Vines . — The Proteolytic Enzyme of Nepenthes. 583 
Martin failed to find peptone among the products of digestion 
of vegetable proteids by papain, though leucin and tyrosin 
were formed. However, it does not necessarily follow that 
because the proteolytic enzyme of Nepenthes apparently does 
not give rise to peptone, no other vegetable enzyme does so. 
For it must be borne in mind that the enzyme of Nepenthes 
has a function to perform which is quite different to that of 
the other enzymes under consideration : they are destined to 
act only on the proteids in the tissues of the plant, whereas 
the enzyme of Nepenthes has to act upon the proteids of 
animals outside the plant, and to change them into substances 
which can be readily absorbed. Still there is one feature 
which all these enzymes undoubtedly possess in common, 
namely this, that they all produce relatively large quantities 
of albumoses. The whole subject of the action of vegetable 
proteolytic enzymes obviously requires careful re-investigation. 
Another peculiarity of the enzyme of Nepenthes is its great 
stability. It resists decomposition, and is indeed antiseptic, 
differing in this respect from papain (and trypsin) which, 
as Martin points out, is readily decomposed ; and its activity 
is not destroyed by treatment with such a proportion of alkali 
as Green has found to destroy that of the enzyme of the 
Lupin-seed. This greater stability is no doubt to be corre- 
lated with the fact that it has to act outside the plant, where 
it may be exposed to conditions which would render it useless 
were it less stable than it is. 
The secretion of the necessary acid by the pitchers is an 
important point to which I have not been able as yet to give 
any attention. I would only lay stress upon the fact that, in 
N. Mastersiana , the liquid in the unopened pitchers is, as 
a rule, distinctly acid, a fact which controverts the prevalent 
idea that the secretion of acid is the result of stimulation by 
the presence of foreign bodies in the pitchers. The whole 
physiology of the glands requires investigation by those 
histological methods which Miss Huie has so successfully 
employed in the study of the glands of Drosera 1 . 
1 Huie, Quarterly Journal of Microscopical Science, 1896. 
