The limited and peculiar activity which arises in matter and which we call vital; which comes and goes; which will not stay to be analyzed; which we in vain try to reproduce in our laboratories; which is inseparable from chemistry and physics, but which is not summed up by them; which seems to use them and direct them to new ends,—an entity which seems to have invaded the kingdom of inert matter at some definite time in the earth's history, and to have set up an insurgent movement there; cutting across the circuits of the mechanical and chemical forces; turning them about, pitting one against the other; availing itself of gravity, of chemical affinity, of fluids and gases, of osmosis and exosmosis, of colloids, of oxidation and hydration, and yet explicable by none of these things; clothing itself with garments of warmth and color and perfume woven from the cold, insensate elements; setting up new activities in matter; building up myriads of new unstable compounds; struggling against the tendency of the physical forces to a dead equilibrium; indeterminate, intermittent, fugitive; limited in time, limited in space; present in some worlds, absent from others; breaking up the old routine of the material forces, and instituting new currents, new tendencies; departing from the linear activities of the inorganic, and setting up the circular activities of living currents; replacing change by metamorphosis, revolution by evolution, accretion by secretion, crystallization by cell-formation, aggregation by growth; and, finally, introducing a new power into the world—the mind and soul of man—this wonderful, and apparently transcendental something which we call life—how baffling and yet how fascinating is the inquiry into its nature and origin! Are we to regard it as Tyndall did, and as others before and since his time did and do, as potential in the constitution of matter, and self-evolved, like the chemical compounds that are involved in its processes?

As mechanical energy is latent in coal, and in all combustible bodies, is vital energy latent in carbon, hydrogen, oxygen, and so forth, needing only the right conditions to bring it out? Mechanical energy is convertible into electrical energy, and vice versa. Indeed, the circle of the physical forces is easily traced, easily broken into, but when or how these forces merge into the vital and psychic forces, or support them, or become them—there is the puzzle. If we limit the natural to the inorganic order, then are living bodies supernatural? Super-mechanical and super-chemical certainly, and chemics and mechanics and electro-statics include all the material forces. Is life outside this circle? It is certain that this circle does not always include life, but can life exist outside this circle? When it appears it is always inside it.

Science can only deal with life as a physical phenomenon; as a psychic phenomenon it is beyond its scope, except so far as the psychic is manifested through the physical. Not till it has produced living matter from dead can it speak with authority upon the question of the origin of life. Its province is limited to the description and analysis of life processes, but when it essays to name what institutes the processes, or to disclose the secret of organization, it becomes philosophy or theology. When Haeckel says that life originated spontaneously, he does not speak with the authority of science, because he cannot prove his assertion; it is his opinion, and that is all. When Helmholtz says that life had no beginning, he is in the same case. When our later biophysicists say that life is of physico-chemical origin, they are in the same case; when Tyndall says that there is no energy in the universe but solar energy, he is in the same case; when Sir Oliver Lodge says that life is an entity outside of and independent of matter, he is in the same case. Philosophy and theology can take leaps in the dark, but science must have solid ground to go upon. When it speculates or theorizes, it must make its speculations good. Scientific prophecy is amenable to the same tests as other prophecy. In the absence of proof by experiment—scientific proof—to get the living out of the non-living we have either got to conceive of matter itself as fundamentally creative, as the new materialism assumes, or else we have got to have an external Creator, as the old theology assumes. And the difference is more apparent than real. Tyndall is "baffled and bewildered" by the fact that out of its molecular vibrations and activities "things so utterly incongruous with them as sensation, thought, and emotion can be derived." His science is baffled and bewildered because it cannot, bound as it is by the iron law of the conservation and correlation of energy, trace the connection between them. But his philosophy or his theology would experience little difficulty. Henri Bergson shows no hesitation in declaring that the fate of consciousness is not involved in the fate of the brain through which it is manifested, but it is his philosophy and not his science that inspires this faith. Tyndall deifies matter to get life out of it—makes the creative energy potential in it. Bergson deifies or spiritualizes life as a psychic, creative principle, and makes matter its instrument or vehicle.

