Robert Ettinger created Cryonics Institute in the 1960s to advance the field of cryonics, which involves preserving humans in liquid nitrogen after death with the goal of future revival when medical technologies allow. By 2015, around 250 people had been cryopreserved in the United States and another 1,500 had made arrangements. Cryonics does not simply freeze the body, but vitrifies it through replacing water with antifreeze chemicals to prevent ice crystals, which scientists demonstrated successfully by reviving a rabbit after transplanting a vitrified kidney.