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The doctrine of definite combinations, as will be 

 shewn in the following lectures, will assist us in gain- 

 ing just views respecting the composition of plants, 

 and the economy of the vegetable kingdom ; but the 

 same accuracy of weight and measure, the same statical 

 results which depend upon the uniformity of the laws 

 that govern dead matter, cannot be expected in opera- 

 tions where the powers of life are concerned, and 

 where a diversity of organs and of functions exists. 

 The classes of definite inorganic bodies, even if we 

 include all the crystalline arrangements of the mineral 

 kingdom, are few, compared with the forms and sub- 

 stances belonging to animated nature* Life gives a 

 peculiar character to all its productions ; the power of 

 attraction and repulsion, combination and decomposi- 

 tion, are subservient to it ; a few elements, by the 

 diversity of their arrangement, are made to form the 

 most different substances ; and similar substances are 

 produced from compounds which, when superficially 

 examined, appear entirely different, 



