Popular Science Monthly/Volume 15/October 1879/Micro-Organisms and their Effects in Nature
|MICRO-ORGANISMS AND THEIR EFFECTS IN NATURE.|
By WILLIAM S. BARNARD, Ph. D.,
PROFESSOR OF INVERTEBRATE ZOÖLOGY IN CORNELL UNIVERSITY.
WHAT is too small to be seen, people are generally apt to regard with contempt or indifference, as of no practical consequence. This is one of the grossest of popular errors. There is not only a profound scientific interest in the realm of microscopic life, which is every day becoming deeper as its organisms are viewed from the standpoint of evolution, but they have a significance in the economy of nature, a usefulness to man, and a value in the industrial arts, of which but few glimpses have as yet been popularly obtained. To the inquiry, Of what service are those swarms of infinitesimal objects which are revealed only through the microscope? do they subserve any other purpose than to amuse infatuated microscopists?—the reply is, that their operations in nature are on a grand and imposing scale, and that their influence on man and other organisms, as well as on the air, the water, and the solid earth, is nothing less than enormous. Although we do not see these infinitesimal creatures at work, their proceedings are none the less real; and though their operations are infinitesimal, the aggregate results are vast and in the highest degree important. It may be shown—1. That, as food, they feed a greater number of beings than any other kind of organisms; 2. That, as scavengers, they eat more refuse than any other group of organisms; 3. That, despite their minuteness, their fossil remains are much greater in bulk and of far more consequence than those of large quadrupeds and serpent-like monsters, such as the mastodon, megatherium, plesiosaurus, ichthyosaurus, etc.; 4. That, as builders, they have produced immense structures, which far surpass in size all the colossal works of man. The evidence of these statements will be presently given; but meantime it may be remarked that such grand results redeem the study of microscopical objects from that pettiness which is often imputed to it.
But not alone because of their stupendous effects are these invisible creatures entitled to our attention. It is in the simplest and smallest creatures that we find the alphabet of the science of life. The rudimentary objects of biology are invisible; and the language of the science could never have been acquired except by first learning its A, B, C with the microscope. It is by the study of the lowest elementary forms of life that we become enabled to comprehend its higher and more complex forms, and we never could have done it otherwise. The anatomy and physiology of our own bodily structures have their roots in the invisible. The grand chain-work of relations that binds all things in order thus loses itself at one extreme in the infinitely great, and at the other in the infinitely small. Embryology, the playground of evolution, shows us microscopic embryos like adult micro-forms as necessary links in the unity of natural phenomena, so that the relationship of living things can only be comprehended by a study of the minutest objects. I do not, however, propose here to enlarge upon this aspect of the subject, but simply to offer a few illustrations of the importance of these micro-organisms.
Let us first consider the relations of microscopic animals to the crust of the earth, and notice what they have had to do with its formation and constitution. From their low grade of organization they are naturally supposed to have been the earliest creatures on our globe, and there is evidence in favor of this. In ancient geological ages, in whose rocks they are scarce, or hardly to be found at all as fossils, there lived numerous worms, mollusks, etc., which could not have subsisted without them as food. We may conclude, with some degree of certainty, that they were almost as plentiful then as now, probably more so; but we could not expect these delicate and minute objects to remain preserved until the present, to have withstood the metamorphoses of the very rocks in which they were imbedded. On this account they are exceedingly rare in the oldest formations, while the shells of various kinds are extremely numerous in modern rocks and earth. Still, the earliest fossil known, the Eozoön Canadense, the organic nature of which was formerly questioned, but now seems certain, belongs to the Azoic rocks. This determination of life in what was formerly regarded as the Azoic or lifeless age, has necessitated the establishment of an age of Dawn-life, hence named Eozoic. Life in Azoic time was also inferred from its immense quantities of carbon and of graphite, the most ancient deposits of which might be of organic origin. But aside from the Eozoön fossils, we appear to have further positive evidence of life in rhizopod fossils of Stromatopore structure, as discovered in the so-called green-stones of the Huronian, as well as in the great bog-ore deposits, which were evidently formed, then as now, through the agency of swampy vegetation.
It now seems most likely that flints, called silicic rocks, because they contain so much of the glass-substance known as silica, were largely produced from silicic organic remains, and the correctness of this view is strongly sustained by the microscope discovering in most flinty masses the crystalline needles of sponges, incasements of diatoms, capsules of infusorians, or spheroid frames of rhizopods. The silica which percolates and hardens petrified wood and other fossils may have originated chiefly from organic structures. Also, we find in chalk the molds of the silicic parts of animals, but the silica is dissolved out and gone.
