Head transplant surgery may appear to be at the very cutting edge of 21st-century medical science, but surgeons have been attempting the feat for more than 100 years, with varying degrees of success and sometimes stomach-turning results.

American physiologist Charles Claude Guthrie successfully grafted one dog's head onto the side of another dog's neck in 1908, a procedure that is believed to have overshadowed his less controversial medical achievements and prevented him from winning a Nobel Prize.

Russian scientist Vladimir Demikhov took up the gauntlet for the Soviet Union in the 1950s, carrying out a series of dog head transplants, all of which led to the animals dying as a result of immune reactions. In the same decade, Dr Ren Xiaoping's predecessors at Harbin Medical University conducted a dog head transplant with a similar outcome.

READ MORE: Chinese surgeon prepares for world's first head transplant

Demikhov went on to pioneer the use of immunosuppressants, inspiring surgeons worldwide and playing a role in making possible the first human heart transplant, in South Africa, in 1967.

The role model for Ren, who hopes to carry out the first human head transplant, is American neurosurgeon Dr Robert White, who, in 1970, conducted his own head transplant operation on a monkey. The animal lived long enough to look around, breathe, sniff at the air and attempt to bite the hand of one of White's colleagues. He repeated the operation in 2001.

White, who died in 2010, is described by Ren as "a very, very smart man who I admire greatly".

His work was highly controversial in a liberal era, however, and was effectively cut short by the uproar over his experiments on animals, which saw anti-vivisectionists label him a butcher. White appeared to take the criticisms lightly, and once turned up at a children's Halloween party dressed as Dr Frankenstein.

A devout Catholic who was an adviser to Pope John Paul II, White challenged the notion that he was somehow interfering with God's work.

"I believe the brain tissue is the physical repository for the human soul," he said in an interview after his retirement. "I don't think the soul is in your arm, in your heart, or in your kidneys."

He did, however, admit to feeling a powerful weight of moral responsibility after conducting his first successful head transplant, on what he conceded was a "very unhappy monkey" in the short time it survived.

White, who was filmed smoking a pipe while conducting the operation, said, "I thought, 'What have I done? Have we reached a point where the human soul can be transplanted? And if so, what does that mean?'"

Before his death, White acknowledged that the possibility of a human head transplant, or as he preferred to call it a "total body transplant", depended not only upon the continued advance of medical science but also on "the moral and social justification" of the operation. That dilemma may be about to come into scalpel-sharp focus.