The adventure of life

Front matter

CIass_BjM^J

Book _3.

CDPffilGHT DEPOSIT

Preface

The life of every one who will read these words has been influenced in some way by the war. It has rudely broken many old and sacred ties ; it has touched with calamitous finger innumerable homes ; it has altered life-long habits and shattered many a fondly cherished belief. It has introduced a ferment into human thought, and men who had accepted without questioning and with little understanding the mysteries of existence are finding their beliefs challenged and their faith shaken by the iron discipline of events. They are asking, as they watch civilization ablaze in the furnace, if there is any answer to the riddle of the universe; if there is any righteousness in the scheme of things ; if there is any purpose in life: or if it is all nothing but an ugly delusion or a hideous dream.

There is a danger that some will find in a crude doctrine of materialism the sole resting-place for their feet ; but the materialistic creed is a creed of pessimism — a foundation from which no useful and enduring edifice of belief can ever arise. That humanity may spring from the ashes of civilization with vigor renewed and vision purified, we must cultivate an invincible spirit of optimism. For such an attitude of mind we have good grounds : we have none for the sterilizing dogmas of materialism.

It is given to the physician to see much of human life. He has many opportunities of beholding its sordidness. He is the daily witness of its high heroism. He is conviii PREFACE

stantly faced by its problems; he can never get away from its mysteries ; his knowledge of its adaptations is intimate, and though there is still much about it that is hidden from his inquiring eyes, he is aware of some of its potentialities.

Personally, I cannot bring myself to believe that life can ever be explained in the terms of sheer materialism, and reduced to mere chemical equations, or expressed entirely in the language of the physical or physiological laboratory. The indomitable logic of facts has driven me to the conclusion that behind all and above all there is an intelligent and beneficent Mind, immanent in nature and in the life of man. If this is true we have good reason to hail the future with a glad confidence.

The chapters which follow have been written in the hope that they may help to illumine with a ray of light, however feeble, the clouds of perplexity with which many an earnest seeker after the truth finds himself surrounded.

The book is neither a scientific monograph nor a philosophical treatise, and will be easily comprehended by all. As far as possible I have endeavored to avoid the use of technical terms. My aim has been to impress upon all who care to read the wonder and the harmony of life, and the complete interdependence that subsists between all forms of life. I believe that the goal of Nature is Life; the aim of Life is the development of Intelligence, and the object of Intelligence is a knowledge of God.

It is not my desire to disarm criticism, but some of the defects in the chapters which follow — of whose existence I am fully conscious — are due to the conditions under which the book has been composed. It was begun on a winter night in a little bell-tent in the

PREFACE ix

North of France, within sight of a horizon lit by the flash of heavy guns. More than once the hurricanelamp had to be extinguished lest its faint light, illuminating the canvas walls, should attract the eye of some questing enemy aviator and tempt him to hurl his bombs upon the sleeping hospital. It was completed in a tent still within the zone of war, but somewhat more remote from actual hostilities. Libraries are no part of the equipment of a war hospital, and I have had no books of reference to fall back upon except a few smuggled over in my kit-bag. Napoleon is said to have carried a library through all his campaigns. An officer of the R.A.M.C. who would dare to attempt to emulate that great example would have his plans rudely frustrated by the Embarkation Officer. But the circumstances which made the task difficult in one direction made it easier in another, for the facts of war have supplied me with an unfailing source of illustration.

Robert W. Mackenna.

March, 1918.

Contents

CHAPTER PAGE

I The Universality of Life 1

II The Origin of Life 9

Chapter I The Universality Of Life

O raickle is the powerful grace that lies In plants, herbs, stones, and their true qualities: For naught so vile that on the earth doth live, But to the earth some special good doth give.

Shakespeare. Borneo and Juliet.

Nothing walks with aimless feet;

That not one life shall be destroyed

Or cast as rubbish to the void, When God hath made the pile complete.

Tennyson. In Mernorianu

Life is the most wonderful thing in the world. We find it everywhere, abundant, prodigal, and luxuriant. Earth, sea, and sky teem with it. The grass in the fields, the flowers on the hillside, the trees in the forest, the birds in the air, the fish in the water, and all things that creep or walk are quick with life. We turn over a stone with our stick and sack a city, for underneath it is a seething colony of ants, which scurry hither and thither in no purposeless panic, but intent on saving themselves, their young, and their hoarded food from destruction by the invader.

