Once described as a ‘hysterical character out of one of Dostoevsky’s novels’,20 he was a study in self-contradiction: a profound pessimist who tried to kill himself at least twice, yet wrote a book called The Prolongation of Life: Optimistic Studies. And in that book, published in 1908, he projected his contradictions onto the world of microbes. On the one hand, Metchnikoff said that intestinal bacteria produce toxins that cause illness, senility, and ageing and were ‘the principal cause of the short duration of human life’. On the other, he also believed that some microbes could prolong life.
