Gut Feelings
In the fourth century BC, Hippocrates, the father of modern medicine, shared a prescient opinion that “bad digestion is the root of all evil,” and that “death sits in the bowels.”
In the seventeenth century, Dutch scientist Antoni van Leeuwenhoek used homemade single-lens microscopes on samples gathered from his own body to make the first observations of bacteria. Describing his remarkable discovery, he said, “I then most always saw, with great wonder, that in the said matter there were many very little living animalcules, very prettily amoving.”
In the nineteenth century, French zoologist Élie Metchnikoff believed that bacteria in fermented milk were beneficial in fighting “autointoxication,” a term used to describe a wide range of symptoms from fatigue to melancholia. His theory that eating yogurt could delay senility and enhance health was popular during his time but soon faded from prominence for more than a century.
Starting in the late
