structures in a specimen. Various types of microscopes use different features of light or electrons to increase
contrast—visible differences between the parts of a specimen (seeSection 2.3). Additionally, dyes that bind to some
structures but not others can be used to improve the contrast between images of relatively transparent objects (see
Section 2.4).
- Explain the difference between magnification and resolution.
- Explain the difference between resolution and contrast.
- Name two factors that affect resolution.
2.2 Peering Into the Invisible World
Learning Objectives
- Describe historical developments and individual contributions that led to the invention and development of the
microscope - Compare and contrast the features of simple and compound microscopes
Some of the fundamental characteristics and functions of microscopes can be understood in the context of the history
of their use. Italian scholar Girolamo Fracastoro is regarded as the first person to formally postulate that disease was
spread by tiny invisibleseminaria, or “seeds of the contagion.” In his bookDe Contagione(1546), he proposed that
these seeds could attach themselves to certain objects (which he calledfomes[cloth]) that supported their transfer
from person to person. However, since the technology for seeing such tiny objects did not yet exist, the existence of
theseminariaremained hypothetical for a little over a century—an invisible world waiting to be revealed.
Early Microscopes
Antonie van Leeuwenhoek, sometimes hailed as “the Father of Microbiology,” is typically credited as the first person
to have created microscopes powerful enough to view microbes (Figure 2.9). Born in the city of Delft in the
Dutch Republic, van Leeuwenhoek began his career selling fabrics. However, he later became interested in lens
making (perhaps to look at threads) and his innovative techniques produced microscopes that allowed him to observe
microorganisms as no one had before. In 1674, he described his observations of single-celled organisms, whose
existence was previously unknown, in a series of letters to the Royal Society of London. His report was initially
met with skepticism, but his claims were soon verified and he became something of a celebrity in the scientific
community.
40 Chapter 2 | How We See the Invisible World
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