i75 
Vines . — The Proteases of Plants (///). 
of solubility : that is, I prepared extracts of various plants and parts of 
plants, either with distilled water or with 2°/ o solution of common salt 
(NaCl), and compared their digestive activities. This method, which is, 
of course, only applicable when solid material has to be dealt with, gave 
interesting results in the case of Yeast ( Saccharomyces Cerevisiae) and of 
the Mushroom (. Agaricus campestris). I found in both cases (4) that 
a rapidly prepared watery extract could not digest fibrin, though it 
peptolysed Witte-peptone : on the other hand, a rapidly prepared extract 
made with NaCl-solution digested fibrin within 24 hours, and also 
peptolysed Witte-peptone. From these facts I inferred that there are 
two proteases in these plants: one, readily soluble in water, digesting 
peptone but not fibrin : the other, less soluble in water, digesting fibrin. 
The former cannot well be anything but erepsin : as to the latter, the 
method gave no certain indication whether it were a pepsin or a trypsin, 
inasmuch as the NaCl-solution dissolved out not only the peptonizing 
enzyme, but the erepsin as well. A decisive result, on this method, could 
only be attained by ensuring the removal by water of the whole of the 
erepsin, leaving the peptonizing enzyme behind alone : but this I had not 
succeeded in doing to my satisfaction. Consequently, I was content to 
regard the peptonizing enzyme, provisionally, as a trypsin, in accordance 
with the prevalent view (4, p. 315). 
I then sought for another method that should be more decisive in its 
results and of more general application. In the before-mentioned experi- 
ments with Yeast and the Mushroom, I had incidentally observed that 
peptolysis and fibrin-digestion were effected in much the same manner, but 
not to the same degree, by the reaction of the liquid, whether acid, alkaline, 
or neutral : it appeared, in fact, that a physiological analysis might be 
effected in this way. I applied this method, in the first instance, to the 
investigation of papain (5), with results that led me to the conclusion that 
this substance contains two proteases, an erepsin, and a fibrin-digesting 
but not peptolytic enzyme which can only be regarded as of the nature of 
a pepsin. Since writing that paper, I have applied the method to the 
Pineapple, Yeast, the Mushroom, Malt, Hyacinth-bulb, and the pitcher- 
liquid of Nepenthes ; in fact, to most of the plants which I knew to be 
capable of digesting fibrin, and in every case with confirmatory results. 
The following is a selection from the very numerous experiments : 
for the sake of completeness I introduce some made with papain, although 
I have already dealt with that substance (5). I may explain that an 
important feature in my method is the simultaneous presentation of fibrin 
and Witte-peptone for digestion. Moreover, the essential point for a 
successful experiment is to add acid or alkali in due proportion to the 
enzyme-strength of the digesting liquid. When the reaction was artificially 
varied, HC1 was the acid used, and Na 2 Co 3 the alkali. The antiseptic 
