The question of whether tuberculosis was due to a transmissible agent or to an inherited disposition was a subject of controversy in the nineteenth century, but the 1868 demonstration by Jean Antoine Villemin that inoculation of tuberculous material from humans and cattle into rabbits elicited characteristic granulomatous lesions swung the argument strongly in favour of an infectious cause. The matter was finally and irrefutably settled on 24 March 1882, when Robert Koch described a series of meticulous studies in which he had not only isolated the causative bacillus but, by means of his well-known postulates, had clearly confirmed its aetiological role in tuberculosis.