<unk>  is a flexible<unk>  of silk suture, later versions of which were wrapped in silver wire. It was an early IUD, a birth control device.<unk>  was the first IUD used by a significant number of women. The<unk>  was introduced by German gynecologist Ernst<unk>  in 1929. It ceased to be in wide use circa 1939. Inserting a foreign device into the uterus causes an inflammatory response, which creates a hostile environment for sperm. The silver wire used to construct later versions of<unk>  was contaminated with copper, which increases this spermicidal effect. In 1934, Japanese physician Tenrei Ota developed a variation of the<unk> <unk>  that contained a supportive structure in the center. The addition of this central disc lowered the IUD's expulsion rate. However, insertion of these devices caused high rates of infection and were condemned by the medical community. Furthermore, their use and development was stifled by World War II politics: contraception was forbidden in both Nazi Germany and Axis-allied Japan. The rest of the Western world did not learn of the work of<unk>  and Ota until well after the war ended.
Gräfenberg's ring
Woronoff's ring
Dennie–Morgan fold
Kronig isthmus
Curschmann's spirals
Soemmering ring
Kock pouch
Pili bifurcati