Anton van Leeuwenhoek (1632- 
1 723) was an early microscopist 
who ground his own lenses as a 
hobby and was the first to observe 
such living cells as sperm and pond 
water microorganisms. 
source of illumination (typically white 
light) to magnify cells. 
One of the most remarkable early 
microscopists was a Dutch draper 
named Anton van Leeuwenhoek, who 
ground his own lenses as a hobby. 
Van Leeuwenhoek, who once made 
a lens from a grain of sand, used 
simple (sing le-lensed) microscopes to 
examine everything from pond water 
to the scum on his teeth. 
In 1702, van Leeuwenhoek 
reported to the Royal (Scientific) Soci- 
ety of London that he had observed 
"a little clear sort of light in the 
middle" of a fish blood cell he had 
been examining. This description of 
what was later called the cell's 
nucleus was the first suggestion that 
animal cells had an internal structure. 
Throughout the 1 8th and 1 9th centu- 
ries, improvements in microscopes 
and techniques for selectively stain- 
ing cell parts enabled cell biologists 
to distinguish other particles within 
the cell. However, researchers could 
not study these minute flecks in detail 
because they met an insuperable 
obstacle: the wavelength of light. 
A light microscope — even one with 
perfect lenses and perfect illumina- 
tion— simply cannot be used to distin- 
guish objects that are smaller than 
one-half fhe wavelength of light. 
White light has an average wave- 
length of 0.55 micrometers, half of 
which is 0.27 micrometers. (One 
micrometer is a thousandth of a milli- 
meter, and there are about 25,000 
micrometers to an inch. Micrometers 
are also called microns.) Any two 
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