Robert Koch, a German physician and microbiologist, is best known for his contributions to the field of bacteriology. In the late 19th century, Koch used a compound microscope to study the causative agents of infectious diseases. One of his most significant discoveries was the identification of the bacterium responsible for causing tuberculosis, Mycobacterium tuberculosis.
Using a combination of staining techniques and microscopic observation, Koch was able to isolate and identify the specific microorganism responsible for tuberculosis. He also developed a series of postulates, known as Koch's postulates, that are still used today to establish a causal relationship between a microorganism and a disease.
Koch's use of the compound microscope was instrumental in advancing the field of bacteriology and revolutionized our understanding of infectious diseases. His work laid the foundation for the development of antibiotics and other treatments for bacterial infections.