IITHE PROBLEM OF ORIGINS
CHAPTER ITHE ORIGIN OF LIFE
Strictly speaking, the theory of Transformism is not concerned with the initial production of organic species, but rather with the subsequent differentiation and multiplication of such species by transmutation of the original forms. This technical sense, however, is embalmed only in the term transformism and not in its synonym evolution. The signification of the latter term is less definite. It may be used to denote any sort of development or origination of one thing from another. Hence the problem of the formation of organic species is frequently merged with the problem of the transformation of species under the common title of evolution.
This extension of the evolutionary concept, in its widest sense, to the problem of the origin of life on our globe is known as the hypothesis of abiogenesis or spontaneous generation. It regards inorganic matter as the source of organic life not merely in the sense of apassive cause, out of which the primordial forms of life were produced, but in the sense of anactive causeinasmuch as it ascribes the origin of life to the exclusive agency of dynamic principles inherent in inorganic matter, namely, the physicochemical energies that are native to mineral matter. Life, in other words, is assumed to have arisen spontaneously, that is, by means of a synthesisand convergence of forces resident in inorganic matter, and not through the intervention of any exterior agency.
The protagonists of spontaneous generation, therefore, assert not merely a passive, but an active, evolution of living, from lifeless matter. As to the fact of the origin of the primal organisms from inorganic matter, there is no controversy whatever. All agree that, at some time or other, the primordial plants and animals emanated from inorganic matter. The sole point of dispute is whether they arose from inorganic matter by active evolution or simply by passive evolution. The passive evolution of mineral matter into plants and animals is an everyday occurrence. The grass assimilates the nitrates of the soil, and is, in turn, assimilated by the sheep, whose flesh becomes the food of man, and mineral substance is thus finally transformed into human substance. In the course of metabolic processes, the inorganic molecule may doff its mineral type and don, in succession, the specificities of plant, animal, and human protoplasm; and this transition from lower to higher degrees of perfection may be termed an evolution. It is an ascent of matter from the lowermost grade of an inert substance, through the intermediate grades of vegetative and animal life, up to the culminating and ultimate term of material perfection, in the partial constitution of a human nature and personality, in the concurrence as a coagent in vegetative and sensile functions, and in the indirect participation, as instrument, in the higher psychic functions of rational thought and volition.
At the present time, the inorganic world is clearly the exclusive source of all the matter found in living beings. All living beings construct their bodies out of inorganic substances in the process of nutrition, and render back to the inorganic world, by dissimilation and death, whatever they have taken from it. We must conclude, therefore, the matter of the primordial organisms was likewise derived from the inorganic world. But we are not warranted in concluding that this process of derivation was an active evolution. On thecontrary, all evidence is against the supposition that brute matter is able to evolve of itself into living matter. It can, indeed, be transformed into plants, animals, and men through the action of an appropriate external agent (i.e.solely through the agency of the living organism), but it cannot acquire the perfections of living matter by means of its own inherent powers. It cannot vitalize, or sensitize, itself through the unaided activity of its own physicochemical energies. Only when it comes under the superior influence of preëxistent life can it ascend to higher degrees of entitive perfection. It does not become of itself life, sensibility, and intelligence. It must first be drawn into communion with what is already alive, before it can acquire life and sensibility, or share indirectly in the honors of intelligence (as the substrate of the cerebral imagery whence the human mind abstracts its conceptual thought). Apart from this unique influence, inorganic matter is impotent to raise itself in the scale of existence, but, if captured, molded, and transmuted by a living being, it may progress to the point of forming with the human soul one single nature, one single substance, one single person. The evolution of matter exemplified in organic metabolism is obviously passive, and such an evolution of the primal organisms out of non-living matter even the opponents of the hypothesis of spontaneous generation concede. But spontaneous generation implies an active evolution of the living from the lifeless, and this is the point around which the controversy wages. It would, of course, be utterly irrational to deny to the Supreme Lord and Author of Life the power of vivifying matter previously inanimate and inert, and hence the origin of organic life from inorganic matter by a formative (not creative) act of the Creator is the conclusion to which the denial of abiogenesis logically leads.
The hypothesis of spontaneous generation is far older than the theory of transformism. It goes back to the Greek predecessors of Aristotle, at least, and may be of far greater antiquity. It was based, as is well known, upon an erroneousinterpretation of natural facts, which was universally accepted up to the close of the 17th century. As we can do no more than recount a few outstanding incidents of its long and interesting history here, the reader is referred to the VII chapter of Wasmann’s “Modern Biology” and the VIII chapter of Windle’s “Vitalism and Scholasticism” for the details which we are obliged to omit.
From time immemorial the sudden appearance of maggots in putrescent meat had been a matter of common knowledge, and the ancients were misled into regarding the phenomenon as an instance of ade novoorigin of life from dead matter. The error in question persisted until the year 1698, when it was decisively disproved by a simple experiment of the Italian physician Francesco Redi. He protected the meat from flies by means of gauze. Under these conditions, no maggots appeared in the meat, while the flies, unable to reach the meat, deposited their eggs on the gauze. Thus it became apparent that the maggots were larval flies, which emerged from fertilized eggs previously deposited in decaying meat by female flies. Antonio Vallisnieri, another Italian, showed that the fruit-fly had a similar life-history. As a result of these discoveries, Redi rejected the theory of spontaneous generation and formulated the first article of the Law of Genetic Vital Continuity:Omne vivum ex vivo.
Meanwhile, the first researches conducted by means of the newly invented compound microscope disclosed what appeared to be fresh evidence in favor of the discarded hypothesis. The unicellular organisms known as infusoria were found to appear suddenly in hay infusions, and their abrupt appearance was ascribed to spontaneous generation. Towards the end of the 18th century, however, a Catholic priest named Lazzaro Spallanzani refuted this new argument by sterilizing the infusions with heat and by sealing the containers as protection against contamination by floating spores or cysts. After theinfusions had been boiled for a sufficient time and then sealed, no organisms could be found in them, no matter how long they were kept. We now know that protozoa and protophytes do not originatede novoin infusions. Their sudden appearance in cultures is due to the deposition of spores or cysts from the air, etc.
The possibility that the non-germination of life in sterilized infusions kept in sealed containers might be due to the absence of oxygen, removed by boiling and excluded by sealing, left open a single loophole, of which the 19th century defenders of abiogenesis proceeded to avail themselves. Pasteur, however, by employing sterilized cultures, which he aerated with filtered air exclusively, succeeded in depriving his opponents of this final refuge, and thereby completely demolished the last piece of evidence in favor of spontaneous generation. Prof. Wm. Sydney Thayer, in an address delivered at the Sorbonne, May 22, 1923, gives the following account of Pasteur’s experiments in this field: “Then, naturally (1860-1876) came the famous studies on spontaneous generation undertaken against the advice of his doubting masters, Biot and Dumas. On the basis of careful and well-conceived experiments he demonstrated the universal presence of bacteria in air, water, dust; he showed the variation in different regions of the bacterial content of the air; he demonstrated the permanent sterility of media protected from contamination, and he insisted on the inevitable derivation of every living organism from one of its kind. ‘No,’ he said, ‘there is no circumstance known today which justifies us in affirming that microscopic organisms have come into the world, without parents like themselves. Those who made this assertion have been the playthings of illusions or ill-made experiments invalidated by errors which they have not been able to appreciate or to avoid.’ In the course of these experiments he demonstrated the necessity of reliable methods of sterilization for instruments or culture media, of exposure for half an hour to moist heat at 120° or to dry air at 180°. And behold! our modernprocedures of sterilization and the basis of antiseptic surgery.” (Science, Dec. 14, 1923, p. 477.) Pasteur brought to a successful completion the work of Redi and Spallanzani. Henceforth spontaneous generation was deprived of all countenance in the realm of biological fact.
