Raul Mora's job gets a lot more stressful in the summertime — so, to kick back, he plays third base and pitcher on a baseball team.

"I play with the Sea Dogs," says Mora. "It's a 53-and-over team."

Mora oversees the distribution of blood to 10 hospitals in the Chicago area. He's manufacturing director for the Red Cross Mid-America Region, so he knows exactly when to expect the summer slowdown.

"We saw it a little earlier this year," says Mora. "I don't know if it's because our transfusions are up or if people just started leaving for vacations early or if they changed the school calendar — I really don't know. But we started seeing it probably two weeks before Memorial Day."

Mora keeps blood supplies in a room-sized, walk-in refrigerator at the Red Cross offices. Yellow plastic bins hold pints of blood, but about 80 percent of the shelves are empty.

"It's built to accommodate up to 5,000 products, but there's only a thousand," Mora says, looking around. "So... it's not good!"

It's about half as much blood as Mora usually keeps in stock.

The same dip in supply happens every year. Mora says blood banks can't stockpile earlier in the year, before summer, because red blood cells only last about 45 days in the refrigerator. After that, they start breaking down.

"Once it hits that shelf life, those products are no good," says Mora. "We have to throw them out."

The Red Cross says, nationwide, its donations decrease by about six percent in the summer. Other blood distributors say their donations can drop 10 to 20 percent. However, nobody is dying from these blood shortfalls. When stocks run low, blood suppliers will hustle and work with hospitals to make sure the blood goes wherever it's needed most.

But if blood suppliers are desperate for more donations in the summer, and the same shortage predictably happens every year, wouldn't it help if they paid people to give blood?

"We think that the evidence is pretty clear that this could be a way to solve when there's temporary shortages," says Robert Slonim, a professor of economics at the University of Sydney, who has studied blood markets and altruism.

Organizations like the Red Cross take donated blood and sell it to hospitals — so why not give blood donors a cut of that money? It's perfectly legal in the United States to pay people for their blood. In fact, for much of the 20th century, it was common.

Then, in 1970, a social policy researcher named Richard Titmuss published a book called "The Gift Relationship." In the book, he argued that paying people for their blood might attract the wrong kind of folks.

"Maybe people who can't hold a steady job," says Slonim. "And so these might be people that have issues with alcohol or with drugs that would actually make their blood less safe."

In "The Gift Relationship," Titmuss argued that it's better to rely on people's good, charitable instincts. Soon after, organizations like the Red Cross and the World Health Organization started advocating for volunteer-only blood donation. Which brings us to the system we have today.

But recently, Slonim and other researchers put this theory to the test. They did several studies to find out what happens when you give people incentives, like a $10 gift card or a T-shirt, for donating blood. They found that these incentives worked — more people did indeed donate. Furthermore, safety was not compromised.

"We never found, that when the incentives were offered, we saw any increase in people being disqualified to donate blood," says Slonim.

His research team wasn't able to offer blood donors money — only small gifts. So how would donors feel about getting paid cold hard cash for their blood? I visited a blood drive in downtown Chicago to ask a few people. Most donors said, 'No thanks.'

Brenda Thompson said even if she received a financial incentive, she would still donate just as regularly as she currently does. "Really. Whenever I can give blood, that's what I'm going to do," she says.

Another blood donor, Jon Mermann, had other, more creative ideas for incentives. Maybe the Red Cross could hold the blood drive on the observation deck of the Willis Tower, that Chicago tourist destination, where donors could look out over the city.

"Or serve cocktails," Mermann suggests.

That's unlikely to happen, and more traditional cash payments aren't likely to happen soon either. So far there has not been enough demand for blood, or concern about supplies, to change the system.

But over the years, scientists have been searching for a breakthrough that could change how things are done. One of the latest attempts comes from Allan Doctor, a physician and researcher at Washington University in Saint Louis. He's the creator of ErythroMer.

"It's an artificial red blood cell that's intended to resuscitate people who might be severely anemic or bleeding," says Doctor.

ErythroMer is a pink powder that you would mix with water. It's designed to be injected into someone's bloodstream. It has not been tested in humans yet, but the idea is that it could be used on soldiers who are wounded on the battlefield, or other places where real blood might be hard to store.

It could also help hospitals and blood banks deal with seasonal shortages. For instance, when someone is rushed to the emergency room after a major accident, doctors could use the powdered substitute to stabilize the patient, freeing up real blood for other uses. Allan Doctor thinks that it could also come in handy during a major incident like the Boston Marathon bombing.

"Boston-area hospitals went to the brink of depleting the local blood bank with that disaster," he says. "We've discussed with government agencies the possibility of stockpiling ErythroMer in urban centers."

Doctor says it will be many, many years before all the extra blood we need comes from a lab. ErythroMer is not a perfect substitute for blood — it doesn't clot or fight infection or circulate like real blood does.

For now, blood banks will continue to depend on people lining up to donate.