Chapter 4

In the first place, it is remarkable, that all the races of animated beings, which are entirely within the range of our powers of observation,--which have such a size and locality that we can study and accurately determine their organization and habits,--are unquestionably produced from parents of their own kind. Only the minute microscopic animals are now supposed to be generated spontaneously; and this alleged fact rests not on direct proof, but only on our inability in certain cases to trace the process of their production in the ordinary way. As many of these animals, in their perfect state, are not more than the twelve thousandth part of an inch in diameter, it is not much to be wondered at, that we should not be able in all cases to discover their ova, or to follow these ova through all their stages of development into the complete being. It is farther remarkable, that these animalcules, when once produced, whether by spontaneous or natural generation, are all found to be provided with the organs or requisite means for continuing their species, and, in fact, for multiplying their number from themselves with astonishing rapidity. As they certainly have children, it seems reasonable to suppose, according to the analogy of all the higher animated tribes, that they also had parents. The ancients supposed, that the worms and insects which appear in decaying organic matter were generated there by the decomposition of the substance, without the previous agency of individuals of the same stock. Every schoolboy is acquainted with Virgil's mode of obtaining a new swarm of bees from the decaying carcass of a heifer. Subsequent researches, made with more care, and perhaps with better instruments of observation, have entirely disproved the hypothesis, and show that the maggots were produced in every case from eggs deposited by flies or other insects, and were afterwards themselves developed into the state of perfect insects. Then it seems reasonable to believe, that the improved observations of future times will clear up the only remaining difficulty, and show how the infusory animalcules also are generated from beings of their own kind.

These minute creatures are prolific to a degree that transcends all calculation; and they exist, either in the egg or maturely developed, in inconceivable numbers. A single wheel-animalcule, _Hydatina senta_, which was watched for more than eighteen days, and which lives still longer, is capable of a fourfold increase in twenty-four or thirty hours; a rate of propagation which would afford in ten days a million of beings. From their tenacity of life, extraordinary powers of reproduction, and incalculable numbers, their united influence may be said to be far more important, in all the great operations of nature, than that of the larger and more perfectly developed organisms. They swarm in all the seas, and play an important part in choking up harbours and forming great deposits at the mouths of rivers. The remains of those which have perished form great beds and strata in the crust of the earth. The silicious stone, called Tripoli, is entirely composed of such remains; at Bilin, in Bohemia, there is one stratum of this substance, fourteen feet thick, one cubic inch of which is estimated to contain forty-one thousand millions of individuals. Their extreme tenacity of life is evinced by the fact, that many of them may be entirely desiccated, and preserved in pure sand for several years, after which, on the application of a drop of water, they may be restored to life. In this dried state, M. Doyere exposed some of them to a heat equal to that of boiling water, and afterwards revived them; though, in an active state, if subjected to a much lower temperature, they perish. If, then, the fully developed and mature can resist such powerful extraneous causes of destruction, how much more must the ova possess the power of enduring them without losing their latent life! The following extract from Professor Owen's Lectures shows the bearing of these facts upon the question of equivocal generation.

"The act of oviparous generation, that sending forth of countless ova through the fatal laceration or dissolution of the parent's body, is most commonly observed in the well-fed _Polygastria_, which crowd together as their little ocean evaporates; and thus each leaves, by the last act of its life, the means of perpetuating and diffusing its species by thousands of fertile germs. When the once thickly tenanted pool is dried up, and its bottom converted into a layer of dust, these inconceivably minute and light ova will be raised with the dust by the first puff of wind, diffused through the atmosphere, and may there remain long suspended; forming, perhaps, their share of the particles which we see flickering in the sunbeam, ready to fall into any collection of water, beaten down by every summer shower into the streams or pools which receive or may be formed by such showers, and, by virtue of their tenacity of life, ready to develope themselves wherever they may find the requisite conditions for their existence.

"The possibility, or, rather, the high probability, that such is the design of the oviparous generation of the _Infusoria_, and such the common mode of the diffusion of their ova, renders the hypothesis of equivocal generation, which has been so frequently invoked to explain their origin in new-formed natural or artificial infusions, quite gratuitous. If organs of generation might, at first sight, seem superfluous in creatures propagating their kind by gemmation and spontaneous fission, equivocal generation is surely still less required to explain the origin of beings so richly provided with the ordinary and recognized modes of propagation."--pp. 31, 32.

