A handful of scientists around the United States are trying to do something that some people find disturbing: make embryos that are part human, part animal.

The researchers hope these embryos, known as chimeras, could eventually help save the lives of people with a wide range of diseases.

One way would be to use chimera embryos to create better animal models to study how human diseases happen and how they progress.

Perhaps the boldest hope is to create farm animals that have human organs that could be transplanted into terminally ill patients.

But some scientists and bioethicists worry the creation of these interspecies embryos crosses the line. "You're getting into unsettling ground that I think is damaging to our sense of humanity," says Stuart Newman, a professor of cell biology and anatomy at the New York Medical College.

The experiments are so sensitive that the National Institutes of Health has imposed amoratorium on funding them while officials explore the ethical issues they raise.

Nevertheless, a small number of researchers are pursuing the work with alternative funding. They hope the results will persuade the NIH to lift the moratorium.

"We're not trying to make a chimera just because we want to see some kind of monstrous creature," says Pablo Ross, a reproductive biologist at the University of California, Davis. "We're doing this for a biomedical purpose."

The NIH is expected to announce soon how it plans to handle requests for funding.

Recently, Ross agreed to let me visit his lab for an unusual look at his research. During the visit, Ross demonstrated how he is trying to create a pancreas that theoretically could be transplanted into a patient with diabetes.

The first step involves using new gene-editing techniques to remove the gene that pig embryos need to make a pancreas.

Working under an elaborate microscope, Ross makes a small hole in the embryo's outer membrane with a laser. Next, he injects a molecule synthesized in the laboratory to home in and delete the pancreas gene inside. (In separate experiments, he has done this to sheep embryos, too.)

After the embryos have had their DNA edited this way, Ross creates another hole in the membrane so he can inject human induced pluripotent stem cells, or iPS for short, into the pig embryos.

Like human embryonic stem cells, iPS cells can turn into any kind of cell or tissue in the body. The researchers' hope is that the human stem cells will take advantage of the void in the embryo to start forming a human pancreas.

Because iPS cells can be made from any adult's skin cells, any organs they form would match the patient who needs the transplant, vastly reducing the risk that the body would reject the new organ.

But for the embryo to develop and produce an organ, Ross has to put the chimera embryos into the wombs of adult pigs. That involves a surgical procedure, which is performed in a large operating room across the street from Ross's lab.

Pablo Ross of the University of California, Davis inserts human stem cells into a pig embryo as part of experiments to create chimeric embryos.

Rob Stein/NPR

The day Ross opened his lab to me, a surgical team was anesthetizing an adult female pig so surgeons could make an incision to get access to its uterus.

Ross then rushed over with a special syringe filled with chimera embryos. He injected 25 embryos into each side of the animal's uterus. The procedure took about an hour. He repeated the process on a second pig.

Every time Ross does this, he then waits a few weeks to allow the embryos to develop to their 28th day — a time when primitive structures such as organs start to form.

Ross then retrieves the chimeric embryos to dissect them so he can see what the human stem cells are doing inside. He examines whether the human stem cells have started to form a pancreas, and whether they have begun making any other types of tissues.

The uncertainty is part of what makes the work so controversial. Ross and other scientists conducting these experiments can't know exactly where the human stem cells will go. Ross hopes they'll only grow a human pancreas. But they could go elsewhere, such as to the brain.

"If you have pigs with partly human brains you would have animals that might actually have consciousness like a human," Newman says. "It might have human-type needs. We don't really know."

That possibility raises new questions about the morality of using the animals for experimentation. Another concern is that the stem cells could form human sperm and human eggs in the chimeras.

"If a male chimeric pig mated with a female chimeric pig, the result could be a human fetus developing in the uterus of that female chimera," Newman says. Another possibility is the animals could give birth to some kind of part-human, part-pig creature.

"One of the concerns that a lot of people have is that there's something sacrosanct about what it means to be human expressed in our DNA," says Jason Robert, a bioethicist at Arizona State University. "And that by inserting that into other animals and giving those other animals potentially some of the capacities of humans that this could be a kind of violation — a kind of, maybe, even a playing God."

Ross defends what his work. "I don't consider that we're playing God or even close to that," Ross says. "We're just trying to use the technologies that we have developed to improve peoples' life."

Still, Ross acknowledges the concerns. So he's moving very carefully, he says. For example, he's only letting the chimera embryos develop for 28 days. At that point, he removes the embryos and dissects them.

If he discovers the stem cells are going to the wrong places in the embryos, he says he can take steps to stop that from happening. In addition, he'd make sure adult chimeras are never allowed to mate, he says.

"We're very aware and sensitive to the ethical concerns," he says. "One of the reasons we're doing this research the way we're doing it is because we want to provide scientific information to inform those concerns."

Venezuelan soldiers outside a supermarket while people lining up to buy basic food items in Caracas, Venezuela, on Sunday.

A week ago residents of the poorer barrios of Venezuela's capital, Caracas, woke up to find soldiers everywhere.

Dressed in black helmets, military fatigues, and bulletproof jackets, a fleet of soldiers on 400 motorcycles flew through narrow, crumbling, streets while being supported by trucks and two helicopters.