Meanwhile, the cytologists and embryologists of the last century were adding article after article to the law of genetic cellular continuity, thus forging link by link the fatal chain of severance that inexorably debars abiogenesis from the domain of natural science. With the formulation of the great Cell Theory by Schleiden and Schwann (1838-1839), it became clear that the cell is the fundamental unit of organization in the world of living matter. It has proved to be, at once, the simplest organism capable of independent existence and the basic unit of structure and function in all the more complex forms of life. The protists (unicellular protozoans and protophytes) consist each of a single cell, and no simpler type of organism is known to science. The cell is the building brick out of which the higher organisms or metists (i.e.the multicellular and tissued metazoans and metaphytes) are constructed, and all multicellular organisms are, at one time or other in their career, reduced to the simplicity of a single cell (v.g.in the zygote and spore stages). The somatic or tissue cells, which are associated in the metists to form one organic whole, are of the same essential type as germ cells and unicellular organisms, although the parallelism is more close between the unicellular organism and the germ cell. The germ cell, like the protist, is equipped with all the potentialities of life, whereas tissue cells are specialized for one function rather than another. The protist is a generalized and physiologically-balanced cell, one which performs all the vital functions, and in which the suppression of one function leads to the destruction of all the rest; while the tissue cell is a specialized and physiologically-unbalanced cell limited to a single function, with the other vital functions in abeyance (though capable of manifesting themselves under certain circumstances). Normally, therefore, the tissue cell is functionally incomplete, a part and not a whole, whereas the protist is an independent individual, being, at once, the highest type of cell and the lowest type of organism.
According to the classic definition of Franz Leydig and Max Schultze, the cell is a mass of protoplasm containing a nucleus, both protoplasm and nucleus arising through division of the corresponding elements of a preëxistent cell. In this form the definition is quite general and applies to all cells, whether tissue cells, germ cells, or unicellular organisms. Moreover, it embodies two principles which still further determine the law of genetic cellular continuity, namely:Omnis cellula ex cellula, enunciated by Virchow in 1855, and Flemming’s principle:Omnis nucleus ex nucleo, proclaimed in 1882. In this way, Cytology supplemented Redi’s formula that every living being is from a preëxistent living being, by adding two more articles, namely, that every living cell is from a preëxistent cell, and every new cellular nucleus is derived by division from a preëxistent cellular nucleus. Now neither the nucleus nor the cell-body (the cytoplasm or extranuclear area of the cell) is capable of an independent existence. The cytoplasm of the severed nerve fibre, when it fails to reëstablish its connection with the neuron nucleus, degenerates. The enucleated amœba, though capable of such vital functions as depend upon destructive metabolism, can do nothing which involves constructive metabolism, and is, therefore, doomed to perish. The sperm cell, which is a nucleus that has sloughed off most of its cytoplasm, disintegrates, unless it regains a haven in the cytoplasm of the egg. Life, accordingly, cannot subsist in a unit more simply organized than the cell. No organism lives which is simpler than the cell, and the origin of all higher forms of life is reducible, as we shall see, to the origin of the cell. Consequently, new life can originate in no other way than by a process of cell-division. All generation or reproduction of new life is dependent upon the division of the cell-body and nucleus of a preëxistent living cell.
Haeckel, it is true, has attempted to question the status of the cell as the simplest of organisms, by alleging the existence of cytodes (non-nucleated cells) among the bacteria and the blue-green algæ. Further study, however, has shown that bacteria and blue-green algæ have a distributed nucleus, like that of certain ciliates, such asDileptus gigasandTrachelocerca. In such forms the entire cell body is filled with scattered granules of chromatin called chromioles, and this diffuse type of nucleus seems to be the counterpart of the concentrated nuclei found in the generality of cells. At any rate, there is a temporary aggregation of the chromioles at critical stages in the life-cycle (such as cell-division), and these scattered chromatin granules undergo division, although their distribution to the daughter-cells is not as regular as that obtaining in mitosis. All this is strongly suggestive of their nuclear nature, and cells with distributed nuclei cannot, therefore, be classified as cytodes. In fact, the polynuclear condition is by no means uncommon.Paramœcium aurelia, for example, has a macronucleus and a micronucleus, and theUroleptus mobilishas eight macronuclei and from two to four micronuclei. The difference between the polynuclear and diffuse condition seems to be relatively unimportant. In fact, the distributed nucleus differs from the morphological nucleus mainly in the absence of a confining membrane. From the functional standpoint, the two structures are identical. Hence the possession of a nucleus or its equivalent is, to all appearances, a universal characteristic of cells. Haeckel’s “cytodes” have proved to be purely imaginary entities. The verdict of modern cytologists is that Shultze’s definition of the cell must stand, and that the status of the cell as the simplest of organic units capable of independent existence is established beyond the possibility of prudent doubt.
With the progressive refinement of microscopic technique, it has become apparent that the law of genetic continuity applies not merely to the cell as a whole and to its major parts, the nucleus and the cell-body, but also to the minor components or organelles, which are seen to be individually self-perpetuating by means of growth and division. The typical cell nucleus, as is well known, is a spherical vesicle containing a semisolid, diphasic network of basichromatin (formerly “chromatin”) and oxychromatin (linin) suspended in more fluid medium or ground called nuclear sap. When the cell is about to divide, the basichromatin resolves itself into a definite number of short threads called chromosomes. Now, Boveri found that, in the normal process of cell-division known as mitosis, these nuclear threads or chromosomes are each split lengthwise and divided into two exactly equivalent halves, the resulting halves being distributed in equal number to the two daughter-cells produced by the division of the original cell. Hence, in the year 1903, Boveri added a fourth article to the law of genetic vital continuity, namely:Omne chromosoma ex chromosomate.
But the law in question applies to cytoplasmic as well as nuclear components. In physical appearance, the cell-body or cytoplasm resembles an emulsion with a clear semiliquid external phase called hyaloplasm and an internal phase consisting mainly of large spheres called macrosomes and minute particles called microsomes, all of which, together with numerous other formed bodies, are suspended in the clear hyaloplasm (hyaline ground-substance). Now certain of these cytoplasmic components have long been known to beself-perpetuatingby means of growth and division, maintaining their continuity from cell to cell. The plastids of plant cells, for example, divide at the time of cell-division, although their distribution to the daughter-cells does not appear to be as definite and regular as that which obtains in the case of the chromosomes. Similarly, the centrioles or division-foci of animal cells are self-propagating by division, but here the distribution to the daughter-cells is exactly equivalent and not at random as in the case of plastids. In the light of recent research it looks as though two other types of cytoplasmic organelles must be added to the list of cellularcomponents, which are individually self-perpetuating by growth and division, namely, the chondriosomes and the Golgi bodies—“both mitochondria and Golgi bodies are able to assimilate, grow, and divide in the cytoplasm.” (Gatenby.) Wilson is of opinion that the law of genetic continuity may have to be extended even to those minute granules and particles of the cytosome, which were formerly thought to arisede novoin the apparently structureless hyaloplasm. Speaking of the emulsified appearance of the starfish and sea urchin eggs, he tells us that their protoplasm shows “a structure somewhat like that of an emulsion, consisting of innumerable spheroidal bodies suspended in a clear continuous basis or hyaloplasm. These bodies are of two general orders of magnitude, namely: larger spheres or macrosomes rather closely crowded and fairly uniform in size, and much smaller microsomes irregularly scattered between the macrosomes, and among these are still smaller granules that graduate in size down to the limit of vision with any power (i.e.of microscope) we may employ.” (Science, March 9, 1923, p. 282.) Now, the limit of microscopic vision by the use of the highest-power oil-immersion objectives is one-half the length of the shortest waves of visible light, that is, about 200 submicrons (the submicron being one millionth of a millimeter). Particles whose diameter is less than this cannot reflect a wave of light, and are, therefore, invisible so far as the microscope is concerned. By the aid of the ultramicroscope, however, we are enabled to see the halos formed by particles not more than four submicrons in diameter, which, however, represents the limit of the ultramicroscope, and is the diameter hypothetically assigned to the protein multimolecule. Since, therefore, we find the particles in the protoplasm of the cell body graduating all the way down to the limit of this latter instrument, and since on the very limit of microscopic vision we find such minute particles as the centrioles “capable of self-perpetuation by growth and division, and of enlargement to form much larger bodies,” we cannot ignore the possibilitythat the ultramicroscopic particles may have the same powers and may be the sources or “formative foci” of the larger formed bodies, which were hitherto thought to arisede novo.
