Lesson 2: Public Health Microbiology

Section I: Introduction

2-5

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2-5. 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:

(1) Micron (µ): 1/1000 millimeter (about 1/25400th of an inch).

 

(2) Millimicron (mµ): 1/1000µ (1 billionth of a meter, or 1 millionth of a millimeter.

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