Volume 5 / Book 11 — DROPS OF WATER.

As all, or very nearly all, the animalcules found in water are invisible to the naked eye, no subject can be more interesting than that of these wonderful atoms, which, we have every reason to suppose, are by far the most numerous of those beings possessing life. The variety of form, the extraordinary construction, the rapid movement of some, the stationary life of others, and many other peculiarities, will prove subjects of interest and delight to the thinking mind. The one idea that a single drop of water may afford amusement and excite astonishment for hours to the investigator, is sufficient proof of the wonderful powers of the Creator in this minute portion of his works. These little creatures prove quite fascinating; and hour after hour will be spent in watching their habits and movements, till the powers of the student are exhausted. A good microscope, in fact, opens a new world to the possessor, a world of beings totally different from any thing we have been accustomed to see; and the substance of which they are composed is in general so transparent, that the internal structure is visible to the eye—even the act of digestion can be perceived, and the food traced from its entrance at the mouth to its passage into the internal cavities; the eggs, also, can be seen within the body. These and many other peculiarities have been discovered only by very patient investigation, and several naturalists, both English and foreign, have almost devoted their lives to the study; and let no one say it is a useless one, for whatever can help to prove the power and wisdom with which this world was created can not be time thrown away. To those who only use the microscope as an amusement (and it is a never-ending one), a short time occasionally is well bestowed on one of the most beautiful parts of the creation.

There are upward of seven hundred species of Infusoria known and described. These are of all shapes and forms, some even assuming a variety in themselves; many possess eyes, others have none; some move so rapidly that the eye can not follow them, and others are attached to various substances; some have very many stomachs, or internal sacs, and others have only one; others, again, form a compound mass, that is, many individuals live in the same transparent case, and some are so minute, that by the aid of the best microscopes they can not be clearly discerned. Many people are disgusted after viewing water through a microscope, and suppose that all water abounds in living creatures, and that, consequently, we drink them in myriads. This is an error: there are none, or very few, in spring water, and, as no one would think of drinking from a ditch or stagnant pool where plants abound, there is little to fear. If necessitated to partake of water abounding in life, the person is either ignorant of its state, or the want is so urgent that the thought does not occur; and even should it arise, these delicate transparent little atoms would not be perceived by the taste—this fear or disgust may therefore be dismissed. Many waters abound in the larvæ of gnats and other insects, and minute creatures of the crustaceous order, but these can generally be seen by the naked eye.

In all parts of the world, and in most waters where aquatic plants in a healthy state abound, these invisible creatures may be met with, and not only in stagnant pools, but in running streams and the broad ocean. Among water-plants these little beings find shelter and food; therefore, when water is brought from these localities, some of the vegetation peculiar to the pool or stream should be procured at the same time. They swarm among duckweed. Many are found also in clear shallow pools, particularly in the spring. When a pond is observed to have a stratum of dust on the surface, or a thin film, it will generally be found almost entirely composed of living creatures. This dust-like appearance consists nearly exclusively of species of the most beautiful colors, such as Pandorina, Gonium, &c. A shining film of various colors is also occasionally seen on standing water: this is composed of Infusoria; a red appearance being often given to water by some species, and by others a yellowish hue. Sheets of water often assume an intense green, from the presence of many of these minute bodies. Lakes have been known to change their color very mysteriously, and to have caused some alarm in the superstitious; but it is now known to arise from Infusoria, as they are attracted to the surface by the sun in the middle of the day, and descend as that luminary declines—thus the lake will be clear, morning and evening, and turbid, or of different colors, in the course of the day. If stalks of flowers are steeped for a few days in water, it will be found to swarm with life; even a few dead leaves, or a bit of dry hay, will produce the same effect. At first monads will appear; these will be succeeded by specimens of the genera Paramecium, Amoeba, and those of the class Rotatoria. I have tried these experiments, and always with success. If the infusion be kept a few weeks (particularly that formed with leaves), one peculiar kind of animalcule will swarm to a most astonishing degree, so that a drop will contain hundreds, so close together that they form quite a crowd, and yet all are in a state of activity, and feeding from the vegetable matter disengaged from the decaying leaves. They are not even confined to these localities, for lakes and rivers, the fluids found in animals and vegetables, strong acids, and also the briny ocean, are full of these interesting creatures. One kind of phosphorescence (an appearance which is so often observed by the seaside and at sea) is occasioned by some species; and, when we remember that this luminosity often extends for miles, we are lost in astonishment at the immensity of their numbers.

