BACTERIA
Visible only under a microscope, bacteria are so tiny that
you may best get an idea of their size through an analogy: If you can imagine
for a moment that all eight million inhabitants of New York City are reduced to
the size of bacteria, all eight million would fit comfortably into a single
drop of water. Different types of bacteria differ considerably in size, shape,
and habits.
For example, streptococci form chains like strings of beads;
others, such as those that produce boils, live in clusters, like bunches of
grapes. Bacteria have a bad press, which only some of them deserve. More of
them are beneficial than destructive. Bacteria, for example, are industrious
workers in sewage plants, helping to dispose of waste.
Bacteria, too, help the growth of many plants on which all
other plants and animals depend. But certainly life would be more pleasant
without those varieties that cause syphilis, pneumonia, boils, abscesses, strep
sore throats, tuberculosis, and many other diseases.
VIRUSES
Far smaller even than bacteria; viruses are not
visible under an ordinary microscope, only under the far more powerful electron
microscope. Much that is known about viruses has been learned only recently.
Once considered nonliving bits of matter, they are now regarded as the lowest
forms of life-parasites that do not grow unless they can occupy living cells in
which they set up reproductive housekeeping. If dried or frozen, they look like
lifeless chemicals and remain inactive for years only to resume activity again
when favorable conditions are provided.
About 500 of them have been identified
by the electron microscope, which magnifies them 25,000 times or more.
They look much like pearls, beautifully cut gems, bricks, or
rods when seen this way. They are extremely potent. Small numbers of them,
given ideal conditions, can start a disease. They cause many diseases including
polio, influenza, yellow fever, rabies, infectious hepatitis, smallpox,
chickenpox, measles, mumps and the common cold.
No comments:
Post a Comment