240 Vines. — Proteolytic Enzymes in Plants. 
The chief source of error to be avoided was the putrefaction 
of the digesting mixtures. When the period of digestion was 
brief, extending over three or four hours or even more, this 
source of error did not arise : in prolonged digestions it was 
eliminated by the use of antiseptics, such as hydrocyanic 
acid (HCN), hydrochloric acid (HC1), or chloroform-water. 
The mixtures without antiseptics generally showed no sign of 
putrefaction in the course of the experiment, but occasionally 
they developed an offensive odour : it is, however, not neces- 
sary to attach importance to those results, as the evidence 
afforded by the antiseptic experiments is conclusive in itself. 
In many instances the results were controlled by parallel 
experiments in which the vegetable matter under investigation 
had previously been boiled. 
The tryptophan e-test was usually applied directly to the 
digested liquid acidified, when necessary, with acetic acid : in 
only a few cases (e.g. leaf and root of Dandelion) did the 
liquid become too highly coloured, in the course of digestion, 
to admit of accurate observation of the tryptophane-reaction. 
In a good many cases (e.g. Apple, leaf of Scolopendrium , 
tuber of Helianthus tuberosus') a marked yellow colour was 
produced on the addition of the chlorine-water ; but this did 
not prevent the detection of the tryptophane-reaction. The 
various intensities of the tryptophane-reaction are described 
by the series of terms — faint, distinct, marked, strong. The 
fact that when the vegetable substance had previously been 
boiled the digested liquid gave no tryptophane-reaction, or 
only a faint one, due to the presence of tryptophane in the 
substance itself, proves that the Witte-peptone and other 
proteids used contained no tryptophane to begin with. 
It should be mentioned that the temperature of the incu- 
bator or thermostat, in which the liquids were set to digest, 
was about 40 ° C. in all cases. 
In some cases acid (either HC1 or citric acid) was added to 
the liquids to be digested : but this is not necessary, since all 
the liquids used were either acid to begin with, or they 
naturally became so in the course of digestion. When acid 
