Ludwik Fleck was born on July 11, 1896, in Lvov (now Lviv), at that time under the rule of Austria-Hungary, to a family of Jewish craftsman. His medical studies at the John Casimir University were interrupted by military service. He graduated in 1922, when Lvov belonged to the reborn Poland. At the end of his studies he was an assistant of the famous typhus specialist Rudolf Weigl. In 1923 Fleck founded a private laboratory of medical analysis and was in charge of the Lvov Sick Fund and the bacteriological-chemical laboratories of the General Public Hospital.