Chapter 13
The "free path" of molecules, both in liquids and in gases, is so minute as to be beyond the reach of the most powerful microscope. This free path in liquids is a zigzag course, owing to the perpetual collisions with other molecules. The molecular behavior of liquids differs from that of gases only in what is called surface tension. Liquids have a skin, a peculiar stress of the surface molecules; gases do not, but tend to dissipate and fill all space. A drop of water remains intact till vaporization sets in; then it too becomes more and more diffused.
When two substances combine chemically, more or less heat is evolved. When the combination is effected slowly, as in an animal's body, heat is slowly evolved. When the combustion is rapid, as in actual fire, heat is rapidly evolved. The same phenomenon may reach the eye as light, and the hand as heat, though different senses get two different impressions of the same thing. So a mechanical disturbance may reach the ear as sound, and be so interpreted, and reach the hand as motion in matter. In combustion, the oxygen combines rapidly with the carbon, giving out heat and light and carbon dioxide, but why it does so admits of no explanation. Herein again is where life differs from fire; we can describe combustion in terms of chemistry, but after we have described life in the same terms something--and this something is the main thing--remains untouched.
The facts of radio-activity alone demonstrate the truth of the atomic theory. The beta rays, or emanations from radium, penetrating one foot of solid iron are very convincing. And this may go on for hundreds of years without any appreciable diminution of size or weight of the radio-active substance. "A gram of such substance," says Sir Oliver Lodge, "might lose a few thousand of atoms a second, and yet we could not detect the loss if we continued to weigh it for a century." The volatile essences of organic bodies which we detect in odors and flavors, are not potent like the radium emanations. We can confine them and control them, but we cannot control the rays of radio-active matter any more than we can confine a spirit. We can separate the three different kinds of rays--the alpha, the beta, and the gamma--by magnetic devices, but we cannot cork them up and isolate them, as we can musk and the attar of roses.
And these emanations are taking place more or less continuously all about us and we know it not. In fact, we are at all times subjected to a molecular bombardment of which we never dream; minute projectiles, indivisible points of matter, are shot out at us in the form of electrons from glowing metals, from lighted candles, and from other noiseless and unsuspected batteries at a speed of tens of thousands of miles a second, and we are none the wiser for it. Indeed, if we could see or feel or be made aware of it, in what a different world we should find ourselves! How many million-or billion-fold our sense of sight and touch would have to be increased to bring this about! We live in a world of collisions, disruptions, and hurtling missiles of which our senses give us not the slightest evidence, and it is well that they do not. There is a tremendous activity in the air we breathe, in the water we drink, in the food we eat, and in the soil we walk upon, which, if magnified till our senses could take it in, would probably drive us mad. It is in this interior world of molecular activity, this world of electric vibrations and oscillations, that the many transformations of energy take place. This is the hiding-place of the lightning, of the electrons which moulded together make the thunderbolt. What an underworld of mystery and power it is! In it slumbers all the might and menace of the storm, the power that rends the earth and shakes the heavens. With the mind's eye one can see the indivisible atoms giving up their electrons, see the invisible hosts, in numbers beyond the power of mathematics to compute, being summoned and marshalled by some mysterious commander and hurled in terrible fiery phalanxes across the battlefield of the storm.
The physicist describes the atom and talks about it as if it were "a tangible body which one could hold in his hand like a baseball." "An atom," Sir Oliver Lodge says, "consists of a globular mass of positive electricity with minute negative electrons embedded in it." He speaks of the spherical form of the atom, and of its outer surface, of its centre, and of its passing through other atoms, and of the electrons that revolve around its centre as planets around a sun. The electron, one hundred thousand times smaller than an atom, yet has surface, and that surface is a dimpled and corrugated sheet--like the cover of a mattress. What a flight of the scientific imagination is that!
The disproportion between the size of an atom and the size of an electron is vastly greater than that between the sun and the earth. Represent an atom, says Sir Oliver Lodge, by a church one hundred and sixty feet long, eighty feet broad, and forty feet high; the electrons are like gnats inside it. Yet on the electric theory of matter, electrons are all of the atom there is; there is no church, but only the gnats rushing about. We know of nothing so empty and hollow, so near a vacuum, as matter in this conception of it. Indeed, in the new physics, matter is only a hole in the ether. Hence the newspaper joke about the bank sliding down and leaving the woodchuck-hole sticking out, looks like pretty good physics. The electrons give matter its inertia, and give it the force we call cohesion, give it its toughness, its strength, and all its other properties. They make water wet, and the diamond hard. They are the fountain-head of the immense stores of the inter-atomic energy, which, if it could be tapped and controlled, would so easily do all the work of the world. But this we cannot do. "We are no more competent," says Professor Soddy, "to make use of these supplies of atomic energy than a savage, ignorant of how to kindle a fire, could make use of a steam-engine." The natural rate of flow of this energy from its atomic sources we get as heat, and it suffices to keep life going upon this planet. It is the source of all the activity we see upon the globe. Its results, in the geologic ages, are stored up for us in coal and oil and natural gas, and, in our day, are available in the winds, the tides, and the waterfalls, and in electricity.
