Gram's method n : a staining technique used to classify bacteria; bacteria are stained with gentian violet and then treated with Gram's solution; after being decolorized with alcohol and treated with safranine and washed in water, those that retain the gentian violet are gram-positive and those that do not retain it are gram-negative [syn: {Gram method}, {Gram's procedure}, {Gram's stain}, {Gram stain}]