By the spring of 1862, a year into the American Civil War, Major General Ulysses S. Grant had pushed deep into Confederate territory along the Tennessee River. In early April, he was camped at Pittsburg Landing, near Shiloh, Tennessee, waiting for Maj. Gen. Don Carlos Buell’s army to meet up with him.

On the morning of April 6, Confederate troops based out of nearby Corinth, Mississippi, launched a surprise offensive against Grant’s troops, hoping to defeat them before the second army arrived. Grant’s men, augmented by the first arrivals from the Ohio, managed to hold some ground, though, and establish a battle line anchored with artillery. Fighting continued until after dark, and by the next morning, the full force of the Ohio had arrived and the Union outnumbered the Confederates by more than 10,000.

The Union troops began forcing the Confederates back, and while a counterattack stopped their advance it did not break their line. Eventually, the Southern commanders realized they could not win and fell back to Corinth until another offensive in August (for a more detailed explanation of the battle, see this animated history).

All told, the fighting at the Battle of Shiloh left more than 16,000 soldiers wounded and more 3,000 dead, and neither federal or Confederate medics were prepared for the carnage.

The bullet and bayonet wounds were bad enough on their own, but soldiers of the era were also prone to infections. Wounds contaminated by shrapnel or dirt became warm, moist refuges for bacteria, which could feast on a buffet of damaged tissue. After months marching and eating field rations on the battlefront, many soldiers’ immune systems were weakened and couldn’t fight off infection on their own. Even the army doctors couldn’t do much; microorganisms weren’t well understood and the germ theory of disease and antibiotics were still a few years away. Many soldiers died from infections that modern medicine would be able to nip in the bud.

A BRIGHT SPOT

Some of the Shiloh soldiers sat in the mud for two rainy days and nights waiting for the medics to get around to them. As dusk fell the first night, some of them noticed something very strange: their wounds were glowing, casting a faint light into the darkness of the battlefield. Even stranger, when the troops were eventually moved to field hospitals, those whose wounds glowed had a better survival rate and had their wounds heal more quickly and cleanly than their unilluminated brothers-in-arms. The seemingly protective effect of the mysterious light earned it the nickname “Angel’s Glow.”

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In 2001, almost one hundred and forty years after the battle, seventeen-year-old Bill Martin was visiting the Shiloh battlefield with his family. When he heard about the glowing wounds, he asked his mom – a microbiologist at the USDA Agricultural Research Service who had studied luminescent bacteria that lived in soil – about it.

“So you know, he comes home and, ‘Mom, you’re working with a glowing bacteria. Could that have caused the glowing wounds?’” Martin told Science Netlinks. “And so, being a scientist, of course I said, ‘Well, you can do an experiment to find out.’”

And that’s just what Bill did.

He and his friend, Jon Curtis, did some research on both the bacteria and the conditions during the Battle of Shiloh. They learned that Photorhabdus luminescens, the bacteria that Bill’s mom studied and the one he thought might have something to do with the glowing wounds, live in the guts of parasitic worms called nematodes, and the two share a strange lifecycle.

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