klinotaxis Amovement in a specific direction rela-
tive to a given stimulus, either directly toward or away
from the source.
Koch, Robert (1843–1910) GermanBacteriologist
Robert Koch was born on December 11, 1843, in
Clausthal in the Upper Harz Mountains and is consid-
ered one of the fathers of modern medical bacteriolo-
gy (along with Louis Pasteur). The son of a mining
engineer, he taught himself to read by age five. He
attended the local high school and developed an inter-
est in biology.
In 1862 Koch attended the University of Göttingen
to study medicine under professor of anatomy Jacob
Henle. In 1840 Henle had published that living, para-
sitic organisms caused infectious diseases. In 1866
Koch married Emmy Fraats and they had one daughter.
After receiving his M.D. degree, Koch went to Berlin
for further study. In 1867, after a period as assistant in
the general hospital at Hamburg, he settled into general
practice at Langenhagen and, in 1869, at Rackwitz, in
the province of Posen. There he passed his district med-
ical officer’s examination, but in 1870 he volunteered
to serve in the Franco-Prussian War. From 1872 to
1880 he was district medical officer for Wollstein and
while there carried out his groundbreaking research.
Studying from his four-room flat, with a micro-
scope and other equipment he purchased, he began
research on anthrax, earlier discovered by other scien-
tists to be caused by a bacillus. Koch wanted to prove
whether or not anthrax was actually caused by the
bacillus, and he used mice and bacilli taken from the
spleens of dead farmanimals. He found that the mice
did die from the bacillus and proved that the blood of
anthrax-infected animals transmitted it. He also showed
that the bacilli could produce resistance spores when
environmental conditions were unfavorable, and that
they could reemerge as viable anthrax-causing organ-
isms when conditions changed. Koch’s work became
internationally known when it was published in 1876.
He was the first person to establish a definite causal
connection between a particular disease and a particular
bacillus. He continued working on methods of studying
bacteria and in 1878 published his results that included
how to control infections caused by bacteria.
In 1880 he was appointed a member of the Reichs-
Gesundheitsamt (Imperial Health Bureau) in Berlin and
continued to refine his methods in bacteriological
research. He invented new methods of cultivating pure
cultures of bacteria on solid media and on agar kept in
the special kind of flat dish invented by his colleague
Petri, which is still in common use (the Petri dish). He
also developed new methods of staining bacteria, mak-
ing them easily visible for identification. All of this
work helped establish the methods to study pathogenic
bacteria easily in pure cultures. Koch also laid down the
conditions, known as Koch’s postulates, that must be
satisfied before it can be accepted that particular bacte-
ria cause particular diseases. These postulates were:- The specific organism should be shown to be present
in every case of the disease. - The specific microorganism should be isolated from
the diseased animal and grown in pure culture on
artificial laboratory media such as in a Petri dish. - The freshly isolated microorganism, when inoculated
into a healthy laboratory animal, should cause the
same disease seen in the original animal. - The microorganism should be recovered from the
experimentally infected animal.
Koch also discovered the tubercle bacillus, the
cause of tuberculosis, and developed a method of
growing it in pure culture, and in 1882, he published
his now classical work on the bacillus. In 1883 he was
sent to Egypt as leader of the German Cholera Com-
mission to investigate a cholera outbreak and soon dis-
covered the bacteria that causes cholera and brought
back pure cultures of it to Germany. He also studied
cholera in India.
Koch formulated rules for the control of epidemics
of cholera in 1893 and formed the basis of the methods
ofcontrol. His work on cholera was rewarded with a
prize of 100,000 German marks.
In 1885 Koch was appointed professor of hygiene
in the University of Berlin and director of the newly
established Institute of Hygiene in the university. Five
years later he was appointed brigadier general (gener-
alarzt)class I and freeman of the city of Berlin. In 1891
he became an honorary professor of the medical faculty
of Berlin and director of the new Institute for Infectious
Diseases. In 1893 Koch married Hedwig Freiberg.
Koch continued to travel and explore the causes of
many other diseases.
Koch was the recipient of many prizes and medals;
honorary doctorates from the Universities of HeidelbergKoch, Robert 189