We look abroad and discover that wherever life could find a foothold it has established itself. There is living lichen on the rocks, and even on some bluff crag thrust up from the earth like the shoulder of a sleeping giant we find that life has seized on every little shelf and slope where a handful of earth has lodged. Not far from where I write there is a great range of limestone hills. Their summits are crowned by vegetation of many kinds, and pine-trees stand defiant in the blast ; but all along the precipitous sides, wherever niche or cranny has afforded a lodgment, some tree has grown, and, hanging between the earth and the sky, where no cragsman would ever venture to tread, it proclaims the triumph of life over death, and the urgency of nature's demand for life, and yet more life.

Life is such an urgent thing that it hastens to repair the devastation and havoc wrought by man. In the fields of Flanders and the fertile land of France the grass and the flowers are constantly seeking to hide the desolation which man has produced with his devilish engines of war. It is as though Nature shuddered at the defilement of Mother Earth and sought to cover her bruised body with pitying and flower-laden hands.

Much of the beauty of the earth is due to the life upon it. Take away all the vegetation, roll up the green carpet of the grass, throw down the awe-inspiring aisles of forest trees, and earth would become a desolate and unlovely place.

We live in a world of life. Much of it we can see with the unaided eye, but beyond the range of our natural vision there is a realm of nature in which life still fulfills itself. In a drop of river-water or a speck of road-dust the microscope reveals to us life in myriad forms, each distinct, but sharing in the one great principle which animates all living things. Every one of these infinitesimal creatures fills a niche of its own in the Universe. One may sit for hours at a time with an eye riveted to the tube of an ultramicroscope in a maze

THE UNIVERSALITY OF LIFE 3

of wonder, watching the dance of life performed by the teeming bacteria present in a minute drop of water from a stagnant pool. The field of vision is thronged by an innumerable multitude of actively moving, infinitely little living things. Some are engaged in a rhythmic dance, scarcely moving from their position. Others dart like some torpedo-craft across the field of vision, and pass out of sight. Others move with more leisurely progression like some sight-seer in an historic town; others again, with sinuous movement, ominous of evil purpose, bore their slow way across the visual field; and now and then, lit up by the reflected light, and all aglow like some barbaric princess loaded with precious stones, there swims into our ken a veritable queen of bacterial life. Royally she moves ; and, as one wonders, she is gone.

All life is bound together in a community of mutual service. The master-chemist, the sun, at work in his laboratory in every blade of grass, is elaborating nourishment for all the cattle of the fields. The whole of the animal kingdom depends for its sustenance upon the green things of the earth. But the green things owe a debt to the animal kingdom in turn. The flower that pours its perfumed chalice into the ocean of the air depends upon the questing bee or other insect for that little speck of magic pollen-dust that will enable it to continue its life in another generation. The bird that tears a berry from a tree bears the seed off, and drops it perhaps many miles away, where haply it may find a resting-place and continue its kind.

All life in Nature is directed to high service, and even death helps Nature to win fresh fields for life. Much of the surface of the earth, as we now know it, once lay at the bottom of the sea. Of itself sand offers but a poor and precarious sustenance for vegetable life;

but the first lowly plant that established itself upon the sand made the conquest of the desert an easier thing for the plants that followed it. It lived a difficult existence, then it died, and its leaves and stem drooped and fell upon its inhospitable bed. But in making its sacrifice it won an empire. It imparted to the sand all the riches it had won from its life in the atmosphere, and the sterile shore was gradually converted into hospitable earth. The fertility of the earth is a perpetual witness to the rejuvenating power of death. Life feeds on death; and out of death new life forever rises. Nothing in Nature lives for its own ends alone ; nothing in Nature dies without bequeathing a heritage of some sort to other things that live. Even the bacillus, man's constant and deadly foe, when vanquished by him, renders up to him spoils of war that may help him to win in another fight. For every micro-organism that is destroyed by his mechanism of defense in the body of a human being, confers upon him some fresh power, some increase of immunity that will help to protect him against a similar attack. The man who walks scatheless through an epidemic of infectious disease does so, in some instances, because there has come to him by heredity a healthy constitution ; but part of his immunity is a legacy left to him by those germs of disease which, in the course of his life, have died within his body. Nothing that lives is valueless, and if only we could see the whole world of Nature spread before us like a picture and could understand all that there is to decipher, we should discover that it constitutes a great and beautiful whole in which, in spite of apparent universal struggle, there is a deep underlying concord whose aim and purpose is life — life more adaptable and more capable of progress.

All forms of life have the same physical basis, a

THE UNIVERSALITY OF LIFE 5

highly complex substance compounded from simple elements, known as protoplasm. This identity of the physical basis of life necessarily implies that life differs more in degree than in kind. We and the higher animals have more activities, more potentialities than the lower forms of life, but, being built up from protoplasm, we are cousins-germane to every roadside weed, or every flower in the field. And for this, if for no other reason, we should walk humbly.

