<prompt> Dark ground microscopy is used for diagnosis ofSpirochaeteMyco-tuberculosisMyco-lepraeMycoplasma  <response>: Ans. a Spirochete. Ref. Harrison, Principles of Medicine, 18thChapter 169. Syphilis Dark ground microscopic examination is useful but negative results does not exclude diagnosis of syphilis. Diagnosis by microscopy is applicable in primary and secondary stages and congenital syphilis. Wet film prepared with exudates is seen under dark ground microscope. T.pallidum show slow movement with slender spiral structure. However, serology remains the best diagnostic test for syphilis.Educational point: In blood transfusion and in congenital syphilis, no chancre occurs. 