<P> The gas chambers worked to their fullest capacity from April to July 1944, during the massacre of Hungary's Jews . Hungary was an ally of Germany during the war, but it had resisted turning over its Jews until Germany invaded that March . A rail spur leading directly into Birkenau was completed that May to deliver the victims closer to the gas chambers . From 14 May until early July 1944, 437,000 Hungarian Jews, half of the pre-war population, were deported to Auschwitz, at a rate of 12,000 a day for a considerable part of that period . The incoming volume was so great that the SS resorted to burning corpses in open - air pits as well as in the crematoria . The last selection took place on 30 October 1944 . </P> <P> German doctors performed a wide 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 . Prof Dr Carl Clauberg injected chemicals into women's uteruses in an effort to glue them shut . Bayer, then a subsidiary of IG Farben, bought prisoners to use as research subjects for testing new drugs . Prisoners were also deliberately infected with spotted fever for vaccination research and exposed to toxic substances to study the effects . </P> <P> The most infamous doctor at Auschwitz was Josef Mengele, known as the "Angel of Death". Particularly interested in research on identical twins, Mengele performed cruel experiments on them, such as inducing diseases in one twin and killing the other when the first died to perform comparative autopsies . He also took a special interest in dwarfs, and he deliberately induced noma in twins, dwarfs, and other prisoners to study the effects . </P> <P> Kurt Heissmeyer took twenty Jewish children from Auschwitz to use in pseudoscientific medical experiments at the Neuengamme concentration camp . In April 1945, the children were killed by hanging to conceal the project . </P>

What was the biggest camp in the holocaust