io Vines . — -The Proteases of Plants ( VI). 
trypsin 5 of Yeast, is, therefore, not a single protease, but a mixture of two ; 
consequently the term may now be dispensed with. 
It will be seen that the results obtained with Yeast agree with those 
obtained with papain, and lead to the same conclusions. 
Review of the Subject. 
Now that my researches upon the proteases of plants have led to a 
definite conclusion, valid at least for the materials that have been subjected 
to experiments, I should like to retrace briefly the steps by which I have 
arrived at that conclusion. 
Without attempting a complete history of the subject, the delivery ot 
Sir Joseph Hooker’s presidential address at the Belfast meeting of the 
British Association in 1874, and the publication of Darwin’s book on 
‘ Insectivorous Plants ’ in the following year, may be taken as the starting- 
point of the scientific investigation of proteolysis in plants. The first conclu- 
sion arrived at was that the secretions of insectivorous plants contain an 
enzyme similar to the pepsin of animals, inasmuch as it digests fibrin and 
the other higher proteins in acid medium. 
The next step was the discovery by von Gorup-Besanez, about the 
same time, of the existence of proteolytic enzymes in ordinary, non-insec- 
tivorous, plants. The fact of the presence of leucin and asparagin in seedlings 
of a Vetch, when grown in darkness, suggested to him that these substances 
must be the products of changes in the reserve-protein of the seed effected 
by a digestive enzyme. Accordingly he examined the seeds of the Vetch, 
but whether germinated or ungerminated he does not say, and succeeded in 
extracting from them, by means of glycerin, an enzyme that converted 
fibrin into peptone in the presence of 0-2 per cent. HC1 (4). He subse- 
quently investigated the seeds of the Hemp {Cannabis sativa) and of the Flax 
(Linum usitatissimuni)> apparently ungerminated, as also Malt, arriving at 
much the same result as in the case of the Vetch (5). He sought in vain for 
leucin, trypsin, and asparagin among the products of the digestion of fibrin. 
Thus he failed to trace the leucin, asparagin, &c., found in seedlings to 
a digestive process ; and though he did not call the enzyme that he found 
by the name c pepsin he described it as * peptonbildendes ferment ’. 
The first general idea as to the nature of the apparently wide-spread 
protease of plants was, therefore, what may be termed the pepsin-idea : that 
is, it was considered to be a peptonizing enzyme acting only in acid 
medium. However, facts soon began to come to light which gradually 
made this view untenable. The investigation of papain by Wurtz, already 
mentioned on p. 2, showed that here was an enzyme which digested 
fibrin not only in acid, but also in neutral and even alkaline media. 
Although Wurtz found nothing but peptone in the products of digestion * he 
realized that enzyme could not be a pepsin, so he regarded it as a kind of 
