Beginner's luck – the first in vivo demonstration of functioning platelets; William Duke, 1910

Blood platelets remained obscure until the early 20th century although from the 1880s claims that low numbers were associated with certain types of ‘purpura’ began to gain favour. This article re‐appraises critically, but with due consideration to the limited technology of the times, the first remarkable in vivo demonstration of the effects of platelets demonstrated by the serial ‘Bleeding Times' reported by William Duke in 1910, when fresh blood was transfused to two thrombocytopenic people. It also speculates on the possible causes of the thrombocytopenia with which Duke's main patient presented.