2 PHYSIOLOGY OF MUSCLES AND NERVES. 



of a different kind. The contraction of a polyp when 

 touched and the voluntary movement of the human 

 arm are phenomena of a peculiar kind, and result from 

 circumstances quite other than those which cause the 

 fall of a stone or the attraction and repulsion exercised 

 between magnetic or electric masses. Moreover, sensa- 

 tion, such as we are conscious of in ourselves, and of the 

 existence of which in other men and in animals we learn 

 either from the statements or from the conduct of those 

 others, seems to be entirely unrepresented in inanimate 

 nature ; it even appears doubtful if it occurs in plants. 

 Upon this task, hard as it is, physiological research has 

 thrown much light; it is the knowledge which has thus 

 already been gained which will form the subject of the 

 following explanations. 



2. Although even in plants movements occur similar 

 to those observable in animals, yet there seems to be an 

 essential difference between the two. For instance, in 

 most animals we lind that special organs are formed to 

 serve principally for movement. Such are the muscles, 

 which form what is ordinarily called flesh. Organs 

 of this sort have never yet been seen in plants. But 

 not all the movements of the animal body are accom- 

 plished by the muscles, and some forms of motion occur 

 in exactly the same way in the plant as in the animal 

 organism. 



These movements are most evident, and are most 

 easily explained in the sensitive plant {M imosa pudica). 

 The stem and branches of the sensitive plant bear leaf- 

 stalks, each of which again bears secondary leaf-stalks, 

 to which latter the individual leaflets are attached. If 

 the plant is shaken, the leaf-stalks suddenly bend and 

 sink, the upper surfaces of the two halves of each leaflet 



