[Stephane Leduc (1853-1939), from medicine to synthetic biology].

At the beginning of the XXth century, Stéphane Leduc (1853-1939), physician and biologist in Nantes (France), believed that he created a new discipline: the synthetic biology. Using his own works on diffusion and osmotic growths, he considered that the structures obtained by him were very closed to living beings. In 1907, his conclusions were strongly criticized and his papers were refused by the Académie des Sciences de Paris, because they questioned spontaneous generations. This paper relates Leduc's experimental works and conclusions and as well analyses his analogical method.