The greatest use of those animalcules which have the body of plasma incased by a cell-membrane, and are called infusorians, will be pointed out further on, yet their influence on the crust of our globe must be noticed here; for a few of these bear shells and hence are found in a petrified state. Their fragmentary shells almost compose the flint rocks at Delitzsch, near Leipsic, Saxony, while some of the living sorts occur as fossils in the coal and chalk formations. Many green-sand rocks, even as far down as the Silurian, consist mainly of similar silicic shells, or the nuclei or molds of their chambers. The whetstones so extensively manufactured from the lower green-sand stone in the Black-Down Hills of England, have probably derived their useful qualities from them. Also, the silicic polishing-stone, called tripoli, or Polirschiefer, in Germany, not only contains such shells, but is entirely composed of them. This substance is used chiefly as a powder for polishing metals and stones. Infusorial formations of similar character are found at Cassel, Planitz, and Bilin. The layer at Bilin, in Bohemia, is fourteen feet thick, and Ehrenberghas estimated that it contains 41,000,000,000 shells in every cubic inch, while all are united and imbedded by an amorphous silicic substance forming compact masses of rock. At Agea, in Bohemia, there is another deposit two miles long, with an average thickness of twenty-eight feet. Its upper layer is about ten feet thick, and consists wholly of such shells; while the lower eighteen feet is a dense mixture of these with a fine granular substance. Other similar deposits appear in many parts of the world.
The many silicic clays owe their peculiar characters to the microscopic fossils they have contained. The sands and mergel of Sienna and Coroncina, in Italy, imbed great quantities. The lanceolets, the lowest of vertebrates, the mud-eating fishes, and the dirt-eaters among men, subsist chiefly from these tiny organisms, for the so-called "edible earths" and "infusorial earths" are made up largely of, and owe their nutritive qualities to, the remains of microscopic animals. These earths are eaten in times of need by the Lapps and Tungusians. They are likewise used in South America, in New Caledonia, Kurdistan, in China, and in some of our own Southern States. The "bread-stone" of China belongs to this kind of food. On the shores of a lake near Uranea, in Sweden, there is a large deposit of infusorial powder called Bergmehl (mountain-meal), which is mixed with flour and eaten. It consists almost entirely of microscopic shells.
The animalcules of plasma without a cover of cell-membrane are known as rhizopods, or root-footed animals. These have been of the greatest benefit in geological history. Those which have a central spore case are called radiolarians, and generally bear beautiful spheroid, radiate, silicic frames, which have assisted largely in producing great flinty deposits in the depths of the sea, constructing extensive masses of rock. There is no doubt that they helped greatly in the formation of the silicic rocks of Virginia, the Nicobar Islands, Sicily, Barbadoes, etc. Indeed, this latter island consists almost entirely of their remains, and two hundred and thirty-two kinds have been described on it alone. Also the barren rocks, twenty feet thick, on which the city of Richmond, Virginia, stands, consist mainly of their discoid shells.
Other rhizopods, called foraminifers, produce porous, calcareous incasements for themselves and help form limestone rocks.
Surprising as it may sound, it is nevertheless true that substantially the rhizopods built the temples and mammoth pyramids of Egypt and the stone walls of Vienna and Paris, for the very rocks of these structures, as well as those which surround the Mediterranean Sea and extend thence to the Himalayan Mountains, are chiefly built up by their infinitely numerous perforated shells. There are extensive limestone formations, which have resulted mainly from their remains, and some of these bear their names, as the miliolithic, of the Paris basin; that of the Vienna basin; the alveolithic, of western France; and the nummulithic, of the Mediterranean. Limestones composed chiefly, sometimes entirely, of their shells, appear in the Grob-Kalk of Gentilly and in very many other localities, also forming a broad belt along both sides of the Mediterranean Sea and eastward therefrom, sometimes hundreds of feet in thickness.
