It is our plan, so far as possible, to discuss the problems of the mind in one section of this book, and the problems of the body in another; but just as we found that we could not separate our duties to ourself from our duties to our neighbors, so we find that the mind and the body are inextricably interwoven, and that whenever we probe deeply into one, we discover the other. The interaction of the mind and the body is a fascinating problem into which we must look for a moment, not because we expect to solve it, but because it illuminates the whole subject.

The human body is a machine. It takes in carbon and oxygen, and burns them, and gives out carbon dioxide and other waste products, and develops energy in proportion to the amount of carbon it consumes. This machine has its elaborate apparatus of action and reaction, its sensory organs where outside stimuli are received, its nerves like telegraph wires to carry these impressions, its brain cells to store them and to transform them into reactions. We know to some extent how these brain cells work. We know what portions of the brain are devoted to this or that activity. We know that if we stick a pin into a certain spot we shall paralyze the left forefinger. We know that by injecting a certain drug, or by breathing a certain gas, we can cause this or that sensation or reaction, such as laughing or weeping or mania. We know what poisons are generated in the system by anger, and what chemical changes take place in a muscle that is tired. All this is part of a vast new science which is called bio-chemistry, or the chemistry of life.

Our bodies, therefore, are part of the material universe, and subject to the laws or ways of being of this universe. The first of these laws that we know is the law of causation. Every change in the universe has its cause, and that in turn had another cause; this chain is never broken, no matter how far we go, and the same causes universally produce the same effects. If you see a ball move on a billiard table, you know that the ball did not move itself; you know that something struck the ball or tilted the table. You discover that the motion of the ball moves the air around it, and the waves of that motion are spread through the room. They strike the walls, and the motion is carried on through the walls, and if we had instruments sensitive enough, we could feel the motion of that billiard ball at the other side of the world, and a few million years from now at the most remote of the stars. This is what is called the law of the conservation of energy, and when we discover something like radium which seems to violate that law by giving out unlimited quantities of energy, we investigate and discover a new form of energy locked up in the atom. In the disintegration of the atom we have a source of power which, when we have learned to use it, will multiply perhaps millions of times the powers we are now able to use on this earth. But energy, no matter how many times it is transformed, and in what strange ways it reappears, always remains, and is never destroyed, and never created out of nothing.

My friend the great physiologist once took me into his laboratory and showed me a little aquarium in which some minute creatures were wiggling about—young sea-urchins, if I remember. The physiologist took a bottle containing some chemical, and dropped a single drop into the water, and instantly all these little black creatures, which had been darting aimlessly in every direction through the water, turned and swam all in one direction, toward the light. They swam until they touched the walls of the aquarium, and there they stuck, trying their best to swim farther. "And now," said my friend, "that is what we call a 'tropism,' and all life is a tropism. What you see in that aquarium means that some day we shall know just what combination of chemicals causes a human being to move this way or that, to do this thing or that. When bio-chemistry has progressed sufficiently, we shall be able to make human qualities, perhaps in the sperm, perhaps in the embryo, perhaps day by day by means of diet or injection."

Said I: "Some day, when bio-chemistry has progressed far enough, you will know what combination of chemicals causes a man to vote the Democratic or Republican ticket."

"Why not?" answered my friend. (He has a sense of humor about all things except this sacred bio-chemistry.)

Said I: "When you have got to that stage, keep the secret carefully, and we will fix up a scheme, and a few days before election we will release some gas in our big cities, and sweep the country for the Socialist ticket."

But jesting aside: if the human body is a material thing, existing in the material world and subject to causation, there must be material reasons for the actions of human bodies, just the same as for the moving of billiard balls. We hear the sound of a billiard ball striking the cushion, and we are prepared to accept the idea that the thing we call hearing in us is caused by the impinging of sound waves upon our eardrums. And if we investigate human beings in the mass, we find every reason to believe that they act according to laws, and that there are material causes for their acts. If you get up and shout fire in a theater, you know how the audience will behave. If you study statistics, you can say that in any large city a certain fixed number of human beings are going to commit suicide every month; you can even say that more are going to commit suicide in the month of June than in any other month. You can say that more people are going to die at two o'clock in the morning than at any other hour. You know that certain changes in the weather will cause all human beings to behave in the same way. You know that an increase of prices or an increase of unemployment will cause a certain additional number of men to commit crimes, and a certain additional number of women to become prostitutes. You know that if a man overeats, his thoughts will change their color; he will have what he calls "the blues." I might cite a thousand other illustrations to prove that human minds are subject to material laws, and therefore to investigation by the bio-chemists.

