gel into a useless soup. And agar gels
remain solid at the ideal temperatures for
bacterial growth, often around 100ºF/38ºC,
a temperature at which gelatin begins to
melt.
How did microbiologists come to use
agar? In the late 19th century, Lina Hesse,
the American wife of a German scientist,
recalled the advice of family friends who
had lived in Asia, and made agar jellies
and puddings that stayed solid in the
summer heat of Dresden. Her husband
relayed his wife’s suggestion to his boss,
the pioneering microbiologist Robert
Koch, who then used agar to isolate the
bacterium that causes tuberculosis.The Nature of Starch
Starch molecules are long chains of thousands
of glucose sugar molecules linked up together.
There are two kinds of starch molecules: long