A Vulcan blood type, considered rare, but possessed by Ambassador Sarek and his son, U.S.S. Enterprise NCC-1701 first officer Mr. Spock. In 2267, Ambassador Sarek fell critically ill while on board the Constitution-class Enterprise and required emergency heart surgery. Without the proper blood donor, Sarek would surely die. Knowing his own was the only blood type that could save Sarek, Mr. Spock -- despite psychological frictions with his father -- offered himself as a donor for the operation.