when the secretion is neutralised by minute drops of the solution of an
alkali, the digestion of albumen is completely stopped, and that on the
addition of a minute dose of hydrochloric acid it immediately
recommences.
The nine following substances, or classes of substances, namely,
epidermic productions, fibro-elastic tissue, mucin, pepsin, urea,
chitine, cellulose, gun-cotton, chlorophyll, starch, fat and oil, are
not acted on by the secretion of Drosera; nor are they, as far as is
known, by the gastric juice of animals. Some soluble matter, however,
was extracted from the mucin, pepsin, and chlorophyll, used by me, both
by the secretion and by artificial gastric juice.
The several substances, which are completely dissolved by the
secretion, and which are afterwards absorbed by the glands, affect the
leaves rather differently. They induce inflection at very different
[page 132] rates and in very different degrees; and the tentacles
remain inflected for very different periods of time. Quick inflection
depends partly on the quantity of the substance given, so that many
glands are simultaneously affected, partly on the facility with which
it is penetrated and liquefied by the secretion, partly on its nature,
but chiefly on the presence of exciting matter already in solution.
Thus saliva, or a weak solution of raw meat, acts much more quickly
than even a strong solution of gelatine. So again leaves which have
re-expanded, after absorbing drops of a solution of pure gelatine or
isinglass (the latter being the more powerful of the two), if given
bits of meat, are inflected much more energetically and quickly than
they were before, notwithstanding that some rest is generally requisite
between two acts of inflection. We probably see the influence of
texture in gelatine and globulin when softened by having been soaked in
water acting more quickly than when merely wetted. It may be partly due
to changed texture, and partly to changed chemical nature, that
albumen, which had been kept for some time, and gluten which had been
subjected to weak hydrochloric acid, act more quickly than these
substances in their fresh state.
The length of time during which the tentacles remain inflected largely
depends on the quantity of the substance given, partly on the facility
with which it is penetrated or acted on by the secretion, and partly on
its essential nature. The tentacles always remain inflected much longer
115