throughout all my later experiments by many valuable suggestions and
assistance given me with the greatest kindness by Dr. Burdon Sanderson.
[page 86]
It may be well to premise for the sake of any reader who knows nothing
about the digestion of albuminous compounds by animals that this is
effected by means of a ferment, pepsin, together with weak hydrochloric
acid, though almost any acid will serve. Yet neither pepsin nor an acid
by itself has any such power.* We have seen that when the glands of the
disc are excited by the contact of any object, especially of one
containing nitrogenous matter, the outer tentacles and often the blade
become inflected; the leaf being thus converted into a temporary cup or
stomach. At the same time the discal glands secrete more copiously, and
the secretion becomes acid. Moreover, they transmit some influence to
the glands of the exterior tentacles, causing them to pour forth a more
copious secretion, which also becomes acid or more acid than it was
before.
As this result is an important one, I will give the evidence. The
secretion of many glands on thirty leaves, which had not been in any
way excited, was tested with litmus paper; and the secretion of
twenty-two of these leaves did not in the least affect the colour,
whereas that of eight caused an exceedingly feeble and sometimes
doubtful tinge of red. Two other old leaves, however, which appeared to
have been inflected several times, acted much more decidedly on the
paper. Particles of clean glass were then placed on five of the leaves,
cubes of albumen on six, and bits of raw meat on three, on none of
which was the secretion at this time in the least acid. After an
interval of 24 hrs., when almost all the tentacles on
* It appears, however, according to Schiff, and contrary to the opinion
of some physiologists, that weak hydrochloric dissolves, though slowly,
a very minute quantity of coagulated albumen. Schiff, Phys. de la
Digestion, tom. ii. 1867, p. 25. [page 87]
these fourteen leaves had become more or less inflected, I again tested
the secretion, selecting glands which had not as yet reached the centre
or touched any object, and it was now plainly acid. The degree of
acidity of the secretion varied somewhat on the glands of the same
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