It’s blue, comes from a creature more ancient than dinosaurs, and saves countless human lives. +

It’s the blood of horseshoe crabs, and for decades it’s proved vital to biomedical companies that must screen vaccines, IV fluids, and medical devices for bacteria that can be fatal in our bloodstream. Thanks to proteins in cells that act like a primitive immune system, the crabs’ blood coagulates instantly when it touches pathogens like E. coli and Salmonella. So sensitive is the test derived from the proteins that it can detect amounts as slight as one part per trillion. That’s like one grain of sugar in an Olympic-size pool, says John Dubczak of test producer Charles River, Endosafe.