He was born in Inawashiro, Fukushima. He worked at the Institute of Infectious Diseases as a doctor. When he was 24, he went to the United States. In 1928, he moved to Ecuador, where there were many cases of yellow fever. He went to find the bacteria that caused it. After arriving there, he was able to identify the bacteria as yellow fever, and developed a vaccine. This quickly reduced the number of people dying of yellow fever in South America.