Certainly, pathology, as we shall see, tells us of ultramicroscopic disease-germs, which are capable of reproduction and maintenance of a specific type, and experimental genetics makes us aware of a linear alignment of submicroscopic genes in the nuclear chromosomes, each gene undergoing periodic division and perpetual transmission from generation to generation. The cytologist, therefore, to quote the words of Wilson, “cannot resist the evidence that the appearance of a simple homogeneous colloidal substance is deceptive; that it is in reality a complex, heterogeneous, or polyphasic system. He finds it difficult to escape the conclusion, therefore, that the visible and the invisible components of the protoplasmic system differ only in their size and degree of dispersion; that they belong to a single continuous series, and that the visible structure of protoplasm may give us a rough magnified picture of the invisible.” (Ibidem, p. 283.)
It would seem, therefore, that we must restore to honor, as the fifth article of the law of cellular continuity, the formula, which Richard Altmann enunciated on purely speculative grounds in 1892, but which the latest research is beginning to place on a solid factual basis, namely:Omne granulum ex granulo. “For my part,” says the great cytologist, Wilson, “I am disposed to accept the probability that many of these particles, as if they were submicroscopical plastids, may have a persistent identity, perpetuating themselves by growth and multiplication without loss of their specific individual type.” And he adds that the facts revealed by experimental embryology (e.g., the existence of differentiated zones of specific composition in the cytoplasm of certain eggs) “drive us to the conclusion that the submicroscopical components of the hyaloplasm are segregated and distributed according to an ordered system.” (Ibidem, p. 283.) The structure of the cell has often been likened to a heterogeneous solution,that is, to a complex polyphasic colloidal system, but this power of perpetual division and orderly assortment possessed by the cell as a whole and by its single components is the unique property of the living protoplasmic system, and is never found in any of the colloidal systems known to physical chemistry, be they organic or inorganic.
Cells, then, originate solely by division of preëxistent cells and even the minor components of the cellular system originate in like fashion, namely: by division of their respective counterparts in the preëxistent living cell. Here we have the sum and substance of the fivefold law of genetic continuity, whose promulgation has relegated the hypothesis of spontaneous generation to the realms of empty speculation. Waiving the possibility of ana prioriargument, by which abiogenesis might be positively excluded, there remains this one consideration, which alone is scientifically significant, that, so far as observation goes and induction can carry us, the living cell has absolute need of a vital origin and can never originate by the exclusive agency of the physicochemical forces native to inorganic matter. If organic life exists in simpler terms than the cell, science knows nothing of it, and no observed process, simple or complicated, of inorganic nature, nor any artificial synthesis of the laboratory, however ingenious, has ever succeeded in duplicating the wonders of the simplest living cell.
In fact, the very notion of a chemical synthesis of living matter is founded on a misconception. It would, indeed, be rash to set limits to the chemist’s power of synthesizing organic compounds, but living protoplasm is not a single chemical compound. Rather it is a complex system of compounds, enzymes and organelles, coördinated and integrated into an organized whole by a persistent principle of unity and finality. Organic life, to say nothing at all of its unique dynamics, is a morphological as well as a chemical problem;and, while it is conceivable that the chemist might synthesize all the compounds found in dead protoplasm, to reproduce a single detail of the ultramicroscopic structure of a living cell lies wholly beyond his power and province. “Long ago,” says Wilson (in the already quoted address on the “Physical Basis of Life”), “it became perfectly plain that what we call protoplasm is not chemically a single substance. It is a mixture of many substances, a mixture in high degree complex, the seat of varied and incessant transformations, yet one which somehow holds fast for countless generations to its own specific type. The evidence from every source demonstrates that the cell is a complex organism, a microcosm, a living system.” (Science, March 9, 1923, p. 278.)
With the chemist, analysis must precede synthesis, and it is only after a structural formula has been determined by means of quantitative analysis supplemented by analogy and comparison, that a given compound can be successfully synthesized. But living protoplasm and its structures elude such analysis. Intravitous staining is inadequate even as a means of qualitative analysis, and tests of a more drastic nature destroy the life and organization, which they seek to analyze. “With one span,” says Amé Pictet, Professor of Chemistry at the University of Geneva, “we will now bridge the entire distance separating the first products of plant assimilation from its final product, namely, living matter. And it should be understood at the outset that I employ this term ‘living matter’ only as an abbreviation, and to avoid long circumlocution. You should not, in reality, attribute life to matter itself; it has not, it cannot have both living molecules and dead molecules. Life requires an organization, which is that of cellular structure, but it remains, in contradistinction to it, outside the domain of strict chemistry. It is none the less true that the content of a living cell must differ in its chemical nature from the content of a dead cell. It is entirely from this point of view that the phenomenon of life pertains to my subject.... A livingcell, both in its chemical composition and in its morphological structure, is an organism of extraordinary complexity. The protoplasm that it incloses is a mixture of very diverse substances. But if there be set aside on the one hand those substances which are in the process of assimilation and on the other those which are the by-products of nutrition, and which are in the process of elimination, there remain the protein or albuminous substances, and these must be considered, if not the essential factor of life, at least the theater of its manifestations.... Chemistry, however, is totally ignorant, or nearly so, of the constitution of living albumen, for chemical methods of investigation at the very outset kill the living cell. The slightest rise in temperature, contact with the solvent, the very powerful effect of even the mildest reactions cause the transformation that needs to be prevented, and the chemist has nothing left but dead albumen.” (Smithson. Inst. Rpt. for 1916, pp. 208, 209.)
Chemical analysis associated with physical analysis by means of the polariscope, spectroscope, x-rays, ultramicroscope, etc. is extremely useful in determining the structure of inorganic units like the atom and the molecule. Both, too, throw valuable light on the problem of the structure of non-living multimolecules such as the crystal units of crystalloids and the ultramicrons of colloids, but they furnish no clue to the submicroscopical morphology of the living cell. Such methods do not enable us to examine anything more than the “physical substrate” of life, and that, only after it has been radically altered; for it is not the same after life has flown. At all events, the integrating principle, the formative determinant, which binds the components of living protoplasm into a unitary system, which makes of them a single totality instead of a mere sum or fortuitous aggregate of disparate and uncoördinated factors, and which gives to them a determinate and persistent specificity that can hold its own amid a perpetual fluxion of matter and continual flow of energy, this is forever inaccessible to the chemist, and constitutes a phenomenon of which the inorganic world affords no parallel.
