1 6 Vines . — The Proteases of Plants (VI). 
The view that I propose in substitution for the f vegetable trypsin ' 
theory is that the proteases of plants belong to two groups, the peptases 
and the ereptases — a view that is now supported by a considerable body 
of evidence, both direct and indirect. It remains now to consider the 
respective properties of these proteases, so far as they are known. 
The Ereptases are enzymes which are readily soluble in water, in watery 
solutions of neutral salts, and in alcohol up to over 65 per cent. ; their 
digestive activity seems to be exclusively peptolytic, and to be especially 
associated with an acid medium. I am unable to give even an approximate 
reaction-range for plant-ereptase, because I have not yet made any ex- 
periments with it in pure solution ; all my experiments, so far, have been 
made with extracts containing other substances in solution, the presence 
of which materially affects the action of acids or alkalies upon the enzyme. 
For instance, I have found ( 17 ) the reaction-range of peptolysis in a 
5 per cent. Yeast extract to be from o-6 per cent. HC 1 to 2 per cent. 
Na 2 C 0 3 , a very wide range which could certainly be very much reduced 
were the experiments to be repeated with a liquid containing only the 
ereptase in solution. 
I have not yet come across any facts to indicate that the ereptases of 
various plants are materially different from each other. 
The Peptases are proteases of which the digestive activity is limited to 
the peptonization of the more complex proteins. 
There is some ground for thinking that there are at any rate two kinds 
of peptases, which differ from each other (a) in the mode of their occurrence, 
and ( b ) in the relation between their respective digestive activities and the 
reaction of the medium. The one kind exists in the tissues of plants, 
fruits, seeds, latex, &c., and may therefore be designated endopeptase ; the 
other kind is to be found in the excretions of plants, for example, in the 
pitcher-liquid of Nepenthes , and may be distinguished as ectopeptase . 
(a) Endopeptase is an enzyme which can be readily extracted from the 
tissues, &c., in which it occurs by NaCl-solutions ; and also, to a less extent, 
by water, and by 50 per cent, alcohol. The extraction by means of water 
is due to the presence of salts and other substances which are extracted 
with the peptase ; for, when obtained as free as possible from foreign bodies, 
it is not soluble in distilled water (vide Yeast, p. 9), but is still soluble 
in 2 per cent. NaCl-solution. Its digestive activity, like that of ereptase, 
is greatest at the natural reaction, generally somewhat acid, of the plant- 
extract which contains it. Very slight addition of mineral acid (0-05 HC 1 ) 
or of a rather larger quantity of organic acid (-3 per cent, citric acid) arrests 
the action of a pure solution of the enzyme, which digests fibrin actively 
when neutral or slightly alkaline ; an increase of alkalinity retards and 
finally stops digestion. 
(b) Ectopeptase is an enzyme which is in solution in the excretion of at 
