MICROMETRY

MICROMETRY

• Microorganisms vary greatly in size and their size can be measured through a microscope
• Micrometry refers to the measurement of microorganisms.
•  The unit used to measure the microorganisms is micrometer or micron,
• which is equal to 1/1000 mm.

There are 2 types of micrometers, namely

1. ocular micrometer and 
2. stage micrometer.

Ocular micrometer 

• ➢ Ocular micrometer is a circular glass piece  
• ➢ with an arbitrary scale in the centre divided into 100 divisions  with ten major divisions.  
• ➢ The major divisions are marked with number or numeral.

Stage micrometer

• ➢ It is a glass slide
• ➢ marked with 1mm length divided into 100 divisions at the centre,  
• ➢ so that each division is equal to 0.01 mm or 10m. I 
• ➢ n this micrometer every tenth division is longer than other lines.  
• ➢ This is used to calibrate the actual value of ocular division.

Standardization of ocular micrometer

•  The ocular micrometer has to be calibrated for each set of objective and ocular lence
•  Place the ocular micrometer in the eye piece and the stage micrometer in the stage.  
•  Observe it under low power.
•  The scales of ocular micrometer and stage micrometer are focused accurately in such a manner they coincide each other.  
•  Count the spaces on ocular micrometer until the lines coincide with the stage micrometer again.  
•  Count the spaces on the stage micrometer in between the coinciding lines. By determining how many ocular units superimposed a known distance on the  stage micrometer, 
•  calculate the value of each ocular division.
  

Measurement of microorganisms

•  To measure the dimensions of microorganisms select the set of ocular and objective lenses under which organisms to be measured.  
•  Calibrate the ocular micrometer with the help of stage micrometer.
•  Remove the stage micrometer and place the slide containing the microorganisms on the stage.  
•  Super impose the ocular micrometer on the cells.
•  Count the number of ocular divisions covered on the breadth or length of the cells.  
•  Then, calculate the size of the cells by converting the ocular division into microns and multiplying with number of divisions.