Principles of Microscope Micrometers for Determination of Cell Size
Principle of Determination of Microbial Cell Size Using a Microscope Micrometer
The size of microbial cells is one of the important basis for microbial classification and identification. Microorganisms are tiny and must
It must be observed with the help of a microscope, and to measure the size of microbial cells, it must also be measured under a microscope with the help of a special micrometer.
The micrometer is composed of two parts: stage micrometer and ocular micrometer.
The stage micrometer is a piece of glass with engraved center (Fig. 2-7), the total length of the scale is l mm, divided into 100 small divisions, each division is 10 μm long,
Dedicated to the calibration of eyepiece micrometers. The eyepiece micrometer can be directly used to measure the cell size, it is a circular slide (Fig.
Place it on the partition in the eyepiece when measuring. The total length of the scale of the eyepiece micrometer is l cm, divided into 100 small divisions, and each division is 100 μm long.
Since the eyepiece micrometer measures the size of the image of the microbial cell after it has been enlarged by the microscope, the actual length represented by the scale varies with the magnification of the eyepiece and objective lens used and the size of the lens barrel.
Therefore, before use, it must be calibrated with the stage micrometer to find the length represented by each small grid of the eyepiece micrometer at a certain magnification, and then use the eyepiece micrometer to directly measure the measured object the size of.
Calculation of an eyepiece micrometer scale correction factor (calibration factor): an eyepiece micrometer scale
(μ = known distance between two overlapping lines on the stage micrometer / the two overlapping lines m) the scale of the eyepiece micrometer
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 the correction factor of each eyepiece micrometer scale = 20 μm / 13 = 1.54 μm
Example 2: If a microorganism is observed with a microscope eyepiece micrometer, and the length is 5 eyepiece micrometer scales, then
Microbe length = number of eyepiece micrometer graduations X correction factor for each eyepiece micrometer graduation = 5 X 1.54 μm = 7.70 μm
