During the American Civil War there were stories of soldiers whose wounds would glow in the dark. Doctor’s noted that the wounds showing this phenomenon were healing faster, giving the soldiers a higher chance of survival than non-glowing wounds. They called the effect “Angel’s Glow”.
It took quite a while to figure out what happened there – apparently some 139 years. It was a high-schooler who figured out in 2001 that the glow was emitted from a bioluminescent bacterium called Photorhabdus luminescens. It is suggested that this bacterium might have eaten other bacteria and pathogens in the wounds, decreasing a risk of infection and leading to an improved outcome for the soldiers.
Pretty amazing story of bacteria in action. Some more details here.
(header image from Madras Courier)