Hans Christian Joachim Gram (September 13, 1853 – November 14, 1938) was a Danish bacteriologist. He was the son of Frederik Terkel Julius Gram, a professor of jurisprudence, and Louise Christiane Roulund.

Gram studied botany at the University of Copenhagen and was an assistant in botany to the zoologist Japetus Steenstrup. His plants introduced him to the basis of pharmacology and the use of the microscope.

He entered medical school in 1878 and graduated in 1883. He travelled throughout Europe between 1878 and 1885. In Berlin, in 1884, he developed a method for distinguishing between two major classes of bacteria. This technique, the Gram Stain, continues to be a standard procedure in medical microbiology.

In 1891, Gram became a lecturer in pharmacology, and later that year was appointed professor at the University of Copenhagen. In 1900 he resigned his Chair in Pharmacology to become Professor of Medicine.

Template:Mainarticle The work that gained him international reputation was his development of a method of staining bacteria. The stain later played a major role in classifying bacteria. Gram was a modest man, and in his initial publication he remarked “I have therefore published the method, although I am aware that as yet it is very defective and imperfect; but it is hoped that also in the hands of other investigators it will turn out to be useful.”

His initial work concerned the study of Red blood cells in men. He was among the first to recognise that macrocytes were characteristic of pernicious anaemia.

After his appointment as professor of Medicine in 1900 he published four volumes of clinical lectures which became widely used in Denmark. He retired in 1923.

• Whitworth, Judith A.; Firkin, Barry G. (2002). Dictionary of medical eponyms. Carnforth, Lancs: Parthenon. ISBN 1-85070-333-7.CS1 maint: Multiple names: authors list (link)
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