No antagonism, it is true, exists between gravitation and etherodynamy. It is no less true that the action of the first is always disturbed in a peculiar manner by that of the second, and that in some phenomena it seems as if the latter would neutralise the former. This fact is most strikingly shown in some of the commonest experiments in physics. The gold leaves of the electroscope separate, the pith-balls are attracted towards electrified bodies in spite of their weight, and are repelled with a rapidity greater than that which would result merely from their own weight. And yet these bodies have no more ceased to possess weight than those masses of iron raised by the powerful magnets of M. Jamin. Etherodynamy in these two cases merely overcame gravitation and either modified or imitated its action. Those terrestrial bodies which present no other phenomena than those which can be referred to either gravitation or etherodynamy have, since the time of Linnæus, been termed _Inanimate Bodies_. Together they constitute the _Mineral Kingdom_. We see that the existence and the distinction of this group are perfectly independent of any hypothesis intended to explain the phenomena. _Two kinds of phenomena_ then are characteristic of the mineral kingdom: _phenomena of the Keplerian movement_ and _physico-chemical phenomena_, which may be attributed to the action of two forces: _gravitation_ and _etherodynamy_. V. The sidereal and mineral kingdoms form the Inorganic Empire. Passing from it we enter the domain of organized and living beings. We have already seen the essential phenomena by which they are distinguished. These phenomena differ essentially from all those which we have observed in inanimate bodies. It seems to me, therefore, necessary to attribute them to a special cause,—to _Life_. I know that in the present day any one making use of this word is readily accused by a great number of physicists and chemists, and by an entire physiological school, of introducing into science a vague and almost mysterious expression. There is, however, nothing in it more vague or mysterious than in the word _gravitation_. It is very true that we do not know _what_ Life _is_; but no more do we know _what_ the force _is_ that set the stars in motion and retains them in their orbits. If astronomers have been right in giving to the _force_, or _unknown cause_, which gives the worlds their mathematical movements, naturalists have a perfect right to designate by a special term that _unknown cause_ which produces filiation, birth and death. It will be apparent that my idea of Life is not the same as it was with many ancient vitalists, that it is no more the _arche_ of van Helmont than the _vital principle_ of Barthez. Its function appears to me very different to that attributed to it by most of our predecessors, and which is still attributed to it by some physiologists.