I have already remarked in a preceding chapter, that all organized beings after death undergo a change, in consequence of which their bodies, as such, disappear from the surface of the earth. In a short time after the event, animal matters lose their cohesion; they are dissipated into the air, leaving only the mineral elements they had derived from the soil. The change commences immediately after death: with the aid of moisture and exposure to the air, the bodies of animals, as well as plants, undergo changes, the last of which are[30] the conversion of their carbonic acid and of their hydrogen into water, of their nitrogen into ammonia, of their sulphur into sulphuric acid. Thus, their elements assume or resume forms in which they can again serve as food to a new generation of plants and animals. “The same atom of carbon which, as the constituent of a muscular fibre in the heart of a man, assists to propel the blood through his frame, was perhaps a constituent of the heart of one of his ancestors, and any atom of nitrogen in our brain has perhaps been a part of the brain of an Egyptian or of a negro. [30] Liebig, 1851. “As the intellect of the men of this generation draws the food required for its development and cultivation from the products of the intellectual activity of former times, so may the constituents or elements of the bodies of a former generation pass into, and become parts of, our own frames. The proximate cause of the changes which occur in organized bodies after death is the action of the oxygen of the air on many of their constituents. This action only takes place when water--that is, moisture--is present, and requires a certain temperature.” The great agent in all these changes is oxygen, as has been already sufficiently explained when speaking of the decomposition of vegetables after death. I shall first attend to the influence these changes have on the soil as producing agents, intended to restore to the soil those vivifying powers which it never seems to lose when man interferes not; and lastly, to consider briefly its influence on man himself.