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. The most infamous doctor at Auschwitz was Josef Mengele, the "Angel of Death", who worked in Auschwitz II from 30 May 1943, at first in the gypsy family camp. Interested in performing research on identical twins, dwarfs, and those with hereditary disease, Mengele set up a kindergarten in barracks 29 and 31 for children he was experimenting on, and for all Romani children under six, where they were given better food rations. From May 1944, he would select twins and dwarfs from among the new arrivals during "selection", reportedly calling for twins with "Zwillinge heraus!" ("twins step forward!"). He and other doctors (the latter prisoners) would measure the twins' body parts, photograph them, and subject them to dental, sight and hearing tests, x-rays, blood tests, surgery, and blood transfusions between them. Then he would have them killed and dissected. Kurt Heissmeyer, another German doctor and SS officer, took 20 Polish Jewish children from Auschwitz to use in pseudoscientific experiments at the Neuengamme concentration camp near Hamburg, where he injected them with the tuberculosis bacilli to test a cure for tuberculosis. In April 1945, the children were murdered by hanging to conceal the project. A Jewish skeleton collection was obtained from among a pool of 115 Jewish inmates, chosen for their perceived stereotypical racial characteristics. Rudolf Brandt and Wolfram Sievers, general manager of the Ahnenerbe (a Nazi research institute),