In one of his essays Huxley pointed out a fact which must have struck any one who has ever sat on a hillside and contemplated the life around him. All the essential processes of life are carried on in silence. The cataract of the sap rising in some giant tree sends no ripple of sound into the atmosphere to call our attention to it. The branches orientate themselves so that the leaves may catch the sunlight, and the leaves carry on their wonderful work of chemical disintegration and chemical synthesis in absolute silence. The boom of the bursting bud is a poetic fancy, divorced from reality. The fruit ripens, and falls mellow to the earth, but no murmur is wrung from the parent tree. The bleat of a straying sheep, the hum of a bee, the rasping crescendo of the grasshopper, the bark of a distant dog, all come to us vibrant and keen in the stillness of nature. But they are not essential processes of the life of the creatures that produce them. They are the witnesses to the joy of life, or its perplexity.

Our muscles contract noiselessly; in the river of our blood millions of little cargo-boats collide and move on again without a sound. Organs like the liver perform marvelous functions of chemical conversion in absolute silence. A stethoscope applied to the chest enables us to hear the rhythmic thud of the closure of the valves in the heart, and we may hear also the rustle of the air as it is sucked into the ramifying passages through the lungs. But we can detect no sound from the processes of assimilation which are occurring so constantly in the heart muscle, to keep it in repair ; nor do we hear any noise and clamor that would tell us that the cells of the lungs are the busiest wharves in the world, where countless millions of cargo-boats are unloading carbonic-acid gas, and taking in a freight of oxygen every moment of the day and night.

Even thought, the highest function of which any living thing is capable, is a silent process.

The question as to whether life exists on any other planet than our own is one of constant allurement, and as yet science has no definite and authoritative declaration to make. It has been pointed out that certain very special conditions are necessary for the maintenance of life, such as an atmosphere of a certain density, containing at least oxygen and carbonic-acid gas, nitrogen and moisture; regularity, within certain limits, of temperature; an adequate amount of solar energy in the form of light and heat ; and an abundance of water. These things are necessary for life as we know it. But there may be other forms of life of which we have neither knowledge nor the power to conceive. To man, to all animals, and to all vegetable life oxygen is essential. But there is a class of micro-organisms, of which the tetanus bacillus is one, to which oxygen is a deadly poison. They cannot live in its presence. They flourish in its absence. So it is obvious that the conditions which we know to be essential for the maintenance of human life upon the earth may not be necessary for other forms of life on other planets. It would indeed be strange if the infinite immensity of space, sprinkled over as it is by an incal-

THE UNIVERSALITY OF LIFE 7

culable number of worlds greater than our own, should offer no habitation to life but the surface of our minor planet, the earth.

Flammarion, the distinguished French astronomer, was convinced that life exists on other planets than our own, and many think with him. But when we remember the remarkable way in which life is affected by environment, we must be prepared to admit that any form of life met with among the stars, being subject to other influences, will probably differ in a marked degree from life as we know it.

The simplest form of life is the unicellular organism — the protozoon. Man is built up from a multitude of such cells, many millions going to make up his body. But he does not consist of a coherent mass of protozoa welded together. His cells are specialized. Some are set aside in one organ to discharge certain functions ; others, in other organs, are devoted to still different ends. Complexity of organization has led to specialization of function, and the complex organism and the specialized function are integrated and controlled by the marvelously developed nervous system of which he is possessed. He is no mere collection of cells. He is a self-determined individual, sharing in common with the lowlier forms of life the power of growth, the functions of assimilation and nutrition, the power of reproduction, and participating with them in the inevitable experience of death. But he has an experience which is his and his alone. Endowed with the golden gift of reason, he is, to some extent, the master of his own destiny. For him life need not be a meaningless repetition of elementary and almost automatic functions. He may scale the dizzy heights of joy, or plumb the depths of sorrow. Made for action, eager for life, capable of self-sacrifice and of worship, ever hungering insatiably for new knowledge, man may make of life no meaningless adventure, but a glorious opportunity.

Though a great chasm divides the inanimate things in Nature from the things that have life, Life is perpetually making use of the inanimate, quickening it to new activities. The iron of the earth, and the limestone rock broken up by atmospheric influences, are absorbed and modified by the plant life of the fields, and become incorporate in the bodies of animals, and may ascend through bird or sheep or oxen to a place in the body of man. Life spins fresh matter into her ever-growing web, and when the web crumbles into dust, Life picks up the separated atoms once again and weaves other and possibly still more beautiful webs. Matter, which some hold to be the only reality, is little more than a delusion : it becomes real only when it subserves the purposes of life.

