IF we have delayed somewhat too long the mention of Dr. Bastian’s learned and powerful treatise on the “ Beginnings of Life,” it has been because of a natural reluctance to approach so vast a subject, on which so much is to be said, while yet so little can be said that is thoroughly satisfactory. If the half of Dr. Bastian’s positions are destined to become substantiated, his work will mark an epoch in biology hardly less important than that which was marked by Mr. Darwin’s “ Origin of Species.” U nfortunately, the kind of proof which is needed for Dr. Bastian’s main thesis is much more difficult, not only to obtain, but also to appreciate properly when obtained, than the kind of proof by which the hypothesis of natural selection has been converted into a scientific theory. In the latter case what was needed was some principle of interpretation which should account for the facts of the classification, embryology, morphology, and distribution of plants and animals, without appealing to any other forces than such as are known to be actually in operation ; and it was because the theory of natural selection furnished such a principle that it met with such ready acceptance from the scientific world. On the other hand, the fate of Dr. Bastian’s theory of archebiosis depends upon the issue of a series of experiments of extraordinary delicacy and difficulty, — experiments which are of value only when performed by scientific experts of consummate training, and which the soundest critic of inductive methods must find it perilous to interpret with confidence, unless he has had something of the training of an expert himself. For, however simple it may seem to the uninitiated to shut up an organizable solution so securely that organic germs from the atmosphere cannot gain access to it, or cannot even be imagined to gain access to it, this is really one of the most desperate tasks which an experimenter has ever had set before him ; yet to such rigor of exclusion is the inquirer forced who aims to settle the question by the direct application of what logicians call the method of difference. And thus the question at issue is reduced to that unpromising state in which both parties to the dispute are called upon to perform the apparently hopeless task of proving a negative. When living things appear in the isolated solution, the adherents of the germ-theory are always able to point out some imaginable way in which germs might have got in ; and on the other hand, when the panspermatists adduce instances in which no living things have been found, the believers in archebiosis are able to maintain, with equal cogency, that the failure was due, not to the complete exclusion of germs from without, but to the neglect of some other condition essential to the evolution of living matter.
But Dr. Bastian strikes out from this closed circle of rebutting arguments with a boldness which deserves success. He takes very strong ground in maintaining that the notion that the atmosphere is forever swarming with the germs of bacteria and vibriones, ready on all occasions to penetrate the pores of glass bottles, to creep in through the capillary neck of a flask from which the air has been expelled by boiling, and to sustain a heat sufficient to disintegrate all known forms of life, is a pure hypothesis, unsustained by a solitary fact, save those in the interpretation of which it is itself taken for granted. Half its force is, indeed, taken away from the germ-theory, when it is stated after this straightforward manner. For Spallanzani to assume that the air is always loaded with such germs was a very happy guess ; but what is to assure us that it was a true one ? and, above all, why are we to go on acquiescing in it as if it were a demonstrated fact ? The only facts to sustain it are such as admit equally well of a totally different explanation. The germ-theory only maintains its ground as a tradition ; and were the scales of prejudice turned ever so little in favor of archebiosis, the germ-theory would be no longer appealed to, and would almost immediately be forgotten. Obviously, these are hardly the characteristics of a valid scientific hypothesis.
From this point of view, one set of Dr. Bastian’s experiments is of striking significance. Two similar flasks, the one containing a boiled “ Pasteur’s solution ” and the other a boiled infusion of turnip, are placed beneath the same bell-jar and allowed to stand for a few days. It is found that the “ Pasteur’s solution ” will remain free from bacteria for an indefinite length of time, while bacteria are always speedily developed in the turnip infusion. Now, the advocates of the germ-theory cannot maintain that atmospheric germs were excluded in the one case but not in the other ; for the two flasks are treated in precisely the same manner, and the possibility of any accidental difference of treatment is eliminated by the frequent repetition of the experiment. Nor can it be urged that all germs of life were destroyed by boiling in the case of the “ Pasteur’s solution,” but not in the case of the turnip infusion ; for both have alike been subjected to a temperature considerably higher than that which is admitted to be fatal to every form of life; while here, again, repetition of the experiment negatives the supposition of any accidental variation in the process. We are, in short, debarred from assuming any physical condition in the one case which is not present in the other. The only imaginable retreat for the panspermatists is in the assumption that the Pasteur’s solution ” is an unfavorable medium for the development of introduced bacteriagerms, while the turnip infusion allows such germs to develop freely. Another experiment, however, cuts off this line of retreat. When bacteria are introduced into “ Pasteur’s solution,” they multiply with great rapidity and soon render the liquid turbid. In view of these striking facts, but one conclusion would appear to be tenable : the bacteria must originate de novo from organizable matter, and their presence in the one case and absence in the other must depend solely on the difference in constitution between the two liquids. The one contains the materials essential for the origination of life, while the other does not. “ We can only infer,” says Dr. Bastian, “that, whilst the boiled saline solution is quite incapable of engendering bacteria, such organisms are able to arise de novo in the boiled organic infusion.”
It is not more than three years since Professor Huxley described the doctrine of the panspermatists as “ victorious along the whole line ” ; yet it is now undeniable that, owing to such experiments as those just cited and others of like implication, that doctrine has been put upon the defensive, with a rather poor prospect of being able to maintain its ground. Until these conclusions have been thoroughly refuted, the probabilities must be regarded as decidedly in favor of archebiosis.
By “ archebiosis ” Dr. Bastian means the genesis of living matter de novo in the absence of living parentage. The bacterium is supposed to be, as it were, precipitated from the solution in much the same way that a crystal is precipitated. As Professor Huxley observes, “ It is not probable that there is any real difference in the nature of the molecular forces which compel the carbonate of lime to assume and retain the crystalline form, and those which cause the albuminoid matter to move and grow, select and form, and maintain its particles in a state of incessant motion. The property of crystallizing is to crystallizable matter what the vital property is to albuminoid matter (protoplasm). The crystalline form corresponds to the organic form, and its internal structure to tissue structure. Crystalline force being a property of matter, vital force is but a property of matter.” When, therefore, the constituent proximate elements of lowest organisms are brought together under suitable conditions, they unite to form bacteria or vibriones or ciliated infusoria, the resulting forms being determined by the operation of principles analogous to those which govern the production of crystals.
However the question may be decided as to the possibility of archebiosis occurring at the present day amid the artificial circumstances of the laboratory, there are few who will deny that archebiosis, or the origination of living matter in accordance with natural laws, must have occurred at some epoch in the past. Let us take note of some of the facts which bear upon this question.
When our earth, refusing to follow in their retreat the heavier portions of the solar nebula, began its independent career as a planet, its surface was by no means so heterogeneous as at present. We may fairly suppose that the temperature of that surface cannot have been lower, but may well have been much higher, than that of the solar surface at the present time, which is estimated at three million degrees Fahrenheit, — or more than fourteen thousand times hotter than boiling water. At such a temperature there could have been no formation of chemical compounds ; so that the chief source of terrestrial heterogeneity did not exist, while physical causes of heterogeneity were equally kept in abeyance by the maintenance of all things in a gaseous state. We have now to show how the mere cooling of this gaseous planet, consequent upon perpetual radiation of heat into surrounding space, must have given rise to the endless variety of structures, organic as well as inorganic, which the earth’s surface now presents. The origination of life will thus appear in its proper place, as an event in the chemical history of the earth. Let us see what must have been the inevitable chemical consequences of the earth’s cooling.
In a large number of cases, heat is favorable to chemical union, as in the familiar instance of lighting a candle, a gas-jet, ora wood-fire. The molecules of carbon and oxygen, which will not unite when simply brought into juxtaposition, nevertheless begin rapidly to unite as soon as their rates of undulation are heightened by the intense heat of the match. In like manner, the phosphoric compound with which the end of the match is equipped refuses to take up molecules of atmospheric oxygen, until its molecules receive an increment of motion supplied by the arrested molar motion of the match along a rough surface. So oxygen and hydrogen do not combine when they are simply mingled together in the same vessel ; but when sufficiently heated they explode, and unite to form steam. In these and in many other cases a certain amount of heat causes substances to enter into chemical union. But it is none the less true that an enormous supply of heat causes such violent molecular undulation as to render chemical union impossible. Since the mode of attractive force known as chemism acts only at infinitesimal distances, the increase of thermal undulation, which at first only causes such a molecular rearrangement as to allow mutually attracting molecules to rush together, must at last cause such a separation of particles that chemism will be unable to act. This inference from known laws of heat is fully verified by experiment in the case of all those compounds -which we can decompose by such thermal means as we have at command. Speaking generally, the most complex compounds are the most unstable, and these are the soonest decomposed by heat. The highly complex organic molecules of fibrine and albumen are often separated by the ordinary heat of a summer’s day, as is witnessed in the spoiling of meat. Supersalts and double salts are decomposed at lower temperatures than simple salts; and these again yield to a less amount of heat than is required to sunder the elements of deutoxides, peroxides, etc. The protoxides, which are only one degree more complex than simple elements, withstand a still higher temperature, and several of them refuse to yield to the greatest heat which we can produce artificially. No chemist, however, doubts that a still greater heat would decompose even these. We may picture to ourselves the earth’s surface as at the outset composed only of uncombined elements, of free oxygen, hydrogen, nitrogen, carbon, sulphur, etc., and of iron, copper, sodium, and other metals in a state of vapor. With the lowering of this nebular temperature by radiation, chemical combinations of greater and greater heterogeneity became gradually possible. First appeared the stable binary compounds, such as water and the inorganic acids and bases. After still further lowering of temperature, some of the less stable compounds, such as salts and double salts, were enabled to appear on the scene. At a later date came the still more heterogeneous and unstable organic acids and ethers. And all this chemical evolution must have taken place before the first appearance of living protoplasm. Upon these statements we may rest with confidence, since they are immediate corollaries from known properties of matter.
When it is asked, then, in what way were brought about the various chemical combinations from which have resulted the innumerable mineral forms which make up the crust of the globe, the reply is that they were primarily due to the unhindered working of the chemical affinities of their constituent molecules as soon as the requisite coolness was obtained. As soon as it became cool enough for oxygen and hydrogen to unite into a stable compound, they did unite to form vapor of water. As soon as it became cool enough for double salts to exist, then the mutual affinities of simple binary compounds and single salts, variously brought into juxtaposition, sufficed to produce double salts. And so on, throughout the inorganic world.
Here we obtain a hint as to the origin of organic life upon the earth’s surface. In accordance with the modern dynamic theory of life, we are bound to admit that the higher and less stable aggregations of molecules which constitute protoplasm were built up in just the same way in which the lower and more stable aggregations of molecules which constitute a single or a double salt were built up. Dynamically, the only difference between carbonate of ammonia and protoplasm, which can be called fundamental, is the greater molecular complexity and consequent instability of the latter. We are bound to admit, then, that, as carbonic acid and ammonia, when brought into juxtaposition, united by virtue of their inherent properties as soon as the diminishing temperature would let them, so also carbon, nitrogen, hydrogen, and oxygen, when brought into juxtaposition, united by virtue of their inherent properties into higher and higher multiples as fast as the diminishing temperature would let them, until at last living protoplasm was the result of the long-continued process.
While by following such considerations as these into greater detail the mode in which protoplasm must have arisen may by and by be partially comprehended, it is at the same time true that the ultimate mystery — the association of vital properties with the enormously complex chemical compound known as protoplasm — remains unsolved. Why the substance protoplasm should manifest sundry properties which are not manifested by any of its constituent substances, we do not know; and very likely we shall never know. But whether the mystery be forever insoluble or not, it can in no wise be regarded as a solitary mystery. It is equally mysterious that starch or sugar or alcohol should manifest properties not displayed by their elements, oxygen, hydrogen, and carbon, when uncombined; it is equally mysterious that a silvery metal and a suffocating gas should, by their union, become transformed into table-salt. Yet, however mysterious, the fact remains that one result of every chemical synthesis is the manifestation of a new set of properties. The case of living matter or protoplasm is in nowise exceptional.
In view of these considerations, it may be held that the evolution of living things is a not improbable concomitant of the cooling down of any planetary body which contains upon its surface the chemical constituents of living matter. It may, perhaps, turn out that we can no more reproduce in the laboratory the precise group of conditions under which living matter was first evolved than we can obtain direct testimony as to the language and civilization of our pre-historic ancestors. But, just as it is conceded to be possible, by reasoning upon established philological principles, to obtain trustworthy results as to the speech and culture of the pre-historsc Aryans, so it must be admitted that, by reasoning upon known facts in physical science, we may get some glimpse of the circumstances which must have attended the origin of living matter. By following this method new light will no doubt eventually be thrown upon the past history of our planet, and a sound basis will be obtained for conjectures regarding the existence of living organisms upon some of our neighboring worlds.