into the properties of yeast, nitrogen fixation, alcohol production and the role of lactic acid bacteria. In 1895 Marken helped to fund for him the Chair of Microbiology at the university, where he remained

Shallow wells in rural areas and often deep wells, too, were contaminated with animal waste and bacteria from surface sewers and drains. Disease was rife and could be often traced to the water supply.

Britain at the start of the 20th century chlorine began to be introduced into the water to kill off bacteria. In Germany, not even a half of all cities possessed a central system of water supplies. But in