The fairy tales of science/The Invisible World
The Invisible World.
"Nor is the stream
Of purest crystal, nor the lucid air,
Though one transparent vacancy it seems,
Void of their unseen people."—Thomson
The revelations of the telescope are not more astounding than those of the microscope. The human eye can only range over a finite portion of the universe, but aided by these magic instruments its sphere of research is greatly augmented. The one familiarizes the mind with the rolling orbs of the infinitely distant world, while the other enables us to examine the marvellous inhabitants of that which is infinitely minute.
Single microscopes, in the form of glass globes containing water, were used by the ancients, and in course of time these crystal bubbles gave place to hemispheres of glass, and these in their turn to lenses. The compound microscope, consisting of two lenses placed at a distance, so that the one next the eye magnifies the enlarged image of any object placed in front of the other, was invented by a spectacle-maker at Middleburg, in Holland, about the year 1590. This Dutch microscope, rudely formed of two lenses and a wooden tube, was the germ of the beautiful and complex instrument of modern times. Let us now peep through this wondrous spy-glass into the invisible world.
In a single drop of stagnant water we may discover a world of marvellous creatures, whose eccentric forms baffle description. In some of these tiny monsters it is not easy to detect any definite shape, as their bodies are destitute of any solid support, and seem to be composed of gelatinous matter, which may take almost any figure. In others, there is still a considerable variety in the forms assumed by the same individual under different circumstances, but the prevailing shape can be recognised. In others, again, the body, although still unprotected by any firm envelope, appears to undergo little change in figure, except when affected by temporary pressure. But there are many that cannot be influenced even by pressure, their soft bodies being inclosed in coats of flinty mail. All these creatures move about in the water with great rapidity, yet they have neither arms, legs, nor fins. Their movements are performed by means of peculiar processes called cilia, which resemble minute hairs. So active are these cilia, and such restless little fellows are those to whom they belong, that it is impossible to conceive a more animated scene than that presented to the eye of the microscopic observer in the examination of a drop of water.
The waters of the earth teem with these minute forms of existence; but as their presence was first detected in certain infusions of vegetable matter, they were named Infusoria—a term which they have been allowed to retain, though it is now known that their sphere of existence embraces all the aqueous portions of the globe. We have said that their quaint forms baffle description; but we will endeavour to give the reader some idea, however inadequate, of one or two individuals of the infusorial race.
The smallest and the most active members of this immense family are the Monads, which so thickly populate the invisible world, that Ehrenberg has declared that a selected drop of water may actually contain as many as there are human beings upon the surface of the great globe itself! These minute creatures are always in motion, and may be seen bustling about in every part of the drop—to them a mighty sea—as though their health and happiness depended on constant exercise.
The little creatures, or rather the congeries of creatures, called the Volvox, and formerly known as the globe animalcule, is not the least remarkable of this group. It consists of a number of monads, invested by a common envelope, each individual maintaining in some mysterious way an organic connexion with its companions. It is not easy to understand how a number of distinct beings can move in such perfect unison as to be frequently mistaken for a single animalcule. Yet so it is; this group of monads rolls round and round the drop of water, with the peculiar revolving or spinning movement which has given rise to its distinctive appellation of volvox, just as if it were a simple being. Six or eight young volvoces may generally be seen through the transparent envelope, from which they make their escape when sufficiently developed to become the envelopes of new broods.
