Hans's Christian Joachim Gram (* 13 September 1853 in Copenhagen; "† 15 November 1938) was a Danish bacteriologist.

Gram studied first Botanik, later also medicine, at the University of Copenhagen up to the conclusion 1883. 1891 became it lecturer and received in the same year a Professur for pharmacology, starting from 1900 for medicine in Copenhagen.

Gram found 1883 and 1885 in a citizen of Berlin hospital a way, exciter of the pneumonia Streptococcus pneumoniae between (grampositiv) and Klebsiella pneumoniae (gramnegativ) differently This coloring method (gram's stain) is based on a then unknown difference in the structure of cell wall of bacteria. Gram positive bacteria have a thick cell wall, mainly consisting of a multilayered situation of Murein. The gramnegativen bacteria possess only a very thin wall from an in up to wenigschichtigen situation of Murein, in addition they have a second Lipidmembran similarly a Cytoplasmamembran outside of cell wall with the colouring with Gentianaviolett form with iodine iodine potassium solution an water-insoluble "lacquer" within the cell. This lacquer can be washed with ethanol from gramnegativen bacteria. Ethanol cannot penetrate however through the thick cell wall of the grampositiven bacteria, therefore the color lacquer remains containing in these cells. In order to make the other bacteria visible, a with Safranin is used.

Reason for the intensive research at coloring methods for bacteria to end 19. Century was their bad visibility in the light field microscopy. Only with the development of the phase contrast in the 30's 20. Century became visible they without colouring.

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