Robert Koch
Techniques in bacteria study

Robert Koch made two important developments in microscopy; he was the first to use an oil immersion lens and a condenser that enabled smaller objects to be seen. In addition, he was also the first to effectively use photography (microphotography) for microscopic observation. He introduced the "bedrock methods" of bacterial staining using methylene blue and Bismarck (Vesuvin) brown dye. In an attempt to grow bacteria, Koch began to use solid nutrients such as potato slices. Through these initial experiments, Koch observed individual colonies of identical, pure cells. He found that potato slices were not suitable media for all organisms, and later began to use nutrient solutions with gelatin. However, he soon realized that gelatin, like potato slices, was not the optimal medium for bacterial growth, as it did not remain solid at 37 °C, the ideal temperature for growth of most human pathogens. And also many bacteria can hydrolyze gelatin making it a liquid. As suggested to him by his post-doctoral assistant Walther Hesse, who got the idea from his wife Fanny Hesse, in 1881, Koch started using agar to grow and isolate pure cultures. Agar is a polysaccharide that remains solid at 37 °C, is not degraded by most bacteria, and results in a stable transparent medium.
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