Science is supreme in its own sphere, the sphere, or hemisphere, of the objective world, but it does not embrace the whole of human life, because human life is made up of two spheres, or hemispheres, one of which is the subjective world. There is a world within us also, the world of our memories, thoughts, emotions, aspirations, imaginings, which overarches the world of our practical lives and material experience, as the sky overarches the earth. It is in the spirit of science that we conquer and use the material world in which we live; it is in the spirit of art and literature, philosophy and religion, that we explore and draw upon the immaterial world of our own hearts and souls. Of course the man of science is also a philosopher—may I not even say he is also a prophet and poet? Not otherwise could he organize his scientific facts and see their due relations, see their drift and the sequence of forces that bind the universe into a whole. As a man of science he traces out the causes of the tides and the seasons, the nature and origin of disease, and a thousand and one other things; but only as a philosopher can he see the body as a whole and speculate about the mystery of its organization; only as a philosopher can he frame theories and compare values and interpret the phenomena he sees about him.

II

We can only know, in the scientific sense, the physical and chemical phenomena of life; its essence, its origin, we can only know as philosophy and idealism know them. We have to turn philosophers when we ask any ultimate question. The feeling we have that the scientific conception of life is inadequate springs from the philosophical habit of mind. Yet this habit is quite as legitimate as the scientific habit, and is bound to supplement the latter all through life.

The great men of science, like Darwin and Huxley, are philosophers in their theories and conclusions, and men of science in their observations and experiments. The limitations of science in dealing with such a problem are seen in the fact that science can take no step till it has life to begin with. When it has got the living body, it can analyze its phenomena and reduce them to their chemical and physical equivalents, and thus persuade itself that the secret of life may yet be hit upon in the laboratory. Professor Czapek, of the University of Prague, in his work on "The Chemical Phenomena of Life" speaks for science when he says, "What we call life is nothing else but a complex of innumerable chemical reactions in the living substance which we call protoplasm." The "living substance" is assumed to begin with, and then we are told that the secret of its living lies in its chemical and physical processes. This is in one sense true. No doubt at all that if these processes were arrested, life would speedily end, but do they alone account for its origin? Is it not like accounting for a baby in terms of its breathing and eating? It was a baby before it did either, and it would seem as if life must in some way ante-date the physical and chemical processes that attend it, or at least be bound up in them in a way that no scientific analysis can reveal.

If life is merely a mode of motion in matter, it is fundamentally unlike any and all other modes of motion, because, while we can institute all the others at will, we are powerless to institute this. The mode of motion we call heat is going on in varying degrees of velocity all about us at all times and seasons, but the vital motion of matter is limited to a comparatively narrow circle. We can end it, but we cannot start it.

The rigidly scientific type of mind sees no greater mystery in the difference in contour of different animal bodies than a mere difference in the density of the germ cells: "one density results in a sequence of cell-densities to form a horse; another a dog; another a cat"; and avers that if we "repeat the same complex conditions, the same results are as inevitable as the sequences of forces that result in the formation of hydrogen monoxide from hydrogen and oxygen."

Different degrees of density may throw light on the different behavior of gases and fluids and solids, but can it throw any light on the question of why a horse is a horse, and a dog a dog? or why one is an herbivorous feeder, and the other a carnivorous?

The scientific explanation of life phenomena is analogous to reducing a living body to its ashes and pointing to them—the lime, the iron, the phosphorus, the hydrogen, the oxygen, the carbon, the nitrogen—as the whole secret.

