Friedrich Loeffler (1852-1915), German bacteriologist and virologist. Loeffler worked as an assistant to Robert Koch and became director of the Koch Institute in Berlin in 1913. In 1882 Loeffler discovered the organism which caused glanders (a contagious horse disease). In 1884 Loeffler isolated the diphtheria bacillus which had first been observed by Theodor Klebs. In doing so he made a number of technical advances in the culturing of cells. In 1898, Loeffler and Paul Frosch inoculated cows with foot-and-mouth disease with cell-free filtrates from infected animals. This proved that viruses caused disease.