564 Vines . — Proteolytic Enzyme of Nepenthes (III). 
that of honey, and often an amber colour which Clautriau 
attributes to tannoid substances derived from the tissue of 
the pitcher, rather than to any chromogen such as is formed 
in tryptic digestion along with amido-acids. 
The acidity of the liquid was the subject of special attention. 
The reaction of the liquid had been found by previous ob- 
servers to be sometimes acid and sometimes neutral : even in 
unopened pitchers it is often acid, as I have pointed out 
(11.#, p. 575), a fact which is not readily accounted for. 
Clautriau made the interesting observation that acidity is 
caused, not only by the introduction of any foreign body, 
but also by mechanical stimulation of the pitcher, whether 
open or unopened. It suffices to shake a pitcher vigorously to 
induce acidity of the contained liquid in the course of a few 
hours. 
Incidentally attention is drawn to the remarkable fact, well 
known in other pitcher-plants such as Sarracenia , that living 
insect-larvae, more especially those of the mosquito, are to be 
found in the pitchers. This fact, Clautriau rightly argues, 
cannot be accepted as evidence against the digestive activity 
of the pitcher-liquid : it is rather to be taken as an indication 
of special adaptation of the larvae. It Is a fact belonging to 
the same physiological category as the presence of living 
parasites in the digestive tract of animals, and as the in- 
digestibility of the gastric mucous membrane by its own 
secretions. It is, however, clear that the pitcher-liquid can 
contain no actively toxic or anaesthetic substances. Clautriau 
observed, in fact, that insects are very slowly killed when 
immersed in the liquid. 
With regard to the actual process of digestion, Clautriau 
found that the albumin which he introduced into vigorous 
pitchers entirely disappeared within two days. The examina- 
tion of the liquid at this stage showed that it gave no pre- 
cipitate on neutralization, or on boiling in the presence of 
acids or of neutral salts : nor was any precipitate caused by 
ferrocyanide of potassium and acetic acid, by double iodide 
of mercury and potassium, or by phosphomolybdic acid. 
