The disease now known as Hansen's disease was for centuries called leprosy. It was once among the most feared of all medical disorders. Patients were commonly isolated from the general community in leper colonies, such as the one founded in the Hawaiian Islands by Father Damien. In fact, the term leper long ago became synonymous with the person who was outcast by society.

Until the mid-nineteenth century, Hansen's disease was thought to be a hereditary condition or a disease of the blood. Researchers had unsuccessfully attempted to induce the disease in animals by injecting them with cells from Hansen's patients. Some scientists had even tried to infect themselves in this way, without success. As a result, most authorities were convinced that the disease was not infectious.

The correct explanation for the disease was provided in about 1869 by the Norwegian physician, Gerhard Henrik Armauer Hansen. Hansen was born in...