Allan Macfadyen (26 May 1860 in Glasgow – 1 March 1907 in Hampstead, London) was a Scottish bacteriologist,[1][2] a pioneer in immunization against bacterial infection.
Upon his return to England, he became, from 1889 to 1892, a research scholar of the Grocers' Company and lecturer on bacteriology at the College of State Medicine in London.
The College was subsequently amalgamated with the British Institute of Preventive Medicine, of which Macfadyen was made director in 1891.
To obtain these endotoxins Macfadyen ground up bacteria, rendered brittle by freezing with liquid nitrogen to –190 °C.
Macfadyen showed that injecting small doses of bacterial endotoxins into experimental animals made them immune to infection by the corresponding living bacteria.