In 1862, tens of thousands of young men set off to kill each other in a field in Shiloh, Tennessee and did an excellent job of it, leaving at least 3,000 people dead and a further 16,000 maimed and wounded. After the battle was over, medics from either side spent the next two days carrying barely-breathing bodies out of the sea of mud and human gore. Some men spent the whole two days too wounded to crawl to shelter, lying where they fell in the rain and freezing sludge around them.
And some of them had many lonely hours in the dark to watch their battle-wounds glow.
For 140 years the stories of blue-green glowing wounds were dismissed as superstition, much like the Angels that soldiers claim they saw at the Battle of Mons during the first world war. The legend goes that the wounds didn’t just glow; the men with glowing wounds were much, much more likely to survive their ordeal on the field of valour than their non-glowing cohorts, leading the wounds to be referred to as “Angel’s Glow”. Curiously, the stories were proven true in 2001 by a pair of teenagers, Bill Martin and Jon Curtis, doing a school science fair project, who went back to the battle site to test the soil for microbes.*
What they found was Photorhabdus luminescens, which is a bacteria that lives in the guts of tiny parasitic worms called nematodes. The nematodes spew up the bacteria on their food (insects) and let the bacteria release toxins and enzymes that kill and partially dissolve that food. Fortunately for the soldiers, the toxins also kill other bacteria, meaning that the nematodes and P. luminescens sterilise the wounds that they infect. This explains why the glowing wounds healed faster and better than the non-glowing wounds.
But wait, why didn’t the P. luminescens make the soldiers sick like the other bacteria would? Well, it turns out that P. luminescens can’t survive at human body temperature. All the soldiers that had the glowing wounds had been lying outside in the freezing cold and rain for hours or days – all of them would have had lower than normal body temperatures and many would have hypothermia, meaning that they could support P. luminescens in their wounds until they were carried inside and warmed up. As their body temperatures returned to normal, the P. luminescens would die off, leaving the wounds free of bacteria – that is, until they had their bandages changed by a field medic in an era where washing your hands wasn’t considered a necessary part of practicing medicine.
* Take this how you will, but we are supposed to accept that these two boys came up with the idea on their own, even though one of their parents is a microbiologist that works with P. luminescens professionally.