And here I may mention the evident use of these wonderful beings. They appear wherever decaying animal or vegetable substances are found in water, and are extremely useful in destroying what would otherwise taint the air with noxious gasses and smells. Minute algæ also assist in preserving the purity of the water in which they live; they serve as food, also, to animals higher in the scale of creation than themselves. Captain Sir James Ross, in his Antarctic Voyage, speaking of a small fish found by him in the South Seas, and stating by what means it and many others are fed, says, "All are eventually nourished and sustained by the minute infusorial animalcules, which we find filling the ocean with an inconceivable multitude of the minutest forms of organic life." We may infer from this, the immense importance of the Infusoria in the scale of existence, for although only remotely supporting the higher animals, yet the want of them would be greatly felt. Ehrenberg states, that a single drop of water may hold five hundred millions of the smallest animalcules. What, then, can be the population of a lake or of the ocean?

I have watched specimens of the genera Floscularia, Vorticella, and Stentor, for hours at a time, and they have never ceased to feed on minute portions of animal and vegetable substances, brought to them by the current they are enabled to make in the water; others eagerly pursue their prey, or feed on the decaying vegetable matter floating about: indeed, the appetite of these little creatures seems insatiable. Many genera have a strong chewing apparatus, like a mouth armed with teeth. All seem employed in the same way, though using different methods. Much decaying matter must thus be taken away by this insatiable, though miniature army, provided for the purpose. They, in their turn, afford sustenance to aquatic insects, which are again preyed on by fishes; and thus food is prepared for more highly organized animals, and lastly for man.

Animalcules have never been observed to rest, or at least to sleep; but this may be partly owing to the light necessarily used in viewing them, which forms an artificial sunlight, exciting their powers of motion: they may rest during darkness, when they can not be seen by us. Many are only attracted to the surface of the water by the light of the sun, and are difficult to be obtained on a dull day; they are, however, not much affected by cold or heat, for they are procurable in winter as in summer, though not in such profusion: they are found even under thick ice, and I have frequently broken, in severe frost, the frozen surface of a pond, and, inserting a bottle, have obtained some most interesting kinds. Many of the Polygastrica will bear a great degree of cold, even more so than those of the class Rotatoria, whose organization is of a higher order.

It has, I believe, been generally observed, that the more simple the organization of animals, the more retentive is the creature of life, and this is the case with these minute beings. The Rotifer vulgaris will even bear revivification several times. Dr. Carpenter relates that he tried the experiment six times with twelve specimens, and each time some were perfectly restored to animation. By allowing the drop of water which held them to evaporate, and at the end of twenty-four hours giving them a fresh supply, he succeeded six times in restoring some of them: at last two only were left, and these unfortunately he lost. Ehrenberg affirms, that if thoroughly desiccated they can not revive, but that they may remain in a lethargic condition if deprived of water for a certain time only. The same naturalist observes that when an animalcule is frozen with the water, it is surrounded by an exceedingly small portion which is unfrozen, occasioned probably by the animal heat of its body; but, should the cold be so great as to freeze this, the creature dies. Animal heat in such an atom! how marvelous! Yet they will bear a great degree of heat also. The same naturalist says, that the Polygastrica, will bear the temperature gradually raised to 120° of Fahrenheit, and some even to 200°, but if raised suddenly they die at 140°. Now, if we consider that water raised to 212° is boiling, we shall be as much astonished at their powers of enduring heat as cold. Sir James Ross, in his Antarctic Expedition, found upward of seventy species of Polygastrica with loricæ, or silicious shells, in fragments of ice.

It will, therefore, be seen, that animalcules are obtainable at all seasons, and in every place where there are ponds or pools of water; or they may be procured from water-butts, or by placing leaves, hay, or almost any vegetable substance in a little water, which has been previously found to have nothing living in it.