Recent accounts show, that the dust collected from the atmosphere at sea, many miles from land, generally contains some of these dried animalcules and their ova. Many of these germs can be developed only in particular localities, or under certain conditions which are rarely fulfilled. Consequently, if there were but few of them, the species might perish, because those few might not find their appropriate home. But such an accident is guarded against by the vast multiplication of these germs and their wide dispersion; for, unlike all the higher tribes of beings except man, the same species is often found in all regions of the globe. Very few, in comparison with the whole number, may find a proper _nidus_; but these few then propagate with such marvellous rapidity, as fully to replenish, if not to increase, the original stock. Thus they have been enabled, as species, to survive even those destroying causes which exterminated all the higher forms of animals. Several species still exist, which were in being at the time of the cretaceous formation, though all the other animated races belonging to that period have perished. "These animalcules," says Ehrenberg, "constitute a chain, which, though in the individual it be microscopic, yet in the mass is a mighty one, connecting the organic life of distant ages of the earth."

In view of facts like these, we may surely say, that the existence of the infusory animalcules, and even of the entozoa, is conceivable, supposing they could only have been produced by parents of their own kind, and without having recourse to the anomalous and hypothetical doctrine of equivocal generation. We may not be able to trace their line of parentage, for our imperfect vision cannot follow the motes which play in the sunbeam, nor track them from their birth-place to their final home. But we know that they must be deposited in every layer of dust that falls from the atmosphere, that they must be inhaled with every breath which an animal draws, and be swallowed with every morsel and drop of its food. The experiments which seem to prove that living beings may be produced from pure inorganic matter are all explicable on the supposition, that adequate precautions were not taken to exclude every animal and germ capable of development from the substances experimented upon, and from the air which was admitted into the apparatus. On this ground, the experiments of Crosse and Weekes, cited by our author, have been quite generally rejected by scientific men, as hardly deserving of notice. We learn that the former was "discouraged by the reception of his experiments," and "soon discontinued them";--with good reason, for it does not appear from our author's account, that he adopted any precautions at all. Mr. Weekes seems to have been a little more cautious, and the consequence was, that he did not observe any appearance of life among the substances experimented upon for "eleven months," at the end of which time we may reasonably suppose, that his precautions ceased to have perfect effect. The only experiment, in which adequate means to guard against causes of error were taken, was that of Professor Schulze, of Berlin, which had a contrary result. We extract Mr. Owen's account of it.

"He filled a glass flask half full of distilled water, in which were various animal and vegetable substances: he then closed it with a good cork, through which were passed two glass tubes, bent at right angles, the whole being air-tight: it was next placed in a sand bath, and heated until the water boiled violently. While the watery vapor was escaping by the glass tubes, the Professor fastened at each end an apparatus which chemists employ for collecting carbonic acid: that at the one end was filled with concentrated sulphuric acid, and the other with a solution of potash. By means of the boiling heat, it is to be presumed that every thing living, and all germs in the flask or in the tubes were destroyed; whilst all access was cut off by the sulphuric acid on the one side, and by the potash on the other. The apparatus was then exposed to the influence of summer light and heat; at the same time, there was placed near it an open vessel, with the same substances that had been introduced into the flask, and also after having subjected them to a boiling temperature. In order to renew constantly the air within the flask, the experimenter sucked with his mouth several times a day the open end of the apparatus, filled with the solution of potash, by which process the air entered his mouth from the flask through the caustic liquid, and the atmospheric air from without entered the flask through the sulphuric acid. The air was of course not at all altered in its composition by passing through the sulphuric acid in the flask; but all the portions of living matter, or of matter capable of becoming animated, were taken up by the sulphuric acid and destroyed. From the 28th of May until the beginning of August, Professor Schulze continued uninterruptedly the renewal of the air in the flask, without being able, by the aid of the microscope, to discover any living animal or vegetable substance; although, during the whole of the time, observations were made almost daily on the edge of the liquid; and when, at last, the Professor separated the different parts of the apparatus, he could not find in the whole liquid the slightest trace of _Infusoria_ or _Confervae_, or of mould; but all three presented themselves in great abundance a few days after he had left the flask standing open. The vessel which he placed near the apparatus contained on the following day _Vibriones_ and _Monads_, to which were soon added larger Polygastric _Infusoria_, and afterwards _Rotifera_."--pp. 32, 33.