With these facts in mind, we can hardly fail to be amused whenever certain simple chemical reactions obtainedin vitroare hailed as “clue to the origin of life.” When it was found, for instance, that, under certain conditions, an aldehyde (probably formaldehyde) is formed in a colloidal solution of chlorophyll in water, if exposed to sunlight, the discovery gave rise to Bach’s formaldehyde-hypothesis; for Alexis Bach saw in this reaction “a first step in the origin of life.” As formaldehyde readily undergoes aldol condensation into a syrupy fluid called formose, when a dilute aqueous solution of formaldehyde is saturated with calcium hydroxide and allowed to stand for several days, there was no difficulty in conceiving the transition from formaldehyde to the carbohydrates; for formose is a mixture containing several hexose sugars, and Fischer has succeeded in isolating therefrom acrose, a simple sugar having the same formula as glucose, namely: C6H12O6. Glyceraldehyde undergoes a similar condensation. In view of these facts, carbohydrate-production in green plants was interpreted as a photosynthesis of these substances from water and carbon dioxide, with chlorophyll acting a sensitizer to absorb the radiant energy necessary for the reaction. The first step in the process was thought to be a reduction of carbonic acid to formic acid and then to formaldehyde, the latter being at once condensed into glucose, which in turn was supposed to be dehydrated and polymerized into starch. From the carbohydrates thus formed and the nitrates of the soil the plant could then synthesize proteins, while oxidation of the carbohydrates into fatty acids would lead to the formation of fats. Hence Bach regarded the formation of formaldehyde in the presence of water, carbon dioxide, chlorophyll, and sunlight as the “first step in the production of life.” Bateson, however, does not find the suggestion a very helpful one, and evaluates it at its true worth in the following contemptuous aside: “We should be greatly helped,” he says,“by some indication as to whether the origin of life has been single or multiple.” Modern opinion is, perhaps, inclined to the multiple theory, but we have no real evidence. Indeed, the problem still stands outside the range of scientific investigation, and when we hear the spontaneous formation of formaldehyde mentioned as a possible first step in the origin of life, we think of Harry Lauder in the character of a Glasgow schoolboy pulling out his treasures from his pocket—“That’s a wassher—for makkin’ motor cars.” (“Presidential Address,” cf. Smithson. Inst. Rpt. for 1915, p. 375.)
Bach, moreover, takes it for granted that the formation of formaldehyde is really the first step in the synthesis performed by the green plant, and he claims that formaldehyde is formed when carbon dioxide is passed through a solution of a salt of uranium in the presence of sunlight. Fenton makes a similar claim in the case of magnesium, asserting that traces of formaldehyde are discernible when metallic magnesium is immersed in water saturated with carbon dioxide. But at present it begins to look as though the spontaneous formation and condensation of formaldehyde had nothing to do with the process that actually occurs in green plants. Certain chemists, while admitting that an aldehyde is formed when chlorophyll, water, and air are brought together in the presence of sunlight, deny that the aldehyde in question is formaldehyde, and they also draw attention to the fact that this aldehyde may be formed in an atmosphere entirely destitute of carbon dioxide. In fact, the researches conducted by Willstätter and Stoll, and later (in 1916) by Jörgensen and Kidd tend to discredit the common notion that carbohydrate-production in plants is the result of a direct union of water and carbon dioxide. Botany textbooks still continue to parrot the traditional view. We cannot any longer, however, be sure but that the term photosynthesis may be a misnomer.
Carbohydrate-formation in plants seems to be more analogous to carbohydrate-formation in animals than was formerly thought to be the case. In animals, as is well known, glycogen or animal starch is formed not by direct synthesis, but by deämination and reduction of proteins. In a similar way, it is thought that the production of carbohydrates in plants may be due to a breaking down of the phytyl ester in chlorophyll, the chromogen group functioning (under the action of light) alternately as a dissociating enzyme in the formation of sugars and a synthesizing enzyme in the reconstruction of chlorophyll. Phytol is an unsaturated alcohol obtained when chlorophyll is saponified by means of caustic alkalis. Its formula is C20H39OH, and chlorophyll consists of a chromogen group containing magnesium (MgN4C32H30O) united to a diester of phytyl and methyl alcohols.
Experimental results are at variance with the theory that chlorophyll acts as a sensitizer in bringing about a reduction of carbonic acid, after the analogy of eosin, which in the presence of light accelerates the decomposition of silver salts on photographic plates. Willstätter found that, when a colloidal solution of the pure extract of chlorophyll in water is exposed to sunlight and an atmosphere consisting of carbon dioxide exclusively, no formaldehyde is formed, but the chlorophyll is changed into yellow phæophytin owing to the removal of the magnesium from the chromogen group by the action of the carbonic acid. Jörgensen, on the other hand, discovered that in an atmosphere of pure oxygen, formaldehyde is formed, apparently by the splitting off and reduction of the phytyl ester of chlorophyll. Soon, however, the formaldehyde is oxidized to formic acid, which replaces the chlorophyllic magnesium with hydrogen, thus causing the green chlorophyll to degenerate into yellow phæophytin and finally to lose its color altogether. The dissociation of the chromogen group may be due to the fact that the reaction takes placein vitro, and may not occur in the living plant. At all events, it would seem that plants, like animals, manufacture carbohydrates by a destructive rather than a constructive process, and that water and carbon dioxide serverather as materials for the regeneration of chlorophyll than as materials out of which sugars are directly synthesized.
A new theory has been proposed by Dr. Oskar Baudisch, who seems to have sensed the irrelevance of the formaldehyde hypothesis, and to have sought another solution in connection with the chromogen group of chlorophyll. He finds a more promising starting-point in formaldoxime, which, he claims, readily unites with such metals as magnesium and iron and with formaldehyde, in the presence of light containing ultra-violet rays, to form organic compounds analogous to the chromogen complexes in chlorophyll and hæmoglobin. Oximes are compounds formed by the condensation of one molecule of an aldehyde with one molecule of hydroxylamine (NH2OH) and the elimination of a molecule of water. Hence Dr. Baudisch imagines that, given formaldoxime (H2C:N·OH), magnesium, and ultra-violet rays, we might expect a spontaneous formation of chlorophyll leading eventually to the production of organic life. “It is his theory that life may have been caused through the direct action of sunlight upon water, air, and carbon dioxide in the ancient geologic past when, he believes, sunlight was more intense and contained more ultra-violet light and the air contained more water vapor and carbon dioxide than at the present time.” (Science, April 6, 1923, Supplement XII.)
This is the old Spencerian evasion, the fatuous appeal to “conditions unlike those we know,” the unverified and unverifiable assumption that an unknown past must have been more favorable to spontaneous generation than the known present. In archæozoic times, the temperature was higher, the partial pressure of atmospheric carbon dioxide greater, the percentage of ultra-violet rays in sunlight larger. Such contentions are interesting, if true, but, for all that, they may, “like the flowers that bloom in the spring,” have nothing to do with the case. Nature does not, and the laboratory cannot, reproduce the conditions which are said to have brought about the spontaneous generation of formaldoxime and its progressive transmutation into phycocyanin, chlorophyll and the blue-green algæ. What value, then, have these conjectures? If it be the function of natural science to discount actualities in favor of possibilities, to draw arguments from ignorance, and to accept the absence of disproof as a substitute for demonstration, then the expedient of invoking the unknown in support of a speculation is scientifically legitimate. But, if the methods of science are observation and induction, if it proceeds according to the principle of the uniformity of nature, and does not utterly belie its claim of resting upon factual realities rather than the figments of fancy, then all this hypothecation, which is so flagrantly at variance with the actual data of experience and the unmistakable trend of inductive reasoning, is not science at all, but sheer credulity and superstition.
