leaf. On some leaves, a few tentacles did not, from some unknown cause,
become inflected, as often happens; and in five instances their
secretion was found not to be in the least acid; whilst the secretion
of the adjoining and inflected tentacles on the same leaf was decidedly
acid. With leaves excited by particles of glass placed on the central
glands, the secretion which collects on the disc beneath them was much
more strongly acid than that poured forth from the exterior tentacles,
which were as yet only moderately inflected. When bits of albumen (and
this is naturally alkaline), or bits of meat were placed on the disc,
the secretion collected beneath them was likewise strongly acid. As raw
meat moistened with water is slightly acid, I compared its action on
litmus paper before it was placed on the leaves, and afterwards when
bathed in the secretion; and there could not be the least doubt that
the latter was very much more acid. I have indeed tried hundreds of
times the state of the secretion on the discs of leaves which were
inflected over various objects, and never failed to find it acid. We
may, therefore, conclude that the secretion from unexcited leaves,
though extremely viscid, is not acid or only slightly so, but that it
becomes acid, or much more strongly so, after the tentacles have begun
to bend over any inorganic or organic object; and still more strongly
acid after the tentacles have remained for some time closely clasped
over any object.
I may here remind the reader that the secretion [page 88] appears to be
to a certain extent antiseptic, as it checks the appearance of mould
and infusoria, thus preventing for a time the discoloration and decay
of such substances as the white of an egg, cheese, &c. It therefore
acts like the gastric juice of the higher animals, which is known to
arrest putrefaction by destroying the microzymes.
[As I was anxious to learn what acid the secretion contained, 445
leaves were washed in distilled water, given me by Prof. Frankland; but
the secretion is so viscid that it is scarcely possible to scrape or
wash off the whole. The conditions were also unfavourable, as it was
late in the year and the leaves were small. Prof. Frankland with great
kindness undertook to test the fluid thus collected. The leaves were
excited by clean particles of glass placed on them 24 hrs. previously.
No doubt much more acid would have been secreted had the leaves been
excited by animal matter, but this would have rendered the analysis
more difficult. Prof. Frankland informs me that the fluid contained no
77