and also a finer pair, the latter with long narrow points; a stout and a fine pair of scissors, and a scalpel. It is well to have a straight pair of scissors, and also a pair curved on the flat (fig. 5.) It is convenient to have a pair of forceps like those shown in fig. 6 for lifting and applying a cover glass to a preparation, or like those in fig. 7 for holding a cover-glass on which a thin filin with bacteria is spread. 7. Camel-Hair Brushes, at least two, the smaller crow-size, and one somewhat larger. 8. A Razor, which is not to be hollow-ground. It must be kept very sharp, and stropped frequently. It is better to have one ground flat on one side. 9. Watch-Glasses.-Instead of the ordinary-sized glasses, the student should provide himself with at least four inches in diameter. 3 10. A Section-Lifter. This may be made by beating out the end of a piece of copper wire (inch thick) until a thin plate is formed. FIG. 6.-Cover-Glass Lifter. The plate is then bent at an angle to the stem. It is better, however, to purchase one made of German silver (fig. 8). 11. Drawing Materials. As great importance is attached in FIG. 7.-Cornet's Cover-Glass Forceps. this laboratory and in this course to making drawings of the microscopic objects, each student must provide himself with a drawing-book-a quarto, with unruled paper, and containing 150 pages or thereby, is sufficient. Suitable drawing-pencils, including an H.B., and a harder one, e.g., H.H.H.; both must be of a good quality of lead. After a sketch has been made in pencil, the sketches should be coloured. This may be done either with coloured pencils or water-colours. The latter are greatly to be preferred. 12. Slips of white bibulous paper, 3 inches by inch, to soak up any superfluous fluid, and to be used for irriga tion. For irrigation purposes use small triangular slips. 13. Small glass pipettes, which the student should make for himself by heating in a gas-flame and drawing out a piece of narrow glass-tubing at two places, close to each other, leaving a small part of the tube of the original width, which acts as the bulb of the pipette. Several may be made at a time, and their capillary ends sealed in the flame, and kept until they are required. 14. A pair of narrow glass rods drawn to a point to tease tissues in such metallic solutions as gold chloride or silver nitrate, which act on metallic instruments. 15. Labels for the slides.-It is well to have a large number of pieces of paper cut, 3 inches by 1 inch, as temporary labels, on which is written the name of the preparation. Each label is placed under its appropriate slide in a tray. These labels are merely temporary. This is specially desirable where the slides have to be " ringed," as in this process a permanent label is apt to be displaced or destroyed. In the case of balsam preparations, they may be labelled at once with the small square permanent labels. In every case the preparation should be labelled, FIG. 8. and the label should bear not only the name of the tissue or organ, but the direction of the section and the medium in which it is mounted, and, if desired, the date of mounting. Labels are now printed so cheaply, that for half-a-crown a student can have a thousand labels printed with his own name. Section Lifter. 16. Reagents. The student should also be provided with the following reagents, placed in a small wooden framework on the work-table. Only those reagents that are most frequently used need be provided for in the framework; the others can be supplied as required. Small bottles-two ounces or thereby-not too tall, and provided with a glass rod, are necessary. The glass rod has a bulge at the junction of its upper and middle thirds, and this bulge prevents it from falling into the bottle, and, at the same time, acts as stopper for the bottle. Failing this, a piece of glass rod passed through the cork will answer the purpose. (1.) Normal Saline, or 6 per cent. salt solution. Dissolve 6 grms. of pure common salt in 1000 cc. of water. As this fluid is apt to undergo change, it should not be kept too long. (2.) Glycerine (either pure or equal parts of glycerine and water). (5.) Dilute Acetic Acid (2 per cent.). (8.) Clove-Oil or Xylol.—This should be provided with a small brush fixed on the end of a wooden rod perforating the cork. 17. Other Apparatus is required, but in a well-equipped laboratory special articles are supplied as required; they are referred to in the context. They include a dissecting microscope, photophore, mounting block, warm stage, eye-piece micrometer, lamp, turntable, polarising apparatus, camera lucida, &c., &c. II.—THE MICROSCOPE AND ITS ACCESSORIES. 1. An account of the optical principles on which the microscope is constructed is purposely omitted. The compound microscope consists of a stand fixed to a heavy, usually horse-shoe shaped, foot. The stand (fig. 9) carries a stage to support the microscopic preparation, the mirror or arrangement for illuminating the object, together with the body tube; the latter consists of a long brass tube, or one tube telescoped into another. To the lower end of this tube is fixed a combination of lenses, constituting the lens or objective, while at its upper end is the eye-piece. 