Bacteriologist, hygienist. After graduating from the University of Tokyo Faculty of Medicine, he went to Germany to study sanitary science and bacteriology. After returning to Japan, he taught the first class of sanitary science in Japan in 1885 and became a professor at the University of Tokyo Faculty of Medicine in 1886. He founded the hygienic laboratory of the Home Ministry and formed the foundation for bacteriology in Japan. In 1896, he discovered that the plague epidemic was due to transmission by fleas. He became the president of the Medical School of the Imperial University of Tokyo. Member of the Japan Imperial Academy.