The making of worlds, we are assured, was not purposeless, and its most obvious purpose to our minds is the preparation of suitable abodes for organic life. No other seems of comparable importance; no other, indeed, comes within the full grasp of our apprehensive intelligence. Yet its limitations must not be forgotten. The human standpoint is not the only one from which the sum of things may be surveyed; and although we be unable to quit it, we can still admit that the view obtainable from it is probably not all-embracing. We only know with certainty that the end which appears to us supreme has, in one case, been successfully attained; how far it was sought to be compassed elsewhere must always remain a matter of speculation.
On our own globe the presence of life is none the less mysterious for being profuse and familiar. We can trace the strange history of its slow unfolding, but the secret of its initiation baffles our utmost scrutiny. The cooled rind of a once molten globe serves as the stage for the drama; beneath it primeval heat still reigns. Temperature rises steadily with descent into the interior of the earth; at a depth of about two miles it must reach the boiling-point of water at the sea-level. This temperature, which is absolutely prohibitive of vitality, was formerly, beyond question, that of the surface. At some long past epoch, accordingly, our future oceans hung suspended as a prodigious envelope of vapour above a hot crust of slag and lava; our teeming planet lay barren; it harboured no promise, no potency, no visible possibility of life.
So it should have remained had the law of continuity been rigidly enforced; but there came a time for a new beginning, and a new beginning was made. A momentous alteration took place; inert Nature was quickened; what had been sterile became all at once fruitful; an immeasurable gulf was bridged, and movement was started along an endless line of advance. That the advance was set on foot and directed by an intelligent Will is the only inference derivable from a rational survey of the known facts.
Life can be studied in its manifestations, not in itself. Attempts to define it have served only to show our inability to 'lift the painted veil.' We can, however, see that its presence is attended by characteristic effects, brought about in harmony with the laws of inorganic nature, although not in blind submission to them. Their operation is somehow restrained, and appears to be subtly though securely guided towards determinate ends prescribed by the vital needs of each animal or plant. This modifying principle unmistakably regulates the economy of every living organism; the cessation of its activity means death.
Science has made no real progress towards solving the enigma of vitality. Its evasiveness becomes, on the contrary, more apparent as inquiry is rendered more exact. Under a laxer discipline of thought the contrast between life and death seemed less glaring. It was easily taken for granted that creeping things were engendered by corruption, aid being invoked, if required, from the virtus cœlestis of the eighth sphere. Thus, the birth of mice from the damp earth was, in the ninth century, held to be signified by the word mus (=humus);[119] and Van Helmont, at the height of the revival of learning, published without misgiving a recipe for the creation of the same animals.[120] Yet there was already better knowledge to be had for the asking; and Francesco Redi, in 1668, crystallized Harvey's opinion in the celebrated maxim, 'Omne vivum ex vivo.' Its truth is incontrovertible. Challenged and tested again and again, it has as often been vindicated, and may now be said, despite certain anomalous effects of radium on veal broth, to stand outside the legitimate range of debate. 'That life is an antecedent to life,' Lord Kelvin declared in 1871, 'seems to me as sure a teaching of science as the law of gravitation.'[121]
But the succession is not easy to start within the terms of a strictly uniformitarian convention. The expedient is tempting, if scarcely satisfactory, of demanding from the past what we dare not claim from the present. Two and a half millenniums ago it was already in vogue. Herodotus dismisses a genealogical embarrassment with the remark, γένοιτο δ'άν πᾶν έν τῶ μακρῶ χρόνω, which may be freely translated, 'In the long run of time anything may happen.' Conditions, we are apt to think, may have been more elastic long ago. The proven impossibility of to-day becomes vaguely thinkable seen through the mist of uncounted yesterdays. 'If it were given to me,' Professor Huxley said,[122] 'to look beyond the abyss of geologically recorded time to the still more remote period when the earth was passing through physical and chemical conditions which it can no more see again than a man can recall his infancy, I should expect to be a witness of the evolution of living protoplasm from non-living matter.' To these first vital compounds he attributed a fungoid nature and mode of growth, and the choice deprived his speculation of any plausibility that might otherwise have belonged to it. Fungi are not self-supporting; they cannot supply themselves with nourishment from the raw materials of the mineral world; they depend upon the hospitality of differently organized beings. They were, then, certainly not among the 'first mercies of nature.' Mr. Herbert Spencer, too, was inclined to regard spontaneous generation as a superannuated process. The leap from the non-vital to the vital, now admitted by the saner kind of biologists to be impracticable, might have been taken, it seemed to him, when 'the heat of the earth's surface was falling through those ranges of temperature at which the higher organic compounds are unstable.' But the 'reason why' is to seek. A sterilized solution is precisely one which has cooled from a high thermal grade; a baked brick is similarly circumstanced. Why should the appearance of life in primeval times have been favoured by a state of things fatal to it here and now?
