On This Day in Science History - September 13 - Hans Gram

September 13th is Hans Christian Joachim Gram's birthday. Gram was a Dutch bacteriologist who discovered a staining technique used in histology and microbiology. The Gram stain test is generally the first test microbiologists perform when identifying bacteria. It quickly divides the bacteria into two types: Gram positive and Gram negative. When the Gram stain is applied, the Gram positive bacteria will absorb the stain and turn purple. The Gram negative bacteria will not absorb the stain and may be colored pink using a counterstain.

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