What is the purpose of heat fixing the smear?

Before bacteria can be stained, a smear of bacteria must be made on a slide and heat fixed. A smear is made by spreading a bacterial suspension on a clean slide and letting it air dry. The dry smear is heated on a hot plate or passed through a flame several times to heat fix it. read more

When preparing bacteria for observation with a microscope, heat fixing the smear on the slide kills the bacteria to stop the potential spread of disease and adheres the smear to the slide. After heat fixing, the smear is stained. read more

a combination of negative staining and simple stain techniques is used. Negative stain allows the background to stain without the heat, leaving the capsule and bacteria negatively stained. After this is complete, you heat fix, damaging the capsule, followed by a simple stain which stains the bacteria. read more