Principles of Microscope Micrometer Determination of Cell Size
The size of microbial cells is one of the important basis for the classification and identification of microorganisms. Microorganisms are tiny and must be observed with the help of a microscope. To measure the size of microbial cells, they must also be measured under a microscope with the help of a special micrometer.
The microscope micrometer consists of two parts: the stage micrometer and the ocular micrometer.
The stage micrometer is a glass slide with an engraving in the center (Fig. 2-7). The total length of the scale is 1 mm.
Dedicated to calibrating eyepiece micrometers. The eyepiece micrometer can be used directly to measure cell size. It is a circular glass slide (Figure 2-8) with an equal division in the center, which is placed on the separator in the eyepiece for measurement. The total length of the eyepiece micrometer scale is 1 cm, and it is divided into 100 small cells, each of which is 100 μm long. Since the eyepiece micrometer measures the size of the image of microbial cells after being magnified by a microscope, the actual scale represents the length. It changes with the magnification of the eyepiece and objective lens used and the length of the lens barrel. Therefore, it must be calibrated with a stage micrometer before use to find out the length represented by each small cell of the eyepiece micrometer under a certain magnification. , and then use the eyepiece micrometer to directly measure the size of the measured object.
Calculation of the calibration factor for an eyepiece micrometer: an eyepiece micrometer scale (μ = the known distance between the double overlapping lines on the stage micrometer / the double overlapping line m) between the eyepiece micrometers scale of ruler
Example 1: If the known distance between two overlapping lines is 2 stage micrometer scales (2 X 10 μ
m), corresponding to 13 eyepiece micrometer scales, then
Correction factor for each eyepiece micrometer scale = 20 μm / 13 = 1.54 μm
Example 2: If a microorganism is observed with a microscope eyepiece micrometer with a length of 5 eyepiece micrometer scales, then
Microbial length = number of divisions measured by eyepiece micrometer X correction factor for each eyepiece micrometer graduation = 5 X 1.54 μm = 7.70 μm
