German doctors performed a variety of experiments on prisoners at Auschwitz. SS doctors tested the efficacy of X-rays as a sterilization device by administering large doses to female prisoners. Carl Clauberg injected chemicals into women's uteruses in an effort to glue them shut. Prisoners were infected with spotted fever for vaccination research and exposed to toxic substances to study the effects. In one experiment Bayer, then part of IG Farben, paid RM 150 each for 150 female inmates from Auschwitz (the camp had asked for RM 200 per woman), who were transferred to a Bayer facility to test an anesthetic. A Bayer employee wrote to Rudolf Höss: "The transport of 150 women arrived in good condition. However, we were unable to obtain conclusive results because they died during the experiments. We would kindly request that you send us another group of women to the same number and at the same price." The Bayer research was led at Auschwitz by Helmuth Vetter of Bayer/IG Farben, who was also an Auschwitz physician and SS captain, and by Auschwitz physicians Friedrich Entress and Eduard Wirths.