290 
Vines. — The Proteases of Plants. 
i proteolysis/ the successive stages of the process may, I would suggest, 
be conveniently distinguished as — (a) peptonization , the conversion of the 
higher proteids into albumoses and peptones ; and ( b ) peptolysis , the 
decomposition of peptones into nitrogenous but non-proteid substances. 
This terminology offers the prospective advantage of simplifying the 
classification of the proteases. But before attempting this, it is necessary 
to draw attention to a recent paper by Vernon (2) in which he announces 
the important discovery that the peptolytic activity hitherto attributed 
to trypsin is largely due to an ereptic enzyme associated with it. This 
enzyme, which may be distinguished as pancreato-erepsin, is not identical 
with the entero-erepsin found by Cohnheim in the small intestine, though 
it belongs to the same group, other members of which will no doubt be dis- 
covered in due time. The effect of this discovery is somewhat to alter the 
position of trypsin proper — that is, trypsin free from pancreato-erepsin — in 
a classification of the proteases, bringing its peptonizing activity into 
relatively greater prominence. Taking this into account, and neglecting 
the somewhat conflicting views as to the possible peptolytic activity of 
pepsin — which may, after all, be due to an associated erepsin hitherto undis- 
covered — the proteases of the animal body may be classified as follows : — 
A. Actively peptonizing, but not at all peptolytic : pepsin. 
B. Actively peptonizing and peptolytic : trypsin. 
C. Feebly peptonizing, actively peptolytic : erepsins. 
There is a question bearing upon the relation between trypsin and 
erepsin that requires special consideration. Trypsin, it is well known, 
forms tryptophane as one of the products of its peptolytic activity : but 
does erepsin produce this substance ? It is not inconceivable that a pepto- 
lytic enzyme might produce leucin and tyrosin without, however, forming 
tryptophane ; and if this were found to be true of any form of erepsin, 
it would afford a clear distinction between tryptic and ereptic proteases. 
It is unfortunate that, so far as I have been able to ascertain, the available 
information on this important point is not altogether conclusive. Cohn- 
heim’s account of the products of digestion by entero-erepsin conveys the 
impression that tryptophane was not among them : but it does not appear 
that the presence or absence of this substance was made the subject of 
special investigation. On the other hand, Dr. Vernon informs me by letter 
that he has detected tryptophane in a digestion of peptone by entero- 
erepsin. For the present, at any rate, I accept the positive rather than the 
negative evidence, adopting the view that tryptophane is a product of 
peptolysis by erepsin as well as by trypsin. 
I have not included the proteases of plants in this survey, as I propose 
to discuss their nature in the concluding section of this paper. 
In dealing with the papers on proteolysis in plants, to which I have 
alluded, I will take first those relating to cases that I have not myself 
