Proceedings of the Linnean Society of London - University Library

LINNEAN SOCIETY OF LONBOX. 2 1
nimjerous experiments made with various plants and parts of
plants in which I have detected digestive action, that the enzymes
act proteolytically. In view of this accumulating evidence, the
only possible conclusion to be drawn is that the proteases of
plants are essentially proteolytic : there is, in fact, no record
of the existence in any plant of a merely or mainly peptonising
enzyme.
This conclusion has not been arrived at without contradiction.
In the case of the pitcher-plant Nepenthes, the lafe Dr. Clautriau
contested the accuracy of my results, asserting that here was
an instance of simple peptonisation. However, I have never
failed to obtain evidence of proteolysis in digestiA-e experiments
with the pitcher-liquid, and can only suggest that the conditions
of Dr. Clautriau's experiments were in some way unsuitable,
probably because the necessary acid was not supplied. More
recently Dr. Mendel has asserted that papain can peptonise but
not proteolyse the higher proteids. tn a paper which is shortly
to be published, I have shown, I think conclusively, that the
cause of the divergence between Dr. Mendel's results and my own
is that the antiseptic which he used in his experiments interfered
with the action of the enzyme.
I may now very briefly describe the methods which I have
adopted for the purpose, (1) of detecting the presence of a
protease, and (2) of determining the nature of its action.
In the first instance, the method employed was the usual one
of submitting some blood-fibrin to the action of the liquid, with
due antiseptic precautions, and observing the more or less
complete solution of it in the course of the experiment. It was
in this way that the digestive activity of Nepenthes-\\C[\x\d, Papaw,
of Pineapple-juice, and of solutions of papain, had been first
discovered ; and it Mas in this ^ay that I detected it in the Yeast,
the Mushroom, the Melon, and other plants. But in many
cases the result was altogether negative, and for the moment
I followed the usual course of accepting this as evidence for the
total absence of digestive power in these cases.
Confining my attention to the positive results, I endeavoured to
ascertain, by an examination of the products of digestion, what
had been the action of the protease in each case, whether merely
peptonising or completely proteolytic. In devising a simple
method for doing this, I remembered that one of the constant
products of pancreatic digestion is a substance termed tryptophane,
which gives a pink or violet colour on the addition of chlorinewater.
As the presence of tryptophane is accepted as evidence
of proteolysis effected by trypsin, it would also be evidence of
proteolysis by vegetable proteases. I accordingly tested the
liquids resulting from fibrin-digestions with the various plantmaterials
just mentioned, and in every case there was unmistak-
able evidence of the presence of tryptophane. The conclusion is
therefore inevitable, that in all these cases the enzyme is, like
trypsin, capable not only of peptonisation but also of proteolysis.