[Ludwig Fraenkel, corpus luteum and discovery of progesterone].
In 1934, after a dramatic neck-and-neck scientific race, four research groups independently from each other reported on the successful purification of progesterone. Two of the groups were from the then-German cities of Breslau and Danzig, the others were from the USA and Switzerland. Possibly, the Breslau group had already had the purified hormone as early as 1933. At that time, gynecologist Ludwig Fraenkel (1870-1951) had been their "spiritus rector" for more than three decades. It was Fraenkel himself who at the beginning of the century, in examining a hypothesis of the anatomist Gustav Jacob Born (1851-1900), had provided experimental proof for an endocrine function of the corpus luteum. Later on, Fraenkel enlisted the help of chemist Karl Heinrich Slotta (1895-1987) in the purification of the hormone. This took place after important requirements for the isolation and for the semiquantitative determination of the hormone (e.g. the Corner-Allen-Test) had been established elsewhere. Also belonging to the Breslau research group were Erich Fels (1897-1981) and Heinrich Ruschig (born in 1906). Fels was an assistant to Fraenkel, Ruschig a PhD-candidate directed by Slotta. Shortly after the group had succeeded in purifying Progesterone the Breslau group was broken apart by the National Socialists' racial policies: Fraenkel, Fels and Slotta were forced into emigration.