Video narration
How can you see a transparent organism without staining it? Think of dust appearing in a flashlight beam in a dark room: scattered light makes what was hard to see stand out. Start with a wet mount on a slide, and place it on the microscope stage. In dark-field microscopy, a special condenser sends light toward the specimen at an angle, rather than straight up through the center. Here's the key: the objective lens does not collect the direct beam. It collects light scattered by the specimen. That scattered light forms a bright image against a dark background. For a clear view, keep the specimen in focus and the illumination and condenser aligned. This approach is useful when you want to observe transparent specimens without staining them. So you see it unstained because scattered light reaches the objective, making it bright against darkness.