Views of the microscopic world : designed for general reading, and as a hand-book for classes in natural science / by John Brocklesby.

  • Brocklesby, John, 1811-1889.
Date:
1851
    sorial animalcules exist in countless numbers—often swarming to such an extent, as even to color the element in which they live. One species tinges the water with a blood-red hue, another causes it to appear of an intensely vivid green ; while a bright orange hue indicates the presence of a diflferent species. They are likewise found in strong acids, and in the fluids contained in animal bodies and living plants, and have also been detected alive in moist earth, sixty feet below the surface of the soil. The broad rivers are their home, and far from shore, upon the tropic seas, the ocean swarms, for leagues, with their congregated myriads; and as the bark of the mariner nightly cuts the wave, the dazzhng track it leaves upon the waters,' and the fiery spray that flashes from its bows, tell of the presence of life enshrined within an infinity of living atoms. Nor is the bed of the ocean without its minute inhabitants ; for the mud brought up by the deep sea-lead, from the depth of sixteen hundred feet, is full of organic life. There is also every reason for believing, that the atmosphere abounds with the eggs of animalcules, as it does with the seeds of minute plants ; and that these germs, being inconceivably light, are raised by evaporation, and borne about by the winds in unseen clouds; ready to burst into life whenever a con- currence of favorable circumstances facilitates their development. Lifted at one time to the loftiest mountain tops, at another carried down to the lowest dells and deepest caverns ; they cross seas, sweep over continents, and interchange climes and seasons. In this manner are these invisible forms disseminated over every part of the world ; for wherever investigation's have been prosecuted, infu- sorial animalcules have been discovered. Through the patient and persevering labors of distinguished naturalists, no less than seven hundred and eighty-six different species of animalcules have been dis- tinctly recognised and delineated, and grouped into families and classes ; distin- guished from each other by their forms, manner of progression, habits, and modes of reproduction. One kind are beheld dwelling harmoniously together within a delicate transparent shell, which in one case assumes a spherical, and in others a quadrangular form ; the living globes with all their inhabitants, as if actuated by a single will, rolling in perfect freedom within the confines of a drop of water. And within each of these globes smaller globes are discerned, enjoy- ing their existence equally with those from which they are separated by the surrounding crystalHne sphere. Other infusoria possess the power of changing their forms at will, and in the space of a few minutes pass through a variety of curious and grotesque shapes. Another class shoot up in the form of beautiful shrubs, crowned with bell- shaped flowers, whose margins are encircled with a fringe of slender hairs ; but the flower-cups are living beings, and the mimic tree is instinct with vitality in every branch. At one moment, it is seen spreading outward and upward from the base, with all its living flowers in full expansion; and at the next, should danger threaten, every shoot suddenly contracts, and the whole group of animal- cules shrink down in spiral coils, into the smallest compass. The great variety of form possessed by these interesting objects, can only be fully conceived by ex-
    amining those works in which they are accurately delineated. In the great work of Dr. Ehrenberg, who has devoted his life to the study of animalcules, they are beheld in all their beautiful and singular proportions. This splendid volume, of foho size, contains sixty-four plates, filled with several hundred infusorial shapes, drawn and colored from nature. Some resemble globes, trumpets, stars, boats, and coins; others assume the forms of eels and serpents ; and many appear in the shape of fruits, necklaces, pitchers, wheels, flasks, cups, funnels, and fans. But the minuteness of these beings is no less surprising than the diversity of their forms. The Monad, the smallest of all known living creatures, swarms by myriads in a drop of water; for it has been computed that within this small space, no less than five hundred millions could be comprised ; and this calculation is not to be regarded as unworthy of confidence, inasmuch as the Monad is never found to attain a length greater than the twelve thousandth part of an inch. In a cubic-inch of a certain kind of mould, consisting entirely of animalcules, more than forty-one millions of distinct beings were estimated by Ehrenberg to exist; a fact which, when taken in connexion with others, of the same nature, render it highly probable, that the Hving beings of the microscopic world surpass in num- ber those which are visible to the naked eye. Structure.