Dark ground microscopy is used to see -

Dark ground/ Darkfield microscope Very slender organisms such as spirochetes and filamentous organisms such as flagella are not visible under ordinary illumination. The contrast in dark field microscopy gives an illusion of increased resolution so that these structures can be seen under the dark field microscope. In darkfield microscopy, reflected light is used instead of the transmitted light used in the ordinary microscope. Dark ground (dark field) microscopy is used for - Flagella - Spirochetes