contrast of living and dead—eating and being eaten—trace matter upwards and life downwards—colloids—cells—protoplasm—monera—composition of protoplasm—essential qualities of life—nutrition and sensation—motion—reproduction—spontaneous generation—organic compounds—polar conditions of life.
polarity having been established as the universal law of the inorganic world, we have now to pass to the organic, or world of life. at first sight there seems to be a great gulf fixed between the living and the dead which no bridge can span. but first impressions are very apt to deceive us, and when things are traced up to their origins we often find them getting nearer and nearer until it is difficult to say where one begins and the other ends. take for instance such an antithesis as ‘eating or being eaten.’ if a hunter meets a grizzly bear in the rocky mountains, one would say that no distinction can be sharper than whether the bear eats the man, or the man the bear. in the one case there is a man, and in the other a bear, less in the world. but look through a microscope at a glass of water, and you may see two specks of jelly-like substance swimming in it. they are living creatures, for they eat and grow, and thrust out and retract processes of their formless mass, which serve as temporary legs and arms for seizing food and for voluntary motion. in short, they are[77] each what may be called strictly individual am?b?, forming separate units of the animated creation as much as the man and the bear. but if the two happen to come in contact, what happens? the two slimy masses involve one another and coalesce, and the resulting am?ba swims away merrily as two gentlemen rolled into one.
now in his case what became of their individualities: did am?ba a eat am?ba b, or vice versa, and is the resulting am?ba a survival of a or of b, or of both or neither of them? and what becomes of the antithesis of ‘eating or being eaten’ which was so clear and distinct in the highly specialised forms of life, and is so evanescent in the simpler forms? this illustration may serve to teach us how necessary it is to trace things up to their origins, before expressing too trenchant and confident opinions as to their nature and relations.
in the case of the organic and inorganic worlds the proper course obviously is, not to draw conclusions from extreme and highly specialised instances, but to follow life downwards to its simplest and most primitive form, and matter upwards to the form which approaches most nearly to this form of life. following matter upwards, we find a regular progression from the simple to the complex. take the diamond, which is one of the simplest of substances, being merely the crystallised form of a single ultimate element, carbon. it is extremely hard and extremely stable. ascending to compounds of two, three, or more elements, we get substances which are more complex and less stable; and at last we arrive at combinations which involve many elements and are extremely complex. among these latter substances are some, called colloids, which[78] are neither solid, like crystals, nor fluid, like liquids, but in an intermediate state, like jelly or the white of an egg, in which the molecules have great mobility and are at a considerable distance apart, so that water can penetrate their mass. these colloids are for the most part very complicated compounds of various elements based on a nucleus of carbon, which, from its atom having four poles with strong mutual attractions, is eminently qualified for forming what may be called the inner skeleton of these complex combinations. colloids of this description form the last stage of the ascending line from inorganic matter to organic life.
next let us trace life downwards towards matter. there is a constant succession from the more to the less complex and differentiated: from man, through mammals, reptiles, fishes, and a long chain of more simple forms, until at its end we come to the two last links, which are the same for all animals, all plants, and all forms of animated existence. the last link but one is the cell, the last of all is protoplasm.
protoplasm, or, as huxley calls it, ‘the physical basis of life,’ is a colourless jelly-like substance, absolutely homogeneous, without parts or structure, in fact a mere microscopic speck of jelly.
the cell is the first step in the specialisation of protoplasm, the outer layer of which, in contact with the surrounding environment, becoming hardened so as to form an enclosing cell-wall, while a portion of the enclosed protoplasm condenses into a nucleus, in which a further condensation makes what is called the nucleolus or second smaller nucleus. this constitutes the nucleated cell, whose repeated subdivision into other similar cells in geometrical progression furnishes the[79] raw material out of which all the varied structures of the world of life are built up. plants and animals, bones, muscles, and organs of sense, are all composed of modified cells, hardened, flattened, or otherwise altered, as the case may require. if we trace life up to its origin in the individual instead of in the species, we arrive at the same result. all plants and animals, whether of the lowest or highest forms, fish, reptile, bird, mammal, man, begin their individual existence as a speck of protoplasm, passing into a nucleated cell, which contains in it the whole principle of its subsequent evolution into the mature and completed form.