—The outer covering of infusorial animalcules is of two kinds; the first soft and yielding, resembling the skin of the leech and slug, and so far capable of expansion and contraction as to adapt itself to the state of the ani- malcule whether distended or not; the second presenting the appearance of a firm, transparent shell, yet possessing a flexibihty like horn. Those animalcules that are protected by the latter integument are termed loricated, from the Latin word lorica, a shell; while the name illoricaied or shelless, is assigned to those which are invested with the softer and more perishable covering. The materials that compose the shell vary in different species ; in many instances it consists entirely of flint, and in others of lime united with oxide of iron; in some cases it is combustible and in others not. In several kinds, the lorica, in the form of a jar or cylinder, entirely surrounds the animalcule, while in others it is shaped like a shield, and protects tlie hving atom to which it belongs, as the shell of the turtle defends its sluggish inhabitant from external danger. When the loricated infusoria die, their shells yet remain, uninjured for ages, and in several parts of the world have been discovered accumulated in such vast quantities as to form extensive deposits of marl, lime, and flint, of which we shall speak' more particularly hereafter. It was formerly believed, that the smaller species of animalcules were entirely destitute of external organs ; but such improvements have now been made in the construction of microscopes, and the organization of the living objects has been rendered so much more distinct, from the practice of feeding them on color- ed substances before examination, that this supposition has been shown to be entirely unfounded, even in the case of monads. These external organs vary in kind in diflferent animalcules, but the one which 2
    is the most remarkable, and is common to all Infusoria, is a slender filament like a hair, situated near the mouth, and from its striking resemblance to an eye-lash is known by the name of cilium, the Latin word for eye-lash. The cilium is employed by the animalcule for the purpose of motion, and also for that of procuring food. Using this member as an oar, the creature moves swiftly through the water, and so curious is the action of this propeller, that the very stroke which effects a progressive motion, causes at the same time a current to set towards the mouth of the animalcule, bearing its prey and food within its reach. In addition to the offices of the cilia* just described, they are supposed by some naturalists to be the principal instruments for respiration to the Infusorial world; inasmuch as similar appendages are found encirchng the gills or beard of the oyster and muscle, and other animals of the like nature. It is by means of the gills that these creatures inhale the air contained in the water, and the cilia by causing currents to flow towards these organs, furnish a continual supply of fresh air. According to Mantell, " recent discoveries have shown that cilia exist also in the internal organs of man and other vertebrated animals, and are agents by which many of the most important functions of the animal economy are per- formed." When an animalcule is examined, this delicate member easily eludes observa- tion, but if the creature is placed in a drop of water colored with indigo or car- mine, the little whirls and currents created by the action of the cilia are readily detected under the microscope ; and upon the evaporation of the water from the glass slide, a fine streak upon the surface indicatesats existence and position. These slender organs are variously arranged in different species of Infusoria. In some they are extended in rows throughout the entire length of the animal- cule, and in others are distributed over the whole surface of the body. Fringes of ciha encircle the mouths of some, while in many kinds, the circles of cilia forming into bands, surround certain projections issuing from the upper part of the body. Numerous species are furnished with only two of these filaments projecting from the mouth, and nearly equal to the body in length. The base of each cilium terminates in a bulb, and when the organ is in motion its point describes a circle, while the globular base simply rolls round upon the surface to which it is attached. An idea may be gained of this motion by holding the arm out stiffly and swinging it round, so as to describe a circle in the air with the point of a finger; the arm then corresponds to one of the cilia, and the ball of the shoulder-joint to the bulb upon which the cilium turns. The motion is doubtless performed by muscles, and Ehrenberg considers that he has not only discovered their existence in some of the larger Infusoria, but also the arrange- ment of the fibres that compose them. The bands and coronets of ciha, which encircle certain classes of animalcules, present when in motion a singular appearance. Though each organ is stationary and revolves only around its bulb, yet the combined action of the circular rows * Cilia, the plural of cilium.