When we ask by what right men of science presume to lift the veil of mystery from a remote past, which no one has observed, we are told that the justification of this procedure is the principle of the uniformity of nature or the invariability of natural laws. Nature’s laws are the same yesterday, today, and forever. Hence the scientist, who wishes to penetrate into the unknown past, has only to “prolong the methods of nature from the present into the past.” (Tyndall.) If we reject the soundness of this principle, we automatically cut ourselves off from all certainty regarding that part of the world’s history which antecedes human observation. Either nature’s laws change, or they do not. If they never change, then Spontaneous Generation is quite as much excluded from the past as it is from the present. If, however, as Hamann and Fechner explicitly maintain, nature’s laws do change, then, obviously, no knowledge whatever is possible respecting the past, since it is solely upon the assumption of the immutable constancy of such laws that we can venture to reconstruct prehistory.
The puerile notion that the synthesis of organic substances in the laboratory furnishes a clue to the origin of organiclife on earth is due to a confusion of organic, with living and organized, substances. It is only in the production of organic substances that the chemist can vie with the plant or animal. These are lifeless and unorganized carbon compounds, which are termed organic because they are elaborated by living organisms as a metaplastic by-product of their metabolism. Such substances, however, are not to be confounded with animate matter,e.g.a living cell and its organelles, or even with organized matter,e.g.dead protoplasm. These the chemist cannot duplicate; for vitality and organization, as we have seen, are things that elude both his analysis and his synthesis. Even with respect to the production of organic substances, the parallelism between the living cell and the chemical laboratory is far from being a perfect one. Speaking of the metaplastic or organic products of cells, Benjamin Moore says: “Most of these are so complex that they have not yet been synthesized by the organic chemist; nay, even of those that have been synthesized, it may be remarked that all proof is wanting that the syntheses have been carried out in identically the same fashion and by the employment of the same forms of energy in the case of the cell as in the chemist’s laboratory. The conditions in the cell are widely different, and at the temperature of the cell and with such chemical materials as are at hand in the cell no such organic syntheses have been artificially carried out by the forms of energy extraneous to living tissue.” (“Recent Advances in Physiology and Bio-Chemistry,” p. 10.) Be that as it may, however, the prospect of a laboratory synthesis of an organic substance like chlorophyll affords no ground whatever for expecting a chemical synthesis of living matter. The chlorophyllic tail is inadequate to the task of wagging the dog of organic life. In this connection, Yves Delage’s sarcastic comment on Schaaffhausen’s theory is worthy of recall. The latter had suggested (in 1892) that life was initiated by a chemical reaction, in which water, air, and mineral salts united under the influence of light and heatto produce a colorlessProtococcus, which subsequently acquired chlorophyll and became aProtococcus viridis. “If the affair is so simple,” writes Delage, “why does not the author produce a few specimens of thisprotococcusin his laboratory? We will gladly supply him with the necessary chlorophyll.” (“La structure du protoplasma et les théories sur l’hérédité,” p. 402.)
Another consideration, which never appears to trouble the visionaries who propound theories of this sort, is the fact that the inert elements and blind forces of inorganic nature are, if left to themselves, utterly impotent to duplicate even so much as the feats of the chemical laboratory, to say nothing at all of the more wonderful achievements possible only to living organisms. In the laboratory, the physicochemical forces of the mineral world are coördinated, regulated, and directed by the guiding intelligence of the chemist. In that heterogeneous conglomerate, which we call brute matter, no such guiding principle exists, and the only possible automatic results are those which the fortuitous concurrence of blind factors avails to produce. Chance of this kind may vie with art in the production of relatively simple combinations or systems, but where the conditions are as complex as those, which the synthesis of chlorophyll presupposes, chance is impotent and regulation absolutely imperative. How much more is this true, when there is question of the production of an effect so complicatedly telic as the living organism! “I venture to think,” says Sir William Tilden, in a letter to the LondonTimes(Sept. 10, 1912), “that no chemist will be prepared to suggest a process by which, from the interaction of such materials (viz., inorganic substances), anything approaching a substance of the nature of a proteid could be formed or, if by a complex series of changes a compound of this kind were conceivably produced, that it would present the characters of living protoplasm.” In the concluding sentence of his letter, the great chemist seems to deprecate even the discussion of a chemical synthesis of living matter, whetherspontaneous or artificial. “Far be it from any man of science,” he says, “to affirm that any given set of phenomena is not a fit subject of inquiry and that there is any limit to what may be revealed in answer to systematic and well-directed investigation. In the present instance, however, it appears to me that this is not a field for the chemist nor one in which chemistry is likely to afford any assistance whatever.” In any case, the idea that a chaos of unassorted elements and undirected forces could succeed where the skill of the chemist fails is preposterous. No known or conceivable process, or group of processes, at work in inorganic nature, is equal to the task. Chance is an explanation only for minds insensible to the beauty and order of organic life.
Darwin inoculated biological science with this Epicurean metaphysics, when, in his “Origin of Species,” he ascribed discriminating and selective powers of great delicacy and precision to the blind factors of a heterogeneous and variable environment. He compared natural selection to artificial selection, and in so doing, he was led astray by a false implication of his own analogy—“I have called this principle,” he says, “by which each slight variation, if useful, is preserved, by the term natural selection, in order to mark its relation to man’s power of selection.” (“Origin of Species,” 6th ed., c. III, p. 58.) Having likened the unintelligent and fortuitous selection and elimination exercised by the environment to the intelligent and purposive selection and elimination practiced by animal breeders and horticulturists, he pressed the analogy to the unwarranted extent of attributing to a blind, lifeless, and impersonal aggregate of minerals, liquids, and gases superhuman powers of discretion. To preserve even the semblance of parity, he ought first to have expurgated the process of artificial selection by getting rid of the element of human intelligence, which lurks therein, and vitiates its parallelism with the unconscious and purposeless havoc wrought at random by the blind and uncoördinated agencies of the environment. If inorganic nature were a vastand multifarious mold, a preformed sieve with holes of different sizes, a separator for sorting coins of various denominations, Darwin’s idea would be, in some degree, defensible, but this would only transfer the problem of cosmic order and intelligence from the organism to the environment. As a matter of fact, the mechanism of the environment is far toosimplein its structure and toogeneralin its influence to account for the complexities and specificities of organisms, that is, for the morphology and specific differences of plants and animals. Hence the selective work of the environment is negligible in the positive sense, and consists, for the most part, in a tendency to eliminate the abnormal and the subnormal. On the other hand, the environment as well as the organism is fundamentally teleological, and the environmental mechanism, though simple and general, is nevertheless expressly preadapted for the maintenance of organic life. Henderson, the bio-chemist of Harvard, has shown conclusively, in his “Fitness of the Environment” (1913), that the environment itself has been expressly selected with this finality in view, and that the inorganic world, while not the active cause, is, nevertheless, the preördained complement of organic life.
