INTRODUCTION. 7 



Life being the most important of all the properties of be- 

 ings, and the highest of all characters, it is not surprising that 

 it has in all ages been made the most general principle of dis- 

 tinction ; and that natural beings have always been separated 

 into two immense divisions, the living and the inanimate. 



Of Living Beings, and Organization in general. 



If, in order to obtain a correct idea of the essence of life, we 

 consider it in those beings in which its effects are the most 

 simple, we quickly perceive that it consists in the faculty pos- 

 sessed by certain corporeal combinations, of continuing for a 

 time and under a determinate form, by constantly attracting 

 into their composition a part of surrounding substances, and 

 rendering to the elements, portions of their own. 



Life then is a vortex, more or less rapid, more or less com- 

 plicated, the direction of which is invariable, and which always 

 carries along molecules of similar kinds, but into which indi- 

 vidual molecules are continually entering, and from which they 

 are continually departing; so that the form of a living body is 

 more essential to it than its matter. 



As long as this motion subsists, the body in which it takes 

 place is living it lives. When it finally ceases, it dies. 

 After death, the elements which compose it, abandoned to the 

 ordinary chemical affinities, soon separate, from which, more 

 or less quickly, results the dissolution of the once living body. 

 It was then by the vital motion that its dissolution was arrest- 

 ed, and its elements were held in a temporary union. 



All living bodies die after a certain period, whose extreme 

 limit is fixed for each species, and death appears to be a ne- 

 cessary consequence of life, which, by its own action, insensi- 

 bly alters the structure of the body, so as to render its conti- 

 nuance impossible. 



In fact, the living body undergoes gradual, but continual 

 changes, during the whole term of its existence. At first, it 

 increases in diAiensions, according to proportions, and within 

 limits, fixed for each species and for each one of its parts ; it 

 then augments in density in the most of its parts: it is this 



