pulpy. It was evident that the protoplasm had been injuriously
affected; and soon afterwards some of the cells appeared quite empty.
These effects differ altogether from those produced by the several
salts of ammonia, as well as by various organic fluids, and by
inorganic particles placed on the glands. A solution of the same
strength of carbonate of soda and carbonate of potash acted in nearly
the same manner as the chloride; and here again, after 2 hrs. 30 m.,
the outer cells of some of the glands had emptied themselves of their
brown pulpy contents. We shall see in the eighth chapter that solutions
of several salts of soda of half the above strength cause inflection,
but do not injure the leaves. Weak solutions of sulphate of quinine, of
nicotine, camphor, poison of the cobra, &c., soon induce well-marked
aggregation; whereas certain other substances (for instance, a solution
of curare) have no such tendency.
Many acids, though much diluted, are poisonous; and though, as will be
shown in the eighth chapter, they cause the tentacles to bend, they do
not excite true aggregation. Thus leaves were placed in a solution of
one part of benzoic acid to 437 of water; and in 15 m. the purple fluid
within the cells had shrunk a little from the walls, yet when carefully
examined after 1 hr. 20 m., there was no true aggregation; and after 24
hrs. the leaf was evidently dead. Other leaves in iodic acid, diluted
to the same degree, showed after 2 hrs. 15 m. the same shrunken
appearance of the purple fluid within the cells; and these, after 6
hrs. 15 m., were seen under a high power to be filled with excessively
minute spheres of dull reddish protoplasm, [page 51] which by the next
morning, after 24 hrs., had almost disappeared, the leaf being
evidently dead. Nor was there any true aggregation in leaves immersed
in propionic acid of the same strength; but in this case the protoplasm
was collected in irregular masses towards the bases of the lower cells
of the tentacles.
A filtered infusion of raw meat induces strong aggregation, but not
very quickly. In one leaf thus immersed there was a little aggregation
after 1 hr. 20 m., and in another after 1 hr. 50 m. With other leaves a
considerably longer time was required: for instance, one immersed for 5
hrs. showed no aggregation, but was plainly acted on in 5 m.; when
placed in a few drops of a solution of one part of carbonate of ammonia
to 146 of water. Some leaves were left in the infusion for 24 hrs., and
these became aggregated to a wonderful degree, so that the inflected
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