Vines . — The Proteolytic Enzyme of Nepenthes. 565 
and phosphotungstic acid: moreover, with saturated solution 
of sodium hydrate and dilute solution of copper sulphate 
it gave a striking rose coloration (biuret-reaction). These 
reactions indicate the presence of peptone in the liquid, and 
demonstrate that the fibrin has undergone peptic digestion. 
In the following year 1 I showed that it is possible to 
obtain^ a glycerin-extract of the pitchers which has a distinct 
digestive action on fibrin, though it acts less rapidly than 
does the pitcher-liquid, thus establishing an analogy between 
the pitchers and the gastric mucous membrane of animals. 
I carried this analogy a step further by experiments tending 
to show that the enzyme of the pitchers, like the pepsin of 
the stomach, is derived from a zymogen formed in the gland- 
cells and subsequently decomposed by the action of acids. 
It might be fairly inferred that the foregoing observations 
together form a body of evidence sufficient to warrant the 
conclusion that the pitchers of Nepenthes secrete a proteolytic 
enzyme ; and such was, in fact, the conclusion which was 
drawn. But of late years the correctness of this conclusion 
has been questioned. Thus Dubois 2 , experimenting with 
the liquid from the pitchers of various species of Nepenthes , 
arrived at the following results, which I give in his own 
words : — £ Le liquide des urnes fermees, sur le point de 
s’ouvrir, puise au moyen cl’une pipette a boule sterilisee et 
avec toutes les precautions convenables pour eviter l’intro- 
duction de germes venus du dehors, est reste limpide pendant 
plusieurs mois. Ce liquide, aussitot apres sa sortie de Turne 
fermee, mis en contact avec des cubes d’albumine coagulee, 
n'a pas attaque les cubes, ni a la temperature du milieu 
ambiant, ni a celle de l’etuve chauffee a 35-40° C. ; le liquide 
reste limpide, filtre au bout de plusieurs heures, ne contenait 
pas de peptone. 5 
‘ La meme experience repetee en puisant le liquide dans 
les urnes fermees, directement au moyen des tubes a culture 
1 Journ. Linn. Soc., XV, 1877, p. 427. 
2 Sur le pretendu pouvoir digestif du liquide de l’urne des Nepenthes ; Comptes 
Rendus, t. cxi, 1890, p. 315. 