They set up street checkpoints and positioned themselves on rooftops to monitor the neighborhoods, while officers scoured alleys and houses holding heavy weaponry.

The military deployment took place in the midst of Venezuela's massive economic crisis triggered by the fall of oil prices and characterized by a shrinking economy and hyperinflation. Blackouts are now constant, in many areas water is severely rationed, and public-sector employees work just two days a week in an effort to save energy.

Patients are dying in hospitals for lack of basic care, desperate families are buying bootleg medication at inflated prices, and standing in huge lines is required to buy basic goods such as toilet paper, condoms, and rice.

At the same time President Nicolás Maduro faces a drive by the political opposition, emboldened by its electoral win in December that gave it control of congress for the first time in 17 years, to force a recall referendum.

The situation is so tense that last week's show of military strength sparked immediate rumors of a coup. What was actually happening was close to the opposite — the launch of a new phase of an anticrime offensive that some observers see as an effort by Maduro to show the unsettled population that he is still in charge and intends to remain so.

The Operation Liberation and Protection, or OLP, began in July. It is the country's 23rd anticrime initiative since President Hugo Chávez took office and launched his Bolivarian revolution in 1999. It is the third since his protegé, Maduro, began his term after Chávez died in 2013.

But, some say, anticrime operations in Venezuela are not necessarily primarily about the rampant criminal gangs that caused Caracas to be named the most violent city in the world in 2015 with a terrifying homicide rate of nearly 120 murders per 100,000 citizens.

"It's a preventative measure in the face of widespread dissatisfaction in Venezuela," criminal lawyer and well-known criminologist Luis Izquiel said. "People want to see a political change with the referendum, because they are hungry and lack most things."

The new stage of the OLP was announced with great fanfare on state-owned TV. Reports detailed the number of soldiers, cars, ambulances, tanks, and helicopters involved, as well as the exact details of the equipment they carried.

When the OLP was first launched in July, it promised to dismantle criminal gangs operating in poor barrios. It consisted of military sweeps that caught up anyone who was allegedly involved and, critics say, many others who were not.

Izquiel, the lawyer, says the second stage of the OLP appears more directed toward political control, with the military now preparing to occupy some areas for longer periods of time.

"Here you can see that the message is the intimidation," he said. "They are going to stay for some time to prevent public dissatisfaction from showing."

Even if the aim is to control crime, critics argue that the OLP should be discontinued because it has both failed to reduce homicide rates — which increased by 7% in the first few months of this year compared with the same period in 2015 — and encourages abuse.

"It's only good for violating human rights and criminalizing poverty," Izquiel said. "When the OLP targets a poor area, it destroys anything that stands in its way, tearing down houses."

A report released last month by a local human-rights group called Provea, in association with the US-based Human Rights Watch, detailed extrajudicial executions, arbitrary detentions, forced evacuations, and the destruction of many homes.

Irene González tells the story of how she lost her house to the OLP last year, and went on to form the Committee of Victims from Ensenada, a poor area in the state of Miranda.

"I woke up early to go to work, around 4 a.m.," she said. "It was raining. I saw a lot of soldiers as I left my home. Then I found out there were 1,500 of them. They told me I could not go out, because it was an OLP. I asked how long it would take, as I had to go to work, and their response made me shiver because they said 'For as long as it takes us to tear down your house.'"

González said the operation led to the capture of two people who were later released, and the formation of the committee of victims by 110 families whose homes were destroyed by what they say they were told was a presidential order.

"There's no excuse to leave all those families in the street," González said. "There were no criminals or drugs in the area."

Perhaps most worrying for the government is that González is not somebody who has been easily turned against the "socialist" project launched by Chávez 17 years ago and is now under the charge of Maduro.

"I'm a Chavista, but I don't like Maduro," she said. "Our beloved president Chávez would have never allowed this atrocity to take place."

The recently implemented second stage of the OLP included an initial claim of success, in the form of the capture and death of José Antonio Tovar Colina, also known as El Picure, who was said to head a criminal group that controls three states.

Jamilton Andrés Suárez Ulloa, also known as El Topo, was also killed in the operation. He reportedly controlled the mining areas in the Bolívar state and was the alleged mastermind behind the death of a group of miners in Tumeremo earlier this year.

"There's a society that is demanding safety after being overwhelmed by criminal leaders," said Inti Rodríguez, member of the human-rights groups Provea, that helped elaborate last month's report. "And the government is answering with the same heavy-handed policy that enables it to say it's doing something."

Rodríguez, however, added that this time the political side to the operation was particularly obvious.

"There's a clear motive behind the launch of the second stage of the OLP. The referendum to revoke Maduro's presidency is on the horizon," he said. "The security operation has a huge propaganda effect and the militarization of poor areas stops an uprising from taking place."

The relaunched OLP came three days before president Maduro declared a 60-day state of emergency that, if approved by the national legislature, would give him wider powers of state intervention in the economy, which are already considerable.

Maduro, meanwhile, has stepped up his already frequent allegations that an internationally backed intervention or coup against him is imminent. This Saturday he told a large gathering of supporters that the military will start exercises in a week in order to ensure it is prepared for "whatever scenario."

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