In 1846, Danish physician Peter Ludvig Panum traveled to the Faroe Islands in search of measles. The rocky outcrops, located about 200 miles[200 km]north of Scotland, were hit by the plague, and Panum was sent by his government to investigate. The voyage took the discovery of viruses and antibodies for several years, but Panum still faced a challenge to test its immune system: Most of the islanders, who had survived a measles epidemic in 1781 – 65 years earlier – were not currently ill. He wrote: “I did not find anyone carefully searched, and he was attacked again.”