This document provides information about gram staining, including: 1) Gram staining is a method developed by Hans Christian Gram that classifies bacteria as either Gram-positive or Gram-negative based on their ability to retain crystal violet dye. Gram-positive bacteria retain the purple crystal violet dye after alcohol washing, while Gram-negative bacteria appear red. 2) The document outlines the principle of gram staining, noting that basic dyes like crystal violet bind to the slightly negatively charged bacterial cells, while acidic dyes stain the background. 3) The requirements and step-by-step method for performing a gram stain are provided, including heat fixing a bacterial sample on a slide, applying crystal violet and