[Expedition, experiment and expertise reflected in Robert Koch's assets].

Basic techniques in bacteriology provided the foundation for the success of experimental medicine. The combination of laboratory experiments and field studies consolidated bacteriology as a paradigm for the development of preventive strategies. Robert Koch's (1843-1910) contribution to this development is crucial in that he integrated the technical facilities of his era into microbiological research. The present study introduces various sources of Koch's assets which, in addition to manuscripts and letters, include also bacteriological slides and photographs. These relicts allow to reconstruct an example of the scientific process as a whole, to investigate his style and purpose as a scientist, and to follow Koch's strategy of visualisation with contemporary technical equipment. The example chosen is Koch's last expedition when the German government sent him to investigate the spreading of sleeping-sickness in Eastern Africa and to test "Atoxyl" as a specific remedy. Most case-studies and laboratory-research took place on the Sese-Islands in Lake Victoria and illustrate the extreme conditions in tropical Africa. The experiments searching for the etiological agent of sleeping-sickness--a typical disease only for central Africa--involved bacteriological slides which were to be the basis for further experimental results and the expertise expected of him.