protoplasm is, therefore, evidently the nearest approach of life to matter; and if life ever originated from atomic and molecular combinations, it was in this form. to suppose that any more complex form of life, however humble, could originate from chemical combinations, would be a violation of the law of evolution, which shows a uniform development from the simple to the complex, and never a sudden jump passing at a bound over intermediate grades. to understand life, therefore, we must understand protoplasm; for protoplasm, closely as it approximates to colloid matter, is thoroughly alive. a whole family, the monera, consist simply of a living globule of jelly, which has not even begun to be differentiated. every molecule, as in a crystal, is of homogeneous chemical composition and an epitome of the whole mass. there are no special parts, no organs told off for particular functions, and yet all life-functions—nutrition, reproduction, sensation, and movement—are performed, but each by the whole body. the jelly-speck becomes a mouth to swallow, and turning inside out, a stomach to digest. it shoots out[80] tongues of jelly to move and feel with, and presently withdraws them.
with these attributes it is impossible to deny to protoplasm the full attributes of life, or to doubt that, like the atom in the material world, it is the primary element of organic or living existence. given the atom, we can trace up, step by step, the whole evolution of matter; so given the protoplasm, we can trace up the evolution of life by progressive stages to its highest development—man. to understand life, therefore, we must begin by trying to understand protoplasm.
what is protoplasm? in its substance it is a nitrogenous carbon compound, differing only from other similar compounds of the albuminous family of colloid by the extremely complex composition of its atoms. it consists of five elements, and its average composition is said by chemists to be 52·55 per cent. carbon, 21·23 oxygen, 15·17 nitrogen, 6·7 hydrogen, 1·2 sulphur. its peculiar qualities, therefore, including life, are not the result of any new and peculiar atom added to the known chemical compounds of the same family, but of the manner of grouping and motions of these well-known material elements. it has in a remarkable degree the faculty of absorbing water, so that its molecules seem to float in it in a condition of semi-fluid aggregation, which seems to be necessary for the complex molecular movements which are the cause or accompaniment of life. thus, many seeds and animalcul?, if perfectly dry, may remain apparently as dead and as unchanging as crystals, for years, or even, as in the case of the mummy wheat, for centuries, to revive into life when moistened.
but in addition to those material qualities in which[81] protoplasm seems to differ only from a whole group of similar compounds of the type of glycerine, by the greater complexity and mobility of its molecules, it has developed the new and peculiar element which is called life. life in its essence is manifested by the faculties of nutrition, sensation, movement, and reproduction.
as regards nutrition there is this essential difference between living and non-living matter. the latter, if it feeds and grows at all, does so only by taking on fresh molecules of its own substance on its outer surface, as in the case of a small nucleus-crystal of ice in freezing water. if it feeds on foreign matter and throughout its mass, it does so only in the way of chemical combination, forming a new product. living matter, on the other hand, feeds internally, and works up foreign substances, by the process we call digestion, into molecules like its own, which it assimilates, rejecting as waste any surplus or foreign matter which it cannot incorporate. it thus grows and decays as assimilation or waste preponderates, remaining always itself. the distinction will be clear if we consider what happens when water rusts iron. in a certain sense the iron may be said to eat the oxygen, reject the hydrogen, and grow, or increase in weight by what it feeds on; but the result is not a bigger piece of iron, but a new substance, rust, or oxide of iron. that living matter should feed internally is not so wonderful, for its semi-fluid condition may well enable foreign molecules to penetrate its mass and come in contact with its own interior molecules; but it is an experience different from anything known in the inorganic world that it should be able to manufacture molecules of protoplasm like its own out of these foreign molecules, and thus grow by assimilation.[82] for instance, when am?b?, bacteria, and other low organisms live and multiply in chemical solutions which contain no protoplasm, but only inorganic compounds containing the requisite atoms for making protoplasm, or when a plant not only chemically decomposes carbonic dioxide, exhaling the oxygen and depositing the carbon in its stem and leaves, but also from this and other elements drawn from the soil or air manufactures the living protoplasm which courses through its channels, the result is that life has manufactured life out of non-living materials.
