Hans Christian Joachim Gram

…devised by a Danish physician, Hans Christian Gram, in 1884. The Gram reaction reflects fundamental differences in the biochemical and structural properties of bacteria. A slide containing a heat-fixed smear of bacterial cells is treated with crystal-violet stain (a basic dye), during which the cells turn purple. The slide is…

In 1884 the Danish microbiologist Hans Christian Gram discovered that crystal violet irreversibly stains certain bacteria but can be washed from others. The dye has been widely used ever since for the Gram stain technique, which identifies bacteria as gram-positive (the stain is retained) or gram-negative (the stain is washed…