INTRODUCTION. 



1. The nature of a body is the aggregate of its peculiar 

 powers, capabilities, and forces. These depend upon the con- 

 dition of its parts and the manner of their connection. 



2. The aggregate of the forces of a purely physical body is 

 termed its physical nature. 



3. The general forces of physical bodies belong to the animal 

 and the human organism, so far as it is considered in its con- 

 stituent parts, and the union of these as a physical body only, 

 and not as a machine ; and to that extent we can philosophically 

 apply the general laws of natural philosophy to the fluids and 

 the matter of the solids. To these general forces particularly 

 belong general and specific gravity, the force of attraction, 

 which, in the matter composing the solids of animals, is the 

 so-called contractility [Reiz], or the dead force of Haller, 

 and which is simply the effect of cohesion; — also heat, elec- 

 tricity, &c. 



4. The aggregate of the forces which a physical body pos- 

 sesses, in so far as it is a machine, is termed its mechanical 

 nature, and depends upon the physical nature and the kind 

 of union of its parts, whereby it becomes a machine. [Its 

 structure.) 



5. In addition to its mechanical nature, the animal or 

 human organism (so far as it is not a living body, but only a 

 mechanical machine), is endowed with the mechanical forces of 

 the machines, and to that extent we can philosophically apply 

 the laws of mechanics to the machines of such a body. The 

 forces of the lever, of hydraulic machines, of the force-pump, 

 &c., belong to this class of mechanical forces. 



Mechanical machines may be divided into the artistic and 

 natural {organic). The latter diff'er principally from the 

 former in having a highly compound structure, so that the 

 wdiole machine, even to its minutest details, is composed of 