Simple constructions may, indeed, be due to pure accident as well as deliberate art, inasmuch as they presuppose but few and easy conditions. Complex constructions, on the contrary, provided they be systematic and not chaotic, are not producible by accident, but only by art, because they require numerous and complicated conditions. Operating individually, the unconscious factors of inorganic nature can produce simple and homogeneous constructions such as crystals. Operating in uncoördinated concurrence with one another, these blind and unrelated agencies produce complex chaotic formations such as mountains and islands, mere heterogeneous conglomerates, destitute of any determinate size, shape, or symmetry, constructions in which every single item and detail is the result of factors each of which is independent of theother. In short, the efficacy of the unconscious and uncoordinated physicochemical factors of inorganic nature is limited to fortuitous results, which serve no purpose, embody no intelligible law, convey no meaning nor idea, and afford no æsthetic satisfaction, being mere aggregates or sums rather than natural units and real totalities. But it does not extend to the production of complex systematic formations such as living organisms or human artefacts. Left to itself, therefore, inorganic nature might conceivably duplicate the simplest artefacts such as the chipped flints of the savage, and it might also construct a complex heterogeneous chaos of driftwood, mud, and sand like the Great Raft of the Red River, but it would be utterly impotent to construct a complicated telic system comparable to an animal, a clock, or even an organic compound, like chlorophyll.
In this connection, it is curious to note how extremely myopic the scientific materialist can be, when there is question of recognizing a manifestation of Divine intelligence in the stupendous teleology of the living organism, and how incredibly lynx-eyed he becomes, when there is question of detecting evidences of human intelligence in the eoliths alleged to have been the implements of a “Tertiary Man.” In the latter case, he is never at a loss to determine the precise degree of chipping, at which an eolith ceases to be interpretable as the fortuitous product of unconscious processes, and points infallibly to the intelligent authorship of man, but he grows strangely obtuse to the psychic implications of teleology, when it comes to explaining the symmetry of a starfish or the beauty of a Bird of Paradise.
In conclusion, it is clear that the hypothesis of a spontaneous origin of organic life from inorganic matter has in its favor neither factual evidence nor aprioristic probability, but is, on the contrary, ruled out of court by the whole force of the scientific principle of induction. To recapitulate, there are no subcellular organisms, and all cellular organisms (which is the same as saying, all organisms), be they unicellular ormulticellular, originate exclusively by reproduction, that is, by generation from living parents of the same organic type or species. This is the law of genetic vital continuity, which, by the way, Aristotle had formulated long before Harvey, when he said: “It appears that all living beings come from a germ, and the germ from parents.” (“De Generatione Animalium,” lib. I, cap. 17.) All reproduction, however, is reducible to a process of cell-division. That such is the case with unicellular organisms is evident from the very definition of a cell. That it is also true of multicellular organisms can be shown by a review of the various forms of reproduction occurring among plants and animals.
Reproduction, the sole means by which the torch of life is relayed from generation to generation, the exclusive process by which living individuals arise and races are perpetuated, consists in the separation of a germ from the parent organism as a physical basis for the development of a new organism. The germ thus separated may be many-celled or one-celled, as we shall see presently, but the separated cells, be they one or many, have their common and exclusive source in the process of mitotic cell-division. In a few cases, this divisional power or energy of the cell seems to be perennial by virtue of an inherent inexhaustibility. In most cases, however, it is perennial by virtue of a restorative process involving nuclear reorganization. In the former cases, which are exceptional, the cellular stream of life appears to flow onward forever with steady current, but as a general rule it ebbs and flows in cycles, which involve a periodic rise and fall of divisional energy. The phenomena of the life-cycle are characteristic of most, perhaps all, organisms. The complete life-cycle consists of three phases or periods, namely: an adolescent period of high vitality, a mature period of balanced metabolism, and a senescent period of decline. Each life-cycle begins with the germination of the new organismand terminates with its death, and it is reproduction which constitutes the connecting link between one life-cycle and another.
Reproduction, as previously intimated, is mainly of two kinds, namely: somatogenic reproduction, which is less general and confined to the metists, and cytogenic reproduction, which is common to metists and protists, and which is the ordinary method by which new organisms originate. Reproduction is termed somatogenic, when the germ separated from the body of the parent consists of a whole mass of somatic or tissue cells not expressly set aside and specialized for reproductive purposes. Reproduction is termed cytogenic, when the germ separated from the parent or parents consists of a single cell (e.g.a spore, gamete, or zygote) dedicated especially to reproductive purposes.
Cytogenic reproduction may be either nonsexual (agamic) or sexual, according as the cell which constitutes the germ is an agamete or a gamete. An agamete is a germ cell not specialized for union with another complementary cell, or, in other words, it is a reproductive cell incapable of syngamy,e.g.a spore. A gamete, on the other hand, is a reproductive cell (germ cell) specialized for the production of a zygote (a synthetic or diploid germ cell) by union with a complementary cell,e.g.an egg, or a sperm.
Nonsexual cytogenic reproduction is of three kinds, according to the nature of the agamete. When a unicellular organism gives rise to two new individuals by simple cell-division, we have fissiparation or binary fission. When a small cell or bud is formed and separated by division from a larger parent cell, we have budding (gemmation) or unequal fission. When the nucleus of the parent cell divides many times to form a number of daughter-nuclei, which then partition the cytoplasm of the parent cell among themselves so as to form a large number of reproductive cells called spores, we have what is known as sporulation or multiple fission. The first and second kind of nonsexualreproduction are confined to the protists, but the third kind (sporulation) also occurs among the metists.
Sexual cytogenic reproduction is based upon gametes or mating germ cells. Since complementary gametes are specialized for union with each other to form a single synthetic cell, the zygote, the number of their nuclear threads or chromosomes is reduced to one half (thehaploid number) at the time of maturation, so that the somatic or tissue cells of the parent organism have double the number (thediploid number) of chromosomes present in the reduced or mature gametes. Hence, when the gametes unite to form a zygote, summation is prevented and the diploid number of chromosomes characteristic of the given species of plant or animal is simply restored by the process of syngamy or union. The process by which the number of chromosomes is reduced in gametes is calledmeiosis, and, among the metists, it is distinct from syngamy, which, in their case, is a separate process called fertilization. Among the protists, we have, besides fertilization, another type of syngamy called conjugation, which combines meiosis with fertilization.
In sexual reproduction, we have three kinds of gametes, namely: isogametes, anisogametes, and heterogametes. In the type of sexual reproduction known as isogamy, the complementary gametes are exactly alike both in size and shape. There is no division of labor between them. Each of the fusing gametes is equally fitted for the double function which they must perform, namely, the kinetic function, which enables them to reach each other and unite by means of movement, and the trophic function which consists in laying up a store of food for the sustenance of the developing embryo. In anisogamy, the complementary gametes are alike in shape, but unlike in size, and here we have the beginning of that division of labor, upon which the difference of gender or sex is based. The larger or female gamete is called a macrogamete. It is specialized for the trophic rather than the kinetic function, being rendered more inert by having a largeamount of yolk or nutrient material stored up within it. The smaller or male gamete is called a microgamete. It is specialized for the kinetic function, since it contains less yolk and is the more agile of the two. In anisogamy, however, the division of labor is not complete, because both functions are still retained by either gamete, albeit in differing measure. In the heterogamy, the differentiation between the male and female gametes is complete, and they differ from each other in structure as well as size. The larger or female gamete has no motor apparatus and retains only the trophic function. The kinetic function is sacrificed to the task of storing up a food supply for the embryo. Such a gamete is called a hypergamete or egg. The smaller or male gamete is known, in this case, as a hypogamete or sperm. It has a motor apparatus, but no stored-up nutrients, and has even sloughed off most of its cytoplasm, in its exclusive specialization for the motor function. In heterogamy, accordingly, the division of labor is complete.
