Vines. — The Proteases of Plants {III). 185 
(, b ) those in which it also occurred with alkaline reaction : 
papain, Pineapple, Hyacinth-bulb. 
Moreover, in the latter group, fibrin-digestion proceeded when the 
alkalinity was relatively strong: papain, 1 * 5 % Na 2 C 0 3 ; Pineapple, acid 
liquid to which 8 °/ o Na 2 C 0 3 had been added; Hyacinth, acid liquid to 
which 3-4 °/ o Na 2 C 0 3 had been added. Out of all this diversity one 
inference of fundamental importance can immediately be drawn, namely 
this, that in every case it is at natural acidity that both fibrin-digestion 
and peptolysis are active ; this is their point of coincidence. 
On further consideration of these results, it will, I think, be generally 
admitted that the method employed does actually afford the means of 
realizing that separation of the proteolytic activities which I postulated 
in the introduction (see p. 174) as being essential to the investigation of the 
nature of the supposed ‘ vegetable trypsin.’ I cannot interpret the evidence 
thus obtained otherwise than as indicating that peptolysis and fibrin- 
digestion are effected by two distinct proteases : that ‘ vegetable trypsin ’ 
is, in fact, not a single protease, but a mixture of two ; the one a peptolytic 
enzyme belonging to the ereptases, the other a peptonizing, fibrin-digesting 
enzyme belonging to the peptases. I do not term the ereptic enzyme 
simply ‘ erepsin,’ or the fibrin-digesting enzyme f pepsin/ because these 
terms have been specifically applied to the proteases of animals, and 
because the properties are not identical in either case : thus ‘ vegetable 
erepsin * differs from animal erepsin in that it is active through a wider 
range of both acid and alkaline reaction, whilst the latter (at least in the 
case of the higher animals) is inactive in the presence of acid ; and 
‘vegetable pepsin’ can, in certain cases at least, act in an alkaline medium, 
whilst animal pepsin cannot. Neither the erepsins nor the pepsins of 
animals and plants are identical. It is convenient to regard the different 
kinds of erepsin as members of the group of ereptases , as being, as it were, 
species of the genus: similarly the pepsins form the group of peptases. 
Ereptases and peptases belong to the larger group of proteases , as being 
enzymes capable of acting upon proteid substances. 
The fact that the ereptase occurs alone, so far as I have been able 
to discover, in many plants, notably in leaves, makes, as I have already 
urged, in favour of the view that all peptolytic action in plants is due to 
this enzyme. The position would be materially strengthened if, in the course 
of investigation, cases of the independent existence of the peptase were 
likewise to be brought to light. But this has not yet been done ; and the 
fact that wherever fibrin-digestion has been observed it has always been 
found to be accompanied by peptolysis, remains to provide an argument 
of some weight against the view of the autonomy of the two enzymes that 
I have been led to adopt. The only immediate reply to this objection is 
the fairly obvious one, that a merely peptonizing enzyme alone would be 