    is such, that they appear to revolve together like a wheel upon its axle, and 80 complete is the illusion that the name of wheel-animalcules, or Rotatoria, is given to those which possess this peculiarity. Besides these organs, stiff hairs or bristles are found upon animalcules, which, unlike the cilia, are devoid of rotation, but serve as supports to the body, and also aid these living atoms in climbing. Animalcules are also found with hook- like projections extending from the under side of the body, which are capable of motion to some extent, but do not possess the pecuhar movement of the ciha. Many Infusoria are also endowed with another kind of member, that more com- pletely subserves the purpose of motion, and which they have the power of pro- truding or withdrawing at pleasure, as the snail extends and retracts its horns. These organs are soft, and by some species can be thrust out from every part of the body; while in others that are partially covered by a shell, they are confined to the uncovered portions. The power of extension possessed by Infusoria over these organs is much greater, in proportion to their size, than in the case of snails and animals of a similar nature. In those Infusoria that are gifted with the highest organization, as the wheel- bearing animalcules, there appears to be a member resembling a claw, by means of which they attach themselves firmly to any object within their grasp. The claw is appended to an extended portion of the body, resembling a foot. Classification.—Dr. Ehrenberg, to whom we are more indebted than to any- other observer, for our knowledge of Infusoria, divides this hving world into two great classes, distinguished from each other by their structure: viz., the Poly- gastrica* or many-stomached animalcule^ and the Rotatoriaf or wheel-animalcule. PoLTGASTRicA.—If au aulmalcule of this class is viewed by the microscope, a number of round spots within its body will be readily detected, which are often quite large compared with the size of the living atom. These spots are so many stomachs, connected together by a single tube, and forming the digestive appa- ratus of the creature. If the water around the animalcule is clear, the stomachs will appear more transparent than the rest of the body ; but if it is tinted with sap-green or carmine (which substances are usually employed) they will be seen more distinctly ; for the animalcule readily imbibes the colored fluid, and the stomachs from their transparency then appear of the same hue as the liquid;— while the tint of the more solid portions of the body remains unchanged. The number of stomachs varies in different species from four to upwards of two hundred. In the annexed cut a highly magnified view of a bell-shaped animalcule is presented, in which the stomachs and coronets of cilia are distinctly exhibited. None of this class of infusoria are more than the twelfth of an inch long, and the smallest species, when full grown, do not exceed in extent the thirty-six thous * From the Greek polus, many, and gaster, a stomach f From the Latin rota, a tvheel.
    andth part of an inch. Uniting, however, in infinite multitudes, the more minute kinds form various colored masses, several feet in length. The young of many- species are doubtless too minute to be visible even un- der the highest powers of the microscope. Most of the Polygastrica reside in fresh water, but many species inhabit the ocean. They are likewise found living in moist earth, in peat bogs, in animal fluids,- and in water in which astringent substances, such as bark, have been infused. It has even been supposed that from their extreme lightness some species may dwell in the moisture of the atmosphere, being driven about in unseen countless numbers, at the sport of every wind. One-half of the kinds composing this class are loricated, the other half illoricated; and from the former are derived those vast collections of minute shells, which often con- stitute for leagues a large portion of the surface of the earth; the enduring me- morials of innumerable beings which perished centuries ago. L BELL-SHAPITD ANIMALCULE. C. Cilia. S. The Stomachs. Figure Rotatoria.—The second class of Infusoria have received the appellation of Rotatoria, as has already been stated, from the circumstance that the circles of cilia which surround the upper part of the body of the animal appear when in motion to revolve like a wheel. The cilia are found upon no other portion of their body, while in the Poly- gastrica they are distributed over the entire surface. In some species the crowns of cilia con- sist of a single set, and in oth- ers several circular rows of dif- ferent forms are distinctly no- ticed. This class of Infusoria is endowed with a highly perfect- ed organization, and on account of their comparatively large size, some of them attaining a leno'th of one-thirtieth of an inch, both their external and internal structure are well re- vealed by the microscope. The Rotatoria possess a single sto- mach, and many kinds are furnished with jaws and teeth. aa. The Cilia, bb. The Eyes. c. The Jaws and Teeth. ^j^j^j^ together with Other parts will be particularly described hereafter, when treating of individual ani-