Which statement describes the staining step in Modified Knott's technique?

• A. 1-2 drops of methylene blue stain
• B. 0.5 ml saline
• C. 1-2 drops of formalin
• D. 3-4 drops of crystal violet

Answer: (A)

Staining with methylene blue provides contrast and makes the microfilariae easier to see after the red blood cells have been lysed and the parasites concentrated. This basic dye binds to cellular components, highlighting the parasite and its internal features such as the nuclei, so the organisms appear blue against a clear background under the microscope. A small amount is used (about 1–2 drops) to color the organisms without over-staining the slide. Saline, formalin, and crystal violet aren’t used for this staining step: saline is for washing or dilution, formalin is the fixative/lysis agent used earlier, and crystal violet isn’t part of this Knott’s staining method.