568 Vines.— Proteolytic Enzyme of Nepenthes (///), 
conclusions and my own is as to the nature of the proteolytic 
enzyme of the pitcher-liquid, as manifested by the products 
of its activity. I need not attempt any reply to his criticisms 
beyond the remark that they appear to be based upon an 
imperfect acquaintance with my papers. The question at 
issue is simply one of fact : is the enzyme a pepsin or 
a trypsin ? — a question of some moment, for if it be a pepsin 
it will be the first instance of such an enzyme having been 
definitely proved to occur in plants. We agree that the 
enzyme produces peptones ; but here, Clautriau asserts, its 
activity ceases ; whilst I have endeavoured to prove that it 
proceeds to the further stage of forming leucin, tyrosin, and 
other substances characteristic of tryptic digestion. Clau- 
triau’s evidence is of a negative character : he states that 
he has failed to detect leucin or tyrosin, but the investigation 
made with this particular object in view was by no means 
exhaustive. On the other hand, I have pointed out (11 a y 
p. 580) that there is to be found among the products of 
digestion a substance which presents some of the char- 
acteristics of leucin, though the presence of tyrosin was not 
detected. 
It may be fairly urged that the evidence which I have 
adduced is inconclusive ; and that the only absolutely con- 
vincing proof would be the separation of leucin, and of tyrosin 
too, in sufficient quantity to admit of ultimate analysis. This 
proof I am not able to give, and for the reason that I have 
not, so far, been able to carry on digestion-experiments on 
a sufficiently large scale. Comparing my results with those 
of Martin (6) in papai'n-digestion, and those of Chittenden 
(1) in bromelin-digestion, I am led to infer that the enzyme 
of Nepenthes , which may be conveniently termed nepenthin , 
produces leucin and tyrosin in smaller quantity than does that 
(papain or papayotin) of the Papaw ( Carica Papaya , L.) or that 
(bromelin) of the Pine- Apple {Ananas sativus, Schult.) ; just 
as these enzymes, in turn, are less active than animal trypsin. 
This remark applies especially to tyrosin, which is always 
produced less abundantly than leucin in tryptic digestion ■ 