IV
The electric constitution of matter is quite beyond anything we can imagine. The atoms are little worlds by themselves, and the whole mystery of life and death is in their keeping. The whole difference in the types of mind and character among men is supposed to be in their keeping. The different qualities and properties of bodies are in their keeping. Whether an object is hot or cold to our senses, depends upon the character of their vibrations; whether it be sweet or sour, poisonous or innocuous to us, depends upon how the atoms select their partners in the whirl and dance of their activities. The hardness and brilliancy of the diamond is supposed to depend upon how the atoms of carbon unite and join hands.
I have heard the view expressed that all matter, as such, is dead matter, that the molecules of hydrogen, oxygen, carbon, nitrogen, iron, phosphorus, calcium, and so on, in a living body, are themselves no more alive than the same molecules in inorganic matter. Nearly nine tenths of a living body is water; is not this water the same as the water we get at the spring or the brook? is it any more alive? does water undergo any chemical change in the body? is it anything more than a solvent, than a current that carries the other elements to all parts of the body? There are any number of chemical changes or reactions in a living body, but are the atoms and molecules that are involved in such changes radically changed? Can oxygen be anything but oxygen, or carbon anything but carbon? Is what we call life the result of their various new combinations? Many modern biologists hold to this view. In this conception merely a change in the order of arrangement of the molecules of a substance--which follows which or which is joined to which--is fraught with consequences as great as the order in which the letters of the alphabet are arranged in words, or the words themselves are arranged in sentences. The change of one letter in a word often utterly changes the meaning of that word, and the changing of a word in the sentence may give expression to an entirely different idea. Reverse the letters in the word "God," and you get the name of our faithful friend the dog. Huxley and Tyndall both taught that it was the way that the ultimate particles of matter are compounded that makes the whole difference between a cabbage and an oak, or between a frog and a man. It is a hard proposition. We know with scientific certainty that the difference between a diamond and a piece of charcoal, or between a pearl and an oyster-shell, is the way that the particles of carbon in the one case, and of calcium carbide in the other, are arranged. We know with equal certainty that the difference between certain chemical bodies, like alcohol and ether, is the arrangement of their ultimate particles, since both have the same chemical formula. We do not spell acetic acid, alcohol, sugar, starch, animal fat, vegetable oils, glycerine, and the like, with the same letters; yet nature compounds them all of the same atoms of carbon, hydrogen, and oxygen, but in different proportions and in different orders.
Chemistry is all-potent. A mechanical mixture of two or more elements is a simple affair, but a chemical mixture introduces an element of magic. No conjurer's trick can approach such a transformation as that of oxygen and hydrogen gases into water. The miracle of turning water into wine is tame by comparison. Dip plain cotton into a mixture of nitric and sulphuric acids and let it dry, and we have that terrible explosive, guncotton. Or, take the cellulose of which cotton is composed, and add two atoms of hydrogen and one of oxygen, and we have sugar. But we are to remember that the difference here indicated is not a quantitative, but a qualitative one, not one affecting bulk, but affecting structure. Truly chemistry works wonders. Take ethyl alcohol, or ordinary spirits of wine, and add four more atoms of carbon to the carbon molecule, and we have the poison carbolic acid. Pure alcohol can be turned into a deadly poison, not by adding to, but simply by taking from it; take out one atom of carbon and two of hydrogen from the alcohol molecule, and we have the poison methyl alcohol. But we are to remember that the difference here indicated is not a quantitative, but a qualitative one, not one affecting bulk, but affecting structure.
In our atmosphere we have a mechanical mixture of nitrogen and oxygen, four parts of nitrogen to one of oxygen. By uniting the nitrogen and oxygen chemically (N_{2}O) we have nitrous oxide, laughing-gas. Ordinary starch is made up of three different elements--six parts of carbon, ten parts of hydrogen, and five parts of oxygen (C_{6}H_{10}O_{5}). Now if we add water to this compound, we have a simple mixture of starch and water, but if we bring about a chemical union with the elements of water (hydrogen and oxygen), we have grape sugar. This sugar is formed in green leaves by the agency of sunlight, and is the basis of all plant and animal food, and hence one of the most important things in nature.
Carbon is a solid, and is seen in its pure state in the diamond, the hardest body in nature and the most valued of all precious stones, but it enters largely into all living bodies and is an important constituent of all the food we eat. As a gas, united with the oxygen of the air, forming carbon dioxide, it was present at the beginning of life, and probably helped kindle the first vital spark. In the shape of wood and coal, it now warms us and makes the wheels of our material civilization go round. Diamond stuff, through the magic of chemistry, plays one of the principle rôles in our physical life; we eat it, and are warmed and propelled by it, and cheered by it. Taken as carbonic acid gas into our lungs, it poisons us; taken into our stomachs, it stimulates us; dissolved in water, it disintegrates the rocks, eating out the carbonate of lime which they contain. It is one of the principal actors in the drama of organized matter.
V
We have a good illustration of the power of chemistry, and how closely it is dogging the footsteps of life, in the many organic compounds it has built up out of the elements, such as sugar, starch, indigo, camphor, rubber, and so forth, all of which used to be looked upon as impossible aside from life-processes. It is such progress as this that leads some men of science to believe that the creation of life itself is within the reach of chemistry. I do not believe that any occult or transcendental principle bars the way, but that some unknown and perhaps unknowable condition does, as mysterious and unrepeatable as that which separates our mental life from our physical. The transmutation of the physical into the psychical takes place, but the secret of it we do not know. It does not seem to fall within the law of the correlation and the conservation of energy.
Free or single atoms are very rare; they all quickly find their mates or partners. This eagerness of the elements to combine is one of the mysteries. If the world of visible matter were at one stroke resolved into its constituent atoms, it would practically disappear; we might smell it, or taste it, if we were left, but we could not see it, or feel it; the water would vanish, the solid ground would vanish--more than half of it into oxygen atoms, and the rest mainly into silicon atoms.
The atoms of different bodies are all alike, and presumably each holds the same amount of electric energy. One wonders, then, how the order in which they are arranged can affect them so widely as to produce bodies so unlike as, say, alcohol and ether. This brings before us again the mystery of chemical arrangement or combination, so different from anything we know among tangible bodies. It seems to imply that each atom has its own individuality. Mix up a lot of pebbles together, and the result would be hardly affected by the order of the arrangement, but mix up a lot of people, and the result would be greatly affected by the fact of who is elbowing who. It seems the same among the mysterious atoms, as if some complemented or stimulated those next them, or had an opposite effect. But can we think of the atoms in a chemical compound as being next one another, or merely in juxtaposition? Do we not rather have to think of them as identified with one another to an extent that has no parallel in the world of ponderable bodies? A kind of sympathy or affinity makes them one in a sense that we only see realized among living beings.
Chemical activity is the first step from physical activity to vital activity, but the last step is taken rarely--the other two are universal. Chemical changes involve the atom. What do vital changes involve? We do not know. We can easily bring about the chemical changes, but not so the vital changes. A chemical change destroys one or more substances and produces others totally unlike them; a vital change breaks up substances and builds up other bodies out of them; it results in new compounds that finally cover the earth with myriads of new and strange forms.
X
THE VITAL ORDER
I
The mechanistic theory of life--the theory that all living things can be explained and fully accounted for on purely physico-chemical principles--has many defenders in our day. The main aim of the foregoing chapters is to point out the inadequacy of this view. At the risk of wearying my reader I am going to collect under the above heading a few more considerations bearing on this point.
A thing that grows, that develops, cannot, except by very free use of language, be called a machine. We speak of the body as a machine, but we have to qualify it by prefixing the adjective living--the living machine, which takes it out of the mechanical order of things fabricated, contrived, built up from without, and puts it in the order we call vital, the order of things self-developed from within, the order of things autonomous, as contrasted with things automatic. All the mechanical principles are operative in the life processes, but they have been vitalized, not changed in any way but in the service of a new order of reality. The heart with its chambers and valves is a pump that forces the blood through the system, but a pump that works itself and does not depend upon pneumatic pressure--a pump in which vital energy takes the place of gravitational energy. The peristaltic movement in the intestines involves a mechanical principle, but it is set up by an inward stimulus, and not by outward force. It is these inward stimuli, which of course involve chemical reactions, that afford the motive power for all living bodies and that put the living in another order from the mechanical. The eye is an optical instrument,--a rather crude one, it is said,--but it cannot be separated from its function, as can a mere instrument--the eye sees as literally as the brain thinks. In breathing we unconsciously apply the principle of the bellows; it is a bellows again which works itself, but the function of which, in a very limited sense, we can inhibit and control. An artificial, or man-made, machine always implies an artificer, but the living machine is not made in any such sense; it grows, it arises out of the organizing principle that becomes active in matter under conditions that we only dimly understand, and that we cannot reproduce.