The Rotifera form a class even more interesting than the monads. The animals of this class have usually an elongated form, and are perfectly symmetrical on the two sides. Near the mouth we observe one or two rows of delicate cilia, which are frequently arranged in a circular manner; and when they are in motion, an appearance of revolving wheels is produced, from which the class derives its appellation. The common wheel animalcule was long a puzzle to philosophers, who were forced to invent many marvellous hypotheses to explain the motion of the pair of paddle-wheels with which this little creature is furnished. We must not always believe our own eyes—for the two little wheels on the anterior part of the body of this rotifer, which seem to be always turning round on their axes, are really stationary. The motion is now allowed to be an optical illusion produced by the motion of the two circular rows of cilia on the fore part of the body. These cilia lash the surrounding waters into a miniature whirlpool, into which innumerable animalcules are drawn, to be swallowed by the voracious rotifer, who is provided with a formidable set of crushing teeth, and a most efficient digestive apparatus. The movements of these strange animals are active and varied. Sometimes they will attach themselves by the tail to a fixed object, and set their cilia in motion to entrap unwary monads; then they will pack up their wheels and swim freely through the water, or crawl along a solid surface after the manner of a leech. Some of the rotifera may be completely dried up and preserved for an indefinite time, without the loss of their vitality. But put one of these withered animalcules in water, and in an hour's time you will see him return to life, though he may have been apparently dead for many years! The multiplication of the rotifera is extremely rapid, twenty-four hours being a sufficient period for an individual to be born, be developed, and to become itself a parent! The reader must not forget that all these wonderful facts are related of a living being not quite the thirty-sixth part of an inch in length—a mere speck in the visible world!
Let us pause for a moment in our examination, to reflect upon these marvellous revelations. How perfect are the works of the Divine Hand! Not long since we allowed our imagination to penetrate the unfathomable ocean of space, wherein "God's name is writ in worlds;" and now as we peep into a drop of water, we find in the structure of its marvellous inhabitants evidences of the same Almighty Wisdom that conceived the harmonious arrangement of the celestial orbs. It has been truly said, that the smallest living object in the world is in itself, and for the part it is destined to perform in nature, as perfect as the largest.
The plants of the invisible world outvie the animals in strangeness and beauty. We call them plants, though they are utterly unlike the vegetable forms of the visible world. All these beings are endowed with powers of motion, and were until quite recently regarded as animals. In nature there is no line of demarcation between the two organic kingdoms, and these moving plants seem to form the link which renders the chain of being complete. The Diatomaceœ, or diatoms, are by far the most abundant forms of microscopic vegetation, and we will therefore devote some space to their consideration. In shape, these beings resemble mathematical figures of minute dimensions, rather than vegetable organisms; and appear to us as living circles, ovals, polygons, triangles, and stars.
The movements of the diatoms are due to the cilia, or eyelashes, with which they are furnished; but it is a disputed point whether these cilia act in obedience to a will, or whether their motion is due to a physical force acting independently of any controlling power. Adopting the latter view of ciliary motion, a clever writer has compared the moving diatom to a little steamer with the fires lighted and the paddles going, but without a crew, a pilot, or a captain.
The distinguishing peculiarity of the Diatomaceœ is, that they possess a solid framework of flint, their vegetable matter being merely a delicate investing membrane. The trees of the forest, having passed through their successive stages of development, undergo the process of decay, their constituents being dissipated as invisible gases; but the tiny diatoms are indestructible, and their constantly accumulating skeletons are gradually being deposited in beds beneath the waters which cover three-fifths of the surface of this planet.
"At first," says a celebrated naturalist, "the effect produced by things so small—thousands of which might be contained in a drop, and millions packed together in a cubic inch—may appear of trifling moment, when speaking of so grand an operation as the deposition of submarine strata. But each moment has its value in the measurement of time, to whatever extent of ages the succession may be prolonged; so each of these atoms has a definite relation to space, and their constant production and deposition will at length result in mountains. The examination of the most ancient of the stratified rocks, and of all others in the ascending scale, and the investigation of deposits now in the course of formation, teach us that, from the first dawn of animated nature up to the present hour, this prolific family has never ceased its activity. England may boast that the sun never sets upon her empire; but here is an ocean-realm whose subjects are literally more numerous than the sands of the sea. We cannot count them by millions simply, but by hundreds of thousands of millions. Indeed, it is futile to speak of numbers in relation to things so uncountable. Extensive rocky strata, chains of hills, beds of marl, almost every description of soil, whether superficial or raised from a great depth, contain the remains of these little plants, in greater or less abundance. Some tracts of country are literally built up of their skeletons. No country is destitute of such monuments; and in some they constitute the leading features in the structure of the soil. The world is a vast catacomb of Diatomaceœ; nor is the growth of those old dwellers on the earth diminished in its latter days!"