if we take sensation, this, in its last analysis, is change, or molecular motion, induced in a body by the action of its environment. here there is a certain analogy between living and non-living matter, for the latter does respond to changes in the surrounding environment, as in the case of heat, electricity, and otherwise; but living matter is far more sensitive, the changes are far more frequent and complex, and in certain cases they are accompanied by a sensation of what is called consciousness, which in the higher organisms rises into a perception of voluntary effort or free-will as a factor in the transformation of energies. thus it happens that in the case of dead matter the changes produced by a change of conditions follow fixed laws and can be predicted and calculated, while those of living matter are apparently uncertain and capricious. we can tell how much an iron bar will expand with heat; but we cannot say whether, if a particle of food is brought within reach of an am?ba, it will or will not shoot out a finger to seize it. if the am?ba is hungry it probably will; if it is enjoying a siesta after a full meal, it probably will not.
[83]
the case of sensation includes that of motion, which is after all only sensation applied in the liberation of energy of position which has by some chemical process become stored up, either in the living mass, or in some special organ of it, such as muscle. iron, for instance, moves when it expands by heat or is attracted by a magnet; but it moves, like the planets, by fixed and calculable laws: while living matter moves, as might be expected from the variable character of its sensation, in a manner which often cannot be calculated. there are cases, however, of reflex or involuntary motion, where, even in the highest living organisms, sensation and motion seem to follow change of environment, in a fixed and invariable sequence, as in shrinking from pain, touching or galvanising a nerve; and it may be that the apparent spontaneousness and variability of living motion is only the result of the almost infinitely greater complexity and mobility of the elements of living matter.
reproduction remains, which is the faculty most characteristic of life, and which distinguishes most sharply the organic from the inorganic world. in the inorganic there is no known process by which dead matter reproduces itself, as the cell does when it contracts in the middle and splits up into two cells, which in their turn propagate an endless number of similar cells, increasing in geometrical progression until they supply the raw material from which all the countless varieties of living organisms are built up, which, in their turn, repeat the process and reproduce themselves in offspring. this is the real mystery of life; we can partly see or suspect how its other faculties might arise from an extension of the known qualities and laws of[84] matter and of energy; but we can discern no analogy between the non-reproductive nitrogenous carbon compound, which makes so near an approach to protoplasm in its chemical composition, and the reproductive protoplasm, which is fertile, increases and multiplies, and replenishes the earth. can the gap be bridged over: can protoplasm be manufactured out of chemical elements? it is done every day by plants which make protoplasm out of inorganic elements, and by the lowest forms of life which live and multiply in chemical solutions. it is done also in the life-history of all individuals whose primitive cell or ovum makes thousands or millions of other cells, each containing within its enclosing membrane as much protoplasm as there was in the unit from which they started. but in all these instances there was the living principle to start with, existing in the primitive speck of protoplasm, from which the rest were developed. can this primitive speck be created; or, in other words, can protoplasm be artificially manufactured by chemical processes?
the answer must be, no; not by any process now known. the similarity of chemical composition, and the increasing conviction of the universality of natural law and of evolution, have led to a very general belief that such a spontaneous generation of life must be possible, and numerous experiments have been made to produce it. for a time the balance seemed to be very evenly held between the supporters and opponents of spontaneous generation. in fact, starting from the assumption, which at first was common to both sides, that heat equal to the boiling point of water destroyed all life organisms, spontaneous generation had the best of it: for it was clearly proved that living organisms did[85] appear in infusions contained in vessels which had been hermetically sealed, after being subjected to this, or even a higher degree of heat. but subsequent and more careful experiments have shown that the germs or spores of bacteria and other animalcul?, which are generally floating in the air, can, when dry, withstand a greater degree of heat, and that when the experiments are made in optically pure air no life ever appears and the infusions never putrefy. on questions of this sort all who are not themselves expert experimentalists must be guided by authority, and we may be content to accept the dictum of huxley that biogenesis, or all life from previous life, was ‘victorious along the whole line.’ but in doing so we must accept huxley’s caution, ‘that with organic chemistry, molecular physics, and physiology yet in their infancy, and every day making prodigious strides, it would be the height of presumption for any man to say that the conditions under which matter assumes the qualities called vital, may not some day be artificially brought together.’
