at present no well-established instance of the 
occurrence of a merely peptonizing enzyme in the Vegetable Kingdom. A 
more important point is, however, that of the reaction of the liquid in which 
the protease will work. The activity of animal pepsin is limited to acid 
liquids ; whilst animal trypsin, though most active in a distinctly alkaline 
liquid, can nevertheless work in a neutral or even in a slightly acid liquid. 
In its range of reaction, the vegetable peptonizing enzyme resembles animal 
trypsin rather than pepsin ; but with this difference, that whereas animal 
trypsin is most active in a distinctly alkaline liquid, the vegetable protease 
is most active in a distinctly acid liquid. It seems therefore probable that 
the protease in question may be a trypsin of a new type, characterized 
by its activity in an acid, rather than an alkaline, liquid. 
On these grounds it is suggested that the yeast and the mushroom 
contain two associated proteases, vegetable erepsin and vegetable trypsin, 
an association that finds its analogue in the pancreatic secretion of animals 
which, as Vernon has recently shown (2), contains both erepsin (pancreato- 
erepsin) and trypsin proper. The term f vegetable trypsin 1 is already 
in common use, but in a wider sense than that in which I have just 
employed it. Hitherto it has been applied to the vegetable proteases 
without taking the presence of erepsin into account, whereas I limit 
the term to the peptonizing enzyme apart from the erepsin. Vernon’s 
results have introduced the same distinction into animal physiology ; 
formerly the term ‘ trypsin ’ was applied to the protease of the pancreas, 
but this, as he has shown, is really a mixture of pancreato-erepsin with true 
trypsin. 
A few lines may be devoted, in conclusion, to the consideration of the 
question as to how far these views are applicable to plants in general. 
It can hardly be doubted that, at some period in their existence, all plants 
and all parts of plants contain a peptolytic enzyme concerned in promoting 
the distribution of proteids in the temporary form of amido-acids, &c. 
But it is not clear that a peptonizing enzyme is of such general occurrence : 
on the contrary, as I have already pointed out (13, p. 262), many parts 
of plants failed to digest fibrin in my experiments. It is possible that 
in those experiments the precise conditions most favourable to peptonization 
were not provided : it may be that, for instance, the use of NaCl extracts 
that have given such good results with the Yeast and the Mushroom, 
will give similar results in other cases. I have not yet had time to make 
