The medical mutation process by which air-breathers are changed into water-breathers is known as "surgo-op." It is practiced by the Aquans of the planet Argo. In 2269, Captain Kirk and Mr. Spock are mutated with this process, giving them webbed hands, secondary eyelids, and other internal mutations. Reverse mutation is achieved by an infusion of concentrated doses of an anti-toxin, made from the ambergris-like venom of a sur-snake. Unfortunately, due to lost records, the exact dosage of the venom to reverse mutations on humans is unknown.