the 1/2400 of a grain (.027 mg.). Three of them had their tentacles
strongly inflected and their blades curled inwards; five were slightly
and somewhat doubtfully affected, having from three to eight of their
exterior tentacles inflected: one leaf was not at all affected, yet was
afterwards acted on by saliva. In six of these cases, a trace of action
was perceptible in [page 149] 7 hrs., but the full effect was not
produced until from 24 hrs. to 30 hrs. had elapsed. Two of the leaves,
which were only slightly inflected, re-expanded after an additional
interval of 19 hrs.
Half-minims of a rather weaker solution, viz. of one part to 1312 of
water (1 gr. to 3 oz.) were tried on fourteen leaves; so that each
received 1/2880 of a grain (.0225 mg.), instead of, as in the last
experiment, 1/2400 of a grain. The blade of one was plainly inflected,
as were six of the exterior tentacles; the blade of a second was
slightly, and two of the exterior tentacles well, inflected, all the
other tentacles being curled in at right angles to the disc; three
other leaves had from five to eight tentacles inflected; five others
only two or three, and occasionally, though very rarely, drops of pure
water cause this much action; the four remaining leaves were in no way
affected, yet three of them, when subsequently tried with urine, became
greatly inflected. In most of these cases a slight effect was
perceptible in from 6 hrs. to 7 hrs., but the full effect was not
produced until from 24 hrs. to 30 hrs. had elapsed. It is obvious that
we have here reached very nearly the minimum amount, which, distributed
between the glands of the disc, acts on the exterior tentacles; these
having themselves not received any of the solution.
In the next place, the viscid secretion round three of the exterior
glands was touched with the same little drop (1/20 of a minim) of a
solution of one part to 437 of water; and after an interval of 2 hrs.
50 m. all three tentacles were well inflected. Each of these glands
could have received only the 1/28800 of a grain, or .00225 mg. A little
drop of the same size and strength was also applied to four other
glands, and in 1 hr. two became inflected, whilst the other two never
moved. We here see, as in the case of the half-minims placed on the
discs, that the nitrate of ammonia is more potent in causing inflection
than the carbonate; for minute drops of the latter salt of this
strength produced no effect. I tried minute drops of a still weaker
solution of the nitrate, viz. one part to 875 of water, on twenty-one
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