Modern Microscopy Gives 
Clear View of Cell Structure 
and Movements 
Using an instrument the size of his palm, Anton 
van Leeuwenhoek was the first person to study the 
movements of living sperm. Modern descen- 
dants of van Leeuwenhoek's light microscope 
can be over 6 feet tall, but they continue to be in- 
dispensable to cell biologists because, unlike 
electron microscopes, light microscopes enable 
the user to see living cells in action. The primary 
challenge for light microscopists since van 
Leeuwenhoek's time has been to enhance the 
contrast between pale cells and their paler sur- 
roundings so that cell structures and movement 
can be seen more easily. Recently, ingenious 
strategies involving video cameras, polarizing 
light, digitizing computers, and other techniques 
have yielded vast improvements in contrast and 
have fueled a renaissance in light microscopy. 
A polarizer causes lightwaves to move in 
parallel planes, thus reducing the distortion that 
results when light scatters across a magnified 
object. This technique was first used in the 
1 950's, and provided many new clues to cellular 
activities, particularly the intricacies of cell 
division. Further enhancements in visualizing the 
cell's interior came in the early 1 980's when mi- 
croscopists Shinya Inoue of the Marine Biological 
Laboratory in Woods Hole, Massachusetts, and 
Robert Allen of Dartmouth College began turning 
video cameras onto living cells. Unlike the eye, a 
video camera can "see" objects clearly even 
when the contrast between subject and back- 
ground is very poor. Inoue and Allen used video 
cameras to watch food-containing vesicles and 
other bodies in the cell move rapidly along 
slender track-like organelles. Video images can 
now be further enhanced by digitizing comput- 
ers, which, when attached io a camera, scan the 
cell, breakdown the image into lightand dark 
bits, and then reconstruct the image so that "visual 
noise" (grayness) is subtracted, while objects of 
interest a re highlighted. 
A new type of microscope, called the confocal 
microscope, promises to have a great impact on 
the study of cell structure. A confocal -microscope 
passes a beam of light over a tiny portion of a 
cell, then focuses the light that reflects off the 
specimen through a pinhole. A sharply focused, 
three-dimensional image of a cell or cell structure 
can be built up by recording the intensity of the 
light beam coming off each scanned pointand 
then reconstructing the whole image on a 
viewing screen. Because confocal microscopes 
can be used on living cells, they allow research- 
ers to see clearly cell movements and the 
interactions of neighboring cells. 
Electron microscopy is also undergoing some 
exciting developments. One new instrument 
that has aroused great interest is the scanning 
tunneling electron microscope. This device 
consists of an ultrathin tube that is held a fraction 
of a millimeter away from a cell or other sample. 
The distance between the sample and the tube is 
reduced until a current of electrons jumps from 
the sample and travels up the tube, a phenome- 
non called tunneling. As the tube is moved over 
the surface of the sample, a computer records 
the distances between the sample and the tube 
and converts this information into a picture of the 
sample's contours. In 1 989, researchers re- 
ported using scanning tunneling electron micros- 
copy to obtain, for the first time, direct images of 
pure DNA. Eventually, this method may be used 
to observe living viruses or the actions of 
molecules on the cell surface. While these latest 
revolutions in microscopy are still in their early 
stages, they are already enabling scientists to 
see the tiniest details of cell structure and activity 
in ways undreamed of a few years ago. 
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