described. A drop of this kind equals on an average 1/20 of a minim,
and therefore contains 1/4800 of a grain (.0135 mg.) of the carbonate.
I touched with it the viscid secretion round three glands, so that each
gland received only [page 144] 1/14400 of a grain (.00445 mg.).
Nevertheless, in two trials all the glands were plainly blackened; in
one case all three tentacles were well inflected after an interval of 2
hrs. 40 m.; and in another case two of the three tentacles were
inflected. I then tried drops of a weaker solution of one part to 292
of water on twenty-four glands, always touching the viscid secretion
round three glands with the same little drop. Each gland thus received
only the 1/19200 of a grain (.00337 mg.), yet some of them were a
little darkened; but in no one instance were any of the tentacles
inflected, though they were watched for 12 hrs. When a still weaker
solution (viz. one part to 437 of water) was tried on six glands, no
effect whatever was perceptible. We thus learn that the 1/14400 of a
grain (.00445 mg.) of carbonate of ammonia, if absorbed by a gland,
suffices to induce inflection in the basal part of the same tentacle;
but as already stated, I was able to hold with a steady hand the minute
drops in contact with the secretion only for a few seconds; and if more
time had been allowed for diffusion and absorption, a much weaker
solution would certainly have acted.
Some experiments were made by immersing cut-off leaves in solutions of
different strengths. Thus four leaves were left for about 3 hrs. each
in a drachm (3.549 ml.) of a solution of one part of the carbonate to
5250 of water; two of these had almost every tentacle inflected, the
third had about half the tentacles and the fourth about one-third
inflected; and all the glands were blackened. Another leaf was placed
in the same quantity of a solution of one part to 7000 of water, and in
1 hr. 16 m. every single tentacle was well inflected, and all the
glands blackened. Six leaves were immersed, each in thirty minims
(1.774 ml.) of a solution of one part to 4375 of water, and the glands
were all blackened in 31 m. All six leaves exhibited some slight
inflection, and one was strongly inflected. Four leaves were then
immersed in thirty minims of a solution of one part to 8750 of water,
so that each leaf received the 1/320 of a grain (.2025 mg.). Only one
became strongly inflected; but all the glands on all the leaves were of
so dark a red after one hour as almost to deserve to be called black,
whereas this did not occur with the leaves which were at the same time
immersed in water; nor did water produce this effect on any other
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