Working Accessories.
Troughs—Live-cages—Compressors.
A glass plate with a ledge, and some pieces of thin glass, although applicable for many purposes, are specially designed for objects in fluid. Thus a drop of fluid containing the object sought for is placed upon the slide and covered by a piece of thin glass; or, the object being put upon the glass slide and the thin glass over it, the fluid is applied near one side, and runs under by capillary attraction.
Fig. 208.—Varley’s Live-box.
Troughs and Live-box.—These are made of various materials, glass, vulcanite, brass, &c., expressly for examining infusoria and live animals. They should be so constructed as to admit of the use of a medium power, a ½-inch at least, under the microscope. They should also admit of being easily cleaned and repaired when broken; matters rarely thought of by those who construct them. An early devised live-box (Varley’s, [Fig. 208]) consists of two circular pieces of brass tubing, one sliding over the other carrying a disc of glass and fitting over another glass with bevelled edges to prevent the fluid flowing away.
Fig. 209.—Ross’s Compressorium.
The Compressorium is used for similar purposes. By a graduated pressure the fluid is thinned out and a higher power can be employed for the examination of the object. Ross’s early compressorium consists of a plate of brass about three inches long, having in its centre a circle of glass like the bottom of the live-box. This piece of glass is set in a frame, B, which slides in and out so that it can be removed for the convenience of preparing any object upon it—under water if desirable. The upper movable part, D, is attached to a screw-motion at C; and at one end of the brass plate, A, which forms the bed of the instrument, is an upright piece of brass grooved so as to receive a vertical plate, to which a downward motion is given by a single fine screw, surrounded by a spiral spring, which elevates the plate as soon as the screw-pressure is removed.
Fig. 210.—Beck’s Parallel-plate Compressor.
Beck’s Parallel-plate Compressor ([Fig. 210]) affords a more exact means of regulating the pressure, and can be used for a variety of purposes. It is also easily cleaned.
Fig. 211.—Rousselet’s Compressorium.
Rousselet’s Compressorium ([Fig. 211]) is a very effective form for general use. It is so arranged that the student has perfect control over the pressure to which the specimen should be subjected. The cover-glass is large in comparison with that beneath; being bevelled causes evaporation to go on very slowly while the pressure between the two glass surfaces is kept perfectly parallel.
Botterill’s Live-trough ([Fig. 212]) consists of two brass plates screwed together by binding screws, and holding between them two plates of thin glass, which are maintained at a proper distance by inserting a semicircular flat disc of india-rubber.
Fig. 212.—Botterill’s Live-trough.
Fig. 213.—Glass Trough.
Glass troughs for chara and polypes (a sectional view of one shown at [Fig. 213]) are made of three pieces of glass, the bottom being a thick strip, and the front (a) of thinner glass than the back (b); the whole is cemented together with Jeffery’s marine-glue. The method adopted for confining objects near the front glass varies according to circumstances. The most convenient is to place in the trough a piece of glass wide enough to stand across diagonally, as at c; then, if the object be heavier than water, it will sink until stopped by the glass plate. At other times, when used to view chara, the diagonal plate may be made to press it close to the front by means of a wedge of glass or cork. When using the trough the microscope should be placed in a nearly horizontal position.
Fig. 214.—Weber’s Slip with Convex Cell for use as a Live-trough.
Fig. 215.—Current-slide Live-cell.
Cells for viewing living objects, and watching their movements, take many forms, usually determined by the makers for the purposes they are required to serve. The smaller glass troughs (Figs. 216, 216a) are made for examining the small infusoria, rotifers, &c., some of which take special forms, as the double or divided trough ([Fig. 217]) intended for viewing the circulation of the blood in the tail of a small fish, and at the same time keep up a supply of water and air.
Fig. 216.
Fig. 216a.
The Frog-plate consists of a strip of plate-glass, or wood, pierced with holes on either side, through which tapes are passed to secure the frog in its place. At the extreme end is a shallow glass trough, made to hold a sufficient quantity of water to keep the web of the foot moist while under examination. In this way a continuous view of the circulation of the blood of the animal is obtained.
Fig. 217.
Growing Cells have received more attention from those who devote attention to the lower forms of life, the construction of which, for the purpose of maintaining a continuous supply of fresh water to objects under observation, and for sustaining their vital energy for a long period, is of some importance. The employment of live-cells is resorted to by microscopists, as doubtless there is much to be discovered concerning the metamorphoses which some of the lower micro-organisms, both of plant and animal life, pass through.
Fig. 218.—Frog-plate.
Holman’s life slide consists of a 3 × 1 inch glass slide, with a deep oval cavity in the middle to receive the specimen for observation. A shallow oval is ground and polished around the deep cavity, forming a bevel. From this bevel a fine cut extends, to furnish fresh air to the living low forms of life which invariably seek the bevelled edge of the cavity, thus bringing them within reach of the highest powers. He also contrived a convenient form of “moist chamber,” or animalcule-cage ([Fig. 220]), for the purpose of studying the growth of minute organisms, without in any way disturbing them for a lengthened period. This is also found useful as a dry chamber for holding minute insects.
