Dark ground microscopy is used to see?

Darkfield / Dark ground microscope in which reflected light is used instead of transmitted light used in the ordinary microscope. Flagella are less than 0.02 um in thickness and hence beyond the limit of resolution of the light microscopes. They may in some instances be seen under dark field / Dark ground illumination. They can be visualized by special staining techniques in which their thickness is increased by mordanting or by electron microscopy. Ref: Textbook of Microbiology; Ananthanarayan and Paniker; 9th edition; Pg no: 11