o\ THE PHYSICAL P.ASIs OF LIFE m 



we rightly name the higher faculties, are not 

 excluded from this classification, inasmuch as to 

 every one but the subject of them, they are known 

 only as transitory changes in the relative positions 

 of parts of the body. Speech, gesture, and every 

 other form of human action are, in the long run, 

 resolvable into muscular contraction, and muscular 

 contraction is but a transitory change in the 

 relative positions of the parts of a muscle. But 

 the scheme which is large enough to embrace the 

 activities of the highest form of life, covers all 

 those of the lower creatures. The lowest plant, or 

 animalcule, feeds, grows, and reproduces its kind. 

 In addition, all animals manifest those transitory 

 changes of form which we class under irritability 

 and contractility ; and, it is more than probable, 

 that when the vegetable world is thoroughly 

 explored, we shall find all plants in possession of 

 the same powers, at one time or other of their 

 existence. 



I am not now alluding to such phenomena, at 

 once rare and conspicuous, as those exhibited by the 

 leaflets of the sensitive plants, or the stamens of the 

 barberry, but to much more widely spread, and at 

 one time, more subtle and hidden, manifes- 

 tations of vegetable contractility. You are doubt- 

 less aware that the common nettle owes its stinging 

 property to the innumerable stiff and needle-like, 

 though exquisitely drlieate, hairs which cover its 

 surface. Each stinging-needle tapers from a broad 



