ORGANIC BODIES. 21 



particles, which is totally unlike every other com- 

 bination of matter. If, for example, we merely 

 place an acid and an alkali together in a glass, the 

 particles will remain in juxtaposition, and yet in 

 perfect quietude, because they are only mechani- 

 cally combined. But water poured on the mass 

 becomes the means of a chemical union, which is 

 strikingly apparent in immediate effervescence. In 

 like manner, a combination of nitre, sulphur, and 

 charcoal, is familiar to us as gunpowder the parti- 

 cles of these substances being mixed mechanically ; 

 but no sooner does a spark fall on the train, than the 

 affinities between these substances produce so inti- 

 mate a union, that we are astounded, perhaps, by 

 the result. Still, as there is a marked distinction 

 between a mechanical and a chemical union, there 

 is one far more palpable between inorganic and 

 organic bodies, as the consequence of vital force. 



In crystals, or any other inorganic bodies, it may 

 also be remarked, we observe a determinate and 

 settled form ; but in those which are organic, a per- 

 petual change is carried on by the agency of vital 

 power. Thus, particles which were lately incorpo- 

 rated, are thrown off, and others, foreign and inor- 

 ganic, are taken up to be incorporated and thrown 

 off, in their turn. Life maintains its triumph over 

 the laws of dead matter, preserving for its appointed 

 time the identity of the plant or the animal, until 

 vitality ceases, and its operations give place to the 

 laws of chemical affinity, which being unopposed, 



