Bacteriologist. In 1896, he graduated from the Medical College of the Imperial University and was mentored by Kitasato Shibasaburo at an institute for studying infectious diseases. He discovered Shigella dysenteriae as the pathogen for bacillary dysentery in 1898. In 1901, he engaged in research of biochemistry, immunology and chemotherapy under Paul Ehrlich in Germany and discovered trypan red, which was regarded as the first chemotherapeutic agent. After returning to Japan, he studied a Shigella vaccine, tuberculosis and Hansen's disease. He became a professor of the Faculty of Medicine of Keio University, a professor of Keijo Imperial University, and an advisor of the Kitasato Institute. Awarded the Order of Culture in 1944.