and further, ‘that as a matter not of proof but of probability, if it were given me to look beyond the abyss of geologically recorded time, to the still more remote period when the earth was passing through chemical and physical conditions which it can never see again, i should expect to be a witness of the evolution of living protoplasms from non-living matter.’ such is the cautious candour with which scientific men approach problems upon which theologians dogmatise with the unerring intrepidity of ignorance.
in the meantime what may be said as to huxley’s reservations is this: a considerable step has been made in the direction indicated, by the success of recent[86] chemistry in forming artificially what are called organic compounds, that is, substances which were previously known only as products of animal or vegetable secretions. urea, for instance, the base of uric acid, with which so many are unfortunately familiar in the form of gout; indigotine, the principle of the blue colouring matter of the indigo plant; and alizarine, that of madder; are all now produced artificially, and have even become important articles of commerce. if chemists can make the indigotine, which the growing plant elaborates at the same time as it elaborates protoplasm, may we not hope some day to make the latter as well as the former product? now organic compounds of this class are being formed artificially every day, and it is said that chemists have already succeeded in producing several hundreds. but even if this expectation is never fulfilled, we may fall back on huxley’s second reservation of the enormous difference of chemical and physical conditions in the early stages of the earth’s life from anything now known. it has been calculated that the earth’s temperature when it first started on its career as an independent planet was something like 3,000,000° fahrenheit. at this heat probably all atoms would be dissociated; but as the temperature diminished they would come closer together, but still with a great deal of motion, and making wide excursions, which might bring many different atoms together in complex though unstable combinations. moreover, carbon, which is the basis of all such combinations of the class of protoplasm, was far more abundant in those early days in the form of carbonic dioxide gas, before the enormous amount of vegetable matter in the form of coal and otherwise, had been subtracted from it. in any case[87] the first protoplasm must be extremely ancient, for the remains of sea-weeds are found in the oldest strata, and vegetation of any sort implies the manufacture of protoplasm from inorganic matter.
the passage from the organic into the inorganic world is best traced by following the line of pasteur’s researches on ferments. how does the world escape being choked up by the accumulation of dead organic matter throughout innumerable ages? by what are called ferments, inducing processes of fermentation and putrefaction, by which the course of life is reversed, and the organic elements are taken to pieces and restored to the inorganic world. pasteur proved, in opposition to the theories of liebig and other older chemists, that this was not done directly by the oxygen of the air, but through the intermediate agency of living microbes, whose spores, floating in the air, took up their abode and multiplied wherever they found an appropriate habitation. given an air purified from germs, or a temperature low enough to prevent them from germinating, and putrescible substances would keep sweet for ever. the practical realisation of this is seen in the enormous commerce in canned meats and fruits, and in the imports of frozen beef and mutton, causing a fall of rents and much lamentation among british landlords and farmers.
but then the question was asked, how are your microscopic organisms disposed of? what are the ferments of your ferments? for even microscopic bacteria and vibrios would, in time, choke up the world by their residue if not got rid of. pasteur answered that the ferments are destroyed by a new series of organisms—aerobes—living in the air, and these by other aerobes in succession until the ultimate products are oxidised.[88] ‘thus, in the destruction of what has lived, all is reduced to the simultaneous action of the three great natural phenomena—fermentation, putrefaction, and slow combustion. a living being, animal or vegetable, or the débris of either, having just died, is exposed to the air. the life that has abandoned it is succeeded by life under other forms. in the superficial parts, accessible to the air, the germs of the infinitely little aerobes flourish and multiply. the carbon, hydrogen, and nitrogen of the organic matter are transformed by the oxygen of the air, and under the vital activity of the aerobes, into carbonic acid, the vapour of water, and ammonia. the combustion continues as long as organic matter and air are present together. at the same time the superficial combustion is going on, fermentation and putrefaction are performing their work in the midst of the mass by means of the developed germs of the original microbes, which, note, do not need oxygen to live, but which oxygen causes to perish. gradually the phenomena of destruction are at last accomplished through the work of latent fermentation and slow combustion.’
