572 Vines. — Proteolytic Enzyme of Nepenthes {III), 
If, however, these enzymes be grouped according to their 
mode of action, the three vegetable enzymes may be associated 
with trypsin, since they induce that disruption of the proteid 
molecule which is marked by the formation of tryptophan 
and other, non-proteid bodies such as leucin and tyrosin : on 
the same ground they would be distinguished from pepsin. 
But it must be borne in mind that the chemistry of peptic 
proteolysis is probably by no means so simple as it has been 
thought to be. Although it has been generally accepted that 
pepsin does no more than to hydrolyse the higher proteids 
into peptones, there have long been physiologists, like Hoppe- 
Seyler, holding the view that non-proteid crystallizable sub- 
stances, such as leucin, tyrosin, and others, are formed in 
prolonged peptic digestion. The most recent researches 
in this direction, those of Zunz (12) and of Lawrow (5), go 
to prove that such substances are in fact among the products 
of peptic digestion, without, however, proving their identity 
with the non-proteid products of tryptic digestion. Lawrow 
asserts that he has detected leucin in a prolonged (two 
months) self-digestion of a pig’s stomach : but, on the other 
hand, he failed to find tyrosin. In no case, so far as I am 
aware, has tryptophan been found in peptic digestion ; and 
until that has been done, the tryptophan-reaction may be taken 
as the distinguishing criterion between the action of trypsin 
and that of pepsin. What exactly the relation between peptic 
and tryptic digestion may be, cannot be determined until 
a great deal more is known as to the chemical details of 
both processes. It is not impossible that they may be found 
to differ, not in kind, as is now generally assumed, but only 
in degree : in which case the vegetable enzymes enumerated 
above would form a series intermediate in properties between 
pepsin on the one hand and trypsin on the other. 
The evidence afforded by the tryptophan-reaction 
strengthens the suggestion which I have already ventured 
to make (11 b> p. 555), that all known proteolytic enzymes 
of plants are tryptic, though some of them, such as that 
of Drosera , still await investigation. 
