Activity 37 Notes: The History of the
Germ Theory of Disease
Robert Hooke: 1635-1703
Wrote Micrographia, a book of drawings
and observations; it included ideas about life
cycles, fossils, and drawings of what saw under
a microscope.
Hooke built his own compound microscope.
He discovered that cork (from a tree) is made of
tiny shapes that he called cells.
Anton van Leeuwenhoek (1632-1723)
Made simple microscopes that could
magnify objects up to 200x.
Leeuwenhoek made very detailed
observations about pondwater and tooth
scrapings.
He was one of the first to observe microbes,
which he called animalcules.
Mattias Jakob Schleiden (1804-1881)
Theodor Schwann (1810-1882)
Karl Theodor Ernst von Siebold (18041885)
Schleiden was a botanist (studied plants)
who used microscopes to study plants (at a time
when most botanists looked only at whole
plants); he suggested that all plants are entirely
made of cells.
Schwann suggested that all animals are
entirely made of cells.
Schleiden and Schwann get credit for Cell
Theory: All organisms are made up of cells.
Von Siebold suggested microbes are also
made up of cells ~ (usually one cell each).
Rudolf Carl Virchow (1821- 1902)
* Virchow said, in the 1850s “all cells arise
from cells,” meaning cells reproduced to create
new cells.
* All organisms begin as a single cell.
* Most microbes are made of ONLY one cell.
* An adult human is made of about 10
trillion cells.
* Virchow thought diseases were caused by
cells not working properly. This is true for
some diseases (such as leukemia), but not all.
Ignaz Philipp Semmelweiss (18181865)
* Semmelweiss was worried about “childbed
fever,” which killed a lot of women. He noticed
that many doctors examined pregnant women
right after doing autopsies.
* Semmelweiss tried washing his hands
between patients: his death rate dropped from
12% to 1%.
* Semmelweiss tried to get hospitals/doctors
to change habits (i.e. wash hands), but people
resisted because he couldn’t explain why
washing hands saved lives.
Louis Pasteur (1822-1895)
* Pasteur discovered that some microbes
caused food and drink to spoil, and that heat
can kill a lot of those microbes (such as
tuberculosis); using heat to kill microbes is now
called “pasteurization.”
* Pasteur thought microbes caused some
infectious diseases; this idea is the basis of the
Germ Theory of Disease.
Robert Koch (1843-1910)
* Koch found scientific evidence that
specific microbes caused specific diseases; he
identified anthrax, tuberculosis, and cholera.
* Koch injected healthy mice with anthrax,
then injected another group of healthy mice
with blood from the infected mice, and
observed. All infected mice died, and anthrax
microbes were found only in infected mice, not
in healthy ones.
* Koch developed agar, a gelatin-like
substance, to culture (grow) bacteria.
Florence Nightingale (1820-1910)
* Nightingale believed that cleanliness was
part of good nursing, and she PUBLISHED her
ideas in 1860.
* Her ideas improved sanitation at military
hospitals and saved many soldiers’ lives.
Joseph Lister (1827-1912)
* Lister heard about Pasteur’s Germ Theory
of Disease, and decided to use chemical
antiseptic to clean surgical instruments. He also
sprayed the air, and required hand washing
and clean aprons.
* After making these changes, the death rate
of patients after surgery dropped from 45% to
15%.
William Stewart Halsted (1852-1922)
* Halstead took germ theory to the next
practical level: he prevented the spread of
germs by wearing rubber gloves during
surgery (gloves are easier to sterilize than
hands).
The Theory of Spontaneous Generation
* Once upon a time, many scientists
believed that living things grew from non-
living things (e.g. plants grow from soil, no
seeds; maggots grow from meat, no eggs
needed). It took lots of experiments to prove
Virchow right: in fact, cells arise from cells (not
from dirt or meat).
* 3 Major Experiments
* In 1668, an Italian doctor named
Francesco Redi did an experiment to prove that
maggots grew from eggs laid by flies (not from
meat). He set up jars of meat, some uncovered,
some sealed, some covered with gauze: maggots
only grew in the open jars, where flies could
reach the meat.
* In 1767 an Italian priest (Spallanzini)
sealed and boiled bottles of liquid: nothing
grew in the bottles. In 1859, Pasteur did a
similar experiment with fancy flasks and yeast
cells. Both experiments showed that microbes
can only grow from other microbes: organisms
cannot come from non-living things.