pressure soon causes a visible change in the protoplasm, which change
is transmitted down the whole length of the tentacle, giving it at last
a mottled appearance, distinguishable even by the naked eye.
In the fourth chapter it was shown that leaves placed for a short time
in water at a temperature of 110 Fahr. (43 .3 Cent.) become somewhat
inflected; they are thus also rendered more sensitive to the action
[page 267] of meat than they were before. If exposed to a temperature
of between 115 and 125 (46 .1-51 .6 Cent.), they are quickly
inflected, and their protoplasm undergoes aggregation; when afterwards
placed in cold water, they re-expand. Exposed to 130 (54 .4 Cent.), no
inflection immediately occurs, but the leaves are only temporarily
paralysed, for on being left in cold water, they often become inflected
and afterwards re-expand. In one leaf thus treated, I distinctly saw
the protoplasm in movement. In other leaves, treated in the same
manner, and then immersed in a solution of carbonate of ammonia, strong
aggregation ensued. Leaves placed in cold water, after an exposure to
so high a temperature as 145 (62 .7 Cent.), sometimes become slightly,
though slowly, inflected; and afterwards have the contents of their
cells strongly aggregated by carbonate of ammonia. But the duration of
the immersion is an important element, for if left in water at 145
(62 .7 Cent.), or only at 140 (60 Cent.), until it becomes cool, they
are killed, and the contents of the glands are rendered white and
opaque. This latter result seems to be due to the coagulation of the
albumen, and was almost always caused by even a short exposure to 150
(65.5 Cent.); but different leaves, and even the separate cells in the
same tentacle, differ considerably in their power of resisting heat.
Unless the heat has been sufficient to coagulate the albumen, carbonate
of ammonia subsequently induces aggregation.
In the fifth chapter, the results of placing drops of various
nitrogenous and non-nitrogenous organic fluids on the discs of leaves
were given, and it was shown that they detect with almost unerring
certainty the presence of nitrogen. A decoction of green peas or of
fresh cabbage-leaves acts almost as powerfully as an infusion of raw
meat; whereas an infusion of cabbage- [page 268] leaves made by keeping
them for a long time in merely warm water is far less efficient. A
decoction of grass-leaves is less powerful than one of green peas or
cabbage-leaves.
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