Proceedings of the Linnean Society of London - University Library

22 PROCEEDINGS OF THE
I now returned to the consideration of the cases in which I had
failed to observe the digestion of fibrin ; and on applying to tliem
the tryptophane-test, 1 was somewhat surprised to find that it
frequently gave a distinct and even strong reaction, especially
when the material used consisted of pieces of the root, leaf, bulb,
etc. under examination. It was clear that a protease was present
which, though it did not act upou fibrin, digested the proteids
contained in the juice or tissue of the plant itself. Seeing that
these proteases, though possessing but slight peptonising power,
were strongly proteolytic, 1 varied the mode of experiment by
submitting to their action such simple proteids
peptones, with most satisfactory results.
as albumoses and
I thus reached the further conclusion that whilst in certain
plants (e. g. Pineapple, Papaw, Nepenthes, Teast, etc.) there are
proteases which closely resemble trypsin in their mode of action,
in the majority of cases there are proteases which differ from
trypsin in that they cannot peptonise fibrin though they resemble
trypsin in proteolysing albumoses and peptones. These pro-
teases seemed to belong to an altogether new type of enzyme ;
a consideration that led me to feel some misgiving as to my
observations. Fortunately I happened, at this junctui'e, to hear of
Cohnheim's recent discovery in the intestine of animals, of an
enzyme possessing somewhat similar properties. This enzyme, to
which he has given the name Erepsin, proteolyses albumoses and
peptones, but cannot peptonise a more complex proteid than
casein. I thus obtained confirmation of the surmise that the
proteases which I had discovered were not tryptic, although they
were proteolytic.
I must not overburden with detail this slight sketch of the
growth of knowledge with regard to the distribution and nature
of proteases in both plants and animals. I will, however, venture
upon a few remarks of a general nature. With regard to the
distribution of the proteases in the body, they have been found,
as I have said, in all parts of the plant—leaves, stems, roots, bulbs,
tubers, fruits, seeds ; and the inference might be drawn that
herein the plant differs from the animal organism, in which these
enzymes are confined to the digestive tract. But this inference
would be only partially true even of the higher animals. No
doubt the enzymes are especially secreted by the digestive organs
but recent researches, more especially those of Hedin, have shown
that they are widely distributed throughout the tissues of the
animal body.
Then as to the I'elation to each other of the three known types
of proteases— the peptic, the tryptic, the ereptic. The relation
between trypsni and erepsin has already been sufficiently indicated.
"With regard to pepsi«, it has long been generally held, though
with some dissentients, that pepsin is an enzyme which can only
peptonise but cannot further decompose proteids. But of late
years there has been an accumulation of evidence tending to
show that this view is too arbitrary : to show that pepsin can, as a
;