Vines . — Tryptophane in Proteolysis . 3 
However, the difficulty would still remain that it is impossible 
at present to prepare equivalent standardized solutions of the 
enzymes to begin with. 
Before proceeding to the description of the experiments, 
a few general remarks as to the methods employed are 
necessary. The digestions were carried on in an incubator 
or thermostat, at a constant temperature of S^°~ 39 ° C. The 
fibrin used had been well-washed in water and in alcohol, and 
preserved in 50 per cent, glycerin ; it was again well-washed 
in water immediately before use : it was not previously swollen 
in dilute HC1. That the results obtained on its digestion 
were not attributable to an enzyme belonging to the fibrin 
itself, is proved by the fact that digestion of some of it in 
0-2 °/ o HC1, for several days, gave rise to no tryptophane; nor 
was any found when the fibrin was digested with water for 
a similar period (see expts. with Bacteria, p. 15). Moreover the 
results obtained with fibrin were checked by those with Witte- 
peptone, with which they were generally concordant, though 
they were produced more slowly and were less marked. 
A point of experimental importance arose in connexion 
with the neutralized or alkaline digestions in which crude 
vegetable juices were used, such as those of the Pine- Apple, 
of the Fig, and of germinating seeds. It was observed that 
the neutral or alkaline reaction of these liquids was main- 
tained for some hours ; but on prolonging the digestions over 
night (20-24 hours) the liquids became more or less strongly 
acid, showing that a secondary development of acid had 
taken place. The results recorded in such cases are those 
that were obtained whilst the liquid was still found to be 
neutral or alkaline. It is noticeable that when a neutralized 
or alkaline liquid thus becomes acid again, the tryptophane- 
reaction that it gives is exceptionally strong, indicating that 
proteolytic action has been more than usually vigorous. 
I am unable at present to account for these facts. It seems 
not improbable that some of the recorded observations as 
to the activity of certain of these enzymes in prolonged 
digestions of neutralized or alkaline liquids, may be to some 
extent vitiated by the failure to recognize this re-acidification. 
