172 Vines — The Proteases of Plants (//!). 
fibrin-digesting (or peptonizing) enzyme : a statement that raises the im- 
portant question of the nature of the latter enzyme, to the discussion of 
which this paper is devoted. 
The Nature of the Fibrin-digesting Protease. 
The original view, propounded on the discovery of proteid-digestion 
by plants (1874), was that the active enzyme is allied to the pepsin of the 
higher animals. For instance, Darwin (6), speaking of Dionaea , says : 
£ When a leaf closes on any object, it may be said to form itself into a 
temporary stomach ; and if the object yields ever so little animal matter 
. . . the glands on the surface pour forth their acid secretion, which acts 
like the gastric juice of animals.’ Similarly, Sir Joseph Hooker ( 7 ) said, 
with regard to Nepenthes'. ‘ From the observations it would appear probable 
that a substance acting as pepsin does is given off from the inner wall 
of the pitcher, but chiefly after placing animal matter in the acid fluid’: 
and von Gorup-Besanez and Will (8) described the pitcher-liquid of 
Nepenthes as ‘a vegetable solution of pepsin.’ Von Gorup-Besanez did 
not actually use the word ‘ pepsin ’ in the account of his discovery ( 9 ) of 
a peptonizing ferment in germinating seeds (Malt, Vetch, &c.), but his 
observations suggest that this was his idea of its nature. 
This view was a fair inference from the fact that the higher proteids 
had been observed, in these cases, to be digested by an acid liquid ; and 
was supported by the discovery, made by von Gorup-Besanez, that peptones 
are formed in the process. Not only did he discover this, but he went on 
to inquire whether or not the peptones so formed underwent further change 
(peptolysis). In an experiment with extract of Vetch seeds acting on 
fibrin swollen with o-2°/ 0 HC 1 , he looked for, but failed to find, leucin, 
tyrosin, asparagin, or asparaginic acid among the products of digestion. 
This negative result must have been a disappointment to the investigator, 
since the object of his research was to account for the presence of leucin 
and asparagin in seedlings, and it had occurred to him that these sub- 
stances might possibly be formed in the germinating seed by a peptolytic 
process analogous to the pancreatic digestion of proteids in the animal 
body. However, the idea seemed untenable in the face of the above 
experiment, so von Gorup-Besanez contented himself with simply recording 
the presence in these seeds of ‘ peptonbildende Fermente.’ 
Within a comparatively short time, the pepsin-theory of the nature 
of the fibrin-digesting protease had to make way for the trypsin-theory 
by which it was replaced. The first step in this direction was the 
observation made by Wurtz ( 10 ), in his investigation of papain, that this 
substance could digest in neutral and alkaline as well as in acid media ; and 
on this account he regarded it as allied rather to the pancreatin (i. e. 