For readers who are not familiar with these subjects, it may be well to mention, that the weight of authority is decidedly against this doctrine of spontaneous generation. It is rejected by Mueller, who ranks among the first physiologists of Germany; by Ehrenberg, one of the most distinguished microscopists in the world; and by Owen, who stands at the head of the school of comparative anatomy in England, if not in Europe. The remark made by Cuvier, more than thirty years ago, is still true at the present day, that, "although the impossibility of spontaneous generation cannot be absolutely demonstrated, yet all the efforts of those physiologists who believe in the possibility of it have not succeeded in showing us a single instance."

Passing over, then, our author's theory of the origination of life from inorganic matter as utterly untenable, we come to the next point in his system,--the most chimerical of all,--the gradual development of the higher orders of being out of those next beneath them in the scale. It is not pretended, that there is _any known instance_ of the transmutation of species, or of the evolution, in the ordinary way, of any being specifically different from its parents. The same animal, indeed, may pass through different grades of development; but these changes affect only the individual, not the race. The progeny of this animal must begin at the same point where its parent did, and run precisely the same cycle. The tadpole becomes a frog, but the young of that frog are tadpoles; the worm becomes a winged insect, but the eggs of that insect are hatched into nothing but worms. These changes in the life of the individual, like the successive periods of the embryotic state, of infancy, and manhood in the human being, are perfectly consistent with persistence of type in the race, and do not indicate even the possibility that a new species may be developed out of an old one. On the contrary, the germ must be considered as _potentially_ equivalent to the whole future being, for it is invariably developed into that being. If there be any one fact unquestionably established by observation, it is that each species invariably produces its like. "All the phenomena," says Mueller, "at present observed in the animal kingdom, seem to prove that the species were originally created distinct, and independent of each other. There is no remote possibility of one species being produced from another."

The doctrine of our author, then, is confessedly a pure hypothesis, and, as such, it might be summarily dismissed into the region of cloud-land and dreams, where it had its origin. The burden of proof is upon him, and as he has failed to produce a single instance in which his theory is exemplified, he may be rightfully debarred the privilege of discussion. But waiving this point, if we look into the grounds of his conjecture, we find bold assumptions more than once substituted for the plain statement of facts, which would destroy every shade of credibility in his doctrine. True, there is an appearance, both in the animal and vegetable kingdoms, of an ascending scale of being, from simply organized forms and imperfect developments up to the complex arrangements and nice adaptations of the advanced tribes. But the progress is not regular, nor are the intervals of constant length. The line is often broken and doubled, and, in fact, the individuals are far more naturally arranged in a number of parallel lines, beginning successively at a somewhat lower point, than in a single series. Man, of course, is placed at the head of the animal tribes; but the interval which separates him from the chimpanzee cannot easily be cleared at one bound. He forms but one genus, and that genus is the only one of its order. But even if the line of gradation were single and perfect, the fact would be of no service to the hypothesis we are now considering; for the interval between two species most nearly allied to each other seems to be quite as impassable as the broadest gulf of separation.

The point chiefly relied upon to show the credibility of this doctrine is the fact, according to our author, that the higher animals pass through a series of changes resembling the permanent forms of the lower tribes. The first form of man himself "is that which is permanent in the animalcule"; and thence he comes to resemble successively a fish, a reptile, a bird, and the lower mammifers, before he attains his specific maturity. It is held, then, that a premature birth from an animal of a higher kind might have instituted a new race of a lower type; and that a birth unusually delayed, permitting an embryo to be still farther advanced in the line of organization, might have created a new species of a higher order than the parent. Here, every thing depends on the _absolute identity_ of the germs of all animals, in the lower stages of their growth. General resemblances and analogies are of no weight whatever; the essential internal organization of the ova of different species must be the same; otherwise, however ripened into a mature being, whether the birth be advanced or postponed, the individual must still belong to its parents' species, of which it possesses the distinctive peculiarity. Now, this point of _the identity of germs is a mere assumption_; not only is it destitute of proof,--the whole evidence is against it. There is a degree of outward resemblance, but there is no sameness. When we trace the origin of life back to the remotest point to which our powers of observation extend, when we come to microscopic vesicles that can be discerned only by the highest magnifiers, general similarity of outward shape is all that can be predicated of them. The specific differences lie below this general resemblance of outward form; we cannot discern them, but we _know_ that they must exist, and that they are _essential_ differences, for each one of these vesicles is invariably developed, if at all, into an individual of the species to which its parent belongs. The germinal vesicles of a tree and a quadruped are somewhat alike, outwardly; so, to the hen's eyes, there is no difference between her own eggs and the duck's eggs which the farmer's wife has put into her nest. But when she has hatched her brood, part of them are found to be web-footed, and these, to her great astonishment and distress, immediately take to the water. Our author commits the same blunder as the poor hen. This want of consciousness that he has got to the end of his tether, this inability to believe that any difference can exist where he is not able to see it, though it is invariably indicated by future consequent differences of the most striking nature, is perfectly characteristic of the rash theorist in science.