Professor Czapek is not entirely consistent. He says that it is his conviction that there is something in physiology that transcends the chemistry and the physics of inorganic nature. At the same time he affirms, "It becomes more and more improbable that Life develops forces which are unknown in inanimate Nature." But psychic forces are a product of life, and they certainly are not found in inanimate nature. But without laying stress upon this fact, may we not say that if no new force is developed by, or is characteristic of, life, certainly new effects, new processes, new compounds of matter are produced by life? Matter undergoes some change that chemical analysis does not reveal. The mystery of isomeric substances appears, a vast number of new compounds of carbon appear, the face of the earth changes. The appearance of life in inert matter is a change analogous to the appearance of the mind of man in animate nature. The old elements and forces are turned to new and higher uses. Man does not add to the list of forces or elements in the earth, but he develops them, and turns them to new purposes; they now obey and serve him, just as the old chemistry and physics obey and serve life. Czapek tells us of the vast number of what are called enzymes, or ferments, that appear in living bodies—"never found in inorganic Nature and not to be gained by chemical synthesis." Orders and suborders of enzymes, they play a part in respiration, in digestion, in assimilation. Some act on the fats, some on the carbohydrates, some produce inversion, others dissolution and precipitation. These enzymes are at once the products and the agents of life. They must exert force, chemical force, or, shall we say, they transform chemical force into life force, or, to use Professor Moore's term, into "biotic energy"?

III

The inorganic seems dreaming of the organic. Behold its dreams in the fern and tree forms upon the window pane and upon the stone flagging of a winter morning! In the Brunonian movement of matter in solution, in crystallization, in chemical affinity, in polarity, in osmosis, in the growth of flint or chert nodules, in limestone formations—like seeking like—in these and in other activities, inert matter seems dreaming of life.

The chemists have played upon this tendency in the inorganic to parody or simulate some of the forms of living matter. A noted European chemist, Dr. Leduc, has produced what he calls "osmotic growths," from purely unorganized mineral matter—growths in form like seaweed and polyps and corals and trees. His seeds are fragments of calcium chloride, and his soil is a solution of the alkaline carbonates, phosphates, or silicates. When his seeds are sown in these solutions, we see inert matter germinating, "putting forth bud and stem and root and branch and leaf and fruit," precisely as in the living vegetable kingdom. It is not a growth by accretion, as in crystallization, but by intussusception, as in life. These ghostly things exhibit the phenomena of circulation and respiration and nutrition, and a crude sort of reproduction by budding; they repair their injuries, and are able to perform periodic movements, just as does an animal or a plant; they have a period of vigorous youthful growth, of old age, of decay, and of death. In form, in color, in texture, and in cell structure, they imitate so closely the cell structures of organic growth as to suggest something uncanny or diabolical. And yet the author of them does not claim that they are alive. They are not edible, they contain no protoplasm—no starch or sugar or peptone or fats or carbohydrates. These chemical creations by Dr. Leduc are still dead matter—dead colloids—only one remove from crystallization; on the road to life, fore-runners of life, but not life. If he could set up the chlorophyllian process in his chemical reactions among inorganic compounds, the secret of life would be in his hands. But only the green leaf can produce chlorophyll; and yet, which was first, the leaf or the chlorophyll?

Professor Czapek is convinced that "some substances must exist in protoplasm which are directly responsible for the life processes," and yet the chemists cannot isolate and identify those substances.

How utterly unmechanical a living body is, at least how far it transcends mere mechanics is shown by what the chemists call "autolysis." Pulverize your watch, and you have completely destroyed everything that made it a watch except the dead matter; but pulverize or reduce to a pulp a living plant, and though you have destroyed all cell structure, you have not yet destroyed the living substance; you have annihilated the mechanism, but you have not killed the something that keeps up the life process. Protoplasm takes time to die, but your machine stops instantly, and its elements are no more potent in a new machine than they were at first. "In the pulp prepared by grinding down living organisms in a mortar, some vital phenomena continue for a long time." The life processes cease, and the substances or elements of the dead body remain as before. Their chemical reactions are the same. There is no new chemistry, no new mechanics, no new substance in a live body, but there is a new tendency or force or impulse acting in matter, inspiring it, so to speak, to new ends. It is here that idealism parts company with exact science. It is here that the philosophers go one way, and the rigid scientists the other. It is from this point of view that the philosophy of Henri Bergson, based so largely as it is upon scientific material, has been so bitterly assailed from the scientific camp.

