In 1847, Daniel Cornelius Danielsen (1815-1894) made an extensive description of leprosy. In 1868 Armauer Hansen (1841-1912) used this work as a basis for his studies of leprosy which in 1874 led to the discovery of the leprosy bacillus. At that time, he was not certain that leprosy was really caused by this micro-organism. It was not possible to infect laboratory animals with the disease, or to cultivate the bacteria. For this reason he implanted matter taken from patients into other individuals, including nurses and patients, but without succeeding in giving rise to a pathological process. One of the patients brought an action against Armauer Hansen on the grounds of these experiments, and Armauer Hansen was removed, by the decision of the court, from his position at the Leprosarium No. 1, where the experiments had taken place. He retained, however, his position as Chief Medical Officer for Leprosy.

In an attempt to throw light on certain aspects of the occurrence of the disease, Armauer Hansen made a journey to the USA, to examine leprous immigrants and to ascertain whether the disease had spread from them to other persons in the USA. It turned out, however, to be extremely difficult to trace patients in their new country, and no definite conclusions could be drawn. As time went by, Armauer Hansen won international recognition. One of the occasions at which this found expression was the Second International Leprosy Congress in Bergen in 1909. In the botanic gardens of the university of Bergen stands a bust of Armauer Hansen, erected by scientists from the whole of Europe and unveiled on his 60th birthday, in 1901. Armauer Hansen's urn has been placed under the bust.