Scientists’ plans to carry out the first human head transplant next year has raised questions about whether such a surgery is even possible or ethically sound.

During a cold, dreary summer in Switzerland 200 years ago, English author Mary Shelley sat down to write her novel “Frankenstein.”

The story — and subsequent adaptations for the screen — has gripped our imaginations ever since.

While reanimating the dead remains a scientific impossibility, scientists are pushing the boundaries of modern medicine closer and closer to Shelley’s vision.

As they do, the public’s uneasiness about the ethical limits of medicine has been stoked.

Take, for example, the announcement last year by Italian neuroscientist Dr. Sergio Canavero that he plans to perform the first human head transplant.

Not sometime in the distant future … but possibly in 2017.

And now he has a volunteer for the procedure — Valery Spiridonov, a 31-year-old Russian man with a degenerative muscle condition.

This has bumped Canavero’s bold plans from the realm of science fiction straight into the real world.

Like Victor Frankenstein, Canavero hopes to make great scientific advances, even if it means working at the fringes of modern medicine.

For some critics, though, transplanting a human head onto a new body crosses a line — one similar to the line that Shelley’s fictional doctor stepped over when he created his “creature.”

Read more: Future of face transplants »

Compared to transplanting a heart or kidney, a head transplant is technically much more challenging.

Surgeons will need to join many tissues of the head and new body, including muscles, skin, ligaments, bones, blood vessels, and most importantly, the nerves of the spinal cord.

But there has already been some groundwork laid for the “audacious plan” of Canavero and his partner, Chinese surgeon Dr. Xiaoping Ren, as described in the September issue of The Atlantic.

In the early 1900s, a Missouri surgeon transplanted the head of one dog onto the neck of another, creating one with two heads. This feat was repeated by Soviet and Chinese surgeons in the 1950s, with the dog living for 29 days.

In the 1970s, a surgeon from Ohio transplanted the heads of rhesus monkeys onto new bodies. They survived and could even eat and follow objects with their eyes. But the doctor hadn’t reconnected their spinal cords, so they remained paralyzed.

Canavero and Ren have different plans.

They hope to fuse the nerves cells of the head and body using a gluelike chemical called polyethylene glycol.

Ren has already tested this chemical on mice with spinal cords that have been severed. The mice were walking within two days of the procedure.

In preparation for Spiridonov’s surgery next year, Ren’s team has also successfully transplanted a mouse’s head onto another body. This was later repeated on a monkey.

These animals, though, were euthanized within a day of the procedure. So future experiments are needed in order to know if a head transplant is a long-term solution.

Read more: Uterus transplant: Is it ethical? »

According to The Atlantic, Canavero says there is a “90 percent plus” chance of success. Ren, though, is less definite about the outcome.

And as with all transplant surgeries, there are many risks.

Before Patrick Hardison underwent one of the world’s most extensive face transplants, doctors gave him a 50 percent chance of survival.

Infection, loss of blood flow to the transplanted organ, and rejection of the new tissue all lower the odds of success.

With a head transplant, loss of blood flow to the brain is an even larger problem. Lack of oxygen can damage the brain and leave a person with severe mental deficiencies.

Cooling both the head and body before and during surgery could allow the cells to survive longer without oxygen. Still, doctors would only have an hour or less to complete the surgery.

One of the most common risks of organ transplants is tissue rejection. With a head transplant, though, it would be the head that would be seen as “foreign” by the new body’s immune system.

Finding a donor body that is a good match for Spiridonov — in this case a male who died of head trauma with no damage to the body — could minimize this risk.

But he would need to take powerful immunosuppressive medications for the rest of his life to limit the chance that the new body’s immune system would attack the tissues of his head.

After surgery, Spiridonov would be kept in a coma for several weeks to allow his spinal nerves to heal.

But if he wakes up before his spinal nerves heal, there is a chance that he would be paralyzed. Or that his nerve cells would fuse incorrectly — with nerves meant to control the arms connected to the legs instead.

In spite of that, Spiridonov is still willing to face those odds.

His genetic condition, known as Werdnig-Hoffmann disease, has left him confined to a wheelchair. He movements are limited to typing, feeding himself, and steering his wheelchair with a joystick.

Werdnig-Hoffmann disease is also fatal, although Spiridonov has already lived longer than his doctors had expected.

Read more: Rich people get donor organs faster »

The fringe nature of Canavero’s and Ren’s plans has led to harsh backlash from scientists and ethicists.

Some have called it “nuts” or scientifically impossible.

Others are concerned that even though Spiridonov is aware of the risks, it still doesn’t make it OK for doctors to perform the surgery.

And then there is the cost — between $10 million and $100 million.

Would this money be better spent on helping the thousands of people who suffer spinal cord injuries each year?

Head transplants also raise issues of who the new body belongs to, especially in terms of its sperm or eggs.

If someone with a new body had a child, would the family of the donated body have visitation rights?

And then there are the more philosophical questions. What does it mean for a person’s sense of self to have a body that they weren’t born with?

There’s not even certainty that someone would be able to accept a new body as part of themselves.

The man who underwent the world’s first hand transplant was uncomfortable with his new hand. So he stopped taking his immunosuppressive drugs and the hand had to be removed.

Public angst about head transplants may subside after a few successful surgeries, the way it has with face transplants.

But for now, Canavero and Ren are still working on the other side of a line that many think we shouldn’t cross.