3 
Vines — The Proteases of Plants ( VI ). 
the presence of alkali (05 per cento Na 2 C0 3 ), results that were confirmed 
by some further observations which were published about a year later (16). 
Returning again to the subject (18), I was struck by the fact that the 
digestion of fibrin and that of peptone were not always similarly affected by 
changes in the experimental conditions ; and consequently expressed the 
opinion that papain may be a mixture of two proteases, the one fibrin- 
digesting but not peptolytic, the other peptolytic but not fibrin-digesting. 
In a supplementary paper, containing some further facts concerning 
papain-digestion amongst others, I suggested that the fibrin-digesting 
enzymes should be classed as peptases , and the peptolysing enzymes as 
ereptases . 
The mode in which I have endeavoured to establish these views, in the 
case of papain by separating the peptase and the ereptase, is based upon the 
observation frequently made in the course of my work, that extracts of 
plant-material made with 2 per cent. NaCl-solution digest fibrin more 
actively than similar extracts made with distilled water. This fact sug- 
gested the possibility of there being a fibrin-digesting enzyme (peptase) 
present, which is less soluble in distilled water than the peptone-digesting 
enzyme (ereptase). If this be so, it should be possible to wash out all the 
ereptase, by treating the material with relatively large quantities of dis- 
tilled water, leaving some, at any rate, of the peptase behind. I tried this 
repeatedly with papain, as well as with other material, but without success ; 
however much water I used, the washings, as shown by experiment, con- 
tinued to contain ereptase: in fact the ereptase in the material seemed 
inexhaustible. 
It occurred to me eventually that extraction of papain with NaCl- 
solution, instead of with water, might lead to the desired result, and this 
proved to be the case. I found that when papain was extracted with 
20-25 times its volume of 2 per cent. NaCl-solution and the liquid 
filtered off, either the residue contained no ereptase, or any remaining in it 
could be washed out by means of water ; and further, that this residue 
treated with 2 per cent. NaCl-solution, yielded, after filtration, a liquid 
which digested fibrin but was without action on peptone. By these means, 
however, only the fibrin-digesting enzyme is separated ; the ereptase not 
being obtained in pure solution. The method is illustrated in detail by the 
following note of an experiment: — 
10 grms. of commercial papain mixed thoroughly in a mortar with 200 cc. 2 per 
cent. NaCl-solution : after standing for an hour or so, the'’ mixture was placed on a 
filter : filtration was slow (it would have been better if 250 cc. of the NaCl-solution 
had been used). 
Filtrate 1. The filtered NaCl-extract was clear, light yellow, acid; it gave a 
dense ppt. on boiling, and on the addition of nitric acid (HN0 3 ) : it also gave a distinct 
tryptophane-reaction. 
