The question of whether cryonics “works” or not is too general and hides the point that progressive breakthroughs can make the concept more plausible. Human cryopreservation consists of a number of procedures culminating in long term care at cryogenic temperatures. An evidence based approach to cryonics dictates that the limits of procedures that can be reversed by contemporary technologies should be investigated and pushed further. Under ideal conditions viability of the brain of the patient can be maintained until the early stages of cryoprotective perfusion. In other words, cryonics procedures can be reversed with no or minimal brain injury up until the stage where exposure of the brain to higher concentrations of the vitrification agent compromises viability. Although we do not have a good understanding of the extent of ice formation in the brain of typical patients in which vitrification is attempted, in ideal cases the current limiting factor to reversibility of cryonics procedures is cryoprotectant toxicity.
During its existence as a research program, cryonics researchers have shown great interest in recovering animals from ultra-profound hypothermic temperatures (lower than 5 degrees Celsius). The ability to routinely lower the temperature of mammals to temperatures close to zero degrees Celsius and recover them without adverse effects to the brain does make the initial stages of cryonics reversible. Although this procedure does not necessarily require that the blood of an animal is removed at the lowest temperatures, theoretical considerations and experimental evidence dictate that the use of an universal organ preservation solution will improve outcome. In the 1980s, the Alcor Life Extension Foundation engaged in a series of experiments that recovered dogs perfused with a mannitol-based organ preservation solution called MHP after 5-hours of bloodless perfusion at 5 degrees Celsius without adverse neurological outcome after rewarming.
Less known than those record setting experiments are earlier explorations in cryonics into whole body asanguineous hypothermia. The following document by cryonics researcher and Alcor patient Jerry Leaf documents a Trans Time experiment during the early days of total body washout experiments in cryonics. This account was published in the November/December 1977 issue of Long Life Magazine and the scan contains an introduction by Art Quaife and an afterword by Saul Kent.