Fig. 219.—Holman’s Life Slide. Full size.
Fig. 220.—Holman’s Moist Chamber.
Zentmayer’s Holman Syphon Slide is used either as a hot or cold water cell. It should be deep enough to hold a small fish or newt, and retain it without any undue pressure. When in use it is only necessary to place the animal into it (as shown in [Fig. 221]), with some water, and secure it with a glass cover; then immerse the upper tube in a jar of water, while another, at a lower level, maintains a current. When the slide is on the stage of the microscope, one jar should stand on a lower level than the other, the slide being made the highest part of the syphon. The pressure of the atmosphere is sufficient to keep the cover-glass in its place.
The examination of the various kinds of infusorial life—rotifers, for instance—is facilitated by the addition of the smallest particle of colouring matter, either carmine or indigo. A small quantity of either of these colours should be rubbed up in a little water in a watch-glass, and a portion taken up on the point of a brush, and the brush run along the edge of the cover-glass; sufficient will be left behind to barely tinge the water with the colour, and this gradually distributes itself over the rotifers. Under the microscope this minute quantity will be seen like a rising cloud of dust, and as it approaches a rotifer it is whirled round in different curves, showing at once the action of its wonderfully rapid cilia. This colouring matter appears to be devoured, as it may be traced from the mouth to the digestive canal. Monads may be detected by this means, and the smaller forms of algæ, Euglena viridis and Protococcus pluvialis.
Fig. 221.—Holman’s Syphon Slide.
Dipping-tubes.—In dealing with infusorial or monad life it is convenient to keep a stock-bottle ready for their reception, and in a light favourable to health. When a live specimen is required for examination, the dipping-tube is brought into requisition. These tubes are open at both ends, and vary in length and diameter. Their ends should be nicely rounded off in the flame of a blow-pipe; in form either straight, or bent and drawn out to a fine point, as represented in [Fig. 222]. When any special specimen is required for examination, then one of the tubes must be passed down into the water, the upper orifice having been previously closed by the forefinger, and kept tightly pressed, until its lower orifice comes in contact with the object. On the finger being removed, the water rushes up and carries the creature sought for with it. The finger is once more replaced at the top of the tube; it is then lifted out, and the contents deposited in one or other of the glass cells described. Tubes with india-rubber covers can be had.
Fig. 222.—Dipping-tubes.
Fig. 223.—Stock-bottle.
Moist and Warm Stages.—In addition to the moist cells and chambers described it is often found necessary in working out the histories of minute organisms to keep them for some time under observation, and as far as possible in an undisturbed condition, and it is equally necessary to prevent evaporation of the water in which they are immersed. One of the best warm stages is that known as Maddox’s growing stage; this can be had of any optician. More elaborate adaptions are required for the study of special organisms, and for experimental research.
Fig. 224.—Bartley’s Warm Stage.
In that case Bartley’s Warm Stage ([Fig. 224]) is recommended. There are other forms of warm stages in use, many of an inexpensive kind and readily adaptable to any stage. Bartley’s has proved useful; it consists of a vessel, E, three parts filled with water and supported on a ring stand. This may be kept at any temperature by the small spirit-lamp, C; a syphon tube d conveys the warm water along f, and through the bent tubing which surrounds the object under observation on the stage, D, and then passes off through the open end, C, into the receptacle, B, placed to receive the overflow. Steam can be used for heating, or iced water for observing the effects of cold upon the organism.
A simple form of warm stage may be made of an oblong copper plate, two inches long by one wide, from one side of which a rod of the same material projects. The plate has a round aperture, the centre half an inch in diameter, and is fastened to an ordinary slide with sealing-wax. The drop or object to be examined is placed on a large-sized cover-glass and covered over with a smaller one. Olive oil or vaseline is painted round the edge of the smaller one to prevent evaporation, and the preparation is placed over the aperture in the plate. The slide bearing the copper plate is clamped to the stage of the microscope. The flame of the spirit-lamp is applied to the extremity of the rod, and the heat is conducted to the plate and thence transmitted to the specimen. In order that the temperature of the copper plate may be approximately that of the body, the lamp is so adjusted that a fragment of cacao butter and wax placed close to the preparation is melted.
Professors Stricker and Schäfer have constructed warm stages for accurate observations, and which fully answer every purpose.
Fig. 225.—Stricker’s Warm Stage.
Stricker’s Stage ([Fig. 225]) consists of a rectangular box with a central opening, C, permitting the passage of light through the specimen under examination. The water makes its exit and entrance at the side tubes B B′, and the temperature is indicated by a thermometer in front. In this apparatus either warm or cold water can be continuously used.
Fig. 226.—Schäfer’s Warm Stage.
Schäfer’s apparatus ([Fig. 226]) consists of a vessel filled with water (seen near the stage) which has been first boiled to expel the air, and then heated by means of a gas flame. The warm water ascends the india-rubber tubing to the brass box on the stage. The box is pierced by a tubular aperture to admit light to the object, and has an exit tube by which the cooled water from the stage returns by another piece of tubing to be reheated by the gas flame. There is a gas-regulator, by means of which any temperature can be maintained.