But now, stop a moment. Here you sit reading a book. Something in the book pleases you, and you say, "Good!" Perhaps you slap your knee or clench your fist. Now here is a motion of your hand, which stirs the air about you, and which, according to the laws of energy, will spread its effects to the other side of the world, and even to the farthest of the stars. Or perhaps the book makes you angry, and you throw it down in disgust; an entirely different motion, which will affect the other side of the world and the farthest of the stars in an entirely different way. The machine of the universe will be forever altered because of that slapping of your knee or that throwing down of your book.

And what was the cause of these things? So far as we can see, the material cause was exactly the same in each case—the reading of certain letters. Two human beings, sitting side by side and reading exactly the same letters, might be affected in exactly opposite ways. It seems hardly rational to maintain that the material difference of two pairs of eyes, moving over exactly the same set of letters, could have resulted in two such different motions of the hands. As a matter of fact, the very same letters may affect the same person in different ways. The composer, Edward MacDowell, once told me how on his birthday his pupils sent him a gift, with a card containing some lines from the opera "Rheingold," beginning, "O singe fort"—that is, "Oh, sing on." But the composer happened, when glancing at the card, to think French instead of German, and got the message, "Oh, powerful monkey!" This, of course, was disconcerting to a famous piano performer, and his pupils, if they had been watching his face, would have seen an unexpected reaction. It seems manifest, does it not, that the cause of this difference of reaction was not any difference of the letters, but purely a difference of thought? So it appears that thoughts may change the material universe; they may break the chain of causation, and interfere with material events.

Compare the two things, a state of consciousness and say, a steam shovel. They are entirely different, and so far as we can see, entirely incompatible and unrelated. Can anyone imagine how a thought can turn into a steam shovel, or a steam shovel into a thought? We can understand how a steam shovel lifts a mass of earth out of the ground, and we can understand how a human hand moves a lever which causes the shovel to act; but we are unable to conceive how a state of mind—whether it be a desire for pay, or an ideal of service, or a vision of the Panama Canal—can so affect a steam shovel as to cause it to move. We can sit and think motion at a billiard ball for a thousand years, and it does not move; but when we think motion at our hand, it moves instantly, and passes on the motion to the billiard ball or the steam shovel. When fire touches our hand it sends some kind of vibration to the brain, and in some inconceivable way that vibration is turned into a state of consciousness called pain, and that is turned, "as quick as thought," into another kind of motion, the jerking back of our hand.

So it seems certain that consciousness really does "butt in" on the chain of natural causation. And yet, just see in what position this leaves the scientist who is investigating life! Imagine if you can, the plight of a doctor who wanted to prescribe a diet for a sick person, if he knew that every piece of chicken and every piece of fish were free to decide of its own impulse whether or not it would be digested in the human stomach. But the plight of this doctor would be nothing to the plight of the chemist or the biologist or the engineer who was asked to do his thinking and his planning in a world containing a billion and a quarter human beings, each one a lawless agent, each one a source of new and unforeseeable energies, each one acting as a "first cause," and starting new chains of activity, tearing the universe to pieces according to his own whims. What kind of a universe would that be? It would simply be a chaos; there could be no thinking, there could be no life in it; there could be no two things the same in it, and no laws of any sort.

So then we fall back into the hands of the "determinists," who assert one unbreakable chain of natural causation, and regard the human body as an automaton. We go back to the bio-chemist, who purposes some day to ascertain for us just exactly what molecules of matter in just what positions and combinations in the brain cells of William Shakespeare caused him to perpetrate a mixed metaphor. We go back to the belief that human beings act as they must act, because the clock of life, wound up and started, must move in such and such a fashion.

But now, let us see what are the implications of that theory! Here am I writing a book, appealing to men to act in certain ways. Of course, I know that not all will follow my advice. Some will be foolish—or what seems to me foolish. Others will be weak, and will resolve to act in certain ways, and then go and act in other ways. But some will be just; some will be free; some will use their brains—because, you see, I am convinced that they can use their brains! I am convinced that ideas will affect and stir them, in complete defiance of the bio-chemist, who tells me that they act that way because of certain chemicals in their brain cells, and that I write my book because of other chemicals, and that my idea that I am writing the book because I want to write it is a delusion, and that the whole thing is happening just so because the universe was wound up that way.

Now, this an unsolved problem, and I have no solution to offer. What I have set forth is in substance one of the four "antinomies" of Kant, and you can see for yourself how it is possible to prove either side, and impossible to be sure of either. Perhaps there is really a duality in life. Perhaps there are two aspects of the universe, the material and the spiritual, and perhaps they do not really interact as they seem to, but both are guided and determined by some higher reality of life of which we know nothing. In that case there would really be a chemical equivalent for every thought, and there would be a trace of consciousness for every material atom in the universe. Maybe the theologians are right, and in the universal consciousness of God the whole future exists predetermined. Maybe to God there is no such thing as time; the past, the present, and the future are all alike to Him.