2. The tube is blackened inside, and to its lower end is screwed the objective, consisting usually of several lenses screwed together. By means of it a magnified inverted aerial image is produced in the body of the tube. The lenses on the objective should not be unscrewed. At least two objectives are required a low power and a high power. At the upper end of the tube is the ocular or eye-piece, composed of two plano-convex lenses, the one next the eye of the observer being called the eye-glass, the lower one the field-glass. The two lenses, with their convex surfaces downwards, are fixed in a brass tube which slips into the upper end of the tube of the microscope. 3. The tube itself is supported in a vertical position on the stand, so that it can be moved upwards and downwards vertically, to bring the objective near to the object, and thus bring the latter clearly into focus. This arrangement is termed the adjustment. The mode in which this is accomplished varies. In the cheaper microscopes the tube of the microscope is moved inside another tube fixed to the stand (fig. 9). This is done by means of the hand, while in the more expensive microscopes there is a rack-and-pinion movement for raising or depressing the tube (fig. 10). Usually there are two adjustments-one the coarse adjustment, whether it be by rotating one tube inside the other or by a rack-and-pinion movement; it is used to bring the outlines of the object dimly into focus. The other, the fine adjustment, is a fine screw, usually placed at the upper and back part of the pillar of the stand of the microscope. By it the object is brought accurately into focus. 4. The stand is provided with a horizontal solid table or stage, placed at a convenient height, and on which the object to be examined is placed. The stage consists of a flat plate of brass blackened on its under surface, or There are two clips of a glass plate fixed on a black-ground. which are used for fixing a preparation in a definite position on the stage. It is perforated by a circular aperture in its centre, into which can be fitted diaphragms of different sizes, or a blackened circular brass plate with holes of different sizes-from a pinhole to half an inch-rotates under the stage, so that the desired size of hole -or diaphragm-can be brought under the central aperture in the stage. The aperture in the stage must not be too small; it should be sufficiently large to enable a section of the spinal cord to be seen as a whole. A small aperture is used with high powers and a large aperture with low powers. In the more expensive, and in some of the cheaper microscopes also, the stand is provided. with a joint, so that the microscope can be inclined as shown in fig. 10. 5. Illumination of the Object.-Under the stage is placed a mirror, movable in all directions, and which is usually provided. with a flat and a concave surface. When it is available, diffuse light-never direct sunlight-reflected from a white cloud, and a northerly exposure are to be preferred. For ordinary illumination the concave side of the mirror is used. The light is reflected from it, and is transmitted through the hole in the stage, the object on the stage, and the tube of the microscope, to the eye of the observer. The flat mirror is used along with a sub-stage condenser (§ 10). 6. Direct and Oblique Illumination.-When the light is reflected from the concave mirror, it strikes the object nearly vertically; this is called direct or central illumination. But sometimes it is of importance to detect very fine variations on the surface of the object; then for this purpose oblique illumination is practised. This may be done by tilting the mirror slightly, so that the rays of light fall somewhat obliquely on the object. In this case there must be no small diaphragm in or under the stage. This may also be done in the more expensive microscopes by introducing a diaphragm which permits light to pass only at its sides, its centre being blocked. This is known as a central stop-diaphragm, which shuts off all the axial, and transmits only the marginal rays, causing what is called dark-ground illumination (fig. 12). use. 7. The Diaphragm, of which there are two forms in common The most common form is a blackened metallic plate--disc diaphragm-perforated with holes of different sizes, placed under the stage, and so arranged as to rotate on a pivot. The edge of the plate usually projects a little beyond the stage, so that it can be readily rotated by the finger, so as to bring the appropriate aperture under the hole in the stage. The diaphragm is usually provided with a slightly projecting pin, which gives a click when the hole in the diaphragm is exactly centred. Another form-cylindrical diaphragm-consists of a small brass cylinder, into which can be |