British bacteriologist (1865–1926)
Leishman was born in Glasgow, the son of the regius professor of medicine at the university there. He himself was educated at the university, where he obtained his MD in 1886. He immediately joined the Army Medical Service and began his career in India, where he served from 1890 to 1897. On his return to England he took up an appointment at the Army Medical School at Netley as an assistant to Almroth Wright, succeeding him in 1903 as professor of pathology when the school moved to Millbank. In 1913 Leishman transferred to the War Office, where he served in various advisory positions before being appointed director of pathology (1919) and director general of Army Medical Services (1923), a post he held until his death.
Leishman's first major success was his discovery in 1900 of the protozoan parasite (Leishmania) responsible for the disease known variously as kala-azar and dumdum fever. As he delayed publication until 1903 he was forced to share his discovery with C. Donovan, who independently repeated his work (the form of the parasite found in humans became known as the Leishman–Donovan body). The disease caused by the parasite is now known as leishmaniasis.
In 1900 he went on to develop the widely used Leishman's stain. This is a compound of methylene blue and eosin that soon became adopted as the standard stain for the detection of such protozoan parasites as Plasmodium (malaria parasite) in the blood.
Leishman also made major contributions to the development of various vaccines, particularly those used against typhoid. By 1896 Wright had developed a safe vaccine of killed typhoid bacilli, which he persuaded the Army to test during the Boer War (1899–1902). The extent of the protection provided by the vaccine became a matter of violent controversy between Wright and the English statistician Karl Pearson; the Army Council therefore invited Leishman in 1904 to resolve the dispute. By 1909 Leishman was able to report that those inoculated in India carried a significantly smaller risk of dying from enteric complaints (5 died out of 10,378 vaccinated, compared with 46 out of the 8936 not vaccinated).
It was mainly as a result of this work, together with improvements introduced by Leishman in the actual quality of the vaccine, that a policy of mass vaccination was adopted in 1914. Consequently only 1191 deaths due to typhoid were reported by the British Army throughout the whole of World War I.
Leishman was knighted in 1909.
