Page 237 - Inventions - A Visual Encyclopedia (DK - Smithsonian)

Louis Pasteur in his laboratory
COMPOUND MICROSCOPE

4. Eyepiece lens Rays of light
magnifies the image
produced by the
objective lens. 3. Objective
lens magnifies
the object.

GERM THEORY IN GOOD HEALTH
1. The specimen
The idea that infectious diseases are spread by
is placed on a
germs, or microorganisms, is known as germ 2. The mirror glass slide.
reflects light
theory. Today, we take it for granted, but this
up through
view was highly controversial when Pasteur the specimen.
proposed it. With the help of the microscope,
he showed that some tiny organisms were
responsible for contaminating milk, while
other microorganisms called yeasts caused A compound microscope operates in roughly the opposite way to a
the fermentation of beer and wine. telescope. Rather than having a large lens for gathering faint light from
far away, a microscope has a small lens for focusing light on small
Robert Koch in objects that are close up. Microscopes usually have a light source, an
his laboratory objective lens that can be focused, and a fixed eyepiece. The lenses
focus by bending light to make the image appear larger.

ELECTRON MICROSCOPES
In the 1930s, the German physicist Ernst Ruska developed
a microscope that could magnify up to 500,000 times.
Instead of using light, the device used a beam of
electrons. It would eventually be possible to produce
images of molecules and atoms. Today’s most powerful
microscopes can magnify up to 30 million times.

Image of bacteria
(yellow) on the tip
of a household pin,
taken by an electron
FINDING BACTERIA microscope
While Pasteur proved that diseases were caused
by bacteria, the German scientist Robert Koch
pinned down specific culprits. Microscopes
enabled him to identify the bacteria that cause
diseases such as anthrax (1876), tuberculosis
(1882), and cholera (1883). For these discoveries,
Koch is known as the “father of bacteriology”
(the study of bacteria).
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