Koch was awarded the 1905 Nobel Prize in physiology and medicine for identifying the bacterium that causes tuberculosis. Until Koch's discovery it was thought that tuberculosis is due to a nutritional disorder. Koch was the first person to show that the disease is an infection caused by bacteria carried through the air on dust particles. In his study of these bacteria, Koch developed a basic method of isolating and identifying any disease-causing bacteria. This method, called Koch's postulates, is still used in microbilogy. Koch also developed a test for diagnosing tuberculosis.
Koch began his career in microbiology with a study of anthrax, an infectious disease of livestock that may be transmitted to man. In 1876 he isolated and identified the anthrax-causing bacterium. By observing their life cycle. he also explained how the disease is spread from one animal to another.
In studying anthrax, Koch used a liquid medium to cultivate the bacteria. However, the medium was not entirely satisfactory because it allowed the bacteria to move freely and they could not be carefully observed. For his study of tuberculosis-causing bacteria, Koch wanted a solid medium on which to grow the microorganisms. With such a medium the bacteria would remain on the surface, where they could be easily seen. After experimenting with various kinds of culture media, Koch finally developed a solid medium using gelatin. Many scientists consider this Koch's greatest contribution to the field of microbiology.
Between 1883 and 1907, Koch traveled throughout India, Egypt, and other parts of Afric, studying the various epidemic diseases of those areas. In India he discovered the bacteria that cause cholera and showed that the disease is spread through polluted water. He also proved that bubonic plague is transmitted to man through the bite of a flea that has lived on an infected rat.