The living cell is a wonderful machine, but if we ask which is first, life or the cell, where are we? There is the synthetical reaction in the cell, and the analytical or splitting reaction—the organizing, and the disorganizing processes—what keeps up this seesaw and preserves the equilibrium? A life force, said the older scientists; only chemical laws, say the new. A prodigious change in the behavior of matter is wrought by life, and whether we say it is by chemical laws, or by a life force, the mystery remains.

The whole secret of life centres in the cell, in the plant cell; and this cell does not exceed .005 millimetres in diameter. An enormous number of chemical reactions take place in this minute space. It is a world in little. Here are bodies of different shapes whose service is to absorb carbon dioxide, and form sugar and carbohydrates. Must we go outside of matter itself, and of chemical reactions, to account for it? Call this unknown factor "vital force," as has so long been done, or name it "biotic energy," as Professor Moore has lately done, and the mystery remains the same. It is a new behavior in matter, call it by what name we will.

Inanimate nature seems governed by definite laws; that is, given the same conditions, the same results always follow. The reactions between two chemical elements under the same conditions are always the same. The physical forces go their unchanging ways, and are variable only as the conditions vary. In dealing with them we know exactly what to expect. We know at what degree of temperature, under the same conditions, water will boil, and at what degree of temperature it will freeze. Chance and probability play no part in such matters. But when we reach the world of animate nature, what a contrast we behold! Here, within certain limits, all is in perpetual flux and change. Living bodies are never two moments the same. Variability is the rule. We never know just how a living body will behave, under given conditions, till we try it. A late spring frost may kill nearly every bean stalk or potato plant or hill of corn in your garden, or nearly every shoot upon your grapevine. The survivors have greater powers of resistance—a larger measure of that mysterious something we call vitality. One horse will endure hardships and exposures that will kill scores of others. What will agitate one community will not in the same measure agitate another. What will break or discourage one human heart will sit much more lightly upon another. Life introduces an element of uncertainty or indeterminateness that we do not find in the inorganic world. Bodies still have their laws or conditions of activity, but they are elastic and variable. Among living things we have in a measure escaped from the iron necessity that holds the world of dead matter in its grip. Dead matter ever tends to a static equilibrium; living matter to a dynamic poise, or a balance between the intake and the output of energy. Life is a peculiar activity in matter. If the bicyclist stops, his wheel falls down; no mechanical contrivance could be devised that could take his place on the wheel, and no combination of purely chemical and physical forces can alone do with matter what life does with it. The analogy here hinted at is only tentative. I would not imply that the relation of life to matter is merely mechanical and external, like that of the rider to his wheel. In life, the rider and his wheel are one, but when life vanishes, the wheel falls down. The chemical and physical activity of matter is perpetual; with a high-power microscope we may see the Brunonian movement in liquids and gases any time and at all times, but the movement we call vitality dominates these and turns them to new ends. I suppose the nature of the activity of the bombarding molecules of gases and liquids is the same in our bodies as out; that turmoil of the particles goes on forever; it is, in itself, blind, fateful, purposeless; but life furnishes, or is, an organizing principle that brings order and purpose out of this chaos. It does not annul any of the mechanical or chemical principles, but under its tutelage or inspiration they produce a host of new substances, and a world of new and beautiful and wonderful forms.