We may distinguish two principal kinds of sexual reproduction, namely: unisexual reproduction and bisexual reproduction. When a single gamete such as an unfertilized egg gives rise (with, or without, chromosomal reduction) to a new organism, we have unisexual reproduction or parthenogenesis. Parthenogenesis from a reduced egg gives rise to an organism having only the haploid number of chromosomes, as is the case with the drone or male bee, but unreduced eggs give rise to organisms having the diploid number of chromosomes. Parthenogenesis, as we shall see presently, can, in some cases, be induced by artificial means. When reproduction takes place from a zygote or diploid germ cell formed by the union of two gametes, we have what is known as bisexual reproduction or syngamy. It is, perhaps, permissible to distinguish a third or intermediate kind of sexual reproduction, for which we might coin the term autosexual. What we refer to as autosexual reproduction is usually known as autogamy, and occurs when a diploid nucleus is formed in a germcell by the union (or, we might say, reunion) of two daughter-nuclei derived from the same mother-nucleus. Autogamy occurs not only among the protists (e. g.Amœba albida), but also among the metists, as is the case with the brine shrimp,Artemia salina, in which the diploid number of chromosomes is restored after reduction by a reunion of the nucleus of the second polar body with the reduced nucleus of the egg. Autogamy is somewhat akin to kleistogamy, which occurs among hermaphroditic metists of both the plant and animal kingdoms. The violet is a well-known example. In kleistogamy or self-fertilization, the zygote is formed by the union of two gametes derived from the same parent organism. Strictly speaking, however, kleistogamy is not autogamy, but syngamy, and must, therefore, be classed as bisexual reproduction. It is, of course, necessarily confined to hermaphrodites.
Loeb’s experiments in artificial parthenogenesis have been sensationally misinterpreted by some as an artificial production of life. What Jacques Loeb really did was to initiate development in an unfertilized egg by the use of chemical and physical excitants. The writer has repeated these experiments with the unfertilized eggs of the common sea urchin,Arbacia punctulata, using very dilute butyric acid and hypertonic sea water as stimulants. Cleavage had started within an hour and a half after the completion of the aforesaid treatment, and the eggs were in the gastrula stage by the following morning (9 hours later). In three days, good specimens of the larval stage known as the pluteus could be found swimming in the normal sea water to which the eggs had been transferred from the hypertonic solution. Since mature sea urchin eggs undergo reduction before insemination takes place, the larval sea urchins arising from these artificially activated eggs had the reduced or haploid number of chromosomes instead of the diploid number possessed by normal larvæ arising from eggs activated by the sperm. For, in fertilization, the sperm not only activates the egg, but is also the means of securing biparental inheritance, by contributing its quota of chromosomes to the zygotic complex. Hence, it is only in the former function,i. e.of initiating cleavage in the egg, that a chemical excitant can replace the sperm. In any case, it is evident that these experiments do not constitute an exception to the law of genetic cellular continuity. The artificially activated egg comes from the ovaries of a living female sea urchin, and in this there is small consolation for the exponent of abiogenesis. The terse comment of an old Irish Jesuit sizes up the situation very aptly: “The Blue Flame Factory,” he said, “has announced another discovery of the secret of life. A scientist made an egg and hatched an egg. The only unfortunate thing was that the egg he hatched was not the egg he made.” How an experiment of this sort could be interpreted as an artificial production of life is a mystery. The only plausible explanation is that given by Professor Wilson, who traces it to the popular superstition that the egg is a lifeless substrate, which is animated by the sperm. The idea owes its origin to the spermists of the 17th century, who defended this doctrine against the older school of preformationists known as ovists. It is now, however, an embryological commonplace that egg and sperm are both equally cellular, equally protoplasmic, and equally vital.
The phenomena of the life-cycle in organisms find their explanation in what, perhaps, is inherent in all living matter, namely, a tendency to involution and senescence. This tendency, in the absence of a remedial process of rejuvenation, leads inevitably to death. Living matter seems to “run down” like a clock, and to stand in similar need of a periodic “rewinding.” This reinvigoration of protoplasm is accomplished by means of several different types of nuclear reorganization. Since no nuclear reorganization occurs in somatogenic reproduction, there seem to be limits to this type of propagation. Plants, like the potato and the apple, cannot be propagated indefinitely by means of tubers, shoots, stems, etc. The stock plays out in time, and, ever and anon, recourse mustbe had to seedlings. Hence a process of nuclear reorganization seems, in most cases, at least, to be essential for the restoration of vitality and the continuance of life. Whether this need of periodic renewal is absolutely universal, we cannot say. The banana has been propagated for over a century by the somatogenic method, and there are a few other instances in which there appears to be no limit to this type of reproduction. Nevertheless, the tendency to decline is so common among living beings that the rare exceptions serve only to confirm (if they do not follow) the general rule.
In cytogenic reproduction three kinds of rejuvenation by means of nuclear reorganization are known: (1) amphimixis or syngamy; (2) automixis or autogamy; (3) endomixis. In amphimixis or syngamy, two gametic (haploid) nuclei of different parental lineage are commingled to form the diploid nucleus of the zygote, which is consequently of biparental origin. In automixis or autogamy, two reduced or haploid nuclei of the same parental lineage unite to form a diploid nucleus, the uniting nuclei being daughter-nuclei derived from a common parent nucleus. In endomixis, the nucleus of the exhausted cell disintegrates and fuses with the cytoplasm, out of which it is reformed or reconstructed as the germinal nucleus of a rejuvenated cellular series. Endomixis occurs as a periodic phenomenon among the protists, and it appears to be homologous with parthenogenesis among metists. In certain ciliates, like the Paramœcium, endomixis and syngamy are facultative methods of rejuvenation. This has been proved most conclusively by Professor Calkins’ work onUroleptus mobilis, an organism in which both endomixis and conjugation are amenable to experimental control. Nonsexual reproduction in this protozoan (by binary fission) is attended with a gradual weakening of metabolic activity, which increases with each successive generation. The initial rate of division and metabolic energy can, however, be restored either by conjugation (of two individuals), or by endomixis, which takes place (in a single individual) during encystment. The race, however, inevitably dies out, if both encystment and conjugation are prevented. Even in such protists as do not exhibit the phenomenon of nuclear reorganization through sexual reproduction, Kofoid points to the phenomenon of alternating periods of rest and rapid cell-division as evidence that some process of periodically-recurrent nuclear organization must exist in the organisms, which do not conjugate. This process of nuclear reorganization manifested by periodic spurts of renewed divisional energy is, according to Kofoid, a more primitive mode of rejuvenation than endomixis. “The phenomenon of endomixis,” he says, “appears to be somewhat more like that of parthenogenesis than a more primitive form of nuclear reorganization.” (Science, April 6, 1923, p. 403.) At all events, it seems safe to conclude that the tendency to senescence is pretty general among living organisms, and that this tendency, unless counteracted by a periodic reorganization of the nuclear genes, results inevitably in the deterioration and final extinction of the race.
