■10 



THE PHILOSOPHY 



varied at pleafure. All plants make the ftrongeft efforts, by incli- 

 ning, turning, and even twifting their ftems and branches, to efcape 

 from darknefs and fliade, and to procure the influences of the fun. 

 Place a wet fpunge under the leaves of a tree, they foon bend 

 downward, and endeavour to apply their inferior furfaces to the 

 fpunge. If a vefTel of water be placed v/ithin fix inches of a grow- 

 ing cucumber, in twenty-four hours the cucumber alters the direc- 

 tion of its .branches, bends either to the right or left, and never flops 

 till it comes into contad: with the water. When a pole is placed at 

 a confiderable dlflance from an unfupported vine, the branches of 

 which are proceeding in a contrary diredtion from that of the pole, 

 in a fhort time, it alters its courfe, and flops not till it clings around 

 the pole. 



Fadls of this kind excite our wonder ; but they by no means 

 prove that vegetables live, or that they are endowed with fenfation, 

 which implies a diftind: perception of pleafure and pain. 



There Is an inferior fpecies of fenfation, which is diflinguiflied 

 by the term irritability. This term denotes that power by which 

 mufcular fibres, even after they are detached from the body, con- 

 trad upon the application of any ftimulating fubflance, whether fo- 

 lid or fluid. The heart of a frog, when pricked with the point of 

 a pin, continues to beat, or to contradt and dilate, for feveral hours 

 after it has been cut out of the animal's body. The heart of a vi- 

 per, or of a turtle, beats diftindly from twenty to thirty hours af- 

 ter the death of thefe animals. The periftaltic motion of the in- 

 teftines is produced by their irritability. When the inteflines of a 

 dog, or any other quadruped, are fuddenly cut into different por- 

 tions, all thefe portions crawl about like worms, and contract upon 

 the flighteft touch. Though irritability be unqueftionably a vital 

 principle, yet it is equally certain, that mufcular fibres, when fepa- 



rated 