this seems a complete demonstration of the passage of the organic into the inorganic world in the way of analysis, or taking the puzzle to pieces. in the opposite way of synthesis, or putting it together, the nearest approach yet made has been in the manufacture of those organic compounds already referred to, such as urea, alizarine, indigotine and other products which had hitherto only been known as products of animal or vegetable life. of these a vast number have been already formed from inorganic elements by chemical processes, and almost every day announces some fresh discovery.
under these circumstances it is unsafe to affirm[89] either, on the one hand, that the problem has been solved and that life has ever been made in a laboratory; or, on the other hand, that there is any such great gulf fixed between the organic and the inorganic, that we can assume a break requiring secondary supernatural interference to surmount it, and ignore the good old maxim that ‘natura nihil facit per saltum.’ positive proof is wanting, but the probabilities point here, as they do everywhere else throughout the universe, to the truth of the theory of ‘original impress’ as opposed to that of ‘secondary interference.’
it remains to show how the fundamental law of polarity affects the more complex relations of life and of its various combinations. and here it is important to bear in mind that as the factors of the problem become more intricate and complex, so also do the laws which regulate their existence and action. polarity is no longer a simple question of attraction and repulsion at the two ends of a magnet or at the opposite poles of an atom. it appears rather as a general law under which as the simple and absolute becomes differentiated by evolution into the complex and manifold, it does so under the condition of developing contrasts. for every plus there is a minus, for every like an unlike; one cannot exist without the other; and, although apparently antagonistic, harmonious order is only possible by their co-existence and mutual balance.
this is so important that it may be well to make the idea clearer by an illustration. the earth revolves round the sun in its annual orbit under the influence of two forces: the centripetal, or force of gravity tending to draw it towards the sun; and the centrifugal, tending to make it dart away into infinite space. during half the[90] orbit the centripetal seems to be gaining ground on the centrifugal, and the earth is approaching nearer to the sun. if this continued it would revolve ever nearer and soon fall into it; but the centrifugal force is gradually recruiting its strength from the increased velocity of the earth, until it first equals the centripetal, and finally outstrips it, and for the remaining half of the orbit it is constantly gaining ground. if this went on, the earth would fly off into the chilly regions of outer space; but the centripetal force in its turn regains the ascendency; and thus by the balance of the two forces our planet describes the beautiful ellipse, its harmonious orbit as a habitable globe; while comets in which one or the other force unduly preponderates for long periods are alternately drawn into fiery proximity to the sun, and sent careering through regions void of heat.
compare this passage from herbert spencer: ‘as from antagonist physical forces, as from antagonist emotions in each man, so from the antagonist social tendencies man’s emotions create, there always results not a medium state, but a rhythm between opposite states. the one force or tendency is not continuously counterbalanced by the other force or tendency; but now the one greatly preponderates, and presently by reaction there comes a preponderance of the other.’
and again: ‘there is nowhere a balanced judgment and a balanced action, but always a cancelling of one another by opposite errors. men pair off in insane parties, as emerson puts it.’
the reader will now begin to understand the sense in which polarity applies to these complex conditions of an advanced evolution.
to return, however, from this digression to the[91] point at which it began, viz. the origin of life, we have to show how the law of polarity prevails in the organic as well as in the inorganic world. in the first place the material to which all life is attached, from the speck of protoplasm to the brain of man, is strictly a chemical product of atoms and molecules bound together by the same polar laws as those of inorganic matter.
in like manner all the essential processes by which life lives, moves, and has its being, are equally mechanical and chemical. if the brain, receiving a telegram from without through the optic nerve, sends a reply along another nerve which liberates energy stored up in a muscle and produces motion, the messages are received and transmitted like those sent by a voltaic battery along the wires of a telegraph, and the energy is stored up by the slow combustion of food in oxygen, just as that of the steam-engine is produced by the combustion of coal. all this is mechanical, inorganic, and therefore polar.
but when we come to the conditions of life proper, we find the influence of polarity mainly in this: that as it develops from simpler into more complex forms, it does so under the law of developing contrasts or opposite polarities, which are necessary complements of each other’s existence. thus, as we ascend in the scale of life, we find two primitive polarities developed: that of plant and animal, and that of male and female.
