6 
Vines. — The Proteases of Plants (VI). 
I may add that neither form of papain is completely soluble in water or 
NaCl-solutions ; after extraction, a considerable insoluble residue remains, 
which, in the case of commercial papain, consists largely of some form of 
coagulated protein, as Martin has already noticed. It should also be 
recorded that all the digestions took place at 39 0 C., and that HCN was the 
antiseptic. 
Turning, now, to the consideration of the bearing of the new facts that 
I have described, the first effect of them will be the disuse, as being no 
longer necessary, of the name ‘ papain ’ or ‘ papayotin ’). The name, in its 
original strict sense, was applied to what was considered to be a single 
substance ; but now that this supposed tryptic protease has been shown to 
be a mixture of two proteases the name has lost its significance, and, if used 
at all, might be applied to the dried latex, whether raw or refined. 
A point of great importance is the relation between the digestive 
activity of the papain-enzymes and the reaction of the medium. As already 
mentioned, Wurtz and Martin both found that digestion of fibrin or albumin 
(peptonization) was most active when the medium was neutral. Martin 
showed further that digestion is even more active in a feebly alkaline medium 
(0*35 per cent. Na 2 C0 3 ), and continues, though with diminishing activity as 
the alkalinity is increased, even when the medium contains 1 per cent. Na 2 C0 3 ; 
and that it is arrested in a medium which is acid to the small extent of 
o°o5 per cent. HC1. The few observations that I have made on this point 
in the course of these experiments confirm these results. Thus (p. 4) 
I found that the NaCl-solution of peptase digested fibrin when neutral or 
alkaline (0-5 per cent. Na 2 C0 3 ), but did not do so in the presence of 
o-i per cent. HC1, or of 0-5 per cent, citric acid. In another experiment 
(p. 5) digestion was prevented by 0*3 per cent citric acid, and by 
0-05 HC1. 
The results of some earlier experiments on this very point (19) had led 
me to form a rather different opinion from that just stated. The conclusion 
drawn from them was that the reaction-range for fibrin-digestion by papain 
extended from an alkalinity = at least 1-5 per cent. Na 2 C0 3 to an acidity = 
°’3“°\5 HC1. The discrepancy on this point between the results of my 
present and of my previous experiments is, I believe, to be accounted for on 
the ground that in the latter the solution used contained more protease ; 
and further that it also contained a good deal of protein in solution, which 
would protect the protease to some extent from the action of the acid, 
whereas, in the former, the amount of protein was very small. 
The question of the relation between the enzymes and the proteins of 
papaw-latex naturally arises here* It has been already mentioned (p. 2) 
that Martin considered the digestive action to be associated with the 
albumose. My experiments seem to show that the fibrin-digesting enzyme 
is associated with the globulin of the latex, inasmuch as it is more soluble in 
