7 
fibers at all. Plant cells have a 
unique ability to use light as a 
source of energy. 
Then what do all these cells 
have in common? Discovering 
their shared properties was 
difficult. At first, scientists 
thought that the cell was just a 
blob of jelly, or some primordial 
soup enclosed in a bag. They 
named the jelly “protoplasm.” 
For a long time they could not 
find anything in the protoplasm, 
which is now known as the 
“cytoplasm.” 
Part of the difficulty in 
studying cells, of course, is 
due to their extremely small 
size. The cells of multicellular 
organisms are impossible to 
see with the unaided eye. 
Schleiden and Schwann, like 
cell biologists before and 
after, relied upon microscopes 
to enlarge the image of cells 
so that they could be studied. 
Microscopes employ one or 
more curved lenses and a 
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 
(single-lensed) microscopes to 
examine everything from pond 
water to the scum on his teeth. 
In 1702, van Leeuwenhoek 
reported to the Royal 
(Scientific) Society of London 
that he had observed “a little 
clear sort of light in the 
middle” of a fish blood cell 
cells whose structures 
vary according to the 
nerve cells , for e 
from spine to toe. The 
orderly structure of 
typical skeletal muscle is 
shown here in such 
muscle cell were drawn 
scale as the 
Hair cell 
Muscle cell 
Rod cell in eye 
