. The microscope; a simple handbook. Microscopes. 62 THE MICROSCOPE Culture plates. chess-board plate be used, then thirty-six squares, six each way, correspond to a cubic millimetre. The most convenient size to select wiU depend upon the class of object to be counted and the object glass that is used. Due to the alternate squares being tinted, a count can be made with much less eye-strain than with the ordinary hsemacytometer, and this method is preferred by some apart from the question of the cost of the apparatus. The preparation of culture plates and the methods of cultiva- tion will be fo
. The microscope; a simple handbook. Microscopes. 62 THE MICROSCOPE Culture plates. chess-board plate be used, then thirty-six squares, six each way, correspond to a cubic millimetre. The most convenient size to select wiU depend upon the class of object to be counted and the object glass that is used. Due to the alternate squares being tinted, a count can be made with much less eye-strain than with the ordinary hsemacytometer, and this method is preferred by some apart from the question of the cost of the apparatus. The preparation of culture plates and the methods of cultiva- tion will be found in text-books on bacteriology. They are large square plates covered on one surface with nutrient gelatine, upon which isolated colonies of bacteria are groAsdng. They should be examined with a low-power IJ-inch (32-mm.) object glass, the mechanical stage having been removed from the surface of the stage for the purpose. The required colonies having been recognised, a morsel of the gelatine can be removed with a platinum needle, while the colony is in the field of the microscope, and can be smeared on a cover glass. A drop of distilled water having been added, it can be spread out on the cover glass and examined in a living state with the high-power dark-ground illuminator or dried in a spirit flame, stained and moimted on a 3 X 1-inch slip with a drop of Canada balsam. Warm stage- A Warm stage is an apparatus for applying warmth to a speci- men under continuous observation. A simple form consists of an oblong copper plate 3x1 inches, from one side of which projects a long narrow strip and which has an aperture 1/2 inch diameter in the centre of the 3 X 1-inch portion. It is placed on the stage of the microscope and held like an ordinary 3x1 glass slip in such a posi- tion that the long strip projects in front of the microscope. A spirit lamp is placed under the far end of the projecting strip and adjusted so that its flame impinges on the strip, or is slightly to one side,
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