In 1602, a Spanish fleet was sailing up the Pacific coast of Mexico when the crew became deathly ill. “The first symptom is pain in the whole body that makes it sensitive to touch,” wrote Antonio de la Ascensión, a priest on the expedition. “Purple spots begin to cover the body, especially from the waist down; then the gums become so swollen that the teeth cannot be brought together, and they can only drink, and finally they die all of a sudden, while talking.” Podcast: Science Times You probably take them every day, but do you know what vitamins really do? The crew was suffering from scurvy, a disease that was then both bitterly familiar and deeply mysterious. No one knew why it struck sailors or how to cure it. But on that 1602 voyage, Ascensión witnessed what he considered a miracle. While the crew was ashore burying the dead, one sick sailor picked up a cactus fruit to eat. He started to feel better, and his crewmates followed his example. “They all began to eat them and bring them back on board so that, after another two weeks, they were all healed,” the priest wrote.