Acids, diluted to the same degree, which do not cause inflection.

1.  Gallic; not poisonous. 2.  Tannic; not poisonous. 3.  Tartaric; not poisonous. 4.  Citric; not poisonous. 5.  Uric; (?) not poisonous.

Nitric Acid.—­Four leaves were placed, each in thirty minims of one part by weight of the acid to 437 of water, so that each received 1/16 of a grain, or 4.048 mg.  This strength was chosen for this and most of the following experiments, as it is the same [page 190] as that of most of the foregoing saline solutions.  In 2 hrs. 30 m. some of the leaves were considerably, and in 6 hrs. 30 m. all were immensely, inflected, as were their blades.  The surrounding fluid was slightly coloured pink, which always shows that the leaves have been injured.  They were then left in water for three days; but they remained inflected and were evidently killed.  Most of the glands had become colourless.  Two leaves were then immersed, each in thirty minims of one part to 1000 of water; in a few hours there was some inflection; and after 24 hrs. both leaves had almost all their tentacles and blades inflected; they were left in water for three days, and one partially re-expanded and recovered.  Two leaves were next immersed, each in thirty minims of one part to 2000 of water; this produced very little effect, except that most of the tentacles close to the summit of the petiole were inflected, as if the acid had been absorbed by the cut-off end.

Hydrochloric Acid.—­One part to 437 of water; four leaves were immersed as before, each in thirty minims.  After 6 hrs. only one leaf was considerably inflected.  After 8 hrs. 15 m. one had its tentacles and blade well inflected; the other three were moderately inflected, and the blade of one slightly.  The surrounding fluid was not coloured at all pink.  After 25 hrs. three of these four leaves began to re-expand, but their glands were of a pink instead of a red colour; after two more days they fully re-expanded; but the fourth leaf remained inflected, and seemed much injured or killed, with its glands white.  Four leaves were then treated, each with thirty minims of one part to 875 of water; after 21 hrs. they were moderately inflected; and on being transferred to water, fully re-expanded in two days, and seemed quite healthy.

Hydriodic Acid.—­One to 437 of water; three leaves were immersed as before, each in thirty minims.  After 45 m. the glands were discoloured, and the surrounding fluid became pinkish, but there was no inflection.  After 5 hrs. all the tentacles were closely inflected; and an immense amount of mucus was secreted, so that the fluid could be drawn out into long ropes.  The leaves were then placed in water, but never re-expanded, and were evidently killed.  Four leaves were next immersed in one part to 875 of water; the action was now slower, but after 22 hrs. all four leaves were closely inflected, and were affected in other respects as above described.  These leaves did not re-expand, though left for four days in water.  This acid acts far more powerfully than hydrochloric, and is poisonous.