CHAP. XIIl. 
IRRITABILITY. 
S51 
stamens close at night to open again in the morning. Putting 
the stem of this plant into dilute prussic acid for four hours, 
occasioned the loss of the contractile property by irritation ; 
the articulation became flexible, and might be inclined in 
any direction by the instrument. The leaves had scarcely * 
begun to fade. On placing the expanded flowers on the 
prussic acid, the same effect took place, but much more 
rapidly. 
The experiment being repeated, with an aqueous solution 
of opium, a similar effect was produced in nine hours. 
Dilute solutions of oxide of arsenic and ai^eniate of potash 
were used: the stamens lost the powder of approaching the 
pistil ; but they were stiff, hard, withdrawn backwards, and 
could not have their direction altered without fracture. It 
seemed like an irritation, or a vegetable inflammation. 
Solution of corrosive sublimate more slowly produced the 
same effects. 
Sensitive plant (Mimosa pudica). — Experiments were now 
made with this vegetable. When a leaf of this plant is 
cut, and allowed to fall on pure water, the leaflets generally 
contract rapidly ; but after a few moments expand, and are 
then susceptible of contraction by the touch of any other 
body. They may thus be preserved in a sensible state two 
or three days. If the section be made with a very sharp 
instrument, and without concussion, the leaves may be sepa- 
rated without any contraction. The branches of this plant 
may be preserved for several days in fresh water. Gum- 
water also effects the same purpose. 
When a cut leaf of this plant falls upon a solution of cor- 
rosive sublimate, the l^af rapidly contracts, and the leaflets 
curl up in an unusual manner, and do not again expand. 
When put into pure water, the sensibility does not return, 
but the whole remains stiff and immovable. A little solution 
of corrosive sublimate being put into a portion of pure water, 
containing an expanded branch of the plant, gradually caused 
curling up of the leaves, which then closed and fell. If the 
solution be very weak, the leaves open on the morrow, and are 
still sensible, but ultimately contract, twist, and remain stiff 
