Mode or Type
Characteristics of the five kingdoms.
OBSERVATION AND MEASUREMENT
a. Observation. Although microbes are considered to be among the first living
things on earth, they were not actually seen until 1675. In this year Anton van
Leeuwenhoek of Holland, the inventor of the microscope, first described protozoa as
viewed under his instrument. His better microscopes had a magnification of about 160.
The standard light microscopes of today magnify an object up to about 1000 diameters.
The electron microscope that differs from the ordinary light microscope by focusing an
indirect image of the specimen on a screen will provide a magnification of 200,000
times. By means of extremely precise photographic methods, we can achieve a further
enlargement of 10 times. This gives us a theoretical capability of examining specimens
with a magnification of two million.
b. Units of Measurement. A special scale can be used on a light microscope
to enable measurement of microorganisms. Objects less than about 0.3 microns cannot
be seen when using a light microscope. The following units of measure are normally
used in the measurement of microscopic objects:
Micron (): 1/1000 millimeter (about 1/25400th of an inch).
Millimicron (m): 1/1000 (1 billionth of a meter, or 1 millionth of a