In cases analogous to that of which we have been treating, the word Force merely indicates the presence of an Unknown Cause, which gives rise to a group of fixed phenomena. In assigning names to each of the Forces or Unknown Causes to which we consider ourselves able to refer certain groups of phenomena, we facilitate the demonstration and discussion of the facts. The scientific man knows very well that he cannot go beyond this.

It is in this sense, and in this sense alone, that I have used above the expressions Force and Life. Astronomers consider gravitation the unknown cause of the movement of the stars; I consider Life as the unknown cause of the phenomena which are characteristic of organised beings. It may be that both gravitation and Life, as well as the other general forces are merely as x, of which the equation has not yet been discovered. I shall presently return to these considerations.

Be this as it may, whatever our real ignorance, whatever the Cause of which we are here treating, and though Impulsion should one day replace Attraction in our Theories, the facts would still remain the same. The stars would still be distributed through space, and subject to the laws of Newton and Kepler; they would still constitute a perfectly distinct whole, in the part assigned to the bodies which compose it, and in the nature of the relations which unite them. They would still form the Sidereal Kingdom.

This kingdom is then characterised by a general phenomenon, the Keplerian Movement, which may be attributed to a single force, namely that of gravitation.

IV. Let us now return to the Earth, the only celestial body which we can study in detail. Modern discoveries, however, judging from the relation of the elements and their mutual action, make it almost certain that the greatest similarity exists between the stars distributed in space, between all those at least which form part of our heavens.

Let us first establish the fact that upon our globe we again meet with the Keplerian Movement in falling bodies.

Attraction is here represented by Weight. Gravitation reappears with all its laws, acting upon grains of dust as it acts upon worlds. The parts of the whole, of cosmos, as Humboldt would have said, cannot escape from, the force which governs the whole.

But upon the surface of our Earth and in its interior, as far as we have been able to penetrate either by direct observation or scientific induction, we notice the appearance of other movements which are not subject to the laws of Kepler or Newton; phenomena appear which are entirely new and perfectly distinct from those due to gravitation. They are the physico-chemical phenomena. From their number and their difference in character they were long attributed to the action of distinct forces which were called Electricity, Heat, Magnetism, etc. Modern science, however, by transforming, so to speak, one into the other, has demonstrated their original unity. Physicists refer them all to nothing more than so many manifestations of the undulations of ether. The vibration of the latter is then the fundamental phenomenon from which all the others rise.

But this ether is absolutely hypothetical; its nature is perfectly unknown; no one knowing whence it acquires this quantity of movement, which, according to actual theory, should be subject neither to increase nor diminution. Now, in reality, we have here the Unknown cause of all physico-chemical phenomena. For this reason, and also for convenience, we shall give a name to this unknown cause, to this force, and call it Etherodynamy (Ethérodynamie).

But is not Etherodynamy only a particular form, a simple modification, or an effect of gravitation? Are not these two forces only different manifestations of a more general force? Many eminent men are much inclined to admit one or other of these hypotheses. Still, up to the present time, the facts do not seem to me to shew much agreement with them. Etherodynamy is displayed even in space and among the stars by variable, localised and temporary phenomena; the action of gravitation is one, universal and

constant. Man has always been able to exercise a certain amount of control over the former; he can produce at will light and heat; modern science cannot act upon the second. We can neither augment nor diminish, reflect or refract, or polarise weight; we cannot arrest its action. Ever. in the fall of bodies the regularity in the acceleration of the motion proves that the cause of this movement is subject to no alteration. Here then is no transmutation of force similar to that in a machine worked by electricity or heat.

But whatever be the progress of science, and though M. de Tessan's theory should be confirmed by experiment, the difference between the phenomena would not be diminished; the conclusions to be drawn from the facts in connection with the question we are here discussing would remain the

same.

It is scarcely necessary to remark that the physicochemical phenomena produced by etherodynamy can act upon masses or be exclusively molecular. They are in all cases similar to those which depend upon gravitation, they are subject to invariable laws and are always repeated in a similar manner when produced under similar circumstances.

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 organised 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.

Far from merely animating the organs, it is closely associated with the forces of which we have already spoken. Living beings are heavy, and therefore subject to gravitation; they are the seat of numerous and various physico-chemical phenomena which are indispensable to their existence and which must be referred to the action of etherodynamy. But these phenomena are here manifested under the influence of another force. It is for this reason that the results of these phenomena are often quite different to those in inanimate bodies, and that living beings have their special products. Life is not antagonistic to the inanimate forces, but it governs and rules their action by its laws. Therefore it makes them produce tissues, organs and individuals instead of crystals; it organises germs, and maintains through space and time, in spite of the most complex metamorphoses, that unity of definite living forms which we call Species.

If the anti-vitalists would only seriously reflect upon the matter, they would acknowledge that, considered from this point of view, there is nothing more mysterious in living beings than in some of the commonest phenomena presented by inanimate bodies. The intervention of Life as a modifying agent of actions purely etherodynamic may be as easily admitted as that of etherodynamy itself modifying and overcoming the action of weight. It is just as strange to see a piece of iron attracted and supported by a magnet, as to see carbon, oxygen, hydrogen and nitrogen combine and dispose themselves so as to form an animal or vegetable cell instead of any imaginable inorganic composition.

I have repeatedly, and for many years, maintained the doctrine which I have summed up here. It seems to me confirmed in the highest degree by the researches undertaken for the elucidation of the problem of which we are treating. The experiences of M. Bernard in particular, relative to the action exercised by anæsthetics upon plants as well as upon animals, makes it impossible for us to doubt for a moment