There is an especial interest in connection with the theory of archigony and its physical basis in the chemical fact that cyanogen and its compounds—cyanide of potassium, cyanic acid, cyanide of hydrogen, etc.—are only formed at incandescent heat; that is to say, when the requisite inorganic nitrogenous compounds are put with glowing coals, or the mixture is heated to incandescence. Other essential constituents of albumin, such as carburetted hydrogen or alcohol-radical, can be formed synthetically in heat. "Thus," says Pflüger, "nothing is clearer than the possibility of the formation of cyanic compounds when the earth was entirely or partially in a state of incandescence or great heat. We see how extraordinarily all the facts of chemistry point to fire as the force that has produced the constituents of albumin by synthesis. Hence life was born from fire, and the chief conditions of its appearance are associated with a time when the earth was a glowing ball of fire. When we remember the incalculably long period in which the surface of the earth was slowly cooling, we see that cyanogen, and the compounds that contained cyanogen, and carburetted hydrogen, had plenty of time and opportunity to follow out to any extent their great tendency to the transposition and formation of polymeria (chains of atoms), and, with the co-operation of oxygen and afterwards of water and salts, to evolve into the self-decomposable albumin which is living matter." In regard to the latter feature, it is well to emphasize the fact that, as will be understood, there must have been a long series of chemical intermediary stages between the incandescent formation of cyanogen and the appearance of the aqueous living plasm.
Pflüger's cyanogen theory does not conflict with my monera theory, but rather supplements it, by its careful and thoroughly scientific study of a much earlier stage of primitive biogenesis—in a sense, the first period of preparation for the formation of albumin. This must be well borne in mind in view of the attacks which have lately been made on it by Neumeister and other vitalists; it is supposed to be untenable, because "there is an impassable gulf between cyanic compounds and proteids." This criticism is answered by the living albumin itself, which always contains in its nitrogenous decomposition products the radical of cyanide or other substances (urea) that can be artificially produced from cyanic compounds. Another objection is that "the cyanic compounds which were formed in the heat must have very quickly perished on the subsequent appearance of water." The objection has no weight, since we can form no definite idea as to the special conditions of chemical activity in those times. We can only say that the conditions during this long period (embracing millions of years) were totally different from those of chemical action at the surface of the earth to-day. The real ground of the opposition of Neumeister and other vitalists is their dualistic conception of nature, which will maintain at all costs the deep gulf between the organic and inorganic worlds.
Max Verworn, in his General Physiology, has fully described and criticised the various theories of the appearance of life on the earth. He rightly attributes a great value to Pflüger's cyanogen theory, because "it makes a strictly scientific study of the problem in close relation to the facts of physiological chemistry, and goes thoroughly into detail." He agrees with Pflüger when he expresses himself as follows: "I would say, therefore, that the first albumin to be formed was in point of fact living matter, endued with the property in all its radicals of attracting especially homogeneous parts with great force and preference, in order to build them chemically into the molecule, and so grow indefinitely. On this view the living albumin need not have a constant molecular weight, because it is a huge molecule in an unceasing process of formation and decomposition, probably acting on the ordinary chemical molecules as a sun does on a small meteor." This theory, which I believe to be correct, is also maintained by many other modern scientists who have made a particular study of the difficult question of the nature and origin of the albuminoids.
Now that we have described the various modern theories of archigony that are worth considering, and recognized with Nägeli that the original development of the organic from the inorganic is a fact, we may glance at the older theories which, under the name of "spontaneous generation," afforded matter for a good deal of controversy. It is true that they are now almost entirely abandoned, but the experiments in connection with them excited a good deal of interest and led to many misunderstandings.
The older hypotheses of "spontaneous generation" do not bear on our problem of archigony (or the first development of living matter from lifeless inorganic carbon compounds) but relate to the formation of lower organisms out of the putrid and decomposing organic elements of higher organisms. In order to distinguish these hypotheses from the totally different theory of archigony, it is better to give them the name of saprobiosis (an earlier name was necrobiosis), which means the birth of living from dead (nekron) or putrid (sapron) organic matter. Saprobiosis is preferable, because necrobiosis is better used in a different sense, for the dead organic parts which gradually bring about the death of the living body (see p. 106). It was believed in ancient times that lower organisms could arise from the dead remains of higher organisms, such as fleas from manure, lice from morbid pustules in the skin, moths from old furs, and mussels from slime in the water. As these stories were supported by the authority of Aristotle, and on that account believed by St. Augustine and other fathers, and reconciled with the faith, they were held until the beginning of the eighteenth century. Even in the year 1713 the botanist Heucherus stated that the green duck-weed (lemna) is only condensed grease from the surface of foul standing water, and that water-cress was formed from it in fresh running water.
