Robert Koch (1843-1910) German bacteriologist and physician in his laboratory © Universal History Archive/Getty Images)

Robert Koch: how he identified one of the 19th Century’s biggest killers

How one of the pioneers of bacteriology single-handedly solved the mystery of one of the biggest killers of the 19th Century – ‘consumption’, what we now know as tuberculosis.

Robert Koch’s important discovery wasn’t actually an experiment but rather more than six months of solitary work. During 1881-2, he tackled the leading cause of death in the 19th Century: consumption, or tuberculosis. Tuberculosis is quite unlike acute contagious diseases, which provided the model for early work in the field.

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Most doctors thought it was an inherited disorder, attributing the familial incidence to bad heredity. The tubercle bacillus is slow-growing, and difficult to stain and cultivate. It was at least easy to grow in guinea pigs, which then developed tubercles in their lungs. Koch managed to find the right medium for the fastidious organism: heat-coagulated sheep serum.

Read more about the history of disease:

He found that a combination of the dyes methylene blue and Bismarck brown stained it, making it visible in his microscope.

In producing the disease in his laboratory animals, and recovering and growing it again, he fulfilled the criteria of what we still call ‘Koch’s Postulates’. Koch’s redefinition of tuberculosis changed how it was understood, justifying public health measures including building tuberculosis sanatoria, in which individuals with the bacillus in their sputum were isolated for long periods.

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There they were also treated with the largely ineffective therapies that remained in place until the antibiotic era of the 1940s.