PRELIMINARY IDEAS. 3 



and to inquire into the fundamental differences which distin- 

 guish a mineral from a living body, a plant from an animal. 



3. Differences between Mineral or Inorganic Sub- 

 stances and Living Beings. These differences are numerous 

 and striking ; they may be thus summed up. They differ in 

 their origin, mode of existence, duration, manner of decay or 

 destruction, general form, intimate structure, and elementary 

 composition. 



4. Thus, as to the mode of origin. When a mineral 

 body is formed, it springs immediately from the union of 

 two or more substances, which, by their nature, differ essen- 

 tially from it, and which combine by reason of the chemical 

 affinities they possess. A living being, on the contrary, is 

 never thus [spontaneously formed; it springs from one re- 

 sembling itself, and the vitality essential to its formation is 

 transmitted in succession from an uninterrupted series of 

 individuals resembling each other. Two substances, in no 

 way resembling each other, chlorine and sodium, for example, 

 by their union form common salt, independent of the presence 

 of this third substance : not so the plant or animal ; for its 

 formation a parent is necessary, that is, a being resembling 

 it and preceding it in point of time. Such beings, then, 

 require for their formation a foreign impulse, and this they 

 can only receive from a parent. 



5. As respects their mode of existence. The two classes 

 of bodies are equally distinct. Rocks and minerals remain 

 internally in a state of rest or repose; if they gain any addi- 

 tional substance, it is by the accretion of matter similar to 

 them; what they lose is accidental, and affects them not. 

 Living bodies, on the contrary, are constantly in a state of 

 composition and decomposition, the consequence of internal 

 movements in their structure. All is in motion. Unceas- 

 ingly they incorporate foreign substances or molecules with 

 their own, and give out to the external world particles of their 

 own. This vortex, or whirlpool as it were, constitutes what 

 is called nutrition, and is essential to life. They grow by 

 intussusception and not by juxtaposition, like minerals; for 

 the molecules by which they increase penetrate into the in- 

 terior of organized beings, and are there deposited. 



6. At length, having existed for a certain period, the 

 extreme limit of which is definite for each species, the living 

 body infallibly perishes : mineral or unorganized bodies, on 

 the contrary, once formed, exist until destroyed by an external 