In this inexhaustible power of self-renewal inherent in all forms of organic life, the mechanist and the upholder of abiogenesis encounter an insuperable difficulty. In inorganic nature, where the perpetual-motion device is a chimera, and the law of entropy reigns in unchallenged supremacy, nothing analogous to it can be found. The activity of all non-living units of nature, from the hydrogen atom to the protein multimolecule, is rigidly determined by the principle of the degradation of energy. The inorganic unit cannot operate otherwise than by externalizing and dissipating irreparably its own energy-content. Nor is its reconstruction and replenishment with energy ever again possible except through the wasteful expenditure of energy borrowed from some more richly endowed inorganic unit. In order to pay Paul a little, Peter must be robbed of much. Wheresoever atoms are built up into complex endothermic molecules, the constructiveprocess is rigidly dependent upon the administration thereto of external energy, which in the process of absorption must of necessity fall from a higher level of intensity. And when the energy thus absorbed by the complex molecule is again set free by combustion, it is degraded to a still lower potential, from which, without external intervention, it can never rise again to its former plane of intensity. The phenomena of radioactivity tell the same tale. All the heavier atoms, at least, are constantly disintegrating with a concomitant discharge of energy. There is no compensating process, however, enabling such an atom to re-integrate and recharge itself at stated intervals; and, once it has broken down into its component protons and electrons, “not all the king’s horses nor all the king’s men can ever put Humpty-Dumpty together again.” In a word, none of the inorganic units of the mineral world exhibits that wonderful power of autonomous recuperation which a unicellular ciliate manifests when it rejuvenates itself by means of endomixis. The inorganic world knows of no constructive process comparable to this. It is only in living beings that we find what James Ward describes as the “tendency to disturb existing equilibria, to reverse the dissipative processes which prevail throughout the inanimate world, to store and build up where they are ever scattering and pulling down, the tendency to conserve individual existence against antagonistic forces, to grow and to progress, not inertly taking the easier way but seemingly striving for the best, retaining every vantage secured, and working for new ones.” (“On the Conservation of Energy,” I, p. 285.)
Summing up, then, we have seen that the reproductive process, whereby the metists or multicellular organism originate, resolves itself ultimately into a process of cell-division. The same is true of the protists or unicellular organisms. For all cells, whether they be protists, germ cells, or somatic cells, originate in but one way, and that is, from a preëxistent living cell by means of cell-division. Neither experimentationnor observation has succeeded in revealing so much as a single exception to the universal law of genetic cellular continuity, and the hypothesis of spontogenesis is outlawed, in consequence, by the logic of scientific induction. Even the hope that future research may bring about an amelioration of its present status is entirely unwarranted in view of the manifest dynamic superiority of the living organism as compared with any of the inert units of the inorganic world. “Whatever position we take on this question,” says Edmund B. Wilson, in the conclusion of his work on the Cell, “the same difficulty is encountered; namely, the origin of that coördinated fitness, that power of active adjustment between internal and external relations, which, as so many eminent biological thinkers have insisted, overshadows every manifestation of life. The nature and origin of this power is the fundamental problem of biology. When, after removing the lens of the eye in the larval salamander, we see it restored in perfect and typical form by regeneration from the posterior layer of the iris, we behold an adaptive response to changed conditions of which the organism can have no antecedent experience either ontogenetic or phylogenetic, and one of so marvelous a character that we are made to realize, as by a flash how far we still are from a solution of this problem.” Then, after discussing the attempt of evolutionists to bridge the enormous gap that separates living, from lifeless nature, he continues: “But when all these admissions are made, and when the conserving action (sic) of natural selection is in the fullest degree recognized, we cannot close our eyes to two facts: first, that we are utterly ignorant of the manner in which the idioplasm of the germ cell can so respond to the influence of the environment as to call forth an adaptive variation; and second, that the study of the cell has on the whole seemed to widen rather than to narrow the enormous gap that separates even the lowest forms of life from the inorganic world.” (“The Cell,” 2nd edit., pp. 433, 434.)
Since true science is out of sympathy with baseless conjectures and gratuitous assumptions, one would scarcely expect to find scientists opposing the inductive trend of the known facts by preferring mere possibilities (if they are even such) to solid actualities. As a matter of fact, however, there are not a few who obstinately refuse to abandon preconceptions for which they can find no factual justification. The bio-chemist, Benjamin Moore, while conceding the bankruptcy of the old theory of spontaneous generation, which looked for ade novoorigin of living cells in sterilized cultures, has, nevertheless, the hardihood to propose what he is pleased to term anewone. Impressed by the credulity of Charlton Bastian and the autocratic tone of Schäfer, he sets out to defend as plausible the hypothesis that the origination of life from inert matter may be a contemporaneous, perhaps, daily, phenomenon, going on continually, but invisible to us, because its initial stages take place in the submicroscopic world. By the time life has emerged into the visible world, it has already reached the stage at which the law of genetic continuity prevails, but at stages of organization, which lie below the limit of the microscope, it is not impossible, he thinks, that abiogenesis may occur. To plausibleize this conjecture, he notes that the cell is a natural unit composed of molecules as a molecule is a natural unit composed of atoms. He further notes, that, in addition to the cell, there is in nature another unit higher than the monomolecule, namely, themultimoleculeoccurring in both crystalloids and colloids. The monomolecule consists of atoms held together by atomic valence, whereas the multimolecule consists of molecules whose atomic valence is completely saturated, and which are, consequently, held together by what is now known asmolecularorresidual valence. Moore cites the crystal units of sodium bromide and sodium iodide as instances of multimolecules. The crystal unit of ordinary salt, sodium chloride, is an ordinary monomolecule, with the formula NaCl. In the case of the former salts the crystal units consist of multimolecules of the formula NaB·(H2O)2and NaI·(H2O)2, the water of crystallization not being mechanically confined in the crystals, but combined with the respective salt in the exact ratio of two molecules of water to one of the salt. Judged by all chemical tests, such as heat of formation, the law of combination in fixed ratios, the manifestation of selective affinity, etc., the multimolecule is quite as much entitled to be considered a natural unit as is the monomolecule.
But it is not in the crystalloidal multimolecule, but in the larger and more complex multimolecule of colloids (viscid substances like gum arabic, gelatine, agar-agar, white of egg, etc.), that Moore professes to see a sort of intermediate between the cell and inorganic units. Such colloids form with a dispersing medium (like water) an emulsion, in which the dispersed particles, known as ultramicrons or “solution aggregates,” are larger than monomolecules. It is among these multimolecules of colloids that Moore would have us search for a transitional link connecting the cell with the inorganic world. Borrowing Herbert Spencer’s dogma of the complication of homogeneity into heterogeneity, he asserts that such colloidal multimolecules would tend to become more and more complex, and consequently more and more instable, so that their instability would gradually approach the chronic instability or constant state of metabolic fluxion manifest in living organisms. The end-result would be a living unit more simply organized than the cell, and evolution seizing upon this submicroscopic unit would, in due time, transform it into cellular life of every variety and kind.Ce n’est que le premier pas qui coûte!
It should be noted that this so-called law is a mere vague formula like the “law” of natural selection and the “law” of evolution. The facts which it is alleged to express are not cited, and its terms are far from being quantitative. It is certainly not a law in the sense of Arrhénius, who says:“Quantitative formulation, that is, the establishing of a connection, expressed by a formula, between different quantitatively measurable magnitudes, is the peculiar feature of a law.” (“Theories of Chemistry,” Price’s translation, p. 3.) Now, chemistry, as an exact science, has no lack of laws of this kind, but no branch of chemistry, whether physical, organic, or inorganic, knows of anylaw of complexity, that can be stated in either quantitative, or descriptive, terms. We will, however, let Moore speak for himself: