Popular Science Monthly/Volume 2/November 1872/Spontaneous Generation
| SPONTANEOUS GENERATION. |
THE appearance of the long-promised work of Dr. Bastian on the "Beginnings of Life"[1] will be welcomed by the students of natural history as an important step forward in the progress of an old and interesting controversy. Whether all the life of the earth came from some primordial spark in the dim beginning, that has spread in multitudinous diversity through earth, sea, and air; or whether all forms of living things sprang into perfect existence after their distinctive kinds by a supernatural fiat; or whether the origination of living things is still within the compass of natural operations, are questions equally fascinating to pursue and difficult to determine. But the radical problem of the origin of life is now accepted as legitimate in the field of science, and much of the world's ablest talent is profoundly occupied with its investigation. We propose to give a brief account of Dr. Bastian's contribution to the inquiry, or rather to point out his line of research, referring those who are interested in the subject to his able work, which is now accessible to American readers.
The doctrine that certain forms of living things originate directly in the operations of Nature, without the agency of parentage, is an ancient speculation. Three centuries before the Christian era, Aristotle believed in the spontaneous origination of eels and other fish out of the slimy mud of rivers and marshes; also, that certain insects took origin from the vernal dew on plants; and that lice were spontaneously engendered in the flesh of animals. He believed also that animals might proceed from vegetables—that the caterpillars of certain butterflies, for instance, were actually the products of the plants upon which they fed. To the authority of Aristotle, which was despotic in the schools for nearly two thousand years, was added in this case the influence of poetry by which the Aristotelian science was popularized. Ovid, who is reputed to have been forty-three years old at the Christian era, sung of spontaneous generation as follows—Dryden being responsible for the English:
"The rest of animals from teeming earth
Produced, in various forms received their birth.
The native moisture, in its close retreat
Digested by the sun's ethereal heat
As in a kindly womb, began to breed,
Then swelled and quickened by the vital seed;
And some in less, and some in longer space,
Were ripened into form and took a several face.
Thus when the Nile from Pharian fields is fled,
And seeks, with ebbing tide, his ancient bed,
The fat manure with heavenly fire is warmed,
And crusted creatures, as in wombs, are formed;
These, when they turn the glebe, the peasants find;
Some rude, and yet unfinished in their kind.
Short of their limbs, a lame, imperfect birth;
One half alive, and one of lifeless earth."
Crude ideas of this kind prevailed universally until the seventeenth century. The celebrated physiologist, Dr. William Harvey, the discoverer of the circulation of the blood, has the credit of first propounding the modern view expressed in the maxim "Omne vivum ex vivo," which being interpreted signifies, "No life without antecedent life." He maintained that all living beings proceed from eggs; but exactly what he meant by "eggs," that is, whether they were always derived from parental organisms, or might originate in some other way, is considered uncertain.
The first distinct announcement of the doctrine that all living matter has sprung from preëxisting living matter, was made by Francesco Redi, an Italian physician, who published his views just two hundred and four years ago. His position is thus stated by Prof. Huxley: "Here are dead animals, or pieces of meat; I expose them to the air in hot weather, and in a few days they swarm with maggots. You tell me that these are generated in the dead flesh; but, if I put similar bodies, while quite fresh, into a jar, and tie some fine gauze over the top of the jar, not a maggot makes its appearance, while the dead substances, nevertheless, putrefy just in the same way as before. It is obvious, therefore, that the maggots are not generated by the corruption of the meat, and that the cause of their formation must be a something which is kept away by gauze. But gauze will not keep away aëriform bodies or fluids. This something must, therefore, exist in the form of solid particles too big to get through the gauze. Nor is one left long in doubt what these solid particles are; for the blow-flies, attracted by the odor of the meat, swarm round the vessel, and urged by a powerful but in this case misleading instinct, lay eggs out of which maggots are immediately hatched upon the gauze. The conclusion, therefore, is unavoidable: the maggots are not generated by the meat, but the eggs which give rise to them are brought through the air by the flies."
These experiments were unanswerable; but the doctrine of spontaneous generation had been too long and firmly believed, to be surrendered merely because of the demonstrated falsity of its grounds. It was held to have the sanction of the Bible, which affirmed that bees were generated from the carcass of a dead lion: Dr. Redi was therefore called upon to defend himself against the charge of impugning Scripture authority.
The views of Redi prevailed for a century, and the hypothesis of spontaneous generation had become completely discredited. But meantime the microscope had been improved, and a new world of life revealed. When animal or vegetable substances are infused for a time in water, swarms of creatures are produced in it, called infusorial animalculæ, and which are so small that they can only be seen with a powerful magnifier. This was a new aspect of the production of life, and favored the view of its spontaneous origin. In the middle of the eighteenth century, an Englishman named Needham took the ground that, although putrefying meat may not engender insects, it may yet give rise to animalculæ. "If," said Needham, "these animalculæ come
Fig. 1.
Some of the Most Common Primordial Forms of Life. (x 800.) A. Plastide-particles; B. Bacteria; C. Torula; D. Vibriones; E. Spirilla; F. Leptothrix.
from germs, these germs must exist, either in the infused substance, the water, or the adjacent air. All germs are killed by heat; if, therefore, I boil the infusion, seal it up, and then heat the whole vessel, I shall destroy the germs." He did this; but, after waiting for a time, the animalculæ still appeared in the closed vessel. The experiment seemed conclusive in favor of spontaneous generation, or life without germs; but, again, a learned Italian appeared and attacked the hypothesis. Spallanzani repeated Needham's experiments with more vigilant precautions. He closed the tubes more effectually, and exposed them to a greater heat, after which the animalculæ failed to appear. The real issue in the case was thus fairly reached, and the question became one of the existence of atmospheric germs, and of their power of resisting heat. The results of Spallanzani were generally held conclusive against the hypothesis of spontaneous generation; but, toward the middle of the present century, the question was again opened, and it has been assiduously investigated and hotly discussed by men of science for the last forty years. We cannot even mention the numerous contributions to it that have been made by eminent scientists, but must refer the reader to Dr. Bastian's work, where the history of recent investigations upon the subject is given in detail.
The growth of new distinctions and more precise ideas in science requires the use of new terms to mark them, while, at the same time, old terms have to be discarded, as conveying erroneous ideas. The term "spontaneous generation," although so long applied to the subject, that it will be apt to continue in popular use, has lost its place in biological science, as it is too indefinite, and conveys a false idea. Those who hold that life originates directly from non-living matter do not consider that its production in this way is any more truly "spontaneous" than its usual production from parental germs. Several words have been introduced by different writers to define their ideas, which it is desirable here to explain.
Biogenesis is the term applied by Prof. Huxley to the derivation of life from previously-existing life; and Abiogenesis to the production of life from non-living matter. The latter term, therefore, corresponds to what is commonly meant by "spontaneous generation."
Homogenesis, or Homogeny, are terms that have been long applied to the production of like from like; that is, the common case in which the living parent gives rise to offspring which pass through the same changes as itself.
Heterogenesis, or Heterogeny, is the name applied to processes by which living things arise from the matter of preexisting organisms, belonging to a totally different species. It has, however, had different meanings, and its use has created some obscurity, but it is customary to apply it to the so-called cases of "spontaneous generation;" and those who hold this doctrine are therefore known as Heterogenists.
Panspermy is the name given to the doctrine of diffused atmospheric germs, as the sources of infusorial life, and those who hold to this view are called Panspermists. "Spontaneous generation," so called, or the production of living creatures without parentage, may take place in two ways: either from preexisting living matter (heterogenesis), or from not-living matter. This production of living forms from inorganic materials is termed by Dr. Bastian Archebiosis, which literally means "beginning to live."
It was in the course of some investigations upon the microscopical characters of the blood of persons suffering from acute diseases that Dr. Bastian's attention was first drawn to the question of the origin of life. He soon became interested in it as an independent scientific problem, and pursued the inquiry experimentally for three years, the results being recorded in the present work. In Part I. he aims to show that the now commonly-accepted doctrine of the Correlation of Forces favors the independent origin of living matter. In this part, also, he has an elaborate chapter showing that the cell cannot be regarded as the ultimate organic unit. In Part II., under the head of Archebiosis, he takes up the real issue of the spontaneous generation of new matter endowed with living properties. The question is thus stated: "It must be considered to turn almost wholly upon the possibility of the de novo origin of bacteria; since, if such a mode of origin can be proved for them, it must also be conceded for other allied fungoid and algoid units. Evidence, which is of the most convincing character when looked at from all sides, now shows that bacteria are killed by a temperature of 140° Fahr. Yet similar organisms will constantly appear and rapidly multiply within closed flasks containing organic fluids, although the flasks and their contents have-been previously exposed for some time to a temperature of 212° Fahr."
As it will be impossible in this article to give the details of Dr. Bastian's experiments, we will try to convey to our readers some notion of these living organisms, which it is now claimed can be produced when all germs are destroyed. When a fluid containing an organic substance in solution is left to itself for a time, which may be variable in different circumstances, the infusion gradually becomes turbid, and there forms upon its surface a thin, semi-translucent scum,
Fig. 2.
Representation of Haeckel's Group Monera. (x 800.) The Common Amœba.
a. Minute Specks of Protoplasm from Fine Surface Mud of Fresh-water Ponds; b. Protomœba Primitiva, two Individuals resulting from a Recent Fission; c. Vampyrella Pendula; d. Amæba Porreta, a Form of Protomœba.
or pellicle, that soon thickens into a membrane. If the fluid be observed by a microscope of the highest power, when it first begins to grow clouded, it will be found swarming with multitudes of moving specks or spherical particles (Fig. 1, A),varying from 1/20000 to 1/100000 of an inch in diameter. These specks have been variously named. They have been called "monads," or "mycrozimes," or "micrococci," and are termed by Dr. Bastian plastide particles. They are regarded by him as the primordial particles of living matter, and as giving origin to organisms of a higher grade.
Among these are the infusorial objects known as bacteria (Fig. 1, B). These are minute, rod-like, jointed bodies, varying in size according to circumstances, but pretty uniform in the same solution. They are in length from to of an inch, and in thickness from to of an inch. The rods are formed of a series of granules placed end to end, and their appearance has been likened to a number of fine needles embedded in a thin film of glue. They often present a joint or line in the middle, dividing them into two equal parts. "Their movements are frequently of a more or less rapid, oscillating, or irregularly rotating character; though at other times they may be seen darting from place to place, either directly or in curves of various descriptions. All gradations exist, in fact, between movements which suffice at once to stamp them as living things, and mere slow oscillations, the presence of which alone may make us doubtful as to whether we have to do with living or dead organisms."
Along with the plastide-particles and the bacteria, there appears one of the lowest and simplest of organic bodies—the Torula, or yeast-plant (Fig. 1, C). The torula is a simple cell, possessing a cell-wall formed of a thin, homogeneous membrane, and containing a soft formative layer composed of protoplasm. These cells are about of an inch and smaller, and multiply by budding or gemmation, being usually seen in chains, or clustered groups. Vibriones (Fig. 1, D) are described as jointed bodies, composed of long, rod-like segments, bent at various angles, which exhibit certain slow movements either as mere bending of the body, or else an actual undulating progression. In size they may vary from that of the largest bacteria, up to a body of an inch in length, by in breadth, though there is no definite limit to their dimensions. The Spirilla (Fig. 1, E) are less common organic forms, characterized by the most active movements, and in which the body is thread-like, though twisted into the form of a helix, or spiral. Leptothrix (Fig. 1 F) is a name applied to certain filamentous objects that are generally motionless, and often not much thicker than vibriones. They may be either straight or undulating in outline, and perfectly plain, or marked by minute segmentations, after the fashion of the larger fungous filaments, into which it is said they sometimes develop.
Within a few years past, attention has been called by Prof. Haeckel to certain of the lowest forms of organic life, which he considers intermediate between the animal and vegetable kingdoms, and by which they are connected. These he calls the Protista, meaning, first of all, primordial. This primordial organic kingdom, Haeckel divides into ten groups, the lowest of which he names the Monera, which includes certain minute jelly-specks termed protomceba and protogenes. Prof. Haeckel says: "I have called these forms of life standing at the lowest grade of organization monera. Their whole body, in a fully-developed and freely-moving condition, consists of an entirely homogeneous and structureless substance, a living particle of albumen capable of nourishment and reproduction. These simplest and most imperfect of all organisms are, in many respects, of the highest interest. For the albumen-like, organic matter meets us here as the material substratum of all life-phenomena, apparently not only under the simplest form as yet actually observed, but also under the simplest form which can well be imagined. Simpler and more incomplete organisms than the monera cannot be conceived. ... Indeed, the whole body of the monera, however strange this may sound, represents nothing more than a single, thoroughly homogeneous particle of albumen, in a firmly adhesive condition. The external form is quite irregular, continually changing, globularly contracted when at rest. Our sharpest discrimination can detect no trace of an internal structure, or of a formation from dissimilar parts. As the homogeneous, albuminous mass of the body of the moner does not even exhibit a differentiation into an inner nucleus and an outer plasma, and as, moreover, the whole body consists of a homogeneous plasma or protoplasma, the organic matter here does not even reach the importance of the simplest cell. It remains in the lowest imaginable grade of organic individuality." Prof. Haeckel afterward says: "The monera are indeed protista. They are neither animals nor plants. They are organisms of the most primitive kind; among which the distinction between animals and plants does not exist."
Fig. 3.
Transformations of Chlorophyll Corpuscles, (x 600.)
a, Pale, unaltered Chlorophyll Corpuscles of Nitella; b, Others lying side by side with former, but larger, of a darker green, and slightly granular; c, Decolorization advancing a few granules still green; d, Similar corpuscles after the protrusion of motionless rays, and formation of a vacuole; e, Similar corpuscles completely decolorized and converted into sluggish specimens of Actinophrys; f, First stage in transformation of Actinophrys. some of which are converted into Amoebae (g), and others into Monads (h) with two flagella; j, Enchelys-like organisms, probably derived from further development of some Monads and Amœbæ.
The common amœba is described as a microscopic animal at the very bottom of the scale of living things. It is a minute, shapeless, structureless mass of semi-fluid jelly or protoplasm, without organs of any kind, but it has the marvellous power of extemporizing organs as it requires them. Thus, if it wishes to move, it shoots out a part of its body as a temporary foot, and retracts it when no longer wanted. If it desires to seize any thing, it protrudes an arm for the purpose; and, when it has in this way got possession of the needed nutriment, becoming all stomachy it wraps itself round its food, and absorbs or digests it.
Dr. Carpenter describes it as "changing itself into a greater variety of forms than the fabled Proteus, laying hold of its food without members, swallowing it without a mouth, digesting it without a stomach, appropriating its nutritious material without absorbent vessels or a circulating system, moving from place to place without muscles, feeling (if it has any power to do so) without nerves, multiplying itself without eggs, and not only this, but, in many instances, forming shelly coverings of a symmetry and complexity not surpassed by those of any testaceous animal."
Fig. 4.
Modes of Origin and Development of Ciliated Infusoria. (x600.)
a, Transforming Euglena. with red "eye-speck" still visible; b, A similar body, having many of its chlorophyll corpuscles still green, fringed with almost motionless cilia; c, A completely decolorized sphere derived from a transformed Euglena. provided with a few partly-motionless cilia; d and e, More advanced forms of a similar embryo developing into a Dileptus (?); f, Vorticella. soon after its emergence from a cyst of Euglena origin, which subsequently develops into a striated variety (g); h, A large Chlorococcus-vesicle, whose contents gradually undergo decolorization (j), and at last becomes converted into an annualized mass (k), which gradually shapes itself into the form of an Oxytricha (l). This after a time ruptures its cyst and soon takes on the characteristics shown at m; n, A form of Plœsconia derived from an embryo produced within other, apparently similar, Chlorococcus-vesicles.
The experiments of Dr. Bastian force upon him the conclusion that the several organisms here considered, bacteria, torula, vibriones, fungus-filaments, protomœba, and monads, are products of the direct development of new-born specks of living matter. His experiments seem to have been conducted with extreme precautions. He hermetically closed the narrow necks of his flasks during violent ebullition, thus producing an almost perfect vacuum above the infusion. After this he subjected the flasks to a heat of from 212° Fahr. to over 400° Fahr. After being left a few days under favorable situations, and then examined, they were found to contain the living creatures we have described. The only remaining question is, Could these organisms or their germs survive this degree of heat? The alternative to which the opponents of spontaneous generation seem to be driven, by these investigations, is thus pointedly stated by Mr. Alfred Russell Wallace, in a late review of Dr. Bastian's book, in Nature. He says: "The only way of escaping from the results of such a series of experiments as that here recorded is by asserting that, although the organisms which are produced in the flasks are killed by a temperature much below that
Fig. 5.
Transformation of a Mass of Chlorococcus Corpuscles into the so-called "Winter-egg" of Hydatina senta. (x 250.)
a, Ovoid mass of bright-green Chlorococcus Corpuscles, about 1/300 in long diameter: b, Such a mass after its transformation into a brown granular body, without distinct bounding wall (should have been intermediate in tint between a and c); c, A similar body at a later stage, when a limiting envelop has made its appearance, upon which villous outgrowths had been produced; d, Later stage, constituting the so-called "winter-egg" of Hydatina; e, Hydatina senta which is produced from such a body—almost adult.
to which the flasks have been subjected, the germs from which they have been produced are not so killed. We are asked, therefore, to accept as facts three pure suppositions: first, that such excessively minute and simple organisms as bacteria, whose only mode of multiplication is by fission or gemmation, have germs which possess different physical properties from themselves; secondly, that these germs, as well as many others, are omnipresent in the atmosphere; and, thirdly, that they are not injured by an exposure for four hours to vapor heated to over 300° Fahr.; and, finally, we are to accept all these suppositions as facts in order to avoid admitting that species of living protoplasm are originated de novo in some fluids just as specks of crystalline matter originate in other fluids, and although some organisms can be seen to make their appearance in fluids independently of all preexisting visible germs, just as crystals do."
In Part III., Dr. Bastian takes up the processes of heterogenesis, whereby the matter of already existing living units gives birth to other living things, wholly different from themselves, and having no tendency to revert to the parental type. The transformations and developments represented in Figs. 3, 4, and 5, will mainly interest those familiar with the objects delineated, but they are of a very remarkable character. It is alleged that the cells of conferva give rise to euglena, a beautiful green organism which abounds in stagnant water, while this undergoes still further transformation into amœba, and ciliated infusoria. And still more surprising, if possible, is the transformation of the minute algoid chlorococcus into the large, complex, and well-known rotifer, Hydatina senta (Fig. 5).
As Dr. Bastian remarks: "The fact that animals with such distinct and specific organs should arise in this definite manner, from the reproductive products of the plant, will doubtless seem to many to flavor more of fable than of fact." This is undoubtedly true. Dr. Bastian's views contravene general experience. The derivation of organisms from preexisting germs is the actual method which we know that Nature employs in all grades from the top to the bottom of the scale of life. We know, moreover, that infusorial germs do exist, and float about, in the atmosphere. Besides, all our past knowledge of life implies the slow operation of the forces of evolution. As for the appearance of infusorial organisms in liquids, which a few hours before did not contain them, they must be explained in accordance with known modes of action, until some other method is demonstrated. To this, Dr. Bastian replies—1. That science now admits that, at some period in the earth's history, the lower forms of life have arisen by the operation of natural causes. 2. That all the considerations bearing upon the case favor the view that such organisms may be produced now, and that it is little else than absurd to suppose that "the simplest and most structureless amœba of the present day can boast a line of ancestors stretching back to such far-remote periods that in comparison with them the primeval men were but as things of yesterday;" and 3. That the de novo origin of living matter, and the transformation of low vegetable organisms into infusoria and animalcula are facts that must now be considered as experimentally established. The whole question will therefore turn on the future testing of these remarkable processes. The subject cannot be allowed to rest here; and, if Dr. Bastian's experiments shall be verified, the publication of his work will constitute an epoch in the progress of biological science. It may be remarked that the "Beginnings of Life" is written in a popular and intelligible style, but, as it was composed while the doctor was absorbed in his investigations, it is somewhat defective in classification and condensation. This is to be regretted, yet it is quite a secondary matter. Mr. Wallace deprecates its literary defects, but cordially concedes its scientific importance. He says: "It is so full of curious and novel facts and experiments, it contains so much excellent reasoning and acute criticism, and it opens up such new and astounding views of the nature and origin of life, that one feels it ought to and might have ranked with such standard works as the 'Origin of Species' and the 'Principles of Biology,' if equal care had been bestowed upon it as a literary composition."
- ↑ "The Beginnings of Life; being some Account of the Nature, Modes of Origin, and Transformations of Lower Organisms." By H. Charlton Bastian, M.A., M.D., F.R.S. In two volumes, pp. 1200; with numerous Illustrations.