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Chapter 11 : The Germ Theory Is Established
To symbolize the magnitude of Robert Koch's discoveries, we need only mention that shortly after the completion of his studies on anthrax he electrified the world by discovering the microbes responsible for cholera and for tuberculosis—two of the most destructive enemies of humankind. In reality, several veterinarians and physicians had suspected long before Pasteur and Koch that bacteria were responsible for anthrax. The three decades that followed the original studies on anthrax saw the discovery of many other bacterial agents of disease by Pasteur, Koch, their associates, and their followers. The great theoretical advance in the germ theory of disease was to be made by Pasteur himself when he discovered that disease can be caused by agents so small as to be invisible under the microscope and able to pass through filters, and so peculiar as to fail to grow in the ordinary culture media of the bacteriologists. These agents of disease are now known as filterable viruses or simply, viruses. The new discovery came from the study of rabies. The general symptoms of rabies suggested that the nervous system was attacked during the disease. Nerve tissue seemed to be an ideal medium for the virus of rabies, and to fulfill the condition of selectivity, which was the foundation of the cultural method.