But what is still more astonishing is the fact that the whole geological formation known as the cretaceous or chalk has been produced almost entirely by their porous shells—that the immense chalk cliffs and downs along the English Channel and elsewhere have resulted from masses of their shells, and that they thus bear the same relation to the Cretaceous or Chalk as do plants to the Carboniferous or Coal age. The very dust of those chalky regions was once alive! Of course, many other kinds of organisms helped to some extent in the formation of cretaceous deposits, but the great bulk was undoubtedly of rhizopod origin. Standing at Dieppe, France, beneath the immense chalk cliffs of the English Channel, one can hardly realize that these beds of solid chalk, hundreds of feet in thickness, are the produce of such diminutive beings. But when we reflect that the chalk is five hundred and thirty-five feet high at Beachy Head, and five hundred feet at Wendover Hill, that it has been bored into five hundred and ten feet at Diss, in Norfolk, and that its average thickness has been estimated by reliable geologists, such as De la Bêche and others, at about seven hundred feet, while it extends through all the northern part of France as far south as Aix-la-Chapelle, thence northward to Denmark and through the south part of England to the Isle of Wight; and that its outcroppings have been traced from the north of Ireland to the south of France and eastward to the borders of Asia Minor, while a belt of cretaceous deposits extends around the earth just north of the equator, and numerous other chalk regions occur, like that reaching from Terra del Fuego to New Granada, in South America, besides those in our own country—very extensive in the Western, less so in the Southern States—we begin to perceive in what overwhelming quantities these organisms have existed, and what a stupendous work they have performed. The microscopic animals of the Cretaceous may be individually insignificant, but en masse they are certainly far more important than such larger fossils as the mosasaurus, pterodactylus, iguanodon, ichthyosaurus, and species of large fossil turtles of the same age, or the elephant-like mastodons and ponderous, sloth-like megatheriums of more modern date. The microscopic shells, which chalk contains, are 'mostly in a fragmentary condition, yet plenty are entire enough to be readily identified, and the number of different kinds (species) involved was very great, for about three hundred species have been described. Twenty of these species are still living and more or less actively engaged, along with other living species, in the construction of modern chalk, or the chalk-mud of the Atlantic basin. Here in the bottom of the sea we have chalk in the actual process of formation to-day. It was long since said by Dr. Mantell that "chalk forms such an assemblage of sedimentary deposits as would probably be presented to observation if a mass of the bed of the Atlantic two thousand feet in thickness were elevated above the waters and became dry land; the only essential difference would be the generic and specific characters of the imbedded animal and vegetable remains," and this view has lately been substantiated by the deep-sea investigations of English naturalists. Wyville Thomson says: "There can be no doubt whatever that we have forming at the bottom of the present ocean a vast sheet of rock which very closely resembles chalk; and there can be as little doubt that the old chalk, the Cretaceous formation, which in some parts of England has been subjected to enormous denudation, and which is overlaid by the beds of the Tertiary series, was produced in the same manner and under closely similar circumstances"; and he also thinks it is "probable that in the deeper parts of the Atlantic a deposit, differing possibly from time to time in composition, but always of the same general character, might have been accumulating continuously from the Cretaceous, or even earlier periods, to the present day." What enormous swarms and successive generations of rhizopods have existed, to effect such amazing results! Were all the extinct chalk animals resurrected at once, they would envelop the earth as did the primitive waters before the land was apart from the sea; we should have an ocean of protoplasm filled with their shells. Figuier truly says: "With these microscopic animals Nature has worked wonders in geological times; nor have those wonders ceased in our days."
Their diminutive size, marvelous reproductive capacity, and tenacity of life, together with the readiness with which they adapt themselves to new and various conditions of existence, not only have insured them a wide distribution in space, but also have enabled them to survive the destructive causes which exterminated higher forms through long and successive ages of geological time. Among about one hundred and twenty-five kinds (genera) of shelled, root-footed animals, only about fifteen are not fossil. Of the one hundred and ten species of those with perforated shells now living in the Atlantic chalk-ooze, the number of species common to it and the various geological formations in England is estimated as fifty-three with the crag, twenty-eight with the London clay, nineteen with the chalk, seven with the Rhsetic and Upper Trias, one with the Permian, and one with the Carboniferous. The survival of so many species in the group is a striking testimony against the theory that the species of each geological division of time ended in a totally demolishing and exterminating catastrophe. The links in their chain are small but numerous, continuously uniting the organic life of remote ages with that of to-day.
At present the immense numbers of their shells on some shores is remarkable; indeed, the sands of some localities are largely composed of them. D'Orbigny obtained 3,800,000 porous shells from a single ounce of sand on the shores of the Antilles. According to Soldani, one ounce of sand from Rimini, on the Adriatic, yields 6,000 shells. This scientist described and figured a great number of these in Italy, publishing an elaborate folio work with 228 copperplate illustrations, and then destroyed the whole edition a few days afterward, because he could find only six purchasers of the work, to the preparation of which he had devoted twenty years of his life! These organisms were as poorly appreciated then as now. Max Shultze reports that he has separated 1,500,000 specimens from one ounce of sifted sand from the coasts of Italy, near Mola di Gaeta. Also the deep-sea sands are in great part made up of their shells. In most of these the perforated forms abound, but in many localities the silicic symmetrical frames are most numerous. Until recently the great depths of the ocean were supposed to be dark, barren wastes; that the lack of oxygen, with the immense pressure of water from above, rendered these abysses impenetrable and uninhabitable. But the success of modern deep-sea soundings, particularly in the region of the Atlantic cable, has shown that the Atlantic ooze or chalk-mud, of which the ocean-bed is so largely composed, is literally alive with protoplasmic animalcules, whose innumerable shells and calcareous deposits give to this ooze its peculiar character, and are virtually constructing beds of chalk. These and other facts have led some of our best authorities to believe that the formation of chalk has been a continuous process from the Cretaceous time to the present.