The first scientific refutation of these old stories was made by the Italian physician, Francisco Redi, in 1674, on the basis of very careful experiment: he was persecuted for "unbelief" on that account. He showed that all these animals arose from eggs that had been deposited by female animals in dung, skin, fur, slime, etc. But at that time the proof could not be extended to the tape-worms, maw-worms, and other intestinal animals (entozoa), which live inside other animals (in the bowels, blood, brain, or liver). It was still believed that these arise from diseased parts of the host-animals in which they live, until about the middle of the nineteenth century. It was not until 1840-1860 that it was shown by the experiments of Siebold, Leuckart, Van Beneden, Virchow, and other famous biologists, that all these intestinal animals have come from without into the animals they live in, and propagate there by eggs. Of late years the proof has been applied all round.
On the other hand, the hypothesis of saprobiosis retained its position until quite recently for one section of the smallest and lowest organisms, the microscopic forms of life, invisible to the naked eye, which were formerly called infusoria, and which we now call by the wider name of protists or unicellulars. When Leeuwenhoek discovered the infusoria in 1675 with the newly invented microscope, and showed that they arise in great quantities in infusions of hay, moss, flesh, and other putrid organic substances, it was generally believed that they were spontaneously generated there. The Abbé Spallanzani showed in 1687 that no infusoria appear in these infusions if they are well boiled and the vessel is carefully closed; the boiling kills the germs in them, and the exclusion of air prevents the entrance of fresh germs. In spite of this, many microscopists still believed that certain infusoria, particularly the very small and simple bacteria, could be born directly from putrid or diseased tissues of organisms, or from decomposing organic fluids; the opinion was maintained by Pouchet at Paris in 1858, and afterwards by Charlton Bastian. The controversy about the subject moved the Paris Academy in 1858 to offer a prize for "careful research that would throw new light on the question of spontaneous generation." It fell to the famous Louis Pasteur, who proved, by a series of ingenious experiments, that there are everywhere in the atmosphere numbers of germs of microbes or microscopic organisms floating among the dust particles, and that these grow and reproduce when they reach water. Not only infusoria, but also small highly organized plants and animals—such as lichens, mosses, rotifers, and tardigrades—can live for months in a desiccated condition, be carried in all directions by the wind, and reawaken into life when they reach water. On the other hand, Pasteur showed convincingly that organisms never appear in infusions of organic substances when they are sufficiently boiled and the atmosphere that reaches them has been chemically purified. He summed up the results of his rigorous experiments, which were confirmed by Robert Koch and other bacteriologists, and gave rise to the modern precautions as to disinfection, in the maxim: "Spontaneous or equivocal generation is a myth."
The famous experiments of Pasteur and his successors had destroyed the myth of saprobiosis, but not the theory of archigony. These entirely different hypotheses are still very frequently confused, because the old title of "spontaneous generation" is used for both. We still read sometimes that the "unscientific" belief in abiogenesis has been definitely refuted by these experiments, and that the question of the origin of life has thus become an insoluble enigma. There is an astonishing superficiality and lack of discernment in such remarks; they would hardly be possible in any other branch of science. But in biology—many of its distinguished representatives continue to say—we have only to observe and correctly describe facts; the formation of clear ideas and the indulgence in reflection on the facts are unnecessary and dangerous, and, therefore, to be avoided! It is due to this pitiable condition of biological methods of research that our hypothesis of archigony is still attacked, or else ignored. Why? Because the false hypothesis of saprobiosis, which has absolutely nothing in common with it but the name "spontaneous generation," has been refuted by the experiments of Pasteur and his colleagues![9] These experiments prove nothing whatever beyond the fact that new organisms are not formed in certain infusions of organic matter—under definite, artificial conditions. They do not even touch the important and pressing question, which alone interests us: "How did the earliest organic inhabitants of our earth, the primitive organisms, arise from inorganic compounds?"
The great popularity of the famous experiments of Pasteur on spontaneous generation, and the unfortunate confusion of ideas which was caused by the false interpretation of his results, make it necessary for me to say a word on the general value of scientific experiments in many questions. Since Bacon introduced experiment into science three hundred years ago, and gave it a logical basis, both our speculative knowledge of nature and the practical application of our knowledge made remarkable progress. New methods of research made it possible for modern workers to penetrate far more deeply into the nature of phenomena than the older thinkers had done, who had no knowledge of experiment. Especially in the nineteenth century the development of the experimental method, or the putting of a question to nature, led to enormous advances in the various sciences.
In the subject we are considering the question to be put to nature is: "Under what conditions and in what manner is living matter (or plasm) formed from lifeless inorganic compounds?" We may confidently assume that in the period when archigony took place—the time when organic life first appeared on the cooled surface of the earth, at the beginning of the Laurentian Age—the conditions of existence were totally different from what they are now; but we are very far from having a clear idea of what they were, or from being able to reproduce them artificially. We are just as far from having a thorough chemical acquaintance with the albuminous compounds to which plasm belongs. We can only assume that the plasma-molecule is extremely large, and made up of more than a thousand atoms, and that the arrangement and connection of the atoms in the molecule are very complicated and unstable. But of the real features of this intricate structure we have as yet no conception. As long as we are ignorant of this complex molecular structure of albumin, it is useless to attempt to produce it artificially. Yet in this position of the matter we would seek to produce that great wonder of life, the plasm, artificially, and when the experiment miscarries (as we should expect) we cry out: "Spontaneous generation is impossible."