All the forces of Nature are leagued in a great conspiracy. The sunbeam which trips daintily over a field of ripening corn, sprinkling the last flecks of gold on the tumid ears, is completing with its living touch the work made possible by myriads of dead and lowly things. Many generations of plant life perished to prepare the soil ; worms and insects and bacteria have labored and died to enrich it. Winter has crumbled it in her ice-cold fingers ; Spring has warmed it with her breath; Summer has sounded her reveille and marshalled the serried ranks of standing corn, teaching them to forage in the limitless acres of the atmosphere ; the rain has poured out its libation, and the wind is come with a promise that the time of harvest shall not fail, and that there will be food for man and beast. For the whole Universe works together in the service of life, which is the goal of Nature and her crown.

Chapter II

" I call the effects of Nature the works of God, whose hand and instrument she only is; and therefore to ascribe His actions unto her is to devolve the honor of the principal agent upon the instrument, which if with reason we may do, then let our hammers rise up and boast that they have built our houses, and our pen receive the honor of our writings."

In all ages the question of the origin of life has allured and perplexed the thinking man. Unable to fathom the mystery, he has either folded his hands and abandoned his search for a solution, or he has fallen back upon his imagination, and some of the most beautiful legends of mythology were the offerings made by fancy to the clamant appeal of the hungering mind for a knowledge of the truth.

From the days of Aristotle down to our own time the idea of the possibility of spontaneous generation has had its supporters. They hold that the line between the non-living and the living, which is passed in the reverse direction by everything that breathes at death, is largely an artificial barrier, and they believe that animate things may rise spontaneously from the inanimate. The careful experiments of Pasteur did much to disprove the doctrine, but of recent years it has received a fresh impetus from the researches of Leduc, and from the observation of Burke of Cambridge, who studied the effects produced by radium emanations upon solutions of gelatine. A great body of scientific opinion is, however, opposed to the possibility of spontaneous generation occurring. It is worthy of note that whenever living things are said to have appeared spontaneously they have been found to belong to animal or vegetable species which are already known. This is in itself a powerful argument against their authenticity. If spontaneous generation ever occurs, either in nature or under laboratory conditions, it would probably present us with entirely new forms of life. This would mean the constant appearance of new species, and we know that the number of species increases only by age-long variations.

Aristotle, no mean scientific observer, who studied the manifestations of life carefully and recognized the unbroken chain which links the lowest plant with the higher animals, believed that certain fishes were produced spontaneously, and Virgil, naturalist and poet, tells in his Georgics how a goddess taught the shepherd to cause living bees to rise from the flanks of a dead bullock. In the De rerum Natura Lucretius expressed the opinion that animals might develop from the action of the sun upon the vapors and moisture of the earth.

At a much later date Van Helmont, who lived in the sixteenth century, stated that living mice and scorpions could be produced at will, like the live rabbit from the conjuror's hat, by mixing together certain ingredients. His recipe for the spontaneous generation of mice consisted of a mixture of dirty linen with wheat, or a piece of cheese, while scorpions could be produced by exposing sweet basil to the heat of the sun in the hollow of a scooped-out brick. These interesting conclusions were the outcome either of inaccurate observation, or of faulty method which left a loop-hole for error to creep in — in one case a vagrant mother-mouse, in the other a scorpion. Holinshed, in whose historical works

Shakespeare dug deep for the ground-work of some of his plays, said in his Description of England, " A horsehair laid in a pailfull of turbid water will in a short time stir and become a living creature." This erroneous idea still persists in some country districts.

In approaching the study of the origin of life we must not forget that the earth existed as a glowing ball of fire for many aeons before it cooled down sufficiently to give to life a fit nidus in which to develop. Though some forms of life are marvelously tolerant of extremes either of heat or cold, life as a rule requires for its maintenance and propagation certain somewhat specialized conditions, and until such conditions were attainable upon our globe there was no life upon it. The late Lord Kelvin calculated that some time between twenty and forty million years ago the conditions upon the earth began to be compatible with the development of life. The margin of twenty million years between the two dates seems a generous and ample concession, though it is only a moment relatively to the immense and incalculable period since the gaseous particles or atoms of meteoric dust that were the prototype of our planet rushed to each other in the cosmic dance, and, blazing through space, Earth started on her pilgrimage along the unbeaten track of her orbit.

Before we proceed to consider how life may have come to earth we must recognize two facts. First, that life on this planet probably began in the sea, and, second, that vegetable life was, almost certainly, the precursor of animal life. The former of these postulates is founded on the knowledge that moisture is necessary for the continuance of life in its full activity, and that the sea would offer a medium whose temperature was less variable than that of the adjacent land. Further, it should not be forgotten that in the water of the sea are found dissolved most of those inorganic or mineral substances that are requisite for the support of plant life, and the constant motion of the sea would bring the necessary pabulum to the growing plant. Vegetable life must have preceded animal life, for not even yet, after these millions of years during which it has succeeded in accommodating itself to many changes of environment, has the animal economy found a way of supporting itself directly from inorganic materials. Plant life is the j ackal, it is the lion's provider : it caters for animal life, and without vegetable life, unless it suddenly acquired new powers, animal life would speedily and inevitably die out.

Probably life appeared in the sea in a form even more elementary than those simple unicellular formations such as the protozoa and the various forms of bacterial life which we know to-day. Some biologists believe that by the time the protozoon was reached, evolution had already many years behind it.

There are several theories as to the origin of life, each of which has its advocates. There is the theory that life is the result of a definite creative act of the great First Cause that lies behind the Universe. Another opinion is that life did not originate on our planet, but came to it as a rich bequest from some other world that perished years ago. In the collision or cataclysm which shattered that planet some particle of living matter, it is suggested, found refuge in a cleft in a piece of rock, and the fragment of rock, rushing through space as a meteorite, fell upon the earth and surrendered its precious burden to the waves of the sea. Both Lord Kelvin and von Helmholtz accepted this hypothesis as a feasible explanation of the manner in which life may have come to earth ; but it has been opposed by other authorities on the ground that in its passage through our atmosphere a meteorite glows with intense heat, and consequently its temperature is raised to a degree that is incompatible with life. On the other hand it has been urged that, if the cleft in the meteorite were sufficiently deep, its little germinal burden might find adequate protection even though the surface of the meteorite were hotter than Nebuchadnezzar's furnace. It has also been suggested that life may have come to earth from some other planet without the intervention of a meteor-* ite to carry it. Cohn put forward the suggestion that, in the cosmic dust which floats through space and falls gently as the dew upon the expectant bosom of the earth, there might be mingled living cells that had wandered or been hurled into space from some other planet. Falling gradually through our atmosphere, these living cells would not attain such a velocity that their temperature would be raised to a degree incompatible with their continued vitality. Svante Arrhenius has suggested that living matter may travel from star to star, impelled by the pressure of the waves of light. But both theories have had their opponents, who believe that the actinic rays of the sun would destroy these elementary living cells in their long passage through the vastnesses of interplanetary space.

In 1872 W. Preyer made a novel suggestion concerning the origin of life upon the earth. He was of opinion that life was present in the midst of the glowing mass of incandescent matter of which the earth consisted before it began to cool. According to his view the molten ball teemed with low forms of life which he called pyrozoa. These life-forms differed radically from any type of living thing that we know to-day in their extraordinary capacity for resisting heat. As the earth cooled the pyrozoa adapted themselves to the new conditions, and became the remote predecessors of those forms of life with which we are acquainted. Preyer's theory did not receive much support, and to-day it is almost forgotten.

Of recent years an attempt has been made to prove that life arose spontaneously when the surface of the cooling earth was covered by chemical substances in a condition of nascent activity. According to this theory creation has not yet ceased. It is still in operation, and life continues to be engendered afresh from non-living materials.

The chemist has divided matter into two great classes — organic substances and inorganic substances. An organic substance is one which contains carbon, while an inorganic substance, such for example as sulphate of iron, oxide of lead, or bichloride of mercury, is carbon-free. For a long period it was believed that the line separating the organic from the inorganic was sharp and well-defined, and that at no point did the substances in the two classes approximate to each other in composition or character. But about the middle of the last century Thomas Graham began to investigate the properties of a series of bodies which he called colloids (from colla — glue) an example of which is gelatine, and he enunciated the opinion that in the colloids we have a large group of substances that come near to bridging the chasm between the organic and the inorganic. As sometimes happens with an epochmaking discovery, his work was neglected and almost forgotten, until about the beginning of the present century, when its importance dawned upon the chemist and physiologist, and the chemistry of the colloids has become one of the most fertile territories for research that the scientific mind has yet discovered. With singular clarity of vision Graham recognized the close relationship subsisting between the character of the colloids and the phenomena of life, and later observers have not hesitated to suggest that through the colloids one may pick one's way from the inorganic to the organic, and from the inanimate to the living.