1905 Nobel Prize in Physiology or Medicine — Robert Koch

What You Will Learn in This Article

You will learn what needs to be proven to say, "This bacterium is the cause of this disease." Koch created a four-step verification protocol – the foundation of modern infectious disease epidemiology, and the archetype of scientific proof of causality. This "Koch's postulates," which is a must-read in the first chapter of university microbiology textbooks, originated here.

How to Prove "the Cause of a Disease"?

We take for granted that "bacteria cause disease." However, until the mid-19th century, most doctors believed that disease was caused by "bad air (miasma)" or "imbalance of bodily fluids." The existence of bacteria began to be visible under a microscope, but proving the causal relationship, "this bacterium is the cause of this disease," was a completely different problem.

Does the mere discovery of bacteria in a patient guarantee that it is the cause? How can causality be proven, rather than just a correlation? Robert Koch provided the answer to this question, and his answer was remarkably systematic.

The Zeitgeist — A Year When the World Was Turned Upside Down

1905 was, in many ways, a year of "the collapse of the existing order."

The Russo-Japanese War ended with Japan's victory (Treaty of Portsmouth, September 1905). It was the first time in modern history that a European power had been defeated by an Asian country. The shockwave spread throughout the world, and in Korea, it directly led to the Eulsa Treaty (November 1905), a tragedy in which Japan forcibly annexed Korea.

In the same year, Albert Einstein, an employee of the patent office in Bern, Switzerland, published his theory of special relativity. And in Russia, the First Revolution broke out, triggered by "Bloody Sunday."

1905, the year Koch received the Nobel Prize, was such a year. It was a period when political and scientific paradigms were being challenged simultaneously. Koch's achievement was precisely of that nature—a challenge to the millennia of ignorance that "we do not know the cause of disease."

Meanwhile, Koch himself was a typical product of the German Empire. As mentioned in the 2001 article about Behring, the German Empire actively utilized science as a tool for national prestige, and Koch's Institute for Infectious Diseases (now the Robert Koch Institute, RKI) was a key institution. The RKI, which led Germany's public health policy during the COVID-19 pandemic, is named after this man.

A Rural Doctor Who Began Bacteriology in His Kitchen

Robert Koch (1843-1910) was born in Clausthal, a mining town at the foot of the Harz Mountains. After studying medicine at the University of Göttingen, he practiced medicine in the Prussian rural town of Wollstein. It was here that something remarkable happened. This rural doctor set up a microscope in a corner of his home office—a microscope his wife had given him as a birthday gift—and began studying bacteriology on his own.

His first target was anthrax. Koch isolated the anthrax bacillus from the blood of infected cattle, injected it into mice, causing the same disease, and successfully isolated the same bacillus from the diseased mice (1876). This study, conducted in a laboratory that was like a rural clinic's kitchen, announced the birth of bacteriology along with Pasteur.

After moving to Berlin, Koch discovered in 1882 the causative agent of tuberculosis, one of the infectious diseases that has claimed the most lives in human history—Mycobacterium tuberculosis. In 19th-century Europe, tuberculosis was called the "White Plague," and one in seven deaths was caused by tuberculosis.

Koch's Postulates — The Most Famous Debugging Protocol in the History of Science

Koch's greatest achievement was not simply discovering the bacillus. He created a methodology for proving "this bacillus is the cause of this disease." This is Koch's postulates.

1. The same microorganism must be found in all cases of the disease.
2. The microorganism must be isolated from the diseased host and grown in pure culture.
3. The cultured microorganism should cause the disease when introduced into a healthy host.
4. The same microorganism must be re-isolated from the experimentally infected host.

In terms of computer science, this is a four-step debugging protocol for determining the cause of a bug.

1. Does the same suspect code exist in all environments where the crash occurs?
2. Can that code be isolated and run independently?
3. When the isolated code is injected into a normal environment, does the same crash occur?
4. Can the code be extracted from the environment in which the crash occurred?

Only after passing all four steps can you say, "This code is the cause of the bug." What Koch created is a protocol for bacteriology, but in essence, it is a universal framework for verifying causality. It is surprising that this principle, which is taught in the first week of university microbiology classes, was created in the 1870s.

However, this analogy also has its limitations. Software bugs are deterministic, but infectious diseases are probabilistic. Not all people infected with the tuberculosis bacillus develop tuberculosis. The outcome varies depending on immune status, nutritional status, and genetic susceptibility. Koch's postulates themselves were later modified and expanded due to this limitation, and are difficult to apply directly to viruses (which cannot be cultured) or prions (infectious agents that do not contain nucleic acids).

Koch and Pasteur — The Greatest Rivalry in the History of Science

When talking about Koch, it is impossible to leave out Louis Pasteur. The two were the twin giants of bacteriology and, at the same time, fierce rivals. Koch, a German, and Pasteur, a Frenchman. Behind the competition between the two was the national pride of France, which had been defeated by Prussia in the Franco-Prussian War (1870-1871), and the scientific prestige of the new German Empire.

Koch publicly criticized Pasteur's experiment on the anthrax vaccine for its lack of reproducibility, and Pasteur questioned the effectiveness of Koch's tuberculosis treatment (tuberculin). The two engaged in heated debates in academic journals. It was a confrontation in which science and national pride were intertwined.

Tuberculin — The Painful Failure of a Great Scientist

Koch had both brilliant achievements and painful failures. In 1890, he announced tuberculin—an extract of the tuberculosis bacillus—as a treatment for tuberculosis. Koch, who declared at the Berlin International Medical Congress that "I have found a cure for tuberculosis," was met with enthusiasm from around the world.

However, tuberculin did not cure tuberculosis. Clinical trials confirmed that it was ineffective and, in some patients, worsened their condition. Koch suffered a serious loss of credibility due to his excessive announcement.

Ironically, tuberculin failed as a treatment, but it was a great success as a diagnostic reagent for tuberculosis. The tuberculin skin test (PPD test), also known as the "tuberculin test," is still used worldwide to screen for tuberculosis infection. In Korea, too, the test you receive in elementary and middle school, in which a solution is injected into the inside of your arm and the size of the swelling is measured 48 hours later, is Koch's tuberculin.

The Door Opened by Bacteriology — The Root of Modern Infectious Disease Epidemiology

After Koch's postulates were established, the discovery of the causative agents of infectious diseases surged. Gonococcus, typhoid bacillus, leprosy bacillus, diphtheria bacillus, plague bacillus, dysentery bacillus, syphilis bacillus—all of these pathogens were identified within the framework of Koch's postulates. Half of the first part of university microbiology textbooks is based on the knowledge established during this period.

And the students trained at the Koch Institute are the other protagonists in this series. Behring (antiserum), in the 2001 article, and Ehrlich (chemotherapy), in the 2008 article—both were trained at Koch's institute. Koch was not only the father of bacteriology, but also the founder of a school that produced Nobel laureates.

In 1905, the debugging protocol created by Koch has not been broken. Whenever new exceptions such as viruses and prions emerge, it has been expanded, but the original four-step logical structure still survives as the gold standard for verifying causality.