IV

Bergson says the intellect is characterized by a natural inability to understand life. Certain it is, I think, that science alone cannot grasp its mystery. We must finally appeal to philosophy; we must have recourse to ideal values—to a non-scientific or super-scientific principle. We cannot live intellectually or emotionally upon science alone. Science reveals to us the relations and inter-dependence of things in the physical world and their relations to our physical well-being; philosophy reveals their relations to our mental and spiritual life, their meanings and their ideal values. Poor, indeed, is the man who has no philosophy, no commanding outlook over the tangles and contradictions of the world of sense. There is probably some unknown and unknowable factor involved in the genesis of life, but that that factor or principle does not belong to the natural, universal order is unthinkable. Yet to fail to see that what we must call intelligence pervades and is active in all organic nature is to be spiritually blind. But to see it as something foreign to or separable from nature is to do violence to our faith in the constancy and sufficiency of the natural order. One star differeth from another in glory. There are degrees of mystery in the universe. The most mystifying thing in inorganic nature is electricity,—that disembodied energy that slumbers in the ultimate particles of matter, unseen, unfelt, unknown, till it suddenly leaps forth with such terrible vividness and power on the face of the storm, or till we summon it through the transformation of some other form of energy. A still higher and more inscrutable mystery is life, that something which clothes itself in each infinitely varied and beautiful as well as unbeautiful form of matter. We can evoke electricity at will from many different sources, but we can evoke life only from other life; the biogenetic law is inviolable.

Professor Soddy says, "Natural philosophy may explain a rainbow but not a rabbit." There is no secret about a rainbow; we can produce it at will out of perfectly colorless beginnings. "But nothing but rabbits will or can produce a rabbit, a proof again that we cannot say what a rabbit is, though we may have a perfect knowledge of every anatomical and microscopic detail."

To regard life as of non-natural origin puts it beyond the sphere of legitimate inquiry; to look upon it as of natural origin, or as bound in a chain of chemical sequences, as so many late biochemists do, is still to put it where our science cannot unlock the mystery. If we should ever succeed in producing living matter in our laboratories, it would not lessen the mystery any more than the birth of a baby in the household lessens the mystery of generation. It only brings it nearer home.

V

What is peculiar to organic nature is the living cell. Inside the cell, doubtless, the same old chemistry and physics go on—the same universal law of the transformation of energy is operative. In its minute compass the transmutation of the inorganic into the organic, which constitutes what Tyndall called "the miracle and the mystery of vitality," is perpetually enacted. But what is the secret of the cell itself? Science is powerless to tell us. You may point out to your heart's content that only chemical and physical forces are discoverable in living matter; that there is no element or force in a plant that is not in the stone beside which it grew, or in the soil in which it takes root; and yet, until your chemistry and your physics will enable you to produce the living cell, or account for its mysterious self-directed activities, your science avails not. "Living cells," says a late European authority, "possess most effective means to accelerate reactions and to cause surprising chemical results."

Behold the four principal elements forming stones and soils and water and air for whole geologic or astronomic ages, and then behold them forming plants and animals, and finally forming the brains that give us art and literature and philosophy and modern civilization. What prompted the elements to this new and extraordinary behavior? Science is dumb before such a question.

Living bodies are immersed in physical conditions as in a sea. External agencies—light, moisture, air, gravity, mechanical and chemical influences—cause great changes in them; but their power to adapt themselves to these changes, and profit by them, remains unexplained. Are morphological processes identical with chemical ones?

In the inorganic world we everywhere see mechanical adjustment, repose, stability, equilibrium, through the action and interaction of outward physical forces; a natural bridge is a striking example of the action of blind mechanical forces among the rocks. In the organic world we see living adaptation which involves a non-mechanical principle. An adjustment is an outward fitting together of parts; an adaptation implies something flowing, unstable, plastic, compromising; it is a moulding process; passivity on one side, and activity on the other. Living things struggle; they struggle up as well as down; they struggle all round the circle, while the pull of dead matter is down only.

