The beef broth remained uncontaminated even after months of being exposed
to the air. The very same flask containing the original beef broth exists today in
Pasteur Institute in Paris and still shows no sign of contamination. Pasteur’s
experiments validated that microorganisms are not spontaneously generated.
Based on Pasteur’s findings, a concerted effort was launched to improve
sterilization techniques to prevent microorganisms from reproducing. Pasteur-
ization, one of the best-known sterilization techniques, was developed and
namedfor Pasteur. Pasteurization kills harmful microorganisms in milk, alco-
holic beverages, and other foods and drinks by heating it enough to kill most
bacteria that cause spoilage.JOHN TYNDALL AND FERDINAND COHN
The work of John Tyndall and Ferdinand Cohn in the late 1800s led to one of the
most important discoveries in sterilization. They learned that some microorgan-
isms are resistant to certain sterilization techniques. Until their discovery, scien-
tists had assumed that no microorganism could survive boiling water, which
became a widely accepted method of sterilization. This was wrong. Some ther-
mophiles resisted heat and could survive a bath in boiling water. This meant that
there was not one magic bullet that killed all harmful microorganisms.Germ Theory
Until the late 1700s, not much was really known about diseases except their
impact. It seemed that anyone who came in contact with an infected person
contracted the disease. A disease that is spread by being exposed to infection is
called a contagious disease. The unknown agent that causes the disease is called
a contagion. Today we know that a contagion is a microorganism, but in the 1700s
many found it hard to believe something so small could cause such devastation.ROBERT KOCH
Opinions changed dramatically following Robert Koch’s study of anthrax in
the late 1800s. Koch noticed a pattern developing: Anyone who worked with or
ingested animals that were infected with anthrax contracted the disease. In fact,(^12) CHAPTER 1 The World of the Microorganism