204 THE PHENOMENA OF MOTION 



but both of these manifestations are confined within 

 certain limits. 



We observe in animals, that the conversion of food 

 into blood, and the contact of the blood with the living 

 tissues, are determined by a mechanical force, whose 

 manifestation proceeds from distinct organs, and is 

 effected by a distinct system of organs, possessing the 

 property of communicating and extending the motion 

 which they receive. We find the power of the animal 

 to change its place, and to produce mechanical effects 

 by means of its limbs, dependent on a second similar 

 system of organs or apparatus. Both of these systems 

 of apparatus, as well as the phenomena of motion pro- 

 ceeding from them, are wanting in plants. 



In order to form a clear conception of the origin and 

 source of the mechanical motions in the animal body, 

 it may be advantageous to reflect on the modus operandi 

 of other forces, which in their manifestations are most 

 closely allied to the vital force. 



When a number of plates of zinc and copper, ar- 

 ranged in a certain order, are brought into contact with 

 an acid, and when the extremities of the apparatus are 

 joined by means of a metallic wire, a chemical action 

 begins at the surface of the plates of zinc, and the wire, 

 in consequence of this action, acquires the most singular 

 and wonderful properties. 



The wire appears as the carrier or conductor of a 

 force, which may be conducted and communicated 

 through it in every direction with amazing velocity. 