There is nothing more painful to the human mind than to have to confess its own impotence. Yet I can see no escape from the dilemma we are here facing. There is not a man alive who does not assume the freedom of the will, who does not show in all his acts that he agrees with old Dr. Samuel Johnson: "We know we are free and there's an end on't." Without a belief in freedom we cannot get beyond the animal, we cannot become the masters of our own souls. And yet, the man who swallows that idea whole, and goes out into the world and preaches personal morality to the neglect of the fundamental economic facts, the facts of the body in its relationship to all other bodies—we know what happens to that man; he becomes a shouting fool. Unless he is literally a fool, or a knave, he quickly discovers his own futility, and proceeds to use his common sense, in spite of all his theories. "Come to Jesus!" cried William Booth, and he went out in the streets of London to save souls with a bass drum; but presently, in day by day contact with the degradation of the London slums, he realized that he could not save souls so long as those souls were dwelling in starved and lousy bodies. So William Booth with his Salvation Army took to starting night shelters and cast-off clothing bureaus!

And of exactly the same sort is the bewilderment which falls to the lot of the scientist who is honest and willing to face the facts. The bio-chemist with his test tubes and his microscopes and his complex apparatus of research sits himself down and accumulates a mass of information about the human body. He investigates the diseases of the body and learns in detail just how these diseases spread and sometimes how they are caused; he can present you with a diagnosis, showing the exact stage to which the degeneration of a certain organ has proceeded, and perhaps he can suggest to you a change of diet or some drug which will, for a time at least, check the process of the breakdown. But in other cases he will be perfectly helpless; he will be, as it were, buried under the mass of detail which he has accumulated; he will find the vital energy depressed, and he will not know any way to renew it. But along will come some mental specialist, who in a half hour's talk with the patient, by a simple change in the patient's ideas, will completely make over the patient's life, and set going a new vital process which will restore the body to its former health. A religious enthusiast may do this, a psychotherapist may do it, a moral genius may do it; and the physician with all his learning will find himself like a man on the outside of a house, peering in through the windows and trying in vain to find out something about the life of the family and its guests.

This is humiliating to the chemist and the medical man, but they have to face it, because it is a fact. In the seat of authority over the human body there sits a higher being which, without any religious implications, we may call the soul; or, if it is impossible to get away from the religious implication of that word, we will call it the consciousness, or the personality. This master of the house of life is in many ways dependent upon the house. If the furnace goes out he freezes, and if the house takes fire and burns up—well, he disappears and leaves no address. But in other ways the master of the house is really master, and is a worker of miracles. He does things which we do not at all understand, and cannot yet even foresee, but which often completely make the house over.

William James, a scientist of real authority, has a wonderful essay, "The Powers of Men," in which he sets forth the fact that human beings as a general rule make use of only a small portion of the energies which dwell in their beings, and that one of our problems is to find the ways by which we can draw upon stores of hidden energy which we have within us. Also, in a fascinating book, "Varieties of the Religious Experience," James has endeavored to study and analyze the phenomena which hitherto the physician and the biologist have been disposed to ridicule and neglect. But unless I am mistaken, every scientist in the end will be forced to come back to the central fact, that life is a unity, and that the heart of it is the spirit; that what we call the will is not an accident, not a delusion, not some by-product of nature, but is the very secret of life; and that behind it is a vast ocean of power, which now and then sweeps away all dykes, and floods into the human consciousness.

The writer of this book is now a patient and plodding teacher of a certain economic doctrine, a preacher of what he might call anti-parasitism. He has come to the conclusion that the habit of men to enslave their fellows and exploit them and draw their substance from them without return—that this habit is destructive to all civilization, and is incompatible with any of the higher forms of life, intellectual, moral or artistic. He has come to the conclusion that there is no use attempting to build a structure of social life until there is a sound foundation; in other words, until the capitalist system has been replaced by cooperation. But in his youth he was, or thought he was, a poet, and touched upon that strange and wonderful thing which we call genius. He saw his own consciousness, as it were a leaf driven before a mighty tempest of spiritual energy. And he believes that this experience was no delusion, but was a revelation of the hidden mysteries of being. He still has memories of this startling experience, still hints of it in his consciousness; something still leaps in his memory, like a race-horse, or like the war-horse of Revelations, which "scenteth the battle afar off, the thunder of the captains and the shouting." Because of these things he can never accept any philosophy which shackles the human spirit, he will never in his thought attempt to set bounds to the possibilities of human life. The very heart of life beats in us, the wonder of it and the glory of it swells like a tide behind us. New universes are born in us, or, if you prefer, they are made by us; and the process is one of endless joy, of rapture beyond anything that the average man can at present imagine, or that any instruments invented by science can weigh or measure.