The vital and the mechanical coöperate in all our bodily functions. Swallowing our food is a mechanical process, the digestion of it is a chemical process and the assimilation and elimination of it a vital process. Inhaling and exhaling the air is a mechanical process, the oxidation of the blood is a chemical process, and the renewal of the corpuscles is a vital process. Growth, assimilation, elimination, reproduction, metabolism, and secretion, are all vital processes which cannot be described in terms of physics and chemistry. All our bodily movements--lifting, striking, walking, running--are mechanical, but seeing, hearing, and tasting, are of another order. And that which controls, directs, coördinates, and inhibits our activities belongs to a still higher order, the psychic. The world of thoughts and emotions within us, while dependent upon and interacting with the physical world without us, cannot be accounted for in terms of the physical world. A living thing is more than a machine, more than a chemical laboratory.
We can analyze the processes of a tree into their mechanical and chemical elements, but there is besides a kind of force there which we must call vital. The whole growth and development of the tree, its manner of branching and gripping the soil, its fixity of species, its individuality--all imply something that does not belong to the order of the inorganic, automatic forces. In the living animal how the psychic stands related to the physical or physiological and arises out of it, science cannot tell us, but the relation must be real; only philosophy can grapple with that question. To resolve the psychic and the vital into the mechanical and chemical and refuse to see any other factors at work is the essence of materialism.
II
Any contrivance which shows an interdependence of parts, that results in unity of action, is super-mechanical. The solar system may be regarded as a unit, but it has not the purposive unity of a living body. It is one only in the sense that its separate bodies are all made of one stuff, and obey the same laws and move together in the same direction, but a living body is a unit because all its parts are in the service of one purposive end. An army is a unit, a flock of gregarious birds, a colony of ants or bees, is a unit because the spirit and purpose of one is the spirit and purpose of all; the unity is psychological.
Only living bodies are adaptive. Adaptation, of course, has its physics or its chemistry, because it is a physical phenomenon; but there is no adaptation of a rock or a clay-bank to its environment; there is only mechanical and chemical adjustment. The influence of the environment may bring about chemical and physical changes in a non-living body, but they are not purposive as in a living body. The fat in the seeds of plants in northern countries is liquid and solid at a lower temperature than in tropical climates. Living organisms alone react in a formative or deformative way to external stimuli. In warm climates the fur of animals and the wool of sheep become thin and light. The colder the climate, the thicker these coverings. Such facts only show that in the matter of adaptation among living organisms, there is a factor at work other than chemistry and physics--not independent of them, but making a purposive use of them. Cut off the central shoot that leads the young spruce tree upwards, and one of the shoots from the whirl of lateral branches below it slowly rises up and takes the place of the lost leader. Here is an action not prompted by the environment, but by the morphological needs of the tree, and it illustrates how different is its unity from the unity of a mere machine. I am only aiming to point out that in all living things the material forces behave in a purposive way to a degree that cannot be affirmed of them in non-living, and that, therefore, they imply intelligence.
Evidently the cells in the body do not all have the same degree of life,--that is, the same degree of irritability. The bone cells and the hair cells, for instance, can hardly be so much alive--or so irritable--as the muscle cells; nor these as intensely alive as the nerve and brain cells. Does not a bird possess a higher degree of life than a mollusk, or a turtle? Is not a brook trout more alive than a mud-sucker? You can freeze the latter as stiff as an icicle and resuscitate it, but not the former. There is a scale of degrees in life as clearly as there is a scale of degrees in temperature. There is an endless gradation of sensibilities of the living cells, dependent probably upon the degree of differentiation of function. Anæsthetics dull or suspend this irritability. The more highly developed and complex the nervous system, the higher the degree of life, till we pass from mere physical life to psychic life. Science might trace this difference to cell structure, but what brings about the change in the character of the cell, or starts the cells to building a complex nervous system, is a question unanswerable to science. The biologist imagines this and that about the invisible or hypothetical molecular structure; he assigns different functions to the atoms; some are for endosmosis, others for contraction, others for conduction of stimuli. Intramolecular oxygen plays a part. Other names are given to the mystery--the micellar strings of Naegeli, the biophores of Weismann, the plastidules of Haeckel; they all presuppose millions of molecules peculiarly arranged in the protoplasm.