252 Vines. — Proteolytic Enzymes in Plants. 
Na 2 C 0 3 ) as when it is acid. Experiments in alkaline medium 
were performed with leaves of Lettuce, Spinach, and Celery ; 
the tuber of the Potato ; the bulbs of the Tulip and the 
Hyacinth ; the fruit of the Banana and of the Orange (peel). 
Experiments with Proteids other than 
WlTTE-PEPTONE. 
Inasmuch as nearly all the proteases known at the time 
when I commenced my experiments had been found to be 
peptonizing as well as proteolytic, it was incumbent upon me 
to ascertain whether or not the newly discovered proteolytic 
enzymes were also capable of peptonizing the higher proteids. 
I therefore proceeded to test some of them with such proteids 
as fibrin, raw egg-albumin, caseinogen (as contained in milk), 
and commercial casein. 
Fibrin. 
Experiments were made with the following: the juice of 
the Melon, the Vegetable Marrow, the Cucumber, the Tomato, 
the Onion ; extract of Euphorbia Characias , and of Wheat- 
Germ ; bruised leaves of Spinach and of Celery (etiolated) ; 
the bruised tissue of the Mushroom. The well-washed fibrin 
used had been preserved in dilute glycerin. The possible tests 
for digestion were (1) the biuret-reaction; (2) the trypto- 
phane-reaction ; (3) the disappearance of the fibrin supplied. 
In many cases (especially leaves) the biuret-test could not be 
applied on account of the presence of a substance that gave 
a strong yellow colour on the addition of the concentrated 
NaHO solution. Nor was the tryptophane-test alone al- 
together reliable, since the reaction might be the result of the 
digestion of proteids in the juice or tissue under examination, 
but together with the disappearance of the fibrin it could be 
depended on. The following instances illustrate the general 
methods of experiment. 
Cucumis sativus. 
50 cc. of the expressed juice of a nearly ripe, somewhat yellow 
Cucumber were placed in each of two bottles ; to each was added 
