But due to the strong reaction of the time's clergy the graft was removed. The first organ transplant was performed in the beginning of the 20th century by Alexis Carrel in Chicago, who in 1906 transplanted a new heart into a dog and a new kidney into a cat. Today, over 600,000 people are on the waiting list for tissues and organs and their number continues to grow. Human organs must be taken quickly from healthy people who have died through trauma. Of all animals, pigs are the favored xenotransplant donors.
Pigs have anatomies very much similar to that of humans.
They are generally healthier than most primates and extremely easy to breed, producing a whole litter of piglets at a time. Moral objections to killing pigs are fewer since they are slaughtered for food. The porcine tissue from immunological point of view are very close to the human tissues. The placenta of the pigs practically does not permit the carrying of micro-organisms and antibodies from the blood circulation of the mother to the fetuses. Due to the above, the new born piglets do not have immune antibodies till the suckling of collastra.