 He worked for a time in Bonn and joined the School of Hygiene and Tropical Medicine in London in 1901.As bacteriologist with the Royal Society Commission on Sleeping Sickness in 1902, he went to Entebbe, Uganda with George Carmichael Low and Cuthbert Christy.He demonstrated the cause and means of transmission of sleeping sickness, discovered the spirochete of yaws, and did other original work in bacteriology and in parasitic diseases of the skin.