1845–1916 · Russian-born biologist at the Pasteur Institute · 1908 Nobel laureate in Physiology or Medicine
Metchnikoff shared the 1908 Nobel Prize in Physiology or Medicine with Paul Ehrlich for work on immunity, then spent his later years at the Pasteur Institute arguing that microbes in the large intestine poison the body and hasten old age — the theory of intestinal auto-intoxication. In The Prolongation of Life: Optimistic Studies he called the human large intestine “certainly useless” and prescribed soured milk to crowd out putrefactive bacteria, which is why he is the figure most often named as the source of this slogan. He never wrote the sentence. The phrase appears nowhere in the 1908 English translation of the book, whose full text is searchable at Project Gutenberg.