Heinrich Hermann Robert Koch
(1843 - 1910)
German physician, one of the founders of the science of bacteriology,
who discovered the tubercle bacillus (1882) and the cholera bacillus
(1883). He won the Nobel Prize for Physiology or Medicine in 1905.
Koch attended the University of Gottingen, where he studied medicine,
graduating in 1866. He then became a physician in various provincial
towns. After serving briefly as a field surgeon during the Franco-Prussian
War of 1870-71, he became district surgeon in Wollstein, in what was
then Germany, where he built a small laboratory. Equipped with a microscope,
a microtome (an instrument for cutting thin slices of tissue), and a
homemade incubator, he began his study of algae, switching later to
One of Koch's teachers at Gottingen had been the anatomist and histologist
Friedrich Gustav Jacob Henle, who, in 1840, published the theory that
infectious diseases were caused by living microscopic organisms. In
1850 the French parasitologist Casimir-Joseph Davaine, who was among
the first to observe organisms in the blood of persons suffering certain
diseases, reported the transmission of anthrax by the inoculation of
healthy sheep with the blood of animals dying of the disease and the
finding of microscopic rod-shaped bodies in the blood of the dead sheep.
Inspired by the work of the French microbiologist Louis Pasteur, Davaine
in 1863 showed that it was highly probable that, because the sheep did
not become diseased in the absence of these rodlike bodies, anthrax
was due to the presence of such organisms in the blood. The natural
history of the disease was, nevertheless, far from complete.
It was at this point that Koch began. He cultivated the anthrax organisms
in suitable media on microscope slides, demonstrated their growth into
long filaments, and discovered the formation within them of oval, translucent
bodies--dormant spores. Koch found that the dried spores could remain
viable for years, even under exposed conditions. This finding explained
the recurrence of the disease in pastures long unused for grazing, for
the dormant spores could, under the right conditions, develop into the
rod-shaped bacilli that cause anthrax. The anthrax life cycle, which
Koch had discovered, was announced and illustrated at Breslau in 1876,
on the invitation of Ferdinand Cohn, an eminent botanist. Julius Cohnheim,
a famous pathologist, was deeply impressed by Koch's presentation. "It
leaves nothing more to be proved," he said. "I regard it as
the greatest discovery ever made with bacteria and I believe that this
is not the last time that this young Robert Koch will surprise and shame
us by the brilliance of his investigations." Cohn, whose discovery
of spores was published earlier in 1876, was also very much impressed
and generously helped to prepare the engraving for Koch's epochal paper,
which he also published. One of Cohn's pupils, Joseph Schroeter, found
that chromogenic (colour-forming) bacteria would grow on such solid
substrates as potato, coagulated egg white, meat, and bread and that
these colonies were capable of forming new colonies of the same colour,
consisting of organisms of the same type. This was the starting point
of Koch's pure-culture techniques, which he worked out a few years later.
That a disease organism might be cultured outside the body was a concept
introduced by Louis Pasteur, but the pure-culture techniques for doing
so were perfected by Koch, whose precise and ingenious experiments demonstrated
the complete life cycle of an important organism. The anthrax work afforded
for the first time convincing proof of the definite causal relation
of a particular bacillus to a particular disease.
In 1877 Koch published an important paper on the investigation, preservation,
and photographing of bacteria. His work was illustrated by superb photomicrographs.
In this paper he described his method of preparing thin layers of bacteria
on glass slides and fixing them by gentle heat. Koch also invented the
apparatus and the procedure for the very useful hanging-drop technique,
whereby microorganisms could be cultured in a drop of nutrient solution
on the underside of a glass slide. In 1878 Koch summarized his experiments
on the etiology of wound infection. By inoculating animals with material
from various sources, he produced six types of infection, each due to
a specific microorganism. He then transferred these infections by inoculation
through several kinds of animals, reproducing the original six types.
In this study, he also observed differences in pathogenicity for different
species of hosts and demonstrated that the animal body is an excellent
apparatus for the cultivation of bacteria.
Discovery of tubercle bacillus
Koch, now recognized as a scientific investigator of the first rank,
obtained a position in Berlin in the German Health Office, where he
set up a laboratory in bacteriology. With his collaborators, he devised
new research methods. To obtain a pure culture outside the body, Koch
mixed the organisms in melted gelatin; then, after solidification of
the gelatin and growth of the organisms, portions of pure colonies were
placed into separate tubes of broth or other media. Koch also concentrated
his efforts on the study of tuberculosis, with the aim of isolating
its cause. Although it was known that tuberculosis was due to an infective
agent, the organism had not yet been isolated and identified. By modifying
the method of staining, the bacillus was discovered and its presence
established in preparations of tuberculous material. A fresh difficulty
arose when, for some time, it proved impossible to grow the organism
in pure culture. But, eventually, Koch succeeded in isolating the organism
on a succession of media. Its etiologic role was now established. On
March 24, 1882, Koch announced before the Physiological Society of Berlin
that he had isolated and grown the tubercle bacillus, which he believed
to be the cause of all forms of tuberculosis.
Meanwhile, Koch's work was interrupted by the appearance of cholera
in Egypt and the danger of its transmission to Europe. As member of
a German government commission, Koch went to Egypt to investigate the
disease; although he soon had reason to suspect a particular comma-shaped
bacillus as the specific cause of cholera, he was frustrated by the
cessation of the epidemic. Nevertheless, he discovered the cause of
amebic dysentery and the bacilli of two varieties of Egyptian conjunctivitis.
Proceeding to India, where cholera is endemic, he completed his task,
discovering the cholera organism and its transmission via drinking water,
food, and clothing.
Resuming his studies of tuberculosis, Koch investigated what effect
an injection of dead bacilli would have on a person who subsequently
received a dose of living ones; he concluded that the local reaction
produced might prove the means by which the disease could not only be
diagnosed but, in the early stages, perhaps even cured. In his studies,
he used as the active agent a sterile liquid produced from cultures
of the bacillus. But this liquid (tuberculin, 1890) proved disappointing
as a curative agent, and, consequently, its importance as a means of
detecting a present or past tubercular state was not immediately recognized.
Additional work on tuberculosis came later in Koch's career, but, after
the seeming debacle of tuberculin, he was occupied (1891-99) with a
great variety of investigations into diseases of humans and animals--studies
of leprosy, rinderpest, bubonic plague, surra, Texas fever, and malaria.
The spread of malaria was still a mystery; Koch had nearly satisfied
himself that it was transmitted by mosquitoes when the British bacteriologist
Ronald Ross published his findings pointing to the same conclusion.
In 1901 Koch reported work done on the pathogenicity of the human tubercle
bacillus for domestic animals. He believed that infection of human beings
by bovine tuberculosis is so rare that it is not necessary to take any
measures against it. This conclusion was rejected by commissions of
inquiry in Europe and America in an extensive and important work that
was stimulated by Koch's theory, even though it proved to be partly
wrong. But, in most cases, the successful measures of prophylaxis were
those firmly laid down by Koch.
Thomas D. Brock, Robert Koch: A Life in Medicine and Bacteriology (1988).