Stored blood (the blood bank)

Karl Landsteiner's blood groups made transfusion safe, but blood still had to travel straight from one body to another: it clotted within minutes. In 1915 Richard Lewisohn, a Jewish surgeon at Mount Sinai in New York, established the exact concentration of sodium citrate that stops blood clotting without poisoning the patient — 0.2 per cent — and showed the blood kept for days. Transfusion became a thing you could store, ship and stockpile. Every blood bank, every battlefield transfusion and every routine operation since rests on that number.

Part of “The Gifts of the Jews” — verified Jewish contributions to the world, with sources.