Robert Koch and the white death: from tuberculosis to tuberculin

The German medical bacteriologist Robert Koch is commonly considered one of the founding fathers of medical bacteriology. His investigations into the aetiology of tuberculosis uncovered the pathogen of this condition, the tubercle bacillus today known as Mycobacterium tuberculosis, in 1882. This work can be seen as a cornerstone of contemporary medical bacteriology, its technologies and methods. It has often been asked how such successful research connected to the tuberculin episode of 1890/91, when Koch produced a medicine for that disease, which spectacularly failed when applied in practice. The analysis concentrates on the path of mostly experimental investigations which Koch followed between 1882 and 1890. From Koch's laboratory notes it becomes clear that tuberculin therapy did in fact work in Koch's laboratory, even though it failed to do so almost anywhere else. The clue to this contradictory picture lies in the peculiar nature of Koch's understanding of tuberculosis as a disease e.g. his reliance an animal experiments, which essentially differed from what many of his contemporaries held as essentials of that condition.