10 
survive under their high 
vacuum, they cannot show 
the ever-changing movements 
that characterize a living cell. 
The first electron microscopes 
were used to study crystals 
and were impractical for the 
study of cell structure. Cell 
researchers had to learn how 
to cut extremely thin slices of 
cells, sometimes down to a 
thickness of only a few hundred 
angstroms, so that electrons 
could pass through them. Also, 
to ensure contrast between 
different parts of the other- 
wise transparent cell, new 
staining techniques had to be 
devised. These techniques use 
special metal-containing 