Behold what a good chemist a plant is! With what skill it analyzes the carbonic acid in the air, retaining the carbon and returning the oxygen to the atmosphere! Then the plant can do what no chemist has yet been able to do; it can manufacture chlorophyll, a substance which is the basis of all life on the globe. Without chlorophyll (the green substance in plants) the solar energy could not be stored up in the vegetable world. Chlorophyll makes the plant, and the plant makes chlorophyll. To ask which is first is to call up the old puzzle, Which is first, the egg, or the hen that laid it?

According to Professor Soddy, the engineer's unit of power, that of the British cart-horse, has to be multiplied many times in a machine before it can do the work of a horse. He says that a car which two horses used to pull, it now takes twelve or fifteen engine-horse to pull. The machine horse belongs to a different order. He does not respond to the whip; he has no nervous system; he has none of the mysterious reserve power which a machine built up of living cells seems to possess; he is inelastic, non-creative, non-adaptive; he cannot take advantage of the ground; his pull is a dead, unvarying pull. Living energy is elastic, adaptive, self-directive, and suffers little loss through friction, or through imperfect adjustment of the parts. A live body converts its fuel into energy at a low temperature. One of the great problems of the mechanics of the future is to develop electricity or power directly from fuel and thus cut out the enormous loss of eighty or ninety per cent which we now suffer. The growing body does this all the time; life possesses this secret; the solar energy stored up in fuel suffers no loss in being transformed into work by the animal mechanism.

Soddy asks whether or not the minute cells of the body may not have the power of taking advantage of the difference in temperature of the molecules bombarding them, and thus of utilizing energy that is beyond the capacity of the machinery of the motor-car. Man can make no machine that can avail itself of the stores of energy in the uniform temperature of the earth or air or water, or that can draw upon the potential energy of the atoms, but it may be that the living cell can do this, and thus a horse can pull more than a one-horse-power engine. Soddy makes the suggestive inquiry: "If life begins in a single cell, does intelligence? does the physical distinction between living and dead matter begin in the jostling molecular crowd? Inanimate molecules, in all their movements, obey the law of probability, the law which governs the successive falls of a true die. In the presence of a rudimentary intelligence, do they still follow that law, or do they now obey another law—the law of a die that is loaded?" In a machine the energy of fuel has first to be converted into heat before it is available, but in a living machine the chemical energy of food undergoes direct transformation into work, and the wasteful heat-process is cut off.

VI

Professor Soddy, in discussing the relation of life to energy, does not commit himself to the theory of the vitalistic or non-mechanical origin of life, but makes the significant statement that there is a consensus of opinion that the life processes are not bound by the second law of thermo-dynamics, namely, the law of the non-availability of the energy latent in low temperatures, or in the chaotic movements of molecules everywhere around us. To get energy, one must have a fall or an incline of some sort, as of water from a higher to a lower level, or of temperature from a higher to a lower degree, or of electricity from one condition of high stress to another less so. But the living machine seems able to dispense with this break or incline, or else has the secret of creating one for itself.

In the living body the chemical energy of food is directly transformed into work, without first being converted into heat. Why a horse can do more work than a one-horse-power engine is probably because his living cells can and do draw upon this molecular energy. Molecules of matter outside the living body all obey the law of probability, or the law of chance; but inside the living body they at least seem to obey some other law—the law of design, or of dice that are loaded, as Soddy says. They are more likely always to act in a particular way. Life supplies a directing agency. Soddy asks if the physical distinction between living and dead matter begins in the jostling molecular crowd—begins by the crowd being directed and governed in a particular way. If so, by what? Ah! that is the question. Science will have none of it, because science would have to go outside of matter for such an agent, and that science cannot do. Such a theory implies intelligence apart from matter, or working in matter. Is that a hard proposition? Intelligence clearly works in our bodies and brains, and in those of all the animals—a controlled and directed activity in matter that seems to be life. The cell which builds up all living bodies behaves not like a machine, but like a living being; its activities, so far as we can judge, are spontaneous, its motions and all its other processes are self-prompted. But, of course, in it the mechanical, the chemical, and the vital are so blended, so interdependent, that we may never hope to separate them; but without the activity called vital, there would be no cell, and hence no body.

