Dark ground microscopy is used for -: (A) TPI, (B) FTA - ABS, (C) Kahn's test, (D) VDRL
Answer is A. In TPI test, the serum of patient is incubated with complement and T. pallidum maintained in a complex medium anaerobically. If the antibodies are present, the treponemes are immobilized, that is, rendered nonmotile, when examined under dark ground illumination.