FUNCTION.] BY POISONS. 153 



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 con- 

 tract 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 separated without 

 any contraction. The branches of this plant may be pre- 

 served 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 leaf 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 immoveable. 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 till they die. Solutions of arsenic and arseniate of potash 

 produce the same effects. 



A leaf of the Sensitive Plant was in a cold diluted solution 

 of opium : in a few moments it opened out as in water, and, 

 after half an hour, gave the usual signs of contractibility. In 

 six hours it was expanded, and had a natural appearance, but 

 could not be excited to move. The leaflets were flexible at 

 the articulations, and offered a singular contrast to the state 

 of irritation produced by corrosive sublimate. Pure water 

 did not recover the plant. A large branch, similarly situated, 

 expanded its leaves; but in half an hour had lost much of 

 its sensibility : the leaflets, though alive, seemed asleep, and 

 required much stimulating to cause contraction. In one 

 hour the contractions ceased : in two hours the branch was 

 dead. 



A leaf placed in prussic acid (Scheele's strength) con- 

 tracted, then slightly dilated, but was quite insensible, and 

 the articulations were flexible : water did not recover it. If 