It were unreasonable to expect that scientific analysis should show that the physics and chemistry of a living body differs from that of the non-living. What is new and beyond the reach of science to explain is the kind of activity of these elements. They enter into new compounds; they build up bodies that have new powers and properties; they people the seas and the air and the earth with living creatures, they build the body and brain of man. The secret of the activity in matter that we call vital is certainly beyond the power of science to tell us. It is like expecting that the paint and oil used in a great picture must differ from those in a daub. The great artist mixed his paint with brains, and the universal elements in a living body are mixed with something that science cannot disclose. Organic chemistry does not differ intrinsically from inorganic; the difference between the two lies in the purposive activity of the elements that build up a living body.

Or is life, as a New England college professor claims, "an x-entity, additional to matter and energy, but of the same cosmic rank as they," and "manifesting itself to our senses only through its power to keep a certain quantity of matter and energy in the continuous orderly ferment we call life"?

I recall that Huxley said that there was a third reality in this universe besides matter and energy, and this third reality was consciousness. But neither the "x-entity" of Professor Ganong nor the "consciousness" of Huxley can be said to be of the same cosmic rank as matter and energy, because they do not pervade the universe as matter and energy do. These forces abound throughout all space and endure throughout all time, but life and consciousness are flitting and uncertain phenomena of matter. A prick of a pin, or a blow from a hammer, may destroy both. Unless we consider them as potential in all matter (and who shall say that they are not?) may we look upon them as of cosmic rank?

It is often urged that it is not the eye that sees, or the brain that thinks, but something in them. But it is something in them that never went into them; it arose in them. It is the living eye and the living brain that do the seeing and the thinking. When the life activity ceases, these organs cease to see and to think. Their activity is kept up by certain physiological processes in the organs of the body, and to ask what keeps up these is like the puppy trying to overtake its own tail, or to run a race with its own shadow.

The brain is not merely the organ of the mind in an external and mechanical sense; it is the mind. When we come to living things, all such analogies fail us. Life is not a thing; thought is not a thing; but rather the effect of a certain activity in matter, which mind alone can recognize. When we try to explain or account for that which we are, it is as if a man were trying to lift himself.

Life seems like something apart. It does not seem to be amenable to the law of the correlation and conservation of forces. You cannot transform it into heat or light or electricity. The force which a man extracts from the food he eats while he is writing a poem, or doing any other mental work, seems lost to the universe. The force which the engine, or any machine, uses up, reappears as work done, or as heat or light or some other physical manifestation. But the energy of foodstuffs which a man uses up in a mental effort does not appear again in the circuit of the law of the conservation of energy. A man uses up more energy in his waking moments, though his body be passive, than in his sleeping. What we call mental force cannot be accounted for in terms of physical force. The sun's energy goes into our bodies through the food we eat, and so runs our mental faculties, but how does it get back again into the physical realm? Science does not know.

It must be some sort of energy that lights the lamps of the firefly and the glow-worm, and it must be some sort or degree of energy that keeps consciousness going. The brain of a Newton, or of a Plato, must make a larger draft on the solar energy latent in food-stuffs than the brain of a day laborer, and his body less. The same amount of food-consumption, or of oxidation, results in physical force in the one case, and mental force in the other, but the mental force escapes the great law of the equivalence of the material forces.

John Fiske solves the problem when he drops his physical science and takes up his philosophy, declaring that the relation of the mind to the body is that of a musician to his instrument, and this is practically the position of Sir Oliver Lodge.

