Ludwig Fraenkel: 'spiritus rector' of the early progesterone research.

The search for the corpus luteum hormone progesterone took more than three decades and the efforts of many scientists all over Europe and the USA. In 1934, after a dramatic neck-and-neck scientific race, four research groups independently from each other reported on the successful isolation of the pure substance. 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. 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 Socialist's racial policies: Fraenkel, Fels and Slotta were forced into emigration.