at different times in water.
There is nothing remarkable in the mere fact of the
one-twenty-millionth of a grain of the phosphate, dissolved in above
two-million times its weight of water, being absorbed by a gland. All
physiologists admit that the roots of plants absorb the salts of
ammonia brought to them by the rain; and fourteen gallons of rain-water
contain* a grain of ammonia, therefore only a little more than twice as
much as in the weakest solution employed by me. The fact which appears
truly wonderful is, that the one-twenty-millionth of a grain of the
phosphate of ammonia (including less than the one-thirty-millionth of
efficient matter), when absorbed by a gland, should induce some change
in it, which leads to a motor impulse being transmitted down the whole
length of the tentacle, causing the basal part to bend, often through
an angle of above 180 degrees.
Astonishing as is this result, there is no sound reason
* Miller s Elements of Chemistry, part ii. p. 107, 3rd edit. 1864.
[page 173]
why we should reject it as incredible. Prof. Donders, of Utrecht,
informs me that from experiments formerly made by him and Dr. De
Ruyter, he inferred that less than the one-millionth of a grain of
sulphate of atropine, in an extremely diluted state, if applied
directly to the iris of a dog, paralyses the muscles of this organ.
But, in fact, every time that we perceive an odour, we have evidence
that infinitely smaller particles act on our nerves. When a dog stands
a quarter of a mile to leeward of a deer or other animal, and perceives
its presence, the odorous particles produce some change in the
olfactory nerves; yet these particles must be infinitely smaller* than
those of the phosphate of ammonia weighing the one-twenty-millionth of
a grain. These nerves then transmit some influence to the brain of the
dog, which leads to action on its part. With Drosera, the really
marvellous fact is, that a plant without any specialised nervous system
should be affected by such minute particles; but we have no grounds for
assuming that other tissues could not be rendered as exquisitely
susceptible to impressions from without if this were beneficial to the
organism, as is the nervous system of the higher animals.
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