facts we may conclude that the protoplasmic fluid within a cell does
not become aggregated unless it be in a living state, and only
imperfectly if the cell has been injured. We have also seen that the
fluid must be in an oxygenated state, in order that the process of
aggregation should travel from cell to cell at the proper rate.
Various nitrogenous organic fluids and salts of ammonia induce
aggregation, but in different degrees and at very different rates.
Carbonate of ammonia is the most powerful of all known substances; the
absorption of 1/134400 of a grain (.000482 mg.) by a gland suffices to
cause all the cells of the same tentacle to become aggregated. The
first effect of the carbonate and of certain other salts of ammonia, as
well as of some other fluids, is the darkening or blackening of the
glands. This follows even from long immersion in cold distilled water.
It apparently depends in chief part on the strong aggregation of their
cell-contents, which thus become opaque, and do not reflect light. Some
other fluids render the glands of a brighter red; whilst certain acids,
though much diluted, the poison of the cobra-snake, &c., make the
glands perfectly white and opaque; and this seems to depend on the
coagulation of their contents without [page 63] any aggregation.
Nevertheless, before being thus affected, they are able, at least in
some cases, to excite aggregation in their own tentacles.
That the central glands, if irritated, send centrifugally some
influence to the exterior glands, causing them to send back a
centripetal influence inducing aggregation, is perhaps the most
interesting fact given in this chapter. But the whole process of
aggregation is in itself a striking phenomenon. Whenever the peripheral
extremity of a nerve is touched or pressed, and a sensation is felt, it
is believed that an invisible molecular change is sent from one end of
the nerve to the other; but when a gland of Drosera is repeatedly
touched or gently pressed, we can actually see a molecular change
proceeding from the gland down the tentacle; though this change is
probably of a very different nature from that in a nerve. Finally, as
so many and such widely different causes excite aggregation, it would
appear that the living matter within the gland-cells is in so unstable
a condition that almost any disturbance suffices to change its
molecular nature, as in the case of certain chemical compounds. And
this change in the glands, whether excited directly, or indirectly by a
stimulus received from other glands, is transmitted from cell to cell,
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