Some of the injured had wounds that glowed blue -- and those who did, seemed to be more

likely to survive.

They called this weird light the Angel's Glow, and figured that it must be a sign of

supernatural protection.

And for more than a hundred years, nobody knew what caused it -- until a pair of high

school scientists figured it out:

The soldiers with glowing wounds were being protected by bacteria.

The American Civil War was a pretty rough place to be.

New developments in weaponry made the battles especially bloody and brutal, resulting in

extremely high numbers of casualties on both sides of the conflict.

The Battle of Shiloh was a particularly awful place to be -- when the battlefields cleared

after two days of fighting, more than 23,000 people had been injured or killed, making

it the bloodiest battle in American history until that point.

The medics on both sides weren't prepared to deal with so many injuries, so many wounded

soldiers had to wait for days before they received medical attention.

And as night fell on the first evening, some soldiers were surprised to discover that their

wounds were glowing with a soft blue light.

It turned out that those soldiers whose wounds had glowed in the dark were more likely to

survive, and their injuries healed more cleanly than those who didn't -- almost as if the

blue light were protecting the soldiers who had it.

In 2001, a 17-year-old named Bill Martin learned about the Angel's Glow and immediately thought

of his mother's research on glowing bacteria for the US Department of Agriculture.

Phyllis Martin was studying a type of bioluminescent bacteria known as Photorhabdus luminescens,

which is found in soil and glows a pale blue.

So Bill, along with his friend John Curtis, decided to see if the blue glow of the soldier's

wounds could be related to the blue glow of the bacteria.

They knew that P. luminescens has a mutualistic relationship -- in other words, one that benefits

both species -- with a roundworm, or nematode.

But the worms have another important relationship in their lives -- they're parasites of some

insects.

When these roundworms infect an insect, they spit up any P. luminescens that the insect

happens to have in its guts.

Then, the bacteria release toxins that kill the insect and enzymes that break down tissue.

So both the worm and the bacteria get a tasty dinner.

The duo took their project to the lab, where they examined strains of the bacteria under

different environmental conditions to figure out what suited them best.

When they compared those results to the conditions described in historical records of the Battle

of Shiloh, they found that the soil would have been a great place for both the bacteria

and the worms to thrive.

And if the bacteria were living in soldiers' wounds, that would explain the Angel's Glow

-- and why the soldiers who had it were more likely to survive.

So here's what they figured happened after the Battle of Shiloh:

There would probably have been insects on or near the soldiers' wounds, because they

were outdoors in a battlefield.

When nematodes infected those insects, P. luminescens would have released the toxins

that normally help kill the insects.

But in this case, those compounds would also have helped kill off other, more dangerous

bacteria, protecting the soldiers from infection.

Then, the worms would have moved on in search of their next meal.

And that whole time, the P. luminescens would be glowing, giving off a faint, ghostly blue

light.

So, it seemed like Martin and Curtis had solved the mystery.

But there was one more wrinkle to iron out:

Normal human body temperatures are too hot for P. luminescens.

So how could the bacteria be living in the soldiers' wounds?

After some more thinking, though, the pair came up with an answer.

The battle occurred in early April in Tennessee, where it would have pretty chilly at night.

The wounded soldiers would have been sitting on the cold, damp ground, waiting for medical

care.

Under those conditions, it wouldn't take long for hypothermia to set in -- and the

soldiers' lowered body temperature would have been just cool enough for P. luminescens

to do their thing.

Then, once the soldiers were found and brought indoors for care, their bodies would warm

back up again, killing off the P. luminescens before they could spread far enough to become

dangerous.

These experiments and conclusions earned Bill Martin and John Curtis the top prize in the

2001 Intel International Science and Engineering Fair.

By combining their knowledge of history and microbiology, and trying a few experiments

of their own, they solved the 139-year-old mystery of the Angel's Glow.

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