The assertion, that man's "first form _is_ that which is permanent in the animalcule,"--even if we do not look to the potentiality of development into a higher being, which experience shows to exist in the human germ, but not in the infusorial,--is a positive misstatement. The lowest monad has a mouth and means for propagating its kind, which do not belong to the primitive ovum of any higher animal. About the succeeding stages in the growth of the embryo our author's language is more cautious. He only says, that they _resemble_, or _typify_, some of the lower orders of being; and this is virtually admitting a specific difference, and giving up his own theory for all the conditions posterior to that of the germ. The brain and heart of the embryo successively _resemble_ the corresponding organs in a fish, a reptile, a bird, and a quadruped; but they are not identical, _even in outward appearance_, with those organs. Of course, if arrested at any stage of its growth, and prematurely born, the embryo would not be one of the lower animals, but only something resembling it in outward shape; and conversely, if it were possible for the birth of a bird to be delayed till it had reached a higher stage of development in the same line in which it was proceeding, it would not become a quadruped, but it would be an anomalous creature somewhat like one. Consequently, no one species now on the earth can have been evolved out of any other existing race; because the germs of any two, at a very early stage in their history, according to our author's own confession, are specifically unlike.

To avoid this difficulty, he is driven to a further supposition, still more gratuitous and improbable; namely, that the germ destined to become one of a different race from its parents, having advanced along its usual line of development so far as that line coincides with the one belonging to the new species, there diverges, and follows a different path up to the period of its birth into a new creature; that is, the embryo of a reptile, having grown for a certain time as if it were to be a reptile, suddenly turns aside, like a young man changing his mind about the choice of a profession, and for the rest of its foetal life follows the proper line of progress in order to be developed into a bird. This is mere dreaming, and reminds one only of the wonderful transformations effected by enchantment in an Arabian tale. We might just as plausibly suppose, that the reptile, after it became mature, was suddenly transformed into a bird, as that it underwent this change before it was hatched. All the evidence attainable goes to show, that the law of development is as immutable before as after birth, the several stages of progress succeeding each other in a constant order, and affecting the individual only, not the race. A young monkey is no more likely to be transmuted into a man than an old one; nor is such a metamorphosis at all more probable in the course of its foetal life.

The view we have now obtained of the specific differences between distinct races of being at separate periods of their existence is precisely what might have been anticipated from the law of gradual development, which holds throughout the organic kingdoms. Between two mature animals, these differences are perfectly obvious and well marked. As we go a step back in their history, the distinction becomes a little more obscure; two worms may resemble each other very closely, though the two winged insects subsequently produced from them may be very unlike. Receding still farther, some of these specific differences may entirely disappear, the organs or parts which should exhibit them being not yet developed. And when we come to the primitive germs, so minute as to be visible only through the microscope, no outward distinction, perhaps, is any longer perceptible, and the radical difference of their internal organization is indicated only by the fact, to be verified by subsequent observation, that the two are invariably developed into perfectly distinct animals, belonging respectively to the same races with their parents. A theorist, whose whole system is based upon the invariable operation of natural agencies, cannot reasonably object to this conclusion.

That our statements in the course of this argument may not appear of the same questionable character as those advanced by our author, we will fortify them with a few brief citations from a work of such unquestionable authority as the Lectures of Professor Owen.