German scientists and doctors conducted medical experiments on selected concentration camp inmates.  The procedures were often deliberately painful or fatal.  Some prisoners were exposed to sub-zero temperatures, immersed in freezing salt water, or killed in low-pressure tanks, all to study the effects of harsh battle conditions.  Others were injected with malaria or hepatitis, or exposed to mustard gas or other poisons, in order to study vaccinations or the course of a disease or poison.  Other prisoners' sexual organs were exposed to x-rays or injected with toxic chemicals, so Nazi doctors could study methods for sterilizing people they considered to be “unworthy of living.”  Experiments were conducted on twin children and disabled inmates for Nazi genetic research, which was considered vital to the development of a German “master race.”  Following the war, some physicians involved in these experiments were sentenced to death or life in prison.