This semi-fluid lining is protoplasm, which thus constitutes a kind of
bag, full of a limpid liquid, and roughly corresponding in form with
the interior of the hair which it fills. When viewed with a sufficiently
high magnifying power, the protoplasmic layer of the nettle hair is seen
to be in a condition of unceasing activity. Local contractions of the
whole thickness of its substance pass slowly and gradually from point to
point, and give rise to the appearance of progressive waves, just as the
bending of successive stalks of corn by a breeze produces the apparent
billows of a cornfield.
But, in addition to these movements, and independently of them, the
granules are driven, in relatively rapid streams, through channels in
the protoplasm which seem to have a considerable amount of persistence.
Most commonly, the currents in adjacent parts of the protoplasm take
similar directions; and, thus, there is a general stream up one side of
the hair and down the other. But this does not prevent the existence of
partial currents which take different routes; and sometimes trains of
granules may be seen coursing swiftly in opposite directions within
a twenty-thousandth of an inch of one another; while, occasionally,
opposite streams come into direct collision, and, after a longer or
shorter struggle, one predominates.
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