these are blackened, and the tentacles are inflected. The glands of the
disc, when excited by a half-minim drop (.0296 ml.), containing 1/960
of a grain (.0675 mg.), transmit a motor impulse to the exterior
tentacles, causing them to bend inwards. A minute drop, containing
1/14400 of a grain (.00445 mg.), if held for a few seconds in contact
with a gland, soon causes the tentacle bearing it to be inflected. If a
leaf is left [page 148] immersed for a few hours in a solution, and a
gland absorbs the 1/134400 of a grain (.0048 mg.), its colour becomes
darker, though not actually black; and the contents of the cells
beneath the gland are plainly aggregated. Lastly, under the same
circumstances, the absorption by a gland of the 1/268800 of a grain
(.00024 mg.) suffices to excite the tentacle bearing this gland into
movement.
NITRATE OF AMMONIA.
With the salt I attended only to the inflection of the leaves, for it
is far less efficient than the carbonate in causing aggregation,
although considerably more potent in causing inflection. I experimented
with half-minims (.0296 ml.) on the discs of fifty-two leaves, but will
give only a few cases. A solution of one part to 109 of water was too
strong, causing little inflection, and after 24 hrs. killing, or nearly
killing, four out of six leaves which were thus tried; each of which
received the 1/240 of a grain (or .27 mg.). A solution of one part to
218 of water acted most energetically, causing not only the tentacles
of all the leaves, but the blades of some, to be strongly inflected.
Fourteen leaves were tried with drops of a solution of one part to 875
of water, so that the disc of each received the 1/1920 of a grain
(.0337 mg.). Of these leaves, seven were very strongly acted on, the
edges being generally inflected; two were moderately acted on; and five
not at all. I subsequently tried three of these latter five leaves with
urine, saliva, and mucus, but they were only slightly affected; and
this proves that they were not in an active condition. I mention this
fact to show how necessary it is to experiment on several leaves. Two
of the leaves, which were well inflected, re-expanded after 51 hrs.
In the following experiment I happened to select very sensitive leaves.
Half-minims of a solution of one part to 1094 of water (i.e. 1 gr. to 2
1/2 oz.) were placed on the discs of nine leaves, so that each received
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