John Berry Haycraft

15 March 1857 – 30 December 1922) was a British physician and professor in physiology who carried out important medical research.

His younger brother was Sir Thomas Haycraft, a judge in the British Colonial Service.

[2] He received his medical education at the University of Edinburgh, where he gained an MD on the history, development, and function of the carapace of the chelonia[3] and also a DSc in public health in 1888.

During his years in Birmingham and Edinburgh, Haycraft had been actively engaged in research and published papers on the coagulation of blood and in 1884, he discovered that the leech secreted a powerful anticoagulant, which he named hirudin, although it was not isolated until the 1950s, nor its structure fully determined until 1976.

Haycraft returned to London in 1892 and was appointed a research scholar of the British Medical Association.