Why is the magnification of an oil lens larger than that of an ordinary objective lens?
Reasons why bacteria need to be fixed before staining in microbiological experiments:
1: Kill cells and make the dye easy to color.
Two: Make the bacteria adhere to the glass slide and not easily washed away by water.
When fixing, dry slowly. If you really want to speed up the process, you can dry it for a few times at a distance above the flame of an alcohol lamp. Do not dry the glass so that it heats up, otherwise it may destroy the bacterial life form.
Gram stain and microscopic observation of bacteria
Experimental principle
Principle of Gram staining: The different reactions of bacteria to Gram staining are due to the different composition and structure of their cell walls. The cell wall of Gram-positive bacteria is mainly a network of peptidoglycans. When treated with ethanol, the pore size of the network structure becomes smaller due to dehydration, and the permeability decreases, thereby causing the complex of crystal violet-iodine to form. The substance is not easily eluted and remains in the cells. After decolorization and counterstaining, the blue-purple color of the primary dye is still retained. The cell wall peptidoglycan layer of Gram-negative bacteria is thin and has a high lipid content. Therefore, during decolorization, the lipids are dissolved by ethanol (or acetone), and the permeability of the cell wall increases, making the crystal violet-iodine complex It is relatively easy to be eluted out. After counterstaining with counterstain, the cells are stained with the red color of the counterstain. Principle of microscope imaging: Modern ordinary optical microscopes use two lens systems, eyepieces and objective lenses, to magnify images, so they are often called compound microscopes. In the optical system of a microscope, the performance of the objective lens is the most critical. The oil lens has the largest magnification and is the most important for microbiological research. The main purpose of adding drops of lens oil between the slide and the lens is to increase the illumination brightness and increase the resolution of the microscope. Using oil instead of air as the light propagation medium reduces the refraction or total reflection of light, making the observed image clearer.
Look for the bacterial colonies to be observed under a low-magnification microscope (keep moving the slide, if you feel a red shadow, stop immediately, adjust the magnification, if it is not a colony, continue to look), raise the lens barrel, and then switch to the oil lens. Add a drop of cedar oil to the sample area, and use the coarse adjuster to carefully lower the lens barrel so that the oil lens is immersed in the lens oil and almost in contact with the specimen. Raise the condenser to the highest position and open the aperture. Use the coarse adjuster to slowly raise the lens barrel until the object image appears in the field of view and use the fine adjuster to make it clear and in focus.
