DEPEND ON CHEMICAL CHANGES. 



be increased in intensity by chemical forces of analogous 

 character, and retarded or put an end to by those of 

 opposite character ; and that we are enabled to exercise 

 an influence on every part of an organ by means of sub- 

 stances possessing a well-defined chemical action. 



As, in the closed galvanic circuit, in consequence of 

 certain changes which an inorganic body, a metal, un- 

 dergoes when placed in contact with an acid, a certain 

 something becomes cognizable by our senses, which we 

 call a current of electricity ; so, in the animal body, in 

 consequence of transformations and changes undergone 

 by matter previously constituting a part of the organism, 

 certain phenomena of motion and activity are perceived, 

 and these we call life, or vitality. 



The electrical current manifests itself in certain phe- 

 nomena of attraction and repulsion, which it excites in 

 other bodies naturally motionless, and by the phenom- 

 ena of the formation and decomposition of chemical 

 compounds, which occur everywhere, when the resist- 

 ance is not sufficient to arrest the current. 



It is from this point of view, and from no other, that 

 chemistry ought to contemplate the phenomena of life. 

 Wonders surround us on every side. The formation 

 of a crystal, of an octahedron, is not less incompre- 

 hensible than the production of a leaf or of a muscular 

 fibre ; and the production of vermilion, from mercury 

 and sulphur, is as much an enigma as the formation of 

 an eye from the substance of the blood. 



The first conditions of animal life are nutritious mat- 

 ters and oxygen, introduced into the system. 