Whether living or dead, diatoms are very beautiful objects under the microscope; but it is impossible to give in words a distinct idea of their complex forms and delicate markings. In the muddy waters of the Thames we meet with some lovely varieties. Amongst them we may find one or two which may be roughly compared with some familiar objects belonging to the visible world. A many-spoked wheel, divested of its felly, will give the reader some idea of a common diatom; but he must imagine the spokes to be formed of innumerable pieces joined together with the utmost nicety, and to be inserted in the nave with far greater regularity than that attainable by any human wheelwright. Yet this delicate wheel is formed of the hardest flint, and is so minute that its spokes are less than the three-hundredth part of an inch in length!
Another diatom has the appearance of a piece of lace edging, with crossing threads and oval openings arranged in a beautiful and perfectly regular pattern. Another resembles a chain of flat beads, or rather, an open bracelet formed of oblong tablets. This simile, however, is far from being perfect; for the living tablets of the diatom are neither strung upon threads, nor connected by hinges, but are joined in some inexplicable manner at their corners.
The boat-shaped diatoms, or Naviculœ, are perhaps the most beautiful of this minute family. One of them, an unnamed variety, has been thus described by an anonymous writer:—"The tiny bark is a boat of cut rock-crystal, fit to float across a sea of light; itself might almost be believed to be fashioned out of solidified light. The central line must be the keel; the translucent planking is clearly visible; and around the sides are cut symmetrical notches, to serve as rullocks for ethereal rowers to navigate this brilliant gondola." In Thames water, Naviculœexist in great abundance, the most common form being that of an Indian canoe, with a gracefully curved prow.
The flint which forms the skeleton of the diatom, and the armour of the animalcule, is withdrawn from its solution in the waters inhabited by these minute organisms by some mysterious operation of the vital force. So prolific are these tiny forms of life, that it has been estimated that a single animalcule can increase to such an extent during one month, that its entire descendants can form a bed of silica or flint twenty-five square miles in extent, and one foot and three-quarters thick! "As a parallel to Archimedes," says Bischof, "who declared he could move the earth if he had a lever long enough, we may say:—Give us a mailed animalcule, and with it we will in a short time separate all the carbonate of lime and silica from the ocean!"
This leads us to consider more minutely the part played by the animals and plants of the invisible world in the formation of the beds of rock which form the solid crust of our globe. Twenty years ago Professor Ehrenberg discovered a wonderful bed of earth which was almost entirely composed of living infusoria, and which extended to twenty, and, in some localities, even to sixty feet in depth. This formation is situated in Berlin, at a depth of about fifteen feet below the pavement of the city. How life is sustained in this subterranean world of infusoria is a mystery, since it is evident that the organisms cannot come in contact with any air except that which is contained in the water which percolates through the mass.
This discovery was followed by others equally astounding. A mass, more than twenty feet in thickness, of light silicious earth, was found at Ebsdorf, in Hanover, and, on examination by the microscope, it appeared that this earth consisted entirely of the minute shields of invisible infusoria. Again, the beds of silicious marls upon which the towns of Richmond and Petersburg, in Virginia, are built, are now known to be almost wholly made up of the skeletons of diatomacœe. The forms that predominate are elegant saucer-shaped shields, elaborately ornamented with hexagonal spots disposed in curves, and resembling the engine-turned sculpturing on a watch. They vary in size from the one-hundredth to the one-thousandth of an inch in diameter.
We need not carry our microscope out of England to discover the remains of infusoria in the earth's crust. The white chalk which underlies or forms the surface of the south-eastern part of England, is a mere aggregation of microscopic shell and corals, so minute that upwards of a million of the former are contained in a single cubic inch of this well-known substance. These little shells, which remind us of those of the nautili, are the calcareous envelopes of the animalcules termed foraminifera, which abound in modern seas, and are constantly contributing to the amount of sediment now forming in the bed of the ocean. The beautiful white stone called calcaire grossier, which furnishes the inhabitants of Paris with a cheap and inexhaustible supply of building material, has almost the same structure as chalk; and Professor Ansted has observed that the capital of France, as well as the towns and villages of the neighbouring departments, are almost entirely built of foraminifera.
