In the mid-nineteenth century, the German speaking countries overtook and surpassed France as the leading supporters of scientific and medical research. German rulers became convinced that scientific and medical research offered enormous practical benefits and was worth supporting. This happened in France too, which was how Louis Pasteur was able to make a career as a scientist. However, the scale of support for scientific research in Germany was larger, and many more men (and a very few women) were able to forge scientific careers in the nineteenth century. Germany was not a unified country until 1871. The political fragmentation of the German states actually helped further the development of science because each German territory (at least, each of the larger territories) had its own state-supported university with research faculty. Each state competed with the others to have the most prestigious faculty and the best research facilities. And in order to try to attract the best professors and the brightest students, different universities offered perks like bigger salaries for professors, better laboratories, larger research budgets, and larger staffs of technical assistants. As universities competed with each other to attract and retain science faculty, financial and institutional support for science increased. By contrast, in France the undisputed intellectual and cultural center was Paris, and a substantial amount of the country’s resources went into Parisian institutions, which naturally limited the number of scientists and universities that received support.

The career of one of the most famous German scientists, Robert Koch (1843-1919), demonstrates the influence of this institutional support. Although Pasteur was the first (by a few years) to articulate the concept of germ theory – that is, that a specific microorganism causes a specific disease – Robert Koch was responsible for the consolidation of field of bacteriology. If you have ever used Petri dishes, cultured bacteria in an agar medium, or stained bacteria in order to visualize them under the microscope, you have employed techniques developed by Koch and his associates. Julius Richard Petri (1852 – 1921), inventor of the Petri dish, was one of Koch’s assistants. Walther Hesse (1846 –1911), another of Koch’s assistants, developed agar as a medium (after learning about its properties from his wife Angelina Hesse). Koch formalized the procedures for identifying the microorganisms that caused specific diseases. These procedures are now known as Koch’s postulates, and you can still find them in science textbooks. It was Koch who firmly established the germ theory of disease and systematically developed its potential.

Look at the following website for an overview of Koch's Postulates.

In order to prove that an organism was responsible for a particular disease, a scientist had to demonstrate four things:

1) The organism is found in every instance of the disease. That is, the microorganism is present in all individuals (human or animal) with the disease. However, the mere fact that the microorganism is present does not demonstrate that it CAUSES the disease. [It was later shown that sometimes disease causing microorganisms are found in healthy individuals. These humans (or animals) are called “healthy carriers.”] The next three steps are crucial to demonstrating that a specific microorganism is the cause of a specific disease.

2) The organism must be isolated and cultured over many generations. That is, a researcher needed to be able to extract the microorganism from the body of a sick animal or human and culture that organism outside of the body.

3) After the microorganism has been isolated and cultured for many generations, the researcher should be able to reproduce the disease in experimental animals using this cultured microorganism. That is, it is not sufficient to take the microorganism out of a sick individual and put it in the body of a healthy individual to see if it will cause the same disease. If you did this, a critic could argue that it was some OTHER substance in the sick person’s body that carried the disease. But if the microorganism has been isolated and cultured for many generations, there is no substance from the sick individual’s body left in the culture. What you have is pure microorganism. So if that microorganism is introduced into a healthy individual and that individual becomes sick with the same disease, you can be certain that it was the microorganism that caused the disease.

4) Finally, the researchjer must be able to retrieve the microorganism from the inoculated animal and culture it.

Koch and his followers could not meet all four criteria in all cases – viruses remained challenging on into the twentieth century because they could not be seen under a microscope and isolated – but they could in most. Koch’s earliest work was with anthrax, an organism that Pasteur also studied. Pasteur identified the microorganism that causes anthrax in 1876. However, Koch really hit the big time with his discovery of the microorganism that causes tuberculosis. On March 24, 1882, Koch announced his discovery of the bacillus that causes tuberculosis paper in a paper he delivered before the Berlin Physiological Society. Tuberculosis was a leading cause of death in the nineteenth century, so there was considerable excitement when Koch made this discovery. It was hoped that, just as in the case of chicken cholera and anthrax, a vaccine could be developed. As it turned out, a vaccine and a cure for tuberculosis was considerably harder to develop, but in the aftermath of his work on tuberculosis Koch became internationally famous.

In 1883, there was a cholera epidemic in Egypt. The French government sent a team headed by a colleague of Louis Pasteur, to invesigate. The German government sent a team headed by Robert Koch. A fierce competition ensued to see who could find the microorganism that causes cholera first. The French team used Pasteurian methods. They tried to reproduce the disease in experimental animals and then look for microorganism. This failed because cholera only affects humans (it’s not the same as chicken cholera). Koch worked directly with human cholera victims. He isolated and identified the bacillus that causes cholera, and showed that it lived in human intestine and was communicated mainly by polluted water. He reported his success to the German government in February of 1884. In the next few decades Koch’s pupils and colleagues rapidly discovered microorganisms responsible for diphtheria, typhoid, pneumonia, gonorrhea, cerebrospinal meningitis, leprosy, plague, tetanus, syphilis, whooping cough and more.

Pasteur’s success with anthrax and rabies vaccines created high expectations. All you needed to do was identify microorganism and vaccine would quickly follow! Unfortunately, this didn’t happen so easily in most cases. Tuberculosis was still untreatable. Attempts to protect individuals by injecting them with killed or attenuated tuberculosis bacilli didn’t work.

One of the early success stories of germ theory involves the disease diphtheria. Diphtheria is an infectious disease characterized by fever, sore throat, and coughing. In severe cases, a leathery membrane forms on the tonsils and palate which blocks the airways and can cause death. Although this disease is almost unheard of in industrialized countries today, it was a major killer of children in the nineteenth century. (There have been less than sixty cases of diphtheria in the US since 1980.) For example, in New York City in the 1870s, two thousand children per year died of diphtheria. The microorganism that causes diphtheria was identified by Edwin Klebs (1834 – 1913) in 1883. When attenuated cultures of diphteria bacilli were injected into guinea pigs, they produced immunity. Thus it was possible to vaccinate guinea pigs, and eventually children, against diphtheria. In 1890, two scientists who worked with Robert Koch, Shibasaburo Kitasato and Emil von Behring, discovered that the blood or serum of an animal rendered immune to diphtheria through vaccination could be used to treat another animal exposed to the disease. This blood or serum was called diphtheria antitoxin. Diphtheria antitoxin was first used to cure a sick child in Berlin in 1891. The antitoxin came into general use in 1895. Within ten years the mortality rate of diphtheria dropped to less than half of what it had been. In 1901, Emil von Behring won the first Nobel Prize in medicine for his work on diphtheria. (It’s not clear to me why Shibasaburo Kitasato did not share this prize.) Diphtheria was a great success story because the discovery of the microorganism led to both a vaccine and a cure.