Inheritance and adaptation, says Haeckel, are sufficient to account for all the variety of animal and vegetable forms on the earth. But is there not a previous question? Do we not want inheritance and adaptation accounted for? What mysteries they hold! Does the river-bed account for the river? How can a body adapt itself to its environment unless it possess an inherent, plastic, changing, and adaptive principle? A stone does not adapt itself to its surroundings; its change is external and not internal. There is mechanical adjustment between inert bodies, but there is no adaptation without the push of life. A response to new conditions by change of form implies something actively responsive—something that profits by the change.

VII

If we could tell what determines the division of labor in the hive of bees or a colony of ants, we could tell what determines the division of labor among the cells in the body. A hive of bees and a colony of ants is a unit—a single organism. The spirit of the body, that which regulates all its economies, which directs all its functions, which coÖrdinates its powers, which brings about all its adaptations, which adjusts it to its environment, which sees to its repairs, heals its wounds, meets its demands, provides more force when more is needed, which makes one organ help do the work of another, which wages war on disease germs by specific ferments, which renders us immune to this or that disease; in fact, which carries on all the processes of our physical life without asking leave or seeking counsel of us,—all this is on another plane from the mechanical or chemical—super-mechanical.

The human spirit, the brute spirit, the vegetable spirit—all are mere names to fill a void. The spirit of the oak, the beech, the pine, the palm—how different! how different the plan or idea or interior economies of each, though the chemical and mechanical processes are the same, the same mineral and gaseous elements build them up, the same sun is their architect! But what physical principle can account for the difference between a pine and an oak, or, for that matter, between a man and his dog, or a bird and a fish, or a crow and a lark? What play and action or interaction and reaction of purely chemical and mechanical forces can throw any light on the course evolution has taken in the animal life of the globe—why the camel is the camel, and the horse the horse? or in the development of the nervous system, or the circulatory system, or the digestive system, or of the eye, or of the ear?

A living body is never in a state of chemical repose, but inorganic bodies usually are. Take away the organism and the environment remains essentially the same; take away the environment and the organism changes rapidly and perishes—it goes back to the inorganic. Now, what keeps up the constant interchange—this seesaw? The environment is permanent; the organism is transient. The spray of the falls is permanent; the bow comes and goes. Life struggles to appropriate the environment; a rock, for example, does not, in the same sense, struggle with its surroundings, it weathers passively, but a tree struggles with the winds, and to appropriate minerals and water from the soil, and the leaves struggle to store up the sun's energy. The body struggles to eliminate poisons or to neutralize them; it becomes immune to certain diseases, learns to resist them; the thing is alive. Organisms struggle with one another; inert bodies clash and pulverize one another, but do not devour one another.

Life is a struggle between two forces, a force within and a force without, but the force within does all the struggling. The air does not struggle to get into the lungs, nor the lime and iron to get into our blood. The body struggles to digest and assimilate the food; the chlorophyll in the leaf struggles to store up the solar energy. The environment is unaware of the organism; the light is indifferent to the sensitized plate of the photographer. Something in the seed we plant avails itself of the heat and the moisture. The relation is not that of a thermometer or hygrometer to the warmth and moisture of the air; it is a vital relation.

Life may be called an aquatic phenomenon, because there can be no life without water. It may be called a thermal phenomenon, because there can be no life below or above a certain degree of temperature. It may be called a chemical phenomenon, because there can be no life without chemical reactions. Yet none of these things define life. We may discuss biological facts in terms of chemistry without throwing any light on the nature of life itself. If we say the particular essence of life is chemical, do we mean any more than that life is inseparable from chemical reactions?

After we have mastered the chemistry of life, laid bare all its processes, named all its transformations and transmutations, analyzed the living cell, seen the inorganic pass into the organic, and beheld chemical reaction, the chief priestess of this hidden rite, we shall have to ask ourselves, Is chemistry the creator of life, or does life create or use chemistry? These "chemical reaction complexes" in living cells, as the biochemists call them, are they the cause of life, or only the effect of life? We shall decide according to our temperaments or our habits of thought.