FROM A VEGETABLE. 197 



which takes place in the disposition of the parts of the 

 sensitive plant on being touched does not proceed from 

 irritability ! I shall therefore apply the word sensation to 

 that peculiar property of the animal kingdom which from 

 muscular or fibrous contraction into itself of the part af- 

 fected, evidently depends on some secondary action of the 

 nervous system ; whereas, I shall for the present ascribe to 

 irritability those phenomena which without any fibrous 

 contraction of the parts merely result from a change in 

 their disposition among themselves, and which, for aught 

 we know, may proceed always from a simple mechanical 

 cause. 



To the latter cause alone, then, or mechanical irritability, 

 will the remarkable properties of the Mimosa sensitiva, the 

 Hedysarwn gyraus, the Dion&a muscipula, and other ve- 

 getables, be referable ; and indeed these opinions are borne 

 out by one of the first botanists on the Continent, who 

 defines vegetables as " sensibilitate, voluntate et matu pro- 

 pria destituta," and animals as acted upon by two natural 

 forces, yi?- vis vitalis and sensibilitas, whereof, the former is 

 according to him " corporibus organicis omnibus communis 

 et sui inscia," and the latter " animalibus propria et sui 

 cQUScia." If these notions be correct, the vis vitalis will 

 be the same with the vital principle described in the pre- 

 ceding chapter by its effects, and the sensibilitas will be 

 no other than that imponderable fluid by which Cuvier 

 supposes the nerve to act on the animal fibre, or still more 

 likely it will be the connexion between some intelligent 

 principle and the nerve itself. When this connexion is 

 interrupted the sensibilitas may be considered as dormant, 

 and the animal as in the case of its sleep remains only 

 acted upon by the vis vitalis, and may be compared to a 