The essence of the biological crux resides in 'protoplasm.' The word was coined by Von Mohl in 1846, with the object of emphasizing the importance of the substance it signified, which indeed forms the bulk of every organism, animal and vegetable, man, mushroom, and amœba. Huxley rightly termed it 'the physical basis of life,' adding, however, the infelicitous conjecture that its production might have been one of the lucky hits of nature. It would have been a hit of incalculable moment, but of incalculable improbability. 'Odds beyond arithmetic' were against that particular throw coming out of the Lucretian dice-box. The 'primal slime' (to use Oken's phrase) is composed of oxygen, nitrogen, hydrogen, and carbon, with minute percentages of phosphates and other salts. But these constituents are put together in a highly artificial manner. Eight or nine hundred elementary atoms, in fact, go to the making of one molecule of protoplasm, forming a structure of extreme complexity, most delicately balanced and eminently unstable. It results, accordingly, from the employment of specially directed forces, and stores, for the benefit of the producing organism, the energy expended in its construction. Left to itself, it promptly goes to pieces, and yields back its component particles to their native inorganic sphere. The laws there ruling are in truth adverse to the existence of protoplasm; abandoned to their unmitigated action, it perishes. We should then as reasonably suppose that in the geological past rivers flowed uphill as that inorganic nature stumbled blindly upon this wonderful postulate and product of life.
Professor Huxley affirmed life to be 'a property of protoplasm,' the inevitable outcome of 'the nature and disposition of its molecules,' and he sought to cover the absurdity of the dictum by claiming as analogous a case wholly disparate. Water, he argued, has qualities totally unlike those of oxygen or hydrogen, and protoplasm may similarly, by mere intricacy of arrangement, and the evoking of latent affinities, become endowed with the transcendant powers connected with animated existence. 'What better philosophical status, then,' he exclaimed, 'has vitality than aquosity?'[123] 'True,' he added, 'protoplasm can only be generated by protoplasm, in a manner that evades our intelligence, but does anybody quite comprehend the modus operandi of an electric spark which traverses a mixture of oxygen and hydrogen?' The illustration is inapt. The electric spark fulfils no constructive function. It simply agitates the molecules so as to bring their native affinities into play. It acts like a mechanical blow on dynamite. Further, water is a stable compound, because its formation is attended by loss of energy; it represents a plane permanently occupied because reached by a steep descent; but protoplasm is, in this respect, the antitype of water. It needs force for its composition; water needs force for its decomposition. Protoplasm needs force plus a suitable apparatus; it can be turned out only by an artfully adapted machine with a head of steam on. It is thus continually manufactured by plants under the stimulus of light. They provide the apparatus, sunbeams the energy. If the supply of power is cut off, the machinery comes to a halt, protoplasm ceases to be generated, the organism dies of inanition.
Many German biologists find themselves compelled, by the impossibility of explaining vital activities in terms of chemistry or physics, to associate protoplasm with some kind of psychical activity.[124] Individuality, at least, implies an ultra-material principle, and it asserts itself at the very base of the animal creation. An amœba is the simplest of living beings. Formerly called the 'Proteus animalcule,' it is 'everything in turn, and nothing long.' It can be round or radiated, spherical or lenticular, as momentary convenience prescribes. Organs it has none, its limbs are conspicuous by absence, it is 'sans everything' that belongs to the ordinary outfit of an animated creature. Yet such-like nucleated globules of protoplasm have flourished exuberantly during countless ages. Adaptability insured survival. An amœba is at home in almost any environment. What it has not ready-made, it can supply at a moment's notice. Out of any part of its substance it can improvise feelers and tentacles for the capture of its prey, as well as a stomach for its digestion, and it thus effectively goes through the full round of animal economy. Some varieties, too, are noted builders. Those called Foraminifera have the faculty of secreting carbonate of lime from sea-water, and construct with it fairy dwellings, perforated in all directions to allow of the protrusion of exploratory filaments. Fossil chambered shells of this type are extraordinarily abundant. Their dense conglomeration in the chalk elicited Buffon's exclamation that 'the very dust had been alive!'[125] The calcaire grossier of which Paris is built consists mainly of them, and to this day, in oceanic depths, the materials of future capitals are in course of preparation by the monumental industry of these unpretending creatures.