In their geographical distribution most have an extremely wide range, and great numbers of species are cosmopolitan in their occurrence, yet there is a general uniformity of the conditions under which they exist. For example, globigerina appears often in such great depths of the ocean that the temperature of its habitat hardly varies with the seasons, or even for different zones, while the same species under different conditions of depth, temperature, etc., does show very strong varieties, which are sometimes so markedly distinct as to be accounted different species and genera, as has often been asserted by Carpenter, Williamson, and others. Professor Carpenter also states that Messrs. Parker and Jones became so familiar with the geographical variations of the species of perforated shells, that they could judge from the appearance of a specimen whence it came.
The infusorians belong chiefly to the fresh water, being plentiful in all lakes, ponds, swamps, rivers, and smaller streams, while only a few are marine; contrariwise, the rhizopods are mostly found in the seas, a small number inhabiting fresh waters. The rhizopods also serve an important function in the depths of the sea by setting free in the water large supplies of carbonic and phosphoric acids. Certain infusorian lash-swimmers (noctiluca, etc.) sometimes make the ocean look red or bloody by day and illumine it with phosphorescence at night. This is often observed in the Red Sea, in the Gulf of Guinea, off the north of France, on the Peruvian coasts, and in the Gulf of California, which on this account was called Mar Vermijo, or Vermilion Sea, by the early Spanish navigators.
With few exceptions, microscopic beings possess the power of moving from place to place, although many enjoy this freedom for only a part of their lifetime, and then become adherent or attached to foreign bodies for the rest of their existence. But even with the most rapid, free swimming forms, so little distance can be accomplished in their almost momentary lives, that their voluntary progressions can have little or no effect on their geographical distribution. In this they are creatures of chance or circumstance. Multiplying in myriads, and being too small and weak to resist the elements, they are constantly swept about in currents of water or air, and in the moisture on the surfaces of moving animals, etc. Well-authenticated observations show that with the evaporation of ponds and other waters containing swarms of these little animals, many encyst themselves within delicate capsules formed of an exudation, which hardens the body-surface; they then dry up and become as particles of dust, which are wafted from place to place by the winds, and for weeks or months may lie in the mud, dust, or snow, on hay, moss, branches of trees, etc. Others decompose, but leave behind their germs, which are distributed in the same way. By these means they are scattered everywhere, and those which chance to fall into favorable situations survive and produce swarms of progeny, while others, falling on bad ground, perish. Thus they are ready to do their appointed work, whenever and wherever it is needed. It is commonly thought that pure drinking-water is filled with these microscopic creatures, and it is sometimes said that they constitute the life of the water, while in their absence it becomes dead, stagnant, and often slimy, green, and unfit for use. All this is the opposite of the facts. Pure water is not inhabited by organisms; on the contrary, stagnant water or impure water alone affords them subsistence. They hasten the destruction of dead animal and vegetable matters the water may contain, causing for the time being an infusion or fermentation, which results finally in the purification of the liquid in question.
The bodily corruption in diseases, whether contagious or not, is not caused alone by the swarms of infesting organisms associated therewith, but is simply their cause, a sustenance for them, itself making their existence and multiplication possible.
The unaccounted-for readiness of these animalcules to spring up wherever decaying organic matter existed, first suggested the name infusoria, and led to the early false opinions that they were generated by the decomposition and fermentation of organic bodies, and to the modern reformed theory of spontaneous generation.
Strangely seeming, yet true, stagnation, death, decay, are replete with life when viewed through lenses, so that it has become a scientific doctrine that all organic decomposition and fermentation is assisted and sustained by these tiny creatures. Hence we may regard them as the most important scavengers of earth, water, and air.
While their devouring work is as a "bottling up" of injurious and infectious matters, thus purifying our world, the substances their little bodies may contain and their parasitic action when inoculated into the bodies of higher living organisms by contact, inhalation, eating, etc., render some kinds extremely dangerous as conveyers of the various contagious diseases, hence to be strenuously avoided by strict cleanliness and rigid hygienic measures of every kind. Such knowledge has done much toward inducing modern purity, and has led to our recently improved treatment of wounds and sores by the antiseptic method, whereby many benefits result and great numbers of lives are saved.