These stupendous results produced by the agency of creatures that are separately invisible to the naked eye, direct our thoughts to the Creator who has thought fit to endow these living atoms with powers that render them such important instruments in effecting the changes in the earth's surface, which His infinite wisdom has planned.
Let us quit the infusoria and glance with our microscopic eye at some other marvellous objects belonging to the invisible world. If we look through our magic tube at the downy mould formed upon any decaying substance, a wonderful forest of delicate thread-like plants will be revealed. These beautiful fungi will be seen to multiply and grow, to swell and finally to burst, scattering their invisible spores into the surrounding air.
If we make use of our microscope to examine the eggs of insects we shall have cause to wonder at their elaborate carving and beautiful forms. It is impossible to convey to the reader an adequate idea of the elegant design and delicate sculpturing of some of these insect-eggs; few of which, be it observed, are what is commonly termed egg-shaped. It is impossible to account for the strange diversities of form in these egglets; thus, in the small and great peacock butterflies, which differ in little but size, the egg of the first is a cylinder with eight prominent ribs, while that of the latter is shaped like a Florence flask and has no ribs. Why the little peacock should escape from a barrel, and the big one from a bottle, is a problem as yet unsolved. Here are the eggs of four different members of the butterfly family. To the unaided eye they appear mere uninteresting dots, about the size of a pin's head, but if we examine them microscopically, we shall find that nature has spared no pains in decorating these minute objects. One of these eggs is an elegant turban, having a round button in the centre of the depressed crown; another is a very elaborate pound-cake; the third a fairy foot ball, covered with a network of extremely minute hexagonal meshes; and the fourth is a little spherical summer-house of rustic-work roofed with flat tiles. The last simile is a little strained, as it is not easy to imagine a rustic arbour shaped like a balloon, but we must remind the reader that we meet with forms in the invisible world that cannot be likened to any object that exists within the sphere of unaided vision. The smaller insects deposit eggs that are still more curious than those of the butterflies and moths. The egg of the lace-fly is like an unripe cherry with a long white transparent stem; that of the blowfly like a white cucumber with longitudinal stripes; and that deposited by the bug has been well compared to a circular game-pie with a standing crust, the lid of which is lifted when the young one makes its exit after hatching.
The microscope reveals many wonderful peculiarities of structure in the beings whose eggs we have just examined. The coloured dust of the butterfly's wing turns out to be feathery-scales of a tapering form, with deeply-cut notches at their broad end. The hairs of the bee are seen to be thickly beset with still finer hairs. The smallest fly is found to possess an elaborate pumping apparatus or trunk, compared with which the pumps constructed by man are clumsy and inefficient. The eyes of insects are composite, each visible eye being made up of thousands that are invisible; no less than twenty thousand of these minute organs have been detected by means of the microscope in the head of the hawk-moth. But our space is limited, and we dare not enter any further into the subject of insect anatomy.
The dust of the butterfly's wing is remarkable enough, but the fertilizing dust or pollen that covers the stamens of flowers, appears still more curious to the microscopic eye. Pollen varies greatly in different plants. An author, who seems to have a happy knack of finding similes for indescribable objects, says that the rose and poppy have pollen like grains of wheat magnified into semi-transparent weavers' shuttles; that of the mallow, he tells us, resembles cannon-balls covered with spikes; the fuchsia has pollen like bits of half-melted sticky sugar-candy, with which a small quantity of horsehair has become entangled; and the passion-flower has pollen grains resembling Chinese carved ivory balls.
The microscope has revealed strange little fissures and cavities in minerals, the latter containing fluids, groups of crystals, and floating balls. Even the diamond, topaz, garnet, and other precious stones, have these minute cavities.
Here we must stop, or our fairy-tale will wear out the patience of the reader. We have glanced at a few of the marvels of the invisible world through that wonderful spy-glass which science has recently brought to a high state of perfection, and which day by day adds to our knowledge of minute things. Our examination has necessarily been imperfect, for it would be an easier task to enumerate all the visible objects upon the face of the earth, than to describe the countless forms that exist in the invisible world.
- The term microscope is derived from two Greek words, the first signifying a small object, and the latter to see or examine.
- Doctor Harvey.
- Navicula hippocampus.
- Dr. Mantell.