The Gram stain is adifferential
stainwhich allows most bacteria to be
divided into two groups, Gram-positive bacteria and Gram-negative bacteria. The
technique is based on the fact that the Gram positive cell wall has a stronger
attraction for crystal violet when Gram's iodine is applied than does the Gram
negative cell wall. Gram's iodine is known as amordant. The procedure was
discovered by Christian Gram in 1884.
