Cryonics is the practice of preserving animals or humans under very low temperatures to halt the decay process. In futurist circles, cryonics is seen as a possible way to cheat death by preserving oneself until medical science can revive the patient without damage. Animals have already been frozen for hours and revived with today's science, although more complex animals such as felines tend to undergo some brain damage.
Freezing is not the only technique employed by cryonicists - in modern cryonics, vitrification is also used. In vitrification, a cryoprotectant such as glycerol is injected into the patient in high concentrations resulting in rapid cooling without ice formation. Glycerol is the same substance used by some species of frog to survive almost completely embedded in ice for days or weeks. Vitrification is distinct from freezing because the patient is cooled so quickly that the biological tissue has no time to warp into a crystalline pattern; the original pattern is preserved with high integrity, hardened like glass.
Critics of cryonics have contended that medical science will never advance to the point of being able to revive a vitrified body, even after thousands or millions of years. Still others contend that no one in the future will care enough to revive human bodies preserved during this era, even if the technology were available and economical. Most cryonics advocates cite molecular nanotechnology as the likely future means of smooth and complete revival for cryopreserved patients.
At least four organizations offer cryonics services in the United States. Patients are cooled to temperatures between -150°C and -200°C (-238°F and -328°F) and stored in secure containers. Over a hundred patients are currently preserved. Probably, the most famous person to be cryopreserved is baseball star Ted Williams. His cryosuspension created controversy in late 2002. Over a thousand people are currently signed up to cryopreserved when their bodies deanimate. As medical science continues to improve, so too will the probability of the successful revival of cryonics patients.