18. Oxygen, hydrogen, nitrogen, and carbon, in combining themselves without the vital principle, form only a mineral or inorganic body. The vital principle, modifying the molecular constitution of this body, gives to it special properties. In place of a mineral molecule is found a molecule of organic matter.
The activity of the vital principle is sustained during life by the action of the organs, as is heat by the rotary movement of a wheel. As this action ceases with death, the vital principle is extinguished, as heat is when the wheel ceases to turn. But the effect produced upon the molecular state of the body by the vital principle lives after its extinction, just as the carbonization of wood continues after the extinction of heat. In the analysis of organic bodies, chemistry finds again the constituent elements, oxygen, hydrogen, nitrogen, and carbon; but it cannot reconstruct them, because the cause exists no more: and thus the effect cannot be reproduced, although it can reconstruct a stone.