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.
