Freezing/Hypothermia-"patients" were subjected to negative temperatures and put in icy vats of water (both while naked), and then attempts were made at revival. few were effective.
Genetics-
One of the most famous doctors involved in the genetic experiments was Joseph Mengele, also known as the angel of death. he took a special interest in twins, and did experiments on them that included sewing a pair of twins together in the attempt to make "Siamese twins". other experiments were conducted on dwarfs and homosexuals as well, such as trying to turn the homosexuals straight. those experiments failed.
Prisoners were infected with diseases such as malaria because the Nazis wanted to find cures.
Killing/Genocide-
A good number of the experiments conducted on prisoners were just to have an excuse to kill them. High Altitude, Pharmalogical, Sterilization, Surgery and Traumatic Injuries.
Josef Mengele
Auschwitz had Joseph Mengele. Dachau performed High Altitude Medical Experiments and Buchenwald tested pharmaceuticals and incendiary devices on prisoners. See the Jewish Virtual Library's section on Medical Experiments for a good list of experiments and those responsible.
Because the Germans were searching for a cure for diseases like Malaria that come from mosquitoes, they also did it to find more things out about the human body (They were also looking for abilities like telekinesis in twins, or if they had some sort of special bond)
Sonar soundings.
Josef Mengele performed gruesome and atrocious medical experiments (more like mad man experiments) on the Jews or with the Jews and the other undesireables. He did this at the Auschwitz-Birkenau concentration camp.
A Lab
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Because they were persecuted because of their religion/ ethicity first by the Russians with their Pogroms and later by the Germans in the 1930's. The Germans brutally murdered 6 million Jews during WW2. Very few Germans paid the price for what they had done. Most Germans viewed Jews as being a lower form of humanity much like animals. Many medical experiments were carried out on captive Jews
Most experiments conducted are medical experiments, but fluid mechanics experiments, various experiments involving weightlessness, and testing of new technologies are also conducted.
Rutherford
laboratory
The medical experiments were gruesome and had little merit for the rest of the medical world. There motivations for the experiments were mostly about studying sub-humans according to their view. See the attached links.