Vines. — Proteolytic Enzymes in Plants (II). 603 
I give an account of my experiments in this direction, so far 
as they have gone. 
In March, 1902, I published in this periodical a paper (3) 
which dealt, among other topics, with the digestive properties 
of papain. I there adduced evidence to prove that this 
protease proteolyses fibrin and Witte-peptone, and is more 
active in acid than in neutral or alkaline liquids, as indicated 
by the tryptophane-reaction. As regards its proteolytic 
action, my results confirmed those of Martin (4), who had 
found leucin and tyrosin among the products of digestion. 
After my MS. had left my hands, I received a paper on the 
subject by Mendel and Underhill (5), which contains observa- 
tions apparently disproving the proteolytic activity of papain, 
and suggesting that it can only peptonize the higher proteids. 
This was followed, after an interval of several months, by 
a second paper (6), w r hich, without adducing fresh experi- 
mental evidence, restates the conclusions of the previous 
paper, criticizing also the view, to which I have more than 
once given expression, that all known vegetable proteases 
decompose the proteid molecule into leucin, tyrosin, trypto- 
phane, & c., that is, are completely proteolytic. 
The facts upon which Mendel and Underhill rely, are that 
in over sixty trials made with four different samples of papain, 
and with casein, fibrin, coagulated egg-albumin, and boiled 
muscle-tissue as the material to be digested, they failed to 
detect leucin, tyrosin, or tryptophane. Only with fresh, 
unboiled muscle were these products obtained, a result that 
these authors attribute to the self-digestion (autolysis) of the 
tissue. In all the experiments, sodium fluoride (NaF i # /J 
was the antiseptic employed. On this evidence they con- 
clude that papain is an enzyme differing from both pepsin 
and trypsin. ‘ While the products of the papain digestion of 
proteids resemble quite closely those of pepsin, . . . the enzyme 
differs from animal pepsin in that it acts readily in both 
neutral and alkaline media. On the other hand, although 
papain is comparable with trypsin in exerting a solvent action 
in fluids of various reactions, the failure to form leucin, tyrosin, 
