Vines, — Proteolytic Enzymes in Plants, 239 
these are the proteids to be employed in the search for 
enzymes in plants. Consequently I have employed as di- 
gestible material in these experiments either the proteids 
naturally present in the juice or in the tissue of the plant ; or, 
when proteid material had to be supplied, the substance sold 
as { Witte-peptone,’ a dry powder consisting of a mixture of 
albumoses and some peptone. Moreover, the immediate 
object of my search was not a peptonizing , but a proteolytic 
enzyme ; not an enzyme, that is, which hydrolyzes the higher 
proteids into the lower, but one that decomposes the proteid 
molecule altogether. The test of digestive activity has ac- 
cordingly been the tryptophane-reaction : that is, the treat- 
ment of the acid digested liquid with chlorine-water which 
produces a characteristic, more or less marked, pink or violet 
colouration if tryptophane be present ; and if tryptophane be 
present, it is presumptive evidence that proteolysis has taken 
place. 
Incidentally, however, I found it necessary to make some 
experiments with the more complex proteids. Whilst they 
were nearly always successful when Witte-peptone was the 
material supplied, the results with fibrin, raw egg-albumin, 
and commercial casein, were often negative : but experiments 
with milk showed that the enzymes detected could act upon 
caseinogen, in several instances. 
The plant-material used was, in many cases, the juice, 
when the parts to be investigated were sufficiently succulent, 
such as fruits, &c. When the parts did not yield enough 
juice, I had recourse, in the first instance, to watery extracts. 
But I sometimes found juices, and especially watery extracts, 
to be unsatisfactory : when unfiltered they were too thick 
or too highly coloured, when filtered they were almost or 
altogether inert. After many trials I found that the best 
method of preparing such material as leaves, stems, roots, &c., 
was to slightly bruise pieces of them in a mortar ; when so 
prepared, they were placed in the experimental bottles with 
distilled water, or other liquid, and the digestible substance 
(Witte-peptone, fibrin, &c.) then added. 
